
<ArticleTitle>7,12-Dimethylbenz[a]anthracene inhibition of steroid production in MA-10 mouse Leydig tumor cells is not directly linked to induction of CYP1B1.</ArticleTitle>
<AbstractText>Testosterone, which is essential for spermatogenesis, is synthesized in the Leydig cells of the testis. This study addresses whether male reproductive toxicity from exposure to polycyclic or polychlorinated aromatic hydrocarbons, such as 7,12-dimethylbenz[a]anthracene (DMBA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), may be due to direct effects on Leydig cell function. Using a cell-based assay, the effects of TCDD, benz[a]anthracene (BA), and DMBA on steroid production and <prot>cytochrome P4501B1</prot> (<prot>CYP1B1</prot>) expression in treated MA-10 mouse Leydig tumor cells or primary cultures of rat Leydig cells was determined. (Bu)(2)<prot>cAMP</prot>-stimulated steroid production was inhibited approximately 25% and approximately 80% by DMBA treatment of MA-10 cells and rat Leydig cells, respectively, while BA or TCDD were without effect. Conversely, male Sprague-Dawley rats treated with TCDD displayed a 75% decrease in serum testosterone levels, while DMBA-treated rats had circulating testosterone levels comparable to control rats. Injection of human <prot>chorionic gonadotropin</prot> (<prot>hCG</prot>) 1 h prior to euthanasia restored testosterone levels in TCDD-treated rats to 79% of the <prot>hCG</prot>-stimulated levels in control rats. Steady-state levels of <prot>CYP1B1</prot> mRNA, as detected by RT-PCR, are present in the MA-10 cells and treatment with TCDD, BA, DMBA, or the <prot>cAMP</prot> analog (Bu)(2)<prot>cAMP</prot> induced <prot>CYP1B1</prot> mRNA expression levels. <prot>CYP1B1</prot> was constitutively expressed in rat testis, adrenal, liver, and kidney tissues while <prot>CYP1A1</prot> was undetectable. TCDD treatment induced <prot>CYP1B1</prot> expression in the adrenal and liver and <prot>CYP1A1</prot> in the kidney and liver. DMBA treatment induced only <prot>CYP1A1</prot> levels in kidney and liver. In sum, DMBA or a reactive DMBA metabolite, but not TCDD, has a direct effect on steroidogenesis in isolated Leydig cells. <prot>CYP1B1</prot> expression levels, however, cannot be directly correlated to potential in vitro or in vivo toxic effects of TCDD or DMBA.</AbstractText>
