Oral supplementation with a combination of L-citrulline and L-arginine rapidly increases plasma L-arginine concentration and enhances NO bioavailability

Supplementation with l-arginine and nitrates vs age and individual physiological reactivity

Ageing is a natural ontogenetic phenomenon that entails a decrease in the adaptive capacity of the organism, as a result of which the body becomes less adaptable to stressful conditions. Nitrate and nitrite enter the body from exogenous sources and from nitrification of ammonia nitrogen by intestinal microorganisms. This review considers the mechanisms of action of l-arginine, a known inducer of nitric oxide (NO) biosynthesis, and nitrates as supplements in the processes of ageing and aggravated stress states, in which mechanisms of individual physiological reactivity play an important role. This approach can be used as an element of individual therapy or prevention of premature ageing processes depending on the different levels of initial reactivity of the functional systems. A search was performed of the PubMed, Scopus, and Google Scholar databases (n = 181 articles) and the author's own research (n = 4) up to May 5, 2023. The review presents analyses of data on targeted treatment of NO generation by supplementation with l-arginine or nitrates, which is a promising means for prevention of hypoxic conditions frequently accompanying pathological processes in an ageing organism. The review clarifies the role of the individual state of physiological reactivity, using the example of individuals with a high predominance of cholinergic regulatory mechanisms who already have a significant reserve of adaptive capacity. In studies of the predominance of adrenergic influences, a poorly trained organism as well as an elderly organism correspond to low resistance, which is an additional factor of damage at increased energy expenditure.

CONCLUSION

It is suggested that the role of NO synthesis from supplementation of dietary nitrates and nitrites increases with age rather than from oxygen-dependent biosynthetic reactions from l-arginine supplementation.

An aberrant fused in sarcoma liquid droplet of amyotrophic lateral sclerosis pathological variant, R495X, accelerates liquid-solid phase transition

Intracellular aggregation of fused in sarcoma (FUS) is associated with the pathogenesis of familial amyotrophic lateral sclerosis (ALS). Under stress, FUS forms liquid droplets via liquid-liquid phase separation (LLPS). Two types of wild-type FUS LLPS exist in equilibrium: low-pressure LLPS (LP-LLPS) and high-pressure LLPS (HP-LLPS); the former dominates below 2 kbar and the latter over 2 kbar. Although several disease-type FUS variants have been identified, the molecular mechanism underlying accelerated cytoplasmic granule formation in ALS patients remains poorly understood. Herein, we report the reversible formation of the two LLPS states and the irreversible liquid-solid transition, namely droplet aging, of the ALS patient-type FUS variant R495X using fluorescence microscopy and ultraviolet-visible absorption spectroscopy combined with perturbations in pressure and temperature. Liquid-to-solid phase transition was accelerated in the HP-LLPS of R495X than in the wild-type variant; arginine slowed the aging of droplets at atmospheric conditions by inhibiting the formation of HP-LLPS more selectively compared to that of LP-LLPS. Our findings provide new insight into the mechanism by which R495X readily forms cytoplasmic aggregates. Targeting the aberrantly formed liquid droplets (the HP-LLPS state) of proteins with minimal impact on physiological functions could be a novel therapeutic strategy for LLPS-mediated protein diseases.

Amino acid profile alteration in age-related atrial fibrillation

BACKGROUND

Amino acids (AAs) are one of the primary metabolic substrates for cardiac work. The correlation between AAs and both atrial fibrillation (AF) and aging has been documented. However, the relationship between AAs and age-related AF remains unclear.

METHODS

Initially, the plasma AA levels of persistent AF patients and control subjects were assessed, and the correlations between AA levels, age, and other clinical indicators were explored. Subsequently, the age-related AF mouse model was constructed and the untargeted myocardial metabolomics was conducted to detect the level of AAs and related metabolites. Additionally, the gut microbiota composition associated with age-related AF was detected by a 16S rDNA amplicon sequencing analysis on mouse fecal samples.

RESULTS

Higher circulation levels of lysine (Student's t-test, P = 0.001), tyrosine (P = 0.002), glutamic acid (P = 0.008), methionine (P = 0.008), and isoleucine (P = 0.014), while a lower level of glycine (P = 0.003) were observed in persistent AF patients. The feature AAs identified by machine learning algorithms were glutamic acid and methionine. The association between AAs and age differs between AF and control subjects. Distinct patterns of AA metabolic profiles were observed in the myocardial metabolites of aged AF mice. Aged AF mice had lower levels of Betaine, L-histidine, L-alanine, L-arginine, L-Pyroglutamic acid, and L-Citrulline compared with adult AF mice. Aged AF mice also presented a different gut microbiota pattern, and its functional prediction analysis showed AA metabolism alteration.

CONCLUSION

This study provided a comprehensive network of AA disturbances in age-related AF from multiple dimensions, including plasma, myocardium, and gut microbiota. Disturbances of AAs may serve as AF biomarkers, and restoring their homeostasis may have potential benefits for the management of age-related AF.

Shuttle between arginine and lysine: influence on cancer immunonutrition

Amino acids which are essential nutrients for all cell types' survival are also recognised to serve as opportunistic/alternative fuels in cancers auxotrophic for specific amino acids. Accordingly, restriction of amino acids has been utilised as a therapeutic strategy in these cancers. Contrastingly, amino acid deficiencies in cancer are found to greatly impair immune functions, increasing mortality and morbidity rates. Dietary and supplemental amino acids in such conditions have revealed their importance as 'immunonutrients' by modulating cellular homeostasis processes and halting malignant progression. L-arginine specifically has attracted interest as an immunonutrient by acting as a nodal regulator of immune responses linked to carcinogenesis processes through its versatile signalling molecule, nitric oxide (NO). The quantum of NO generated directly influences the cytotoxic and cytostatic processes of cell cycle arrest, apoptosis, and senescence. However, L-lysine, a CAT transporter competitor for arginine effectively limits arginine input at high L-lysine concentrations by limiting arginine-mediated effects. The phenomenon of arginine-lysine antagonism can, therefore, be hypothesised to influence the immunonutritional effects exerted by arginine. The review highlights aspects of lysine's interference with arginine-mediated NO generation and its consequences on immunonutritional and anti-cancer effects, and discusses possible alternatives to manage the condition. However, further research that considers monitoring lysine levels in arginine immunonutritional therapy is essential to conclude the hypothesis.

Increased nitric oxide availability worsens the cardiac performance during early re-perfusion period in adult rats

OBJECTIVES

Re-perfusion is the standard therapy for acute myocardial infarction, despite the associated pathologies that may contribute to irreversible myocardial injury. The present study aims to clarify the alterations in cardiac activities in response to experimental cardiac ischemic arrest followed by re-perfusion in isolated hearts perfused with nitric oxide (NO) donor, l-arginine, or NO inhibitor, Nω-Nitro-l-arginine methyl ester hydrochloride (l-NAME), to shed light on the possible role of NO in the re-perfusion process.

