Regional blood flow in compression-induced brain edema in rats: effect of dietary vitamin E

Therapies targeting lipid peroxidation in traumatic brain injury

Lipid peroxidation can be broadly defined as the process of inserting a hydroperoxy group into a lipid. Polyunsaturated fatty acids present in the phospholipids are often the targets for peroxidation. Phospholipids are indispensable for normal structure of membranes. The other important function of phospholipids stems from their role as a source of lipid mediators - oxygenated free fatty acids that are derived from lipid peroxidation. In the CNS, excessive accumulation of either oxidized phospholipids or oxygenated free fatty acids may be associated with damage occurring during acute brain injury and subsequent inflammatory responses. There is a growing body of evidence that lipid peroxidation occurs after severe traumatic brain injury in humans and correlates with the injury severity and mortality. Identification of the products and sources of lipid peroxidation and its enzymatic or non-enzymatic nature is essential for the design of mechanism-based therapies. Recent progress in mass spectrometry-based lipidomics/oxidative lipidomics offers remarkable opportunities for quantitative characterization of lipid peroxidation products, providing guidance for targeted development of specific therapeutic modalities. In this review, we critically evaluate previous attempts to use non-specific antioxidants as neuroprotectors and emphasize new approaches based on recent breakthroughs in understanding of enzymatic mechanisms of lipid peroxidation associated with specific death pathways, particularly apoptosis. We also emphasize the role of different phospholipases (calcium-dependent and -independent) in hydrolysis of peroxidized phospholipids and generation of pro- and anti-inflammatory lipid mediators. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Animal modelling of traumatic brain injury in preclinical drug development: where do we go from here?

Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. Survivors of TBI frequently suffer from long-term personality changes and deficits in cognitive and motor performance, urgently calling for novel pharmacological treatment options. To date, all clinical trials evaluating neuroprotective compounds have failed in demonstrating clinical efficacy in cohorts of severely injured TBI patients. The purpose of the present review is to describe the utility of animal models of TBI for preclinical evaluation of pharmacological compounds. No single animal model can adequately mimic all aspects of human TBI owing to the heterogeneity of clinical TBI. To successfully develop compounds for clinical TBI, a thorough evaluation in several TBI models and injury severities is crucial. Additionally, brain pharmacokinetics and the time window must be carefully evaluated. Although the search for a single-compound, 'silver bullet' therapy is ongoing, a combination of drugs targeting various aspects of neuroprotection, neuroinflammation and regeneration may be needed. In summary, finding drugs and prove clinical efficacy in TBI is a major challenge ahead for the research community and the drug industry. For a successful translation of basic science knowledge to the clinic to occur we believe that a further refinement of animal models and functional outcome methods is important. In the clinical setting, improved patient classification, more homogenous patient cohorts in clinical trials, standardized treatment strategies, improved central nervous system drug delivery systems and monitoring of target drug levels and drug effects is warranted.

Oxidative damage after severe head injury and its relationship to neurological outcome

OBJECTIVE

We sought to establish the time course of reactive oxygen species after severe head injuries in humans and to investigate their relationship with clinical outcomes.

METHODS

Both the markers of oxidative damage-malonylaldehyde (MDA) and the enzymatic and nonenzymatic antioxidant defenses (i.e., superoxide dismutase [SOD] and vitamin E [VE], respectively)-were studied. To assess the time course of MDA, SOD, and VE, jugular bulb (JB) and peripheral venous blood samples were obtained from 30 patients within 8 hours of severe head trauma onset (T(0)) and 6 (T(1)), 12 (T(2)), 24 (T(3)), and 48 hours (T(4)) after trauma onset. Patients were divided into good and poor outcome groups according to their 6-month neurological outcome as determined on the basis of their Glasgow Outcome Scale scores and biochemical profiles.

RESULTS

In JB samples, MDA levels increased significantly at T(1), T(2), T(3), and T(4) as compared with T(0); SOD activity increased significantly at T(2) and T(3) as compared with T(0); and VE levels decreased significantly at T(1), T(2), and T(3) as compared with T(0). The same variables did not change significantly over time in peripheral venous blood samples. Moreover, the MDA levels and SOD activity detected in JB samples were significantly higher in the poor outcome group at T(1) and T(2). No significant difference in VE levels was observed between the two outcome groups.

