Early changes in extracellular amino acids and calcium concentrations in rabbit hippocampus following complete 15-min cerebral ischemia

Trans- and Cis-Phosphorylated Tau Protein: New Pieces of the Puzzle in the Development of Neurofibrillary Tangles in Post-Ischemic Brain Neurodegeneration of the Alzheimer's Disease-like Type

Recent evidence indicates that experimental brain ischemia leads to dementia with an Alzheimer's disease-like type phenotype and genotype. Based on the above evidence, it was hypothesized that brain ischemia may contribute to the development of Alzheimer's disease. Brain ischemia and Alzheimer's disease are two diseases characterized by similar changes in the hippocampus that are closely related to memory impairment. Following brain ischemia in animals and humans, the presence of amyloid plaques in the extracellular space and intracellular neurofibrillary tangles was revealed. The phenomenon of tau protein hyperphosphorylation is a similar pathological feature of both post-ischemic brain injury and Alzheimer's disease. In Alzheimer's disease, the phosphorylated Thr231 motif in tau protein has two distinct trans and cis conformations and is the primary site of tau protein phosphorylation in the pre-entanglement cascade and acts as an early precursor of tau protein neuropathology in the form of neurofibrillary tangles. Based on the latest publication, we present a similar mechanism of the formation of neurofibrillary tangles after brain ischemia as in Alzheimer's disease, established on trans- and cis-phosphorylation of tau protein, which ultimately influences the development of tauopathy.

A Look at the Etiology of Alzheimer's Disease based on the Brain Ischemia Model

Alzheimer's disease (AD) is the frequent form of dementia in the world. Despite over 100 years of research into the causes of AD, including amyloid and tau protein, the research has stalled and has not led to any conclusions. Moreover, numerous projects aimed at finding a cure for AD have also failed to achieve a breakthrough. Thus, the failure of anti-amyloid and anti-tau protein therapy to treat AD significantly influenced the way we began to think about the etiology of the disease. This situation prompted a group of researchers to focus on ischemic brain episodes, which, like AD, mostly present alterations in the hippocampus. In this context, it has been proposed that cerebral ischemic incidents may play a major role in promoting amyloid and tau protein in neurodegeneration in AD. In this review, we summarized the experimental and clinical research conducted over several years on the role of ischemic brain episodes in the development of AD. Studies have shown changes typical of AD in the course of brain neurodegeneration post-ischemia, i.e., progressive brain and hippocampal atrophy, increased amyloid production, and modification of tau protein. In the post-ischemic brain, the diffuse and senile amyloid plaques and the development of neurofibrillary tangles characteristic of AD were revealed. The above data evidently showed that after brain ischemia, there are modifications in protein folding, leading to massive neuronal death and damage to the neuronal network, which triggers dementia with the AD phenotype.

Alpha-, Beta-, and Gamma-Secretase, Amyloid Precursor Protein, and Tau Protein Genes in the Hippocampal CA3 Subfield in an Ischemic Model of Alzheimer's Disease with Survival up to 2 Years

Background

Understanding the phenomena underlying the non-selective susceptibility to ischemia of pyramidal neurons in the CA3 is important from the point of view of elucidating the mechanisms of memory loss and the development of dementia.

Objective

The aim of the study was to investigate changes in genes expression of amyloid precursor protein, its cleaving enzymes and tau protein in CA3 post-ischemia with survival of 12-24 months.

Methods

We used an ischemic model of Alzheimer's disease to study the above genes using an RT-PCR protocol.

Results

The expression of the amyloid precursor protein gene was above the control values at all times post-ischemia. The expression of the α-secretase gene also exceeded the control values post-ischemia. The expression of the β-secretase gene increased 12 and 24 months post-ischemia, and 18 months was below control values. Presenilin 1 and 2 genes expression was significantly elevated at all times post-ischemia. Also, tau protein gene expression was significantly elevated throughout the observation period, and peak gene expression was present 12 months post-ischemia.

Conclusions

The study suggests that the genes studied are involved in the non-amyloidogenic processing of amyloid precursor protein. Additionally data indicate that brain ischemia with long-term survival causes damage and death of pyramidal neurons in the CA3 area of the hippocampus in a modified tau protein-dependent manner. Thus defining a new and important mechanism of pyramidal neuronal death in the CA3 area post-ischemia. In addition expression of tau protein gene modification after brain ischemia is useful in identifying ischemic mechanisms occurring in Alzheimer's disease.

Blood and Brain Metabolites after Cerebral Ischemia

The study of an organism's response to cerebral ischemia at different levels is essential to understanding the mechanism of the injury and protection. A great interest is devoted to finding the links between quantitative metabolic changes and post-ischemic damage. This work aims to summarize the outcomes of the most studied metabolites in brain tissue-lactate, glutamine, GABA (4-aminobutyric acid), glutamate, and NAA (N-acetyl aspartate)-regarding their biological function in physiological conditions and their role after cerebral ischemia/reperfusion. We focused on ischemic damage and post-ischemic recovery in both experimental-including our results-as well as clinical studies. We discuss the role of blood glucose in view of the diverse impact of hyperglycemia, whether experimentally induced, caused by insulin resistance, or developed as a stress response to the cerebral ischemic event. Additionally, based on our and other studies, we analyze and critically discuss post-ischemic alterations in energy metabolites and the elevation of blood ketone bodies observed in the studies on rodents. To complete the schema, we discuss alterations in blood plasma circulating amino acids after cerebral ischemia. So far, no fundamental brain or blood metabolite(s) has been recognized as a relevant biological marker with the feasibility to determine the post-ischemic outcome or extent of ischemic damage. However, studies from our group on rats subjected to protective ischemic preconditioning showed that these animals did not develop post-ischemic hyperglycemia and manifested a decreased metabolic infringement and faster metabolomic recovery. The metabolomic approach is an additional tool for understanding damaging and/or restorative processes within the affected brain region reflected in the blood to uncover the response of the whole organism via interorgan metabolic communications to the stressful cerebral ischemic challenge.

Apitherapy in Post-Ischemic Brain Neurodegeneration of Alzheimer's Disease Proteinopathy: Focus on Honey and Its Flavonoids and Phenolic Acids

Neurodegeneration of the brain after ischemia is a major cause of severe, long-term disability, dementia, and mortality, which is a global problem. These phenomena are attributed to excitotoxicity, changes in the blood-brain barrier, neuroinflammation, oxidative stress, vasoconstriction, cerebral amyloid angiopathy, amyloid plaques, neurofibrillary tangles, and ultimately neuronal death. In addition, genetic factors such as post-ischemic changes in genetic programming in the expression of amyloid protein precursor, β-secretase, presenilin-1 and -2, and tau protein play an important role in the irreversible progression of post-ischemic neurodegeneration. Since current treatment is aimed at preventing symptoms such as dementia and disability, the search for causative therapy that would be helpful in preventing and treating post-ischemic neurodegeneration of Alzheimer's disease proteinopathy is ongoing. Numerous studies have shown that the high contents of flavonoids and phenolic acids in honey have antioxidant, anti-inflammatory, anti-apoptotic, anti-amyloid, anti-tau protein, anticholinesterase, serotonergic, and AMPAK activities, influencing signal transmission and neuroprotective effects. Notably, in many preclinical studies, flavonoids and phenolic acids, the main components of honey, were also effective when administered after ischemia, suggesting their possible use in promoting recovery in stroke patients. This review provides new insight into honey's potential to prevent brain ischemia as well as to ameliorate damage in advanced post-ischemic brain neurodegeneration.

