Absorption of α-ketoglutarate by the gastrointestinal tract of pigs

Elevation of Intracellular Alpha-Ketoglutarate Levels Inhibits Osteoclastogenesis by Suppressing the NF-κB Signaling Pathway in a PHD1-Dependent Manner

Age-related osteoporosis, a high-prevalence disease in the aged population, is generally attributed to the excessive activity of osteoclasts. Most approved drugs treat osteoporosis by inhibition of osteoclasts. Although in vivo studies have shown that alpha-ketoglutarate (AKG), an intermediate in the TCA cycle, can ameliorate age-related osteoporosis, the effects of AKG on osteoclastogenesis and the underlying mechanism of its action have not been studied yet. Here, we showed that the elevation of intracellular AKG levels by supplementing dimethyl AKG (DM-AKG, a cell-permeable derivative of AKG) inhibits the receptor activator of NF-κB ligand (RANKL)-induced osteoclasts differentiation from primary bone marrow-derived macrophages (BMMs) and RAW264.7 cells in vitro. We further found that DM-AKG treatment suppresses NF-κB signaling and oxidative phosphorylation (OXPHOS) during RANKL-induced osteoclastogenesis in RAW264.7 cells. Interestingly, dimethyl oxalylglycine (DMOG), an AKG competitive inhibitor of AKG-dependent prolyl hydroxylases (PHDs), antagonizes the suppression of the RANKL-activated NF-κB signaling pathway caused by DM-AKG treatment. Furthermore, blocked PHD1 expression (also known as EglN2), instead of PHD2 or PHD3, was confirmed to reverse the DM-AKG treatment-induced suppression of the RANKL-activated NF-κB signaling pathway. Accordingly, blocked PHD1 expression antagonized the inhibitory effects of DM-AKG on osteoclastogenesis. Together, our finding suggests that the elevation of intracellular AKG levels inhibits osteoclastogenesis by suppressing RANKL-activated NF-κB signaling in a PHD1-dependent manner, which may provide a novel nutritional strategy for osteoporosis treatment.

Dietary Alpha-Ketoglutarate Partially Abolishes Adverse Changes in the Small Intestine after Gastric Bypass Surgery in a Rat Model

Alpha-ketoglutarate (AKG) is one of the key metabolites that play a crucial role in cellular energy metabolism. Bariatric surgery is a life-saving procedure, but it carries many gastrointestinal side effects. The present study investigated the beneficial effects of dietary AKG on the structure, integrity, and absorption surface of the small intestine after bariatric surgery. Male 7-week-old Sprague Dowley rats underwent gastric bypass surgery, after which they received AKG, 0.2 g/kg body weight/day, administered in drinking water for 6 weeks. Changes in small intestinal morphology, including histomorphometric parameters of enteric plexuses, immunolocalization of claudin 3, MarvelD3, occludin and zonula ocludens 1 in the intestinal mucosa, and selected hormones, were evaluated. Proliferation, mucosal and submucosal thickness, number of intestinal villi and Paneth cells, and depth of crypts were increased; however, crypt activity, the absorption surface, the expression of claudin 3, MarvelD3, occludin and zonula ocludens 1 in the intestinal epithelium were decreased after gastric bypass surgery. Alpha-ketoglutarate supplementation partially improved intestinal structural parameters and epithelial integrity in rats undergoing this surgical procedure. Dietary AKG can abolish adverse functional changes in the intestinal mucosa, enteric nervous system, hormonal response, and maintenance of the intestinal barrier that occurred after gastric bypass surgery.

Alpha-ketoglutarate, a key molecule involved in nitrogen circulation in both animals and plants, in the context of human gut microbiota and protein metabolism

PURPOSE

Nitrogen (N₂) is an indispensable metabolite required for the synthesis of protein. In animals, gut bacteria and, to a certain extent, even hepatocytes, are able to assimilate nitrogen from ammonium (NH₄⁺), which is essentially derived from the amine group (-NH₂) and which is at the same time a very toxic metabolite. Initially, NH₄⁺ is coupled to alpha-ketoglutarate (AKG), a reaction which results in the appearance of glutamate (one amine group), and after that, in the appearance of glutamine - containing two amine groups. The surplus of NH₄⁺ which is not utilized by AKG/glutamate/glutamine is eliminated as urea in the urine, via the urea cycle in hepatocytes. Plants bacteria also assimilate nitrogen from NH₄⁺, by its fixation to ammonia (NH₃)/NH₄⁺.

