The origin of H-1 NMR-visible triacylglycerol in human neutrophils - High fatty acid environments result in preferential sequestration of palmitic acid into plasma membrane triacylglycerol

Human neutrophils incubated for 1 h in vitro with 10% commercial pooled, hu man serum containing high levels of free fatty acids (1141 mu m) displayed a distinct lipid signal, typical of triacylglycerol, in the H-1 NMR spectru m. Concurrently their plasma membrane triacylglycerol mass increased 4.6-fo ld with a selective rise in the content of palmitic and linoleic acids. Alt hough qualitatively similar, these effects were much greater than those obs erved after incubating neutrophils with 50 mu g.mL(-1) of lipopolysaccharid e in the presence of 10% AB serum with normal free fatty acid content (345 mu m, LPS/S). Incubation of neutrophils with an artificial mixture of free fatty acids at concentrations found in commercial serum, or with the fatty acid fraction isolated from commercial serum increased the H-1 NMR-detectab le triacylglycerol. The signal intensity of the H-1 NMR-detectable triacylg lycerol depended on the triacylglycerol composition, and correlated with in creased membrane triacylglycerol mass. Cellular uptake of H-3-labelled palm itic or oleic acids increased in the presence of commercial serum but not w ith LPS/S, with little contribution in either case to the triacylglycerol p ool that increased in mass. Pulse-chase experiments demonstrated that with LPS/S and commercial serum, radiolabelled palmitic acid was preferentially incorporated into triacylglycerol located in the plasma membrane. This proc ess could occur at the plasma membrane, as cytoplasts efficiently convert e xogenous fatty acids into triacylglycerol. We propose that LPS/S and serum containing high levels of free fatty acid, important in conditions of sepsi s and inflammation, may facilitate the sequestration of palmitic acid into triacylglycerol by different pathways. This triacylglycerol originates from exogenous and endogenous free fatty acids, is H-1 NMR-visible, and may hav e a role in regulating apoptosis.