Diminished global arginine bioavailability as a metabolic defect in chronic systolic heart failure

A Low Arginine/Ornithine Ratio is Associated with Long-Term Cardiovascular Mortality

AIMS

The long-term prognostic value of the bioavailability of L-arginine, an important source of nitric oxide for the maintenance of vascular endothelial function, has not been investigated fully. We therefore investigated the relationship between amino acid profile and long-term prognosis in patients with a history of standby coronary angiography.

METHODS

We measured the serum concentrations of L-arginine, L-citrulline, and L-ornithine by high-speed liquid chromatography. We examined the relationship between the L-arginine/L-ornithine ratio and the incidence of all-cause death, cardiovascular death, and major adverse cardiovascular events (MACEs) in 262 patients (202 men and 60 women, age 65±13 years) who underwent coronary angiography over a period of ≤ 10 years.

RESULTS

During the observation period of 5.5±3.2 years, 31 (12%) patients died, including 20 (8%) of cardiovascular death, while 32 (12%) had MACEs. Cox regression analysis revealed that L-arginine/L-ornithine ratio was associated with an increased risk for all-cause death (unadjusted hazard ratio, 95% confidence interval) (0.940, 0.888-0.995) and cardiovascular death (0.895, 0.821-0.965) (p＜0.05 for all). In a model adjusted for age, sex, hypertension, hyperlipidemia, diabetes, current smoking, renal function, and log10-transformed brain natriuretic peptide level, cardiovascular death (0.911, 0.839-0.990, p=0.028) retained an association with a low L-arginine/ L-ornithine ratio. When the patients were grouped according to an L-arginine/L-ornithine ratio of 1.16, the lower L-arginine/L-ornithine ratio group had significantly higher incidence of all-cause death, cardiovascular death, and MACEs.

CONCLUSION

A low L-arginine/L-ornithine ratio may be associated with increased 10-year cardiac mortality.

Arginine Dysregulation and Myocardial Dysfunction in a Mouse Model and Children with Chronic Kidney Disease

Cardiovascular disease is the leading cause of death in chronic kidney disease (CKD). Arginine, the endogenous precursor for nitric oxide synthesis, is produced in the kidneys. Arginine bioavailability contributes to endothelial and myocardial dysfunction in CKD. Plasma from 129X1/SvJ mice with and without CKD (5/6th nephrectomy), and banked plasma from children with and without CKD were analyzed for amino acids involved in arginine metabolism, ADMA, and arginase activity. Echocardiographic measures of myocardial function were compared with plasma analytes. In a separate experiment, a non-specific arginase inhibitor was administered to mice with and without CKD. Plasma citrulline and glutamine concentrations correlated with multiple measures of myocardial dysfunction. Plasma arginase activity was significantly increased in CKD mice at 16 weeks vs. 8 weeks (p = 0.002) and ventricular strain improved after arginase inhibition in mice with CKD (p = 0.03). In children on dialysis, arginase activity was significantly increased vs. healthy controls (p = 0.04). Increasing ADMA correlated with increasing RWT in children with CKD (r = 0.54; p = 0.003). In a mouse model, and children, with CKD, arginine dysregulation correlates with myocardial dysfunction.

L-arginine and Its Derivatives Correlate with Exercise Capacity in Patients with Advanced Heart Failure

Methylated arginine metabolites interrupt nitric oxide synthesis, which can result in endothelium dysfunction and inadequate vasodilation. Since little is known about the dynamics of arginine derivatives in patients with heart failure (HF) during physical exercise, we aimed to determine this as well as its impact on the patient outcomes. Fifty-one patients with HF (left ventricle ejection fraction-LVEF ≤ 35%, mean 21.7 ± 5.4%) underwent the cardiopulmonary exercise test (CPET). Plasma concentrations of L-arginine, citrulline, ornithine, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA) were measured before and directly after CPET. All patients were followed for a mean of 23.5 ± 12.6 months. The combined endpoint was: any death, urgent heart transplantation, or urgent LVAD implantation. L-arginine concentrations increased significantly after CPET (p = 0.02), when ADMA (p = 0.01) and SDMA (p = 0.0005) decreased. The parameters of better exercise capacity were positively correlated with post-CPET concentration of L-arginine and inversely with post-CPET changes in ADMA, SDMA, and baseline and post-CPET SDMA concentrations. Baseline and post-CPET SDMA concentrations increased the risk of endpoint occurrence (HR 1.02, 95% CI 1.009–1.03, p = 0.04 and HR 1.02, 95% CI 1.01–1.03, p = 0.02, respectively). In conclusion, in patients with HF, extensive exercise is accompanied by changes in arginine derivatives that can reflect endothelium function. These observations may contribute to the explanation of the pathophysiology of exercise intolerance in HF.

