Role of C-5 chiral center in R-(+)-pulegone-mediated hepatotoxicity: metabolic disposition and toxicity of 5, 5-dimethyl-2-(1-Methylethylidene)-cyclohexanone in rats.
Metabolic disposition of 5, 5-dimethyl-2-(1-methylethylidene)-cyclohexanone (I) was examined in rats. Compound (I) was administered orally (250 mg/kg of body weight/day) to rats for 5 days. The following urinary metabolites were isolated and identified: 4,5,6,7-tetrahydro-3,6, 6-trimethylbenzofuran (III), 3,3-dimethylcyclohexanone (VI), 5, 5-dimethyl-3-hydroxy-2-(1-methylethylidene)-cyclohexanone (X), 5, 5-dimethyl-2-(1-hydroxymethylethyl)-cyclohexanone (IX), 3-hydroxy-5-hydroxymethyl-5-methyl-2-(1-methylethylidene)-cyclo hexano ne (XI), 5,6-dihydro-3,6,6-trimethyl-2(4H)-benzofuranone (VIII), and 5,5-dimethyl-3-hydroxy-2-(1-carboxy ethylidene)-cyclohexanone (XIII). Incubation of compound (I) with phenobarbital (PB)-induced rat liver microsomes in the presence of NADPH resulted in the formation of a metabolite, tentatively identified as a furanoterpene (III) based on proton magnetic resonance, gas chromatography, and gas chromatography-mass spectroscopy analyses. The formation of III was inhibited to a significant extent by carbon monoxide, metyrapone, SKF 525-A, and cytochrome c, suggesting the participation of PB-induced microsomal cytochrome P-450 system in the conversion of I to III. Compound I gave type I spectral change in the PB-induced liver microsomes and the dissociation constant (Ks) for I was 38.5 microM. Intraperitoneal administration of a single dose (250 mg/kg) of I to rats resulted in 26, 23, and 41% decreases in the levels of cytochrome P-450, glucose-6-phosphatase, and aminopyrine N-demethylase, respectively, at the end of 24 h. During this period, a 11-fold increase in serum glutamate pyruvate transaminase level was also observed. However, a decrease in the level of cytochrome P-450 and glucose-6-phosphatase, and an increase in serum glutamate pyruvate transaminase values were comparatively more pronounced when R-(+)-pulegone (250 mg/kg) or CCl(4) (0.6 ml/kg) was administered to rats. Pretreatment of rats with PB potentiated the hepatotoxicity caused by I, whereas pretreatment with 3-methylcholanthrene protected from it. This suggests that PB-induced cytochrome P-450-catalyzed reactive metabolites may be responsible for the toxic effects caused by I. (+info)
Studies on the formation of lipid peroxides and on some enzymic activities in the liver of vitamin E-deficient rats.
Rats were fed a 5 or 20% casein diet that causes liver necrosis unless supplemented with vitamin E or selenite. The following activities were studied in liver subcellar fractions: enzymic formation of lipid peroxides, NADPH-cytochrome c reductase, oxidative demethylation of aminopyrine, and incorporation of [14C]leucine into protein (with microsomes); xanthine oxidase (with soluble supernatant); and RNA polymerases I and II (with nuclei). Formation of lipid peroxides was higher in rats fed diets without vitamin E and was not reduced significantly by dietary selenite. The activity of xanthine oxidase was higher in animals fed the 20% casein than in those fed the 5% casein diet; however, a higher activity was observed in the rats fed the latter diet without vitamin E or selenite than in those receiving these supplements. The activity of RNA polymerase I was higher in rats fed the low casein diet. Other activities examined were not affected significantly by the level of dietary casein or by vitamin E or selenits. (+info)
Effect of repeated exposure to aniline, nitrobenzene, and benzene on liver microsomal metabolism in the rat.
Exposure of rats to aniline at daily doses of 50 mg/kg of body weight over a month stimulated the microsomal metabolism as manifested by (1) acceleration of p-hydroxylation of anilin and N-demethylation of aminopyrine in 9-000 times g postmitochondrial supernatant of the liver, (2) shortening the sleeping time after hexobarbital, and (3) reduction of the antipyretic effect of phenacetin. In the rats exposed to nitrobenzene in a similar manner to aniline, nitroreduction of nitrobenzene and p-hydroxylation of aniline remained unaffected; the antipyretic effect of phenacetin was decreased, whereas hexobarbital sleeping time remained unchanged. Exposure of rats to benzene (50 mg/kg of body weight daily for a month) had no effect on the rate of hydroxylation of benzene and N-demethylation of aminopyrine. In benzene-exposed rats hexobarbital sleeping time was prolonged whereas the antipyretic effect of phenacetin was unaffected. Microsomal metabolism of aniline, nitrobenzene, and benzene was stimulated and inhibited when the rats were pretreated with phenobarbital and SKF 525-A, respectively. (+info)
Induction of drug metabolism-related enzymes by methylcholanthrene and phenobarbital in transgenic mice carrying human prototype c-Ha-ras gene and their wild type littermates.
