Hypothermia but not NMDA receptor antagonism protects against stroke induced by distal middle cerebral arterial occlusion in mice

Microglia through MFG-E8 signaling decrease the density of degenerating neurons and protect the brain from the development of cortical infarction after stroke

Neuronal loss is a hallmark of stroke and other neurodegenerative diseases, and as such, neuronal loss caused by microglia has been thought to be a contributing factor to disease progression. Here, we show that microglia indeed contribute significantly to neuronal loss in a mouse model of stroke, but this microglial-dependent process of neuronal clearance specifically targets stressed and degenerating neurons in the ischemic cortical region and not healthy non-ischemic neurons. Nonspecific stimulation of microglia decreased the density of neurons in the ischemic cortical region, whereas specific inhibition of MFG-E8 signaling, which is required for microglial phagocytosis of neurons, had the opposite effect. In both scenarios, the effects were microglia specific, as the same treatments had no effect in mice whose microglia were depleted prior to stroke. Finally, even though the inhibition of MFG-E8 signaling increased neuronal density in the ischemic brain region, it substantially exacerbated the development of cortical infarction. In conclusion, microglia through MFG-E8 signaling contribute to the loss of ischemic neurons and, in doing so, minimize the development of cortical infarction after stroke.

The underlying mechanism of calcium toxicity-induced autophagic cell death and lysosomal degradation in early stage of cerebral ischemia

Cerebral ischemia is the important cause of worldwide disability and mortality, that is one of the obstruction of blood vessels supplying to the brain. In early stage, glutamate excitotoxicity and high level of intracellular calcium (Ca2+) are the major processes which can promote many downstream signaling involving in neuronal death and brain tissue damaging. Moreover, autophagy, the reusing of damaged cell organelles, is affected in early ischemia. Under ischemic conditions, autophagy plays an important role to maintain energy of the brain and its function. In the other hand, over intracellular Ca2+ accumulation triggers excessive autophagic process and lysosomal degradation leading to autophagic process impairment which finally induce neuronal death. This article reviews the association between intracellular Ca2+ and autophagic process in acute stage of ischemic stroke.

Decreased levels of hydrogen sulfide in the hypothalamic paraventricular nucleus contribute to sympathetic hyperactivity induced by cerebral infarction

Paroxysmal sympathetic hyperactivity (PSH) is a common clinical feature secondary to ischemic stroke (IS), but its mechanism is poorly understood. We aimed to investigate the role of H2S in the pathogenesis of PSH. IS patients were divided into malignant (MCI) and non-malignant cerebral infarction (NMCI) group. IS in rats was induced by the right middle cerebral artery occlusion (MCAO). H2S donor (NaHS) or inhibitor (aminooxy-acetic acid, AOAA) were microinjected into the hypothalamic paraventricular nucleus (PVN). Compared with the NMCI group, patients in the MCI group showed PSH, including tachycardia, hypertension, and more plasma norepinephrine (NE) that was positively correlated with levels of creatine kinase, glutamate transaminase, and creatinine respectively. The 1-year survival rate of patients with high plasma NE levels was lower. The hypothalamus of rats with MCAO showed increased activity, especially in the PVN region. The levels of H2S in PVN of the rats with MCAO were reduced, while the blood pressure and renal sympathetic discharge were increased, which could be ameliorated by NaHS and exacerbated by AOAA. NaHS completely reduced the disulfide bond of NMDAR1 in PC12 cells. The inhibition of NMDAR by MK-801 microinjected in PVN of rats with MCAO also could lower blood pressure and renal sympathetic discharge. In conclusion, PSH may be associated with disease progression and survival in patients with IS. Decreased levels of H2S in PVN were involved in regulating sympathetic efferent activity after cerebral infarction. Our results might provide a new strategy and target for the prevention and treatment of PSH.

