Amino acid supplementation is anabolic during the acute phase of endotoxin-induced inflammation: A human randomized crossover trial

Acute effects of testosterone on whole body protein metabolism in hypogonadal and eugonadal conditions: a randomized, placebo-controlled, crossover study

Chronic testosterone (T) substitution and short-term T administration positively affect protein metabolism, however, data on acute effects in humans are sparse. This study aimed to investigate T's acute effects on whole body protein metabolism in hypogonadal and eugonadal conditions. We designed a randomized, double-blind, placebo-controlled, crossover study, including 12 healthy young males. Whole body protein metabolism was evaluated during 1) eugonadism, and after medically induced hypogonadism, with application of a gel on each trial day containing either 2) placebo, 3) T 50 mg, or 4) T 150 mg; under basal (5-h basal period) and insulin-stimulated conditions (3-h clamp). The main outcome measure was a change in net protein balance. The net protein loss was 62% larger in the placebo-treated hypogonadal state compared with the eugonadal state during the basal period (-5.5 ± 3.5 µmol/kg/h vs. -3.4 ± 1.2 µmol/kg/h, P = 0.038), but not during the clamp (P = 0.06). Also, hypogonadism resulted in a 25% increase in whole body urea flux (P = 0.006). However, T did not result in any significant changes in protein breakdown, synthesis, or net balance during either the basal period or clamp (all P > 0.05). Protein breakdown was reduced during clamp compared with the basal period regardless of gonadal status or T exposure (all P ≤ 0.001). In conclusion, the application of transdermal T did not counteract the negative effects of hypogonadism with no effects on protein metabolism within 5 h of administration. Insulin (during clamp) mitigated the effects of hypogonadism. This study is the first to investigate acute protein metabolic effects of T in hypogonadal men.NEW & NOTEWORTHY In a model of medically induced hypogonadism in male volunteers, we found increased whole body urea flux and net protein loss as an expected consequence of hypogonadism. Our study demonstrates the novel finding that the application of transdermal testosterone had no acute effects on whole body protein metabolism under eugonadal conditions, nor could it mitigate the hypogonadism-induced changes in protein metabolism. In contrast, insulin (during clamp) mitigated the effects of hypogonadism on protein metabolism.

Nutrient sensing: LEAP2 concentration in response to fasting, glucose, lactate, and β-hydroxybutyrate in healthy young males

BACKGROUND

The appetite-suppressing potential of liver-expressed antimicrobial peptide 2 (LEAP2), and its antagonistic effects on the hunger-inducing hormone ghrelin have attracted scientific interest. It is unclear how LEAP2 is influenced by fasting and how it responds to specific nutrients.

OBJECTIVES

The purpose of this investigation was to assess whether LEAP2 concentration 1) decreases after fasting, 2) increases postprandially, and 3) is regulated by nutrient sensing in the splanchnic bed.

METHODS

Plasma LEAP2 concentration was measured in blood samples from 5 clinical cross-over trials, following 1) 36 h of fasting (n = 8), 2) 10 h of fasting (n = 37, baseline data pooled from 4 of the clinical trials), 3) Oral and intravenous glucose administration (n = 11), 4) Oral and intravenous Na-lactate administration (n = 10), and 5) Oral and intravenous Na-β-hydroxybutyrate (BHB) administration (n = 8). All 5 trials included healthy males.

RESULTS

Compared with a 10-h fasting period, the median LEAP2 concentration was 38% lower following 36 h of fasting (P < 0.001). Oral administration of glucose elevated, whereas intravenous glucose administration lowered LEAP2 concentration (intervention x time, P = 0.001), resulting in a mean difference of 9 ng/mL (95% confidence interval [CI]: 1, 17) after 120 min. Oral lactate increased, and intravenous lactate decreased LEAP2 (intervention x time, P = 0.007), with a mean difference between interventions of 10 ng/mL (95% CI: 6, 15) after 120 min. In contrast, oral and intravenous administration of BHB reduced the LEAP2 concentration (main effect of time, P < 0.001).

CONCLUSIONS

Our investigations show that LEAP2 concentration was lower after a 36-h fast than an overnight fast and that oral delivery of glucose and lactate elevated LEAP2 concentration compared with intravenous administration, whereas LEAP2 concentrations decreased with both oral and intravenous BHB. This indicates that the LEAP2 concentration is sensitive to intestinal exposure to specific substrates, highlighting the need for future studies exploring the relationship between nutrients and LEAP2. This trial was registered at clinicaltrials.gov as NCT01840098, NCT03204877, NCT04299815, NCT03935841, and NCT01705782.

International Society of Sports Nutrition Position Stand: Effects of essential amino acid supplementation on exercise and performance

Position Statement: The International Society of Sports Nutrition (ISSN) presents this position based on a critical examination of literature surrounding the effects of essential amino acid (EAA) supplementation on skeletal muscle maintenance and performance. This position stand is intended to provide a scientific foundation to athletes, dietitians, trainers, and other practitioners as to the benefits of supplemental EAA in both healthy and resistant (aging/clinical) populations. EAAs are crucial components of protein intake in humans, as the body cannot synthesize them. The daily recommended intake (DRI) for protein was established to prevent deficiencies due to inadequate EAA consumption. The following conclusions represent the official position of the Society: 1. Initial studies on EAAs' effects on skeletal muscle highlight their primary role in stimulating muscle protein synthesis (MPS) and turnover. Protein turnover is critical for replacing degraded or damaged muscle proteins, laying the metabolic foundation for enhanced functional performance. Consequently, research has shifted to examine the effects of EAA supplementation - with and without the benefits of exercise - on skeletal muscle maintenance and performance. 2. Supplementation with free-form EAAs leads to a quick rise in peripheral EAA concentrations, which in turn stimulates MPS. 3. The safe upper limit of EAA intake (amount), without inborn metabolic disease, can easily accommodate additional supplementation. 4. At rest, stimulation of MPS occurs at relatively small dosages (1.5-3.0 g) and seems to plateau at around 15-18 g. 5. The MPS stimulation by EAAs does not require non-essential amino acids. 6. Free-form EAA ingestion stimulates MPS more than an equivalent amount of intact protein. 7. Repeated EAA-induced MPS stimulation throughout the day does not diminish the anabolic effect of meal intake. 8. Although direct comparisons of various formulas have yet to be investigated, aging requires a greater proportion of leucine to overcome the reduced muscle sensitivity known as "anabolic resistance." 9. Without exercise, EAA supplementation can enhance functional outcomes in anabolic-resistant populations. 10. EAA requirements rise in the face of caloric deficits. During caloric deficit, it's essential to meet whole-body EAA requirements to preserve anabolic sensitivity in skeletal muscle.

Effects of whey and soy protein supplementation on inflammatory cytokines in older adults: a systematic review and meta-analysis

BACKGROUND AND AIMS

Low-grade inflammation is a mediator of muscle proteostasis. This study aimed to investigate the effects of isolated whey and soy proteins on inflammatory markers.

METHODS

We conducted a systematic literature search of randomised controlled trials (RCT) through MEDLINE, Web of Science, Scopus and Cochrane Library databases from inception until September 2021. To determine the effectiveness of isolated proteins on circulating levels of C-reactive protein (CRP), IL-6 and TNF-α, a meta-analysis using a random-effects model was used to calculate the pooled effects (CRD42021252603).

