HIV Reverse Cholesterol Transport Study

HIV infection is associated with low HDL-cholesterol, an independent risk-factor for cardiovascular disease (CVD). NNRTI-based HAART increases HDL-c, with nevirapine shown to increase production of its major apolipoprotein ApoA-I. In contrast, initiation of PI-based HAART leads to persistently low HDL-c despite a reduction in HIV RNA and immunologic recovery.

HDL-c is formed through reverse cholesterol transport (RCT), the process where cholesterol is transferred from intracellular pools to circulating lipoproteins which are then eliminated by the liver. Accumulation of intracellular cholesterol in cells such as macrophages and their precursor (circulating monocytes) has been implicated in atherogenesis.

In vitro data suggests the HIV protein Nef directly interferes with cellular proteins involved in RCT such as ATP-binding cassette transporter A1 (ABCA1) in monocyte-derived macrophages. ABCA1 expression is controlled by peroxisome proliferator-activated receptor gamma (PPARG) and the intracellular cholesterol sensor sterol regulatory element binding protein 2 (SREBP2). In adipose tissue it is known that PI treatment downregulates SREBP and PPARG expression.

Preliminary work in the investigators lab has reproduced these findings in monocytes in untreated HIV infection in vivo and demonstrated relationships between gene expression for ABCA1, SREBP2, monocyte intracellular cholesterol and circulating lipoproteins. These early data suggest that defects in RCT determine intracellular cholesterol levels in HIV-infected subjects whereas increased LDL-c is a greater determinant of intracellular cholesterol in HIV negative subjects. This suggests a potentially pivotal role for RCT abnormalities in low HDL-c, increased intracellular cholesterol and atherogenesis in HIV infection.

The investigator's aim to examine the impact of initiation of ART with either PI or NNRTI on RCT in circulating monocytes in vivo and how this impact correlates with changes in amount and size of circulating HDL-c.