CYP3A4
Cytochrome P450 3A4 (EC 1.14.14.1) (1,4-cineole 2-exo-monooxygenase) (1,8-cineole 2-exo-monooxygenase) (EC 1.14.14.56) (Albendazole monooxygenase (sulfoxide-forming)) (EC 1.14.14.73) (Albendazole sulfoxidase) (CYPIIIA3) (CYPIIIA4) (Cholesterol 25-hydroxylase) (Cytochrome P450 3A3) (Cytochrome P450 HLp) (Cytochrome P450 NF-25) (Cytochrome P450-PCN1) (Nifedipine oxidase) (Quinine 3-monooxygenase) (EC 1.14.14.55) [CYP3A3]
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We previously verified a physiologically based pharmacokinetic (PBPK) model for mirabegron in healthy subjects using the Simcyp Simulator by incorporating data on the inhibitory effect on cytochrome P450 (CYP) 2D6 and a multi-elimination pathway mediated by CYP3A4, uridine 5'-diphosphate-glucuronosyltransferase (UGT) 2B7 and butyrylcholinesterase (BChE). The aim of this study was to use this PBPK model to assess the magnitude of drug-drug interactions (DDIs) in an elderly population with severe renal impairment (sRI), which has not been evaluated in clinical trials. We first determined the system parameters, and meta-analyses of literature data suggested that the abundance of UGT2B7 and the BChE activity in an elderly population with sRI was almost equivalent to and 20% lower than that in healthy young subjects, respectively. Other parameters, such as the CYP3A4 abundance, for an sRI population were used according to those built into the Simcyp Simulator. Second, we confirmed that the PBPK model reproduced the plasma concentration-time profile for mirabegron in an sRI population (simulated area under the plasma concentration-time curve (AUC) was within 1.5-times that of the observed value). Finally, we applied the PBPK model to simulate DDIs in an sRI population. The PBPK model predicted that the AUC for mirabegron with itraconazole (a CYP3A4 inhibitor) was 4.12-times that in healthy elderly subjects administered mirabegron alone, and predicted that the proportional change in AUC for desipramine (a CYP2D6 substrate) with mirabegron was greater than that in healthy subjects. In conclusion, the PBPK model was verified for the purpose of DDI assessment in an elderly population with sRI.
MeSH Terms
- Acetanilides
- Adolescent
- Adrenergic beta-3 Receptor Agonists
- Adult
- Aged
- Aging
- Butyrylcholinesterase
- Cytochrome P-450 CYP2D6 Inhibitors
- Cytochrome P-450 CYP3A
- Cytochrome P-450 CYP3A Inhibitors
- Desipramine
- Drug Interactions
- Female
- Gemfibrozil
- Glucuronosyltransferase
- Humans
- Itraconazole
- Lorazepam
- Male
- Middle Aged
- Models, Biological
- Renal Insufficiency
- Thiazoles
- Young Adult
- Zidovudine
Keywords drug-drug mirabegron, physiologically-based pharmacokinetic model, renal impairment, the Simcyp Simulator
The interindividual variability of cyclosporin A (CsA) pharmacokinetics might be explained by heterogeneity in the cytochrome P450 3A (CYP3A) subfamily. Altered CYP3A enzyme activity was associated with variant allele of P450 oxidoreductase gene (POR*28). The aim of this study was to assess the impact of age, CYP3A5*3, CYP3A4*22, and POR*28 alleles on CsA pharmacokinetics in pediatric renal transplant recipients. Renal transplant patients receiving CsA (n = 47) were genotyped for CYP3A5*3, CYP3A4*22, and POR*28. CYP3A5 nonexpressers had higher overall dose-adjusted predose concentration (C0/dose; ng/mL per mg/kg) compared with expressers (31.48 ± 12.75 versus 22.44 ± 7.12, P = 0.01). CYP3A5 nonexpressers carrying POR*28 allele had a lower overall dose-adjusted concentration (C2/dose) than those with POR*1/*1 genotype (165.54 ± 70.40 versus 210.55 ± 79.98, P = 0.02), with age as covariate. Children aged 6 years and younger had a lower overall C0/dose (18.82 ± 4.72 versus 34.19 ± 11.89, P = 0.001) and C2/dose (106.75 ± 26.99 versus 209.20 ± 71.57, P < 0.001) compared with older children. Carriers of CYP3A5*3 allele aged ≤6 years required higher dose of CsA and achieved lower C0/dose and C2/dose, at most time points, than older carriers of this allele. Carriers of POR*28 allele aged ≤6 years required higher doses of CsA, whereas they achieved lower C0/dose and C2/dose, at most time points, in comparison to older carriers of this allele. The significant effect of age (P < 0.002) and CYP3A5 variation (P < 0.02) was shown for overall C0/dose, whereas age (P < 0.00001) and POR variation (P = 0.05) showed significant effect on C2/dose. Regression summary for overall C2/dose in patients aged 6 years younger showed a significant effect of both CYP3A5 and POR variations (P < 0.016). Younger age, POR*28 allele, and CYP3A5*3 allele were associated with higher CsA dosing requirements and lower concentration/dose ratio. Pretransplant screening of relevant polymorphisms in accordance with age should be considered to adjust therapy.
MeSH Terms
- Adolescent
- Aging
- Alleles
- Child
- Cyclosporine
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Female
- Gene Expression Regulation
- Genetic Variation
- Humans
- Immunosuppressive Agents
- Kidney Transplantation
- Male
- Serbia
- Transplant Recipients
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
Sex and age differences in hepatic expression of drug-metabolizing enzyme genes could cause variations in drug metabolism, but has not been fully elucidated, especially in Asian population. In this study, the global expression of human hepatic genes was analyzed by microarrays in 40 Japanese subjects (27 males and 13 females). Thirty-five sex-biased genes were identified (P < 0.005). Whereas, 60 age-biased genes in two age groups, <60 years and ≥70 years (P < 0.001), were identified in males. By Gene Ontology analysis, the sex-biased genes were related to protein catabolism and modification, while the age-biased genes were related to transcription regulation and cell death. Quantitative polymerase chain reaction confirmed the female-biased expression of drug-metabolizing enzyme genes BChE, CYP4X1, and SULT1E1 (≥1.5-fold, P < 0.05). Further analysis of drug-metabolizing enzyme genes indicated that expression of CYP2A6 and CYP3A4 in females in the ≥70 age group was less than in the <60 age group (≥1.5-fold, P < 0.05), and this trend was also observed for PXR expression in males (≥1.5-fold, P < 0.05). The results presented provide important insights into hepatic physiology and function, especially drug metabolism, with respect to sex and age.
MeSH Terms
- Aged
- Aging
- Butyrylcholinesterase
- Cytochrome P-450 Enzyme System
- Female
- Gene Expression Profiling
- Gene Expression Regulation, Enzymologic
- Humans
- Liver
- Male
- Middle Aged
- Oligonucleotide Array Sequence Analysis
- Pharmaceutical Preparations
- Pregnane X Receptor
- Receptors, Steroid
- Sex Characteristics
- Sulfotransferases
Keywords
- Age
- Cytochrome P450
- Drug metabolism
- Gene expression
- Liver
- Sex
Members of the human CYP3A family of metabolizing enzymes exhibit developmental changes in expression whereby CYP3A7 is expressed in fetal tissues, followed by a transition to expression of CYP3A4 in the first months of life. Despite knowledge about the general pattern of CYP3A activity in human development, the mechanisms that regulate developmental expression remain poorly understood. Epigenetic changes, including cytosine methylation, have been suggested to play a role in the regulation of CYP3A expression. The objective of this study was to investigate changes in cytosine methylation of the CYP3A4 and CYP3A7 genes in human pediatric and prenatal livers. The methylation status of cytosine-phospho-guanine dinucleotides was determined in 16 pediatric liver samples using methyl-seq and confirmed by bisulfite sequencing of 48 pediatric and 34 prenatal liver samples. Samples were separated by age into five groups (prenatal, < 1 year of age, 1.8-6 years, 7-11 years, and 12-17 years). Methyl-seq anaylsis revealed that cytosines in the proximal promoter of CYP3A7 are hypomethylated in neonates compared with adolescents (P < 0.001). In contrast, a cytosine 383 base pair upstream of CYP3A4 is hypermethylated in liver samples from neonates compared with adolescents (P = 0.00001). Developmental changes in methylation of cytosines in the proximal promoters of CYP3A4 and CYP3A7 in pediatric livers were confirmed by bisulfite sequencing. In addition, the methylation status of cytosine in the CYP3A4 and CYP3A7 proximal promoters correlated with changes in developmental expression of mRNA for the two enzymes.
