Drug-metabolizing Enzymes In Rat Liver Research Articles

Pharmacokinetics of active ingredients of Pudilan Xiaoyan Oral Liquid in rats and effect on liver drug-metabolizing enzymes

This study is aimed to establish a method for the determination of baicalin,baicalin and purpurin in the plasma of rats after oral administration of Pudilan Xiaoyan Oral Liquid( PDL) by using liquid chromatography-mass spectrometry( LC-MS),analyze the pharmacokinetics of three components in rats,and investigate the effects of PDL on drug-metabolizing enzymes in rat liver. C18 column was used for liquid chromatography separation,with acetonitrile-water( containing 0. 2% formic acid) as the mobile phase for gradient elution. The mass spectrometry was detected by electrospray ion source( ESI) under multi-reaction monitoring mode( MRM),as well as positive and negative ion alternating mode. Plasma sample collection was performed by using an automatic blood collection meter for small animals. The pharmacokinetic parameters were calculated by Win Nonlin software. The total protein concentration of rat liver microsomes and the total enzyme content of CYP450 were determined by BCA method and spectrophotometry respectively. The methodological study in terms of linear range,recovery rate,precision and sample stability,was used to confirm that the LC-MS analysis method established in this experiment was simple,exclusive,accurate and reliable,and can meet the requirement of determining the content of baicalin,oroxindin and corynoline in plasma after PDL administration in rats. The drug-time curve showed that baicalin and oroxindin had a bimodal phenomenon,and the pharmacokinetic parameters indicated that baicalin,oroxindin and corynoline in PDL had certain drug-like properties. After 7 consecutive days of PDL administration,the rat liver coefficient,total liver microparticle protein and CYP450 enzyme content were increased,but there was no significant difference,indicating that PDL was less likely to develop drug-drug interaction based on CYP enzyme. The results of this experiment can provide reference for the research on in vivo efficacy and drug interaction of PDL as well as on its clinical application.

Effects of Buyang Huanwu Decoction on antioxidant and drug-metabolizing enzymes in rat liver

AimTo study the effect of Buyang Huanwu Decoction (BYHWD) on the antioxidant enzymes and drug-metabolizing enzymes in rat liver. MethodFollowing treatment of rats with BYHWD at 6.42, 12.83, or 25.66 g·kg−1 per day for 15 days, microsomes and cytosols isolated from the liver tissues were prepared by differential centrifugation according to standard procedures. The activities of the antioxidant enzymes and cytochrome b5, NADPH-cytochrome P450 reductase, CYP3A, CYP2E1, UGT, and GST of the rat livers were determined by UV-Vis spectrophotometer. ResultsThe activities of ALT, AST, antioxidant enzymes, and the Hepatosomatic Index in serum were not significantly affected. In cytosols, the activity of CAT was significantly increased at the dosage of 12.83 g·kg−1, and all the other antioxidant activities and MDA levels were not affected by this treatment. BYHWD had no effect on cytochrome b5, NADPH-cytochrome P450 reductase, CYP3A, and UGT. At the highest dose (25.66 g·kg−1), the activity of CYP2E1 was significantly inhibited, and the activities of GST and the level of GSH were increased. ConclusionBYHWD is safe for the liver, and has the functions of detoxification and antioxidant. Patients should be cautioned about the herb-drug interaction of BYHWD and CYP2E1 substrates.

Andrographis paniculataExtract and Andrographolide Modulate the Hepatic Drug Metabolism System and Plasma Tolbutamide Concentrations in Rats

Andrographolide is the most abundant terpenoid of A. paniculata which is used in the treatment of diabetes. In this study, we investigated the effects of A. paniculata extract (APE) and andrographolide on the expression of drug-metabolizing enzymes in rat liver and determined whether modulation of these enzymes changed the pharmacokinetics of tolbutamide. Rats were intragastrically dosed with 2 g/kg/day APE or 50 mg/kg/day andrographolide for 5 days before a dose of 20 mg/kg tolbutamide was given. APE and andrographolide reduced the AUC0–12 h of tolbutamide by 37% and 18%, respectively, compared with that in controls. The protein and mRNA levels and enzyme activities of CYP2C6/11, CYP1A1/2, and CYP3A1/2 were increased by APE and andrographolide. To evaluate whether APE or andrographolide affected the hypoglycemic action of tolbutamide, high-fat diet-induced obese mice were used and treated in the same manner as the rats. APE and andrographolide increased CYP2C6/11 expression and decreased plasma tolbutamide levels. In a glucose tolerance test, however, the hypoglycemic effect of tolbutamide was not changed by APE or andrographolide. These results suggest that APE and andrographolide accelerate the metabolism rate of tolbutamide through increased expression and activity of drug-metabolizing enzymes. APE and andrographolide, however, do not impair the hypoglycemic effect of tolbutamide.

