Effect of zinc on tPA induced thrombolysis

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Stroke is the second leading cause of death worldwide, and the fifth leading cause of death in the US. With the aging of the population, the number of stroke patients is likely to grow. Despite enormous research efforts including many clinical trials, effective therapy has remained elusive. A large number of previous preclinical studies was performed on non-embolic stroke, which could be one of the factors for translational failure. Tissue plasminogen activator (tPA) remains the only FDA-approved treatment for acute ischemic stroke. Unfortunately, only 2-5% of stroke patients in the US receive this therapy because of the narrow time window and severe side effects for using tPA. The most deadly and damaging side effect of tPA is the risk of intracranial bleeding or hemorrhage. For that reason, the dose of tPA and its overall administration are under tight control, while the effect of thrombolysis may be compromised. Studies have been focused on improving efficacy of tPA for higher rate of reperfusion, and for enhancement of safety and less adverse bleeding episode. In this proposal, we will investigate how metal ion zinc (Zn2+) affect thrombolysis in vitro and in vivo. We have proposed a method to improve tPA-induced thrombolysis. The overall hypothesis behind the proposed research is that study is that the presence of Zn2+ alters tPA-induced thrombolysis. This hypothesis is based on the following key observations based on the available literature, and our published and preliminary studies: 1st. In the bloodstream there is the most Zn2+-enriched site, α-granule of platelets, where the zinc concentration reaches 500µM (almost 30 fold higher zinc level in platelets than in the serum). 2nd. Zn2+ play critical roles in blood coagulation and platelets aggregation. 3rd. During the clot formation, a large amount of Zn2+ are released from platelets leading to the surge in Zn2+ concentrations in the local microenvironment and subsequent platelet aggregation. Therefore, thrombi become a source of Zn2+ as Zn2+ is “trapped” in the thrombi. 4th. Results from our published study showed that Zn2+ attenuated streptokinase-induced thrombolysis. In the preliminary studies, we observed the similar interaction between Zn2+ and tPA. The specific Aim 1 will determine the effect of Zn2+ on tPA-induced thrombolysis in vitro. Specific Aim 2 will investigate the promoting effect of Zn2+ chelation on tPA-induced thrombolysis in embolic MCAO in vivo. The major finding in the preliminary study is that Zn2+ has an inhibitory effect on thrombolysis when it is co-applied with tPA. We hypothesize that Zn2+ chelation can facilitate the tPA-induced thrombolysis in the clot model of ischemic stroke. The application of smaller amount tPA, in combination with a zinc chelator, can achieve the same or better therapeutic outcome in the treatment of stroke. Therefore, this proposal is a basic translation research addressing priorities of NIH stroke research, and addressing complex issues such as timing, therapeutic window, cytotoxicity and reperfusion of a potential combination therapy.