The Effect of Propofol on the Hippocampus in Chronic Cerebral Hypoxia in a Rat Model Through Klotho Regulation.

BACKGROUND/AIM: Chronic cerebral hypoxia often leads to brain damage and inflammation. Propofol is suggested to have neuroprotective effects under anaesthesia. MATERIALS AND METHODS: This study used rat models with carotid artery coarctation or closure. Four groups of rats were compared: a control group, a propofol-treated group, a group with bilateral common carotid artery blockage (BCAO), and a BCAO group treated with propofol post-surgery. RESULTS: The Morris water maze test indicated cognitive impairment in BCAO rats, which also showed hippocampal structure changes, oxidative stress markers alteration, and reduced Klotho expression. Propofol treatment post-BCAO surgery improved these outcomes, suggesting its potential in mitigating chronic cerebral hypoxia effects. CONCLUSION: Propofol may increase klotho levels and reduce apoptosis and inflammation linked to oxidative stress in cognitively impaired mice.

Fatty acid-binding protein 5 is a functional biomarker and indicator of ferroptosis in cerebral hypoxia.

The progression of human degenerative and hypoxic/ischemic diseases is accompanied by widespread cell death. One death process linking iron-catalyzed reactive species with lipid peroxidation is ferroptosis, which shows hallmarks of both programmed and necrotic death in vitro. While evidence of ferroptosis in neurodegenerative disease is indicated by iron accumulation and involvement of lipids, a stable marker for ferroptosis has not been identified. Its prevalence is thus undetermined in human pathophysiology, impeding recognition of disease areas and clinical investigations with candidate drugs. Here, we identified ferroptosis marker antigens by analyzing surface protein dynamics and discovered a single protein, Fatty Acid-Binding Protein 5 (FABP5), which was stabilized at the cell surface and specifically elevated in ferroptotic cell death. Ectopic expression and lipidomics assays demonstrated that FABP5 drives redistribution of redox-sensitive lipids and ferroptosis sensitivity in a positive-feedback loop, indicating a role as a functional biomarker. Notably, immunodetection of FABP5 in mouse stroke penumbra and in hypoxic postmortem patients was distinctly associated with hypoxically damaged neurons. Retrospective cell death characterized here by the novel ferroptosis biomarker FABP5 thus provides first evidence for a long-hypothesized intrinsic ferroptosis in hypoxia and inaugurates a means for pathological detection of ferroptosis in tissue.

Neuroimaging mimics of anoxic brain injury: A review.

Diffuse cortical diffusion changes on magnetic resonance imaging (MRI) are characteristically ascribed to global cerebral anoxia, typically after cardiac arrest. Far from being pathognomonic, however, this neuroimaging finding is relatively nonspecific, and can manifest in a myriad of disease states including hypoxia, metabolic derangements, infections, seizure, toxic exposures, and neuroinflammation. While these various conditions can all produce a neuroimaging pattern of widespread cortical diffusion restriction, many of these underlying causes do have subtly unique imaging features that are appreciable on MRI and can be of clinical and diagnostic utility. Specific populations of neurons are variably sensitive to certain types of injury, whether due to differences in perfusion, receptor type density, or the unique tropisms of infectious organisms. In this narrative review, we discuss a number of distinct etiologies of diffuse cortical diffusion restriction on MRI, the unique pathophysiologies responsible for tissue injury, and the resulting neuroimaging characteristics that can be of assistance in differentiating them. As widespread cortical injury from any cause often presents with altered mental status or coma, the differential diagnosis can be enhanced with rapid acquisition of MRI when clinical history or detailed physical examination is limited. In such settings, the distinct imaging features discussed in this article are of interest to both the clinician and the radiologist.

Hypothermic preconditioning attenuates hypobaric hypoxia induced spatial memory impairment in rats.

