Thinking outside the cleft to understand synaptic activity: contribution of the cystine-glutamate antiporter (System xc-) to normal and pathological glutamatergic signaling

Ferritinophagy and Ferroptosis in Cerebral Ischemia Reperfusion Injury

Cerebral ischemia-reperfusion injury (CIRI) is the second leading cause of death worldwide, posing a huge risk to human life and health. Therefore, investigating the pathogenesis underlying CIRI and developing effective treatments are essential. Ferroptosis is an iron-dependent mode of cell death, which is caused by disorders in iron metabolism and lipid peroxidation. Previous studies demonstrated that ferroptosis is also a form of autophagic cell death, and nuclear receptor coactivator 4(NCOA4) mediated ferritinophagy was found to regulate ferroptosis by interfering with iron metabolism. Ferritinophagy and ferroptosis are important pathogenic mechanisms in CIRI. This review mainly summarizes the link and regulation between ferritinophagy and ferroptosis and further discusses their mechanisms in CIRI. In addition, the potential treatment methods targeting ferritinophagy and ferroptosis for CIRI are presented, providing new ideas for the prevention and treatment of clinical CIRI in the future.

Recent advances in potential therapeutic targets of ferroptosis‑associated pathways for the treatment of stroke (Review)

Stroke is a severe neurological disease that is associated with high rates of morbidity and mortality, and the underlying pathological processes are complex. Ferroptosis fulfills a significant role in the progression and treatment of stroke. It is well established that ferroptosis is a type of programmed cell death that is distinct from other forms or types of cell death. The process of ferroptosis involves multiple signaling pathways and regulatory mechanisms that interact with mechanisms inherent to stroke development. Inducers and inhibitors of ferroptosis have been shown to exert a role in the onset of this cell death process. Furthermore, it has been shown that interfering with ferroptosis affects the occurrence of stroke, indicating that targeting ferroptosis may offer a promising therapeutic approach for treating patients of stroke. Hence, the present review aimed to summarize the latest progress that has been made in terms of using therapeutic interventions for ferroptosis as treatment targets in cases of stroke. It provides an overview of the relevant pathways and molecular mechanisms that have been investigated in recent years, highlighting the roles of inducers and inhibitors of ferroptosis in stroke. Additionally, the intervention potential of various types of Traditional Chinese Medicine is also summarized. In conclusion, the present review provides a comprehensive overview of the potential therapeutic targets afforded by ferroptosis‑associated pathways in stroke, offering new insights into how ferroptosis may be exploited in the treatment of stroke.

Ferroptosis: a potential bridge linking gut microbiota and chronic kidney disease

Ferroptosis is a novel form of lipid peroxidation-driven, iron-dependent programmed cell death. Various metabolic pathways, including those involved in lipid and iron metabolism, contribute to ferroptosis regulation. The gut microbiota not only supplies nutrients and energy to the host, but also plays a crucial role in immune modulation and metabolic balance. In this review, we explore the metabolic pathways associated with ferroptosis and the impact of the gut microbiota on host metabolism. We subsequently summarize recent studies on the influence and regulation of ferroptosis by the gut microbiota and discuss potential mechanisms through which the gut microbiota affects ferroptosis. Additionally, we conduct a bibliometric analysis of the relationship between the gut microbiota and ferroptosis in the context of chronic kidney disease. This analysis can provide new insights into the current research status and future of ferroptosis and the gut microbiota.

ATF3-CBS signaling axis coordinates ferroptosis and tumorigenesis in colorectal cancer

The induction of ferroptosis is promising for cancer therapy. However, the mechanisms enabling cancer cells to evade ferroptosis, particularly in low-cystine environments, remain elusive. Our study delves into the intricate regulatory mechanisms of Activating transcription factor 3 (ATF3) on Cystathionine β-synthase (CBS) under cystine deprivation stress, conferring resistance to ferroptosis in colorectal cancer (CRC) cells. Additionally, our findings establish a positively correlation between this signaling axis and CRC progression, suggesting its potential as a therapeutic target. Mechanistically, ATF3 positively regulates CBS to resist ferroptosis under cystine deprivation stress. In contrast, the suppression of CBS sensitizes CRC cells to ferroptosis through targeting the mitochondrial tricarboxylic acid (TCA) cycle. Notably, our study highlights that the ATF3-CBS signaling axis enhances ferroptosis-based CRC cancer therapy. Collectively, the findings reveal that the ATF3-CBS signaling axis is the primary feedback pathway in ferroptosis, and blocking this axis could be a potential therapeutic approach for colorectal cancer.

Baicalein improves renal interstitial fibrosis by inhibiting the ferroptosis in vivo and in vitro

Evidence indicates that Baicalein can ameliorate renal interstitial fibrosis by inducing myofibroblast apoptosis and inhibit the RLS3-induced ferroptosis in melanocytes. However, the relationship between renal interstitial fibrosis and anti-ferroptosis affected by Baicalein remains unclear. In our study, the anti-fibrosis and anti-ferroptosis effects of Baicalein were assessed in a rat model induced by the UUO method in vivo, and the effects of Baicalein on Erastin-induced ferroptosis of renal MPC-5 cells were examined by Western blot of fibrosis-related and ferroptosis-related proteins in vitro. In the UUO-induced rat model, Baicalein decreased kidney weight loss, improved renal function assessed the biomarks of urinary albumin excretion, serum creatine, and BUN levels, and reduced renal tubular injury. Furthermore, Baicalein inhibited renal ferroptosis by reducing ROS and MDA levels and increasing SOD and GSH levels in the UUO rat model. In addition, Baicalein potently reduced the expression of fibrosis-related proteins such as TGF-β1, a-SMA, and Smad-2 to prevent renal interstitial fibrosis, and increased the expression of ferroptosis-related proteins such as SLC7A11, GPX4, and FTH to inhibit ferroptosis both in vitro and in vivo. Taken together, Baicalein exerts anti-fibrosis activity by reducing the ferroptosis response on the UUO-induced rat model and renal MPC5 cells. Therefore, Baicalein, as a novel therapeutic method on kidney diseases with strong activity in suppressing ferroptosis, could be a potential alternative treatment for renal interstitial fibrosis.

Irisin attenuates type 1 diabetic cardiomyopathy by anti-ferroptosis via SIRT1-mediated deacetylation of p53

BACKGROUND

Diabetic cardiomyopathy (DCM) is a serious complication in patients with type 1 diabetes mellitus (T1DM), which still lacks adequate therapy. Irisin, a cleavage peptide off fibronectin type III domain-containing 5, has been shown to preserve cardiac function in cardiac ischemia-reperfusion injury. Whether or not irisin plays a cardioprotective role in DCM is not known.

METHODS AND RESULTS

T1DM was induced by multiple low-dose intraperitoneal injections of streptozotocin (STZ). Our current study showed that irisin expression/level was lower in the heart and serum of mice with STZ-induced TIDM. Irisin supplementation by intraperitoneal injection improved the impaired cardiac function in mice with DCM, which was ascribed to the inhibition of ferroptosis, because the increased ferroptosis, associated with increased cardiac malondialdehyde (MDA), decreased reduced glutathione (GSH) and protein expressions of solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4), was ameliorated by irisin. In the presence of erastin, a ferroptosis inducer, the irisin-mediated protective effects were blocked. Mechanistically, irisin treatment increased Sirtuin 1 (SIRT1) and decreased p53 K382 acetylation, which decreased p53 protein expression by increasing its degradation, consequently upregulated SLC7A11 and GPX4 expressions. Thus, irisin-mediated reduction in p53 decreases ferroptosis and protects cardiomyocytes against injury due to high glucose.

CONCLUSION

This study demonstrated that irisin could improve cardiac function by suppressing ferroptosis in T1DM via the SIRT1-p53-SLC7A11/GPX4 pathway. Irisin may be a therapeutic approach in the management of T1DM-induced cardiomyopathy.

