N-Acetylaspartylglutamate (NAAG) Pretreatment Reduces Hypoxic-Ischemic Brain Damage and Oxidative Stress in Neonatal Rats

Emerging ferroptosis inhibitors as a novel therapeutic strategy for the treatment of neonatal hypoxic-ischemic encephalopathy

Neonatal hypoxia-ischemia encephalopathy (NHIE), an oxygen deprivation-mediated brain injury due to birth asphyxia or reduced cerebral blood perfusion, often leads to lifelong sequelae, including seizures, cerebral palsy, and mental retardation. NHIE poses a significant health challenge, as one of the leading causes of neonatal morbidity and mortality globally. Despite this, available therapies are limited. Numerous studies have recently demonstrated that ferroptosis, an iron-dependent non-apoptotic regulated form of cell death characterized by lipid peroxidation (LPO) and iron dyshomeostasis, plays a role in the genesis of NHIE. Moreover, recently discovered compounds have been shown to exert potential therapeutic effects on NHIE by inhibiting ferroptosis. This comprehensive review summarizes the fundamental mechanisms of ferroptosis contributing to NHIE. We focus on various emerging therapeutic compounds exhibiting characteristics of ferroptosis inhibition and delineate their pharmacological benefits for the treatment of NHIE. This review suggests that pharmacological inhibition of ferroptosis may be a potential therapeutic strategy for NHIE.

Deletion of glutamate carboxypeptidase II (GCPII), but not GCPIII, provided long-term benefits in mice with traumatic brain injury

MAIN PROBLEM

N-acetylaspartylglutamate (NAAG) has neuroprotective effects in traumatic brain injury (TBI) by activating metabotropic glutamate receptor 3 (mGluR3) and reducing glutamate release. Glutamate carboxypeptidase II (GCPII) is the primary enzyme responsible for the hydrolysis of NAAG. It remains unclear whether glutamate carboxypeptidase III (GCPIII), a homolog of GCPII, can partially compensate for GCPII's function.

METHODS

GCPII-/- , GCPIII-/- , and GCPII/III-/- mice were generated using CRISPR/Cas9 technology. Mice brain injury model was established through moderate controlled cortical impact (CCI). The relationship between GCPII and GCPIII was explored by analyzing injury response signals in the hippocampus and cortex of mice with different genotypes at the acute (1 day) and subacute (7 day) phase after TBI.

RESULTS

In this study, we found that deletion of GCPII reduced glutamate production, excitotoxicity, and neuronal damage and improved cognitive function, but GCPIII deletion had no significant neuroprotective effect. Additionally, there was no significant difference in the neuroprotective effect between the combination of GCPII and GCPIII deletion and GCPII deletion alone.

CONCLUSION

These results suggest that GCPII inhibition may be a therapeutic option for TBI, and that GCPIII may not act as a complementary enzyme to GCPII in this context.

Functional imaging and neurochemistry identify in vivo neuroprotection mechanisms counteracting excitotoxicity and neurovascular changes in the hippocampus and visual cortex of obese and type 2 diabetic animal models

Functional MRI (fMRI) with 1 H-MRS was combined on the hippocampus and visual cortex of animal models of obesity (high-fat diet, HFD) and type 2 diabetes (T2D) to identify the involved mechanisms and temporal evolution of neurometabolic changes in these disorders that could serve as potentially reliable clinical biomarkers. HFD rats presented elevated levels of N-acetylaspartylglutamate (NAAG) (p = 0.0365 vs. standard diet, SD) and glutathione (GSH) (p = 0.0494 vs. SD) in the hippocampus. NAAG and GSH levels in this structure proved to be correlated (r = 0.4652, p = 0.0336). This mechanism was not observed in diabetic rats. Combining MRS and fMRI-evaluated blood-oxygen-level-dependent (BOLD) response, elevated taurine (p = 0.0326 vs. HFD) and GABA type A receptor (GABAA R) (p = 0.0211 vs. SD and p = 0.0153 vs. HFD) were observed in the visual cortex of only diabetic rats, counteracting the elevated BOLD response and suggesting an adaptative mechanism against hyperexcitability observed in the primary visual cortex (V1) (p = 0.0226 vs. SD). BOLD amplitude was correlated with the glutamate levels (r = 0.4491; p = 0.0316). Therefore, here we found evidence for several biological dichotomies regarding excitotoxicity and neuroprotection in different brain regions, identifying putative markers of their different susceptibility and response to the metabolic and vascular insults of obesity and diabetes.