Hi1a Improves Sensorimotor Deficit following Endothelin-1-Induced Stroke in Rats but Does Not Improve Functional Outcomes following Filament-Induced Stroke in Mice

Activation of acid-sensing ion channel 1a (ASIC1a) plays a major role in mediating acidosis-induced neuronal injury following a stroke. Therefore, the inhibition of ASIC1a is a potential therapeutic avenue for the treatment of stroke. Venom-peptide Hi1a, a selective and highly potent ASIC1a inhibitor, reduces the infarct size and functional deficits when injected into the brain after stroke in rodents. However, its efficacy when administered using a clinically relevant route of administration remains to be established. Therefore, the current investigation aims to examine the efficacy of systemically administered Hi1a, using two different models of stroke in different species. Mice were subjected to the filament model of middle cerebral artery occlusion (MCAO) and treated with Hi1a systemically using either a single- or multiple-dosing regimen. 24 h poststroke, mice underwent functional testing, and the brain infarct size was assessed. Rats were subjected to endothelin-1 (ET-1)-induced MCAO and treated with Hi1a intravenously 2 h poststroke. Rats underwent functional tests prior to and for 3 days poststroke, when infarct volume was assessed. Mice receiving Hi1a did not show any improvements in functional outcomes, despite a trend toward reduced infarct size. This trend for reduced infarct size in mice was consistent regardless of the dosing regimen. There was also a trend toward lower infarct size in rats treated with Hi1a. More specifically, Hi1a reduced the amount of damage occurring within the somatosensory cortex, which was associated with an improved sensorimotor function in Hi1a-treated rats. Thus, this study suggests that Hi1a or more brain-permeable ASIC1a inhibitors are a potential stroke treatment.

Research progress and perspectives of N-methyl-D-aspartate receptor in myocardial and cerebral ischemia-reperfusion injury: A review

There is an urgent need to find common targets for precision therapy, as there are no effective preventive therapeutic measures for combined clinical heart-brain organ protection and common pathways associated with glutamate receptors are involved in heart-brain injury, but current glutamate receptor-related clinical trials have failed. Ischemia-reperfusion injury (IRI) is a common pathological condition that occurs in multiple organs, including the heart and brain, and can lead to severe morbidity and mortality. N-methyl-D-aspartate receptor (NMDAR), a type of ionotropic glutamate receptor, plays a crucial role in the pathogenesis of IRI. NMDAR activity is mainly regulated by endogenous activators, agonists, antagonists, and voltage-gated channels, and activation leads to excessive calcium influx, oxidative stress, mitochondrial dysfunction, inflammation, apoptosis, and necrosis in ischemic cells. In this review, we summarize current research advances regarding the role of NMDAR in myocardial and cerebral IRI and discuss potential therapeutic strategies to modulate NMDAR signaling to prevent and treat IRI.

TAT peptide at treatment-level concentrations crossed brain endothelial cell monolayer independent of receptor-mediated endocytosis or peptide-inflicted barrier disruption

The peptide domain extending from residues 49 to 57 of the HIV-1 Tat protein (TAT) has been widely shown to facilitate cell entry of and blood-brain barrier (BBB) permeability to covalently bound macromolecules; therefore, TAT-linked therapeutic peptides trafficked through peripheral routes have been used to treat brain diseases in preclinical and clinical studies. Although the mechanisms underlying cell entry by similar peptides have been established to be temperature-dependent and cell-type specific and to involve receptor-mediated endocytosis, how these peptides cross the BBB remains unclear. Here, using an in vitro model, we studied the permeability of TAT, which was covalently bound to the fluorescent probe fluorescein isothiocyanate (FITC), and evaluated whether it crossed the "in vitro BBB", a monolayer of brain endothelial cells, and whether the mechanisms were similar to those involved in TAT entry into cells. Our results show that although TAT crossed the monolayer of brain endothelial cells in a temperature-dependent manner, in contrast to the reported mechanism of cell entry, it did not require receptor-mediated endocytosis. Furthermore, we revisited the hypothesis that TAT facilitates brain delivery of covalently bound macromolecules by causing BBB disruption. Our results demonstrated that the dose of TAT commonly used in preclinical and clinical studies did not exert an effect on BBB permeability in vitro or in vivo; however, an extremely high TAT concentration caused BBB disruption in vitro. In conclusion, the BBB permeability to TAT is temperature-dependent, but at treatment-level concentrations, it does not involve receptor-mediated endocytosis or BBB disruption.