Post-Ischemic Permeability of the Blood-Brain Barrier to Amyloid and Platelets as a Factor in the Maturation of Alzheimer's Disease-Type Brain Neurodegeneration

The aim of this review is to present evidence of the impact of ischemic changes in the blood-brain barrier on the maturation of post-ischemic brain neurodegeneration with features of Alzheimer's disease. Understanding the processes involved in the permeability of the post-ischemic blood-brain barrier during recirculation will provide clinically relevant knowledge regarding the neuropathological changes that ultimately lead to dementia of the Alzheimer's disease type. In this review, we try to distinguish between primary and secondary neuropathological processes during and after ischemia. Therefore, we can observe two hit stages that contribute to Alzheimer's disease development. The onset of ischemic brain pathology includes primary ischemic neuronal damage and death followed by the ischemic injury of the blood-brain barrier with serum leakage of amyloid into the brain tissue, leading to increased ischemic neuronal susceptibility to amyloid neurotoxicity, culminating in the formation of amyloid plaques and ending in full-blown dementia of the Alzheimer's disease type.

Selected Biomarkers of Oxidative Stress and Energy Metabolism Disorders in Neurological Diseases

Neurological diseases can be broadly divided according to causal factors into circulatory system disorders leading to ischemic stroke; degeneration of the nerve cells leading to neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) diseases, and immune system disorders; bioelectric activity (epileptic) problems; and genetically determined conditions as well as viral and bacterial infections developing inflammation. Regardless of the cause of neurological diseases, they are usually accompanied by disturbances of the central energy in a completely unexplained mechanism. The brain makes up only 2% of the human body's weight; however, while working, it uses as much as 20% of the energy obtained by the body. The energy requirements of the brain are very high, and regulatory mechanisms in the brain operate to ensure adequate neuronal activity. Therefore, an understanding of neuroenergetics is rapidly evolving from a "neurocentric" view to a more integrated picture involving cooperativity between structural and molecular factors in the central nervous system. This article reviewed selected molecular biomarkers of oxidative stress and energy metabolism disorders such as homocysteine, DNA damage such as 8-oxo2dG, genetic variants, and antioxidants such as glutathione in selected neurological diseases including ischemic stroke, AD, PD, and epilepsy. This review summarizes our and others' recent research on oxidative stress in neurological disorders. In the future, the diagnosis and treatment of neurological diseases may be substantially improved by identifying specific early markers of metabolic and energy disorders.

Melatonin: A Potential Candidate for the Treatment of Experimental and Clinical Perinatal Asphyxia

Perinatal asphyxia is considered to be one of the major causes of brain neurodegeneration in full-term newborns. The worst consequence of perinatal asphyxia is neurodegenerative brain damage, also known as hypoxic-ischemic encephalopathy. Hypoxic-ischemic encephalopathy is the leading cause of mortality in term newborns. To date, due to the complex mechanisms of brain damage, no effective or causal treatment has been developed that would ensure complete neuroprotection. Although hypothermia is the standard of care for hypoxic-ischemic encephalopathy, it does not affect all changes associated with encephalopathy. Therefore, there is a need to develop effective treatment strategies, namely research into new agents and therapies. In recent years, it has been pointed out that natural compounds with neuroprotective properties, such as melatonin, can be used in the treatment of hypoxic-ischemic encephalopathy. This natural substance with anti-inflammatory, antioxidant, anti-apoptotic and neurofunctional properties has been shown to have pleiotropic prophylactic or therapeutic effects, mainly against experimental brain neurodegeneration in hypoxic-ischemic neonates. Melatonin is a natural neuroprotective hormone, which makes it promising for the treatment of neurodegeneration after asphyxia. It is supposed that melatonin alone or in combination with hypothermia may improve neurological outcomes in infants with hypoxic-ischemic encephalopathy. Melatonin has been shown to be effective in the last 20 years of research, mainly in animals with perinatal asphyxia but, so far, no clinical trials have been performed on a sufficient number of newborns. In this review, we summarize the advantages and limitations of melatonin research in the treatment of experimental and clinical perinatal asphyxia.

Alzheimer's Disease Connected Genes in the Post-Ischemic Hippocampus and Temporal Cortex

It is considered that brain ischemia can be causative connected to Alzheimer’s disease. In the CA1 and CA3 regions of the hippocampus and temporal cortex, genes related to Alzheimer’s disease, such as the amyloid protein precursor (APP), β-secretase (BACE1), presenilin 1 (PSEN1) and 2 (PSEN2), are deregulated by ischemia. The pattern of change in the CA1 area of the hippocampus covers all genes tested, and the changes occur at all post-ischemic times. In contrast, the pattern of gene changes in the CA3 subfield is much less intense, does not occur at all post-ischemic times, and is delayed in time post-ischemia relative to the CA1 field. Conversely, the pattern of gene alterations in the temporal cortex appears immediately after ischemia, and does not occur at all post-ischemic times and does not affect all genes. Evidence therefore suggests that various forms of dysregulation of the APP, BACE1 and PSEN1 and PSEN2 genes are associated with individual neuronal cell responses in the CA1 and CA3 areas of the hippocampus and temporal cortex with reversible cerebral ischemia. Scientific data indicate that an ischemic episode of the brain is a trigger of amyloidogenic processes. From the information provided, it appears that post-ischemic brain injury additionally activates neuronal death in the hippocampus and temporal cortex in an amyloid-dependent manner.

Cross-Talk between Amyloid, Tau Protein and Free Radicals in Post-Ischemic Brain Neurodegeneration in the Form of Alzheimer’s Disease Proteinopathy

Recent years have seen remarkable progress in research into free radicals oxidative stress, particularly in the context of post-ischemic recirculation brain injury. Oxidative stress in post-ischemic tissues violates the integrity of the genome, causing DNA damage, death of neuronal, glial and vascular cells, and impaired neurological outcome after brain ischemia. Indeed, it is now known that DNA damage and repair play a key role in post-stroke white and gray matter remodeling, and restoring the integrity of the blood-brain barrier. This review will present one of the newly characterized mechanisms that emerged with genomic and proteomic development that led to brain ischemia to a new level of post-ischemic neuropathological mechanisms, such as the presence of amyloid plaques and the development of neurofibrillary tangles, which further exacerbate oxidative stress. Finally, we hypothesize that modified amyloid and the tau protein, along with the oxidative stress generated, are new key elements in the vicious circle important in the development of post-ischemic neurodegeneration in a type of Alzheimer’s disease proteinopathy.

Post-Ischemic Neurodegeneration of the Hippocampus Resembling Alzheimer's Disease Proteinopathy

In this review, we summarize, inter alia, the protein and gene changes associated with Alzheimer’s disease and their role in post-ischemic hippocampal neurodegeneration. In the hippocampus, studies have revealed dysregulation of the genes for the amyloid protein precursor metabolism and tau protein that is identical in nature to Alzheimer’s disease. Data indicate that amyloid and tau protein, derived from brain tissue and blood due to increased permeability of the blood–brain barrier after ischemia, play a key role in post-ischemic neurodegeneration of the hippocampus, with concomitant development of full-blown dementia. Thus, the knowledge of new neurodegenerative mechanisms that cause neurodegeneration of the hippocampus after ischemia, resembling Alzheimer’s disease proteinopathy, will provide the most important therapeutic development goals to date.

The Many Faces of Post-Ischemic Tau Protein in Brain Neurodegeneration of the Alzheimer's Disease Type

Recent data suggest that post-ischemic brain neurodegeneration in humans and animals is associated with the modified tau protein in a manner typical of Alzheimer’s disease neuropathology. Pathological changes in the tau protein, at the gene and protein level due to cerebral ischemia, can lead to the development of Alzheimer’s disease-type neuropathology and dementia. Some studies have shown increased tau protein staining and gene expression in neurons following ischemia-reperfusion brain injury. Recent studies have found the tau protein to be associated with oxidative stress, apoptosis, autophagy, excitotoxicity, neuroinflammation, blood-brain barrier permeability, mitochondrial dysfunction, and impaired neuronal function. In this review, we discuss the interrelationship of these phenomena with post-ischemic changes in the tau protein in the brain. The tau protein may be at the intersection of many pathological mechanisms due to severe neuropathological changes in the brain following ischemia. The data indicate that an episode of cerebral ischemia activates the damage and death of neurons in the hippocampus in a tau protein-dependent manner, thus determining a novel and important mechanism for the survival and/or death of neuronal cells following ischemia. In this review, we update our understanding of proteomic and genomic changes in the tau protein in post-ischemic brain injury and present the relationship between the modified tau protein and post-ischemic neuropathology and present a positive correlation between the modified tau protein and a post-ischemic neuropathology that has characteristics of Alzheimer’s disease-type neurodegeneration.

