3-nitrotyrosine and Brain-Injuries--Traumatic

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality among military service members and civilians in the United States. Despite significant advances in the understanding of TBI pathophysiology, several clinical reports indicate that multiple genetic and epigenetic factors can influence outcome. Homocysteine (HCY) is a non-proteinogenic amino acid, the catabolism of which can be dysregulated by stress, lifestyle, aging, or genetic abnormalities leading to hyperhomocysteinemia (HHCY). HHCY is a neurotoxic condition and a risk factor for multiple neurological and cardiovascular disorders that occurs when HCY levels is clinically > 15 µM. Although the deleterious impact of HHCY has been studied in human and animal models of neurological disorders such as stroke, Alzheimer's disease and Parkinson's disease, it has not been addressed in TBI models. This study tested the hypothesis that HHCY has detrimental effects on TBI pathophysiology. Moderate HHCY was induced in adult male Sprague Dawley rats via daily administration of methionine followed by impact-induced traumatic brain injury. In this model, HHCY increased oxidative stress, upregulated expression of proteins that promote blood coagulation, exacerbated TBI-associated blood-brain barrier dysfunction and promoted the infiltration of inflammatory cells into the cortex. We also observed an increase of brain injury-induced lesion size and aggravated anxiety-like behavior. These findings show that moderate HHCY exacerbates TBI outcomes and suggest that HCY catabolic dysregulation may be a significant biological variable that could contribute to TBI pathophysiology heterogeneity.

Topics: Animals; Anxiety; Behavior, Animal; Blood Coagulation; Blood-Brain Barrier; Brain Injuries, Traumatic; Cerebral Cortex; Homocysteine; Hyperhomocysteinemia; Inflammation; Intercellular Adhesion Molecule-1; Male; Methionine; Occludin; Oxidative Stress; Rats, Sprague-Dawley; Tyrosine; Zonula Occludens-1 Protein

Traumatic brain injury (TBI) contributes to one third of injury related deaths in the US. Treatment strategies for TBI are supportive, and the pathophysiology is not fully understood. Secondary mechanisms of injury in TBI, such as oxidative stress and inflammation, are points at which intervention may reduce neuropathology. Evidence suggests that reactive oxygen species (ROS) propagate blood-brain barrier (BBB) hyperpermeability and inflammation following TBI. We hypothesized that targeted detoxification of ROS may improve the pathological outcomes of TBI. Following TBI, endothelial activation results in a time dependent increase in vascular expression of ICAM-1. We conjugated catalase to anti-ICAM-1 antibodies and administered the conjugate to 8 wk old C57BL/6J mice 30 min after moderate controlled cortical impact injury. Results indicate that catalase targeted to ICAM-1 reduces markers of oxidative stress, preserves BBB permeability, and attenuates neuropathological indices more effectively than non-targeted catalase and anti-ICAM-1 antibody alone. Furthermore, the study of microglia by two-photon microscopy revealed that anti-ICAM-1/catalase prevents the transition of microglia to an activated phenotype. These findings demonstrate the use of a targeted antioxidant enzyme to interfere with oxidative stress mechanisms in TBI and provide a proof-of-concept approach to improve acute TBI management that may also be applicable to other neuroinflammatory conditions.

Topics: Animals; Blood-Brain Barrier; Brain Injuries, Traumatic; Catalase; Endothelial Cells; Hydrogen Peroxide; Intercellular Adhesion Molecule-1; Mice; Microglia; Neuroglia; Oxidative Stress; Protective Agents; Reactive Oxygen Species; Tyrosine

Gastrointestinal dysfunction is one of several physiologic complications in patients with traumatic brain injury (TBI). TBI can result in increased intestinal permeability resulting from apoptosis of intestinal epithelial cells, which contain a large number of mitochondria for persisting barrier function. Autophagy of damaged mitochondria (mitophagy) controls the quality of the mitochondria and regulates cellular homeostasis. However, the exact mechanism of mitophagy that underlies the pathological changes induced by TBI is unknown. Here, we report that mitophagy decreases the intestinal epithelial cell damage and apoptosis that are activated in a rat model of controlled cortical impact (CCI). CCI-induced mitophagy is associated with an increase in 3-nitrotyrosine and 4-hydroxynonenal, indicating that oxidative stress may increase in response to mitochondrial disturbance. CCI also results in the expression of the tight junction proteins zonula occludens-1 (ZO-1) and occludin, which may regulate the in vivo intestinal hyperpermeability induced by CCI. Additionally, CCI-induced mitophagy was shown to be mediated by the oxidative stress-related extracellular signal-regulated kinase (ERK)/nuclear factor-erythroid2-like2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway, which may serve to reduce the apoptosis induced by oxidative stress. These results suggest that CCI-induced mitophagy serves to diminish apoptosis-mediated intestinal epithelial cell damage and to improve intestinal permeability, via ERK/Nrf2/HO-1 signaling. These findings may be useful in the design of rational approaches for the prevention and treatment of symptoms associated with TBI.

Topics: Aldehydes; Animals; Brain Injuries, Traumatic; Epithelial Cells; Extracellular Signal-Regulated MAP Kinases; Heme Oxygenase-1; Intestinal Mucosa; Male; Mitophagy; NF-E2-Related Factor 2; Oxidative Stress; Rats; Rats, Sprague-Dawley; Signal Transduction; Tyrosine

Injury severity in blast induced Traumatic Brain Injury (bTBI) increases with blast overpressure (BOP) and impulse in dose-dependent manner. Pure primary blast waves were simulated in compressed gas shock-tubes in discrete increments. Present work demonstrates 24 hour survival of rats in 0-450 kPa (0-800 Pa∙s impulse) range at 10 discrete levels (60, 100, 130, 160, 190, 230, 250, 290, 350 and 420 kPa) and determines the mortality rate as a non-linear function of BOP. Using logistic regression model, predicted mortality rate (PMR) function was calculated, and used to establish TBI severities. We determined a BOP of 145 kPa as upper mild TBI threshold (5% PMR). Also we determined 146-220 kPa and 221-290 kPa levels as moderate and severe TBI based on 35%, and 70% PMR, respectively, while BOP above 290 kPa is lethal. Since there are no standards for animal bTBI injury severity, these thresholds need further refinements using histopathology, immunohistochemistry and behavior. Further, we specifically investigated mild TBI range (0-145 kPa) using physiological (heart rate), pathological (lung injury), immuno-histochemical (oxidative/nitrosative and blood-brain barrier markers) as well as blood borne biomarkers. With these additional data, we conclude that mild bTBI occurs in rats when the BOP is in the range of 85-145 kPa.

Topics: Aldehydes; Animals; Blast Injuries; Blood-Brain Barrier; Bradycardia; Brain; Brain Injuries, Traumatic; Explosions; Lung Injury; Male; Microvessels; NADPH Oxidases; Nitric Oxide Synthase Type II; Nitrosative Stress; Rats, Sprague-Dawley; Tyrosine