Pharmacokinetics of intravenous and oral L-arginine in normal volunteers

Gut microbial alterations in arginine metabolism determine bone mechanical adaptation

Although mechanical loading is essential for maintaining bone health and combating osteoporosis, its practical application is limited to a large extent by the high variability in bone mechanoresponsiveness. Here, we found that gut microbial depletion promoted a significant reduction in skeletal adaptation to mechanical loading. Among experimental mice, we observed differences between those with high and low responses to exercise with respect to the gut microbial composition, in which the differential abundance of Lachnospiraceae contributed to the differences in bone mechanoresponsiveness. Microbial production of L-citrulline and its conversion into L-arginine were identified as key regulators of bone mechanoadaptation, and administration of these metabolites enhanced bone mechanoresponsiveness in normal, aged, and ovariectomized mice. Mechanistically, L-arginine-mediated enhancement of bone mechanoadaptation was primarily attributable to the activation of a nitric-oxide-calcium positive feedback loop in osteocytes. This study identifies a promising anti-osteoporotic strategy for maximizing mechanical loading-induced skeletal benefits via the microbiota-metabolite axis.

Fragment-based drug discovery for disorders of the central nervous system: designing better drugs piece by piece

Fragment-based drug discovery (FBDD) has emerged as a powerful strategy to confront the challenges faced by conventional drug development approaches, particularly in the context of central nervous system (CNS) disorders. FBDD involves the screening of libraries that comprise thousands of small molecular fragments, each no greater than 300 Da in size. Unlike the generally larger molecules from high-throughput screening that limit customisation, fragments offer a more strategic starting point. These fragments are inherently compact, providing a strong foundation with good binding affinity for the development of drug candidates. The minimal elaboration required to transition the hit into a drug-like molecule is not only accelerated, but also it allows for precise modifications to enhance both their activity and pharmacokinetic properties. This shift towards a fragment-centric approach has seen commercial success and holds considerable promise in the continued streamlining of the drug discovery and development process. In this review, we highlight how FBDD can be integrated into the CNS drug discovery process to enhance the exploration of a target. Furthermore, we provide recent examples where FBDD has been an integral component in CNS drug discovery programs, enabling the improvement of pharmacokinetic properties that have previously proven challenging. The FBDD optimisation process provides a systematic approach to explore this vast chemical space, facilitating the discovery and design of compounds piece by piece that are capable of modulating crucial CNS targets.

Nitric oxide: A potential etiological agent for vaso-occlusive crises in sickle cell disease

Nitric oxide (NO), a vasodilator contributes to the vaso-occlusive crisis associated with the sickle cell disease (SCD). Vascular nitric oxide helps in vasodilation, controlled platelet aggregation, and preventing adhesion of sickled red blood cells to the endothelium. It decreases the expression of pro-inflammatory genes responsible for atherogenesis associated with SCD. Haemolysis and activated endothelium in SCD patients reduce the bioavailability of NO which promotes the severity of sickle cell disease mainly causes vaso-occlusive crises. Additionally, NO depletion can also contribute to the formation of thrombus, which can cause serious complications such as stroke, pulmonary embolism etc. Understanding the multifaceted role of NO provides valuable insights into its therapeutic potential for managing SCD and preventing associated complications. Various clinical trials and studies suggested the importance of artificially induced nitric oxide and its supplements in the reduction of severity. Further research on the mechanisms of NO depletion in SCD is needed to develop more effective treatment strategies and improve the management of this debilitating disease.

The Emerging Role of Prediabetes and Its Management: Focus on L-Arginine and a Survey in Clinical Practice

The worldwide impressive growth of metabolic disorders observed in the last decades, especially type 2 diabetes mellitus and obesity, has generated great interest in the potential benefits of early identification and management of patients at risk. In this view, prediabetes represents a high-risk condition for the development of type 2 diabetes mellitus and cardiovascular diseases, and an ideal target to intercept patients before they develop type 2 diabetes gaining a prominent role even in international guidelines. For prediabetic individuals, lifestyle modification is the cornerstone of diabetes prevention, with evidence of about 50% relative risk reduction. Accumulating data also show potential benefits from pharmacotherapy. In this context, the only available data pertain to metformin as a pharmaceutical drug and vitamin D and L-arginine as nutraceuticals. L-arginine appears to be a very interesting tool in the clinical management of patients with pre-diabetes. In this review we summarize the current knowledge on the role of L-arginine in prediabetes as a potentially useful preventive strategy against the progression to type 2 diabetes, with a particular focus on the underlying molecular mechanisms and the past and ongoing trials. In this article we also report the interesting data about the perception of the prediabetic condition and its therapeutic management in the clinical practice in Italy. An early identification and a prompt management of people with prediabetes appears to be of paramount importance to prevent the progression to diabetes and avoid its cardiovascular consequences.

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.

The pathogenic pathways of cardiovascular disease in perimenopausal women

Introduction

Menopause is associated with disturbed cardiovascular health. The objective of the study was to compare the effect of hormonal replacement therapy (HRT) and its combination with diet, L-arginine, and xylitol solutions on metabolic processes and cardiovascular health in perimenopausal women.

Material and methods

In total 106 women were enrolled in the cross-sectional study. The 36 patients of Group II received HRT. 35 women who had been prescribed additionally to HRT a diet, L-arginine, and also xylitol were included in Group III. 35 healthy reproductive-aged women were included in Group I (control). The variables body mass index (BMI), heart rate (HR), blood pressure (BP), lipid and carbohydrate metabolism and C-reactive protein, and menopausal Cooperman's score were determined before and after the 3-month program.

Results

The obtained results showed the homogeneity of average age, BMI, HR, BP, and Cooperman's score in Group II and Group III before inclusion in the study. But several variables changed significantly after a 3-month period. The study showed the effect of the 3-month program on BMI and Cooperman's score. We also found the restoration of the lipid profiles in Group III. The patients of perimenopausal age featured elevated levels of insulin and C-RP (C-reactive protein). The restoration of levels of insulin and CRP occurred in the process of the 3-month program.

Conclusions

The use of a 3-month program including diet, xylitol, and L-arginine solutions contributed to the reduction of Cooperman's score, chronic inflammation, and restoration of lipid and carbohydrate metabolism.

Alternative Excipients for Protein Stabilization in Protein Therapeutics: Overcoming the Limitations of Polysorbates

Given their safety and efficiency in protecting protein integrity, polysorbates (PSs) have been the most widely used excipients for the stabilization of protein therapeutics for years. In recent decades, however, there have been numerous reports about visible or sub-visible particles in PS-containing biotherapeutic products, which is a major quality concern for parenteral drugs. Alternative excipients that are safe for parenteral administration, efficient in protecting different protein drugs against various stress conditions, effective in protein stabilization in high-concentrated liquid formulations, stable under the storage conditions for the duration of the product's shelf-life, and compatible with other formulation components and the primary packaging are highly sought after. The aim of this paper is to review potential alternative excipients from different families, including surfactants, carbohydrate- and amino acid-based excipients, synthetic amphiphilic polymers, and ionic liquids that enable protein stabilization. For each category, important characteristics such as the ability to stabilize proteins against thermal and mechanical stresses, current knowledge related to the safety profile for parenteral administration, potential interactions with other formulation components, and primary packaging are debated. Based on the provided information and the detailed discussion thereof, this paper may pave the way for the identification or development of efficient excipients for biotherapeutic protein stabilization.

A Translational Randomized Trial of Perioperative Arginine Immunonutrition on Natural Killer Cell Function in Colorectal Cancer Surgery Patients

BACKGROUND

Surgery results in severe impairment of natural killer (NK) cell cytotoxicity (NKC) and activity (NKA, cytokine secretion), and a dramatic drop in arginine levels. Postoperative immunosuppression is associated with increased complications and recurrence. Perioperative arginine is reported to reduce postoperative complications. Because arginine modulates NK cell function, this study aimed to determine whether perioperative consumption of arginine-enriched supplements (AES) can improve NK cell function in colorectal cancer (CRC) surgery patients.

