Hepatic Microsomal Cytochrome P-450 Content Research Articles

Mode of action analysis for fluxapyroxad-induced rat liver tumour formation: evidence for activation of the constitutive androstane receptor and assessment of human relevance

The fungicide fluxapyroxad (BAS 700 F) has been shown to significantly increase the incidence of liver tumours in male Wistar rats at dietary levels of 1500 and 3000 ppm and in female rats at a dietary level of 3000 ppm via a non-genotoxic mechanism. In order to elucidate the mode of action (MOA) for fluxapyroxad-induced rat liver tumour formation a series of in vivo and in vitro investigative studies were undertaken. The treatment of male and female Wistar rats with diets containing 0 (control), 50, 250, 1500 and 3000 ppm fluxapyroxad for 1, 3, 7 and 14 days resulted in a dose-dependent increases in relative weight at 1500 and 3000 ppm from day 3 onwards in both sexes, with an increase in relative liver weight being also observed in male rats given 250 ppm fluxapyroxad for 14 days. Examination of liver sections revealed a centrilobular hepatocyte hypertrophy in some fluxapyroxad treated male and female rats. Hepatocyte replicative DNA synthesis (RDS) was significantly increased in male rats given 1500 and 3000 ppm fluxapyroxad for 3 and 7 days and in female rats given 50–3000 ppm fluxapyroxad for 7 days and 250–3000 ppm fluxapyroxad for 3 and 14 days; the maximal increases in RDS in both sexes being observed after 7 days treatment. The treatment of male and female Wistar rats with 250–3000 ppm fluxapyroxad for 14 days resulted in significant increases in hepatic microsomal total cytochrome P450 (CYP) content and CYP2B subfamily-dependent enzyme activities. Male Wistar rat hepatocytes were treated with control medium and medium containing 1–100 μM fluxapyroxad or 500 μM sodium phenobarbital (NaPB) for 4 days. Treatment with fluxapyroxad and NaPB increased CYP2B and CYP3A enzyme activities and mRNA levels but had little effect on markers of CYP1A and CYP4A subfamily enzymes and of the peroxisomal fatty acid β-oxidation cycle. Hepatocyte RDS was significantly increased by treatment with fluxapyroxad, NaPB and 25 ng/ml epidermal growth factor (EGF). The treatment of hepatocytes from two male human donors with 1–100 μM fluxapyroxad or 500 μM NaPB for 4 days resulted in some increases in CYP2B and CYP3A enzyme activities and CYP mRNA levels but had no effect on hepatocyte RDS, whereas treatment with EGF resulted in significant increase in RDS in both human hepatocyte preparations. Hepatocytes from male Sprague-Dawley wild type (WT) and constitutive androstane receptor (CAR) knockout (CAR KO) rats were treated with control medium and medium containing 1–16 μM fluxapyroxad or 500 μM NaPB for 4 days. While both fluxapyroxad and NaPB increased CYP2B enzyme activities and mRNA levels in WT hepatocytes, only minor effects were observed in CAR KO rat hepatocytes. Treatment with both fluxapyroxad and NaPB only increased RDS in WT and not in CAR KO rat hepatocytes, whereas treatment with EGF increased RDS in both WT and CAR KO rat hepatocytes. In conclusion, a series of in vivo and in vitro investigative studies have demonstrated that fluxapyroxad is a CAR activator in rat liver, with similar properties to the prototypical CAR activator phenobarbital. A robust MOA for fluxapyroxad-induced rat liver tumour formation has been established. Based on the lack of effect of fluxapyroxad on RDS in human hepatocytes, it is considered that the MOA for fluxapyroxad-induced liver tumour formation is qualitatively not plausible for humans.

