| BackgroundCadmium(Cd)is an extremely toxic environmental and occupational pollutant that endangers human health.The rapidly increasing Cd levels in the environment have provoked public concerns regarding its potential harmful effects on human health,especially in China.Although Cd is known to be general toxicity,recently the hepatotoxicity of Cd has raised increasing public concerns.Epidemiological data revealed that Cd exposure is positive correlation with hepatic necroinflammation and non-alcoholic/alcoholic fatty liver disease.Growing evidence indicates that inflammation,apoptosis and oxidative stress play crucial roles in Cd-induced toxicity.What is more,the NOD-like receptor pyrin domain containing 3(NLRP3)inflammasome is found to be a key signalling platform that detects pathogen-associated molecular patterns(PAMPs)and danger-associated molecular patterns(DAMPs).Upon NLRP3 inflammasome activation,pro-inflammatory factor such as IL-1β and IL-18 will be elicited,which contributes to the innate immune response.However,whether NLRP3 inflammasome is involved in Cd-induced liver inflammation have not been reported.Melatonin(N-acetyl-5-methoxytryptamine),an indoleamine mainly produced by the pineal gland,skin and gut,has been shown to exert biological activities,including antioxidative,anti-inflammatory and anti-apoptotic properties.Based on the fact that oxidative stress and inflammation participate in Cd-induced injury,melatonin may be a potential therapeutic agent for the treatment of Cd-induced toxicity.However,the molecular mechanism of how melatonin ameliorates Cd-induced injury remains unknown.Therefore,our present study was conducted to investigate whether Cd-induced inflammatory injury in the liver through the NLRP3 inflammasome pathway.We further tested the hypothesis that melatonin could confer hepatoprotection via inhibiting TXNIP-NLRP3 inflammasome activation.Methods(1)Male C57BL/6 mice were randomly assigned into control group and Cd treatment group.Cd treatment group were intraperitoneally injected with CdCl2(2 mg/kg);the control group mice received an equal volume of normal saline.At 0,6,12,and 24 h after Cd administration,mice liver and blood samples were immediately collected.Liver function,histological damage and inflammation were measured by serum levels of alanine aminotransferase(ALT),aspartate aminotransferase(AST),LDH,IL-1β,IL-6,TNF-α and hematoxylin and eosin(H&E)staining.NLRP3 inflammasome activation was measured by western blot of NLRP3,caspase-1 and IL-1β and caspase-1 activity.NLRP3-/-mice was used to verify the role of the NLRP3 inflammasome in Cd-induced hepatotoxicity.(2)Before CdCl2 treatment,mice was intraperitoneally pre-treatment with melatonin(10 mg/kg)once a day for 3 days to investigate the protective effects of melatonin against Cd-induced hepatotoxicity by detecting the serum levels of ALT/AST and LDH as well as H&E staining.Further examing the hepatic oxidative stress,TXNIP expression levels and NLRP3 inflammasome activation to verify the role of TXNIP-NLRP3 inflammasome in melatonin against Cd-induced hepatotoxicity.Results(1)Cd exposure progressively increased the serum ALT/AST and LDH activities.What is more,the plasma levels of IL-1β,IL-6 and TNF-α and MPO expression in liver were elevated after Cd exposure.The histopathological analysis showed that Cd exposure resulted in hepatocyte swelling and necrosis,liver inflammatory infiltration and hemorrhage,which indicated that Cd exposure induced liver injury and inflammation.Cd exposure significantly increased the expression levels of NLRP3,caspase-1 and IL-1β as well as the activities of caspase-1.When compared with the WT mice,deficiency of NLRP3 inhibited the activation of NLRP3 inflammasome and improved liver injury induced by Cd exposure.This suggested that NLRP3 inflammasome play a vital role in Cd-induced liver injury.(2)Melatonin pretreatment markedly alleviated Cd-induced liver injury,hepatocyte necrosis and inflammatory cell infiltration.The ELISA and real time RT-PCR results showed that melatonin pretreatment effectively decreased the elevated plasma levels and liver gene expression levels of IL-1β,IL-6 and TNF-α caused by Cd treatment.Furthermore,melatonin pretreatment significantly reduced MDA content and restored the activities of SOD,CAT and GSH in Cd-treated mice.Moreover,Cd treatment not only induced the expression of TXNIP mRNA and protein,but it also enhanced the interaction between TXNIP and NLRP3,which was significantly blunted by the pretreatment of melatonin.ConclusionsIn conclusion,we propose an intriguing mechanism that Cd-induced liver inflammation is dependent the activation of the NLRP3 inflammasome.Most importantly,our study is the first time to document that the protective effect of melatonin is mediated by the TXNIP-NLRP3 inflammasome pathway.Taken together,our findings provide new insight and pharmacological evidence for the application of melatonin as an antagonist for Cd toxicity. |
