Abstract
Acute stroke causes complex, pathological, and systemic responses that have not been treatable by any single medication. In this study, using a murine transient middle cerebral artery occlusion stroke model, a novel therapeutic strategy is proposed, where blood replacement (BR) robustly reduces infarctions and improves neurological deficits in mice. Our analyses of immune cell subsets suggest that BR therapy substantially decreases neutrophils in blood following a stroke. Electrochemiluminescence detection demonstrates that BR therapy reduces cytokine storm in plasma and ELISA demonstrates reduced levels of matrix metalloproteinase-9 (MMP-9) in the plasma and brains at different time points post-stroke. Further, we have demonstrated that the addition of MMP-9 to the blood diminishes the protective effect of the BR therapy. Our study is the first to show that BR therapy leads to profoundly improved stroke outcomes in mice and that the improved outcomes are mediated via MMP-9. These results offer new insights into the mechanisms of stroke damage.
Introduction
A stroke remains a major cause of morbidity and mortality globally1. Current treatments for acute stroke include thrombolytic therapy through the administration of tissue plasminogen activator and the surgical removal of the clot. However, these methods have limited time windows. In the clinical field of stroke, the mantra is “time is brain,” because infarct evolves every minute following a stroke.
A stroke is more than just a disruption of blood flow to the brain; stroke pathophysiology is a progressive and systemic response to brain injury2. Dynamic breaches of the blood–brain barrier (BBB) has been observed in experimental stroke animal models3,4 and stroke patients5. Following BBB disruption after ischemic stroke, a pathological and systemic reaction may be initiated. A hyperinflammatory condition, including an increase in inflammatory cells, cytokines, and chemokines in circulating blood has been documented in stroke6. Activated neutrophils secret proteinases such as matrix metalloproteinase-9 (MMP-9), which may cause BBB leakage, extracellular matrix degradation, and evolution of cerebral ischemia7. MMP-9 also interacts with chemokines8 and cytokines9,10,11, causing a further cascade of post-ischemic cerebral inflammation that leads to degeneration in brain tissue and exacerbates stroke outcomes.
In this study, using a murine transient middle cerebral artery occlusion (tMCAO) stroke model, we present a therapeutic strategy for stroke—a blood replacement (BR) that substitutes stroke mouse blood with whole blood obtained from naive, healthy donor mice. We have demonstrated that the BR performed at 6.5~7 h following a stroke robustly reduces infarct volume and improves neurological deficits. Following the treatment, we demonstrate that the BR therapy significantly reduces the cytokine storm in the plasma. In addition, flow cytometry and enzyme-linked immunosorbent assay (ELISA) have demonstrated substantially reduced neutrophils and decreased levels of MMP-9 in the blood and brains of stroke mice, which received whole blood obtained from naive donor mice. Further, addition of MMP-9 in blood diminishes therapeutic effects of the BR therapy. These results reveal a possible therapy of using blood for brain protection from a stroke….
