Comparison of chlorzoxazone one-sample methods to estimate CYP2E1 activity in humans

Objective Comparison of a one-sample with a multi-sample method (the metabolic fractional clearance) to estimate CYP2E1 activity in humans.Methods Healthy, male Caucasians (n=19) were included. The multi-sample fractional clearance (Cl_fe) of chlorzoxazone was compared with one-time-point clearance estimation (Cl_est) at 3, 4, 5 and 6 h. Furthermore, the metabolite/drug ratios (MRs) estimated from one-time-point samples at 1, 2, 3, 4, 5 and 6 h were compared with Cl_fe.Results The concordance between Cl_est and Cl_fe was highest at 6 h. The minimal mean prediction error (MPE) of Cl_est as a percentage of actual mean Cl_fe was –4.2% at 6 h. Furthermore, regarding Cl_fe, there was a negligible difference (P=0.56) of bias between Cl_est at 3 h (MPE=–8.9%) and 6 h (MPE=–4.2%). The best concordance between MR and Cl_fe was found at 3 h (r=0.74; P<0.001).Conclusion All three single-dose-sample estimates, Cl_est at 3 h or 6 h, and MR at 3 h, can serve as reliable markers of CYP2E1 activity. The one-sample clearance method is an accurate, renal function-independent measure of the intrinsic activity; it is simple to use and easily applicable to humans.     

Study on influence of piperine treatment on the pharmacokinetics of diclofenac in healthy volunteers

1.?Diclofenac sodium (DIC) is a widely used anti-inflammatory drug and its administration in humans receiving long-term therapy with herbal drugs containing piperine (PIP) may occur, which leads to drug–phytochemical interactions. The purpose of the present study was to investigate the influence of PIP treatment on the pharmacokinetics of DIC in healthy volunteers.

2.?The open-label, two period, sequential study was conducted in 12 healthy volunteers. PIP 20?mg was administered once daily for 10 days during treatment phase. A single dose of DIC 100?mg was administered during control and after treatment phases under fasting conditions. The blood samples were collected after DIC dosing at predetermined time intervals and analyzed by HPLC.

3.?Treatment with PIP significantly enhanced maximum plasma concentration (C_max) (2.24–3.68?μg/mL, p?<?0.05), area under the curve (AUC) (7.09–11.81?μg h/mL, p?<?0.05), half-life (T_1/2) (1.23–1.65?h, p?<?0.05) and significantly decreased elimination rate constant (K_el) (0.62–0.41?h^?1, p?<?0.05), apparent oral clearance (CL/F) (7.57–4.52?L/h, p?<?0.05) of DIC as compared to that of control phase.

4.?The results suggest that the altered pharmacokinetics of DIC might be attributed to PIP mediated inhibition of CYP2C9 enzyme, which indicates the clinically significant interaction present between DIC and PIP. Therefore, the combination therapy of DIC along with PIP may represent a novel approach to reduce dosage and result in reduced incidence of gastrointestinal side effects seen with DIC alone at higher doses.     

Effect of 1-aminobenzotriazole on the in vitro metabolism and single-dose pharmacokinetics of chlorzoxazone,a selective CYP2E1 substrate in Wistar rats

