Glutamine: metabolism and application in nutrition support.

Glutamine is the most abundant free amino acid in the body. It is avidly consumed by rapidly dividing cells, such as those lining the gut, because its 5-carbon skeleton can provide energy whilst the nitrogen molecules support the synthesis of nucleic acids. Patients who are maintained using conventional solutions of parenteral nutrients become depleted in glutamine, which has led to the reclassification of glutamine as a conditionally essential nutrient. Unfortunately, glutamine is unstable in solution and produces toxic byproducts on decomposition. This means that solutions of nutrients containing glutamine have a relatively short half-life, which has led to the commercialisation of stable dipeptides containing glutamine. Although it is evident that glutamine enhances nitrogen metabolism, there is a lack of consistent evidence from the initial clinical trials demonstrating that supplementation with glutamine has specific clinical advantages. The next few years will witness the performance of larger scale clinical trials and the results of these studies should define a more certain role for glutamine in routine clinical practice.

Role of specific amino acids in nutritional support.

Attempts have been made over the past decade to evaluate the role of specific amino acids in the nutritional support of surgical patients. Particular attention has been paid to the branched-chain amino acids, glutamine, and a collection of compounds that have been referred to as 'immunonutrients'. The present review provides an overview of the rationale behind the use of these nutrients and reviews information about their role in patients undergoing surgery. In general, although the use of immunonutrients enhances the nutritional status of patients, and although a number of clinical trials have claimed clinical advantages, there are still doubts about their clinical utility and concerns about their high cost.

Glutathione.

Glutathione (GSH) is an ubiquitous thiol-containing tripeptide that plays a key role in cell biology. It modulates cell response to redox changes associated with the reactive oxygen species, detoxifies the metabolites of drugs; regulates gene expression and apoptosis, and is involved in the transmembrane transport of organic solutes. Polymorphism has been observed in key enzymes of GSH metabolism and some alleles have been associated with an impaired redox buffer system downsteam diseases, and susceptibility to ischaemia. These varied activities make GSH an attractive target for a more reductionist approach to the prevention and management of many conditions of interest to surgeons.

The role of glutathione in intestinal dysfunction.

Glutathione plays an important cytoprotective role in the gut. Animal studies have demonstrated that the provisions of glutathione precursors are protective for different types of free-radical-mediated cellular injury. There is a need to clarify the potential role of glutathione supplementation in ischemia-reperfusion injury and inflammatory bowel disease. More speculative is whether treatment with glutathione precursors can modify the progress of colorectal cancer.

The management of patients with the short bowel syndrome.

The surgeon is invariably the primary specialist involved in managing patients with short bowel syndrome. Because of this they will play an important role in co-ordinating the management of these patients. The principal aims at the initial surgery are to preserve life, then to preserve gut length, and maintain its continuity. In the immediate postoperative period, there needs to be a balance between keeping the patient alive through the use of TPN and antisecretory agents and promoting gut adaptation with the use of oral nutrition. If the gut fails to adapt during this period, then the patient may require therapy with more specific agents to promote gut adaptation such as growth factors and glutamine. If following this, the patient still has a short gut syndrome, then the principal options remain either long term TPN, or intestinal transplantation which remains a difficult and challenging procedure with a high mortality and morbidity due to rejection.