Protective effect of HIF-1α against hippocampal apoptosis and cognitive dysfunction in an experimental rat model of subarachnoid hemorrhage

Role of hypoxia-inducible factor in postoperative delirium of aged patients: A review

Postoperative delirium is common, especially in older patients. Delirium is associated with prolonged hospitalization, an increased risk of postoperative complications, and significant mortality. The mechanism of postoperative delirium is not yet clear. Cerebral desaturation occurred during the maintenance period of general anesthesia and was one of the independent risk factors for postoperative delirium, especially in the elderly. Hypoxia stimulates the expression of hypoxia-inducible factor-1 (HIF-1), which controls the hypoxic response. HIF-1 may have a protective role in regulating neuron apoptosis in neonatal hypoxia-ischemia brain damage and may promote the repair and rebuilding process in the brain that was damaged by hypoxia and ischemia. HIF-1 has a neuroprotective effect during cerebral hypoxia and controls the hypoxic response by regulating multiple pathways, such as glucose metabolism, angiogenesis, erythropoiesis, and cell survival. On the other hand, anesthetics have been reported to inhibit HIF activity in older patients. So, we speculate that HIF plays an important role in the pathophysiology of postoperative delirium in the elderly. The activity of HIF is reduced by anesthetics, leading to the inhibition of brain protection in a hypoxic state. This review summarizes the possible mechanism of HIF participating in postoperative delirium in elderly patients and provides ideas for finding targets to prevent or treat postoperative delirium in elderly patients.

Hydrogen inhalation therapy regulates lactic acid metabolism following subarachnoid hemorrhage through the HIF-1α pathway

The neuroprotective effects of hydrogen have been demonstrated, but the mechanism is still poorly understood. In a clinical trial of inhaled hydrogen in patients with subarachnoid hemorrhage (SAH), we found that hydrogen reduced the accumulation of lactic acid in the nervous system. There are no studies demonstrating the regulatory effect of hydrogen on lactate and in this study we hope to further clarify the mechanism by which hydrogen regulates lactate metabolism. In cell experiments, PCR and Western Blot showed that HIF-1α was the target related to lactic acid metabolism that changed the most before and after hydrogen intervention. HIF-1α levels were suppressed by hydrogen intervention treatment. Activation of HIF-1α inhibited the lactic acid-lowering effect of hydrogen. We have also demonstrated the lactic acid-lowering effect of hydrogen in animal studies. Our work clarifies that hydrogen can regulate lactate metabolism via the HIF-1αpathway, providing new insights into the neuroprotective mechanisms of hydrogen.

SIRT1 Activation Promotes Long-Term Functional Recovery After Subarachnoid Hemorrhage in Rats

BACKGROUND

An increase in sirtuin 1 (SIRT1) reportedly attenuates early brain injury, delayed cerebral ischemia, and short-term neurologic deficits in rodent models of subarachnoid hemorrhage (SAH). This study investigates the effect of resveratrol, a SIRT1 activator, on long-term functional recovery in a clinically relevant rat model of SAH.

METHODS

Thirty male Wistar rats were subjected to fresh arterial blood injection into the prechiasmatic space and randomized to receive 7 days of intraperitoneal resveratrol (20 mg/kg) or vehicle injections. Body weight and rotarod performance were measured on days 0, 3, 7, and 34 post SAH. The neurologic score was assessed 7 and 34 days post SAH. Morris water maze performance was evaluated 29-33 days post SAH. Brain SIRT1 activity and CA1 neuronal survival were also assessed.

RESULTS

Blood pressure rapidly increased in all SAH rats, and no between-group differences in blood pressure, blood gases, or glucose were detected. SAH induced weight loss during the first 7 days, which gradually recovered in both groups. Neurologic score and rotarod performance were significantly improved after resveratrol treatment at 34 days post SAH (p = 0.01 and 0.04, respectively). Latency to find the Morris water maze hidden platform was shortened (p = 0.02). In the resveratrol group, more CA1 neurons survived following SAH (p = 0.1). An increase in brain SIRT1 activity was confirmed in the resveratrol group (p < 0.05).

CONCLUSIONS

Treatment with resveratrol for 1 week significantly improved the neurologic score, rotarod performance, and latency to find the Morris water maze hidden platform 34 days post SAH. These findings indicate that SIRT1 activation warrants further investigation as a mechanistic target for SAH therapy.

Potential role of serum hypoxia-inducible factor 1alpha as a biomarker of delayed cerebral ischemia and poor clinical outcome after human aneurysmal subarachnoid hemorrhage: A prospective, longitudinal, multicenter, and observational study

Objective

Hypoxia-inducible factor 1alpha (HIF-1α) functions as a crucial transcriptional mediator in hypoxic and ischemic brain response. We endeavored to assess the prognostic significance of serum HIF-1α in human aneurysmal subarachnoid hemorrhage (aSAH).

Methods

In this prospective, longitudinal, multicenter, and observational study of 257 patients with aSAH and 100 healthy controls, serum HIF-1α levels were quantified. Univariate analyses, followed by multivariate analyses, were performed to discern the relationship between serum HIF-1α levels and severity and delayed cerebral ischemia (DCI) plus poststroke 6-month poor outcome [extended Glasgow outcome scale (GOSE) scores of 1-4]. Predictive efficiency was determined under the receiver operating characteristic (ROC) curve.

