Non-overweight depressed patients who respond to antidepressant treatment have a higher risk of later metabolic syndrome: findings from the METADAP cohort

BACKGROUND

Major depressive disorder (MDD) is a complex disorder with a significant public health burden. Depression remission is often associated with weight gain, a major risk factor for metabolic syndrome (MetS). The primary objective of our study was to assess prospectively the impact of response to antidepressant treatment on developing MetS in a sample of MDD patients with a current major depressive episode (MDE) and who are newly initiating their treatment.

METHODS

In the 6-month prospective METADAP cohort, non-overweight patients, body mass index <25 kg/m2, with MDD and a current MDE were assessed for treatment response after 3 months of treatment, and incidence of MetS after 3 and 6 months of treatment. Outcome variables were MetS, number of MetS criteria, and each MetS criterion (high waist circumference, high blood pressure, high triglyceridemia, low high-density lipoprotein-cholesterolemia, and high fasting plasma glucose).

RESULTS

In total, 98/169 patients (58%) responded to treatment after 3 months. A total of 2.7% (1/38) developed MetS out of which 12.7% (10/79) (p value < 0.001) had responded to treatment after 3 months. The fixed-effect regression models showed that those who responded to treatment after 3 months of follow-up had an 8.6 times higher odds of developing MetS (odds ratio = 8.58, 95% confidence interval 3.89-18.93, p value < 0.001).

CONCLUSION

Compared to non-responders, non-overweight patients who responded to treatment after 3 months of antidepressant treatment had a significantly higher risk of developing MetS during the 6 months of treatment. Psychiatrists and nurses should closely monitor the metabolic profile of their patients, especially those who respond to treatment.

Nitric Oxide Synthase activity in major depressive episodes before and after antidepressant treatment: Results of a large case-control treatment study

BACKGROUND

Nitric oxide synthase (NOS) activity, an enzyme potentially involved in the major depressive episodes (MDE), could be indirectly measured by the L-Citrulline/L-Arginine ratio (L-Cit/L-Arg). The aim of this study was: (1) to compare the NOS activity of patients with a MDE to that of healthy controls (HC); (2) to assess its change after antidepressant treatment.

METHODS

A total of 460 patients with a current MDE in a context of major depressive disorder (MDD) were compared to 895 HC for NOS activity (L-Cit/L-Arg plasma ratio). L-Arg and L-Cit plasma levels were measured using a MS-based liquid chromatography method. Depressed patients were assessed at baseline, and after 3 and 6 months of antidepressant treatment for depression severity and clinical response.

RESULTS

Depressed patients had a lower NOS activity than HC at baseline [0.31 ± 0.09 v. 0.38 ± 0.12; 95% confidence interval (CI) -0.084 to -0.062, p < 0.0001]. Lower NOS activity at baseline predicted a higher response rate [odds ratio (OR) = 29.20; 95% CI 1.58-536.37; p = 0.023]. NOS activity in depressed patients increased significantly up to 0.34 ± 0.08 after antidepressant treatment (Est = 0.0034; 95% CI 0.0002-0.0067; p = 0.03).

CONCLUSIONS

Depressed patients have a decreased NOS activity that improves after antidepressant treatment and predicts drug response. NOS activity may be a promising biomarker for MDE in a context of MDD.

Relationship between achieved personalized glycaemic targets and monitoring of clinical events in elderly diabetic patients

AIM

Recent guidelines for the management of type 2 diabetes (T2DM) in the elderly recommend adjusting the therapeutic target (HbA_1c) according to the patient's health. Our study aimed to explore the association between achieving the recommended personalized HbA_1c target and the occurrence of major clinical events under real-life conditions.

METHODS

The T2DM S.AGES cohort was a prospective multicentre study into which 213 general practitioners recruited 983 non-institutionalized T2DM patients aged>65 years. The recommended personalized HbA_1c targets were<7%, <8% and <9% for healthy, ill and very ill patients, respectively. Major clinical events (death from any cause, major vascular events and/or hospitalization) were recorded during the 3-year follow-up. Mixed-effects logistic regression models were used for the analyses.

RESULTS

Of the 747 patients analyzed at baseline, 551 (76.8%) were at their recommended personalized HbA_1c target. During follow-up, 391 patients (52.3%) experienced a major clinical event. Of the patients who did not achieve their personalized HbA_1c target (compared with those who did), the risk (OR) of a major clinical event was 0.95 (95% CI: 0.69-1.31; P=0.76). The risk of death, major vascular event and hospitalization were 0.88 (95% CI: 0.40-1.94; P=0.75), 1.14 (95% CI: 0.7-1.83; P=0.59) and 0.84 (95% CI: 0.60-1.18; P=0.32), respectively.

CONCLUSION

Over a 3-year follow-up period, our results showed no difference in risk of a major clinical event among patients, regardless of whether or not they achieved their personalized recommended HbA_1c target. These results need to be confirmed before implementing a more permissive strategy for treating T2DM in elderly patients.

Therapeutic management in ambulatory elderly patients with atrial fibrillation: the S.AGES cohort

Few epidemiologic studies have specifically focused on very old community dwelling population with atrial fibrillation (AF). The objectives of the AF-S.AGES cohort were to describe real-life therapeutic management of non-institutionalized elderly patients with AF according to age groups, i.e., 65-79 and ≥ 80 and to determine the main factors associated with anticoagulant treatment in both groups.

METHODS

Observational study (N=1072) aged ≥ 65 years old, recruited by general practitioners. Characteristics of the sample were first evaluated in the overall sample and according to age (< 80 or ≥ 80 years) and to use of anticoagulant treatment at inclusion. Logistic models were used to analyze the determinants of anticoagulant prescription among age groups.

RESULTS

Mean age was 78.0 (SD=6.5) years and 42% were ≥ 80 years. Nineteen percent had paroxysmal AF, 15% persistent, 56% permanent and 10% unknown type, 77% were treated with vitamin K antagonists (VKA), 17% with antiplatelet therapy with no differences between age groups. Rate-control drugs were more frequently used than rhythm-control drugs (55% vs. 37%, p < 0.001). VKA use was associated with permanent AF, younger age and cancer in patients ≥ 80 years old and with permanent AF and preserved functional autonomy in patients < 80 years old. Hemorrhagic scores were independently associated with non-use of VKA whereas thromboembolic scores were not associated with VKA use.

CONCLUSIONS

In this elderly AF outpatient population, use of anticoagulant therapy was higher even after 80 years than in previous studies suggesting that recent international guidelines are better implemented in the elderly population.

The therapeutic management of chronic pain in ambulatory care patients aged 65 and over in France: the S.AGES Cohort. Baseline data

OBJECTIVE

The main objective of the S.AGES (Elderly Subjects) cohort study is to describe the current therapeutic strategy for chronic pain in non-institutionalised elderly patients in France.

