Implication of steady state concentrations of nitrite and nitrate metabolites of nitric oxide in plasma and whole blood in healthy human subjects

Is vitamin C a booster of the effects of dietary nitrate on endothelial function? Physiologic rationale and implications for research

Endothelial dysfunction (ED) is an early marker of vascular damage linked to the loss of integrity of the endothelial lining and represents a key step in the pathogenesis of atherosclerosis and cardiovascular diseases (CVDs). ED may be reversible, hence the development and testing of effective early interventions could be beneficial for the prevention and treatment of CVDs. Recent studies have demonstrated that the consumption of dietary nitrate (NO₃^-), an inorganic anion that serves as a substrate for the gas transmitter nitric oxide (NO), can lower blood pressure, improve endothelial function and, in observational studies, reduce the risk for CVD. We hypothesize that the co-consumption of NO₃^- with vitamin C, which is a potent antioxidant, could enhance the "yield" of NO produced from a given NO₃^- dose byThis could translate into greater NO-dependent effects on endothelial function (EF) and overall vascular health (than may be experienced with NO₃^- supplementation alone). This review presents evidence to suggest that the combination of vitamin C and dietary nitrate could represent a promising and effective approach to improve EF and reduce CVD risk, and discuss opportunities for future research.

Plasma Nitrate and Incidence of Cardiovascular Disease and All-Cause Mortality in the Community: The Framingham Offspring Study

BACKGROUND

Nitrate is a dietary component as well as an endogenously formed metabolite and source of the signaling molecule nitric oxide. Harmful as well as beneficial effects of nitrate have been advocated. Data regarding the prognostic relevance of plasma nitrate are limited. The aim of this study was to evaluate the prospective association of plasma nitrate with cardiovascular disease (CVD) and all-cause mortality.

METHODS AND RESULTS

We assayed plasma nitrate in 2855 Framingham Offspring Study participants (mean age 59 years, 54% women) by gas chromatography-mass spectrometry and evaluated its association with all-cause mortality and incident CVD. On follow-up (median 17.3 years), 775 participants died and 522 developed new-onset CVD (of 2546 participants free of CVD at baseline). In multivariable models adjusting for standard risk factors, plasma nitrate was associated with an increased risk of death in participants (hazard ratio per unit increase in log-nitrate 1.21; 95% confidence interval, 1.04-1.40 [P=0.015]). The strength of the association was attenuated by additional adjustment for estimated glomerular filtration rate (hazard ratio, 1.16; 95% confidence interval, 1.00-1.35 [P=0.057]). In contrast, no evidence was found for an association of plasma nitrate with incident CVD (multivariable-adjusted hazard ratio per unit increase log-nitrate 1.08; 95% confidence interval, 0.89-1.31 [P=0.42]).

CONCLUSIONS

In our prospective community-based investigation, a higher plasma nitrate concentration was associated with all-cause mortality but not with incident CVD. The association of nitrate with mortality may at least in part be attributable to its association with renal function.

The presence of the NOS3 gene polymorphism for intron 4 mitigates the beneficial effects of exercise training on ambulatory blood pressure monitoring in adults

The number of studies that have evaluated exercise training (ET) and nitric oxide synthase (NOS)3 gene polymorphisms is scarce. The present study was designed to evaluate the relationship between exercise training and NOS3 polymorphisms at -786T>C, 894G>T, and intron 4b/a on blood pressure (BP) using 24-h ambulatory BP monitoring (ABPM), nitrate/nitrite levels (NOx), and redox state. Eighty-six volunteers (51 ± 0.6 yr old) were genotyped into nonpolymorphic and polymorphic groups for each of the three positions of NOS3 polymorphisms. Auscultatory BP, ABPM, SOD activity, catalase activity, NOx levels, and malondialdehyde levels were measured. DNA was extracted from leukocytes, and PCR followed by sequencing was applied for genotype analysis. Aerobic ET consisted of 24 sessions for 3 days/wk for 40 min at moderate intensity. This study was performed in a double-blind and crossover format. ET was effective in lowering office BP (systolic BP: 3.2% and diastolic BP: 3%) as well as ABPM (systolic BP: 2% and diastolic BP: 1.3%). Increased SOD and catalase activity (42.6% and 15.1%, respectively) were also observed. The NOS3 polymorphism for intron 4 mitigated the beneficial effect of ET for systolic BP (nonpolymorphic group: -3.0% and polymorphic group: -0.6%) and diastolic BP (nonpolymorphic group: -3.2% and polymorphic group: -0.5%), but it was not associated with NOx level and redox state. Paradoxical responses were found for positions T786-C and G894T for the NOS3 gene. Consistently, the presence of the polymorphism for intron 4 blunted the beneficial effects of ET in middle-aged adults. Possibly, this effect might be as consequence of intron 4 acting as a short intronic repeat RNA controlling endothelial NOS activity epigenetically.