Effects of chitosan oligosaccharides on drug-metabolizing enzymes in rat liver and kidneys

To investigate the effect of chitosan oligosaccharides (COS) on drug-metabolizing enzymes in rat liver and kidneys, male Spraque–Dawley rats were fed a diet containing 1% or 3% COS for 5weeks. The activities of cytochrome P450 (CYP) enzymes, UDP-glucurosyltransferase (UGT) and glutathione S-transferase (GST) in the liver and kidneys were determined. Significant decreases in microsomal CYP3A-catalyzed testosterone 6β-hydroxylation, CYP2C-catalyzed diclofenac 4-hydroxylation, and CYP4A-catalyzed lauric acid 12-hydroxylation in the liver of rats fed the COS diets were observed compared with those rats fed the control diet. Immunoblot analyses of CYP proteins showed the same trend as with enzyme activities. Increased glutathione content in liver was found in rats fed the 1% COS diet. Increased hepatic NADPH: quinone oxidoreductase 1 (NQO1) activity was found in rats fed the COS diets. In kidneys, COS had little or no effect on CYP enzyme activities. However, increased GST activity was observed in rats fed the COS diets. Moreover, a higher UGT activity was found in rats fed the 1% COS diet. Our results indicate that COS may suppress hepatic CYP enzymes and induce phase II detoxifying reactions in the liver and kidneys of rats.

Dose-related inhibition of the drug-metabolizing enzymes of rat liver by the pyrrolizidine alkaloid, monocrotaline.

Adult, male Sprague-Dawley rats were given 0, 10, 20, 40 or 80 mg kg-1 of monocrotaline intraperitoneally and the following toxicity parameters determined 24 h post treatment. Compared with the control none of the doses caused significant change in either the relative liver weight or the hepatic microsomal protein concentration. Microsomal cytochrome P450 content and activities of benzphetamine N-demethylase and aniline hydroxylase did not differ from the control at 10 or 20 mg kg-1 dosage. But, there was a significant loss of cytochrome P450 at 40 and 80 mg kg-1 dosages and decrease in the activity of the two enzymes only at the highest dose. Similarly, the highest dose caused a marked elevation of serum sorbitol dehydrogenase and glutamic pyruvic transaminase activity suggestive of severe liver damage.

INDUCTION OF GENES FOR METABOLISM AND TRANSPORT BY TRANS-STILBENE OXIDE IN LIVERS OF SPRAGUE-DAWLEY AND WISTAR-KYOTO RATS

trans-Stilbene oxide (TSO) is a synthetic proestrogen that induces phase I and II drug-metabolizing enzymes in rat liver. The purpose of this study was to determine whether TSO also induces transporter expression in rat liver and whether gene induction in rat liver after TSO occurs in a constitutive androstane receptor (CAR)-dependent manner. Total RNA was isolated from male rat livers after treatment with TSO for up to 4 days (200 mg/kg, i.p., twice daily), and the mRNA levels for each gene were quantified. CYP2B1/2, CYP3A1, epoxide hydrolase, heme oxygenase-1, UGT1A6, UGT2B1, multiple drug resistance protein (Mdr) 1a and 1b, as well as multidrug resistance-associated protein (Mrp) 2, 3, and 4 mRNA were increased in livers after TSO treatment. To determine whether TSO activates gene expression in a CAR-dependent manner, male and female Wistar-Kyoto (WKY) rats were treated with TSO for 3 days. TSO induced CYP2B1/2, UGT2B1, and Mdr1b in males more than in females, suggesting that TSO could increase their expression via CAR. Conversely, TSO induced CYP3A1, epoxide hydrolase, UGT1A6, and Mrp3 similarly in both genders, indicating that induction of these genes occurs independently of CAR. TSO treatment also increased the activity of a CAR binding element luciferase reporter construct in HepG2 cells transfected with rat CAR and in mouse liver. Additionally, TSO increased antioxidant response element/electrophile response element luciferase reporter construct activity in HepG2 cells. In conclusion, in WKY rat liver, TSO increases CYP2B1/2, UGT2B1, and Mdr1b mRNA expression in a gender-dependent manner and CYP3A1, epoxide hydrolase, UGT1A6, and Mrp3 in a gender-independent manner.

