Oral L-arginine supplementation improves endothelial function and ameliorates insulin sensitivity and inflammation in cardiopathic nondiabetic patients after an aortocoronary bypass

Role of Argininosuccinate Synthase 1 -Dependent L-Arginine Biosynthesis in the Protective Effect of Endothelial Sirtuin 3 Against Atherosclerosis

Atherosclerosis is initiated with endothelial cell (EC) dysfunction and vascular inflammation under hyperlipidemia. Sirtuin 3 (SIRT3) is a mitochondrial deacetylase. However, the specific role of endothelial SIRT3 during atherosclerosis remains poorly understood. The present study aims to study the role and mechanism of SIRT3 in EC function during atherosclerosis. Wild-type Sirt3f/f mice and endothelium-selective SIRT3 knockout Sirt3f/f; Cdh5Cre/+ (Sirt3EC-KO) mice are injected with adeno-associated virus (AAV) to overexpress PCSK9 and fed with high-cholesterol diet (HCD) for 12 weeks to induce atherosclerosis. Sirt3EC-KO mice exhibit increased atherosclerotic plaque formation, along with elevated macrophage infiltration, vascular inflammation, and reduced circulating L-arginine levels. In human ECs, SIRT3 inhibition resulted in heightened vascular inflammation, reduced nitric oxide (NO) production, increased reactive oxygen species (ROS), and diminished L-arginine levels. Silencing of SIRT3 results in hyperacetylation and deactivation of Argininosuccinate Synthase 1 (ASS1), a rate-limiting enzyme involved in L-arginine biosynthesis, and this effect is abolished in mutant ASS1. Furthermore, L-arginine supplementation attenuates enhanced plaque formation and vascular inflammation in Sirt3EC-KO mice. This study provides compelling evidence supporting the protective role of endothelial SIRT3 in atherosclerosis and also suggests a critical role of SIRT3-induced deacetylation of ASS1 by ECs for arginine synthesis.

Metabolomics of cerebrospinal fluid reveals prognostic biomarkers in pediatric status epilepticus

AIMS

Status epilepticus (SE) is the most common neurological emergency in pediatric patients. This study aimed to screen for prognostic biomarkers of SE in the cerebrospinal fluid (CSF) using metabolomics.

METHODS

Ultra-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (UPLC-QTOF-MS) was conducted to identify prognostic biomarkers in CSF metabolomics by comparing the poor outcome group (N = 13) with the good outcome group (N = 15) of children with SE. Differentially expressed metabolites were identified using Mann-Whitney U test corrected by Benjamini-Hochberg and partial least squares discriminant analysis (PLS-DA).

RESULTS

The PLS-DA model identified and validated significant metabolic differences between the poor and good outcome groups of children with SE (PLS-DA with R2 Y = 0.992 and Q2  = 0.798). A total of 49 prognosis-related metabolites were identified. Of these metabolites, 20 including glutamyl-glutamine, 3-iodothyronamine, and L-fucose had an area under the curve (AUC) ≥ 80% in prognostic prediction of SE. The logistic regression model combining glutamyl-glutamine and 3-iodothyronamine produced an AUC value of 0.976, with a sensitivity of 0.863 and specificity of 0.956. Pathway analysis revealed that dysregulation of the citrate cycle (TCA) and arginine biosynthesis may contribute to poor SE prognosis.

CONCLUSIONS

This study highlighted the prognosis-related metabolomic disturbances in the CSF of children with SE and identified potential prognostic biomarkers. A prognostic prediction model combining glutamyl-glutamine and 3-iodothyronamine with high predictive value was established.

Peanut skin procyanidins reduce intestinal glucose transport protein expression, regulate serum metabolites and ameliorate hyperglycemia in diabetic mice

One of diabetic characteristics is the postprandial hyperglycemia. Inhibiting glucose uptake may be beneficial for controlling postprandial blood glucose levels and regulating the glucose metabolism Peanut skin procyanidins (PSP) have shown a potential for lowering blood glucose; however, the underlying mechanism through which PSP regulate glucose metabolism remains unknown. In the current study, we investigated the effect of PSP on intestinal glucose transporters and serum metabolites using a mouse model of diabetic mice. Results showed that PSP improved glucose tolerance and systemic insulin sensitivity, which coincided with decreased expression of sodium-glucose cotransporter 1 and glucose transporter 2 in the intestinal epithelium induced by an activation of the phospholipase C β2/protein kinase C signaling pathway. Moreover, untargeted metabolomic analysis of serum samples revealed that PSP altered arachidonic acid, sphingolipid, glycerophospholipid, bile acids, and arginine metabolic pathways. The study provides new insight into the anti-diabetic mechanism of PSP and a basis for further research.

The effects of a comparatively higher dose of 1000 mg/kg/d of oral L- or D-arginine on the L-arginine metabolic pathways in male Sprague-Dawley rats

Oral L-arginine supplements are popular mainly for their nitric oxide mediated vasodilation, but their physiological impact is not fully known. L-arginine is a substrate of several enzymes including arginase, nitric oxide synthase, arginine decarboxylase, and arginine: glycine amidinotransferase (AGAT). We have published a study on the physiological impact of oral L- and D-arginine at 500 mg/kg/day for 4 wks in male Sprague-Dawley rats. We investigated the effects of oral L-arginine and D-arginine at a higher dose of 1000 mg/kg/d for a longer treatment duration of 16 wks in 9-week-old male Sprague-Dawley rats. We measured the expression and activity of L-arginine metabolizing enzymes, and levels of their metabolites in the plasma and various organs. L-arginine did not affect the levels of L-arginine and L-lysine in the plasma and various organs. L-arginine decreased arginase protein expression in the upper small intestine, and arginase activity in the plasma. It also decreased AGAT protein expression in the liver, and creatinine levels in the urine. L-arginine altered arginine decarboxylase protein expression in the upper small intestine and liver, with increased total polyamines plasma levels. Endothelial nitric oxide synthase protein was increased with D-arginine, the presumed metabolically inert isomer, but not L-arginine. In conclusion, oral L-arginine and D-arginine at a higher dose and longer treatment duration significantly altered various enzymes and metabolites in the arginine metabolic pathways, which differed from alterations produced by a lower dose shorter duration treatment published earlier. Further studies with differing doses and duration would allow for a better understanding of oral L-arginine uses, and evidence based safe and effective dose range and duration.

A Critical Review on Vasoactive Nutrients for the Management of Endothelial Dysfunction and Arterial Stiffness in Individuals under Cardiovascular Risk

Pathophysiological conditions such as endothelial dysfunction and arterial stiffness, characterized by low nitric oxide bioavailability, deficient endothelium-dependent vasodilation and heart effort, predispose individuals to atherosclerotic lesions and cardiac events. Nitrate (NO₃^-), L-arginine, L-citrulline and potassium (K⁺) can mitigate arterial dysfunction and stiffness by intensifying NO bioavailability. Dietary compounds such as L-arginine, L-citrulline, NO₃^- and K⁺ exert vasoactive effects as demonstrated in clinical interventions by noninvasive flow-mediated vasodilation (FMD) and pulse-wave velocity (PWV) prognostic techniques. Daily L-arginine intakes ranging from 4.5 to 21 g lead to increased FMD and reduced PWV responses. Isolated L-citrulline intake of at least 5.6 g has a better effect compared to watermelon extract, which is only effective on endothelial function when supplemented for longer than 6 weeks and contains at least 6 g of L-citrulline. NO₃^- supplementation employing beetroot at doses greater than 370 mg promotes hemodynamic effects through the NO₃^--NO2-/NO pathway, a well-documented effect. A potassium intake of 1.5 g/day can restore endothelial function and arterial mobility, where decreased vascular tone takes place via ATPase pump/hyperpolarization and natriuresis, leading to muscle relaxation and NO release. These dietary interventions, alone or synergically, can ameliorate endothelial dysfunction and should be considered as adjuvant therapies in cardiovascular diseases.

