Mechanism of mahanine-induced apoptosis in human leukemia cells (HL-60).

Mahanine, a carbazole alkaloid occurs in the edible part of Micromelum minutum, Murraya koenigii and related species has been found to induce apoptosis in human myeloid cancer cell (HL-60). Concentration of 10 microM mahanine caused a complete inhibition of cell proliferation and the induction of apoptosis in a time dependent manner. Mahanine-induced cell death was characterized with the changes in nuclear morphology, DNA fragmentation, activation of caspase like activities, poly(ADP-ribose) polymerase cleavage, release of cytochrome c into cytosol and stimulation of reactive oxygen species generation. The cell death was completely prevented by a pancaspase inhibitor benzyloxycarbonyl-L-aspart-1-yl-[(2,6-dichlorobenzoyl)oxy]methane (Z-Asp-CH(2)-DCB). Mahanine activated various caspases such as caspase-3, -6, -8 and -9 (like) activities but not caspase-1 like activity. More than 70% cell survival was observed in the presence of a caspase-3 inhibitor. In addition, co-treatment of cyclosporin A markedly increased the survival of mahanine-treated HL-60 cells. Flow cytometric analysis revealed that mahanine decreased the mitochondrial membrane potential of intact cells, and disrupted cell cycle progression by increasing the number of cells in sub-diploid region, concomitantly with the decrease of cells in diploid phases, particularly at late hours of apoptosis. The overall results suggest that mahanine down regulates cell survival factors by activation of caspase-3 through mitochondrial dependent pathway, and disrupts cell cycle progression.