Microsomal Cytochrome P-450 Content Research Articles

Characterization of cytochrome P450 dependent mixed-function oxidase system of gilthead seabream ( sparus aurata; sparidae) liver

1. 1. The average cytochrome P450 content of gilthead seabeam liver microsomes was found to be 0.078 ± 0.012 ( n = 4) nmol/mg protein, which was about 50%, 24% and 13% of that measured in trout, sturgeon and scup liver microsomes, respectively. 2. 2. Gilthead seabream liver microsomes contained a relatively higher amount of cytochrome b5, as 0.32 ± 0.05 ( n = 4) nmol/mg protein. 3. 3. Effects of microsomal protein amount and temperature ranging from 15 to 30°C on aniline 4-hydroxylation and ethylmorphine N-demethylation activities were examined. No significant differences were observed between the enzyme activities at these temperatures. 4. 4. The liver microsomal aniline 4-hydroxylase activity of gilthead seabream in the 1990 fall (0.016–0.021 nmol p-aminophenol/min/mg protein) was 4.5–6 times higher than that in the 1991 spring (0.003–0.004 nmol p-aminophenol/min/mg protein). 5. 5. Liver microsomal ethylmorphine N-demethylase activity measured in 1991 spring (0/371) nm ol formaldehyde/min/mig protein) was 41% higher than that in 1990 fall (0.263 nmol formaldehyde/min/mg protein).

Effects of in vivo benzene treatment on cytochrome P450 and mixed-function oxidase activities of gilthead seabream ( sparus aurata) liver microsomes

1. Treatment of gilthead seabream ( Spams aurata) with benzene 0.6 ml/kg/day, s.c., for four consecutive days resulted in a marked 78% and 73% decrease in total cytochrome P450 content and 7-ethoxyresorufin O-deethylase activity of liver microsomes, respectively. 2. In contrast, benzene treatment did not affect aniline 4-hydroxylase, ethylmorphine N-demethylase and cytochrome b5 content of fish liver microsomes, significantly. 3. The study revealed a distinct difference in the mixed-function oxidation of xenobiotics in mammalian and fish liver microsomes in response to benzene treatment.

Hepatic cytochrome P450 induction in goats: Effects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with β-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2–3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16α-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA probe, rather than with a rat 3A1 probe. BNF selectively induced EROD, whereas TST hydroxylation and ETM dealkylation were inhibited. With BNF-treated animals, increased concentrations of a protein cross-reactive with anti-rat P450 1A1/1A2 and of an mRNA that showed homology with a human 1A1 cDNA probe, but not with a mouse 1A1/1A2 probe, were observed.

Effects of methyl tertiary-butyl ether on hepatic lipid peroxidation in mice

The effect of one-shot or repeated treatment with methyl tertiary-butyl ether (MTBE) on lipid peroxidation and cytochrome P-450 in mouse liver was examined. One-shot treatment at the 500 mg/kg dose level caused a transient decrease in leukocyte number after 24 h. An increased level of lipid peroxide was observed in the liver homogenates 24 h after one-shot treatment and four weeks of repeated 200 mg/kg treatment. The hepatic cytochrome P-450 content increased after one and four weeks of repeated treatment (50, 200 mg/kg). On the other hand, the treatment did not affect glutathione content and glutathione-S-transferase activity. These results indicate that MTBE treatment caused lipid peroxidation in the liver homogenate and induction of hepatic microsomal cytochrome P-450 content.

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

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

Characterization of an azole-resistant Candida glabrata isolate.

