Triglyceride Synthesis in Epididymal Adipose Tissue CONTRIBUTION OF GLUCOSE AND NON-GLUCOSE CARBON SOURCES

The obesity epidemic has generated interest in determining the contribution of various pathways to triglyceride synthesis, including an elucidation of the origin of triglyceride fatty acids and triglyceride glycerol. We hypothesized that a dietary intervention would demonstrate the importance of using glucose versus non-glucose carbon sources to synthesize triglycerides in white adipose tissue. C57BL/6J mice were fed either a low fat, high carbohydrate (HC) diet or a high fat, carbohydrate-free (CF) diet and maintained on (H2O)-H-2 (to determine total triglyceride dynamics) or infused with [6,6-H-2] glucose (to quantify the contribution of glucose to triglyceride glycerol). The (H2O)-H-2 labeling data demonstrate that although de novo lipogenesis contributed similar to 80% versus similar to 5% to the pool of triglyceride palmitate in HC-versus CF-fed mice, the epididymal adipose tissue synthesized similar to 1.5-fold more triglyceride in CF-versus HC-fed mice, i.e. 37 +/- 5 versus 25 +/- 3 mu mol x day(-1). The [6,6-H-2] glucose labeling data demonstrate that similar to 69 and similar to 28% of triglyceride glycerol is synthesized from glucose in HC-versus CF-fed mice, respectively. Although these data are consistent with the notion that non-glucose carbon sources (e. g. glyceroneogenesis) can make substantial contributions to the synthesis of triglyceride glycerol (i.e. the absolute synthesis of triglyceride glycerol from non-glucose substrates increased from similar to 8 to similar to 26 mu mol x day(-1) in HC-versus CF-fed mice), these observations suggest (i) the importance of nutritional status in affecting flux rates and (ii) the operation of a glycerol-glucose cycle.