Results

There were significantly increased serum HIF-lα levels after aSAH, in comparison to controls (median, 288.0 vs. 102.6 pg/ml; P < 0.001). Serum HIF-lα levels were independently correlated with Hunt-Hess scores [β, 78.376; 95% confidence interval (CI): 56.446-100.305; P = 0.001] and modified Fisher scores (β, 52.037; 95% CI: 23.461-80.614; P = 0.002). Serum HIF-lα levels displayed significant efficiency for discriminating DCI risk [area under ROC curve (AUC), 0.751; 95% CI: 0.687-0.815; P < 0.001] and poor outcome (AUC, 0.791; 95% CI: 0.736-0.846; P < 0.001). Using the Youden method, serum HIF-1α levels >229.3 pg/ml predicted the development of DCI with 92.3% sensitivity and 48.4% specificity and serum HIF-1α levels >384.0 pg/ml differentiated the risk of a poor prognosis with 71.4% sensitivity and 81.1% specificity. Serum HIF-1α levels >229.3 pg/ml were independently predictive of DCI [odds ratio (OR), 3.061; 95% CI: 1.045-8.965; P = 0.041] and serum HIF-1α levels >384.0 pg/ml were independently associated with a poor outcome (OR, 2.907; 95% CI: 1.403-6.024; P = 0.004). The DCI predictive ability of their combination was significantly superior to those of Hunt-Hess scores (AUC, 0.800; 95% CI: 0.745-0.855; P = 0.039) and modified Fisher scores (AUC, 0.784; 95% CI: 0.726-0.843; P = 0.004). The prognostic predictive ability of their combination substantially exceeded those of Hunt-Hess scores (AUC, 0.839; 95% CI: 0.791-0.886; P < 0.001) and modified Fisher scores (AUC, 0.844; 95% CI: 0.799-0.890; P < 0.001).

Conclusion

Elevated serum HIF-lα levels after aSAH, in independent correlation with stroke severity, were independently associated with DCI and 6-month poor outcome, substantializing serum HIF-lα as a potential prognostic biomarker of aSAH.

The Role of Inflammation in Cognitive Impairment of Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) has become a major worldwide public health concern, given its global prevalence. It has clear links with multiple comorbidities and mortality. Cognitive impairment is one related comorbidity causing great pressure on individuals and society. The clinical manifestations of cognitive impairment in OSAS include decline in attention/vigilance, verbal–visual memory loss, visuospatial/structural ability impairment, and executive dysfunction. It has been proven that chronic intermittent hypoxia (CIH) may be a main cause of cognitive impairment in OSAS. Inflammation plays important roles in CIH-induced cognitive dysfunction. Furthermore, the nuclear factor kappa B and hypoxia-inducible factor 1 alpha pathways play significant roles in this inflammatory mechanism. Continuous positive airway pressure is an effective therapy for OSAS; however, its effect on cognitive impairment is suboptimal. Therefore, in this review, we address the role inflammation plays in the development of neuro-impairment in OSAS and the association between OSAS and cognitive impairment to provide an overview of its pathophysiology. We believe that furthering the understanding of the inflammatory mechanisms involved in OSAS-associated cognitive impairment could lead to the development of appropriate and effective therapy.

Rethinking the initial changes in subarachnoid haemorrhage: Focusing on real-time metabolism during early brain injury

Over the last two decades, neurological researchers have uncovered many pathophysiological mechanisms associated with subarachnoid haemorrhage (SAH), with early brain injury and delayed cerebral ischaemia both contributing to morbidity and mortality. The current dilemma in SAH management inspired us to rethink the nature of the insult in SAH: sudden bleeding into the subarachnoid space and hypoxia due to disturbed cerebral circulation and increased intracranial pressure, generating exogenous stimuli and subsequent pathophysiological processes. Exogenous stimuli are defined as factors which the brain tissue is not normally exposed to when in the healthy state. Intersections of these initial pathogenic factors lead to secondary brain injury with related metabolic changes after SAH. Herein, we summarized the current understanding of efforts to monitor and analyse SAH-related metabolic changes to identify those precise pathophysiological processes and potential therapeutic strategies; in particular, we highlight the restoration of normal cerebrospinal fluid circulation and the normalization of brain-blood interface physiology to alleviate early brain injury and delayed neurological deterioration after SAH.

Cardamonin attenuates cerebral ischemia/reperfusion injury by activating the HIF-1α/VEGFA pathway

Cardamonin is a chalcone with neuroprotective activity. The aim of our study was to explore the functions and mechanism of action of cardamonin in ischemic stroke. Oxygen-glucose deprivation and reperfusion (OGD/R)-induced human brain microvascular endothelial cells (HBMECs) and middle cerebral artery occlusion (MCAO) mouse model were utilized to mimic ischemic stroke. Cell viability was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide. Permeability was investigated via fluorescein isothiocyanate-dextran assay. Apoptosis was detected by TdT-Mediated dUTP Nick End Labeling staining. Hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor A (VEGFA) protein levels were measured using Western blotting. Brain injury was evaluated by 2,3,5-triphenyltetrazolium chloride staining, neurological score and brain water content. The 37 overlapping targets of ischemic stroke and cardamonin were predicted to be associated with the HIF-1/VEGFA signaling. Cardamonin alleviated OGD/R-induced viability reduction and increase of permeability and apoptosis in HBMECs. Cardamonin increased OGD/R-induced activation of the HIF-1α/VEGFA pathway. Inhibition of the HIF-1α/VEGFA signaling using inhibitor relieved the effect of cardamonin on cell viability, permeability and apoptosis in HBMECs under OGD/R. Cardamonin mitigated brain injury and promoted activation of the HIF-1α/VEGFA signaling in MCAO-treated mice. Overall, cardamonin protected against OGD/R-induced HBMEC damage and MACO-induced brain injury through activating the HIF-1α/VEGFA pathway.

