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 microM), human liver microsomes (3194 pmol mg protein(-1) min(-1) and 335 microM) and pure isozyme (3423 pmol mg protein(-1) min(-1) and 403 microM), 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 microM and 0.12 min(-1); human: 27.19 microM and 0.14 min(-1)) and pure isozyme (3.18 microM 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 approximately 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.     

Effect of piperine on CYP2E1 enzyme activity of chlorzoxazone in healthy volunteers

1.?The purpose of the present study was to investigate the effect of piperine (PIP) on CYP2E1 enzyme activity and pharmacokinetics of chlorzoxazone (CHZ) in healthy volunteers.

2.?An open-label, two period, sequential study was conducted in 12 healthy volunteers. A single dose of PIP 20?mg was administered daily for 10 days during treatment phase. A single dose of CHZ 250?mg was administered during control and after treatment phases under fasting conditions. The blood samples were collected at predetermined time intervals after CHZ dosing and analyzed by HPLC.

3.?Treatment with PIP significantly enhanced maximum plasma concentration (C_max) (3.14–4.96?μg/mL)_, area under the curve (AUC) (10.46–17.78?μg h/mL), half life (T_1/2) (1.26–1.82?h) and significantly decreased elimination rate constant (K_el) (0.57–0.41?h?^??¹), apparent oral clearance (CL/F) (24.76–13.65?L/h) of CHZ when compared to control. In addition, treatment with PIP significantly decreased C_max (0.22–0.15?μg/mL), AUC (0.94–0.68?μg h/mL), T_1/2 (2.54–1.68?h) and significantly increased K_el (0.32–0.43?h?^??¹) of 6-hydroxychlorzoxazone (6-OHCHZ) as compared to control. Furthermore, treatment with PIP significantly decreased metabolite to parent (6-OHCHZ/CHZ) ratios of C_max, AUC, T_1/2 and significantly increased K_el ratio of 6-OHCHZ/CHZ, which indicate the decreased formation of CHZ to 6-OHCHZ.

4.?The results suggest that altered pharmacokinetics of CHZ might be attributed to PIP mediated inhibition of CYP2E1 enzyme, which indicate significant pharmacokinetic interaction present between PIP and CHZ. The inhibition of CYP2E1 by PIP may represent a novel therapeutic benefit for minimizing ethanol induced CYP2E1 enzyme activity and results in reduced hepatotoxicity of ethanol.     

Effects of cysteine on the pharmacokinetics of intravenous chlorzoxazone in rats with protein-calorie malnutrition

The effects of cysteine on the pharmacokinetics of chlorzoxazone (CZX) and one of its metabolites, 6-hydroxychlorzoxazone (OH-CZX), were investigated after intravenous administration of CZX, 25 mg/kg, to control rats (4-week fed on 23% casein diet) and rats with PCM (4-week fed on 5% casein diet) and PCMC (PCM with oral cysteine supplementation, 250 mg/kg, twice daily during the fourth week). In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity (AUC) of OH-CZX (436 compared with 972 microgmin/ml) and the percentages of intravenous dose of CZX excreted in 8-h urine as OH-CZX (20.2 compared with 38.5%) were significantly smaller than those in control rats. The above data indicated that the formation of OH-CZX from CZX decreased significantly in rats with PCM due to a significant decrease in chlorzoxazone-6-hydroxylase activity (328 compared with 895 pmol/min/mg protein) in the rats. The results were expected since in rats with PCM, hepatic CYP2E1 expression and its mRNA levels decreased significantly as compared to control, and CZX was metabolized to OH-CZX primarily by CYP2E1 in rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters restored fully (hepatic microsomal chlorzoxazone 6-hydroxylation activity based on both mg protein and nmol CYP450) or partially (total body clearance and apparent volume of distribution at steady state of CZX, and AUC, terminal half-life and 8-h urinary excretion of OH-CZX) to control levels.     

