Early Brain Edema is a Predictor of In-Hospital Mortality in Traumatic Brain Injury.

BACKGROUND: Identifying patients who may progress to a poor clinical outcome will encourage earlier appropriate therapeutic interventions. Brain edema may contribute to secondary injury in traumatic brain injury (TBI) and thus, may be a useful prognostic indicator. OBJECTIVE: We determined whether the presence of brain edema on the initial computed tomography (CT) scan of TBI patients would predict poor in-hospital outcome. METHODS: We performed a retrospective review of all trauma patients with nonpenetrating head trauma at a Level I Trauma Center. International Classification of Diseases, Ninth Revision codes indicated the presence of brain edema and we evaluated the validity of this pragmatic assessment quantitatively in a random subset of patients. In-hospital mortality was the primary outcome variable. Univariate analysis and logistic regression identified predictors of mortality in all TBI patients and those with mild TBI. RESULTS: Over 7200 patients were included in the study, including 6225 with mild TBI. Measurements of gray and white matter CT density verified radiological assessments of brain edema. Patients with documented brain edema had a mortality rate over 10 times that of the entire study population. With logistic regression accounting for Injury Severity Score, Glasgow Coma Scale score, other CT findings, and clinical variables, brain edema predicted an eightfold greater mortality rate in all patients (odds ratio 8.0, 95% confidence interval 4.6-14.0) and fivefold greater mortality rate for mild TBI patients (odds ratio 4.9, 95% confidence interval 2.0-11.7). CONCLUSIONS: Brain edema is an independent prognostic variable across all categories of TBI severity. By alerting emergency physicians to patients with poor predicted clinical outcomes, this finding will drive better resource allocation, earlier intervention, and reduced patient mortality.

Intranasal naloxone administration by police first responders is associated with decreased opioid overdose deaths.

OBJECTIVE: This study sought to answer the question, "Can police officers administer intranasal naloxone to drug overdose victims to decrease the opioid overdose death rate?" METHODS: This prospective interventional study was conducted in Lorain County, OH, from January 2011 to October 2014. Starting October 2013, trained police officers administered naloxone to suspected opioid overdose victims through a police officer naloxone prescription program (NPP). Those found by the county coroner to be positive for opioids at the time of death and those who received naloxone from police officers were included in this study. The rate of change in the total number of opioid-related deaths in Lorain County per quarter year, before and after initiation of the NPP, and the trend in the survival rate of overdose victims who were given naloxone were analyzed by linear regression. Significance was established a priori at P < .05. RESULTS: Data from 247 individuals were eligible for study inclusion. Opioid overdose deaths increased significantly before initiation of the police officer NPP with average deaths per quarter of 5.5 for 2011, 15.3 for 2012, and 16.3 for the first 9 months of 2013. After initiation of the police officer NPP, the number of opioid overdose deaths decreased each quarter with an overall average of 13.4. Of the 67 participants who received naloxone by police officers, 52 (77.6%) survived, and 8 (11.9%) were lost to follow-up. CONCLUSIONS: Intranasal naloxone administration by police first responders is associated with decreased deaths in opioid overdose victims.

Taurine release by astrocytes modulates osmosensitive glycine receptor tone and excitability in the adult supraoptic nucleus.

Cells can release the free amino acid taurine through volume-regulated anion channels (VRACs), and it has been hypothesized that taurine released from glial cells is capable of inhibiting action potential (AP) firing by activating neuronal glycine receptors (GlyRs) (Hussy et al., 1997). Although an inhibitory GlyR tone is widely observed in the brain, it remains unknown whether this specifically reflects gliotransmission because most neurons also express VRACs and other endogenous molecules can activate GlyRs. We found that VRACs are absent in neurons of the rat supraoptic nucleus (SON), suggesting that glial cells are the exclusive source of taurine in this nucleus. Application of strychnine to rat hypothalamic explants caused a depolarization of SON neurons associated with a decrease of chloride conductance and could excite these cells in the absence of fast synaptic transmission. This inhibitory GlyR tone was eliminated by pharmacological blockade of VRACs, by cellular taurine depletion, by metabolic inactivation of glia with fluorocitrate, and after retraction of astrocytic processes that intercalate neuronal somata and dendrites. Finally, GlyR tone varied inversely with extracellular fluid tonicity to mediate the osmotic control of AP firing by SON neurons. These findings establish taurine as a physiological gliotransmitter and show that gliotransmission is a spatially constrained process that can be modulated by the morphological rearrangement of astrocytes.

