Effects of acidosis on brain capillary endothelial cells and cholinergic neurons: relevance to vascular dementia and Alzheimer's disease

Sulfur-bridging the gap: investigating the electrochemistry of novel copper chelating agents for Alzheimer's disease applications

There is currently an unmet demand for multi-functional precision treatments for Alzheimer's disease (AD) after several failed attempts at designing drugs based on the amyloid hypothesis. The focus of this work is to investigate sulfur-bridged quinoline ligands that could potentially be used in chelation therapies for a subpopulation of AD patients presenting with an overload of labile copper ions, which are known to catalyze the production of reactive oxygen species (ROS) and exacerbate other markers of AD progression. The ligands 1-(2'-thiopyridyl)isoquinoline (1TPIQ) and 2-(2'-thiopyridyl)quinoline (2TPQ) were synthesized and characterized before being electrochemically investigated in the presence of different oxidizing and reducing agents in solution with a physiological pH relevant to the brain. The electrochemical response of each compound with copper was studied by employing both hydrogen peroxide (H2O2) as an oxidizing agent and ascorbic acid (AA) as an antioxidant during analysis using cyclic voltammetry (CV). The cyclic voltammograms of each quinoline were compared with similar ligands that contained aromatic N-donor groups but no sulfur groups to provide relative electrochemical properties of each complex in solution. In a dose-dependent manner, it was observed that AA exerted dual-efficacy when combined with these chelating ligands: promoting synergistic metal binding while also scavenging harmful ROS, suggesting AA is an effective adjuvant therapeutic agent. Overall, this study shows how coordination by sulfur-bridged quinoline ligands can alter copper electrochemistry in the presence of AA to limit ROS production in solution.

Involvement of brain metabolism in neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) affect a significant portion of the global population and have a substantial social and economic impact worldwide. Most NDDs manifest in early childhood and are characterized by deficits in cognition, communication, social interaction and motor control. Due to a limited understanding of the etiology of NDDs, current treatment options primarily focus on symptom management rather than on curative solutions. Moreover, research on NDDs is problematic due to its reliance on a neurocentric approach. However, recent studies are broadening the scope of research on NDDs, to include dysregulations within a diverse network of brain cell types, including vascular and glial cells. This review aims to summarize studies from the past few decades on potential new contributions to the etiology of NDDs, with a special focus on metabolic signatures of various brain cells. In particular, we aim to convey how the metabolic functions are intimately linked to the onset and/or progression of common NDDs such as autism spectrum disorders, fragile X syndrome, Rett syndrome and Down syndrome.

Recent advancements on in vitro blood-brain barrier model: A reliable and efficient screening approach for preclinical and clinical investigation

INTRODUCTION

The efficiency of brain therapeutics is greatly hindered by the blood-brain barrier (BBB). BBB's protective function, selective permeability, and dynamic functionality maintain the harmony between the brain and peripheral region. Thus, the design of any novel drug carrier system requires the complete study and investigation of BBB permeability, efflux transport, and the effect of associated cellular and non-vascular unit trafficking on BBB penetrability. The in vitro BBB models offer a most promising, and reliable mode of initial investigation of BBB permeability and associated factors as strong evidence for further preclinical and clinical investigation.

AREA COVERED

This review work covers the structure and functions of BBB components and different types of in vitro BBB models along with factors affecting BBB model development and model selection criteria.

EXPERT OPINION

In vivo models assume to reciprocate the physiological environment to the maximum extent. However, the interspecies variability, NVUs trafficking, dynamic behavior of BBB, etc., lead to non-reproducible results. The in vitro models are comparatively less complex, and flexible, as per the study design, could generate substantial evidence and help identify suitable in vivo animal model selection.

A synapsin Ⅰ cleavage fragment contributes to synaptic dysfunction in Alzheimer's disease

Synaptic dysfunction is a key feature of Alzheimer's disease (AD). However, the molecular mechanisms underlying synaptic dysfunction remain unclear. Here, we show that synapsin Ⅰ, one of the most important synaptic proteins, is fragmented by the cysteine proteinase asparagine endopeptidase (AEP). AEP cleaves synapsin at N82 in the brains of AD patients and generates the C‐terminal synapsin Ⅰ (83–705) fragment. This fragment is abnormally distributed in neurons and induces synaptic dysfunction. Overexpression of AEP in the hippocampus of wild‐type mice results in the production of the synapsin Ⅰ (83–705) fragment and induces synaptic dysfunction and cognitive deficits. Moreover, overexpression of the AEP‐generated synapsin Ⅰ (83–705) fragment in the hippocampus of tau P301S transgenic mice and wild‐type mice promotes synaptic dysfunction and cognitive deficits. These findings suggest a novel mechanism of synaptic dysfunction in AD.

