CYP3A5 rather than MDR1 gene polymorphism of recipient is related to tacrolimus individual dose requirement in Chinese liver transplant patients

AIM： Tacrolimus shows considerable interindividual pharmacokinetic variability, therapeutic drug monitoring of trough blood concentration is necessary to avoid adverse effects. CYP3A5 and P-glycoprotein （P-gp, encoded by MDR1） are involved in tacrolimus＇ metabolism and absorption process. This study is to investigate whether tacrolimus dosage adjustment is affected by the polymorphism in CYP3A5 and MDR1 in Chinese liver transplant patients. METHODS： Forty-nine liver transplant patients treated with tacrolimus were enrolled in this study. Polymerase chain reaction-restriction fragment length polymorphism （PCR-RFLP） analysis was applied to determine the genotype of CYP3A5 and MDR1. Tacrolimus blood tough concentration was measured by FPIA, and concentration/dose ratio（C/D） was investigated at day 7, day 14 and 1 month after liver transplantation.[第一段]     

Effects of donor–recipient combinational CYP3A5 genotypes on tacrolimus dosing in Chinese DDLT adult recipients

BackgroundFor liver transplant (LT) recipients, the liver CYP3A5 metabolic enzymes are determined by the donor’s genes, whereas the intestinal enzymes are encoded by the recipient’s genes. This combinational form confuses the metabolism of tacrolimus (Tac) in vivo. This retrospective study was conducted to investigate the combined effects of donor–recipient CYP3A5 genotype on tacrolimus pharmacokinetics in Chinese LT adult patients.MethodsThree hundred seventy-three LT patients from two Chinese organ transplant centers were enrolled, and both recipients and donors were genotyped for CYP3A5. Patients were divided into four groups (R_ND_N, R_ED_N, R_ND_E, R_ED_E) according to CYP3A5*3 allele expressers (E) and non-expressers (N) in recipients (R) and donors (D). The dose-adjusted trough levels (C/D ratio) of tacrolimus were assessed for six months among the four groups. Multiple linear regression analysis was performed to assess the effects of the CYP3A5 genotype and several clinical variables on the C/D ratio.ResultsThe R_ND_N group consistently had the largest C/D ratio throughout the entire study period, whereas the R_ED_E group had the smallest C/D ratio, and the R_ED_N/R_ND_E group had an intermediate (R_ND_N > R_ED_N/R_ND_E > R_ED_E) ratio. The C/D ratio in the R_ND_N and R_ND_E groups was higher than that in the R_ED_N and R_ED_E groups within three months, respectively; the ratio in the R_ND_N group was higher than that in the R_ND_E group, and the ratio in the R_ED_N group was higher than that in the R_ED_E group at six months. The effect of the donor CYP3A5 genotype on C/D values was observed throughout the timeline, and the recipient’s genetics correlated only in the first three months. Among non-genetic factors, hemoglobin (HGB) and albumin (ALB) were correlated with Tac C/D values at a few time points.ConclusionsTo predict the initial dose of tacrolimus in LT patients, both donor and recipient CYP3A5 genotypes must be taken into account; during the maintenance phase of targeted blood concentration, the donor’s CYP3A5 genotype may be of prime importance, especially at three months after transplantation.     

