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.