Application of proton NMR spectroscopy to measurement of whole-body RNA degradation rates: effects of surgical stress in human patients.

The urinary catabolites, N2,N2-dimethylguanosine (DMG), pseudouridine (PSU) and 7-methylguanine (m7-Gua) are formed from post-transcriptional methylation of RNA bases and are not reincorporated into RNA upon its degradation. Their quantitative urinary excretion may be used to determine rates of whole body degradation of individual RNA species since DMG occurs exclusively in tRNA, PSU occurs in rRNA and tRNA and m7-Gua occurs in all RNA species. Conventional HPLC analysis has several drawbacks since pre-analytical steps may involve selective losses and, under certain conditions, other urinary analytes may co-elute. In the present paper, we report analysis of these compounds by high-field 1H-nuclear magnetic resonance (1H-NMR) spectroscopy. Urinary concentrations of these metabolites were found to be in agreement with previously published HPLC and ELISA determinations. However, NMR analysis required minimal sample preparation (other than lyophilisation and reconstitution) and was capable of the simultaneous determination of other relevant analytes such as creatinine. This technique was therefore applied to urine samples from patients who had undergone surgical stress and insulin-like growth factor-1 (IGF-I) therapy. Surgical stress increased the excretion of DMG and m7-Gua. Degradation rates for tRNA and mRNA were also higher in surgically stressed subjects when compared with controls but degradation rates of rRNA decreased by approx. 30%. However, injection of IGF-I (40 micrograms/kg s.c.) had no significant effect on the excretion of these nucleosides. These data indicated that IGF-I therapy has no marked effects on RNA turnover following trauma. We suggest that this technique can be applied to study of RNA metabolism in any surgical or medical condition. Furthermore, since only 0.6 ml of urine is required, studies in neonates seem to be feasible.

Do fibre containing enteral diets have advantages over existing low residue diets?

This study investigated the influence of fibre on the pattern of absorption of protein and carbohydrate following administration of polymeric enteral diet and also the effect of added fibre on frequency of bowel action, stool weight and gastrointestinal side effects during enteral nutrition. No difference was seen in frequency of bowel action, stool weight or gastrointestinal side effects in five patients fed with either a fibre free polymeric diet or with the same diet augmented with 24 g fibre/24 h. Addition of fibre did not significantly alter breath hydrogen excretion. In an oral tolerance test on six normal subjects, the post prandial rises in blood glucose and levels of 17 amino acids were similar on ingestion of a fibre containing or fibre free test meal.

Effect of providing fortified meals and between-meal snacks on energy and protein intake of hospital patients.

This study aimed to evaluate whether food fortification and snacks could increase the energy and protein intakes of hospital patients. The control group of 82 consecutive admissions on medical, elderly care and orthopaedic wards ate freely from the hospital menu. Subsequently, an intervention group of 62 patients were offered fortified food and snacks, providing an extra 22.2|g protein/day and 966 kcal/day in addition to the standard menu. Fortification significantly increased energy intake in the intervention group (P = 0.007, independent samples t-test), having the greatest effect on groups with the lowest energy intake, that is male and female orthopaedic, female medical and female elderly patients (84 cent of total). The increases in energy intake were 21.3 cent, 21.4 cent, 23 cent and 19.6 cent respectively. Although the increased energy and protein intake represented 25.6 cent and 22.5 cent respectively, of the supplements given, and suggested that wastage was high, it was nevertheless sufficient to remove energy deficit. We therefore propose that provision of fortified food and snacks is a convenient method of improving the nutritional intakes of hospital patients.

Artificial nutrition support in hospitals in the United Kingdom--1994: Third national survey.

OBJECTIVE: To determine how artificial nutrition support is used in hospitals in the United Kingdom and to determine whether there have been any alterations in practice when compared to similar studies in 1988 (1) and 1991 (2). DESIGN: A 94-question survey about artificial nutrition support (ANS) was sent to all district dietitians registered with the British Dietetic Association on 1 January 1994. Information was collected additionally from pharmacists, nutrition nurses and clinicians. RESULTS: 66.6% of questionnaires distributed were returned with analysable information. Of the respondents, 37.3% had access to nutrition support teams, compared with 27% in 1988. The documentation of usage of nutrition support was poor, only 33% of respondents being able to accurately quantify administration of enteral nutrition (EN), and 53% parenteral nutrition (PN). CONCLUSIONS: Despite increasing awareness about the role of artificial nutrition support, and the value of nutrition support teams there has only been a modest increase in the provision and monitoring of NSTs in the last 3 years. This has important implications when considering audit of such practices.

Artificial nutrition support in hospitals in the United Kingdom - 1991: Second national survey.