The role of regulated necrosis in diabetes and its complications

Morphologically, cell death can be divided into apoptosis and necrosis. Apoptosis, which is a type of regulated cell death, is well tolerated by the immune system and is responsible for hemostasis and cellular turnover under physiological conditions. In contrast, necrosis is defined as a form of passive cell death that leads to a dramatic inflammatory response (also referred to as necroinflammation) and causes organ dysfunction under pathological conditions. Recently, a novel form of cell death named regulated necrosis (such as necroptosis, pyroptosis, and ferroptosis) was discovered. Distinct from apoptosis, regulated necrosis is modulated by multiple internal or external factors, but meanwhile, it results in inflammation and immune response. Accumulating evidence has indicated that regulated necrosis is associated with multiple diseases, including diabetes. Diabetes is characterized by hyperglycemia caused by insulin deficiency and/or insulin resistance, and long-term high glucose leads to various diabetes-related complications. Here, we summarize the mechanisms of necroptosis, pyroptosis, and ferroptosis, and introduce recent advances in characterizing the associations between these three types of regulated necrosis and diabetes and its complications.

Using Redox Proteomics to Gain New Insights into Neurodegenerative Disease and Protein Modification

Antioxidant defenses in biological systems ensure redox homeostasis, regulating baseline levels of reactive oxygen and nitrogen species (ROS and RNS). Oxidative stress (OS), characterized by a lack of antioxidant defenses or an elevation in ROS and RNS, may cause a modification of biomolecules, ROS being primarily absorbed by proteins. As a result of both genome and environment interactions, proteomics provides complete information about a cell's proteome, which changes continuously. Besides measuring protein expression levels, proteomics can also be used to identify protein modifications, localizations, the effects of added agents, and the interactions between proteins. Several oxidative processes are frequently used to modify proteins post-translationally, including carbonylation, oxidation of amino acid side chains, glycation, or lipid peroxidation, which produces highly reactive alkenals. Reactive alkenals, such as 4-hydroxy-2-nonenal, are added to cysteine (Cys), lysine (Lys), or histidine (His) residues by a Michael addition, and tyrosine (Tyr) residues are nitrated and Cys residues are nitrosylated by a Michael addition. Oxidative and nitrosative stress have been implicated in many neurodegenerative diseases as a result of oxidative damage to the brain, which may be especially vulnerable due to the large consumption of dioxygen. Therefore, the current methods applied for the detection, identification, and quantification in redox proteomics are of great interest. This review describes the main protein modifications classified as chemical reactions. Finally, we discuss the importance of redox proteomics to health and describe the analytical methods used in redox proteomics.

Safety and tolerability of topiramate and N-acetyl cysteine combination in individuals with alcohol use disorder: a 12 week, randomized, double-blind, pilot study

Topiramate (TPM), a GABA/glutamate modulator, has shown positive results for treating alcohol use disorder (AUD), but causes significant cognitive adverse effects. TPM causes cognitive side effects by reducing glutathione levels in the frontal lobe. N-acetyl cysteine (NAC) increases level of intracellular glutathione. We hypothesized that combining NAC with TPM may mitigate the possible cognitive side effects of TPM, as well as working synergistically in reducing alcohol consumption more efficaciously than using TPM alone. A 12-week, double-blind randomized trial assessing the effects of combining NAC (1200 mg/day) with TPM (200 mg/day) vs TPM alone (i) cognitive side effects caused by TPM, (ii) percentage of heavy drinking days (PHDD) and percentage of days abstinent (PDA) using weekly calendar, and (iii) craving outcomes using the obsessive-compulsive drinking scale. Seventeen participants were randomized into the study (nine received TPM + NAC and eight matching TPM + Placebo). Cognitive adverse events were not significantly different between the treatment arms (P = 0.581). There was no difference in PHDD (P = 0.536) and in PDA over the entire study period (P = 0.892). However, both treatment groups at study end, compared with the baseline, significantly reduced their PHDD and increased their PDA. As for cravings: TPM + NAC group has shown higher level in automaticity of drinking (P = 0.029) and interference due to drinking (P = 0.014) subscales compared with the TPM + Placebo group. No difference was observed between groups in terms of Drinking Obsessions and Alcohol Consumption subscales. This pilot study indicates that combining NAC with TPM is overall safe, but the addition of NAC has no significant benefit over placebo in the incidence of TPM-related cognitive impairment, and alcohol drinking. Furthermore, craving outcomes may become worse with the addition of NAC.

Potential applications of ferroptosis inducers and regulatory molecules in hematological malignancy therapy

Ferroptosis, a novel form of iron-dependent cell death, has emerged as a potential avenue for promoting tumor cell death by causing cell membrane rupture and the accumulation of lipid peroxides (LPO) in the cell. Since its discovery in 2012, extensive research has been conducted to explore the mechanism of ferroptosis inducers, including erastin, sulfasalazine, and sorafenib. These compounds inhibit system XC-, while Ras-selective lethal small molecule 3 (RSL3) and FION2 specifically target GPX4 to promote ferroptosis. Therefore, targeting ferroptosis presents a promising therapeutic approach for malignant tumors. While the study of ferroptosis in solid tumors has made significant progress, there is limited information available on its role in hematological tumors. This review aims to summarize the molecular mechanisms of ferroptosis inducers and discuss their clinical applications in hematological malignancies. Furthermore, the identification of non-coding RNAs (ncRNAs) and genes that regulate key molecules in the ferroptosis pathway could provide new targets and establish a molecular theoretical foundation for exploring novel ferroptosis inducers in hematological malignancies.

Iron and copper: critical executioners of ferroptosis, cuproptosis and other forms of cell death

Regulated cell death (RCD) is a regulable cell death that involves well-organized signaling cascades and molecular mechanisms. RCD is implicated in fundamental processes such as organ production and tissue remodeling, removing superfluous structures or cells, and regulating cell numbers. Previous studies have not been able to reveal the complete mechanisms, and novel methods of RCD are constantly being proposed. Two metal ions, iron (Fe) and copper (Cu) are essential factors leading to RCDs that not only induce ferroptosis and cuproptosis, respectively but also lead to cell impairment and eventually diverse cell death. This review summarizes the direct and indirect mechanisms by which Fe and Cu impede cell growth and the various forms of RCD mediated by these two metals. Moreover, we aimed to delineate the interrelationships between these RCDs with the distinct pathways of ferroptosis and cuproptosis, shedding light on the complex and intricate mechanisms that govern cellular survival and death. Finally, the prospects outlined in this review suggest a novel approach for investigating cell death, which may involve integrating current therapeutic strategies and offer a promising solution to overcome drug resistance in certain diseases. Video Abstract.

Changes in glutamate and glutamine distributions in the retinas of cystine/glutamate antiporter knockout mice

Purpose

The cystine/glutamate antiporter is involved in the export of intracellular glutamate in exchange for extracellular cystine. Glutamate is the main neurotransmitter in the retina and plays a key metabolic role as a major anaplerotic substrate in the tricarboxylic acid cycle to generate adenosine triphosphate (ATP). In addition, glutamate is also involved in the outer plexiform glutamate-glutamine cycle, which links photoreceptors and supporting Müller cells and assists in maintaining photoreceptor neurotransmitter supply. In this study, we investigated the role of xCT, the light chain subunit responsible for antiporter function, in glutamate pathways in the mouse retina using an xCT knockout mouse. As xCT is a glutamate exporter, we hypothesized that loss of xCT function may influence the presynaptic metabolism of photoreceptors and postsynaptic levels of glutamate.

Methods

Retinas of C57BL/6J wild-type (WT) and xCT knockout (KO) mice of either sex were analyzed from 6 weeks to 12 months of age. Biochemical assays were used to determine the effect of loss of xCT on glycolysis and energy metabolism by measuring lactate dehydrogenase activity and ATP levels. Next, biochemical assays were used to measure whole-tissue glutamate and glutamine levels, while silver-intensified immunogold labeling was performed on 6-week and 9-month-old retinas to visualize and quantify the distribution of glutamate, glutamine, and related neurochemical substrates gamma-aminobutyric acid (GABA) and glycine in the different layers of the retina.

Results

Biochemical analysis revealed that loss of xCT function did not alter the lactate dehydrogenase activity, ATP levels, or glutamate and glutamine contents in whole retinas in any age group. However, at 6 weeks of age, the xCT KO retinas revealed altered glutamate distribution compared with the age-matched WT retinas, with accumulation of glutamate in the photoreceptors and outer plexiform layer. In addition, at 6 weeks and 9 months of age, the xCT KO retinas also showed altered glutamine distribution compared with the WT retinas, with glutamine labeling significantly decreased in Müller cell bodies. No significant difference in GABA or glycine distribution were found between the WT and xCT KO retinas at 6 weeks or 9 months of age.

