Chronic intermittent hypoxic preconditioning suppresses pilocarpine-induced seizures and associated hippocampal neurodegeneration

Neurogenesis, A Potential Target for Intermittent Hypoxia Leading to Cognitive Decline

As a sleep breathing disorder, characterized by intermittent hypoxia (IH) and Obstructive sleep apnea (OSA), is believed to decrease the cognitive function of patients. Many factors are thought to be responsible for cognitive decline in OSA patients. Neurogenesis, a process by which neural stem cells (NSCs) differentiate into new neurons in the brain, is a major determinant affecting cognitive function. However, there is no clear relationship between IH or OSA and neurogenesis. In recent years, increasing numbers of studies on IH and neurogenesis are documented. Therefore, this review summarizes the effects of IH on neurogenesis; then discusses the influencing factors that may cause these effects and the potential signaling pathways that may exist. Finally, based on this impact, we discuss potential methods and future directions for improving cognition.

Chronic intermittent hypobaric hypoxia ameliorates osteoporosis after spinal cord injury through balancing osteoblast and osteoclast activities in rats

INTRODUCTION

As a common complication of spinal cord injury (SCI), most SCI patients suffer from osteoporosis. In our previous study, chronic intermittent hypobaric hypoxia (CIHH) could promote bone fracture healing. We speculated that it may act a role in the progression of osteoporosis. The current study purposed to explore the role of CIHH in the osteoporosis triggered by SCI in rats.

METHODS

A SCI-induced SCI model was established by completed transection at T9-T10 spinal cord of Wistar rats. One week after SCI, the rats were conducted to CIHH treatment (PB = 404 mmHg, Po2 = 84 mmHg) 6 hours a day for continuously 7 weeks.

RESULTS

The results of X-radiography and Micro-CT assessment demonstrated that compared with sham rats, the areal bone mineral density (BMD), bone volume to tissue volume, volumetric BMD, trabecular thickness, trabecular number, and trabecular connectivity were decreased. Trabecular bone pattern factor, trabecular separation, as well as structure model index were increased at the distal femur and proximal tibia of SCI rats, which were effectively reversed by CIHH treatment. Histomorphometry showed that CIHH treatment increased bone formation of SCI rats, as evidenced by the increased osteoid formation, the decreased number and surface of TRAP-positive osteoclasts. Furthermore, ELISA and real time PCR results showed that the osteoblastogenesis-related biomarkers, such as procollagen type 1 N-terminal propeptide, osteocalcin in serum, as well as ALP and OPG mRNAs in bone tissue were decreased, while the osteoclastogenesis-related biomarkers, including scleorostin in serum and RANKL and TRAP mRNAs in bone tissue were increased in SCI rats. Importantly, the deviations of aforementioned biomarkers were improved by CIHH treatment. Mechanically, the protective effects of CIHH might be at least partly mediated by hypoxia-inducible factor-1 alpha (HIF-1α) signaling pathway.

CONCLUSION

The present study testified that CIHH treatment ameliorates osteoporosis after SCI by balancing osteoblast and osteoclast activities in rats.

Incidence and predictors of epilepsy in children with congenital heart disease

OBJECTIVE

Children with CHD may be at increased risk for epilepsy. While the incidence of perioperative seizures after surgical repair of CHD has been well-described, the incidence of epilepsy is less well-defined. We aim to determine the incidence and predictors of epilepsy in patients with CHD.

METHODS

Retrospective cohort study of patients with CHD who underwent cardiopulmonary bypass at <2 years of age between January, 2012 and December, 2013 and had at least 2 years of follow-up. Clinical variables were extracted from a cardiac surgery database and hospital records. Seizures were defined as acute if they occurred within 7 days after an inciting event. Epilepsy was defined based on the International League Against Epilepsy criteria.

RESULTS

Two-hundred and twenty-one patients were identified, 157 of whom were included in our analysis. Five patients (3.2%) developed epilepsy. Acute seizures occurred in 12 (7.7%) patients, only one of whom developed epilepsy. Predictors of epilepsy included an earlier gestational age, a lower birth weight, a greater number of cardiac surgeries, a need for extracorporeal membrane oxygenation or a left ventricular assist device, arterial ischaemic stroke, and a longer hospital length of stay.

CONCLUSIONS

Epilepsy in children with CHD is rare. The mechanism of epileptogenesis in these patients may be the result of a complex interaction of patient-specific factors, some of which may be present even before surgery. Larger long-term follow-up studies are needed to identify risk factors associated with epilepsy in these patients.

