Fatty Acid Storage from Systemic FFA and VLDL-triglyceride Between Visceral and Subcutaneous Adipose Tissue Depots in Morbid Obesity (OR09-06-19)

Abstract

ObjectivesUnderstanding both systemic and cellular factors that govern lipid storage in different tissue depots may be essential for understanding the genesis of differences in body fat distribution. MethodsWe assessed fatty acid (FA) storage in upper body subcutaneous adipose (UBSQ), visceral (omental) adipose (VAT), and liver from systemic free fatty acids (FFA) using [9,10–3H] palmitate tracer and from very low density lipoprotein (VLDL) triglycerides (TG) using autologous [1–14C]VLDL-TG tracers combined with carefully timed biopsies in patients undergoing bariatric surgery. We measured the activity of 4 enzymes that regulate adipocyte FA storage: lipoprotein lipases (LPL) – an extracellular enzyme, and 3 intracellular enzymes - acyl-CoA synthase (ACS), glycerol-3-phospate acyltransferase (GPAT) and diacylglycerol transferase (DGAT). Finally, we examined systemic factors (fasting plasma insulin and resting energy expenditure (REE)) that might relate to lipid storage. ResultsStorage of systemic FFA was well correlated between VAT and UBSQ (r = 0.53, P < 0.006), UBSQ and liver (r = 0.69, P = 0.0003), but not between VAT and liver. Storage of VLDL-TG was positively correlated between all three depots. Fasting LPL activity was positively correlated with storage of VLDL-TG in VAT (r = 0.47, P < 0.05) but not UBSQ. Fasting palmitate was correlated with storage rates of systemic FFA in both VAT (r = 0.45, P < 0.03) and UBSQ (r = 0.48, P < 0.03). The activities of intracellular storage enzymes (ACS, DGAT, and GPAT) were unrelated to UBSQ storage of systemic FFA or VLDL-TG. None of the intracellular enzymes correlated with storage of systemic FFA in VAT; only ACS (r = 0.50, P < 0.03) was positively correlated with VLDL-TG storage; DGAT and GPAT tended to correlate (P = 0.056 and P = 0.0719, respectively). Plasma insulin was unrelated to storage of either lipid in both depots. Interestingly, REE was negatively correlated to VAT storage of VLDL-TG (r = 0.45, P < 0.03) but not systemic FFA, whereas REE was negatively correlated to UBSQ storage of systemic FFA (r = 0.50, P < 0.05) but not VLDL-TG. ConclusionsIn morbid obesity, differences in cellular and systemic factors contribute to variations in storage of VLDL-TG versus systemic FFA between VAT and UBSQ; however, within each subject there is no preferential partitioning of FA to either VAT or UBSQ. Funding SourcesDK40484, DK45343, DK50456.