Piperonyl butoxide: Mode of action analysis for mouse liver tumour formation and human relevance

In a 79 week bioassay the pesticide synergist piperonyl butoxide (PBO) was shown to significantly increase the incidence of hepatocellular adenoma (but not hepatocellular carcinoma) in male CD-1 mice at dietary levels of 100 and 300 mg/kg/day PBO and in female mice at a dietary level of 300 mg/kg/day. As PBO is not a genotoxic agent, a series of investigative studies were undertaken to elucidate the mode of action (MOA) for PBO-induced mouse liver tumour formation. Male CD-1 mice were fed diets to provide intakes of 0 (control), 30, 100 and 300 mg/kg/day PBO and for purposes of comparison 500 ppm sodium phenobarbital (NaPB), a known constitutive androstane receptor (CAR) activator, for 7 and 14 days. Treatment with 100 and 300 mg/kg/day PBO and 500 ppm NaPB increased relative liver weight which was associated with hepatocyte hypertrophy, with hepatocyte replicative DNA synthesis (RDS) being increased after 7 days treatment. The treatment of CD-1 mice with 30−300 mg/kg/day PBO for 14 days resulted in significant dose-dependent increases in hepatic microsomal cytochrome P450 (CYP) content and 7-pentoxyresorufin O-depentylase (PROD) activity and in hepatic Cyp2b10 mRNA levels. In contrast, PBO produced a biphasic effect on markers of activation of the peroxisome proliferator-activated receptor alpha (PPARα), with small increases in microsomal lauric acid 12-hydroxylase activity and hepatic Cyp4a10 mRNA levels being observed in mice given 100 mg/kg/day with PBO, with either no increase or a significant inhibition being observed in mice given 300 mg/kg/day PBO. The hepatic effects of PBO in male CD-1 mice were generally similar to those produced by NaPB and were reversible after the cessation of treatment for 28 days. Studies were also performed in male C57BL/6J (wild type) mice and in hepatic CAR and pregnane X receptor (PXR) knockout mice (CAR KO/PXR KO mice), where in the CAR KO/PXR KO mice PBO had little effect on markers of CAR activation, but produced some increases in markers of PPARα activation. The treatment of male CD-1 mouse hepatocytes for 4 days with 5−50 μM PBO, 10−1000 μM NaPB and 25 ng/mL epidermal growth factor (EGF) resulted in significant increases in hepatocyte RDS. While treatment of hepatocytes from one male and one female human donor with 5−500 μM PBO and 10−1000 μM NaPB for 4 days had no effect on hepatocyte RDS, treatment with EGF resulted in significant increases in RDS in both human hepatocyte preparations. In summary, PBO is predominantly a hepatic CAR activator at carcinogenic dose levels in CD-1 mice, with activation of hepatic CAR resulting in a suppression of the effect of PBO on hepatic PPARα. A robust MOA for PBO-induced mouse liver tumour formation has been established, this MOA being similar to that previously identified for NaPB and some other rodent liver CAR activators. Based on the lack of effect of PBO on RDS in human hepatocytes, it is considered that the MOA for PBO-induced mouse liver tumour formation is qualitatively not plausible for humans.

Metazachlor: Mode of action analysis for rat liver tumour formation and human relevance

