Sequence diversity in CYP3A promoters and characterization of the genetic basis of polymorphic CYP3A5 expression

In vitro inhibitory effect of West African medicinal and food plants on human cytochrome P450 3A subfamily

AIM OF THE STUDY

In Africa, medicinal plants are used intensively and concomitantly with allopathic medicines in the treatment of opportunity diseases by many patients or by healthy person to prevent diseases. However, there is little information about the interactions between medicines and botanical products used currently in West Africa area. Therefore, the aim of the present investigation is to study the effect of some plant products on CYP3A4, CYP3A5 and CYP3A7, three individual enzymes of CYP3A subfamily, in vitro.

MATERIALS AND METHODS

Teas and ethanolic extracts of medicinal, food and co-administered plants were evaluated on CYP3A4, CYP3A5 and CYP3A7 individual enzymes in vitro using fluorometric assays.

RESULTS

Extracts of adjuvant plants such as Aframomum cuspidatum, and Aframomum melegueta, as well as one medicinal plant (Harrisonia abyssinica) inhibited CYP3A4, CYP3A5 and CYP3A7 activity more than 90%. Phyllanthus amarus showed high inhibition of CYP3A5 and CYP3A7. Food plants (Solanum macrocarpon and Talinum triangulare) inhibited CYP3A4 and CYP3A5 less than 20%.

CONCLUSION

These results indicate that plants tested in this study affect in vitro the activity of the main three CYP3A subfamily enzymes. These active plants could interfere with the metabolism at phase I of conventional drugs in vivo as well act as pharmacoenhancers in herbal mixtures.

Effect of CYP2D6, CYP3A5, and MDR1 genetic polymorphisms on the pharmacokinetics of risperidone and its active moiety

Clinical studies suggest that plasma levels of risperidone and its active moiety (risperidone + 9-hydroxyrisperidone) correlate with adverse drug effects. The aim of this study is to evaluate the pharmacogenetic variability in the disposition of risperidone and the active moiety in healthy Chinese subjects. A 2-mg single dose of risperidone is orally administered to 23 healthy Chinese subjects. The risperidone and 9-hydroxyrisperidone serum concentrations are measured. The polymorphic alleles of CYP2D6*10, CYP3A5*3, MDR1 C1236T, G2677T/A, and C3435T are determined in each subject. The mean maximum plasma concentration and area under the time-concentration curve extrapolated to infinity for risperidone are significantly higher in subjects possessing the CYP2D6*10 allele than in those with the CYP2D6*1/*1 and *1/*10 genotype. For active moiety, the subjects who carry both homozygous CYP2D6*10 and homozygous CYP3A5*3 have 98% higher area under the time-concentration curve extrapolated to infinity and 59% higher maximum plasma concentration compared with other CYP2D6 EM subjects. The MDR1 2677GA genotype may also play a role in risperidone pharmacokinetics. Further studies are needed to explore the impact of MDR1 2677GA and CYP3A5 polymorphisms on risperidone therapy.

Sex and CYP3A5 genotype influence total CYP3A activity: high CYP3A activity and a unique distribution of CYP3A5 variant alleles in Ethiopians

The objectives of the this study were to assess the influence of CYP3A5 genotype and sex on the variability in total CYP3A activity and to compare 4β-hydroxycholesterol and omeprazole sulfoxidation as phenotypic markers for CYP3A activity in Ethiopians. Healthy subjects (n=150) were genotyped for CYP3A5*3, *6 and *7 using allele-specific PCR and Taqman genotyping assays. Plasma levels of 4β-hydroxycholesterol, 3 h post-dose omeprazole and omeprazole sulfone, were determined by gas chromatography-mass spectrometry and high performance liquid chromatography, respectively. The frequency of CYP3A5*1, *3, *6 and *7 was 20.5, 67.3, 12.2 and 0%, respectively. The mean plasma 4β-hydroxycholesterol level was 35.4 ng ml⁻¹. The mean 4β-hydroxycholesterol level (P=0.0001) and the 4β-hydroxycholesterol/cholesterol ratio (P=0.004) were higher in women than in men. CYP3A5 genotype significantly correlated with the plasma 4β-hydroxycholesterol concentration (P=0.003) and 4β-hydroxycholesterol/cholesterol ratio (P=0.0002). The omeprazole/omeprazole sulfone ratio was significantly correlated with 4β-hydroxycholesterol and 4β-hydroxycholesterol/cholesterol ratio in CYP3A5*0/*0 genotypes but not in individuals carrying the CYP3A5*1 allele. No correlation of omeprazole/omeprazole sulfone ratio with sex or CYP3A5 genotype was observed. A clear gene-dose effect implies plasma 4β-hydroxycholesterol level as a useful endogenous biomarker for total CYP3A activity (CYP3A5 plus CYP3A4) whereas the omeprazole/omeprazole sulfone ratio reflects mainly CYP3A4 activity. Sex and CYP3A5 genotype influence total CYP3A activity. Ethiopians display high total CYP3A activity and a unique distribution of CYP3A5 variant alleles not described hitherto.

Polymorphisms in cytochromes P450 2C8 and 3A5 are associated with paclitaxel neurotoxicity

Neurotoxicity is one of the most relevant dose-limiting toxicities of the anticancer drug paclitaxel. It exhibits substantial interindividual variability of unknown molecular basis, and represents one of the major challenges for the improvement of paclitaxel therapy. The extensive variability in paclitaxel clearance and metabolism lead us to investigate the association between polymorphisms in paclitaxel elimination pathway and neurotoxicity. We selected 13 relevant polymorphisms in genes encoding paclitaxel metabolizing enzymes (CYP2C8, CYP3A4 and CYP3A5) and transporters (organic anion transporting polypeptide (OATP) 1B1, OATP1B3 and P-glycoprotein) and genotyped them in 118 Spanish cancer patients treated with paclitaxel. After adjusting for age and treatment schedule, CYP2C8 Haplotype C and CYP3A5*3 were associated with protection (hazard ratio (HR) (per allele)=0.55; 95% confidence interval (CI)=0.34-0.89; P=0.014 and HR (per allele)=0.51; 95%CI=0.30-0.86; and P=0.012, respectively) and CYP2C8*3 with increased risk (HR (per allele)=1.72; 95%CI=1.05-2.82; and P=0.032). In each case, the allele causing increased paclitaxel metabolism was associated with increased neurotoxicity, suggesting an important role for metabolism and hydroxylated paclitaxel metabolites. We estimated the HR per paclitaxel-metabolism increasing allele carried across the three polymorphisms to be HR=1.64 (95% CI=1.26-2.14; P=0.0003). The results for P-glycoprotein were inconclusive, and no associations were observed for the other genes studied. The incorporation of this genetic data in treatment selection could help to reduce neurotoxicity events, thereby individualizing paclitaxel pharmacotherapy. These results warrant validation in independent series.

