Synthesis of guanidinoacetate and creatine from amino acids by rat pancreas

Screening of Amino Acids as a Safe Energy Source for Isolated Rat Pancreatic Acini

OBJECTIVES

Amino acids play an essential role in protein synthesis, metabolism, and survival of pancreatic acini. Adequate nutritional support is important for acute pancreatitis treatment. However, high concentrations of arginine and lysine may induce acute pancreatitis. The study aimed to identify the most suitable l -amino acids as safe energy sources for pancreatic acinar cells.

MATERIALS AND METHODS

Pancreatic acini were isolated from male Wistar rats. Effects of amino acids (0.1-20 mM) on uncoupled respiration of isolated acini were studied with a Clark electrode. Cell death was evaluated with fluorescent microscopy and DNA gel electrophoresis.

RESULTS

Among the tested amino acids, glutamate, glutamine, alanine, lysine, and aspartate were able to stimulate the uncoupled respiration rate of isolated pancreatic acini, whereas arginine, histidine, and asparagine were not. Lysine, arginine, and glutamine (20 mM) caused complete loss of plasma membrane integrity of acinar cells after 24 hours of incubation. Glutamine also caused early (2-4 hours) cell swelling and blebbing. Aspartate, asparagine, and glutamate only moderately decreased the number of viable cells, whereas alanine and histidine were not toxic. DNA fragmentation assay and microscopic analysis of nuclei showed no evidence of apoptosis in cells treated with amino acids.

CONCLUSIONS

Alanine and glutamate are safe and effective energy sources for mitochondria of pancreatic acinar cells.

Acute toxicity profiling of medicinal herb Ardisia elliptica leaf extract by conventional evaluations and proton nuclear magnetic resonance (NMR) metabolomics

Background and aim

Interest in the safety of herbal medicine is growing rapidly regarding knowledge and challenges in natural products. Hence, this study aimed to reveal the toxicological profile of Ardisia elliptica, a traditional medicinal plant used in the treatment of various illnesses.

Experimental procedure

Acute toxicity study was performed on female and male Sprague Dawley rats with a single oral administration of 2000 mg/kg BW of 70% ethanolic A. elliptica leaf extract, using a combination of conventional investigations and 1H-NMR-based metabolomics approaches.

Results

Physical, hematological, biochemical, and histopathological assessments demonstrated the usual rat profile, with no mortality and delayed toxicity 14 days after administration. 1H NMR serum metabolomics depicted similar metabolites between normal and treated groups. Nevertheless, 1H NMR of urinary metabolomics revealed perturbation in carbohydrate, amino acid, and energy metabolism within 24h after extract administration, while no accumulation of toxic biomarkers in the collected biological fluids on Day 14. A minor gender-based difference revealed the influence of sex hormones and different energy expenditure on response to extract treatment.

Conclusion

This study suggested that 2000 mg/kg BW of 70% ethanolic A. elliptica leaf extract is considered as safe for consumption and offered a comprehensive overview of the response of physiological and metabolic aspects applicable to food and herbal product development.

Creatine homeostasis and the kidney: comparison between kidney transplant recipients and healthy controls

Creatine is a natural nitrogenous organic acid that is integral to energy metabolism and crucial for proper cell functioning. The kidneys are involved in the first step of creatine production. With kidney transplantation being the gold-standard treatment for end-stage kidney disease, kidney transplant recipients (KTR) may be at risk of impaired creatine synthesis. We aimed to compare creatine homeostasis between KTR and controls. Plasma and urine concentrations of arginine, glycine, guanidinoacetate, creatine and creatinine were measured in 553 KTR and 168 healthy controls. Creatine intake was assessed using food frequency questionnaires. Iothalamate-measured GFR data were available in subsets of 157 KTR and 167 controls. KTR and controls had comparable body weight, height and creatine intake (all P > 0.05). However, the total creatine pool was 14% lower in KTR as compared to controls (651 ± 178 vs. 753 ± 239 mmol, P < 0.001). The endogenous creatine synthesis rate was 22% lower in KTR as compared to controls (7.8 ± 3.0 vs. 10.0 ± 4.1 mmol per day, P < 0.001). Despite lower GFR, the plasma guanidinoacetate and creatine concentrations were 21% and 41% lower in KTR as compared to controls (both P < 0.001). Urinary excretion of guanidinoacetate and creatine were 66% and 59% lower in KTR as compared to controls (both P < 0.001). In KTR, but not in controls, a higher measured GFR was associated with a higher endogenous creatine synthesis rate (std. beta: 0.21, 95% CI: 0.08; 0.33; P = 0.002), as well as a higher total creatine pool (std. beta: 0.22, 95% CI: 0.11; 0.33; P < 0.001). These associations were fully mediated (93% and 95%; P < 0.001) by urinary guanidinoacetate excretion which is consistent with production of the creatine precursor guanidinoacetate as rate-limiting factor. Our findings highlight that KTR have a disturbed creatine homeostasis as compared to controls. Given the direct relationship of measured GFR with endogenous creatine synthesis rate and the total creatine pool, creatine supplementation might be beneficial in KTR with low kidney function.Trial registration ID: NCT02811835.Trial registration URL: https://clinicaltrials.gov/ct2/show/NCT02811835 .

