Scavenging of blood glutamate for enhancing brain-to-blood glutamate efflux

Low serum alanine aminotransferase (ALT) levels are associated with poor outcomes in acute ischemic stroke patients regardless of age

Studies have indicated that reduced serum ALT levels are commonly linked to aging and are known to predict poor outcomes in many clinical conditions as potential frailty indicators. There are close connections between the brain and peripheral organs, particularly the liver. In patients with acute ischemic stroke (AIS), the interactive effects may change ALT levels, which in turn influence stroke outcomes. Whether ALT has potential neuroprotective effects or is an indicator of frailty in AIS patients remains unknown. This retrospective analysis examined 572 AIS patients in Beijing Luhe Hospital between August 2020 and June 2021. Patient demographics and laboratory results were assembled. The National Institutes of Health Stroke Scale (NIHSS) was used to analyze stroke severity. Modified Rankin Score (mRS) determined stroke outcome 3 months after AIS, with mRS≤2 indicating a favorable outcome. Based on serum ALT measurements, patients were classified into three tertiles (T1-T3). Binary logistic regression analysis evaluated the correlation between ALT tertiles and AIS outcomes. Of the patients, 66 exhibited unfavorable outcomes. The median ALT level in this group was 13 (IQR: 11-18.25), which was lower than in the favorable outcomes cohort (16; IQR: 11-22). A decline in ALT corresponded with a higher incidence of poor outcomes at 3 months (T1, 15.5 %; T2, 11.4 %; T3, 7.0 %; p = 0.03). The lowest ALT tertile (T1) was independently linked to an adverse 3-month outcome (OR 2.50 95 %CI 1.24-5.07, p = 0.038) compared to the highest tertile. ALT levels demonstrated no correlation with age (T1, 62.59 ± 12.64; T2, 64.01 ± 11.47; T3, 65.12 ± 11.27; p > 0.05). Regardless of age, lower serum ALT levels are independently associated with poorer outcomes in AIS patients. This finding suggests the potential pivotal part of the liver in AIS outcomes, highlighting the need to consider both neurological and liver functions post-stroke.

Glutamate Neurotoxicity and Destruction of the Blood–Brain Barrier: Key Pathways for the Development of Neuropsychiatric Consequences of TBI and Their Potential Treatment Strategies

Traumatic brain injury (TBI) is associated with significant cognitive and psychiatric conditions. Neuropsychiatric symptoms can persist for years following brain injury, causing major disruptions in patients’ lives. In this review, we examine the role of glutamate as an aftereffect of TBI that contributes to the development of neuropsychiatric conditions. We hypothesize that TBI causes long-term blood–brain barrier (BBB) dysfunction lasting many years and even decades. We propose that dysfunction in the BBB is the central factor that modulates increased glutamate after TBI and ultimately leads to neurodegenerative processes and subsequent manifestation of neuropsychiatric conditions. Here, we have identified factors that determine the upper and lower levels of glutamate concentration in the brain after TBI. Furthermore, we consider treatments of disruptions to BBB integrity, including repairing the BBB and controlling excess glutamate, as potential therapeutic modalities for the treatment of acute and chronic neuropsychiatric conditions and symptoms. By specifically focusing on the BBB, we hypothesize that restoring BBB integrity will alleviate neurotoxicity and related neurological sequelae.

Glutamate Efflux across the Blood–Brain Barrier: New Perspectives on the Relationship between Depression and the Glutamatergic System

Depression is a significant cause of disability and affects millions worldwide; however, antidepressant therapies often fail or are inadequate. Current medications for treating major depressive disorder can take weeks or months to reach efficacy, have troubling side effects, and are limited in their long-term capabilities. Recent studies have identified a new set of glutamate-based approaches, such as blood glutamate scavengers, which have the potential to provide alternatives to traditional antidepressants. In this review, we hypothesize as to the involvement of the glutamate system in the development of depression. We identify the mechanisms underlying glutamate dysregulation, offering new perspectives on the therapeutic modalities of depression with a focus on its relationship to blood–brain barrier (BBB) permeability. Ultimately, we conclude that in diseases with impaired BBB permeability, such as depression following stroke or traumatic brain injury, or in neurogenerative diseases, the glutamate system should be considered as a pathway to treatment. We propose that drugs such as blood glutamate scavengers should be further studied for treatment of these conditions.