METHODS

In this prospective cohort study, non-institutionalised patients aged 65 years and over with chronic pain were recruited by general practitioners (GP) across France. All medicinal and non- medicinal prescriptions were recorded at inclusion and will be followed up over 3 years via an eCRF. Data recorded at baseline are presented in this paper.

RESULTS

Two hundred and sixty GPs enrolled 1379 evaluable patients between June 3rd, 2009 and June 3rd, 2011. Pain was mainly of a mechanical nature, due to osteoarthritis or common back pain. 80% of the patients had moderate or severe pain. More than a third of patients were treated with a step 1 analgesic (mainly paracetamol), and approximately 30% received a step 2 analgesic (23% dextropropoxyphene and 40.3% tramadol/paracetamol combination). Only 3% received step 3 analgesics; this rate remained low even in patients with severe pain. The proportion of patients treated with an antiepileptic was higher in case of neuropathic pain. More than 25% of patients did not receive any analgesic medication.

CONCLUSION

The baseline S.AGES study results exhibit a well-balanced therapeutic management of chronic pain by GPs for ambulatory elderly patients. Clinicaltrials.org NCT01065909.

Identifying and preventing adverse drug events in elderly hospitalised patients: a randomised trial of a program to reduce adverse drug effects

OBJECTIVES

Evaluate the impact of educational intervention in decreasing ADEs in elderly patients in a hospital setting.

DESIGN

Randomised prospective study.

SETTING

The study was performed in France in the Paris area, in 16 rehabilitation geriatric centres of APHP (Assistance Publique - Hôpitaux de Paris). Patient capacity per centre varied from 15 to 57 with a total of 526.

PARTICIPANTS

All the patients > or = 65 years hospitalized during the 4 week study period were included.

MEASUREMENTS

During a first 2 week phase without intervention ADE's were recorded in all centres. Then units were then randomised for an educational intervention or not. The educational phase lasted 1 week, without ADE tracking. Then, both types of units (I+ and I-) recorded ADEs for 2 weeks. Possible drug-related incidents were detected using a standardized check list (nurses) and a weekly review of all charts by investigators. Possible drug-related incidents were analysed by a group of reviewers selected from the authors to classify them as ADE or not.

RESULTS

576 patients (mean age: 83.6 +/- 7.9 years) were consecutively included. The mean number of drugs at inclusion was 9.4 +/- 4.24 drugs per patient. 223 out of 755 events were considered "probable" ADEs (29.5%). Among the 223 ADEs, 62 (28%) could have been prevented. The main outcome of this trial was the change in the proportion of ADEs in elderly patients in the intervention-units, compared to the control group. The main errors were: to high a dose (26%), double therapy (21%), under dose (13%), inappropriate drug (13%), drug-drug interaction (6%), previous same adverse drug reaction (3%) and miscellaneous (11.18%). After a specific educational intervention program, there were fewer ADEs in the intervention group (n = 38, 22%) than in the control group (n = 63, 36%; p = 0.004).

CONCLUSION

Educational programs could help reduce the prevalence of ADEs by 14% and encourage physicians to change outdated prescription habits.

Vitamin K epoxide reductase genetic polymorphism is associated with venous thromboembolism: results from the EDITH Study

BACKGROUND

The vitamin K epoxide reductase complex subunit 1 (VKORC1) recycles endogenous vitamin K, a cofactor for vitamin K-dependent coagulation factor synthesis. Common polymorphisms in VKORC1, the gene coding for VKORC1, have been found to affect the dose response to vitamin K antagonists, and to confer an increased risk of vascular diseases in a Chinese population. The aim of this study was to evaluate the association between the VKORC1 1173C > T polymorphism and venous thromboembolism (VTE).

METHODS

We report the results of a case-control study designed to evaluate interactions between acquired and inherited risk factors of VTE. We studied 439 cases hospitalized with a first venous thromboembolic event that was not related to a major acquired risk factor for VTE, and 439 matched controls. The VKORC1 1173C > T polymorphism was selected for genotyping as the tagging single-nucleotide polymorphism for previously identified VKORC1 haplotypes.

RESULTS

The relationship between VTE and the VKORCI 1173C > T polymorphism was consistent with a recessive model. The frequency of the VKORCI TT genotype was lower in cases than in controls. The odds ratio (OR) (95% CI) was 0.62 (0.41-0.94) for the TT genotype as compared to CT/CC genotypes. Adjustment on cardiovascular diseases, body mass index, factor V (FV) and prothrombin gene mutations did not alter the results.

CONCLUSIONS

In this case-control study, the frequency of the VKORCI TT genotype was lower in patients with VTE than in matched controls. The clinical consequence of these results remains to be determined, but gives new perspectives for exploration of the role of VKORCI polymorphism in the pathogenesis of VTE.

Amiodarone Interacts with Simvastatin but not with Pravastatin Disposition Kinetics

The aim of this study was to determine the influence of amiodarone on the pharmacokinetics of simvastatin and pravastatin in humans. This was a prospective, crossover, randomized, open-label study performed in 12 healthy volunteers comparing the pharmacokinetics of a single oral dose of simvastatin (40 mg) or pravastatin (40 mg) taken alone and after 3 days of amiodarone (400 mg/day). Amiodarone increased simvastatin acid AUC (area under the plasma concentration-time curve)0-24 h, peak plasma concentration (Cmax), and t1/2 by 73% (P=0.02), 100% (P=0.02), and 48% (P=0.06), respectively, whereas it did not significantly alter pravastatin pharmacokinetics. Point estimates and 90% confidence intervals for simvastatin acid, simvastatin lactone, and pravastatin AUC0-24 h were 154% (109-216%), 155% (109-227%), and 86% (63-118%), respectively. If amiodarone and a statin have to be simultaneously prescribed, pravastatin should be preferred to simvastatin in order to avoid a drug interaction.

[A new, rapid and robust genotyping method for CYP2C9 and MDR1]

Single nucleotide polymorphisms (SNPs) can significantly affect human phenotypes. Detection of allelic variant carriers has become a major goal for clinical pharmacologists in order to study phenotype-genotype relationships. However, there is a crucial need for rapid, and validated pharmacogenetic tests. The aim of the study was to validate a new fluorescence PCR strategy for cytochrome P450 2C9 (CYP2C9) and multidrug resistance gene (MDR1) genotyping. Results of CYP2C9 and MDR1 genotypes determined with reference techniques were compared to those obtained by allelic discrimination assays employing fluorescent TaqMan probes. Sixteen subjects carrying CYP2C9*2 and CYP2C9*3 allelic variants (heterozygous and homozygous) previously identified by sequencing and 55 subjects previously genotyped for MDR1 exon 26 (C3435T) SNP by conventional PCR-RFLP were genotyped with fluorescent PCR. Fluorescent PCR gave 100 % accuracy with the results obtained with reference genotyping strategies for each of the 3 SNPs. Genotyping results with fluorescent PCR repeated on three consecutive occasions remained constant over time for each of the 3 SNPs. Allelic discrimination assays based on fluorescent PCR gave entire satisfaction for CYP2C9 and MDR1 genotyping. This reliable genotyping strategy can be easily used in clinical practice and should be further developed for additional SNPs identification.

