Transient ischemic attack before nonlacunar ischemic stroke in the elderly

Defective interferon signaling in the circulating monocytes of type 2 diabetic mice

Type 2 diabetes mellitus (T2DM) is associated with poor outcome after stroke. Peripheral monocytes play a critical role in the secondary injury and recovery of damaged brain tissue after stroke, but the underlying mechanisms are largely unclear. To investigate transcriptome changes and molecular networks across monocyte subsets in response to T2DM and stroke, we performed single-cell RNA-sequencing (scRNAseq) from peripheral blood mononuclear cells and bulk RNA-sequencing from blood monocytes from four groups of adult mice, consisting of T2DM model db/db and normoglycemic control db/+ mice with or without ischemic stroke. Via scRNAseq we found that T2DM expands the monocyte population at the expense of lymphocytes, which was validated by flow cytometry. Among the monocytes, T2DM also disproportionally increased the inflammatory subsets with Ly6C+ and negative MHC class II expression (MO.6C+II-). Conversely, monocytes from control mice without stroke are enriched with steady-state classical monocyte subset of MO.6C+II+ but with the least percentage of MO.6C+II- subtype. Apart from enhancing inflammation and coagulation, enrichment analysis from both scRNAseq and bulk RNAseq revealed that T2DM specifically suppressed type-1 and type-2 interferon signaling pathways crucial for antigen presentation and the induction of ischemia tolerance. Preconditioning by lipopolysaccharide conferred neuroprotection against ischemic brain injury in db/+ but not in db/db mice and coincided with a lesser induction of brain Interferon-regulatory-factor-3 in the brains of the latter mice. Our results suggest that the increased diversity and altered transcriptome in the monocytes of T2DM mice underlie the worse stroke outcome by exacerbating secondary injury and potentiating stroke-induced immunosuppression.

Significance Statement

The mechanisms involved in the detrimental diabetic effect on stroke are largely unclear. We show here, for the first time, that peripheral monocytes have disproportionally altered the subsets and changed transcriptome under diabetes and/or stroke conditions. Moreover, genes in the IFN-related signaling pathways are suppressed in the diabetic monocytes, which underscores the immunosuppression and impaired ischemic tolerance under the T2DM condition. Our data raise a possibility that malfunctioned monocytes may systemically and focally affect the host, leading to the poor outcome of diabetes in the setting of stroke. The results yield important clues to molecular mechanisms involved in the detrimental diabetic effect on stroke outcome.

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

Background

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

Materials and methods

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

Results

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

Conclusion

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

Volatile Sedation With Isoflurane in Neurocritical Care Patients After Poor-grade Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE

Volatile sedation after aneurysmal subarachnoid hemorrhage (aSAH) promises several advantages, but there are still concerns regarding intracranial hypertension due to vasodilatory effects. We prospectively analyzed cerebral parameters during the switch from intravenous to volatile sedation with isoflurane in patients with poor-grade (World Federation of Neurosurgical Societies grade 4-5) aSAH.

METHODS

Eleven patients were included in this prospective observational study. Between day 3 and 5 after admission, intravenous sedation was switched to isoflurane using the Sedaconda Anesthetic Conserving Device (Sedana Medical, Danderyd, Sweden). Intracranial pressure (ICP), cerebral perfusion pressure (CPP), brain tissue oxygenation (PBrO2), cerebral mean flow velocities (MFVs; transcranial Doppler ultrasound) and regional cerebral oxygen saturation (rSO2, near-infrared spectroscopy monitoring), as well as cardiopulmonary parameters were assessed before and after the sedation switch (-12 to +12 hours). Additionally, perfusion computed tomography data during intravenous and volatile sedation were analyzed retrospectively for changes in cerebral blood flow.

RESULTS

There were no significant changes in mean ICP, CPP, and PBrO2 after the sedation switch to isoflurane. Mean rSO2 showed a non-significant trend towards higher values, and mean MFV in the middle cerebral arteries increased significantly after the initiation of volatile sedation. Isoflurane sedation resulted in a significantly increased norepinephrine administration. Despite an increase in mean inspiratory pressure, we observed a significant increase in mean partial arterial pressure of carbon dioxide.

CONCLUSIONS

Isoflurane sedation does not compromise ICP or cerebral oxygenation in poor-grade aSAH patients, but the significant depression of CPP could limit the use of volatiles in case of hemodynamic instability or high vasopressor demand.

Ischemia preconditioning induces an adaptive response that defines a circulating metabolomic signature in ischemic stroke patients

Transient ischemic attacks (TIAs) before an acute ischemic stroke (AIS) could induce ischemic tolerance (IT) phenomena. with an endogenous neuroprotective role (Ischemic preconditioning. IPC). A consecutive prospective cohort of patients with AIS were recruited from 8 different hospitals. Participants were classified by those with non-previous recent TIA vs. previous TIA (within seven days. TIA ≤7d). A total of 541 AIS patients were recruited. 40 (7.4%). of them had previous TIA ≤7d. In line with IPC. patients with TIA ≤7d showed: 1) a significantly less severe stroke at admission by NIHSS score. 2) a better outcome at 7-90 days follow-up and reduced infarct volumes. 3) a specific upregulated metabolomics/lipidomic profile composed of diverse lipid categories. Effectively. IPC activates an additional adaptive response on increasing circulation levels of structural and bioactive lipids to facilitate functional recovery after AIS which may support biochemical machinery for neuronal survival. Furthermore. previous TIA before AIS seems to facilitate the production of anti-inflammatory mediators that contribute to a better immune response. Thus. the IT phenomena contributes to a better adaptation of further ischemia. Our study provides first-time evidence of a metabolomics/lipidomic signature related to the development of stroke tolerance in AIS patients induced by recent TIA.

