Isoflurane provides neuroprotection in neonatal hypoxic ischemic brain injury by suppressing apoptosis

GABAergic system and chloride cotransporters as potential therapeutic targets to mitigate cell death in ischemia

Gamma aminobutyric acid (GABA) is a critical inhibitory neurotransmitter in the central nervous system that plays a vital role in modulating neuronal excitability. Dysregulation of GABAergic signaling, particularly involving the cotransporters NKCC1 and KCC2, has been implicated in various pathologies, including epilepsy, schizophrenia, autism spectrum disorder, Down syndrome, and ischemia. NKCC1 facilitates chloride influx, whereas KCC2 mediates chloride efflux via potassium gradient. Altered expression and function of these cotransporters have been associated with excitotoxicity, inflammation, and cellular death in ischemic events characterized by reduced cerebral blood flow, leading to compromised tissue metabolism and subsequent cell death. NKCC1 inhibition has emerged as a potential therapeutic approach to attenuate intracellular chloride accumulation and mitigate neuronal damage during ischemic events. Similarly, targeting KCC2, which regulates chloride efflux, holds promise for improving outcomes and reducing neuronal damage under ischemic conditions. This review emphasizes the critical roles of GABA, NKCC1, and KCC2 in ischemic pathologies and their potential as therapeutic targets. Inhibiting or modulating the activity of these cotransporters represents a promising strategy for reducing neuronal damage, preventing excitotoxicity, and improving neurological outcomes following ischemic events. Furthermore, exploring the interactions between natural compounds and NKCC1/KCC2 provides additional avenues for potential therapeutic interventions for ischemic injury.

Differential Age-Dependent Mitochondrial Dysfunction, Oxidative Stress, and Apoptosis Induced by Neonatal Hypoxia-Ischemia in the Immature Rat Brain

Neonatal hypoxia-ischemia (HI) is among the main causes of mortality and morbidity in newborns. Experimental studies show that the immature rat brain is less susceptible to HI injury, suggesting that changes that occur during the first days of life drastically alter its susceptibility. Among the main developmental changes observed is the mitochondrial function, namely, the tricarboxylic acid (TCA) cycle and respiratory complex (RC) activities. Therefore, in the present study, we investigated the influence of neonatal HI on mitochondrial functions, redox homeostasis, and cell damage at different postnatal ages in the hippocampus of neonate rats. For this purpose, animals were divided into four groups: sham postnatal day 3 (ShP3), HIP3, ShP11, and HIP11. We initially observed increased apoptosis in the HIP11 group only, indicating a higher susceptibility of these animals to brain injury. Mitochondrial damage, as determined by flow cytometry showing mitochondrial swelling and loss of mitochondrial membrane potential, was also demonstrated only in the HIP11 group. This was consistent with the decreased mitochondrial oxygen consumption, reduced TCA cycle enzymes, and RC activities and induction of oxidative stress in this group of animals. Considering that HIP3 and the sham animals showed no alteration of mitochondrial functions, redox homeostasis, and showed no apoptosis, our data suggest an age-dependent vulnerability of the hippocampus to hypoxia-ischemia. The present results highlight age-dependent metabolic differences in the brain of neonate rats submitted to HI indicating that different treatments might be needed for HI newborns with different gestational ages.

Isoflurane reduces septic neuron injury by HO‑1‑mediated abatement of inflammation and apoptosis

Sepsis-associated encephalopathy (SAE) frequently occurs in critically ill patients with severe systemic infections. Subanesthetic isoflurane (0.7% ISO) possesses anti-inflammatory, antioxidant and anti-apoptotic properties against a number of human diseases, including brain injury. The activation of heme oxygenase-1 (HO-1) impedes inflammation, oxidation and apoptosis, thus alleviating sepsis-induced brain damage. However, whether 0.7% ISO affords protection against septic neuronal injury involving HO-1 activation is unclear. The present study aimed to investigate the neuroprotective effects of 0.7% ISO and its potential underlying mechanisms in SAE using a mouse model established by cecal ligation and puncture (CLP). The results indicated that the expression and activity of HO-1 in the mouse hippocampus were increased by CLP, and further enhanced by ISO. ISO reduced the death rate, brain water content and blood-brain barrier disruption, but improved the learning and memory functions of CLP-treated mice. ISO significantly decreased the production of pro-inflammatory cytokines and the levels of oxidative indictors in the serum and hippocampus, as well as the number of apoptotic neurons and the expression of pro-apoptotic proteins in the hippocampus. Inversely, anti-inflammatory factors, antioxidative enzymes and anti-apoptotic proteins were markedly increased by ISO administration. However, the neuroprotective effects of ISO were abolished by a HO-1 inhibitor. Overall, these findings suggested that 0.7% ISO alleviated SAE via its anti-inflammatory, antioxidative and anti-apoptotic properties, which involved the activated form of HO-1.