Intermittent fasting alleviates type 1 diabetes-induced cognitive dysfunction by improving the frontal cortical metabolic disorder

Intermittent fasting (IF) is an ecological strategy to control various metabolic disorder symptoms, but its protective effect on type 1 diabetes (T1D)-induced cognitive dysfunction and the underlying mechanisms remain poorly defined. Herein, we examined the efficacy of IF in altering the behaviors and brain metabolome in T1D mice and investigated the potential molecular mechanisms. We demonstrated that IF remarkably improved frontal cortical-dependent memory in T1D mice and reduced the loss of neuronal cells. Metabolomics and targeted mass spectrometry assay showed that IF reprogrammed the frontal cortical metabolome composition, including activated the aspartate and glutamate pathway and reversed glycerophospholipid and sphingolipid depositions in T1D mice. Mechanistically, IF attenuated the levels of oxidative stress proteins, such as NOX2, NOX4, 8-OHdG, 4-HNE, and inhibited the levels of pro-apoptotic factors Bax and cleaved Caspase-3, finally improved the memory ability of T1D mice. In vitro studies confirmed the protective effect of the supplemented N-acetylaspartate, a pivotal metabolite involved in IF-regulated T1D-induced cognitive dysfunction, in high glucose-stimulated SH-SY5Y cells by eliminating toxic lipids accumulation, oxidative stress and apoptosis. To conclude, the frontal cortical metabolites mediated the protective effects of IF against T1D-induced cognitive dysfunction by attenuating oxidative stress and apoptotic signaling. Thus, IF can be a potential therapeutic strategy for T1D-induced cognitive dysfunction.

Dendrimer-Conjugated Glutamate Carboxypeptidase II Inhibitor Restores Microglial Changes in a Rabbit Model of Cerebral Palsy

We have previously shown that maternal endotoxin exposure leads to a phenotype of cerebral palsy and pro-inflammatory microglia in the brain in neonatal rabbits. "Activated" microglia overexpress the enzyme glutamate carboxypeptidase II (GCPII) that hydrolyzes N-acetylaspartylglutamate to N-acetylaspartate and glutamate, and we have shown previously that inhibiting microglial GCPII is neuroprotective. Glutamate-induced injury and associated immune signaling can alter microglial responses including microglial process movements for surveillance and phagocytosis. We hypothesize that inhibition of GCPII activity could alter microglial phenotype and normalize microglial process movement/dynamics. Newborn rabbit kits exposed to endotoxin in utero, when treated with dendrimer-conjugated 2-(phosphonomethyl)-pentanedioic acid (D-2PMPA), a potent and selective inhibitor of microglial GCPII, showed profound changes in microglial phenotype within 48 h of treatment. Live imaging of hippocampal microglia in ex vivo brain slice preparations revealed larger cell body and phagocytic cup sizes with less stable microglia processes in CP kits compared to healthy controls. D-2PMPA treatment led to significant reversal of microglial process stability to healthy control levels. Our results emphasize the importance of microglial process dynamics in determining the state of microglial function in the developing brain and demonstrate how GCPII inhibition specifically in microglia can effectively change the microglial process motility to healthy control levels, potentially impacting migration, phagocytosis, and inflammatory functions.

NMDA Receptor Activation Stimulates Hypoxia-Induced TRPM2 Channel Activation, Mitochondrial Oxidative Stress, and Apoptosis in Neuronal Cell Line: Modular Role of Memantine

TRPM2 channel is activated by the increase of hypoxia (HYP)-mediated excessive mitochondrial (mROS) and cytosolic (cROS) free reactive oxygen species generation and intracellular free Ca²⁺ ([Ca²⁺]_i) influx. The stimulations of the N-methyl-d-aspartate(NMDA) receptor and TRPM2 channel induce mROS and apoptosis in the neurons, although their inhibitions via the treatments of memantine (MEM) and MK-801 decrease mROS and apoptosis. However, the molecular mechanisms underlying MEM treatment and NMDA inhibition' neuroprotection via TRPM2 inhibition in the HYP remain elusive. We investigated the modulator role of MEM and NMDA via the modulation of TRPM2 on oxidative neurodegeneration and apoptosis in SH-SY5Y neuronal cells. Six groups were induced in the SH-SY5Y and HEK293 cells as follows: Control, MEM, NMDA blocker (MK-801), HYP (CoCl₂), HYP + MEM, and HYP + MK-801. The HYP caused to the increases of TRPM2 and PARP-1 expressions, and TRPM2 agonist (H₂O₂ and ADP-ribose)-induced TRPM2 current density and [Ca²⁺]_i concentration via the upregulation of mitochondrial membrane potential, cROS, and mROS generations. The alterations were not observed in the absence of TRPM2 in the HEK293 cells. The increase of cROS, mROS, lipid peroxidation, cell death (propidium iodide/Hoechst) rate, apoptosis, caspase -3, caspase -8, and caspase -9 were restored via upregulation of glutathione and glutathione peroxidase by the treatments of TRPM2 antagonists (ACA or 2-APB), MEM, and MK-801. In conclusion, the inhibition of NMDA receptor via MEM treatment modulated HYP-mediated mROS, apoptosis, and TRPM2-induced excessive [Ca²⁺]_i and may provide an avenue for protecting HYP-mediated neurodegenerative diseases associated with the increase of mROS, [Ca²⁺]_i, and apoptosis.

