Dietary nitrite attenuates oxidative stress and activates antioxidant genes in rat heart during hypobaric hypoxia

Lifelong exposure to high-altitude hypoxia in humans is associated with improved redox homeostasis and structural-functional adaptations of the neurovascular unit

High-altitude (HA) hypoxia may alter the structural-functional integrity of the neurovascular unit (NVU). Herein, we compared male lowlanders (n = 9) at sea level (SL) and after 14 days acclimatization to 4300 m (chronic HA) in Cerro de Pasco (CdP), Péru (HA), against sex-, age- and body mass index-matched healthy highlanders (n = 9) native to CdP (lifelong HA). Venous blood was assayed for serum proteins reflecting NVU integrity, in addition to free radicals and nitric oxide (NO). Regional cerebral blood flow (CBF) was examined in conjunction with cerebral substrate delivery, dynamic cerebral autoregulation (dCA), cerebrovascular reactivity to carbon dioxide (CVRCO2 ) and neurovascular coupling (NVC). Psychomotor tests were employed to examine cognitive function. Compared to lowlanders at SL, highlanders exhibited elevated basal plasma and red blood cell NO bioavailability, improved anterior and posterior dCA, elevated anterior CVRCO2 and preserved cerebral substrate delivery, NVC and cognition. In highlanders, S100B, neurofilament light-chain (NF-L) and T-tau were consistently lower and cognition comparable to lowlanders following chronic-HA. These findings highlight novel integrated adaptations towards regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia. KEY POINTS: High-altitude (HA) hypoxia has the potential to alter the structural-functional integrity of the neurovascular unit (NVU) in humans. For the first time, we examined to what extent chronic and lifelong hypoxia impacts multimodal biomarkers reflecting NVU structure and function in lowlanders and native Andean highlanders. Despite lowlanders presenting with a reduction in systemic oxidative-nitrosative stress and maintained cerebral bioenergetics and cerebrovascular function during chronic hypoxia, there was evidence for increased axonal injury and cognitive impairment. Compared to lowlanders at sea level, highlanders exhibited elevated vascular NO bioavailability, improved dynamic regulatory capacity and cerebrovascular reactivity, comparable cerebral substrate delivery and neurovascular coupling, and maintained cognition. Unlike lowlanders following chronic HA, highlanders presented with lower concentrations of S100B, neurofilament light chain and total tau. These findings highlight novel integrated adaptations towards the regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia.

Dissolved oxygen gradient on three dimensionally printed microfluidic platform for studying its effect on fish at three levels: cell, embryo, and larva

A simple and low-cost dissolved oxygen gradient platform of three dimensionally (3D) printed microfluidic chip was developed for cultivating cells, embryos, and larvae of fish. "Christmas tree" structure channel networks generated a dissolved oxygen gradient out of two fluids fed to the device. Polydimethylsiloxane (PDMS) membrane with high biocompatibility was used as the substrate for cell culture in the 3D-printed microfluidic chip, which made the cell analysis easy. The embryos and larvae of fish could be cultured directly in the chip, and their development can be observed in real time with a microscope. Using zebrafish as a model, we assessed the effect of different dissolved oxygen on its cells, embryos, and larvae. Hypoxia induced production of reactive oxygen species (ROS) in zebrafish cells, embryos, and larvae, eventually leading to cell apoptosis and developmental impairment. Hypoxia also increased nitric oxide content in zebrafish cells, which might be a defensive strategy to overcome the adverse effect of hypoxia in fish cells. This is the first platform that could comprehensively investigate the effects of different dissolved oxygen on fish at the cell, embryo, and larva levels, which has great potential in studying the responses of aquatic organisms under different oxygen concentrations.

Long-lasting blood pressure lowering effects of nitrite are NO-independent and mediated by hydrogen peroxide, persulfides, and oxidation of protein kinase G1α redox signalling

AIMS

Under hypoxic conditions, nitrite (NO2-) can be reduced to nitric oxide (NO) eliciting vasorelaxation. However, nitrite also exerts vasorelaxant effects of potential therapeutic relevance under normal physiological conditions via undetermined mechanisms. We, therefore, sought to investigate the mechanism(s) by which nitrite regulates the vascular system in normoxia and, specifically, whether the biological effects are a result of NO generation (as in hypoxia) or mediated via alternative mechanisms involving classical downstream targets of NO [e.g. effects on protein kinase G1α (PKG1α)].

