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

Abstract

Extract: 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 obses individual. After undergoing transformation to a fibroblastlike 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 < 0.005, Table 2 and Fig. 5), whereas in cultures of skin fibroblasts, only the activities of G6PDH dropped significantly (P < 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.

Speculation: Some evidence suggests that adipose cells are derived from stromal precursors present in the adipose depot. The data presented in this study suggest that, although cultured adipose cells may be similar in some respects to skin fibroblasts, they have some important differences from skin fibroblasts. The differences may reflect the fact that, as a consequence of differentiation, enzymatic patterns develop which determine how they will perform their special functions of lipid synthesis, storage, and release, It is argued that adipocytes and their precursors are not fibroblasts which happen to be able to store lipids.

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