Age-dependent changes in the glutamate-nitric oxide pathway in the hippocampus of the triple transgenic model of Alzheimer's disease: implications for neurometabolic regulation

Embelin Mitigates Amyloid-β-Induced Neurotoxicity and Cognitive Impairment in Rats: Potential Therapeutic Implications for Alzheimer's Disease

Alzheimer's disease (AD) is a significant form of dementia. Embelin (EMB) is a natural compound with varied actions that could help prevent AD pathology. Herein, we have investigated the neuroprotective potential of EMB against Aβ1-42-induced neurotoxicity in rats. In this experiment, Alzheimer-like dementia was induced in rats by infusing Aβ1-42 oligomers directly into the brain's ventricles. Subsequently, the Aβ1-42-intoxicated rats received treatment with varying doses of EMB (2.5, 5, and 10 mg/kg, administered intraperitoneally) over 2 weeks. The spatial and non-spatial memory of animals was assessed at different time intervals, and various biochemical, neurochemical, and neuroinflammatory parameters in the hippocampal brain tissue of the rats were analyzed. Infusion of Aβ1-42 in rat brain caused cognitive impairment and was accompanied by increased acetylcholinesterase activity, oxidative stress, and elevated levels of pro-inflammatory cytokines (such as TNF-α, IL-1β, and IL-6) in the hippocampal tissue. Moreover, a significant decline in the levels of monoamines and an imbalance of GABA and glutamate levels were also observed. EMB treatment significantly mitigated Aβ1-42-induced cognitive deficit and other biochemical changes, including Aβ levels. The EMB-treated rats showed improved learning and consolidation of memory. EMB also attenuated Aβ-induced oxidative stress and neuroinflammation and restored the levels of monoamines and the balance between GABA and glutamate. The observed cognitive benefits following EMB treatment in Aβ1-42-infused rats may be attributed to its antioxidant and anti-inflammatory properties and ability to restore hippocampal neurochemistry and Aβ levels. The above findings indicate the therapeutic potential of EMB in neurodegenerative pathologies associated with cognitive decline, such as Alzheimer's disease.

Nitric Oxide/Nitric Oxide Synthase System in the Pathogenesis of Neurodegenerative Disorders-An Overview

Nitric oxide, a ubiquitous molecule found throughout the natural world, is a key molecule implicated in many central and benefic molecular pathways and has a well-established role in the function of the central nervous system, as numerous studies have previously shown. Dysregulation of its metabolism, mainly the upregulation of nitric oxide production, has been proposed as a trigger and/or aggravator for many neurological affections. Increasing evidence supports the implication of this molecule in prevalent neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, or amyotrophic lateral sclerosis. The mechanisms proposed for its neurotoxicity mainly center around the increased quantities of nitric oxide that are produced in the brain, their cause, and, most importantly, the pathological metabolic cascades created. These cascades lead to the formation of neuronal toxic substances that impair the neurons' function and structure on multiple levels. The purpose of this review is to present the main causes of increased pathological production, as well as the most important pathophysiological mechanisms triggered by nitric oxide, mechanisms that could help explain a part of the complex picture of neurodegenerative diseases and help develop targeted therapies.

Lithium Provides Broad Therapeutic Benefits in an Alzheimer's Disease Mouse Model

BACKGROUND

Alzheimer's disease (AD) is a chronic neurodegenerative disorder with a progressive loss of cognitive function. Currently, no effective treatment regimen is available. Lithium, a mood stabilizer for bipolar disorder, exerts broad neuroprotective and neurotrophic actions and improves cognitive function.

OBJECTIVE

The study investigated if lithium stabilizes Ca2+ signaling abnormalities in hippocampal neurons and subsequently normalize downstream effects on AD neuropathology and synaptic plasticity in young AD mice.

METHODS

Four-month-old 3xTg-AD mice were treated with a LiCl diet chow for 30 days. At the end of the lithium treatment, a combination of two-photon Ca2+ imaging, electrophysiology, and immunohistochemistry assays were used to assess the effects of the LiCl treatment on inositol trisphosphate receptor (IP3R)-dependent endoplasmic reticulum (ER) Ca2+ and voltage-gated Ca2+ channel (VGCC)-mediated Ca2+ signaling in CA1 neurons, neuronal nitric oxide synthase (nNOS) and hyperphosphorylated tau (p-tau) levels and synaptic plasticity in the hippocampus and overlying cortex from 3xTg-ADmice.

