Protective Effect of Aliskiren in Experimental Ischemic Stroke: Up-Regulated p-PI3K, p-AKT, Bcl-2 Expression, Attenuated Bax Expression

The Protective Role of Transcript-Induced in Spermiogenesis 40 in Cerebral Ischemia-Reperfusion Injury

Prompt reperfusion after cerebral ischemia is important to maintain neuronal survival and reduce permanent disability and death. However, the resupply of blood can induce oxidative stress, inflammatory response and apoptosis, further leading to tissue damage. Here, we report the versatile biological roles of transcript-induced in spermiogenesis 40 (Tisp40) in ischemic stroke. We found that the expression of Tisp40 was upregulated in ischemia/reperfusion-induced brain tissues and oxygen glucose deprivation/returned -stimulated neurons. Tisp40 deficiency increased the infarct size and neurological deficit score, and promoted inflammation and apoptosis. Tisp40 overexpression played the opposite role. In vitro, the oxygen glucose deprivation/returned model was established in Tisp40 knockdown and overexpression primary cultured cortical neurons. Tisp40 knockdown can aggravate the process of inflammation and apoptosis, and Tisp40 overexpression ameliorated the aforementioned processes. Mechanistically, Tisp40 protected against ischemic stroke via activating the AKT signaling pathway. Tisp40 may be a new therapeutic target in brain ischemia/reperfusion injury.

Dantrolene alleviates mitochondrial dysfunction and neuroinflammation in traumatic brain injury by modulating the NF-ĸβ/Akt pathway

Traumatic brain injury (TBI) triggers a bevy of changes including mitochondrial dysfunction, apoptosis, oxidative stress, neurobehavioural impairment, and neuroinflammation, among others. Dantrolene (DNT), a muscle relaxant which inhibits intracellular Ca2+ signaling from the ER, has been repurposed as a potential neuroprotective agent in various neurological diseases. However, there have been limited studies on whether it can mitigate TBI-induced deficits and restore impaired mitochondrial dynamics. This study sought to evaluate whether Dantrolene can potentially provide neuroprotection in an in vivo model of TBI. Male wistar rats subjected to TBI were treated with DNT (10 mg/kg) 1 h and 12 h post surgery. Animals were assessed 24 h post-TBI to evaluate neurobehavioural deficits and cerebral edema. We evaluated the protein expressions of apoptotic, autophagic, and neuroinflammatory markers by immunoblotting, as well as Mitochondrial Membrane Potential (MMP) and Reactive Oxygen Species (ROS) via Flow Cytometry to ascertain the effects of DNT on TBI. We further analysed immunofluorescence staining with Glial Fibrillary Acidic Protein (GFAP) and immunohistochemistry with NF-κβ to investigate neuroinflammation. H&E staining was also performed post-TBI. Our findings revealed DNT administration inhibits mitochondria-mediated apoptotis and reduces heightened oxidative stress. DNT treatment was also found to reverse neurobehavioural impairments and offer neuroprotection by preserving neuronal architechture. We also demonstrated that DNT inhibits neuronal autophagy and alleviates neuroinflammation following TBI by modulating the NF-κβ/Akt signaling pathway. Thus, our results suggest a novel application of DNT in ameliorating the multitude of deficits induced by TBI, thereby conferring neuroprotection.

Effects of an Akt-activating peptide obtained from walnut protein degradation on the prevention of memory impairment in mice

Akt acts as a central protein influencing multiple pathologies in neurodegenerative diseases including AD and PD, and using Akt activators is a promising management strategy. The current study characterized the effects of an Akt-activating peptide (Glu-Pro-Glu-Val-Leu-Pro, EPEVLR) obtained from walnut protein degradation on D-gal-induced memory impairment in mice. EPEVLR was obtained by hydrolysis of walnut proteins, identification of peptide sequences, and screening for molecular docking sequentially. The MWM test in mice indicated that the oral administration of EPEVLR (80, 200 and 400 mg per kg per day) significantly (p < 0.05) reversed D-gal-induced memory impairment. WB tests of the mouse hippocampus confirmed that EPEVLR could activate Akt by promoting its phosphorylation. In addition, further characterization (including TEM, ELISA, and immunohistochemistry) related to Akt phosphorylation showed lower Aβ and p-tau levels, as well as more autophagosomes than those in the model group. Moreover, the EPEVLR treatment significantly increased Lactobacillus abundance and reduced Helicobacter abundance in the gut microbiome and caused up-regulation of SCFAs and down-regulation of LPS of serum metabolites. Therefore, EPEVLR ingestion reversed cognitive impairment symptoms, possibly related to the activation of Akt and regulation of the intestinal flora pathway. Consumption of an EPEVLR-containing diet is beneficial for treating cognitive dysfunction.

Intranasal Delivery of Anti-Apoptotic siRNA Complexed with Fas-Signaling Blocking Peptides Attenuates Cellular Apoptosis in Brain Ischemia

Ischemic stroke-induced neuronal cell death leads to the permanent impairment of brain function. The Fas-mediating extrinsic apoptosis pathway and the cytochrome c-mediating intrinsic apoptosis pathway are two major molecular mechanisms contributing to neuronal injury in ischemic stroke. In this study, we employed a Fas-blocking peptide (FBP) coupled with a positively charged nona-arginine peptide (9R) to form a complex with negatively charged siRNA targeting Bax (FBP9R/siBax). This complex is specifically designed to deliver siRNA to Fas-expressing ischemic brain cells. This complex enables the targeted inhibition of Fas-mediating extrinsic apoptosis pathways and cytochrome c-mediating intrinsic apoptosis pathways. Specifically, the FBP targets the Fas/Fas ligand signaling, while siBax targets Bax involved in mitochondria disruption in the intrinsic pathway. The FBP9R carrier system enables the delivery of functional siRNA to hypoxic cells expressing the Fas receptor on their surface-a finding validated through qPCR and confocal microscopy analyses. Through intranasal (IN) administration of FBP9R/siCy5 to middle cerebral artery occlusion (MCAO) ischemic rat models, brain imaging revealed the complex specifically localized to the Fas-expressing infarcted region but did not localize in the non-infarcted region of the brain. A single IN administration of FBP9R/siBax demonstrated a significant reduction in neuronal cell death by effectively inhibiting Fas signaling and preventing the release of cytochrome c. The targeted delivery of FBP9R/siBax represents a promising alternative strategy for the treatment of brain ischemia.

