A preliminary study of subject factors associated with poor differentiation capacity of visceral and subcutaneous adipose tissue in human obesity
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BACKGROUND: Fat is stored in adipose tissue. In obesity, differentiation of preadipocytes to new adipocytes (fat cells) is required for energy storage. Otherwise fat accumulation in non-adipocytes contributes to fatty liver and diabetes. Our goal was to assess subject characteristics associated with poor in-vitro differentiation capacity of preadipocytes from omental (OM) and abdominal subcutaneous (SC) fat. APPROACH: A convenience sample of, 4 males and 20 females, age 39±2 (range 20-56) years, BMI 42 ± 2 (23-63) kg/m2 (i.e. from lean to obese), 7 Caucasian, 8 Hispanic, 1 other and 8 African Americans) undergoing elective surgery was studied. Fat samples collected during surgery were used for histology and preadipocyte isolation. Fat cell diameters and their distribution (normal or bimodal) were analyzed from histology. Preadipocyte differentiation capacity was measured in vitro. RESULTS: In the OM depot, no effect of ethnicity, sex or HbA1c was found. Unexpectedly, subjects with preadipocytes with poor differentiation capacity tended to be younger (poor differentiation group 36 ± 2 years versus high 43 ± 3 years, p=0.09) and to have lower fasting glucose (poor 97 ± 3.65 mg/dl versus high 111 ± 7.08 mg/dl, p=0.06). In SC, no differences were noted. Fat cell size was not associated with differentiation capacity in either depot. Bimodal distribution, which may show formation of new adipocytes, was seen mostly in Caucasian subjects (5 out of 7) compared to Hispanic (3 out of 8) and African Americans (2 out of 8). CONCLUSION: It is important to investigate the associations between age/ethnicity and OM preadipocyte differentiation/cell distribution in adequately powered cross-sectional studies.