RESULTS

Thirty-day LiCl treatment reduced aberrant IP3R-dependent ER Ca2+ and VGCC-mediated Ca2+ signaling in CA1 pyramidal neurons from 3xTg-AD mice and restored neuronal nitric oxide synthase (nNOS) and hyperphosphorylated tau (p-tau) levels to control levels in the hippocampal subfields and overlying cortex. The LiCl treatment enhanced post-tetanic potentiation (PTP), a form of short-term plasticity in the hippocampus.

CONCLUSION

The study found that lithium exerts therapeutic effects across several AD-associated early neuronal signaling abnormalities including aberrant Ca2+ signaling, nNOS, and p-tau formation and enhances short-term synaptic plasticity. Lithium could serve as an effective treatment or co-therapeutic for AD.

Neurovascular coupling mechanisms in health and neurovascular uncoupling in Alzheimer's disease

To match the metabolic demands of the brain, mechanisms have evolved to couple neuronal activity to vasodilation, thus increasing local cerebral blood flow and delivery of oxygen and glucose to active neurons. Rather than relying on metabolic feedback signals such as the consumption of oxygen or glucose, the main signalling pathways rely on the release of vasoactive molecules by neurons and astrocytes, which act on contractile cells. Vascular smooth muscle cells and pericytes are the contractile cells associated with arterioles and capillaries, respectively, which relax and induce vasodilation.

Much progress has been made in understanding the complex signalling pathways of neurovascular coupling, but issues such as the contributions of capillary pericytes and astrocyte calcium signal remain contentious. Study of neurovascular coupling mechanisms is especially important as cerebral blood flow dysregulation is a prominent feature of Alzheimer’s disease. In this article we will discuss developments and controversies in the understanding of neurovascular coupling and finish by discussing current knowledge concerning neurovascular uncoupling in Alzheimer’s disease.

Nitric oxide impairs spatial learning and memory in a rat model of Alzheimer's disease via disturbance of glutamate response in the hippocampal dentate gyrus during spatial learning

Nitric oxide (NO)-dependent pathways may play a significant role in the decline of synaptic and cognitive functions in Alzheimer's disease (AD). However, whether NO in the hippocampal dentate gyrus (DG) is involved in the spatial learning and memory impairments of AD by affecting the glutamate (Glu) response during these processes is not well-understood. Here, we prepared an AD rat model by long-term i.p. of D-galactose into ovariectomized rats, and then the effects of L-NMMA (a NO synthase inhibitor) on Glu concentration and amplitude of field excitatory postsynaptic potential (fEPSP) were measured in the DG region during the Morris water maze (MWM) test in freely-moving rats. During the MWM test, compared with the sham group, the escape latency was increased in the place navigation trial, and the percentage of time spent in target quadrant and the number of platform crossings were decreased in the spatial probe trial, in addition, the increase of fEPSP amplitude in the DG was significantly attenuated in AD group rats. L-NMMA significantly attenuated the spatial learning and memory impairment in AD rats, and reversed the inhibitory effect of AD on increase of fEPSP amplitude in the DG during the MWM test. In sham group rats, the Glu level in the DG increased significantly during the MWM test, and this response was markedly enhanced in AD rats. Furthermore, the response of Glu in the DG during spatial learning was recovered by microinjection of L-NMMA into the DG. Our results suggest that NO in the DG impairs spatial learning and memory and related synaptic plasticity in AD rats, by disturbing the Glu response during spatial learning.

A High Fat/Cholesterol Diet Recapitulates Some Alzheimer's Disease-Like Features in Mice: Focus on Hippocampal Mitochondrial Dysfunction

BACKGROUND

Ample evidence from clinical and pre-clinical studies suggests mid-life hypercholesterolemia as a risk factor for developing Alzheimer's disease (AD) at a later age. Hypercholesterolemia induced by dietary habits can lead to vascular perturbations that increase the risk of developing sporadic AD.

OBJECTIVE

To investigate the effects of a high fat/cholesterol diet (HFCD) as a risk factor for AD by using a rodent model of AD and its correspondent control (healthy animals).

METHODS

We compared the effect of a HFCD in normal mice (non-transgenic mice, NTg) and the triple transgenic mouse model of AD (3xTgAD). We evaluated cognitive performance in relation to changes in oxidative metabolism and neuron-derived nitric oxide (•NO) concentration dynamics in hippocampal slices as well as histochemical staining of markers of the neurovascular unit.

