CYP1A2
Cytochrome P450 1A2 (EC 1.14.14.1) (CYPIA2) (Cholesterol 25-hydroxylase) (Cytochrome P(3)450) (Cytochrome P450 4) (Cytochrome P450-P3) (Hydroperoxy icosatetraenoate dehydratase) (EC 4.2.1.152)
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Cytochrome P450s (CYPs) are phase-I metabolic enzymes playing important roles in drug metabolism, dietary chemicals and endogenous molecules. Age is a key factor influencing P450s expression. Thus, age-related changes of CYP 1-4 families and bile acid homeostasis-related CYPs, the corresponding nuclear receptors and a few phase-II genes were examined. Livers from male Sprague-Dawley rats at fetus (-2 d), neonates (1, 7, and 14 d), weanling (21 d), puberty (28 and 35 d), adulthood (60 and 180 d), and aging (540 and 800 d) were collected and subjected to qPCR analysis. Liver proteins from 14, 28, 60, 180, 540 and 800 days of age were also extracted for selected protein analysis by western blot. In general, there were three patterns of their expression: Some of the drug-metabolizing enzymes and related nuclear receptors were low in fetal and neonatal stage, increased with liver maturation and decreased quickly at aging (AhR, Cyp1a1, Cyp2b1, Cyp2b2, Cyp3a1, Cyp3a2, Ugt1a2); the majority of P450s (Cyp1a2, Cyp2c6, Cyp2c11, Cyp2d2, Cyp2e1, CAR, PXR, FXR, Cyp7a1, Cyp7b1. Cyp8b1, Cyp27a1, Ugt1a1, Sult1a1, Sult1a2) maintained relatively high levels throughout the adulthood, and decreased at 800 days of age; and some had an early peak between 7 and 14 days (CAR, PXR, PPARα, Cyp4a1, Ugt1a2). The protein expression of CYP1A2, CYP2B1, CYP2E1, CYP3A1, CYP4A1, and CYP7A1 corresponded the trend of mRNA changes. In summary, this study characterized three expression patterns of 16 CYPs, five nuclear receptors, and four phase-II genes during development and aging in rat liver, adding to our understanding of age-related CYP expression changes and age-related disorders.
Keywords
- Aging
- Cytochrome P450’s
- Nuclear receptors
- Ontogeny
- Rat liver
- mRNA/protein expression
The vast majority of physiological and biological data required for physiologically based predictions are primarily available in Caucasians rather than other ethnic populations, which leads to a lack of confidence in the application of physiologically based pharmacokinetic (PBPK) modeling for ethnicity-specific prediction of pharmacokinetics in the Chinese population. In this study we recalibrate the system parameters of Chinese-specific PBPK modeling and explore for the first time the relative importance of ethnicity-specific microsomal protein per gram of liver (MPPGL), liver weight, and cytochrome P450 (CYP) 1A2 abundance to the projection of drug disposition mediated by CYP1A2 in young and elderly Chinese adults. Chinese MPPGL levels and associated variability were parameterized and incorporated for the first time into ethnicity-specific PBPK models for the Chinese adults. Parameterization of Chinese liver weights was also recalibrated on the basis of autopsy data from Chinese individuals (n = 4081) across the entire adult age range. Uncertainty surrounding the Chinese-specific CYP1A2 content has also been explored and clarified by conducting ethnicity-related PBPK simulations under different scenarios. Various ethnicity-related or 'what-if' scenarios for PBPK modeling were implemented to assess the predictive performance and explore the relative importance of ethnicity-specific MPPGL and liver weight to the projection of drug disposition mediated by CYP1A2 in terms of two typical CYP1A2 substrates, caffeine and theophylline, in young and elderly Chinese adults by comparing the predicted concentration-time data and associated pharmacokinetic parameter estimates with observations. Compared with 0.85, the liver scalar of 0.9 generally produced more accurate liver weight levels in virtual Chinese peers. Additionally, simulated MPPGL levels on the basis of Caucasian data were not able to reflect the age-independent pattern observed in Chinese adults, dissimilar to that on the basis of Chinese-specific adult MPPGL data. The modeling Scenarios A and B provided similar predictions for theophylline pharmacokinetics in young Chinese adults across different age groups, while Scenario B provided the most accurate prediction for theophylline pharmacokinetics in elderly Chinese adults. However, the use of a stratified value of CYP1A2 content derived from a Han Chinese cohort with a small sample size instead of the pooled value of all Chinese cohorts involved regardless of Chinese sub-ethnicity resulted in inadequate prediction of CYP1A2-mediated pharmacokinetics in terms of caffeine and theophylline in either young or elderly Chinese subjects. Additionally, the impact of ethnic-specific MPPGL on predictive accuracy of theophylline pharmacokinetics in elderly Chinese subjects is more evident than that of liver weight. We provided quantitative information pertaining to Chinese-specific levels of liver weight and MPPGL, and recalibrated these system parameters for PBPK modeling for young and elderly Chinese subjects. Uncertainty surrounding the Chinese-specific CYP1A2 content has also been clarified. PBPK modeling based on the recalibrated system parameters can accurately simulate CYP1A2-mediated pharmacokinetics in both young and elderly Chinese adults, particularly in elderly individuals.
MeSH Terms
- Adult
- Aged
- Aging
- Asian Continental Ancestry Group
- Cytochrome P-450 CYP1A2
- Female
- Healthy Volunteers
- Humans
- Liver
- Male
- Microsomes, Liver
- Middle Aged
- Models, Biological
- Organ Size
- Young Adult
Variable drug responses depend on individual variation in the activity of drug-metabolizing enzymes, including cytochrome P450 enzymes (CYP). As the most common chronic liver disease in children and adults, nonalcoholic steatohepatitis (NASH) has been identified as a source of significant interindividual variation in hepatic drug metabolism. Compared with adults, children present age-related differences in pharmacokinetics and pharmacodynamics. The purpose of this study was to determine the impact of fatty liver disease severity on the activity of a variety of CYP enzymes in children and adolescents. Healthy and nonalcoholic fatty liver disease pediatric subjects aged 12-21 years inclusive received an oral cocktail of four probe drugs: caffeine (CYP1A2, 100 mg), omeprazole (CYP2C19, 20 mg), losartan (CYP2C9, 25 mg), and midazolam (CYP3A4, 2 mg). Venous blood and urine were collected before administration and 1, 2, 4, and 6 hours after administration. Concentrations of the parent drugs and CYP-specific metabolites were quantified in plasma and urine using liquid chromatography with tandem mass spectrometry. In plasma, the decreased metabolic area under the curve (AUC) ratio, defined as the metabolite AUC to parent AUC, of omeprazole indicated significant decreases of CYP2C19 ([i]P[/i] = 0.002) enzymatic activities in NASH adolescents, while the urine analyses did not show significant differences and were highly variable. A comparison between the present in vivo pediatric studies and a previous ex vivo study in adults indicates distinct differences in the activities of CYP1A2 and CYP2C9. These data demonstrate that pediatric NASH presents an altered pattern of CYP activity and NASH should be considered as a confounder of drug metabolism for certain CYP enzymes. These differences could lead to future investigations that may reveal unexpected variable drug responses that should be considered in pediatric dosage recommendations.
MeSH Terms
- Adolescent
- Adult
- Aging
- Area Under Curve
- Child
- Chromatography, High Pressure Liquid
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2C9
- Cytochrome P-450 Enzyme System
- Female
- Genotype
- Humans
- Male
- Non-alcoholic Fatty Liver Disease
- Pharmaceutical Preparations
- Young Adult
The elderly constitute a significant, potentially sensitive, subpopulation within the general population, which must be taken into account when performing risk assessments including determining an acceptable daily exposure (ADE) for the purpose of a cleaning validation. Known differences in the pharmacokinetics of drugs between young adults (who are typically the subjects recruited into clinical trials) and the elderly are potential contributors affecting the interindividual uncertainty factor (UF ) component of the ADE calculation. The UF values were calculated for 206 drugs for young adult and elderly groups separately and combined (with the elderly assumed to be a sensitive subpopulation) from published studies where the pharmacokinetics of the young adult and elderly groups were directly compared. Based on the analysis presented here, it is recommended to use a default UF value of 10 for worker populations (which are assumed to be approximately equivalent to the young adult groups) where no supporting pharmacokinetic data exist, while it is recommended to use a default UF value of 15 for the general population, to take the elderly into consideration when calculating ADE values. The underlying reasons for the large differences between the exposures in the young adult and elderly subjects for the 10 compounds which show the greatest separation are different in almost every case, involving the OCT2 transporter, glucuronidation, hydrolysis, CYP1A2, CYP2A6, CYP2C19, CYP2D6, CYP3A4 or CYP3A5. Therefore, there is no consistent underlying mechanism which appears responsible for the largest differences in pharmacokinetic parameters between young adult and elderly subjects.
MeSH Terms
- Aged
- Aged, 80 and over
- Aging
- Cytochrome P-450 Enzyme System
- Female
- Humans
- Male
- Middle Aged
- Organic Cation Transporter 2
- Pharmacokinetics
- Risk Assessment
- Uncertainty
- Young Adult
Keywords
- Acceptable daily exposure
- Cleaning validation
- Elderly
- Pharmacokinetics
Predicting age-specific metabolism is important for evaluating age-related drug and chemical sensitivity. Multiple cytochrome P450s and carboxylesterase enzymes are responsible for human pyrethroid metabolism. Complete ontogeny data for each enzyme are needed to support in vitro to in vivo extrapolation (IVIVE). This study was designed to determine age-dependent human hepatic CYP2C8 expression, for which only limited ontogeny data are available, and to further define CYP1A2 ontogeny. CYP2C8 and 1A2 protein levels were measured by quantitative Western blotting using liver microsomal samples prepared from 222 subjects with ages ranging from 8 weeks gestation to 18 years after birth. The median CYP2C8 expression was significantly greater among samples from subjects older than 35 postnatal days ([i]n =[/i] 122) compared with fetal samples and those from very young infants (fetal to 35 days postnatal, [i]n =[/i] 100) (0.00 vs. 13.38 pmol/mg microsomal protein; [i]p[/i] < 0.0001). In contrast, the median CYP1A2 expression was significantly greater after 15 months postnatal age ([i]n =[/i] 55) than in fetal and younger postnatal samples (fetal to 15 months postnatal, [i]n =[/i] 167) (0.0167 vs. 2.354 pmol/mg microsomal protein; [i]p[/i] < 0.0001). CYP2C8, but not CYP1A2, protein levels significantly correlated with those of CYP2C9, CYP2C19, and CYP3A4 ([i]p[/i] < 0.001), consistent with CYP2C8 and CYP1A2 ontogeny probably being controlled by different mechanisms. This study provides key data for the physiologically based pharmacokinetic model-based prediction of age-dependent pyrethroid metabolism, which will be used for IVIVE to support pyrethroid risk assessment for early life stages.
MeSH Terms
- Adolescent
- Adult
- Aging
- Child
- Child, Preschool
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2C8
- Female
- Fetal Development
- Gene Expression
- Gene Ontology
- Gestational Age
- Humans
- In Vitro Techniques
- Infant
- Infant, Newborn
- Liver
- Male
- Microsomes, Liver
- Risk Assessment
- Xenobiotics
- Young Adult
The purpose of this study was to explore clinical markers reflecting developmental changes in drug clearance by preterm infants. Preterm infants administered aminophylline or theophylline to treat apnoea of prematurity were enrolled in this study. Trough and one of 2 h, 4 h or 6 h post-dose blood samples and urine samples were collected during steady state, to determine the concentrations of theophylline and its targeted metabolites. CYP1A2*1C and CYP1A2*1F genotypes were analyzed. Total, renal and nonrenal clearances of theophylline were calculated, and cytochrome P450 1A2 (CYP1A2) activity was obtained from the ratio of 1-methyluric acid and 3-methylxanthine to theophylline in urine. Multiple linear regression analysis was performed to evaluate the relationships between theophylline clearance and the clinical characteristics of preterm infants. A total of 152 samples from 104 preterm infants were analyzed. A strong association between the serum trough and urine theophylline concentrations was found (P < 0.001). Total, renal and nonrenal clearances of theophylline were 0.50 ± 0.29 ml kg min , 0.16 ± 0.06 ml kg min and 0.34 ± 0.28 ml kg min , respectively. CYP1A2 activity correlated positively with the postnatal age and postmenstrual age. However, CYP1A2 genotype was not associated with CYP1A2 activity, which was significantly associated with nonrenal clearance. CYP1A2 activity, postnatal age , weight and 24-h urine output were significantly associated with total theophylline clearance. CYP1A2 activity can be monitored using noninvasive random urine samples, and it can be used to assess developmental changes in theophylline clearance by preterm infants.
