Exposure to chlorothalonil in zebrafish: modulation and biotransformation potential of two cytosolic GST isoforms

Glutathione S-transferases (GSTs) are enzymes involved in the Phase II biotransformation of xenobiotics, including chlorothalonil (CLT), an organochlorine biocide used in agriculture, and antifouling paints. However, GSTs comprise a family of related enzymes and specific isoforms that are preferentially involved in CLT metabolism have not yet been identified. Thus, the objective of this study was to identify whether the two cytosolic GST isoforms expressed in zebrafish gills (GSTP and GSTA) were modulated by CLT exposure and their potential to participate in CLT metabolism in this species. Initially, the activity of both GST isoforms was evaluated in zebrafish gills after chlorothalonil exposure (to 0.1 and 10 μg/L) for 4 and 7 days. The highest CLT concentration tested (10 μg/L) significantly increased GSTP activity after 4 days of exposure and the activity of GSTA after 7 days of exposure. The mRNA levels of the gstp (gstp1 and gstp1) and gsta (gsta1 and gsta2) isoforms were also evaluated in fish gills after exposure to the same CLT concentration, but no significant alteration was observed. Finally, in silico analysis strongly suggests that CLT could interact with the active site of both GST isoforms with good binding affinity, following a spontaneous thermodynamic process (ΔG < 0 kcal/mol). The approach employed here indicated that both GST isoforms could be involved in the biotransformation of CLT in the gills of D. rerio while protecting the fish against the deleterious effects of contaminants.