METHODS

This study randomized 24 CRC patients to receive the AES or isocaloric/isonitrogenous control supplement three times a day for five days before and after surgery. The AES contained 4.2 g of arginine per dose (12.6 g/day). The primary objective was to determine whether AES improved NKC by 50 % compared with the control group after surgery.

RESULTS

On surgery day (SD) 1, NKC was significantly reduced postoperatively in the control group by 50 % (interquartile range [IQR], 36-55 %; p = 0.02) but not in the AES group (25 % reduction; IQR, 28-75 %; p = 0.3). Furthermore, AES had no benefit in terms of NKA or NK cell number. Compliance was much greater preoperatively (>91 %) than postoperatively (<46 %). However, despite excellent preoperative compliance, arginine was rapidly cleared from the blood within 4 h after consumption and therefore, did not prevent the postoperative drop in arginine.

CONCLUSIONS

Oral consumption of arginine immunonutrition resulted in a modest improvement in NKC after surgery but was unable to prevent postoperative arginine depletion or the suppression of NKA (ClinicalTrials.gov NCT02987296).

The effects of acute and chronic oral l-arginine supplementation on exercise-induced ammonia accumulation and exercise performance in healthy young men: A randomised, double-blind, cross-over, placebo-controlled trial

Objective

This study examined the effects of a single and chronic oral intake of l-arginine supplementation on blood ammonia concentration and exercise performance.

Methods

Sixteen healthy young men (mean ± standard deviation, 23 ± 3 years) participated in a randomised, double-blind, cross-over, placebo-controlled study. For the acute trials, the participants consumed 200 mL of water containing either l-arginine (5 g) or placebo (dextrin; 5.5 g) and performed cycling exercise at 75% of heart rate reserve for 60 min, followed by a 15-min cycling performance test. For the chronic trials, the participants continued to consume each designated supplement twice a day for another 13 days, and then repeated the same protocol as the acute trials at day 15. After a 14-day washout period, the participants changed the supplement and repeated the same protocol as above.

Results

Plasma ammonia concentrations were lower in the chronic arginine trial than those in both acute placebo (mean difference - 4.5 μmol/L) and acute arginine (mean difference - 5.1 μmol/L) trials (p < 0.05). There was no difference in plasma ammonia concentration between the chronic arginine and chronic placebo trials (mean difference - 1.2 μmol/L). No differences were found in mean power output during the performance test between the chronic arginine and chronic placebo trials (mean difference 0.5 W) or between the acute arginine and acute placebo trials (mean difference 0.0 W).

Conclusions

An acute and chronic oral intake of l-arginine supplementation did not attenuate exercise-induced increases in ammonia accumulation or had no significant impact on cycling performance.

The effects of acute arginine supplementation on neuroendocrine, metabolic, cardiovascular, and mood outcomes in younger men: a double-blind placebo controlled trial

Objectives:

Arginine is an amino-acid supplement and precursor for nitric-oxide synthesis, which affects various biologic processes. The objective of this study was to determine the effects of arginine supplementation on growth hormone (GH) and metabolic parameters.

Methods:

Thirty physically active, healthy men (age 18–39 y; body mass index: 18.5–25 kg/m²) were randomized in a double-blind, placebo-controlled, crossover trial. Arginine (10 g) and placebo (0 g) beverages were consumed after an overnight fast. Blood samples were collected at baseline and 1.5, 3.0, and 24 h after supplementation. The primary outcomes were serum GH and metabolomics. Also, amino acids, glucose, insulin, triacylglycerols, thyroid hormones, testosterone, cortisol, dehydroepiandrosterone, and mood state were assessed. Individuals with detectable increases in GH were analyzed separately (responders: n = 16; < 0.05 ng/mL at 1.5 h). Repeated-measure analyses of variance estimated the treatment effects at each timepoint.

Results:

Arginine levels increased at 1.5 h (146%) and 3.0 h (95%; P ≤ 0.001) and GH (193%) and thyroid-stimulating hormone (TSH; 10%) levels at 24 h (P < 0.05) after arginine versus placebo consumption. Arginine versus placebo increased glucose levels at 1.5 h (5%) and 3.0 h (3%; P ≤ 0.001). Arginine versus placebo did not affect other dependent measures, including mood state (P > 0.05), but changes in the urea, glutamate, and citric-acid pathways were observed. Among responders, arginine versus placebo increased GH at 1.5 h (37%), glucose at 1.5 h (4%) and 3.0 h (4%), and TSH at 24 h (9%; P < 0.05). Responders had higher levels of benzoate metabolites at baseline and 1.5 h, and an unknown compound (X-16124) at baseline, 1.5 h, and 24 h that corresponds to a class of gut microbes (P < 0.05).

Conclusions:

Arginine supplementation modestly increased GH, glucose, and TSH levels in younger men. Responders had higher benzoate metabolites and an unknown analyte attributed to the gut microbiome. Future studies should examine whether the increased prevalence of these gut microorganisms corresponds with GH response after arginine supplementation.

Effect of dietary amino acids L-arginine and lysine on implant osseointegration

Background:

Low protein diets have been linked to decreased bone strength in humans. Arginine and lysine can help improve the healing process and stimulate growth factors.

Aim:

To evaluate if dietary arginine and lysine combination aids in reducing the time frame for osseo-integration process and bone formation in animal models.

Materials and Methods:

Controls (Group I) and Experimental (Group II) consisted of twelve New Zealand rabbits. Animals in the experimental group were fed a conventional pellet food, water, and the amino acids L-Lysine and L-Arginine (Biovea, USA), whereas those in the control group were offered a standard diet. In both groups of animals, titanium implants measuring 2.5mm* 6mm were implanted in each tibial osteotomy. At the end of two weeks, four weeks, and eight weeks, the animals were euthanized. The tibial bone was removed and preserved in 1% formalin. The samples were analysed histologically for presence or absence of Necrosis, presence or absence of clot formation, Vascularization, Fibroblast, Osteoblasts and Osteoid Bone growth.

Results:

Histological outcomes on vascularization, fibroblasts, osteoblasts, osteoid bone growth inferred no significant variation between the control and experimental groups after 8 weeks (P>.05).

Conclusion:

Vascularity, clot organisation, osteoblasts, fibroblasts, and osteoid bone production in the protein fed experimental group animals were better in initial stages of healing when compared to control groups.

The Effects of L-Arginine in Hypertensive Patients: A Literature Review

Hypertension (HTN) is a chronic disease that affects more than 972 million people throughout the world, which is usually associated with endothelial dysfunction. Scientists are closely investigating endothelial dysfunction and have recently discovered the endothelium-derived relaxing factor (EDRF) known as NO (nitric oxide), which is derived from a semi-essential amino acid, L-arginine, by the action of endothelial nitric oxide synthase (eNOS). Production of adequate amounts of NO by vascular endothelial cells is essential to maintain normal blood pressure and prevent the development of HTN. Asymmetrical dimethylarginine (ADMA) is an endogenous NOS inhibitor that is increased in those with HTN especially in patients with renal dysfunction. In the present review, the role of L-arginine, arginine transporters, and ADMA in the pathobiology of HTN and their potential clinical significance are discussed.

Inhibition of arginase modulates T-cell response in the tumor microenvironment of lung carcinoma

Immunotherapy has demonstrated significant activity in a broad range of cancer types, but still the majority of patients receiving it do not maintain durable therapeutic responses. Amino acid metabolism has been proposed to be involved in the regulation of immune response. Here, we investigated in detail the role of arginase 1 (Arg1) in the modulation of antitumor immune response against poorly immunogenic Lewis lung carcinoma. We observed that tumor progression is associated with an incremental increase in the number of Arg1⁺ myeloid cells that accumulate in the tumor microenvironment and cause systemic depletion of ʟ-arginine. In advanced tumors, the systemic concentrations of ʟ-arginine are decreased to levels that impair the proliferation of antigen-specific T-cells. Systemic or myeloid-specific Arg1 deletion improves antigen-induced proliferation of adoptively transferred T-cells and leads to inhibition of tumor growth. Arginase inhibitor was demonstrated to modestly inhibit tumor growth when used alone, and to potentiate antitumor effects of anti-PD-1 monoclonal antibodies and STING agonist. The effectiveness of the combination immunotherapy was insufficient to induce complete antitumor responses, but was significantly better than treatment with the checkpoint inhibitor alone. Together, these results indicate that arginase inhibition alone is of modest therapeutic benefit in poorly immunogenic tumors; however, in combination with other treatment strategies it may significantly improve survival outcomes.