Differential benefits of physical training associated or not with L-arginine supplementation in rats with metabolic syndrome: evaluation of cardiovascular, autonomic and metabolic parameters

Metabolic syndrome (MetS) is characterized by endocrine-metabolic and cardiac alterations that increase the risk of cardiovascular disease, dyslipidemia, and type-2 diabetes mellitus. Dietary supplementation with L-Arginine (L-Arg) is beneficial for fat loss, while chronic aerobic exercise has several benefits in reversing cardiovascular, autonomic, and metabolic dysfunctions caused by obesity. However, the association between these two approaches has not yet been described. This study aimed to evaluate the possible benefits of physical training, with or without L-Arg supplementation, on cardiovascular, autonomic, and metabolic parameters in rats with MetS, which was induced by the subcutaneous administration of monosodium glutamate at 4 mg g^-1day^-1 in rats from the first to fifth day of life. Physical training on a treadmill and supplementation with L-Arg in adulthood were carried out concomitantly for 8 weeks. After this, the animals underwent femoral artery catheterization to record their cardiovascular parameters and autonomic modulation. Organs and blood were removed to measure levels of nitrite, glucose, and hepatic steatosis. In adult rats with MetS, supplementation with L-Arg in combination with physical training reduced hypertension, tachycardia, adipose tissue mass, free fatty acids, and hepatic steatosis. Supplementation with L-Arg and physical training separately was beneficial in reducing several aspects of MetS, but a combination of both was especially effective in reducing adipose tissue and hepatic steatosis. Together, the two therapies can form a good strategy to combat MetS.

Short-Term L-Citrulline Supplementation Does Not Affect Inspiratory Muscle Oxygenation and Respiratory Performance in Older Adults

In sports nutrition, nitric oxide (NO^•) precursors such as L-citrulline are widely used to enhance NO^• bioavailability, which is considered an ergogenic aid. Our study aimed to examine the effect of short-term L-citrulline supplementation on respiratory muscles' performance, fatigue, and oxygenation in older adults. Fourteen healthy older males took 6 g of L-citrulline or a placebo for seven days in a double-blind crossover design. Pulmonary function via spirometry (i.e., forced expired volume in 1 s (FEV₁), forced vital capacity (FVC), and their ratio)), fractional exhaled nitric oxide (NO^•), maximal inspiratory pressure (MIP), rate of perceived exertion, and sternocleidomastoid muscle oxygenation (i.e., oxyhemoglobin (Δ[O₂Hb]) and de-oxyhemoglobin (Δ[HHb]), total hemoglobin concentration (Δ[tHb]), and tissue saturation index (TSI%)) were evaluated at baseline, after seven days of L-citrulline supplementation, and after incremental resistive breathing to task failure of the respiratory muscles. The exhaled NO^• value was only significantly increased after the supplementation (26% p < 0.001) in the L-citrulline condition. Pulmonary function, MIP, rate of perceived exertion, and sternocleidomastoid muscle oxygenation were not affected by the L-citrulline supplementation. In the present study, although short-term L-citrulline supplementation increased exhaled NO^•, no ergogenic aids were found on the examined parameters at rest and after resistive breathing to task failure in older adults.

Alcohol Drinks Induce Acute Lowering in Circulating l-Arginine in Obese and Type 2 Diabetic Subjects

Since low serum l-arginine (Arg) and high asymmetric dimethylarginine (ADMA) can predict microvascular complications in type 2 diabetes mellitus (T2DM), we tested whether Arg and ADMA are affected by diet and physical activity in overweight/obese and T2DM subjects. We tested the effects on serum Arg and ADMA of single loads of dextrose, protein, fat, or alcohol (∼300 calories each); one episode of physical exercise; and 12 weeks of standard lifestyle modification (dietary and physical activity counseling). Alcohol drink was followed by ∼30% lowering in Arg. Arg and ADMA increased after a protein load but remained stable after glucose or fat load or 30 min of treadmill walk. Following 12 weeks of lifestyle modification, ADMA declined only in subjects achieving weight loss >5%. In conclusion, alcohol is a previously unrecognized acute suppressor of serum Arg. Lifestyle modification lowers ADMA in subjects who achieve weight loss >5%. Clinical Trial Registration Number: NCT04406402.

L-Arginine Improves Cognitive Impairment in Hypertensive Frail Older Adults

Cognitive impairment is a prevailing event in hypertensive patients and in frail older adults. Endothelial dysfunction has been shown to underlie both hypertension and cognitive dysfunction. Our hypothesis is that L-Arginine, which is known to ameliorate endothelial dysfunction, could counteract cognitive impairment in a high-risk population of hypertensive frail older adults. We designed a clinical trial to verify the effects of 4-weeks oral supplementation of L-Arginine on global cognitive function of hypertensive frail older patients. The study was successfully completed by 35 frail hypertensive elderly patients assigned to L-Arginine and 37 assigned to placebo. At follow-up, we found a significant difference in the Montreal Cognitive Assessment (MoCA) test score between the L-Arginine treated group and placebo (p: 0.0178). Moreover, we demonstrated that L-Arginine significantly attenuates Angiotensin II-induced mitochondrial oxidative stress in human endothelial cells. In conclusion, our findings indicate for the first time that oral L-Arginine supplementation significantly improves cognitive impairment in frail hypertensive older adults.

The Role of Amino Acids in Endothelial Biology and Function

The vascular endothelium acts as an important component of the vascular system. It is a barrier between the blood and vessel wall. It plays an important role in regulating blood vessel tone, permeability, angiogenesis, and platelet functions. Several studies have shown that amino acids (AA) are key regulators in maintaining vascular homeostasis by modulating endothelial cell (EC) proliferation, migration, survival, and function. This review summarizes the metabolic and signaling pathways of AAs in ECs and discusses the importance of AA homeostasis in the functioning of ECs and vascular homeostasis. It also discusses the challenges in understanding the role of AA in the development of cardiovascular pathophysiology and possible directions for future research.

Obesity Is Associated with Sustained Symptomatology and Unique Inflammatory Features in Children with Asthma

BACKGROUND

Obesity complicates the clinical manifestations of asthma in children. However, few studies have examined longitudinal outcomes or markers of systemic inflammation in obese asthmatic children.

OBJECTIVE

We hypothesized that obese children with asthma would have: (1) poorer clinical outcomes over 12 months, (2) decreased responsiveness to systemic corticosteroid administration, (3) greater markers of systemic inflammation, and (4) unique amino acid metabolites associated with oxidative stress.

METHODS

Children 6 to 17 years of age (lean, N = 257; overweight, N = 99; obese, N = 138) completed a baseline visit and follow-up visit at 12 months. Outcome measures included asthma control, quality of life, lung function, and exacerbations. A subset received intramuscular triamcinolone and were re-evaluated at 7(+7) days. Leptin, adiponectin, C-reactive protein, total cholesterol, interleukin (IL)-1β, IL-6, IL-17, interferon gamma, tumor necrosis factor alpha, monocyte-chemoattractant protein-1, and amino acid metabolites were also quantified in plasma as potential biomarkers of outcomes in obese children.

RESULTS

Obesity was associated with more symptoms, poorer quality life, and more exacerbations that persisted over 1 year despite greater medication requirements. Obese children also had minimal clinical improvement in asthma control and lung function after intramuscular triamcinolone. Leptin, C-reactive protein, and amino acid metabolites associated with glutathione synthesis and oxidative stress differed in obese children. Within the obese group, lower concentrations of arginine-related metabolites also distinguished uncontrolled from controlled asthma at 12 months.

CONCLUSION

Obesity is associated with poorer asthma outcomes and unique systemic inflammatory features that may not be adequately modified with conventional asthma therapies. Novel approaches may be needed given increased symptoms and unique inflammation and oxidative stress in obese children with asthma.

The Potential of L-Arginine in Prevention and Treatment of Disturbed Carbohydrate and Lipid Metabolism—A Review

L-arginine, an endogenous amino acid, is a safe substance that can be found in food. The compound is involved in synthesis of various products responsible for regulatory functions in the body. Particularly noteworthy is, among others, nitric oxide, a signaling molecule regulating carbohydrate and lipid metabolism. The increasing experimental and clinical data indicate that L-arginine supplementation may be helpful in managing disturbed metabolism in obesity, regulate arterial blood pressure or alleviate type 2 diabetes symptoms, but the mechanisms underlying these effects have not been sufficiently elucidated. This review aims to present the up-to-date information regarding the current uses and health-promoting potential of L-arginine, its effects on nitric oxide, carbohydrate and lipid metabolisms, based on the results of in vivo, in vitro studies, and clinical human trials. Available literature suggests that L-arginine may have beneficial effects on human health. However, some studies found that higher dietary L-arginine is associated with worsening of an existing disease or may be potential risk factor for development of some diseases. The mechanisms of regulatory effects of L-arginine on carbohydrate and lipid metabolism have not been fully understood and are currently under investigation.