Transient Ischemic Attacks Preceding Ischemic Stroke and the Possible Preconditioning of the Human Brain: A Systematic Review and Meta-Analysis

Stroke is a leading cause of mortality and disability worldwide. Transient ischemic attack (TIA) is defined as transient brain ischemia with temporary neurological deficits. In animal models, prior TIA seems to enhance brain ischemic tolerance to withstand further ischemic events, which might be explained by brain preconditioning. Thus, this review aims to formulate evidence of whether TIAs can induce positive preconditioning and enhance the functional outcomes in patients suffering from subsequent ischemic strokes. Five databases were searched (PubMed, Embase, SAGE, Web of Science, and Scopus), and twelve studies were included in the quantitative analysis. Studies were eligible when comparing patients with acute ischemic stroke (AIS) and previous TIA with those with AIS without TIA. Comparisons included the National Institute of Health Stroke Scale (NIHSS) score at admission and 7 days from the stroke event, modified Rankin score (mRS), and Trial of ORG 10,172 in Acute Stroke Treatment (TOAST) classification. Odds ratio (OR), mean difference (MD), and 95% confidence interval (CI) were used to describe our results using the random effect model. Our results revealed that patients with stroke and prior TIAs had lower NIHSS scores at admission than those without prior TIAs. However, the NIHSS score was not significantly different between the two groups at 7 days. Furthermore, there was no statistically significant difference between both groups in terms of mortality. Despite the differences in the admission mRS score groups, patients with prior TIAs had lower mRS scores at discharge.

Preconditioning by Preceding Ischemic Cerebrovascular Events

Background Emerging yet contrasting evidence from animal and human studies associates ischemic preconditioning with improvement of subsequent stroke severity, although long-term outcome remains unclear. The purpose of this study was to analyze how preceding cerebral ischemic events influence subsequent stroke severity and outcome. Methods and Results Data for this retrospective cohort study were extracted from ASTRAL (Acute Stroke Registry and Analysis of Lausanne). This registry includes a sample of all consecutive patients with acute ischemic strokes admitted to the stroke unit and/or intensive care unit of the Lausanne University Hospital, Switzerland. We investigated associations between preceding ischemic events (transient ischemic attacks or ischemic strokes) and the impact on subsequent stroke severity and clinical improvement within 24 hours, measured through National Institute of Health Stroke Scale, as well as 3-month outcome, determined through a shift in the modified Rankin Scale. Of 3530 consecutive patients with ischemic stroke (43% women, median age 73 years), 1001 (28%) had ≥1 preceding cerebral ischemic events (45% transient ischemic attack, 55% ischemic stroke; 31% multiple events). After adjusting for multiple prehospital, clinical, and laboratory confounders, admission stroke severity was significantly lower in patients preconditioned through a preceding ischemic event, but 24-hour improvement was not significant and 3-month outcome was unfavorable. Conclusions Preceding ischemic events were independently associated with a significant reduction in subsequent stroke severity but worsened long-term clinical outcome. These results, if confirmed by future randomized studies, may help design neuroprotective strategies. The unfavorable effect on stroke outcome is probably a consequence of the cumulative disability burden after multiple ischemic events.

Metabolic Reprogramming: Strategy for Ischemic Stroke Treatment by Ischemic Preconditioning

Stroke is one of the leading causes of death and permanent disability worldwide. Ischemic preconditioning (IPC) is an endogenous protective strategy, which has been reported to exhibit a significant neuroprotective effect in reducing the incidence of ischemic stroke. However, the underlying neuroprotective mechanisms of IPC remain elusive. An increased understanding of the pathogenic mechanisms of stroke and IPC serves to highlight the importance of metabolic reprogramming. In this review, we summarize the metabolic disorder and metabolic plasticity in the incidence and progression of ischemic stroke. We also elaborate how IPC fully mobilizes the metabolic reprogramming to maintain brain metabolic homeostasis, especially for energy and redox homeostasis, and finally protects brain function in the event of an ischemic stroke.

[Into thin air - Altitude training and hypoxic conditioning: From athlete to patient]

INTRODUCTION

Hypoxic exposure should be considered as a continuum, the effects of which depend on the dose and individual response to hypoxia. Hypoxic conditioning (HC) represents an innovative and promising strategy, ranging from improved human performance to therapeutic applications.

STATE OF THE ART

With the aim of improving sports performance, the effectiveness of hypoxic exposure, whether natural or simulated, is difficult to demonstrate because of the large variability of the protocols used. In therapeutics, the benefits of HC are described in many pathological conditions such as obesity or cardiovascular pathologies. If the HC benefits from a strong preclinical rationale, its application to humans remains limited.

PERSPECTIVES

Advances in training and acclimation will require greater personalization and precise periodization of hypoxic exposures. For patients, the harmonization of HC protocols, the identification of biomarkers and the development and subsequent validation of devices allowing a precise control of the hypoxic stimulus are necessary steps for the development of HC.

CONCLUSIONS

From the athlete to the patient, HC represents an innovative and promising field of research, ranging from the improvement of human performance to the prevention and treatment of certain pathologies.