METHODS

Hearts isolated from adult Wistar rats were studied on Langendorff preparation under basal conditions and during 30 min re-perfusion following 30 min of total global ischemia. Rats were randomly divided into three groups; control and l-arginine or l-NAME infused heart groups. Cardiac tissue content of malondialdhyde, catalase and nitrite was also measured.

RESULTS

Compared to the control group, both l-arginine and l-NAME infused hearts showed increased basal chronotropy and myocardial flow rate. Following ischemia and during the whole period of re-perfusion, the three groups demonstrated significant deterioration in the inotropic activity and compromised myocardial flow rate. l-arginine infused hearts revealed depressed inotropy and chronotropy, weak systolic and diastolic functions with compromised myocardial flow at early 5 min of re-perfusion, yet with significantly higher myocardial flow rate by the end of re-perfusion.

CONCLUSIONS

Reducing NO availability by l-NAME revealed mild impact on the ischemia re-perfusion induced contractile dysfunction, whereas excess NO worsens cardiac performance at the early re-perfusion period.

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

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

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

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

Regulated Arginine Metabolism in Immunopathogenesis of a Wide Range of Diseases: Is There a Way to Pass between Scylla and Charybdis?

More than a century has passed since arginine was discovered, but the metabolism of the amino acid never ceases to amaze researchers. Being a conditionally essential amino acid, arginine performs many important homeostatic functions in the body; it is involved in the regulation of the cardiovascular system and regeneration processes. In recent years, more and more facts have been accumulating that demonstrate a close relationship between arginine metabolic pathways and immune responses. This opens new opportunities for the development of original ways to treat diseases associated with suppressed or increased activity of the immune system. In this review, we analyze the literature describing the role of arginine metabolism in the immunopathogenesis of a wide range of diseases, and discuss arginine-dependent processes as a possible target for therapeutic approaches.

Combined Citrulline and Glutathione Supplementation Improves Endothelial Function and Blood Pressure Reactivity in Postmenopausal Women

Postmenopausal women (PMW) may experience endothelial dysfunction associated with arginine (ARG) deficiency relative to asymmetric dimethylarginine (ADMA) caused by oxidative stress. Endothelial dysfunction contributes to increased blood pressure (BP) responsiveness to sympathoexcitation induced by the cold pressor test (CPT). We investigated the effects of citrulline alone (CIT) and combined with the antioxidant glutathione (CIT+GSH) on vascular function. Forty-four healthy PMW were randomized to CIT (6 g), CIT+GSH (2 g + 200 mg: Setria^®) or placebo (PL) for 4 weeks. Brachial artery flow-mediated dilation (FMD), aortic stiffness (pulse wave velocity, PWV), brachial and aortic BP reactivity to CPT, and serum fasting blood glucose (FBG), ARG, and ARG/ADMA ratio were measured. Baseline FBG was higher in CIT+GSH vs. PL. FMD increased after CIT+GSH vs. PL (p < 0.05). CIT and CIT+GSH increased ARG/ADMA (p < 0.05), but did not affect aortic PWV. CIT+GSH attenuated the brachial and aortic systolic BP and mean arterial pressure (MAP) responses to CPT vs. PL and CIT (p < 0.05). The improvements in FMD were related to baseline FMD (r = -0.39, p < 0.05) and aortic MAP response to CPT (r = -0.33, p < 0.05). This study showed that CIT+GSH improved FMD and attenuated systolic BP and MAP reactivity in PMW. Although CIT increased ARG/ADMA, it did not improve FMD in healthy PMW.

Dietary Arginine and Citrulline Supplements for Cardiovascular Health and Athletic Performance: A Narrative Review

The global market for nutritional supplements (NS) is growing rapidly, and the use of L-arginine (Arg), L-citrulline (Cit), and citrulline malate (CitMal) supplements has been shown to enhance cardiovascular health and athletic performance. Over the past decade, Arg, Cit, and CitMal supplements have received considerable attention from researchers in the field of exercise nutrition, who have investigated their potential effects on hemodynamic function, endothelial function, aerobic and anaerobic capacity, strength, power, and endurance. Previous studies were reviewed to determine the potential impact of Arg, Cit, and CitMal supplements on cardiovascular health and exercise performance. By synthesizing the existing literature, the study aimed to provide insight into the possible uses and limitations of these supplements for these purposes. The results showed that both recreational and trained athletes did not see improved physical performance or increased nitric oxide (NO) synthesis with 0.075 g or 6 g doses of Arg supplement per body weight. However, 2.4 to 6 g of Cit per day for 7 to 16 days of various NSs had a positive impact, increasing NO synthesis, enhancing athletic performance indicators, and reducing feelings of exertion. The effects of an 8 g acute dose of CitMal supplement were inconsistent, and more research is needed to determine its impact on muscle endurance performance. Based on the positive effects reported in previous studies, further testing is warranted in various populations that may benefit from nutritional supplements, including aerobic and anaerobic athletes, resistance-trained individuals, elderly people, and clinical populations, to determine the impact of different doses, timing of ingestion, and long-term and acute effects of Arg, Cit, and CitMal supplements on cardiovascular health and athletic performance.

Streptococcal arginine deiminase regulates endothelial inflammation, mTOR pathway and autophagy

Endothelial cells (EC) are active participants in the inflammation process. During the infection, the change in endothelium properties provides the leukocyte infiltrate formation and restrains pathogen dissemination due to coagulation control. Pathogenic microbes are able to change the endothelium properties and functions in order to invade the bloodstream and disseminate in the host organism. Arginine deiminase (ADI), a bacterial arginine-hydrolyzing enzyme, which causes the amino acid deficiency, important for endothelium biology. Previous research implicates altered metabolism of arginine in the development of endothelial dysfunction and inflammation. It was shown that arginine deficiency, as well as overabundance affects the balance of mechanical target of rapamycin (mTOR)/S6 kinase (S6K) pathway, arginase and endothelial nitric oxide synthase (eNOS) resulted in reactive oxygen species (ROS) production and EC activation. ADI creating a deficiency of arginine can interfere cellular arginine-dependent processes. Thus, this study was aimed at investigation of the influence of streptococcal ADI on the metabolism and inflammations of human umbilical vein endothelial cells (HUVEC). The action of ADI was studied by comparing the effect Streptococcus pyogenes M49-16 paternal strain expressing ADI and its isogenic mutant M49-16delArcA with the inactivated gene ArcA. Based on comparison of the parental and mutant strain effects, it can be concluded, that ADI suppressed mTOR signaling pathway and enhanced autophagy. The processes failed to return to the basic level with arginine supplement. Our study also demonstrates that ADI suppressed endothelial proliferation, disrupted actin cytoskeleton structure, increased phospho-NF-κB p65, CD62P, CD106, CD54, CD142 inflammatory molecules expression, IL-6 production and lymphocytes-endothelial adhesion. In spite of the ADI-mediated decrease in arginine concentration in the cell-conditioned medium, the enzyme enhanced the production of nitric oxide in endothelial cells. Arginine supplementation rescued proliferation, actin cytoskeleton structure, brought NO production to baseline and prevented EC activation. Additional evidence for the important role of arginine bioavailability in the EC biology was obtained. The results allow us to consider bacterial ADI as a pathogenicity factor that can potentially affect the functions of endothelium.

