Decreased white fat cell thermogenesis in obese individuals

Abstract

OBJECTIVE: To investigate whether white adipocyte thermogenesis and energy metabolism are reduced in obese individuals. SUBJECTS: Eight lean and 15 obese men and women; BMI 19–41. DESIGN: Isolated subcutaneous adipocytes were maintained in agarose gel for 20 h under basal conditions and subsequently for 10 h after stimulation with 1 µM isoprenaline. Direct microcalorimetry was performed continuously over 30 h while biochemical measures were obtained after 0, 20, 25 and 30 h. MEASUREMENTS: Total cellular thermogenesis, oxygen consumption, glycolysis, lipolysis, triglyceride/FFA substrate cycle, adenine nucleotides, DNA content as basis of reference. RESULTS: Under basal and stimulated conditions, thermogenesis (5.6 and 8.6 µW/µgDNA, respectively; P<0.0001) correlated negatively (P<0.01 and P<0.05, respectively) with the BMI and positively with O₂ and glucose consumption, lactate, glycerol, FFA release and FFA re-esterification. Reduced basal lactate production with increased BMI (P<0.05) indicates a more aerobic adipocyte metabolism in obese individuals. Negative correlation between BMI and stimulated triglyceride/FFA substrate cycle activity (P<0.01) explains the decreased hormone induced adipocyte heat production in the obese. CONCLUSIONS: The results suggest that a reduction of total body energy expenditure, which is discussed to cause obesity, can be associated with distinct metabolic alterations at a cellular level. However, since the estimated total body fat cell thermogenesis does not exceed 7% of the resting metabolic rate, the observed decrease of adipocyte heat production in the face of augmented BMI can only in part be responsible for the development of obesity.