MeSH Terms
- Adolescent
- Age Factors
- Aging
- Child
- Child, Preschool
- Cytochrome P-450 CYP3A
- Cytosine
- DNA Methylation
- Epigenesis, Genetic
- Female
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Enzymologic
- Gestational Age
- Humans
- Infant
- Infant, Newborn
- Liver
- Male
- Promoter Regions, Genetic
- RNA, Messenger
The activity of several key enzymes involved in the metabolism of many drugs is subject to change closely related to the age of patients. This possibility must also be considered in the case of tacrolimus, the most important calcineurins inhibitor, which is widely used in pediatric kidney transplantation. As well as in the liver and intestine, some of the enzymes involved in the metabolism of tacrolimus were also isolated in the peripheral blood mononuclear cells (PBMCs), where also appear to play an important regulatory action. Therefore, the influence of some external factors on the expression of specific mRNA can be determined noninvasively. The correlation between the levels of mRNA specific for key enzymes SXR, CYP3A and ABCB1 involved in the metabolism of tacrolimus was evaluated in PBMCs obtained from a selected population of 29 young kidney transplant recipients. A possible correlation between the expression of these specific mRNAs and tacrolimus pharmacokinetics was also investigated. The patients' age and their blood concentrations of SXR mRNA were directly correlated with the expression of CYP3A4, CYP3A5 mRNAs, but not of ABCB1 mRNA in the PBMCs. tacrolimus-normalized daily dose was strongly correlated with patient's age and multivariable regression indicates the CYP3A4-specific mRNA as the sole independent variable influencing tacrolimus concentration-to-dose ratio. Aging and SXR mRNA significantly affect the expression of CYP3A4- and CYP3A5-specific mRNA as measured by their concentration in PBMC.
MeSH Terms
- ATP Binding Cassette Transporter, Subfamily B
- Adolescent
- Aging
- Cytochrome P-450 CYP3A
- Female
- Humans
- Immunosuppressive Agents
- Kidney Transplantation
- Male
- Monocytes
- Pregnane X Receptor
- RNA, Messenger
- Receptors, Steroid
- Tacrolimus
Keywords
- ABCB1
- CYP3A4
- CYP3A5
- SXR
- mRNA
- pediatric kidney transplant
- peripheral blood mononuclear cells
- tacrolimus
In view of paediatric drug development, regulatory authorities often request safety studies in juvenile animals, including minipigs. Unfortunately, knowledge on the ontogeny of the biotransformation processes in animal models remains scarce and impedes a correct interpretation of the toxicity findings. CYP3A4 is one of the most important drug-metabolizing enzymes in human beings and shows important similarities with CYP3A in the minipig. Therefore, the aim of this study was to assess the abundance and activity of CYP3A in liver microsomes from foetal, juvenile (days 1, 3, 7 and 28) and adult male and female Göttingen minipigs. CYP3A abundance was studied by an indirect enzyme-linked immunosorbent assay (ELISA), whereas CYP3A activity was assessed by a biotransformation assay with Luciferin-IPA. CYP3A abundance could not be detected until day 3. From day 7 onwards, a gradual increase in expression was noted, leading to the highest abundance in adult animals. CYP3A activity was not detectable in foetuses and 1-day-old animals. The CYP3A activity was detectable, but below the LLOQ in day 3 animals and increased gradually with age to reach the highest level in adults. The CYP3cide and ketoconazole inhibition, and testosterone and midazolam reduction of Luciferin-IPA metabolism in minipig liver microsomes substantiate that Luciferin-IPA is metabolized by CYP3A in minipigs. A positive correlation was found between CYP3A abundance and biotransformation of Luciferin-IPA (Pearson r = 0.863; p < 0.0001). In conclusion, both abundance and activity of CYP3A increased gradually in juvenile minipigs, but remained below the levels observed in adult animals.
MeSH Terms
- Age Factors
- Aging
- Animals
- Biotransformation
- Cytochrome P-450 CYP3A
- Enzyme-Linked Immunosorbent Assay
- Female
- Firefly Luciferin
- Kinetics
- Liver
- Male
- Microsomes, Liver
- Substrate Specificity
- Swine
- Swine, Miniature
Although both POPPK and physiologically based pharmacokinetic (PBPK) models can account for age and other covariates within a paediatric population, they generally do not account for real-time growth and maturation of the individuals through the time course of drug exposure; this may be significant in prolonged neonatal studies. The major objective of this study was to introduce age progression into a paediatric PBPK model, to allow for continuous updating of anatomical, physiological and biological processes in each individual subject over time. The Simcyp paediatric PBPK model simulator system parameters were reanalysed to assess the impact of re-defining the individual over the study period. A schedule for re-defining parameters within the Simcyp paediatric simulator, for each subject, over a prolonged study period, was devised to allow seamless prediction of pharmacokinetics (PK). The model was applied to predict concentration-time data from multiday studies on sildenafil and phenytoin performed in neonates. Among PBPK system parameters, CYP3A4 abundance was one of the fastest changing covariates and a 1-h re-sampling schedule was needed for babies below age 3.5 days in order to seamlessly predict PK (<5% change in abundance) with subject maturation. The re-sampling frequency decreased as age increased, reaching biweekly by 6 months of age. The PK of both sildenafil and phenytoin were predicted better at the end of a prolonged study period using the time varying vs fixed PBPK models. Paediatric PBPK models which account for time-varying system parameters during prolonged studies may provide more mechanistic PK predictions in neonates and infants.
MeSH Terms
- Aging
- Anticonvulsants
- Bronchodilator Agents
- Child
- Child, Preschool
- Clinical Trials as Topic
- Humans
- Infant
- Infant, Newborn
- Models, Biological
- Pediatrics
- Pharmaceutical Preparations
- Pharmacokinetics
- Phenytoin
- Piperazines
- Purines
- Reproducibility of Results
- Sildenafil Citrate
- Sulfones
- Theophylline
- Vasodilator Agents
First-dose-in-children relies on the prediction of clearance from adults for which little information is available on the accuracy of the scaling-approaches applied. For CYP3A-metabolized compounds, scaling of clearance is further challenged by different isoforms and by the CYP3A7 to CYP3A4 switch at young ages. This investigation aimed to evaluate the accuracy of two frequently used scaling approaches and to gain insights into the ontogeny of CYP3A. Hence, a literature database was compiled containing 203 clearance values from term-neonates to adults for 18 CYP3A-metabolized compounds. The clearances in adults were scaled to children using (i) allometric scaling plus maturation function and (ii) a mechanistic approach based on the well-stirred model. Three maturation functions were separately evaluated. In children >3 months, all approaches were interchangeable heeding the maturation function applied and biases were mostly observed in children <3 months. The results from a sensitivity analysis indicate that these biases are possibly caused by disregarding the CYP3A7 activity which could account for up to 86% of the metabolism in term-neonates. Only the mechanistic approach using an overall-CYP3A maturation function led to unbiased predictions of clearances across all ages. The current investigation adds to the predictions of the first-dose-in-children of compounds (partially) metabolized by CYP3A.
MeSH Terms
- Adolescent
- Adult
- Aging
- Algorithms
- Body Weight
- Child
- Child, Preschool
- Cytochrome P-450 CYP3A
- Hepatic Artery
- Humans
- Infant
- Infant, Newborn
- Liver
- Models, Biological
- Pharmaceutical Preparations
- Pharmacokinetics
- Portal Vein
- Regional Blood Flow
Keywords
- bridging
- children
- extrapolation
- pediatrics
- scaling
The magnitude of any metabolic drug-drug interactions (DDIs) depends on fractional importance of inhibited pathway which may not necessarily be the same in young children when compared to adults. The ontogeny pattern of cytochrome P450 (CYP) enzymes (CYPs 1A2, 2B6, 2C8, 2C9, 2C18/19, 2D6, 2E1, 3A4) and renal function were analyzed systematically. Bootstrap methodology was used to account for variability, and to define the age range over which statistical differences existed between each pair of specific pathways. A number of DDIs were simulated (Simcyp Pediatric v12) for virtual compounds to highlight effects of age on fractional elimination and consequent magnitude of DDI. For a theoretical drug metabolized 50% by each of CYP2D6 and CYP3A4 pathways at birth, co-administration of ketoconazole (3 mg/kg) resulted in a 1.65-fold difference between inhibited versus uninhibited AUC compared to 2.4-fold in 1 year olds and 3.2-fold in adults. Conversely, neonates could be more sensitive to DDI than adults in certain scenarios. Thus, extrapolation from adult data may not be applicable across all pediatric age groups. The use of pediatric physiologically based pharmacokinetic (p-PBPK) models may offer an interim solution to uncovering potential periods of vulnerability to DDI where there are no existing clinical data derived from children.
