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, a-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.