Endothelial NO synthase as a source of NO and superoxide

Endothelial dysfunction due to eNOS uncoupling: molecular mechanisms as potential therapeutic targets

Nitric oxide (NO) is one of the most important molecules released by endothelial cells, and its antiatherogenic properties support cardiovascular homeostasis. Diminished NO bioavailability is a common hallmark of endothelial dysfunction underlying the pathogenesis of the cardiovascular disease. Vascular NO is synthesized by endothelial nitric oxide synthase (eNOS) from the substrate L-arginine (L-Arg), with tetrahydrobiopterin (BH₄) as an essential cofactor. Cardiovascular risk factors such as diabetes, dyslipidemia, hypertension, aging, or smoking increase vascular oxidative stress that strongly affects eNOS activity and leads to eNOS uncoupling. Uncoupled eNOS produces superoxide anion (O₂^-) instead of NO, thus becoming a source of harmful free radicals exacerbating the oxidative stress further. eNOS uncoupling is thought to be one of the major underlying causes of endothelial dysfunction observed in the pathogenesis of vascular diseases. Here, we discuss the main mechanisms of eNOS uncoupling, including oxidative depletion of the critical eNOS cofactor BH₄, deficiency of eNOS substrate L-Arg, or accumulation of its analog asymmetrical dimethylarginine (ADMA), and eNOS S-glutathionylation. Moreover, potential therapeutic approaches that prevent eNOS uncoupling by improving cofactor availability, restoration of L-Arg/ADMA ratio, or modulation of eNOS S-glutathionylation are briefly outlined.

Pathological changes in the brain after peripheral burns

Brain injuries are common complications in patients with thermal burns and are associated with unpleasant outcomes. In clinical settings, it was once believed that brain injuries were not major pathological processes after burn, at least in part due to the unavailability of specific clinical manifestations. Burn-related brain injuries have been studied for more than a century, but the underlying pathophysiology has not been completely clarified. This article reviews the pathological changes in the brain following peripheral burns at the anatomical, histological, cytological, molecular and cognitive levels. Therapeutic indications based on brain injury as well as future directions for research have been summarized and proposed.

ACTIVITY OF NITRO-OXIDATIVE PROCESSES IN PREGNANT WOMEN WITH IDIOPATHIC ARTERIAL HYPOTENSION

Primary violation of vascular tone and reactivity is considered the main hemodynamic link in the pathogenesis of idiopathic arterial hypotension (IAH). Two gaseous messengers - nitric oxide (NO) and hydrogen sulfide (H2S) play an important role in the regulation of vascular tone. The research aims at determining the state of the NO system and the level of H2S in women with IAH and their effect on the uteroplacental blood flow. Material and Methods. A number of 20 pregnant women with IAH at 40-41 weeks of gestation were examined (group I); the second group included 20 pregnant women with normotony at 39-40 weeks of gestation. The concentration of the complex of nitrates and nitrites was determined by the reaction of formation of a colored complex by Griss reagent. The content and production of peroxynitrite in alkali and alkaline earth metals were determined according to the procedure described by Vanuffelen et al. Detection of hydrogen sulfide content in blood plasma was performed by the method of Dombkowski et al. Studies of uteroplacental blood flow were performed on ultrasonic diagnostic device "SA-8000 EX" using color Doppler mapping and pulse mapping dopplerometry of the blood flow in the uterine arteries (UA). The assessment of blood flow velocity curves was carried out by determining the pulsation index (PI) in both arteries taking into account the average value. Results. The results of the study showed that an average level of nitrites and nitrates in pregnant women with IAH was 37.0% higher than in women with normotension, and peroxynitrite values were 2.4 times higher, respectively. In contrast, the concentration of H2S in pregnant women with IAH was almost 1.4 times lower, than in pregnant women with normal blood pressure. Doppler study of blood flow indices in UA showed a moderate increase in PI in 28.0% of pregnant women with IAH. Thus, indices of vascular resistance in UA of pregnant women with IAH were higher, on average, by 19.0% than in pregnant women with normotension. Conclusions. High levels of nitrites and nitrates in pregnant women with IAH form the basis for the development of nitrosatous stress, which is accompanied by increasing concentration of highly toxic peroxynitrite. Significant increase in peroxynitrite is one of the causes of endothelial dysfunction. In pregnant women with IAH due to the low content of H2S - its vasoconstrictive effects are prevalent, which may indicate an indirect interaction between both of these systems of vasoregulation.

Blood Flow Restriction Training: To Adjust or Not Adjust the Cuff Pressure Over an Intervention Period?

Blood flow restriction (BFR) training combines exercise and partial reduction of muscular blood flow using a pressured cuff. BFR training has been used to increase strength and muscle mass in healthy and clinical populations. A major methodological concern of BFR training is blood flow restriction pressure (BFRP) delivered during an exercise bout. Although some studies increase BFRP throughout a training intervention, it is unclear whether BFRP adjustments are pivotal to maintain an adequate BFR during a training period. While neuromuscular adaptations induced by BFR are widely studied, cardiovascular changes throughout training intervention with BFR and their possible relationship with BFRP are less understood. This study aimed to discuss the need for BFRP adjustment based on cardiovascular outcomes and provide directions for future researches. We conducted a literature review and analyzed 29 studies investigating cardiovascular adaptations following BFR training. Participants in the studies were healthy, middle-aged adults, older adults and clinical patients. Cuff pressure, when adjusted, was increased during the training period. However, cardiovascular outcomes did not provide a plausible rationale for cuff pressure increase. In contrast, avoiding increments in cuff pressure may minimize discomfort, pain and risks associated with BFR interventions, particularly in clinical populations. Given that cardiovascular adaptations induced by BFR training are conflicting, it is challenging to indicate whether increases or decreases in BFRP are needed. Based on the available evidence, we suggest that future studies investigate if maintaining or decreasing cuff pressure makes BFR training safer and/or more comfortable with similar physiological adaptation.

Peroxynitrite decomposition catalyst enhances respiratory function in isolated brain mitochondria

Peroxynitrite (PN), generated from the reaction of nitric oxide (NO) and superoxide, is implicated in the pathogenesis of ischemic and neurodegenerative brain injuries. Mitochondria produce NO from mitochondrial NO synthases and superoxide by the electron transport chain. Our objective was to detect the generation of PN of mitochondrial origin and characterize its effects on mitochondrial respiratory function. Freshly isolated brain nonsynaptosomal mitochondria from C57Bl/6 (wild type, WT) and endothelial NO synthase knockout (eNOS-KO) mice were treated with exogenous PN (0.1, 1, 5 µmol/L) or a PN donor (SIN-1; 50 µmol/L) or a PN scavenger (FeTMPyP; 2.5 µmol/L). Oxygen consumption rate (OCR) was measured using Agilent Seahorse XFe24 analyzer and mitochondrial respiratory parameters were calculated. Mitochondrial membrane potential, superoxide, and PN were determined from rhodamine 123, dihydroethidium, and DAX-J2 PON green fluorescence measurements, respectively. Mitochondrial protein nitrotyrosination was determined by Western blots. Both exogenous PN and SIN-1 decreased respiratory function in WT isolated brain mitochondria. FeTMPyP enhanced state III and state IVo mitochondrial respiration in both WT and eNOS-KO mitochondria. FeTMPyP also elevated state IIIu respiration in eNOS-KO mitochondria. Unlike PN, neither SIN-1 nor FeTMPyP depolarized the mitochondria. Although mitochondrial protein nitrotyrosination was unaffected by SIN-1 or FeTMPyP, FeTMPyP reduced mitochondrial PN levels. Mitochondrial superoxide levels were increased by FeTMPyP but were unaffected by PN or SIN-1. Thus, we present the evidence of functionally significant PN generation in isolated brain mitochondria. Mitochondrial PN activity was physiologically relevant in WT mice and pathologically significant under conditions with eNOS deficiency.NEW & NOTEWORTHY Mitochondria generate superoxide and nitric oxide that could potentially react with each other to produce PN. We observed eNOS and nNOS immunoreactivity in isolated brain and heart mitochondria with pharmacological inhibition of nNOS found to modulate the mitochondrial respiratory function. This study provides evidence of generation of functionally significant PN in isolated brain mitochondria that affects respiratory function under physiological conditions. Importantly, the mitochondrial PN levels and activity were exaggerated in the eNOS-deficient mice, suggesting its pathological significance.