A novel, multitargeted endogenous metabolic modulator composition impacts metabolism, inflammation, and fibrosis in nonalcoholic steatohepatitis-relevant primary human cell models

Nonalcoholic steatohepatitis (NASH) is a complex metabolic disease of heterogeneous and multifactorial pathogenesis that may benefit from coordinated multitargeted interventions. Endogenous metabolic modulators (EMMs) encompass a broad set of molecular families, including amino acids and related metabolites and precursors. EMMs often serve as master regulators and signaling agents for metabolic pathways throughout the body and hold the potential to impact a complex metabolic disease like NASH by targeting a multitude of pathologically relevant biologies. Here, we describe a study of a novel EMM composition comprising five amino acids and an amino acid derivative (Leucine, Isoleucine, Valine, Arginine, Glutamine, and N-acetylcysteine [LIVRQNac]) and its systematic evaluation across multiple NASH-relevant primary human cell model systems, including hepatocytes, macrophages, and stellate cells. In these model systems, LIVRQNac consistently and simultaneously impacted biology associated with all three core pathophysiological features of NASH—metabolic, inflammatory, and fibrotic. Importantly, it was observed that while the individual constituent amino acids in LIVRQNac can impact specific NASH-related phenotypes in select cell systems, the complete combination was necessary to impact the range of disease-associated drivers examined. These findings highlight the potential of specific and potent multitargeted amino acid combinations for the treatment of NASH.

Asymmetric dimethylarginine predicts perioperative cardiovascular complications in patients undergoing medium-to-high risk non-cardiac surgery

Objectives

Perioperative cardiovascular events remain an important factor that affects surgery outcome. We assessed if asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis, predicts perioperative risk, and if pre-operative supplementation with L-arginine/L-citrulline improves the plasma L-arginine/ADMA ratio.

Methods

In this prospective study, planned thoracic and/or abdominal surgery patients were randomized to receive L-arginine/L-citrulline (5 g/day) or placebo 1 to 5 days before surgery. We measured perioperative plasma ADMA and L-arginine levels. The primary outcome was a 30-day combined cardiovascular endpoint.

Results

Among 269 patients, 23 (8.6%) experienced a major adverse cardiovascular event. ADMA and C-reactive protein were significantly associated with the incidence of cardiovascular complications in the multivariable-adjusted analysis. The L-arginine plasma concentration was significantly higher on the day of surgery with L-arginine/L-citrulline supplementation compared with placebo. In patients with high pre-operative ADMA, there was a non-significant trend towards reduced incidence of the primary endpoint with L-arginine/L-citrulline supplementation (six vs. nine events).

Conclusions

ADMA is a predictor of major adverse cardiovascular complications in the perioperative period for patients who are undergoing major abdominal and/or thoracic surgery. Supplementation with L-arginine/L-citrulline increased the L-arginine plasma concentration, enhanced the L-arginine/ADMA ratio, and induced a trend towards fewer perioperative events.

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.

The Impact of Amino Acids on Postprandial Glucose and Insulin Kinetics in Humans: A Quantitative Overview

Different amino acids (AAs) may exert distinct effects on postprandial glucose and insulin concentrations. A quantitative comparison of the effects of AAs on glucose and insulin kinetics in humans is currently lacking. PubMed was queried to identify intervention studies reporting glucose and insulin concentrations after acute ingestion and/or intravenous infusion of AAs in healthy adults and those living with obesity and/or type 2 diabetes (T2DM). The systematic literature search identified 55 studies that examined the effects of l-leucine, l-isoleucine, l-alanine, l-glutamine, l-arginine, l-lysine, glycine, l-proline, l-phenylalanine, l-glutamate, branched-chain AAs (i.e., l-leucine, l-isoleucine, and l-valine), and multiple individual l-AAs on glucose and insulin concentrations. Oral ingestion of most individual AAs induced an insulin response, but did not alter glucose concentrations in healthy participants. Specific AAs (i.e., leucine and isoleucine) co-ingested with glucose exerted a synergistic effect on the postprandial insulin response and attenuated the glucose response compared to glucose intake alone in healthy participants. Oral AA ingestion as well as intravenous AA infusion was able to stimulate an insulin response and decrease glucose concentrations in T2DM and obese individuals. The extracted information is publicly available and can serve multiple purposes such as computational modeling.

Therapeutic Potential of Citrulline as an Arginine Supplement: A Clinical Pharmacology Review

Supplemental arginine has shown promise as a safe therapeutic option to improve endogenous nitric oxide (NO) regulation in cardiovascular diseases associated with endothelial dysfunction. In clinical studies in adults, L-arginine, an endogenous amino acid, was reported to improve cardiovascular function in hypertension, pulmonary hypertension, preeclampsia, angina, and MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome. L-citrulline, a natural precursor of L-arginine, is more bioavailable than L-arginine because it avoids hepatic first-pass metabolism and has a longer circulation time. Although not yet well-studied, arginine/citrulline has immense therapeutic potential in some life-threatening diseases in children. However, the optimal clinical development of arginine or citrulline in children requires more information about pharmacokinetics and exposure-response relationships at appropriate ages and under relevant disease states. This article summarizes the preclinical and clinical studies of arginine/citrulline in both adults and children, including currently available pharmacokinetic information. The pharmacology of arginine/citrulline is confounded by several patient-specific factors such as variations in baseline arginine/citrulline due to developmental ages and disease states. Currently available pharmacokinetic studies are insufficient to inform the optimal design of clinical studies, especially in children. Successful bench-to-bedside clinical translation of arginine supplementation awaits information from well-designed pharmacokinetic/pharmacodynamic studies, along with pharmacometric approaches.

Myeloid Cell-Derived Arginase in Cancer Immune Response

Amino acid metabolism is a critical regulator of the immune response, and its modulating becomes a promising approach in various forms of immunotherapy. Insufficient concentrations of essential amino acids restrict T-cells activation and proliferation. However, only arginases, that degrade L-arginine, as well as enzymes that hydrolyze L-tryptophan are substantially increased in cancer. Two arginase isoforms, ARG1 and ARG2, have been found to be present in tumors and their increased activity usually correlates with more advanced disease and worse clinical prognosis. Nearly all types of myeloid cells were reported to produce arginases and the increased numbers of various populations of myeloid-derived suppressor cells and macrophages correlate with inferior clinical outcomes of cancer patients. Here, we describe the role of arginases produced by myeloid cells in regulating various populations of immune cells, discuss molecular mechanisms of immunoregulatory processes involving L-arginine metabolism and outline therapeutic approaches to mitigate the negative effects of arginases on antitumor immune response. Development of potent arginase inhibitors, with improved pharmacokinetic properties, may lead to the elaboration of novel therapeutic strategies based on targeting immunoregulatory pathways controlled by L-arginine degradation.

Effect of Preoperative Administration of Oral Arginine and Glutamine in Patients with Enterocutaneous Fistula Submitted to Definitive Surgery: a Prospective Randomized Trial

BACKGROUND

The use of glutamine and arginine has shown several advantages in postoperative outcomes in patients after gastrointestinal surgery. We determined the effects of its use in patients with enterocutaneous fistula after operative treatment.

PATIENTS AND METHODS

Forty patients with enterocutaneous fistula were randomly assigned to one of two groups. The control group received the standard medical care while the patients of the experimental group were supplemented with enteral administration of 4.5 g of arginine and 10 g of glutamine per day for 7 days prior to the surgery. The primary outcome variable was the recurrence of the fistula and the secondary outcomes were preoperative and postoperative serum concentrations of interleukin 6 and C-reactive protein and postoperative infectious complications.

RESULTS

Twenty patients were assigned to each group. The fistula recurred in two patients (10%) of the experimental group and in nine patients (45%) of the control group (P < 0.001). We found a total of 13 infectious complications in six patients of the control group (all with fistula recurrence) and none in the experimental group. Mean preoperative serum concentrations of interleukin 6 and C-reactive protein were lower in patients from the experimental group. In addition, these levels were lower in patients who had recurrence if compared to patients that did not recur.

