Study Of Antioxidant Responses And Nrf2 Transcript Levels In Mytilus Coruscus Exposed To Single And Mixtures Of Cadmium And Benzo(a)pyrene

Exposure to heavy metals and polyaromatic hydrocarbons(PAHs)has been demonstrated to induce an oxidative stress response in bivalves,the combined effect of heavy metals and PAHs on the oxidative stress response has not been reported extensively and little is known about in bivalves.In addition,The Nrf2 antioxidant response pathway plays a pivotal role in in antioxidant defense against oxidative stress and it is a major player in antioxidant protection.As a representative species of marine mussels,thick shell mussels is one kind of common model organism in aquatic environment due to its wide distribution and sensitivity to environmental stresses.Based on the above,in present study,we assessed the antioxidant system potential,lipid peroxidative effects(MDA)and mRNA levels of Nrf2 in the gill and digestive gland of thick shell mussel M.coruscus exposed to individual and binary mixtures(BaP 56 ?g/L + Cd 0.31 mg/L,BaP 56 ?g/L + Cd 0.93 mg/L)of cadmium(0.31 mg/L,0.93mg/L)and benzo(a)pyrene(56 ?g/L)at different exposure times(0,6,12,24,48,and 96 h).The main conclusions are as follows:1.In general,activities of tested enzymes tended to be induced in the gills and inhibited in digestive glands,MDA contents increased both in gills and digestive glands,digestive glands show higher lipid peroxidation than than gills,despite gill antioxidant enzymatic capacity stimulation by contaminants exposure further lipid peroxidative damage occurred.2.In majority exposure scenarios,Cd and BaP interactions induced an antagonistic effect on lipid peroxidation and antioxidant enzymes(SOD,CAT,GPX,GST)(did not significantly increase on the basis of additivity).Interestingly,lipid peroxidation was limited by the combination of Cd and BaP,especially in the gills,which would be related to faster antioxidant response.3.A significant increase in mRNA levels of Nrf2 was observed,and secondly,mRNA levels of Nrf2 in the digestive glands were much higher than that of gills,Additionally,combination of both toxicants produced a clear interaction,specially by refraining Nrf2 expression,which was possibly associated to a lower antioxidant response.In summary,A tissue-specific response showing unique alteration in gill and digestive gland were investigated,indicating the different function of tissues during stress responses.Single and complex contaminant mixtures interact differently based on target tissue which may lead to an imbalance in the thick shell mussel health status.To our knowledge,this is the first study on the role of Nrf2 in mollusk exposed to mixtures of BaP and Cd,which will contribute to further understanding the defense characteristics,molecular mechanism of PAHs and heavy metals on antioxidant responses in bivalves,valuable information for marine pollution monitoring and provide a theoretical basis for the healthy breeding of shellfish.