Metabolism of (−)-fenchone by CYP2A6 and CYP2B6 in human liver microsomes

The in vitro metabolism of (?)-fenchone was examined in human liver microsomes and recombinant enzymes. The biotransformation of (?)-fenchone was investigated by gas chromatography-mass spectrometry. (?)-Fenchone was found to be oxidized to 6-exo-hydroxyfenchone, 6-endo-hydroxyfenchone and 10-hydroxyfenchone by human liver microsomal P450 enzymes. The formation of metabolites was determined by the relative abundance of mass fragments and retention times on gas chromatography (GC). CYP2A6 and CYP2B6 were major enzymes involved in the hydroxylation of (?)-fenchone by human liver microsomes, based on the following lines of evidence. First, of 11 recombinant human P450 enzymes tested, CYP2A6 and CYP2B6 catalysed the oxidation of (?)-fenchone. Second, oxidation of (?)-fenchone was inhibited by thioTEPA and (+)-menthofuran. Finally, there was a good correlation between CYP2A6, CYP2B6 contents and (?)-fenchone hydroxylation activities in liver microsomes of 11 human samples. CYP2A6 may be more important than CYP2B6 in human liver microsomes. Kinetic analysis showed that the V_max/K_m values for (?)-fenchone 6-endo-, 6-exo- and 10-hydroxylation catalysed by liver microsomes of human sample HG-03 were 24.3, 44.0 and 1.3?nM^?1?min^?1, respectively. Human recombinant CYP2A6 and CYP2B6 catalysed (?)-fenchone 6-exo-hydroxylation with V_max values of 2.7 and 12.9?nmol?min^?1?nmol^?1 P450 and apparent K_m values of 0.18 and 0.15?mM and (?)-fenchone 6-endo-hydroxylation with V_max values of 1.26 and 5.33?nmol?min^?1?nmol^?1 P450 with apparent K_m values of 0.29 and 0.26?mM. (?)-Fenchone 10-hydroxylation was catalysed by CYP2B6 with K_m and V_max values of 0.2?mM and 10.66?nmol?min^?1?nmol^?1 P450, respectively.     

Activation of CYP3A-mediated testosterone 6β-hydroxylation by tanshinone IIA and midazolam 1-hydroxylation by cryptotanshinone in human liver microsomes

This study evaluated the in vitro activation of CYP3A-mediated midazolam 1-hydroxylation and testosterone 6β-hydroxylation by tanshinone I, tanshinone IIA, and cryptotanshinone. The abilities of tanshinones to activate CYP3A-mediated midazolam 1-hydroxylation and testosterone 6β-hydroxylation in human liver microsomes (HLMs) were tested. Substrate- and effector-dependent activation of CYP3A by tanshinones were both observed. Cryptotanshinone was shown to activate CYP3A-mediated midazolam 1-hydroxylation in a concentration-dependent manner. In contrast, tanshinone IIA and tanshinone I did not activate this hydroxylation reaction. In addition, tanshinone IIA activated CYP3A-mediated testosterone 6β-hydroxylation, whereas cryptotanshinone and tanshinone I did not. The results from our study enhance the understanding of CYP3A activation by tanshinone IIA and cryptotanshinone in HLMs. Additionally, these data allow for an accurate prediction of the magnitude and likelihood of Danshen-drug interactions.     

Activation of CYP3A-mediated testosterone 6β-hydroxylation by tanshinone IIA and midazolam 1-hydroxylation by cryptotanshinone in human liver microsomes

1. This study evaluated the in vitro activation of CYP3A-mediated midazolam 1-hydroxylation and testosterone 6β-hydroxylation by tanshinone I, tanshinone IIA, and cryptotanshinone.

2. The abilities of tanshinones to activate CYP3A-mediated midazolam 1-hydroxylation and testosterone 6β-hydroxylation in human liver microsomes (HLMs) were tested. Substrate- and effector-dependent activation of CYP3A by tanshinones were both observed.

3. Cryptotanshinone was shown to activate CYP3A-mediated midazolam 1-hydroxylation in a concentration-dependent manner. In contrast, tanshinone IIA and tanshinone I did not activate this hydroxylation reaction. In addition, tanshinone IIA activated CYP3A-mediated testosterone 6β-hydroxylation, whereas cryptotanshinone and tanshinone I did not.

4. The results from our study enhance the understanding of CYP3A activation by tanshinone IIA and cryptotanshinone in HLMs. Additionally, these data allow for an accurate prediction of the magnitude and likelihood of Danshen-drug interactions.

