Ischemic preconditioning: a novel target for neuroprotective therapy

Endothelial Progenitor Cells Count after Acute Ischemic Stroke Predicts Functional Outcome in Patients with Carotid Atherosclerosis

OBJECTIVES

Circulating Endothelial Progenitor Cells (EPCs) predict cardiovascular outcomes in patients with coronary disease. However, the predictive value of EPCs after ischemic stroke is not well established. We aimed to study the prognostic role of EPCs in patients with acute ischemic stroke and carotid atherosclerosis, focusing on post-stroke functional outcome and stroke recurrences.

MATERIALS AND METHODS

We studied consecutive adult patients with an acute (<7 days) anterior circulation ischemic stroke and carotid atherosclerosis. Cardioembolic strokes were excluded. We measured circulating EPCs by flow cytometry (CD34+/CD133+/KDR+) at inclusion (7±1 days after stroke) and at one year of follow-up. At three months and at one year we registered the modified Rankin Scale score, stroke recurrences and coronary syndromes during the follow-up.

RESULTS

We studied 80 patients with a mean age of 74.3±10.4 years. We divided the population in tertiles according to the EPCs count. At three months we observed a favorable outcome in 25/36 (69.4%) patients in the lowest, 19/22 (86.4%) in the medium and 21/22 (95.5%) in the highest tercile (p=0.037). In the multivariable analysis a higher EPCs count was associated with favorable functional outcome after adjusting for age and baseline NIHSS score (OR=3.61, 95%CI 1.34-9.76; p=0.011). This association persisted at one year of follow-up. We did not find association between counts of EPCs and stroke recurrence.

CONCLUSIONS

In patients with acute ischemic stroke and carotid atherosclerosis, a higher count of EPCs was associated with favorable functional outcome in the mid and long-term follow-up. Counts of EPCs did not predict stroke recurrences.

Intermittent Hypobaric Hypoxic Preconditioning Provides Neuroprotection by Increasing Antioxidant Activity, Erythropoietin Expression and Preventing Apoptosis and Astrogliosis in the Brain of Adult Rats Exposed to Acute Severe Hypoxia

BACKGROUND

Exposure to intermittent hypoxia has been demonstrated to be an efficient tool for hypoxic preconditioning, preventing damage to cells and demonstrating therapeutic benefits. We aimed to evaluate the effects of respiratory intermittent hypobaric hypoxia (IHH) to avoid brain injury caused by exposure to acute severe hypoxia (ASH).

METHODS

biomarkers of oxidative damage, mitochondrial apoptosis, and transcriptional factors in response to hypoxia were assessed by Western blot and immunohistochemistry in brain tissue. Four groups of rats were used: (1) normoxic (NOR), (2) exposed to ASH (FiO2 7% for 6 h), (3) exposed to IHH for 3 h per day over 8 days at 460 mmHg, and (4) ASH preconditioned after IHH.

RESULTS

ASH animals underwent increased oxidative-stress-related parameters, an upregulation in apoptotic proteins and had astrocytes with phenotype forms compatible with severe diffuse reactive astrogliosis. These effects were attenuated and even prevented when the animals were preconditioned with IHH. These changes paralleled the inhibition of NF-κB expression and the increase of erythropoietin (EPO) levels in the brain.

CONCLUSIONS

IHH exerted neuroprotection against ASH-induced oxidative injury by preventing oxidative stress and inhibiting the apoptotic cascade, which was associated with NF-κB downregulation and EPO upregulation.

Hypoxic Preconditioning Induces Neuronal Differentiation of Infrapatellar Fat Pad Stem Cells through Epigenetic Alteration

Hypoxia is considered a key factor in cellular differentiation and proliferation, particularly during embryonic development; the process of early neurogenesis also occurs under hypoxic conditions. Apart from these developmental processes, hypoxia preconditioning or mild hypoxic sensitization develops resistance against ischemic stroke in deteriorating tissues. We therefore hypothesized that neurons resulting from hypoxia-regulated neuronal differentiation could be the best choice for treating brain ischemia, which contributes to neurodegeneration. In this study, infrapatellar fat pad (IFP), an adipose tissue present beneath the knee joint, was used as the stem cell source. IFP-derived stem cells (IFPSCs) are totally adherent and are mesenchymal stem cells. The transdifferentiation protocol involved hypoxia preconditioning, the use of hypoxic-conditioned medium, and maintenance in maturation medium with α-lipoic acid. The differentiated cells were characterized using microscopy, reverse transcription PCR, real time PCR, and immunocytochemistry. To evaluate the epigenetic reprogramming of IFPSCs to become neuron-like cells, methylation microarrays were performed. Hypoxia preconditioning stabilized and allowed for the translocation of hypoxia inducible factor 1α into the nucleus and induced achaete-scute homologue 1 and doublecortin expression. Following induction, the resultant cells expressed neuronal markers neuron-specific enolase, neurofilament-light chain, growth associated protein 43, synaptosome associated protein 25, and β-III tubulin. The differentiated neural-lineage cells had functional gene expression pertaining to neurotransmitters, their release, and their receptors. The molecular signaling mechanisms regulated developmental neurogenesis. Furthermore, the in vitro physiological condition regulated neurotransmitter respecification or switching during IFPSC differentiation to neurons. Thus, differentiated neurons were fabricated against the ischemic region to treat neurodegenerative diseases.

