Arginine de novo and nitric oxide production in disease states

"Nutraceuticals" in relation to human skeletal muscle and exercise

Skeletal muscles have a fundamental role in locomotion and whole body metabolism, with muscle mass and quality being linked to improved health and even lifespan. Optimizing nutrition in combination with exercise is considered an established, effective ergogenic practice for athletic performance. Importantly, exercise and nutritional approaches also remain arguably the most effective countermeasure for muscle dysfunction associated with aging and numerous clinical conditions, e.g., cancer cachexia, COPD, and organ failure, via engendering favorable adaptations such as increased muscle mass and oxidative capacity. Therefore, it is important to consider the effects of established and novel effectors of muscle mass, function, and metabolism in relation to nutrition and exercise. To address this gap, in this review, we detail existing evidence surrounding the efficacy of a nonexhaustive list of macronutrient, micronutrient, and "nutraceutical" compounds alone and in combination with exercise in relation to skeletal muscle mass, metabolism (protein and fuel), and exercise performance (i.e., strength and endurance capacity). It has long been established that macronutrients have specific roles and impact upon protein metabolism and exercise performance, (i.e., protein positively influences muscle mass and protein metabolism), whereas carbohydrate and fat intakes can influence fuel metabolism and exercise performance. Regarding novel nutraceuticals, we show that the following ones in particular may have effects in relation to 1) muscle mass/protein metabolism: leucine, hydroxyl β-methylbutyrate, creatine, vitamin-D, ursolic acid, and phosphatidic acid; and 2) exercise performance: (i.e., strength or endurance capacity): hydroxyl β-methylbutyrate, carnitine, creatine, nitrates, and β-alanine.

Mangiferin from Pueraria tuberosa reduces inflammation via inactivation of NLRP3 inflammasome

Recent reports have demonstrated the role of phyto-constituents in modulating inflammatory responses. Mangiferin isolated from Mangifera indica is known to induce potent anti-oxidative, anti-diabetic and anti-inflammatory activity. However, the molecular mechanism of its anti-inflammatory activity is not properly understood. In this study we have isolated Mangiferin from the tubers of Pueraria tuberosa (PT-Mangiferin) and analysed the mechanism of its potent anti-inflammatory effects in LPS stimulated RAW 264.7 mouse macrophage cell line and in a carrageenan induced air pouch model. PT-Mangiferin was non-toxic to primary cells but showed significant toxicity and apoptotic effect on cancerous cells. It significantly reduced the production of pro-inflammatory mediators (COX-2, iNOS and TNF-α) in LPS stimulated RAW 264.7 cells. Further, it has also reduced the generation of ROS and inhibited LPS induced NF-kB translocation in these cells. Additionally, PT-Mangiferin significantly reduced inflammation in a mouse air pouch model by inhibiting the infiltration of monocytes and neutrophils and reducing the production of cytokines. These effects were mediated via inactivation of NLRP3 inflammasome complex and its downstream signalling molecules. Taken together these results suggest that PT-Mangiferin is potent anti-inflammatory compound that reduces inflammation and holds promise in development of herbal based anti-inflammatory therapeutics in future.

Serum asymmetric dimethylarginine and arginine levels predict microvascular and macrovascular complications in type 2 diabetes mellitus

BACKGROUND

Increased oxidative stress in diabetes increases nitric oxide (NO) oxidation and low l-arginine (Arg) could further reduce NO and impair vascular function, thereby accelerating, in the long run, vascular complications. We therefore measured Arg and asymmetric dimethylarginine (ADMA) levels in patients with type 2 diabetes mellitus (T2DM) and healthy controls. Additionally, we observed the diabetic individuals over time to see if Arg and asymmetric dimethylarginine predicted T2DM complications.

METHODS

We examined baseline serum Arg and ADMA levels in a cohort of 105 participants with type 2 diabetes and compared them with an age- and weight-matched nondiabetic group of 137 individuals who served as a reference population. Additionally, we assessed whether Arg and/or ADMA predicted macrovascular and microvascular complications over 6 years of follow-up.

RESULTS

Serum Arg was lower in individuals with T2DM than in controls (64 ± 28 vs 75 ± 31 μmol/L; P = .009) and inversely related to hemoglobin A1c (r = -0.2; P = .002). Over follow-up, we observed that participants with T2DM in the lowest quartile of Arg had increased risk for the subsequent evolution of nephropathy, peripheral neuropathy, and composite microvascular complications (odds ratio [OR] = 5.5; 95% confidence interval [CI] -1.9 to 16; P = .002). The highest ADMA quartile was associated with increased risk for both microvascular (OR = 4.5; 95% CI -1.4 to 14.1; P = .009) and 6.5-year incident macrovascular complications (OR = 8.3; 95% CI 1.9-35.5; P = .004).

CONCLUSION

l-Arginine levels are lower in individuals with T2DM than in matched controls. Both low Arg and high ADMA, independent of each other and adjusted for classical risk factors, predict the incidence of microvascular complications.

Effects of a chronic l-arginine supplementation on the arginase pathway in aged rats

While ageing is frequently associated with l-arginine deficiency, clinical and experimental studies provided controversial data on the interest of a chronic l-arginine supplementation with beneficial, no or even deleterious effects. It was hypothesized that these discrepancies might relate to a deviation of l-arginine metabolism towards production of l-ornithine rather than nitric oxide as a result of age-induced increase in arginase activity. This study investigated the effect of ageing on arginase activity/expression in target tissues and determined whether l-arginine supplementation modulated the effect of ageing on arginase activity. Arginase activity and expression were measured in the heart, vessel, brain, lung, kidney and liver in young rats (3-months old) and aged Wistar rats (22-24-months-old) with or without l-arginine supplementation (2.25% in drinking water for 6weeks). Plasma levels of l-arginine and l-ornithine were quantified in order to calculate the plasma l-arginine/l-ornithine ratio, considered as a reflection of arginase activity. Cardiovascular parameters (blood pressure, heart rate) and aortic vascular reactivity were also studied. Ageing dramatically reduced plasma l-arginine and l-arginine/l-ornithine ratio, decreased liver and kidney arginase activities but did not change activities in other tissues. l-Arginine supplementation normalized plasma l-arginine and l-arginine/l-ornithine ratio, improved endothelial function and decreased systolic blood pressure. These effects were associated with decreased arginase activity in aorta along with no change in the other tissues except in the lung in which activity was increased. A strong mismatch was therefore observed between arginase activity and expression in analyzed tissues. The present study reveals that ageing selectively changes arginase activity in clearance tissues, but does not support a role of the arginase pathway in the potential deleterious effect of the l-arginine supplementation in aged patients. Moreover, our data argue against the use of the measurement of plasma l-arginine/l-ornithine ratio to estimate arginase activity in aged patients.

Parenteral or Enteral Arginine Supplementation Safety and Efficacy

Arginine supplementation has the potential to improve the health of patients. Its use in hospitalized patients has been a controversial topic in the nutrition literature, especially concerning supplementation of septic patients. In this article, we review the relevant literature both for and against the use of arginine in critically ill, surgical, and hospitalized patients. The effect of critical illness on arginine metabolism is reviewed, as is its use in septic and critically ill patients. Although mounting evidence supports immunonutrition, there are only a few studies that suggest that this is safe in patients with severe sepsis. The use of arginine has been shown to benefit a variety of critically ill patients. It should be considered for inclusion in combinations of immunonutrients or commercial formulations for groups in whom its benefit has been reported consistently, such as those who have suffered trauma and those in acute surgical settings. The aims of this review are to discuss the role of arginine in health, the controversy surrounding arginine supplementation of septic patients, and the use of arginine in critically ill patients.

Safety and Effectiveness of Arginine in Adults

l-Arginine (Arg) appears to have a beneficial effect on the regulation of nutrient metabolism to enhance lean tissue deposition and on insulin resistance in humans. The observed safe level for oral administration of Arg is ∼20 g/d, but higher levels have been tested in short-term studies without serious adverse effects; however, more data are needed in both animal models and humans to fully evaluate safety as well as efficacy. The primary objective of this review is to summarize the current knowledge of the safety, pharmacokinetics, and effectiveness of oral Arg in adults. Arg supplementation has been used safely in vulnerable populations, such as pregnant women, preterm infants, and individuals with cystic fibrosis. Several recent studies have shown beneficial effects of Arg in individuals with obesity, insulin resistance, and diabetes. Collectively, the data suggest that Arg supplementation is a safe and generally well-tolerated nutriceutical that may improve metabolic profiles in humans.