RESULTS

Thirty-one RCT met the inclusion criteria and were included in the systematic review and meta-analysis. A significant reduction of circulating IL-6 levels following whey protein [Mean Difference (MD): -0·79, 95 % CI: -1·15, -0·42, I² = 96 %] and TNF-α levels following soy protein supplementation (MD: -0·16, 95 % CI: -0·26, -0·05, I² = 68 %) was observed. The addition of soy isoflavones exerted a further decline in circulating TNF-α levels (MD: -0·20, 95 % CI: -0·31, -0·08, I² = 34 %). According to subgroup analysis, whey protein led to a statistically significant decrease in circulating IL-6 levels in individuals with sarcopenia and pre-frailty (MD: -0·98, 95 % CI: -1·56, -0·39, I² = 0 %). These findings may be dependent on participant characteristics and treatment duration.

CONCLUSIONS

These data support that whey and soy protein supplementation elicit anti-inflammatory effects by reducing circulating IL-6 and TNF-α levels, respectively. This effect may be enhanced by soy isoflavones and may be more prominent in individuals with sarcopenia.

[Whey protein and caseinate supplementation in oncological patients undergoing elective surgery for the modification of functional capacity]

INTRODUCTION

the nutritional intervention has become a critical point to achieve the reduction of perioperative morbidity and mortality in cancer patients. There are different factors that will play a fundamental role in the evolution and prognosis of this pathology, being the state of nutrition and diet a cornerstone in these aspects.

OBJECTIVE

to evaluate the perioperative effect of whey protein isolate (WPI) and calcium caseinate (CaCNT) in cancer patients undergoing elective surgery.

METHODS

randomized controlled clinical trial with three groups: the control group (n = 15), consisting in conventional management by the oncology surgery services, and two intervention groups, one with calcium caseinate supplementation (n = 15) and another one with whey protein isolate supplementation (n = 15) for six weeks perioperatively. Handgrip strength, six-minute walk, and body composition were assessed pre and postoperatively.

RESULTS

those who were supplemented with WPI maintained their handgrip strength and showed less extracellular water (p < 0.02); also an increase in visceral mass was shown (p < 0.02). Finally, a correlation was found with variables associated with body composition and patient evolution when compared to the control group.

CONCLUSIONS

nutritional supplementation needs to be approached from the functional and metabolic point of view to identify factors that have a favorable impact, as well as the distinction between carcinoma and the type of supplementation to be implemented.

Investigating effects of sodium beta-hydroxybutyrate on metabolism in placebo-controlled, bilaterally infused human leg with focus on skeletal muscle protein dynamics

Systemic administration of beta-hydroxybutyrate (BHB) decreases whole-body protein oxidation and muscle protein breakdown in humans. We aimed to determine any direct effect of BHB on skeletal muscle protein turnover when administered locally in the femoral artery. Paired design with each subject being investigated on one single occasion with one leg being infused with BHB and the opposing leg acting as a control. We studied 10 healthy male volunteers once with bilateral femoral vein and artery catheters. One artery was perfused with saline (Placebo) and one with sodium-BHB. Labelled phenylalanine and palmitate were used to assess local leg fluxes. Femoral vein concentrations of BHB were significantly higher in the intervention leg (3.4 (3.2, 3.6) mM) compared with the placebo-controlled leg (1.9 (1.8, 2.1) mM) with a peak difference of 1.4 (1.1, 1.7) mM, p < 0.0005. Net loss of phenylalanine for BHB vs Placebo -6.7(-10.8, -2.7) nmol/min vs -8.7(-13.8, -3.7) nmol/min, p = 0.52. Palmitate flux and arterio-venous difference of glucose did not differ between legs. Under these experimental conditions, we failed to observe the direct effects of BHB on skeletal muscle protein turnover. This may relate to a combination of high concentrations of BHB (close to 2 mM) imposed systemically by spillover leading to high BHB concentrations in the saline-infused leg and a lack of major differences in concentration gradients between the two sides-implying that observations were made on the upper part of the dose-response curve for BHB and the relatively small number of subjects studied.

A New Serum Macrophage Checkpoint Biomarker for Innate Immunotherapy: Soluble Signal-Regulatory Protein Alpha (sSIRPα)

Background and Aims: The macrophage “don’t eat me” pathway CD47/SIRPα is a target for promising new immunotherapy. We hypothesized that a soluble variant of SIRPα is present in the blood and may function as a biomarker. Methods: Monocyte derived macrophages (MDMs) from human buffy-coats were stimulated into macrophage subtypes by LPS and IFN-γ (M1), IL-4 and IL-13 (M2a), IL-10 (M2c) and investigated using flow cytometry. Soluble SIRPα (sSIRPα) was measured in cell cultures and serum by Western blotting and an optimized ELISA. Serum samples were obtained from 120 healthy individuals and from 8 individuals challenged by an LPS injection. Results: All macrophage phenotypes expressed SIRPα by flowcytometry, and sSIRPα was present in all culture supernatants including unstimulated cells. M1 macrophages expressed the lowest level of SIRPαand released the highest level of sSIRPα (p < 0.05). In vivo, the serum level of sSIRPα increased significantly (p < 0.0001) after an LPS challenge in humans. The median concentration in healthy individuals was 28.7 µg/L (19.8−41.1, 95% reference interval), and 20.5 µg/L in an IFCC certified serum reference material. The protein was stable in serum for prolonged storage and repeated freeze/thawing. Conclusions: We demonstrate that sSIRPα is produced constitutively and the concentration increases upon macrophage activation both in vitro and in vivo. It is present in human serum where it may function as a biomarker for the activity of tumor-associated macrophages (TAMs), and for monitoring the effect of immunotherapy.

LPS induces rapid increase in GDF15 levels in mice, rats, and humans but is not required for anorexia in mice

Growth differentiation factor 15 (GDF15), a TGFβ superfamily cytokine, acts through its receptor, cell line-derived neurotrophic factorfamily receptor α-like (GFRAL), to suppress food intake and promote nausea. GDF15 is broadly expressed at low levels but increases in states of disease such as cancer, cachexia, and sepsis. Whether GDF15 is necessary for inducing sepsis-associated anorexia and body weight loss is currently unclear. To test this we used a model of moderate systemic infection in GDF15KO and GFRALKO mice with lipopolysaccharide (LPS) treatment to define the role of GDF15 signaling in infection-mediated physiologic responses. Since physiological responses to LPS depend on housing temperature, we tested the effects of subthermoneutral and thermoneutral conditions on eliciting anorexia and inducing GDF15. Our data demonstrate a conserved LPS-mediated increase in circulating GDF15 levels in mouse, rat, and human. However, we did not detect differences in LPS-induced anorexia between WT and GDF15KO or GFRALKO mice. Furthermore, there were no differences in anorexia or circulating GDF15 levels at either thermoneutral or subthermoneutral housing conditions in LPS-treated mice. These data demonstrate that GDF15 is not necessary to drive food intake suppression in response to moderate doses of LPS.NEW & NOTEWORTHY Although many responses to LPS depend on housing temperature, the anorexic response to LPS does not. LPS results in a potent and rapid increase in circulating levels of GDF15 in mice, rats, and humans. Nevertheless, GDF15 and its receptor (GFRAL) are not required for the anorexic response to systemic LPS administration. The anorexic response to LPS likely involves a myriad of complex physiological alterations.