The aim of this study was to study the effect of 1-aminobenzotriazole (ABT) on in vitro metabolism, oral, and intravenous (IV) pharmacokinetics of chlorzoxazone (CZX) in rats. Enzyme kinetics of CZX was performed with rat and human liver microsomes and pure isozyme (CYP2E1) with and without ABT. The enzyme kinetics (V_max and K_m) of the formation of 6-hydroxychlorzoxazone (OH-CZX) was found to be similar among rat liver microsomes (3486?pmol?mg?protein^?1?min^?1 and 345?µM), human liver microsomes (3194?pmol?mg?protein^?1?min^?1 and 335?µM) and pure isozyme (3423?pmol?mg?protein^?1?min^?1 and 403?µM), but K_I and K_inact values for ABT towards the ability to inhibit the formation of OH-CZX from CZX varied between liver microsomes (rat: 32.09?µM and 0.12?min^?1; human: 27.19?µM and 0.14?min^?1) and pure isozyme (3.18?µM and 0.29?min^?1). The novel robust analytical method was capable of quantifying CZX, OH-CZX, and ABT simultaneously in a single run, and the method was used for both in vitro and in vivo studies. Pre-treatment of rats with ABT prior to oral and IV administration of CZX significantly decreased the clearance (threefold) and consequently increased the AUC of CZX (approx. three- to fourfold). When rats were pre-treated with ABT, the formation of OH-CZX was completely blocked after oral and IV administration; however, we were able to measure OH-CZX in rats administered with CZX by oral and IV routes without pre-treatment of ABT. The oral bioavailability of CZX was ～71% when dosed alone and reached 100% under pre-treatment with ABT. The t_1/2 values of CZX was significantly prolonged for oral dosing compared with IV dosing under pre-treated conditions with ABT, suggesting an involvement of pre-systemic component in the disposition of CZX. The pharmacokinetic parameters of ABT did not change when it was dosed along with CZX (oral and IV), indicating that either CZX or OH-CZX had no effect on disposition of ABT. The plasma concentrations of ABT were above and beyond the required levels to inhibit CYP2E1 enzyme for at least 36?h post-treatment.     

糖尿病模型大鼠肝脏CYP2E1酶活性的变化

采用四氧嘧啶诱发糖尿病大鼠模型,测定肝苯胺羟化酶及其他药酶活性,同时用氯唑沙宗探针间接评价CYP2E1的活性。结果表明,糖尿病大鼠苯胺羟化酶活性增加80%,伴有其他药酶活性增加。大鼠单次po氯唑沙宗50mg·kg^-1,糖尿病组氯唑沙宗的C_max和AUC分别减少37%和34%,6 羟氯唑沙宗的Tpeak缩短,羟化指数(OH-CZX与CZX的AUC比或浓度比)升高表明糖尿病大鼠可诱导CYP2E1活性。提示糖尿病患者服用经CYP2E1酶代谢的药物应慎重。     

复方银杏叶胶囊对肝损伤大鼠CYP2E1、CYP3A4的影响

目的研究复方银杏叶胶囊(CGB)对酒精性肝损伤大鼠CYP2E1、CYP3A4活性的影响。方法正常组和酒精性肝损伤模型组均以CGB[(250 mg/(kg.d)]灌胃,分别在灌胃CGB前及灌胃1周后,灌胃探针药氯唑沙宗(50 mg/kg)及氨苯砜(20 mg/kg),于探针药灌后24 h内不同时间点采血,测定各探针药血药浓度。结果灌胃CGB前,模型组氯唑沙宗和氨苯砜的AUC0-24、Cmax均显著低于正常组(P<0.05或P<0.01)。灌胃CGB后,模型组氯唑沙宗和氨苯砜的AUC0-24、Cmax均较灌胃前显著升高(P<0.05或P<0.01);且氯唑沙宗的t1/2灌胃CGB后明显高于灌胃前(P<0.05)。结论 CGB能够明显抑制酒精性肝损伤大鼠CYP2E1、CYP3A4酶活性。     

慢性间断性低氧对大鼠肝脏CYP3A_2和CYP2E_1的影响研究

目的研究慢性间断性低氧对大鼠肝脏CYP3A2和CYP2E1的影响。方法将大鼠随机分为对照组、低氧3d组、低氧7d组、低氧14d组、低氧28d组,低氧处理结束24h后,常规腹腔注射麻醉,摘取眼球血液2ml制备血清,并测定丙氨酸氨基转移酶(ALT)、天门冬酸氨基转移酶(AST)、红霉素N-脱甲基酶(ERD)、苯胺羟化酶(ANH)活性;取新鲜肝组织以制备微粒体和提取核糖核酸(RNA),并以RT-PCR进行基因片段扩增以检测大鼠肝脏细胞色素CYP3A2、CYP2E1的mRNA表达水平。结果慢性间断性低氧对血清ALT、AST活性无明显影响;低氧7d后,大鼠肝脏ERD、ANH活性明显升高,28d时诱导率分别为155.5%、42.2%;同时,CYP3A2、CYP2E1mRNA的表达水平也分别增加了220.5%、102.8%。结论慢性间断性低氧能显著增加大鼠肝脏ERD、ANH活性,其机制可能与其在转录水平上提高肝脏CYP3A2和CYP2E1的基因表达水平有关。     