RESULTS

In NTg, the HFCD produced only moderate hypercholesterolemia but significant decline in spatial memory was observed. A tendency for decrease in •NO production was accompanied by compromised mitochondrial function with decrease in spare respiratory capacity. In 3xTgAD mice, a robust increase in plasma cholesterol levels with the HFCD did not worsen cognitive performance but did induce compromise of mitochondrial function and significantly decreased •NO production. We found increased staining of biomarkers for astrocyte endfeet and endothelial cells in 3xTgAD hippocampi, which was further increased by the HFCD.

CONCLUSION

A short term (8 weeks) intervention with HFCD can produce an AD-like phenotype even in the absence of overt systemic hypercholesterolemia and highlights mitochondrial dysfunction as a link between hypercholesterolemia and sporadic AD.

Age-related alterations in the cerebrovasculature affect neurovascular coupling and BOLD fMRI responses: Insights from animal models of aging

The present and future research efforts in cognitive neuroscience and psychophysiology rely on the measurement, understanding, and interpretation of blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to effectively investigate brain function. Aging and age-associated pathophysiological processes change the structural and functional integrity of the cerebrovasculature which can significantly alter how the BOLD signal is recorded and interpreted. In order to gain an improved understanding of the benefits, drawbacks, and methodological implications for BOLD fMRI in the context of cognitive neuroscience, it is crucial to understand the cellular and molecular mechanism of age-related vascular pathologies. This review discusses the multifaceted effects of aging and the contributions of age-related pathologies on structural and functional integrity of the cerebral microcirculation as they has been investigated in animal models of aging, including age-related alterations in neurovascular coupling responses, cellular and molecular mechanisms involved in microvascular damage, vascular rarefaction, blood-brain barrier disruption, senescence, humoral deficiencies as they relate to, and potentially introduce confounding factors in the interpretation of BOLD fMRI.

Contrasting Metabolic Insufficiency in Aging and Dementia

Metabolic insufficiency and neuronal dysfunction occur in normal aging but is exaggerated in dementia and Alzheimer's disease (AD). Metabolic insufficiency includes factors important for both substrate supply and utilization in the brain. Metabolic insufficiency occurs through a number of serial mechanisms, particularly changes in cerebrovascular supply through blood vessel abnormalities (ie, small and large vessel vasculopathy, stroke), alterations in neurovascular coupling providing dynamic blood flow supply in relation to neuronal demand, abnormalities in blood brain barrier including decreased glucose and amino acid transport, altered glymphatic flow in terms of substrate supply across the extracellular space to cells and drainage into CSF of metabolites, impaired transport into cells, and abnormal intracellular metabolism with more reliance on glycolysis and less on mitochondrial function. Recent studies have confirmed abnormal neurovascular coupling in a mouse model of AD in response to metabolic challenges, but the supply chain from the vascular system into neurons is disrupted much earlier in dementia than in equivalently aged individuals, contributing to the progressive neuronal degeneration and cognitive dysfunction associated with dementia. We discuss several metabolic treatment approaches, but these depend on characterizing patients as to who would benefit the most. Surrogate biomarkers of metabolism are being developed to include dynamic estimates of neuronal demand, sufficiency of neurovascular coupling, and glymphatic flow to supplement traditional static measurements. These surrogate biomarkers could be used to gauge efficacy of metabolic treatments in slowing down or modifying dementia time course.

Nitrergic modulation of neuronal excitability in the mouse hippocampus is mediated via regulation of Kv2 and voltage-gated sodium channels

Regulation of neuronal activity is a necessity for communication and information transmission. Many regulatory processes which have been studied provide a complex picture of how neurons can respond to permanently changing functional requirements. One such activity-dependent mechanism involves signaling mediated by nitric oxide (NO). Within the brain, NO is generated in response to neuronal NO synthase (nNOS) activation but NO-dependent pathways regulating neuronal excitability in the hippocampus remain to be fully elucidated. This study was set out to systematically assess the effects of NO on ion channel activities and intrinsic excitabilities of pyramidal neurons within the CA1 region of the mouse hippocampus. We characterized whole-cell potassium and sodium currents, both involved in action potential (AP) shaping and propagation and determined NO-mediated changes in excitabilities and AP waveforms. Our data describe a novel signaling by which NO, in a cGMP-independent manner, suppresses voltage-gated Kv2 potassium and voltage-gated sodium channel activities, thereby widening AP waveforms and reducing depolarization-induced AP firing rates. Our data show that glutathione, which possesses denitrosylating activity, is sufficient to prevent the observed nitrergic effects on potassium and sodium channels, whereas inhibition of cGMP signaling is also sufficient to abolish NO modulation of sodium currents. We propose that NO suppresses both ion channel activities via redox signaling and that an additional cGMP-mediated component is required to exert effects on sodium currents. Both mechanisms result in a dampened excitability and firing ability providing new data on nitrergic activities in the context of activity-dependent regulation of neuronal function following nNOS activation.

