Skip to main content Accessibility help
×
Home
Hostname: page-component-5c569c448b-ckh7h Total loading time: 0.683 Render date: 2022-07-02T18:47:23.023Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "useRatesEcommerce": false, "useNewApi": true } hasContentIssue true

Role of specific dietary amino acids in clinical conditions

Published online by Cambridge University Press:  01 August 2012

Renate Jonker
Affiliation:
Department of Health & Kinesiology, Texas A&M University, Suite #210, 1700 Research Parkway, College Station, Texas, 77843-4253, USA
Mariëlle P. K. J. Engelen
Affiliation:
Department of Health & Kinesiology, Texas A&M University, Suite #210, 1700 Research Parkway, College Station, Texas, 77843-4253, USA
Nicolaas E. P. Deutz*
Affiliation:
Department of Health & Kinesiology, Texas A&M University, Suite #210, 1700 Research Parkway, College Station, Texas, 77843-4253, USA
*
*Corresponding author: Nicolaas E. P. Deutz, MD, PhD., email nep.deutz@ctral.org
Rights & Permissions[Opens in a new window]

Abstract

In a variety of chronic and acute disease states, alterations in protein synthesis, breakdown and protein turnover rates occur that are related to the loss of body protein and skeletal muscle wasting. A key observation is the stimulation of protein breakdown in muscle and the stimulation of protein synthesis in the splanchnic area; mainly liver. An altered splanchnic extraction of amino acids as well as an anabolic resistance to dietary protein, related to stress, disuse and aging play a key role in the pathogenesis of muscle wasting in these conditions. To overcome these factors, specific dietary protein and amino acid diets have been introduced. The main focus of these diets is the quantity and quality of dietary proteins and whether a balanced mixture or solely dietary essential amino acids are required with or without higher intake levels of specific amino acids. Specifically in cancer patients, stimulated muscle protein synthesis has been obtained by increasing the amount of protein in a meal and by providing additional leucine. Also in other chronic diseases such as chronic obstructive pulmonary disease and cystic fibrosis, meals with specific dietary proteins and specific combinations of dietary essential amino acids are able to stimulate anabolism. In acute diseases, a special role for the amino acid arginine and its precursor citrulline as anabolic drivers has been observed. Thus, there is growing evidence that modifying the dietary amino acid composition of a meal will positively influence the net balance between muscle protein synthesis and breakdown, leading to muscle protein anabolism in a variety of chronic and acute disease states. Specific amino acids with anabolic potential are leucine, arginine and citrulline.

Type
Full Papers
Copyright
Copyright © The Authors 2012

Introduction

The importance of dietary amino acids (AAs) in protein synthesis and breakdown in health and disease has been widely discussed. AAs are ingested daily via the diet, followed by digestion, absorption and ultimately distribution to many important sites in the body. The net balance between protein synthesis and breakdown in the body during a day is the result of metabolic and physiological homeostasis. When this homeostasis is disturbed by disease, between meals a shift towards a more negative protein balance often occurs, ultimately resulting in loss of (skeletal muscle) protein. In these circumstances, an overall increase in protein turnover, a stimulation of protein breakdown in muscle, and an enhanced uptake of AAs by the splanchnic bed are key factors.

Alterations in the metabolic function and regulation of the gut and liver are often present in acute and chronic disease states, associated with an increased stress-response (i.e. inflammation). As a consequence, the extraction of AAs between meals is often increased to support a higher energy expenditure, hepatic gluconeogenesis, the production of acute phase proteins and other substrates related to the present condition. Importantly, the increased need for AAs by the splanchnic tissues potentially stimulates the breakdown of protein in muscle, draining muscle protein stores.

We and others have shown that high-grade inflammatory states such as sepsis and burn injury as well as low-grade systemic inflammatory conditions like cancer, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) are all characterized by changes in the interorgan exchange of several AAs.

When during a day, net protein breakdown exceeds net protein synthesis, catabolism will occur. To optimize the anabolic response to a meal, more specifically of muscle, detailed insight in the underlying mechanisms is needed.

Stimulation and inhibition of muscle protein synthesis are two metabolic pathways potentially regulated by different mechanisms(Reference Wolfe1). However, both depend on the availability of AAs in the extracellular pool (i.e., blood stream). As dietary protein is digested and absorbed by the gut, dietary AAs are extracted by the splanchnic area (i.e. portal drained viscera and liver) during their first pass or alternatively released into the systemic circulation (Fig. 1). The extent of their extraction reflects on their availability in the systemic circulation. Likely, it is the increase in extracellular AA concentrations after a meal that gives signal for protein synthesis(Reference Wolfe and Miller2) and consequently AAs are transported into the muscle. To the contrary, a fall in extracellular AA concentrations below basal levels inhibits the stimulation of muscle protein synthesis(Reference Wolfe1).

Fig. 1 Concept of splanchnic extraction of amino acids during feeding and availability to muscle for protein synthesis (PS).

Animal and human clinical trials in health and disease have investigated whether dietary protein and amino acid diets can positively modify the accretion of protein during a meal, thereby improving the overall protein balance throughout the day. However, there is concern for an anabolic resistance of skeletal muscle related to aging, disuse and the presence of inflammation that in various disease states could ultimately lead to more protein wasting. In the diets that have been introduced it appears that the quantity, as well as the dietary protein or amino acid composition of a meal is of crucial importance. Most recent studies have focused on the effects of adding the AA leucine (LEU) in combination with other ingredients to the diet. It appears that muscle protein synthesis can be stimulated with LEU diets under certain conditions. However, we still lack insight into the role of specific dietary amino acids like LEU in attenuating or preventing the loss of skeletal muscle in chronic or critically ill patients, which is of crucial importance in relation to their recovery, functional status, and overall outcome. Our main goal is to develop dietary modifications that lead to improved outcome and function of chronic and acute disease states based on translation of available knowledge from animal and human clinical research.

Important modifying factors for protein anabolism

There are two factors that play a key role in modifying the capacity for protein anabolism during feeding in situations where a chronic or acute disease is present: first-pass splanchnic extraction (SPE) of dietary AAs and anabolic resistance to dietary AAs.

First-pass splanchnic extraction of dietary amino acids

The splanchnic tissues play a key role in the regulation of protein turnover, because these tissues are responsible for the first-pass extraction of the dietary AAs and their release to the peripheral tissues (Fig. 1)(Reference Stoll and Burrin3). Dietary AAs absorbed by the splanchnic bed are used either for incorporation into protein of the splanchnic area (constitutive or labile proteins (e.g. pancreatic enzymes, mucus, mucosal villi)) or are converted into other products such as other AAs that subsequently can be used for protein synthesis or are to be oxidized(Reference Stoll and Burrin3). Splanchnic tissues are known for their high protein turnover rates. In situations of an altered metabolic function of these tissues (i.e. acute or chronic disease) this could potentially limit the flow and availability of dietary AAs to the peripheral tissues, thereby negatively influencing the metabolic response to a meal.