Disparate Effect of Antioxidant Supplements on the Basal Tone and Vascular Remodeling of the Aorta in Hypertensive Rats

BACKGROUND

Oxidative stress plays an essential role in the vascular tone in hypertension; however, the mechanisms remain unclear.

AIM

This study aimed to determine the antioxidant effect of tempol and vitamin C (Vit-C) on the basal tone and vascular remodeling of the aorta in nitric oxide (NO) deficiency-induced hypertensive rats.

METHOD

Male Sprague-Dawley rats were induced to hypertension by Nω-nitro-L-arginine methyl ester (L-NAME). Animals were randomized as follows: vehicle (Control: CR), CR-tempol, CR-Vit-C, L-NAME, L-NAME-tempol, and L-NAME-Vit-C. After 6 weeks of treatment, the basal aortic tone was evaluated by sodium nitroprusside (SNP) and calcium-free medium. Endothelial function, NO, reduced-to-oxidized glutathione (GSH/GSSG) ratio, resting membrane potential (mP), and vascular remodeling were also measured.

RESULTS

L-NAME rats showed an increased basal tone that was blunted by both SNP (-547 ± 69; n = 7 vs. CR: -7.5 ± 6.7 mg; n = 7; p < 0.001) and calcium-free medium. Tempol or Vit-C did not reverse hypertension, and the high basal tone was decreased only with tempol. In L-NAME rats, only tempol partially improved endothelial function, GSH-to-GSSG ratio, mP values, and vascular remodeling.

CONCLUSIONS

Tempol decreased calcium-dependent basal aortic tone and improved vascular homeostasis in L-NAME rats. Vit-C did not lead to a similar effect, suggesting that alterations in the superoxide dismutase pathway may play a role in the basal aortic tone.

Intraplatelet L-Arginine-Nitric Oxide Metabolic Pathway: From Discovery to Clinical Implications in Prevention and Treatment of Cardiovascular Disorders

Despite the development of new drugs and other therapeutic strategies, cardiovascular disease (CVD) remains still the major cause of morbidity and mortality in the world population. A lot of research, performed mostly in the last three decades, revealed an important correlation between "classical" demographic and biochemical risk factors for CVD, (i.e., hypercholesterolemia, hyperhomocysteinemia, smoking, renal failure, aging, diabetes, and hypertension) with endothelial dysfunction associated directly with the nitric oxide deficiency. The discovery of nitric oxide and its recognition as an endothelial-derived relaxing factor was a breakthrough in understanding the pathophysiology and development of cardiovascular system disorders. The nitric oxide synthesis pathway and its regulation and association with cardiovascular risk factors were a common subject for research during the last decades. As nitric oxide synthase, especially its endothelial isoform, which plays a crucial role in the regulation of NO bioavailability, inhibiting its function results in the increase in the cardiovascular risk pattern. Among agents altering the production of nitric oxide, asymmetric dimethylarginine-the competitive inhibitor of NOS-appears to be the most important. In this review paper, we summarize the role of L-arginine-nitric oxide pathway in cardiovascular disorders with the focus on intraplatelet metabolism.

Enhanced Nitric Oxide (NO) and Decreased ADMA Synthesis in Pediatric ADHD and Selective Potentiation of NO Synthesis by Methylphenidate

Attention deficit hyperactivity disorder (ADHD) is a common pediatric psychiatric disorder, frequently treated with methylphenidate (MPH). Recently, MPH’s cardiovascular safety has been questioned by observational studies describing an increased cardiovascular risk in adults and blood pressure alterations in children. We considered members of the L-arginine (Arg)/nitric oxide (NO) pathway as possible early cardiovascular risk factors in pediatric ADHD children. They include the NO metabolites, nitrite and nitrate, the NO precursor Arg, and asymmetric dimethylarginine (ADMA), an endogenous NO synthase (NOS) inhibitor and a cardiovascular risk factor in adults. We conducted a prospective clinical trial with 42 ADHD children (aged 6–16 years) with (n = 19) and without (n = 23) MPH treatment. Age-matched children without ADHD (n = 43) served as controls. All plasma and urine metabolites were determined by gas chromatography-mass spectrometry. We observed higher plasma nitrite and lower plasma ADMA concentrations in the ADHD children. MPH-treated ADHD children had higher plasma nitrite concentrations than MPH-untreated ADHD children. As NOS activity is basally inhibited by ADMA, MPH treatment seems to have decreased the inhibitory potency of ADMA. Percentiles of systolic blood pressure were higher in MPH-treated ADHD children. The underlying mechanisms and their implications in the MPH therapy of pediatric ADHD with MPH remain to be elucidated in larger cohorts.

Pathogenetic role of endothelial nitric oxide synthase uncoupling during lung ischaemia-reperfusion injury

OBJECTIVES

Ischaemia-reperfusion injury is a necessary part of organ transplantation and a key determinant of both acute and chronic graft failure. We have assessed the contribution of endothelial nitric oxide synthase (eNOS) and eNOS uncoupling to oxidative and nitrosative stress formation during lung ischaemia-reperfusion injury dependent on ischaemia time.

METHODS

Forty eNOS wild-type mice (eNOS +/+ ) and 40 eNOS knock-out mice (eNOS -/- ) received either a sham thoracotomy or 60 or 90 min of ischaemia, followed by 0, 1 or 24 h of reperfusion. Lung tissue was analysed with electron spin resonance for NO production and reactive oxygen species content. Protein nitrosation, eNOS and eNOS uncoupling were determined using western blotting. In peripheral blood, arterial blood gases were taken and reactive oxygen species content was determined.

RESULTS

eNOS +/+ mice had lower reactive oxygen species production in their peripheral circulation but worse blood gas values after 1 h of reperfusion. Lung tissue of eNOS -/- mice showed lower reactive oxygen species and NO production and lower protein nitrosation compared with wild-type mice. Longer ischaemia times result in more elaborate oxidative and nitrosative stress dependent on eNOS genotype. Structural eNOS uncoupling was present after 60 min of ischaemia but diminished after 90 min of ischaemia.

CONCLUSIONS

eNOS uncoupling may contribute to lung ischaemia-reperfusion injury and inflammation. This ultimately leads to worse clinical outcome. Stabilizing eNOS may therefore be a new approach to extend pulmonary graft survival.

Results, meta-analysis and a first evaluation of UNOxR, the urinary nitrate-to-nitrite molar ratio, as a measure of nitrite reabsorption in experimental and clinical settings

We recently found that renal carbonic anhydrase (CA) is involved in the reabsorption of inorganic nitrite (NO₂^-), an abundant reservoir of nitric oxide (NO) in tissues and cells. Impaired NO synthesis in the endothelium and decreased NO bioavailability in the circulation are considered major contributors to the development and progression of renal and cardiovascular diseases in different conditions including diabetes. Isolated human and bovine erythrocytic CAII and CAIV can convert nitrite to nitrous acid (HONO) and its anhydride N₂O₃ which, in the presence of thiols (RSH), are further converted to S-nitrosothiols (RSNO) and NO. Thus, CA may be responsible both for the homeostasis of nitrite and for its bioactivation to RSNO/NO. We hypothesized that enhanced excretion of nitrite in the urine may contribute to NO-related dysfunctions in the renal and cardiovascular systems, and proposed the urinary nitrate-to-nitrite molar ratio, i.e., U_NOxR, as a measure of renal CA-dependent excretion of nitrite. Based on results from clinical and experimental animal studies, here, we report on a first evaluation of U_NOxR. We determined U_NOxR values in preterm neonates, healthy children, and adults, in children suffering from type 1 diabetes mellitus (T1DM) or Duchenne muscular dystrophy (DMD), in elderly subjects suffering from chronic rheumatic diseases, type 2 diabetes mellitus (T2DM), coronary artery disease (CAD), or peripheral arterial occlusive disease (PAOD). We also determined U_NOxR values in healthy young men who ingested isosorbide dinitrate (ISDN), pentaerythrityl tetranitrate (PETN), or inorganic nitrate. In addition, we tested the utility of U_NOxR in two animal models, i.e., the LEW.1AR1-iddm rat, an animal model of human T1DM, and the APOE*3-Leiden.CETP mice, a model of human dyslipidemia. Mean U_NOxR values were lower in adult patients with rheumatic diseases (187) and in T2DM patients of the DALI study (74) as compared to healthy elderly adults (660) and healthy young men (1500). The intra- and inter-variabilities of U_NOxR were of the order of 50% in young and elderly healthy subjects. U_NOxR values were lower in black compared to white boys (314 vs. 483, P = 0.007), which is in line with reported lower NO bioavailability in black ethnicity. Mean U_NOxR values were lower in DMD (424) compared to healthy (730) children, but they were higher in T1DM children (1192). ISDN (3 × 30 mg) decreased stronger U_NOxR compared to PETN (3 × 80 mg) after 1 day (P = 0.046) and after 5 days (P = 0.0016) of oral administration of therapeutically equivalent doses. In healthy young men who ingested NaNO₃ (0.1 mmol/kg/d), U_NOxR was higher than in those who ingested the same dose of NaCl (1709 vs. 369). In LEW.1AR1-iddm rats, mean U_NOxR values were lower than in healthy rats (198 vs. 308) and comparable to those in APOE*3-Leiden.CETP mice (151).