Effects of treatment with SGLT-2 inhibitors on arginine-related cardiovascular and renal biomarkers

BACKGROUND

In patients with type 2 diabetes (T2D) sodium-glucose cotransporter 2 (SGLT-2) inhibitors improve glycaemic control as well as cardiovascular and renal outcomes. Their effects on L-arginine (Arg) related risk markers asymmetric and symmetric dimethylarginine (ADMA and SDMA) and the protective biomarker L-homoarginine (hArg) linking T2D to cardiovascular and renal disease have not yet been reported.

METHODS

Plasma and 24-h urine samples taken before and after 6 weeks of treatment were available from two prospective, randomized, double-blind, placebo-controlled, cross-over trials with empagliflozin (71 patients analyzed, NCT02471963) and dapagliflozin (59 patients analyzed, NCT02383238). In these samples, concentrations of hArg, Arg, ADMA, SDMA, and creatinine were determined by liquid-chromatography coupled to tandem mass-spectrometry. Additionally, intraindividual changes of the biomarkers in plasma were correlated with intraindividual changes of clinical parameters.

RESULTS

Treatment with empagliflozin and dapagliflozin was associated with a reduction of plasma hArg by 17.5% and 13.7% (both p < 0.001), respectively, and increase in plasma SDMA concentration of 6.7% and 3.6%, respectively (p < 0.001 and p < 0.05), while plasma Arg and ADMA concentrations were not significantly altered. 24-h urinary excretion of ADMA was reduced by 15.2% after treatment with empagliflozin (p < 0.001) but not after dapagliflozin treatment, while excretion of the other markers was not significantly altered. Renal clearance of SDMA was reduced by 9.1% and 3.9% for both drugs (both p < 0.05). A reduction in ADMA clearance was observable after empagliflozin treatment only (- 15.5%, p < 0.001), but not after dapagliflozin. Renal clearance of hArg and Arg was not significantly altered. Treatment effects on L-arginine related biomarkers were not constantly correlated with effects on glycated hemoglobin, fasting plasma glucose, body mass index, and systolic blood pressure.

CONCLUSIONS

Treatment with SGLT-2 inhibitors has divergent effects on Arg-related biomarkers and could affect risk estimates associated with these markers. The observed effects are unlikely to explain the known cardiovascular and renal benefits of treatment with empagliflozin or dapagliflozin but still may indicate new therapeutic approaches in patients treated with SGLT-2 inhibitors. Trial registration http://www.clinicaltrials.gov : NCT02471963 (registered 15th June 2015, retrospectively registered) and NCT02383238.

Effect of l-Arginine Supplementation on Blood Pressure in Adults: A Systematic Review and Dose-Response Meta-analysis of Randomized Clinical Trials

A decade-old meta-analytic work indicated that l-arginine supplementation might have a blood pressure (BP)-lowering effect in different populations. However, several relevant investigations have emerged in the last 10 y, and an up-to-date systematic review and meta-analysis on this topic is currently lacking. Therefore, we aimed to examine the impact of l-arginine supplementation on BP by conducting a systematic review and dose-response meta-analysis of randomized placebo-controlled clinical trials (RCTs). We searched online databases using relevant keywords up to April 2021 to identify RCTs using oral l-arginine on systolic BP (SBP) and diastolic BP (DBP) in adults. Inclusion criteria were adult participants and an intervention duration ≥4 d. Exclusion criteria were the use of l-arginine infusion and acute interventions. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% CI. Twenty-two RCTs with 30 effect sizes were included in this meta-analysis. The pooled analysis demonstrated significant decreases in SBP (WMD = -6.40 mmHg; 95% CI: -8.74, -4.05; P < 0.001) and DBP (WMD = -2.64 mmHg; 95% CI: -3.94, -1.40; P < 0.001) after l-arginine supplementation. Subgroup analysis showed significant reductions in SBP and DBP regardless of baseline BP category (normotensive, hypertensive), study duration (≤24 d, >24 d), sex (female, male), health status (healthy, unhealthy), and BMI (normal, overweight, obese). No significant changes were observed with dosages >9 g/d, trial duration >24 d, or in obese individuals. l-Arginine supplementation also appears to decrease DBP more effectively in females than in males. Moreover, meta-regression analysis for DBP demonstrated a significant relation between the dose of l-arginine intake and changes in DBP (P = 0.020). In the nonlinear dose-response analysis, the effective dosage of l-arginine supplementation was detected to be ≥4 g/d for SBP (P = 0.034), independent of trial duration. Overall, l-arginine supplementation may be effective for decreasing BP. This study was registered at PROSPERO as CRD42021242772.

Long lasting protective effects of early l-arginine treatment on endothelium in an in vitro study

BACKGROUND & AIMS

Excess nutrient supply, such as high fat and high glucose intake, promotes oxidative stress and advanced glycation end products accumulation. Oxidative stress and AGE accumulation cause pathological elevation of arginase activity and pro-inflammatory signaling implicated in endothelial dysfunction. Several studies showed positive effects of l-arginine supplementation in endothelial function but little is currently known about the role of l-arginine as prevention of endothelial dysfunction caused by excessive nutrient supply (overfeeding). Our aim was to evaluate a possible protective effect of l-arginine on endothelial dysfunction caused by excessive nutrient supply (overfeeding), using human endothelial cells line in an in vitro study.

METHODS

Endothelial EA.hy926 cells were pre-treated with 1.72 mM of l-arginine for 24 h and afterwards subjected to nutritional stress (high lipid, high insulin and high glucose concentrations) for further 24 h. After treatment discontinuation, the cells were kept in culture for 48 h, in physiological condition, to evaluate the effects of treatments after normalization.

RESULTS

Excess nutrient supply in EA.hy926 cell line showed an increase of oxidative and nitrosative stress, a rise of AGEs production, high arginase activity, leading the cells to acidosis and to cell death. l-arginine pretreatment protects the cells by reducing apoptosis, acidosis, oxidative and nitrosative stress, arginase activity and AGE accumulation. l-arginine pretreatment reduces AGEs generation and accumulation by regulating STAB1 and RAGE gene expression levels. STAB1, acting as receptor scavenger of AGEs, interferes with AGE-RAGE binding and thus prevents activation of intracellular signaling pathways leading to cell damage. Moreover the reduction of oxidative stress promotes a decrease of excessive activation of arginase involved in endothelial dysfunction. The effects of pretreatment with l-arginine last even in the absence of stimuli and despite after treatment discontinuation.

CONCLUSIONS

An early l-arginine treatment is able to prevent oxidative stress and AGEs accumulation caused by overfeeding in human endothelial cell line by regulating STAB1/RAGE gene expression and by reducing excess arginase activity. The positive effects of l-arginine pretreatment continue even after treatment discontinuation in normal conditions.

Endogenous flux of nitric oxide: Citrulline is preferred to Arginine

Both arginine (Arg) and its precursor citrulline (Cit) have received much interest in the past two decades because of their potential effects on whole-body nitric oxide (NO) production and augmentation of NO-dependent signalling pathways. However, the usefulness of Arg supplementation for NO production is questionable because of its high splanchnic first pass metabolism (FPM), which limits its systemic availability. Both hepatic- and extrahepatic arginases critically limit the availability of Arg for the NO synthase enzymes (NOSs) and therefore, a limited amount of oral Arg can reach the systemic circulation for NO synthesis. Arg also has some undesired effects including induction of arginase activity, an increase of urea levels, a decrease of cellular uptake of Cit and decrease of recycling of Arg from Cit. In contrast, Cit has more availability as an NO precursor because of its high intestinal absorption, low FPM and high renal reabsorption. At the cellular level, co-localization of Cit transport systems and the enzymes involved in the Cit-Arg-NO pathway facilitates channelling of Cit into NO. Furthermore, cells preferably use Cit rather than either intra- or extracellular Arg to improve NO output, especially in high-demand situations. In conclusion, available evidence strongly supports the concept that Cit leads to higher NO production and suggests that Cit may have a better therapeutic effect than Arg for NO-disrupted conditions.

