The use of alpha-ketoglutarate salts in clinical nutrition and metabolic care

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.

Psat1-generated α-ketoglutarate and glutamine promote muscle stem cell activation and regeneration

By satisfying bioenergetic demands, generating biomass, and providing metabolites serving as cofactors for chromatin modifiers, metabolism regulates adult stem cell biology. Here, we report that a branch of glycolysis, the serine biosynthesis pathway (SBP), is activated in regenerating muscle stem cells (MuSCs). Gene inactivation and metabolomics revealed that Psat1, one of the three SBP enzymes, controls MuSC activation and expansion of myogenic progenitors through production of the metabolite α-ketoglutarate (α-KG) and α-KG-generated glutamine. Psat1 ablation resulted in defective expansion of MuSCs and impaired regeneration. Psat1, α-KG, and glutamine were reduced in MuSCs of old mice. α-KG or glutamine re-established appropriate muscle regeneration of adult conditional Psat1 -/- mice and of old mice. These findings contribute insights into the metabolic role of Psat1 during muscle regeneration and suggest α-KG and glutamine as potential therapeutic interventions to ameliorate muscle regeneration during aging.

Alpha-ketoglutarate supplementation reduces inflammation and thrombosis in type 2 diabetes by suppressing leukocyte and platelet activation

The interplay between platelets and leukocytes contributes to the pathogenesis of inflammation, thrombosis, and cardiovascular diseases (CVDs) in type 2 diabetes (T2D). Our recent studies described alpha-ketoglutarate (αKG), a Krebs cycle intermediate metabolite as an inhibitor to platelets and leukocytes activation by suppressing phosphorylated-Akt (pAkt) through augmentation of prolyl hydroxylase-2 (PHD2). Dietary supplementation with a pharmacological concentration of αKG significantly inhibited lung inflammation in mice with either SARS-CoV-2 infection or exposed to hypoxia treatment. We therefore investigated if αKG supplementation could suppress hyperactivation of these blood cells and reduce thromboinflammatory complications in T2D. Our study describes that dietary supplementation with αKG (8 mg/100 g body wt. daily) for 7 days significantly reduced the activation of platelets and leukocytes (neutrophils and monocytes), and accumulation of IL1β, TNFα, and IL6 in peripheral blood of T2D mice. αKG also reduced the infiltration of platelets and leukocytes, and accumulation of inflammatory cytokines in lungs by suppressing pAkt and pP65 signaling. In a cross-sectional investigation, our study also described the elevated platelet-leukocyte aggregates and pro-inflammatory cytokines in circulation of T2D patients. T2D platelets and leukocytes showed an increased aggregation and thrombus formation in vitro. Interestingly, a pre-incubation of T2D blood samples with octyl αKG significantly suppressed the activation of these blood cells and ameliorated aggregate/thrombus formation in vitro. Thus, suggesting a potential therapeutic role of αKG against inflammation, thrombosis, and CVDs in T2D.

Alpha-ketoglutarate supplementation and BiologicaL agE in middle-aged adults (ABLE)-intervention study protocol

Targeting molecular processes of aging will enable people to live healthier and longer lives by preventing age-related diseases. Geroprotectors are compounds with the potential to increase healthspan and lifespan. Even though many of them have been tested in animal models, the translation to humans is limited. Alpha-Ketoglutarate (AKG) has been studied widely in model animals, but there are few studies testing its geroprotective properties in humans. ABLE is a double blinded placebo-controlled randomized trial (RCT) of 1 g sustained release Ca-AKG versus placebo for 6 months of intervention and 3 months follow up including 120 40-60-year-old healthy individuals with a higher DNA methylation age compared to their chronological age. The primary outcome is the decrease in DNA methylation age from baseline to the end of the intervention. A total of 120 participants will be randomized to receive either sustained release Ca-AKG or placebo. Secondary outcomes include changes in the inflammatory and metabolic parameters in blood, handgrip strength and leg extension strength, arterial stiffness, skin autofluorescence, and aerobic capacity from baseline to 3 months, 6 months, and 9 months. This study will recruit middle-aged participants with an older DNA methylation age compared to their chronological age, and test whether supplementation with Ca-AKG can reduce DNA methylation age. This study is unique in its inclusion of biologically older participants.

Relationship between plasma glutamate and cardiovascular disease risk in Chinese patients with type 2 diabetes mellitus by gender

Objectives

This study aimed to assess the association between plasma glutamate (Glu) and the risk of cardiovascular disease (CVD) in patients with type 2 diabetes mellitus (T2DM) and whether this association differs by gender.

Material and methods

We retrieved clinical information on 1032 consecutive patients with T2DM from a same tertiary care center from May 2015 to August 2016. Glu was quantified by liquid chromatography-tandem mass spectrometry analysis. Glu was converted into a categorical variable based on the median concentration in the whole population, while logistic regression was used to obtain the odds ratio (OR) and 95% confidence interval (CI), and the correlation between Glu and various biochemical indices was analyzed.

Results

We found that Glu was positively associated with the risk of CVD in patients with T2DM. This correlation was more significant in women. In T2DM patients, the higher the age, body mass index (BMI), weight and systolic blood pressure (SBP), the lower the glycosylated hemoglobin (HbA1C) concentration and the higher the Glu. In female patients, the correlation between age, weight, BMI, SBP, and plasma Triglycerides (TG), and Glu was also statistically significant.

Conclusion

In conclusion, female T2DM patients with high levels of Glu have a higher risk of developing CVD.

Enhancement of α-Ketoglutaric Acid Production by Yarrowia lipolytica Grown on Mixed Renewable Carbon Sources through Adjustment of Culture Conditions

α-Ketoglutaric acid (KGA) is a valuable compound with a wide range of applications, e.g., in the cosmetics, pharmaceutical, chemical and food industries. The present study aimed to enhance the efficiency of KGA production by Yarrowia lipolytica CBS146773 from renewable carbon sources. In the investigation, various factors that may potentially affect KGA biosynthesis were examined in bioreactor cultures performed on a simple medium containing glycerol (20 g/L) and fed with four portions of a substrate mixture (15 + 15 g/L of glycerol and rapeseed oil). It was found that the process may be stimulated by regulation of the medium pH and aeration, application of selected neutralizing agents, supplementation with thiamine and addition of sorbitan monolaurate, whereas presence of biotin and iron ions had no positive effect on KGA biosynthesis. Adjustment of the parameters improved the process efficiency and allowed 82.4 g/L of KGA to be obtained, corresponding to productivity of 0.57 g/L h and yield of 0.59 g/g. In addition, the production of KGA was characterized by a low level (≤6.3 g/L) of by-products, i.e., citric and pyruvic acids. The results confirmed the high potential of renewable carbon sources (glycerol + rapeseed oil) for effective KGA biosynthesis by Yarrowia lipolytica.

