Efficacy of ornithine-alpha-ketoglutarate (OKGA) as a dietary supplement in growing rats

Effects of low-protein diet supplementation with alpha-ketoglutarate on growth performance, nitrogen metabolism and mTOR signalling pathway of skeletal muscle in piglets

Excessive protein levels in diets result in incomplete digestion of nitrogenous nutrients that are excreted from the body, causing environment pollution. Alpha-ketoglutarate (AKG) has been reported to decrease dietary protein levels, promote intestinal health in piglets and reduce environmental pollution. However, the underlying mechanisms of AKG are largely unknown. The objective of this study was to determine the effects of low-protein diet supplementation of AKG on the growth performance, nitrogen metabolism, relative expression of amino acid transporter genes and mTOR signalling pathway of skeletal muscle in piglets. Forty-eight piglets with an initial weight of 11.53 ± 0.04 kg were randomly divided into four groups. Each group had four replicates, and each replicate had three pigs. A low-protein (LP) diet (crude protein was 14.96%) served as the control without AKG, while 0.5%, 1.0% and 1.5% AKG were added to the LP diet for the other experimental groups. The trial period lasted for 28 days. Compared with the LP group, the LP + 1.0%A and LP + 1.5%A groups increased the growth performance (p < .05);increased the mRNA levels of amino acid transporters in the duodenum, anterior jejunum and posterior jejunum (p < .05); and reduced faecal nitrogen and urine nitrogen emissions (p < .05). They also showed greater mRNA levels and phosphorylated protein levels for S6 kinase beta (S6K) (p < .05), mammalian target of rapamycin (mTOR) (p < .05) and 4E-binding protein 1 (4EBP1) (p < .05) in skeletal muscle. An LP diet supplemented with AKG activated the mTOR signalling and promoted the ability of the small intestine to absorb protein, thereby increasing protein deposition. Taken together, an LP diet supplemented with AKG provides a theoretical basis for the promotion and application of AKG in piglet production.

Supplementation with α-ketoglutarate to a low-protein diet enhances amino acid synthesis in tissues and improves protein metabolism in the skeletal muscle of growing pigs

α-Ketoglutarate (AKG) is a crucial intermediate in the tricarboxylic acid (TCA) cycle and can be used for the production of ATP and amino acids in animal tissues. However, the effect of AKG on the expression patterns of genes involved in muscle protein metabolism is largely unknown, and the underlying mechanism remains to be elucidated. Therefore, we used young pigs to investigate the effects of a low crude protein (CP) diet and a low CP diet supplemented with AKG on protein accretion in their skeletal muscle. A total of 27 growing pigs with an initial body weight of 11.96 ± 0.18 kg were assigned randomly to one of the three diets: control (normal recommended 20% CP, NP), low CP (17% CP, LP), or low CP supplemented with 1% AKG (ALP). The pigs were fed their respective diets for 35 days. Free amino acid (AA) profile and hormone levels in the serum, and the expression of genes implicated in protein metabolism in skeletal muscle were examined. Results showed that compared with the control group or LP group, low-protein diets supplemented with AKG enhanced serum and intramuscular free AA concentrations, the mRNA abundances of AA transporters, and serum concentrations of insulin-like growth factor-1 (IGF-1), activated the mammalian target of rapamycin (mTOR) pathway, and decreased serum urea concentration and the mRNA levels for genes related to muscle protein degradation (P < 0.05). In conclusion, these results indicated that addition of AKG to a low-protein diet promotes amino acid synthesis in tissues and improves protein metabolism in skeletal muscle.

Effects of alpha-ketoglutarate (AKG) on growth performance and non-specific immunity of juvenile red drum fed diets with low or adequate phosphorus levels

This study evaluated the effects of α-ketoglutarate (AKG) on the growth performance, body, and skeletal composition, as well as non-specific immunity of juvenile red drum (Sciaenops ocellatus) fed adequate or low-phosphorus diets. A 2 × 2 factorial design was arranged with two levels of total phosphorus (1.0 or 1.6%) and two levels (0 or 1%) of AKG. Each diet was fed to red drum in four replicate 110-L aquaria (15 fish/aquarium) twice daily for 7 weeks. The results indicated that the low-P diets significantly (P < 0.05) decreased weight gain, feed efficiency, and condition factor of red drum, but increased moisture content and decreased ash content of whole body, as well as decreased ash content of skeletal tissue and decreased plasma lysozyme. Supplementation of AKG significantly improved the fillet yield and plasma lysozyme and tended to improve neutrophil oxidative radical production (P = 0.097). Based on these results, phosphorus level had the greatest effect on growth performance and non-specific immunity of red drum, while AKG supplementation had limited positive effects on immunological responses and fillet yield of juvenile red drum.

