A C-13 NUCLEAR-MAGNETIC-RESONANCE STUDY OF FREE FATTY-ACID INCORPORATION IN ACYLATED LIPIDS IN DIFFERENTIATING PREADIPOCYTES

To understand the role of free fatty acid (FFA) incorporation in the a ccumulation of lipids in the adipocyte and ultimately in the developme nt of obesity, C-13 nuclear magnetic resonance was used to study lipid metabolism in differentiating preadipocytes, The incorporation of C-1 3=O-labeled FFA into cellular lipids in primary cultured rat preadipoc ytes and 3T3L1 preadipocytes at different stages of differentiation wa s monitored by the C-13 carbonyl chemical shift. Significant incorpora tion of palmitic acid into phosphatidylcholine in both the alpha and b eta acyl chain positions was found in cells at early stages of differe ntiation. At later differentiation stages or after extended incubation periods, most of the C-13=O signals were found in the triacylglycerol (TG) molecules. Unsaturated C-13=O-labeled acyl chains were detected in the TG molecules when cells were incubated with saturated C-13=O-la beled FFA, indicating that intracellular dehydrogenation had occurred in the C-13=O-labeled palmitoyl chain. By using C-13-labeled methyl my ristate as an internal intensity reference, incorporation of C-13 FFA into each acyl chain position of the major intracellular lipids was de termined quantitatively.