Increased CYP1A2 content and capacity to activate Glu-P-1 and Trp-P-2 in liver microsomes of scorbutic ODS rats

Osteogenic Disorder Shionogi (ODS) rats, which cannot synthesizeascorbic acid due to a deficiency of L-gulonolactone oxidase,become scorbutic when not supplied with dietary ascorbic acid.We used the deficient rats to study the effects of ascorbicacid on the amount of cytochrome P450 enzymes in liver microsomes.The total amount of hepatic cytochrome P450 in ODS rats deprivedof ascorbic acid was lower by 40%, whereas ODS rats fed withascorbic acid and the wild strain had the same level of totalhepatic cytochrome P450. Western blot analysis for various formsof cytochrome P450 in liver microsomes indicated that the amountof CYP1A2 was significantly higher in ascorbic acid deficientrats. On the other hand, amounts of CYP2B2 and 3A were lower,and those of CYP2E1 and CYP2C6/11 were unaffected. In accordancewith the higher amount of CYP1A2, Northern blot analysis showedincreased expression of CYP1A2 mRNA. The capacity of microsomesto produce mutagens from 2-amino-6-methyl-dipyrido1, 2-a:3',2'-d]imidazole acetate (Glu-P-1) and 3-amino-1-methyl-5H-pyrido4,3-b]indole acetate (Trp-P-2) was higher in scorbutic ODS ratsby the Ames test. These results indicate that the effects ofascorbic acid deficiency on the expression of cytochrome P450in ODS rat livers are form-specific and that the increased CYP1A2is associated with increased metabolic activation of promutagensin the scorbutic state.