In previous studies, we and others have shown that the first-pass SPE of the AAs LEU and phenylalanine increases with age(Reference Tessari, Inchiostro and Barazzoni4Reference Luiking, Deutz and Jakel8) (Fig. 2). Although the exact reason for this elevated SPE in the elderly is still unknown, it is suggested that it may contribute to the development of sarcopenia as hypothetically less AAs could be available to the peripheral tissues. Interestingly, Boirie and colleagues(Reference Boirie, Gachon and Beaufrere5) found a positive correlation between the SPE of dietary LEU and BMI in a small study group and this relationship appeared to be more pronounced in the elderly. The relatively large contribution of adipose tissue to an increased BMI in the elderly as well as the fat distribution could possibly enhance levels of inflammatory markers and therefore lead to a higher hepatic extraction of LEU. Limited data are available as to whether acute or chronic diseases further aggravate the age-related disturbances found in splanchnic amino acid extraction, Interestingly, a lower SPE was found in patients with moderate COPD associated with an enhanced anabolic response to a protein meal (Fig. 3), suggesting that the metabolic efficiency of feeding was increased in this COPD group(Reference Engelen, Rutten and De Castro9, Reference Engelen, Rutten and De Castro10). The reduced SPE in COPD is remarkable as COPD is a low-grade systemic inflammatory condition(Reference Gan, Man and Senthilselvan11, Reference Pinto-Plata, Mullerova and Toso12). Besides an adaptation to increased needs elsewhere in the body, the reduced SPE might reflect a reduced splanchnic protein turnover rate rather than a reduced splanchnic amino acid net utilization. Factors known to influence splanchnic protein turnover are nicotine use and the intake of certain drugs (e.g. non-steroidal anti-inflammatory drugs known to reduce blood flow in the splanchnic region)(Reference Hashimoto, Yoneda and Shimada13). We hypothesize that a reduced first-pass SPE is a compensatory mechanism of the body to keep an overall protein balance (Fig. 4). When this adaptive mechanism starts to fail, patients will lose their ability to counteract the protein loss during catabolic conditions.

Fig. 2 Values are means ± SE. Splanchnic extraction (SPE) of phenylalanine (PHE) or leucine (LEU) stable isotopes in young (open bar) and elderly (striped bar) individuals(48) and unpublished results from Engelen et al., 2011. Significance of difference between young and elderly individuals *P < 0·05.

Fig. 3 Values are means ± SE. Net anabolism in COPD patients (striped bar) as reflected by the net increase in whole-body protein synthesis (WbPS) is associated with a reduced splanchnic extraction (SPE) of meal-derived amino acids as compared to healthy controls (open bar)(9, 10) and unpublished results from Engelen et al., 2011. Significance of difference between COPD patients and healthy controls *P < 0·05, **P < 0·01.

Fig. 4 Reduced splanchnic extraction during disease as an adaptive mechanism (refer Fig. 1) to make more amino acids available for muscle protein synthesis (PS) to compensate for the stimulated protein breakdown between meals.

Anabolic resistance to dietary protein

Aging

A relatively large portion of human research on protein metabolism has been performed in healthy young and elderly individuals. It has been shown that elderly who are active and have no evidence of an inflammatory condition, have comparable values for basal muscle protein turnover (synthesis and breakdown rates) as young adults(Reference Volpi, Sheffield-Moore and Rasmussen14Reference Symons, Schutzler and Cocke17). Recent research does indicate the possibility of a gender related difference in muscle protein synthesis(Reference Smith, Atherton and Villareal18), explaining the slower progression of muscle loss in elderly women compared to men.

Although there are strong indications that the first-pass SPE of dietary AAs is higher in the elderly(Reference Tessari, Inchiostro and Barazzoni4Reference Luiking, Deutz and Jakel8), Volpi and others showed that the amino acid availability to the muscle, subsequent amino acid uptake and muscle protein synthesis were not affected(Reference Volpi, Mittendorfer and Wolf7, Reference Koopman, Walrand and Beelen19). In line with this, but on a whole-body level, we found that although the SPE of several dietary AAs was higher in response to a whey protein meal in the elderly, protein synthesis was not affected (Engelen et al., unpublished results) (Fig. 5). Alternatively, Cuthbertson and colleagues did observe a blunted anabolic response on a muscle level to a mixture of free dietary essential amino acids (EAAs), ranging from 2·5 to 40 g, independent of insulin availability or dose of AAs(Reference Cuthbertson, Smith and Babraj16). A possible explanation for this could be a decreased activation of amino acid signaling proteins, such as mammalian target of rapamycin (mTOR), p70 S6 kinase and eukaryotic initiation factors, in the elderly.

Fig. 5 Values are means ± SE. Net whole-body protein synthesis (Net WbPS) 2 h after continuous intake of a whey protein+carbohydrate meal in young and elderly individuals (unpublished results from Engelen et al., 2011). The complete drink supplied 8·1 g protein and 21 g maltodextrin (based on a 75 kg subject) over 2 h. No statistically significant interaction was observed between group and protein.

Disuse

Exercise, besides dietary protein, is an important stimulus of muscle protein synthesis. However in chronic as well as in acute disease states, patients are often subject to prolonged inactivity, caused by hospitalization, bed rest or a more gradual decline in daily activities. The disuse of skeletal muscle triggers certain metabolic alterations in protein turnover, resulting in disuse atrophy. As described in a recent review by Rennie et al. (Reference Rennie, Selby and Atherton20), disuse primarily affects muscle protein synthesis, with no concomitant increase but rather a reduction in muscle protein breakdown. Different models of disuse (i.e. knee immobilization or bed rest for 10 to 28 d) have shown this down regulation of muscle protein synthesis(Reference Paddon-Jones, Sheffield-Moore and Cree21Reference Ferrando, Paddon-Jones and Hays23). In addition, it could be that longer periods of disuse are associated with a more progressive reduction in protein synthesis, as a study in healthy elderly showed that the total mean nitrogen balance was significantly lower in the second half of a 10 d period of bed rest(Reference Kortebein, Ferrando and Lombeida24).

More importantly, attempts to increase protein synthesis after inactivity, by amino acid supplementation has revealed an anabolic resistance of skeletal muscle to feeding. After 14 d of unilateral knee immobilization in healthy young adults, 4 h of infusion with a low as well as a high dose of mixed AAs was not able to acutely stimulate muscle protein synthesis to the same extent as in the mobilized leg(Reference Glover, Phillips and Oates22). The low and high dose resulted in an increase (55 % vs. 70 %, respectively) in anabolic response in the mobilized leg(Reference Glover, Phillips and Oates22). Interestingly, a recent study by Ferrando and colleagues(Reference Ferrando, Paddon-Jones and Hays23) showed that supplementation with dietary EAAs (high in LEU) was capable of maintaining muscle protein synthesis at baseline level during 10 d of bed rest, which otherwise decreased by 30 %, indicating the anabolic potential of dietary EAAs.

Systemic inflammation

It is suggested that a systemic inflammatory response contributes to the pathogenesis of muscle wasting. Systemic inflammation is a condition characterized by increased plasma concentrations of several inflammatory markers, such as C-reactive protein, fibrinogen, leukocytes, IL-6 and 8 and tumor necrosis factor-α. In healthy elderly, increased concentrations of plasma C-reactive protein, IL-6 and tumor necrosis factor receptor II were all negatively related to muscle protein synthesis(Reference Toth, Matthews and Tracy25). The liver, as the main production site of acute phase reactants, extracts an increased proportion of alimentary AAs to support the accelerated acute phase response. Thus, if and when the availability of AAs to muscle is decreased, the response of muscle protein synthesis could be blunted. In addition, the delivery of dietary AAs to the liver appears to result in an enhanced splanchnic consumption of certain dietary EAAs(Reference Reeds, Fjeld and Jahoor26) and therefore the amino acid profile may be unbalanced for the skeletal muscle, thereby negatively influencing skeletal muscle anabolism.