MeSH Terms
- Aging
- Apnea
- Bronchodilator Agents
- Cytochrome P-450 CYP1A2
- Female
- Genotype
- Gestational Age
- Humans
- Infant
- Infant, Newborn
- Infant, Premature
- Male
- Theophylline
- Uric Acid
- Xanthines
Keywords
- cytochrome P450 1A2
- drug monitoring
- pharmacokinetics
- premature infants
- theophylline
On a sample of 1240 persons from Bashkortostan, including Russian, Bashkirs and Tatars, the analysis of allele and genotype frequencies distribution of CYP1A2 gene polymorphism -163C>A was performed by PCR-RFLP in view of belonging to a particular age cohort. In Russian and Bashkirs ethnic groups we observed age-dependent decrease of CYP1A2*C allele and CYP1A2*CI*C genotype frequencies (in Russian statistically significant for allele and genotype, the Bashkirs--only for allele) and a statistically significant increase of CYP1A2*A allele and CYP1A2*A/*A genotype frequencies. The set reduction in the frequency of the wild allele CYP1A2*C and increasing the frequency of the mutant allele CYP1A2*A with age may be due to greater survival of persons who are carriers of that allelic variants of CYP1A2 gene, providing a more efficient metabolism of xenobiotics.
MeSH Terms
- Adult
- Aged
- Aged, 80 and over
- Aging
- Bashkiria
- Cytochrome P-450 CYP1A2
- Ethnic Groups
- European Continental Ancestry Group
- Gene Frequency
- Genotype
- Humans
- Middle Aged
- Polymorphism, Genetic
- Xenobiotics
- Young Adult
Process of aging is accompanied by changes in the biotransformation of xenobiotics and impairment of normal cellular functions by free radicals. Therefore, this study was designed to determine age-related differences in the activities and/or expressions of selected drug-metabolizing and antioxidant enzymes in young and old rats. Specific activities of 8 drug-metabolizing enzymes and 4 antioxidant enzymes were assessed in hepatic subcellular fractions of 6-week-old and 21-month-old male Wistar rats. Protein expressions of carbonyl reductase 1 (CBR1) and glutathione S-transferase (GST) were determined using immunoblotting. Remarkable age-related decrease in specific activities of CYP2B, CYP3A, and UDP-glucuronosyl transferase was observed, whereas no changes in activities of CYP1A2, flavine monooxygenase, aldo-keto reductase 1C, and antioxidant enzymes with advancing age were found. On the other hand, specific activity of CBR1 and GST was 2.4 folds and 5.6 folds higher in the senescent rats compared with the young ones, respectively. Interindividual variability in CBR1 activity increased significantly with rising age. We suppose that elevated activities of GST and CBR1 may protect senescent rats against xenobiotic as well as eobiotic electrophiles and reactive carbonyls, but they may alter metabolism of drugs, which are CBR1 and especially GSTs substrates.
MeSH Terms
- Aging
- Animals
- Antioxidants
- Enzyme Activation
- Inactivation, Metabolic
- Liver
- Male
- Metabolic Clearance Rate
- Oxidoreductases
- Pharmaceutical Preparations
- Rats
- Rats, Wistar
- Xenobiotics
In Meishan and Landrace pigs, sex differences in the constitutive expression of hepatic cytochrome P4501A (CYP1A) subfamily enzymes were examined in terms of their mRNA, protein, and enzyme activity. All the results from the real-time RT-PCR, western blotting, and enzyme assays for CYP1A subfamily enzymes indicated that, in 5-month-old Meishan pigs, the expression levels of CYP1A1 and CYP1A2 in males were significantly low as compared with those in females. In contrast, there were no such significant sex differences in Landrace pigs. Castration of male Meishan pigs led to a female-type expression of the CYP1A subfamily enzymes, whereas no such effect was observed in male Landrace pigs after castration. In both breeds of pigs, the administration of testosterone propionate to the females and castrated males led to marked decreases in the expression levels of mRNAs and proteins in the CYP1A subfamily enzymes, and also in their enzyme activities. Furthermore, the correlation analyses between the serum testosterone level and the gene expression levels of CYP1A subfamily enzymes in different sex-matured (1-5-month-old) male pigs revealed that the clear decrease in expression levels of hepatic CYP1A subfamily enzymes occurred at concentrations of more than 33 ng/ml of serum testosterone. Incidentally, the mean concentrations of serum testosterone in 5-month-old Landrace and Meishan pigs were around 18 and 50 ng/ml respectively. In conclusion, we demonstrated for the first time that the serum testosterone level is one of the physiological factors which regulate constitutive expression of hepatic CYP1A1 and CYP1A2 in pigs.
MeSH Terms
- Aging
- Androgens
- Animals
- Cytochrome P-450 CYP1A1
- Cytochrome P-450 CYP1A2
- Down-Regulation
- Female
- Gene Expression Regulation, Enzymologic
- Male
- Microsomes, Liver
- Multigene Family
- RNA, Messenger
- Sex Characteristics
- Swine
- Testosterone Propionate
Non-differentiated cells are attractive targets for cell therapy. During liver regeneration oval cells intensively proliferate and differentiate extending their metabolic activity. Hepatic cytochromes P450 (CYPs) can be linked either with metabolic activation of toxic compounds or drug metabolism. We investigated the differentiation and biotransformative potential of non-differentiated cells in primary cell cultures isolated from livers of fetuses (16-days-old), young (4-months-old) and old (20-months-old) rats. Under the conditions of experimental hepatocarcinogenesis, adult rats were fed for three weeks with CDE diet. Liver cells were cultured and precursor cells were differentiated to hepatocytes following induction with sodium butyrate (SB) or dimethyl sulphoxide (DMSO) in culture on MesenCult medium. We identified a number of cells expressing Thy-1, CD34, alpha-fetoprotein, cytokeratines--CK18 or CK19 and glutathione transferases--GSTpi or GSTalpha. In vitro differentiation of these cells, isolated from CDE-treated rats begun earlier as compared to non-treated ones. Age-dependent changes in the cell differentiation sequence, as well as CYPmRNA expression sequence accompanying precursor cells differentiation, were also observed. mRNA expression of CYP1A2, CYP2B1/2 and CYP3A1 was higher in the cells of young rats, but in the case of CYP2E1--in the cells of old rats. It was concluded that both proliferation and differentiation potential of oval cells, decreased with age.
MeSH Terms
- Aging
- Animals
- Biomarkers
- Cell Count
- Cell Differentiation
- Cell Proliferation
- Cytochrome P-450 Enzyme System
- Fetus
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Enzymologic
- Hepatocytes
- Ki-67 Antigen
- Liver
- Male
- RNA, Messenger
- Rats
- Rats, Sprague-Dawley
- Stem Cells
- alpha-Fetoproteins
Age-related changes in hepatic expression and activity of cytochrome P450 (CYP) were investigated in male rats aged 3 (weanling), 12 (young), 26 (adult), and 104 (old) weeks. Levels of microsomal protein, total CYP, and cytochrome b(5) increased fully after puberty. CYP1A1 was detected only in 3-week-old rats, and CYP1A2, CYP2B1, and CYP2E1 were maximally expressed at 3 weeks but decreased at 12 and 26 weeks. CYP2C11 and CYP3A2 increased markedly after puberty and decreased with aging. Ethoxyresorufin-O-deethylase, methoxyresorufin-O-demethylase, pentoxyresorufin-O-depenthylase, and p-nitrophenol hydroxylase activities were at their highest in 3-week-old rats, and midazolam hydroxylase activity was at a maximum in 12-week-old rats but decreased with aging. The present results show that increasing age caused significant alterations in hepatic expression/activity of CYP isoforms in an isoform-specific manner. These results suggest that age-related changes in hepatic CYP isoforms may be an important factor for deciding the efficacy and safety of xenobiotics.
MeSH Terms
- Aging
- Animals
- Aryl Hydrocarbon Hydroxylases
- Cytochrome P-450 CYP1A1
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2B1
- Cytochrome P-450 CYP2E1
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Cytochrome P450 Family 2
- Isoenzymes
- Liver
- Male
- Membrane Proteins
- Microsomes, Liver
- Rats
- Rats, Sprague-Dawley
- Steroid 16-alpha-Hydroxylase
Apixaban is an oral, direct, and highly selective factor Xa inhibitor in late-stage clinical development for the prevention and treatment of thromboembolic diseases. The metabolic drug-drug interaction potential of apixaban was evaluated in vitro. The compound did not show cytochrome P450 inhibition (IC(50) values >20 microM) in incubations of human liver microsomes with the probe substrates of CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, or 3A4/5. Apixaban did not show any effect at concentrations up to 20 muM on enzyme activities or mRNA levels of selected P450 enzymes (CYP1A2, 2B6, and 3A4/5) that are sensitive to induction in incubations with primary human hepatocytes. Apixaban showed a slow metabolic turnover in incubations of human liver microsomes with formation of O-demethylation (M2) and hydroxylation products (M4 and M7) as prominent in vitro metabolites. Experiments with human cDNA-expressed P450 enzymes and P450 chemical inhibitors and correlation with P450 activities in individual human liver microsomes demonstrated that the oxidative metabolism of apixaban for formation of all metabolites was predominantly catalyzed by CYP3A4/5 with a minor contribution of CYP1A2 and CYP2J2 for formation of M2. The contribution of CYP2C8, 2C9, and 2C19 to metabolism of apixaban was less significant. In addition, a human absorption, distribution, metabolism, and excretion study showed that more than half of the dose was excreted as unchanged parent (f(m CYP) <0.5), thus significantly reducing the overall metabolic drug-drug interaction potential of apixaban. Together with a low clinical efficacious concentration and multiple clearance pathways, these results demonstrate that the metabolic drug-drug interaction potential between apixaban and coadministered drugs is low.
MeSH Terms
- Aging
- Anticoagulants
- Cells, Cultured
- Cytochrome P-450 CYP3A
- Cytochrome P-450 CYP3A Inhibitors
- Cytochrome P-450 Enzyme Inhibitors
- Cytochrome P-450 Enzyme System
- Drug Evaluation, Preclinical
- Drug Interactions
- Factor Xa Inhibitors
- Hepatocytes
- Humans
- Hydroxylation
- Isoenzymes
- Kinetics
- Metabolic Detoxication, Phase I
- Microsomes
- Organ Specificity
- Pyrazoles
- Pyridones
- RNA, Messenger
- Recombinant Proteins
We previously reported an ontogeny model of hepatic cytochrome P450 (P450) activity that predicts in vivo P450 elimination from in vitro intrinsic clearance. The purpose of this study was to conduct investigations into key assumptions of the P450 ontogeny model using the developing rat model system. We used two developmentally dissimilar enzymes, CYP2E1 and CYP1A2, and male rats (n = 4) at age groups representing critical developmental stages. Total body and liver weights and hepatic microsomal protein contents were measured. Following high-performance liquid chromatography analysis, apparent K(M) and V(max) estimates were calculated using nonlinear regression analysis for CYP2E1- and CYP1A2-mediated chlorzoxazone 6-hydroxylation and methoxyresorufin O-dealkylation, and V(max) estimates for p-nitrophenol and phenacetin hydroxylations, respectively. Hepatic scaling factors and V(max) values provided estimates for infant scaling factors (ISF). The data show microsomal protein contents increased with postnatal age and reached adult values after postnatal day (PD) 7. Apparent K(M) values were similar at all developmental stages except at < or =PD7. Developmental increases in probe substrate V(max) values did not correlate with the biphasic increase in immunoquantifiable P450. The activity of two different probe substrates for each P450 covaried as a function of age. A plot of observed ISF values as a function of age reflected the developmental pattern of rat hepatic P450. In summation, these observations diverge from several of the model's assumptions. Further investigations are required to explain these inconsistencies and to investigate whether the developing rat may provide a predictive paradigm for pediatric risk assessment for P450-mediated elimination processes.