MeSH Terms
- Aging
- Cytochrome P-450 Enzyme System
- Drug Interactions
- Humans
- Liver
- Models, Biological
- Pharmaceutical Preparations
Keywords
- drug-drug interaction
- ontogeny
- pediatric
With the aging population and its rapidly increasing prevalence, dementia has become an important public health concern in developed and developing countries. To date, the pharmacological treatment is symptomatic and based on the observed neurotransmitter disturbances. The four most commonly used drugs are donepezil, galantamine, rivastigmine and memantine. Donepezil, galantamine and rivastigmine are acetylcholinesterase inhibitors with different pharmacodynamic and pharmacokinetic profiles. Donepezil inhibits selectively the acetylcholinesterase and has a long elimination half-life (t(1/2)) of 70 h. Galantamine is also a selective acetylcholinesterase inhibitor, but also modulates presynaptic nicotinic receptors. It has a t(1/2) of 6-8 h. Donepezil and galantamine are mainly metabolised by cytochrome P450 (CYP) 2D6 and CYP3A4 in the liver. Rivastigmine is a so-called 'pseudo-irreversible' inhibitor of acetylcholinesterase and butyrylcholinesterase. The t(1/2) of the drug is very short (1-2 h), but the duration of action is longer as the enzymes are blocked for around 8.5 and 3.5 h, respectively. Rivastigmine is metabolised by esterases in liver and intestine. Memantine is a non-competitive low-affinity antagonist of the NMDA receptor with a t(1/2) of 70 h. Its major route of elimination is unchanged via the kidneys. Addressing the issue of inter-patient variability in treatment response might be of special importance for the vulnerable population taking anti-dementia drugs. Pharmacogenetic considerations might help to avoid multiple medication changes due to non-response and/or adverse events. Some pharmacogenetic studies conducted on donepezil and galantamine reported an influence of the CYP2D6 genotype on the pharmacokinetics of the drugs and/or on the response to treatment. Moreover, polymorphisms in genes of the cholinergic markers acetylcholinesterase, butyrylcholinesterase, choline acetyltransferase and paraoxonase were found to be associated with better clinical response to acetylcholinesterase inhibitors. However, confirmation studies in larger populations are necessary to establish evidence of which subgroups of patients will most likely benefit from anti-dementia drugs. The aim of this review is to summarize the pharmacodynamics and pharmacokinetics of the four commonly used anti-dementia drugs and to give an overview on the current knowledge of pharmacogenetics in this field.
MeSH Terms
- Aging
- Alzheimer Disease
- Cholinesterase Inhibitors
- Donepezil
- Excitatory Amino Acid Antagonists
- Galantamine
- Humans
- Indans
- Memantine
- Pharmacogenetics
- Phenylcarbamates
- Piperidines
- Receptors, N-Methyl-D-Aspartate
- Rivastigmine
Stiripentol is a third generation antiepileptic, marketed since 2007 under the name of Diacomit(®). It is indicated, always in combination, in the treatment of severe myoclonic epilepsy in infancy or Dravet syndrome. Its pharmacokinetics is not linear. It is a potent inhibitor of CYP3A4, 1A2 and 2C19 and increases the plasma concentrations of many other antiepileptic drugs. Without this being considered as a validated therapeutic range, the trough plasma concentrations at steady-state, corresponding to the usual doses are between 10 and 15 mg/L. The concentration-efficacy relationship is not established, but there is some evidence for a concentration-related toxicity. However, because of its non-linear kinetics, stiripentol should be a good candidate for therapeutic drug monitoring (TDM). Nonetheless, the current level of evidence for the advantage of TDM is "remains to be estimated".
MeSH Terms
- Aging
- Anticonvulsants
- Chromatography, High Pressure Liquid
- Critical Illness
- Dioxolanes
- Dose-Response Relationship, Drug
- Drug Monitoring
- Epilepsies, Myoclonic
- Epilepsy
- Humans
- Kidney Diseases
- Liver Diseases
The urine levels of cortisol and 6-beta-hydroxycortisol in 30 healthy children were determined with high performance liquid chromatography. The activity of cytochrome P450 isoenzyme CYP3A4 was estimated by the ratio of 6-beta-hydroxycortisol and cortisol. Differences in the CYP3A4 activity depended on the age sex. At the age of 4 to 9 years the value of the ratio was 9.21 /- 0.67 which in fact was statistically higher than that in the children at the age of 0 to 3 years (p<0.001). In the female children at the age of 0 to 3 years the value of the isoenzyme CYP3A4 activity was actually lower (p<0,05) vs. the female children of the higher ages and the male children at the age of 0 to 3 years. The results are useful for further researches on improvement of drugs dosing and prevention of adverse reactions.
MeSH Terms
- Adolescent
- Age Factors
- Aging
- Child
- Child, Preschool
- Cytochrome P-450 CYP3A
- Female
- Humans
- Hydrocortisone
- Infant
- Infant, Newborn
- Isoenzymes
- Male
- Phenotype
- Sex Characteristics
Sufentanil is a potent synthetic opioid. Like other opioids, sufentanil creates a stable hemodynamic environment in cardiovascularly compromised pediatric patients. Clearance, expressed as per kilogram, is increased in children compared to adults. The P450 CYP3A4 enzyme is responsible for the major metabolic N-dealkylation pathway. Enzyme activity is reduced in neonates but the maturation of sufentanil clearance is not described. The free active fraction is affected by age because of the reduced α(1) -acid glycoprotein plasma concentrations in neonates. Intranasal administration of sufentanil is a possible option for premedication, procedural sedation and analgesia in children, as this option has been found to be safe and effective. Studies concerning the pharmacokinetics and dynamics of sufentanil administered as a bolus or continuous infusion in children are few.
MeSH Terms
- Administration, Intranasal
- Aging
- Analgesics, Opioid
- Anesthesia, Epidural
- Anesthesia, Intravenous
- Blood Proteins
- Cardiovascular Diseases
- Child
- Child, Preschool
- Cytochrome P-450 CYP3A
- Half-Life
- Hemodynamics
- Humans
- Infant
- Injections, Spinal
- Kidney Failure, Chronic
- Protein Binding
- Reference Values
- Sufentanil
Voriconazole is a broad spectrum antifungal agent for treating life-threatening fungal infections. Its clearance is approximately 3-fold higher in children compared with adults. Voriconazole is cleared predominantly via hepatic metabolism in adults, mainly by CYP3A4, CYP2C19, and flavin-containing monooxygenase 3 (FMO3). In vitro metabolism of voriconazole by liver microsomes prepared from pediatric and adult tissues (n = 6/group) mirrored the in vivo clearance differences in children versus adults, and it showed that the oxidative metabolism was significantly faster in children compared with adults as indicated by the in vitro half-life (T(1/2)) of 33.8 or - 15.3 versus 72.6 or - 23.7 min, respectively. The K(m) for voriconazole metabolism to N-oxide, the major metabolite formed in humans, by liver microsomes from children and adults was similar (11 or - 5.2 versus 9.3 or - 3.6 microM, respectively). In contrast, apparent V(max) was approximately 3-fold higher in children compared with adults (120.5 or - 99.9 versus 40 or - 13.9 pmol/min/mg). The calculated in vivo clearance from in vitro data was found to be approximately 80% of the observed plasma clearance values in both populations. Metabolism studies in which CYP3A4, CYP2C19, or FMO was selectively inhibited provided evidence that contribution of CYP2C19 and FMO toward voriconazole N-oxidation was much greater in children than in adults, whereas CYP3A4 played a larger role in adults. Although expression of CYP2C19 and FMO3 is not significantly different in children versus adults, these enzymes seem to contribute to higher metabolic clearance of voriconazole in children versus adults.