Midazolam Prevents the Adverse Outcome of Neonatal Asphyxia

OBJECTIVE

Birth asphyxia (BA) is the most frequent cause of neonatal death as well as central nervous system (CNS) injury. BA is often associated with neonatal seizures, which only poorly respond to anti-seizure medications and may contribute to the adverse neurodevelopmental outcome. Using a non-invasive rat model of BA, we have recently reported that the potent benzodiazepine, midazolam, prevents neonatal seizures in ~50% of rat pups. In addition to its anti-seizure effect, midazolam exerts anti-inflammatory actions, which is highly relevant for therapeutic intervention following BA. The 2 major aims of the present study were to examine (1) whether midazolam reduces the adverse outcome of BA, and (2) whether this effect is different in rats that did or did not exhibit neonatal seizures after drug treatment.

METHODS

Behavioral and cognitive tests were performed over 14 months after asphyxia, followed by immunohistochemical analyses.

RESULTS

All vehicle-treated rats had seizures after asphyxia and developed behavioral and cognitive abnormalities, neuroinflammation in gray and white matter, neurodegeneration in the hippocampus and thalamus, and hippocampal mossy fiber sprouting in subsequent months. Administration of midazolam (1 mg/kg i.p.) directly after asphyxia prevented post-asphyctic seizures in ~50% of the rats and resulted in the prevention or decrease of neuroinflammation and the behavioral, cognitive, and neurodegenerative consequences of asphyxia. Except for neurodegeneration in the thalamus, seizures did not seem to contribute to the adverse outcome of asphyxia.

INTERPRETATION

The disease-modifying effect of midazolam identified here strongly suggests that this drug provides a valuable option for improving the treatment and outcome of BA. ANN NEUROL 2023;93:226-243.

Blood-Brain Barrier Disruption in Preclinical Mouse Models of Stroke Can Be an Experimental Artifact Caused by Craniectomy

The pathophysiological features of ischemia-related blood-brain barrier (BBB) disruption are widely studied using preclinical stroke models. However, in many of these models, craniectomy is required to confirm arterial occlusion via laser Doppler flowmetry or to enable direct ligation of the cerebral artery. In the present study, mice were used to construct a distal middle cerebral artery occlusion (dMCAO) model, a preclinical stroke model that requires craniectomy to enable direct ligation of the cerebral artery, or were subjected to craniectomy alone. dMCAO but not craniectomy caused neurodegeneration and cerebral infarction, but both procedures induced an appreciable increase in BBB permeability to Evans blue dye, fluorescein, and endogenous albumin but not to 10 kDa dextran-FITC, leading to cerebral edema. Using rats, we further showed that BBB disruption induced by craniectomy with no evidence of dural tearing was comparable to that induced by craniectomy involving tearing of the dura. In conclusion, our data demonstrated that craniectomy can be a major contributor to BBB disruption and cerebral edema in preclinical stroke models. The implications of this experimental artifact for translational stroke research and preclinical data interpretation are discussed.

Prophylactic Zinc Administration Combined with Swimming Exercise Prevents Cognitive-Emotional Disturbances and Tissue Injury following a Transient Hypoxic-Ischemic Insult in the Rat

Exercise performance and zinc administration individually yield a protective effect on various neurodegenerative models, including ischemic brain injury. Therefore, this work was aimed at evaluating the combined effect of subacute prophylactic zinc administration and swimming exercise in a transient cerebral ischemia model. The prophylactic zinc administration (2.5 mg/kg of body weight) was provided every 24 h for four days before a 30 min common carotid artery occlusion (CCAO), and 24 h after reperfusion, the rats were subjected to swimming exercise in the Morris Water Maze (MWM). Learning was evaluated daily for five days, and memory on day 12 postreperfusion; anxiety or depression-like behavior was measured by the elevated plus maze and the motor activity by open-field test. Nitrites, lipid peroxidation, and the activity of superoxide dismutase (SOD) and catalase (CAT) were assessed in the temporoparietal cortex and hippocampus. The three nitric oxide (NO) synthase isoforms, chemokines, and their receptor levels were measured by ELISA. Nissl staining evaluated hippocampus cytoarchitecture and Iba-1 immunohistochemistry activated the microglia. Swimming exercise alone could not prevent ischemic damage but, combined with prophylactic zinc administration, reversed the cognitive deficit, decreased NOS and chemokine levels, prevented tissue damage, and increased Iba-1 (+) cell number. These results suggest that the subacute prophylactic zinc administration combined with swimming exercise, but not the individual treatment, prevents the ischemic damage on day 12 postreperfusion in the transient ischemia model.