Alternative substrate metabolism depends on cerebral metabolic state following traumatic brain injury

Decreases in energy metabolism following traumatic brain injury (TBI) are attributed to impairment of glycolytic flux and oxidative phosphorylation. Glucose utilization post-TBI is decreased while administration of alternative substrates has been shown to be neuroprotective. Changes in energy metabolism following TBI happens in two phases; a period of hyper-metabolism followed by prolonged hypo-metabolism. It is not understood how different cerebral metabolic states may impact substrate metabolism and ultimately mitochondrial function. Adult male or female Sprague Dawley rats were given sham surgery or controlled cortical impact (CCI) and were assigned one of two administration schemes. Glucose, lactate or beta-hydroxybutyrate (BHB) were infused i.v. either starting immediately after injury or beginning 6 h post-injury for 3 h to reflect the hyper- and hypo-metabolic stages. Animals were euthanized 24 h post-injury. The peri-contusional cortex was collected and assayed for mitochondrial respiration peroxide production, and citrate synthase activity. Tissue acetyl-CoA, ATP, glycogen and HMGB1 were also quantified. Sex differences were observed in injury pattern. Administration based on cerebral metabolic state identified that only early lactate and late BHB improved mitochondrial function and peroxide production and TCA cycle intermediates in males. In contrast, both early and late BHB had deleterious effects on all aspects of metabolic measurements in females. These data stress there is no one optimal alternative substrate, but rather the fuel type used should be guided by both cerebral metabolic state and sex.

Metabolomic markers of fertility in bull seminal plasma

Metabolites play essential roles in biological systems, but detailed identities and significance of the seminal plasma metabolome related to bull fertility are still unknown. The objectives of this study were to determine the comprehensive metabolome of seminal plasma from Holstein bulls and to ascertain the potential of metabolites as biomarkers of bull fertility. The seminal plasma metabolome from 16 Holstein bulls with two fertility rates were determined by gas chromatography-mass spectrometry (GC-MS). Multivariate and univariate analyses of the data were performed, and the pathways associated with the seminal plasma metabolome were identified using bioinformatics approaches. Sixty-three metabolites were identified in the seminal plasma of all bulls. Fructose was the most abundant metabolite in the seminal fluid, followed for citric acid, lactic acid, urea and phosphoric acid. Androstenedione, 4-ketoglucose, D-xylofuranose, 2-oxoglutaric acid and erythronic acid represented the least predominant metabolites. Partial-Least Squares Discriminant Analysis (PLSDA) revealed a distinct separation between high and low fertility bulls. The metabolites with the greatest Variable Importance in Projection score (VIP > 2) were 2-oxoglutaric acid and fructose. Heat-map analysis, based on VIP score, and univariate analysis indicated that 2-oxoglutaric acid was less (P = 0.02); whereas fructose was greater (P = 0.02) in high fertility than in low fertility bulls. The current study is the first to describe the metabolome of bull seminal plasma using GC-MS and presented metabolites such as 2-oxoglutaric acid and fructose as potential biomarkers of bull fertility.

