Altered regulation of cytochrome P-450 enzymes in choline-deficient cirrhotic male rat liver: impaired regulation and activity of the male-specific androst-4-ene-3,17-dione 16 alpha-hydroxylase, cytochrome P-450UT-A, in hepatic cirrhosis.

Total microsomal cytochrome P-450 levels were decreased, to about 50% of control, in liver of male rats made cirrhotic by the prolonged intake of a choline-deficient diet. We have suggested previously that this decrease in cytochrome P-450 levels is not a generalized one, but is selective for certain forms of the enzyme. In the present study, levels of six cytochrome P-450 forms including the sex-specific cytochrome P-450 forms, P-450UT-A, P-450PCN-E, and P-450UT-l, were quantitated immunochemically in hepatic microsomes prepared from control and cirrhotic male rats and were related to changes in the regioselectivity of cytochrome P-450-mediated androst-4-ene-3,17-dione hydroxylation in these fractions. The principal finding of this study was that the male-specific androst-4-ene-3,17-dione 16 alpha-hydroxylase was decreased in cirrhotic microsomes to about 20% of control. The content of P-450UT-A decreased concurrently from about 0.40 to less than 0.01 nmol/mg of microsomal protein. Other pathways of androst-4-ene-3,17-dione hydroxylation were also affected, but to different extents than the 16 alpha-hydroxylase. 6 beta-Hydroxylation decreased in cirrhotic microsomes to about 45% of control, despite a marked decrease in P-450PCN-E from 0.27 to less than 0.002 nmol/mg of microsomal protein. The rate of androst-4-ene-3,17-dione 7 alpha-hydroxylation underwent a less pronounced reduction in cirrhosis to about two-thirds of control microsomal activity, and levels of the cytochrome P-450 associated with this activity, P-450UT-F, were decreased in proportion with the decrease in total microsomal cytochrome P-450. 16 beta-Hydroxylase activity was unaffected by the cirrhotogenic process. From spectral binding studies it was apparent that androst-4-ene-3,17-dione elicited a high affinity type I interaction in control microsomal fractions (Ks = 4.5 microM), whereas no interaction was apparent in cirrhotic liver microsomes. Levels of three other forms of cytochrome P-450--P-450PB-C (a constitutive form inducible by phenobarbital), P-450ISF-G (a major isosafrole-inducible form), and P-450UT-I (the major female sexually-differentiated isozyme)--were apparently unaltered in cirrhosis. These findings are consistent with the assertion that specific forms of cytochrome P-450 are subject to altered regulation in hepatic cirrhosis.