Comparative Effects of Acute and Chronic Carbofuran Exposure on Oxidative Stress and Drug-Metabolizing Enzymes in Liver

The current study has been designed to examine the comparative effects of acute and chronic carbofuran exposure on lipid peroxidation, glutathione levels, and drug-metabolizing enzymes in rat liver. Activity of acetylcholinesterase, a bona fide marker of carbofuran exposure, was markedly inhibited after acute carbofuran exposure, whereas the extent of inhibition was much less after chronic exposure. Lipid peroxidation was accentuated after chronic carbofuran exposure. However, acute exposure resulted in relatively less increase in lipid peroxidation levels than with chronic exposure. Glutathione levels were significantly increased in liver of animals chronically exposed to carbofuran; on the contrary, there was a drastic reduction in glutathione levels after acute exposure. Cytochrome P450 was significantly induced in liver of animals treated with acute as well as chronic carbofuran. The activity of glutathione-S-transferase was induced after both acute and chronic carbofuran exposure; the increase was much higher in chronically exposed animals as compared with animals exposed acutely. Based on the results, it is clear that acute and chronic carbofuran exposure have differential effects on oxidative stress and drug-metabolizing enzymes in liver.

Suppressive Effect of (-)-Epigallocatechin Gallate on Aflatoxin B1-induced Chromosome Aberrations in Rat Bone Marrow Cells.

The suppressive effect of (-)-epigallocatechin gallate (EGCG), the major polyphenolic constituent present in green tea, on aflatoxin B1 (AFB1)-induced chromosome aberrations (CA) in rat bone marrow cells was studied. The administration of EGCG 24 hr before the AFB1 injection significantly suppressed AFB1-induced CA. The suppression was observed 18 hr, 24 hr and 48 hr after the AFB1 treatment but no suppressive effect was observed at the early period (6 hr and 12 hr) after the AFB1 treatment. Furthermore, the suppression was observed in all doses of AFB1 (1, 5, 10 and 20 mg/kg) investigated. Rats given EGCG 2 hr before the AFB1 injection displayed no suppressive effect. The suppressive effect of EGCG paralleled the dose of EGCG when given in a dose range of 10-60 mg/kg body weight. The administration of (-)-epicatechin gallate 24 hr before the AFB1 injection significantly suppressed AFB1-induced CA as well as EGCG. On the other hand, in rats given green tea polyphenols (GTP) 2 hr before the AFB1 injection, (-)-epigallocatechin and gallic acid significantly suppressed AFB1-induced CA. The pretreatment with EGCG or gallic acid did not induce the drug-metabolizing enzymes in rat liver, such as cytochrome P450 and glutathione S-transeferase. Rats given 2% green tea infusion as the sole source of drinking water for four days before sacrifice displayed significantly suppressed AFB1-induced CA. However, rats given various kinds of canned tea for four days showed no suppressive effect. The amount of GTP in canned tea determined by high performance liquid chromatography (HPLC) analysis was much less than that in 2% green tea infusion.

Sex-related effect of hemin on cytochrome P450 and drug-metabolizing enzymes in rat liver.

We examined the effect of hemin on rat hepatic microsomal cytochrome P450 (P450) and its molecular species (P450 2E1, 3A2, 2C11 and 2C12) under the induction of heme oxygenase activity in male and female rats. Hemin produced an inverse relationship between the induction of heme oxygenase activity and the decrease of P450 content in a dose-dependent manner. A time course study revealed that hemin produced a significant decrease in total P450 content in male rats to about 37% that of the controls at 24 hr after its administration. Western and Northern blot analyses revealed that the increase in both heme oxygenase-1 (HO-1) protein and HO-1 mRNA reached a maximum at 24 hr and returned to control levels within 120 hr in both sexes. With respect to P450-dependent monooxygenase activities, we found that there was a significant decrease of aniline p-hydroxylase activity to about 30% of the control animals, but not in erythromycin N-demethylase activity at various time intervals. Immunoblot analysis revealed that P450 2E1 in male rat liver was dramatically decreased at 24 hr to about 20% of the controls, but not P450 3A2. Parallel to the decrease of androstenedione 16 alpha-hydroxylase activity, there was a marked decrease of P450 2C11 or 2C12 in male or female rats, respectively, at 72 hr after the treatment; however, hemin did not decrease androstenedione 16 alpha-hydroxylase activity in phenobarbital-pretreated rat liver. These findings suggest that hemin predominantly affects constitutively expressed isozymes rather than inducible P450 species in rat liver.

