Effects of dietary α-ketoglutarate supplementation on the growth performance, glutamine synthesis and amino acid concentrations of juvenile hybrid sturgeon Acipenser schrenckii ♀×Acipenser baerii ♂ fed high levels of soy protein concentrate

In ovo feeding of α-ketoglutaric acid improves hepatic antioxidant-gene expression, plasma antioxidant activities and decreases body temperature without affecting broiler body weight under cyclic heat stress

The broiler industry is adversely affected by the rise in global temperature. This study investigated the effects of in ovo feeding of α-ketoglutaric acid (AKG) on growth performance, organ weight, plasma metabolite, plasma oxidative stress, rectal temperature (RT), and hepatic mRNA expression of antioxidant-related genes in Arbor Acres broilers subjected to cyclic heat stress (HS). Three hundred fifty fertile eggs during incubation were divided into 5 groups according to AKG concentrations and temperature conditions. After dissolving AKG in distilled water at 0, 0.5, 1.0, and 1.5, 0% AKG was in ovo administered to 2 of the 5 groups whereas the remaining 3 groups received 0.5, 1.0, and 1.5%, respectively. From d 29 to 34 of age, 4 groups of birds received heat stress (HS) at 31°C ± 1°C for 6 h per day while the other group was kept at room temperature (21°C ± 1°C; NT). So, the 5 treatment groups were: 1) 0AKG-NT, where chicks hatched from eggs receiving 0% AKG were reared under thermoneutral conditions. 2) 0AKG-HS, where chicks hatched from eggs receiving 0% AKG were reared under cyclic HS conditions. 3) 0.5AKG-HS, where chicks hatched from eggs receiving 0.5% AKG were reared under cyclic HS conditions. 4) 1.0AKG-HS, where chicks hatched from eggs receiving 1.0% AKG were reared under cyclic HS conditions. 5) 1.5AKG-HS, where chicks hatched from eggs receiving 1.5% AKG were reared under cyclic HS conditions. HS significantly reduced body weight change (ΔBW %) and average daily gain (ADG) without affecting average daily feed intake (ADFI). Feed conversion ratio (FCR) was significantly increased (P = 0.003) in all HS-treated groups. A significant linear decrease in the final RT (P = 0.005) and a change in RT (P = 0.003) were detected with increasing AKG concentration. Total antioxidant capacity (P = 0.029) and antioxidant balance (P = 0.001) in plasma increased linearly with increasing AKG concentration whereas malondialdehyde concentrations were linearly decreased (P = 0.001). Hepatic gene expression of CAT (P = 0.026) and GPX1 (P = 0.001) were dose-dependently upregulated while nicotinamide adenine dinucleotide phosphate oxidase (NOX)1, NOX4, and heat shock protein (HSP)70 were linearly downregulated (P < 0.05). Hence, in ovo injection of AKG was effective in mitigating HS-induced oxidative stress without attenuating the adverse effects on broiler growth.

Effect of phosphorus on growth performance, intestinal tight junctions, Nrf2 signaling pathway and immune response of juvenile mirror carp (Cyprinus carpio) fed different α-ketoglutarate levels

Previous research has shown that dietary α-ketoglutarate (AKG) supplementation can promote growth performance, phosphorus metabolism, and skeletal development of juvenile mirror carp (Cyprinus carpio) fed low phosphorous diets. In the current study, we tested the hypothesis that 1% AKG dietary supplementation reduces the dietary phosphorus requirements of juvenile mirror carp. A total of 12 experimental isoproteic and isolipidic diets containing available phosphorus levels of 0.21%, 0.38%, 0.55%, 0.72%, 0.89%, and 1.07% dry matter with either 0 or 1% AKG supplementation were used in the study. A total of 1080 juvenile fish of similar initial weight (0.90 ± 0.03 g) were selected and randomly assigned to 36 tanks. There were three replicates for each experimental group, with a density of 30 fish per tank. Fish were fed to satiation for 8 weeks. The results indicated that fish fed the diet supplemented with 1% AKG showed a significant increase in final body weight (FBW), weight gain rate (WGR), feed intake (FI) and phosphorus intake (PI) compared to the diet without AKG (P < 0.05). FBW and WGR increased significantly with increasing available phosphorus levels from 0.21% to 0.89% (P < 0.05). The mRNA expression of ZO-1, claudin 11, and occludin was significantly increased by dietary AKG and phosphorus (P < 0.05). The mRNA expression of Nrf2, GPx1a, and CAT in the Nrf2 signaling pathway was significantly increased by dietary AKG and phosphorus (P < 0.05). The expression levels of IL-10 and TGF-β2 were significantly increased by dietary AKG and phosphorus, but the expression levels of IL-1β, IL-8, IL-10, TNF-a and NF-κB were significantly decreased with dietary AKG and phosphorus supplementation (P < 0.05). Based on second-order polynomial regression analysis of WGR against dietary phosphorus levels, the optimal dietary phosphorus level was found to be 0.79% of dry feed for juvenile mirror carp fed a diet with 1% AKG supplementation and 0.93% of dry feed without AKG supplementation. This study confirmed that AKG supplementation can reduce the phosphorus requirements of juvenile mirror carp by promoting growth performance, intestinal tight junctions, Nrf2 signaling pathways and immune response.

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.

