Action of enterally administered ornithine alpha-ketoglutarate on protein breakdown in skeletal muscle and liver of the burned rat

Alpha-Ketoglutarate as a Molecule with Pleiotropic Activity: Well-Known and Novel Possibilities of Therapeutic Use

Alpha-ketoglutarate (AKG), an endogenous intermediary metabolite in the Krebs cycle, is a molecule involved in multiple metabolic and cellular pathways. It functions as an energy donor, a precursor in the amino acid biosynthesis, a signalling molecule, as well as a regulator of epigenetic processes and cellular signalling via protein binding. AKG is an obligatory co-substrate for 2-oxoglutarate-dependent dioxygenases, which catalyse hydroxylation reactions on various types of substrates. It regulates the activity of prolyl-4 hydroxylase, which controls the biosynthesis of collagen, a component of bone tissue. AKG also affects the functioning of prolyl hydroxylases, which, in turn, influences the function of the hypoxia-inducible factor, an important transcription factor in cancer development and progression. Additionally, it affects the functioning of enzymes that influence epigenetic modifications of chromatin: ten-eleven translocation hydroxylases involved in DNA demethylation and the Jumonji C domain containing lysine demethylases, which are the major histone demethylases. Thus, it regulates gene expression. The metabolic and extrametabolic function of AKG in cells and the organism open many different fields for therapeutic interventions for treatment of diseases. This review presents the results of studies conducted with the use of AKG in states of protein deficiency and oxidative stress conditions. It also discusses current knowledge about AKG as an immunomodulatory agent and a bone anabolic factor. Additionally, the regulatory role of AKG and its structural analogues in carcinogenesis as well as the results of studies of AKG as an anticancer agent are discussed.

Effects of ornithine alpha-ketoglutarate on protein metabolism in Yoshida sarcoma-bearing rats

BACKGROUND & AIMS

Ornithine alpha-ketoglutarate (OKG) is recognized to improve nutritional status in various catabolic states, such as burn injury, trauma, and sepsis. However, in wasting diseases, such as induced by cancer, the data are scarce and the precise mechanisms by which OKG acts on protein metabolism are still unclear. The aim of this study was to evaluate the ability of OKG to affect protein metabolism in an aggressive model of cancer and to modulate the ubiquitin-proteasome-dependent pathway, which in skeletal muscle is the critical degradative pathway implicated in many catabolic states, including cancer-associated cachexia.

METHODS

Experiments were carried out in Yoshida sarcoma-bearing and healthy pair-fed rats. Three groups of 16 young male rats were studied during 9 days following tumor implantation: two groups of tumor-bearing rats fed a balanced regimen enriched with either OKG (5 g/kg body weight/day, OKG-K) or an isonitrogenous mixture of non-essential amino acids (C-K), and one group of healthy pair-fed rats (PF).

RESULTS

As expected, Yoshida sarcoma induced muscle atrophy, decreased nitrogen balance, enhanced 3-methylhistidine (3-MH) excretion and increased mRNA levels for ubiquitin and 14-kDa ubiquitin-conjugating enzyme E2. OKG supplementation did not improve muscle mass or protein balance and did not reduce enhanced 3-MH excretion in Yoshida sarcoma-bearing rats. Furthermore, OKG did not suppress in the cancer rats the enhanced expression of ubiquitin and 14-kDa E2, despite OKG decreased by 23% the ubiquitination rate in cancer rats (OKG-K vs. C-K, P<0.05).

CONCLUSIONS

These data suggest that OKG action is not universal; i.e. depending upon the model under study. In the circumstances, OKG did not counteract the increase in ubiquitin-proteasome-dependent proteolysis observed in Yoshida sarcoma-bearing rats.

Effect of an immune-enhancing diet on lymphocyte in head-injured rats: What is the role of arginine?

OBJECTIVE

The benefit of immune-enhancing diets (IEDs) in the intensive care unit remains controversial. Considering their complexity, the role of each component, in particular arginine (Arg), in their properties is largely unknown. The aim of this study was to determine the role of arginine in the immunomodulatory effects of an IED (Crucial) in head-injured rats.

DESIGN

Thirty-four rats were randomized into five groups: AL (ad libitum), HI (head-injured), HI-STD (HI + standard enteral nutrition, EN), HI-STD-Arg (HI + standard EN + Arg in equimolar concentration to Arg in IED), and HI-IED (HI + IED). These isocaloric and isonitrogenous diets were administered over 4 days. After death, the thymus was removed and weighed. The density of CD25, CD4 and CD8 on lymphocytes from blood and from Peyer patches was evaluated. Mesenteric lymph nodes, liver and spleen were cultured for analysis of enterobacterial translocation and dissemination.

