Effect of alpha-ketoglutarate infusions on organ balances of glutamine and glutamate in anaesthetized dogs in the catabolic state

Glutamine concentration and tissue exchange with intravenously administered alpha-ketoglutaric acid and ammonium: a dose-response study in the pig

OBJECTIVE

We investigated the effects of an intravenous load of alpha-ketoglutaric acid, ammonium (NH(4)(+)), and metabolic acidosis on plasma concentration and splanchnic and hindleg tissue exchange of glutamine, glutamate, alanine, and arginine in postabsorptive, anesthetized pigs.

METHODS

Sixteen anesthetized piglets received a constant infusion of NH(4)Cl for 4 h and alpha-ketoglutaric acid in incremental dosages for 3 h (group 1, n = 8) or a constant infusion of alpha-ketoglutaric acid for 4 h and NH(4)Cl in incremental dosages for 3 h (group 2, n = 8). Plasma amino acids were analyzed and splanchnic blood flow was calculated according to the indocyanine green dye infusion technique. Femoral artery blood flow was measured with ultrasound flowmetry. Statistical evaluation of within-group differences was made with the Wilcoxon signed rank test.

RESULTS

Plasma glutamine levels increased dose-dependently in group 2 (P < 0.05) but not in group 1. Glutamate concentration increased, mainly in group 2 (P < 0.05), whereas the plasma concentration of alanine decreased in both groups (P < 0.05). Plasma concentration of arginine increased in both groups (P < 0.05). Splanchnic uptake and skeletal muscle release of glutamine did not change in either group compared with baseline values. Splanchnic glutamate release decreased (P < 0.05) in group 1 at 240 min; muscular uptake was unaffected in both groups. Splanchnic uptake and muscular release of alanine were unaffected in both groups. The significance level was set at 0.05.

CONCLUSION

Our findings indicate that the splanchnic bed or hindleg skeletal muscle was not the source of the increased plasma concentration of glutamine in this study.

Glutamine supplementation promotes anaplerosis but not oxidative energy delivery in human skeletal muscle

The aims of the present study were twofold: first to investigate whether TCA cycle intermediate (TCAI) pool expansion at the onset of moderate-intensity exercise in human skeletal muscle could be enhanced independently of pyruvate availability by ingestion of glutamine or ornithine alpha-ketoglutarate, and second, if it was, whether this modification of TCAI pool expansion had any effect on oxidative energy status during subsequent exercise. Seven males cycled for 10 min at approximately 70% maximal O2) uptake 1 h after consuming either an artificially sweetened placebo (5 ml/kg body wt solution, CON), 0.125 g/kg body wt L-(+)-ornithine alpha-ketoglutarate dissolved in 5 ml/kg body wt solution (OKG), or 0.125 g/kg body wt L-glutamine dissolved in 5 ml/kg body wt solution (GLN). Vastus lateralis muscle was biopsied 1 h postsupplement and after 10 min of exercise. The sum of four measured TCAI (SigmaTCAI; citrate, malate, fumarate, and succinate, approximately 85% of total TCAI pool) was not different between conditions 1 h postsupplement. However, after 10 min of exercise, SigmaTCAI (mmol/kg dry muscle) was greater in the GLN condition (4.90 +/- 0.61) than in the CON condition (3.74 +/- 0.38, P < 0.05) and the OKG condition (3.85 +/- 0.28). After 10 min of exercise, muscle phosphocreatine (PCr) content was significantly reduced (P < 0.05) in all conditions, but there was no significant difference between conditions. We conclude that the ingestion of glutamine increased TCAI pool size after 10 min of exercise most probably because of the entry of glutamine carbon at the level of alpha-ketoglutarate. However, this increased expansion in the TCAI pool did not appear to increase oxidative energy production, because there was no sparing of PCr during exercise.

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.

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.

Renal effects of alpha-ketoglutarate early after coronary operations

BACKGROUND

Alpha-ketoglutarate (alpha-KG) is a Krebs cycle intermediate and the carbon skeleton of glutamate. Alpha-ketoglutarate has provoked interest in heart surgery because of its proposed critical role in myocardial metabolism. This study investigates the role of alpha-KG in renal function after cardiac surgical procedures.