Hypobaric Hypoxia (HH) is known to cause oxidative stress in the brain that leads to spatial memory deficit and neurodegeneration. For decades therapeutic hypothermia is used to treat global and focal ischemia in preserving brain functions that proved to be beneficial in humans and rodents. Considering these previous reports, the present study was designed to establish the therapeutic potential of hypothermia preconditioning on HH induced spatial memory, biochemical and morphological changes in adult rats. Male Sprague Dawley rats were exposed to HH (7620 m, ~ 282 mmHg) for 1, 3 and 7 days with and without hypothermic preconditioning. Spatial learning memory was assessed by Morris water maze (MWM) test along with evaluation of hippocampal pyramidal neuron damage by histological study. Oxidative stress was measured by studying the levels of nitric oxide (NO), reactive oxygen species (ROS), lipid peroxidation (LPO), oxidized and reduced glutathione (GSSG and GSH). Results of MWM test indicated prolonged path length and latency to reach the platform in HH groups that regained to normal in cold pre-treated groups. A likely neurodegeneration was evident in HH groups that lessen in the cold pre-treated groups. Hypothermic preconditioning prevented spatial memory impairment and neurodegeneration in animals subjected to HH via decreasing the NO, ROS and LPO compared to control animals. The GSH level and GSH/GSSG ratio was found to be higher in preconditioned animals as compared to respective HH exposed animals, indicative of redox scavenging and restoration of hippocampal neuronal structure as well as spatial memory. Therefore, hypothermic preconditioning improves spatial memory deficit by reducing HH induced oxidative stress and hippocampal neurodegeneration, hence can be used as a multi-target prophylactic measure to combat HH induced neurodegeneration.

Human amniotic fluid derived-exosomes alleviate hypoxic encephalopathy by enhancing angiogenesis in neonatal mice after hypoxia.

Neonatal hypoxic encephalopathy is a type of central nervous system dysfunction manifested by high mortality and morbidity. Exosomes play a crucial role in neuroprotection by enhancing angiogenesis. The objective of this study was to investigate the effect of human amniotic fluid-derived exosomes (hAFEXOs) on functional recovery in neonatal hypoxic encephalopathy. The transwell assay, scratch wound healing assay, and tube formation assay were used to evaluate the effect of hAFEXOs on the angiogenesis of human umbilical vein endothelial cells (HUVECs) after oxygen and glucose deprivation (OGD). The angiogenesis of microvascular endothelial cells (MECs) in the cortex was tested in neonatal mice treated with hAFEXOs or phosphate-buffered saline (PBS) after hypoxia. Expressions of hypoxia-inducible factor 1 α (HIF-1α) and vascular endothelial growth factor (VEGF) in the cerebral cortex were also tested by western blot. The Morris Water Maze Test (MWM) was carried out to detect the performance of spatial memory after processing with hAFEXOs or PBS. The results indicated that hAFEXOs favored tubing formation and migration of HUVECs after in vitro OGD. The hAFEXOs also favored the expression of CD31 in neonatal mice following hypoxia. The expressions of both HIF-1α and VEGF were significantly augmented in the cerebral cortex of neonatal mice which were treated with hAFEXOs. Moreover, the MWM test results showed that the performance of the spatial memory was better in the hAFEXO-treated group than in the PBS-treated group. Our study indicates that hAFEXOs alleviated hypoxic encephalopathy and enhanced angiogenesis in neonatal mice after hypoxia. In addition, hAFEXOs  promoted migration and tube formation of HUVECs after OGD in vitro. These findings confirm that hAFEXOs show great potential for further studies aimed at developing therapeutic agents for hypoxic encephalopathy.

Sevoflurane preconditioning protects experimental ischemic stroke by enhancing anti-inflammatory microglia/macrophages phenotype polarization through GSK-3ß/Nrf2 pathway.

AIMS: Sevoflurane preconditioning (SPC) results in cerebral ischemic tolerance; however, the mechanism remains unclear. Promoting microglia/macrophages polarization from pro-inflammatory state to anti-inflammatory phenotype has been indicated as a potential treatment target against ischemic stroke. In this study, we aimed to assess the effect of SPC on microglia polarization after stroke and which signaling pathway was involved in this transition. METHODS: Mouse primary microglia with SPC were challenged by oxygen-glucose deprivation (OGD) or lipopolysaccharide (LPS), and mice with SPC were subjected to middle cerebral artery occlusion (MCAO). Then, the mRNA and protein levels of pro-inflammatory/anti-inflammatory factors were analyzed. GSK-3ß phosphorylation and Nrf2 nuclear translocation were measured. The mRNA and protein expression of pro-inflammatory/anti-inflammatory factors, neurological scores, infarct volume, cellular apoptosis, the proportion of pro-inflammatory/anti-inflammatory microglia/macrophages, and the generation of super-oxidants were examined after SPC or GSK-3ß inhibitor TDZD treatment with or without Nrf2 deficiency. RESULTS: Sevoflurane preconditioning promoted anti-inflammatory and inhibited pro-inflammatory microglia/macrophages phenotype both in vitro and in vivo. GSK-3ß phosphorylation at Ser9 was increased after SPC. Both SPC and TDZD administration enhanced Nrf2 nuclear translocation, reduced pro-inflammatory microglia/macrophages markers expression, promoted anti-inflammatory markers level, and elicited a neuroprotective effect. Nrf2 deficiency abolished the promoted anti-inflammatory microglia/macrophages polarization and ischemic tolerance induced by TDZD treatment. The reduced percentage of pro-inflammatory positive cells and super-oxidants generation induced by SFC or TDZD was also reversed by Nrf2 knockdown. CONCLUSIONS: Our results indicated that SPC exerts brain ischemic tolerance and promotes anti-inflammatory microglia/macrophages polarization by GSK-3ß-dependent Nrf2 activation, which provides a novel mechanism for SPC-induced neuroprotection.