MEASUREMENTS AND RESULTS

HI induced an atrophy of the thymus which was not corrected by the standard diet (HI 0.27 +/- 0.03, HI-STD 0.35 +/- 0.03 vs. AL 0.49 +/- 0.02 g; p < 0.05). However, the standard diet supplemented with arginine limited the thymic atrophy and the IED restored thymus weight. CD25 density and interleukin-2 production were increased only in the HI-STD-Arg and HI-IED groups (p < 0.05). Head injury induced enterobacterial translocation and dissemination which were blunted only in the HI-STD-Arg group (p < 0.05).

CONCLUSIONS

In this rat HI model, arginine appears to be safe, contributes to a large extent to the immunomodulatory effects of the IED, and seems to limit enterobacterial translocation and dissemination more efficiently alone than in an IED.

Dose dependency of the effect of ornithine α-ketoglutarate on tissue glutamine concentrations and hypercatabolic response in endotoxaemic rats

The optimal dosage of ornithine α-ketoglutarate (OKG) for repleting tissue glutamine (Gln) concentrations and maintaining N homeostasis after injury is unknown. We set out to perform ‘dose-ranging’ of OKG supplementation after an endotoxaemic challenge. Sixty-one male Wistar rats were injected with 3 mg lipopolysaccharide (LPS) from Escherichia coli/kg (n 50) or saline vehicle (9 g NaCl/l; controls n 11). After a 24 h fast, survivors were fed by gavage for 48 h with a polymeric standard diet (879 kJ/kg per d and 1·18 g N/kg per d) supplemented with non-essential amino acids (control, n 11; LPS-OKG-0·0, n 9), or with 0·5 g OKG/kg per d (LPS-OKG-0·5, n 12), 1·5 OKG/kg per d (LPS-OKG-1.5, n 11) or 4·5 g OKG/kg per d (LPS-OKG-4·5, n 10). The diets for all groups were made isonitrogenous with the LPS-OKG-4·5 diet by adding an appropriate amount of non-essential amino acids. Rats were killed on day 3 for blood and tissue sampling (muscle, jejunum mucosa, liver). Urine was collected daily for 3-methylhistidine and total N assays. The OKG dose was correlated with Gln concentrations in every tissue and with cumulative N balance (Spearman test, P<0·01). 3-Methylhistidine excretion was increased in endotoxaemic groups compared with controls (ANOVA, P<0·05) except in the LPS-OKG-4·5 group. Only the LPS-OKG-4·5 group achieved a positive post-injury N balance (t test, P<0·05). In conclusion, OKG exerted a dose-dependent effect on tissue Gln concentration and N balance, but only the highest dosage counteracted myofibrillar hypercatabolism and caused a positive N balance.

Does the ornithine-alpha-ketoglutarate ratio influence ornithine alpha-ketoglutarate metabolism in healthy rats?

Ornithine alpha-ketoglutarate (OKG) is a salt composed of 2 molecules of ornithine (ORN) and one molecule of alpha-ketoglutarate (alphaKG). OKG has been used successfully via oral, enteral, and parenteral routes to improve protein status in patients with chronic and acute protein depletion, but its mechanism of action, which is probably multifactorial, is still unclear. A specific metabolic interaction between alphaKG and ORN has been shown to be a key factor in the effects of OKG, but the impact of the ORN/alphaKG ratio (2 molecules of ORN for 1 molecule of alphaKG) has never been discussed. To clarify this point, young (3 weeks old) male Wistar rats in the postabsorptive state received 5 g/kg of either OKG or a mono-ornithine alphaKG (MOKG) salt (ORN/alphaKG ratio = 1:1) in amounts that were either isonitrogenous or isomolar to OKG, or a saline solution (controls) and were killed 1 hour later. In a second experiment, a kinetic study was performed in which rats were killed 1, 2, 3, or 6 hours after OKG, MOKG, or saline administration. Amino acid contents were analyzed in the plasma, liver, jejunal and ileal mucosae, and the extensor digitorum longus (EDL) muscle. The major metabolites detected after intake of OKG or MOKG (ie, ORN, proline [PRO], and glutamate; OKG and MOKG vs control, P < .05) together with the absence of increased arginine and citrulline levels suggested that ORN was mainly metabolized by the ORN aminotransferase pathway, leading to glutamate and PRO production with accumulation persisting at 6 hours postadministration. This study provides new and important data on the influence of the ORN/alphaKG ratio on OKG metabolism: MOKG-treated rats presented less intestinal ORN than OKG-treated rats (MOKG vs OKG, P < .05), suggesting that ORN/alphaKG ratio influences the rate of ORN availability and metabolism. In addition, the metabolic interaction between ORN and alphaKG (ie, in the presence of alphaKG, ORN metabolism is partially diverted toward PRO production), which is characteristic of OKG metabolism, still takes place even if the salt contains only 1 molecule of ORN instead of two.

