Neuroprotective potential of ceftriaxone in in vitro models of stroke

A Review on Neuroinflammatory Pathway Mediating Through Ang-II/AT1 Receptors and a Novel Approach for the Treatment of Cerebral Ischemia in Combination with ARB's and Ceftriaxone

Background

Ischemic stroke is one of the prevalent neurodegenerative disorders; it is generally characterized by sudden abruption of blood flow due to thromboembolism and vascular abnormalities, eventually impairing the supply of oxygen and nutrients to the brain for its metabolic needs. Oxygen-glucose deprived conditions provoke the release of excessive glutamate, which causes excitotoxicity.

Summary

Recent studies suggest that circulatory angiotensin-II (Ang-II) has an imperative role in initiating detrimental events through binding central angiotensin 1 (AT1) receptors. Insufficient energy metabolites and essential ions often lead to oxidative stress during ischemic reperfusion, which leads to the release of proinflammatory mediators such as interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and cytokines like interleukin-18 (IL-18) and interleukin- 1beta (IL-1β). The transmembrane glutamate transporters, excitatory amino acid transporter-2 (EAAT-2), which express in astroglial cells, have a crucial role in the clearance of glutamate from its releasing site and convert glutamate into glutamine in normal circumstances of brain physiology.

Key Message

During cerebral ischemia, an impairment or dysfunction of EAAT-2 attributes the risk of delayed neuronal cell death. Earlier studies evidencing that angiotensin receptor blockers (ARB) attenuate neuroinflammation by inhibiting the Ang-II/AT1 receptor-mediated inflammatory pathway and that ceftriaxone ameliorates the excitotoxicity-induced neuronal deterioration by enhancing the transcription and expression of EAAT-2 via the nuclear transcriptional factor kappa-B (NF-kB) signaling pathway. The present review will briefly discuss the mechanisms involved in Ang-II/AT1-mediated neuroinflammation, ceftriaxone-induced EAAT-2 expression, and the repurposing hypothesis of the novel combination of ARBs and ceftriaxone for the treatment of cerebral ischemia.

The Interplay between Gut Microbiota and Parkinson's Disease: Implications on Diagnosis and Treatment

The bidirectional interaction between the gut microbiota (GM) and the Central Nervous System, the so-called gut microbiota brain axis (GMBA), deeply affects brain function and has an important impact on the development of neurodegenerative diseases. In Parkinson’s disease (PD), gastrointestinal symptoms often precede the onset of motor and non-motor manifestations, and alterations in the GM composition accompany disease pathogenesis. Several studies have been conducted to unravel the role of dysbiosis and intestinal permeability in PD onset and progression, but the therapeutic and diagnostic applications of GM modifying approaches remain to be fully elucidated. After a brief introduction on the involvement of GMBA in the disease, we present evidence for GM alterations and leaky gut in PD patients. According to these data, we then review the potential of GM-based signatures to serve as disease biomarkers and we highlight the emerging role of probiotics, prebiotics, antibiotics, dietary interventions, and fecal microbiota transplantation as supportive therapeutic approaches in PD. Finally, we analyze the mutual influence between commonly prescribed PD medications and gut-microbiota, and we offer insights on the involvement also of nasal and oral microbiota in PD pathology, thus providing a comprehensive and up-to-date overview on the role of microbial features in disease diagnosis and treatment.

Brain-immune interaction mechanisms: Implications for cognitive dysfunction in psychiatric disorders

Objectives

Cognitive dysfunction has been identified as a major symptom of a series of psychiatric disorders. Multidisciplinary studies have shown that cognitive dysfunction is monitored by a two‐way interaction between the neural and immune systems. However, the specific mechanisms of cognitive dysfunction in immune response and brain immune remain unclear.

Materials and methods

In this review, we summarized the relevant research to uncover our comprehension of the brain–immune interaction mechanisms underlying cognitive decline.

Results

The pathophysiological mechanisms of brain‐immune interactions in psychiatric‐based cognitive dysfunction involve several specific immune molecules and their associated signaling pathways, impairments in neural and synaptic plasticity, and the potential neuro‐immunological mechanism of stress.

Conclusions

Therefore, this review may provide a better theoretical basis for integrative therapeutic considerations for psychiatric disorders associated with cognitive dysfunction.

Use of Ceftriaxone as a Predictor of Good Outcome in Stroke Patients: A Retrospective Chart Review

Background:

Whether ceftriaxone (CEFT) has any added advantage other than its antibiotics effect in stroke as a neuroprotective agent is not known, and this forms the base of this study.

Purpose:

We tried to assess the predictive role of the use of CEFT with respect to outcome in stroke patients.

Methods:

A retrospective chart review was conducted from a stroke registry over consecutive stroke patients admitted at a tertiary teaching institute from January 2017 to December 2018. Patients were categorized into three groups on the basis of antibiotics they received; patients without antibiotic treatment (NAB), piperacillin plus tazobactam treatment, and the CEFT treatment group. The outcome was assessed by the modified Rankin Scale at three months in good (0–3) and poor outcomes (4–6).

Results:

A total of 390 stroke patients were analyzed with ages ranging between 20 and 95 years and 151 of them were females. It was found that the severity at three months was significantly lower in those patients who were given CEFT antibiotic ( P = 0.04; OR = 0.626; 95% CI [0.396, 0.990]).

Conclusion:

Stroke patients in CEFT-treated group have a better outcome compared to piperacillin–tazobactam therapy or without antibiotics use at three months. This study indicates the possibility of an additional neuroprotective effect of CEFT apart from its antibacterial property.

The GLT-1 enhancer clavulanic acid suppresses cocaine place preference behavior and reduces GCPII activity and protein levels in the rat nucleus accumbens

The β-lactam antibiotic ceftriaxone (CTX) is a glutamate transporter subtype 1 (GLT-1) enhancer that reduces cocaine reinforcing efficacy and relapse in rats, but pharmacokinetic liabilities limit translational utility. An attractive alternative is clavulanic acid (CLAV), a structurally related β-lactamase inhibitor and component of FDA-approved Augmentin. CLAV retains the GLT-1 enhancing effects of CTX but displays greater oral bioavailability, brain penetrability and negligible antibacterial activity. CLAV reduces morphine conditioned place preference (CPP) and ethanol consumption in rats, but knowledge about the efficacy of CLAV in preclinical models of drug addiction remains sparse. Here, we investigated effects of CLAV (10 mg/kg, IP) on the acquisition, expression, and maintenance of cocaine CPP in rats, and on two glutamate biomarkers associated with cocaine dependence, GLT-1 and glutamate carboxypeptidase II (GCPII). CLAV administered during cocaine conditioning (10 mg/kg, IP x 4 d) did not affect the development of cocaine CPP. However, a single CLAV injection, administered after the conditioning phase, reduced the expression of cocaine CPP. In rats with established cocaine preference, repeated CLAV administration facilitated extinction of cocaine CPP. In the nucleus accumbens, acute CLAV exposure reduced GCPII protein levels and activity, and a 10-d CLAV treatment regimen enhanced GLT-1 levels. These results suggest that CLAV reduces expression and maintenance of cocaine CPP but lacks effect against development of CPP. Moreover, the ability of a single injection of CLAV to reduce both GCPII activity and protein levels, as well as expression of cocaine CPP, points toward studying GCPII as a therapeutic target of CLAV.

Neuroprotective Effects of Ceftriaxone Involve the Reduction of Aβ Burden and Neuroinflammatory Response in a Mouse Model of Alzheimer's Disease

Ceftriaxone (CEF) is a safe and multipotent antimicrobial agent that possesses neuroprotective properties. Earlier, we revealed the restoration of cognitive function in OXYS rats with signs of Alzheimer's disease (AD)-like pathology by CEF along with its modulating the expression of genes related to the system of amyloid beta (Aβ) metabolism in the brain. The aim of this study was to determine the effects of CEF on behavior, Aβ deposition, and associated neuroinflammation using another model of an early AD-like pathology induced by Aβ. Mice were injected bilaterally i.c.v. with Aβ fragment 25-35 to produce the AD model, while the CEF treatment (100 mg/kg/day, i.p., 36 days) started the next day after the surgery. The open field test, T-maze, Barnes test, IntelliCage, and passive avoidance test were used for behavioral phenotyping. Neuronal density, amyloid accumulation, and the expression of neuroinflammatory markers were measured in the frontal cortex and hippocampus. CEF exhibited beneficial effects on some cognitive features impaired by Aβ neurotoxicity including complete restoration of the fear-induced memory and learning in the passive avoidance test and improved place learning in the IntelliCage. CEF significantly attenuated amyloid deposition and neuroinflammatory response. Thus, CEF could be positioned as a potent multipurpose drug as it simultaneously targets proteostasis network and neuroinflammation, as well as glutamate excitotoxicity, oxidative pathways, and neurotrophic function as reported earlier. Together with previous reports on the positive effects of CEF in AD models, the results confirm the potential of CEF as a promising treatment against cognitive decline from the early stages of AD progression.