In Vivo Monitoring of pH in Subacute PD Mouse Brains with a Ratiometric Electrochemical Microsensor Based on Poly(melamine) Films

In vivo monitoring of cerebral pH is of great significance because its disturbance is related to some pathological processes such as neurodegenerative diseases, for example, Parkinson's disease (PD). In this study, we developed an electrochemical microsensor based on poly(melamine) (P_Mel) films for ratiometric monitoring of pH in subacute PD mouse brains. In this microsensor, P_Mel films were prepared from a simple electropolymerization approach in a melamine-containing solution, serving as the selective pH recognition membrane undergoing a 2H⁺/2e^- process. Meanwhile, electrochemically oxidized graphene oxide (EOGO) produced a built-in correction signal which helped avoid the environmental interference of the complicated brain systems. The potential difference between the peaks generated from EOGO and P_Mel gradually decreased with the aqueous pH increasing from 4.0 to 9.0, constituting the detection foundation of the ratiometric electrochemical microsensor (REM). The in vitro studies demonstrated that this proposed method exhibited a high sensitivity (a Nernstian response of -61.35 mV/pH) and remarkable selectivity against amino acids, anions, cations, and biochemical and reactive oxygen species coexisting in the brain. Coupled with its excellent stability and reproducibility and good antibiofouling based on short-term detection, the developed REM could serve as a disposable sensor for the determination of cerebral pH in vivo. Its following successful application in the real-time measurement of pH in the striatum, hippocampus, and cortex of rat brains in the events of global cerebral ischemia/reperfusion verified the reliability of this method. Finally, we adopted this robust REM to systematically analyze and compare the average pH in different regions of normal and subacute PD mouse brains.

A γ-adducin cleavage fragment induces neurite deficits and synaptic dysfunction in Alzheimer's disease

Neurite deficits and synaptic dysfunction contribute to cognitive impairments in Alzheimer's disease (AD). However, the underlying molecular mechanisms remain unclear. Here, we show that γ-adducin, a cytoskeleton-associated protein that assembles the spectrin-actin framework, is cleaved by a lysosomal cysteine proteinase named asparagine endopeptidase (AEP). AEP is upregulated and activated during aging and cleaves γ-adducin at N357, disrupting spectrin-actin assembly. Moreover, γ-adducin (1-357) fragment downregulates the expression of Rac2, leading to defects in neurite outgrowth. Expression of the γ-adducin (1-357) fragment in the hippocampus of tau P301S transgenic mice resulted in significant AD-like pathology and cognitive deficits. In summary, AEP-mediated fragmentation of γ-adducin plays a vital role in AD. Blocking the activity of AEP might be a novel therapeutic target for AD.

Hypoxia, Acidification and Inflammation: Partners in Crime in Parkinson’s Disease Pathogenesis?

Like in other neurodegenerative diseases, protein aggregation, mitochondrial dysfunction, oxidative stress and neuroinflammation are hallmarks of Parkinson’s disease (PD). Differentiating characteristics of PD include the central role of α-synuclein in the aggregation pathology, a distinct vulnerability of the striato-nigral system with the related motor symptoms, as well as specific mitochondrial deficits. Which molecular alterations cause neurodegeneration and drive PD pathogenesis is poorly understood. Here, we summarize evidence of the involvement of three interdependent factors in PD and suggest that their interplay is likely a trigger and/or aggravator of PD-related neurodegeneration: hypoxia, acidification and inflammation. We aim to integrate the existing knowledge on the well-established role of inflammation and immunity, the emerging interest in the contribution of hypoxic insults and the rather neglected effects of brain acidification in PD pathogenesis. Their tight association as an important aspect of the disease merits detailed investigation. Consequences of related injuries are discussed in the context of aging and the interaction of different brain cell types, in particular with regard to potential consequences on the vulnerability of dopaminergic neurons in the substantia nigra. A special focus is put on the identification of current knowledge gaps and we emphasize the importance of related insights from other research fields, such as cancer research and immunometabolism, for neurodegeneration research. The highlighted interplay of hypoxia, acidification and inflammation is likely also of relevance for other neurodegenerative diseases, despite disease-specific biochemical and metabolic alterations.

Decreased pH in the aging brain and Alzheimer's disease

Using publicly available data sets, we compared pH in the human brain and the cerebrospinal fluid (CSF) of postmortem control and Alzheimer's disease cases. We further investigated the effects of long-term acidosis in vivo in the APP-PS1 mouse model of Alzheimer's disease. We finally examined in vitro whether low pH exposure could modulate the release of proinflammatory cytokines and the uptake of amyloid beta by microglia. In the human brain, pH decreased with aging. Similarly, we observed a reduction of pH in the brain of C57BL/6 mice with age. In addition, independent database analyses revealed that postmortem brain and CSF pH is further reduced in Alzheimer's disease cases compared with controls. Moreover, in vivo experiments showed that low pH CSF infusion increased amyloid beta plaque load in APP-PS1 mice. We further observed that mild acidosis reduced the amyloid beta 42-induced release of tumor necrosis factor-alpha by microglia and their capacity to uptake this peptide. Brain acidosis is associated with aging and might affect pathophysiological processes such as amyloid beta aggregation or inflammation in Alzheimer's disease.

Role of antioxidants and a nutrient rich diet in Alzheimer's disease

The joint attack on the body by metabolic acidosis and oxidative stress suggests that treatment in degenerative diseases, including Alzheimer's disease (AD), may require a normalizing of extracellular and intracellular pH with simultaneous supplementation of an antioxidant combination cocktail at a sufficiently high dose. Evidence is also accumulating that combinations of antioxidants may be more effective, taking advantage of synergistic effects of appropriate antioxidants as well as a nutrient-rich diet to prevent and reverse AD. This review focuses on nutritional, nutraceutical and antioxidant treatments of AD, although they can also be used in other chronic degenerative and neurodegenerative diseases.