Pretreatment of starved rats with ornithine alpha-ketoglutarate: effects on hepatic mRNA levels and plasma concentrations of three liver-secreted proteins

OBJECTIVE

Ornithine alpha-ketoglutarate (OKG) displays anabolic properties at the hepatic level, but the mechanisms involved remain unclear. This study investigated in vivo the ability of OKG to modulate hepatic gene expression of three liver-secreted proteins: albumin, transthyretin, and retinol binding protein.

METHODS

One hundred eighty rats were fed for 5 d with a balanced regimen enriched with OKG (5 g.kg(-1).d(-1)) or an isonitrogenous mixture (alanine, glycine, and serine). Hepatic mRNA levels and plasma concentrations of the three proteins studied were determined at the end of the nutrition period and after 1, 2, and 3 d of food deprivation. Results were compared by analysis of variance and Bonferroni-Dunn tests.

RESULTS

At the end of the nutrition period, hepatic mRNA levels and plasma concentrations of the three proteins were not modified by OKG supplementation. However, OKG largely increased mRNA levels of albumin, transthyretin, and retinol binding protein on the first day of starvation compared with control animals (+68%, +64% and +51%, respectively; P < 0.01 versus control). OKG precociously increased albuminemia (on day 2) but had no effect on plasma concentrations of transthyretin and retinol binding protein. Neither regulation of polyamine hepatic concentration nor alteration in hepatic amino acid content seemed to be implicated in these actions.

CONCLUSION

This study is the first to demonstrate that OKG regulates in vivo liver gene expression during acute malnutrition by modulating hepatic mRNA levels.

Ornithine alpha-ketoglutarate metabolism in the healthy rat in the postabsorptive state

To gain further insight into the ability of ornithine alpha-ketoglutarate (OKG) to generate key metabolites, the aim of this work was to study the short-term metabolism, that is, 1 hour after administration, of OKG in plasma and tissues. Particular attention was paid to keto acids (alpha-ketoglutarate and branched-chain keto acids). Young (3 weeks old) male Wistar rats in the postabsorptive state received either 1.5 g/kg of monohydrated OKG (OKG group, n = 8) diluted in distilled water or an equivalent volume of saline solution at 0.9% (control group, n = 8) by gavage and were killed 1 hour later. Plasma, liver, jejunal and ileal mucosa, and the extensor digitorum longus muscle were removed to analyze amino and keto acid contents. Major metabolites detected after OKG ingestion (ornithine [ORN], alpha-ketoglutarate, proline and glutamate; OKG vs control, P < .05) and the absence of increased arginine (and even a decrease in jejunum and muscle) and citrulline levels suggested that ORN was mainly metabolized by the ORN aminotransferase pathway. In addition, significantly decreased plasma branched-chain keto acids and increased hepatic branched-chain amino acids (OKG vs control, P < .05) were observed upon OKG ingestion. Finally, glutamine accumulation restricted to the intestine, as evidenced in this short-term study, suggests that the effects of OKG on glutamine pools in other tissues in various pathological states after several days of treatment, as observed in previous studies, may be related to a long-term induction of glutamine synthetase.

Caffeic Acid Phenethyl Ester Improves Oxidative Erythrocyte Damage in a Rat Model of Thermal Injury

Oxygen-derived free radicals impair cell membrane functions and induce circulatory disturbances, and free radicals, such as superoxide anion, hydrogen peroxide, hydroxyl radicals, and peroxynitrite, have been suggested to play important roles in the pathogenesis of major burn injuries. The present study investigated the effects of thermal injury on erythrocyte lipid peroxidation and antioxidant status and investigated the effects of caffeic acid phenethyl ester (CAPE), a new antioxidant and anti-inflammatory agent, in rats subjected to thermal injury. Burn injury caused a remarkable increase in erythrocyte lipid peroxidation, levels of nitric oxide (NO), and activities of antioxidant enzymes and xanthine oxidase (XO). The treatment with CAPE decreased both activity of burn-induced XO activity and levels of NO in the erythrocytes. In conclusion, CAPE treatment resulted in decreased erythrocyte lipid peroxidation in thermal injury and helped to prevent oxidative damage by decreasing activity of XO and levels of NO.