METHODS AND RESULTS

Ex vivo myography revealed that, unlike in thoracic aorta (conduit vessels), the vasorelaxant effects of nitrite in mesenteric resistance vessels from wild-type (WT) mice were NO-independent. Oxidants such as H2O2 promote disulfide formation of PKG1α, resulting in NO- cyclic guanosine monophosphate (cGMP) independent kinase activation. To explore whether the microvascular effects of nitrite were associated with PKG1α oxidation, we used a Cys42Ser PKG1α knock-in (C42S PKG1α KI; 'redox-dead') mouse that cannot transduce oxidant signals. Resistance vessels from these C42S PKG1α KI mice were markedly less responsive to nitrite-induced vasodilation. Intraperitoneal (i.p.) bolus application of nitrite in conscious WT mice induced a rapid yet transient increase in plasma nitrite and cGMP concentrations followed by prolonged hypotensive effects, as assessed using in vivo telemetry. In the C42S PKG1α KI mice, the blood pressure lowering effects of nitrite were lower compared to WT. Increased H2O2 concentrations were detected in WT resistance vessel tissue challenged with nitrite. Consistent with this, increased cysteine and glutathione persulfide levels were detected in these vessels by mass spectrometry, matching the temporal profile of nitrite's effects on H2O2 and blood pressure.

CONCLUSION

Under physiological conditions, nitrite induces a delayed and long-lasting blood pressure lowering effect, which is NO-independent and occurs via a new redox mechanism involving H2O2, persulfides, and PKG1α oxidation/activation. Targeting this novel pathway may provide new prospects for anti-hypertensive therapy.

Protective effects of two novel nitronyl nitroxide radicals on heart failure induced by hypobaric hypoxia

AIMS

Hypobaric hypoxia (HH), linked to oxidative stress, impairs cardiac function. We synthesized a novel nitronyl nitroxide radical, an HPN derivative (HEPN) and investigated the protective effects of HEPN and HPN against HH-induced heart injury in mice and the underlying mechanisms of action.

MAIN METHODS

Mice were administered with HPN (200 mg/kg) or HEPN (200 mg/kg) 30 min before exposed to HH. The cardiac function was measured. Serum AST, CK, LDH and cTnI were estimated. Heart tissue oxidase activity, SOD, CAT, GSH-Px, ROS and MDA were estimated. ATP content, Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activity was measured. The expression of HIF-1, VEGF, Nrf2, HO-1, Bax, Bcl-2, Caspase-3 was estimated.

KEY FINDINGS

Results showed that pretreatment with HEPN or HPN led to a dramatic decrease in the activity of biochemical markers AST, CK, LDH and cTnI in murine serum. They increased the activity of SOD, CAT and GSH-Px and reduced the level of ROS and MDA in the hearts of mice. HEPN and HPN could increase the expression of Nrf2 and OH-1. They could maintain the ATPase activity. The Bax and Caspase-3 expression as well as the ratio of Bax/Bcl-2 were significantly downregulated and the Bcl-2 expression was upregulated by HPN or HEPN compared to the HH group. They may attenuate the HH-induced oxidant stress via free radical scavenging activity.

SIGNIFICANCE

The present study showed that the nitronyl nitroxide radical HEPN and HPN may be potential therapeutic agents for treatment of HH-induced cardiac dysfunction.

Circulating markers of nitric oxide homeostasis and cardiometabolic diseases: insights from population-based studies

Emerging data suggest that impaired nitric oxide (NO) homeostasis has a key role in development of cardiometabolic disorders. The association between circulating levels of NO metabolites, i.e. nitrate and nitrite (NOx), and risk of chronic diseases has not yet been fully clarified. This work aims to address epidemiologic aspects of NO metabolism and discusses different physiologic and pathophysiologic conditions influencing circulating NOx. Further, cross-sectional associations of serum NOx with metabolic disorders are described and along the way, potential short-term and long-term power of serum NOx for predicting cardiometabolic outcomes are reviewed. Results from population-based studies show that circulating NOx is affected by aging, smoking habits, pregnancy, menopause status, thyroid hormones, and various pathologic conditions including type 2 diabetes, insulin resistance, hypertension, and renal dysfunction. Lifestyle factors, especially dietary habits, but also smoking habits and the degree of physical activity influence NO homeostasis and the circulating levels of NOx. Elevated serum NOx, due to increased iNOS activity, is associated with increased incidence of metabolic syndrome, different obesity phenotypes, and cardiovascular events.

Competing trends of ROS and RNS-mediated protein modifications during hypoxia as an alternate mechanism of NO benefits

Hypoxia, especially altitude associated hypoxia is known to cause severe physiological alterations and life-threatening conditions. Impaired redox balance along with oxidative stress, protein carbonylation and instigation of apoptotic events are common sub-cellular events that follow the hypoxic insult. The role of nitric oxide (NO) is very dynamic and versatile in preventing the ill effects of hypoxia vis-a-vis reacting with oxidative species and causing protein nitrosylation. Although several mechanisms of NO-mediated cytoprotection are known during hypoxic insult, limited pieces of evidence are available to support the relationship between two downstream events of oxidative stress, protein carbonylation (caused by carbonyl; CO radical) and protein nitrosylation/nitration (caused by NO/peroxynitrite; ONOO radical). In this study, we investigated an entirely new aspect of NO protection in hypoxia involving crosstalk between carbonylation and nitrosylation. Using standard NO inhibitor l-NAME and simulated hypoxic conditions in hypoxia-sensitive cell line H9c2, we evaluated the levels of radicals, cell death, mitochondrial membrane potential, levels of protein nitrosylation, protein nitration and carbonylation and glutathione content. The results were then carefully analyzed in light of NO bioavailability. Our study shows that reducing NO during hypoxia caused cell death via the increased degree of carbonylation in proteins. This provides a new aspect of NO benefits which furthers opens new possibilities to explore potential mechanisms and effects of cross-talk between nitrosylation, protein nitration and carbonylation, especially through some common antioxidant mediators such as glutathione and thioredoxin.