Use of lanthanum for water treatment A matter of concern?

Among several other eutrophication management tools, Phoslock®, a lanthanum modified bentonite (LMB) clay, is now frequently used. Concerns have been raised as to whether exposure to Phoslock®-treated water may lead to lanthanum accumulation/toxicity in both animals and humans. In the present experimental study, rats were administered lanthanum orally as either lanthanum carbonate, lanthanum chloride or Phoslock® at doses of either 0.5 or 17 mg/L during 10 weeks. Controls received vehicle. The gastrointestinal absorption and tissue distribution of lanthanum was investigated. Extremely strict measures were implemented to avoid cross-contamination between different tissues or animals. Results showed no differences in gastrointestinal absorption between the different compounds under study as reflected by the serum lanthanum levels and concentrations found in the brain, bone, heart, spleen, lung, kidney and testes. At sacrifice, significant but equally increased lanthanum concentrations versus vehicle were observed in the liver for the highest dose of each compound which however, remained several orders of magnitude below the liver lanthanum concentration previously measured after long-term therapeutic administration of lanthanum carbonate and for which no hepatotoxicity was noticed in humans. In conclusion, (i) the use of LMB does not pose a toxicity risk (ii) gastrointestinal absorption of lanthanum is minimal and independent on the type of the compound, (iii) with exception of the liver, no significant increase in lanthanum levels is observed in the various organs under study, (iv) based on previous studies, the slightly increased liver lanthanum levels observed in a worst case scenario do not hold any risk of hepatotoxicity.

Normal brain aging and Alzheimer's disease are associated with lower cerebral pH: an in vivo histidine 1H-MR spectroscopy study

It is unclear whether alterations in cerebral pH underlie Alzheimer's disease (AD) and other dementias. We performed proton spectroscopy after oral administration of histidine in healthy young and elderly persons and in patients with mild cognitive impairment and dementia (total N = 147). We measured cerebral tissue pH and ratios of common brain metabolites in relation to phosphocreatine and creatine (Cr) in spectra acquired from the hippocampus, the white matter (WM) of the centrum semiovale, and the cerebellum. Hippocampal pH was inversely associated with age in healthy participants but did not differ between patients and controls. WM pH was low in AD and, to a lesser extent, mild cognitive impairment but not in frontotemporal dementia spectrum disorders and pure vascular dementia. Furthermore, WM pH provided incremental diagnostic value in addition to N-acetylaspartate to Cr ratio. Our study suggests that in vivo assessment of pH may be a useful marker for the differentiation between AD and other types of dementia.

Role of monocarboxylate transporter 4 in Alzheimer disease

The pathological process of Alzheimer disease (AD) is closely related to energy metabolism disorders. In the nervous system, monocarboxylate transporter 4 (MCT4) is expressed in the glial cell membrane and is responsible for transporting intracellular lactic acid. In this study, we found that MCT4 expression was elevated in the cerebrospinal fluid of patients with mild cognitive impairment. Two- and three-month-old APPswe/PS1dE9 (APP/PS1) mice and C57 mice were studied. The APP/PS1 mice began to show cognitive decline at 3 months of age and MCT4 in the hippocampus of 2- and 3-month old APP/PS1 mice was higher than that of C57 mice. This change is similar to that in people with mild cognitive impairment. Subsequently, MCT4 overexpression/siRNA lentiviral particles were used to establish stable primary astrocytes. Overexpression and knockdown of MCT4 had no significant effect on glial cell apoptosis. Transfected astrocytes were co-cultured with neurons. Overexpression of cytoplasmic MCT4 increased the expression of Aβ42, γ-secretase, and CD147 in the co-culture system; in addition, the growth ability of primary neurons decreased significantly, extracellular lactic acid increased, and neuronal apoptosis increased. In AD model mice, siMCT4 injection improved cognitive ability, reduced neuronal apoptosis, and reduced γ-secretase expression. Taken together, these results suggest that MCT4 is involved in energy metabolism during early pathological processes in AD, and suppression of MCT4 represents a new potential neuroprotective factor for AD.

The evidence for the physiological effects of lactate on the cerebral microcirculation: a systematic review

Abstract

Lactate's role in the brain is understood as a contributor to brain energy metabolism, but it may also regulate the cerebral microcirculation. The purpose of this systematic review was to evaluate evidence of lactate as a physiological effector within the normal cerebral microcirculation in reports ranging from in vitro experiments to in vivo studies in animals and humans. Following pre‐registration of a review protocol, we systematically searched the PubMed, EMBASE, and Cochrane databases for literature covering themes of ‘lactate’, ‘the brain’, and ‘microcirculation’. Abstracts were screened, and data extracted independently by two individuals. We excluded studies evaluating lactate in disease models. Twenty‐eight papers were identified, 18 of which were in vivo animal experiments (65%), four on human studies (14%), and six on in vitro or ex vivo experiments (21%). Approximately half of the papers identified lactate as an augmenter of the hyperemic response to functional activation by a visual stimulus or as an instigator of hyperemia in a dose‐dependent manner, without external stimulation. The mechanisms are likely to be coupled to NAD⁺/NADH redox state influencing the production of nitric oxide. Unfortunately, only 38% of these studies demonstrated any control for bias, which makes reliable generalizations of the conclusions insecure. This systematic review identifies that lactate may act as a dose‐dependent regulator of cerebral microcirculation by augmenting the hyperemic response to functional activation below 5 mmol/kg, and by initiating a hyperemic response above 5 mmol/kg.