An interaction between the cytochrome P450 probe substrates chlorzoxazone (CYP2E1) and midazolam (CYP3A)

AIMS: The use of multiple probe substrates to evaluate the activity of drug metabolizing enzymes requires that there are no inter-substrate interactions. As part of a series of studies to develop a clinically useful collection of probe substrates that could be given alone or in any combination, we observed an interaction between midazolam (MDZ) and another component of the six-drug cocktail. Published data indicated that the interacting component was likely to be chlorzoxazone. This was investigated as part of a second study. The data relating to the interaction from both studies are reported here. METHODS: Both studies were performed in 16 healthy subjects. All treatments were given orally after an overnight fast. In study 1, which was performed to a four-period, open, crossover design, subjects received on separate occasions MDZ 5 mg, diclofenac 25 mg, a four drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg and chlorzoxazone 250 mg) and a six drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg, chlorzoxazone 250 mg, diclofenac 25 mg and MDZ 5 mg). In study 2, which was performed to a two-period, open, crossover design, subjects received a five drug cocktail (as the six drug cocktail in the first study, but without chlorzoxazone and with diclofenac dose increased to 50 mg) and a six drug cocktail (as five drug cocktail, with chlorzoxazone 250 mg). In both studies, blood samples were taken for measurement of plasma MDZ and 1-hydroxy MDZ (1-OH MDZ) concentrations. In study 1, blood samples were taken up to 12 h post-dose while in study 2 a single sample was taken 2 h after dosing. In study 1, the potential interaction between MDZ and the other components of the six drug cocktail was assessed by comparing AUClast ratios (1-OH MDZ/MDZ) between the two treatments. Additionally, a single sampling timepoint of 2 h post-dose for determination of concentration, rather than AUC, ratios was established. The 2 h plasma concentration ratios from studies 1 and 2 were combined and a pooled analysis performed to compare ratios within each study (to determine the change in ratio when MDZ was dosed with and without chlorzoxazone) and between studies (to determine the consistency of the ratios when MDZ was given either as part of the two six drug cocktails or when given alone and as part of the five drug cocktail). RESULTS: In study 1, both the AUClast ratio and the 2 h post-dose plasma concentration ratio were reduced when MDZ was given as part of the six drug cocktail in comparison with those for MDZ alone. This was the result of an increase in MDZ, rather than decrease in 1-OH MDZ, concentrations and was considered to result from a reduction in first pass metabolism of MDZ. The geometric mean AUClast values (with 95% CI) for MDZ were 95.6 (79.0, 115.7) and 160.4 (133.6, 192.6) microg l(-1) h when given alone and as part of the six drug cocktail, respectively. The corresponding values for 1-OH MDZ were 789.6 (697.6, 893.6) and 791.4 (701.7, 892.6) microg l(-1) h. The ratio of adjusted geometric mean AUClast ratios for the two treatments was 1.82 (90% CI 1.48, 2.23, P < 0.001). The pooled plasma 1-OH MDZ/MDZ ratio data from both studies showed that the differences in MDZ metabolism observed in study 1 were replicated in study 2. The adjusted geometric mean 1-OH MDZ/MDZ ratios when MDZ was given alone and as part of the six drug cocktail were 7.79 and 4.59, respectively, for study 1 (ratio 1.70, 95% CI 1.36, 2.11, P < 0.001) and 7.64 and 4.60 for study 2 (ratio 1.66, 95% CI 1.34, 2.06, P < 0.001). These data indicate that when given orally chlorzoxazone interacts with MDZ, increasing plasma MDZ concentrations. In contrast, there was no difference between the plasma 1-OH MDZ/MDZ ratios when MDZ was given alone and as part of the five drug cocktail indicating that there were no interactions between MDZ and any of the other components of that cocktail. CONCLUSIONS: Chlorzoxazone appears to significantly influence the pharmacokinetics of oral MDZ, probably through inhibition of first pass metabolism by CYP3A in the GI tract. Data from these studies and literature evidence showing a further interaction between chlorzoxazone and CYP1A2 substrates and questions concerning the specificity of chlorzoxazone as a probe substrate for CYP2E1, indicate that the use of chlorzoxazone in multisubstrate probe cocktails should be avoided.     