Neuroinflammation in Post-Ischemic Neurodegeneration of the Brain: Friend, Foe, or Both?

One of the leading causes of neurological mortality, disability, and dementia worldwide is cerebral ischemia. Among the many pathological phenomena, the immune system plays an important role in the development of post-ischemic degeneration of the brain, leading to the development of neuroinflammatory changes in the brain. After cerebral ischemia, the developing neuroinflammation causes additional damage to the brain cells, but on the other hand it also plays a beneficial role in repair activities. Inflammatory mediators are sources of signals that stimulate cells in the brain and promote penetration, e.g., T lymphocytes, monocytes, platelets, macrophages, leukocytes, and neutrophils from systemic circulation to the brain ischemic area, and this phenomenon contributes to further irreversible ischemic brain damage. In this review, we focus on the issues related to the neuroinflammation that occurs in the brain tissue after ischemia, with particular emphasis on ischemic stroke and its potential treatment strategies.

Participation of Amyloid and Tau Protein in Post-Ischemic Neurodegeneration of the Hippocampus of a Nature Identical to Alzheimer's Disease

Recent evidence suggests that amyloid and tau protein are of vital importance in post-ischemic death of CA1 pyramidal neurons of the hippocampus. In this review, we summarize protein alterations associated with Alzheimer's disease and their gene expression (amyloid protein precursor and tau protein) after cerebral ischemia, as well as their roles in post-ischemic hippocampus neurodegeneration. In recent years, multiple studies aimed to elucidate the post-ischemic processes in the development of hippocampus neurodegeneration. Their findings have revealed the dysregulation of genes for amyloid protein precursor, β-secretase, presenilin 1 and 2, tau protein, autophagy, mitophagy, and apoptosis identical in nature to Alzheimer's disease. Herein, we present the latest data showing that amyloid and tau protein associated with Alzheimer's disease and their genes play a key role in post-ischemic neurodegeneration of the hippocampus with subsequent development of dementia. Therefore, understanding the underlying process for the development of post-ischemic CA1 area neurodegeneration in the hippocampus in conjunction with Alzheimer's disease-related proteins and genes will provide the most important therapeutic development goals to date.

Myricetin as a Promising Molecule for the Treatment of Post-Ischemic Brain Neurodegeneration

The available drug therapy for post-ischemic neurodegeneration of the brain is symptomatic. This review provides an evaluation of possible dietary therapy for post-ischemic neurodegeneration with myricetin. The purpose of this review was to provide a comprehensive overview of what scientists have done regarding the benefits of myricetin in post-ischemic neurodegeneration. The data in this article contribute to a better understanding of the potential benefits of myricetin in the treatment of post-ischemic brain neurodegeneration, and inform physicians, scientists and patients, as well as their caregivers, about treatment options. Due to the pleiotropic properties of myricetin, including anti-amyloid, anti-phosphorylation of tau protein, anti-inflammatory, anti-oxidant and autophagous, as well as increasing acetylcholine, myricetin is a promising candidate for treatment after ischemia brain neurodegeneration with full-blown dementia. In this way, it may gain interest as a potential substance for the prophylaxis of the development of post-ischemic brain neurodegeneration. It is a safe substance, commercially available, inexpensive and registered as a pro-health product in the US and Europe. Taken together, the evidence available in the review on the therapeutic potential of myricetin provides helpful insight into the potential clinical utility of myricetin in treating neurodegenerative disorders with full-blown dementia. Therefore, myricetin may be a promising complementary agent in the future against the development of post-ischemic brain neurodegeneration. Indeed, there is a scientific rationale for the use of myricetin in the prevention and treatment of brain neurodegeneration caused by ischemia.

The Role of Gut Microbiota in an Ischemic Stroke

The intestinal microbiome, the largest reservoir of microorganisms in the human body, plays an important role in neurological development and aging as well as in brain disorders such as an ischemic stroke. Increasing knowledge about mediators and triggered pathways has contributed to a better understanding of the interaction between the gut-brain axis and the brain-gut axis. Intestinal bacteria produce neuroactive compounds and can modulate neuronal function, which affects behavior after an ischemic stroke. In addition, intestinal microorganisms affect host metabolism and immune status, which in turn affects the neuronal network in the ischemic brain. Here we discuss the latest results of animal and human research on two-way communication along the gut-brain axis in an ischemic stroke. Moreover, several reports have revealed the impact of an ischemic stroke on gut dysfunction and intestinal dysbiosis, highlighting the delicate play between the brain, intestines and microbiome after this acute brain injury. Despite our growing knowledge of intestinal microflora in shaping brain health, host metabolism, the immune system and disease progression, its therapeutic options in an ischemic stroke have not yet been fully utilized. This review shows the role of the gut microflora-brain axis in an ischemic stroke and assesses the potential role of intestinal microflora in the onset, progression and recovery post-stroke.

Participation of Amyloid and Tau Protein in Neuronal Death and Neurodegeneration after Brain Ischemia

Current evidence indicates that postischemic brain injury is associated with the accumulation of folding proteins, such as amyloid and tau protein, in the intra- and extracellular spaces of neuronal cells. In this review, we summarize protein changes associated with Alzheimer’s disease and their gene expression (amyloid protein precursor and tau protein) after brain ischemia, and their roles in the postischemic period. Recent advances in understanding the postischemic mechanisms in development of neurodegeneration have revealed dysregulation of amyloid protein precursor, α-, β- and γ-secretase and tau protein genes. Reduced expression of the α-secretase gene after brain ischemia with recirculation causes neuronal cells to be less resistant to injury. We present the latest data that Alzheimer’s disease-related proteins and their genes play a crucial role in postischemic neurodegeneration. Understanding the underlying processes of linking Alzheimer’s disease-related proteins and their genes in development of postischemic neurodegeneration will provide the most significant goals to date for therapeutic development.

Neuroprotection by Phytoestrogens in the Model of Deprivation and Resupply of Oxygen and Glucose In Vitro: The Contribution of Autophagy and Related Signaling Mechanisms

Phytoestrogens can have a neuroprotective effect towards ischemia-reperfusion-induced neuronal damage. However, their mechanism of action has not been well described. In this work, we investigate the type of neuronal cell death induced by oxygen and glucose deprivation (OGD) and resupply (OGDR) and pinpoint some of the signaling mechanisms whereby the neuroprotective effects of phytoestrogens occur in these conditions. First, we found that autophagy initiation affords neuronal protection upon neuronal damage induced by OGD and OGDR. The mammalian target of rapamycin/ribosomal S6 kinase (mTOR/S6K) pathway is blocked in these conditions, and we provide evidence that this is mediated by modulation of both the 5′ AMP-activated protein kinase (AMPK) and phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) pathways. These are dampened up or down, respectively, under OGDR-induced neuronal damage. In contrast, the MAPK-Erk kinase/extracellular signal-regulated kinase (MEK/ERK) pathway is increased under these conditions. Regarding the pathways affected by phytoestrogens, we show that their protective properties require autophagy initiation, but at later stages, they decrease mitogen-activated protein kinase (MAPK) and AMPK activation and increase mTOR/S6K activation. Collectively, our results put forward a novel mode of action where phytoestrogens play a dual role in the regulation of autophagy by acting as autophagy initiation enhancers when autophagy is a neuroprotective and pro-survival mechanism, and as autophagy initiation inhibitors when autophagy is a pro-death mechanism. Finally, our results support the therapeutic potential of phytoestrogens in brain ischemia by modulating autophagy.