Effects of long-term nitrate supplementation on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in male obese type 2 diabetic rats

PURPOSE

Supplementation with inorganic nitrate to boost the nitrate-nitrite-nitric oxide (NO) pathway, may act as a potential therapeutic agent in diabetes. The aim of this study was to determine the effects of nitrate on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in obese type 2 diabetic rats.

METHODS

Male Wistar rats were divided into 4 groups: Control, control + nitrate, diabetes, and diabetes + nitrate. Diabetes was induced using a high-fat diet and low-dose of streptozotocin. Sodium nitrate (100 mg/L in drinking water) was administered simultaneously for two months. Serum levels of fasting glucose, insulin, and lipid profiles were measured every 2-weeks. Glycated hemoglobin (HbA1c) was measured monthly. Serum thiobarbituric reactive substances (TBARS) level and catalase activity were measured before and after treatment. At the end of the study, glucose, pyruvate, and insulin tolerance tests were done. Glucose-stimulated insulin secretion (GSIS) and insulin content from isolated pancreatic islets were also assessed; mRNA expression of iNOS as well as mRNA expression and protein levels of GLUT4 in insulin-sensitive tissues, and serum IL-1β were determined.

RESULTS

Nitrate supplementation in diabetic rats significantly improved glucose tolerance, lipid profiles, and catalase activity as well as decreased gluconeogenesis, fasting glucose, insulin, and IL-1β; although it had no significant effect on GSIS, islet insulin content, HbA1c, and serum TBARS. Compared to the controls, in diabetic rats, mRNA expression and protein levels of GLUT4 were significantly lower in the soleus muscle (54% and 34%, respectively) and epididymal adipose tissue (67% and 41%, respectively). In diabetic rats, nitrate administration increased GLUT4 mRNA expression and protein levels in both soleus muscle (215% and 17%, respectively) and epididymal adipose tissue (344% and 22%, respectively). In diabetic rats, nitrate significantly decreased elevated iNOS mRNA expression in both the soleus muscle and epididymal adipose tissue.

CONCLUSION

Chronic nitrate supplementation in obese type 2 diabetic rats improved glucose tolerance, insulin resistance, and dyslipidemia; these favorable effects were associated with increased mRNA and protein expression of GLUT4 and decreased mRNA expression of iNOS in insulin-sensitive tissues, and with decreased gluconeogenesis, inflammation, and oxidative stress.

Chronic administration of sodium nitrite prevents hypertension and protects arterial endothelial function by reducing oxidative stress in angiotensin II-infused mice

AIM

Endothelial dysfunction accompanied by an increase in oxidative stress is a key event leading to hypertension. As dietary nitrite has been reported to exert antihypertensive effect, the present study investigated whether chronic oral administration of sodium nitrite improves vascular function in conduit and resistance arteries of hypertensive animals with elevated oxidative stress.

METHODS

Sodium nitrite (50mg/L) was given to angiotensin II-infused hypertensive C57BL/6J (eight to ten weeks old) mice for two weeks in the drinking water. Arterial systolic blood pressure was measured using the tail-cuff method. Vascular responsiveness of isolated aortae and renal arteries was studied in wire myographs. The level of nitrite in the plasma and the cyclic guanosine monophosphate (cGMP) content in the arterial wall were determined using commercially available kits. The production of reactive oxygen species (ROS) and the presence of proteins (nitrotyrosine, NOx-2 and NOx-4) involved in ROS generation were evaluated with dihydroethidium (DHE) fluorescence and by Western blotting, respectively.

RESULTS

Chronic administration of sodium nitrite for two weeks to mice with angiotensin II-induced hypertension decreased systolic arterial blood pressure, reversed endothelial dysfunction, increased plasma nitrite level as well as vascular cGMP content. In addition, sodium nitrite treatment also decreased the elevated nitrotyrosine and NOx-4 protein level in angiotensin II-infused hypertensive mice.

CONCLUSIONS

The present study demonstrates that chronic treatment of hypertensive mice with sodium nitrite improves impaired endothelium function in conduit and resistance vessels in addition to its antihypertensive effect, partly through inhibition of ROS production.