Serum hypoxia-inducible factor 1alpha emerges as a prognostic factor for severe traumatic brain injury

BACKGROUND

Hypoxia-inducible factor 1alpha (HIF-1α) is implicated in the cell's response to hypoxia. We investigated whether serum HIF-1α concentrations are correlated with the severity and clinical outcome of severe traumatic brain injury (sTBI).

METHODS

Serum HIF-1α concentrations were quantified in 104 sTBI patients and 80 healthy controls. Trauma severity was assessed using Glasgow coma scale (GCS). Glasgow outcome scale (GOS) score of 1-3 at post-trauma 90 days was defined as a poor outcome. Multivariate analyses were performed to discern the relationship between serum HIF-1α concentrations and outcome.

RESULTS

Patients displayed significantly higher serum HIF-1α concentrations than controls (median, 294.9 versus 102.7 pg/ml). HIF-1α concentrations were intimately related to GCS scores (r = -0.62) and GOS scores (r = -0.64). 48 patients (46.2%) experienced a poor outcome. Serum HIF-1α concentrations > 280.2 pg/ml significantly distinguished patients with the development of poor outcome with 77.1% sensitivity and 69.6% specificity (AUC, 0.750; 95% CI: 0.655-0.829). Serum HIF-1α concentrations > 280.2 pg/ml emerged as an independent predictor for poor outcome (OR: 4.179; 95% CI: 1.024-17.052).

CONCLUSIONS

Serum HIF-1α concentrations are tightly associated with trauma severity and poor 90-day outcome, substantializing serum HIF-1α as a promising prognostic biomarker for sTBI.

Circulating lncRNAs HIF1A-AS2 and LINLK-A: Role and Relation to Hypoxia-Inducible Factor-1α in Cerebral Stroke Patients

Long noncoding RNAs (lncRNAs) have been recently recognized as key players of gene expression in cerebral pathogenesis. Thus, their potential use in stroke diagnosis, prognosis, and therapy is actively pursued. Due to the complexity of the disease, identifying stroke-specific lncRNAs remains a challenge. This study investigated the expression of lncRNAs HIF1A-AS2 and LINK-A, and their target gene hypoxia-inducible factor-1 (HIF-1) in Egyptian stroke patients. It also aimed to determine the molecular mechanism implicated in the disease. A total of 75 stroke patients were divided into three clinical subgroups, besides 25 healthy controls of age-matched and sex-matched. Remarkable upregulation of lncRNA HIF1A-AS2 and HIF1-α along with a downregulation of lncRNA LINK-A was noticed in all stroke groups relative to controls. Serum levels of phosphatidylinositol 3-kinase (PI3K), phosphorylated-Akt (p-Akt), vascular endothelial growth factor (VEGF), and angiopoietin-1 (ANG1) as well as their receptors, malondialdehyde (MDA), and total antioxidant capacity (TAC) were significantly increased, whereas brain-derived neurotrophic factor (BDNF) levels were significantly decreased particularly in hemorrhagic stroke versus ischemic groups. Eventually, these findings support the role of lncRNAs HIF1A-AS2 and LINK-A as well as HIF1-α in activation of angiogenesis, neovascularization, and better prognosis of stroke, especially the hemorrhagic type.

Empagliflozin alleviates neuronal apoptosis induced by cerebral ischemia/reperfusion injury through HIF-1α/VEGF signaling pathway

Ischemic stroke is a serious condition associated with severe functional disability and high mortality, however; effective therapy remains elusive. Empagliflozin, a sodium-glucose cotransporter 2 inhibitor, has been shown to exert additional non-glycemic benefits including anti-apoptotic effects in different disease settings. Thereby, this study was designed to investigate the ameliorative effect of empagliflozin on the neuronal apoptosis exhibited in cerebral ischemia/reperfusion (I/R) in a rat model targeting HIF-1α/VEGF signaling which is involved in this insult. Global cerebral I/R injury was induced in male Wistar rats through occlusion of the bilateral common carotid arteries for 30 min followed by one-hour reperfusion. Empagliflozin doses of 1 and 10 mg/kg were administered 1 and 24 h after reperfusion. In I/R-injured rats, empagliflozin treatments significantly reduced infarct size and enhanced neurobehavioral functions in a dose-dependent manner. The drug alleviated neuronal death and cerebral injury inflicted by global ischemia as it suppressed neuronal caspase-3 protein expression. In parallel, protein expressions of HIF-1α and its downstream mediator VEGF were upregulated in the ischemic brain following empagliflozin treatment. The results indicated that empagliflozin attenuates cerebral I/R-induced neuronal death via the HIF-1α/VEGF cascade.