CVN-AD Alzheimer's mice show premature reduction in neurovascular coupling in response to spreading depression and anoxia compared to aged controls

We compared the efficacy of neurovascular coupling and substrate supply in cerebral cortex during severe metabolic challenges in transgenic Alzheimer's [CVN-AD] and control [C57Bl/6] mice, to evaluate the hypothesis that metabolic insufficiency is a critical component of degeneration leading to dementia. We analyzed cerebral blood flow and metabolic responses to spreading depression (induced by K⁺ applied to the cortex) and anoxia across aging in CVN-AD + C57Bl/6 genotypes. In the CVN-AD genotype progression to histological and cognitive hallmarks of dementia is a stereotyped function of age. We correlated physiology and imaging of the cortex with the blood flow responses measured with laser doppler probes. The results show that spreading depression resulted in a hyperemic blood flow response that was dramatically reduced (24% in amplitude, 70% in area) in both middle-aged and aged CVN-AD mice compared to C57Bl/6 age-matched controls. However, spreading depression amplitude and conduction velocity (≈6 mm/min) did not differ among groups. Anoxia (100% N₂ ) showed significantly decreased (by 62%) reactive blood flow and autoregulation in aged AD-CVN mice compared to aged control animals. Significantly reduced neurovascular coupling occurred prematurely with aging in CVN-AD mice. Abbreviated physiological hyperemia and decreased resilience to anoxia may enhance early-onset metabolic deficiency through decreased substrate supply to the brain. Metabolic deficiency may contribute significantly to the degeneration associated with dementia as a function of aging and regions of the brain involved.

The bioactivity of neuronal-derived nitric oxide in aging and neurodegeneration: Switching signaling to degeneration

The small and diffusible free radical nitric oxide (^•NO) has fascinated biological and medical scientists since it was promoted from atmospheric air pollutant to biological ubiquitous signaling molecule. Its unique physical chemical properties expand beyond its radical nature to include fast diffusion in aqueous and lipid environments and selective reactivity in a biological setting determined by bioavailability and reaction rate constants with biomolecules. In the brain, ^•NO is recognized as a key player in numerous physiological processes ranging from neurotransmission/neuromodulation to neurovascular coupling and immune response. Furthermore, changes in its bioactivity are central to the molecular pathways associated with brain aging and neurodegeneration. The understanding of ^•NO bioactivity in the brain, however, requires the knowledge of its concentration dynamics with high spatial and temporal resolution upon stimulation of its synthesis. Here we revise our current understanding of the role of neuronal-derived ^•NO in brain physiology, aging and degeneration, focused on changes in the extracellular concentration dynamics of this free radical and the regulation of bioenergetic metabolism and neurovascular coupling.

Amyloid Beta-Related Alterations to Glutamate Signaling Dynamics During Alzheimer's Disease Progression

Alzheimer’s disease (AD) ranks sixth on the Centers for Disease Control and Prevention Top 10 Leading Causes of Death list for 2016, and the Alzheimer’s Association attributes 60% to 80% of dementia cases as AD related. AD pathology hallmarks include accumulation of senile plaques and neurofibrillary tangles; however, evidence supports that soluble amyloid beta (Aβ), rather than insoluble plaques, may instigate synaptic failure. Soluble Aβ accumulation results in depression of long-term potentiation leading to cognitive deficits commonly characterized in AD. The mechanisms through which Aβ incites cognitive decline have been extensively explored, with a growing body of evidence pointing to modulation of the glutamatergic system. The period of glutamatergic hypoactivation observed alongside long-term potentiation depression and cognitive deficits in later disease stages may be the consequence of a preceding period of increased glutamatergic activity. This review will explore the Aβ-related changes to the tripartite glutamate synapse resulting in altered cell signaling throughout disease progression, ultimately culminating in oxidative stress, synaptic dysfunction, and neuronal loss.