Conclusion

Loss of xCT function results in glutamate metabolic disruption through the accumulation of glutamate in photoreceptors and a reduced uptake of glutamate by Müller cells, which in turn decreases glutamine production. These findings support the idea that xCT plays a role in the presynaptic metabolism of photoreceptors and postsynaptic levels of glutamate and derived neurotransmitters in the retina.

Clavulanic Acid Improves Memory Dysfunction and Anxiety Behaviors through Upregulating Glutamatergic Transporters in the Nucleus Accumbens of Mice Repeatedly Exposed to Khat Extract

Khat (Catha edulis) is an evergreen shrub whose buds and leaves give a state of delight and euphoria when chewed. Cathinone, an amphetamine-like stimulant that is among the active ingredients in khat, is able to downregulate glutamate transporter subtype I (GLT-1). Neurobehavioral dysfunctions such as altered locomotor activity, anorexia, and nociception have been observed in animals exposed to cathinone. Interestingly, treatment with a β-lactam antibiotic such as ceftriaxone, which upregulates GLT-1, normalizes cathinone-induced conditioned place preference, and alters repetitive movements in rats. However, little is known about the role of the glutamatergic system in memory dysfunction and anxiety-like behaviors in mice exposed to khat. We found here that clavulanic acid, a β-lactam-containing compound and GLT-1 upregulator, would modulate the neurobehavioral changes, including memory impairment and anxiety-like behaviors, associated with repeated exposure of mice to khat. Our data supported that clavulanic acid could improve memory impairment and anxiety-like behaviors through upregulating GLT-1 in the nucleus accumbens (NAc), an effect abolished with a selective GLT-1 blocker. This upregulation was associated with restored glutamate/cystine antiporter expression in the NAc using a Western blotting assay. Cathine and cathinone were identified in khat extract using the gas chromatography technique. Our work provides preclinical insight into the efficacy of β-lactam-containing compounds for the attenuation of neurobehavioral changes induced by khat exposure.

The Ying and Yang of Hydrogen Sulfide as a Paracrine/Autocrine Agent in Neurodegeneration: Focus on Amyotrophic Lateral Sclerosis

Ever since its presence was reported in the brain, the nature and role of hydrogen sulfide (H2S) in the Central Nervous System (CNS) have changed. Consequently, H2S has been elected as the third gas transmitter, along with carbon monoxide and nitric oxide, and a number of studies have focused on its neuromodulatory and protectant functions in physiological conditions. The research on H2S has highlighted its many facets in the periphery and in the CNS, and its role as a double-faced compound, switching from protective to toxic depending on its concentration. In this review, we will focus on the bell-shaped nature of H2S as an angiogenic factor and as a molecule released by glial cells (mainly astrocytes) and non-neuronal cells acting on the surrounding environment (paracrine) or on the releasing cells themselves (autocrine). Finally, we will discuss its role in Amyotrophic Lateral Sclerosis, a paradigm of a neurodegenerative disease.

N-acetylcysteine Pharmacology and Applications in Rare Diseases-Repurposing an Old Antioxidant

N-acetylcysteine (NAC), a precursor of cysteine and, thereby, glutathione (GSH), acts as an antioxidant through a variety of mechanisms, including oxidant scavenging, GSH replenishment, antioxidant signaling, etc. Owing to the variety of proposed targets, NAC has a long history of use as a prescription product and in wide-ranging applications that are off-label as an over-the-counter (OTC) product. Despite its discovery in the early 1960s and its development for various indications, systematic clinical pharmacology explorations of NAC pharmacokinetics (PK), pharmacodynamic targets, drug interactions, and dose-ranging are sorely limited. Although there are anecdotal instances of NAC benefits in a variety of diseases, a comprehensive review of the use of NAC in rare diseases does not exist. In this review, we attempt to summarize the existing literature focused on NAC explorations in rare diseases targeting mitochondrial dysfunction along with the history of NAC usage, approved indications, mechanisms of action, safety, and PK characterization. Further, we introduce the research currently underway on other structural derivatives of NAC and acknowledge the continuum of efforts through pre-clinical and clinical research to facilitate further therapeutic development of NAC or its derivatives for rare diseases.

Basic mechanisms and novel potential therapeutic targets for ferroptosis in acute myeloid leukemia

Ferroptosis is a form of cell death that is regulated by iron and characterized by the buildup of lipid peroxides (LPO) and subsequent rupture of the cell membrane. The molecular mechanisms of ferroptosis involve metabolic pathways related to iron, lipids, and amino acids, which contribute to the production of lipid reactive oxygen species (ROS). In recent years, there has been increasing attention on the occurrence of ferroptosis in various diseases. Ferroptosis has been found to play a crucial role in cardiovascular diseases, digestive diseases, respiratory and immunological diseases, and particularly in malignancies. However, there is still a lack of studies on ferroptosis in acute myeloid leukemia (AML). This paper provides a comprehensive review of the mechanism of ferroptosis and its regulatory molecules and therapeutic agents in AML. It also evaluates the relationship between ferroptosis-related genes (FRGs), non-coding RNAs (ncRNAs), and prognosis to develop prognostic molecular models in AML. The study also explores the association between ferroptosis and immune infiltration in AML, to identify novel potential target regimens for AML.

COCHLEAR GLIAL CELLS MEDIATES GLUTAMATE UPTAKE THROUGH A SODIUM-INDEPENDENT TRANSPORTER

Since glutamate is the primary excitatory neurotransmitter in the mammalian cochlea, the mechanisms for the removal of glutamate from the synaptic and extrasynaptic spaces are critical for maintaining normal function of this region. Glial cells of inner ear are crucial for regulation of synaptic transmission throughout since it closely interacts with neurons along the entire auditory pathway, however little is known about the activity and expression of glutamate transporters in the cochlea. In this study, using primary cochlear glial cells cultures obtained from newborn Balb/C mice, we determined the activity of a sodium-dependent and sodium-independent glutamate uptake mechanisms by means of High Performance Liquid Chromatography. The sodium-independent glutamate transport has a prominent contribution in cochlear glial cells which is similar to what has been demonstrated in other sensory organs, but it is not found in tissues less susceptible to continuous glutamate-mediated injuries. Our results showed that x_CG^- system is expressed in CGCs and is the main responsible for sodium-independent glutamate uptake. The identification and characterization of the x_CG^- transporter in the cochlea suggests a possible role of this transporter in the control of extracellular glutamate concentrations and regulation of redox state, that may aid in the preservation of auditory function.

Early onset of age-related changes in the retina of cystine/glutamate antiporter knockout mice

To determine the role of the cystine/glutamate antiporter on retinal structure and function, retinas of C57Bl/6J wild-type and xCT knockout mice, lacking the xCT subunit of the cystine/glutamate antiporter were examined from 6 weeks to 12 months of age. Fundoscopy, optical coherence tomography (OCT), and whole mount retinal autofluorescence imaging were used to visualise age-related retinal spots. Glial fibrillary acidic protein (GFAP) immunolabelling was used to assess retinal stress. Retinal function was evaluated using full-field and focal electroretinograms. Examinations revealed retinal spots in both wild-type and xCT knockout mice with the number of spots greater at 9 months in the knockout compared to wild-type. OCT confirmed these discrete spots were located at the retinal pigment epithelium (RPE)-photoreceptor junction and did not label with drusen markers. Whole mount lambda scans of the 9 month xCT knockout retinas revealed that the photoreceptor autofluorescence matched the spots, suggesting these spots were retinal debris. GFAP labelling was increased in knockout retinas compared to wild-type indicative of retinal stress, and the discrete spots were associated with migration of microglia/macrophages to the RPE-retina intersection. OCT revealed that the superior retina was thinner at 9 months in knockout compared to wild-type mice due to changes to the outer nuclear and photoreceptor layers. While global retinal function was not affected by loss of xCT, focal changes in retinal function were detected in areas where spots were present. Tother these results suggest that the xCT KO mice exhibit features of accelerated ageing and suggests that this mouse model may be useful for studying the underlying cellular pathways in retinal ageing.

Astrocyte regulation of synaptic signaling in psychiatric disorders

Over the last 15 years, the field of neuroscience has evolved toward recognizing the critical role of astroglia in shaping neuronal synaptic activity and along with the pre- and postsynapse is now considered an equal partner in tripartite synaptic transmission and plasticity. The relative youth of this recognition and a corresponding deficit in reagents and technologies for quantifying and manipulating astroglia relative to neurons continues to hamper advances in understanding tripartite synaptic physiology. Nonetheless, substantial advances have been made and are reviewed herein. We review the role of astroglia in synaptic function and regulation of behavior with an eye on how tripartite synapses figure into brain pathologies underlying behavioral impairments in psychiatric disorders, both from the perspective of measures in postmortem human brains and more subtle influences on tripartite synaptic regulation of behavior in animal models of psychiatric symptoms. Our goal is to provide the reader a well-referenced state-of-the-art understanding of current knowledge and predict what we may discover with deeper investigation of tripartite synapses using reagents and technologies not yet available.