Combined Ischemic Preconditioning and Resveratrol Improved Bloodbrain Barrier Breakdown via Hippo/YAP/TAZ Signaling Pathway

BACKGROUND

Transient Ischemia/Reperfusion (I/R) is the main reason for brain injury and results in disruption of the Blood-Brain Barrier (BBB). It had been reported that BBB injury is one of the main risk factors for early death in patients with cerebral ischemia. Numerous investigations focus on the study of BBB injury which have been carried out.

OBJECTIVE

The objective of this study was to investigate the treatment function of the activation of the Hippo/Yes-Associated Protein (YAP) signaling pathway by combined Ischemic Preconditioning (IPC) and resveratrol (RES) before brain Ischemia/Reperfusion (BI/R) improves Blood-Brain Barrier (BBB) disruption in rats.

METHODS

Sprague-Dawley (SD) rats were pretreated with 20 mg/kg RES and IPC and then subjected to 2 h of ischemia and 22 h of reperfusion. The cerebral tissues were collected; the cerebral infarct volume was determined; the Evans Blue (EB) level, the brain Water Content (BWC), and apoptosis were assessed; and the expressions of YAP and TAZ were investigated in cerebral tissues.

RESULTS

Both IPC and RES preconditioning reduced the cerebral infarct size, improved BBB permeability, lessened apoptosis, and upregulated expressions of YAP and transcriptional co-activator with PDZ-binding motif (TAZ) compared to the Ischemia/Reperfusion (I/R) group, while combined IPC and RES significantly enhanced this action.

CONCLUSION

combined ischemic preconditioning and resveratrol improved blood-brain barrier breakdown via Hippo/YAP/TAZ signaling pathway.

Modulation of Cerebral Store-operated Calcium Entry-regulatory Factor (SARAF) and Peripheral Orai1 Following Focal Cerebral Ischemia and Preconditioning in Mice

Store-operated Ca²⁺ entry (SOCE) contributes to Ca²⁺ refilling of endoplasmic reticulum (ER), but also provides Ca²⁺ influx involved in physiological and pathological signalling functions. Upon depletion of Ca²⁺ store, the sensor protein stromal interaction molecule (STIM) activates Orai1, forming an ion-conducting pore highly selective for Ca²⁺. SOCE-associated regulatory factor (SARAF) associates with STIM1 to facilitate a slow form of Ca²⁺-dependent inactivation of SOCE or interacts with Orai1 to stimulate SOCE in STIM1-independent manner. We have investigated whether cerebral ischemic damage and neuroprotection conferred by ischemic preconditioning (PC) in mouse are associated with changes in the expression of the molecular components of SOCE. Ischemic PC induced by 15-min occlusion of the middle cerebral artery (MCAo) resulted in significant amelioration of histological and functional outcomes produced, 72 h later, by a more severe ischemia (1 h MCAo). Neither ischemia, nor PC affected the expression of Orai1 in the frontoparietal cortex. However, the number of Orai1-immunopositive cells, mostly corresponding to Ly-6G+ neutrophils, was significantly elevated in the blood after the ischemic insult, regardless of previous PC. The expression of Stim1 and SARAF, mainly localised in NeuN-immunopositive neurons, was reduced in the ischemic cortex. Interestingly, neuroprotection by ischemic PC prevented the reduction of SARAF expression in the lesioned cortex and this could be interpreted as a compensatory mechanism to restore ER Ca²⁺ refilling in neurons in the absence of STIM1. Thus, preventing SARAF downregulation may represent a pivotal mechanism implicated in neuroprotection provided by ischemic PC and should be exploited as an original target for novel stroke therapies.

Lupeol Alleviates Cerebral Ischemia-Reperfusion Injury in Correlation with Modulation of PI3K/Akt Pathway

BACKGROUND/AIM

This study aimed to investigate the effect and mechanism of lupeol on cerebral ischemia-reperfusion injury in rats.

METHODS

The effects of lupeol on cerebral infarction, cerebral water content, neurological symptoms and cerebral blood flow in rats were evaluated. Nissl staining was carried out to assess the neuronal damage of ischemic brain after I/R in rats. Apoptosis of ischemic brain neurons after I/R was detected by TUNEL staining. Western blotting was carried out to detect the effects of lupeol on the expression of p-PDK1, p-Akt, pc-Raf, p-BAD, cleaved caspase-3 and p-PTEN.

RESULTS

Lupeol significantly increased cerebral blood flow after I/R in rats, reduced brain water content and infarct volume, and decreased neurological function scores. It significantly reduced neuronal damage after I/R in rats, and significantly reduced neuronal cell loss. PI3K inhibitor (LY294002) can eliminate the effect of lupeol on I/R in rats. In addition, lupeol significantly increased the protein expression of p-PDK1, p-Akt, pc-Raf, p-BAD, and down-regulated the expression of cleaved caspase-3. LY294002 reversed the effects of lupeol on the expression of PI3K/Akt signaling pathway-related proteins and cleaved caspase-3 after I/R in rats.

