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Polynitroxyl Albumin Reduces Infarct Size in Transient Focal Cerebral Ischemia in the Rat: Potential Mechanisms Studied by Magnetic Resonance Imaging

Nitroxide free radicals are known to protect cells from oxidative damage. Diffusion-weighted and perfusion-weighted magnetic resonance imaging was used to evaluate the effects of polynitroxyl albumin(PNA) in a middle cerebral artery intraluminal suture model of transient focal cerebral ischemia in the rat. Three groups of Sprague-Dawley rats were investigated: (1) PNA(N = 6), (2) human serum albumin (N = 6), and (3) saline (N = 7). The middle cerebral artery was occluded for 2 hours. Treatment was started 30 minutes after induction of ischemia. A total dose of 1% body weight (volume/weight) of PNA (23.5 mg/dL protein and 110 mmol/L nitroxide), albumin (23.5 mg/dL), or saline was injected intravenously at three time points: 0.5% at 0.5 hours, 0.25% at 2 hours (i.e., just before reperfusion), and 0.25% at 4 hours after occlusion. Six sets of diffusion- and perfusion-weighted magnetic resonance images were acquired throughout the 2 hours of ischemia and the 2 hours of reperfusion. The rats were killed at 24 hours, and the brains were stained with 2,3,5-triphenyltetrazolium chloride (TTC). Diffusion-weighted imaging showed that the growth of the ischemic lesion was suppressed in the PNA-treated group. The 4 hours diffusion-weighted imaging-derived hemispheric lesion volume in the PNA-treated group (25% ± 9%) was significantly smaller than that in the saline-treated(43% ± 13%; P = 0.016) or albumintreated groups (38% ± 6%; P = 0.017). A larger difference was observed for the 24-hour TTC-derived lesion volumes in the PNA (8% ± 7%), saline (35% ± 8%; P< 0.001), and albumin (31% ± 6%; P < 0.001) groups. Perfusion-weighted imaging demonstrated a marked improvement in cerebral perfusion in the PNA-treated group during ischemia and reperfusion. In conclusion, treatment with PNA results in an improvement in perfusion and a reduction of infarct volume in a model of transient focal cerebral ischemia in the rat.