Effects of oral L-arginine supplementation on exercise-induced QT dispersion and exercise tolerance in stable angina pectoris

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.

Cardiovascular disease: primary prevention, disease modulation and regenerative therapy

Cardiovascular primary prevention and regeneration programs are the contemporary frontiers in functional metabolic vascular medicine. This novel science perspective harnesses our inherent ability to modulate the interface between specialized gene receptors and bioavailable nutrients in what is labeled as the nutrient-gene interaction. By mimicking a natural process through the conveyance of highly absorbable receptor specific nutrients, it is feasible to accelerate cell repair and optimize mitochondrial function, thereby achieving cardiovascular cure. We performed a comprehensive review of PubMed, EMBASE and Cochrane Review databases for articles relating to cardiovascular regenerative medicine, nutrigenomics and primary prevention, with the aim of harmonizing their roles within contemporary clinical practice. We searched in particular for large-scale randomized controlled trials on contemporary cardiovascular pharmacotherapies and their specific adverse effects on metabolic pathways which feature prominently in cardiovascular regenerative programs, such as nitric oxide and glucose metabolism. Scientific research on 'cardiovascular-free' centenarians delineated that low sugar and low insulin are consistent findings. As we age, our insulin level increases. Those who can decelerate the rapidity of this process are prompting their cardiovascular rejuvenation. It is beginning to dawn on some clinicians that contemporary treatments are not only failing to impact on our most prevalent diseases, but they may be causing more damage than good. Primary prevention programs are crucial elements for a better outcome. Cardiovascular primary prevention and regeneration programs have enhanced clinical efficacy and quality of life and complement our conventional endovascular practice.

Effects of L-arginine supplementation on blood flow, oxidative stress status and exercise responses in young adults with uncomplicated type I diabetes

BACKGROUND AND AIMS

Vascular disease is the principal cause of death and disability in patients with diabetes, and endothelial dysfunction seems to be the major cause in its pathogenesis. Since L-arginine levels are diminished in conditions such as type 1 and type 2 diabetes, in this work we aimed to verify the effects of L-arginine supplementation (7 g/day) over the endothelial function and oxidative stress markers in young male adults with uncomplicated type 1 diabetes. We also investigated the influences of L-arginine administration on vascular/oxidative stress responses to an acute bout of exercise.

METHODS

Ten young adult male subjects with uncomplicated type 1 diabetes and twenty matched controls volunteered for this study. We analysed the influence of L-arginine supplementation (7 g/day during 1 week) over lower limb blood flow (using a venous occlusion plethysmography technique), oxidative stress marker (TBARS, Carbonyls), anti-oxidant parameters (uric acid and TRAP) and total tNOx in rest conditions and after a single bout of submaximal exercise (VO₂ at 10 % below the second ventilatory threshold). Data described as mean ± standard error (SE). Alpha level was P < 0.05.

RESULTS

Glycaemic control parameters were altered in type 1 diabetic subjects, such as HbA1c (5.5 ± 0.03 vs. 8.3 ± 0.4 %) and fasted glycaemia (94.8 ± 1.4 vs. 183 ± 19 mg/dL). Oxidative stress/damage markers (carbonyls and TBARS) were increased in the diabetic group, while uric acid was decreased. Rest lower limb blood flow was lower in type 1 diabetic subjects than in healthy controls (3.53 ± 0.35 vs. 2.66 ± 0.3 ml 100 ml⁻¹ min⁻¹). L-Arginine supplementation completely recovered basal blood flow to normal levels in type 1 diabetics' subjects (2.66 ± 0.3 to 4.74 ± 0.86 ml 100 ml⁻¹ min⁻¹) but did not interfere in any parameter of redox state or exercise.

CONCLUSION

Our findings highlight the importance of L-arginine for the improvement of vascular function in subjects with diabetes, indicating that L-arginine supplementation could be an essential tool for the treatment for the disease complications, at least in non-complicated diabetes. However, based on our data, it is not possible to draw conclusions regarding the mechanisms by which L-arginine therapy is inducing improvements on cardiovascular function, but this important issue requires further investigations.