Arginine Metabolism Revisited

Mammalian arginine metabolism is complex due to the expression of multiple enzymes that utilize arginine as substrate and to interactions or competition between specific enzymes involved in arginine metabolism. Moreover, cells may contain multiple intracellular arginine pools that are not equally accessible to all arginine metabolic enzymes, thus presenting additional challenges to more fully understanding arginine metabolism. At the whole-body level, arginine metabolism ultimately results in the production of a biochemically diverse range of products, including nitric oxide, urea, creatine, polyamines, proline, glutamate, agmatine, and homoarginine. Included in this group of compounds are the methylated arginines (e.g., asymmetric dimethylarginine), which are released upon degradation of proteins containing methylated arginine residues. Changes in arginine concentration also can regulate cellular metabolism and function via a variety of arginine sensors. Although much is known about arginine metabolism, elucidation of the physiologic or pathophysiologic roles for all of the pathways and their metabolites remains an active area of investigation, as exemplified by current findings highlighted in this review.

Genome-wide association reveals that common genetic variation in the kallikrein-kinin system is associated with serum L-arginine levels

L-arginine is the essential precursor of nitric oxide, and is involved in multiple key physiological processes, including vascular and immune function. The genetic regulation of blood L-arginine levels is largely unknown. We performed a genome-wide association study (GWAS) to identify genetic factors determining serum L-arginine levels, amongst 901 Europeans and 1,394 Indian Asians. We show that common genetic variations at the KLKB1 and F12 loci are strongly associated with serum L-arginine levels. The G allele of single nucleotide polymorphism (SNP) rs71640036 (T/G) in KLKB1 is associated with lower serum L-arginine concentrations (10 µmol/l per allele copy, p=1×10-24), while allele T of rs2545801 (T/C) near the F12 gene is associated with lower serum L-arginine levels (7 µmol/l per allele copy, p=7×10-12). Together these two loci explain 7 % of the total variance in serum L-arginine concentrations. The associations at both loci were replicated in independent cohorts with plasma L-arginine measurements (p<0.004). The two sentinel SNPs are in nearly complete LD with the nonsynonymous SNP rs3733402 at KLKB1 and the 5'-UTR SNP rs1801020 at F12, respectively. SNPs at both loci are associated with blood pressure. Our findings provide new insight into the genetic regulation of L-arginine and its potential relationship with cardiovascular risk.

L-Arginine and B vitamins improve endothelial function in subjects with mild to moderate blood pressure elevation

Purpose

The aim of this trial was to investigate the influence of a dietetic product consisting of a unique combination of l-arginine with the vitamins B₆, folic acid and B₁₂ (Telcor^® Arginin plus) on endothelial dysfunction.

Methods

Subjects aged 40–65 years with mild to moderate blood pressure (BP) elevation not treated with anti-hypertensive drugs were randomly assigned to either the dietetic product (n = 40) or a matching placebo (n = 41) for 3 months with open follow-up for a further 3 months. Postprandial change in endothelial function was assessed using the validated reactive hyperaemia index (RHI) at 3 months compared to the study onset (RHI post–pre, visit 3–visit 1; ΔΔRHI). Secondary parameters included BP and plasma homocysteine concentration.

Results

The primary efficacy analysis revealed superiority of the nutritional intervention over placebo (p = 0.0349) in reducing the deterioration of endothelial function. While in the active group ΔΔRHI increased (0.371 ± 0.122), almost no change could be detected in the placebo group (0.031 ± 0.100), thus demonstrating a significant improvement in vascular function in the intervention group. Moreover, the intervention reduced BP and homocysteine levels. Non-serious adverse events were equally distributed in both groups, and none of the events were assessed as possibly intervention-related by the investigators.

Conclusions

This trial confirmed the effective and safe use of dietary management with l-arginine in combination with B vitamins. The primary efficacy analysis demonstrated a statistically significant superiority of the combination of l-arginine with B vitamins over placebo in improving and restoring impaired endothelial function and lowering BP in patients with mild to moderate blood pressure elevation.

Arginine intake is associated with oxidative stress in a general population

OBJECTIVE

The aim of this study was to assess the association between protein and arginine from meat intake and oxidative stress in a general population.

METHODS

Data came from the Health Survey for Sao Paulo (ISA-Capital), a cross-sectional population-based study in Brazil (N = 549 adults). Food intake was estimated by a 24-h dietary recall. Oxidative stress was estimated by malondialdehyde (MDA) concentration in plasma. Analyses were performed using general linear regression models adjusted for some genetic, lifestyle, and biochemical confounders.

RESULTS

MDA levels were associated with meat intake (P for linear trend = 0.031), protein from meat (P for linear trend = 0.006), and arginine from meat (P for linear trend = 0.044) after adjustments for confounders: age, sex, body mass index, smoking, physical activity, intake of fruit and vegetables, energy and heterocyclic amines, C-reactive protein levels, and polymorphisms in GSTM1 (glutathione S-transferase Mu 1) and GSTT1 (glutathione S-transferase theta 1) genes. Results were not significant for total protein and protein from vegetable intake (P > 0.05).

CONCLUSIONS

High protein and arginine from meat intake were associated with oxidative stress independently of genetic, lifestyle, and biochemical confounders in a population-based study. Our results suggested a novel link between high protein/arginine intake and oxidative stress, which is a major cause of age-related diseases.

Alterations in whole-body arginine metabolism in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a condition characterized by systemic low-grade inflammation that could increase the production of nitric oxide (NO), of which arginine is the sole precursor. Arginine is derived from the breakdown of protein and through the conversion of citrulline to arginine (de novo arginine production).

OBJECTIVE

Our objective was to study whole-body arginine and citrulline and related metabolism in stable COPD patients.

DESIGN

With the use of stable isotope methodology, we studied whole-body arginine and citrulline rates of appearance, de novo arginine (citrulline-to-arginine flux) and NO (arginine-to-citrulline flux) production, protein synthesis and breakdown rates, and plasma amino acid concentrations in a heterogeneous group of patients with moderate-to-severe COPD [n = 23, mean ± SE age: 65 ± 2 y, forced expiratory volume in 1 s (FEV1): 40% ± 2% of predicted], and a group of healthy older adults (n = 19, mean ± SE age: 64 ± 2 y, FEV1: 95% ± 4% of predicted).

RESULTS

Although plasma arginine and citrulline concentrations were comparable between COPD patients and controls, whole-body arginine (P = 0.015) and citrulline (P = 0.026) rates of appearance were higher in COPD patients and related to a 57% greater de novo arginine production (P < 0.0001). Despite a higher whole-body arginine clearance in COPD patients (P < 0.0001), we found no difference in NO production.

CONCLUSION

In stable patients with moderate-to-severe COPD, endogenous arginine production is upregulated to support a higher arginine utilization that is unrelated to whole-body NO production. This trial was registered at clinicaltrials.gov as NCT01173354 and NCT01172314.

Catabolism and safety of supplemental L-arginine in animals

L-arginine (Arg) is utilized via multiple pathways to synthesize protein and low-molecular-weight bioactive substances (e.g., nitric oxide, creatine, and polyamines) with enormous physiological importance. Furthermore, Arg regulates cell signaling pathways and gene expression to improve cardiovascular function, augment insulin sensitivity, enhance lean tissue mass, and reduce obesity in humans. Despite its versatile roles, the use of Arg as a dietary supplement is limited due to the lack of data to address concerns over its safety in humans. Data from animal studies are reviewed to assess arginine catabolism and the safety of long-term Arg supplementation. The arginase pathway was responsible for catabolism of 76-85 and 81-96 % Arg in extraintestinal tissues of pigs and rats, respectively. Dietary supplementation with Arg-HCl or the Arg base [315- and 630-mg Arg/(kg BW d) for 91 d] had no adverse effects on male or female pigs. Similarly, no safety issues were observed for male or female rats receiving supplementation with 1.8- and 3.6-g Arg/(kg BW d) for at least 91 d. Intravenous administration of Arg-HCl to gestating sheep at 81 and 180 mg Arg/(kg BW d) is safe for at least 82 and 40 d, respectively. Animals fed conventional diets can well tolerate large amounts of supplemental Arg [up to 630-mg Arg/(kg BW d) in pigs or 3.6-g Arg/(kg BW d) in rats] for 91 d, which are equivalent to 573-mg Arg/(kg BW d) for humans. Collectively, these results can help guide studies to determine the safety of long-term oral administration of Arg in humans.

