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

Zhilong Huoxue Tongyu capsule attenuates intracerebral hemorrhage induced redox imbalance by modulation of Nrf2 signaling pathway

Background: One of the severely debilitating and fatal subtypes of hemorrhagic stroke is intracerebral hemorrhage (ICH), which lacks an adequate cure at present. The Zhilong Huoxue Tongyu (ZLHXTY) capsule has been utilized effectively since last decade to treat ICH, in some provinces of China but the scientific basis for its mechanism is lacking. Purpose: To investigate the neuroprotective role of ZLHXTY capsules for ICH-induced oxidative injury through the regulation of redox imbalance with the Nrf2 signaling pathway. Methods: Autologous blood injection model of ICH in C57BL/6J mice was employed. Three treatment groups received ZLHXTY once daily through oral gavage at doses 0.35 g/kg, 0.7 g/kg, and 1.4 g/kg, started after 2 h and continued for 72 h of ICH induction. The neurological outcome was measured using a balance beam test. Serum was tested for inflammatory markers IL-1β, IL-6, and TNF-α through ELISA, oxidative stress through hydrogen peroxide content assay, and antioxidant status by total antioxidant capacity (T-AOC) assay. Nuclear extract from brain tissue was assayed for Nrf2 transcriptional factor activity. RT-qPCR was performed for Nfe2l2, Sod1, Hmox1, Nqo1, and Mgst1; and Western blotting for determination of protein expression of Nrf2, p62, Pp62, Keap, HO1, and NQO1. Fluoro-jade C staining was also used to examine neuronal damage. Results: ZLHXTY capsule treatment following ICH demonstrated a protective effect against oxidative brain injury. Neurological scoring showed improvement in behavioral outcomes. ELISA-based identification demonstrated a significant decline in the expression of serum inflammatory markers. Hydrogen peroxide content in serum was found to be reduced. The total antioxidant capacity was also reduced in serum, but the ZLHXTY extract showed a concentration-dependent increase in T-AOC speculating at its intrinsic antioxidant potential. Nrf2 transcriptional factor activity, mRNA and protein expression analyses revealed normalization of Nrf2 and its downstream targets, which were previously elevated as a result of oxidative stress induced by ICH. Neuronal damage was also reduced markedly after ZLHXTY treatment as revealed by Fluoro-jade C staining. Conclusion: ZLHXTY capsules possess an intrinsic antioxidant potential that can modulate the ICH-induced redox imbalance in the brain as revealed by the normalization of Nrf2 and its downstream antioxidant targets.

Maintained high sustained serum malondialdehyde levels after severe brain trauma injury in non-survivor patients

Objective

Higher blood malondialdehyde (biomarker of lipid peroxidation) levels in the first hours of traumatic brain injury (TBI) have been found in patients with a worst prognosis. The objective of this study was to determine whether serum malondialdehyde levels during the first week of severe TBI could be used as mortality biomarkers. This was a multicenter, prospective and observational study performed in six Spanish Intensive Care Units. We included patients with severe TBI (defined as Glasgow Coma Scale < 9), and with Injury Severity Score in non-cranial aspects < 9. We determined serum malondialdehyde concentrations at days 1, 4 and 8 of TBI. We stablished 30-day mortality as the end-point study.

Results

We found that serum malondialdehyde concentrations at days 1 (p < 0.001), 4 (p < 0.001), and 8 (p < 0.001) of TBI were higher in non-survivor (n = 34) than in survivor (n = 90) patients. We found an area under curve of serum malondialdehyde concentrations at days 1, 4, and 8 of TBI to predict 30-day mortality of 77% (p < 0.001), 87% (p < 0.001) and 84% (p < 0.001) respectively. Thus, the new and most relevant findings of our study were serum malondialdehyde levels during the first week of TBI could be used as mortality biomarkers.