In conclusion, several factors such as aging, disuse and systemic inflammation play a key role in modifying the anabolic capacity of the body. It is expected that these effects might be even more pronounced when a chronic or acute disease state is present.

Protein and amino acid supplementation

Can we overcome the discussed factors by modifying the diet? Dietary protein and amino acid supplements are the most likely candidates to do this and both appear to be primarily capable of stimulating muscle protein synthesis, whereas muscle protein breakdown rates often remain unchanged(Reference Biolo, Tipton and Klein27, Reference Volpi, Mittendorfer and Wolf7, Reference Katsanos, Kobayashi and Sheffield-Moore28, Reference Dillon, Volpi and Wolfe29).

Protein quantity and quality

Supplementation of dietary protein in healthy individuals stimulates muscle protein synthesis and is responsible for a net anabolic response to feeding. However, the capacity for muscle protein synthesis is determined to a certain degree by the amount of protein intake. A recent study in healthy young and elderly showed that a threefold higher dietary protein intake was not favourable above a single dose of 30 g dietary protein ( = 0·4 g /kg body weight for a person of 75 kg, ~1/3th of average daily protein intake)(Reference Symons, Sheffield-Moore and Wolfe30) and muscle protein synthesis was equally stimulated by 50 %. On the other end, a study by Katsanos and others showed that a small protein meal (7 g) did not result in comparable stimulation of muscle protein synthesis in young and elderly, indicating a higher threshold for protein synthesis in the elderly(Reference Katsanos, Kobayashi and Sheffield-Moore28). This higher threshold for protein synthesis could be another important factor in the development of sarcopenia and therefore a recommended dietary allowance for protein intake of 1·5 g protein/day should be aimed for to maintain muscle mass and function in the elderly(Reference Wolfe, Miller and Miller31).

There is still some controversy as to whether the quality of dietary protein is an important factor influencing muscle protein synthesis. We recently performed a study in healthy young individuals and showed that the quality of the protein provided did not differentially influence muscle protein kinetics(Reference Luiking, Engelen and Soeters32). The mixed muscle fractional synthetic response and net muscle protein breakdown were comparable after intake of soya protein versus an isonitrogenous amount of casein protein (Fig. 6). Adversely, in a recent study by Tang(Reference Tang, Moore and Kujbida33), the proteins whey and soya, were favourable in comparison to the casein protein in stimulating skeletal muscle protein synthesis in healthy young men. The differences found between casein, whey and soya protein may largely be related to how quickly the proteins are digested (fast vs. slow) instead of the quality of the amino acid composition of the proteins. A possible explanation for the greater muscle synthetic response after whey and soya protein ingestion could be the more rapid and high plasma appearance of AAs compared to the slower and moderate hyperaminoacidaemia resulting from casein intake(Reference Boirie, Dangin and Gachon34). However, it may well be the case that the observed differences in the capacity of different proteins to stimulate muscle protein synthesis are related to the duration of the observation period after intake of the protein meals. A recent study from Denmark(Reference Reitelseder, Agergaard and Doessing35) clearly showed that when muscle protein synthesis was measured in the first 3 h after the meal, whey protein was more anabolic, whereas casein protein was more anabolic when measuring between 3 and 6 h after the meal. Interestingly, no differences were found between casein and whey proteins in their muscle anabolic effect when measuring over the whole 0–6 h period after meal intake. This might also explain our own observation when comparing soy and casein proteins(Reference Luiking, Engelen and Soeters32). It could well be that the essential amino acid content and composition of the different dietary proteins, and especially the LEU content are more decisive factors for a positive effect on muscle protein synthesis in situations where a chronic or acute disease is present. The differences between the types of proteins that we eat are probably not large enough to make a difference in healthy, young individuals in an unstressed condition. However, it might well be possible that the prandial observation periods when comparing different proteins are often chosen to be too short and that therefore certain (wrong) conclusions have been made.

Fig. 6 Values are means ±  SE. Mixed muscle fractional synthesis rate (FSR) 4 h after continues intake of dietary casein protein (CAPM) or soya protein (SOPM) in healthy young subjects(32). The complete drink supplied 0·2 g protein/kg BW/4 h (about 14 g/subject/4 h) and 42 g carbohydrates. No significant interaction was observed between group and protein.

Free total and dietary essential amino acids

Muscle protein synthesis in the elderly can be stimulated by continuous infusion of mixed AAs in the post-absorptive state(Reference Volpi, Ferrando and Yeckel36) and also by a bolus ingestion of dietary EAAs(Reference Paddon-Jones, Sheffield-Moore and Zhang15). However, increasing evidence indicates that only dietary EAAs appear to be required for the stimulation of muscle protein synthesis in healthy elderly(Reference Volpi, Kobayashi and Sheffield-Moore37, Reference Paddon-Jones, Sheffield-Moore and Katsanos38). A research study performed in healthy young men showed a similar effect, as only the dietary EAAs were able to increase the incorporation of L-[1-13C]LEU into muscle protein.

Specific role of leucine

The dietary EAA leucine (LEU), isoleucine and valine (identified as the branched-chain amino acids (BCAA)) form a group of AAs primarily prevalent in skeletal muscle. LEU is of particular interest due to the increasing evidence indicating the diverse roles of LEU and the specific regulatory role that LEU plays in stimulation of muscle protein synthesis. LEU alters muscle protein synthesis by regulating the translation initiation of several eukaryotic initiation factors (eIF4E, eIF4G) and ribosomal protein kinase S6 (p70S6)(Reference Kimball and Jefferson39). LEU furthermore functions as a nitrogen donor for the production of alanine and glutamine (GLN) in muscle(Reference Rennie and Tipton40) and LEU is one of the relatively small number of AAs which are known to enhance insulin secretion from the primary islet cells and β-cell lines(Reference Newsholme, Brennan and Rubi41). Previous studies have shown that infusion of the amino acid LEU resulted in the strongest insulin increase compared to other AAs(Reference Floyd, Fajans and Conn42).

In a healthy population, the anabolic response to LEU appears to be distinct between the young and elderly(Reference Cuthbertson, Smith and Babraj16), which could be related to the enhanced extraction by the gut, liver or both described in the elderly by Boirie et al. (Reference Boirie, Gachon and Beaufrere5). Consistent with the notion that LEU plays a regulatory role in the stimulation of muscle protein synthesis, it has recently been shown that dietary supplementation with extra LEU improves the response of muscle protein synthesis in elderly subjects(Reference Katsanos, Kobayashi and Sheffield-Moore43Reference Rieu, Balage and Sornet45), whereas in young adults the addition of extra LEU did not facilitate an increased stimulatory effect(Reference Katsanos, Kobayashi and Sheffield-Moore43). Therefore, raising the plasma concentration of LEU by the provision of a LEU-enriched medical food potentially can overcome impaired responsiveness of muscle protein synthesis in the elderly and creates a rationale for using LEU as an important anabolic substrate for patients with increased muscle loss(Reference Cuthbertson, Smith and Babraj16). It can be argued that supplementation of LEU without co-ingestion of the other BCAAs valine and isoleucine could result in a lower muscle protein synthesis, the so-called BCAA-antagonism, as all three precursors are required for skeletal muscle protein synthesis(Reference Tipton, Elliott and Ferrando46).