Glutamate receptor-mediated taurine release from the hippocampus during oxidative stress.

BACKGROUND: Hippocampal slices swell and release taurine during oxidative stress. The influence of cellular signalling pathways on this process is unclear. Glutamate signalling can facilitate volume regulation in other CNS preparations. Therefore, we hypothesize activation of taurine release by oxidative stress results from tissue swelling and is coupled to activation of glutamate receptors. METHODS: Rat hippocampi were incubated at room temperature for 2 hr in artificial cerebrospinal fluid (aCSF) equilibrated with 95% O2 plus 5% CO2. For some slices, 1 mM taurine was added to the aCSF to maintain normal tissue taurine content. Slices then were perfused with aCSF at 35 degrees C and baseline data recorded before 2 mM H2O2 was added. For some studies, mannitol or inhibitors of glutamate receptors or the volume-regulated anion channel (VRAC) were added before and during H2O2 treatment. The intensity of light transmitted through the slice (the intrinsic optical signal, IOS) was determined at 1-min intervals. Samples of perfusate were collected at 2-min intervals and amino acid contents determined by HPLC. Data were analyzed by repeated measures ANOVA and post hoc Dunnett's test with significance indicated for p<0.05. RESULTS: IOS of slices prepared without taurine treatment increased significantly by 3.3+/-1.3% (mean+/-SEM) during oxidative stress. Little taurine was detected in the perfusate of these slices and the rate of taurine efflux did not change during H2O2 exposure. The alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate antagonist, 25 microM CNQX, but not the N-methyl-D-aspartate (NMDA) receptor antagonist, 10 microM MK-801, inhibited the increase in IOS during H2O2 treatment. Taurine-treated slices exposed to H2O2 showed no change in IOS; however, taurine efflux increased by 335+/-178%. When these slices were perfused with hypertonic aCSF (350 mOsm) or exposed to the VRAC inhibitor, 20 microM DCPIB, no increase in the taurine efflux rate was observed during H2O2 exposure. Taurine-treated slices perfused with 10 microM MK-801 during H2O2 exposure showed a 4.6+/-1.9% increase in IOS but no increase in the taurine efflux rate. CONCLUSIONS: Taurine efflux via VRAC is critical for volume regulation of hippocampal slices exposed to oxidative stress. This increased taurine efflux does not result from direct activation of the taurine release pathway by H2O2. NMDA receptor activation plays an important role in taurine release during oxidative stress.

Ischemia-induced brain damage is enhanced in human renin and angiotensinogen double-transgenic mice.

To investigate the role of brain angiotensin II (ANG II) in the pathogenesis of injury following ischemic stroke, mice overexpressing renin and angiotensinogen (R+A+) and their wild-type control animals (R-A-) were used for experimental ischemia studies. Focal brain ischemia was induced by middle cerebral artery occlusion (MCAO). The severity of ischemic injury was determined by measuring neurological deficits and histological damage at 24 and 48 h after MCAO, respectively. To exclude the influence of blood pressure and local collateral blood flow, brain slices were used for oxygen and glucose deprivation (OGD) studies. The severity of OGD-induced damage was determined by measuring indicators of tissue swelling and cell death, the intensity of the intrinsic optical signal (IOS), and the number of propidium iodide (PI) staining cells, respectively. Results showed 1) R+A+ mice showed higher neurological deficit score (3.8 +/- 0.5 and 2.5 +/- 0.3 for R+A+ and R-A-, respectively, P < 0.01) and larger infarct volume (22.2 +/- 1.6% and 14.1 +/- 1.2% for R+A+ and R-A-, respectively, P < 0.01); 2) The R+A+ brain slices showed more severe tissue swelling and cell death in the cortex (IOS: 140 +/- 6% and 114 +/- 10%; PI: 139 +/- 20 cells/field and 39 +/- 9 cells/field for R+A+ and R-A-, respectively, P < 0.01); 3) treatment with losartan (20 micromol/l) abolished OGD-induced exaggeration of cell injury seen in R+A+ mice. The data indicate that activation of ANG II/AT(1) signaling is harmful to brain exposed to ischemia.