Hepatic metabolism and transporter gene variants enhance response to rosuvastatin in patients with acute myocardial infarction: the GEOSTAT-1 Study

BACKGROUND

Pharmacogenetics aims to maximize benefits and minimize risks of drug treatment. Our objectives were to examine the influence of common variants of hepatic metabolism and transporter genes on the lipid-lowering response to statin therapy.

METHODS AND RESULTS

The Genetic Effects On STATins (GEOSTAT-1) Study was a genetic substudy of Secondary Prevention of Acute Coronary Events-Reduction of Cholesterol to Key European Targets (SPACE ROCKET) (a randomized, controlled trial comparing 40 mg of simvastatin and 10 mg of rosuvastatin) that recruited 601 patients after myocardial infarction. We genotyped the following functional single nucleotide polymorphisms in the genes coding for the cytochrome P450 (CYP) metabolic enzymes, CYP2C9*2 (430C>T), CYP2C9*3 (1075A>C), CYP2C19*2 (681G>A), CYP3A5*1 (6986A>G), and hepatic influx and efflux transporters SLCO1B1 (521T>C) and breast cancer resistance protein (BCRP; 421C>A). We assessed 3-month LDL cholesterol levels and the proportion of patients reaching the current LDL cholesterol target of <70 mg/dL (<1.81 mmol/L). An enhanced response to rosuvastatin was seen for patients with variant genotypes of either CYP3A5 (P=0.006) or BCRP (P=0.010). Furthermore, multivariate logistic-regression analysis revealed that patients with at least 1 variant CYP3A5 and/or BCRP allele (n=186) were more likely to achieve the LDL cholesterol target (odds ratio: 2.289; 95% CI: 1.157, 4.527; P=0.017; rosuvastatin 54.0% to target vs simvastatin 33.7%). There were no differences for patients with variants of CYP2C9, CYP2C19, or SLCO1B1 in comparison with their respective wild types, nor were differential effects on statin response seen for patients with the most common genotypes for CYP3A5 and BCRP (n=415; odds ratio: 1.207; 95% CI: 0.768, 1.899; P=0.415).

CONCLUSION

The LDL cholesterol target was achieved more frequently for the 1 in 3 patients with CYP3A5 and/or BCRP variant genotypes when prescribed rosuvastatin 10 mg, compared with simvastatin 40 mg. Clinical Trial Registration- URL: http://isrctn.org. Unique identifier: ISRCTN 89508434.

Factors associated with clopidogrel nonresponsiveness

Clopiodgrel therapy is the standard of care in patients with acute coronary syndrome and in those undergoing percutaneous coronary intervention. However, there is a significant amount of interindividual variability in clopidogrel responsiveness. Clopidogrel is a prodrug and requires metabolism via several CYP450 enzymes in order to exert its antiplatelet effects. Interference in these activation steps is the primary cause of clopidogrel nonresponsiveness. This review focuses on genetic polymorphisms in, and drug interactions with, the CYP450 enzymes that are associated with clopidogrel nonresponsiveness. In addition, clinical factors that effect clopidogrel responsiveness are also reviewed. Particular emphasis is placed on those factors that are not only associated with a change in clopidogrel pharmacokinetics or pharmacodynamics, but are also associated with an increased risk of adverse cardiovascular events. Currently, the majority of data assessing clopidogrel nonresponsiveness focus on genetic variation in CYP2C19 and drug interactions with proton pump inhibitors. However, genetic variation in other CYP450 enzymes, other drug interactions and clinical causes have been studied and are also reviewed here. It is important for healthcare practitioners to recognize all of the causes of clopidogrel nonresponsiveness, especially as novel antiplatelet alternatives become available.

The missing linkage: what pharmacogenetic associations are left to find in CYP3A?

IMPORTANCE OF THE FIELD

An enormous amount of drugs and endogenous substrates are metabolized by the enzymes encoded in the CYP3A gene cluster, making variation at this locus of utmost importance in the field of pharmacogenetics. However, the identification of genetic variation that contributes to the wide phenotypic variability at this locus has been elusive. While dozens of studies have investigated the effects of coding variants, none have found the definitive answer to what variant or variants explain the distribution of enzyme activity and clinical effects seen with the drug metabolized by these genes.

AREAS COVERED IN THIS REVIEW

This review highlights the recent pharmacogenetic work at the CYP3A locus, in particular studies on known functional variants in CYP3A4 and CYP3A5. In addition, common pharmacogenetic strategies as well as considerations specific to the CYP3A locus are discussed.

WHAT THE READER WILL GAIN

The reader will gain a greater understanding of the complexities involved in studying the CYP3A locus, population differences that may affect pharmacogenetic studies at this locus and the importance of variation that affect gene regulation.

TAKE HOME MESSAGE

More innovative and comprehensive methods to assay this region are needed, with particular attention paid to the role of gene regulation and non-coding sequence.

Errors and reproducibility of DNA array-based detection of allelic variants in ADME genes: PHARMAchip™

Aims: Differences in adverse drug reactions can be explained by genetic variations, especially if they determine the expression of certain protein effectors and/or drug-metabolizing enzymes. Over the last decade, several tests screening for the most frequent polymorphisms in drug-metabolizing enzymes have been marketed for research and diagnostic purposes. The aim of this study was to assess the suitability of PHARMAchip™ for the genotyping of polymorphisms of genes associated with drug metabolism and response as an alternative to Jurilab Ltd’s DrugMEt® Test. Materials & methods: In this observational study, performed using 100 previously genotyped DNA samples, we report on common genes included in the two different tests examined: the former DrugMEt test and the recently introduced PHARMAchip test. Results & conclusion: Although these tests are based on different methodological approaches, we have found a high concordance of results between both methods. Some of the discrepancies between tests were related to allelic variants not monitored in a particular microarray and the quality of the genomic DNA used.

