Pii: s0753-3322(02)00291-3

Dossier: Free amino acids in human health and pathologies Arginine and immunity: a unique perspective Carmelo Nieves Jr, Bobbi Langkamp-Henken * Food Science and Human Nutrition Department, University of Florida, PO Box 110370, Gainesville, FL 32611-0370, USA Abstract
Arginine functions in the body as a free amino acid, a component of most proteins, and the substrate for several non-protein, nitrogen-containing compounds, many of which function in immunity. Although arginine is synthesized in the body, it is not made insufficient quantities to support growth or meet metabolic requirements during periods of stress. Based on the biochemical and physiologicalrole of arginine in maintaining health and immunity, arginine is being added at pharmacologic concentrations to enteral formulas to boostimmune function. Unfortunately, animal and human studies that investigate enteral arginine supplementation as the single variable do notshow clear immunologic benefit. The inconsistent effects of arginine supplementation on immune function are due to numerous factors, suchas the amount and timing of arginine supplementation, the animal species or strain of species, and the experimental model. Systematic studyis required to determine whether a basal dietary intake of arginine is required to maintain immune function during health and how mucharginine is required to meet metabolic requirements during periods of growth or stress. 2002 Éditions scientifiques et médicales ElsevierSAS. All rights reserved.
Keywords: Arginine; Immune function; Arginase; Nitric oxide 1. Introduction
2. Arginine metabolism
Arginine functions in the body as a free amino acid, a Classification of arginine as an essential or non-essential component of most proteins, and as the substrate for several amino acid has been difficult. By the classical definition, non-protein, nitrogen-containing compounds. As a free essential amino acids cannot be synthesized in the body to amino acid, arginine functions as an intermediate in the urea meet the needs for optimal growth. In 1930, Scull and Rose cycle. As one of the 20 common α-amino acids, arginine is observed that arginine was synthesized in vivo, and classi- an integral component of mammalian proteins. As a sub- fied arginine as a non-essential amino acid . Nitrogen strate for several non-protein, nitrogen-containing com- balance studies, which are currently used to classify an pounds, arginine indirectly participates in the rapid regen- amino acid as essential or non-essential for humans, also classified arginine as non-essential . Some con- vasodilatation, neurotransmission, calcium release, and ulti- sider this to be an inaccurate evaluation and argue that mately immunity. This review will briefly address the arginine may need to be reclassified as a semi-essential or biochemical basis for arginine in health and disease and conditionally essential amino acid (reviewed in ).
discuss animal and human studies available in the literature Support for this argument comes from animal studies (rats that investigate the role of arginine supplementation on and dogs) in which sub-optimal weight gain is observed when arginine is excluded from the diet during growthUnder these conditions (growth) in vivo synthe-sis of arginine is not sufficient, hence the term conditionallyessential. During times of physiologic stress, arginine syn- thesis may not be able to keep up with metabolic demands.
E-mail address: rjhenken@mail.ifas.ufl.edu (B. Langkamp-Henken).
2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
PII: S 0 7 5 3 - 3 3 2 2 ( 0 2 ) 0 0 2 9 1 - 3 C. Nieves Jr, B. Langkamp-Henken / Biomed Pharmacother 56 (2002) 471–482 This is another ‘condition’ where arginine may become virtually all tissues including the kidney, brain, liver, skel- etal muscle and lungs However, the purpose of this One of the major functions of arginine within the body is as an intermediate in the urea cycle. The free amino acid Another function of arginine is protein synthesis. Argin- arginine contains a guanidino group, which is essential for ine can be converted into proline, glutamate and glutamine the synthesis of urea in most mammals. Urea is primarily (see all of which are common amino acids found synthesized in the liver and excreted by the kidneys. In the within most proteins. Synthesis of these three amino acids cytosol of hepatocytes, arginase-I removes the guanidino begins with arginine being converted into ornithine. Orni- group from arginine to produce urea and ornithine (see thine is then converted into pyrroline-5-carboxylate. The Urea is then transported from the hepatocyte into the enzyme for this reaction is ornithine aminotransferase.
bloodstream and ornithine is used to regenerate arginine Pyrroline-5-carboxylate can be converted into either proline within the hepatocyte. It is important to note that a second using pyrroline-5-carboxylate reductase or in two-steps form of arginase (arginase-II) exists and is expressed in converted into glutamyl-γ-semialdehyde, then glutamate.
