Effect of high sucrose diet on liver enzyme content and activity and aflatoxin B1-induced mutagenesis

Aflatoxin B1 (AFB1) is a fungal toxin and contaminant that has been implicated in human liver carcinogenesis. In this study we evaluated the effect of a 65% of total calories from sucrose diet (HSD) for 90 days on hepatic cytochrome P450 (CYP450) and glutathione-S-transferase (GST) activity compared to rats maintained on standard lab chow (0% sucrose). There was a statistically significant increase in the number of S. typhimurium His+ revertants (p < 0.001) generated from the incubation of AFB1 with hepatic microsomes from rats fed a HSD. The HSD did not affect the total microsomal CYP450 content nor content of CYP450 1A2, 2B1, 2 isoforms which activate AFB1. Alkoxyresorufin O-dealkylase activity (MROD, PROD) of microsomes from animals fed HSD was decreased by 73% and 49%, respectively. MROD activity is linked to CYP 1A2 activity while PROD is linked to CYP 2B1,2 activity. Although the amount of CYP 3A was significantly decreased in rats fed a HSD, its activity, determined by the presence of the fluorometric metabolite 7-hydroxyquinidine, was unchanged. GST activity was significantly lower in the rats fed HSD.     

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 5 weeks. 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.     

Ginkgo biloba extract markedly induces pentoxyresorufin O-dealkylase activity in rats

We examined the effect of Ginkgo biloba extract (GBE) on hepatic drug-metabolizing enzymes, particularly cytochrome P450 (CYP), in rats. Rats were fed a GBE-containing diet or received GBE by intragastric gavage. The concentration of CYP and activity of various CYP enzymes in the liver were increased in a dose- and time-dependent manner. Significant increases in the concentration and activities of CYP enzymes were detected on day 1 of feeding of a 0.5% GBE diet and after administration of 10 mg GBE/kg body weight for 5 days by intragastric gavage. Among the CYP enzymes, the activity of pentoxyresorufin O-dealkylase (PROD), a CYP2B enzyme, was especially markedly increased. The induction of CYP2B enzyme by GBE was confirmed by Western blot analysis. Addition of GBE to a CYP assay system in vitro caused concentration-dependent inhibition of various CYP enzyme activities. The inhibition was more marked for the microsomal enzymes from GBE-treated rats than for those from control rats and more marked against PROD activity among the CYP enzymes tested. When the inhibition of various CYP enzymes activities by GBE in vitro was compared, no marked difference was observed between rat and human hepatic microsomal enzymes. These results indicate that excess intake of GBE induces CYP enzymes, particularly PROD, and may modify the efficacy of drugs taken simultaneously.     

Ethanol-a direct inducer of drug metabolism.

The inductive effects of chronic phenobarbital and ethanol ingestion on hepatic microsomal drug metabolism were examined in rats consuming different proportions of dietary fat. Eight groups of rats were fed for 1 week on matched amounts of nutritionally adequate liquid diets providing 2, 5, 10 or 41% of calories as fat (safflower oil), two groups at each level. One group at each level received phenobarbital (80 mg/kg daily by intubation), the other getting water. In a parallel experiment, one group at each fat level received 36% of calories as ethanol, the other as sucrose, and these regimens were continued for 1 month. Dietary fat content per se had no significant effect on body weight, liver weight, microsomal protein, cytochrome P-450 content, or hepatic triglycerides (TG) during the 1-week experiment, but significantly increased all these measures in the 1-month experiment. Both phenobarbital and ethanol treatment increased all these measures except body weight, but phenobarbital had a greater effect on liver weight, microsomal protein and cytochrome P-450, while ethanol had a greater effect on hepatic TG and a significant interaction with dietary fat content in relation to TG levels. In contrast, microsomal metabolism of aminopyrine, aniline and meprobamate in vitro was increased approximately equally by phenobarbital and ethanol, while dietary fat content had no effect alone, and no significant interaction with phenobarbital or ethanol. Ethanol, like phenobarbital, therefore, appears to induce microsomal drug metabolism independently of its effects on TG metabolism.     