Antioxidant Enzyme-Mimetic Activity and Neuroprotective Effects of Cerium Oxide Nanoparticles Stabilized with Various Ratios of Citric Acid and EDTA.

Cerium oxide (CeO2) nanoparticles (CeNPs) are potent antioxidants that are being explored as potential therapies for diseases in which oxidative stress plays an important pathological role. However, both beneficial and toxic effects of CeNPs have been reported, and the method of synthesis as well as physico-chemical, biological, and environmental factors can impact the ultimate biological effects of CeNPs. In the present study, we explored the effect of different ratios of citric acid (CA) and EDTA (CA/EDTA), which are used as stabilizers during synthesis of CeNPs, on the antioxidant enzyme-mimetic and biological activity of the CeNPs. We separated the CeNPs into supernatant and pellet fractions and used commercially available enzymatic assays to measure the catalase-, superoxide dismutase (SOD)-, and oxidase-mimetic activity of each fraction. We tested the effects of these CeNPs in a mouse hippocampal brain slice model of ischemia to induce oxidative stress where the fluorescence indicator SYTOX green was used to assess cell death. Our results demonstrate that CeNPs stabilized with various ratios of CA/EDTA display different enzyme-mimetic activities. CeNPs with intermediate CA/EDTA stabilization ratios demonstrated greater neuroprotection in ischemic mouse brain slices, and the neuroprotective activity resides in the pellet fraction of the CeNPs. The neuroprotective effects of CeNPs stabilized with equal proportions of CA/EDTA (50/50) were also demonstrated in two other models of ischemia/reperfusion in mice and rats. Thus, CeNPs merit further development as a neuroprotective therapy for use in diseases associated with oxidative stress in the nervous system.

Trpv4 Mediates Hypotonic Inhibition of Central Osmosensory Neurons via Taurine Gliotransmission.

The maintenance of hydromineral homeostasis requires bidirectional detection of changes in extracellular fluid osmolality by primary osmosensory neurons (ONs) in the organum vasculosum laminae terminalis (OVLT). Hypertonicity excites ONs in part through the mechanical activation of a variant transient receptor potential vanilloid-1 channel (dn-Trpv1). However, the mechanism by which local hypotonicity inhibits ONs in the OVLT remains unknown. Here, we show that hypotonicity can reduce the basal activity of dn-Trpv1 channels and hyperpolarize acutely isolated ONs. Surprisingly, we found that mice lacking dn-Trpv1 maintain normal inhibitory responses to hypotonicity when tested in situ. In the intact setting, hypotonicity inhibits ONs through a non-cell-autonomous mechanism that involves glial release of the glycine receptor agonist taurine through hypotonicity activated anion channels (HAAC) that are activated subsequent to Ca2+ influx through Trpv4 channels. Our study clarifies how Trpv4 channels contribute to the inhibition of OVLT ONs during hypotonicity in situ.

Physiologic effects of simulated + Gx orbital reentry in primate models of hemorrhagic shock.