Heterogeneity in brain distribution of activated microglia and astrocytes in a rat ischemic model of Alzheimer's disease after 2 years of survival

The present study was designed to follow neuroinflammation after ischemic brain injury in the long-term survival rat model. Immunohistochemistry was performed 2 years after 10 min global brain ischemia due to cardiac arrest. For the visualization of the cellular inflammatory reaction microglial marker Iba1 and astrocyte marker GFAP were used. In post-ischemic animals our study revealed significant activation of astrocytes in all tested brain regions (hippocampal CA1 and CA3 areas and dentate gyrus, motor and somatosensory cortex, striatum and thalamus), while microglial activation was only found in CA1 and CA3 areas, and the motor cortex. In the specifically sensitive brain areas microglia and astrocytes showed simultaneously significant activation, while in the resistant brain areas only astrocytes were activated. Thus, there was clear evidence of less intensive neuroinflammation in brain areas resistant to ischemia. Such neuroinflammatory processes are backed by microglia and astrocytes activity even up to 2 years after ischemia-reperfusion brain injury. Our study thus revealed a chronic effect of global cerebral ischemia on the neuroinflammatory reaction in the rat brain even 2 years after the insult.

Shared Genomic and Proteomic Contribution of Amyloid and Tau Protein Characteristic of Alzheimer's Disease to Brain Ischemia

Post-ischemic brain damage is associated with the deposition of folding proteins such as the amyloid and tau protein in the intra- and extracellular spaces of brain tissue. In this review, we summarize the protein changes associated with Alzheimer's disease and their gene expression (amyloid protein precursor and tau protein) after ischemia-reperfusion brain injury and their role in the post-ischemic injury. Recent advances in understanding the post-ischemic neuropathology have revealed dysregulation of amyloid protein precursor, α-secretase, β-secretase, presenilin 1 and 2, and tau protein genes after ischemic brain injury. However, reduced expression of the α-secretase in post-ischemic brain causes neurons to be less resistant to injury. In this review, we present the latest evidence that proteins associated with Alzheimer's disease and their genes play a key role in progressive brain damage due to ischemia and reperfusion, and that an ischemic episode is an essential and leading supplier of proteins and genes associated with Alzheimer's disease in post-ischemic brain. Understanding the underlying processes of linking Alzheimer's disease-related proteins and their genes in post-ischemic brain injury with the risk of developing Alzheimer's disease will provide the most significant goals for therapeutic development to date.

Proteomic and Genomic Changes in Tau Protein, Which Are Associated with Alzheimer's Disease after Ischemia-Reperfusion Brain Injury

Recent evidence suggests that transient ischemia of the brain with reperfusion in humans and animals is associated with the neuronal accumulation of neurotoxic molecules associated with Alzheimer’s disease, such as all parts of the amyloid protein precursor and modified tau protein. Pathological changes in the amyloid protein precursor and tau protein at the protein and gene level due to ischemia may lead to dementia of the Alzheimer’s disease type after ischemic brain injury. Some studies have demonstrated increased tau protein immunoreactivity in neuronal cells after brain ischemia-reperfusion injury. Recent research has presented many new tau protein functions, such as neural activity control, iron export, protection of genomic DNA integrity, neurogenesis and long-term depression. This review discusses the potential mechanisms of tau protein in the brain after ischemia, including oxidative stress, apoptosis, autophagy, excitotoxicity, neurological inflammation, endothelium, angiogenesis and mitochondrial dysfunction. In addition, attention was paid to the role of tau protein in damage to the neurovascular unit. Tau protein may be at the intersection of many regulatory mechanisms in the event of major neuropathological changes in ischemic stroke. Data show that brain ischemia activates neuronal changes and death in the hippocampus in a manner dependent on tau protein, thus determining a new and important way to regulate the survival and/or death of post-ischemic neurons. Meanwhile, the association between tau protein and ischemic stroke has not been well discussed. In this review, we aim to update the knowledge about the proteomic and genomic changes in tau protein following ischemia-reperfusion injury and the connection between dysfunctional tau protein and ischemic stroke pathology. Finally we present the positive correlation between tau protein dysfunction and the development of sporadic Alzheimer’s disease type of neurodegeneration.

Substantiation for the Use of Curcumin during the Development of Neurodegeneration after Brain Ischemia

Currently available pharmacological treatment of post-ischemia-reperfusion brain injury has limited effectiveness. This review provides an assessment of the current state of neurodegeneration treatment due to ischemia-reperfusion brain injury and focuses on the role of curcumin in the diet. The purpose of this review was to provide a comprehensive overview of what was published about the benefits of curcumin influence on post-ischemic brain damage. Some data on the clinical benefits of curcumin treatment of post-ischemic brain in terms of clinical symptoms and adverse reactions have been reviewed. The data in this review contributes to a better understanding of the potential benefits of curcumin in the treatment of neurodegenerative changes after ischemia and informs scientists, clinicians, and patients, as well as their families and caregivers about the possibilities of such treatment. Due to the pleotropic properties of curcumin, including anti-amyloid, anti-tau protein hyperphosphorylation, anti-inflammatory, anti-apoptotic, and neuroprotective action, as well as increasing neuronal lifespan and promoting neurogenesis, curcumin is a promising candidate for the treatment of post-ischemic neurodegeneration with misfolded proteins accumulation. In this way, it may gain interest as a potential therapy to prevent the development of neurodegenerative changes after cerebral ischemia. In addition, it is a safe substance and inexpensive, easily accessible, and can effectively penetrate the blood–brain barrier and neuronal membranes. In conclusion, the evidence available in a review of the literature on the therapeutic potential of curcumin provides helpful insight into the potential clinical utility of curcumin in the treatment of neurological neurodegenerative diseases with misfolded proteins. Therefore, curcumin may be a promising supplementary agent against development of neurodegeneration after brain ischemia in the future. Indeed, there is a rational scientific basis for the use of curcumin for the prophylaxis and treatment of post-ischemic neurodegeneration.

Expression of the Tau Protein and Amyloid Protein Precursor Processing Genes in the CA3 Area of the Hippocampus in the Ischemic Model of Alzheimer's Disease in the Rat

Understanding the mechanisms underlying the selective susceptibility to ischemia of the CA3 region is very important to explain the neuropathology of memory loss after brain ischemia. We used a rat model to study changes in gene expression of the amyloid protein precursor and its cleaving enzymes and tau protein in the hippocampal CA3 sector, after transient 10-min global brain ischemia with survival times of 2, 7, and 30 days. The expression of the α-secretase gene was below control values at all times studied. But, the expression of the β-secretase gene was below the control values at 2-7 days after ischemia and the maximal increase in its expression was observed on day 30. Expression of the presenilin 1 gene was significantly elevated above the control values at 2-7 days after ischemia and decreased below the control values at day 30. Expression of the presenilin 2 gene showed an opposite trend to the expression of presenilin 1. Expression of the amyloid protein precursor gene after ischemia was at all times above the control values with a huge significant overexpression on day 7. Additionally, the expression of the tau protein gene was below the control values 2 days after ischemia, but the significant increase in its expression was observed on days 7-30. Data show that brain ischemia activates neuronal changes and death in the CA3 region of the hippocampus in a manner dependent on amyloid and tau protein, thus determining a new and important way to regulate the survival and/or death of ischemic neurons.