Genetic variants of CYP3A4 and CYP3A5 in cynomolgus and rhesus macaques

Cynomolgus and rhesus macaques are frequently used in preclinical trials due to their close evolutionary relationships to humans. We conducted an initial screening for genetic variants in cynomolgus and rhesus macaque genes orthologous to human CYP3A4 and CYP3A5. Genetic screening of 78 Indochinese and Indonesian cynomolgus macaques and 34 Chinese rhesus macaques revealed a combined total of 42 CYP3A4 genetic variants, including 12 nonsynonymous variants, and 34 CYP3A5 genetic variants, including nine nonsynonymous variants. Four of these nonsynonymous variants were located at substrate recognition sites or the heme-binding region, domains essential for protein function, including c.886G>A (V296M) and c.1310G>A (S437N) in CYP3A4 and c.1437C>G (N479K) and c.1310G>C (T437S) in CYP3A5. The mutant proteins of these genetic variants were expressed in Escherichia coli and purified. Metabolic activity of these proteins measured using midazolam and nifedipine as substrates showed that none of these protein variants substantially influences the drug-metabolizing capacity of CYP3A4 or CYP3A5 protein. In Indonesian cynomolgus macaques, we also found IVS3+1delG in CYP3A4 and c.625A>T in CYP3A5, with which an intact protein cannot be produced due to a frameshift generated. Screening additional genomes revealed that two of 239 animals and three of 258 animals were heterozygous for IVS3+1delG of CYP3A4 and c.625A>T of CYP3A5, respectively. Some genetic variants were unevenly distributed between Indochinese and Indonesian cynomolgus macaques and between cynomolgus and rhesus macaques. Information on genetic diversity of macaque CYP3A4 and CYP3A5 presented here could be useful for successful drug metabolism studies conducted in macaques.

Cytochrome P450-mediated metabolism in the human gut wall

Objective

Although the human small intestine serves primarily as an absorptive organ for nutrients and water, it also has the ability to metabolise drugs. Interest in the small intestine as a drug-metabolising organ has been increasing since the realisation that it is probably the most important extrahepatic site of drug biotransformation.

Key findings

Among the metabolising enzymes present in the small intestinal mucosa, the cytochromes P450 (CYPs) are of particular importance, being responsible for the majority of phase I drug metabolism reactions. Many drug interactions involving induction or inhibition of CYP enzymes, in particular CYP3A, have been proposed to occur substantially at the level of the intestine rather than exclusively within the liver, as originally thought. CYP3A and CYP2C represent the major intestinal CYPs, accounting for approximately 80% and 18%, respectively, of total immunoquantified CYPs. CYP2J2 is also consistently expressed in the human gut wall. In the case of CYP1A1, large interindividual variation in the expression levels has been reported. Data for the intestinal expression of the polymorphic CYP2D6 are conflicting. Several other CYPs, including the common hepatic isoform CYP2E1, are expressed in the human small intestine to only a very low extent, if at all. The distribution of most CYP enzymes is not uniform along the human gastrointestinal tract, being generally higher in the proximal regions of the small intestine.

Summary

This article reviews the current state of knowledge of CYP enzyme expression in human small intestine, the role of the gut wall in CYP-mediated metabolism, and how this metabolism limits the bioavailability of orally administered drugs. Possible interactions between drugs and CYP activity in the small intestine are also discussed.

Pharmacogenetics of calcineurin inhibitors in renal transplantation

Cyclosporine A and tacrolimus (Tac) are inmunosuppresive drugs with a narrow therapeutic range. Underdosing is associated with organ rejection, whereas overdosing could result in toxicity. Therapeutic drug monitoring at different postdose times is necessary to maintain the blood concentrations within a target window. These calcineurin inhibitors are characterized by a broad interindividual pharmacokinetics variability, which makes the determination of the initial dose difficult. In a patient receiving a dose, the amount of the drug that is measured in the blood determines its bioavailability, which depends on the absorption, biotransformation, and elimination of the drug. These processes are primarily controlled by efflux pumps and enzymes of the cytochrome P (CYP) 450 family. DNA variants at the genes encoding these proteins contribute to the interindividual heterogeneity for calcineurin inhibitors metabolism. Cyclosporine A and Tac are metabolized by CYP3A4 and CYP3A5, and several single nucleotide polymorphisms in the two genes have been associated with differences in drug clearance. Carriers of the CYP3A5 wild-type allele have a higher CYP3A5 expression compared with individuals who are homozygous for a common DNA variant that affects gene splicing (CYP3A5*3). For renal transplant recipients receiving Tac, homozygotes for this nonexpression allele would exhibit significantly lower Tac clearance and may require a lower dose to remain within the blood target concentration compared with CYP3A5 expressors. To date, this CYP3A5 variant is the only reported genetic factor to predict the appropiate starting dosage of Tac, avoiding overdosing and improving the outcome of renal transplantation.

Vincristine: Can its therapeutic index be enhanced?

Vincristine is one of the most widely used and more effective drugs in paediatric oncology. The dose-limiting toxicity of neuropathy, lack of proven neuroprotective measures and an incomplete understanding of the pharmacokinetics and pharmacogenetics of vincristine have limited its therapeutic potential. Recent advances in the understanding of vincristine pharmacokinetics and pharmacogenetics, and potential methods of preventing neurotoxicity are reviewed which could enable dose escalation and dose individualisation in order to enhance the therapeutic index.

Genetic polymorphism of metabolic enzymes P450 (CYP) as a susceptibility factor for drug response, toxicity, and cancer risk

The polymorphic P450 (CYP) enzyme superfamily is the most important system involved in the biotransformation of many endogenous and exogenous substances including drugs, toxins, and carcinogens. Genotyping for CYP polymorphisms provides important genetic information that help to understand the effects of xenobiotics on human body. For drug metabolism, the most important polymorphisms are those of the genes coding for CYP2C9, CYP2C19, CYP2D6, and CYP3A4/5, which can result in therapeutic failure or severe adverse reactions. Genes coding for CYP1A1, CYP1A2, CYP1B1, and CYP2E1 are among the most responsible for the biotransformation of chemicals, especially for the metabolic activation of pre-carcinogens. There is evidence of association between gene polymorphism and cancer susceptibility. Pathways of carcinogen metabolism are complex, and are mediated by activities of multiple genes, while single genes have a limited impact on cancer risk. Multigenic approach in addition to environmental determinants in large sample studies is crucial for a reliable evaluation of any moderate gene effect. This article brings a review of current knowledge on the relations between the polymorphisms of some CYPs and drug activity/toxicity and cancer risk.