Effects of Iron on Efficacy of Photodynamic Therapy Using Photolon in a Mouse Model of CT26 Colon Cancer

BACKGROUND

Photodynamic therapy (PDT) -a minimally invasive anti-cancer therapy-is undergoing experimental studies to increase its anti-cancer effects. This study investigated the influence of iron on the anti-cancer effects of PDT.

METHODS

PDT was performed in a cancer-bearing mouse model, which was created by using a murine colon carcinoma (CT26) cell line after administration of Photolon and iron. Tumor volume and the results of TdT-mediated dUTP-biotin nick end labeling (TUNEL), 8-OHdG, and TBARS assays were used to measure anti-cancer effect.

RESULTS

On day 14, tumor volume had increased by 49% in the PDT group and decreased by 72% in the iron+PDT group. The percentage of TUNEL-positive cells in tumor tissues was 45% in the PDT group and 69% in the iron+PDT group, suggesting that the proportion of TUNEL-positive cells had increased in the iron+PDT group. The 8-OHdG content in tumor tissues was 33% higher in the iron+PDT group than in the PDT group. The TBARS content in tumor tissues was 46% higher in the iron+PDT group than in the PDT group.

CONCLUSIONS

Iron enhances the anti-cancer effect of PDT using Photolon, most likely by increasing oxidative damage.

Longitudinal evaluation of neuroinflammation and oxidative stress in a mouse model of Alzheimer disease using positron emission tomography

Background

Validation of new biomarkers of Alzheimer disease (AD) is crucial for the successful development and implementation of treatment strategies. Additional to traditional AT(N) biomarkers, neuroinflammation biomarkers, such as translocator protein (TSPO) and cystine/glutamine antiporter system (x_c^-), could be considered when assessing AD progression. Herein, we report the longitudinal investigation of [¹⁸F]DPA-714 and [¹⁸F]FSPG for their ability to detect TSPO and x_c^- biomarkers, respectively, in the 5xFAD mouse model for AD.

Methods

Expression of TSPO and x_c^- system was assessed longitudinally (2–12 months of age) on 5xFAD mice and their respective controls by positron emission tomography (PET) imaging using radioligands [¹⁸F]DPA-714 and [¹⁸F]FSPG. In parallel, in the same mice, amyloid-β plaque deposition was assessed with the amyloid PET radiotracer [¹⁸F]florbetaben. In vivo findings were correlated to ex vivo immunofluorescence staining of TSPO and x_c^- in microglia/macrophages and astrocytes on brain slices. Physiological changes of the brain tissue were assessed by magnetic resonance imaging (MRI) in 12-month-old mice.

Results

PET studies showed a significant increase in the uptake of [¹⁸F]DPA-714 and [¹⁸F]FSPG in the cortex, hippocampus, and thalamus in 5xFAD but not in WT mice over time. The results correlate with Aβ plaque deposition. Ex vivo staining confirmed higher TSPO overexpression in both, microglia/macrophages and astrocytes, and overexpression of x_c^- in non-glial cells of 5xFAD mice. Additionally, the results show that Aβ plaques were surrounded by microglia/macrophages overexpressing TSPO. MRI studies showed significant tissue shrinkage and microstructural alterations in 5xFAD mice compared to controls.

Conclusions

TSPO and x_c^- overexpression can be assessed by [¹⁸F]DPA-714 and [¹⁸F]FSPG, respectively, and correlate with the level of Aβ plaque deposition obtained with a PET amyloid tracer. These results position the two tracers as promising imaging tools for the evaluation of disease progression.

Graphical abstract

Longitudinal in vivo study in the 5xFAD mouse model shows that TSPO and oxidative stress assessment through [¹⁸F]DPA-714 and [¹⁸F]FSPG-PET imaging, respectively, could serve as a potential tool for the evaluation of Alzheimer disease progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01016-5.

Structural investigation of human cystine/glutamate antiporter system xc− (Sxc−) using homology modeling and molecular dynamics

The cystine/glutamate antiporter system xc− (Sxc−) belongs to the SLC7 family of plasma membrane transporters. It exports intracellular glutamate along the latter’s concentration gradient as a driving force for cellular uptake of cystine. Once imported, cystine is mainly used for the production of glutathione, a tripeptide thiol crucial in maintenance of redox homeostasis and protection of cells against oxidative stress. Overexpression of Sxc− has been found in several cancer cells, where it is thought to counteract the increased oxidative stress. In addition, Sxc− is important in the central nervous system, playing a complex role in regulating glutamatergic neurotransmission and glutamate toxicity. Accordingly, this transporter is considered a potential target for the treatment of cancer as well as neurodegenerative diseases. Till now, no specific inhibitors are available. We herein present four conformations of Sxc− along its transport pathway, obtained using multi-template homology modeling and refined by means of Molecular Dynamics. Comparison with a very recently released cryo-EM structure revealed an excellent agreement with our inward-open conformation. Intriguingly, our models contain a structured N-terminal domain that is unresolved in the experimental structures and is thought to play a gating role in the transport mechanism of other SLC7 family members. In contrast to the inward-open model, there is no direct experimental counterpart for the other three conformations we obtained, although they are in fair agreement with the other stages of the transport mechanism seen in other SLC7 transporters. Therefore, our models open the prospect for targeting alternative Sxc− conformations in structure-based drug design efforts.

Is depression the missing link between inflammatory mediators and cancer?

Patients with cancer are at greater risk of developing depression in comparison to the general population and this is associated with serious adverse effects, such as poorer quality of life, worse prognosis and higher mortality. Although the relationship between depression and cancer is now well established, a common underlying pathophysiological mechanism between the two conditions is yet to be elucidated. Existing theories of depression, based on monoamine neurotransmitter system dysfunction, are insufficient as explanations of the disorder. Recent advances have implicated neuroinflammatory mechanisms in the etiology of depression and it has been demonstrated that inflammation at a peripheral level may be mirrored centrally in astrocytes and microglia serving to promote chronic levels of inflammation in the brain. Three major routes to depression in cancer in which proinflammatory mediators are implicated, seem likely. Activation of the kynurenine pathway involving cytokines, increases tryptophan catabolism, resulting in diminished levels of serotonin which is widely acknowledged as being the hallmark of depression. It also results in neurotoxic effects on brain regions thought to be involved in the evolution of major depression. Proinflammatory mediators also play a crucial role in impairing regulatory glucocorticoid mediated feedback of the hypothalamic-pituitary-adrenal axis, which is activated by stress and considered to be involved in both depression and cancer. The third route is via the glutamatergic pathway, whereby glutamate excitotoxicity may lead to depression associated with cancer. A better understanding of the mechanisms underlying these dysregulated and other newly emerging pathways may provide a rationale for therapeutic targeting, serving to improve the care of cancer patients.

Effects of a Novel Beta Lactam Compound, MC-100093, on the Expression of Glutamate Transporters/Receptors and Ethanol Drinking Behavior of Alcohol-Preferring Rats

Chronic ethanol exposure affects the glutamatergic system in several brain reward regions including the nucleus accumbens (NAc). Our laboratory has shown that chronic exposure to ethanol reduced the expression of glutamate transporter 1 (GLT-1) and cystine/glutamate exchanger (xCT) and, as a result, increased extracellular glutamate concentrations in the NAc of alcohol-preferring (P) rats. Moreover, previous studies from our laboratory reported that chronic ethanol intake altered the expression of certain metabotropic glutamate receptors in the brain. In addition to central effects, chronic ethanol consumption induced liver injury, which is associated with steatohepatitis. In the present study, we investigated the effects of chronic ethanol consumption in the brain and liver. Male P rats had access to a free choice of ethanol and water bottles for five weeks. Chronic ethanol consumption reduced GLT-1 and xCT expression in the NAc shell but not in the NAc core. Furthermore, chronic ethanol consumption increased fat droplet content as well as peroxisome proliferator-activated receptor alpha (PPAR-α) and GLT-1 expression in the liver. Importantly, treatment with the novel beta-lactam compound, MC-100093, reduced ethanol drinking behavior and normalized the levels of GLT-1 and xCT expression in the NAc shell as well as normalized GLT-1 and PPAR-α expression in the liver. In addition, MC-100093 attenuated ethanol-induced increases in fat droplet content in the liver. These findings suggest that MC-100093 may be a potential lead compound to attenuate ethanol-induced dysfunction in the glutamatergic system and liver injury. SIGNIFICANCE STATEMENT: This study identified a novel beta-lactam, MC-100093, that has demonstrated upregulatory effects on GLT-1. MC-100093 reduced ethanol drinking behavior and normalized levels of GLT-1 and xCT expression in the NAc shell as well as normalized GLT-1 and PPAR-α expression in the liver. In addition, MC-100093 attenuated ethanol-induced increases in fat droplet content in the liver.