Objective - to determine current clinical practice of nutrition support in hospitals in the UK and to determine whether there have been any apparent changes in practices since 1988. Design - An 81 question survey about enteral and parenteral nutriton was sent to all District Dietitians registered with the British Dietetic Association. Information was collected additionally from pharmacists and clinicians. Results - 61.2% of questionnaires distributed were completed and returned. 32.5% of respondents had access to nutrition support teams, compared with 27% in 1988. The documentation of usage of nutrition support was poor, only 33% being able to accurately quantify administation of enteral nutrition, and 53% parenteral nutrition. Since 1988 the number of respondents using peripheral parenteral nutrition had doubled to 15%. Those using percutaneous gastrostomies had increased from 6% to 74%. Those using respiratory enteral diet formulations had quadrupled to 33%. There have been no other apparent major changes in nutrition support practice in the UK, in the last 3 years. Conclusions - Despite increasing awareness about the role of artificial nutrition support, and the value of Nutrition Support Teams there has been little or no progress in the provision or monitoring of support in the last 3 years. This has important implications when considering audit of such practices.

Immunonutrition: role of sulfur amino acids, related amino acids, and polyamines.

Pro-inflammatory cytokines mediate widespread changes in protein metabolism. Amino acids released from peripheral tissues fulfill a number of functions. They act as substrate for acute phase protein and immunoglobulin synthesis and, together with polyamines, in the replication of immune cells. Demands for specific amino acids may outstrip the supply from endogenous sources. A number of strands of evidence suggest that sulphur amino acids, and amino acids that are metabolically related to them, may be required in increased amounts. Protein deficiency impairs the acute phase response. However, sulfur amino acid insufficiency compromises glutathione synthesis, to a greater extent than hepatic protein synthesis, in the presence and absence of an inflammatory stimulus. The resulting effect may be compromised antioxidant defences. Functioning of T cells is dependent on intracellular glutathione concentrations and may also be affected by sulphur amino acid insufficiency. It has been suggested that the increased N excretion, which occurs during the immune response, is a reflection of a relative imbalance in the profile of amino acids released from peripheral tissues and the requirements imposed by the synthesis of substances involved in the acute phase response. Phenylalanine, tyrosine, tryptophan serine, and cysteine are released in amounts closest to requirements. Polyamine synthesis may be important for the fidelity of the enhanced level DNA transcription and RNA translation that occurs in response to infection and during tissue repair, gut growth after surgery, and in gut barrier functions. Although synthesized de novo from ornithine, arginine and S-adenosyl methionine (SAM), substantial recycling is a key feature of polyamine metabolism. The recycling may be a reflection of the need to maintain adequate tissue SAM during periods of rapid cell growth. During an immune/inflammatory response the combination of enhanced utilization of cysteine for glutathione synthesis and cell replication may lead to depletion of cellular SAM. A relatively small addition of polyamines to the diet may improve gut-associated aspects of the hosts' antibacterial defenses.

Influence of three different fiber-supplemented enteral diets on bowel function and short-chain fatty acid production.

BACKGROUND: Dietary fiber is known to influence bowel habit and gastrointestinal mucosal cell morphology and function. large-bowel function is particularly influenced by insoluble, poorly fermentable fiber sources, whereas mucosal function is affected by fiber sources that are soluble and highly fermentable. The aim of the present study was to compare bowel function during consumption of a self-selected diet, a fiber-free enteral diet, and three polymeric enteral diets, each supplemented with a fiber with different fermentation characteristics. The fiber sources used were oat, soy oligosaccharide, and soy polysaccharide. METHODS: Seven healthy subjects consumed four diets in random order for 4 to 7 days. These were a self-selected diet, a 2-L polymeric enteral diet, and a 2-L polymeric enteral diet supplemented with 15 g of total dietary fiber per liter derived from either soy oligosaccharide fiber (75 g/L) or oat fiber (15 g/L). An additional six healthy subjects were randomly assigned to three diets (4 to 7 days): a self-selected diet, a 2-L polymeric enteral diet, or the same 2-L polymeric enteral diet supplemented with 20 g of soy polysaccharide fiber per liter (15 g of total dietary fiber per liter). Bowel function was assessed by measuring whole-gut transit time, mean daily stool wet weights, and bowel movement frequency per day. Fermentation characteristics of the different fiber sources were determined quantitatively and qualitatively by measuring short-chain fatty acids produced during in vitro stool culture. RESULTS: Total short-chain fatty acid and butyric acid production with soy oligosaccharide fiber were significantly higher compared with values observed for soy polysaccharide fiber (p < .003), oat fiber (p < .005), and self-selected (control) diet (p < .003). Compared with the fiber-free diet, consumption of the soy polysaccharide, oat, and soy oligosaccharide-fiber-supplemented enteral diets did not significantly (p > .05) alter whole-gut transit time or stool wet weight. However, bowel frequency was significantly improved by consumption of the soy polysaccharide-fiber-supplemented diet but not the oat fiber or soy oligosaccharide-fiber-supplemented diets. CONCLUSION: Compared with a fiber-free polymeric enteral diet, the daily consumption of an enteral diet supplemented with 30 g of total dietary fiber per day derived from a poorly fermentable oat fiber, a highly fermentable soy oligosaccharide fiber, or a moderately fermentable soy polysaccharide fiber has little impact, if any, on bowel function.

