Oral nitrite restores age-dependent phenotypes in eNOS-null mice.

Alterations in the synthesis and bioavailability of NO are central to the pathogenesis of cardiovascular and metabolic disorders. Although endothelial NO synthase-derived (eNOS-derived) NO affects mitochondrial long-chain fatty acid ß-oxidation, the pathophysiological significance of this regulation remains unclear. Accordingly, we determined the contributions of eNOS/NO signaling in the adaptive metabolic responses to fasting and in age-induced metabolic dysfunction. Four-month-old eNOS-/- mice are glucose intolerant and exhibit serum dyslipidemia and decreased capacity to oxidize fatty acids. However, during fasting, eNOS-/- mice redirect acetyl-CoA to ketogenesis to elevate circulating levels of ß-hydroxybutyrate similar to wild-type mice. Treatment of 4-month-old eNOS-/- mice with nitrite for 10 days corrected the hypertension and serum hyperlipidemia and normalized the rate of fatty acid oxidation. Fourteen-month-old eNOS-/- mice exhibited metabolic derangements, resulting in reduced utilization of fat to generate energy, lower resting metabolic activity, and diminished physical activity. Seven-month administration of nitrite to eNOS-/- mice reversed the age-dependent metabolic derangements and restored physical activity. While the eNOS/NO signaling is not essential for the metabolic adaptation to fasting, it is critical for regulating systemic metabolic homeostasis in aging. The development of age-dependent metabolic disorder is prevented by low-dose replenishment of bioactive NO.

Puerarin attenuates diabetic kidney injury through the suppression of NOX4 expression in podocytes.

Radix puerariae, a traditional Chinese herbal medication, has been used to treat patients with diabetic nephropathy (DN). Several studies demonstrated that puerarin, the active compound of radix puerariae, reduces diabetic injury in streptozotocin (STZ)-induced diabetic rodent models. However, as STZ injection alone results in mild kidney injury, the therapeutic benefit afforded by puerarin in DN remained inconclusive. Thus we sought to clarify the role of puerarin by employing an accelerated DN model, STZ-induced diabetes in the endothelial nitric oxide synthase-null (eNOS-/-) mice. Puerarin treatment of diabetic eNOS-/- mice significantly attenuated albuminuria and diabetic kidney injury, which were associated with reduced oxidative stress and reduced NAPDH oxidase 4 (NOX4) in glomeruli of diabetic eNOS-/- mice. Puerarin treatment of murine podocytes culture in high glucose conditions led to reduced superoxide production and NOX4 expression. We further determined that that puerarin treatment increased both mRNA and protein levels of SIRT1 in podocytes and that puerarin led to SIRT1-mediated deacetylation of NF-κB and suppression of NOX4 expression. Our findings confirm the renoprotective effects of puerarin in an experimental model of advanced DN and provide a molecular mechanism by which puerarin exerts the anti-oxidative effects in podocytes  in the diabetic milieu.

Enhanced XOR activity in eNOS-deficient mice: Effects on the nitrate-nitrite-NO pathway and ROS homeostasis.

Xanthine oxidoreductase (XOR) is generally known as the final enzyme in purine metabolism and as a source of reactive oxygen species (ROS). In addition, this enzyme has been suggested to mediate nitric oxide (NO) formation via reduction of inorganic nitrate and nitrite. This NO synthase (NOS)-independent pathway for NO generation is of particular importance during certain conditions when NO bioavailability is diminished due to reduced activity of endothelial NOS (eNOS) or increased oxidative stress, including aging and cardiovascular disease. The exact interplay between NOS- and XOR-derived NO generation is not fully elucidated yet. The aim of the present study was to investigate if eNOS deficiency is associated with changes in XOR expression and activity and the possible impact on nitrite, NO and ROS homeostasis. Plasma levels of nitrate and nitrite were similar between eNOS deficient (eNOS-/-) and wildtype (wt) mice. XOR activity was upregulated in eNOS-/- compared with wt, but not in nNOS-/-, iNOS-/- or wt mice treated with the non-selective NOS inhibitor L-NAME. Following an acute dose of nitrate, plasma nitrite increased more in eNOS-/- compared with wt, and this augmented response was abolished by the selective XOR inhibitor febuxostat. Livers from eNOS-/- displayed higher nitrite reducing capacity compared with wt, and this effect was attenuated by febuxostat. Dietary supplementation with nitrate increased XOR expression and activity, but concomitantly reduced superoxide generation. The latter effect was also seen in vitro after nitrite administration. Treatment with febuxostat elevated blood pressure in eNOS-/-, but not in wt mice. A high dose of dietary nitrate reduced blood pressure in naïve eNOS-/- mice, and again this effect was abolished by febuxostat. In conclusion, eNOS deficiency is associated with an upregulation of XOR facilitating the nitrate-nitrite-NO pathway and decreasing the generation of ROS. This interplay between XOR and eNOS is proposed to play a significant role in NO homeostasis and blood pressure regulation.

