Rationale:Most of the current anti-platelet drugs inhibit platelet function permanently and have systemic side effects, including thrombocytopenia and hemorrhage. We previously found that thymidine phosphorylase (TYMP), a platelet cytoplasmic protein, facilitates multiple agonist induced platelet activation and enhances thrombosis. A specific TYMP inhibitor, namely, tipiracil hydrochloride (TPI), has been approved by the U.S. Food and Drug Administration for clinical use as an auxiliary drug making it possible to be repositioned as an anti-platelet medicine.
Objective:We aimed to test the hypothesis that TPI is a novel and safe anti-platelet drug by examining its role in platelet activation and thrombosis using both in vitro and in vivo studies.
Methods and Results:By co-expression of TYMP and Lyn or Lyn-SH3 domain tagged with glutathione S-transferase, we showed the direct evidence that TYMP binds to the SH3 domain in its partners. TYMP haplodeficiency is sufficient to inhibit thrombosis in vivo regardless of gender. TPI treatment rapidly inhibited collagen-and ADP-induced platelet aggregation, which copied the phenotype of TYMP deficient platelets. Under both normal and hyperlipidemic conditions, treating wild type (WT) mice with TPI via intraperitoneal injection, intravenous injection, or gavage feeding dramatically inhibited thrombosis without inducing significant bleeding. Even administered above the effective dose, TPI has a lower bleeding side effect compared to aspirin and clopidogrel. Most importantly, intravenously delivery of TPI alone or combined with tissue plasminogen activator dramatically inhibited the growth of developing thrombi. Dual administration of very low dose of aspirin and TPI also dramatically inhibited thrombosis without disturbing hemostasis.
Conclusion:This pharmacological study demonstrated that TYMP participates in multiple signaling pathways in platelet and plays a mechanistic role in regulating platelet activation and thrombosis. TPI, a specific TYMP inhibitor, would be a novel safe anti-platelet and anti-thrombosis medicine.
Cellix flow chamber-based platelet adhesion and aggregation assayCellix flow chambers were coated with collagen 10 μg/mL in PBS. Whole blood was drawn from mouse inferior vena cava using 0.109 M sodium citrate as an anticoagulant, stained with Rhodamine 6G, and then used for the flow chamber mediated adhesion and aggregation assay. Some of the whole blood was treated with or without TPI before it was perfused into the chamber.Compare the therapeutic effect of TPI to aspirin and clopidogrel 5 8 to 10 week-old male WT mice were gavage fed with either TPI, aspirin, or clopidogrel once daily for one week, then subsequently used in an in vivo thrombosis study. Tail bleeding assay was conducted on these mice immediately after the thrombosis study.
Examine the effect of TYMP inhibition on thrombosis under hyperlipidemiaWT mice were fed a western diet (WD, TD.88137) for a total of 4 weeks. For a separate group of mice, the diet was changed to a customized diet (TD.1...