The Effect Of Ethanol On The Viability Of Nerve Cells And The Preliminary Mechanisms

Excessive alcohol drinking damages the nervous system,resulting in brain atrophy and decline of cognitive function.Epidemiological studies have shown that in comparison to abstainers,heavy drinkers have higher risk of developing cognitive dysfunction and neurodegenerative diseases such as Alzheimer's disease(AD),while moderate drinkers do not have increased risk of cognitive impairment or AD.In AD patients,heavy drinking causes a faster cognitive decline compared to the abstainers,while light to moderate alcohol drinking leads to a slower cognitive decline.Neuronal cell loss is an important mechanism underlying the brain damages and cognitive impairment in both alcoholics and AD patients.However,the concentration dependent effect of alcohol on neuronal cell survival and its mechanism are not completely understood.In this study,neuro-2a(N2a)cells were used to investigate the toxic effects of ethanol on neuronal cells.The results from MTT assays showed that high concentration of ethanol(175-400 m M)significantly reduced the viability of N2 a cells.In contrast,ethanol treatment with concentration less than 150 m M for 24 h did not alter the viability of N2 a cells.When cocultured with amyloid beta(A?),ethanol treatment with concentration above 10 m M increased while concentration between 0.1 to 1.6 m M decreased A?-induced cytotoxicity.Further studies showed that higher concentration of ethanol promoted while lower concentration of ethanol inhibitied A? aggregation,consistant with their effects on A?-induced cytotoxicity.When the ethanol treatment with concentration between 0.5 to 50 m M was prolonged to 48 h or longer,it was found that the number of cells after ethanol treatment was significantly higher than that of control,with 1 m M ethanol had the most obvious effect.5-bromo-2-deoxyuridine(Brd U)incorporation assay and flow cytometry analyses revealed that the number of cells in the S-phase was increased after ethanol treatment in 36 h or 60 h.The result from Western blot showed that the level of cyclin D1 was elevated.Mitogen-activated protein kinases(MAPKs)and phosphoinositide 3-kinase(PI3Ks)/Akt/mammalian target of rapamycin(m TOR)cell signaling pathways play important roles in the regulation of cell survival and proliferation.In this study,it was found that treatment with lo w concentration of ethanol increased the activation of extracellular signal-regulated kinase 1/2(ERK 1/2)and c-Jun N-terminal kinase(JNK),while decreased the activation of p38 MAPK.In addition,low-concentration ethanol treatment increased the activation of Akt,enhanced the activity of m TOR,which subsequently increased the activation of ribosomal protein S6 kinases(p70S6K).The modulation of above cell signals might be an important mechanism by which low concentration of ethanol increased the number of cells in S-phase.Aldehyde dehydrogenase 2(ALDH2)catalyzes the oxidation and detoxification of acetaldehyde,a toxic intermetabolite of ethanol metabolism.About 40% of Asian population have lower ALDH2 activity because of a single nucleotide polymorph ism of ALDH2 gene.It has been shown that the beneficial effects of low-dose alcohol may be related to the induction of ALDH2.In N2 a cells,treatment with low concentration of ethanol increased the levels of ALDH2.Meanwhile,low concentration of ethanol no longer promoted the cell activity in ALDH2 knockout cells.Therefore,the effect of low concentration ethanol on the growth of N2 a cells is dependent on the activity of ALDH2.Above results showed that high concentration of ethanol induced cytotoxicity,while low concentration of ethanol promoted the survival and the proliferative potential of N2 a cells,which may be related to its modulation of the activation of MAPKs and Akt/m TOR cell signaling pathways.The results may partially explain the role of excessive drinking in promoting cognitive decline and moderate drinking in delaying the pathological development of AD.As the activity of ALDH2 is essential for the promotion of cell activity by ethanol,the effect of alcohol on neuronal cell survival is not only dependent on the dose of alcohol,but also related to the genotype of ALDH2 gene.