The Peculiar Facets of Nitric Oxide as a Cellular Messenger: From Disease-Associated Signaling to the Regulation of Brain Bioenergetics and Neurovascular Coupling

In this review, we address the regulatory and toxic role of ^·NO along several pathways, from the gut to the brain. Initially, we address the role on ^·NO in the regulation of mitochondrial respiration with emphasis on the possible contribution to Parkinson's disease via mechanisms that involve its interaction with a major dopamine metabolite, DOPAC. In parallel with initial discoveries of the inhibition of mitochondrial respiration by ^·NO, it became clear the potential for toxic ^·NO-mediated mechanisms involving the production of more reactive species and the post-translational modification of mitochondrial proteins. Accordingly, we have proposed a novel mechanism potentially leading to dopaminergic cell death, providing evidence that NO synergistically interact with DOPAC in promoting cell death via mechanisms that involve GSH depletion. The modulatory role of NO will be then briefly discussed as a master regulator on brain energy metabolism. The energy metabolism in the brain is central to the understanding of brain function and disease. The core role of ^·NO in the regulation of brain metabolism and vascular responses is further substantiated by discussing its role as a mediator of neurovascular coupling, the increase in local microvessels blood flow in response to spatially restricted increase of neuronal activity. The many facets of NO as intracellular and intercellular messenger, conveying information associated with its spatial and temporal concentration dynamics, involve not only the discussion of its reactions and potential targets on a defined biological environment but also the regulation of its synthesis by the family of nitric oxide synthases. More recently, a novel pathway, out of control of NOS, has been the subject of a great deal of controversy, the nitrate:nitrite:NO pathway, adding new perspectives to ^·NO biology. Thus, finally, this novel pathway will be addressed in connection with nitrate consumption in the diet and the beneficial effects of protein nitration by reactive nitrogen species.

The effect of nitric oxide on mitochondrial respiration

This article reviews the interactions between nitric oxide (NO) and mitochondrial respiration. Mitochondrial ATP synthesis is responsible for virtually all energy production in mammals, and every other process in living organisms ultimately depends on that energy production. Furthermore, both necrosis and apoptosis, that summarize the main forms of cell death, are intimately linked to mitochondrial integrity. Endogenous and exogenous •NO inhibits mitochondrial respiration by different well-studied mechanisms and several nitrogen derivatives. Instantaneously, low concentrations of •NO, specifically and reversibly inhibit cytochrome c oxidase in competition with oxygen, in several tissues and cells in culture. Higher concentrations of •NO and its derivatives (peroxynitrite, nitrogen dioxide or nitrosothiols) can cause irreversible inhibition of the respiratory chain, uncoupling, permeability transition, and/or cell death. Peroxynitrite can cause opening of the permeability transition pore and opening of this pore causes loss of cytochrome c, which in turn might contribute to peroxynitrite-induced inhibition of respiration. Therefore, the inhibition of cytochrome c oxidase by •NO may be involved in the physiological and/or pathological regulation of respiration rate, and its affinity for oxygen, which depend on reactive nitrogen species formation, pH, proton motriz force and oxygen supply to tissues.

Dysregulation of stress systems and nitric oxide signaling underlies neuronal dysfunction in Alzheimer's disease

Stress is a multimodal response involving the coordination of numerous body systems in order to maximize the chance of survival. However, long term activation of the stress response results in neuronal oxidative stress via reactive oxygen and nitrogen species generation, contributing to the development of depression. Stress-induced depression shares a high comorbidity with other neurological conditions including Alzheimer's disease (AD) and dementia, often appearing as one of the earliest observable symptoms in these diseases. Furthermore, stress and/or depression appear to exacerbate cognitive impairment in the context of AD associated with dysfunctional catecholaminergic signaling. Given there are a number of homologous pathways involved in the pathophysiology of depression and AD, this article will highlight the mechanisms by which stress-induced perturbations in oxidative stress, and particularly NO signaling, contribute to neurodegeneration.