Mechanism of induction of hepatic drug-metabolizing enzymes by ethanol—I: Limited role of microsomal phospholipids

Two groups of female Sprague-Dawley rats were pair-fed nutritionally adequate liquid diets containing 36 per cent of total calories as ethanol or additional carbohydrate (controls). One group was fed a high fat diet (35 per cent of total calories as fat); the other group was fed a low fat diet (2 per cent of total calories as linoleate as the only source of fat). When given with the high fat diet, ethanol increased cytochrome P-450 and microsomal phospholipid content per g of liver. When given with a low fat diet, it increased cytochrome P-450 to a lesser extent and did not alter the microsomal phospholipid content when expressed per g of liver or per 100 g of body weight. Phosphatidylcholine accounted for the greater porportion of phospholipids and was increased by ethanol only with the high fat diet. L-Methionine-methyl[³H] and [¹⁴C]choline incorporation into phosphatidylcholine was unaltered by ethanol in either model. The fatty acid composition of phosphatidylcholine was altered by ethanol more significantly with the high fat diet. Since ethanol similarly enhances the activity of benzphetamine demethylation in both dietary models, quantitative and qualitative differences in microsomal phospholipids produced by ethanol are probably not responsible for the induction by ethanol of this drug-metabolizing enzyme activity. Further evidence to that effect was obtained from the measurement of benzphetamine demethylation in vitro by partially purified cytochrome P-450, reductase and lipid fractions of ethanol-fed and control rats fed a high fat diet. The stimulation of benzphetamine demethylation by the lipid fraction was identical whether using lipids from microsomes of ethanol-fed animals or control animals. Dietary fat plays a role in the induction by ethanol of cytochrome P-450 and NADPH-cytochrome P-450 reductase and on microsomal phospholipid content and composition. The effects of ethanol on microsomal phospholipids are probably not related to the induction of benzphetamine demethylation activity.     

双环醇对肝脏部分切除大鼠CYP450酶活性和表达的影响(英文)

本研究考察双环醇对肝脏部分切除(PH)后大鼠肝脏微粒体细胞色素P450(CYP)活性、基因和蛋白表达的影响及相关机制。大鼠PH前灌胃给予双环醇(300 mg.kg-1)3次,PH后处死大鼠,取其血清和肝组织进行检测,依次测定血清谷丙转氨酶(ALT)、肝微粒体丙二醛(MDA)和肝脏总CYP含量、4种CYP同工酶活性、基因和蛋白表达。结果显示,双环醇可显著抑制PH大鼠血清ALT和肝微粒体MDA的升高,抑制肝脏总CYP含量的减少,抑制CYP2C6、2C11活性和mRNA表达的下降,明显抑制CYP3A1/2活性的下降,并上调CYP3A1和2E1的mRNA和蛋白表达。结果表明,双环醇对PH大鼠肝脏CYP450酶及部分同工酶活性和表达的改变有明显改善作用,其作用机制可能与其抗氧化作用和酶诱导作用密切相关。     

Effects of dietary pectin and cellulose on hepatic and intestinal mixed-function oxidations and hepatic 3-hydroxy-3-methylglutaryl-coenzyme a reductase in the rat

The aim of this study was to determine if feeding dietary fiber (cellulose or pectin) to male rats could influence hepatic and intestinal mixed-function oxidation. We simultaneously compared hepatic drug-oxidizing activity with the activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, the rate-controlling enzyme for cholesterol biosynthesis. Three groups of six animals were fed a purified diet containing by weight either 10.4% cellulose or 10.4% pectin, or a standard cereal-based diet containing 4.5% crude fiber; the caloric contributions by carbohydrate, protein and fat in the three diets were similar. In the cellulose-fed rats, the hepatic microsomal cytochrome P-450 content and the activities of ethylmorphine N-demethylase and aniline hydroxylase were significantly lower when compared with those of rats fed pectin or the cereal-based diet. The hepatic microsomal cytochrome P-450 content and the activities of ethylmorphine N-demethylase and aniline hydroxylase were similar in the pectin-fed and cereal diet-fed rats. Hepatic HMG-CoA reductase activity, hepatic microsomal cytochrome b₅ content, and intestinal benzo[a]pyrene hydroxylase activity were comparably lower in rats fed the purified diet with either dietary fiber when compared to those fed the cereal diet. It is concluded that dietary pectin and cellulose exert distinctly different influences on the hepatic microsomal mixed-function oxidase system for drug metabolism, but not on liver cholesterol synthesis or intestinal benzo[a]pyrene hydroxylation, suggesting that different physiological mechanisms control these enzyme systems.     

