Elevated concentrations of free fatty acids are associated with increased insulin response to standard glucose challenge in human immunodeficiency virus-infected subjects with fat redistribution

Abstract

Fat redistribution, defined by both increased abdominal visceral fat and/or decreased abdominal, extremity, and facial subcutaneous fat, is increasingly recognized among human immunodeficiency virus (HIV)-infected patients treated with combination antiretroviral therapy. Fat redistribution in this population is associated with insulin resistance and dyslipidemia and is often referred to as the HIV lipodystrophy syndrome (LIPO). Fatty acids are known to modulate insulin resistance in other disease states, but a comprehensive evaluation of fatty acids has not been undertaken among HIV-infected patients with fat redistribution. In this study, we investigated fatty acid concentrations in 64 HIV-infected individuals (45 men and 19 women) with evidence of fat redistribution (LIPO) in comparison to 30 HIV-infected individuals (20 men and 10 women) without evidence of fat redistribution (NONLIPO) and 32 HIV-negative healthy control subjects (C) (21 males and 11 females) of similar age and body mass index (BMI). Glucose, insulin, and free fatty acid (FFA) levels were measured in response to a 75-g oral glucose tolerance test (OGTT) in the LIPO, NONLIPO, and C subjects. In addition, fasting lipids were obtained, and body composition was determined by anthropometric measurements and dual-energy x-ray absorptiometry (DXA). Fasting FFA concentrations were significantly increased in the LIPO group as compared with NONLIPO and C subjects (0.74 [plusmn] 0.03 v 0.60 [plusmn] 0.04 [mean [plusmn] SEM] mmol/L, P = .002, LIPO v NONLIPO; 0.74 [plusmn] 0.03 v 0.59 [plusmn] 0.03 mmol/L, P = .001, LIPO v C). In contrast, fasting FFA concentrations were not increased in the NONLIPO group (0.60 [plusmn] 0.04 v 0.59 [plusmn] 0.03, P = .909, NONLIPO v C). Similarly, fasting triglycerides and 120-minute OGTT FFA were significantly increased in the LIPO group as compared with the NONLIPO and C group. FFA decreased in HIV-infected LIPO, NONLIPO, and C subjects in response to OGTT, but the 120-minute FFA concentrations remained significantly elevated in LIPO patients compared with NONLIPO and C subjects. In a multivariate regression model of LIPO patients, fasting FFA ( P = .027) was a strong independent predictor of insulin area under the curve (AUC), controlling for age, BMI, gender, and body composition ( r 2 for model = .31). No differences were observed in FFA concentrations in the LIPO group in an analysis based on current protease inhibitor (PI) use. These data suggest that FFA concentrations are increased in HIV-infected patients with fat redistribution. Increased fasting concentrations of fatty acids are associated with abnormal insulin responses to standard glucose challenge in HIV-infected patients with fat redistribution. Further studies are necessary to determine the mechanism of increased fatty acid concentrations and the role played by increased FFA in mediating insulin resistance in this population.