Hypoxic-preconditioning induces neuroprotection against hypoxia–ischemia in newborn piglet brain

Research hotspots and frontiers of preconditioning in cerebral ischemia: A bibliometric analysis

Background

Preconditioning is a promising strategy against ischemic brain injury, and numerous studies in vitro and in vivo have demonstrated its neuroprotective effects. However, at present there is no bibliometric analysis of preconditioning in cerebral ischemia. Therefore, a comprehensive overview of the current status, hot spots, and emerging trends in this research field is necessary.

Materials and methods

Studies on preconditioning in cerebral ischemia from January 1999-December 2022 were retrieved from the Web of Science Core Collection (WOSCC) database. CiteSpace was used for data mining and visual analysis.

Results

A total of 1738 papers on preconditioning in cerebral ischemia were included in the study. The annual publications showed an upwards and then downwards trend but currently remain high in terms of annual publications. The US was the leading country, followed by China, the most active country in recent years. Capital Medical University published the largest number of articles. Perez-Pinzon, Miguel A contributed the most publications, while KITAGAWA K was the most cited author. The focus of the study covered three areas: (1) relevant diseases and experimental models, (2) types of preconditioning and stimuli, and (3) mechanisms of ischemic tolerance. Remote ischemic preconditioning, preconditioning of mesenchymal stem cells (MSCs), and inflammation are the frontiers of research in this field.

Conclusion

Our study provides a visual and scientific overview of research on preconditioning in cerebral ischemia, providing valuable information and new directions for researchers.

Vascular Endothelial Growth Factor and Erythropoietin Show Different Expression Patterns in the Early and Late Hypoxia Preconditioning Phases and May Correlate with DNA Methylation Status in the Mouse Hippocampus

Liu, Na, Yanbo Zhang, Pu Zhang, Kerui Gong, Chunyang Zhang, Kai Sun, and Guo Shao. Vascular endothelial growth factor and erythropoietin show different expression patterns in the early and late hypoxia preconditioning phases and may correlate with DNA methylation status in the mouse hippocampus. High Alt Med Biol. 23:361-368, 2022. Background: Vascular endothelial growth factor (VEGF) and erythropoietin (EPO) have been proven to participate in neuroprotection induced by hypoxia preconditioning (HPC), and they can be regulated by hypoxia-inducible factor 1 (HIF-1). It has been reported that DNA methylation can affect VEGF and EPO expression. This study aimed to explore the expression of VEGF and EPO in the early phase and late phase of HPC and whether their expression was affected by DNA methylation. Method: Acute repeated HPC mice were used as the animal model, and detection of molecular changes was performed immediately (early phase) and 1 day (late phase) after HPC treatment. The mRNA and protein expression levels of VEGF, EPO, and DNA methyltransferases (DNMTs) in the hippocampi were measured by real-time polymerase chain reaction and western blotting, respectively. The activity of DNMTs and global methylation levels were analyzed by enzyme-linked immunosorbent assay. DNA methylation levels of VEGF and EPO promoters, which were catalyzed by DNMTs, were determined by bisulfite-modified DNA sequencing. Results: The expression of VEGF was increased in the early phase and late phase of HPC (p < 0.05), whereas the expression of EPO was unchanged in the early phase (p > 0.05) of HPC and was increased in the late phase (p < 0.05). VEGF and EPO expression were negatively correlated with the DNA methylation levels of their promoters. DNMT3A and DNMT3B were decreased in the early phase and late phase (p < 0.05), whereas DNMT1 was unchanged in the early phase and late phase (p > 0.05). Conclusions: Our data demonstrated that DNMTs affect VEGF and EPO expression by regulating the DNA methylation levels of the promoters of VEGF and EPO.

Mimicking partial to total placental insufficiency in a rabbit model of cerebral palsy

All placental abruptions begin as partial abruptions, which sometimes manifest as fetal bradycardia. The progression from partial to total abruption was mimicked by a new rabbit model of placental insufficiency, and we compared it, with sufficient statistical power, with the previous model mimicking total placental abruption. The previous model uses total uterine ischemia at E22 or E25 (70% or 79% term, respectively), in pregnant New Zealand white rabbits for 40 min (Full H-I). The new model, Partial+Full H-I, added a 30-min partial ischemia before the 40-min total ischemia. Fetuses were delivered either at E31.5 (full term) vaginally for neurobehavior testing, or by C-section at E25 for ex vivo brain cell viability evaluation. The onset of fetal bradycardia was within the first 2 min of either H-I protocol. There was no difference between Full H-I (n = 442 for E22, 312 for E25) and Partial+Full H-I (n = 154 and 80) groups in death or severely affected kits at E22 (76% vs. 79%) or at E25 (66% vs. 64%), or normal kits at E22 or E25, or any of the individual newborn neurobehavioral tests at any age. No sex differences were found. Partial+Full H-I (n = 6) showed less cell viability than Full H-I (n = 8) at 72-hr ex vivo in the brain regions studied. Partial+Full H-I insult produced similar cerebral palsy phenotype as our previous Full H-I model in a sufficiently powered study and may be more suitable for testing of potential neuroprotectants.

Pathophysiology of Perinatal Asphyxia in Humans and Animal Models

Perinatal asphyxia is caused by lack of oxygen delivery (hypoxia) to end organs due to an hypoxemic or ischemic insult occurring in temporal proximity to labor (peripartum) or delivery (intrapartum). Hypoxic–ischemic encephalopathy is the clinical manifestation of hypoxic injury to the brain and is usually graded as mild, moderate, or severe. The search for useful biomarkers to precisely predict the severity of lesions in perinatal asphyxia and hypoxic–ischemic encephalopathy (HIE) is a field of increasing interest. As pathophysiology is not fully comprehended, the gold standard for treatment remains an active area of research. Hypothermia has proven to be an effective neuroprotective strategy and has been implemented in clinical routine. Current studies are exploring various add-on therapies, including erythropoietin, xenon, topiramate, melatonin, and stem cells. This review aims to perform an updated integration of the pathophysiological processes after perinatal asphyxia in humans and animal models to allow us to answer some questions and provide an interim update on progress in this field.