Role of human liver microsomal CYP3A4 and CYP2B6 in catalyzing N-dechloroethylation of cyclophosphamide and ifosfamide

The anticancer alkylating agents cyclophosphamide (CPA) and ifosfamide (IFA) are prodrugs that undergo extensive P450-catalyzed metabolism to yield both active (4-hydroxylated) and therapeutically inactive but neurotoxic (N-dechloroethylated) metabolites. Whereas the human liver microsomal P450 catalysts of CPA and IFA 4-hydroxylation are well characterized, the P450 enzyme catalysts of the alternative N-dechloroethylation pathway are poorly defined. Analysis of a panel of fifteen human P450 cDNAs in the baculovirus expression system ('Supersomes') demonstrated that CYP3A4 exhibited the highest N-dechloroethylation activity toward both CPA and IFA, whereas CYP2B6 displayed high N-dechloroethylation activity toward IFA, but not CPA. The contributions of each human P450 to overall liver microsomal N-dechloroethylation were calculated using a recently described relative substrate-activity factor method, and were found to be in excellent agreement with the results of inhibition studies using the CYP3A inhibitor troleandomycin and an inhibitory monoclonal antibody to CYP2B6. With CPA as substrate, CYP3A4 was shown to catalyze >/=95% of liver microsomal N-dechloroethylation, whereas with IFA as substrate, CYP3A4 catalyzed an average of approximately 70% of liver microsomal N-dechloroethylation (range = 40-90%), with the balance of this activity catalyzed by CYP2B6 (range = 10-70%, dependent on the CYP2B6 content of the liver). Because CYP2B6 can make a significant contribution to human liver microsomal IFA N-dechloroethylation, but only a minor contribution to IFA 4-hydroxylation, the selective inhibition of hepatic CYP2B6 activity in individuals with a high hepatic CYP2B6 content may provide a useful approach to minimize the formation of therapeutically inactive but toxic N-dechloroethylated IFA metabolites.     

Effects of dietary R-goitrin on hepatic and intestinal glutathione S-transferase, microsomal epoxide hydratase and ethoxycoumarin O-deethylase activities in the rat

The influence of dietary R-goitrin on components of the xenobiotic-metabolizing system was examined in the liver and small intestine of male Sprague-Dawley rats. Given at a level of 200 ppm in the diet for 14 days, the R-goitrin caused a statistically significant (P less than 0.05) 21% increase in liver weight relative to body weight. A less pronounced, but statistically significant, 11% increase in relative liver weight resulted from the administration of R-goitrin at 40 ppm in the diet. Hepatic glutathione S-transferase (GST) activity was significantly increased 1.5- and 2-fold over the basal level at concentrations of 40 and 200 ppm R-goitrin, respectively. Hepatic microsomal epoxide hydratase (EH) activity was also significantly increased. Hepatic EH activity was 1.6- and 3.3-fold greater in the 40- and 200-ppm R-goitrin groups, respectively, than in the control group given the basal diet. R-Goitrin at 200 ppm in the diet produced significant 1.2- and 1.4-fold increases of GST and microsomal EH activities, respectively, in the mucosa of the small intestine. The administration of R-goitrin at 40 or 200 ppm in the diet had no significant effect on either hepatic or intestinal ethoxycoumarin O-deethylase activity.     

Concurrent subacute exposure to arsenic through drinking water and malathion via diet in male rats: effects on hepatic drug-metabolizing enzymes