CONCLUSION

Preoperative administration of oral arginine and glutamine could be valuable in the postoperative recovery of patients with enterocutaneous fistulas submitted to definitive surgery.

Potential roles of Citrulline and watermelon extract on metabolic and inflammatory variables in diabetes mellitus, current evidence and future directions: A systematic review

OBJECTIVE

Diabetes mellitus is a prevalent endocrine disorder worldwide. Citrulline is an α-amino acid, which is abundant in watermelon, and a precursor of arginine and nitric oxide. Decreased bioavailability of nitric oxide is associated with insulin resistance. The present systematic review focused on the existing evidence of citrulline and watermelon extract effects on metabolic and inflammatory parameters in diabetes mellitus.

METHODS

A systematic search of the databases PubMed, Scopus, EMBASE, ProQuest and Google Scholar was conducted for relevant papers published from inception until October 2018. All clinical trials, animal and in vitro studies published in the English language that assessed the role of citrulline and watermelon extract on diabetes mellitus, were eligible. Studies providing inadequate information were excluded.

RESULTS

Out of 1262 articles we found, only eight articles met the inclusion criteria for analysis. In three studies an increase in the synthesis of nitric oxide was reported with citrulline and watermelon extract supplementation. Four studies showed a significant reduction in blood glucose after supplementation with watermelon extract, and two studies reported a decrease in a number of inflammatory biomarkers following citrulline supplementation. Although citrulline intake caused a significant reduction in HOMA-IR in one study, inconsistent results were revealed on the effects of citrulline and watermelon extract on insulin levels and lipid profile.

CONCLUSION

Citrulline and watermelon extract could improve nitric oxide synthesis, glycaemic status and inflammation in diabetes mellitus. However, further studies are required to shed light on the underlying mechanisms.

The Arginine Deiminase Operon Is Responsible for a Fitness Trade-Off in Extended-Spectrum-β-Lactamase-Producing Strains of Escherichia coli

We previously identified an operon involved in an arginine deiminase (ADI) pathway (arc operon) on a CTX-M-producing plasmid from an O102-ST405 strain of Escherichia coli As the ADI pathway was shown to be involved in the virulence of various Gram-positive bacteria, we tested whether the ADI pathway could be involved in the epidemiological success of extended-spectrum-β-lactamase (ESBL)-producing E. coli strains. We studied two collections of human E. coli isolated in France (n = 493) and England (n = 1,509) and show that the prevalence of the arc operon (i) is higher in ESBL-producing strains (12.1%) than in nonproducers (2.5%), (ii) is higher in CTX-M-producing strains (16%) than in other ESBL producers (3.5%), and (iii) increased over time in ESBL-producing strains from 0% before 2000 to 43.3% in 2011 to 2012. The arc operon, found in strains from various phylogenetic backgrounds, is carried by IncF plasmids (85%) or chromosomes (15%) in regions framed by numerous insertion sequences, indicating multiple arrivals. Competition experiments showed that the arc operon enhances fitness of the strain in vitro in lysogeny broth with arginine. In vivo competition experiments showed that the arc operon is advantageous for the strain in a mouse model of urinary tract infection (UTI), whereas it is a burden in a mouse model of intestinal colonization. In summary, we have identified a trait linked to CTX-M-producing strains that is responsible for a trade-off between two main E. coli lifestyles, UTI and gut commensalism. This trait alone cannot explain the wide spread of ESBLs in E. coli but merits epidemiological surveillance.

The Effects of Oral l-Arginine and l-Citrulline Supplementation on Blood Pressure

Nitric oxide (NO) is a well-known vasodilator produced by the vascular endothelium via the enzyme endothelial nitric oxide synthase (eNOS). The inadequate production of NO has been linked to elevated blood pressure (BP) in both human and animal studies, and might be due to substrate inaccessibility. This review aimed to investigate whether oral administration of the amino acids l-arginine (Arg) and l-citrulline (Cit), which are potential substrates for eNOS, could effectively reduce BP by increasing NO production. Both Arg and Cit are effective at increasing plasma Arg. Cit is approximately twice as potent, which is most likely due to a lower first-pass metabolism. The current data suggest that oral Arg supplementation can lower BP by 5.39/2.66 mmHg, which is an effect that is comparable with diet changes and exercise implementation. The antihypertensive properties of Cit are more questionable, but are likely in the range of 4.1/2.08 to 7.54/3.77 mmHg. The exact mechanism by which Cit and Arg exert their effect is not fully understood, as normal plasma Arg concentration greatly exceeds the Michaelis constant (K_m) of eNOS. Thus, elevated plasma Arg concentrations would not be expected to increase endogenous NO production significantly, but have nonetheless been observed in other studies. This phenomenon is known as the "l-arginine paradox".

Effect of ranolazine on plasma arginine derivatives and urinary isoprostane 8-iso-PGF2α in patients with myocardial infarction in the randomized RIMINI-Trial

The purpose of the present study was to assess whether 6-week ranolazine application on top of guideline-based treatment impacts on the arginine/NO pathway and urinary isoprostane 8-iso-PGF_2α as marker of oxidative stress in patients directly after a myocardial infarction. 20 patients with unstable angina pectoris and proof of acute cardiac ischemia entered the study. 10 subjects received the study drug ranolazine in addition to standard treatment, the others received only standard treatment. Urine and venous blood were collected before and after treatment. At the end of the study and compared to baseline, homoarginine levels had increased in the control group. This was not the case in ranolazine-patients. Interestingly, in ranolazine-treated-patients arginine plasma levels were significantly higher at the end of the study than at baseline (difference +26 µmol/L, 95% CI 8.6 to 44 µmol/L). ADMA and SDMA levels were not different. Urine levels of the oxidative stress marker 8-iso-PGF_2α tended to be lower in ranolazine-treated patients (−144 pmol/mg creatinine). Findings of this hypothesis-driven study give evidence that ranolazine treatment enhances arginine plasma levels and lowers oxidative stress.

Acute Effects of L-Arginine Supplementation on Oxygen Consumption Kinetics and Muscle Oxyhemoglobin and Deoxyhemoglobin during Treadmill Running in Male Adults

L-arginine is used as a nitric oxide related supplement intended to improve sports performance, and to enhance muscular recovery during exercise. However, the literature is inconclusive. The aim of this study was to determine the effects of acute oral L-arginine supplementation on O2 consumption kinetics and local muscle blood volume and oxygenation during treadmill running at two different intensities. Using a double-blind, crossover and placebo-controlled design, 11 young healthy male adults were randomly assigned to 6 g of L-arginine (ARG) or placebo (PLA) supplementation that was ingested 60 min before the exercise test. Tests consisted of treadmill run at two different intensities (5 min each; moderate, 90% of ventilatory threshold, VT; and heavy, 50% of the difference between VT and VO2peak) interspersed by 1-min walking. Respiratory gas exchange variables were measured continuously with an automated metabolic cart. Near infrared spectroscopy (NIRS) was used to continuously monitor muscle oxyhemoglobin and deoxyhemoglobin and total hemoglobin. Blood samples were collected before supplementation and 6 min after exercise. Two-way repeated measures ANOVA did not show differences in plasma nitrite concentrations between ARG or PLA conditions during the running tests. No significant differences were observed between ARG and PLA conditions for O2 kinetics as well as for NIRS variables. ARG supplementation does not improve physiological responses associated with oxygen cost and NIRS variables during running treadmill tests. Hence, our results do not support the use of L-arginine as an ergogenic aid for running performance in young healthy males.