Anabolic effects of oral leucine-rich protein with and without β-hydroxybutyrate on muscle protein metabolism in a novel clinical model of systemic inflammation-a randomized crossover trial

BACKGROUND

β-lactoglobulin (BLG) stimulates muscle protein synthesis and β-hydroxybutyrate (BHB) inhibits muscle breakdown. Whether combining the 2 can additively attenuate disease-induced muscle loss is unknown.

OBJECTIVE

Based on previous observations of anticatabolic effects of protein and ketone bodies during inflammation, and using a novel model combining ongoing systemic inflammation, fasting, and immobilization, we tested whether the anticatabolic muscle response to oral amino acids is altered compared with control conditions, as well as whether coadministration of oral BHB and BLG further improves the muscle anabolic response. Muscle net balance (NBphe) was the primary outcome and intramyocellular signals were assessed.

METHODS

In a randomized crossover design, 8 young men underwent either preconditioning with LPS (prestudy day: 1 ng/kg, study day: 0.5 ng/kg) combined with a 36-h fast and bed rest to mimic catabolic inflammatory disease (CAT) or an overnight fast (control [CTR]) prior to isocaloric nutritional interventions on 3 occasions separated by ∼6 wk (range 42 to 83 d).

RESULTS

NBphe increased similarly upon all conditions (interaction P = 0.65). From comparable baseline rates, both Rdphe [muscle synthesis, median ratio (95% CI): 0.44 (0.23, 0.86) P = 0.017] and Raphe [muscle breakdown, median ratio (95% CI): 0.46 (0.27, 0.78) P = 0.005] decreased following BHB + BLG compared with BLG. BLG increased Rdphe more under CAT conditions compared with CTR (interaction P = 0.02). CAT increased inflammation, energy expenditure, and lipid oxidation and decreased Rdphe and anabolic signaling [mammalian target of rapamycin (mTOR) and eukaryotic translation initiation factor 4E-binding protein 1 (4EPB1) phosphorylation].

CONCLUSION

In contrast to our initial hypothesis, NBphe increased similarly following BLG during CAT and CTR conditions; CAT however, specifically stimulated the BLG-mediated increase in protein synthesis, whereas BHB coadministration did not affect NBphe, but distinctly dampened the BLG-induced increase in muscle amino acid fluxes thereby liberating circulating amino acids for anabolic actions elsewhere.

IGF-1 and IGFBP-3 in Inflammatory Cachexia

Inflammation induces a wide response of the neuroendocrine system, which leads to modifications in all the endocrine axes. The hypothalamic–growth hormone (GH)–insulin-like growth factor-1 (IGF-1) axis is deeply affected by inflammation, its response being characterized by GH resistance and a decrease in circulating levels of IGF-1. The endocrine and metabolic responses to inflammation allow the organism to survive. However, in chronic inflammatory conditions, the inhibition of the hypothalamic–GH–IGF-1 axis contributes to the catabolic process, with skeletal muscle atrophy and cachexia. Here, we review the changes in pituitary GH secretion, IGF-1, and IGF-1 binding protein-3 (IGFBP-3), as well as the mechanism that mediated those responses. The contribution of GH and IGF-1 to muscle wasting during inflammation has also been analyzed.

Mini-review: Glucagon responses in type 1 diabetes - a matter of complexity

In recent years the role of altered alpha cell function and glucagon secretion in type 1 diabetes has attracted scientific attention. It is well established that glucagon responses to hypoglycemia are absent in type 1 diabetes, but more uncertain whether it is intact following other physiological and metabolic stimuli compared with nondiabetic individuals. The aim of this review is to (i) summarize current knowledge on glucagon responses during hypoglycemia in normal physiology and type 1 diabetes, and (ii) review human in vivo studies investigating glucagon responses after other stimuli in individuals with type 1 diabetes and nondiabetic individuals. Available data suggest that in type 1 diabetes the absence of glucagon secretion after hypoglycemia is irreversible. This is a scenario specific to hypoglycemia, since other stimuli, including administration of amino acids, insulin withdrawal, lipopolysaccharide exposure and exercise lead to substantial glucagon responses though attenuated compared to nondiabetic individuals in head-to-head studies. The derailed glucagon secretion is not confined to hypoglycemia as individuals with type 1 diabetes, as opposed to nondiabetic individuals display glucagon hypersecretion after meals, thereby potentially contributing to insulin resistance. The complexity of these phenomena may relate to activation of distinct regulatory pathways controlling glucagon secretion i.e., intra-islet paracrine signaling, direct and autonomic nervous signaling.

β-Lactoglobulin Is Insulinotropic Compared with Casein and Whey Protein Ingestion during Catabolic Conditions in Men in a Double-Blinded Randomized Crossover Trial

BACKGROUND

Muscle loss during acute infectious disease is mainly triggered by inflammation, immobilization, and malnutrition.

OBJECTIVE

The objective was to compare muscle protein kinetics and metabolism following ingestion of the dairy protein supplements β-lactoglobulin (BLG), casein (CAS), and whey (WHE) during controlled catabolic conditions.

METHODS

We used a randomized crossover design (registered at clinicaltrials.gov as NCT03319550) to investigate 9 healthy male participants [age: 20-40 y; BMI (in kg/m2) 20-30] who were randomly assigned servings of BLG, CAS, or WHE (0.6 g protein/kg, one-third as bolus and two-thirds as sip every 20 min) on 3 separate occasions separated by ∼6-8 wk. The participants received an infusion of lipopolysaccharide (1 ng/kg) combined with 36 h of fasting and bed rest before each study day, mimicking a clinical catabolic condition. The forearm model and isotopic tracer techniques were used to quantify muscle protein kinetics. Muscle biopsy specimens were obtained and intramyocellular signaling investigated using Western blot.

RESULTS

BLG, CAS, and WHE improved the net balance of phenylalanine (NBphe) from baseline with ∼75% (P < 0.001) with no difference between interventions (primary outcome, P < 0.05). No difference in rates of appearance and disappearance of phenylalanine or in intramyocellular signaling activation was found between interventions (secondary outcomes). The incremental AUC for serum insulin was 62% higher following BLG compared with CAS (P < 0.001) and 30% higher compared with WHE (P = 0.002), as well as 25% higher in WHE compared with CAS (P = 0.006). Following BLG consumption, plasma concentrations of glucose-dependent insulinotropic peptide (GIP) increased 70% compared with CAS (P = 0.001) and increased 34% compared with WHE (P = 0.06). No significant difference was found between WHE and CAS (P = 0.12).

CONCLUSION

BLG, WHE, and CAS have similar effects on muscle in young male participants during catabolic conditions. BLG showed specific, possibly GIP-dependent, insulinotropic properties, which may have future clinical implications.

Pre- and Post-Surgical Nutrition for Preservation of Muscle Mass, Strength, and Functionality Following Orthopedic Surgery

Nutritional status is a strong predictor of postoperative outcomes and is recognized as an important component of surgical recovery programs. Adequate nutritional consumption is essential for addressing the surgical stress response and mitigating the loss of muscle mass, strength, and functionality. Especially in older patients, inadequate protein can lead to significant muscle atrophy, leading to a loss of independence and increased mortality risk. Current nutritional recommendations for surgery primarily focus on screening and prevention of malnutrition, pre-surgical fasting protocols, and combating post-surgical insulin resistance, while recommendations regarding macronutrient composition and timing around surgery are less established. The goal of this review is to highlight oral nutrition strategies that can be implemented leading up to and following major surgery to minimize atrophy and the resultant loss of functionality. The role of carbohydrate and especially protein/essential amino acids in combating the surgical stress cascade and supporting recovery are discussed. Practical considerations for nutrient timing to maximize oral nutritional intake, especially during the immediate pre- and post- surgical periods, are also be discussed.