Pathophysiology of Preeclampsia and L-Arginine/L-Citrulline Supplementation as a Potential Strategy to Improve Birth Outcomes

In preeclampsia, the shallow invasion of cytotrophoblast cells to uterine spiral arteries, leading to a reduction in placental blood flow, is associated with an imbalance of proangiogenic/antiangiogenic factors to impaired nitric oxide (NO) production. Proangiogenic factors, such as vascular endothelial growth factor (VEGF) and placental growth factor (PlGF), require NO to induce angiogenesis through antioxidant regulation mechanisms. At the same time, there are increases in antiangiogenic factors in preeclampsia, such as soluble fms-like tyrosine kinase type 1 receptor (sFIt1) and toll-like receptor 9 (TLR9), which are mechanism derivates in the reduction of NO bioavailability and oxidative stress in placenta.Different strategies have been proposed to prevent or alleviate the detrimental effects of preeclampsia. However, the only intervention to avoid the severe consequences of the disease is the interruption of pregnancy. In this scenario, different approaches have been analysed to treat preeclamptic pregnant women safely. The supplementation with amino acids is one of them, especially those associated with NO synthesis. In this review, we discuss emerging concepts in the pathogenesis of preeclampsia to highlight L-arginine and L-citrulline supplementation as potential strategies to improve birth outcomes. Clinical and experimental data concerning L-arginine and L-citrulline supplementation have shown benefits in improving NO availability in the placenta and uterine-placental circulation, prolonging pregnancy in patients with gestational hypertension and decreasing maternal blood pressure.

New perspectives for investigating muscular perfusion response after dietary supplement intake: an exploratory, randomized, double-blind, placebo-controlled crossover trial in healthy young athletes using contrast-enhanced ultrasound (CEUS)

Background

Various dietary supplements have been reported to enhance muscular perfusion in athletes practicing resistance training, especially through modulation of nitric oxide signaling.

Objectives

The aim of this study was therefore to investigate selected ‘NO-boosting’ supplements in a real-life setting i) to generate novel hypotheses and perfusion estimates for power calculation in view of a definitive trial and ii) to assess the feasibility of the study design with particular focus on the use of contrast-enhanced ultrasound (CEUS) for perfusion quantification.

Methods

Thirty young male athletes (24 ± 4 years) regularly practicing resistance training were enrolled in this three-arm, placebo(PL)-controlled crossover trial with ingestion of two commercially available supplements: an amino acid combination (AA) (containing 3 g of L-arginine-hydrochloride and 8 g of L-citrulline-malate) and 300 mg of a specific green tea extract (GTE). After intake, CEUS examinations of the dominant biceps brachii muscle were performed under resting conditions and following standardized resistance exercising. Quantitative parameters of biceps perfusion (peak enhancement, PE; wash-in perfusion index, WiPI) and caliber were derived from corresponding CEUS video files. Additionally, subjective muscle pump was determined after exercise.

Results

For PE, WiPI, and biceps caliber, the standard deviation (SD) of the within-subject differences between PL, AA, and GTE was determined, thereby allowing future sample size calculations. No significant differences between PL, AA, and GTE were observed for biceps perfusion, caliber, or muscle pump. When comparing resting with post-exercise measurements, the increase in biceps perfusion significantly correlated with the caliber increase (PE: r = 0.266, p = 0.0113; WiPI: r = 0.269, p = 0.0105). Similarly, the biceps perfusion correlated with muscle pump in the post-exercise conditions (PE: r = 0.354, p = 0.0006; WiPI: r = 0.350, p = 0.0007). A high participant adherence was achieved, and the acquisition of good quality CEUS video files was feasible. No adverse events occurred.

Conclusion

Based on our novel examination protocol, CEUS seems to be feasible following higher-load resistance exercising and may be used as a new method for high-resolution perfusion quantification to investigate the effects of pre-exercise dietary supplementation on muscle perfusion and related muscle size dynamics.

Wild Watermelon-Extracted Juice Ingestion Reduces Peripheral Arterial Stiffness with an Increase in Nitric Oxide Production: A Randomized Crossover Pilot Study

Wild watermelon contains various nutrients, but the effect of its acute ingestion on arterial stiffness is unclear. This study aimed to investigate whether a single bout of acute ingestion of wild watermelon-extracted juice decreased arterial stiffness concomitant with an increase in nitric oxide (NO) production. Twelve healthy young female participants were tested under two conditions in a randomized, double-blind crossover study: (1) a beverage containing 90 g of wild watermelon extract and (2) a control beverage: a placebo. Pulse wave velocity (PWV), an index of arterial stiffness, blood flow, and plasma nitrate/nitrite (NOx) levels were measured in the supine position at 30, 60, and 90 min after the intake of each beverage. The changes in femoral-ankle PWV were significantly reduced after wild watermelon-extracted juice intake compared to those in the placebo group. Additionally, the changes in blood flow in the posterior tibial artery and plasma NOx levels after intake of wild watermelon-extracted juice were significantly increased compared to those in the placebo group. These data show that acute ingestion of wild watermelon-extracted juice reduces peripheral (lower limb) arterial stiffness and increases NO bioavailability. To confirm these associations, more detailed investigations of the nutrients that influence these effects should be conducted.

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.