Effects of dietary glutamine on antioxidant enzyme activity and immune response in burned mice

OBJECTIVES

We investigated the effect of dietary glutamine (Gln) on specific antibody production and antioxidant enzyme activities in burned mice vaccinated with detoxified Pseudomonas exotoxin A linked with the outer membrane proteins I and F (PEIF). We also evaluated the survival rate of vaccinated and non-vaccinated burned mice infected with Pseudomonas aeruginosa.

METHODS

There were three consecutive experiments. In experiment 1, 30 BALB/c mice were assigned to one of two groups. The control group was fed casein as the protein source; the Gln group received 4% Gln (w/w) to replace part of the casein. Mice were immunized twice with PEIF, and the production of specific antibodies against PEIF was measured every week. Eight weeks after immunization, all mice received a 30% body surface area burn injury. Mice were killed 24 h after the burn. The antioxidant enzyme activities and lipid peroxides in the tissues and specific antibody production were analyzed. In experiment 2, 12 mice were assigned to a control or a Gln group and fed with one the experimental diets for 4 wk. Then burn injury was induced, and mice were killed 24 h later. In vitro, splenocytes were cultured, and interleukin (IL)-4 and IL-10 were measured after mitogen stimulation. In experiment 3, survival rates of vaccinated and non-vaccinated burned mice complicated with P. aeruginosa infection were evaluated. The survival rate was observed for 8 d after the burn.

RESULTS

Antioxidant enzyme activities and lipid peroxides in tissues tended to be lower in the Gln group than in the control group after the burn. Specific antibody production against P. aeruginosa increased significantly in the Gln group at 4 and 7 wk after immunization and at 24 h after the burn. IL-4 concentrations in mitogen-stimulated splenocytes were significantly higher in the Gln group than in the control group. Survival rates of non-vaccinated burned mice in the Gln group were significantly higher than those in the control group, whereas there was no difference in the survival of vaccinated burned mice after bacterial infection.

CONCLUSIONS

These results suggested that vaccinated mice receiving a Gln-enriched diet may have enhanced humoral immunity and attenuated oxidative stress induced by burn injury. Also, Gln supplementation improved the survival of burned mice complicated with P. aeruginosa infection.

Immune-enhancing diets for stressed patients with a special emphasis on arginine content: analysis of the analysis

PURPOSE OF REVIEW

After two decades of intensive research, whether arginine-enriched diets for oral/enteral administration are beneficial or harmful for stressed patients remains uncertain. An American consensus and a meta-analysis provide divergent conclusions. The main goal of the present review is to analyze these documents.

RECENT FINDINGS

The so-called immune-enhancing diets have been found to be beneficial to postoperative patients. Nothing proves, however, that arginine is responsible for these beneficial effects since immune-enhancing diets contain other pharmacologically active components (e.g. omega3 free fatty acids, RNAs, antioxidant vitamins). In fact, arginine-enriched diets may be harmful in hemodynamically unstable patients and those presenting with multiple organ failure.

SUMMARY

In light of the current doubts and until convincing data are produced, immune-enhancing diets should not be used in unstable critically ill patients.

In vivo induction of insulin secretion by ornithine alpha-ketoglutarate: involvement of nitric oxide and glutamine

We previously demonstrated that ornithine alpha-ketoglutarate (OKG), known for its anabolic properties, induces insulin secretion in vitro. The present study was undertaken to further characterize this effect in vivo and investigate a possible interaction with glucose both in vivo and in vitro. Male Wistar rats received an intravenous bolus of OKG (25 mg/kg) and/or glucose (0.8 g/kg) or saline, and their plasma insulin and glucose levels were monitored for 30 minutes. OKG alone increased plasma insulin to a similar extent to glucose. In combination with glucose, OKG significantly increased glucose-induced insulin secretion in vivo and in vitro, and led to a significant increase in glucose utilization in vivo. The absence of significant variations in plasma arginine and glutamine suggests a direct effect of OKG on the pancreas. To assess the involvement of the synthesis of nitric oxide and glutamine in OKG-induced insulin secretion, the experiments were repeated in the presence of inhibitors of these 2 pathways, respectively L-nitroarginine-methylester (L-NAME) and methionine sulfoximine (MSO). Both inhibitors were able significantly to reduce OKG-induced insulin secretion without affecting either basal or glucose-induced insulin release. Thus OKG acts directly with glucose on islets to induce insulin secretion via mechanisms involving NO and glutamine synthesis. In addition, our results suggest that OKG and glucose act via separate pathways.