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Associations between Sleep, Cortisol Regulation, and Diet: Possible Implications for the Risk of Alzheimer Disease

Accumulation of proteinaceous amyloid β plaques and tau oligomers may occur several years before the onset of Alzheimer disease (AD). Under normal circumstances, misfolded proteins get cleared by proteasome degradation, autophagy, and the recently discovered brain glymphatic system, an astroglial-mediated interstitial fluid bulk flow. It has been shown that the activity of the glymphatic system is higher during sleep and disengaged or low during wakefulness. As a consequence, poor sleep quality, which is associated with dementia, might negatively affect glymphatic system activity, thus contributing to amyloid accumulation. The diet is another important factor to consider in the regulation of this complex network. Diets characterized by high intakes of refined sugars, salt, animal-derived proteins and fats and by low intakes of fruit and vegetables are associated with a higher risk of AD and can perturb the circadian modulation of cortisol secretion, which is associated with poor sleep quality. For this reason, diets and nutritional interventions aimed at restoring cortisol concentrations may ease sleep disorders and may facilitate brain clearance, consequentially reducing the risk of cognitive impairment and dementia. Here, we describe the associations that exist between sleep, cortisol regulation, and diet and their possible implications for the risk of cognitive impairment and AD.

Interaction of the Heparin-Binding Consensus Sequence of β-Amyloid Peptides with Heparin and Heparin-Derived Oligosaccharides

Alzheimer's disease (AD) is characterized by the presence of amyloid plaques in the AD brain. Comprised primarily of the 40- and 42-residue β-amyloid (Aβ) peptides, there is evidence that the heparan sulfate (HS) of heparan sulfate proteoglycans (HSPGs) plays a role in amyloid plaque formation and stability; however, details of the interaction of Aβ peptides with HS are not known. We have characterized the interaction of heparin and heparin-derived oligosaccharides with a model peptide for the heparin- and HS-binding domain of Aβ peptides (Ac-VHHQKLV-NH2; Aβ(12-18)), with mutants of Aβ(12-18), and with additional histidine-containing peptides. The nature of the binding interaction was characterized by NMR, binding constants and other thermodynamic parameters were determined by isothermal titration calorimetry (ITC), and relative binding affinities were determined by heparin affinity chromatography. The binding of Aβ(12-18) by heparin and heparin-derived oligosaccharides is pH-dependent, with the imidazolium groups of the histidine side chains interacting site-specifically within a cleft created by a trisaccharide sequence of heparin, the binding is mediated by electrostatic interactions, and there is a significant entropic contribution to the binding free energy as a result of displacement of Na(+) ions from heparin upon binding of cationic Aβ(12-18). The binding constant decreases as the size of the heparin-derived oligosaccharide decreases and as the concentration of Na(+) ion in the bulk solution increases. Structure-binding relationships characterized in this study are analyzed and discussed in terms of the counterion condensation theory of the binding of cationic peptides by anionic polyelectrolytes.

Acid-sensing ion channel 1a contributes to the effect of extracellular acidosis on NLRP1 inflammasome activation in cortical neurons

Background

Acid-sensing ion channels (ASICs) are cation channels which were activated by extracellular acidosis and involved in various physiological and pathological processes in the nervous system. Inflammasome is a key component of the innate immune response in host against harmful and irritable stimuli. As the first discovered molecular platform, NLRP1 (nucleotide-binding oligomerization domain (NOD)-like receptor protein 1) inflammasome is expressed in neurons and implicated in many nervous system diseases such as brain injury, nociception and epilepsy. However, little is known about the effect of ASICs on NLRP1 inflammasome activation under acidosis.

Methods

The expression of inflammasome complex protein (NLRP1, ASC (apoptosis-associated speck-like protein containing a caspase-activating recruitment domain) and caspase-1), inflammatory cytokines (IL-1β and IL-18), and apoptosis-related protein (Bax, Bcl-2, and activated caspase-3) was detected by Western blot. Large-conductance Ca²⁺ and voltage-activated K⁺ (BK) channel currents were recorded by whole-cell patch-clamp technology. Measurement of [K⁺]_i was performed by fluorescent ion imaging system. Co-expression of ASICs and BK channels was determined by dual immunofluorescence. Cell viability was assessed by MTT and LDH kit.

Results

ASICs and BK channels were co-expressed in primary cultured cortical neurons. Extracellular acidosis increased the expression of NLRP1, ASC, caspase-1, IL-1β, and IL-18. Further mechanistic studies revealed that acidosis-induced ASIC1a activation results in the increase of BK channel currents, with the subsequent K⁺ efflux and a low concentration of intracellular K⁺, which activated NLRP1 inflammasome. Furthermore, these effects of acidosis could be blocked by specific ASIC1a inhibitor PcTX1 and BK channel inhibitor IbTX. The data also demonstrated neutralization of NLRP1-protected cortical neurons against injury induced by extracellular acidosis.

