Enzymatic adaptations by cultured adipocytes of human infants and children: effect of obese serum on the activities of lactate-, malate-, and glucose-6-phosphate dehydrogenases.

To determine whether there are any biochemical characteristics which distinguish human adipose cells from human skin fibroblasts, assays of lactate dehydrogenase with pyruvate as substrate (LDH-P), malate dehydrogenase (MDH), and glucose-6-phosphate dehydrogenase (G6PDH) were done on both cell types after they had been successfully adapted to artificial medium in tissue culture and also while they were growing temporarily in serum from an obese individual. After undergoing transformation to a fibroblast-like appearance, the adipose cells (adipofibroblasts) contained significantly more of each enzyme than did the initial adipose cell isolates. The level of activities of LDH-P and G6PDH increased to the same levels as in skin fibroblasts (Table 2); however, MDH activities rose to much higher levels than those found in skin fibroblasts (Table 2). In obese serum, activities of LDH-P did not significantly change but the activities of MDH and G6PDH dropped sharply in adipofibroblasts (P less than 0.005, Table 2 and Fig. 5), whereas in cultures of skin fibroblasts, only the activities of G6PDH dropped significantly (P less than 0.025 Table 2), the other enzyme activities being unchanged. It is concluded that, on the basis of the biochemical behaviors of these two cell lines in culture, adipose cells are biochemically different from skin fibroblasts and are not to be regarded as just fibroblasts with lipid-storing ability.