Acute oral dose of sodium nitrite induces redox imbalance, DNA damage, metabolic and histological changes in rat intestine

Industrialization and unchecked use of nitrate/nitrite salts for various purposes has increased human exposure to high levels of sodium nitrite (NaNO₂) which can act as a pro-oxidant and pro-carcinogen. Oral exposure makes the gastrointestinal tract particularly susceptible to nitrite toxicity. In this work, the effect of administration of a single acute oral dose of NaNO₂ on rat intestine was studied. Animals were randomly divided into four groups and given single doses of 20, 40, 60 and 75 mg NaNO₂/kg body weight. Untreated animals served as the control group. An NaNO₂ dose-dependent decline in the activities of brush border membrane enzymes, increase in lipid peroxidation, protein oxidation, hydrogen peroxide levels and decreased thiol content was observed in all treated groups. The activities of various metabolic and antioxidant defense enzymes were also altered. NaNO₂ induced a dose-dependent increase in DNA damage and DNA-protein crosslinking. Histopathological studies showed marked morphological damage in intestinal cells. The intestinal damage might be due to nitrite-induced oxidative stress, direct action of nitrite anion or chemical modification by reaction intermediates.

ARM-microcontroller based portable nitrite electrochemical analyzer using cytochrome c reductase biofunctionalized onto screen printed carbon electrode

Nitrite (NO₂^-) supplementation limits hypoxia-induced oxidative stress and activates the alternate NO pathway which may partially account for the nitrite-mediated cardioprotection. So, sensitive and selective biosensors with point-of-care devices need to be explored to detect the physiological nitrite level due to its important role in human pathophysiology. In this work, cytochrome c reductase (CcR) biofunctionalized self assembled monolayer (SAM) functionalized on gold nanoparticles (GNPs) in polypyrrole (PPy) nanocomposite onto the screen printed carbon electrode (SPCE) was investigated as a biosensor for the detection of nitrite based on its electrochemical and catalytic properties. CcR was covalently coupled with SAM layers on GNPs by using EDC and NHS. Direct electrochemical response of CcR biofunctionalized electrodes showed a couple of well-defined and nearly reversible cyclic voltammetric peaks at -0.34 and -0.45 vs. Ag/AgCl. Under optimal conditions, the biosensor could be used for the determination of NO₂^- with a linear range from 0.1-1600µm and a detection limit of 60nM with a sensitivity of 0.172µAµM^-1cm^-2. Further, we have designed and developed a novel and cost effective portable electrochemical analyzer for the measurement of NO₂^- in hypoxia induced H9c2 cardiac cells using ARM microcontroller. The results obtained here using the developed portable electrochemical nitrite analyzer were also compared with the standard cyclic voltammetry instrument and found in agreement with each other.

Revisiting cobalt chloride preconditioning to prevent hypobaric hypoxia-induced damage: identification of global proteomic alteration and key networks

Several studies have supported the hypoxia mimetic roles and cytoprotective properties of cobalt chloride in vitro and in vivo. However, a clear understanding of biological process-based mechanism that integrates the available information remains unknown. This study was aimed to explore the potential mechanism of cobalt chloride deciphering its benefits and well-known physiological challenge caused by hypobaric hypoxia that reportedly affects nearly 24 % of the global population. In order to explore the mechanism of CoCl2, we used global proteomic and systems biology approach in rat model to provide a deeper insight into molecular mechanisms of preconditioning. Furthermore, key conclusions were drawn based on biological network analysis and their enrichment with ontological overlaps. The study was further strengthened by consistent identification of validation of proteins using immunoblotting. CoCl2-pretreated animals exposed to hypoxia showed two significant networks, one lipid metabolism and other cell cycle associated, with a total score of 23 and eight focus molecules. In this study, we delineated two primary routes: one, by direct modulation of reactive oxygen species metabolism and, second, by regulation of lipid metabolism which was not known until now. The previously known benefits of cobalt chloride during physiological challenge by hypobaric hypoxia are convincing and could be explained by some basic set of metabolic and molecular reorganization within the hypoxia model. Interestingly, we also observed some of the completely unknown roles of cobalt chloride such as regulation of lipid that could undulate the translational roles of cobalt chloride supplementation beyond hypoxia preconditioning.

Protective effect of exogenous nitrite in postoperative ileus

BACKGROUND AND PURPOSE

As the pathogenesis of postoperative ileus (POI) involves inflammation and oxidative stress, comparable to ischaemia/reperfusion injury which can be ameliorated with nitrite, we investigated whether nitrite can protect against POI and explored the mechanisms involved.

EXPERIMENTAL APPROACH

We used intestinal manipulation (IM) of the small intestine to induce POI in C57BL/6J mice. Sodium nitrite (48 nmol) was administered intravenously just before IM. Intestinal transit was assessed using fluorescent imaging. Bethanechol-stimulated jejunal circular muscle contractions were measured in organ baths. Inflammatory parameters, neutrophil infiltration, inducible NOS (iNOS) activity, reactive oxygen species (ROS) levels, mitochondrial complex I activity and cGMP were measured in the intestinal muscularis.