Arsenic is a known global groundwater contaminant, while malathion is one of the most widely used pesticides in agriculture and public health practices in the world. Here, we investigated whether repeated exposure to arsenic at the groundwater contamination levels and to malathion at sublethal levels exerts adverse effects on the hepatic drug-metabolizing system in rats, and whether concurrent exposure is more hazardous than the single agent. Male Wistar rats were exposed daily to 4 or 40 ppm of arsenic via drinking water, 50 or 500 ppm of malathion-mixed feed and in a similar fashion co-exposed to 4 ppm of arsenic and 50 ppm of malathion or 40 ppm of arsenic and 500 ppm of malathion for 28 days. At term, toxicity was assessed by evaluating changes in body weight, liver weight, levels of cytochrome P(450) (CYP), cytochrome b (5) and microsomal and cytosolic proteins, and activities of aminopyrine-N-demethylase (ANDM), aniline-P-hydroxylase (APH), glutathione-S-transferase (GST) and uridine diphosphate glucuronosyltransferase (UGT) in liver. Arsenic and malathion alone did not alter body weight and liver weight, but these were significantly decreased in both the co-exposed groups. These treatments decreased the activities of ANDM and APH and the levels of liver microsomal and cytosolic proteins, increased GST activity and had no effect on UGT activity. The effects of exposure to low-dose and high-dose combinations on the activities of either phase I or phase II drug-metabolizing enzymes and protein content were mostly similar to that produced by the respective low and high dose of either arsenic or malathion, except APH activity. The effect of arsenic (40 ppm) on APH activity was partially, but significantly, inhibited by malathion (500 ppm). Results indicate that the body or liver weights and the biochemical parameters were differentially affected in male rats following concurrent subacute exposure to arsenic and malathion, with the co-exposure appearing more hazardous to physical variables based on body or liver weights whilst producing biochemical changes comparable to those caused by the individual agents. From these findings, no specific toxicological interaction between arsenic and malathion can be conclusively generalized.     

Mixed-function oxidase system induction and propylene hepatotoxicity

Propylene is hepatotoxic to male Charles River COBS Sprague-Dawley rats pretreated with polychlorinated biphenyls (PCB: Aroclor 1254). Four-hour inhalation exposure to 50,000 ppm propylene increased liver weight/body weight ratios and elevated serum enzyme activities in PCB-pretreated animals. Hepatic microsomal cytochrome P-450 content of PCB-pretreated rats dropped profoundly during propylene exposure and remained depressed for at least 24 h. In addition, PCB-pretreated, propylene-exposed rats exhibited a decrease in the specific activity of hepatic microsomal aniline hydroxylase. However, there was no change in activities of either hepatic microsomal aminopyrine demethylase or glucose-6-phosphatase. Propylene exposure of rats pretreated with beta-naphthoflavone (BNF), phenobarbital (PB), or a mixture of BNF and PB was not hepatotoxic. However, there was, in these animals, a substantial decline in hepatic microsomal cytochrome P-450 levels 24 h after the start of propylene exposure. Hence, the propylene-dependent process resulting in hepatic cytochrome P-450 destruction is qualitatively or quantitatively different from the process that causes acute hepatotoxicity. Preexposure fasting had no effect on the hepatotoxicity resulting from a 4-h exposure of PCB-pretreated rats to 50,000 ppm propylene. Administration of SKF-525A to PCB-pretreated rats immediately prior to propylene exposure completely prevented elevations in serum enzyme activities and liver weight/body weight ratios. In vitro incubation of hepatic microsomes prepared from either BNF-, PB-, or PCB-pretreated rats with an atmosphere of 20% propylene/80% air produced in NADPH-dependent decrease in cytochrome P-450 content. These results suggest that PCB pretreatment is a prerequisite for propylene hepatotoxicity in the rat. Cytochrome P-450-dependent bioactivation of propylene is associated with this hepatotoxicity, but further studies are needed to characterize the mechanism of the PCB-propylene interaction.     

Induction and recovery of hepatic drug metabolizing enzymes in rats treated with Ginkgo biloba extract.

Herb-drug interactions, especially cytochrome P450 (CYP)-mediated interactions, cause an enhancement or attenuation in efficacy of co-administered drugs. In a previous study, we reported that repeated oral ingestion of Ginkgo biloba extract (GBE) markedly induced hepatic drug metabolizing enzymes in rats. In this study, we focused on the recovery of GBE-induced hepatic drug metabolizing enzymes after the discontinuation of GBE in rats. Feeding of a 0.5% GBE diet to rats for 1 week markedly increased liver weight, content of total CYP, activities of 6 CYP subtypes and glutathione S-transferase (GST). The content and activities of CYP enzymes were recovered to almost basal levels within 1 week after the discontinuation of GBE, while the activity of GST gradually decreased and recovered to the control level after 3 weeks. These results indicated that GBE-induced hepatic drug metabolizing enzymes in rats, especially CYPs, were rapidly recovered by discontinuation of GBE in rats even after excess treatment, and suggested that interactions of GBE with drugs could be avoided by discontinuation of GBE.     