Genetic and Pharmacological Modulation of P75 Neurotrophin Receptor Attenuate Brain Damage After Ischemic Stroke in Mice

The precursor nerve growth factor (ProNGF) and its receptor p75 neurotrophin receptor (p75NTR) are upregulated in several brain diseases, including ischemic stroke. The activation of p75NTR is associated with neuronal apoptosis and inflammation. Thus, we hypothesized that p75NTR modulation attenuates brain damage and improves functional outcomes after ischemic stroke. Two sets of experiments were performed. (1) Adult wild-type (WT) C57BL/6 J mice were subjected to intraluminal suture-middle cerebral artery occlusion (MCAO) to induce cerebral ischemia. Pharmacological inhibitor of p75NTR, LM11A-31 (50 mg/kg), or normal saline was administered intraperitoneally (IP) 1 h post-MCAO, and animals survived for 24 h. (2) Adult p75NTR heterozygous knockout (p75NTR+/-) and WT were subjected to photothrombotic (pMCAO) to induce ischemic stroke, and the animals survived for 72 h. The sensory-motor function of animals was measured using Catwalk XT. The brain samples were collected to assess infarction volume, edema, hemorrhagic transformation, neuroinflammation, and signaling pathway at 24 and 72 h after the stroke. The findings described that pharmacological inhibition and genetic knocking down of p75NTR reduce infarction size, edema, and hemorrhagic transformation following ischemic stroke. Additionally, p75NTR modulation significantly decreased several anti-apoptosis markers and improved sensory motor function compared to the WT mice following ischemic stroke. Our observations exhibit that the involvement of p75NTR in ischemic stroke and modulation of p75NTR could improve the outcome of ischemic stroke by increasing cell survival and enhancing motor performance. LM11A-31 has the potential to be a promising therapeutic agent for ischemic stroke. However, more evidence is needed to illuminate the efficacy of LM11A-31 in ischemic stroke.

The cellular mechanisms associated with the anesthetic and neuroprotective properties of xenon: a systematic review of the preclinical literature

Introduction

Xenon exhibits significant neuroprotection against a wide range of neurological insults in animal models. However, clinical evidence that xenon improves outcomes in human studies of neurological injury remains elusive. Previous reviews of xenon's method of action have not been performed in a systematic manner. The aim of this review is to provide a comprehensive summary of the evidence underlying the cellular interactions responsible for two phenomena associated with xenon administration: anesthesia and neuroprotection.

Methods

A systematic review of the preclinical literature was carried out according to the PRISMA guidelines and a review protocol was registered with PROSPERO. The review included both in vitro models of the central nervous system and mammalian in vivo studies. The search was performed on 27th May 2022 in the following databases: Ovid Medline, Ovid Embase, Ovid Emcare, APA PsycInfo, and Web of Science. A risk of bias assessment was performed utilizing the Office of Health Assessment and Translation tool. Given the heterogeneity of the outcome data, a narrative synthesis was performed.

Results

The review identified 69 articles describing 638 individual experiments in which a hypothesis was tested regarding the interaction of xenon with cellular targets including: membrane bound proteins, intracellular signaling cascades and transcription factors. Xenon has both common and subtype specific interactions with ionotropic glutamate receptors. Xenon also influences the release of inhibitory neurotransmitters and influences multiple other ligand gated and non-ligand gated membrane bound proteins. The review identified several intracellular signaling pathways and gene transcription factors that are influenced by xenon administration and might contribute to anesthesia and neuroprotection.

Discussion

The nature of xenon NMDA receptor antagonism, and its range of additional cellular targets, distinguishes it from other NMDA antagonists such as ketamine and nitrous oxide. This is reflected in the distinct behavioral and electrophysiological characteristics of xenon. Xenon influences multiple overlapping cellular processes, both at the cell membrane and within the cell, that promote cell survival. It is hoped that identification of the underlying cellular targets of xenon might aid the development of potential therapeutics for neurological injury and improve the clinical utilization of xenon.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier: 336871.

GLP-1R knockdown abrogates the protective effects of liraglutide on ischaemic stroke via inhibition of M2 polarisation and activation of NLRP3 inflammasome by reducing Nrf2 activation

Liraglutide has been recently discovered to penetrate the blood-brain barrier to exert neuroprotective effects. However, relevant mechanisms of the protective effects of liraglutide on ischaemic stroke remain to be elucidated. This study examined the mechanism of GLP-1R in regulating the protective effect of liraglutide against ischaemic stroke. Middle cerebral artery occlusion (MCAO) male Sprague-Dawley rat model with/without GLP-1R or Nrf2 knockdown was established and subjected to liraglutide treatment. Then neurological deficit and brain oedema of rats was evaluated and brain tissues were subjected to TTC, Nissl, TUNEL and immunofluorescence staining. Rat primary microglial cells firstly underwent lipopolysaccharide (LPS) treatment, then GLP-1R or Nrf2 knockdown treatment, and finally Liraglutide treatment to research the NLRP3 activation. As a result, Liraglutide protected rats' brain tissues after MCAO, which attenuated brain oedema, infarct volume, neurological deficit score, neuronal apoptosis and Iba1 expression but enhanced live neurons. However, GLP-1R knockdown abrogated these protective effects of liraglutide on MCAO rats. According to in vitro experiments, Liraglutide promoted M2 polarisation, activated Nrf2 and inhibited NLRP3 activation in LPS-induced microglial cells, but GLP-1R or Nrf2 knockdown reversed these effects of Liraglutide on LPS-induced microglial cells. Further, Nrf2 knockdown counteracted the protection of liraglutide on MCAO rats, whereas sulforaphane (agonist of Nrf2) counteracted the effect of Nrf2 knockdown on liraglutide-treated MCAO rats. Collectively, GLP-1R knockdown abrogated the protection of liraglutide on MCAO rats by activating NLRP3 via inactivating Nrf2.

