Substrate-endocrine interactions and protein metabolism

Rationale and design of a proof-of-concept trial investigating the effect of uninterrupted perioperative (par)enteral nutrition on amino acid profile, cardiomyocytes structure, and cardiac perfusion and metabolism of patients undergoing coronary artery bypass grafting

Background

Malnutrition is very common in patients undergoing cardiac surgery. Malnutrition can change myocardial substrate utilization which can induce adverse effects on myocardial metabolism and function. We aim to investigate the hypothesis that there is a disturbed amino acids profile in the cardiac surgical patient which can be normalized by (par)enteral nutrition before, during and after surgery, subsequently improving cardiomyocyte structure, cardiac perfusion and glucose metabolism.

Methods/Design

This randomized controlled intervention study investigates the effect of uninterrupted perioperative (par)enteral nutrition on cardiac function in 48 patients undergoing coronary artery bypass grafting. Patients are given enteral nutrition (n = 16) or parenteral nutrition (n = 16), at least two days before, during, and two days after coronary artery bypass grafting, or are treated according to the standard guidelines (control) (n = 16). We will illustrate the effect of (par)enteral nutrition on differences in concentrations of amino acids and asymmetric dimethylarginine and in activity of dimethylarginine dimethylaminohydrolase and arginase in cardiac tissue and blood plasma. In addition, cardiomyocyte structure by histological, immuno-histochemical and ultrastructural analysis will be compared between the (par)enteral and control group. Furthermore, differences in cardiac perfusion and global left ventricular function and glucose metabolism, and their changes after coronary artery bypass grafting are evaluated by electrocardiography-gated myocardial perfusion scintigraphy and ¹⁸F-fluorodeoxy-glucose positron emission tomography respectively. Finally, fat free mass is measured before and after intervention with bioelectrical impedance spectrometry in order to evaluate nutritional status.

Trial registration

Netherlands Trial Register (NTR): NTR2183

Stimulation of muscle protein degradation by murine and human epidermal cytokines: relationship to thermal injury

Accelerated muscle proteolysis is a characteristic of systemic reaction following trauma, sepsis, or extensive thermal injury. The factors involved in this accelerated muscle breakdown have not been fully described. However, recently leukocytic pyrogen or interleukin 1 (IL-1) have been implicated in the induction of muscle protein degradation in septicemia or trauma. The epidermal cytokine epidermal cell-derived thymocyte activating factor (ETAF) is biochemically and functionally similar to IL-1. Injury to skin can augment ETAF activity. Using a murine model, we found that thermal injury can significantly enhance ETAF/IL-1 activity in a dose-dependent fashion. In addition, ETAF can cause net muscle protein breakdown in vitro. Thus, increased amounts of ETAF produced by thermally injured skin may contribute to the accelerated muscle breakdown in extensive thermal injury.

Parenteral nourishment of patients undergoing surgical or traumatic stress

Severe surgical or other traumatic stress initiates an integrated central nervous system and metabolic response characterized by catabolism which selectively preserves vital organs, drawing on peripheral tissue proteins for required amino acids. When oral intake is prohibited adequate intravenous nutritional support hastens convalescence and may be life-saving. Intravenous nutrients routinely consist of amino acids for replacement of lost protein, a nonprotein calorie source--usually glucose, and vitamins and minerals. Lipid, infrequently used in routine surgery as part of the calorie source, supplies essential fatty acids and prevents side effects resulting with large amounts of intravenous glucose. Lipid has other benefits. Stress-induced hormones stimulate lipid catabolism. When lipid is used for part of the calorie requirement in intravenous feedings, the plasma insulin level is reduced and peripheral amino acids become available for synthesis of critically needed visceral proteins. Recent work has shown that the branched chain amino acids carnitine and some species of lipid added to intravenous nutrient formulations postoperatively affect the nitrogen retention and may hasten convalescence. Further work should be directed at understanding the unique biochemical changes occurring after injury, devising objective assay procedures to measure the severity of the response and improving intravenous formulations for the acutely ill surgical patient.

Branched chain amino acid-enriched solutions in the septic patient. A randomized, prospective trial

A prospective, randomized trial was undertaken to compare the nutritional efficacy in surgical stress of a standard amino acid solution and two branched chain-enriched amino acid solutions: one enriched primarily with valine, the other with leucine. The study comprised 37 patients in the surgical intensive care unit who received isocaloric, isonitrogenous parenteral nutrition started within 24 hours of the onset of major operation, injury, or sepsis. Nitrogen retention was marginally but statistically significantly better on days 5, 7, and 10 in both groups of patients receiving the branched chain-enriched solutions, but differences in cumulative nitrogen balance were not statistically significant. Amino acid composition appeared to be important in that the group receiving the leucine-enriched solution appeared to maintain hepatic protein synthesis better (as manifest by higher short-turnover plasma protein concentrations) and required less exogenous insulin to maintain euglycemia. Improved outcome was not seen in the groups receiving the branched chain-enriched solutions.