Low Protein Diets Supplemented With Alpha-Ketoglutarate Enhance the Growth Performance, Immune Response, and Intestinal Health in Common Carp (Cyprinus carpio)

To investigate the effects of alpha-ketoglutarate (AKG) supplementation in a low protein (LP) diet on the growth performance, immune response, and intestinal health of common carp (Cyprinus carpio), 600 carp were randomly divided into five dietary groups: a normal protein (NP) diet containing 32% crude protein, an LP diet formulated with 28% crude protein, and LP with AKG at 0.4%, 0.8%, and 1.2% (dry matter). After an 8-week trial period, the results demonstrated that an LP diet led to a decrease in performance, immune response, and intestinal barrier function. Compared with the LP group, the final body weight and weight gain rate in the LP+0.4% AKG group were significantly higher, the feed conversion ratio was significantly decreased with the addition of 0.4% and 0.8% AKG. The supplementation with 0.4% and 0.8% AKG markedly increased the activities of T-SOD and GSH-Px, as well as the expression levels of GPX1a and GPX1b relative to the LP group, whereas the MDA content was significantly decreased in the LP+0.4% AKG group. In addition, the expression levels of tight junctions including claudin-3, claudin-7, ZO-1, and MLCK were significantly up-regulated in the LP+0.4% AKG group, and the relative expression levels of the pro-inflammatory factors IL-1β and IL-6α were significantly lower with the addition of 0.4%, 0.8%, and 1.2% AKG. Moreover, the abundance of Proteobacteria in the LP+0.4% AKG group was lower than that in the LP group, and the abundance of Firmicutes and Fusobacteria was higher at the phylum level. The abundance of Citrobacter in the LP+0.4% AKG group was decreased compared to the LP group, while the abundance of Aeromonas was increased at the genus level. In short, the effects of AKG on the intestinal health of the common carp were systematically and comprehensively evaluated from the perspectives of intestinal physical barrier, chemical barrier, biological barrier, and immune barrier. We found that an LP diet supplemented with 0.4% AKG was beneficial to the growth performance and intestinal health of common carp.

Alpha-Ketoglutarate dietary supplementation to improve health in humans

Alpha-ketoglutarate (AKG) is an intermediate in the Krebs cycle involved in various metabolic and cellular pathways. As an antioxidant, AKG interferes in nitrogen and ammonia balance, and affects epigenetic and immune regulation. These pleiotropic functions of AKG suggest it may also extend human healthspan. Recent studies in worms and mice support this concept. A few studies published in the 1980s and 1990s in humans suggested the potential benefits of AKG in muscle growth, wound healing, and in promoting faster recovery after surgery. So far there are no recently published studies demonstrating the role of AKG in treating aging and age-related diseases; hence, further clinical studies are required to better understand the role of AKG in humans. This review will discuss the regulatory role of AKG in aging, as well as its potential therapeutic use in humans to treat age-related diseases.

Serum glutamate and glutamine-to-glutamate ratio are associated with coronary angiography defined coronary artery disease

BACKGROUND AND AIMS

Serum concentrations of glutamate (Glu), Glutamine (Gln) and Gln/Glu ratio have consistently been reported to be associated with metabolic disorders and diabetes. The aim of this study was to examine the relationship between these metabolites with the presence of coronary artery disease (CAD) and CAD severity in Chinese patients.

METHODS AND RESULTS

2970 Chinese patients undergoing coronary angiography (CAG) in Beijing Hospital were enrolled. Baseline demographics and medical history data was recorded by questionnaires. Serum Glu and Gln concentrations were analyzed by isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS). Statistical analysis showed that CAD patients had significantly higher levels of Glu and lower Gln/Glu ratios compared with non-CAD control group. Glu was significantly positively associated with body mass index (BMI), fasting blood glucose (FBG), triglycerides (TG), creatinine (Crea), and uric acid (UA), and negatively associated with high-density lipoprotein cholesterol (HDL-C), while inverse associations between Gln/Glu ratio and these risk factors were observed. Glu levels increased and Gln/Glu decreased with the increase of CAD severity as represented by either the number of stenosed vessels or the Gensini scores. Logistic regression analysis demonstrated that, after adjusting for smoking status, obesity or overweight, hypertension, dyslipidemia, diabetes, stroke and family history of premature CAD, high Glu level and low Gln/Glu ratio were positively associated with CAG defined CAD as well as CAD severity expressed by Gensini score.

CONCLUSIONS

We identified Glu and Gln/Glu ratio independently associated with CAG defined CAD as well as CAD severity in Chinese patients undergoing CAG.

Protein networks linking Warburg and reverse Warburg effects to cancer cell metabolism

It was 80 years after the Otto Warburg discovery of aerobic glycolysis, a major hallmark in the understanding of cancer. The Warburg effect is the preference of cancer cell for glycolysis that produces lactate even when sufficient oxygen is provided. "reverse Warburg effect" refers to the interstitial tissue communications with adjacent epithelium, that in the process of carcinogenesis, is needed to be explored. Among these cell-cell communications, the contact between epithelial cells; between epithelial cells and matrix; and between fibroblasts and inflammatory cells in the underlying matrix. Cancer involves dysregulation of Warburg and reverse Warburg cellular metabolic pathways. How these gene and protein-based regulatory mechanisms have functioned has been the basis for this review. The importance of the Warburg in oxidative phosphorylation suppression, with increased glycolysis in cancer growth and proliferation is emphasized. Studies that are directed at pathways that would be expected to shift cell metabolism to an increased oxidation and to a decrease in glycolysis are emphasized. Key enzymes required for oxidative phosphorylation, and affect the inhibition of fatty acid metabolism and glutamine dependence are conferred. The findings are of special interest to cancer pharmacotherapy. Studies described in this review are concerned with the effects of therapeutic modalities that are intimately related to the Warburg effect. These interactions described may be helpful as adjuvant therapy in controlling the process of proliferation and metastasis.

Application of a New Engineered Strain of Yarrowia lipolytica for Effective Production of Calcium Ketoglutarate Dietary Supplements

The present study aimed to develop a technology for the production of dietary supplements based on yeast biomass and α-ketoglutaric acid (KGA), produced by a new transformant of Yarrowia lipolytica with improved KGA biosynthesis ability, as well to verify the usefulness of the obtained products for food and feed purposes. Transformants of Y. lipolytica were constructed to overexpress genes encoding glycerol kinase, methylcitrate synthase and mitochondrial organic acid transporter. The strains were compared in terms of growth ability in glycerol- and oil-based media as well as their suitability for KGA biosynthesis in mixed glycerol-oil medium. The impact of different C:N:P ratios on KGA production by selected strain was also evaluated. Application of the strain that overexpressed all three genes in the culture with a C:N:P ratio of 87:5:1 allowed us to obtain 53.1 g/L of KGA with productivity of 0.35 g/Lh and yield of 0.53 g/g. Finally, the possibility of obtaining three different products with desired nutritional and health-beneficial characteristics was demonstrated: (1) calcium α-ketoglutarate (CaKGA) with purity of 89.9% obtained by precipitation of KGA with CaCO3, (2) yeast biomass with very good nutritional properties, (3) fixed biomass-CaKGA preparation containing 87.2 μg/g of kynurenic acid, which increases the health-promoting value of the product.

