Adrenal activation of carbon tetrachloride: role of microsomal P450 isozymes

Abstract

Previous investigations demonstrated that carbon tetrachloride (CCl 4) was activated by adrenal microsomes, resulting in various functional changes and ultimately in necrosis of the zona reticularis of the gland. Experiments were done to identify the adrenal P450 isozyme(s) involved in the bioactivation of CCl 4. Incubation of microsomes from the zona reticularis (ZR) of the guinea pig adrenal cortex with CCl 4 plus NADPH caused initiation of lipid peroxidation, covalent binding of CCl 4-derived radioactivity to protein, and degradation of cytochrome(s) P450. Preincubation of the microsomal preparations with inhibitory antibodies to P450 17α or P450 C12 decreased the corresponding enzyme activities (17α-hydroxylation and 21-hydroxylation), but did not affect the activation of CCl 4. 1-Aminobenzotriazole (ABT), a suicide inhibitor of some P450 isozymes, decreased the enzyme activities catalysed by an adrenal 52 000 Da (52 kDa) isozyme, but had no effect on the function of P450 17α or P450 C21. However, ABT completely inhibited the CCl 4-induced LP and covalent binding in adrenal microsomes. The results indicate that adrenal CCl 4 activation is catalysed by the 52 kDa P450 isozyme and not by the steroid hydroxylases. Localization of the 52 kDa isozyme to the ZR probably accounts for the selective necrosis of this region of the gland by CCl 4.