Therapeutic potential of nutraceuticals to protect brain after stroke

Stroke leads to significant neuronal death and long-term neurological disability due to synergistic pathogenic mechanisms. Stroke induces a change in eating habits and in many cases, leads to undernutrition that aggravates the post-stroke pathology. Proper nutritional regimen remains a major strategy to control the modifiable risk factors for cardiovascular and cerebrovascular diseases including stroke. Studies indicate that nutraceuticals (isolated and concentrated form of high-potency natural bioactive substances present in dietary nutritional components) can act as prophylactic as well as adjuvant therapeutic agents to prevent stroke risk, to promote ischemic tolerance and to reduce post-stroke consequences. Nutraceuticals are also thought to regulate blood pressure, delay neurodegeneration and improve overall vascular health. Nutraceuticals potentially mediate these effects by their powerful antioxidant and anti-inflammatory properties. This review discusses the studies that have highlighted the translational potential of nutraceuticals as stroke therapies.

Effects of Hypoxic and Ischemic Clinical Conditions on the Outcomes of Acute Ischemic Stroke Patients

Background

Several studies have shown the neuroprotective role afforded by hypoxic and ischemic preconditioning in cerebrovascular disorders. There are several clinical conditions which simulate the hypoxic and ischemic conditioning in humans. The aim of this retrospective study is to identify whether the presence of any clinical scenarios mimicking the hypoxic and ischemic conditions prior to the current acute ischemic stroke (AIS) has a neuroprotective role in these patients.

Materials and methods

Data were collected for patients >18 years of age who underwent endovascular treatment for AIS from January 2009 to June 2015. A good outcome was defined as modified Rankin score (mRS) of 0 to 3 at discharge and a poor outcome as mRS of 4-6. A logistic regression analysis was performed to identify independent predictors of outcomes at discharge in both groups. A p value of <0.05 was considered statistically significant for all analyses.

Results

A total of 102 patients, aged 67 ± 16 years with median preprocedural National Institute of Health Stroke Scale (NIHSS) score 17.5 (1-36), were included. Twenty-one (21%) patients had a good outcome (mRS: 0-3) and 81 (79%) had a poor outcome (mRS: 4-6). A logistic regression analysis identified higher NIHSS score [odds ratio (OR): 1.251, confidence interval (CI): 1.11-1.40, p = 0.0002] and history of transient ischemic attack (TIA; OR: 7.881, CI: 1.05-21.01, p < 0.04) as predictors of a poor outcome at discharge.

Conclusion

Our data suggest that the occurrence of TIA preceding an AIS may be associated with the poor outcomes in patients with AIS, although this finding needs confirmation in larger studies.

How to cite this article

Athiraman U, Tempelhoff R, Karanikolas M. Effects of Hypoxic and Ischemic Clinical Conditions on the Outcomes of Acute Ischemic Stroke Patients. Indian J Crit Care Med 2020;24(2):104-108.

Age-Dependent Levels of Protein Kinase Cs in Brain: Reduction of Endogenous Mechanisms of Neuroprotection

Neurodegenerative diseases are among the leading causes of mortality and disability worldwide. However, current therapeutic approaches have failed to reach significant results in their prevention and cure. Protein Kinase Cs (PKCs) are kinases involved in the pathophysiology of neurodegenerative diseases, such as Alzheimer's Disease (AD) and cerebral ischemia. Specifically ε, δ, and γPKC are associated with the endogenous mechanism of protection referred to as ischemic preconditioning (IPC). Existing modulators of PKCs, in particular of εPKC, such as ψεReceptor for Activated C-Kinase (ψεRACK) and Resveratrol, have been proposed as a potential therapeutic strategy for cerebrovascular and cognitive diseases. PKCs change in expression during aging, which likely suggests their association with IPC-induced reduction against ischemia and increase of neuronal loss occurring in senescent brain. This review describes the link between PKCs and cerebrovascular and cognitive disorders, and proposes PKCs modulators as innovative candidates for their treatment. We report original data showing εPKC reduction in levels and activity in the hippocampus of old compared to young rats and a reduction in the levels of δPKC and γPKC in old hippocampus, without a change in their activity. These data, integrated with other findings discussed in this review, demonstrate that PKCs modulators may have potential to restore age-related reduction of endogenous mechanisms of protection against neurodegeneration.

Enhancing and Extending Biological Performance and Resilience

Human performance, endurance, and resilience have biological limits that are genetically and epigenetically predetermined but perhaps not yet optimized. There are few systematic, rigorous studies on how to raise these limits and reach the true maxima. Achieving this goal might accelerate translation of the theoretical concepts of conditioning, hormesis, and stress adaptation into technological advancements. In 2017, an Air Force-sponsored conference was held at the University of Massachusetts for discipline experts to display data showing that the amplitude and duration of biological performance might be magnified and to discuss whether there might be harmful consequences of exceeding typical maxima. The charge of the workshop was "to examine and discuss and, if possible, recommend approaches to control and exploit endogenous defense mechanisms to enhance the structure and function of biological tissues." The goal of this white paper is to fulfill and extend this workshop charge. First, a few of the established methods to exploit endogenous defense mechanisms are described, based on workshop presentations. Next, the white paper accomplishes the following goals to provide: (1) synthesis and critical analysis of concepts across some of the published work on endogenous defenses, (2) generation of new ideas on augmenting biological performance and resilience, and (3) specific recommendations for researchers to not only examine a wider range of stimulus doses but to also systematically modify the temporal dimension in stimulus inputs (timing, number, frequency, and duration of exposures) and in measurement outputs (interval until assay end point, and lifespan). Thus, a path forward is proposed for researchers hoping to optimize protocols that support human health and longevity, whether in civilians, soldiers, athletes, or the elderly patients. The long-term goal of these specific recommendations is to accelerate the discovery of practical methods to conquer what were once considered intractable constraints on performance maxima.