Metabolomics and Biomarker Discovery in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of disability and mortality worldwide. The TBI pathogenesis can induce broad pathophysiological consequences and clinical outcomes attributed to the complexity of the brain. Thus, the diagnosis and prognosis are important issues for the management of mild, moderate, and severe forms of TBI. Metabolomics of readily accessible biofluids is a promising tool for establishing more useful and reliable biomarkers of TBI than using clinical findings alone. Metabolites are an integral part of all biochemical and pathophysiological pathways. Metabolomic processes respond to the internal and external stimuli resulting in an alteration of metabolite concentrations. Current high-throughput and highly sensitive analytical tools are capable of detecting and quantifying small concentrations of metabolites, allowing one to measure metabolite alterations after a pathological event when compared to a normal state or a different pathological process. Further, these metabolic biomarkers could be used for the assessment of injury severity, discovery of mechanisms of injury, and defining structural damage in the brain in TBI. Metabolic biomarkers can also be used for the prediction of outcome, monitoring treatment response, in the assessment of or prognosis of post-injury recovery, and potentially in the use of neuroplasticity procedures. Metabolomics can also enhance our understanding of the pathophysiological mechanisms of TBI, both in primary and secondary injury. Thus, this review presents the promising application of metabolomics for the assessment of TBI as a stand-alone platform or in association with proteomics in the clinical setting.

Location-dependent effects of trauma on oxidative stress in humans

Though circulating antioxidant capacity in plasma is homeostatically regulated, it is not known whether acute stressors (i.e. trauma) affecting different anatomical locations could have quantitatively different impacts. For this reason, we evaluated the relationship between the anatomical location of trauma and plasma total antioxidant capacity (TAC) in a prospective study, where the anatomical locations of trauma in polytraumatic patients (n = 66) were categorized as primary affecting the brain -traumatic brain injury (TBI)-, thorax, abdomen and pelvis or extremities. We measured the following: plasma TAC by 2 independent methods, the contribution of selected antioxidant molecules (uric acid, bilirubin and albumin) to these values and changes after 1 week of progression. Surprisingly, TBI lowered TAC (919 ± 335 μM Trolox equivalents (TE)) in comparison with other groups (thoracic trauma 1187 ± 270 μM TE; extremities 1025 ± 276 μM TE; p = 0.004). The latter 2 presented higher hypoxia (PaO₂/FiO₂ 272 ± 87 mmHg) and hemodynamic instability (inotrope use required in 54.5%) as well. Temporal changes in TAC are also dependent on anatomical location, as thoracic and extremity trauma patients’ TAC values decreased (1187 ± 270 to 1045 ± 263 μM TE; 1025 ± 276 to 918 ± 331 μM TE) after 1 week (p < 0.01), while in TBI these values increased (919 ± 335 to 961 ± 465 μM TE). Our results show that the response of plasma antioxidant capacity in trauma patients is strongly dependent on time after trauma and location, with TBI failing to induce such a response.

Oxidized phospholipid signaling in traumatic brain injury

Oxidative stress is a major contributor to secondary injury signaling cascades following traumatic brain injury (TBI). The role of lipid peroxidation in the pathophysiology of a traumatic insult to neural tissue is increasingly recognized. As the methods to quantify lipid peroxidation have gradually improved, so has the understanding of mechanistic details of lipid peroxidation and related signaling events in the injury pathogenesis. While free-radical mediated, non-enzymatic lipid peroxidation has long been studied, recent advances in redox lipidomics have demonstrated the significant contribution of enzymatic lipid peroxidation to TBI pathogenesis. Complex interactions between inflammation, phospholipid peroxidation, and hydrolysis define the engagement of different cell death programs and the severity of injury and outcome. This review focuses on enzymatic phospholipid peroxidation after TBI, including the mechanism of production, signaling roles in secondary injury pathology, and temporal course of production with respect to inflammatory response. In light of the newly identified phospholipid oxidation mechanisms, we also discuss possible therapeutic targets to improve neurocognitive outcome after TBI. Finally, we discuss current limitations in identifying oxidized phospholipids and possible methodologic improvements that can offer a deeper insight into the region-specific distribution and subcellular localization of phospholipid oxidation after TBI.