In a 2-year study the herbicide metazachlor (BAS 479H) was shown to significantly increase the incidence of liver tumours in female Wistar rats at a dietary level of 8000 ppm. As metazachlor is not a genotoxic agent, a series of in vivo and in vitro investigative studies were undertaken to elucidate the mode of action (MOA) for metazachlor-induced female rat liver tumour formation. Male and female Wistar rats were given diets containing 0 (control), 200 and 8000 ppm metazachlor for 3, 7, 14 and 28 days. The treatment of male rats with 200 and 8000 ppm metazachlor and female rats with 8000 ppm metazachlor resulted in significant increases in relative liver weight, which was associated with a centrilobular hepatocyte hypertrophy. Hepatocyte replicative DNA synthesis (RDS) was significantly increased in male rats given 8000 ppm metazachlor for 3 and 7 days and in female rats given 200 ppm metazachlor for 7–28 days and 8000 ppm metazachlor for 3–28 days. Significant increases in relative liver weight, centrilobular hepatocyte hypertrophy and hepatocyte RDS were also observed in male and female Wistar rats given and 500 ppm sodium phenobarbital (NaPB) for 3–28 days. The treatment of female Wistar rats with either 8000 ppm metazachlor for 7 days or with 500 ppm NaPB for 3 and 7 days resulted in the nuclear translocation of the hepatic constitutive androstane receptor (CAR). Treatment of male and female Wistar rats with 8000 ppm metazachlor for 14 days resulted in significant increases in hepatic microsomal total cytochrome P450 (CYP) content, CYP2B subfamily-dependent enzyme activities and mRNA levels, together with some increases in CYP3A enzyme activity and mRNA levels. The treatment of male Wistar rat hepatocytes with metazachlor (concentration range 0.5–50 μM) and NaPB (500 μM) for 4 days resulted in increased CYP2B enzyme activities and mRNA levels; with metazachlor and NaPB also producing significant increases in hepatocyte RDS levels. Studies were also performed with hepatocytes from male Sprague-Dawley wild type (WT) rats and CAR knockout (CAR KO) rats. While both treatment with metazachlor and NaPB for 4 days increased CYP2B enzyme activities and mRNA levels in WT rat hepatocytes, only minor effects were observed in CAR KO rat hepatocytes. Treatment with both metazachlor and NaPB only increased RDS in WT but not in CAR KO rat hepatocytes. The treatment of hepatocytes from two male human donors with 0.5–25 μM metazachlor or 500 μM NaPB for 4 days resulted in increases in CYP2B6 and CYP3A4 mRNA levels but had no effect on hepatocyte RDS. EGF as concurrently used positive control demonstrated the expected RDS response in all rat and human hepatocyte cultures. In conclusion, a series of in vivo and in vitro investigative studies have demonstrated that metazachlor is a CAR activator in rat liver, with similar properties to the prototypical CAR activator phenobarbital. A robust MOA for metazachlor-induced female rat liver tumour formation has been established. Based on the lack of effect of metazachlor on RDS in human hepatocytes, it is considered that the MOA for metazachlor-induced rat liver tumour formation is qualitatively not plausible for humans.

Role of Kupffer cells in ischemic injury in alcoholic fatty liver

BackgroundThis study was designed to evaluate the role of Kupffer cells (KCs) in hepatic drug metabolizing dysfunction after hepatic ischemia–reperfusion (IR) in alcoholic fatty liver. Materials and methodsRats were fed the Lieber-DeCarli diet for 5 wk to develop alcoholic fatty liver, then were subjected to 90 min of hepatic ischemia and 5 h of reperfusion. For ablation of KCs, rats were pretreated with gadolinium chloride (GdCl3) 48 and 24 h before the IR procedure. ResultsAfter the IR procedure, ethanol diet (ED)-fed rats had higher serum aminotransferase activity compared with the control diet-fed rats. These changes were attenuated by GdCl3. The ED-fed rats exhibited increased hepatic microsomal total cytochrome P450 (CYP) content and nicotinamide adenine dinucleotide phosphate-CYP reductase and CYP1A1, 1A2, 2B1, and 2E1 isozyme activity. After hepatic IR, these increases were reduced to lower levels than observed in the sham group, except CYP2E1 activity. Increases in CYP2E1 activity and its expression were augmented after hepatic IR in ED-fed animals, but were attenuated by GdCl3. Finally, toll-like receptor 4 and myeloid differentiation primary response gene 88 protein expression, nuclear translocation of nuclear factor-κB and activator protein 1, and levels of proinflammatory mediators were further increased in ED-fed animals compared with control diet-fed animals after IR. These increases were attenuated by GdCl3. ConclusionsWe suggest that KCs contribute to hepatic drug metabolizing dysfunction during hepatic IR in alcoholic fatty liver via the toll-like receptors 4-mediated inflammatory response.

Sex-related differences in rat liver microsomal enzymes and their induction by doxapram.

The effects of doxapram on the hepatic microsomal mono-oxygenase system of male and female rats were investigated. Male and female rats were administered doxapram (10-120 mg kg-1 day-1, i.p.) for 4 days. In female rats, administration of doxapram (20, 40, 60, 80, 100 and 120 mg kg-1) elevated the parameters in a dose-dependent manner while doxapram (100 and 120 mg kg-1) elevated the levels of cytochrome P450 and hexobarbitone hydroxylase in male rats. Doxapram (40 mg kg-1) caused induction of hepatic drug metabolism typified by an increase of hepatic microsomal cytochrome P450 content and activities of hexobarbitone hydroxylase, benzphetamine N-demethylase and ethylmorphine N-demethylase in female rats, but no change in male rats. These findings were supported by the results of SDS/polyacrylamide-gel electrophoresis. However, 7-ethoxycoumarin O-de-ethylase and arylhydrocarbon hydroxylase activities were significantly increased in male rats. NADPH-cytochrome c reductase and NADH-cytochrome c reductase activities, and cytochrome b5 content were unaffected in rats of both sexes. The sex-dependent cytochrome P450 species may be selectively sensitive to the action of doxapram.