Effect of head-out water immersion on vascular function in healthy subjects

Immersion in thermoneutral water increases cardiac output and peripheral blood flow and reduces systemic vascular resistance. This study examined the effects of head-out water immersion on vascular function. Twelve healthy middle-aged males were immersed during 60 min in the seated position, with water at the level of xiphoid. Local and central vascular tone regulating systems were studied during that time. Brachial artery diameter and blood flow were recorded using ultrasonography and Doppler. Endothelial function was assessed with flow-mediated dilation. Results were compared with the same investigations performed under reference conditions in ambient air. During water immersion, brachial artery diameter increased (3.7 ± 0.2 mm in ambient air vs. 4 ± 0.2 mm in water immersion; p < 0.05). Endothelium-mediated dilation was significantly lower in water immersion than in ambient air (10% vs. 15%; p = 0.01). Nevertheless, the difference disappeared when the percentage vasodilatation of the brachial artery was normalized to the shear stimulus. Smooth muscle-mediated dilation was similar in the 2 conditions. Spectral analysis of systolic blood pressure variability indicated a decrease in sympathetic vascular activity. Plasma levels of nitric oxide metabolites remained unchanged, whereas levels of natriuretic peptides were significantly elevated. An increase in brachial blood flow, a decrease in sympathetic activity, a warming of the skin, and an increase in natriuretic peptides might be involved in the increase in reference diameter observed during water immersion. Endothelial cell reactivity and smooth muscle function did not appear to be altered.

Impacts of lisinopril and lisinopril plus simvastatin on erythrocyte and plasma arginase, nitrite, and nitrate in hypertensive patients

Angiotensin-converting enzyme inhibitors are effective at reducing blood pressure, whereas statins decrease plasma cholesterol, impeding atherosclerosis. The authors hypothesize that these medications may improve blood pressure by modifying the arginase-nitric oxide synthase system of erythrocytes. In this study, the effects of lisinopril alone versus lisinopril + simvastatin on erythrocyte and plasma arginase enzyme and nitric oxide metabolites are compared. Patients with atherosclerosis and hypertension are randomly assigned to receive lisinopril 10 to 20 mg/d or lisinopril 10 to 20 mg/d plus simvastatin 20 mg/d for 24 weeks. Higher arginase activity is observed in erythrocytes from 100% of patients and mainly recovered after 12 and 24 weeks of treatment with lisinopril or lisinopril + simvastatin. Plasma arginase activity is 3 orders of magnitude lower than erythrocyte arginase activity in all participants, suggesting a lack of its clinical significance. Both treatments cause the increase in plasma $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ , $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ , and $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ + $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ in 100% of patients. Erythrocyte $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ + $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ concentration is greatly decreased in hypertensive patients but recovers after monotherapy and combined therapy. The results show for the first time that lisinopril monotherapy and combined lisinopril + simvastatin therapy exhibit pronounced and equipotential normalizing effects on erythrocyte arginase and nitric oxide synthase activities.