The maintenance of adult peripheral adult nerve and microvascular networks in the rat mesentery culture model

BACKGROUND

Neurovascular patterning is an emerging area of microvascular research. While overlapping molecular signals highlight links between angiogenesis and neurogenesis, advancing our understanding is limited by a lack of in vitro models containing both systems. One potential model is the rat mesentery culture model, which our laboratory has recently introduced as an ex vivo tool to investigate cellular dynamics during angiogenesis in a microvascular network scenario. The objective of this study was to demonstrate the use of the rat mesentery culture model as an ex vivo platform for maintaining the spatiotemporal relationship between blood vessels and peripheral nerves during angiogenesis in adult microvascular networks.

METHODS

Adult male Wistar rat mesenteric tissue windows were harvested, rinsed in sterile DPBS and medium and then cultured per group: 1) MEM alone and 2) NBM with NGF and 20 % FBS (nerve culture medium). On day 3 post culture tissues were labeled for endothelial (PECAM) and neural (class III β-tubulin, NG2, tyrosine hydroxylase, CGRP) markers.

RESULTS

In MEM alone tissues nerve segment degeneration was supported by discontinuous nerve or absence of nerve marker labeling. Nerve presence at the arteriole level and capillary level was maintained for the nerve culture medium group compared to day 0, non-cultured control group (unstimulated).

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

The results support the use of specific medium types to maintain nerve presence across cultured microvascular networks and implicates the rat mesentery culture model as a novel ex vivo tool for investigating neurovascular patterning in adult tissues.

An appropriate level of autophagy reduces emulsified isoflurane-induced apoptosis in fetal neural stem cells

Autophagy plays essential roles in cell survival. However, the functions and regulation of the autophagy-related proteins Atg5, LC3B, and Beclin 1 during anesthetic-induced developmental neurotoxicity remain unclear. This study aimed to understand the autophagy pathways and mechanisms that affect neurotoxicity, induced by the anesthetic emulsified isoflurane, in rat fetal neural stem cells. Fetal neural stem cells were cultured, in vitro, and neurotoxicity was induced by emulsified isoflurane treatment. The effects of pretreatment with the autophagy inhibitors 3-methyladenine and bafilomycin and the effects of transfection with small interfering RNA against ATG5 (siRNA-Atg5) were observed. Cell viability was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and apoptosis was assessed using flow cytometry. Ultrastructural changes were analyzed through transmission electron microscopy. The levels of the autophagy-related proteins LC3B, Beclin 1, Atg5, and P62 and the pro-apoptosis-related protein caspase-3 were analyzed using western blot assay. The inhibition of cell proliferation and that of apoptosis rate increased after treatment with emulsified isoflurane. Autophagolysosomes, monolayer membrane formation due to lysosomal degradation, were observed. The autophagy-related proteins LC3B, Beclin 1, Atg5, and P62 and caspase-3 were upregulated. These results confirm that emulsified isoflurane can induce toxicity and autophagy in fetal neural stem cells. Pre-treatment with 3-methyladenine and bafilomycin increased the apoptosis rate in emulsified isoflurane-treated fetal neural stem cells, which indicated that the complete inhibition of autophagy does not alleviate emulsified isoflurane-induced fetal neural stem cell toxicity. Atg5 expression was decreased significantly by siRNA-Atg5 transfection, and cell proliferation was inhibited. These results verify that the Atg5 autophagy pathway can be regulated to maintain appropriate levels of autophagy, which can inhibit the neurotoxicity induced by emulsified isoflurane anesthetic in fetal neural stem cells.

HDAC2 hyperexpression alters hippocampal neuronal transcription and microglial activity in neuroinflammation-induced cognitive dysfunction

Background

Inflammation can induce cognitive dysfunction in patients who undergo surgery. Previous studies have demonstrated that both acute peripheral inflammation and anaesthetic insults, especially isoflurane (ISO), are risk factors for memory impairment. Few studies are currently investigating the role of ISO under acute peri-inflammatory conditions, and it is difficult to predict whether ISO can aggravate inflammation-induced cognitive deficits. HDACs, which are essential for learning, participate in the deacetylation of lysine residues and the regulation of gene transcription. However, the cell-specific mechanism of HDACs in inflammation-induced cognitive impairment remains unknown.