Is age a key factor contributing to the disparity between success of neuroprotective strategies in young animals and limited success in elderly stroke patients? Focus on protein homeostasis

Neuroprotection strategies to improve stroke outcome have been successful in the laboratory but not in clinical stroke trials, and thus have come under scrutiny by the medical community. Experimental stroke investigators are therefore under increased pressure to resolve this problem. Acute ischemic stroke represents a severe form of metabolic stress that activates many pathological processes and thereby impairs cellular functions. Traditionally, neuroprotection strategies were designed to improve stroke outcome by interfering with pathological processes triggered by ischemia. However, stroke outcome is also dependent on the brain's capacity to restore cellular functions impaired by ischemia, and this capacity declines with age. It is, therefore, conceivable that this age-dependent decline in the brain's self-healing capacity contributes to the disparity between the success of neuroprotective strategies in young animals, and limited success in elderly stroke patients. Here, prosurvival pathways that restore protein homeostasis impaired by ischemic stress should be considered, because their capacity decreases with increasing age, and maintenance of proteome fidelity is pivotal for cell survival. Boosting such prosurvival pathways pharmacologically to restore protein homeostasis and, thereby, cellular functions impaired by ischemic stress is expected to counterbalance the compromised self-healing capacity of aged brains and thereby help to improve stroke outcome.

Hypoxic conditioning and the central nervous system: A new therapeutic opportunity for brain and spinal cord injuries?

Central nervous system diseases are among the most disabling in the world. Neuroprotection and brain recovery from either acute or chronic neurodegeneration still represent a challenge in neurology and neurorehabilitation as pharmacology treatments are often insufficiently effective. Conditioning the central nervous system has been proposed as a potential non-pharmacological neuro-therapeutic. Conditioning refers to a procedure by which a potentially deleterious stimulus is applied near to but below the threshold of damage to the organism to increase resistance to the same or even different noxious stimuli given above the threshold of damage. Hypoxic conditioning has been investigated in several cellular and preclinical models and is now recognized as inducing endogenous mechanisms of neuroprotection. Ischemic, traumatic, or chronic neurodegenerative diseases can benefit from hypoxic conditioning strategies aiming at preventing the deleterious consequences or reducing the severity of the pathological condition (preconditioning) or aiming at inducing neuroplasticity and recovery (postconditioning) following central nervous system injury. Hypoxic conditioning can consist in single (sustained) or cyclical (intermittent, interspersed by short period of normoxia) hypoxia stimuli which duration range from few minutes to several hours and that can be repeated over several days or weeks. This mini-review addresses the existing evidence regarding the use of hypoxic conditioning as a potential innovating neuro-therapeutic modality to induce neuroprotection, neuroplasticity and brain recovery. This mini-review also emphasizes issues which remain to be clarified and future researches to be performed in the field. Impact statement Neuroprotection and brain recovery from either acute or chronic neurodegeneration still represent a challenge in neurology and neurorehabilitation. Hypoxic conditioning may represent a harmless and efficient non-pharmacological new therapeutic modality in the field of neuroprotection and neuroplasticity, as supported by many preclinical data. Animal studies provide clear evidence for neuroprotection and neuroplasticity induced by hypoxic conditioning in several models of neurological disorders. These studies show improved functional outcomes when hypoxic conditioning is applied and provides important information to translate this intervention to clinical practice. Some studies in humans provide encouraging data regarding the tolerance and therapeutic effects of hypoxic conditioning strategies. The main issues to address in future research include the definition of the appropriate hypoxic dose and pattern of exposure, the determination of relevant physiological biomarkers to assess the effects of the treatment and the evaluation of combined strategies involving hypoxic conditioning and other pharmacological or non-pharmacological treatments.

Preconditioning in neuroprotection: From hypoxia to ischemia

Sublethal hypoxic or ischemic events can improve the tolerance of tissues, organs, and even organisms from subsequent lethal injury caused by hypoxia or ischemia. This phenomenon has been termed hypoxic or ischemic preconditioning (HPC or IPC) and is well established in the heart and the brain. This review aims to discuss HPC and IPC with respect to their historical development and advancements in our understanding of the neurochemical basis for their neuroprotective role. Through decades of collaborative research and studies of HPC and IPC in other organ systems, our understanding of HPC and IPC-induced neuroprotection has expanded to include: early- (phosphorylation targets, transporter regulation, interfering RNA) and late- (regulation of genes like EPO, VEGF, and iNOS) phase changes, regulators of programmed cell death, members of metabolic pathways, receptor modulators, and many other novel targets. The rapid acceleration in our understanding of HPC and IPC will help facilitate transition into the clinical setting.