Serum acylcarnitines and amino acids and risk of type 2 diabetes in a multiethnic Asian population

INTRODUCTION

We evaluated whether concentrations of serum acylcarnitines and amino acids are associated with risk of type 2 diabetes and can improve predictive diabetes models in an Asian population.

RESEARCH DESIGN AND METHODS

We used data from 3313 male and female participants from the Singapore Prospective Study Program cohort who were diabetes-free at baseline. The average age at baseline was 48.0 years (SD: 11.9 years), and participants were of Chinese, Malay, and Indian ethnicity. Diabetes cases were identified through self-reported physician diagnosis, fasting glucose and glycated hemoglobin concentrations, and linkage to national disease registries. We measured fasting serum concentrations of 45 acylcarnitines and 14 amino acids. The association between metabolites and incident diabetes was modeled using Cox proportional hazards regression with adjustment for age, sex, ethnicity, height, and parental history of diabetes, and correction for multiple testing. Metabolites were added to the Atherosclerosis Risk in Communities (ARIC) predictive diabetes risk model to assess whether they could increase the area under the receiver operating characteristic curve (AUC).

RESULTS

Participants were followed up for an average of 8.4 years (SD: 2.1 years), during which time 314 developed diabetes. Branched-chain amino acids (HR: 1.477 per SD; 95% CI 1.325 to 1.647) and the alanine to glycine ratio (HR: 1.572; 95% CI 1.426 to 1.733) were most strongly associated with diabetes risk. Additionally, the acylcarnitines C4 and C16-OH, and the amino acids alanine, combined glutamate/glutamine, ornithine, phenylalanine, proline, and tyrosine were significantly associated with higher diabetes risk, and the acylcarnitine C8-DC and amino acids glycine and serine with lower risk. Adding selected metabolites to the ARIC model resulted in a significant increase in AUC from 0.836 to 0.846.

CONCLUSIONS

We identified acylcarnitines and amino acids associated with risk of type 2 diabetes in an Asian population. A subset of these modestly improved the prediction of diabetes when added to an established diabetes risk model.

The Emerging Role of l-Glutamine in Cardiovascular Health and Disease

Emerging evidence indicates that l-glutamine (Gln) plays a fundamental role in cardiovascular physiology and pathology. By serving as a substrate for the synthesis of DNA, ATP, proteins, and lipids, Gln drives critical processes in vascular cells, including proliferation, migration, apoptosis, senescence, and extracellular matrix deposition. Furthermore, Gln exerts potent antioxidant and anti-inflammatory effects in the circulation by inducing the expression of heme oxygenase-1, heat shock proteins, and glutathione. Gln also promotes cardiovascular health by serving as an l-arginine precursor to optimize nitric oxide synthesis. Importantly, Gln mitigates numerous risk factors for cardiovascular disease, such as hypertension, hyperlipidemia, glucose intolerance, obesity, and diabetes. Many studies demonstrate that Gln supplementation protects against cardiometabolic disease, ischemia-reperfusion injury, sickle cell disease, cardiac injury by inimical stimuli, and may be beneficial in patients with heart failure. However, excessive shunting of Gln to the Krebs cycle can precipitate aberrant angiogenic responses and the development of pulmonary arterial hypertension. In these instances, therapeutic targeting of the enzymes involved in glutaminolysis such as glutaminase-1, Gln synthetase, glutamate dehydrogenase, and amino acid transaminase has shown promise in preclinical models. Future translation studies employing Gln delivery approaches and/or glutaminolysis inhibitors will determine the success of targeting Gln in cardiovascular disease.

5-Hydroxymethylfurfural and Alpha-Ketoglutaric Acid as an Ergogenic Aid During Intensified Soccer Training: A Placebo Controlled Randomized Study

Intensified training may lead to fatigue or even a state of overreaching with temporary reductions in performance. Any aid helping to prevent these consequences and to better tolerate such a training regime would be of great importance. 5-hydroxymethylfurfural (5-HMF) and α-ketoglutaric acid (α-KG) supplementation has been suggested to support favorable training outcomes but its effectiveness to facilitate adaptations during an intensified training period has never been investigated. During an in-season competition break (2 weeks), seventeen young outfield soccer players (age:14.7 ± 0.4 yr) performed a 9-day lasting shock microcyle including 5-7 repeated sprint exercise sessions in addition to the regular training (∼6 sessions/wk) and match (1-2 matches/wk) schedule. Before the training period a treadmill test to exhaustion, a YOYO intermittent recovery level 2 (YYIR2) and a repeated sprint ability (RSA) test were performed. The treadmill test was repeated 3 days after the shock microcycle whereas the YYIR2 and the RSA test on day 10 after the training. Magnitude based inference analysis showed likely positive effects of the 5-HMF/α-KG compared to the control group for changes in the maximal running velocity (+0.3 ± 0.7 vs. -0.3 ± 0.8 km/h) and running velocity at lactate turn-point 1 (+0.2 ± 0.4 vs. -0.2 ± 0.6) and lactate turn-point 2 (+0.4 ± 0.4 vs. -0.2 ± 0.6 km/h, for the 5-HMF/α-KG and placebo group, respectively). Training improved YYIR2 performance (+180 ± 67 vs. +200 ± 168m) and RSA (mean time: -0.1 ± 0.1 vs. -0.1 ± 0.1s, for the 5-HMF/α-KG and placebo group, respectively) in both groups and to the same extent. In conclusion, an in-season shock microcyle including repeated sprint training improves YYIR2 performance and RSA in youth soccer players. Supplementation with 5-HMF/α-KG did not modify training adaptations but led to likely positive exercise performance responses shortly after the intensified training regime.

Wild-type IDH2 promotes the Warburg effect and tumor growth through HIF1α in lung cancer

Hotspot mutations of isocitrate dehydrogenase 1 and 2 (IDH1/2) have been studied in several cancers. However, the function of wild-type IDH2 in lung cancer and the mechanism of its contribution to growth of cancer cells remain unknown. Here, we explored the role and mechanism of wild-type IDH2 in promoting growth of lung cancer.

Methods: Information regarding genomic and clinical application focusing on IDH2 in cancer was examined in several databases of more than 1,000 tumor samples. IDH2 expression was assessed by immunohistochemistry in tissues from lung cancer patients. The biological functions of IDH2 were evaluated by using cell-based assays and in vivo xenograft mouse models.

Results: Here we reported that wild-type IDH2 is up-regulated and is an indicator of poor survival in lung cancer and several other cancers. Targeting IDH2 with shRNA resulted in decreased HIF1α expression, leading to the attenuation of lung cancer cell proliferation and tumor growth. Treatment of lung cancer cells with AGI-6780 (a small molecule inhibitor of IDH2), PX-478 (an inhibitor of HIF1α) or incubation with octyl-α-KG inhibited lung cancer cell proliferation.

