HYPERINSULINEMIA IS RELATED TO ERYTHROCYTE PHOSPHOLIPID-COMPOSITION AND MEMBRANE FLUIDITY CHANGES IN OBESE NONDIABETIC WOMEN

It has been suggested that changes in the properties of cell membranes are involved in an altered insulin action. However, the influence of changes in the distribution of phospholipid classes has not been explo red. We investigated 69 obese nondiabetic normoglycemic women (17 pati ents with impaired glucose tolerance) with varying degrees of insulin sensitivity to determine the phospholipid composition and fluid state of their erythrocyte plasma membranes. The fasting plasma insulin, the homeostasis model analysis of insulin resistance (HOMA), and the inte grated area under the insulin curve (AUC-I) alter an oral glucose chal lenge were used as markers of insulin resistance. Results were divided into normal glucose tolerance (NGT) and impaired glucose tolerance. T here was a positive correlation in NGT group between the membrane sphi ngomyelin (SM) content and the fasting plasma insulin (r = 0.523; P < 0.0001), HOMA value (r = 0.483; P < 0.0005), and AUC-I (r = 0.352; P < 0.05) and negative correlations between membrane fluidity determined with two fluorescent probes and plasma fasting insulin (r = -0.320; r = -0.365; P < 0.05) and HOMA value (r = -0.321; r = -0.382; P < 0.05). There were also correlations between SM and the three markers of insu lin resistance in the impaired glucose tolerance group. There was no c orrelation between insulin resistance and other membrane components. S tepwise multiple regression analysis in the NGT group confirmed that t he membrane SM content was an independent predictor of plasma fasting insulin, HOMA values, and AUC-I variations. Sphingomyelin could be one of the membrane parameters contributing to insulin resistance.