Effects of cytochrome P450 inducers and inhibitors on the pharmacokinetics of intravenous furosemide in rats: involvement of CYP2C11, 2E1, 3A1 and 3A2 in furosemide metabolism

Objectives It has been reported that the non‐renal clearance of furosemide was significantly faster in rats pretreated with phenobarbital but was not altered in rats pretreated with 3‐methylcholanthrene. However, no studies on other cytochrome P450 (CYP) isozymes have yet been reported in rats. Method Furosemide 20 mg/kg was administered intravenously to rats pretreated with various CYP inducers –3‐methylcholanthrene, orphenadrine citrate and isoniazid, inducers of CYP1A1/2, 2B1/2 and 2E1, respectively, in rats – and inhibitors – SKF‐525A (a nonspecific inhibitor of CYP isozymes), sulfaphenazole, cimetidine, quinine hydrochloride and troleandomycin, inhibitors of CYP2C6, 2C11, 2D and 3A1/2, respectively, in rats. Key findings The non‐renal clearance of furosemide was significantly faster (55.9% increase) in rats pretreated with isoniazid, but slower in those pretreated with cimetidine or troleandomycin (38.5% and 22.7% decreases, respectively), than controls. After incubation of furosemide with baculovirus‐infected insect cells expressing CYP2C11, 2E1, 3A1 or 3A2, furosemide was metabolized via CYP2C11, 2E1, 3A1 and 3A2. Conclusions These findings could help explain possible pharmacokinetic changes of furosemide in various rat disease models (where CYP2C11, 2E1, 3A1 and/or CYP3A2 are altered) and drug–drug interactions between furosemide and other drugs (mainly metabolized via CYP2C11, 2E1, 3A1 and/or 3A2).     

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.     

Time‐dependent effects of Klebsiella pneumoniae endotoxin on the pharmacokinetics of chlorzoxazone and its main metabolite, 6‐hydroxychlorzoxazone,in rats: restoration of the parameters in 96 hour in KPLPS rats to control levels

It has been reported that chlorzoxazone (CZX) was primarily metabolized via hepatic Cyp2e1 to form 6‐hydroxychlorzoxazone (OH‐CZX) in rats, and the activity of aniline hydroxylase (a Cyp2e1 marker) in the liver was significantly decreased in rats at 24 h after pretreatment with lipopolysaccharide derived from Klebsiella pneumoniae (24 h KPLPS rats), whereas the levels were not changed at 2 h and 96 h in the KPLPS rats. Thus, the time‐dependent pharmacokinetic parameters of CZX and OH‐CZX were evaluated after the intravenous administration of CZX (20 mg/kg) to control rats, and the 2 h, 24 h and 96 h KPLPS rats along with the time‐dependent changes in the protein expression of hepatic Cyp2e1. After the intravenous administration of CZX to 24 h KPLPS rats, the AUC_{0–2 h} of OH‐CZX and AUC_{OH‐CZX, 0–2 h}/AUC_CZX were significantly smaller (by 40.5% and 71.2%, respectively) than those of controls due to the significant decrease (by 75.3%) in the protein expression of hepatic Cyp2e1. However, in 96 h KPLPS rats, the pharmacokinetic parameters of both CZX and OH‐CZX were unchanged compared with controls due to the restoration of the protein expression of hepatic Cyp2e1 to control levels. These observations highlighted the existence of the time‐dependent effects of KPLPS on the pharmacokinetics of CZX and OH‐CZX in rats. Copyright © 2009 John Wiley & Sons, Ltd.     

Pharmacokinetics of intravenous chlorzoxazone in rats with dehydration and rehydration: effects of food intakes