Decreased sigmoidal ABCB1 (P-glycoprotein) expression in ulcerative colitis is associated with disease activity

Aims: The modulation of the intestinal expression of detoxifying proteins by relevant transcription factors, intracellular receptors and cytokines in ulcerative colitis (UC) is poorly understood. Here, we compared the intestinal expression of drug transporters, metabolizing enzymes and putative regulatory genes between inflamed and noninflamed tissue and studied their modulation by disease activity. Materials & methods: Sigmoidal biopsies of 18 UC patients and 18 healthy volunteers matched for age, gender and ABCB1 3435C>T genotype were investigated for mRNA expression levels of 43 systematically selected candidate genes by low-density array real-time PCR. Additionally, the ABCB1 gene product P-glycoprotein was visualized by immunohistochemistry and quantified by western blotting. Disease phenotype was categorized by clinical, endoscopic and histopathological examination. Disease activity was quantified by clinical activity index. Results: In inflamed sigmoidal tissue from UC patients, 11 genes (NAT1, NR2B1, CEBPB, IFG, IL8, IL10, S100A12, SPP1, DEFA5, DEFA6 and HAMP) were overexpressed. By contrast, only the major human efflux transporter ABCB1 showed significantly lower expression levels, that were inversely correlated with those of certain antimicrobial peptides (DEFA5/6) and cytokines (IL1β and IL8). Cell culture experiments revealed a time-dependent decrease of ABCB1 expression upon IL8 exposure. Disease activity profoundly modified ABCB1 expression, indicated by an inverse correlation of clinical activity index values with ABCB1 mRNA expression (r = -0.603; p = 0.017) and markedly reduced protein expression in UC patients with moderate and severe symptomology (p = 0.011). Conclusion: Cytokine-mediated downregulation of the major human efflux transporter ABCB1 in inflamed intestine of UC patients is presumably dependent on disease activity, with a possible contribution from IL8.

Pharmacogenomic discovery using cell-based models

Quantitative variation in response to drugs in human populations is multifactorial; genetic factors probably contribute to a significant extent. Identification of the genetic contribution to drug response typically comes from clinical observations and use of classic genetic tools. These clinical studies are limited by our inability to control environmental factors in vivo and the difficulty of manipulating the in vivo system to evaluate biological changes. Recent progress in dissecting genetic contribution to natural variation in drug response through the use of cell lines has been made and is the focus of this review. A general overview of current cell-based models used in pharmacogenomic discovery and validation is included. Discussion includes the current approach to translate findings generated from these cell-based models into the clinical arena and the use of cell lines for functional studies. Specific emphasis is given to recent advances emerging from cell line panels, including the International HapMap Project and the NCI60 cell panel. These panels provide a key resource of publicly available genotypic, expression, and phenotypic data while allowing researchers to generate their own data related to drug treatment to identify genetic variation of interest. Interindividual and interpopulation differences can be evaluated because human lymphoblastoid cell lines are available from major world populations of European, African, Chinese, and Japanese ancestry. The primary focus is recent progress in the pharmacogenomic discovery area through ex vivo models.

Effect of CYP3A5*3 genotype on serum carbamazepine concentrations at steady-state in Korean epileptic patients

BACKGROUND AND OBJECTIVE

Carbamazepine (CBZ) is metabolized mainly by the CYP3A family of enzymes, which includes CYP3A4 and CYP3A5. Several studies have suggested that the CYP3A5*3 genotype influences the pharmacokinetics of CYP3A substrates. The present study aimed to assess the effect of the CYP3A5*3 genotype on serum concentration of CBZ at the steady-state in Korean epileptic patients.

METHOD

The serum concentrations of CBZ in 35 Korean epileptic patients were measured and their CYP3A5 genotype was determined. Fourteen patients were CYP3A5 expressors (two for CYP3A5*1/*1 and 12 for CYP3A5*1/*3) and 21 patients were CYP3A5 non-expressors (CYP3A5*3/*3). Dose-normalized concentrations (mean +/- SD) of CBZ were 9.9 +/- 3.4 ng/mL/mg for CYP3A5 expressors and 13.1 +/- 4.5 ng/mL/mg for CYP3A5 non-expressors (P = 0.032). The oral clearance of CBZ was significantly higher in CYP3A5 non-expressors than that of CYP3A5 expressors (0.056 +/-0.017 L/h/kg vs. 0.040 +/- 0.014 L/h/kg, P = 0.004). The CYP3A5 genotype affected the CBZ concentrations in Korean epileptic patients and is a factor that may contribute to inter-individual variability in CBZ disposition in epileptic patients.

CYP3A4 and CYP3A5 polymorphisms and blood pressure response to amlodipine among African-American men and women with early hypertensive renal disease

PURPOSE

To explore the association between CYP3A4 and CYP3A5 gene polymorphisms and blood pressure response to amlodipine among participants from the African-American Study of Kidney Disease and Hypertension Trial randomized to amlodipine (n = 164).

METHODS

Cox proportional hazards models were used to determine the risk of reaching a target mean arterial pressure (MAP) of < or =107 mm Hg by CYP3A4 (A-392G and T16090C) and CYP3A5 (A6986G) gene polymorphisms, stratified by MAP randomization group (low or usual) and controlling for other predictors for blood pressure response.

RESULTS

Women randomized to a usual MAP goal with an A allele at CYP3A4 A-392G were more likely to reach a target MAP of 107 mm Hg. The adjusted hazard ratio (AA/AG compared to GG) with 95% confidence interval was 3.41 (1.20-9.64; p = 0.020). Among participants randomized to a lower MAP goal, those with the C allele at CYP3A4 T16090C were more likely to reach target MAP: The adjusted hazard ratio was 2.04 (1.17-3.56; p = 0.010). After adjustment for multiple testing using a threshold significance level of p = 0.016, only the CYP3A4 T16090C SNP remained significant. CYP3A5 A6986G was not associated with blood pressure response.

CONCLUSIONS

Our findings suggest that blood pressure response to amlodipine among high-risk African-Americans appears to be determined by CYP3A4 genotypes, and sex specificity may be an important consideration. Clinical applications of CYP3A4 genotype testing for individualized treatment regimens warrant further study.