     

4β-hydroxycholesterol as an endogenous CYP3A marker in cancer patients treated with taxanes

Aim

Taxanes are anti-cancer agents used to treat several types of solid tumours. They are metabolized by cytochrome P450 (CYP) 3A, displaying a large pharmacokinetic (PK) variability. In this study, we evaluated the endogenous CYP3A4 marker 4β-hydroxycholesterol (4β-OHC) as a potential individual taxane PK predictor.

Methods

Serum 4β-OHC and cholesterol concentrations were determined in 291 paclitaxel and 151 docetaxel-treated patients, and were subsequently correlated with taxane clearance.

Results

In the patients treated with paclitaxel, no clinically relevant correlations between the 4β-OHC or 4β-OHC : cholesterol ratio and paclitaxel clearance were found. In the patients treated with docetaxel, 4β-OHC concentration was weakly correlated with docetaxel clearance in males (r = 0.35 P = 0.01, 95% CI 0.08, 0.58). Of the 10% patients with taxane outlier clearance values, 4β-OHC did correlate with docetaxel clearance in males (r = 0.76, P = 0.03, 95% CI 0.12, 0.95).

Conclusion

There was no clinical correlation between paclitaxel clearance and the CYP3A4 activity markers 4β-OHC or the 4β-OHC : cholesterol ratio. A weak correlation was observed between 4β-OHC and docetaxel clearance, but only in males. This endogenous CYP3A4 marker has limited predictive value for taxane clearance in patients.     

Regulation of VDR expression in rat and human intestine and liver – Consequences for CYP3A expression

The vitamin D receptor (VDR) regulates the expression of drug metabolizing enzymes and transporters in intestine and liver, but the regulation of VDR expression in intestine and liver is incompletely understood. We studied the regulation of VDR mRNA expression by ligands for VDR, farnesoid X receptor (FXR), glucocorticoid receptor (GR) and protein kinase C α (PKCα) in rat and human ileum and liver using precision-cut slices. 1,25(OH)₂D₃ induced VDR expression in rat ileum and liver, and human ileum but not in liver. Chenodeoxycholic acid (CDCA), but not lithocholic acid (LCA) and GW4064 induced VDR mRNA expression in rat ileum and liver. The PKCα activator, phorbol-12-myristate-13-acetate (PMA) induced the expression of VDR in the rat liver, and the induction of VDR by 1,25(OH)₂D₃ and CDCA was inhibited by the PKCα inhibitor, bisindolyl maleimide I (Bis I). These results show that the expression of VDR is likely to be regulated by PKC but not by FXR or VDR activation at least in the rat liver. The VDR mediated induction of its target genes CYP3A1 and CYP3A2 by 1,25(OH)₂D₃ or LCA in the rat ileum was strongly reduced in the presence of CDCA despite the higher VDR expression. Thus, CDCA might potentiate the toxicity of LCA by inhibiting its metabolism.     

CYP3A activity in severe liver cirrhosis correlates with Child–Pugh and model for end-stage liver disease (MELD) scores

Aims

Impaired liver function often necessitates drug dose adjustment to avoid excessive drug accumulation and adverse events, but a marker for the extent of the required adjustment is lacking. The aim of this study was to investigate whether Child–Pugh (CP) and model for end-stage liver disease (MELD) scores correlate with drug clearance.

Methods

Midazolam was used as a CYP3A probe and its pharmacokinetics were analyzed in 24 patients with mild to severe liver cirrhosis (n = 4, 10 and 10 with CP class A, B and C, respectively) and six patients without liver disease.

Results

Both scores correlated well with unbound midazolam clearance (CL_u), unbound midazolam fraction and half-life (all P < 0.01), whereas the unbound steady-state volume of distribution was not significantly changed. In patients with severe liver cirrhosis unbound midazolam clearance was only 14% of controls (CP C: CL_u = 843 ± 346 l h⁻¹, MELD ≥ 15: CL_u = 805 ± 474 l h⁻¹, controls: CL_u = 5815 ± 2649 l h⁻¹, P < 0.01).

