The Effectiveness of L-arginine in Clinical Conditions Associated with Hypoxia.

The review summarises the data of the last 50 years on the effectiveness of the amino acid L-arginine in therapeutic practice in conditions accompanied by different-origin hypoxia. The aim of this review was to analyse the literature and our research data on the role of nitric oxide in the modulation of individual physiological reactivity to hypoxia. The review considers the possibility of eliminating methodological conflicts in the case of L-arginine, which can be solved by taking into account individual physiological reactivity (or the hypoxia resistance factor). Considerable attention is paid to genetic and epigenetic mechanisms of adaptation to hypoxia and conditions of adaptation in different models. The article presents data on the clinical effectiveness of L-arginine in cardiovascular system diseases (hypertension, atherosclerosis, coronary heart disease, etc.) and stress disorders associated with these diseases. The review presents a generalised analysis of techniques, data on L-arginine use by athletes, and the ambiguous role of NO in the physiology and pathology of hypoxic states shown via nitric oxide synthesis. Data on the protective effects of adaptation in the formation of individual high reactivity in sportsmen are demonstrated. The review demonstrates a favourable effect of supplementation with L-arginine and its application depending on mitochondrial oxidative phosphorylation processes and biochemical indices in groups of individuals with low and high capacity of adaptation to hypoxia. In individuals with high initial anti-hypoxic reserves, these favourable effects are achieved by the blockade of NO-dependent biosynthesis pathways. Therefore, the methodological tasks of physiological experiments and the therapeutic consequences of treatment should include a component depending on the basic level of physiological reactivity.

Single Nucleotide Polymorphisms in the Arginase 1 and 2 Genes Are Differentially Associated with Circulating l-Arginine Concentration in Unsupplemented and l-Arginine-Supplemented Adults.

BACKGROUND: Genetic variation in arginase may underlie variability in whole blood l-arginine concentrations in unsupplemented and l-arginine-supplemented adults. OBJECTIVES: We aimed to study whether single nucleotide polymorphisms (SNPs) in the arginase 1 (ARG1) and arginase 2 (ARG2) genes are associated with blood l-arginine concentrations in unsupplemented and l-arginine-supplemented individuals. METHODS: In 374 adults (mean ± SD age: 59.6 ± 14.6 y; 180 males), we analyzed SNPs in the ARG1 (rs2246012 and rs2781667) and ARG2 genes (rs3742879 and rs2759757) and their associations with blood l-arginine concentrations. We analyzed associations of haplotypes for the ARG1 gene and for the ARG1 and ARG2 genes combined with blood l-arginine concentrations in supplement users and unsupplemented participants. RESULTS: Of study participants, 120 had low (<42 µmol/L), 133 had medium (42-114 µmol/L), and 121 had high blood l-arginine concentrations (>114 µmol/L); 58 individuals were current l-arginine supplement users. We found a significantly higher prevalence of the minor allele of ARG1 rs2246012 in supplement users with higher blood l-arginine concentrations (P = 0.03). Mean ± SEM l-arginine concentration was 263 ± 9.76 µmol/L in supplement users homozygous for the minor allele of ARG1 rs2246012 (P = 0.004); it was 70.4 ± 25.6 µmol/L in unsupplemented participants homozygous for the minor allele of ARG2 rs3759757 (P = 0.03). The ARG1 haplotype was significantly associated with blood l-arginine concentrations in supplement users (P = 0.046), whereas the combined ARG1/ARG2 haplotype was significantly associated with blood l-arginine concentrations in the cohort as a whole (P = 0.012). CONCLUSIONS: Genetic variability in the ARG1 and ARG2 genes is associated with blood l-arginine concentrations in humans: ARG1 is associated with blood l-arginine concentrations in l-arginine supplement users, whereas ARG2 is associated with blood l-arginine concentrations in unsupplemented participants. Our study is the first to describe a possible functional relation between ARG1 and ARG2 SNPs and blood l-arginine concentrations; genetic variability in ARG1 may explain variation in blood l-arginine concentrations during supplement use and discrepant study results.

The essential role of hypothalamic paraventricular nucleus nNOS in the modulation of autonomic control in exercised rats.

