Hepatic Drug-metabolizing Enzyme System Research Articles

In vitro interactions of malachite green and leucomalachite green with hepatic drug-metabolizing enzyme systems in the rainbow trout (Onchorhyncus mykiss)

Malachite green (MG) has been widely used in aquaculture to treat a number of microbial and parasitic diseases. It is currently banned in the EU because of the high cytotoxicity and carcinogenic activity, which is also shared by leucomalachite green (LMG), a reduced MG metabolite that can persist in fish tissues for months. There is scant information about the ability of either compound to interact with drug metabolizing enzymes in fish. Therefore we evaluated the in vitro effects of MG and LMG (25, 50 and 100μM) on some DMEs and glutathione (GSH) content in rainbow trout liver subfractions. LMG did not affect any of the examined parameters. In contrast, MG proved to deplete GSH and to depress to a various extent the activities of NAD(P)H cytochrome c reductase, 7-ethoxycoumarin O-deethylase, 1-naphthol uridindiphosphoglucuronyl-transferase and maximally those of 7-ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST) accepting 1-chloro2,4-dinitrobenzene (CDNB) as substrate. The inhibition mechanisms of EROD and GST were investigated by means of non-linear Michaelis-Menten kinetics and Lineweaver-Burk plots using 0.175–8μM MG. The calculated IC50 for EROD was 7.1μM, and the inhibition appeared to be competitive (Ki 2.78±0.24μM). In the case of GST, the calculated IC50 was 0.53μM. The inhibition was best described as competitive toward GSH (Ki 0.39±0.02μM) and of mixed-type toward CDNB (Ki 0.64±0.06μM). Our findings indicate that, contrary to LMG, MG behaves as a relatively strong inhibitor of certain liver DMEs and can reversibly bind GSH.

Influence of curcumin, capsaicin, and piperine on the rat liver drug-metabolizing enzyme system in vivo and in vitro

The effect of dietary supplementation of spice-active principles, curcumin (0.2%), capsaicin (0.015%), and piperine (0.02%) on the activities of the liver drug-metabolizing enzyme system was examined. All the 3 dietary spice principles significantly stimulated the activity of aryl hydroxylase. A synergistic action of dietary curcumin and capsaicin with respect to stimulating the activity of aryl hydroxylase was also evidenced when fed in combination. The activity of N-demethylase essentially remained unaffected by dietary curcumin, capsaicin, or their combination, but was significantly lowered as a result of piperine feeding. Uridine dinucleotide phosphate (UDP)-glucuronyl transferase activity was decreased by dietary piperine and the combination of curcumin and capsaicin. NADPH-cytochrome c reductase activity was significantly decreased by dietary piperine. The levels of hepatic microsomal cytochrome P450 and cytochrome b5 were not influenced by any of the dietary spice-active principles. These spice-active principles were also examined for their possible in vitro influence on the components of the hepatic drug-metabolizing enzyme system in rat liver microsomal preparation. Piperine significantly decreased the activity of liver microsomal aryl hydroxylase activity when included in the assay medium at 1 x 10(-6) mol/L, 1 x 10(-5) mol/L, and 1x 10(-4) mol/L level. Lowered activity of N-demethylase was observed in presence of capsaicin or piperine at 1 x 10(-6) mol/L in the assay medium. Hepatic microsomal glucuronyl transferase activity was significantly decreased in vitro by addition of capsaicin or piperine. Capsaicin and piperine brought about significant decrease in liver microsomal cytochrome P450 when included at 1 x 10(-6) mol/L and 1 x 10(-5) mol/L, the effect being much higher in the case of piperine. The results suggested that whereas the 3 spice principles have considerable similarity in structure, piperine is exceptional in its influence on the liver drug-metabolizing enzyme system. The study also indicated that a combination of curcumin and capsaicin does not produce any significant additive effect on the liver drug-metabolizing enzyme system.

