Search

The stomach chemical environment promotes the production of new molecules that can induce post-translational modifications of endogenous proteins with physiological impact. The nitrate-nitrite-nitric oxide pathway is relevant in this process via production of nitric oxide ( • NO) and nitric oxide-derived nitrogen oxides (NOx) at high concentrations. Using a highly sensitive and selective chemiluminescence approach, we found that exposure the stomach of rats to nitrite yielded S - and N -nitroso derivatives in gastric mucus cysteine-rich glycoproteins (mucins). To lesser extent, the underlying epithelial cell layers also suffered nitrite-driven S - and N -nitroso modifications which increased upon mucus removal, indicating that, under normal nitrite load, • NO and NOx can reach inner layers of the stomach wall and locally modify proteins. S -nitrosation was by large the predominant modification. In vitro and ex vivo experiments indicated that the gastric nitrosation pattern is triggered by dietary nitrite in a concentration dependent manner, encompassing the intermediary formation of • NO and is susceptible to modulation by dietary reductants, notably red wine polyphenols. Collectively, these results suggest a protective action of the mucus and potential • NO-dependent biochemical effects at deeper cells layers of the mucosa. [ABSTRACT FROM AUTHOR]

Abstract: During the last two decades nitric oxide (·NO) gas has emerged as a novel and ubiquitous intercellular modulator of cell functions. In the brain, ·NO is implicated in mechanisms of synaptic plasticity but it is also involved in cell death pathways underlying several neurological diseases. Because of its hydrophobicity, small size, and rapid diffusion properties, the rate and pattern of ·NO concentration changes are critical determinants for the understanding of its diverse actions in the brain. ·NO measurement in vivo has been a challenging task due to its low concentration, short half‐life, and high reactivity with other biological molecules, such as superoxide radical, thiols, and heme proteins. Electrochemical methods are versatile approaches for detecting and monitoring various neurotransmitters. When associated with microelectrodes inserted into the brain they provide high temporal and spatial resolution, allowing measurements of neurochemicals in physiological environments in a real‐time fashion. To date, electrochemical detection of ·NO is the only available technique that provides a high sensitivity, low detection limit, selectivity, and fast response to measure the concentration dynamics of ·NO in vivo. We have used carbon fiber microelectrodes coated with two layers of Nafion and o‐phenylenediamine to monitor the rate and pattern of ·NO change in the rat brain in vivo. The analytical performance of microelectrodes was assessed in terms of sensitivity, detection limit, and selectivity ratios against major interferents: ascorbate, dopamine, noradrenaline, serotonin, and nitrite. For the in vivo recording experiments, we used a microelectrode/micropipette array inserted into the brain using a stereotaxic frame. The characterization of in vivo signals was assessed by electrochemical and pharmacological verification. Results support our experimental conditions that the measured oxidation current reflects variations in the ·NO concentration in brain extracellular space. We report results from recordings in hippocampus and striatum upon stimulation of N‐methyl‐d‐aspartate‐subtype glutamate receptors. Moreover, the kinetics of ·NO disappearance in vivo following pressure ejection of a ·NO solution is also addressed. [Copyright &y& Elsevier]

Alzheimer's disease (AD) is a multifactorial disease characterized by extracellular deposits of amyloid plaques and intracellular neurofibrillary tangles. These hallmark alterations are preceded by synaptic deterioration, changes in neuromolecular plasticity phenomena, mitochondrial dysfunction, increase in oxidative damage to cellular constituents and decreased energy metabolism. The hippocampus is a structure of the temporal medial lobe implicated in specific forms of memory processes. It is also one of the first and most affected regions of the CNS in AD. Here we present a novel approach to the study if mitochondrial function/disfunction in 2 rodent models of AD: an acute rat model obtained by intracerebroventricular injection of the toxin streptozotocin (STZ) and a progressive triple transgenic mouse model (3TgAD) harboring PS1 M146V , APP Swe , and tau P301L transgenes. Mitochondrial dysfunction has classically been assessed in such models by isolating mitochondria, synaptossoms or working with cell cultures. Anyone of these approaches destroys the intricate intercellular connectivity and cytoarchitecture of neuronal tissue. We used acute hippocampal slices obtained from the 2 models of AD and evaluated changes in mitochondrial function as a function of disease and/or age. Mitochondrial stress test were performed on the high resolution respirometry (Oroboros 2 K Oxymeter). Upon analysis of oxygen consumption rates (OCR) we observed significant decreases in basal OCR, maximal respiratory capacity, ATP turnover and a tendency for decrease in sparing capacity in the STZ rat model compared to shame injected animals. Regarding the 3TgAD model we observed an age-dependent decrease in all parameters evaluated in the mitochondrial stress test, in both 3TgAD and NTg animals. However, although a tendency towards decreased OCR was observed when comparing 3TgAD and age-matched NTg animals, no statistically significant difference was observed. [ABSTRACT FROM AUTHOR]