Biomarkers Associated with the Outcome of Traumatic Brain Injury Patients

This review focuses on biomarkers associated with the outcome of traumatic brain injury (TBI) patients, such as caspase-3; total antioxidant capacity; melatonin; S100B protein; glial fibrillary acidic protein (GFAP); glutamate; lactate; brain-derived neurotrophic factor (BDNF); substance P; neuron-specific enolase (NSE); ubiquitin carboxy-terminal hydrolase L-1 (UCH-L1); tau; decanoic acid; and octanoic acid.

Serum melatonin levels in survivor and non-survivor patients with traumatic brain injury

Background

Circulating levels of melatonin in patients with traumatic brain injury (TBI) have been determined in a little number of studies with small sample size (highest sample size of 37 patients) and only were reported the comparison of serum melatonin levels between TBI patients and healthy controls. As to we know, the possible association between circulating levels of melatonin levels and mortality of patients with TBI have not been explored; thus, the objective of our current study was to determine whether this association actually exists.

Methods

This multicenter study included 118 severe TBI (Glasgow Coma Scale <9) patients. We measured serum levels of melatonin, malondialdehyde (to assess lipid peroxidation) and total antioxidant capacity (TAC) at day 1 of severe TBI. We used mortality at 30 days as endpoint.

Results

We found that non-survivor (n = 33) compared to survivor (n = 85) TBI patients showed higher circulating levels of melatonin (p < 0.001), TAC (p < 0.001) and MDA (p < 0.001). We found that serum melatonin levels predicted 30-day mortality (Odds ratio = 1.334; 95% confidence interval = 1.094–1.627; p = 0.004), after to control for GCS, CT findings and age. We found a correlation between serum levels of melatonin levels and serum levels of TAC (rho = 0.37; p < 0.001) and serum levels of MDA (rho = 0.24; p = 0.008).

Conclusions

As to we know, our study is the largest series providing circulating melatonin levels in patients with severe TBI. The main findings were that non-survivors had higher serum melatonin levels than survivors, and the association between serum levels of melatonin levels and mortality, peroxidation state and antioxidant state.

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.

New Prognostic Biomarkers in Patients With Traumatic Brain Injury

CONTEXT

Traumatic brain injury (TBI) is a leading cause of death, disability, and resource consumption per year. There are two kinds of brain injury in TBI, primary and secondary injuries. Primary injury refers to the initial physical forces applied to the brain at the moment of impact. Secondary injury occurs over a period of hours or days following the initial trauma and results from the activation of different pathways such as inflammation, coagulation, oxidation, and apoptosis.

EVIDENCE ACQUISITION

This review focuses on new prognostic biomarkers of mortality in TBI patients related to inflammation, coagulation, oxidation, and apoptosis.

RESULTS

Recently circulating levels of substance P (SP), soluble CD40 ligand (sCD40L), tissue inhibitor of matrix metalloproteinases (TIMP)-1, malondialdehyde (MDA), and cytokeratin (CK)-18 fragmented have been found to be associated with mortality in TBI patients. Substance P is a neuropeptide of the tachykinin family, mainly synthesized in the central and peripheral nervous system, with proinflammatory effects when binding to their neurokinin-1 receptor (NK1R). Soluble CD40 ligand, a member of the tumor necrosis factor (TNF) family that is released into circulation from activated platelets, exhibit proinflamatory, and procoagulant properties on binding to their cell surface receptor CD40. Matrix metalloproteinases (MMPs) are a family of zinc-containing endoproteinases involved neuroinflammation and TIMP-1 is the inhibitor of some of them. Malondialdehyde is an end-product formed during lipid peroxidation due to degradation of cellular membrane phospholipids, that is released into extracellular space and finally into the blood. Cytokeratin -18 is cleaved by the action of caspases during apoptosis, and CK-18 fragmented is released into the blood.

CONCLUSIONS

Circulating levels of some biomarkers, such as SP, sCD40L, TIMP-1, MDA, and CK-18 fragmented, related to inflammation, coagulation, oxidation, and apoptosis have been recently associated with mortality in patients with TBI. These biomarkers could help in the prognostic classification of the patients and open new research lines in the treatment of patients with TBI.