A model mimicking catabolic inflammatory disease; a controlled randomized study in humans

Objective

Inflammatory disease is catabolic and associated with insulin resistance, increased energy expenditure, lipolysis and muscle protein loss. The main contributors to these metabolic adaptations are inflammation, malnutrition and immobilisation. Controlled experimental models incorporating these central elements of hospitalisation are lacking. The aim of this study was to validate such a human experimental model.

Methods

In a randomized crossover design, six healthy young men underwent; (i) overnight fast (CTR), or (ii) exposure to systemic lipopolysaccharide (1 ng/kg) combined with 36-hour fast and bed rest (CAT). The difference in insulin sensitivity between CAT and CTR was the main outcome, determined by a hyperinsulinemic euglycemic glucose clamp. Palmitate, glucose, urea, phenylalanine and tyrosine tracers were infused to estimate metabolic shifts during interventions. Indirect calorimetry was used to estimate energy expenditure and substrate oxidation.

Results

Insulin sensitivity was 41% lower in CAT than in CTR (M-value, mg/kg/min): 4.3 ± 0.2 vs 7.3 ± 1.3, p<0.05. The median (min max) palmitate flux (μmol/min) was higher during CAT than in CTR (257.0 (161.7 365.4) vs 131.6 (92.3 189.4), p = 0.004), and protein kinetics did not differ between interventions. C-reactive peptide (mg/L) was elevated in CAT compared with CTR (30.57 ± 4.08 vs 1.03 ± 0.19, p<0.001). Energy expenditure increased by 6% during CAT compared with CTR (1869 ± 94 vs 1756 ± 58, p = 0.04), CAT having higher lipid oxidation rates (p = 0.01) and lower glucose oxidation rates (p = 0.03). Lipopolysaccharide caused varying abdominal discomfort 2 hours post-injection, which had disappeared the following day.

Conclusion

We found that combined systemic inflammation, fasting and bed rest induced marked insulin resistance and increased energy expenditure and lipolysis, rendering this controlled experimental model suitable for anti-catabolic intervention studies, mimicking clinical conditions.

Effects of protein intake prior to carbohydrate-restricted endurance exercise: a randomized crossover trial

Background

Deliberately training with reduced carbohydrate availability, a paradigm coined training low, has shown to promote adaptations associated with improved aerobic capacity. In this context researchers have proposed that protein may be ingested prior to training as a means to enhance the protein balance during exercise without spoiling the effect of the low carbohydrate availability. Accordingly, this is being practiced by world class athletes. However, the effect of protein intake on muscle protein metabolism during training low has not been studied.

This study aimed to examine if protein intake prior to exercise with reduced carbohydrate stores benefits muscle protein metabolism in exercising and non-exercising muscles.

Methods

Nine well-trained subjects completed two trials in random order both of which included a high-intensity interval ergometer bike ride (day 1), a morning (day 2) steady state ride (90 min at 65% VO₂peak, 90ss), and a 4-h recovery period. An experimental beverage was consumed before 90ss and contained either 0.5 g whey protein hydrolysate [WPH]/ kg lean body mass or flavored water [PLA]. A stable isotope infusion (L-[ring-¹³C₆]-phenylalanine) combined with arterial-venous blood sampling, and plasma flow rate measurements were used to determine forearm protein turnover. Myofibrillar protein synthesis was determined from stable isotope incorporation into the vastus lateralis.

Results

Forearm protein net balance was not different from zero during 90ss exercise (nmol/100 ml/min, PLA: 0.5 ± 2.6; WPH: 1.8, ± 3.3) but negative during the 4 h recovery (nmol/100 ml/min, PLA: − 9.7 ± 4.6; WPH: − 8.7 ± 6.5); no interaction (P = 0.5) or main effect of beverage (P = 0.11) was observed. Vastus lateralis myofibrillar protein synthesis rates were increased during 90ss exercise (+ 0.02 ± 0.02%/h) and recovery (+ 0.02 ± 0.02%/h); no interaction (P = 0.3) or main effect of beverage (P = 0.3) was observed.

Conclusion

We conclude that protein ingestion prior to endurance exercise in the energy- and carbohydrate-restricted state does not increase myofibrillar protein synthesis or improve net protein balance in the exercising and non-exercising muscles, respectively, during and in the hours after exercise compared to ingestion of a non-caloric control.

Trial registration

clinicaltrials.gov, NCT01320449. Registered 10 May 2017 – Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03147001

Effect of citrulline on muscle protein turnover in an in vitro model of muscle catabolism

OBJECTIVE

Muscle net catabolism, as seen after severe trauma or sepsis or in postoperative situations, is mediated by hormones (e.g., cortisol) and proinflammatory cytokines (e.g., tumor necrosis factor alpha [TNF-α]). Specific amino acids may be able to limit this muscle mass loss. Citrulline (CIT) stimulates muscle protein synthesis in various situations, but little data exist on hypercatabolic situations and the effects on protein breakdown are unknown. Our aim was to assess the effect of CIT on protein turnover in an in vitro model of muscle hypercatabolism.

METHODS

Myotubes derived from C2C12 myoblasts were treated with 150 nM dexamethasone (DEX), 10 ng/mL TNF-α, or 0.006% ethanol (as control [CON]) for 24 h. Subsequently, myotubes were incubated with or without 5 mM CIT for 6 h. Muscle protein synthesis rate was evaluated by the surface sensing of translation method and by l-[3,5-³H]tyrosine (Tyr) incorporation. The muscle protein breakdown rate was evaluated from Tyr release into culture medium. CIT action was analyzed by non-parametric Kruskal-Wallis and Mann-Whitney tests.

RESULTS

CIT treatment significantly increased protein synthesis rates compared with the DEX or TNF-α group (surface sensing of translation method; DEX + CIT versus DEX; P = 0.03 and TNF-α+CIT versus TNF-α; P = 0.05) and significantly decreased protein breakdown rate in the CON and DEX groups (CON + CIT versus CON; P = 0.05 and DEX + CIT versus DEX; P = 0.05).

CONCLUSIONS

CIT treatment regulated muscle protein turnover in an in vitro model of muscle net catabolism. Exploring the underlying mechanisms would also be of interest.

New advances in stable tracer methods to assess whole-body protein and amino acid metabolism

PURPOSE OF REVIEW

Stable isotope methods have been used for many years to assess whole-body protein and amino acid kinetics in healthy conditions and in response to aging, exercise and (clinically stable) disease states.

RECENT FINDINGS

In recent years, tracer research expanded to the anabolic response to feeding in critical illness and its use during acute metabolic stressors. Furthermore, new isotope approaches and tracer insights have been obtained. In the postabsorptive state, the novel tracer pulse approach has several advantages above the established continuous tracer approach because of the metabolic information that can be obtained, easy applicability, and low tracer costs. The use of bolus versus sip-feeding approaches to assess the anabolic response to a meal is dependent on the research question and its feasibility. Promising new tracer approaches have been developed to measure the anabolic capacity, and protein digestibility and absorption. Advances have been made in the field of mass spectrometry in low enrichment analysis.

