Comparison of surrogate and direct measurement of insulin resistance in chronic hepatitis C virus infection: impact of obesity and ethnicity.

UNLABELLED: Studies using surrogate estimates show high prevalence of insulin resistance in hepatitis C infection. This study prospectively evaluated the correlation between surrogate and directly measured estimates of insulin resistance and the impact of obesity and ethnicity on this relationship. Eighty-six nondiabetic, noncirrhotic patients with hepatitis C virus (age = 48 +/- 7 years, 74% male, 44% white, 22% African American, 26% Latino, 70% genotype 1) were categorized into normal-weight (body mass index [BMI] < 25, n = 30), overweight (BMI = 25-29.9, n = 38), and obese (BMI > or = 30, n = 18). Insulin-mediated glucose uptake was measured by steady-state plasma glucose (SSPG) concentration during a 240-minute insulin suppression test. Surrogate estimates included: fasting glucose and insulin, glucose/insulin, homeostasis model assessment (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), insulin (I-AUC) and glucose (G-AUC) area under the curve during oral glucose tolerance test, and the Belfiore and Stumvoll indexes. All surrogate estimates correlated with SSPG, but the magnitude of correlation varied (r = 0.30-0.64). The correlation coefficients were highest in the obese. I-AUC had the highest correlation among all ethnic and weight groups (r = 0.57-0.77). HOMA-IR accounted for only 15% of variability in SSPG in the normal weight group. The common HOMA-IR cutoff of < or =3 to define insulin resistance had high misclassification rates especially in the overweight group independent of ethnicity. HOMA-IR > 4 had the lowest misclassification rate (75% sensitivity, 88% specificity). Repeat HOMA-IR measurements had higher within-person variation in the obese (standard deviation = 0.77 higher than normal-weight, 95% confidence interval = 0.25-1.30, P = 0.005). CONCLUSION: Because of limitations of surrogate estimates, caution should be used in interpreting data evaluating insulin resistance especially in nonobese, nondiabetic patients with HCV.

Apolipoprotein E promotes the regression of atherosclerosis independently of lowering plasma cholesterol levels.

OBJECTIVE: The mechanisms by which apolipoprotein E (apoE) can promote the regression of atherosclerosis are not well understood. This study examined whether apoE can promote atherosclerosis regression independently of lowering plasma cholesterol levels. METHODS AND RESULTS: We studied hypomorphic apoE mice (Apoe(h/h)), which express an apoE4-like form of mouse apoE at approximately 2% to 5% of normal levels in plasma and are normolipidemic. After 18 weeks of diet-induced hypercholesterolemia, which resulted in advanced aortic atherosclerotic lesions composed of a lipid-rich layer of foam cells covering a fibrotic core, 2 groups of mice were fed a chow diet for 16 weeks. One group continued to express low levels of apoE; the other was induced to express physiological levels of plasma apoE by Cre-mediated recombination of the hypomorphic Apoe allele. In both groups, plasma cholesterol levels fell rapidly to similar levels, and histological analysis at 16 weeks revealed elimination of the foam-cell layer. However, physiological levels of plasma apoE also enhanced the removal of neutral lipids from the fibrotic cores. CONCLUSIONS: These findings demonstrate for the first time that apolipoprotein E promotes the regression of atherosclerosis independently of lowering plasma cholesterol levels. Using Apoeh/hMx1-Cre mice we have begun to address apolipoprotein E-mediated mechanisms of atherosclerosis regression. We report the existence of a cholesterol-independent role of apolipoprotein E in atherosclerosis regression. This mechanism is critical for lipid removal from the fibrotic component of the plaque but not from the foam cell-rich layer beneath the endothelium.