Ketogenic Diet Alleviates Hippocampal Neurodegeneration Possibly via ASIC1a and the Mitochondria-Mediated Apoptotic Pathway in a Rat Model of Temporal Lobe Epilepsy

BACKGROUND

The ketogenic diet (KD) is a proven therapy for refractory epilepsy. Although the anti-seizure properties of this diet are understood to a certain extent, the exploration of its neuroprotective effects and underlying mechanisms is still in its infancy. Tissue acidosis is a common feature of epileptogenic foci. Interestingly, the activation of acid-sensing ion channel 1a (ASIC1a), which mediates Ca²⁺-dependent neuronal injury during acidosis, has been found to be inhibited by ketone bodies in vitro. This prompted us to investigate whether the neuroprotective effects induced by the KD occur via ASIC1a and interconnected downstream mechanisms in a rat model of temporal lobe epilepsy.

METHODS

Male Sprague-Dawley rats were fed either the KD or a normal diet for four weeks after undergoing pilocarpine-induced status epilepticus (SE). The effects of KD on epileptogenesis, cognitive impairment and hippocampal neuron injury in the epileptic rats were subsequently evaluated by video electroencephalogram, Morris water maze test and Nissl staining, respectively. The expression of ASIC1a and cleaved caspase-3 in the hippocampus were determined using Western blot analysis during the chronic period following SE. Moreover, the intracellular Ca²⁺ concentration, mitochondrial membrane potential (MMP), mitochondrial reactive oxygen species (mROS) and cell apoptosis of hippocampal cells were detected by flow cytometry.

RESULTS

We found that the KD treatment strongly attenuated the spontaneous recurrent seizures, ameliorated learning and memory impairments and prevented hippocampal neuronal injury and apoptosis. The KD was also shown to inhibit the upregulation of ASIC1a and the ensuing intracellular Ca²⁺ overload in the hippocampus of the epileptic rats. Furthermore, the seizure-induced structure disruption of neuronal mitochondria, loss of MMP and accumulation of mROS were reversed by the KD treatment, suggesting that it has protective effects on mitochondria. Finally, the activation of caspase-3 was also inhibited by the KD.

CONCLUSION

These findings indicate that the KD suppresses mitochondria-mediated apoptosis possibly by regulating ASIC1a to exert neuroprotective effects. This may provide a mechanistic explanation of the therapeutic effects of KD.

Chronic Intermittent Hypobaric Hypoxia Restores Hippocampus Function and Rescues Cognitive Impairments in Chronic Epileptic Rats via Wnt/β-catenin Signaling

Epilepsy is a complex neurological disorder with frequent psychiatric, cognitive, and social comorbidities in addition to recurrent seizures. Cognitive impairment, one of the most common comorbidities, has severe adverse effects on quality of life. Chronic intermittent hypobaric hypoxia (CIHH) has demonstrated neuroprotective efficacy in several neurological disease models. In the present study, we examined the effects of CIHH on cognition and hippocampal function in chronic epileptic rats. CIHH treatment rescued deficits in spatial and object memory, hippocampal neurogenesis, and synaptic plasticity in pilocarpine-treated epileptic rats. The Wnt/β-catenin pathway has been implicated in neural stem cell proliferation and synapse development, and Wnt/β-catenin pathway inhibition effectively blocked the neurogenic effects of CIHH. Our findings indicate that CIHH rescues cognitive deficits in epileptic rats via Wnt/β-catenin pathway activation. This study establishes CIHH and Wnt/β-catenin pathway regulators as potential treatments for epilepsy- induced cognitive impairments.

Elevating the level of hypoxia inducible factor may be a new potential target for the treatment of depression

Hypoxia inducible factor-1 (HIF-1) is a transcriptional factor that regulates gene expressions in response to decreased oxygen levels in the tissue, or hypoxia. HIF-1 exerts protective effects against hypoxia by mediating mitochondrial metabolism and consequently reducing oxidative stress. Recently, increased levels of oxidative stress and abnormal energy metabolism in the brain have been suggested to play essential roles in the pathogenesis of depression. Given that HIF-1 activates creatine metabolism and increases phosphocreatine levels in the intestinal epithelial cells, we assume that HIF-1 may induce similar processes in the brain. Elevated phosphocreatine levels in the brain, as measured by magnetic resonance spectroscopy, were associated with better treatment response to the antidepressants in individuals with depression. In addition, oral creatine supplements, which led to increased phosphocreatine levels in the brain, also enhanced the effects of antidepressants in individuals with depression. As such, we hypothesized that increasing the HIF-1, which potentially facilitates creatine metabolism in the brain, might be a new therapeutic target in depression. With this regard, we suggested that interventions to elevate the HIF-1 levels in the brain, including the intermittent hypoxia conditioning and hyperbaric oxygen therapy, might be considered as new additional treatments for depression.