Nitric oxide (NO), an intercellular signaling molecule is relevant for circulatory autonomic control. Brain NO synthase (NOS) and NO levels were downregulated in pathological conditions, but rescued after exercise training. We hypothesized that exercise training was also able to improve NO modulation within the hypothalamic paraventricular nucleus (PVN) of healthy rats. Male Wistar rats were submitted to two 4-weeks protocols: i) swimming training (T) or kept sedentary (S), ii) l-arginine (62,5 mg/mL, 1 mL/day p. o.) or vehicle supplementation. Rats underwent stereotaxic surgery (PVN bilateral guide cannulas) and chronic catheterization of artery/vein. Arterial pressure (AP), heart rate (HR) and baroreflex sensitivity were recorded in conscious rats at rest and following a selective nNOS inhibitor (Nw-Propyl-l-Arginine, 4 nmol/100 nL) within the PVN. Rats were deeply anesthetized for brain perfusion/harvesting after respiratory arrest. In separate groups (T and S, l-arginine and Vehicle supplemented) not submitted to PVN cannulation, fresh and fixed brains were obtained for gene and protein nNOS expression (qPCR and immunohistochemistry) and nitrite levels (Griess reaction). T and l-arginine treatment were accompanied by resting bradycardia, augmented parasympathetic and reduced sympathetic activity to heart and vessels (power spectral analysis) and increased baroreflex sensitivity (†P < 0.05). In contrast, PVN nNOS inhibition blocked/attenuated these effects in addition to significantly increase in resting MAP and HR (with larger effects in T and l-arginine treated rats vs. respective controls, †P < 0.05). T increased nNOS gene and protein expression within the ventromedial and posterior PVN nuclei (†P < 0.05). PVN nitirite levels were also increased in T and l-arginine groups (†P < 0.05). Data strongly suggest that training by increasing NO availability within PVN preautonomic nuclei favors both the slow down of sympathetic and the augmentation of parasympathetic activity and facilitates baroreflex control, therefore improving autonomic regulation of the heart in healthy rats.

Benefits of L-alanine or L-arginine supplementation against adiposity and glucose intolerance in monosodium glutamate-induced obesity.

PURPOSE: L-alanine (Ala) and L-arginine (Arg) have been reported to regulate pancreatic ß-cell physiology and to prevent body fat accumulation in diet-induced obesity. Here, we assessed growth and adiposity parameters, glucose tolerance, insulin secretion and the expression of insulin and nutrient-regulated proteins in monosodium glutamate (MSG)-obese mice supplemented with either Ala or Arg. METHODS: Male newborn C57Bl/6 mice received a daily subcutaneous injection of MSG or saline solution (CTL group), during the first 6 days of life. From 30 to 90 days of age, MSG and CTL mice received or not 2.55 % Ala (CAla or MArg groups) or 1.51 % Arg-HCl (CArg or MArg groups) in their drinking water. RESULTS: Adult MSG mice displayed higher adiposity associated with lower phosphorylation of the adipogenic enzyme, ACC, in adipose tissue. Glucose intolerance in MSG mice was linked to lower insulin secretion and to lower expression of IRß in adipose tissue, as well as AS160 phosphorylation in skeletal muscle. Perigonadal fat depots were smaller in Ala and Arg mice, while retroperitoneal fat pads were decreased by Ala supplementation only. Both Ala and Arg improved fed-state glycemia as well as IRß and pAS160 content, but only Ala led to improved glucose tolerance and insulin secretion. Adipostatic signals were increased in MAla mice, as indicated by enhanced AMPK phosphorylation and pACC content in fat depots. CONCLUSIONS: Ala supplementation led to more pronounced metabolic improvements compared to Arg, possibly due to suppression of lipogenesis through activation of the AMPK/ACC pathway.

l-arginine supplementation improved neonatal outcomes in pregnancies with hypertensive disorder or intrauterine growth restriction: A systematic review and meta-analysis of randomized controlled trials.

BACKGROUND & AIMS: Previous research established that the availability of l-arginine affects placental vascular development and fetal growth. However, practical details associated with the effects of l-arginine supplementation on the neonatal outcomes of hypertensive disorder (HD) and intrauterine growth restriction (IUGR) pregnancies are limited. METHODS: The PubMed, ScienceDirect, and Web of Science databases were searched for peer-reviewed literature published by September 30, 2021 to investigate the operational details of l-arginine supplementation in improving neonatal outcomes in complicated pregnancies. Standardized mean difference (SMD) and weighted mean difference (WMD) of continuous variables, as well as the risk ratio (RR) for categorical variables were pooled by random-effects models. RESULTS: The results indicated that l-arginine supplementation increased the plasma nitric oxide (NO) concentrations in IUGR pregnancies (SMD: 0.71; 95% CI: 0.45, 0.97; I2 = 0%), but decreased the risk of preeclampsia in HD mothers (RR: 0.49; 95% CI: 0.31, 0.76; I2 = 0%). Administration with l-arginine elevated birth weights both in hypertensive and IUGR pregnant women, with WMDs of 194.70 g (95% CI: 58.21, 331.20; I2 = 44.2%) and 134.00 g (95% CI: 43.53, 224.46; I2 = 42.4%), respectively. However, the intervention had no effect on gestational age except in HD pregnancies (WMD: 7.05 d; 95% CI: 3.16, 10.95; I2 = 36.5%). l-arginine administration during pregnancy significantly reduced the small for gestational age (SGA) risk of fetus both in HD (RR: 0.51; 95% CI: 0.31, 0.83; I2 = 0.0%) and IUGR mothers (RR: 0.46; 95% CI: 0.25, 0.88; I2 = 0.0%). Subgroup analyses revealed that l-arginine supplementation at <4 g/d dosage or for ≥1-month duration or in the third trimester had a greater effect on birth weights in HD women without proteinuria, but a higher l-arginine dosage was more beneficial for extending gestational age and reducing the risk of SGA in older pregnancies. Additionally, intravenous infusion of l-arginine, but not oral administration, significantly increased birth weight in IUGR pregnancies with elevated NO concentrations, although the recommended amount should be confined to <4 g/d. CONCLUSIONS: These findings provide practical guidelines for l-arginine supplementation to improve the birth outcomes of complicated pregnancies. REGISTRY NUMBER: CRD42021246290 (https://www.crd.york.ac.uk/PROSPERO).