Glyoxalase 1 Modulation in Obesity and Diabetes

Significance: Obesity and type 2 diabetes mellitus are increasing globally. There is also increasing associated complications, such as non-alcoholic fatty liver disease (NAFLD) and vascular complications of diabetes. There is currently no licensed treatment for NAFLD and no recent treatments for diabetic complications. New approaches are required, particularly those addressing mechanism-based risk factors for health decline and disease progression. Recent Advances: Dicarbonyl stress is the abnormal accumulation of reactive dicarbonyl metabolites such as methylglyoxal (MG) leading to cell and tissue dysfunction. It is a potential driver of obesity, diabetes, and related complications that are unaddressed by current treatments. Increased formation of MG is linked to increased glyceroneogenesis and hyperglycemia in obesity and diabetes and also down-regulation of glyoxalase 1 (Glo1)-which provides the main enzymatic detoxification of MG. Glo1 functional genomics studies suggest that increasing Glo1 expression and activity alleviates dicarbonyl stress; slows development of obesity, related insulin resistance; and prevents development of diabetic nephropathy and other microvascular complications of diabetes. A new therapeutic approach constitutes small-molecule inducers of Glo1 expression-Glo1 inducers-exploiting a regulatory antioxidant response element in the GLO1 gene. A prototype Glo1 inducer, trans-resveratrol (tRES)-hesperetin (HESP) combination, in corrected insulin resistance, improved glycemic control and vascular inflammation in healthy overweight and obese subjects in clinical trial. Critical Issues: tRES and HESP synergize pharmacologically, and HESP likely overcomes the low bioavailability of tRES by inhibition of intestinal glucuronosyltransferases. Future Directions: Glo1 inducers may now be evaluated in Phase 2 clinical trials for treatment of NAFLD and vascular complications of diabetes.

Amino acid arginine and adducts: autoimmune activity

Arginine is derived from dietary intake, body protein breakdown, or endogenous de novo arginine production. Arginine methylation of non-histone proteins is used in transcriptional regulation. Protein-arginine methylation is used for regulation of transcriptional and various physiological pathological processes. Protein methylation may affect protein-protein, protein-DNA, or protein-RNA interaction. Arginine has an effect on the DNA-binding activity of NF-κB, a dominant transcriptional factor in inflammation. Adduct formation results in increased secretion of messenger molecules such as cytokines and chemokines that mediate communication among cells and promote inflammation. Arginine and lysine amino acid-rich histones in nucleosomes on modification by environmental agents form histone-DNA adducts, making it immunogenic. Alteration of DNA resulting from photomodification could lead to the development of antibodies or mutations to modified DNA. Lysine and arginine-rich histones in nucleosomes on modification by environmental agents form histone-DNA adducts, making it immunogenic. Alteration of DNA resulting from photomodification could lead to the development of antibodies or mutations to modified DNA. Therefore, the DNA-arginine photoadduct and modified photoadduct could have important implications in various pathophysiological conditions such as toxicology, carcinogenesis, and autoimmune phenomena. Abbreviations: Arg: Arginine; SLE: systemic lupus erythematosus; UV: ultraviolet; Tm: thermal melting temperature; NO: nitric oxide; O₂.^-: superoxide anion.

Absent increase in vertebral artery blood flow during l-arginine infusion in hypertensive men

Endothelial dysfunction is observed in the peripheral vasculature of hypertensive patients, but it is unclear how the cerebral circulation is affected. More specifically, little is known about the impact of human hypertension on vertebral artery (VA) endothelial function. This study evaluated whether the endothelial function of the VA is impaired in hypertensive men. For 13 male hypertensive subjects (46 ± 3 yr) and eight age-matched male controls (46 ± 4 yr), blood pressure (BP; photoplethysmography), VA, and common carotid (CC) blood flow (duplex ultrasound) were determined at rest and during 30 min of intravenous l-arginine (30 g; a precursor of nitric oxide) or isotonic saline infusion. Controls and hypertensive subjects demonstrated a similar resting CC (601 ± 30 vs. controls 570 ± 43 ml/min; P = 0.529) and VA blood flow (119 ± 11 vs. controls 112 ± 9 ml/min; P = 0.878). During administration of l-arginine, CC blood flow increased similarly between groups (hypertensive 12 ± 3%, controls 13 ± 2%; P = 0.920). In contrast, the increase in VA blood flow was nonexistent in the hypertensive subjects (0.8 ± 3% vs. controls: 16 ± 4%; P = 0.015) with no significant change in BP. Both CC and VA flow returned to near-resting values within 30 min after the infusion, and for four hypertensive subjects and three controls, time-control experiments using 0.9% saline did not affect VA or CC blood flow significantly. The results demonstrate endothelial dysfunction in the posterior cerebral circulation of middle-aged hypertensive men.

l-Arginine supplementation does not improve muscle function during recovery from resistance exercise

The purpose of this study was to investigate the effects of l-arginine supplementation on muscle recovery after a single session of high-intensity resistance exercise (RE). Twenty healthy young adult participants (22.8 ± 3.4 years old) were assigned to 1 of 2 groups (N = 10 per group): a placebo-supplement group or an l-arginine-supplement group. The groups completed a session of high-intensity RE (0 h) and 3 subsequent fatigue test sessions (at 24, 48, and 72 h postexercise) to assess the time course of muscle recovery. During the test sessions, we assessed the following dependent variables: number of maximum repetitions, electromyographic signal (i.e., root mean square (RMS) and median frequency (MF) slope), muscle soreness, perceived exertion, blood levels of creatine kinase (CK) and lactate, and testosterone:cortisol ratio. Number of maximum repetitions increased at 48 and 72 h postexercise in both groups (time, P < 0.05). CK levels and muscle soreness increased at 24 h postexercise and then progressively returned to baseline at 72 h post exercise in both groups (time, P < 0.05). Lactate levels increased immediately postexercise but were reduced at 24 h postexercise in both groups (time, P < 0.05). Testosterone:cortisol ratio, RMS, and MF slope remained unchanged during the recovery period in both groups (time, P > 0.05). No significant (P > 0.05) group × time interaction was found for all dependent variables during the recovery period. In conclusion, our data indicate that l-arginine supplementation does not improve muscle recovery following a high-intensity RE session in young adults.

The clinical effects of l-arginine and asymmetric dimethylarginine: implications for treatment in secondary Raynaud's phenomenon

Secondary Raynaud's phenomenon (RP) is often the sentinel clinical finding in systemic sclerosis and may precede systemic disease by several years. Altered nitric oxide metabolism plays a critical role in both fibrosis and severe secondary RP phenotypes in these patients. Increased flux through inducible nitric oxide synthase (iNOS) drives cutaneous fibrosis. Failure of flux through endothelial nitric oxide synthase (eNOS) contributes to increased vasoconstriction and decreased vasorelaxation. The underproduction of nitric oxide by eNOS is in part due to increased levels of asymmetric dimethylarginine (ADMA), an endogenous competitive inhibitor of nitric oxide synthase. The inhibitory effects of increased ADMA levels may be counteracted increasing serum l‐arginine, which is often an effective treatment strategy in these patients. As such, l‐arginine‐based therapies should be considered in managing secondary RP, particularly given their favourable safety and tolerability profile. While there is no established dosing regimen, studies of oral l‐arginine in secondary RP suggest that divided dosing may begin at 1–2 g/day and may be titrated up to 10 g/day. Conversely, primary RP is not associated with increased ADMA production which likely accounts for the failure of l‐arginine trials to show benefit in primary RP.

The effect of l-Arginine on Ciliary Beat Frequency in PCD patients, non-PCD respiratory patients and healthy controls

OBJECTIVES

Few studies have examined the potentially therapeutic effect of increasing the production of endogenous nitric oxide (NO) in Primary Ciliary Dyskinesia (PCD) and other chronic respiratory conditions. Nasal NO is low in PCD and has been found to correlate with compromised Ciliary Beat Frequency (CBF). In this study we assessed the effect of increasing l-Arginine, as the substrate of NO synthases, on CBF in biopsies of human respiratory ciliated epithelium.

METHODOLOGY

A total of 28 suspect cases with chronic respiratory manifestations referred for PCD diagnostic testing and 8 healthy controls underwent nasal brushing. Obtained epithelial cells were divided between three culture medium 199 solutions, containing different levels of l-Arginine (0.33 mM as baseline, 1 mM and 10 Mm as increased levels). CBF measurements were obtained at 37 °C and 25 °C at 1, 3 and 24 h after sample acquisition.