Glutamate, T cells and multiple sclerosis

Glutamate is the major excitatory neurotransmitter in the nervous system, where it induces multiple beneficial and essential effects. Yet, excess glutamate, evident in a kaleidoscope of acute and chronic pathologies, is absolutely catastrophic, since it induces excitotoxicity and massive loss of brain function. Both the beneficial and the detrimental effects of glutamate are mediated by a large family of glutamate receptors (GluRs): the ionotropic glutamate receptors (iGluRs) and the metabotropic glutamate receptors (mGluRs), expressed by most/all cells of the nervous system, and also by many non-neural cells in various peripheral organs and tissues. T cells express on their cell surface several types of functional GluRs, and so do few other immune cells. Furthermore, glutamate by itself activates resting normal human T cells, and induces/elevates key T cell functions, among them: T cell adhesion, chemotactic migration, cytokine secretion, gene expression and more. Glutamate has also potent effects on antigen/mitogen/cytokine-activated T cells. Furthermore, T cells can even produce and release glutamate, and affect other cells and themselves via their own glutamate. Multiple sclerosis (MS) and its animal model Experimental Autoimmune Encephalomyelitis (EAE) are mediated by autoimmune T cells. In MS and EAE, there are excess glutamate levels, and multiple abnormalities in glutamate degrading enzymes, glutamate transporters, glutamate receptors and glutamate signaling. Some GluR antagonists block EAE. Enhancer of mGluR4 protects from EAE via regulatory T cells (Tregs), while mGluR4 deficiency exacerbates EAE. The protective effect of mGluR4 on EAE calls for testing GluR4 enhancers in MS patients. Oral MS therapeutics, namely Fingolimod, dimethyl fumarate and their respective metabolites Fingolimod-phosphate and monomethyl fumarate, can protect neurons against acute glutamatergic excitotoxic damage. Furthermore, Fingolimod reduce glutamate-mediated intracortical excitability in relapsing-remitting MS. Glatiramer acetate -COPAXONE®, an immunomodulator drug for MS, reverses TNF-α-induced alterations of striatal glutamate-mediated excitatory postsynaptic currents in EAE-afflicted mice. With regard to T cells of MS patients: (1) The cell surface expression of a specific GluR: the AMPA GluR3 is elevated in T cells of MS patients during relapse and with active disease, (2) Glutamate and AMPA (a selective agonist for glutamate/AMPA iGluRs) augment chemotactic migration of T cells of MS patients, (3) Glutamate augments proliferation of T cells of MS patients in response to myelin-derived proteins: MBP and MOG, (4) T cells of MS patients respond abnormally to glutamate, (5) Significantly higher proliferation values in response to glutamate were found in MS patients assessed during relapse, and in those with gadolinium (Gd)+ enhancing lesions on MRI. Furthermore, glutamate released from autoreactive T cells induces excitotoxic cell death of neurons. Taken together, the evidences accumulated thus far indicate that abnormal glutamate levels and signaling in the nervous system, direct activation of T cells by glutamate, and glutamate release by T cells, can all contribute to MS. This may be true also to other neurological diseases. It is postulated herein that the detrimental activation of autoimmune T cells by glutamate in MS could lead to: (1) Cytotoxicity in the CNS: T cell-mediated killing of neurons and glia cells, which would subsequently increase the extracellular glutamate levels, and by doing so increase the excitotoxicity mediated by excess glutamate, (2) Release of proinflammatory cytokines, e.g., TNFα and IFNγ that increase neuroinflammation. Finally, if excess glutamate, abnormal neuronal signaling, glutamate-induced activation of T cells, and glutamate release by T cells are indeed all playing a key detrimental role in MS, then optional therapeutic tolls include GluR antagonists, although these may have various side effects. In addition, an especially attractive therapeutic strategy is the novel and entirely different therapeutic approach to minimize excess glutamate and excitotoxicity, titled: 'brain to blood glutamate scavenging', designed to lower excess glutamate levels in the CNS by 'pumping it out' from the brain to the blood. The glutamate scavanging is achieved by lowering glutamate levels in the blood by intravenous injection of the blood enzyme glutamate oxaloacetate transaminase (GOT). The glutamate-scavenging technology, which is still experimental, validated so far for other brain pathologies, but not tested on MS or EAE yet, may be beneficial for MS too, since it could decrease both the deleterious effects of excess glutamate on neural cells, and the activation of autoimmune T cells by glutamate in the brain. The topic of glutamate scavenging, and also its potential benefit for MS, are discussed towards the end of the review, and call for research in this direction.

Blood glutamate grabbing does not reduce the hematoma in an intracerebral hemorrhage model but it is a safe excitotoxic treatment modality

Recent studies have shown that blood glutamate grabbing is an effective strategy to reduce the excitotoxic effect of extracellular glutamate released during ischemic brain injury. The purpose of the study was to investigate the effect of two of the most efficient blood glutamate grabbers (oxaloacetate and recombinant glutamate oxaloacetate transaminase 1: rGOT1) in a rat model of intracerebral hemorrhage (ICH). Intracerebral hemorrhage was produced by injecting collagenase into the basal ganglia. Three treatment groups were developed: a control group treated with saline, a group treated with oxaloacetate, and a final group treated with human rGOT1. Treatments were given 1 hour after hemorrhage. Hematoma volume (analyzed by magnetic resonance imaging (MRI)), neurologic deficit, and blood glutamate and GOT levels were quantified over a period of 14 days after surgery. The results observed showed that the treatments used induced a significant reduction of blood glutamate levels; however, they did not reduce the hematoma, nor did they improve the neurologic deficit. In the present experimental study, we have shown that this novel therapeutic strategy is not effective in case of ICH pathology. More importantly, these findings suggest that blood glutamate grabbers are a safe treatment modality that can be given in cases of suspected ischemic stroke without previous neuroimaging.