Effects of dietary arginine supplementation on antibody production and antioxidant enzyme activity in burned mice

This study investigated the effect of arginine (Arg) supplementation on specific antibody production and antioxidant enzyme activities in burned mice vaccinated with detoxified Pseudomonas exotoxin A linked with the outer membrane proteins I and F, named PEIF. Also, the survival rate of burned mice complicated with Pseudomonas aeruginosa was evaluated. Experiment 1: Thirty BALB/c mice were assigned to two groups. One group was fed a control diet with casein as the protein source, while the other group was supplemented with 2% Arg in addition to casein. The two groups were isonitrogenous. The mice were immunized twice with PEIF, and the production of specific antibodies against PEIF was measured every week. After 8 weeks, all mice received a 30% body surface area burn injury. Mice were sacrificed 24h after the burn. The antioxidant enzyme activities and lipid peroxides in the tissues as well as the specific antibody production were analyzed. Experiment 2: Twenty-eight mice were divided into two groups and vaccinated as described in experiment 1. After the burn the mice were infected with P. aeruginosa, and the survival rate was observed for 8 days. The results demonstrated that antioxidant enzyme activities and lipid peroxides in tissues were significantly lower in the Arg group than in the control group after the burn. The production of specific antibodies against P. aeruginosa significantly increased in the Arg group at 4 and 7 weeks after immunization, and 24h after the burn. The survival rates of vaccinated burned mice after bacterial infection did not significantly differ between the two groups. These results suggest that vaccinating mice with Arg supplementation may enhance humoral immunity and attenuate the oxidative stress induced by burn injury. However, Arg supplementation did not improve survival in vaccinated mice complicated with P. aeruginosa infection.

Effects of alpha-ketoglutarate on antioxidants and lipid peroxidation products in rats treated with ammonium acetate

The effects of alpha-ketoglutarate (alpha-KG) on hyperammonemia induced by ammonium acetate were studied biochemically in experimental rats. The levels of circulatory urea and non-protein nitrogen increased significantly in rats treated with ammonium acetate and decreased significantly in rats treated with alpha-KG and ammonium acetate. In liver and kidney tissues, similar patterns of alterations across groups were observed in the levels of thiobarbituric acid-reactive substances and lipid profile variables (free fatty acids, triacylglycerols, phospholipids, and cholesterol). Further, enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) and non-enzymatic (reduced glutathione) antioxidants in both tissues decreased significantly in rats treated with ammonium acetate and increased significantly in rats treated with alpha-KG and ammonium acetate. The biochemical alterations during alpha-KG treatment might have been due to 1) the detoxification of excess ammonia, 2) participation in the non-enzymatic oxidative decarboxylation during hydrogen peroxide decomposition, and 3) enhancement of the proper metabolism of fats that could suppress oxygen radical generation and thus prevent lipid peroxidative damages in rats.

Effects of arginine supplementation on antioxidant enzyme activity and macrophage response in burned mice

This study investigated the effect of arginine (Arg) supplementation on antioxidant enzyme activities and macrophage response in burned mice. Experiment 1: 60 male BALB/c mice were assigned to two groups. One group was fed a control diet with casein as the protein source, the other group was supplemented with 2% Arg in addition to casein. The two groups were isonitrogenous. After 4 weeks, all mice received a 30% body surface area burn injury. The antioxidant enzyme activities and lipid peroxides in the tissues were analyzed. Experiment 2: 20 mice were divided into two groups and burn injury was induced after feeding for 4 weeks as described in experiment 1. Twenty-four hours after the burn, tumor necrosis factor-alpha (TNF-alpha) secreted by cultured peritoneal macrophages was measured. The results show that antioxidant enzyme activities and lipid peroxides in tissues tended to be lower in the Arg group than in the control group after the burn. Production of TNF-alpha by peritoneal macrophages after stimulation with lipopolysacchride (LPS) was significantly elevated in the Arg group, whereas no response was observed in the control group. These results suggest that dietary Arg supplementation attenuates the oxidative stress induced by burn injury, and a better macrophage response was observed when Arg was administered.

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.

Ornithine alpha-ketoglutarate improves wound healing in severe burn patients: a prospective randomized double-blind trial versus isonitrogenous controls

OBJECTIVE

To compare the effectiveness on wound healing time in severe burn patients of ornithine alpha-ketoglutarate supplementation of enteral feeding vs. an isonitrogenous control. Previous clinical and experimental studies suggest a beneficial effect of enterally administered ornithine alpha-ketoglutarate supplementation on protein metabolism in burn patients, but few data deal with clinical outcome.

DESIGN

Prospective double-blind randomized trial.

SETTING

Burn treatment center of an army hospital.