Citrulline as an alternative stimulator

Citrulline (CIT), produced by the gut from GLN and ARG (approximately 80–90 % of CIT is produced via this conversion) is metabolized to ARG in the kidneys. After the release by the kidneys, ARG becomes available in the circulation for uptake by peripheral (muscle) tissue. ARG availability is dependent on dietary intake and the de novo synthesis of ARG from CIT. A possible role of CIT in modifying protein kinetics is through the availability of CIT in the kidney and the conversion of CIT to ARG, regulated by plasma CIT availability(Reference van de Poll, Siroen and van Leeuwen47).

It has been observed that dietary intake of both ARG(Reference Bruins48Reference Zhang, Chinkes and Wolfe53) and (more recently) CIT(Reference Cynober, Moinard and De Bandt54) stimulate muscle protein synthesis, and that CIT per gram is more effective than ARG. Probably this is related to the fact that CIT escapes hepatic uptake and because of a more efficient dietary absorption of CIT in the gut. Through the GLN-CIT-ARG pathway, CIT as a precursor for ARG might well be a more potent stimulator of protein synthesis than ARG itself.

Protein metabolism and the response to feeding in acute and chronic wasting diseases

It is well known that in acute and chronic diseases alterations in protein synthesis and breakdown have a detrimental effect on muscle protein stores. As muscle protein stores become depleted, patients experience muscle wasting, negatively influencing their prognosis and functional capabilities. As the available research in chronic disease states (such as cancer, COPD, CF) and acute diseases has so far mainly been on the potential anabolic properties of certain proteins (i.e. whey and casein) and AAs (i.e. EAAs, LEU, ARG and CIT), this review is specifically focused on these specific proteins and AAs.

Cancer

Cancer is often associated with a constellation of responses which together lead to cachexia, the syndrome of anorexia, muscle wasting and progressive depletion of adipose tissue. In addition to a loss of appetite, metabolic changes occur in cancer patients that may amplify the loss of muscle. These metabolic changes may result from inflammation, insulin resistance, hypogonadism, or other causes(Reference Tisdale55). To continue, the rate of muscle protein synthesis has been reported to be reduced in patients with established cancer cachexia(Reference Dillon, Volpi and Wolfe29, Reference Durham, Dillon and Sheffield-Moore56) and whole-body protein turnover was found to be elevated in cancer patients unrelated to the presence of weight loss(Reference Melville, McNurlan and Calder57). Previously, we and others showed that metabolic changes are also apparent in the plasma amino acid profile of patients with breast, colonic, pancreatic and lung cancer, even without weight loss being present, with strong indications for a disturbed ARG metabolism(Reference Melville, McNurlan and Calder57, Reference Vissers, Dejong and Luiking58). Besides, in skeletal muscle the catabolic machinery is already activated (enhanced ubiquitin mRNA levels and proteasome activity) prior to significant weight loss(Reference Bossola, Muscaritoli and Costelli59, Reference Bossola, Muscaritoli and Costelli60).

It has been suggested that the metabolic response to cancer (i.e. hepatic acute phase response) prevents the efficient use of food and in combination with a reduced intake, gains in lean mass are difficult to achieve. A recent study in cachectic patients with advanced ovarian cancer showed that patients responded less anabolically following receiving a balanced mixture of 40 g of dietary EAAs and non-EAAs compared to healthy controls. The data indicated that while these cancer patients were able to mount an acute anabolic response to a high amount of AAs during the absorptive period, anabolism was attenuated(Reference Dillon, Volpi and Wolfe29). We recently compared two different nutritional supplements and observed that muscle protein synthesis was stimulated by a high leucine/high protein supplement, but not by a conventional supplement(Reference Deutz, Safar and Schutzler61). Further human research in cancer is needed to confirm these findings and to examine whether only high dosages of dietary AAs are capable of stimulating anabolism. Although human studies examining the specific role of LEU in stimulating protein anabolism in cancer have, to our knowledge, not been described yet, animal studies show promising results. A study performed in mice bearing a cachexia-inducing tumour showed that muscle protein synthesis was increased and protein breakdown attenuated in response to a high amount of LEU (1 g kg− 1 d− 1)(Reference Eley, Russell and Tisdale62). In another study, using tumour-bearing cachectic mice(Reference Peters, van Helvoort and Kegler63), muscle-mass loss was counteracted dose-dependently by leucine supplementation (0 vs 1 vs 8 g of supplemented leucine per kg feed, for 21 d), however a change in markers of protein breakdown was not seen. Very limited research has been performed in cancer patients in relation to muscle protein stimulation by specific AAs and therefore, in our opinion, amelioration of muscle loss in these patients is still very difficult to target.

Chronic Obstructive Pulmonary Disease

In moderate to severe COPD basal protein turnover is enhanced, reflected by an increase in whole-body protein synthesis and whole-body protein breakdown (WbPB)(Reference Engelen, Deutz and Wouters64). Therefore, even though the net catabolic response resembles the response that is seen in healthy individuals, turnover rates are increased, indicating a higher metabolic demand in COPD, creating a drain on the body protein stores. Other important observations relating to interorgan metabolism in COPD are reduced levels of muscle glutamate (GLU) and plasma BCAAs(Reference Engelen and Schols65), mostly due to a fall in LEU(Reference Hofford, Milakofsky and Vogel66, Reference Engelen, Wouters and Deutz67).

Besides changes in basal protein turnover and amino acid levels, an altered inter-organ response to feeding is also seen in COPD. We observed that patients with moderate COPD have a higher anabolic response to a casein-based protein meal than healthy controls, caused by both a stimulation of whole-body protein synthesis and attenuation of WbPB(Reference Engelen, Rutten and De Castro9). The larger reduction in WbPB in COPD patients compared to healthy controls was explained by a lower SPE of phenylalanine by the gut, liver, or both during feeding, which could lead to a higher peripheral availability of dietary phenylalanine(Reference Engelen, Rutten and De Castro9). Furthermore, a recent study investigating the effects of soya feeding with or without added BCAAs in COPD and healthy controls(Reference Engelen, Rutten and De Castro10) showed that soya feeding with added BCAAs only improved whole-body protein synthesis in COPD (Fig. 7). In both groups, BCAA supplementation reduced splanchnic protein synthesis, suggesting that BCAA supplementation alters inter-organ metabolism in favour of the peripheral (i.e. muscle) compartment. When comparing whey, casein and soya protein with and without BCAAs, it is even more clear that net anabolism in COPD patients is likely associated with a reduced SPE of meal-derived AAs (Fig. 3).

Fig. 7 Values are means ± SE. Net increase in whole-body protein synthesis (WbPS) after intake of soya protein (open bar) or co-ingestion of branched-chain amino acids (BCAAs) and soya protein (striped bar) in COPD and healthy controls(10). Significance of difference between ingestion of soya protein and soya protein with co-ingestion of BCAAs in COPD group *P < 0·05.

