Carboxylesterase activities in chondrichthyans of the western Mediterranean Sea

Sharks, rays, skates and chimaeras play an important role as predators in the ecosystems. These species could serve as potential sentinels for the presence of xenobiotics in marine ecosystems. In this study, liver carboxylesterase (CbE) activity was determined for 20 species of chondrichthyans. Carboxylesterase activity, a known esterase involved in the metabolism of pesticides, lipids and certain drugs, was measured using two substrates: 4-nitrophenyl acetate (pNPA) and α-naphthyl acetate (αNA). Rajiformes (rays and skates) showed higher CbE activity than sharks, and the order Chimaeriformes showed the lowest values. In vitro sensitivity to CbE inhibitors was assessed in the shark Scyliorhinus canicula. The substrate αNA was found to be the most adequate as it displayed the highest activity and was more sensitive to the organophosphate dichlorvos in the liver (IC50 = 2.37 μM) and plasma (IC50 = 0.051 μM). The high interspecific variation of CbE activity and its sensitivity to inhibition by fenofibrate suggest that this enzyme could contribute to species-specific differences in drug detoxification.