Effect of Docosahexaenoic Acid on Rate of Differentiation of HL-60 Human Leukemia¹ Free

We have utilized an experimental model of cell lipid modification that allows study of the effect of a polyunsaturated fatty acid on the linked processes of cellular differentiation and growth arrest. HL-60 human leukemia cells were grown in media supplemented with 10 µm concentrations of the fatty acid docosahexaenoic acid (22:6) or oleic acid (18:1) or in unsupplemented media. Gas chromatographic analysis of phospholipid extracts from HL-60 cells grown in unmodified or 18:1-supplemented media revealed 39% and 36% 18:1, 13 and 12% polyenoics, and 2 and 3% 22:6, respectively. In contrast, cells from 22:6-supplemented cultures had 22% 18:1, 18% total polyunsaturated fatty acids, and 10% 22:6. Retinoic acid was added to cells grown in the various media, and phorbol ester-induced superoxide generation, nitroblue tetrazolium reduction, and growth arrest were determined as measures of differentiation. Unmodified and 18:1-enriched cells showed inducible oxidative burst activity beginning at 48 h after the addition of retinoic acid and continuing to increase for 5 days. In marked contrast, the 22:6-enriched leukemia cells exhibited an increased oxidative activity as early as 24 h which is equivalent to about one division cycle time. G_1/0-specific growth arrest was associated with the oxidative phenotypic differentiation in all three cell types. However, cells enriched with 22:6 demonstrated early growth arrest and differentiation considerably in advance of 18:1-modified or unmodified cells. An effect on the cellular differentiation process could be detected after even a brief 1-h exposure of the cells to 22:6. Therefore, a highly polyunsaturated fatty acid which is actively incorporated into membrane structures appreciably accelerates the differentiation process of this human neoplastic cell.