In summary, it can be suggested that feeding of a protein supplement high in BCAAs and the addition of LEU might counterbalance the low plasma concentration of these AAs, optimally stimulate muscle protein synthesis and reduce SPE in COPD.

Cystic Fibrosis

In CF, disease-related factors including anorexia, inflammation, hypoxia, inactivity, and impaired glucose tolerance all contribute to the loss of skeletal muscle by altering the balance between protein synthesis and breakdown. Children with CF with acute exacerbations of their lung disease appear to have a strongly attenuated protein synthesis rate as compared to healthy children (about 50 % lower) and children with chronic but stable pulmonary disease (about 43 % lower)(Reference Holt, Ward and Francis68). In the latter group, a greater WbPB was found as compared to healthy children and CF patients suffering from an acute exacerbation.

Information about the anabolic effects of specific nutritional modulation on protein metabolism in diseased children is limited and therefore strategies to improve muscle gain via food intake are difficult to achieve. However, children with stable CF prove to be capable of improving protein metabolism in response to a high dose of protein (4 g kg− 1 d− 1), since whole-body protein synthesis was increased by 23 % with no concomitant effect on WbPB, resulting in a net anabolic response(Reference Geukers, Oudshoorn and Taminiau69). In a similar group of children without CF this high dose of protein significantly increased WbPB, indicating that feeding affects protein turnover differently in children with stable CF(Reference Kien, Zipf and Horswill70). Another study in stunted children with stable CF showed similar results and a dose-response effect on protein synthesis was observed when protein was provided at 1·5, 3 and 5 g protein kg− 1 d− 1, respectively, for 4 d. The protein synthesis rate was 30 % higher in the high-protein group compared to the low-protein group and resulted in a much greater net anabolic response(Reference Geukers, Oudshoorn and Taminiau69). The specific role of insulin in inhibiting protein loss in CF should also be a focus of attention. Due to a reduced production of insulin (as a result of pancreatic insufficiency)(Reference Kien, Horswill and Zipf71) and the diminished ability of insulin to suppress endogenous protein breakdown(Reference Hardin, LeBlanc and Lukenbaugh72, Reference Moran, Milla and Ducret73) new protein accretion might be hampered.

More extensive research in CF and also in other disease states of children is required to determine the specific nutritional requirements of these children and whether they respond more anabolically to specific amino acid mixtures, with a special role for the amino acid LEU as an anabolic stimulus and for its insulinotropic properties.

Acute disease

On the Intensive Care Unit, the net catabolic response of skeletal muscle is a key observation in patients with sepsis and burn injury, and is strongly associated with their severe inflammatory condition. Mostly by reference to animal studies, it has been shown that during high levels of inflammation, muscle protein synthesis is decreased(Reference Lang, Frost and Vary74, Reference Lang, Frost and Bronson75). We previously showed that reduced plasma levels of ARG and CIT are present in the acute phase of critical illness in children, related to an increased level of C-reactive protein(Reference van Waardenburg, de Betue and Luiking76). The reduced level of plasma ARG can be explained by an increased usage of ARG for nitric oxide production, increased arginase activity(Reference Argaman, Young and Noviski77), decreased renal de novo ARG synthesis from conversion of its precursor CIT(Reference Luiking, Engelen and Deutz78), or can be the result of an elevated protein synthesis in the liver (formation of acute phase reactants) or decreased dietary intake. We hypothesize that a decreased plasma concentration of CIT could be caused by a decreased GLN and GLU availability in the gut or a decreased gut function associated with the severe inflammatory milieu. A depletion of plasma ARG and CIT in critical illness may inhibit peripheral skeletal muscle protein synthesis because ARG is needed as a precursor for the formation of a complete protein.

Goals of nutritional support in acute disease are clear in terms of stimulating synthesis of proteins in the muscle, gut and liver. At the same time, it is essential that nutritional support has no adverse effects (e.g. further blood acidification and increase in plasma urea concentration). Endogenous non-EAAs are generally available in excess during sepsis because of accelerated release from muscle protein catabolism(Reference Bruins, Deutz and Soeters79) and increased de novo synthesis resulting from oxidation of dietary EAAs(Reference Bruins, Deutz and Soeters79). Therefore, we anticipate that, as shown in elderly populations, only dietary EAAs are necessary in acute critical illness to improve net protein synthesis and would be beneficial above complete amino acid mixtures by reducing the chance of adverse effects. The initiation of protein synthesis involves a series of steps involving eukaryotic initiation factors(Reference Rhoads, Niu and Odle80) and it has been shown that LEU, and more recently ARG can activate these factors(Reference Rhoads, Niu and Odle80, Reference Corl, Odle and Niu81). And although in sepsis a “leucine resistance” is described caused by an attenuated phosphorylation of initiation factors(Reference Lang, Frost and Vary74), both LEU and ARG could play a specific role in muscle protein synthesis beyond their role as a precursor for protein synthesis. In addition, CIT instead of ARG could be preferred as a dietary stimulus, since a greater stimulation of muscle protein synthesis was found with CIT(Reference Cynober, Moinard and De Bandt54).

In conclusion, more clinical research is needed examining the specific protein metabolic effects of dietary EAAs, CIT, ARG and LEU supplementation in acute critical illness.

Conclusions

A higher SPE of dietary AAs, caused by aging and inflammation, alters the amino acid availability for the skeletal muscle and along with the anabolic resistance to dietary protein, as observed in the elderly and in increased states of inflammation, negatively affecting protein anabolism. Muscle disuse, often a characteristic of acute and chronic disease appears to amplify the anabolic resistance to dietary protein, therefore further aggravating muscle loss. Dietary interventions with specific proteins, amino acid mixtures and EAAs appear to be mostly capable of stimulating (muscle) protein synthesis. The majority of research so far has been performed in healthy subjects (young and old). The available research in disease states shows a most promising role for the dietary EAAs LEU and ARG, with new perspectives on the role of CIT that need to be further explored. Moreover, it would be of scientific and clinical interest to investigate in more detail whether in certain disease states combinations of proteins and/or amino acids have the potential to induce even higher levels of anabolism. More research in disease states is crucial to establish specific dietary recommendations for various chronic and acute diseases.

Acknowledgements

The authors declare no conflict of interest.

The work described was supported in part by The National Heart, Lung and Blood Institute (award number R-01HL095903). The content is solely the responsibility of the authors and does not necessarily represent official views of the National Heart, Lung and Blood Institute or the National Institutes of Health.

All authors have made substantial contributions and have given approval to the conception, drafting, and final version of the manuscript.

