Characterization of two cellular superoxide dismutases in Protohermes xanthodes (Megaloptera: Corydalidae) in response to sublethal chlorpyrifos stress

Abstract

Pesticides released into the environment are increasingly recognized as a global threat to freshwater ecosystems because of their adverse effects on non-target organisms, particularly aquatic insects and other arthropods. Superoxide dismutases (SODs) are important antioxidant enzymes that play a crucial role in protecting organisms from oxidative stress induced by harmful materials. In this study, we identified 2 cellular SODs (PxSOD1 and PxSOD2) in Protohermes xanthodes Navás (Megaloptera: Corydalidae), an freshwater predatory insect, and determined the oxidative stress induced in P. xanthodes larvae by sublethal exposure to chlorpyrifos (CPF). PxSOD1 and PxSOD2 are members of the cytoplasmic Cu/ZnSODs and mitochondrial MnSODs, respectively, and differ substantially in protein structure. Both PxSOD1 and PxSOD2 recombinant proteins demonstrated catalytic activity toward O2•- in the activity assays. After exposure to sublethal concentrations of CPF, malondialdehyde (MDA) content and SOD activities were increased in P. xanthodes larvae in a dose-dependent manner. PxSOD1 expression was decreased in the 0.42 and 4.2 μg/L CPF groups and increased in the 4.2 μg/L CPF group. PxSOD2 was upregulated by 0.42, 4.2, and 8.4 μg/L CPF treatments and the expression levels in the 4.2 and 8.4 μg/L CPF groups were significantly higher than that in the no CPF control. Our results suggest that sublethal concentrations of CPF can induce oxidative stress in P. xanthodes larvae, and the cellular SODs in P. xanthodes larvae may contribute to the protection against CPF-induced oxidative stress.

Keywords: Protohermes xanthodes; Chlorpyrifos; expression; oxidative stress; superoxide dismutase.