MATERIALS/METHODS

Previous studies have shown that AKG (also known as 2-oxo-glutaric acid or 2-oxopentanedioic acid), the primary metabolite of Rhizobium and gut bacteria, is essential for the assimilation of nitrogen.

RESULTS

Symbiotic bacteria produce AKG, which together with glutamate dehydrogenase (GDH), 'generates' primarily amine groups from NH₄⁺. The final product is glutamate - the first amino acid. Glutamate has the capacity to be converted to glutamine, through the action of glutamine synthetase, after the assimilation of the second nitrogen from NH₄⁺.

CONCLUSION

Glutamate/glutamine, derivatives of AKG metabolism, are capable of donating amine groups for the creation of other amino acids, following NH₂ transamination to certain metabolites e.g., short chain fatty acids (SCFA).

From Acidifiers to Intestinal Health Enhancers: How Organic Acids Can Improve Growth Efficiency of Pigs

Organic acids have been used successfully in pig production as a cost-effective performance-enhancing option and they continue to be the number one alternative to antibiotic growth promoters. The aim of this review is to provide the biological rationale behind organic acids use in pig production, focusing on their different effects along the gastrointestinal tract of pigs. Organic acids are reviewed for their antimicrobial properties and for their classic use as acidifiers, with particular attention to pH modulation and microflora control. Additional beneficial effects on intestinal health and general metabolism are presented and we explain the advantage of microencapsulation as a tool to deliver organic acids along the intestine.

Diet-induced changes in brain structure and behavior in old gerbils

Background/Objectives:

Aging is associated with many physiological alterations such as changes in metabolism, food intake and brain dysfunction. Possible ways to correct age-related brain dysfunction using dietary treatments still remains undeveloped. The aim of our research was to investigate whether long-term dietary treatment with 2-oxoglutarate (2-OX), which is involved in many regulatory pathways, together with pancreatic-like enzymes of microbial origin (PLEM), which ensure appropriate digestion and absorption of nutrients, affects age-related changes in the brain morphology and cognitive function in old Mongolian gerbils.

Materials/methods:

Experiment was comprised of two separate studies. Samples of the hippocampus were obtained from male Mongolian gerbils of different ages (n=63 in the first study, n=74 in the second study). Immunohistochemistry was used for visualization of the nestin/NeuN-positive neuronal progenitors. Changes in amount of neural cell adhesion molecules (NCAMs) were estimated using enzyme-linked immunosorbent assay. For assessment of cognitive and sensorimotor functions, the T-maze spontaneous alternation test and the adhesive removal test (ART) were used. The ultrastructure of the CA1 hippocampal area was visualized using transmission electron microscopy.

Results:

Long-term treatment with 2-OX+PLEM led to a significantly increased amount of nestin/NeuN-positive cells in the CA1 hippocampal area and positive changes in learning and sensorimotor functions. As for synaptic transmission, changes in the spatial distribution of synaptic vesicles, as well as the redistribution of NCAM forms, were observed in the hippocampal synapses of the old gerbils.

Conclusions:

Taken together, our data show that dietary supplementation with 2-OX+PLEM not only enhances the proliferation and differentiation of neuronal progenitors, but also improves age-related deficits in the morphological and functional state of the brain of old gerbils. Thus, suggesting that a 2-OX+PLEM-enriched diet could also improve brain functions that have deteriorated with age.

Accelerated stability and bioassay of a new oral α-ketoglutarate formulation for treating cyanide poisoning

CONTEXT

Due to several limitations of existing cyanide antidotes, α-ketoglutarate (α-KG) has been proposed as a promising treatment for cyanide.

