Shaun E. Gruenbaum

The neuroprotective effects of oxaloacetate in closed head injury in rats is mediated by its blood glutamate scavenging activity: evidence from the use of maleate.

Introduction Treatment with oxaloacetate after traumatic brain injury has been shown to decrease blood glutamate levels and protect against the neurotoxic effects of glutamate on the brain. A number of potential mechanisms have been suggested to explain oxaloacetate-induced neuroprotection. We hypothesize that the primary mechanism by which intravenous oxaloacetate provides neuroprotection is by activation of the blood glutamate-scavenging enzyme glutamate-oxaloacetate transaminase, increasing thereby the driving force for the efflux of excess glutamate from brain interstitial fluids into blood. If so, coadministration of maleate, a glutamate-oxaloacetate transaminase-blocker is expected to prevent the neuroprotective effects of oxaloacetate. Materials and Methods A neurological severity score (NSS) was measured 1 hour after closed head injury (CHI) in rats. Then, rats received 30 μL/min/100 g infusion of saline, or 1 mmol/100 g solution of oxaloacetate, maleate, or a mixture of oxaloacetate and maleate. NSS was reassessed at 24 and 48 hour after CHI. Blood glutamate and glucose levels were measured at 0, 60, 90, and 120 minutes. Results NSS improved significantly at 24 hour (P<0.001) and 48 hour (P<0.001) only in the rats treated with oxaloacetate. Blood glutamate decreased significantly in the oxaloacetate-treated group at 90 minute (at the conclusion of oxaloacetate administration) (P<0.00001), but not in the control, maleate or oxaloacetate+maleate groups. A strong correlation r2=0.86 was found to exist between the percent decrease in blood glutamate levels and percent improvement in NSS. Discussion The results of this study demonstrate that the primary mechanism by which oxaloacetate provides neuroprotective activity after CHI is related to its blood glutamate scavenging activity. Management of blood glutamate concentration may have important implications in the treatment of acute brain conditions, including CHI and stroke.

Effect of Glutamate and Blood Glutamate Scavengers Oxaloacetate and Pyruvate on Neurological Outcome and Pathohistology of the Hippocampus after Traumatic Brain Injury in Rats

Background: Decreasing blood glutamate concentrations after traumatic brain injury accelerates brain-to-blood glutamate efflux, leading to improved neurologic outcomes. The authors hypothesize that treatment with blood glutamate scavengers should reduce neuronal cell loss, whereas administration of glutamate should worsen outcomes. The authors performed histologic studies of neuronal survival in the rat hippocampus after traumatic brain injury and treatment with blood glutamate scavengers. Methods: Traumatic brain injury was induced on anesthetized male Sprague-Dawley rats by a standardized weight drop. Intravenous treatment groups included saline (control), oxaloacetate, pyruvate, and glutamate. Neurologic outcome was assessed using a Neurological Severity Score at 1 h, and 1, 2, 7, 14, 21, 28 days. Blood glutamate was determined at baseline and 90 min. Four weeks after traumatic brain injury, a histologic analysis of surviving neurons was performed. Results: Oxaloacetate and pyruvate treatment groups demonstrated increased neuronal survival (oxaloacetate 2,200 ± 37, pyruvate 2,108 ± 137 vs. control 1,978 ± 46, P < 0.001, mean ± SD). Glutamate treatment revealed decreased neuronal survival (1,715 ± 48, P < 0.001). Treatment groups demonstrated favorable neurologic outcomes at 24 and 48 h (Neurological Severity Score at 24 and 48 h: 5.5 (1–8.25), 5 (1.75–7.25), P = 0.02 and 3(1–6.5), 4 (1.75–4.5), P = 0.027, median ± corresponding interquartile range). Blood glutamate concentrations were decreased in the oxaloacetate and pyruvate treatment groups. Administration of oxaloacetate and pyruvate was not shown to have any adverse effects. Conclusions: The authors demonstrate that the blood glutamate scavengers oxaloacetate and pyruvate provide neuroprotection after traumatic brain injury, expressed both by reduced neuronal loss in the hippocampus and improved neurologic outcomes. The findings of this study may bring about new therapeutic possibilities in a variety of clinical settings.