Conclusions

Our data showed that NLRP1 inflammasome could be activated by extracellular acidosis though ASIC-BK channel K⁺ signal pathway and was involved in extracellular acidosis-induced cortical neuronal injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0465-7) contains supplementary material, which is available to authorized users.

Acid-Sensing Ion Channels as Potential Pharmacological Targets in Peripheral and Central Nervous System Diseases

Acid-sensing ion channels (ASICs) are widely expressed in the body and represent good sensors for detecting protons. The pH drop in the nervous system is equivalent to ischemia and acidosis, and ASICs are very good detectors in discriminating slight changes in acidity. ASICs are important pharmacological targets being involved in a variety of pathophysiological processes affecting both the peripheral nervous system (e.g., peripheral pain, diabetic neuropathy) and the central nervous system (e.g., stroke, epilepsy, migraine, anxiety, fear, depression, neurodegenerative diseases, etc.). This review discusses the role played by ASICs in different pathologies and the pharmacological agents acting on ASICs that might represent promising drugs. As the majority of above-mentioned pathologies involve not only neuronal dysfunctions but also microvascular alterations, in the next future, ASICs may be also considered as potential pharmacological targets at the vasculature level. Perspectives and limitations in the use of ASICs antagonists and modulators as pharmaceutical agents are also discussed.

Organotypic brain slice cultures as a model to study angiogenesis of brain vessels

Brain vessels are the most important structures in the brain to deliver energy and substrates to neurons. Brain vessels are composed of a complex interaction between endothelial cells, pericytes, and astrocytes, controlling the entry of substrates into the brain. Damage of brain vessels and vascular impairment are general pathologies observed in different neurodegenerative disorders including e.g., Alzheimer's disease. In order to study remodeling of brain vessels, simple 3-dimensional in vitro systems need to be developed. Organotypic brain slices of mice provide a potent tool to explore angiogenic effects of brain vessels in a complex 3-dimensional structure. Here we show that organotypic brain slices can be cultured from 110 μm thick sections of postnatal and adult mice brains. The vessels are immunohistochemically stained for laminin and collagen IV. Co-stainings are an appropriate method to visualize interaction of brain endothelial cells with pericytes and astrocytes in these vessels. Different exogenous stimuli such as fibroblast growth factor-2 or vascular endothelial growth factor induce angiogenesis or re-growth, respectively. Hyperthermia or acidosis reduces the vessel density in organotypic slices. In conclusion, organotypic brain slices exhibit a strong vascular network which can be used to study remodeling and angiogenesis of brain vessels in a 3-dimensional in vitro system.

Systemic physiology and neuroapoptotic profiles in young and adult rats exposed to surgery: A randomized controlled study comprising four different anaesthetic techniques

BACKGROUND

Experimental evidence indicates that general anaesthetics can induce apoptotic neurodegeneration in the developing brain. The majority of these studies have been performed in the absence of surgery and it currently remains unclear how the presence of surgical stimuli would influence neuroapoptosis as well as systemic homeostasis. Here we explored this possibility by performing dorsal skin flap surgery in young and adult rats under four distinct currently used anaesthesia regimens.

METHODS

Young (21-days) and adult (2 months) male Sprague-Dawley rats were randomized to 150 min exposure to one of four anaesthetics regimens: (i) sevoflurane/dexmedetomidine, (ii) sevoflurane/fentanyl; (iii) propofol/dexmedetomidine, and (iv) propofol/fentanyl. Animals underwent a dorsal skin flap procedure while physiologic, metabolic and biochemical parameters were closely monitored. Neuroapoptotic profiles were evaluated in the cortex, thalamus and hippocampus (CA1 and CA3) at the end of the procedure in each experimental group.

RESULTS

Significant perturbations of systemic homeostasis were found under all anaesthetic regimens. Hyperglycemia and decreased heart rate were particularly relevant in experimental groups receiving dexmedetomidine, while propofol administration was associated with increased systemic lactate levels and metabolic acidosis. A substantial difference in anaesthesia/surgery-induced neuroapoptosis was found between young and adult rats in several brain regions. Combination of sevoflurane and dexmedetomidine resulted in the highest number of caspase-3 positive cells, although the extent of cell death remained relatively low in all experimental groups.

CONCLUSION

Combination of anaesthesia and surgery induces significant perturbations of physiological parameters in both young and adult spontaneously breathing rats undergoing surgery. These observations further enlighten the need for detailed physiological monitoring under these experimental conditions. Although some statistically significant differences in activated caspase-3 profiles were detected between experimental groups, the overall extent of neuronal cell death remained very low under all conditions questioning, thereby, the physiological significance of apoptotic neurodegeneration in the context of anaesthesia and surgery.

Does closure of acid-sensing ion channels reduce ischemia/reperfusion injury in the rat brain?