A Candida (Torulopsis) glabrata strain (B57149) became resistant to fluconazole after a patient carrying the organism was treated with the drug at 400 mg once daily for 9 days. Growth of the pretreatment isolate (B57148) was inhibited by 50% with 0.67 microM ketoconazole, 1.0 microM itraconazole, and 43 microM fluconazole, whereas growth of B57149 was inhibited slightly by 10 microM ketoconazole but was unaffected by 10 microM itraconazole or 100 microM fluconazole. This indicates cross-resistance to all three azole antifungal agents. The cellular fluconazole content of B57149 was from 1.5- to 3-fold lower than that of B57148, suggesting a difference in drug uptake between the strains. However, this difference was smaller than the measured difference in susceptibility and, therefore, cannot fully explain the fluconazole resistance of B57149. Moreover, the intracellular contents of ketoconazole and itraconazole differed by less than twofold between the strains, so that uptake differences did not account for the azole cross-resistance of B57149. The microsomal cytochrome P-450 content of B57149 was about twice that of B57148, a difference quantitatively similar to the increased subcellular ergosterol synthesis from mevalonate or lanosterol. These results indicate that the level of P-450-dependent 14 alpha-demethylation of lanosterol is higher in B57149. Increased ergosterol synthesis was also seen in intact B57149 cells, and this coincided with a decreased susceptibility of B57149 toward all three azoles and amphotericin B. B57149 also had higher squalene epoxidase activity, and thus, more terbinafine was needed to inhibit the synthesis of 2,3-oxidosqualene from squalene. P-450 content and ergosterol synthesis both decreased when isolate B57149 was subcultured repeatedly on drug-free medium. This repeated subculture also fully restored the strain's itraconazole susceptibility, but only partly increased its susceptibility to fluconazole. The results suggest that both lower fluconazole uptake and increased P-450-dependent ergosterol synthesis are involved in the mechanism of fluconazole resistance but that only the increased ergosterol synthesis contributes to itraconazole cross-resistance.

Hepatic chemiluminescence and lipid peroxidation in mild iron overload

The effect of iron-overload on both hepatic lipid peroxidation and chemiluminescence was studied in early stages after iron-dextran injection. Total hepatic iron content was markedly elevated over control values 2–6 h after iron dose. A 4-fold increase in light emission was detected after 4–6 h after iron injection. Plasma GOT, GPT and LDH activities were not affected by the treatment suggesting that cell permeability was not affected by necrosis. Increases in the generation of thiobarbituric acid reactive substances (TBARS) and chemiluminescence in liver homogenates, were determined as a function of time after iron administration, in the presence of NADPH as cofactor. Under the same experimental conditions, microsomal cytochrome P-450 content was decreased by 40%, 2 h after iron treatment. To evaluate liver antioxidant defenses, catalase, superoxide dismutase and glutathione peroxidase activities were determined. Glutathione peroxidase activity in the homogenate was not affected by the treatment. Catalase and superoxide dismutase activities declined by 25 and 36%, respectively, compared with control values 4 h after the iron dose. Our data suggest that lipid peroxidation occurs after mild iron overload even though the liver remains functional.

Interaction of monocrotophos and its novel thion analogues with microsomal cytochrome P-450: in vivo and in vitro studies in rat

The binding of monocrotophos (MCP) and its two thion analogues (coded as RPR-II and RPR-V) to rat hepatic microsomal cytochrome P-450 (HMC) were investigated in vitro by difference spectroscopy. These three organophosphorus insecticides were found to bind stoichiometrically to HMC with very high affinity ( Ks 34–50 μM). RPR-V showed the highest binding affinity followed by RPR-II and MCP. Association of these compounds with HMC occured within 2 min of addition in the cuvette and therefore, appeared to be tight binding ligands of cytochrome P-450. In vivo studies at equitoxic doses of the three compounds 24 h after oral treatment in rats revealed that they all caused reduction in MC content in liver, lung, kidney and brain, as against induction in cardiac and spleenic cytochrome P-450. These in vivo results suggest organ specificity in modulating the microsomal cytochrome P-450 (MC) content of hepatic and extra-hepatic tissues by the three compounds. Apparently, their binding affinity with HMC is strongly correlated with their LD 50 value and has a substantial co-relationship with the cytochrome P-450 level in the liver.