Blood metabolomes as non-invasive biomarkers and targets of metabolic interventions for doxorubicin and trastuzumab-induced cardiotoxicity

This study aimed to identify the alterations of blood metabolome levels and their association with cardiac dysfunction and cardiac injury following treatment with doxorubicin and trastuzumab. Eight-week-old male Wistar rats were divided into four groups (n = 6 per group) to receive intraperitoneal injection with either: (1) 1 mL of normal saline solution (NSS) at days 0, 4, 8, 15, 22, and 29 (control group for doxorubicin); (2) 3 mg/kg/day of doxorubicin at days 0, 4, 8, 15, 22, and 29 (doxorubicin group); (3) 1 mL of NSS at days 0-6 (control group for trastuzumab); or (4) 4 mg/kg/day of trastuzumab at days 0-6 (trastuzumab group). Four days after the last injected dose, cardiac function was determined. The rats were then euthanized to collect venous blood and the heart for the quantification of 107 serum and 100 cardiac metabolomes using mass spectrometry-based targeted metabolomics. We observed strong relationships between 72 cardiac versus 61 serum metabolomes in doxorubicin and trastuzumab groups. Moreover, significant correlations between cardiac function and the cardiac injury biomarker versus 28 and 58 serum metabolomes were revealed in doxorubicin and trastuzumab-treated rats, respectively. Interestingly, the patterns of both serum and cardiac metabolome alterations differed between doxorubicin and trastuzumab groups. Our findings emphasize the potential role of the constituents of the blood metabolome as non-invasive biomarkers to assess severity and prognosis of heart failure induced by doxorubicin and trastuzumab. These findings may contribute to the development of metabolic-targeted therapy specific for cardioprotection during different phases of cancer treatment.

Homoarginine in the cardiovascular system: Pathophysiology and recent developments

Upcoming experimental and epidemiological data have identified the endogenous non-proteinogenic amino acid L-homoarginine (L-hArg) not only as a novel biomarker for cardiovascular disease but also as being directly involved in the pathogenesis of cardiac dysfunction. The association of low L-hArg levels with adverse cardiovascular events and mortality has proposed the idea of nutritional supplementation to rescue pathways inversely associated with cardiovascular health. Subsequent clinical and experimental studies contributed significantly to our knowledge of potential effects on the cardiorenal axis, acting either as a biomarker or a cardiovascular active agent. In this review article, we provide a comprehensive summary of the L-hArg metabolism, pathophysiological aspects, and current developments in the field of experimental and clinical evidence in favor of protective cardiovascular effects. Establishing a reliable biomarker to identify patients at high risk to die of cardiovascular disease represents one of the main goals for tackling this disease and providing individual therapeutic guidance.

Implications for the Metabolic Fate of Oral Glutamine Supplementation within Plasma and Erythrocytes of Patients with Sickle Cell Disease: A Pharmacokinetics Study

OBJECTIVES

L-Glutamine is FDA-approved for sickle cell disease (SCD), yet the mechanism(s)-of-action are poorly understood. We performed a pharmacokinetics (pK) study to determine the metabolic fate of glutamine supplementation on plasma and erythrocyte amino acids in patients with SCD.

DESIGN

A pK study was performed where patients with SCD fasting for >8hours received oral L-glutamine (10 grams). Blood was analyzed at baseline, 30/60/90minutes/2/3/4/8 hrs. A standardized diet was administered to all participants at 3 established time-points (after 2/5/7hrs). A subset of patients also had pK studies performed without glutamine supplementation to follow normal diurnal fluctuations in amino acids.

SETTING

Comprehensive SCD Center in Oakland, California RESULTS: Five patients with SCD were included, three of whom performed pK studies both with and without glutamine supplementation. Average age was 50.6 ± 5.6 years, 60% were female, 40% SS, 60% SC. Plasma glutamine levels increased significantly after oral glutamine supplementation, compared to minimal fluctuations with diet. Plasma glutamine concentration peaked within 30-minutes of ingestion (p=0.01) before decreasing to a plateau by 2-hours that remained higher than baseline by 8hours. Oral glutamine also increased plasma arginine concentration, which peaked by 4-hrs (p=0.03) and remained elevated through 8-hrs. Erythrocyte glutamine levels began to increase by 8-hours, while erythrocyte arginine concentration peaked at 4-hours.

CONCLUSIONS

Oral glutamine supplementation acutely improved glutamine and arginine bioavailability in both plasma and erythrocytes. This is the first study to demonstrate that glutamine therapy increases arginine bioavailability and may provide insight into shared mechanisms-of-action between these conditionally-essential amino acids.

Metabolomic Profiling of Adults with Congenital Heart Disease

Metabolomic analysis may provide an integrated assessment in genetically and pathologically heterogeneous populations. We used metabolomic analysis to gain mechanistic insight into the small and diverse population of adults with congenital heart disease (ACHD). Consecutive ACHD patients seen at a single institution were enrolled. Clinical variables and whole blood were collected at regular clinical visits. Stored plasma samples were analyzed for the concentrations of 674 metabolites and metabolic markers using mass spectrometry with internal standards. These samples were compared to 28 simultaneously assessed healthy non-ACHD controls. Principal component analysis and multivariable regression modeling were used to identify metabolites associated with clinical outcomes in ACHD. Plasma from ACHD and healthy control patients differed in the concentrations of multiple metabolites. Differences between control and ACHD were greater in number and in degree than those between ACHD anatomic groups. A metabolite cluster containing amino acids and metabolites of amino acids correlated with negative clinical outcomes across all anatomic groups. Metabolites in the arginine metabolic pathway, betaine, dehydroepiandrosterone, cystine, 1-methylhistidine, serotonin and bile acids were associated with specific clinical outcomes. Metabolic markers of disease may both be useful as biomarkers for disease activity and suggest etiologically related pathways as possible targets for disease-modifying intervention.