LncRNA CEBPA-AS1 knockdown prevents neuronal apoptosis against oxygen glucose deprivation/reoxygenation by regulating the miR-455/GPER1 axis

Ischemic stroke (IS) is a common nervous system disease, which is a major cause of disability and death in the world. In present study, we demonstrated a regulatory mechanism of CCAAT/enhancer binding protein-alpha antisense 1 (CEBPA-AS1) in oxygen glucose deprivation/reoxygenation (OGD/R)-induced SH-SY5Y cells, with a focus on neuronal apoptosis. CEBPA-AS1, miR-455, and GPER1 expressions were evaluated by using qRT-PCR and Western blotting. The binding relationship among CEBPA-AS1, miR-455, and GPER1 was determined by a dual luciferase reporter assay. Neuronal viability and apoptosis were examined using MTT and flow cytometry assays, followed by determination of apoptosis-related factors (caspase 3, caspase 8, caspase 9, Bax, and Bcl-2). CEBPA-AS1 and GPER1 levels were upregulated, and miR-455 level was downregulated in the cell model of OGD/R induced. CEBPA-AS1 knockdown increased SH-SY5Y viability and reduced OGD/R-induced apoptosis. CEBPA-AS1 could act as a sponge of miR-455, and CEBPA-AS1 knockdown was found to elevate miR-455 expression. miR-455 overexpression also promoted SH-SY5Y cell viability and rescued them from OGD/R-induced apoptosis by binding to GPER1. GPER1 overexpression or miR-455 inhibition reversed the anti-apoptotic effect of CEBPA-AS1 knockdown. These findings suggest a regulatory network of CEBPA-AS1/miR-455/GPER1 that mediates neuronal cell apoptosis in the OGD model, providing a better understanding of pathogenic mechanisms after IS.

The Effect of Angelica sinensis Polysaccharide on Neuronal Apoptosis in Cerebral Ischemia-Reperfusion Injury via PI3K/AKT Pathway

In the present study, the protective effects and mechanism of Angelica sinensis polysaccharide (ASP) were investigated in rats with cerebral ischemia-reperfusion injury (CIRI). Rats were randomly divided into sham group, CIRI group, ASP treatment group, and ASP and LY294002 treatment group. H&E results confirmed the successful induction of CIRI in Sprague-Dawley rats. Compared with the sham group, the neurological function score, percentage of myocardial infarction area, neuronal apoptosis, oxidative stress, and inflammation in the CIRI group were significantly increased. Compared with the CIRI group, the ASP group’s neurological function score, percentage of myocardial infarction area, neuronal apoptosis, oxidative stress, and inflammation were significantly reduced. However, compared with the ASP group, LY294002 inhibited the effect of ASP in CIRI rats. CIRI downregulated the PI3K/AKT pathway and upregulated the apoptosis level. And ASP activated the PI3K/AKT pathway and Bcl-2 protein expression, while it inhibited caspase-3 and Bax expression. LY294002 could significantly inhibit the protective effect of ASP on nerve injury and the expression and phosphorylation of PI3K and Akt protein in CIRI rats. ASP could effectively improve nerve function and nerve cell apoptosis of CIRI rats by activating the PI3K/AKT signaling pathway.

Expression of Long Non-coding RNA RGD1566344 in the Brain Cortex of Male Mice After Focal Cerebral Ischemia-Reperfusion and the Neuroprotective Effect of a Non-coding RNA RGD1566344 Inhibitor

Ischemic stroke (IS) remains a major cause of disability and death. The changes in long non-coding RNA (lncRNA) RGD1566344 expression in the mouse cerebral cortex, including the infarct and penumbra regions after IS, are not clear. Less is known about the impact and underlying mechanisms of RGD1566344 in IS. In this study, we found that RGD1566344 levels were elevated in the ischemic infarct and penumbra regions 12 h after middle cerebral artery occlusion/reperfusion (MCAO/R) in male mice and in PC12 cells with oxygen glucose deprivation/reperfusion (OGD/R). The inhibition of RGD1566344 by small interference RNA (siRNA) significantly alleviated apoptosis in OGD/R PC12 cells. In cell transfection, quantitative real-time PCR, and Western blot experiments, we demonstrated the possible interaction of non-POU domain-containing octamer-binding protein (NONO) with RGD1566344. The NONO level in OGD/R PC12 cells was obviously increased after inhibiting the RGD1566344 treatment; subsequently the protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway was activated. This demonstrated the effect of the RGD1566344-NONO-AKT axis on neural protection after IS. These results revealed a new molecular mechanism of lncRNA RGD1566344 inhibitors through targeting NONO/AKT/mTOR signaling to protect against ischemic neuronal injury, providing strong evidence for the development of promising therapeutic strategies against IS.

Serum Levels of B-cell Lymphoma-2 Anti-Apoptotic Protein and Malignant Middle Cerebral Artery Infarction Mortality

INTRODUCTION AND GOAL

There is scarce and contradictory data on B-cell lymphoma 2 (Bcl2), member of the Bcl-2 antiapoptotic molecules family of intrinsic apoptosis pathway, in ischemic stroke patients. The objective of this study was to determine whether there is an association between blood Bcl2 concentrations and mortality of ischemic stroke patients.

MATERIAL AND METHODS

Five Intensive Care Units participated in this prospective and observational study of patients with severe malignant middle cerebral artery infarction (MMCAI). Severe MMCAI was diagnosed when acute infarction was present in 50% or more of said region and with a Glasgow Coma Scale (GCS) score of less than 9 points. Serum samples were collected at the time of MMCAI diagnosis.

FINDINGS

Higher serum Bcl2 concentrations (p = 0.001), lower platelet count (p = 0.01) and lower GCS (p = 0.002) were found in non-survivors (n = 28) than in MMCAI survivors (n = 28). Serum Bcl2 levels had an area under the curve for mortality prediction of 75% (95% CI = 62%-88%; p < 0.001). Patients with serum Bcl2 levels > 43.6 ng/mL had higher mortality rate according to Kaplan-Meier analysis (Hazard ratio=10.0; 95% CI = 3.4-29.5; p < 0.001). Multiple logistic regression showed an association between serum Bcl2 and mortality at 30 days (OR = 1.041; 95% CI = 1.006-1.077; p = 0.02) controlling for GCS and platelet count.

