Cellular and molecular responses of earthworm coelomocytes and antioxidant enzymes to naphthalene and a major metabolite (1-naphthol)

Abstract

Naphthalene exerts potential threats on the soil environment and soil-dwelling species. The toxic effects on soil organisms, the response of antioxidant enzymes and the underlying molecular mechanisms for naphthalene metabolites remain to be fully elucidated. Here we report the cytotoxicity and oxidative stress induced by naphthalene and a major metabolite (1-naphthol) on Eisenia fetida coelomocytes and the interaction mechanism between 1-naphthol and the critical antioxidant enzymes (CAT and SOD). Earthworm coelomocytes were more susceptible to 1-naphthol than to naphthalene. At the molecular level, 1-naphthol preferentially bound to the active site of CAT with catalytic residues (His 74, Tyr 357 and Asn147) and the surface of SOD via hydrophobic forces and hydrogen bonds. Direct exposure to 1-naphthol resulted in the unfolding of the CAT skeleton accompanied by secondary structure changes, though only changes in SOD skeleton were observed, without a change in the secondary structure. Static fluorescence quenching of CAT and SOD were initiated with 1-naphthol by the formation of a non-fluorescent complex. Direct 1-naphthol binding inhibited the activity of CAT but presented no adverse effects on the activity of SOD. This paper provides a theoretical basis for the elucidation and better understanding of the toxicity of naphthalene and its metabolites.