Methods

Three-month-old C57BL/6 mice were treated with single versus combined exposure to LPS injected intraperitoneally (i.p.) to simulate acute abdominal inflammation and isoflurane to investigate the role of anaesthesia and acute peripheral inflammation in cognitive impairment. Behavioural tests, Western blotting, ELISA, immunofluorescence, qRT-PCR, and ChIP assays were performed to detect memory, the expressions of inflammatory cytokines, HDAC2, BDNF, c-Fos, acetyl-H3, microglial activity, Bdnf mRNA, c-fos mRNA, and Bdnf and c-fos transcription in the hippocampus.

Results

LPS, but not isoflurane, induced neuroinflammation-induced memory impairment and reduced histone acetylation by upregulating histone deacetylase 2 (HDAC2) in dorsal hippocampal CaMKII⁺ neurons. The hyperexpression of HDAC2 in neurons was mediated by the activation of microglia. The decreased level of histone acetylation suppressed the transcription of Bdnf and c-fos and the expressions of BDNF and c-Fos, which subsequently impaired memory. The adeno-associated virus ShHdac2, which suppresses Hdac2 after injection into the dorsal hippocampus, reversed microglial activation, hippocampal glutamatergic BDNF and c-Fos expressions, and memory deficits.

Conclusions

Reversing HDAC2 in hippocampal CaMKII⁺ neurons exert a neuroprotective effect against neuroinflammation-induced memory deficits.

Upregulation of aryl hydrocarbon receptor nuclear translocator 2 in the hippocampi of post-stroke depression rats

Aryl hydrocarbon receptor nuclear translocator protein 2 (ARNT2), a member of the basic helix-loop-helix superfamily of transcription factors, may serve a vital role in neuronal survival and cell proliferation via formation of heterodimers with hypoxia-inducible factor-1α. Previous studies indicated that ARNT2 levels were elevated in the brains of ischemic rats; however, the involvement of ARNT2 in post-stroke depression (PSD) rats is not well understood. Therefore, the present study aimed to investigate the levels of ARNT2 in the hippocampi of PSD rats, and to clarify the potential association between ARNT2 and behavioral performance. A PSD rat model was established by middle cerebral artery occlusion (MCAO) followed by a 4-week chronic unpredictable mild stress (CUMS) regimen. A sucrose preference test and open field test (OFT) were conducted, and body weight was measured. In addition, reverse transcription-polymerase chain reaction and immunohistochemistry were performed to measure ARNT expression. Results indicated that MCAO+CUMS rats had lower weight gain, consumed less sucrose and moved less compared with controls. Furthermore, the mRNA and protein levels of ARNT in MCAO+CUMS rats were increased compared with in controls. The sucrose preference index and horizontal movement distance in the OFT were positively correlated with ARNT mRNA level. Thus, from these findings it was suggested that ARNT2 may be positively associated with improvement of cognitive impairment, and therefore may be a potential target in PSD treatment.

Effects of compound 21, a non‑peptide angiotensin II type 2 receptor agonist, on general anesthesia‑induced cerebral injury in neonatal rats

General anesthesia has a great impact on neurodevelopment. However, the mechanisms underlying this effect and therapeutic methods to address it remain limited. The present study aimed to investigate the effects of compound (C)21, a non-peptide angiotensin II type 2 receptor agonist, on general anesthesia-induced cerebral injury in neonatal rats. Neonatal Sprague Dawley rats (postnatal day 7) were randomly divided into three groups (n=6 per group): The control, isoflurane and C21+ isoflurane (C21) group. General anesthesia was induced through inhalation of 1.3% isoflurane. Apoptosis and synaptic structure were analyzed. The levels of peroxisome proliferator-activated receptor (PPAR)-α were detected using an enzyme-linked immunosorbent assay. BCL2, apoptosis regulator (Bcl-2) expression was also measured. Compared with the control group, the cerebral cortex, hippocampus, amygdala and hypothalamus in the isoflurane group had significantly more apoptotic cells (P<0.05). The nuclei of the control group were round and transparent, while shrunken nuclei and condensed chromatin were visible in the isoflurane group. A reduction in synapse number was observed in the isoflurane group compared with the control. By contrast, nuclei shrinkage and the decrease in synaptic number was improved in the C21 group. PPAR-α and Bcl-2 expression, at the mRNA and protein levels, was significantly reduced in the isoflurane group compared with the control (P<0.05). C21 treatment reduced the decrease in PPAR-α and Bcl-2 in the cerebral cortex, hippocampus, amygdala and hypothalamus (P<0.05). Collectively, it was demonstrated that C21 prevented apoptosis and synaptic loss induced by general anesthesia in neonatal rats by enhancing the expression of PPAR-α and Bcl-2.