Effects of perfluoro fatty acids on xenobiotic-metabolizing enzymes, enzymes which detoxify reactive forms of oxygen and lipid peroxidation in mouse liver

Male mice were exposed via their diet to perfluoro fatty acids of various chain-lengths (2–10 carbon atoms) at different doses (0.02 and 0.1% weight) and for different periods of time (2–10 days). Thereafter, we monitored effects on liver and body weights and a number of hepatic parameters, including mitochondrial protein content, microsomal contents of cytochromes P450 and b 5, NADPH-cytochrome P450 reductase activity [measured as NADPH-cytochrome c reductase (EC 1.6.2.3)], microsomal and cytosolic epoxide hydrolase (EC 3.3.2.3) activities, cytosolic DT-diaphorase (EC 1.6.99.2), glutathione transferase (EC 2.5.1.18), glutathione peroxidase (EC 1.11.1.9) and super-oxide dismutase (EC 1.15.1.1) activities, and levels of thiobarbituric acid-reactive material (as an indicator of lipid peroxidation) in the mitochondrial subtraction. The most dramatic changes observed were a 5–9-fold increase in mitochondrial protein, a 3–6-fold increase in the microsomal content of cytochrome P450, a 3–10-fold increase in cytosolic DT-diaphorase activity, an approximately 2-fold increase in cytosolic epoxide hydrolase activity and as much as a 60% decrease in the level of thiobarbituric acid-reactive compounds in the mitochondrial fraction. Smaller increases in microsomal epoxide hydrolase activity and decreases in cytosolic glutathione peroxidase activity were also observed. Of the perfluoro fatty acids tested, perfluorooctanoic acid caused the largest changes in the parameters examined here. Dietary exposure of mice to a 0.02% dose of this substance for 10 days results in a maximal or near-maximal effect in most cases.

Inhibition of rat methylbenzylnitrosamine metabolism by dietary zinc and zinc in vitro

Methylbenzylnitrosamine is an esophageal-specific carcinogen in the rat, and the incidence of methylbenzylnitrosamine-induced esophageal carcinoma is increased by dietary zinc deficiency. Methylbenzylnitrosamine requires activation by cytochrome P-450 to be mutagenic; the present study examined the role of dietary zinc deficiency and the in vitro addition of zinc on the cytochrome P-450-dependent microsomal metabolism of methylbenzylnitrosamine. Dietary zinc deficiency significantly increased the cytochrome P-450-dependent esophageal and hepatic microsomal metabolism of methylbenzylnitrosamine. These changes occurred without alteration in the specific content of total microsomal cytochrome P-450 of the esophagus or liver. The addition of zinc in vitro, at concentrations found in normal tissues, irreversibly inhibited the esophageal and hepatic cytochrome P-450-dependent microsomal metabolism of methylbenzylnitrosamine. These results suggest that physiological levels of zinc may be an endogenous inhibitor of methylbenzylnitrosamine metabolism. Dietary zinc deficiency appears to reduce this inhibition of cytochrome P-450 activity, resulting in an increase in carcinogen activation.

Reversibility of secondary biliary fibrosis by biliodigestive anastomosis in the rat

Biliary cirrhosis with portal hypertension and hepatocellular failure is a well-known complication of extrahepatic obstruction. It is unclear to what extent these changes are reversible by biliodigestive anastomosis. Therefore a rat model of relief of biliary obstruction was developed by performing Roux-en-Y choledochojejunostomy in rats after bile duct obstruction. Patency of the biliodigestive anastomosis was documented by biliary scintigraphy. Microsomal function was assessed in vivo by the aminopyrine breath test and portal hypertension by spleen pulp pressure. Microsomal function was markedly impaired in obstructed animals but recovered after biliodigestive anastomosis. Microsomal cytochrome P450 content paralleled these changes. Similarly, portal hypertension was reversed after successful relief of obstruction. Stereologic analysis showed that biliodigestive anastomosis partially reversed bile ductular proliferation and fibrosis. Studying the time course of recovery showed that restoration of microsomal function was achieved after 2 weeks whereas recovery from portal hypertension required 4 weeks of biliary drainage. Recovery of microsomal function was paralleled by normalization of microsomal lipid composition while resolution of portal hypertension occurred parallel to resolution of the histologic abnormalities.

