A tracer bolus method for investigating glutamine kinetics in humans

Comprehensive metabolic amino acid flux analysis in critically ill patients

Amino acid (AA) metabolism is severely disturbed in critically ill ICU patients. To be able to make a more scientifically based decision on the type of protein or AA nutrition to deliver in ICU patients, comprehensive AA phenotyping with measurements of plasma concentrations and whole body production (WBP) is needed. Therefore, we studied ICU patients and matched control subjects using a novel pulse isotope method to obtain in-depth metabolic analysis. In 51 critically ill ICU patients (SOFA~6.6) and 49 healthy controls, we measured REE and body composition/phase-angle using BIA. In the postabsorptive state, we collected arterial (ized) blood for CRP and AA. Then, we administered an 8 mL solution containing 18 stable AA tracers as a pulse and calculated WBP. Enrichments: LC-MS/MS and statistics: t-test, ANCOVA. Compared to healthy, critically ill ICU patients had lower phase-angle (p < 0.00001), and higher CRP (p < 0.0001). Most AA concentrations were lower in ICU patients (p < 0.0001), except tau-methylhistidine and phenylalanine. WBP of most AA were significantly (p < 0.0001) higher with increases in glutamate (160%), glutamine (46%), and essential AA. Remarkably, net protein breakdown was lower. There were only weak relationships between AA concentrations and WBP. Critically ill ICU patients (SOFA 8-16) had lower values for phase angle (p = 0.0005) and small reductions of most plasma AA concentrations, but higher tau-methylhistidine (p = 0.0223) and hydroxyproline (p = 0.0028). Remarkably, the WBP of glutamate and glutamine were lower (p < 0.05), as was their clearance, but WBP of tau-methylhistidine (p = 0.0215) and hydroxyproline (p = 0.0028) were higher. Our study in critically ill ICU patients shows that comprehensive metabolic phenotyping was able to reveal severe disturbances in specific AA pathways, in a disease severity dependent way. This information may guide improving nutritional compositions to improve the health of the critically ill patient. CLINICAL TRIAL REGISTRY: Data are from the baseline measurements of study NCT02770092 (URL: https://clinicaltrials.gov/ct2/show/NCT02770092) and NCT03628365 (URL: https://clinicaltrials.gov/ct2/show/NCT03628365).

Endogenous production of glutamine and plasma glutamine concentration in critically ill patients

BACKGROUND

Glutamine plasma concentrations outside the normal range at intensive care unit (ICU) admission are associated with unfavorable outcomes. Based on the hypothesis that hypoglutaminemia in the ICU is the result of an increased utilization of glutamine which cannot be fully met by endogenous production, extra glutamine supplementation has been advocated to ICU patients with hypoglutaminemia. However, it is still unclear whether there is a causal relation between hypo- and hyperglutaminemia and outcomes. Present guidelines advise against supplementation, although there is no evidence available for patients with hypoglutaminemia. The pathophysiology of abnormal glutamine levels and whether glutamine production or glutamine utilization is compromised is largely unknown. Therefore, the aim of this study was to elucidate the relationship between plasma glutamine levels and the endogenous glutamine production in ICU patients.

METHOD

In this observational study, a technique using a small bolus of intravenous glutamine with an isotopic label was used to measure glutamine production.

RESULTS

There was a statistically significant correlation between de novo endogenous production of glutamine (not emanating directly from protein breakdown) and plasma glutamine concentrations in the low and normal range in circulatory stabilized ICU patients (n = 19), R² = 0.35 (P ≤ 0.01).

CONCLUSION

The predictive value of a low plasma glutamine concentration at ICU admission on outcomes may thus be related to a low endogenous production, which may need to be supplemented in the best interest of this cohort of patients.

Dietary Amino Acids and Immunonutrition Supplementation in Cancer-Induced Skeletal Muscle Mass Depletion: A Mini-Review

Cancer patients display systemic inflammation, which leads to an increase in protein catabolism, thus promoting the release of free amino acids to further support metabolism and remodelling of muscle proteins. Inflammation associated with tumor growth leads to malnutrition, a factor that increases the risk of developing cachexia. With cancer-induced cachexia, nutritional interventions have gained traction as a preventative method to manage this condition. Currently, cancer consensus recommendations suggest a protein intake above 1.0 g/kg.day-1 up to 2.0 g/k.day-1 for cancer patients, although an ideal amount for some amino acids in isolation has yet to be determined. Due to controversy in the literature regarding the benefits of the biochemical mechanisms of various muscle mass supplements, such as L-leucine (including whey protein and BCAA), β-hydroxy-beta-methyl butyrate (HMβ), arginine, glutamine and creatine, several studies have carefully examined their effects. L-leucine and its derivatives appear to regulate protein synthesis by direct or indirect activation of the mTORC1 pool of kinases, further promoting muscle protein balance. Arginine and glutamine may act by reducing inflammation and infection progression, thus promoting improvements in food intake. Creatine exerts anabolic activity, acting as an immediate energy substrate to support muscle contraction further increasing lean mass, mainly due to greater water uptake by the muscle. In this narrative review, we highlighted the main findings regarding protein consumption and amino acids to mitigate cancer-induced skeletal muscle depletion.