MeSH Terms
- Adult
- Aging
- Antifungal Agents
- Aryl Hydrocarbon Hydroxylases
- Biocatalysis
- Child
- Child, Preschool
- Cytochrome P-450 CYP2C19
- Cytochrome P-450 CYP3A
- Cytochrome P-450 CYP3A Inhibitors
- Cytochrome P-450 Enzyme Inhibitors
- Cytochrome P-450 Enzyme System
- Enzyme Inhibitors
- Humans
- Kinetics
- Liver
- Microsomes, Liver
- Middle Aged
- Models, Biological
- Oxygenases
- Pyrimidines
- Triazoles
- Voriconazole
- Young Adult
Fesoterodine, a new antimuscarinic agent for overactive bladder, undergoes immediate and extensive hydrolysis by nonspecific esterases to 5-hydroxymethyl tolterodine (5-HMT), the metabolite principally responsible for its antimuscarinic activity. Formation of 5-HMT does not require cytochrome P450 (CYP)-mediated metabolism, but its further metabolism and inactivation involves CYP3A4 and CYP2D6 isoenzymes. Subject age, gender, and race can play a key role in inter-subject variability in pharmacokinetics and thus efficacy and safety of drugs. This article examines the effects of age, gender, and race on the pharmacokinetics and pharmacodynamics of fesoterodine. Data from two randomized, double-blind, placebo-controlled, parallel-group trials in healthy subjects are presented: Study 1 investigated the effects of race (white vs. black men) and Study 2 investigated the effects of age (young vs. old men) and gender (elderly men vs. elderly women) on the pharmacokinetics and pharmacodynamics of single doses of fesoterodine 8 mg. In both studies, the primary endpoints were area under the concentration-time curve up to the last sample (AUC0-tz) and maximum concentration (Cmax) of 5-HMT in plasma. Pharmacodynamic variables included spontaneous salivary secretion (Studies 1 and 2) and residual urine volume (Study 2 only). The two studies included 5 groups of 16 subjects each (randomized 3 : 1 to fesoterodine or placebo): white men aged 18 - 45 years, black men aged 18 - 45 years (Study 1); young white men aged 18 - 40 years, elderly white men aged > 65 years, and elderly white women aged > 65 years (Study 2). There were no clinically meaningful differences in the primary endpoints between white and black subjects or between young white men, elderly white men, and elderly white women. Mean AUC0-tz was 70.7 ng/ml x h in whites and 64.1 ng/ml x h in blacks; mean Cmax was 6.1 and 5.5 ng/ml in whites and blacks, respectively. Mean AUC0-tz in young white men, elderly white men, and elderly white women was 49, 48, and 54 ng/ml x h, respectively; mean Cmax in young white men, elderly white men, and elderly white women was 4.1, 3.8, and 4.6 ng/ml, respectively. Consistent with the anticholinergic pharmacology of fesoterodine, declines in salivary volume were observed in both studies, and elevations in residual urinary volume were observed, especially in elderly subjects, in Study 2. Fesoterodine was well tolerated, with common adverse events such as headache and dry mouth recognized as antimuscarinic class effects. Subject demographics, such as age, gender, and race, do not have a clinically meaningful effect on 5-HMT pharmacokinetics or pharmacodynamics after single-dose administration of fesoterodine 8 mg; thus, no dosage adjustment is required for fesoterodine based on age, gender, or race.
MeSH Terms
- Adolescent
- Adult
- African Continental Ancestry Group
- Aged
- Aging
- Area Under Curve
- Benzhydryl Compounds
- Double-Blind Method
- Ethnic Groups
- European Continental Ancestry Group
- Female
- Humans
- Male
- Middle Aged
- Muscarinic Antagonists
- Salivation
- Sex Characteristics
- Urodynamics
- Young Adult
Currently, >50% of candidates for solid organ transplantation in Europe and the US are aged >50 years while approximately 15% of potential recipients are aged >or=65 years. Elderly transplant candidates are characterized by specific co-morbidity profiles that compromise graft and patient outcome after transplantation. The presence of coronary artery or peripheral vascular disease, cerebrovascular disease, history of malignancy, chronic obstructive lung disease or diabetes mellitus further increases the early post-transplant mortality risk in elderly recipients, with infections and cardiovascular complications as the leading causes of death. Not only are elderly patients more prone to developing drug-related adverse effects, but they are also more susceptible to pharmacokinetic and pharmacodynamic drug interactions because of polypharmacy. The majority of currently used immunosuppressant drugs in organ transplantation are metabolized by cytochrome P450 (CYP) or uridine diphosphate-glucuronosyltransferases and are substrates of the multidrug resistance (MDR)-1 transporter P-glycoprotein, the MDR-associated protein 2 or the canalicular multispecific organic anion transporter, which predisposes these immunosuppressant compounds to specific interactions with commonly prescribed drugs. In addition, important drug interactions between immunosuppressant drugs have been identified and require attention when choosing an appropriate immunosuppressant drug regimen for the frail elderly organ recipient. An age-related 34% decrease in total body clearance of the calcineurin inhibitor ciclosporin was observed in elderly renal recipients (aged >65 years) compared with younger patients, while older recipients also had 44% higher intracellular lymphocyte ciclosporin concentrations. Similarly, using a Bayesian approach, an inverse relationship was noted between sirolimus clearance and age in stable kidney recipients. Ciclosporin and tacrolimus have distinct pharmacokinetics, but both are metabolized by intestinal and hepatic CYP3A4/3A5 and transported across the cell membrane by P-glycoprotein. The most common drug interactions with ciclosporin are therefore also observed with tacrolimus, but the two drugs do not interact identically when administered with CYP3A inhibitors or inducers. The strongest effects on calcineurin-inhibitor disposition are observed with azole antifungals, macrolide antibacterials, rifampicin, calcium channel antagonists, grapefruit juice, St John's wort and protease inhibitors. Drug interactions with mycophenolic acids occur mainly through inhibition of their enterohepatic recirculation, either by interference with the intestinal flora (antibacterials) or by limiting drug absorption (resins and binders). Rifampicin causes a reduction in mycophenolic acid exposure probably through induction of uridine diphosphate-glucuronosyltransferases. Proliferation signal inhibitors (PSIs) such as sirolimus and everolimus are substrates of CYP3A4 and P-glycoprotein and have a macrolide structure very similar to tacrolimus, which explains why common drug interactions with PSIs are comparable to those with calcineurin inhibitors. Ciclosporin, in contrast to tacrolimus, inhibits the enterohepatic recirculation of mycophenolic acids, resulting in significantly lower concentrations and hence risk of underexposure. Therefore, when switching from tacrolimus to ciclosporin and vice versa or when reducing or withdrawing ciclosporin, this interaction needs to be taken into account. The combination of ciclosporin with PSIs requires dose reductions of both drugs because of a synergistic interaction that causes nephrotoxicity when left uncorrected. Conversely, when switching between calcineurin inhibitors, intensified monitoring of PSI concentrations is mandatory. Increasing age is associated with structural and functional changes in body compartments and tissues that alter absorptive capacity, volume of distribution, hepatic metabolic function and renal function and ultimately drug disposition. While these age-related changes are well-known, few specific effects of the latter on immunosuppressant drug metabolism have been reported. Therefore, more clinical data from elderly organ recipients are urgently required.
MeSH Terms
- Aged
- Aged, 80 and over
- Aging
- Comorbidity
- Drug Interactions
- Female
- Geriatrics
- Humans
- Immunosuppressive Agents
- Male
- Organ Transplantation
- Pharmacokinetics
- Polypharmacy
Aging involves progressive impairments in the functional reserve of multiple organs, which might also affect drug metabolism and pharmacokinetics. In addition, the elderly population will develop multiple diseases and, consequently, often has to take several drugs. As the hepatic first-pass effect of highly cleared drugs could be reduced (due to decreases in liver mass and perfusion), the bioavailability of some drugs can be increased in the elderly. Significant changes in body composition occur with advancing age. Lipophilic drugs may have an increased volume of distribution (Vd) with a prolonged half-life, and water-soluble drugs tend to have a smaller Vd. In the elderly, hepatic drug clearance of some drugs can be reduced by up to 30% and CYP-mediated phase I reactions are more likely to be impaired than phase II metabolism, which is relatively preserved in the elderly. Concerning the most important CYP3A4 studies with human liver microsomes and clinical studies with the validated probe, midazolam, it is indicated that there are no significant differences in CYP3A4 activity between young and old populations. Finally, renal excretion is decreased (up to 50%) in about two thirds of elderly subjects, but confounding factors such as hypertension and coronary heart disease account also for a decline in kidney function. In conclusion, age-related physiological and pharmacokinetic changes as well as the presence of comorbidity and polypharmacy will complicate drug therapy in the elderly.