Comprehensive analysis of the L-arginine/L-homoarginine/nitric oxide pathway in preterm neonates: potential roles for homoarginine and asymmetric dimethylarginine in foetal growth

L-Arginine (Arg) and L-homoarginine (hArg) are precursors of nitric oxide (NO), a signalling molecule with multiple important roles in human organism. In the circulation of adults, high concentrations of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) and low concentrations of hArg emerged as cardiovascular risk factors. Yet, the importance of the Arg/hArg/NO pathway, especially of hArg and ADMA, in preterm neonates is little understood. We comprehensively investigated the Arg/hArg/NO pathway in 106 healthy preterm infants (51 boys, 55 girls) aged between 23 + 6 and 36 + 1 gestational weeks. Babies were divided into two groups: group I consisted of 31 babies with a gestational age of 23 + 6 - 29 + 6 weeks; group II comprised 75 children with a gestational age of 30 + 0 - 36 + 1 weeks. Plasma and urine concentrations of ADMA, SDMA, hArg, Arg, dimethylamine (DMA) which is the major urinary ADMA metabolite, as well as of nitrite and nitrate, the major NO metabolites, were determined by GC-MS and GC-MS/MS methods. ADMA and hArg plasma levels, but not the hArg/ADMA molar ratio, were significantly higher in group II than in group I: 895 ± 166 nM vs. 774 ± 164 nM (P = 0.001) for ADMA and 0.56 ± 0.04 µM vs. 0.48 ± 0.08 µM (P = 0.010) for hArg. There was no statistical difference between the groups with regard to urinary ADMA (12.2 ± 4.6 vs 12.8 ± 3.6 µmol/mmol creatinine; P = 0.61) and urinary SDMA. Urinary hArg, ADMA, SDMA correlated tightly with each other. Urinary excretion of DMA was slightly higher in group I compared to group II: 282 ± 44 vs. 247 ± 35 µmol/mmol creatinine (P = 0.004). The DMA/ADMA molar ratio in urine was tendentiously higher in neonates of group I compared to group II: 27 ± 13 vs. 20 ± 5 (P = 0.065). There were no differences between the groups with respect to Arg in plasma and to nitrite and nitrate in plasma and urine. In preterm neonates, ADMA and hArg biosynthesis increases with gestational age without remarkable changes in the hArg/ADMA ratio or NO biosynthesis. Our study suggests that ADMA and hArg are involved in foetal growth.

Regular Exercise Reduces Endothelial Cortical Stiffness in Western Diet-Fed Female Mice

We recently showed that Western diet-induced obesity and insulin resistance promotes endothelial cortical stiffness in young female mice. Herein, we tested the hypothesis that regular aerobic exercise would attenuate the development of endothelial and whole artery stiffness in female Western diet-fed mice. Four-week-old C57BL/6 mice were randomized into sedentary (ie, caged confined, n=6) or regular exercise (ie, access to running wheels, n=7) conditions for 16 weeks. Exercise training improved glucose tolerance in the absence of changes in body weight and body composition. Compared with sedentary mice, exercise-trained mice exhibited reduced endothelial cortical stiffness in aortic explants (sedentary 11.9±1.7 kPa versus exercise 5.5±1.0 kPa; P<0.05), as assessed by atomic force microscopy. This effect of exercise was not accompanied by changes in aortic pulse wave velocity (P>0.05), an in vivo measure of aortic stiffness. In comparison, exercise reduced femoral artery stiffness in isolated pressurized arteries and led to an increase in femoral internal artery diameter and wall cross-sectional area (P<0.05), indicative of outward hypertrophic remodeling. These effects of exercise were associated with an increase in femoral artery elastin content and increased number of fenestrae in the internal elastic lamina (P<0.05). Collectively, these data demonstrate for the first time that the aortic endothelium is highly plastic and, thus, amenable to reductions in stiffness with regular aerobic exercise in the absence of changes in in vivo whole aortic stiffness. Comparatively, the same level of exercise caused destiffening effects in peripheral muscular arteries, such as the femoral artery, that perfuse the working limbs.

Vasoactive enzymes and blood flow responses to passive and active exercise in peripheral arterial disease

BACKGROUND

Peripheral arterial disease (PAD) is characterised by impaired leg blood flow, which contributes to claudication and reduced exercise capacity. This study investigated to what extent vasoactive enzymes might contribute to altered blood flow in PAD (Fontaine stage II).

METHODS

We compared femoral artery blood flow during reactive hyperaemia, leg-extension exercise and passive leg movement, and determined the level of vasoactive enzymes in skeletal muscle samples from the vastus lateralis in PAD (n = 10, 68.5 ± 6.5 years) and healthy controls (CON, n = 9, 62.1 ± 12.3 years). Leg blood flow was measured with Doppler ultrasound and muscle protein levels of phosphorylated endothelial nitric oxide synthase, NADPH oxidase, cyclooxygenase 1 and 2, thromboxane synthase, and prostacyclin synthase were determined.

RESULTS

Leg blood flow during the initial 90 s of passive leg movement (242 ± 33 vs 441 ± 75 ml min(-1), P = 0.03) and during reactive hyperaemia (423 ± 100 vs 1255 ± 175 ml min(-1), P = 0.002) was lower in PAD than CON, whereas no significant difference was observed for leg blood flow during exercise (1490 ± 250 vs 1887 ± 349 ml min(-1), P = 0.37). PAD had higher NADPH oxidase than CON (1.04 ± 0.19 vs 0.50 ± 0.06 AU, P = 0.02), with no differences for other enzymes. Leg blood flow during exercise was correlated with prostacyclin synthase (P = 0.001).

CONCLUSION

Elevated NADPH oxidase indicates that oxidative stress may be a primary cause of low nitric oxide availability and impaired blood flow in PAD.

Association between hypertriglyceridemia and protein oxidation and proinflammatory markers in normocholesterolemic and hypercholesterolemic individuals

BACKGROUND

Although hypercholesterolemia is a well-established risk factor for coronary heart disease, evidence suggests that increased triglyceride (TG) concentrations are also an independent risk factor. TG concentrations >150mg/dl are observed nearly twice as often in subjects with atherosclerosis. We assessed the association between hypertriglyceridemia and protein oxidation and proinflammatory markers in normocholesterolemic and hypercholesterolemic individuals.

METHODS

We included 127 volunteers enrolled in Cruz Alta, RS, Brazil. The patients were stratified based on total cholesterol and TG concentrations for analysis of associations with inflammation (high-sensitivity C-reactive protein - hs-CRP), endothelial dysfunction (nitric oxide - NOx) and oxidative stress (advanced oxidation protein products - AOPPs; ischemia-modified albumin - IMA). Correlations between variables were determined and multiple regression analysis was employed to investigate whether some variables correlate with TG concentrations.

RESULTS

Hypertriglyceridemia was related to oxidative stress and proinflammatory markers in individuals independent of total cholesterol concentrations. Moreover, the results indicate a stronger association of tested biomarkers with TG concentrations than with total cholesterol. The results indicate a positive correlation between oxidative stress and TG concentrations in the sera of hypercholesterolemia subjects. AOPPs and IMA concentrations were associated with the presence of hypertriglyceridemia in a manner that was independent of age, gender, hypertension and diabetes mellitus disease, smoking habits, sedentary lifestyle, BMI, waist circumference, LDL, HDL and total cholesterol concentrations.

CONCLUSIONS

We speculate that TG concentrations can reflect the enhancement of protein oxidation and proinflammation.