Conclusion: IDH2 promotes the Warburg effect and lung cancer cell growth, which is mediated through HIF1α activation followed by decreased α-KG. Therefore, IDH2 could possibly serve as a novel therapeutic target for lung cancer.

Anaplerotic therapy in propionic acidemia

BACKGROUND

Propionic acidemia is a rare metabolic disorder caused by a deficiency of propionyl- CoA carboxylase, the enzyme converting propionyl-CoA to methylmalonyl-CoA that subsequently enters the citric acid cycle as succinyl-CoA. Patients with propionic acidemia cannot metabolize propionic acid, which combines with oxaloacetate to form methylcitric acid. This, with the defective supply of succinyl-CoA, may lead to a deficiency in citric acid cycle intermediates.

PURPOSE

The objective of this study was to determine whether supplements with glutamine (400mg/kg per day), citrate (7.5mEq/kg per day), or ornithine α-ketoglutarate (400mg/kg per day) (anaplerotic agents that could fill up the citric acid cycle) would affect plasma levels of glutamine and ammonia, the urinary excretion of Krebs cycle intermediates, and the clinical outcome in 3 patients with propionic acidemia.

METHODS

Each supplement was administered daily for four weeks with a two week washout period between supplements. The supplement that produced the most favorable changes was supplemented for 30 weeks following the initial study period and then for a 2 year extension.

RESULTS

The urinary excretion of the Krebs cycle intermediates, α-ketoglutarate, succinate, and fumarate increased significantly compared to baseline during citrate supplementation, but not with the other two supplements. For this reason, citrate supplements were continued in the second part of the study. The urinary excretion of methylcitric acid and 3-hydroxypropionic acid did not change with any intervention. No significant changes in ammonia or glutamine levels were observed with any supplement. However, supplementation with any anaplerotic agents normalized the physiological buffering of ammonia by glutamate, with plasma glutamate and alanine levels significantly increasing, rather than decreasing with increasing ammonia levels. No significant side effects were observed with any therapy and safety labs (blood counts, chemistry and thyroid profile) remained unchanged. Motor and cognitive development was severely delayed before the trial and did not change significantly with therapy. Hospitalizations per year did not change during the trial period, but decreased significantly (p<0.05) in the 2years following the study (when citrate was continued) compared to the 2years before and during the study.

CONCLUSIONS

These results indicate that citrate entered the Krebs cycle providing successful anaplerotic therapy by increasing levels of the downstream intermediates of the Krebs cycle: α-ketoglutarate, succinate and fumarate. Citrate supplements were safe and might have contributed to reduce hospitalizations in patients with propionic acidemia.

Dietary α-ketoglutarate supplementation improves hepatic and intestinal energy status and anti-oxidative capacity of Cherry Valley ducks

α-Ketoglutarate (AKG) is an extensively used dietary supplement in human and animal nutrition. The aim of the present study was to investigate effects of dietary AKG supplementation on the energy status and anti-oxidative capacity in liver and intestinal mucosa of Cherry Valley ducks. A total of 80 1-day-old ducks were randomly assigned into four groups, in which ducks were fed basal diets supplemented with 0% (control), 0.5%, 1.0% and 1.5% AKG, respectively. Graded doses of AKG supplementation linearly decreased the ratio of adenosine monophosphate (AMP) to adenosine triphosphate (ATP) in the liver, but increased ATP content and adenylate energy charge (AEC) in a quadratic and linear manner, respectively (P < 0.05). Increasing dietary AKG supplemental levels produced linear positive responses in ATP content and AEC, and negative responses in AMP concentration, the ratio of AMP to ATP and total adenine nucleotide in the ileal mucosa (P < 0.05). All levels of dietary AKG reduced the production of jejunal hydrogen peroxide and hepatic malondialdehyde (P < 0.05). Hepatic and ileal messenger RNA expression of AMP kinase α-1 and hypoxia-inducible factor-1α were linearly up-regulated as dietary AKG supplemental levels increased (P < 0.05). In conclusion, dietary AKG supplementation linearly or quadratically enhanced hepatic and intestinal energy storage and anti-oxidative capacity of Cherry Valley ducks.

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.

Towards metabolic biomarkers of insulin resistance and type 2 diabetes: progress from the metabolome

The complex aetiology of type 2 diabetes makes effective screening, diagnosis and prognosis a substantial challenge for the physician. The rapidly developing area of metabolomics, which uses analytical techniques such as mass spectrometry and nuclear magnetic resonance, has emerged as a promising approach to identify biomarkers of diabetes and the insulin-resistant state that precedes overt pathology. Initial successes with metabolomic studies have indicated potential biomarkers for insulin resistance and for identifying people at risk of developing diabetes, with particular focus on aminoacids and lipid metabolism. These biomarkers will help to improve research and management of diabetes. In particular, several biomarkers identified could be used for early identification of diabetes risk. Furthermore, changes in selected biomarkers can indicate effectiveness of therapeutic interventions for type 2 diabetes and the metabolic syndrome. Indeed, there is much promise that branched-chain aminoacids might provide a screening biomarker for type 2 diabetes risk, allowing early dietary and exercise interventions to treat or even prevent the disease.

Neuroprotective effects of alpha-ketoglutarate and ethyl pyruvate against motor dysfunction and oxidative changes caused by repeated 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine exposure in mice

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin associated with drug abuse and causes permanent symptoms of Parkinson's disease (PD) by destroying dopaminergic neurons in the substantia nigra of the brain. In the present study, the neuroprotective effects of two carboxylic acid compounds, viz. alpha-ketoglutarate (A-KG), a Kreb’s cycle intermediate and ethyl pyruvate (EP), a lipid-soluble analogue of pyruvate, were evaluated against MPTP intoxication in mice and compared with madopar (MD; combination of levodopa plus benserazide), a standard drug. Animals received oral treatment of A-KG (500 mg/kg), EP (100 mg/kg) or MD (5 mg/kg) daily for 5 days followed by intraperitoneal administration of MPTP (20 mg/kg) and posttreatment (+10 min) of A-KG, EP or MD daily for the remaining 5 days. MPTP caused the inhibition of complex I of electron transport chain accompanied by oxidative stress in the brain. It also caused cytotoxicity in the midbrain region as characterized by histology and immunohistochemistry. Treatments of A-KG and EP were found to resolve the loss of motor coordination, oxidative stress, diminished complex I activity and tyrosine hydroxylase–positive neurons in midbrain. A-KG and EP also regressed the histological damage in the brain and minimized the accumulation of alpha-synuclein in the midbrain region. The data suggest that A-KG and EP which are nontoxic carboxylic acid compounds could be of potential therapeutic value in the treatment of PD.