MeSH Terms
- Aged
- Aging
- Area Under Curve
- Biological Availability
- Body Composition
- Cytochrome P-450 CYP3A
- Humans
- Liver
- Pharmaceutical Preparations
Evaluation of: Fanta S, Niemi M, Jönsson S et al.: Pharmacogenetics of cyclosporine in children suggests an age-dependent influence of ABCB1polymorphisms. Pharmacogenet. Genomics 18(2), 77-90 (2008). The clinical use of the immunosuppressive agent cyclosporine is complicated by its toxicity, narrow therapeutic window and highly variable pharmacokinetics between individuals. In adults, genetic polymorphisms in the genes encoding the cyclosporine-metabolizing enzymes CYP3A4 and CYP3A5, as well as the ABCB1 gene, which encodes the efflux-pump P-glycoprotein, seem to have a limited effect, if any, on cyclosporine pharmacokinetics. However, the authors have now reported for the first time an association between cyclosporine oral bioavailability and the ABCB1 c.1236C>T and c.2677G>T polymorphisms, as well as the related haplotype c.1199G-c.1236C-c.2677G-c.3435C, in children with end-stage renal disease older than 8 years of age. Carriers of the variant alleles had a cyclosporine oral bioavailability that was around 1.5-times higher compared with noncarriers. This association was not observed in children younger than 8 years of age. In addition, no relation between cyclosporine disposition and genetic variation in the CYP3A4, CYP3A5, ABCC2, SLCO1B1 and NR1I2 genes was observed. These data suggest that the effect of ABCB1 polymorphisms on cyclosporine pharmacokinetics is related to age, and thus developmental stage. Although further study is necessary to establish the predictive value of ABCB1 genotyping for individualization of cyclosporine therapy in children older than 8 years, an important step towards further personalized immunosuppressive drug therapy has been made.
MeSH Terms
- ATP Binding Cassette Transporter, Subfamily B
- ATP Binding Cassette Transporter, Subfamily B, Member 1
- Adult
- Aging
- Child
- Cyclosporine
- Humans
- Immunosuppressive Agents
- Inactivation, Metabolic
- Kidney Transplantation
- Pharmacogenetics
- Polymorphism, Single Nucleotide
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
Maturational expression of carboxylesterase activity in laboratory animals has been correlated with age-related differences in sensitivity to many organophosphorus insecticides including chlorpyrifos. Little information is available, however, on the maturational expression of liver carboxylesterases in humans. Human liver carboxylesterase activity was compared in tissues from infants (2-24 months) and adults (20-36 years). There was no significant difference between mean infant and adult carboxylesterase activities. The carboxylesterase activity rank order was: 2 months<3 months<20 years<24 months<4 months<36 years<21 years<8 months<34 years<35 years. Proteins (3 microg) were separated and blotted using antibodies against rat hydrolase S (HS), human carboxylesterase (HCE) types 1 and 2, and CYP3A4. Again, there were no significant differences in staining density between infant and adult tissues with any isozyme. Aliquots of each sample were pre-incubated (30 min, 37 degrees C) with chlorpyrifos oxon to evaluate in vitro sensitivity. Based on 95% confidence intervals, no significant differences in IC50 values were obtained in 3-month to 36-year samples (range: 1.42-2.12 nM), while the IC50 was significantly lower in the 2-month sample (0.45 nM). Carboxylesterase activity across samples was correlated with cytochrome b5 content and HS immunosignal but not with other microsomal activities (total cyt P450 content, testosterone hydroxylation, coumarin hydroxylation, and EROD). The results suggest that, in contrast to rodents, human liver carboxylesterase expression changes relatively little during postnatal maturation.
MeSH Terms
- Adult
- Aging
- Carboxylesterase
- Chlorpyrifos
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Humans
- Infant
- Isoenzymes
- Liver
Repeated administration of agents (e.g., cancer chemotherapy) that can cause drug-induced nephrotoxicity may lead to acute or chronic renal damage. This will adversely affect the health and well-being of children, especially when the developing kidney is exposed to toxic agents that may lead to acute glomerular, tubular or combined toxicity. We have previously shown that the cancer chemotherapeutic ifosfamide (IF) causes serious renal damage substantially more in younger children (less than 3 years of age) than among older children. The mechanism of the age-related IF-induced renal damage is not known. Our major hypothesis is that renal CYP P450 expression and activity are responsible for IF metabolism to the nephrotoxic chloroacetaldehyde. Presently, the ontogeny of these catalytic enzymes in the kidney is sparsely known. The presence of CYP3A4, 3A5 and 2B6 was investigated in human fetal, pediatric and adult kidney as was the metabolism of IF (both R-IF and S-IF enantiomers) by renal microsomes to 2-dechloroethylifosfamide (2-DCEIF) and 3-dechloroethylifosfamide (3-DCEIF). Our analysis shows that CYP 3A4 and 3A5 are present as early as 8 weeks of gestation. IF is metabolized in the kidney to its two enantiomers. This metabolism can be inhibited with CYP 3A4/5 and 2B6 specific monoclonal inhibitory antibodies, whereby the CYP3A4/5 inhibitory antibody decreased the production of R-3-DCEIF by 51%, while the inhibitory CYP2B6 antibody decreased the production of S-2-DCEIF and S-3-DCEIF by 44 and 43%, respectively, in patient samples. Total renal CYP content is approximately six-fold lower than in the liver.
MeSH Terms
- Adolescent
- Adult
- Aged
- Aged, 80 and over
- Aging
- Antibodies, Monoclonal
- Antineoplastic Agents, Alkylating
- Aryl Hydrocarbon Hydroxylases
- Blotting, Western
- Child
- Child, Preschool
- Cyclophosphamide
- Cytochrome P-450 CYP2B6
- Cytochrome P-450 CYP3A
- Fetus
- Humans
- Ifosfamide
- Immunohistochemistry
- Infant
- Kidney
- Microsomes
- Middle Aged
- Oxidoreductases, N-Demethylating
- Stereoisomerism
Previously, a human CYP3A4-transgenic (Tg-CYP3A4) mouse line was reported to exhibit enhanced metabolism of midazolam by cytochrome P450 3A4 (CYP3A4) expressed in small intestine. Here we show that expression of CYP3A4 and murine cyp3a and cyp2b was both age and sex dependent. CYP3A4 was expressed in the livers of male and female Tg-CYP3A4 mice at 2 and 4 wk of age. Since 6 wk, CYP3A4 was undetectable in male livers, whereas it was constitutively expressed in female livers at decreased levels (3- to 5-fold). Pregnenolone 16alpha-carbonitrile markedly induced hepatic CYP3A4 expression, and the level was higher in females than males. Induction of intrinsic murine cyp3a and cyp2b was also sex dependent. Tg-CYP3A4 females were found to be deficient in lactation, leading to a markedly lower pup survival. The mammary glands of the Tg-CYP3A4 lactating mothers had underdeveloped alveoli with low milk content. Furthermore, beta-casein and whey acidic protein mRNAs were expressed at markedly lower levels in Tg-CYP3A4 pregnant and nursing mouse mammary glands compared with wild-type mice. This impaired lactation phenotype was associated with significantly reduced serum estradiol levels in Tg-CYP3A4 mice. A pharmacokinetic study revealed that the clearance of iv administrated [(3)H]estradiol was markedly enhanced in Tg-CYP3A4 mice compared with wild-type mice. These results suggest that CYP3A4 may play an important role in estradiol homeostasis. This may be of concern for treatment of pregnant and lactating women because CYP3A4 gene expression and enzymatic activity can be potentially modified by CYP3A4 inhibitors or inducers in medications, supplements, beverages, and diet.
MeSH Terms
- Aging
- Animals
- Aryl Hydrocarbon Hydroxylases
- Caseins
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Estradiol
- Female
- Gene Expression
- Homeostasis
- Humans
- Lactation
- Liver
- Male
- Mammary Glands, Animal
- Mice
- Mice, Transgenic
- Milk Proteins
- Oxidoreductases, N-Demethylating
- Phenotype
- Pregnenolone Carbonitrile
- Sex Factors
- Transgenes
The pharmacokinetics of almotriptan are linear over a range of oral doses up to 200mg in healthy volunteers. The compound has a half-life of approximately 3 hours. Almotriptan is well absorbed after oral administration and the mean absolute bioavailability is 69.1%. Maximal plasma concentrations are achieved between 1.5 and 4 hours after dose administration; however, within 1 hour after administration, plasma concentrations are approximately 68% of the value at 3 hours after administration. Food does not significantly affect almotriptan absorption. Almotriptan is not highly protein bound and is extensively distributed in the body. Approximately 50% of an almotriptan dose is excreted unchanged in the urine; this is the predominant single mechanism of elimination. Renal clearance is mediated, in part, through active tubular secretion, while the balance of the almotriptan dose is metabolised to inactive compounds. The predominant route of metabolism is via monoamine oxidase-A, and cytochrome P450 (CYP) mediated oxidation (via CYP3A4 and CYP2D6) occurs to a minor extent. Almotriptan clearance is moderately reduced in elderly subjects, but the magnitude of this effect does not warrant a dose reduction. Sex has no significant effect on almotriptan pharmacokinetics. Almotriptan pharmacokinetic parameters do not differ between adolescents and adults, and absorption is not affected during a migraine attack. As expected, renal dysfunction results in reduced clearance of almotriptan. Patients with moderate-to-severe renal dysfunction should use the lowest dose of almotriptan and the total daily dose should not exceed 12.5 mg. Similar dosage recommendations are valid for patients with hepatic impairment, based on the clearance mechanisms for almotriptan. Drug-drug interaction studies were conducted between almotriptan and the following compounds: fluoxetine, moclobemide, propranolol, verapamil and ketoconazole. No significant pharmacokinetic or pharmacodynamic interactions with almotriptan were observed for fluoxetine or propranolol. Almotriptan clearance was reduced, to a modest degree, by moclobemide and verapamil, which was consistent with the contribution of monoamine oxidase-A and CYP3A4 to the metabolic clearance of almotriptan. Although ketoconazole has a greater effect on almotriptan clearance than verapamil, no dosage adjustment is required when almotriptan is given with these drugs.
