Creatine synthesis: hepatic metabolism of guanidinoacetate and creatine in the rat in vitro and in vivo

Global 13C tracing and metabolic flux analysis of intact human liver tissue ex vivo

Liver metabolism is central to human physiology and influences the pathogenesis of common metabolic diseases. Yet, our understanding of human liver metabolism remains incomplete, with much of current knowledge based on animal or cell culture models that do not fully recapitulate human physiology. Here, we perform in-depth measurement of metabolism in intact human liver tissue ex vivo using global 13C tracing, non-targeted mass spectrometry and model-based metabolic flux analysis. Isotope tracing allowed qualitative assessment of a wide range of metabolic pathways within a single experiment, confirming well-known features of liver metabolism but also revealing unexpected metabolic activities such as de novo creatine synthesis and branched-chain amino acid transamination, where human liver appears to differ from rodent models. Glucose production ex vivo correlated with donor plasma glucose, suggesting that cultured liver tissue retains individual metabolic phenotypes, and could be suppressed by postprandial levels of nutrients and insulin, and also by pharmacological inhibition of glycogen utilization. Isotope tracing ex vivo allows measuring human liver metabolism with great depth and resolution in an experimentally tractable system.

Effect of Guanidinoacetic Acid Supplementation on the Performance of Calves Fed Milk Replacer

Guanidinoacetic acid (GAA) is the direct precursor to creatine, which serves as an energy reserve mechanism in the body. We evaluated the effects of GAA supplementation on the growth performance of calves fed milk replacer. Forty-five Holstein-Angus steer calves (40.9 kg, approximately 1 week old) were assigned to 1 of 3 treatments to assess growth performance and data from 41 calves were analyzed. Treatments were provided in the milk replacer for 42 d and included 0, 1, or 2 g GAA/d. Calves were fed 2.84 L milk replacer twice daily with ad libitum access to starter feed and water. Treatments ended on day 42 prior to a 17-day weaning period. Supplementation of GAA increased (p < 0.01) plasma concentrations of GAA (0.42, 0.51, and 0.67 mg/L for 0, 1, and 2 g GAA/d, respectively) and creatine (18.7, 22.1, and 24.4 mg/L for 0, 1, and 2 g GAA/d, respectively). Bodyweight tended to linearly increase (p = 0.09) with increasing GAA on d 59 (91.2, 98.3, and 98.6 kg for 0, 1, and 2 g GAA/d, respectively). Daily gains from day 0 to 59 tended to increase with GAA provision (p = 0.09; 0.86, 0.97, and 0.98 kg/d for 0, 1, and 2 g GAA/d, respectively). Starter feed dry matter intake tended to linearly increase (p = 0.06) with GAA supplementation (0.201, 0.278, and 0.286 kg/d for 0, 1, and 2 g GAA/d, respectively). Treatments providing 1 and 2 g GAA/d affected performance similarly. No differences among treatments were observed for health (respiratory and fecal) scores during the application of treatments or during the subsequent weaning period. The inclusion of GAA in milk replacer tended to increase the gain of calves, and this was associated with elevated starter feed intake.

NMR-based metabolomics analysis reveals the effect of environmental contamination exposure on fishermen living around the Mundaú Lagoon in Maceió (Alagoas, Brazil)

The Mundaú lagoon in Maceió (Alagoas, Brazil) is a crucial resource for the local population, particularly fishing communities. Recent studies have revealed potential toxic metal contamination in the lagoon, particularly with mercury (Hg) levels exceeding the maximum regulated values. This inorganic contaminant may be impacting the health of fishermen and the local population. In this context, metabolomics, a study of small-molecule metabolites, can offer insights into the physiological impact of environmental contamination on humans. Thus, volunteers from the control and exposed groups were selected, considering the main exposure criteria primarily defined by their proximity and interaction with the lagoon. Blood and urine samples were collected from the volunteers and subjected to analysis using NMR spectroscopy. The data underwent Principal Component Analysis (PCA) and Orthogonal Partial Least-Squares Discriminant Analysis (OPLS-DA) based on metabolic patterns to establish group discrimination or identification. Metabolic pathways were assessed through enrichment analysis. The study revealed several metabolic disturbances in the exposed group's urine and plasma samples compared to control group. Noteworthy findings included arginine and proline metabolism disruptions, indicative of ammonia recycling and urea cycle impairment. These changes suggest compromised ammonia detoxification in the exposed group. Disturbances in the tricarboxylic acid (TCA) cycle and the transfer of acetyl groups into mitochondria suggested systemic metabolic stress in energy metabolism. Furthermore, elevated carnitine and ketone levels may indicate compensatory responses to low TCA cycle activity. Alterations in glutamate and glutathione metabolism and imbalances in glutathione levels indicate oxidative stress and impaired detoxification. This study highlights significant metabolic changes in fishermen exposed to contaminated environments, which can affect various metabolic pathways, including energy metabolism and antioxidant processes, potentially making individuals more vulnerable to the adverse effects of environmental contaminants. Finally, this work highlights insights into the relationship between environmental contamination and metabolic pathways, particularly in regions with limited studies.

NMR-based metabolomics for investigating urinary profiles of metal carpentry workers exposed to welding fumes and volatile organic compounds

Introduction

Metal carpentry includes a wide range of work activities such as welding and cutting metallic components, use of solvents and paints. Therefore, the employees in these types of activities are mainly exposed to welding fumes and volatile organic solvents. Here, we present an NMR-based metabolomic approach for assessing urinary profiles of workers in the same company that are exposed to two different risk factors.

Methods

The study enrolled 40 male subjects exposed to welding fumes, 13 male subjects exposed to volatile organic compounds of a metal carpentry company, and 24 healthy volunteers. All samples were collected, in the middle of the working week at fast. Thirty-five urinary metabolites belonging to different chemical classes such as amino acids, organic acids and amines were identified and quantified. Results were processed by multivariate statistical analysis for identifying significant metabolites for each working group examined, compared to controls.

Results

Workers exposed to welding fumes displayed urinary increase in glutamine, tyrosine, taurine, creatine, methylguanidine and pseudouridine associated to oxidative impairment, while workers exposed to volatile organic compounds showed higher urinary levels of branched chain aminoacids.

Conclusion

Our work identified specific urinary profile related to each occupational exposure, even if it is below the threshold limit values.

Oat protein modulates cholesterol metabolism and improves cardiac systolic function in high fat, high sucrose fed rats

Oats are recognized to provide many health benefits that are mainly associated with its dietary fibre, β-glucan. However, the protein derived from oats is largely understudied with respect to its ability to maintain health and attenuate risk factors of chronic diseases. The goal of the current study was to investigate the metabolic effects of oat protein consumption in lieu of casein as the protein source in high fat, high sucrose (HF/HS) fed Wistar rats. Four-week-old rats were divided into three groups and were fed three different experimental diets: a control diet with casein as the protein source, an HF/HS diet with casein, or an HF/HS diet with oat protein for 16 weeks. Heart structure and function were determined by echocardiography. Blood pressure measurements, an oral glucose tolerance test, and markers of cholesterol metabolism, oxidative stress, inflammation, and liver and kidney damage were also performed. Our study results show that incorporation of oat protein in the diet was effective in preserving systolic heart function in HF/HS fed rats. Oat protein significantly reduced serum total and low-density lipoprotein cholesterol levels. Furthermore, oat protein normalized liver HMG-CoAR activity, which, to our knowledge, is the first time this has been reported in the literature. Therefore, our research suggests that oat protein can provide hypocholesterolemic and cardioprotective benefits in a diet-induced model of metabolic syndrome.

Membrane transporters in cell physiology, cancer metabolism and drug response

By controlling the passage of small molecules across lipid bilayers, membrane transporters influence not only the uptake and efflux of nutrients, but also the metabolic state of the cell. With more than 450 members, the Solute Carriers (SLCs) are the largest transporter super-family, clustering into families with different substrate specificities and regulatory properties. Cells of different types are, therefore, able to tailor their transporter expression signatures depending on their metabolic requirements, and the physiological importance of these proteins is illustrated by their mis-regulation in a number of disease states. In cancer, transporter expression is heterogeneous, and the SLC family has been shown to facilitate the accumulation of biomass, influence redox homeostasis, and also mediate metabolic crosstalk with other cell types within the tumour microenvironment. This Review explores the roles of membrane transporters in physiological and malignant settings, and how these roles can affect drug response, through either indirect modulation of sensitivity or the direct transport of small-molecule therapeutic compounds into cells.