MeSH Terms
- Age Factors
- Aging
- Animals
- Body Weight
- Chlorzoxazone
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2E1
- Cytochromes
- Dealkylation
- Hydroxylation
- Isoenzymes
- Kinetics
- Liver
- Male
- Microsomes, Liver
- Models, Biological
- Nitrophenols
- Organ Size
- Oxazines
- Phenacetin
- Proteins
- Rats
- Rats, Sprague-Dawley
- Reproducibility of Results
- Risk Assessment
- Substrate Specificity
We report a comprehensive examination of rat hepatic CYP1A2 and CYP2E1 ontogeny. We compare the data to human data to determine the rat's capacity as a model to identify CYP-mediated mechanisms underlying age-dependent differences in susceptibility to toxicity. We evaluated CYP expression using real-time RT-PCR, immunoblot and immunohistochemistry, and specific probe activity in male rat livers (n = 4) at critical developmental life stages. CYP2E1 mRNA expression was low at birth, then increased rapidly to peak prior to weaning. CYP1A2 transcript levels remained very low postnatally and then increased dramatically to reach peak expression during weaning. Immunoreactive CYP1A2 and CYP2E1 was first detected at postnatal day 3 (PD3), and reached 50% of adult levels after weaning, and adult levels by puberty. CYP1A2 and CYP2E1 probe activity (pmol/(min mg)) was detected at PD3 and peaked during weaning and late neonatal period, respectively. CYP activity fell to adult values by puberty, a pattern that closely mirrored the temporal changes in mRNA but not protein. An increasing preferential localization of CYP1A2 and CYP2E1 immunoreactivity in perivenous hepatocytes was observed with maturation to adulthood. Although differences in CYP1A2 and CYP2E1 ontogeny between rats and humans exist, knowledge of these differences will aid interspecies extrapolation of developmental toxicokinetic data.
MeSH Terms
- Aging
- Animals
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2E1
- Cytochrome P-450 Enzyme System
- Female
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Enzymologic
- Humans
- Liver
- Oxidoreductases
- RNA, Messenger
- Rats
- Rats, Sprague-Dawley
The effects of conjugated equine estrogens (CEE) 0.625 mg daily on cytochrome P450 (CYP) were quantified in 12 middle-aged and 13 elderly postmenopausal women at baseline and 6 months later. CYP phenotype was characterized by caffeine (CYP1A2), chlorzoxazone (CYP2E1), dapsone (CYP, N-acetyltransferase 2), dextromethorphan (CYP2D6), and mephenytoin (CYP2C19) metabolism. CEE significantly decreased CYP1A2 (caffeine metabolic ratio: 0.57 /- 0.20 before, 0.40 /- 0.20 after, P = .001) and significantly increased CYP2D6 (dextromethorphan/dextrorphan ratio: 0.0116 /- 0.0143 before, 0.0084 /- 0.0135 after, P = .022) metabolism. CEE had no overall effect on CYP2C19, CYP2E1, CYP-mediated dapsone metabolism, and N-acetyltransferase 2. The dextromethorphan metabolic ratio decreased only in the seniors. The dapsone recovery ratio decreased in the middle-aged group and increased in the seniors. CEE significantly influenced CYP1A2, CYP2D6, and CYP-mediated dapsone oxidative metabolism but not CYP2C19, CYP2E1, or N-acetyltransferase 2 metabolism in postmenopausal women. Age influenced CYP2D6 metabolism and dapsone hydroxylation.
MeSH Terms
- Aged
- Aging
- Aryl Hydrocarbon Hydroxylases
- Arylamine N-Acetyltransferase
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2C19
- Cytochrome P-450 CYP2D6
- Cytochrome P-450 CYP2E1
- Dapsone
- Estrogens, Conjugated (USP)
- Female
- Humans
- Hydroxylation
- Metabolic Detoxication, Phase I
- Middle Aged
- Mixed Function Oxygenases
- Postmenopause
Clearance is an important pharmacokinetic concept for scaling dosage, understanding the risks of drug-drug interactions and environmental risk assessment in children. Accurate clearance scaling to children requires prior knowledge of adult clearance mechanisms and the age-dependence of physiological and enzymatic development. The objective of this research was to develop and evaluate ontogeny models that would provide an assessment of the age-dependence of clearance. Using in vitro data and/or in vivo clearance values for children for eight compounds that are eliminated primarily by one process, models for the ontogeny of renal clearance, cytochrome P450 (CYP) 3A4, CYP2E1, CYP1A2, uridine diphosphate glucuronosyltransferase (UGT) 2B7, UGT1A6, sulfonation and biliary clearance were developed. Resulting ontogeny models were evaluated using six compounds that demonstrated elimination via multiple pathways. The proportion of total clearance attributed to each clearance pathway in adults was delineated. Each pathway was individually scaled to the desired age, inclusive of protein-binding prediction, and summed to generate a total plasma clearance for the child under investigation. The paediatric age range included in the study was premature neonates to sub-adults. There was excellent correlation between observed and predicted clearances for the model development (R2 = 0.979) and test sets (Q2 = 0.927). Clearance in premature neonates could also be well predicted (development R2 = 0.951; test Q2 = 0.899). Paediatric clinical trial development could greatly benefit from clearance scaling, particularly in guiding dosing regimens. Furthermore, since the proportion of clearance via different elimination pathways is age-dependent, information could be gained on the developmental extent of drug-drug interactions.
MeSH Terms
- Aging
- Bile
- Child
- Cytochrome P-450 Enzyme System
- Glomerular Filtration Rate
- Glucuronides
- Humans
- Kidney
- Liver
- Models, Statistical
- Pharmaceutical Preparations
- Pharmacokinetics
- Sulfonic Acids
There are few data describing levobupivacaine pharmacokinetics in infants (<3 months) after caudal administration. An open-label study was undertaken to examine the pharmacokinetics of levobupivacaine 2.5 mg ml(-1), 2 mg kg(-1) in children aged less than 3 months after single-shot caudal epidural administration. Plasma concentrations were determined at intervals from 0.5 to 4 h after injection. A population pharmacokinetic analysis of levobupivacaine time-concentration profiles (84 observations) from 22 infants with mean postnatal age (PNA) 2.0 (range 0.6-2.9) months was undertaken using non-linear mixed effects models (NONMEM). Time-concentration profiles were analysed using a one-compartment model with first-order input and first-order elimination. Estimates were standardized to a 70 kg adult using allometric size models. Population parameter estimates (between-subject variability) for total levobupivacaine were clearance (CLt) 12.8 [coefficient of variation (CV) 50.6%] litre h(-1) 70 kg(-1), volume of distribution (Vt) 202 (CV 31.6%) litre 70 kg(-1), absorption half-life (Tabs) 0.323 (CV 18.6%) h 70 kg(-1). Estimates for the unbound drug were clearance (CLfree) 104 (CV 43.5%) litre h(-1) 70 kg(-1), volume of distribution (Vfree) 1700 (CV 44.9%) litre 70 kg(-1), absorption half-life (Tabsfree) 0.175 (CV 83.7%) h 70 kg(-1). There was no effect attributable to PNA on CL or V. Time to peak plasma concentration (Tmax) was 0.82 (CV 18%) h. Peak plasma concentration (Cmax) was 0.69 (CV 25%) microg ml(-1) for total levobupivacaine and 0.09 (CV 37%) microg ml(-1) for unbound levobupivacaine. Clearance in infants is approximately half that described in adults, suggesting immaturity of P450 CYP3A4 and CYP1A2 enzyme isoforms that metabolize levobupivacaine in infants. This lower clearance delays Tmax, which was noted to occur approximately 50 min after administration of caudal epidural levobupivacaine.
MeSH Terms
- Aging
- Anesthesia, Caudal
- Anesthetics, Local
- Body Weight
- Bupivacaine
- Female
- Humans
- Infant
- Infant, Newborn
- Levobupivacaine
- Male
To create a general physiologically based pharmacokinetic (PBPK) model for drug disposition in infants and children, covering the age range from birth to adulthood, and to evaluate it with theophylline and midazolam as model drugs. Physiological data for neonates, 0.5-, 1-, 2-, 5-, 10- and 15-year-old children, and adults, of both sexes were compiled from the literature. The data comprised body weight and surface area, organ weights, vascular and interstitial spaces, extracellular body water, organ blood flows, cardiac output and glomerular filtration rate. Tissue: plasma partition coefficients were calculated from rat data and unbound fraction (f u) of the drug in human plasma, and age-related changes in unbound intrinsic hepatic clearance were estimated from CYP1A2 and CYP2E1 (theophylline) and CYP3A4 (midazolam) activities in vitro. Volume of distribution (V dss), total and renal clearance (CL and CL R) and elimination half-life (t(1/2)) were estimated by PBPK modelling, as functions of age, and compared with literature data. The predicted V dss of theophylline was 0.4-0.6 l kg(-1) and showed only a modest change with age. The median prediction error (MPE) compared with literature data was 3.4%. Predicted total CL demonstrated the time-course generally reported in the literature. It was 20 ml h(-1) kg(-1) in the neonate, rising to 73 ml h(-1) kg(-1) at 5 years and then decreasing to 48 ml h(-1) kg(-1) in the adult. Overall, the MPE was - 4.0%. Predicted t(1/2) was 18 h in the neonate, dropping rapidly to 4.6-7.2 h from 6 months onwards, and the MPE was 24%. The predictions for midazolam were also in good agreement with literature data. V dss ranged between 1.0 and 1.7 l kg(-1) and showed only modest change with age. CL was 124 ml h(-1) kg(-1) in the neonate and peaked at 664 ml h(-1) kg(-1) at 5 years before decreasing to 425 ml h(-1) kg(-1) in the adult. Predicted t(1/2) was 6.9 h in the neonate and attained 'adult' values of 2.5-3.5 h from 1 year onwards. A general PBPK model for the prediction of drug disposition over the age range neonate to young adult is presented. A reference source of physiological data was compiled and validated as far as possible. Since studies of pharmacokinetics in children present obvious practical and ethical difficulties, one aim of the work was to utilize maximally already available data. Prediction of the disposition of theophylline and midazolam, two model drugs with dissimilar physicochemical and pharmacokinetic characteristics, yielded results that generally tallied with literature data. Future use of the model may demonstrate further its strengths and weaknesses.