KEY RESULTS

Pre-treatment with nitrite markedly improved the delay in intestinal transit and restored the reduced intestinal contractility observed 24 h following IM. This was accompanied by reduced protein levels of TNF-α, IL-6 and the chemokine CCL2, along with reduced iNOS activity and ROS levels. The associated neutrophil influx at 24 h was not influenced by nitrite. IM reduced mitochondrial complex I activity and cGMP levels; treatment with nitrite increased cGMP levels. Pre-treatment with the NO scavenger carboxy-PTIO or the soluble guanylyl cyclase inhibitor ODQ abolished nitrite-induced protective effects.

CONCLUSIONS AND IMPLICATIONS

Exogenous nitrite deserves further investigation as a possible treatment for POI. Nitrite-induced protection of POI in mice was dependent on NO and this effect was not related to inhibition of mitochondrial complex I, but did involve activation of soluble guanylyl cyclase.

Consistent antioxidant and antihypertensive effects of oral sodium nitrite in DOCA-salt hypertension

Hypertension is a common disease that includes oxidative stress as a major feature, and oxidative stress impairs physiological nitric oxide (NO) activity promoting cardiovascular pathophysiological mechanisms. While inorganic nitrite and nitrate are now recognized as relevant sources of NO after their bioactivation by enzymatic and non-enzymatic pathways, thus lowering blood pressure, mounting evidence suggests that sodium nitrite also exerts antioxidant effects. Here we show for the first time that sodium nitrite exerts consistent systemic and vascular antioxidant and antihypertensive effects in the deoxycorticosterone-salt (DOCA-salt) hypertension model. This is particularly important because increased oxidative stress plays a major role in the DOCA-salt hypertension model, which is less dependent on activation of the renin-angiotensin system than other hypertension models. Indeed, antihypertensive effects of oral nitrite were associated with increased plasma nitrite and nitrate concentrations, and completely blunted hypertension-induced increases in plasma 8-isoprostane and lipid peroxide levels, in vascular reactive oxygen species, in vascular NADPH oxidase activity, and in vascular xanthine oxidoreductase activity. Together, these findings provide evidence that the oral administration of sodium nitrite consistently decreases the blood pressure in association with major antioxidant effects in experimental hypertension.

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Nitrite is known to recycle back to NO under specific conditions.

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Antihypertensive effects have been shown for sodium nitrite in some animal models.

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The DOCA-salt hypertension model includes oxidative stress as a major pathogenetic mechanism.

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This study shows antihypertensive effects of nitrite in the DOCA-salt hypertension model.

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Reduction in arterial blood pressure was associated with important antioxidant effects of sodium nitrite.

Sodium nitrite supplementation improves motor function and skeletal muscle inflammatory profile in old male mice

Aging is associated with motor declines that lead to functional limitations and disability, necessitating the development of therapies to slow or reverse these events. We tested the hypothesis that sodium nitrite supplementation attenuates declines in motor function in older C57BL/6 mice. Motor function was assessed using a battery of tests (grip strength, open-field distance, rota-rod endurance) in old animals (age 20-24 mo) at baseline and after 8 wk of sodium nitrite (old nitrite, n = 22, 50 mg/liter) or no treatment (old control, n = 40), and in young reference animals (3 mo, n = 87). Eight weeks of sodium nitrite supplementation improved grip strength (old nitrite, +12.0 ± 14.9% vs. old control, +1.5 ± 15.2%, P < 0.05) and open field distance (old nitrite, +9.5 ± 7.7%, P < 0.01 vs. old control, -28.1 ± 2.0%) and completely restored rota-rod endurance-run time (old nitrite, +3.2 ± 7.1%, P < 0.01 vs. old control, -21.5 ± 7.2%; old nitrite after treatment P > 0.05 vs. young reference). Inflammatory cytokines were markedly increased in quadriceps of old compared with young reference animals (by ELISA, interleukin-1β [IL-1β] 3.86 ± 2.34 vs. 1.11 ± 0.74, P < 0.05; interferon-gamma [INF-γ] 8.31 ± 1.59 vs. 3.99 ± 2.59, P < 0.01; tumor necrosis factor-alpha [TNF-α] 1.69 ± 0.44 vs. 0.76 ± 0.30 pg/ml, P < 0.01), but were reduced to young reference levels after treatment (old nitrite, IL-1β 0.67 ± 0.95; INF-γ 5.22 ± 2.01, TNF-α 1.21 ± 0.39 pg/ml, P < 0.05 vs. old control, P > 0.05 vs. young reference). Cytokine expression and treatment (old nitrite vs. old control) predicted strength (R(2) = 0.822, P < 0.001, IL-1β, INF-γ, group), open field distance (R(2) = 0.574, P < 0.01, IL-1β, group) and endurance run time (R(2) = 0.477, P < 0.05, INF-γ). Our results suggest that sodium nitrite improves motor function in old mice, in part by reducing low-grade inflammation in muscle.

