Background/Purpose: The antiplatelet drugs Ticagrelor and clopidogrel are P2Y₁₂ antagonists but ticagrelor also inhibits cellular adenosine uptake via ENT1 and thereby increases extracellular adenosine levels. Dipyridamole induces its antiplatelet effect indirectly via adenosine, and like ticagrelor, inhibits ENT1. We have demonstrated that dipyridamole stimulates bone regeneration in mice by an A2AR-dependent mechanism. Both adenosine A2AR or A2BR stimulation inhibits osteoclast differentiation. We asked whether the antiplatelet agents ticagrelor and clopidogrel regulated osteoclast differentiation and, if so, A_2AR or A2BR stimulation played a role in this effect.

Methods: Osteoclast and osteoblast differentiation were studied in primary murine bone marrow culture as the number of TRAP-positive or Alizarin Red-positive cells, respectively, after challenge with ticagrelor, the active metabolite of clopidrogrel or dipyridamole (1nM-100mM) (n=5 each), in the presence/absence of ZM241385 (A2AR antagonist) or GS6201 (A2BR antagonist) 1mM. Male C57Bl/6 mice were anesthetized, a trephine defect was created in the calvariae, and covered using a collagen scaffold soaked in saline or 10-100mM ticagrelor or clopidogrel (n=5 each). Animals received the appropriate treatment daily until sacrifice 4 weeks after surgery when calvariae were harvested and prepared for microCT and histology.

Results: TRAP staining reveals a dose-dependent reduction in osteoclast differentiation in the presence of ticagrelor (IC50=10µM), clopidogrel (IC50=10µM) and dipyridamole (IC50=1µM), been these concentrations above the clinical exposures. TRAP staining revealed that ZM241385 blocked the effect of both ticagrelor and dipyridamole, whereas the effect of clopidogrel was reversed by GS6021. Alizarin Red staining revealed a slight but non-significant increase by ticagrelor, clopidogrel and dipyridamole treatment. ZM241385 reversed the effect of both ticagrelor and dipyridamole on osteoblast differentiation but the effects of clopidogrel were reversed by GS6021. microCT showed that blockade of adenosine uptake by treatment with either ticagrelor or clopidogrel markedly enhanced bone regeneration (28±1% and 27±2% respectively, vs. 15±3% in control, p<0.01). Bone regeneration was similar to that produced by BMP2 treatment. In ticagrelor- and clopidogrel-treated mice there was a decrease in TRAP-positive osteoclasts that correlated with a decrease in Cathepsin K immunostaining. We observed an increase in Alkaline Phosphatase immunostaining , in ticagrelor or clopidogrel treated bony defects.

Conclusion: Ticagrelor inhibits osteoclast differentiation via blockade of adenosine uptake and resulting increases in extracellular adenosine levels stimulate A2ARs, as we have previously reported for dipyridamole.. Both ticagrelor and the active metabolite of clopidogrel promoted bone regeneration in a murine trephination model. Local treatment with the antiplatelet agents ticagrelor, clopidogrel or dipyridamole may be useful for inhibition of bone destruction or promoting bone growth.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ticagrelor-regulates-osteoblast-and-osteoclast-function-and-promotes-bone-formation-in-vivo-by-increasing-adenosine-levels/