Pyruvate’s blood glutamate scavenging activity contributes to the spectrum of its neuroprotective mechanisms in a rat model of stroke

In previous studies, we have shown that by increasing the brain‐to‐blood glutamate efflux upon scavenging blood glutamate with either oxaloacetate or pyruvate, one achieves highly significant neuroprotection particularly in the context of traumatic brain injury. The current study examines, for the first time, how the blood glutamate scavenging properties of glutamate–pyruvate transaminase (GPT), alone or in combination with pyruvate, may contribute to the spectrum of its neuroprotective mechanisms and improve the outcome of rats exposed to brain ischemia, as they do after head trauma. Rats that were exposed to permanent middle cerebral artery occlusion (MCAO) and treated with intravenous 250 mg/kg pyruvate had a smaller volume of infarction and reduced brain edema, resulting in an improved neurological outcome and reduced mortality compared to control rats treated with saline. Intravenous pyruvate at the low dose of 31.3 mg/kg did not demonstrate any neuroprotection. However, when combined with 0.6 mg/kg of GPT there was a similar neuroprotection observed as seen with pyruvate at 250 mg/kg. Animals treated with 1.69 g/kg glutamate had a worse neurological outcome and a larger extent of brain edema. The decrease in mortality, infarcted brain volume and edema, as well as the improved neurological outcome following MCAO, was correlated with a decrease in blood glutamate levels. We therefore suggest that the blood glutamate scavenging activity of GPT and pyruvate contributes to the spectrum of their neuroprotective mechanisms and may serve as a new neuroprotective strategy for the treatment of ischemic stroke.

Brain to blood glutamate scavenging as a novel therapeutic modality: a review

Abstract It is well known that abnormally elevated glutamate levels in the brain are associated with secondary brain injury following acute and chronic brain insults. As such, a tight regulation of brain glutamate concentrations is of utmost importance in preventing the neurodegenerative effects of excess glutamate. There has been much effort in recent years to better understand the mechanisms by which glutamate is reduced in the brain to non-toxic concentrations, and in how to safely accelerate these mechanisms. Blood glutamate scavengers such as oxaloacetate, pyruvate, glutamate–oxaloacetate transaminase, and glutamate-pyruvate transaminase have been shown to reduce blood glutamate concentrations, thereby increasing the driving force of the brain to blood glutamate efflux and subsequently reducing brain glutamate levels. In the past decade, blood glutamate scavengers have gained increasing international interest, and its uses have been applied to a wide range of experimental contexts in animal models of traumatic brain injury, ischemic stroke, subarachnoid hemorrhage, epilepsy, migraine, and malignant gliomas. Although glutamate scavengers have not yet been used in humans, there is increasing evidence that their use may provide effective and exciting new therapeutic modalities. Here, we review the laboratory evidence for the use of blood glutamate scavengers. Other experimental neuroprotective treatments thought to scavenge blood glutamate, including estrogen and progesterone, beta-adrenergic activation, hypothermia, insulin and glucagon, and hemodialysis and peritoneal dialysis are also discussed. The evidence reviewed here will hopefully pave the way for future clinical trials.

Neuroprotection by Estrogen and Progesterone in Traumatic Brain Injury and Spinal Cord Injury

In recent years there has been a growing body of clinical and laboratory evidence demonstrating the neuroprotective effects of estrogen and progesterone after traumatic brain injury (TBI) and spinal cord injury (SCI). In humans, women have been shown to have a lower incidence of morbidity and mortality after TBI compared with age-matched men. Similarly, numerous laboratory studies have demonstrated that estrogen and progesterone administration is associated with a mortality reduction, improvement in neurological outcomes, and a reduction in neuronal apoptosis after TBI and SCI. Here, we review the evidence that supports hormone-related neuroprotection and discuss possible underlying mechanisms. Estrogen and progesterone-mediated neuroprotection are thought to be related to their effects on hormone receptors, signaling systems, direct antioxidant effects, effects on astrocytes and microglia, modulation of the inflammatory response, effects on cerebral blood flow and metabolism, and effects on mediating glutamate excitotoxicity. Future laboratory research is needed to better determine the mechanisms underlying the hormones’ neuroprotective effects, which will allow for more clinical studies. Furthermore, large randomized clinical control trials are needed to better assess their role in human neurodegenerative conditions.