Intestinal Microbiota in Cardiovascular Health and Disease: JACC State-of-the-Art Review

Despite major strides in reducing cardiovascular disease (CVD) burden with modification of classic CVD risk factors, significant residual risks remain. Recent discoveries that linked intestinal microbiota and CVD have broadened our understanding of how dietary nutrients may affect cardiovascular health and disease. Although next-generation sequencing techniques can identify gut microbial community participants and provide insights into microbial composition shifts in response to physiological responses and dietary exposures, provisions of prebiotics or probiotics have yet to show therapeutic benefit for CVD. Our evolving understanding of intestinal microbiota-derived physiological modulators (e.g., short-chain fatty acids) and pathogenic mediators (e.g., trimethylamine N-oxide) of host disease susceptibility have created novel potential therapeutic opportunities for improved cardiovascular health. This review discusses the roles of human intestinal microbiota in normal physiology, their associations with CVD susceptibilities, and the potential of modulating intestinal microbiota composition and metabolism as a novel therapeutic target for CVD.

Novel Markers of the Metabolic Impact of Exogenous Retinoic Acid with A Focus on Acylcarnitines and Amino Acids

Treatment with all-trans retinoic acid (ATRA), the carboxylic form of vitamin A, lowers body weight in rodents by promoting oxidative metabolism in multiple tissues including white and brown adipose tissues. We aimed to identify novel markers of the metabolic impact of ATRA through targeted blood metabolomics analyses, with a focus on acylcarnitines and amino acids. Blood was obtained from mice treated with a high ATRA dose (50 mg/kg body weight/day, subcutaneous injection) or placebo (controls) during the 4 days preceding collection. LC-MS/MS analyses with a focus on acylcarnitines and amino acids were conducted on plasma and PBMC. Main results showed that, relative to controls, ATRA-treated mice had in plasma: increased levels of carnitine, acetylcarnitine, and longer acylcarnitine species; decreased levels of citrulline, and increased global arginine bioavailability ratio for nitric oxide synthesis; increased levels of creatine, taurine and docosahexaenoic acid; and a decreased n-6/n-3 polyunsaturated fatty acids ratio. While some of these features likely reflect the stimulation of lipid mobilization and oxidation promoted by ATRA treatment systemically, other may also play a causal role underlying ATRA actions. The results connect ATRA to specific nutrition-modulated biochemical pathways, and suggest novel mechanisms of action of vitamin A-derived retinoic acid on metabolic health.

l-arginine alleviates doxorubicin-induced endothelium-dependent dysfunction by promoting nitric oxide generation and inhibiting apoptosis

BACKGROUND/AIMS

Patients with doxorubicin (Dox) treatment have a high risk of developing vascular toxicity with an unknown mechanism. l-arginine is a substrate for nitric oxide (NO). The decreased level of arginine-NO metabolite in Dox-treated cancer patients was associated with increased level of vascular damage, which promoted us to investigate the mechanism of Dox-induced vascular dysfunction and verify whether l-arginine supplement could alleviate this vasculotoxic effect.

METHOD

Within a mouse model of Dox injection (5 mg/kg i.p., 2 or 4 weeks), we measured vascular relaxation, blood pressure, vascular NO generation, apoptosis, and oxidative stress. We tested the efficacy of l-arginine (1.5 mg/g/day, 4 weeks) on Dox-induced vascular relaxation, blood pressure, vascular NO generation, apoptosis, as well as oxidative stress.

RESULTS

Dox induced endothelium-dependent vascular dysfunction, which was associated with increased reactive oxidative stress (ROS) production and reduced NO generation in the vessel. ROS was required for Dox-induced apoptosis of both smooth muscle cells and endothelial cells. Dox treatment in mice increased blood pressure, but had no effect on vascular inflammation and fibrosis. L-aringine restored Dox-induced vascular dysfunction via enhancing vascular NO production and alleviating ROS-mediated apoptosis.

CONCLUSION

We for the first time demonstrated l-arginine was effectively in suppressing Dox-induced vascular dysfunction, by attenuating vascular NO release and apoptosis. Our results provide a therapeutic target or a circulating marker for assessing vascular dysfunction which response to Dox treatment, and advance our understanding of the mechanisms of Dox-induced vascular dysfunction.

Targeted Metabolomic Profiling of Plasma and Survival in Heart Failure Patients

OBJECTIVES

This study sought to derive and validate plasma metabolite associations with survival in heart failure (HF) patients.

BACKGROUND

Profiling of plasma metabolites to predict the course of HF appears promising, but validation and incremental value of these profiles are less established.

METHODS

Patients (n = 1,032) who met Framingham HF criteria with a history of reduced ejection fraction were randomly divided into derivation and validation cohorts (n = 516 each). Amino acids, organic acids, and acylcarnitines were quantified using mass spectrometry in fasting plasma samples. We derived a prognostic metabolite profile (PMP) in the derivation cohort using Lasso-penalized Cox regression. Validity was assessed by 10-fold cross validation in the derivation cohort and by standard testing in the validation cohort. The PMP was analyzed as both a continuous variable (PMPscore) and dichotomized at the median (PMPcat), in univariate and multivariate models adjusted for clinical risk score and N-terminal pro-B-type natriuretic peptide.