Citrulline protects against LPS‑induced acute lung injury by inhibiting ROS/NLRP3‑dependent pyroptosis and apoptosis via the Nrf2 signaling pathway

Acute lung injury (ALI) is a common complication in patients with sepsis and is accompanied by high mortality. The present study aimed to investigate if the organic compound citrulline has a protective against lipopolysaccharide (LPS)-stimulated ALI and its potential mechanisms. ALI was induced in mice by intraperitoneal (i.p.) injection of LPS (10 mg/kg). Citrulline (1 g/kg/day) was administrated i.p. 7 days prior to LPS injection. Mouse lung vascular endothelial cells (MLVECs) were divided into five groups: Control, LPS, LPS + Cit, LPS + N-acetyl-L-cysteine (NAC) and LPS + Cit + ML385. Lung injury was determined by morphology changes. Apoptosis and pyroptosis were detected using western blot analysis and immunofluorescence. The present results indicated that citrulline can significantly attenuate ALI. Citrulline pretreatment decreased the expression of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome and decreased pyroptosis and apoptosis. Intervention with the total reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine attenuated NLRP3 inflammasome-associated pyroptosis and apoptosis in LPS-treated MLVECs. Citrulline pretreatment inhibited pyroptotic cell death and apoptosis induced by LPS. Citrulline decreased accumulation of intracellular ROS and activated the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. Furthermore, the Nrf2 inhibitor ML385 reversed ROS generation, NLRP3 inflammasome-mediated pyroptosis and apoptosis suppressed by citrulline. In summary, the present data demonstrated that citrulline may confer protection against ALI via inhibition of ROS/NLRP3 inflammasome-dependent pyroptosis and apoptosis via the Nrf2 signaling pathway.

Mechanism underlying liquid-to-solid phase transition in fused in sarcoma liquid droplets

The RNA-binding protein fused in sarcoma (FUS) forms ribonucleoprotein granules via liquid-liquid phase separation (LLPS) in the cytoplasm. The phase separation of FUS accelerates aberrant liquid-solid phase separation and leads to the onset of familial amyotrophic lateral sclerosis (ALS). We previously found that FUS forms two types of liquid condensates in equilibrium, specifically LP-LLPS (i.e., normal type) and HP-LLPS (i.e., aberrant type), each with different partial molar volumes. However, it is unclear how liquid condensates are converted to the pathogenic solid phase. Here, we report a mechanism underlying the aberrant liquid-to-solid phase transition of FUS liquid condensates and the inhibition of this transition with small molecules. We found that the liquid condensate formed via HP-LLPS had greatly reduced dynamics, which is a common feature of aged wild-type FUS droplets and the droplet-like assembly of the ALS patient-type FUS variant. The longer FUS remained on the HP-LLPS, the harder it was to transform it into a mixed state (i.e., one-phase). These results indicate that liquid-to-solid phase transition, namely the aging of droplets, is accelerated with HP-LLPS. Interestingly, arginine suppressed the aging of droplets and HP-LLPS formation more strongly than LP-LLPS formation. These data indicate that the formation of HP-LLPS via the one-phase state or LP-LLPS is a pathway leading to irreversible solid aggregates. Dopamine and pyrocatechol also suppressed HP-LLPS formation. Our data highlight the potential of HP-LLPS to be used as a therapeutic target and arginine as a plausible drug candidate for ALS-causing FUS.

The Effects of Consuming Amino Acids L-Arginine, L-Citrulline (and Their Combination) as a Beverage or Powder, on Athletic and Physical Performance: A Systematic Review

Consumption of amino acids L-arginine (L-Arg) and L-citrulline (L-Cit) are purported to increase nitric oxide (NO) production and improve physical performance. Clinical trials have shown relatively more favorable outcomes than not after supplementing with L-Cit and combined L-Arg and L-Cit. However, in most studies, other active ingredients such as malate were included in the supplement. Therefore, the aim of this study was to determine the efficacy of consuming standalone L-Arg, L-Cit, and their combination (in the form of powder or beverage) on blood NO level and physical performance markers. A systematic review was undertaken following PRISMA 2020 guidelines (PROSPERO: CRD42021287530). Four electronic databases (PubMed, Ebscohost, Science Direct, and Google scholar) were used. An acute dose of 0.075 g/kg of L-Arg or 6 g L-Arg had no significant increase in NO biomarkers and physical performance markers (p > 0.05). Consumption of 2.4 to 6 g/day of L-Cit over 7 to 16 days significantly increased NO level and physical performance markers (p < 0.05). Combined L-Arg and L-Cit supplementation significantly increased circulating NO, improved performance, and reduced feelings of exertion (p < 0.05). Standalone L-Cit and combined L-Arg with L-Cit consumed over several days effectively increases circulating NO and improves physical performance and feelings of exertion in recreationally active and well-trained athletes.

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

With the growing global demand for animal protein and rising temperatures caused by climate change, heat stress (HS) is one of the main emerging environmental challenges for the poultry industry. Commercially-reared birds are particularly sensitive to hot temperatures, so adopting production systems that mitigate the adverse effects of HS on bird performance is essential and requires a holistic approach. Feeding and nutrition can play important roles in limiting the heat load on birds; therefore, this review aims to describe the effects of HS on feed intake (FI) and nutrient digestibility and to highlight feeding strategies and nutritional solutions to potentially mitigate some of the deleterious effects of HS on broiler chickens. The reduction of FI is one of the main behavioral changes induced by hot temperatures as birds attempt to limit heat production associated with the digestion, absorption, and metabolism of nutrients. Although the intensity and length of the heat period influences the type and magnitude of responses, reduced FI explains most of the performance degradation observed in HS broilers, while reduced nutrient digestibility appears to only explain a small proportion of impaired feed efficiency following HS. Targeted feeding strategies, including feed restriction and withdrawal, dual feeding, and wet feeding, have showed some promising results under hot temperatures, but these can be difficult to implement in intensive rearing systems. Concerning diet composition, feeding increased nutrient and energy diets can potentially compensate for decreased FI during HS. Indeed, high energy and high crude protein diets have both been shown to improve bird performance under HS conditions. Specifically, positive results may be obtained with increased added fat concentrations since lipids have a lower thermogenic effect compared to proteins and carbohydrates. Moreover, increased supplementation of some essential amino acids can help support increased amino acid requirements for maintenance functions caused by HS. Further research to better characterize and advance these nutritional strategies will help establish economically viable solutions to enhance productivity, health, welfare, and meat quality of broilers facing HS.

Nitric Oxide Synthesis Metabolites-As Potential Markers in Chronic Kidney Disease in Children

Nitric oxide (NO) is an important signaling molecule for many physiological and pathological processes. Diseases associated with abnormal NO synthesis include cardiovascular diseases, insulin-dependent diabetes, or chronic kidney disease (CKD). The aim of the paper was to evaluate NO synthesis metabolites, i.e., asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), dimethylamine (DMA), arginine, citrulline in plasma of patients with different severity of CKD and to seek possible links between these parameters and the development of this disease. Forty-eight CKD children and thirty-three age-matched controls were examined. Patients were divided into groups depending on the CKD stages (Group II-stage II, Group III-stage III, Group IV-stage IV, and Group RRT children on dialysis). To determine the concentrations of the above-mentioned metabolites in plasma liquid chromatography-mass spectrometry was used. There were significant differences observed in levels of ADMA, SDMA, DMA, and citrulline between control vis CKD groups (p values ranging from <0.001 to 0.029). Plasma arginine concentration was also higher in CKD patients compared to the control group but statistically insignificant. ADMA levels in CKD children were statistically significantly higher in relation to particular stages of CKD (RRT vis II stage of CKD: p = 0.01; RRT vis III-IV stages of CKD: p < 0.046). Citrulline levels in CKD children were statistically significantly higher in RRT group vis control (p < 0.001). Children with CKD develop disturbances in most metabolites of NO synthesis. Dialysis children treated show the greatest disturbances of plasma ADMA and citrulline levels. ADMA seems to be a good indicator of the gradual progression of the CKD, which is proved by the negative correlation with eGFR.