Population pharmacokinetics and pharmacogenetics of tacrolimus in de novo pediatric kidney transplant recipients

The aim of this study was to develop a population pharmacokinetic model of tacrolimus in pediatric kidney transplant patients, identify factors that explain variability, and determine dosage regimens. Pharmacokinetic samples were collected from 50 de novo pediatric kidney transplant patients (age 2-18 years) who were on tacrolimus treatment. Population pharmacokinetic analysis of tacrolimus was performed using NONMEM, and the impact of variables (demographic and clinical factors, and CYP3A4-A5, ABCB1, and ABCC2 polymorphisms) was tested. The pharmacokinetic data were described by a two-compartment model that incorporated first-order absorption and lag time. The apparent oral clearance (CL/F) was significantly related to body weight (allometric scaling); in addition, it was higher in patients with low hematocrit levels and lower in patients with CYP3A5*3/*3. The population pharmacokinetic-pharmacogenetic model developed in de novo pediatric kidney transplant patients demonstrated that, in children, tacrolimus dosage should be based on weight, hematocrit levels, and CYP3A5 polymorphism. Individualization of therapy will enable the optimization of tacrolimus exposure, with resultant beneficial effects on kidney function in the initial post-transplantation period.

Immunotherapy in elderly transplant recipients: a guide to clinically significant drug interactions

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.

Genetic polymorphism of CYP3A5 in Indian chronic myeloid leukemia patients

CYP3A5 is an important genetic contributor to inter-individual differences in CYP3A-dependent clinically important drugs of metabolism and also of various endogenous compounds and environmental contaminants. The CYP3A5*3 allele results in a truncated protein with loss of CYP3A5 expression and CYP3A5*6 is associated with lower CYP3A5 catalytic activity. The polymorphism analysis was performed by PCR-RFLP and some representative cases by direct sequencing. Our case control study involved 183 consecutive North Indian CML patients in chronic phase of disease and 208 geographically and racially matched healthy controls. PCR-RFLP was carried out to determine the frequency of CYP3A5*3 and CYP3A5*6 genotypes. The relationship between these allelic variants and risk of CML was assessed by means of odds ratio (OR) with 95% confidence limits calculated by logistic regression. The frequencies of CYP3A5*1/*1, CYP3A5*1/*3, and CYP3A5*3/*3 genotypes in CML and controls were examined, and the quantitative comparison of the frequency distributions between CML versus control were performed, showing no significant differences among these comparison pairs (P = 0.88, 0.65, and 0.80, respectively). However, we did not find the CYP3A5*6 allele in any of the controls and leukemia patients. It is concluded that there is no association of this polymorphism with the risk of chronic myeloid leukemia.

CYP3A5 polymorphism and sensitivity of blood pressure to dietary salt in Japanese men

The cytochrome P-450 3A5 (CYP3A5) gene has recently been implicated in renal sodium reabsorption and blood pressure regulation. The genetic effect of CYP3A5*1 (expressor) and *3 (reduced-expressor) variants on blood pressure has been studied in African Americans and Caucasians, but not yet in the Asian population. In this cross-sectional study, 238 Japanese male workers were examined to determine whether CYP3A5 *1*3 affects the blood pressure level, taking daily salt intake into account as a potential gene-environment interaction. The A6986G polymorphism was determined by melting curve analysis, and the salt intake level was inferred from spot urine specimen by calculating 24-h urinary sodium excretion. CYP3A5 *1*3 per se had no association with systolic blood pressure (SBP) and only a weak association was detected for diastolic blood pressure (DBP) (*1/*1 vs *3/*3, P=0.038), which was strengthened after adjustment with age and body mass index (*1/*1 vs*3/*3, P=0.007; *1/*1 vs*1/*3, P=0.045). Significant interactions between the genotype and salt intake were observed in both SBP (P=0.046) and DBP (P=0.003). SBP and DBP were significantly associated with the level of salt intake in*3/*3 (P<0.001) but not in *1 carriers. *1carrier had higher blood pressure than *3/*3, but only in those with low salt intake. These results suggest that CYP3A5 variants may be a determinant of salt sensitivity of blood pressure in Japanese men.

Molecular population genetics of human CYP3A locus: signatures of positive selection and implications for evolutionary environmental medicine

BACKGROUND

The human CYP3A gene cluster codes for cytochrome P450 (CYP) subfamily enzymes that catalyze the metabolism of various exogenous and endogenous chemicals and is an obvious candidate for evolutionary and environmental genomic study. Functional variants in the CYP3A locus may have undergone a selective sweep in response to various environmental conditions.

OBJECTIVE

The goal of this study was to profile the allelic structure across the human CYP3A locus and investigate natural selection on that locus.

METHODS

From the CYP3A locus spanning 231 kb, we resequenced 54 genomic DNA fragments (a total of 43,675 bases) spanning four genes (CYP3A4, CYP3A5, CYP3A7, and CYP3A43) and two pseudogenes (CYP3AP1 and CYP3AP2), and randomly selected intergenic regions at the CYP3A locus in Africans (24 individuals), Caucasians (24 individuals), and Chinese (29 individuals). We comprehensively investigated the nucleotide diversity and haplotype structure and examined the possible role of natural selection in shaping the sequence variation throughout the gene cluster.

RESULTS

Neutrality tests with Tajima's D, Fu and Li's D* and F*, and Fay and Wu's H indicated possible roles of positive selection on the entire CYP3A locus in non-Africans. Sliding-window analyses of nucleotide diversity and frequency spectrum, as well as haplotype diversity and phylogenetically inferred haplotype structure, revealed that CYP3A4 and CYP3A7 had recently undergone or were undergoing a selective sweep in all three populations, whereas CYP3A43 and CYP3A5 were undergoing a selective sweep in non-Africans and Caucasians, respectively.

CONCLUSION

The refined allelic architecture and selection spectrum for the human CYP3A locus highlight that evolutionary dynamics of molecular adaptation may underlie the phenotypic variation of the xenobiotic disposition system and varied predisposition to complex disorders in which xenobiotics play a role.