Effect of l-arginine on cardiac reverse remodeling and quality of life in patients with heart failure

BACKGROUND & AIMS

Heart failure (HF), as a major cardiac disease, is associated with considerable mortality, morbidities and poor quality of life. The aim of this study was to investigate the effect of l-arginine supplementation on cardiac outcomes and quality of life in patients with ischemic HF.

METHODS

This double-blind randomized controlled clinical trial was conducted in 50 patients with ischemic HF. Patients were randomly assigned to receive either 3 gr/d l-arginine or placebo, for 10 weeks. Cardiac function (based on echocardiography and six-minute walk test), blood pressure, and quality of life (based on the Minnesota living with heart failure questionnaire) were assessed.

RESULTS

The results showed significant improvements in ejection fraction (-6.5 ± 8.7 vs. -0.7 ± 7.8%, P = 0.037), left ventricular function (P = 0.043), diastolic dysfunction (P = 0.01) and marginally improvement in changes of left ventricular dimension during diastole (LVDd) (4 ± 6 vs. 0.3 ± 6.9 mm, P = 0.065) in the l-arginine compared to the placebo group. At the end of the study, physical aspect (5.7 ± 3.3 vs. 1.2 ± 6.1, P = 0.002) and total score (10 ± 6.7 vs. 4.1 ± 9.4, P = 0.011) of quality of life improved significantly in the l-arginine compared with the placebo group. Additionally, pre-to post-values of diastolic blood pressure, mean arterial pressure, LVDd, LV ejection fraction, left ventricular function, diastolic dysfunction as well as physical and total scores of quality of life improved significantly within the intervention, but not the placebo, group (all P < 0.05).

CONCLUSION

This study showed that 3 gr/d l-arginine supplementation for 10 weeks could improve cardiac recovery and function, and quality of life in patients with HF. This study was registered at the Iranian Clinical Trial Registration Center (www.irct.ir) with IRCT20170202032367N4 code.

Effects of L-arginine supplementation on biomarkers of glycemic control: a systematic review and meta-analysis of randomised clinical trials

The present meta-analysis aimed to determine the effectiveness of L-arginine supplementation in improving biomarkers of glycemic control in adults. Electronic databases including PubMed, ISI Web of Science, Scopus, and the Cochrane Collaboration Library were searched up to January 2020. The meta-analysis of twelve randomised clinical trials indicated that L-arginine had no significant effect on serum fasting blood sugar (FBS) (weighted mean difference [WMD]: -3.38 mg/dl, 95% CI: -6.79 to 0.04, p = .53), serum insulin (WMD: -0.12 Hedges' g 95% CI: -0.33 to 0.09, p = .27), glycated haemoglobin A1c (HbA1c; WMD: -0.04%, 95% CI: -0.25 to 0.17, p = .71), and homeostasis model assessment for insulin resistance (WMD: -0.48, 95% CI: -1.15 to 0.19, p = .15). Although several animal studies have proposed that L-arginine supplementation might improve blood glucose control, the present study could not confirm this benefit in humans.

[Asymmetric dimethylarginine (ADMA) in retinal vein occlusion-Results from the Gutenberg RVO study]

BACKGROUND

Asymmetric dimethylarginine (ADMA) is considered an independent cardiovascular risk factor (cvRF) and thus represents a potential new biomarker for retinal vein occlusion (RVO).

METHODS

Overall, 92 patients with RVO and the same number of matched controls were included in the Gutenberg RVO study. All patients underwent a standardized examination for cvRF at the study center of the population-based Gutenberg health study (GHS) as well as ophthalmological examinations and intensive laboratory tests. This article presents a substudy of patients (≤65 years old) and the controls in whom ADMA was additionally determined by high performance liquid chromatography (HPLC) at baseline and 4-6 weeks later.

RESULTS

Out of 44 patients with RVO 22 had central retinal vein occlusion (CRVO), 15 had branch retinal vein occlusion (BRVO) and 7 had hemiretinal vein occlusion (hemi-RVO). The ADMA levels were 0.383 ± 0.094 µM (mean ± standard deviation) in RVO patients at baseline and 0.380 ± 0.093 µM (p = 0.514, initial vs. follow-up) after the follow-up period versus 0.360 ± 0.077 µM (p = 0.175, controls vs. RVO) in controls (n = 44). Arterial hypertension was the most prevalent risk factor in 22 (50%) of the patients and in 11 (25%) of the controls (odds ratio, OR 2.77, 95% confidence interval, CI 0.97-7.95; p = 0.058). The ADMA values above the 95th percentile (>0.530 µM) were detected in 4 patients with RVO (9.1%) but not in any of the controls (p = 0.041, RVO vs. controls).

CONCLUSION

Hypertension is the most important risk factor for RVO. Due to the high number of hypertensive patients in the cohort, the relevance of ADMA as an independent risk factor could neither be confirmed nor disproved.

The association between serum omentin level and bodyweight: A systematic review and meta-analysis of observational studies

BACKGROUND AND AIMS

A number of studies have examined the association between omentin and body weight, but the findings have been inconclusive. Here in, we systematically reviewed available observational studies to elucidate the overall relationship between omentin and body weight, by comparison of serum omentin level in overweight/obese and normal weight subjects.

METHODS

PubMed, Science direct, Scopus and ISI web of science databases were searched for all available literature until January 2020 for studies assessing the association between omentin and body weight. The Newcastle-Ottawa Quality Assessment Scale was used to assess the quality of each study.

RESULTS

A total of 27 articles met the inclusion criteria and were included in our systematic review and meta-analysis. There was a significant association between omentin serum level and body weight (Standard Mean Difference (SMD) -0.43; 95% CI, -0.70 to -0.15; P = 0.002; I² = 93.2%). In order to find the probable source of heterogeneity subgroup analysis based on the participants' age (adolescent, adult), gender (male, female, both gender), health status (healthy, unhealthy), geographical location (Asian, non-Asian countries), study quality (low, medium, high), study design (case-control, cross-sectional), participants' health status (healthy, unhealthy) and BMI (obese, overweight) was carried out.

CONCLUSION

According to what was discussed, we found that serum omentin level is significantly lower in overweight subjects but not obese ones. This finding should be interpreted cautiously because of significant heterogeneity among included studies.

A Paradoxical Vasodilatory Nutraceutical Intervention for Prevention and Attenuation of Migraine-A Hypothetical Review

Studies suggest that migraine pain has a vascular component. The prevailing dogma is that peripheral vasoconstriction activates baroreceptors in central, large arteries. Dilatation of central vessels stimulates nociceptors and induces cortical spreading depression. Studies investigating nitric oxide (NO) donors support the indicated hypothesis that pain is amplified when acutely administered. In this review, we provide an alternate hypothesis which, if substantiated, may provide therapeutic opportunities for attenuating migraine frequency and severity. We suggest that in migraines, heightened sympathetic tone results in progressive central microvascular constriction. Suboptimal parenchymal blood flow, we suggest, activates nociceptors and triggers headache pain onset. Administration of NO donors could paradoxically promote constriction of the microvasculature as a consequence of larger upstream central artery vasodilatation. Inhibitors of NO production are reported to alleviate migraine pain. We describe how constriction of larger upstream arteries, induced by NO synthesis inhibitors, may result in a compensatory dilatory response of the microvasculature. The restoration of central capillary blood flow may be the primary mechanism for pain relief. Attenuating the propensity for central capillary constriction and promoting a more dilatory phenotype may reduce frequency and severity of migraines. Here, we propose consideration of two dietary nutraceuticals for reducing migraine risk: L-arginine and aged garlic extracts.

Effects of l-arginine supplementation on glycemic profile: Evidence from a systematic review and meta-analysis of clinical trials

BACKGROUND

The effects of l-arginine supplementation on indices of glycemic control and the role of many factors influencing this intervention have been controversial in clinical trials.

OBJECTIVE

This meta-analysis was performed to assess the effects of l-arginine supplementation on indices of glycemic control, including fasting blood glucose (FBG), hemoglobin A1c (HbA1c), serum insulin and homeostatic model assessment of insulin resistance (HOMA-IR) levels in randomized controlled trials (RCTs).

SEARCH STRATEGY

This study conducted a systematic review of RCTs published in PubMed, Scopus, Web of Science, Cochrane Library and Embase, up to 5 May, 2018.