Acclimatization to long-term hypoxia: gene expression in ovine carotid arteries

Exposure to acute high-altitude hypoxia is associated with an increase in cerebral blood flow (CBF) as a consequence of low arterial O2 tension. However, in response to high altitude acclimatization, CBF returns to levels similar to those at sea level, and tissue blood flow is maintained by an increase in angiogenesis. Of consequence, dysregulation of the acclimatization responses and CBF can result in acute mountain sickness, acute cerebral and/or pulmonary edema. To elucidate the signal transduction pathways involved in successful acclimatization to high altitude, in ovine carotid arteries, we tested the hypothesis that high altitude-associated long-term hypoxia results in changes in gene expression of critical signaling pathways. We acclimatized nonpregnant adult sheep to 3,801 m altitude for ∼110 days and conducted oligonucleotide microarray experiments on carotid arteries. Of a total of 116 regulated genes, 58 genes were significantly upregulated and 58 genes were significantly downregulated (each >2-fold, P < 0.05). Major upregulated genes included suprabasin and myelin basic protein, whereas downregulated genes included BAG2. Several of these genes are known to activate the ERK canonical signal transduction pathway and the process of angiogenesis. We conclude that among other changes, the altered signal transduction molecules involved in high-altitude acclimatization are associated ERK activation and angiogenesis.

The antihypertensive effects of sodium nitrite are not associated with circulating angiotensin converting enzyme inhibition

Nitrite-derived nitric oxide (NO) formation exerts antihypertensive effects. Because NO inhibits angiotensin converting enzyme (ACE) activity, we carried a comprehensive series of experiments in rats to test the hypothesis that sodium nitrite exerts antihypertensive effects by inhibiting ACE. We examined whether sodium nitrite (15 mg/kg; or vehicle; by gavage): (I) attenuates the pressor responses to angiotensin I at doses of 0.03, 0.1, 0.3, 1, 3, and 10 μg/kg intravenously; (II) attenuates the acute hypertension induced by L-NAME (100 mg/kg; or vehicle; by gavage); (III) attenuates the chronic hypertension induced by L-NAME (1 g/L in drinking water; or vehicle) administered for 6 weeks; (IV) attenuates the hypertension in the 2 kidney-1 clip (2K1C) chronic hypertension model. Blood samples were collected at the end of each study and plasma angiotensin converting enzyme (ACE) activity was measured with a fluorimetric assay using Hippuryl-His-Leu as substrate. ACE inhibitors were used as positive controls. Plasma nitrite concentrations were measured by ozone-based reductive chemiluminescence. The in vitro effects of sodium nitrite (0, 1, 3, 10, 30, 100 μmol/L) on plasma ACE activity were also determined. We found that sodium nitrite did not affect the pressor responses to angiotensin I. Moreover, while sodium nitrite exerted significant antihypertensive effects in acute and chronic hypertension models, no significant effects on plasma ACE activity were found. In vitro experiments showed no effects of sodium nitrite on plasma ACE activity. This is the first study to demonstrate that the acute and chronic antihypertensive effects of sodium nitrite are not associated with significant inhibition of circulating ACE activity.

Inorganic nitrite supplementation for healthy arterial aging

Aging is the major risk factor for cardiovascular diseases (CVD). This is attributable primarily to adverse changes in arteries, notably, increases in large elastic artery stiffness and endothelial dysfunction mediated by inadequate concentrations of the vascular-protective molecule, nitric oxide (NO), and higher levels of oxidative stress and inflammation. Inorganic nitrite is a promising precursor molecule for augmenting circulating and tissue NO bioavailability because it requires only a one-step reduction to NO. Nitrite also acts as an independent signaling molecule, exerting many of the effects previously attributed to NO. Results of recent studies indicate that nitrite may be effective in the treatment of vascular aging. In old mice, short-term oral sodium nitrite supplementation reduces aortic pulse wave velocity, the gold-standard measure of large elastic artery stiffness, and ameliorates endothelial dysfunction, as indicated by normalization of NO-mediated endothelium-dependent dilation. These improvements in age-related vascular dysfunction with nitrite are mediated by reductions in oxidative stress and inflammation, and may be linked to increases in mitochondrial biogenesis and health. Increasing nitrite levels via dietary intake of nitrate appears to have similarly beneficial effects in many of the same physiological and clinical settings. Several clinical trials are being performed to determine the broad therapeutic potential of increasing nitrite bioavailability on human health and disease, including studies related to vascular aging. In summary, inorganic nitrite, as well as dietary nitrate supplementation, represents a promising therapy for treatment of arterial aging and prevention of age-associated CVD in humans.

Hypobaric hypoxia induced arginase expression limits nitric oxide availability and signaling in rodent heart

BACKGROUND

This study was aimed to evaluate regulation of cardiac arginase expression during hypobaric hypoxia and subsequent effect on nitric oxide availability and signaling.

