Abstract 17802: pH Sensitive Polyethylene Glycol-urokinase Nanogels Ameliorates the Severity of Ischemic Stroke in Rats by Effective Thrombolysis and Protection of Blood-brain Barrier

Abstract

Background: pH sensitive polyethylene glycol-urokinase nanogels(PEG-UK) was reported previously as a new form of UK, which could release UK at certain pH value and has the same thrombolytic effect as naked UK on human clots in vitro. In this study, we evaluated its effect in rat model of ischemic stroke and further investigated possible mechanisms. Methods: Persistent middle cerebral artery occlusion were induced in adult Sprague-Dawley rats. pH distribution in the brain was mapped at 1 hour after ischemia through Needle type pH micro sensor and pH Optica Micro system. Thrombolytic effect of PEG-UK, such as dynamic levels of D-dimer, neurological deficts and infarction volume, were examined respectively. In spite of the overall performances, possible mechanisms were also explored, for example, the permeability of blood-brain barrier(BBB) reflected by Evans Blue(EB) leakage, BBB’s integrity via matrix metalloproteinase 9 (MMP9), tissue inhibitor of metalloproteinase protein-1 (TIMP-1) and Claudin5, and extent of apoptosis and neurotoxicity standed by Caspase9 and N-methyl-D-aspartic acid receptor 1(NMDAR1). Results: In ischemic hemisphere, pH value near cortex was obviously lower than that in deeper white matter. Averagely, occlusion for 1 hour induced the decline of pH value for about 0.49, and the lowest value reached to 6.32. Treatment with PEG-UK brought obvious alleviation of neurological deficts in acute phase( P =0.001). A significant reduction of relative infarction volume was also proved in PEG-UK rats( P <0.001). As to the permeability of BBB, the leakage of EB in PEG-UK group was the least among three groups( P =0.001). What’s more, the sustain of the expression of TIMP-1( P =0.032) and Claudin5( P <0.001) and the inhibition of upregulation of MMP9( P <0.001) were all concluded in PEG-UK group. Besides, both the expression of NMDAR1( P <0.001) and Caspase9( P =0.013) in PEG-UK treated rats were much less. Conclusions: Our findings indicated that treatment with PEG-UK ameliorated the severity of ischemic stroke, accompanied by neuroprotection through keeping the integrity of BBB and inhibiting apoptosis and neurotoxicity. PEG-UK may further inhibit hemorrhagic transformation by its BBB protection effect.