PATIENTS

Forty-seven severe burn patients with total burned body surface areas of 25% to 95% and presence of full thickness burn who were prescribed early exclusive enteral nutrition. Either ornithine alpha-ketoglutarate or isonitrogenous control (soy protein mixture, Protil-1) were administered twice a day as a bolus (2 x 10 g) at 9 am and 9 pm for 3 wks. The patients were evaluated for wound healing time (primary end point), antibiotic use, tolerance, duration of enteral nutrition, and nutritional status.

INTERVENTIONS

Serial blood samples were collected in each patient for determination of serum transthyretin and plasma phenylalanine, and urine sampling was performed for determination of 3-methylhistidine excretion at day 4 and day 21 after burn injury.

MEASUREMENTS AND MAIN RESULTS

Wound healing times in patients receiving ornithine alpha-ketoglutarate or Protil-1 were 60 +/- 7 and 90 +/- 12 days, respectively (p < .05) for similar grafted surfaces. Based on increased serum transthyretin concentrations, both groups showed an improvement of nutritional status at day 21 after burn. Taking a cut-off value of 110 unit burn standard for severity of injury, plasma phenylalanine concentrations, and urinary 3-methylhistidine/creatinine ratio were significantly reduced (p < .05) in the less severe burn patients (<110 unit burn standard) supplemented with ornithine alpha-ketoglutarate.

CONCLUSIONS

Ornithine alpha-ketoglutarate supplementation of enteral feeding significantly shortens wound healing time in severe burn patients. In addition, ornithine alpha-ketoglutarate administration was safe and well tolerated and decreased protein hypercatabolism in the less severe burn patients.

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.

Is the L-arginine-nitric oxide pathway involved in endotoxemia-induced muscular hypercatabolism in rats?

We investigated the role of the nitric oxide (NO) synthase (NOS) pathway in muscular metabolism during endotoxemia in four groups of male Wistar rats. Two groups were injected with the lipopolysaccharide (LPS) of Escherichia coli (3 mg/kg), with one group treated using N(G)-nitro-L-arginine methylester ([L-NAME] 85 mg/kg/d) and the other not. The two control groups included one treated with L-NAME and the other not. After 24 hours of fasting, the rats were fed by controlled enteral nutrition and killed on day 3. The results showed that (1) NOS inhibition was detrimental during endotoxemia, increasing lethality from 20% to 80.5%, and (2) NOS inhibition did not modify the hypercatabolic state consecutive to endotoxemia, particularly at the muscular level (nitrogen balance, total-body and muscular weight loss, and muscular protein and glutamine concentrations). However, myofibrillar catabolism was delayed in the LPS-NAME group. In conclusion, NO production is of major importance for survival after an endotoxemic challenge, but contributes weakly to the metabolic response of muscle to injury.

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.

A randomized controlled trial of the influence of the mode of enteral ornithine alpha-ketoglutarate administration in burn patients

To investigate appropriate mode and daily dose of enteral ornithine alpha-ketoglutarate (OKG) administration, 54 burn patients (total burn surface area: 20-50%) were included in a randomized controlled trial and assigned to receive either a supplement of OKG (10, 20 or 30 g/d) as bolus or continuous infusion, or a continuous infusion of an isonitrogenous amount of a soy protein mixture (Protil-1: 10, 20 or 30 g/d) in addition to their enteral diet. The influence of these treatments on clinical outcome and biological indices was evaluated. OKG administration significantly improved nitrogen balance and reduced 3-methylhistidine and hydroxyproline urinary elimination. This was associated with a gradual rise in plasma glutamine over time. Given as a bolus, OKG significantly improved wound healing, assessed both clinically [day of last graft: (mean +/- SEM) OKG bolus 23.7 +/- 2.1 d versus Protil-1, 39.9 +/- 9.9 d; P < 0.05] and by hydroxyproline excretion, and biological markers of nitrogen metabolism, and tended to reduce duration of enteral nutrition (P = 0.12). The higher catabolic status in the patients administered 20 g OKG/d at the onset of the study, despite randomization, precludes any definite conclusion (concerning the dose-effect relationship). However, based on 3-methylhistidine elimination, our data indicate a benefit of 30 g OKG/d administration over 10 g/d. This study further supports OKG supplementation in burn patients. In addition, this is the first trial based on objective data that favors bolus over continuous infusion of OKG in critically ill patients.

