Therapeutic Effects of Systemic Administration of the Novel RANKL-Modified Peptide, MHP1, for Ischemic Stroke in Mice

Microglial healing peptide 1, "MHP1", is a newly developed synthetic peptide composed of the DE and a part of the EF loop of the receptor activator of nuclear factor-кB (NFκB) ligand (RANKL). Our previous report demonstrated that MHP1 significantly inhibits Toll-like receptor (TLR) 2- and 4-induced inflammation in microglia/macrophages through RANK signaling without osteoclast activation. However, its inhibitory effects on ischemic stroke when administered intravenously have not been clarified. First, we examined whether MHP1 could penetrate the brain parenchyma. Intravenous injection of FITC-conjugated MHP1 demonstrated that MHP1 could cross the blood-brain-barrier in peri-infarct regions, but not in intact regions. Because MHP1 in the parenchyma was reduced at 60 minutes after injection, we speculated that continuous injection was necessary to achieve the therapeutic effects. To check the possible deactivation of MHP1 by continuous injection, the anti-inflammatory effects were checked in MG6 cells after incubation in 37°C for 24 hours. Although the inhibitory effects for IL6 and TNFα were reduced compared to nonincubated MHP1, its anti-inflammatory efficacy remained, indicating that continuous administration with pump was possible. The single and successive continuous administration of MHP1 starting from 4 or 6 hours after cerebral ischemia successfully reduced infarct volume and prevented the exacerbation of neurological deficits with reduced activation of microglia/macrophages and inflammatory cytokines. Different from recombinant RANKL, MHP1 did not activate osteoclasts in the paralytic arm. Although further modification of MHP1 is necessary for stabilization, the MHP1 could be a novel agent for the treatment ischemic stroke.

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