Xenobiotic-metabolizing enzymes and enzymes involved in the metabolism of reactive oxygen species in the porcine ovary : subcellular distributions and levels of expression during follicular maturation and in the non-pregnant and pregnant corpus luteum

Abstract: The polycyclic aromatic hydrocarbon (PAH) 7,12-dimethylbenz(a)anthracene (DMBA) is metabolized by both porcine ovarian microsomes and mitochondria, with the highest activity being seen in the corpus luteum. Microsomal DMBA monooxygenase activity is inhibited by inhibitors of the CYP450 system and by 17-bestradiol, thus indicating involvement of CYP1B1. Mitochondrial DMBA monooxygenase activity is located in the inner membrane/matrix and is not affected by inhibitors of the CYP450-system, by 17-bestradiol or by inhibitors of the respiratory chain. Mass spectral analysis of metabolites produced by microsomal and mitochondrial fractions showed both common and specific metabolites for each fraction. Both fractions produce reactive intermediates with the capacity to bind covalently to protein, and, in the case of mitochondria, to mitochondrial DNA. The metabolism of DMBA by both porcine ovarian microsomes and mitochondria seems to involve pathways other than the CYP450 system, and the involvement of reactive oxygen species is suggested.The level of expression of certain enzymes indirectly or directly involved in cellular defenses against metabolites of xenobiotics and reactive oxygen species (i. e, catalase, sulphotransferase, DT-diaphorase, glutathione peroxidase and glutathione reductase) are elevated in the pregnant corpus luteum compared to the non-pregnant corpus luteum.GST activity toward CDNB is higher in non-pregnant corpora lutea than in both follicles and pregnant corpora lutea. Western blotting revealed the presence of the GST subunits A1/2,A3, A4, A5, M1/2, M2 and P1 in the cytosol from follicles of different levels of maturation and in corpora lutea. In general, the highest levels of expression of these subunits are observed in corpora lutea. GSTP1 is the only subunit expressed at higher levels in follicles.