Central nervous system entry of peripherally injected umbilical cord blood cells is not required for neuroprotection in stroke

Abstract

Background and Purpose - To date, stem cell graft-mediated neuroprotection is equated with graft survival and secretion of neurotrophic factors in the brain. Here, we examined whether neuroprotection by systemically delivered human umbilical cord blood (HUCB) cells was dependent on their entry into the central nervous system in a rodent model of acute stroke. Methods - Adult male Sprague-Dawley rats were subjected to right middle cerebral artery occlusion for 60 minutes. During the 1-hour occlusion, animals were randomly assigned to 1 of the following treatments: intravenous injection of HUCB (a subtherapeutic dose of 200 000 cells in 10 μL) with blood-brain barrier (BBB) permeabilizer (1.1 mol/L mannitol at 4°C) or vehicle, intravenous vehicle alone, or intravenous mannitol alone. Behavioral tests, using elevated body swing test and passive avoidance test, were conducted at day 3 poststroke, and thereafter, animals were euthanized for: (1) immunohistochemical examination of HUCB, which were lentivirally labeled with green fluorescent protein; (2) cerebral infarction analysis using 2,3,5-triphenyl-tetrazolium chloride; and (3) enzyme-linked immunosorbent assay of trophic factors within the striatal region. Results - We did not detect intravenously administered low dose of HUCB cells in the brains of animals at day 3 after stroke even when cells were coinfused with a BBB permeabilizer (mannitol). However, HUCB-mannitol treatment significantly increased brain levels of neurotrophic factors, which correlated positively with reduced cerebral infarcts and improved behavioral functions. Conclusions - Our data show that central nervous system availability of grafted cells is not a prerequisite for acute neuroprotection provided that therapeutic molecules secreted by these cells could cross the BBB.