Fig. 1. Diagram of arginine metabolites. Metabolites are bolded and enzymes/proteins are italicized.
Abbreviations: ADC, arginine decarboxylase; A:GAT, arginine:glycine amidinotransferase; DAO, diamine oxidase; Glu synthase, glutamine synthase; GMT,guanidinoacetate-N-methyltransferase; NOS-1, nitric oxide synthase-1; NOS-2, nitric oxide synthase-2; NOS-3, nitric oxide synthase-3; OAT, ornithineaminotransferase; ODC, ornithine decarboxylase; P-5-C dehydrogenase, pyrroline-5-carboxylate dehydrogenase; P-5-C reductase, pyrroline-5-carboxylatereductase; and PT, polyamine transporter.
C. Nieves Jr, B. Langkamp-Henken / Biomed Pharmacother 56 (2002) 471–482 The conversion of pyrroline-5-carboxylate into glutamyl-γ- arginine indirectly provide the substrate for polyamine semialdehyde is spontaneous and requires no enzyme; synthesis, it also indirectly stimulates polyamine synthesis however, conversion of glutamyl-γ-semialdehyde into by stimulating the release of growth hormone . In glutamate requires the enzyme pyrroline-5-carboxylate de- turn, growth hormone stimulates the release of insulin-like hydrogenase. Synthesis of glutamine from glutamate is growth factor-1, which stimulates polyamine synthesis by catalyzed by glutamine synthase and requires ammonia. In increasing ornithine decarboxylase activity .
addition to protein formation, glutamine prevents the accu- While ornithine decarboxylase is the rate-limiting en- mulation of ammonia in extrahepatic tissue by transporting zyme in polyamine production a second enzyme, arginine ammonia through the bloodstream to the hepatocytes for decarboxylase, also synthesizes polyamines In a study conducted in rats, arginine decarboxylase was shown to Arginine metabolism also generates several essential decarboxylate ornithine (K = 0.25 mM) to produce pu- non-protein, nitrogen-containing compounds. Some ex- trescine or to decarboxylate arginine (K = 0.75 mM) to amples of these compounds are creatine, polyamines, agma- produce agmatine . Moreover, both human and animal tine and nitric oxide. Creatine is primarily synthesized in the studies have shown that the enzyme agmatinase can use liver and transported through the blood stream to muscle agmatine as a substrate to produce putrescine tissue. Creatine functions as a carrier for phosphate and is In addition to being a substrate for polyamine synthesis, needed for the rapid regeneration of adenosine triphosphate agmatine also regulates intracellular concentrations of in the muscles. Synthesis of creatine is dependent on the polyamines. Regulation of intracellular polyamine produc- guanidino group of arginine and is a two-step reaction (see tion is important because high levels of polyamines are ). In the first reaction arginine:glycine amidinotrans- toxic to cells (reviewed in Agmatine regulates ferase, transfers the guanidino group from arginine onto polyamine production by decreasing ornithine decarboxy- glycine, this produces guanidinoacetate and ornithine. Next, lase activity and enhancing the transcription of antizyme the enzyme guanidinoacetate N-methyltransferase transfers . Antizyme is an endogenous protein that decreases a methyl group from S-adenosylmethionine to guanidinoac- intracellular polyamine synthesis through two different etate. Products from this reaction are creatine and mechanisms. First, antizyme decreases ornithine decarboxy- lase activity and second, antizyme accelerates the degrada- (phosphocreatine) occurs at the guanidino group in the tion of ornithine decarboxylase . Although, regulating the production polyamines decreases intracellular Approximately 10% of arginine in the plasma is used to polyamines levels, it does not prevent the uptake of synthesize creatine, even though creatine is regenerated polyamines from extracellular sources via the polyamine when phosphocreatine phophorylates adenosine diphos- transporter. Another function of agmatine and antizyme is to phate . This is due to the fact that phosphocreatine decrease the activity of the polyamine transporter, thus undergoes spontaneous degradation to creatinine. Creatinine limiting the uptake of extracellular polyamines cannot be degraded by mammals and is excreted by the In addition to regulating polyamine levels, agmatine and kidneys. A study conducted by Cockroft and Gault esti- arginine also regulate production of nitric oxide. Nitric mated creatinine excretion to be 23.6 ± 5 mg/kg over 24 h in oxide is an antimicrobial agent that is effective against males 18–29 years old . Using a 70 kg male as a intracellular pathogens, extracellular parasites and bacteria reference, 2.0–3.1 g of arginine is needed daily to replace Nitric oxide is also a neurotransmitter (reviewed creatine loss. A typical gram of dietary protein provides in and vasodilator . The enzyme that produces 54 mg of readily available arginine If our reference nitric oxide is nitric oxide synthase. The substrate for this male consumes the recommended daily allowance of 0.8 g reaction is arginine and the products are nitric oxide and of protein per kg of body weight, this supplies 3.0 g of citrulline (see There are three isoforms of nitric arginine. This means that the dietary intake of arginine may oxide synthase; these are NOS-1, NOS-2 and NOS-3.