Glutamate homeostasis and dopamine signaling: Implications for psychostimulant addiction behavior

Cocaine, amphetamine, and methamphetamine abuse disorders are serious worldwide health problems. To date, there are no FDA-approved medications for the treatment of these disorders. Elucidation of the biochemical underpinnings contributing to psychostimulant addiction is critical for the development of effective therapies. Excitatory signaling and glutamate homeostasis are well known pathophysiological substrates underlying addiction-related behaviors spanning multiple types of psychostimulants. To alleviate relapse behavior to psychostimulants, considerable interest has focused on GLT-1, the major glutamate transporter in the brain. While many brain regions are implicated in addiction behavior, this review focuses on two regions well known for their role in mediating the effects of cocaine and amphetamines, namely the nucleus accumbens (NAc) and the ventral tegmental area (VTA). In addition, because many investigators have utilized Cre-driver lines to selectively control gene expression in defined cell populations relevant for psychostimulant addiction, we discuss potential off-target effects of Cre-recombinase that should be considered in the design and interpretation of such experiments.

Astrocytes in rare neurological conditions: Morphological and functional considerations

Astrocytes are a population of central nervous system (CNS) cells with distinctive morphological and functional characteristics that differ within specific areas of the brain and are widely distributed throughout the CNS. There are mainly two types of astrocytes, protoplasmic and fibrous, which differ in morphologic appearance and location. Astrocytes are important cells of the CNS that not only provide structural support, but also modulate synaptic activity, regulate neuroinflammatory responses, maintain the blood-brain barrier, and supply energy to neurons. As a result, astrocytic disruption can lead to widespread detrimental effects and can contribute to the pathophysiology of several neurological conditions. The characteristics of astrocytes in more common neuropathologies such as Alzheimer's and Parkinson's disease have significantly been described and continue to be widely studied. However, there still exist numerous rare neurological conditions in which astrocytic involvement is unknown and needs to be explored. Accordingly, this review will summarize functional and morphological changes of astrocytes in various rare neurological conditions based on current knowledge thus far and highlight remaining neuropathologies where astrocytic involvement has yet to be investigated.

CNS and peripheral immunity in cerebral ischemia: partition and interaction

Stroke elicits excessive immune activation in the injured brain tissue. This well-recognized neural inflammation in the brain is not just an intrinsic organ response but also a result of additional intricate interactions between infiltrating peripheral immune cells and the resident immune cells in the affected areas. Given that there is a finite number of immune cells in the organism at the time of stroke, the partitioned immune systems of the central nervous system (CNS) and periphery must appropriately distribute the limited pool of immune cells between the two domains, mounting a necessary post-stroke inflammatory response by supplying a sufficient number of immune cells into the brain while maintaining peripheral immunity. Stroke pathophysiology has mainly been neurocentric in focus, but understanding the distinct roles of the CNS and peripheral immunity in their concerted action against ischemic insults is crucial. This review will discuss stroke-induced influences of the peripheral immune system on CNS injury/repair and of neural inflammation on peripheral immunity, and how comorbidity influences each.

Selective toxicity of antibacterial agents-still a valid concept or do we miss chances and ignore risks?

BACKGROUND

Selective toxicity antibacteribiotics is considered to be due to interactions with targets either being unique to bacteria or being characterized by a dichotomy between pro- and eukaryotic pathways with high affinities of agents to bacterial- rather than eukaryotic targets. However, the theory of selective toxicity oversimplifies the complex modes of action of antibiotics in pro- and eukaryotes.

METHODS AND OBJECTIVE

This review summarizes data describing multiple modes of action of antibiotics in eukaryotes.

RESULTS

Aminoglycosides, macrolides, oxazolidinones, chloramphenicol, clindamycin, tetracyclines, glycylcyclines, fluoroquinolones, rifampicin, bedaquillin, ß-lactams inhibited mitochondrial translation either due to binding to mitosomes, inhibition of mitochondrial RNA-polymerase-, topoisomerase 2ß-, ATP-synthesis, transporter activities. Oxazolidinones, tetracyclines, vancomycin, ß-lactams, bacitracin, isoniazid, nitroxoline inhibited matrix-metalloproteinases (MMP) due to chelation with zinc and calcium, whereas fluoroquinols fluoroquinolones and chloramphenicol chelated with these cations, too, but increased MMP activities. MMP-inhibition supported clinical efficacies of ß-lactams and daptomycin in skin-infections, and of macrolides, tetracyclines in respiratory-diseases. Chelation may have contributed to neuroprotection by ß-lactams and fluoroquinolones. Aminoglycosides, macrolides, chloramphenicol, oxazolidins oxazolidinones, tetracyclines caused read-through of premature stop codons. Several additional targets for antibiotics in human cells have been identified like interaction of fluoroquinolones with DNA damage repair in eukaryotes, or inhibition of mucin overproduction by oxazolidinones.

CONCLUSION

The effects of antibiotics on eukaryotes are due to identical mechanisms as their antibacterial activities because of structural and functional homologies of pro- and eukaryotic targets, so that the effects of antibiotics on mammals are integral parts of their overall mechanisms of action.

Increased vulnerability to impulsive behavior after streptococcal antigen exposure and antibiotic treatment in rats

RATIONALE

The inflammation induced by Group A Streptococcus (GAS) infection has been viewed as a vulnerability factor in mental disorders characterized by inhibitory control deficits, such as attention-deficit/hyperactivity disorder or obsessive-compulsive disorder. Antibiotic treatment reduces GAS symptoms; however, its effects on impulsivity have not been fully assessed.

OBJECTIVES

We investigated whether GAS exposure during early adolescence might be a vulnerability factor for adult impulsivity, if antibiotic treatment acts as a protective factor, and whether these differences are accompanied by changes in the inflammatory cytokine frontostriatal regions.

METHODS

Male Wistar rats were exposed to the GAS antigen or to vehicle plus adjuvants at postnatal day (PND) 35 (with two boosts), and they received either ampicillin (supplemented in the drinking water) or water alone from PND35 to PND70. Adult impulsivity was assessed using two different models, the 5-choice serial reaction time task (5-CSRT task) and the delay discounting task (DDT). The levels of interleukin-6 (IL-6) and IL-17 were measured in the prefrontal cortex (PFc), and the tumor necrosis factor α levels (TNFα) were measured in the PFc and nucleus accumbens (NAcc).

RESULTS

GAS exposure and ampicillin treatment increased the waiting impulsivity by a higher number of premature responses when the animals were challenged by a long intertrial interval during the 5-CSRT task. The GAS exposure revealed higher impulsive choices at the highest delay (40 s) when tested by DDT, while coadministration with ampicillin prevented the impulsive choice. GAS exposure and ampicillin reduced the IL-6 and IL-17 levels in the PFc, and ampicillin treatment increased the TNFα levels in the NAcc. A regression analysis revealed a significant contribution of GAS exposure and TNFα levels to the observed effects.

CONCLUSIONS

GAS exposure and ampicillin treatment induced an inhibitory control deficit in a different manner depending on the form of impulsivity measured here, with inflammatory long-term changes in the PFc and NAcc that might increase the vulnerability to impulsivity-related neuropsychiatric disorders.

Transport rate of EAAT2 is regulated by amino acid located at the interface between the scaffolding and substrate transport domains

Excitatory Amino Acid Transporters (EAATs) are plasma membrane proteins responsible for maintenance of low extracellular concentrations of glutamate in the CNS. Dysfunction in their activity is implicated in various neurological disorders. Glutamate transport by EAATs occurs through the movement of the central transport domain relative to the scaffold domain in the EAAT membrane protein. Previous studies suggested that residues located within the interface of these two domains in EAAT2, the main subtype of glutamate transporter in the brain, are involved in regulating transport rates. We used mutagenesis, structure-function relationship, surface protein expression and electrophysiology studies, in transfected COS-7 cells and oocytes, to examine residue glycine at position 298, which is located within this interface. Mutation G298A results in increased transport rate without changes in surface expression, suggesting a more hydrophobic and larger alanine results in facilitated transport movement. The increased transport rate does not involve changes in sodium affinity. Electrophysiological currents show that G298A increase both transport and anion currents, suggesting faster transitions through the transport cycle. This work identifies a region critically involved in setting the glutamate transport rate.

