Racial differences in in vivo adipose lipid kinetics in humans

The storage of lipids in the form of triglycerides (TGs) and the de novo synthesis (lipogenesis) of fatty acids from nonlipid precursors [de novo lipogenesis (DNL)] are important functions of adipose tissue (AT) that influence whole-body metabolism. Yet, few studies have reported in vivo estimates of adipose lipid kinetics in humans. Fifty-two women with obesity (27 African-American and 25 Caucasian; 29.7 ± 5.5 years; BMI 32.2 ± 2.8 kg/m²; 44.3 ± 4.0% body fat) were enrolled in the study. In vivo synthesis (or replacement) of TGs (f_TG) as well as the synthesis of the fatty acid, palmitate [a measure of adipose DNL (f_DNL)], were assessed using an 8 week incorporation of deuterium into lipids (glycerol and palmitate moieties of TGs) in subcutaneous abdominal (scABD) and subcutaneous femoral (scFEM) AT. We report, for the first time, significant race differences in both TG synthesis and absolute DNL, with Caucasians having higher f_TG and f_DNL as compared with African-Americans. The DNL contribution to newly synthesized TG (corrected f_DNL) was not different between races. Interestingly, our findings also show that the scFEM adipose depot had higher TG replacement rates relative to the scABD. Finally, the replacement rate of TG (f_TG) was negatively correlated with changes in body weight over the 8 week labeling period. Our results provide the first evidence that in vivo TG replacement (synthesis and breakdown) rates differ by ethnicity. In addition, TG turnover varies by depot location in humans, implying an increased capacity for TG storage and higher lipolytic activity in the scFEM AT.