CONCLUSION

Lupeol had significant neuroprotective effects on brain I/R injury and neuronal apoptosis, and its mechanism may be related to the activation of PI3K/Akt signaling pathway.

Effects of dietary 5-methoxyindole-2-carboxylic acid on brain functional recovery after ischemic stroke

Stroke leads to devastating outcomes including impairments of sensorimotor and cognitive function that may be long lasting. New intervention strategies are needed to overcome the long-lasting effects of ischemic injury. Previous studies determined that treatment with 5-methoxyindole-2-carboxylic acid (MICA) conferred chemical preconditioning and neuroprotection against stroke. The purpose of the current study was to determine whether the preconditioning can lead to functional improvements after stroke (done by transient middle cerebral artery occlusion). After 4 weeks of MICA feeding, half the rats underwent ischemic injury, while the other half remained intact. After one week recovery, all the rats were tested for motor and cognitive function (rotorod and water maze). At the time of euthanasia, measurements of long-term potentiation (LTP) were performed. While stroke injury led to motor and cognitive dysfunction, MICA supplementation did not reverse these impairments. However, MICA supplementation did improve stroke-related impairments in hippocampal LTP. The dichotomy of the outcomes suggest that more studies are needed to determine optimum duration and dosage for MICA to lead to substantial motor and cognitive improvements, along with LTP change and neuroprotection.

Administration of 5-methoxyindole-2-carboxylic acid that potentially targets mitochondrial dihydrolipoamide dehydrogenase confers cerebral preconditioning against ischemic stroke injury

The objective of this study was to investigate a possible role of mitochondrial dihydrolipoamide dehydrogenase (DLDH) as a chemical preconditioning target for neuroprotection against ischemic injury. We used 5-methoxyindole-2-carboxylic acid (MICA), a reportedly reversible DLDH inhibitor, as the preconditioning agent and administered MICA to rats mainly via dietary intake. Upon completion of 4 week's MICA treatment, rats underwent 1h transient ischemia and 24h reperfusion followed by tissue collection. Our results show that MICA protected the brain against ischemic stroke injury as the infarction volume of the brain from the MICA-treated group was significantly smaller than that from the control group. Data were then collected without or with stroke surgery following MICA feeding. It was found that in the absence of stroke following MICA feeding, DLDH activity was lower in the MICA treated group than in the control group, and this decreased activity could be partly due to DLDH protein sulfenation. Moreover, DLDH inhibition by MICA was also found to upregulate the expression of NAD(P)H-ubiquinone oxidoreductase 1(NQO1) via the Nrf2 signaling pathway. In the presence of stroke following MICA feeding, decreased DLDH activity and increased Nrf2 signaling were also observed along with increased NQO1 activity, decreased oxidative stress, decreased cell death, and increased mitochondrial ATP output. We also found that MICA had a delayed preconditioning effect four weeks post MICA treatment. Our study indicates that administration of MICA confers chemical preconditioning and neuroprotection against ischemic stroke injury.

Prior transient ischemic attacks may have a neuroprotective effect in patients with ischemic stroke

INTRODUCTION

Although functional recovery and survival after ischemic infarction seem to improve in patients with prior transient ischemic attack (TIA), little is known about the role of characteristics of prior TIA in subsequent cerebral infarction. Thus, the objective of this study was to explore how the characteristics of prior TIA have a neuroprotective effect on patients with ischemic stroke.

MATERIAL AND METHODS

A total of 221 patients admitted consecutively to a primary care center for first-ever ischemic stroke were divided into two groups on the basis of the presence or absence of prior TIAs. The initial NIHSS modified Rankin Scale was used to measure the severity and disability after the stroke. Subgroups were based on the TIA duration (< 10 min, 10 to 60 min, and > 60 min), TIA frequency (1 time, 2-3 times, more than 3 times), and the interval of stroke (< 1 week, 1-4 weeks, > 4 weeks). The severity of the neurologic picture on admission and functional disability after stroke were compared between patients with and without TIAs and subgroups as well.

RESULTS

A total of 132 (59.73%) of the 221 patients had prior TIAs before stroke. Risk factors and the initial clinical picture did not differ between patients with or without TIAs. Patients with prior TIA had a more favorable outcome than those without TIA (59.09% vs. 43.82%), and a significant difference between the two groups was observed (χ² = 4.976, p = 0.026). Furthermore, neurological outcome in patients with prior TIA lasting for 60 min, less than 3 times and shorter intervals within 4 weeks was significantly different from that in the non-TIA group (p < 0.05).

CONCLUSIONS

Prior transient ischemic attacks may have a neuroprotective effect on the subsequent ischemic stroke, and this effect might be affected by the characteristics of TIAs. Patients with TIAs of low frequency, short duration and short interval are considered to have better neurological outcomes.