CONCLUSIONS

This study reports for the first time the higher blood Bcl2 concentrations in non-surviving ischemic stroke patients than in survivors and the association between elevated blood Bcl2 and mortality in ischemic stroke patients.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

Effect of aliskiren on the anticonvulsant activity of antiepileptic drugs against 6 Hz-induced psychomotor seizures in mice

Drug-drug interactions should be considered during the pharmacological treatment in patients with epilepsy and coexisting hypertension. Experimental studies in rodents showed that antihypertensive drugs which block the renin-angiotensin system (RAS) are able to decrease seizure severity. The anticonvulsant efficacy of several antiepileptic drugs (AEDs) was enhanced in different seizure models following concomitant treatment with RAS inhibitors. The current study examined the combined treatment with AEDs (carbamazepine, valproate, phenobarbital, clonazepam, ethosuximide, levetiracetam) and aliskiren, the first inhibitor of renin for treating hypertension, in the mouse 6 Hz psychomotor seizure model. The convulsive threshold was not affected by the renin inhibitor up to a dose of 75 mg/kg i.p. However, aliskiren (75 mg/kg) enhanced the anticonvulsant action of valproate reducing its ED₅₀ value from 96.7 to 25.6 mg/kg (P < 0.01). The anticonvulsant potency of other AEDs was unaffected by aliskiren treatment. The combinations of aliskiren with AEDs did not cause adverse effects in mice evaluated in the rota-rod or passive avoidance task. Administration of the renin inhibitor did not significantly alter either plasma or brain concentration of valproate. The obtained results confirm earlier findings from other seizure tests (maximal electroshock and pentylenetetrazole-induced seizure test) that aliskiren has a neutral or positive effect on the anticonvulsant efficacy of AEDs, which suggest its safe use for the treatment of high blood pressure in patients with epilepsy. The beneficial anticonvulsant effect of the concomitant treatment with aliskiren and valproate is worthy of recommendation to further both preclinical and clinical studies.

Epothilone B Facilitates Peripheral Nerve Regeneration by Promoting Autophagy and Migration in Schwann Cells

The search for drugs that can facilitate axonal regeneration and elongation following peripheral nerve injury has been an area of increasing interest in recent years. Epothilone B (EpoB) is an FDA-approved antineoplastic agent, which shows the capacity to induce α-tubulin polymerization and to improve the stability of microtubules. Recently, it has been increasingly recognized that EpoB has a regenerative effect in the central nervous system. However, the information currently available regarding the potential therapeutic effect of EpoB on peripheral nerve regeneration is limited. Here, we used a rat sciatic crush injury model system to determine that EpoB strikingly improved axonal regeneration and recovery of function. Also, EpoB (1 nM) did not result in significant apoptosis in Schwann cells (SCs) and showed little effect on their viability either. Interestingly, EpoB (1 nM) significantly enhanced migration in SCs, which was inhibited by autophagy inhibitors 3-methyladenine (3-MA). Since PI3K/Akt signaling has been implicated in regulating autophagy, we further examined the involvement of PI3K/Akt in the process of EpoB-induced SC migration. We found that EpoB (1 nM) significantly inhibited phosphorylation of PI3K and Akt in SCs. Further studies showed that both EpoB-enhanced migration and autophagy were increased/inhibited by inhibition/activation of PI3K/Akt signaling with LY294002 or IGF-1. In conclusion, EpoB can promote axonal regeneration following peripheral nerve injury by enhancing the migration of SCs, with this activity being controlled by PI3K/Akt signaling-mediated autophagy in SCs. This underscores the potential therapeutic value of EpoB in enhancing regeneration and functional recovery in cases of peripheral nerve injury.

Decades-old renin inhibitors are still struggling to find a niche in antihypertensive therapy. A fleeting look at the old and the promising new molecules

Hypertension is a diverse illness interlinked with cerebral, cardiovascular (CVS) and renal abnormalities. Presently, the malady is being treated by focusing on Renin- angiotensin system (RAS), voltage-gated calcium channels, peripheral vasodilators, renal and sympathetic nervous systems. Cardiovascular and renal abnormalities are associated with the overactivation of RAS, which can be constrained by angiotensin- converting enzyme inhibitors (ACEIs), angiotensin II (Ang-II) -AT1 receptor blockers (ARBs) and renin inhibitors. The latter is a new player in the old system. The renin catalyzes the conversion of angiotensinogen to Angiotensin I (Ang-I). This can be overcome by inhibiting renin, a preliminary step, eventually hinders the occurrence of the cascade of events in the RAS. Various peptidomimetics, the first-generation renin inhibitors developed six decades ago have limited drug-like properties as they suffered from poor intestinal absorption, high liver first-pass metabolism and low oral bioavailability. The development of chemically diverse molecules from peptides to nonpeptides expanded the horizon to achieving direct renin inhibition. Aliskiren, a blockbuster drug that emerged as a clinical candidate and got approved by the US FDA in 2007 was developed by molecular modeling studies. Aliskiren indicated superior to average efficacy and with minor adverse effects relative to other RAS inhibitors. However, its therapeutic use is limited by poor oral bioavailability of less than 2% that is similar to first-generation peptidic compounds. In this review, we present the development of direct renin inhibitors (DRIs) from peptidic to nonpeptidics that lead to the birth of aliskiren, its place in the treatment of cardiovascular diseases and its limitations.

A review of clinically significant drug-drug interactions involving angiotensin II receptor antagonists and antiepileptic drugs

INTRODUCTION

Angiotensin II receptor blockers are widely used for the treatment of arterial hypertension and heart failure. However, recent studies on animal models of seizures showed that in the brain, the renin-angiotensin-aldosterone system might be involved in neuroinflammation; therefore, the administration of angiotensin II receptor blockers that cross the blood/brain barrier, reduces not only blood pressure but reduces neuroinflammation-induced neuronal injury. Apart from this neuroprotective effect, these drugs exhibit anticonvulsant activity in animal models of seizures, and losartan is associated with a probable anti-epileptogenic activity.

AREAS COVERED

In this review, we intended to highlight the role of drug-drug interactions involving angiotensin II receptor antagonists with antiepileptic drugs accompanied by a brief characteristic of the role of RAS in neuroinflammation.

EXPERT OPINION

Some combinations of antiepileptic drugs (lamotrigine or valproate) with sartans are particularly effective in terms of enhanced seizure control. Considering a possible anti-epileptogenic activity of losartan, its combinations with antiepileptic drugs may prove especially beneficial in epileptogenesis inhibition.