Insights into the Potential Role of Mercury in Alzheimer's Disease

Mercury (Hg), which is a non-essential element, is considered a highly toxic pollutant for biological systems even when present at trace levels. Elevated Hg exposure with the growing release of atmospheric pollutant Hg and rising accumulations of mono-methylmercury (highly neurotoxic) in seafood products have increased its toxic potential for humans. This review aims to highlight the potential relationship between Hg exposure and Alzheimer's disease (AD), based on the existing literature in the field. Recent reports have hypothesized that Hg exposure could increase the potential risk of developing AD. Also, AD is known as a complex neurological disorder with increased amounts of both extracellular neuritic plaques and intracellular neurofibrillary tangles, which may also be related to lifestyle and genetic variables. Research reports on AD and relationships between Hg and AD indicate that neurotransmitters such as serotonin, acetylcholine, dopamine, norepinephrine, and glutamate are dysregulated in patients with AD. Many researchers have suggested that AD patients should be evaluated for Hg exposure and toxicity. Some authors suggest further exploration of the Hg concentrations in AD patients. Dysfunctional signaling pathways in AD and Hg exposure appear to be interlinked with some driving factors such as arachidonic acid, homocysteine, dehydroepiandrosterone (DHEA) sulfate, hydrogen peroxide, glucosamine glycans, glutathione, acetyl-L carnitine, melatonin, and HDL. This evidence suggests the need for a better understanding of the relationship between AD and Hg exposure, and potential mechanisms underlying the effects of Hg exposure on regional brain functions. Also, further studies evaluating brain functions are needed to explore the long-term effects of subclinical and untreated Hg toxicity on the brain function of AD patients.

Altered Nup153 Expression Impairs the Function of Cultured Hippocampal Neural Stem Cells Isolated from a Mouse Model of Alzheimer's Disease

Impairment of adult hippocampal neurogenesis is an early event in Alzheimer's disease (AD), playing a crucial role in cognitive dysfunction associated with this pathology. However, the mechanisms underlying defective neurogenesis in AD are still unclear. Recently, the nucleoporin Nup153 has been described as a new epigenetic determinant of adult neural stem cell (NSC) maintenance and fate. Here we investigated whether Nup153 dysfunction could affect the plasticity of NSCs in AD. Nup153 expression was strongly reduced in AD-NSCs, as well as its interaction with the transcription factor Sox2, a master regulator of NSC stemness and their neuronal differentiation. Similar Nup153 reduction was also observed in WT-NSCs treated with amyloid-β (Aβ) or stimulated with a nitric oxide donor. Accordingly, AD-NSCs treated with either a γ-secretase inhibitor or antioxidant compounds showed higher Nup153 levels suggesting that both nitrosative stress and Aβ accumulation affect Nup153 expression. Of note, restoration of Nup153 levels in AD-NSCs promoted their proliferation, as assessed by BrdU incorporation, neurosphere assay, and stemness gene expression analysis. Nup153 overexpression also recovered AD-NSC response to differentiation, increasing the expression of pro-neuronal genes, the percentage of cells positive for neuronal markers, and the acquisition of a more mature neuronal phenotype. Electrophysiological recordings revealed that neurons differentiated from Nup153-transfected AD-NSCs displayed higher Na⁺ current density, comparable to those deriving from WT-NSCs. Our data uncover a novel role for Nup153 in NSCs from animal model of AD and point to Nup153 as potential target to restore physiological NSC behavior and fate in neurodegenerative diseases.

Age-Dependent Impairment of Neurovascular and Neurometabolic Coupling in the Hippocampus

Neurovascular and neurometabolic coupling are critical and complex processes underlying brain function. Perturbations in the regulation of these processes are, likely, early dysfunctional alterations in pathological brain aging and age-related neurodegeneration. Evidences support the role of nitric oxide (•NO) as a key messenger both in neurovascular coupling, by signaling from neurons to blood vessels, and in neurometabolic coupling, by modulating O₂ utilization by mitochondria. In the present study, we investigated the functionality of neurovascular and neurometabolic coupling in connection to •NO signaling and in association to cognitive performance during aging. For this, we performed in vivo simultaneous measurements of •NO, O₂ and cerebral blood flow (CBF) in the hippocampus of F344 rats along chronological age in response to glutamatergic activation and in correlation with cognitive performance. Firstly, it is evidenced the temporal sequence of events upon glutamate stimulation of hippocampal dentate gyrus, encompassing the local and transitory increase of •NO followed by transitory local changes of CBF and pO₂. Specifically, the transient increase of •NO is followed by an increase of CBF and biphasic changes of the local pO₂. We observed that, although the glutamate-induced •NO dynamics were not significantly affected by aging, the correspondent hemodynamic was progressively diminished accompanying a decline in learning and memory. Noteworthy, in spite of a compromised blood supply, in aged rats we observed an increased ΔpO₂ associated to the hemodynamic response, suggestive of a decrease in the global metabolic rate of O₂. Furthermore, the impairment in the neurovascular coupling observed along aging in F344 rats was mimicked in young rats by promoting an unbalance in redox status toward oxidation via intracellular generation of superoxide radical. This observation strengthens the idea that oxidative stress may have a critical role in the neurovascular uncoupling underlying brain aging and dysfunction. Overall, data supports an impairment of neurovascular response in connection with cognition decline due to oxidative environment-dependent compromised •NO signaling from neurons to vessels during aging.

