Transport of fluorescent derivatives of fatty acids into cultured human leukemic myeloid cells and their subsequent metabolic utilization

Transport of fluorescent derivatives of fatty acids across the cell membrane of cultured human leukemic myeloid cells (HL 60) and their subsequent metabolic utilization were studied. The rates of uptake of these derivatives and their incorporation into cellular lipids were compared with that of radioactively labelled palmitic acid. Three groups of fluorescent derivatives were observed: A, those transported into the cells and subsequently incorporated into neutral lipids and phospholipids, B, fatty acids which were taken up by the cells but not utilized metabolically, and C, fatty acids which were not transported across the cell membrane. Fatty acids of the latter group, except the hydrophobic probe, also contained functional groups such as hydroxy, acetylamino or sulfonylamino. When observed in fluorescence microscopy, cells incubated with group A fatty acids contained intracellular fluorescent granules, whereas those incubated with group B fatty acids showed diffuse fluorescence. HL 60 cells undergo differentiation into granulocytes or macrophages upon treatment with dimethylsulfoxide or a phorbol ester, respectively. When compared to the uninduced cells, the transport of the fluorescent fatty acids or palmitic acid as well as their subsequent incorporation into lipids were considerably lower in the granulocytes and higher in the macrophages. The use of the fluorescent derivatives as a tool for studying transport of fatty acids across the cell membrane is discussed.