Lack of evidence for induction of CYP2B1, CYP3A23, and CYP1A2 gene expression by Panax ginseng and Panax quinquefolius extracts in adult rats and primary cultures of rat hepatocytes.

Treatment of rats with a single oral dose (10-30 mg/kg) of a crude Panax ginseng extract of unknown ginsenoside content has been reported to modestly increase hepatic microsomal cytochrome P450-mediated aminopyrine N-demethylation activity. In the present study, we compared the effect of P. ginseng and Panax quinquefolius extracts on rat hepatic CYP2B1, CYP3A23, and CYP1A2 gene expression. Adult male Sprague-Dawley rats (250-275 g) received, by oral gavage or i.p., P. ginseng extract [4% (w/w) total ginsenosides; 30 or 100 mg/kg/day for 1 or 4 days], P. quinquefolius extract [10% (w/w) total ginsenosides; 100 or 400 mg/kg/day for 21 consecutive days), or an equivalent volume (2 ml/kg) of the vehicle (0.9% NaCl or 0.3% carboxymethylcellulose) and were terminated 1 day after the last dose. P. ginseng and P. quinquefolius extracts did not affect body weight gain, absolute or relative liver weight, hepatic CYP2B1, CYP3A23, or CYP1A2 mRNA expression, or microsomal CYP2B-mediated 7-benzyloxyresorufin O-dealkylation (BROD) or CYP1A-mediated 7-ethoxyresorufin O-dealkylation (EROD) activity. In contrast, results from positive control experiments indicated that phenobarbital increased CYP2B1 mRNA and BROD activity, dexamethasone increased CYP3A23 mRNA, and beta-naphthoflavone increased CYP1A2 mRNA and EROD activity levels. Treatment of primary cultures of rat hepatocytes with either of the ginseng extracts (0.1-1000 microg/ml for 2 days) also did not affect CYP2B1 or CYP3A23 mRNA expression. Overall, our data indicate that P. ginseng and P. quinquefolius extracts do not increase rat hepatic CYP2B1, CYP3A23, or CYP1A2 gene expression.     

Cytochrome P4502E1 induction increases thioacetamide liver injury in diet-restricted rats.

Earlier studies have shown highly exaggerated mechanism-based liver injury of thioacetamide (TA) in rats following moderate diet restriction (DR) and in diabetes. The objective of the present study was to investigate the mechanism of higher liver injury of TA in DR rats. Since both DR and diabetes induce CYP2E1, we hypothesized that hepatic CYP2E1 plays a major role in the bioactivation-based liver injury of TA. When male Sprague-Dawley rats (250-275 g) were maintained on diet restriction (DR, 35% of ad libitum fed rats, 21 days) the total hepatic microsomal cytochrome P450 (CYP450) was increased 2-fold along with a 4.6-fold increase in CYP2E1 protein, which corresponded with a 3-fold increase in CYP2E1 activity as measured by chlorzoxazone hydroxylation. To further test the involvement of CYP2E1, 24 and 18 h after pretreatment with pyridine (PYR) and isoniazid (INZ), specific inducers of CYP2E1, male Sprague-Dawley rats received a single administration of 50 mg of TA/kg (i.p.). TA liver injury was >2.5- and >3-fold higher at 24 h in PYR + TA and INZ + TA groups, respectively, compared with the rats receiving TA alone. Pyridine pretreatment resulted in significantly increased total CYP450 content accompanied by a 2.2-fold increase in CYP2E1 protein and 2-fold increase in enzyme activity concordant with increased liver injury of TA, suggesting mechanism-based bioactivation of TA by CYP2E1. Hepatic injury of TA in DR rats pretreated with diallyl sulfide (DAS), a well known irreversible in vivo inhibitor of CYP2E1, was significantly decreased (60%) at 24 h. CCl(4) (4 ml/kg i.p.), a known substrate of CYP2E1, caused lower liver injury and higher animal survival confirming inhibition of CYP2E1 by DAS pretreatment. The role of flavin-containing monooxygenase (FMO) in TA bioactivation implicated by previous in vitro studies, and consequent increased TA-induced liver injury in DR rats was tested in vivo with a relatively selective inhibitor of FMO, indole-3-carbinol, and then treated with 50 mg of TA/kg. FMO activity and alanine aminotransferase levels measured at different time points revealed that TA liver injury was not decreased although FMO activity was significantly decreased, suggesting that hepatic FMO is unlikely to bioactivate TA. These findings suggest induction of CYP2E1 as the primary mechanism of increased bioactivation-based liver injury of TA in DR rats.     