Nitric Oxide-Dependent Pathways as Critical Factors in the Consequences and Recovery after Brain Ischemic Hypoxia.

Brain ischemia is one of the leading causes of disability and mortality worldwide. Nitric oxide (NO•), a molecule that is involved in the regulation of proper blood flow, vasodilation, neuronal and glial activity constitutes the crucial factor that contributes to the development of pathological changes after stroke. One of the early consequences of a sudden interruption in the cerebral blood flow is the massive production of reactive oxygen and nitrogen species (ROS/RNS) in neurons due to NO• synthase uncoupling, which leads to neurotoxicity. Progression of apoptotic or necrotic neuronal damage activates reactive astrocytes and attracts microglia or lymphocytes to migrate to place of inflammation. Those inflammatory cells start to produce large amounts of inflammatory proteins, including pathological, inducible form of NOS (iNOS), which generates nitrosative stress that further contributes to brain tissue damage, forming vicious circle of detrimental processes in the late stage of ischemia. S-nitrosylation, hypoxia-inducible factor 1α (HIF-1α) and HIF-1α-dependent genes activated in reactive astrocytes play essential roles in this process. The review summarizes the roles of NO•-dependent pathways in the early and late aftermath of stroke and treatments based on the stimulation or inhibition of particular NO• synthases and the stabilization of HIF-1α activity.

Brain tissue oxygenation guided therapy and outcome in non-traumatic subarachnoid hemorrhage.

Brain hypoxia can occur after non-traumatic subarachnoid hemorrhage (SAH), even when levels of intracranial pressure (ICP) remain normal. Brain tissue oxygenation (PbtO2) can be measured as a part of a neurological multimodal neuromonitoring. Low PbtO2 has been associated with poor neurologic recovery. There is scarce data on the impact of PbtO2 guided-therapy on patients' outcome. This single-center cohort study (June 2014-March 2020) included all patients admitted to the ICU after SAH who required multimodal monitoring. Patients with imminent brain death were excluded. Our primary goal was to assess the impact of PbtO2-guided therapy on neurological outcome. Secondary outcome included the association of brain hypoxia with outcome. Of the 163 patients that underwent ICP monitoring, 62 were monitored with PbtO2 and 54 (87%) had at least one episode of brain hypoxia. In patients that required treatment based on neuromonitoring strategies, PbtO2-guided therapy (OR 0.33 [CI 95% 0.12-0.89]) compared to ICP-guided therapy had a protective effect on neurological outcome at 6 months. In this cohort of SAH patients, PbtO2-guided therapy might be associated with improved long-term neurological outcome, only when compared to ICP-guided therapy.

Effects of omega 3 polyunsaturated fatty acids, antioxidants, and/or non-steroidal inflammatory drugs in the brain of neonatal rats exposed to intermittent hypoxia.