Cerebral plasticity: Windows of opportunity in the developing brain

BACKGROUND

Neuroplasticity refers to the inherently dynamic biological capacity of the central nervous system (CNS) to undergo maturation, change structurally and functionally in response to experience and to adapt following injury. This malleability is achieved by modulating subsets of genetic, molecular and cellular mechanisms that influence the dynamics of synaptic connections and neural circuitry formation culminating in gain or loss of behavior or function. Neuroplasticity in the healthy developing brain exhibits a heterochronus cortex-specific developmental profile and is heightened during "critical and sensitive periods" of pre and postnatal brain development that enable the construction and consolidation of experience-dependent structural and functional brain connections.

PURPOSE

In this review, our primary goal is to highlight the essential role of neuroplasticity in brain development, and to draw attention to the complex relationship between different levels of the developing nervous system that are subjected to plasticity in health and disease. Another goal of this review is to explore the relationship between plasticity responses of the developing brain and how they are influenced by critical and sensitive periods of brain development. Finally, we aim to motivate researchers in the pediatric neuromodulation field to build on the current knowledge of normal and abnormal neuroplasticity, especially synaptic plasticity, and their dependence on "critical or sensitive periods" of neural development to inform the design, timing and sequencing of neuromodulatory interventions in order to enhance and optimize their translational applications in childhood disorders of the brain.

METHODS

literature review.

RESULTS

We discuss in details five patterns of neuroplasticity expressed by the developing brain: 1) developmental plasticity which is further classified into normal and impaired developmental plasticity as seen in syndromic autism spectrum disorders, 2) adaptive (experience-dependent) plasticity following intense motor skill training, 3) reactive plasticity to pre and post natal CNS injury or sensory deprivation, 4) excessive plasticity (loss of homeostatic regulation) as seen in dystonia and refractory epilepsy, 6) and finally, plasticity as the brain's "Achilles tendon" which induces brain vulnerability under certain conditions such as hypoxic ischemic encephalopathy and epileptic encephalopathy syndromes. We then explore the unique feature of "time-sensitive heightened plasticity responses" in the developing brain in the in the context of neuromodulation.

CONCLUSION

The different patterns of neuroplasticity and the unique feature of heightened plasticity during critical and sensitive periods are important concepts for researchers and clinicians in the field of pediatric neurology and neurodevelopmental disabilities. These concepts need to be examined systematically in the context of pediatric neuromodulation. We propose that critical and sensitive periods of brain development in health and disease can create "windows of opportunity" for neuromodulatory interventions that are not commonly seen in adult brain and probably augment plasticity responses and improve clinical outcomes.

Chemical Conditioning as an Approach to Ischemic Stroke Tolerance: Mitochondria as the Target

It is well established that the brain can be prepared to resist or tolerate ischemic stroke injury, and mitochondrion is a major target for this tolerance. The preparation of ischemic stroke tolerance can be achieved by three major approaches: ischemic conditioning, hypoxic conditioning and chemical conditioning. In each conditioning approach, there are often two strategies that can be used to achieve the conditioning effects, namely preconditioning (Pre-C) and postconditioning (Post-C). In this review, we focus on chemical conditioning of mitochondrial proteins as targets for neuroprotection against ischemic stroke injury. Mitochondrial targets covered include complexes I, II, IV, the ATP-sensitive potassium channel (mitoKATP), adenine dinucleotide translocase (ANT) and the mitochondrial permeability transition pore (mPTP). While numerous mitochondrial proteins have not been evaluated in the context of chemical conditioning and ischemic stroke tolerance, the paradigms and approaches reviewed in this article should provide general guidelines on testing those mitochondrial components that have not been investigated. A deep understanding of mitochondria as the target of chemical conditioning for ischemic stroke tolerance should provide valuable insights into strategies for fighting ischemic stroke, a leading cause of death in the world.

Molecular programs induced by heat acclimation confer neuroprotection against TBI and hypoxic insults via cross-tolerance mechanisms

Neuroprotection following prolonged exposure to high ambient temperatures (heat acclimation HA) develops via altered molecular programs such as cross-tolerance Heat Acclimation-Neuroprotection Cross-Tolerance (HANCT). The mechanisms underlying cross-tolerance depend on enhanced "on-demand" protective pathways evolving during acclimation. The protection achieved is long lasting and limits the need for de novo recruitment of cytoprotective pathways upon exposure to novel stressors. Using mouse and rat acclimated phenotypes, we will focus on the impact of heat acclimation on Angiotensin II-AT2 receptors in neurogenesis and on HIF-1 as key mediators in spontaneous recovery and HANCT after traumatic brain injury (TBI). The neuroprotective consequences of heat acclimation on NMDA and AMPA receptors will be discussed using the global hypoxia model. A behavioral-molecular link will be crystallized. The differences between HANCT and consensus preconditioning will be reviewed.