Methionine: An Indispensable Amino Acid in Cellular Metabolism and Health of Atlantic Salmon

Methionine is an indispensable amino acid with an important role as the main methyl donor in cellular metabolism for both fish and mammals. Metabolization of methionine to the methyl donor S-adenosylmethionine (SAM) has consequence for polyamine, carnitine, phospholipid, and creatine synthesis as well as epigenetic modifications such as DNA- and histone tail methylation. Methionine can also be converted to cysteine and contributes as a precursor for taurine and glutathione synthesis. Moreover, methionine is the start codon for every protein being synthetized and thereby serves an important role in initiating translation. Modern salmon feed is dominated by plant ingredients containing less taurine, carnitine, and creatine than animal-based ingredients. This shift results in competition for SAM due to an increasing need to endogenously synthesize associated metabolites. The availability of methionine has profound implications for various metabolic pathways including allosteric regulation. This necessitates a higher nutritional need to meet the requirement as a methyl donor, surpassing the quantities for protein synthesis and growth. This comprehensive review provides an overview of the key metabolic pathways in which methionine plays a central role as methyl donor and unfolds the implications for methylation capacity, metabolism, and overall health particularly emphasizing the development of fatty liver, oxidation, and inflammation when methionine abundance is insufficient focusing on nutrition for Atlantic salmon (Salmo salar).

The value of prospective metabolomic susceptibility endotypes: broad applicability for infectious diseases

BACKGROUND

As new infectious diseases (ID) emerge and others continue to mutate, there remains an imminent threat, especially for vulnerable individuals. Yet no generalizable framework exists to identify the at-risk group prior to infection. Metabolomics has the advantage of capturing the existing physiologic state, unobserved via current clinical measures. Furthermore, metabolomics profiling during acute disease can be influenced by confounding factors such as indications, medical treatments, and lifestyles.

METHODS

We employed metabolomic profiling to cluster infection-free individuals and assessed their relationship with COVID severity and influenza incidence/recurrence.

FINDINGS

We identified a metabolomic susceptibility endotype that was strongly associated with both severe COVID (ORICUadmission = 6.7, p-value = 1.2 × 10-08, ORmortality = 4.7, p-value = 1.6 × 10-04) and influenza (ORincidence = 2.9; p-values = 2.2 × 10-4, βrecurrence = 1.03; p-value = 5.1 × 10-3). We observed similar severity associations when recapitulating this susceptibility endotype using metabolomics from individuals during and after acute COVID infection. We demonstrate the value of using metabolomic endotyping to identify a metabolically susceptible group for two-and potentially more-IDs that are driven by increases in specific amino acids, including microbial-related metabolites such as tryptophan, bile acids, histidine, polyamine, phenylalanine, and tyrosine metabolism, as well as carbohydrates involved in glycolysis.

INTERPRETATIONS

These metabolites may be identified prior to infection to enable protective measures for these individuals.

FUNDING

The Longitudinal EMR and Omics COVID-19 Cohort (LEOCC) and metabolomic profiling were supported by the National Heart, Lung, and Blood Institute and the Intramural Research Program of the National Center for Advancing Translational Sciences, National Institutes of Health.

Creatine Supplementation to Improve Sarcopenia in Chronic Liver Disease: Facts and Perspectives

Creatine supplementation has been one of the most studied and useful ergogenic nutritional support for athletes to improve performance, strength, and muscular mass. Over time creatine has shown beneficial effects in several human disease conditions. This review aims to summarise the current evidence for creatine supplementation in advanced chronic liver disease and its complications, primarily in sarcopenic cirrhotic patients, because this condition is known to be associated with poor prognosis and outcomes. Although creatine supplementation in chronic liver disease seems to be barely investigated and not studied in human patients, its potential efficacy on chronic liver disease is indirectly highlighted in animal models of non-alcoholic fatty liver disease, bringing beneficial effects in the fatty liver. Similarly, encephalopathy and fatigue seem to have beneficial effects. Creatine supplementation has demonstrated effects in sarcopenia in the elderly with and without resistance training suggesting a potential role in improving this condition in patients with advanced chronic liver disease. Creatine supplementation could address several critical points of chronic liver disease and its complications. Further studies are needed to support the clinical burden of this hypothesis.

Supply and demand of creatine and glycogen in broiler chicken embryos

Optimal embryonic development and growth of meat-type chickens (broilers) rely on incubation conditions (oxygen, heat, and humidity), on nutrients and on energy resources within the egg. Throughout incubation and according to the embryo's energy balance, the main energy storage molecules (creatine and glycogen) are continuously utilized and synthesized, mainly in the embryonic liver, breast muscle, and the extraembryonic yolk sac (YS) tissue. During the last phase of incubation, as the embryo nears hatching, dynamic changes in energy metabolism occur. These changes may affect embryonic survival, hatchlings' uniformity, quality and post hatch performance of broilers, hence, being of great importance to poultry production. Here, we followed the dynamics of creatine and glycogen from embryonic day (E) 11 until hatch and up to chick placement at the farm. We showed that creatine is stored mainly in the breast muscle while glycogen is stored mainly in the YS tissue. Analysis of creatine synthesis genes revealed their expression in the liver, kidney, YS tissue and in the breast muscle, suggesting a full synthesis capacity in these tissues. Expression analysis of genes involved in gluconeogenesis, glycogenesis, and glycogenolysis, revealed that glycogen metabolism is most active in the liver. Nevertheless, due to the relatively large size of the breast muscle and YS tissue, their contribution to glycogen metabolism in embryos is valuable. Towards hatch, post E19, creatine levels in all tissues increased while glycogen levels dramatically decreased and reached low levels at hatch and at chick placement. This proves the utmost importance of creatine in energy supply to late-term embryos and hatchlings.

Isolated Pancreatic Metastases of Renal Cell Carcinoma-Clinical Particularities and Seed and Soil Hypothesis

A meta-analysis of 1470 isolated pancreatic metastases of renal cell carcinoma revealed, that, in addition to the unusual exclusive occurrence of pancreatic metastases and the favourable treatment results, the isPMRCC is characterised by further peculiarities of the clinical course: The lack of prognostic significance of volume and growth rate dependent risk factors and the independence of treatment results from standard or local resections. As an explanation for all these peculiarities, according to today's knowledge, a strong acting seed and soil mechanism can serve, which allows embolized tumour cells to grow to metastases only in the pancreas, and prevents them definitively or for years in all other organs. The good prognosis affects not only isolated PM, but also multi-organ metastases of the RCC, in which the additional occurrence of PM is also associated with a better prognosis. Genetic studies revealed specific changes in cases of PM of RCC: Lack of loss of 9p21.3 and 14q31.2, which are otherwise specific gene mutations at the onset of generalization, a low weight genome instability index, i.e., high genetic stability, and a low rate of PAB1 and a high rate of BPRM1 alterations, which signal a more favourable course. The cause of pancreatic organotropism in isPMRCC is still unclear, so only those factors that have been identified as promoting organotropism in other, more frequent tumour entities can be presented: Formation of the pre-metastatic niche, chemokine receptor-ligand mechanism, ability to metabolic adaptation, and immune surveillance.

Hepatic urea, creatinine and uric acid metabolism in dairy cows with divergent milk urea concentrations

Milk urea concentration is an indicator for dietary nitrogen (N)-supply and urinary N-excretion. Dairy cows with high (HMU) compared to low milk urea (LMU) concentration have greater plasma urea, creatinine and uric acid concentrations, but if the liver metabolism accounts for these differences is unknown. Eighteen HMU and 18 LMU cows were fed a diet with a low (LP) or normal (NP) crude protein concentration. A N balance study was performed and a ¹³C-urea bolus was administered to measure urea pool size. Liver samples were analyzed by 2D-gel-based proteomics and RT-qPCR. Although HMU cows had a greater urea pool, plasma urea, uric acid, and hippuric acid concentrations, these differences were not associated with altered expressions of genes related to urea cycling or N-metabolism. Instead, HMU cows had higher oxidative stress levels. Conclusively, other factors than hepatic urea metabolism account for milk urea concentrations. Despite higher plasma urea concentrations and argininosuccinate synthase 1 protein expression on the LP diet, urea cycle mRNA expressions were not affected, indicating that its activity is not controlled at transcriptional level. Feeding the LP diet resulted in increased expressions of enzymes catabolizing fatty acids, but the reason remains to be investigated in future studies.

Maternal serum uric acid, creatinine and blood urea levels in the prediction of pre-eclampsia among pregnant women attending ANC and delivery services at Bahir Dar city public hospitals, northwest Ethiopia: A case-control study

Background

Pre-eclampsia (PE) is a metabolic disorder that adversely affects the lives of mother and their infants. Even though, several studies have been conducted on PE, no effective diagnostic and therapeutic agents were developed so far. Hence, this study was designed to evaluate serum uric acid, blood urea and creatinine levels in the prediction of PE.