MeSH Terms
- Adolescent
- Aging
- Animals
- Biotransformation
- Female
- Food-Drug Interactions
- Humans
- Indoles
- Kidney Diseases
- Liver Diseases
- Male
- Migraine Disorders
- Receptor, Serotonin, 5-HT1B
- Serotonin Receptor Agonists
- Sex Characteristics
- Tissue Distribution
- Tryptamines
The steroid and xenobiotic receptor (SXR) has been demonstrated to play an important role in the regulation of the cytochrome P450 3A4 gene (CYP3A4) and multidrug resistance gene 1 (MDR1) by both endogenous and xenobiotic substrates. SXR and its rodent ortholog PXR exhibit marked differences in their ability to be activated by xenobiotic inducers. This suggests that results obtained by rodent models may not always accurately predict responses to the same compounds in humans. SXR expression was demonstrated in the human liver and intestine, but its systemic distribution remains unknown. Therefore in this study, we first characterized the expression of SXR and its target genes CYP3A4, and MDR1 in human adult and fetal tissues using quantitative RT-PCR, immunoblotting, and combined laser capture microscopy and RT-PCR analysis. SXR mRNA and protein are expressed in adult and fetal liver, lung, kidney, and intestine. There is a close association between the expression of SXR and its target genes in all of the tissues examined. The amounts of SXR mRNA in the liver and intestine reached maximal levels in young adults (15-38 years old) and then subsequently decreased to less than half of the maximal levels with aging. These findings demonstrated age-related differences in the body's capacity to metabolize steroids and xenobiotic compounds and suggest an important role for SXR and its target genes, CYP3A4 and MDR1 in this process.
MeSH Terms
- Adolescent
- Adult
- Aging
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Female
- Fetus
- Gene Expression Regulation
- Genes, MDR
- Humans
- Male
- Organ Specificity
- Pregnane X Receptor
- RNA, Messenger
- Receptors, Steroid
- Tissue Distribution
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
Many reports of interactions between drugs metabolized by CYP3A4 and influenza vaccine have been made. The authors hypothesized that changes in CYP3A4 activity following influenza immunization would correlate with cytokine production or age. Twenty-four subjects had an erythromycin breath test (ERMBT) and blood draw for lymphocyte culture prior to and on day 7 following influenza immunization. Cytokine production by lymphocytes cultured with influenza antigen was measured by ELISA. Eight men and sixteen women ranging in age from 20 to 66 years (mean = 38.7 years; SE = 2.9) participated in the study. Interferon gamma (IFNgamma) production inversely correlated with change in ERMBT (correlation coefficient = -0.614; p < 0.02), although the overall change in ERMBT was not statistically significant (mean = -4%; p = 0.28). The IFNgamma production correlates with change in ERMBT. This correlation supports in vitro findings of decreased CYP3A4 expression and activity with IFNgamma exposure.
MeSH Terms
- Adult
- Aged
- Aging
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Cytokines
- Erythromycin
- Female
- Humans
- Influenza Vaccines
- Male
- Middle Aged
The influence of ageing on the pharmacokinetics of zolpidem, an extensively prescribed hypnotic medication, was evaluated in healthy human volunteers. A series of 16 elderly (age: 61-85 years) and 24 young (age: 22-42 years) volunteers received single 5 mg oral doses of zolpidem tartrate. Serum zolpidem concentrations were determined by HPLC with fluorescence detection in samples drawn during 8 h after dosage. The effect of testosterone on zolpidem biotransformation was evaluated in vitro using human liver microsomes. Possible induction of CYP3A protein expression and function was studied in cultured human hepatocytes. Among men, apparent oral clearance of zolpidem was decreased in elderly compared to young subjects (3.8 vs 11.0 ml min-1 kg-1, P < 0.01), Cmax was increased (93 vs 40 ng ml-1, P < 0.01), and half-life increased (2.7 vs 1.5 h, P < 0.03). Among women, zolpidem oral clearance was decreased in the elderly (3.0 vs 5.8 ml min-1 kg-1, P < 0.02), Cmax increased (108 vs 60 ng ml-1, P < 0.001), with no difference in t1/2 (2.3 vs 2.4 h). Among male subjects, free serum testosterone concentrations were lower in the elderly (10.5 vs 19.0 pg ml-1, P < 0.01), and were significantly correlated with zolpidem clearance (r2 = 0.46, P < 0.001). Multiple regression analysis indicated a greater relative contribution of serum testosterone than age to the oral clearance of zolpidem among men. In human liver microsomes, co-incubation of zolpidem (10 micro m) with varying concentrations of testosterone produced activation of biotransformation of zolpidem to its principal hydroxylated metabolite. Maximum activation was achieved at equimolar concentrations of testosterone (10 micro m). However, testosterone did not induce immunoactive CYP3A4 expression or catalytic function in cultured human hepatocytes. The increased Cmax and lower oral clearance of zolpidem in the elderly are consistent with recommendations of lower clinical doses of zolpidem in the elderly. Our clinical and in vitro data both suggest that reduced free serum testosterone may have a modulatory role in age-dependent changes in zolpidem pharmacokinetics in men.
MeSH Terms
- Administration, Oral
- Adult
- Aged
- Aged, 80 and over
- Aging
- Chromatography, High Pressure Liquid
- Drug Interactions
- Female
- GABA Agonists
- Half-Life
- Hepatocytes
- Humans
- Hypnotics and Sedatives
- Male
- Microsomes, Liver
- Middle Aged
- Pyridines
- Testosterone
- Zolpidem
Rabeprazole is the most recently approved proton pump inhibitor in Germany. The substance has an absolute bioavailability upon oral administration of approximately 52% which is robust against food intake or administration of antacids. Maximal plasma concentrations are reached after approximately 3-4 h. Concentrations increase proportionally with the dose. Rabeprazole undergoes an almost complete, mainly non-enzymatic metabolism with renal elimination of the metabolites. CYP3A4 and CYP2C19 contribute to the fraction of metabolism mediated enzymatically. Elimination half-life is about 1 h. The extent of rabeprazole concentration increase by old age, poor metabolizer status for CYP2C19 and impairment of liver function is not greater than two-fold, impaired renal function does not affect the elimination. Even in patients with delayed elimination, no relevant accumulation of rabeprazole was observed upon long-term administration. In in vivo studies, rabeprazole had no noteworthy effect on the metabolism of other drugs. This statement however must be made with reservation because of shortcomings in published studies with respect to the methods used and presentation and because of lacking investigations about possible effects on the cytochrome P-450 enzymes CYP3A4 and CYP2D6. A slight reduction in ketoconazole absorption and a moderate increase in digoxin concentrations should be taken into account for concomitant therapy, but is expected to be clinically relevant only in isolated cases. Based on these partially incomplete data, in summary it is to be expected that rabeprazole can be administered at a standard dose for the respective disease in almost any patient for the entire duration of therapy, and that usually no dose adjustment of other drugs is required when rabeprazole is coadministered.