The Western Diet Regulates Hippocampal Microvascular Gene Expression: An Integrated Genomic Analyses in Female Mice

Hyperlipidemia is a risk factor for dementia, and chronic consumption of a Western Diet (WD) is associated with cognitive impairment. However, the molecular mechanisms underlying the development of microvascular disease in the memory centers of the brain are poorly understood. This pilot study investigated the nutrigenomic pathways by which the WD regulates gene expression in hippocampal brain microvessels of female mice. Five-week-old female low-density lipoprotein receptor deficient (LDL-R−/−) and C57BL/6J wild type (WT) mice were fed a chow or WD for 8 weeks. Metabolics for lipids, glucose and insulin were determined. Differential gene expression, gene networks and pathways, transcription factors, and non-protein coding RNAs were evaluated by genome-wide microarray and bioinformatics analysis of laser captured hippocampal microvessels. The WD resulted in differential expression of 2,412 genes. The majority of differential gene expression was attributable to differential regulation of cell signaling proteins and their transcription factors, approximately 7% was attributable to differential expression of miRNAs, and a lesser proportion was due to other non-protein coding RNAs, primarily long non-coding RNAs (lncRNAs) and small nucleolar RNAs (snoRNAs) not previously described to be modified by the WD in females. Our findings revealed that chronic consumption of the WD resulted in integrated multilevel molecular regulation of the hippocampal microvasculature of female mice and may provide one of the mechanisms underlying vascular dementia.

Osteopontin-Enhanced Autophagy Attenuates Early Brain Injury via FAK-ERK Pathway and Improves Long-Term Outcome after Subarachnoid Hemorrhage in Rats

Osteopontin (OPN) enhances autophagy, reduces apoptosis, and attenuates early brain injury (EBI) after a subarachnoid hemorrhage (SAH). A total of 87 Sprague–Dawley rats were subjected to sham or SAH operations to further investigate the signaling pathway involved in osteopontin-enhanced autophagy during EBI, and the potential effect of recombinant OPN (rOPN) administration to improve long-term outcomes after SAH. Rats were randomly divided into five groups: Sham, SAH + Vehicle (PBS, phosphate-buffered saline), SAH + rOPN (5 μg/rat recombinant OPN), SAH + rOPN + Fib-14 (30 mg/kg of focal adhesion kinase (FAK) inhibitor-14), and SAH + rOPN + DMSO (dimethyl sulfoxide). Short-term and long-term neurobehavior tests were performed, followed by a collection of brain samples for assessment of autophagy markers in neurons, pathway proteins expression, and delayed hippocampal injury. Western blot, double immunofluorescence staining, Nissl staining, and Fluoro-Jade C staining assay were used. Results showed that rOPN administration increased autophagy in neurons and improved neurobehavior in a rat model of SAH. With the administration of FAK inhibitor-14 (Fib-14), neurobehavioral improvement and autophagy enhancement induced by rOPN were abolished, and there were consistent changes in the phosphorylation level of ERK1/2. In addition, early administration of rOPN in rat SAH models improved long-term neurobehavior results, possibly by alleviating hippocampal injury. These results suggest that FAK–ERK signaling may be involved in OPN-enhanced autophagy in the EBI phase after SAH. Early administration of rOPN may be a preventive and therapeutic strategy against delayed brain injury after SAH.

The insights into molecular pathways of hypoxia-inducible factor in the brain

The objectives of this present work were to review recent developments on the role of hypoxia-inducible factor (HIF) in the survival of cells under normoxic versus hypoxic and inflammatory brain conditions. The dual nature of HIF effects appears well established, based on the accumulated evidence of HIF playing both the role of adaptive factor and mediator of cell demise. Cellular HIF responses depend on pathophysiological conditions, developmental phase, comorbidities, and administered medications. In addition, HIF-1α and HIF-2α actions may vary in the same tissues. The multiple roles of HIF in stem cells are emerging. HIF not only regulates expression of target genes and thereby influences resultant protein levels but also contributes to epigenetic changes that may reciprocally provide feedback regulations loops. These HIF-dependent alterations in neurological diseases and its responses to treatments in vivo need to be examined alongside with a functional status of subjects involved in such studies. The knowledge of HIF pathways might be helpful in devising HIF-mimetics and modulating drugs, acting on the molecular level to improve clinical outcomes, as exemplified here by clinical and experimental data of selected brain diseases, occasionally corroborated by the data from disorders of other organs. Because of complex role of HIF in brain injuries, prospective therapeutic interventions need to differentially target HIF responses depending on their roles in the molecular mechanisms of neurologic diseases.

Tolfenamic Acid Attenuates 3-Nitropropionic Acid-Induced Biochemical Alteration in Mice

Tolfenamic acid (TA), a nonsteroidal anti-inflammatory drug, shows neuroprotective effects and alleviates cognitive deficits in transgenic mouse models of Alzheimer's disease. However, whether TA can prevent the biochemical alterations induced by intraperitoneal injection of 3-nitropropionic acid (3-NP) in mice is still unknown. In this study, the striatal lesion area was measured by 2,3,5-triphenyltetrazolium chloride staining. Glutamate, SDH and ATP levels were tested using colorimetric assay kits. The neuroinflammatory cytokine levels were tested by ELISA kits. The expression of synaptic proteins and the subtypes of the NMDA receptor were tested by western blotting. TA was orally administered 10 days before 3-NP injection (pretreatment) or on the same day as 3-NP injection (co-treatment). TA pretreatment showed the strongest neuroprotective effects: pretreatment significantly attenuated the 3-NP-induced muscular weakness in the forelimb and alterations in glutamate level, mitochondrial function, and pro-inflammatory cytokine release in the brains of mice. These results suggest that TA has preventive and protective effects on 3-NP-induced neurotoxicity.