Methods

A hospital-based case-control study was conducted among pregnant women. A simple random sampling technique was applied to select study participants. The socio-demographic and clinical data were collected using an interview-administered questionnaire. Serum samples were used to determine the maternal uric acid, urea and creatinine levels via an automated chemistry analyzer. Independent sample t-test, Pearson correlation test and receiver operating characteristic (ROC) curve analysis were performed to check the association and diagnostic accuracy of variables to PE.

Results

The mean ages (in years) of the case and control groups were 27.98 ± 5.64 and 27.33 ± 4.45, respectively. The mean serum uric acid and blood urea levels were significantly higher in pre-eclamptic women than in normotensive pregnant women (6.27 ± 0.20 vs 4.43 ± 0.15, and 8.50 ± 3.99 vs 5.67 ± 2.19), respectively but the serum creatinine level is non-significantly increased in cases as compared to controls (0.70 ± 0.05 vs 0.50 ± 0.01). The areas under the ROC curve of serum uric acid, creatinine and blood urea levels were 0.785, 0.735 and 0.764 (sensitivity: 69%, 60.7%, 67.9%; specificity: 73.8%, 75%, 71.4%) with the cutoff points of ≥5.25 mg/dL, ≥0.565 mg/dL and ≥6.5 mg/dL, respectively.

Conclusion

In this study, we observed a significantly higher concentration of serum uric acid and blood urea values in pre-eclampsia as compared with normotensive pregnant women. Therefore, this suggested that serum uric acid; blood urea and creatinine values can be associated with PE. Moreover, serum uric acid, blood urea and creatinine levels could be carefully utilized as a diagnostic marker for PE, but their inclusion in routine diagnostic test to PE requires large-scale multi-center prospective studies that corroborate our findings.

Influence of homoarginine on creatine accumulation and biosynthesis in the mouse

Organisms obtain creatine from their diet or by de novo synthesis via AGAT (L-arginine:glycine amidinotransferase) and GAMT (Guanidinoacetate N-methyltrasferase) in kidney and liver, respectively. AGAT also synthesizes homoarginine (hArg), low levels of which predict poor outcomes in human cardiovascular disease, while supplementation maintains contractility in murine heart failure. However, the expression pattern of AGAT has not been systematically studied in mouse tissues and nothing is known about potential feedback interactions between creatine and hArg. Herein, we show that C57BL/6J mice express AGAT and GAMT in kidney and liver respectively, whereas pancreas was the only organ to express appreciable levels of both enzymes, but no detectable transmembrane creatine transporter (Slc6A8). In contrast, kidney, left ventricle (LV), skeletal muscle and brown adipose tissue must rely on creatine transporter for uptake, since biosynthetic enzymes are not expressed. The effects of creatine and hArg supplementation were then tested in wild-type and AGAT knockout mice. Homoarginine did not alter creatine accumulation in plasma, LV or kidney, whereas in pancreas from AGAT KO, the addition of hArg resulted in higher levels of tissue creatine than creatine-supplementation alone (P < 0.05). AGAT protein expression in kidney was downregulated by creatine supplementation (P < 0.05), consistent with previous reports of end-product repression. For the first time, we show that hArg supplementation causes a similar down-regulation of AGAT protein (P < 0.05). These effects on AGAT were absent in the pancreas, suggesting organ specific mechanisms of regulation. These findings highlight the potential for interactions between creatine and hArg that may have implications for the use of dietary supplements and other therapeutic interventions.

Isolated Pancreatic Metastases of Renal Cell Cancer: Genetics and Epigenetics of an Unusual Tumour Entity

Isolated pancreatic metastases of renal cell carcinoma (isPMRCC) are a rare manifestation of metastatic renal cell carcinoma (mRCC) characterized by two peculiarities: (1). The definite or at least long-term exclusive occurrence of metastases in the pancreas and (2). an unusual low tumour aggressiveness with slow tumour progression and consecutive, good treatment results. According to current knowledge, the exclusive occurrence of pancreatic metastases is due to a highly specific and highly selective seed and soil mechanism, which does not allow metastases settlement outside the pancreas, and whose detailed genetic/epigenetic causes are not yet elucidated. Recent studies have shed light on some of the pathways involved for the protracted course of the disease and highlighted a special genetic profile (lack of loss of 9p, lower weight genome instability index, low frequency of BAP1 alterations, and a high frequency of PBRM1 loss), which deviates from the conventional mRCC profile. Finally, the question of the reasons for the long-term relative genetic stability of the involved cell clones, which is an essential prerequisite for a favourable prognosis, remains unanswered.

Biosynthesis of Guanidinoacetate by Bacillus subtilis Whole-Cell Catalysis

Guanidinoacetate (GAA) is a naturally occurring amino acid derivative and the direct precursor of creatine, which is widely used in feed additives and the pharmaceutical industry. The current industrial synthesis of GAA is based on chemical methods, which limits the application of GAA. Here, a biological approach is developed for food safety GAA production via whole-cell biocatalysis by the generally regarded as safe (GRAS) bacterium Bacillus subtilis. First, we introduced a heterologous arginine: glycine amidinotransferase (AgaT) from Amycolatopsis kentuckyensis into B. subtilis and optimized its expression level using strategies including: promoter optimization, ribosome binding site (RBS) and N-terminal coding sequence (NCS) screening. In order to alleviate the waste of arginine and the inhibition of AgaT by ornithine, we optimized the natural ornithine cycle in B. subtilis. At the same time, the first gene in the glycine degradation pathway was knocked out. After optimization using these strategies, the titer of GAA was 4.26 g/L with a productivity of 0.21 g/L/h in 20 h, which provides a new method for the biosynthesis of GAA.

SLC6A and SLC16A family of transporters: Contribution to transport of creatine and creatine precursors in creatine biosynthesis and distribution

Creatine (Cr) is needed to maintain high energy levels in cells. Since Cr plays reportedly a critical role in neurodevelopment and the immune system, Cr dynamics should be strictly regulated to control these physiological events. This review focuses on the role of transporters that recognize Cr and/or Cr precursors. Our previous studies revealed physiological roles of SLC6A and SLC16A family transporters in Cr dynamics. Creatine transporter (CRT/SLC6A8) contributes to the influx transport of Cr in Cr distribution. γ-Aminobutyric acid transporter 2 (GAT2/SLC6A13) mediates incorporation of guanidinoacetate (GAA), a Cr precursor, in the process of Cr biosynthesis. Monocarboxylate transporter 12 (MCT12/SLC16A12) functions as an efflux transporter for Cr and GAA, and contributes to the process of Cr biosynthesis. Accordingly, the SLC6A and SLC16A family of transporters play important roles in the process of Cr biosynthesis and distribution via permeation of Cr and Cr precursors across the plasma membrane.

Bioavailability, Efficacy, Safety, and Regulatory Status of Creatine and Related Compounds: A Critical Review

In 2011, we published a paper providing an overview about the bioavailability, efficacy, and regulatory status of creatine monohydrate (CrM), as well as other “novel forms” of creatine that were being marketed at the time. This paper concluded that no other purported form of creatine had been shown to be a more effective source of creatine than CrM, and that CrM was recognized by international regulatory authorities as safe for use in dietary supplements. Moreover, that most purported “forms” of creatine that were being marketed at the time were either less bioavailable, less effective, more expensive, and/or not sufficiently studied in terms of safety and/or efficacy. We also provided examples of several “forms” of creatine that were being marketed that were not bioavailable sources of creatine or less effective than CrM in comparative effectiveness trials. We had hoped that this paper would encourage supplement manufacturers to use CrM in dietary supplements given the overwhelming efficacy and safety profile. Alternatively, encourage them to conduct research to show their purported “form” of creatine was a bioavailable, effective, and safe source of creatine before making unsubstantiated claims of greater efficacy and/or safety than CrM. Unfortunately, unsupported misrepresentations about the effectiveness and safety of various “forms” of creatine have continued. The purpose of this critical review is to: (1) provide an overview of the physiochemical properties, bioavailability, and safety of CrM; (2) describe the data needed to substantiate claims that a “novel form” of creatine is a bioavailable, effective, and safe source of creatine; (3) examine whether other marketed sources of creatine are more effective sources of creatine than CrM; (4) provide an update about the regulatory status of CrM and other purported sources of creatine sold as dietary supplements; and (5) provide guidance regarding the type of research needed to validate that a purported “new form” of creatine is a bioavailable, effective and safe source of creatine for dietary supplements. Based on this analysis, we categorized forms of creatine that are being sold as dietary supplements as either having strong, some, or no evidence of bioavailability and safety. As will be seen, CrM continues to be the only source of creatine that has substantial evidence to support bioavailability, efficacy, and safety. Additionally, CrM is the source of creatine recommended explicitly by professional societies and organizations and approved for use in global markets as a dietary ingredient or food additive.