Oxidative stress and tissue pathology caused by subacute exposure to ammonium acetate in rats and their response to treatments with alpha-ketoglutarate and N-acetyl cysteine

Ammonia is a widely used industrial chemical that is recognized as a potent neurotoxin and environmental pollutant. The present study addresses the oxidative stress and tissue pathology caused by 4 weeks of exposure to ammonium acetate (AMA; 100 mg/kg daily; orally) in rats, and their response to oral treatments with alpha-ketoglutarate (A-KG; 1.0 g/kg), a potential cyanide antidote, and/or N-acetyl cysteine (NAC; 10 mg/kg), an antioxidant. The organ-body weight index of brain and liver was significantly increased by AMA but kidney was unaffected. Also, plasma ammonia levels were significantly elevated without any concomitant change in blood gas status and hematology but levels of catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase and reduced glutathione (GSH) in the brain and liver were diminished, accompanied by elevated levels of malondialdehyde. Levels of glutathione disulfide (GSSG) were unaffected, but the ratio of GSH:GSSG was reduced. Plasma alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase and total bilirubin were raised but urea, uric acid and creatinine levels were not altered. AMA also caused temporal, hepatic and renal pathology. However, the renal pathology was not supported by any biochemical alterations. A-KG or NAC alone afforded less protection against AMA as compared to both given together. The protective efficacy of A-KG can be ascribed to its ability to detoxify ammonia and additionally both A-KG and NAC have antioxidant properties as well. The study suggests a new therapeutic regimen for ammonia poisoning.

Enhanced α-ketoglutaric acid production in Yarrowia lipolytica WSH-Z06 by an improved integrated fed-batch strategy

This study aimed at enhancing α-ketoglutaric acid (α-KG) production by Yarrowia lipolytica WSH-Z06. Batch culture experiments demonstrated that CaCO(3) and a relatively low pH (3.0) in the α-KG production phase contributed to α-KG synthesis. Using a two-stage pH control strategy, in which pH was buffered by CaCO(3) in the growth phase and then maintained at 3.0 in the α-KG production phase, the yield of α-KG reached 53.4 g L(-1). In the later phase of batch fermentation, the glycerol was exhausted but synthesis of α-KG did not cease. Therefore, glycerol was fed with an integrated fed-batch mode, and α-KG production increased to 66.2 g L(-1) with a productivity of 0.35 g L(-1) h(-1). Compared to optimal batch culture, α-KG production and productivity were enhanced by 23.9% and 16.7%, respectively. The two-stage pH control strategy, constant feeding approach and lower pH in later phase would be useful for α-KG industrial production.

Metabolite profiling identifies pathways associated with metabolic risk in humans

BACKGROUND

Although metabolic risk factors are known to cluster in individuals who are prone to developing diabetes mellitus and cardiovascular disease, the underlying biological mechanisms remain poorly understood.

METHODS AND RESULTS

To identify pathways associated with cardiometabolic risk, we used liquid chromatography/mass spectrometry to determine the plasma concentrations of 45 distinct metabolites and to examine their relation to cardiometabolic risk in the Framingham Heart Study (FHS; n=1015) and the Malmö Diet and Cancer Study (MDC; n=746). We then interrogated significant findings in experimental models of cardiovascular and metabolic disease. We observed that metabolic risk factors (obesity, insulin resistance, high blood pressure, and dyslipidemia) were associated with multiple metabolites, including branched-chain amino acids, other hydrophobic amino acids, tryptophan breakdown products, and nucleotide metabolites. We observed strong associations of insulin resistance traits with glutamine (standardized regression coefficients, -0.04 to -0.22 per 1-SD change in log-glutamine; P<0.001), glutamate (0.05 to 0.14; P<0.001), and the glutamine-to-glutamate ratio (-0.05 to -0.20; P<0.001) in the discovery sample (FHS); similar associations were observed in the replication sample (MDC). High glutamine-to-glutamate ratio was associated with lower risk of incident diabetes mellitus in FHS (odds ratio, 0.79; adjusted P=0.03) but not in MDC. In experimental models, administration of glutamine in mice led to both increased glucose tolerance (P=0.01) and decreased blood pressure (P<0.05).

CONCLUSIONS

Biochemical profiling identified circulating metabolites not previously associated with metabolic traits. Experimentally interrogating one of these pathways demonstrated that excess glutamine relative to glutamate, resulting from exogenous administration, is associated with reduced metabolic risk in mice.

Effect of alpha-ketoglutarate and N-acetyl cysteine on cyanide-induced oxidative stress mediated cell death in PC12 cells

Cyanide is a mitochondrial poison, which is ubiquitously present in the environment. Cyanide-induced oxidative stress is known to play a key role in mediating the neurotoxicity and cell death in rat pheochromocytoma (PC12) cells. PC12 cells are widely used as a model for neurotoxicity assays in vitro. In the present study, we investigated the protective effects of alpha-ketoglutarate (A-KG), a potential cyanide antidote, and N-acetyl cysteine (NAC), an antioxidant against toxicity of cyanide in PC12 cells. Cells were treated with various concentrations (0.625—1.25 mM) of potassium cyanide (KCN) for 4 hours, in the presence or absence of simultaneous treatment of A-KG (0.5 mM) and NAC (0.25 mM). Cyanide caused marked decrease in the levels of cellular antioxidants like superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR). Lipid peroxidation indicated by elevated levels of malondialdehyde (MDA) was found to be accompanied by decreased levels of reduced glutathione (GSH) and total antioxidant status (TAS) of the cells. Cyanide-treated cells showed notable increase in caspase-3 activity and induction of apoptotic type of cell death after 24 hours. A-KG and NAC alone were very effective in restoring the levels of GSH and TAS, but together they significantly resolved the effects of cyanide on antioxidant enzymes, MDA levels, and caspase-3 activity. The present study reveals that combination of A-KG and NAC has critical role in abbrogating the oxidative stress-mediated toxicity of cyanide in PC12 cells. The results suggest potential role of A-KG and NAC in cyanide antagonism.

Activity and gene expression profile of certain antioxidant enzymes in different organs of rats after subacute cyanide exposure: effect of alpha-ketoglutarate

Oxidative stress plays a crucial role in mediating cyanide toxicity. The present study addresses the effect of cyanide on activity and gene-expression profile of certain antioxidant enzymes and the expression of heat shock protein (HSP-70) in different organs of rats. Rats were treated with 0.50 LD(50) (7.0 mg/kg) of potassium cyanide (KCN; oral) and/or alpha-ketoglutarate (A-KG; 1.0 g/kg; oral) daily for 14 days, and various biochemical variables were measured in brain, liver, and kidney after 7 and 14 days of treatments and a 7-day recovery period. Cyanide significantly reduced the activity of glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CA) in all the organs after 7 days, while the activity of GPx in brain, liver, and kidney, GR in liver, and CA in brain remained diminished up to 14 days. The gene-expression profile of corresponding enzymes did not show any difference between the control and treatment groups. Elevated levels of malondialdehyde were observed in brain and kidney 7 and 14 days after cyanide. Cyanide also increased the expression of HSP-70 activity in brain after 7 days alone. Regression of toxicity was observed after the withdrawal of KCN. Treatment of A-KG was found to prevent all the biochemical alterations caused by cyanide. This study reveals that oxidative stress caused by cyanide was independent of the expression of antioxidant enzyme activity at the gene level, and all changes responded favorably to A-KG, indicating its therapeutic potential.