Central and peripheral effects of L-citrulline on thermal physiology and nitric oxide regeneration in broilers

The mechanism that mediates L-citrulline (L-Cit) hypothermia is poorly understood, and the involvement of nitric oxide signaling has not been fully elucidated. Therefore, this study aimed to determine L-Cit's influence on body temperature and to ascertain the central and peripheral mechanisms associated with this response. Chicks responded to intracerebroventricular (ICV) injection of L-Cit with high and low body temperatures (P < 0.05) depending on the dose tested, for both the surface and rectal temperatures. Peripheral (i.p.) L-Cit injection did not affect body temperature responses. Nitric oxide (NO) concentration and NO synthase (NOS) were influenced with varying doses of L-Cit. Hypothalamic NO was increased at 4 µg L-Cit whereas, plasma iNOS was elevated at 2µg L-Cit treatment. However, i.p. L-Cit did not change the NO content, rather it induced higher (P < 0.05) plasma tNOS and iNOS activity, and further upregulated iNOS and nNOS gene expression in the hypothalamus. In addition, ICV L-Cit potentiated a pro- versus anti-inflammatory milieu with the induction of IL-8, IL-10, and TGFβ (P < 0.05), which may be related to the changes in body temperature. Following ICV L-Cit administration, it was observed that L-Cit caused dose variable changes in the ultrastructure of hypothalamic neurons. The lowest dose was associated with a higher number of dead or degenerating neurons, whereas the highest L-Cit dose had fewer neuronal numbers with larger sizes. Therefore, this study shows that central and peripheral L-Cit administration imposes changes in body temperature, nitric oxide production, and inflammatory responses, in a dose-dependent manner.

Oral administration of l-citrulline alters the vascular delivery of substances to rat skeletal muscles

Vascular endothelial function deteriorates with age and disease, and the production of vasodilator factors like nitric oxide (NO) decreases. The free amino acid l-citrulline increases vasodilation and blood flow through increased NO production. We examined the effects of oral l-citrulline administration on vascular delivery of substances to skeletal muscles. In Experiment 1, following oral l-citrulline administration and subsequent intravenous Evans blue dye (EBD) administration to rats, EBD levels delivered to skeletal muscles were measured after 60 min. In Experiment 2, plasma concentrations of amino acids and NOx, an indicator of vasodilation, were measured over time after oral l-citrulline administration. In Experiment 3, we measured EBD levels in skeletal muscles of streptozotocin-induced type 1 diabetic rats following l-citrulline administration. In these experiments, EBD levels in the soleus muscle were higher in the l-citrulline group than in the control group (19.9 ± 0.7 vs. 22.5 ± 1.9 μg/g tissue, p < 0.05). Plasma l-arginine, l-citrulline, and NOx levels were increased within 30 min after l-citrulline administration. EBD levels in the soleus and gastrocnemius muscles were higher in diabetic rats with l-citrulline administration (18.7 ± 2.2 vs. 25.0 ± 4.3 μg/g tissue, p < 0.05 and 8.0 ± 0.5 vs. 9.2 ± 0.8 μg/g tissue, p = 0.05, respectively). These data suggest that oral l-citrulline administration may increase the level of substances delivered to skeletal muscles by increasing the NO production in both normal and vascular endothelial dysfunction models.

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l-Citrulline (CIT) increases blood flow and induces vasorelaxation.

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CIT increased dye delivery to soleus but not gastrocnemius muscles in normal rats.

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CIT administration increased the blood levels of l-arginine and NOx.

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CIT led to higher dye delivery to soleus and gastrocnemius muscles in diabetic rats.

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CIT increase vascular delivery in skeletal muscles through increasing NO production.

Potential Implications of Citrulline and Quercetin on Gut Functioning of Monogastric Animals and Humans: A Comprehensive Review

The importance of gut health in animal welfare and wellbeing is undisputable. The intestinal microbiota plays an essential role in the metabolic, nutritional, physiological, and immunological processes of animals. Therefore, the rapid development of dietary supplements to improve gut functions and homeostasis is imminent. Recent studies have uncovered the beneficial effects of dietary supplements on the immune response, microbiota, gut homeostasis, and intestinal health. The application of citrulline (a functional gut biomarker) and quercetin (a known potent flavonoid) to promote gut functions has gained considerable interest as both bioactive substances possess anti-inflammatory, anti-oxidative, and immunomodulatory properties. Research has demonstrated that both citrulline and quercetin can mediate gut activities by combating disruptions to the intestinal integrity and alterations to the gut microbiota. In addition, citrulline and quercetin play crucial roles in maintaining intestinal immune tolerance and gut health. However, the synergistic benefits which these dietary supplements (citrulline and quercetin) may afford to simultaneously promote gut functions remain to be explored. Therefore, this review summarizes the modulatory effects of citrulline and quercetin on the intestinal integrity and gut microbiota, and further expounds on their potential synergistic roles to attenuate intestinal inflammation and promote gut health.

