CYP3A5 phenotype-genotype correlations in a British population

Parenteral nutrition emulsion inhibits CYP3A4 in an iPSC derived liver organoids testing platform

OBJECTIVES

Parenteral nutrition (PN) is used for patients of varying ages with intestinal failure to supplement calories. Premature newborns with low birth weight are at a high risk for developing PN associated liver disease (PNALD) including steatosis, cholestasis, and gallbladder sludge/stones. To optimize nutrition regimens, models are required to predict PNALD.

METHODS

We have exploited induced pluripotent stem cell derived liver organoids to provide a testing platform for PNALD. Liver organoids mimic the developing liver and contain the different hepatic cell types. The organoids have an early postnatal maturity making them a suitable model for premature newborns. To mimic PN treatment we used medium supplemented with either clinoleic (80% olive oil/20% soybean oil) or intralipid (100% soybean oil) for 7 days.

RESULTS

Homogenous HNF4a staining was found in all organoids and PN treatments caused accumulation of lipids in hepatocytes. Organoids exhibited a dose dependent decrease in CYP3A4 activity and expression of hepatocyte functional genes. The lipid emulsions did not affect overall organoid viability and glucose levels had no contributory effect to the observed results.

CONCLUSIONS

Liver organoids could be utilized as a potential screening platform for the development of new, less hepatotoxic PN solutions. Both lipid treatments caused hepatic lipid accumulation, a significant decrease in CYP3A4 activity and a decrease in the RNA levels of both CYP3A4 and CYP1A2 in a dose dependent manner. The presence of high glucose had no additive effect, while Clinoleic at high dose, caused significant upregulation of interleukin 6 and TLR4 expression.

Ethnicity-based classifications and medical genetics: One Health approaches from a Western Pacific perspective

A new era presently dawns for medical genetics featuring individualised whole genome sequencing and promising personalised medical genetics. Accordingly, we direct readers attention to the continuing value of allele frequency data from Genome-Wide Association Surveys (GWAS) and single gene surveys in well-defined ethnic populations as a guide for best practice in diagnosis, therapy, and prescription. Supporting evidence is drawn from our experiences working with Austronesian volunteer subjects across the Western Pacific. In general, these studies show that their gene pool has been shaped by natural selection and become highly diverged from those of Europeans and Asians. These uniquely evolved patterns of genetic variation underlie contrasting schedules of disease incidence and drug response. Thus, recognition of historical bonds of kinship among Austronesian population groups across the Asia Pacific has distinct public health advantages from a One Health perspective. Other than diseases that are common among them like gout and diabetes, Austronesian populations face a wide range of climate-dependent infectious diseases including vector-borne pathogens as they are now scattered across the Pacific and Indian Oceans. However, we caution that the value of genetic survey data in Austronesians (and other groups too) is critically dependent on the accuracy of attached descriptive information in associated metadata, including ethnicity and admixture.

Representation of CYP3A4, CYP3A5 and UGT1A4 Polymorphisms within Croatian Breast Cancer Patients' Population

Single nucleotide polymorphism (SNP) in genes encoding drug-metabolizing enzymes (DME) could have a critical role in individual responses to anastrozole. Frequency of CYP3A4*1B, CYP3A5*3 and UGT1A4*2 SNPs in 126 Croatian breast cancer (BC) patients and possible association with anastrozole-induced undesirable side effects were analyzed. Eighty-two postmenopausal patients with estrogen receptor (ER)-positive BC treated with anastrozole and 44 postmenopausal ER-positive BC patients before hormonal adjuvant therapy were included in the study. Genomic DNA was genotyped by TaqMan Real-Time PCR. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry. The homozygotes for the variant G allele of CYP3A5*3 were predominant (88%), and the homozygotes for the reference A allele were not detected. While homozygotes for the variant G allele of CYP3A4*1B were not detected, predominantly wild type homozygotes for A allele (94%) were present. CYP3A4*1B and CYP3A5*3 SNPs were in 84.3% linkage disequilibrium (D’ = 0.843) and 95.1% (D’ = 0.951) in group treated with anastrozole and w/o treatment, respectively. Homozygotes for the A allele of UGT1A4*2 were not detected in our study groups. Although the variant CYP3A5*3 allele, which might result in poor metabolizer phenotype and more pronounced side effects, was predominant, significant association with BMD changes induced by anastrozole were not confirmed.

A Minimal Physiologically-Based Pharmacokinetic Model for Tacrolimus in Living-Donor Liver Transplantation: Perspectives Related to Liver Regeneration and the cytochrome P450 3A5 (CYP3A5) Genotype

In adult patients after living‐donor liver transplantation, postoperative days and the cytochrome P450 3A5 (CYP3A5) genotype are known to affect tacrolimus pharmacokinetics. In this study, we constructed a physiologically‐based pharmacokinetic model adapted to the clinical data and evaluated the contribution of liver regeneration as well as hepatic and intestine CYP3A5 genotypes on tacrolimus pharmacokinetics. As a result, liver function recovered immediately and affected the total body clearance of tacrolimus only during a limited period after living‐donor liver transplantation. The clearance was about 1.35‐fold higher in the recipients who had a liver with the CYP3A5*1 allele than in those with the CYP3A5*3/*3 genotype, whereas bioavailability was ~0.7‐fold higher in the recipients who had intestines with the CYP3A5*1 allele than those with CYP3A5*3/*3. In conclusion, the constructed physiologically‐based pharmacokinetic model clarified that the oral clearance of tacrolimus was affected by the CYP3A5 genotypes in both the liver and intestine to the same extent.

Effects of UGT1A1, CYP3A5 and ABCB1 Genetic Variants on Pharmacokinetics of Antihistamine Drug Mizolastine in Chinese Healthy Volunteers

Mizolastine is a selective histamine H1 receptor antagonist for chronic urticaria or allergic rhinitis. We investigated whether the variant genotypes of metabolic enzymes UGT1A1, CYP3A5 and transporter ABCB1 influence pharmacokinetic phenotype of substrate mizolastine in Chinese volunteers. Genotyping of single nucleotide polymorphisms in UGT1A1*6 (G211A), CYP3A5*3 (A6986G) and ABCB1 (C3435T) was determined by the pyrosequencing method. After a single oral dose of 10 mg mizolastine, the plasma concentrations were measured using validated high-performance liquid chromatography in 24 Chinese healthy volunteers. The results showed that the distributions of wild-type homozygotes and variant allele carriers (the sum of variant heterozygotes and variant homozygotes) were as follows: 17 cases (70.8%) versus seven cases (29.2%) in UGT1A1*6 genotypes, five cases (20.8%) versus 19 cases (79.2%) in CYP3A5*3 genotypes and seven cases (29.2%) versus 17 cases (70.8%) in ABCB1 3435T genotypes, respectively. There were no significant differences in pharmacokinetic parameters of mizolastine between the variant allele UGT1A1*6, CYP3A5*3 and ABCB1 3435T carriers and the wild-type homozygotes, and the ratios were as follows: C_max was 101.03%, 86.02% and 105.78%; T_max was 162.35%, 98.98% and 144.90%; AUC_0-28 was 113.04%, 77.35% and 112.71%; and t_1/2 was 95.77%, 72.40% and 100.97%, respectively. In conclusion, these results suggested that the UGT1A1, CYP3A5 and ABCB1 genetic polymorphisms might be not contributed to the interindividual variation of mizolastine pharmacokinetic phenotype in the Chinese population.