INTRODUCTION: While the physiologic effects of space travel are documented in healthy individuals, little is known about its impact on medically ill or injured persons. In this study, hemorrhagic shock in primates was used to model a potentially common pathophysiologic condition during exposure to gravitational forces simulating return from Earth orbit. This experiment did not model the effects of cardiovascular deconditioning that normally occur during spaceflight. METHODS: Using invasive hemodynamic monitoring, serial cardiovascular and laboratory parameters in baboons (Papio papio) were studied. Subjects were centrifuged at either a low +Gx (3.3 G maximum) or high +Gx (7.8 G maximum) acceleration reentry profile before and after being subjected to either class II (20% volume loss) or class IV (40% volume loss) hemorrhagic shock. RESULTS: Significant alterations in cardiovascular and laboratory parameters occurred during shock and exposure to high and low +Gx acceleration. Shock classification was the primary determinant of change in cardiovascular function. During the experimental protocol, 31 of 32 animals survived (97% survival). After a 1-wk post-protocol observation period, 28 of 32 subjects survived (88% survival). CONCLUSIONS: This preliminary study presents data that suggest that the emergent return of a medically compromised individual without resuscitation may be potentially survivable. However, medical stabilization with volume resuscitation, supplemental oxygen, and noninvasive monitoring would likely optimize clinical outcomes in the event of significant hemorrhagic shock states necessitating emergent deorbit.

Calcium/calmodulin-modulated chloride and taurine conductances in cultured rat astrocytes.

Osmotically swollen rat cerebral astrocytes develop an increased anion conductance which can mediate chloride and taurine release. We used whole cell patch clamp to study mechanisms that modulate this conductance. Astrocyte chloride conductance increased within 4 min of exposure to 200 mOsm medium and was 670+/-123% of its initial value after 15 min (mean+/-S.E.M.). This conductance was substantially reduced in 0.1 mM extracellular calcium with 20 mM BAPTA added to the electrode solution and was completely inhibited with calcium-free perfusion solution containing 1 mM EDTA (n=4). The conductance increase in 200 mOsm medium also was inhibited in a dose-dependent manner by nimodipine with a calculated K(i) of 0.31+/-0.4 microM and mean+/-S.E.M. inhibition of 84.4+/-4% at 100 microM nimodipine. In the presence of 100 microM W-7, a calmodulin antagonist, the mean+/-S.E.M. conductance increase after 15 min was 223+/-40% of the initial value while 300 microM W-7 or 100 microM trifluoperazine inhibited the conductance increase completely (n=6). With taurine as the major anion in electrode and perfusion solutions, a significant conductance increase was observed in 200 mOsm medium. This conductance increase was inhibited by 300 microM W-7 or 100 microM nimodipine. We conclude extracellular calcium influx via L-type calcium channels leads to increased astrocyte anion conductance in 200 mOsm conditions via calmodulin-dependent activation of anion channels. Efflux of anionic taurine from swollen astrocytes also may be affected by calcium influx through a similar calcium/calmodulin-dependent process.

Altitude decompression sickness symptom resolution during descent to ground level.

INTRODUCTION: Altitude decompression sickness (DCS) is a health risk associated with the conduct of high altitude airdrop operations, high altitude reconnaissance, future fighter operations, hypobaric chamber training, unpressurized flight, and extravehicular activity (EVA) in space. The treatment for DCS includes the provision of 100% oxygen (O2) at ground level (GLO) and/or hyperbaric oxygen therapy (HBO). In this paper we examine the effect of repressurization to ground level from hypobaric conditions on DCS symptoms. Timely recompression (descent at first recognition of any DCS symptom) may be a safe, effective treatment for the large majority of DCS symptoms. METHODS: Data from altitude chamber exposures recorded in the Air Force Research Laboratory (AFRL) Altitude DCS Database were reviewed to determine the level of recompression required for complete resolution of 1,699 observed symptoms. RESULTS: Of the 1,699 DCS symptoms reviewed, 66 (3.9%) resolved at altitude, 117 (6.9%) resolved at ground level, and 1,433 (84.3%) resolved during descent. Increasing the pressure by 138 mmHg from the altitude of exposure where symptoms occurred resolved roughly 50% of symptoms. Little resolution of symptoms was noted with recompressions of < 50 mmHg. The greatest rate of symptom resolution occurred with recompressions of 50-250 mmHg. CONCLUSION: These findings support the concept that descent and postflight, ground-level oxygen may be sufficient to relieve the majority of altitude DCS symptoms. HBO may be reserved for serious, recurring, delayed, or refractory symptoms. The findings also suggest a need for further study of DCS symptom resolution.