only be sufficient to replace arginine lost in creatine NOS-1 (also known as nNOS, NOS-I and Type I NOS) is production. However, keep in mind that protein turnover constitutive and is predominately located in neuronal tissue.
and de novo synthesis also add to plasma arginine levels.
NOS-2 (also known as iNOS, NOS-II and Type II NOS) is Another metabolic pathway that involves arginine is the inducible and is located in a variety of tissue. NOS-3 (also synthesis of polyamines. Polyamines (putrescine, spermine known as eNOS, NOS-3 and Type III) is constitutive and is and spermidine) function in membrane transport, (reviewed primarily localized in endothelial tissue. Both NOS-1 and in ), cell growth, cell proliferation and cell differentia- NOS-3 produce low levels of nitric oxide and are calcium tion . Arginine and products of arginine metabo- dependent. Agmatine increases activity of NOS-1 and lism are necessary in both the regulation and the synthesis NOS-3 by stimulating the release of calcium (reviewed in However, agmatine indirectly decreases NOS-2 activ- C. Nieves Jr, B. Langkamp-Henken / Biomed Pharmacother 56 (2002) 471–482 ity. Agmatine is converted to agmatine aldehyde by diamine the control diet. Researchers have used arginine-free diets or oxidase, in turn, agmatine aldehyde inhibits NOS-2 “standard” diets. The standard diets vary in arginine content from 0.4 to 2% arginine. Ronnenberg et al. compared anarginine-free diet to a standard diet (1% arginine) in‘healthy’ young and aged rats . They showed an 3. Arginine and immunity
increase in concanavalin A-induced splenocyte inter-leukin-2 production with the standard diet compared withthe arginine-free diet. Supplementing arginine in the diet The importance of arginine in metabolic pathways result- (3% arginine) did not increase interleukin-2 production ing in protein formation and removal of nitrogenous waste above that seen with the standard diet . Kobayashi et al.
as well as cell signaling, proliferation and differentiation has compared antigen-specific mucosal immune responses in been well established. What remains to be clarified is mice fed an arginine-free diet with verses fed an arginine- whether dietary arginine can be supplemented at pharmaco- supplemented diet containing 8.7 g/l of arginine Mice logic levels to manipulate metabolic outcome. Currently, fed the arginine-supplemented diet had a higher level of clinicians are adding arginine to enteral formulas at a antigen-specific fecal immunoglobulin A. Mice fed the concentration of five times that found in a typical diet in arginine-free and arginine-supplemented diets did not differ attempt to boost immune function and improve clinical in daily consumption of the diet or in body weight .
outcome in critically ill patients. The rationale for thispractice is based on a number of studies demonstrating the While arginine may not be required in the diet of a benefit of arginine supplementation on immune function.
healthy adult animal to maintain weight or nitrogen balance, However, missing from critical reviews and possibly even it may be required in the diet to maintain normal immune the literature in general have been the studies showing no function. In fact, some studies using lymphocytes from effect or a detrimental effect of arginine supplementation on healthy animals demonstrate depressed in vitro lymphocyte immune function or outcome. Twenty-one animal studies in proliferation when cultured in media containing low levels which arginine was supplemented enterally are summarized of arginine and maximal proliferation when arginine is in The effect of arginine supplementation on added back to the media at physiologic plasma concentra- various immune parameters is listed as an increase, no tions If a minimal amount of arginine is required change, or a decrease in the immune parameter. From this to maintain immune function, the question becomes how table it becomes evident that the effects of arginine supple- much arginine is enough? This question is difficult to mentation on immune function are not consistent. For answer due to the lack of uniformity in the amount of example, five studies report an increase in thymus weight arginine supplemented in the experimental diets, the large with arginine supplementation while five studies report no variation in arginine content of the “standard” control diets, change in thymus weight with supplementation. Two studies and the nitrogen source and/or content of diets.