Aliskiren and captopril improve cognitive deficits in poorly controlled STZ-induced diabetic rats via amelioration of the hippocampal P-ERK, GSK3β, P-GSK3β pathway

Learning and memory deficits are obvious symptoms that develop over time in patients with poorly controlled diabetes. Hyperactivity of the renin-angiotensin system (RAS) is directly associated with β-cell dysfunction and diabetic complications, including cognitive impairment. Here, we investigated the protective and molecular effects of two RAS modifiers, aliskiren; renin inhibitor and captopril; angiotensin converting enzyme inhibitor, on cognitive deficits in the rat hippocampus. Injection of low dose streptozotocin for 4 days resulted in type 1 diabetes. Then, poorly controlled diabetes was mimicked with ineffective daily doses of insulin for 4 weeks. The hyperglycaemia and pancreatic atrophy caused memory disturbance that were identifiable in behavioural tests, hippocampal neurodegeneration, and the following significant changes in the hippocampus, increases in the inflammatory marker interleukin 1β, cholinesterase, the oxidative stress marker malondialdehyde and protein expression of phosphorylated extracellular-signal-regulated kinase and glycogen synthase kinase-3 beta versus decrease in the antioxidant reduced glutathione and protein expression of phosphorylated glycogen synthase kinase-3 beta. Blocking RAS with either drugs along with insulin amended all previously mentioned parameters. Aliskiren stabilized the blood glucose level and restored normal pancreatic integrity and hippocampal malondialdehyde level. Aliskiren showed superior protection against the hippocampal degeneration displayed in the earlier behavioural modification in the passive avoidance test, and the aliskiren group outperformed the control group in the novel object recognition test. We therefore conclude that aliskiren and captopril reversed the diabetic state and cognitive deficits in rats with poorly controlled STZ-induced diabetes through reducing oxidative stress and inflammation and modulating protein expression.

A Network-Based Method for Mechanistic Investigation and Neuroprotective Effect on Post-treatment of Senkyunolid-H Against Cerebral Ischemic Stroke in Mouse

Senkyunolide-H (SEH), a major bioactive compound extracted from Ligusticum chuanxiong, has been reported to be effective in preventing cerebral ischemic stroke (CIS). In this study, we employed network pharmacology to reveal potential mechanism of SEH against CIS on a system level and confirmed the therapeutic effects of SEH on CIS by models of cerebral ischemia-reperfusion in vivo and in vitro. Through protein-protein interaction networks construction of SEH- and CIS-related targets, a total of 62 key targets were obtained by screening topological indices and analyzed for Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment. Gene Ontology analysis indicated that SEH might have a role in treating CIS via regulating some biological processes including regulation of transcription from RNA polymerase II promoter, epidermal growth factor receptor signaling pathway, phosphatidylinositol-mediated signaling, and some molecular function, such as transcription factor and protein phosphatase binding and nitric oxide synthase regulator activity. Meanwhile, the Kyoto Encyclopedia of Genes and Genomes analysis showed that phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway was significantly enriched. In addition, our result showed that SEH posttreatment significantly decreased the neurological scores, infarct volume, and neuronal death in the middle cerebral artery occlusion mice. Moreover, the PI3K/Akt/nuclear factor kappa B signaling pathway was activated by intragastric administration of 40 mg/kg SEH, as verified by Western blot. In vitro, treatment of PC12 cells with 100 μM SEH markedly reduced cell death induced by oxygen-glucose deprivation through the activation of PI3K/Akt/nuclear factor kappa B pathway, and the therapeutic effect of SEH was obviously inhibited by 10 μM LY294002. In summary, these results suggested that SEH carries a therapeutic potential in CIS involving multiple targets and pathways, and the most crucial mechanism might be through the activation of PI3K/Akt/nuclear factor kappa B (NF-κB) signaling pathway to inhibit inflammatory factor releases and increase the antiapoptosis capacity. Our study furnishes the future traditional Chinese medicine research with a network pharmacology framework.

Central Application of Aliskiren, a Renin Inhibitor, Improves Outcome After Experimental Stroke Independent of Its Blood Pressure Lowering Effect

Epidemiological studies suggest that pharmacological reduction of systemic hypertension lowers incidence and severity of stroke. However, whether the reduction of blood pressure per se or the compounds used to reduce hypertension are responsible for this effect received little attention. In the current study we therefore aimed to investigate whether Aliskiren, a renin-inhibitor used to treat arterial hypertension, may improve outcome in a mouse model of ischemic stroke when applied centrally and in a dose not affecting blood pressure. Male C57BL/6 mice received 0.6, 2.0, or 6.0 μg Aliskiren or vehicle by intracerebroventricular injection as a pre-treatment and were then subjected to 60 min of middle cerebral artery occlusion (MCAo). Infarct volume, brain edema formation, mortality, antioxidant effects, and functional outcome were assessed up to seven days after MCAo. Central administration of Aliskiren (0.6 or 2.0 μg) had no effect on systemic blood pressure but significantly reduced infarct volume and brain edema formation, blunted mortality, and improved neurological outcome up to 1 week after MCAo. Due to the central and prophylactic administration of the compound, we cannot make any conclusions about the potency of Aliskiren for acute stroke treatment, however, our study clearly demonstrates, that in addition to lowering blood pressure Aliskiren seems to have a direct neuroprotective effect. Hence, renin-inhibitors may be an effective addition to prophylactic treatment regimens in stroke patients.

SOD3 overexpression alleviates cerebral ischemia-reperfusion injury in rats

Background

Ischemic stroke is a deadly disease that poses a serious threat to human life. Superoxide dismutase 3 (SOD3, ECSOD) is the main antioxidant enzyme that removes superoxide anions from cells. This study aimed to investigate the effect of SOD3 overexpression on cerebral ischemia‐reperfusion injury in rats.

Methods

GV230‐EGFP‐ECSOD, the recombinant SOD3‐overexpressed vector, was constructed by genetic engineering technology, and mesenchymal stem cells (MSCs) were infected with lentiviral packaging. In animal experiment, cerebral ischemia‐reperfusion injury model rats were successfully established. ECSOD‐MSCs are the MSCs that successfully transfected with SOD3 overexpression vector. The animals were injected with ECSOD‐MSCs (ECSOD‐MSC group), normal MSCs (MSCs group), PBS (PBS group), and not do any processing (Model group) via the tail vein. Then MRI was used to detect the infarct volume of rats, modified Neurological Severity Scores (mNSS), and immunohistochemistry were used to evaluate the expression of neurological function and apoptosis‐related genes in rats.

Results

Western blot analysis revealed that the SOD3 was highly expressed in MSCs. Animal experiments showed that the transplantation of ECSOD‐MSCs significantly reduced the infarct volume of ischemic stroke rats (p < 0.05), significantly improved neurological function in rats (p < 0.05), and found proapoptotic gene, Bax, expression was significantly decreased (p < 0.05), the expression of anti‐apoptotic gene, Bcl‐2, was significantly increased (p < 0.05). The highly expressed SOD3 has no correction with brain infarct volume, and the highly expressed SOD3 has a positive correlation with cell apoptosis. It is speculated that overexpression of SOD3 affects the expression of Bax and Bcl‐2, and improves apoptosis to alleviate ischemic stroke.