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

The aim of this study was to analyze the possible protective effects of a glutamine and arginine precursor (ornithine-alpha-ketoglutarate [OKG]) on the mucosa of a transplanted intestine when administered with either a defined formula oral diet (DFD) or a standard chow. Isogenic male Lewis rats (250 g) were submitted to a laparotomy (groups 1 and 2) or to an orthotopic small bowel transplantation (SBT; groups 3-6). Groups 1, 3, and 5 received a DFD 14 days after surgery. Groups 2, 4, and 6 received standard chow. In addition, groups 5 and 6 received a daily oral supplementation of 1.4 g/kg of OKG. Weight changes and food intake were recorded daily. At the end of the study, bacterial translocation (BT) was measured in mesenteric lymph nodes, liver, and spleen. The protein/DNA index was also determined in intestinal mucosa. SBT induced BT in all transplanted groups, especially in those fed DFD. Addition of OKG (groups 5 and 6) significantly reduced BT in comparison with groups 3 and 4 and improved the protein/DNA index as well as weight gain. It is concluded that OKG supplementation protects the intestinal barrier after SBT, and that this effect is more marked when it is added to a standard chow.

Enteral administration of ornithine alpha-ketoglutarate or arginine alpha-ketoglutarate: a comparative study of their effects on glutamine pools in burn-injured rats

OBJECTIVES

Ornithine alpha-ketoglutarate has proved to be an efficient nutritional support in trauma situations, especially after burn injury. To determine whether the action of ornithine alpha-ketoglutarate is due to its alpha-ketoglutarate moiety (as a glutamine precursor), we studied the effects of alpha-ketoglutarate administered to rats as ornithine alpha-ketoglutarate, or in combination with arginine salt (arginine alpha-ketoglutarate), as the two closely related amino acids have similar metabolic behavior.

DESIGN

Prospective, randomized trial.

SETTING

Animal laboratory.

SUBJECTS

Forty-six male Wistar rats, weighing approximately 90 g.

INTERVENTIONS

Rats were burned over 20% of their body surface area, starved for 24 hrs, with water ad libitum, and then enterally refed for 48 hrs using Osmolite (210 kcal/kg/day, 1.2 g of nitrogen/kg/day), supplemented with one of the following: a) an amount of glycine isonitrogenous to ornithine alpha-ketoglutarate (group 1); b) 5 g of monohydrated ornithine alpha-ketoglutarate/kg/day (group 2); c) an amount of arginine alpha-ketoglutarate isonitrogenous to ornithine alpha-ketoglutarate (group 3); or d) an amount of arginine alpha-ketoglutarate isomolar to ornithine alpha-ketoglutarate (group 4).

MEASUREMENTS AND MAIN RESULTS

We measured amino acid concentrations in plasma, muscle, and liver, and plasma urea concentration. At refeeding, ornithine alpha-ketoglutarate increased plasma glutamine concentration (p < .05 vs. the three other groups), and counteracted the increase in plasma phenylalanine concentration. In muscle, although the three alpha-ketoglutarate combinations induced similar increases in the glutamate pool, ornithine alpha-ketoglutarate induced the highest increase in glutamine (7.0 +/- 0.3 vs. 5.4 +/- 0.3 micromol/g in group 3, 6.3 +/- 0.3 in group 4, and 4.6 +/- 0.2 in group 1, p < .01 between group 2 and groups 3 or 1). Also, only ornithine alpha-ketoglutarate increased liver glutamine concentration. Finally, isomolar arginine alpha-ketoglutarate increased plasma urea concentration (+50% vs. the three other groups, p < .01).

CONCLUSIONS

Our results demonstrate, for the first time, the following: a) the action of ornithine alpha-ketoglutarate as a glutamine precursor cannot solely be ascribed to alpha-ketoglutarate since arginine alpha-ketoglutarate combinations did not exhibit this effect to the same extent; and b) the action of ornithine alpha-ketoglutarate is not due to its nitrogen content since isonitrogenous arginine alpha-ketoglutarate did not reproduce the effects of ornithine alpha-ketoglutarate.

Ornithine alpha-ketoglutarate counteracts thymus involution and glutamine depletion in endotoxemic rats

This work studied the action of ornithine a-ketoglutarate (OKG) supplementation in an experimental model of endotoxemia in the rat. Male Wistar rats were injected intraperitoneally with lipopolysaccharide (LPS) from Escherichia coli (0127:B8). They were fasted for 24 h, then refed for 48 h with an enteral diet supplemented with either OKG (66 mg N x kg(-1) x d(-1)) or glycine, isonitrogenous to the OKG group. A control (sham) group was also studied. LPS treatment induced a decrease in thymus and muscle weights compared to controls, and a decrease in glutamine and arginine concentrations in the anterior tibialis muscle. Supplementation with OKG restored thymus weight and muscle arginine level and increased muscle glutamine concentration, when compared to controls. We conclude that OKG counteracts the thymic involution that occurs with endotoxemia, and restores the muscular content of glutamine and arginine, both of which are involved in the regulation of immune function.

