The Microbiome and Protein Carbamylation: Potential Targets for Protein-Restricted Diets Supplemented with Ketoanalogues in Predialysis Chronic Kidney Disease

In chronic kidney disease (CKD), metabolic derangements resulting from the interplay between decreasing renal excretory capacity and impaired gut function contribute to accelerating disease progression and enhancing the risk of complications. To protect residual kidney function and improve quality of life in conservatively managed predialysis CKD patients, current guidelines recommend protein-restricted diets supplemented with essential amino acids (EAAs) and their ketoanalogues (KAs). In clinical studies, such an approach improved nitrogen balance and other secondary metabolic disturbances, translating to clinical benefits, mainly the delayed initiation of dialysis. There is also increasing evidence that a protein-restricted diet supplemented with KAs slows down disease progression. In the present review article, recent insights into the role of KA/EAA-supplemented protein-restricted diets in delaying CKD progression are summarized, and possible mechanistic underpinnings, such as protein carbamylation and gut dysbiosis, are elucidated. Emerging evidence suggests that lowering urea levels may reduce protein carbamylation, which might contribute to decreased morbidity and mortality. Protein restriction, alone or in combination with KA/EAA supplementation, modulates gut dysbiosis and decreases the generation of gut-derived uremic toxins associated, e.g., with cardiovascular disease, inflammation, protein energy wasting, and disease progression. Future studies are warranted to assess the effects on the gut microbiome, the generation of uremic toxins, as well as markers of carbamylation.

Parenteral trace element provision: recent clinical research and practical conclusions

The aim of this systematic review (PubMed, www.ncbi.nlm.nih.gov/pubmed and Cochrane, www.cochrane.org; last entry 31 December 2014) was to present data from recent clinical studies investigating parenteral trace element provision in adult patients and to draw conclusions for clinical practice. Important physiological functions in human metabolism are known for nine trace elements: selenium, zinc, copper, manganese, chromium, iron, molybdenum, iodine and fluoride. Lack of, or an insufficient supply of, these trace elements in nutrition therapy over a prolonged period is associated with trace element deprivation, which may lead to a deterioration of existing clinical symptoms and/or the development of characteristic malnutrition syndromes. Therefore, all parenteral nutrition prescriptions should include a daily dose of trace elements. To avoid trace element deprivation or imbalances, physiological doses are recommended.

Cost containment through L-alanyl-L-glutamine supplemented total parenteral nutrition after major abdominal surgery: a prospective randomized double-blind controlled study

BACKGROUND & AIMS

Glutamine is recognized as a conditionally essential amino acid. Recent studies indicate that glutamine-containing total parenteral nutrition improves nitrogen economy, enhances gastrointestinal and immune functions and shortens hospital stay.

METHODS

Thirty-seven patients (19 w and 18 m; age 61. 4+/-10.4 years; BMI 23.7+/-2.8 kg/m(2)) following major abdominal surgery receiving an isonitrogenous isoenergetic TPN with or without alanyl-glutamine supplementation (0.5 g/kg BW/day), were evaluated in a double-blind, randomized, controlled trial over a five-day period by measuring nitrogen balance, selected biochemical parameters and length of hospital stay.

RESULTS

Supplemental alanyl-glutamine improved the overall mean (-3.5+/-1.6 vs. -5.5+/-1. 4 g N;P<0.05) and cumulative nitrogen balance (-14.1+/-9.1 vs. -21.7+/-11.4 g N;P<0.05) compared with the isonitrogenous, isoenergetic standard regimen. Alanyl-glutamine normalized plasma glutamine concentration and reduced the length of hospital stay (12.8+/-2.6 vs. 17.5+/-6.4 days;P<0.05).

CONCLUSIONS

The results of the study confirm that supplementation with synthetic alanyl-glutamine dipeptide is associated with cost containment due to shortened hospitalization and improved nitrogen economy.

The scientific basis of immunonutrition

Substrates with immune-modulating actions have been identified among both macro- and micronutrients. Currently, the modes of action of individual immune-modulating substrates, and their effects on clinical outcomes, are being examined. At present, some enteral formulas are available for the clinical setting which are enriched with selected immune-modulating nutrients. The purpose of the present paper is to review the scientific rationale of enteral immunonutrition. The major aspects considered are mucosal barrier structure and function, cellular defence function and local or systemic inflammatory response. It is notable that in critical illness the mucosal barrier and cellular defence are impaired and a reinforcement with enteral immunonutrition is desirable, while local or systemic inflammatory response should be down regulated by nutritional interventions. The results available from clinical trials are conflicting. Meta-analyses of recent trials show improvements such as reduced risk of infection, fewer days on a ventilator, and reduced length of intensive care unit and hospital stay. Thus, a grade A recommendation was proclaimed for the clinical use of enteral immune-modulating diets. Improvement in outcome was only seen when critical amounts of the immune-modulating formula were tolerated in patients classified as being malnourished. However, in other patients with severe sepsis, shock and organ failure, no benefit or even disadvantages from immunonutrition were reported. In such severe conditions we hypothesize that systemic inflammation might be undesirably intensified by arginine and unsaturated fatty acids, directly affecting cellular defence and inflammatory response. We therefore recommend that in patients suffering from systemic inflammatory response syndrome great caution should be exercised when immune-enhancing substrates are involved which may aggravate systemic inflammation.