Conclusion

Our results indicated that MSCs transfected with SOD3 can effectively alleviate cerebral ischemia‐reperfusion injury in rats.

Up-regulated microRNA-199b-3p represses the apoptosis of cerebral microvascular endothelial cells in ischemic stroke through down-regulation of MAPK/ERK/EGR1 axis

MicroRNAs (miRNAs) have emerged as key mediators of posttranscriptional gene silencing in both pathogenic and pathological aspects of ischemic stroke biology. Therefore, the purpose of present study was to explore the effect of microRNA-199b-3p (miR-199b-3p) on the cerebral microvascular endothelial cells (CMECs) in middle cerebral artery occlusion-reperfusion (MCAO-R) mice by regulating MAPK/ERK/EGR1 axis. Mice were used to establish MCAO-R models and to measure the expression of miR-199b-3p and the MAPK/ERK/EGR1 axis-related genes. CMECs were extracted from the MCAO-R mice. A series of mimic or inhibitor for miR-199b-3p, or U0126 (an inhibitor for the MAPK/ERK/EGR1 axis) were introduced to treat these CMECs. The levels of miR-199b-3p and MAPK/ERK/EGR1 axis-related genes in tissues and cells were detected. The effects miR-199b-3p on the process of CMECs, including cell viability, cell cycle and cell apoptosis were evaluated. miR-199b-3p expressed poorly in the brain tissues after MCAO-R, along with activated MAPK/ERK/EGR1 axis and increased CMECs apoptosis. CMECs transfected with miR-199b-3p mimics and U0126 manifested with increased cell viability, more cells arrested at the S stage, and inhibited apoptosis of CMECs. In conclusion, these key results demonstrated up-regulated miR-199b-3p could protect mice against ischemic stroke by inhibiting the apoptosis of CMECs through blockade of MAPK/ERK/EGR1 axis.

The differential neuroprotection of HSP70-hom gene single nucleotide polymorphisms: In vitro (neuronal hypoxic injury model) and in vivo (rat MCAO model) studies

To investigate the effect of HSP70-hom+2437 single nucleotide polymorphisms (SNPs) on hypoxia and ischemia condition, we constructed the neuronal hypoxic injury model and the rat middle cerebral artery occlusion (MCAO) model to compare the inhibition rate of neurons and detect the infarct volume as well as the expression of related apoptotic proteins in order to explore the possible mechanisms. The neuroblastoma cells SHSY5Y were divided into the OE (transfected with the C allele) group, OEmu (transfected with the T allele) group and negative control (NC, transfected with the empty lentiviral vector CON195) group. Varying degrees of hypoxia were induced by deferoxamine (DFO). The inhibition rate of hypoxic neurons and the expression of related apoptotic proteins were detected in the three genotype groups. While in the rat MCAO model, we built five groups including the sham group, the blank control group (injected with physiological saline), the negative control group (injected with lentivirus and physiological saline), the C allele group and the T allele group (injected with lentivirus overexpressing C and T allele). The MCAO model operation was then underwent in all five groups, the infarct volume by TTC staining and the expression of related apoptotic proteins were detected after 24 h. The results in neuronal hypoxic injury model showed a significant difference in the inhibition rate between the three groups (P < 0.05), and the average inhibition rates for the OEmu, OE and NC groups were 13.2%, 19.2% and 23.3%, respectively. The inhibition rates also differed between lower and higher DFO concentrations (P < 0.05). Compared with the NC group, Bax decreased significantly in the OE and OEmu groups, whereas PI3K and HSPA1L (HSP70-hom) increased. However, the expression of Bax in the OEmu group decreased significantly more than in the OE group, whereas PI3K and HSPA1L levels showed no difference between the two groups. Corresponding with the results above, overexpressing HSP70-hom could reduce the infarct volume of ischemic injury by TTC staining in rat MCAO model and the T allele group also had less infarct volume than C allele group. Compared with the sham group, blank control group and negative control group, Bax decreased significantly in the C and T allele groups, while HSPA1L and p- AKT increased. Furthermore, the expression of Bax in the T allele group decreased significantly more than that in the C allele group, while there were no significant differences in HSPA1L and p-AKT levels between the two groups. Therefore, the overexpression of HSP70-hom+2437 could play a protective role in hypoxic neurons and ischemic brain tissue by upregulating the expression of HSPA1L and PI3K/p-AKT and downregulating the expression of BAX. The neuroprotective effect of the T allele was stronger than that of the C allele, which may be related to the strengthened downregulation of BAX.

Role of the Angiotensin Pathway and its Target Therapy in Epilepsy Management

Despite extensive research on epileptogenesis, there is still a need to investigate new pathways and targeted therapeutic approaches in this complex process. Inflammation, oxidative stress, neurotoxicity, neural cell death, gliosis, and blood–brain barrier (BBB) dysfunction are the most common causes of epileptogenesis. Moreover, the renin–angiotensin system (RAS) affects the brain’s physiological and pathological conditions, including epilepsy and its consequences. While there are a variety of available pharmacotherapeutic approaches, information on new pathways is in high demand and the achievement of treatment goals is greatly desired. Therefore, targeting the RAS presents an interesting opportunity to better understand this process. This has been supported by preclinical studies, primarily based on RAS enzyme, receptor-inhibition, and selective agonists, which are characterized by pleiotropic properties. Although there are some antiepileptic drugs (AEDs) that interfere with RAS, the main targeted therapy of this pathway contributes in synergy with AEDs. However, the RAS-targeted treatment alone, or in combination with AEDs, requires clinical studies to contribute to, and clarify, the evidence on epilepsy management. There is also a genetic association between RAS and epilepsy, and an involvement of pharmacogenetics in RAS, so there are possibilities for the development of new diagnostic and personalized treatments for epilepsy.

CXCL8 gene silencing promotes neuroglial cells activation while inhibiting neuroinflammation through the PI3K/Akt/NF-κB-signaling pathway in mice with ischemic stroke

OBJECTIVE

Ischemic stroke is known as a neurodegenerative disorder, which induces long-period tissue damage. Chemokine (C-X-C motif) ligand 8 (CXCL8) is involved in acute inflammation and tumor progression through the phosphoinositide-3-kinase/protein kinase B/nuclear factor-κB (PI3K/Akt/NF-κB)-signaling pathway. In this study, we aimed to explore the mechanism of CXCL8 in ischemic stroke in relation to the PI3K/Akt/NF-κB-signaling pathway.