Genetic and environmental risk factors for oral anticoagulant overdose

BACKGROUND

Cytochrome P450 2C9 (CYP2C9) allelic variant carriers have been shown to experience hyper-responsiveness to small doses of oral anticoagulants (OAs) (warfarin or acenocoumarol) and a higher bleeding rate.

OBJECTIVES

To determine the relative frequencies of different risk factors for OA overdose including diet, concomitant diseases, drug interactions, recent increment of OA dose and CYP2C9 genetic polymorphism among hospitalised patients.

MATERIALS AND METHODS

Frequencies of the different risk factors for OA overdose were determined in a prospective case-control study. Seventy-five consecutive patients with an International normalised ratio (INR) greater than 4 were matched with seventy-five control patients with an INR greater than 2 but less than 3.5 with respect to age, prescribed OA and daily dose. Genotyping of CYP2C9*2 and CYP2C9*3 allelic variants was detected by the TaqMan allelic discrimination assay.

RESULTS

Drug interactions and a recent increment of OA dose were the only significant independent risk factors identified in the first analysis with odds ratio 2.13 (95% CI: 1.06-4.28) and 3.38 (95%CI: 1.51-7.57), respectively. A recent increment of OA dose was the only significant independent risk factor identified among the patients treated with coumarin derivatives (acenocoumarol or warfarin), excluding those treated with fluindione; the odds ratio was 4.3 (95% CI: 1.5-12.3). CYP2C9 genetic polymorphism did not significantly predict the increased risk of OA overanticoagulation in this study. However three homozygous CYP2C9*3/CYP2C9*3 genotype patients were found among the cases, whereas no such patients could be identified among controls.

CONCLUSION

This is the first observational study investigating the role of CYP2C9 genetic polymorphism together with other environmental OA overdose risk factors. Our results support the view that although the CYP2C9*3/CYP2C9*3 genotype is associated soon after the introduction of OA with dramatic overanticoagulation, OA overdose is mostly related to environmental factors.

Semiautomatic macroencapsulation of fresh or cryopreserved porcine hepatocytes maintain their ability for treatment of acute liver failure

We have previously demonstrated that fresh or cryopreserved xenogeneic hepatocytes manually macroencapsulated in AN69 polymer and transplanted intraperitoneally in rats were able to improve the survival rate after 95% hepatectomy without immunosuppression. In addition, we developed a semiautomatic device where porcine hepatocytes were coextruded with AN69 hydrogel in order to macroencapsulate large amounts of cells. The purpose of the present study was to 1) test whether transplanted porcine hepatocytes macroencapsulated in this device remained functional as evaluated by their ability to prevent death from acute liver failure, and 2) compare the efficiency of cryopreserved or freshly isolated hepatocytes. Fresh or cryopreserved porcine hepatocytes were macroencapsulated in the semiautomatic device by coextrusion in AN69 polymer in 2-m minitubes containing 6 x 10(7) cells. Acute liver failure was induced in rats by two-step 95% hepatectomy. At the time of completion of liver resection, rats were either not transplanted with minitubes (control group I, n = 13), or were implanted with two minitubes containing culture medium (control group II, n = 11), hepatocytes killed by heat treatment (control group III, n = 10), coextruded fresh hepatocytes (group IV, n = 11), or coextruded cryopreserved hepatocytes (group V, n = 11), without immunosuppression. The survival rate at day 7 was between 0% and 31% in the three control groups. By contrast, coextruded fresh hepatocytes significantly improved the survival rate (group IV, 82%) as did cryopreserved cells (group V, 91% survival). In surviving rats, minitubes were explanted after 20 days; either fresh or cryopreserved hepatocytes appeared morphologically viable and their ultrastructure was preserved. Their detoxification capacities evaluated by the activity of the cyt P450 CYP3A4 were partly maintained. In conclusion, porcine hepatocytes macroencapsulated by coextrusion using a semiautomatic device and transplanted without immunosuppression were able to prevent death from acute liver failure in rats. Cryopreserved cells were as efficient as fresh hepatocytes.

Variability of cytochrome P450 1A2 activity over time in young and elderly healthy volunteers

AIMS

To assess the age-associated changes over time of plasma paraxanthine/caffeine (PAX/CAF) ratios used as a probe for CYP1A2 activity.

METHODS

Intraindividual and interindividual variabilities in PAX/CAF ratio were compared by phenotyping with caffeine, 16 young and 16 elderly healthy subjects on five occasions.

RESULTS

PAX/CAF ratio variability was comparable regardless of age (intraindividual CV: 17.6 +/- 6% and 16.2 +/- 5.9%, interindividual CV: 48.1 +/- 2.9% and 42.7 +/- 3.6% in young and elderly, respectively). The PAX/CAF ratio was lower in elderly than in young subjects (95% CI for the difference: 0.004, 0.32) but the difference was not significant in nonsmokers compared separately.

CONCLUSIONS

The variability over time of the PAX/CAF ratio is not influenced by age.

Early acenocoumarol overanticoagulation among cytochrome P450 2C9 poor metabolizers

Cytochrome P450 2C9 (CYP2C9) is the enzyme that terminates the anticoagulant effect of warfarin. The heterozygous carriers of the two allelic variants CYP2C9*2 and CYP2C9*3 have been associated with impaired warfarin metabolism and a higher risk of haemorrhage. Only three CYP2C9 poor metabolizers (CYP2C9*3/CYP2C9*3) initiating warfarin treatment have so far been identified, all of them with a dramatic overdose occurring a few days after treatment initiation. Acenocoumarol, another coumarinic anticoagulant, has recently been shown to be metabolized by CYP2C9. We report, for the first time, two cases of dramatic overanticoagulation occurring in patients starting acenocoumarol treatment while taking recommended doses (4 mg/day). In both cases, the overdose was discovered at the first INR control with values above 9. Genotyping revealed that the two patients were homozygous for the CYP2C9*3 allele. Our report highlights the need for CYP2C9 genotyping before starting oral anticoagulants in order to prevent early overanticoagulation episodes.