Chronic mild hypoxia accelerates recovery from preexisting EAE by enhancing vascular integrity and apoptosis of infiltrated monocytes

While several studies have shown that hypoxic preconditioning suppresses development of the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS), no one has yet examined the important clinically relevant question of whether mild hypoxia can impact the progression of preexisting disease. Using a relapsing-remitting model of EAE, here we demonstrate that when applied to preexisting disease, chronic mild hypoxia (CMH, 10% O₂) markedly accelerates clinical recovery, leading to long-term stable reductions in clinical score. At the histological level, CMH led to significant reductions in vascular disruption, leukocyte accumulation, and demyelination. Spinal cord blood vessels of CMH-treated mice showed reduced expression of the endothelial activation molecule VCAM-1 but increased expression of the endothelial tight junction proteins ZO-1 and occludin, key mechanisms underlying vascular integrity. Interestingly, while equal numbers of inflammatory leukocytes were present in the spinal cord at peak disease (day 14 postimmunization; i.e., 3 d after CMH started), apoptotic removal of infiltrated leukocytes during the remission phase was markedly accelerated in CMH-treated mice, as determined by increased numbers of monocytes positive for TUNEL and cleaved caspase-3. The enhanced monocyte apoptosis in CMH-treated mice was paralleled by increased numbers of HIF-1α+ monocytes, suggesting that CMH enhances monocyte removal by amplifying the hypoxic stress manifest within monocytes in acute inflammatory lesions. These data demonstrate that mild hypoxia promotes recovery from preexisting inflammatory demyelinating disease and suggest that this protection is primarily the result of enhanced vascular integrity and accelerated apoptosis of infiltrated monocytes.

Intermittent Hypoxic Conditioning Alleviates Post-Traumatic Stress Disorder-Induced Damage and Dysfunction of Rat Visceral Organs and Brain

Posttraumatic stress disorder (PTSD) causes mental and somatic diseases. Intermittent hypoxic conditioning (IHC) has cardio-, vaso-, and neuroprotective effects and alleviates experimental PTSD. IHC’s ability to alleviate harmful PTSD effects on rat heart, liver, and brain was examined. PTSD was induced by 10-day exposure to cat urine scent (PTSD rats). Some rats were then adapted to 14-day IHC (PTSD+IHC rats), while PTSD and untreated control rats were cage rested. PTSD rats had a higher anxiety index (AI, X-maze test), than control or PTSD+IHC rats. This higher AI was associated with reduced glycogen content and histological signs of metabolic and hypoxic damage and of impaired contractility. The livers of PTSD rats had reduced glycogen content. Liver and blood alanine and aspartate aminotransferase activities of PTSD rats were significantly increased. PTSD rats had increased norepinephrine concentration and decreased monoamine oxidase A activity in cerebral cortex. The PTSD-induced elevation of carbonylated proteins and lipid peroxidation products in these organs reflects oxidative stress, a known cause of organ pathology. IHC alleviated PTSD-induced metabolic and structural injury and reduced oxidative stress. Therefore, IHC is a promising preventive treatment for PTSD-related morphological and functional damage to organs, due, in part, to IHC’s reduction of oxidative stress.

The Effects of High-Altitude Environment on Brain Function in a Seizure Model of Young-Aged Rats

In this study, we examined the effects of high-altitude environment on the brain function of a young-rat seizure model. Two-hundred healthy, 3-week old, male rats were selected and equally divided into the plateau and plain groups. The plateau group was preconditioned in a simulated 5,000-m altitude (barometric pressure [PB], 405 mmHg; partial pressure of oxygen [PO₂], 84 mmHg) for 6 h/day for 7 days, while the plain group was kept in the ordinary atmospheric environment (PB, 760 mmHg; PO₂, 157 mmHg) for 7 days. After preconditioning, rats were administered pentylenetetrazol (PTZ) to generate level-4 or stronger seizures. Electroencephalogram (EEG) signals were recorded (16 rats/group); the histology and apoptosis of hippocampal tissue were evaluated (6 rats/group); and spatial learning and memory were examined in the Morris water maze (12 rats/group; 6-weeks old). To induce a level 4 or stronger seizure successfully, a significantly higher PTZ dose was used in the plateau (81.32 ± 21.57 mg/kg) than in the plain group (63.41 ± 19.77 mg/kg, p < 0.01); however, the plateau group survival rate was significantly lower than that of the plain group (26.2 vs. 42.9%, p < 0.05). EEG parameters did not differ between the two groups. Histological analysis revealed that in the plateau group, more neurons were observed (p < 0.001), especially in DG and CA1 areas, and less apoptotic cells were found in DG areas (p = 0.035), comparing with the plain group. No differences were found between the two groups in any of the parameters examined in the Morris water maze. Our results show that the disease outcome caused by low pressure and low oxygen environment in the plateau group was different to that in the plain group. The high drug dosage to induce seizures in the plateau group, accompanied by increased mortality rates after seizures, indicates that the seizure threshold may be higher in the plateau than in the plain group. Moreover, based on the histological findings, the plateau environment seems to exert a protective effect on brain development after seizures only for survived individuals with mild conditions.