Association between ABCC2 polymorphism and lopinavir accumulation in peripheral blood mononuclear cells of HIV-infected patients

Aim: Lopinavir (LPV) is a potent protease inhibitor used in combination with low doses of ritonavir in the treatment of HIV-infected patients. LPV pharmacokinetics is characterized by a large interindividual variability requiring the use of therapeutic drug monitoring in different clinical situations. While the sources of this variability are still unknown, several genetic polymorphisms in biotransformation enzymes or transporter proteins involved in the metabolism and/or the distribution of LPV appear as good candidates. Therefore, the aim of the present study was to investigate the influence of selected genetic polymorphisms on LPV trough plasma concentrations ([LPV]Cmin), LPV concentrations in peripheral blood mononuclear cells ([LPV]CC) and the LPV accumulation ratio ([LPV]CC:[LPV]Cmin). Materials & methods: A total of 53 patients receiving Kaletra® (Abbott Laboratories, IL, USA) (LPV+ritonavir) were genotyped for 14 different polymorphisms in biotransformation enzymes and transporter proteins. [LPV]Cmin, [LPV]CC and [LPV]CC:[LPV]Cmin were compared according to the patient’s genotypes. Results & conclusion: The 4544G>A (rs8187710)polymorphism in ABCC2 was associated with a higher accumulation of LPV in peripheral blood mononuclear cells of HIV-treated patients. As already observed in previous studies, ABCB1 or CYP3A5 polymorphisms had no impact on [LPV]Cmin and we did not detect any influence of these polymorphisms on [LPV]CC and its accumulation in mononuclear cells. In conclusion, this pilot study suggests, for the first time, that the 4544G>A polymorphism in ABCC2 could explain a significant part of the interindividual variability in LPV pharmacokinetics. Further investigations are needed to confirm this association and to explore its real pharmacodynamic impact.

A case-control association study between the CYP3A4 and CYP3A5 genes and schizophrenia in the Chinese Han population

In this study, variants of two genes coding for cytochrome P450 enzyme (CYP3A4 and CYP3A5) were analysed in a case-control sample using 398 schizophrenic patients and 391 healthy controls. All subjects were unrelated Han Chinese from Shanghai. No difference was observed on the allelic or genotypic distribution of CYP3A4 and CYP3A5 gene polymorphisms between the groups. However, the two-marker haplotypes covering components CYP3A41G and CYP3A53 were observed to be significantly associated with schizophrenia (corrected global p=0.0009). In addition, we identified one common risk haplotype, G/G (present in 59.5% of the general population). The results suggest that CYP3A4 and CYP3A5 might play a role in genetic susceptibility to schizophrenia. However, confirmatory studies in independent samples are needed.

Association of genotypes of the CYP3A cluster with midazolam disposition in vivo

The genes that encode for CYP3A4 and CYP3A5 are located in the same region (CYP3A cluster) on chromosome 7. Midazolam (MDZ) is a substrate for both CYP3A4 and CYP3A5. We hypothesize that MDZ disposition in vivo is associated with genotypes of the CYP3A cluster. A meta-analysis of the pharmacokinetic (PK) parameters from seven clinical trials was carried out, in which MDZ was administered both intravenously and orally. DNA samples were available from 116 patients. There were significant ethnic differences in the allelic frequencies of these four common single-nucleotide polymorphisms (SNPs) in the CYP3A cluster. Significant linkage disequilibrium was found between CYP3A5(*)3 and CYP3A4(*)1A in Caucasians, and between CYP3A5(*)1 and CYP3A4(*)1B in African Americans. There were no differences in MDZ disposition in vivo between different genotypes, haplotypes and diplotypes in the CYP3A cluster (P>0.05). No significant differences in MDZ PK parameters were observed between Caucasians and African Americans. Women had higher weight-corrected systemic and oral clearance than men, but dose-adjusted AUC and bioavailability differences were not observed between sexes. The clinical importance of elevated CYP3A activity in women remains to be determined. The r(GC)'s of MDZ PK parameters were between 0.3 and 13.6%. In conclusion, the meta-analysis of seven studies suggests that environmental factors explain the majority of CYP3A activity variation. Further studies are necessary to define the functional significance of SNPs in the CYP3A cluster and the effects of CYP3A genotypes on MDZ disposition in vivo.

Effect of cytochrome P450 3A5*3 genotype on the stereoselective pharmacokinetics of amlodipine in healthy subjects

Amlodipine is a racemic mixture composed of S- and R-form and metabolized stereoselectively. Cytochrome P450 3A (CYP3A) including CYP3A5 are involved in the metabolism of amlodipine and it was reported that polymorphic CYP3A5 genotype modulates the plasma levels of amlodipine and thus affect its pharmacokinetics. This study was conducted to find whether stereoselective pharmacokinetics of amlodipine was affected by the polymorphic CYP3A5 genotype. Seventeen healthy subjects were genotyped for CYP3A5*3 variant. After a single dose of 10-mg amlodipine, enantiomers of amlodipine were analyzed using HPLC-MS/MS equipped with an AGP column. Amlodipine showed stereoselective pharmacokinetics. S-amlodipine exhibited higher plasma levels than R-amlodipine in both genotype groups. S-amlodipine showed 15% higher mean peak plasma concentrations (Cmax) in CYP3A5*1/*3 carriers (3.28 ng/ml) than CYP3A5*3/*3 carriers (2.85 ng/ml) (P = 0.194) and R-amlodipine also showed 21% higher Cmax in CYP3A5*1/*3 carriers (3.33 ng/ml) than CYP3A5*3/*3 carriers (2.75 ng/ml) (P = 0.114). CYP3A5*1/*3 carriers also have 23 and 12% higher mean area under the time versus concentration curve of R-amlodipine and S-amlodipine than CYP3A5*3/*3 carriers, respectively (for R-amlodipine, 147.1 ng*h/ml for CYP3A5*1/*3 carriers versus 121.8 ng*h/ml for CYP3A5*3/*3 carriers, P = 0.234; for S-amlodipine, 161.6 ng*h/ml for CYP3A5*1/*3 carriers vs. 144.2 ng*h/ml for CYP3A5*3/*3 carriers, P = 0.353). Other pharmacokinetic parameters also showed no significant difference between them. In conclusion, the present study showed that despite the evidence that amlodipine is stereoselectively metabolized, CYP3A5*3 genotype did not affect stereoselective disposition of amlodipine. It provides the evidence that CYP3A5*3genotype plays a minor role in the interindividual variability of stereoselective disposition of amlodipine in humans.

