Insulin-like peptides stimulate metabolism but not proliferation of human fibroblasts

Abstract

The ability of a partially purified preparation of peptides with insulin-like activity (ILA) prepared from human plasma to stimulate several metabolic, synthetic and proliferative responses in diploid human fibroblasts was examined. ILA at 4 ng insulin equivalents/ml stimulated the uptake of the glucose analog, 2-deoxy-D-glucose 96 .+-. 17% (mean .+-. SE) and the amino acid analog, .alpha.-aminoisobutyrate 78 .+-. 15%, which was more effective than either insulin at 6.4-6400 ng/ml or 15% fetal calf serum. Kinetic analysis of uptake indicated that ILA increased the Vmax for 2-deoxy-D-glucose 100 .+-. 16% and had no significant effect on Km; for .alpha.-aminoisobutyrate it increased the Vmax 26 .+-. 9% and decreased the Km 38 .+-. 4%. ILA at 4 ng insulin equivalents/ml stimulated glucose consumption and the incorporation of isotopically labeled phenylalanine into protein and thymidine into DNA to a 2- to 5-fold greater extent than 6.4 ng/ml insulin. Very high insulin concentrations (6400 ng/ml) stimulated glucose consumption more than ILA although protein and DNA synthesis were still 2-fold lower than with ILA. Cells treated with fetal calf serum showed the greatest glucose consumption, protein and DNA synthesis and cell proliferation. The anabolic effects of ILA were followed by a modest increase in cell number (23 .+-. 3%), but neither refeeding nor subculturing in ILA could sustain cell proliferation. ILA isolated from human plasma evidently elicits a diverse response in cultured human fibroblasts of increased metabolism and macromolecular synthesis, but additional factors are needed to promote cell division.