Transgenic mice hemizygously carrying human c-Ha-ras proto-oncogene, Tg-rasH2 show very sensitive and facilitated carcinogenicity to various carcinogens. In this study, activities of certain enzymes related to drug metabolism and energy metabolism were measured in microsome and cytosol fractions of livers of Tg-rasH2 mice and their wild type littermates with both sexes treated with 3-methylcholanthrene (MC) and phenobarbital (PB). Aminopyrine N-demethylase activities increased significantly in livers of all mice treated with PB. MC and PB treatments induced significant increases in activities of UDP-glucuronosyltransferase and S-adenosyl homocysteinase compared to those in the non-treated groups in microsome fractions from all mice. In cytosol fractions of livers of all mice, glutathione S-transferase activity was significantly induced in the PB treated groups. There were no significant differences in activities of lactate dehydrogenase, glucose 6-phosphate dehydrogenase, pyruvate kinase and glucose 6-phosphatase related to energy metabolism in livers and kidneys among all mice. Tg-rasH2 mice showed stable activities of enzymes related to drug detoxication and energy metabolism similar to those of non-transgenic mice. These results suggest that the human c-Ha-ras transgene may not affect drug metabolism-related enzymes, and the facilitated carcinogenic response in the Tg-rasH2 mouse is not due to these enzymatic disorders. (+info)
Further experiments on lipid peroxidation in transplanted and experimental hepatomas.
The results of experiments on the subject of lipid peroxidation in hepatomas are described. It is now clear that lipid peroxidation is strongly decreased in most highly dedifferentiated hepatomas. It seems evident that the extent of the decline is strictly related to the degree of dedifferentiation. The model of diethylnitrosamine carcinogenesis, according to the method by Solt, Medline and Farber, has been now adopted to study the stages of carcinogenesis. It was shown that a net decline in lipid peroxidation occurs as early as at the stage of reversible nodules and progresses until the development of clear hepatomas. This change is practically simultaneous with a decline in the efficiency of the enzymes of the drug metabolizing system and in the content of cytochrome P450-Glutathione content and metabolism show also important changes. In fact, a dramatic increase in gamma-glutamyl-transpeptidase takes place very early during carcinogenesis, and is responsible for large decline in total glutathione during incubation of the homogenates. Glutathione peroxidase activity, on the contrary, is decreased, whereas glutathione reductase does not show significant changes. The supernatant of highly anaplastic tumors inhibits lipid peroxidation in normal liver homogenates, suggesting the presence of substances provided with antioxidant properties. These cannot be, however, related to a higher glutathione content. Supernatants from early nodules seem to be unable to block lipid peroxidation in normal liver homogenates. Preliminary experiments done to study the aldehyde pattern produced during lipid peroxidation, both in hepatomas and in nodules, confirm the presence of very poor lipid peroxidation and possibly of different peroxidation kinetics. (+info)
Studies on the evaluation of the toxicity of various salts of lead, manganese, platinum, and palladium.
Preliminary studies have been conducted on various parameters in order to assess the possible and relative toxicities of a number of metallic salts. Upon oral administration in lethal-dose experiments, two soluble Pt4+ salts were more toxic than the other salts tested. Following intraperiotneal injection in lethal-dose experiments, PbCl2 was less toxic than several of the soluble or partially soluble salts of Pt4+, Pd2+, and Mn2+. An intake of a total of approximately 250 mg of Pt4+ per rat in the drinking fluid over a 30-day interval did not affect the activities of aniline hydroxylase and aminopyrine demethylase in rat liver microsomes. In rats receiving soluble Pt4+ salts in the drinking fluid, the highest concentration of Pt was found in the kidney and an appreciiable concentration was found in the liver. (+info)
Inhibition of human hepatic cytochrome P450s and steroidogenic CYP17 by nonylphenol.
Effect of nonylphenol on aminopyrine N-demethylase activity, a typical drug-metabolizing enzyme activity, by ten kinds of human hepatic cytochrome P450s (CYP) and on progesterone 17alpha-hydroxylase activity by steroidogenic CYP17 was investigated. When determined at 2 mM substrate concentration, nonylphenol (1 mM) most efficiently inhibited aminopyrine N-demethylation by CYP2C9 and CYP2C19, by 61% and 59%, respectively, followed by CYP2D6, CYP1A2, CYP2C18 and CYP2C8 (46-51%), whereas inhibition of the activities by other CYPs was less than 27%. Additionally, nonylphenol competitively inhibited diclofenac 4'-hydroxylation by CYP2C9 and S-mephenytoin 4'-hydroxylation by CYP2C19 with Ki values of 5.3 and 37 microM, respectively. Furthermore, nonylphenol exhibited a competitive inhibition of progesterone 17alpha-hydroxylase activity by CYP17 with Ki value of 62 microM. These results suggest that nonylphenol inhibits human hepatic CYPs, especially CYP2C9 and CYP2C19, and steroidogenic CYP17 activities. (+info)
Leaves from a standard, insect-susceptible cauliflower variety and an insect-resistant strain were formulated at either 10 or 25% into semipurified diets for male and female weanling rats. After 3 weeks, relative liver weights, microsomal protein, cytochrome P-450, and activities of hepatic microsomal aminopyrine N-demethylase, aniline hydroxylase, p-nitroanisole O-demethylase, and N-methylaniline N-demethylase were determined. Growth, feed intake, and feed efficiency of male rats were not affected by the inclusion of the dried cauliflower leaf in the diet. However, female rats exhibited a depressed feed intake and increased feed efficiency with cauliflower leaf supplemental diets. Relative liver weights increased with increasing percentage of cauliflower leaves in the diet. Hepatic microsomal enzyme response to cauliflower leaf supplementation of the diet was greater in males than in females. Only aniline hydroxylase activity remained unchanged by the test diets. Male rats showed significant increases in N- and O-demethylation with both the 10 and 25% cauliflower diets, and increased values for microsomal protein and cytochrome P-450 at the 25% supplemental level. Female rats did not show significant hepatic microsomal induction from cauliflower leaf consumption at the 10% level. However, cytochrome P-450 and the metabolism of aminopyrine and p-nitroanisole were enhanced by consumption of cauliflower leaves at 25% of their diet. None of the parameters tested in this study evidenced a difference between the two cauliflower cultivars fed to either sex. (+info)