The relationship among microsomal enzyme induction, liver weight, and histological change in cynomolgus monkey toxicology studies

The purpose of this investigation was to examine the relationship among hepatic microsomal enzyme induction, liver weight, histological evidence of hepatic injury, and serum clinical chemistry markers of hepatic origin in the cynomolgus monkey. We report here the results from independent toxicology studies for 10 investigative drug candidates representing four therapeutic classes. Study conditions were selected to elicit target organ toxicity. We found that six of the 10 compounds altered cytochrome P450-associated activities in both male and female monkeys, two in females only, and one altered similar activities in males only. Frequently, significant treatment-related elevations in NADPH cytochrome c reductase and ethylmorphine N-demethylase were noted. When the results from all 10 studies were pooled, 14 cytochrome P450-associated activities were significantly increased and five were decreased in males compared to 15 significantly increased and three decreased in the females. Treatment-associated liver weight increases were noted in four studies. Except for hepatocellular hypertrophy in one study, no significant treatment-related microscopic changes in liver and no elevations of serum biomarkers commonly associated with liver toxicity were observed in any of the studies that demonstrated significant hepatic enzyme induction. Compared to parallel rat studies, one compound was an inducer only in monkeys and one was an inducer only in rats. Significant elevations of microsomal drug-metabolizing enzymes in the cynomolgus monkey liver are not accompanied by substantial hepatic changes except for hepatomegaly. These alterations in the hepatic drug-metabolizing enzyme system were benign based the absence of histopathological lesions and serum biomarkers of hepatobiliary toxicity.

Modulatory influence of noscapine on the ethanol-altered hepatic biotransformation system enzymes, glutathione content and lipid peroxidation in vivo in rats

The modulatory potential of noscapine, an opium alkaloid was assessed on the ethanol-induced changes in hepatic drug metabolizing enzyme systems, glutathione content and microsomal lipid peroxidation. Noscapine was administered orally to male Wistar rats at a dose level of 200 mg/kg bw alone as well as in combination with 50% ethanol (v/v) for 5 days. Noscapine administration was associated with a approximately 91% decrease in hepatic microsomal cytochrome P-450 content. A decline of approximately 36% was observed in the NADPH-cytochrome c reductase activity on noscapine administration. The lowering of cytochrome P-450 levels on noscapine administration was accompanied by a concomitant increase in heme oxygenase activity as well as serum bilirubin levels. Our results indicate that the combination dosage of noscapine and ethanol antagonised the ethanol-induced elevation of cytochrome P-450 levels. Noscapine fed rats had decreased glutathione (GSH) content and enhanced lipid peroxidation compared to control rats as indexed by MDA method. Further, noscapine and ethanol coexposure produced a more pronounced elevation in lipid peroxidation and the glutathione levels also decreased significantly. We speculate on the basis of our results that the significant enhancement of lipid peroxidation on combination dosage of noscapine and ethanol is a consequence of depletion of glutathione to certain critical levels. The inhibition of glutathione-S-transferase (GST) as well as lowering of cytochrome P-450 suggests that the biotransformation of noscapine and ethanol is significantly altered following acute coexposures.

Metabolic Fate of NKH477. (2). Blood Concentration, Distribution, Excretion and Effects on Drug-Metabolizing Enzyme System in Rats after Repeated Intravenous Administration.

The blood concentration, distribution and excretion of radioactivity were investigated in male rats after daily intravenous administration of 14C-NKH477 for 21 days. The effects of NKH477 on hepatic drug metabolizing enzyme system were also investigated in male rats. 1. The radioactivity in the blood at 24 hr after daily administration rose as number of dose increased, the elimination of radioactivity from the blood after the last dosing was slower than that after a single dosing. 2. In most tissues, the radioactivity accumulated during the period of repeated administration, especially in the spleen, blood, kidney and mesenteric lymph node that rose markedly. Disappearance of radioactivity from most tissues after the last dosing was slower compared with that after a single dosing. 3. Within 168 hr after a repeated administration for 21 days, urinary and fecal excretion amounted to 7.8% and 88.9% of cumulative dose, respectively. The ratio of excretion between urine and feces was approximately the same as after a single dosing. 4. Repeated administration of NKH477 at doses of 0.3 and 1.0 mg/kg/day for 7 days had no effect on liver weight, microsomal cytochrome P-450 contents and hepatic drug-metabolizing enzyme system.

Metabolic Fate of a Novel Antiulcer Agent, T-593. (III). Blood Concentration, Distribution, Metabolism, Excretion and Effects on Hepatic Drug Metabolizing Enzyme System after Repeated Oral Administration to Rats.

Metabolic Fate of a Novel Antiulcer Agent, T-593. (III). Blood Concentration, Distribution, Metabolism, Excretion and Effects on Hepatic Drug Metabolizing Enzyme System after Repeated Oral Administration to Rats.

Disposition of Components of New Anti-cancer Drug S-1(3): Absorption, Excretion of Components of S-1 and Effects on Hepatic Drug Metabolizing Enzyme System after Repeated Administration of S-1 to Rats.