Tonic Activation of Extrasynaptic NMDA Receptors Decreases Intrinsic Excitability and Promotes Bistability in a Model of Neuronal Activity

NMDA receptors (NMDA-R) typically contribute to excitatory synaptic transmission in the central nervous system. While calcium influx through NMDA-R plays a critical role in synaptic plasticity, experimental evidence indicates that NMDAR-mediated calcium influx also modifies neuronal excitability through the activation of calcium-activated potassium channels. This mechanism has not yet been studied theoretically. Our theoretical model provides a simple description of neuronal electrical activity that takes into account the tonic activity of extrasynaptic NMDA receptors and a cytosolic calcium compartment. We show that calcium influx mediated by the tonic activity of NMDA-R can be coupled directly to the activation of calcium-activated potassium channels, resulting in an overall inhibitory effect on neuronal excitability. Furthermore, the presence of tonic NMDA-R activity promotes bistability in electrical activity by dramatically increasing the stimulus interval where both a stable steady state and repetitive firing can coexist. These results could provide an intrinsic mechanism for the constitution of memory traces in neuronal circuits. They also shed light on the way by which β-amyloids can alter neuronal activity when interfering with NMDA-R in Alzheimer’s disease and cerebral ischemia.

Tau Protein Dysfunction after Brain Ischemia

Brain ischemia comprises blood-brain barrier, glial, and neuronal cells. The blood–brain barrier controls permeability of different substances and the composition of the neuronal cells ‘milieu’, which is required for their physiological functioning. Recent evidence indicates that brain ischemia itself and ischemic blood-brain barrier dysfunction is associated with the accumulation of neurotoxic molecules within brain tissue, e.g., different parts of amyloid-β protein precursor and changed pathologically tau protein. All these changes due to ischemia can initiate and progress neurodegeneration of the Alzheimer’s disease-type. This review presents brain ischemia and ischemic blood-brain barrier as a trigger for tau protein alterations. Thus, we hypothesize that the changes in pattern of phosphorylation of tau protein are critical to microtubule function especially in neurons, and contribute to the neurodegeneration following brain ischemia-reperfusion episodes with Alzheimer’s disease phenotype.

Neuroprotective and Neurological/Cognitive Enhancement Effects of Curcumin after Brain Ischemia Injury with Alzheimer's Disease Phenotype

In recent years, ongoing interest in ischemic brain injury research has provided data showing that ischemic episodes are involved in the development of Alzheimer's disease-like neuropathology. Brain ischemia is the second naturally occurring neuropathology, such as Alzheimer's disease, which causes the death of neurons in the CA1 region of the hippocampus. In addition, brain ischemia was considered the most effective predictor of the development of full-blown dementia of Alzheimer's disease phenotype with a debilitating effect on the patient. Recent knowledge on the activation of Alzheimer's disease-related genes and proteins-e.g., amyloid protein precursor and tau protein-as well as brain ischemia and Alzheimer's disease neuropathology indicate that similar processes contribute to neuronal death and disintegration of brain tissue in both disorders. Although brain ischemia is one of the main causes of death in the world, there is no effective therapy to improve the structural and functional outcomes of this disorder. In this review, we consider the promising role of the protective action of curcumin after ischemic brain injury. Studies of the pharmacological properties of curcumin after brain ischemia have shown that curcumin has several therapeutic properties that include anti-excitotoxic, anti-oxidant, anti-apoptotic, anti-hyperhomocysteinemia and anti-inflammatory effects, mitochondrial protection, as well as increasing neuronal lifespan and promoting neurogenesis. In addition, curcumin also exerts anti-amyloidogenic effects and affects the brain's tau protein. These results suggest that curcumin may be able to serve as a potential preventive and therapeutic agent in neurodegenerative brain disorders.

Exosomes as possible spread factor and potential biomarkers in Alzheimer's disease: current concepts

Increasing evidence points that important factors during development/spread of Alzheimer's disease in brain tissue are small extracellular vesicles, called exosomes. Exosomes comprise disease-related biomolecules such as the amyloid protein precursor, β-amyloid peptide and tau protein. Exosomes are hypothesized to facilitate the spread of β-amyloid peptide and tau protein from their cells of origin (e.g., neurons) to the extracellular space and to recipient cells to alter their phenotype and function. The roles of exosomes carry a rich biomolecules cargo in physiology and pathology is poorly understood. In this review, we will consider new information about the role of exosomes in Alzheimer's disease spreading and progression and underline their possible usefulness as the future diagnostic antemortem biomarkers in this devastating disorder.

Autophagy, mitophagy and apoptotic gene changes in the hippocampal CA1 area in a rat ischemic model of Alzheimer's disease

BACKGROUND

Postichemic brain injury correlates with poor prognosis since selectively vulnerable parts of brain are associated with apoptotic neuronal death. But autophagy has been recognized, as a probable survival mechanism following brain ischemia.

METHODS

We have analyzed, by quantitative reverse-transcriptase PCR assay protocol, three genes: autophagy, mitophagy and caspase 3 for neuronal death response in ischemic hippocampal CA1 area.

RESULTS

We have found that autophagy gene was not significantly modified at all time points after ischemia, whereas mitophagy and caspase 3 genes were upregulated at day 2 and decreased to basal values at days 7 and 30.

CONCLUSION

It may be inferred that mitophagy process markedly accompanies apoptosis during delayed neuronal death in hippocampal CA1 area following brain ischemia.

Neuroprotection of Ro25-6981 Against Ischemia/Reperfusion-Induced Brain Injury via Inhibition of Autophagy

In this study, we investigated the neuroprotective effect of Ro25-6981 against cerebral ischemia/reperfusion injury. Ro25-6981 alone or in combination with rapamycin was intracerebroventricularly administered to rats which suffered transient forebrain ischemia inducing by 4-vessel occlusion and reperfusion. Nissl staining was used to determine the survival of CA1 pyramidal cells of the hippocampus, while immunohistochemistry was performed to measure neuron-specific enolase (NSE) expression. The expression of autophagy-related proteins, such as microtubule-associated protein l light chain 3 (LC3), Beclin 1, and sequestosome 1 (p62), was assessed by immunoblotting. Nissl staining showed that neuronal damage was reduced in the hippocampal CA1 pyramidal layer in rats that received Ro25-6981. The protective effect of Ro25-6981 was dose-dependent, with a significant effect in the middle-dose range. The expression of NSE increased after Ro25-6981 treatment. Ro25-6981 significantly decreased LC3II (which is membrane bound) and Beclin 1, and increased p62. In addition, Ro25-6981 decreased rapamycin-induced neuronal damage and excessive activation of autophagy after I/R. Taken together, the results suggest that Ro25-6981 could suppress ischemic brain injury by regulating autophagy-related proteins during ischemia/reperfusion.

Dysregulation of Amyloid-β Protein Precursor, β-Secretase, Presenilin 1 and 2 Genes in the Rat Selectively Vulnerable CA1 Subfield of Hippocampus Following Transient Global Brain Ischemia

The interaction between brain ischemia and Alzheimer’s disease (AD) has been intensively investigated recently. Nevertheless, we have not yet understood the nature and mechanisms of the ischemic episodes triggering the onset of AD and how they influence its slow progression. The assumed connection between brain ischemia and the accumulation of amyloid-β (Aβ) peptide awaits to be clearly explained. In our research, we employed a rat cardiac arrest model to study the changes in gene expression of amyloid-β protein precursor (AβPP) and its cleaving enzymes, β- and γ-secretases (including presenilins) in hippocampal CA1 sector, following transient 10-min global brain ischemia. The quantitative reverse-transcriptase PCR assay demonstrated that the expression of all above genes that contribute to Aβ peptide generation was dysregulated during 30 days in postischemic hippocampal CA1 area. It suggests that studied Aβ peptide generation-related genes can be involved in AβPP metabolism, following global brain ischemia and will be useful to identify the molecular mechanisms underpinning that cerebral ischemia might be an etiological cause of AD via dysregulation of AβPP and its cleaving enzymes, β- and γ-secretases genes, and subsequently, it may increase Aβ peptide production and promote the gradual and slow development of AD neuropathology. Our data demonstrate that brain ischemia activates delayed neuronal death in hippocampus in an AβPP-dependent manner, thus defining a new and important mode of ischemic cell death.

Is the ischemic blood–brain barrier insufficiency responsible for full-blown Alzheimer's disease?