In vitro and in vivo antiproliferative and trypanocidal activities of ruthenium NO donors

BACKGROUND AND PURPOSE

Many compounds liberating NO (NO donors) have been used as therapeutic agents. Here we test two ruthenium nitrosyls, which release NO when activated by biological reducing agents, for their effects in vitro and in vivo against Trypanosoma cruzi, the agent responsible for the American trypanosomiasis (Chagas' disease).

EXPERIMENTAL APPROACH

Ruthenium NO donors were incubated with a partially drug-resistant strain of T. cruzi and the anti-proliferative and trypanocidal activities evaluated. In a mouse model of acute Chagas' disease, trypanocidal activity was evaluated by measuring parasitemia, survival rate of infected mice and elimination of amastigotes in myocardial tissue.

KEY RESULTS

In vitro, the observed anti-proliferative and trypanocidal activities of trans-[Ru(NO)(NH(3))(4)isn](BF(4))(3) and trans-[Ru(NO)(NH(3))(4)imN](BF(4))(3) were due to NO liberated upon reduction of these nitrosyls. Ru(NO)isn had a lower IC(50 epi) (67 microM) than the NO donor, sodium nitroprusside (IC(50 epi)=244 microM) and Ru(NO)imN (IC(50 try)=52 microM) was more potent than gentian violet (IC(50 try)=536 microM), currently used in the treatment of blood. Both ruthenium nitrosyls eliminated, in vivo, extracellular as well as intracellular forms of T. cruzi in the bloodstream and myocardial tissue and allowed survival of up to 80% of infected mice at a dose (100 nmol kg(-1) day(-1)) much lower than the optimal dose for benznidazole (385 micromol kg(-1) day(-1)).

CONCLUSIONS AND IMPLICATIONS

Our data strongly suggest that NO liberated is responsible for the anti-proliferative and trypanocidal activities of the ruthenium NO donors and that these compounds are promising leads for novel and effective anti-parasitic drugs.

Analysis of nitrite and nitrate in biological samples using high-performance liquid chromatography

Various analytical techniques have been developed to determine nitrite and nitrate, oxidation metabolites of nitric oxide (NO), in biological samples. HPLC is a widely used method to quantify these two anions in plasma, serum, urine, saliva, cerebrospinal fluid, tissue extracts, and fetal fluids, as well as meats and cell culture medium. The detection principles include UV and VIS absorbance, electrochemistry, chemiluminescence, and fluorescence. UV or VIS absorbance and electrochemistry allow simultaneous detection of nitrite and nitrate but are vulnerable to the severe interference from chloride present in biological samples. Chemiluminescence and fluorescence detection improve the assay sensitivity and are unaffected by chloride but cannot be applied to a simultaneous analysis of nitrite and nitrate. The choice of a detection method largely depends on sample type and facility availability. The recently developed fluorometric HPLC method, which involves pre-column derivatization of nitrite with 2,3-diaminonaphthalene (DAN) and the enzymatic conversion of nitrate into nitrite, offers the advantages of easy sample preparation, simple derivatization, stable fluorescent derivatives, rapid analysis, high sensitivity and specificity, lack of interferences, and easy automation for determining nitrite and nitrate in all biological samples including cell culture medium. To ensure accurate analysis, care should be taken in sample collection, processing, and derivatization as well as preparation of reagent solutions and mobile phases, to prevent environmental contamination. HPLC methods provide a useful research tool for studying NO biochemistry, physiology and pharmacology.

Peroxidative stress and antioxidant enzymes in children with beta-thalassemia major

OBJECTIVE

Regular blood transfusions and secondary iron overload make thalassemic erythrocytes prone to peroxidative injury. Although some reports suggest endogenous free radical damage in thalassemia, there remains discrepancy in the status of antioxidant enzymes. The aim of this study was to evaluate the extent of lipid peroxidation and status of antioxidant enzyme in children with beta-thalassemia.

METHODS

Fifty transfusion-dependent beta-thalassemics were subjected to analysis of lipoperoxides as malondialdehyde (MDA), nitric oxide (NOx), superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GPx) along with serum iron and ferritin, liver functions and uric acid. Plasma MDA was analyzed to indicate the oxidative parameters, whereas the erythrocyte SOD, GPx, and plasma NOx were measured to show the antioxidant status of the children. All these parameters in 30 non-anemic healthy controls attending the child health promotion clinic of hospital were also studied.