Disposition of Components of New Anti-cancer Drug S-1(3): Absorption, Excretion of Components of S-1 and Effects on Hepatic Drug Metabolizing Enzyme System after Repeated Administration of S-1 to Rats.

Caffeine increases its own metabolism through cytochrome P4501A induction in rats

Caffeine is one of the most widely used - and may be abused - xenobiotic compounds in the world. If numerous pharmacological properties of caffeine have been reported, the effects of caffeine treatment on the hepatic drug-metabolizing enzyme system have been scarcely studied. Pretreatment of rats for 3 days with 150 mg/kg/day of caffeine dramatically increased P4501A and P4502B dependent catalytic activities determined in vitro. Furthermore, N-demethylations and C-8 oxidation of caffeine were increased by about 2 fold by caffeine treatment. Immunoblot analysis demonstrated that the liver contents of P4501A2 and P4502B1/2B2, known to be involved in these monooxygenase activities, increased also by about 2 fold. Cytochrome P4503A1 and 2E1 were not modified. Taken together, there data suggest that caffeine increases its own metabolism through P4501A induction.

Characterization of hepatic microsomal cytochrome P-450 from rats treated with methylsulphonyl metabolites of polychlorinated biphenyl congeners

The inducing potency of 3-methylsulphonyl(MeSO 2)-2,2′,4′,5,5′-pentachlorobiphenyl (pentaCB), which was one of the major MeSO 2 metabolites of polychlorinated biphenyls (PCBs) present in seal blubber[1], on the hepatic drug metabolizing enzyme activities was examined in comparison with that of the parent compound and phenobarbital (PB). The inducing fashion of the above enzymes and changes in the contents of PB-inducible P-450 forms by 2,3′,4′,5-tetrachlorobiphenyl (tetraCB) (IU-70), 2,2′,3′,4′,5-pentaCB (IU-87), 2,2′,4′,5,5′-pentaCB (IU-101) and 2,2′,3′,4′,5,5′-hexachlorobiphenyl (hexaCB) (IU-141), and their MeSO 2 metabolites were investigated in rats. Administration at various doses (0.2-1.0 μmol/kg) of 3-MeSO 2-2,2′,4′,5,5′-pentaCB produced nearly dose-related increases in the hepatic concentration of this methyl sulphone, in the contents of cytochromes P-450 and b 5, and in activities of aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase and benzo[ a]pyrene hydroxylase of liver microsomes. Major PB-inducible forms, CYP2B1, CYP2B2, CYP3A2 and CYP2C6 were induced with four PCBs (342 μmol/kg) and their 3-MeSO 2 metabolites (0.5–10 μmol/kg), indicating that 3-MeSO 2 metabolites were strong PB-type inducers of hepatic drug-metabolizing enzymes. 3-MeSO 2-2,2′,4′,5,5′-pentaCB was an especially strong inducer. On the other hand, four PB-inducible forms of cytochrome P-450 were not induced with the 4-MeSO 2 isomers. The relation between liver concentrations of the corresponding 3-MeSO 2 derivatives and induction of four PB-inducible forms of cytochrome P-450 after administration of four PCBs and their 3-MeSO 2 derivatives further confirmed that the 3-MeSO 2 metabolites played an important role in the induction which parent PCB congeners caused on the hepatic drug-metabolizing enzyme system.

Induction of hepatic microsomal drug-metabolizing enzymes by methylsulphonyl metabolites of polychlorinated biphenyl congeners in rats

The effect of methylsulphonyl (MeSO 2) metabolites of 2,3′,4′,5-tetrachlorobiphenyl (tetraCB) (IU-70), 2,2′,3′,4′,5-pentachlorobiphenyl (pentaCB) (IU-87), 2,2′,4′,5,5′ -pentaCB (IU-101) and 2,2′,3′,4′,5,5′-hexachlorobiphenyl (hexaCB) (IU-141), on the hepatic microsomal drug-metabolizing enzyme system was investigated in rats. The administration of 3-MeSO 2-2,3′,4′,5-tetraCB (10 μmol/kg), 3-MeSO 2-2,2′,3′,4′,5-pentaCB (0.5 μmol/kg), 3-MeSO 2-2,2′,4′,5,5′-pentaCB (0.5 μmol/kg) and 3-MeSO 2-2,2′,3′,4′,5,5′-hexaCB (2 μmol/kg) to rats significantly increased the contents of cytochromes P-450 and b 5 and the activities of aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase and benzo[ a]pyrene hydroxylase. From these results, it is suggested that the 3-MeSO 2 derivatives studied are possibly potent phenobarbital-like inducers of microsomal drug-metabolizing enzymes. On the other hand, 4-MeSO 2-2,3′,4′,5-tetraCB, 4-MeSO 2-2,2′,3′,4′,5-pentaCB, 4-MeSO 2-2,2′, 4′,5,5′-pentaCB and 4-MeSO 2-2,2′,3′,4′,5,5′-hexaCB had almost no effect on both cytochrome contents and these enzyme activities. After 96 h, following administration of 2,3′,4′,5-tetraCB, 2,2′,3′,4′,5-pentaCB, 2,2′,4′,5,5′-pentaCB and 2,2′,3′,4′,5,5′-hexaCB

