Acides aminés et immunité

Modulation of immune response with ornithine A-ketoglutarate in burn injury: an arginine or glutamine dependency?

Enterally administered ornithine alpha-ketoglutarate (OKG) is an efficient complement of nutritional support in trauma situations, especially after burn injury. A typical feature observed in this intense catabolic state is insufficient production of glutamine (Gln) and arginine (Arg), two amino acids (AAs) involved in the immune response. As OKG in vivo metabolism generates these two AAs, we investigated, in burned rats, the action of OKG with regard to modulation of immunity. Male Wistar rats were randomly allocated to four groups. On day 0, 12 rats were burned with boiling water (20% body surface area). After a 24-h fast, they were enterally refed for 48 h using Osmolite, as a low-calorie low-nitrogen regimen, supplemented with either 5 g OKG x kg(-1) x d(-1) (n = 6) or an equivalent amount of nitrogen in the form of glycine (n = 6). Non-burned pair-fed controls treated with glycine (n = 6) and healthy rats fed ad libitum (n = 6) were also studied. Nitrogen balance was assessed from daily measurement of total nitrogen excretion. On day 3, thymus, Anterior tibialis muscle and proximal jejunum weights were recorded. Muscle and intestinal AA concentrations were also quantified. OKG counteracted (P<0.01) the thymic involution that occurs with burn injury, and increased the concentrations of Gln and Arg in both the muscle (P<0.01 and P<0.05, respectively) and the jejunum (P<0.01 for Gln). When all groups were taken together, a positive correlation was found between thymus weight, and Gln and Arg muscle concentrations (r = 0.71, P<0.001 and r = 0.58, P<0.01, respectively). Furthermore, as expected, OKG improved nitrogen balance. As it is known that total number of thymocytes parallels thymic weight, and as Gln and Arg are essential nutrients for activated immune cells, our results suggest that Gln and Arg derived from OKG are responsible for the immunomodulating properties of this molecule in burn injury.

Bacterial dissemination, rather than translocation, mediates hypermetabolic response in endotoxemic rats

OBJECTIVE

To study the pathogenesis of the host response during bacterial translocation, a rat model was designed for prolonged follow-up after injury.

DESIGN

A prospective, controlled animal study.

SETTING

Animal laboratory.

SUBJECTS

Young male Wistar rats.

INTERVENTIONS

Antibiotic decontamination of rats was performed 4 days before intragastric inoculation with a selected Escherichia coli strain (10(10) bacteria/kg of body weight). Two days later, the rats received a lipopolysaccharide injection or not (control group) and were observed for 3 days. They were then killed. A reference group (pair-fed healthy animals) was studied in parallel.

MEASUREMENTS AND MAIN RESULTS

During observations, urinary total nitrogen loss and 3-methylhistidine excretion were determined daily. When the rats were killed, mesenteric lymph nodes (MLNs), spleen, and liver were aseptically removed and cultured. Colonies identified as translocated E. coli were counted in each organ. Intracellular amino acid free pools were measured in extensor digitorum longus and anterior tibialis. Endotoxin induces bacterial translocation of bacteria from gut lumen to MLNs (100% vs. 59% in the lipopolysaccharide-untreated control group; p < .05) and dissemination to spleen and liver (65% and 45% of positive cultures after endotoxemia, respectively, vs. 6% and 12% in the control groups). No translocation occurred in the reference group. Evidence for the hypermetabolic response was seen in lipopolysaccharide-treated and infected rats, but protein catabolism was more closely related to the occurrence of bacterial dissemination to spleen and liver than to translocation alone (e.g., the cumulative 3-methylhistidine excretion during the observation period was 4.07+/-0.18 micromol in uninfected rats, 4.48+/-0.29 in rats with positive MLN cultures alone and 6.17+/-0.30 in MLN, spleen, or liver infected rats; 1 vs. 2, NS; 3 vs. 1, and 3 vs. 2, p < .05).

CONCLUSIONS

Gut barrier failure is associated with a deep excessive catabolic response in the host. The mechanism by which the metabolic state affects the resistance to infection apparently involves amino acid metabolism.