OBJECTIVE

This study reports the accelerated stability and bioassay of a new oral α-KG formulation.

MATERIALS AND METHODS

Amber-colored PVDF bottles containing 100 ml of 10% α-KG in 70% sorbitol, preservative (sodium methyl paraben and sodium propyl paraben), sweetener (sodium saccharine), flavor (American ice-cream soda and peppermint) and color (tartrazine), at pH 7.0-8.0 were stored in stability chamber (40 ± 2 °C and 75 ± 5% humidity) for 6 months in a GMP compliant facility. Various physical (pH, color, evaporation, extractable volume and clarity), chemical (identification and quantification of active ingredient) and microbiological (total aerobic count) analyses, together with protection studies were carried periodically in mice. Acute toxicity of the formulation and bioavailability of α-KG were assessed in rats at the beginning of the experiment.

RESULTS

No physical changes and microbiological growth were observed in the formulation. After 6 months, α-KG content in the formulation diminished by ∼24% but its protective efficacy against cyanide remained at 5.9-fold. Protection was further characterized spectrophotometrically by disappearance of α-KG spectrum in the presence of cyanide, confirming cyanohydrin formation. Oral LD50 of α-KG formulation in rats was >7.0 g/kg body weight, and did not produce any acute toxicity of clinical significance. Also, an appreciable amount of α-KG was measured in blood.

CONCLUSION

As per the guidelines of International Conference on Harmonization, the new α-KG formulation exhibited satisfactory stability, bioefficacy and safety as cyanide antidote.

Metabolic fate and function of dietary glutamate in the gut

Glutamate is a main constituent of dietary protein and is also consumed in many prepared foods as an additive in the form of monosodium glutamate. Evidence from human and animal studies indicates that glutamate is a major oxidative fuel for the gut and that dietary glutamate is extensively metabolized in first pass by the intestine. Glutamate also is an important precursor for bioactive molecules, including glutathione, and functions as a key neurotransmitter. The dominant role of glutamate as an oxidative fuel may have therapeutic potential for improving function of the infant gut, which exhibits a high rate of epithelial cell turnover. Our recent studies in infant pigs show that when glutamate is fed at higher (4-fold) than normal dietary quantities, most glutamate molecules are either oxidized or metabolized by the mucosa into other nonessential amino acids. Glutamate is not considered to be a dietary essential, but recent studies suggest that the level of glutamate in the diet can affect the oxidation of some essential amino acids, namely leucine. Given that substantial oxidation of leucine occurs in the gut, ongoing studies are investigating whether dietary glutamate affects the oxidation of leucine in the intestinal epithelial cells. Our studies also suggest that at high dietary intakes, free glutamate may be absorbed by the stomach as well as the small intestine, thus implicating the gastric mucosa in the metabolism of dietary glutamate. Glutamate is a key excitatory amino acid, and metabolism and neural sensing of dietary glutamate in the developing gastric mucosa, which is poorly developed in premature infants, may play a functional role in gastric emptying. These and other recent reports raise the question as to the metabolic role of glutamate in gastric function. The physiologic significance of glutamate as an oxidative fuel and its potential role in gastric function during infancy are discussed.

First-pass metabolism limits the intestinal absorption of enteral alpha-ketoglutarate in young pigs

