Analysis and quantitation of ceramide

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It is now well appreciated that many membrane lipids play important roles in the specific responses of cells to various stimuli. The sphingolipid ceramide has emerged as a relatively new addition to the group of bioactive lipid molecules, with suggested roles in the regulation of the stress response. Indeed, many inflammatory cytokines, stresses such as heat, ischemia/reperfusion, and oxidation, and cytotoxic agents affect ceramide metabolism and induce increases of its cellular levels. On the other hand, treatment with exogenous ceramides or agents that induce accumulation of endogenous ceramide can mimic many of the responses to a stress stimulus. These include effects on cell differentiation, apoplosis, and cell senescence. Such effects are not induced by closely related compounds such as dihydroceramide and stereoisomers of the natural ceramides. Intracellular levels of ceramide can be increased by its de novo synthesis (a multistep pathway involving several enzymes) or by the hydrolysis of more complex sphingolipids. Reciprocally, ceramide levels can be decreased via metabolic and/or catabolic reactions, including incorporation of ceramide into other sphingolipids via activation of enzymes such as sphingomyefin syntfiase or cerebroside synthase or its hydrolysis into fatty acids and sphingosine (by the action of ceramidases).