O-110 - The effect of submaxillariectomy on hepatic drug metabolizing enzyme system and heme metabolism.

O-110 - The effect of submaxillariectomy on hepatic drug metabolizing enzyme system and heme metabolism.

Absorption, Distribution, Excretion and Effects on Drug Metabolizing Enzyme Activities of a New Antiplatelet Drug, Ethyl 2-(4,5-bis(4-methoxyphenyl)thiazol-2-yl)pyrrol-1-ylacetate(KBT-3022), after Multiple Oral Administration in Mice.

Absorption, distribution, excretion, enzyme induction and effect to platelet were investigated in male mice after oral administration of an antiplatelet drug, KBT-3022. 1. Radioactivity levels in the plasma 24 hr after daily oral administration of 14C-KBT-3022 reached a steady state by the 4th dosing. The radioactivity levels after the 21st dosing showed a broad peak with about half of the Cmax after single dosing but had a similar AUC0-24 h.2. Radioactivity levels in tissues 24 hr after daily oral administration of 14CKBT-3022 increased with the number of doses and reached a steady state by the 21st dosing except the spleen. The radioactivity levels in the lung, heart and testis after the 21st dosing were 5-6 times higher than those after single dosing, but those in the other tissues were lower than 4 times. Elimination of radioactivity from tissues after the 21st dosing was slower than that after single dosing. At 72 hr after the 21st dosing, the radioactivity level in the aorta was 50% of the maximum and those in the skin, testis, lung, fat and spleen were 24-35% of the maximum. High level of radioactivity was noted in the deferent duct as revealed by whole body autoradiography. 3. No marked difference was observed in plasma concentration of 6-keto-PGF1α and serum concentration of TXB2 between the single and repeated dosing groups, although the accumulation of radioactivity was noted in the aorta after multiple doses of 14C-KBT-3022. From these results, metabolites in the aorta would not inhibit the production of PGI2. 4. Excretion of radioactivity in the urine and feces did not change with the number of doses and was 1.3 and 92.7% of the cumulative dose, respectively, within 120 hr after the 21st dosing. 5. No significant effect on hepatic drug-metabolizing enzyme system was observed after repeated dosing of KBT-3022.

The prolongation effect on the duration of pentobarbital anesthesia by submaxillariectomy in male rats

The present study was performed to investigate the effects of submaxillariectomy (Subx) on the anesthetic effect (sleeping time) of pentobarbital, the concentration-time profile of plasma pentobarbital and the hepatic drug metabolizing enzyme systems in male rats of the Donryu strain. Subx was performed when the rats were 60 days old. Subx prolonged the duration of pentobarbital (30 mg/kg, i.p.) anesthesia at 10, 23 and 43 days after the operation, respectively. At 43 days after Subx, the plasma pentobarbital concentration was higher in the Subx group until 30 min after the administration. There was no significant difference in the hepatic microsomal cytochrome P-450 content between the Subx and control groups. Cytochrome b5 content, aminopyrine N-demethylase and aniline hydroxylase activities were increased significantly in the Subx group. The activity of heme oxygenase, the rate limiting enzyme in the heme catabolic pathway, tended to increase in the Subx group. Furthermore, the activity of delta-aminolevulinic acid synthetase, the rate limiting enzyme in the heme synthetic pathway, was significantly decreased to 51 percent of the control group by Subx. These results may suggest that the prolongation of the duration of pentobarbital anesthesia is caused by Subx due to the change in the pharmacokinetics of pentobarbital, especially the inhibitory effects of the hepatic pentobarbital metabolizing enzyme system.