Neuroprotective effects and mechanisms of ischemic/hypoxic preconditioning on neurological diseases

As the organ with the highest demand for oxygen, the brain has a poor tolerance to ischemia and hypoxia. Despite severe ischemia/hypoxia induces the occurrence and development of various central nervous system (CNS) diseases, sublethal insult may induce strong protection against subsequent fatal injuries by improving tolerance. Searching for potential measures to improve brain ischemic/hypoxic is of great significance for treatment of ischemia/hypoxia related CNS diseases. Ischemic/hypoxic preconditioning (I/HPC) refers to the approach to give the body a short period of mild ischemic/hypoxic stimulus which can significantly improve the body's tolerance to subsequent more severe ischemia/hypoxia event. It has been extensively studied and been considered as an effective therapeutic strategy in CNS diseases. Its protective mechanisms involved multiple processes, such as activation of hypoxia signaling pathways, anti-inflammation, antioxidant stress, and autophagy induction, etc. As a strategy to induce endogenous neuroprotection, I/HPC has attracted extensive attention and become one of the research frontiers and hotspots in the field of neurotherapy. In this review, we discuss the basic and clinical research progress of I/HPC on CNS diseases, and summarize its mechanisms. Furthermore, we highlight the limitations and challenges of their translation from basic research to clinical application.

Multitarget neuroprotection by quercetin: Changes in gene expression in two perinatal asphyxia models

Hypoxic-ischemic encephalopathy (HIE) causes mortality and long-term neurologic morbidities in newborns, affecting pathways related to energy failure, excitotoxicity and oxidative stress that often lead to cell death. The whole process of HIE injury is coupled to changes in the expression of a great array of proteins. A nanoliposomal preparation of the flavonoid quercetin has been shown to exert neuroprotective effects in perinatal asphyxia models. This study aimed to identify neonatal HIE markers and explore the effect of quercetin administration in two perinatal asphyxia models: newborn rats and piglets. In the rat model, nanoliposomal quercetin administration reduced mortality after asphyxia. In the piglet model, quercetin partially overrode the reduction of HIF-1α mRNA levels in the cortex induced by asphyxia. Quercetin administration also reduced increased level of HO-1 mRNA in asphyctic piglets. These results suggest that quercetin neuroprotection might be involved in the regulation of HIF-1α, HO-1 and their targets. A proteomic approach revealed that the glycolytic pathway is strongly regulated by quercetin in both species. We also identified a set of proteins differentially expressed that could be further considered as markers. In piglets, this set includes Acidic Leucine-rich nuclear phosphoprotein 32 (ANP32A), associated with nervous system differentiation, proteins related with death pathways and alpha-enolase which can be converted to neuron-specific enolase, a glycolytic enzyme that may promote neuroprotection. In newborn rats, other promising proteins associated with neurogenesis and neuroprotection emerged, such as dihydropyrimidinase-related proteins, catalytic and regulatory subunits of phosphatases and heterogeneous nuclear ribonucleoprotein K (hnRNPK). Our results show that a nanoliposomal preparation of quercetin, with protective effect in two HIE mammal models, modulates the expression of proteins involved in energy metabolism and other putative neuroprotective signals in the cortex. Identification of these signals could reveal potential molecular pathways involved in disease onset and the novel quercetin neuroprotective strategy.

A Genome-Wide Analysis of the Gene Expression and Alternative Splicing Events in a Whole-Body Hypoxic Preconditioning Mouse Model

Exposure to specific doses of hypoxia can trigger endogenous neuroprotective and neuroplastic mechanisms of the central nervous system. These molecular mechanisms, together referred to as hypoxic preconditioning (HPC), remain poorly understood. In the present study, we applied RNA sequencing and bioinformatics analyses to study HPC in a whole-body HPC mouse model. The preconditioned (H4) and control (H0) groups showed 605 differentially expressed genes (DEGs), of which 263 were upregulated and 342 were downregulated. Gene Ontology enrichment analysis indicated that these DEGs were enriched in several biological processes, including metabolic stress and angiogenesis. The Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that the FOXO and Notch signaling pathways were involved in hypoxic tolerance and protection during HPC. Furthermore, 117 differential alternative splicing events (DASEs) were identified, with exon skipping being the dominant one (48.51%). Repeated exposure to systemic hypoxia promoted skipping of exon 7 in Edrf1 and exon 9 or 13 in Lrrc45. This study expands the understanding of the endogenous protective mechanisms of HPC and the DASEs that occur during HPC.

Brain Contrast-Enhanced Ultrasound Evaluation of a Pediatric Swine Model

ABSTRACT

Brain injury remains a leading cause of morbidity and mortality in children. We evaluated the feasibility of using a pediatric swine model to develop contrast-enhanced ultrasound (CEUS)-based measures of brain perfusion for clinical application in various types of brain injury monitoring. Six-week-old, 10-kg swine (N = 10) were anesthetized, and an acoustic window was created in the right frontal cranium to provide visualization of an oblique coronal plane and bilateral thalami. Ultrasound contrast agent was administered via a femoral venous catheter as a weight-based (0.03 mL/kg) bolus. After localization of the imaging plane, CEUS cine clips were acquired for 90 seconds. Bolus injection of contrast agent provided global visualization of cerebral perfusion and highlighted microvasculature in the brain. Preliminary evaluation of bolus kinetics in piglets showed a central gray nuclei-to-cortex ratio similar to human infants with a steep wash-in that crossed and remained above the 1.0 threshold for most of the enhancement period. We demonstrated the similarity in brain perfusion between piglets and human infants, specifically central gray nuclei-to-cortex ratio, showing preliminary feasibility of its use as a pediatric model of brain perfusion. Contrast-enhanced ultrasound can be performed at the bedside as a minimally invasive procedure, and quantitative CEUS may provide critical information regarding changes in brain perfusion as a result of injury or as a response to therapy.

