Ontogeny of methionine utilization and splanchnic uptake in critically ill children

Effects of improved amino acid balance diet on lysine mammary utilization, whole body protein turnover and muscle protein breakdown on lactating sows

BACKGROUND

The study objective was to test the hypothesis that low crude protein (CP) diet with crystalline amino acids (CAA) supplementation improves Lys utilization efficiency for milk production and reduces protein turnover and muscle protein breakdown. Eighteen lactating multiparous Yorkshire sows were allotted to 1 of 2 isocaloric diets (10.80 MJ/kg net energy): control (CON; 19.24% CP) and reduced CP with "optimal" AA profile (OPT; 14.00% CP). Sow body weight and backfat were recorded on d 1 and 21 of lactation and piglets were weighed on d 1, 14, 18, and 21 of lactation. Between d 14 and 18, a subset of 9 sows (CON = 4, OPT = 5) was infused with a mixed solution of 3-[methyl-2H3]histidine (bolus injection) and [13C]bicarbonate (priming dose) first, then a constant 2-h [13C]bicarbonate infusion followed by a 6-h primed constant [1-13C]lysine infusion. Serial blood and milk sampling were performed to determine plasma and milk Lys enrichment, Lys oxidation rate, whole body protein turnover, and muscle protein breakdown.

RESULTS

Over the 21-d lactation period, compared to CON, sows fed OPT had greater litter growth rate (P < 0.05). Compared to CON, sows fed OPT had greater efficiency of Lys (P < 0.05), Lys mammary flux (P < 0.01) and whole-body protein turnover efficiency (P < 0.05). Compared to CON, sows fed OPT tended to have lower whole body protein breakdown rate (P = 0.069). Muscle protein breakdown rate did not differ between OPT and CON (P = 0.197).

CONCLUSION

Feeding an improved AA balance diet increased efficiency of Lys and reduced whole-body protein turnover and protein breakdown. These results imply that the lower maternal N retention observed in lactating sows fed improved AA balance diets in previous studies may be a result of greater partitioning of AA towards milk rather than greater body protein breakdown.

Homocysteine exchange across skeletal muscle in patients with chronic kidney disease

Sites and mechanisms regulating the supply of homocysteine (Hcy) to the circulation are unexplored in humans. We studied the exchange of Hcy across the forearm in CKD patients (n = 17, eGFR 20 ± 2 ml/min), in hemodialysis (HD)-treated patients (n = 14) and controls (n = 9). Arterial Hcy was ~ 2.5 folds increased in CKD and HD patients (p < 0.05-0.03 vs. controls). Both in controls and in patients Hcy levels in the deep forearm vein were consistently greater (+~7%, p < 0.05-0.01) than the corresponding arterial levels, indicating the occurrence of Hcy release from muscle. The release of Hcy from the forearm was similar among groups. In all groups arterial Hcy varied with its release from muscle (p < 0.03-0.02), suggesting that muscle plays an important role on plasma Hcy levels. Forearm Hcy release was inversely related to folate plasma level in all study groups but neither to vitamin B12 and IL-6 levels nor to muscle protein net balance. These data indicate that the release of Hcy from peripheral tissue metabolism plays a major role in influencing its Hcy plasma levels in humans and patients with CKD, and that folate is a major determinant of Hcy release.

Protein Requirements of the Critically Ill Pediatric Patient

This article includes a review of protein needs in children during health and illness, as well as a detailed discussion of protein metabolism, including nitrogen balance during critical illness, and assessment and prescription/delivery of protein to critically ill children. The determination of protein requirements in children has been difficult and challenging. The protein needs in healthy children should be based on the amount needed to ensure adequate growth during infancy and childhood. Compared with adults, children require a continuous supply of nutrients to maintain growth. The protein requirement is expressed in average requirements and dietary reference intake, which represents values that cover the needs of 97.5% of the population. Critically ill children have an increased protein turnover due to an increase in whole-body protein synthesis and breakdown with protein degradation leading to loss of lean body mass (LBM) and development of growth failure, malnutrition, and worse clinical outcomes. The results of protein balance studies in critically ill children indicate higher protein needs, with infants and younger children requiring higher intakes per body weight compared with older children. Monitoring the side effects of increased protein intake should be performed. Recent studies found a survival benefit in critically ill children who received a higher percentage of prescribed energy and protein goal by the enteral route. Future randomized studies should evaluate the effect of protein dosing in different age groups on patient outcomes, including LBM, muscle structure and function, duration of mechanical ventilation, intensive care unit and hospital length of stay, and mortality.

