Mechanism of apoptosis in HL-60 cells induced by n-3 and n-6 polyunsaturated fatty acids

The biochemical properties and specificity of n-3 and n-6 polyunsaturated f atty acids (PUFAs) are not well known. Because PUFAs induce apoptosis of di fferent cells, we studied the effect of various PUFAs, such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosapentaenoic acid (DPA), on the fate of cultured human promyelocytic leukemia cells (HL-60) to elucida te the mechanism of apoptosis and the difference in action between n-3 and n-6 PUFAs. Fairly low concentrations of PUFAs inhibited the growth of HL-60 cells and induced their apoptosis by a mechanism that is sensitive to DMSO , an antioxidant, and z-Val-Ala-Asp(OMe)-fluoromethylketone (z-VAD-fmk), a pan-caspase inhibitor. PUFAs stimulated the generation of reactive oxygen s pecies (ROS) and activated various types of caspase-like proteases, such as caspase-3, -6, -8, and -9, but not caspase-1. In addition, PUFAs triggered the reaction leading to the cleavage of Bid, a death agonist member of the Bcl-2 family, and also released cytochrome c from mitochondria into the cy tosol. PUFAs also decreased the mitochondrial membrane potential of intact HL-60 cells. All of these actions of n-3 PUFAs were stronger than those of AA, an n-6 PUFA, although the mechanism is not known. PUFAs stimulate swell ing and membrane depolarization of isolated mitochondria in a cyclosporin A -sensitive manner. The results indicated that PUFA-induced apoptosis of HL- 60 cells may be caused, in part, by direct action on the cells and by activ ation of the caspase cascade through cytochrome c release coupled with mito chondrial membrane depolarization. (C) 2001 Elsevier Science Inc. All right s reserved.