Oxidative stress mediated cytotoxicity of cyanide in LLC-MK2 cells and its attenuation by alpha-ketoglutarate and N-acetyl cysteine

Cyanide is a rapidly acting mitochondrial poison that inhibits cellular respiration and energy metabolism leading to histotoxic hypoxia followed by cell death. Cyanide is predominantly a neurotoxin but its toxic manifestations in non-neuronal cells are also documented. This study addresses the oxidative stress mediated cytotoxicity of cyanide in Rhesus monkey kidney epithelial cells (LLC-MK2). Cells were treated with various concentrations of potassium cyanide (KCN) for different time intervals and cytotoxicity was evidenced by increased leakage of intracellular lactate dehydrogenase, mitochondrial dysfunction (MTT assay) and depleted energy status of cells (ATP assay). Cytotoxicity was accompanied by lipid peroxidation indicated by elevated levels of malondialdehyde (MDA), reactive oxygen species (ROS) and reactive nitrogen species (RNS) (DCF-DA staining), diminished cellular antioxidant status (reduced glutathione (GSH), glutathione peroxidase, superoxide dismutase and catalase). These cascading events triggered an apoptotic kind of cell death characterized by oligonucleosomal DNA fragmentation and nuclear fragmentation (Hoechst 33342 staining). Apoptosis was further confirmed by increased caspase-3 activity. Cyanide-induced cytotoxicity, oxidative stress, and DNA fragmentation were prevented by alpha-ketoglutarate (A-KG) and N-acetyl cysteine (NAC). A-KG is a potential cyanide antidote that confers protection by interacting with cyanide to form cyanohydrin complex while NAC is a free radical scavenger and enhances the cellular GSH levels. The study reveals cytotoxicity of cyanide in cells of renal origin and the protective efficacy of A-KG and NAC.

The impact of preoperative micronutrient supplementation in lung surgery. A prospective randomized trial of oral supplementation of combined alpha-ketoglutaric acid and 5-hydroxymethylfurfural

OBJECTIVE

Preoperative micronutrient supplementation in fast-track surgery programs have shown to reduce complications, shorten recovery, and thereby lower costs. In a prospective randomized study, the metabolic effects of a combination of alpha-ketoglutaric acid (alpha-KG) and 5-hydroxymethylfurfural (5-HMF) were evaluated concerning their impact on improvement of exercise capacity and reduction of oxidative stress in lung surgery.

METHODS

Thirty-two consecutive patients admitted for lung resection due to NSCLC were randomized to the study protocol. All patients received preoperative nutritional guidelines according to general recommendations. In 16 (study group), a supplementation of 7.2g alpha-KG and 720 mg 5-HMF/day (SANOPAL) was administered from days 1 to 10. Spiroergometric evaluation was carried out at baseline and day 10 after micronutrient supplementation. Blood samples for the determination of oxidative stress, i.e. carbonyl proteins (CPs) and isoprostanes (IPs) were taken on at baseline, in the operating room just before resection treatment, and 25 min after single lung ventilation (SLV).

RESULTS

Spiroergometric re-evaluation showed a significant increase of VO2max (p=0.0108) and Watt's (p=0.011) in favor of the study group. Determination of oxidative stress showed a significant reduction of CPs before (p=0.048) and after SLV (p=0.0001) for the study group compared to the control group. The same is true for IPs before (p=0.003) and after SLV (p=0.02). Hospitalization and intensive care unit (ICU) of the study group showed a significant reduction compared to the control group (p=0.03 and p=0.02, respectively).

CONCLUSIONS

Simple oral supplementation using a combination of alpha-KG and 5-HMF of preoperative micronutrition may therefore be one further step in a multimodality approach of fast-track surgery programs also in lung surgery.

Effects of ornithine alpha-ketoglutarate on protein metabolism in Yoshida sarcoma-bearing rats

BACKGROUND & AIMS

Ornithine alpha-ketoglutarate (OKG) is recognized to improve nutritional status in various catabolic states, such as burn injury, trauma, and sepsis. However, in wasting diseases, such as induced by cancer, the data are scarce and the precise mechanisms by which OKG acts on protein metabolism are still unclear. The aim of this study was to evaluate the ability of OKG to affect protein metabolism in an aggressive model of cancer and to modulate the ubiquitin-proteasome-dependent pathway, which in skeletal muscle is the critical degradative pathway implicated in many catabolic states, including cancer-associated cachexia.

METHODS

Experiments were carried out in Yoshida sarcoma-bearing and healthy pair-fed rats. Three groups of 16 young male rats were studied during 9 days following tumor implantation: two groups of tumor-bearing rats fed a balanced regimen enriched with either OKG (5 g/kg body weight/day, OKG-K) or an isonitrogenous mixture of non-essential amino acids (C-K), and one group of healthy pair-fed rats (PF).

RESULTS

As expected, Yoshida sarcoma induced muscle atrophy, decreased nitrogen balance, enhanced 3-methylhistidine (3-MH) excretion and increased mRNA levels for ubiquitin and 14-kDa ubiquitin-conjugating enzyme E2. OKG supplementation did not improve muscle mass or protein balance and did not reduce enhanced 3-MH excretion in Yoshida sarcoma-bearing rats. Furthermore, OKG did not suppress in the cancer rats the enhanced expression of ubiquitin and 14-kDa E2, despite OKG decreased by 23% the ubiquitination rate in cancer rats (OKG-K vs. C-K, P<0.05).

CONCLUSIONS

These data suggest that OKG action is not universal; i.e. depending upon the model under study. In the circumstances, OKG did not counteract the increase in ubiquitin-proteasome-dependent proteolysis observed in Yoshida sarcoma-bearing rats.

Dose dependency of the effect of ornithine α-ketoglutarate on tissue glutamine concentrations and hypercatabolic response in endotoxaemic rats

The optimal dosage of ornithine α-ketoglutarate (OKG) for repleting tissue glutamine (Gln) concentrations and maintaining N homeostasis after injury is unknown. We set out to perform ‘dose-ranging’ of OKG supplementation after an endotoxaemic challenge. Sixty-one male Wistar rats were injected with 3 mg lipopolysaccharide (LPS) from Escherichia coli/kg (n 50) or saline vehicle (9 g NaCl/l; controls n 11). After a 24 h fast, survivors were fed by gavage for 48 h with a polymeric standard diet (879 kJ/kg per d and 1·18 g N/kg per d) supplemented with non-essential amino acids (control, n 11; LPS-OKG-0·0, n 9), or with 0·5 g OKG/kg per d (LPS-OKG-0·5, n 12), 1·5 OKG/kg per d (LPS-OKG-1.5, n 11) or 4·5 g OKG/kg per d (LPS-OKG-4·5, n 10). The diets for all groups were made isonitrogenous with the LPS-OKG-4·5 diet by adding an appropriate amount of non-essential amino acids. Rats were killed on day 3 for blood and tissue sampling (muscle, jejunum mucosa, liver). Urine was collected daily for 3-methylhistidine and total N assays. The OKG dose was correlated with Gln concentrations in every tissue and with cumulative N balance (Spearman test, P<0·01). 3-Methylhistidine excretion was increased in endotoxaemic groups compared with controls (ANOVA, P<0·05) except in the LPS-OKG-4·5 group. Only the LPS-OKG-4·5 group achieved a positive post-injury N balance (t test, P<0·05). In conclusion, OKG exerted a dose-dependent effect on tissue Gln concentration and N balance, but only the highest dosage counteracted myofibrillar hypercatabolism and caused a positive N balance.