The effect of combined inositol supplementation on maternal metabolic profile in pregnancies complicated by metabolic syndrome and obesity.

BACKGROUND: Myoinositol and D-chiroinositol improve insulin resistance in women with obesity and gestational diabetes and in postmenopausal women with metabolic syndrome. We previously reported that offspring born to hypertensive dams lacking endothelial nitric oxide synthase and fed a high-fat diet develop metabolic-like syndrome phenotype. OBJECTIVE: The objective of the study was to investigate the effect of a mixture of myoinositol/D-chiroinositol supplementation during pregnancy on the maternal metabolic profile in pregnancies complicated by the metabolic-like syndrome and obesity using a pregnant mouse model. STUDY DESIGN: Female heterozygous endothelial nitric oxide synthase(-/+) mice with moderate hypertension were placed on a high-fat diet for 4 weeks to induce a metabolic-like syndrome phenotype. Similarly, wild-type C57BL/6 mice were placed on a high-fat diet for 4 weeks to induce a murine obesity model. Mice were then bred with wild-type males. On gestational day 1, dams were randomly allocated to receive either a mixture of myoinositol/D-chiroinositol in water (7.2/0.18 mg/mL, respectively) or water as control (placebo). At term (gestational day 18), maternal weights, systolic blood pressure, and a glucose tolerance test were obtained. Dams were then killed; pups and placentas were weighed and maternal blood collected. Serum levels of metabolic biomarkers relevant to diabetes and obesity (ghrelin, gastric inhibitory peptide, glucagon-like peptide 1, glucagon, insulin, leptin, resistin) were measured by a multiplex enzyme-linked immunosorbent assay. Analysis was done comparing metabolic-like syndrome-myoinositol/D-chiroinositol-treated vs metabolic-like syndrome-nontreated mice and obese-myoinositol/D-chiroinositol-treated vs obese nontreated mice. RESULTS: Mean systolic blood pressure was lower in metabolic-like syndrome pregnant mice treated with myoinositol/D-chiroinositol compared with placebo (P = .04), whereas there was no difference in systolic blood pressure between treated and placebo-treated obese pregnant mice. Pregnant metabolic-like syndrome mice treated with myoinositol/D-chiroinositol showed lower glucose values during the glucose tolerance test and in the area under the curve (myoinositol/D-chiroinositol: 17512.5 ± 3984.4 vs placebo: 29687.14 ± 8258.7; P = .003), but no differences were seen in the obese pregnant mice. Leptin serum levels were lower in the metabolic-like syndrome-myoinositol/D-chiroinositol-treated mice compared with the placebo group (myoinositol/D-chiroinositol: 16985 ± 976.4 pg/dL vs placebo: 24181.9 ± 3128.2 pg/dL, P = .045). No other differences were seen in any of the remaining serum metabolic biomarkers studied in metabolic-like syndrome and in obese pregnant mice. Maternal weight gain was not different in the pregnant metabolic-like syndrome dams, whereas it was lower in the obese myoinositol/D-chiroinositol-treated dams compared with the placebo group (myoinositol/D-chiroinositol: 10.9 ± 0.5 g vs 12.6 ± 0.6 g, P = .04). Fetal and placental weights did not differ between myoinositol/D-chiroinositol-treated and nontreated pregnant dams with metabolic-like syndrome and obesity. CONCLUSION: Combined inositol treatment during pregnancy improves blood pressure, glucose levels at the glucose tolerance test, and leptin levels in pregnant dams with metabolic-like syndrome phenotype but not in obese pregnant dams. In addition, inositol treatment was associated with lower gestational weight gain in the obese but not in the metabolic-like syndrome pregnant dams.

