Effect of oral supplementation of ornithine-alpha-ketoglutarate on the intestinal barrier after orthotopic small bowel transplantation

Gastrointestinal disorders of the critically ill. Bacterial translocation in the gut

The human gastrointestinal tract is colonized by a dense population of microorganisms, referred to as the bacterial flora. Although the gut provides a functional barrier between these organisms and the host, bacterial translocation is a common event in the healthy person. However, in critically ill patients, with various underlying diseases, this bacterial translocation may lead to infections and consequently to a further reduction in general health status. The mechanism of bacterial translocation is widely, and somehow controversially investigated in vitro and in animal models. In human studies, several diseases have been associated with bacterial translocation. However, methodological shortcomings, insufficient populations and conflicting results leave many open questions. This is also reflected in the various published therapeutic strategies. To overcome this problem more investigations in humans are needed, especially in techniques for detecting bacterial translocation.

Bacterial translocation in clinical intestinal transplantation

BACKGROUND

Bacterial translocation (BT) has been suggested to be responsible for the high incidence of infections occurring after small bowel transplantation (SBTx). Bacterial overgrowth, alteration of the mucosal barrier function as a consequence of preservation injury or acute rejection (AR), and potent immunosuppression are all associated with BT. The aim of this study was to evaluate and quantify the correlation of BT with these events.

METHODS

Fifty pediatric SBTx recipients on tacrolimus and prednisone immunosuppression were analyzed. Blood, stool, and liver biopsies and peritoneal fluid were cultured (circa 4000 total specimens) when infection was clinically suspected or as part of follow-up. BT episodes were considered when microorganisms were found simultaneously in blood or liver biopsy and stool.

RESULTS

BT (average of 2.0 episodes/patient) was evident in 44% of patients and was most frequently caused by Enterococcus, Staphylococcus, Enterobacter, and Klebsiella. The presence of a colon allograft was associated with a higher rate of BT (75% vs. 33.3%). Furthermore, the transplantation procedure (colon vs. no colon) affected the rate of BT: SBTx=40% vs. 25%, combined liver and SBTx=100% vs. 30%, multivisceral transplantation=25% vs. 50%. AR was associated with 39% of BT episodes. BT followed AR in 9.6% of the cases. In 5.2% of the cases, positive blood cultures without stool confirmation of the bacteria were seen. Prolonged cold ischemia time (CIT) affected BT rate significantly (CIT>9 hr 76% vs. CIT<9 hr 20.8%).

CONCLUSIONS

This study shows that 1) a substantial percentage of, but not all, BT is associated with AR, 2) the presence of a colon allograft increases the risk for BT, and 3) a long CIT is associated with a high incidence of BT after SBTx.

Bacterial dissemination and metabolic changes in rats induced by endotoxemia following intestinal E. coli overgrowth are reduced by ornithine alpha-ketoglutarate administration

The efficacy of ornithine alpha-ketoglutarate (OKG) in preventing bacterial translocation and dissemination, metabolic disorders and changes in mucosal enzyme activities was assessed in a model of bacterial translocation in rats. Antibiotic decontamination was performed 4 d before intragastric inoculation with an Escherichia coli strain (10(10) bacteria/kg body). Two days later, the rats were given either a lipopolysaccharide (LPS) 0127:B8 or a saline injection and were deprived of food for 24 h. Enteral nutrition, [Osmolite, 880 kJ/(kg. d)] supplemented with either OKG (LPS + OKG) or glycine (Saline + Gly or LPS + Gly), was then given for 2 d. Urinary total nitrogen losses and 3-methylhistidine excretion were determined daily. On killing at d 3, bacterial translocation to the mesenteric lymph nodes (MLN) and dissemination to the spleen and liver were evaluated, jejunal mucosa enzyme activities were assayed and tissue free amino acids in muscles were measured. Endotoxin induced translocation from the gut lumen to the MLN in all groups, whereas dissemination occurred only in LPS-treated rats. OKG significantly reduced dissemination of the bacteria in the spleen. 3-Methylhistidine excretion was greater in the LPS + Gly group (+25%, P: < 0.05) than in either the LPS + OKG or Saline + Gly group. The group fed the OKG-enriched diet had higher muscular glutamine, ornithine and arginine concentrations than did the Gly-supplemented groups (P: < 0.05). Intestinal sucrase and aminopeptidase activities were higher in the LPS + OKG group than in the LPS + Gly group (-30%, P: < 0.05). OKG supplementation limits bacterial dissemination and metabolic changes after injury in rats and thus may be useful in the prevention of gut-derived sepsis in critically ill patients.

The use of alpha-ketoglutarate salts in clinical nutrition and metabolic care

Theoretically, alpha-ketoglutarate is a precursor of glutamine, a fact that may be of importance given the key regulatory properties of this amino acid. Although the literature suggests that glutamine synthesis accounts only for a marginal part of the disposal of exogenously supplied alpha-ketoglutarate, administered alpha-ketoglutarate has a potent 'sparing' effect on endogenous glutamine pools. When alpha-ketoglutarate is supplied as an ornithine salt, a synergistic effect of the two parts of the molecule increases the synthesis of glutamine or the 'sparing' of endogenous glutamine pools. In addition, alpha-ketoglutarate in combination with ornithine dramatically increases the synthesis of arginine, proline and polyamines, which also play key roles in metabolic adaptation to trauma. The recent literature suggests that the administration of alpha-ketoglutarate in combination with ornithine improves gut morphology and functions, counteracts trauma-induced dysimmunity and exerts anabolic/anticatabolic actions on protein metabolism.

Enteral ornithine alpha-ketoglutarate enhances intestinal adaptation to massive resection in rats

Ornithine alpha-ketoglutarate (OKG) has been advocated in the treatment of critically ill patients for its anabolic effect on protein metabolism. Since OKG is a precursor of glutamine, arginine, and polyamines, key substrates of intestinal metabolism and function, we investigated the influence of OKG on intestinal adaptation and trophicity and on glutamine status after small bowel resection. After massive (80%) small bowel resection, rats were enterally fed for 7 days with a standard diet supplemented with either OKG (2 g/kg/d) or an isonitrogenous amount of glycine. OKG induced an adaptative hyperplasia of the villi, demonstrated in the jejunum by an increase in the villus height to crypt depth ratio (OKG v control, 4.3+/-0.4 v 3.3+/-0.5, P < .01) along with an increase (P < .05) in ornithine decarboxylase (ODC) activity (+80%) and ornithine content (+102%). Plasma glutamine (+25%) and muscle glutamine (anterior tibialis [AT], +43%; extensor digitorum longus [EDL], +54%) and protein (AT, +32%) were significantly higher (P < .05) after OKG administration, supporting its role in the restoration of glutamine pools. In summary, enterally administered OKG, which enhances intestinal adaptation after massive resection and improves muscle glutamine and protein content, could contribute significantly to nutritional management after small bowel resection.

Amino acids with anabolic properties

Experimental studies have clearly demonstrated both the indispensability in stress situations of amino acids, previously considered to be non-essential, and the importance of the specific properties of these same amino acids. Glutamine, arginine and their precursors/metabolites, ornithine and alpha-ketoglutarate, exert anabolic or anticatabolic effects through their involvement in protein metabolism, in the immune response and in cell proliferation. Clinical studies suggest that the supplementation of nutritional therapy with these amino acids can be of significant benefit for injured patients.