Apoptosis induction by ceramide derivatives and its potential mechanisms through domain formation

Ceramides, which are recognized as pivotal signaling agents in cell differentiation and proliferation, elicit apoptosis in response to anticancer drugs and stress. Although the 1-hydroxy group of ceramide is considered to play an important role in inducing apoptosis, the detailed mechanism underlying ceramide-induced apoptosis remains elusive. We previously synthesized ceramide derivatives by transforming the 1-hydroxy group into amino and carboxy groups, and assessed their ability to form domains in artificial membranes. In this study, we evaluated the apoptotic activities of these derivatives against living cells. Surprisingly, despite the lack of the 1-hydroxy group, most of the derivatives exhibited apoptotic activity, with some being more active than ceramide. Confocal microscopy using fluorescent-ceramide and coherent anti-Stokes Raman scattering microscopy utilizing deuterated ceramide suggested the formation of large domains on living cell membranes. These findings suggest a potential relationship between domain formation and apoptotic activity. Liquid chromatography-mass spectrometry showed that the differences in apoptotic activity among the derivatives were unlikely attributed to variations in cellular uptake. Consequently, we propose that these ceramide derivatives accumulate and form distinct domains within the cellular membranes, inducing apoptosis. Intracellular ceramides synthesized in response to external stimuli may trigger apoptosis through the same mechanism.