Reduced arginine availability and nitric oxide synthesis in cancer is related to impaired endogenous arginine synthesis

Reduced plasma arginine (ARG) concentrations are found in various types of cancer. ARG and its product nitric oxide (NO) are important mediators in the immune function and the defense against tumour cells. It remains unclear whether the diminished systemic ARG availability in cancer is related to insufficient endogenous ARG synthesis, negatively affecting NO synthesis, and whether a dietary amino acid mixture is able to restore this. In 13 patients with advanced non-small cell lung cancer (NSCLC) and 11 healthy controls, whole body ARG and CIT (citrulline) rates of appearance were measured by stable isotope methodology before and after intake of a mixture of amino acids as present in whey protein. The conversions of CIT to ARG (indicator of de novo ARG synthesis) and ARG to CIT (marker of NO synthesis), and ARG clearance (reflecting ARG disposal capacity) were calculated. Plasma isotopic enrichments and amino acid concentrations were measured by LC-MS/MS. Conversions of CIT to ARG and ARG to CIT (P<0.05), and CIT rate of appearance (P=0.07) were lower in NSCLC. ARG rate of appearance and clearance were comparable suggesting no enhanced systemic ARG production and disposal capacity in NSCLC. After intake of the mixture, ARG rate of appearance and concentration increased (P<0.001), and ARG to CIT conversion was restored in NSCLC. In conclusion, an impaired endogenous ARG synthesis plays a role in the reduced systemic ARG availability and NO synthesis in advanced NSCLC. Nutritional approaches may restore systemic ARG availability and NO synthesis in cancer, but the clinical implication remains unclear.

The Nitric Oxide Synthase Inhibitor NG-Nitro-L-Arginine Methyl Ester Diminishes the Immunomodulatory Effects of Parental Arginine in Rats with Subacute Peritonitis

The combined treatment of parenteral arginine and the nitric oxide synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) have been shown to improve liver function and systemic inflammation in subacute peritonitic rats. Here, we investigated the effects of single and combined parenteral arginine and L-NAME treatments on leukocyte and splenocyte immunity. Male Wistar rats were subjected to cecal punctures and were intravenously given total parenteral nutrition solutions with or without arginine and/or L-NAME supplementations for 7 days. Non-surgical and sham-operated rats with no cecal puncture were given a chow diet and parenteral nutrition, respectively. Parenteral feeding elevated the white blood cell numbers and subacute peritonitis augmented the parenteral nutrition-induced alterations in the loss of body weight gain, splenomegaly, and splenocyte decreases. Parenteral arginine significantly increased the B-leukocyte level, decreased the natural killer T (NKT)-leukocyte and splenocyte levels, alleviated the loss in body weight gain and total and cytotoxic T-splenocyte levels, and attenuated the increases in plasma nitrate/nitrite and interferon-gamma production by T-splenocytes. L-NAME infusion significantly decreased NKT-leukocyte level, tumor-necrosis factor (TNF)-alpha production by T-splenocytes and macrophages, and interferon-gamma production by T-leukocytes, monocytes, and T-splenocytes, as well as increased interleukin-6 production by T-leukocytes and monocytes and nitrate/nitrite production by T-leukocytes. Combined treatment significantly decreased plasma nitrate/nitrite, the NKT-leukocyte level, and TNF-alpha production by T-splenocytes. Parenteral arginine may attenuate immune impairment and L-NAME infusion may augment leukocyte proinflammatory response, eliminate splenocyte proinflammatory and T-helper 1 responses, and diminish arginine-induced immunomodulation in combined treatment in subacute peritonitic rats.

Effect of Pneumoperitoneum on Oxidative Stress and Inflammation via the Arginase Pathway in Rats

PURPOSE

Oxidative stress during CO₂ pneumoperitoneum is reported to be associated with decreased bioactivity of nitric oxide (NO). However, the changes in endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and arginase during CO₂ pneumoperitoneum have not been elucidated.

MATERIALS AND METHODS

Thirty male Sprague-Dawley rats were randomized into three groups. After anesthesia induction, the abdominal cavities of the rats of groups intra-abdominal pressure (IAP)-10 and IAP-20 were insufflated with CO₂ at pressures of 10 mm Hg and 20 mm Hg, respectively, for 2 hours. The rats of group IAP-0 were not insufflated. After deflation, plasma NO was measured, while protein expression levels and activity of eNOS, iNOS, arginase (Arg) I, and Arg II were analyzed with aorta and lung tissue samples.

RESULTS

Plasma nitrite concentration and eNOS expression were significantly suppressed in groups IAP-10 and IAP-20 compared to IAP-0. While expression of iNOS and Arg I were comparable between the three groups, Arg II expression was significantly greater in group IAP-20 than in group IAP-0. Activity of eNOS was significantly lower in groups IAP-10 and IAP-20 than in group IAP-0, while iNOS activity was significantly greater in group IAP-20 than in groups IAP-0 and IAP-10. Arginase activity was significantly greater in group IAP-20 than in groups IAP-0 and IAP-10.

CONCLUSION

The activity of eNOS decreases during CO₂ pneumoperitoneum, while iNOS activity is significantly increased, a change that contributes to increased oxidative stress and inflammation. Moreover, arginase expression and activity is increased during CO₂ pneumoperitoneum, which seems to act inversely to the NO system.

Responses in whole-body amino acid kinetics to an acute, sub-clinical endotoxin challenge in lambs

Some effects of parasitism, endotoxaemia or sepsis can be mitigated by provision of extra protein. Supplemented protein may encompass a metabolic requirement for specific amino acids (AA). The current study investigates a method to identify and quantify the amounts of AA required during inflammation induced by an endotoxin challenge. One of each pair of six twin sheep was infused in the jugular vein for 20 h with either saline (control) or lipopolysaccharide (LPS, 2 ng/kg body weight per min) fromEscherichia coli. Between 12 and 20 h a mixture of stable isotope-labelled AA was infused to measure irreversible loss rates. From 16 to 20 h all sheep were supplemented with a mixture of unlabelled AA infused intravenously. Blood samples were taken before the start of infusions, and then continuously over intervals between 14 and 20 h. At 20 h the sheep were euthanised, and liver and kidney samples were taken for measurement of serine-threonine dehydratase (SDH) activity. LPS infusion decreased plasma concentrations of most AA (P<0·05;P<0·10 for leucine and tryptophan), except for phenylalanine (which increasedP=0·022) and tyrosine. On the basis of the incremental response to the supplemental AA, arginine, aspartate, cysteine, glutamate, lysine (tendency only), glycine, methionine, proline, serine and threonine were important in the metabolic response to the endotoxaemia. The AA infusion between 16 and 20 h restored the plasma concentrations in the LPS-treated sheep for the majority of AA, except for glutamine, isoleucine, methionine, serine and valine. LPS treatment increased (P<0·02) SDH activity in both liver and kidney. The approach allows quantification of key AA required during challenge situations.

Acute ingestion of citrulline stimulates nitric oxide synthesis but does not increase blood flow in healthy young and older adults with heart failure

To determine if age-associated vascular dysfunction in older adults with heart failure (HF) is due to insufficient synthesis of nitric oxide (NO), we performed two separate studies: 1) a kinetic study with a stable isotope tracer method to determine in vivo kinetics of NO metabolism, and 2) a vascular function study using a plethysmography method to determine reactive hyperemic forearm blood flow (RH-FBF) in older and young adults in the fasted state and in response to citrulline ingestion. In the fasted state, NO synthesis (per kg body wt) was ∼ 50% lower in older vs. young adults and was related to a decreased rate of appearance of the NO precursor arginine. Citrulline ingestion (3 g) stimulated de novo arginine synthesis in both older [6.88 ± 0.83 to 35.40 ± 4.90 μmol · kg body wt(-1) · h(-1)] and to a greater extent in young adults (12.02 ± 1.01 to 66.26 ± 4.79 μmol · kg body wt(-1) · h(-1)). NO synthesis rate increased correspondingly in older (0.17 ± 0.01 to 2.12 ± 0.36 μmol · kg body wt(-1) · h(-1)) and to a greater extent in young adults (0.36 ± 0.04 to 3.57 ± 0.47 μmol · kg body wt(-1) · h(-1)). Consistent with the kinetic data, RH-FBF in the fasted state was ∼ 40% reduced in older vs. young adults. However, citrulline ingestion (10 g) failed to increase RH-FBF in either older or young adults. In conclusion, citrulline ingestion improved impaired NO synthesis in older HF adults but not RH-FBF, suggesting that factors other than NO synthesis play a role in the impaired RH-FBF in older HF adults, and/or it may require a longer duration of supplementation to be effective in improving RH-FBF.

