Objective: Leptin is an adipocyte secreted hormone and an important regulator of neuroendocrine, metabolic, and immune function. Both r-metHuLeptin and IGF1 administration result in reduced central adipose tissue in subjects with highly active antiretroviral therapy-induced metabolic syndrome (HAART-MS) but whether the effects of leptin are mediated through increasing IGF levels remains unknown.
Methods: To assess whether r-metHuLeptin improves the HAART-MS by regulating circulating IGF and IGFBPs, we first conducted a cross-sectional study of 118 men and women with HIV infection and >6 months of exposure to antiretroviral medications to examine any association between circulating IGF1 and leptin levels. We also performed a randomized, double-blinded, placebo-controlled, crossover trial of recombinant human leptin (r-metHuLeptin) administration to seven HIV positive men with lipoatrophy and leptin deficiency (leptin <3 ng/ml) related to antiretroviral medication use.
Results: In the observational study, leptin levels were inversely associated with circulating IGF1 levels after adjusting for age and gender (r=0.27 P=0.002), but this inverse association became non-significant after adjustment for % body fat and exercise. In the interventional leptin study, leptin levels increased significantly during r-metHuLeptin treatment (from 1.34+/-0.20 ng/ml at baseline to 17+/-5.05 ng/ml after 8 weeks P=0.046) and metabolic parameters improved including reduced fasting insulin levels and reduced homeostasis model assessment-insulin resistance (HOMA-IR). Despite the increase in circulating leptin levels, there was no change in IGF1, IGF2, free IGF1, or IGF-binding proteins during the 2-month treatment period.
Conclusion: The effects of r-metHuLeptin in patients with HAART-MS are not mediated through increasing IGF or IGFBP levels.