No effect of short-term arginine supplementation on nitric oxide production, metabolism and performance in intermittent exercise in athletes

Arginine supplementation has been shown to alleviate endothelial dysfunction and improve exercise performance through increasing nitric oxide production in patients with cardiopulmonary diseases. In addition, arginine supplementation could decrease accumulations of lactate and ammonia, metabolites involved in development of muscular fatigue. The aim of this study was to investigate the effect of short-term arginine supplementation on performance in intermittent anaerobic exercise and the underlying mechanism in well-trained male athletes. Ten elite male college judo athletes participated with a randomized crossover, placebo-controlled design. The subjects consumed 6 g/day arginine (ARG trial) or placebo (CON trial) for 3 days then performed an intermittent anaerobic exercise test on a cycle ergometer. Blood samples were collected before supplementation, before and during exercise and 0, 3, 6, 10, 30 and 60 min after exercise. ARG trial had significantly higher arginine concentrations than CON trial at the same time point before, during and after exercise. In both trials, nitrate and nitrite concentration was significantly higher during and 6 min after exercise comparing to the basal concentration. The increase in nitrate and nitrite concentration during exercise in both trials was parallel to the increase in plasma citrulline concentrations. There was no significant difference between the 2 trials in plasma nitrate and nitrite, lactate and ammonia concentrations and peak and average power in the exercise. The results of this study suggested that short-term arginine supplementation had no effect on nitric oxide production, lactate and ammonia metabolism and performance in intermittent anaerobic exercise in well-trained male athletes.

L-Arginine therapy in cardiovascular pathologies: beneficial or dangerous?

PURPOSE OF REVIEW

L-Arginine is the precursor for nitric oxide synthesis. In the brain, nitric oxide acts as a neurotransmitter; in the immune system, nitric oxide acts as a mediator of host defense; in the cardiovascular system, nitric oxide mediates the protective effects of the intact endothelium, acting as an endogenous antiatherogenic molecule.

RECENT FINDINGS

About 5 g of L-arginine is taken up each day. L-Arginine plasma levels are not significantly reduced in most diseases, except end-stage renal failure during hemodialysis treatment. Nonetheless, intravenous or oral administration of L-arginine results in enhanced nitric oxide elaboration in subjects with impaired endothelial function. In clinical trials short to medium-term administration of L-arginine improved the symptoms of cardiovascular disease. In other trials, however, L-arginine was not beneficial and in one recent long-term study higher mortality of subjects receiving L-arginine than those receiving placebo was reported. These contradictory results were not understood for a long time. The endogenous inhibitor of nitric oxide synthase, asymmetric dimethylarginine, may determine a subject's response to L-arginine. L-Arginine appears to exert no effect in subjects with low asymmetric dimethylarginine levels, whereas in subjects with high asymmetric dimethylarginine levels L-arginine restores the L-arginine/asymmetric dimethylarginine ratio to normal and normalizes endothelial function.

SUMMARY

The effects of L-arginine supplementation on human physiology appear to be multicausal and dose related. Criteria need to be developed to define patients who benefit from L-arginine supplementation.

l -Arginine Supplementation in Peripheral Arterial Disease

Background— l -Arginine is the precursor of endothelium-derived nitric oxide, an endogenous vasodilator. l -Arginine supplementation improves vascular reactivity and functional capacity in peripheral arterial disease (PAD) in small, short-term studies. We aimed to determine the effects of long-term administration of l -arginine on vascular reactivity and functional capacity in patients with PAD.

Methods and Results— The Nitric Oxide in Peripheral Arterial Insufficiency (NO-PAIN) study was a randomized clinical trial of oral l -arginine (3 g/d) versus placebo for 6 months in 133 subjects with intermittent claudication due to PAD in a single-center setting. The primary end point was the change at 6 months in the absolute claudication distance as assessed by the Skinner-Gardner treadmill protocol. l -Arginine supplementation significantly increased plasma l -arginine levels. However, measures of nitric oxide availability (including flow-mediated vasodilation, vascular compliance, plasma and urinary nitrogen oxides, and plasma citrulline formation) were reduced or not improved compared with placebo. Although absolute claudication distance improved in both l -arginine- and placebo-treated patients, the improvement in the l -arginine-treated group was significantly less than that in the placebo group (28.3% versus 11.5%; P =0.024).

Conclusions— In patients with PAD, long-term administration of l -arginine does not increase nitric oxide synthesis or improve vascular reactivity. Furthermore, the expected placebo effect observed in studies of functional capacity was attenuated in the l -arginine-treated group. As opposed to its short-term administration, long-term administration of l -arginine is not useful in patients with intermittent claudication and PAD.