References

1Wolfe, RR (2002) Regulation of muscle protein by amino acids. J Nutr 132, 3219S3224S.CrossRefGoogle ScholarPubMed
2Wolfe, RR & Miller, SL (1999) Amino acid availability controls muscle protein metabolism. Diabetes Nutr and Metab 12, 322328.Google ScholarPubMed
3Stoll, B & Burrin, DG (2006) Measuring splanchnic amino acid metabolism in vivo using stable isotopic tracers. J Anim Sci 84, Suppl, E60E72.CrossRefGoogle ScholarPubMed
4Tessari, P, Inchiostro, S, Barazzoni, R, et al. (1994) Fasting and postprandial phenylalanine and leucine kinetics in liver cirrhosis. Am J Physiol – Endocrinol Metab 267, E140E149.CrossRefGoogle ScholarPubMed
5Boirie, Y, Gachon, P & Beaufrere, B (1997) Splanchnic and whole-body leucine kinetics in young and elderly men. Am J Clin Nutr 65, 489495.CrossRefGoogle Scholar
6Matthews, DE, Harkin, R, Battezzati, A, et al. (1999) Splanchnic bed utilization of enteral [alpha]-ketoisocaproate in humans. Metabolism 48, 15551563.CrossRefGoogle ScholarPubMed
7Volpi, E, Mittendorfer, B, Wolf, SE, et al. (1999) Oral amino acids stimulate muscle protein anabolism in the elderly despite higher first-pass splanchnic extraction. Am J Physiol 277, E513E520.Google ScholarPubMed
8Luiking, YC, Deutz, NE, Jakel, M, et al. (2005) Casein and soy protein meals differentially affect whole-body and splanchnic protein metabolism in healthy humans. J Nutr 135, 10801087.CrossRefGoogle ScholarPubMed
9Engelen, MP, Rutten, EP, De Castro, CL, et al. (2005) Altered interorgan response to feeding in patients with chronic obstructive pulmonary disease. Am J Clin Nutr 82, 366372.CrossRefGoogle ScholarPubMed
10Engelen, MP, Rutten, EP, De Castro, CL, et al. (2007) Supplementation of soy protein with branched-chain amino acids alters protein metabolism in healthy elderly and even more in patients with chronic obstructive pulmonary disease. Am J Clin Nutr 85, 431439.CrossRefGoogle ScholarPubMed
11Gan, WQ, Man, SF, Senthilselvan, A, et al. (2004) Association between chronic obstructive pulmonary disease and systemic inflammation: a systematic review and a meta-analysis. Thorax 59, 574580.CrossRefGoogle ScholarPubMed
12Pinto-Plata, VM, Mullerova, H, Toso, JF, et al. (2006) C-reactive protein in patients with COPD, control smokers and non-smokers. Thorax 61, 2328.CrossRefGoogle ScholarPubMed
13Hashimoto, T, Yoneda, M, Shimada, T, et al. (2004) Intraportal nicotine infusion in rats decreases hepatic blood flow through endothelin-1 and both endothelin A and endothelin B receptors. Toxicol Appl Pharmacol 196, 110.CrossRefGoogle ScholarPubMed
14Volpi, E, Sheffield-Moore, M, Rasmussen, BB, et al. (2001) Basal muscle amino acid kinetics and protein synthesis in healthy young and older men. JAMA 286, 12061212.CrossRefGoogle Scholar
15Paddon-Jones, D, Sheffield-Moore, M, Zhang, XJ, et al. (2004) Amino acid ingestion improves muscle protein synthesis in the young and elderly. Am J Physiol Endocrinol Metab 286, E321E328.CrossRefGoogle Scholar
16Cuthbertson, D, Smith, K, Babraj, J, et al. (2005) Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB J 19, 422424.CrossRefGoogle ScholarPubMed
17Symons, TB, Schutzler, SE, Cocke, TL, et al. (2007) Aging does not impair the anabolic response to a protein-rich meal. Am J Clin Nutr 86, 451456.CrossRefGoogle Scholar
18Smith, GI, Atherton, P, Villareal, DT, et al. (2008) Differences in muscle protein synthesis and anabolic signaling in the postabsorptive state and in response to food in 65–80 year old men and women. PLoS One 3, e1875.CrossRefGoogle ScholarPubMed
19Koopman, R, Walrand, S, Beelen, M, et al. (2009) Dietary protein digestion and absorption rates and the subsequent postprandial muscle protein synthetic response do not differ between young and elderly men. J Nutr 139, 17071713.CrossRefGoogle ScholarPubMed
20Rennie, MJ, Selby, A, Atherton, P, et al. (2010) Facts, noise and wishful thinking: muscle protein turnover in aging and human disuse atrophy. Scand J Med Sci Sports 20, 59.CrossRefGoogle ScholarPubMed
21Paddon-Jones, D, Sheffield-Moore, M, Cree, MG, et al. (2006) Atrophy and impaired muscle protein synthesis during prolonged inactivity and stress. J Clin Endocrinol Metab 91, 48364841.CrossRefGoogle Scholar
22Glover, EI, Phillips, SM, Oates, BR, et al. (2008) Immobilization induces anabolic resistance in human myofibrillar protein synthesis with low and high dose amino acid infusion. J Physiol 586, 60496061.CrossRefGoogle ScholarPubMed
23Ferrando, AA, Paddon-Jones, D, Hays, NP, et al. (2010) EAA supplementation to increase nitrogen intake improves muscle function during bed rest in the elderly. Clin Nutr 29, 1823.CrossRefGoogle ScholarPubMed
24Kortebein, P, Ferrando, A, Lombeida, J, et al. (2007) Effect of 10 days of bed rest on skeletal muscle in healthy older adults. JAMA 297, 17721774.CrossRefGoogle ScholarPubMed
25Toth, MJ, Matthews, DE, Tracy, RP, et al. (2005) Age-related differences in skeletal muscle protein synthesis: relation to markers of immune activation. Am J Physiol Endocrinol Metab 288, E883E891.CrossRefGoogle ScholarPubMed
26Reeds, PJ, Fjeld, CR & Jahoor, F (1994) Do the differences between the amino acid compositions of acute-phase and muscle proteins have a bearing on nitrogen loss in traumatic states? J Nutr 124, 906910.CrossRefGoogle ScholarPubMed
27Biolo, G, Tipton, KD, Klein, S, et al. (1997) An abundant supply of amino acids enhances the metabolic effect of exercise on muscle protein. Am J Physiol 273, E122E129.Google ScholarPubMed
28Katsanos, CS, Kobayashi, H, Sheffield-Moore, M, et al. (2005) Aging is associated with diminished accretion of muscle proteins after the ingestion of a small bolus of essential amino acids. Am J Clin Nutr 82, 10651073.CrossRefGoogle ScholarPubMed
29Dillon, EL, Volpi, E, Wolfe, RR, et al. (2007) Amino acid metabolism and inflammatory burden in ovarian cancer patients undergoing intense oncological therapy. Clin Nutr 26, 736743.CrossRefGoogle ScholarPubMed
30Symons, TB, Sheffield-Moore, M, Wolfe, RR, et al. (2009) A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects. J Am Diet Assoc 109, 15821586.CrossRefGoogle Scholar
31Wolfe, RR, Miller, SL & Miller, KB (2008) Optimal protein intake in the elderly. Clin Nutr 27, 675684.CrossRefGoogle ScholarPubMed
32Luiking, YC, Engelen, MP, Soeters, PB, et al. (2010) Differential metabolic effects of casein and soy protein meals on skeletal muscle in healthy volunteers. Clin Nutr 30, 6572.CrossRefGoogle ScholarPubMed
33Tang, JE, Moore, DR, Kujbida, GW, et al. (2009) Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol 107, 987992.CrossRefGoogle ScholarPubMed
34Boirie, Y, Dangin, M, Gachon, P, et al. (1997) Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A 94, 1493014935.CrossRefGoogle ScholarPubMed
35Reitelseder, Sr, Agergaard, J, Doessing, S, et al. (2011) Whey and casein labeled with l-[1-13C]leucine and muscle protein synthesis: effect of resistance exercise and protein ingestion. Am J Physiol – Endocrinol Metab 300, E231E242.CrossRefGoogle Scholar
36Volpi, E, Ferrando, AA, Yeckel, CW, et al. (1998) Exogenous amino acids stimulate net muscle protein synthesis in the elderly. J Clin Invest 101, 20002007.CrossRefGoogle ScholarPubMed
37Volpi, E, Kobayashi, H, Sheffield-Moore, M, et al. (2003) Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults. Am J Clin Nutr 78, 250258.CrossRefGoogle ScholarPubMed
38Paddon-Jones, D, Sheffield-Moore, M, Katsanos, CS, et al. (2006) Differential stimulation of muscle protein synthesis in elderly humans following isocaloric ingestion of amino acids or whey protein. Exp Gerontol 41, 215219.CrossRefGoogle ScholarPubMed
39Kimball, SR & Jefferson, LS (2001) Regulation of protein synthesis by branched-chain amino acids. Curr Opin Clin Nutr Metab Care 4, 3943.CrossRefGoogle ScholarPubMed
40Rennie, MJ & Tipton, KD (2000) Protein and amino acid metabolism during and after exercise and the effects of nutrition. Annu Rev Nutr 20, 457483.CrossRefGoogle ScholarPubMed
41Newsholme, P, Brennan, L, Rubi, B, et al. (2005) New insights into amino acid metabolism, beta-cell function and diabetes. Clin Sci (Lond) 108, 185194.CrossRefGoogle ScholarPubMed