RESULTS

Overall, 48% of patients were African American, 35% were women, and the average age was 69 years. After a median follow-up of 34 months, there were 256 deaths (127 and 129 in derivation and validation cohorts, respectively). Optimized modeling defined the 13 metabolite PMPs, which was cross validated as both the PMPscore (hazard ratio [HR]: 3.27; p < 2 × 10^-16) and PMPcat (HR: 3.04; p = 2.93 × 10^-8). The validation cohort showed similar results (PMPscore HR: 3.9; p < 2 × 10^-16 and PMPcat HR: 3.99; p = 3.47 × 10^-9). In adjusted models, PMP remained associated with mortality in the cross-validated derivation cohort (PMPscore HR: 1.63; p = 0.0029; PMPcat HR: 1.47; p = 0.081) and the validation cohort (PMPscore HR: 1.54; p = 0.037; PMPcat HR: 1.69; p = 0.043).

CONCLUSIONS

Plasma metabolite profiles varied across HF subgroups and were associated with survival incremental to conventional predictors. Additional investigation is warranted to define mechanisms and clinical applications.

Elevated levels of plasma symmetric dimethylarginine and increased arginase activity as potential indicators of cardiovascular comorbidity in rheumatoid arthritis

Background

Rheumatoid arthritis (RA) patients are at high risk of developing cardiovascular disease (CVD). In RA, chronic inflammation may lead to endothelial dysfunction, an early indicator of CVD, owing to diminished nitric oxide (NO) production. Because l-arginine is the sole precursor of NO, we hypothesized that levels of l-arginine metabolic products reflecting NO metabolism are altered in patients with RA.

Methods

Plasma samples from patients with RA (n = 119) and age- and sex-matched control subjects (n = 238) were used for this study. Using LC-MS/MS, we measured plasma levels of free l-arginine, l-ornithine, l-citrulline, l-N^G-monomethyl arginine (MMA), asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). We compared global arginine bioavailability ratio (GABR) (i.e., ratio of l-arginine to l-ornithine + l-citrulline) and arginine methylation index (ArgMI) (i.e., ADMA + SDMA/MMA) in patients with RA vs. control subjects. Plasma arginase activity was measured using a sensitive arginase assay kit. The relationship of l-arginine metabolites and arginase activity to CVD risk factors was evaluated using Pearson’s chi-square test.

Results

Compared with healthy control subjects, the RA cohort showed significantly lower levels of plasma l-arginine (46.11 ± 17.29 vs. 74.2 ± 22.53 μmol/L, p < 0.001) and GABR (0.36 ± 0.16 vs. 0.73 ± 0.24, p < 0.001), elevated levels of ADMA (0.76 ± 0.12 vs. 0.62 ± 0.12 μmol/L, p < 0.001), SDMA (0.54 ± 0.14 vs. 0.47 ± 0.13 μmol/L, p < 0.001), and ArgMI (6.51 ± 1.86 vs. 5.54 ± 1.51, p < 0.001). We found an approximately fourfold increase in arginase activity (33.8 ± 1.1 vs. 8.4 ± 0.8 U/L, p < 0.001), as well as elevated levels of arginase-mediated l-arginine catalytic product l-ornithine (108.64 ± 30.26 vs. 69.3 ± 20.71 μmol/L, p < 0.001), whereas a nitric oxide synthase (NOS) catalytic product, the l-citrulline level, was diminished in RA (30.32 ± 9.93 vs. 36.17 ± 11.64 μmol/L, p < 0.001). Patients with RA with existing CVD had higher arginase activity than patients with RA without CVD (p = 0.048).

Conclusions

Global l-arginine bioavailability was diminished, whereas plasma arginase activity, ADMA, and SDMA levels were elevated, in patients with RA compared with healthy control subjects. Plasma SDMA was associated with hypertension and hyperlipidemia in patients with RA. This dysregulated l-arginine metabolism may function as a potential indicator of CVD risk in patients with RA.

A relative L-arginine deficiency contributes to endothelial dysfunction across the stages of the menopausal transition