Chronic intermittent hypobaric hypoxia attenuates skeletal muscle ischemia-reperfusion injury in mice

AIM

The aim of this study was to investigate the protective effect of chronic intermittent hypobaric hypoxia (CIHH) against skeletal muscle ischemia-reperfusion (IR) injury and to determine the underlying mechanism.

MAIN METHODS

C57BL/6 mice were randomly divided into 3 groups: skeletal muscle IR injury group (IR), CIHH pretreatment following IR group (IR + CIHH), and sham operation group (Sham). The skeletal muscle IR injury model was induced by the unilateral application of a tourniquet on a hind limb for 3 h and then releasing it for 24 h. CIHH pretreatment simulating a 5000-m altitude was applied 6 h per day for 28 days. The functional and morphological performance of IR-injured gastrocnemius muscle was evaluated using contraction force, H&E staining, and transmission electron microscopy. IR injury-induced CD68⁺ macrophage infiltration was assessed by immunofluorescence. TNFα levels in serum and muscle were measured by ELISA and western blotting, respectively. Apoptosis was examined by TUNEL staining and Cleaved Caspase-3 protein expression.

KEY FINDINGS

Acute IR injury resulted in reduced contraction tension, morphological destruction, macrophage infiltration, increased TNFα levels, and apoptosis in gastrocnemius muscle. CIHH pretreatment significantly ameliorated contraction function and morphological performance in IR-injured skeletal muscle. In addition, CIHH pretreatment resulted in marked decreases in CD68⁺ macrophage infiltration, TNFα levels, and apoptosis.

SIGNIFICANCE

These data demonstrated that CIHH has a protective effect against acute IR injury in skeletal muscle via inhibition of inflammation and apoptosis.

Chronic mild hypoxia promotes hippocampal neurogenesis involving Notch1 signaling in epileptic rats

Cognitive impairment is one of the most common and disabling co-morbidities of epilepsy. It is therefore imperative to find novel treatment approaches to rescue cognitive function among epilepsy patients. Adult neurogenesis is strongly implicated in cognitive function, and mild hypoxia is known to promote the proliferation and differentiation of both embryonic and adult neural stem cells (NSCs). In the present study, we investigated the effect of mild hypoxia on cognitive function and hippocampal neurogenesis of rats with pilocarpine-induced chronic epilepsy. Chronic epilepsy induced marked spatial learning and memory deficits in the Morris water maze that were rescued by consecutively 28 days mild hypoxia exposure (6 h/d at 3000 m altitude equivalent) during the chronic phase. Moreover, mild hypoxia reversed the suppression of hippocampal neurogenesis and the downregulation of NT-3 and BDNF expression in hippocampus and cortex of epileptic rats. Mild hypoxia in vitro also promoted hippocampus-derived NSC proliferation and neuronal differentiation. In addition, mild hypoxia enhanced Notch1 and Hes1 expression, suggesting that Notch1 signaling may be involved in neuroprotection of hypoxia. Our data may help to pave the way for identifying new therapeutic targets for rescuing cognition conflicts in epileptic patients by using hypoxia to promote hippocampus neurogenesis.

Rat Strain and Housing Conditions Alter Oxidative Stress and Hormone Responses to Chronic Intermittent Hypoxia

Sleep apnea has been associated with elevated risk for metabolic, cognitive, and cardiovascular disorders. Further, the role of hypothalamic–pituitary–adrenal (HPA) activation in sleep apnea has been controversial in human studies. Chronic intermittent hypoxia (CIH) is a rodent model, which mimics the hypoxemia experienced by patients with sleep apnea. Most studies of CIH in rats have been conducted in the Sprague Dawley rat strain. Previously published literature suggests different strains of rats exhibit various responses to disease models, and these effects can be further modulated by the housing conditions experienced by each strain. This variability in response is similar to what has been observed in clinical populations, especially with respect to the HPA system. To investigate if strain or housing (individual or pair-housed) can affect the results of CIH (AHI 8 or 10) treatment, we exposed individual and pair-housed Sprague Dawley and Long-Evans male rats to 7 days of CIH treatment. This was followed by biochemical analysis of circulating hormones, oxidative stress, and neurodegenerative markers. Both strain and housing conditions altered oxidative stress generation, hyperphosphorylated tau protein (tau tangles), circulating corticosterone and adrenocorticotropic hormone (ACTH), and weight metrics. Specifically, pair-housed Long-Evans rats were the most sensitive to CIH, which showed a significant association between oxidative stress generation and HPA activation under conditions of AHI of 8. These results suggest both strain and housing conditions can affect the outcomes of CIH.

