The long-term effect of α-ketoglutarate, given early in postnatal life, on both growth and various bone parameters in pigs

α-Ketoglutarate downregulates thiosulphate metabolism to enhance antibiotic killing

Potentiation of the effects of currently available antibiotics is urgently required to tackle the rising antibiotics resistance. The pyruvate (P) cycle has been shown to play a critical role in mediating aminoglycoside antibiotic killing, but the mechanism remains unexplored. In this study, we investigated the effects of intermediate metabolites of the P cycle regarding the potentiation of gentamicin. We found that α-ketoglutarate (α-KG) has the best synergy with gentamicin compared to the other metabolites. This synergistic killing effect was more effective with aminoglycosides than other types of antibiotics, and it was effective against various types of bacterial pathogens. Using fish and mouse infection models, we confirmed that the synergistic killing effect occurred in vivo. Furthermore, functional proteomics showed that α-KG downregulated thiosulphate metabolism. Upregulation of thiosulphate metabolism by exogenous thiosulphate counteracted the killing effect of gentamicin. The role of thiosulphate metabolism in antibiotic resistance was further confirmed using thiosulphate reductase knockout mutants. These mutants were more sensitive to gentamicin killing, and less tolerant to antibiotics compared to their parental strain. Thus, our study highlights a strategy for potentiating antibiotic killing by using a metabolite that reduces antibiotic resistance.

Heritability and genetic correlations of plasma metabolites of pigs with production, resilience and carcass traits under natural polymicrobial disease challenge

Metabolites in plasma of healthy nursery pigs were quantified using nuclear magnetic resonance. Heritabilities of metabolite concentration were estimated along with their phenotypic and genetic correlations with performance, resilience, and carcass traits in growing pigs exposed to a natural polymicrobial disease challenge. Variance components were estimated by GBLUP. Heritability estimates were low to moderate (0.11 ± 0.08 to 0.19 ± 0.08) for 14 metabolites, moderate to high (0.22 ± 0.09 to 0.39 ± 0.08) for 17 metabolites, and highest for l-glutamic acid (0.41 ± 0.09) and hypoxanthine (0.42 ± 0.08). Phenotypic correlation estimates of plasma metabolites with performance and carcass traits were generally very low. Significant genetic correlation estimates with performance and carcass traits were found for several measures of growth and feed intake. Interestingly the plasma concentration of oxoglutarate was genetically negatively correlated with treatments received across the challenge nursery and finisher (− 0.49 ± 0.28; P < 0.05) and creatinine was positively correlated with mortality in the challenge nursery (0.85 ± 0.76; P < 0.05). These results suggest that some plasma metabolite phenotypes collected from healthy nursery pigs are moderately heritable and genetic correlations with measures of performance and resilience after disease challenge suggest they may be potential genetic indicators of disease resilience.

Alpha-Ketoglutaric Acid Production from a Mixture of Glycerol and Rapeseed Oil by Yarrowia lipolytica Using Different Substrate Feeding Strategies

The microbiological biosynthesis of α-ketoglutaric acid (KGA) has recently captured the attention of many scientists as an alternative to its common chemical synthesis. The present study aimed to evaluate the effect of the feeding strategy of substrates, i.e., glycerol (G = 20 g·dm−3) and rapeseed oil (O = 20 g·dm−3), on yeast growth and the parameters of KGA biosynthesis by a wild strain Yarrowia lipolytica A-8 in fed-batch and repeated-batch cultures. The effectiveness of KGA biosynthesis was demonstrated to depend on thiamine concentration and the substrate feeding method. In the fed-batch culture incubated with 3 µg·dm−3 of thiamine and a substrate feeding variant 2G(_OGO), KGA was produced in the amount of 62.1 g·dm−3 at the volumetric production rate of 0.37 g·dm−3·h−1. These values of KGA production parameters were higher than these obtained in the control culture (with rapeseed oil only). During 10 cycles of the 1788-h repeated-batch culture carried out acc. to the feeding strategy 2G(_OGO), in the last 5 cycles the yeast produced from 55.6 to 58.2 g·dm−3 of KGA and maximally 2.9 g·dm−3 of the pyruvic acid as a by-product.