Mass spectrometry and 3-nitrotyrosine: strategies, controversies, and our current perspective

Reactive-nitrogen species (RNS) such as peroxynitrite (ONOO(-)), that is, the reaction product of nitric oxide ((•)NO) and superoxide (O2(-•)), nitryl chloride (NO2Cl) and (•)NO2 react with the activated aromatic ring of tyrosine to form 3-nitrotyrosine. This modification, which has been known for more than a century, occurs to both the free form of the amino acid (i.e., soluble/free tyrosine) and to tyrosine residues covalently bound within the backbone of peptides and proteins. Nitration of tyrosine is thought to be of biological significance and has been linked to health and disease, but determining its role has proved challenging. Several key questions have been the focus of much of the research activity: (a) to what extent is free/soluble tyrosine nitrated in biological tissues and fluids, and (b) are there specific site(s) of nitration within peptides/proteins and to what extent (i.e., stoichiometry) does this modification occur? These issues have been addressed in a wide range of sample types (e.g., blood, urine, CSF, exhaled breath condensate and various tissues) and a diverse array of physiological/pathophysiological scenarios. The accurate determination of nitrated tyrosine is, however, a stumbling block. Despite extensive study, the extent to which nitration occurs in vivo, the specificity of the nitration reaction, and its importance in health and disease, remain unclear. In this review, we highlight the analytical challenges and discuss the approaches adopted to address them. Mass spectrometry, in combination with either gas chromatography (GC-MS, GC-MS/MS) or liquid chromatography (LC-MS/MS), has played the central role in the analysis of 3-nitrotyrosine and tyrosine-nitrated biological macromolecules. We discuss its unique attributes and highlight the role of stable-isotope labeled 3-nitrotyrosine analogs in both accurate quantification, and in helping to define the biological relevance of tyrosine nitration. We show that the application of sophisticated mass spectrometric techniques is advantageous if not essential, but that this alone is by no means a guarantee of accurate findings. We discuss the important analytical challenges in quantifying 3-nitrotyrosine, possible workarounds, and we attempt to make sense of the disparate findings that have been reported so far.

Effects of paracetamol on NOS, COX, and CYP activity and on oxidative stress in healthy male subjects, rat hepatocytes, and recombinant NOS

Paracetamol (acetaminophen) is a widely used analgesic drug. It interacts with various enzyme families including cytochrome P450 (CYP), cyclooxygenase (COX), and nitric oxide synthase (NOS), and this interplay may produce reactive oxygen species (ROS). We investigated the effects of paracetamol on prostacyclin, thromboxane, nitric oxide (NO), and oxidative stress in four male subjects who received a single 3 g oral dose of paracetamol. Thromboxane and prostacyclin synthesis was assessed by measuring their major urinary metabolites 2,3-dinor-thromboxane B₂ and 2,3-dinor-6-ketoprostaglandin F_1α, respectively. Endothelial NO synthesis was assessed by measuring nitrite in plasma. Urinary 15(S)-8-iso-prostaglanding F_2α was measured to assess oxidative stress. Plasma oleic acid oxide (cis-EpOA) was measured as a marker of cytochrome P450 activity. Upon paracetamol administration, prostacyclin synthesis was strongly inhibited, while NO synthesis increased and thromboxane synthesis remained almost unchanged. Paracetamol may shift the COX-dependent vasodilatation/vasoconstriction balance at the cost of vasodilatation. This effect may be antagonized by increasing endothelial NO synthesis. High-dosed paracetamol did not increase oxidative stress. At pharmacologically relevant concentrations, paracetamol did not affect NO synthesis/bioavailability by recombinant human endothelial NOS or inducible NOS in rat hepatocytes. We conclude that paracetamol does not increase oxidative stress in humans.

Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Cardiovascular disease is the primary cause of morbidity and mortality among the diabetic population. Both experimental and clinical evidence suggest that diabetic subjects are predisposed to a distinct cardiomyopathy, independent of concomitant macro- and microvascular disorders. 'Diabetic cardiomyopathy' is characterized by early impairments in diastolic function, accompanied by the development of cardiomyocyte hypertrophy, myocardial fibrosis and cardiomyocyte apoptosis. The pathophysiology underlying diabetes-induced cardiac damage is complex and multifactorial, with elevated oxidative stress as a key contributor. We now review the current evidence of molecular disturbances present in the diabetic heart, and their role in the development of diabetes-induced impairments in myocardial function and structure. Our focus incorporates both the contribution of increased reactive oxygen species production and reduced antioxidant defenses to diabetic cardiomyopathy, together with modulation of protein signaling pathways and the emerging role of protein O-GlcNAcylation and miRNA dysregulation in the progression of diabetic heart disease. Lastly, we discuss both conventional and novel therapeutic approaches for the treatment of left ventricular dysfunction in diabetic patients, from inhibition of the renin-angiotensin-aldosterone-system, through recent evidence favoring supplementation of endogenous antioxidants for the treatment of diabetic cardiomyopathy. Novel therapeutic strategies, such as gene therapy targeting the phosphoinositide 3-kinase PI3K(p110α) signaling pathway, and miRNA dysregulation, are also reviewed. Targeting redox stress and protective protein signaling pathways may represent a future strategy for combating the ever-increasing incidence of heart failure in the diabetic population.

Mitochondrial dysfunction in brain cortex mitochondria of STZ-diabetic rats: effect of l-Arginine

Mitochondrial dysfunction has been implicated in many diseases, including diabetes. It is well known that oxygen free radical species are produced endogenously by mitochondria, and also nitric oxide (NO) by nitric oxide synthases (NOS) associated to mitochondrial membranes, in consequence these organelles constitute main targets for oxidative damage. The aim of this study was to analyze mitochondrial physiology and NO production in brain cortex mitochondria of streptozotocin (STZ) diabetic rats in an early stage of diabetes and the potential effect of L-arginine administration. The diabetic condition was characterized by a clear hyperglycaemic state with loose of body weight after 4 days of STZ injection. This hyperglycaemic state was associated with mitochondrial dysfunction that was evident by an impairment of the respiratory activity, increased production of superoxide anion and a clear mitochondrial depolarization. In addition, the alteration in mitochondrial physiology was associated with a significant decrease in both NO production and nitric oxide synthase type I (NOS I) expression associated to the mitochondrial membranes. An increased level of thiobarbituric acid-reactive substances (TBARS) in brain cortex homogenates from STZ-diabetic rats indicated the presence of lipid peroxidation. L-arginine treatment to diabetic rats did not change blood glucose levels but significantly ameliorated the oxidative stress evidenced by lower TBARS and a lower level of superoxide anion. This effect was paralleled by improvement of mitochondrial respiratory function and a partial mitochondrial repolarization.In addition, the administration of L-arginine to diabetic rats prevented the decrease in NO production and NOSI expression. These results could indicate that exogenously administered L-arginine may have beneficial effects on mitochondrial function, oxidative stress and NO production in brain cortex mitochondria of STZ-diabetic rats.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

The role of oxidative stress in postprandial endothelial dysfunction

Endothelial dysfunction is a turning point in the initiation and development of atherosclerosis and its complications and is predictive of future cardiovascular events. Ingestion of high-carbohydrate or high-fat meals often results in postprandial hyperglycaemia and/or hypertriacylglycerolaemia that may lead to a transient impairment in endothelial function. The present review will discuss human studies evaluating the impact of high-carbohydrate and high-fat challenges on postprandial endothelial function as well as the potential role of oxidative stress in such postprandial metabolic alterations. Moreover, the present review will differentiate the postprandial endothelial and oxidative impact of meals rich in varying fatty acid types.

The impact of acute mental stress on vascular endothelial function: evidence, mechanisms and importance

Cardiovascular disease is a principle cause of morbidity and mortality worldwide, and it has a complex etiology that involves lifestyle factors such as psychosocial stress. Recent evidence suggests that temporary impairments in vascular endothelial cell function may contribute to the relationship between stress and cardiovascular disease. Indeed, impaired endothelial function has been observed to occur transiently (lasting up to 1.5h) following mental stress, and such periods of impairment could accumulate to become clinically relevant over the long term. The finding of acute stress induced endothelial dysfunction is not universal however, and both physiological (e.g. sympathetic nervous system and hypothalamic-pituitary-adrenal axis reactivity), and methodological factors contribute to the conflicting results. A clear understanding of the interaction between stress response activation and endothelial function is critical to elucidating the complexities of the relationship between psychosocial stress and cardiovascular disease. Therefore, the purpose of this review is: 1) to briefly describe the importance of vascular endothelial function and how it is assessed, 2) to review the literature investigating the impact of acute mental stress on endothelial function in humans, identifying factors that may explain contradictory results, and 3) to summarize our current understanding of the mechanisms that may mediate an acute mental stress-endothelial function interaction.