Elucidation of the Structure and Synthesis of Neuroprotective Low Molecular Mass Components of the Parawixia bistriata Spider Venom

The South American social spider Parawixia bistriata produces a venom containing complex organic compounds with intriguing biological activities. The crude venom leads to paralysis in termites and stimulates l-glutamate uptake and inhibits GABA uptake in rat brain synaptosomes. Glutamate is the major neurotransmitter at the insect neuromuscular junction and at the mammalian central nervous system, suggesting a modulation of the glutamatergic system by the venom. Parawixin1, 2, and 10 (Pwx1, 2 and 10) are HPLC fractions that demonstrate this bioactivity. Pwx1 stimulates l-glutamate uptake through the main transporter in the brain, EAAT2, and is neuroprotective in in vivo glaucoma models. Pxw2 inhibits GABA and glycine uptake in synaptosomes and inhibits seizures and neurodegeneration, and Pwx10 increases l-glutamate uptake in synaptosomes and is neuroprotective and anticonvulsant, shown in in vivo epilepsy models. Herein, we investigated the low molecular mass compounds in this venom and have found over 20 small compounds and 36 unique acylpolyamines with and without amino acid linkers. The active substances in fractions Pwx1 and Pwx2 require further investigation. We elucidated and confirmed the structure of the active acylpolyamine in Pwx10. Both fraction Pwx10 and the synthesized component enhance the activity of transporters EAAT1 and EAAT2, and, importantly, offer in vitro neuroprotection against excitotoxicity in primary cultures. These data suggest that compounds with this mechanism could be developed into therapies for disorders in which l-glutamate excitotoxicity is involved.

Molecular changes evoked by the beta-lactam antibiotic ceftriaxone across rodent models of substance use disorder and neurological disease

Ceftriaxone is a beta-lactam antibiotic that increases the expression of the major glutamate transporter, GLT-1. As such, ceftriaxone ameliorates symptoms across multiple rodent models of neurological diseases and substance use disorders. However, the mechanism behind GLT-1 upregulation is unknown. The present review synthesizes this literature in order to identify commonalities in molecular changes. We find that ceftriaxone (200 mg/kg for at least two days) consistently restores GLT-1 expression in multiple rodent models of neurological disease, especially when GLT-1 is decreased in the disease model. The same dose given to healthy/drug-naive rodents does not reliably upregulate GLT-1 in any brain region except the hippocampus. Increased GLT-1 expression does not consistently arise from transcriptional regulation, and is likely to be due to trafficking changes. In addition to altered transporter expression, ceftriaxone ameliorates neuropathologies (e.g. tau, amyloid beta, cell death) and aberrant protein expression associated with a number of neurological disease models. Taken together, these results indicate that ceftriaxone remains a strong candidate for treatment of multiple disorders in the clinic.

Hippocampal Synaptic Dysfunction in a Mouse Model of Huntington Disease Is Not Alleviated by Ceftriaxone Treatment

Glutamate transporters, particularly glutamate transporter 1 (GLT-1), help to prevent the adverse effects associated with glutamate toxicity by rapidly clearing glutamate from the extracellular space. Since GLT-1 expression and/or function are reduced in many neurodegenerative diseases, upregulation of GLT-1 is a favorable approach to treat the symptoms of these diseases. Ceftriaxone, a β-lactam antibiotic reported to increase GLT-1 expression, can exert neuroprotective effects in a variety of neurodegenerative diseases; however, many of these diseases do not exhibit uniform brain pathology. In contrast, as a drug that readily crosses the blood–brain barrier, ceftriaxone administration is likely to increase GLT-1 levels globally throughout the neuroaxis. In Huntington disease (HD), low GLT-1 expression is observed in the striatum in postmortem tissue and animal models. While ceftriaxone was reported to increase striatal GLT-1 and ameliorate the motor symptoms in a mouse model of HD, the extrastriatal effects of ceftriaxone in HD are unknown. Using electrophysiology and high-speed imaging of the glutamate biosensor iGluSnFR, we quantified real-time glutamate dynamics and synaptic plasticity in the hippocampus of the Q175FDN mouse model of HD, following intraperitoneal injections of either saline or ceftriaxone. We observed an activity-dependent increase in extracellular glutamate accumulation within the HD hippocampus, which was not the result of reduced GLT-1 expression. Surprisingly, ceftriaxone had little effect on glutamate clearance rates and negatively impacted synaptic plasticity. These data provide evidence for glutamate dysregulation in the HD hippocampus but also caution the use of ceftriaxone as a treatment for HD.

Neuroprotective Effects of Emodin against Ischemia/Reperfusion Injury through Activating ERK-1/2 Signaling Pathway

Background: Stroke is one of the leading causes of death and disability worldwide and places a heavy burden on the economy in our society. Current treatments, such as the use of thrombolytic agents, are often limited by a narrow therapeutic time window. However, the regeneration of the brain after damage is still active days, even weeks, after stroke occurs, which might provide a second window for treatment. Emodin, a traditional Chinese medicinal herb widely used to treat acute hepatitis, has been reported to possess antioxidative capabilities and protective effects against myocardial ischemia/reperfusion injury. However, the underlying mechanisms and neuroprotective functions of Emodin in a rat middle cerebral artery occlusion (MCAO) model of ischemic stroke remain unknown. This study investigates neuroprotective effects of Emodin in ischemia both in vitro and in vivo. Methods: PC12 cells were exposed to oxygen-glucose deprivation to simulate hypoxic injury, and the involved signaling pathways and results of Emodin treatment were evaluated. The therapeutic effects of Emodin in ischemia animals were further investigated. Results: Emodin reduced infarct volume and cell death following focal cerebral ischemia injury. Emodin treatment restored PC12 cell viability and reduced reactive oxygen species (ROS) production and glutamate release under conditions of ischemia/hypoxia. Emodin increased Bcl-2 and glutamate transporter-1 (GLT-l) expression but suppressed activated-caspase 3 levels through activating the extracellular signal-regulated kinase (ERK)-1/2 signaling pathway. Conclusion: Emodin induced Bcl-2 and GLT-1 expression to inhibit neuronal apoptosis and ROS generation while reducing glutamate toxicity via the ERK-1/2 signaling pathway. Furthermore, Emodin alleviated nerve cell injury following ischemia/reperfusion in a rat MCAO model. Emodin has neuroprotective effects against ischemia/reperfusion injury both in vitro and in vivo, which may be through activating the ERK-1/2 signaling pathway.

Hippocampal and Cerebellar Changes in Acute Restraint Stress and the Impact of Pretreatment with Ceftriaxone

Acute restraint stress (ARS) is an unavoidable stress situation and may be encountered in different clinical situations. The aim of the current study was to investigate the effects of ARS on the hippocampus and cerebellum, assess the impact of these effects on the behavior and cognitive function, and determine whether pretreatment with ceftriaxone would attenuate the damages produced by ARS on the hippocampus and cerebellum. Four groups of male mice were included in this study: The control group, ARS group, ceftriaxone group, and ARS + ceftriaxone group. Tail suspension test, Y-maze task, and open field tests were used to assess depression, working spatial memory, and anxiety. The biochemical analyses included measurements of serum cortisol, tumor necrotic factor (TNF), interleukin-6, hippocampal expression of bone morphogenetic protein 9 (BMP9), lysosomal-associated membrane protein 1 (LAMP1), glutamate transporter 1 (GLT1), heat shock protein 90, cerebellar expression of S100 protein, glutamic acid decarboxylase (GAD), and carbon anhydrase. Histopathological examination of the brain sections was conducted on the hippocampus and cerebellum by hematoxylin and eosin stains in addition to ultrastructure evaluation using electron microscopy. Our results suggested that ceftriaxone had neuroprotective properties by attenuating the effects of ARS on the hippocampus and cerebellum in mice. This effect was demonstrated by the improvement in the cognitive and behavioral tests as well as by the preservation of the hippocampal and cerebellar architecture.

