UBC Theses and Dissertations
Constitutive expression of xenobiotic-metabolizing enzymes in rat testis : immunochemical characterization and regulation by 17-beta-estradiol benzoate and bisphenol A Gilibili, Ravindranath Reddy
Relatively little is known about the expression, localization and regulation of rat testicular xenobiotic-metabolizing enzymes, including cytochrome P450s (CYP) and microsomal epoxide hydrolase (mEH), which are involved in the metabolism of xenobiotics including drugs and toxicants, and of endobiotics such as steroid hormones and prostaglandins. Suppression or induction of these enzymes in testis may alter the magnitude of tissue exposure to xenobiotics and endobiotics levels. In the present study, constitutive expression of various xenobiotic-metabolizing enzymes (Study 1) and their regulation by 17β-estradiol benzoate (EB) (Study 2) and an endocrine disrupting chemical, bisphenol A (BPA) (Study 3), were investigated in adult rat testis. As shown in Study 1, immunoblot analysis of testicular microsomes prepared from untreated rats revealed the presence of CYP1B1, CYP2A1, CYP17A1, NADPH-cytochrome P450 reductase (POR) and mEH, and absence of CYP1A1, CYP1A2, CYP2B1, CYP2E1, CYP2D1, CYP2D2, CYP2C6, CYP2C7, CYP2C11, CYP2C12, CYP2C13, CYP3A1, CYP3A2, CYP4A1, CYP4A2 and CYP4A3. Immunohistochemical analysis of tissue sections prepared from frozen testis indicated that CYP1B1, CYP2A1 and CYP17A1 were localized in interstitial cells, but not in seminiferous tubules, whereas mEH and POR were localized in both interstitial cells and in seminiferous tubules. In Study 2, subcutaneous (sc) treatment of EB at 0.004, 0.04, 0.4 or 4 μmol/kg once daily for 14 days suppressed testicular expression of CYP1B1, CYP2A1 and CYP17A1 at each of the dosages tested. EB also suppressed mEH and POR protein expression at dosages > 0.04 μmol/kg. In Study 3, administration of BPA at 400, 800 or 1600 μmol/kg sc once daily for 14 days decreased testicular CYP1B1, CYP2A1, CYP17A1, mEH and POR protein expression at each of the dosages tested. EB and BPA did not produce a general down-regulation of testicular protein expression because neither of these chemicals decreased calnexin protein (endoplasmic reticulum marker) levels. In summary, CYP1B1, CYP2A1, CYP17A1, mEH and POR were detected in rat testis and their expression was confined to interstitial cells (CYP1B1, CYP2A1, CYP17A1, mEH and POR) and seminiferous tubules (mEH and POR). Constitutive expression of these rat testicular enzymes was suppressed by exogenous administration of 17β-estradiol and BPA.
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