Angiotensin converting enzyme 2/Ang-(1-7)/mas axis protects brain from ischemic injury with a tendency of age-dependence.

BACKGROUND: The angiotensin (Ang) converting enzyme 2 (ACE2)/Ang-(1-7)/Mas receptor pathway is an important component of the renin-angiotensin system and has been suggested to exert beneficial effects in ischemic stroke. AIMS: This study explored whether the ACE2/Ang-(1-7)/Mas pathway has a protective effect on cerebral ischemic injury and whether this effect is affected by age. METHODS: We used three-month and eight-month transgenic mice with neural over-expression of ACE2 (SA) and their age-matched nontransgenic (NT) controls. Neurological deficits and ischemic stroke volume were determined following middle cerebral artery occlusion (MCAO). In oxygen and glucose deprivation (OGD) experiments on brain slices, the effects of the Mas receptor agonist (Ang1-7) or antagonist (A779) on tissue swelling, Nox2/Nox4 expression reactive oxygen species (ROS) production and cell death were measured. RESULTS: (1) Middle cerebral artery occlusion -induced ischemic injury and neurological deficit were reduced in SA mice, especially in eight-month animals; (2) OGD-induced tissue swelling and cell death were decreased in SA mice with a greater reduction seen in eight-month mice; (3) Ang-(1-7) and A779 had opposite effects on OGD-induced responses, which correlated with changes in Nox2/Nox4 expression and ROS production. CONCLUSIONS: Angiotensin converting enzyme 2/Ang-(1-7)/Mas axis protects brain from ischemic injury via the Nox/ROS signaling pathway, with a greater effect in older animals.

Purinergic activation of anion conductance and osmolyte efflux in cultured rat hippocampal neurons.

The majority of mammalian cells demonstrate regulatory volume decrease (RVD) following swelling caused by hyposmotic exposure. A critical signal initiating RVD is activation of nucleotide receptors by ATP. Elevated extracellular ATP in response to cytotoxic cell swelling during pathological conditions also may initiate loss of taurine and other intracellular osmolytes via anion channels. This study characterizes neuronal ATP-activated anion current and explores its role in net loss of amino acid osmolytes. To isolate anion currents, we used CsCl as the major electrolyte in patch electrode and bath solutions and blocked residual cation currents with NiCl(2) and tetraethylammonium. Anion currents were activated by extracellular ATP with a K(m) of 70 microM and increased over fourfold during several minutes of ATP exposure, reaching a maximum after 9.0 min (SD 4.2). The currents were blocked by inhibitors of nucleotide receptors and volume-regulated anion channels (VRAC). Currents showed outward rectification and inactivation at highly depolarizing membrane potentials, characteristics of swelling-activated anion currents. P2X agonists failed to activate the anion current, and an inhibitor of P2X receptors did not block the effect of ATP. Furthermore, current activation was observed with extracellular ADP and 2-(methylthio)adenosine 5'-diphosphate, a P2Y(1) receptor-specific agonist. Much less current activation was observed with extracellular UTP, suggesting the response is mediated predominantly by P2Y(1) receptors. ATP caused a dose-dependent loss of taurine and alanine that could be blocked by inhibitors of VRAC. ATP did not inhibit the taurine uptake transporter. Thus extracellular ATP triggers a loss of intracellular organic osmolytes via activation of anion channels. This mechanism may facilitate neuronal volume homeostasis during cytotoxic edema.