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 O 2 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. [ABSTRACT FROM AUTHOR]

Acetylcholine (ACh) modulates neuronal network activities implicated in cognition, including theta and gamma oscillations but the mechanisms remain poorly understood. Joint measurements of cholinergic activity and neuronal network dynamics with high spatio-temporal resolution are critical to understand ACh neuromodulation. However, current electrochemical biosensors are not optimized to measure nanomolar cholinergic signals across small regions like hippocampal sub-layers. Here, we report a novel oxidase-based electrochemical biosensor that matches these constraints. The approach is based on measurement of H 2 O 2 generated by choline oxidase (ChOx) in the presence of choline (Ch). The microelectrode design consists of a twisted pair of 50 µm diameter Pt/Ir wires (sensor and sentinel), which is scalable, provides high spatial resolution and optimizes common mode rejection. Microelectrode coating with ChOx in chitosan cross-linked with benzoquinone is simple, mechanically robust and provides high sensitivity (324±46 nA µM −1 cm −2 ), a limit of detection of 16 nM and a t 50 response time of 1.4 s. Local field potential (LFP)-related currents dominate high-frequency component of electrochemical recordings in vivo . We significantly improved signal-to-noise-ratio compared to traditional sentinel subtraction by a novel frequency domain common mode rejection procedure that accounts for differential phase and amplitude of LFP-related currents on the two channels. We demonstrate measurements of spontaneous nanomolar Ch fluctuations, on top of which micromolar Ch increases occurred during periods of theta activity in anesthetized rats. Measurements were not affected by physiological O 2 changes, in agreement with the low biosensor Km for O 2 (2.6 µM). Design and performance of the novel biosensor opens the way for multisite recordings of spontaneous cholinergic dynamics in behaving animals. [ABSTRACT FROM AUTHOR]

Background. Nitric oxide ( ∙ NO), a ubiquitous molecule involved in a plethora of signaling pathways, is produced from dietary nitrate in the gut through the so-called nitrate–nitrite–NO pathway. In the stomach, nitrite derived from dietary nitrate triggers a network of chemical reactions targeting endogenous and exogenous biomolecules, thereby producing new compounds with physiological activity. Objective. The aim of this study was to ascertain whether compounds with physiological relevance are produced in the stomach upon consumption of nitrate- and ethanol-rich foods. Design. Human volunteers consumed a serving of lettuce (source of nitrate) and alcoholic beverages (source of ethanol). After 15 min, samples of the gastric headspace were collected and ethyl nitrite was identified by GC–MS. Wistar rats were used to study the impact of ethyl nitrite on gastric smooth muscle relaxation at physiological pH. Result. Nitrogen oxides, produced from nitrite in the stomach, induce nitrosation of ethanol from alcoholic beverages in the human stomach yielding ethyl nitrite. Ethyl nitrite, a potent vasodilator, is produced in vivo upon the consumption of lettuce with either red wine or whisky. Moreover, at physiological pH, ethyl nitrite induces gastric smooth muscle relaxation through a cGMP-dependent pathway. Overall, these results suggest that ethyl nitrite is produced in the gastric lumen and releases ∙ NO at physiological pH, which ultimately may have an impact on gastric motility. Systemic effects may also be expected if ethyl nitrite diffuses through the gastric mucosa reaching blood vessels, therefore operating as a ∙ NO carrier throughout the body. Conclusion. These data pinpoint posttranslational modifications as an underappreciated mechanism for the production of novel molecules with physiological impact locally in the gut and highlight the notion that diet may fuel compounds with the potential to modulate gastrointestinal welfare. [ABSTRACT FROM AUTHOR]