METHODS

Microarray-based gene expression profiling of peripheral blood mononuclear cells was used to identify ischemic stroke-related differentially expressed genes and explore role of CXCL8 in ischemic stroke. Next, the ischemic mice model was successfully established, with transfection efficiency detected. After that, deflection index, recovery of nervous system, infarct sizes, ischemia-induced apoptosis, and neuroinflammatory response in ischemic stroke were measured. At last, the content of inflammatory factors as well as the expression of CXCL8, caspase-3, caspase-9, Bad, interleukin-6 (IL-6), IL-1β, tumor necrosis factor-α (TNF-α), Akt, PI3K, and NF-κB were determined.

RESULTS

Comprehensive gene expression profiling analysis identified that CXCL8 might affect the development of ischemic stroke through regulating the PI3K/Akt/NF-κB-signaling pathway. CXCL8 silencing significantly reduced deflection index and infarct size, improved neurological function, and suppressed neuroglial cell loss and apoptosis index. In addition, glial fibrillary acidic portein (GFAP) and ionized calcium-binding adapter molecule 1 (IBA-1) expressions were decreased following CXCL8 suppression, suggesting CXCL8 affected neuroglial activation. Importantly, we also found that CXCL8 silencing activated neuroglial cell and suppressed inflammatory cytokine production in ischemic stroke mice.

CONCLUSION

Taken together, these findings highlight that functional suppression of CXCL8 promotes neuroglial activation and inhibits neuroinflammation by regulating the PI3K/Akt/NF-κB-signaling pathway in mice with ischemic stroke, which might provide new insight for ischemic stroke treatment.

Effect of aliskiren, a direct renin inhibitor, on the protective action of antiepileptic drugs against pentylenetetrazole-induced clonic seizures in mice

It has been demonstrated that certain angiotensin-converting enzyme (ACE) inhibitors and angiotensin AT₁ receptor antagonists can possess anticonvulsant activity. The purpose of the current study was to examine the effect of aliskiren, a direct renin inhibitor and a novel antihypertensive drug, against pentylenetetrazole (PTZ)-induced clonic seizures in mice and on the protective activity of conventional antiepileptic drugs (AEDs) in this seizure model. Effects of aliskiren on the PTZ threshold and the protective efficacy of AEDs, such as clonazepam (CLO), phenobarbital (PB), valproate (VPA), and ethosuximide (ETX) in the PTZ test, were evaluated in adult Swiss mice. Aliskiren and AEDs were administered intraperitoneally (i.p.) while PTZ (50-100 mg/kg) was injected subcutaneously (s.c.). The rota-rod and passive avoidance test were used to assess the adverse effects of the combined treatment with aliskiren and AEDs. Aliskiren, at the dose of 75 mg/kg, significantly raised the PTZ threshold (P < 0.05). Furthermore, aliskiren, at the subthreshold dose of 50 mg/kg, significantly enhanced the protective action of CLO (P < 0.01), PB (P < 0.01), and VPA (P < 0.05) but not ETX (P > 0.05) in the s.c. PTZ test. Motor coordination in the rota-rod test and long-term memory in the passive avoidance task were not impaired by the combined treatment of the drugs. This study suggests that treatment with aliskiren can be useful in hypertensive patients with myoclonic seizures. Certainly, a clinical verification of using aliskiren in such patients would be necessary.

Expression of Bcl-2 and Bad in hippocampus of status epileptic rats and molecular mechanism of intervened recombinant human erythropoietin

Injury of hippocampal neurons in status epilepticus (SE) SD rats kindled by pentylenetetrazol (PTZ) were studied, and the changes of apoptosis neurons, protein expression of Bad and Bcl-2 alone and combined application of phosphatidyl inositol 3-kinase (PI3K) inhibitor LY294002 and recombinant human erythropoietin (rHuEpo) were evaluated for the possible mechanisms of rHuEpo. The SE rats kindled by the PTZ were randomly divided into normal control group [normal saline (NS)], model group (PTZ + NS), rHuEpo treated group (PTZ + rHuEpo), LY294002 treated group (PTZ + LY294002 + rHuEpo) and LY294002 control group (rHuEpo + PTZ + DMSO). Apoptosis of hippocampal neurons was detected by TUNEL method; expression of phosphorylation protein kinase B (p-PKB/p-Akt), Bcl-2 and Bad were detected by immunohistochemistry; the expression of Bcl-2 mRNA, Bad mRNA in hippocampal neurons of rats were detected through reverse transcription polymerase chain reaction (RT-PCR); the expression of Akt, p-Akt and Bcl-2, Bad protein in hippocampal neurons of rats were detected by western blotting. The amount of apoptotic neurons was less in the rHuEpo treated group and the LY294002 control group than in the LY294002 treated group (P<0.05). The expression of p-Akt protein and Bcl-2 protein increased while the Bad protein decreased significantly in the rHuEpo treated group and the LY294002 control group compared with the LY294002 treated group (P<0.05). The expression of Bad protein and Bad mRNA in hippocampus increased while the p-Akt, Bcl-2, Bcl-2 mRNA decreased significantly in the LY294002 treated group compared with the rHuEpo treated group (P<0.05). The PI3K/Akt signaling pathway is one of the pathways of rHuEpo neuroprotective effects and was confirmed from both the of positive and negative aspects. rHuEpo regulates the expression of mitochondrial apoptotic pathway related factors Bad and Bcl-2 to inhibit apoptosis and promotes neuronal survival.

Neural Stem Cell-Conditioned Medium Ameliorated Cerebral Ischemia-Reperfusion Injury in Rats

Introduction

Our previous study suggested that NSC-CM (neural stem cell-conditioned medium) inhibited cell apoptosis in vitro. In addition, many studies have shown that neurotrophic factors and microparticles secreted into a conditioned medium by NSCs had neuroprotective effects. Thus, we hypothesized that NSC-CM had the capacity of protecting against cerebral I/R injury.

Methods

Adult male Sprague-Dawley rats receiving middle cerebral artery occlusion surgery as an animal model of cerebral I/R injury were randomly assigned to two groups: the control group and NSC-CM-treated group. 1.5 ml NSC-CM or PBS (phosphate buffer saline) was administrated slowly by tail vein at 3 h, 24 h, and 48 h after ischemia onset.