Preterm infants experience frequent arterial oxygen desaturations during oxygen therapy, or intermittent hypoxia (IH). Neonatal IH increases oxidative distress which contributes to neuroinflammation and brain injury. We tested the hypotheses that exposure to neonatal IH is detrimental to the immature brain and that early supplementation with antioxidants and/or omega 3 polyunsaturated fatty acids (n-3 PUFAs) combined with non-steroidal anti-inflammatory drugs (NSAIDs) is protective. Newborn rats were exposed to brief hypoxia (12% O2 ) during hyperoxia (50% O2 ) from the first day of life (P0) until P14 during which they received daily oral supplementation with antioxidants, namely coenzyme Q10 (CoQ10) or glutathione nanoparticles (nGSH), n-3 PUFAs and/or topical ocular ketorolac. Placebo controls received daily oral olive oil and topical ocular saline. Room air (RA) littermates remained in 21% O2 from birth to P21 with all treatments identical. At P14 animals were allowed to recover in RA until P21 with no further treatment. Whole brains were harvested for histopathology and morphometric analyses, and assessed for biomarkers of oxidative stress and inflammation, as well as myelin injury. Neonatal IH resulted in higher brain/body weight ratios, an effect that was reversed with n-3 PUFAs and n-3 PUFAs+CoQ10 with or without ketorolac. Neonatal IH was also associated with hemorrhage, oxidative stress, and elevations in inflammatory prostanoids. Supplementation with n-3 PUFAs and nGSH with and without ketorolac were most beneficial for myelin growth and integrity when administered in RA. However, the benefit of n-3 PUFAs was significantly curtailed in neonatal IH. Neonatal IH during a critical time of brain development causes inflammation and oxidative injury. Loss of therapeutic benefits of n-3 PUFAs suggest its susceptibility to oxidation in neonatal IH and therefore indicate that co-administration with antioxidants may be necessary to sustain its efficacy.

Recovery of Hypoxic Regions in a Rat Model of Microembolism.

OBJECTIVES: Endovascular treatment (EVT) has become the standard of care for acute ischemic stroke. Despite successful recanalization, a limited subset of patients benefits from the new treatment. Human MRI studies have shown that during removal of the thrombus, a shower of microclots is released from the initial thrombus, possibly causing new ischemic lesions. The aim of the current study is to quantify tissue damage following microembolism. MATERIALS AND METHODS: In a rat model, microembolism was generated by injection of a mixture of polystyrene fluorescent microspheres (15, 25 and 50 µm in diameter). The animals were killed at three time-points: day 1, 3 or 7. AMIRA and IMARIS software was used for 3D reconstruction of brain structure and damage, respectively. CONCLUSIONS: Microembolism induces ischemia, hypoxia and infarction. Infarcted areas persist, but hypoxic regions recover over time suggesting that repair processes in the brain rescue the regions at risk.

Recombinant Human Growth Hormone Activates Neuroprotective Growth Factors in Hypoxic Brain Injury in Neonatal Mice.

Perinatal hypoxia severely disrupts cerebral metabolic and maturational programs beyond apoptotic cell death. Antiapoptotic treatments such as erythropoietin are suggested to improve outcomes in hypoxic brain injury; however, the results are controversial. We analyzed the neuroprotective effects of recombinant human growth hormone (rhGH) on regenerative mechanisms in the hypoxic developing mouse brain in comparison to controls. Using an established model of neonatal acute hypoxia (8% O2, 6 hours), P7 mice were treated intraperitoneally with rhGH (4000 µg/kg) 0, 12, and 24 hours after hypoxic exposure. After a regeneration period of 48 hours, expression of hypoxia-inducible neurotrophic factors (erythropoietin [EPO], vascular endothelial growth factor A [VEGF-A], insulin-like growth factors 1 and 2 [IGF-1/-2], IGF binding proteins) and proinflammatory markers was analyzed. In vitro experiments were performed using primary mouse cortical neurons (E14, DIV6). rhGH increased neuronal gene expression of EPO, IGF-1, and VEGF (P < .05) in vitro and diminished apoptosis of hypoxic neurons in a dose-dependent manner. In the developing brain, rhGH treatment led to a notable reduction of apoptosis in the subventricular zone and hippocampus (P < .05), abolished hypoxia-induced downregulation of IGF-1/IGF-2 expression (P < .05), and led to a significant accumulation of endogenous EPO protein and anti-inflammatory effects through modulation of interleukin-1ß and tumor necrosis factor α signaling as well as upregulation of cerebral phosphorylated extracellularly regulated kinase 1/2 levels (ERK1/2). Indicating stabilizing effects on the blood-brain barrier (BBB), rhGH significantly modified cerebrovascular occludin expression. Thus, we conclude that rhGH mediates neuroprotective effects by the activation of endogenous neurotrophic growth factors and BBB stabilization. In addition, the modification of ERK1/2 pathways is involved in neuroprotective actions of rhGH. The present study adds further evidence that pharmacologic activation of neurotrophic growth factors may be a promising target for neonatal neuroprotection.