SAM, a cystathionine beta-synthase activator, promotes hydrogen sulfide to promote neural repair resulting from massive cerebral infarction induced by middle cerebral artery occlusion

Neurologic deterioration after massive cerebral infarct should be identified at an early stage for medical and surgical treatments. We investigated the effect of hydrogen sulfide on the excitotoxity of PC12 cells exposed to oxygen-glucose deprivation (OGD) and its effect on the apoptosis of brain tissues in rats with middle cerebral artery occlusion (MCAO). Rats with MCAO were treated with SAM, a cystathionine beta-synthase (CBS) activator, or AOAA, a CBS inhibitor. Hydrogen sulfide content in the brain tissues of infarcted patients or rats with MCAO was decreased, whereas glutamate (GLU) content was increased. In addition, SAM reduced reactive oxygen species content, lactate dehydrogenase release, and apoptosis levels in the brain tissues of rats with MCAO. The PC12 cells that were exposed to OGD were also treated with 20 mM GLU and later treated with SAM or AOAA. In PC12 cells, SAM reduced the apoptosis caused by GLU after OGD. The protective effects of hydrogen sulfide was elicited through the sulfur-sulfhydrylation modification of NMDAR and the induction of ERK/MAPK signaling. Our results showed that hydrogen sulfide exerts a protective effect on the PC12 cells and the rats with MCAO, which might represent a possible therapeutic agent against massive cerebral infarct.

Pre-hospital mild therapeutic hypothermia for patients with severe traumatic brain injury

BACKGROUND

We aimed to assess the effects of pre-hospital mild therapeutic hypothermia (MTH) on patients with severe traumatic brain injury (sTBI).

METHODS

Eighty-six patients with sTBI were prospectively enrolled into the pre-hospital MTH group and the late MTH group (initiated in hospital). Patients in the pre-hospital MTH group were maintained at a tympanic temperature of 33°C-35°C before admission and continued to be treated with a therapeutic hypothermia device for 4 days. Patients in the late MTH group were treated with the same MTH parameters. Intracranial pressure (ICP), complications and Glasgow Outcome Scale (GOS) scores were monitored.

RESULTS

ICP was significantly lower for patients in the pre-hospital MTH group 24, 48, and 72 h after treatment (17.38 ± 4.88 mmHg, 18.40 ± 4.50 mmHg, and 16.40 ± 4.13 mmHg, respectively) than that in the late MTH group (20.63 ± 3.00 mmHg, 21.80 ± 6.00 mmHg, and 18.81 ± 4.50 mmHg) (P < .05). The favorable prognosis (GOS scores 4-5) rate in the pre-hospital MTH group was higher tha n the late MTH group (65.1% vs. 37.2%, respectively; P < .05) without complications .

CONCLUSION

Pre-hospital MTH for patients with STBI can reduce ICP and improve neurological outcomes.

Drug-Induced Hyperglycemia as a Potential Contributor to Translational Failure of Uncompetitive NMDA Receptor Antagonists

Hyperglycemia is a comorbidity in 60–80% of stroke patients; nevertheless, neuroprotective drugs like NMDA receptor (NMDAR) antagonists are typically assessed in normoglycemic animals at the preclinical stage before they are approved to enter clinical trials. Interestingly, as a possible explanation for the translational failure of NMDAR antagonists, it was recently reported that stroke occurring during nighttime causes smaller infarctions in rodents and therefore has a smaller window for neuroprotection. To investigate why stroke occurring during different circadian phases confers a difference in severity, we reanalyzed the published source data and found that some mice that were used in the daytime have higher blood glucose than mice that were used in the nighttime. We then repeated the experiments but found no difference in blood glucose concentration or infarct volume regardless of the circadian phase during which stroke occurs. On the other hand, induction of hyperglycemia by glucose injection reproducibly increased stroke severity. Moreover, although hyperglycemia increases infarction volume, which presumably would provide a larger window for neuroprotection, uncompetitive NMDAR antagonists were unexpectedly found to exacerbate stroke outcome by worsening hyperglycemia. Taken together, our new data and reanalysis of the published source data suggested that blood glucose during stroke, rather than the circadian phase during which stroke occurs, affects the size of the ischemic infarction; moreover, we have revealed drug-induced hyperglycemia as a potential reason for the translational failure of uncompetitive NMDAR antagonists. Future trials for this class of neuroprotective drugs should monitor patients’ blood glucose at enrollment and exclude hyperglycemic patients.