SUMMARY

Novel tracer approaches are available that can more readily be used in critical illness and during acute metabolic stressors. Besides the use of tracer application in various clinical conditions, more research is needed on how to incorporate isotopes on an individual level.

Susceptibility-Related Factor and Biomarkers of Dietary Supplement Polygonum multiflorum-Induced Liver Injury in Rats

Polygonum multiflorum [PM, synonym Reynoutria multiflora (Thunb.) Moldenke.], a well-known and commonly used Traditional Chinese Medicine and herbal dietary supplement for nourishing the kidney and liver, etc., has aroused wide concern for its reported potential hepatotoxicity. Previous clinical cases and experimental studies have suggested that mild immune stress (MIS) may be one of the susceptibility-related factors of idiosyncratic drug-induced liver injury (IDILI) caused by PM. In this paper, we found that the same dose of PM caused abnormal liver biochemical indicators and liver tissue damage in MIS model rats, while it did not result in liver injury in normal rats, further confirming that MIS is a susceptibility factor for PM-IDILI. Plasma chemokine/cytokine profiling indicated that the MIS model group was significantly different from the other groups, showing a significant upregulation of plasma chemokines, while the MIS/PM group showed upregulated expression of chemokines or pro-inflammatory cytokines. Liver histopathological examination indicated a small amount of inflammatory cytokine infiltration in the MIS group, but no hepatocyte injury, consistent with the plasma profiles of increased chemokines and unchanged inflammatory cytokines. Notably, metabolomics characterization showed that MIS caused reprogramming of these metabolic pathways (such as phenylalanine and glutamate pathways), which was associated with acute phase reactions and inflammatory responses. These results suggested that MIS may promote an immune response to the initial cellular injury induced by PM in the liver, and MIS-induced upregulation of chemokines and metabolic reprogramming may an important mechanism that mediates the susceptibility to PM-IDILI. Furthermore, via receiver operating characteristic (ROC) curves analysis, we identified 12 plasma cytokines (e.g., IP-10, MCP-1 and MIP-1α) and nine metabolomics biomarkers (e.g., L-Phenylalanine, Creatinine, and L-glutamine) with differential capabilities (all ROC AUC > 0.9) of identifying susceptibility model animals from normal ones, which might be of referable value for the clinical recognition of PM-IDILI susceptible individuals.

Citrulline and muscle protein homeostasis in three different models of hypercatabolism

Supplementation of enteral nutrition (EN) by specific amino acids (AAs) has been proposed to prevent muscle protein loss in intensive care unit (ICU) patients. Citrulline (Cit), which has been shown to stimulate muscle protein synthesis in other situations, may be of interest in this setting. Our aim was to assess the effect of Cit in three catabolic models relevant to critical illness: endotoxemia (LPS), traumatic brain injury (TBI), and TBI with infectious complications (TBI-Ec), which are characterized by different alterations in protein homeostasis. Fifty-eight male Sprague-Dawley rats (200-220 g) were randomized to receive a standard diet ad libitum (CON, n = 9) or to undergo catabolic injuries on day 0 (D0, n = 49), and EN (Sondalis HP energy® 290 kcal/kg/d) from day 1 (D1) combined with Cit (2 g/kg/d) or isonitrogenous non-essential AAs (NEAAs) until day 3 (D3). Endotoxemia was induced by IP injection of LPS from E. coli (3 mg/kg), TBI by hydraulic percussion, and infectious complications (TBI-Ec) by administration of luminescent E. coli on D1. Nitrogen balance (ΔN) and 3-methylhistidine (3-MHis) were measured daily. Muscle protein synthesis (MPS, measured by the SUnSET method) and mTORC1 activation (S6K-1 and 4E-BP1 phosphorylation) were measured on D3 2 h after the arrest of enteral nutrition in soleus, extensor digitorum longus (EDL), gastrocnemius and tibialis muscles. ΔN was lower (p < 0.001) in all three models of injury compared with basal and CON from D1 to D3, and more negative in the LPS-CIT (p < 0.05) than in the LPS group. The 3-MHis/creatinine ratio was significantly increased on D1 in all groups compared with CON, and on D2 only in the LPS and TBI groups (p < 0.0001, LPS and TBI vs. CON). MPS was similar in all groups in soleus and tibialis but significantly higher in EDL in LPS-CIT [LPS-CIT: 4.5 ± 1.7 (mean ± SD) vs. CON: 2.3 ± 1.2; and vs. LPS-NEAA: 3.1 ± 2.3] and in gastrocnemius (LPS-CIT vs. CON; p = 0.05). S6K-1 phosphorylation in the EDL was also higher in LPS-CIT vs. CON (LPS-CIT: 0.94 ± 0.51 CON: 0.42 ± 0.28), but not in gastrocnemius. IL-6 plasma level was significantly higher in all the catabolic groups vs. CON (p < 0.005) with no difference between treatments (Cit or NEAAs). In conclusion, the TBI model showed only a rise in muscle proteolysis, whereas the LPS model displayed a rise in both protein synthesis and proteolysis. Secondly, our results show that the Cit effect varies according to the type of injury and to the muscle under study. The stimulation of MPS rate and the mTOR pathway in LPS-treated rats contrasts with degraded ΔN, suggesting that the Cit effect on protein metabolism in critically ill rats is limited at the whole-body level.

Effects of 3-hydroxybutyrate and free fatty acids on muscle protein kinetics and signaling during LPS-induced inflammation in humans: anticatabolic impact of ketone bodies

Background

Acute inflammation, and subsequent release of bacterial products (e.g. LPS), inflammatory cytokines, and stress hormones, is catabolic, and the loss of lean body mass predicts morbidity and mortality. Lipid intermediates may reduce protein loss, but the roles of free fatty acids (FFAs) and ketone bodies during acute inflammation are unclear.

Objective

We aimed to test whether infusions of 3-hydroxybutyrate (3OHB), FFAs, and saline reduce protein catabolism during exposure to LPS and Acipimox (to restrict and control endogenous lipolysis).

Design

A total of 10 healthy male subjects were randomly tested 3 times, with: 1) LPS, Acipimox (Olbetam) and saline, 2) LPS, Acipimox, and nonesterified fatty acids (Intralipid), and 3) LPS, Acipimox, and 3OHB, during a 5-h basal period and a 2-h hyperinsulinemic, euglycemic clamp. Labeled phenylalanine, tyrosine, and urea tracers were used to estimate protein kinetics, and muscle biopsies were taken for Western blot analysis of protein metabolic signaling.

Results

3OHB infusion increased 3OHB concentrations (P < 0.0005) to 3.5 mM and decreased whole-body phenylalanine-to-tyrosine degradation. Basal and insulin-stimulated net forearm phenylalanine release decreased by >70% (P < 0.005), with both appearance and phenylalanine disappearance being profoundly decreased. Phosphorylation of eukaryotic initiation factor 2α at Ser51 was increased in skeletal muscle, and S6 kinase phosphorylation at Ser235/236 tended (P = 0.074) to be decreased with 3OHB infusion (suggesting inhibition of protein synthesis), whereas no detectable effects were seen on markers of protein breakdown. Lipid infusion did not affect phenylalanine kinetics, and insulin sensitivity was unaffected by interventions.