Serial exposure to ethanol drinking and methamphetamine enhances glutamate excitotoxicity

A significant comorbidity exists between alcohol and methamphetamine (Meth) abuse but the neurochemical consequences of this co-abuse are unknown. Alcohol and Meth independently and differentially affect glutamatergic transmission but the unique effects of their serial exposure on glutamate signaling in mediating damage to dopamine neurons are unknown. Sprague-Dawley rats had intermittent voluntary access to 10% ethanol (EtOH) every other day and water over 28 days and were then administered a binge injection regimen of Meth or saline. EtOH drinking decreased the glutamate aspartate transporter and increased basal extracellular concentrations of glutamate within the striatum when measured after the last day of drinking. Ceftriaxone is known to increase the expression and/or activity of glutamate transporters in the brain and prevented both the decreases in glutamate aspartate transporter and the increases in basal extracellular glutamate when administered during EtOH drinking. EtOH drinking also exacerbated the acute increases in extracellular glutamate observed upon Meth exposure, the subsequent increases in spectrin proteolysis, and the long-term decreases in dopamine content in the striatum, all of which were attenuated by ceftriaxone administration during EtOH drinking only. These results implicate EtOH-induced increases in extracellular glutamate and corresponding decreases in glutamate uptake as mechanisms that contribute to the vulnerability produced by EtOH drinking and the unique neurotoxicity observed after serial exposure to Meth that is not observed with either drug alone. Open Science: This manuscript was awarded with the Open Materials Badge For more information see: https://cos.io/our-services/open-science-badges/.

Novel Positive Allosteric Modulators of Glutamate Transport Have Neuroprotective Properties in an in Vitro Excitotoxic Model

Dysfunction of excitatory amino acid transporters (EAATs) has been implicated in the pathogenesis of various neurological disorders, such as stroke, brain trauma, epilepsy, and several neurodegenerative disorders. EAAT2 is the main transporter subtype responsible for glutamate clearance in the brain, and plays a key role in regulating neurotransmission and preventing excitotoxicity. Therefore, compounds that increase the activity of EAAT2 have therapeutic potential for neuroprotection. In previous studies, we used virtual screening approaches to identify novel positive allosteric modulators (PAMs) of EAAT2. These compounds were shown to selectively increase the activity of EAAT2 and increase V_max of transport, without changing substrate affinity. In this work, our major effort was to investigate whether increasing the activity of EAAT2 by allosteric modulation would translate to neuroprotection in in vitro primary culture models of excitotoxicity. To investigate potential neuroprotective effects of one EAAT2 PAM, GT949, we subjected cultures to acute and prolonged excitotoxic insults by exogenous application of glutamate, or oxidative stress by application of hydrogen peroxide. GT949 administration did not result in neuroprotection in the oxidative stress model, likely due to damage of the glutamate transporters. However, GT949 displayed neuroprotective properties after acute and prolonged glutamate-mediated excitotoxicity. We propose that this compound prevents excess glutamate signaling by increasing the rate of glutamate clearance by EAAT2, thereby preventing excitotoxic damage and cell death. This novel class of compounds is therefore an innovative approach for neuroprotection with potential for translation in in vivo animal models of excitotoxicity.

Repurposing of the β-Lactam Antibiotic, Ceftriaxone for Neurological Disorders: A Review

To date, there is no cure or disease-modifying agents available for most well-known neurological disorders. Current therapy is typically focused on relieving symptoms and supportive care in improving the quality of life of affected patients. Furthermore, the traditional de novo drug discovery technique is more challenging, particularly for neurological disorders. Therefore, the repurposing of existing drugs for these conditions is believed to be an efficient and dynamic approach that can substantially reduce the investments spent on drug development. Currently, there is emerging evidence that suggests the potential effect of a beta-lactam antibiotic, ceftriaxone (CEF), to alleviate the symptoms of different experimentally-induced neurological disorders: Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, epileptic-seizure, brain ischemia, traumatic brain injuries, and neuropathic pain. CEF also affects the markers of oxidative status and neuroinflammation, glutamatergic systems as well as various aggregated toxic proteins involved in the pathogenesis of different neurological disorders. Moreover, it was found that CEF administration to drug dependent animal models improved the withdrawal symptoms upon drug discontinuation. Thus, this review aimed to describe the effects of CEF against multiple models of neurological illnesses, drug dependency, and withdrawal. It also emphasizes the possible mechanisms of neuroprotective actions of CEF with respective neurological maladies.

Sulbactam Protects Hippocampal Neurons Against Oxygen-Glucose Deprivation by Up-Regulating Astrocytic GLT-1 via p38 MAPK Signal Pathway

Sulbactam is an atypical β-lactam medication and reported to be neuroprotective by up-regulating glial glutamate transporter-1 (GLT-1) in rats. The present study was undertaken to study the role of p38 MAPK signal pathway in sulbactam induced up-regulation of GLT-1 expression in astrocytes and anti-ischemic effect. Neuron-astrocyte co-cultures and astrocyte cultures from neonatal Wistar rats were used. Cerebral ischemia was mimicked by oxygen-glucose deprivation (OGD). Hoechst (HO)/propidium iodide (PI) double fluorescence staining and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay were used to evaluate neuronal death and cell viability, respectively. Immunocytochemistry and Western blot were used to detect protein expressions. Sulbactam pre-incubation significantly and dose-dependently prevented neuronal death and decline in cell viability induced by OGD in neuron-astrocyte co-cultures, and upregulated GLT-1 expression in astrocyte cultures endured OGD, which suggested that sulbactam might protect neurons against OGD by up-regulating astrocytic GLT-1 expression. It was further shown that the phosphorylated-p38 MAPK expression in astrocytes was up-regulated after the sulbactam pre-incubation and this up-regulation was moderate in amplitude. Especially, the time course of the up-regulation of phosphorylated-p38 MAPK was obviously earlier than that of GLT-1, which suggested possibility that p38 MAPK might be an upstream signal for GLT-1 up-regulation induced by sulbactam. We further found that SB203580, the specific inhibitor of p38 MAPK, dose-dependently inhibited the GLT-1 up-regulation induced by sulbactam either in non- or OGD-treated astrocytes and the protective effect of sulbactam on co-cultured neurons against OGD. Taken together, it might be concluded that sulbactam protects cerebral neurons against OGD by up-regulating astrocytic GLT-1 expression via p38 MAPK signal pathway.

Global untargeted serum metabolomic analyses nominate metabolic pathways responsive to loss of expression of the orphan metallo β-lactamase, MBLAC1

The C. elegans gene swip-10 encodes an orphan metallo β-lactamase that genetic studies indicate is vital for limiting neuronal excitability and viability. Sequence analysis indicates that the mammalian gene Mblac1 is the likely ortholog of swip-10, with greatest sequence identity localized to the encoded protein's single metallo β-lactamase domain. The substrate for the SWIP-10 protein remains unknown and to date no functional roles have been ascribed to MBLAC1, though we have shown that the protein binds the neuroprotective β-lactam antibiotic, ceftriaxone. To gain insight into the functional role of MBLAC1 in vivo, we used CRISPR/Cas9 methods to disrupt N-terminal coding sequences of the mouse Mblac1 gene, resulting in a complete loss of protein expression in viable, homozygous knockout (KO) animals. Using serum from both WT and KO mice, we performed global, untargeted metabolomic analyses, resolving small molecules via hydrophilic interaction chromatography (HILIC) based ultra-performance liquid chromatography, coupled to mass spectrometry (UPLC-MS/MS). Unsupervised principal component analysis reliably segregated the metabolomes of MBLAC1 KO and WT mice, with 92 features subsequently nominated as significantly different by ANOVA, and for which we made tentative and putative metabolite assignments. Bioinformatic analyses of these molecules nominate validated pathways subserving bile acid biosynthesis and linoleate metabolism, networks known to be responsive to metabolic and oxidative stress. Our findings lead to hypotheses that can guide future targeted studies seeking to identify the substrate for MBLAC1 and how substrate hydrolysis supports the neuroprotective actions of ceftriaxone.