Background Ascorbate and neuronal-derived nitric oxide ( NO) play regulatory roles in the brain that tare dependent on their compartmentalization and diffusion. Glutamatergic activation triggers both ascorbate fluxes toward extracellular medium and NO production. The information on the profiles of change in time and space upon glutamatergic activation is scarce and yet this knowledge is important for the understanding of ascorbate and NO functions in vivo, in particular in the case of a coupled interaction between both dynamics. Hypothesis NO produced upon NMDA receptor activation is a modulator of ascorbate release to the extracellular space. Methods In this work, carbon fiber microelectrodes for simultaneous measurements of these substances in the hippocampus were used to collect information about ascorbate and NO dynamic profiles in real time. Results Glutamate stimulation evoked transient ascorbate and NO signals with high degree of spatial and temporal correlation between them. Combined experiments encompassing direct stimulus with NO and inhibitors of glutamate uptake and nNOS provided additional evidence supporting the modulator role of NO in the release of ascorbate to the extracellular space. Conclusions The coupling between NO and ascorbate upon glutamatergic activation points to a functional impact on the activities of both compounds and, although the precise molecular mechanism needs to be clarified, such a coupling lays the foundations for new regulatory mechanisms in the brain. [ABSTRACT FROM AUTHOR]

The coupling between neuronal activity and cerebral blood flow (CBF) is essential for normal brain function. The mechanisms behind this neurovascular coupling process remain elusive, mainly because of difficulties in probing dynamically the functional and coordinated interaction between neurons and the vasculature in vivo. Direct and simultaneous measurements of nitric oxide (NO) dynamics and CBF changes in hippocampus in vivo support the notion that during glutamatergic activation nNOS-derived NO induces a time-, space-, and amplitude-coupled increase in the local CBF, later followed by a transient increase in local O2 tension. These events are dependent on the activation of the NMDA-glutamate receptor and nNOS, without a significant contribution of endothelial-derived NO or astrocyte-neuron signaling pathways. Upon diffusion of NO from active neurons, the vascular response encompasses the activation of soluble guanylate cyclase. Hence, in the hippocampus, neurovascular coupling is mediated by nNOS-derived NO via a diffusional connection between active glutamatergic neurons and blood vessels. [ABSTRACT FROM AUTHOR]

Abstract: Dietary nitrate is reduced to nitrite and nitric oxide (•NO) in the gut, producing reactive species able to nitrate proteins and lipids. We investigated intragastric production of •NO and nitrating agents in vivo by examining selective nitration of pepsinogen and pepsin. We further addressed the functional impact of nitration on peptic activity by evaluating the progression of secretagogue-induced ulcers. Pepsinogen nitration was assessed in healthy and diclofenac-induced ulcerated rat stomachs. Both groups were fed nitrite or water by oral gavage. Protein nitration was studied by immunofluorescence and immunoprecipitation. In parallel experiments, pentagastrin was administered to rats and nitrite was then instilled intragastrically. •NO levels were measured before and after nitrite administration by chemiluminescence. Macroscopic damage was assessed and nitrated pepsin was examined in the margin of ulcers. Protein nitration was detected physiologically in the stomach of healthy animals. Nitrite had a dual effect on intragastric nitration: overall nitration was decreased under physiological conditions but enhanced by acute inflammation. Pepsin and pepsinogen were also nitrated via a nitrite-dependent pathway. Nitration of both pepsin and its zymogen led to decreased peptic activity in response to classical substrates (e.g., collagen). Under conditions of acute ulceration, nitrite-dependent pepsin nitration prevented the development of gastric ulcers. Dietary nitrite generates nitrating agents in the stomach in vivo, markedly decreasing peptic activity. Under inflammatory and ulcerogenic conditions pepsin nitration attenuates the progression of gastric ulceration. These results suggest that dietary nitrite-dependent nitration of pepsin may have a novel antiulcerogenic effect in vivo. [Copyright &y& Elsevier]