Prognosis Biomarkers of Severe Sepsis and Septic Shock by 1H NMR Urine Metabolomics in the Intensive Care Unit

Early diagnosis and patient stratification may improve sepsis outcome by a timely start of the proper specific treatment. We aimed to identify metabolomic biomarkers of sepsis in urine by ¹H-NMR spectroscopy to assess the severity and to predict outcomes. Urine samples were collected from 64 patients with severe sepsis or septic shock in the ICU for a ¹H NMR spectra acquisition. A supervised analysis was performed on the processed spectra, and a predictive model for prognosis (30-days mortality/survival) of sepsis was constructed using partial least-squares discriminant analysis (PLS-DA). In addition, we compared the prediction power of metabolomics data respect the Sequential Organ Failure Assessment (SOFA) score. Supervised multivariate analysis afforded a good predictive model to distinguish the patient groups and detect specific metabolic patterns. Negative prognosis patients presented higher values of ethanol, glucose and hippurate, and on the contrary, lower levels of methionine, glutamine, arginine and phenylalanine. These metabolites could be part of a composite biopattern of the human metabolic response to sepsis shock and its mortality in ICU patients. The internal cross-validation showed robustness of the metabolic predictive model obtained and a better predictive ability in comparison with SOFA values. Our results indicate that NMR metabolic profiling might be helpful for determining the metabolomic phenotype of worst-prognosis septic patients in an early stage. A predictive model for the evolution of septic patients using these metabolites was able to classify cases with more sensitivity and specificity than the well-established organ dysfunction score SOFA.

Comparison of arginase isoform expression in patients with different subtypes of chronic rhinosinusitis

Objective:

Although human paranasal sinuses are critical organs for nitric oxide production, little information is available regarding the role of arginase in alterations of arginine metabolism and nasal nitric oxide levels that may be informative for classifying chronic rhinosinusitis subtypes.

Methods:

The expression and localisation of arginase and nitric oxide synthase isoforms in paranasal sinus mucosa were examined, and the fractional exhaled nitric oxide was measured in chronic rhinosinusitis without nasal polyps (n=18) and chronic rhinosinusitis with nasal polyps (n = 27) patients.

Results:

Increased arginase-2 activities in chronic rhinosinusitis without nasal polyps patients were associated with significantly lower levels of nasal fractional exhaled nitric oxide. Chronic rhinosinusitis with nasal polyps patients showed significant NOS2 messenger RNA upregulation with concomitant higher levels of oral and nasal fractional exhaled nitric oxide.

Conclusion:

These results indicate that fractional exhaled nitric oxide is a valid marker for differentiating chronic rhinosinusitis phenotypes based on a delicate balance between arginase and nitric oxide synthase activities in nitric oxide production.

Pharmacokinetic-Pharmacodynamic Model for the Effect of l-Arginine on Endothelial Function in Patients with Moderately Severe Falciparum Malaria

Impaired organ perfusion in severe falciparum malaria arises from microvascular sequestration of parasitized cells and endothelial dysfunction. Endothelial dysfunction in malaria is secondary to impaired nitric oxide (NO) bioavailability, in part due to decreased plasma concentrations of l-arginine, the substrate for endothelial cell NO synthase. We quantified the time course of the effects of adjunctive l-arginine treatment on endothelial function in 73 patients with moderately severe falciparum malaria derived from previous studies. Three groups of 10 different patients received 3 g, 6 g, or 12 g of l-arginine as a half-hour infusion. The remaining 43 received saline placebo. A pharmacokinetic-pharmacodynamic (PKPD) model was developed to describe the time course of changes in exhaled NO concentrations and reactive hyperemia-peripheral arterial tonometry (RH-PAT) index values describing endothelial function and then used to explore optimal dosing regimens for l-arginine. A PK model describing arginine concentrations in patients with moderately severe malaria was extended with two pharmacodynamic biomeasures, the intermediary biochemical step (NO production) and endothelial function (RH-PAT index). A linear model described the relationship between arginine concentrations and exhaled NO. NO concentrations were linearly related to RH-PAT index. Simulations of dosing schedules using this PKPD model predicted that the time within therapeutic range would increase with increasing arginine dose. However, simulations demonstrated that regimens of continuous infusion over longer periods would prolong the time within the therapeutic range even more. The optimal dosing regimen for l-arginine is likely to be administration schedule dependent. Further studies are necessary to characterize the effects of such continuous infusions of l-arginine on NO and microvascular reactivity in severe malaria.

Glucagon-Like Peptide 2 (GLP-2) Stimulates Postprandial Chylomicron Production and Postabsorptive Release of Intestinal Triglyceride Storage Pools via Induction of Nitric Oxide Signaling in Male Hamsters and Mice

The intestinal overproduction of apolipoprotein B48 (apoB48)-containing chylomicron particles is a common feature of diabetic dyslipidemia and contributes to cardiovascular risk in insulin resistant states. We previously reported that glucagon-like peptide-2 (GLP-2) is a key endocrine stimulator of enterocyte fat absorption and chylomicron output in the postprandial state. GLP-2's stimulatory effect on chylomicron production in the postabsorptive state has been confirmed in human studies. The mechanism by which GLP-2 regulates chylomicron production is unclear, because its receptor is not expressed on enterocytes. We provide evidence for a key role of nitric oxide (NO) in mediating the stimulatory effects of GLP-2 during the postprandial and postabsorptive periods. Intestinal chylomicron production was assessed in GLP-2-treated hamsters administered the pan-specific NO synthase (NOS) inhibitor L-N(G)-nitroarginine methyl ester (L-NAME), and in GLP-2-treated endothelial NOS knockout mice. L-NAME blocked GLP-2-stimulated apoB48 secretion and reduced triglycerides (TGs) in the TG-rich lipoprotein (TRL) fraction of the plasma in the postprandial state. Endothelial NOS-deficient mice were resistant to GLP-2 stimulation and secreted fewer large apoB48-particles. When TG storage pools were allowed to accumulate, L-NAME mitigated the GLP-2-mediated increase in TRL-TG, suggesting that NO is required for early mobilization and secretion of stored TG and preformed chylomicrons. Importantly, the NO donor S-nitroso-L-glutathione was able to elicit an increase in TRL-TG in vivo and stimulate chylomicron release in vitro in primary enterocytes. We describe a novel role for GLP-2-mediated NO-signaling as a critical regulator of intestinal lipid handling and a potential contributor to postprandial dyslipidemia.

Update on protein intake: importance of milk proteins for health status of the elderly

Loss of lean body mass that occurs with aging is the primary endpoint with which sarcopenia is defined. Furthermore, loss of muscle mass is central to the development of many adverse health issues in the elderly. Consequently, the response of lean body mass to nutritional interventions, particularly to dietary protein, has been a commonly measured endpoint. However, increased protein intake has been associated with improved markers for cardiovascular health, improved bone health, management of weight and metabolic diseases, and reduced all-cause mortality. Strength, rather than lean body mass, may be a more accurate indicator of health, especially in the elderly. The recommended dietary allowance for protein has been set at 0.8 g/kg/day. Because the average protein intake in the United States is approximately 1.2 g/kg/day, it appears that the average protein intake is above the recommended dietary allowance but below the low end of the acceptable macronutrient distribution range recommended by expert committees of the National Academy of Sciences and below the dietary intake levels suggested by the US Department of Agriculture in the Dietary Guidelines.

Asymmetric dimethyl arginine induces pulmonary vascular dysfunction via activation of signal transducer and activator of transcription 3 and stabilization of hypoxia-inducible factor 1-alpha

Pulmonary hypertension (PH), associated with imbalance in vasoactive mediators and massive remodeling of pulmonary vasculature, represents a serious health complication. Despite the progress in treatment, PH patients typically have poor prognoses with severely affected quality of life. Asymmetric dimethyl arginine (ADMA), endogenous inhibitor of endothelial nitric oxide synthase (eNOS), also represents one of the critical regulators of pulmonary vascular functions. The present study describes a novel mechanism of ADMA-induced dysfunction in human pulmonary endothelial and smooth muscle cells. The effect of ADMA was compared with well-established model of hypoxia-induced pulmonary vascular dysfunction. It was discovered for the first time that ADMA induced the activation of signal transducer and activator of transcription 3 (STAT3) and stabilization of hypoxia inducible factor 1α (HIF-1α) in both types of cells, associated with drastic alternations in normal cellular functions (e.g., nitric oxide production, cell proliferation/Ca(2+) concentration, production of pro-inflammatory mediators, and expression of eNOS, DDAH1, and ICAM-1). Additionally, ADMA significantly enhanced the hypoxia-mediated increase in the signaling cascades. In summary, increased ADMA may lead to manifestation of PH phenotype in human endothelial and smooth muscle cells via the STAT3/HIF-1α cascade. Therefore this signaling pathway represents the potential pathway for future clinical interventions in PH.