The following results were obtained recently from our laboratories; in rats with 72-h water deprivation (rats with dehydration), the hepatic cytochrome P450 2E1 (CYP2E1) was three-fold induced with an increase in the mRNA. Rehydration of 48-h water-deprived rats for the next 24 h with free access of food (rats with rehydration) restored CYP2E1 level to that of control. However, rehydration of 48-h water-deprived rats for the next 24 h with limited food supply (20% of control) failed to restore the CYP2E1 level to that of control. Hence, the CYP2E1 changes in rats with dehydration and rehydration resulted from differences in food intakes but not from dehydration or rehydration per'se. Chlorzoxazone (CZX) is metabolized to 6-hydroxychlorzoxazone (OH-CZX) mainly by CYP2E1 in rats. Therefore, the pharmacokinetics of CZX and OH-CZX were compared after intravenous administration of CZX, 25 mg/kg, to control rats and rats with dehydration and rehydration with free access of food. In rats with dehydration, the amount of 24-h urinary excretion of free OH-CZX plus its glucuronide conjugates (Ae (OH-CZX, 0-24 h,) expressed in terms of intravenous dose of CZX) was significantly greater (45.6 compared with 35.6%) and area under the plasma concentration-time curve from time zero to time infinity (AUC) of CZX was significantly smaller (2190 compared with 3200 micro g min/ml) than those in control rats. The above data indicated that the formation of OH-CZX increased significantly in rats with dehydration due to 3-fold induction of CYP2E1. In rats with rehydration with free access of food, the Ae (OH-CZX, 0-24 h) (39.0 compared with 35.6%) and AUC of CZX (2870 compared with 3200 micro g min/ml) were restored (comparable) to control levels since the expression of CYP2E1 in rats with dehydration returned to control level by rehydration. The above data indicate that CZX could be used as a chemical probe to assess the activity of CYP2E1 in rats with dehydration and rehydration.     

Preclinical evaluation of the pharmacokinetics, brain uptake and metabolism of E121, an antiepileptic enaminone ester, in rats

The present study describes the brain uptake, pharmacokinetics and metabolism of an anticonvulsant enaminone ester E121, which belongs to a new and active series of compounds with potential in vivo anticonvulsant activity in rodent models, in rats. A single dose of E121 was administered i.p. to male Sprague Dawley rats at 10 mg E121/kg body weight. Cohorts of animals (n=3) were killed at varying times over 0-24 h to collect plasma and brain samples. Urinary excretion of E121 was studied in a separate group of five rats at the same dose. A validated HPLC method was used to quantify E121 and its metabolites in plasma, brain and urine. LC-MS/MS was used to characterize the metabolites. The plasma and brain Cmax of 11.0+/-3.0 mg/l and 10.4+/-1.4 mg/kg, respectively, were observed for E121 at 15 min post dose and they declined in a mono-exponential fashion. The plasma Cl/F and t1/2 were 0.57 l/h/kg and 0.75 h, respectively. The brain uptake ratio of E121 was 0.9. Mass spectral analysis of urine showed two major metabolites (m/z 280) and one minor metabolite (m/z 236) that were consistent with initial hydrolysis of the compound to the acid followed by further decarboxylation and appears to be the major route of elimination of E121. The rapid and moderate brain uptake of E121 correlates well with its potential anticonvulsant activity (ED50 3.0 mg/kg p.o. in rats). The brain uptake, pharmacokinetic and metabolic profile of E121 supports the need to further evaluate this compound for its potential as an antiepileptic.     

Circadian rhythm of cytochrome P4502E1 and its effect on disposition kinetics of chlorzoxazone in rats

The aim of this report is to study the circadian rhythm of cytochrome P4502E1 (CYP2E1) and its effect on the disposition kinetics of chlorzoxazone in male Wistar rats. The rats were housed under a 12-h light/dark cycle (lights from 9:00 to 21:00) with food and water ad libitum for 3 months. It was found that the expression of microsomal CYP2E1 mRNA in the liver during the dark phase was significantly lower than during the light phase, whereas the content of CYP2E1 protein and its hydroxylation activity were significantly higher. Therefore, chlorzoxazone 20 mg/kg was intravenously administered at 12:00 (light phase group) or 24:00 (dark phase group) to determine the effect on the disposition kinetics. The value of the area under the plasma concentration-time curve from 0 to 8 h (AUC(0-8 h)) of chlorzoxazone showed no significant difference between the two groups. However, the value of chlorzoxazone half-life in plasma of the light phase group was significant longer than the dark phase group. The AUC(0-8 h) of 6-hydroxychlorzoxazone, a metabolite formed from chlorzoxazone mainly by CYP2E1, was significantly higher in the dark phase than in the light phase. In conclusion, microsomal CYP2E1 shows a substantial circadian variation in rats, and this was associated with a decrease of chlorzoxazone half life, and an increase of 6-hydroxychlorzoxazone production. Therefore, the temporal variations of therapeutic response and toxicological effects may have to be taken into consideration for other xenobiotics that are predominantly metabolized by CYP2E1, particularly those with a short half-life.     