The Effect of Fever on Quinine and Quinidine Disposition in the Rat

The pharmacokinetics of quinine and its diastereoisomer quinidine has been investigated in normal and febrile rats. Endotoxin-induced fever in rats resulted in an increased quinine clearance (CL) (4.49 +/- 1.45 vs 1.38 +/- 0.65 L h-1 kg-1, P less than 0.001) and volume of distribution (Vd) (42.6 +/- 8.8 vs 28.9 +/- 10.3 L kg-1, P less than 0.05) with a concomitant shortening of the elimination half-life (t1/2) (7.1 +/- 2.5 vs 15.9 +/- 5.9 h, P less than 0.01). With quinidine, however, fever resulted in an increased CL (3.95 +/- 1.05 vs 1.89 +/- 0.60 L h-1 kg-1, P less than 0.002) with no change in Vd and a significant decrease in t1/2 (5.1 +/- 0.7 vs 10.1 +/- 2.8 h, P less than 0.001). In both studies there was no significant difference in hepatic microsomal protein or cytochrome P450 content. Neither drug accumulated in the liver but low concentrations of quinidine were present in the heart 24 h after administration. In-vitro studies suggest that temperature does not alter the binding of either drug. These data suggest that fever enhances the clearance of quinine and quinidine. These findings may offer some additional explanation of the lack of serious quinine and quinidine toxicity during the treatment of malaria infection, even after large dosages of the drug administered during the initial period of treatment when fever is most intense.

Impairment of drug metabolism by the liver in experimental fascioliasis in the rat.

Fascioliasis has been produced in the rat by an oral administration of 20 metacercariae of Fasciola hepatica. Hepatic microsomal cytochrome P450 and b5 contents and both aminopyrine demethylase and aniline hydroxylase activities have been measured during the course of the experimental distomiasis. The cytochrome P450 concentration and microsomal drug metabolizing enzymes generally fell by weeks 3 to 8 post-infestation and recovered to normal values thereafter. For the same period, both the histoenzymatically assayed liver cytochrome oxidase and arylsulphatase activities were reduced whereas there were correlated increases in glutamic pyruvic and glutamic oxaloacetic plasma transaminases. Tissue inflammation and destruction provoked by young histophagous migrating flukes could be responsible for these changes that have already been observed in several hepatic diseases. The possible influence of naturally-induced fasciolasis on liver drug metabolism is discussed.

Mode of Action Analysis for the Synthetic Pyrethroid Metofluthrin-Induced Rat Liver Tumors: Evidence for Hepatic CYP2B Induction and Hepatocyte Proliferation

Two-year treatment with high doses of Metofluthrin produced hepatocellular tumors in both sexes of Wistar rats. To understand the mode of action (MOA) by which the tumors are produced, a series of studies examined the effects of Metofluthrin on hepatic microsomal cytochrome P450 (CYP) content, hepatocellular proliferation, hepatic gap junctional intercellular communication (GJIC), oxidative stress and apoptosis was conducted after one or two weeks of treatment. The global gene expression profile indicated that most genes with upregulated expression with Metofluthrin were metabolic enzymes that were also upregulated with phenobarbital. Metofluthrin induced CYP2B and increased liver weights associated with centrilobular hepatocyte hypertrophy (increased smooth endoplasmic reticulum [SER]), and induction of increased hepatocellular DNA replication. CYP2B1 mRNA induction by Metofluthrin was not observed in CAR knockdown rat hepatocytes using the RNA interference technique, demonstrating that Metofluthrin induces CYP2B1 through CAR activation. Metofluthrin also suppressed hepatic GJIC and induced oxidative stress and increased antioxidant enzymes, but showed no alteration in apoptosis. The above parameters related to the key events in Metofluthrin-induced liver tumors were observed at or below tumorigenic dose levels. All of these effects were reversible upon cessation of treatment. Metofluthrin did not cause cytotoxicity or peroxisome proliferation. Thus, it is highly likely that the MOA for Metofluthrin-induced liver tumors in rats is through CYP induction and increased hepatocyte proliferation, similar to that seen for phenobarbital. Based on analysis with the International Life Sciences Institute/Risk Science Institute MOA framework, it is reasonable to conclude that Metofluthrin will not have any hepatocarcinogenic activity in humans, at least at expected levels of exposure.