The Role of Nitric Oxide Synthase Uncoupling in Tumor Progression

Here, evidence suggests that nitric oxide synthases (NOS) of tumor cells, in contrast with normal tissues, synthesize predominantly superoxide and peroxynitrite. Based on high-performance liquid chromatography analysis, the underlying mechanism for this uncoupling is a reduced tetrahydrobiopterin:dihydrobiopterin ratio (BH4:BH2) found in breast, colorectal, epidermoid, and head and neck tumors compared with normal tissues. Increasing BH4:BH2 and reconstitution of coupled NOS activity in breast cancer cells with the BH4 salvage pathway precursor, sepiapterin, causes significant shifts in downstream signaling, including increased cGMP-dependent protein kinase (PKG) activity, decreased β-catenin expression, and TCF4 promoter activity, and reduced NF-κB promoter activity. Sepiapterin inhibited breast tumor cell growth in vitro and in vivo as measured by a clonogenic assay, Ki67 staining, and 2[18F]fluoro-2-deoxy-D-glucose-deoxyglucose positron emission tomography (FDG-PET). In summary, using diverse tumor types, it is demonstrated that the BH4:BH2 ratio is lower in tumor tissues and, as a consequence, NOS activity generates more peroxynitrite and superoxide anion than nitric oxide, resulting in important tumor growth-promoting and antiapoptotic signaling properties.

IMPLICATIONS

The synthetic BH4, Kuvan, is used to elevate BH4:BH2 in some phenylketonuria patients and to treat diseases associated with endothelial dysfunction, suggesting a novel, testable approach for correcting an abnormality of tumor metabolism to control tumor growth.

Changes in plasma levels of asymmetric dimethylarginine, symmetric dimethylarginine, and arginine after a single dose of vardenafil in patients with pulmonary hypertension

OBJECTIVE

We investigated whether vardenafil, a phosphodiesterase-5 inhibitor, alters plasma levels of asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and arginine.

PATIENTS AND METHODS

ADMA, SDMA, and arginine were measured (0-540 min) in 12 patients with pulmonary hypertension after a single oral dose of vardenafil. Invasive hemodynamic data were collected at baseline and after 60 min.

RESULTS

A reduction in ADMA was observed at 30 and 45 min with a median change of -11.1% (P=0.021) and -12.5% (P=0.002). SDMA decreased with a median -5.3% change (P=0.032) at 45 min. An increase in arginine, median 40.3% (P=0.002), 45.0% (P=0.010), and 77.1% (P=0.008) was observed at 120, 300, and 540 min respectively. An increase in the arginine/ADMA ratio, median 11.7% (P=0.012), 32.5% (P=0.003), 26.5% (P=0.021), 33% (P=0.007), 48.5% (P=0.007), and 63.1% (P=0.008) was observed at 15, 45, 60, 120, 300, and 540 min respectively. There was a positive correlation between vardenafil exposure and the percent change in the arginine/ADMA ratio from baseline to 540 min (r=0.80; P=0.01). A correlation between baseline mean right atrial pressure (mRAP) and baseline ADMA (r=0.65; P=0.023), and baseline SDMA (r=0.61; P=0.035) was observed. A correlation between the baseline arginine/ADMA ratio and baseline cardiac output (CO) (r=0.59; P=0.045) and baseline cardiac index (CI) (r=0.61; P=0.036) was observed. Baseline arginine/ADMA ratio correlated with baseline mRAP (r=-0.79; P=0.002). A correlation between change (0-60 min) in CI and change in arginine (r=0.77; P=0.003) as well as change in the arginine/ADMA ratio (r=0.61; P=0.037) was observed.

CONCLUSIONS

Vardenafil induced changes in ADMA, SDMA, arginine, and the arginine/ADMA ratio in patients with PH. An increase in arginine and the arginine/ADMA ratio was associated with improvement in CI.

Arginine and citrulline and the immune response in sepsis

Arginine, a semi-essential amino acid is an important initiator of the immune response. Arginine serves as a precursor in several metabolic pathways in different organs. In the immune response, arginine metabolism and availability is determined by the nitric oxide synthases and the arginase enzymes, which convert arginine into nitric oxide (NO) and ornithine, respectively. Limitations in arginine availability during inflammatory conditions regulate macrophages and T-lymfocyte activation. Furthermore, over the past years more evidence has been gathered which showed that arginine and citrulline deficiencies may underlie the detrimental outcome of inflammatory conditions, such as sepsis and endotoxemia. Not only does the immune response contribute to the arginine deficiency, also the impaired arginine de novo synthesis in the kidney has a key role in the eventual observed arginine deficiency. The complex interplay between the immune response and the arginine-NO metabolism is further underscored by recent data of our group. In this review we give an overview of physiological arginine and citrulline metabolism and we address the experimental and clinical studies in which the arginine-citrulline NO pathway plays an essential role in the immune response, as initiator and therapeutic target.

[Citrulline and arginine kinetics and its value as a prognostic factor in pediatric critically ill patients]

INTRODUCTION

Low concentrations of plasma citrulline and arginine have been reported in children under various pathological conditions.

HYPOTHESIS

Plasma citrulline and arginine levels undergo different kinetics during the early days of critical illness in children according to the severity of symptoms and can be correlated with other clinical and laboratory parameters associated with the SIR.

PATIENTS AND METHODS

A single-center prospective observational study in patients 7 days to 14 years admitted to pediatric intensive care unit (PICU). Citrulline and arginine blood levels (blood in dry paper, analysis by mass spectrometry in tandem), acute phase reactants and clinical data were collected on admission, at 12 h, 24 h, 3 and 7 days.

RESULTS

A total of 44 critically ill patients were included and control group was formed by 42 healthy children. The citrulline and arginine kinetic analysis showed: 1) Citrulline falls significantly (P<.05) at 12 h of admission; levels remain low until day 7 and begin progressive increase again. 2) Arginine is already lowered at 6h, although an earlier rise occurs (3rd day). 3. The decrease of citrulline in the first 3 days of admission positively correlates with arginine kinetics. Bivariate analysis showed: 1) Correlation of elevated citrulline on the 7th day with shorter duration of mechanical ventilation, lower PICU stay and lower occurrence of complications. The levels of citrulline still descended at day 7 are associated with increased CRP/procalcitonin elevation at first 24 h. 2) The greatest decrease of arginine in the first 12 h is associated with a longer PICU stay and greater number of complications and increase of acute phase reactants at 3 days.

CONCLUSIONS

There are decreased levels of arginine and citrulline in the first days at PICU, with recovery at the 3rd and 7th day respectively, and a relationship between a greater decrease and a worse outcome and between a longer income and a higher serum CRP/procalcitonin.

l-Arginine administration attenuates airway inflammation by altering l-arginine metabolism in an NC/Nga mouse model of asthma

Changes in l-arginine metabolism, including increased arginase levels and decreased nitric oxide production, are involved in the pathophysiology of asthma. In this study, using an intranasal mite-induced NC/Nga mouse model of asthma, we examined whether administration of l-arginine ameliorated airway hyperresponsiveness and inflammation by altering l-arginine metabolism. Experimental asthma was induced in NC/Nga mice via intranasal administration of mite crude extract (50 µg/day) on 5 consecutive days (days 0-4, sensitization) and on day 11 (challenge). Oral administration of l-arginine (250 mg/kg) was performed twice daily on days 5-10 for prevention or on days 11-13 for therapy. On day 14, we evaluated the inflammatory airway response (airway hyperresponsiveness, the number of cells in the bronchoalveolar lavage fluid, and the changes in pathological inflammation of the lung), arginase expression and activity, l-arginine bioavailability, and the concentration of NOx, the end products of nitric oxide. Treatment with l-arginine ameliorated the mite-induced inflammatory airway response. Furthermore, l-arginine administration attenuated the increases in arginase expression and activity and elevated the NOx levels by enhancing l-arginine bioavailability. These findings indicate that l-arginine administration may contribute to the improvement of asthmatic symptoms by altering l-arginine metabolism.

Improvement of the physical performance is associated with activation of NO/PGC-1α/mtTFA signaling pathway and increased protein expressions of electron transport chain in gastrocnemius muscle from rats supplemented with L-arginine

AIM

To examine the influence of l-arginine supplementation in combination with physical training on mitochondrial biomarkers from gastrocnemius muscle and its relationship with physical performance.