METHODS

Rats were exposed to hypobaric hypoxia (282mmHg for 3h) and ARG1 expression was monitored. The expression levels of eNOS and eNOS(Ser1177) were determined by Western blotting, cGMP levels were measured by ELISA and amino acid concentrations were measured by HPLC analysis. Transcription regulation of arginase was monitored by chromatin immunoprecipitation (ChIP) assay with anti-c-Jun antibody for AP-1 consensus binding site on ARG1 promoter. Arginase activity was inhibited by intra-venous dose of N-(ω)-hydroxy-nor-l-arginine (nor-NOHA) prior to hypoxia exposure and subsequent effect on NO availability and oxidative stress were evaluated.

RESULTS

Hypobaric hypoxia induced cardiac arginase expression by recruiting c-Jun to AP-1 binding site on ARG1 promoter. This increased expression redirected l-arginine towards arginase and resulted in limited endothelial nitric oxide synthase (eNOS) activity, nitric oxide (NO) availability and cGMP mediated signaling. Inhibition of arginase restored the eNOS activity, promoted cardiac NO availability and ameliorated peroxynitrite formation during hypoxia.

CONCLUSIONS

Hypoxic induced arginase under transcription control of AP-1 reciprocally regulates eNOS activity and NO availability in the heart. This also results in cardiac oxidative stress.

GENERAL SIGNIFICANCE

This study provides understanding of hypoxia-mediated transcriptional regulation of arginase expression in the heart and its subsequent effect on eNOS activity, NO availability and signaling as well as cardiac oxidative stress. This information will support the use of arginase inhibitors as therapeutics for pathological hypoxia.

Cerium oxide nanoparticles protect rodent lungs from hypobaric hypoxia-induced oxidative stress and inflammation

BACKGROUND

Cerium oxide nanoparticles (nanoceria) are effective at quenching reactive oxygen species (ROS) in cell culture and animal models. Although nanoceria reportedly deposit in lungs, their efficacy in conferring lung protection during oxidative stress remains unexplored. Thus, the study evaluated the protective efficacy of nanoceria in rat lung tissue during hypobaric hypoxia.

METHODS

A total of 48 animals were randomly divided into four equal groups (control [C], nanoceria treated [T], hypoxia [H], and nanoceria treated plus hypoxia [T+H]). Animals were injected intraperitoneally with either a dose of 0.5 μg/kg body weight/week of nanoceria (T and T+H groups) or vehicle (C and H groups) for 5 weeks. After the final dose, H and T+H animals were challenged with hypobaric hypoxia, while C and T animals were maintained at normoxia. Lungs were isolated and homogenate was obtained for analysis of ROS, lipid peroxidation, glutathione, protein carbonylation, and 4-hydroxynonenal-adduct formation. Plasma was used for estimating major inflammatory cytokines using enzyme-linked immunosorbent assay. Intact lung tissues were fixed and both transmission electron microscopy and histopathological examinations were carried out separately for detecting internalization of nanoparticles as well as altered lung morphology.

RESULTS

Spherical nanoceria of 7-10 nm diameter were synthesized using a microemulsion method, and the lung protective efficacy of the nanoceria evaluated during hypobaric hypoxia. With repeated intraperitoneal injections of low micromole concentration, we successfully localized the nanoceria in rodent lung without any inflammatory response. The lung-deposited nanoceria limited ROS formation, lipid peroxidation, and glutathione oxidation, and prevented oxidative protein modifications like nitration and carbonyl formation during hypobaric hypoxia. We also observed reduced lung inflammation in the nanoceria-injected lungs, supporting the anti-inflammatory properties of nanoceria.

CONCLUSION

Cumulatively, these results suggest nanoceria deposit in lungs, confer protection by quenching noxious free radicals during hypobaric hypoxia, and do not evoke any inflammatory response.

Blood substitutes: evolution from noncarrying to oxygen- and gas-carrying fluids

The development of oxygen (O2)-carrying blood substitutes has evolved from the goal of replicating blood O2 transport properties to that of preserving microvascular and organ function, reducing the inherent or potential toxicity of the material used to carry O2, and treating pathologies initiated by anemia and hypoxia. Furthermore, the emphasis has shifted from blood replacement fluid to "O2 therapeutics" that restore tissue oxygenation to specific tissues regions. This review covers the different alternatives, potential and limitations of hemoglobin-based O2 carriers (HBOCs) and perfluorocarbon-based O2 carriers (PFCOCs), with emphasis on the physiologic conditions disturbed in the situation that they will be used. It describes how concepts learned from plasma expanders without O2-carrying capacity can be applied to maintain O2 delivery and summarizes the microvascular responses due to HBOCs and PFCOCs. This review also presents alternative applications of HBOCs and PFCOCs namely: 1) How HBOC O2 affinity can be engineered to target O2 delivery to hypoxic tissues; and 2) How the high gas solubility of PFCOCs provides new opportunities for carrying, dissolving, and delivering gases with biological activity. It is concluded that the development of current blood substitutes has amplified their applications horizon by devising therapeutic functions for O2 carriers requiring limited O2 delivery capacity restoration. Conversely, full, blood-like O2-carrying capacity reestablishment awaits the control of O2 carrier toxicity.