A mode of action for induction of liver tumors by Pyrethrins in the rat

High doses of Pyrethrins produce liver tumors in female rats. To elucidate the mode of action for tumor formation, the hepatic effects of Pyrethrins have been investigated. Male Sprague-Dawley CD rats were fed diets containing 0 (control) and 8000 ppm Pyrethrins and female rats' diets containing 0, 100, 3000 and 8000 ppm Pyrethrins for periods of 7, 14 and 42 days and 42 days followed by 42 days of reversal. As a positive control, rats were also fed diets containing 1200-1558 ppm sodium Phenobarbital (NaPB) for 7 and 14 days. The treatment of male rats with 8000 ppm Pyrethrins, female rats with 3000 and 8000 ppm Pyrethrins and both sexes with NaPB resulted in increased liver weights, which were associated with hepatocyte hypertrophy. Hepatocyte replicative DNA synthesis was also increased by treatment with Pyrethrins and NaPB. The treatment of male and female rats with Pyrethrins and NaPB produced significant increases in hepatic microsomal cytochrome P450 (CYP) content and a marked induction of CYP2B-dependent 7-pentoxyresorufin O-depentylase and testosterone 16beta-hydroxylase activities. Significant increases were also observed in CYP3A-dependent testosterone 6beta-hydroxylase activity. The hepatic effects of Pyrethrins were dose-dependent in female rats with 100 ppm being a no effect level and on cessation of treatment were reversible in both sexes. This study demonstrates that Pyrethrins are mitogenic CYP2B form inducers in rat liver. The mode of action for Pyrethrins-induced rat liver tumor formation appears to be similar to that of NaPB and some other non-genotoxic CYP2B inducers of hepatic xenobiotic metabolism.

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.

The contribution of 2,3,5-trichlorophenyl methyl sulfone, a metabolite of 1,2,4-trichlorobenzene, to the δ-aminolevulinic acid synthetase induction by 1,2,4-trichlorobenzene in rat liver

In the present study, we investigated the contribution of methylsulfonyl metabolite derived from 1,2,4-trichlorobenzene (1,2,4-TCB) on the δ-aminolevulinic acid (ALA) synthetase induction by the parent compound in rats. The time courses of increasing of hepatic microsomal total cytochrome P450 content after a single ip administration of 1,2,4-TCB (1.36 mmol/kg), and 2,3,5- and 2,4,5-trichlorophenyl methyl sulfones (2,3,5- and 2,4,5-TCPSO 2Mes) (50 μmol/kg each) were in parallel with those of increasing of the total heme content in liver microsomes. 1,2,4-TCB significantly increased the heme oxygenase activity, but 2,3,5- and 2,4,5-TCPSO 2Mes did not. On the other hand, 1,2,4-TCB and 2,3,5-TCPSO 2Me markedly enhanced the ALA synthetase activity. No change was observed in this enzyme activity after the administration of 2,4,5-TCPSO 2Me. After the administration of 1,2,4-TCB to the rats treated with dl-buthionine-( S, R)-sulfoximine (BSO) and to the non-BSO-treated rats, the concentrations of both 2,3,5- and 2,4,5-TCPSO 2Mes were significantly lower in liver of the BSO-treated rats than in liver of the non-BSO-treated rats. Additionally, the 1,2,4-TCB did not elevate the ALA synthetase activity in the BSO-treated rats. On the other hand, the administration of 2,3,5-TCPSO 2Me to BSO-treated rats resulted in induction of ALA synthetase. The results strongly suggest that the methyl sulfone derived from 1,2,4-TCB, i.e., 2,3,5-TCPSO 2Me, contributes highly to the induction of the ALA synthetase activity by the parent compound.