CYP3A polymorphisms and immunosuppressive drugs in solid-organ transplantation

Most immunosuppressive drugs have a narrow therapeutic index and large interpatient variabilities in their pharmacokinetic and pharmacodynamic profiles. Identification of functional single-nucleotide polymorphisms in genes encoding for drug metabolizing enzymes has great potential to improve the drug efficacy and safety profiles, since these genetic factors may be important biomarkers for individualization of immunosuppressive therapy. This article summarizes current knowledge regarding the impact of CYP3A polymorphisms on immunosuppressive drug pharmacokinetics. Many retrospective studies have shown a clear relationship between CYP3A5*1/*3 polymorphism and tacrolimus pharmacokinetics, while the influence of CYP3A5*1/*3 or CYP3A4*/*1B on ciclosporin and sirolimus exposure are still questionable. CYP3A polymorphisms may partially contribute to the clinical variability of the enzyme-mediated drug interactions. Drug-drug interactions may also influence the phenotypic consequence of CYP3A polymorphisms. Population pharmacodynamic/kinetic/genomic modeling was proposed as an emerging and promising approach to quantitatively explore the contribution of genetic polymorphisms to the large interpatient variability in the pharmacokinetic and pharmacodynamic profiles of immunosuppressive drugs. Prospective, randomized studies in large patient populations are needed to further clarify the genetic effects of CYP3A on immunosuppressive drug exposure and response.

Statin regulation of CYP3A4 and CYP3A5 expression

CYP3A4 and CYP3A5 are cytochrome P450 enzymes that are highly expressed in the liver and gut and metabolize endogenous compounds and xenobiotics. Statins are cholesterol-lowering drugs that are extensively metabolized by CYP3A4 and CYP3A5. The bioavailability of statins is affected by CYP3A4 and CYP3A5 and glucuronidases metabolism as well as uptake and efflux transporters that affect drug disposition. CYP3A4 and CYP3A5 variants have been demonstrated to influence the pharmacokinetics, efficacy and safety of statins. Inducers and inhibitors of CYP3A4 and CYP3A5 play an important role in reducing statin efficacy and increase the risk of adverse effects, respectively. Statins have been demonstrated to increase CYP3A expression in vitro, most likely because they are ligands to nuclear receptors (pregnane X receptor and constitutive androsterone receptor) that form heterodimers with retinoid X receptors and bind to responsive elements in the CYP3A4 and CYP3A5 promoter regions. This special report outlines the earlier studies on variability of response to statins owing to CYP3A variants and highlights findings on the induction of CYP3A4 and CYP3A5 expression by statins.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

CYP3A5*1/*3 genotype influences the blood concentration of tacrolimus in response to metabolic inhibition by ketoconazole

OBJECTIVES

Ketoconazole retards metabolic degradation of tacrolimus through its effect on the cytochrome P-450 enzyme system and allows reduction in treatment costs. Enzyme activity is determined by a single nucleotide polymorphism (*1/*3) in the CYP3A5 gene.

METHODS

We prospectively investigated the impact of this polymorphism on tacrolimus concentration in a cohort of 79 renal transplant recipients on ketoconazole. Genotyping was carried out by using polymerase chain reaction-restriction fragment length polymorphism technique. Dose-adjusted trough level (C0) was calculated at baseline and at 3, 7, 15, 30, and 60 days.

RESULTS

The baseline C0 was significantly lower in those with at least one *1 allele [44.95+/-14.12 vs. 63.43+/-14.72 (ng/ml)/(mg/kg/day), P<0.0001]. After starting ketoconazole in all genotypes, dose-normalized C0 increased and the cost of therapy decreased. Compared with baseline, the magnitude of increase was 112% and 79% in those without and with *1 allele, respectively (P<0.001). The cost savings were 32% and 39% in mycophenolate mofetil-treated and 47% and 61% in azathioprine-treated patients who were with and without one *1 allele, respectively.

CONCLUSION

We show that the CYP3A5*1/*3 polymorphism is an important determinant of the response to inhibition of tacrolimus metabolism by ketoconazole, with a 30% greater inhibition in those lacking *1 allele. This finding will allow better dose adjustment and minimize exposure to subtherapeutic or toxic concentrations.

Inflammatory stress and idiosyncratic hepatotoxicity: hints from animal models

Adverse drug reactions (ADRs) present a serious human health problem. They are major contributors to hospitalization and mortality throughout the world (Lazarou et al., 1998; Pirmohamed et al., 2004). A small fraction (less than 5%) of ADRs can be classified as "idiosyncratic." Idiosyncratic ADRs (IADRs) are caused by drugs with diverse pharmacological effects and occur at various times during drug therapy. Although IADRs affect a number of organs, liver toxicity occurs frequently and is the primary focus of this review. Because of the inconsistency of clinical data and the lack of experimental animal models, how IADRs arise is largely undefined. Generation of toxic drug metabolites and induction of specific immunity are frequently cited as causes of IADRs, but definitive evidence supporting either mechanism is lacking for most drugs. Among the more recent hypotheses for causation of IADRs is that inflammatory stress induced by exogenous or endogenous inflammagens is a susceptibility factor. In this review, we give a brief overview of idiosyncratic hepatotoxicity and the inflammatory response induced by bacterial lipopolysaccharide. We discuss the inflammatory stress hypothesis and use as examples two drugs that have caused IADRs in human patients: ranitidine and diclofenac. The review focuses on experimental animal models that support the inflammatory stress hypothesis and on the mechanisms of hepatotoxic response in these models. The need for design of epidemiological studies and the potential for implementation of inflammation interaction studies in preclinical toxicity screening are also discussed briefly.

Atazanavir pharmacokinetics in genetically determined CYP3A5 expressors versus non-expressors

OBJECTIVES

The objective of this study was to compare atazanavir pharmacokinetics in genetically determined CYP3A5 expressors versus non-expressors.

METHODS

HIV-negative adult volunteers were pre-screened for CYP3A5 *3, *6 and *7 polymorphisms and enrollment was balanced for CYP3A5 expressor status, gender and race (African-American versus non-African-American). Participants received atazanavir 400 mg daily for 7 days followed by atazanavir/ritonavir 300 mg/100 mg daily for 7 days with pharmacokinetic studies on days 7 and 14. Other measures collected were bilirubin, UGT1A1 *28, and ABCB1 1236C > T, 2677G > T/A and 3435C > T genotypes. Data analyses utilized least squares regression.

