Rationale: Hemorrhagic complications represent a major limitation of intravenous thrombolysis using tissue plasminogen activator (tPA) in patients with ischemic stroke. The expression of tPA receptors on immune cells raises the question of what effects tPA exerts on these cells and whether these effects contribute to thrombolysis-related hemorrhagic transformation. Objective: We aim to determine the impact of tPA on immune cells and investigate the association between observed immune alteration with hemorrhagic transformation in ischemic stroke patients and in a rat model of embolic stroke. Methods and Results: Paired blood samples were collected before and 1 hour after tPA infusion from 71 ischemic stroke patients. Control blood samples were collected from 27 ischemic stroke patients without tPA treatment. A rat embolic middle cerebral artery occlusion model was adopted to investigate the underlying mechanisms of hemorrhagic transformation. We report that tPA induces a swift surge of circulating neutrophils and T cells with profoundly altered molecular features in ischemic stroke patients and a rat model of focal embolic stroke. tPA exacerbates endothelial injury, increases adhesion and migration of neutrophils and T cells, which are associated with brain hemorrhage in rats subjected to embolic stroke. Genetic ablation of annexin A2 in neutrophils and T cells diminishes the effect of tPA on these cells. Decoupling the interaction between mobilized neutrophils/T cells and the neurovascular unit, achieved via a sphingosine-1-phosphate receptor 1 modulator RP101075 and a CCL2 synthesis inhibitor bindarit, which block lymphocyte egress and myeloid cell recruitment, respectively, attenuates hemorrhagic transformation and improves neurological function after tPA thrombolysis. Conclusions: Our findings suggest that immune invasion of the neurovascular unit represents a previously unrecognized mechanism underlying tPA-mediated brain hemorrhage, which can be overcome by precise immune modulation during thrombolytic therapy.

Background and Purpose — Apoptotic-like pathways may contribute to brain cell death after intracerebral hemorrhage. In this study, we used a simplified in vitro model of hemoglobin neurotoxicity to map the caspase cascades involved and to document the role of oxidative stress. Methods — Primary neuronal cultures were obtained from rat cerebral cortex and exposed to hemoglobin to induce cell death. Cytotoxicity was assessed via measurements of mitochondrial viability (MTT assay) and lactate dehydrogenase (LDH assay). Activation of caspase-3, -8, and -9 was measured by Western blot and enzyme activity assays. Various caspase inhibitors (zVADfmk, zDEVDfmk, zIETDfmk, and zLEHDfmk) were tested for neuroprotective efficacy. The role of oxidative stress was assessed with the use of U83836E as a potent scavenger of free radicals. Results — Exposure of primary cortical neurons to hemoglobin induced a dose- and time-dependent cytotoxicity. Western blots showed upregulation of cleaved caspase-3. Enzyme assays showed an increase in caspase-9–like and caspase-3–like activity. However, caspase inhibition did not result in neuroprotection. In contrast, the free radical scavenger U83836E significantly reduced hemoglobin-induced neuronal death. Combination treatment with both U83836E and the broad spectrum caspase inhibitor zVADfmk did not yield additional protection. Conclusions — Upstream and downstream caspases were upregulated after hemoglobin-induced neurotoxicity in vitro, but only an antioxidant approach with a potent free radical scavenger significantly improved neuronal survival. These data suggest that in addition to the activation of caspase cascades, parallel pathways of oxidative stress may predominate in this model of hemoglobin neurotoxicity.

Background and Purpose— Emerging data suggest that neuroglobin (Ngb) may protect against hypoxic/ischemic neuronal insults. However, the underlying mechanisms in vivo and implications for long-term outcomes are still not well understood. Methods— Using our newly created Ngb overexpressing transgenic (Ngb-Tg) mice, we measured brain infarction on day 1 and day 14 after transient focal cerebral ischemia and performed neurobehavioral assessments in sensorimotor deficits on days 1, 3, 7, and 14. To test the hypothesis that Ngb may play a role in reducing oxidative stress after stroke, intracellular malondialdehyde levels were measured and compared in Ngb-Tg and wild-type mice. Results— Increased Ngb mRNA and protein levels were identified in Ngb-Tg brains. Malondialdehyde levels in ischemic hemispheres of Ngb-Tg were significantly reduced compared with wild-type controls at 8 hours and 22 hours after transient focal cerebral ischemia. Compared with wild-type controls, brain infarction volumes 1 day and 14 days after transient focal cerebral ischemia were significantly reduced in Ngb-Tg mice. However, there were no significant improvements in sensorimotor deficits for up to 14 days after stroke in Ngb-Tg mice compared with wild-type controls. Conclusions— Ngb reduces tissue infarction and markers of oxidative stress after stroke. Tissue protection by overexpressing Ngb can be sustained for up to 2 weeks.