Effect of scutellarin on the metabolism and pharmacokinetics of clopidogrel in rats

Erigeron breviscapus (Vant.) Hand‐Mazz, a traditional Chinese medicine, is often co‐prescribed with clopidogrel for the treatment of ischemic vascular diseases. Scutellarin is the representative bioactive flavonoid isolated from this herb. The aim of this study was to explore the effect of scutellarin on the metabolism and pharmacokinetics of clopidogrel. The in vitro studies using rat liver microsomes showed that scutellarin significantly inhibited the metabolism of clopidogrel. The IC₅₀ value was 2.1 µm . Ten male rats were employed to investigate the effect of scutellarin on the pharmacokinetics of clopidogrel in vivo. After pretreatment with scutellarin, there were significant increases in the AUC_0–∞ (from 0.9 ± 0.4 to 1.7 ± 0.6 ng/ml h; p <0.05) and C_max (from 0.4 ± 0.1 to 0.9 ± 0.1 ng/ml; p <0.05) of clopidogrel. The pharmacokinetic data for clopidogrel active metabolite showed significant decreases in AUC_0–∞ (18.2 ± 5.6 to 11.4 ± 3.7 ng/ml h; p <0.05) and C_max (from 8.2 ± 1.2 to 4.3 ± 0.3 ng/ml; p <0.05) after pretreatment with scutellarin. Collectively, the metabolism and pharmacokinetics of clopidogrel were significantly affected by scutellarin. This study indicated that potential herb–drug interaction between scutellarin and clopidogrel should be taken into consideration in clinical use. Copyright © 2014 John Wiley & Sons, Ltd.     

Phenobarbital induces monkey brain CYP2E1 protein but not hepatic CYP2E1, in vitro or in vivo chlorzoxazone metabolism

Cytochrome P450 2E1 (CYP2E1) is expressed in the brain and liver, and can metabolize clinical drugs and activate toxins. The effect of phenobarbital on hepatic and brain CYP2E1 is unclear. We investigated the effect of chronic phenobarbital treatment on in vivo chlorzoxazone disposition (a CYP2E1 probe drug), in vitro chlorzoxazone metabolism, and hepatic and brain CYP2E1 protein levels in African Green monkeys (Cercopithecus aethiops). Monkeys were given oral saccharine or saccharine supplemented with 20 mg/kg phenobarbital (N = 6/group) for 22 days. Phenobarbital did not induce in vivo chlorzoxazone disposition, in vitro chlorzoxazone metabolism or hepatic CYP2E1 protein levels (all P > 0.05). However, phenobarbital induced brain CYP2E1 protein levels, using immunoblotting, by 1.26-fold in the cerebellum (P = 0.01) and 1.46-fold in the putamen (P = 0.04). Phenobarbital also increased cell-specific CYP2E1 expression, for example in the frontal cortical pyramidal neurons and cerebellar Purkinje cells. This data indicates that phenobarbital does not alter hepatic metabolism, but may alter metabolism of CYP2E1 substrates within the brain.     

Effect of Morin on pharmacokinetics of Piracetam in rats,in vitro enzyme kinetics and metabolic stability assay using rapid UPLC method