MeSH Terms
- Adolescent
- Aging
- Body Composition
- Bronchodilator Agents
- Cardiac Output
- Child
- Child, Preschool
- Female
- Half-Life
- Humans
- Infant
- Infant, Newborn
- Liver Circulation
- Male
- Midazolam
- Models, Biological
- Organ Size
- Regional Blood Flow
- Theophylline
Previously we have reported our analyses of cytochrome P450 (CYP) expression in rat ocular tissues and in our current study we have extended these analyses to the different stages of growth in both male and female rats. Additionally, we have examined the expression levels of the different conjugation enzymes, sulfotransferases (SULTs), UDP-glucuronosyl transferases (UGTs) and glutathione S-transferases (GSTs), in ocular tissues. In 5-week-old animals, the CYP genes, CYP2B2 and CYP3A1, were abundantly expressed in the lens, with higher CYP1A1 expression detectable in the extra-lenticular tissues, of both genders. However, the expression of CYP1A2 and CYP2E1 in female ocular tissues was more extensive than in male. Moreover, in females the expression of the phenol-sulfating SULTs, ST1A1, ST1B1 and ST1C1, was more abundant in the extra-lenticular tissues, whereas the levels of the hydroxysteroid-sulfating SULTs, ST2A1 and ST2A5, predominated in the lens. The expression levels of the UGTs, UGT1A1, UGT1A6 and UGT2B1, were also higher in the female extra-lenticular tissues but the expression of the GSTA subfamily (GSTA1 and GSTA2) was very weak in the ocular tissues of both genders. The overall gene expression profiles were found to change with the age of the animals (from 3 to 8 weeks) and, in general, the expression levels of the CYPs and SULTs declined with age, whereas the levels of the UGTs and GSTs increased. These results demonstrate that the expression profiles of drug metabolising enzymes show both region- and gender-specific patterns in rat ocular tissues.
MeSH Terms
- Aging
- Animals
- Biotransformation
- Cytochrome P-450 Enzyme System
- Eye
- Female
- Gene Expression Profiling
- Gene Expression Regulation, Enzymologic
- Glucuronosyltransferase
- Male
- Rats
- Rats, Sprague-Dawley
- Reverse Transcriptase Polymerase Chain Reaction
- Sex Characteristics
- Sulfotransferases
The present study compared the relative expression pattern of 10 orthologous CYP forms from families 1-4 in cDNA panels of human and mouse fetal and adult tissues. Except for CYP1A2, all of these CYPs exhibited specific patterns of expression during mouse ontogeny, suggesting possible involvement in development. Cyp1a1 and Cyp2r1 were the only two of the orthologs to be expressed only in the E7 mouse; Cyp2s1 was expressed in all stages, including E7, while Cyp2e1 appeared only at E17. Highest expression of the individual CYPs in the different late term human fetal tissues was: thymus, CYP1B1 and CYP2U1; liver, CYP2E1; brain, CYP2R1, CYP1A1 and CYP4X1; and lung, CYP4B1 and CYP2W1. In general, the level of individual human CYP transcripts was lower in the fetal than the corresponding adult tissues. The pattern of expression in adult mouse and human tissues was fairly similar for CYP1A1, CYP1A2, CYP1B1, CYP2S1, and CYP2U1 orthologs.
MeSH Terms
- Adult
- Aging
- Animals
- Base Sequence
- Cytochrome P-450 Enzyme System
- DNA, Complementary
- Embryo, Mammalian
- Gene Expression Profiling
- Gene Expression Regulation, Developmental
- Humans
- Mice
- Organ Specificity
The activity of cytochrome P450 (CYP) enzymes, which determine the rate of elimination of lipid-soluble drugs, demonstrates considerable interindividual variability. The extent to which age and sex influence CYP activity remains unclear in humans. Our objectives were to determine whether in vivo activity of selected CYP enzymes is affected by age or sex and to evaluate sex bioequivalence in a large sample size. We have assessed in vivo activity of the CYP1A2, 2C19, 2D6, 2E1, and 3A4 enzymes in 161 normal subjects (51% female subjects and 40% aged >50 years). After simultaneous administration of a cocktail of selective probes (caffeine, mephenytoin, debrisoquin [INN, debrisoquine], chlorzoxazone, and dapsone, respectively), phenotypic indices for metabolism of these drugs were used as measures of individual CYP activity. Sex bioequivalence analysis used the bootstrap method. There were no sex differences associated with CYP1A2 activity. A significant negative correlation (r = -0.572, P < .01) between enzyme activity and age was observed for CYP2C19, but there were no sex differences. CYP2D6 activity showed no dependence on age or sex. In contrast, CYP2E1 activity showed an age-associated increase (r = 0.393, P < .01), which developed earlier in life in male subjects compared with female subjects. These results were further supported by the sex bioequivalence analysis of CYP phenotypic activity, which revealed that sexes were equivalent with respect to CYP2C19 (90% confidence interval [CI], 0.874-1.04), CYP3A4 (90% CI, 0.95-1.176), and CYP2D6 (90% CI, 0.928-1.09) phenotype and just exceeded the 0.8 to 1.25 limits to be equivalent with respect to CYP2E1 (90% CI, 0.785-1.08) and CYP1A2 (90% CI, 0.736-1.03) phenotype. These observations suggest that the presence of selective mechanisms of regulation for individual CYP enzymes can be influenced by age and sex. However, we suggest that sex has a limited ability to explain intersubject variation of activity for these phenotypic measures of CYP enzyme activity.
MeSH Terms
- Adolescent
- Adult
- Aged
- Aged, 80 and over
- Aging
- Algorithms
- Chromatography, High Pressure Liquid
- Cytochrome P-450 Enzyme System
- Female
- Genotype
- Humans
- Isoenzymes
- Male
- Middle Aged
- Models, Statistical
- Phenotype
- Sex Characteristics
- Therapeutic Equivalency
We have measured cytochrome P450 (CYP) activity in nearly 150 samples of human liver microsomes and 64 samples of cryopreserved human hepatocytes, and we have performed induction studies in over 90 preparations of cultured human hepatocytes. We have analyzed these data to examine whether the expression of CYP enzyme activity in liver microsomes and isolated hepatocytes or the inducibility of CYP enzymes in cultured hepatocytes is influenced by the gender, age, or ethnicity of the donor (the latter being limited to Caucasians, African Americans, and Hispanics due to a paucity of livers from Asian donors). In human liver microsomes, there were no statistically significant differences (P > 0.05) in CYP activity as a function of age, gender, or ethnicity with one exception. 7-Ethoxyresorufin O-dealkylase (CYP1A2) activity was greater in males than females, which is consistent with clinical observation. Liver microsomal testosterone 6beta-hydroxylase (CYP3A4) activity was slightly greater in females than males, but the difference was not significant. However, in cryopreserved human hepatocytes, the gender difference in CYP3A4 activity (females = twice males) did reach statistical significance, which supports the clinical observation that females metabolize certain CYP3A4 substrates faster than do males. Compared with those from Caucasians and African Americans, liver microsomes from Hispanics had about twice the average activity of CYP2A6, CYP2B6, and CYP2C8 and half the activity of CYP1A2, although this apparent ethnic difference may be a consequence of the relatively low number of Hispanic donors. Primary cultures of hepatocytes were treated with beta-naphthoflavone, an inducer of CYP1A2, phenobarbital or rifampin, both of which induce CYP2B6, CYP2C9, CYP2C19, and CYP3A4, albeit it to different extents. Induction of these CYP enzymes in freshly cultured hepatocytes did not appear to be influenced by the gender or age of the donor. Furthermore, CYP3A4 induction in hepatocytes isolated from cirrhotic liver was comparable to that in normal hepatocytes, which supports the "healthy hepatocyte, sick environment" hypothesis of liver cirrhosis. This review summarizes these findings and discusses their implications for the use of human liver microsomes and hepatocytes for in vitro studies of drug metabolism and enzyme induction, which play a key role in drug development.
MeSH Terms
- Aging
- Alcohol Drinking
- Animals
- Cells, Cultured
- Cytochrome P-450 Enzyme System
- Enzyme Induction
- Ethnic Groups
- Female
- Hepatocytes
- Humans
- Isoenzymes
- Liver Cirrhosis
- Male
- Microsomes, Liver
- Sex Characteristics
- Smoking
Children's risks from environmental toxicant exposure can be affected by pharmacokinetic factors that affect the internal dose of parent chemical or active metabolite. There are numerous physiologic differences between neonates and adults that affect pharmacokinetics including size of lipid, and tissue compartments, organ blood flows, protein binding capacity, and immature function of renal and hepatic systems. These factors combine to decrease the clearance of many therapeutic drugs, which can also be expected to occur with environmental toxicants in neonates. The net effect may be greater or lesser internal dose of active toxicant depending upon how the agent is distributed, metabolized, and eliminated. Child/adult pharmacokinetic differences decrease with increasing postnatal age, but these factors should still be considered in any children's age group, birth through adolescence, for which there is toxicant exposure. Physiologically based pharmacokinetic (PBPK) models can simulate the absorption, distribution, metabolism, and excretion of xenobiotics in both children and adults, allowing for a direct comparison of internal dose and risk across age groups. This review provides special focus on the development of hepatic cytochrome P-450 enzymes (CYPs) in early life and how this information, along with many factors unique to children, can be applied to PBPK models for this receptor population. This review describes a case study involving the development of neonatal PBPK models for the CYP1A2 substrates caffeine and theophylline. These models were calibrated with pharmacokinetic data in neonates and used to help understand key metabolic differences between neonates and adults across these two drugs.
MeSH Terms
- Adult
- Aging
- Child
- Environmental Pollutants
- Growth
- Humans
- Kidney
- Models, Biological
- Risk Assessment
To assess the pharmacokinetics of alosetron, its effect on in vivo enzyme activities, and influence of demographic factors during repeated dosing. Thirty healthy men and women received 1 mg oral alosetron twice-daily for 29.5 days and a single oral dose of a metabolic probe cocktail before and on the last day of alosetron dosing. Serum alosetron concentrations were measured on days 1, 8, 15, 22 and 29. Probe-substrate and metabolite concentrations were measured after each cocktail dose. Alosetron accumulation in serum was negligible. Exposure to alosetron did not alter probe-metabolite/substrate ratios associated with CYP2C19, 2E1, 2C9, or 3A4 activity, but modestly decreased those associated with CYP1A2 and N-acetyltransferase activity. Systemic exposure to alosetron was higher in women, positively correlated with age and body mass index, and negatively correlated with CYP1A2 activity. Incidence of constipation was higher in women, but not associated with alosetron concentration. Single dose data can reliably predict the pharmacokinetics of alosetron after repeated doses. Alosetron exhibits limited potential for inhibition of cytochrome P450-mediated metabolism. Interindividual differences in alosetron pharmacokinetics associated with demographic factors may be related to strong dependence on metabolism by CYP1A2.
MeSH Terms
- Administration, Oral
- Adult
- Aging
- Area Under Curve
- Aryl Hydrocarbon Hydroxylases
- Arylamine N-Acetyltransferase
- Body Mass Index
- Carbolines
- Constipation
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2C19
- Female
- Gastrointestinal Agents
- Half-Life
- Humans
- Male
- Middle Aged
- Mixed Function Oxygenases
- Retrospective Studies
- Sex Characteristics
Children's risks can differ from those in adults for numerous reasons, one being differences in the pharmacokinetic handling of chemicals. Immature metabolism and a variety of other factors in neonates can affect chemical disposition and clearance. These factors can be incorporated into physiologically based pharmacokinetic (PBPK) models that simulate the fate of environmental toxicants in both children and adults. PBPK models are most informative when supported by empirical data, but typically pediatric pharmacokinetic data for toxicants are not available. In contrast, pharmacokinetic data in children are readily available for therapeutic drugs. The current analysis utilizes data for caffeine and theophylline, closely related xanthines that are both cytochrome P-450 (CYP) 1A2 substrates, in developing PBPK models for neonates and adults. Model development involved scale-up of in vitro metabolic parameters to whole liver and adjusting metabolic function for the ontological pattern of CYP1A2 and other CYPs. Model runs were able to simulate the large differences in half-life and clearance between neonates and adults. Further, the models were able to reproduce the faster metabolic clearance of theophylline relative to caffeine in neonates. This differential between xanthines was found to be due primarily to an extra metabolic pathway available to theophylline, back-methylation to caffeine, that is not available to caffeine itself. This pathway is not observed in adults exemplifying the importance of secondary or novel routes of metabolism in the immature liver. Greater CYP2E1 metabolism of theophylline relative to caffeine in neonates also occurs. Neonatal PBPK models developed for these drugs may be adapted to other CYP1A2 substrates (e.g., arylamine toxicants). A stepwise approach for modeling environmental toxicants in children is proposed.
