Effect And Affecting Mechanism Of NTiO₂ On Hemocytes Phagocytosis Of Blood Clam,Tegillarca Granosa

With the rapid development of nano-technology,nanoparticles(NPs)are increasingly used in the production of all kinds of industrial goods,daily necessities,and even pharmaceutical products.According to the predictions,the annual production of NPs will reach 500,000 tons by the year of 2020.Under this circumstance,NPs would inevitably escape into the environment during the production,usage,and disposal of NP and NP-containing products.Through the process of surface runoff and precipitation,NP contaminations will eventually converge into its ultimate sink,the ocean,and pose a potential threat to all kinds of marine organisms and the ocean ecosystem.Inhabiting the water-substrate layer of intertidal zone,where NP contaminations are usually condensed,sessile filter feeding bivalves are severely challenged by NP pollution.Though it has been suggested that immune system is one of the targets of NPs,the immunotoxicity of NPs and the affecting mechanisms underlying still remain poorly understood in marine bivalve species to date.Therefore,in the present study,the immune-toxic impact of titanium dioxide nanoparticles(nTiO2),one of the most widely used nanoparticle,on a typical marine bivalve species,the blood clam(Tegillarca granosa),were investigated.Results showed that the phagocytic rate,cell viability,and intracellular Ca2+ concentration of hemocytes were significantly suppressed,whereas the intracellular ROS concentration of hemocytes significantly increased upon nTiO2 exposure.Exposure to nTiO2 also led to the significant downregulation of apoptosis and Ca2+signaling-related genes.Meanwhile,the toxic impacts of nTiO2 were partially mitigated by the addition of exogenous Ca2+,as indicated by the recovery tendency in almost all the measured parameters,indicating an important role of Ca2+signaling in the immunotoxicity of nTiO2.Furthermore,the concentrations of the three neurotransmitters(DA,GABA,and ACh)were significantly induced,whereas AChE activity and the gene expression of modulatory enzymes and receptors of these neurotransmitters were significantly suppressed upon nTiO2 exposure,indicating an evident neurotoxic impact of nTiO2 on T.granosa.In summary,nTiO2 hampers the phagocytic activity of hemocytes probably through disrupting the neuro-immune regulation and subsequently intracellular calcium hemeostasis and Ca2+-signaling,which reduces the effective number and physiological condition of hemocytes and eventually leads to hampered hemocyte phagocytosis.