The pharmacodynamics of L-arginine

L-arginine is a precursor for nitric oxide (NO) synthesis. NO is a ubiquitous mediator that is formed by a family of enzymes named NO synthases. In the brain, NO acts as a neurotransmitter; in the immune system, NO acts as a mediator of host defense; and in the cardiovascular system, NO mediates the protective effects of the intact endothelium, acting as a vasodilator and endogenous antiatherogenic molecule. About 5 g of L-arginine is ingested each day in a normal Western diet. L-arginine plasma levels are not significantly reduced in most disease conditions, except end-stage renal failure during hemodialysis treatment. Nonetheless, intravenous or dietary (oral) administration of relatively large doses of L-arginine has been shown to result in enhanced NO formation in subjects with impaired endothelial function at baseline. In several controlled clinical trials, long-term administration of L-arginine has been shown to improve the symptoms of cardiovascular disease. However, in other trials L-arginine was not beneficial, and in a recent study, the authors reported higher mortality of subjects receiving L-arginine than those receiving placebo. Recently it became clear that endogenous levels of asymmetric dimethylarginine (ADMA), a competitive inhibitor of L-arginine metabolism by NO synthase, may determine a subject's response to L-arginine supplementation. L-arginine appears to exert no effect in subjects with low ADMA levels, whereas in subjects with high ADMA levels, L-arginine restores the L-arginine/ADMA ratio to normal levels and thereby normalizes endothelial function. In conclusion, the effects of L-arginine supplementation on human physiology appear to be multicausal and dose-related. Doses of 3-8 g/d appear to be safe and not to cause acute pharmacologic effects in humans.

Oster rediscovered--mega-dose folate for symptomatic atherosclerosis

Thirty years ago, Kurt Oster promulgated the avant-garde theory that bovine xanthine oxidase, absorbed intact from homogenized milk, promoted atherogenesis by oxidatively damaging membrane plasmalogens. Under the mistaken impression that folic acid is a xanthine oxidase inhibitor, he administered high-dose folate (80 mg daily) to hundreds of patients afflicted with symptomatic atherosclerosis, and reported marked improvements in angina, intermittent claudication, and wound healing; he also suspected that this regimen was decreasing heart attack risk. The xanthine oxidase theory has since fallen by the wayside, but there is now evidence that folic acid can lessen endothelial oxidative stress by improving the function of "uncoupled" nitric oxide synthase deficient in tetrahydrobiopterin. In light of these new findings, a properly controlled assessment of Oster's mega-dose folate therapy is warranted.

Physical training and metabolic supplementation reduce spontaneous atherosclerotic plaque rupture and prolong survival in hypercholesterolemic mice

Moderate physical exercise (PE) combined with metabolic treatment (MT) (antioxidants and l-arginine) are well known to reduce atherosclerotic lesion formation in hypercholesterolemic mice. However, the long-term beneficial effects on unstable atheroma remain poorly understood. We started early PE training in large groups of 6-week-old hypercholesterolemic mice (by graduated swimming) alone or in combination with nutritional supplementation (1.0% vitamin E added to the chow and 0.05% vitamin C and 6% l-arginine added to the drinking water). Inactive controls did not receive PE. The spontaneous development of atherosclerotic plaque rupture (associated with advanced atherosclerosis) and survival rates were evaluated. Moderate PE elicited an increase in plasma levels of nitric oxide. Early combined treatment with PE and MT in the hypercholesterolemic mice significantly reduced lesions (also detected noninvasively at 10 months) and spontaneous atherosclerotic plaque rupture and prolonged survival more effectively than each intervention alone. Thus, early concerted actions of MT and PE improve the natural history of atherosclerotic lesions and reduce the plaque instability in hypercholesterolemic mice.