Expression of hepatic drug-metabolizing cytochrome p450 enzymes and their intercorrelations: a meta-analysis

Cytochrome P450 is a family of enzymes that catalyze reactions involved in the metabolism of drugs and other xenobiotics. These enzymes are therefore important in pharmacologic and toxicologic studies, and information on their abundances is of value in the process of scaling in vitro data to in vivo metabolic parameters. A meta-analysis was applied to data on the abundance of human hepatic cytochrome P450 enzymes in Caucasian adult livers (50 studies). Despite variations in the methods used to measure the abundance of enzymes, agreement between the studies in 26 different laboratories was generally good. Nonetheless, some heterogeneity was detected (Higgins and Thompson heterogeneity test). More importantly, large interindividual variability was observed in the collated data. Positive correlations between the expression levels of some cytochrome P450 enzymes were found in the abundance data, including the following pairs: CYP3A4/CYP3A5*1/*3 (Rs = 0.70, P < 0.0001, n = 52), CYP3A4/CYP2C8 (Rs = 0.68, P < 0.0001, n = 134), CYP3A4/CYP2C9 (Rs = 0.55, P < 0.0001, n = 71), and CYP2C8/CYP2C9 (Rs = 0.55, P < 0.0001, n = 99). These correlations can be used to demonstrate common genetic transcriptional mechanisms.

Relationship between genotypes Sult1a2 and Cyp2d6 and tamoxifen metabolism in breast cancer patients

Tamoxifen is a pro-drug widely used in breast cancer patients to prevent tumor recurrence. Prior work has revealed a role of cytochrome and sulfotransferase enzymes in tamoxifen metabolism. In this descriptive study, correlations were examined between concentrations of tamoxifen metabolites and genotypes for CYP2D6, CYP3A4, CYP3A5, SULT1A1, SULT1A2 and SULT1E1 in 135 patients with estrogen receptor-positive breast cancer. Patients were genotyped using the Roche-AmpliChip® CYP450 Test, and Real-Time and conventional PCR-RFLP. Plasma tamoxifen, 4-hydroxy-tamoxifen, N-desmethyl-tamoxifen, endoxifen and tamoxifen-N-oxide were isolated and quantified using a high-pressure liquid chromatography-tandem mass spectrometry system. Significantly higher endoxifen levels were detected in patients with the wt/wt CYP2D6 compared to the v/v CYP2D6 genotype (p<0.001). No differences were detected in the remaining tamoxifen metabolites among CYP2D6 genotypes. Patients featuring the SULT1A2*2 and SULT1A2*3 alleles showed significantly higher plasma levels of 4-hydroxy-tamoxifen and endoxifen (p = 0.025 and p = 0.006, respectively), as likely substrates of the SULT1A2 enzyme. Our observations indicate that besides the CYP2D6 genotype leading to tamoxifen conversion to potent hydroxylated metabolites in a manner consistent with a gene-dose effect, SULT1A2 also seems to play a role in maintaining optimal levels of both 4-hydroxy-tamoxifen and endoxifen.

From gut to kidney: transporting and metabolizing calcineurin-inhibitors in solid organ transplantation

Since their introduction circa 35 years ago, calcineurin-inhibitors (CNI) have become the cornerstone of immunosuppressive therapy in solid organ transplantation. However, CNI's possess a narrow therapeutic index with potential severe consequences of drug under- or overexposure. This demands a meticulous policy of Therapeutic Drug Monitoring (TDM) to optimize outcome. In clinical practice optimal dosing is difficult to achieve due to important inter- and intraindividual variation in CNI pharmacokinetics. A complex and often interdependent set of factors appears relevant in determining drug exposure. These include recipient characteristics such as age, race, body composition, organ function, and food intake, but also graft-related characteristics such as: size, donor-age, and time after transplantation can be important. Fundamental (in vitro) and clinical studies have pointed out the intrinsic relation between the aforementioned variables and the functional capacity of enzymes and transporters involved in CNI metabolism, primarily located in intestine, liver and kidney. Commonly occurring polymorphisms in genes responsible for CNI metabolism (CYP3A4, CYP3A5, CYP3A7, PXR, POR, ABCB1 (P-gp) and possibly UGT) are able to explain an important part of interindividual variability. In particular, a highly prevalent SNP in CYP3A5 has proven to be an important determinant of CNI dose requirements and drug-dose-interactions. In addition, a discrepancy in genotype between graft and receptor has to be taken into account. Furthermore, common phenomena in solid organ transplantation such as inflammation, ischemia- reperfusion injury, graft function, co-medication, altered food intake and intestinal motility can have a differential effect on the expression enzymes and transporters involved in CNI metabolism. Notwithstanding the built-up knowledge, predicting individual CNI pharmacokinetics and dose requirements on the basis of current clinical and experimental data remains a challenge.

Role of pharmacogenetics on adjuvant chemotherapy-induced neutropenia in Chinese breast cancer patients

BACKGROUND

Breast cancer patients regularly undergo adjuvant chemotherapies following surgery. However, these treatments are largely associated with chemotherapeutic toxicities ranging from nausea to severe myelosuppression. In this investigation, we examined the effects of four SNPs in NR1I2, CYP3A4 and CYP3A5 genes on chemotherapy-induced severe neutropenia in 311 female Chinese breast cancer patients undergoing a standard adjuvant chemotherapy regimen.

METHODS

Patients were monitored for adverse reactions throughout the treatment, then divided into "none or mild" (80 %) or "severe" (20 %) toxicity groups according to whether they suffered grade 4 neutropenia defined as having an absolute neutrophil counts (ANC) of less than 0.5 × 10(9)/L anytime during the treatment. DNA was extracted from patients' peripheral blood samples, then genotyped using allele-specific Tm-shift PCR and melting analysis.

RESULTS

Logistic regression revealed that rs776746 or CYP3A5*3 strongly associated with grade 4 neutropenia (OR = 2.56, P = 0.023) after adjustment for covariates, one of which more significant factor was baseline ANC (OR = 0.68, P = 0.020). Although univariate analysis in all patients did not reveal any association at first, further analysis indicated that rs776746 is significantly associated with severe neutropenia in subgroup of breast cancer patients with normal baseline ANC (≥2.0 × 10(9)/L). These carriers of A-allele have 3.14-fold increased risk of developing severe neutropenia (P = 0.004).