Parkinson's disease and CYP1A2 activity

AIMS MPTP, a neurotoxin which induces parkinsonism is partially metabolized by the enzyme CYP1A2. Smoking appears to protect against Parkinson's disease (PD) and cigarette smoke induces CYP1A2 activity. Thus, we investigated the hypothesis that idiopathic PD is associated with lower CYP1A2 activity using caffeine as a probe compound. METHODS CYP1A2 activity was assessed using saliva paraxanthine (PX) to caffeine (CA) ratios. Caffeine half-life was also estimated from salivary concentrations of caffeine at 2 and 5 h post dose. 117 treated and 40 untreated patients with PD and 105 healthy control subjects were studied. RESULTS PX/CA ratios were 0. 57, 0.93 and 0.77 in treated patients, untreated patients and healthy control subjects, respectively, with no significant differences between study groups (95% CI: treated patients vs controls -0.24, 0.57; untreated patients vs controls -0.75, 0.35). However, patients with PD (treated or untreated) had caffeine half-lives shorter than that in controls (treated patients: 262 min, untreated patients: 244 min, controls: 345 min; 95% CI: controls vs treated patients 23, 143 (P = 0.003); controls vs untreated patients 19, 184 (P = 0.011)). Amongst the patients with PD, caffeine half-life was also inversely related to the age of onset of disease (P = 0.012); gender and concomitant drugs did not influence this significantly. CONCLUSIONS: Based on PX/CA ratio, there was no evidence of decreased CYP1A2 activity in patients compared with control subjects. The observed decrease in the elimination half-life of caffeine in PD may be caused by increased CYP2E1 activity, an enzyme that also contributes to the metabolism of caffeine. The latter warrants further investigation.     

Effect of sodium tanshinone II A sulfonate on the activity of CYP1A2 in healthy volunteers

1. Sodium tanshinone IIA sulfonate (STS) is a water-soluble derivative of tanshinone IIA, a famous Chinese medicine which has been used in the treatment of cardiovascular disorders for many years. Using caffeine as a probe drug, this project was designed to investigate the effect of STS on the activity of CYP1A2 in humans.

2. Sixteen unrelated healthy volunteers were recruited for this two-phase, randomized and crossover study. The volunteers received either placebo or 60?mg day^?1 of STS injections through vein for 13 days. Pharmacokinetics of caffeine and the metabolite paraxanthine was determined by high-performance liquid chromatography. CYP1A2 activity was monitored by the ratio of paraxanthine to caffeine at 6?h in plasma.

3. Enzyme activity analysis showed that STS significantly increased the activity of CYP1A2 by 41.1% [90% confidence interval (CI), 17.4–64.8%] (p = 0.036). The area under the curve [AUC_(0–24h)] of caffeine significantly decreased by 13.3% [90% CI = 7.0–19.6%] (p = 0.005) with 13 days of treatment of STS. AUC_(0–24h) of paraxanthine significantly increased by 17.4% [90% CI = 4.3–30.5%] (p = 0.035). No significant difference was found for other parameters of caffeine and paraxanthine between two phases.

4. STS has significantly induced the activity of CYP1A2 in vivo. Simultaneously, AUC_(0–24h) of caffeine and paraxanthine were significantly affected by STS. The findings have provided some useful information for safe and effective usage of STS in clinic.

     

In vivo CYP2E1 phenotyping as a new potential biomarker of occupational and experimental exposure to benzene