report an increase in mitogen-induced in vitro interleukin-2 Nutritionists tend to compare arginine supplementation production while five studies report no change in to an isonitrogenous control diet to differentiate between the interleukin-2 production with arginine supplementation.
non-specific effects of arginine (high nitrogen content) and Recommendations for pharmacologic supplementation of the specific effects of arginine and arginine metabolites.
arginine to enhance immunity in human health and patholo- While normalizing the nitrogen load between treatment gies cannot be made until we have a clearer picture of the groups may not be as big of a concern in healthy animals basis for and/or outcomes of these recommendations.
and humans, it does become an issue with stress models Many factors contribute to the inconsistent effects of (e.g. sepsis and trauma), which result in negative nitrogen enteral arginine supplementation on immune function. One of the most evident factors is the amount of arginine Commonly, glycine, alanine, or a mixture of nonessential supplemented in the diet. Researchers have provided 5 g of amino acids is added to the control diet to balance the arginine per kg diet (with half provided in the diet and half nitrogen load between arginine-supplemented and control provided in the drinking water) to 17 g of arginine per liter diets. Because arginine is a nitrogen-rich amino acid, of liquid diet. Others have provided 100 mg arginine HCl non-physiologic concentrations of single amino acids must via gavage (see The different concentrations of be added to make the control diet to make it isonitrogenous.
supplemental arginine and methods of administration may Unfortunately this is not without consequence. Pharmaco- contribute to the inconsistent effects of arginine supplemen- logic doses of glycine have been reported to alter free amino tation on immunity. Additionally, these differences also acid patterns and intestinal enzyme activity in a sepsis make it difficult to compare studies.
model Glycine may also have cytoprotective effects Another factor that may contribute to the inconsistent (reviewed in While the addition of alanine for a effects of arginine supplementation on immune function is nitrogen control in a sepsis model appears to preserve Table 1Summary of animal studies showing the effect of arginine administered enterally on various immune parameters and outcomes Effect of arginine on immune parameters and outcomes Standard a diet with added arginine (2% total arginine) vs. a standard diet a madeisonitrogenous with added alanine for 14 d Purified amino acid diet with 3% total arginine vs. 1.1% total arginine (control diet) vs.
Standard diet with 1% arginine in the drinking NK activity, IL-2R expression, T DTH, IL-2 productionwater vs. standard diet with an isonitrogenous cell cytotoxicity level of glycine in the drinking water for 10 d Standard diet (1.8% arginine) with added 0.5, 1, 2, or 3% arginine—half provided in the diet proliferation d and half in the drinking water vs. standard diet(1.8% arginine) for 6 d Liquid diet with 8.7 g/l arginine vs. arginine- free liquid diet made isonitrogenous withadded non-essential amino acids for 14–21 d Standard diet with 1.2 vs. 0% arginine in the Liquid diet with 7.7 g/l vs. 0 g/l total arginine Isonitrogenous liquid diets with 2.4, 4.5, 7.2 or DTH with 7.2 g/l 12 g total arginine per l via gastrostomy for14 d Standard diet with added 2% arginine vs.
standard diet made isonitrogenous with added Standard diet with added 2% arginine vs.
with E. coli, and 20% whole standard diet made isonitrogenous with added Standard diet (1.6% arginine) with 0.75 vs. 0% Liquid diet via gastrostomy containing 5, 11, or 17 g/l arginine HCl vs. 0.7 g/l total arginine Standard diet (1.8% arginine) with 100 mg arginine HCl vs. water via gavage for 4–7 d Standard diet plus 1, 2, or 5% arginine vs.