Effect of grapefruit juice on digoxin pharmacokinetics in humans

OBJECTIVES

Grapefruit juice is responsible for drug interactions mediated by intestinal cytochrome P4503A4 inhibition and possibly P-glycoprotein inhibition in enterocytes. Our main objective was to determine whether grapefruit juice alters the bioavailability of digoxin, a P-glycoprotein substrate. The secondary objective was to determine whether the magnitude of the pharmacokinetic interaction was influenced by P-glycoprotein genetic polymorphism.

METHODS

Twelve healthy volunteers participated in this open randomized crossover study comparing the effect of grapefruit juice consumption (versus water) on the pharmacokinetics of a single oral dose of digoxin (0.5 mg). The P-glycoprotein genotype was determined according to MDR1 genetic polymorphism in exon 26 (C3435T).

RESULTS

Grapefruit juice had no significant effect on the maximum plasma drug concentration (C(max)) of digoxin or the area under the plasma concentration-time curve (AUC) from time zero to 48 hours. However, there was a 9% increase in the digoxin AUC from time zero to 4 hours and from time zero to 24 hours (P =.01) during grapefruit juice administration. The digoxin renal clearance remained unchanged during both periods. No relationship between MDR1 C3435T genotype and early digoxin pharmacokinetic changes could be detected.

CONCLUSION

The modest changes in digoxin pharmacokinetics observed during grapefruit juice ingestion do not support an important P-glycoprotein inhibition. Under our experimental conditions, grapefruit juice-mediated P-glycoprotein inhibition does not appear to play a relevant role in drug interactions, at least when assessed by use of digoxin disposition kinetics.

Survival and differentiation of porcine hepatocytes encapsulated by semiautomatic device and allotransplanted in large number without immunosuppression

BACKGROUND/AIMS

The aim of this study was to evaluate the survival and functions of porcine hepatocytes transplanted in large quantities in the peritoneal cavity of allogeneic animals following semiautomatic encapsulation.

METHODS

Isolated porcine hepatocytes and a polymer solution composed of AN69 were coextruded through a double lumen spinneret. Minitubes containing hepatocytes were transplanted in the peritoneal cavity of 12 pigs (4 x 10(9) cells/animal) in the absence of immunosuppressive therapy. Seven, 15, and 21 days after transplantation, minitubes was collected and processed for analyses. The morphology was examined under light and electron microscopy. Albumin synthesis was assessed by semi-quantitative reverse transcription-polymerase chain reaction. Cytochrome P450 3A (CYP3A) gene expression was analyzed by Western blot and by testosterone 6-beta-hydroxylation assay.

RESULTS

The device allowed to encapsulate 55 x 10(6) hepatocytes/min. Hepatocytes exhibited normal structural and ultrastructural features up to day 21. Albumin gene expression decreased progressively between days 0 and 21. The amount of CYP3A protein and 6-beta-hydroxylase activity were approximately 2-fold lower at days 7 and 15 than in freshly encapsulated hepatocytes, and further decreased thereafter.

CONCLUSIONS

The preservation of hepatocyte functions during 1-2 weeks is encouraging for potential short-term use of such bioartificial liver in future clinical application.

Indirect cytotoxicity of flucloxacillin toward human biliary epithelium via metabolite formation in hepatocytes

Flucloxacillin, an isoxazolyl-penicillin, causes cholestasis and biliary epithelium injury. The aim of the study was to determine whether flucloxacillin, either directly or through metabolite formation, may induce cytotoxicity in hepatic or biliary cells. Cytotoxicity was assessed by lactate dehydrogenase release in primary cultures of human hepatocytes and of gallbladder-derived biliary epithelial cells (BEC). Metabolite production in microsome and cell preparations was analyzed by chromatography, nuclear magnetic resonance spectroscopy, and mass spectrometry. While flucloxacillin induced no direct cytotoxicity in any of the hepatocyte (n = 12) and BEC (n = 19) preparations, the conditioned media from cultured hepatocytes preincubated with flucloxacillin (50-500 mg/L) triggered a significant increase in lactate dehydrogenase release over controls in approximately 50% of BEC preparations (7/12), and this effect depended upon flucloxacillin concentration. Remaining BEC preparations exhibited no toxic response. Cytotoxicity in BEC preparations (9/13) was also induced by the supernatants of human liver microsomes and of recombinant human cytochrome P450 (CYP)3A4 preincubated with flucloxacillin (500 mg/L). Supernatants from both liver microsome and CYP3A4 preparations contained one major metabolite which was identified as 5'-hydroxymethylflucloxacillin. The production of this metabolite was inhibited following CYP3A4 inhibition by troleandomycin in human liver microsomes, and markedly enhanced following CYP3A induction by dexamethasone in rat liver microsomes. As opposed to BEC, cultured hepatocytes displayed significant CYP3A activity and produced low amounts of this metabolite. The purified metabolite (0.01-5 mg/L) exerted toxic effects in BEC but not in hepatocytes. In conclusion, hepatocytes mainly via CYP3A4 activity, generate flucloxacillin metabolite(s) including 5'-hydroxymethylflucloxacillin that may induce cytotoxicity in susceptible BEC. These metabolic events may contribute to the pathogenesis of drug-induced cholangiopathies.

Survival and functions of encapsulated porcine hepatocytes after allotransplantation or xenotransplantation without immunosuppression

BACKGROUND

This study evaluated the survival and functions of encapsulated porcine hepatocytes after intraperitoneal allotransplantation and xenotransplantation without immunosuppression.

METHODS

Isolated porcine hepatocytes were encapsulated in AN 69 polymer capsules (45.10(6)/capsule) and transplanted intraperitoneally in 12 rats and 12 pigs. Fifteen, 30, and 60 days after transplantation, capsules were removed and the viability and morphology of explanted hepatocytes were examined under light and electronic microscopy. The potential to produce albumin was assessed by evaluating the level of albumin messenger RNA, using semiquantitative reverse transcription-polymerase chain reaction. 6beta-Hydroxylase activity was measured by high-performance liquid chromatography. In addition, cytochrome P450 3A proteins were detected by Western blot only in allogeneic hepatocytes.

RESULTS

Similar results were observed after allotransplantation and xenotransplantation. Histologic studies showed that hepatocytes were well-preserved and arranged in cords for up to 30 days. The expression of porcine albumin gene was maintained up to 15 days. 6beta-Hydroxylase activity was 2.5-fold lower at day 15 than in freshly encapsulated hepatocytes, which were not transplanted. In allogeneic hepatocytes, the expression of CYP 3A protein was detected up to 60 days after transplantation.

CONCLUSIONS

Encapsulated porcine hepatocytes remain viable and functional for at least 15 days after allotransplantation and xenotransplantation without immunosuppression. The demonstration of maintained hepatic functions in transplanted porcine hepatocytes up to 15 days is a first step toward application in the treatment of acute liver failure.