Group II Metabotropic Glutamate Receptors Reduce Apoptosis and Regulate BDNF and GDNF Levels in Hypoxic-Ischemic Injury in Neonatal Rats

Birth asphyxia causes brain injury in neonates, but a fully successful treatment has yet to be developed. This study aimed to investigate the effect of group II mGlu receptors activation after experimental birth asphyxia (hypoxia-ischemia) on the expression of factors involved in apoptosis and neuroprotective neurotrophins. Hypoxia-ischemia (HI) on 7-day-old rats was used as an experimental model. The effects of intraperitoneal application of mGluR2 agonist LY379268 (5 mg/kg) and the specific mGluR3 agonist NAAG (5 mg/kg) (1 h or 6 h after HI) on apoptotic processes and initiation of the neuroprotective mechanism were investigated. LY379268 and NAAG applied shortly after HI prevented brain damage and significantly decreased pro-apoptotic Bax and HtrA2/Omi expression, increasing expression of anti-apoptotic Bcl-2. NAAG or LY379268 applied at both times also decreased HIF-1α formation. HI caused a significant decrease in BDNF concentration, which was restored after LY379268 or NAAG administration. HI-induced increase in GDNF concentration was decreased after administration of LY379268 or NAAG. Our results show that activation of mGluR2/3 receptors shortly after HI prevents brain damage by the inhibition of excessive glutamate release and apoptotic damage decrease. mGluR2 and mGluR3 agonists produced comparable results, indicating that both receptors may be a potential target for early treatment in neonatal HI.

Relationship of ozone application and time in rats with hypoxic-ischemic brain injury

BACKGROUND

Despite the important advances in pregnancy and newborn follow-up, hypoxic-ischemic encephalopathy is still one of the prominent causes of newborn mortality and disability worldwide, and there is no sufficiently effective treatment for it yet. This study aimed to investigate whether the ozone injection, administered in a single-dose as a preconditioning agent before the hypoxia and in single and repeated doses on different days following the hypoxia, would affect the spatial memory performance of the rats in the Morris water maze test or on their apoptotic cell numbers.

METHODS

The study consisted of 102 seven-day-old male Wistar baby rats randomly divided into five groups. Rats in all groups were induced with hypoxic-ischemic brain injury (HIBI) except for the Sham group, and 1.2 mg/kg ozone was administered intraperitoneally. For the apoptosis evaluation, eight rats from each of the first four groups were decapitated by cervical dislocation. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay was used for immunohistochemical quantification of apoptosis in the excised brains. Blood malondialdehyde (MDA) and superoxide dismutase (SOD) levels were measured in the blood samples collected through cardiac puncture. Fourteen-week-old rats underwent the Morris water maze test to test their long-term spatial memory.

RESULTS

On apoptotic quantification in the right hemisphere using the TUNEL assay, the numbers of apoptotic neurons in the ozone preconditioning group (Group 3) and the group given ozone on the day of hypoxia (Group 4) were found to be significantly higher than the Sham group (Group 1), but significantly lower than the non-treatment group (Group 2) (p <0.001; p <0.001, respectively). Group 3 rats had the highest mean MDA level and SOD activity. Considering the platform finding times in the first four days of the tests, Group 4 had the shortest times after Group 1; and on Day 4, Group 4 found the platforms significantly sooner than Groups 2, 3, and 5 (p <0.001). Comparison of Groups 1 and 4 revealed significantly shorter times for Group 1 for each day except for Day 2.

CONCLUSIONS

Other studies have shown that controlled application of ozone would result in oxidative preconditioning and reduce the damage induced by reactive oxygen species through enabling adaptation to oxidative stress. Our study obtained remarkable and encouraging findings for ozone administration in HIBI by examining Group 4's performance in the first four days and the difference in its platform finding times between Day 1 and Day 4. HIPPOKRATIA 2021, 25 (2):56-62.