The Dietary Supplement Creatyl-l-Leucine Does Not Bioaccumulate in Muscle, Brain or Plasma and Is Not a Significant Bioavailable Source of Creatine

Creatine is an important energy metabolite that is concentrated in tissues such as the muscles and brain. Creatine is reversibly converted to creatine phosphate through a reaction with ATP or ADP, which is catalyzed by the enzyme creatine kinase. Dietary supplementation with relatively large amounts of creatine monohydrate has been proven as an effective sports supplement that can enhances athletic performance during acute high-energy demand physical activity. Some side effects have been reported with creatine monohydrate supplementation, which have stimulated research into new potential molecules that could be used as supplements to potentially provide bioavailable creatine. Recently, a popular supplement, creatyl-l-leucine, has been proposed as a potential dietary ingredient that may potentially provide bioavailable creatine. This study tests whether creatyl-l-leucine is a bioavailable compound and determines whether it can furnish creatine as a dietary supplement. Rats were deprived of dietary creatine for a period of two weeks and then given one of three treatments: a control AIN-93G creatine-free diet, AIN-93G supplemented with creatine monohydrate or AIN-93G with an equimolar amount of creatyl-l-leucine supplement in the diet for one week. When compared to the control and the creatine monohydrate-supplemented diet, creatyl-l-leucine supplementation resulted in no bioaccumulation of either creatyl-l-leucine or creatine in tissue.

Current and potential new treatment strategies for creatine deficiency syndromes

Creatine deficiency syndromes (CDS) are inherited metabolic disorders caused by mutations in GATM, GAMT and SLC6A8 and mainly affect central nervous system (CNS). AGAT- and GAMT-deficient patients lack the functional brain endogenous creatine (Cr) synthesis pathway but express the Cr transporter SLC6A8 at blood-brain barrier (BBB), and can thus be treated by oral supplementation of high doses of Cr. For Cr transporter deficiency (SLC6A8 deficiency or CTD), current treatment strategies benefit one-third of patients. However, as their phenotype is not completely reversed, and for the other two-thirds of CTD patients, the development of novel more effective therapies is needed. This article aims to review the current knowledge on Cr metabolism and CDS clinical aspects, highlighting their current treatment possibilities and the most recent research perspectives on CDS potential therapeutics designed, in particular, to bring new options for the treatment of CTD.

Development of a Longitudinal Diagnosis and Prognosis in Patients with Chronic Kidney Disease: Intelligent Clinical Decision-Making Scheme

Previous studies on CKD patients have mostly been retrospective, cross-sectional studies. Few studies have assessed the longitudinal assessment of patients over an extended period. In consideration of the heterogeneity of CKD progression. It’s critical to develop a longitudinal diagnosis and prognosis for CKD patients. We proposed an auto Machine Learning (ML) scheme in this study. It consists of four main parts: classification pipeline, cross-validation (CV), Taguchi method and improve strategies. This study includes datasets from 50,174 patients, data were collected from 32 chain clinics and three special physical examination centers, between 2015 and 2019. The proposed auto-ML scheme can auto-select the level of each strategy to associate with a classifier which finally shows an acceptable testing accuracy of 86.17%, balanced accuracy of 84.08%, sensitivity of 90.90% and specificity of 77.26%, precision of 88.27%, and F1 score of 89.57%. In addition, the experimental results showed that age, creatinine, high blood pressure, smoking are important risk factors, and has been proven in previous studies. Our auto-ML scheme light on the possibility of evaluation for the effectiveness of one or a combination of those risk factors. This methodology may provide essential information and longitudinal change for personalized treatment in the future.

Metabolic Profiling of Praziquantel-mediated Prevention of Opisthorchis viverrini-induced Cholangiocyte Transformation in the Hamster Model of Cholangiocarcinoma

BACKGROUND

Opisthorchis viverrini (Ov) infection-induced cholangiocarcinoma (CCA) is a major public health problem in northeastern Thailand. Praziquantel was shown to prevent CCA development in an Ov-infected hamster model; however, the molecular mechanism remains unknown.

MATERIALS AND METHODS

In this study, we used a hamster model with Ov and N-nitrosodimethylamine-induced CCA to study the mechanisms of praziquantel action. The liver tissues from the hamsters with and without praziquantel treatment were analyzed using ¹H nuclear magnetic resonance spectroscopy.

RESULTS

A total of 14 metabolites were found to be significantly different between the two groups. Furthermore, the combination of acetate, inosine and sarcosine was shown to exert an anti-inflammatory effect through interleukin-6 inhibition in a macrophage cell line, suggesting a mechanism by which praziquantel may prevent inflammation caused by Ov, cholangiocyte transformation and further CCA develpoment.

CONCLUSION

These findings might avail the development of a preventive strategy for CCA in high-risk populations.

Aflatoxin B1 Induces Gut-Inflammation-Associated Fecal Lipidome Changes in F344 Rats

Aflatoxin B1 (AFB1) induced intestinal epithelial damage in rodent models, which indicates that long-term exposure to AFB1 may cause chronic gut disorders. In this study we tested the hypothesis that AFB1-induced adverse effects on gut is mediated by gut-microbiota, which is partially reflected by the changes of fecal microbiome and metabolome. F344 rats were orally exposed to AFB1 of 0, 5, 25 and 75 µg kg-1 body weight for 4 weeks and fecal samples were collected. An ion-fragmentation-spectrum-based metabolomics approach was developed to investigate the fecal microbiota-associated metabolic changes in fecal samples. We found that AFB1 inhibited the hepatic and intestinal metabolism of bile constituents. As compared to the controls, bile acid synthesis-associated cholesterols in rats treated with 25 µg kg-1 (the middle-dose group) were significantly decreased in the fecal samples, e.g., lathosterol (45% reduction), cholesterol ester (21% reduction), chenodeoxycholic acid (20% reduction), dihydroxycholesterol (55% reduction), hydroxycholesterol (20% reduction), and 5-cholestene (29% reduction). While disease-associated lipids were not detectable in the feces of the control group, they were found in AFB1-treated groups, including diglyceride, monoacylglyceride, 19,20-dihydroxy-docosapentaenoic acid, and phosphatidylethanolamine. Metabolisms of carbohydrates and production of short chain fatty acids were remarkedly decreased in all treated groups. Moreover, an inflammatory-bowel-disease (IBD)-associated taxonomic structure of fecal microbiota was observed as ∼25% Lachnospiraceae, ∼25% Ruminococcaceae, < 1% Lactobacillales, which was similar to the composition pattern found in IBD patients. These results suggest that AFB1-induced disruption on gut-microbiota, partially reflected by fecal microbiome and metabolome, may play important roles in the pathogenesis of chronic gut disorders.

Contribution of monocarboxylate transporter 12 to blood supply of creatine on the sinusoidal membrane of the hepatocytes

Creatine (Cr)/phosphocreatine has the ability to buffer the high-energy phosphate, thereby contributing to intracellular energy homeostasis. As Cr biosynthetic enzyme deficiency is reported to increase susceptibility to colitis under conditions of inflammatory stress, Cr is critical for maintaining intestinal homeostasis under inflammatory stress. Cr is mainly produced in the hepatocytes and then distributed to other organs of the body by the circulatory system. Since monocarboxylate transporter 9 (MCT9) and monocarboxylate transporter 12 (MCT12) have been reported to accept Cr as a substrate, these transporters are proposed as candidates for Cr efflux transporter in the liver. The aim of this study was to elucidate the transport mechanism on Cr supply from the hepatocytes. Immunohistochemical staining of the rat liver sections revealed that both MCT9 and MCT12 were localized on the sinusoidal membrane of the hepatocytes. In the transport studies using Xenopus laevis oocyte expression system, [¹⁴C]Cr efflux from MCT9- or MCT12-expressing oocytes was significantly greater than that from water-injected oocytes. [¹⁴C]Cr efflux from primary cultured hepatocytes was significantly decreased following MCT12 mRNA knockdown, whereas this efflux was not decreased after mRNA knockdown of MCT9. Based on the extent of MCT12 protein downregulation and Cr efflux after knockdown of MCT12 in primary cultured rat hepatocytes, the contribution ratio of MCT12 in Cr efflux was calculated as 76.4%. Our study suggests that MCT12 substantially contributes to the efflux of Cr at the sinusoidal membrane of the hepatocytes.NEW & NOTEWORTHY Our study is the first to identify the role of monocarboxylate transporter 12 (MCT12) as a transporter of creatine (Cr) in the liver. MCT12 was found to significantly contribute to the efflux of Cr on the sinusoidal membrane of the hepatocytes. Since hepatocytes are known to be involved in creatine biosynthesis, the present findings can be beneficial for the regulation of Cr biosynthesis and supply.

