Induction and inhibition of aromatase (CYP19) activity by various classes of pesticides in H295R human adrenocortical carcinoma cells.

Various pesticides known or suspected to interfere with steroid hormone function were screened in H295R cells for effects on catalytic activity and mRNA expression of aromatase. Dibutyl-, tributyl-, and triphenyltin chloride decreased aromatase and ethoxyresorufin O-deethylase activities concentration dependently (1-300 nM; 24-h exposure). However, these decreases occurred only at cytotoxic concentrations, indicated by decreases in mitochondrial MTT reduction and intracellular neutral red uptake. The organotins did not cause direct inhibition during the catalytic assay (1-1000 nM; 1.5-h exposure). The same was true for p,p'-DDT, and o,p-DDT, and o,p-DDE, which decreased aromatase activity only at cytotoxic concentrations (> or =10 microM; 24-h exposure). p,p'-DDE had no effect on aromatase activity or cell viability at 1 and 10 microM. Various imidazole-like fungicides were aromatase inhibitors. Imazalil and prochloraz were potent mixed inhibitors (K(i)/K(i)(') = 0.04/0.3 and 0.02/0.3 microM, respectively), whereas propiconazole, difenoconazole, and penconazole were less potent competitive inhibitors (K(i) = 1.9, 4.5, and 4.7 microM, respectively). Fenarimol, tebuconazole, and hexaconazole decreased aromatase activity close to cytotoxic concentrations. Vinclozolin, as was shown previously for atrazine, induced aromatase activity and CYP19 mRNA levels about 2.5- and 1.5-fold, respectively. To investigate the mechanism of aromatase induction in H295R cells, the ability of the pesticides to increase intracellular cAMP levels was examined. Vinclozolin (100 microM) and atrazine (30 microM) increased cAMP levels about 1.5-fold above control. Forskolin and isobutyl methylxanthine (IBMX) increased cAMP levels 3 and 1.8-fold, respectively. Time-response curves for cAMP induction and concentration-response curves for aromatase induction by vinclozolin, atrazine, and IBMX were similar, suggesting that the mechanism of aromatase induction by these pesticides is mediated through inhibition of phosphodiesterase activity.