The Effects of Methylene Blue on Autophagy and Apoptosis in MRI‐defined Normal Tissue, Ischemic Penumbra and Ischemic Core

Background and purposeMethylene blue (MB) USP, which has energy‐enhancing and antioxidant properties, is currently used to treat methemoglobinemia and cyanide poisoning in humans. We recently showed that MB administration reduces infarct volume and behavioral deficits in rat models of ischemic stroke and traumatic brain injury. This study reportsthe underlying molecular mechanisms of MB neuroprotection following transient ischemic stroke in rats.MethodsRats were subjected to transient ischemic stroke. Multimodal MRI during the acute phaseand at 24hrs was used to define three regions of interest (ROIs): i) the perfusion‐diffusion mismatch salvaged by reperfusion, ii) the perfusion‐diffusion mismatch not salvaged by reperfusion, and iii) the ischemic core. These ROIswere extracted for western blot analyses of autophagic and apoptotic markers.ResultsThe major findings were: 1) MB treatment reduced infarct volume and behavioral deficits, 2) MB improved CBF to perfusion‐diffusion mismatch tissue after reperfusion and minimized harmful hyperperfusion24hrs after stroke, 3) MB inhibited apoptosis and enhanced autophagyin the perfusion‐diffusion mismatch tissue, 4) MB inhibited apoptotic signaling cascades (p53‐Bax‐Bcl2‐Caspase3), and 5) MB enhanced autophagic signaling cascades (p53‐AMPK‐TSC2‐mTOR).ConclusionsMB induced neuroprotection,at least in part,by enhancing autophagy and reducing apoptosis in perfusion‐diffusion mismatch tissue following ischemic stroke.