Prodromal Transient Ischemic Attack or Minor Stroke and Outcome in Basilar Artery Occlusion

BACKGROUND

The presence of prodromal transient ischemic attacks (TIAs) has been associated with a favorable outcome in anterior circulation stroke. We aimed to determine the association between prodromal TIAs or minor stroke and outcomes at 1 month, in the Basilar Artery International Cooperation Study, a registry of patients presenting with an acute symptomatic and radiologically confirmed basilar artery occlusion.

METHODS

A total of 619 patients were enrolled in the registry. Information on prodromal TIAs was available for 517 patients and on prodromal stroke for 487 patients. We calculated risk ratios and corresponding 95% confidence intervals (CIs) for poor clinical outcome (modified Rankin Scale score ≥4) according to the variables of interest.

RESULTS

Prodromal minor stroke was associated with poor outcome (crude risk ratio [cRR], 1.26; 95% CI, 1.12-1.42), but TIAs were not (cRR, .93; 95% CI, .79-1.09). These associations remained essentially the same after adjustment for confounding variables.

CONCLUSIONS

Prodromal minor stroke was associated with an unfavorable outcome in patients with basilar artery occlusion, whereas prodromal TIA was not.

Hypoxic Conditioning as a New Therapeutic Modality

Preconditioning refers to a procedure by which a single noxious stimulus below the threshold of damage is applied to the tissue in order to increase resistance to the same or even different noxious stimuli given above the threshold of damage. Hypoxic preconditioning relies on complex and active defenses that organisms have developed to counter the adverse consequences of oxygen deprivation. The protection it confers against ischemic attack for instance as well as the underlying biological mechanisms have been extensively investigated in animal models. Based on these data, hypoxic conditioning (consisting in recurrent exposure to hypoxia) has been suggested a potential non-pharmacological therapeutic intervention to enhance some physiological functions in individuals in whom acute or chronic pathological events are anticipated or existing. In addition to healthy subjects, some benefits have been reported in patients with cardiovascular and pulmonary diseases as well as in overweight and obese individuals. Hypoxic conditioning consisting in sessions of intermittent exposure to moderate hypoxia repeated over several weeks may induce hematological, vascular, metabolic, and neurological effects. This review addresses the existing evidence regarding the use of hypoxic conditioning as a potential therapeutic modality, and emphasizes on many remaining issues to clarify and future researches to be performed in the field.

Ischemic tolerance in an in vivo model of glutamate preconditioning

Ischemia initiates a complicated biochemical cascade of events that triggers neuronal death. This study focuses on glutamate-mediated neuronal tolerance to ischemia-reperfusion. We employed an animal model of lifelong excess release of glutamate, the glutamate dehydrogenase 1 transgenic (Tg) mouse, as a model of in vivo glutamate preconditioning. Nine- and twenty-two-month-old Tg and wild-type (wt) mice were subjected to 90 min of middle cerebral artery occlusion, followed by 24 hr of reperfusion. The Tg mice suffered significantly reduced infarction and edema volume compared with their wt counterparts. We further analyzed proteasomal activity, level of ubiquitin immunostaining, and microtubule-associated protein-2A (MAP2A) expression to understand the mechanism of neuroprotection observed in the Tg mice. We found that, in the absence of ischemia, the Tg mice exhibited higher activity of the 20S and 26S proteasomes, whereas there was no significant difference in the level of hippocampal ubiquitin immunostaining between wt and Tg mice. A surprising, significant increase was observed in MAP2A expression in neurons of the Tg hippocampus following ischemia-reperfusion compared with that in wt hippocampus. The results suggest that increased proteasome activity and MAP2A synthesis and transport might account for the effectiveness of glutamate preconditioning against ischemia-reperfusion.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

Preconditioning the human brain: practical considerations for proving cerebral protection

Ischemic preconditioning has evolved as one of the most powerful strategies for cerebral protection in laboratory models of ischemia. Translating the success of laboratory studies to human cerebral protection will necessitate an approximation of laboratory conditions. This would require a practical, easily implemented method of preconditioning and clinical settings in which cerebral ischemia is anticipated, thereby allowing cerebral preconditioning prior to ischemia onset. Remote limb ischemic preconditioning is readily instituted and used in several ongoing cardiac studies for ischemic myocardial protection. It is a potentially promising intervention for brain protection as well. Suitable clinical settings, in which a preliminary study of ischemic preconditioning in neurological disorders appears feasible, include carotid endarterectomy or stenting, cardiac surgery, and subarachnoid hemorrhage with the accompanying risk of vasospasm. These are settings, in which there is substantial risk of brain ischemia, which occurs over a short and predictable period, allowing for preconditioning to be implemented prior to ischemia onset.

Is there a place for cerebral preconditioning in the clinic?

Preconditioning (PC) describes a phenomenon whereby a sub-injury inducing stress can protect against a later injurious stress. Great strides have been made in identifying the mechanisms of PC-induced protection in animal models of brain injury. While these may help elucidate potential therapeutic targets, there are questions over the clinical utility of cerebral PC, primarily because of questions over the need to give the PC stimulus prior to the injury, narrow therapeutic windows and safety. The object of this review is to address the question of whether there may indeed be a clinical use for cerebral PC and to discuss the deficiencies in our knowledge of PC that may hamper such clinical translation.

Age-related reduction of cerebral ischemic preconditioning: myth or reality?