Effect of Oxidized Frying Oil and Vitamin C Levels on the Hepatic Xenobiotic-Metabolizing Enzyme System of Guinea Pigs.

The influence of oxidized frying oil (OFO) on the guinea pig hepatic microsomal xenobiotic-metabolizing enzyme system in the presence of different amounts dietary vitamin C was investigated. Weanling male guinea pigs were divided into four groups and were fed 15% oxidized frying oil diets supplemented with vitamin C at 300, 600, or 1,500 mg/kg (experimental diets) or a control diet that contained 15% fresh untreated soybean oil with 300 mg/kg of vitamin C, respectively. After 60 d, guinea pigs were euthanized and phase I and phase II xenobiotic-metabolizing enzymes in the liver were determined. Compared with the fresh oil diet fed the control group, the relative liver weight was higher in the OFO-fed groups. Hepatic microsomal protein and cytochrome P450 contents were significantly higher in OFO-fed guinea pigs than in the control group. Both values increased in response to increased intake of vitamin C. The activities of phase II relative components, including UDP-glucuronyl transferase, UDP-glucuronyl dehydrogenase and beta-glucuronidase, of guinea pigs fed the OFO diets supplemented with 300 mg vitamin C/kg were significantly higher than those of guinea pigs fed the control diet. However, the phase II relative components decreased with increasing vitamin C content in the diet. The results demonstrate that both dietary OFO and vitamin C in guinea pigs induce hepatic xenobiotic-metabolizing enzymes, but the level of induction is modulated by the dietary vitamin C level.

High induction of cytochrome p4501a activity without changes in retinoid and thyroid hormone levels in flounder (Platichthys flesus) exposed to 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin

AbstractOal dosesof 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) were administered twice within 7 d (total concentration 0.01, 0.1, 1, 10, or 100 μg TCDD/kg body weight) to flounder (Platichthys flesus). After 10 d of exposure, flounder were sacrificed, and the effects of TCDD exposure on hepatic microsomal total cytochrome P450 content, 7‐ethoxyresorufin‐O‐deethylase (EROD) activity, and glutathione‐S‐transferase activity were examined. In addition, plasma and hepatic retinoid and plasma thyroid hormone levels were analyzed. Overall a good correlation existed between the dose and liver concentrations of TCDD. However, only 0.75% of the total dose of TCDD was retained in the flounder liver. The TCDD caused a dose‐related, statistically significant induction of the hepatic microsomal total cytochrome P450 content (4.4‐fold; p < 0.001) and associated EROD activity (27‐fold; p < 0.001), without obvious changes in body weight, liver weight, and condition factor. Total glutathione‐S‐transferase activity was not induced in livers of flounder exposed to TCDD. No TCDD‐induced changes in liver retinoid, plasma retinol, and plasma thyroid hormone parameters were observed. These results indicate that the flounder is an aryl hydrocarbon (Ah) receptor‐responsive species with respect to CYP1A induction but not with respect to other mammalian Ah receptor‐associated responses.

Microsomal and Peroxisomal Fatty Acid Oxidation in Liver of Rats With Bile Duct Ligation and Two-Thirds Hepatectomy

Microsomal cytochrome P450 and peroxisomal activity were studied in liver of rats 7 days after two-thirds hepatectomy or bile duct ligation (BDL). Both surgical models decreased the hepatic microsomal cytochrome P450 content, but only cholestasis, produced by BDL, decreased the microsomal metabolism of lauric acid and aminopyrine, peroxisomal fatty acid β-oxidation and catalase activity. The microsomal and peroxisomal activities responded in a coordinate way to cholestasis and two-thirds hepatectomy. These results suggest a cause-effect relationship between the microsomal cytochrome P450 and peroxisomal activity.

Influence of amphotericin B treatment duration of hepatic microsomal enzyme function in rats.