Conclusion

The correlation with unbound midazolam clearance suggests that either score predicts the metabolic capacity of CYP3A, the most relevant drug metabolizing enzyme subfamily in humans.     

CYP3A induction and inhibition by different antiretroviral regimens reflected by changes in plasma 4β-hydroxycholesterol levels

OBJECTIVE AND METHODS: A member of the major human cytochrome P450 superfamily of hemoproteins, CYP3A4/5, converts cholesterol into 4beta-hydroxycholesterol. We studied plasma 4beta-hydroxycholesterol levels prior to and 4 weeks after initiating antiretroviral therapy that included efavirenz, ritonavir-boosted atazanavir or ritonavir-boosted lopinavir with the aim of exploring the usefulness of plasma 4beta-hydroxycholesterol levels as an endogenous biomarker of CYP3A activity. Efavirenz is an inducer of CYP3A, whereas the ritonavir-boosted regimens are net inhibitors of CYP3A. RESULTS: In patients treated with efavirenz, the median plasma 4beta-hydroxycholesterol level increased by 46 ng/mL (p = 0.004; n = 11). In contrast, patients given ritonavir-boosted atazanavir showed a median decrease in plasma 4beta-hydroxycholesterol of -9.4 ng/mL (p = 0.0003; n = 22), and those given ritonavir-boosted lopinavir showed a median change from baseline of -5.8 ng/mL (p = 0.38; n = 19). There were significant between-group differences in the effects of antiretroviral treatment on plasma 4beta-hydroxycholesterol levels (p < 0.0001). CONCLUSION: Changes in plasma 4beta-hydroxycholesterol following the initiation of efavirenz- or atazanavir/ritonavir-based antiretroviral therapy reflected the respective net increase and decrease of CYP3A activity of these regimens. The plasma 4beta-hydroxycholesterol level did not indicate a net CYP3A inhibition in the lopinavir/ritonavir arm, possibly because of concomitant enzyme induction.     

β-Naphthoflavone induced CYP1A1 and 1A3 proteins in the liver of rainbow trout (Oncorhynchus mykiss)

1. Two CYP1A proteins, designated HAP 1 andHAP 2, were isolated from the liver of the β-naphthoflavone(BNF)-treated rainbow trout. The proteins were initially resolved by chromatography on a DEAE sepharose column and were further purified by hydroxylapatite chromatography. 2. Both HAP 1 and HAP 2 proteins exhibited high 7-ethoxyresorufin, methoxy resorufin and phenacetin O-dealkylase activities and were good catalysts for the oxidation of 7,12-dimethylbenz[a]anthracene (DMBA). No qualitative difference was observed between the two proteins in their ability to catalyse the formation of the individual metabolites of DMBA. 3. The two purified proteins showed identical amino acid sequence for the first 13 amino acids. However, the 14th amino acid was valine for HAP 1 protein and alanine for HAP 2 protein. 4. Alignment ofthe amino acid sequences showed that HAP 1 protein was identical to the deduced protein ofthe previously reported troutCYP1A2 (renamed CYP1A1) gene for the first 24 amino acids at the N-terminal region. HAP 2 protein corresponded to the deduced protein sequence of CYP1A3 gene for the first 14 amino acids. However, unlike the deduced sequences of CYP1A1 and 1A3 the N -terminal methionine was absent in the purified proteins. 5. We conclude thatHAP 1 and HAP 2 are the products ofthe CYP1A1 and CYP1A3 genes respectively, and are found in the liver of the BNF-treated rainbow trout.     