Blood flow restricted exercise and vascular function

It is established that regular aerobic training improves vascular function, for example, endothelium-dependent vasodilatation and arterial stiffness or compliance and thereby constitutes a preventative measure against cardiovascular disease. In contrast, high-intensity resistance training impairs vascular function, while the influence of moderate-intensity resistance training on vascular function is still controversial. However, aerobic training is insufficient to inhibit loss in muscular strength with advancing age; thus, resistance training is recommended to prevent sarcopenia. Recently, several lines of study have provided compelling data showing that exercise and training with blood flow restriction (BFR) leads to muscle hypertrophy and strength increase. As such, BFR training might be a novel means of overcoming the contradiction between aerobic and high-intensity resistance training. Although it is not enough evidence to obtain consensus about impact of BFR training on vascular function, available evidences suggested that BFR training did not change coagulation factors and arterial compliance though with inconsistence results in endothelial function. This paper is a review of the literature on the impact of BFR exercise and training on vascular function, such as endothelial function, arterial compliance, or other potential factors in comparison with those of aerobic and resistance training.

Brachial artery flow-mediated dilation following exercise with augmented oscillatory and retrograde shear rate

Background

Acute doses of elevated retrograde shear rate (SR) appear to be detrimental to endothelial function in resting humans. However, retrograde shear increases during moderate intensity exercise which also enhances post-exercise endothelial function. Since SR patterns differ with the modality of exercise, it is important to determine if augmented retrograde SR during exercise influences post-exercise endothelial function. This study tested the hypothesis that (1) increased doses of retrograde SR in the brachial artery during lower body supine cycle ergometer exercise would attenuate post-exercise flow-mediated dilation (FMD) in a dose-dependent manner, and (2) antioxidant vitamin C supplementation would prevent the attenuated post-exercise FMD response.

Methods

Twelve men participated in four randomized exercise sessions (90 W for 20 minutes) on separate days. During three of the sessions, one arm was subjected to increased oscillatory and retrograde SR using three different forearm cuff pressures (20, 40, 60 mmHg) (contralateral arm served as the control) and subjects ingested placebo capsules prior to exercise. A fourth session with 60 mmHg cuff pressure was performed with 1 g of vitamin C ingested prior to the session.

Results

Post-exercise FMD following the placebo conditions were lower in the cuffed arm versus the control arm (arm main effect: P < 0.05) and without differences between cuff pressures (20 mmHg: 5.7 ± 2.2%; 40 mmHg: 4.7 ± 1.3%; 60 mmHg: 5.4 ± 2.4%) (P > 0.05). Following vitamin C treatment, post-exercise FMD in the cuffed and control arm increased from baseline (P < 0.05) but were not different (control: 7.1 ± 3.5% vs. cuffed: 6.6 ± 3.3%) (P > 0.05).

Conclusions

These results indicate that augmented oscillatory and retrograde SR in non-working limbs during lower body exercise attenuates post-exercise FMD without an evident dose–response in the range of cuff pressures evaluated. Vitamin C supplementation prevented the attenuation of FMD following exercise with augmented oscillatory and retrograde SR suggesting that oxidative stress contributes to the adverse effects of oscillatory and retrograde shear during exercise on FMD.

Glutathione in cerebral microvascular endothelial biology and pathobiology: implications for brain homeostasis

The integrity of the vascular endothelium of the blood-brain barrier (BBB) is central to cerebrovascular homeostasis. Given the function of the BBB as a physical and metabolic barrier that buffers the systemic environment, oxidative damage to the endothelial monolayer will have significant deleterious impact on the metabolic, immunological, and neurological functions of the brain. Glutathione (GSH) is a ubiquitous major thiol within mammalian cells that plays important roles in antioxidant defense, oxidation-reduction reactions in metabolic pathways, and redox signaling. The existence of distinct GSH pools within the subcellular organelles supports an elegant mode for independent redox regulation of metabolic processes, including those that control cell fate. GSH-dependent homeostatic control of neurovascular function is relatively unexplored. Significantly, GSH regulation of two aspects of endothelial function is paramount to barrier preservation, namely, GSH protection against oxidative endothelial cell injury and GSH control of postdamage cell proliferation in endothelial repair and/or wound healing. This paper highlights our current insights and hypotheses into the role of GSH in cerebral microvascular biology and pathobiology with special focus on endothelial GSH and vascular integrity, oxidative disruption of endothelial barrier function, GSH regulation of endothelial cell proliferation, and the pathological implications of GSH disruption in oxidative stress-associated neurovascular disorders, such as diabetes and stroke.

Brachial artery modifications to blood flow-restricted handgrip training and detraining

Low load resistance training with blood flow restriction (BFR) can increase muscle size and strength, but the implications on the conduit artery are uncertain. We examined the effects of low-load dynamic handgrip training with and without BFR, and detraining, on measures of brachial artery function and structure. Nine male participants (26 ± 4 yr, 178 ± 3 cm, 78 ± 10 kg) completed 4 wk (3 days/wk) of dynamic handgrip training at 40% 1 repetition maximum (1RM). In a counterbalanced manner, one forearm trained under BFR (occlusion cuff at 80 mmHg) and the other under nonrestricted (CON) conditions. Brachial artery function [flow-mediated dilation (FMD)] and structure (diameter) were assessed using Doppler ultrasound. Measurements were made before training (pretraining), after training (posttraining), and after 2-wk no training (detraining). Brachial artery diameter at rest, in response to 5-min ischemia (peak diameter), and ischemic exercise (maximal diameter) increased by 3.0%, 2.4%, and 3.1%, respectively, after BFR training but not after CON. FMD did not change at any time point in either arm. Vascular measures in the BFR arm returned to baseline after 2 wk detraining with no change after CON. The data demonstrate that dynamic low-load handgrip training with BFR induced transient adaptations to conduit artery structure but not function.

The exercise dose affects oxidative stress and brachial artery flow-mediated dilation in trained men

The aim of this investigation was to establish whether changes in oxidative stress and endothelial function following acute aerobic exercise are dose-dependent. Ten healthy trained men completed four exercise sessions: 50% VO(2peak) for 30 min (moderate intensity moderate duration, MIMD), 50% VO(2peak) for 60 min (moderate intensity long duration, MILD), 80% VO(2peak) for 30 min (high intensity moderate duration, HIMD), and 80% VO(2peak) for the time to reach the caloric equivalent of MIMD (high intensity short duration, HISD). Thiobarbituric acid reactive substances (TBARS) were measured as an index of oxidative stress and brachial artery flow-mediated dilation (FMD) was assessed as an index of endothelial function. Variables were measured at baseline, immediately post-exercise, 1 and 2 h post-exercise. Both HIMD (14.2 ± 2.5 μmol/L) and HISD (14.7 ± 1.9 μmol/L) TBARS differed from MIMD (11.8 ± 1.5 μmol/L) immediately post-exercise. TBARS increased from pre to immediately post-exercise for HIMD (12.6 ± 2.1 vs.14.2 ± 2.5 μmol/L) and HISD (12.3 ± 2.8 vs. 14.7 ± 1.9 μmol/L). Both MIMD (7.2 ± 2.2%) and HISD (7.6 ± 2.7%) FMD immediately post-exercise were greater than HIMD (4.7 ± 2.2%). An increase of FMD from pre to immediately post-exercise was found for MIMD (5.0 ± 2.5 vs. 7.2 ± 2.2%) and HISD (5.9 ± 2.4 vs. 7.6 ± 2.7%). These data suggest that acute exercise-induced TBARS are exercise intensity-dependent whereas FMD appears to improve following energy expenditure equivalent to 30 min 50% VO(2peak), regardless of intensity or duration.