Conclusion

During acute inflammation, 3OHB has potent anticatabolic actions in muscle and at the whole-body level; in muscle, reduction of protein breakdown overrides inhibition of synthesis. This trial was registered at clinicaltrials.gov as NCT01752348.

The impact of immobilisation and inflammation on the regulation of muscle mass and insulin resistance: different routes to similar end-points

Loss of muscle mass and insulin sensitivity are common phenotypic traits of immobilisation and increased inflammatory burden. The suppression of muscle protein synthesis is the primary driver of muscle mass loss in human immobilisation, and includes blunting of post‐prandial increases in muscle protein synthesis. However, the mechanistic drivers of this suppression are unresolved. Immobilisation also induces limb insulin resistance in humans, which appears to be attributable to the reduction in muscle contraction per se. Again mechanistic insight is missing such that we do not know how muscle senses its “inactivity status” or whether the proposed drivers of muscle insulin resistance are simply arising as a consequence of immobilisation. A heightened inflammatory state is associated with major and rapid changes in muscle protein turnover and mass, and dampened insulin‐stimulated glucose disposal and oxidation in both rodents and humans. A limited amount of research has attempted to elucidate molecular regulators of muscle mass loss and insulin resistance during increased inflammatory burden, but rarely concurrently. Nevertheless, there is evidence that Akt (protein kinase B) signalling and FOXO transcription factors form part of a common signalling pathway in this scenario, such that molecular cross‐talk between atrophy and insulin signalling during heightened inflammation is believed to be possible. To conclude, whilst muscle mass loss and insulin resistance are common end‐points of immobilisation and increased inflammatory burden, a lack of understanding of the mechanisms responsible for these traits exists such that a substantial gap in understanding of the pathophysiology in humans endures.

Alkalinization with potassium bicarbonate improves glutathione status and protein kinetics in young volunteers during 21-day bed rest

BACKGROUND & AIMS

Physical inactivity is associated with lean body mass wasting, oxidative stress and pro-inflammatory changes of cell membrane lipids. Alkalinization may potentially counteract these alterations. We evaluated the effects of potassium bicarbonate supplementation on protein kinetics, glutathione status and pro- and anti-inflammatory polyunsaturated fatty acids (PUFA) in erythrocyte membranes in humans, during experimental bed rest.

METHODS

Healthy, young, male volunteers were investigated at the end of two 21-day bed rest periods, one with, and the other without, daily potassium bicarbonate supplementation (90 mmol × d^-1), according to a cross-over design. Oxidative stress in erythrocytes was evaluated by determining the ratio between reduced (GSH) and oxidized glutathione (GSSG). Glutathione turnover and phenylalanine kinetics, a marker of whole body protein metabolism, were determined by stable isotope infusions. Erythrocyte membranes PUFA composition was analyzed by gas-chromatography.

RESULTS

At the end of the two study periods, urinary pH was 10 ± 3% greater in subjects receiving potassium bicarbonate supplementation (7.23 ± 0.15 vs. 6.68 ± 0.11, p < 0.001). Alkalinization increased total glutathione concentrations by 5 ± 2% (p < 0.05) and decreased its rate of clearance by 38 ± 13% (p < 0.05), without significantly changing GSH-to-GSSG ratio. After alkalinization, net protein balance in the postabsorptive state improved significantly by 17 ± 5% (p < 0.05) as well as the sum of n-3 PUFA and the n-3-to-n-6 PUFA ratio in erythrocyte membranes (p < 0.05).

CONCLUSIONS

Alkalinization during long-term inactivity is associated with improved glutathione status, anti-inflammatory lipid pattern in cell membranes and reduction in protein catabolism at whole body level. This study suggests that, in clinical conditions characterized by inactivity, oxidative stress and inflammation, alkalinization could be a useful adjuvant therapeutic strategy.

Barriers to cancer nutrition therapy: excess catabolism of muscle and adipose tissues induced by tumour products and chemotherapy

Cancer-associated malnutrition is driven by reduced dietary intake and by underlying metabolic changes (such as inflammation, anabolic resistance, proteolysis, lipolysis and futile cycling) induced by the tumour and activated immune cells. Cytotoxic and targeted chemotherapies also elicit proteolysis and lipolysis at the tissue level. In this review, we summarise specific mediators and chemotherapy effects that provoke excess proteolysis in muscle and excess lipolysis in adipose tissue. A nutritionally relevant question is whether and to what degree these catabolic changes can be reversed by nutritional therapy. In skeletal muscle, tumour factors and chemotherapy drugs activate intracellular signals that result in the suppression of protein synthesis and activation of a transcriptional programme leading to autophagy and degradation of myofibrillar proteins. Cancer nutrition therapy is intended to ensure adequate provision of energy fuels and a complete repertoire of biosynthetic building blocks. There is some promising evidence that cancer- and chemotherapy-associated metabolic alterations may also be corrected by certain individual nutrients. The amino acids leucine and arginine provided in the diet at least partially reverse anabolic suppression in muscle, while n-3 PUFA inhibit the transcriptional activation of muscle catabolism. Optimal conditions for exploiting these anabolic and anti-catabolic effects are currently under study, with the overall aim of net improvements in muscle mass, functionality, performance status and treatment tolerance.

Macrophage activation marker sCD163 correlates with accelerated lipolysis following LPS exposure: a human-randomised clinical trial

BACKGROUND

Macrophage activation determined by levels of soluble sCD163 is associated with obesity, insulin resistance, diabetes mellitus type 2 (DM2) and non-alcoholic fatty liver disease (NAFLD). This suggests that macrophage activation is involved in the pathogenesis of conditions is characterised by adaptions in the lipid metabolism. Since sCD163 is shed to serum by inflammatory signals including lipopolysaccharides (LPS, endotoxin), we investigated sCD163 and correlations with lipid metabolism following LPS exposure.

METHODS

Eight healthy male subjects were investigated on two separate occasions: (i) following an LPS exposure and (ii) following saline exposure. Each study day consisted of a four-hour non-insulin-stimulated period followed by a two-hour hyperinsulinemic euglycemic clamp period. A ³H-palmitate tracer was used to calculate the rate of appearance (Ra_palmitate). Blood samples were consecutively obtained throughout each study day. Abdominal subcutaneous adipose tissue was obtained for western blotting.

RESULTS

We observed a significant two-fold increase in plasma sCD163 levels following LPS exposure (P < 0.001), and sCD163 concentrations correlated positively with the plasma concentration of free fatty acids, Ra_palmitate, lipid oxidation rates and phosphorylation of the hormone-sensitive lipase at serine 660 in adipose tissue (P < 0.05, all). Furthermore, sCD163 concentrations correlated positively with plasma concentrations of cortisol, glucagon, tumour necrosis factor (TNF)-α, interleukin (IL)-6 and IL-10 (P < 0.05, all).

CONCLUSION

We observed a strong correlation between sCD163 and stimulation of lipolysis and fat oxidation following LPS exposure. These findings support preexisting theory that inflammation and macrophage activation play a significant role in lipid metabolic adaptions under conditions such as obesity, DM2 and NAFLD.

Metabolic effects of insulin in a human model of ketoacidosis combining exposure to lipopolysaccharide and insulin deficiency: a randomised, controlled, crossover study in individuals with type 1 diabetes

AIMS/HYPOTHESIS

Diabetic ketoacidosis (DKA) is often caused by concomitant systemic inflammation and lack of insulin. Here we used an experimental human model to test whether and how metabolic responses to insulin are impaired in the early phases of DKA with a specific focus on skeletal muscle metabolism.