Acidosis is a common characteristic of brain damage. Because studies have shown that permeable Ca²⁺-acid-sensing ion channels can mediate the toxic effects of calcium ions, they have become new targets against pain and various intracranial diseases. However, the mechanism associated with expression of these channels remains unclear. This study sought to observe the expression characteristics of permeable Ca²⁺-acid-sensing ion channels during different reperfusion inflows in rats after cerebral ischemia. The rat models were randomly divided into three groups: adaptive ischemia/reperfusion group, one-time ischemia/reperfusion group, and severe cerebral ischemic injury group. Western blot assays and immunofluorescence staining results exhibited that when compared with the one-time ischemia/reperfusion group, acid-sensing ion channel 3 and Bcl-x/l expression decreased in the adaptive ischemia/reperfusion group. Calmodulin expression was lowest in the adaptive ischemia/reperfusion group. Following adaptive reperfusion, common carotid artery flow was close to normal, and the pH value improved. Results verified that adaptive reperfusion following cerebral ischemia can suppress acid-sensing ion channel 3 expression, significantly reduce Ca²⁺ influx, inhibit calcium overload, and diminish Ca²⁺ toxicity. The effects of adaptive ischemia/reperfusion on suppressing cell apoptosis and relieving brain damage were better than that of one-time ischemia/reperfusion.

Delivery of Polymeric Nanoparticles to Target Vascular Diseases

Current advances in nanotechnology have paved the way for the early detection, prevention and treatment of various diseases such as vascular disorders and cancer. These advances have provided novel approaches or modalities of incorporating or adsorbing therapeutic, biosensor and targeting agents into/on nanoparticles. With significant progress, nanomedicine for vascular therapy has shown significant advantages over traditional medicine because of its ability to selectively target the disease site and reduce adverse side effects. Targeted delivery of nanoparticles to vascular endothelial cells or the vascular wall provides an effective and more efficient way for early detection and/or treatment of vascular diseases such as atherosclerosis, thrombosis and Cerebrovascular Amyloid Angiopathy (CAA). Clinical applications of biocompatible and biodegradable polymers in areas such as vascular graft, implantable drug delivery, stent devices and tissue engineering scaffolds have advanced the candidature of polymers as potential nano-carriers for vascular-targeted delivery of diagnostic agents and drugs. This review focuses on the basic aspects of the vasculature and its associated diseases and relates them to polymeric nanoparticle-based strategies for targeting therapeutic agents to diseased vascular site.

The acidic pH-induced structural changes in Pin1 as revealed by spectral methodologies

Pin1 is closely associated with the pathogenesis of cancers and Alzheimer's disease (AD). Previously, we have shown the characteristics of the thermal denaturation of Pin1. Herein, the acid-induced denaturation of Pin1 was determined by means of fluorescence emission, synchronous fluorescence, far-UV CD, ANS fluorescence and RLS spectroscopies. The fluorescence emission spectra and the synchronous fluorescence spectra suggested the partially reversible unfolding (approximately from pH 7.0 to 4.0) and refolding (approximately from pH 4.0 to 1.0) of the structures around the chromophores in Pin1, apparently with an intermediate state at about pH 4.0-4.5. The far-UV CD spectra indicated that acidic pH (below pH 4.0) induced the structural transition from α-helix and random coils to β-sheet in Pin1. The ANS fluorescence and the RLS spectra further suggested the exposure of the hydrophobic side-chains of Pin1 and the aggregation of it especially below pH 2.3, and the aggregation possibly resulted in the formation of extra intermolecular β-sheet. The present work primarily shows that acidic pH can induce kinds of irreversible structural changes in Pin1, such as the exposure of the hydrophobic side-chains, the transition from α-helix to β-sheet and the aggregation of Pin1, and also explains why Pin1 loses most of its activity below pH 5.0. The results emphasize the important role of decreased pH in the pathogenesis of some Pin1-related diseases, and support the therapeutic approach for them by targeting acidosis and modifying the intracellular pH gradients.

Homocysteine has anti-inflammatory properties in a hypercholesterolemic rat model in vivo

Inflammation is a hallmark in many neurodegenerative diseases like Alzheimer's disease or vascular dementia. Cholesterol and homocysteine are both vascular risk factors which have been associated with dementia, inflammation and blood–brain barrier dysfunction. In previous studies we found that hypercholesterolemia but not hyperhomocysteinemia induced inflammation in rats in vivo. The aim of the present study was to investigate the effect of a combined treatment of Sprague Dawley rats with cholesterol and homocysteine for 5 months on spatial learning and memory, blood–brain barrier integrity and inflammation. Cholesterol treated rats showed severe learning deficits, while rats treated with cholesterol and homocysteine (Mix) counteracted the cholesterol-induced inflammation and partly the cortical blood–brain barrier disruptions, although cognition was still impaired. To study the potential protective effect of homocysteine, inflammation was induced in organotypic rat brain cortex slices and primary microglial cells by treatment with different inflammatory stimuli (e.g. lipopolysaccharide or tissue plasminogen activator). Tissue plasminogen activator-induced inflammation was counteracted by homocysteine. In conclusion, our data demonstrate that homocysteine significantly ameliorates cholesterol-induced inflammation and blood–brain barrier disruption but not the memory impairment, possibly involving a tissue plasminogen activator-related mechanism.