Abstract: Inorganic nitrite, derived from the reduction of nitrate in saliva, has recently emerged as a protagonist in nitric oxide (•NO) biology as it can be univalently reduced to •NO, in the healthy human stomach. Important physiological implications have been attributed to nitrite-derived •NO in the gastrointestinal tract, namely modulation of host defense, blood flow, mucus formation and motility. At acidic pH, nitrite generates different nitrogen oxides depending on the local microenvironment (redox status, gastric content, pH, inflammatory conditions), including •NO, nitrogen dioxide (•NO2), dinitrogen trioxide (N2O3), and peroxynitrite. Thus, the gastric environment is a significant source of nitrating and nitrosating agents, especially in individuals consuming a nitrate/nitrite-rich diet on a daily basis. Both, the gastric lumen and mucosa contain putative targets for nitration, not only proteins and lipids from ingested aliments but also endogenous proteins secreted by the oxyntic glands. The physiological and functional consequences of nitration of gastric mediators will impact on local processes including food digestion and ulcerogenesis. Additionally, gastric nitration products (such as nitrated lipids) may be absorbed and affect systemic pathways. Thus, dietary ingestion of nitrate will have direct consequences for endogenous protein nitration, as indicated by our preliminary data. [Copyright &y& Elsevier]

Abstract: Nitrite, considered a biological waste and toxic product, is being regarded as an important physiological molecule in nitric oxide (emistry. Because the interaction of dietary phenolic compounds and nitrite would be kinetically (due to the high concentrations achieved) and thermodynamically (on basis of the redox potentials) feasible in the stomach, we have studied the potential reduction of nitrite by polyphenols present in several dietary sources. By measuring the time courses of tion in simulated gastric juice (pH 2), the efficiency of the compounds studied is as follows: Epicatechin-3-O-gallate>quercetin>procyanidin B8 dimer>oleuropein>procyanidin B2 dimer>chlorogenic acid>epicatechin>catechin>procyanidin B5 dimer. The initial rates of tion fall in a narrow range (ca. 1–5μMs−1) but the distinct kinetics of the decay of s suggest that competition reactions for erative. The proof of concept that, in the presence of nitrite, phenol-containing dietary products induce a strong increase of stomach was established in an in vivo experiment with healthy volunteers consuming lettuce, onions, apples, wine, tea, berries and cherries. Moreover, selected mixtures of oleuropein and catechin with low nitrite (1μM) were shown to induce muscle relaxation of stomach strips in a structure-dependent way. Data presented here brings strong support to the concept that polyphenols consumed in a variety of dietary products, under gastric conditions, reduce nitrite to in turn, may exert a biological impact as a local relaxant. [Copyright &y& Elsevier]

Abstract: Nitrite may be a source for nitric oxide ( NO), particularly in highly acidic environments, such as the stomach. Diet products contribute also with reductants that dramatically increase the production of NO from nitrite. Red wine has been attributed health promoting properties largely on basis of the reductive antioxidant properties of its polyphenolic fraction. We show in vitro that wine, wine anthocyanin fraction and wine catechol (caffeic acid) dose- and pH-dependently promote the formation of NO when mixed with nitrite, as measured electrochemically. The production of NO promoted by wine from nitrite was substantiated in vivo in healthy volunteers by measuring NO in the air expelled from the stomach, following consumption of wine, as measured by chemiluminescence. Mechanistically, the reaction involves the univalent reduction of nitrite, as suggested by the formation of NO and by the appearance of EPR spectra assigned to wine phenolic radicals. Ascorbic and caffeic acids cooperate in the reduction of nitrite to NO. Moreover, reduction of nitrite is critically dependent on the phenolic structure and nitro-derivatives of phenols are also formed, as suggested by caffeic acid UV spectral modifications. The reduction of nitrite may reveal previously unrecognized physiologic effects of red wine in connection with NO bioactivity. [Copyright &y& Elsevier]