Tumour Evolution and Seed and Soil Mechanism in Pancreatic Metastases of Renal Cell Carcinoma

In metastatic renal cell carcinoma, pancreatic metastases can appear in two clinical manifestations: (a) very rarely as isolated pancreatic metastases and (b) in the context with multi-organ metastatic disease. Both courses are characterised by rare, unusual clinical features. For isolated pancreatic metastases, the literature shows no effect on survival in all 11 publications that examined the effect of singular versus multiple pancreatic metastases; a lack of effect on survival time was also present in all 8 studies on pancreatic metastases size, in 7 of 8 studies on the influence of disease-free interval (DFI), and in 6 of 7 studies on the influence of synchronous versus metachronous metastases. In multi-organ site metastases observations, on the other hand, all five available references showed significantly better results in patients with concurrent pancreatic metastases compared to those without pancreatic metastases, although the total number of affected organs in the pancreatic metastases cohort was larger. Tumour volume-dependent risk factors thus remain surprisingly ineffective in both groups, which contradicts the usual behaviour of solid tumours. The reasons for this unusual behaviour and possible relations to tumour evolution and the hypothesis of an influence of a seed and soil mechanism in the occurrence of pancreatic metastases in metastatic renal cell carcinoma are discussed.

Metabolomic-based clinical studies and murine models for acute pancreatitis disease: A review

Acute pancreatitis (AP) is one of the most common gastroenterological disorders requiring hospitalization and is associated with substantial morbidity and mortality. Metabolomics nowadays not only help us to understand cellular metabolism to a degree that was not previously obtainable, but also to reveal the importance of the metabolites in physiological control, disease onset and development. An in-depth understanding of metabolic phenotyping would be therefore crucial for accurate diagnosis, prognosis and precise treatment of AP. In this review, we summarized and addressed the metabolomics design and workflow in AP studies, as well as the results and analysis of the in-depth of research. Based on the metabolic profiling work in both clinical populations and experimental AP models, we described the metabolites with potential utility as biomarkers and the correlation between the altered metabolites and AP status. Moreover, the disturbed metabolic pathways correlated with biological function were discussed in the end. A practical understanding of current and emerging metabolomic approaches applicable to AP and use of the metabolite information presented will aid in designing robust metabolomics and biological experiments that result in identification of unique biomarkers and mechanisms, and ultimately enhanced clinical decision-making.

Neonatal Piglets Can Synthesize Adequate Creatine, but Only with Sufficient Dietary Arginine and Methionine, or with Guanidinoacetate and Excess Methionine

BACKGROUND

Suckling piglets synthesize most of their creatine requirement, which consumes substantial amounts of arginine in order to synthesize guanidinoacetic acid (GAA) and methionine in order to transmethylate GAA to creatine.

OBJECTIVES

To determine whether supplemental GAA or creatine spare arginine and/or methionine for protein synthesis and, if GAA is supplemented, whether excess methionine is needed for conversion to creatine.

METHODS

Yucatan miniature piglets (9-11 days old; both sexes) were fed 1 of 5 elemental diets for 5 days: 1) low arginine (0.3 g·kg-1·d-1) and low methionine (0.20 g·kg-1·d-1; Base); 2) Base plus GAA (0.093 g·kg-1·d-1; +GAA); 3) Base plus GAA plus excess methionine (0.5 g·kg-1·d-1; +GAA/Met); 4) Base plus creatine (0.12 g·kg-1·d-1; +Cre); or 5) excess arginine (1.8 g·kg-1·d-1) and excess methionine (+Arg/Met). Isotope tracers were infused to determine whole-body GAA, creatine, and protein synthesis; tissues were analyzed for creatine synthesis enzymes and metabolite concentrations. Data were analyzed by 1-way ANOVA.

RESULTS

: GAA and creatine syntheses were 115% and 32% higher, respectively, with the +Arg/Met diet (P < 0.0001), in spite of 33% lower renal L-arginine: glycine amidinotransferase activity (P < 0.0001) compared to Base, suggesting substrate availability dictates synthesis rather than enzyme capacity. GAA or creatine supplementation reduced arginine conversion to creatine by 46% and 43%, respectively (P < 0.01), but did not spare amino acids for whole-body protein synthesis, suggesting that limited amino acids were diverted to protein at the expense of creatine synthesis. The +GAA/Met diet led to higher creatine concentrations in the kidney (2.6-fold) and liver (7.6-fold) than the +GAA diet (P < 0.01), suggesting excess methionine is needed for GAA conversion to creatine.

CONCLUSIONS

Piglets are capable of synthesizing sufficient creatine from the precursor amino acids arginine and methionine, or from GAA plus methionine.

Mechanism of Intestinal Flora and Proteomics on Regulating Immune Function of Durio zibethinus Rind Polysaccharide

In this study, cyclophosphamide was injected intraperitoneally to establish an immunosuppressive mouse model to study the immune regulating effects of Durio zibethinus Murr rind polysaccharide (DZMP) through proteomics and intestinal flora. The results showed that the thymus and spleen indexes of the high-dose DZMP (200 mg/kg) group were significantly increased, and the tissue structure of the spleen was improved compared with the model group ( $P<0.01$ ). The contents of IL-2, IL-4, IL-6, and TNF-α in the high-dose group of DZMP were significantly increased ( $P<0.001$ ). Activities of acid phosphatase (ACP), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) were increased in serum ( $P<0.01$ ). In the liver, catalase (CAT) activity was increased ( $P<0.001$ ) while the malondialdehyde (MDA) content was decreased and immune activity was increased ( $P<0.001$ ). Proteomics studies showed that the drug group could significantly increase the low-affinity immunoglobulin gamma Fc receptor III (FcγRIII) protein and protein kinase C-α (PKC-α) compared with the model group ( $P<0.001$ ). In addition, the result showed that those proteins were likely involved in the regulation of the metabolic pathways of autoimmune thyroid disease, Staphylococcus aureus infection, and NF-κB signaling pathway. Intestinal microbial studies showed that short-chain fatty acid (SCFA) content was increased as well as the relative abundance of beneficial bacteria Akkermansia, Bacteroides, and Paraprevotella, while the relative abundance of Ruminococcus and Oscillospira was decreased compared with the model group ( $P<0.001$ ). The results showed that DZMP might play a beneficial role in immune regulation by improving intestinal flora.

Creatine in Health and Disease

Although creatine has been mostly studied as an ergogenic aid for exercise, training, and sport, several health and potential therapeutic benefits have been reported. This is because creatine plays a critical role in cellular metabolism, particularly during metabolically stressed states, and limitations in the ability to transport and/or store creatine can impair metabolism. Moreover, increasing availability of creatine in tissue may enhance cellular metabolism and thereby lessen the severity of injury and/or disease conditions, particularly when oxygen availability is compromised. This systematic review assesses the peer-reviewed scientific and medical evidence related to creatine's role in promoting general health as we age and how creatine supplementation has been used as a nutritional strategy to help individuals recover from injury and/or manage chronic disease. Additionally, it provides reasonable conclusions about the role of creatine on health and disease based on current scientific evidence. Based on this analysis, it can be concluded that creatine supplementation has several health and therapeutic benefits throughout the lifespan.

Metabolic Effects of Doxorubicin on the Rat Liver Assessed With Hyperpolarized MRI and Metabolomics

Doxorubicin (DOX) is a successful chemotherapeutic widely used for the treatment of a range of cancers. However, DOX can have serious side-effects, with cardiotoxicity and hepatotoxicity being the most common events. Oxidative stress and changes in metabolism and bioenergetics are thought to be at the core of these toxicities. We have previously shown in a clinically-relevant rat model that a low DOX dose of 2 mg kg^-1 week^-1 for 6 weeks does not lead to cardiac functional decline or changes in cardiac carbohydrate metabolism, assessed with hyperpolarized [1-¹³C]pyruvate magnetic resonance spectroscopy (MRS). We now set out to assess whether there are any signs of liver damage or altered liver metabolism using this subclinical model. We found no increase in plasma alanine aminotransferase (ALT) activity, a measure of liver damage, following DOX treatment in rats at any time point. We also saw no changes in liver carbohydrate metabolism, using hyperpolarized [1-¹³C]pyruvate MRS. However, using metabolomic analysis of liver metabolite extracts at the final time point, we found an increase in most acyl-carnitine species as well as increases in high energy phosphates, citrate and markers of oxidative stress. This may indicate early signs of steatohepatitis, with increased and decompensated fatty acid uptake and oxidation, leading to oxidative stress.

