Acid Sphingomyelinase/ceramide Mediates Hepatocytic Injury Of Mice Induced By Noise Exposure

Background Noise pollution is an increasingly serious public health problem in modern society and an important component of military aviation environment.Long-term noise exposure leads to not only hearing loss but also non-hearing impairment,such as sleep disturbance,declined mental function and cardiovascular diseases,lowering health and working ability of flight and ground crews.Epidemiological survey showed that there was high incidence of hyperlipidemia or fatty liver in noise exposed population.Animal study indicated the activity of transaminase in serum was enhanced after noise exposure suggesting it might evoke hepatocytic injury.However,it is still unclear how the noise affects the structure or functions of hepatocytes,what mechanism underlies the changes and how to prevent it from happening.Sphingolipids(SLs)are active lipid constituents controlling multiple crucial cellular activities,among which acid sphingomyelinase(ASM)hydrolyzes sphingomyeline(SM)producing ceramide(Cer)to prevent the accumulation of SM inside cells.However,the over-activation of ASM or over-generation of Cer contributes to cellular apoptosis,inflammation and oxidative stress involved in the occurring of hepaticinflammation,steatosis and fibrosis.But the changes of ASM/Cer upon noise exposure and the role of it in noise induced liver damage(NILD)are still to be elucidated.Docosahexaenoic acid(DHA)is one of omega-3 polyunsaturated fatty acids(ω-3 PUFA),which reduces inflammatory response in tissues and has been proven inhibiting the activity of ASM.Meanwhile,DHA ameliorates liver damage caused by alcohol,high fat diet or virus infection prominently.The effect of DHA on NILD has never been reported before.Aims 1.To elucidate the effect of noise on hepatocytic structure,morphology,lipid metabolism,apoptosis,fibrosis and oxidative stress in mice.2.To explore the role of ASM/Cer pathway in NILD.3.To investigate the protective role of DHA in NILD and mechanism involved.Methods Male Kunming(KM)mice were exposed to a broad band noise(90-110 d B,20-20 k Hz).Doxepine hydrochloride(DOX)and DHA were used as ASM inhibitor,given to the mice by intragastric administration.1.Hematoxylin-eosin(HE)staining was used to examine the morphological structure of liver tissue.2.Oil red O(ORO)staining was used to detect lipid deposition.3.Transferase-mediated d UTP nick end labeling(TUNEL)was used to count the apoptotic cells.4.Western blot,immunohistochemistry(IHC)staining and quantitative real time polymerase chain reaction(q RT-PCR)were used to detect protein or m RNA content as well as Cer level.5.Masson trichrome staining was used to detect liver fibrosis.6.Dihydroethidium(DHE)fluorescence probe was applied to measure superoxide anion(O2-·)levels.7.Malondialdehyde(MDA),total antioxidant capacity(T-AOC),xanthine oxidase(XOD)and nicotinamide adenine dinucleotide oxidase(NADH oxidase)kits were used to detect oxidative stress.8.Alanine aminotransferase(ALT)and aspartate transaminase(AST)kits were used to test liver function.Results 1.Compared with control group,mice exposed to noise showed significant hepatic cord derangement with edema,vacuolization and karyolysis of hepatocytes.The noise exposure also caused remarkable lipid deposition and apoptosis in hepatocytes and with the prolongation of exposure,pathological changes were gradually aggravated.2.Compared with control group,the ASM gene and protein expression as well as Cer generation in liver tissue of noise exposed mice was significantly increased,which could be restored substantially by DOX treatment.At the same time,DOX mitigated the noise induced structural disorder,lipid deposition,increased apoptosis and higher oxidative stress in hepatocytes significantly.DOX also reversed the noise raised ALT or AST activity in serum.3.DHA attenuated noise elicited hepatic structural disorder of mice significantly.It also restored the hepatocytic lipid deposition,apoptosis and oxidative stress induced by noise exposure substantially.Meanwhile,the increased ASM gene or protein expression and Cer production in liver tissue of noise exposed mice was normalized significantly by DHA treatment.Conclusions 1.Broad band noise exposure led to hepatic cord derangement and promoted lipid deposition,apoptosis and oxidative stress in hepatocytes of mice.2.Noise up-regulated the ASM/Cer pathway in liver tissue of mice which mediated the occurring of hepatocytic injury.3.DHA mitigated the noise induced hepatocytic injury by normalizing the over-activatedASM/Cer pathway in liver tissue of mice.