Galactose counteracts hypoglycemia-induced decline of cholinergic neurons at low pH in organotypic rat brain slices of the basal nucleus of Meynert

A growing body of evidence indicates that hypoglycemia and acidosis may contribute to the development of Alzheimer's disease (AD). The cell death of basal forebrain cholinergic neurons constitutes a hallmark of AD and directly correlates with cognitive impairment. The aim of the present study was to investigate, in an organotypic rat brain slice model of the basal nucleus of Meynert, the effects of glucose deprivation on cholinergic neurons under normal and acidic conditions. Furthermore, we were interested to explore whether different saccharides (galactose, fructose, saccharose, lactose) can replace glucose under low pH conditions. Our data show a pH-dependent survival of cholinergic neurons at a high (37.1 mmol/l) glucose level, which was markedly decreased at a low (5.6 mmol/l) glucose level. Galactose (+31.5 mmol/l) significantly counteracted the loss of choline acetyltransferase-positive neurons in low-glucose-treated slices, while fructose, lactose and saccharose only partly protected cholinergic neurons. In conclusion, our results indicate that replacement of glucose with different saccharides, but most potently with galactose, protects cholinergic neurons against hypoglycemia at a low pH.

Acidosis, acid-sensing ion channels, and neuronal cell death

Acidosis is a common feature of many neuronal diseases and often accompanied with adverse consequences such as pain and neuronal injury. Before the discovery of acid-sensing ion channels (ASICs), protons were usually considered as a modulator of other ion channels, such as voltage-gated calcium channels, N-methyl-D-aspartate, and γ-amino butyric acid(A) receptor channels. Accordingly, the functional effects of acidosis were considered as consequences of modulations of these channels. Since the first cloning of ASICs in 1997, the conventional view on acidosis-mediated pain and cell injury has been dramatically changed. To date, ASICs, which are directly activated by extracellular protons, are shown to mediate most of the acidosis-associated physiological and pathological functions. For example, ASIC1a channels are reported to mediate acidosis-induced ischemic neuronal death. In this article, we will review the possible mechanisms that underlie ASIC1a channel-mediated neuronal death and discuss ASIC1a channel modulators involved in this process.

Differential effects of short- and long-term hyperhomocysteinaemia on cholinergic neurons, spatial memory and microbleedings in vivo in rats

Hyperhomocysteinaemia (HHcy) has been identified as a cardiovascular risk factor for neurodegenerative brain diseases. The aim of the present study was to investigate the effects of short (5 months) or long (15 months) HHcy in Sprague–Dawley rats in vivo. Short- and long-term HHcy differentially affected spatial memory as tested in a partially baited eight-arm radial maze. HHcy significantly reduced the number of choline acetyltransferase (ChAT)-positive neurons in the basal nucleus of Meynert and ChAT-positive axons in the cortex only after short-term but not long-term treatment, while acetylcholine levels in the cortex were decreased at both time points. Nerve growth factor (NGF) was significantly enhanced in the cortex only after 15 months of HHcy. HHcy did not affect cortical levels of amyloid precursor protein, beta-amyloid(1-42), tau and phospho-tau181 and several inflammatory markers, as well as vascular RECA-1 and laminin density. However, HHcy induced cortical microbleedings, as illustrated by intensive anti-rat IgG-positive spots in the cortex. In order to study the regulation of the key enzyme ChAT, organotypic rat brain slices were incubated with homocysteine, which induced a decline of ChAT that was counteracted by NGF treatment. In conclusion, our data demonstrate that chronic short- and long-term HHcy differentially caused memory impairment, cholinergic dysfunction, NGF expression and vascular microbleedings.

Chronic mild cerebrovascular dysfunction as a cause for Alzheimer's disease?

Alzheimer's disease (AD) is a progressive chronic disorder and is characterized by β-amyloid plaques and angiopathy, tau pathology, neuronal cell death, and inflammatory responses. The reasons for this disease are not known. This review proposes the hypothesis that a chronic mild longlasting cerebrovascular dysfunction could initiate a cascade of events leading to AD. It is suggested that (vascular) risk factors (e.g. hypercholesterolemia, type 2 diabetes, hyperhomocysteinemia) causes either damage of the cerebrovascular system including silent strokes or causes dysregulation of beta-amyloid clearance at the blood-brain barrier resulting in increased brain beta-amyloid. A cascade of subsequent downstream events may lead to disturbed metabolic changes, and neuroinflammation and tau pathology. The role of NGF on the cell death of cholinergic neurons is discussed. Additional risk factors (e.g. acidosis, metals) contribute to plaque development.

Autoantibodies to the adenosine triphosphate synthase play a pathogenetic role in Alzheimer's disease

It has become evident that an autoimmune component could play a role in Alzheimer's disease (AD) onset and/or progression. The aim of this study was to identify neuronal antigenic targets specifically recognized by serum autoantibodies and to investigate their cellular effects and their possible pathogenetic role. We identified, by an immunoproteomic approach using mouse brain proteins, the adenosine triphosphate (ATP) synthase β subunit as a new autoantigen in AD. Using an ELISA assay we found that serum anti-ATP synthase autoantibodies were present in 38% of patients with AD, but in no age-matched healthy subjects or in patients with Parkinson's disease or atherosclerosis. Analytical cytology studies, using SH-SY5Y neuroblastoma cell line, showed that ATP synthase autoantibodies were capable of inducing the inhibition of ATP synthesis, alterations of mitochondrial homeostasis and cell death by apoptosis. These findings suggest that autoantibodies specific to ATP synthase can exert a pathogenetic role via a mechanism that brings into play the impairment of the extracellular ATP homeostasis and the alteration of mitochondrial function triggering cell death by apoptosis.