RESULTS

Among a total of 36 recruited subjects, 8 had PCD confirmed (PCD n = 8), 20 had PCD excluded (non-PCD n = 20) and 8 were healthy controls (Healthy Controls = 8). Among PCD subjects, ciliary motility was characterized by rotational (n = 5) or dyskinetic (n = 3) beating. At 37 °C, compared to baseline, higher levels of l-Arginine resulted in up to 9% CBF increase at 1 h (p = 0.007), up to 9% CBF increase at 3 h (p < 0.001) and up to 12% CBF increase at 24 h (p = 0.002). Similar although smaller scale increases were recorded at 25 °C. The effect of l-Arginine was time dependent (interaction p = 0.002) and was similar in PCD patients, non-PCD chronic respiratory patients and healthy controls (interaction p = 0.800).

CONCLUSIONS

l-Arginine increases CBF and merits to be evaluated as a potential stimulator of mucociliary clearance in chronic respiratory conditions and congenital ciliary disorders with residual motility. Larger human studies are needed to confirm these findings.

Population pharmacokinetics of arginine glutamate in healthy Chinese volunteers

1. The present study developed population pharmacokinetic models of arginine and glutamate in healthy Chinese volunteers. Two nonlinear mixed-effect models were developed using NONMEM® software (ICON Development Solutions, Ellicott City, MD) to describe the pharmacokinetic properties and to assess the relevant parameters as well as the inter-individual variability. The potential covariates were screened using stepwise approach and the stability and predictive capability of the models were performed using bootstrap and visual predictive check. 2. The concentration time curves of arginine and glutamate were best described by a first-order elimination two-compartment model and a nonlinear elimination one-compartment model, respectively. The final parameter estimation of arginine for CL was 44.1 L/h. Q, V₁ and V₂ were 23 L/h, 20.3 L and 46 L, respectively. The final parameter estimation of glutamate for V_max and K_m were 18.8 mg/h and 77.2 mg/L, respectively. V for low dose and high dose was 23.1 L and 36.3 L, respectively. 3. For arginine, weight was significant covariate on the apparent distribution volume of peripheral compartment. The gain in weight remarkably increases V_2. For glutamate, dose as a significant covariate on the apparent distribution volume was included, subjects received high dose (20 g) have remarkably higher V compared to subjects received low dose (10 g).

Safety and performance benefits of arginine supplements for military personnel: a systematic review

CONTEXT

Dietary supplements are widely used by military personnel and civilians for promotion of health.

OBJECTIVE

The objective of this evidence-based review was to examine whether supplementation with l-arginine, in combination with caffeine and/or creatine, is safe and whether it enhances athletic performance or improves recovery from exhaustion for military personnel.

DATA SOURCES

Information from clinical trials and adverse event reports were collected from 17 databases and 5 adverse event report portals.

STUDY SELECTION

Studies and reports were included if they evaluated the safety and the putative outcomes of enhanced performance or improved recovery from exhaustion associated with the intake of arginine alone or in combination with caffeine and/or creatine in healthy adults aged 19 to 50 years.

DATA EXTRACTION

Information related to population, intervention, comparator, and outcomes was abstracted. Of the 2687 articles screened, 62 articles meeting the inclusion criteria were analyzed. Strength of evidence was assessed in terms of risk of bias, consistency, directness, and precision.

RESULTS

Most studies had few participants and suggested risk of bias that could negatively affect the results. l-Arginine supplementation provided little enhancement of athletic performance or improvements in recovery. Short-term supplementation with arginine may result in adverse gastrointestinal and cardiovascular effects. No information about the effects of arginine on the performance of military personnel was available.

CONCLUSIONS

The available information does not support the use of l-arginine, either alone or in combination with caffeine, creatine, or both, to enhance athletic performance or improve recovery from exhaustion. Given the information gaps, an evidence-based review to assess the safety or effectiveness of multi-ingredient dietary supplements was not feasible, and therefore the development of a computational model-based approach to predict the safety of multi-ingredient dietary supplements is recommended.

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.

Combined effects of aerobic exercise and l-arginine ingestion on blood pressure in normotensive postmenopausal women: A crossover study

After menopause the incidence of cardiovascular diseases increases in women. A decrease in nitric oxide (NO) bioavailability has been pointed out to play a major role in this phenomenon. Since it is believed that l-arginine administration could improve NO bioavailability, the aim of this study was to examine the effects of acute l-arginine administration associated with aerobic exercise on blood pressure (BP), redox state and inflammatory biomarkers in normotensive postmenopausal women (NPW). Sixteen volunteers (57±6yr) were subjected to four experimental sessions (crossover design): arginine+exercise (A-E); arginine (ARG); exercise+placebo (EXE); control (CON). Each session was initiated with either 9g of l-arginine ingestion (ARG or A-E days), placebo (EXE day), or nothing (CON day). The participants performed 30min of aerobic exercise (A-E and EXE days) or sitting rest (CON and ARG days). Blood samples were collected before each session and 45min after the intervention. Office BP and ambulatory blood pressure monitoring (ABPM) were evaluated. NO/cGMP pathway, redox state and inflammatory biomarkers were measured. Systolic BP decreased during the 24-hour in A-E and EXE sessions. However, diastolic BP reduced only in A-E session. No changes were found in the biomarkers concentrations. In conclusion, the association was effective in lowering diastolic BP in NPW. Additionally, physical exercise alone promoted a long lasting effect on systolic BP measured by ABPM in this population, although this beneficial effect was not associated with changes in the cardio-inflammatory biomarkers. Possibly, other factors such as neural influences could be mediating this effect.

Arginine behaviour after arginine or citrulline administration in older subjects

Arginine (ARG) and its precursor citrulline (CIT) are popular dietary supplements, especially for the elderly. However, age-related reductions in lean body mass and alterations in organ functions could change their bioavailability. Pharmacokinetics and tolerance to amino acid (AA) loads are poorly documented in elderly subjects. The objective here was to characterise the plasma kinetics of CIT and ARG in a single-dosing study design. Eight fasting elderly men underwent two separate isomolar oral loading tests (10 g of CIT or 9·94 g of ARG). Blood was withdrawn over an 8-h period to measure plasma AA concentrations. Only CIT, ornithine and ARG plasma concentrations were changed. Volume of distribution was not dependent on AA administered. Conversely, parameters related to ARG kinetics were strongly dependent on AA administered: after ARG load, elimination was higher (ARG>CIT; P=0·041) and admission period+time at peak concentration was lower (ARG<CIT; P=0·033), and the combination of both phenomena results in a marked increase in ARG availability when CIT was administered (ARG<CIT; P=0·033) compared with ARG administration itself. In conclusion, a single CIT administration in the elderly is safe and well tolerated, and CIT proves to be a better in vivo ARG precursor than ARG itself in healthy elderly subjects.

Combining citrulline with atorvastatin preserves glucose homeostasis in a murine model of diet-induced obesity

BACKGROUND AND PURPOSE

NO is a crucial regulator of energy and lipid metabolism, whose homeostasis is compromised during obesity. Combination of citrulline and atorvastatin potentiated NO production in vitro. Here we have assessed the effects of this combination in mice with diet-induced obesity (DIO).

EXPERIMENTAL APPROACH

C57BL/6J male mice were given a standard diet (control) or a high fat-high sucrose diet (DIO) for 8 weeks. DIO mice were then treated with DIO alone, DIO with citrulline, DIO with atorvastatin or DIO with citrulline and atorvastatin (DIOcit-stat) for 3 weeks. Thereafter, body composition, glucose tolerance, insulin sensitivity and liver fat metabolism were measured.

KEY RESULTS

DIOcit-stat mice showed lower body weight, fat mass and epididymal fat depots compared with other DIO groups. Unlike other DIO groups, glucose tolerance and insulin sensitivity of DIOcit-stat, along with blood glucose and insulin concentrations in response to feeding, were restored to control values. Refeeding-induced changes in liver lipogenic activity were also reduced in DIOcit-stat mice compared with those of DIO animals. This was associated with decreased gene expression of the transcription factor SREBP-1, liver X receptor α, ChREBP and of target lipogenic enzymes in the liver of DIOcit-stat mice compared with those of other DIO groups.

CONCLUSIONS AND IMPLICATIONS

The citrulline-atorvastatin combination prevented fat mass accumulation and maintained glucose homeostasis in DIO mice. Furthermore, it potentiated inhibition of hepatic de novo lipogenesis activity. This combination has potential for preservation of glucose homeostasis in patients receiving statin therapy.