Inhibiting effect of ethinylestradiol/levonorgestrel combination on microsomal enzymatic activities in rat liver and kidney.

The aim of the study was to evaluate the effects of two therapeutic combinations of ethinylestradiol (EE) and levonorgestrel (LE), which are used in triphasic contraceptives, on the activities of drug-metabolizing enzymes in rat liver and kidney. Sexually mature female Wistar rats were given 0.03 mg EE and 0.05 mg LE, or 0.03 mg EE and 0.125 mg LE for 6 or 18 sexual cycles, i.e. for 30 or 90 days. EE/LE inhibited not only the metabolic capacity of P450, a protein which directly undergoes suicide inhibition, but also the level of rat liver cytochrome b5 (dependent on the heme pool) as well as the activities of NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase in the liver and kidney. The majority of these effects were independent of the gestagen dose and of the duration of treatment, suggesting that estrogen is a predominant inhibiting factor in the EE/LE combination. The study has revealed differences in the enzyme activities between the liver and kidney, which may result from the fact that these organs display different sets of P450 isoforms and, therefore, their monooxygenase systems show distinct capacities to metabolize exogenous steroids.

Effect of the spine venom from the crown-of-thorns starfish, Acanthaster planci, on drug-metabolizing enzyme in rat liver.

The effect of spine venom from the crown-of-thorns starfish (Acanthaster planci) on drug-metabolizing enzymes in rat liver was studied. The spine venom was prepared by saturation of spine homogenate with ammonium sulfate and the protein fraction precipitating 50% saturation was used as venom B. Venom A was the protein precipitated between 50 and 100% saturation. When venom B (100-200 mg/kg) was given to rats, liver microsomal GSH S-transferase and cytochrome P450 activities decreased while cytosolic GSH S-transferase activity was not changed. The decrease in these microsomal enzyme activities was seen from 12 hr to 24 hr after giving 100 mg/kg of venom B. Rats given venom A died, suggesting an involvement of the lethal factor in venom A. The data showed that the spine venom B from A. planci depressed microsomal GSH S-transferase and cytochrome P450 activities in rat liver and that this venom was distinct from the lethal factor of the spine venom.

Induction of cytochromes P450 2B and 2E1 in rat liver by isomeric picoline N-oxides

Pyridine derivatives are widely used solvents and precursors for the synthesis of chemicals of industrial importance. Oxidized metabolites have been implicated in the observed toxicity of pyridines and are known to induce drug-metabolizing enzymes in rat liver. In this study the three isomeric picoline (methylpyridine) N-oxides, as major oxidized metabolites of 2-, 3- and 4-picoline, were evaluated as inducers of cytochrome P450 (CYP) enzymes in rat liver. After a single dose of 100 mg/kg 24 h before sacrifice the 3- and 4-isomers were effective inducers of microsomal substrate oxidations associated with the phenobarbital-inducible CYPs 2B; upregulation of CYP2B protein was confirmed by immunoblotting. In contrast, the 2-isomer did not increase CYP2B protein or activity in rat liver but CYP2E1 protein expression was upregulated by the isomers to 160–200% of control. The three chemicals increased aniline 4-hydroxylation activity in rat liver, which is consistent with induction of CYPs 2B or 2E1 and 4-nitrophenol 2-hydroxylation activity was increased in microsomal fractions from 3- and 4-picoline N-oxide-treated rats. The activities of several other CYPs were also determined and CYP1A-dependent 7-ethylresorufin O-deethylation was increased (to ∼6- and 2-fold of control) by the 3- and 4-isomer, respectively, whereas the activity of CYP3A-mediated androstenedione 6 β-hydroxylation was decreased by the agents-most notably by the 2-isomer. During NADPH-supported oxidation of CCl 4, lipid peroxidation was increased in microsomes from 3- and 4-picoline N-oxide-pretreated rats and was modulated in vitro by the CYP2B inhibitor orphenadrine, but not by the CYP2E1 inhibitor 4-methylpyrazole. These findings establish that particular isomers of picoline N-oxide rapidly upregulate CYP2B or, to a lesser extent, CYP2E1 and implicate CYP2B in the enhanced lipid peroxidation observed in microsomes from rats treated with 3- and 4-picoline N-oxides. Such induction process may contribute to the hepatotoxicity of pyridines by enhancing the capacity for microsomal lipid peroxidation.