Nitric oxide (NO⋅) is a diffusible regulatory molecule involved in a wide range of physiological and pathological events. At the tissue level, a local and temporary increase in NO⋅ concentration is translated into a cellular signal. From our current knowledge of biological synthesis and decay, the kinetics and mechanisms that determine NO⋅ concentration dynamics in tissues are poorly understood. Generally, NO⋅ mediates its effects by stimulating (e.g., guanylate cyclase) or inhibiting (e.g., cytochrome oxidase) transition metal-containing proteins and by post-translational modification of proteins (e.g., formation of nitrosothiol adducts). The borderline between the physiological and pathological activities of NO⋅ is a matter of controversy, but tissue redox environment, supramolecular organization and compartmentalisation of NO⋅ targets are important features in determining NO⋅ actions. In brain, NO⋅ synthesis in the dependency of glutamate NMDA receptor is a paradigmatic example; the NMDA-subtype glutamate receptor triggers intracellular signalling pathways that govern neuronal plasticity, development, senescence and disease, suggesting a role for NO⋅ in these processes. Measurements of NO⋅ in the different subregions of hippocampus, in a glutamate NMDA receptor-dependent fashion, by means of electrochemical selective microsensors illustrate the concentration dynamics of NO⋅ in the sub-regions of this brain area. The analysis of NO⋅ concentration–time profiles in the hippocampus requires consideration of at least two interrelated issues, also addressed in this review. NO⋅ diffusion in a biological medium and regulation of NO⋅ activity. [Copyright &y& Elsevier]

The brain has a very high energetic demand requiring a constant supply of O 2 and glucose. Coping with these requirements implies that only a restricted number of neuronal cells fire simultaneously and their metabolic needs are satisfied through the local and transient increase in cerebral blood flow (CBF) via the mechanism of neurovascular coupling (NYC), in a process mediated by • NO. However, when O 2 supply is diminished, this pathway for NYC is impaired. In this work we tested the hypothesis that under hypoxic conditions nitrite is a source of • NO in the brain, through its reduction by ascorbate. For that, we used an in vivo approach to monitor • NO and CBF dynamics in the hippocampus, involving the insertion of selective microelectrodes and arrays. Results show that the local microinjection of nitrite in animals submitted to short-term hypercapnia induced a transient increase of • NO in the nM range, concomitantly with transient increases in CBF. Furthermore, it was observed a decrease in extracellular levels of ascorbate timely coupled with the production of • NO. Results suggest that reduction of nitrite to • NO by ascorbate occurs in the brain, thus constituting a pathway for • NO mediated NYC when nNOS function is impaired due to limited availability of O 2 . [ABSTRACT FROM AUTHOR]

Alterations in nitric oxide ( • NO) concentration dynamics and bioactivity with age may play an important role in the decay of synaptic and metabolic functions in Alzheimer's disease (AD) by affecting plasticity and mitochondrial function. Here we performed a longitudinal study of the glutamate-NO signaling axis in the hippocampus of the triple transgenic mouse model of AD (3xTgAD). We found that, in the CA1 region, NMDAr-evoked • NO transients exhibited a progressive decrease in intensity with age, more pronounced in 3xTgAD as compared to non-transgenic groups. Age-dependent decrease in basal oxygen consumption was accompanied by a significant decrease in maximal respiratory rate. This prompted us to investigate whether • NO bioactivity may be shifted toward oxidative chemistry associated with neurotoxicity and indeed we observed age-dependent increase in 3-nitrotyrosine staining in the hippocampus, more pronounced in the 3xTgAD groups. We conclude that the biphasic change in • NO dynamics in the hippocampus may, at an early age, mitigate loss of synaptic strength but ultimately is diverted towards increased oxidative damage, which may contribute to energetic crisis. [ABSTRACT FROM AUTHOR]