MAIN METHODS

Male Wistar rats were divided into four groups: control sedentary (SD), sedentary supplemented with l-arginine (SDLA), trained (TR) and trained supplemented with l-arginine (TRLA). Supplementation of l-arginine was administered by gavage (62.5mg/ml/day/rat). Physical training consisted of 60min/day, 5days/week, 0% grade, speed of 1.2km/h. The study lasted 8weeks. Skeletal muscle mitochondrial enriched fraction as well as cytoplasmic fractions were obtained for Western blotting and biochemical analyses. Protein expressions of transcriptor coactivator (PGC-1α), transcriptor factors (mtTFA), ATP synthase subunit c, cytochrome oxidase (COXIV), constitutive nitric oxide synthases (eNOS and nNOS), Cu/Zn-superoxide dismutase (SOD) and manganese-SOD (Mn-SOD) were evaluated. We also assessed in plasma: lipid profile, glycemia and malondialdehyde (MDA) levels. The nitrite/nitrate (NOx(-)) levels were measured in both plasma and cytosol fraction of the gastrocnemius muscle.

KEY FINDINGS

8-week l-arginine supplementation associated with physical training was effective in promoting greater tolerance to exercise that was accompanied by up-regulation of the protein expressions of mtTFA, PGC-1α, ATP synthase subunit c, COXIV, Cu/Zn-SOD and Mn-SOD. The upstream pathway was associated with improvement of NO bioavailability, but not in NO production since no changes in nNOS or eNOS protein expressions were observed.

SIGNIFICANCE

This combination would be an alternative approach for preventing cardiometabolic diseases given that in overt diseases a profound impairment in the physical performance of the patients is observed.

Plasma arginine/ADMA ratio as a sensitive risk marker for atherosclerosis: Shimane CoHRE study

BACKGROUND

Asymmetric dimethylarginine (ADMA), which acts an endogenous inhibitor of nitric oxide synthase (NOS), is involved in the pathogenesis of cardiovascular disease. Arginine (Arg) may regulate vascular endothelial function, since Arg is the substrate of NO competing with ADMA. In our previous study, low Arg/ADMA ratio is an independent risk for microangiopathy-related cerebral damage.

PURPOSE

Here, we performed a cross-sectional study to evaluate the association between the Arg/ADMA ratio and the maximal intima-media thickness (IMT) in the carotid artery.

SUBJECTS AND METHODS

Participants were 785 community-dwelling Japanese people without any severe disorders. Plasma concentration of Arg and ADMA in fasting blood sample was determined using HPLC. IMT was measured in the bilateral carotid artery by ultrasonography.

RESULTS

Among quartiles stratified by the Arg/ADMA ratio, ANOVA showed a significant difference in IMT and the IMT in Q1 (the lowest quartile) was significantly higher than that in Q4 (the highest quartile). In multiple linear regression analysis, age, the male gender, lower BMI, the presence of hypertension and lower Arg/ADMA ratio were independently correlated with IMT, while IMT was not correlated with Arg or ADMA alone. In addition, the Arg/ADMA ratio was associated with IMT independent of age, sex, BMI and the presence of hypertension with odds ratio 0.21 (95%CI: 0.05-0.88) in multiple logistic regression analysis for IMT 1.5 mm or more.

CONCLUSION

Imbalance of Arg and ADMA is independently involved in the progression of atherosclerosis, and the Arg/ADMA ratio may be a sensitive marker for atherosclerosis.

Arginine infusion in patients with septic shock increases nitric oxide production without haemodynamic instability

Arginine deficiency in sepsis may impair nitric oxide (NO) production for local perfusion and add to the catabolic state. In contrast, excessive NO production has been related to global haemodynamic instability. Therefore, the aim of the present study was to investigate the dose-response effect of intravenous arginine supplementation in post-absorptive patients with septic shock on arginine-NO and protein metabolism and on global and regional haemodynamics. Eight critically ill patients with a diagnosis of septic shock participated in this short-term (8 h) dose-response study. L-Arginine-HCl was continuously infused [intravenously (IV)] in three stepwise-increasing doses (33, 66 and 99 μmol·kg-1·h-1). Whole-body arginine-NO and protein metabolism were measured using stable isotope techniques, and baseline values were compared with healthy controls. Global and regional haemodynamic parameters were continuously recorded during the study. Upon infusion, plasma arginine increased from 48±7 to 189±23 μmol·l-1 (means±S.D.; P<0.0001). This coincided with increased de novo arginine (P<0.0001) and increased NO production (P<0.05). Sepsis patients demonstrated elevated protein breakdown at baseline (P<0.001 compared with healthy controls), whereas protein breakdown and synthesis both decreased during arginine infusion (P<0.0001). Mean arterial and pulmonary pressure and gastric mucosal-arterial partial pressure of carbon dioxide difference (Pr-aCO2) gap did not alter during arginine infusion (P>0.05), whereas stroke volume (SV) increased (P<0.05) and arterial lactate decreased (P<0.05). In conclusion, a 4-fold increase in plasma arginine with intravenous arginine infusion in sepsis stimulates de novo arginine and NO production and reduces whole-body protein breakdown. These potential beneficial metabolic effects occurred without negative alterations in haemodynamic parameters, although improvement in regional perfusion could not be demonstrated in the eight patients with septic shock who were studied.

Berteroin present in cruciferous vegetables exerts potent anti-inflammatory properties in murine macrophages and mouse skin

Berteroin (5-methylthiopentyl isothiocyanate) is a sulforaphane analog present in cruciferous vegetables, including Chinese cabbage, rucola salad leaves, and mustard oil. We examined whether berteroin exerts anti-inflammatory activities using lipopolysaccharide (LPS)-stimulated Raw 264.7 macrophages and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mouse skin inflammation models. Berteroin decreased LPS-induced release of inflammatory mediators and pro-inflammatory cytokines in Raw 264.7 macrophages. Berteroin inhibited LPS-induced degradation of inhibitor of κBα (IκBα) and nuclear factor-κB p65 translocation to the nucleus and DNA binding activity. Furthermore, berteroin suppressed degradation of IL-1 receptor-associated kinase and phosphorylation of transforming growth factor β activated kinase-1. Berteroin also inhibited LPS-induced phosphorylation of p38 MAPK, ERK1/2, and AKT. In the mouse ear, berteroin effectively suppressed TPA-induced edema formation and down-regulated iNOS and COX-2 expression as well as phosphorylation of AKT and ERK1/2. These results demonstrate that berteroin exhibits potent anti-inflammatory properties and suggest that berteroin can be developed as a skin anti-inflammatory agent.

Mitochondrial injury and dysfunction in hypertension-induced cardiac damage

Hypertension remains an important modifiable risk factor for cardiovascular disease, associated with increased morbidity and mortality. Deciphering the mechanisms involved in the pathogenesis of hypertension is critical, as its prevalence continues increasing worldwide. Mitochondria, the primary cellular energy producers, are numerous in parenchymal cells of the heart, kidney, and brain, major target organs in hypertension. These membrane-bound organelles not only maintain cellular respiration but also modulate several functions of the cell including proliferation, apoptosis, generation of reactive oxygen species, and intracellular calcium homeostasis. Therefore, mitochondrial damage and dysfunction compromise overall cell functioning. In recent years, significant advances increased our understanding of mitochondrial morphology, bioenergetics, and homeostasis, and in turn of their role in several diseases, so that mitochondrial abnormalities and dysfunction have been identified in experimental models of hypertension. In this review, we summarize current knowledge of the contribution of dysfunctional mitochondria to the pathophysiology of hypertension-induced cardiac damage, as well as available evidence of mitochondrial injury-induced damage in other organs. Finally, we discuss the capability of antihypertensive therapy to ameliorate hypertensive mitochondrial injury, and the potential position of mitochondria as therapeutic targets in patients with hypertension.