TIME COURSE OF INDUCTION OF RAT HEPATIC DRUG METABOLIZING ENZYME ACTIVITIES FOLLOWING DIETARY ADMINISTRATION OF FLAVONOIDS

Effects of continuous feeding flavonoids (flavone, flavanone, and tangeretin) on drug-metabolizing enzymes in rat liver were investigated to ascertain how long feeding is required to reach maximal induction and to determine whether maximal induction is maintained for a long period of feeding. In the first experiment rats received a diet containing 10 mmol flavonoid/kg dry matter for 4, 8, 16, or 32 d. The second experiment was designed to examine the time course for induction during the first 4 d. The kinetics of induction depended on the chemical structure of the flavonoid and was different from one enzyme to another. Flavone increased P450 1A and P450 2B apoproteins and stimulated many enzyme activities. A significant increase of P450 1A1/2 proteins, ethoxyresorufin O-deethylase (EROD), and methoxyresorufin O-demethylase (MROD) activities occurred as early as 6 h after the first administration, and a gradual increase was observed up to 4 d of feeding. P450 2B1/2 proteins and pentoxyresorufin O-depentylase (PROD) activity were also increased but after a lag period when compared with P450 1A1/2 proteins. EROD and MROD activities declined after 4 d, whereas PROD activity remained steady during 32 d of flavone feeding. Glutathione transferase (GST) and p-nitrophenol UDP-glucuronosyl transferase (UGT) activities were also increased. The maximal induction was reached by 4 d of feeding for UGT and after a longer duration of feeding (16 d) for GST. Flavanone treatment induced mostly P450 2B1/2 proteins and PROD, GST, and UGT activites. After 4 d of feeding, P450 2B1/2 proteins and PROD activity declined whereas GST and UGT activities remained steady. Tangeretin treatment produced changes similar to flavone but of lesser magnitude and after a longer delay.

Comparative effects of flavonoids and model inducers on drug-metabolizing enzymes in rat liver

The inducing effects of some flavonoids (flavone, flavanone, tangeretin and quercetin) and model substances have been studied in rats, and the activity and the expression of drug-metabolizing enzymes have been compared in rats. The addition of flavonoids to the diet (0.3% w/w) for 2 weeks did not change the liver cytochrome P450 content nor the activities of the NADPH-cytochrome P450 and NADH-cytochrome b 5 reductases, but it affected the activities of phase I and phase II enzymes. Flavone, and to a lesser extent tangeretin, increased the activities mediated by the P450 1A1,2 (EROD) and 2B1,2 (PROD) as well as the activities of p-nitrophenol UDP-glucuronyl transferase (UGT) and glutathione transferase (GST). Flavanone mainly enhanced PROD, UGT and GST, whereas quercetin did not modify any enzyme activities. None of the tested flavonoids modulated the activities catalyzed by P450 2E1, 3A and 4A. Immunoblotting studies showed that flavone and tangeretin increased the expression of cytochrome P450 1A and 2B forms, whereas flavanone only induced cytochrome P450 2B. Flavone and to a lesser extent flavanone, markedly increased the phenol-UGT protein level. Both flavone and flavanone also increased the androsterone- and testosterone-UGTs, whereas tangeretin and quercetin did not increase any UGT isoform. We concluded that the flavonoids tested specifically affected the expression of the drug-metabolizing isozymes in rat liver, their inducing properties were dependent on their chemical structures.

Induction of rat liver drug-metabolizing enzymes by tetrachloroethylene.

