Metabolic markers, regional adiposity, and adipose cell size: relationship to insulin resistance in African-American as compared to Caucasian women

BACKGROUND/OBJECTIVES: African-American women have the greatest prevalence of obesity in the U.S., and higher rates of type 2 diabetes (T2D) than Caucasian women, yet paradoxically lower plasma triglycerides (TG), visceral fat and intrahepatic fat, and higher high-density lipoprotein (HDL)-cholesterol. Visceral fat has not been evaluated against insulin resistance in African-American women, and TG/HDL-cholesterol has been criticized as a poor biomarker for insulin resistance in mixed-sex African-American populations. Adipocyte hypertrophy, reflecting adipocyte dysfunction, predicts insulin resistance in Caucasians, but has not been studied in African-Americans. Our goal was to assess whether traditional correlates of insulin resistance, measures of adiposity and adipocyte characteristics similarly predict peripheral insulin resistance in African-American and Caucasian women. SUBJECTS/METHODS: Thirty-four healthy African-American (n=17) and Caucasian (n=17) women, matched for age (mean=53.0 yrs) and BMI (mean=30 kg/m(2)), underwent a steady-state plasma glucose (SSPG) test to measure insulin sensitivity; computed tomography (fat distribution); and a periumbilical scalpel biopsy (adipocyte characterization). By-race analyses utilized ANCOVA; linear regressions evaluated relationships between metabolic/adipose variables. All analyses adjusted for BMI and menopausal status. RESULTS: Insulin sensitivity did not differ between groups (p=0.65). BMI, %body fat nor thigh fat predicted insulin resistance in African-American women. Fasting TG (p=0.046), HDL-cholesterol (p=0.0006) and TG/HDL-cholesterol ratio (p=0.009) strongly predicted insulin resistance in African-American women. Despite being lower in African-American women, hepatic fat and VAT correlated with insulin resistance in both groups, as did fasting glucose, VAT/SAT ratio and %SAT (inverse). CONCLUSIONS: Total adiposity measures and adipocyte hypertrophy did not predict insulin resistance in African-American women, but did in Caucasian women. Plasma TG and HDL-cholesterol were significant predictors of insulin resistance in African-American women. Our findings demonstrate the need to identify race and sex-specific biomarkers for metabolic risk profiling.