Assessing CYP2E1 phenotype in vivo may be important to predict individual susceptibility to those chemicals, including benzene, which are metabolically activated by this isoenzyme. Chlorzoxazone (CHZ), a specific CYP2E1 substrate, is readily hydroxylated to 6-OH-chlorzoxazone (6-OH-CHZ) by liver CYP2E1 and the metabolic ratio 6-OH-CHZ/CHZ in serum (MR) is a specific and sensitive biomarker of CYP2E1 activity in vivo in humans. We used this MR as a potential biomarker of effect in benzene-treated rats and, also, in humans occupationally exposed to low levels of benzene. Male Sprague-Dawley rats (375–400 g b.w.) were treated i.p. for 3 days with either a 0.5 ml solution of benzene (5 mmol/kg b.w.) in corn oil, or 0.5 ml corn oil alone. Twenty-four hours after the last injection, a polyethylene glycol (PEG) solution of CHZ (20 mg/kg b.w.) was injected i.p. in both treated and control animals. After 2, 5, 10, 15, 20, 30, 45, 60, 90, 120, 180, and 240 min from injection, 0.2 ml blood was taken from the tip tail and stored at −20 °C until analysis. A modified reverse phase HPLC method using a 5 μm Ultrasphere C18 column equipped with a direct-connection ODS guard column, was used to measure CHZ and its metabolite 6-OH-CHZ in serum. No statistically significant difference in the MR was observed, at any sampling time, between benzene-treated and control rats. The concentration-versus-time area under the curve (AUC), however, was lower (p < 0.05, Mann–Whitney test), whereas the systemic clearance was higher (p < 0.05) in treated than in control rats. Eleven petrochemical workers occupationally exposed to low levels of airborne benzene (mean ± SD, 25.0 ± 24.4 μg/m³) and 13 non-exposed controls from the same factory (mean ± SD, 6.7 ± 4.0 μg/m³) signed an informed consent form and were administered 500 mg CHZ p.o. Two hours later a venous blood sample was taken for CHZ and 6-OH-CHZ measurements. Despite exposed subjects showed significantly higher levels of t,t-MA and S-PMA, two biomarkers of exposure to benzene, than non-exposed workers, no difference in the MR mean values ± SD was found between exposed (0.59 ± 0.29) and non-exposed (0.57 ± 0.23) subjects. So, benzene was found to modify CHZ disposition, but not CYP2E1 phenotype in benzene-treated rats, nor in workers exposed to benzene, probably due to the levels of exposure being too low.     

CYP2E1 overexpression inhibits microsomal Ca-ATPase activity in HepG2 cells

Cytochrome P450 2E1 (CYP2E1) is a microsomal enzyme that generates reactive oxygen species during its catalytic cycle. We previously found an important role for calcium in CYP2E1-potentiated injury in HepG2 cells. The possibility that CYP2E1 may oxidatively damage and inactivate the microsomal Ca²⁺-ATPase in intact liver cells was evaluated, in order to explain why calcium is elevated during CYP2E1 toxicity. Microsomes were isolated by differential centrifugation from two liver cell line: E47 cells (HepG2 cells transfected with the pCI neo expression vector containing the human CYP2E1 cDNA, which overexpress active microsomal CYP2E1), and control C34 cells (HepG2 cells transfected with the pCI neo expression vector alone, which do not express significantly any cytochrome P450). The Ca²⁺-dependent ATPase activity was determined by measuring the accumulation of inorganic phosphate from ATP hydrolysis. CYP2E1 overexpression produced a 45% decrease in Ca²⁺-dependent ATPase activity (8.6 nmol Pi/min/mg protein in C34 microsomes versus 4.7 nmol Pi/min/mg protein in microsomes). Saturation curves with Ca²⁺ or ATP showed that CYP2E1 overexpression produced a decrease in V_max but did not affect the K_m for either Ca²⁺ or ATP. The decrease in activity was not associated with a decrease in SERCA protein levels. The ATP-dependent microsomal calcium uptake was evaluated by fluorimetry using fluo-3 as the fluorogenic probe. Calcium uptake rate in E47 microsomes was 28% lower than in C34 microsomes. Treatment of E47 cells with 2 mM N-acetylcysteine prevented the decrease in microsomal Ca²⁺-ATPase found in E47 cells. These results suggest that CYP2E1 overexpression produces a decrease in microsomal Ca²⁺-ATPase activity in HepG2 cells mediated by reactive oxygen species. This may contribute to elevated cytosolic calcium and to CYP2E1-potentiated injury.     