Splenocyte proliferation, survival Survival with 5% arginine Effect of arginine on immune parameters and outcomes Standard diet (2% arginine) with 1.8 vs. 0% arginine in the drinking water (0% madeisonitrogenous with added glycine) for 21 d Standard diet with added arginine (3% total arginine) vs. standard diet (1.6% arginine) made isonitrogenous with added alanine for Liquid diet with 2.93 g/l total arginine vs.
arginine-free liquid diet made isonitrogenous bacterial killing, splenocyteproliferation, IL-2 production Standard diet (1.8% arginine) with added 1% arginine—half provided in the diet and half in proliferation the drinking water vs. standard diet (1.8%arginine) for 6 d Standard diet plus 49 g/kg arginine vs.
standard diet made isonitrogenous with added Chemical-induced colorectal Standard diet with 1 vs. 0% arginine in the Thymus weight after 10 week of Thymus weight after 22 week of Tumor incidence, burden, and Standard diet with 1% arginine in drinking water vs. standard diet with an isonitrogenous IL-2 production, splenocytelevel of glycine in the drinking water for a Unless otherwise noted, standard diets contain approximately 0.4 to 0.98% arginine.
b Abbreviations: DTH, delayed-type hypersensitivity; IgA, immunoglobulin A; IL-1 , interleukin-1 beta; IL-2R, interleuking-2 receptor; mRNA, messenger RNA; NK, natural killer; and TNF-α, c In vitro production of IL-2 from mitogen-stimulated lymphocyte cultures.
d Unless stated otherwise splenocyte and thymocyte proliferation is mitogen induced.
C. Nieves Jr, B. Langkamp-Henken / Biomed Pharmacother 56 (2002) 471–482 plasma and tissue-free amino acid concentrations In addition to differences in lymphocyte cytokine pro- observations from our laboratory suggest that alanine is not duction between different strains of mice, macrophages from different strains of mice respond differently. Resident In 2000, we showed that arginine supplementation en- peritoneal macrophages from C57BL/6 are more easily hanced delayed-type hypersensitivity responses in young, activated to produce nitric oxide upon stimulation with adult, and aged male CB6F1 (BALB/c × C57BL/6) mice interferon-γ than macrophages from BALB/c mice given a 2% arginine diet versus an isonitrogenous control Based on differences in lymphocyte cytokine production diet The control diet was made isonitrogenous with the and macrophage activation among strains of mice, it may be addition of alanine. Recently we have repeated this experi- possible that arginine supplementation yields different im- ment in female BALBc mice, but this time a third diet was mune outcomes in different strains of mice. Similar obser- added to the protocol. Mice received the standard diet with vations may also become apparent between species with added arginine (2% total arginine), the standard diet made arginine supplementation (and reviewed in ).
isonitrogenous to the arginine diet with the addition of Up until this point in the review, the experimental model alanine, or the standard diet. Delayed-type hypersensitivity used to examine the effect of arginine supplementation on responses were not different between mice receiving the 2% immune function has been largely ignored. The amount of arginine diet and the mice that received the standard diet.
arginine required in the diet and ultimately the effect of However, the delayed-type hypersensitivity response was arginine supplementation on outcome might largely depend significantly lower in the mice fed the alanine-supplemented on the experimental model. Sepsis and inflammation in- (isonitrogenous diet) than the standard diet (unpublished crease nitric oxide production via upregulation of NOS-2 data). These data in conjunction with the previously re- Mice that lack NOS-2 are susceptible to infection ported data suggest that arginine supplementation did Trauma, on the other hand, is associated with not enhance delayed-type hypersensitivity responses but decreased nitric oxide production and increased extrahe- that the addition of alanine to the standard diet depressed patic arginase-I expression and activity these responses. Other explanations for these data could be The greatest increase in extrahepatic arginase activity is that male and female mice or different strains of mice found in splenic macrophages . In humans, general respond differently to arginine supplementation. The latter surgery and trauma increase peripheral mononuclear cell explanation could also help justify some of the conflicting arginase-I activity and decrease plasma nitric oxide effects of arginine supplementation on immune function that In general surgery patients, the increase in mononuclear arginase activity was only evident when the T 2 cytokine, Mitogen-stimulated splenocytes from different strains of interleukin 10, was increased Bernard et al. demon- mice have a propensity to secrete different cytokines. For strated that in vitro macrophage arginase activity increases example, splenocytes from C57BL/6 mice secrete higher concentrations of interferon-γ and lower concentrations of -adrenoceptor blockade prior to trauma decreases murine interleukin-4, while splenocytes from BALB/c mice secrete splenic arginase activity These data suggest a role for lower concentrations of interferon-γ and higher concentra- catecholamines and cytokines in switching arginine metabo- tions of interleukin-4 Helper T lymphocytes that lism between an antimicrobial and a tissue repair pathway.
