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Insulin Increases Lipogenic Enzyme Activity in Human Adipocytes in Primary Culture^1,2,3,

University of Tennessee, Department of Nutrition, Agricultural Experiment Station and Physiology Program, Knoxville, TN 37996 ^* University of Tennessee Medical Center, Department of Surgery, Division of Plastic Surgery, Knoxville, TN 37920

Studies with human adipose tissue have demonstrated the presence of key enzymes of fat synthesis. However, long-term regulation of these enzymes has not been reported. To address this issue, we used human adipocytes in primary culture. Human adipose tissue was obtained from abdominal fat of patients undergoing abdominal surgery. Adipocytes were isolated by collagenase digestion and cultured in media supplemented with 1% fetal bovine serum. To evaluate metabolic activity of cultured cells, we assessed the following during the culture: DNA pattern, cell size, glucose consumption and activities for two lipogenic enzymes, fatty acid synthase (FAS) and glycerol-3-phosphate dehydrogenase (GPDH). Analysis of DNA pattern showed that human adipocytes cultured under the above conditions did not undergo cell apoptosis. In addition, no significant change in the cell size occureed during 22 d of culture. Glucose consumption by cultured cells was also constant during the culture and was 60% greater in the presence of 10 nmol/L of insulin. Treatment of cultured human adipocytes with insulin for 3–22 d increased GPDH and FAS activity by 60% and 2.8-fold, respectively, compared to cells cultured without insulin. Furthermore, the increase in FAS activity due to insulin treatment was dose dependent and maximal at 10 nmol/L. Our studies show for the first time that human adipocytes can be maintained viable and metabolically active for 2–3 wk in culture. Interestingly, cultured cells remain responsive to insulin. Therefore, this system will allow further characterization of long-term regulation of lipogenesis in human adipocytes and will be useful for developing pharmacological treatments of obesity.

KEY WORDS: • human adipocytes • primary culture • fatty acid synthase • glycerol-3-phosphate dehydrogenase • insulin

¹ Funded in part by the New Foundation for Diabetes.

² Presented in part at the Southeastern Lipid Conference, October 1994, Cashiers, NC (Moustaï, N. Lipogenic activity and insulin responsiveness of primary cultured human adipocytes), and at the FASEB meeting in Atlanta, GA, April, 1995 (Moustaïd, N., Jones, B. H. & Cagle, M. Insulin increases lipogenic activity of primary cultured human adipocytes).

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

⁵ Recipient of a UTK Professional Development Award and supported by a Career Development Award from the American Diabetes Association, and by Tennessee Agricultural Experiment Station.

⁶ Recipients of a research grant from the Physicians Medical Education and Research Foundation of the University of Tennessee Medical Center in Knoxville, TN.

Manuscript received 24 April 1995. Revision accepted 6 December 1995.