Effect of γ-ray on metabolic enzyme CYP3A1 in rat liver on multiple levels北大核心CSCD

Aim To explore the effect of γ-ray on the mRNA,protein expression levels and metabolic activity level of the key drug metabolic enzyme CYP3A1 in rat liver. Methods Wistar rats were randomly divided into control group, 24 h post-radiation group and 72 h post-radiation group. The experimental group was exposed to total body irradiation of single 6 Gy γ-ray. Blood was collected from the orbital venous plexus for blood routine examination and biochemical analysis 24 h and 72 h after irradiation, and liver tissue was prepared for quantifying expression of CYP3A1 mRNA and liver-specific microRNA (miR-122-5p) through RT-PCR. The expression level of CYP3A1 protein was analyzed by Western blot, and the metabolic activity level of CYP3A1 detected by the specific substrate midazolam combined with LC-MS method. Results Com¬pared with the control group, the weights of the rats in the radiation group significantly decreased, and the number of white blood cells was markedly reduced. Simultaneously, the activities of alanine aminotrans-ferase and alkaline phosphatase continuously descended, as well as the levels of total bilirubin and bile acid significantly increased, which indicated that the liver may be damaged after radiation. The relative expression of CYP3A1 mRNA continued to increase significantly 24 h and 72 h after irradiation. CYP3A1 protein expression and metabolic activity levels showed an obvious increasing trend 24 h after irradiation, and rose significantly 72 h after irradiation compared with the control group. At the same time, the expression of miR-122-5p in liver of rats in the 24 h and 72 h post-radiation group continued to decrease rapidly compared with the control group. Conclusions γ-ray radiation may arouse damage effect on liver, which leads to the continuous up-regulation of the mRNA and protein expression levels of the capital metabolic enzyme CYP3A1 in liver tissue, as well as the elevation of the metabolic activity level. The regulatory mechanism might be related to miR-122-5p. © 2023 Publication Centre of Anhui Medical University. All rights reserved.     

Assessment of the impact of CYP3A polymorphisms on the formation of α-hydroxytamoxifen and N-desmethyltamoxifen in human liver microsomes

Tamoxifen, an antiestrogen used in the prevention and treatment of breast cancer, is extensively metabolized by cytochrome P450 enzymes. Its biotransformation to α-hydroxytamoxifen (α-OHT), which may be genotoxic, and to N-desmethyltamoxifen (N-DMT), which is partially hydroxylated to 4-hydroxy-N-DMT (endoxifen), a potent antiestrogen, is mediated by CYP3A enzymes. However, the potential contribution of CYP3A5 and the impact of its low-expression variants on the formation of these metabolites are not clear. Therefore, we assessed the contributions of CYP3A4 and CYP3A5 and examined the impact of CYP3A5 genotypes on the formation of α-OHT and N-DMT, by using recombinant CYP3A4 and CYP3A5 and human liver microsomes (HLM) genotyped for CYP3A5 variants. We observed that the catalytic efficiency [intrinsic clearance (CL(int))] for α-OHT formation with recombinant CYP3A4 was 5-fold higher than that with recombinant CYP3A5 (0.81 versus 0.16 nl · min?1 · pmol cytochrome P450?1). There was no significant difference in CL(int) values between the three CYP3A5-genotyped HLM (*1/*1, *1/*3, and *3/*3). For N-DMT formation, the CL(int) with recombinant CYP3A4 was only 1.7-fold higher, relative to that with recombinant CYP3A5. In addition, the CL(int) for N-DMT formation by HLM with CYP3A5*3/*3 alleles was approximately 3-fold lower than that for HLM expressing CYP3A5*1/*1. Regression analyses of tamoxifen metabolism with respect to testosterone 6β-hydroxylation facilitated assessment of CYP3A5 contributions to the formation of the two metabolites. The CYP3A5 contributions to α-OHT formation were negligible, whereas the contributions to N-DMT formation ranged from 51 to 61%. Our findings suggest that polymorphic CYP3A5 expression may affect the formation of N-DMT but not that of α-OHT.     