Glial loss of the metallo β-lactamase domain containing protein, SWIP-10, induces age- and glutamate-signaling dependent, dopamine neuron degeneration

Across phylogeny, glutamate (Glu) signaling plays a critical role in regulating neural excitability, thus supporting many complex behaviors. Perturbed synaptic and extrasynaptic Glu homeostasis in the human brain has been implicated in multiple neuropsychiatric and neurodegenerative disorders including Parkinson's disease, where theories suggest that excitotoxic insults may accelerate a naturally occurring process of dopamine (DA) neuron degeneration. In C. elegans, mutation of the glial expressed gene, swip-10, results in Glu-dependent DA neuron hyperexcitation that leads to elevated DA release, triggering DA signaling-dependent motor paralysis. Here, we demonstrate that swip-10 mutations induce premature and progressive DA neuron degeneration, with light and electron microscopy studies demonstrating the presence of dystrophic dendritic processes, as well as shrunken and/or missing cell soma. As with paralysis, DA neuron degeneration in swip-10 mutants is rescued by glial-specific, but not DA neuron-specific expression of wildtype swip-10, consistent with a cell non-autonomous mechanism. Genetic studies implicate the vesicular Glu transporter VGLU-3 and the cystine/Glu exchanger homolog AAT-1 as potential sources of Glu signaling supporting DA neuron degeneration. Degeneration can be significantly suppressed by mutations in the Ca2+ permeable Glu receptors, nmr-2 and glr-1, in genes that support intracellular Ca2+ signaling and Ca2+-dependent proteolysis, as well as genes involved in apoptotic cell death. Our studies suggest that Glu stimulation of nematode DA neurons in early larval stages, without the protective actions of SWIP-10, contributes to insults that ultimately drive DA neuron degeneration. The swip-10 model may provide an efficient platform for the identification of molecular mechanisms that enhance risk for Parkinson's disease and/or the identification of agents that can limit neurodegenerative disease progression.

Identification of Novel Allosteric Modulators of Glutamate Transporter EAAT2

Dysfunction of excitatory amino acid transporters (EAATs) has been implicated in the pathogenesis of various neurological disorders, such as stroke, brain trauma, epilepsy, and neurodegenerative diseases, among others. EAAT2 is the main subtype responsible for glutamate clearance in the brain, having a key role in regulating transmission and preventing excitotoxicity. Therefore, compounds that increase the expression or activity of EAAT2 have therapeutic potential for neuroprotection. Previous studies identified molecular determinants for EAAT2 transport stimulation in a structural domain that lies at the interface of the rigid trimerization domain and the central substrate binding transport domain. In this work, a hybrid structure based approach was applied, based on this molecular domain, to create a high-resolution pharmacophore. Subsequently, virtual screening of a library of small molecules was performed, identifying 10 hit molecules that interact at the proposed domain. Among these, three compounds were determined to be activators, four were inhibitors, and three had no effect on EAAT2-mediated transport in vitro. Further characterization of the two best ranking EAAT2 activators for efficacy, potency, and selectivity for glutamate over monoamine transporters subtypes and NMDA receptors and for efficacy in cultured astrocytes is demonstrated. Mutagenesis studies suggest that the EAAT2 activators interact with residues forming the interface between the trimerization and transport domains. These compounds enhance the glutamate translocation rate, with no effect on substrate interaction, suggesting an allosteric mechanism. The identification of these novel positive allosteric modulators of EAAT2 offers an innovative approach for the development of therapies based on glutamate transport enhancement.

Metallo-β-lactamase Domain-Containing Protein 1 (MBLAC1) Is a Specific, High-Affinity Target for the Glutamate Transporter Inducer Ceftriaxone

Ceftriaxone, a β-lactam antibiotic, has been reported to act independently of its antimicrobial actions to normalize perturbed central nervous system glutamate levels, principally by elevating expression of glial glutamate transporters. Identification of a specific, high-affinity target for ceftriaxone could significantly impact therapeutic development for multiple brain disorders, ranging from neurodegenerative disorders to addiction. Recently, we identified a glial-expressed Caenorhabditis elegans gene, swip-10, that encodes a metallo-β-lactamase domain-containing protein, and limits glutamate-dependent changes in dopamine neuron excitability. Bioinformatic analyses identified MBLAC1 as the likely mammalian orthologue of swip-10. Using cyanogen bromide immobilized ceftriaxone for affinity capture experiments and backscattering interferometry to monitor MBLAC1 binding of unmodified ceftriaxone, we obtained evidence for specific, high affinity (K_D = 2.2 μM) binding of ceftriaxone to MBLAC1. We discuss our findings with respect to MBLAC1 as a potentially exclusive, high-affinity binding partner of ceftriaxone in the CNS, and the path forward in the development of novel, MBLAC1-based therapeutics.

The β-lactam clavulanic acid mediates glutamate transport-sensitive pain relief in a rat model of neuropathic pain

BACKGROUND

Following nerve injury, down-regulation of astroglial glutamate transporters (GluTs) with subsequent extracellular glutamate accumulation is a key factor contributing to hyperexcitability within the spinal dorsal horn. Some β-lactam antibiotics can up-regulate GluTs, one of which, ceftriaxone, displays analgesic effects in rodent chronic pain models.

METHODS

Here, the antinociceptive actions of another β-lactam clavulanic acid, which possesses negligible antibiotic activity, were compared with ceftriaxone in rats with chronic constriction injury (CCI)-induced neuropathic pain. In addition, the protein expression of glutamate transporter-1 (GLT1), its splice variant GLT1b and glutamate-aspartate transporter (GLAST) was measured in the spinal cord of CCI rats. Finally, protein expression of the same GluTs was evaluated in cultured astrocytes obtained from rodents and humans.

RESULTS

Repeated injection of ceftriaxone or clavulanic acid over 10 days alleviated CCI-induced mechanical hypersensitivity, whilst clavulanic acid was additionally able to affect the thermal hypersensitivity. In addition, clavulanic acid up-regulated expression of GLT1b within the spinal cord of CCI rats, whereas ceftriaxone failed to modulate expression of any GluTs in this model. However, both clavulanic acid and ceftriaxone up-regulated GLT1 expression in rat cortical and human spinal astrocyte cultures. Furthermore, clavulanic acid increased expression of GLT1b and GLAST in rat astrocytes in a dose-dependent manner.

CONCLUSIONS

Thus, clavulanic acid up-regulates GluTs in cultured rodent- and human astroglia and alleviates CCI-induced hypersensitivity, most likely through up-regulation of GLT1b in spinal dorsal horn.

SIGNIFICANCE

Chronic dosing of clavulanic acid alleviates neuropathic pain in rats and up-regulates glutamate transporters both in vitro and in vivo. Crucially, a similar up-regulation of glutamate transporters in human spinal astrocytes by clavulanic acid supports the development of novel β-lactam-based analgesics, devoid of antibacterial activity, for the clinical treatment of chronic pain.

The role of glutamate in neuronal ion homeostasis: A case study of spreading depolarization

Simultaneous changes in ion concentrations, glutamate, and cell volume together with exchange of matter between cell network and vasculature are ubiquitous in numerous brain pathologies. A complete understanding of pathological conditions as well as normal brain function, therefore, hinges on elucidating the molecular and cellular pathways involved in these mostly interdependent variations. In this paper, we develop the first computational framework that combines the Hodgkin-Huxley type spiking dynamics, dynamic ion concentrations and glutamate homeostasis, neuronal and astroglial volume changes, and ion exchange with vasculature into a comprehensive model to elucidate the role of glutamate uptake in the dynamics of spreading depolarization (SD)-the electrophysiological event underlying numerous pathologies including migraine, ischemic stroke, aneurysmal subarachnoid hemorrhage, intracerebral hematoma, and trauma. We are particularly interested in investigating the role of glutamate in the duration and termination of SD caused by K+ perfusion and oxygen-glucose deprivation. Our results demonstrate that glutamate signaling plays a key role in the dynamics of SD, and that impaired glutamate uptake leads to recovery failure of neurons from SD. We confirm predictions from our model experimentally by showing that inhibiting astrocytic glutamate uptake using TFB-TBOA nearly quadruples the duration of SD in layers 2-3 of visual cortical slices from juvenile rats. The model equations are either derived purely from first physical principles of electroneutrality, osmosis, and conservation of particles or a combination of these principles and known physiological facts. Accordingly, we claim that our approach can be used as a future guide to investigate the role of glutamate, ion concentrations, and dynamics cell volume in other brain pathologies and normal brain function.