Modeling of Hypoxic Brain Injury through 3D Human Neural Organoids.

Brain organoids have emerged as a novel model system for neural development, neurodegenerative diseases, and human-based drug screening. However, the heterogeneous nature and immature neuronal development of brain organoids generated from pluripotent stem cells pose challenges. Moreover, there are no previous reports of a three-dimensional (3D) hypoxic brain injury model generated from neural stem cells. Here, we generated self-organized 3D human neural organoids from adult dermal fibroblast-derived neural stem cells. Radial glial cells in these human neural organoids exhibited characteristics of the human cerebral cortex trend, including an inner (ventricular zone) and an outer layer (early and late cortical plate zones). These data suggest that neural organoids reflect the distinctive radial organization of the human cerebral cortex and allow for the study of neuronal proliferation and maturation. To utilize this 3D model, we subjected our neural organoids to hypoxic injury. We investigated neuronal damage and regeneration after hypoxic injury and reoxygenation. Interestingly, after hypoxic injury, reoxygenation restored neuronal cell proliferation but not neuronal maturation. This study suggests that human neural organoids generated from neural stem cells provide new opportunities for the development of drug screening platforms and personalized modeling of neurodegenerative diseases, including hypoxic brain injury.

Occlusion of activity dependent synaptic plasticity by late hypoxic long term potentiation after neonatal intermittent hypoxia.

To elucidate the mechanisms of memory impairment after chronic neonatal intermittent hypoxia (IH), we employed a mice model of severe IH administered at postnatal days 3 to 7. Since prior studies in this model did not demonstrate increased cell death, our primary hypothesis was that IH causes a functional disruption of synaptic plasticity in hippocampal neurons. In vivo recordings of Schaffer collateral stimulation-induced synaptic responses during and after IH in the CA1 region of the hippocampus revealed pathological late phase hypoxic long term potentiation (hLTP) (154%) that lasted more than four hours and could be reversed by depotentiation with low frequency stimulation (LFS), or abolished by NMDA and PKA inhibitors (MK-801 and CMIQ). Furthermore, late phase hLTP partially occluded normal physiological LTP (pLTP) four hours after IH. Early and late hLTP phases were induced by neuronal depolarization and Ca2+ influx, determined with manganese enhanced fMRI, and had increased both AMPA and NMDA - mediated currents. This was consistent with mechanisms of pLTP in neonates and also consistent with mechanisms of ischemic LTP described in vitro with OGD in adults. A decrease of pLTP was also recorded on hippocampal slices obtained 2 days after IH. This decrease was ameliorated by MK-801 injections prior to each IH session and restored by LFS depotentiation. Occlusion of pLTP and the observed decreased proportion of NMDA-only silent synapses after neonatal hLTP may explain long term memory, behavioral deficits and abnormal synaptogenesis and pruning following neonatal IH.

Metformin ameliorates brain damage caused by cardiopulmonary resuscitation via targeting endoplasmic reticulum stress-related proteins GRP78 and XBP1.

Cerebral damage after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) is a primary cause of death. Endoplasmic reticulum stress (ERS) is very important during these situations. This study aimed to explore the role of metformin in protecting brain endoplasmic reticulum post CA/CPR. Male SD rats (n = 132) were treated with 6-min CA-posted asphyxia and sham surgery. Before CA/CPR, metformin (200 mg/kg/day) or a vehicle (0.9% saline) were administered randomly for two weeks. The neurological deficit scores were assessed 24 h, 48 h, 72 h, and 7 days after CA/CPR, and the rat brains were analyzed by Western blotting and qRT-PCR. Apoptosis was detected by the TUNEL assay according to the mitochondrial membrane potential (MMP). Oxidative stress and ERS-related protein expression were also investigated. The Western blotting and qRT-PCR results revealed that the resuscitated animals had time-dependent elevated GRP78 and XBP1 levels compared with the sham operative rats. Moreover, our results showed that the rats treated with metformin had increased neurological deficit scores (NDS), an improved seven-day survival rate, decreased cell apoptosis within the hippocampus CA1 area, and less oxidative stress compared with the CA/CPR group. Furthermore, metformin inhibited the mRNA and protein expressions of glucose-regulated protein 78 (GRP78) and X-box binding protein 1 (XBP1) in the CA/CPR rat model. We confirmed that CA/CPR can induce ERS-related apoptosis and oxidative stress in the brain; moreover, inhibiting ERS-related proteins GRP78 and XBP1 with metformin might attenuate cerebral injury post CA/CPR.