Total parenteral nutrition with different ratios of fat/carbohydrate at two energy levels: an animal study

Different regimens of total parenteral nutrition were evaluated in 64 growing rats, during a 10-day period. Thirty-two rats were kept at a low energy regimen (270 kcal/kg body weight per day), and the remaining rats were infused with a high energy solution (350 kcal/kg/day). At each energy level, four fat/carbohydrate (CHO) nonprotein energy ratios were tested: 0% fat/100% CHO (no fat); 6% fat/94% CHO (low fat); 30% fat/70% CHO (medium fat); 60% fat/40% CHO (high fat). A daily supply of 0.9 g nitrogen/kg of a well balanced amino acid solution was administered to all rats. Growth, nitrogen balance, net nitrogen utilization, and blood status were evaluated. Carcass, liver, and muscle composition were investigated with respect to protein, fat, and water content. Liver and body composition was similar between groups at the same energy level. At the higher energy level the fat deposition was increased. At the low energy level, rats from no fat and low fat groups lost weight during the first 3 days of the experimental period. The medium fat groups showed the highest weight gain at each energy level. This suggests the importance of the presence of fat in total parenteral nutrition programs. During the last days of the experimental period, all rats gained weight, and showed a positive nitrogen balance. All groups given 350 kcal/kg/day gained weight more rapidly and showed a better nitrogen balance and utilization than the corresponding group given 270 kcal/kg/day. This study emphasizes that a well-balanced proportion of energy and substrates is important.

Branched chain metabolic support. A prospective, randomized, double-blind trial in surgical stress

A prospective, randomized, double-blind trial of the nutritional effects of branched chain modified amino acid solutions was undertaken in 23 surgical patients within 24 hours of the onset of major general surgery, polytrauma, or sepsis. The effects were evaluated in the absence of abnormalities of oxygen transport and perfusion in an isocaloric/isonitrogenous setting where the major difference between the groups was the amount of branched chain amino acids received. Both groups received balanced parenteral nutrition with 1.5 gm/kg/day of amino acids, 30 calories/kg/day of glucose, and 7 calories/kg/day of fat. At the end of the 7-day study interval, the group receiving the branched chain enriched therapy at 0.7 gm/kg/day of branched chain amino acids had improved nitrogen retention; an elevation of their absolute lymphocyte count from 800 to 1800/mm3, a reversal of anergy to recall skin test antigens in 60% of the patients, and improved plasma transferrin levels (p less than 0.03). Nutritional support using the modified amino acid metabolic support solutions has beneficial effects during the stress interval that do not seem as achievable with current commercially available nutritional support regimens.

Does modified amino acid total parenteral nutrition alter immune-response in high level surgical stress

A randomized prospective double-blinded study was conducted in patients in moderate to high level surgical stress to ascertain the effect of high dose branched-chain (BcAA) hyperalimentation on skin test reactivity and lymphocyte count. Isocaloric, isonitrogenous balanced total parenteral nutrition solutions were administered to two treatment groups. The study group received the high dose (45% BcAA) solution while the control group received a standard amino acid solution (24.2% BcAA). All patients received 1 to 1.5 g/kg/day of amino acids and 30 nonprotein cal/kg/day, with 30% of them as fat. Immune function was assessed by absolute lymphocyte count and delayed cutaneous hypersensitivity on days 0 and 7 of therapy. Absolute lymphocyte count showed a marked improvement in patients receiving high dose aBcAA (p less than 0.03). All patients were anergic at baseline; a much greater percentage of skin test reactivity was observed in the BcAA group on day 7 (p less than 0.03). They were also in positive nitrogen balance. The data suggest that improved nitrogen retention and immune-competence is possible with branched-chain-enriched hyperalimentation in high level surgical stress.

[Advantage of xylitol compared to glucose as an energy source during early postoperative parenteral feeding]

After a 5-day preoperative preparing period, 24 metabolically healthy patients, who had to undergo gastric resection, were fed postoperatively by hypocaloric total parenteral nutrition for a 5-day period. Group I, n = 13; received 0.11 g Xylitol/kg BW . h; Group II, n = 11, received 0.11 g Glucose/kg BW . h. Both groups received 1.71 g L-crystalline amino acids/kg BW . day. During the whole postoperative period, group II had significantly higher serum glucose and insulin levels. Due to the high postoperative insulin concentration in group II, free fatty acids, acetoacetate, beta-hydroxybutyrate and branched chained amino acids were significantly lower. The augmented release of muscle amino acids and the covering of a part of the energy expenditure by increased fatty acid oxidation in group I led to a higher postoperative synthesis rate of visceral proteins. From postoperative day 3 on transferrin and from postoperative day 6 on albumin and total protein were significantly higher in group I. This study could demonstrate that due to its special role in the intermediary metabolism during the postoperative period xylitol leads to a significantly higher regeneration rate of visceral proteins compared to glucose during total parenteral nutrition.