GC-MS and HPLC methods for peroxynitrite (ONOO- and O15NOO-) analysis: a study on stability, decomposition to nitrite and nitrate, laboratory synthesis, and formation of peroxynitrite from S-nitrosoglutathione (GSNO) and KO2

Nitric oxide (˙NO) and superoxide (O(2)(-)˙) are ubiquitous in nature. Their reaction product peroxynitrite (ONOO(-)) and notably its conjugated peroxynitrous acid (ONOOH) are highly unstable in aqueous phase. ONOO(-)/ONOOH (referred to as peroxynitrite) isomerize and decompose to NO(3)(-), NO(2)(-) and O(2). Here, we report for the first time GC-MS and HPLC methods for the analysis of peroxynitrite in aqueous solution. For GC-MS analysis peroxynitrite in alkaline solution was derivatized to a pentafluorobenzyl derivative using pentafluorobenzyl bromide. O(15)NOO(-) was synthesized from H(2)O(2) and (15)NO(2)(-) and used as internal standard. HPLC analysis was performed on stationary phases consisting of Nucleosil® 100-5C(18)AB or Nucleodur® C(18) Gravity. The mobile phase consisted of a 10 mM aqueous solution of tetrabutylammonium hydrogen sulfate and had a pH value of 11.5. UV absorbance detection at 300 nm was used. HPLC allows simultaneous analysis of ONOO(-), NO(2)(-) and NO(3)(-). The GC-MS and HPLC methods were used to study stability, synthesis, formation from S-[(15)N]nitrosoglutathione (GS(15)NO) and KO(2), and isomerization/decomposition of peroxynitrite to NO(2)(-) and NO(3)(-) in aqueous buffer.

Postprandial lipaemia, oxidative stress and endothelial function: a review

AIMS

Postprandial lipaemia-induced endothelial dysfunction is felt to be mediated by increases in oxidative stress. In this review, we have examined the cross-sectional relationships found among these three variables.

METHODS

We found 20 studies conducted by 16 independent investigative teams through a Medline search from 1980 to 2008; studies were required to report correlations between at least two of the three variables of interest in studies of humans. This review is divided into (i) discussions on the biomarkers and other measures of postprandial lipaemia, oxidative stress and endothelial function; (ii) associations reported among the three variables; and (iii) other considerations including alternative intervention studies.

RESULTS

Triglycerides and free fatty acids are robust and well-standardised biomarkers of lipaemia. Measures of oxidative stress ranged from electron spin techniques to measures of lipid peroxidation and are limited by lack of standardisation. Brachial artery flow-mediated dilatation is the most commonly used measure of endothelial function. The associations between postprandial lipaemia and oxidative stress and between postprandial lipaemia and endothelial function are strong and consistent. However, the association between postprandial oxidative stress and endothelial function appears weak, at least using current approaches to measurement of oxidative stress.

DISCUSSION AND CONCLUSIONS

These observations are consistent with the proposed concept that oxidative stress mediates the adverse effects of postprandial lipaemia on endothelial function; they are limited by the difficulties in measuring oxidative stress. Efforts directed at optimising and standardising the measurement of oxidative stress will be of value in future works in this area.

The oxidative stress-induced niacin sink (OSINS) model for HIV pathogenesis

Although several specific micronutrient deficiencies are associated with disease progression and increased mortality risk in HIV/AIDS, and even a simple multivitamin/mineral supplement can prolong survival, this is typically viewed merely as nutritional support of the immune system, and only necessary if there are deficiencies to be rectified. However, the reality is more complex. Several striking nutrient-related metabolic abnormalities have been consistently documented in HIV infection. One is chronic oxidative stress, including a drastic depletion of cysteine from the glutathione pool, and a progressive decline of serum selenium that is correlated with disease progression and mortality. Another is decreased blood levels of tryptophan, with an associated intracellular niacin deficiency. Tryptophan depletion or "deletion" by induction of indoleamine-2,3-dioxygenase (IDO), the first step in oxidative tryptophan metabolism, is a known mechanism for immune suppression that is of critical importance in cancer and pregnancy, and, potentially, in HIV/AIDS. Existing evidence supports the hypothesis that these nutrient-related metabolic abnormalities in HIV infection regarding antioxidants, selenium, sulfur, tryptophan and niacin are interrelated, because HIV-associated oxidative stress can induce niacin/NAD+ depletion via activation of poly(ADP-ribose) polymerase (PARP), which could lead to tryptophan oxidation for compensatory de novo niacin synthesis, thereby contributing to immune tolerance and T-cell loss via tryptophan deletion and PARP-induced cell death. This "oxidative stress-induced niacin sink" (OSINS) model provides a mechanism whereby the oxidative stress associated with HIV infection can contribute to immunosuppression via tryptophan deletion. This model is directly supported by evidence that antioxidants can counteract indoleamine-2,3-dioxygenase (IDO), providing the critical link between oxidative stress and tryptophan metabolism proposed here. The OSINS model can be used to guide the design of nutraceutical regimens that can effectively complement antiretroviral therapy for HIV/AIDS.

Reactive oxygen-induced reactive oxygen formation during human sperm capacitation

Physiological processes are often activated by reactive oxygen species (ROS), such as the superoxide anion (O(2)(*)(-)) and nitric oxide (NO*) produced by cells. We studied the interactions between NO* and O(2)(*)(-), and their generators (NO* synthase, NOS, and a still elusive oxidase), in human spermatozoa during capacitation (transformations needed for acquisition of fertility). Albumin, fetal cord serum ultrafiltrate, and L-arginine triggered capacitation and ROS generation (NO* and O(2)(*)(-)) and superoxide dismutase (SOD) and NOS inhibitors prevented all these effects. Surprisingly, capacitation due to exogenous NO* (or O(2)(*)(-)) was also blocked by SOD (or NOS inhibitors). Probes used were proven specific and innocuous on spermatozoa. Whereas O(2)(*)(-) was needed only for 30 min, the continuous NO* generation was essential for hours. Capacitation caused a time-dependent increase in protein tyrosine nitration that was prevented by SOD and NOS inhibitors, suggesting that O(2)(*)(-) and NO*. also act via the formation of ONOO(-). Spermatozoa treated with NO* (or O(2)(*)(-)) initiated a dose-dependent O(2)(*)(-) (or NO*) production, providing, for the first time in cells, a strong evidence for a two-sided ROS-induced ROS generation. Data presented show a close interaction between NO* and O(2)(*)(-) and their generators during sperm capacitation.

Potential role of tryptophan derivatives in stress responses characterized by the generation of reactive oxygen and nitrogen species

To face physicochemical and biological stresses, living organisms evolved endogenous chemical responses based on gas exchange with the atmosphere and on formation of nitric oxide (NO(*)) and oxygen derivatives. The combination of these species generates a complex network of variable extension in space and time, characterized by the nature and level of the reactive oxygen (ROS) and nitrogen species (RNS) and of their organic and inorganic scavengers. Among the latter, this review focusses on natural 3-substituted indolic structures. Tryptophan-derived indoles are unsensitive to NO(*), oxygen and superoxide anion (O(2)(*-)), but react directly with other ROS/RNS giving various derivatives, most of which have been characterized. Though the detection of some products like kynurenine and nitroderivatives can be performed in vitro and in vivo, it is more difficult for others, e.g., 1-nitroso-indolic compounds. In vitro chemical studies only reveal the strong likelihood of their in vivo generation and biological effects can be a sign of their transient formation. Knowing that 1-nitrosoindoles are NO donors and nitrosating agents indicating they can thus act both as mutagens and protectors, the necessity for a thorough evaluation of indole-containing drugs in accordance with the level of the oxidative stress in a given pathology is highlighted.

Determination of asymmetric dimethylarginine in biological fluids: a paradigm for a successful analytical story

PURPOSE OF REVIEW

To review recently reported analytical methods for the quantification in biological fluids of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthesis, and to evaluate their impact on clinical research.

RECENT FINDINGS

Recently developed and increasingly used analytical methods in this area are based on mass spectrometry coupled with gas chromatography (i.e., gas chromatography-mass spectrometry and gas chromatography-mass spectrometry/mass spectrometry) or liquid chromatography (i.e., liquid chromatography-mass spectrometry and liquid chromatography-mass spectrometry/mass spectrometry). These approaches revealed asymmetric dimethylarginine concentrations in plasma and serum of healthy adults in the range 400-500 nmol/l. High-performance liquid chromatography methods with fluorescence detection provide asymmetric dimethylarginine plasma/serum concentrations comparable to those of mass spectrometry-based methods. This interval for circulating asymmetric dimethylarginine and the mass spectrometry/mass spectrometry-based methods have the potential to serve as reference values and analytical methods, respectively. An enzyme-linked immunosorbent assay method for asymmetric dimethylarginine has become commercially available and is increasingly used in clinical studies. Comparative studies revealed that the enzyme-linked immunosorbent assay method produces considerably higher asymmetric dimethylarginine concentrations in plasma or serum in healthy humans in the basal state than mass spectrometry and high-performance liquid chromatography methods and runs varyingly in different laboratories.