The goal of this paper is to provide scientists with a comprehensive review of the state-of-the-art influence the ischemic blood-brain barrier (BBB) has on the final development of Alzheimer's disease and to provide detailed food-for-thought which will hopefully stimulate more researchers in this area of neuroscience. Understanding new and fundamental concepts about the behavior of the BBB during long-term reperfusion after ischemia with a variety of new neuropathogenic factors can hopefully provide some interesting clues related to the pathologic processes issues that have been receiving considerable attention in the human clinic. We present the recent data to understand the role of the BBB in maturation of both diseases and try to differentiate between primary and secondary pathologic mechanisms. In conclusion, the neuropathogenesis of Alzheimer's disease involves an initial ischemic neuronal alterations leading to enhanced neuronal vulnerability to beta-amyloid peptide and the ischemic breakdown of the BBB with leakage of serum borne beta-amyloid peptide into brain parenchyma, activation of beta-amyloid peptide-dependent toxicity culminating in the formation of amyloid plaques and finally end in full-blown Alzheimer's disease. In summary, probably we have combined mechanism(s) of ischemia processes, ischemic and chronic BBB dysfunction and beta-amyloid peptide-dependent injury in pathology of neurodegeneration that is observed in Alzheimer's disease. We speculate that Alzheimer's disease may be caused by silent and sublethal ischemic episodes that attack and slowly steal the minds of its victims. Finally, our review proposes the ischemic BBB-dependent mechanism(s) that probably are responsible for full-blown Alzheimer's disease.

Alzheimer's mechanisms in ischemic brain degeneration

There is increasing evidence for influence of Alzheimer's proteins and neuropathology on ischemic brain injury. This review investigates the relationships between beta-amyloid peptide, apolipoproteins, presenilins, tau protein, alpha-synuclein, inflammation factors, and neuronal survival/death decisions in brain following ischemic episode. The interactions of these molecules and influence on beta-amyloid peptide synthesis and contribution to ischemic brain degeneration and finally to dementia are reviewed. Generation and deposition of beta-amyloid peptide and tau protein pathology are important key players involved in mechanisms in ischemic neurodegeneration as well as in Alzheimer's disease. Current evidence suggests that inflammatory process represents next component, which significantly contribute to degeneration progression. Although inflammation was initially thought to arise secondary to ischemic neurodegeneration, recent studies present that inflammatory mediators may stimulate amyloid precursor protein metabolism by upregulation of beta-secretase and therefore are able to establish a vicious cycle. Functional brain recovery after ischemic lesion was delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and beta-amyloid peptide. Moreover, ischemic neurodegeneration is strongly accelerated with aging, too. New therapeutic alternatives targeting these proteins and repairing related neuronal changes are under development for the treatment of ischemic brain consequences including memory loss prevention.

Neuroprotective effects of the agonist of metabotropic glutamate receptors ABHxD-I in two animal models of cerebral ischaemia

The neuroprotective efficacy of 2-aminobicyclo[2.1.1]hexane-2,5-dicarboxylic acid-I (ABHxD-I), a rigid agonist of metabotropic glutamate receptors, was studied using a 3-min global cerebral ischaemia model in Mongolian gerbils and the hypoxia/ischaemia model in 7-day-old rats. The effects on brain damage of ABHxD-I (30 mg/kg, intraperitoneally or 7.5 microg intracerebroventricularly) administered 30 min before global ischaemia or 30 min after hypoxia/ischaemia was evaluated 14 days after the insults. Treatment of adult gerbils with ABHxD-I injected i.c.v. but not systemically, prevented post-ischaemic hyperthermia and substantially reduced brain damage. These effects may reflect low permeability of the adult blood-brain barrier to ABHxD-I, and the role of reduced body and brain temperature in neuroprotection after its i.c.v. administration. ABHxD-I given either i.p. or i.c.v. to developing rats reduced brain damage by 55 and 37%, respectively, without affecting the body temperature. Due to immaturity and increased post-ischaemic permeability of the blood-brain barrier in developing rats, ABHxD-I may induce neuroprotection by direct interference with brain metabotropic glutamate receptors.

Regulation of phosphatidylethanolamine degradation by enzyme(s) of subcellular fractions from cerebral cortex

Hydrolysis of 1-acyl-2-[14C]arachidonoyl-sn-glycero-3-phosphoethanolamine was studied in cerebral cortex homogenate and subcellular fractions. The enzyme(s) confined to the synaptic plasma membrane (SPM) hydrolyze(s) [14C-arachidonoyl]phosphatidylethanolamine (PE) in the presence of EGTA to [14C-arachidonoyl]diacylglycerol (DAG) and a small amount of [14C]arachidonic acid (AA). Degradation of PE is time-, protein- and substrate-dependent with a pH optimum of 7.8. The highest activity of PE degradation was observed in the presence of 10 mM EGTA. Under this condition GTP gamma S has no effect on PE hydrolysis. In the presence of Ca2+ ions degradation of PE was significantly lower as compared to the conditions with EGTA. However, the percentage distribution of free AA in the sum of both products of PE hydrolysis (AA + DAG) increases from 16 and 20% observed in the presence of EGTA 2 mM and 10 mM to 34% and 43% in the presence of 0.5 mM CaCl2 alone and together with GTP gamma S, respectively. Cytosolic enzymes also degrade PE in the presence of 2 mM EGTA with the formation of DAG and AA. Radioactivity in the AA represents about 80% of the total radioactivity of the products of PE degradation. The hydrolysis of PE by cytosolic enzymes is almost completely inhibited by neomycin but the hydrolysis by the SPM-bound enzyme(s) is inhibited only 70%. Other studies with quinacrine indicated that only a small pool of PE is degraded by SPM-bound Ca(2+)-independent phospholipase A2 (PLA2). All of these data suggest that PE in cerebral cortex is mainly degraded by cytosolic and SPM-bound Ca(2+)-independent phospholipase C. Further studies towards a better understanding of the mechanisms of cerebral degradation and the physiological significance of Ca(2+)-independent pathways of PE hydrolysis are necessary.

Ultrastructural studies of cerebral vascular spasm after cardiac arrest-related global cerebral ischemia in rats

The present investigation was undertaken to study the ultrastructural morphology of brain blood vessels during vasospasm following total cerebral ischemia. Global cerebral ischemia was produced in rats by compression of the cardiac vessel bundle (i.e., cardiac arrest) using a metal hook that was introduced into the mediastinum. Ischemia lasted for 10 min with blood recirculation for 6, 12 and 24 h. Rat brains were perfusion-fixed and regions from the cerebral cortex and associated leptomeningeal vessels were evaluated by scanning and transmission electron microscopy. We noted three general vasoconstrictive responses in vessels of various sizes including veins and arteries. These alterations related to the smooth muscle cell arrangement associated with each constricted vessel including a circumferential, and longitudinal arrangement, or a combination of both types. Other features in the three types of vasoconstricted vessels included thickening of the vessel basement membranes with increased endothelial microfilaments and vesicular profiles. Our studies present evidence that ischemia of 10-min duration with blood reflow for 6, 12 and 24 h produces profound and variable vasospastic changes in some but not all vessels. These vascular alterations are thought to be caused in part by vasoactive substances released both by endothelial and blood cells and by perivascular cellular elements in response to the ischemic episode.

Complete cerebral ischemia with short-term survival in rat induced by cardiac arrest. II. Extracellular and intracellular accumulation of apolipoproteins E and J in the brain

The distribution of apolipoprotein E (apo E) and apolipoprotein J (apo J) was investigated immunocytochemically in rats at various time intervals after 10 min global cerebral ischemia (GCI) induced by cardiac arrest. Strong apo E and weaker apo J immunoreactivity was found extracellularly in multiple deposits located close to the microvessels. These deposits appeared 3 h after GCI and were present, but not in all the animals, at all time intervals studied post-GCL. In some rats, apo E immunoreactivity was also found in small necrotic foci. Widespread, neuronal apo E immunostaining appeared 6 h post-GCI. However, the strongest neuronal apo E immunoreactivity was found 7 days post-GCI in those neurons, most often observed in the CA1 hippocampal region, exhibiting signs of ischemic cell damage. These ischemically damaged neurons displayed weaker immunoreactivity to apo J, despite its increase in the response to GCI in the various brain regions examined. Our data show that mechanisms operating in ischemia are able to supply large amounts of apo E and apo J to the brain tissue and suggest involvement of both apo E and apo J in a complex series of events occurring in the ischemic brain. Perivascular deposits of apo E/apo J colocalized with amyloid beta protein precursor epitopes that have been disclosed by us previously in this model. Whether this phenomenon is limited to postischemic brain tissue, or can be encountered also in other pathological conditions will require further elaboration.