Effect of the CYP2D6*10 genotype on venlafaxine pharmacokinetics in healthy adult volunteers

AIMS: Interindividual differences in the pharmacokinetics of venlafaxine, a new antidepressant, were shown during early clinical trials in Japan. Venlafaxine is metabolized mainly by CYP2D6 to an active metabolite, O-desmethylvenlafaxine (ODV). Therefore, the influence of the CYP2D6 genotypes on venlafaxine pharmacokinetics was examined in a Japanese population. METHODS: Twelve adult Japanese men in good health participated in this study. Genomic DNA was isolated from peripheral lymphocytes, and the CYP2D6 genotypes were determined by codon 188C/T, 1934G/A, 2938G/A and 4268G/C mutations using endonuclease tests based on PCR and by Xba I-RFLP analysis. Subjects were categorized into the following 3 groups (n=4 in each group); Group1: CYP2D6*10/*10, *5/*10, Group2: CYP2D6*1/*10, *2/*10 and Group3: CYP2D6*1/*1, CYP2D6*1/*2. Venlafaxine (25 mg, n=6; 37.5 mg, n=6) was administered orally at 09.00 h following an overnight fast. Plasma concentrations of venlafaxine and ODV were monitored by h.p.l.c. for 48 h. RESULTS: The Cmax and AUC of venlafaxine were 184% and 484% higher in the group 1 subjects than in the group 3 subjects, and 101% and 203% higher in the group 1 than in the group 2, respectively. CONCLUSIONS: These results suggest that CYP2D6*10 influences the pharmacokinetics of venlafaxine in a Japanese population.     

Effect of glycyrrhizin on CYP2C19 and CYP3A4 activity in healthy volunteers with different CYP2C19 genotypes

1. The objective of this study was to investigate the interaction between glycyrrhizin and omeprazole and observe the effects of glycyrrhizin on CYP2C19 and CYP3A4 activities in healthy Chinese male volunteers with different CYP2C19 genotypes.

2. Eighteen healthy subjects (six CYP2C19*1/*1, five CYP2C19*1/*2, one CYP2C19*1/*3, five CYP2C19*2/*2 and one CYP2C19*2/*3) were enrolled in a two-phase randomized crossover trial. In each phase, all subjects received placebo or glycyrrhizin salt tablet 150?mg twice daily for 14 consecutive days. The pharmacokinetics of omeprazole (20?mg orally on day 15) was determined for up to 12?h following administration by high-performance liquid chromatography.

3. After 14-day treatment of glycyrrhizin, plasma omeprazole significantly decreased, and those of omeprazole sulfone significantly increased. However, plasma concenetrations of 5-hydroxyomeprazole did not significantly change. The ratio of AUC_0–∞ of omeprazole to omeprazole sulfone decreased by 43.93% ± 13.56% (p?=?0.009) in CYP2C19*1/*1, 44.85% ± 14.84% (p?=?0.002) in CYP2C19*1/*2 or *3 and 36.16% ± 7.52% (p?<?0.001) in CYP2C19*2/*2 or *3 while those of omeprazole to 5-hydroxyomeprazole did not change significantly in all three genotypes. No significant differences in glycyrrhizin response were found among CYP2C19 genotypes.

4. Glycyrrhizin induces CYP3A4-catalyzed sulfoxidation of omeprazole and leads to decreased omeprazole plasma concentrations, but has no significant impact on CYP2C19-dependent hydroxylation of omeprazole.

     

抑制CYP2E1增强何首乌水提物肝毒性作用及其毒性成分筛选研究

目的 研究肝细胞色素氧化酶P450(CYP450)亚型CYP2E1与何首乌肝毒性的关系并筛选有关毒性成分.方法 MTT法检测CYP2E1特异性抑制剂二乙基二硫代氨基甲酸钠(DDTC)作用后何首乌水提物(PMR)对人肝细胞L02的毒性作用,及PMR和6种成分2,3,5,4'-四羟基二苯乙烯-2-O-β-D-葡萄糖苷(2,...     