Vascular endothelial function declines across the menopause transition in women. We tested the hypothesis that reduced availability of the endothelial nitric oxide synthase [eNOS] substrate L‐arginine is an underlying mechanism to vascular endothelial dysfunction across menopause stages. Endothelial function (brachial artery flow‐mediated dilation [FMD]) and plasma markers of L‐arginine metabolism (citrulline, N^G‐mono‐methyl‐ւ‐arginine [L‐NMMA] asymmetric dimethylarginine [ADMA] and N^G‐N^′G‐dimethyl‐l‐arginine [SDMA]), were measured in 129 women: 36 premenopausal (33 ± 7 years), 16 early‐ (49 ± 3 years) or 21 late‐ (50 ± 4 years) perimenopausal, and 21 early‐ (55 ± 3 years) or 35 late‐ (61 ± 4 years) postmenopausal. FMD was progressively reduced across menopause stages (P < 0.001). Menopause stage was associated with L‐arginine concentrations (P = 0.012), with higher levels in early postmenopausal compared to early and late perimenopausal women (P < 0.05). The methylarginine and eNOS inhibitor L‐NMMA was higher in early and late postmenopausal women compared to premenopausal and early and late perimenopausal women (all P < 0.001), and was inversely correlated with FMD (r = −0.30, P = 0.001). The L‐arginine/L‐NMMA ratio, a potential biomarker of relative L‐arginine levels, was lower in postmenopausal compared to either premenopausal or perimenopausal women (both P < 0.001), and was positively correlated with FMD (r = 0.33, P < 0.001). There were no differences in plasma citrulline, ADMA or SDMA across groups. These data suggest that a relative L‐arginine deficiency may be a mechanism underlying the decline in endothelial function with the menopause transition in women. The relative L‐arginine deficiency may be related to elevated levels of the methylarginine L‐NMMA, which would compete with L‐arginine for eNOS and for intracellular transport, reducing NO biosynthesis.

Metabolic Biomarkers in Heart Failure

Metabolomics is the study of small, organic molecules within biochemical pathways. With advancement of technology, nuclear magnetic resonance, gas chromatography, and mass spectrometry have allowed for the discovery and analysis of large databases of metabolites implicated in heart failure. Metabolomics also explores the patient and environment interactions and unlocks the link between environmental exposures and the development of cardiovascular disease. Although a relatively new field, metabolomics is poised to become a clinically impactful field that develops novel biomarkers and explores new therapeutic interventions in heart failure.

Alterations in plasma L-arginine and methylarginines in heart failure and after heart transplantation

OBJECTIVE

Endothelial function, including the nitric oxide (NO)-pathway, has previously been extensively investigated in heart failure (HF). In contrast, studies are lacking on the NO pathway after heart transplantation (HT). We therefore investigated substances in the NO pathway prior to and after HT in relation to hemodynamic parameters.

DESIGN

12 patients (median age 50.0 yrs, 2 females), heart transplanted between June 2012 and February 2014, evaluated at our hemodynamic lab, at rest, prior to HT, as well as four weeks and six months after HT were included. All patients had normal left ventricular function post-operatively and none had post-operative pulmonary hypertension or acute cellular rejection requiring therapy at the evaluations. Plasma concentrations of ADMA, SDMA, L-Arginine, L-Ornithine and L-Citrulline were analyzed at each evaluation.

RESULTS

In comparison to controls, the plasma L-Arginine concentration was low and ADMA high in HF patients, resulting in low L-Arginine/ADMA-ratio pre-HT. Already four weeks after HT L-Arginine was normalized whereas ADMA remained high. Consequently the L-Arginine/ADMA-ratio improved, but did not normalize. The biomarkers remained unchanged at the six-month evaluation and the L-Arginine/ADMA-ratio correlated inversely to pulmonary vascular resistance (PVR) six months post-HT.

CONCLUSIONS

Plasma L-Arginine concentrations normalize after HT. However, as ADMA is unchanged, the L-Arginine/ADMA-ratio remained low and correlated inversely to PVR. Together these findings suggest that (i) the L-Arginine/ADMA-ratio may be an indicator of pulmonary vascular tone after HT, and that (ii) NO-dependent endothelial function is partly restored after HT. Considering the good postoperative outcome, the biomarker levels may be considered "normal" after HT.

Effects of l-arginine supplementation associated with continuous or interval aerobic training on chronic heart failure rats

OBJECTIVE

Chronic heart failure (CHF) is related with exercise intolerance and impaired nitric oxide (NO) production, which can lead to several functional capacity alterations. Considering the possible superiority of aerobic interval training compared to continuous training and the capacity of l-arginine to restore the NO pathway, the aim of the present study was to investigate whether these treatments are beneficial to exercise capacity, muscle mass preservation and hemodynamic, inflammatory and oxidative stress parameters in CHF rats.

METHODS

Thirty-eight male Wistar rats post 6weeks of myocardial infarction (MI) surgery were randomly assigned into 6 CHF groups: sedentary (SED, n=6); SED+Arg (n=7); ACT (n=8); ACT+Arg (n=5); AIT (n=7); AIT+Arg (n=5). Exercise test capacity (ETC) was performed pre and post 8weeks of intervention. Supplemented rats received Arg (1g/kg) by oral gavage (7×/week). Exercise training was performed on a rat treadmill (5×/week). Hemodynamic variables, tissue collection, congestion, inflammatory cytokines, and oxidative parameters were evaluated at the end of protocols.

RESULTS

All trained groups showed a superior exercise capacity compared to SED groups on the post-intervention test (p<0.0001). Pulmonary congestion was attenuated in AIT and AIT+Arg compared with the SED group (p<0.05). Left ventricular end-diastolic pressure (LVEDP) was lower in ACT+Arg, AIT, and AIT+Arg groups than SED group (p<0.05). Association of AIT with Arg supplementation was able to improve hemodynamic responses (left ventricular systolic pressure (LVSP), systolic blood pressure (SBP), +dP/dt_max, and -dP/dt_max (p<0.05), likewise, decrease muscular and renal lipid peroxidation and tumor necrosis factor (TNF)-α, and increase interleukin (IL)-10/TNF-α plasmatic levels (p<0.01). Groups that associated aerobic exercise with Arg supplementation (ACT+Arg and AIT+Arg) revealed higher gastrocnemius mass compared to the SED group (p<0.01).

