Effects of Combined Exposures of Microcystin-Lr and Benzo[A]Pyrene on Detoxification Mechanisms in the Fish Liver Cell Line (Plhc-1)

Abstract

This study focuses on mixture toxicity between representatives of two classes of common aquatic contaminants, microcystin-LR (MCLR) and benzo[a]pyrene (BaP) on detoxification in a fish liver cell line (PLHC-1). Cells were exposed to MCLR (0.01, 1 µM) or BaP (0.01, 0.1, 1 µM) or mixtures of both chemicals for 1 to 48 h. Cytotoxicity, function and regulation of cytochrome P450 1A (CYP1A) and P-glycoprotein (Pgp) were analyzed. Exposure to MCLR, BaP individually or in different mixture combinations induced CYP1A enzyme activity and CYP1A mRNA expression with differences between individual and mixed exposures. An antagonistic mixture effect was seen on induction of CYP1A enzyme activity. The half maximal inhibition concentration of BaP on CYP1A activity was 1.7 µM, whereas MCLR had no inhibitory effect, suggesting that the antagonistic mixture effect is no due to inhibition of the CYP1A enzyme by MCLR. In contrast, a synergistic mixture effect was seen on induction of CYP1A mRNA levels at early exposure times (1 and 3 h). At 6 h or longer exposures times, only the highest BaP concentration tested (1 µM) induced CYP1A mRNA expression. Function and regulation of Pgp were not significantly affected in any of the exposure experiments. Besides, none of tested concentrations or mixtures caused cytotoxicity. This study suggests mixture effects between MCRL and BaP at lower concentrations (maximum 1 µM) on function and regulation of CYP1A in a fish liver cell line, providing new insights into the potential adverse mixture effects between these two different classes of aquatic contaminants.

Keywords: cyanotoxins, polycyclic aromatic hydrocarbons, chemical mixtures, cytochrome P450 1A, P-glycoprotein, fish