Metabolic Signature of Articular Cartilage Following Mechanical Injury: An Integrated Transcriptomics and Metabolomics Analysis

Mechanical injury to the articular cartilage is a key risk factor in joint damage and predisposition to osteoarthritis. Integrative multi-omics approaches provide a valuable tool to understand tissue behavior in response to mechanical injury insult and help to identify key pathways linking injury to tissue damage. Global or untargeted metabolomics provides a comprehensive characterization of the metabolite content of biological samples. In this study, we aimed to identify the metabolic signature of cartilage tissue post injury. We employed an integrative analysis of transcriptomics and global metabolomics of murine epiphyseal hip cartilage before and after injury. Transcriptomics analysis showed a significant enrichment of gene sets involved in regulation of metabolic processes including carbon metabolism, biosynthesis of amino acids, and steroid biosynthesis. Integrative analysis of enriched genes with putatively identified metabolite features post injury showed a significant enrichment for carbohydrate metabolism (glycolysis, galactose, and glycosylate metabolism and pentose phosphate pathway) and amino acid metabolism (arginine biosynthesis and tyrosine, glycine, serine, threonine, and arginine and proline metabolism). We then performed a cross analysis of global metabolomics profiles of murine and porcine ex vivo cartilage injury models. The top commonly modulated metabolic pathways post injury included arginine and proline metabolism, arginine biosynthesis, glycolysis/gluconeogenesis, and vitamin B6 metabolic pathways. These results highlight the significant modulation of metabolic responses following mechanical injury to articular cartilage. Further investigation of these pathways would provide new insights into the role of the early metabolic state of articular cartilage post injury in promoting tissue damage and its link to disease progression of osteoarthritis.

Betaine Supplementation May Improve Heat Tolerance: Potential Mechanisms in Humans

Betaine has been demonstrated to increase tolerance to hypertonic and thermal stressors. At the cellular level, intracellular betaine functions similar to molecular chaperones, thereby reducing the need for inducible heat shock protein expression. In addition to stabilizing protein conformations, betaine has been demonstrated to reduce oxidative damage. For the enterocyte, during periods of reduced perfusion as well as greater oxidative, thermal, and hypertonic stress (i.e., prolonged exercise in hot-humid conditions), betaine results in greater villi length and evidence for greater membrane integrity. Collectively, this reduces exercise-induced gut permeability, protecting against bacterial translocation and endotoxemia. At the systemic level, chronic betaine intake has been shown to reduce core temperature, all-cause mortality, markers of inflammation, and change blood chemistry in several animal models when exposed to heat stress. Despite convincing research in cell culture and animal models, only one published study exists exploring betaine's thermoregulatory function in humans. If the same premise holds true for humans, chronic betaine consumption may increase heat tolerance and provide another avenue of supplementation for those who find that heat stress is a major factor in their work, or training for exercise and sport. Yet, this remains speculative until data demonstrate such effects in humans.

Multiorgan Metabolomics and Lipidomics Provide New Insights Into Fat Infiltration in the Liver, Muscle Wasting, and Liver-Muscle Crosstalk Following Burn Injury

Burn injury mediated hypermetabolic syndrome leads to increased mortality among severe burn victims, due to liver failure and muscle wasting. Metabolic changes may persist up to 2 years following the injury. Thus, understanding the underlying mechanisms of the pathology is crucially important to develop appropriate therapeutic approaches. We present detailed metabolomic and lipidomic analyses of the liver and muscle tissues in a rat model with a 30% body surface area burn injury located at the dorsal skin. Three hundred and thirty-eight of 1587 detected metabolites and lipids in the liver and 119 of 1504 in the muscle tissue exhibited statistically significant alterations. We observed excessive accumulation of triacylglycerols, decreased levels of S-adenosylmethionine, increased levels of glutamine and xenobiotics in the liver tissue. Additionally, the levels of gluconeogenesis, glycolysis, and tricarboxylic acid cycle metabolites are generally decreased in the liver. On the other hand, burn injury muscle tissue exhibits increased levels of acyl-carnitines, alpha-hydroxyisovalerate, ophthalmate, alpha-hydroxybutyrate, and decreased levels of reduced glutathione. The results of this preliminary study provide compelling observations that liver and muscle tissues undergo distinctly different changes during hypermetabolism, possibly reflecting liver-muscle crosstalk. The liver and muscle tissues might be exacerbating each other's metabolic pathologies, via excessive utilization of certain metabolites produced by each other.

The Role of Pi, Glutamine and the Essential Amino Acids in Modulating the Metabolism in Diabetes and Cancer

Purpose

Re-examine the current metabolic models.

Methods

Review of literature and gene networks.

Results

Insulin activates Pi uptake, glutamine metabolism to stabilise lipid membranes. Tissue turnover maintains the metabolic health. Current model of intermediary metabolism (IM) suggests glucose is the source of energy, and anaplerotic entry of fatty acids and amino acids into mitochondria increases the oxidative capacity of the TCA cycle to produce the energy (ATP). The reduced cofactors, NADH and FADH2, have different roles in regulating the oxidation of nutrients, membrane potentials and biosynthesis. Trans-hydrogenation of NADH to NADPH activates the biosynthesis. FADH2 sustains the membrane potential during the cell transformations. Glycolytic enzymes assume the non-canonical moonlighting functions, enter the nucleus to remodel the genetic programmes to affect the tissue turnover for efficient use of nutrients. Glycosylation of the CD98 (4F2HC) stabilises the nutrient transporters and regulates the entry of cysteine, glutamine and BCAA into the cells. A reciprocal relationship between the leucine and glutamine entry into cells regulates the cholesterol and fatty acid synthesis and homeostasis in cells. Insulin promotes the Pi transport from the blood to tissues, activates the mitochondrial respiratory activity, and glutamine metabolism, which activates the synthesis of cholesterol and the de novo fatty acids for reorganising and stabilising the lipid membranes for nutrient transport and signal transduction in response to fluctuations in the microenvironmental cues. Fatty acids provide the lipid metabolites, activate the second messengers and protein kinases. Insulin resistance suppresses the lipid raft formation and the mitotic slippage activates the fibrosis and slow death pathways.

Arginine and Endothelial Function

Arginine (L-arginine), is an amino acid involved in a number of biological processes, including the biosynthesis of proteins, host immune response, urea cycle, and nitric oxide production. In this systematic review, we focus on the functional role of arginine in the regulation of endothelial function and vascular tone. Both clinical and preclinical studies are examined, analyzing the effects of arginine supplementation in hypertension, ischemic heart disease, aging, peripheral artery disease, and diabetes mellitus.

Serious analytical inconsistencies challenge the validity of the energy balance theory

Energy metabolism theory affirms that body weight stability is achieved as over time the average energy intake equals the average energy expenditure, a state known as energy balance. Here it is demonstrated, however, that weight stability coexists with a persistent energy imbalance. Such unexpected result emerges as a consequence of the answers to three fundamental problems: 1. Is it possible to model body weight fluctuations without the energy balance theory? And if so, what are the benefits over the energy balance strategy? 2. During energy balance, how the oxidized macronutrient distribution that underlies the average energy expenditure is related to the macronutrient distribution of the average energy intake? 3. Is energy balance possible under a low-fat diet that simultaneously satisfies the following conditions? (a) The fat fraction of the absorbed energy intake is always less than the oxidized fat fraction of the energy expenditure. (b) The carbohydrate fraction of the absorbed energy intake is always greater or equal to the oxidized carbohydrate fraction of the energy expenditure. The first of these issues is addressed with the axiomatic method while the rest are managed through analythical arguments. On the whole, this analysis identifies inconsistencies in the principle of energy balance. The axiomatic approach results also in a simple mass balance model that fits experimental data and explains body composition alterations. This model gives rise to a convincing argument that appears to elucidate the advantage of low-carbohydrate diets over isocaloric low-fat diets. It is concluded, according to the aforementioned model, that weight fluctuations are ultimately dependent on the difference between daily food mass intake and daily mass loss (e.g., excretion of macronutrient oxidation products) and not on energy imbalance. In effect, it is shown that assuming otherwise may caused unintended weight gain.

