Differential Induction of Apoptosis of Leukemic Cells by Rhizochalin, Two Headed Sphingolipids from Sponge and Its Derivatives

Two-headed sphingolipids bear a certain similarity with sphingolipids in the structure and but differing from classical sphingolipids in α,ω-position of the basic groups. We analyzed the apoptotic effects of some two-headed sphingolipids including rhizochalin (Rhz) and its derivatives isolated from sponge Rhizochalina incrustata on human leukemia HL-60 cells. Direct addition of Rhz induced apoptosis of HL-60 cells. The aglycon of Rhz, which has no galactosyl residue, showed a stronger ability to induce apoptotic activity than Rhz. Rhz congeners with acetate derivatives only weakly induced apoptosis. The usual mitochondrial membrane permeability changes and the decrease of protein levels of procaspases-8, -9, and -3 correlated with the apoptotic activity of Rhzs. These results suggest that derivatives of two-headed sphingolipids potently induce apoptosis in mammalian cells when administered exogenously and this cell death was dependent on caspase activation pathways.