Isoflurane‑induced postoperative cognitive dysfunction is mediated by hypoxia‑inducible factor‑1α‑dependent neuroinflammation in aged rats

Elderly patients are at high risk of developing postoperative cognitive dysfunction (POCD) after prolonged exposure to inhaled anesthetics. However, the pathogenesis of POCD remains unknown. Hypoxia-inducible factor-1α (HIF-1α) is activated by inhaled anesthetics. The aim of the present study was to determine the role of HIF-1α in isoflurane-induced neuroinflammation and the resulting cognitive impairment. Following a 4-h exposure to 1.5% isoflurane in 20-month-old rats, increased expression of HIF-1α protein, activation of nuclear factor (NF)-κB signaling and increased expression of TNF-1α were observed in the hippocampus of isoflurane-exposed rats compared with the control group. Pharmacological inhibition of HIF-1α activation by 5-[1-(phenylmethyl)-1H-indazol-3-yl]-2-furanmethanol (YC-1) markedly suppressed the enhanced expression of HIF-1α, disrupted NF-κB signaling pathway activity and inhibited the isoflurane-induced increase of TNF-1α expression. YC-1 pretreatment also significantly attenuated isoflurane-induced cognitive deficits according to the results of the Morris water maze task. These results suggest that hippocampal HIF-1α appears to be involved in an upstream mechanism of isoflurane-induced cognitive impairment. Further research is warranted to fully clarify the pathogenesis and investigate HIF-1α as a potential therapeutic target for POCD.

Neurobehavioral testing in subarachnoid hemorrhage: A review of methods and current findings in rodents

The most important aspect of a preclinical study seeking to develop a novel therapy for neurological diseases is whether the therapy produces any clinically relevant functional recovery. For this purpose, neurobehavioral tests are commonly used to evaluate the neuroprotective efficacy of treatments in a wide array of cerebrovascular diseases and neurotrauma. Their use, however, has been limited in experimental subarachnoid hemorrhage studies. After several randomized, double-blinded, controlled clinical trials repeatedly failed to produce a benefit in functional outcome despite some improvement in angiographic vasospasm, more rigorous methods of neurobehavioral testing became critical to provide a more comprehensive evaluation of the functional efficacy of proposed treatments. While several subarachnoid hemorrhage studies have incorporated an array of neurobehavioral assays, a standardized methodology has not been agreed upon. Here, we review neurobehavioral tests for rodents and their potential application to subarachnoid hemorrhage studies. Developing a standardized neurobehavioral testing regimen in rodent studies of subarachnoid hemorrhage would allow for better comparison of results between laboratories and a better prediction of what interventions would produce functional benefits in humans.

Role of HIF-1a in regulating autophagic cell survival during cerebral ischemia reperfusion in rats

Hypoxia-inducible factor-1a (HIF-1a) plays a beneficial role during cerebral ischemia reperfusion (IR), but the underlying molecular mechanisms are not completely understood. Here, we aimed to investigate the effects and molecular regulation of HIF-1a on brain cell apoptosis and autophagy during IR. We found that augmentation of HIF-1a in re-perfused hematopoietic cells significantly reduced brain damage, alleviated brain edema and improved neural function during IR, seemingly through two HIF-1a target genes BNIP3 and NIX, which were critical regulators for cell apoptosis and autophagic cell survival. in vitro, HIF-1a induced up-regulation of BNIP3 and NIX in human cortical neuron cells, HCN-1A. Inhibition of BNIP3 and NIX significantly attenuated HIF-1a-suppressed cell apoptosis and HIF-1a-induced cell autophagy. Together, these data suggest that HIF-1a may ameliorate brain damages during IR through BNIP3 and NIX -dependent augmentation of autophagic cell survival and reduction in cell apoptosis.

Autophagy in hemorrhagic stroke: Mechanisms and clinical implications

Accumulating evidence advances the critical role of autophagy in brain pathology after stroke. Investigations employing autophagy induction or inhibition using pharmacological tools or autophagy-related gene knockout mice have recently revealed the biological significance of intact and functional autophagy in stroke. Most of the reported cases attest to a pro-survival role for autophagy in stroke, by facilitating removal of damaged proteins and organelles, which can be recycled for energy generation and cellular defenses. However, these observations are difficult to reconcile with equally compelling evidence demonstrating stroke-induced upregulation of brain cell death index that parallels enhanced autophagy. This begs the question of whether drug-induced autophagy during stroke culminates in improved or worsened pathological outcomes. A corollary fascinating hypothesis, but presents as a tricky conundrum, involves the effects of autophagy on cell death and inflammation, which are two main culprits in the disease progression of stroke-induced brain injury. Evidence has extended the roles of autophagy in inflammation via cytokine regulation in an unconventional secretion manner or by targeting inflammasomes for degradation. Moreover, in the recently concluded Vancouver Autophagy Symposium (VAS) held in 2014, the potential of selective autophagy for clinical treatment has been recognized. The role of autophagy in ischemic stroke has been reviewed previously in detail. Here, we evaluate the strength of laboratory and clinical evidence by providing a comprehensive summary of the literature on autophagy, and thereafter we offer our perspectives on exploiting autophagy as a drug target for cerebral ischemia, especially in hemorrhagic stroke.

