OBJECTIVE Reperfusion therapy with intravenous recombinant tissue plasminogen activator (rtPA) is the standard of care for acute ischemic stroke. However, hemorrhagic complications can result. Intravenous infusion of mesenchymal stem cells (MSCs) reduces stroke volume and improves behavioral function in experimental stroke models. One suggested therapeutic mechanism is inhibition of vascular endothelial dysfunction. The objective of this study was to determine whether MSCs suppress hemorrhagic events after rtPA therapy in the acute phase of transient middle cerebral artery occlusion (tMCAO) in rats. METHODS After induction of tMCAO, 4 groups were studied: 1) normal saline [NS]+vehicle, 2) rtPA+vehicle, 3) NS+MSCs, and 4) rtPA+MSCs. The incidence rate of intracerebral hemorrhage, both hemorrhagic and ischemic volume, and behavioral performance were examined. Matrix metalloproteinase-9 (MMP-9) levels in the brain were assessed with zymography. Quantitative analysis of regional cerebral blood flow (rCBF) was performed to assess hemodynamic change in the ischemic lesion. RESULTS The MSC-treated groups (Groups 3 and 4) experienced a greater reduction in the incidence rate of intracerebral hemorrhage and hemorrhagic volume 1 day after tMCAO even if rtPA was received. The application of rtPA enhanced activation of MMP-9, but MSCs inhibited MMP-9 activation. Behavioral testing indicated that both MSC-infused groups had greater improvement than non-MSC groups had, but rtPA+MSCs provided greater improvement than MSCs alone. The rCBF ratio of rtPA groups (Groups 2 and 4) was similar at 2 hours after reperfusion of tMCAO, but both were greater than that in non-rtPA groups. CONCLUSIONS Infused MSCs may inhibit endothelial dysfunction to suppress hemorrhagic events and facilitate functional outcome. Combined therapy of infused MSCs after rtPA therapy facilitated early behavioral recovery.
Keywords: BBB = blood-brain barrier; DWI = diffusion-weighted imaging; EvB = Evans Blue; GFP = green fluorescent protein; IL = interleukin; MCA = middle cerebral artery; MMP = matrix metalloproteinase; MSC = mesenchymal stem cell; NF-κβ = nuclear factor kappa light-chain enhancer of activated B cells; NS = normal saline; PBS = phosphate-buffered saline; PWI = perfusion-weighted imaging; ROI = region of interest; TNF = tumor necrosis factor; intracranial hemorrhage; mesenchymal stem cell; middle cerebral artery occlusion; rCBF = regional cerebral blood flow; recombinant tissue plasminogen activator; rodent; rtPA = recombinant tissue plasminogen activator; stroke; tMCAO = transient MCA occlusion; transplantation.