Splanchnic first pass disappearance of threonine and lysine do not differ in healthy men in the fed state

We previously showed that the splanchnic bed of neonates takes up a significantly higher amount (43%) of threonine in contrast to lysine (12%). We questioned whether this same pattern applied in adult humans and found no information in the literature. Therefore, our objective in the current study was to determine the difference in splanchnic first pass disappearance of threonine and lysine in adult humans during the fed state. During two 5-d study periods, 6 healthy men received l-[1-(13)C]threonine or l-[1-(13)C]lysine enterally or parenterally randomized to either study d 3 or 5, respectively. The diets were in the form of an amino acid mixture providing a protein intake of 1 g · kg(-1) · d(-1) and an energy intake of 1.5 times the resting energy expenditure. Blood and breath samples were collected at baseline and plateau for amino acid and 11CO(2) enrichment. Splanchnic disappearances in adult males were similar for threonine and lysine. The splanchnic disappearance of threonine as a percentage of intake was 17.9% (8.4 mg · kg(-1) · d(-1)) in the healthy men compared with 18.5% (11.2 mg · kg(-1) · d(-1)) for lysine. We conclude that the threonine requirement of the gut of healthy men consuming a liquid formula diet based on free amino acids is similar to the lysine requirement, which is in contrast to our previous findings for neonates.

Current recommended parenteral protein intakes do not support protein synthesis in critically ill septic, insulin-resistant adolescents with tight glucose control

OBJECTIVE

To investigate the effects of insulin infusion and increased parenteral amino acid intakes on whole body protein balance, glucose kinetics, and lipolysis in critically ill, insulin-resistant, septic adolescents.

DESIGN

A single-center, randomized, crossover study.

SETTING

A medicosurgical intensive care unit in a tertiary university hospital.

PATIENTS

Nine critically ill, septic adolescents (age 15.0 ± 1.2 yrs, body mass index 20 ± 4 kg m(-2)) receiving total parenteral nutrition.

INTERVENTIONS

Patients received total parenteral nutrition with standard (1.5 g · kg(-1) · day(-1)) and high (3.0 g · kg(-1) · day(-1)) amino acid intakes in a 2-day crossover setting, randomized to the order in which they received it. On both study days, we conducted a primed, constant, 7-hr stable isotope tracer infusion with [1-(13)C]leucine, [6,6-(2)H(2)]glucose, and [1,1,2,3,3-(2)H(5)]glycerol, in combination with a hyperinsulinemic euglycemic clamp during the last 3 hrs.

MEASUREMENTS AND MAIN RESULTS

Insulin decreased protein synthesis at standard amino acid and high amino acid intakes (p < .01), while protein breakdown decreased with insulin at standard amino acid intake (p < .05) but not with the high amino acid intake. High amino acid intake improved protein balance (p < .05), but insulin did not have an additive effect. There was significant insulin resistance with an M value of ~3 (mg · kg(-1) · min(-1))/(mU · mL(-1)) which was 30% of reported normal values. At high amino acid intake, endogenous glucose production was not suppressed by insulin and lipolysis rates increased.

CONCLUSION

The current recommended parenteral amino acid intakes are insufficient to maintain protein balance in insulin-resistant patients during tight glucose control. During sepsis, insulin decreases protein synthesis and breakdown, and while high amino acid intake improves protein balance, its beneficial effects may be offset by enhanced endogenous glucose production and lipolysis, raising concerns that insulin resistance may have been exacerbated and that gluconeogenesis may have been favored by high amino acid intakes. Dose-response studies on the effect of the level of amino acid intakes (protein) on energy metabolism are needed.

Reducing glucose infusion safely prevents hyperglycemia in post-surgical children

BACKGROUND & AIMS

To investigate the effects of two different glucose infusions on glucose homeostasis and amino acid metabolism in post-surgical children.

METHODS

This randomized crossover study evaluated glucose and amino acid metabolism in eight children (age 9.8 ± 1.9 months, weight 9.5 ± 1.1 kg) admitted to a pediatric intensive care unit in a tertiary university hospital after surgical correction for non-syndromal craniosynostosis. Patients were randomized to receive low (LG; 2.5 mg kg(-1) min(-1)) and standard (SG; 5.0 mg kg(-1) min(-1)) glucose infusion in a crossover setting. After a bolus (4 g kg(-1)) of deuterium oxide, we conducted a primed, constant, 8 h tracer infusion with [6,6-²H₂]Glucose, [1-¹³C]Leucine, [ring-²H₅]Phenylalanine and [3,3-²H₂]Tyrosine.

RESULTS

SG resulted in hyperglycemia (defined as > 6.1 mmol L(-1)), while during LG plasma glucose levels were normoglycemic (5.9 ± 0.6 vs. 7.5 ± 1.7 mmol L(-1); LG vs. SG respectively, p = 0.02). Hypoglycemia did not occur during LG infusion. Endogenous glucose production was not fully suppressed during the hyperglycemic state under SG and increased with reduced glucose infusion (2.6 ± 1.5 vs. 1.1 ± 1.4 mg kg(-1) min(-1); LG vs. SG; p = 0.05). Whole body protein balance derived from leucine and phenylalanine kinetics was slightly negative but not further affected with a decrease in glucose infusion.

CONCLUSIONS

The current recommended glucose infusion induces hyperglycemia in post-surgical children. A reduced glucose infusion safely reduced high glucose levels, while children were capable to sustain normoglycemia with increased endogenous glucose production. The reduced glucose infusion did not exacerbate the mild catabolic state in which the patients were.