Carbohydrate-stimulated fatty acid synthesis de novo in human adipose tissue of different cellular types.

Abstract

Abstract. Fatty acid (FA) synthesis in vitro by human adipose tissue has been determined as glucose incorporation into FA by slices and as the overall enzyme capacity for incorporation of acetyl units into FA from acetate and citrate by an optimal cytoplasmic assay system. Twelve subjects with normal, hypertrophic, hyperplastic or combined hypertrophic‐hyperplastic adipose tissue were examined during basal, weight stable conditions and after 3 and 22 days on a high‐carbohydrate low‐fat chemically defined diet (Vivasorb®) administered in amounts resulting in a moderately negative energy balance. Incorporations obtained with the cytoplasmic assay were several times higher than those with the whole cell technique. During carbohydrate feeding FA synthesis increased 3 and 11 times, respectively, as measured with the subcellular and the whole cell techniques. However, FA synthesis de novo was of little quantitative importance in human adipose tissue even during stimulated conditions. Expressed per g adipose tissue triglyceride (TG), there were no differences in FA synthesis between the four cellular groups before or during high‐carbohydrate feeding. Expressed per cell, large fat cells demonstrated a higher enzyme capacity for FA synthesis than did cells of normal size. The correlation between fat cell size and enzyme capacity for FA synthesis increased during the course of high‐carbohydrate feeding. During but not before high‐carbohydrate feeding there were several correlations between different whole cell and subcellular activities of adipose tissue and also strong correlations between FA synthesis in adipose tissue and serum TG. The latter correlation was most likely not related to a direct dependence between the two factors. Contrary to earlier reports, this investigation indicates the presence of ATP citrate lyase [E.C.4.1.3.8] in human adipose tissue and demonstrates that, in vitro, the enzyme capacity for citrate incorporation is at least as large as the capacity for acetate incorporation into FA if optima! conditions are used for both precursors.