Intermittent Hypoxia and Its Impact on Nrf2/HIF-1α Expression and ABC Transporters: An in Vitro Human Blood-Brain Barrier Model Study.

BACKGROUND/AIMS: Obstructive sleep apnea (OSA) is characterized by repeated episodes of complete or partial obstruction of the upper airways, leading to chronic intermittent hypoxia (IH). OSA patients are considered at high cerebrovascular risk and may also present cognitive impairment. One hypothesis explored is that disturbances may be linked to blood-brain barrier (BBB) dysfunction. The BBB is a protective barrier separating the brain from blood flow. The BBB limits the paracellular pathway through tight and adherens junctions, and the transcellular passage by efflux pumps (ABC transporters). The aims of this study were to evaluate the impact of IH and sustained hypoxia (SH) on a validated in vitro BBB model and to investigate the factors expressed under both conditions. METHODS: Exposure of endothelial cells (HBEC-5i) in our in vitro model of BBB to hypoxia was performed using IH cycles: 1% O2-35 min/18% O2-25 min for 6 cycles or 6 h of SH at 1% O2. After exposure, we studied the cytotoxicity and the level of ROS in our cells. We measured the apparent BBB permeability using sodium fluorescein, FITC-dextran and TEER measurement. Whole cell ELISA were performed to evaluate the expression of tight junctions, ABC transporters, HIF-1α and Nrf2. The functionality of ABC transporters was evaluated with accumulation studies. Immunofluorescence assays were also conducted to illustrate the whole cell ELISAs. RESULTS: Our study showed that 6 h of IH or SH induced a BBB disruption marked by a significant decrease in junction protein expressions (claudin-5, VE-cadherin, ZO-1) and an increase in permeability. We also observed an upregulation in P-gp protein expression and functionality and a downregulation in BCRP. Hypoxia induced production of ROS, Nrf2 and HIF-1α. They were expressed in both sustained and intermittent conditions, but the expression and the activity of P-gp and BCRP were different. CONCLUSION: Understanding these mechanisms seems essential in order to propose new therapeutic strategies for patients with OSA.

Molecular Basis of Sex Difference in Neuroprotection induced by Hypoxia Preconditioning in Zebrafish.

Hypoxia, the major cause of ischemic injury, leads to debilitating disease in infants via birth asphyxia and cerebral palsy, whereas in adults via heart attack and stroke. A widespread, natural protective phenomenon termed 'hypoxic preconditioning' (PH) occurs when prior exposures to hypoxia eventually result in robust hypoxia resistance. Accordingly, we have developed and optimized a novel model of hypoxic preconditioning in adult zebrafish to mimic the tolerance of mini stroke(s) in human, which appears to protect against the severe damage inflicted by a major stroke event. Here, we observed a remarkable difference in the progression pattern of neuroprotection between preconditioning hypoxia followed by acute hypoxia (PH) group, and acute hypoxia (AH) only group, with noticeable sex difference when compared with normoxia behaviour upon recovery. Since gender difference has been reported in stroke risk factors and disease history, it was pertinent to investigate whether any such sex difference also exists in PH's protective mechanism against acute ischemic stroke. In order to elucidate the neural molecular mechanisms behind sex difference in neuroprotection induced by PH, a high throughput proteomics approach utilizing iTRAQ was performed, followed by protein enrichment analysis using ingenuity pathway analysis (IPA) tool. Out of thousands of significantly altered proteins in zebrafish brain, the ones having critical role either in neuroglial proliferation/differentiation or neurotrophic functions were validated by analyzing their expression levels in preconditioned (PH), acute hypoxia (AH), and normoxia groups. The data indicate that female zebrafish brains are more protected against the severity of AH when exposed to the hypoxic preconditioning. The study also sheds light on the involvement of many signalling pathways underlying sex difference in preconditioning-induced neuroprotective mechanism, which can be further validated for the therapeutic approach.

Demonstrating a reduced capacity for removal of fluid from cerebral white matter and hypoxia in areas of white matter hyperintensity associated with age and dementia.