Mangiferin Potentiates Neuroprotection by Isoflurane in Neonatal Hypoxic Brain Injury by Reducing Oxidative Stress and Activation of Phosphatidylinositol-3-Kinase/Akt/Mammalian Target of Rapamycin (PI3K/Akt/mTOR) Signaling

Background

Hypoxic-ischemic brain injury in the perinatal period is a main cause of perinatal mortality and neurologic complications in neonates and children. Recent studies have focused on the neuroprotective effect of anesthetic drugs. The volatile anesthetic isoflurane has been shown to exert neuroprotective effects in cerebral ischemia. Mangiferin is a natural polyphenol with various pharmacological properties, including antioxidant and ant-tumor effects. This study aimed to determine whether mangiferin potentiates the neuroprotective effects of isoflurane and also if mangiferin when administered alone exerts neuroprotective effects following hypoxic-ischemic brain injury.

Material/Methods

Sprague-Dawley rats were subjected to cerebral hypoxic ischemia on postnatal day 10 (P10). Mangiferin (50, 100, or 200 mg/kg b.w.) was intragastrically administered from P3 to P12 and 1 h prior to insult on the day of ischemic induction. At 3 h after hypoxia-ischemia (HI) insult, separate groups of rat pups were exposed to isoflurane (1.5%) for 6 h. Following 48 h of HI, the rats were sacrificed and brain tissues were used for analysis.

Results

Mangiferin treatment attenuated neuronal apoptosis and reduced cerebral infarct volume. The expression of cleaved caspase-3 and apoptotic cascade proteins were regulated. The levels of reactive oxygen species (ROS) and malondialdehyde were reduced by mangiferin and/or isoflurane exposure. The levels of antioxidant glutathione were considerably raised under HI injury, which was modulated by mangiferin and isoflurane exposure. The PI3K/Akt signaling pathway, which was downregulated following HI insult, was activated by mangiferin and/or isoflurane.

Conclusions

This study reveals the potent neuroprotective efficacy of mangiferin against HI-induced brain injury via effectively modulating apoptotic pathways, ROS levels, and PI3K/Akt cascades while potentiating protective effects of isoflurane.

Estrogen and propofol combination therapy inhibits endoplasmic reticulum stress and remarkably attenuates cerebral ischemia-reperfusion injury and OGD injury in hippocampus

AIM

Endoplasmic reticulum stress (ERS) is vital in inducing apoptosis via caspase-12 and C/EBP homologous protein (CHOP) apoptotic pathway in the hippocampus after ischemia-reperfusion injury. The study aimed to estimate the efficacy of estrogen and propofol combination therapy against ERS-induced apoptosis after cerebral ischemia-reperfusion injury and oxygen-glucose deprivation (OGD) injury in the hippocampus in vivo and in vitro.

METHODS

Rat model of cerebral ischemia-reperfusion injury was generated by middle cerebral artery occlusion (MCAO) strategy with ischemic intervention for 90 min and reperfusion for 24 h. Propofol processing ischemia-reperfusion group (Propofol group) infused 50 mg/kg/h of propofol via the femoral vein at the onset of reperfusion for 30 min. Estrogen processing ischemia-reperfusion group (estrogen group) received 0.0125 mg/kg of estrogen via tail vein at 30 min prior to MCAO. Combination therapy for ischemia-reperfusion group (combination group) received simultaneous processing with propofol and estrogen. In vitro, brain slices were randomly exposed to dimethylsulfoxide (DSMO), 10 μm of propofol, 10 nm of estrogen, or propofol and estrogen. Changes in the orthodromic population spike (OPS) at the end of reoxygenation were recorded. Neurological deficit examination, Nissl staining, and 2,3,5-triphenyltetrazolium chloride (TTC) staining were employed to evaluate the level of cerebral ischemia-reperfusion injury. The expression of caspase-3, caspase-12, glucose-regulated protein 78 (GRP78), and CHOP were investigated by Western blot and immunofluorescence staining assays. Neural apoptotic rate in hippocampus was detected by the flow cytometry trial.

