N-Acetylcysteine Alleviates PCB 52-induced Hepatotoxicity By Repressing Oxidative Stress And Inflammatory Responses

BACKGROUNDPolychlorinated biphenyls(PCBs),a class of persistent organic pollutants and human carcinogens,exert toxic effects on human,such as hepatotoxicity and neurotoxicity.Although they have been banned for over 30 years,high levels of PCBs can still be detected in our environment.According to the data of environmental epidemiological,PCBs in the air are mainly low-chlorinated PCBs,especially tri-and tetra-chlorinated congeners.Moreover,PCBs can accumulate in human fatty tissue by food chain and respiratory tract.Human liver is the main metabolic organ of exogenous chemicals.PCBs can induce oxidative stress and inflammatory response,and participate in the occurrence and development of various chronic diseases.However,the mechanisms of the toxic effects and effective prevention and treatment for exposure of PCBs need further investigations.The initiation of oxidative stress can be resulted from the imbalance of redox homeostasis,which is manifested as excessive production of intracellular reactive oxygen species(ROS)and/or dysfunction of the antioxidant defense system.Oxidative stress is involved in the occurrence and development of various diseases by activating the TLR4-MyD88-Traf6 inflammatory signaling pathway.N-Acetylcysteine(NAC),a ROS scavenger,can reduce excess ROS in vivo and in vitro as well as oxidative stress-induced damage.ObjectivesThe aims of the present study are to clarify the underlying mechanisms of PCB52-induced hepatotoxicity in vitro and provide some experimental evidence for the treatment for PCB52 exposure.MethodsRat(Brl-3A)and human(L-02)normal liver cells were exposed to PCB52(40μM).The cell viability was determined by cell counting kit 8(CCK-8).Flow cytometry was used to detect the level of reactive oxygen species(ROS)in hepatocytes,and malondialdehyde(MDA)was detected using MDA test kit.The mRNA expression levels of inflammatory-realted factors in cells were examined by RT-qPCR method,while their protein levels were determined by western blotting method.After the pretreatment of NAC,the cell viability,ROS level,MDA content,mRNA expression of inflammatory-related factors and their protein levels were further examined by the above mentioned methods.Results1.PCB 52 exposure decreased the cell viability in normal rat and human hepatocytes.2.PCB 52 exposure resulted in accumulation of ROS and increase of MDA in hepatocytes.3.PCB 52 exposure increased expression of inflammatory-related genes and proteins.In rat hepatocytes,expression of Traf6,Myd88,Tnf-α,Hmox1 and Nqo1 were significantly increased compared with the control,while no significant change of Keap1 and Nfe2l2 expression was observed.In human hepatocytes,expression of MYD88,TNF-α and IL1B were significantly increased compared with the control,while no significant change of KEAP1,NFE2L2,HMOX1,NQO1 was detected.4.The pretreatment of NAC significantly improved the cellular viability of the hepatocytes.5.Intracellular ROS accumulation and MDA content were significantly alleviated in hepatocytes by the pretreatment of NAC compared with the PCB52-treated cells.6.Expression of Traf6,Myd88,Tnf-α,Hmox1 in rat hepatocytes and MYD88,TNF-α,IL1B in human hepatocytes were significantly decreased by the pretreatment of NAC compared with the PCB52-treated cells.Protein expression of TLR4,Traf6,MyD88 were significantly decreased by the NAC pretreatment,although no significant changes of mRN A levels of Keap1,Nfe2l2 and protein expression of Nrf2,Keapl,HO-1 were observed.Conclusions1.PCB 52 exposure resulted in ROS accumulation and increase of MDA content in hepatocytes,which might initiate inflammatory response and induced hepatotoxicity.2.NAC pretreatment effectively alleviated PCB 52-induced hepatotoxicity by repressing oxidative stress and inflammatory responses.