SUMMARY

At present, many analytical methods allow for the accurate and precise quantification of asymmetric dimethylarginine in biological fluids. However, reliable quantification of biological asymmetric dimethylarginine remains an analytical challenge in basic and clinical research.

Relation of the Glu298Asp polymorphism of the nitric oxide synthase gene to hypertension and serum cholesterol in Japanese workers

OBJECTIVE

To assess whether the Glu298Asp polymorphism of the endothelial nitric oxide synthase (eNOS) gene possibly mediates the relation of blood pressure and serum cholesterol.

METHOD

Regular health examination in 2003 of 1,694 Japanese workers from the Shimane Prefecture, Japan.

RESULTS

The frequencies of the Glu/Glu, Glu/Asp, and Asp/Asp genotypes were 85.9%, 13.4%, and 0.7%, respectively. After adjustment for age, sex, BMI, and lifestyle (drinking, smoking, exercise and stress), the odds ratio (OR) of hypertension associated with high (> or = 220 mg/dl or under treatment) total cholesterol was 2.08 (95% Confidence Interval (CI) 1.02-4.24) among carriers of the eNOS 298Asp allele versus 1.18 (95% CI 0.89-1.55, p for interaction=0.50) among non-carriers. Similarly, the ORs of hypertension associated with counseling-need (120-139 mg/dl) and high (> or = 140 mg/dl) levels of LDL cholesterol among carriers of the eNOS 298Asp allele were significantly higher than those among non-carriers, at 2.65 (95% CI 1.16-6.01) versus 1.03 (95% CI 0.77-1.39, p for interaction=0.01), and 2.80 (95% CI 1.33-5.89) versus 0.95 (95% CI 0.71-1.26, p for interaction=0.04), respectively.

CONCLUSION

These results indicate that the eNOS 298Asp allele, which is weakly associated with hypertension, may increase the risk of hypertension when associated with high serum lipid levels.

Hypoxic conditioning suppresses nitric oxide production upon myocardial reperfusion

Physiologically modulated concentrations of nitric oxide (NO) are generally beneficial, but excessive NO can injure myocardium by producing cytotoxic peroxynitrite. Recently we reported that intermittent, normobaric hypoxia conditioning (IHC) produced robust cardioprotection against infarction and lethal arrhythmias in a canine model of coronary occlusion-reperfusion. This study tested the hypothesis that IHC suppresses myocardial nitric oxide synthase (NOS) activity and thereby dampens explosive, excessive NO formation upon reperfusion of occluded coronary arteries. Mongrel dogs were conditioned by a 20 d program of IHC (FIO(2) 9.5-10%; 5-10 min hypoxia/cycle, 5-8 cycles/d with intervening 4 min normoxia). One day later, ventricular myocardium was sampled for NOS activity assays, and immunoblot detection of the endothelial NOS isoform (eNOS). In separate experiments, myocardial nitrite (NO(2)(-)) release, an index of NO formation, was measured at baseline and during reperfusion following 1 h occlusion of the left anterior descending coronary artery (LAD). Values in IHC dogs were compared with respective values in non-conditioned, control dogs. IHC lowered left and right ventricular NOS activities by 60%, from 100-115 to 40-45 mU/g protein (P < 0.01), and decreased eNOS content by 30% (P < 0.05). IHC dampened cumulative NO(2)(-) release during the first 5 min reperfusion from 32 +/- 7 to 14 +/- 2 mumol/g (P < 0.05), but did not alter hyperemic LAD flow (15 +/- 2 vs. 13 +/- 2 ml/g). Thus, IHC suppressed myocardial NOS activity, eNOS content, and excessive NO formation upon reperfusion without compromising reactive hyperemia. Attenuation of the NOS/NO system may contribute to IHC-induced protection of myocardium from ischemia-reperfusion injury.

Contribution of xanthine oxidase-derived superoxide to chronic hypoxic pulmonary hypertension in neonatal rats

Xanthine oxidase (XO)-derived reactive oxygen species (ROS) formation contributes to experimental chronic hypoxic pulmonary hypertension in adults, but its role in neonatal pulmonary hypertension has received little attention. In rats chronically exposed to hypoxia (13% O2) for 14 days from birth, we examined the effects of ROS scavengers (U74389G 10 mg·kg−1·day−1 or Tempol 100 mg·kg−1·day−1 ip) or a XO inhibitor, Allopurinol (50 mg·kg−1·day−1 ip). Both ROS scavengers limited oxidative stress in the lung and attenuated hypoxia-induced vascular remodeling, confirming a critical role for ROS in this model. However, both interventions also significantly inhibited somatic growth and normal cellular proliferation in distal air spaces. Hypoxia-exposed pups had evidence of increased serum and lung XO activity, increased vascular XO-derived superoxide production, and vascular nitrotyrosine formation. These changes were all prevented by treatment with Allopurinol, which also attenuated hypoxia-induced vascular remodeling and partially reversed inhibited endothelium-dependent arterial relaxation, without affecting normal growth and proliferation. Collectively, our findings suggest that XO-derived superoxide induces endothelial dysfunction, thus impairing pulmonary arterial relaxation, and contributes to vascular remodeling in hypoxia-exposed neonatal rats. Due to the potential for adverse effects on normal growth, targeting XO may represent a superior “antioxidant” strategy to ROS scavengers for neonates with pulmonary hypertension.

Exogenous arginine in sepsis

Sepsis is a severe condition in critically ill patients and is considered an arginine deficiency state. The rationale for arginine deficiency in sepsis is mainly based on the reduced arginine levels in sepsis that are associated with the specific changes in arginine metabolism related to endothelial dysfunction, severe catabolism, and worse outcome. Exogenous arginine supplementation in sepsis shows controversial results with only limited data in humans and variable results in animal models of sepsis. Since in these studies the severity of sepsis varies but also the route, timing, and dose of arginine, it is difficult to draw a definitive conclusion for sepsis in general without considering the influence of these factors. Enhanced nitric oxide production in sepsis is related to suggested detrimental effects on hemodynamic instability and enhanced oxidative stress. Potential mechanisms for beneficial effects of exogenous arginine in sepsis include enhanced (protein) metabolism, improved microcirculation and organ function, effects on immune function and antibacterial effects, improved gut function, and an antioxidant role of arginine. We recently performed a study indicating that arginine can be given to septic patients without major effects on hemodynamics, suggesting that more studies can be conducted on the effects of arginine supplementation in septic patients.

Interaction between serum cholesterol levels and the renin–angiotensin system on the new onset of arterial hypertension in subjects with high-normal blood pressure

OBJECTIVES

To investigate the possible interactions between serum cholesterol levels and the renin-angiotensin system on the development of stable hypertension in subjects with high-normal blood pressure (BP).

BACKGROUND

Hypercholesterolemia increases angiotensin-II type 1 (AT1) receptor density and pressor responsiveness to angiotensin II, and has been reported to contribute to the development of hypertension. The effects of elevated serum cholesterol levels on BP control might be exaggerated by concomitant activation of the renin-angiotensin system, and their combination might contribute to the development of stable hypertension.

METHODS

We investigated the relationship between serum cholesterol levels, plasma renin activity (PRA) and the long-term development of hypertension in 66 young (age < 45 years) patients with high-normal BP and elevated (> 200 mg/dl, n = 46: HC) or normal (</=200 mg/dl, n = 20: NC) serum cholesterol levels and in 20 normotensive, normocholesterolemic controls (C). The main outcome measure was the prospective evaluation of the 15-year incidence of stable hypertension in the different populations.

RESULTS

New-onset hypertension was higher in patients with high-normal BP and HC when compared to NC patients [relative risk (RR) = 1.9; 95% confidence interval (CI), 1.1-4.3, P < 0.001] and control subjects (RR = 3.1; 95% CI = 1.4-5.3, P < 0.001). High PRA increased the overall rate of hypertension in both HC and NC. The interaction between HC and PRA was more evident in patients with borderline high cholesterol levels (200-240 mg/dl) where the adjusted relative risk of new onset of hypertension was 2.17 (95% CI 1.2-3.74; P < 0.05) in high PRA subjects and 1.17 (95% CI 0.67-2.23; P = 0.87) in subjects with normal PRA.