Since arginase and nitric oxide synthase utilize arginine interleukin-2 and tumor-necrosis factor- are referred to as as a substrate, increased expression of arginase-I increases T helper-1 (T 1) cells, whereas T lymphocytes that pre- intracellular ornithine and polyamines and reduces basal dominantly produce interleukin-4, -5, -6 and -10 are re- nitric oxide synthesis by endothelial cells . Nitric oxide ferred to as T 2 cells. Cell-mediated immune functions, derived from NOS-3 produces vasorelaxation and inhibits such as delayed-type hypersensitivity and activation of platelet aggregation and neutrophil infiltration—important cytotoxic T lymphocytes and inflammatory macrophages, functions for maintaining organ blood flow following are associated with T 1 responses, while B lymphocyte, trauma A series of studies examined whether mast cell and eosinophil activation are associated with T 2 intravenous arginine administration during resuscitation responses. The balance between T 1 and T 2 responses improved blood flow to various organs following trauma predicts the metabolic fate of arginine and possibly the and hemorrhage . Rats underwent a sham operation or difference between cell proliferation and connective tissue laparotomy (trauma), were bled to a mean arterial pressure production or antimicrobial capacity. In vitro and in vivo of 40 mmHg, and resuscitated. Arginine (300 mg/kg) or studies demonstrate that NOS-2 and arginase-1 are differ- saline was infused intravenously during the first 15 min of entially regulated by T 1- and T 2-driven immune reac- resuscitation. At 3 h post trauma-hemorrhage and resusci- tions with T 1 cytokines inducing NOS-2 and T 2 cytok- tation, plasma arginine (corrected for the plasma protein concentration) decreased 87% compared with shamoperated C. Nieves Jr, B. Langkamp-Henken / Biomed Pharmacother 56 (2002) 471–482 group. Infusion of arginine during resuscitation temporarily Two of the trials show an increase in mitogen-induced corrected plasma arginine concentrations and significantly lymphocyte proliferation, while three of the trials show no increased corrected plasma citrulline concentrations increase or a decrease in lymphocyte proliferation with Cardiac output and blood flow to the heart, skin, muscle, arginine supplementation. No studies demonstrate improved kidneys, stomach, pancreas, small intestine, large intestine, clinical outcomes with arginine supplementation.
mesentery, brain, liver, and spleen were increased with A large part of the rationale for supplementing arginine to intravenous arginine administration during resuscitation enhance immune function is based on studies that show an . Arginine infusion during resuscitation was also asso- increase in mitogen-induced in vitro lymphocyte prolifera- ciated with decreased liver injury and plasma interleukin-6 tion (see In vitro lymphocyte proliferation and increased splenocyte interleukin-2 production com- is a convenient measure of immune function, especially in pared with animals resuscitated without arginine human studies, and appears to correlate with mortality Mitogen-induced splenocyte proliferation was significantly However, the mechanism by which arginine supplementa- lower following trauma-hemorrhage and resuscitation with- tion in vivo may enhance in vitro lymphocyte proliferation out arginine infusion compared with sham-operated con- is still unknown. Is it possible that mitogen-induced in vitro trols. Arginine infusion prevented this decrease Based lymphocyte proliferation represents a completely artificial on the kinetics of nitric oxide produc tion in the blood flow condition? For example, Barbul et al. gave healthy volun- studies, the authors concluded that the intravenous arginine teers 24.8 g of free arginine per day for 14 d . Plasma increased blood flow via the production of nitric oxide by arginine concentrations were 66.3 µM at baseline and in- creased to 114 µM after 14 d of supplementation. Peripheral While this series of studies showed benefit of intravenous blood lymphocytes were obtained at baseline and day 14 infusion of arginine at the time of resuscitation, it is and stimulated with mitogen in culture media (RPMI 1640) unknown and perhaps doubtful that enteral arginine would containing approximately 1150 µM arginine Any have the same affect. In a healthy animal, approximately changes that occur in vivo due to the difference in plasma 40% of dietary arginine is degraded in the intestine in the arginine concentrations may be abolished in vitro. Ochoa et al. demonstrated that interleukin-2 accumulation was sig- hemorrhage, blood flow to the intestines and portal blood nificantly less when splenocytes, stimulated with anti-CD3, flow are reduced which may alter the absorption process were cultured in media containing 100 or 1000 µM arginine Madden et al. demonstrated that providing arginine compared with cells cultured with 0 or 10 µM arginine (100 mg arginine HCl every 12 h) via gavage immediately Additionally, CD45RA negative CD8+ (memory) T cells after and for 4 d following cecal ligation and puncture that and the number of CD8 and CD3 receptors were upregu- overall survival was not altered compared with unsupple- lated with the addition of arginine to the culture media mented controls When the arginine was gavaged daily Rodriguez et al. demonstrated that T cell receptor CD3 for 3 d prior to and after the insult following the same chain expression was regulated by arginine in the culture administration regimen, survival improved significantly.