Dietary supplements for improving nitric-oxide synthesis.

Nitric oxide (NO) is an essential component of the human body, involved in blood vessel dilation, stimulation of hormone release, signaling and regulation of neurotransmission. Nitric oxide is synthesized by nitric-oxide-synthase-dependent and -independent pathways. Nitric oxide supplementation improves cardiac health, enhances performance during exercise, reduces high blood pressure during pregnancy, reduces erectile dysfunction and improves healing processes and respiratory response. Nitric-oxide-associated benefits are mostly apparent in untrained or moderately trained individuals. L-arginine and L-citrulline supplementation contributes to nitric oxide levels because L-arginine is directly involved in NO synthesis, whereas L-citrulline acts as an L-arginine precursor that is further converted to NO by a reaction catalyzed by NO synthase. L-arginine supplements increase respiratory response and enhance performance during exercise, while L-citrulline with malate and other molecules increase working capacity. Various studies involving beetroot juice have reported a significant increase in plasma nitrite levels, regarded as markers of NO, after intake of beetroot juice. Although NO supplementation may have mild to moderate side-effects, using smaller or divided doses could avoid some of these side-effects. Since nitric oxide supplementation may worsen certain health conditions and may interfere with certain medicines, it should only be taken under medical supervision.

The effect of l-arginine supplementation and surgical trauma on the frequency of myeloid-derived suppressor cells and T lymphocytes in tumour and blood of colorectal cancer patients.

PURPOSE: l-arginine (L-arg) deficiency causes immunosuppression, but it is unknown if L-arg supplementation in colorectal cancer (CRC) patients restores immune system activity. Our objective was to investigate the effect of L-arg supplementation on the frequency of monocytic (M) and polymorphonuclear (PNM) myeloid-derived suppressor cells (M-MDSCs and PMN-MDSCs, respectively). METHODS: We enrolled 65 CRC patients (34 males, 31 females) aged 69 â€‹± â€‹10 years into a prospective, randomised, double-blind study. Twenty-eight patients received L-arg and 37 received placebo for 9 days at a dose of 10 â€‹g/day. The frequency changes in MDSC, CD4+ cells and the concentration of C-reactive protein (CRP) were assessed before supplementation with L-arg (test 1), after 9 days of supplementation (test 2), and after surgery on day 11 (test 3). RESULTS: The frequency of M-MDSC in the tumours of patients receiving L-arg supplementation was higher than in placebo-treated patients, as was the frequency of PMN-MDSC and M-MDSC in the mucosa. CRP concentration in the serum of placebo-treated patients in test 2 was higher than in test 1, and the concentration in the serum of patients with L-arg supplementation in test 2 was lower than in test 1. Moreover, the expression pattern of the argininosuccinate synthase 1 (ASS1) suggests that CRC is not auxotrophic for L-arg. CONCLUSIONS: The results of this study do not support the hypothesis that L-arg supplementation in CRC patients can reduce immunosuppression by decreasing the frequency of suppressor cells and increasing the frequency of effector CD4+ T cells.

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

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

Effect of L-arginine supplementation on insulin resistance and serum adiponectin concentration in rats with fat diet.

OBJECT: The purpose of this study was to determine whether supplementation with L-arginine, a substrate used in the production of nitric oxide, had an effect on adiponectin concentration in rats fed a high-fat diet. The influence of L-arginine on insulin resistance was also evaluated. MATERIALS AND METHODS: The experiment was performed using 36 Wistar rats divided into three groups: group 1 was fed a standard diet, group 2 a high-fat (HF) diet, group 3 a HF diet supplemented with L-arginine. After 42 days, serum levels of lipids, glucose, insulin, NO, and adiponectin were measured. Insulin resistance (IR) was estimated by the Homeostasis Model Assessment (HOMA). RESULTS: Body mass was equal in all 3 groups, at the beginning as well as at the end of the study, however, in group 2 the amount of visceral fat was greater after 42 days. In group 3, there was a tendency for visceral fat to decrease. An increase in cholesterol, triglycerides, insulin and HOMA-IR, as well as a decrease in NO and adiponectin were seen in group 2, while in group 3, L-arginine supplementation ameliorated these disturbances. CONCLUSIONS: Our study shows that L-arginine supplementation in rats fed a HF diet is associated with an increase in insulin sensitivity. Our findings suggest that the underlying mechanism could be at least partially related to an increase in adiponectin concentration.

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.