MeSH Terms
- 2-Pyridinylmethylsulfinylbenzimidazoles
- Adult
- Aging
- Anti-Ulcer Agents
- Benzimidazoles
- Biological Availability
- Child
- Clinical Trials as Topic
- Drug Interactions
- Female
- Food-Drug Interactions
- Humans
- Intestinal Absorption
- Male
- Omeprazole
- Rabeprazole
Cholinesterase inhibitors are the 'first-line' agents in the treatment of Alzheimer's disease. This article presents the latest information on their pharmacokinetic properties and pharmacodynamic activity. Tacrine was the first cholinesterase inhibitor approved by regulatory agencies, followed by donepezil, rivastigmine and recently galantamine. With the exception of low doses of tacrine, the cholinesterase inhibitors exhibit a linear relationship between dose and area under the plasma concentration-time curve. Cholinesterase inhibitors are rapidly absorbed through the gastrointestinal tract, with time to peak concentration usually less than 2 hours; donepezil has the longest absorption time of 3 to 5 hours. Donepezil and tacrine are highly protein bound, whereas protein binding of rivastigmine and galantamine is less than 40%. Tacrine is metabolised by hepatic cytochrome P450 (CYP) 1A2, and donepezil and galantamine are metabolised by CYP3A4 and CYP2D6. Rivastigmine is metabolised by sulfate conjugation. Two cholinesterase enzymes are present in the body, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Tacrine and rivastigmine inhibit both enzymes, whereas donepezil and galantamine specifically inhibit AChE. Galantamine also modulates nicotine receptors, thereby enhancing acetylcholinergic activity at the synapse. These different pharmacological profiles provide distinctions between these agents. Cholinesterase inhibitors show a nonlinear relationship between dose and cholinesterase inhibition, where a plateau effect occurs. Cholinesterase inhibitors display a different profile as each agent achieves its plateau at different doses. In clinical trials, cholinesterase inhibitors demonstrate a dose-dependent effect on cognition and functional activities. Improvement in behavioural symptoms also occurs, but without a dose-response relationship. Gastrointestinal adverse events are dose-related. Clinical improvement occurs with between 40 and 70% inhibition of cholinesterase. A conceptual model for cholinesterase inhibitors has been proposed, linking enzyme inhibition, clinical efficacy and adverse effects. Currently, measurement of enzyme inhibition is used as the biomarker for cholinesterase inhibitors. New approaches to determining the efficacy of cholinesterase inhibitors in the brain could involve the use of various imaging techniques. The knowledge base for the pharmacokinetics and pharmacodynamics of cholinesterase inhibitors continues to expand. The increased information available to clinicians can optimise the use of these agents in the management of patients with Alzheimer's disease.
MeSH Terms
- Aging
- Alzheimer Disease
- Biological Availability
- Carbamates
- Cholinesterase Inhibitors
- Donepezil
- Drug Interactions
- Half-Life
- Humans
- Indans
- Intestinal Absorption
- Liver
- Phenylcarbamates
- Piperidines
- Protein Binding
- Rivastigmine
- Tacrine
- Tissue Distribution
With the aging of the population, death from coronary heart disease (CHD) and stroke has become more prevalent. Cardiovascular disease (CVD) risk factors, such as hypertension, obesity, and diabetes mellitus increase with age as well. Recent secondary-prevention studies have established the positive effect of statins in decreasing the risk of CHD mortality through the lowering of cholesterol. Statins have an excellent safety record, at least with users under age 65, and provide a cheaper alternative to more costly medical options. The most serious side effect associated with their use is myopathy, which is infrequent. Drug interactions have been found with drugs that compete for the same CYP450 isoenzymes as statins. Several drugs have been shown to significantly inhibit the CYP3A4 pathway; in combination with statins such as lovastatin, simvastatin, atorvastatin, and cerivastatin, they have been shown to elevate serum concentrations of these statins, or may increase the risk of myopathy. Alternatively, other drugs can inhibit the CYP2C9 pathway and may elevate serum concentration of fluvastatin. Due to the number of medications the elderly receive, an understanding of the various metabolic pathways is of vital importance to minimize the potential for drug interactions. The elderly population, while at high risk for CVD, is currently undertreated. Statins can effectively lower low-density lipoprotein cholesterol levels and lessen the risk of CVD for this population.
MeSH Terms
- Aged
- Aging
- Cardiovascular Diseases
- Drug Interactions
- Humans
- Hydroxymethylglutaryl CoA Reductases
- Hydroxymethylglutaryl-CoA Reductase Inhibitors
- Risk Factors
Our objective was to assess the effect of rifampin (INN, rifampicin) on the pharmacokinetics of fexofenadine and to assess the influence of advanced age and sex. Twelve young volunteers (6 men and 6 women; age range, 22 to 35 years) and twelve elderly volunteers (6 men and 6 women; age range, 65 to 76 years) received a 60-mg oral dose of fexofenadine before and after treatment with 600 mg of oral rifampin for 6 days. Blood and urine were collected for 48 hours and assayed for fexofenadine, azacyclonol, and rifampin by HPLC with either fluorescence or mass spectrometry detection. All of the groups had a significant increase (P <.05) in the oral clearance of fexofenadine after rifampin treatment: young men, 2955 /- 1516 versus 5524 /- 3410 mL/min; young women, 2632 /- 996 versus 7091 /- 5,379 mL/min; elderly men, 1760 /- 850 versus 4608 /- 1159 mL/min; and elderly women, 2210 /- 554 versus 4845 /- 1600 mL/min. The peak serum concentration of fexofenadine was also significantly reduced (P <.05) by rifampin treatment: young men, 77 /- 31 versus 52 /- 17 ng/mL; young women, 72 /- 19 versus 36 /- 14 ng/mL; elderly men, 106 /- 42 versus 52 /- 14 ng/mL; elderly women, 76 /- 23 versus 46 /- 19 ng/mL. Half-life (150 to 230 minutes), time to maximum concentration (130 to 205 minutes), renal clearance (95 to 153 mL/min), and fraction unbound (2.9% to 3.7%) of fexofenadine showed no significant difference between control and treatment. The amount of azacyclonol, a CYP3A4 mediated metabolite of fexofenadine, eliminated renally increased on average 2-fold after rifampin dosing; however, this pathway accounted for less than 0.5% of the dose. No effect of age or sex on fexofenadine disposition or serum trough rifampin concentration (0.2 microg/mL to 1.8 microg/mL) was observed before or after rifampin treatment. This study showed that rifampin effectively increased fexofenadine oral clearance and that this effect was independent of age and sex. We conclude that the cause of the increased oral clearance of fexofenadine is a reduced bioavailability caused by induction of intestinal P-glycoprotein.
MeSH Terms
- ATP Binding Cassette Transporter, Subfamily B, Member 1
- Administration, Oral
- Adult
- Aged
- Aging
- Analysis of Variance
- Chromatography, High Pressure Liquid
- Drug Interactions
- Enzyme Inhibitors
- Female
- Half-Life
- Histamine H1 Antagonists
- Humans
- Male
- Metabolic Clearance Rate
- Rifampin
- Sex Characteristics
- Terfenadine
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
We observed significant strain differences [Dark Agouti (DA) > Wistar] in 1,3,7-trimethyluric acid formation (C-8 hydroxylation) during caffeine metabolism, though not in N-demethylations, in adult male DA and Wistar rats. In contrast, adult female and immature male rats of both DA and Wistar strains did not show significant differences in activity levels of C-8 hydroxylation. Kinetic studies using liver microsomes revealed that adult male DA rats have a larger Vmax for C-8 hydroxylation than do Wistar rats. Troleandomycin (TAO), known as a cytochrome P450 (CYP) 3A inhibitor, and an anti-rat CYP3A2 polyclonal antibody effectively reduced C-8 hydroxylation by rat liver microsomes in a concentration-dependent manner, suggesting that C-8 hydroxylation in rats is mediated largely by an isoform(s) of the CYP3A subfamily. Troleandomycin and the antibody did not inhibit the N-demethylations of caffeine by rat liver microsomes. Treatment of rats with CYP3A inducers caused a marked increase in C-8 hydroxylase activity. These results indicate that the rat CYP3A subfamily is capable of catalyzing C-8 hydroxylation of caffeine as is the case for human CYP3A4. The results of western blotting analysis using anti CYP3A antiserum showed that the staining intensity of the protein band in DA rat liver microsomes was higher than that in Wistar rat liver microsomes. We concluded that marked sex-dependent strain differences in C-8 hydroxylation of caffeine between Wistar and DA rats are due to the differences in the levels of expression of CYP3A in these strains of rats.