Comparative induction of cytochrome P-450-dependent monooxygenases in the livers and gills of tilapia and carp

The induction properties of liver and gill microsomal monooxygenases were determined using freshwater fish tilapia ( Oreochromis mossambicus) and carp ( Cyprinus carpio), which are relatively pollution resistant and nonresistant, respectively. Pretreatments with 3-methylcholanthrene (3-MC) and polychlorinated biphenyls (PCBs) markedly increased microsomal cytochrome P-450 (P-450) contents and P-450-dependent monooxygenase activities toward benzo(a)pyrene, 7-ethoxyresorufin and 7-ethoxycoumarin, in the fish tissues. In the liver, the elevated levels of benzo(a)pyrene and 7-ethoxyresorufin oxidation activities in tilapia were higher than the corresponding levels in carp. Conversely, in the gill, the elevated levels in carp were higher than or similar to tilapia. Gel electrophoresis and immunoblotting analyses of liver and gill microsomes revealed that the xenobiotic pretreatments induced specific tilapia and carp proteins recognized by the monoclonal antibody (MAb) 1-12-3 to marine fish scup P-450E, a teleost orthologue of P-450 1A1. In contrast to 3-MC and PCBs, phenobarbital (PB) failed to induce monooxygenases in the fish tissues except in carp liver where PB increased 7-ethoxycoumarin O-deethylase activity and weakly induced a protein with which MAb 1-12-3 was cross-reactive. The results of field studies showed that the hepatic levels of P-450 1A1 and associated monooxygenase activities were elevated in tilapia collected from a polluted river, relative to tilapia and carp collected from nonpolluted water.

Herbicide-insecticide interaction in maize: Malathion inhibits cytochrome P450-dependent primisulfuron metabolism

Tolerance of maize to sulfonylurea herbicides such as primisulfuron has recently been reported to be impaired by the use of some organophosphorus insecticides. In an effort to elucidate the mechanism of this interaction, the effect of the insecticide, malathion, on the metabolism of primisulfuron was studied in whole plants, in excised leaves, and in a microsomal in vitro system from maize. Foliar application of malathion to 7-day-old plants had no influence on leaf uptake and translocation of primisulfuron, but caused a decrease in the rate of herbicide metabolism. In excised leaves, malathion increased the metabolic half-life of primisulfuron. In microsomal preparations, malathion inhibited cytochrome P450-dependent primisulfuron phenyl- and pyrimidinering hydroxylation. Loss of primisulfuron phenyl-ring hydroxylase activity was time-dependent, saturable with respect to malathion concentration, and attenuated in the absence of NADPH. The kinetic data suggest a mechanism-based cytochrome P450 inactivation by malathion. The oxoanalogue of malathion, malaoxon, did not influence the metabolic half-life of primisulfuron in excised leaves and was a poor inhibitor of microsomal primisulfuron hydroxylation. Neither insecticide had any effect in vitro on total microsomal cytochrome P450 content. From the present results it may be concluded that malathion affects primisulfuron tolerance of maize due to the inhibition of cytochrome P450 monooxygenases involved in herbicide metabolism.

Cyclophosphamide and its metabolite acrolein. Some studies on their porphyrinogenic action in 17 day old chick embryo

1. Some studies of cyclophosphamide (CP) and its metabolite acrolein in chick embryo liver were carried out in order to investigate the mechanism of the porphyrinogenic action of CP. 2. in vitro and in vivo studies revealed that CP induced but did not activate (5-aminolaevulinic acid (ALA) synthase. 3. Pretreatments with phenobarbital (PB) or SKF-525A did not modify ALA-synthase induction produced by CP. 4. Acrolein administration neither induced ALA-synthase activity nor increased cytochrome P-450 content or led to hepatic porphyrin accumulation. 5. Time course induction of cytochrome P-450 content after administration of CP or PB was similar. 6. The results obtained would indicate that CP is a strong inducer of both ALA-synthase activity and microsomal cytochrome P-450 content in liver of 17 day-old chick embryos and that its porphyrinogenic activity is not mediated by its metabolite acrolein.