Stroke injury induced by distal middle cerebral artery occlusion is resistant to N-methyl-d-aspartate receptor antagonism in FVB/NJ mice

Although N-methyl-d-aspartate receptor (NMDAR) antagonism has been shown to have a neuroprotective effect in many preclinical stroke models, the efficacy of this antiexcitotoxicity strategy in clinical trials in stroke patients has been disappointing. Interestingly, it has been reported that NMDAR antagonism is not neuroprotective in C57BL/6 mice subjected to distal middle cerebral artery occlusion (dMCAO), supporting the notion that whether these treatments are neuroprotective depends on the type of cerebral ischemia. However, because C57BL/6 mice are inherently resistant to excitotoxicity, the reported lack of neuroprotection could also be explained by the difference in the mouse strain studied rather than the stroke model used. Here we examined the neuroprotective efficacy of NMDAR antagonism in FVB/NJ mice, an excitotoxicity-prone mouse strain, subjected to dMCAO. Although C57BL/6 mice are known to have an excitotoxicity-resistant genetic background and FVB/NJ mice are known to have an excitotoxicity-prone genetic background, the infarct volume and density of neurodegenerating neurons were similar in the two mouse strains following dMCAO. In addition, none of the antiexcitotoxicity agents studied, including the canonical NMDAR antagonist MK801 and the therapeutic peptides Tat-NR2B9c and L-JNKI-1, protected the FVB/NJ mouse brain against ischemic damage induced by dMCAO. In conclusion, our data demonstrated that FVB/NJ mice are no more susceptible to cerebral ischemia than C57BL/6 mice and that NMDAR antagonism is ineffective in mice, even in an excitotoxicity-prone strain, subjected to dMCAO.

Microglia depletion by PLX3397 has no effect on cocaine-induced behavioral sensitization in male mice

Cocaine and other addictive drugs are known to stimulate microglia, and microglia in turn have been shown to play roles in both the development and mitigation of drug dependence. For instance, cocaine can directly bind to surface receptors on microglia and trigger their release of interleukin-1β, which promotes addictive behaviors; however, cocaine also indirectly stimulates microglia by elevating dopamine, which causes microglia to impair long-lasting neuronal changes related to cocaine use. The seemingly opposing roles of microglia beg the question of what the net effect of microglial presence is on cocaine-induced behavioral changes. Here, we depleted microglia from the mouse brain by treating mice with PLX3397 and subjected the mice to cocaine-induced behavioral sensitization, a model for studying long-lasting neuronal changes associated with drugs of abuse. Although cocaine treatment had little effect on microglial abundance, PLX3397 treatment dramatically decreased the number of microglia in the nucleus accumbens and hippocampus in control mice and in mice subjected to cocaine sensitization. Importantly, loss of microglia did not appear to affect either the acute locomotor response to cocaine treatment or sensitization after repeated doses of cocaine. In conclusion, while our data do not contradict previous findings indicating that different microglial-derived factors can have seemingly opposite effects on behaviors associated with cocaine use, they suggest that microglia do not have a net effect on cocaine-induced long-lasting behavioral changes.

The Function of the NMDA Receptor in Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is one of the main forms of neonatal brain injury which could lead to neonatal disability or even cause neonatal death. Therefore, HIE strongly affects the health of newborns and brings heavy burden to the family and society. It has been well studied that N-methyl-D-aspartate (NMDA) receptors are involved in the excitotoxicity induced by hypoxia ischemia in adult brain. Recently, it has been shown that the NMDA receptor also plays important roles in HIE. In the present review, we made a summary of the molecular mechanism of NMDA receptor in the pathological process of HIE, focusing on the distinct role of GluN2A- and GluN2B-containing NMDA receptor subtypes and aiming to provide some insights into the clinical treatment and drug development of HIE.