METHODS

Nine individuals with type 1 diabetes from a previously published cohort were investigated twice at Aarhus University Hospital using a 120 min infusion of insulin (3.0/1.5 mU kg^-1 min^-1) after an overnight fast under: (1) euglycaemic conditions (CTR) or (2) hyperglycaemic ketotic conditions (KET) induced by an i.v. bolus of lipopolysaccharide and 85% reduction in insulin dosage. The primary outcome was insulin resistance in skeletal muscle. Participants were randomly assigned to one of the two arms at the time of screening using www.randomizer.org . The study was not blinded.

RESULTS

All nine volunteers completed the 2 days and are included in the analysis. Circulating concentrations of glucose and 3-hydroxybutyrate increased during KET (mean ± SEM 17.7 ± 0.6 mmol/l and 1.6 ± 0.2 mmol/l, respectively), then decreased after insulin treatment (6.6 ± 0.7 mmol/l and 0.1 ± 0.07 mmol/l, respectively). Prior to insulin infusion (KET vs CTR) isotopically determined endogenous glucose production rates were 17 ± 1.7 μmol kg^-1 min^-1 vs 8 ± 1.3 μmol kg^-1 min^-1 (p = 0.003), whole body phenylalanine fluxes were 2.9 ± 0.5 μmol kg^-1 min^-1 vs 3.1 ± 0.4 μmol kg^-1 min^-1 (p = 0.77) and urea excretion rates were 16.9 ± 2.4 g/day vs 7.3 ± 1.7 g/day (p = 0.01). Insulin failed to stimulate forearm glucose uptake and glucose oxidation in KET compared with CTR (p < 0.05). Glycogen synthase phosphorylation was impaired in skeletal muscle.

CONCLUSIONS/INTERPRETATION

In KET, hyperglycaemia is primarily driven by increased endogenous glucose production. Insulin stimulation during early phases of DKA is associated with reduced glucose disposal in skeletal muscle, impaired glycogen synthase function and lower glucose oxidation. This underscores the presence of muscle insulin resistance in the pathogenesis of DKA. Trial registration www.clinicaltrials.gov (ID number: NCT02157155). Funding This work was funded by the Danish Council for Strategic Research (grant no. 0603-00479B).

Despite Inflammation, Supplemented Essential Amino Acids May Improve Circulating Levels of Albumin and Haemoglobin in Patients after Hip Fractures

Essential amino acids (EAAs) are nutritional substrates that promote body protein synthesis; thus we hypothesised that their supplementation may improve circulating albumin (Alb) and haemoglobin (Hb) in rehabilitative elderly patients following hip fractures (HF). Out of the 145 HF patients originally enrolled in our study, 112 completed the protocol. These subjects were divided into two randomised groups, each containing 56 patients. For a period of two months, one group (age 81.4 ± 8.1 years; male/female 27/29) received a placebo, and the other (age 83.1 ± 7.5 years; male/female 25/31) received 4 + 4 g/day oral EAAs. At admission, the prevalence of both hypoAlb (<3.5 g/dL) and hypoHb (<13 g/dL male, <12 g/dL female) was similar in the placebo group (64.3% hypoAlb, 66% hypoHb) and the treated group of patients (73.2% hypoAlb, 67.8% hypoHb). At discharge, however, the prevalence of hypoAlb had reduced more in EAAs than in placebo subjects (31.7% in EAAs vs. 77.8% in placebo; p < 0.001). There was a 34.2% reduction of anaemia in hypoHb in EAA subjects and 18.9% in placebo subjects, but the difference was not statistically significant. Oral supplementation of EAAs improves hypoAlb and, to a lesser extent, Hb in elderly rehabilitative subjects with hip fractures. Anaemia was reduced in more than one third of patients, which, despite not being statistically significant, may be clinically relevant.

Presence of early stage cancer does not impair the early protein metabolic response to major surgery

BACKGROUND

Combined bilateral mastectomy and reconstruction is a common major surgical procedure in women with breast cancer and in those with a family history of breast cancer. As this large surgical procedure induces muscle protein loss, a preserved anabolic response to nutrition is warranted for optimal recovery. It is unclear whether the presence of early stage cancer negatively affects the protein metabolic response to major surgery as this would mandate perioperative nutritional support.

METHODS

In nine women with early stage (Stage II) breast malignancy and nine healthy women with a genetic predisposition to breast cancer undergoing the same large surgical procedure, we examined whether surgery influences the catabolic response to overnight fasting and the anabolic response to nutrition differently. Prior to and within 24 h after combined bilateral mastectomy and reconstruction surgery, whole body protein synthesis and breakdown rates were assessed after overnight fasting and after meal intake by stable isotope methodology to enable the calculation of net protein catabolism in the post-absorptive state and net protein anabolic response to a meal.

RESULTS

Major surgery resulted in an up-regulation of post-absorptive protein synthesis and breakdown rates (P < 0.001) and lower net protein catabolism (P < 0.05) and was associated with insulin resistance and increased systemic inflammation (P < 0.01). Net anabolic response to the meal was reduced after surgery (P < 0.05) but higher in cancer (P < 0.05) indicative of a more preserved meal efficiency. The significant relationship between net protein anabolism and the amount of amino acids available in the circulation (R²  = 0.85, P < 0.001) was independent of the presence of non-cachectic early stage breast cancer or surgery.

CONCLUSIONS

The presence of early stage breast cancer does not enhance the normal catabolic response to major surgery or further attenuates the anabolic response to meal intake within 24 h after major surgery in patients with non-cachectic breast cancer. This indicates that the acute anabolic potential to conventional feeding is maintained in non-cachectic early stage breast cancer after major surgery.

Insight on the impacts of free amino acids and their metabolites on the immune system from a perspective of inborn errors of amino acid metabolism

INTRODUCTION

Amino acids (AAs) support a broad range of functions in living organisms, including several that affect the immune system. The functions of the immune system are affected when free AAs are depleted or in excess because of external factors, such as starvation, or because of genetic factors, such as inborn errors of metabolism. Areas covered: In this review, we discuss the current insights into how free AAs affect immune responses. When possible, we make comparisons to known disease states resulting from inborn errors of metabolism, in which changed levels of AAs or AA metabolites provide insight into the impact of AAs on the human immune system in vivo. We also explore the literature describing how changes in AA levels might provide pharmaceutical targets for safe immunomodulatory treatment. Expert opinion: The impact of free AAs on the immune system is a neglected topic in most immunology textbooks. That neglect is undeserved, because free AAs have both direct and indirect effects on the immune system. Consistent choices of pre-clinical models and better strategies for creating formulations are required to gain clinical impact.

Roles of Dietary Amino Acids and Their Metabolites in Pathogenesis of Inflammatory Bowel Disease

Inflammatory Bowel Disease (IBD) is a kind of chronic inflammation, which has increasing incidence and prevalence in recent years. IBD mainly divides into Crohn's disease (CD) and ulcerative colitis (UC). It is hard to cure IBD completely, and novel therapies are urgently needed. Amino acids (AAs) and their metabolites are regarded as important nutrients for humans and animals and also play an important role in IBD amelioration. In the present study, the potential protective effects of AAs and their metabolites on IBD had been summarized with the objective to provide insights into IBD moderating using dietary AAs and their metabolites as a potential adjuvant therapy.