INCLUSION CRITERIA

Studies were included in this meta-analysis if they were RCTs with parallel design and reported sufficient data on participants before and after intervention, and outcomes of glycemic profile parameters in both the arginine supplementation and control groups.

DATA EXTRACTION AND ANALYSIS

The screening of titles and abstracts was performed independently by two reviewers. Selected articles were considered if they met the study's inclusion criteria. The quality of included studies was assessed by using the Cochrane Collaboration modified tool. From 710 articles retrieved in the initial search, only 10 trials were suitable for pooling the effects of arginine supplementation on serum glucose, insulin, HOMA-IR and HbA1c levels, with effect sizes of nine, eight, five and five, respectively.

RESULTS

Pooled random-effect analysis revealed that l-arginine supplementation could significantly decrease FBG level (weighted mean difference [WMD]: 3.35 mg/dL; 95% confidence interval [CI] = [-6.55, -0.16]; P = 0.04) and serum insulin level (WMD: -2.19 μIU/mL; 95% CI = [-3.70, -0.67]; P = 0.005). However, the effects of l-arginine supplementation on HOMA-IR and HbA1c were not significant. Results of subgroup analysis showed that supplementation with l-arginine could significantly decrease serum insulin levels when the dosage of l-arginine is > 6.5 g/d (WMD: -3.49 μIU/mL; 95% CI = [-5.59, -1.38]; P = 0.001), when the duration of supplementation is ≤ 12.8 weeks (WMD: -3.76; 95% CI = [-6.50, -0.98]; P = 0.008), when the participants are not diabetic patients (WMD: -2.54 μIU/mL; 95% CI = [-4.50, -0.50]; P = 0.01) and when the baseline serum level of insulin was > 20 μIU/mL (WMD: -3.98; 95% CI = [-6.31, -1.65]; P = 0.001).

CONCLUSION

Although the results of this study confirmed that supplementation with l-arginine could have significant effects on some glycemic profile indices of participants in clinical trials, the clinical importance of this reduction may not be meaningful.

L-arginine effect on inflammatory mediators: A systematic review of randomized controlled clinical trials

L-arginine is an important factor in several physiological and biochemical processes. Recently, scientists studied L-arginine effect on inflammatory mediators such as C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). We conducted a systematic review on randomized controlled trials assessing L-arginine effect on inflammatory mediators. We searched data bases including Google scholar, ISI web of science, SCOPUS, and PubMed/Medline up to April 2019. Randomized clinical trials assessing the effect of L-arginine on inflammatory mediators in human adults were included. Our search retrieved eleven articles with 387 participants. Five articles were on patients with cancer and 6 articles were on adults without cancer. L-arginine was applied in enteral form in 5 articles and in oral form in 6 articles. Eight articles were on both genders, two articles were on women, and one article was on men. L-arginine could not reduce inflammatory mediators among patients with and without cancer except one article which indicated that taking L-arginine for 6 months decreased IL-6 among cardiopathic nondiabetic patients. Our results indicated that L-arginine might not be able to reduce selected inflammatory mediators, but for making a firm decision more studies are needed to be conducted with longer intervention duration, separately on male and female and with different doses of L-arginine.

Exogenous l-ARGININE does not stimulate production OF NO or cGMP within the rat corporal smooth muscle cells in culture

BACKGROUND AND AIM

Nitric oxide (NO) is the intracellular chemical responsible for initiating a penile erection. Despite conflicting clinical data, it continues to be publicized and promoted that orally administered l-arginine, the putative substrate for NO, enhances the erectile response presumably by stimulating NO production by the corporal tissues resulting in an increase in cGMP production. To shed light on this issue, an in vitro study was conducted to explore the effect of direct exogenous administration of l-arginine as well as its precursor and metabolite, l-citrulline, on the NO-cGMP pathway within the cavernosal smooth muscle (CSM) cell.

MATERIALS AND METHODS

CSM cells obtained from 8 to 10 week old Sprague-Dawley rats were grown in Dulbecco media with 20% fetal calf serum and then incubated with or without l-arginine (L-ARG) or l-citrulline (L-CIT) in a time course and dose-response manner. Sildenafil (0.4 mM), IBMX (1 mM), l-NAME (3 μM), ODQ (5 μM) and Deta Nonoate (10 μM) were used as either inhibitors or stimulators of the NO-cGMP pathway. mRNA and protein were extracted and used for the determination of the phosphodiesterase 5 (PDE5). PDE5 activity was determined by luminometry. cGMP content was determined by ELISA. Nitrite formation, an indicator of NO production, was measured in the cell culture media by a colorimetric assay. The cationic (CAT-1) and neutral (SNAT-1) amino acid transporters for L-ARG and L-CIT, respectively, were determined by Western blot.

RESULTS

When compared to untreated CSM cells, incubation with 0.25-4.0 mM of L-ARG or 0.3-4.8 mM of L-CIT anywhere between 3 and 24 h did not result in any additional nitrite or cGMP production. The addition of l-NAME, IBMX or ODQ to these L-ARG and L-CIT treated cells did not alter these results. L-CIT but not L-ARG increased PDE5 mRNA and protein content as well as the activity of the PDE5 enzyme. Both CAT-1 and SNAT-1 were expressed in the CSM cells.

CONCLUSIONS

This in vitro study demonstrates that exogenous administration of L-ARG or L-CIT failed to stimulate production of either NO or cGMP by the corporal CSM cells. A re-evaluation of the presumptive role of the exogenous administration of L-ARG in improving the synthesis of NO at least at the level of the CSM cells appears warranted.

The effect of L-arginine supplementation on obesity-related indices: A systematic review and meta-analysis of randomized clinical trials

The clinical studies regarding the effect of L-arginine in human anthropometry have not been fully consistent, therefore, we carried out a systematic review and meta-analysis of randomized clinical trials in order to precisely evaluate and quantify the efficacy of L-arginine on weight, waist circumference, and BMI. We searched online databases including PubMed, SCOPUS, and Google Scholar for relevant articles up to September 2017. Eligible articles were reviewed by two independent investigators. Mean differences of the outcomes were used for calculation of weighted mean difference (WMD) derived from the random-effects model. Statistical heterogeneity between studies was examined using Cochran's Q-test and I² index. Funnel plot and Egger's tests were performed to assess the publication bias. In our initial search, we found 1598 publications, of which 8 RCTs (9 treatment arms) were included. The results of the meta-analysis displayed a significant reduction in WC following L-arginine supplementation (WMD: -2.97 cm; 95% CI: -4.75 to -1.18, P = 0.001). However, L-arginine intervention had not elicited a significant effect on BMI (WMD: -0.51 kg/m²; 95% CI: -1.11 to .08, P = 0.09) and body weight (WMD: -0.57 kg; 95% CI: -1.77 to 0.61, P = 0.34). Subgroup analyses displayed that longer-term interventions (≥8 weeks) had a positive effect on body weight and using < 8 g/day L-arginine with longer duration (≥8 weeks) could significantly decrease BMI. In conclusion, this meta-analysis result suggested L-arginine supplementation could reduce waist circumference without any significant effect on body weight and body mass index.

Exploratory metabolomics of metabolic syndrome: A status report

Metabolic syndrome (MetS) is as a cluster of cardio-metabolic factors that greatly increase the risk of chronic diseases such as type II diabetes mellitus and atherosclerotic cardiovascular disease. In the United States, obesity, physical inactivity, aging, and genetics (to a minor extent) have arisen as risk factors for developing MetS. Although 35% of American adults suffer from MetS, its pathogenesis largely remains unknown. Worse, there is a lack of screening and optimum therapy for this disease. Researchers have consequently turned towards metabolomics to identify biomarkers to better understand MetS. The purpose of this review is to characterize various metabolites and their potential connections to MetS. Numerous studies have also characterized MetS as a disease of increased inflammation, and therefore this review also explores how metabolites play a role in various inflammatory pathways. Our review explores a broad range of metabolites including biogenic amines, branched chain amino acids, aromatic amines, phosphatidylcholines, as well as a variety of other molecules. We will explore their biochemical pathways and their potential role in serving as biomarkers.