Expression and activity of CYP2E1 in circulating lymphocytes are not altered in diabetic individuals

Cytochrome P4502E1 (CYP2E1) plays an important role in ROS production thus favouring accelerated membrane lipid peroxidation. This isoform is strongly expressed in the liver but it can be also found in lymphocytes. As such, lymphocyte may provide a non-invasive accessible pool for screening CYP2E1 expression in man. We have, therefore, analysed CYP2E1 expression and activity in lymphocyte microsomes from 12 healthy controls, 11 type 1 and 12 type 2 diabetic subjects by using Western blot and enzymatic activities. Immunoblotting did not show difference among CYP2E1 protein bands in controls, type 1 and type 2 diabetics. To assess CYP2E1 activity we used the 7-ethoxy-4-trifluoromethylcoumarin (7-EFC), as a fluorescent substrate. The rate of deethylation of 7-EFC from controls did not differ from type 1 and type 2 diabetic subjects. The lack of any difference in CYP2E1 activity also was confirmed by the NADPH-dependent microsomal lipid peroxidation CCL4-induced assay showing similar peroxidation rates among controls and diabetic subjects. The results show that CYP2E1 expression/activity in lymphocytes is not enhanced in diabetes.     

淫羊藿苷对小鼠肝微粒体细胞色素P450酶及其亚型CYP2E1活性的影响

目的 研究淫羊藿苷对小鼠肝脏微粒体细胞色素P450(CYP)总酶含量及其亚型CYP2E1、CYP3A和CYP1A1活性的影响.方法 给予小鼠ig淫羊藿苷(50、100、200 mg·kg-1·d-1),3d后钙沉淀法制备肝细胞微粒体,UV法测定肝微粒体CYP的含量及其亚型CYP2E1与CYP3A的活性;荧光分光光度法测定肝微粒体CYP1A1的活性.结果 高剂量淫羊藿苷可降低小鼠肝脏微粒体CYP的含量(约54%)、抑制CYP2E1的活性(抑制率为53.1%),对CYP3A和CYP1A1的活性无影响.结论 大剂量淫羊藿苷可降低小鼠肝脏微粒体CYP的总含量,并抑制其亚型CYP2E1的活性.     

Differential effects of diabetes on CYP2E1 and CYP2B4 proteins and associated drug metabolizing enzyme activities in rabbit liver

The effects of diabetes on cytochrome P450 (CYP)-dependent drug metabolizing enzymes are yet to be clarified. The most widely used animals in these studies have been rats, and information on the effects of diabetes on rabbit liver drug metabolizing enzymes have been unavailable until now. In this study, for the first time, a significant induction of liver CYP2E1 is demonstrated via immunoblot analysis in alloxan-induced rabbits. The CYP2E1 content of diabetic microsomes was highly correlated with the activities of liver aniline 4-hydroxylase (r=0.82, p<0.05), and p-nitrophenol hydroxylase (r=0.86, p<0.01), and diabetes increased the activities of the enzymes associated with CYP2E1. The activities of aniline 4-hydroxylase and p-nitrophenol hydroxylase were significantly increased by 1.7 and 1.8-fold, respectively compared to those of control rabbits. In marked contrast, diabetes had no effect on the protein levels of CYP2B4 as determined by immunoblotting and on benzphetamine N-demethylase activity, which is known to be specifically metabolized by CYP2B4 in rabbit liver. The present study demonstrates that diabetes increases the activities of CYP2E1 and associated enzymes but does not change the activity levels of CYP2B4 and associated enzymes in diabetic rabbits. These findings are in contrast to those of mice, hamsters and rats, and that suggest the presence of species-dependent responses of CYP-dependent drug metabolizing enzymes to diabetes.An account of this work was presented at the 19th European Workshop on Drug Metabolism, DMW-2004, in Antalya, Turkey, on 3–8 October 2004     

Chronic administration of caderofloxacin,a new fluoroquinolone,increases hepatic CYP2E1 expression and activity in rats

Aim:

Caderofloxacin is a new fluoroquinolone that is under phase III clinical trials in China. Here we examined the effects of caderofloxacin on rat hepatic cytochrome P450 (CYP450) isoforms as well as the potential of caderofloxacin interacting with co-administered drugs.

Methods:

Male rats were treated with caderofloxacin (9 mg/kg, ig) once or twice daily for 14 consecutive days. The effects of caderofloxacin on CYP3A, 2D6, 2C19, 1A2, 2E1 and 2C9 were evaluated using a “cocktail” of 6 probes (midazolam, dextromethorphan, omeprazole, theophylline, chlorzoxazone and diclofenac) injected on d 0 (prior to caderofloxacin exposure) and d 15 (after caderofloxacin exposure). Hepatic microsomes from the caderofloxacin-treated rats were used to assess CYP2E1 activity and chlorzoxazone metabolism. The expression of CYP2E1 mRNA and protein in hepatic microsomes was analyzed with RT-PCR and Western blotting, respectively.