CONCLUSION

Our results suggested that polymorphisms in CYP3A5 might be useful pharmacogenetic markers for the prediction of severe neutropenia during chemotherapy, however, only after screening patients by their baseline ANC in the presence of gene-environmental interaction. We demonstrate an approach of pharmacogenetic analysis, in which the genetic data should be analyzed in the perspective of other clinical parameters.

Pharmacogenomics of Cytochrome P450 3A4: Recent Progress Toward the "Missing Heritability" Problem

CYP3A4 is the most important drug metabolizing enzyme in adult humans because of its prominent expression in liver and gut and because of its broad substrate specificity, which includes drugs from most therapeutic categories and many endogenous substances. Expression and function of CYP3A4 vary extensively both intra- and interindividually thus contributing to unpredictable drug response and toxicity. A multitude of environmental, genetic, and physiological factors are known to influence CYP3A4 expression and activity. Among the best predictable sources of variation are drug–drug interactions, which are either caused by pregnane X-receptor (PXR), constitutive androstane receptor (CAR) mediated gene induction, or by inhibition through coadministered drugs or other chemicals, including also plant and food ingredients. Among physiological and pathophysiological factors are hormonal status, age, and gender, the latter of which was shown to result in higher levels in females compared to males, as well as inflammatory processes that downregulate CYP3A4 transcription. Despite the influence of these non-genetic factors, the genetic influence on CYP3A4 activity was estimated in previous twin studies and using information on repeated drug administration to account for 66% up to 88% of the interindividual variation. Although many single nucleotide polymorphisms (SNPs) within the CYP3A locus have been identified, genetic association studies have so far failed to explain a major part of the phenotypic variability. The term “missing heritability” has been used to denominate the gap between expected and known genetic contribution, e.g., for complex diseases, and is also used here in analogy. In this review we summarize CYP3A4 pharmacogenetics/genomics from the early inheritance estimations up to the most recent genetic and clinical studies, including new findings about SNPs in CYP3A4 (*22) and other genes (P450 oxidoreductase (POR), peroxisome proliferator-activated receptor alpha (PPARA)) with possible contribution to CYP3A4 variable expression.

Genetic polymorphisms of the CYP3A4, CYP3A5, CYP3A7 and CYP1A2 among the Jordanian population

Cytochromes P450 (CYP450) plays an extremely vital role in oxidation, reduction, and peroxidation of numerous endogenous and exogenous compounds, like drugs and procarcinogens. Mainly, expression occurs in the liver, in varying polymorphic forms. Therefore, proposed as biomarkers of susceptibility to carcinogenicity and toxicity. The objective of this study was to find the allelic frequencies of CYP3A5*2,*3,*4,*5,*6,*7, CYP3A4*1B, CYP3A7*1C and CYP1A2*1C, *1D, *1E, *1F enzymes in Jordanians, and to compare them with other ethnic groups. We used polymerase chain reaction-restriction fragment length (PCR-RFLP) to genotype alleles, and we calculated frequencies using Hardy Weinberg's equation (HWE). Allelic frequencies results were: CYP3A5*2 (0.2%), CYP3A5*3 (86.6%), CYP3A5*6 (1.7%), CYP*3A5*4,*5*7 not detected, CYP3A4*1B (11.7%), CYP3A7*1C (1.7%). Finally 6.5%, 18.2%, 6.0%, 67.3% were the results of CYP1A2*1C, 1D, 1E and 1F, respectively. In conclusion, genotyping method and results of this study can be adopted or used in pharmacotherapy, toxicity and carcinogenic studies in Jordan.

Dimovski A. Frequency of the most common CYP3A5 polymorphisms in the healthy population of the Republic of Macedonia

The genetic polymorphism affecting the CYP3A5 enzyme is responsible for inter-individual and interethnic variability in the metabolism of CYP3A5 substrates. The aim of this study was to analyze the distribution of the most common CYP3A5*3 allelic variants in the healthy population of R. Macedonia and to investigate if the allelic frequency falls within the assumed range for European Caucasians. The total of 174 healthy volunteers from the general population were included. The genotyping of the CYP3A5*3 variant alleles, *3A (rs15524) and *3E (rs28365095), was performed with Real-Time PCR based on the allelic discrimination method using a TaqMan SNP genotyping assay according to the manufacturer’s instructions. The CYP3A5*3 allele is abundantly present displaying an allelic frequency of 0.922. We estimate that 0.82 of the Macedonian population are homozygotes for the variant and do not have a CYP3A5 enzymatic activity. Our study demonstrated a high prevalence of CYP3A5*3 allele in the Macedonian population. The distribution of CYP3A5 alleles was similar to that found in other European Caucasians. As the goals of personalized medicine are beginning to be realized, this provides basic information on the CYP3A5 allele frequency for the future pharmacogenetic research in R. Macedonia.

Tacrolimus and 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors: An interaction study in CYP3A5 non-expressors, renal transplant recipients

OBJECTIVES

Atherosclerosis is a significant factor affecting long-term outcome in renal transplant recipients. Studies have been conducted to determine the pharmacogenomic pathways involved in statin efficacy, efficiency, and adverse effect likelihood. However, little is known about the influence of statins on tacrolimus kinetics. The aim of this study was to investigate possible pharmacological interactions between tacrolimus and statins in CYP3A5 non-expressors, renal transplant recipients.

MATERIALS AND METHODS

Twenty-four patients, treated with tacrolimus (n=24), methylprednisolone (n=24), and mycophenolate mofetil (n=19)/azathioprine (n=1)/everolimus (n=4), participated in the study. After an observation time of 112±36 days, statins, namely, atorvastatin (n=12), simvastatin (n=8), pravastatin (n=2), or fluvastatin (n=2), were administered for additional 101±34 days. DNA was extracted from whole blood sample and polymerase chain reaction followed by restriction fragment length polymorphism analysis was used for CYP3A5 genotyping. Student's t-test and Mann-Whitney test were used to test the significance of difference in variables that passed or did not pass Kolmogorov's normality test, respectively.

RESULTS

No statistically significant difference was observed in tacrolimus daily dose, concentration, concentration/dose ratio, and volume of distribution before and during the administration of statins. Statistically significant decrease in serum cholesterol was observed after initiation of statins. Renal and hepatic function remained unchanged and no skeletal muscle abnormalities were reported.

CONCLUSIONS

The results of this study show that tacrolimus and statins do not interact in terms of efficacy, efficiency, and adverse effect likelihood. No significant clinical interaction or effect was observed, even with the use of atorvastatin or simvastatin, which are metabolized by CYP3A4 such as tacrolimus.

Impact of CYP2D6, CYP3A5, CYP2C9 and CYP2C19 polymorphisms on tamoxifen pharmacokinetics in Asian breast cancer patients

AIM

To investigate the impact of genetic polymorphisms in CYP2D6, CYP3A5, CYP2C9 and CYP2C19 on the pharmacokinetics of tamoxifen and its metabolites in Asian breast cancer patients.