METHODS

Twenty-two patients with normal preoperative renal function were included in a prospective, randomized, and controlled study. Eleven patients received intravenous infusion of 30 g alpha-KG/hour after the operation. Measurements were performed before operation, immediately after operation, and after 30 minutes of alpha-KG infusion.

RESULTS

Renal blood flow was higher during alpha-KG infusion, 297% +/- 97% (of preoperative value), than in controls, 125% +/- 20% (p < 0.05). Filtration fraction was lower (12.3% +/- 0.05% versus 17.2% +/- 1.1%, p < 0.01), which prevented a significant difference in glomerular filtration rate. The renal arteriovenous differences of lactate, glutamate, glutamine, and glycine changed toward a net release during alpha-KG infusion.

CONCLUSIONS

Infusion of alpha-KG enhances renal blood flow early after coronary surgical procedures in patients with normal renal function. The mechanism is unclear, but could be associated with primarily metabolic effects, and may potentially convey a beneficial effect for renal function.

Addition of alpha-ketoglutarate to blood cardioplegia improves cardioprotection

BACKGROUND

We hypothesized that myocardial content of alpha-ketoglutarate (alpha-KG), an intermediate of the Krebs cycle, can be critically low during heart operations, and that provision of alpha-KG could reduce metabolic abnormalities and lead to improved myocardial protection.

METHODS

Twenty-four men aged 46 to 78 years who were undergoing heart operations participated in a prospective, controlled, randomized study. In 13 patients, an average of 28 g of alpha-KG was added to blood cardioplegia. Plasma creatine kinase isoenzyme MB and troponin T, and myocardial extraction of oxygen, substrates, and amino acids were measured.

RESULTS

alpha-Ketoglutarate treatment was associated with lower creatine kinase isoenzyme MB (F = 39.6, df = 1.172, p < 0.001) and lower troponin (F = 12.9, df = 1.172, p < 0.001). The values at 4 hours were 31 +/- 2.4 microg/L versus 49 +/- 4.9 microg/L (creatine kinase isoenzyme MB) and 1.1 +/- 0.05 microg/L versus 2.0 +/- 0.34 microg/L (troponin T). Myocardial oxygen extraction was higher during alpha-KG cardioplegia (p < 0.01), but there were no significant differences in myocardial uptake or release of substrates or amino acids. Lactate release was observed in both groups during cardioplegia. Myocardial lactate release had ceased after 30 minutes of reperfusion in nearly half the alpha-KG-treated patients (6 of 13) but remained in all the control patients (11 of 11, p = 0.016). There were no other differences after 30 minutes of reperfusion.

CONCLUSION

Provision of alpha-KG during blood cardioplegia improves myocardial protection in patients undergoing coronary operations. This may be linked to enhanced oxidation.

Acute effects of insulin-like growth factor I on inter-organ amino acid flux in protein-catabolic dogs

The effects of acute administration of human recombinant insulin-like growth factor-I (rhIGF-I) on amino acid (AA) flux between hindlimbs, liver and gut were investigated in anaesthetized post-operative dogs. rhIGF-I produced about a 10-fold increase in plasma IGF-I concentrations above baseline values (P < 0.001), increased the plasma levels of glucagon and adrenaline (P < 0.05), and evoked a fall in plasma glucose (-55 +/- 8%; (P < 0.001) and plasma total AA levels (-23 +/- 8%; P < 0.05). AA flux in post-absorptive dogs under NaCl infusions was characterized by an efflux of AA from the hindlimbs (as a result of the protein-catabolic situation), an equal AA balance across the gut and an AA uptake by the liver. The administration of rhIGF-I increased hepatic AA uptake in the NaCl group from 3.51 +/- 0.8 to 7.5 +/- 0.4 mumol/min per kg (P < 0.01) and in the AA-infused group from 16.8 +/- 0.6 to 22.4 +/- 1.5 mumol/min per kg (P < 0.05), but did not influence the AA balance across hindlimbs and gut. Glucose infusions normalized the plasma concentrations of counter-regulatory hormones without influencing the inter-organ AA balances. We conclude that hypoaminoacidaemia caused by rhIGF-I infusions is the result of a stimulated AA uptake by the liver, but is unrelated to alterations of AA exchange across the hindlimbs.

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.