Endothelial Nitric Oxide Synthase-Derived Nitric Oxide Prevents Dihydrofolate Reductase Degradation via Promoting S-Nitrosylation.

OBJECTIVE: Dihydrofolate reductase (DHFR) is a key protein involved in tetrahydrobiopterin (BH4) regeneration from 7,8-dihydrobiopterin (BH2). Dysfunctional DHFR may induce endothelial nitric oxide (NO) synthase (eNOS) uncoupling resulting in enzyme production of superoxide anions instead of NO. The mechanism by which DHFR is regulated is unknown. Here, we investigate whether eNOS-derived NO maintains DHFR stability. APPROACH AND RESULTS: DHFR activity, BH4 content, eNOS activity, and S-nitrosylation were assessed in human umbilical vein endothelial cells and in aortas isolated from wild-type and eNOS knockout mice. In human umbilical vein endothelial cells, depletion of intracellular NO by transfection with eNOS-specific siRNA or by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO)-both of which had no effect on DHFR mRNA levels-markedly reduced DHFR protein levels in parallel with increased DHFR polyubiquitination. Supplementation of S-nitroso-l-glutathione (GSNO), a NO donor, or MG132, a potent inhibitor of the 26S proteasome, prevented eNOS silencing and PTIO-induced DHFR reduction in human umbilical vein endothelial cells. PTIO suppressed S-nitrosylation of DHFR, whereas GSNO promoted DHFR S-nitrosylation. Mutational analysis confirmed that cysteine 7 of DHFR was S-nitrosylated. Cysteine 7 S-nitrosylation stabilized DHFR from ubiquitination and degradation. Experiments performed in aortas confirmed that PTIO or eNOS deficiency reduces endothelial DHFR, which can be abolished by MG132 supplementation. CONCLUSIONS: We conclude that S-nitrosylation of DHFR at cysteine 7 by eNOS-derived NO is crucial for DHFR stability. We also conclude that NO-induced stabilization of DHFR prevents eNOS uncoupling via regeneration of BH4, an essential eNOS cofactor.

Protective effect of hexane extracts of Uncaria sinensis against photothrombotic ischemic injury in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Uncaria sinensis (US) has been used in traditional Korean medicine to treat vascular disease and to relieve various neurological symptoms. AIM OF THE STUDY: Scientific evidence related to the effectiveness or action mechanism of US on cerebrovascular disease has not been examined experimentally. Here, we investigated the cerebrovascular protective effect of US extracts on photothrombotic ischemic injury in mice. MATERIALS AND METHODS: US hexane extracts (HEUS), ethyl acetate extracts (EAEUS) and methanol extracts (MEUS) were administered intraperitoneally 30 min before ischemic insults. Focal cerebral ischemia was induced in C57BL/6J mice and endothelial nitric oxide synthase knockout (eNOS KO) mice by photothrombotic cortical occlusion. We evaluated the infarct volume, neurological score and the activation of Akt and eNOS in ischemic brain. RESULTS: HEUS more significantly reduced infarct volume and edema than did EAEUS and MEUS following photothrombotic cortical occlusion. HEUS produced decreased infarct volume and edema size, and improved neurological function in a concentration-dependent manner (10, 50, and 100 mg/kg). However, HEUS did not reduce brain infarction in eNOS KO mice, suggesting that the protective effect of HEUS is primarily endothelium-dependent. Furthermore, HEUS (10-300 µg/ml) produced a concentration-dependent relaxation in mouse aorta and rat basilar artery, which was not seen in eNOS KO mouse aorta, suggesting that HEUS cause vasodilation via an eNOS-dependent mechanism. This correlated with increased phosphorylation of Akt and eNOS in the brains of HEUS-treated mice. CONCLUSION: HEUS prevent cerebral ischemic damage by regulating Akt/eNOS signaling. US, herbal medicine, may be the basis of a novel strategy for the therapy of stroke.