LPS infusion suppresses serum FGF21 levels in healthy adult volunteers

CONTEXT

During the inflammatory acute phase response, plasma glucose and serum triglycerides are increased in humans. Fibroblast growth factor (FGF) 21 has plasma glucose and lipid-reducing actions, but its role in the acute inflammatory response in human is unknown.

OBJECTIVE

To investigate circulating levels of FGF21 after lipopolysaccharide (LPS) infusion.

DESIGN

Two randomized, single-blinded, placebo-controlled crossover trials were used.

SETTING

The studies were performed at a university hospital clinical research center.

PATIENTS AND INTERVENTIONS

Study 1 (LPS bolus): Eight young, healthy, lean males were investigated two times: (1) after isotonic saline injection and (2) after LPS injection (bolus of 1 ng/kg). Each study day lasted 4 h. Study 2 (continuous LPS infusion): Eight, healthy males were investigated two times: (1) during continuously isotonic saline infusion and (2) during continuous LPS infusion (0.06 ng/kg/h). Each study day lasted 4 h. Circulating FGF21 levels were quantified every second hour by an immunoassay.

RESULTS

A LPS bolus resulted in a late suppression (t = 240 min) of serum FGF21 (P = 0.035). Continuous LPS infusion revealed no significant effects on FGF21 levels (P = 0.82).

CONCLUSIONS

Our studies show that a bolus of LPS results in decreased FGF21 levels 4 h from exposure.

Regulation of Lipolysis and Adipose Tissue Signaling during Acute Endotoxin-Induced Inflammation: A Human Randomized Crossover Trial

Background

Lipolysis is accelerated during the acute phase of inflammation, a process being regulated by pro-inflammatory cytokines (e.g. TNF-α), stress-hormones, and insulin. The intracellular mechanisms remain elusive and we therefore measured pro- and anti-lipolytic signaling pathways in adipocytes after in vivo endotoxin exposure.

Methods

Eight healthy, lean, male subjects were investigated using a randomized cross over trial with two interventions: i) bolus injection of saline (Placebo) and ii) bolus injection of lipopolysaccharide endotoxin (LPS). A ³H-palmitate tracer was used to measure palmitate rate of appearance (Ra_palmitate) and indirect calorimetry was performed to measure energy expenditures and lipid oxidation rates. A subcutaneous abdominal fat biopsy was obtained during both interventions and subjected to western blotting and qPCR quantifications.

Results

LPS caused a mean increase in serum free fatty acids (FFA) concentrations of 90% (CI-95%: 37–142, p = 0.005), a median increase in Ra_palmitate of 117% (CI-95%: 77–166, p<0.001), a mean increase in lipid oxidation of 49% (CI-95%: 1–96, p = 0.047), and a median increase in energy expenditure of 28% (CI-95%: 16–42, p = 0.001) compared with Placebo. These effects were associated with increased phosphorylation of hormone sensitive lipase (pHSL) at ser⁶⁵⁰ in adipose tissue (p = 0.03), a trend towards elevated pHSL at ser⁵⁵² (p = 0.09) and cAMP-dependent protein kinase A (PKA) phosphorylation of perilipin 1 (PLIN1) (p = 0.09). Phosphatase and tensin homolog (PTEN) also tended to increase (p = 0.08) while phosphorylation of Akt at Thr³⁰⁸ tended to decrease (p = 0.09) during LPS compared with Placebo. There was no difference between protein or mRNA expression of ATGL, G0S2, and CGI-58.

Conclusion

LPS stimulated lipolysis in adipose tissue and is associated with increased pHSL and signs of increased PLIN1 phosphorylation combined with a trend toward decreased insulin signaling. The combination of these mechanisms appear to be the driving forces behind the increased lipolysis observed in the early stages of acute inflammation and sepsis.

Trial Registration

ClinicalTrials.gov NCT01705782

The Hip Functional Retrieval after Elective Surgery May Be Enhanced by Supplemented Essential Amino Acids

It is not known whether postsurgery systemic inflammation and plasma amino acid abnormalities are still present during rehabilitation of individuals after elective hip arthroplasty (EHA). Sixty subjects (36 females; age 66.58 ± 8.37 years) were randomized to receive 14-day oral EAAs (8 g/day) or a placebo (maltodextrin). At admission to and discharge from the rehabilitation center, serum C-reactive protein (CRP) and venous plasma amino acid concentrations were determined. Post-EHA hip function was evaluated by Harris hip score (HHS) test. Ten matched healthy subjects served as controls. At baseline, all patients had high CRP levels, considerable reduction in several amino acids, and severely reduced hip function (HHS 40.78 ± 2.70 scores). After treatment, inflammation decreased both in the EAA group and in the placebo group. Only EAA patients significantly improved their levels of glycine, alanine, tyrosine, and total amino acids. In addition, they enhanced the rate of hip function recovery (HHS) (from baseline 41.8 ± 1.15 to 76.37 ± 6.6 versus baseline 39.78 ± 4.89 to 70.0 ± 7.1 in placebo one; p = 0.006). The study documents the persistence of inflammation and plasma amino acid abnormalities in post-EHA rehabilitation phase. EAAs enhance hip function retrieval and improve plasma amino acid abnormalities.

Correlation of deglutition in subacute ischemic stroke patients with peripheral blood adaptive immunity: Essential amino acid improvement

We aimed to document in stroke patients peripheral blood immune cell profiles, their relations with neuro-functional tests, and any possible influence of supplemented essential amino acids (EAAs) may have on both the immune system and the relationship of the latter with neuro-function.Forty-two dysphagic stroke patients (27 men; 71±9 years) underwent bio-humoral measurements, neuro-functional tests, including Functional Independence Measure (FIM) and Dysphagia Outcome and Severity Scale (DOSS), and were randomized to receive EAAs 8 g/d (EAA group) or isocaloric maltodextrin (placebo group).At discharge all measurements were repeated 38±1 days after randomization.At admission, total white cell (TWC), neutrophil (N), and lymphocyte (Lymph) counts were normal and the N/Lymph ratio was higher than normal values (<3.0). At discharge, both TWC and N decreased while Lymph increased significantly. As a result, the N/Lymph ratio significantly decreased (P <0.001) returning to normal levels. Absolute Lymph counts and Lymph % TWC correlated positively with DOSS (r = +0.235, P = 0.04 and r = +0.224, P = 0.05, respectively), negatively with C-reactive protein natural logarithm (ln CRP) (P = 0.02 and P = 0.0001, respectively), which is an inflammation marker. N correlated positively with ln CRP (P = 0.001) and had a slight negative association with FIM (P = 0.07). The N/Lymph ratio was inversely related to FIM (r = -0.262, P = 0.02) and DOSS (r = -0.279, P = 0.01). Finally, FIM correlated with DOSS (r = +0.35, P = 0.05).For the regression analysis, the overtime changes of Lymph % TWC correlated significantly with DOSS (P = 0.01). There was a positive correlation between Lymph % TWC and DOSS for the entire stroke population (P = 0.015). While this correlation was not important for the placebo group (P = 0.27), it was significant in the EAA subgroup (P = 0.018).In the sub-acute stroke stage, there may be slight alterations of peripheral blood immune cells. Lymph cells are associated with improved neuro-function tests with evidence that this association is enhanced by supplementing EAAs.