Direct measurement of glucose in the brain extracellular space with high spatial and temporal resolution is needed for understanding of brain energy metabolism. In this work we developed and extensively characterized an amperometric glucose microbiosensor using ceramic-based platinum multisite microelectrode arrays (MEAs) for measuring extracellular glucose in the rat brain in vivo . Glucose-oxidase (GOx) was immobilized at the microelectrode surface by cross-linking with glutaraldehyde in the presence of BSA. The in vitro evaluations supported the high analytical performance of these microbiosensors for application in the brain, including high selectivity and sensitivity, adequate linear range and limit of detection, good operational stability and response time, minimal oxygen-, pH- and temperature-dependencies. The microbiosensors were successfully used for measurements of glucose with high temporal and spatial resolution in the hippocampus of anesthetized rats in response to systemic, local glucose changes and upon glutamatergic stimulation. Overall, the results support the suitability of these microbiosensors for measuring rapid changes of extracellular glucose in the rat brain. [ABSTRACT FROM AUTHOR]

Age-dependent changes in nitric oxide ( • NO) concentration dynamics may play a significant role in both decaying synaptic and metabolic functions in Alzheimer's disease (AD). This neuromodulator acts presynaptically to increase vesicle release and glutamatergic transmission and also regulates mitochondrial function. Under conditions of altered intracellular redox environment, • NO may react and produce reactive species such as peroxynitrite. Using the triple transgenic mouse model of AD (3xTgAD), we investigated age-dependent changes in the glutamate- • NO axis in the hippocampus. Direct measurement of • NO concentration dynamics revealed a significant increase in N -methyl-D-aspartate type receptor–evoked peak • NO in the 3xTgAD model at an early age. Aging produced a decrease in peak • NO accompanied by significant decrease in production and decay rates in the transgenic model. Evaluation of energy metabolism revealed age-dependent decrease in basal oxygen consumption rate, a general decrease in mitochondrial oxidative phosphorylation parameters, and loss in mitochondrial sparing capacity in both genotypes. Finally, we observed age-dependent increase in 3-nitrotyrosine residues in the hippocampus, consistent with a putative shift in • NO bioactivity toward oxidative chemistry associated with neurotoxicity. [ABSTRACT FROM AUTHOR]

Abstract: Nitric oxide ( NO) is a diffusible messenger that conveys information based on its concentration dynamics, which is dictated by the interplay between its synthesis, inactivation and diffusion. Here, we characterized NO diffusion in the rat brain in vivo. By direct sub-second measurement of NO, we determined the diffusion coefficient of NO in the rat brain cortex. The value of 2.2×10−5 cm2/s obtained in vivo was only 14% lower than that obtained in agarose gel (used to evaluate NO free diffusion). These results reinforce the view of NO as a fast diffusing messenger but, noticeably, the data indicates that neither NO diffusion through the brain extracellular space nor homogeneous diffusion in the tissue through brain cells can account for the similarity between NO free diffusion coefficient and that obtained in the brain. Overall, the results support that NO diffusion in brain tissue is heterogeneous, pointing to the existence of a pathway that facilitates NO diffusion, such as cell membranes and other hydrophobic structures. [Copyright &y& Elsevier]

Abstract: By acting as a bioreactor, affording chemical and mechanical conditions for the reaction between dietary components, the stomach may be a source of new bioactive molecules. Using gas chromatography-mass spectrometry we here demonstrate that, under acidic gastric conditions, ethyl nitrite is formed in µM concentrations from the reaction of red wine or distilled alcoholic drinks with physiological amounts of nitrite. Rat femoral artery rings and gastric fundus strips dose-dependently relaxed upon exposure to nitrite:ethanol mixtures. In contrast, when administered separately in the same dose ranges, nitrite evoked only minor vasorelaxation while ethanol actually caused a slight vasoconstriction. Mechanistically, the relaxation effect was assigned to generation of nitric oxide (•NO) as supported by direct demonstration of •NO release from ethyl nitrite and the absence of relaxation in the presence of the soluble guanylyl cyclase inhibitor, ODQ. In conclusion, these results suggest that ethanol in alcoholic drinks interacts with salivary-derived nitrite in the acidic stomach leading to the production of the potent smooth muscle relaxant ethyl nitrite. These findings reveal an alternative chemical reaction pathway for dietary nitrate and nitrite with possible impact on gastric physiology and pathophysiology. [Copyright &y& Elsevier]