Effects of intra-hippocampal microinjection of vitamin B12 on the orofacial pain and memory impairments induced by scopolamine and orofacial pain in rats

In the present study, we investigated the effects of microinjection of vitamin B₁₂ into the hippocampus on the orofacial pain and memory impairments induced by scopolamine and orofacial pain. In ketamine-xylazine anesthetized rats, the right and left sides of the dorsal hippocampus (CA1) were implanted with two guide cannulas. Orofacial pain was induced by subcutaneous injection of formalin (1.5%, 50μl) into the right vibrissa pad, and the durations of face rubbing were recorded at 3-min blocks for 45min. Morris water maze (MWM) was used for evaluation of learning and memory. Finally, locomotor activity was assessed using an open-field test. Vitamin B₁₂ attenuated both phases of formalin-induced orofacial pain. Prior administration of naloxone and naloxonazine, but not naltrindole and nor-binaltorphimine, prevented this effect. Vitamin B₁₂ and physostigmine decreased latency time as well as traveled distance in Morris water maze. In addition, these chemicals improved scopolamine-induced memory impairment. The memory impairment induced by orofacial pain was improved by vitamin B₁₂ and physostigmine used alone. Naloxone prevented, whereas physostigmine enhanced the memory improving effect of vitamin B₁₂ in the pain-induced memory impairment. All the above-mentioned chemicals did not alter locomotor activity. The results of the present study showed that at the level of the dorsal hippocampus, vitamin B₁₂ modulated orofacial pain through a mu-opioid receptor mechanism. In addition, vitamin B₁₂ contributed to hippocampal cholinergic system in processing of memory. Moreover, cholinergic and opioid systems may be involved in improving effect of vitamin B₁₂ on pain-induced memory impairment.

Neuronal prolyl-4-hydroxylase 2 deficiency improves cognitive abilities in a murine model of cerebral hypoperfusion

Episodes of cerebral hypoxia/ischemia increase the risk of dementia, which is associated with impaired learning and memory. Previous studies in rodent models of dementia indicated a favorable effect of the hypoxia-inducible factor (HIF) targets VEGF (vascular endothelial growth factor) and erythropoietin (Epo). In the present study we thus investigated whether activation of the entire adaptive HIF pathway in neurons by cell-specific deletion of the HIF suppressor prolyl-4-hydroxylase 2 (PHD2) improves cognitive abilities in young (3months) and old (18-28months) mice suffering from chronic brain hypoperfusion. Mice underwent permanent occlusion of the left common carotid artery, and cognitive function was assessed using the Morris water navigation task. Under conditions of both normal and decreased brain perfusion, neuronal PHD2 deficiency resulted in improved and faster spatial learning in young mice, which was preserved to some extent also in old animals. The loss of PHD2 in neurons resulted in enhanced hippocampal mRNA and protein levels of Epo and VEGF, but did not alter local microvascular density, dendritic spine morphology, or expression of synaptic plasticity-related genes in the hippocampus. Instead, better cognitive function in PHD2 deficient animals was accompanied by an increased number of neuronal precursor cells along the subgranular zone of the dentate gyrus. Overall, our current pre-clinical findings indicate an important role for the endogenous oxygen sensing machinery, encompassing PHDs, HIFs and HIF target genes, for proper cognitive function. Thus, pharmacological compounds affecting the PHD-HIF axis might well be suited to treat cognitive dysfunction and neurodegenerative processes.

Hypoxia promotes apoptosis of neuronal cells through hypoxia-inducible factor-1α-microRNA-204-B-cell lymphoma-2 pathway

Neuronal cells are highly sensitive to hypoxia and may be subjected to apoptosis when exposed to hypoxia. Several apoptosis-related genes and miRNAs involve in hypoxia-induced apoptosis. This study aimed to examine the role of HIF1α-miR-204-BCL-2 pathway in hypoxia-induced apoptosis in neuronal cells. Annexin V/propidium iodide assay was performed to analyze cell apoptosis in AGE1.HN and PC12 cells under hypoxic or normoxic conditions. The expression of BCL-2 and miR-204 were determined by Western blot and qRT-PCR. The effects of miR-204 overexpression or knockdown on the expression of BCL-2 were evaluated by luciferase assay and Western blot under hypoxic or normoxic conditions. HIF-1α inhibitor YC-1 and siHIF-1α were employed to determine the effect of HIF-1α on the up-regulation of miR-204 and down-regulation of BCL-2 induced by hypoxia. Apoptosis assay showed the presence of apoptosis induced by hypoxia in neuronal cells. Moreover, we found that hypoxia significantly down-regulated the expression of BCL-2, and increased the mRNA level of miR-204 in neuronal cells than that in control. Bioinformatic analysis and luciferase reporter assay demonstrated that miR-204 directly targeted and regulated the expression of BCL-2. Specifically, the expression of BCL-2 was inhibited by miR-204 mimic and enhanced by miR-204 inhibitor. Furthermore, we detected that hypoxia induced cell apoptosis via HIF-1α/miR-204/BCL-2 in neuronal cells. This study demonstrated that HIF-1α-miR-204-BCL-2 pathway contributed to apoptosis of neuronal cells induced by hypoxia, which could potentially be exploited to prevent spinal cord ischemia-reperfusion injury.