Hypoxic pre-conditioning suppresses experimental autoimmune encephalomyelitis by modifying multiple properties of blood vessels

While hypoxic pre-conditioning protects against neurological disease the underlying mechanisms have yet to be fully defined. As chronic mild hypoxia (CMH, 10% O₂) triggers profound vascular remodeling in the central nervous system (CNS), the goal of this study was to examine the protective potential of hypoxic pre-conditioning in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS) and then determine how CMH influences vascular integrity and the underlying cellular and molecular mechanisms during EAE. We found that mice exposed to CMH at the same time as EAE induction were strongly protected against the development of EAE progression, as assessed both at the clinical level and at the histopathological level by reduced levels of inflammatory leukocyte infiltration, vascular breakdown and demyelination. Mechanistically, our studies indicate that CMH protects, at least in part, by enhancing several properties of blood vessels that contribute to vascular integrity, including reduced expression of the endothelial activation molecules VCAM-1 and ICAM-1, maintained expression of endothelial tight junction proteins ZO-1 and occludin, and upregulated expression of the leukocyte inhibitory protein laminin-111 in the vascular basement membrane. Taken together, these data suggest that optimization of BBB integrity is an important mechanism underlying the protective effect of hypoxic pre-conditioning.

Intermittent hypoxia improves behavioral and adrenal gland dysfunction induced by posttraumatic stress disorder in rats

Nonpharmacological treatments of stress-induced disorders are promising, since they enhance endogenous stress defense systems, are free of side effects, and have few contraindications. The present study tested the hypothesis that intermittent hypoxia conditioning (IHC) ameliorates behavioral, biochemical, and morphological signs of experimental posttraumatic stress disorder (PTSD) induced in rats with a model of predator stress (10-day exposure to cat urine scent, 15 min daily followed by 14 days of stress-free rest). After the last day of stress exposure, rats were conditioned in an altitude chamber for 14 days at a 1,000-m simulated altitude for 30 min on day 1 with altitude and duration progressively increasing to 4,000 m for 4 h on day 5. PTSD was associated with decreased time spent in open arms and increased time spent in closed arms of the elevated X-maze, increased anxiety index, and increased rate of freezing responses. Functional and structural signs of adrenal cortex degeneration were also observed, including decreased plasma concentration of corticosterone, decreased weight of adrenal glands, reduced thickness of the fasciculate zone, and hydropic degeneration of adrenal gland cells. The thickness of the adrenal fasciculate zone negatively correlated with the anxiety index. IHC alleviated both behavioral signs of PTSD and morphological evidence of adrenal cortex dystrophy. Also, IHC alone exerted an antistress effect, which was evident from the increased time spent in open arms of the elevated X-maze and a lower number of rats displaying freezing responses. Therefore, IHC of rats with experimental PTSD reduced behavioral signs of the condition and damage to the adrenal glands.

NEW & NOTEWORTHY Intermittent hypoxia conditioning (IHC) has been shown to be cardio-, vaso-, and neuroprotective. For the first time, in a model of posttraumatic stress disorder (PTSD), this study showed that IHC alleviated both PTSD-induced behavioral disorders and functional and morphological damage to the adrenal glands. Also, IHC alone exerted an antistress effect. These results suggest that IHC may be a promising complementary treatment for PTSD-associated disorders.

Hypoxic Preconditioning Protects SH-SY5Y Cell against Oxidative Stress through Activation of Autophagy