CONCLUSION

Reactive oxygen species-mediated oxidative damage can play an important role in determining the prognosis of severe brain injury in humans.

Stilbazulenyl nitrone, a novel azulenyl nitrone antioxidant: improved neurological deficit and reduced contusion size after traumatic brain injury in rats

OBJECT

Stilbazulenyl nitrone (STAZN) is a second-generation azulenyl nitrone that has markedly enhanced antioxidant properties compared with those of conventional alpha-phenyl nitrones. In this study, the authors assessed the potential efficacy of STAZN in a rodent model of fluid-percussion brain injury, which results in a consistent cortical contusion.

METHODS

After anesthesia had been induced in normothermic Sprague-Dawley rats (brain temperature 36-36.5 degrees C) by halothane-nitrous oxide, the animals were subjected to a right parietooccipital parasagittal fluid-percussion injury (1.5-2 atm). The agent (STAZN, 30 mg/kg: eight animals) or vehicle (dimethyl sulfoxide; eight animals) was administered intraperitoneally at 5 minutes and 4 hours after trauma. The neurological status of each rat was evaluated on Days 1, 2, and 7 postinjury (normal score 0, maximum injury 12). Seven days after trauma, the rat brains were perfusion fixed, coronal sections at various levels were digitized, and areas of contusion were measured. Treatment with STAZN significantly improved neurological scores on Days 2 and 7 postinjury compared with vehicle-treated rats. Administration of STAZN also significantly reduced the total contusion area by 63% (1.8 +/- 0.5 mm2 in STAZN-treated animals compared with 4.8 +/- 2.1 mm2 in vehicle-treated animals; p = 0.04) and the deep cortical contusion area by 60% (1.2 +/- 0.2 mm2 in STAZN-treated animals compared with 2.9 +/- 1.2 mm2 in vehicle-treated animals; p = 0.03). By contrast, hippocampal cell loss in the CA3 sector was unaffected by STAZN treatment.

CONCLUSIONS

Therapy with STAZN, a novel potent antioxidant, administered following traumatic brain injury, markedly improves neurological and histological outcomes. Azulenyl nitrones appear to represent a promising class of neuroprotective agents for combating this devastating condition.

Protective effect of a novel vitamin E derivative on experimental traumatic brain edema in rats--preliminary study

Oxygen free radicals have been proposed to be one of the major mechanisms of secondary brain damage in traumatic brain injury. Protective effect by vitamin E against oxidative damage has attracted much attention. Recent studies have demonstrated a novel vitamin E derivative, 2-(alpha-D-glucopyranosyl)methyl-2,5,7,8-tetramethylchroman-6-ol (TMG), has excellent water-solubility and antioxidant activity. The purpose of this study was to investigate protective effects of TMG on experimental traumatic brain edema (BE). Male Wistar rats were anaesthetized with chloral hydrate. Traumatic BE was produced by a cortical freezing lesion. Animals were separated into three groups: saline-treated rats (n = 4), TMG-treated (4 mg/kg) rats (n = 7) and TMG-treated (40 mg/kg) rats (n = 8). Saline or TMG was administered intravenously before lesion production. Animals were sacrificed at 6 hours after lesion production and the brain water content was determined by the dry-wet weight method. Half-life of TMG after intravenous administration of TMG was also investigated. The half life of TMG was approximately 5 minutes. TMG (40 mg/kg) significantly attenuated BE following cryogenic brain injury (p < 0.01). In conclusion, this preliminary study has demonstrated that a novel vitamin E derivative might be promising in the treatment of traumatic BE.

Time-level relationship for lipid peroxidation and the protective effect of alpha-tocopherol in experimental mild and severe brain injury

OBJECTIVE

Oxygen free radical-mediated lipid peroxidation has been proposed to be one of the major mechanisms of secondary damage in traumatic brain injury. The first purpose of this study was to establish the time-level relationship for lipid peroxidation in injured brain tissue. The second purpose was to examine the protective effect of alpha-tocopherol against lipid peroxidation.