The effect of narcotics on ferroptosis-related molecular mechanisms and signalling pathways

Ferroptosis is a novel programmed cell death form characterized by iron-mediated reactive oxygen species-induced lipid peroxidation and subsequent cell damage that is distinct from apoptosis, necroptosis, pyroptosis, and autophagy. Most studies on ferroptosis are based on its function and mechanism, but there have been relatively few studies on the effects of drugs, especially anaesthetics, on ferroptosis. Therefore, we summarized the recent literature on the effects of anaesthetics on ferroptosis to understand the underlying mechanism. In particular, we focused on the targets of various anaesthetics in different mechanisms of ferroptosis and the effects of ferroptosis induction or inhibition by narcotics on various diseases. The aims of this review are to provide a relatively reasonable drug regimen for clinicians, to explore potential ferroptosis protection drugs and targets, to reduce perioperative complications and to improve the postoperative performance of patients, especially those who are critically ill.

The role of ferroptosis in esophageal cancer

Esophageal cancer is one of the most common cancers with high mortality rate around the world. Although the treatment strategy of this disease has made great progress, the prognosis of advanced patients is not ideal. Ferroptosis, a novel regulatory cell death model, that is different from traditional apoptosis and characterized by increased Fenton reaction mediated by intracellular free iron and lipid peroxidation of cell membrane. Ferroptosis has been proved to be closely linked to a variety of diseases, especially cancer. This review aims to summarize the core mechanism of ferroptosis in esophageal cancer, the regulation of ferroptosis signaling pathway and its current application. At the same time, we emphasize the potential and prospect of ferroptosis in the treatment of esophageal cancer. Collectively, targeting ferroptosis pathway may provide new insights into the diagnosis, treatment and prognosis of esophageal cancer.

The Involvement of Polyamines Catabolism in the Crosstalk between Neurons and Astrocytes in Neurodegeneration

In mammalian cells, the content of polyamines is tightly regulated. Polyamines, including spermine, spermidine and putrescine, are involved in many cellular processes. Spermine oxidase specifically oxidizes spermine, and its deregulated activity has been reported to be linked to brain pathologies involving neuron damage. Spermine is a neuromodulator of a number of ionotropic glutamate receptors and types of ion channels. In this respect, the Dach-SMOX mouse model overexpressing spermine oxidase in the neocortex neurons was revealed to be a model of chronic oxidative stress, excitotoxicity and neuronal damage. Reactive astrocytosis, chronic oxidative and excitotoxic stress, neuron loss and the susceptibility to seizure in the Dach-SMOX are discussed here. This genetic model would help researchers understand the linkage between polyamine dysregulation and neurodegeneration and unveil the roles of polyamines in the crosstalk between astrocytes and neurons in neuroprotection or neurodegeneration.

New Insights on Ferroptosis and Gynecological Malignancies

Ferroptosis is a new type of cell death different from apoptosis and necrosis, which can regulate the accumulation of lipid peroxidation through different pathways, ultimately leading to cell death. An increasing number of studies have revealed that the relationship between ferroptosis and cancer is extremely complex, which holds promise as a new treatment. In gynecological malignancies, ferroptosis has been found to have excellent antitumor activity, which can regulate the proliferation, metastasis and radiochemotherapy resistance. With the continuous progress of research, nanodrugs, gene therapy and other new therapeutic techniques for inducing ferroptosis have been proposed. However, the study of ferroptosis in gynecological malignancies is still in its infancy, and further research is needed to design safe and effective cancer therapies based on ferroptosis. This article reviews the mechanism of ferroptosis and the latest research progress and prospects in gynecological malignancies.

Disruption of Glutamate Homeostasis in the Brain of Rat Offspring Induced by Prenatal and Early Postnatal Exposure to Maternal High-Sugar Diet

A high-calorie diet has contributed greatly to the prevalence of overweight and obesity worldwide for decades. These conditions also affect pregnant women and have a negative impact on the health of both the woman and the fetus. Numerous studies indicate that an unbalanced maternal diet, rich in sugars and fats, can influence the in utero environment and, therefore, the future health of the child. It has also been shown that prenatal exposure to an unbalanced diet might permanently alter neurotransmission in offspring. In this study, using a rat model, we evaluated the effects of a maternal high-sugar diet on the level of extracellular glutamate and the expression of key transporters crucial for maintaining glutamate homeostasis in offspring. Glutamate concentration was assessed in extracellular fluid samples collected from the medial prefrontal cortex and hippocampus of male and female offspring. Analysis showed significantly increased glutamate levels in both brain structures analyzed, regardless of the sex of the offspring. These changes were accompanied by altered expression of the EAAT1, VGLUT1, and x_c⁻ proteins in these brain structures. This animal study further confirms our previous findings that a maternal high-sugar diet has a detrimental effect on the glutamatergic system.

Astrocytic Glutamatergic Transmission and Its Implications in Neurodegenerative Disorders

Several neurodegenerative disorders involve impaired neurotransmission, and glutamatergic neurotransmission sets a prototypical example. Glutamate is a predominant excitatory neurotransmitter where the astrocytes play a pivotal role in maintaining the extracellular levels through release and uptake mechanisms. Astrocytes modulate calcium-mediated excitability and release several neurotransmitters and neuromodulators, including glutamate, and significantly modulate neurotransmission. Accumulating evidence supports the concept of excitotoxicity caused by astrocytic glutamatergic release in pathological conditions. Thus, the current review highlights different vesicular and non-vesicular mechanisms of astrocytic glutamate release and their implication in neurodegenerative diseases. As in presynaptic neurons, the vesicular release of astrocytic glutamate is also primarily meditated by calcium-mediated exocytosis. V-ATPase is crucial in the acidification and maintenance of the gradient that facilitates the vesicular storage of glutamate. Along with these, several other components, such as cystine/glutamate antiporter, hemichannels, BEST-1, TREK-1, purinergic receptors and so forth, also contribute to glutamate release under physiological and pathological conditions. Events of hampered glutamate uptake could promote inflamed astrocytes to trigger repetitive release of glutamate. This could be favorable towards the development and worsening of neurodegenerative diseases. Therefore, across neurodegenerative diseases, we review the relations between defective glutamatergic signaling and astrocytic vesicular and non-vesicular events in glutamate homeostasis. The optimum regulation of astrocytic glutamatergic transmission could pave the way for the management of these diseases and add to their therapeutic value.

Ferroptosis and Ferritinophagy in Diabetes Complications

With long-term metabolic malfunction, diabetes can cause more serious damage to the whole body tissue and organs, resulting in a variety of complications. Therefore, it is particularly important to further explore the pathogenesis of diabetes complications and develop drugs for prevention and treatment. In recent years, ferroptosis has been recognized as a new regulatory mode of cell death different from apoptosis and necrosis, which involves the regulation of nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy. Evidence shows that ferroptosis and ferritinophagy provide a significant role in the occurrence and development of diabetes complications. This article systematically reviews the current understanding of ferroptosis and ferritinophagy, focusing on their potential mechanisms, connection, and regulation. We discuss their involvement in diabetes complications and consider emerging therapeutic opportunities and the associated challenges with future prospects.