Modulation of Cellular Respiration by Endogenously Produced Nitric Oxide in Rat Hippocampal Slices

Nitric oxide (^•NO) is an ubiquitous signaling molecule that participates in molecular processes associated with several neural phenomena ranging from memory formation to excitotoxicity. In the hippocampus, neuronal ^•NO production is coupled to the activation of NMDA type glutamate receptors. Cytochrome c oxidase has emerged as a novel target for ^•NO, which competes with O₂ for binding to this mitochondrial complex. This reaction establishes ^•NO as a regulator of cellular metabolism and, possibly, mitochondrial production of reactive oxygen species which participate in cellular signaling. A major gap in the understanding of ^•NO bioactivity, namely, in the hippocampus, has been the lack of knowledge of its concentration dynamics. Here, we present a detailed description of the simultaneous recording of ^•NO and O₂ concentration dynamics in rat hippocampal slices. Carbon fiber microelectrodes are fabricated and applied for real-time measurements of both gases in a system close to in vivo models. This approach allows for a better understanding of the current paradigm by which an intricate interplay between ^•NO and O₂ regulates cellular respiration.

Activation of brain glucose metabolism ameliorating cognitive impairment in APP/PS1 transgenic mice by electroacupuncture

An essential feature of Alzheimer's disease (AD) is implicated in brain energy metabolic impairment that is considered underlying pathogenesis of cognitive impairment. Therefore, therapeutic interventions to allay cognitive deficits that target energy metabolism may be an efficacy strategy in AD. In this study, we found that electroacupuncture (EA) at the DU20 acupoint obviously increased glucose metabolism in specific brain regions such as cortex, hippocampus, cingulate gyrus, basal forebrain septum, brain stem, and cerebellum in APP/PS1 transgenic mice by animal ¹⁸F-Fluoro-2-deoxy-D-Glucose (¹⁸F-FDG)/positron emission tomography (PET) imaging, accompanied by cognitive improvements in the spatial reference learning and memory and memory flexibility and novel object recognition performances. Further evidence shown energy metabolism occurred in neurons or non-neuronal cells of the cortex and hippocampus in terms of the co-location of GLUT3/NeuN and GLUT1/GFAP. Simultaneously, metabolic homeostatic factors were critical for glucose metabolism, including phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and AKT serine/threonine kinase. Furthermore, EA-induced phosphorylated AMPK and AKT inhibited the phosphorylation level of the mammalian target of rapamycin (mTOR) to decrease the accumulation of amyloid-beta (Aβ) in the cortex and hippocampus. These findings are concluded that EA is a potential therapeutic target for delaying memory decline and Aβ deposition of AD. The AMPK and AKT are implicated in the EA-induced cortical and hippocampal energy metabolism, which served as a contributor to improving cognitive function and Aβ deposition in a transgenic mouse model of AD.

A Cystine-Rich Whey Supplement (Immunocal®) Provides Neuroprotection from Diverse Oxidative Stress-Inducing Agents In Vitro by Preserving Cellular Glutathione

Oxidative stress is a principal mechanism underlying the pathophysiology of neurodegeneration. Therefore, nutritional enhancement of endogenous antioxidant defenses may represent a viable treatment option. We investigated the neuroprotective properties of a unique whey protein supplement (Immunocal®) that provides an essential precursor (cystine) for synthesis of the endogenous antioxidant, glutathione (GSH). Primary cultures of rat cerebellar granule neurons (CGNs), NSC34 motor neuronal cells, or HT22 hippocampal cells were preincubated in medium containing Immunocal and then subsequently treated with agents known to induce oxidative stress. Immunocal protected CGNs against neurotoxicity induced by the Bcl-2 inhibitor, HA14-1, the nitric oxide donor, sodium nitroprusside, CuCl₂, and AlCl₃. Immunocal also significantly reduced NSC34 cell death due to either H₂O₂ or glutamate and mitigated toxicity in HT22 cells overexpressing β-amyloid_1-42. The neuroprotective effects of Immunocal were blocked by inhibition of γ-glutamyl-cysteine ligase, demonstrating dependence on de novo GSH synthesis. These findings indicate that sustaining GSH with Immunocal significantly protects neurons against diverse inducers of oxidative stress. Thus, Immunocal is a nutritional supplement worthy of testing in preclinical animal models of neurodegeneration and in future clinical trials of patients afflicted by these diseases.

