Cytochrome P450-dependent Enzyme Activities Research Articles

Stimulation of microsomal drug oxidation in liver and kidney of rats treated with the oncolytic agent cis-dichlorodiammineplatinum-II.

In vitro drug metabolism from liver and kidney of rats was studied for up to 12 days following a single intraperitoneal injection of the antineoplastic drug cisplatinum. At 3,5, and 8 days posttreatment, hepatic cytochrome P-450 dependent enzyme activity was increased 20-45%, but levels of cytochromes P-450 and b5 were unaltered. Hepatic in vitro stimulated thiobarbituric acid reactive (TBAR) substances were increased at all times, with a maximum of 20 times normal on day 5. Renal aniline hydroxylase activity was elevated 25-95% throughout the first 8 days. Renal in vitro stimulated TBAR substances were not significantly altered. In vitro addition of cisPt to control microsomes resulted in no consistent, dose-related changes in substrate metabolism.

Effect of hepatocarcinogens on epoxide hydrolase and other xenobiotic metabolizing enzymes.

Hepatocarcinogens cause marked biochemical changes in the liver at short intervals after administration. The studies described were designed to investigate the effects of hepatocarcinogens and hepatotoxicants on the microsomal mixed function oxidase system. DT-diaphorase and epoxide hydrolase. Following 5 day p.o. treatment of male F-344 rats with aflatoxin B1 (AFB), 2-acetylaminofluorene (AAF), technical grade dinitrotoluene (DNT), or 2,4-diaminotoluene, microsomal cytochrome P450 dependent enzyme activities were depressed while epoxide hydrolase activity was markedly elevated (3-8 times control). Diethylnitrosamine (DEN) given at 5 mg/kg/day and DL-ethionine at 1000 mg/kg/day failed to increase epoxide hydrolase. 3-Methylcholanthrene, methylnitrosourea, carbon tetrachloride, bromobenzene and vinyl chloride all failed to increase epoxide hydrolase activity. Using 3 daily i.p. injections, dose-response relationships for increases in epoxide hydrolase were generated for the hepatocarcinogens. With the exception of p-dimethylaminoazobenzene (DAB) and DEN, the carcinogens studied produced log-linear dose response curves for increase in epoxide hydrolase. Both DEN and DAB caused increases in epoxide hydrolase but classical sigmoidal dose-response curves were not obtained. The order of potency for increasing epoxide hydrolase was AFB greater than AAF greater than 2,6-dinitrotoluene greater than 3'-methyl-N,N-dimethyl-4-aminoazobenzene greater than DNT greater than 2, 4-dinitrotoluene. The slopes of the linear portions of the log dose-response curves were not statistically different from the slope of the dose-response curve obtained with AAF suggesting that structurally diverse carcinogens elicit increases in epoxide hydrolase by a common mechanism.

Actions of danazol in vivo on cytochrome P-450 and steroidogenic enzymes in rat testis and liver microsomal preparations

The mechanism of action of danazol has not been established and the drug may act at multiple loci. Effects suggesting inhibition of pituitary gonadotropin release have been described while some in vitro studies have demonstrated competitive inhibition of steroidogenic enzymes. In addition, destruction of cytochrome P-450 by the acetylenic moiety of danazol is a possible mechanism. Following 14 days of danazol treatment (10 mg/kg/day), the specific content of rat testis microsomal cytochrome P-450 and the serum testosterone were decreased, in spite of no significant change in serum luteinizing hormone. Furthermore, simultaneous administration of human chorionic gonadotropin with danazol still resulted in a decrease in cytochrome. The activities of two testicular microsomal steroid-converting enzymes (17 alpha-hydroxylase and 17,20-lyase) were not altered when based on cytochrome P-450 content but were markedly depressed when based on microsomal protein. In liver, danazol showed a similar but less marked dimunition of the cytochrome. Surprisingly, steroid 17 alpha-hydroxylase activity in liver was significantly increased while other cytochrome P-450 dependent enzyme activities were not altered.

Determination of plasma trimethadione and its metabolite carbon tetrachloride-intoxicated rat liver: a useful tool for estimation of hepatic drug metabolizing capacity.

1. The relationship between the plasma concentration ratio of 5,5-dimethyl-2,4-oxazolidinedione (DMO) to trimethadione (TMO) and cytochrome P-450 dependent drug-metabolizing enzyme activities after administration of TMO to rats pretreated with different dose levels of carbon tetrachloride (CCl4) was investigated. 2. Pretreatment of rats with different dose levels of CCl4 resulted in a prolongation of TMO half-life, and increase of the area under the curve (AUC), and a decrease of clearance, but the apparent volume of distribution (Vd) was not significantly decreased. 3. Depending on the extent of liver-injury by CCl4, there was a good correlation between the ratio of DMO to TMO in plasma and hepatic cytochrome P-450 dependent drug -metabolizing enzyme activities such as cytochrome P-450 content (r=0.796 at 1 h, r=0849 at 2 h), aminopyrine N-demethylase activity (r=0.877 t 1 h, r=0905 at 2 h), TMO N-demethylase activity (r=0.876 at 1 h,r=0.928 at 2 h) and aniline hydroxylase activity (r=0.900 at 1 h, r=0.936 at 2 h). 4. These results, together with the previous findings, indicate determination of the plasma levels of TMO and DMO might be a useful tool as an index of drug metabolizing capacity of rat livers.