Our results in a previous study indicated that the portal absorption of intragastrically fed alpha-ketoglutarate (AKG) was limited in young pigs. Our aim was to quantify the net portal absorption, first-pass metabolism, and whole-body flux of enterally infused AKG. In study 1, we quantified the net portal nutrient absorption in young pigs (n = 9) given an intraduodenal infusion of milk replacer [10 mL/(kg . h)] and either saline (control) or 930 micromol/(kg . h) AKG for 4 h. In study 2, we quantified the luminal disappearance of a duodenal AKG bolus in young pigs (n = 7). In study 3, we quantified the whole-body kinetics of (13)C-AKG metabolism when infused either enterally (n = 9) or intravenously (n = 9) in young pigs. In study 1, when compared with the control group, enteral AKG infusion increased (P < 0.01) the arterial (13.8 +/- 1.7 vs. 27.4 +/- 3.6 micromol/L) and portal (22.0 +/- 1.4 vs. 64.6 +/- 5.9 micromol/L) AKG concentrations and the net portal absorption of AKG [19.7 +/- 2.8 vs. 95.2 +/- 12.0 micromol/(kg . h)]. The mean fractional portal appearance of enterally infused AKG was 10.23 +/- 1.3%. In study 2, the luminal disappearance of AKG was 663 micromol/(kg . h), representing 63% of the intraduodenal dose. In study 3, the whole-body (13)C-AKG flux [4685 +/- 666 vs. 801 +/- 67 micromol/(kg . h)] was higher (P < 0.05) when given enterally than intravenously, but (13)CO(2) recovery was not different (37.3 +/- 1.0 vs. 36.2 +/- 0.7%dose). The first-pass splanchnic (13)C-AKG utilization was approximately 80%, of which 30% was oxidized to (13)CO(2). We conclude that the intestinal absorption of AKG is limited in young pigs largely due to substantial first-pass gastrointestinal metabolism.

Intraduodenal infusion of α-ketoglutarate decreases whole body energy expenditure in growing pigs

BACKGROUND AND AIMS

alpha-Ketoglutarate (AKG) has been suggested to play a particular role as an oxidative fuel for the gut, and thus may have a sparing function for fuels such as glutamate and aspartate. Using the pig model we aimed to quantify how the route of administration (intravenous, i.v.; intragastric, i.g.; intraduodenal, i.d.) affects AKG utilization, whole body energy expenditure (EE) and nutrient oxidation.

METHODS

Pigs (15 kg) were supplied with a complete nutrient solution (NS) via catheters. To explore the metabolic effects of AKG, 1.0 g AKG kgBW(-1)d(-1) was infused simultaneously with the NS using either the i.d., i.v. or i.g. route. [1-(13)C]AKG (15 mg kgBW(-1)) was infused i.d., i.v. or i.g., respectively, for 3h. AKG utilization (AKG UTIL) was estimated as AKG UTIL=100-(13)C recovery (% of (13)C dose). (13)C recovery was calculated from the (13)C enrichment in breath CO(2) and the whole-body CO(2) production.

RESULTS

AKG infusion and NS via the i.d. route resulted in a reduced AKG UTIL (40.1+/-6.7) as compared to the i.v. route (62.9+/-2.4, P<0.001) and i.g. route (62.3+/-1.6, P<0.001). The total EE was lower with the i.d. route of AKG and NS (745+/-68 kJkgBW(-0.62)d(-1)) as compared to the i.v. route (965+/-54 kJkgBW(-0.62)d(-1), P<0.005) and i.g. route (918+/-43 kJkgBW(-0.62)d(-1), P<0.005). Carbohydrate oxidation was increased with the i.d. route (38.2g+/-3.4 kgBW(-0.62)d(-1)) as compared to the i.v. route (27.8+/-2.9 gkgBW(-0.62)d(-1), P<0.08) and i.g. route (23.9+/-8.5 gkgBW(-0.62)d(-1), P<0.05). Fat oxidation was decreased (2.1+/-1.9 gkgBW(-0.62)d(-1); P<0.001) with the i.d. route as compared to the i.v. route (11.5+/-1.4 gkgBW(-0.62)d(-1), P<0.001) and i.g. route (11.9+/-3.1 gkgBW(-0.62)d(-1), P<0.001).

CONCLUSIONS

The i.d. infusion of AKG in combination with the NS affected the whole body EE and nutrient oxidation, in comparison to that obtained with the i.v. and i.g. routes. It was concluded that the i.d. administration of AKG markedly controlled the nutrient partitioning in the oxidation processes. Finally, in contrary to the observations with glutamine or glutamate, a considerable percentage of the AKG infusion was retained in the body irrespective of the route of administration.