Metabolism of sanguinarine in human and in rat: Characterization of oxidative metabolites produced by human CYP1A1 and CYP1A2 and rat liver microsomes using liquid chromatography–tandem mass spectrometry

The quaternary benzo[c]phenanthridine alkaloid, sanguinarine (SA), has been detected in the mustard oil contaminated with Argemone mexicana, which produced severe human intoxications during epidemic dropsy in India. Today, SA metabolism in human and in rat has not yet been fully elucidated. The goal of this study is to investigate the oxidative metabolites of SA formed during incubations with rat liver microsomes (RLM) and recombinant human cytochrome P450 (CYP) and to tentatively identify the CYP isoforms involved in SA detoxification. Metabolites were analyzed by liquid chromatography combined with electrospray ionization-tandem mass spectrometry. Up to six metabolites were formed by RLM and their modified structure has been proposed using their mass spectra and mass shifts from SA (m/z 332). The main metabolite M2 (m/z 320) resulted from ring-cleavage of SA followed by demethylation, whereas M4 (m/z 348) is oxidized by CYP in the presence of NADPH. The diol-sanguinarine metabolite M6 (m/z 366) formed by RLM might derive from a putative epoxy-sanguinarine metabolite M5 (m/z 348). M4 and M6 could be detected in rat urine as their respective glucuronides. 5,6-Dihydrosanguinarine is the prominent derivative formed from SA in cells expressing no CYP. Oxidative biotransformation of SA was investigated using eight human CYPs: only CYP1A1 and CYP1A2 displayed activity.     

Effect of buffer conditions on CYP2C8-mediated paclitaxel 6α-hydroxylation and CYP3A4-mediated triazolam α- and 4-hydroxylation by human liver microsomes

Abstract

1.?Buffer conditions in in vitro metabolism studies using human liver microsomes (HLM) have been reported to affect the metabolic activities of several cytochrome P450 (CYP) isozymes in different ways, although there are no reports about the dependence of CYP2C8 activity on buffer conditions.

2.?The present study investigated the effect of buffer components (phosphate or Tris-HCl) and their concentration (10–200?mM) on the CYP2C8 and CYP3A4 activities of HLM, using paclitaxel and triazolam, respectively, as marker substrates.

3.?The K_m (or S₅₀) and V_max values for both paclitaxel 6α-hydroxylation and triazolam α- and 4-hydroxylation, estimated by fitting analyses based on the Michaelis–Menten or Hill equation, greatly depended on the buffer components and their concentration.

4.?The CL_int values in phosphate buffer were 1.2–3.0-fold (paclitaxel) or 3.1–6.4-fold (triazolam) higher than in Tris-HCl buffer at 50–100?mM. These values also depended on the buffer concentration, with a maximum 2.3-fold difference observed between 50 and 100?mM which are both commonly used in drug metabolism studies.

5.?These findings suggest the necessity for optimization of the buffer conditions in the quantitative evaluation of metabolic clearances, such as in vitro–in vivo extrapolation and also estimating the contribution of a particular enzyme in drug metabolism.     

Roles of human cytochrome P450 3A4/5 in dexamethasone 6β-hydroxylation mediated by liver microsomes and humanized liver in chimeric mice metabolically suppressed with azamulin

The urinary metabolic ratio of 6β-hydroxydexamethasone to dexamethasone reportedly acts as a noninvasive marker for human cytochrome P450 (P450) 3A4/5, which is induced by rifampicin in humanized-liver mice. In the current study, the pharmacokinetics of dexamethasone in humanized-liver mice after intravenous administration (10 mg/kg) were investigated using azamulin (a time-dependent P450 3A4/5 inhibitor). After intravenous dexamethasone administration, significant differences were observed in the time-dependent plasma and 24-h urinary concentrations of 6β-hydroxydexamethasone between untreated humanized-liver mice and humanized-liver mice treated with azamulin (daily oral doses of 15 mg/kg for 3 days). The mean ratios of 6β-hydroxydexamethasone to dexamethasone for the maximum concentrations, the areas under the plasma concentration-versus-time curves, and urinary concentrations were significantly lower in the azamulin-treated group (59%, 58%, and 41% of the untreated values, respectively). 6β-Hydroxydexamethasone formation was suppressed by 93% by replacing control human liver microsomes with P450 3A4/5-inactivated liver microsomes. These results suggest that the oxidation of dexamethasone in humans is mediated mainly by P450 3A4/5 (which is suppressed by azamulin), and that humanized-liver mice orally treated with azamulin may constitute an in vivo model for metabolically inactivated P450 3A4/5 in human hepatocytes transplanted into chimeric mice.     