The aim of this study was to investigate the effect of Morin on the pharmacokinetics of Piracetam in rats, in vitro enzyme kinetics and metabolic stability (high throughput) studies using human liver microsomes in UPLC. For pharmacokinetics studies, male Wistar rats were pretreated with Morin (10 mg/kg) for one week and on the last day, a single dose of Piracetam (50 mg/kg) was given orally. In another group, both Morin and Piracetam were co‐administered to evaluate the acute effect of Morin on Piracetam. The control group received oral distilled water for one week and administered with Piracetam on the last day. As Morin is an inhibitor of P‐ Glycoprotein (P‐gp) and CYP 3A, it was anticipated to improve the bioavailability of Piracetam. Amazingly, relative to control, the areas under the concentration time curve and peak plasma concentration of Piracetam were 1.50‐ and 1.45‐fold, respectively, greater in the Morin‐pretreated group. However, co‐administration of Morin had no significant effect on these parameters. Apart from the aforementioned merits, the results of this study are further confirmed by clinical trials; Piracetam dosages should be adjusted to avoid potential drug interaction when Piracetam is used clinically in combination with Morin and Morin‐containing dietary supplements. The in vitro enzyme kinetics were performed to determined km, V_max & CL_ins. The in vitro metabolic stability executed for the estimation of metabolic rate constant and half‐life of Piracetam. These studies also extrapolate to in vivo intrinsic hepatic clearance (Cl_{int, in vivo}) from in vitro intrinsic hepatic clearance (CL_{int, in vitro})_. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of acute renal failure on the pharmacokinetics of telithromycin in rats: negligible effects of increase in CYP3A1 on the metabolism of telithromycin

It was reported that the expression of CYP3A1 increased in rats with acute renal failure induced by uranyl nitrate (rat model of U-ARF) compared with controls. It was shown that telithromycin was mainly metabolized via CYP3A1/2 in rats in this study. Hence, the pharmacokinetic parameters of telithromycin were compared after both intravenous and oral administration at a dose of 50 mg/kg to control rats and a rat model of U-ARF. After intravenous administration of telithromycin to rats with U-ARF, the AUC and renal clearance (Cl(r)) were significantly greater (35.0% increase) and slower (99.1% decrease), respectively, than the controls. Unexpectedly, the nonrenal clearance (Cl(nr)) of telithromycin was comparable between the two groups of rats, suggesting that CYP3A isozyme responsible for the metabolism of telithromycin seemed not to be expressed considerably in the rat model of U-ARF. After oral administration of telithromycin to rats with U-ARF, the AUC was also significantly greater (127% increase) than the controls and the value, 127%, was considerably greater than 35.0% after intravenous administration of telithromycin. This may be due mainly to the decrease in the intestinal first-pass effect of telithromycin compared with controls in addition to significantly slower Cl(r) than controls.     

Pharmacokinetics and metabolism of diltiazem in rats: comparing single vs repeated subcutaneous injections in vivo

The objective of the study was to determine the effect of repeated administration on the pharmacokinetics and metabolism of diltiazem (DTZ) using an in vivo rat model. Male SD rats (n = 6-10 per group) weighing 350-450 g were used. Each rat received either a single 20 mg/kg dose of DTZ by subcutaneous (s.c.) injection or 5 mg/kg s.c. twice daily for five doses. Plasma concentrations of DTZ and its major metabolites were determined by HPLC for up to 8 h. Compared with the single dose, repeated administration resulted in higher dose normalized plasma concentrations of DTZ (AUC 26.4+/-14.2 vs 13.9+/-11.5 microg-h/ml), longer apparent half-life (t(1/2) = 12.5+/-14.6 vs 3.7+/-1.4 h) and lower systemic clearance (CL = 1.1+/-1.0 vs 2.9+/-2.7 l/h/kg). Higher dose normalized plasma concentrations, longer t(max), but shorter apparent t(1/2) of the major metabolites were observed following the repeated administration. The results also suggest that possible binding of DTZ may occur at the site of injection when administered subcutaneously in the higher dose.     

Effects of tesmilifene,a substrate of CYP3A and an inhibitor of P‐glycoprotein,on the pharmacokinetics of intravenous and oral docetaxel in rats

