Validation of Brain Extracellular Glycerol as an Indicator of Cellular Membrane Damage due to Free Radical Activity after Traumatic Brain Injury

Abstract

Following severe traumatic brain injury (TBI), increasing oxygen delivery to the brain has been advocated as a useful strategy to reverse mitochondrial dysfunction and improve neurological outcome. However, this might also promote overproduction of free radicals, responsible for lipid peroxidation and hence brain cell damage. Therefore, a method for monitoring this potential adverse effect in humans is desirable. Glycerol, an end product of phospholipid breakdown, easily detectable in the human brain by means of microdialysis, might represent a reliable indicator of free radical-induced cell membrane damage. Brain microdialysates were collected from 24 adult male Sprague-Dawley rats over a 3-hour period following sham operation (n=6), chemical brain injury via administration of Fenton's reagent (n=6), a powerful hydroxyl radical generator, and lateral fluid percussion injury (FPI; n=12). In the FPI animals, post-traumatic i.v. administration of either normal saline or the free radical scavenger Tempol (10 mg/kg, followed by an infusion of 30 mg/kg/h over 3 h) was carried out to evaluate the effect of blockade of free radical generation. Samples were analyzed for the presence of glycerol and the marker of hydroxyl radical (OH.) by generation of 2,3-DHBA (dihydroxybenzoic acid). Brain tissue staining with TTC (2,3,5-triphenyltetrazoium chloride) was performed for lesion size assessment. Rats subjected to either Fenton's reagent administration or FPI exhibited significantly higher levels of glycerol as compared with shams (p=0.05). However, when the FPI was followed by Tempol administration, concentration of both glycerol and 2,3-DHBA decreased significantly (p=0.05). Furthermore, TCC staining revealed a significant reduction of secondary brain tissue damage in Tempol-treated animals (p=0.05). Our data suggest that injury-induced increases in microdialysate glycerol levels are a valid indicator of free radical activity, and their amelioration following Tempol treatment accords with less histological damage in response to FPI.

A prospective, randomized Phase II clinical trial to evaluate the effect of combined hyperbaric and normobaric hyperoxia on cerebral metabolism, intracranial pressure, oxygen toxicity, and clinical outcome in severe traumatic brain injury

“…3,4,17,35 Glycerol is an end product of phospholipid degradation in neural tissue cell membranes and is a marker of cell damage whether caused by O 2 toxicity via free radical formation and lipid peroxidation or secondarily from ischemia. 16,19,32 Levels of CSF F2-isoprostanes as well as microdialysate glycerol were significantly decreased following combined HBO 2 /NBH treatment. These findings may not only signify that there were no signs of O 2 toxicity from the combined HBO 2 /NBH treatment, but, in fact, that there was a protective effect against neuroinflammation and free radical-mediated damage.…”

Characterization of the Ionic Profile of the Extracellular Space of the Injured and Ischemic Brain: A Microdialysis Study

“…15,16 Peerdeman et al in a small cohort of TBI patients found that although the extracellular concentration of Glycerol [Gly] o was not useful for early detection of secondary adverse events. 15 However, values of [Gly] o > 150 µmol/L in the normal-appearing regions of the brain had a positive predictive value of 100% for an unfavorable outcome.…”

Free-Radical Scavenger Edaravone Treatment Confers Neuroprotection Against Traumatic Brain Injury in Rats

“…Elevation of free radicals damages all cellular components, including DNA, lipids, and proteins, leading to injuries of neurons, glial cells, nerve fibers, and blood vessels. Oxidative stress damages the BBB, leading to vasogenic brain edema, neuronal degeneration, and deteriorating neurological function, probably caused by the accelerated formation of several ROS including superoxide, hydroxyl radical (OH), NO (Dohi et al, 2006;Eghwrudjakpor and Allison, 2010;Merenda et al, 2008).…”

“…Oxidative stress occurs when there is an imbalance between cellular production of free radicals and the intrinsic ability of cells to sequester and eliminate these free radicals (Gilgun-Sherki et al, 2002). It begins immediately after TBI and initiates the cascade resulting in neuronal dysfunction and death, and thus plays a major role in the morbidity and mortality following TBI (Merenda et al, 2008). Importantly, enhancement of cellular defense mechanisms through the use of exogenous antioxidants is known to be neuroprotective in animal models of cerebral ischemia (Clausen et al, 2004).…”