A clinical evaluation to determine the safety, pharmacokinetics, and pharmacodynamics of an inositol-stabilized arginine silicate dietary supplement in healthy adult males

Purpose

The purpose of this study was to characterize the pharmacokinetics (PKs) and pharmacodynamics (PDs) of an oral inositol-stabilized arginine silicate dietary supplement.

Subjects and methods

Ten healthy males, 26.7±5.4 years, took three 500 mg arginine silicate capsules (active product) for 14 days. The subjects attended test visits on Days 1 and 14. Fasting blood and saliva collections were performed predose and at 0.5 hours, 1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours postdose for plasma arginine, serum silicon, and salivary nitric oxide (NO) + nitrite.

Results

Day 1 PK parameters (adjusted for body weight) for arginine were peak serum concentration (C_Max) 30.06±7.80 μg/mL, time it takes to reach peak serum concentration (t_Max) 1.13±0.52 hours, and time required to reach half its original concentration (t_1/2) 15.93±9.55 hours and for silicon were C_Max 2.99±0.63 μg/mL, t_Max 2.44±2.05 hours, and t_1/2 34.56±16.56 hours. After Day 1 dose, arginine levels increased at 0.5 hours, 1 hour, 1.5 hours, 2 hours, 3 hours, and 5 hours (P<0.01) and silicon levels increased at 1 hour and 1.5 hours (P<0.05). After Day 14 dose, arginine levels increased at 0.5 hours, 1 hour, and 1.5 hours (P<0.05) and silicon levels increased at 1 hour, 1.5 hours, 2 hours, and 3 hours (P<0.01). After 14 days of use, baseline arginine trended toward being higher than baseline Day 1 (P=0.0645), and 4-hour postdose plasma arginine was significantly higher (P=0.0488) at Day 14 than Day 1. Although not a significant difference, NO, as measured as salivary nitrate, increased in four subjects and stayed the same in six subjects at 0.5 hours after the first dose (P=0.125). After 14 days of use, baseline NO levels increased in six subjects and stayed the same in four subjects; this shift was significant (P=0.031).

Conclusion

The arginine silicate dietary supplement increases blood levels of arginine after a single dose within 30 minutes and blood levels of silicon for up to 1.5 hours. Blood levels of arginine, silicon, and NO (salivary nitrite) were elevated consistently after 14 days of use. The observed increase in baseline salivary nitrite is supporting information that there was some improvement in NO production. Further study on the effect of this supplement on NO production and the resulting physiological effect is warranted. Within the specific protocol of this study, the product was found to be safe.

Arginine protects muscle cells from wasting in vitro in an mTORC1-dependent and NO-independent manner

Amino acids are potent regulators of muscle protein synthesis and breakdown and have received considerable attention for the treatment of muscle wasting conditions. Arginine is critically involved in numerous physiological functions including providing substrate for the production of creatine, urea and nitric oxide (NO) and in the synthesis of new proteins. However, little is known about the direct effects of arginine on skeletal muscle protein synthesis during catabolic conditions. The aims of this study were to determine whether exogenous arginine could protect skeletal muscle cells from wasting directly and whether this effect was dependent on production of NO and/or activation of the rapamycin-sensitive mechanistic target of rapamycin complex 1 (mTORC1) signalling pathway. To explore these aims, we deprived mature C2C12 myotubes from nutrients and growth factors by incubating them in HEPES buffered saline with arginine or equimolar concentrations of alanine (control). Our results show that arginine: increased the ratio of phosphorylated to total mTOR (146 %), S6 (40 %) and 4EBP1 (69 %); increased protein synthesis (69 %) during the first hour of treatment; and increased myotube diameter by ~15 %. Experiments using the NO synthase inhibitor L-NG-Nitroarginine Methyl Ester showed a NO-independent protection from muscle wasting. On the other hand, the mTORC1 inhibitor rapamycin prevented increases in phosphorylated S6, protein synthesis and myotube diameter. The activation of mTORC1 and protein synthesis by arginine was not associated with changes in the phosphorylation status of Akt, but rather increased the expression of the amino acid-sensitive type III PI3-kinase Vps34 signalling protein. These data support a direct role for arginine in the regulation of mTORC1 in skeletal muscle.

Myocardial protection by co-administration of L-arginine and tetrahydrobiopterin during ischemia and reperfusion

BACKGROUND

Reduced bioavailability of nitric oxide (NO) is a key factor contributing to myocardial ischemia and reperfusion injury. The mechanism behind the reduction of NO is related to deficiency of the NO synthase (NOS) substrate L-arginine and cofactor tetrahydrobiopterin (BH4) resulting in NOS uncoupling. The aim of the study was to investigate if the combination of L-arginine and BH4 given iv or intracoronary before reperfusion protects from reperfusion injury.

METHODS

Sprague-Dawley rats and pigs were subjected to myocardial ischemia and reperfusion. Rats received vehicle, L-arginine, BH4, L-arginine+BH4 with or without the NOS-inhibitor L-NMMA iv 5 min before reperfusion. Pigs received infusion of vehicle, L-arginine, BH4 or L-arginine+BH4 into the left main coronary artery for 30 min starting 10 min before reperfusion.

RESULTS

Infarct size was significantly smaller in the rats (50 ± 2%) and pigs (54 ± 5%) given L-arginine+BH4 in comparison with the vehicle groups (rats 65 ± 3% and pigs 86 ± 5%, P<0.05). Neither L-arginine nor BH4 alone significantly reduced infarct size. Administration of L-NMMA abrogated the cardioprotective effect of L-arginine+BH4. Myocardial BH4 levels were 3.5- to 5-fold higher in pigs given L-arginine+BH4 and BH4 alone. The generation of superoxide in the ischemic-reperfused myocardium was reduced in pigs treated with intracoronary L-arginine+BH4 versus the vehicle group (P<0.05).

CONCLUSION

Administration of L-arginine+BH4 before reperfusion protects the heart from ischemia-reperfusion injury. The cardioprotective effect is mediated via NOS-dependent pathway resulting in diminished superoxide generation.

Effect of oral L-arginine administration on exhaled nitric oxide (NO) concentration in healthy volunteers

We previously reported a case of pulmonary hypertension, where the symptoms were improved by oral L-arginine (arginine) administration. Arginine may increase nitric oxide (NO) production in the pulmonary artery. Exhaled NO may reflect pulmonary artery NO production. It has been demonstrated that exhaled NO concentration is higher in patients with allergic diseases, but whether oral arginine administration alters exhaled NO is unknown. Therefore, in this study, we investigated whether oral arginine administration increases exhaled NO among healthy volunteers with and without a history of allergy. Eleven subjects were given a single oral dose (200 mg/kg) of arginine, and their plasma arginine concentrations and exhaled NO were measured up to 150 minutes. Baseline values of exhaled NO concentration were significantly higher in those with a history of allergy (56.4±20.3 ppb, n=5, P< 0.05) than those without (16.8±4.0 ppb, n=6). Oral arginine increased exhaled NO, which peaked at 60 minutes after the administration in those with a history of allergy (85.2±44.8 ppb, n=5). However, the increase in exhaled NO was not significant compared to the baseline values. In contrast, plasma arginine concentration was increased significantly by arginine administration (P< 0.01), regardless of an allergy history. These results suggested that the difference in exhaled NO concentration was not due to a difference in arginine absorption. Serum IgE level was significantly higher in the group with a history of allergy. Eosinophils and white blood cells were within normal range in all subjects. We conclude that oral arginine administration does not significantly increase exhaled NO, regardless of allergy history. However, as arginine administration has been reported to be effective in patients with pulmonary hypertension, it will be necessary to test exhaled NO in subjects with pulmonary hypertension in the future.

AMP-activated protein kinase regulates L-arginine mediated cellular responses

Background

Our prior study revealed the loss in short-term L-Arginine (ARG) therapeutic efficacy after continuous exposure; resulting in tolerance development, mediated by endothelial nitric oxide synthase (eNOS) down-regulation, secondary to oxidative stress and induced glucose accumulation. However, the potential factor regulating ARG cellular response is presently unknown.