Cerebral embolism accompanied by remarkable diffusion-weighted imaging reversal in a 10 month-old infant with congenital heart disease

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The case of infant ischemic stroke with remarkable DWI reversal.

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A mismatch between core volume and visually DWI lesion predicts DWI reversal.

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Chronic hypoxia and early recanalization may contribute to large DWI reversal.

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Mismatch between DWI-ASPECTS and core volume may occur in infant brain.

Neuroprotection of hypoxic/ischemic preconditioning in neonatal brain with hypoxic-ischemic injury

The neonatal brain is susceptible to hypoxic-ischemic injury due to its developmental characteristics. Hypoxia-ischemia means a decreased perfusion of oxygen and glucose, which can lead to severe encephalopathy. Although early initiation of therapeutic hypothermia was reported to provide neuroprotection for infants after HI, hypothermia administered alone after the acute insult cannot reverse the severe damage that already has occurred or improve the prognosis of severe hypoxic-ischemic encephalopathy. Therefore, exploring new protective mechanisms for treating hypoxic-ischemic brain damage are imperative. Until now, many studies reported the neuroprotective mechanisms of hypoxic/ischemic preconditioning in protecting the hypoxic-ischemic newborn brains. After hypoxia and ischemia, hypoxia-inducible factor signaling pathway is involved in the transcriptional regulation of many genes and is also play a number of different roles in protecting brains during hypoxic/ischemic preconditioning. Hypoxic/ischemic preconditioning could protect neonatal brain by several mechanisms, including vascular regulation, anti-apoptosis, anti-oxidation, suppression of excitotoxicity, immune regulation, hormone levels regulation, and promote cell proliferation. This review focused on the protective mechanisms underlying hypoxic/ischemic preconditioning for neonatal brain after hypoxia-ischemia and emphasized on the important roles of hypoxia inducible factor 1 signaling pathway.

Ischemic Postconditioning Mitigates Retinopathy in Tree Shrews with Diabetic Cerebral Ischemia

Ischemic postconditioning (PC) is proved to efficiently protect diabetic patients with acute myocardial infarction from ischemia-reperfusion injury. We aimed to explore the protective roles of ischemic PC on diabetic retinopathy in tree shrews with diabetic cerebral ischemia. A diabetic tree shrew model was established through high-fat diet feeding combined with streptozotocin (STZ) injection, while cortical thrombotic cerebral ischemia was induced photochemically. Tree shrews were divided into the normal control group, sham operation group, diabetes mellitus group, diabetes mellitus+cerebral ischemia group, and diabetes mellitus+cerebral ischemia+PC group (in which the tree shrews with diabetic cerebral ischemia were treated with ischemic PC). H&E staining was used to examine the pathological changes in the retina, and immunohistochemistry was performed to determine the retinal expression of VEGF (vascular endothelial growth factor). The modeling resulted in 77% tree shrews with diabetes. Ischemic PC reduced the blood glucose levels in the tree shrews with diabetic cerebral ischemia. Tree shrews with diabetes had thinned retina with disordered structures, and these pathological changes were aggravated after cerebral ischemia. The retinopathy was alleviated after ischemic PC. Retina expression of VEGF was mainly distributed in the ganglion cell layer in tree shrews. Diabetes and cerebral ischemia increased retinal VEGF expression in a step-wise manner, while additional ischemic PC reduced retinal VEGF expression. Therefore, ischemic PC effectively alleviates retinopathy in tree shrews with diabetic cerebral ischemia, and this effect is associated with reduced retinal VEGF expression.

Remote Ischemic Conditioning Protects Diabetic Retinopathy in Streptozotocin-induced Diabetic Rats via Anti-Inflammation and Antioxidation

Ischemic conditioning inhibits oxidative stress and inflammatory response in diabetes. However, whether limb remote ischemic conditioning (LRIC) has beneficial effects on diabetic retinopathy (DR) remains unknown. This study aims to investigate the protective effects of LRIC in retinal ganglion cell in streptozotocin (STZ) induced Type 1 diabetic rats. A total of 48 healthy male Sprague-Dawley (200-220g) rats were randomly assigned to the normal group, normal+LRIC group, diabetes mellitus (DM) group and DM+LRIC group. Streptozotocin (STZ, 60 mg/kg) was intraperitoneally injected into the rats to establish the diabetic model. LRIC was conducted by tightening a tourniquet around the upper thigh and releasing for three cycles daily (10 mins x 3 cycles). Retinas were harvested after 12 weeks of LRIC treatment for histopathologic, Western blot and ELISA analysis. Plasma were collected at the same time for ELISA analysis. LRIC alleviated diabetic retinopathy symptoms as evidenced by the increased number of retinal ganglion cells (P<0.01) and decreased glial fibrillary acidic protein (GFAP) expression level (P<0.01) in the rat retina. LRIC in DM rats exhibited anti-inflammatory and antioxidative effects as confirmed by the down-regulation of pro-inflammatory cytokine: interleukin-6 (IL-6), and the up-regulation of antioxidants: superoxide dismutase (SOD), and glutathione (GSH)/oxidized glutathione (GSSG). Furthermore, LRIC significantly downregulated VEGF protein expression in the retina (P<0.01). These results suggest that the antioxidative and anti-inflammatory activities of LRIC may be important mechanisms involved in the protective effect of LRIC in STZ-induced diabetic rats.

Effects of Ischemic and Proton Pump Inhibitors Preconditioning on Oxidative Stress of Isolated Rat Heart

Aim of present study was to determine the participation of various biomarkers of oxidative damage: nitrite (NO2 −), superoxide anion radicals (O2 −), index of lipid peroxidation (TBARS) and hydrogen peroxide (H2O2) in coronary circulation after application of the different models of preconditioning such as ischemic and preconditioning with proton pump inhibitors.