The effect of tetrachloroethylene on Phase I and II drug-metabolizing enzymes in rat liver was examined. Rats were treated orally with tetrachloroethylene daily for five days, at doses of 125, 250, 500, 1,000 and 2,000 mg/kg. The higher doses (> 500 mg/kg) of tetrachloroethylene induced the hepatic microsomal 7-pentoxyresorufin O-depentylase and 7-benzyloxyresorufin O-debenzylase activities associated with the CYP2B subfamily. 7-ethoxyresorufin O-deethylase activity was also induced about 2-fold compared with that of control rats at 500, 1,000, and 2,000 mg/kg dose levels of tetrachloroethylene. However, 7-ethoxycoumarin O-deethylase and 7-methoxyresorufin O-demethylase activities were increased significantly at only the 1,000 mg/kg dose level of tetrachloroethylene (1.4- and 1.5-fold). Although other cytochrome P450-mediated monooxygenase activities such as nitrosodimethylamine N-demethylase, aminopyrine N-demethylase and erythromycin N-demethylase were also induced by tetrachloroethylene, the relative induction to control activity was lower than those of 7-pentoxyresorufin O-depentylase and 7-benzyloxyresorufin O-debenzylase. Western immunoblotting showed that the levels of CYP2B1 and CYP2B2 proteins in liver microsomes were increased at doses of 1,000 and 2,000 mg/kg of tetrachloroethylene. In addition to cytochrome P450-mediated monooxygenases, there was significant induction of the Phase II drug-metabolizing enzymes, DT-diaphorase, glutathione S-transferase activities towards 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene, and UDP-glucuronyltransferase activities towards 4-nitrophenol and 7-hydroxycoumarin. The results indicate that tetrachloroethylene induces both Phase I (CYP2B-mediated monooxygenase) and Phase II drug-metabolizing enzymes (DT-diaphorase, glutathione S-transferase and UDP-glucuronyltransferase) in the rat liver.

Microsomal metabolism of N, N-diethylacetamide and N, N-dimethylacetamide and their effects on drug-metabolizing enzymes of rat liver

This study was undertaken to investigate: (1) the effect of N, N-diethylacetamide (DEAC) and N, N-dimethylacetamide (DMAC) administration to rats on drug-metabolizing enzymes in the liver; (2) the in vitro dealkylation of DEAC and DMAC by hepatic microsomes from rats treated with various P450 inducers and purified P450 (2B1 and 2E1). DEAC administration at doses of 100–300 mg/kg i.p. for 3 days mostly induced P450 2B1/2-associated hepatic microsomal monooxygenase activities (pentoxyresorufin O-depenthylase and the 16 β-testosterone hydroxylase) and its own dealkylation (DEAC deethylase activity). P4502E1-linked monooxygenase activities, such as aniline and p-nitrophenol hydroxylases, were not affected. DEAC treatment increased the amount of P4502B1/2 in microsomes in a dose-dependent manner, but depressed the amount of P-4502C11 as assayed by western blotting. DMAC treatment did not alter any microsomal monooxygenases or phase II enzymatic activity. The oxidative metabolism of DEAC and DMAC with control and induced microsomes resulted in the dealkylation of these solvents, giving rise to acetaldehyde and formaldehyde, respectively. The kinetic parameters for these N-dealkylations were investigated. It was found that phenobarbital-, dexamethasone- and DEAC-induced microsomes deethylated DEAC with a V max ∼3-fold of control-, ethanol- or β-naphtoflavone-induced microsomes, although with a similar affinity; ethanol- or acetone- induced microsomes demethylated DMAC with a V max higher than that of control microsomes. In a reconstituted system, the purified P4502B1 dealkylated DEAC, but not DMAC, at the rate of 6.2 nmol/min/nmol P450, whereas purified P4502E1 dealkylated DMAC, but not DEAC, at the rate of 7.9 nmol/min/nmol P450. Oxidation of DEAC and DMAC were markedly inhibited in microsomes from DEAC-treated rats by anti-P4502B1 IgG and in microsomes from acetone-treated rats by anti-P4502El IgG, respectively. These results indicate that DMAC and DEAC are predominantly oxidated by different P450 isozymes and that only DEAC, when administered to rat, is capable of altering the expression of the hepatic P450 system. This latter feature could be related to the higher toxicity reported for DEAC.