Method

Human umbilical vein endothelial cells were incubated with 100 μM ARG for 2 h in buffer (short-term or acute), or for 7 days in culture medium and challenged for 2 h in buffer (continuous or chronic), in the presence or absence of other agents. eNOS activity was determined by analyzing cellular nitrite/nitrate (NO₂^–/NO₃^–), and AMP-activated protein kinase (AMPK) activity was assayed using SAMS peptide. ¹³C₆ glucose was added to medium to measure glucose uptake during cellular treatments, which were determined by LC-MS/MS. Cellular glucose was identified by o-toluidine method. Superoxide (O₂^•–) was identified by EPR-spin-trap, and peroxynitrite (ONOO^–) was measured by flow-cytometer using aminophenyl fluorescein dye.

Results

Short-term incubation of cells with 100 μM ARG in the presence or absence of 30 μM L-N^G-Nitroarginine methyl ester (L-NAME) or 30 μM AMPK inhibitor (compound C, CMP-C) increased cellular oxidative stress and overall glucose accumulation with no variation in glucose transporter-1 (GLUT-1), or AMPK activity from control. The increase in total NO₂^–/NO₃^– after 2 h 100 μM ARG exposure, was suppressed in cells co-incubated with 30 μM CMP-C or L-NAME. Long-term exposure of ARG with or without CMP-C or L-NAME suppressed NO₂^–/NO₃^–, glucose uptake, GLUT-1, AMPK expression and activity below control, and increased overall cellular glucose, O₂^•– and ONOO^–. Gluconeogenesis inhibition with 30 μM 5-Chloro-2-N-2,5-dichlorobenzenesulfonamido-benzoxazole (CDB) during ARG exposure for 2 h maintained overall cellular glucose to control, but increased cellular glucose uptake. Continuous co-incubation with CDB and ARG increased NO₂^–/NO₃^–, glucose uptake, GLUT-1, AMPK expression and activity, and maintained overall cellular glucose, O₂^•– and ONOO^– to control conditions.

Conclusion

The present study provides the fundamental evidence for AMPK as the primary modulator of ARG cellular responses and for regulating the mode of glucose accumulation during short-term and continuous ARG treatments.

Stimulation of insulin secretion by large-dose oral arginine administration in healthy adults

The effects of large-dose oral arginine administration on the secretion of insulin by islet β-cells in healthy adults were determined. Eight non-obese healthy volunteers with normal glucose tolerance participated randomly in tests with four stages (with an interval of at least 3 days): the 300 ml purified water stage (PWS), the 75 g glucose stage (GSS), the 30 g arginine stage (ARS) and the 75 g glucose with 30 g arginine stage (GAS). Venous blood samples were collected to detect the concentrations of glucose and insulin at baseline (0) and at 15, 30, 45, 60 and 120 min after drug administration. The glucose and insulin levels were steady in the PWS. The remaining three stages had similarly shaped insulin concentration-time curves, which differed from that of the PWS. The peak concentration of blood insulin and the net incremental area under the curve of blood insulin in the GSS, ARS and GAS were significantly higher compared with those in the PWS (P<0.05). In the ARS, the glucose levels remained stable; however, the net incremental area under the curve for blood insulin in the ARS was much lower compared with that in the GSS or GAS (P<0.05). Large-dose oral arginine administration may slightly stimulate insulin secretion by islet β-cells in healthy adults with normal glucose tolerance in a manner that is independent of glucose concentration.

Kinetics of the utilization of dietary arginine for nitric oxide and urea synthesis: insight into the arginine-nitric oxide metabolic system in humans

BACKGROUND

The systemic availability of oral/dietary arginine and its utilization for nitric oxide (NO) synthesis remains unknown and may be related to a competitive hydrolysis of arginine into urea in the splanchnic area and systemic circulation.

OBJECTIVES

We investigated the kinetics and dose-dependency of dietary arginine utilization for NO compared with urea synthesis and studied the characteristics of the arginine-NO metabolic system in healthy humans.

DESIGN

We traced the metabolic fate and analyzed the utilization dynamics of dietary arginine after its ingestion at 2 nutritional amounts in healthy humans (n = 9) in a crossover design by using [(15)N-(15)N-(guanido)]-arginine, isotope ratio mass spectrometry techniques, and data analysis with a compartmental modeling approach.

RESULTS

Whatever the amount of dietary arginine, 60 ± 3% (±SEM) was converted to urea, with kinetics indicative of a first-pass splanchnic phenomenon. Despite this dramatic extraction, intact dietary arginine made a major contribution to the postprandial increase in plasma arginine. However, the model identified that the plasma compartment was a very minor (~2%) precursor for the conversion of dietary arginine into NO, which, in any case, was small (<0.1% of the dose). The whole-body and plasma kinetics of arginine metabolism were consistent with the suggested competitive metabolism by the arginase and NO synthase pathways.

CONCLUSIONS

The conversion of oral/dietary arginine into NO is not limited by the systemic availability of arginine but by a tight metabolic compartmentation at the systemic level. We propose an organization of the arginine metabolic system that explains the daily maintenance of NO homeostasis in healthy humans.

Influence of Circulation System on Estimation of Absorption and Elimination Constant after per oral Drug Administration: A Reanalysis

This study aimed to identify the cause of atypical shape of measured concentration-time profile in the peak area by one compartment open model with a lag time (Bateman function with a lag) after single dose oral administration of drug published in "Pharmacokinetic and Pharmacodynamic Data Analysis: Concepts and Application" by Gabrielsson and Weiner (1997) and two concentration profiles after frequent sampling oral glucose tolerance test. Following the oral administration of 100 μg of substance A to human volunteer, frequent sampling was carried out and concentration-time profiles were obtained. Our hemodynamic circulatory structural model capable of parameters estimation of circulation and gastrointestinal subsystem to explain the plateau within the interval 40-100 min (substance A) and 15-30 min (glucose) of the measured concentration-time profile was developed. The mean residence time, the rate constants of absorption and elimination parameters of our model were calculated. Comparing to the Bateman function, our results demonstrate better approximation of the substance A and glucose concentration-time profile and estimation of absorption rate constant by our structural model. Obtained model results indicate that the atypical shape of measured concentration-time profile of single dose oral administration of drug was probably caused by the gastrointestinal and circulation system with deep compartment. This applies to the substances with high coefficient of absorption.

Increased plasma availability of L-arginine in the postprandial period decreases the postprandial lipemia in older adults

OBJECTIVE

Older adults have exaggerated postprandial lipemia, which increases their risk for cardiovascular disease. We sought to determine the effects of increased plasma L-arginine (L-ARG) availability on the oxidation of ingested fat (enriched with [1,1,1-(13)C]-triolein) and plasma triacylglycerol (TG) concentrations during the postprandial period in older subjects.

METHODS

On one day, eight healthy subjects (67.8 ± 1.3 y old) received an intravenous infusion of L-ARG during the first hour of the postprandial period (L-ARG trial), while on a separate day, and in a randomized order, they received saline (control trial).

RESULTS

The 8-h area under the plasma concentration-time curve describing the postprandial plasma TG concentrations was considerably lower in the L-ARG trial than in the control trial (-4 ± 21 versus 104 ± 21 mg ∙ dL(-1) ∙ h(-1), P < 0.01). The rate of the postprandial oxidation of the ingested lipid was not different between the trials, but the average contribution of the ingested oleate to the oleate of the TG of the plasma small TG-rich lipoproteins (Svedberg flotation index 20-400) was lower in the L-ARG trial (11 ± 1 versus 18 ± 2%, P < 0.01). L-ARG infusion also decreased the 8-h area under the plasma concentration-time curve of the plasma free fatty acid concentrations derived from the ingested fat compared with the saline infusion (0.77 ± 0.09 versus 1.11 ± 0.08; mmol ∙ L(-1) ∙ h(-1), P < 0.01).

CONCLUSION

Increasing the plasma L-ARG availability during the postprandial period decreases the postprandial lipemia in older adults, in association with a decrease in the postprandial contribution of ingested lipids into TGs of the plasma small TG-rich lipoproteins.