Effect of bifendate on the pharmacokinetics of cyclosporine in relation to the CYP3A4＊18B genotype in healthy subjects

Aim： To evaluate the potential drug-drug interactions between bifendate and cyclosporine, a substrate of CYP3A4, in relation to different CYP3A4＊18B genotype groups.
Methods： Eighteen unrelated healthy subjects （six CYP3A4＊1＊1, six CYP3A4＊1/＊18B, and six CYP3A4＊18/＊18B） were selected for this study. After repeated oral administration of a placebo or bifendate （three times daily for 14 d）, the wholeblood level of cyclosporine was measured using high performance liquid chromatography-electrospray mass spectrometry （HPLC/ESI-MS）. This study was carried out in a two-phase randomized crossover manner.
Results： After the treatment with bifendate, the areas under the curve （AUC0-24 and AUC0-∞） decreased significantly by 9.7%±3.7% （P=0.01） and 19.2%±16.8% （P=0.001） in CYP3A4＊1/＊1 subjects, 11.3%±9.4% （P=0.03） and 10.5%±9.6% （P=0.043） in CYP3A4＊1/＊18B subjects, and 40.2%＋14.7% （P=0.02） and 37.5%±15.8% （P=0.003） in CYP3A4＊18B/＊18B subjects. Meanwhile, the decreases in the AUC0-24 and AUC0-∞ values in the three groups were significantly different （using one-way analysis of variance, P=0.001 and P=0.001）, and the change in the CYP3A4＊18B/＊18B group was greater than that in the other two groups. The oral clearance of cyclosporine was altered in all the subjects, with substantial increases by 10.2%±4.4% （P=0.004） in CYP3A4＊1/＊1 subjects, 14.0%±12.0% （P=0.048） in CYP3A4＊1/＊18B subjects, and 32.4%±21.7% （P=0.013） in CYP3A4＊18B/＊18B subjects.
Conclusion： These results suggest that bifendate decreases the plasma concentration of cyclosporine in a CYP3A4 genotype- dependent manner.     

Variability in PXR-mediated induction of CYP3A4 by commercial preparations and dry extracts of St. John’s wort

St. John’s wort (SJW, Hypericum perforatum) is a well-tolerated herbal medicine widely used for the treatment of mild and moderate depressions. In the last 5 years, SJW has been implicated in drug interactions, which are largely mediated by the induction of the drug metabolizing enzymes, especially CYP3A4. There is still some controversy regarding the exact mechanism of induction and the identity of the SJW constituents involved. We investigated in LS174T cells the induction of CYP3A4 by ten SJW extracts, six commercial preparations, and the purified SJW constituent hyperforin. The content of hyperforin among the commercial preparations of SJW varied 62-fold (range 0.49–30.57 mg/dose). The CYP3A4 induction was mediated by PXR, but not by CAR. The magnitude of the induction correlated statistically significantly with the content of hyperforin in commercial SJW preparations (R = 0.87, p = 0.004) and in dry extracts (R = 0.65, p = 0.03), but not with their content of flavonoids or hypericin. Most of the CYP3A4 induction response occurred in the hyperforin range encountered in the blood of patients treated with SJW preparations. A temperature-induced decrease in the hyperforin content of a selected dry SJW extract abolished the induction of CYP3A4. In conclusion, commercial SJW preparations still exhibit an enormous variability in CYP3A4 induction, which is mediated by hyperforin and PXR. SJW preparations with lower hyperforin content should reduce the frequency of clinical interactions involving this herbal drug. This work was partly funded by the Deutsche Forschungsgemeinschaft (DFG) grant WO505/2-2.