Stroke is one of the leading causes of death in industrialized countries for people older than 65 years of age. The reasons are still unclear. A reduction of endogenous mechanisms against ischemic insults has been proposed to explain this phenomenon. The “cerebral” ischemic preconditioning mechanism is characterized by a brief episode of ischemia that renders the brain more resistant against subsequent longer ischemic events. This ischemic tolerance has been shown in numerous experimental models of cerebral ischemia. This protective mechanism seems to be reduced with aging both in experimental and clinical studies. Alterations of mediators released and/or intracellular pathways may be responsible for age-related ischemic preconditioning reduction. Agents able to mimic the “cerebral” preconditioning effect may represent a new powerful tool for the treatment of acute ischemic stroke in the elderly. In this article, animal and human cerebral ischemic preconditioning, its age-related difference, and its potential therapeutical applications are discussed.

Genetics and genomics of ischemic tolerance: focus on cardiac and cerebral ischemic preconditioning

A subthreshold ischemic insult applied to an organ such as the heart and/or brain may help to reduce damage caused by subsequent ischemic episodes. This phenomenon is known as ischemic tolerance mediated by ischemic preconditioning (IPC) and represents the most powerful endogenous mechanism against ischemic injury. Various molecular pathways have been implicated in IPC, and several compounds have been proposed as activators or mediators of IPC. Recently, it has been established that the protective phenotype in response to ischemia depends on a coordinated response at the genomic, molecular, cellular and tissue levels by introducing the concept of 'genomic reprogramming' following IPC. In this article, we sought to review the genetic expression profiles found in cardiac and cerebral IPC studies, describe the differences between young and aged organs in IPC-mediated protection, and discuss the potential therapeutic application of IPC and pharmacological preconditioning based on the genomic response.

Physical activity is inversely related to drug consumption in elderly patients with cardiovascular events

Elderly patients with cardiovascular events are characterized by high drug consumptions. Whether high drug consumptions are related to physical activity is not known. In order to examine whether physical activity is related to drug consumption in the elderly, patients older than 65 years (n = 250) with a recent cardiovascular event were studied. Physical activity was analyzed according to the Physical Activity Scale for the Elderly (PASE) score and related to drug consumption. PASE score was 72.4 ± 45.0 and drug consumption was 8.3 ± 2.2. Elderly patients with greater comorbidity took more drugs (8.7 ± 2.1) and are less active (PASE = 64.4 ± 50.6) than patients with Cumulative Illness Rating Scale severity score higher than 1.8 than those with a score lower than 1.8 (76.3 ± 41.4, p < 0.05, and 8.0 ± 2.0, p = 0.006, respectively). Multivariate analysis correlation confirmed that PASE score is negatively associated with drug consumption (β = −0.149, p = 0.031), independently of several variables including comorbidity. Thus, physical activity is inversely related to drug consumption in elderly patients with cardiovascular events. This inverse relationship may be attributable to the high degree of comorbidity observed in elderly patients in whom poor level of physical activity and high drug consumption are predominant.

Poised for success: implementation of sound conditioning strategies to promote endogenous protective responses to stroke in patients

The following perspective represents our summary of questions, ideas, concerns, and recommendations expressed by speakers and discussants at the second Biennial Translational Preconditioning Workshop held in Miami in December 2011.

Clinical application of preconditioning and postconditioning to achieve neuroprotection

Ischemic conditioning is a form of endogenous protection induced by transient, subcritical ischemia in a tissue. Organs with high sensitivity to ischemia, such as the heart, the brain, and spinal cord, represent the most critical and potentially promising targets for potential therapeutic applications of ischemic conditioning. Numerous preclinical investigations have systematically studied the molecular pathways and potential benefits of both pre- and postconditioning with promising results. The purpose of this review is to summarize the present knowledge on cerebral pre- and postconditioning, with an emphasis in the clinical application of these forms of neuroprotection. A systematic MEDLINE search for the terms preconditioning and postconditioning was performed. Publications related to the nervous system and to human applications were selected and analyzed. Pre- and postconditioning appear to provide similar levels of neuroprotection. The preconditioning window of benefit can be subdivided into early and late effects, depending on whether the effect appears immediately after the sublethal stress or with a delay of days. In general, early effects have been associated posttranslational modification of critical proteins (membrane receptors, mitochondrial respiratory chain) while late effects are the result of gene up- or downregulation. Transient ischemic attacks appear to represent a form of clinically relevant preconditioning by inducing ischemic tolerance in the brain and reducing the severity of subsequent strokes. Remote forms of ischemic pre- and postconditioning have been more commonly used in clinical studies, as the remote application reduces the risk of injuring the target tissue for which protection is pursued. Limb transient ischemia is the preferred method of induction of remote conditioning with evidence supporting its safety. Clinical studies in a variety of populations at risk of central nervous damage including carotid disease, cervical myelopathy, and subarachnoid hemorrhage have shown improvement in surrogate markers of injury. Promising preclinical and early clinical studies noting improvement in surrogate markers of central nervous injury after the use of remote pre- and postconditioning treatments demand follow-up systematic investigations to address effectiveness. Challenges in the application of these techniques to pressing clinical cerebrovascular disease ought to be overcome through careful, well-designed, translational investigations.