Association of l-Arginine Supplementation with Markers of Endothelial Function in Patients with Cardiovascular or Metabolic Disorders: A Systematic Review and Meta-Analysis

l-Arginine supplementation is a potential therapy for treating cardiovascular and metabolic diseases. However, the use of distinct l-arginine sources, intervened populations, and treatment regimens may have yielded confusion about their efficacy. This research constitutes a systematic review and meta-analysis summarizing the effects of l-arginine supplementation compared to placebo in individuals with cardiovascular disease (CVD), obesity, or diabetes. Eligibility criteria included randomized clinical trials and interventions based on oral supplementation of l-arginine with a minimum duration of three days; comparison groups consisted of individuals with the same disease condition receiving an oral placebo substance. The primary outcome was flow-mediated dilation, and secondary outcomes were nitrite/nitrate (NOx) rate and asymmetric dimethylarginine (ADMA). Statistical heterogeneity among studies included in the meta-analyses was assessed using the inconsistency index (I2). Fifty-four full-text articles from 3761 retrieved references were assessed for eligibility. After exclusions, 13 studies were included for data extraction. There was no difference in blood flow after post-ischemic hyperemia between the supplementation of l-arginine and placebo groups before and after the intervention period (standardized mean difference (SMD) = 0.30; 95% confidence intervals (CIs) = −0.85 to 1.46; I2 = 96%). Sensitivity analysis showed decreased heterogeneity when the studies that most favor arginine and placebo were removed, and positive results in favor of arginine supplementation were found (SMD = 0.59; 95% CIs = 0.10 to 1.08; I2 = 75%). No difference was found in meta-analytical estimates of NOx and ADMA responses between arginine or placebo treatments. Overall, the results indicated that oral l-arginine supplementation was not associated with improvements on selected variables in these patients (PROSPERO Registration: CRD42017077289).

Rate of appearance of amino acids after a meal regulates insulin and glucagon secretion in patients with type 2 diabetes: a randomized clinical trial

Background

Meal composition regulates the postprandial response of pancreatic and gastrointestinal hormones and plays an important role in patients with type 2 diabetes (T2D). Proteins have glucagon and insulinotropic effects, which may differ depending on amino acid composition, form of intake, and rate of digestibility and absorption.

Objective

The aim of this study was to test effects of isolated pea protein-based (PP) compared with casein protein-based (CP) meals differing in amino acid compositions on endocrine responses to meal tolerance tests (MTTs) in patients with T2D.

Design

Thirty-seven individuals with T2D [mean ± SD age: 64 ± 6 y; mean ± SD body mass index (kg/m2): 30.2 ± 3.6; mean ± SD glycated hemoglobin: 7.0% ± 0.6%] were randomly assigned to receive either high-animal-protein (∼80% of total protein) or high-plant-protein (∼72% of total protein) diets (30% of energy from protein, 40% of energy from carbohydrate, 30% of energy from fat) for 6 wk. MTTs were performed at study onset and after 6 wk. Participants received standardized high-protein (30% of energy) meals 2 times/d containing either CP-rich (∼85% wt:wt) or PP-rich (∼95% wt:wt) foods.

Results

The CP and PP meals produced differences in insulin, C-peptide, glucagon, and glucose-dependent insulinotropic peptide (GIP) release. Total areas under the curve after CP were significantly lower than after the PP lunch by 40% for insulin and 23% for glucagon. Indexes of insulin sensitivity and secretion were significantly improved for the second CP MTT. This was accompanied by differential rates of appearance of amino acids. The ingestion of PP resulted in significant increases in amino acids after both meals, with a decline between meals. By contrast, CP intake resulted in increases in most amino acids after breakfast, which remained elevated but did not increase further after lunch.

Conclusions

PP elicits greater postprandial increases in glucagon than does CP and consequently requires higher insulin to control glucose metabolism, which appears to be related to the rate of amino acid appearance. The metabolic impact of protein quality could be used as a strategy to lower insulin needs in patients with T2D. This trial was registered at www.clinicaltrials.gov as NCT02402985.

Integrative Medicine and Cardiovascular Disorders

Integrative medicine (IM) has developed an increasingly significant role in health care worldwide, including cardiovascular diseases (CVD). This review describes the commonly used IM in CVD, with particular attention placed with dietary supplements and mind-body therapies. More rigorous research continues to be needed to determine the mechanisms and efficacy of IM cardiovascular morbidity and mortality. Health care providers will need to develop skills in open communication and nonjudgmental dialogue around IM use in discussing treatment plans with their patients.

Arginine reverses growth hormone resistance through the inhibition of toll-like receptor 4-mediated inflammatory pathway

OBJECTIVE

Growth hormone stimulates growth by increasing insulin-like growth factor 1 expression and secretion. In the presence of insufficient nutrients, GH increases, whereas IGF-1 expression becomes severely suppressed, leading to GH resistance. This study aimed to explore the effect of arginine (Arg) on GH resistance during malnutrition and to describe its underlying mechanism.

METHODS

C57BL/6J mice were injected intraperitoneally with Arg for 1h or subjected to caloric restriction with Arg supplement in drinking water for 18days. HepG2 cells were exposed to different Arg concentrations for 24h. Signaling pathway agonists/inhibitors, siRNA, and overexpression plasmids were used to investigate the underlying molecular mechanism. Liver-specific toll-like receptor (TLR4) knockout mice were utilized to clarify the role of TLR4 in Arg-induced IGF-I expression and secretion.

RESULTS

Arg inhibited the TLR4 downstream pathway by binding to TLR4 and consequently activated Janus kinase 2/signal transducer and activator of transcription 5 signaling pathway. As a result, IGF-1 transcription and secretion increased. Arg activity was absent in liver-specific TLR4 knockout mice and was greatly suppressed in liver with overexpressed TLR4, suggesting that hepatic TLR4 was required and sufficient to induce GH resistance. By contrast, the mammalian target of rapamycin pathway was unnecessary for Arg activity. Arg not only significantly increased IGF-1 expression and secretion under acute fasting and chronic CR conditions but also attenuated body weight loss.

CONCLUSIONS

Our results demonstrate a previously unappreciated pathway involving Arg that reverses GH resistance and alleviates malnutrition-induced growth restriction through the inhibition of TLR4-mediated inflammatory pathway.

Decreased diabetes risk over 9 year after 18-month oral L-arginine treatment in middle-aged subjects with impaired glucose tolerance and metabolic syndrome (extension evaluation of L-arginine study)

Purpose

This study aimed to determine whether l-arginine supplementation lasting for 18 months maintained long-lasting effects on diabetes incidence, insulin secretion and sensitivity, oxidative stress, and endothelial function during 108 months among subjects at high risk of developing type 2 diabetes.

Methods

One hundred and forty-four middle-aged subjects with impaired glucose tolerance and metabolic syndrome were randomized in 2006 to an l-arginine supplementation (6.4 g orally/day) or placebo therapy lasting 18 months. This period was followed by a 90-month follow-up. The primary outcome was a diagnosis of diabetes during the 108 month study period. Secondary outcomes included changes in insulin secretion (proinsulin/c-peptide ratio), insulin sensitivity (IGI/HOMA-IR), oxidative stress (AOPPs), and vascular function. After the 18 month participation, subjects that were still free of diabetes and willing to continue their participation (104 subjects) were further followed until diabetes diagnosis, with a time span of about 9 years from baseline.

Results

Although results derived from the 18 month of the intervention study demonstrated no differences in the probability of becoming diabetics, at the end of the study, the cumulative incidence of diabetes was of 40.6% in the l-arginine group and of 57.4% in the placebo group. The adjusted HR for diabetes (l-arginine vs. placebo) was 0.66; 95% CI 0.48, 0.91; p < 0.02). Proinsulin/c-peptide ratio (p < 0.001), IGI/HOMA-IR (p < 0.01), and AOPP (p < 0.05) levels were ameliorated in l-arginine compared to placebo.

Conclusions

These results may suggest that the administration of l-arginine could delay the development of T2DM for a long period. This effect could be mediated, in some extent, by l-arginine-induced reduction in oxidative stress.