Oxidative stress plays a role in many neurological diseases. Hypoxic preconditioning (HPC) has been proposed as an intervention that protects neurons from damage by altering their response to oxidative stress. The aim of this study was to investigate the mechanisms by which HPC results in neuroprotection in cultured SH-SY5Y cells subjected to oxidative stress to provide a guide for future investigation and targeted interventions. SH-SY5Y cells were subjected to HPC protocols or control conditions. Oxidative stress was induced by H₂O₂. Cell viability was determined via adenosine triphosphate assay. Rapamycin and 3-methyxanthine (3-MA) were used to induce and inhibit autophagy, respectively. Monodansylcadaverine staining was used to observe the formation of autophagosomes. Levels of Microtubule-associated protein light chain 3 B (LC3B), Beclin 1, and p53 were measured by Western blot. Reactive oxygen species (ROS) were also determined. Cell viability in the HPC group following 24-h exposure to 600 μM H₂O₂ was 65.04 ± 12.91% versus 33.14 ± 5.55% in the control group. LC3B, Beclin 1, and autophagosomes were increased in the HPC group compared with controls. Rapamycin mimicked the protection and 3-MA decreased the protection. There was a moderate increase in ROS after HPC, but rapamycin can abolish the increase and 3-MA can enhance the increase. p53 accumulated in a manner consistent with cell death, and HPC-treated cells showed reduced accumulation of p53 as compared with controls. Treatment with rapamycin decreased p53 accumulation, and 3-MA inhibited the decrease in p53 induced by HPC. HPC protects against oxidative stress in SH-SY5Y cells. Mechanisms of protection may involve the activation of autophagy induced by ROS generated from HPC and the following decline in p53 level caused by activated autophagy in oxidative stress state. This is in line with recent findings in nonneuronal cell populations and may represent an important advance in understanding how HPC protects neurons from oxidative stress.

Hypoxia in CNS Pathologies: Emerging Role of miRNA-Based Neurotherapeutics and Yoga Based Alternative Therapies

Cellular respiration is a vital process for the existence of life. Any condition that results in deprivation of oxygen (also termed as hypoxia) may eventually lead to deleterious effects on the functioning of tissues. Brain being the highest consumer of oxygen is prone to increased risk of hypoxia-induced neurological insults. This in turn has been associated with many diseases of central nervous system (CNS) such as stroke, Alzheimer's, encephalopathy etc. Although several studies have investigated the pathophysiological mechanisms underlying ischemic/hypoxic CNS diseases, the knowledge about protective therapeutic strategies to ameliorate the affected neuronal cells is meager. This has augmented the need to improve our understanding of the hypoxic and ischemic events occurring in the brain and identify novel and alternate treatment modalities for such insults. MicroRNA (miRNAs), small non-coding RNA molecules, have recently emerged as potential neuroprotective agents as well as targets, under hypoxic conditions. These 18-22 nucleotide long RNA molecules are profusely present in brain and other organs and function as gene regulators by cleaving and silencing the gene expression. In brain, these are known to be involved in neuronal differentiation and plasticity. Therefore, targeting miRNA expression represents a novel therapeutic approach to intercede against hypoxic and ischemic brain injury. In the first part of this review, we will discuss the neurophysiological changes caused as a result of hypoxia, followed by the contribution of hypoxia in the neurodegenerative diseases. Secondly, we will provide recent updates and insights into the roles of miRNA in the regulation of genes in oxygen and glucose deprived brain in association with circadian rhythms and how these can be targeted as neuroprotective agents for CNS injuries. Finally, we will emphasize on alternate breathing or yogic interventions to overcome the hypoxia associated anomalies that could ultimately lead to improvement in cerebral perfusion.

Impaired hippocampal glucose metabolism during and after flurothyl-induced seizures in mice: Reduced phosphorylation coincides with reduced activity of pyruvate dehydrogenase

OBJECTIVE

To determine changes in glucose metabolism and the enzymes involved in the hippocampus ictally and postictally in the acute mouse flurothyl seizure model.

METHODS

[U-¹³ C]-Glucose was injected (i.p.) prior to, or following a 5 min flurothyl-induced seizure. Fifteen minutes later, mice were killed and the total metabolite levels and % ¹³ C enrichment were analyzed in the hippocampal formation using gas chromatography-mass spectrometry. Activities of key metabolic and antioxidant enzymes and the phosphorylation status of pyruvate dehydrogenase were measured, along with lipid peroxidation.

RESULTS

During seizures, total lactate levels increased 1.7-fold; however, [M + 3] enrichment of both lactate and alanine were reduced by 30% and 43%, respectively, along with a 28% decrease in phosphofructokinase activity. Postictally the % ¹³ C enrichments of all measured tricarboxylic acid (TCA) cycle intermediates and the amino acids were reduced by 46-93%. At this time, pyruvate dehydrogenase (PDH) activity was 56% of that measured in controls, and there was a 1.9-fold increase in the phosphorylation of PDH at ser232. Phosphorylation of PDH is known to decrease its activity.