Association between serum malondialdehyde levels and mortality in patients with severe brain trauma injury

There is a hyperoxidative state in patients with trauma brain injury (TBI). Malondialdehyde (MDA) is an end-product formed during oxidative stress, concretely lipid peroxidation. In small studies (highest sample size 50 patients), higher levels of MDA have been found in nonsurviving than surviving patients with TBI. An association between serum MDA levels and mortality in patients with TBI, however, has not been reported. Thus, the objective of this prospective, observational, multicenter study, performed in six Spanish intensive care units, was to determine whether MDA serum levels are associated with early mortality in a large series of patients with severe TBI. Serum MDA levels were measured in 100 patients with severe TBI on day 1 and in 75 healthy controls. The end-point of the study was 30-day mortality. We found higher serum MDA levels in patients with severe TBI than in healthy controls (p < 0.001). Nonsurviving patients with TBI (n = 27) showed higher serum MDA levels (p < 0.001) than survivors (n = 73). Logistic regression analysis showed that serum MDA levels were associated with 30-day mortality (odds ratio [OR] = 4.662; 95% confidence interval [CI] = 1.466-14.824; p = 0.01), controlling for Glasgow Coma Score, age, and computed tomography findings. Survival analysis showed that patients with serum MDA levels higher than 1.96 nmol/mL presented increased 30-day mortality than patients with lower levels (hazard ratio = 3.5; 95% CI = 1.43-8.47; p < 0.001). Thus, the most relevant new finding of our study, the largest to date on serum MDA levels in patients with severe TBI, was an association between serum MDA levels and early mortality.

Total antioxidant capacity is associated with mortality of patients with severe traumatic brain injury

Background

Previously, circulating total antioxidant capacity (TAC) in traumatic brain injury (TBI) patients has been scarcely studied and only in studies of small sample size (lower than 55 TBI patients). In one study were found higher serum TAC in non-survivor than in survivor TBI patients; however, an association between circulating TAC and mortality in patients with TBI has not been previously reported. Thus, the objective of this study was to determine whether there is an association between circulating TAC, peroxidation state and mortality in patients with severe TBI.

Methods

This was a multicenter, observational and prospective study was carried out in six Spanish Intensive Care Units. We included patients with severe TBI defined as Glasgow Coma Scale (GCS) lower than 9. We excluded patients with Injury Severity Score (ISS) in non-cranial aspects higher than 9. We measured serum TAC on day 1 of TBI. The 30-day mortality was established as endpoint.

Results

Non-surviving TBI patients (N = 27) showed higher serum TAC (P < 0.001) than survivor ones (N = 73). Logistic regression analyses showed that serum TAC higher than 2.59 nmol/mL were associated with 30-day mortality controlling for APACHE-II and CT classification (OR = 4.40; 95 % CI = 1.14–16.98; P = 0.03), controlling for GCS and age (OR = 5.88; 95 % CI = 1.57–22.06; P = 0.009), and controlling for CT classification and admission abnormal pupils (OR = 3.89; 95 % CI = 1.30–11.61; P = 0.02). There was an association between serum TAC and malondialdehyde (a biomarker of lipid peroxidation) levels (rho = 0.25; p = 0.01), APACHE-II score (rho = 0.23; p = 0.03) and GCS (rho = −0.21; p = 0.04).

Conclusions

To our knowledge, our series is the largest reporting data on circulating TAC in patients with severe TBI. The most relevant and new findings of our study were that there is an association between circulating TAC and peroxidation state and mortality in patients with severe TBI.

Traumatic Brain Injury Increases Cortical Glutamate Network Activity by Compromising GABAergic Control

Traumatic brain injury (TBI) is a major risk factor for developing pharmaco-resistant epilepsy. Although disruptions in brain circuitry are associated with TBI, the precise mechanisms by which brain injury leads to epileptiform network activity is unknown. Using controlled cortical impact (CCI) as a model of TBI, we examined how cortical excitability and glutamatergic signaling was altered following injury. We optically mapped cortical glutamate signaling using FRET-based glutamate biosensors, while simultaneously recording cortical field potentials in acute brain slices 2-4 weeks following CCI. Cortical electrical stimulation evoked polyphasic, epileptiform field potentials and disrupted the input-output relationship in deep layers of CCI-injured cortex. High-speed glutamate biosensor imaging showed that glutamate signaling was significantly increased in the injured cortex. Elevated glutamate responses correlated with epileptiform activity, were highest directly adjacent to the injury, and spread via deep cortical layers. Immunoreactivity for markers of GABAergic interneurons were significantly decreased throughout CCI cortex. Lastly, spontaneous inhibitory postsynaptic current frequency decreased and spontaneous excitatory postsynaptic current increased after CCI injury. Our results suggest that specific cortical neuronal microcircuits may initiate and facilitate the spread of epileptiform activity following TBI. Increased glutamatergic signaling due to loss of GABAergic control may provide a mechanism by which TBI can give rise to post-traumatic epilepsy.