Induction of P-glycoprotein, glutathione-S-transferase and cytochrome P450 in rat liver by atrazine

We studied the effects of intraperitoneally administered atrazine on two hepatic neoplastic markers, P-glycoprotein (P-gp), and glutathione-S-transferase (GST), and several phase I drug-metabolizing enzyme cytochrome P450 (CYP) subfamilies in hepatic microsomes and cytosol of Fischer rats. The P-gp content was increased after 24 h of atrazine administration at 50 mg/kg, and maximum P-gp induction was observed at 300 mg/kg for 3 days. GST-P was induced at a lower dose than P-gp, from 10 mg/kg, but no other form of GST, such as GST1A1, was induced by the same dose. Among the CYP families, CYP1A2 was highly and CYP2B was slightly induced by atrazine while the CYP3A content remained unchanged. The liver plasma membrane marker alkaline phosphatase (AP) was not induced by the same doses. The inductions of P-gp, GST-P and CYP1A2 observed may explain some of the reported tumor-promoting properties and toxicity of atrazine in vivo.     

Changes in hepatic phase I and phase II biotransformation enzyme expression and glutathione levels following atrazine exposure in female rats

1. To determine the effects of repeated atrazine (ATR) treatment on hepatic phase I and II enzymes, adult female rats were treated with vehicle or 100?mg/kg of ATR for 1, 2, 3 or 4 days. Glutathione-s-transferases (GST) mRNA expression, protein levels (mu, pi, alpha, omega), and activity (cytosolic and microsomal), along with bioavailable glutathione (GSH) were assayed.

2. GST expression, concentrations and activity were increased, along with GSH levels, in animals treated with ATR for 3 and 4 days.

3. A subsequent study was performed with animals treated with vehicle, 6.5, 50 or 100?mg/kg/day for 4, 8 or 14 days. Expression of hepatic phase I CYP 450 enzymes was evaluated in conjugation with GST expression, protein and activity. Nineteen of the 45 CYP enzymes assayed displayed increased mRNA levels after eight?days of treatment in animals treated with 50 or 100?mg/kg/day. After 14 days of treatment, all CYP expression levels returned to control levels except for CYP2B2, CYP2B3, CYP2C7, CYP2C23, CYP2E1, CYP3A9, CYP4A3 and CYP27A1, which remained elevated.

4. Results indicate that there may be a habituation or adaptation of liver phase I and phase II expression following repeated ATR treatment.     

Modulation of testosterone-metabolizing hepatic cytochrome P-450 enzymes in developing Sprague-Dawley rats following in utero exposure to p,p'-DDE.

1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) causes sexual developmental aberrations in male rats through a likely mechanism of androgen receptor antagonism. DDE is also known to induce liver cytochrome P-450 (CYP). The expression of CYP enzymes is regulated by steroid hormones, which, in turn, are inactivated in the liver by CYP-catalyzed hydroxylations and subsequent conjugations. This study was undertaken to examine the potential of in utero DDE exposure to affect the developmental expression of the hepatic CYP enzymes that are responsible for testosterone hydroxylations. Pregnant Sprague-Dawley rats were dosed daily by gavage with DDE at 0, 10, or 100 mg/kg body weight or with flutamide at 40 mg/kg body weight from gestation day 14 to 18. Additional adult male rats were given seven daily doses of DDE at 100 mg/kg. Liver samples were collected from the offspring of the dosed dams on postnatal days (PND) 10 and 21 and from the adult rats a day after the last dosing. Assays for regioselective and sterospecific testosterone hydroxylase activities were performed using hepatic microsomal preparations. Specific liver CYP proteins were detected by immunoblotting. While the CYP2B1 and 3A1 and their hydroxylated testosterone products were highly elevated by the DDE treatments in both adult and developing rats, the responses of 2C11 and 2A1 were development-dependent. The flutamide treatment had little effect on CYP enzyme expression. This study demonstrated that developing offspring rats are susceptible to the hepatic CYP enzyme-modulating action of DDE following its administration to the pregnant dams.     