The influence of amphotericin B on various cytochrome P450-dependent mixed-function oxidases, antipyrine clearance and glucose-6-phosphatase was investigated in rats treated daily with deoxycholate amphotericin B (3 mg/kg body weight, intravenously) either for 1 or 4 days. Enzyme activity was measured ex vivo in hepatic microsomes. Following amphotericin B plus deoxycholate application for day 1, ethoxycoumarin-O-deethylase activity decrease significantly whereas microsomal cytochrome P450 concentration, cytochrome c reductase activity, antipyrine clearance and glucose-6-phosphatase activity did not change significantly. In contrast, following application of amphotericin B plus deoxycholate for 4 days the cytochrome P450 concentration was reduced by 50% (p < 0.05) as well as ethoxycoumarin-O-deethylase activity, antipyrine clearance and glucose-6-phosphatase activity: ethoxycoumarin-O-deethylase 232 +/- 68 pmol/mg/min, control 442 +/- 99 pmol/mg/min (p < 0.01); antipyrine clearance 0.56 +/- 0.21 ml/min, control 0.96 +/- 0.18 ml/min (p < 0.01), and glucose-6-phosphatase 193 +/- 28 mU/mg, control 351 +/- 95 mU/mg (p < 0.05). Cytochrome c reductase activity did not decrease significantly. Besides an increase in cytochrome c reductase activity, sodium deoxycholate (a vehicle of amphotericin B) alone induced no significant changes. Microsomal protein related to liver wet weight was significantly reduced by 50% (p < 0.01) only in animals treated for 4 days with amphotericin B plus deoxycholate. The results show that a 1-day treatment of rats with amphotericin B decreases ethoxycoumarin-O-deethylase activity, whereas the hepatic microsomal cytochrome P450 content, cytochrome c reductase and glucose-6-phosphatase activity did not change. Amphotericin B given for 4 days significantly decreases hepatic microsomal enzyme function. The inhibitory effect of amphotericin B on hepatic cytochrome P450 may be due to inhibition of hepatic protein synthesis.

Effects of deltamethrin on hepatic microsomal cytochrome p450‐dependent monooxygenases in carp

Abstract The in vivo effects of sublethal concentrations of deltamethrin (DM), a pyrethroid insecticide, on the hepatic microsomal cytochrome P450 (Cyt P450) content and the Cyt P450‐dependent monooxygenase activities (para‐nitrophenetole‐O‐deethylase, pNPOD; aminopyrene‐N‐demethylase, APND; ethylmorphine‐N‐demethylase, EMND; 7‐ethoxycoumarin‐O‐deethylase, ECOD; and ethoxyresorufin‐O‐deethylase, EROD) were examined in adult carp (Cyprinus carpió L.). 0.2 μg/1 DM treatment resulted in significant increases in APND, EMND and ECOD activities, whereas 2 μg/1 DM resulted in significant inhibitions of all studied isoenzyme activities with the exceptions of pNPOD and APND after 72 h. EROD was the only enzyme for which a slight increase in activity was observed. On repeated treatment, Cyt P450 could not be detected after 48 h, but the Cyt P420 level increased. All tested isoenzyme activities were inhibited, with the exception ofthat of EROD, which was enhanced. All these changes in enzyme activities and Cyt P450 content demonstrate the effects of DM on fish. DM treatment at low concentration is presumed to cause induction of the Cyt P450‐dependent monooxygenases which may lead to faster metabolization of the insecticide. In contrast, DM at higher concentration strongly inhibited the activities of the studied enzymes. This finding may be due to the damaging effect of DM on the xenobiotic metabolizing enzyme systems offish.

P-785 - Temporal variation of hepatic microsomal cytochrome P-450 activities and contents in Long Evans rats.

P-785 - Temporal variation of hepatic microsomal cytochrome P-450 activities and contents in Long Evans rats.

Influence of long-term ethanol treatment on rat liver aniline and p-nitrophenol hydroxylation