Experimental subarachnoid hemorrhage in rats: comparison of two endovascular perforation techniques with respect to success rate, confounding pathologies and early hippocampal tissue lesion pattern

Recently aside from the “classic” endovascular monofilament perforation technique to induce experimental subarachnoid hemorrhage (SAH) a modification using a tungsten wire advanced through a guide tube has been described. We aim to assess both techniques for their success rate (induction of SAH without confounding pathologies) as primary endpoint. Further, the early tissue lesion pattern as evidence for early brain injury will be analyzed as secondary endpoint. Sprague Dawley rats (n=39) were randomly assigned to receive either Sham surgery (n=4), SAH using the “classic” technique (n=18) or using a modified technique (n=17). Course of intracranial pressure (ICP) and regional cerebral blood flow (rCBF) was analyzed; subsequent pathologies were documented either 6 or 24 h after SAH. Hippocampal tissue samples were analyzed via immunohistochemistry and western blotting. SAH-induction, regardless of confounding pathologies, was independent from type of technique (p=0.679). There was no significant difference concerning case fatality rate (classic: 40%; modified: 20%; p=0.213). Successful induction of SAH without collateral ICH or SDH was possible in 40% with the classic and in 86.7% with the modified technique (p=0.008). Peak ICP levels differed significantly between the two groups (classic: 94 +/- 23 mmHg; modified: 68 +/- 19 mmHg; p=0.003). Evidence of early cellular stress response and activation of apoptotic pathways 6 h after SAH was demonstrated. The extent of stress response is not dependent on type of technique. Both tested techniques successfully produce SAH including activation of an early stress response and apoptotic pathways in the hippocampal tissue. However, the induction of SAH with less confounding pathologies was more frequently achieved with the modified tungsten wire technique.

HIF-1α Mediates Isoflurane-Induced Vascular Protection in Subarachnoid Hemorrhage

Objective

Outcome after aneurysmal subarachnoid hemorrhage (SAH) depends critically on delayed cerebral ischemia (DCI) – a process driven primarily by vascular events including cerebral vasospasm, microvessel thrombosis, and microvascular dysfunction. This study sought to determine the impact of postconditioning – the phenomenon whereby endogenous protection against severe injury is enhanced by subsequent exposure to a mild stressor – on SAH-induced DCI.

Methods

Adult male C57BL/6 mice were subjected to sham, SAH, or SAH plus isoflurane postconditioning. Neurological outcome was assessed daily via sensorimotor scoring. Contributors to DCI including cerebral vasospasm, microvessel thrombosis, and microvascular dysfunction were measured 3 days later. Isoflurane-induced changes in hypoxia-inducible factor 1alpha (HIF-1α)-dependent genes were assessed via quantitative polymerase chain reaction. HIF-1α was inhibited pharmacologically via 2-methoxyestradiol (2ME2) or genetically via endothelial cell HIF-1α-null mice (EC-HIF-1α-null). All experiments were performed in a randomized and blinded fashion.

Results

Isoflurane postconditioning initiated at clinically relevant time points after SAH significantly reduced cerebral vasospasm, microvessel thrombosis, microvascular dysfunction, and neurological deficits in wild-type (WT) mice. Isoflurane modulated HIF-1α-dependent genes – changes that were abolished in 2ME2-treated WT mice and EC-HIF-1α-null mice. Isoflurane-induced DCI protection was attenuated in 2ME2-treated WT mice and EC-HIF-1α-null mice.

Interpretation

Isoflurane postconditioning provides strong HIF-1α-mediated macro- and microvascular protection in SAH, leading to improved neurological outcome. These results implicate cerebral vessels as a key target for the brain protection afforded by isoflurane postconditioning, and HIF-1α as a critical mediator of this vascular protection. They also identify isoflurane postconditioning as a promising novel therapeutic for SAH.

Neurovascular events after subarachnoid hemorrhage: focusing on subcellular organelles

Subarachnoid hemorrhage (SAH) is a devastating condition with high morbidity and mortality rates due to the lack of effective therapy. Early brain injury (EBI) and cerebral vasospasm (CVS) are the two most important pathophysiological mechanisms for brain injury and poor outcomes for patients with SAH. CVS has traditionally been considered the sole cause of delayed ischemic neurological deficits after SAH. However, the failure of antivasospastic therapy in patients with SAH supported changing the research target from CVS to other mechanisms. Currently, more attention has been focused on global brain injury within 3 days after ictus, designated as EBI. The dysfunction of subcellular organelles, such as endoplasmic reticulum stress, mitochondrial failure, and autophagy-lysosomal system activation, has developed during EBI and delayed brain injury after SAH. To our knowledge, there is a lack of review articles addressing the direction of organelle dysfunction after SAH. In this review, we discuss the roles of organelle dysfunction in the pathogenesis of SAH and present the opportunity to develop novel therapeutic strategies of SAH via modulating the functions of organelles.

Pharmacologic stabilization of hypoxia-inducible transcription factors protects developing mouse brain from hypoxia-induced apoptotic cell death

OBJECTIVE

Accumulation of hypoxia-inducible transcription factors (HIFs) by prolyl-4-hydroxylase inhibitors (PHI) has been suggested to induce neuroprotection in the ischemic rodent brain. We aimed to investigate in vivo effects of a novel PHI on HIF-regulated neurotrophic and pro-apoptotic factors in the developing normoxic and hypoxic mouse brain.