Objectives It has been reported that docetaxel is a P‐glycoprotein substrate and is metabolized via the cytochrome P450 (CYP) 3A subfamily in rats. Tesmilifene is a substrate of the CYP3A subfamily and is an inhibitor of P‐glycoprotein. Thus, the effects of various doses of tesmilifene on the pharmacokinetics of intravenous and orally administered docetaxel have been investigated in rats. Methods Docetaxel (20 mg/kg as base) was administered intravenously and orally without and with tesmilifene (5, 10, and 20 mg/kg) in rats. Key findings After intravenous administration of docetaxel with tesmilifene, the values of nonrenal clearance (CL_NR) and area under the plasma concentration–time (AUC) for docetaxel were comparable with those without tesmilifene. Tesmilifene did not increase the values of AUC or of absolute oral bioavailability (F) for docetaxel after oral administration of docetaxel with tesmilifene. Conclusions The inhibition for the metabolism of docetaxel via hepatic and intestinal CYP3A subfamily, and inhibition of P‐glycoprotein‐mediated efflux of docetaxel in the intestine by tesmilifene were almost negligible. The extremely low value of F for docetaxel was due to the incomplete absorption from the gastrointestinal tract and considerable first‐pass metabolism of docetaxel in rats.     

Effect of the acute-phase response on the pharmacokinetics of chlorzoxazone and cytochrome P-450 2E1 in vitro activity in rats.

The acute-phase response is known to produce alterations in hepatic cytochrome P-450 (CYP) expression. Lipopolysaccharide (LPS), a well known inducer of acute-phase response decreases hepatic CYP2E1 in vitro activity in rats. This study was designed to determine if LPS administration produced alterations in the pharmacokinetics of chlorzoxazone (CZN), a marker for CYP2E1 expression. Sprague-Dawley rats were administered a single i.p. injection of LPS (5 mg/kg) or saline control approximately 24 h before a single i.v. bolus dose of CZN (15 mg/kg). Serial blood samples were collected over a 120-min period to quantitate CZN plasma concentrations and protein binding. In addition, livers were removed and processed for evaluating in vitro CYP2E1 protein concentrations and activity. Systemic clearance decreased by 35% in LPS-treated rats, whereas half-life and steady-state volume of distribution increased by 167 and 66%, respectively. The plasma free-fraction of CZN increased 2-fold after LPS treatment. The CZN intrinsic clearance decreased in LPS rats by 71% compared with control values. The CYP2E1 liver microsomal activity decreased between 55 and 75% along with a 41% decrease in CYP2E1 protein concentration. The CZN intrinsic clearance was significantly correlated with both the CZN and p-nitrophenol liver microsomal activity (r = 0.97 and r = 0.91, respectively). This study demonstrated that LPS administration produced expected reductions in the in vivo intrinsic clearance of CZN, and these changes were highly correlated with in vitro activity studies. In addition, LPS produced significant increases in the steady-state volume of distribution of CZN secondary to reductions in its plasma protein binding.     

Cocktail法研究脉络宁注射液对大鼠CYP1A2、CYP2E1和CYP3A4活性的影响

目的：研究脉络宁注射液对大鼠CYP1A2、CYP2E1和CYP3A4活性的影响。方法：14只大鼠随机均分成临床等效剂量组和高剂量组,连续2周静脉给予脉络宁注射液（临床等效剂量纽,2mL／kg;高剂量组,4mL／kg）前后,均同时灌胃给予3个探针底物（茶碱,30mg／kg;氯唑沙宗,50rag／kg;氨苯砜,20mg/kg）,进行采血试验。用HPLC法同时测定大鼠体内各探针的血药浓度,DAS1．0软件计算药动学参数,并以配对t检验对各组大鼠前后两轮主要药动学参数进行差异性比较。结果：在1个给药疗程（14d）内,临床等效剂量组大鼠用药前后,3个探针的药动学参数均无显著性变化（P〉0．05）;高剂量组大鼠用药后,与用药前相比,茶碱的药动学参数没有显著变化（P〉0．05）;氨苯砜和氯唑沙宗的AUC0-24h均有升高趋势（P〈0．05）,给药后分别是给药前的1．44倍和1．28倍,同时氯唑沙宗的CL显著降低（P〈0．05）。结论：临床等效剂量脉络宁对大鼠CYP1A2、CYP2E1和CYP3A4活性均无显著影响,而高剂量脉络宁对大鼠CYP2E1和CYP3A4均有弱抑制作用。     