CONCLUSION

We support the hypothesis that the presence of hypercholesterolemia can promote the development of stable hypertension through its interaction with the circulating renin-angiotensin system in patients with high-normal blood pressure.

Deficiency of endothelial nitric-oxide synthase confers susceptibility to diabetic nephropathy in nephropathy-resistant inbred mice

Recent studies have implicated dysfunctional endothelial nitric-oxide synthase (eNOS) as a common pathogenic pathway in diabetic vascular complications. However, functional consequences are still incompletely understood. To determine the role of eNOS-derived nitric oxide (NO) in diabetic nephropathy, we induced diabetes in eNOS knockout (KO) and wild-type (WT) mice on the C57BL6 background, using low-dose streptozotocin injection, and we investigated their glomerular phenotype at up to 20 weeks of diabetes. Although the severity of hyperglycemia in diabetic eNOS KO mice was similar to diabetic WT mice, diabetic eNOS KO mice developed overt albuminuria, hypertension, and glomerular mesangiolysis, whereas diabetic WT and nondiabetic control mice did not. Glomerular hyperfiltration was also significantly reduced in diabetic eNOS KO mice. Electron micrographs from diabetic eNOS KO mice revealed an injured endothelial morphology, thickened glomerular basement membrane, and focal foot process effacement. Furthermore, the anionic sites at glomerular endothelial barrier estimated by cationic ferritin binding were reduced in diabetic eNOS KO mice. In aggregate, these results demonstrate that deficiency of eNOS-derived NO causes glomerular endothelial injury in the setting of diabetes and results in overt albuminuria and glomerular mesangiolysis in nephropathy-resistant inbred mice. The findings indicate a vital role for eNOS-derived NO in the pathogenesis of diabetic nephropathy.

Aging enhances pressure-induced arterial superoxide formation

The purpose of this study was to investigate the mechanisms that regulate superoxide (O(2)(*-)) production as a function of an acute elevation of intravascular pressure and age. Mesenteric arteries isolated from young (6 mo) and aged (24 mo) male Fischer 344 rats were used. O(2)(*-) production in vessels in response to 80 (normal pressure, NP) and 180 (high pressure, HP) mmHg was determined by the superoxide dismutase-inhibitable nitroblue tetrazolium (NBT) reduction assay. In vessels exposed to NP, O(2)(*-) production was significantly higher in aged than in young vessels (32.7 +/- 7.0 vs. 15.4 +/- 2.4 nmol.mg(-1).30 min(-1)). HP enhanced O(2)(*-) production in vessels of both groups, but the enhancement was significantly greater in aged than in young vessels (63.4 +/- 6.7 vs. 32.7 +/- 4.3 nmol.mg(-1).30 min(-1)). Apocynin (100 micromol/l) attenuated HP-induced increases in O(2)(*-) production in both groups, whereas allopurinol (100 micromol/l) and N(omega)-nitro-L-arginine methyl ester (100 mumol/l) inhibited the response only in aged vessels. Confocal microscopy showed increases in O(2)(*-) in response to HP in endothelial and smooth muscle layers of both groups, with much greater fluorescent staining in aged than in young rats and in the endothelium than in smooth muscle cells. No significant changes in NAD(P)H oxidase gene and protein expressions were observed in vessels of the two groups. Upregulation of protein expression of xanthine oxidase was detected in aged vessels. We conclude that NAD(P)H oxidase contributes importantly to HP-induced enhanced O(2)(*-) production in vessels of both young and aged rats, whereas xanthine oxidase and nitric oxide synthase-dependent O(2)(*-) production also contribute to the enhancement in mesenteric arteries of aged rats.

Clinical pharmacology and therapeutic use of antioxidant vitamins

The clinical use of antioxidants has gained considerable interest during the last decade. It was suggested from epidemiological studies that diets high in fruits and vegetables might help decrease the risk of cardiovascular disease. Therefore, supplements of vitamins C and E were applied through protocols aimed to prevent diseases such as atherosclerosis, preeclampsia or hypertension, thought to be mediated by oxidative stress. Despite the biological properties of these vitamins could account for an effective protection, as shown by several clinical and experimental studies, their efficacy remains controversial in the light of some recent clinical trials and meta-analyses. However, the methodology of these studies, criteria for selection of patients, the uncertain extent of progression of the disease when initiating supplementation, the lack of mechanistic studies containing basic scientific aspects, such as the bioavailability, pharmacokinetic properties, and the nature of the antioxidant sources of vitamins, could account for the inconsistency of the various clinical trials and meta-analyses assessing the efficacy of these vitamins to prevent human diseases. This review presents a survey of the clinical use of antioxidant vitamins E and C, proposing study models based on the biological effects of these compounds likely to counteract the pathophysiological mechanisms able to explain the structural and functional organ damage.

Mechanistic studies on the intramolecular one-electron transfer between the two flavins in the human endothelial NOS reductase domain

The object of this study was to clarify the mechanism of electron transfer in the human endothelial nitric oxide synthase (eNOS) reductase domain using recombinant eNOS reductase domains; the FAD/NADPH domain containing FAD- and NADPH-binding sites and the FAD/FMN domain containing FAD/NADPH-, FMN-, and a calmodulin-binding sites. In the presence of molecular oxygen or menadione, the reduced FAD/NADPH domain is oxidized via the neutral (blue) semiquinone (FADH(*)), which has a characteristic absorption peak at 520 nm. The FAD/NADPH and FAD/FMN domains have high activity for ferricyanide, but the FAD/FMN domain has low activity for cytochrome c. In the presence or absence of calcium/calmodulin (Ca(2+)/CaM), reduction of the oxidized flavins (FAD-FMN) and air-stable semiquinone (FAD-FMNH(*)) with NADPH occurred in at least two phases in the absorbance change at 457nm. In the presence of Ca(2+)/CaM, the reduction rate of both phases was significantly increased. In contrast, an absorbance change at 596nm gradually increased in two phases, but the rate of the fast phase was decreased by approximately 50% of that in the presence of Ca(2+)/CaM. The air-stable semiquinone form was rapidly reduced by NADPH, but a significant absorbance change at 520 nm was not observed. These findings indicate that the conversion of FADH(2)-FMNH(*) to FADH(*)-FMNH(2) is unfavorable. Reduction of the FAD moiety is activated by CaM, but the formation rate of the active intermediate, FADH(*)-FMNH(2) is extremely low. These events could cause a lowering of enzyme activity in the catalytic cycle.

Increased oxidative stress in the streptozotocin-induced diabetic apoE-deficient mouse: Changes in expression of NADPH oxidase subunits and eNOS

Elevated oxidative stress plays a key role in the development of atherosclerosis and endothelial dysfunction in diabetes-associated vascular disease. Glucose-induced changes in the activity of NADPH oxidase and endothelial nitric oxide synthase (eNOS) may result in vascular endothelial cell dysfunction via dysregulation of eNOS and/or changes in the expression of the subunits of NADPH oxidase. In this study, we have investigated whether changes in the expression of the subunits of NADPH oxidase, or eNOS mRNA, can be associated with oxidative stress in the streptozotocin-induced type 1 diabetic apolipoprotein E-deficient (apoE(-/-)) diabetic mouse. Oxidative stress was assessed in aorta and mesenteric arteries by immunofluorescence labelling with dihydroethidium and levels of NADPH oxidase subunits and eNOS were determined by a real-time polymerase chain reaction protocol. Blood glucose levels and oxidative stress were significantly increased following 4, 8 and 16 weeks after treatment with streptozotocin in both streptozotocin-apoE(-/-) aorta and mesenteric arteries compared to the time- and age-matched vehicle (citrate buffer)-treated non-diabetic apoE(-/-). In the mesenteric arteries the expression of nox4 (4 weeks) and gp91phox (nox2) (8 weeks) subunits of NADPH oxidase from streptozotocin-apoE(-/-) were enhanced as were eNOS mRNA and protein (P<0.05). However, only eNOS mRNA and protein remained increased at 16 weeks. These data indicate that increased oxidative stress in the vasculature of streptozotocin-apoE(-/-) mice is linked to changes in eNOS, superoxide dismutase (SOD) and NADPH oxidase expression.