RESULTS

Fifteen CYP3A5 expressors and 16 non-expressors participated. The day 7 atazanavir oral clearance (CL/F) was 1.39-fold faster (0.25 versus 0.18 L/h/kg; P = 0.045) and the C(min) was half (87 versus 171 ng/mL; P = 0.044) in CYP3A5 expressors versus non-expressors. Non-African-American CYP3A5 expressor males had 2.1-fold faster CL/F (P = 0.003) and <20% the C(min) (P = 0.0001) compared with non-African-American non-expressor males. No overall CYP3A5 expressor effects were observed during the ritonavir phase. One or two copies of wild-type ABCB1 haplotype (1236C/2677G/3435C) was predictive of slower atazanavir and ritonavir CL/F compared with zero copies (P < 0.06). Indirect bilirubin increased 1.6- to 2.8-fold more in subjects with UGT1A1 *28/*28 versus *1/*28 or *1/*1.

CONCLUSIONS

CYP3A5 expressors had faster atazanavir CL/F and lower C(min) than non-expressors. The effect was most pronounced in non-African-American men. Ritonavir lessened CYP3A5 expressor effects. The wild-type ABCB1 CGC haplotype was associated with slower CL/F and the UGT1A1 *28 genotype was associated with increased bilirubin. Thus, CYP3A5, ABCB1 and UGT1A1 polymorphisms are associated with atazanavir pharmacokinetics and pharmacodynamics in vivo.

Expressed sequence tags (ESTs) and single nucleotide polymorphisms (SNPs): What large-scale sequencing projects can tell us about ADME

To date over 800 complete genomes have been sequenced, with many more partially complete. Coupled with the large amount of mRNA transcript sequence data being produced from expression studies, there is now a daunting amount of information available to the research scientist. This review examines how this information may be best used, focusing on examples from sequences encoding absorption, distribution, metabolism and excretion (ADME)-related proteins in particular. Through the use of phylogenetic, splice variant and single nucleotide polymorphism (SNP) analysis, the review examines not only how insights into species-specific responses to drug exposure may be gained, but also how best to utilize this information to predict both individual human responses and the impact of population variance in response.

Ethnic differences in the distribution ofCYP3A5gene polymorphisms

The genetic polymorphism affecting the CYP3A5 enzyme is responsible for interindividual and interethnic variability in the metabolism of CYP3A5 substrates. The full extent of the CYP3A5 genetic polymorphism was analysed in French Caucasian, Gabonese and Tunisian populations using a polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) strategy. In the three populations, eight, 17 and ten single nucleotide polymorphisms (SNPs), respectively, were identified, among which nine correspond to rare new mutations. Also identified were 16 alleles including eight new allelic variants. Significant differences were observed in the distribution of these alleles. Particularly, the frequency of the CYP3A5*3C null allele in French Caucasians (81.3%) and in Tunisians (80.0%) is higher than in the Gabonese population (12.5%) (p < 0.001). Considering the CYP3A5 genotypes of the tested individuals, only 10.4% of French Caucasians and 30.0% of Tunisians were identified as CYP3A5 expressors. In contrast, 90.0% of Gabonese subjects appear to express the CYP3A5 protein.

Gene conversion causing human inherited disease: evidence for involvement of non-B-DNA-forming sequences and recombination-promoting motifs in DNA breakage and repair

A variety of DNA sequence motifs including inverted repeats, minisatellites, and the chi recombination hotspot, have been reported in association with gene conversion in human genes causing inherited disease. However, no methodical statistically based analysis has been performed to formalize these observations. We have performed an in silico analysis of the DNA sequence tracts involved in 27 nonoverlapping gene conversion events in 19 different genes reported in the context of inherited disease. We found that gene conversion events tend to occur within (C+G)- and CpG-rich regions and that sequences with the potential to form non-B-DNA structures, and which may be involved in the generation of double-strand breaks that could, in turn, serve to promote gene conversion, occur disproportionately within maximal converted tracts and/or short flanking regions. Maximal converted tracts were also found to be enriched (P<0.01) in a truncated version of the chi-element (a TGGTGG motif), immunoglobulin heavy chain class switch repeats, translin target sites and several novel motifs including (or overlapping) the classical meiotic recombination hotspot, CCTCCCCT. Finally, gene conversions tend to occur in genomic regions that have the potential to fold into stable hairpin conformations. These findings support the concept that recombination-inducing motifs, in association with alternative DNA conformations, can promote recombination in the human genome.

Pharmacogenomics of CYP3A: considerations for HIV treatment

The understanding of the cytochrome P450 3A SNP in antiretroviral therapy is important, because it is highly inducible, extremely polymorphic and metabolizes many of the drugs that are key components of highly active antiretroviral therapy regimens. This enzyme is prolific and promiscuous towards drug and xenobiotic substrate selection and it is also unpredictable among individuals, having a 5- to 20-fold variability in its ability to contribute to drug clearance. The importance of human CYP3A pharmacogenetics is also gaining attention in other established areas of pharmacotherapy as it may contribute to the goal of predicting efficacy and/or toxicity, specifically with the discovery of null allele CYP3A4*20. This review summarizes the current understanding, implications of genetic variation in the CYP3A enzymes, the central role of CYP3A in linking human genetics, the pharmacokinetics and resulting pharmacodynamic responses to certain antiretroviral drugs, and their eventual place in applied clinical pharmacotherapy.

Genetic polymorphisms in CYP3A5 and MDR1 genes and their correlations with plasma levels of tacrolimus and cyclosporine in renal transplant recipients

Immunosuppressive drugs, such as tacrolimus (FK506) and cyclosporine (CsA), play an essential role in graft survival, preventing rejection. Large interindividual differences in drug-metabolizing enzymes as well as in drug transporters make the task of reaching the optimal concentrations difficult. The bioavailability of CsA and FK506 seems to be associated with the cytocrhome P450 IIIA (CYP3A) gene. It has also been described that the Multi Drug Resistance 1 (MDR1) gene that encodes for polyglycoprotein-P (P-gp) may influence the metabolizing action of FK506 and CsA. Therefore, we sought, to correlate single nucleotide polymorphisms (SNPs) in the CYP3A and MDR1 genes with the concentrations of FK506 and CsA. For this purpose we analyzed 2 groups of renal transplant recipients by sequencing: one receiving a CsA immunosuppressive regime, and other, an FK506-immunosuppression. This study showed that subjects in the FK506 group who had encoded the 1236C>T substitution in the MDR1 gene displayed 44.4% higher drug concentrations compared with ("wild-type") individuals. Individuals carrying the 2677G>T,A mutation showed FK506 concentrations that were 44.7% higher than the wild-type individuals. Concerning the CsA group, individuals carrying the 22915A>C substitution displayed CsA concentrations 52.1% higher than wild-type individuals.