Ornithine alpha-ketoglutarate increases mineralization and mechanical properties of tibia in turkeys

Skeletal disorders in rapidly growing poultry are commonplace. This study was performed to investigate the effect of ornithine alpha-ketoglutarate (OKG) administration during the last 7 weeks of life on structural properties, mineralization, and mechanical endurance of skeleton in turkeys at slaughter. Healthy HB Medium Bronze female turkeys were randomly assigned to two weight-matched groups at the age of 12 weeks. OKG was administered orally to the experimental group (N=17) at the dose of 0.4 g/kg body weight per day, while the control group (N=16) received an equal dose of the vehicle. The turkeys were slaughtered at the age of 19 weeks and the tibiae were isolated for analysis. The effect of OKG on skeletal system development in turkeys was evaluated in relation to both geometrical and mechanical properties as well as quantitative computed tomography (QCT). Free amino acids concentrations were assessed with the use of ion-exchange chromatography. Significantly increased bone mineral density of the trabecular and the cortical bone of tibia in the turkeys given OKG for the last 7 weeks of production cycle were observed (P<0.05). OKG administration improved mechanical endurance of the tibia estimated by the three-point bending test (P<0.01). Plasma amino acid analyses showed increased level of aspartate, proline, alanine, valine, isoleucine, leucine, and ornithine (all P<0.05) after OKG treatment, whereas cystathionine concentration was decreased (P=0.03). Obtained results indicate that oral OKG administration has beneficial effects on skeletal development in fast growing turkeys and this effect is connected with increased amino acid synthesis. These observations may serve to improve skeletal properties in birds, especially when considering that skeletal disorders often affect the tibia and the proper function of the skeletal system plays an essential role in animal welfare and poultry production.

Pretreatment of starved rats with ornithine alpha-ketoglutarate: effects on hepatic mRNA levels and plasma concentrations of three liver-secreted proteins

OBJECTIVE

Ornithine alpha-ketoglutarate (OKG) displays anabolic properties at the hepatic level, but the mechanisms involved remain unclear. This study investigated in vivo the ability of OKG to modulate hepatic gene expression of three liver-secreted proteins: albumin, transthyretin, and retinol binding protein.

METHODS

One hundred eighty rats were fed for 5 d with a balanced regimen enriched with OKG (5 g.kg(-1).d(-1)) or an isonitrogenous mixture (alanine, glycine, and serine). Hepatic mRNA levels and plasma concentrations of the three proteins studied were determined at the end of the nutrition period and after 1, 2, and 3 d of food deprivation. Results were compared by analysis of variance and Bonferroni-Dunn tests.

RESULTS

At the end of the nutrition period, hepatic mRNA levels and plasma concentrations of the three proteins were not modified by OKG supplementation. However, OKG largely increased mRNA levels of albumin, transthyretin, and retinol binding protein on the first day of starvation compared with control animals (+68%, +64% and +51%, respectively; P < 0.01 versus control). OKG precociously increased albuminemia (on day 2) but had no effect on plasma concentrations of transthyretin and retinol binding protein. Neither regulation of polyamine hepatic concentration nor alteration in hepatic amino acid content seemed to be implicated in these actions.

CONCLUSION

This study is the first to demonstrate that OKG regulates in vivo liver gene expression during acute malnutrition by modulating hepatic mRNA levels.

Ornithine alpha-ketoglutarate supplementation influences motor activity in healthy rats

BACKGROUND

Ornithine alpha-ketoglutarate (OKG) improves nutritional status in malnourished patients. Published and unpublished data suggest OKG may have effects on the central nervous system that may contribute to its action.

OBJECTIVE

We investigated the effect of an OKG-enriched diet on behaviour in healthy rats.

DESIGN

Thirty male Wistar rats were randomised in three groups: the OKG group was fed for 5 days (D0-D5) at 90% of spontaneous food intake with an OKG-enriched diet (5 g/kg/d). The non-essential amino acids (NEAA) group was fed similarly with a regimen enriched with NEAA (glycine, alanine, histidine and serine) to be isonitrogenous to OKG group. The ad libitum (AL) group had no treatment and was fed ad libitum with a standard regimen throughout. Rats were tested at D4 for motor activity by actimetry, and at D5 first for spontaneous alternation behaviour measured in the Y-maze, and then for exploratory behaviour measured using the open-field test (stressful environment).

RESULTS

We found that OKG supplementation enhanced global motricity by actimetry (AL 772 +/- 55, NEAA 811 +/- 54 vs. OKG 966 +/- 24 arbitrary units, P < 0.05) and total numbers of arms visited in the Y-maze (AL 26 +/- 2, NEAA 30 +/- 3 vs. OKG 38 +/- 3, P < 0.05). The lack of any effect of the OKG-enriched diet in the open-field test shows that the enhancement of locomotion activity was most probably not due to an increase in anxiety or fear in the rats.

CONCLUSION

An OKG-enriched diet can induce beneficial stimulant effects that may be involved in the mechanism of action of OKG.

Ornithine alpha-ketoglutarate as a potent precursor of arginine and nitric oxide: a new job for an old friend

Ornithine alpha-ketoglutarate (OKG) is a salt formed of 2 molecules of ornithine and 1 alpha-ketoglutarate. Its administration improves nutritional status in chronically malnourished (e.g., elderly) and acutely malnourished patients (especially burn and trauma patients). There is evidence that OKG activity is not the simple addition of the effects of ornithine (Orn) and alpha-ketoglutarate (alphaKG), because the presence of both moieties is required to induce the generation of key metabolites such as glutamine, proline, and arginine (Arg), whereas this does not occur when one or the other is given separately. This observation is related to the fact that the main feature of Orn at the whole-body level is to be metabolized through the Orn aminotransferase-dependent pathway, whereas the simultaneous administration of Orn and alphaKG saturates this pathway, diverting Orn toward metabolism into Arg. For years, OKG activity has been associated with its ability to induce the secretion of anabolic hormones, such as insulin and growth hormone, and to increase glutamine and polyamine synthesis. Recent studies using chemical inhibitors of nitric oxide synthase (NOS) suggest that nitric oxide derived from Arg could be partly involved in OKG activity. The use of genetically modified animals (i.e., knockout for NOS expression) is required to confirm this hypothesis.