CONCLUSIONS

Both aerobic training protocols were capable to improve aerobic capacity, and the association with Arg supplementation was important to attenuate muscle loss. Moreover, interval training associated with Arg supplementation elicits greater improvements in hemodynamic parameters, contributing to reduction in pulmonary congestion, and demonstrated particular responses in the inflammatory profile and in the antioxidant status.

Pathways to pulmonary hypertension in sickle cell disease: the search for prevention and early intervention

INTRODUCTION

Pulmonary hypertension (PH) develops in a significant number of patients with sickle cell disease (SCD), resulting in increased morbidity and mortality. This review focuses on PH pathophysiology, risk stratification, and new recommendations for screening and treatment for patients with SCD. Areas covered: An extensive PubMed literature search was performed. While the pathophysiology of PH in SCD is yet to be fully deciphered, it is known that the etiology is multifactorial; hemolysis, hypercoagulability, hypoxemia, ischemic-reperfusion injury, oxidative stress, and genetic susceptibility all contribute in varying degrees to endothelial dysfunction. Hemolysis, in particular, seems to play a key role by inciting an imbalance in the regulatory axis of nitric oxide and arginine metabolism. Systematic risk stratification starting in childhood based on clinical features and biomarkers that enable early detection is necessary. Multi-faceted, targeted interventions, before irreversible vasculopathy develops, will allow for improved patient outcomes and life expectancy. Expert commentary: Despite progress in our understanding of PH in SCD, clinically proven therapies remain elusive and additional controlled clinical trials are needed. Prevention of disease starts in childhood, a critical window for intervention. Given the complex and multifactorial nature of SCD, patients will ultimately benefit from combination therapies that simultaneously targets multiple mechanisms.

Arginine-Nitric Oxide Metabolites and Cardiac Dysfunction in Patients With Breast Cancer

BACKGROUND

Oxidative/nitrosative stress and endothelial dysfunction are hypothesized to be central to cancer therapeutics-related cardiac dysfunction (CTRCD). However, the relationship between circulating arginine-nitric oxide (NO) metabolites and CTRCD remains unstudied.

OBJECTIVES

This study sought to examine the relationship between arginine-NO metabolites and CTRCD in a prospective cohort of 170 breast cancer patients treated with doxorubicin with or without trastuzumab.

METHODS

Plasma levels of arginine, citrulline, ornithine, asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and N-monomethylarginine (MMA) were quantified at baseline, 1 month, and 2 months after doxorubicin initiation. Determinants of baseline biomarker levels were identified using multivariable linear regression, and Cox regression defined the association between baseline levels and 1- or 2-month biomarker changes and CTRCD rate in 139 participants with quantitated echocardiograms at all time points.

RESULTS

Age, hypertension, body mass index, and African-American race were independently associated with ≥1 of baseline citrulline, ADMA, SDMA, and MMA levels. Decreases in arginine and citrulline and increases in ADMA were observed at 1 and 2 months (all p < 0.05). Overall, 32 participants experienced CTRCD over a maximum follow-up of 5.4 years. Hazard ratios for ADMA and MMA at 2 months were 3.33 (95% confidence interval [CI]: 1.12 to 9.96) and 2.70 (95% CI: 1.35 to 5.41), respectively, and 0.78 (95% CI: 0.64 to 0.97) for arginine at 1 month.

CONCLUSIONS

In breast cancer patients undergoing doxorubicin therapy, early alterations in arginine-NO metabolite levels occurred, and early biomarker changes were associated with a greater CTRCD rate. Our findings highlight the potential mechanistic and translational relevance of this pathway to CTRCD.

Relation between change in exercise capacity and change in blood amino acids in patients with chronic heart failure

[Purpose] Although cardiac rehabilitation (CR) is recommended for patients with chronic heart failure (CHF), adequate exercise effect cannot be obtained in elderly patients. Administration of amino acids (AA) to CHF patients has been reported to improve exercise capacity, but the changes in AA composition in plasma before and after CR had not been reported. This study aimed to measure plasma levels of AA in CHF patients and compare with values of normal range. In addition the relationship between the change of exercise capacity and AA were examined. [Subjects and Methods] Twelve CHF patients (60% males, aged 68 ± 12 years) were studied. The correction between the rates of changes in exercise capacity parameters and in plasma AA levels was investigated. [Results] Anaerobic threshold (AT) and peak oxygen uptake (VO2) improved significantly after CR. The AA profile showed no specific pattern, and citrulline (Cit) was the amino acid showing a significant positive correlation with exercise capacity (∆Cit vs. ∆AT: r=0.602, ∆Cit vs. ∆AT-work rate (WR): r=0.681, ∆Cit vs. ∆VO2/WR: r=0.635). A tendency of positive correlation was observed between ∆Cit and ∆peak VO2 (r=0.456). [Conclusion] The AA profile showed no specific pattern, but a relationship between change in exercise capacity and Cit were found.