Cysteinyl-leukotriene generation as a biomarker for survival in the critically ill

OBJECTIVE

To evaluate the capacity of cysteinyl-leukotriene generation in the progression of critical illness compared with that in healthy volunteers and to clarify interrelationships between the rate of leukotriene generation, severity of the disease, and clinical outcome.

DESIGN

Prospective, observational study.

SETTING

Surgical intensive care unit (ICU) in a German university hospital.

PATIENTS

We studied 14 ICU patients (nine men, five women; aged 42-82 yrs) suffering from systemic inflammatory response syndrome, sepsis, or sepsis syndrome, with a calculated sepsis severity score of 17.7+/-4.2 and a Simplified Acute Physiology score of 17.6+/-3.0. In addition, five healthy volunteers (three men, two women; aged 34-38 yrs) were included in the study.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood samples were obtained every second day from septic patients until discharge from the ICU or death. Leukotriene C4 (LTC4) synthesizing capacity was assessed in isolated and stimulated leukocytes (Ca-ionophore) by using combined reversed-phase, high-pressure liquid chromatography and radioimmunoassay methods. Initially, all patients synthesized less LTC4 than the healthy subjects. In patients who did not survive, the low LTC4 generation persisted throughout the observation period, whereas in surviving patients, its formation was normalized during convalescence. In surviving patients, LTC4 concentrations correlated with sepsis severity score.

CONCLUSIONS

LTC4 generation is impaired in sepsis and may serve as a biomarker for survival in the critical ill.

Determination of glutamine in muscle protein facilitates accurate assessment of proteolysis and de novo synthesis-derived endogenous glutamine production

BACKGROUND

Results of tracer studies indicate that skeletal muscle contributes to approximately 70% of overall glutamine production in healthy adults; the contribution of de novo synthesis being estimated at approximately 60%. However, measurement of the de novo synthesis rate in muscle tissue requires knowledge of the appearance rate of glutamine in plasma and the quantity of glutamine derived from intracellular proteolysis. Thus, the content of glutamine in muscle protein is a prerequisite for an accurate calculation.

OBJECTIVE

The objective of the study was to measure glutamine in muscle protein.

DESIGN

Muscle specimens (open biopsies) were obtained from humans (10 men and 4 women), rats (n = 4), cows (n = 4), and pigs (n = 4). Glutamine was assessed via prehydrolysis derivatization, rapid microwave-enhanced acid hydrolysis, and 5-dimethylaminonaphthalene-1-sulfonyl chloride (dansyl chloride) reversed-phase HPLC, and expressed per mg alkali-soluble protein (ASP) and DNA.

RESULTS

Glutamine concentrations in muscle cell protein of various species ranged from 41 to 49 microg/mg ASP; the differences were not species related. The combined means (+/-SDs) for the 4 species were 43.6 +/- 4.9 microg/mg ASP and 11.9 +/- 2.0 mg/mg DNA, respectively. In humans, there was no apparent influence of age, sex, or BMI.

CONCLUSIONS

Direct and specific measurements of glutamine in intact muscle protein were 50% lower than assumed previously. We used data compiled from earlier studies to recalculate the contributions of proteolysis and de novo synthesis to the endogenous production of glutamine in selected age groups of healthy humans; these contributions remained remarkably constant at approximately 13% and approximately 87%, respectively.

Glutamine content of protein and peptide-based enteral products

BACKGROUND

Glutamine is a conditionally essential amino acid for patients with severe catabolic illness, intestinal dysfunction, or immunodeficiency syndromes. Glutamine is a natural component in many enteral preparations, yet lacking methodology hampers its quantitative determination in dietary products.

OBJECTIVE

The present study was assigned to assess glutamine contents in selected enteral products by using a newly developed method enabling the assessment of protein/peptide bound glutamine.

METHODS

Fourteen commercially available enteral diets (10 protein based and 4 peptide based) were investigated. After removal of interfering fat and carbohydrates, the nitrogen content of the purified preparations was determined by chemiluminescence and protein/peptide bound glutamine was assessed using a three-step procedure; by using a novel prehydrolysis derivatization technique with bis(1,1-trifluoroacetoxy)iodobenzene, glutamine is converted to acid stable diaminobutyric acid. The derivatives are hydrolyzed with a new microwave technology, and subsequently the amino acid composition is determined by reversed phase-high-performance liquid chromatography after dansyl-chloride derivatization.

RESULTS

The content in the protein-based preparations varied between 5.2 and 8.1 g/16 g nitrogen. In the peptide-based products, considerably lower glutamine contents were measured (1.3 to 5.6 g/16 g nitrogen).

CONCLUSION

In the present study, we report for the first time glutamine contents in ready to use enteral products. The daily amount might be satisfactory for healthy individuals but probably not sufficient for the adequate support of the stressed patient. Reliable assessment of glutamine in enteral formulae is a prerequisite t perform clinical studies investigating glutamine requirements in the catabolic state.