L-Citrulline Influences the Body Temperature, Heat Shock Response and Nitric Oxide Regeneration of Broilers Under Thermoneutral and Heat Stress Condition

Heat stress (HS) adversely affects several physiological responses in organisms, but the underlying molecular mechanisms involved are yet to be fully understood. L-Citrulline (L-Cit) is a nutraceutical amino acid that is gaining research interest for its role in body temperature regulation and nitric oxide synthesis. This study investigated whether dietary supplementation with L-Cit (1% of basal diet) could ameliorate the effects of acute HS on thermotolerance, redox balance, and inflammatory responses of broilers. Ross 308 broilers (288 chicks) were subjected to two environments; thermoneutral at 24°C (TNZ) or HS at 35°C for 5 h, and fed two diets; control or L-Cit. The results showed that HS increased the ear, rectal (RT), and core body (CBT) temperatures of broilers, along with higher respiratory rate. The RT and CBT readings were intermittently affected with time effect, whereas, L-Cit supplementation lowered the mean CBT than the control diet. Antioxidant assays showed that superoxide dismutase was increased during HS, while, catalase was promoted by L-Cit supplementation. In addition, L-Cit induced glutathione peroxidase activity compared to the control diet during HS. Hypothalamic heat shock protein (HSP)-90 was upregulated by HS, but L-Cit downregulated heat shock factor (HSF)-1, and HSP 60 mRNA expressions. HSF 3 mRNA expression was downregulated by L-Cit under TNZ condition. More so, HS increased the plasma nitric oxide (NO) concentration but lowered the total NO synthase (tNOS) activity. In contrast, L-Cit supplementation limited NO production but increased the tNOS activity. Arginase activity was increased in the control fed group during HS but L-Cit supplementation lowered this effect. The NOS-COX pathway was significantly affected under TNZ condition, since L-Cit supplementation downregulated the mRNA expression of iNOS-COX2 in the hypothalamus, and further reduced the serum PGE2 concentration. Together, these data indicates that L-Cit influenced the antioxidant defense, heat shock response and nitric oxide regeneration both under thermoneutral and HS conditions; and that L-Cit may be directly and/or indirectly involved in the central regulation of body temperature.

The Mechanisms of L-Arginine Metabolism Disorder in Endothelial Cells

L-arginine is a key metabolite for nitric oxide production by endothelial cells, as well as signaling molecule of the mTOR signaling pathway. mTOR supports endothelial cells homeostasis and regulates activity of L-arginine-metabolizing enzymes, endothelial nitric oxide synthase, and arginase II. Disruption of the L-arginine metabolism in endothelial cells leads to the development of endothelial dysfunction. Conflicting results of the use of L-arginine supplement to improve endothelial function reveals a controversial role of the amino acid in the endothelial cell biology. The review is aimed at analysis of the current data on the role of L-arginine metabolism in the development of endothelial dysfunction.

The Etiology and Pathophysiology Genesis of Benign Prostatic Hyperplasia and Prostate Cancer: A New Perspective

Background: The etiology of benign prostatic hyperplasia and prostate cancer are unknown, with ageing being the greatness risk factor. Methods: This new perspective evaluates the available interdisciplinary evidence regarding prostate ageing in terms of the cell biology of regulation and homeostasis, which could explain the timeline of evolutionary cancer biology as degenerative, inflammatory and neoplasm progressions in these multifactorial and heterogeneous prostatic diseases. Results: This prostate ageing degeneration hypothesis encompasses the testosterone-vascular-inflamm-ageing triad, along with the cell biology regulation of amyloidosis and autophagy within an evolutionary tumorigenesis microenvironment. Conclusions: An understanding of these biological processes of prostate ageing can provide potential strategies for early prevention and could contribute to maintaining quality of life for the ageing individual along with substantial medical cost savings.

The Effects of L-Citrulline on Blood-Lactate Removal Kinetics Following Maximal-Effort Exercise

The accumulation of lactate in muscle and blood during high-intensity exercise is negatively correlated with the duration exercise can be sustained. Removal of lactate is a key component of acute recovery between consecutive bouts of such exercise. Low-intensity exercise enhances recovery by accelerating lactate turnover in metabolically active tissues, largely mediated by blood flow to these tissues. Therefore, the purpose of this research was to clarify if L-citrulline, a nutritional supplement purported to promote vasodilation via enhanced nitric oxide availability, would augment the removal of blood lactate during active recovery (AR). L-citrulline ingestion will augment the rate of blood lactate concentration decrease during AR, reduce the oxygen-cost of submaximal exercise, and increase time-to-exhaustion and peak oxygen uptake (V̇O2peak) during a test of maximal aerobic power. Healthy university students (five males & five females) participated in this double-blind, randomized, placebo-controlled study. Participants exercised on a cycle ergometer at submaximal steady-state intensities followed by progressively increasing intensity to exhaustion, 10 min of AR, and then supramaximal intensity exercise to exhaustion. Oxygen uptake was measured throughout the trial and blood lactate was sampled repeatedly during AR. The protocol elicited very high peak blood lactate concentrations after exercise (11.3 + 1.3 mmol/L). L-citrulline supplementation did not significantly alter blood lactate kinetics during AR, the oxygen cost of exercise, V̇O2peak, or time-to-exhaustion. Despite a strong theoretical basis by which L-citrulline could augment lactate removal from the blood, L-citrulline supplementation showed no effect as an exercise-recovery supplement.

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.

L-Citrulline ameliorates the attenuation of acetylcholine-induced vasodilation of retinal arterioles in diabetic rats

In our previous study, we found that the vasodilation of retinal arterioles induced by acetylcholine and BMS-191011, a large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel opener, were diminished in diabetic rats. Currently, few agents ameliorate the impaired vasodilator responses of retinal blood vessels. Our recent finding that the intravenous infusion of L-citrulline dilated retinal arterioles, suggests that L-citrulline could be a potential therapeutic agent for circulatory disorders of the retina. In this study, we determined the effect of an oral L-citrulline treatment on impaired acetylcholine- and BMS-191011-induced vasodilation in the retinal arterioles of diabetic rats. To induce diabetes, rats were administered an intravenous dose of streptozotocin (65 mg/kg) and a 5% D-glucose solution as drinking water. The L-citrulline (2 g/kg/day) and L-arginine (2 g/kg/day) treatments commenced either 15 days before or just after the streptozotocin injection and continued throughout the experimental period. A 29-day treatment with L-citrulline, but not L-arginine, significantly ameliorated the impaired acetylcholine- and BMS-191011-induced retinal vasodilation in diabetic rats without affecting their plasma glucose levels. The 2-week L-citrulline treatment tended to ameliorate the dysfunction of the acetylcholine-induced retinal vasodilation in diabetic rats. In conclusion, these results showed that the retinal blood vessel dysfunction induced by diabetes mellitus could be prevented by the long-term administration of L-citrulline and suggest that the latter could play a potentially prophylactic role in diabetic retinopathy.

L-Citrulline: A Non-Essential Amino Acid with Important Roles in Human Health

L-Arginine (Arg) has been widely used due to its functional properties as a substrate for nitric oxide (NO) generation. However, L-citrulline (CIT), whose main natural source is watermelon, is a non-essential amino acid but which has important health potential. This review provides a comprehensive approach to different studies of the endogenous synthesis of CIT, metabolism, pharmacokinetics, and pharmacodynamics as well as its ergogenic effect in exercise performance. The novel aspect of this paper focuses on the different effects of CIT, citrulline malate and CIT from natural sources such as watermelon on several topics, including cardiovascular diseases, diabetes, erectile dysfunction, cancer, and exercise performance. CIT from watermelon could be a natural food-sourced substitute for pharmacological products and therefore the consumption of this fruit is promoted.