Acquired Amino Acid Deficiencies: A Focus on Arginine and Glutamine

Nonessential amino acids are synthesized de novo and therefore not diet dependent. In contrast, essential amino acids must be obtained through nutrition since they cannot be synthesized internally. Several nonessential amino acids may become essential under conditions of stress and catabolic states when the capacity of endogenous amino acid synthesis is exceeded. Arginine and glutamine are 2 such conditionally essential amino acids and are the focus of this review. Low arginine bioavailability plays a pivotal role in the pathogenesis of a growing number of varied diseases, including sickle cell disease, thalassemia, malaria, acute asthma, cystic fibrosis, pulmonary hypertension, cardiovascular disease, certain cancers, and trauma, among others. Catabolism of arginine by arginase enzymes is the most common cause of an acquired arginine deficiency syndrome, frequently contributing to endothelial dysfunction and/or T-cell dysfunction, depending on the clinical scenario and disease state. Glutamine, an arginine precursor, is one of the most abundant amino acids in the body and, like arginine, becomes deficient in several conditions of stress, including critical illness, trauma, infection, cancer, and gastrointestinal disorders. At-risk populations are discussed together with therapeutic options that target these specific acquired amino acid deficiencies.

Global arginine bioavailability, a marker of nitric oxide synthetic capacity, is decreased in PTSD and correlated with symptom severity and markers of inflammation

INTRODUCTION

Psychiatric, physical and biological aspects of posttraumatic stress disorder (PTSD) may be associated with dysfunctions in several cellular processes including nitric oxide (NO) production. NO is synthesized from arginine in a reaction carried out by NO synthase (NOS) enzymes. The recently introduced "global arginine bioavailability ratio" (GABR; ratio of arginine to [ornithine+citrulline]) has been proposed as a reliable approximation of NO synthetic capacity in vivo. The objectives of the present study were to test the hypotheses that (i) subjects with combat-related PTSD have lower GABR scores than combat controls, (ii) GABR score is inversely associated with the severity of psychopathological measures, (iii) GABR score is inversely associated with markers of inflammation.

METHODS

Metabolic profiling for plasma samples (i.e. arginine, citrulline and ornithine) and inflammation markers (interleukin [IL]-6, IL-1β, tumor necrosis factor [TNF]-α, interferon [IFN]-γ and C-reactive protein [CRP]) were assessed in 56 combat-exposed males with PTSD and 65 combat-exposed males without PTSD. We assessed severity of PTSD (Clinician Administered PTSD Scale [CAPS]) and depression (Beck Depression Inventory-II [BDI-II]) as well as history of early life trauma (Early Trauma Inventory [ETI]) and affectivity (Positive and Negative Affect Schedule [PANAS]).

RESULTS

The GABR value was (i) significantly lower in PTSD subjects compared to controls (p=0.001), (ii) significantly inversely correlated with markers of inflammation including IL6 (p=0.04) and TNFα (p=0.02), and (iii) significantly inversely correlated with CAPS current (p=0.001) and lifetime (p<0.001) subscales, ETI (p=0.045) and PANAS negative (p=0.006). Adding antidepressant use or MDD diagnosis as covariates led to similar results. Adding age and BMI as covariates also led to similar results, with the exception of IL6 and ETI losing their significant association with GABR.

DISCUSSION

This study provides the first evidence that global arginine bioavailability, a marker of NO synthetic capacity in vivo, is lower in veterans with PTSD and is negatively associated with some markers of inflammation as well as with measures of PTSD symptom severity, negative affectivity and childhood adverse experiences. These findings add to the accumulating evidence that specific cellular dysfunction may be associated with the symptomatology of PTSD and may help to explain the higher burden of cardio-metabolic disturbances seen in this disorder.

Strategies to increase nitric oxide signalling in cardiovascular disease

Nitric oxide (NO) is a key signalling molecule in the cardiovascular, immune and central nervous systems, and crucial steps in the regulation of NO bioavailability in health and disease are well characterized. Although early approaches to therapeutically modulate NO bioavailability failed in clinical trials, an enhanced understanding of fundamental subcellular signalling has enabled a range of novel therapeutic approaches to be identified. These include the identification of: new pathways for enhancing NO synthase activity; ways to amplify the nitrate-nitrite-NO pathway; novel classes of NO-donating drugs; drugs that limit NO metabolism through effects on reactive oxygen species; and ways to modulate downstream phosphodiesterases and soluble guanylyl cyclases. In this Review, we discuss these latest developments, with a focus on cardiovascular disease.