Arginine and aerobic training prevent endothelial and metabolic alterations in rats at high risk for the development of the metabolic syndrome

Endothelial function is a key mechanism in the development of CVD. Arginine and exercise are important non-pharmacological strategies for mitigating the impact of metabolic changes in the metabolic syndrome, but the effect of their combined administration is unknown. Thus, the aim of this study was to investigate the isolated and combined effects of aerobic training and arginine supplementation on metabolic variables and vascular reactivity in rats at high risk for developing the metabolic syndrome. Wistar rats were divided into two groups: control and fructose (F – water with 10 % fructose). After 2 weeks, the F group was divided into four groups: F, fructose+arginine (FA, 880 mg/kg per d of l-arginine), fructose+training (FT) and fructose+arginine+training (FTA); treatments lasted for 8 weeks, and no difference was observed in body mass gain. Arginine did not improve the body protein content, and both the FA and FT groups show a reversal of the increase in adipose tissue. Insulin increase was prevented by training and arginine, without additive effect, and the increase in serum TAG was prevented only by training. The F group showed impaired endothelium-dependent vasodilation and hyperreactivity to phenylephrine, but arginine and training were capable of preventing these effects, even separately. Higher nitric oxide level was observed in the FA and FT groups, and no potentiating effect was detected. Thus, only training was able to prevent the increase in TAG and improve the protein mass, and training and arginine exert similar effects on fat content, insulin and endothelial function, but these effects are not additive.

The effect of l-arginine supplementation on body composition and performance in male athletes: a double-blinded randomized clinical trial

BACKGROUND/OBJECTIVE

Athletes used a lot of dietary supplements to achieve the more muscle mass and improve their athletic performance. The objective of this study was to investigate the effect of l-arginine supplementation on sport performance and body composition in male soccer players.

SUBJECTS/METHODS

This double-blinded, randomized and placebo-controlled trial was conducted on 56 male soccer players, with age range of 16-35, who referred to sport clubs in Isfahan, Iran. Subjects were randomly assigned to either l-arginine or placebo groups. Athletes received daily either 2 g per day l-arginine supplement or the same amount of placebo (maltodextrin) for 45 days. Sport performance and also body mass index (BMI), body fat mass (BFM) and lean body mass (LBM) were measured at the beginning and end of the study. Also, 3-day dietary records were collected at three different time points (before, in the middle of, and at the end of the study).

RESULTS

The mean age of subjects was 20.85±4.29 years. Sport performance (VO₂ max) significantly increased in l-arginine supplementation group (4.12±6.07) compared with placebo group (1.23±3.36) (P=0.03). This increase remained significant even after adjustment of baseline values, physical activity and usual dietary intake of subjects throughout the study. No significant effect of l-arginine supplementation was found on weight, BMI, BFM and LBM.

CONCLUSIONS

l-arginine supplementation (2 g per day) could increase the sport performance in male athletes, but had no effect on anthropometric measurements, including BMI, BFM and LBM. So, further studies are needed to shed light our findings.

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.

Is arginase a potential drug target in tobacco-induced pulmonary endothelial dysfunction?

Background

Tobacco-induced pulmonary vascular disease is partly driven by endothelial dysfunction. The bioavailability of the potent vasodilator nitric oxide (NO) depends on competition between NO synthase-3 (NOS3) and arginases for their common substrate (L-arginine). We tested the hypothesis whereby tobacco smoking impairs pulmonary endothelial function via upregulation of the arginase pathway.

Methods

Endothelium-dependent vasodilation in response to acetylcholine (Ach) was compared ex vivo for pulmonary vascular rings from 29 smokers and 10 never-smokers. The results were expressed as a percentage of the contraction with phenylephrine. We tested the effects of L-arginine supplementation, arginase inhibition (by N(omega)-hydroxy-nor-l-arginine, NorNOHA) and NOS3 induction (by genistein) on vasodilation. Protein levels of NOS3 and arginases I and II in the pulmonary arteries were quantified by Western blotting.

Results

Overall, vasodilation was impaired in smokers (relative to controls; p < 0.01). Eleven of the 29 smokers (the ED⁺ subgroup) displayed endothelial dysfunction (defined as the absence of a relaxant response to Ach), whereas 18 (the ED⁻ subgroup) had normal vasodilation. The mean responses to 10⁻⁴ M Ach were −23 ± 10% and 31 ± 4% in the ED⁺ and ED⁻ subgroups, respectively (p < 0.01). Supplementation with L- arginine improved endothelial function in the ED⁺ subgroup (−4 ± 10% vs. -32 ± 10% in the presence and absence of L- arginine, respectively; p = 0.006), as did arginase inhibition (18 ± 9% vs. -1 ± 9%, respectively; p = 0.0002). Arginase I protein was overexpressed in ED⁺ samples, whereas ED⁺ and ED⁻ samples did not differ significantly in terms of NOS3 expression. Treatment with genistein did not significantly improve endothelial function in ED⁺ samples.

Conclusion

Overexpression and elevated activity of arginase I are involved in tobacco-induced pulmonary endothelial dysfunction.

The effects of L-arginine, alone and combined with vitamin C, on mineral status in relation to its antidiabetic, anti-inflammatory, and antioxidant properties in male rats on a high-fat diet

The aim of this study was to evaluate the influence of the intake of L-arginine alone and of L-arginine with vitamin C on mineral concentration in rats fed with a high-fat diet, and to assess the lipid glucose, insulin, and total antioxidant status (TAS) and tumor necrosis factor (TNF) alpha serum levels that result. Wistar rats were assigned to groups fed with either a standard control diet (C), a diet high in fat (FD), a diet high in fat with L-arginine, or a diet high in fat with L-arginine and vitamin C. After 6 weeks, the length and weight of the rats were measured, and the animals were euthanized. The liver, spleen, kidneys, pancreas, heart, and gonads were collected, as were blood samples. The total serum cholesterol, triglyceride, fasting glucose, insulin, TAS, and TNF alpha levels were measured. The tissue calcium, magnesium, iron, zinc, and copper concentrations were determined. It was found that L-arginine supplementation diminished the effect of the modified diet on the concentration of iron in the liver and spleen and of copper in heart. At the same time, it was observed that L-arginine supplementation reduced the effect of the high-fat diet on insulin, TNF alpha, and TAS. The combination of L-arginine and vitamin C produced a similar effect on the mineral levels in the tissues as did L-arginine used alone. Moreover, positive correlations between serum insulin and iron in the liver, between TNF alpha and iron in the liver, and between TNF alpha and copper in the heart were observed. The level of TAS in serum was inversely correlated with the copper level in the heart and the iron level in the liver. We concluded that the beneficial influence of L-arginine on insulin, TAS, and TNF alpha serum level is associated with changes in the iron and copper status in rats fed with a high-fat diet. No synergistic effect of L-arginine and vitamin C in the biochemical parameters or in the mineral status in rats fed with the modified diet was observed.

Supplementation with apple enriched with L-arginine may improve metabolic control and survival rate in alloxan-induced diabetic rats

Supplementation with L-arginine or fresh food with high content of this amino acid is associated with favorable effects in the metabolic control of diabetes. We aimed to determine whether supplementation with apples enriched with L-arginine offer additional benefits compared to L-arginine by itself in a preclinical study of diabetes. This study combines food-engineer technologies with in vivo and in vitro analysis. In vitro experiments show that cells derived from non-diabetic animals and exposed to high glucose (25 mM, 12 H) and cells isolated from alloxan-induced diabetic animals exhibited a reduction (∼50%) in the L-arginine uptake. This effect was reverted by L-arginine pretreatment (12 H) in both the normal and diabetes-derived cells. In preclinical studies, normoglycemic (n = 25) and diabetic groups (n = 50) were divided into subgroups that received either L-arginine (375 mg/kg per 10 days) or apple enriched with L-arginine or vehicle (control). In a preliminary analysis, supplementation with L-arginine by itself (50%) or apple enriched with L-arginine (100%) improve survival rate in the diabetic group compared to control (0%) at the end of the follow up (17 days). This phenomenon was associated with a partial but sustained high plasma level of L-arginine, as well as plasma concentration of nitrites and insulin in the L-arginine or apple + L-arginine groups after supplementation. Apple + L-arginine supplementation in diabetic animals induced the highest and longest effects in the level of these three markers among the studied groups. Therefore, apple enriched by L-arginine offers more benefits than L-arginine by itself in this preclinical study.