MeSH Terms
- Adult
- Aging
- Caffeine
- Environmental Exposure
- Half-Life
- Humans
- Infant, Newborn
- Liver
- Metabolic Clearance Rate
- Models, Biological
- Risk Factors
- Theophylline
- Tissue Distribution
Nitric oxide (NO) is responsible for cytochrome P450 (CYP450) loss during isolation and cytokine treatment of primary rat hepatocytes. As P450s mediate the metabolism of toxic chemicals, their inhibition could compromise the cells competence to eliminate toxins, a condition potentially relevant in neurological diseases involving constitutive activation of nitric oxide synthase (NOS) and NO over-production. Here, we have investigated the correlation between NO accumulation and CYP1A2 down-regulation during maturation of mouse cerebellar granule cells (CGC). As neurons matured in culture, the inducible levels of CYP1A2 protein and catalytic activity decreased to almost undetectable values. In parallel, a significant increase in NO concentration was observed. Neuronal NOS remained constitutively active during maturation, thus contributing to NO accumulation. The NOS inhibitor l-NAME, restored CYP1A2 catalytic activity up to 9 days in vitro, supporting a role for NO in the inhibition process. Maturation was also followed by increased NMDA receptor activity and intracellular Ca2 concentration. We suggest that maintained NOS activity during CGC maturation could lead to NO accumulation and to decreased CYP1A2 inducibility. Increased NMDA receptor activity and Ca2 entry could contribute to this process. Thus, neurodegeneration could diminish the induction of specific P450s and impair the metabolism of foreign and/or endogenous chemicals in the CNS.
MeSH Terms
- Aging
- Aniline Compounds
- Animals
- Animals, Newborn
- Calcimycin
- Calcium
- Cells, Cultured
- Cellular Senescence
- Cerebellum
- Citrulline
- Copper Sulfate
- Cytochrome P-450 CYP1A2
- DNA-Binding Proteins
- Dizocilpine Maleate
- Down-Regulation
- Enzyme Induction
- Enzyme Inhibitors
- Excitatory Amino Acid Agonists
- Excitatory Amino Acid Antagonists
- Fluoresceins
- Ionophores
- Mice
- Mice, Inbred C57BL
- N-Methylaspartate
- NG-Nitroarginine Methyl Ester
- Neurons
- Nitric Oxide
- Nitric Oxide Synthase
- RNA, Messenger
- Repressor Proteins
- Reverse Transcriptase Polymerase Chain Reaction
- Time Factors
- Tritium
- Xanthenes
Age-related changes in the expression of xenobiotic biotransformation enzymes can result in differences in the rates of chemical activation and detoxification, affecting responses to the therapeutic and/or toxic effects of chemicals. Despite recognition that children and adults may exhibit differences in susceptibility to chemicals, information about when in development specific biotransformation enzymes are expressed is incomplete. N-acetyltransferases (NATs) are phase II enzymes that catalyze the acetylation of arylamine and hydrazine carcinogens and therapeutic drugs. The postnatal expression of NAT1 and NAT2 was investigated in C57Bl/6 mice. Hepatic NAT1 and NAT2 messenger RNAs (mRNAs) increased with age from neonatal day (ND) 4 to adult in a nonlinear fashion. The presence of functional proteins was confirmed by measuring NAT activities with the isoform selective substrates p-aminobenzoic acid and isoniazid, as well as the carcinogens 2-aminofluorene and 4-aminobiphenyl (4ABP). Neonatal liver was able to acetylate all of the substrates, with activities increasing with age. Protein expression of CYP1A2, another enzyme involved in the biotransformation of arylamines, showed a similar pattern. The genotoxicity of 4ABP was assessed by determining hepatic 4ABP-DNA adducts. There was an age-dependent increase in 4ABP-DNA adducts during the neonatal period. Thus, developmental increases in expression of NAT1 and NAT2 genes in neonates are associated with less 4ABP genotoxicity. The age-related pattern of expression of biotransformation enzymes in mice is consistent with human data for NATs and suggests that this may play a role in developmental differences in arylamine toxicity.
MeSH Terms
- 4-Aminobenzoic Acid
- Acetyltransferases
- Aging
- Amino Acid Transport System A
- Amino Acid Transport Systems
- Aminobiphenyl Compounds
- Animals
- Animals, Newborn
- Arylamine N-Acetyltransferase
- Biotransformation
- Carrier Proteins
- Cytochrome P-450 CYP1A2
- DNA Adducts
- Fluorenes
- Isoenzymes
- Isoniazid
- Liver
- Mice
- Mice, Inbred C57BL
- Mutagens
- RNA, Messenger
- Reverse Transcriptase Polymerase Chain Reaction
To characterize the distribution of mathematically derived human hepatic CYP1A1 activity using differential inhibition of ethoxyresorufin O-deethylation (EROD) by fluvoxamine. Quantitative CYP1A1- and CYP1A2-mediated EROD activities were determined in 42 human livers using differential inhibition of EROD by fluvoxamine. CYP1A2-specific activity was also measured by phenacetin O-deethylation and caffeine 3-demethylation. Distributions of CYP1A1-mediated EROD and CYP1-A2 probe activities were analyzed using cumulative distribution (probit) plots and the Kolgomorov-Smirnov test. Age effect on CYP1A1- and CYP1A2-mediated EROD activities was evaluated using descriptive statistics and analysis of variance. The derived CYP1A1 protein concentration of 0.58 /- 1.04 pmol/mg was only 4% of the derived CYP1A2. Since CYP1A1 is intrinsically far more active than CYP1A2 in mediating EROD, contribution of CYP1A1 to EROD represented approximately 25-40% of CYP1A2 contribution. Three of the 42 livers exhibited no CYP1A1-mediated EROD. Approximately 8% of the individuals showed high CYP1A1 activity phenotype based on cumulative distribution curve analysis. Hepatic CYP1A1 activity was more variable than that of CYP1A2. The variance of CYP1A1-mediated EROD was significantly different from that of CYP1A2, using the Kolgomorov-Smirnov statistical test. Even though not statistically significant, an age-related pattern in CYP1A1-mediated activity was identified: activity was high in the pre-puberty group, then decreased in the young/mature adult group and, finally, a slight increase was observed in old age. Distribution pattern in CYP1A1-mediated EROD suggests that the low derived CYP1A1 expression is most likely induced rather than constitutive. CYP1A1 activity deviates from log-normal distribution; the variations in hepatic CYP1A1 activity may affect the conversion of procarcinogens to carcinogens. The age-related trend in CYP1A1-mediated EROD activity hints that CYP1A1 responsiveness to inducers may change with age as well as with exposure to environmental inducers. These findings prompt (1) future genotyping studies to determine whether increased CYP1A1 inducibility is a result of genetic factors and (2) studies to address whether CYP1A1 inducibility changes with age.
MeSH Terms
- Aging
- Caffeine
- Cytochrome P-450 CYP1A1
- Cytochrome P-450 CYP1A2
- Enzyme Inhibitors
- Fluvoxamine
- Humans
- Isoenzymes
- Kinetics
- Microsomes, Liver
- Models, Statistical
- Molecular Probes
- Phenacetin
- Substrate Specificity
Previously, we established a method to assess drug metabolism capacity based on a pharmacokinetic estimation of the quantity of cytochrome P450 (CYP) in vivo (PKCYP-test) by introducing an apparent liver-to-blood free concentration gradient in vivo (qg). The qg values were determined as the ratio of in vivo-in vitro clearance. In this study, we examined the application of the PKCYP-test to the clearance of acetanilide and caffeine mediated by CYP1A2 using rat models in which the levels of CYP enzymes were reduced. Rats fed a choline-deficient diet (CD-fed) and aged rats were used as models for a low level of CYP in the liver. In both rat models, the contribution (fCYP) of CYP1A2 to the in vivo intrinsic clearance values (CLint) of acetanilide and caffeine metabolism was less than unity, suggesting that other metabolic pathways are involved in the CLint. The in vivo clearance for CYP1A2 was estimated by multiplying fCYP by CLint, then the value of qg was determined as the ratio of in vivo-in vitro clearance. We predicted the level of CYP1A2 in CD-fed and aged rats, based on the clearance of acetanilide mediated by CYP1A2, using the qg value of control rats. The clearance of caffeine mediated by CYP1A2 in CD-fed and aged rats, as estimated from the predicted level of CYP1A2, correlated with the observed values. In conclusion, we have demonstrated that the PKCYP-test can be applied to CYP1A2 for drugs metabolized by multiple CYP isozymes, and/or to models involving reduced CYP.
MeSH Terms
- Acetanilides
- Aging
- Algorithms
- Animals
- Antibodies, Blocking
- Caffeine
- Central Nervous System Stimulants
- Choline Deficiency
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP1A2 Inhibitors
- Cytochrome P-450 Enzyme Inhibitors
- Cytochrome P-450 Enzyme System
- Diet
- Disease Models, Animal
- Enzyme Inhibitors
- Isoenzymes
- Liver Circulation
- Male
- Methylcholanthrene
- Microsomes, Liver
- Rats
- Rats, Sprague-Dawley
The naphthylamine derivative sertraline is a potent and selective inhibitor of serotonin reuptake into presynaptic terminals. Sertraline has a linear pharmacokinetic profile and a half-life of about 26 h. Its major metabolite, desmethylsertraline does not appear to inhibit serotonin reuptake. Sertraline mildly inhibits the CYP2D6 isoform of the cytochrome P450 system but has little effect on CYP1A2, CYP3A3/4, CYP2C9, or CYP2C19. It is, however, highly protein bound and may alter blood levels of other highly protein bound agents. Sertraline is a widely used serotonin reuptake inhibitor that has been shown to have both antidepressant and antianxiety effects. Many clinical trials have demonstrated its efficacy in depression compared with both placebo and other antidepressant drugs. Its efficacy has also been demonstrated in randomized, controlled trials of patients with obsessive-compulsive disorder, panic disorder, social phobia, and premenstrual dysphoric disorder. In short-term, open-label studies it has appeared efficacious and tolerable in children and adolescents and in the elderly, and data are positive for its use in pregnant or lactating women. Typical side effects include gastrointestinal and central nervous system effects as well as treatment-emergent sexual dysfunction; withdrawal reactions may be associated with abrupt discontinuation of the agent. The safety profile of sertraline in overdose is very favorable. Sertraline's efficacy for both mood and anxiety disorders, relatively weak effect on the cytochrome P450 system, and tolerability profile and safety in overdose are factors that contribute to make it a first-line agent for treatment in both primary and tertiary care settings.
MeSH Terms
- Aging
- Animals
- Antidepressive Agents, Second-Generation
- Humans
- Mental Disorders
- Serotonin Uptake Inhibitors
- Sertraline
Hepatic cytochrome P450 (CYP)1A1 and 1A2 enzymes were studied in male Sprague-Dawley rats derived from 5-7 litters fed diets in which the protein source was casein, soy protein isolate or whey. At age 65 d, rats were gavaged with corn oil (vehicle), 40 mg/kg 3-methylcholanthrene (3-MC) or 75 mg/kg isosafrole (ISO). Hepatic expression of CYP1A1 and CYP1A2 mRNA, apoprotein and associated monooxygenase activities were measured 17 h later. No significant dietary effects were observed on basal expression of either enzyme. However, interactions between diet and the two inducers (3-MC and ISO) were observed in soy-fed rats for ethoxy- and methoxyresorufin O-dealkylase activity, CYP1A1 and CYP1A2 apoprotein and mRNA (P < 0.05). The level of induction of CYP1A1 mRNA and apoprotein was lower in rats fed soy diets than in rats fed casein diets (P < 0.05), and the level of induced CYP1A2 mRNA was lower in rats fed soy or whey (P < 0.05) after treatment with the aryl hydrocarbon (Ah) receptor-dependent inducer 3-MC. This was accompanied by a 50% reduction in constitutive levels of the Ah receptor in liver cytosol of soy-fed, relative to casein-fed rats, and a slightly smaller reduction in whey-fed rats. Expression of the Ah receptor correlated with 3-MC-inducibility of CYP1A1 mRNA in rats fed the three diets. In contrast, in rats induced with ISO, which does not bind to the Ah receptor and induces CYP1As via different mechanisms than 3-MC, ethoxyresorufin O-deethylase activity and levels of CYP1A1 apoprotein and mRNA were elevated to a greater degree in soy-fed than in casein- or whey-fed rats (P < 0.05). Moreover, after ISO treatment, induction of methoxyresorufin O-demethylase activity, CYP1A2 apoprotein and mRNA levels was observed only in rats fed soy (P < 0.05). These data suggest potential effects of dietary protein source on metabolism of a wide variety of CYP1A substrates, including environmental and dietary carcinogens, many of which induce their own metabolism.