Examining a biochemical markers of oxidative damage we did not notice any increased production values of any parameter, according to that we can hypothesize that possible occurrence of reperfusion injury after ischemia and PPIs preconditioning is not mediated by this mechanism.

Due to the very difficult and controversial application of ischemic preconditioning in clinical practice, the results of this study suggest that in the future proton pump inhibitors can contribute to the prevention of myocardial damage following ischemia

Effect of Intranasally Delivered rh-VEGF165 on Angiogenesis Following Cerebral Hypoxia-Ischemia in the Cerebral Cortex of Newborn Piglets

Background: Vascular endothelial growth factor (VEGF) stimulates vascular genesis and angiogenesis. Cerebral Hypoxia-Ischemia (HI) leads to the reduction of vasculature in the cerebral cortex of newborn piglets. Objective: The present study tests the hypothesis that post-hypoxia intranasal administration of recombinant human VEGF₁₆₅ (rh-VEGF165) for 3 days increases the vascular density in the cerebral cortex of newborn piglets without promoting neovascularization. Design/Methods: Ventilated newborn piglets were divided into three groups (n = 5/group): normoxic (Nx), hypoxic-ischemic (HI), and HI treated with intranasal rh-VEGF165rh-VEGF165 (HI-VEGF). HI piglets were exposed to HI (0.05 FiO2) for 30 min. Recombinant h-VEGF165 (100 ng/kg) was administered 15 min after HI and then once daily for 3 days. The animals were perfused transcardially and coronal brains sections were processed for Isolectin, Hoechst, and ki-67 cell proliferation marker staining. To assess the vascular density, 30–35 fields per animal section were manually counted using image J software. Results: The vascular density (vessels/mm²) was 42.0 ± 8.0 in the Nx group, 26.4 ± 4.8 (p < 0.05 vs. Nx) in the HI group, and 46.0 ± 11.9 (p < 0.05 vs. HI) in the HI-VEGF group. When stained for newly formed vessels, via Ki-67 staining, the vascular density was 5.4 ± 3.6 in the Nx group (p < 0.05 vs. HI), 10.2 ± 2.1 in the HI group, and 10.9 ± 2.9 in the HI-VEGF group (p = 0.72 vs. HI). HI resulted in a decrease in vascular density. Intranasal rh-VEGF165rh-VEGF165 resulted in the attenuation of the HI-induced decrease in vascular density. However, rh-VEGF165 did not result in the formation of new vascularity, as evident by ki-67 staining. Conclusions: Intranasal rh-VEGF165 may prevent the HI-induced decrease in the vascular density of the brain and could serve as a promising adjuvant therapy for hypoxic-ischemic encephalopathy (HIE).

Vulnerability to a Metabolic Challenge Following Perinatal Asphyxia Evaluated by Organotypic Cultures: Neonatal Nicotinamide Treatment

The hypothesis of enhanced vulnerability following perinatal asphyxia was investigated with a protocol combining in vivo and in vitro experiments. Asphyxia-exposed (AS) (by 21 min water immersion of foetuses containing uterine horns) and caesarean-delivered control (CS) rat neonates were used at P2-3 for preparing triple organotypic cultures (substantia nigra, neostriatum and neocortex). At DIV 18, cultures were exposed to different concentrations of H₂O₂ (0.25-45 mM), added to the culture medium for 18 h. After a 48-h recovery period, the cultures were either assessed for cell viability or for neurochemical phenotype by confocal microscopy. Energy metabolism (ADP/ATP ratio), oxidative stress (GSH/GSSG) and a modified ferric reducing/antioxidant power assay were applied to homogenates of parallel culture series. In CS cultures, the number of dying cells was similar in substantia nigra, neostriatum and neocortex, but it was several times increased in AS cultures evaluated under the same conditions. A H₂O₂ challenge led to a concentration-dependent increase in cell death (>fourfold after 0.25 mM of H₂O₂) in CS cultures. In AS cultures, a significant increase in cell death was only observed after 0.5 mM of H₂O₂. At higher than 1 mM of H₂O₂ (up to 45 mM), cell death increased several times in all cultures, but the effect was still more prominent in CS than in AS cultures. The cell phenotype of dying/alive cells was investigated in formalin-fixed cultures exposed to 0 or 1 mM of H₂O₂, co-labelling for TUNEL (apoptosis), MAP-2 (neuronal phenotype), GFAP (astroglial phenotype) and TH (tyrosine hydroxylase; for dopamine phenotype), counterstaining for DAPI (nuclear staining), also evaluating the effect of a single dose of nicotinamide (0.8 nmol/kg, i.p. injected in 100 μL, 60 min after delivery). Perinatal asphyxia produced a significant increase in the number of DAPI/TUNEL cells/mm³, in substantia nigra and neostriatum. One millimolar of H₂0₂ increased the number of DAPI/TUNEL cells/mm³ by ≈twofold in all regions of CS and AS cultures, an effect that was prevented by neonatal nicotinamide treatment. In substantia nigra, the number of MAP-2/TH-positive cells/mm³ was decreased in AS compared to CS cultures, also by 1 mM of H₂0₂, both in CS and AS cultures, prevented by nicotinamide. In agreement, the number of MAP-2/TUNEL-positive cells/mm³ was increased by 1 mM H₂O₂, both in CS (twofold) and AS (threefold) cultures, prevented by nicotinamide. The number of MAP-2/TH/TUNEL-positive cells/mm³ was only increased in CS (>threefold), but not in AS (1.3-fold) cultures. No TH labelling was observed in neostriatum, but 1 mM of H₂O₂ produced a strong increase in the number of MAP-2/TUNEL-positive cells/mm³, both in CS (>2.9-fold) and AS (>fourfold), decreased by nicotinamide. In neocortex, H₂O₂ increased the number of MAP-2/TUNEL-positive cells/mm³, both in CS and AS cultures (≈threefold), decreased by nicotinamide. The ADP/ATP ratio was increased in AS culture homogenates (>sixfold), compared to CS homogenates, increased by 1 mM of H₂0₂, both in CS and AS homogenates. The GSH/GSSG ratio was significantly decreased in AS, compared to CS cultures. One millimolar of H₂O₂ decreased that ratio in CS and AS homogenates. The present results demonstrate that perinatal asphyxia induces long-term changes in metabolic pathways related to energy and oxidative stress, priming cell vulnerability with both neuronal and glial phenotype. The observed effects were region dependent, being the substantia nigra particularly prone to cell death. Nicotinamide administration in vivo prevented the deleterious effects observed after perinatal asphyxia in vitro, a suitable pharmacological strategy against the deleterious consequences of perinatal asphyxia.

