Background/Purpose: Adenosine, generated from the catabolism of adenine nucleotides, modulates cell function by interacting with specific cell-surface receptors (A₁R, A_2AR, A_2BR, A₃R). Inhibition of osteoclast formation via adenosine A2A receptor stimulation or increasing local adenosine concentration stimulates new bone formation as well as rhBMP-2. Bone alterations have been observed in HIV (Human Immunodeficiency Virus) disease for nearly two decades, in particular a higher risk of low bone mineral density (BMD) and fragility fractures. Treatment with Tenofovir leads to changes in bone catabolism markers and significant reductions in BMD in children and young adults. Tenofovir is taken up by cells and phosphorylated and inhibits HIV-reverse transcriptase by mimicking AMP. We have recently found that Tenofovir inhibits Pannexin-1/Connexin-43-mediated ATP release from cells and decreases extracellular adenosine levels and fibrosis in murine models. Here we determined if Tenofovir directly affects bone and if Dipyridamole, may be a useful treatment to counteract the effects.

Methods: M-CSF/RANKL-induced osteoclast (OC) were studied in primary murine bone marrow culture as the number of TRAP-positive cells after challenge with Tenofovir (1nM-100μM) alone or in combination with Dipyridamole (1nM-100μM). OC differentiation markers were study by RT-PCR. Male C57Bl/6 mice were divided into four groups: saline 0.9% (control), Tenofovir 75mg/Kg/day, Dipyridamole 25mg/Kg/day, combination Tenofovir/Dipyridamole for 4 weeks (n=10 each). Double labelling of bone with calcein /Alizarin Red was performed to analized bone formation and long bones prepared for microCT and histology.

Results: Tenofovir produced a dose-dependent increase in OC differentiation (EC50=44.5nM) that was reversed by Dipyridamole (IC50=0.3µM). Tenofovir increases Cathepsin K and NFATc1 mRNA levels during OC differentiation, and the effect was reverted by Dipyridamole. In vivo, mice treated with Tenofovir lost nearly 10% of body weight (p<0.001) and DXA analysis revealed a decrease in % fat (p<0.05), effect reverted by Dipyridamole. Tenofovir reduced bone formation in vivo (19±2µm bone apposition vs 35±4µm in control, p<0.05) and this effect was reverted by Dipyridamole (30±3µm, p<0.05 vs Tenofovir alone). microCT analysis revealed decrease BMD and altered trabecular bone in Tenofovir-treated mice, been reverted in the presence of Dipyridamole. TRAP-staining showed increased OC in vivo in Tenofovir-treated mice (88±31 vs 27±1 OC/hpf in control, p<0.005) that was reverted inn the pressence of Dipyridamole (30±2OC/hpf, p<0.05 vs Tenofovir alone). Similar results were obtained for Cathepsin K and CD68. RANKL positive cells were increased in the presence of Tenofovir meanwhile OPG positive cells decreases, and both effets were reverted in the presence of Dipyridamole.

Conclusion: These results indicate that Tenofovir enhances osteoclast differentiation and inhibits osteoblast differentiation by an adenosine-ATP-dependent mechanism and suggests that treatment with agents that increase local adenosine concentrations, like Dipyridamole, might prevent bone loss following Tenofovir treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/dipyridamole-an-ent-1-adenosine-transporter-inhibitor-reverts-de-osteoclastic-phenotype-induced-by-tenofovir/