Sodium lactate differently alters relative EEG power and functional connectivity in Alzheimer's disease patients' brain regions

Bilateral temporo-parietal hypoperfusion and decreased glucose metabolism are characteristic in vivo findings in Alzheimer's disease (AD). Lactate is a metabolic vasodilator and is known to induce increased cerebral blood flow in healthy adults. The present study addresses the issue whether sodium lactate infusion affects functional state and resulting electroencephalographic patterns of AD patients. Twelve late-onset sporadic AD probands participated in this self-control study. The relative power and synchronization likelihood (SL) values of the electroencephalographic samples were calculated and compared off-line before and after sodium lactate infusion (0.5 M, 5 ml/kg body weight). Based on the reactivity to sodium lactate the scalp could be divided into three parts; no significant changes were seen in the seriously damaged (P3-P4) areas. The moderately affected regions in the close neighborhood showed a paradoxic inactivation with electroencephalographic slowing, a likely consequence of the metabolic-like steal effect of the near-normal areas outside. These results indicate a diminished vascular and/or metabolic reserve capacity to sodium lactate challenge in AD and confirm the formerly described electroencephalographic abnormalities.

Influence of galantamine on vasomotor reactivity in Alzheimer's disease and vascular dementia due to cerebral microangiopathy

BACKGROUND AND PURPOSE

Recent reports suggest that vascular factors play a crucial role in the development and progression of Alzheimer's disease. We aimed to assess vasomotor reactivity in patients with Alzheimer's disease and vascular dementia due to microangiopathy using transcranial Doppler sonography and near-infrared spectroscopy during a CO(2) exposition task.

METHODS

The normalized CO(2) reactivity assessed at the middle cerebral artery and the oxygenated and deoxygenated hemoglobin of the frontal cortex were obtained. To investigate the impact of cholinergic deficiency known for Alzheimer's disease on vasomotor reactivity, both groups were reinvestigated during treatment with the acetylcholine esterase inhibitor galantamine.

RESULTS

Transcranial Doppler analysis revealed significantly reduced normalized CO(2) reactivity for Alzheimer's disease and vascular dementia. Vasomotor reactivity assessed by near-infrared spectroscopy was decreased in patients with vascular dementia, but not in Alzheimer's disease. Galantamine treatment showed a beneficial effect, normalizing these parameters close to age-matched control levels.

CONCLUSIONS

Our results suggest that Alzheimer's disease is associated with a lack of vasomotor reactivity, which might be associated with disturbed autoregulation indicating a potential risk for a decreased protection of brain tissue against blood pressure changes. Additionally, a diminished increase of cortical oxygenated hemoglobin during the CO(2) test was apparent in patients with vascular dementia. Galantamine treatment influenced vascular reactivity in the CO(2) test, thus providing evidence for the cholinergic deficiency, thereby adding to vascular dysregulation in Alzheimer's disease, but also indicating an important role of cholinergic system dysfunction for vascular dementia.

The enigma of vascular cognitive disorder and vascular dementia

The prevalence, morphology and pathogenesis of vascular dementia (VaD), recently termed vascular cognitive impairment, are a matter of discussion, and currently used clinical diagnostic criteria show moderate sensitivity (average 50%) and variable specificity (range 64-98%). In Western clinic-based series, VaD is suggested in 8-10% of cognitively impaired aged subjects. Its prevalence in autopsy series varies from 0.03 to 58%, with reasonable values of 8-15%, while in Japan it is seen in 22-35%. Neuropathologic changes associated with cognitive impairment include multifocal and/or diffuse disease and focal lesions: multi-infarct encephalopathy, white matter lesions or arteriosclerotic subcortical (leuko)encephalopathy, multilacunar state, mixed cortico-subcortical type, borderline/watershed lesions, rare granular cortical atrophy, post-ischemic encephalopathy and hippocampal sclerosis. They result from systemic, cardiac and local large or small vessel disease. Recent data indicate that cognitive decline is commonly associated with widespread small ischemic/vascular lesions (microinfarcts, lacunes) throughout the brain with predominant involvement of subcortical and functionally important brain areas. Their pathogenesis is multifactorial, and their pathophysiology affects neuronal networks involved in cognition, memory, behavior and executive functioning. Vascular lesions often coexist with Alzheimer disease (AD) and other pathologies. Minor cerebrovascular lesions, except for severe amyloid angiopathy, appear not essential for cognitive decline in full-blown AD, while both mild Alzheimer pathology and small vessel disease may interact synergistically. The lesion pattern of "pure" VaD, related to arteriosclerosis and microangiopathies, differs from that in mixed-type dementia (AD with vascular encephalopathy), more often showing large infarcts, which suggests different pathogenesis of both types of lesions. Due to the high variability of cerebrovascular pathology and its causative factors, no validated neuropathologic criteria for VaD are available, and a large variability across laboratories still exists in the procedures for morphologic examination and histology techniques.