Dysregulated arginine metabolism and cardiopulmonary dysfunction in patients with thalassaemia

Pulmonary hypertension (PH) commonly develops in thalassaemia syndromes, but is poorly characterized. The goal of this study was to provide a comprehensive description of the cardiopulmonary and biological profile of patients with thalassaemia at risk for PH. A case-control study of thalassaemia patients at high versus low PH-risk was performed. A single cross-sectional measurement for variables reflecting cardiopulmonary status and biological pathophysiology were obtained, including Doppler-echocardiography, 6-min-walk-test, Borg Dyspnoea Score, New York Heart Association functional class, cardiac magnetic resonance imaging (MRI), chest-computerized tomography, pulmonary function testing and laboratory analyses targeting mechanisms of coagulation, inflammation, haemolysis, adhesion and the arginine-nitric oxide pathway. Twenty-seven thalassaemia patients were evaluated, 14 with an elevated tricuspid-regurgitant-jet-velocity (TRV) ≥ 2·5 m/s. Patients with increased TRV had a higher frequency of splenectomy, and significantly larger right atrial size, left atrial volume and left septal-wall thickness on echocardiography and/or MRI, with elevated biomarkers of abnormal coagulation, lactate dehydrogenase (LDH) levels and arginase concentration, and lower arginine-bioavailability compared to low-risk patients. Arginase concentration correlated significantly to several echocardiography/MRI parameters of cardiovascular function in addition to global-arginine-bioavailability and biomarkers of haemolytic rate, including LDH, haemoglobin and bilirubin. Thalassaemia patients with a TRV ≥ 2·5 m/s have additional echocardiography and cardiac-MRI parameters suggestive of right and left-sided cardiac dysfunction. In addition, low arginine bioavailability may contribute to cardiopulmonary dysfunction in β-thalassaemia.

Alterations of the arginine metabolome in sickle cell disease: a growing rationale for arginine therapy

Low global arginine bioavailability (GAB) is associated with numerous complications of SCD including early mortality. Mechanisms of arginine dysregulation involve a complex paradigm of excess activity of the arginine-consuming enzyme arginase, elevated levels of asymmetric dimethylarginine, altered intracellular arginine transport, and nitric oxide synthase dysfunction. Restoration of GAB through exogenous supplementation is therefore, a promising therapeutic target. Studies of arginine therapy demonstrate efficacy in treating patients with leg ulcers, pulmonary hypertension risk, and pain. Co-administration with hydroxyurea increases levels of nitrite and fetal hemoglobin. Addressing the alterations in the arginine metabolome may result in new strategies for treatment of SCD.

Arginase inhibition augments nitric oxide production and facilitates left ventricular systolic function in doxorubicin-induced cardiomyopathy in mice

A metabolizing enzyme arginase can decrease nitric oxide (NO) production by competing with NO synthase for arginine as a substrate, but its pathophysiological role in heart failure remains unknown. We aimed to investigate the effect of pharmacological inhibition of arginase on left ventricular function in doxorubicin‐induced cardiomyopathy in mice. Doxorubicin administration for 5 weeks significantly increased protein expression levels or activity of arginase in the lungs and liver, and caused moderate increase in arginase 2 expression in the aorta. In the lungs, accumulated interstitial cells strongly expressed both arginase 1 and arginase 2 by doxorubicin administration. Echocardiography revealed that administration of a potent, reversible arginase inhibitor N‐omega‐hydroxy‐nor‐l‐arginine completely reversed doxorubicin‐induced decrease in the ejection fraction, in parallel with expression levels of BNP mRNA, without affecting apoptosis, hypertrophy, fibrosis, or macrophage infiltration in the left ventricle. Arginase inhibition reversibly lowered systolic blood pressure, and importantly, it recovered doxorubicin‐induced decline in NO concentration in the serum, lungs, and aorta. Furthermore, arginase inhibition stimulated NO secretion from aortic endothelial cells and peritoneal macrophages in vitro. In conclusion, pharmacological inhibition of arginase augmented NO concentration in the serum, lungs, and aorta, promoted NO‐mediated decrease in afterload for left ventricle, and facilitated left ventricular systolic function in doxorubicin‐induced cardiomyopathy in mice.

e12130

This figure shows that administration of an arginase inhibitor nor‐ NOHA facilitates LV systolic function in murine Dox‐induced cardiomyopathy.

Novel metabolic roles of L-arginine in body energy metabolism and possible clinical applications

Although the body can synthesize L-arginine, exogenous supplementation may be sometimes necessary, especially in particular conditions which results in depleted endogenous source. Among diseases and states when exogenous supplementation may be necessary are: burns, severe wounds, infections, insufficient circulation, intensive physical activity or sterility. In recent time, the attention was paid to the use of L-arginine supplementation by athletes during intensive sport activity, to enhance tissue growth and general performance, to potentiate the ergogenic potential and muscle tolerance to high intensive work and gas exchange threshold, to decrease ammonia liberation and recovery performance period and to improve wound healing. High-intensity exercise produces transient hyperammoniemia, presumably due to AMP catabolism. Catabolic pathways of AMP may involve its deamination or dephosphorylation, mainly in order to compensate fall in adenylate enrgy charge (AEC), due to AMP rise. The enzymes of purine metabolism have been documented to be particularly sensitive to the effect of dietary L-arginine supplementation. L-arginine supplementation leads to redirection of AMP deamination on account of increased AMP dephosphorylation and subsequent adenosine production and may increase ATP regeneration via activation of AMP kinase (AMPK) pathway. The central role of AMPK in regulating cellular ATP regeneration, makes this enzyme as a central control point in energy homeostasis. The effects of L-arginine supplementation on energy expenditure were successful independently of age or previous disease, in young sport active, elderly, older population and patients with angina pectoris.