Alterations in hepatic Phase I and Phase II biotransformation enzymes by garlic oil in rats

Studies were conducted to examine the effect of a single and repeated administrations of garlic oil (diallyl sulfide) on Phase I and Phase II biotransformation enzymes in rats. Adult, male Sprague-Dawley rats treated with a single dose of garlic oil (500 mg kg i.p.) showed a significant depression of hepatic cytochrome P-450, aminopyrine Ndemethylase and aniline hydroxylase while microsomal protein content, cytochrome b 5, NADPH-cytochrome c reducase, benzphetamine N-demethylase and cytosolic glutathione, S-transferase remained unaffected 24 h following the treatment. Although certain microsomal enzymes were depressed, there was no liver damage caused by garlic oil as judged by the putative serum enzyme test. On the other hand, daily administration of garlic oil (50 mg kg ) i.p. for 5 days) produced a significant increase in hepatic cytochrome P-450, aminopyrine N-demethylase and benzphetamine N-demethylase activities, but not in the rest of the aforementioned parameters of biotransformation reactions. These data indicate that the effect of garlic oil on the hepatic drug-metabolizing enzyme system is dose-dependent.

COMPARISON OF THE EFFECTS OF PIPERINE ADMINISTERED INTRAGASTRICALLY AND INTRAPERITONEALLY ON THE LIVER AND LIVER MIXED-FUNCTION OXIDASES IN RATS

Piperine, a major pungent constituent of black and red peppers, was administered to rats intragastrically and intraperitoneally to study whether it alters the activities of hepatic mixed-function oxidases (MFO) and serum enzymes as specific markers of hepatotoxicity. An intragastric dose of 100 mg/kg of piperine to adult, male Sprague-Dawley rats caused an increase in hepatic microsomal cytochrome P-450 and cytochrome b5, NADPH-cytochrome c reductase, benzphetamine N-demethylase, aminopyrine N-demethylase and aniline hydroxylase 24 h following treatment. On the other hand, a 10 mg/kg dose given i.p. exhibited no effect on the activities of the aforementioned parameters of the hepatic drug-metabolizing enzyme system. However, when the intragastric and intraperitoneal doses were increased to 800 mg/kg and 100 mg/kg, respectively, the black pepper alkaloid produced a significant decrease in the levels of cytochrome P-450, benzphetamine N-demethylase, aminopyrine N-demethylase and aniline hydroxylase 24 h after treatment. None of the treatments significantly elevated the activities of serum sorbitol dehydrogenase (SDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and isocitrate dehydrogenase (ICD), suggesting that piperine is not a hepatotoxic agent.

Differences in the Effects of Piperine and Piperonyl Butoxide on Hepatic Drug-Metabolizing Enzyme System in Rats

An i.p. administration of rats with piperine (100 mg/kg) and piperonyl butoxide (400 mg/kg) produced a significant decrease in hepatic cytochrome P-450, and activities of benzphetamine N-demethylase, aminopyrine N-demethylase and aniline hydroxylase 1 hr after the treatment. Twenty-four hr later, these parameters along with cytochrome b5 and NADPH-cytochrome c reductase remained depressed only in piperine-treated rats. In contrast, piperonyl butoxide caused a significant induction of these parameters with the exception of cytochrome b5 and aminopyrine N-demethylase, which were up by 36 and 33% over their respective controls but not significantly. These results point up that effect of piperine on hepatic mixed-function oxidases is monophasic while that of piperonyl butoxide is biphasic.

Studies on the Metabolic Fate of (.+-.)-2-(Dimethylamino)-1-((o-(m-methoxyphenethyl)-phenoxy)methyl)ethyl hydrogen succinate hydrochloride (MCI-9042). (III). Absorption, Distribution, Metabolism, Excretion, Accumulation and Effect on the Hepatic Drug-Metabolizing Enzyme Activities after Repeated Oral Administration to Rats.

