Update on host defense and immunonutrients

Metabolic implications of severe burn injuries and their management: a systematic review of the literature

BACKGROUND

Severe burn patients are some of the most challenging critically ill patients, with an extreme state of physiologic stress and an overwhelming systemic metabolic response. A major component of severe burn injury is a hypermetabolic state associated with protein losses and a significant reduction of lean body mass. The second prominent component is hyperglycemia. Reversal of the hypermetabolic response by manipulating the patient's physiologic and biochemical environment through the administration of specific nutrients, growth factors, or other agents, often in pharmacologic doses, is emerging as an essential component of the state of the art in severe burn management. The present review aims at summarizing the new treatment modalities established to reduce the catabolic burden of severe burn injuries, for which there is some evidence-based support.

METHODS

A systematic review of the literature was conducted. Search tools included Elsevier ScienceDirect, EMBASE.com, Medline (OVID), MedlinePlus, and PubMed. Topics searched were Nutrition and Burns, Metabolic Response and Burns, Hypermetabolism and Burns, Hyperglycemia and Burns, and several more specific topics when indicated. With a focus on the most recently published articles, abstracts were reviewed and, when found relevant, were included as references. Full text articles, whenever available, were retrieved.

RESULTS

Many issues remain unanswered. Unfortunately, the present state of our knowledge does not allow the formulation of clear-cut guidelines. Only general trends can be outlined, and these will certainly have some practical applications but above all will dictate future research in the field.

Necrotizing enterocolitis: a practical guide to its prevention and management

Neonatal necrotizing enterocolitis is the second most common cause of morbidity in premature infants and requires intensive care over an extended period. Despite advances in medical and surgical techniques, the mortality and long-term morbidity due to necrotizing enterocolitis remain very high. Recent advances have shifted the attention of researchers from the classic triad (ischemia, bacteria, and the introduction of a metabolic substrate into the intestine) of necrotizing enterocolitis, to gut maturation, feeding practices, and inflammation. The focus on inflammation includes proinflammatory cytokines such as tumor necrosis factor-alpha, interleukin (IL)-6, IL-18, and platelet-activating factor. Research related to the etiology of necrotizing enterocolitis has moved quickly from clostridial toxin to bacterial and other infectious agents. More recently, the pattern of bacterial colonization has been given emphasis rather than the particular species or strain of bacteria or their virulence. Gram-negative bacteria that form part of the normal flora are now speculated as important factors in triggering the injury process in a setting where there is a severe paucity of bacterial species and possible lack of protective Gram-positive organisms. Although the incidence of necrotizing enterocolitis has increased because of the survival of low birthweight infants, clinicians are more vigilant in their detection of the early gastrointestinal symptoms of necrotizing enterocolitis; however, radiographic demonstration of pneumatosis intestinalis remains the hallmark of necrotizing enterocolitis. With prompt diagnosis, a large proportion of infants with necrotizing enterocolitis are now able to be managed medically with intravenous fluid and nutrition, nasogastric suction, antibacterials, and close monitoring of physiologic parameters. In the advanced cases that require surgery, clinicians tend to opt for either simple peritoneal drainage (for very small and sick infants) or laparotomy and resection of the affected part. Intestinal transplantation later in life is available as a viable option for those who undergo resection of large segments of the intestine. It is becoming more evident that treatment of this devastating disease is expensive and comes with the toll of significant long-term sequelae. This has resulted in renewed interest in designing alternative strategies to prevent this serious gastrointestinal disease. Simple trophic feeding and the use of L-glutamine and arginine are novel avenues that have been examined. The use of probiotics ('friendly' bacterial flora) has been introduced as a promising tool for establishing healthy bacterial flora in the newborn gut to block the injury process that may ultimately lead to necrotizing enterocolitis.

Changes in intestinal morphology and permeability in the biobreeding rat before the onset of type 1 diabetes

OBJECTIVE

Type 1 diabetes is an autoimmune disorder that occurs in genetically susceptible individuals. It has been hypothesized that the disease could be triggered by environmental agents that gain entry into the body through small intestinal absorption. Increased intestinal permeability has been reported both in spontaneous animal models of type 1 diabetes and human type 1 diabetes. In these studies, we examined both the physical and functional permeability characteristics of the small intestine in diabetes-prone and control rats.

METHODS

In a series of studies, BioBreeding diabetes-prone(n = 31), BioBreeding diabetes-resistant (n = 20) and control Wistar (n = 25) rats were examined at intervals from 21 to 125 days of age.

RESULTS

The percentage of goblet cells and the mucosal crypt depth were significantly greater in BioBreeding diabetes-prone than BioBreeding diabetes-resistant rats (P < 0.001 and P = 0.01, respectively). BioBreeding diabetes-prone and BioBreeding diabetes-resistant rats expressed less of the tight junction protein claudin (P < 0.05) and exhibited greater intestinal permeability (P < 0.001) than did Wistar rats. Intestinal permeability measured both in vivo and ex vivo decreased in all rat strains as age increased (P < 0.001).

CONCLUSIONS

In a genetically susceptible rodent model of diabetes, early increased intestinal permeability might allow unregulated passage of environmental antigens that could potentially trigger the autoimmune response leading to type 1 diabetes.

New perspectives on nutrition enhance outcomes for premature infants

Significant advances have occurred during the past 20 years in the understanding of the complex relationships of the environment, the developing gut-associated immune system, the bacterial flora, the barrier functions of the gut, and the effects of nutrient intake. These advances have produced a profoundly different way of interpreting the nutritional requirements for normal growth and development of premature infants throughout their entire life.

Protective nutrients

Recognition that specific nutrients can be beneficial when consumed in amounts above the accepted daily requirements has provided a major impetus for the critical examination of dietary approaches with single or multiple nutrient supplements chosen to modulate the inflammatory response, enhance immune function, or improve the blood-gut barrier. Patients suffering the effects of hypercatabolism caused by surgery, cancer, or extensive burns are prime candidates for immunonutrition, as the intervention has come to be known, as are immunosuppressed patients with the human immunodeficiency virus or other overwhelming infections. This review focuses on key nutrients used in clinical trials for which a body of information on the mode of action and metabolic pathways is available. The topics covered include the amino acids, glutamine and arginine; omega-3 fatty acids, eicosapentaenoic acid and docosahexanoic acid; vitamin A; and zinc. Lastly, we address the area of pre- and probiotics and how "friendly" microorganisms are being incorporated into therapeutic regimens aimed at sustaining health. The use of immunonutrition requires judicious consideration of the potential undesirable effects of certain additives in clinical settings where enhanced immune responsiveness can translate into tissue damage and altered mucosal defenses.