Neuroinflammation and cerebrovascular disease in old age: a translational medicine perspective

The incidence of cerebrovascular disease is highest in the elderly population. However, the pathophysiological mechanisms of brain response to cerebral ischemia in old age are currently poorly understood. Ischemic changes in the commonly used young animal stroke models do not reflect the molecular changes associated with the aged brain. Neuroinflammation and oxidative stress are important pathogenic processes occurring during the acute phase of cerebral ischemia. Free radical generation is also implicated in the aging process, and the combination of these effects in elderly stroke patients could explain the higher risk of morbidity and mortality. A better understanding of stroke pathophysiology in the elderly patient would assist in the development of new therapeutic strategies for this vulnerable age group. With the increasing use of reperfusion therapies, inflammatory pathways and oxidative stress remain attractive therapeutic targets for the development of adjuvant neuroprotective agents. This paper will discuss these molecular aspects of acute stroke and senescence from a bench-to-bedside research perspective.

Why do acute ischemic stroke patients with a preceding transient ischemic attack present with less severe strokes? Insights from the German Stroke Study

BACKGROUND

The effect of ischemic preconditioning (IP) is well established in animal models of brain ischemia. There are conflicting data from human observational studies whether IP is also induced by a preceding transient ischemic attack (TIA) resulting in a lower stroke severity in these patients.

METHODS

Data from 7,611 consecutive patients with first-ever acute ischemic stroke from the prospective German Stroke Study Collaboration were analyzed. A multivariate linear regression analysis was used to evaluate whether a preceding TIA was associated with a lower National Institutes of Health Stroke Scale (NIH-SS) score at admission. Furthermore, stroke severity was stratified by the latency between a preceding TIA and subsequent acute ischemic stroke (≤7 days vs. >7 days and ≤72 h vs. >72 h).

RESULTS

A previous TIA was documented in 452 (5.9%) patients, and a significantly lower NIH-SS score at admission was found in these patients compared with patients without TIA. A previous TIA remained significantly associated with a lower NIH-SS score in multivariate analysis corrected for the Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification, cardiovascular risk factors, age, sex and premorbid disability. The NIH-SS score at admission did not significantly differ in 96 patients with a TIA within 7 days compared with 137 patients with a TIA more than 7 days before ischemic stroke. Similarly, there were no significant differences in stroke severity in patients with a TIA within 72 h.

CONCLUSIONS

The significantly lower stroke severity observed in patients with a preceding TIA is not confounded by stroke etiology in our large-scale observational study. Data on latency between the TIA and subsequent ischemic stroke do not support a neuroprotective effect caused by TIA-induced IP in human ischemic stroke.

Relation of aortic arch complex plaques to risk of cerebral infarction in patients with aortic stenosis

Aortic stenosis (AS) and systemic atherosclerosis have been shown to be closely related. We evaluated the prevalence of aortic arch plaques and their possible association with the risk of cerebral infarction in patients with severe AS. Transesophageal echocardiography was performed in 116 patients with severe AS (55 men, mean age 71 ± 7 years, mean aortic valve area 0.68 ± 0.15 cm(2)) who were scheduled for aortic valve replacement. The presence, thickness, and morphology of the aortic arch plaques were evaluated using transesophageal echocardiography. Cerebral infarcts (chronic cerebral infarction and cerebral infarction after cardiac catheterization and aortic valve replacement) were assessed in all patients. Compared to age- and gender-matched control subjects, the patients with severe AS had a significantly greater prevalence of aortic arch plaques (74% vs 41%; p <0.0001) and complex arch plaques such as large plaques (≥4 mm), ulcerated plaques, or mobile plaques (30% vs 10%; p = 0.004). Multivariate logistic analyses showed that the presence of complex arch plaques was independently associated with cerebral infarction in patients with AS after adjusting for traditional atherosclerotic risk factors and coronary artery disease (odds ratio 8.46, 95% confidence interval 2.38 to 30.12; p = 0.001). In conclusion, the results from the present study showed that there is a greater prevalence of aortic arch plaques in patients with AS and that the presence of complex plaques is independently associated with cerebral infarction in these patients. Therefore, the identification of complex arch plaques using transesophageal echocardiography is important for risk stratification of cerebrovascular events in patients with severe AS.

Platinum-based compounds and risk for cardiovascular toxicity in the elderly: role of the antioxidants in chemoprevention

Cancer in elderly patients is an increasingly common problem. Older patients have more co-morbidity, therefore the toxic effects of chemotherapy treatment are less tolerable compared to younger patients. Platinum-based compounds (PBCs) are commonly used cytotoxic agents in the treatment of several solid tumors; however, their application is still limited in elderly patients, due to the risks in cardiovascular toxicity. The increased risk for myocardial ischemia, stroke, and vascular thrombosis linked with PBCs treatment is mainly due to reactive oxygen species (ROS) production and the subsequent induction of oxidative stress and switch to a prothrombotic condition. Recently, studies have shown a different genetic susceptibility in cardiovascular toxicity induced by therapy with PBCs. Antioxidants, such as vitamin E, selenium, lycopene, melatonin, and resveratrol, have been implicated in cancer treatment by their property to suppress the oxidant injury. Resveratrol, especially, has been shown to increase the antineoplastic activity of cisplatin. In addition, resveratrol's ability to activate the sirtuin1 (SIRT1) pathway has been heavily implicated in the mechanisms controlling longevity and quality of life in the aged population. This article reviews the current state of treatment with PBCs and their associated risk for cardiovascular disease. It discusses the most powerful antioxidant supplementation options as a possible strategy to reduce the cardiovascular toxicity effects of chemotherapy in the elderly.