Neurovascular-neuroenergetic coupling axis in the brain: master regulation by nitric oxide and consequences in aging and neurodegeneration

The strict energetic demands of the brain require that nutrient supply and usage be fine-tuned in accordance with the specific temporal and spatial patterns of ever-changing levels of neuronal activity. This is achieved by adjusting local cerebral blood flow (CBF) as a function of activity level - neurovascular coupling - and by changing how energy substrates are metabolized and shuttled amongst astrocytes and neurons - neuroenergetic coupling. Both activity-dependent increase of CBF and O₂ and glucose utilization by active neural cells are inextricably linked, establishing a functional metabolic axis in the brain, the neurovascular-neuroenergetic coupling axis. This axis incorporates and links previously independent processes that need to be coordinated in the normal brain. We here review evidence supporting the role of neuronal-derived nitric oxide (^•NO) as the master regulator of this axis. Nitric oxide is produced in tight association with glutamatergic activation and, diffusing several cell diameters, may interact with different molecular targets within each cell type. Hemeproteins such as soluble guanylate cyclase, cytochrome c oxidase and hemoglobin, with which ^•NO reacts at relatively fast rates, are but a few of the key in determinants of the regulatory role of ^•NO in the neurovascular-neuroenergetic coupling axis. Accordingly, critical literature supporting this concept is discussed. Moreover, in view of the controversy regarding the regulation of catabolism of different neural cells, we further discuss key aspects of the pathways through which ^•NO specifically up-regulates glycolysis in astrocytes, supporting lactate shuttling to neurons for oxidative breakdown. From a biomedical viewpoint, derailment of neurovascular-neuroenergetic axis is precociously linked to aberrant brain aging, cognitive impairment and neurodegeneration. Thus, we summarize current knowledge of how both neurovascular and neuroenergetic coupling are compromised in aging, traumatic brain injury, epilepsy and age-associated neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, suggesting that a shift in cellular redox balance may contribute to divert ^•NO bioactivity from regulation to dysfunction.

Neurovascular uncoupling in the triple transgenic model of Alzheimer's disease: Impaired cerebral blood flow response to neuronal-derived nitric oxide signaling

Nitric oxide (NO)-dependent pathways and cerebrovascular dysfunction have been shown to contribute to the cognitive decline and neurodegeneration observed in Alzheimer's disease (AD) but whether they represent initial factors or later changes of the disease is still a matter of debate. In this work, we aimed at investigating whether and to what extent neuronal-derived NO signaling and related neurovascular coupling are impaired along aging in the hippocampus of the triple transgenic mouse model of Alzheimer's Disease (3xTg-AD). We performed a longitudinal study combining behavior studies, in vivo simultaneous measurements of NO concentration gradients and cerebral blood flow (CBF), along with detection of NO synthase (NOS) and markers of nitroxidative stress. Our results revealed an impairment in the neurovascular coupling along aging in the 3xTg-AD mice which preceded obvious cognitive decline. This impairment was characterized by diminished CBF changes in response to normal or even increased NO signals and associated with markers of nitroxidative stress. The results suggest that impairment in neurovascular coupling is primarily due to cerebrovascular dysfunction, rather than due to dysfunctional NO signaling from neurons to blood vessels. Overall, this work supports cerebrovascular dysfunction as a fundamental underlying process in AD pathology.

NO-Releasing Enmein-Type Diterpenoid Derivatives with Selective Antiproliferative Activity and Effects on Apoptosis-Related Proteins

A series of nine enmein-type ent-kaurane diterpenoid and furoxan-based nitric oxide (NO) donor hybrids (10a-i) were designed and synthesized from commercially available oridonin (1). These hybrids were evaluated for their antiproliferative activity against Bel-7402, K562, MGC-803, and CaEs-17 human cancer cell lines and L-02 normal liver cells. The antiproliferative activity against tumor cells was stronger than the lead compound 1 and parent molecule 9 in most cases. Especially, compound 10f showed the strongest activity against human hepatocarcinoma Bel-7402 cell line with an IC50 of 0.81 μM and could also release 33.7 μmol/L NO at the time point of 60 min. Compounds 10a-i also showed cytotoxic selectivity between tumor and normal liver cells with IC50 ranging from 22.1 to 33.9 μM. Furthermore, the apoptotic properties on Bel-7402 cells revealed that 10f could induce S phase cell cycle arrest and apoptosis at low micromolar concentrations. The effects of 10f on apoptosis-related proteins were also investigated. The potent antiproliferative activities and mechanistic studies warrant further preclinical investigations.