Salvianolic acid B and tanshinone IIA attenuate myocardial ischemia injury in mice by NO production through multiple pathways.

OBJECTIVE: Salvia miltiorrhiza (Danshen) has been widely used for the treatment of cardiac and cerebrovascular disease throughout history. The objective of this study is to further elucidate the mechanisms underlying Danshen's cardiac protective effects to support its clinical evidence. METHODS: AND RESULTS: Salvianolic acid B (Sal B) and Tanshinone IIA (Tan IIA) are two of the major components in Danshen. We observed that Sal B and Tan IIA have cardioprotective effects in an in vivo myocardial infarction model of C57 mice, have vasodilator action in a ex vivo micro-artery system through the endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) pathway and are involved in the regulation of the L-arginine/eNOS/NO pathways in human umbilical vein endothelial cells (HUVECs). Both Sal B and Tan IIA inhibited cardiac hypertrophy and infarction sizes and improved cardiac function at 4 weeks after induction of infarction. Furthermore, an eNOS inhibitor (L-NAME) obliterated the observed effects. Sal B and Tan IIA mediated vasodilatation in mice coronaries ex vivo, the effect of which was decreased with either L-NAME or PI3K inhibitor (LY294002). In addition, Sal B and Tan IIA-induced vasodilatation was observed ex vivo in the microvessels of eNOS-/- mice. Sal B and Tan IIA also stimulated eNOS phosphorylation in a concentration- and time-dependent manner in the HUVEC culture, which was diminished by LY294002. In addition, Sal B and Tan IIA were found to stimulate the phosphorylation of AMPK (Thr(172)) and Akt (Ser(473)), while compound C significantly decreased the phosphorylation of Akt (Ser(473)) mediated by both. Finally, Sal B and Tan IIA were found to increase NO production, induce [(3)H]-L-arginine uptake and increase the CAT-1 and CAT-2B mRNA levels in HUVEC culture. CONCLUSIONS: These findings suggest that both Sal B and Tan IIA have cardioprotective function in certain levels through multiple targets related with NO production, such as eNOS phosphorylation, L-arginine uptake and CAT expression, which may have major clinical implications.

Dietary inorganic nitrate reverses features of metabolic syndrome in endothelial nitric oxide synthase-deficient mice.

The metabolic syndrome is a clustering of risk factors of metabolic origin that increase the risk for cardiovascular disease and type 2 diabetes. A proposed central event in metabolic syndrome is a decrease in the amount of bioavailable nitric oxide (NO) from endothelial NO synthase (eNOS). Recently, an alternative pathway for NO formation in mammals was described where inorganic nitrate, a supposedly inert NO oxidation product and unwanted dietary constituent, is serially reduced to nitrite and then NO and other bioactive nitrogen oxides. Here we show that several features of metabolic syndrome that develop in eNOS-deficient mice can be reversed by dietary supplementation with sodium nitrate, in amounts similar to those derived from eNOS under normal conditions. In humans, this dose corresponds to a rich intake of vegetables, the dominant dietary nitrate source. Nitrate administration increased tissue and plasma levels of bioactive nitrogen oxides. Moreover, chronic nitrate treatment reduced visceral fat accumulation and circulating levels of triglycerides and reversed the prediabetic phenotype in these animals. In rats, chronic nitrate treatment reduced blood pressure and this effect was also present during NOS inhibition. Our results show that dietary nitrate fuels a nitrate-nitrite-NO pathway that can partly compensate for disturbances in endogenous NO generation from eNOS. These findings may have implications for novel nutrition-based preventive and therapeutic strategies against cardiovascular disease and type 2 diabetes.

Ventromedial hypothalamic nitric oxide production is necessary for hypoglycemia detection and counterregulation.