Elemental diet administered nasogastrically without starter regimens to patients with inflammatory bowel disease.

The present study questions the concept of routinely using 'starter regimens' at the outset of enteral feeding with chemically defined elemental diets. A hypertonic elemental diet with an osmolality of 630 mOsm/kg was administered by 24-hr nasogastric infusion to 12 patients with exacerbations of inflammatory bowel disease and to two patients with short bowel syndrome. Starter regimens were not used. Upper gastrointestinal symptoms of nausea, abdominal bloating, and colicky pain occurred transiently in only five of 14 patients. Stool frequency did not increase during full-strength feeding, and daily stool weights decreased significantly (p less than 0.01). These findings show that it is safe to administer undiluted hypertonic elemental diets by constant nasogastric infusion to patients with inflammatory bowel disease. Avoiding starter regimens leads to increased nutrient intake and improved nitrogen balance.

Administration of fat emulsions with nutritional mixtures from the 3-liter delivery system in total parenteral nutrition.

A series of studies was performed to test the efficacy and safety of a parenteral lipid emulsion, Lipofundin S, when given as part of a complete nutritive mixture from the three-liter bag total parenteral nutrition (TPN) delivery system. In vitro stability studies with mixtures corresponding to high and low nutritional intakes showed the fat emulsion to be stable during refrigerated storage for at least 6 days. The clinical use of Lipofundin S in 3-liter TPN bags was studied in 39 consecutive patients requiring TPN, and there were no untoward side-effects. Nitrogen balance was maintained in patients with pancreatitis, those recovering postoperatively, and those with miscellaneous conditions. However, patients with multiple trauma remained in negative balance. The ability of sera, from patients on TPN to agglutinate Lipofundin S was compared to that from healthy controls, and acutely ill patients not on TPN. Patients on TPN showed a higher degree of in vitro creaming than acutely ill controls, and this may have been related to the severity of the underlying illness. These studies suggest that this parenteral lipid emulsion can be safely administered to patients requiring TPN when given from the 3-liter bag delivery system.

Assessment of an automated chemiluminescence nitrogen analyzer for routine use in clinical nutrition.

An automated method of chemiluminescence analysis of nitrogen used routinely for 4 yr. Liquid samples (urine, enteral, and parenteral feeds) required simple dilution, whereas feces required a modified acid-digestion procedure, before analysis. For urine samples, the coefficient of variation was within batch from 0.9-3.6%, and between batch 4.3-7.6%. At a sample injection rate of 2 microliter/sec, the useful dynamic range, for urine diluted 1:200, was 0-14 g N/liter. Precision for fecal nitrogen analysis was 3.8-6.7% for samples of low to high nitrogen content. The correlation between this technique and an established Kjeldahl method for fecal analysis was studied (r = 0.96, slope = 1.30). The discrepancy between the methods was due to inefficient conversion of nitrogen to NH4+ during Kjeldahl digestion of feces, rather than systematic errors in chemiluminescence analysis. Reliability was as good as for other automated clinical analyzers and sample cost was ca. 0.22 pounds. It has proved possible to analyze approximately 80 samples in the working day. The efficiency of measuring 24-hr urine urea-nitrogen (UUN) and total urine nitrogen (TUN) in patients on general wards was measured. Results were obtained on 87% of TPN days, but large variations were noted in UUN/TUN from less than 30% to greater than 90% (average 75.7%) in patients receiving TPN, and from less than 55% to 100% (average 83.8%) in patients receiving enteral nutrition. In contrast, UUN/TUN was 87.0% and 84.0% in healthy subjects, fasted or receiving iv nutrition, respectively. We therefore expect that clinical nutritionists will find increasing applications for this method of nitrogen analysis.

Dietary nucleotides and gut mucosal defence.