Pretreatment with mGluR2 or mGluR3 Agonists Reduces Apoptosis Induced by Hypoxia-Ischemia in Neonatal Rat Brains

Hypoxia-ischemia (HI) in an immature brain results in energy depletion and excessive glutamate release resulting in excitotoxicity and oxidative stress. An increase in reactive oxygen species (ROS) production induces apoptotic processes resulting in neuronal death. Activation of group II mGluR was shown to prevent neuronal damage after HI. The application of agonists of mGluR3 (N-acetylaspartylglutamate; NAAG) or mGluR2 (LY379268) inhibits the release of glutamate and reduces neurodegeneration in a neonatal rat model of HI, although the exact mechanism is not fully recognized. In the present study, the effects of NAAG (5 mg/kg) and LY379268 (5 mg/kg) application (24 h or 1 h before experimental birth asphyxia) on apoptotic processes as the potential mechanism of neuroprotection in 7-day-old rats were investigated. Intraperitoneal application of NAAG or LY379268 at either time point before HI significantly reduced the number of TUNEL-positive cells in the CA1 region of the ischemic brain hemisphere. Both agonists reduced expression of the proapoptotic Bax protein and increased expression of Bcl-2. Decreases in HI-induced caspase-9 and caspase-3 activity were also observed. Application of NAAG or LY379268 24 h or 1 h before HI reduced HIF-1α formation likely by reducing ROS levels. It was shown that LY379268 concentration remains at a level that is required for activation of mGluR2 for up to 24 h; however, NAAG is quickly metabolized by glutamate carboxypeptidase II (GCPII) into glutamate and N-acetyl-aspartate. The observed effect of LY379268 application 24 h or 1 h before HI is connected with direct activation of mGluR2 and inhibition of glutamate release. Based on the data presented in this study and on our previous findings, we conclude that the neuroprotective effect of NAAG applied 1 h before HI is most likely the result of a combination of mGluR3 and NMDA receptor activation, whereas the beneficial effects of NAAG pretreatment 24 h before HI can be explained by the activation of NMDA receptors and induction of the antioxidative/antiapoptotic defense system triggered by mild excitotoxicity in neurons. This response to NAAG pretreatment is consistent with the commonly accepted mechanism of preconditioning.

Neuroprotective effects of a dendrimer-based glutamate carboxypeptidase inhibitor on superoxide dismutase transgenic mice after neonatal hypoxic-ischemic brain injury

The result of a deprivation of oxygen and glucose to the brain, hypoxic-ischemic encephalopathy (HIE), remains the most common cause of death and disability in human neonates globally and is mediated by glutamate toxicity and inflammation. We have previously shown that the enzyme glutamate carboxypeptidase (GCPII) is overexpressed in activated microglia in the presence of inflammation in fetal/newborn rabbit brain. We assessed the therapeutic utility of a GCPII enzyme inhibitor called 2-(3-Mercaptopropyl) pentanedioic acid (2MPPA) attached to a dendrimer (D-2MPPA), in order to target activated microglia in an experimental neonatal hypoxia-ischemia (HI) model using superoxide dismutase transgenic (SOD) mice that are often more injured after hypoxia-ischemia than wildtype animals. SOD overexpressing and wild type (WT) mice underwent permanent ligation of the left common carotid artery followed by 50 min of asphyxiation (10% O₂) to induce HI injury on postnatal day 9 (P9). Cy5-labeled dendrimers were administered to the mice at 6 h, 24 h or 72 h after HI and brains were evaluated by immunofluorescence analysis 24 h after the injection to visualize microglial localization and uptake over time. Expression of GCPII enzyme was analyzed in microglia 24 h after the HI injury. The expression of pro- and anti-inflammatory cytokines were analyzed 24 h and 72 h post-HI. Brain damage was analyzed histologically 7 days post-HI in the three randomly assigned groups: control (C); hypoxic-ischemic (HI); and HI mice who received a single dose of D-2MPPA 6 h post-HI (HI+D-2MPPA). First, we found that GCPII was overexpressed in activated microglia 24 h after HI in the SOD overexpressing mice. Also, there was an increase in microglial activation 24 h after HI in the ipsilateral hippocampus which was most visible in the SOD+HI group. Dendrimers were mostly taken up by microglia by 24 h post-HI; uptake was more prominent in the SOD+HI mice than in the WT+HI. The inflammatory profile showed significant increase in expression of KC/GRO following injury in SOD mice compared to WT at 24 and 72 h. A greater and significant decrease in KC/GRO was seen in the SOD mice following treatment with D-2MPPA. Seven days after HI, D-2MPPA treatment decreased brain injury in the SOD+HI group, but not in WT+HI. This reduced damage was mainly seen in hippocampus and cortex. Our data indicate that the best time point to administer D-2MPPA is 6 h post-HI in order to suppress the expression of GCPII by 24 h after the damage since dendrimer localization in microglia is seen as early as 6 h with the peak of GCPII upregulation in activated microglia seen at 24 h post-HI. Ultimately, treatment with D-2MPPA at 6 h post-HI leads to a decrease in inflammatory profiles by 24 h and reduction in brain injury in the SOD overexpressing mice.