Serial cytokine alterations and abnormal neuroimaging in newborn infants with encephalopathy

AIM

Inflammatory cytokines may play a role in the final common pathway in the pathogenesis of hypoxic-ischaemic injury in experimental models. We aimed to profile the systemic pro-and anti-inflammatory response over the first week of life in term infants at risk of neonatal encephalopathy.

METHOD

In a tertiary referral university neonatal intensive care unit, serial blood samples were analysed from 41 term infants (requiring resuscitation at birth) in this prospective observational pilot study. Serum levels of 10 pro-and anti-inflammatory cytokines were evaluated including interleukin(IL)-1α, IL-1β, IL-6, IL-8, IL-10, tumour necrosis factor(TNF)-α, interferon (IFN)-γ, vascular endothelial growth factor (VEGF), granulocyte/colony-stimulating factor (G-CSF) and granulocyte macrophage/colony-stimulating factor (GM-CSF).

RESULTS

Infants with neonatal encephalopathy and abnormal neuroimaging (n = 15) had significantly elevated granulocyte macrophage/colony-stimulating factor at 0-24 h and interleukin-8, interleukin-6 and interleukin-10 at 24-48 hour. Tumour necrosis factor-α and vascular endothelial growth factor levels were lower at 72-96 hour (p < 0.05). Significantly elevated levels of interleukin-10 were associated with mortality.

CONCLUSION

Serum cytokine changes and innate immune dysregulation in the first week of life may be indicators of outcome in neonatal encephalopathy but require validation in larger studies.

Risk factors and clinical features in ischemic stroke patients with different tongue conditions

OBJECTIVE

To investigate the risk factors and clinical features in ischemic stroke patients with different tongue conditions.

METHODS

A total of 168 successive acute ischemic stroke inpatients (within 7 days of stroke onset) were recruited. Patients were assigned to groups according to tongue color (pink, pale, red, purple), tongue coating (no coating, thin coating, thick coating) and sublingual vessel (normal, abnormal). Risk factors and clinical features including National Institutes of Health Stroke Scale (NIHSS), modified Rankin Scale (mRS) and Barthel Index (BI), clinical classification, laboratory data and pulmonary infection complications were compared.

RESULTS

There were no significant differences in risk factors and clinical features among groups with different tongue colors. The incidence of smoking (4.5%) was lower in the no coating group compared with the thin (30.0%) and thick (39.3%) coating groups (P<0.017). NIHSS (19.05±10.68) in the no coating group was higher than the thin (6.40±6.18) and thick (7.41±7.05) coating groups (P<0.017), BI (20.91±29.99) was lower than the thin (67.61±28.78) and thick (63.02±33.54) coating groups (P<0.017), and the percentage of mRS >3 (90.9%) was higher than the thin (42.2%) and thick (42.9%) coating groups (P<0.017). The percentage of partial anterior circulation infarction patients in the no coating group was higher than the thin coating group (77.3% vs. 42.2%), and the percentage of lacunar infarction patients was lower than the thin coating group (4.5% vs. 37.8%, P<0.017). NIHSS in the abnormal sublingual vessel group was lower than the normal group (5.28±4.38 vs. 10.57±9.58, P=0.000), and BI was higher than the normal group (67.61±29.29 vs. 54.64±36.23, P=0.015).

CONCLUSION

Tongue conditions of acute stroke patients were relevant to clinical features.

Mechanisms of Neuronal Protection against Excitotoxicity, Endoplasmic Reticulum Stress, and Mitochondrial Dysfunction in Stroke and Neurodegenerative Diseases

In stroke and neurodegenerative disease, neuronal excitotoxicity, caused by increased extracellular glutamate levels, is known to result in calcium overload and mitochondrial dysfunction. Mitochondrial deficits may involve a deficiency in energy supply as well as generation of high levels of oxidants which are key contributors to neuronal cell death through necrotic and apoptotic mechanisms. Excessive glutamate receptor stimulation also results in increased nitric oxide generation which can be detrimental to cells as nitric oxide interacts with superoxide to form the toxic molecule peroxynitrite. High level oxidant production elicits neuronal apoptosis through the actions of proapoptotic Bcl-2 family members resulting in mitochondrial permeability transition pore opening. In addition to apoptotic responses to severe stress, accumulation of misfolded proteins and high levels of oxidants can elicit endoplasmic reticulum (ER) stress pathways which may also contribute to induction of apoptosis. Two categories of therapeutics are discussed that impact major pro-death events that include induction of oxidants, calcium overload, and ER stress. The first category of therapeutic agent includes the amino acid taurine which prevents calcium overload and is also capable of preventing ER stress by inhibiting specific ER stress pathways. The second category involves N-methyl-D-aspartate receptor (NMDA receptor) partial antagonists illustrated by S-Methyl-N, N-diethyldithiocarbamate sulfoxide (DETC-MeSO), and memantine. DETC-MeSO is protective through preventing excitotoxicity and calcium overload and by blocking specific ER stress pathways. Another NMDA receptor partial antagonist is memantine which prevents excessive glutamate excitation but also remarkably allows maintenance of physiological neurotransmission. Targeting of these major sites of neuronal damage using pharmacological agents is discussed in terms of potential therapeutic approaches for neurological disorders.