Nitric oxide and energy metabolism in mammals

Nitric oxide (NO) is a signaling molecule synthesized from L-arginine by NO synthase in animals. Increasing evidence shows that NO regulates the mammalian metabolism of energy substrates and that these effects of NO critically depend on its concentrations at the reaction site and the period of exposure. High concentrations of NO (in the micromolar range) irreversibly inhibit complexes I, II, III, IV, and V in the mitochondrial respiratory chain, whereas physiological levels of NO (in the nanomolar range) reversibly reduce cytochomrome oxidase. Thus, NO reduces oxygen consumption by isolated mitochondria to various extents. In intact cells, through cGMP and AMP-activated protein kinase signaling, physiological levels of NO acutely stimulate uptake and oxidation of glucose and fatty acids by skeletal muscle, heart, liver, and adipose tissue, while inhibiting the synthesis of glucose, glycogen and fat in the insulin-sensitive tissues, and enhancing lipolysis in white adipocytes. Chronic effects of physiological levels of NO in vivo include stimulation of angiogenesis, blood flow, mitochondrial biogenesis, and brown adipocyte development. Modulation of NO-mediated pathways through dietary supplementation with L-arginine or its precursor L-citrulline may provide an effective, practical strategy to prevent and treat metabolic syndrome, including obesity, diabetes, and dyslipidemia in mammals, including humans.

L-arginine enriched biscuits improve endothelial function and glucose metabolism: a pilot study in healthy subjects and a cross-over study in subjects with impaired glucose tolerance and metabolic syndrome

OBJECTIVE

The aim of this study was to evaluate the effects of a new L-arginine-enriched biscuit on endothelial function, insulin sensitivity/secretion and body composition.

MATERIALS/METHODS

The project was composed of two studies. The first study was an acute pilot postprandial study in 7 healthy subjects that evaluated bio-availability and vascular effects of L-arginine-enriched biscuits that contained 6.6 gL-arginine, 21.9 g carbohydrates, 3.6 g protein, 7.5 g fat and 4.3 g dietary fiber compared with placebo biscuits and 6.6 g powdered L-arginine. Subjects underwent the tests in random order, in at least 14-day intervals. The second study was a double-blind crossover study in 15 obese subjects with IGT and MS. These subjects consumed 6.6 g of L-arginine-enriched biscuits or placebo biscuits in a 1600 kcal diet. Each study period lasted 2 weeks with a 2-week washout in between. Endothelial function, glucose tolerance, insulin sensitivity and insulin secretion were evaluated at the end of each intervention period.

RESULTS

In the first study, the groups that received the L-arginine-enriched biscuits and the powdered L-arginine had similarly increased L-arginine, NOx and cGMP levels and post-ischemic blood flow (PI-BF). In both cases, these levels were significantly higher than those in the placebo biscuit recipient group. In the second study, the L-arginine-enriched biscuit recipient group displayed increased L-arginine, NOx, cGMP, PI-BF, and Matsuda index levels, whereas their circulating glucose, proinsulin/insulin ratio and fat mass were decreased compared with the placebo biscuit recipient group.

CONCLUSIONS

L-Arginine-enriched biscuits with low sugar and protein content enhance endothelial function and improve glucose metabolism, insulin sensitivity and insulin secretion in subjects with IGT and MS.

L-Arginine enhances glucose and lipid metabolism in rat L6 myotubes via the NO/ c-GMP pathway

OBJECTIVE

The amino acid Arginine (Arg) is the main biological precursor of nitric oxide (NO) and has been described to improve insulin sensitivity in diabetes and obesity. We investigated the molecular mechanisms involved in the long-term effects of Arg on glucose and lipid metabolism.

MATERIALS AND METHODS

L6 myotubes were treated with Arg (7 mmol/L) for 6 days. D-Mannitol (7 mmol/L) was used as control; spermine NONOate (10 μmol/L) and L-NAME (100 μmol/L) were used to evaluate the NO/c-GMP pathway role. Basal and insulin-induced (120 nmol/L) glycogen synthesis, glucose uptake and lipid oxidation, c-GMP and nitrite levels, and the intracellular signaling pathways were evaluated.

RESULTS

Arg-treatment increased: 1) basal and insulin-stimulated glycogen synthesis; 2) glucose uptake; 3) palmitate oxidation; 4) p-Akt (Ser(473)), total and plasma membrane GLUT4 content, total and p-AMPK-α and p-ACC (Ser(79)), p-GSK-3α/β (Ser(21/9)) and 5) nitrite and c-GMP levels. L-NAME treatment suppressed Arg effects on: 1) nitrite and c-GMP content; 2) glycogen synthesis and glucose uptake; 3) basal and insulin-stimulated p-Akt (Ser(473)), total and p-AMPK-α and ACC, and nNOS expression.

CONCLUSION

We provide evidence that Arg improves glucose and lipid metabolism in skeletal muscle, in parallel with increased phosphorylation of Akt and AMPK-α. These effects were mediated by the NO/c-GMP pathway. Thus, arginine treatment enhances signal transduction and has a beneficial effect of metabolism in skeletal muscle through direct activation of Akt and AMPK pathways.

Changes in activities of daily living, nutrient intake, and systemic inflammation in elderly adults receiving recuperative care

OBJECTIVES

To determine the relationships between physical function, systemic inflammation, and nutrient intake in elderly adults who are deconditioned or recovering from medical illness.

DESIGN

Prospective observational study.

SETTING

Recuperative care and rehabilitation setting of a Veterans Affairs hospital.

PARTICIPANTS

Older adults assessed to be in need of and likely to benefit from specialized inpatient care (N = 336, aged 78.9 ± 7.5, median length of stay 24 days).

MEASUREMENTS

Functional assessments and plasma analyses for albumins and inflammatory markers were performed at admission and discharge. Complete nutrient intake assessments were performed daily. Katz (independence in activities of daily living) and walking endurance (distance capability and summation of need for assistive device and human help) scores were based on direct observation and provider query. Data were analyzed using least-squares and logistic regression analyses.

RESULTS

Changes in physical function between admission and discharge were positively correlated with change in nutrient intake and inversely correlated with inflammation at admission and its change. Participants in the upper quartile of change for nutrient intake (particularly improved protein intake) were two to three times as likely to experience a clinically significant change in functional status during the hospitalization. Similarly, the odds of experiencing an improvement in physical function were two to four times as great for participants whose C-reactive protein levels declined as for those whose levels increased. These relationships remained significant after controlling for age, length of stay, and other baseline indicators of health status.

CONCLUSION

Protein intake and inflammation are significantly correlated with functional recovery for aging individuals undergoing recuperative care and rehabilitation. Future studies should investigate whether combined interventions that target these factors improve recovery during hospitalization for this population.

Effect of a long-term oral l-arginine supplementation on glucose metabolism: a randomized, double-blind, placebo-controlled trial

AIM

This study assessed the efficacy of long-term l-arginine (l-arg) therapy in preventing or delaying type 2 diabetes mellitus.

METHODS

A mono-centre, randomized, double-blind, parallel-group, placebo-controlled, phase III trial (l-arg trial) was conducted on 144 individuals affected by impaired glucose tolerance (IGT) and metabolic syndrome (MS). l-Arg/placebo was administered (6.4 g/day) on a background structured lifestyle intervention for 18 months plus a 12-month extended follow-up period after study drug termination. Fasting glucose levels and glucose tolerance after oral glucose tolerance test were evaluated throughout the study.

RESULTS

After 18 months, l-arg as compared with placebo did not reduce the cumulative incidence of diabetes [21.4 and 20.8%, respectively, hazard ratio (HR), 1.04; 95% confidence interval (CI), 0.58-1.86] while the cumulative probability to become normal glucose tolerant (NGT) increased (42.4 and 22.1%, respectively, HR, 2.60; 95% CI, 1.51-4.46, p < 0.001). The higher cumulative probability to become of NGT was maintained during the extended period in subjects previously treated with l-arg (HR, 3.21; 95% CI, 1.87-5.51; p < 0.001). At the end of the extended period, the cumulative incidence of diabetes in subjects previously treated with l-arg was reduced as compared with placebo (27.2 and 47.1%, respectively, HR, 0.42; 95% CI, 0.24-0.75, p < 0.05). During both periods, l-arg significantly improved insulin sensitivity and β-cell function.

CONCLUSION

Among persons with IGT and MS, the supplementation of l-arg for 18 months does not significantly reduce the incidence of diabetes but does significantly increase regression to NGT.