Ischemic Conditioning Is Safe and Effective for Octo- and Nonagenarians in Stroke Prevention and Treatment

Symptomatic intracranial arterial stenosis (SIAS) is very common in octo- and nonagenarians, especially in the Chinese population, and is likely the most common cause of stroke recurrence worldwide. Clinical trials demonstrate that endovascular treatment, such as stenting, may not be suitable for octogenarians with systemic diseases. Hence, less invasive methods for the octogenarian patients are urgently needed. Our previous study (unique identifier: NCT01321749) showed that repetitive bilateral arm ischemic preconditioning (BAIPC) reduced the incidence of stroke recurrence by improving cerebral perfusion (confirmed by single photon emission computed tomography and transcranial Doppler sonography) in patients younger than 80 years of age; however, the safety and effectiveness of BAIPC on stroke prevention in octo- and nonagenarians with SIAS are still unclear. The objective of this study was to evaluate the safety and effectiveness of BAIPC in reducing stroke recurrence in octo- and nonagenarian patients with SIAS. Fifty-eight patients with SIAS were enrolled in this randomized controlled prospective study for 180 consecutive days. All patients enrolled in the study received standard medical management. Patients in the BAIPC group (n = 30) underwent 5 cycles consisting of bilateral arm ischemia followed by reperfusion for 5 min each twice daily. Those in the control group (n = 28) underwent sham-BAIPC twice daily. Blood pressure, heart rate, local skin status, plasma myoglobin, and plasma levels of thrombotic and inflammatory markers were documented in both groups before beginning the study and for the first 30 days. Finally, the incidences of stroke recurrence and magnetic resonance imaging during the 180 days of treatment were compared. Compared with the control, BAIPC had no adverse effects on blood pressure, heart rate, local skin integrity, or plasma myoglobin, and did not induce cerebral hemorrhage in the studied cohort. BAIPC reduced plasma high sensitive C-reactive protein, interleukin-6, plasminogen activator inhibitor-1, leukocyte count, and platelet aggregation rate and elevated plasma tissue plasminogen activator (all p < 0.01). In 180 days, 2 infarctions and 7 transient ischemic attacks were observed in the BAIPC group compared with 8 infarctions and 11 transient ischemic attacks in the sham BAIPC group (p < 0.05). BAIPC may safely inhibit stroke recurrence, protect against brain ischemia, and ameliorate plasma biomarkers of inflammation and coagulation in octo- and nonagenarians with SIAS. A multicenter trial is ongoing.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov, unique identifier: NCT01570231.

Persimmon leaf flavonoid induces brain ischemic tolerance in mice

The persimmon leaf has been shown to improve cerebral ischemic outcomes; however, its mechanism of action remains unclear. In this study, mice were subjected to 10 minutes of ischemic preconditioning, and persimmon leaf flavonoid was orally administered for 5 days. Results showed that the persimmon leaf flavonoid significantly improved the content of tissue type plasminogen activator and 6-keto prostaglandin-F1 α in the cerebral cortex, decreased the content of thromboxane B2, and reduced the content of plasminogen activator inhibitor-1 in mice. Following optical microscopy, persimmon leaf flavonoid was also shown to reduce cell swelling and nuclear hyperchromatism in the cerebral cortex and hippocampus of mice. These results suggested that persimmon leaf flavonoid can effectively inhibit brain thrombosis, improve blood supply to the brain, and relieve ischemia-induced pathological damage, resulting in brain ischemic tolerance.

Protein redox modification as a cellular defense mechanism against tissue ischemic injury

Protein oxidative or redox modifications induced by reactive oxygen species (ROS) or reactive nitrogen species (RNS) not only can impair protein function, but also can regulate and expand protein function under a variety of stressful conditions. Protein oxidative modifications can generally be classified into two categories: irreversible oxidation and reversible oxidation. While irreversible oxidation usually leads to protein aggregation and degradation, reversible oxidation that usually occurs on protein cysteine residues can often serve as an “on and off” switch that regulates protein function and redox signaling pathways upon stress challenges. In the context of ischemic tolerance, including preconditioning and postconditioning, increasing evidence has indicated that reversible cysteine redox modifications such as S-sulfonation, S-nitrosylation, S-glutathionylation, and disulfide bond formation can serve as a cellular defense mechanism against tissue ischemic injury. In this review, I highlight evidence of cysteine redox modifications as protective measures in ischemic injury, demonstrating that protein redox modifications can serve as a therapeutic target for attenuating tissue ischemic injury. Prospectively, more oxidatively modified proteins will need to be identified that can play protective roles in tissue ischemic injury, in particular, when the oxidative modifications of such identified proteins can be enhanced by pharmacological agents or drugs that are available or to be developed.

Positive oxidative stress in aging and aging-related disease tolerance

It is now well established that reactive oxygen species (ROS), reactive nitrogen species (RNS), and a basal level of oxidative stress are essential for cell survival. It is also well known that while severe oxidative stress often leads to widespread oxidative damage and cell death, a moderate level of oxidative stress, induced by a variety of stressors, can yield great beneficial effects on adaptive cellular responses to pathological challenges in aging and aging-associated disease tolerance such as ischemia tolerance. Here in this review, I term this moderate level of oxidative stress as positive oxidative stress, which usually involves imprinting molecular signatures on lipids and proteins via formation of lipid peroxidation by-products and protein oxidation adducts. As ROS/RNS are short-lived molecules, these molecular signatures can thus execute the ultimate function of ROS/RNS. Representative examples of lipid peroxidation products and protein oxidation adducts are presented to illustrate the role of positive oxidative stress in a variety of pathological settings, demonstrating that positive oxidative stress could be a valuable prophylactic and/or therapeutic approach targeting aging and aging-associated diseases.