MeSH Terms
- Aging
- Animals
- Blotting, Northern
- Blotting, Western
- Caseins
- Cytochrome P-450 CYP1A1
- Cytochrome P-450 CYP1A2
- Cytosol
- Dietary Proteins
- Enzyme Induction
- Female
- Fertilization
- Liver
- Male
- Methylcholanthrene
- Milk Proteins
- Rats
- Rats, Sprague-Dawley
- Receptors, Aryl Hydrocarbon
- Safrole
- Soybean Proteins
- Whey Proteins
Reboxetine is a novel selective norepinephrine inhibitor that has been evaluated in the treatment of patients with depression. Reboxetine is a racemic mixture, and the (S,S)-( )-enantiomer appears to be the more potent inhibitor. However, the ratio of the areas under the concentration-time curves of the (S,S)-( )- and (R,R)-(-)-enantiomers in vivo is approximately 0.5. There is no evidence for chiral inversion. Differences in the clearances of the 2 enantiomers may be explained by differences in protein binding. The pharmacokinetics of reboxetine are linear following both single and multiple oral doses up to a dosage of 12 mg/day. The plasma concentration-time profile following oral administration is best described by a 1-compartment model, and the mean half-life (approximately 12 hours) is consistent with the recommendation to administer the drug twice daily. Reboxetine is well absorbed after oral administration. The absolute bioavailability is 94.5%, and maximal concentrations are generally achieved within 2 to 4 hours. Food affects the rate, but not the extent, of absorption. The distribution of reboxetine appears to be limited to a fraction of the total body water due to its extensive (>97%) binding to plasma proteins. The primary route of reboxetine elimination appears to be through hepatic metabolism. Less than 10% of the dose is cleared renally. A number of metabolites formed through hepatic oxidation have been identified, but reboxetine is the major circulating species in plasma. In vitro studies show that reboxetine is predominantly metabolised by cytochrome P450 (CYP) 3A4; CYP2D6 is not involved. Reboxetine plasma concentrations are increased in elderly individuals and in those with hepatic or renal dysfunction, probably because of reduced metabolic clearance. In these populations, reboxetine should be used with caution, and a dosage reduction is indicated. Ketoconazole decreases the clearance of reboxetine, so that the dosage of reboxetine may need to be reduced when potent inhibitors of CYP3A4 are coadministered. Quinidine does not affect the in vivo clearance of reboxetine, confirming the lack of involvement of CYP2D6. There is no pharmacokinetic interaction between reboxetine and lorazepam or fluoxetine. Reboxetine at therapeutic concentrations has no effect on the in vitro activity of CYP1A2, 2C9, 2D6, 2E1 or 3A4. The lack of effect of reboxetine on CYP2D6 and CYP3A4 was confirmed by the lack of effect on the metabolism of dextromethorphan and alprazolam in healthy volunteers. Thus, reboxetine is not likely to affect the clearance of other drugs metabolised by CYP isozymes.
MeSH Terms
- Administration, Oral
- Aged
- Aging
- Antidepressive Agents
- Area Under Curve
- Biological Availability
- Female
- Half-Life
- Humans
- Intestinal Absorption
- Male
- Metabolic Clearance Rate
- Middle Aged
- Morpholines
- Protein Binding
- Reboxetine
- Stereoisomerism
- Tissue Distribution
To assess the effect of gender, age, and smoking habits on the in vivo activities of CYP1A2, flavin-containing monooxygenase (FMO), and xanthine oxidase in Korean subjects. One hundred thirty-three age- and gender-matched healthy Korean volunteers (age range, 21 to 78 years; mean age, 35.3 /- 16.6 years) with and without smoking habits participated. After drinking a cup of coffee (200 mL) that contained 110 mg caffeine, a 1-hour urine sample (between 4 and 5 hours) was collected and caffeine metabolites were analyzed by HPLC. There were marked individual variations in CYP1A2 [(1,7-dimethylurate paraxanthine)/caffeine], FMO (theobromine/caffeine), and xanthine oxidase (1-methylurate/1-methylxanthine) activities (14-, 42-, and 9-fold, respectively). However, the mean values of these enzyme activities in the nonsmokers were not different between men and women. In the nonsmoking subjects in their 20s, the mean values of CYP1A2 and FMO activities (13.5 /- 5.9 and 2.1 /- 1.9, respectively) were higher than those (7.9 /-1.8 and 0.95 /- 0.22) of older decennial age groups. Xanthine oxidase activities were the same for all age groups (subjects in their 20s through their 70s). CYP1A2 activity of the smokers (20.0 /- 9.6) was higher than that of the nonsmokers (10.8 /- 5.8; P < .001). Similarly, the FMO activity in smokers (3.4 /- 2.7) was higher than that of the nonsmokers (1.8 /- 1.7; P < .001). The xanthine oxidase activity (1.3 /- 0.5) was not increased in smokers (1.4 /- 0.5; P = .46). Results of this caffeine metabolism study conducted with age- and gender-matched healthy Korean volunteers with and without smoking habits provided the baseline and the widely varying interindividual activities of CYP1A2, FMO, and xanthine oxidase in a Korean population. The results also suggested that drugs metabolized by CYP1A2 and FMO may require individualized dose adjustment according to the age and smoking habits of the subjects.
MeSH Terms
- Adult
- Aged
- Aging
- Asian Continental Ancestry Group
- Caffeine
- Case-Control Studies
- Chromatography, High Pressure Liquid
- Cytochrome P-450 CYP1A2
- Female
- Humans
- Korea
- Male
- Middle Aged
- Oxygenases
- Reference Values
- Smoking
- Xanthine Oxidase
To characterize the effect(s) of gender, age (glycemic status) and obese state, on hepatic biotransformation activities, expression of cytochrome P450 (CYP450) mRNAs and glutathione transferase activity in the ob/ob mouse. Male and female, ob/ob or ob/ mice were killed at 3-4 months or 7-8 months of age. Hepatic microsomes, cytosol and RNA were prepared from each animal. Male and female ob/ob and ob/ mice, 3-4 or 7-8 months of age. CYP450 form-specific activities of CYP1A1/1A2, CYP3A and CYP2B were estimated by determining the 0-dealkylation of alkoxyresorufin substrates (ethoxy-EROD, benzoxy-BROD and pentoxy-resorufin, PROD, respectively). CYP2E1-dependent, 4-nitrophenol hydroxylase (PNP-OH) and CYP3A-dependent erythromycin N-demethylase (ERY-DM) were also measured in hepatic microsomes. CYP1A2, CYP2E1 and CYP3A protein in microsomal fractions was determined by ELISA. Glutathione transferase activity (GST) was determined in hepatic cytosol and CYP1A2 and CYP2E1 mRNA was estimated by Northern blot analysis. Female mice, regardless of glycemic status, showed an obesity enhanced level of CYP2E1-dependent PNP-OH activity and CYP2E1 protein as shown by ELISA. These increases were observed to be independent of the diabetic state, since 7-8 month-old mice had blood glucose levels identical to lean mice. The mRNA level of CYP2E1 in female mice also exhibited age-and obesity-influenced decreases in expression. No significant differences in CYP2E1 activity or expression were observed in male mice. CYP3A-dependent ERY-DM activity was significantly higher in young males, regardless of phenotype. CYP3A and CYP2B activities did not differ among any animals; however, CYP1A activity, while depressed in obese animals of both genders, was significantly different in old animals. Glutathione S-transferase activity was lower in obese male mice, whereas no difference was observed between lean and obese females This study supports earlier observations in man and rats that the obese state produces alterations in the expression of important oxidation and conjugation pathways. In addition, this report more thoroughly examines the role of gender and glycemic status on biotransformation activities in the ob/ob mouse as demonstrated by increased CYP2E1 protein and CYP2E1-dependent activity in obese females, decreased CYP1A2 protein and CYP1A2-dependent activity in obese animals, and obesity had no effect of glutathione transferase in female mice, in contrast with the previously reported obesity-dependent decrease of this activity in male mice.
MeSH Terms
- Aging
- Animals
- Aryl Hydrocarbon Hydroxylases
- Biotransformation
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 CYP2E1
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Diabetes Mellitus
- Female
- Gene Expression Regulation, Enzymologic
- Glutathione Transferase
- Liver
- Male
- Mice
- Mice, Obese
- Obesity
- Oxidoreductases, N-Demethylating
- RNA, Messenger
We investigated the developmental changes in the pattern of urinary metabolites of theophylline, a substrate for CYP1A2, to study when CYP1A2, which is absent in the perinatal period, fully develops during childhood. The urinary ratios of three metabolites (1-methyluric acid, 3-methylxanthine, and 1,3-dimethyluric acid) to theophylline in patients over 3 y of age show a much larger interindividual variation compared with those under 3 y of age, and the mean values of the ratios in patients over 3 y of age were greater than those in patients under 1 y of age. The urinary ratio of 1,3-dimethyluric acid (a metabolite generated by several cytochrome P450s) to 3-methylxanthine or 1-methyluric acid (metabolites generated by CYP1A2 exclusively) seemed to be relatively constant over 3 y of age; in patients under 3 y of age, these ratios were much higher than those in patients over 3 y of age. The urinary ratio of 1-methyluric acid to 3-methylxanthine or 3-methylxanthine to 1-methyluric acid seemed to be relatively invariable in all patients except those less than 1 y of age. These findings suggest that CYP1A2 activity may be programmed to mature by around 3 y of age and that CYP1A2 probably plays a major role in theophylline 8-hydroxylation at a therapeutic concentration after the full development of CYP1A2 activity.
MeSH Terms
- Aging
- Apnea
- Asthma
- Child, Preschool
- Cytochrome P-450 CYP1A2
- Humans
- Infant
- Infant, Newborn
- Theophylline
- Uric Acid
- Xanthines
Very few studies have been carried out looking at how the effects of drugs and their toxicity in humans change during their lifespan (developing and ageing). The purpose of this study is to review the literature on the changes in probe-drug metabolism, classified by cytochrome P450 (P450 or CYP) at five stages in life: neonates < 4 weeks, infants < 12 months, children < 19 years, young/mature adults 20-64 years, and elderly adults > 65 years. The main probe drugs include caffeine and theophylline, whose metabolism is catalysed by CYP1A2, tolbutamide, phenytoin and ibuprofen, catalysed by CYP2C9, amitriptyline and nortriptyline, catalysed by CYP2C19, acetaminophen, catalysed by CYP2E1 and lidocaine, midazolam and terfenadine, catalysed by 3A3/4. From the published in vivo studies two different patterns of drug metabolism can be identified: (i) activity is low immediately after birth, increases, then peaks at the young/mature adult level and, finally, decreases in old age (drugs catalysed by CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A3/4) and (ii) activity increases rapidly after birth to reach a level equivalent to that in the young/mature adult, then gradually decreases and finally decreasing faster in old age (drugs catalysed by CYP2E1). Further study of the changes in P450 with age is warranted to help prevent adverse reactions and to guide us in tailoring therapy better for the individual patient.
