A ¹³C 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 accumulation of lipids in the adipocyte and ultimately in the development of obesity, ¹³C nuclear magnetic resonance was used to study lipid metabolism in differentiating preadipocytes. The incorporation of ¹³C=O-labeled FFA into cellular lipids in primary cultured rat preadipocytes and 3T3L1 preadipocytes at different stages of differentiation was monitored by the ¹³C carbonyl chemical shift. Significant incorporation of palmitic acid into phosphatidylcholine in both the α and β acyl chain positions was found in cells at early stages of differentiation. At later differentiation stages or after extended incubation periods, most of the ¹³C=O signals were found in the triacylglycerol (TG) molecules. Unsaturated ¹³C=O-labeled acyl chains were detected in the TG molecules when cells were incubated with saturated ¹³C=O-labeled FFA, indicating that intracellular dehydrogenation had occurred in the ¹³C=O-labeled palmitoyl chain. By using ¹³C-labeled methyl myristate as an internal intensity reference, incorporation of ¹³C FFA into each acyl chain position of the major intracellular lipids was determined quantitatively.