In-vivo and in-vitro metabolic clearance of midazolam, a cytochrome P450 3A substrate, by the liver under normal and increased enzyme activity in rats.

The metabolic clearance of midazolam, a cytochrome P450 (CYP) 3A substrate, by the liver under normal and increased enzyme activity in rats was determined in-vivo and in-vitro to elucidate the reproducibility of the in-vivo hepatic extraction ratio of midazolam from the in-vitro study. The hepatic enzyme activity was modified by pretreating rats with a CYP inducer such as dexamethasone and clotrimazole. The in-vivo hepatic extraction ratio (ERh,obs) of midazolam under a steady-state plasma concentration (approx. 3 nmolmL(-1)) in untreated (control) rats was 0.864. This value increased to 0.984 in dexamethasone-pretreated rats and to 0.964 in clotrimazole-pretreated rats. The in-vitro hepatic intrinsic clearance (CL(int,in-vitro)), expressed as mLmin(-1) (mg microsomal protein)(-1), of midazolam was estimated as Vmax (Km)(-1) by in-vitro metabolism studies using liver microsomes. The CL(int,in-vitro) value was converted to the CL(int,cal) value, expressed as mLmin(-1)kg(-1), by considering the microsomal protein content (g liver)(-1) and the microsomal protein content (g liver)(-1)kg(-1). The estimated CL(int,cal) value was then converted to the ERh value (ER(h,cal)) according to the well-stirred, the parallel-tube and the dispersion models. The ERh(h,cal) values obtained by the parallel-tube model were in good agreement with corresponding in-vivo ERh(h,obs) values. In conclusion, it was demonstrated that high hepatic clearances of midazolam under normal and increased CYP3A activity were reasonably predicted from in-vitro metabolism studies using liver microsomes.     

Effect of commercially available green and black tea beverages on drug-metabolizing enzymes and oxidative stress in Wistar rats

The effect of commercially available green tea (GT) and black tea (BT) drinks on drugmetabolizing enzymes (DME) and oxidative stress in rats was investigated. Male Wistar rats were fed a laboratory chow diet and GT or BT drink for 5 weeks. Control rats received de-ionized water instead of the tea drinks. Rats received the GT and BT drinks treatment for 5 weeks showed a significant increase in hepatic microsomal cytochrome P450 (CYP) 1A1 and CYP1A2, and a significant decrease in CYP2C, CYP2E1 and CYP3A enzyme activities. Results of immunoblot analyses of enzyme protein contents showed the same trend with enzyme activity. Significant increase in UDP-glucuronosyltransferase activity and reduced glutathione content in liver and lungs were observed in rats treated with both tea drinks. A lower lipid peroxide level in lungs was observed in rats treated with GT drink. Electrophoretic mobility shift assay revealed that both tea drinks decreased pregnane X receptor binding to DNA and increased nuclear factor-erythroid 2 p45-related factor 2 binding to DNA. These results suggest that feeding of both tea drinks to rats modulated DME activities and reduced oxidative stress in liver and lungs. GT drink is more effective on reducing oxidative stress than BT drink.     

Subchronic toxicity of vomitoxin in Sprague-Dawley rats

Purified vomitoxin was incorporated into the diet at a level of 20 ppm and fed to male Sprague-Dawley rats ad lib. for 90 days. Few clinical signs of toxicity were observed. Rats in the vomitoxin treatment group were less efficient in converting feed into body mass, but there was no feed refusal. Terminal body weight was reduced in the vomitoxin treatment group. There were no statistically significant effects on serum enzyme levels, haematological parameters or tissue lesions, or on liver detoxification systems, as reflected in levels of microsomal cytochrome P-450 or in glutathione S-transferase activity.