METHODS

A total of 165 Asian breast cancer patients receiving 20 mg tamoxifen daily and 228 healthy Asian subjects (Chinese, Malay and Indian; n= 76 each) were recruited. The steady-state plasma concentrations of tamoxifen and its metabolites were quantified using high-performance liquid chromatography. The CYP2D6 polymorphisms were genotyped using the INFINITI™ CYP450 2D6I assay, while the polymorphisms in CYP3A5, CYP2C9 and CYP2C19 were determined via direct sequencing.

RESULTS

The polymorphisms, CYP2D6*5 and *10, were significantly associated with lower endoxifen and higher N-desmethyltamoxifen (NDM) concentrations. Patients who were *1/*1 carriers exhibited 2.4- to 2.6-fold higher endoxifen concentrations and 1.9- to 2.1-fold lower NDM concentrations than either *10/*10 or *5/*10 carriers (P < 0.001). Similarly, the endoxifen concentrations were found to be 1.8- to 2.6-times higher in *1/*5 or *1/*10 carriers compared with *10/*10 and *5/*10 carriers (P≤ 0.001). Similar relationships were observed between the CYP2D6 polymorphisms and metabolic ratios of tamoxifen and its metabolites. No significant associations were observed with regards to the polymorphisms in CYP3A5, CYP2C9 and CYP2C19.

CONCLUSIONS

The present study in Asian breast cancer patients showed that CYP2D6*5/*10 and *10/*10 genotypes are associated with significantly lower concentrations of the active metabolite of tamoxifen, endoxifen. Identifying such patients before the start of treatment may be useful in optimizing therapy with tamoxifen. The role of CYP3A5, CYP2C9 and CYP2C19 seem to be minor.

Impact of CYP3A5 and CYP3A4 gene polymorphisms on dose requirement of calcineurin inhibitors, cyclosporine and tacrolimus, in renal allograft recipients of North India

The present study investigated pharmacogenetic associations of common cytochrome P450 3A (CYP3A5 and CYP3A4) polymorphisms with dose requirements of calcineurin inhibitors, cyclosporine (CsA) and tacrolimus (Tac) in renal transplant recipients of North India. Two hundred twenty four patients on CsA and 73 patients on Tac-based immunosuppression regimen were genotyped for CYP3A5*3 (6986A>G) and CYP3A4*1B (-290A>G) and correlated with CsA/Tac dose requirement (mg/kg/day) and dose-adjusted CsA (C(2))/Tac (T (0)) blood levels (concentration/dose ratio) at 1 month and 3 months posttransplantation. The dose-adjusted levels were significantly lower in CYP3A5 expressers for CsA (p = 0.037; 3 months) and Tac (p < 0.001; 1 month and p < 0.001; 3 months) compared to the non-expressers, suggesting that for a given dose their CsA/Tac blood concentration is lower. The CYP3A5 non-expresser genotype was associated with reduced risk for allograft rejection (HR-0.18, 95% CI 0.03-0.99). No influence of CYP3A4*1B on CsA/Tac pharmacokinetics was observed. CYP3A5 expressers were associated with significantly lower dose-adjusted CsA/Tac concentrations and higher allograft rejection episodes in patients on Tac therapy.

Antiplatelet effect of clopidogrel in patients with aspirin therapy undergoing percutaneous coronary interventions--limited inhibition of the P2Y12 receptor

INTRODUCTION

Large individual variability in clopidogrel responses has been reported. However, mechanisms of the non-responsiveness are unclear. Our aim was to study the extent of platelet inhibition at the receptor level by in vitro receptor antagonists of P2Y(12) (AR-C69931MX, cangrelor) and P2Y(1) (adenosine 3',5'diphosphate) in aspirin treated patients with coronary artery disease (CAD) prior to and after in vivo clopidogrel.

MATERIALS AND METHODS

51 aspirin-treated (100 mg/day) patients participated. Blood was collected before and after administration of clopidogrel at 300 mg loading dose on day one, followed by 75 mg/d for four days. Aggregation in platelet-rich plasma was assessed.

RESULTS

In 20% of patients clopidogrel failed to inhibit platelet responses to ADP. These non-responders had also decreased sensitivity to an in vitro P2Y(12)-receptor antagonist compared with the responders (mean inhibition of aggregation 25 vs. 32%, difference of means 7% (95% CI 2-12%), P<0.02). Moreover, the P2Y(12)-receptor inhibition by in vivo clopidogrel correlated with the inhibition by in vitro ARMX measured prior to administration of clopidogrel. Neither P2Y(1)-receptor activity, thrombin generation while on aspirin nor basal platelet activity associated with clopidogrel responses.

CONCLUSIONS

Concomitant aspirin and clopidogrel treatment failed to suppress platelet activity in 20% of patients. Non-responders to clopidogrel had decreased responses also to another ADP receptor antagonist, which suggests that the impaired response occurs at the level of P2Y(12)-receptor.

CYP2C19 genotype is a major factor contributing to the highly variable pharmacokinetics of voriconazole

In vitro data on the metabolism of the antifungal voriconazole suggest that its pharmacokinetics might be influenced by the activity of CYP2C19, CYP2C9, and CYP3A. To elucidate the genetic influence of polymorphic enzymes on voriconazole metabolism, the authors pooled the pharmacokinetic data from 2 interaction studies in which 35 participants were enrolled according to their CYP2C19 genotype to receive a single 400-mg oral dose of voriconazole. Nine participants were homozygous for CYP2C19(*)1/(*)1, 8 heterozygous for (*)1/(*)17, 11 heterozygous for (*)1/(*)2, 2 heterozygous for (*)2/(*)17, 4 homozygous for (*)2/(*)2, and 1 with a double mutation CYP2C19(*)2/(*)2(*)17. Nine (heterozygous) individuals were carriers of the CYP2C9(*)2 or (*)3 variant alleles. Twenty-five participants did not express the CYP3A5 isozyme ((*)3/(*)3), whereas in 5 individuals, the (*)1/(*)3 combination was present (active enzyme). In addition, the CYP2D6 genotype and 2 variants of the drug transporter MDR1 (C3435T and G2677T) were determined. Multiple regression analysis of voriconazole apparent oral clearance revealed that 49% of its variance can be explained solely by the CYP2C19 polymorphism (P < .0001). Including the other polymorphisms into the regression model did not show any significant contribution. The number of variant CYP2C19 alleles therefore explains a substantial part of the wide variability of voriconazole pharmacokinetics, whereas the presence of functional CYP3A5 and the CYP2C9 genotype had no significant impact on voriconazole exposure. Some minor contribution results from the MDR1 C3435T genotype.