Is diclofenac a valuable CYP2C9 probe in humans?

INTRODUCTION

Besides the low therapeutic index drug tolbutamide, there is no validated in vivo probe to assess the genetically determined CYP2C9 activity in humans. The in vitro CYP2C9-specific substrate diclofenac might be a valuable, well-tolerated probe candidate. In order to validate diclofenac as an in vivo CYP2C9 probe, we planned to show that urinary 4'-hydroxydiclofenac/diclofenac metabolic ratio (MR) would correlate to the apparent partial metabolic clearance of diclofenac into 4'-hydroxydiclofenac (Clmet).

PATIENTS AND METHODS

Eighteen healthy volunteers received a single oral dose of 50 mg diclofenac in its enteric-coated form. Blood and urinary pharmacokinetics of diclofenac were studied over 48 h. Identification of the CYP2C9 alleles (CYP2C9*1, CYP2C9*2, and CYP2C9*3) was performed with genomic DNA sequencing.

RESULTS

We observed a dramatic inter-individual variability in the delay of diclofenac intestinal absorption since its first detectable blood concentration ranged from 0.5 h to more than 12 h after drug intake. The Clmet of diclofenac could not be determined in two subjects who started to absorb the drug after 12 h. No correlation could be observed between Clmet of diclofenac and the different MRs calculated at 0-4 h, 0-8 h, 0-12 h, 0-24 h and 0-48 h urinary collections. The Clmet of diclofenac in heterozygous subjects tended to be lower than among wild-type homozygous subjects, but this difference did not reach statistical significance due to an insufficient number of subjects studied.

CONCLUSION

Diclofenac, in its enteric-coated form, is not a useful in vivo CYP2C9 probe probably because of its highly variable intestinal absorption rate. However, since we found a lower metabolic clearance of diclofenac in heterozygous CYP2C9 subjects, as observed with other CYP2C9 substrates, diclofenac, in another galenic form, might be a potential probe to quantify CYP2C9 activity in humans.

Lymphocyte P-glycoprotein expression and activity before and after rifampicin in man

It has recently been shown that P-glycoprotein (P-gp) is inducible by rifampicin in the human gut as shown in intestinal biopsies. The present study was performed in order to test the hypothesis that human peripheral lymphocytes can be used to assess such an inducibility. We also assessed inter- and intra-individual variability of P-gp expression and activity in peripheral lymphocytes. Blood samples from 13 healthy volunteers were collected 1.7, 14 and 19 days after inclusion. Rifampicin treatment (600 mg/day) was administered from day 15 to day 18. Lymphocyte P-gp expression was measured at the messenger RNA level by semi-quantitative RT-PCR and at the protein level by immunostaining flow cytometry. P-gp activity was determined by flow cytometry with rhodamine 123 efflux. Cytochrome P4503A4 (CYP3A4) inducibility was measured by comparing the urinary metabolic ratio of 6beta-hydroxycortisol/cortisol on day 14 and 19, Lymphocyte P-gp expression and activity was not induced by rifampicin, while it increased CYP3A4 activity from 5.0 +/- 4.0 to 22.9 +/- 16.6 (P < 0.001). There was a 3 - 4-fold inter-individual variability and a 3 - 44 % intra-individual variability of lymphocyte P-gp expression and activity. Peripheral lymphocytes are not an appropriate material to assess P-gp inducibility in humans. P-gp shows significant inter- and intra-individual variability in human lymphocytes.

[Drug-drug interactions: predictive in vitro models of in vivo interactions. Round table no. 6.XV]

Liver drug metabolism is a major source of drug interactions. Three major human in vitro models are employed to detect drug interactions in the preclinical phases of drug development: recombinant enzymes, human liver microsomes and primary human hepatocyte cell cultures. Results obtained from these models may vary during the different phases of drug development. Identification of the metabolic pathways, enzymes involved in drug metabolism (mainly cytochrome P450s), enzyme induction or inhibition allow us to detect the major pharmacokinetic drug interactions which can occur in man and to identify specific populations at risk for such interactions. In vitro models are essential to decide if and which future drug interaction studies should be performed in man. However, the clinical relevance of the potential pharmacokinetic drug interactions detected by these in vitro models remains to be determined and confirmed by human studies.

Low levels of lymphocyte MDR1 gene expression during early renal transplantation in patients treated with tacrolimus

P-glycoprotein (P-gp) is a membrane efflux pump increasing the transport of drugs such as tacrolimus out of the cells. The aim of the study was to determine the kinetics of lymphocyte P-gp expression in patients treated with tacrolimus during the first 3 months following renal transplantation. Lymphocyte MDR1 gene expression was measured by semi-quantitative RT-PCR a few hours before transplantation, 3 weeks and 3 months after the graft. Lymphocyte MDR1 gene expression was low in all the 10 patients compared to 10 healthy volunteers: 0.30 +/- 0.07 arbitrary units (patients) vs. 1.74 +/- 0. 55 (healthy volunteers) (P = 0.0002). MDR1 gene expression decreased among the patients during the study: 0.28 +/- 0.12 (3 weeks later) and 0.12 +/- 0.09 (3 months later) (P = 0.006). We can conclude that lymphocyte MDR1 gene expression among patients before renal transplantation is low and remains low during the first 3 months following the graft.

Combined glutathione-S-transferase M1 and T1 genetic polymorphism and tacrine hepatotoxicity

BACKGROUND

Glutathione conjugation of tacrine reactive metabolites depends in part on the activity of glutathione-S-transferases (GST), of which two isozymes (GST M1 and GST T1) are polymorphically expressed.

OBJECTIVE AND METHODS

To determine whether GST M1, GST T1, and the combined GST M1 and GST T1 null genotypes predict individual susceptibility to tacrine hepatotoxicity, 141 patients with mild to moderate Alzheimer's disease treated with tacrine were genotyped.

RESULTS

During the treatment period, 52 patients had elevated alanine aminotransferase (ALT) levels at least three times the upper limit of normal, whereas 89 patients had normal ALT values (< or = upper limit of normal). Both groups were comparable in demographic and clinical characteristics. Twenty-eight patients were found to be GST T1-negative (20%; with a 95% confidence interval [95% CI] from 13% to 27%), and 68 patients (48%; 95% CI from 40% to 57%) were GST M1-negative. The combined GST M1-T1 null genotype was observed in 18 patients (13%; 95% CI from 7% to 18%) of whom 13 had an elevated plasma ALT at least three times the upper limit of normal during the study period. Although the cumulative percentage of elevated plasma ALT tended to be higher in the GST M1 null genotype, neither GST M1 nor GST T1 alone could predict individual susceptibility to tacrine hepatotoxicity. Multivariate Cox hazards model showed that the association of the GST M1-T1 null genotype was an independent risk factor of hepatotoxicity.