Early blood-brain barrier changes in the rat following transient complete cerebral ischemia induced by cardiac arrest

This study examined regional patterns of increased vascular permeability following transient global cerebral ischemia. Rats underwent 3.5, 5 or 10 min of cardiac vessel bundle occlusion, i.e. cardiac arrest. The animals were killed at 2, 3, 5 and 15 min, or 1, 3, 6 and 24 h after global cerebral ischemia. Thirty minutes before the end of each blood recirculation period, the electron dense protein tracer--horseradish peroxidase (HRP) was intravenously injected and rats were perfusion-fixed for light and electron microscopic analysis. Control rats showed no HRP leakage. Post-ischemic rats demonstrated random blood-brain barrier (BBB) alterations. Permeability alterations were spotty and widespread in cortical, thalamic, basal ganglia, hippocampal, brain stem regions, cerebellum and white matter. Peroxidase extravasation frequently involved arterioles, veins and venules surrounded by perivascular spaces. Routes of increased HRP permeability included endothelial cell (EC) vesiculo-canalicular profiles and diffuse leakage through damaged ECs. Barrier damage determined by HRP permeability revealed a biphasic nature. The first stage appeared immediately after ischemia at the 2nd min and involved the 1st post-insult hour. There was no HRP leakage in rats sacrificed 3 h after insult. BBB opening appeared again 6 h after ischemia and remained open 24 h after cardiac arrest. The openings of BBB did not increase in frequency with longer periods of ischemia and recirculation. These results demonstrate that cardiac arrest produces a spotty BBB disturbances at vessel bifurcations and suggest that BBB changes associated with cardiac arrest may be multifactorial in time course and location.

Microdialysis of interstitial amino acids during spreading depression and anoxic depolarization in rat neocortex

We have examined the effect of cortical spreading depression (SD) and anoxic depolarization (AD) on the interstitial concentration changes of amino acids (AA) in the neocortex of anesthetized rats using microdialysis and HPLC. Accompanying SD alanine increased to 126 +/- 11%, arginine to 116 +/- 3%, aspartate to 160 +/- 17%, glutamate to 163 +/- 9%, glycine to 158 +/- 21%, serine to 125 +/- 9%, and taurine to 172 +/- 15% (mean +/- 1 S.E.M.). The increases lasted for about 1 min. Histidine decreased to 74% +/- 4% at 1 min following SD, and returned to normal 4 min later. Cardiac arrest triggered AD after approximately 2 min, immediately followed by changes of interstitial AAs. At 5 min after AD alanine had increased to 183 +/- 13%, aspartate to 3,458 +/- 656%, GABA to 338 +/- 35%, glutamate to 1,696 +/- 546%, glycine to 297 +/- 37%, serine to 153 +/- 12%, and taurine to 1721 +/- 98% as compared to control values (mean +/- 1 S.E.M.). Histidine decreased to 78 +/- 2% at 3 min following AD while arginine exhibited insignificant variations around the baseline. The increase of glutamate during SD is consistent with activation of NMDA-receptors as an essential requirement for this reaction. The increase of AAs may also contribute to the sequence of events leading to AD, though the exact mechanism remains unknown. SD is an important pathophysiological mechanism of the ischemic penumbra associated with focal cerebral ischemia, while AD reflects the electrophysiological status of the infarct core.(ABSTRACT TRUNCATED AT 250 WORDS)

Detoxification with hemabsorption after cardiac arrest does not improve neurologic recovery. Review and outcome study in dogs

We and others hypothesized that noxious substances released after prolonged cardiac arrest from malfunctioning liver, kidneys, or intestine (e.g. bacterial toxins, aromatic amino acids), might hamper recovery of the brain. The highly detoxifying effect of hemabsorption (i.e. hemoperfusion) with microencapsulated activated carbon has been demonstrated in other diseases. We used our dog model of ventricular fibrillation cardiac arrest of 15 min (n = 2 x 4) or 12.5 min (n = 2 x 6), reversed by brief (high flow) cardiopulmonary bypass (CPB). In half of the dogs in each insult group, a charcoal filter (HemoKart) was inserted into the circuit of CPB at low flow, from start of reperfusion to 4 h. Intermittent positive pressure ventilation was to 20 h and intensive care to 96 h after cardiac arrest. Bacterial blood cultures were positive in most of the dogs in both groups 30 min to 20 h after cardiac arrest (but not later) and were uninfluenced by hemabsorption. In the control groups to 4 h after cardiac arrest, serum levels of potentially injurious aromatic amino acids (e.g. phenylalanine, tyrosine) and of branched-chain/aromatic amino acid ratios, remained unchanged. From 12 to 48 h after cardiac arrest, aromatic amino acid levels increased (worsened). The branched-chain/aromatic amino acid ratios changed accordingly in the opposite direction. In the hemabsorption groups to 4 h after cardiac arrest, all amino acid levels were reduced, aromatic amino acids more so than branched-chain amino acids, thus increasing (improving) the ratio, compared with controls (P < 0.01). There was no group difference after discontinuance of hemabsorption at 4 h. Outcome in terms of overall performance categories and neurologic deficit scores from 24 to 96 h and brain histopathologic damage scores 96 h after cardiac arrest, were not significantly different between groups. The lack of a beneficial outcome effect of hemabsorption to 4 h after cardiac arrest does not support the self-intoxication hypothesis. The amino acid levels later after cardiac arrest suggest that more prolonged hemabsorption and more encompassing detoxification treatments, such as plasma phoresis or total body blood washout, might be evaluated.

Effect of brain ischemia on protein kinase C

We examined the influence of brain ischemia on the activity and subcellular distribution of protein kinase C (PKC). Two different models of ischemic brain injury were used: postdecapitative ischemia in rat forebrain and transient (6-min) cerebral ischemia in gerbil hippocampus. In the rat forebrain model, at 5 and 15 min postdecapitation there was a steady decrease of total PKC activity to 60% of control values. This decrease occurred without changes in the proportion of the particulate to the soluble enzyme pools. Isolated rat brain membranes also exhibited a concomitant decrease of [3H]phorbol 12,13-dibutyrate ([3H]PDBu) binding with an apparent increase of the ligand affinity to the postischemic membranes. On the other hand, the ischemic gerbil hippocampus model displayed a 40% decrease of total PKC activity, which was accompanied by a relative increase of PKC activity in its membrane-bound form. This resulted in an increase in the membrane/total activity ratio, indicating a possible enzyme translocation from cytosol to the membranes after ischemia. Moreover, after 1 day of recovery, a statistically significant enhancement of membrane-bound PKC activity resulted in a further increase of its relative activity up to 162% of control values. In vitro experiments using a synaptoneurosomal particulate fraction were performed to clarify the mechanism of the rapid PKC inhibition observed in cerebral tissue after ischemia. These experiments showed a progressive, Ca(2+)-dependent, antiprotease-insensitive down-regulation of PKC during incubation. This down-regulation was significantly enhanced by prior phorbol (PDBu) treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Early postanoxic changes of polyphosphoinositides and bound Ca2+ content in relation to neuronal activity in brain cortex

We studied the changes in the content of membrane-bound calcium (Cab) and the polyphosphoinositides (poly-PI): bis- and trisphosphoinositide (PIP and PIP2) in the cat brain cortex during the early period (up to 30 min) of reoxygenation after 2.5 min and 5 min of anoxia. In vivo experiments were performed on a living cat cortical preparation. Studies included Cab estimation with clortetracycline, a calcium fluorescent chelate probe, and simultaneous registration of neuronal activity. Anoxia resulted in a significant drop of Cab and PIP2 in the cortex along with an absence of neuronal activity. During reoxygenation after 2.5 min of anoxia we observed an increase of Cab, however the Cab did not recover to the preanoxic level. An elevation of PIP and PIP2 content to 20% above the preanoxic level and recovery of neuronal activity with symptoms of hyperactivation were also observed. After 5 min of anoxia two qualitatively different types of changes were disclosed for the 30 min period of reoxygenation. In one half of the animals only slight symptoms of recovery in some of the indices were found. In the other group Cab and PIP2 content increased to a level significantly exceedingly the preanoxic one and abnormal spike activity appeared. Based on these results we suggest that disturbances in Ca- and poly-PI-related second messenger systems may significantly affect the recovery of neuronal function after anoxia.