SIGNIFICANCE

Here, we show that the increase of lactate levels during flurothyl seizures is from a source other than [U-¹³ C]-glucose, such as glycogen. Surprisingly, although we saw a reduction in phosphofructokinase activity during the seizure, metabolism of [U-¹³ C]-glucose into the TCA cycle seemed unaffected. Similar to our recent findings in the chronic phase of the pilocarpine model, postictally the metabolism of glucose by glycolysis and the TCA cycle was impaired along with reduced PDH activity. Although this decrease in activity may be a protective mechanism to reduce oxidative stress, which is observed in the flurothyl model, ATP is critical to the recovery of ion and neurotransmitter balance and return to normal brain function. Thus we identified promising novel strategies to enhance energy metabolism and recovery from seizures.

Metyrapone prevents brain damage induced by status epilepticus in the rat lithium-pilocarpine model

The status epilepticus (SE) induced by lithium-pilocarpine is a well characterized rodent model of the human temporal lobe epilepsy (TLE) which is accompanied by severe brain damage. Stress and glucocorticoids markedly contribute to exacerbate neuronal damage induced by seizures but the underlying mechanisms are poorly understood. Herein we sought to investigate whether a single administration of metyrapone (150 mg/kg, i.p.), an 11β-hydroxylase inhibitor, enzyme involved in the peripheral and central synthesis of corticosteroids, had neuroprotective properties in this model. Two experiments were carried out. In exp. 1, metyrapone was administered 3 h before pilocarpine injection whereas in exp. 2, metyrapone administration took place at the onset of the SE. In both experiments, 3 days after the insult, brain metabolism was assessed by in vivo 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) positron emission tomography (PET). Brains were processed for analyses of markers of hippocampal integrity (Nissl staining), neurodegeneration (Fluoro-Jade C), astrogliosis (glial fibrillary acidic protein (GFAP) immunohistochemistry) and, for a marker of activated microglia by in vitro autoradiography with the TSPO (18 kDa translocator protein) radioligand [¹⁸F]GE180. The SE resulted in a consistent hypometabolism in hippocampus, cortex and striatum and neuronal damage, hippocampal neurodegeneration, neuronal death and gliosis. Interestingly, metyrapone had neuroprotective effects when administered before, but not after the insult. In summary, we conclude that metyrapone administration prior but not after the SE protected from brain damage induced by SE in the lithium-pilocarpine model. Therefore, it seems that the effect of metyrapone is preventive in nature and likely related to its antiseizure properties.

Chronic intermittent hypobaric hypoxia ameliorates diabetic nephropathy through enhancing HIF1 signaling in rats

AIM

Our previous study demonstrated that chronic intermittent hypobaric hypoxia (CIHH) had anti-diabetes effect. The present study was to explore the renal protective effect of CIHH in diabetic rats.

METHODS

Sprague-Dawley rats were randomly divided into three groups: diabetes mellitus group (DM, induced by high-fat diet combined with low-dose streptozotocin), diabetes plus CIHH treatment group (DM+CIHH, simulated 5000-m altitude, 6h per day for 28days, after diabetes model confirmed) and control group (CON). Systolic arterial blood pressure (SAP), blood biochemicals, urinary albumin, and histopathology of kidney were determined. The superoxide dismutase (SOD) activity, malondialdehyde (MDA) level, protein levels of hypoxia induced factors (HIFs) and transforming growth factor β1 (TGF-β1) in kidney were assayed.

RESULTS

The increased SAP, urinary albumin, hyperplasia of glomerular, fibrosis in mesangial and glomerular, and abnormal lipid metabolism in diabetic rats were ameliorated by CIHH treatment. And decreased superoxide dismutase (SOD) activity and increased malondialdehyde (MDA) level in diabetic kidney were reversed in CIHH-treated DM rats. In addition up-regulated TGF-β1 and down-regulated HIF1α in diabetic kidney returned back to normal level in CIHH-treated DM rats.

CONCLUSIONS

These data demonstrated for the first time that CIHH had protective effects against the early stage damage of diabetic nephropathy through activating HIF1 signaling, improving anti-oxidation and inhibiting TGF-β1 signaling in diabetic rats.