An Interethnic Comparison of Polymorphisms of the Genes Encoding Drug-Metabolizing Enzymes and Drug Transporters: Experience in Singapore

Much of the interindividual variability in drug response is attributable to the presence of single nucleotide polymorphisms (SNPs) in genes encoding drug-metabolizing enzymes and drug transporters. In recent years, we have investigated the polymorphisms in a number of genes encoding phase I and II drug-metabolizing enzymes including CYPIA1, CYP3A4, CYP3A5, GSTM1, NAT2, UGT1A1, and TPMT and drug transporter (MDR1) in three distinct Asian populations in Singapore, namely the Chinese, Malays, and Indians. Significant differences in the frequencies of common alleles encoding these proteins have been observed among these three ethnic groups. For example, the frequency of the variant A2455G polymorphism of CYP1A1 was 28% in Chinese and 31% in Malays, but only 18% in Indians. CYP3A4*4 was detected in two of 110 Chinese subjects, but absent in Indians and Malays. Many Chinese and Malays (61-63%) were homozygous for the GSTM1*0 null genotype compared with 33% of Indians. The frequency of the UGTIA1*28 allele was highest in the Indian population (35%) compared to similar frequencies that were found in the Chinese (16%) and Malay (19%) populations. More importantly, our experience over the years has shown that the pharmacogenetics of these drug-metabolizing enzymes and MDR1 in the Asian populations are different from these in the Caucasian and African populations. For example, the CYP3A4*1B allele, which contains an A-290G substitution in the promoter region of CYP3A4, is absent in all three Asian populations of Singapore studied, but occurs in more than 54% of Africans and 5% of Caucasians. There were no difference in genotype and allelic variant frequencies in exon 12 of MDR1 between the Chinese, Malay, and Indian populations. When compared with other ethnic groups, the distribution of the wild-type C allele in exon 12 in the Malays (34.2%) and Indians (32.8%) was relatively high and similar to the Japanese (38.55%) and Caucasians (41%) but different from African-Americans (15%). The frequency of wild-type TT genotype in Asians (43.5% to 52.1%) and Japanese (61.5%) was much higher than those found in Caucasians (13.3%). All the proteins we studied represent the primary hepatic or extrahepatic enzymes, and their polymorphic expression may be implicated in disease risk and the disposition of drugs or endogenous substances. As such, dose requirements of certain drugs may not be optimal for Asian populations, and a second look at the factors responsible for this difference is necessary.

Global pharmacogenetics: genetic substructure of Eurasian populations and its effect on variants of drug-metabolizing enzymes

AIMS

To study the frequency distribution of cytochrome P450 (CYP) functional genetic variants in five Eurasian populations from the territory of Siberia in Russia.

MATERIALS & METHODS

Unrelated healthy Tuvinians, Buryats, Altaians, Yakuts and Russians (n = 87-88) were genotyped for CYP2C9*2, CYP2C9*3, CYP2C19*2, CYP2C19*3, CYP3A5*3 and CYP3A5*6. Standard pairwise genetic distances, locus-specific and global Fst statistics were calculated.

RESULTS

CYP allele and genotype frequencies demonstrated significant variability. Overall, the degree of between-population variance displayed by CYP SNPs was lower than that recorded from neutral short tandem repeats and Alu-insertion polymorphism, indicating evolutionary conservation of CYP polymorphisms. CYP-based genetic distances were well correlated with the geographic distances across populations (r = 0.822, p = 0.008).

CONCLUSIONS

Although the tested variants were present in the neighboring, yet secluded, populations at the expected range of frequencies, the observed frequencies were significantly variable across Eurasian populations, indicating potential relevance to clinical decision making.

Disparity in holoprotein/apoprotein ratios of different standards used for immunoquantification of hepatic cytochrome P450 enzymes

An analysis of reported hepatic abundances of CYP3A4 and 3A5 indicated that values determined by immunoquantification using commercially available, unpurified recombinant enzymes as standards are significantly lower than those determined using purified enzymes or human liver microsomes characterized with lysosomal peptides (CYP3A4: mean 45 versus 121 pmol/mg protein, p < 0.01; CYP3A5: mean 28 versus 83 pmol/mg protein, p < 0.05). When immunoquantifying cytochromes P450 (P450s), it is assumed that the holoprotein (holo)/apoprotein ratio is the same in the samples and the standard. Estimates of holo/apoprotein ratios from data reported for a range of P450s purified from human liver and non-commercial recombinant systems indicated less than complete and variable heme coupling dependent on enzyme and system.

Genetic polymorphisms of drug-metabolizing enzymes CYP2D6, CYP2C9, CYP2C19 and CYP3A5 in the Greek population

The aim of the present study was to determine the prevalence of the most common allelic variants of the polymorphic cytochrome P450 (CYP) enzymes CYP2D6, CYP2C9, CYP2C19 and CYP3A5 and to predict the genotype frequency for each polymorphism in the Greek population. DNA isolated from peripheral blood samples derived from 283 non-related Greek ethnic subjects was used to determine the frequency of CYP2D6*3, CYP2D6*4, CYP2C9*2, CYP2C9*3 and CYP3A5*3 allelic variants by the polymerase chain reaction (PCR)-restriction fragment length polymorphism method, CYP2C19*2 and CYP2C19*3 with allelic specific amplification (PCR-ASA), and CYP2D6*2 (gene duplications) by long PCR analysis. The allelic frequencies (out of a total of 566 alleles) for CYP2D6*3 and CYP2D6*4, were 2.3% and 17.8%, respectively, while gene duplications (CYP2D6*2) were found in 7.4% of the subjects tested. For CYP2C9*2 and CYP2C9*3 polymorphisms the allelic frequencies were 12.9% and 8.13% respectively. For CYP2C19, the *2 polymorphism was present at an allelic frequency of 13.1%, while no subjects were found carrying the CYP2C19*3 allele. Finally, the CYP3A5*3 allele was abundantly present in the Greek population with an allelic frequency of 94.4%. Overall our results show that the frequencies of the common defective allelic variants of CYP2C9, CYP2C19 and CYP3A5 in Greek subjects are similar to those reported for several other Caucasian populations. Finally, a high prevalence of CYP2D6 gene duplication among Greeks was found, a finding that strengthens the idea that a South/North gradient exists in the occurrence of CYP2D6 ultrarapid metabolizers in European populations.

CYP3A5 genotype has an impact on the metabolism of the HIV protease inhibitor saquinavir

CYP3A is the main enzyme subfamily involved in the metabolism of the HIV protease-inhibitor saquinavir. We hypothesized that individuals homozygous for CYP3A5*1 might have a higher oral clearance of saquinavir, compared with subjects lacking functional CYP3A5 alleles. A single-dose pharmacokinetic trial of saquinavir soft gel capsules, 1,200 mg, was performed in 16 black Tanzanian healthy volunteers with two functional CYP3A5 alleles (*1/*1) and in 18 volunteers without functional CYP3A5 alleles (both alleles being either *3, *6, or *7). The median area under the plasma concentration-time curve (AUC)0-24 reached among subjects with two functional alleles was 1,410 ng h/ml (interquartile range (IQR) 826-1,929), whereas it was 2,138 ng h/ml (IQR 1,380-3,331) in subjects without (P=0.0533, Mann-Whitney U-test). The median ratio of saquinavir over its M2 plus M3 hydroxy metabolites in urine was 64 (IQR 52-73) in subjects with two functional alleles, whereas it was 145 (IQR 89-181) in those without (P=0.000078, Mann-Whitney U-test). In conclusion, saquinavir is metabolized by CYP3A5. The median AUC0-24 for saquinavir among individuals with two functional CYP3A5 alleles was 34% lower than among those with no functional alleles. To clarify the clinical importance of the CYP3A5 polymorphism, further studies should be conducted on saquinavir, dosed to steady state, in the presence of ritonavir boosting.

