Osteopenia and fragility fractures have been associated with human immunodeficiency virus (
HIV) infection.
Tenofovir, a common
antiviral in HIV treatment, also leads to increases in bone catabolism markers and decreased BMD in children and young adults. In murine models and human cell lines,
tenofovir inhibits
adenosine triphosphate release and decreases extracellular
adenosine levels.
Adenosine and
adenosine A2A receptor inhibit osteoclast formation, and increase local
adenosine concentration with
dipyridamole, an agent that blocks
adenosine cellular uptake and stimulates new bone formation as well as bone morphogenic
protein 2. We hypothesized that
tenofovir regulates
bone resorption by diminishing endogenous
adenosine levels and questioned whether
dipyridamole may be a useful treatment to counteract the deleterous bone effects of
tenofovir. Primary murine osteoclasts were induced by
M-CSF/RANKL, and the number of TRAP-positive-cells was studied after challenge with
tenofovir alone or in combination with
dipyridamole.
Differentiation markers were studied by RT-PCR and MAPK/NFkB expression by Western blot. Male C57Bl/6 mice were treated as follows:
saline 0.9% (control),
tenofovir 75 mg/kg/day,
dipyridamole 25 mg/kg/day, combination
tenofovir/
dipyridamole (n = 10, 4 weeks).
Calcein/
Alizarin Red-labeling of newly formed bone was used, and long bones were prepared for micro-computed tomography (μCT)/histology.
Tenofovir produced a dose-dependent increase in osteoclast differentiation (EC50 = 44.5nM) that was reversed by
dipyridamole (IC50 = 0.3 μM).
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. Mice treated with
tenofovir lost nearly 10% of their
body weight (p < 0.001). μCT revealed decreased 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. RANKL-positive cells were increased in
tenofovir-treated mice, whereas
osteoprotegerin-positive cells were decreased; both effects were reversed by
dipyridamole. These results suggest that treatment with agents that increase local
adenosine concentrations, like
dipyridamole, might prevent bone loss following
tenofovir treatment. © 2019 American Society for Bone and
Mineral Research.