Supplemental Conditionally Essential Nutrients in Cardiovascular Disease Therapy

Conditionally essential nutrients (CENs) are organic compounds that are ordinarily produced by the body in amounts sufficient to meet its physiological requirements. However, in disorders, such as cardiovascular disease (CVD), and in other physiologically stressful conditions, their biosynthesis may be inadequate. Under these circumstances, CENs become essential nutrients, comparable to vitamins. The CENs of primary importance in CVD, based on the quantity and quality of human clinical studies, are l-arginine, l-carnitine, propionyl-l-carnitine, and coenzyme Q10. Controlled studies of these CENs are reviewed in depth. Taurine is a CEN of secondary importance caused by a limited human database. Other putative CENs include alpha-lipoic acid, betaine, chondroitin sulfate, glutamine, and d-ribose, each of which is mentioned in passing. Collectively, CENs have demonstrated favorable clinical effects in CVDs, including chronic heart failure, myocardial infarction, angina pectoris, and in CVD risk factors, such as hypertension, hyperlipidemia, and lipoprotein(a). Limited research has pointed to possible benefits in CVD therapy accruing from supplementation with several CENs in combination. Additional controlled clinical studies of CENs in CVD are urgently needed. In view of the efficacy and safety of appropriate supplementation with CENs, it is strongly suggested that healthcare professionals become knowledgeable of these potentially important additions to the CVD therapeutic armamentarium.

Therapeutic potential of nitric oxide donors in the prevention and treatment of atherosclerosis

Well-known risk factors for atherosclerosis include hypercholesterolaemia, hypertension, diabetes, and smoking. These conditions are associated with endothelial dysfunction, which itself is associated with reduced endothelial generation of nitric oxide (NO). This is an overview of the implications of NO generation in atherosclerosis and of the potential therapeutic benefit of drugs which donate NO, such as organic nitrates, nicorandil, and sydnonimines, or those which increase the availability of endogenous NO, such as statins, angiotensin-converting enzyme inhibitors, L-arginine, and tetrahydrobiopterin.

Potential ergogenic effects of arginine and creatine supplementation

The rationale for the use of nutritional supplements to enhance exercise capacity is based on the assumption that they will confer an ergogenic effect above and beyond that afforded by regular food ingestion alone. The proposed or advertised ergogenic effect of many supplements is based on a presumptive metabolic pathway and may not necessarily translate to quantifiable changes in a variable as broadly defined as exercise performance. L-arginine is a conditionally essential amino acid that has received considerable attention due to potential effects on growth hormone secretion and nitric oxide production. In some clinical circumstances (e.g., burn injury, sepsis) in which the demand for arginine cannot be fully met by de novo synthesis and normal dietary intake, exogenous arginine has been shown to facilitate the maintenance of lean body mass and functional capacity. However, the evidence that supplemental arginine may also confer an ergogenic effect in normal healthy individuals is less compelling. In contrast to arginine, numerous studies have reported that supplementation with the arginine metabolite creatine facilitates an increase in anaerobic work capacity and muscle mass when accompanied by resistance training programs in both normal and patient populations. Whereas improvement in the rate of phosphocreatine resynthesis is largely responsible for improvements in acute work capacity, the direct effect of creatine supplementation on skeletal muscle protein synthesis is less clear. The purpose of this review is to summarize the role of arginine and its metabolite creatine in the context of a nutrition supplement for use in conjunction with an exercise stimulus in both healthy and patient populations.

Naturoceutical agents in the management of cardiovascular disease

During the past decade, complementary and alternative medicine (CAM) has grown in attractiveness to the Western public, and in recognition by practitioners of traditional medicine. The incorporation of effective CAM therapies into traditional practice is termed 'integrative medicine'. One form of CAM demonstrating exponential growth through mass public consumerism is the use of naturoceuticals. Naturoceutical (or nutraceutical) agents are defined as mega-dose vitamins, herbal products or other 'natural' supplements purchased and consumed with premeditated 'pharmaceutical' intention to treat or prevent an illness or disease. Dietary supplements per se, are intended to supply adequate nutrients that may be lacking from the diet, and are thus, generally health promoting. A regulatory paradox exists since naturoceuticals are classified as dietary supplements although many possess measurable pharmacologic activity. In reference to cardiovascular disorders, consumers use naturoceuticals for three distinctly recognizable purposes. These are the primary and secondary prevention of cardiovascular diseases and the treatment of diagnosed disorders such as heart failure, angina pectoris or arrhythmia. The evidence base supporting the routine use of naturoceutical products for these intentions is sparse, although the likelihood of harm from their consumption is low for an average, healthy adult. Evidence of significant harm (including fatalities) has been observed when certain herbal products are used in excess or in combination with, other herbs or prescription drugs. The safety of use at the extremes of age, or by persons with cardiac, renal or hepatic impairment is also a concern. Healthcare professionals should routinely document patient naturoceutical use, be alert for and report suspected adverse effects. Until well-designed clinical trials determine the proper indication(s), dose safety profile and risk/benefit ratio for these products, their routine use should not be advocated. Thus, the role of naturoceutical agents in the integrative management of cardiovascular disorders remains undefined.