MeSH Terms
- Aging
- Cytochrome P-450 Enzyme System
- Humans
- Isomerism
This article surveys the development of human hepatic P450 cytochromes (CYPs) involved in xenobiotic metabolism from the fetus through the life span and explores possible clinical consequences of developmental issues. These hepatic P450 CYPs come "on line" at different times during fetal and infant development, and each one is discussed in that temporal sequence. CYP3A7. the major fetal hepatic cytochrome, is present during organogenesis, and it is involved in steroid metabolism. Variably expressed in some fetuses, CYP3A5 is also present at significant levels in about half of all children. In adults, CYP3A4 is the major functional member of the CYP3A subfamily. CYP1A1 is also present during organogenesis, and it metabolizes exogenous toxins, some of which are procarcinogens. CYP2E1 may be present in some second-trimester fetuses, and it may be involved in prenatal alcohol metabolism. After birth, hepatic CYP2D6 and CYP2C8/9 and CYP2C18/19 become active. Both CYP2D6 and CYP2C19 have genetic polymorphisms that can bring about differing capacities to metabolize exogenous drugs, including psychotropic drugs. CYP1A2 becomes active in the fourth to fifth postfetal months. It provides the best current examples of the importance of developmental changes in xenobiotic-metabolizing P450 CYPs through its metabolism of caffeine and theophylline in premature infants, neonates, and adolescents.
MeSH Terms
- Aging
- Animals
- Cytochrome P-450 Enzyme System
- Female
- Fetus
- Humans
- Liver
- Pregnancy
- Xenobiotics
The ontogenesis of CYP1A proteins was investigated in a human liver bank composed of fetal, neonatal and adult samples. In immunoblots, a polyclonal antibody raised against rat CYP1A1, cross-reacted with cDNA-expressed human CYP1A1 and CYP1A2. In adult liver microsomes, this antibody reacted with a single band identified as the CYP1A2 protein, while no CYP1A1 could be detected. CYP1A2 protein was absent in microsomes prepared from fetal and neonatal livers and its levels increased in infants aged 1-3 months to attain 50% of the adult value at one year. Enzymatic activities supported by CYP1A proteins were assayed on these samples. Methoxyresorufin demethylase supported by the CYP1A2 recombinant protein followed the same ontogenic profile as the CYP1A2 protein. In liver microsomes, the demethylation of imipramine was essentially due to CYP1A2 and to a smaller extent to CYP3A. In fetuses and early neonates, CYP3A proteins were responsible for the low demethylation of imipramine (3-4% of the adult activity) before the onset of CYP1A2 and the subsequent rise of activity. Immunodetection and enzymatic activities were consistent with the absence of CYP1A1 and the late expression of CYP1A2 in the human liver, compared to the early rise of CYP3A4, CYP2C, CYP2D6, and CYP2E1 proteins.
MeSH Terms
- Adult
- Aging
- Animals
- COS Cells
- Cell Line
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 Enzyme System
- Fetus
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Enzymologic
- Humans
- Infant
- Infant, Newborn
- Liver
- Microsomes, Liver
- Rats
- Recombinant Proteins
- Substrate Specificity
- Transfection
We immunochemically measured the contents of 9 different cytochrome P450 (CYP) isoenzymes expressed in the liver and compared them between two groups: one group of 6 infant and 4 perinatal patients and one group of 10 patients after infancy (over 1 year old). CYP protein expressed in human liver can be divided into three groups on the basis of expression pattern: (a) CYP2A6, 2C9, 2D6, 2E1, and 3A were present in all samples and no difference was observed between the two groups; (b) CYP1A2, 2B6, and 2C8 were expressed more after infancy than during infancy; and (c) CYP3A7, which has been considered a major CYP enzyme in fetal liver microsomes, was expressed in all infants as well as the four perinatal patients, whereas it was detected in only 2 patients after infancy. These results implied that CYP2A6, 2C9, 2D6, 2E1, and 3A are already expressed during perinatal and infant period, while CYP1A2, 2B6, and 2C8 are expressed highly in subjects over 1 year old, and CYP3A7 disappeared after infancy.
MeSH Terms
- Adolescent
- Adult
- Aged
- Aging
- Blotting, Western
- Child
- Child, Preschool
- Cytochrome P-450 Enzyme System
- Female
- Fetus
- Gestational Age
- Humans
- Infant
- Infant, Newborn
- Isoenzymes
- Liver
- Male
- Middle Aged
The pharmacokinetics of brofaromine, a selective inhibitor of monoamine oxidase A, was evaluated in 12 frail elderly patients (66-92 y) and 12 healthy volunteers (20-35 y). Quantitative liver function tests were performed to show whether brofaromine elimination in the elderly could be predicted from noninvasive assessment of CYP1A2 activity (caffeine clearance) or liver plasma flow (sorbitol clearance). In the elderly the AUC of brofaromine was significantly increased (e.g. for the 75 mg dose 43.2 vs 19.9 mumol*h.l-1, clearance was reduced (5.0 vs. 11.8 l.h-1), the volume of distribution was smaller (130 vs. 230 l), and the half-life was slightly increased (19.0 vs. 14.2 h). No significant correlation was observed between hepatic plasma flow and brofaromine clearance (r = 0.41, P = 0.05), whereas CYP1A2 activity and brofaromine clearance were tightly correlated (r = 0.94, P < 0.0001). Caffeine clearance, a simple, noninvasive test of CYP1A2 activity, is predictive of brofaromine clearance.
MeSH Terms
- Administration, Oral
- Adult
- Aged
- Aged, 80 and over
- Aging
- Caffeine
- Chromatography, Gas
- Cross-Over Studies
- Cytochrome P-450 CYP1A2
- Female
- Frail Elderly
- Half-Life
- Humans
- Liver Function Tests
- Male
- Monoamine Oxidase Inhibitors
- Piperidines
- Regression Analysis
- Sorbitol
The homozygous recessive jaundiced Gunn rat lacks expression of bilirubin UDP-glucuronosyltransferase and serves as a model for Crigler-Najjar syndrome type I, in which high and toxic plasma levels of bilirubin result from this genetic defect in bilirubin conjugation. Both rats and humans dispose of this heme waste product by an alternate metabolic route that involves oxidation of the compound, followed by biliary excretion of the more polar metabolites. To determine the role of cytochrome P450 in this process, hepatic levels of cytochrome P450 mRNA and protein were measured in jaundiced and nonjaundiced Gunn rats as a function of age and sex. The mRNA and protein levels of cytochrome P450(CYP) 1A1 and CYP1A2 were markedly elevated in the jaundiced rats at the age of 10 days, compared with their nonjaundiced littermates. Levels of CYP2E1 mRNA and protein did not differ between these rats, indicating that the CYP1A P450 genes were specifically induced. CYP1A1 mRNA and protein levels increased further in the jaundiced animals between 10 days and 1 month of postnatal life but remained undetectable in the nonjaundiced littermates. On the other hand, CYP1A2 mRNA and protein content increased during this time period in both jaundiced and nonjaundiced rats, but at the age of 1 month there were no major differences between the two groups. CYP1A2 mRNA and protein levels were indistinguishable in 3-month-old jaundiced and nonjaundiced Gunn rats, whereas CYP1A1 could not be detected in either group. These data suggest that young jaundiced Gunn rats cope with the degradation of toxic bilirubin by increasing hepatic levels of CYP1A1 and CYP1A2. On the other hand, normal developmental activation of CYP1A2 may provide the alternative pathway for bilirubin degradation in adult animals. This is the first demonstration of the induction of cytochrome P450 gene expression to permit the elimination of an endogenously generated neurotoxic chemical in a genetic disease in which the normal excretory mechanism is impaired.
MeSH Terms
- Aging
- Animals
- Crigler-Najjar Syndrome
- Cytochrome P-450 Enzyme System
- Disease Models, Animal
- Female
- Gene Expression Regulation, Enzymologic
- Male
- Microsomes, Liver
- RNA, Messenger
- Rats
- Rats, Gunn
Aggregating fetal liver cell cultures were tested for their ability to metabolize xenobiotics using ethoxycoumarin-O-deethylase (ECOD), as marker of phase I metabolism, and glutathione S-transferase (GST), as marker for phase II reactions. Significant basal activities, stable over 14 days in culture were measured for both ECOD and GST activities. The prototype cytochrome P450 inducers, 3-methylcholanthrene (3-MC) and phenobarbital (PB), increased ECOD and GST activities reaching an optimum 7 days after culturing, followed by a decline in activity. This decline was partially prevented by 1% dimethyl sulfoxide (DMSO) added chronically to the culture medium. DMSO was also found to induce ECOD activity and to a lesser extent GST activity. Furthermore, it potentiated in a dose-dependent manner the induction of ECOD by PB. The food-borne carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is metabolically transformed through a number of pathways in vivo. It was therefore used to examine the metabolic capacity in fetal and adult liver cell aggregates. Metabolism of MeIQx was mainly through N2-conjugation, resulting in formation of the N2-glucuronide and sulfamate conjugates for non-induced fetal liver cells. These metabolites were also found in large amounts in non-induced adult liver cells. Low levels of cytochrome P450-mediated ring-hydroxylated metabolites were detected in both non-induced fetal and adult liver cells. After induction with arochlor (PCB) or 3-MC, the major pathway was ring-hydroxylation (cytochrome P450 dependent), followed by conjugation to beta-glucuronic or sulfuric acid. The presence of the glucuronide conjugate of N-hydroxy-MeIQx, a mutagenic metabolite, suggested an induction of P450 CYP1A2. The metabolism of MeIQx by liver cell aggregates is very similar to that observed in vivo and suggests that aggregating liver cell cultures are a useful model for in vitro metabolic studies in toxicology.
MeSH Terms
- 7-Alkoxycoumarin O-Dealkylase
- Aging
- Animals
- Cells, Cultured
- Dimethyl Sulfoxide
- Drug Synergism
- Enzyme Induction
- Glutathione Transferase
- Liver
- Methylcholanthrene
- Phenobarbital
- Quinoxalines
- Rats
- Xenobiotics
We investigated the expression, distribution, and inducibility of 3-methylcholanthrene (MC)-inducible P450 enzymes, CYP1A1 and 1A2, in livers of rabbits at different stages of development, ranging from 4 days before birth (-4 days of age) to adulthood. These enzymes were identified by immunoblotting and immunocytochemistry and quantified by dot-blotting, utilizing previously characterized monoclonal antibodies, 107 and 3/4/2, specific for CYP1A2 and both CYP1A1 and 1A2, respectively, and a polyclonal antibody that recognizes both enzymes. Expression of CYP1A2 is always greater than that of CYP1A1 in livers of untreated rabbits, regardless of age. Moreover, immunocytochemistry showed that CYP1A1 is evenly distributed throughout the liver at all ages, whereas CYP1A2 is highly localized to only a few scattered cells at 1 day before birth. More hepatocytes express this enzyme perinatally. By 6 days of age, expression of CYP1A2 is confined to a narrow band of centrilobular cells, but with increasing age the enzyme is expressed in more hepatocytes until weaning, when all hepatocytes are positive. Although CYP1A1 is induced by MC treatment at most ages, there is no change in its distribution. In contrast, induction of CYP1A2 was shown immunocytochemically to occur in only a limited number of hepatocytes in fetal rabbits. There is a progressive increase with age in the number of hepatocytes that are inducible for CYP1A2. The greatest fold-induction of hepatic CYP1A2 by MC in the rabbit is a 9-11 days of age, when, for MC-treated rabbits, CYP1A2 represents > 60% of the total P450 pool. The modulation of enzyme expression caused by MC treatment of fetuses/neonates leads to developmentally advanced livers with respect to P450 and could have a significant impact on the fetal and neonatal toxicity of some foreign compounds. These data demonstrate, for the first time, that the ontogenetic expression and localization of CYP1A1 and 1A2 within the liver are differentially regulated at the level of the individual cell.