The absorption, distribution, metabolism, excretion and accumulation of MCI-9042 were investigated after repeated oral administration of 14C-MCI-9042 (20mg/kg/day) to male rats for 21 days. The effect of MCI-9042 on the hepatic drug-metabolizing enzyme activities was also investigated after repeated oral administration of MCI-9042 (20 or 100mg/kg/day) to male rats for 21 days. 1. The Tmax and Cmax of radioactivity in the blood after single oral administration to unfasted rats were delayed and decreased compared with those after single administration to fasted rats. Area under the time versus blood concentration curve (AUC0)∞ of radioactivity in unfasted rats was decreased about 18% compared with that in fasted rats. 2. Blood levels of radioactivity at 30 min after each dosing were nearly constant during repeated administration, and those at 24hr after each dosing were increasing up to the 12th day and then after reaching plateau remained constant. The half-life of blood levels of radi oactivity after 21 days repeated oral administration was 10.3hr (t1/2β), which was almost similar to that after single administration. 3.The tissue levels of radioactivity at 24hr after each dosing increased gradually till the 7th or 14th administration, and thereafter remaining at almost same levels. The tissue levels of radioactivity after 21 days repeated administration decreased gradually.4. The excretion rates of radioactivity into the urine and feces were nearly constant during the period of repeated administration of 14C-MCI-9042. Within 96hr after the last dosing, 21.8% and 74.3% of the administered radioactivity were recovered into urine and feces, respecti vely.5. The percentage of unchanged MCI-9042 and its metabolites to total radioactivity present in the plasma, liver, urine and feces after repeated administration were almost same as tho se after a single administration. 6. After repeated administration of MCI-9042 for 21 days, any effect on the hepatic micro somal drug-metabolizing enzyme system was not observed.

Bioactivity of neolignans from fructus Schizandrae.

Fructus Schizandrae sinensis Baill, a traditional Chinese medicine, used as tonic and sedative, has been shown at the beginning of 70's to lower the elevated serum glutamic-pyruvic transaminase (SGPT) levels of patients suffering from chronic viral hepatitis. During past 20 years, a series of neolignans have been isolated and identified as effective principles. Pharmacological studies revealed that they increased liver protein and glycogen synthesis, antagonized liver injuries from CCl4 and thioacetamide. The mechanism of SGPT lowering was considered as a hepato-protective and membrane stabilize action, although inhibition of the activity of liver GPT may also be existed. It was found that some principles of Schizandrae have an inducing effect on hepatic microsomal drug-metabolizing enzyme system P-450, thus explained their anti-toxic, anti-carcinogenic and anti-mutagenic effects. A synthetic derivative compound of Schisandrin called DDB has most of the above mentioned actions now used widely in China as a hepato-protective drug with high effectiveness in normalizing liver functions and very low side effects. From natural Schisandrin to synthesized DDB, pointed out a successful way in the development of new drugs from natural products.

Formation of an Antibacterial Metabolite from a New Macrolide Compound 23-O-Benzyl-5-mycaminosyl-tylonolide (TMC-101), by a Hepatic Microsomal Drug-Metabolizing Enzyme System.

Upon incubation of 23-O-benzyl-5-mycaminosyl-tylonolide (TMC-101) with liver microsomes in the presence of an nicotinamide adenine dinucleotide phosphate-generating system, at least four metabolites were formed: two of them were also formed by an enzyme(s) in rat serum. One of the metabolites formed by liver microsomes possessed antibacterial activity comparable to TMC-101 as examined by bioautography using Micrococcus luteus ATCC 9341 as a tester strain. Incubation of TMC-101 with rat serum degraded most of the parent compound and did not form the active metabolite. The capacity of liver microsomes to produce the active metabolite was increased by pretreatment of rats with 3-methylcholanthrene, phenobarbital and polychlorinated biphenyl. The metabolite with the antibacterial activity was estimated not to be formed by the N-demethylation of TMC-101, and was chemically unstable.

Inhibition of hepatic microsomal cytochrome P450 by cannabidiol in adult male rats.

The mechanism of inhibitory effect of cannabidiol (CBD) on the hepatic drug-metabolizing enzyme system was studied in adult male rats in vivo. Time course studies revealed that microsomal d-benzphetamine N-demethylation and testosterone 2 alpha-, 16 alpha- and 17-oxidation were markedly suppressed 6 to 48 h after the single administration of CBD (10 mg/kg, intraperitoneally). Decreases in activities of aniline hydroxylation and p-nitroanisole O-demethylation and in content of total cytochrome P450 were intermittent and moderate. On the other hand, no change was observed in reduced nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome c reductase activity or cytochrome b5 content in the hepatic microsomes of the CBD-treated rats. Western blotting analysis showed a marked decrease in the male-specific cytochrome P450 UT-2 in the hepatic microsomes, especially 24 to 48 h after pretreatment with CBD. It is possible that CBD given 6 to 12 h before the sacrifice might interact with cytochrome P450 as a substrate, resulting in inhibition of the drug-metabolizing enzyme activities in the earlier stages. In the later stages from 24 to 48 h after CBD treatment, the reduction in content of the male-specific cytochrome P450 UT-2 may play a major role in the inhibitory effect of CBD on the hepatic drug-metabolizing enzyme system in the adult male rat in vivo.