CONCLUSIONS

The presence of combined alleles M1 and T1 deficiencies in glutathione-S-transferase genes increases the susceptibility to tacrine hepatotoxicity.

[Viability and differentiation of human hepatocytes immunoprotected by macroencapsulation and transplanted in rats]

OBJECTIVES

To determine the viability and differentiation of human hepatocytes immunoprotected by encapsulation and transplanted in rats without immunosuppression.

METHODS

Freshly isolated human hepatocytes were encapsulated in hollow fibers and transplanted in the peritoneal cavity of immunocompetent rats. The fibers were explanted for analysis at D3, D7 and D14 following transplantation. Morphological features under light and electron microscopy and gene expression were compared to those of non-transplanted encapsulated hepatocytes (D0). Human cytochrome P450 3A and albumin mRNAs were quantified by Northern blot. Cytochrome P450 3A proteins were detected by Western blot and cytochrome P450 3A enzyme activity was assessed by measuring the formation of 6beta-hydroxytestosterone by high performance liquid chromatography.

RESULTS

Transplanted hepatocytes were more than 60 % viable and exhibited morphological criteria of hepatocytic differentiation up to D7. Albumin and cytochrome P450 3A transcripts were also detected up to D14. At D3 and D7, albumin mRNA levels were of 30 %, compared to control D0 hepatocytes, while cytochrome P450 3A5 and cytochrome P450 3A4 mRNA levels were 65 % and 0 %, respectively. Cytochrome P450 3A immunoreactivity was detected by Western blot up to D14 and 6beta-hydroxylase activity was 17 % at D3 compared to D0, supporting with disappearance of cytochrome P450 3A4 mRNA.

CONCLUSIONS

Human hepatocytes remain viable for a short period, following encapsulation and intraperitoneal transplantation in rat. Other experimental conditions need to be tested to prevent or delay a decrease in hepatocyte specific gene expression.

Prolonged sedation requiring mechanical ventilation and continuous flumazenil infusion after routine doses of clorazepam for alcohol withdrawal syndrome

We report the cases of two patients who developed prolonged sedation after routine doses of clorazepam for alcohol withdrawal syndrome. They required prolonged mechanical ventilation (10 days for both patients) followed by continuous flumazenil infusion (16 days for one patient and 3 days for the other) to avoid reintubation. In the two patients, nordazepam accumulation (main active metabolite of clorazepam) was demonstrated as the cause of the coma. This accumulation could be attributed, in one case, to impaired hepatic cytochrome P 450 3A4 activity. Caution is required when prescribing benzodiazepines to alcoholic patients and the use of benzodiazepine which do not undergo hepatic oxidation by cytochrome P 450 such as oxazepam or lorazepam is suggested.

Phase I and phase II drug-metabolizing enzymes are expressed and heterogeneously distributed in the biliary epithelium

Tissue expression of drug-metabolizing enzymes influences susceptibility to drugs and carcinogens. Because the biliary epithelium, exposed to bile-borne chemicals, may give rise to drug-induced cholangiopathies and to cholangiocarcinomas, we determined the pattern of expression of drug-metabolizing enzymes in this epithelium. We first demonstrated by blot analyses that biliary epithelial cells (BEC) isolated from human gallbladders display cytochrome P450 (CYP) 1A, 2E1, and 3A, microsomal epoxide hydrolase (mEH), alpha, mu, and pi glutathione S-transferase (GST), transcripts and proteins. We also identified CYP-associated steroid 6beta-hydroxylase activity in BEC. CYP and mEH expression was 5- to 20-fold lower in BEC than in autologous hepatocytes, and further differed by a higher ratio of CYP3A5/CYP3A4, and by CYP1A1 predominance over CYP1A2. alphaGST was highly expressed in both hepatocytes and BEC, while piGST was restricted to BEC. In approximately 50% of individuals, muGST was expressed in hepatocytes and at lower levels in BEC. By using the same antibodies as those used in immunoblots, we could show by immunohistochemistry that CYP2E1, CYP3A, mEH, alpha, mu, and piGST immunoreactivities are expressed and display a heterogeneous distribution in the epithelium lining the entire biliary tract except for small intrahepatic bile ducts that were devoid of CYP3A and alphaGST immunoreactivities. In conclusion, BEC contribute to phase II, and although to a lesser extent than hepatocytes, to phase I biotransformation. The distribution of drug-metabolizing enzymes in BEC suggest that they are heterogeneous in their ability to generate and detoxicate reactive metabolites, which may contribute to specific distributions of cholangiopathies.

Assessment of CYP2D6 and CYP2C19 activity in vivo in humans: a cocktail study with dextromethorphan and chloroguanide alone and in combination

OBJECTIVES

Dextromethorphan and chloroguanide (INN, proguanil) are used as prototypic phenotyping substrates of polymorphically expressed CYP2D6 and CYP2C19 in humans. We determined whether the dextromethorphan/dextrorphan and chloroguanide/cycloguanil metabolic ratios, obtained after administration of the parent drugs either alone or in combination, are equivalent.

METHODS

Thirty-six healthy male volunteers received single oral doses of 80 mg dextromethorphan and 200 mg chloroguanide during a three-period, randomized crossover study. Plasma and urine were collected to calculate metabolic ratios and analyze the disposition kinetics of the probe drugs.

RESULTS

All subjects were extensive metabolizers for both CYP2D6 and CYP2C19. Chloroguanide kinetics and urinary metabolic ratio were not altered after dextromethorphan administration. Dextromethorphan urinary metabolic ratio increased from -2.52 +/- 0.67 to -2.03 +/- 0.58 (P < .001) in the presence of chloroguanide. This was caused by an increase of dextromethorphan without a significant change of dextrorphan in both urine and plasma. Inhibition of CYP3A-dependent biotransformation of dextromethorphan to methoxymorphinan did not appear to be responsible for this change because the log(dextromethorphan/methoxymorphinan) urinary ratio, an index of CYP3A activity, did not significantly change during chloroguanide coadministration. The chloroguanide and dextromethorphan metabolic ratio determined from urine collection correlated with the corresponding metabolic ratio determined from plasma obtained 3 hours after oral administration.

CONCLUSION

When CYP2D6 and CYP2C19 activity are assessed, dextromethorphan and chloroguanide cannot be associated in a cocktail because chloroguanide increases the dextromethorphan metabolic ratio. CYP2D6 and CYP2C19 activity can be determined from a blood sample drawn 3 hours after oral administration of dextromethorphan and chloroguanide, respectively.