Neuroprotective agents for neonatal hypoxic-ischemic brain injury

Hypoxic-ischemic (H-I) brain injury in newborns is a major cause of morbidity and mortality that claims thousands of lives each year. In this review, we summarize the promising neuroprotective agents tested on animal models and pilot clinical studies of neonatal H-I brain injury according to the different phases of the disease. These agents target various phases of injury including the early phase of excitotoxicity, oxidative stress and apoptosis as well as late-phase inflammatory reaction and neural repair. We analyze the cell survival and cell death pathways modified by these agents in neonatal H-I brain injury. We aim to 'build a bridge' between animal trials of neuroprotective agents and potential candidate treatments for future clinical applications against H-I encephalopathy.

Cerebral Ischemic Preconditioning: the Road So Far…

Cerebral preconditioning constitutes the brain's adaptation to lethal ischemia when first exposed to mild doses of a subtoxic stressor. The phenomenon of preconditioning has been largely studied in the heart, and data from in vivo and in vitro models from past 2-3 decades have provided sufficient evidence that similar machinery exists in the brain as well. Since preconditioning results in a transient protective phenotype labeled as ischemic tolerance, it can open many doors in the medical warfare against stroke, a debilitating cerebrovascular disorder that kills or cripples thousands of people worldwide every year. Preconditioning can be induced by a variety of stimuli from hypoxia to pharmacological anesthetics, and each, in turn, induces tolerance by activating a multitude of proteins, enzymes, receptors, transcription factors, and other biomolecules eventually leading to genomic reprogramming. The intracellular signaling pathways and molecular cascades behind preconditioning are extensively being investigated, and several first-rate papers have come out in the last few years centered on the topic of cerebral ischemic tolerance. However, translating the experimental knowledge into the clinical scaffold still evades practicality and faces several challenges. Of the various preconditioning strategies, remote ischemic preconditioning and pharmacological preconditioning appears to be more clinically relevant for the management of ischemic stroke. In this review, we discuss current developments in the field of cerebral preconditioning and then examine the potential of various preconditioning agents to confer neuroprotection in the brain.

Effects of ischemic preconditioning on VEGF and pFlk-1 immunoreactivities in the gerbil ischemic hippocampus after transient cerebral ischemia

Ischemia preconditioning (IPC) displays an important adaptation of the CNS to sub-lethal ischemia. In the present study, we examined the effect of IPC on immunoreactivities of VEGF-, and phospho-Flk-1 (pFlk-1) following transient cerebral ischemia in gerbils. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+) sham-operated-group, and IPC+ischemia-operated-group). IPC was induced by subjecting gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated-group, a significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) alone 5 days after ischemia-reperfusion, however, in all the IPC+ischemia-operated-groups, pyramidal neurons in the SP were well protected. In immunohistochemical study, VEGF immunoreactivity in the ischemia-operated-group was increased in the SP at 1 day post-ischemia and decreased with time. Five days after ischemia-reperfusion, strong VEGF immunoreactivity was found in non-pyramidal cells, which were identified as pericytes, in the stratum oriens (SO) and radiatum (SR). In the IPC+sham-operated- and IPC+ischemia-operated-groups, VEGF immunoreactivity was significantly increased in the SP. pFlk-1 immunoreactivity in the sham-operated- and ischemia-operated-groups was hardly found in the SP, and, from 2 days post-ischemia, pFlk-1 immunoreactivity was strongly increased in non-pyramidal cells, which were identified as pericytes. In the IPC+sham-operated-group, pFlk-1 immunoreactivity was significantly increased in both pyramidal and non-pyramidal cells; in the IPC+ischemia-operated-groups, the similar pattern of VEGF immunoreactivity was found in the ischemic CA1, although the VEGF immunoreactivity was strong in non-pyramidal cells at 5 days post-ischemia. In brief, our findings show that IPC dramatically augmented the induction of VEGF and pFlk-1 immunoreactivity in the pyramidal cells of the CA1 after ischemia-reperfusion, and these findings suggest that the increases of VEGF and Flk-1 expressions may be necessary for neurons to survive from transient ischemic damage.

Ischemia-reperfusion injury in stroke

Despite ongoing advances in stroke imaging and treatment, ischemic and hemorrhagic stroke continue to debilitate patients with devastating outcomes at both the personal and societal levels. While the ultimate goal of therapy in ischemic stroke is geared towards restoration of blood flow, even when mitigation of initial tissue hypoxia is successful, exacerbation of tissue injury may occur in the form of cell death, or alternatively, hemorrhagic transformation of reperfused tissue. Animal models have extensively demonstrated the concept of reperfusion injury at the molecular and cellular levels, yet no study has quantified this effect in stroke patients. These preclinical models have also demonstrated the success of a wide array of neuroprotective strategies at lessening the deleterious effects of reperfusion injury. Serial multimodal imaging may provide a framework for developing therapies for reperfusion injury.

Should the STAIR criteria be modified for preconditioning studies?

Diverse preconditioning (PC) stimuli protect against a wide variety of neuronal insults in animal models, engendering enthusiasm that PC could be used to protect the brain clinically. Candidate clinical applications include cardiac and vascular surgery, after subarachnoid hemorrhage, and prior to conditions in which acute neuronal injury is anticipated. However, disappointments in clinical validation of multiple neuroprotectants suggest potential problems translating animal data into successful human therapies. Thus, despite strong promise of preclinical PC studies, caution should be maintained in translating these findings into clinical applications. The Stroke Therapy Academic Industry Roundtable (STAIR) working group and the National institute of Neurological Diseases and Stroke (NINDS) proposed working guidelines to improve the utility of preclinical studies that form the foundation of therapies for neurological disease. Here, we review the applicability of these consensus criteria to preconditioning studies and discuss additional considerations for PC studies. We propose that special attention should be paid to several areas, including 1) safety and dosage of PC treatments; 2) meticulously matching preclinical modeling to the human condition to be tested; and 3) timing of both the initiation and discontinuation of the PC stimulus relative to injury ictus.