The Effect of Citrulline Supplementation on Lactic Acid Blood Level and Oxygen Saturation (SaO2) in Submaximal Physical Activity

An achievement in sport is one of the benchmarks of success of every athlete. One of the causes of the performance degradation is fatigue due to the formation of lactic acid. Supplements are proved to improve the performance in athletes. The purpose of this study was to determine the effect of citrulline supplementation on lactic acid levels and oxygen saturation on submaximal physical activity. Fatigue can be seen from lactic acid levels in subjects who have performed physical activity. This research method used randomized group pretest postest group design. The subjects used were male students of pencak silat airlangga university, and divided into two groups. The first group was given placebo and the second group was given citrulline. Each group was given the same treatment of three minutes of submaximal physical activity using an ergocycle. Before and after doing the activity the blood lactic acid and oxygen saturation of the subject was checked. The result of the data showed that lactic acid and oxygen saturation in both groups had p<0,05. Citrulline supplementation had effect on lactic acid and oxygen saturation. The results of the research showed that the group given with citrulline had significant effect on lactic acid and oxygen saturation before and after treatment.

Contrast-enhanced ultrasound for determining muscular perfusion after oral intake of L-citrulline, L-arginine, and galloylated epicatechines: A study protocol

INTRODUCTION

The market for dietary supplements in the sports sector has been growing rapidly for several years, though there is still lacking evidence regarding their claimed benefits. One group is that of nitric oxide increasing supplements, so-called "NO-boosters," which are claimed to improve the supply of oxygen and nutrients to the muscle by enhancing vasodilation.The aim of this study was to investigate 3 of these supplements in healthy male athletes for their muscle perfusion-enhancing potential using contrast-enhanced ultrasound (CEUS).

METHODS

This placebo-controlled, double-blind, randomized cross-over trial will be carried out at the Center for Orthopedics, Trauma Surgery and Spinal Cord Injury of the University Hospital Heidelberg. Three commercial NO enhancing products including 300 mg of the specific green tea extract VASO6 and a combination of 8 g L-citrulline malate and 3 g L-arginine hydrochloride will be examined for their potential to increase muscular perfusion in 30-male athletes between 18 and 40 years and will be compared with a placebo. On each of the 3 appointments CEUS of the dominant biceps muscle will be performed at rest and after a standardized resistance training. Every athlete receives each of the 3 supplements once after a wash-out period of at least 1 week. Perfusion will be quantified via VueBox quantification software. The results of CEUS perfusion measurements will be compared intra- and interindividually and correlated with clinical parameters.

DISCUSSION

The results of this study may help to establish CEUS as a suitable imaging modality for the evaluation of potentially vasodilatory drugs in the field of sports. Other supplements could also be evaluated in this way to verify the content of their advertising claims.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS), ID: DRKS00016972, registered on 25.03.2019.

L-Arginine-Nitric Oxide-Asymmetric Dimethylarginine Pathway and the Coronary Circulation: Translation of Basic Science Results to Clinical Practice

By 1980, it was thought that we already knew most of the major mechanisms regulating vascular tone. However, after the somewhat serendipity discovery that endothelium is involved in mediation of relaxation to acetylcholine, a whole new world opened up and we had to rewrite our concept regarding vascular function and its regulation (not to mention many other fields). The new player was an endothelium derived relaxing factor, which molecular constitution has been identified to be nitric oxide (NO). This review summarizes the major molecular steps concerning how NO is synthetized from L-arginine. Also, the fate of L-arginine is described via the arginase and methylation pathways; both of them are affecting substantially the level and efficacy of NO. In vitro and in vivo effects of L-arginine are summarized and controversial clinical findings are discussed. On the basis of the use of methylated L-arginines, the vasomotor effects of endothelial NO released to agonists and increases in flow/wall shear stress (a major biological stimulus) is summarized. In this review the role of NO in the regulation of coronary vascular resistance, hence blood flow, is delineated and the somewhat questionable clinical use of NO donors is discussed. We made an attempt to summarize the biosynthesis, role, and molecular mechanisms of endogenously produced methylated L-arginine, asymmetric dimethylarginine (ADMA) in modulating vascular resistance, affecting the function of the heart. Additionally, the relationship between ADMA level and various cardiovascular diseases is described, such as atherosclerosis, coronary artery disease (CAD), ischemia/reperfusion injuries, and different types of coronary revascularization. A novel aspect of coronary vasomotor regulation is identified in which the pericardial fluid ADMA and endothelin play putative roles. Finally, some of the open possibilities for future research on L-arginine-NO-ADMA signaling are highlighted.

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

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

Pharmacokinetic Parameters of Watermelon (Rind, Flesh, and Seeds) Bioactive Components in Human Plasma: A Pilot Study to Investigate the Relationship to Endothelial Function

This study aimed to investigate the metabolic fate of bioactive components in watermelon and explore their effect on endothelial function. Six healthy overweight/obese (BMI: 28.7 ± 1.6 kg/m²) adults received 100 kcal of watermelon flesh (WF), rind (WR), seeds (WS), or control meal. l-Citrulline, arginine, and (poly)phenolic metabolites were characterized in plasma over 24 h using UHPLC-MS. Endothelial function was assessed using a flow mediated dilation (FMD) technique over 7 h. Maximum concentration (C_max) and area under the curve (AUC_0-8h) of l-citrulline were significantly higher after WF- and WR-containing test meals compared to control (p < 0.05). Likewise, several individual phenolic metabolites in plasma had significantly higher C_max after WR, WF, or WS intake compared to control. FMD responses were not different among test meals. Our results provide insights on circulating metabolites from watermelon flesh, seed, and rind and lay the foundation for future clinical trials on vascular benefits of watermelon.

L-Citrulline Supports Vascular and Muscular Benefits of Exercise Training in Older Adults

Age-associated reduction in endothelial nitric oxide (NO) synthesis contributes to the development of cardiovascular diseases and sarcopenia. L-Citrulline is a precursor of NO with the ability to improve vascular function and muscle protein synthesis. We hypothesize that vascular and muscular benefits associated with oral L-citrulline supplementation might be augmented by concomitant supplementation with exercise training in older adults.