METHODS

Neonatal mice (P7) were treated with PHI FG-4497 (30-100mg/kg, i.p.) followed by exposure to systemic hypoxia (8% O2, 6h) 4h later. Cerebral expression of HIFα-subunits, specific neurotrophic and vasoactive target genes (vascular endothelial growth factor (VEGF), adrenomedullin (ADM), erythropoietin (EPO), inducible nitric oxide synthase (iNOS)) as well as pro-apoptotic (BCL2/adenovirus E1B 19-kDa protein-interacting protein 3 gene (BNIP3), immediate early response 3 (IER3)) and migratory factors (chemokine receptor 4 (CXCR4), stromal cell-derived factor 1 (SDF-1)) was determined (quantitative real-time (RT)., Western blot analysis) in comparison to controls. Apoptotic cell death was analyzed by terminal desoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) and cleaved caspase 3 (CC3) staining.

RESULTS

Under normoxic conditions, FG-4497 treatment significantly induced the accumulation of both HIF-1α and HIF-2α isoforms in developing mouse brain. In addition, there was a significant up-regulation of HIF target genes (VEGF, ADM, EPO, CXCR4, p<0.01) with FG-4497 treatment compared to controls supporting functional activation of the HIF proteins. Under hypoxia, differential target gene activation was observed in the developing brain including additive effects of FG-4497 and hypoxia on mRNA expression of VEGF and ADM as well as a dose-dependent down-regulation of iNOS. BNIP3 but not IER3 mRNA levels significantly increased in hypoxic brains pre-treated with high-dose FG-4497 compared to controls. Of special interest, FG-4497 treatment significantly diminished apoptotic cell death, quantified by TUNEL and CC3-positive cells, in hypoxic developing brains compared to controls.

CONCLUSIONS

PHI treatment modulates neurotrophic factors known to be crucially involved in hypoxia-induced cerebral adaptive mechanisms as well as early brain maturation. Pre-treatment with FG-4497 seems to protect the developing brain from hypoxia-induced apoptosis. Present observations provide basic information for further evaluation of neuroprotective properties of PHI treatment in hypoxic injury of the developing brain. However, potential effects on maturational processes need special attention in experimental research targeting HIF-dependent neuroprotective interventions during the very early stage of brain development.

Protective effect of quercetin against oxidative stress and brain edema in an experimental rat model of subarachnoid hemorrhage

Quercetin has been demonstrated to play an important role in altering the progression of ischemic brain injuries and neurodegenerative diseases by protecting against oxidative stress. The effects of quercetin on brain damage after subarachnoid hemorrhage (SAH), however, have not been investigated. This study was designed to explore the effects of quercetin on oxidative stress and brain edema after experimental SAH using four equal groups (n = 16) of adult male Sprague-Dawley (SD) rats, including a sham group, an SAH + vehicle group, an SAH + quercetin10 group, and an SAH + quercetin50 group. The rat SAH model was induced by injection of 0.3 ml of non-heparinised arterial blood into the prechiasmatic cistern. In the SAH + quercetin10 and SAH + quercetin50 groups, doses of 10 mg/kg and 50 mg/kg quercetin, respectively, were directly administered by intraperitoneal injection at 30 min, 12 h, and 24 h after SAH induction. Cerebral tissue samples were extracted for enzymatic antioxidant determination, lipid peroxidation assay, caspase-3 activity and water content testing 48 h after SAH. Treatment with a high dose (50 mg/kg) of quercetin markedly enhanced the activities of copper/zinc superoxide dismutase (CuZn-SOD) and glutathione peroxidase (GSH-Px), and treatment with this dose significantly reduced the level of malondialdehyde (MDA). Caspase-3 and brain edema was ameliorated and neurobehavioral deficits improved in rats that received the high dose of quercetin. The findings suggest that the early administration of optimal dose of quercetin may ameliorate brain damage and provide neuroprotection in the SAH model, potentially by enhancing the activity of endogenous antioxidant enzymes and inhibiting free radical generation.

Inflammation in intracerebral hemorrhage: from mechanisms to clinical translation

Intracerebral hemorrhage (ICH) accounts for 10-15% of all strokes and is associated with high mortality and morbidity. Currently, no effective medical treatment is available to improve functional outcomes in patients with ICH. Potential therapies targeting secondary brain injury are arousing a great deal of interest in translational studies. Increasing evidence has shown that inflammation is the key contributor of ICH-induced secondary brain injury. Inflammation progresses in response to various stimuli produced after ICH. Hematoma components initiate inflammatory signaling via activation of microglia, subsequently releasing proinflammatory cytokines and chemokines to attract peripheral inflammatory infiltration. Hemoglobin (Hb), heme, and iron released after red blood cell lysis aggravate ICH-induced inflammatory injury. Danger associated molecular patterns such as high mobility group box 1 protein, released from damaged or dead cells, trigger inflammation in the late stage of ICH. Preclinical studies have identified inflammatory signaling pathways that are involved in microglial activation, leukocyte infiltration, toll-like receptor (TLR) activation, and danger associated molecular pattern regulation in ICH. Recent advances in understanding the pathogenesis of ICH-induced inflammatory injury have facilitated the identification of several novel therapeutic targets for the treatment of ICH. This review summarizes recent progress concerning the mechanisms underlying ICH-induced inflammation. We focus on the inflammatory signaling pathways involved in microglial activation and TLR signaling, and explore potential therapeutic interventions by targeting the removal of hematoma components and inhibition of TLR signaling.