HBOC vasoactivity: interplay between nitric oxide scavenging and capacity to generate bioactive nitric oxide species

SIGNIFICANCE

Despite many advances in blood substitute research, the development of materials that are effective in maintaining blood volume and oxygen delivery remains a priority for emergency care and trauma. Clinical trials on hemoglobin (Hb)-based oxygen carriers (HBOCs) have not provided information on the mechanism of toxicity, although all commercial formulations have safety concerns. Specifically, it is important to reconcile the different hypotheses of Hb toxicity, such as nitric oxide (NO) depletion and oxidative reactions, to provide a coherent molecular basis for designing a safe HBOC.

RECENT ADVANCES

HBOCs with different sizes often exhibit differences in the degree of HBOC-induced vasoactivity. This has been attributed to differences in the degree of NO scavenging and in the extent of Hb extravasation. Additionally, it is appears that Hb can undergo reactions that compensate for NO scavenging by generating bioactive forms of NO.

CRITICAL ISSUES

Engineering modifications to enhance bioactive NO production can result in diminished oxygen delivery by virtue of increased oxygen affinity. This strategy can prevent the HBOC from fulfilling the intended goal on preserving oxygenation; however, the NO production effects will increase perfusion and oxygen transport.

FUTURE DIRECTIONS

Hb modifications influence NO scavenging and the capacity of certain HBOCs to compensate for NO scavenging through nitrite-mediated reactions that generate bioactive NO. Based on the current understanding of these NO-related factors, possible synthetic strategies are presented that address how HBOC formulations can be prepared that: (i) effectively deliver oxygen, (ii) maintain tissue perfusion, and (iii) limit/reverse underlying inflammation within the vasculature.

Therapeutic efficacy of silymarin from milk thistle in reducing manganese-induced hepatic damage and apoptosis in rats

Oxidative stress has been proposed as a possible mechanism involved in manganese (Mn) toxicity. Using natural antioxidants against metal-induced hepatotoxicity is a modern approach. The present study investigated the beneficial role of silymarin, a natural flavonoid, in Mn-induced hepatotoxicity focusing on histopathology and biochemical approaches. Male Wistar rats were exposed orally to manganese chloride (20 mg/mL) for 30 days followed by intraperitoneal cotreatment with silymarin (100 mg/kg). Exposure to Mn resulted in a significant elevation of the plasma marker enzyme activities and bilirubin level related to liver dysfunction of reactive oxygen species (ROS) production and hepatic oxidative stress indices. This metal reduced the activities of superoxide dismutase, catalase and glutathione peroxidase and nonenzymatic antioxidant levels such as reduced glutathione, total sulfhydryl groups and vitamin C. In addition, it caused hepatic hemorrhage, cellular degeneration and necrosis of hepatocytes as indicated by liver histopathology and DNA fragmentation studies. Coadministration of silymarin alleviated Mn oxidative damage effects by inhibiting ROS generation. Histological studies also supported the beneficial role of silymarin against Mn-induced hepatic damages. Combining all, results suggested that silymarin could protect hepatic tissues against Mn-induced oxidative stress probably through its antioxidant activity. Therefore, its supplementation could provide a new approach for the reduction in hepatic complication due to Mn poisoning.

A key role of toll-like receptor 3 in tissue factor activation through extracellular signal regulated kinase 1/2 pathway in a murine hypoxia model

Hypoxemia in the circulation can lead to venous thrombosis (VT) through tissue factor (TF) activation, but the mechanism of TF activation in hypoxia remains obscure. Ligands released from damaged tissues or cells due to hypoxia are identified by various pattern-recognition receptors (PRR), including Toll-like receptor3 (TLR3). In the present study, we investigated the mechanism of TF activation during acute hypoxia in a rat model. The expression of TLR3 and TF was analyzed by immunoblotting and RT-PCR. The TF activity was evaluated by two-stage chromogenic assay and fibrin deposition was detected by immunohistochemistry. The expression of TLR3, TF, and TF activity was increased significantly 6 h post acute hypoxia and then decreased gradually. The contribution of TLR3 in TF activation was investigated by poly I:C and TLR3 neutralizing antibody. We also found increased ERK phosphorylation both in acute hypoxia and poly I:C treatment. We further showed that the pre-treatment of TLR3 neutralizing antibody or ERK inhibitor (PD98059) 2 h prior to acute hypoxia or poly I:C treatment completely abrogated ERK phosphorylation and TF activation. The pre-treatment of TLR3 neutralizing antibody also inhibited fibrin deposition in lung vasculature. These data indicate that acute hypoxia induced TF activation is mediated through TLR3-ERK1/2 pathway.