MeSH Terms
- Aging
- Animals
- Blotting, Western
- Cytochrome P-450 Enzyme System
- Enzyme Induction
- Female
- Isoenzymes
- Liver
- Male
- Methylcholanthrene
- Microsomes, Liver
- Rabbits
1. Caffeine metabolism was studied in human liver microsomes from foetuses (n = 10), neonates (n = 10), infants (n = 9) and adults (n = 5). Caffeine and its metabolites, 1-3-7-trimethyluric acid, paraxanthine, theophylline and theobromine, were assayed by h.p.l.c. Methoxyresorufin-O-demethylase activity (MEROD) was determined and immunoquantifiable levels of CYP1A2 were measured. 2. The formation of the dimethylxanthines by N-3, N-7 or N-1-demethylation was significantly less in foetuses, neonates and infants than in adults, as shown previously in vivo. The formation of 1-3-7-trimethyluric acid (C-8-hydroxylation) was not significantly different between age groups. The production of total dimethylxanthines, paraxanthine and theophylline increased significantly with age within the neonate-infant group over at least the 0-300 day range (rs = 0.739, 0.667, 0.682, respectively). These data differ from those reported in vivo which suggested that N-3 and N-7-demethylations matured at about 120 days. The difference in maturational profiles of each metabolic pathway suggests that the reactions depend on different isoenzymes. The delay in the maturation of N-1 compared with N-3 and N-7-demethylation is in agreement with previous in vivo data. 3. In the neonate-infant group, only N-3-demethylation correlated with both MEROD activity (rs = 0.681; P < 0.05) and CYP1A2 microsomal concentration (rs = 0.454; P approximately 0.05), suggesting that, as in adults, this reaction depends on CYP1A2. 4. In the foetal samples, the production of total dimethylxanthines, paraxanthine and theobromine decreased significantly (rs = -0.879, -0.767, -0.708, respectively) with increasing gestational age.(ABSTRACT TRUNCATED AT 250 WORDS)
MeSH Terms
- Adult
- Aging
- Biotransformation
- Caffeine
- Chromatography, High Pressure Liquid
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 Enzyme System
- Female
- Fetus
- Gestational Age
- Humans
- Infant
- Infant, Newborn
- Male
- Microsomes, Liver
- Oxidoreductases
The metabolic activation of food-borne heterocyclic amines to colon carcinogens in humans is hypothesized to occur via N-oxidation followed by O-acetylation to form the N-acetoxy arylamine that binds to DNA to give carcinogen-DNA adducts. These steps are catalyzed by hepatic cytochrome P4501A2 (CYP1A2) and acetyltransferase-2 (NAT-2), respectively, which are known to be polymorphic in humans. On the basis of this proposed metabolic activation pathway, patients at greatest risk to develop colorectal cancer or nonfamilial polyps should be those who possess both the rapid NAT-2 and rapid CYP1A2 phenotypes and are exposed to high dietary levels of carcinogenic heterocyclic amines. Using a method that involves caffeine administration and high pressure liquid chromatographic analysis of urinary metabolites, we have determined the CYP1A2 and NAT-2 phenotypes of 205 controls and 75 cancer/polyp cases. Exposure information was obtained using a dietary and health habits questionnaire. Both the rapid CYP1A2 and rapid NAT2 phenotypes were each slightly more prevalent in cases versus controls (57% and 52% versus 41% and 45%, respectively). However, the combined rapid CYP1A2-rapid NAT-2 phenotype was found in 35% of cases and only 16% of the controls, giving an odds ratio of 2.79 (P = 0.002). Univariate analysis of the questionnaire indicated that age, rapid-rapid phenotype, and consumption of well done red meat were associated with increased risk of colorectal neoplasia. Furthermore, a logistic regression model that included age (as a continuous variable), consumption of well done red meat, and rapid-rapid phenotype as independent covariates gave odds ratios of 1.08, 2.08, and 2.91, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
MeSH Terms
- Acetyltransferases
- Adult
- Aged
- Aging
- Biotransformation
- Colonic Polyps
- Colorectal Neoplasms
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 Enzyme System
- Feeding Behavior
- Female
- Heterocyclic Compounds
- Humans
- Male
- Middle Aged
- Oxidoreductases
- Risk Factors
- Smoking
Developmental expression of CYP1A1, CYP1A2 and CYP3A6 in the rabbit have been studied. Cytochromes P450IA1, P450IA2 and P450IIIA6 exhibited comparable patterns of developmental expression. Present at low level (less than 0.05 nmol/mg) in the new born animal up to week 3, these proteins sharply accumulated between weeks 3 and 4 to reach a maximum by week 4 (P450IA1, 0.2 nmol/mg; P450IA2, 0.8 nmol/mg; P450IIIA6, 0.12 nmol/mg) and decreased in the adult (P450IA1, 0.2 nmol/mg; P450IA2, 0.4 nmol/mg; P450IIIA6, 0.09 nmol/mg). Cytochromes P450IA1 and P450IA2 were not expressed in the untreated fetus. Onset of CYP3A6 gene expression occurred at day 30 of gestation and both transcription and mRNA accumulation were transplacentally inducible by rifampicin only shortly before birth, i.e. after treatment of the females between days 28 and 30 of gestation. Both long (1.85 kb) and short (1.7 kb) mRNA transcripts were expressed in untreated or rifampicin-treated fetuses. CYP3A6 gene expression was also induced by rifampicin in 1-week-old and 2-week-old animals. Developmental expression of CYP1A1 and CYP1A2 genes was shown to be closely related to the diet change accompanying weaning which occurs at weeks 3-4. In animals subjected to either delayed (week 6) or early (week 2) weaning, sharp accumulation of messages, proteins and related activities were delayed or anticipated accordingly with respect to normal weaning. Artificially scheduled weaning gave similar results when repeated with biological-grade lucern (grown in the absence of chemical fertilizers, pesticides, etc.), the main constituent of commercial rabbit chow. While CYP3A6 gene expression could be brought forward by early weaning at week 2, both message and protein did not exhibit increased accumulation after delayed weaning at week 6, and remained at the low level of the new born animal. Treatment of 1-week-old and 2-week-old animals with triiodothyronine or of 3-week-old animals with propylthiouracil, an antithyroid factor, did not modify the normal pattern of developmental expression of genes CYP1A1, CYP1A2 and CYP3A6. It is concluded that (a) the onset of CYP3A6 gene expression in the fetus occurs at day 30 of gestation, (b) expression of this gene may be induced transplacentally by rifampicin, (c) CYP1A1, CYP1A2 and CYP3A6 gene expression is sharply activated at weaning, and (d) thyroid hormones appear not to be responsible for the pattern of developmental expression of these genes in the rabbit.
MeSH Terms
- Aging
- Animals
- Animals, Newborn
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 Enzyme System
- Enzyme Induction
- Female
- Gene Expression Regulation, Enzymologic
- Gestational Age
- Liver
- Maternal-Fetal Exchange
- Microsomes, Liver
- Oxidoreductases
- Pregnancy
- RNA, Messenger
- Rabbits
- Rifampin
- Transcription, Genetic
- Weaning
In adult rabbits, the CYP1A1 and CYP1A2 genes are expressed constitutively. Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads to elevations in both CYP1A1 and CYP1A2 gene products (S. T. Okino et al., 1985, Proc. Natl. Acad. Sci. USA 82, 5310-5314). In this report, we have characterized the rabbit CYP1A1 and CYP1A2 genes, and analyzed the pattern of expression of these genes in neonatal animals following exposure to TCDD. Genomic clones encoding the entire rabbit CYP1A1 and CYP1A2 genes were characterized. Restriction enzyme analysis and partial DNA sequence analysis identified the seven exons for the CYP1A1 and CYP1A2 genes. Primer extension analysis using mRNA from TCDD-treated neonatal rabbits helped confirm the start of transcription for the CYP1A genes. The length of the noncoding first exon of the CYP1A1 gene was 74 bases, compared to 90 and 88 bases for the human and rodent CYP1A1 genes. The length of the noncoding CYP1A2 gene first exon was 53 bases, similar to its counterpart in human and rodents. DNA sequence analysis of the 5' regulatory regions and comparison to the rodent and human CYP1 genes demonstrated that the rabbit CYP1A1 and CYP1A2 genes were most similar to their human orthologs. The 5' region of the CYP1A1 gene contained several consensus dioxin (Ah)-receptor responsive elements (XREs), while no functional XRE sequences were identified in the CYP1A2 gene. When expression of the two genes were monitored, a small amount of constitutive P4501A1 mRNA was detected in neonatal rabbits from the ages of 1 to 17 days, while P4501A2 mRNA levels could not be observed until 8-12 days postpartum. In response to TCDD treatment, P4501A1 mRNA levels were inducible at all neonatal time points, while P4501A2 mRNA levels could not be induced until the animals were 3-5 days postpartum. While the dioxin Ah-receptor most likely plays a major role in the induction of these genes by TCDD, early expression of the CYP1A1 and CYP1A2 genes is differentially regulated in a developmental fashion.
MeSH Terms
- Aging
- Animals
- Base Sequence
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 Enzyme System
- DNA
- Enzyme Induction
- Exons
- Gene Expression Regulation, Enzymologic
- Humans
- Liver
- Molecular Sequence Data
- Oligodeoxyribonucleotides
- Oxidoreductases
- Polychlorinated Dibenzodioxins
- RNA, Messenger
- Rabbits
- Restriction Mapping
- Sequence Homology, Nucleic Acid
- Software
- Transcription, Genetic
The urinary molar concentration ratios of several caffeine metabolites are indicators of specific drug metabolizing enzyme activities. The ratios of 5-acetyl-amino-6-formylamino-3-methyluracil (AFMU) to 1-methylxanthine (1X), AFMU to 1X plus 1-methyluric acid (1U), and AFMU to 1X 1U AFMU are indicative of N-acetyltransferase (NAT) activity; the ratios of 1U to 1X and 1U to 1U 1X indicate xanthine oxidase activity; and the ratio of the sum of 7-demethylated metabolites (AFMU 1X 1U) to the precursor for all three compounds, paraxanthine (PX), is a putative indicator of CYP1A2 oxidative activity. Our objective was to discern whether there are race-, gender-, and age-related differences in these indexes of drug-metabolizing activity. In 342 normal healthy unrelated subjects, metabolites were measured in urine collected after administration of low-dose caffeine. By two-way analysis of variance, NAT activity was higher in black subjects than in white subjects when assessed as AFMU/(1U 1X) or as AFMU/(AFMU 1U 1X) (p = 0.001 and p = 0.002, respectively), but less so by use of AFMU/1X (p = 0.08). Xanthine oxidase activity, as assessed by 1U/1X or as 1U/(1U 1X), was lower in black subjects than in white subjects (p = 0.02 and p = 0.001, respectively) and was lower in males than in females (p = 0.001 for both ratios). Females had higher AFMU/1X ratios (p = 0.03) because of higher xanthine oxidase activity. In a model in which AFMU/1X was the dependent variable and race, sex, age, and an index of xanthine oxidase (1U/1X) were independent variables, only race and 1U/1X were significant determinants of this NAT index (p = 0.003 and p < 0.001, respectively). The CYP1A2 ratio was lower in black subjects (p = 0.036) and in females (p = 0.015). Racial and gender differences in xanthine oxidase activity render the AFMU/1X ratio less reliable as an assessment of NAT activity in a heterogeneous population compared with the AFMU/(1U 1X) or AFMU/(AFMU 1U 1X) ratios. The observed racial and gender differences in NAT, xanthine oxidase, and CYP1A2 activities may have implications for racial and gender differences in drug effects and carcinogen biotransformation.
MeSH Terms
- Adolescent
- Adult
- Aging
- Analysis of Variance
- Arylamine N-Acetyltransferase
- Caffeine
- Child
- Child, Preschool
- Continental Population Groups
- Cytochrome P-450 CYP1A2
- Cytochrome P-450 Enzyme System
- Female
- Humans
- Male
- Middle Aged
- Oxidoreductases
- Reference Values
- Sex Characteristics
- Xanthine Oxidase