Inhibition of liver RNA breakdown during acute inflammation in the rat

Liver RNA- and protein-degradation rates were measured after the induction of acute inflammation in the rat. A preliminary study determined changes in hepatic RNA and protein content 12, 18 and 24 h after a turpentine oil injection. The RNA content in turpentine-treated rats compared with pair-fed animals increased significantly and sharply from 12 h (+ 11%) to 18 h (+ 32%) and slightly thereafter (+ 37% at 24 h). The liver protein content was significantly enhanced only at 24 h (+ 11%) in response to inflammation. RNA-degradation rates were determined in livers perfused cyclically in situ for 15 min by measuring the accumulation of radioactive cytidine in the medium 60 h after in vivo labelling of RNA by [5-3H]cytidine instead of [6-14C]orotic acid, the most commonly used radioactive marker. Several validation procedures showed that the method employed was a valid alternative to the use of radioactive orotic acid. RNA-degradation rates, which mainly reflect rRNA breakdown, were significantly lower in the turpentine-treated rats than in respective pair-fed animals at 18 and 24 h (57 and 45% decrease respectively). Proteolysis rates measured at 24 h together with RNA breakdown by valine accumulation in the perfusion medium were not modified after turpentine treatment. The main factors known to regulate RNA degradation (amino acids, insulin/glucagon ratio) were measured in the portal blood 24 h after induction of acute inflammation. Of the known regulatory amino acids, only glutamine and to a lesser extent methionine were increased in the turpentine-treated rats as compared with their pair-fed counterparts. The insulin/glucagon molar ratio was similar in both groups. In conclusion, the reduced breakdown of RNA, especially rRNA, is largely responsible for the accumulation of hepatic RNA during acute inflammation. This inhibition of RNA degradation could possibly be related to the increase in glutamine.

Ornithine alpha-ketoglutarate limits muscle protein breakdown without stimulating tumor growth in rats bearing Yoshida ascites hepatoma

The growth of the Yoshida ascites hepatoma AH130 (YAH) is associated with early wasting, depletion of intracellular amino acid pools, and a pronounced activation of protein degradation in skeletal muscle of the host animal. Ornithine alpha-ketoglutarate (OKG) is used in the treatment of hypercatabolic states, and it has been suggested that it may improve nitrogen balance through repletion of free amino acid pools and suppression of protein catabolism. In cancer, OKG might similarly improve host nutritional status or stimulate tumor growth if its metabolites are limiting for tumor growth. Enteral supplementation with OKG was investigated in Sprague-Dawley rats bearing YAH. Tumor-bearing rats were compared with ad libitum- and pair-fed controls. Rats received OKG (3.4 to 4.0 g/kg body weight/d) or an equal amount of nitrogen as glycine (n = 8 in each group) for 5 days. Tumor implantation decreased cumulative food intake (-40%), host weight (-6%), skeletal muscle weight, and free amino acid levels in muscle and plasma. Muscle protein balance was estimated in vitro; decreased protein synthesis (-30%) and increased proteolysis (+113%) were observed in epitrochlearis muscles (EPI) of YAH-bearing rats compared with control groups. OKG had no effect on the wet weight (10 +/- 1 g) and nitrogen content of the tumor, or on free amino acid levels in the tumor. In tumor-bearing rats, OKG improved muscle protein balance by reducing breakdown by 33% and overall amino acid release of incubated EPI by 46%.

Ornithine alpha-ketoglutarate and glutamine supplementation during refeeding of food-deprived rats

The aim of this study was to compare the efficiency of ornithine alpha-ketoglutarate (OKG) and glutamine supplementation in an experimental model of denutrition that provides well-characterized disturbances of amino acid patterns. Male Wistar rats (187 +/- 11 g; five in each group) were starved for 3 days and then refed for 7 days with an oral diet (192 kcal kg-1.day-1 and 2.25 g of nitrogen kg-1.day-1), supplemented with 0.19 g of nitrogen kg-1.day-1 in the form of OKG, glutamine, or casein (control group). Food deprivation induced a fall in most tissue amino acids, with the notable exception of muscle leucine and liver glutamate, which increased by 43% (p < .01), and 11% (p < .05), respectively. The main effect of OKG was seen in the viscera, with a normalization of most amino acid pools (including proline and branched-chain amino acids) in the small bowel and liver. The main effect of glutamine was observed in the muscle, with a normalization of the glutamine and leucine pools. We conclude that, in this model and with the doses used, OKG and glutamine act in different target tissues, ie, splanchnic areas and muscle, respectively.