Towards understanding the cell surface phenotype, metabolic properties and immune functions of resident macrophages of the peritoneal cavity and splenic red pulp using high resolution quantitative proteomics

Background:Resident macrophages (Mϕs) are distributed throughout the body and are important for maintaining tissue homeostasis and for defence against infections. Tissue Mϕs are highly adapted to their microenvironment and thought to mediate tissue-specific functions involving metabolism and immune defence that are not fully elucidated. Methods:We have used high resolution quantitative proteomics to gain insights into the functions of two types of resident tissue Mϕs: peritoneal cavity Mϕs and splenic red pulp Mϕs.  The cellular expression levels of many proteins were validated by flow cytometry and were consistently in agreement with the proteomics data.Results:Peritoneal and splenic red pulp macrophages displayed major differences in cell surface phenotype reflecting their adaptation to different tissue microenvironments and tissue-specific functions. Peritoneal Mϕs were shown to be enriched in a number of key enzymes and metabolic pathways normally associated with the liver, such as metabolism of fructose, detoxification, nitrogen homeostasis and the urea cycle. Supporting these observations, we show that peritoneal Mϕs are able to utilise glutamine and glutamate which are rich in peritoneum for urea generation.  In comparison, splenic red pulp Mϕs were enriched in proteins important for adaptive immunity such as antigen presenting MHC molecules, in addition to proteins required for erythrocyte homeostasis and iron turnover. We also show that these tissue Mϕs may utilise carbon and nitrogen substrates for different metabolic fates to support distinct tissue-specific roles.Conclusions:This study provides new insights into the functions of tissue Mϕs in immunity and homeostasis.  The comprehensive proteomics data sets are a valuable resource for biologists and immunologists.

Activated whole-body arginine pathway in high-active mice

Our previous studies suggest that physical activity (PA) levels are potentially regulated by endogenous metabolic mechanisms such as the vasodilatory roles of nitric oxide (NO) production via the precursor arginine (ARG) and ARG-related pathways. We assessed ARG metabolism and its precursors [citrulline (CIT), glutamine (GLN), glutamate (GLU), ornithine (ORN), and phenylalanine (PHE)] by measuring plasma concentration, whole-body production (WBP), de novo ARG and NO production, and clearance rates in previously classified low-active (LA) or high-active (HA) mice. We assessed LA (n = 23) and HA (n = 20) male mice by administering a stable isotope tracer pulse via jugular catheterization. We measured plasma enrichments via liquid chromatography tandem mass spectrometry (LC-MS/MS) and body compostion by echo-MRI. WBP, clearance rates, and de novo ARG and NO were calculated. Compared to LA mice, HA mice had lower plasma concentrations of GLU (71.1%; 36.8 ± 2.9 vs. 17.5 ± 1.7μM; p<0.0001), CIT (21%; 57.3 ± 2.3 vs. 46.4 ± 1.5μM; p = 0.0003), and ORN (40.1%; 55.4 ± 7.3 vs. 36.9 ± 2.6μM; p = 0.0241), but no differences for GLN, PHE, and ARG. However, HA mice had higher estimated NO production ratio (0.64 ± 0.08; p = 0.0197), higher WBP for CIT (21.8%, 8.6 ± 0.2 vs. 10.7 ± 0.3 nmol/g-lbm/min; p<0.0001), ARG (21.4%, 35.0 ± 0.6 vs. 43.4 ± 0.7 nmol/g-lbm/min; p<0.0001), PHE (7.6%, 23.8 ± 0.5 vs. 25.6 ± 0.5 nmol/g-lbm/min; p<0.0100), and lower GLU (78.5%; 9.4 ± 1.1 vs. 4.1 ± 1.6 nmol/g lbm/min; p = 0.0161). We observed no significant differences in WBP for GLN, ORN, PHE, or de novo ARG. We concluded that HA mice have an activated whole-body ARG pathway, which may be associated with regulating PA levels via increased NO production.

One-Carbon Metabolism in Fatty Liver Disease and Fibrosis: One-Carbon to Rule Them All

Nonalcoholic fatty liver disease (NAFLD) is a term used to characterize a range of disease states that involve the accumulation of fat in the liver but are not associated with excessive alcohol consumption. NAFLD is a prevalent disease that can progress to organ damage like liver cirrhosis and hepatocellular carcinoma. Many animal models have demonstrated that one-carbon metabolism is strongly associated with NAFLD. Phosphatidylcholine is an important phospholipid that affects hepatic lipid homeostasis and de novo synthesis of this phospholipid is associated with NAFLD. However, one-carbon metabolism serves to support all cellular methylation reactions and catabolism of methionine, serine, glycine, choline, betaine, tryptophan, and histidine. Several different pathways within one-carbon metabolism that play important roles in regulating energy metabolism and immune function have received less attention in the study of fatty liver disease and fibrosis. This review examines what we have learned about hepatic lipid metabolism and liver damage from the study of one-carbon metabolism thus far and highlights unexplored opportunities for future research.

The Determinants of the Human Milk Metabolome and Its Role in Infant Health

Human milk is needed for optimal growth as it satisfies both the nutritional and biological needs of an infant. The established relationship between breastfeeding and an infant’s health is attributable to the nutritional and non-nutritional, functional components of human milk including metabolites such as the lipids, amino acids, biogenic amines and carbohydrates. These components have diverse roles, including protecting the infant against infections and guiding the development of the infant’s immature immune system. In this review, we provide an in-depth and updated insight into the immune modulatory and anti-infective role of human milk metabolites and their effects on infant health and development. We also review the literature on potential determinants of the human milk metabolome, including maternal infectious diseases such as human immunodeficiency virus and mastitis.

Effects of supplemental creatine and guanidinoacetic acid on spatial memory and the brain of weaned Yucatan miniature pigs

The emergence of creatine as a potential cognitive enhancement supplement for humans prompted an investigation as to whether supplemental creatine could enhance spatial memory in young swine. We assessed memory performance and brain concentrations of creatine and its precursor guanidinoacetic acid (GAA) in 14-16-week-old male Yucatan miniature pigs supplemented for 2 weeks with either 200 mg/kg∙d creatine (+Cr; n = 7) or equimolar GAA (157 mg/kg∙d) (+GAA; n = 8) compared to controls (n = 14). Spatial memory tests had pigs explore distinct sets of objects for 5 min. Objects were spatially controlled, and we assessed exploration times of previously viewed objects relative to novel objects in familiar or novel locations. There was no effect of either supplementation on memory performance, but pigs successfully identified novel objects after 10 (p < 0.01) and 20 min (p < 0.01) retention intervals. Moreover, pigs recognized spatial transfers after 65 min (p < 0.05). Regression analyses identified associations between the ability to identify novel objects in memory tests and concentrations of creatine and GAA in cerebellum, and GAA in prefrontal cortex (p < 0.05). The concentration of creatine in brain regions was not influenced by creatine supplementation, but GAA supplementation increased GAA concentration in cerebellum (p < 0.05), and the prefrontal cortex of +GAA pigs had more creatine/g and less GAA/g compared to +Cr pigs (p < 0.05). Creatine kinase activity and maximal reaction velocity were also higher with GAA supplementation in prefrontal cortex (p < 0.05). In conclusion, there appears to be a relationship between memory performance and guanidino compounds in the cerebellum and prefrontal cortex, but the effects were unrelated to dietary supplementation. The cerebellum is identified as a target site for GAA accretion.

Guanidinoacetic acid deficiency: a new entity in clinical medicine?

Guanidinoacetic acid (GAA, also known as glycocyamine or betacyamine) is a naturally-occurring derivative of glycine and a direct metabolic precursor of creatine, a key player in high-phosphate cellular bioenergetics. GAA is found in human serum and urine, with circulating GAA likely reflects an equilibrium between its endogenous production and utilization/excretion. GAA deficiency (as indicated by low serum GAA) has been reported in various conditions yet this intriguing clinical entity appears to be poorly characterized as yet, either as a primary deficit or a sequel of secondary disease. This minireview article summarizes the inherited and acquired disorders with apparent GAA deficiency and discusses a possible relevance of GAA shortfall in clinical medicine.

Guanidinoacetic acid is efficacious in improving growth performance and muscle energy homeostasis in broiler chicks fed arginine-deficient or arginine-adequate diets

Two studies were conducted to test the efficacy of guanidinoacetic acid (GAA) to spare Arg and serve as a precursor of creatine (Cr) by evaluating growth performance and muscle cellular energy homeostasis in broiler chicks. In both studies, 12 replicate pens of 6 chicks received dietary treatments beginning at day 2 post-hatch. At conclusion of each study, muscle biopsy samples were collected within 60 s of euthanasia for analysis of Cr-related energy metabolites. In study 1, Arg-deficient starter and grower basal diets were supplemented with 0 (negative control, NC), 0.06, 0.12, or 0.18% GAA, or supplemental Arg (positive control, PC; 0.37 and 0.32% L-Arg in starter and grower phases, respectively). Dietary GAA elicited graded improvements, with final BW, overall BW gain, and overall G:F being increased (P < 0.05) by 0.12% GAA compared with the NC diet with no difference to PC diet. Increases (P < 0.001) of phosphocreatine (PCr), total Cr (tCr), and glycogen concentrations, as well as the PCr-to-adenosine triphosphate (ATP) and glycogen:ATP ratios, were observed with supplementation of 0.12% GAA compared with the NC diet, even exceeding responses to the PC diet. In study 2, Arg-adequate starter and grower basal diets were supplemented with 0 (negative control, NC), 0.06, or 0.12% GAA, 0.12% Cr monohydrate (PC1), or salmon protein (PC2; containing total Arg concentrations equal to those of the NC diet in each phase and containing similar Cr as in PC1). Overall G:F was increased (P < 0.05) by PC1, but not by PC2, compared with the NC, while GAA supplementation elicited a response intermediate to NC and PC1 diets. However, GAA supplementation increased (P < 0.01) concentrations of tCr and glycogen, as well as the PCr:ATP and glycogen:ATP ratios, when compared with the NC (Arg-adequate) diet. Collectively, these data indicate that GAA can be used to replace Arg in practical, Arg-deficient diets and improve muscle energy homeostasis in broiler chicks receiving either Arg-deficient or Arg-adequate practical diets.