Transgenic Mouse Overexpressing Spermine Oxidase in Cerebrocortical Neurons: Astrocyte Dysfunction and Susceptibility to Epileptic Seizures

Polyamines are organic polycations ubiquitously present in living cells. Polyamines are involved in many cellular processes, and their content in mammalian cells is tightly controlled. Among their function, these molecules modulate the activity of several ion channels. Spermine oxidase, specifically oxidized spermine, is a neuromodulator of several types of ion channel and ionotropic glutamate receptors, and its deregulated activity has been linked to several brain pathologies, including epilepsy. The Dach-SMOX mouse line was generated using a Cre/loxP-based recombination approach to study the complex and critical functions carried out by spermine oxidase and spermine in the mammalian brain. This mouse genetic model overexpresses spermine oxidase in the neocortex and is a chronic model of excitotoxic/oxidative injury and neuron vulnerability to oxidative stress and excitotoxic, since its phenotype revealed to be more susceptible to different acute oxidative insults. In this review, the molecular mechanisms underlined the Dach-SMOX phenotype, linked to reactive astrocytosis, neuron loss, chronic oxidative and excitotoxic stress, and susceptibility to seizures have been discussed in detail. The Dach-SMOX mouse model overexpressing SMOX may help in shedding lights on the susceptibility to epileptic seizures, possibly helping to understand the mechanisms underlying epileptogenesis in vulnerable individuals and contributing to provide new molecular mechanism targets to search for novel antiepileptic drugs.

Aged xCT-Deficient Mice Are Less Susceptible for Lactacystin-, but Not 1-Methyl-4-Phenyl-1,2,3,6- Tetrahydropyridine-, Induced Degeneration of the Nigrostriatal Pathway

The astrocytic cystine/glutamate antiporter system x _c ^- (with xCT as the specific subunit) imports cystine in exchange for glutamate and has been shown to interact with multiple pathways in the brain that are dysregulated in age-related neurological disorders, including glutamate homeostasis, redox balance, and neuroinflammation. In the current study, we investigated the effect of genetic xCT deletion on lactacystin (LAC)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced degeneration of the nigrostriatal pathway, as models for Parkinson's disease (PD). Dopaminergic neurons of adult xCT knock-out mice (xCT^-/-) demonstrated an equal susceptibility to intranigral injection of the proteasome inhibitor LAC, as their wild-type (xCT^+/+) littermates. Contrary to adult mice, aged xCT^-/- mice showed a significant decrease in LAC-induced degeneration of nigral dopaminergic neurons, depletion of striatal dopamine (DA) and neuroinflammatory reaction, compared to age-matched xCT^+/+ littermates. Given this age-related protection, we further investigated the sensitivity of aged xCT^-/- mice to chronic and progressive MPTP treatment. However, in accordance with our previous observations in adult mice (Bentea et al., 2015a), xCT deletion did not confer protection against MPTP-induced nigrostriatal degeneration in aged mice. We observed an increased loss of nigral dopaminergic neurons, but equal striatal DA denervation, in MPTP-treated aged xCT^-/- mice when compared to age-matched xCT^+/+ littermates. To conclude, we reveal age-related protection against proteasome inhibition-induced nigrostriatal degeneration in xCT^-/- mice, while xCT deletion failed to protect nigral dopaminergic neurons of aged mice against MPTP-induced toxicity. Our findings thereby provide new insights into the role of system x _c ^- in mechanisms of dopaminergic cell loss and its interaction with aging.

Ferroptosis in Intracerebral Hemorrhage: A Panoramic Perspective of the Metabolism, Mechanism and Theranostics

Iron is one of the most crucial elements in the human body. In recent years, a kind of programmed, non-apoptotic cell death closely related to iron metabolism-called ferroptosis- has aroused much interest among many scientists. Ferroptosis also interacts with other pathways involved in cell death including iron abnormality, the cystine/glutamate antiporter and lipid peroxidation. Together these pathological pathways exert great impacts on intracerebral hemorrhage (ICH), a lethal cerebrovascular disease with a high incidence rate and mortality rate. Furthermore, the ferroptosis also affects different brain cells (neurons and neuroglial cells) and different organelles (mitochondria and endoplasmic reticulum). Clinical treatments for ferroptosis in ICH have been closely investigated recently. This perspective provides a comprehensive summary of ferroptosis mechanisms after ICH and its interaction with other cell death patterns. Understanding the role of ferroptosis in ICH will open new windows for the future treatments and preventions for ICH and other intracerebral diseases.

Rapid Regulation of Glutamate Transport: Where Do We Go from Here?

Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). A family of five Na⁺-dependent transporters maintain low levels of extracellular glutamate and shape excitatory signaling. Shortly after the research group of the person being honored in this special issue (Dr. Baruch Kanner) cloned one of these transporters, his group and several others showed that their activity can be acutely (within minutes to hours) regulated. Since this time, several different signals and post-translational modifications have been implicated in the regulation of these transporters. In this review, we will provide a brief introduction to the distribution and function of this family of glutamate transporters. This will be followed by a discussion of the signals that rapidly control the activity and/or localization of these transporters, including protein kinase C, ubiquitination, glutamate transporter substrates, nitrosylation, and palmitoylation. We also include the results of our attempts to define the role of palmitoylation in the regulation of GLT-1 in crude synaptosomes. In some cases, the mechanisms have been fairly well-defined, but in others, the mechanisms are not understood. In several cases, contradictory phenomena have been observed by more than one group; we describe these studies with the goal of identifying the opportunities for advancing the field. Abnormal glutamatergic signaling has been implicated in a wide variety of psychiatric and neurologic disorders. Although recent studies have begun to link regulation of glutamate transporters to the pathogenesis of these disorders, it will be difficult to determine how regulation influences signaling or pathophysiology of glutamate without a better understanding of the mechanisms involved.

Genetic Profiles of Ferroptosis in Malignant Brain Tumors and Off-Target Effects of Ferroptosis Induction

Glioblastoma represents the most devastating form of human brain cancer, associated with a very poor survival rate of patients. Unfortunately, treatment options are currently limited and the gold standard pharmacological treatment with the chemotherapeutic drug temozolomide only slightly increases the survival rate. Experimental studies have shown that the efficiency of temozolomide can be improved by inducing ferroptosis – a recently discovered form of cell death, which is different from apoptosis, necrosis, or necroptosis and, which is characterized by lipid peroxidation and reactive oxygen species accumulation. Ferroptosis can also be activated to improve treatment of malignant stages of neuroblastoma, meningioma, and glioma. Due to their role in cancer treatment, ferroptosis-gene signatures have recently been evaluated for their ability to predict survival of patients. Despite positive effects during chemotherapy, the drugs used to induce ferroptosis – such as erastin and sorafenib – as well as genetic manipulation of key players in ferroptosis – such as the cystine-glutamate exchanger xCT and the glutathione peroxidase GPx4 – also impact neuronal function and cognitive capabilities. In this review, we give an update on ferroptosis in different brain tumors and summarize the impact of ferroptosis on healthy tissues.

Psychologically Traumatic Oxidative Stress; A Comprehensive Review of Redox Mechanisms and Related Inflammatory Implications

The organism's energy requirements for homeostatic balance are covered by the redox mechanisms. Yet in case of psychologically traumatic stress, allostatic regulations activate both pro-oxidant and antioxidant molecules as well as respective components of the inflammatory system. Thus a new setpoint of dynamic interactions among redox elements is reached. Similarly, a multifaceted interplay between redox and inflammatory fields is activated with the mediation of major effector systems such as the immune system, Hypothalamic-Pituitary-Adrenal axis, kynurenine, and the glycaemic regulatory one. In case of sustained and/or intense traumatic stress the prophylactic antioxidant components are inadequate to provide the organism with neuroprotection finally culminating in Oxidative Stress and subsequently to cellular apoptosis. In parallel multiple inflammatory systems trigger and/or are triggered by the redox systems in tight fashion so that the causation sequence appears obscure. This exhaustive review aims at the comprehension of the interaction among components of the redox system as well as to the collection of disperse findings relative to the redox-inflammatory interplay in the context of traumatic stress so that new research strategies could be developed.

