Polycyclic aromatic hydrocarbons inhibit in vitro ovarian steroidogenesis in the flounder ( Platichthys flesus L.)

Abstract

The in vitro effect of polycyclic aromatic hydrocarbons (PAHs) on ovarian steroidogenesis of the flounder ( Platichthys flesus L.) was determined. Fully vitellogenic ovary tissue was in vitro incubated in the presence of phenanthrene, benzo[a]pyrene or chrysene, using 17 α-hydroxyprogesterone or androstenedione as precursors. Androstenedione (A), testosterone (T) and 17 β-estradiol (E 2) synthesised in the presence of PAHs were assayed by radioimmunoassay and results compared with control incubations. In order to establish the effect of PAHs on the steroidogenic enzyme systems cytochrome P450 17,20-lyase (P450-17,20l), 17 β-hydroxysteroid dehydrogenase (17 β-HSD) and cytochrome P450 aromatase (P450-arom), results were also compared with the action of ketoconazole (KCZ) and aminoglutethimide (AMG), wich are, respectively, inhibitors of cytochrome P450 steroidogenic enzymes and of P450-arom. KCZ inhibited secretion of A and E 2 in 65% and T in 40%, as a consequence of inhibited P450-17,20l and P450-arom. AMG inhibited P450-arom, which resulted in decreased E 2 synthesis to approximately 50% of control incubations. All the three PAHs inhibited A secretion by approximately 50% and E 2 from 10 to 40%. Because steroid conjugation was also inhibited by phenanthrene, it could be concluded that PAH action was mediated by an inhibitory effect over P450-17,20l, 17 β-HSD and P450-arom. Except for 17 β-HSD, PAHs resembled KCZ, and P450-17,20l was the most sensitive to their inhibitory effect. In conclusion, PAHs strongly blocked the activity of P450-17,20l, a rate-limiting enzyme for conversion of C21 to C19 steroids, and showed, therefore, the potential to disrupt the reproductive cycle of fish living in polluted environments, due to impairment of steroid biosynthesis.