振源胶囊对细胞色素P_(450)酶CYP1A2、CYP3A4、CYP2E1的影响

目的:研究振源胶囊对细胞色素P450酶CYP1A2、CYP3A4、CYP2E1的影响。方法:用Cocktail探针药物法,将Wistar大鼠随机分组,灌胃给予振源胶囊溶液,以生理盐水组为空白对照,诱导10d,于股动脉插管,注射给予3种探针药物咖啡因、氨苯砜、氯唑沙宗,通过高效液相色谱法检测各探针药物的代谢率来评价各组CYP1A2、CYP3A4、CYP2E1亚型酶的活性;药动学计算采用DAS2.0软件完成。结果:给予振源胶囊的大鼠,咖啡因代谢加快,半衰期缩短;氨苯砜代谢减慢,半衰期延长;氯唑沙宗半衰期与空白对照组比较无显著差异(P>0.05)。结论:振源胶囊对大鼠CYP1A2有诱导作用,对CYP3A4有抑制作用,对CYP2E1的作用不明显。     

Effect of hepatic CYP inhibitors on the metabolism of sildenafil and formation of its metabolite,N‐desmethylsildenafil,in rats in vitro and in vivo

Objectives It has been reported that hepatic cytochrome P450 (CYP)2C9 and CYP3A4 are responsible for the metabolism of sildenafil and formation of its metabolite, N‐desmethylsildenafil, in humans. However, in‐vivo studies in rats have not been reported. Methods Sildenafil (20 mg/kg) was administered intravenously to rats pretreated with sulfaphenazole, cimetidine, quinine hydrochloride or troleandomycin, inhibitors of CYP2C6, CYP2C11, CYP2D subfamily and CYP3A1/2, respectively. In‐vitro studies using rat liver microsomes were also performed. Key findings The area under the plasma‐concentration time curve (AUC) was increased and clearance of sildenafil decreased in rats pretreated with cimetidine or troleandomycin. The AUC ratio for N‐desmethylsildenafil (0–4 h): sildenafil (0–∞) was significantly decreased only in rats pretreated with cimetidine. Similar results were obtained in the in‐vitro study using rat liver microsomes. Conclusions Sildenafil is metabolised via hepatic CYP2C11 and 3A1/2, and N‐desmethylsildenafil is mainly formed via hepatic CYP2C11 in rats. Thus, rats could be a good model for pharmacokinetic studies of sildenafil and N‐desmethylsildenafil in humans.     

Effect of hesperidin on the oral pharmacokinetics of diltiazem and its main metabolite,desacetyldiltiazem, in rats

Objectives This study was to investigate the effect of hesperidin, an antioxidant, on the bioavailability and pharmacokinetics of diltiazem and its active major metabolite, desacetyldiltiazem, in rats. Methods A single dose of diltiazem was administered orally (15 mg/kg) in the presence or absence of hesperidin (1, 5 or 15 mg/kg), which was administered 30 min before diltiazem. Key findings Compared with the control group (given diltiazem alone), hesperidin (5 or 15 mg/kg) significantly altered the pharmacokinetic parameters of diltiazem, except for 1 mg/kg hesperidin. The area under the plasma concentration‐time curve from time 0 h to infinity (AUC_0‐∞) was significantly (5 mg/kg, P < 0.05; 15 mg/kg, P < 0.01) increased by 48.9–65.3% and the peak plasma concentration (C_max) was significantly (P < 0.05) increased by 46.7–62.4% in the presence of hesperidin (5 or 15 mg/kg). Consequently, the absolute bioavailability (F) of diltiazem with hesperidin was significantly (5 mg/kg, P < 0.05; 15 mg/kg, P < 0.01) higher than that in the control group. Hesperidin (5 or 15 mg/kg) significantly (P < 0.05) increased the AUC_0‐∞ and 15 mg/kg of hesperidin significantly (P < 0.05) increased the C_max of desacetyldiltiazem. However, the metabolite‐parent ratio (MR) of desacetyldiltiazem was not significantly changed in the presence of hesperidin. Conclusions Hesperidin significantly enhanced the oral bioavailability of diltiazem in rats. It might be considered that hesperidin increased the intestinal absorption and reduced the first‐pass metabolism of diltiazem in the intestine and in the liver via an inhibition of cytochrome P450 3A or P‐glycoprotein.