In vivo induction of insulin secretion by ornithine alpha-ketoglutarate: involvement of nitric oxide and glutamine

We previously demonstrated that ornithine alpha-ketoglutarate (OKG), known for its anabolic properties, induces insulin secretion in vitro. The present study was undertaken to further characterize this effect in vivo and investigate a possible interaction with glucose both in vivo and in vitro. Male Wistar rats received an intravenous bolus of OKG (25 mg/kg) and/or glucose (0.8 g/kg) or saline, and their plasma insulin and glucose levels were monitored for 30 minutes. OKG alone increased plasma insulin to a similar extent to glucose. In combination with glucose, OKG significantly increased glucose-induced insulin secretion in vivo and in vitro, and led to a significant increase in glucose utilization in vivo. The absence of significant variations in plasma arginine and glutamine suggests a direct effect of OKG on the pancreas. To assess the involvement of the synthesis of nitric oxide and glutamine in OKG-induced insulin secretion, the experiments were repeated in the presence of inhibitors of these 2 pathways, respectively L-nitroarginine-methylester (L-NAME) and methionine sulfoximine (MSO). Both inhibitors were able significantly to reduce OKG-induced insulin secretion without affecting either basal or glucose-induced insulin release. Thus OKG acts directly with glucose on islets to induce insulin secretion via mechanisms involving NO and glutamine synthesis. In addition, our results suggest that OKG and glucose act via separate pathways.

Effects of ornithine alpha-ketoglutarate on insulin secretion in rat pancreatic islets: implication of nitric oxide synthase and glutamine synthetase pathways

Ornithine alpha-ketoglutarate (OKG) administration in human subjects elicits insulin secretion. We investigated whether this action was related to an effect of OKG on islets of Langerhans, and addressed the underlying mechanisms of action. For this purpose the influence of OKG on insulin secretion was measured in isolated rat islets of Langerhans under two different conditions. In incubated islets, OKG (0.25 to 2.5 mmol/l) significantly and dose-relatedly increased insulin secretion (1.7- to 4.2-fold; P<0.05 v. basal). To study the kinetics of OKG-stimulated insulin secretion, perifusion experiments were performed, which showed that OKG affected insulin secretion in both initial and later phases. Experiments using alpha-ketoglutarate (alpha-KG) (1 mmol/l) or ornithine (Orn) (2 mmol/l) alone, in concentrations equal to that of OKG, showed that the OKG-induced insulin secretion could not be obtained by either component alone, suggesting that an alpha-KG-Orn interaction is mandatory for the insulin-secreting effect to occur. Since data obtained in vivo suggest that effects of OKG may depend on the synthesis of NO, glutamine and/or polyamines, three metabolic pathways potentially involved in insulin secretion, we then evaluated their contribution by means of their respective inhibitors: l-NG-nitroarginine methyl ester (l-NAME), methionine sulfoximine (MSO) and difluoromethylornithine (DFMO). Both l-NAME and MSO were able significantly to reduce OKG-induced insulin secretion (30 and 40 % respectively; P<0.05), while DFMO was ineffective. Thus OKG is an effective stimulator of insulin secretion, requiring the joint presence of both Orn and alpha-KG, and acting mainly via the synthesis of NO and glutamine. A better understanding of OKG insulino-secretory properties and its mechanisms of action are a prerequisite for its use in insulin-compromised situations.

Alpha-ketoglutarate-supplemented enteral nutrition: effects on postoperative nitrogen balance and muscle catabolism

Enteral feeding in the early postoperative phase may improve gut integrity and reduce infectious complications after trauma and surgery. The aim of the current study was to evaluate the feasibility of alpha-ketoglutarate enrichment of enteral feeding and the effect on protein metabolism after major surgery. Patients undergoing elective abdominal surgery were randomly allocated to receive a standard whole-protein-based enteral nutrition solution (n = 9) or an isonitrogenous, isocaloric solution enriched with alpha-ketoglutarate (n = 11) for 5 d postoperatively. The nutritional goals by day 4 were 25 kcal and 0.17 g of nitrogen, respectively, per kilogram of body weight every 24 h. Standard blood analysis, including prealbumin and C-peptide, was performed preoperatively and on days 1, 3, and 6. Urine was collected daily for nitrogen and 3-methylhistidine analyses. Due to restricted tolerance to enteral feeding, the nitrogen delivery reached only 0.10 g of nitrogen per kilogram of body weight. Transthyretin decreased by 25% in both groups, and albumin decreased significantly in the enriched group compared with the standard nutrition. There were no significant differences in nitrogen balance, excretion of 3-methylhistidine, or clinical outcome between groups. Enrichment of a whole-protein-based formula with alpha-ketoglutarate did not improve protein metabolism or decrease muscle catabolism after major abdominal surgery.

Effects of ornithine alpha-ketoglutarate on circulatory antioxidants and lipid peroxidation products in ammonium acetate treated rats

The effects of ornithine alpha-ketoglutarate (OKG) on ammonium acetate induced hepatotoxicity were studied biochemically in rats. The levels of urea, nonprotein nitrogen, and thiobarbituric acid reactive substances were significantly increased in ammonium acetate treated rats; these levels were significantly decreased in rats treated with ammonium acetate and OKG. Similar patterns of alterations were observed in the levels of free fatty acids, triglycerides, and phospholipids. Furthermore, nonenzymatic antioxidants (vitamins C and E) were significantly decreased in ammonium acetate treated rats, when compared with control rats, and increased in OKG and ammonium acetate treated rats. The biochemical alterations during OKG treatment could be (1) by detoxifying excess ammonia; (2) by participating in nonenzymatic oxidative decarboxylation in the hydrogen peroxide decomposition process, and (3) by enhancing the proper metabolism of fats which could suppress oxygen radical generation and thus prevent the lipid peroxidative damages in rats.

Nutraceuticals: a pharmaceutical viewpoint: I

PURPOSE OF REVIEW

To review pharmaceutical aspects of selected amino acids, antioxidants and related nutraceuticals, deemed to be important for clinical nutrition.

RECENT FINDINGS

New clinical applications of nutraceuticals are increasingly being reported, but there are fundamental differences between formulation, production and the evidence supporting clinical use. Nutraceuticals generally fall within the novel foods and ingredients regulations but their purity, dosage requirements and clinical consequences exceed those of most 'healthfoods'. Replacement of one nutrient or antioxidant is unlikely to correct the cascade of interconnected metabolic abnormalities associated with many diseases. However, it is difficult to ascertain whether the reported benefits of complex mixtures, with little published stability data, are due to one or more individual substrates or some in-vitro interaction between them. Many clinical studies have suffered from inconsistencies of dose, formulation discrepancies and unproven outcome. These contradictory results weaken any firm evidence base to substantiate their effectiveness.

SUMMARY

Nutraceuticals are destined to play an important role in future therapeutic developments but their success will be governed by control of purity, safety and efficacy without inhibiting innovation. The straightforward application of pharmaceutical standards, especially across national borders, is likely to be a difficult challenge and could effectively paralyse the industry. Nevertheless more standardized formulations, dosage forms and production controls are called for. A place for nutraceuticals in clinical practice is emerging, but important pharmaceutical and clinical issues need to be addressed by further research.