RESULTS

All the patients were iron overloaded. Markers of free radical injury such as MDA and antioxidant enzyme SOD and NOx levels were significantly elevated in thalassemic children while mean GPx levels were decreased in patients compared to controls (P < 0.001). All these markers significantly correlated with serum ferritin levels. There was no significant difference in levels of GSH measured but it correlated with serum iron levels.

CONCLUSION

Our study results suggest that iron overload causes peroxidative damage in beta-thalassemia and antioxidant systems try to compensate for reducing lipid peroxidation to lower tissue damage.

Immobilization of the [RuII(edta)NO+] Ion on the surface of functionalized silica gel

The reaction of NO and the immobilized dimer complex (edta)(2)Ru(2)(III(1/2),III(1/2)) on silica gel chemically modified with [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEATS) produces the corresponding immobilized nitrosyl complex AEATS/Ru(II)NO(+). This compound, a monomer, was obtained by reducing the immobilized ruthenium dimer either electrochemically or with Eu(II) and reacting this species with NO(2)(-) ions. The properties of [Ru(edta)NO](-) in solution and anchored (AEATS/Ru(II)NO(+)) on silica were compared using electrochemical (DPV, CV) and spectroscopic (IR, UV-vis, and ESR) techniques. The results indicate that immobilization does not alter the reactivity of the ruthenium complex and confirm that [Ru(edta)(H(2)O)](2)(-) may be used, either in solution or immobilized, as a catalyst for the conversion of NO(2)(-) to NO(+). Both the anchored nitrosyl complex AEATS/Ru(II)NO(+) and the [Ru(edta)NO](-) species in solution, upon one-electron reduction, liberate NO at comparable rates.

Divergent contractile and structural responses of the murine PKC-epsilon null pulmonary circulation to chronic hypoxia

Loss of PKC-epsilon limits the magnitude of acute hypoxic pulmonary vasoconstriction (HPV) in the mouse. Therefore, we hypothesized that loss of PKC-epsilon would decrease the contractile and/or structural response of the murine pulmonary circulation to chronic hypoxia (Hx). However, the pattern of lung vascular responses to chronic Hx may or may not be predicted by the acute HPV response. Adult PKC-epsilon wild-type (PKC-epsilon(+/+)), heterozygous null, and homozygous null (PKC-epsilon(-/-)) mice were exposed to normoxia or Hx for 5 wk. PKC-epsilon(-/-) mice actually had a greater increase in right ventricular (RV) systolic pressure, RV mass, and hematocrit in response to chronic Hx than PKC-epsilon(+/+) mice. In contrast to the augmented PA pressure and RV hypertrophy, pulmonary vascular remodeling was increased less than expected (i.e., equal to PKC-epsilon(+/+) mice) in both the proximal and distal PKC-epsilon(-/-) pulmonary vasculature. The contribution of increased vascular tone to this pulmonary hypertension (PHTN) was assessed by measuring the acute vasodilator response to nitric oxide (NO). Acute inhalation of NO reversed the increased PA pressure in hypoxic PKC-epsilon(-/-) mice, implying that the exaggerated PHTN may be due to a relative deficiency in nitric oxide synthase (NOS). Despite the higher PA pressure, chronic Hx stimulated less of an increase in lung endothelial (e) and inducible (i) NOS expression in PKC-epsilon(-/-) than PKC-epsilon(+/+) mice. In contrast, expression of nNOS in PKC-epsilon(+/+) mice decreased in response to chronic Hx, while lung levels in PKC-epsilon(-/-) mice remained unchanged. In summary, loss of PKC-epsilon results in increased vascular tone, but not pulmonary vascular remodeling in response to chronic Hx. Blunting of Hx-induced eNOS and iNOS expression may contribute to the increased vascular tone. PKC-epsilon appears to be an important signaling intermediate in the hypoxic regulation of each NOS isoform.