Lipoprotein Insulin Resistance Score: Validation and Utility in African Ancestry Populations

Abstract

Lipoprotein insulin resistance (LPIR) is an emerging biomarker of insulin resistance (IR), and a score of >48 is a strong predictor of incident cardiometabolic disease disease in a predominantly European ancestry population. LPIR is derived from a composite score of nuclear magnetic resonance (NMR) lipoprotein (Lp) parameters: triglyceride-rich (TRLp), low density (LDLp), and high density (HDLp). Yet, there is a paucity of data in African ancestry population, in whom there is low-normal TRLp despite high rates of IR and diabetes. Therefore, we examined Lp profiles and LPIR in a large African ancestry cohort, stratified by sex to determine the relationship of LPIR with established markers of IR. This is a secondary analysis from 2 studies (The Africans in America and Federal Women’s Study) designed to evaluate the genetic, biological and socio-environmental factors of diabetes risk in those of African ancestry. All participants self-identified as healthy and lived in the DC metro area, n= 518: 87.7% African immigrant,12.3% African American; age 39±10 (20-65y); BMI 28.1±4.8 (18.2–45.2 kg/m2); 58% male; 31% with obesity, and 37% with abnormal glucose tolerance; mean±SD (range); median (25th-75th percentile). Fasting measures of IR (LPIR, triglyceride/HDL (TG/HDL) ratio and homeostasis model of insulin resistance (HOMA-IR)) were compared with the whole-body insulin sensitivity index (WBISI) obtained during a multi-sample 75g OGTT, using spearman correlations. Lp particle size and subclass concentrations were measured by the amplitudes of the lipid-methyl group signals (NMR LipoProfile®). Men had lower BMI (27.1±3.9 vs 29.3±5.6 kg/m2), fat mass (23.5±5.5 vs 37.9±6.8 %), insulin resistance (WBISI: 6.2 (3.7–10.1) vs 4.9 (3.2–8.6), HOMA-IR: 1.3 (0.7–2.0) vs 1.6 (0.9–2.4), TG/HDL: 1.4 (1.0–2.2) vs 1.1 (0.8–1.5)), all P<0.001. LDLp (1226 (959–1531) vs 1239 (981–1553) nmol/L) and HDLp (17.6 (16.2–19) vs 17.5 (15.9–19.7) µmol/L) were similar by sex, P>0.6, while small LDLp 734 (523–1039) vs 541 (370–805) nmol/L and TRLp 80.5 (52.2–116.4) vs 53.6 (28.7 -89.3) nmol/L were higher in men. The total mean LPIR score was 28.9±18.7 and was higher in men (34±19 vs. 23±17), P<0.001. LPIR and TG/HDL ratio correlated with WBISI (r≥-0.40) and HOMA-IR (r≥0.40), P<0.001 with no differences by sex. HOMA-IR correlated with WBISI (r=-0.95, P<0.001). Overall, African ancestry individuals had high rates of abnormal glucose tolerance, obesity and LDLp but LPIR was 20 points lower than the established score for predicting cardiometabolic disease. It’s utility for detecting IR was modest but it may be an important adjunct for early cardiometabolic risk stratification in African ancestry populations in whom traditional screening methods have lower sensitivity.