BACKGROUND: The cell functions involved in the action of insulin--receptor binding, enzyme and transporter activities--are controlled by membrane properties. We have previously shown that the fasting plasma insulin (FPI) concentration and the homeostasis model assessment (HOMA) estimate of insulin resistance are associated with the sphingomyelin concentration in the erythrocyte membranes of obese women. OBJECTIVES: (1) To study the distribution of phospholipid classes in the plasma membrane and their association with insulin resistance markers in the adipocyte, an insulin-sensitive cell in obese women. (2) To investigate the influence of diabetes in a small group of obese women treated by diet alone. (3) To compare the distribution of phospholipids in erythrocyte membranes in a subgroup of obese nondiabetic and diabetic women. SUBJECTS: Subcutaneous fat biopsies were taken from the abdominal region of 19 obese non-diabetic and seven obese type 2 diabetic women. Erythrocyte membrane assessment was performed in a subgroup of 10 of the 19 obese nondiabetic and in the seven diabetic patients. METHODS: The phospholipid composition of adipocyte and erythrocyte plasma membranes was analyzed by high performance liquid chromatography. RESULTS: FPI was positively correlated with the adipocyte membrane contents of sphingomyelin (P < 0.001), phosphatidylethanolamine (P < 0.05), and phosphatidylcholine (P < 0.01) in the obese nondiabetic women. Similar correlations were obtained with HOMA. A stepwise multiple regression analysis indicated that sphingomyelin accounted for 45.6 and 43.8% of the variance in FPI and HOMA values as an independent predictor. There was a similar positive independent association between FPI and SM in the erythrocyte membranes of the studied subgroup. Diabetes per se did not influence the independent association between SM membrane contents and FPI in both cell types. CONCLUSION: These results suggest a link between membrane phospholipid composition, especially SM, and hyperinsulinemia in obese women.
BACKGROUND: The cell functions involved in the action of insulin--receptor binding, enzyme and transporter activities--are controlled by membrane properties. We have previously shown that the fasting plasma insulin (FPI) concentration and the homeostasis model assessment (HOMA) estimate of insulin resistance are associated with the sphingomyelin concentration in the erythrocyte membranes of obesewomen. OBJECTIVES: (1) To study the distribution of phospholipid classes in the plasma membrane and their association with insulin resistance markers in the adipocyte, an insulin-sensitive cell in obesewomen. (2) To investigate the influence of diabetes in a small group of obesewomen treated by diet alone. (3) To compare the distribution of phospholipids in erythrocyte membranes in a subgroup of obese nondiabetic and diabeticwomen. SUBJECTS: Subcutaneous fat biopsies were taken from the abdominal region of 19 obese non-diabetic and seven obese type 2 diabeticwomen. Erythrocyte membrane assessment was performed in a subgroup of 10 of the 19 obese nondiabetic and in the seven diabeticpatients. METHODS: The phospholipid composition of adipocyte and erythrocyte plasma membranes was analyzed by high performance liquid chromatography. RESULTS: FPI was positively correlated with the adipocyte membrane contents of sphingomyelin (P < 0.001), phosphatidylethanolamine (P < 0.05), and phosphatidylcholine (P < 0.01) in the obese nondiabeticwomen. Similar correlations were obtained with HOMA. A stepwise multiple regression analysis indicated that sphingomyelin accounted for 45.6 and 43.8% of the variance in FPI and HOMA values as an independent predictor. There was a similar positive independent association between FPI and SM in the erythrocyte membranes of the studied subgroup. Diabetes per se did not influence the independent association between SM membrane contents and FPI in both cell types. CONCLUSION: These results suggest a link between membrane phospholipid composition, especially SM, and hyperinsulinemia in obesewomen.