42Floyd, JC Jr, Fajans, SS, Conn, JW, et al. (1966) Stimulation of insulin secretion by amino acids. J Clin Invest 45, 14871502.CrossRefGoogle ScholarPubMed
43Katsanos, CS, Kobayashi, H, Sheffield-Moore, M, et al. (2006) A high proportion of leucine is required for optimal stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly. Am J Physiol Endocrinol Metab 291, E381E387.CrossRefGoogle ScholarPubMed
44Koopman, R, Verdijk, L, Manders, RJ, et al. (2006) Co-ingestion of protein and leucine stimulates muscle protein synthesis rates to the same extent in young and elderly lean men. Am J Clin Nutr 84, 623632.CrossRefGoogle Scholar
45Rieu, I, Balage, M, Sornet, C, et al. (2006) Leucine supplementation improves muscle protein synthesis in elderly men independently of hyperaminoacidaemia. J Physiol 575, 305315.CrossRefGoogle ScholarPubMed
46Tipton, KD, Elliott, TA, Ferrando, AA, et al. (2009) Stimulation of muscle anabolism by resistance exercise and ingestion of leucine plus protein. Appl Physiol Nutr Metab 34, 151161.CrossRefGoogle ScholarPubMed
47van de Poll, MC, Siroen, MP, van Leeuwen, PA, et al. (2007) Interorgan amino acid exchange in humans: consequences for arginine and citrulline metabolism. Am J Clin Nutr 85, 167172.CrossRefGoogle ScholarPubMed
48Bruins, MJ (2001) l-arginine treatment during acute and long-term endotoxemia in the pig - Effects on jejunal motility and interorgan protein, arginine and nitric oxide metabolism. PhD thesis, Maastricht University.Google Scholar
49Bruins, MJ, Soeters, PB, Lamers, WH, et al. (2002) L-arginine supplementation in pigs decreases liver protein turnover and increases hindquarter protein turnover both during and after endotoxemia. Am J Clin Nutr 75, 10311044.CrossRefGoogle ScholarPubMed
50Bruins, MJ, Soeters, PB, Lamers, WH, et al. (2002) L-Arginine supplementation in hyperdynamic endotoxemic pigs: Effect on nitric oxide synthesis by the different organs. Crit Care Med 30, 508517.CrossRefGoogle ScholarPubMed
51Bruins, MJ, Luiking, YC, Soeters, PB, et al. (2004) Effects of long-term intravenous and intragastric L-arginine intervention on jejunal motility and visceral nitric oxide production in the hyperdynamic compensated endotoxaemic pig. Neurogastroenterol Motil 16, 819828.CrossRefGoogle ScholarPubMed
52Yao, K, Yin, Y-L, Chu, W, et al. (2008) Dietary Arginine Supplementation Increases mTOR Signaling Activity in Skeletal Muscle of Neonatal Pigs. J Nutr 138, 867872.CrossRefGoogle ScholarPubMed
53Zhang, XJ, Chinkes, DL & Wolfe, RR (2008) The anabolic effect of arginine on proteins in skin wound and muscle is independent of nitric oxide production. Clin Nutr 27, 649656.CrossRefGoogle ScholarPubMed
54Cynober, L, Moinard, C & De Bandt, JP (2009) The Sir ESPEN David Cuthbertson. Citrulline: a new major signaling molecule or just another player in the pharmaconutrition game? Clin Nutr 29, 545551.CrossRefGoogle Scholar
55Tisdale, MJ (2009) Mechanisms of Cancer Cachexia. Physiol Rev 89, 381410.CrossRefGoogle ScholarPubMed
56Durham, WJ, Dillon, EL & Sheffield-Moore, M (2009) Inflammatory burden and amino acid metabolism in cancer cachexia. Curr Opin Clin Nutr Metab Care 12, 7277.CrossRefGoogle ScholarPubMed
57Melville, S, McNurlan, MA, Calder, AG, et al. (1990) Increased protein turnover despite normal energy metabolism and responses to feeding in patients with lung cancer. Cancer Res 50, 11251131.Google ScholarPubMed
58Vissers, YL, Dejong, CH, Luiking, YC, et al. (2005) Plasma arginine concentrations are reduced in cancer patients: evidence for arginine deficiency? Am J Clin Nutr 81, 11421146.CrossRefGoogle ScholarPubMed
59Bossola, M, Muscaritoli, M, Costelli, P, et al. (2001) Increased muscle ubiquitin mRNA levels in gastric cancer patients. Am J Physiol Regul Integr Comp Physiol 280, R1518R1523.CrossRefGoogle ScholarPubMed
60Bossola, M, Muscaritoli, M, Costelli, P, et al. (2003) Increased muscle proteasome activity correlates with disease severity in gastric cancer patients. Ann Surg 237, 384389.CrossRefGoogle ScholarPubMed
61Deutz, NE, Safar, A, Schutzler, S, et al. (2011) Muscle protein synthesis in cancer patients can be stimulated with an alternatively composed medical food. Clinical Nutr 30, 759768.CrossRefGoogle Scholar
62Eley, HL, Russell, ST & Tisdale, MJ (2007) Effect of branched-chain amino acids on muscle atrophy in cancer cachexia. Biochem J 407, 113120.CrossRefGoogle ScholarPubMed
63Peters, SJ, van Helvoort, A, Kegler, D, et al. (2011) Dose-dependent effects of leucine supplementation on preservation of muscle mass in cancer cachectic mice. Oncol Rep 26, 247254.Google ScholarPubMed
64Engelen, MP, Deutz, NE, Wouters, EF, et al. (2000) Enhanced levels of whole-body protein turnover in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 162, 14881492.CrossRefGoogle ScholarPubMed
65Engelen, MP & Schols, AM (2003) Altered amino acid metabolism in chronic obstructive pulmonary disease: new therapeutic perspective? Curr Opin Clin Nutr Metab Care 6, 7378.CrossRefGoogle ScholarPubMed
66Hofford, JM, Milakofsky, L, Vogel, WH, et al. (1990) The nutritional status in advanced emphysema associated with chronic bronchitis. A study of amino acid and catecholamine levels. Am Rev Respir Dis 141, 902908.CrossRefGoogle ScholarPubMed
67Engelen, MP, Wouters, EF, Deutz, NE, et al. (2000) Factors contributing to alterations in skeletal muscle and plasma amino acid profiles in patients with chronic obstructive pulmonary disease. Am J Clin Nutr 72, 14801487.CrossRefGoogle ScholarPubMed
68Holt, TL, Ward, LC, Francis, PJ, et al. (1985) Whole body protein turnover in malnourished cystic fibrosis patients and its relationship to pulmonary disease. Am J Clin Nutr 41, 10611066.CrossRefGoogle ScholarPubMed
69Geukers, VG, Oudshoorn, JH, Taminiau, JA, et al. (2005) Short-term protein intake and stimulation of protein synthesis in stunted children with cystic fibrosis. Am J Clin Nutr 81, 605610.CrossRefGoogle ScholarPubMed
70Kien, CL, Zipf, WB, Horswill, CA, et al. (1996) Effects of feeding on protein turnover in healthy children and in children with cystic fibrosis. Am J Clin Nutr 64, 608614.CrossRefGoogle ScholarPubMed
71Kien, CL, Horswill, CA, Zipf, WB, et al. (1995) Elevated Hepatic Glucose Production in Children with Cystic Fibrosis. Pediatr Res 37, 600605.CrossRefGoogle ScholarPubMed
72Hardin, DS, LeBlanc, A, Lukenbaugh, S, et al. (1998) Proteolysis associated with insulin resistance in cystic fibrosis. Pediatrics 101, 433437.CrossRefGoogle ScholarPubMed
73Moran, A, Milla, C, Ducret, R, et al. (2001) Protein metabolism in clinically stable adult cystic fibrosis patients with abnormal glucose tolerance. Diabetes 50, 13361343.CrossRefGoogle ScholarPubMed
74Lang, CH, Frost, RA & Vary, TC (2007) Regulation of muscle protein synthesis during sepsis and inflammation. Am J Physiol Endocrinol Metab 293, E453E459.CrossRefGoogle ScholarPubMed
75Lang, CH, Frost, RA, Bronson, SK, et al. (2010) Skeletal muscle protein balance in mTOR heterozygous mice in response to inflammation and leucine. Am J Physiol Endocrinol Metab 298, E1283E1294.CrossRefGoogle ScholarPubMed
76van Waardenburg, DA, de Betue, CT, Luiking, YC, et al. (2007) Plasma arginine and citrulline concentrations in critically ill children: strong relation with inflammation. Am J Clin Nutr 86, 14381444.CrossRefGoogle ScholarPubMed
77Argaman, Z, Young, VR, Noviski, N, et al. (2003) Arginine and nitric oxide metabolism in critically ill septic pediatric patients. Crit Care Med 31, 591597.CrossRefGoogle ScholarPubMed
78Luiking, YC, Engelen, MP & Deutz, NE (2010) Regulation of nitric oxide production in health and disease. Curr Opin Clin Nutr Metab Care 13, 97104.CrossRefGoogle ScholarPubMed
79Bruins, MJ, Deutz, NE & Soeters, PB (2003) Aspects of organ protein, amino acid and glucose metabolism in a porcine model of hypermetabolic sepsis. Clin Sci (Lond) 104, 127141.CrossRefGoogle Scholar
80Rhoads, JM, Niu, X, Odle, J, et al. (2006) Role of mTOR signaling in intestinal cell migration. Am J Physiol Gastrointest Liver Physiol 291, G510G517.CrossRefGoogle ScholarPubMed
81Corl, BA, Odle, J, Niu, X, et al. (2008) Arginine activates intestinal p70(S6k) and protein synthesis in piglet rotavirus enteritis. J Nutr 138, 2429.CrossRefGoogle ScholarPubMed
Figure 0