Pharmacologic Neuroprotection for Functional Outcomes After Traumatic Brain Injury: A Systematic Review of the Clinical Literature

IntroductionTraumatic brain injury (TBI) is a major cause of death and disability worldwide. The deleterious effects of secondary brain injury may be attenuated by early pharmacological therapy in the emergency room and intensive care unit (ICU). Current medical management of acute TBI is primarily supportive, aimed at reducing intracranial pressure (ICP) and optimizing cerebral perfusion. There are no pharmacological therapies to date that have been unequivocally demonstrated to improve neurological outcomes after TBI.ObjectivesThe purpose of this systematic review was to evaluate the recent clinical studies from January 2013 through November 2015 that investigated neuroprotective functional outcomes of pharmacological agents after TBI.MethodsThe following databases were searched for relevant studies: MEDLINE (OvidSP January Week 1, 2013–November Week 2 2015), Embase (OvidSP 2013 January 1–2015 November 24), and the unindexed material in PubMed (National Library of Medicine/National Institutes of Health [NLM/NIH]). This systematic review included only full-length clinical studies and case series that included at least five patients and were published in the English language. Only studies that examined functional clinical outcomes were included.ResultsTwenty-five of 527 studies met our inclusion criteria, which investigated 15 independent pharmacological therapies. Eight of these therapies demonstrated possible neuroprotective properties and improved functional outcomes, of which five were investigated with randomized clinical trials: statins, N-acetyl cysteine (NAC), Enzogenol, Cerebrolysin, and nitric oxide synthase inhibitor (VAS203). Three pharmacological agents did not demonstrate neuroprotective effects, and four agents had mixed results.ConclusionsWhile there is currently no single pharmacological therapy that will unequivocally improve clinical outcomes after TBI, several agents have demonstrated promising clinical benefits for specific TBI patients and should be investigated further.

The effects of peritoneal dialysis on blood glutamate levels: implementation for neuroprotection.

Background: Previous study has demonstrated the efficacy of hemodialysis in reducing blood glutamate levels. The purpose of the present study is to investigate whether peritoneal dialysis (PD) may be effective in lowering blood glutamate levels, which may serve as a potential tool for improving neurological function after brain injury. Methods: Two liters of dialysis solution were infused over 10 minutes into 18 patients with stage V chronic kidney disease. Blood samples were collected immediately before initiation of PD, and hourly for a total of 5 blood samples. Blood samples were sent for determination of glutamate, creatinine, urea, glucose, glutamate oxaloacetate transaminase, and glutamate pyruvate transaminase. PD samples were collected and analyzed for glutamate, creatinine, urea, and glucose at the same time points as the blood samples. Results: Blood glutamate concentrations were significantly reduced by 60 minutes after the infusion of dialysis solution (P<0.0001), whereas levels of glutamate in the dialysis solution were increased significantly by 60 minutes (P<0.0001). Conclusions: We demonstrated that PD is an effective modality in reducing blood glutamate concentrations. This method may be potentially utilized for the treatment of acute and chronic brain disorders that are accompanied by elevated glutamate in the brain’s extracellular fluid. Considering the rapid saturation of the PD solution with glutamate, we recommend frequent dwelling of the PD solution in order to maintain low concentrations of blood glutamate.

Establishment of an animal model of depression contagion.

BACKGROUND Depression is a common and important cause of morbidity, and results in a significant economic burden. Recent human studies have demonstrated that that depression is contagious, and depression in family and friends might cumulatively increase the likelihood that a person will exhibit depressive behaviors. The mechanisms underlying contagion depression are poorly understood, and there are currently no animal models for this condition. METHODS Rats were divided into 3 groups: depression group, contagion group, and control group. After induction of depression by 5 weeks of chronic unpredictable stress, rats from the contagion group were housed with the depressed rats (1 naïve rat with 2 depressed rats) for 5 weeks. Rats were then subjected to sucrose preference, open field, and forced swim tests. RESULTS The sucrose preference was significantly reduced in the depressed rats (p<0.01) and contagion depression rats (p<0.01). Climbing time during forced swim test was reduced in the depression and contagion depression groups (p<0.001), whereas immobility time was significantly prolonged in only the depression group (p<0.001). Rats in both the depression (p<0.05) and depression contagion group (p<0.005) had decreased total travel distance and decreased mean velocity in the open field test, whereas the time spent in the central part was significantly shorter in only the depression group (p<0.001). CONCLUSIONS In this study, for the first time we demonstrated depression contagion in an animal model. A reliable animal model may help better understand the underlying mechanisms of contagion depression, and may allow for future investigations of the studying therapeutic modalities.