Amyloid-β 25-35 Induces Neurotoxicity through the Up-Regulation of Astrocytic System Xc. Antioxidants (Basel) 2021;10:antiox10111685. [PMID: 34829555 PMCID: PMC8615014 DOI: 10.3390/antiox10111685]

Amyloid-β (Aβ) deposition, a hallmark of Alzheimer’s disease, is known to induce free radical production and oxidative stress, leading to neuronal damage. During oxidative stress, several cell types (including astrocytes) can activate the nuclear factor erythroid 2-related factor 2 (Nrf2), a regulator of several phase II detoxifying and antioxidant genes, such as the System X_c⁻ subunit xCT. Here, we studied (i) the effect of the Aβ fragment 25-35 (Aβ_25-35) on Nrf2-dependent System X_c⁻ expression in U373 human astroglial cells and (ii) the effect of Aβ_25-35-induced astrocytic response on neuronal cell viability using an in vitro co-culture system. We found that Aβ_25-35 was able to activate an antioxidant response in astrocytes, by inducing both Nrf2 activation and System X_c⁻ up-regulation. However, this astrocytic response caused an enhanced cell mortality of co-cultured SH-SY5Y cells, taken as a neuronal model. Consistently, the specific System X_c⁻ inhibitor sulfasalazine prevented the increase of both neuronal mortality and extracellular glutamate levels, thus indicating that the neurotoxic effect was due to an augmented release of glutamate through the transporter. The involvement of NMDA receptor activation in this pathway was also demonstrated using the specific inhibitor MK801 that completely restored neuronal viability at the control levels. The present study sheds light on the Nrf2/system X_c⁻ pathway in the toxicity induced by Aβ_25-35 and may help to better understand the involvement of astrocytes in neuronal death during Alzheimer’s disease.

Cystine/Glutamate Antiporter in Schizophrenia: From Molecular Mechanism to Novel Biomarker and Treatment

Glutamate, a crucial excitatory neurotransmitter, plays a major role in the modulation of schizophrenia’s pathogenesis. New drug developments for schizophrenia have been prompted by the hypoglutamatergic hypothesis of schizophrenia. The cystine/glutamate antiporter system x_c⁻ is related to glutamate-release regulation. Patients with schizophrenia were recently discovered to exhibit downregulation of x_c⁻ subunits—the solute carrier (SLC) family 3 member 2 and the SLC family 7 member 11. We searched for relevant studies from 1980, when Bannai and Kitamura first identified the protein subunit system x_c⁻ in lung fibroblasts, with the aim of compiling the biological, functional, and pharmacological characteristics of antiporter x_c⁻, which consists of several subunits. Some of them can significantly stimulate the human brain through the glutamate pathway. Initially, extracellular cysteine activates neuronal x_c⁻, causing glutamate efflux. Next, excitatory amino acid transporters enhance the unidirectional transportation of glutamate and sodium. These two biochemical pathways are also crucial to the production of glutathione, a protective agent for neural and glial cells and astrocytes. Investigation of the expression of system x_c⁻ genes in the peripheral white blood cells of patients with schizophrenia can facilitate better understanding of the mental disorder and future development of novel biomarkers and treatments for schizophrenia. In addition, the findings further support the hypoglutamatergic hypothesis of schizophrenia.

Current Therapies for Neonatal Hypoxic-Ischaemic and Infection-Sensitised Hypoxic-Ischaemic Brain Damage

Neonatal hypoxic-ischaemic brain damage is a leading cause of child mortality and morbidity, including cerebral palsy, epilepsy, and cognitive disabilities. The majority of neonatal hypoxic-ischaemic cases arise as a result of impaired cerebral perfusion to the foetus attributed to uterine, placental, or umbilical cord compromise prior to or during delivery. Bacterial infection is a factor contributing to the damage and is recorded in more than half of preterm births. Exposure to infection exacerbates neuronal hypoxic-ischaemic damage thus leading to a phenomenon called infection-sensitised hypoxic-ischaemic brain injury. Models of neonatal hypoxia-ischaemia (HI) have been developed in different animals. Both human and animal studies show that the developmental stage and the severity of the HI insult affect the selective regional vulnerability of the brain to damage, as well as the subsequent clinical manifestations. Therapeutic hypothermia (TH) is the only clinically approved treatment for neonatal HI. However, the number of HI infants needed to treat with TH for one to be saved from death or disability at age of 18-22 months, is approximately 6-7, which highlights the need for additional or alternative treatments to replace TH or increase its efficiency. In this review we discuss the mechanisms of HI injury to the immature brain and the new experimental treatments studied for neonatal HI and infection-sensitised neonatal HI.

Ferroptosis as a New Mechanism in Parkinson's Disease Therapy Using Traditional Chinese Medicine

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases. To date, among medications used to treat PD, only levodopa exhibits a limited disease-modifying effect on early-onset PD, but it cannot delay the progression of the disease. In 2018, for the first time, the World Health Organization included traditional Chinese medicine (TCM) in its influential global medical compendium. The use of TCM in the treatment of PD has a long history. At present, TCM can help treat and prevent PD. Iron metabolism is closely associated with PD. Ferroptosis, which is characterized by the accumulation of lipid peroxides, is a recently discovered form of iron-dependent cell death. The research literature indicates that ferroptosis in dopaminergic neurons is an important pathogenetic mechanism of PD. TCM may thus play unique roles in the treatment of PD and provide new ideas for the treatment of PD by regulating pathways associated with ferroptosis.

Glutamate - A multifaceted molecule: Endogenous neurotransmitter, controversial food additive, design compound for anti-cancer drugs. A critical appraisal

One of the most widely used flavour enhancers in the food industry is monosodium glutamate (MSG). MSG consumption has been on an upward trend, worrying in terms of potential toxic effects. This review is focused on the long-term toxicity of MSG and the experimental evidence that supports it. The article's primary purpose was to survey recently published data regarding the consumption of MSG within safe limits. The administered doses in animal models are very varied and have given rise to controversy. Also, the paper comprises pathways to lower MSG toxicity and highlight other underexploited biological effects, as anti-cancer potential. The administration of MSG, combined with various compounds, has been shown benefit against toxic effects. Several recent studies have identified a possible mechanism that recommends MSG and some derivatives as potential anti-cancer agents. New anti-cancer compounds based on the glutamic acid structure must be studied and further exploited. International regulations require harmonization of safe doses of MSG based on current scientific studies. Replacing MSG with other umami flavour enhancers may be a safer alternative for human health in the future. The biological consequences of MSG consumption or therapeutical administration have not been fully deciphered yet.

Long access to cocaine self-administration dysregulates the glutamate synapse in the nucleus accumbens core of serotonin transporter knockout rats

Background and Purpose

It is well established that the nucleus accumbens and glutamate play a critical role in the motivation to take drugs of abuse. We have previously demonstrated that rats with ablation of the serotonin (5‐HT) transporter (SERT^−/− rats) show increased cocaine intake reminiscent of compulsivity.

Experimental Approach

By comparing SERT^−/− to SERT^+/+ rats, we set out to explore whether SERT deletion influences glutamate neurotransmission under control conditions as well as after short access (1 h/session) or long access (6 h/session) to cocaine self‐administration.

Key Results

Rats were killed at 24 h after the final self‐administration session for ex vivo molecular analyses of the glutamate system (vesicular and glial transporters, post‐synaptic subunits of NMDA and AMPA receptors and their related scaffolding proteins). Such analyses were undertaken in the nucleus accumbens core. In cocaine‐naïve animals, SERT deletion evoked widespread abnormalities in markers of glutamatergic neurotransmission that, overall, indicate a reduction of glutamate signalling. These results suggest that 5‐HT is pivotal for the maintenance of accumbal glutamate homeostasis. We also found that SERT deletion altered glutamate homeostasis mainly after long access, but not short access, to cocaine.

Conclusion and Implications

Our findings reveal that SERT deletion may sensitize the glutamatergic synapses of the nucleus accumbens core to the long access but not short access, intake of cocaine.

LINKED ARTICLES

This article is part of a themed issue on New discoveries and perspectives in mental and pain disorders. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.17/issuetoc

Endogenous hydrogen sulfide regulates xCT stability through persulfidation of OTUB1 at cysteine 91 in colon cancer cells

Increased xCT and transsulfuration pathway has been associated with metabolic reprogramming of colorectal cancer. However, the correlation between these 2 events and the underlying molecular mechanism remains obscure. xCT expression was determined in tissue microarrays of colorectal cancer. RNA sequencing and functional assays in vitro was adopted to delineate the involvement of transsulfuration pathway in the proper function of xCT in maintaining the chemoresistant phenotype. The synthetic lethality of blocking xCT and the transsulfuration pathway was investigated both in vitro and in vivo. The up-regulation of the transsulfuration pathway after inhibiting xCT in colon cancer cells was evident and exogenous H₂S partially reversed the loss of chemoresistance phenotype after inhibiting xCT. Mechanistically, CTH derived H₂S increased the stability of xCT through persulfidation of OTU domain-containing ubiquitin aldehyde-binding protein 1 at cysteine 91. AOAA and Erastin resulted in synthetic lethality both in vitro and in vivo, which was mediated through increased ferroptosis and apoptosis. Our findings suggest that a reciprocal regulation exists between xCT and the transsulfuration pathway, which is a targetable metabolic vulnerability. Mechanistically, CTH derived H₂S increased the stability of xCT through persulfidation of OTU domain-containing ubiquitin aldehyde-binding protein 1 at cysteine 91.