Ammonia metabolism and hyperammonemic disorders

Human adults produce around 1000 mmol of ammonia daily. Some is reutilized in biosynthesis. The remainder is waste and neurotoxic. Eventually most is excreted in urine as urea, together with ammonia used as a buffer. In extrahepatic tissues, ammonia is incorporated into nontoxic glutamine and released into blood. Large amounts are metabolized by the kidneys and small intestine. In the intestine, this yields ammonia, which is sequestered in portal blood and transported to the liver for ureagenesis, and citrulline, which is converted to arginine by the kidneys. The amazing developments in NMR imaging and spectroscopy and molecular biology have confirmed concepts derived from early studies in animals and cell cultures. The processes involved are exquisitely tuned. When they are faulty, ammonia accumulates. Severe acute hyperammonemia causes a rapidly progressive, often fatal, encephalopathy with brain edema. Chronic milder hyperammonemia causes a neuropsychiatric illness. Survivors of severe neonatal hyperammonemia have structural brain damage. Proposed explanations for brain edema are an increase in astrocyte osmolality, generally attributed to glutamine accumulation, and cytotoxic oxidative/nitrosative damage. However, ammonia neurotoxicity is multifactorial, with disturbances also in neurotransmitters, energy production, anaplerosis, cerebral blood flow, potassium, and sodium. Around 90% of hyperammonemic patients have liver disease. Inherited defects are rare. They are being recognized increasingly in adults. Deficiencies of urea cycle enzymes, citrin, and pyruvate carboxylase demonstrate the roles of isolated pathways in ammonia metabolism. Phenylbutyrate is used routinely to treat inherited urea cycle disorders, and its use for hepatic encephalopathy is under investigation.

Intravenous glutamine supplementation enhances renal de novo arginine synthesis in humans: a stable isotope study

BACKGROUND

Arginine plays a role in many different pathways in multiple cell types. Consequently, a shortage of arginine, caused by pathologic conditions such as cancer or injury, has the potential to disturb many cellular and organ functions. Glutamine is the ultimate source for de novo synthesis of arginine in humans via the intestinal-renal axis. Therefore, we hypothesized that parenteral glutamine supplementation may stimulate the interorgan pathway of arginine production.

OBJECTIVES

The objectives were to quantify arginine production from its precursor glutamine and to establish the contribution of the kidneys to de novo synthesis of arginine in patients receiving intravenous supplementation of glutamine dipeptide during major abdominal surgery.

DESIGN

Whole-body and renal metabolism of glutamine, citrulline, and arginine was assessed by stable isotope techniques in 7 patients receiving a perioperative supplement of intravenous alanyl-glutamine (0.5 g · kg(-1) · d(-1)).

RESULTS

Plasma glutamine, citrulline, and arginine concentrations increased significantly in patients receiving intravenous glutamine dipeptide. At whole-body level, 91% of total citrulline turnover was derived from glutamine, whereas 49% of whole-body citrulline turnover was used for de novo synthesis of arginine. The kidneys were responsible for 75% of whole-body arginine production from citrulline.

CONCLUSIONS

Glutamine and citrulline are important sources for de novo arginine synthesis. The kidneys are the main production site for endogenous arginine. After comparison of these results with previous similar studies, our data suggest that an intravenous glutamine supplement doubles renal arginine production from citrulline. This trial was registered at www.trialregister.nl as NTR2914.

Increases in exhaled nitric oxide after acute stress: association with measures of negative affect and depressive mood

BACKGROUND

Increases in fractional exhaled nitric oxide (FeNO) have been observed after acute laboratory stress, which could indicate a strengthening of immune defenses in acute stress because of the quick onset of the response and the role of nitric oxide in airway-protective functions. In addition, because sustained psychological distress and depression are known to deteriorate immune defenses systems, they may dampen the FeNO response to acute stress.

METHODS

FeNO and negative affect were measured before and after a speech and mental arithmetic stressor. We examined the association of stress-induced FeNO changes with momentary negative affect and questionnaires of perceived stress, anxious mood, and depressive mood in 39 asthma patients and 41 healthy controls.

RESULTS

FeNO increased from baseline to stress in participants with asthma (from 3.38 [0.102] to 3.46 [0.103] ln(ppb)) and controls (2.86 [0.098] to 2.92 [0.099]; F(4,141) = 3.26, p = .014), but the magnitude of the FeNO response did not differ between groups (F < 1). Only low levels of depressive mood were associated with FeNO increases after stress (most pronounced at 0 minute poststress; t(76) = 3.87, p < .001). In contrast, only higher perceived stress was associated with FeNO increases (most pronounced at 0 minute poststress; t(75) = 4.09, p < .001), and momentary negative affect was associated with higher FeNO throughout assessments (β = 0.08, t(114) = 8.27, p = .005). Associations of FeNO with psychological variables were largely unrelated to asthma status and inhaled corticosteroid use.

CONCLUSIONS

Depressive mood is associated with a reduced mobilization of airway nitric oxide in acute stress, whereas other indicators of negative affect are positively associated with overall FeNO levels and reactivity.

Association between brachial-ankle pulse wave velocity and the ratio of l-arginine to asymmetric dimethylarginine in patients undergoing coronary angiography

BACKGROUND

Endothelial dysfunction causes vasomotor dysregulation and vascular stiffening in addition to structural changes. By influencing NO synthesis, deficiency of l-arginine relative to asymmetric dimethylarginine (ADMA), which is an l-arginine derivative that acts as a competitive NO synthase inhibitor, may lead to the promotion of arterial stiffness. This study investigated the relationship between the l-arginine/ADMA ratio and brachial-ankle pulse wave velocity (baPWV), an indicator of arterial stiffness.

METHODS AND RESULTS

This cross-sectional study enrolled 74 patients (62 men, 12 women; mean age, 67±10 years) undergoing elective coronary angiography. A total of 54 (73%) patients had coronary artery disease. Serum l-arginine and ADMA were measured by high-performance liquid chromatography with fluorescence detection. The ratio of l-arginine to ADMA and the serum l-arginine level was associated with baPWV in univariate regression analysis (l-arginine/ADMA ratio: β=-0.323, p=0.005; l-arginine: β=-0.247, p=0.034). In addition, baPWV was related to blood hemoglobin concentration, hematocrit, brain natriuretic peptide level, symmetric dimethylarginine, renal function, blood pressure, and heart rate. In multivariate analysis, the l-arginine/ADMA ratio was a significant predictor of baPWV (β=-0.310, p<0.001). In subgroup analyses, the l-arginine/ADMA ratio was associated with baPWV in elderly patients (n=46, β=-0.359, p=0.004), and in younger patients (n=28, β=-0.412, p=0.006).

CONCLUSION

A low l-arginine/ADMA ratio may be associated with high baPWV in patients undergoing coronary angiography.

Nitric oxide is a positive regulator of the Warburg effect in ovarian cancer cells

Ovarian cancer (OVCA) is among the most lethal gynecological cancers leading to high mortality rates among women. Increasing evidence indicate that cancer cells undergo metabolic transformation during tumorigenesis and growth through nutrients and growth factors available in tumor microenvironment. This altered metabolic rewiring further enhances tumor progression. Recent studies have begun to unravel the role of amino acids in the tumor microenvironment on the proliferation of cancer cells. One critically important, yet often overlooked, component to tumor growth is the metabolic reprogramming of nitric oxide (NO) pathways in cancer cells. Multiple lines of evidence support the link between NO and tumor growth in some cancers, including pancreas, breast and ovarian. However, the multifaceted role of NO in the metabolism of OVCA is unclear and direct demonstration of NO's role in modulating OVCA cells' metabolism is lacking. This study aims at indentifying the mechanistic links between NO and OVCA metabolism. We uncover a role of NO in modulating OVCA metabolism: NO positively regulates the Warburg effect, which postulates increased glycolysis along with reduced mitochondrial activity under aerobic conditions in cancer cells. Through both NO synthesis inhibition (using L-arginine deprivation, arginine is a substrate for NO synthase (NOS), which catalyzes NO synthesis; using L-Name, a NOS inhibitor) and NO donor (using DETA-NONOate) analysis, we show that NO not only positively regulates tumor growth but also inhibits mitochondrial respiration in OVCA cells, shifting these cells towards glycolysis to maintain their ATP production. Additionally, NO led to an increase in TCA cycle flux and glutaminolysis, suggesting that NO decreases ROS levels by increasing NADPH and glutathione levels. Our results place NO as a central player in the metabolism of OVCA cells. Understanding the effects of NO on cancer cell metabolism can lead to the development of NO targeting drugs for OVCAs.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

GENERAL SIGNIFICANCE

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

Airway nitric oxide and psychological processes in asthma and health: a review

OBJECTIVE

The fraction of exhaled nitric oxide (FeNO) has been widely used as a marker of airway inflammation in asthma in recent years. However, NO serves multiple functions throughout the organism, and various influences on FeNO levels beyond inflammation have been documented. Emerging literature indicates that psychological processes are systematically linked to FeNO.

DATA SOURCES

Academic Search Complete, PubMed, PsychArticles, and PsychInfo databases.