OBJECTIVE: The response of ventromedial hypothalamic (VMH) glucose-inhibited neurons to decreased glucose is impaired under conditions where the counterregulatory response (CRR) to hypoglycemia is impaired (e.g., recurrent hypoglycemia). This suggests a role for glucose-inhibited neurons in the CRR. We recently showed that decreased glucose increases nitric oxide (NO) production in cultured VMH glucose-inhibited neurons. These in vitro data led us to hypothesize that NO release from VMH glucose-inhibited neurons is critical for the CRR. RESEARCH DESIGN AND METHODS: The CRR was evaluated in rats and mice in response to acute insulin-induced hypoglycemia and hypoglycemic clamps after modulation of brain NO signaling. The glucose sensitivity of ventromedial nucleus glucose-inhibited neurons was also assessed. RESULTS: Hypoglycemia increased hypothalamic constitutive NO synthase (NOS) activity and neuronal NOS (nNOS) but not endothelial NOS (eNOS) phosphorylation in rats. Intracerebroventricular and VMH injection of the nonselective NOS inhibitor N(G)-monomethyl-l-arginine (l-NMMA) slowed the recovery to euglycemia after hypoglycemia. VMH l-NMMA injection also increased the glucose infusion rate (GIR) and decreased epinephrine secretion during hyperinsulinemic/hypoglycemic clamp in rats. The GIR required to maintain the hypoglycemic plateau was higher in nNOS knockout than wild-type or eNOS knockout mice. Finally, VMH glucose-inhibited neurons were virtually absent in nNOS knockout mice. CONCLUSIONS: We conclude that VMH NO production is necessary for glucose sensing in glucose-inhibited neurons and full generation of the CRR to hypoglycemia. These data suggest that potentiating NO signaling may improve the defective CRR resulting from recurrent hypoglycemia in patients using intensive insulin therapy.

S-nitrosothiols signal hypoxia-mimetic vascular pathology.

NO transfer reactions between protein and peptide cysteines have been proposed to represent regulated signaling processes. We used the pharmaceutical antioxidant N-acetylcysteine (NAC) as a bait reactant to measure NO transfer reactions in blood and to study the vascular effects of these reactions in vivo. NAC was converted to S-nitroso-N-acetylcysteine (SNOAC), decreasing erythrocytic S-nitrosothiol content, both during whole-blood deoxygenation ex vivo and during a 3-week protocol in which mice received high-dose NAC in vivo. Strikingly, the NAC-treated mice developed pulmonary arterial hypertension (PAH) that mimicked the effects of chronic hypoxia. Moreover, systemic SNOAC administration recapitulated effects of both NAC and hypoxia. eNOS-deficient mice were protected from the effects of NAC but not SNOAC, suggesting that conversion of NAC to SNOAC was necessary for the development of PAH. These data reveal an unanticipated adverse effect of chronic NAC administration and introduce a new animal model of PAH. Moreover, evidence that conversion of NAC to SNOAC during blood deoxygenation is necessary for the development of PAH in this model challenges conventional views of oxygen sensing and of NO signaling.

Irradiation promotes Akt-targeting therapeutic gene delivery to the tumor vasculature.

PURPOSE: To determine whether radiation-induced increases in nitric oxide (NO) production can influence tumor blood flow and improve delivery of Akt-targeting therapeutic DNA lipocomplexes to the tumor. METHODS AND MATERIALS: The contribution of NO to the endothelial response to radiation was identified using NO synthase (NOS) inhibitors and endothelial NOS (eNOS)-deficient mice. Reporter-encoding plasmids complexed with cationic lipids were used to document the tumor vascular specificity and the efficacy of in vivo lipofection after irradiation. A dominant-negative Akt gene construct was used to evaluate the facilitating effects of radiotherapy on the therapeutic transgene delivery. RESULTS: The abundance of eNOS protein was increased in both irradiated tumor microvessels and endothelial cells, leading to a stimulation of NO release and an associated increase in tumor blood flow. Transgene expression was subsequently improved in the irradiated vs. nonirradiated tumor vasculature. This effect was not apparent in eNOS-deficient mice and could not be reproduced in irradiated cultured endothelial cells. Finally, we combined low-dose radiotherapy with a dominant-negative Akt gene construct and documented synergistic antitumor effects. CONCLUSIONS: This study offers a new rationale to combine radiotherapy with gene therapy, by directly exploiting the stimulatory effects of radiation on NO production by tumor endothelial cells. The preferential expression of the transgene in the tumor microvasculature underscores the potential of such an adjuvant strategy to limit the angiogenic response of irradiated tumors.