In vitro modulation of 17-beta-estradiol-induced vitellogenin synthesis: Effects of cytochrome P4501A1 inducing compounds on rainbow trout (Oncorhynchus mykiss) liver cells

Cytochrome P4501A1 (CYP1A1) induction, particularly in liver, is a useful marker of exposure of fish to polycyclic- and halogenated-aromatic hydrocarbons. However, the relationship between toxicity and CYP1A1 induction in fish is uncertain. Some compounds that induce CYP1A1 are antiestrogenic in mammalian bioassay, and this effect is linked to aryl hydrocarbon (Ah) receptor and/or increased catabolism of 17-beta-estradiol. Liver of fish synthesizes estrogen-inducible egg yolk precursor protein vitellogenin (Vg) which is critical for oocyte maturation and ovarian development. To determine if CYP1A1-associated endocrine modulation could occur in fish liver, primary cultures of rainbow trout liver cells were co-administered 17-beta-estradiol and CYP1A1 inducing compounds or mixtures. Protein synthesis and enzyme activity of cells were optimal when cultured in a modified HEPES buffered Medium 199 at 15 degrees C. Vg and albumin (Alb), estimated by ELISA measurement of concentration in the media 48 h after treatment, formed the basis for the test. Equivalent viability (mitochondrial dehydrogenase activity) and secretory functional capacity (Alb synthesis) were estimated and correlated with other results. In descending order, 2,3,4,7,8-pentachlorodibenzofuran (10(-12) to 10(-8) M) > 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) congruent to 2,3,7,8-tetrachlorodibenzofuran (10(-12) to 10(-8) M) > beta-naphthoflavone (10(-7) to 10(-6) M) inhibited Vg synthesis in 17-beta-estradiol treated liver cells. Potency of inhibition directly related to strength as an inducer of CYP1A1 protein. At 10(-8) M, PCB congeners 77, 126, 156 did not inhibit Vg synthesis and induced no to moderate levels of CYP1A1 protein or EROD activity. At 10(-8) M, congener 114, a weak EROD inducer, potentiated Vg synthesis relative to cells treated with 17-beta-estradiol alone. The results of this study increase our understanding of the consequences of hepatic CYP1A1 induction, forewarn of reproductive impairment of sexually maturing fishes exposed to CYP1A1 inducing compounds and argue for further, more detailed in vivo investigation.