The informational aspects of nucleic acid synthesis have attracted much more attention than the quantitative significance of DNA, rRNA, tRNA, and nucleotide synthesis. Animal and human studies suggest that in energetic terms, 5-10% of the energy used in synthesising tissue protein is expended in manufacturing an appropriate amount of synthetic machinery, that is the ribosome and tRNA. The two sources for synthesis of nucleotides are salvage of nucleotides released by intracellular degradation or derived from the diet, and nucleotides synthesised de novo from amino acids (for example, glutamine) and sugars (glucose). The comparative importance of these two processes is not well defined, but rRNA production requires a high de novo input in cell types with the capacity for rapid division (for example, lymphocytes). The gut is unusual in requiring a ready arterial supply of nucleotides synthesised by hepatic de novo pathways. Animal studies show that an exogenous supply of nucleotides (salvage) can improve liver regrowth, immune responsiveness to a microbial challenge, and gut morphology in diarrhoea models. Humans adapt to dietary nucleotide intake by downregulating de novo pathways. All total parental nutrition regimens, and most enteral regimens lack nucleotides, which may predispose to an inadequate supply of preformed nucleotides to gut and immune cells in the critically ill, artificially fed patient. Unfortunately, there are no clinical studies that answer this point at present.

Methods for assessing intestinal absorptive function in relation to enteral nutrition.

The success of nasoenteral nutrition support can be limited by intestinal impairment. In particular, reduced absorptive area, mucosal atrophy and abnormal motility may reduce absorption of macronutrients and micronutrients, and diarrhoea remains a commonly encountered complication. We review how basic physiological techniques can be used to investigate such pathophysiology. Lumenal nutrients control mucosal growth, expression of mucosal transporters and regional gut motility. Cell biology techniques now complement classical intestinal perfusion methods in determining the 'safety factor' of excess absorptive capacity. The controversial role of the sodium-glucose linked transporter in dietary glucose assimilation is described in terms of its control, its true function and its role in uptake of other solutes. Techniques that involve brush-border membrane vesicles, Caco-2 cells, mucosal immunohistochemistry and gene expression probes are described. Together, these techniques describe a picture of an organ with remarkable ability to maintain digestive and absorptive function in response to a wide variety of nutritional intakes, often in the face of inflammatory illness.

Nucleotides as immunomodulators in clinical nutrition.

Dietary nucleotides, like glutamine, have attracted attention as a key ingredient missing from nutritional formulae for many years. They are the building blocks of tissue RNA and DNA and of ATP and their presence in breast milk has stimulated research in babies which has indicated that supplementation of infant formula milk leads to improved growth and reduced susceptibility to infection. Animal studies have confirmed some of these data. In particular, dietary nucleotides modulate immune function, promote faster intestinal healing and have trophic effects on the intestine of parenterally-fed rats which are similar to those resulting from glutamine supplementation, but at much lower intakes. Nucleotide supplementation has also been shown to improve some aspects of tissue recovery from ischaemia/reperfusion injury or radical resection. There is, however, a fundamental paradox. The intestine and liver possess powerful homeostatic mechanisms which degrade intake of purines and pyrimidines (i.e. salvage) and replace it with de novo synthesised output. It is possible that peripheral tissues receive only small amounts of nucleotides of dietary origin. Previously, nucleotides have been proposed as being conditionally-essential nutrients that provide an adequate supply of purines and pyrimidines for nucleic acid synthesis in neonates or in the stressed patient. This review explores this puzzle in the light of recent data from nutritional studies and from research into purinergic signalling in the intestine, heart and cells of the immune system. We propose that dietary nucleotides should be considered within a pharmacological and metabolic framework.

Methods for measuring tissue RNA turnover.

Measuring RNA turnover is important because of the significance of rRNA, tRNA and mRNA in tissue protein synthesis. Changes in turnover of each of these species precede important cellular events such as hormone or cytokine action or cell-division itself. Isotopic methods have relied on decay of pulse-labelled RNA or on incorporation of isotopically-labelled precursors. However, recycling of labels may lead to under or overestimation of synthesis rates respectively. The labelling of the intracellular precursor pool must be known if accurate RNA synthesis rates are to be calculated from the degree of incorporation. However, the intracellular nucleotide pools may be anatomically or metabolically compartmented (i.e. via de novo or salvage synthesis routes) and this complicates many study designs. The use of[methyl-14C]- or [methyl-3H]methionine as a means of labelling methylated nucleosides in RNA and protein simultaneously is described in addition to new stable isotopic techniques based on 13C-glycine as a de novo label. Urinary excretion of the numerous modified nucleosides in cellular RNA can be used to calculate whole-body turnover rates of each of the major RNA species. Examples of the effects of critical-illness and glutamine supplementation on RNA turnover are given. We conclude by suggesting that whole-body RNA turnover rates have been significantly underestimated and that this has implications for nutritional therapy, especially with regard to nucleotide supplementation.