The composition and biosynthesis of lipids in human adipose tissues.

The capacity of adipose tissue in rats and mice to synthesize fatty acids and triglycerides from acetate, glucose and long chain fatty acids and to oxidize these substrates to CO. has been well established (1-5). In this investigation, a study has been made of lipid biosynthesis and lipid composition of human adipose tissues. Human subjects provide a unique opportunity to compare the metabolism of normal subcutaneous adipose tissue with a benign neoplasm of fat tissue, the lipoma. Comparative studies of most tumors with their normal tissue counterpart have been difficult because of cellular nonhomogeneity of both normal tissues and tumors and the inability to obtain tumor and normal control tissue from the same subject. The lipoma, on the other hand, arises most frequently in the subcutaneous adipose tissue and morphologically is indistinguishable from normal adipose tissue. This makes it possible to examine the synthetic and catabolic activities and composition of the tumor and control tissue in the same subject under identical environmental conditions. In the present studies, it has been found, in vitro, that lipomas had a significantly higher rate of acetate incorporation into the mixed lipids than the normal subcutaneous adipose tissue of the same subject. Although the rate of synthesis of individual fatty acids was greater in the lipoma than in the normal fat, the relative distribution of radioactivity among the fatty acids was the same in the two tissues. These tissues did not differ significantly with respect to the rate of oxidation of acetate to CO., or the rate of transfer of newly synthesized lipids into the medium.