Beneficial effects on survival were also observed when the signal transduction element and the rate-limiting step in the arginine was infused intravenously immediately after insult.
assembly and membrane expression of the T cell receptor These data suggest that enteral arginine supplementation prior to injury or intravenous arginine supplementation at not interleukin-2 production or interleukin-2 receptor the time of injury may provide the most benefit . Thus chains) was reduced when Jurkat cells (helper T-cell line) timing of enteral arginine supplementation appears to be were cultured in arginine-free media. The inhibition of the another factor contributing to the inconsistent outcomes chain expression was completely reversed with the addition associated with arginine supplementation.
of arginine to the culture media This arginine-mediated The strongest evidence supporting the role of arginine effect was attributed to a change in CD3 mRNA half-life supplementation on immune-modulation in humans comes from double-blind, randomized controlled trials. However, Changes in macrophage function with altered cell culture there are few such trials and fewer that investigate or arginine concentrations have also been described. Albina et demonstrate clinical outcomes (this does not include clinical al. demonstrated that macrophage superoxide production, trials that compare immune-enhancing enteral formulas of phagocytosis, protein synthesis, and tumoricidal activity which arginine is one of many added nutrients). Of 15 were greatest in culture media containing 6 µM arginine, clinical trials that examined the effect of arginine supple- decreased as the arginine concentration in the media ap- proached physiologic concentrations (∼100 µM), and con- tinued to decrease or maintained lower levels of function at the study was a double-blind, randomized controlled trial.
pharmacologic concentrations observed in common cell C. Nieves Jr, B. Langkamp-Henken / Biomed Pharmacother 56 (2002) 471–482 Table 2Double-blind, randomized controlled trials investigating the effect of enteral arginine supplementation on immune function No differences in lymphocyte No difference in preoperatively via oral intake proliferation or endotoxin- lymphocyte proliferation and complications 20, 10, or 0 g/d for 4 weeks, No change in viral load and 17, 8.5, or 0 g/d for 4 weeks No change to possibly a in residents with pressure ulcers via oral intake lymphocyte proliferation andno change in IL-2 production a Abbreviations: IL-2, interleukin-2; GI, gastrointestinal.
culture media (∼1200 µM) These data suggest that arginine supplementation, the animal species or strain of macrophage function would be enhanced at low plasma species, and the experimental model. Systematic study is arginine concentrations and inhibited at concentrations typi- required to determine whether a basal dietary intake of cally found in plasma or culture media. While there are very arginine is required to maintain immune function during few in vivo measures of immune function that can be used health and how much arginine is required to meet metabolic to assess the immune effects of arginine supplementation requirements during periods of growth or stress.
(especially in humans), caution should be used wheninterpreting in vitro studies with immune cells cultured inmedia containing nonphysiologic concentrations of argin- Acknowledgments
In summary, arginine functions in the body as a free This research was supported by the Florida Agricultural amino acid, a component of most proteins, and the substrate Experiment Station, and approved for publication as Journal for several non-protein, nitrogen-containing compounds, many of which function in immunity. Although arginine issynthesized in the body, it is not made in sufficient quanti-ties to support growth or meet metabolic requirements References
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