Brain response characteristics associated with subclavian steal phenomenon

BACKGROUND

Chronic, repetitive, and sublethal hypoperfusion by intra- or extracranial artery stenosis promotes collateral development and conditions the brain toward preventing subsequent lethal ischemia, although these latent properties have rarely been demonstrated in the clinical setting. This study assessed the previously unexplored role of subclavian steal syndrome (SSS) on inciting and protecting brain damage.

METHODS

We enrolled patients diagnosed with SSS associated with subclavian artery stenosis. Subclavian steal was determined by transcranial Doppler and/or digital subtraction angiography. We analyzed the prevalences and predictors of posterior ischemic symptoms and infarcts in SSS patients and also investigated individual cases to demonstrate a clinical evidence of brain conditioning, focusing on cytotoxic and vasogenic edema.

RESULTS

Of 54 SSS patients, 36 (66.7%) had been asymptomatic and incidentally diagnosed with SSS, whereas 18 (33.3%) patients had presented with posterior ischemic symptoms. Symptoms and infarcts including old silent lesions occurred more frequently as unstable hemodynamics of the anterior circulation were combined. Of 18 symptomatic patients, 13 patients (72.2%) had transient ischemic attack and 5 (27.8%) patients had an infarct in the posterior circulation territory. Four patients with cytotoxic edema had mild neurologic deficits and rapid and complete recovery, whereas 1 patient had prolonged, severe vasogenic edema after acute hypertension.

CONCLUSIONS

Although we noted low rates of disabling or fatal strokes in patients with SSS, a variety of vascular and neural factors beyond severity of subclavian steal could influence the likelihood of brain damage.

Ischemic preconditioning increases endothelial progenitor cell number to attenuate partial nephrectomy-induced ischemia/reperfusion injury

OBJECTIVES

The objective of this study was to investigate the role of endothelial progenitor cells (EPCs) in the modulation of ischemia-reperfusion injury (IRI) in a partial nephrectomy (PN) rat model using early-phase ischemic preconditioning (IPC).

MATERIALS AND METHODS

Ninety male Sprague-Dawley rats were randomly divided into three groups following right-side nephrectomy: Sham-operated rats (surgery without vascular clamping); PN rats (renal blood vessels were clamped for 40 min and PN was performed); and IPC rats (pretreated with 15 min ischemia and 10 min reperfusion). At 1, 3, 6, 12, 24 h, and 3 days after reperfusion, the pool of circulating EPCs and kidneys were harvested. The extent of renal injury was assessed, along with EPC number, cell proliferation, angiogenesis, and vascular growth factor expression.

RESULTS

Pretreated rats exhibited significant improvements in renal function and morphology. EPC numbers in the kidneys were increased at 12 h following reperfusion in the IPC group as compared to the PN or Sham groups. Cell proliferation (including endothelial and tubular epithelial cells) and angiogenesis in peritubular capillaries were markedly increased in kidneys treated with IPC. In addition, vascular endothelial growth factor-A (VEGF-A) and stromal cell-derived factor-1α (SDF-1α) expression in the kidneys of pretreated rats was increased compared to rats subjected to PN.

CONCLUSIONS

OUR INVESTIGATION SUGGESTED THAT: (1) the early phase of IPC may attenuate renal IRI induced by PN; (2) EPCs play an important role in renal protection, involving promotion of cell proliferation and angiogenesis through release of several angiogenic factors.

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.

The role of glutamate in neuronal ischemic injury: the role of spark in fire

Although being a physiologically important excitatory neurotransmitter, glutamate plays a pivotal role in various neurological disorders including ischemic neurological diseases. Its level is increased during cerebral ischemia with excessive neurological stimulation causing the glutamate-induced neuronal toxicity, excitotoxicity, and this is considered the triggering spark in the ischemic neuronal damage. The glutamatergic stimulation will lead to rise in the intracellular sodium and calcium, and the elevated intracellular calcium will lead to mitochondrial dysfunction, activation of proteases, accumulation of reactive oxygen species and release of nitric oxide. Interruption of the cascades of glutamate-induced cell death during ischemia may provide a way to prevent, or at least reduce, the ischemic damage. Various therapeutic options are suggested interrupting the glutamatergic pathways, e.g., inhibiting the glutamate synthesis or release, increasing its clearance, blocking of its receptors or preventing the rise in intracellular calcium. Development of these strategies may provide future treatment options in the management of ischemic stroke.