Brain endothelial cells induce astrocytic expression of the glutamate transporter GLT-1 by a Notch-dependent mechanism

Neuron-secreted factors induce astrocytic expression of the glutamate transporter, GLT-1 (excitatory amino acid transporter 2). In addition to their elaborate anatomic relationships with neurons, astrocytes also have processes that extend to and envelop the vasculature. Although previous studies have demonstrated that brain endothelia contribute to astrocyte differentiation and maturation, the effects of brain endothelia on astrocytic expression of GLT-1 have not been examined. In this study, we tested the hypothesis that endothelia induce expression of GLT-1 by co-culturing astrocytes from mice that utilize non-coding elements of the GLT-1 gene to control expression of reporter proteins with the mouse endothelial cell line, bEND.3. We found that endothelia increased steady state levels of reporter and GLT-1 mRNA/protein. Co-culturing with primary rat brain endothelia also increases reporter protein, GLT-1 protein, and GLT-1-mediated glutamate uptake. The Janus kinase/signal transducer and activator of transcription 3, bone morphogenic protein/transforming growth factor β, and nitric oxide pathways have been implicated in endothelia-to-astrocyte signaling; we provide multiple lines of evidence that none of these pathways mediate the effects of endothelia on astrocytic GLT-1 expression. Using transwells with a semi-permeable membrane, we demonstrate that the effects of the bEND.3 cell line are dependent upon contact. Notch has also been implicated in endothelia-astrocyte signaling in vitro and in vivo. The first step of Notch signaling requires cleavage of Notch intracellular domain by γ-secretase. We demonstrate that the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester blocks endothelia-induced increases in GLT-1. We show that the levels of Notch intracellular domain are higher in nuclei of astrocytes co-cultured with endothelia, an effect also blocked by N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester. Finally, infection of co-cultures with shRNA directed against recombination signal binding protein for immunoglobulin kappa J, a Notch effector, also reduces endothelia-dependent increases in enhanced green fluorescent protein and GLT-1. Together, these studies support a novel role for Notch in endothelia-dependent induction of GLT-1 expression. Cover Image for this issue: doi. 10.1111/jnc.13825.

Brain endothelial cells induce astrocytic expression of the glutamate transporter GLT-1 by a Notch-dependent mechanism

Neuron-secreted factors induce astrocytic expression of the glutamate transporter, GLT-1 (excitatory amino acid transporter 2). In addition to their elaborate anatomic relationships with neurons, astrocytes also have processes that extend to and envelop the vasculature. Although previous studies have demonstrated that brain endothelia contribute to astrocyte differentiation and maturation, the effects of brain endothelia on astrocytic expression of GLT-1 have not been examined. In this study, we tested the hypothesis that endothelia induce expression of GLT-1 by co-culturing astrocytes from mice that utilize non-coding elements of the GLT-1 gene to control expression of reporter proteins with the mouse endothelial cell line, bEND.3. We found that endothelia increased steady state levels of reporter and GLT-1 mRNA/protein. Co-culturing with primary rat brain endothelia also increases reporter protein, GLT-1 protein, and GLT-1-mediated glutamate uptake. The Janus kinase/signal transducer and activator of transcription 3, bone morphogenic protein/transforming growth factor β, and nitric oxide pathways have been implicated in endothelia-to-astrocyte signaling; we provide multiple lines of evidence that none of these pathways mediate the effects of endothelia on astrocytic GLT-1 expression. Using transwells with a semi-permeable membrane, we demonstrate that the effects of the bEND.3 cell line are dependent upon contact. Notch has also been implicated in endothelia-astrocyte signaling in vitro and in vivo. The first step of Notch signaling requires cleavage of Notch intracellular domain by γ-secretase. We demonstrate that the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester blocks endothelia-induced increases in GLT-1. We show that the levels of Notch intracellular domain are higher in nuclei of astrocytes co-cultured with endothelia, an effect also blocked by N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester. Finally, infection of co-cultures with shRNA directed against recombination signal binding protein for immunoglobulin kappa J, a Notch effector, also reduces endothelia-dependent increases in enhanced green fluorescent protein and GLT-1. Together, these studies support a novel role for Notch in endothelia-dependent induction of GLT-1 expression. Cover Image for this issue: doi. 10.1111/jnc.13825.

Glutamate Transport System as a Novel Therapeutic Target in Chronic Pain: Molecular Mechanisms and Pharmacology

The vast majority of peripheral neurons sensing noxious stimuli and conducting pain signals to the dorsal horn of the spinal cord utilize glutamate as a chemical transmitter of excitation. High-affinity glutamate transporter subtypes GLAST/EAAT1, GLT1/EAAT2, EAAC1/EAAT3, and EAAT4, differentially expressed on sensory neurons, postsynaptic spinal interneurons, and neighboring glia, ensure fine modulation of glutamate neurotransmission in the spinal cord. The glutamate transport system seems to play important roles in molecular mechanisms underlying chronic pain and analgesia. Downregulation of glutamate transporters (GluTs) often precedes or occurs simultaneously with development of hypersensitivity to thermal or tactile stimuli in various models of chronic pain. Moreover, antisense knockdown or pharmacological inhibition of these membrane proteins can induce or aggravate pain. In contrast, upregulation of GluTs by positive pharmacological modulators or by viral gene transfer to the spinal cord can reverse the development of such pathological hypersensitivity. Furthermore, some multi-target drugs displaying analgesic properties (e.g., tricyclic antidepressant amitriptyline, riluzole, anticonvulsant valproate, tetracycline antibiotic minocycline, β-lactam antibiotic ceftriaxone and its structural analog devoid of antibacterial activity, clavulanic acid) can significantly increase the spinal glutamate uptake. Thus, mounting evidence points at GluTs as prospective therapeutic target for chronic pain treatment. However, design and development of new analgesics based on the modulation of glutamate uptake will require more precise knowledge of molecular mechanisms underlying physiological or aberrant functioning of this transport system in the spinal cord.

Mapping synaptic glutamate transporter dysfunction in vivo to regions surrounding Aβ plaques by iGluSnFR two-photon imaging

Amyloid-β (Aβ) plaques, a hallmark of Alzheimer's disease (AD), are surrounded by regions of neuronal and glial hyperactivity. We use in vivo two-photon and wide-field imaging of the glutamate sensor iGluSnFR to determine whether pathological changes in glutamate dynamics in the immediate vicinity of Aβ deposits in APPPS1 transgenic mice could alter neuronal activity in this microenvironment. In regions close to Aβ plaques chronic states of high spontaneous glutamate fluctuations are observed and the timing of glutamate responses evoked by sensory stimulation exhibit slower decay rates in two cortical brain areas. GLT-1 expression is reduced around Aβ plaques and upregulation of GLT-1 expression and activity by ceftriaxone partially restores glutamate dynamics to values in control regions. We conclude that the toxic microenvironment surrounding Aβ plaques results, at least partially, from enhanced glutamate levels and that pharmacologically increasing GLT-1 expression and activity may be a new target for early therapeutic intervention.

In Alzheimer's disease (AD), neural hyperactivity has been shown to occur in the regions surrounding Aβ plaques. Here, the authors use in vivo two-photon imaging in mouse models of AD and report abnormal glutamate dynamics in the vicinity of plaques which can be partially restored via GLT-1 upregulation through Ceftriaxone treatment.

Effects of repeated high-dose methamphetamine and ceftriaxone post-treatments on tissue content of dopamine and serotonin as well as glutamate and glutamine

Repeated exposure to high doses of methamphetamine (METH) is known to alter several neurotransmitters in certain brain regions. Little is known about the effects of ceftriaxone (CEF), a β-lactam antibiotic, known to upregulate glutamate transporter subtype 1, post-treatment on METH-induced depletion of dopamine and serotonin (5-HT) tissue content in brain reward regions. Moreover, the effects of METH and CEF post-treatment on glutamate and glutamine tissue content are not well understood. In this study, Wistar rats were used to investigate the effects of METH and CEF post-treatment on tissue content of dopamine/5-HT and glutamate/glutamine in the nucleus accumbens (NAc) and prefrontal cortex (PFC). Rats received either saline or METH (10mg/kg, i.p. every 2h×4) followed by either saline or CEF (200mg/kg, i.p, every day×3) post-treatment. METH induced a significant depletion of dopamine and 5-HT in the NAc and PFC. Importantly, dopamine tissue content was completely restored in the NAc following CEF post-treatment. Additionally, METH caused a significant decrease in glutamate and glutamine tissue content in PFC, and this effect was attenuated by CEF post-treatment. These findings demonstrate for the first time the attenuating effects of CEF post-treatment on METH induced alterations in the tissue contents of dopamine, glutamate, and glutamine.