Lactate kinetics in ICU patients using a bolus of 13C-labeled lactate

Background

Plasma lactate concentrations and their trends over time are used for clinical prognosis, and to guide treatment, in critically ill patients. Although heavily relied upon for clinical decision-making, lactate kinetics of these patients is sparsely studied.

Aim

To establish and validate a feasible method to study lactate kinetics in critically ill patients.

Methods

Healthy volunteers (n = 6) received a bolus dose of ¹³C-labeled lactate (20 μmol/kg body weight), and 43 blood samples were drawn over 2 h to determine the decay in labeled lactate. Data was analyzed using non-compartmental modeling calculating rates of appearance (R_a) and clearance of lactate. The area under the curve (AUC) was calculated using a linear-up log-down trapezoidal approach with extrapolation beyond 120 min using the terminal slope to obtain the whole AUC. After evaluation, the same protocol was used in an unselected group of critically ill patients (n = 10).

Results

R_a for healthy volunteers and ICU patients were 12.8 ± 3.9 vs 22.7 ± 11.1 μmol/kg/min and metabolic clearance 1.56 ± 0.39 vs 1.12 ± 0.43 L/min, respectively. ICU patients with normal lactate concentrations showed kinetics very similar to healthy volunteers. Simulations showed that reducing the number of samples from 43 to 14 gave the same results. Our protocol yielded results on lactate kinetics very similar to previously published data using other techniques.

Conclusion

This simple and user-friendly protocol using an isotopically labeled bolus dose of lactate was accurate and feasible for studying lactate kinetics in critically ill ICU patients.

Trial registration

ANZCTR, ACTRN12617000626369, registered 8 March 2017. https://anzctr.org.au/Trial/Registration/TrialReview.aspx?id=372507&isReview=true

[Clinical effect of alanyl-glutamine-enriched nutritional support in the treatment of children with abdominal Henoch-Schönlein purpura]

OBJECTIVE

To study the clinical effect of alanyl-glutamine-enriched nutritional support in the treatment of children with abdominal Henoch-Schönlein purpura.

METHODS

Children with abdominal Henoch-Schönlein purpura who needed nutritional support were enrolled and stratified according to age, sex and the severity of disease, and were randomly divided into a control group (n=118) and an enriched nutritional support group (n=107). The control group was given nutritional support without using alanyl-glutamine, while the enriched nutritional support group was given alanyl-glutamine-enriched nutritional support. Intravenous steroids were used according to the severity of disease in both groups. Other therapies were the same in the two groups. The two groups were compared in terms of the length of hospital stay, the rate and duration of use of intravenous steroids, the recurrence rate of symptoms during hospitalization, the rate of total parenteral nutrition (TPN), the rate of weight loss and the rate of fasting for more than 5 days. All patients were followed up for 3 months after discharge to monitor the recurrence of symptoms.

RESULTS

There were no significant differences in the length of hospital stay, the rate of TPN and the rate of fasting for more than 5 days between the two groups (P>0.05). Compared with the enriched nutritional support group, the control group showed significant increases in the rate and duration of use of intravenous steroids, the recurrence rate of symptoms and the rate of weight loss (P<0.05). After the 3-month follow-up, all the children resumed normal diet, and the recurrence rate of digestive symptoms was less than 20% in each group. Abdominal pain was the most common symptom (83.33%, 30/36), followed by vomiting and abdominal distention. No digestive hemorrhage was observed. All the symptoms were relieved after symptomatic treatment. No significant difference was found between the two groups in the recurrence rate of digestive symptoms (P=0.693).

CONCLUSIONS

Alanyl-glutamine-enriched nutritional support in the treatment of children with abdominal Henoch-Schönlein purpura can reduce the use of intravenous steroids and weight loss, but without impact on the length of hospital stay and post-discharge recurrence.

[Clinical effect of alanyl-glutamine-enriched nutritional support in the treatment of children with abdominal Henoch-Schönlein purpura]

OBJECTIVE

To study the clinical effect of alanyl-glutamine-enriched nutritional support in the treatment of children with abdominal Henoch-Schönlein purpura.