Connexin43 phosphorylation and cytoprotection in the heart

The fundamental role played by connexins including connexin43 (Cx43) in forming intercellular communication channels (gap junctions), ensuring electrical and metabolic coupling between cells, has long been recognized and extensively investigated. There is also increasing recognition that Cx43, and other connexins, have additional roles, such as the ability to regulate cell proliferation, migration, and cytoprotection. Multiple phosphorylation sites, targets of different signaling pathways, are present at the regulatory, C-terminal domain of Cx43, and contribute to constitutive as well as transient phosphorylation Cx43 patterns, responding to ever-changing environmental stimuli and corresponding cellular needs. The present paper will focus on Cx43 in the heart, and provide an overview of the emerging recognition of a relationship between Cx43, its phosphorylation pattern, and development of resistance to injury. We will also review our recent work regarding the role of an enhanced phosphorylation state of Cx43 in cardioprotection. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Experimental models for assaying microvascular endothelial cell pathophysiology in stroke

It is important to understand the molecular mechanisms underlying neuron death following stroke in order to develop effective neuroprotective strategies. Since studies on human stroke are extremely limited due to the difficulty in collecting post-mortem tissue at different time points after the onset of stroke, brain ischaemia research focuses on information derived from in-vitro models of neuronal death through ischaemic injury [1]. This review aims to provide an update on the different in-vitro stroke models with brain microvascular endothelial cells that are currently being used. These models provide a physiologically relevant tool to screen potential neuroprotective drugs in stroke and to study the molecular mechanisms involved in brain ischaemia.

Activation of Akt/FoxO signaling pathway contributes to induction of neuroprotection against transient global cerebral ischemia by hypoxic pre-conditioning in adult rats

It is well established that pre-conditioning protects neuronal injury against ischemia. However, the molecular mechanisms underlying ischemic tolerance are not completely understood. The purpose of the present study was to investigate the role of Akt/forkhead transcription factor, class O (FoxO) pathway in hypoxic pre-conditioning (HPC) using a newly developed HPC to transient global cerebral ischemia (tGCI) model in adult rats. HPC for 30-120 min significantly reduced cell death in the CA1 subregion after 10 min of tGCI. HPC was effective only when applied 1-4 days before ischemia. The maximum protection was observed with 30 min of hypoxia and 1 day interval between hypoxia and ischemia. The phosphorylated Akt and FoxOs measured by western blot and immunohistochemistry were significantly increased after hypoxia-ischemia except for a transient decrease in the HPC group. Lateral ventricular infusion of LY294002 before HPC blocked the increase in phosphorylated Akt and FoxOs and increased neuronal damage in HPC animals. These results suggest that pre-exposure to hypoxia induces protection against tGCI in adult rats. Activation of Akt results in the inactivation of FoxOs which may mediate ischemic tolerance after HPC.

Neuroprotective effect of combined hypoxia-induced VEGF and bone marrow-derived mesenchymal stem cell treatment

PURPOSES

To avoid unwanted adverse effects of higher doses of single treatment of stem cells and gene therapy and increase the therapeutic efficacies, we hypothesized the combined therapy with stem cells and gene therapy. This study assessed the neuroprotective effects of combined gene therapy and stem cell treatment under ischemic hypoxia conditions using hypoxia-inducible vascular endothelial growth factor (VEGF) and bone marrow-derived mesenchymal stem cells (BMSC).

METHODS

Experimental groups included the control which was N2A cells transfected with empty vectors, the transfection only group which was N2A cells treated with pEpo-SV-VEGF alone, the BMSC only group which was N2A cells transfected with empty vectors and cocultured with BMSCs, and the combined treatment group which was N2A cells treated with pEpo-SV-VEGF and cocultured with BMSCs. Each group was transfected for 4 h and cultured at 37 degrees C and 5% CO2 for 24 h. Each group was then cultivated under hypoxic conditions (1% O2) for 12 h. Neuroprotective effects were assessed by reverse transcription polymerase chain reaction, annexin V, and cytotoxicity assay.

RESULTS

Neurons exposed to hypoxic conditions exhibited neuronal apoptosis. Compared to single treatments, the combined hypoxia-inducible VEGF and BMSC treatment demonstrated a significant increase in VEGF expression and decreased neuronal apoptosis.

CONCLUSIONS

These results suggest that combined pEpo-SV-VEGF and BMSC treatment is effective in protecting neurons against hypoxic ischemic injury.

Does remote ischemic preconditioning prevent delayed hippocampal neuronal death following transient global cerebral ischemia in rats?

OBJECTIVE

To determine if remote ischemic preconditioning (RIPC) induced by transient limb ischemia is protective against delayed hippocampal neuronal death in rats undergoing transient global cerebral ischemia (GCI).

METHOD

Animals were randomized into 3 groups: Group I (Control, n = 5) underwent sham procedure, namely, general anesthesia x 2, without cerebral ischemia; Group II (RIPC + GCI, n = 5) was subjected to RIPC, induced by transient left hind limb ischemia under general anesthesia prior to GCI; Group III (GCI only, n = 5) underwent sham procedure under general anesthesia prior to GCI. Twenty-four hours after the RIPC or sham procedure, a transient GCI was induced for 8 minutes in Groups II and III by means of bilateral common carotid artery occlusion and hypotension. Hippocampal CA1 neurons were histologically examined at 7 days after ischemia.

