Objectives : Understanding 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.
Methods : We 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.
Results : Storage 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.
Conclusions : In 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 Sources :
DK40484, DK45343, DK50456