Effects of genetic polymorphisms of CYP3A4, CYP3A5 and MDR1 on cyclosporine pharmacokinetics after renal transplantation

1. The calcineurin inhibitor cyclosporine is widely used to prevent allograft rejection after solid organ transplantation. It has a narrow therapeutic index and shows considerable interindividual differences in its pharmacokinetics. Interindividual differences in the activity and expression of the metabolising enzymes cytochrome P450 (CYP) 3A4 and 3A5 and the multidrug efflux pump P-glycoprotein (P-gp) contribute considerably to cyclosporine pharmacokinetics. Variability in the activity of CYP3A4, CYP3A5 and P-gp could be considered to result from genetic polymorphisms encoding their genes. 2. The aim of the present study was to evaluate retrospectively the effects of genetic polymorphisms of CYP3A4, CYP3A5 and MDR1 on cyclosporine dose adjusted trough blood concentration during the early period after renal transplantation in Chinese patients. 3. One hundred and six renal transplant recipients in China were genotyped by polymerase chain reaction-restriction fragment length polymorphism for CYP3A4*18A, CYP3A5*3 and MDR1 C3435T. Cyclosporine whole blood levels were measured by fluorescence polarization immunoassay. Dose-adjusted trough blood concentrations (C(0)) were determined and compared among the different genotype groups. 4. The frequency of the CYP3A4*18A, CYP3A5*3 and MDR1 C3435T variant alleles were 0.005 (95% confidence interval (CI) 0.048, 0.0049), 0.783 (95% CI 0.781, 0.785) and 0.528 (95% CI 0.526, 0.531), respectively, and these alleles exhibited incomplete linkage disequilibrium. The median cyclosporine dose-adjusted C(0) in CYP3A5*1/*1 genotype subjects (n = 6) was 14.8 ng/mL per mg per kg (range 11.1-26.8 ng/mL per mg per kg), in CYP3A5*1/*3 patients (n = 34) it was 23.7 ng/mL per mg per kg (range 9.0-61.0 ng/mL per mg per kg) and for CYP3A5*3/*3 patients (n = 66) it was 26.4 ng/mL per mg per kg (range 9.8-85.8 ng/mL per mg per kg; P = 0.012, Kruskal-Wallis test). Accordingly, cyclosporine dose-adjusted C0 was larger in CYP3A5 non-expressors than expressors in the first week after renal transplantation. In addition, wild-type homozygotes (n = 21) for MDR1 C3435T had a slight but significantly lower dose-adjusted C0 compared with heterozygotes (n = 58): 17.7 (10.3-60.8) versus 26.4 (9.0-67.3) ng/mL per mg per kg, respectively (P = 0.014, Mann-Whitney U-test). 5. In conclusion, the present study shows that genetic polymorphisms in CYP3A5 may be responsible, in part, for the large interindividual variability of cyclosporine pharmacokinetics during the early phase after renal transplantation in Chinese patients. Patients with the CYP3A5*3 variant genotype require a low dose of cyclosporine to reach target levels compared with those with the CYP3A5*1 allele.

Genetic susceptibility to diclofenac-induced hepatotoxicity: contribution of UGT2B7, CYP2C8, and ABCC2 genotypes

BACKGROUND & AIMS

Diclofenac is a widely used nonsteroidal anti-inflammatory drug and is among the most common drugs causing idiosyncratic hepatotoxicity in several recent series with up to 20% mortality in jaundiced subjects. We hypothesized that susceptibility to hepatotoxicity would be associated with genetic polymorphisms in the genes encoding the enzymes UGT2B7 and CYP2C8, which determine the formation of reactive diclofenac metabolites and in ABCC2 encoding the transporter MRP2 contributing to the biliary excretion of the reactive metabolite.

METHODS

Twenty-four patients (19 female) aged 24-70 (mean, 50.8) years who had suffered diclofenac hepatotoxicity, 48 subjects (35 female) aged 22-77 (mean, 52) years who were taking diclofenac for 0.3-20 (mean, 4) years without developing hepatotoxicity (hospital controls), and 112 healthy controls were investigated. Genotyping for several polymorphisms in the genes encoding UGT2B7, CYP2C8, and ABCC2 was performed and haplotypes assigned.

RESULTS

The UGT2B7*2 allele was more common in diclofenac hepatotoxicity patients compared with hospital controls (odds ratio [OR], 8.5, P = .03) and healthy controls (OR, 7.7, P = .03). The ABCC2 C-24T variant was more common in hepatotoxicity patients compared with hospital (OR, 5.0, P = .005) and healthy controls OR: 6.3, P = .0002). Haplotype distributions for CYP2C8 were different in patients compared with hospital controls (P = .04).

CONCLUSIONS

Allelic variants of UGT2B7, CYP2C8, and ABCC2, which may predispose to the formation and accumulation of reactive diclofenac metabolites are associated with diclofenac hepatotoxicity. Increased level of reactive metabolites may lead to higher levels of protein-diclofenac adducts and subsequently hepatotoxicity.

CYP3A5 genotype markedly influences the pharmacokinetics of tacrolimus and sirolimus in kidney transplant recipients

It is currently not clear whether the concentration-time curves of the immunosuppressants differ with respect to the CYP3A5, MDR1, or MRP2 genotype in dose-adapted stable kidney transplant patients. Dose/trough concentration ratios were obtained in 134 tacrolimus and 20 sirolimus-treated patients, and plasma concentration-time profiles were obtained from 16 (tacrolimus) and 10 (sirolimus) patients. Genotyping was carried out for CYP3A5 6986A>G; ABCB1 2677G>T/A, 3435C>T and ABCC2 -24C>T; 1249G>A; 3972C>T. Dose/trough concentration ratios were 0.67+/-0.3 and 1.36+/-0.73 x 10(3) l (P<0.00001) for tacrolimus and 0.42+/-0.17 and 0.84+/-0.46 x 10(3) l (P=0.18) for sirolimus in CYP3A5 non-expressors and expressors. The unadjusted tacrolimus area under curve (AUC)(0-12) was 106.8+/-17.5 ng/ml x h compared with 133.3+/-42.2 ng/ml x h (P=0.37) without affecting serum creatinine. Mean unadjusted AUC(0-24) of sirolimus did not differ significantly either. Therefore, CYP3A5 expressor status and not transporter variants is a main determinant of oral clearance, particularly for tacrolimus. Dose adaptation according to trough levels, however, appears to be sufficient to maintain similar concentration-time profiles.

