Pilot MRI study of carbon monoxide (CO) against ischemic stroke in mice: blood brain barrier integrity and metabolic pattern

Although stroke is the main cause of brain damage worldwide, stroke therapies are based on blood reperfusion and do not target cerebral parenchyma. Ischemic stroke (representing 87% of all strokes) causes cerebral damage due to oxygen and tissue energy depletion, which lead to acidosis, inflammation, excitotoxicity and oxidative stress. Carbon monoxide (CO) is an endogenous gasotransmitter produced by heme oxygenase cleavage of the heme group. CO promotes cytoprotection by limiting inflammation and preventing cell death in several tissues including the brain. Previous studies have demonstrated the protective role of CO in the mouse ischemic stroke model, middle cerebral artery occlusion (MCAo) by histological analysis when CO is when applied before ischemia. Herein, there are two main novelties. First CO is administrated following stroke, which better mimics its potential future use as therapeutic drug. Secondly, imaging techniques were used to elucidate the effect of this gasotransmitter at the metabolic, vascular and anatomic levels.The putative neuroprotective effects of CO following MCAo were assessed by 3 i.p. injections of the CO-releasing molecule CORM-A1 (3 mg/kg), administered 6, 24 and 48h after reperfusion. Magnetic Resonance Imaging was performed 1 day and 7 days after reperfusion using T2-weighted, diffusion weighted images, proton spectroscopy (1H-MRS) and perfusion (dynamic contrast enhanced images).1H-MRS also allowed the comparison between metabolite signatures at day 1 versus 7 day following MCAo. Furthermore, CORM-A1 limited the loss of blood-brain barrier (BBB) integrity as it reduced the edema formation. Furthermore, the CO donor minimized the metabolite load loss at an early stage after MCAo, both in striatum and cortex.In conclusion and based on MRI analysis, CO has a protective role in the recovery from stroke injury, mainly by acting on BBB integrity and brain metabolism.