METHODS

For this study, 65 guinea pigs in five groups were studied. Five of the animals were identified as a control group, and the remaining 60 animals were divided equally into four groups (Groups A, B, C, and D). Mild injury (200 g x cm) (Groups A and C) and severe injury (1000 g x cm) (Groups B and D) were produced by the method of Feeney et al. Alpha-tocopherol (100 mg/kg) was administered intraperitoneally before brain injury in Groups C and D. Five animals from each group were killed immediately after trauma, five after 1 hour, and the remaining five animals after 36 hours. Lipid peroxidation in traumatized brain tissues was assessed using the thiobarbituric acid method.

RESULTS

In all groups with traumatic brain injuries, levels of malondialdehyde, a lipid peroxidation product, were higher than in the control group. The amount of lipid peroxidation was increased by the severity of the trauma. Alpha-tocopherol significantly suppressed the rise in lipid peroxide levels in traumatized brain tissues.

CONCLUSION

This study demonstrates that lipid peroxidation is increased by the severity of trauma and that alpha-tocopherol has a protective effect against oxygen free radical-mediated lipid peroxidation in mild and severe brain injury.

Attenuation of decompressive hypoperfusion and cerebral edema by superoxide dismutase

This study tested the hypothesis that ischemia-reperfusion injury initiated by the superoxide anion radical is a major component of postdecompression hypoperfusion and cerebral edema, and could be attenuated by superoxide dismutase (SOD). A supratentorial extradural balloon was placed in 20 fasting, lightly anesthetized, mechanically ventilated dogs and inflated in 0.5-ml increments (0.07 ml/sec) at 15-minute intervals. The end-point of balloon expansion was the onset of an isoelectric electroencephalogram, near-arrest of hemispheric cerebral blood flow (CBF) (measured by H2 clearance), and the appearance of a suprainfratentorial intracranial pressure gradient, which was held for 15 minutes. The in vivo development of brain edema was detected by measuring brain elastic response (BER) extradurally, and was correlated with postmortem measurement of brain water content (gravimetry); blood-brain barrier integrity was tested by Evans blue dye given after the insult. After decompression, the dogs were randomly assigned to one of four treatment groups: Group I received hyperventilation (PaCO2 28 +/- 1 mm Hg, mean +/- standard deviation); Group II received furosemide (2.4 mg/kg) and pentobarbital (10 mg/kg) every 8 hours; Group III received 20% mannitol in a 1.4-gm/kg bolus plus furosemide, 0.5 mg/kg; and Group IV received SOD, 15,000 U/kg every 15 minutes for 3 hours. At 4 hours of decompression Group IV had significantly greater recovery in local CBF and BER than Groups I, II, and III (p less than 0.05). The 24-hour survival rate was 20% for Group I, 60% for Group II, 80% for Group III, and 100% for Group IV. The survival rate appeared to correlate with a variable degree of postmortem intraparenchymal hemorrhages, blood-brain barrier disruption, and moderate to severe brain edema for Groups I, II, and III. In contrast, Group IV had the least brain edema (p less than 0.05) and Evans blue dye extravasation (p less than 0.05) and the fewest intraparenchymal hemorrhages. These data support the hypothesis that, under the experimental conditions described here, the superoxide anion plays a major role in the pathophysiology of postdecompression ischemic edema.

Vitamin E and neurologic function in man

Despite the well-known detrimental effect of vitamin E deficiency on the nervous system of many experimental animal models for decades, only over the past decade has vitamin E become recognized as essential for the maintenance of the structure and function of the human nervous system. This discovery of the neurologic role of vitamin E in man is due primarily to the identification of a degenerative neurologic syndrome in children and adults with chronic vitamin E deficiency caused by gastrointestinal diseases impairing fat and vitamin E absorption. A compelling body of clinical, neuropathologic, and therapeutic response evidence conclusively demonstrates that vitamin E deficiency is responsible for the neurologic disorder seen in such patients. In addition, an inborn error in vitamin E metabolism, the Isolated Vitamin E Deficiency Syndrome, causes vitamin E deficiency and similar neurologic degeneration in the absence of fat malabsorption. Guidelines for the evaluation and treatment of vitamin E deficiency in relevant clinical circumstances are provided. The possible role of vitamin E in treating other neurologic diseases is discussed.