Interactive effects of cadmium and benzo(a)pyrene on cellular structure and biotransformation enzymes of the liver of the European eel Anguilla anguilla

Interactive effects of cadmium and benzo(a)pyrene (BaP) on eel Anguilla anguilla liver were studied at the ultrastructural and biotransformation enzyme levels. Seawater-adapted eels were held for 24 days in either clean or cadmium-containing (5 μg Cd −1) seawater. then given a single intraperitoneal injection of BaP (20 mg kg −1 body weight) and finally sacrificed 24 h later. Cadmium exposure alone caused a hepatic perivascular fibrosis. whereas the short-term BaP intoxication alone produced marked lipid droplet accumulation associated with glycogen depletion. When eels were exposed to both toxicants together, the liver showed a complete disorganisation of the hepatic parenchyma including nuclear degeneration. The existence of elements of a biotransformation enzyme system, i.e. cytochrome P-450 monooxygenase system and glutathione-S-transferase (GST). was demonstrated in the liver. BaP injection alone had no detectable effect on microsomal cytochrome P-450 content and NADPH-cytochrome c reductase activity but markedly increased 7-ethoxyresorufin O-deethylase (EROD) and benzo(a)pyrene hydroxylase (BaPMO) activities (induction factors of 15- and 35-fold, respectively). In contrast, cytosolic GST activity was slightly decreased by this treatment. In cadmium-exposed eels, BaP treatment elicited a higher increase in EROD and BaPMO activities (induction factors of 19- and 71-fold. respectively) and also causes a 1.8-fold increase in cylochrome P-450 microsomal content. The effects of cadmium on biotransformation enzymes are discussed in relation to the ultrastructural effects of both toxicants.

Effect of amphotericin B on hepatic cytochrome P-450 and glucose-6-phosphatase in the rat

The effect of amphotericin B on hepatic microsomal cytochrome P-450 ( P-450) concentration was measured in vitro, in vivo and ex vivo in the rat. In vitro, both amphotericin B (0–500 μg/ml) and its vehicle, sodium deoxycholate (0–410 μg/ml), caused similar dose-dependent decreases of P-450 concentrations and glucose-6-phosphatase activity. Intravenous amphotericin B (3 mg/kg) given daily for 3 days decreased antipyrine clearance from control values of 1.24 ± 0.24 ml/min to 0.67 ± 0.12 ml/min ( p < 0.001); whereas antipyrine clearance was unchanged by sodium deoxycholate. The P-450 concentration on the third day was reduced from 0.74 ± 0.14 nmol/mg protein in control rats to 0.33 ± 0.09 nmol/mg protein in rats treated with amphotericin B ( p < 0.001). Sodium deoxycholate had no effect on P-450 concentration. In contrast, amphotericin B had no effect on either antipyrine clearance or P-450 concentration following enzyme induction by phenobarbital. Amphotericin B had no effect on microsomal glucose-6-phosphatase activity in vivo. Neither amphotericin B nor sodium deoxycholate induced lipid peroxidation, measured as malondialdehyde production. These results show that amphotericin B decreases hepatic cytochrome P-450 content and function in the rat. These effects can not be observed in the enzyme induced state. Amphotericin B has no effect on glucose-6-phosphatase in vivo, the key enzyme of the gluconeogenesis, indicating selective effects on hepatic microsomal function.

Reversible bile acid changes in bile duct obstruction and its potential for hepatocellular injury

The etiology of hepatocellular dysfunction resulting from chronic biliary obstruction is not clearly understood. Alterations in bile acid metabolism due to changes in microsomal cytochrome P-450 enzyme activities may have a fundamental role in cholestatic liver injury. This study examines the very early changes in both biliary bile acids and hepatic microsomal cytochrome P-450 content after bile duct obstruction in the rat and the effects of the restoration of bile flow after 3 days of biliary obstruction. We found that early induction of cytochrome P-450 may be a fundamental step in the generation of cholestatic liver injury mediated by hepatotoxic bile acids. The rapid reversal of bile acid changes with reconstituted bile flow indicate that the liver is able to quickly recover when obstruction is relieved. Characterization of this fundamental process may ultimately provide a means of modulation of cholestatic hepatotoxicity.