MeSH Terms
- Aging
- Animals
- Aryl Hydrocarbon Hydroxylases
- Caffeine
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Debrisoquin
- Dexamethasone
- Female
- Humans
- Hydroxylation
- Male
- Methylcholanthrene
- Microsomes, Liver
- Oxidoreductases, N-Demethylating
- Phenobarbital
- Pregnenolone Carbonitrile
- Rats
- Rats, Wistar
- Sex Characteristics
- Species Specificity
- Troleandomycin
- Uric Acid
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
CYP3A isoforms are responsible for the biotransformation of a wide variety of exogenous chemicals and endogenous steroids in human tissues. Two members of the CYP3A subfamily display developmentally regulated expression in the liver; CYP3A7 is expressed in the fetal liver, whereas CYP3A4 is the major cyrochrome P-450 isoform present in the adult liver. To gain insight into the descriptive ontogenesis of CYP3A isoforms during the neonatal period, we have developed several approaches to explore a neonatal liver bank. Although CYP3A4 and CYP3A7 are structurally closely related, they differ in their capacity to carry out monooxygenase reactions. We have cloned CYP3A4 and CYP3A7 and established stable transfectants in Ad293 cells to investigate their substrate specificities. The 16alpha hydroxylation of dehydroepiandrosterone is catalyzed by both proteins, but CYP3A7 has a higher affinity and maximal velocity than CYP3A4. Conversely, the conversion of testosterone into its 6beta derivative is essentially supported by CYP3A4. We used these two probes to determine the ontogenic evolution at the protein level; CYP3A7 was very active in the fetal liver and its activity was maximal during the first week following birth before to progressively decline and reached a very low level in adult livers. Conversely, the activity of CYP3A4 was extremely weak in the fetus and began to raise after birth to reach 30-40% of the adult activity after one month. CYP3A4 RNA accumulation displays a similar pattern of evolution; when probed with an oligonucleotide, its concentration increased rapidly after birth to reach a plateau as soon as the first week of age. These data supports the assumption that CYP3A4 expression is transcriptionally activated during the first week after birth and is accompanied by a simultaneous decrease of CYP3A7 expression, in such a way that the overall CYP3A protein content and the level of pentoxyresorufin dealkylase catalyzed by the two proteins remain nearly constant.
MeSH Terms
- Adult
- Aging
- Animals
- Aryl Hydrocarbon Hydroxylases
- COS Cells
- Cell Line
- Child
- Child, Preschool
- Cloning, Molecular
- Cytochrome P-450 CYP2C8
- Cytochrome P-450 CYP2C9
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- Embryonic and Fetal Development
- Female
- Fetus
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Enzymologic
- Gestational Age
- Humans
- Infant
- Infant, Newborn
- Liver
- Microsomes, Liver
- Mixed Function Oxygenases
- Pregnancy
- Recombinant Proteins
- Steroid 16-alpha-Hydroxylase
- Substrate Specificity
- Transcription, Genetic
- Transfection
Depression is a significant problem in the elderly. Because of aging-related pharmacokinetic and pharmacodynamic changes, it is not possible to automatically extrapolate findings on the efficacy or tolerability of antidepressants from younger to older populations. Venlafaxine inhibits both noradrenaline (norepinephrine) and serotonin (5-hydroxytryptamine; 5-HT) reuptake. Analysis of data from phase II and III trials showed that venlafaxine was comparably effective in the young and in a subset of over 350 elderly patients. Venlafaxine dosage needs to be lowered in the elderly with renal impairment. As a weak cytochrome P450 (CYP) inhibitor, it is unlikely to have clinically significant drug interactions. Venlafaxine may be associated with some increase in supine diastolic blood pressure, especially at dosages above 150 mg/day. Nefazodone is a serotonin uptake inhibitor and serotonin 5-HT2A receptor antagonist. Pooled analysis of about 250 patients found nefazodone to be effective in elderly individuals with moderate or severe depressive symptoms, with or without melancholia, in both primary and recurrent episodes. Nefazodone clearance is reduced in patients with hepatic impairment, and plasma concentrations have been reported to be higher in the elderly. Nefazodone is an inhibitor of the CYP3A4 family. There does not appear to be any increase in the frequency or severity of adverse effects in the elderly. Moclobemide is a selective inhibitor of monoamine oxidase type A. Studies in the elderly have found it to be well tolerated and meta-analysis has shown it to be comparably effective in young and elderly populations, and comparable to other antidepressants in terms of efficacy. Neither age nor renal impairment necessitate dosage adjustment, but hepatic impairment does necessitate dosage reduction. Dietary restrictions are not required. Overall, there is a relative paucity of data on the tolerability and efficacy of newer antidepressants in the elderly, especially those with concomitant medical disorders. Data that are available indicate that venlafaxine, nefazodone and moclobemide have comparable efficacy in older and younger patients.
MeSH Terms
- Aged
- Aging
- Antidepressive Agents
- Benzamides
- Cyclohexanols
- Cytochrome P-450 Enzyme Inhibitors
- Drug Interactions
- Enzyme Inhibitors
- Humans
- Moclobemide
- Monoamine Oxidase Inhibitors
- Piperazines
- Serotonin Uptake Inhibitors
- Triazoles
- Venlafaxine Hydrochloride
To assess whether CYP3A4 and CYP3A7 have a similar capacity to activate carcinogenic mycotoxins, we established cell lines stably expressing human CYP3A4 and CYP3A7, which are adult- and fetal-specific forms of cytochrome P450 in human livers, respectively. Each cDNA was introduced into CR-119 cells which had been established by introducing guinea pig NADPH-cytochrome P450 reductase cDNA into Chinese hamster lung cells. The cell lines (4-line and 7-line) stably expressed the mRNA and the protein corresponding to CYP3A4 and CYP3A7, respectively. The concentration-response for aflatoxin B1 (AFB1) cytotoxicity in 4-line and 7-line, respectively, was compared. 4-10 and 7-40 cells were approximately 17- and 20 times more sensitive to AFB1 than the parental CR-119 cells, respectively. In addition, the sensitivities to AFB1 of both 4-10 and 7-40 cells were enhanced approximately seven times by the addition of 10 microM alpha-naphthoflavone, a known activator of CYP3A enzyme, while the sensitivities were suppressed approximately four times by the addition of 100 microM troleandomycin, which forms a metabolite intermediate complex with CYP3A enzyme. Moreover, both cell lines showed approximately 10 and 2 times higher sensitivity to sterigmatocystin and aflatoxin G1 than CR-119 cells, respectively. These results indicate that CYP3A4 and CYP3A7 have essentially similar capacities to activate AFB1, sterigmatocystin, and aflatoxin G1 to produce toxic metabolites.
MeSH Terms
- Adult
- Aflatoxin B1
- Aging
- Animals
- Aryl Hydrocarbon Hydroxylases
- Benzoflavones
- Biotransformation
- Carcinogens
- Cell Line
- Clone Cells
- Cricetinae
- Cricetulus
- Cytochrome P-450 CYP3A
- Cytochrome P-450 Enzyme System
- DNA, Complementary
- Drug Interactions
- Fetus
- Gene Expression
- Guinea Pigs
- Humans
- Mycotoxins
- Sensitivity and Specificity
- Transfection
- Transformation, Genetic
- Troleandomycin
Lansoprazole, a benzimidazole derivative with antisecretory and antiulcer activities, inhibits the acid pump activity at the final stage of the enzyme process and therefore reduces the acid secretion of parietal cells. Lansoprazole is converted to active metabolites in the acid environment of these cells. It is rapidly absorbed from a gastric acid-resistant formulation and is approximately 97% bound in human plasma. Single dose pharmacokinetics of lansoprazole appear to be linear over the range from 15 to 60mg. Food and time of dose influence absorption after single doses, but do not modify the antisecretory effect of multiple doses. Lansoprazole is extensively metabolised following oral administration into sulphone and 5-hydroxylated metabolites by the cytochrome P450 enzymes CYP3A4 and CYP2C18. Two other metabolites have been identified in plasma: sulphide and hydroxylated sulphone. Mean plasma elimination half-life (t1/2) is between 1.3 and 2.1 hours in healthy volunteers. 15 to 23% of the total dose is found in urine as free and conjugated hydroxylated metabolites, while unchanged lansoprazole is not detected. The pharmacokinetic profile of the drug is not modified by multiple administration. In healthy elderly volunteers, area under the plasma concentration-time curve (AUC) and t1/2 are significantly greater after single administration occurs to the same extent as in young volunteers. Renal failure has no influence on the pharmacokinetics of lansoprazole, but severe hepatic failure causes a significant decrease in clearance and an increase in the AUC and t1/2 of lansoprazole. This is accompanied by modifications in the AUC of metabolites, but severe hepatic failure has minimal effect on accumulation of the drug after multiple administration. The pharmacokinetics of lansoprazole in patients with acid-related disorders do not differ from those in healthy volunteers. Studies of interactions of lansoprazole with warfarin, prednisone, theophylline, phenazone (antipyrine), diazepam, phenytoin and oral contraceptives suggest minimal risk of any clinically significant interaction.
MeSH Terms
- 2-Pyridinylmethylsulfinylbenzimidazoles
- Aging
- Anti-Ulcer Agents
- Drug Interactions
- Gastrointestinal Diseases
- Humans
- Lansoprazole
- Liver Failure
- Omeprazole
- Renal Insufficiency