Alpha-Ketoglutarate in Low-Protein Diets for Growing Pigs: Effects on Cecal Microbial Communities and Parameters of Microbial Metabolism

Alpha-ketoglutarate (AKG), a critical molecule in the tricarboxylic acid cycle, is beneficial to intestinal functions. However, its influence on intestinal microbiota and metabolism is not fully understood. We investigated the effects of a low-protein (LP) diet supplemented with AKG on cecal microbial communities and the parameters of microbial metabolism in growing pigs. Twenty-seven young pigs (Large White × Landrace) with an average initial body weight of 11.96 ± 0.18 kg were randomly allotted into three groups (n = 9): a normal protein (NP) diet containing 20% crude protein (CP); LP diet formulated with 17% CP (LP diet); or LP diet supplemented with 10 g kg^-1 of AKG (ALP diet). After a 35-day trial period, the digesta of the cecum were collected to analyze the concentrations of ammonia and short-chain fatty acids (SCFAs). We also performed a microbial analysis. Although no significant differences were found in performance among the diet groups, pigs fed the ALP diet had greater average daily gain (ADG) when compared with those in the LP group. Experimental diet did not affect cecal bacterial richness or diversity, as determined by Chao1 and ACE species richness measures and Shannon and Simpson indices, respectively. The predominant phyla Firmicutes, Bacteroidetes, and Proteobacteria increased in relative abundances in the cecum of pigs fed ALP diet. At the genus level, compared to the LP diet, the ALP diet significantly increased the abundances of Lachnospiraceae UCG-005, Lachnospiraceae NK4A136 group, Phascolarctobacterium and Parabacteroides, while decreased Vibrio and Maritalea. Pigs fed the ALP diet increased Oribacterium and Lachnoclostridium when compared with the NP diet. Non-metric multidimensional scaling analysis revealed that the distribution of microbiota at each group was distinctly clustered separately along principal coordinate. In addition, quantitative PCR revealed that the ALP diet was also associated with increases in the amounts of Bacteroides, Bifidobacterium, and Lactobacillus, but a decrease in the level of Escherichia coli. Compared with the NP diet, the ALP diet enhanced the concentrations of valerate and propionate. This ALP diet also increased the concentrations of valerate and isobutyrate when compared with the LP diet. Moreover, the ALP diet was linked with a significant decline in the concentration of ammonia in the cecum. These results indicate that a LP diet supplemented with AKG can alter the balance in microbial communities, increasing the population of SCFA-producing bacteria and the amounts of Bacteroides and Bifidobacterium, while reducing the counts of Escherichia coli and the amount of ammonia in the cecum.

Alpha-ketoglutarate (AKG) lowers body weight and affects intestinal innate immunity through influencing intestinal microbiota

Alpha-ketoglutarate (AKG), a precursor of glutamate and a critical intermediate in the tricarboxylic acid cycle, shows beneficial effects on intestinal function. However, the influence of AKG on the intestinal innate immune system and intestinal microbiota is unknown. This study explores the effect of oral AKG administration in drinking water (10 g/L) on intestinal innate immunity and intestinal microbiota in a mouse model. Mouse water intake, feed intake and body weight were recorded throughout the entire experiment. The ileum was collected for detecting the expression of intestinal proinflammatory cytokines and innate immune factors by Real-time Polymerase Chain Reaction. Additionally, the ileal luminal contents and feces were collected for 16S rDNA sequencing to analyze the microbial composition. The intestinal microbiota in mice was disrupted with an antibiotic cocktail. The results revealed that AKG supplementation lowered body weight, promoted ileal expression of mammalian defensins of the alpha subfamily (such as cryptdins-1, cryptdins-4, and cryptdins-5) while influencing the intestinal microbial composition (i.e., lowering the Firmicutes to Bacteroidetes ratio). In the antibiotic-treated mouse model, AKG supplementation failed to affect mouse body weight and inhibited the expression of cryptdins-1 and cryptdins-5 in the ileum. We concluded that AKG might affect body weight and intestinal innate immunity through influencing intestinal microbiota.

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.

Alpha-ketoglutarate suppresses the NF-κB-mediated inflammatory pathway and enhances the PXR-regulated detoxification pathway

Alpha-ketoglutarate (AKG) is a critical nutritional factor in the maintenance of intestinal homeostasis. However, the relative mechanism of AKG has not been well understood. It was recently shown that the interaction between nuclear factor kappa B (NF-κB)-mediated inflammatory pathway and pregnane X receptor (PXR)-regulated detoxification pathway is a check and balance mechanism for keeping the homeostatic state of the intestine, preventing the onset of intestinal inflammation which may lead to cancer. In the current study we used lipopolysaccharide (LPS)-challenged piglet and intestinal porcine epithelial cells-J2 models to investigate the effects of dietary AKG supplementation on the intestinal immune system and PXR regulated target expression. We found that LPS induced significant activation of the NF-κB-mediated inflammatory pathway with concomitant impairment of intestinal nutrient absorption. AKG administration increased intracellular AKG and its metabolite concentrations and enhanced the mRNA expression of alpha-ketoglutarate dehydrogenase in vivo and in vitro. Thus dietary AKG supplementation reversed the adverse effects induced by LPS. We also found a strong inhibitory effects on the NF-κB-mediated inflammatory pathway, especially, in the AKG-treated intestinal tissues, LPS-induced NF-κB phosphorylation was inhibited and TNF-α was suppressed. Interestingly, AKG has potent effects in regulating the PXR and its downstream targets such as CYP3As and CYP2Bs in vivo and in vitro, although AKG is not a known PXR ligand. One potential mechanism for the up-regulation of the PXR pathway is through the down-regulation of NF-κB pathway which in turn de-represses the PXR-regulated target expression. Taken together, our results suggest that AKG improves intestinal immune system through modulating the interaction between PXR and NF-κB. Our findings have important implications for the prevention and treatment of intestinal inflammatory diseases in neonates.