Intermittent hypoxia training protects cerebrovascular function in Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of death and disability among older adults. Modifiable vascular risk factors for AD (VRF) include obesity, hypertension, type 2 diabetes mellitus, sleep apnea, and metabolic syndrome. Here, interactions between cerebrovascular function and development of AD are reviewed, as are interventions to improve cerebral blood flow and reduce VRF. Atherosclerosis and small vessel cerebral disease impair metabolic regulation of cerebral blood flow and, along with microvascular rarefaction and altered trans-capillary exchange, create conditions favoring AD development. Although currently there are no definitive therapies for treatment or prevention of AD, reduction of VRFs lowers the risk for cognitive decline. There is increasing evidence that brief repeated exposures to moderate hypoxia, i.e. intermittent hypoxic training (IHT), improve cerebral vascular function and reduce VRFs including systemic hypertension, cardiac arrhythmias, and mental stress. In experimental AD, IHT nearly prevented endothelial dysfunction of both cerebral and extra-cerebral blood vessels, rarefaction of the brain vascular network, and the loss of neurons in the brain cortex. Associated with these vasoprotective effects, IHT improved memory and lessened AD pathology. IHT increases endothelial production of nitric oxide (NO), thereby increasing regional cerebral blood flow and augmenting the vaso- and neuroprotective effects of endothelial NO. On the other hand, in AD excessive production of NO in microglia, astrocytes, and cortical neurons generates neurotoxic peroxynitrite. IHT enhances storage of excessive NO in the form of S-nitrosothiols and dinitrosyl iron complexes. Oxidative stress plays a pivotal role in the pathogenesis of AD, and IHT reduces oxidative stress in a number of experimental pathologies. Beneficial effects of IHT in experimental neuropathologies other than AD, including dyscirculatory encephalopathy, ischemic stroke injury, audiogenic epilepsy, spinal cord injury, and alcohol withdrawal stress have also been reported. Further research on the potential benefits of IHT in AD and other brain pathologies is warranted.

Neuroprotective Role of Intermittent Hypobaric Hypoxia in Unpredictable Chronic Mild Stress Induced Depression in Rats

Hypoxic exposure results in several pathophysiological conditions associated with nervous system, these include acute and chronic mountain sickness, loss of memory, and high altitude cerebral edema. Previous reports have also suggested the role of hypoxia in pathogenesis of depression and related psychological conditions. On the other hand, sub lethal intermittent hypoxic exposure induces protection against future lethal hypoxia and may have beneficial effect. Therefore, the present study was designed to explore the neuroprotective role of intermittent hypobaric hypoxia (IHH) in Unpredictable Chronic Mild Stress (UCMS) induced depression like behaviour in rats. The IHH refers to the periodic exposures to hypoxic conditions interrupted by the normoxic or lesser hypoxic conditions. The current study examines the effect of IHH against UCMS induced depression, using elevated plus maze (EPM), open field test (OFT), force swim test (FST), as behavioural paradigm and related histological and molecular approaches. The data indicated the UCMS induced depression like behaviour as evident from decreased exploration activity in OFT with increased anxiety levels in EPM, and increased immobility time in the FST; whereas on providing the IHH (5000m altitude, 4hrs/day for two weeks) these behavioural changes were ameliorated. The morphological and molecular studies also validated the neuroprotective effect of IHH against UCMS induced neuronal loss and decreased neurogenesis. Here, we also explored the role of Brain-Derived Neurotrophic Factor (BDNF) in anticipatory action of IHH against detrimental effect of UCMS as upon blocking of BDNF-TrkB signalling the beneficial effect of IHH was nullified. Taken together, the findings of our study demonstrate that the intermittent hypoxia has a therapeutic potential similar to an antidepressant in animal model of depression and could be developed as a preventive therapeutic option against this pathophysiological state.

Current insights into the molecular mechanisms of hypoxic pre- and postconditioning using hypobaric hypoxia

Exposure of organisms to repetitive mild hypoxia results in development of brain hypoxic/ischemic tolerance and cross-tolerance to injurious factors of a psycho-emotional nature. Such preconditioning by mild hypobaric hypoxia functions as a “warning” signal which prepares an organism, and in particular the brain, to subsequent more harmful conditions. The endogenous defense processes which are mobilized by hypoxic preconditioning and result in development of brain tolerance are based on evolutionarily acquired gene-determined mechanisms of adaptation and neuroprotection. They involve an activation of intracellular cascades including kinases, transcription factors and changes in expression of multiple regulatory proteins in susceptible areas of the brain. On the other hand they lead to multilevel modifications of the hypothalamic-pituitary-adrenal endocrine axis regulating various functions in the organism. All these components are engaged sequentially in the initiation, induction and expression of hypoxia-induced tolerance. A special role belongs to the epigenetic regulation of gene expression, in particular of histone acetylation leading to changes in chromatin structure which ensure access of pro-adaptive transcription factors activated by preconditioning to the promoters of target genes. Mechanisms of another, relatively novel, neuroprotective phenomenon termed hypoxic postconditioning (an application of mild hypoxic episodes after severe insults) are still largely unknown but according to recent data they involve apoptosis-related proteins, hypoxia-inducible factor and neurotrophins. The fundamental data accumulated to date and discussed in this review open new avenues for elaboration of the effective therapeutic applications of hypoxic pre- and postconditioning.