Effects of guanidinoacetic acid on growth performance, creatine metabolism and plasma amino acid profile in broilers

The objective of this study was to assess the effects of guanidinoacetic acid (GAA) on growth performance, creatine deposition and blood amino acid (AA) profile on broiler chickens. In Exp. 1, a total of 540 one-day-old Arbor Acres male broilers (average initial body weight, 45.23 ± 0.35 g) were divided randomly into five treatments with six replicates of 18 chicks each. Broilers were fed corn-soybean meal-basal diets supplemented with 0, 600, 800, 1,000 or 1,200 mg/kg GAA for 42 days respectively. Results showed that dietary GAA inclusion increased average daily gain (ADG) and improved gain-to-feed ratio (G:F) from 1 to 42 days (p < 0.01). However, average daily feed intake was unaffected by dietary supplementation of GAA. As GAA inclusion increased, the contents of creatine in plasma and kidney were increased (linear, p < 0.01), while the contents of GAA and creatine in liver were decreased (linear, p < 0.01). Similarly, GAA supplementation was inversely related to concentrations of most essential AA in plasma. In Exp. 2, a total of 432 one-day-old Arbor Acres male broilers (average initial body weight, 39.78 ± 0.58 g) were divided randomly into four treatments with six replicates of 18 chicks each. Birds were fed a corn-soybean meal-basal diet supplemented with 0, 200, 400 or 600 mg/kg GAA for 42 days respectively. Dietary inclusion of 600 mg/kg GAA significantly increased ADG and G:F of broilers (p < 0.05). In conclusion, dietary supplementation of 600-1,200 mg/kg GAA can effectively improve the growth performance in broiler chickens by affecting creatine metabolism and utilization efficiency of essential AA, and 600 mg/kg GAA is the minimum dose for improving performance.

Choline Supplementation in Cystic Fibrosis-The Metabolic and Clinical Impact

Background: Choline is essential for the synthesis of liver phosphatidylcholine (PC), parenchymal maintenance, bile formation, and lipoprotein assembly to secrete triglycerides. In choline deficiency, the liver accretes choline/PC at the expense of lung tissue, thereby impairing pulmonary PC homoeostasis. In cystic fibrosis (CF), exocrine pancreas insufficiency results in impaired cleavage of bile PC and subsequent fecal choline loss. In these patients, the plasma choline concentration is low and correlates with lung function. We therefore investigated the effect of choline supplementation on plasma choline/PC concentration and metabolism, lung function, and liver fat. Methods: 10 adult male CF patients were recruited (11/2014–1/2016), and orally supplemented with 3 × 1 g choline chloride for 84 (84–91) days. Pre-/post-supplementation, patients were spiked with 3.6 mg/kg [methyl-D₉]choline chloride to assess choline/PC metabolism. Mass spectrometry, spirometry, and hepatic nuclear resonance spectrometry served for analysis. Results: Supplementation increased plasma choline from 4.8 (4.1–6.2) µmol/L to 10.5 (8.5–15.5) µmol/L at d84 (p < 0.01). Whereas plasma PC concentration remained unchanged, D₉-labeled PC was decreased (12.2 [10.5–18.3] µmol/L vs. 17.7 [15.5–22.4] µmol/L, p < 0.01), indicating D₉-tracer dilution due to higher choline pools. Supplementation increased Forced Expiratory Volume in 1 second percent of predicted (ppFEV1) from 70.0 (50.9–74.8)% to 78.3 (60.1–83.9)% (p < 0.05), and decreased liver fat from 1.58 (0.37–8.82)% to 0.84 (0.56–1.17)% (p < 0.01). Plasma choline returned to baseline concentration within 60 h. Conclusions: Choline supplementation normalized plasma choline concentration and increased choline-containing PC precursor pools in adult CF patients. Improved lung function and decreased liver fat suggest that in CF correcting choline deficiency is clinically important. Choline supplementation of CF patients should be further investigated in randomized, placebo-controlled trials.

Dietary Guanidinoacetic acid modulates testicular histology and expression of c-Kit and STRA8 genes in roosters

Decline in semen quality is considered as a major contributing factor in age-related subfertility of broiler breeder flocks. This study was aimed to investigate the effect of dietary supplementation of Guanidinoacetic acid (GAA), as an alternative energy source along with antioxidant potential, on testicular histology and relative gene expression of some spermatogonial markers (c-Kit and STRA8) in aged roosters. Sixteen 24-week-old male broiler breeders were randomly allocated into four groups and fed a basal diet supplemented with increasing levels of GAA including 0 (GAA-0), 600 (GAA-600), 1200 (GAA-1200) or 1800 (GAA-1800) mg/kg diet/day for 26 successive weeks. At the end of the experiment, all the birds were killed and two ipsilateral testicle samples were taken to either quantify relative gene expression or do histology. Except for seminiferous tubules' diameter, testicular weight, and the number of blood vessels, dietary supplementation of GGA improved the epithelium thickness of seminiferous tubules, the number of spermatogonia and Leydig cells and the relative gene expression of c-Kit and STRA8 (P < 0.01). Increasing levels of GAA cubically affected (P < 0.01) the diameter of seminiferous tubules and their epithelium thickness as well as the number of spermatogonia. However, number of Leydig cells and relative expression of c-Kit were linearly, and relative expression of STRA8 was quadratically (P < 0.01) enhanced in response to graded levels of GAA supplementation. Taking all parameters into account, daily supplementation of 1300-1450 mg of GAA/kg diet was estimated as an optimum dosage maximizing the evaluated traits.

Choline and choline-related nutrients in regular and preterm infant growth

BACKGROUND

Choline is an essential nutrient, with increased requirements during development. It forms the headgroup of phosphatidylcholine and sphingomyelin in all membranes and many secretions. Phosphatidylcholine is linked to cell signaling as a phosphocholine donor to synthesize sphingomyelin from ceramide, a trigger of apoptosis, and is the major carrier of arachidonic and docosahexaenoic acid in plasma. Acetylcholine is important for neurodevelopment and the placental storage form for fetal choline supply. Betaine, a choline metabolite, functions as osmolyte and methyl donor. Their concentrations are all tightly regulated in tissues.

CLINCAL IMPACT

During the fetal growth spurt at 24-34-week postmenstrual age, plasma choline is higher than beyond 34 weeks, and threefold higher than in pregnant women [45 (36-60) µmol/L vs. 14 (10-17) µmol/L]. The rapid decrease in plasma choline after premature birth suggests an untimely reduction in choline supply, as cellular uptake is proportional to plasma concentration. Supply via breast milk, with phosphocholine and α-glycerophosphocholine as its major choline components, does not prevent such postnatal decrease. Moreover, high amounts of liver PC are secreted via bile, causing rapid hepatic choline turnover via the enterohepatic cycle, and deficiency in case of pancreatic phospholipase A2 deficiency or intestinal resection. Choline deficiency causes hepatic damage and choline accretion at the expense of the lungs and other tissues.

CONCLUSION

Choline deficiency may contribute to the impaired lean body mass growth and pulmonary and neurocognitive development of preterm infants despite adequate macronutrient supply and weight gain. In this context, a reconsideration of current recommendations for choline supply to preterm infants is required.

Acute Kidney Injury Before and After Liver Transplant

The development of acute kidney injury in the setting of liver disease is a significant event both before and after liver transplant. Whether acute kidney injury is the cause of or merely associated with worse outcomes, the development of renal failure is significant from a prognostic as well as from a diagnostic and therapeutic standpoint. Although not every etiology is reversible, there are number of etiologies that are correctable, to include hypovolemia, nephrotoxic medications, and acute tubular necrosis. In the post-liver transplant period, renal failure is associated with graft failure as well as worse outcomes overall. Prompt recognition, workup, and intervention can significantly impact outcomes and survival both before and after liver transplant.