The present study investigates the influence of long-term ethanol (EtOH) treatment of rats [10% (v/v) for 1, 4, 12, and 36 weeks] on hepatic microsomal cytochrome P450 (P450) content and liver aniline and p-nitrophenol hydroxylation. Total P450 per liver was stimulated after EtOH treatment for 1, 4, and 12 weeks. In the case of longer EtOH treatment no additional stimulation in P450 content was observed. Aniline and p-nitrophenol hydroxylase activity increased in direct relation with the duration of EtOH consumption. The stimulation of both enzymatic activities was different. In comparison to controls, in rats treated with 10% (v/v) EtOH for 1, 4, 12, and 36 weeks, an increase in nitrocatechol formation (1.1-, 1.2-, 2.2-, and 2.8-fold, respectively) was found. In contrast, no effect was observed on the metabolism of aniline after 1 and 4 weeks of EtOH consumption. Aniline hydroxylation increased after 12 and 36 weeks of EtOH treatment only. Addition of EtOH in vitro had an inhibitory effect on both aniline and p-nitrophenol hydroxylation. With liver microsomes from controls as well as EtOH-treated rats the inhibition of p-nitrophenol hydroxylation was competitive in nature ( K i = 5.6 mM and K i = 5.9 mM). In contrast, there was a competitive inhibition of aniline hydroxylation with liver microsomes from controls only. With microsomes from EtOH-treated rats a mixed inhibition was found.

Modulation of rat hepatic cytochrome P-450 activity by garlic organosulfur compounds.

Garlic organosulfur compounds exert chemopreventive effects at several organ sites in rodents after administration of chemical carcinogens, possibly by inhibiting carcinogen activation via cytochrome P-450-mediated oxidative metabolism. It has been suggested that the variability in potency of tumor inhibition by garlic sulfur compounds is due to structural differences, such as the number of allyl and sulfur groups. In this study, diallyl sulfide (DAS), diallyl disulfide (DADS), and allyl methyl sulfide (AMS) were administered to acetone-treated adult male Sprague-Dawley rats by gastric gavage at a dose of 1.75 mmol/kg in cottonseed oil. After 15 hours, hepatic microsomal cytochrome P-450 activity and content were examined. The activity of p-nitrophenol (pNP) hydroxylase (E.C. 1.14.13.29) was significantly decreased by all garlic compounds, whereas benzphetamine N-demethylase and ethoxyresorufin O-deethylase activities were not changed. The activity of pNP hydroxylase was decreased to 31%, 54%, and 65% of control activity, and immunodetectable CYP2E1 protein levels were decreased in a similar manner by DAS, DADS, and AMS, respectively. Additional acetone-treated rats were given 4-methyl pyrazole, a ligand specific for CYP2E1, intraperitoneally five hours after garlic compound administration. Ten hours later, pNP hydroxylase activity was decreased to 73%, 78%, and 67% of control levels by DAS, DADS, and AMS, respectively. Further studies are needed to determine whether the variable potency of inhibition of CYP2E1 enzyme activity is related to chemopreventive efficacy of garlic sulfur compounds.

Downregulation of male-specific cytochrome P450s 2C11 and 3A2 in bile duct–ligated male rats: Importance to reduced hepatic content of cytochrome P450 in cholestasis

The effects of bile duct ligation (BDL) on the activity and content of individual hepatic mixed-function oxidases (MFOs) was examined. Five days after BDL, hepatic microsomal total cytochrome P450 (CYP) content and NADPH-cytochrome P450-reductase (P450-reductase) activity were reduced to 56% and 57% of control, respectively. MFO activities attributable to the sexually undifferentiated CYPs 1A, 2A1, 2C6, and 2E1 were decreased to 32% to 52% of control, but the activities of two male sex-specific CYPs, 2C11 and 3A2, were reduced to a significantly greater extent (P < .05). The microsomal contents of CYP proteins 2C6 and 2E1 were decreased after BDL to 61% and 63% of control, whereas 2C11 and 3A2 proteins were 21% and 45% of control. Corresponding reductions of the messenger RNA (mRNA) species for CYP 2C11 (9% of control) and 3A2 (37%) were detected, whereas there was no reduction of 2C6 mRNA. These findings are consistent with downregulation of the CYP 2C11 and 3A2 genes. Nuclear run-on studies performed 3 days after BDL showed that there was a generalized impairment of gene transcription after BDL, but a disproportionate reduction in transcription of CYPs 2C11 and 3A2. A possible explanation for downregulation of CYP 2C11 and 3A2 was provided by the observation that serum estradiol concentrations were threefold greater in BDL male rats, while serum testosterone was reduced; estradiol is known to downregulate CYPs 2C11 and 3A2. It is concluded that male sex-specific CYP enzymes are decreased to a greater extent than other microsomal proteins in BDL male rats.(ABSTRACT TRUNCATED AT 250 WORDS)