Gender-related differences in the formation of skatole metabolites by specific CYP450 in porcine hepatic S9 fractions

Higher accumulation of skatole in the fat of male pigs compared with female pigs might be due to gender-related differences in the rate of skatole degradation. In the present study, skatole metabolites and cytochrome P450 (CYP450) isoforms involved in skatole metabolism were for the first time investigated in hepatic S9 fractions from six male and four female pigs (crossbred Landrace x Yorkshire dams and Duroc boar). Surprisingly, the rates of production of major skatole metabolites were similar in male and female pigs. The most abundant metabolite of skatole was 3-hydroxy-3-methyloxindole (HMOI) followed by 3-methyloxindole and indole-3-carbinol in both male and female S9 fractions. Concentrations of formed HMOI and 3-methyloxindole did not differ between the genders (P = 0.124 for HMOI, and P = 0.575 for 3-methyloxindole). Indole-3-carbinol formation was higher in S9 fractions from the females compared with male pigs (P = 0.0001). Enzyme kinetic parameters were similar for both genders (P > 0.05). In both male and female pigs, ellipticine, diallyl sulphide (DAS) and quercetin inhibited HMOI formation, confirming the involvement of CYP1A1 and CYP2E1. The formation of 3-methyloxindole was reduced in the presence of the CYP2E1 inhibitor DAS, and formation of indole-3-carbinol was reduced in the presence of CYP1A1 and CYP2A19 inhibitors. We found only minor differences in skatole metabolism between male and female pigs, particularly the involvement of CYP2C and CYP3A in indole-3-carbinol formation in female but not in male pigs. This is a very essential finding, suggesting the involvement of larger number of CYP450 isoforms in female pigs. On the other hand, indole-3-carbinol is a minor skatole metabolite, and the physiological significance of CYP2C and CYP3A involvement in its formation in female pigs, but not in male pigs, needs to be elucidated. Our results, however, should be interpreted with caution because of the low number of animals and possibility of breed and age effects on skatole metabolism.