White matter hyperintensities (WMH) occur in association with dementia but the aetiology is unclear. Here we test the hypothesis that there is a combination of impaired elimination of interstitial fluid from the white matter together with a degree of hypoxia in WMH. One of the mechanisms for the elimination of amyloid-ß (Aß) from the brain is along the basement membranes in the walls of capillaries and arteries (Intramural Peri-Arterial Drainage - IPAD). We compared the dynamics of IPAD in the grey matter of the hippocampus and in the white matter of the corpus callosum in 10 week old C57/B16 mice by injecting soluble Aß as a tracer. The dynamics of IPAD in the white matter were significantly slower compared with the grey matter and this was associated with a lower density of capillaries in the white matter. Exposing cultures of smooth muscle cells to hypercapnia as a model of cerebral hypoperfusion resulted in a reduction in fibronectin and an increase in laminin in the extracellular matrix. Similar changes were detected in the white matter in human WMH suggesting that hypercapnia/hypoxia may play a role in WMH. Employing therapies to enhance both IPAD and blood flow in the white matter may reduce WMH in patients with dementia.

Exosomal shuttled miR-424-5p from ischemic preconditioned microglia mediates cerebral endothelial cell injury through negatively regulation of FGF2/STAT3 pathway.

Exosomes secreted by microglia have been found to play a role in neurovascular unit injury under the ischemic/hypoxic state. However, the modulatory effect of exosomes shuttled miRNAs produced by microglia in endothelial cells remains undefined. Here, an oxygen-glucose deprivation (OGD) model was constructed both in microglia and brain microvascular endothelial cells (BMEC). The exosomes secreted by microglia were isolated, and the exosomal miRNA profile was detected. Next, gain- and loss- functions of miR-424-5p, one of the most differentially expressed miRNAs in microglia derived exosomes, were conducted in BMEC. The results demonstrated that exosomes from OGD-activated microglia aggravated OGD induced BMEC viability and integrity damage as well as the loss of vascular formation. While the damaging effects were markedly attenuated by inhibiting miR-424-5p. In addition, miR-424-5p overexpression significantly aggravated OGD induced BMEC damage and permeability. Mechanistically, bioinformatics analysis indicated that miR-424-5p targeted the FGF2 mediated STAT3 signaling pathway, which was verified via dual luciferase activity assay and RIP experiment. Furthermore, in vivo experiments in the middle cerebral artery occlusion (MCAO) model mice were conducted. The results revealed that inhibition of miR-424-5p markedly reduced neurological dysfunctions and endothelial cell injury induced by MCAO. The above results confirmed that exosomes from OGD activated microglia induced significant cell damage and permeability of BMEC, in which the upregulated miR-424-5p in the exosomes functioned by regulating FGF2/STAT3 pathway.

Flavin Adenine Dinucleotide Fluorescence as an Early Marker of Mitochondrial Impairment During Brain Hypoxia.

Multimodal continuous bedside monitoring is increasingly recognized as a promising option for early treatment stratification in patients at risk for ischemia during neurocritical care. Modalities used at present are, for example, oxygen availability and subdural electrocorticography. The assessment of mitochondrial function could be an interesting complement to these modalities. For instance, flavin adenine dinucleotide (FAD) fluorescence permits direct insight into the mitochondrial redox state. Therefore, we explored the possibility of using FAD fluorometry to monitor consequences of hypoxia in brain tissue in vitro and in vivo. By combining experimental results with computational modeling, we identified the potential source responsible for the fluorescence signal and gained insight into the hypoxia-associated metabolic changes in neuronal energy metabolism. In vitro, hypoxia was characterized by a reductive shift of FAD, impairment of synaptic transmission and increasing interstitial potassium [K+]o. Computer simulations predicted FAD changes to originate from the citric acid cycle enzyme α-ketoglutarate dehydrogenase and pyruvate dehydrogenase. In vivo, the FAD signal during early hypoxia displayed a reductive shift followed by a short oxidation associated with terminal spreading depolarization. In silico, initial tissue hypoxia followed by a transient re-oxygenation phase due to glucose depletion might explain FAD dynamics in vivo. Our work suggests that FAD fluorescence could be readily used to monitor mitochondrial function during hypoxia and represents a potential diagnostic tool to differentiate underlying metabolic processes for complementation of multimodal brain monitoring.