Brown adipose tissue lipid metabolism in morbid obesity: the effect of bariatric surgery-induced weight loss.

Objective: We aimed to investigate the effect of bariatric surgery on lipid metabolism in supraclavicular brown adipose tissue in morbidly obese women. We hypothesized that lipid metabolism improves after surgery-induced weight loss. Materials and methods: A total of 23 morbidly obese women (BMI, 42.1 +/- 4.2 kg/m(2); age, 43.8 +/- 9.8 years) were assessed before and 6 months after bariatric surgery and 15 age-and sex-matched controls (22.6 +/- 2.8 kg/m(2)) were assessed once. In the supraclavicular fat depot, fractional (FUR) and NEFA uptake rates were measured with F-18-FTHA-PET. We assessed tissue morphology (triglyceride content) using computed tomography (CT)-radiodensity (in Hounsfield Units[HU]) and the proportion of fat with high density (sBAT [%]) in the entire supraclavicular fat depot. Results: The supraclavicular fractional uptake rate was lower in obese women compared to controls (0.0055 +/- 0.0035 vs 0.0161 +/- 0.0177 1/min, P=.001). Both FUR (to 0.0074 +/- 0.0035 1/min, P=.01) and NEFA uptake rates (to 0.50 +/- 0.50 mu mol/100 g/min, P=.001) increased after surgery. Compared to controls, obese women had lower CT-radiodensity (-101.2 +/- 10.1 vs -82.5 +/- 5.8 HU, P <.001) and sBAT (43.4 +/- 8.4% vs 64.5 +/- 12.4%, P <.001). After surgery, CTradiodensity increased (to -82.5 +/- 9.6 HU, P <.001), signifying decreased triglyceride content and sBAT improved (to 58.0 +/- 10.7%, P <.001), indicating an increased proportion of brown fat. The change in tissue morphology, reflected as increase in CT-radiodensity and sBAT (%), was associated with a decrease in adiposity indices and an increase in whole-body insulin sensitivity. Conclusions: A decrease in triglyceride content, coupled with the increased proportion of brown adipose tissue in the supraclavicular fat depot, may play a role in the improvement of whole-body insulin sensitivity observed in morbidly obese women after surgery-induced weight loss.