Prophylactic Antibiotic Therapy for Preventing Poststroke Infection

Infections, in particular pneumonia, are common complications in patients with acute stroke and are associated with a less favorable neurologic and functional outcome. Patients with severe stroke and dysphagia are at highest risk of infection. Experimental and clinical data suggest stroke-induced immunodeficiency as a major factor contributing to the high incidence of infection after stroke. Preclinical studies support the potential benefit of preventive antibiotic therapy in acute stroke for lowering the incidence of infection and improving clinical outcome. Several smaller clinical trials on preventive antibiotic therapy in patients with stroke conducted during the last 10 years yielded inconclusive results. Recently, 2 large, open-label, controlled trials failed to demonstrate an improved clinical outcome after preventive antibiotic therapy in patients with acute stroke treated in specialized stroke units. In the "Preventive Antibiotics in Stroke Study", antibiotic therapy lowered the rate of infection but did not influence outcome. In the STROKE-INF study, performed in patients with dysphagia after stroke, antibiotic therapy did not lower the incidence of pneumonia and had no prognostic significance. At present, preventive antibiotic therapy cannot be recommended as a therapeutic option for acute stroke.

Preventive Ceftriaxone in Patients with Stroke Treated with Intravenous Thrombolysis: Post Hoc Analysis of the Preventive Antibiotics in Stroke Study

BACKGROUND

The Preventive Antibiotics in Stroke Study (PASS), a randomized open-label masked endpoint trial, showed that preventive ceftriaxone did not improve functional outcome at 3 months in patients with acute stroke (adjusted common OR 0.95; 95% CI 0.82-1.09). Post-hoc analyses showed that among patients who received intravenous thrombolysis (IVT), patients who received ceftriaxone had a significantly better outcome as compared with the control group. This study aimed to gain more insight into the characteristics of these patients.

METHODS

In PASS, 2,550 patients were randomly assigned to preventive antibiotic treatment with ceftriaxone or standard care. In current post-hoc analysis, 836 patients who received IVT were included. Primary outcome included functional status on the modified Rankin Scale, analyzed with adjusted ordinal regression. Secondary outcomes included infection rate and symptomatic intracerebral hemorrhage (sICH) rate.

RESULTS

For all patients in PASS, the p value for the interaction between IVT and preventive ceftriaxone regarding functional outcome was 0.03. Of the 836 IVT-treated patients, 437 were administered ceftriaxone and 399 were allocated to the control group. Baseline characteristics were similar. In the IVT subgroup, preventive ceftriaxone was associated with a significant reduction in unfavorable outcome (adjusted common OR 0.77; 95% CI 0.61-0.99; p = 0.04). Mortality at 3 months was similar (OR 0.75; 95% CI 0.48-1.18). Preventive ceftriaxone was associated with a reduction in infections (OR 0.43; 95% CI 0.28-0.66), and a trend towards an increased risk for sICH (OR 3.09; 95% CI 0.85-11.31). Timing of ceftriaxone administration did not influence the outcome (aOR 1.00; 95% CI 0.98-1.03; p = 0.85).

CONCLUSIONS

According to the post-hoc analysis of PASS, preventive ceftriaxone may improve the functional outcome in IVT-treated patients with acute stroke, despite a trend towards an increased rate of post-IVT-sICH.

GLT-1-Dependent Disruption of CNS Glutamate Homeostasis and Neuronal Function by the Protozoan Parasite Toxoplasma gondii

The immune privileged nature of the CNS can make it vulnerable to chronic and latent infections. Little is known about the effects of lifelong brain infections, and thus inflammation, on the neurological health of the host. Toxoplasma gondii is a parasite that can infect any mammalian nucleated cell with average worldwide seroprevalence rates of 30%. Infection by Toxoplasma is characterized by the lifelong presence of parasitic cysts within neurons in the brain, requiring a competent immune system to prevent parasite reactivation and encephalitis. In the immunocompetent individual, Toxoplasma infection is largely asymptomatic, however many recent studies suggest a strong correlation with certain neurodegenerative and psychiatric disorders. Here, we demonstrate a significant reduction in the primary astrocytic glutamate transporter, GLT-1, following infection with Toxoplasma. Using microdialysis of the murine frontal cortex over the course of infection, a significant increase in extracellular concentrations of glutamate is observed. Consistent with glutamate dysregulation, analysis of neurons reveal changes in morphology including a reduction in dendritic spines, VGlut1 and NeuN immunoreactivity. Furthermore, behavioral testing and EEG recordings point to significant changes in neuronal output. Finally, these changes in neuronal connectivity are dependent on infection-induced downregulation of GLT-1 as treatment with the ß-lactam antibiotic ceftriaxone, rescues extracellular glutamate concentrations, neuronal pathology and function. Altogether, these data demonstrate that following an infection with T. gondii, the delicate regulation of glutamate by astrocytes is disrupted and accounts for a range of deficits observed in chronic infection.

The protozoan parasite Toxoplasma gondii infects a third of the world’s population and causes a chronic lifelong infection in the brain of the host. The consequences of such an infection are poorly understood. Here, we demonstrate that Toxoplasma infection can induce profound changes in astrocyte physiology leading to significant disruption of neuronal networks. Pathology can be rescued by upregulating the astrocytic glutamate transporter, GLT-1, restoring concentrations of extracellular glutamate and EEG power. We suggest that such global dysregulation of neurotransmitters should be considered when determining the effects of infection on the CNS.

Effects of Amoxicillin and Augmentin on Cystine-Glutamate Exchanger and Glutamate Transporter 1 Isoforms as well as Ethanol Intake in Alcohol-Preferring Rats

Alcohol dependence is associated with alteration of glutamate transport and glutamate neurotransmission. Glutamate transporter 1 (GLT-1) is a major transporter that regulates the majority of extracellular glutamate concentration, which is also regulated by cystine-glutamate exchanger (xCT). Importantly, we recently reported that amoxicillin and Augmentin (amoxicillin/clavulanate) upreglulated GLT-1 expression in nucleus accumbens (NAc) and prefrontal cortex (PFC) as well as reduced ethanol consumption in male P rats. In this study, we examined the effects of amoxicillin and Augmentin on GLT-1 isoforms (GLT-1a and GLT-1b), xCT, and glutamate/aspartate transporter (GLAST) expression in NAc and PFC as well as ethanol intake in male P rats. We found that both compounds significantly reduced ethanol intake, and increased GLT-1a, GLT-1b, and xCT expression in NAc. However, only Augmentin increased GLT-1a, GLT-1b, and xCT expression in PFC. There were no effects of these compounds on GLAST expression in NAc and PFC. These findings demonstrated that Augmentin and amoxicillin have the potential to upregulate GLT-1 isoforms and xCT expression, and consequently attenuate ethanol dependence.

Simultaneous recording of brain extracellular glucose, spike and local field potential in real time using an implantable microelectrode array with nano-materials

Glucose is the main substrate for neurons in the central nervous system. In order to efficiently characterize the brain glucose mechanism, it is desirable to determine the extracellular glucose dynamics as well as the corresponding neuroelectrical activity in vivo. In the present study, we fabricated an implantable microelectrode array (MEA) probe composed of platinum electrochemical and electrophysiology microelectrodes by standard micro electromechanical system (MEMS) processes. The MEA probe was modified with nano-materials and implanted in a urethane-anesthetized rat for simultaneous recording of striatal extracellular glucose, local field potential (LFP) and spike on the same spatiotemporal scale when the rat was in normoglycemia, hypoglycemia and hyperglycemia. During these dual-mode recordings, we observed that increase of extracellular glucose enhanced the LFP power and spike firing rate, while decrease of glucose had an opposite effect. This dual mode MEA probe is capable of examining specific spatiotemporal relationships between electrical and chemical signaling in the brain, which will contribute significantly to improve our understanding of the neuron physiology.