A shift in myocardial substrate, improved endothelial function, and diminished sympathetic activity may contribute to the anti-anginal impact of very-low-fat diets

A new category of anti-anginal drug - exemplified by ranolazine - is believed to work by partially inhibiting cardiac oxidation of fatty acids; oxidation of glucose requires less oxygen per mol of ATP generated, and thus is preferable to fat oxidation when oxygen availability is limiting in underperfused cardiac tissue. Unfortunately, there is no reason to believe that these drugs inhibit fat oxidation selectively in the heart; thus, chronic use of these drugs can be expected to increase body fat stores until the original rate of fat oxidation is restored by mass action - presumably negating the therapeutic benefit in angina, while exacerbating the manifold adverse effects of insulin resistance syndrome. The rational way to decrease cardiac metabolic reliance on fatty acids is to consume a very-low-fat quasi-vegan diet (i.e., 10% fat calories). Indeed, such diets are known to have a rapid and substantial therapeutic impact on anginal symptoms, while concurrently benefiting insulin sensitivity, markedly improving serum lipid profile, promoting leanness, and lessening coronary risk. A reduction in diurnal insulin secretion might also be achieved, which would be expected to decrease sympathetic activity. While reduced myocardial demand for oxygen doubtless contributes to the beneficial impact of such diets on angina, it is likely that improved cardiac perfusion consequent to improved endothelium-dependent vasodilation also plays a role in this regard. Supplemental carnitine, also beneficial in angina, appears to improve utilization of glucose in the ischemic myocardium by lowering elevated acetyl-coA levels and thereby disinhibiting pyruvate dehydrogenase. Certain other nutraceuticals may aid control of angina by improving endothelial function. In the longer term, these measures have the potential to slow or reverse the progression of stenotic lesions that underlie most cases of angina. These safe and relatively inexpensive nutritional strategies for coping with angina deserve far more attention than orthodox medical practice has thus far accorded them.

Randomized trial of a medical food for the dietary management of chronic, stable angina

OBJECTIVES

We determined the electrocardiographic, vascular and clinical effects of a medical food bar enriched with L-arginine and a combination of other nutrients known to enhance endothelium-derived nitric oxide (NO) in patients with stable angina.

BACKGROUND

Enhancement of vascular NO by supplementation with L-arginine and other nutrients has been shown to have clinical benefits in patients with angina secondary to atherosclerotic coronary artery disease (CAD). However, the amounts and combinations of these nutrients required to achieve a clinical effect make traditional delivery by capsules and pills less suitable than alternative delivery methods such as a specially formulated nutrition bar.

METHODS

Thirty-six stable outpatients with CAD and class II or III angina participated in a randomized, double-blind, placebo-controlled, crossover trial with two treatment periods each of two weeks' duration (two active bars or two placebo bars per day). Flow-mediated brachial artery dilation was measured by ultrasound. Electrocardiographic measures of ischemia, exercise capacity and angina onset time were measured by treadmill exercise testing and by Holter monitor during routine daily activities. Quality of life was assessed by SF-36 and Seattle Angina Questionnaires and by diary.

RESULTS

The medical food improved flow-mediated vasodilation (from 5.5 +/- 4.5 to 8.0 +/- 4.9, p = 0.004), treadmill exercise time (by 20% over placebo, p = 0.05) and quality-of-life scores (SF-36 summary score; 68 +/- 13 vs. 63 +/- 21 after placebo, p = 0.04, Seattle Angina Questionnaire summary score; 67 +/- 10 vs. 62 +/- 18, p = 0.04) without affecting electrocardiographic manifestations of ischemia or angina onset time.

CONCLUSIONS

These findings reveal that this arginine-rich medical food, when used as an adjunct to traditional therapy, improves vascular function, exercise capacity and aspects of quality of life in patients with stable angina.