The Effect of GLT-1 Upregulation on Extracellular Glutamate Dynamics

Pharmacological upregulation of glutamate transporter-1 (GLT-1), commonly achieved using the beta-lactam antibiotic ceftriaxone, represents a promising therapeutic strategy to accelerate glutamate uptake and prevent excitotoxic damage in neurological conditions. While excitotoxicity is indeed implicated in numerous brain diseases, it is typically restricted to select vulnerable brain regions, particularly in early disease stages. In healthy brain tissue, the speed of glutamate uptake is not constant and rather varies in both an activity- and region-dependent manner. Despite the widespread use of ceftriaxone in disease models, very little is known about how such treatments impact functional measures of glutamate uptake in healthy tissue, and whether GLT-1 upregulation can mask the naturally occurring activity-dependent and regional heterogeneities in uptake. Here, we used two different compounds, ceftriaxone and LDN/OSU-0212320 (LDN), to upregulate GLT-1 in healthy wild-type mice. We then used real-time imaging of the glutamate biosensor iGluSnFR to investigate functional consequences of GLT-1 upregulation on activity- and regional-dependent variations in glutamate uptake capacity. We found that while both ceftriaxone and LDN increased GLT-1 expression in multiple brain regions, they did not prevent activity-dependent slowing of glutamate clearance nor did they speed basal clearance rates, even in areas characterized by slow uptake (e.g., striatum). Unexpectedly, ceftriaxone but not LDN decreased glutamate release in the cortex, suggesting that ceftriaxone may alter release properties independent of its effects on GLT-1 expression. In sum, our data demonstrate the complexities of glutamate uptake by showing that GLT-1 expression does not necessarily translate to accelerated uptake. Furthermore, these data suggest that the mechanisms underlying activity- and regional-dependent differences in glutamate dynamics are independent of GLT-1 expression levels.

l-Cystine is associated with the dysconnectivity of the default-mode network and salience network in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder. Distributed dysconnectivity within both the default-mode network (DMN) and the salience network (SN) has been observed in ADHD. L-cystine may serve as a neuroprotective molecule and signaling pathway, as well as a biomarker of ADHD. The purpose of this study was to explore whether differential brain network connectivity is associated with peripheral L-cystine levels in ADHD patients. We recruited a total of 31 drug-naïve patients with ADHD (mean age: 10.4 years) and 29 healthy controls (mean age: 10.3 years) that underwent resting state functional magnetic resonance imaging scans. Functional connectomes were generated for each subject, and we examined the cross-sectional group difference in functional connectivity (FC) within and between DMN and SN. L-cystine plasma levels were determined using high-performance chemical isotope labeling (CIL)-based liquid chromatography-mass spectrometry (LC-MS). Compared to the control group, the ADHD group showed decreased FC of dorsal DMN (p = 0.031), as well as decreased FC of precuneus-post SN (p = 0.006) and ventral DMN-post SN (p = 0.001). The plasma L-cystine levels of the ADHD group were significantly higher than in the control group (p = 0.002). Furthermore, L-cystine levels were negatively correlated with FC of precuneus-post SN (r = -0.404, p = 0.045) and ventral DMN-post SN (r = -0.540, p = 0.007). The findings suggest that decreased synergies of DMN and SN may serve as neurobiomarkers for ADHD, while L-cystine may be involved in the pathophysiology of network dysconnectivity. Future studies on the molecular mechanism of the cystine-glutamate system in brain network connectivity are warranted.

Corticostriatal dysfunction and social interaction deficits in mice lacking the cystine/glutamate antiporter

The astrocytic cystine/glutamate antiporter system x_c^- represents an important source of extracellular glutamate in the central nervous system, with potential impact on excitatory neurotransmission. Yet, its function and importance in brain physiology remain incompletely understood. Employing slice electrophysiology and mice with a genetic deletion of the specific subunit of system x_c^-, xCT (xCT^-/- mice), we uncovered decreased neurotransmission at corticostriatal synapses. This effect was partly mitigated by replenishing extracellular glutamate levels, indicating a defect linked with decreased extracellular glutamate availability. We observed no changes in the morphology of striatal medium spiny neurons, the density of dendritic spines, or the density or ultrastructure of corticostriatal synapses, indicating that the observed functional defects are not due to morphological or structural abnormalities. By combining electron microscopy with glutamate immunogold labeling, we identified decreased intracellular glutamate density in presynaptic terminals, presynaptic mitochondria, and in dendritic spines of xCT^-/- mice. A proteomic and kinomic screen of the striatum of xCT^-/- mice revealed decreased expression of presynaptic proteins and abnormal kinase network signaling, that may contribute to the observed changes in postsynaptic responses. Finally, these corticostriatal deregulations resulted in a behavioral phenotype suggestive of autism spectrum disorder in the xCT^-/- mice; in tests sensitive to corticostriatal functioning we recorded increased repetitive digging behavior and decreased sociability. To conclude, our findings show that system x_c^- plays a previously unrecognized role in regulating corticostriatal neurotransmission and influences social preference and repetitive behavior.

Antioxidant Effect of Propofol in Gliomas and Its Association With Divalent Metal Transporter 1

Background

Oxidative stress enhances tumor invasion and metastasis in brain cancer. The activation of divalent metal transporter 1 (DMT1), which is regulated by glutamate receptors, can result in the increase of oxidative stress and risk of cancer development. Propofol, an anesthetic with antioxidant capacity, has been shown to decrease oxidative stress in several different types of cancer. However, the underlying mechanism remains unclear. Therefore, the present study aimed to elucidate the mechanism underlying the suppression of oxidative stress in glioma cells by propofol. It was hypothesized that propofol may inhibit oxidative stress in gliomas via suppressing Ca²⁺-permeable α-amino-3-hydroxyl-5-methylisoxazole-4-propionic acid (AMPA) receptor (CPAR)-DMT1 signaling.

Methods

Male Wistar rats with C6 gliomas, which were established by intracranial injection of C6 glioma cells, were either treated with propofol or not for 6 h before being sacrificed. The levels of AMPA receptor subunit GluR2 and DMT1 protein expression were assessed using western blotting. The association between CPARs and DMT1 was confirmed in vitro using the AMPA receptor activator (R, S)-AMPA. Glutathione and reactive oxygen species assay kits were used to evaluate tumor oxidative stress. The effect of propofol on glioma proliferation was evaluated by determining tumor weight, cell cycles and a growth curve.

Results

Propofol infusion at either 20 or 40 mg/kg^-1/h^-1 increased GluR2 levels and downregulated DMT1 expression as well as glutathione content markedly in the periphery compared with that in the glioma core. The in vitro results revealed that (R, S)-AMPA increased DMT1 expression and reactive oxygen species levels, which were partly reversed by propofol treatment.

Conclusion

Propofol regulated DMT1 expression by modulating CPARs, resulting in the inhibition of tumor oxidative stress and glioma growth. The present study provides evidence for optimizing the selection of anesthetic drugs in perioperative management and prognosis of patients with glioma.

The Role of Iron, Its Metabolism and Ferroptosis in Traumatic Brain Injury

Traumatic brain injury (TBI) is a structural and physiological disruption of brain function caused by external forces. It is a major cause of death and disability for patients worldwide. TBI includes both primary and secondary impairments. Iron overload and ferroptosis highly involved in the pathophysiological process of secondary brain injury. Ferroptosis is a form of regulatory cell death, as increased iron accumulation in the brain leads to lipid peroxidation, reactive oxygen species (ROS) production, mitochondrial dysfunction and neuroinflammatory responses, resulting in cellular and neuronal damage. For this reason, eliminating factors like iron deposition and inhibiting lipid peroxidation may be a promising therapy. Iron chelators can be used to eliminate excess iron and to alleviate some of the clinical manifestations of TBI. In this review we will focus on the mechanisms of iron and ferroptosis involving the manifestations of TBI, broaden our understanding of the use of iron chelators for TBI. Through this review, we were able to better find novel clinical therapeutic directions for further TBI study.