Results:

Fourteen-day administration of caderofloxacin significantly increased the activity of hepatic CYP2E1, leading to enhanced metabolism of chlorzoxazone. In vitro microsomal study confirmed that CYP2E1 was a major metabolic enzyme involved in chlorzoxazone metabolism, and the 14-d administration of caderofloxacin significantly increased the activity of CYP2E1 in hepatic microsomes, resulting in increased formation of 6-hydroxychlorzoxazone. Furthermore, the 14-d administration of caderofloxacin significantly increased the expression of CYP2E1 mRNA and protein in liver microsomes, which was consistent with the pharmacokinetic results.

Conclusion:

Fourteen-day administration of caderofloxacin can induce the expression and activity of hepatic CYP2E1 in rats. When caderofloxacin is administered, a potential drug-drug interaction mediated by CYP2E1 induction should be considered.     

Association between CYP1A2 activity and riluzole clearance in patients with amyotrophic lateral sclerosis

AIMS: Riluzole is used in a fixed dosing schedule of 50 mg twice daily to treat patients with amyotropic lateral sclerosis (ALS), one form of motor neurone disease. The large variability in the pharmacokinetics of riluzole may be a factor contributing to its limited therapeutic benefit. Riluzole is assumed to be mainly metabolized by the cytochrome P450 enzyme 1A2 (CYP1A2). The aim of the study was to investigate the relationship between CYP1A2 activity and riluzole clearance with a view to optimize drug treatment. METHODS: A group of 30 ALS patients participated in the study. In each patient the CYP1A2 activity was determined using caffeine as a metabolic probe. Riluzole clearance was estimated from serum drug concentration measurements followed by Bayesian fitting. RESULTS: Riluzole clearance and the serum paraxanthine : caffeine (P/C) ratio showed a positive correlation (r = 0.693; P = 0.0002). Linear regression analysis identified the P/C ratio (beta: 1.16) and height (beta: 0.027) as independent predictors of riluzole clearance (adjusted r2 = 0.369). CONCLUSIONS: The P/C ratio, used as measure of CYP1A2 activity, significantly correlated with the riluzole clearance, although only 37% of the observed variability could be explained.     

Effect of caffeine on clozapine pharmacokinetics in healthy volunteers

AIMS: To assess the effects of caffeine on the pharmacokinetics of clozapine in healthy volunteers. METHODS: This was an open label randomized crossover study in 12 nonsmoking healthy male volunteers. The subjects received a single oral dose of 12.5 mg clozapine in each phase with or without concomitant intake of caffeine (mean dose: 550 mg day-1, range: 400-1000 mg day-1 ). Serum concentrations of clozapine and its metabolites desmethyl-clozapine and clozapine-N-oxide were measured during a 48 h period in each phase. In addition, serum concentrations of caffeine and the metabolite paraxanthine were monitored. RESULTS: A 19% increase in mean clozapine AUC(0,infinity) (P=0.05) and a 14% decrease of mean oral clearance of clozapine were observed during concomitant intake of caffeine (P=0.05) compared with intake of only clozapine. Statistically significant decreases of mean ratios between AUC(0, 12h) for desmethyl-clozapine and AUC(0,12h) for clozapine (-18%), and between AUC(0,12h) for clozapine-N-oxide and AUC(0,12h) for clozapine (-23%) were observed during the caffeine phase (P=0.03 and 0.02, respectively). Oral clearance of clozapine and the ratio AUC(0, 12h) for desmethyl-clozapine/AUC(0,12h) for clozapine were correlated with the paraxanthine/caffeine ratio in serum after intake of caffeine (rs=0.62; P=0.03 and rs=0.77; P=0.003, respectively). CONCLUSIONS: These results suggest that caffeine in daily doses of 400-1000 mg inhibits the metabolism of clozapine to an extent that might be clinically significant in certain individuals.