Stimulatory Effect of Cytochrome b5 Induced by p-Nitroanisole and Diisopropyl 1,3-dithiol-2-ylidenemalonate on Rat Liver Microsomal Drug Hydroxylations1

Abstract

The relationship between the changes in the amount of the components of the liver microsomal electron transport systems and drug hydroxylase activities on administration of p-nitroanisole was investigated. The content of cytochrome P-450 in the p-nitroanisole-treated rats was not significantly different from that in the controls during the treatment. The cytochrome b5 content increased 2.2-fold over that of the controls after 14 days of treatment. Demethylation activities per mg microsomal protein of p-nitroanisole, aminopyrine, and benzphetamine were enhanced 2.7-, 2.4-, and 2.8-fold, respectively, but aniline hydroxylase activity was not enhanced. Similar results were obtained with microsomes from diisopropyl 1,3-dithiol-2-ylidenemalonate (NKK-105)-treated rats. The time-course study of changes in the amount of the components of drug hydroxylase systems suggested that the increase in cytochrome b5 content enhanced the demethylation activities. In the reconstituted system containing cytochrome P-450 partially purified from p-nitroanisole- or NKK-105-treated rats, cytochrome b5 was required for the maximal activities of the demethylation reactions, but did not participate in aniline hydroxylation. These findings showed good correlation between the change of cytochrome b5 content and the demethylation activities and suggested that the increase in cytochrome b5 content might enhance the demethylation activity by stimulating supply of a second electron to cytochrome P-450.

Effect of malotilate (diisopropyl 1,3-dithiol-2-ylidenemalonate) on drug metabolizing activity in rat liver microsomes.

“…They also reported that p-nitroanisole 0-demethylase activity and N-demethylase activities toward amino pyrine, benzphetamine and ethylmorphine were enhanced, but aniline hydroxylase activity was reduced by malotilate adminis tration (12). Recently, Kawata et al (13) showed similar results. However, there are no reports concerning the effect of malo tilate on any other substrate-metabolizing activity.…”

“…The effect of malotilate on the activities of aniline hydroxylase, aminopyrine N-demethylase, benzo(a)pyrene (B(a)P) hydroxylase and 7-ethoxycoumarin (7-EC) 0-deethylase per nmol cytochrome P-450. (10)(11)(12)(13).…”

“…Studies using the antibody for b5 (23) and reconstituted systems (13,24) have shown that b5 is not involved in aniline hydroxylation. Therefore, in the case of aniline hydroxylation, P-450 and b5 may compete for the second electron from NADPH-cytochrome c reductase, and the increase in the content of b5 by the malotilate treatment, thus, may inhibit aniline hydroxy lase activity, though the increase in the activity of NADPH-cytochrome c reductase may have partially reversed this inhibition.…”

Hepatoprotection by malotilate against carbon tetrachloride-alcohol-induced liver fibrosis

“…An interaction of malotilate with the bioactivation of CC14 can be excluded as malotilate did not suppress the activities of the microsomai monooxygenase system [6][7][8]. Whether this effect of malotilate allows the assumption of an antifibrotic action remains unclear, as the antinecrotic potency of this compound cannot be separated from its effect on the connective tissue accumulation.…”

“…This hepatoprotective activity was not related to an inhibition of the microsomal mixed-function oxidase system which activates many hepatotoxic agents to reactive intermediates [6][7][8]. In our model we compared the hepatoprotective efficacy of malotilate with that of Dpenicillamine, colchicine and cianidanol which had been previously shown to exert antifibrotic activities in different models of hepatic fibrosis [9][10][11].…”