[Neuroprotective effect of transient ischemic attack]

Transient ischemic attack (TIA) is a well-recognized risk factor of ischemic stroke. Hence, 7 to 25% of ischemic stroke patients have a history of TIA, and the risk of ischemic stroke after TIA is about 15% at 3 months. However, epidemiological studies have demonstrated that among patients with ischemic stroke, those with a history of TIA have better functional and vital prognoses. This protective effect is particularly found in case of recent and short TIA, and in case of non-lacunar ischemic stroke. Hence, TIA can induce endogenous neuroprotection by the ischemic tolerance phenomenon that decreases the neurodegeneration usually caused by a severe cerebral ischemia in a non-preconditioned brain. The mechanisms of ischemic tolerance appear complex, multiple, and not fully understood. They involve changes in cellular gene expression, metabolic and signaling pathways, and enzymatic expression. The evidence of the neuroprotective effect of TIA offers interesting perspectives for the development of therapeutic strategies targeting the ischemic tolerance phenomenon.

Preconditioning and postconditioning for neuroprotection: the most recent evidence

Stroke is a leading cause of morbidity and mortality, with perioperative stroke being an important complication in the practice of anaesthesia. Unfortunately, pharmacological treatment options are very limited and often not applicable in the perioperative period. The notion of applying a subtoxic stimulus prior to an otherwise lethal event is termed preconditioning. The main focus of the article is on describing the different concepts of preconditioning, including remote ischaemic preconditioning and anaesthetic preconditioning, as well as postconditioning and summarizing the most recent discoveries in this exciting field.

Neuron specific metabolic adaptations following multi-day exposures to oxygen glucose deprivation

Prior exposure to sub toxic insults can induce a powerful endogenous neuroprotective program known as ischemic preconditioning. Current models typically rely on a single stress episode to induce neuroprotection whereas the clinical reality is that patients may experience multiple transient ischemic attacks (TIAs) prior to suffering a stroke. We sought to develop a neuron-enriched preconditioning model using multiple oxygen glucose deprivation (OGD) episodes to assess the endogenous protective mechanisms neurons implement at the metabolic and cellular level. We found that neurons exposed to a five minute period of glucose deprivation recovered oxygen utilization and lactate production using novel microphysiometry techniques. Using the non-toxic and energetically favorable five minute exposure, we developed a preconditioning paradigm where neurons are exposed to this brief OGD for three consecutive days. These cells experienced a 45% greater survival following an otherwise lethal event and exhibited a longer lasting window of protection in comparison to our previous in vitro preconditioning model using a single stress. As in other models, preconditioned cells exhibited mild caspase activation, an increase in oxidized proteins and a requirement for reactive oxygen species for neuroprotection. Heat shock protein 70 was upregulated during preconditioning, yet the majority of this protein was released extracellularly. We believe coupling this neuron-enriched multi-day model with microphysiometry will allow us to assess neuronal specific real-time metabolic adaptations necessary for preconditioning.

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells.

Ischemic tolerance in stroke treatment

Although outcome after stroke treatment has significantly improved over the last 30 years, there has been no revolutionary breakthrough. Among different combined approaches, systemic thrombolysis in combination with neuroprotection became a favorite research target. Recent studies suggest that transient ischemic attacks may represent a clinical model of such ischemic tolerance; thus, a new focus on this research has emerged. In this review, we show the parallels between ischemia and neuroprotection and discuss the potential therapeutic options that may be opened by this new molecular knowledge.

Neuronal plasticity after ischemic preconditioning and TIA-like preconditioning ischemic periods

Transient ischemic attacks (TIAs) have recently become the center of attention since they are thought to share some characteristics with experimental ischemic preconditioning (IPC). This phenomenon describes the situation that a brief, per se harmless, cerebral ischemic period renders the brain resistant to a subsequent severe and normally damaging ischemia. Preconditioning (PC) is not restricted to the brain but also occurs in other organs. Furthermore, apart from a short ischemia, the PC event may comprise nearly any noxious stimulus which, however, must not exceed the threshold to tissue damage. In the last two decades, our knowledge concerning the underlying molecular basis of PC has substantially grown and there is hope to potentially imitate the induction of an endogenous neuroprotective state in patients with a high risk of cerebral ischemia. While, at present, there is virtually no neuropathological data on changes after TIAs or TIA-like PC ischemic periods in human brains, the following review will briefly summarize the current knowledge of plastic neuronal changes after PC in animal models, still awaiting their detection in the human brain.

Preconditioning and tolerance against cerebral ischaemia: from experimental strategies to clinical use

Neuroprotection and brain repair in patients after acute brain damage are still major unfulfilled medical needs. Pharmacological treatments are either ineffective or confounded by adverse effects. Consequently, endogenous mechanisms by which the brain protects itself against noxious stimuli and recovers from damage are being studied. Research on preconditioning, also known as induced tolerance, over the past decade has resulted in various promising strategies for the treatment of patients with acute brain injury. Several of these strategies are being tested in randomised clinical trials. Additionally, research into preconditioning has led to the idea of prophylactically inducing protection in patients such as those undergoing brain surgery and those with transient ischaemic attack or subarachnoid haemorrhage who are at high risk of brain injury in the near future. In this Review, we focus on the clinical issues relating to preconditioning and tolerance in the brain; specifically, we discuss the clinical situations that might benefit from such procedures. We also discuss whether preconditioning and tolerance occur naturally in the brain and assess the most promising candidate strategies that are being investigated.