Relationship between neurological outcome and early oxidative changes in erythrocytes in head injury patients

BACKGROUND

Experimental data indicate that destructive oxidative events reach their peak within the first 24 h after trauma in head injury (HI) and that brain damage occurring due to this impact can be the cause of death or irreversible permanent disabilities in affected patients.

METHODS

Venous blood samples were obtained from 50 HI patients within 24 h of trauma onset and from 30 age- and sex-matched normal controls (NC). Patients were divided into three different neurological outcome groups: those who died within 10 days of trauma (D), and those with severe neurological deficits (SD) or mild/no neurological deficits (MD) at 90 days after trauma. Early oxidative changes in erythrocytes were assessed by estimating an indicator of lipid peroxidative damage - thiobarbituric acid-reactive substances (TBARS) - and antioxidants [reduced glutathione (GSH) levels and superoxide dismutase (SOD) activity].

RESULTS

In the D group, erythrocyte TBARS levels were significantly higher compared to the NC, SD and MD groups (p<0.001); GSH levels were significantly lower compared to the NC (p<0.001) and MD (p<0.01) groups and SOD activity was significantly higher than in the NC (p<0.01) and MD (p<0.01) groups. In the SD group, TBARS levels were significantly higher than in the NC (p<0.001) and MD (p<0.05) groups; GSH levels were significantly lower than in the NC (p<0.001) and MD (p<0.01) groups and SOD activity was higher compared to the NC and MD (p<0.01) groups. In the MD group, TBARS levels were significantly higher and GSH levels significantly lower compared to the NC group (p<0.001). However, we did not observe any significant change in SOD activity compared to the NC group.

CONCLUSIONS

These findings indicate that early oxidative changes may reflect the severity of neurological insult and provide an early indication of patient outcome in traumatic HI.

Does edaravone (MCI- 186) act as an antioxidant and a neuroprotector in experimental traumatic brain injury?

Edaravone (MCI-186) is a novel synthetic free radical scavenger intended to have neuroprotective effect against ischemic insult. It is currently used on patients with cerebral infarction. Here, we note beneficial pharmaceutical effects of edaravone in rat experimental traumatic brain injury. Under specific experimental conditions, edaravone minimized traumatic brain injury by functioning as a synthetic antioxidant. Clinical trials testing the efficacy of edaravone are warranted.

Dietary omega-3 fatty acids normalize BDNF levels, reduce oxidative damage, and counteract learning disability after traumatic brain injury in rats

Omega-3 fatty acids (i.e., docosahexaenoic acid; DHA) regulate signal transduction and gene expression, and protect neurons from death. In this study we examined the capacity of dietary omega3 fatty acids supplementation to help the brain to cope with the effects of traumatic injury. Rats were fed a regular diet or an experimental diet supplemented with omega-3 fatty acids, for 4 weeks before a mild fluid percussion injury (FPI) was performed. FPI increased oxidative stress, and impaired learning ability in the Morris water maze. This type of lesion also reduced levels of brain-derived neurotrophic factor (BDNF), synapsin I, and cAMP responsive element-binding protein (CREB). It is known that BDNF facilitates synaptic transmission and learning ability by modulating synapsin I and CREB. Supplementation of omega-3 fatty acids in the diet counteracted all of the studied effects of FPI, that is, normalized levels of BDNF and associated synapsin I and CREB, reduced oxidative damage, and counteracted learning disability. The reduction of oxidative stress indicates a benevolent effect of this diet on mechanisms that maintain neuronal function and plasticity. These results imply that omega-3 enriched dietary supplements can provide protection against reduced plasticity and impaired learning ability after traumatic brain injury.