Midlife hypercholesterolemia may contribute to onset of Alzheimer's disease (AD) in later life, however the mechanistic link between the two is poorly understood. Here we compared the effect of a 6-week high-fat/cholesterol diet (HFCD) in young (6-mo) mice with a genetic model of AD (3xTgAD), evaluating cognitive function, hippocampal synaptic plasticity, oxidative metabolism and the integrity of the blood-brain barrier (BBB). Despite producing a modest increase in serum cholesterol levels (10%), the HFCD induced significant alterations in cognitive function (novel object recognition, y-maze and water maze tests) comparable to those observed in age-matched 3xTgAD mice. At the synaptic level, HFCD and AD-genotype induced similar loss of LTP strength, accompanied by a decrease in maximal NMDAr-evoked NO production in hippocampal slices. HFCD-induced synaptic dysfunction was mainly post synaptic as revealed by PPF, while in the 3xTgAD mice a presynaptic component was also evident. HFCD also induced significant comprise of mitochondrial oxidative metabolism, including sparing capacity, while slightly affecting BBB integrity. We conclude that HFCD may, to an extent, induce Alzheimer's like disease in young mice similar to that observed in age-matched 3xTgAD mice. [ABSTRACT FROM AUTHOR]

The increase in lifespan is accompanied by an increased risk of developing neurodegenerative disorders. Several studies have suggested age-dependent alterations in nitric oxide ( • NO) signaling, cerebral blood flow (CBF) and brain metabolism, but the putative connection and the temporal pattern between them still requires demonstration. In this work, we performed in vivo simultaneous measurements of • NO, O 2 and CBF in response to glutamatergic activation in the hippocampus of F344 rats along age progression and correlated them with cognitive performance. We found that glutamate-induced • NO dynamics were not significantly affected but the correspondent hemodynamic changes were progressively diminished during aging coupled to a decline in learning and memory. In spite of a compromised blood supply, aged rats exhibited an increased ∆pO 2 suggestive of decreased global metabolic rate. We were able to mimic in young rats the neurovascular uncoupling observed with aging by promoting an unbalance in redox status toward oxidation suggesting a prominent role of oxidative stress. Overall, data supports an impairment of microvascular response in connection with cognitive decline and suggests the contribution of oxidative environment-dependent compromised NO signaling from neurons to vessels. [ABSTRACT FROM AUTHOR]

Nitrate from green-leafy vegetables is sequentially reduced to nitrite in the oral cavity and to nitric oxide (ŸNO) in the stomach. Here, ŸNO increases mucosal blood flow, mucus thickness and prevents microbial infections. Gut microbiota is pivotal in the maintenance of local and systemic welfare as dysbiosis is associated with increased epithelial permeability and with the activation of inflammatory pathways. Herein, we investigated the impact of nitrate on gut microbiome and ensued mucosal effects. Wistar rats were divided in 4 groups and the drinking water was supplemented with 1) antibiotic cocktail (neomycin, bacitracin, imipenem), 2) antibiotic cocktail nitrate, 3) nitrate, 4) tap water (control). Animals were weighted daily. After 7 days they were anesthetized and euthanized. Feces were collected before and after the treatment. Ceca were collected and weighted. The stomach and ascending colon were isolated and occludin, claudin-5, -15 as well as myeloperoxidase (MPO) and iNOS were analyzed. Bacterial DNA was analyzed by DGGE. Antibiotics induced weight loss and cecamegalia (p<0.05) in all animals but nitrate supplementation prevented such effects, likely through a more efficient harvesting of nutrients and preserved motility. The gastric expression of occludin and claudin-5 was decreased during dysbiosis, but both protein levels were recovered by nitrate (p<0.05). Similarly, nitrate prevented MPO and iNOS overexpression under dysbiosis (p<0.05) in the rat stomach. In the large intestine, nitrate increased claudin-5 expression under dysbiosis (p<0.01) but had the opposite effect on occludin (p<0.001). Rats treated with antibiotics and nitrate showed a microflora richness similar to control animals, which suggests that gastric generation of ŸNO recovers gut microbiota during dysbiosis. This data supports that dietary nitrate may rescue gastric epithelial integrity and gut microbiota during dysbiosis and therefore its consumption may be useful when antibiotics are prescribed to treat infections. [ABSTRACT FROM AUTHOR]