Cytochrome P-450 3A4 and 2C8 are involved in zopiclone metabolism

Zopiclone is a widely prescribed, nonbenzodiazepine hypnotic that is extensively metabolized by the liver in humans. The aim of the present study was to identify the human cytochrome P-450 (CYP) isoforms involved in zopiclone metabolism in vitro. Zopiclone metabolism was studied with different human liver microsomes and a panel of heterologously expressed human CYPs (CYP1A2, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, and 3A4). In human liver microsomes, zopiclone was metabolized into N-desmethyl-zopiclone (ND-Z) and N-oxide-zopiclone (NO-Z) with the following K(m) and V(m) of 78 +/- 5 and 84 +/- 19 microM, 45 +/- 1 and 54 +/- 5 pmol/min/mg for ND-Z and NO-Z generation, respectively. Ketoconazole (CYP3A inhibitor) inhibited approximately 40% of the generation of both metabolites, sulfaphenazole (CYP2C inhibitor) inhibited the formation of ND-Z, whereas alpha-naphtoflavone (CYP1A), quinidine (CYP2D6), and chlorzoxazone (CYP2E1) did not affect zopiclone metabolism. The generation of ND-Z and NO-Z were highly correlated to testosterone 6beta-hydroxylation (CYP3A activity, r = 0.95 and 0.92, respectively; p =.0001), and ND-Z was highly correlated to CYP2C8 activity (paclitaxel 6alpha-hydroxylase; r = 0.76, p =.004). Recombinant CYP2C8 had the highest enzymatic activity toward zopiclone metabolism into both its metabolites, followed by CYP2C9 and 3A4. CYP3A4 is the major enzyme involved in zopiclone metabolism in vitro, and CYP2C8 contributes significantly to ND-Z formation.

Mibefradil, a potent CYP3A inhibitor, does not alter pravastatin pharmacokinetics

Dramatic drug-drug interactions have been observed between several HMG-CoA reductase inhibitors and cytochrome P450 3A (CYP3A) inhibitors. The aim of the present study was to investigate the effects of mibefradil, a potent CYP3A inhibitor, on pravastatin pharmacokinetics. 12 healthy volunteers were included in this open-label one-period study. Pravastatin pharmacokinetics (following a single oral dose of 40 mg) was studied in the absence of mibefradil (day 1) and after repeated doses (100 mg/day) of mibefradil (day 8). Pravastatin pharmacokinetics after repeated doses of 40 mg/day was also studied in association with repeated doses (100 mg/day) of mibefradil (day 16). Pravastatin area under the plasma concentration vs. time curve (AUC0-infinity) and Cmax in the absence of mibefradil on day 1 (170 [117 to 395] ng h/mL and 91 [72 to 200] ng/mL respectively, geometric mean [95% confidence intervals]) were not significantly altered in the presence of mibefradil on day 8 (224 [174 to 381] ng h/mL and 124 [72 to 200] ng/mL) and on day 16 (200 [137 to 555] ng h/mL and 91 [74 to 184] ng/mL). Tmax of pravastatin in the absence of mibefradil (0.9 +/- 0.1 h, arithmetic mean +/- SD) was slightly delayed in the presence of mibefradil on day 8 and 16 (1.1 +/- 0.3 and 1.2 +/- 0.3 h respectively, p < 0.01 for both comparisons). The results of the present study confirm the lack of pharmacokinetic interactions between mibefradil and pravastatin and indicate that pravastatin may be safely prescribed in the presence of potent CYP3A inhibitors.

Halofantrine metabolism in microsomes in man: major role of CYP 3A4 and CYP 3A5

We have clarified the contribution of the different enzymes involved in the N-debutylation of halofantrine in liver microsomes in man. The effect of ketoconazole and cytochrome P450 (CYP) 3A substrates on halofantrine metabolism has also been studied. The antimalarial drug halofantrine is metabolized into one major metabolite, N-debutylhalofantrine. In microsomes from nine livers from man, N-debutylation of halofantrine was highly variable with apparent Michaelis-Menten constant V(max) and K(m) values of 215+/-172 pmol min(-1) mg(-1) and 48+/-26 micromol L(-1), respectively, (mean+/-standard deviation). Formation of N-debutylhalofantrine was cytochrome P450 (CYP)-mediated. Studies using selective inhibitors of individual CYPs revealed the role of CYP 3As in the formation of N-debutylhalofantrine. alpha-Naphthoflavone, a CYP 3A activator, increased metabolite formation. In microsomes from 12 livers from man the rate of N-debutylation of halofantrine correlated strongly with CYP 3A4 relative levels (P = 0.002) and less strongly, but significantly, with CYP 2C8 levels (P = 0.025). To characterize CYP-mediated metabolism of halofantrine further, incubations were performed with yeast microsomes expressing specific CYP 3A4, CYP 3A5, CYP 2D6, CYP 2C8 and CYP 2C19 from man. The rate of formation of N-debutylhalofantrine was six- and twelvefold with CYP 3A4 than with CYP 3A5 and CYP 2C8, respectively. CYP 2D6 and CYP 2C19 did not mediate the N-debutylation of halofantrine, but, because in-vivo CYP 2C8 is present at lower concentrations than CYP 3A in the liver in man, the involvement of CYP 3As would be predominant. Diltiazem, erythromycin, nifedipine and cyclosporin (CYP 3A substrates) inhibited halofantrine metabolism. Similarly, ketoconazole inhibited, non-competitively, formation of N-debutylhalofantrine with an inhibition constant, K(i), of 0.05 microM. The theoretical percentage inhibition of halofantrine metabolism in-vivo by ketoconazole was estimated to be 99%. These results indicate that both CYP 3A4 and CYP 3A5 metabolize halofantrine, with major involvement of CYP 3A4. In-vivo, the other CYPs have a minor role only. Moreover, strong inhibition, and consequently increased halofantrine cardiotoxicity, might occur with the association of ketoconazole or other CYP 3A4 substrates.