Competitive HIF Prolyl Hydroxylase Inhibitors Show Protection against Oxidative Stress by a Mechanism Partially Dependent on Glycolysis

The hypoxia inducible factor 1 (HIF-1) is a central transcription factor involved in the cellular and molecular adaptation to hypoxia and low glucose supply. The level of HIF-1 is to a large degree regulated by the HIF prolyl hydroxylase enzymes (HPHs) belonging to the Fe(II) and 2-oxoglutarate-dependent dioxygenase superfamily. In the present study, we compared competitive and noncompetitive HPH-inhibitor compounds in two different cell types (SH-SY5Y and PC12). Although the competitive HPH-inhibitor compounds were found to be pharmacologically more potent than the non-competitive compounds at inhibiting HPH2 and HPH1, this was not translated into the cellular effects of the compounds, where the non-competitive inhibitors were actually more potent than the competitive in stabilizing and translocatingHIF1αto the nucleus (quantified with Cellomics ArrayScan technology). This could be explained by the high cellular concentrations of the cofactor 2-oxoglutarate (2-OG) as the competitive inhibitors act by binding to the 2-OG site of the HPH enzymes. Both competitive and non-competitive HPH inhibitors protected the cells against 6-OHDA induced oxidative stress. In addition, the protective effect of a specific HPH inhibitor was partially preserved when the cells were serum starved and exposed to 2-deoxyglucose, an inhibitor of glycolysis, indicating that other processes than restoring energy supply could be important for the HIF-mediated cytoprotection.

Long-lasting changes in DNA methylation following short-term hypoxic exposure in primary hippocampal neuronal cultures

While the effects of hypoxia on gene expression have been investigated in the CNS to some extent, we currently do not know what role epigenetics plays in the transcription of many genes during such hypoxic stress. To start understanding the role of epigenetic changes during hypoxia, we investigated the long-term effect of hypoxia on gene expression and DNA methylation in hippocampal neuronal cells. Primary murine hippocampal neuronal cells were cultured for 7 days. Hypoxic stress of 1% O2, 5% CO2 for 24 hours was applied on Day 3, conditions we found to maximize cellular hypoxic stress response without inducing cell death. Cells were returned to normoxia for 4 days following the period of hypoxic stress. On Day 7, Methyl-Sensitive Cut Counting (MSCC) was used to identify a genome-wide methylation profile of the hippocampal cell lines to assess methylation changes resulting from hypoxia. RNA-Seq was also done on Day 7 to analyze changes in gene transcription. Phenotypic analysis showed that neuronal processes were significantly shorter after 1 day of hypoxia, but there was a catch-up growth of these processes after return to normoxia. Transcriptome profiling using RNA-Seq revealed 369 differentially expressed genes with 225 being upregulated, many of which form networks shown to affect CNS development and function. Importantly, the expression level of 59 genes could be correlated to the changes in DNA methylation in their promoter regions. CpG islands, in particular, had a strong tendency to remain hypomethylated long after hypoxic stress was removed. From this study, we conclude that short-term, sub-lethal hypoxia results in long-lasting changes to genome wide DNA methylation status and that some of these changes can be highly correlated with transcriptional modulation in a number of genes involved in functional pathways that have been previously implicated in neural growth and development.

Redox signaling pathways involved in neuronal ischemic preconditioning

There is extensive evidence that the restoration of blood flow following cerebral ischemia contributes greatly to the pathophysiology of ischemia mediated brain injury. The initiating stimulus of reperfusion injury is believed to be the excessive production of reactive oxygen (ROS) and nitrogen (RNS) species by the mitochondria. ROS and RNS generation leads to mitochondrial protein, lipid and DNA oxidation which impedes normal mitochondrial physiology and initiates cellular death pathways. However not all ROS and RNS production is detrimental. It has been demonstrated that low levels of ROS production are protective and may serve as a trigger for activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sublethal ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Numerous proteins and signaling pathways have been implicated in the ischemic preconditioning neuroprotective response. In this review we examine the origin and mechanisms of ROS and RNS production following ischemic/reperfusion and the role of free radicals in modulating proteins associated with ischemic preconditioning neuroprotection.

Hypoxic-preconditioning enhances the regenerative capacity of neural stem/progenitors in subventricular zone of newborn piglet brain

Perinatal hypoxia-ischemia (HI) results in brain injury, whereas mild hypoxic episodes result in preconditioning, which can significantly reduce the vulnerability of the brain to subsequent severe hypoxia-ischemia. Hypoxic-preconditioning (PC) has been shown to enhance cell survival and differentiation of progenitor cells in the central nervous system (CNS). The purpose of this study was to determine whether pretreatment with PC prior to HI stimulates subventricular zone (SVZ) proliferation and neurogenesis in newborn piglets. One-day-old piglets were subjected to PC (8% O2/92% N2) for 3h and 24h later were exposed to HI produced by combination of hypoxia (5% FiO2) for a pre-defined period of 30min and ischemia induced by a period of 10min of hypotension. Here we demonstrate that SVZ derived neural stem/progenitor cells (NSPs) from PC, HI and PC+HI piglets proliferated as neurospheres, expressed neural progenitor and neurodevelopmental markers, and that greater proportion of the spheres generated are multipotential. Neurosphere assay revealed that preconditioning pretreatment increased the number of NSP-derived neurospheres in SVZ following HI compared to normoxic and HI controls. NSPs from preconditioned SVZ generated twice as many neurons and astrocytes in vitro. Injections with 5-Bromo-2-deoxyuridine (BrdU) after PC revealed a robust proliferative response within the SVZ that continued for one week. PC also increased neurogenesis in vivo, doublecortin positive cells with migratory profiles were observed streaming from the SVZ to striatum and neocortex. These findings show that the induction of proliferation and neurogenesis by PC might be a positive adaptation for an efficient repair and plasticity in the event of a hypoxic-ischemic insult.