Cerebral phosphoinositide, triacylglycerol, and energy metabolism in reversible ischemia: origin and fate of free fatty acids

Levels of phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol (PI), phosphatidic acid, diacylglycerol (DAG), triacylglycerol (TAG), and free fatty acids (FFAs), as well as their fatty acid composition, were determined in rat forebrain during ischemia and postischemic recirculation. Cerebral energy state and electroencephalograms (EEGs) were also studied. Fifteen minutes of ischemia resulted in a decrease in PIP2 and PIP contents but not in PI content, concurrent with an enlargement of the FFA and DAG pools. The latter were enriched in stearate and arachidonate. Prolongation of ischemia did not produce further changes in content of any of the inositol phospholipids, but the increase in levels of FFAs and DAG continued. At the end of 45 min of ischemia, levels of both PIP2 and PIP decreased by 45-50%, and the total phosphoinositide content (PIP2 + PIP + PI) decreased by 21%, whereas levels of FFAs and DAG increased to 14- and 3.6-fold of control levels, respectively. During ischemia, the TAG-palmitate level decreased, but the TAG-arachidonate level increased; the tissue energy state deteriorated severely; and the EEG was suppressed. A 30-min recirculation period after 15 or 45 min of ischemia led to increases in PIP2, PIP, and total phosphoinositide contents, whereas levels of FFAs and DAG promptly decreased toward control values. The TAG-arachidonate level peaked and the TAG-palmitate level returned to a low control value during early recirculation. The ischemic changes in tissue lipids were completely reversed within 3 h of recirculation after both periods of ischemia. Adenylates were fully phosphorylated with as little as 30 min of reflow. The EEG activity partially recovered during reflow after 15 min of ischemia, whereas it remained depressed after prolonged ischemia. Thus, phosphodiesteric cleavage of PIP2 and PIP followed by deacylation of DAG is likely to contribute to the production of FFAs in early ischemia. Deacylation of undetermined lipids plays a role for the increment in levels of FFAs in the later period of ischemia. The rapid postischemic increase in levels of PIP2 and PIP indicates active synthesis not only from existing PI, but probably also by means of accumulated FFAs and DAG. These results indicate that the impaired resynthesis of inositol phospholipids cannot be a cause of the poor EEG activity after prolonged ischemia. Degradation and resynthesis of polyphosphoinositides and formation of TAG-arachidonate may be important for modulation of free arachidonic acid levels in the brain during temporary ischemia.

Regional brain energy metabolism after complete versus incomplete ischemia in the rat in the absence of severe lactic acidosis

Levels of energy metabolites were measured in forebrain regions in fasted rats subjected to 4-h recirculation after 1 h of either incomplete or complete ischemia. Both models of ischemia were produced by a procedure combining bilateral common carotid artery occlusion, systemic hypotension, and CSF pressure elevation; the degree of intracranial hypertension was varied to produce incomplete and complete ischemia. Levels of brain lactate at the end of ischemia ranged from 16 to 19 mmol/kg in incomplete ischemia and from 11 to 13 mmol/kg in complete ischemia. Energy metabolism recovered evenly in the neocortical and subcortical regions with recirculation after incomplete ischemia. The metabolic recovery in the cerebral cortex after complete ischemia was similar to that observed after incomplete ischemia; however, recovery in the subcortical regions after complete ischemia was less extensive, NADH fluorescence remained high, and there was a fall in total creatine. Intracellular pH in the dorsal thalamus was more alkalotic after complete than incomplete ischemia. Thus, in the absence of profound tissue lactic acidosis, residual CBF during prolonged ischemia helps postischemic restitution of brain energy metabolism in subcortical regions. The pattern of poor recovery in these regions after complete ischemia suggests inadequate reperfusion. The decreased total creatine and the severe tissue alkalosis may be biochemical markers of advanced tissue injury during reflow.