Significance of the minor cytochrome P450 3A isoforms

Cytochrome P450 (CYP) 3A4 is responsible for most CYP3A-mediated drug metabolism but the minor isoforms CYP3A5, CYP3A7 and CYP3A43 also contribute. CYP3A5 is the best studied of the minor CYP3A isoforms. It is well established that only approximately 20% of livers express CYP3A5. The most common reason for the absence of expression is a splice site mutation. The frequency of variant alleles shows interethnic differences, with the wild-type CYP3A5*1 allele more common in Africans than Caucasians and Asians. In individuals who express CYP3A5, the percentage contributed to total hepatic CYP3A by this isoform is still unclear, with estimates ranging from 17% to 50%. CYP3A5 is also expressed in a range of extrahepatic tissues. Only limited information is available on the regulation of CYP3A5 expression but it appears to be inducible via the glucocorticoid receptor, pregnane X receptor and constitutive androstane receptor-beta, as for CYP3A4. Although information on the substrate specificity of CYP3A5 is limited compared with CYP3A4, there have been a number of recent pharmacokinetic studies on a small range of substrates in individuals of known genotype to investigate the contribution of CYP3A5. In the case of midazolam, ciclosporin, nifedipine and docetaxel, clearance by individuals with a CYP3A5-expressing genotype did not differ from that for nonexpressors, but in the case of tacrolimus, eight independent studies have demonstrated faster clearance by those carrying one or two CYP3A5*1 alleles. This may reflect faster turnover of tacrolimus by CYP3A5 than the other substrates. CYP3A5 genotype may affect cancer susceptibility. Certain combined CYP3A4/CYP3A5 haplotypes show differential susceptibility to prostate cancer and there is a nonsignificant increase in the risk of small-cell lung cancer for a CYP3A5*1/*1 genotype. Females positive for CYP3A5*1 appear to reach puberty earlier, which may affect breast cancer risk. CYP3A5*1 homozygotes may have higher systolic blood pressure.CYP3A7 is predominantly expressed in fetal liver but is also found in some adult livers and extrahepatically. The molecular basis for expression in adult liver relates to upstream polymorphisms, which appear to increase homology to CYP3A4 and make regulation of expression more similar. CYP3A7 has a specific role in hydroxylation of retinoic acid and 16alpha-hydroxylation of steroids, and is therefore of relevance both to normal development and carcinogenesis.CYP3A43 is the most recently discovered CYP3A isoform. In addition to a low level of expression in liver, it is expressed in prostate and testis. Its substrate specificity is currently unclear. Polymorphisms predicting absence of active enzyme have been identified.

Identification by single-strand conformational polymorphism analysis of known and new mutations of the CYP3A5 gene in a French population

The cytochrome P450 3A5 (CYP3A5) has been shown to be highly involved in the metabolism of many therapeutic agents. To date, several polymorphisms affecting the CYP3A5 gene have been identified but few studies have shown a complete description of the variability of the CYP3A5 in the French population. Therefore, the extent of CYP3A5 genetic polymorphism was investigated in a French population of 114 patients. The screening of the coding region with their intron-exon boundaries and the proximal flanking regions was performed using a PCR-SSCP strategy. Eighteen polymorphisms were identified, including four new mutations. They correspond to -19 T>C upstream of the exon 1, 7360 T>C in intron 4, 12991 T>C in intron 5 and 29788 delG in exon 12. We also identified 13 alleles including six new alleles. As expected, the most frequent allelic variant is CYP3A5*3, with a frequency of 87% of all alleles. These data confirmed that CYP3A5 gene is highly polymorphic. Furthermore, it will be now interesting to evaluate the impact of this polymorphism on the pharmacokinetic parameters of different drugs.

Association of cyclophosphamide pharmacokinetics to polymorphic cytochrome P450 2C19

Cyclophosphamide (CP), a widely used cytostatic, is metabolized by polymorphic drug metabolizing enzymes particularly cytochrome P450 (CYP) enzymes. Its side effects and clinical efficacy exhibit a broad interindividual variability, which might be due to differences in pharmacokinetics. CP-kinetics were determined in 60 patients using a global and a population pharmacokinetic model considering functionally relevant polymorphisms of CYP2B6, CYP2C9, CYP2C19, CYP3A5, and GSTA1. Moreover, metabolic ratios were calculated for selected CP metabolites, analyzed by (31)P-NMR-spectroscopy. Analysis of variance revealed that the CYP2C19*2 genotype influenced significantly pharmacokinetics of CP at doses </=1000 mg/m(2), whereas there was no evidence of an association of other genotypes to CP elimination or clearance. Mean (+/-SD) CP elimination constants k(e) (h(-1)) were 0.109+/-0.025 in 44 CYP2C19*1/*1 subjects, 0.088+/-0.018 in 13 CYP2C19*1/*2, and 0.076+/-0.014 in three inactive CYP2C19*2/*2 carriers (P=0.009). At CP doses higher than 1000 mg/m(2), a significantly increase of elimination was observed (P=0.001), possibly due to CYP induction. Further studies should link these findings with the clinical outcome.

Upstream and coding region CYP2C9 polymorphisms: correlation with warfarin dose and metabolism

OBJECTIVES

To assess whether CYP2C9 alleles other than CYP2C9*2 and *3 are associated with a low-warfarin dose requirement and the relevance of upstream CYP2C9 polymorphisms to dose requirement and metabolism.

METHODS

CYP2C9 exons, intron-exon boundaries and 3 kb of upstream sequence in 20 patients requiring <or= 1.5 mg warfarin per day and with apparently homozygous wild-type or heterozygous CYP2C9*2 genotypes were screened for novel polymorphisms by single-strand conformational polymorphism analysis. PCR-based genotyping assays for novel upstream and other known polymorphisms were used to screen a larger patient population of known CYP2C9*2 and *3 genotype requiring a range of warfarin doses.

RESULTS

Polymorphisms at eight different upstream sites were found, five of which were already described. We found that the majority of the upstream polymorphisms were in complete linkage disequilibrium with previously described coding region polymorphisms. However, two polymorphisms, T-1188C and the novel DeltaG-2664DeltaT-2665, occurred both in individuals who were otherwise wild-type and in individuals positive for coding region polymorphisms. Evidence for 11 haplotypes, including 8 with frequencies >or= 0.01, was obtained. In individuals negative for coding region polymorphisms, neither individual genotypes for T-1188C or DeltaG-2664DeltaT-2665 or particular combinations of haplotype pairs were predictive of dose requirement or S-warfarin total clearance, suggesting neither upstream polymorphism was functionally significant. Dose requirements in CYP2C9*11 heterozygotes were not statistically significantly different from homozygous wild-type individuals.

CONCLUSIONS

The coding region non-synonymous polymorphisms associated with the CYP2C9*2 and CYP2C9*3 alleles are the major CYP2C9-related factor affecting warfarin dose in UK Caucasians. Upstream CYP2C9 polymorphisms do not appear to be important independent determinants of dose requirement.