Ceftriaxone prevents the neurodegeneration and decreased neurogenesis seen in a Parkinson's disease rat model: An immunohistochemical and MRI study

Manganese-enhanced magnetic resonance imaging (MEMRI) is a widely used technique for detecting neuronal activity in the brain of a living animal. Ceftriaxone (CEF) has been shown to have neuroprotective effects in neurodegenerative diseases. The present study was aimed at clarifying whether, in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) rat model, the known CEF-induced neuronal protection was accompanied by neurogenesis and decreased loss of neuronal activity. After MPTP lesioning (day 0), the rats were treated with CEF (100mg/kg/day, i.p.) or saline for 15 days. They were then injected with MnCl2 (40mg/kg, i.p.) on day 13 and underwent a brain MRI scan on day 14, then the brain was taken for histological evaluation on day 15. The results showed that MPTP lesioning resulted in decreased neuronal activity and density in the nigrostriatal dopaminergic (DAergic) system and the hippocampal CA1, CA3, and dentate gyrus (DG) areas and reduced neurogenesis in the DG, but in hyperactivity in the subthalamic nucleus (STN). These neuronal changes were prevented by CEF treatment. Positive correlations between MEMRI R1 values and neuronal density in the hippocampus were evidenced. Neuronal densities in the hippocampus and SNc were positively correlated. In addition, the R1 value of the STN showed a positive correlation with its neuronal activity but showed a negative correlation with the density of DAergic neurons in the SNc. Therefore, MEMRI R1 value may serve as a good indicator for PD severity and the effect of treatment. To our knowledge, this is the first study showing that CEF prevents loss of neuronal activity and neurogenesis in the brain of PD rats. CEF may therefore have clinical potential in the treatment of PD.

Preclinical Rodent Toxicity Studies for Long Term Use of Ceftriaxone

A 6-month rodent toxicology and pharmacokinetic (PK) study was performed to provide supportive safety data for long-term use of intravenous ceftriaxone in a clinical trial in patients with amyotrophic lateral sclerosis (ALS). Ceftriaxone was administered by subcutaneous injection at up to 2 g/kg/day to Sprague-Dawley Crl:CD (SD) rats. Ceftriaxone was found to be safe and well tolerated. Specifically, no significant differences in body weight and food consumption were observed between the treatment and control groups. With the exception of in red cell parameters decrease, there were no ceftriaxone-related changes in hematology, coagulation, clinical chemistry and urinalysis parameters. Injection site trauma and associated reversible anemia, likely due to chronic blood loss at the injection site, were all attributable to subcutaneous route of administration. Cecum dilatation and some skin changes were reversible after recovery period, while bile duct dilatation, observed only in a few animals, persisted. Changes in the non-glandular stomach do not have a human correlate. The no-observed-adverse-effect dose level (NOAEL) was 0.5 g/kg/day ceftriaxone in both sexes. Ceftriaxone showed rapid absorption with half-life values ranging between 1 and 1.5 hours. Additionally, there was no evidence of accumulation and a virtually complete elimination by 16 hours after the last dose. Overall there were no toxicologically meaningful drug-related animal findings associated with the long-term administration (6 months) of ceftriaxone. These results support safety of long-term use of ceftriaxone in human clinical trials.

Astroglial cradle in the life of the synapse

Astroglial perisynaptic sheath covers the majority of synapses in the central nervous system. This glial coverage evolved as a part of the synaptic structure in which elements directly responsible for neurotransmission (exocytotic machinery and appropriate receptors) concentrate in neuronal membranes, whereas multiple molecules imperative for homeostatic maintenance of the synapse (transporters for neurotransmitters, ions, amino acids, etc.) are shifted to glial membranes that have substantially larger surface area. The astrocytic perisynaptic processes act as an 'astroglial cradle' essential for synaptogenesis, maturation, isolation and maintenance of synapses, representing the fundamental mechanism contributing to synaptic connectivity, synaptic plasticity and information processing in the nervous system.

Clavulanic acid enhances glutamate transporter subtype I (GLT-1) expression and decreases reinforcing efficacy of cocaine in mice

The β-lactam antibiotic ceftriaxone (CTX) reduces cocaine reinforcement and relapse in preclinical assays through a mechanism involving activation of glutamate transporter subtype 1 (GLT-1). However, its poor brain penetrability and intravenous administration route may limit its therapeutic utility for indications related to CNS diseases. An alternative is clavulanic acid (CA), a structural analog of CTX that retains the β-lactam core required for GLT-1 activity but displays enhanced brain penetrability and oral activity relative to CTX. Here, we tested the hypothesis that CA (1, 10 mg/kg ip) would enhance GLT-1 expression and decrease cocaine self-administration (SA) in mice, but at lower doses than CTX. Experiments revealed that GLT-1 transporter expression in the nucleus accumbens of mice treated with repeated CA (1, 10 mg/kg) was enhanced relative to saline-treated mice. Repeated CA treatment (1 mg/kg) reduced the reinforcing efficacy of cocaine (0.56 mg/kg/inf) in mice maintained on a progressive-ratio (PR) schedule of reinforcement but did not affect acquisition of cocaine SA under fixed-ratio responding or acquisition or retention of learning. These findings suggest that the β-lactamase inhibitor CA can activate the cellular glutamate reuptake system in the brain reward circuit and reduce cocaine's reinforcing efficacy at 100-fold lower doses than CTX.

Multifaceted roles for astrocytes in spreading depolarization: A target for limiting spreading depolarization in acute brain injury?

Spreading depolarizations (SDs) are coordinated waves of synchronous depolarization, involving large numbers of neurons and astrocytes as they spread slowly through brain tissue. The recent identification of SDs as likely contributors to pathophysiology in human subjects has led to a significant increase in interest in SD mechanisms, and possible approaches to limit the numbers of SDs or their deleterious consequences in injured brain. Astrocytes regulate many events associated with SD. SD initiation and propagation is dependent on extracellular accumulation of K(+) and glutamate, both of which involve astrocytic clearance. SDs are extremely metabolically demanding events, and signaling through astrocyte networks is likely central to the dramatic increase in regional blood flow that accompanies SD in otherwise healthy tissues. Astrocytes may provide metabolic support to neurons following SD, and may provide a source of adenosine that inhibits neuronal activity following SD. It is also possible that astrocytes contribute to the pathophysiology of SD, as a consequence of excessive glutamate release, facilitation of NMDA receptor activation, brain edema due to astrocyte swelling, or disrupted coupling to appropriate vascular responses after SD. Direct or indirect evidence has accumulated implicating astrocytes in many of these responses, but much remains unknown about their specific contributions, especially in the context of injury. Conversion of astrocytes to a reactive phenotype is a prominent feature of injured brain, and recent work suggests that the different functional properties of reactive astrocytes could be targeted to limit SDs in pathophysiological conditions.

Synergistic effects of ceftriaxone and erythropoietin on neuronal and behavioral deficits in an MPTP-induced animal model of Parkinson's disease dementia

Both ceftriaxone (CEF) and erythropoietin (EPO) show neuroprotection and cognitive improvement in neurodegenerative disease. The present study was aimed at clarifying whether combined treatment with CEF and EPO (CEF+EPO) had superior neuroprotective and behavioral effects than treatment with CEF or EPO alone in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) rat model. The rats were injected with CEF (5 mg/kg/day), EPO (100 IU/kg/day), or CEF+EPO after MPTP lesioning and underwent the bar-test, T-maze test, and object recognition test, then the brains were taken for histological evaluation. MPTP lesioning resulted in deficits in working memory and in object recognition, but the cognitive deficits were markedly reduced or eliminated in rats treated with CEF or CEF+EPO, with the combination having a greater effect. Lesioning also caused neurodegeneration in the nigrostriatal dopaminergic system and the hippocampal CA1 area and these changes were reduced or eliminated by treatment with CEF, EPO, or CEF+EPO, with the combination having a greater effect than single treatment in the densities of DAergic terminals in the striatum and neurons in the hippocampal CA1 area. Thus, compared to treatment with CEF or EPO alone, combined treatment with CEF+EPO had a greater inhibitory effect on the lesion-induced behavioral and neuronal deficits. To our knowledge, this is the first study showing a synergistic effect of CEF and EPO on neuroprotection and improvement in cognition in a PD rat model. Combined CEF and EPO treatment may have clinical potential for the treatment of the dementia associated with PD.

Aberrant RNA homeostasis in amyotrophic lateral sclerosis: potential for new therapeutic targets?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive motor neuron degeneration. The disease pathogenesis is multifaceted in that multiple cellular and molecular pathways have been identified as contributors to the disease progression. Consequently, numerous therapeutic targets have been pursued for clinical development, unfortunately with little success. The recent discovery of mutations in RNA modulating genes such as TARDBP/TDP-43, FUS/TLS or C9ORF72 changed our understanding of neurodegenerative mechanisms in ALS and introduced the role of dysfunctional RNA processing as a significant contributor to disease pathogenesis. This article discusses the latest findings on such RNA toxicity pathways in ALS and potential novel therapeutic approaches.