Fig. 1 Concept of splanchnic extraction of amino acids during feeding and availability to muscle for protein synthesis (PS).

Figure 1

Fig. 2 Values are means ± SE. Splanchnic extraction (SPE) of phenylalanine (PHE) or leucine (LEU) stable isotopes in young (open bar) and elderly (striped bar) individuals(48) and unpublished results from Engelen et al., 2011. Significance of difference between young and elderly individuals *P < 0·05.

Figure 2

Fig. 3 Values are means ± SE. Net anabolism in COPD patients (striped bar) as reflected by the net increase in whole-body protein synthesis (WbPS) is associated with a reduced splanchnic extraction (SPE) of meal-derived amino acids as compared to healthy controls (open bar)(9,10) and unpublished results from Engelen et al., 2011. Significance of difference between COPD patients and healthy controls *P < 0·05, **P < 0·01.

Figure 3

Fig. 4 Reduced splanchnic extraction during disease as an adaptive mechanism (refer Fig. 1) to make more amino acids available for muscle protein synthesis (PS) to compensate for the stimulated protein breakdown between meals.

Figure 4

Fig. 5 Values are means ± SE. Net whole-body protein synthesis (Net WbPS) 2 h after continuous intake of a whey protein+carbohydrate meal in young and elderly individuals (unpublished results from Engelen et al., 2011). The complete drink supplied 8·1 g protein and 21 g maltodextrin (based on a 75 kg subject) over 2 h. No statistically significant interaction was observed between group and protein.

Figure 5

Fig. 6 Values are means ±  SE. Mixed muscle fractional synthesis rate (FSR) 4 h after continues intake of dietary casein protein (CAPM) or soya protein (SOPM) in healthy young subjects(32). The complete drink supplied 0·2 g protein/kg BW/4 h (about 14 g/subject/4 h) and 42 g carbohydrates. No significant interaction was observed between group and protein.

Figure 6

Fig. 7 Values are means ± SE. Net increase in whole-body protein synthesis (WbPS) after intake of soya protein (open bar) or co-ingestion of branched-chain amino acids (BCAAs) and soya protein (striped bar) in COPD and healthy controls(10). Significance of difference between ingestion of soya protein and soya protein with co-ingestion of BCAAs in COPD group *P < 0·05.

You have Access
41
Cited by

Save article to Kindle

To save this article to your Kindle, first ensure coreplatform@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Role of specific dietary amino acids in clinical conditions
Available formats
×

Save article to Dropbox

To save this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Dropbox account. Find out more about saving content to Dropbox.

Role of specific dietary amino acids in clinical conditions
Available formats
×

Save article to Google Drive

To save this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Google Drive account. Find out more about saving content to Google Drive.

Role of specific dietary amino acids in clinical conditions
Available formats
×
×

Reply to: Submit a response

Please enter your response.

Your details

Please enter a valid email address.

Conflicting interests

Do you have any conflicting interests? *