RESULTS

There was no significant difference between the RIPC group and the ischemia only group. The number of neurons in the RIPC group were 0.90 (95% CI 0.20, 4.08) times the number in the ischemia group (p=0.89). The number of neurons in the RIPC group were 0.03 (95% CI 0.01, 0.10) times the number in the Control group (p=0.0001).

CONCLUSION

Second window of the RIPC does not prevent hippocampal CA1 neuronal death at 7 days after transient global cerebral ischemia.

The effect of extracellular glutamate release on repetitive transient ischemic injury in global ischemia model

During operations, neurosurgeons usually perform multiple temporary occlusions of parental artery, possibly resulting in the neuronal damage. It is generally thought that neuronal damage by cerebral ischemia is associated with extracellular concentrations of the excitatory amino acids. In this study, we measured the dynamics of extracellular glutamate release in 11 vessel occlusion (VO) model to compare between single occlusion and repeated transient occlusions within short interval. Changes in cerebral blood flow were monitored by laser-Doppler flowmetry simultaneously with cortical glutamate level measured by amperometric biosensor. From real time monitoring of glutamate release in 11 VO model, the change of extracellular glutamate level in repeated transient occlusion group was smaller than that of single occlusion group, and the onset time of glutamate release in the second ischemic episode of repeated occlusion group was delayed compared to the first ischemic episode which was similar to that of single 10 min ischemic episode. These results suggested that repeated transient occlusion induces less glutamate release from neuronal cell than single occlusion, and the delayed onset time of glutamate release is attributed to endogeneous protective mechanism of ischemic tolerance.

Methamphetamine preconditioning: differential protective effects on monoaminergic systems in the rat brain

Pretreatment with methamphetamine (METH) can attenuate toxicity due to acute METH challenges. The majority of previous reports have focused mainly on the effects of the drug on the striatal dopaminergic system. In the present study, we used a regimen that involves gradual increases in METH administration to rats in order to mimic progressively larger doses of the drug used by some human METH addicts. We found that this METH preconditioning was associated with complete protection against dopamine depletion caused by a METH challenge (5 mg/kg x 6 injections given 1 h apart) in the striatum and cortex. In contrast, there was no preconditioning-mediated protection against METH-induced serotonin depletion in the striatum and hippocampus, with some protection being observed in the cortex. There was also no protection against METH-induced norepinephrine (NE) depletion in the hippocampus. These results indicate that, in contrast to the present dogmas, there might be differences in the mechanisms involved in METH toxicity on monoaminergic systems in the rodent brain. Thus, chronic injections of METH might activate programs that protect against dopamine toxicity without influencing drug-induced pathological changes in serotoninergic systems. Further studies will need to evaluate the cellular and molecular bases for these differential responses.

Are nutrition-induced epigenetic changes the link between socioeconomic pathology and cardiovascular diseases?

The prevalence of cardiovascular diseases (CVD) and diabetes mellitus type 2 (DM 2) is decreasing in developed countries despite the increase in the percentage of subjects with obesity and other well-recognized cardiovascular risk factors. In contrast, the recent transition of the economic model experienced by developing countries, characterized by the adoption of a Western lifestyle, that we have named "socioeconomic pathology," has led to an increase in the burden of CVD. It has been demonstrated that conventional cardiovascular risk factors in developed and developing countries are the same. Why then does the population of developing countries currently have a higher incidence of CVD than that of developed countries if they share the same risk factors? We have proposed the existence of a higher susceptibility to the development of systemic inflammation at low levels of abdominal obesity in the population of developing countries and the consequent endothelial dysfunction, insulin resistance, DM 2, and CVD. In contrast, an important percentage of obese people living in developed countries have a healthy phenotype and low risk of developing CVD and DM 2. Human epidemiologic studies and experimental dietary interventions in animal models have provided considerable evidence to suggest that nutritional imbalance and metabolic disturbances early in life may later have a persistent effect on an adult's health that may even be transmitted to the next generations. Epigenetic changes dependent on nutrition could be key in this evolutionary health behavior, acting as a buffering system, permitting the adaptation to environmental conditions by silencing or increasing the expression of certain genes.

Heat acclimation: a unique model of physiologically mediated global preconditioning against traumatic brain injury

Sub-lethal exposure to practically any harmful stimulus has been shown to induce consequent protection against more severe stress. This preconditioning (PC) effect may be achieved by exposure to different stressors, indicating that the induction of tolerance involves activation of common protective pathways. Chronic exposure to moderate heat (heat acclimation, HA) is a unique PC model, since this global physiological adaptation, as opposed to discrete organ PC, has been shown to induce cross-tolerance against other stressors, including closed head injury (CHI). HA animals show accelerated functional recovery after injury which is accompanied by reduced secondary brain damage. However, the precise mechanisms underlying this phenomenon have not been thoroughly studied until recently. Here we will address the concept of PC, highlighting the unique properties of HA as a model which can be used for the study of endogenous protective pathways triggered by PC procedures. Several molecular mechanisms which are suggested to mediate HA-induced neuroprotection will also be discussed, bringing to light their potential contribution to the development of traumatic brain injury treatment strategies utilizing therapeutic augmentation of endogenous defense mechanisms.