Use of heterologously expressed human cytochrome P450 1A2 to predict tacrine-fluvoxamine drug interaction in man

The aim of the present study was to evaluate the use of recombinant human cytochrome P-450 1A2 (rH-CYP1A2) in studies performed in vitro in order to predict metabolic drug-drug interactions occurring in man. In vitro metabolism of tacrine (a CYP1A2 probe) in the presence and absence of fluvoxamine, a CYP1A2 inhibitor, was investigated in human liver mircrosomes and with different rH-CYP. Vmax, Km and Ki determined with human liver microsomes were compared with those observed using rH-CYP1A2, assuming that 1 mg of liver microsomes contains, on average, 69 pmol of CYP1A2. The extent of tacrine metabolism inhibition procured by fluvoxamine with rH-CYP1A2, was compared with previous results observed in man. The Vax and Km for 1-hydroxytacrine formation rates obtained with rH-CYP1A2 were in good agreement with those observed in human liver microsomes (175+/-9 versus 140+/-60 pmol/min/mg for Vmax and 14+/-2 versus 16+/-2 microM for Km, respectively. The Ki of fluvoxamine on 1-hydroxytacrine formation rate observed with rH-CYP1A2 was similar to that observed with human liver microsome (0.35+/-0.05 versus 0.20+/-0.20 microM, respectively). Using the Km, Vmax and Ki determined with rH-CYP1A2, we calculated that fluvoxamine produced an inhibition of 1-, 2- and 4-hydroxytacrine formation rate of 91, 87 and 88%, respectively, in the range of tacrine and fluvoxamine concentrations observed in man. These percentages of inhibition calculated in vitro were in agreement with the percentage of fluvoxamine-dependent decrease in tacrine apparent oral clearance previously observed in man (83+/-13%). We conclude that human CYP1A2 expressed in yeast is a powerful tool to predict and to quantify drug-drug interactions in man.

Influence of the CYP1A2 inhibitor fluvoxamine on tacrine pharmacokinetics in humans

OBJECTIVE

Tacrine is extensively metabolized by cytochrome P4501A2 (CYP1A2). Fluvoxamine, a potent CYP1A2 inhibitor, may be coadministered with tacrine. The aim of this study was to examine the influence of fluvoxamine administration on the disposition kinetics of single-dose tacrine administration.

METHODS

Thirteen healthy volunteers participated in this double-blind, randomized crossover study, which compared the effects of fluvoxamine (100 mg/day during 6 days) and placebo on the pharmacokinetics of a single oral dose of tacrine (40 mg).

RESULTS

Fluvoxamine caused a significant increase in tacrine area under the plasma concentration versus time curve (AUC): arythmetic mean, 27 (95% confidence interval [CI], 19 to 38) ng.hr/ml versus 224 (95% CI, 166 to 302) ng. hr/ml. Fluvoxamine caused a decrease in the apparent oral clearance of tacrine from 1683 +/- 802 to 200 +/- 106 L/hr (mean +/- SD), which was explained by a decrease in its nonrenal clearance. Five subjects had gastrointestinal side effects during fluvoxamine administration. Fluvoxamine administration was associated with significant increases in the plasma AUC values of three monohydroxylated tacrine metabolites and in the total urinary recovery measurements of tacrine and its metabolites (9.1% +/- 4.6% versus 24.0% +/- 2.6% of recovery). These results may be attributable to fluvoxamine-dependent inhibition of CYP1A/, which is responsible of the biotransformation of tacrine into its monohydroxylated metabolites and further into dihydroxylated and reactive metabolites.

CONCLUSION

Fluvoxamine inhibits the metabolism of tacrine. CYP1A2 may be the target of this inhibition. Fluvoxamine may modulate the hepatotoxicity of tacrine, depending on the relative contribution of tacrine and its reactive metabolites to this toxicity.

Inhibition by omeprazole of proguanil metabolism: mechanism of the interaction in vitro and prediction of in vivo results from the in vitro experiments

Both the antimalarial prodrug proguanil and the gastric proton pump inhibitor omeprazole are substrates for cytochrome P450 (CYP)2C19 and CYP3A. However, the relative contribution of each enzyme to proguanil bioactivation to cycloguanil and to the metabolism of omeprazole, as well as their potential to interact, remains to be examined. The bioactivation of proguanil to its active metabolite cycloguanil was studied in vitro in human liver microsomes and in vivo in 12 healthy subjects, in the absence and in the presence of omeprazole. The formation of cycloguanil from proguanil exhibited biphasic kinetic behavior in four of six human livers, indicating that at least two enzymes are responsible for this metabolic step. Cycloguanil formation activity did not correlate with immunoreactive CYP3A4 content or with CYP3A4 activity, as measured by testosterone 6beta-hydroxylation, suggesting that CYP3A4 plays a limited role in cycloguanil formation. Furthermore, troleandomycin (10 microM) inhibited only 10 to 17% of cycloguanil formation at proguanil concentrations of 100 and 500 microM. At a proguanil concentration of 20 microM, omeprazole at 10 microM inhibited cycloguanil formation in vitro by 47 +/- 59%. These in vitro results were consistent with the results of our in vivo study in healthy subjects, which showed a 32 +/- 11% decrease in proguanil apparent oral clearance and a 65 +/- 8% decrease in proguanil partial metabolic clearance to cycloguanil in the presence of omeprazole (both P < .001). We conclude that in vitro studies of proguanil metabolism and interactions are predictive of in vivo situations, that CYP2C19 is the main enzyme responsible for proguanil bioactivation to cycloguanil and that omeprazole inhibits this biotransformation in vitro and in vivo by inhibiting this enzyme.

Inhibition of CYP1A2 and CYP3A4 by oltipraz results in reduction of aflatoxin B1 metabolism in human hepatocytes in primary culture

Dithiolethiones are thought to act as potent chemoprotective agents against aflatoxin B1 (AFB1)-induced hepatocarcinogenesis in the rat by inducing glutathione S-transferases (GSTs). To determine whether these antioxidants can be similarly effective in human beings, we have investigated metabolism of AFB1, in primary human hepatocytes with or without pretreatment by oltipraz (OPZ), a synthetic derivative of the natural 1,2-dithiole-3-thione. Aflatoxin M1 (AFM1), glutathione conjugates of AFB1 oxides (AFBSGs), and unchanged AFB1 were quantitated in cultures derived from eight human liver donors. Parenchymal cells obtained from the three GST M1-positive livers metabolized AFB1 to AFM1 and to AFBSGs derived from the isomeric exo-and endo-8,9-oxides, whereas no AFBSGs were formed in the GST M1-null cells. Pretreatment of the cells with 3-methylcholanthrene or rifampicin, inducers of CYP1A2 and CYP3A4, respectively, caused a significant increase in AFB1 metabolism. Although OPZ induced GST A2, and to a lesser extent GST A1 and GST M1, it decreased formation of AFM1 and AFBSG, which involves CYP1A2 and CYP3A4. Inhibition by OPZ of AFB1 metabolism by reducing CYP1A2 and CYP3A4 was also demonstrated by decreased activity of their monooxygenase activities toward ethoxyresorufin and nifedipine, respectively. The significant inhibition by OPZ of human recombinant yeast CYP1A2 and CYP3A4 was also shown. These results demonstrate that AFBSG can be formed by GST M1-positive human hepatocytes only, and suggest that chemoprotection with OPZ is due to an inhibition of activation of AFB1, in addition to a GST-dependent inactivation of the carcinogenic exo-epoxide.