Genetic animal models of preconditioning

The preconditioning phenomena have been well established in heart as well as brain. In this review, we detail some of the original studies on preconditioning as well as studies from our lab using rodents and a genetic model system (fruit fly). We have used Drosophila in our lab to solve some of the questions related to tolerance or susceptibility to hypoxia. We believe that these pro-survival strategies and genetic pathways help us understand some of the preconditioning mechanisms that protect the brain from ischemia or ischemia.

Neuronal responses to physiological stress

Physiological stress can be defined as any external or internal condition that challenges the homeostasis of a cell or an organism. It can be divided into three different aspects: environmental stress, intrinsic developmental stress, and aging. Throughout life all living organisms are challenged by changes in the environment. Fluctuations in oxygen levels, temperature, and redox state for example, trigger molecular events that enable an organism to adapt, survive, and reproduce. In addition to external stressors, organisms experience stress associated with morphogenesis and changes in inner chemistry during normal development. For example, conditions such as intrinsic hypoxia and oxidative stress, due to an increase in tissue mass, have to be confronted by developing embryos in order to complete their development. Finally, organisms face the challenge of stochastic accumulation of molecular damage during aging that results in decline and eventual death. Studies have shown that the nervous system plays a pivotal role in responding to stress. Neurons not only receive and process information from the environment but also actively respond to various stresses to promote survival. These responses include changes in the expression of molecules such as transcription factors and microRNAs that regulate stress resistance and adaptation. Moreover, both intrinsic and extrinsic stresses have a tremendous impact on neuronal development and maintenance with implications in many diseases. Here, we review the responses of neurons to various physiological stressors at the molecular and cellular level.

Training the brain to survive stroke

Background

Presently, little can be done to repair brain tissue after stroke damage. We hypothesized that the mammalian brain has an intrinsic capacity to adapt to low oxygen which would improve outcome from a reversible hypoxic/ischemic episode. Acclimation to chronic hypoxia causes increased capillarity and tissue oxygen levels which may improve the capacity to survive ischemia. Identification of these adaptations will lead to protocols which high risk groups could use to improve recovery and reduce costs.

Methods and Findings

Rats were exposed to hypoxia (3 weeks living at ½ an atmosphere). After acclimation, capillary density was measured morphometrically and was increased by 30% in the cortex. Novel implantable oxygen sensors showed that partial pressure of oxygen in the brain was increased by 40% in the normal cortex. Infarcts were induced in brain with 1 h reversible middle cerebral artery occlusions. After ischemia (48 h) behavioural scores were improved and T2 weighted MRI lesion volumes were reduced by 52% in acclimated groups. There was a reduction in inflammation indicated by reduced lymphocytes (by 27–33%), and ED1 positive cells (by 35–45%).

Conclusions

It is possible to stimulate a natural adaptive mechanism in the brain which will reduce damage and improve outcome for a given ischemic event. Since these adaptations occur after factors such as HIF-1α have returned to baseline, protection is likely related more to morphological changes such as angiogenesis. Such pre-conditioning, perhaps with exercise or pharmaceuticals, would not necessarily reduce the incidence of stroke, but the severity of damage could be reduced by 50%.

Preconditioning triggered by carbon monoxide (CO) provides neuronal protection following perinatal hypoxia-ischemia

Perinatal hypoxia-ischemia is a major cause of acute mortality in newborns and cognitive and motor impairments in children. Cerebral hypoxia-ischemia leads to excitotoxicity and necrotic and apoptotic cell death, in which mitochondria play a major role. Increased resistance against major damage can be achieved by preconditioning triggered by subtle insults. CO, a toxic molecule that is also generated endogenously, may have a role in preconditioning as low doses can protect against inflammation and apoptosis. In this study, the role of CO-induced preconditioning on neurons was addressed in vitro and in vivo. The effect of 1 h of CO treatment on neuronal death (plasmatic membrane permeabilization and chromatin condensation) and bcl-2 expression was studied in cerebellar granule cells undergoing to glutamate-induced apoptosis. CO's role was studied in vivo in the Rice-Vannucci model of neonatal hypoxia-ischemia (common carotid artery ligature +75 min at 8% oxygen). Apoptotic cells, assessed by Nissl staining were counted with a stereological approach and cleaved caspase 3-positive profiles in the hippocampus were assessed. Apoptotic hallmarks were analyzed in hippocampal extracts by Western Blot. CO inhibited excitotoxicity-induced cell death and increased Bcl-2 mRNA in primary cultures of neurons. In vivo, CO prevented hypoxia-ischemia induced apoptosis in the hippocampus, limited cytochrome c released from mitochondria and reduced activation of caspase-3. Still, Bcl-2 protein levels were higher in hippocampus of CO pre-treated rat pups. Our results show that CO preconditioning elicits a molecular cascade that limits neuronal apoptosis. This could represent an innovative therapeutic strategy for high-risk cerebral hypoxia-ischemia patients, in particular neonates.

Hypoxic preconditioning in an autohypoxic animal model

Hypoxic preconditioning refers to the exposure of organisms, systems, organs, tissues or cells to moderate hypoxia/ischemia that results in increased resistance to a subsequent episode of severe hypoxia/ischemia. In this article, we review recent research based on a mouse model of repeated exposure to autohypoxia. Pre-exposure markedly increases the tolerance to or protection against hypoxic insult, and preserves the cellular structure of the brain. Furthermore, the hippocampal activity amplitude and frequency of electroencephalogram, latency of cortical somatosensory-evoked potential and spinal somatosensory-evoked potential progressively decrease, while spatial learning and memory improve. In the brain, detrimental neurochemicals such as free radicals are down-regulated, while beneficial ones such as adenosine are up-regulated. Also, antihypoxia factor(s) and gene(s) are activated. We propose that the tolerance and protective effects depend on energy conservation and plasticity triggered by exposure to hypoxia via oxygen-sensing transduction pathways and hypoxia-inducible factor-initiated cascades. A potential path for further research is the development of devices and pharmaceuticals acting on antihypoxia factor(s) and gene(s) for the prevention and treatment of hypoxia and related syndromes.