METHODS

Children with abdominal Henoch-Schönlein purpura who needed nutritional support were enrolled and stratified according to age, sex and the severity of disease, and were randomly divided into a control group (n=118) and an enriched nutritional support group (n=107). The control group was given nutritional support without using alanyl-glutamine, while the enriched nutritional support group was given alanyl-glutamine-enriched nutritional support. Intravenous steroids were used according to the severity of disease in both groups. Other therapies were the same in the two groups. The two groups were compared in terms of the length of hospital stay, the rate and duration of use of intravenous steroids, the recurrence rate of symptoms during hospitalization, the rate of total parenteral nutrition (TPN), the rate of weight loss and the rate of fasting for more than 5 days. All patients were followed up for 3 months after discharge to monitor the recurrence of symptoms.

RESULTS

There were no significant differences in the length of hospital stay, the rate of TPN and the rate of fasting for more than 5 days between the two groups (P>0.05). Compared with the enriched nutritional support group, the control group showed significant increases in the rate and duration of use of intravenous steroids, the recurrence rate of symptoms and the rate of weight loss (P<0.05). After the 3-month follow-up, all the children resumed normal diet, and the recurrence rate of digestive symptoms was less than 20% in each group. Abdominal pain was the most common symptom (83.33%, 30/36), followed by vomiting and abdominal distention. No digestive hemorrhage was observed. All the symptoms were relieved after symptomatic treatment. No significant difference was found between the two groups in the recurrence rate of digestive symptoms (P=0.693).

CONCLUSIONS

Alanyl-glutamine-enriched nutritional support in the treatment of children with abdominal Henoch-Schönlein purpura can reduce the use of intravenous steroids and weight loss, but without impact on the length of hospital stay and post-discharge recurrence.

Is the glutamine story over?

Glutamine has been launched as a conditionally indispensible amino acid for the critically ill. Supplementation has been recommended in guidelines from international societies. Although data have been presented pointing out that glutamine supplementation may not be for everybody, recommendations for treatments and design of study protocols have included all critically ill patients. Results from more recent studies and meta-analyses indicate that indiscriminate use of glutamine supplementation in critically ill patients may actually cause harm rather than beneficial effects. This viewpoint sorts out arguments of controversy in the glutamine story.

Human Protein and Amino Acid Requirements

Human protein and amino acid nutrition encompasses a wide, complex, frequently misunderstood, and often contentious area of clinical research and practice. This tutorial explains the basic biochemical and physiologic principles that underlie our current understanding of protein and amino acid nutrition. The following topics are discussed: (1) the identity, measurement, and essentiality of nutritional proteins; (2) the definition and determination of minimum requirements; (3) nutrition adaptation; (4) obligatory nitrogen excretion and the minimum protein requirement; (5) minimum versus optimum protein intakes; (6) metabolic responses to surfeit and deficient protein intakes; (7) body composition and protein requirements; (8) labile protein; (9) N balance; (10) the principles of protein and amino acid turnover, including an analysis of the controversial indicator amino acid oxidation technique; (11) general guidelines for evaluating protein turnover articles; (12) amino acid turnover versus clearance; (13) the protein content of hydrated amino acid solutions; (14) protein requirements in special situations, including protein-catabolic critical illness; (15) amino acid supplements and additives, including monosodium glutamate and glutamine; and (16) a perspective on the future of protein and amino acid nutrition research. In addition to providing practical information, this tutorial aims to demonstrate the importance of rigorous physiologic reasoning, stimulate intellectual curiosity, and encourage fresh ideas in this dynamic area of human nutrition. In general, references are provided only for topics that are not well covered in modern textbooks.

Endogenous glutamine production in critically ill patients: the effect of exogenous glutamine supplementation

Introduction

Glutamine rate of appearance (R_a) may be used as an estimate of endogenous glutamine production. Recently a technique employing a bolus injection of isotopically labeled glutamine was introduced, with the potential to allow for multiple assessments of the glutamine R_a over time in critically ill patients, who may not be as metabolically stable as healthy individuals. Here the technique was used to evaluate the endogenous glutamine production in critically ill patients in the fed state with and without exogenous glutamine supplementation intravenously.

Methods

Mechanically ventilated patients (n = 11) in the intensive care unit (ICU) were studied on two consecutive days during continuous parenteral feeding. To allow the patients to be used as their own controls, they were randomized for the reference measurement during basal feeding without supplementation, before or after the supplementation period. Glutamine R_a was determined by a bolus injection of ¹³C-glutamine followed by a period of frequent sampling to establish the decay-curve for the glutamine tracer. Exogenous glutamine supplementation was given by intravenous infusion of a glutamine containing dipeptide, L-alanyl-L-glutamine, 0.28 g/kg during 20 hours.

Results

A 14% increase of endogenous glutamine R_a was seen at the end of the intravenous supplementation period as compared to the basal measurements (P = 0.009).

Conclusions

The bolus injection technique to measure glutamine R_a to estimate the endogenous production of glutamine in critically ill patients was demonstrated to be useful for repetitive measurements. The hypothesized attenuation of endogenous glutamine production during L-alanyl-L-glutamine infusion given as a part of full nutrition was not seen.