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.

A metabolomics comparison between sheep's and goat's milk

Despite the worldwide consumption of bovine milk, dairy products from small ruminants, such as goat's and sheep's milk, are gaining a large interest especially in the Mediterranean area. The aim of this work was to study the metabolite profiles of 30 sheep's and 28 goat's milk using an untargeted metabolomics approach by a gas chromatography coupled with mass spectrometry (GC-MS) analysis. Results showed several differences in the metabolite profiles: arabitol, citric acid, α-ketoglutaric acid, glyceric acid, myo-inositol, and glycine were more abundant in sheep's milk, while goat's milk had higher levels of mannose-6-phosphate, isomaltulose, valine, pyroglutamic acid, leucine, and fucose. Associations between metabolite profile and milk compositional traits were also found. Predictive capabilities of statistical models indicated a good correlation between the metabolite profile and the protein content in sheep's milk, and with the fat content in goat's milk. This work leads to a better understanding of milk metabolites in small ruminants and their role in the evaluation of milk properties.

Alpha-Ketoglutarate: Physiological Functions and Applications

Alpha-ketoglutarate (AKG) is a key molecule in the Krebs cycle determining the overall rate of the citric acid cycle of the organism. It is a nitrogen scavenger and a source of glutamate and glutamine that stimulates protein synthesis and inhibits protein degradation in muscles. AKG as a precursor of glutamate and glutamine is a central metabolic fuel for cells of the gastrointestinal tract as well. AKG can decrease protein catabolism and increase protein synthesis to enhance bone tissue formation in the skeletal muscles and can be used in clinical applications. In addition to these health benefits, a recent study has shown that AKG can extend the lifespan of adult Caenorhabditis elegans by inhibiting ATP synthase and TOR. AKG not only extends lifespan, but also delays age-related disease. In this review, we will summarize the advances in AKG research field, in the content of its physiological functions and applications.

The effect of dietary administration of 2-oxoglutaric acid on the cartilage and bone of growing rats

2-Oxoglutaric acid (2-Ox), a precursor to hydroxyproline - the most abundant amino acid in bone collagen, exerts protective effects on bone development during different stages of organism development; however, little is known about the action of 2-Ox on cartilage. The aim of the present study was to elucidate the influence of dietary 2-Ox supplementation on the growth plate, articular cartilage and bone of growing rats. A total of twelve male Sprague-Dawley rats were used in the study. Half of the rats received 2-oxoglutarate at a dose of 0·75 g/kg body weight per d in their drinking-water. Body and organ weights were measured. Histomorphometric analyses of the cartilage and bone tissue of the femora and tibiae were conducted, as well as bone densitometry and peripheral quantitative computed tomography (pQCT). Rats receiving 2-Ox had an increased body mass (P<0·001) and absolute liver weight (P=0·031). Femoral length (P=0·045) and bone mineral density (P=0·014), overall thickness of growth plate (femur P=0·036 and tibia P=0·026) and the thickness of femoral articular cartilage (P<0·001) were also increased. 2-Ox administration had no effect on the mechanical properties or on any of the measured pQCT parameters for both bones analysed. There were also no significant differences in histomorphometric parameters of tibial articular cartilage and autofluorescence of femoral and tibial growth plate cartilage. Dietary supplementation with 2-Ox to growing rats exerts its effects mainly on cartilage tissue, having only a slight influence on bone. The effect of 2-Ox administration was selective, depending on the particular bone and type of cartilage analysed.