RESULTS

Neurological deficit score, infarct volume, the expression of caspase-3 (P <  0.05), caspase-12, GRP78, CHOP, and neural apoptotic rate of I/R group increased markedly (P <  0.01). When obtaining drug treatment, neurological deficit score (P <  0.05), infarct volume, the expression levels of caspase-12 and GRP78, and neural apoptotic rate of the propofol group decreased significantly (P <  0.01). Furthermore, neurological deficit score, infarct volume, expression levels of caspase-3, caspase-12, GRP78, and CHOP (P <  0.05), and neural apoptotic rate decreased in the estrogen group (P <  0.01) and especially in the combination group (P <  0.01). Compared with the propofol group, the neurological deficit score (P <  0.05), infarct volume, caspase-3, caspase-12, GRP78, CHOP, and neural apoptotic rate of the combination group decreased (P <  0.01). Compared with the estrogen group, the infarct volume, caspase-3 (P <  0.05), GRP78, CHOP, and neural apoptotic rate (P <  0.05) of the combination group decreased (P <  0.01). Compared with the propofol group, the infarct volume, caspase-3, caspase-12 (P <  0.05), and GRP78 (P <  0.05) of the estrogen group decreased (P <  0.01). Propofol and estrogen treatment can delay the abolishing time of OPS and increase the recovery rate and amplitude of OPS, compared with OGD group (P <  0.01), especially in the combination therapy (P <  0.01).

CONCLUSION

The neuroprotection of propofol and estrogen combination therapy inhibited excessive ERS-induced apoptosis against cerebral ischemia-reperfusion injury and OGD injury in the hippocampus of rats. Furthermore, the outcomes demonstrated that combination therapy yielded synergistic effects.

Role of spinal GABA receptors in the acute antinociceptive response of mice to hyperbaric oxygen

New pain treatments are in demand due to the pervasive nature of pain conditions. Hyperbaric oxygen (HBO₂) has shown potential in treating pain in both clinical and preclinical settings, although the mechanism of this effect is still unknown. The aim of this study was to investigate whether the major inhibitory neurotransmitter γ-aminobutyric acid (GABA) is involved in HBO₂-induced antinociception in the central nervous system (CNS). To accomplish this goal, pharmacological interactions between GABA drugs and HBO₂ were investigated using the behavioral acetic acid abdominal constriction test. Western blotting was used to quantify protein changes that might occur as a result of the interactions. GABA_A but not GABA_B receptor antagonists dose-dependently reduced HBO₂ antinociception, while antagonism of the GABA reuptake transporter enhanced this effect. Western blot results showed an interaction between the pain stimulus and HBO₂ on expression of the phosphorylated β3 subunit of the GABA_A receptor at S408/409 in homogenates of the lumbar but not thoracic spinal cord. A significant interaction was also found in neuronal nitric oxide synthase (nNOS) expression in the lumbar but not thoracic spinal cord. These findings support the notion that GABA may be involved in HBO₂-induced antinociception at the GABA_A receptor but indicate that more study will be needed to understand the intricacies of this interaction.

Attenuation of Retinal Vascular Development in Neonatal Mice Subjected to Hypoxic-Ischemic Encephalopathy

A significant proportion of children that survive hypoxic-ischemic encephalopathy (HIE) develop visual impairment. These visual deficits are generally attributed to injuries that occur in the primary visual cortex and other visual processing systems. Recent studies suggested that neuronal damage might also occur in the retina. An important structure affecting the viability of retinal neurons is the vasculature. However, the effects of HIE on the retinal neurovasculature have not been systemically evaluated. Here we investigated whether exposure of postnatal day 9 (P9) neonatal mice to HIE is sufficient to induce neurovascular damage in the retina. We demonstrate that the blood vessels on the surface of the retina, from mice subjected to HIE, were abnormally enlarged with signs of degeneration. The intermediate and deep vascular layers in these retinas failed to form normally, particularly in the periphery. All the vascular damages observed here were irreversible in nature up to 100 days post HIE. We also observed loss of retinal neurons, together with changes in both astrocytes and Müller cells mainly in the inner retina at the periphery. Collectively, our findings suggest that HIE results in profound alterations in the retinal vasculature, indicating the importance of developing therapeutic strategies to protect neurovascular dysfunction not only in the brain but also in the retina for infants exposed to HIE.

Neuroprotection provided by isoflurane pre-conditioning and post-conditioning

Isoflurane, a volatile and inhalational anesthetic, has been extensively used in perioperative period for several decades. A large amount of experimental studies have indicated that isoflurane exhibits neuroprotective properties when it is administrated before or after (pre-conditioning and post-conditioning) neurodegenerative diseases (e.g., hypoxic ischemia, stroke and trauma). Multiple mechanisms are involved in isoflurane induced neuroprotection, including activation of glycine and γ-aminobutyric acid receptors, antagonism of ionic channels and alteration of the function and activity of other cellular proteins. Although neuroprotection provided by isoflurane is observed in many animal studies, convincing evidence is lacking in human trials. Therefore, there is still a long way to go before translating its neuroprotective properties into clinical practice.