Anales RANF

P.100 TENOFOVIR CAUSES BONE LOSS VIA DECREASED BONE FORMATION AND INCREASED BONE RESORPTION, WHICH CAN BE COUNTERACTED BY ADENOSINE A2A RECEPTOR IN MICE F.M. Conesa-Buendía 1 , P. Llamas-Granda 1 , A. Larrañaga-Vera 2 , P. Gratal 1 , T. Wilder 2 , R. Largo 1 , G. Herrero-Beaumont 1 , B. Cronstein 2 , A. Mediero 1 ,2 1 IIS-Fundación Jiménez Díaz UAM. Madrid, Spain; 2 NYU School of Medicine, New York, USA. Background or Introduction : Osteopenia and fragility fractures have been associated with HIV infection and Tenofovir, a common antiviral in HIV treatment. In murine models and human cell lines, tenofovir inhibits ATP release and decreases extracellular adenosine levels. Adenosine, and adenosine A2A receptor, inhibits osteoclast formation, and increasing local adenosine concentration with dipyridamole, an agent that blocks adenosine cellular uptaken, stimulates new bone formation as well as rhBMP-2. We hypothesized that tenofovir regulates bone resorption by diminishing endogenous adenosine levels and determined whether dipyridamole and A2A receptor may counteract the effects. Material and methods: M -CSF/RANKL-induced-primary murine osteoclasts were studied as the number of TRAP-positive-cells after challenge with tenofovir alone or in combination with dipyridamole. Differentiation markers were study by RT-PCR, and MAPK/NFkB expression by Western Blot. Male C57Bl/6 mice and A2AKO littermates were treated as follow: saline 0.9% (control), tenofovir 75mg/Kg/day, dipyridamole 25mg/Kg/day, combination tenofovir/dipyridamole (n=10, 4 weeks). Calcein/AlizarinRed-labelling of newly formed bone was used, and long bones were prepared for microCT/histology. Results: Tenofovir produced a dose-dependent increase in osteoclast differentiation (EC 50 =44.5nM) that was reversed by dipyridamole (IC 50 =0.3µM). Tenofovir increased Cathepsin K and NFATc1 mRNA levels and dipyridamole reversed the effect. Dipyridamole reversed the effect of tenofovir on pERK1/2, pp38 and NFkB nuclear translocation. WT mice treated with tenofovir lost nearly 10% of body weight (p<0.001). MicroCT revealed decrease BMD and altered trabecular bone in tenofovir- treated mice, reversed by dipyridamole. TRAP-staining showed increased osteoclasts in tenofovir-treated mice (p<0.005) an effect reversed by dipyridamole. Similar results were obtained for Cathepsin K and CD68 and RANKL-positive-cells, whereas OPG- positive-cells decreased with tenofovir. Similar results were obtained for tenofovir in A2AKO mice, but dipyridamole was not able to reverse the effect. Conclusions: These results suggest that treatment with agents that increase local adenosine concentrations, like dipyridamole, and activate adenosine A2A receptor might prevent bone lost following tenofovir treatment.