A study of the metabolism of apolipoprotein B100 in relation to insulin resistance in African American males

The purpose of this study was to determine the relationship between insulin resistance and apoB100 metabolism in African American males. Fifteen subje cts, 33 +/- 7.6 years old, were divided into two groups, insulin-resistant (IR) or insulin-sensitive (IS), based on the sum of the plasma insulin conc entrations during an oral glucose tolerance test. The IR group (n = 8) diff ered significantly from the IS group (n = 7) with respect to body mass inde x (BMI) (30.1 vs 23.1 kg/m(2); P = 0.0003), fasting triglycerides, (118 vs 54 mg/dl, P = 0.013), and total plasma apolipoprotein B100 (80 vs 59 mg/dl, P = 0.014), Significantly elevated apoB100 levels in the IR group were see n in very low density lipoprotein (VLDL) (5.1 vs 3.4 mg/dl, P = 0.045) and intermediate density lipoprotein (IDL) (18 vs 12 mg/dl, P = 0.017) but not in low density lipoprotein (LDL) (57 vs 46 mg/dl, P = 0.19). Total choleste rol, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), apolipoprotein A-I, and blood pressure were not signif icantly different between the two groups. There was a high correlation betw een the sum of insulins during the oral glucose tolerance test and the BMI (rho = 0.88, P = 0.0001), In five IR and five IS subjects, apoB100 kinetics were determined in the fa sting state using a bolus dose of deuteroleucine and multicompartmental mod eling. IR subjects had significantly lower fractional catabolic rates (FCR) in the larger VLDL, (-70%), the smaller VLDL2 (-71%), and the IDL (-53%) f ractions. No significant differences in production rates were observed for any lipoprotein class. There was a significant correlation between the sum of insulins and the FCR of the apoB100 of VLDL, (rho = -0.65, P = 0.05) and of IDL (rho = -0.85, P = 0.004). The correlation coefficient of the sum of insulins and the FCR of VLDL, was -0.61 with P = 0.067. We conclude that i n this population of African American males, IF is correlated with a decrea sed FCR of apoB100 in VLDL and IDL and elevated plasma levels of apoB and t riglycerides (TG), These changes might be explained by decreased clearance of the TG-rich lipoproteins, We postulate that this may reflect decreased l ipoprotein and/or hepatic lipase activity related to insulin resistance and its association with obesity.