Serum untargeted metabolomic changes in response to diet intervention in dogs with preclinical myxomatous mitral valve disease

Myocardial energy deprivation plays a causal role in the development of heart failure. A cardiac protection blend (CPB) of nutrients including medium chain triglycerides, fish oil and other key nutrients was developed to slow the progression of canine myxomatous mitral valve disease (MMVD). A six-month dietary intervention demonstrated efficacy of CPB in slowing MMVD progression. Untargeted metabolomic analysis of serum from these dogs identified 102 differential metabolites (adjusted P < 0.05). The ratios of omega-6 to omega-3 fatty acid (FA) changed from 2.41 and 1.46 in control and CPB groups at baseline to 4.30 and 0.46 at 6 months respectively. A 2.7-fold increase of α-aminobutyrate, a myocardial modulator of glutathione homeostasis, was found in CPB dogs compared to 1.3-fold increase in control dogs. Arginine and citrulline, precursors of nitric oxide biosynthesis, were both increased 2-fold; caprate, a medium chain FA, was increased 3-fold; and deoxycarnitine, precursor of carnitine biosynthesis, was increased 2.5-fold in CPB dogs. Margarate and methylpalmitate decreased in response to CPB, a potential benefit in MMVD dogs as positive correlations were found between changes in both these FAs and left atrial diameter (r = 0.69, r = 0.87 respectively, adjusted P < 0.05). Sphingomyelins with very long chain saturated FAs associated with decreased risk of heart failure in humans were increased in MMVD dogs fed the CPB diet. Our data supports the hypothesis that CPB improves FA utilization and energetics, reduces oxidative stress and inflammation in MMVD dogs. More studies are needed to understand the roles of specific metabolites in MMVD.

Supplementation of l-arginine boosts the therapeutic efficacy of anticancer chemoimmunotherapy

Myeloid‐derived suppressor cells (MDSCs) play a crucial role in immunosuppression in tumor‐bearing hosts. MDSCs express arginase‐I and indoleamine 2,3‐dioxygenase; they suppress T‐cell function by reducing the levels of l‐arginine and l‐tryptophan, respectively. We examined the anticancer effects of supplementation of these amino acids in CT26 colon carcinoma‐bearing mice. Oral supplementation of l‐arginine or l‐tryptophan (30 mg/mouse) did not affect tumor growth, whereas oral supplementation of d‐arginine was lethal. Supplementation of l‐arginine showed a tendency to augment the efficacy of cyclophosphamide (CP). CP reduced the proportions of granulocytic MDSCs and increased the proportions of monocytic MDSCs in the spleen and tumor tissues of CT26‐bearing mice. l‐Arginine supplementation alone did not affect the MDSC subsets. CP treatment tended to reduce the plasma levels of l‐arginine in CT26‐bearing mice and significantly increased the number of tumor‐infiltrating CD8⁺ T cells. In addition, l‐arginine supplementation significantly increased the proportions of tumor peptide‐specific CD8⁺ T cells in draining lymph nodes. Importantly, additional supplementation of l‐arginine significantly increased the number of cured mice that were treated with CP and anti‐PD‐1 antibody. Totally, l‐arginine supplementation shows promise for boosting the therapeutic efficacy of chemoimmunotherapy.

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.

The Physiological Effects of Amino Acids Arginine and Citrulline: Is There a Basis for Development of a Beverage to Promote Endurance Performance? A Narrative Review of Orally Administered Supplements

Nutritional and ergogenic aid supplementation is prevalent within athletic or general fitness populations, and is only continuing to gain momentum. Taken in isolation or as a combination, amino acid (AA) supplementation has the potential to increase endurance performance among other benefits. L-Arginine (L-Arg) and L-Citrulline (L-Cit) are two AAs proposed to increase endothelial nitric oxide (NO) synthesis, with potential additional physiological benefits, and therefore may contribute to enhanced performance outcomes such as increased power output, or time to exhaustion. However, the appropriate dose for promoting physiological and performance benefits of these AAs, and their potential synergistic effects remains to be determined. Therefore, the aim of this review was to evaluate the varied concentrations used in the current literature, assess the effects of L-Arg and L-Cit in combination on physiological responses and endurance performance, and consider if there is a fundamental basis for providing these supplements in the form of a beverage. A total of six studies were considered eligible for the review which utilized a range of 3–8 g of the AA constituents. The findings support the notion that supplementing with a combination of L-Arg and L-Cit may increase NO production, enhance vasodilation, and therefore increase performance capacity in athletes. A beverage as a carrier for the two AAs is worth considering; however, there remains limited research assessing these outcomes across a consistent range of concentrations in order to see their full potential.

Amino Acids in Circulatory Function and Health

Cardiovascular disease is the major cause of global mortality and disability. Abundant evidence indicates that amino acids play a fundamental role in cardiovascular physiology and pathology. Decades of research established the importance of L-arginine in promoting vascular health through the generation of the gas nitric oxide. More recently, L-glutamine, L-tryptophan, and L-cysteine have also been shown to modulate vascular function via the formation of a myriad of metabolites, including a number of gases (ammonia, carbon monoxide, hydrogen sulfide, and sulfur dioxide). These amino acids and their metabolites preserve vascular homeostasis by regulating critical cellular processes including proliferation, migration, differentiation, apoptosis, contractility, and senescence. Furthermore, they exert potent anti-inflammatory and antioxidant effects in the circulation, and block the accumulation of lipids within the arterial wall. They also mitigate known risk factors for cardiovascular disease, including hypertension, hyperlipidemia, obesity, and diabetes. However, in some instances, the metabolism of these amino acids through discrete pathways yields compounds that fosters vascular disease. While supplementation with amino acid monotherapy targeting the deficiency has ameliorated arterial disease in many animal models, this approach has been less successful in the clinic. A more robust approach combining amino acid supplementation with antioxidants, anti-inflammatory agents, and/or specific amino acid enzymatic pathway inhibitors may prove more successful. Alternatively, supplementation with amino acid-derived metabolites rather than the parent molecule may elicit beneficial effects while bypassing potentially harmful pathways of metabolism. Finally, there is an emerging recognition that circulating levels of multiple amino acids are perturbed in vascular disease and that a more holistic approach that targets all these amino acid derangements is required to restore circulatory function in diseased blood vessels.

Targeting Foam Cell Formation in Atherosclerosis: Therapeutic Potential of Natural Products

Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of atherosclerotic lesions. Targeting foam cell formation in the atherosclerotic lesions can be a promising approach to treat and prevent atherosclerosis. The formation of foam cells is determined by the balanced effects of three major interrelated biologic processes, including lipid uptake, cholesterol esterification, and cholesterol efflux. Natural products are a promising source for new lead structures. Multiple natural products and pharmaceutical agents can inhibit foam cell formation and thus exhibit antiatherosclerotic capacity by suppressing lipid uptake, cholesterol esterification, and/or promoting cholesterol ester hydrolysis and cholesterol efflux. This review summarizes recent findings on these three biologic processes and natural products with demonstrated potential to target such processes. Discussed also are potential future directions for studying the mechanisms of foam cell formation and the development of foam cell-targeted therapeutic strategies.