Anti-osteopenic effect of alpha-ketoglutarate sodium salt in ovariectomized rats

The purpose of the study was to determine the effect of alpha-ketoglutarate sodium salt (AKG) treatment on the mineralization of the tibia in female rats during the development of osteopenia (Experiment-1) and in the condition of established osteopenia (Experiment-2). Thirty-two female rats were ovariectomized (OVX) to induce osteopenia and osteoporosis and another 32 female rats were sham-operated (SHO) and then randomly divided between the two experiments. In Experiment-1, the treatment with AKG started after a 7-day period of convalescence, whereas in Experiment-2 the rats were subjected to a 60-day period of osteopenia fixation, after which the actual experimental protocol commenced. AKG was administered in the experimental solution for drinking at a concentration of 1.0 mol/l and a placebo (PLC) was used as a control solution. After 60 days of experimental treatment the rats in both experiements were sacrificed, the body weight recorded, and blood serum and isolated tibia were stored for further analysis. The bones were analyzed using tomography and densitometry, and for estimation of mechanical properties the 3-point bending test was used. Serum concentrations of osteocalcin and collagen type I crosslinked C-telopeptide were measured. The anabolic effects of AKG on bone during osteopenia development in Experiment-1 not only stopped the degradation of bone tissue, but also stimulated its mineralization. The usage of AKG in animals with established osteopenia (Experiment-2) was not able to prevent bone atrophy, but markedly reduced its intensity. The stimulation of tibia mineralization after AKG treatment has been also argued in healthy SHO animals. The results obtained prove the effectiveness of AKG usage in the prophylaxis and therapy of osteopenia and osteoporosis, induced by bilateral gonadectomy. Additionally, the results clearly prove that treatment with AKG improves the mineralization of bone tissue in healthy animals.

Effects of combined maternal administration with alpha-ketoglutarate (AKG) and β-hydroxy-β-methylbutyrate (HMB) on prenatal programming of skeletal properties in the offspring

BACKGROUND

Nutritional manipulations during fetal growth may induce long-term metabolic effects in postnatal life. The aim of the study was to test whether combined treatment of pregnant sows with alpha-ketoglutarate and β-hydroxy-β-methylbutyrate induces additive long-term effects on skeletal system properties in the offspring.

METHODS

The study was performed on 290 pigs obtained from 24 sows divided into 4 equal groups and subjected to experimental treatment during two weeks before delivery. The first group consisted of control sows, while the second group received alpha-ketoglutarate. The third group was treated with β-hydroxy-β-methylbutyrate and the fourth group underwent combined administration of alpha-ketoglutarate and β-hydroxy-β-methylbutyrate. Piglets obtained from sows were reared until slaughter age to perform morphometric, densitometric and mechanical analyses of femur. Serum evaluations of growth hormone, insulin-like growth factor-1, bone-specific alkaline phosphatase and osteocalcin were performed in newborns and 90-day old piglets; additionally, plasma amino acid concentration was measured in newborns.

RESULTS

Maternal treatment with alpha-ketoglutarate and β-hydroxy-β-methylbutyrate significantly reduced fattening time and increased birth body weight, daily body weight gain, bone weight, volumetric bone mineral density, geometrical parameters and mechanical endurance of femur. These effects were associated with increased serum concentrations of growth hormone, insulin-like growth factor-1, bone-specific alkaline phosphatase and osteocalcin. Furthermore, alpha-ketoglutarate and β-hydroxy-β-methylbutyrate administered solely or in combination significantly increased plasma level of 19 amino acids.

CONCLUSIONS

Hormonal and amino acid evaluations in pigs indicate additive effects of AKG and HMB on systemic growth and development; however, determination of bone properties has not shown such phenomenon.

Consumption of pasteurized human lysozyme transgenic goats' milk alters serum metabolite profile in young pigs

Nutrition, bacterial composition of the gastrointestinal tract, and general health status can all influence the metabolic profile of an organism. We previously demonstrated that feeding pasteurized transgenic goats' milk expressing human lysozyme (hLZ) can positively impact intestinal morphology and modulate intestinal microbiota composition in young pigs. The objective of this study was to further examine the effect of consuming hLZ-containing milk on young pigs by profiling serum metabolites. Pigs were placed into two groups and fed a diet of solid food and either control (non-transgenic) goats' milk or milk from hLZ-transgenic goats for 6 weeks. Serum samples were collected at the end of the feeding period and global metabolite profiling was performed. For a total of 225 metabolites (160 known, 65 unknown) semi-quantitative data was obtained. Levels of 18 known and 4 unknown metabolites differed significantly between the two groups with the direction of change in 13 of the 18 known metabolites being almost entirely congruent with improved health status, particularly in terms of the gastrointestinal tract health and immune response, with the effects of the other five being neutral or unknown. These results further support our hypothesis that consumption of hLZ-containing milk is beneficial to health.