monodehydroascorbate and Brain-Ischemia

The formation of free radicals and lipid peroxidation in the brain after hypoxic ischemia was investigated. Seven-day-old rats were subjected to unilateral (left) carotid artery ligation followed by 70 min of hypoxia with 8% oxygen at 36 degrees C. The animals were randomized into six groups as follows: control animals (no anesthesia, ligation or hypoxia) and animals decapitated at 0, 15, 30, 60 and 180 min into the reoxygenation period. Lipid peroxidation was quantified in brain homogenates using the thiobarbituric acid assay (TBA). The TBA-malondialdehyde (MDA) complex was measured with HPLC. The semi-dehydroascorbate radical was measured using electron spin resonance (ESR) spectroscopy. The semi-dehydroascorbate radical levels increased more than 3-fold in the left HI hemisphere compared to the left control hemisphere 15 min posthypoxic ischemia. The amount of MDA was significantly increased in the hypoxic ischemic (HI) hemisphere ipsilateral to the carotid ligation compared with contralateral hypoxic hemisphere. The MDA level in the left HI hemisphere was also significantly elevated at 0, 15, 30 and 60 min, but not at 180 min into the reoxygenation period. Reoxygenation after hypoxic ischemia thus induced formation of semi-dehydroascorbate radicals and lipid peroxidation.

Topics: Animals; Animals, Newborn; Brain Damage, Chronic; Brain Ischemia; Cerebral Arteries; Dehydroascorbic Acid; Electron Spin Resonance Spectroscopy; Free Radicals; Functional Laterality; Hypoxia, Brain; Lipid Peroxidation; Malondialdehyde; Rats; Thiobarbituric Acid Reactive Substances

Oxygen radicals produced by activated neutrophils have been involved in brain injury during ischemia-reperfusion. Platelet-activating factor (PAF) is a candidate as one of the mediators of neutrophil activation during cerebral ischemia-reperfusion. Recent evidence indicates that PAF-induced neutrophil activation is mediated by thromboxane A2 (TXA2). To study the role of PAF and TXA2 in radical production during cerebral ischemia-reperfusion, we evaluated the effects of a PAF antagonist, Y-24180, and a TXA2 antagonist, S-1452, on radical formation in rats with 1 h middle cerebral artery (MCA) occlusion. In the present study, we employed a new electron spin resonance (ESR) method coupled with brain microdialysis. The method uses the endogenous ascorbyl radical (AR) concentration as a marker of oxygen radicals and requires no spin-trapping agents. In the vehicle controls, extracellular AR from the ischemic brain cortex decreased during MCA occlusion. Following reperfusion, AR significantly increased at 30 mm and 1 h, returned to near the basal levels at 2 h, and increased again at 24 h after reperfusion. In the rats treated with S-1452 or Y-24180, AR decreased during MCA occlusion to the same extent as in the vehicle control. However, pretreatment with Y-24180 or S-1452 significantly attenuated the increase in extracellular AR after reperfusion, while it exerted no effect on the changes in extracellular ascorbate or tissue pO2 throughout the experimental period. In conclusion, PAF and TXA2 might contribute to cerebral ischemia-reperfusion injury by increasing the generation of oxygen radicals.

Topics: Animals; Ascorbic Acid; Azepines; Brain; Brain Ischemia; Bridged Bicyclo Compounds; Dehydroascorbic Acid; Extracellular Space; Fatty Acids, Monounsaturated; Free Radicals; Male; Oxygen; Partial Pressure; Peroxidase; Platelet Activating Factor; Platelet Aggregation Inhibitors; Rats; Rats, Wistar; Reactive Oxygen Species; Reperfusion; Thromboxane A2; Triazoles

A growing body of experimental data indicate that oxygen radicals may mediate the brain injury during ischemia-reperfusion. One potential source of oxygen radicals is activated neutrophils. To study the role of neutrophils in radical production during cerebral ischemia-reperfusion, we evaluated the effects of depletion of circulating neutrophils by administration of an anti-neutrophil monoclonal antibody (RP3) on radical formation in rats with 1-h middle cerebral artery (MCA) occlusion. In the present study, we employed a new electron spin resonance method coupled with brain microdialysis. The method uses the endogenous ascorbyl radical (AR) concentration as a marker of oxygen radicals and requires no spin-trapping agents. In the vehicle controls, extracellular AR decreased during MCA occlusion. After reperfusion, AR significantly increased at 30 min and 1 h, returned to near basal level until 2 h, and increased again at 24 h after reperfusion. In the rats treated with RP3, AR decreased during MCA occlusion to the same extent as in the vehicle control. However, RP3 treatment completely inhibited the increase in extracellular AR after reperfusion. RP3 treatment exerted no effect on the changes in extracellular ascorbate or tissue PO2 throughout the experimental period. In conclusion, neutrophils are a major source of oxygen radicals during reperfusion after focal cerebral ischemia.

Topics: Animals; Brain; Brain Ischemia; Dehydroascorbic Acid; Extracellular Space; Free Radicals; Leukocyte Count; Male; Neutrophils; Oxygen; Partial Pressure; Rats; Rats, Wistar; Reactive Oxygen Species; Reperfusion