Induction of cytochrome P450 1A2 by musk analogues and other inducing agents in rat liver

We characterized the inducing effects of two musk analogues, musk xylene and musk ambrette, on phase I and phase II drug-metabolizing enzymes in rat liver and compared their effects with 3-methylcholanthrene, isosafrole and 2(3)-tert-butylhydroxyanisole (BHA) at 0.1 mmol/kg dose level. Musk xylene and isosafrole increased more efficiently the metabolic activation of 2-amino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole (Glu-P-1) to mutagen than that of benzo(a)pyrene. Musk ambrette increased both the activation of Glu-P-1 and benzo(a)pyrene to the same extent. Western blot analyses revealed that musk xylene, musk ambrette, isosfrole and BHA induced more stronly cytochrome P450 1A2 (CYP1A2) in microsomes than CYP1A1. 3-Methylcholanthrene induced CYP1A1 in preference to CYP1A2. On the other hand, all drugs except for 3-methylcholanthrene did not show remarkable increases in phase II enzyme activities, such as DT-diaphorase, glutathione S-transferase and UDP-glucuronyltransferase, at 0.1 mmol/kg dose level. These results show that musk xylene, musk ambrette, isosafrole and BHA at the dose level used in this study posses the potency to induce CYP1A2 without remarkable induction of CYP1A1 and phase II enzyme activities as observed for 3-methylcholanthrene, although they have been considered to induce both phase I and phase II drug-metabolizing enzymes at higher doses.

An unusual profile of musk xylene-induced drug-metabolizing enzymes in rat liver

We have demonstrated previously that musk xylene, a non-mutagenic carcinogen, is a novel and specific inducer of CYP1A2 in rats (Iwata et al., Biochem Biophys Res Commun 184: 149–153, 1992). In the present study, the effects of musk xylene (50, 100 or 200 mg/kg body weight, i.p., for 5 consecutive days) on both Phase I and Phase II metabolizing enzymes in rat liver were investigated further and more completely. Among the mixed-function oxidases monitored, 7-ethoxycoumarin deethylase and 7-pentoxyresorufin depentylase activities were increased at all dose levels from 1.6- to 1.7-fold and 2.6- to 3.1-fold, respectively. Benzo[a]pyrene hydroxylase activity was increased significantly at only the 200 mg/kg dose level of musk xylene (1.5-fold). Regarding Phase II enzymes, activities of both cytosolic DT-diaphorase and glutathione S-transferase (GST) were increased up to 2.0- to 2.4-fold by musk xylene in a dose-dependent manner. Western blot analysis revealed that the changes in these activities were caused by increases in the amounts of DT-diaphorase and GST Ya subunit. Microsomal UDP-glucuronyltransferase (UDPGT) activity assayed with p-nitrophenol as substrate was increased 1.6- to 2.0-fold. These results show that musk xylene induces both Phase I cytochrome P450 mixed-function oxidase (CYP1A2 specific) and Phase II metabolizing enzyme systems (DT-diaphorase, GST Ya subunit and UDPGT) in rat liver.

Induction potential of fluconazole toward drug-metabolizing enzymes in rats

The induction of drug-metabolizing enzymes in rat liver was studied after subchronic administration of the new triazole antifungal agent fluconazole. The administered doses were 10, 40, and 160 mg/kg per day for 7 days. Fluconazole behaved as a high-magnitude inducer and significantly increased cytochrome P-450 concentrations already at 10 mg/kg (+42%). Cytochrome P-450 induction by fluconazole was dose dependent and reached a value of 302% of the control value at the dose of 160 mg/kg. The induction effects on cytochrome P-450 were also reflected in the drug-metabolizing enzyme activities in hepatic microsomes of pretreated rats. Fluconazole (160 mg/kg per day) preferentially induced the demethylase activities of N,N-dimethylaniline and p-nitroanisole to 258 and 281% of the control values, respectively. The detoxification enzyme UDP-glucuronosyltransferase was significantly lowered by fluconazole at the highest dose. A possible link between the induction potential and the pharmacokinetic properties of triazole antifungal agents is discussed.

Effects of Capsaicin on Drug-Metabolizing Enzymes in Rat Liver

The effects of capsaicin on the drug-metabolizing systems were investigated in rat liver. Capsaicin (50mg/kg b. w., p. o.) produced no alteration of the appearance and body weight for a period of 14 days. The sleeping time induced by pentobarbital (50mg/kg b. w., i. p.), which is an index of the mixed function oxidase system activity, was prolonged in the rats given capsaicin. However, the cytochrome P-450 content and aniline hydroxylase and aminopyrine demethylase in vitro activities were almost unchanged in the rats treated with capsaicin. On the other hand, the activities of conjugation enzymes, UDP-glucuronyltransferase and glutathione S-transferase, were significantly reduced by the capsaicin treatment.These results suggest that capsaicin can increase the toxicity of many xenobiotics by decreasing both phase I and II reactions in drug metabolism.