Ethanol-induced changes in the content of triglycerides, ceramides, and glucosylceramides in cultured neurons.

BACKGROUND

Ethanol induces apoptosis in cultured neurons. To assess the involvement of sphingolipids and neutral lipids in the apoptotic process, ethanol-induced alterations in lipid content and metabolism were examined by using primary cultured rat cerebellar granule neurons (CGNs), human neuroblastoma SK-N-SH cells, and mouse neuroblastoma Neuro2a cells. Ethanol treatment conditions that induced apoptosis in CGNs and SK-N-SH cells but not in Neuro2a cells were used for these experiments.

METHODS

Cultured neurons were treated with and without 100 mM ethanol for one to three days, and the amounts of cellular sphingolipids [ceramide, glucosylceramide (GlcCer), and sphingomyelin] and neutral lipids [cholesterol, triglyceride (TG), and cholesterol ester (ChE)] were analyzed by high-performance thin-layer chromatography, using a Coomassie brilliant blue staining method. The incorporation of [C] acetate into each lipid fraction was measured in CGNs treated with and without ethanol. Also, the effect of delipidated serum, sterols, myriocin (a serine-palmitoyltransferase inhibitor), and desipramine (an acid sphingomyelinase inhibitor) on ethanol-induced lipid changes was studied by using Neuro2a cells.

RESULTS

The most prominent change common to CGN, SK-N-SH, and Neuro2a cells was ethanol-induced TG accumulation. Higher incorporation of radioactivity into TG was also observed in ethanol-treated cultures when cellular lipids were metabolically labeled with [C] acetate in CGNs. In addition, ethanol elevated ceramide levels in all these neurons. However, ethanol induced decreases in GlcCer along with the reduction of cell viability in SK-N-SH cells and CGNs, whereas it increased GlcCer in Neuro2a cells that remained viable. Myriocin, which reduced ceramide levels, attenuated ethanol-induced cell death in SK-N-SH cells. Ethanol-induced accumulation of TG was sterol-independent, whereas changes in ceramide and GlcCer were affected in Neuro2a cells by the presence of sterols in the medium. Staurosporine, which induced cell death in SK-N-SH cells, increased levels of TG, ChE, and ceramides and reduced the level of GlcCer.

CONCLUSIONS

The results showing that ethanol induces accumulation of TG and ceramide in cultured neurons suggest that ethanol enhances lipogenesis and/or reduces fatty acid degradation in neurons, as previously observed in other cell types. Further, ethanol-induced changes in lipid metabolism, specifically those of ceramide and GlcCer, may be related to the ethanol-induced apoptotic pathway.