β2 adrenergic-mediated reduction of blood glutamate levels and improved neurological outcome after traumatic brain injury in rats.

Background: Isoflurane-anesthetized rats subjected to traumatic brain injury (TBI) show a transient reduction in blood L-glutamate levels. Having previously observed that isoproterenol produces a sustained decrease in blood glutamate levels in naive rats, we investigated the possible effects of nonselective and selective &bgr;1 and &bgr;2 adrenergic agonists and antagonists both on blood glutamate levels and on the neurological outcomes of rats subjected to TBI. Methods: Rats received either 10 mL/kg of isotonic saline 1 hour after TBI, 50 µg/kg of isoproterenol pretreatment 30 minutes before TBI, 10 mg/kg of propranolol pretreatment 60 minutes before TBI, 10 mg/kg of metoprolol pretreatment 60 minutes before TBI, or 10 mg/kg of butaxamine pretreatment 40 minutes before TBI and 10 minutes before pretreatment with 50 µg/kg isoproterenol or 10 mg/kg of propranolol 60 minutes after TBI. A neurological severity score (NSS) was measured at 1, 24, and 48 hours after TBI. Blood glutamate, blood glucose, mean arterial blood pressure, and heart rate were measured at the time of drug injection, at the time of TBI, 60 minutes after TBI, and 90 minutes after TBI. Results: Blood glutamate levels decreased spontaneously by 60 minutes after TBI in the control group (P<0.05), reverting to baseline levels by 90 minutes after TBI. A pretreatment with either 10 mg/kg of metoprolol 60 minutes before TBI or with 50 µg/kg of isoproterenol 30 minutes before TBI also reduced blood glutamate levels (P<0.05) both at 90 minutes after TBI and improved the NSS measured 24 and 48 hours after TBI in comparison with the control saline-treated group. However, a 10-mg/kg butoxamine pretreatment 40 minutes before TBI and 10 minutes before pretreatment with 50 µg/kg of isoproterenol or 10 mg/kg of propranolol 60 minutes before TBI neither affected blood glutamate levels across time after TBI nor caused any significant change in the NSS measured 24 and 48 hours after TBI in comparison with the control saline-treated group. A strong correlation (r2=0.73) was demonstrated between the percent decrease in blood glutamate levels at 90 minutes after TBI and the percent improvement of NSS measured 24 hours after TBI. Conclusions: The results suggest that the transient blood glutamate reduction seen after TBI is the result of a stress response and of the activation of the sympathetic nervous system through the &bgr;2 adrenergic receptors, causing an increase of the brain-to-blood efflux of glutamate observed with excess brain glutamate levels after a brain insult. This strongly correlates with the neurological improvement observed 24 hours after TBI.

Extracorporeal methods of blood glutamate scavenging: a novel therapeutic modality

Pathologically elevated glutamate concentrations in the brain’s extracellular fluid are associated with several acute and chronic brain insults. Studies have demonstrated that by decreasing the concentration of glutamate in the blood, thereby increasing the concentration gradient between the brain and the blood, the rate of brain-to-blood glutamate efflux can be increased. Blood glutamate scavengers, pyruvate and oxaloacetate have shown great promise in providing neuroprotection in many animal models of acute brain insults. However, glutamate scavengers’ potential systemic toxicity, side effects and pharmacokinetic properties may limit their use in clinical practice. In contrast, extracorporeal methods of blood glutamate reduction, in which glutamate is filtered from the blood and eliminated, may be an advantageous adjunct in treating acute brain insults. Here, we review the current evidence for the glutamate-lowering effects of hemodialysis, peritoneal dialysis and hemofiltration. The evidence reviewed here highlights the need for clinical trials.