The effects of memantine on lipid peroxidation following closed-head trauma in rats

Memantine is an uncompetitive N-methyl-D: -aspartate (NMDA) receptor antagonist. Unlike other NMDA antagonists, it has been used clinically for years for the treatment of Parkinson's disease, spasticity, and dementia without serious side effects. We aimed to investigate the therapeutic efficacy of memantine on a closed head trauma model. A total of 132 adult male Sprague-Dawley rats were randomly divided into four groups: sham-operated, control (closed head trauma), sham-vehicle (closed head trauma + saline), treatment (closed head trauma + memantine, 10 mg/kg, i.p.). A cranial impact was delivered to the skull, just in front of the coronal suture, over the left hemisphere, from the height of 7 cm. Saline or memantine were applied 15 min after trauma. Rats were euthanased 0.5, 1, 2, 6, 24, 48 h after trauma. Brain tissue samples were taken 5 mm away from the left frontal pole and also from the corresponding point of the contralateral hemispheres. Malondialdehyde activity (MDA) was considered to reflect the degree of lipid peroxidation. The MDA levels continued to increase for the first 2 h after the injury, then started to decrease gradually. Memantine treatment significantly reduced lipid peroxidation levels in the treatment group compared with other groups (P<0.01). The findings of the present study indicate that memantine provides beneficial effects after closed head trauma in rats.

Lesional Expression of RhoA and RhoB following Traumatic Brain Injury in Humans

Inhibition of the small GTPase Rho or of its downstream target Rho-associated kinase (ROCK) has been shown to promote axon regeneration and to improve functional recovery following traumatic CNS lesions in the adult rat. In order to determine the expression pattern of RhoA and RhoB following human traumatic brain injury (TBI) and to assess whether Rho is a possible target for pharmacological intervention in humans, we investigated expression patterns of RhoA and RhoB in brain specimens from 25 patients who died after closed TBI in comparison to brain tissue derived from four neuropathologically unaffected control patients by immunohistochemistry. A highly significant lesional upregulation of both RhoA and RhoB was observed beginning several hours after the traumatic event and continuing for months after TBI. The cellular sources of both molecules included polymorphonuclear granulocytes, monocytes/macrophages, and reactive astrocytes. Additionally, expression of RhoA was also detected in neuronal cells in some of the cases. From our data, we conclude that inhibition of Rho is a promising mechanism for the development of new pharmacological interventions in human TBI. As the observed upregulation of RhoA and RhoB was still detectable months after TBI, we speculate that even delayed treatment with Rho inhibitors might be a therapeutic option.

Time Course Analysis of Hippocampal Nerve Growth Factor and Antioxidant Enzyme Activity following Lateral Controlled Cortical Impact Brain Injury in the Rat

Gradual secondary injury processes, including the release of toxic reactive oxygen species, are important components of the pathogenesis of traumatic brain injury (TBI). The extent of oxidative stress is determined in part by the effectiveness of the antioxidant response, involving the enzymes glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD). Since nerve growth factor (NGF) may be involved in the initiation of antioxidant activity, we employed a controlled cortical impact injury model in rats to produce secondary hippocampal damage and determined the subsequent time course of changes in NGF production and GPx, CAT, and SOD activity in this brain region. Hippocampal NGF production showed a rapid increase with a biphasic response after TBI. NGF protein was increased at 6 h, plateaued at 12 h, declined by 7 days, and exhibited a second rise at 14 days after injury. Similar to NGF, hippocampal GPx activity also showed a biphasic response, increasing by 12 h, declining at 24 h, and exhibiting a second peak at 7 days. In contrast, increased CAT activity occured steadily from 1 day through 7 days after injury. SOD activity was decreased at 6 h after injury, and continued to decline through 14 days. The initial rise in NGF preceded that of CAT, and coincided with an increase in GPX and a drop in SOD activity. These data demonstrate a complex temporal spectrum of antioxidant enzyme activation following secondary brain injury in the hippocampus, and suggest a selective regulatory role for NGF in this response.