Effect of α-tocopherol on hepatic mixed function oxidases in hepatic ischemia/reperfusion

This study was done to determine the relationship between microsomal lipid peroxidation during hepatic ischemia/reperfusion and alteration in cytochrome P-450-dependent drug metabolism. Rats were pretreated with alpha-tocopherol to inhibit lipid peroxidation or with vehicle (soybean oil) and then subjected to 60 min no-flow hepatic ischemia in vivo. Control animals were time-matched sham-ischemic animals. After 1, 5 or 24 hr of reperfusion, liver microsomes were isolated and cytochrome P-450 and mixed function oxidases were studied. In vehicle-treated ischemic rats, serum ALT levels peaked at 5 hr (5,242 +/- 682 U/L) and were significantly reduced by alpha-tocopherol pretreatment (1,854 +/- 229 U/L, p less than 0.01). Similarly, microsomal lipid peroxidation was elevated in the vehicle-treated ischemic group, but this elevation was prevented by alpha-tocopherol pretreatment. Microsomal cytochrome P-450 content and aminopyrine-N-demethylase activity were both decreased in vehicle-treated ischemic rats to 60% and 70% of sham-ischemic control levels, respectively. Although alpha-tocopherol restored cytochrome P-450 content to the level of sham-ischemic control rats, aminopyrine-N-demethylase activity remained at 76% of control with alpha-tocopherol treatment (p less than 0.01 compared with sham-ischemic control). In contrast to what was seen with cytochrome P-450 and aminopyrine-N-demethylase, aniline p-hydroxylase activity was elevated in the vehicle-treated ischemic rats compared with sham-ischemic control rats. These increases were prevented by alpha-tocopherol pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of [3- 14C]coumarin to polar and covalently bound products by hepatic microsomes from the rat, syrian hamster, gerbil and humans

The metabolism of 0.19 and 2.0 m m-[3- 14C]coumarin to polar products and covalently bound metabolites has been studied with hepatic microcomes from the rat, Syrian hamster, Mongolian gerbil and humans. [3- 14C]Coumarin was metabolized by liver microsomes from all species to a number of polar products and to metabolite(s) that became covalently bound to microsomal proteins. The polar products included 3-, 5- and 7-hydroxycoumarins, o-hydroxyphenylacetaldehyde and o-hydroxyphenylacetic acid. Coumarin 7-hydroxylation was observed in all species except the rat. With 0.19 m m-[3- 14C]coumarin, 7-hydroxycoumarin was the major metabolite in human liver microsomes, whereas in the other species with 0.19 m m substrate and in all species with 2.0 m m substrate o-hydroxyphenylacetaldehyde was the major metabolite. Of the three animal species studied the gerbil most resembled humans as this species also had a high coumarin 7-hydroxylase activity. The administration of Aroclor 1254 to the rat and Syrian hamster induced both microsomal cytochrome P-450 content and [3- 14C]coumarin metabolism. With liver microsomes from all species a good correlation between rates of [3- 14C]coumarin metabolism and covalent binding was observed at both substrate concentrations. However, in view of the known species difference between the rat and Syrian hamster in coumarin-induced hepatotoxicity, the present data are not consistent with microsomal coumarin metabolite covalent binding being an indicator of potential liver damage.

酸化エチレン慢性吸入曝露のマウスに及ぼす影響

Male ddY mice were exposed to ethylene oxide (EO) at a concentration of 400 ppm, 6 hours a day, 3 days a week for 13 weeks and the effects of EO on the hepatic drug metabolizing enzymes were investigated. The liver and spleen weight per body weight did not change. Compared to the control group, the kidney weight of the exposed group increased while the testis weight decreased significantly. Hematological examination showed macrocytic anemia in the exposed group. Contents of microsomal cytochrome P-450 in the exposed group increased twice as much as that in the control group, while microsomal protein, cytochrome b5, protoheme and NADPH-cytochrome C reductase activity did not change. NADH-ferricyanide reductase activity of the exposed group increased significantly. Among the glutathione related enzymes in the liver, glutathione reductase and glutathione peroxidase activities in the exposed group decreased but glutathione-S-transferase activity increased significantly.