CYP3A5*3 and CYP3A4*18 single nucleotide polymorphisms in a Chinese population

BACKGROUND

Human cytochrome P450 3A evolved to catalyze the metabolism of numerous common therapy drugs and endogenous molecules. Members of the CYP3A are the majority expressed in human liver and intestine, and there are marked interindividual differences in their protein expression and activity. The activity of CYP3A enzyme in Chinese is highly variable, exceeding 14-fold, and contributes greatly to variation in oral bioavailability and systemic clearance of CYP3A substrates. The genetic factors play an important role in the interindividual variability in CYP3A activity. Detection of CYP3A5 and CYP3A4 variant alleles and knowledge about their allelic frequency in specific ethnic groups are important to lead to individualized drug dosing and improved therapeutics.

METHODS

We determined the allelic frequency of the CYP3A5*3 and CYP3A4*18 in a group of 302 Chinese subjects by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays.

RESULTS

In the group of 302 unrelated individuals, the frequency of the CYP3A5*3 and CYP3A4*18 variant allele in Chinese population were 0.778 (95% CI: 0.754, 0.802) and 0.01 (95% CI: 0, 0.02), respectively.

CONCLUSIONS

We developed a simple assay for the detection of the CYP3A4*18 allele and showed that in a Chinese population, CYP3A4*18 and CYP3A5*3 allelic frequencies are similar to that reported previously in Chinese resident in Taiwan. The frequency of the CYP3A5*3 allele in Chinese population is similar to the Japanese but lower than Caucasians. Meanwhile, our findings suggest that an approximate 62% of the Chinese population carrying CYP3A5*3/*3 genotype may appear not to express CYP3A5 protein.

Lipid-lowering response to statins is affected by CYP3A5 polymorphism

Individuals expressing the polymorphic CYP3A5 enzyme might show a more than average efficiency in the metabolism of lovastatin, simvastatin and atorvastatin. We studied whether the expression of CYP3A5 is associated with an impaired lipid-lowering response to statins in 69 Caucasian patients. Lovastatin, simvastatin and atorvastatin were significantly less effective in CYP3A5 expressors than in non-expressors. The mean serum total cholesterol concentration at 1 year was 23% higher (P = 0.0014) and the mean serum low-density lipoprotein cholesterol concentration was 24% higher (P = 0.036) in subjects possessing the CYP3A5*1 allele (CYP3A5 expressors, n = 7) than in subjects homozygous for the CYP3A5*3 allele (non-expressors, n = 39). The mean percentage reduction in serum total cholesterol from baseline was significantly smaller in CYP3A5 expressors than in non-expressors (17% versus 31%, P = 0.026). No association between hypolipidemic efficacy and CYP3A5 polymorphism was observed among 23 subjects taking statins that are not dependent on CYP3A5 (fluvastatin, pravastatin). These findings suggest that CYP3A5 may be a genetic determinant of interindividual differences in response to certain statins.

Recombinant CYP3A4*17 is defective in metabolizing the hypertensive drug nifedipine, and the CYP3A4*17 allele may occur on the same chromosome as CYP3A5*3, representing a new putative defective CYP3A haplotype

Genetic variation in CYP3A activity may influence the rate of the metabolism and elimination of CYP3A substrates in humans. We previously reported four new CYP3A4 coding variants in three different racial groups. In the present study, we examined metabolism of nifedipine by the recombinant forms of these allelic variants. Metabolism of nifedipine by the L293P (CYP3A4*18), M445T (CYP3A4*3), and P467S (CYP3A4*19) allelic variants was not significantly different from wild-type CYP3A4*1. However, F189S (CYP3A4*17) exhibited a >99% decrease in both V(max) and CL(max) of nifedipine compared with CYP3A4*1. Of 72 racially diverse individuals, CYP3A4*17 was identified in 1 of 24 Caucasian samples [1:5 Eastern European (Adygei ethnic group)]. Genotyping of an extended set of 276 genomic DNAs of Caucasians (100 from the Coriell Repository and an additional 176 from the United States) for CYP3A4*17 detected no additional individuals containing the CYP3A4*17 allele. However, additional genotyping of four more Adygei samples available from Coriell detected an additional individual carrying the CYP3A4*17 allele. New specific polymerase chain reaction-restriction fragment length polymorphism genotyping procedures were developed for the major splice variant of CYP3A5 (CYP3A5*3) and CYP3A4*17. Genotyping revealed that the two individuals carrying CYP3A4*17 were either homozygous or heterozygous for the more frequent CYP3A5*3 allele, suggesting that the two alleles may exist on the same chromosome as a new putative CYP3A poor metabolizer haplotype. We predict that individuals who are homozygous for defective alleles of both of these genes would metabolize CYP3A substrates poorly. The new genetic tests will be useful in future clinical studies to investigate genotype/phenotype associations.

CYP3A5 Genotype is Associated with Diagnosis of Hypertension in Elderly Patients

OBJECTIVE

The aim of this study was to address the presently controversial question of whether cytochrome P450 (CYP) 3A5 polymorphism is associated with hypertension.

METHOD

We studied 373 elderly (age > or =75 years) Finnish (Caucasian) patients from the ongoing DEBATE (Drugs and Evidence Based Medicine in the Elderly) trial. The patients were classified into those with a history of hypertension (n = 229) and those without a history of hypertension (n = 144) on the basis of a detailed questionnaire on each patient's medical history and an interview. The patients were genotyped for the CYP3A5 6986A/G single nucleotide polymorphism (SNP) [CYP3A5*1/*3 alleles].

RESULTS

The proportion of individuals with the CYP3A5*1/*3 genotype, i.e. CYP3A5 expressors, was significantly higher among patients with a diagnosis of hypertension than among patients without (18.3% vs 9.0%, p = 0.016). The corresponding odds ratio was 2.26 (95% CI 1.17, 4.38). The allele and genotype frequencies for the two control SNPs, ABCB1 (MDR1) 3435C/T and SLCO1B1 521T/C, did not differ between the two groups.

CONCLUSION

This work lends support to the theory that the polymorphic CYP3A5 enzyme may be involved in regulation of blood pressure. The possible role of CYP3A5 as a genetic contributor to hypertension susceptibility warrants further study.

Genetic variability in CYP3A5 and its possible consequences

The cytochrome P450 3A (CYP3A) subfamily members are the most abundant and important drug-metabolizing enzymes in humans, and wide interindividual variability in CYP3A expression and function is present. CYP3A4 alone cannot fully explain the observed constitutive variability because its genetic variants are relatively uncommon and have limited functional significance, whereas CYP3A5 expression in humans is highly variable and may be contributory. However, it is difficult to delineate the relative contribution of CYP3A4 and CYP3A5, and to differentiate their effects on drug metabolism as their protein structure, function and substrates are so similar. By contrast, molecular biology methods provide the ability to identify CYP3A4 and CYP3A5 genotypes with certainty. This review collates currently available data on CYP3A5 polymorphisms, provides information on the population frequency of each genetic variant in major ethnic groups, and describes in vitro and in vivo studies that have attempted to identify genotype-phenotype associations.