Results

NSC-CM significantly ameliorated neurological defects and reduced cerebral infarct volume, accompanied by preserved mitochondrial ultrastructure. In addition, we also found that NSC-CM significantly inhibited cell apoptosis in the ischemic hemisphere via improving the expression of Bcl-2 (B-cell lymphoma-2).

Conclusion

NSC-CM might be an alternative and effective therapeutic intervention for ischemic stroke.

Sevoflurane post-conditioning attenuates traumatic brain injury-induced neuronal apoptosis by promoting autophagy via the PI3K/AKT signaling pathway

Background

Sevoflurane post-conditioning exerts nerve-protective effects through inhibiting caspase-dependent neuronal apoptosis after a traumatic brain injury (TBI). Autophagy that is induced by the endoplasmic reticulum stress plays an important role in the secondary neurological dysfunction after a TBI. However, the relationship between autophagy and caspase-dependent apoptosis as well as the underlying nerve protection mechanism that occurs with sevoflurane post-conditioning following a TBI remains unclear.

Methods

The Feeney TBI model was used to induce brain injury in rats. Evaluation of the modified neurological severity scores, measurement of brain water content, Nissl staining, and terminal deoxynucleotidyl transferase dUTP nick end labeling assay were used to determine the neuroprotective effects of the sevoflurane post-conditioning. Both immunofluorescence and Western blot analyses were used to detect the expression of autophagy-related proteins microtubule-associated protein 1 light chain 3-II and Beclin-1, pro-apoptotic factors, as well as the activation of the phosphatidylinositide 3-kinase/protein kinase B (PI3K/AKT) signaling pathway within the lesioned cortex.

Results

Autophagy and neuronal apoptosis were activated in the lesioned cortex following the TBI. Sevoflurane post-conditioning enhanced early autophagy, suppressed neuronal apoptosis, and alleviated brain edema, which improved nerve function after a TBI (all P < 0.05). Sevoflurane post-conditioning induced the activation of PI3K/AKT signaling after the TBI (P < 0.05). The neuroprotective effects of sevoflurane post-conditioning were reversed through the autophagy inhibitor 3-methyladenine treatment.

Conclusion

Neuronal apoptosis and the activation of autophagy were involved in the secondary neurological injury following a TBI. Sevoflurane post-conditioning weakened the TBI-induced neuronal apoptosis by regulating autophagy via PI3K/AKT signaling.

Aliskiren Improves Ischemia- and Oxygen Glucose Deprivation-Induced Cardiac Injury through Activation of Autophagy and AMP-Activated Protein Kinase

Aliskiren is a direct renin inhibitor that has been effective in anti-hypertension. We investigated whether aliskiren could improve the ischemia-induced cardiac injury and whether the autophagy was involved in this effect. A myocardial infarction (MI) model was created by the ligation of the left anterior coronary artery in C57J/BL6 mice. They were treated for 1, 3, 7, and 14 days with vehicle or aliskiren (25 mg/kg/day via subcutaneous injection). In vivo, the MI mice exhibited worse cardiac function by echocardiographic assessment and showed larger myocardial scarring by light microscopy, whereas aliskiren treatment reversed these effects, which were also associated with the changes in caspase-3 and Bcl-2 expression as well as in the number of apoptotic cells. Aliskiren increased autophagy, as demonstrated by LC3B-II expression and transmission electron microscopy. Furthermore, H9c2 cardiomyocytes were employed as an in vitro model to examine the effects of aliskiren on apoptosis and autophagy under oxygen glucose deprivation (OGD)-induced injury. Aliskiren significantly increased cell viability in a dose-dependent manner. The beneficial effects of aliskiren were associated with decreased apoptosis and mitochondrial membrane potential as well as increased autophagy via increased autophagosome formation. We also found that aliskiren-induced cardiomyocyte survival occurred via AMP-activated protein kinase (AMPK)-dependent autophagy. Taken together, these results indicated that aliskiren increased cardiomyocyte survival through increased autophagosomal formation and decreased apoptosis and necrosis via modulating AMPK expression. AMPK-dependent autophagy may represent a novel mechanism for aliskiren in ischemic cardiac disease therapy.

Brain adaptation to hypoxia and hyperoxia in mice

Aims

Hyperoxic breathing might lead to redox imbalance and signaling changes that affect cerebral function. Paradoxically, hypoxic breathing is also believed to cause oxidative stress. Our aim is to dissect the cerebral tissue responses to altered O₂ fractions in breathed air by assessing the redox imbalance and the recruitment of the hypoxia signaling pathways.

Results

Mice were exposed to mild hypoxia (10%O₂), normoxia (21%O₂) or mild hyperoxia (30%O₂) for 28 days, sacrificed and brain tissue excised and analyzed. Although one might expect linear responses to %O₂, only few of the examined variables exhibited this pattern, including neuroprotective phospho- protein kinase B and the erythropoietin receptor. The major reactive oxygen species (ROS) source in brain, NADPH oxidase subunit 4 increased in hypoxia but not in hyperoxia, whereas neither affected nuclear factor (erythroid-derived 2)-like 2, a transcription factor that regulates the expression of antioxidant proteins. As a result of the delicate equilibrium between ROS generation and antioxidant defense, neuron apoptosis and cerebral tissue hydroperoxides increased in both 10%O₂ and 30%O₂, as compared with 21%O₂. Remarkably, the expression level of hypoxia-inducible factor (HIF)−2α (but not HIF-1α) was higher in both 10%O₂ and 30%O₂ with respect to 21%O₂

Innovation

Comparing the in vivo effects driven by mild hypoxia with those driven by mild hyperoxia helps addressing whether clinically relevant situations of O₂ excess and scarcity are toxic for the organism.

Conclusion

Prolonged mild hyperoxia leads to persistent cerebral damage, comparable to that inferred by prolonged mild hypoxia. The underlying mechanism appears related to a model whereby the imbalance between ROS generation and anti-ROS defense is similar, but occurs at higher levels in hypoxia than in hyperoxia.

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Both oxygen scarcity and oxygen excess are harmful for the brain.

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Hypoxia increases ROS more than hyperoxia.

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Hypoxia increases the antioxidant defenses to an extent larger than hyperoxia.

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Both hypoxia and hyperoxia imbalance the ROS generation/ antiROS defense equilibrium.

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These findings have implications for those who need supplemental oxygen therapy.