Leptin for Abnormal Lipid Kinetics in HIV Lipodystrophy Syndrome

• Rates of lipolysis [ Time Frame: Change from Baseline at 2 and 4 months ] [ Designated as safety issue: No ]
  Rates of total and net lipolysis will be measured in plasma samples by mass spectrometry following stable isotope infusions of labeled glycerol and palmitate
  
  

• Rates of fatty acid oxidation [ Time Frame: Change from Baseline at 2 and 4 months. ] [ Designated as safety issue: No ]
  Rates of fatty acid oxidation will be measured in breath samples following stable isotope infusions of 13C-labeled palmitate.
  
  
• Fasting plasma lipids [ Time Frame: Change from Baseline at 2 and 4 months. ] [ Designated as safety issue: No ]
  Fasting plasma cholesterol, HDL-cholesterol and triglycerides will be measured.
  
  
• Glucose levels after glucose challenge [ Time Frame: Change from Baseline at 2 and 4 months. ] [ Designated as safety issue: No ]
  An oral glucose tolerance test will be performed, with measurements of glucose at each time point.
  
  
• Insulin levels after oral glucose challenge. [ Time Frame: Change from Baseline at 2 and 4 months. ] [ Designated as safety issue: No ]
  An oral glucose tolerance test will be performed, with measurements of insulin at each time point
  
  

The HIV lipodystrophy syndrome (HLS) is characterized by peripheral fat wasting and central obesity, and hyperlipidemia (mainly hypertriglyceridemia), which results in insulin resistance. HLS patients are at high risk for cardiovascular disease, diabetes mellitus and the metabolic syndrome.

The investigators have previously shown that the alterations in lipid metabolism in the so-called mixed form of HLS are due to dysregulation of lipid kinetics at two levels. First, there appears to be an acceleration in lipid kinetics, with higher total and net lipolysis despite higher intra-adipocyte re-esterification. However, the percentage of fatty acid flux being oxidized remains the same, leading to increased hepatic recycling of fatty acids to triglycerides (TG), and export of TG-rich VLDL into the circulation. Second, there is reduced clearance of chylomicron and VLDL-TG from the plasma, resulting in the striking hypertriglyceridemia associated with this syndrome. The investigators propose that these alterations in lipid kinetics account for the phenotypic changes characteristic of this syndrome: increased lipolysis would facilitate peripheral lipoatrophy, increased intra-adipocyte re-esterification (if selective in intrabdominal depots) would contribute to the central obesity, and increased hepatic re-esterification together with impaired VLDL- and chylomicron-TG clearance would lead to hypertriglyceridemia.

Rational treatment of HLS should be targeted at these fundamental kinetic defects. Leptin is in many ways an ideal agent, since it increases fat oxidation, and shifts the ratio of utilization of free fatty acids derived from lipolysis towards oxidation and away from re-esterification, and decreases plasma triglyceride levels. HLS patients with lipoatrophy have low circulating levels of leptin. Moreover, leptin has been shown to be effective in correcting similar defects in fat redistribution and circulating lipids in non-HIV forms of lipodystrophy. Hence, the investigators propose to study (using a blinded, placebo-controlled, dose escalating design) the effect of leptin therapy on lipid kinetics and fat distribution in adult subjects with the lipoatrophic and mixed (peripheral lipoatrophy and central adiposity) forms of HLS. The investigators will use state of the art stable isotope tracer techniques and gas chromatography mass spectrometry (GCMS) to measure whole body lipolysis, lipid oxidation, lipid re-esterification and hepatic lipid recycling.