Reassessment of a new model of complete cerebral ischemia in rats. Method of induction of clinical death, pathophysiology and cerebrovascular pathology

The present study was undertaken to ascertain the role of the microcirculation in the phenomenon of hypoperfusion following complete cerebral ischemia. The experiments were performed on rats under superficial ether anesthesia. Cerebral ischemia was induced by cardiac arrest for 3.5 or 10 min, with survival periods that lasted from 3 min to 7 days. A special metal hook-like device was inserted into the chest cavity at the third intercostal spaces for occluding the cardiac vessel bundle. The effect of this procedure was total cessation of systemic circulation, i.e., clinical death. In 52% of animals with 10-min clinical death, resuscitation (external heart massage and artificial ventilation) restored heart activity. When brain circulation was restored, respiratory activity, pain reaction, corneal reflex, bioelectric activity of the cortex, and normal activities of the rats returned. Scanning electron microscopy was applied to study the effect of ischemia on the vessel wall and endothelial cells (EC). Ischemia produced a remarkable increase in the numbers of microvilli and pit-like invaginations on the luminal EC surface. The luminal wall surface of many of the microvessels (MV) formed ridges. Frequently, microthrombi of varying sizes were observed. The most prominent changes were noted from 3 min to 6 h of recirculation, and they correlated with hypoperfusion after ischemia. Seven days later, these changes completely disappeared. The data presented here indicate that progressive hypoperfusion after ischemia occurs with significant alterations in the MV walls. These studies collectively suggest that the focal responses in select MVs may be associated with receptor molecule up-regulation of some, but not all, affected ECs. Our data provide further characterization of a new and unique chronic model of brain ischemia that can be applied to relevant clinical studies.

Prostacyclin attenuates in the rabbit hippocampus early consequences of transient complete cerebral ischemia

The effects of prostacyclin (PGI2) on ischemic changes of extracellular calcium concentration (CaE+2) and the blood-brain barrier (BBB) permeability were studied by microdialysis of the rabbit hippocampus. This was combined with morphological and neurophysiological observations. Complete cerebral ischemia lasting 15 min was produced by ligation of the brachiocephalic trunk, the left subclavian and both internal thoracic arteries. PGI2 was infused continuously i.v. in the last 3 min of ischemia and for 40 min after it, at a rate of 2 micrograms/kg/min. Control rabbits were submitted to untreated 15-min complete cerebral ischemia. The animals treated with PGI2 were found to have recovered bioelectric activity of the cortex and hippocampus in half the time that it took the untreated group. Application of PGI2 reduced by 60% the depth of ischemia-evoked drop of CaE+2 without acceleration of recovery during recirculation. The postischemic increase of BBB permeability to fluorescein was diminished. The number of morphologically changed neurons in the hippocampus of PGI2-treated animals was significantly lower than in the untreated group.

NMDA-, kainate- and quisqualate-stimulated release of taurine from electrophysiologically monitored rat hippocampal slices

While excitatory amino acids (EAAs) are known to evoke the release of taurine in the hippocampus, we have found that taurine is localized primarily in dendrites and only to a lesser extent in terminals in this region. To determine whether taurine is released as a neurotransmitter by non-toxic concentrations of EAAs, or exclusively as a neuroprotectant in response to excitotoxicity, we monitored the release of amino acids from hippocampal slices during simultaneous electrophysiological recording in the CA1 region to assess tissue viability. N-methyl-D-aspartate (NMDA) was the most potent of the EAA agonists tested for stimulating release of taurine. Exposure of slices to 120 microM NMDA increased the concentration of taurine in the perfusate to 1325% of its basal value. Kainate (KA) at a concentration of 128 microM increased taurine to 543% of baseline while quisqualate (Quis) at a concentration of 120 microM increase taurine to only 202% of its baseline value. Release of taurine in response to NMDA and KA peaked during the period when the concentration of the agonist was declining in the bath and did not return to its baseline value until 20 min after removal of the agonist. Increases in release of taurine were associated with concentrations of NMDA, KA, and Quis that caused an incomplete recovery of the CA1 field potential. These results suggest that taurine is primarily released by concentrations of glutamate receptor agonists that exhibit evidence of excitotoxicity in the CA1 region.

Blockade of N-methyl-D-aspartate-sensitive excitatory amino acid receptors with 2-amino-5-phosphonovalerate reduces ischemia-evoked calcium redistribution in rabbit hippocampus

To evaluate the participation of excitatory amino acid receptors sensitive to N-methyl-D-aspartate (NMDA) in ischemia-evoked redistribution of Ca2+ ions from the extra- to the intracellular compartment of the hippocampus, 2-amino-5-phosphonovalerate (APV), a specific antagonist of NMDA receptors, was administered to the rabbit hippocampus through a dialysis probe before, during, and after complete reversible 15-min cerebral ischemia. Microdialysis of the hippocampus allowed us to determine the changes in extracellular calcium and amino acid concentrations and to monitor the permeability of the blood-brain barrier (BBB) to fluorescein. Moreover, EEG and general physiological parameters were registered. APV significantly reduced the ischemic drop of calcium and increased the taurine and phosphoethanolamine content in the extracellular compartment, whereas changes in concentrations of other amino acids and BBB permeability were not modified. Local administration of APV also improved the recovery of EEG activity after ischemia. Inhibition by APV of ischemia-induced calcium redistribution in the hippocampus suggests a major role of NMDA receptors in the influx of calcium to hippocampal neurons during cerebral ischemia.

Beneficial effect of nimodipine on metabolic and functional disturbances in rabbit hippocampus following complete cerebral ischemia

We investigated the effects of intravenous application of nimodipine on the neurophysiologic, biochemical, and morphologic consequences of 15 minutes of global cerebral ischemia in seven rabbits. In vivo dialysis of the hippocampus was used to determine changes in extracellular concentrations of extracellular calcium and amino acids and blood-brain barrier permeability. Ischemia without treatment produced a rapid disappearance of electroencephalographic activity, a decrease in the concentration of extracellular calcium, the release of neuroactive amino acids, and leakage of methionine to the tissue fluid, plus a significant increase of the blood-brain barrier permeability to fluorescein. Except for permeability and electroencephalographic activity, these parameters normalized during 45 minutes of recirculation; permeability and activity failed to normalize completely during 3 hours of recirculation. After 3 hours of recirculation, morphologic changes in the CA1 hippocampal area were observed. Treatment with nimodipine significantly enhanced electroencephalographic activity recovery and normalization during recirculation, reduced the decrease in extracellular calcium concentration, and prevented the increased permeability of the blood-brain barrier. Nimodipine protected the CA1 area from early morphologic changes and reduced leakage of methionine from brain cells. The beneficial cytoprotective effect of nimodipine, probably related to normalization of calcium homeostasis and blood-brain barrier permeability after ischemia, may reflect both vascular and cellular sites of action.