STUDY SELECTIONS

Relevant studies were identified using keywords exhaled nitric oxide paired with psychological stress, stress psychology, emotion, major depression, anxiety, or psychopathology. Studies measuring FeNO during naturalistic observation of emotion and stress, laboratory stress and emotion-induction protocols, and correlational designs using psychological questionnaires were included.

RESULTS

Acute stress, anxiety, and negative affect have been repeatedly linked with higher FeNO levels, whereas more prolonged states of stress, in particular depression, have been associated with lower FeNO levels. The literature on FeNO is paralleled by research on NO in the cardiovascular and central nervous systems, which also shows systematic associations with psychosocial variables. Potential mechanisms of association include stimulation of NO release from different cells, including the epithelia and macrophages, through noradrenaline, interferon-γ, or vascular endothelial growth factor, changes in oxidative stress or arginase levels, or facilitation of diffusion by mechanical factors.

CONCLUSION

Psychosocial factors may need to be considered in the interpretation of longitudinal FeNO changes in monitoring and management of patients with asthma. The distinction between constitutive and inducible sources of NO will be essential for future research.

L-Arginine Supplementation in Type II Diabetic Rats Preserves Renal Function and Improves Insulin Sensitivity by Altering the Nitric Oxide Pathway

Rat studies demonstrated that type II diabetes mellitus (T2DM) decreases both the production and bioavailability of nitric oxide (NO). L-arginine (LA) provides the precursor for the production of NO. We hypothesized that LA dietary supplementation will preserve NO production via endothelial nitric oxide synthase (eNOS) causing renal microvascular vasodilation and increased glomerular blood flow and thus increasing glomerular filtration rate (GFR). This would impede the formation of reactive oxygen species which contributes to cell damage and death. LA supplementation preserved GFR in the treated diabetic rats compared to untreated diabetic rats. We provide evidence that this effect may be due to increased levels of eNOS and urinary cyclic guanosine monophosphate, which leads to renal microvascular vasodilation. Plasma nitrotyrosine was decreased in the LA treated rats; however, plasma nitrite levels remained unaffected as expected. Marked improvements in glucose tolerance were also observed in the LA treated diabetic rats. These results demonstrate that LA supplementation preserves NO activity and may delay the onset of insulin resistance and renal dysfunction during hyperglycemic stress. These results suggest the importance of the NO pathway in consequent renal dysfunction and in the development of insulin resistance in diabetic rats.

Neurovascular unit dysfunction with blood-brain barrier hyperpermeability contributes to major depressive disorder: a review of clinical and experimental evidence

About one-third of people with major depressive disorder (MDD) fail at least two antidepressant drug trials at 1 year. Together with clinical and experimental evidence indicating that the pathophysiology of MDD is multifactorial, this observation underscores the importance of elucidating mechanisms beyond monoaminergic dysregulation that can contribute to the genesis and persistence of MDD. Oxidative stress and neuroinflammation are mechanistically linked to the presence of neurovascular dysfunction with blood-brain barrier (BBB) hyperpermeability in selected neurological disorders, such as stroke, epilepsy, multiple sclerosis, traumatic brain injury, and Alzheimer’s disease. In contrast to other major psychiatric disorders, MDD is frequently comorbid with such neurological disorders and constitutes an independent risk factor for morbidity and mortality in disorders characterized by vascular endothelial dysfunction (cardiovascular disease and diabetes mellitus). Oxidative stress and neuroinflammation are implicated in the neurobiology of MDD. More recent evidence links neurovascular dysfunction with BBB hyperpermeability to MDD without neurological comorbidity. We review this emerging literature and present a theoretical integration between these abnormalities to those involving oxidative stress and neuroinflammation in MDD. We discuss our hypothesis that alterations in endothelial nitric oxide levels and endothelial nitric oxide synthase uncoupling are central mechanistic links in this regard. Understanding the contribution of neurovascular dysfunction with BBB hyperpermeability to the pathophysiology of MDD may help to identify novel therapeutic and preventative approaches.

Nitric oxide deficiency and endothelial dysfunction in pulmonary arterial hypertension

Nitric oxide (NO) signaling plays a major role in modulating vascular tone and remodeling in the pulmonary circulation, but its role in the pathogenesis of pulmonary vascular diseases is still not completely understood. Numerous abnormalities of NO synthesis and signaling have been identified in animal models of pulmonary vascular disease and in humans with pulmonary hypertension. Many of these abnormalities have become targets of new therapies for the treatment of pulmonary hypertension. However, it is unclear to what extent alterations in NO signaling contribute to pulmonary hypertensive responses or merely reflect abnormalities induced by the underlying disease. This perspective examines the current understanding of altered NO signaling in pulmonary hypertensive diseases and discusses how these alterations may contribute to the pathogenesis of pulmonary hypertension. The efficacy and limitations of presently available therapies for pulmonary hypertension that target NO signaling are reviewed along with an update on investigational therapies that use this pathway to reverse pulmonary hypertensive changes.

Arginine appearance and nitric oxide synthesis in critically ill infants can be increased with a protein-energy-enriched enteral formula

BACKGROUND

Arginine is considered an essential amino acid during critical illness in children, and supplementation of arginine has been proposed to improve arginine availability to facilitate nitric oxide (NO) synthesis. Protein-energy-enriched enteral formulas (PE-formulas) can improve nutrient intake and promote anabolism in critically ill infants. However, the effect of increased protein and energy intake on arginine metabolism is not known.

OBJECTIVE

We investigated the effect of a PE-formula compared with that of a standard infant formula (S-formula) on arginine kinetics in critically ill infants.

DESIGN

A 2-h stable-isotope tracer protocol was conducted in 2 groups of critically ill infants with respiratory failure because of viral bronchiolitis, who received either a PE-formula (n = 8) or S-formula (n = 10) in a randomized, blinded, controlled setting. Data were reported as means ± SDs.

RESULTS

The intake of a PE-formula in critically ill infants (aged 0.23 ± 0.14 y) resulted in an increased arginine appearance (PE-formula: 248 ± 114 μmol · kg(-1) · h(-1); S-formula: 130 ± 53 μmol · kg(-1) · h(-1); P = 0.012) and NO synthesis (PE-formula: 1.92 ± 0.99 μmol · kg(-1) · h(-1); S-formula: 0.84 ± 0.36 μmol · kg(-1) · h(-1); P = 0.003), whereas citrulline production and plasma arginine concentrations were unaffected.

CONCLUSION

In critically ill infants with respiratory failure because of viral bronchiolitis, the intake of a PE-formula increases arginine availability by increasing arginine appearance, which leads to increased NO synthesis, independent of plasma arginine concentrations. This trial was registered at www.trialregister.nl as NTR515.

An NO donor approach to neuroprotective and procognitive estrogen therapy overcomes loss of NO synthase function and potentially thrombotic risk

Selective estrogen receptor modulators (SERMs) are effective therapeutics that preserve favorable actions of estrogens on bone and act as antiestrogens in breast tissue, decreasing the risk of vertebral fractures and breast cancer, but their potential in neuroprotective and procognitive therapy is limited by: 1) an increased lifetime risk of thrombotic events; and 2) an attenuated response to estrogens with age, sometimes linked to endothelial nitric oxide synthase (eNOS) dysfunction. Herein, three 3(rd) generation SERMs with similar high affinity for estrogen receptors (ERα, ERβ) were studied: desmethylarzoxifene (DMA), FDMA, and a novel NO-donating SERM (NO-DMA). Neuroprotection was studied in primary rat neurons exposed to oxygen glucose deprivation; reversal of cholinergic cognitive deficit was studied in mice in a behavioral model of memory; long term potentiation (LTP), underlying cognition, was measured in hippocampal slices from older 3×Tg Alzheimer's transgenic mice; vasodilation was measured in rat aortic strips; and anticoagulant activity was compared. Pharmacologic blockade of GPR30 and NOS; denudation of endothelium; measurement of NO; and genetic knockout of eNOS were used to probe mechanism. Comparison of the three chemical probes indicates key roles for GPR30 and eNOS in mediating therapeutic activity. Procognitive, vasodilator and anticoagulant activities of DMA were found to be eNOS dependent, while neuroprotection and restoration of LTP were both shown to be dependent upon GPR30, a G-protein coupled receptor mediating estrogenic function. Finally, the observation that an NO-SERM shows enhanced vasodilation and anticoagulant activity, while retaining the positive attributes of SERMs even in the presence of NOS dysfunction, indicates a potential therapeutic approach without the increased risk of thrombotic events.