Bone Loss and Immune Reconstitution in HIV/AIDS (BLIR-HIV)

With the increasing age of people living with HIV/AIDS, age-induced osteoporosis is likely to be compounded by HIV/AIDS and HAART-associated bone loss. Mechanistically, osteoclasts the cells responsible for bone resorption form under the influence of the key osteoclastogenic cytokine receptor activator of nuclear factor kappa-Β ligand (RANKL). The osteoclastogenic and proresorptive activities of RANKL are moderated by its physiological decoy receptor osteoprotegerin (OPG). Imbalance in the ratio of RANKL to OPG alters osteoclastic bone resorption and lead to osteoporosis. Activated T- and B-cells are a major source of RANKL, while normal physiological B-cells are a major source of OPG. T-cells regulate the production of OPG by B-cells. Thus changes in the immune system induced by HIV/AIDS and/or by HAART could affect B-cell and T-cells RANKL and OPG production. Indeed, data from our group shows that in an animal model of HIV/AIDS, the HIV-1 Transgenic rat, the development of osteoporosis is recapitulated as observed in HIV-infected patients, and B-cell OPG and RANKL production are concurrently down regulated and upregulated respectively. Furthermore, preliminary data in HIV-infected subjects suggests dramatic acute upswing in bone resorption following HAART initiation that peaks at 12 weeks and then declines. Based on these findings, the investigators hypothesize HAART associated bone loss is driven by immune reconstitution. Because this effect of HAART is dramatic in magnitude but short in duration, the investigators propose to apply antiresorptive agent (zoledronic acid, reclast®) to specifically spare patients from this dramatic but acute bone damage.