Substrate fuel kinetics in enterally fed trauma patients supplemented with ornithine alpha ketoglutarate

BACKGROUND

Ornithine-alpha-ketoglutarate (OKG) is a promising anticatabolic agent and the mechanisms of its potential use in trauma patients are not clearly understood.

AIM

To determine the altered whole-body protein, lipid and glucose substrate kinetics in trauma victims in the early flow-phase of injury when they were fed enterally with or without OKG.

METHODS

Fourteen adult, multiple trauma patients who were highly catabolic and hypermetabolic were studied. Whole-body protein ((15)N glycine), fat (2 stage glycerol infusion) and glucose ((3H)glucose) kinetics (t/o) and plasma parameters were measured (A) within 48-60 h after injury before starting nutritional support and then (B) after 4 days of enteral feeding. Group A (n=7, control) received a defined enteral formula (Two Cal HN, 1.4 times BEE calories) and Group B (n=7, OKG) received same isonitrogenous diet replacing 2.62gN/d from the enteral diet by OKG-N (20g OKG/d). RESULTS (Mean+/-SEM): Protein turnover is significantly (P<==0.05) increased in OKG treated patients (4.68+/-0. 15 vs 3.90+/-0.23, gP/kg/day) and glycerol turnover is decreased (0. 87+/-0.16 vs 1.46+/-0.16, micro mole/kg/min). Glucose turnover is not changed. Significant (P<== 0.05) increases in circulating plasma levels of hormones (insulin, 44.2+/-8.4 vs 15.7+/-5.0 ulU/ml, growth hormone 1.68+/-0.33 vs 0.92+/-0.16, ng/ml and IGF-1, 106+/-13 vs 75+/-18, ng/ml) and free amino acids (glutamine, 383+/-20 vs 306+/-25, Proline, 203+/-18 vs 146+/-13 and ornithine, 164+/-27 vs 49+/-5 micro mole/l) are found in OKG treated patients, compared to non OKG patients.

CONCLUSION

Increased hormone secretion due to OKG and the rapid interaction between the metabolites of OKG at the intermediary metabolism level may be responsible for altered substrate fuel kinetics.

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.

Altered tissue polyamine levels due to ornithine-alpha-ketoglutarate in traumatized growing rats

All cells contain significant amounts of polyamines (PA), and their concentrations are highly regulated. Metabolic activity within a tissue may be reflected in the amount of intracellular PA. Since trauma involves accelerated death and regeneration of tissues, the related levels of PA in extracellular and intracellular fluids may reflect altered protein metabolism. Trauma induces an increased excretion of urinary PA, and the tissues responsible for this whole-body activity are not known. During posttraumatic nutritional management, supplementation with ornithine-alpha-ketoglutarate (OKG) seems to improve nitrogen economy. The present study evaluates the significance of muscle, liver, and intestine PA responses in traumatized (bilateral femur fractures) rats to the feeding of an isonitrogenous liquid diet supplemented with or without OKG. Uninjured control rats were pair-fed with respective traumatized rats. After 2 days of starvation and 4 days of feeding, the traumatized and control rats were killed and the tissues were excised and analyzed. Starvation decreases and refeeding increases urinary PA excretion. Trauma-induced PA response is predominantly seen in muscle tissues, and this may be responsible for parallel increases in PA excretion. Liver PA responses show a varying tendency confirming the increased protein synthetic activity due to trauma. Intestine has the highest intracellular PA levels, and there is a general smaller (statistically insignificant) increase in all the individual PA contents due to trauma. OKG supplementation augments tissue and urine PA responses in control rats; however, in trauma rats muscle PA levels show very little change, although nitrogen retention is significantly better (88% to 77%). Mechanistic studies are needed to evaluate the significances of the time-dependent, injury-induced, individual intracellular PA levels.