Cytochrome P450 Inhibition by Antimicrobials and Their Mixtures in Rainbow Trout Liver Microsomes In Vitro.

Abstract

Antimicrobials are ubiquitous in the environment and can bioaccumulate in fish. In the present study, we determined the half-maximal inhibitory concentrations (IC50) of seven environmentally abundant antimicrobials (ciprofloxacin, clarithromycin, clotrimazole, erythromycin, ketoconazole, miconazole, and sulfamethoxazole) on the cytochrome P450 (CYP) system in rainbow trout (Oncorhynchus mykiss) liver microsomes, using 7-ethoxyresorufin O-deethylation (EROD, CYP1A) and 7-benzyloxy-4-trifluoromethylcoumarin O-debenzylation (BFCOD, CYP3A) as model reactions. Apart from ciprofloxacin and sulfamethoxazole, all antimicrobials inhibited either EROD or BFCOD activities or both at concentrations below 500 µM. Erythromycin was the only selective and also time-dependent inhibitor of BFCOD. Compared with environmental concentrations, the IC50s of individual compounds were generally high (>mg/L), but as mixtures, the antimicrobials resulted in strong, indicatively synergistic inhibitions of both EROD and BFCOD at sub-micromolar (~µg/L) mixture concentrations. The cumulative inhibition of the BFCOD activity was detectable even at picomolar (~ng/L) mixture concentrations and potentiated over time, likely because of the strong inhibition of CYP3A by ketoconazole (IC50=1.7±0.3 µM) and clotrimazole (IC50=1.2±0.2 µM). The results suggest that if taken up by fish, the mixtures of these antimicrobials may result in broad CYP inactivation and increase the bioaccumulation risk of any other xenobiotic normally cleared by the hepatic CYPs even at biologically relevant concentrations. This article is protected by copyright. All rights reserved.