Efficient biosynthesis of creatine by whole-cell catalysis from guanidinoacetic acid in Corynebacterium glutamicum

Creatine is a naturally occurring derivative of an amino acid commonly utilized in functional foods and pharmaceuticals. Nevertheless, the current industrial synthesis of creatine relies on chemical processes, which may hinder its utilization in certain applications. Therefore, a biological approach was devised that employs whole-cell biocatalysis in the bacterium Corynebacterium glutamicum, which is considered safe for use in food production, to produce safe-for-consumption creatine. The objective of this study was to identify a guanidinoacetate N-methyltransferase (GAMT) with superior catalytic activity for creatine production. Through employing whole-cell biocatalysis, a gamt gene from Mus caroli (Mcgamt) was cloned and expressed in C. glutamicum ATCC 13032, resulting in a creatine titer of 3.37 g/L. Additionally, the study employed a promoter screening strategy that utilized nine native strong promoters in C. glutamicum to enhance the expression level of GAMT. The highest titer was achieved using the P1676 promoter, reaching 4.14 g/L. The conditions of whole-cell biocatalysis were further optimized, resulting in a creatine titer of 5.42 g/L. This is the first report of successful secretory creatine expression in C. glutamicum, which provides a safer and eco-friendly approach for the industrial production of creatine.

Evidence of an intracellular creatine-sensing mechanism that modulates creatine biosynthesis via AGAT expression in human HAP1 cells

Cellular homeostasis of creatine (CT), integral part of the energy buffering and transducing system connecting intracellular sites of ATP production and utilization, comprises of mechanisms that increase CT, i.e., biosynthesis and cellular uptake, and CT-lowering processes, such as export and non-enzymatic conversion to creatinine. The biosynthesis of CT is controlled by negative feedback loop via suppression of the rate-limiting enzyme arginine:glycine amidinotransferase (AGAT). Although the regulatory mechanism involved is not well understood, AGAT suppression is successfully used in patients with guanidinoacetate methyltransferase (GAMT) deficiency to reduce the neurotoxic accumulation of the AGAT-mediated guanidinoacetate production by supplementing patients with CT. Utilizing the CT-dependent feedback loop for the upregulation of AGAT expression may well represent a therapeutic target for an additional CT deficiency syndrome, the CT transporter (CrT) defect, for which no effective treatment option is available so far. We have used CRISPR to tag the C-terminus of AGAT with a nanoluc luciferase (NLuc) reporter in HAP1 cells. A biphasic decay of AGAT-NLuc in response to increasing extracellular CT was observed, whereas the decrease in AGAT-NLuc expression was directly proportional to the rise in intracellular CT levels with an approximate IC50 of 1-2 mM. CRISPR generated HAP1 CrT null cells and HAP1 CrT null cells stably expressing a CrT-GFP fusion protein further demonstrated that the biphasic response to extracellular CT is mediated by a high-affinity (Km 9-10 µM) CrT dependent, saturable mechanism and a CrT independent, unsaturable uptake process. The direct response to intracellular CT suggests the existence of an intracellular CT sensing system enabling a dynamic cell response to changing CT concentration that is relevant for cellular CT homeostasis.

The potential role of creatine supplementation in neurodegenerative diseases

PURPOSE

The maintenance of energy balance in the body, especially in energy-demanding tissues like the muscles and the central nervous system, depends on creatine (Cr). In addition to improving muscle function, Cr is necessary for the bioenergetics of the central nervous system because it replenishes adenosine triphosphate without needing oxygen. Furthermore, Cr possesses anti-oxidant, anti-apoptotic, and anti-excitotoxic properties. Clinical research on neurodegenerative illnesses has shown that Cr supplementation results in less effective outcomes. With a brief update on the possible role of Cr in human, animal, and in vitro experiments, this review seeks to offer insights into the ideal dosage regimen.

METHODS

Using specified search phrases, such as "creatine and neurological disorder," "creatine supplementation and neurodegenerative disorders," and "creatine and brain," we searched articles in the PubMed database and Google Scholar. We investigated the association between creatine supplementation and neurodegenerative illnesses by examining references.

RESULTS

The neuroprotective effects of Cr were observed in in vitro and animal models of certain neurodegenerative diseases, while clinical trials failed to reproduce favorable outcomes.

CONCLUSION

Determining the optimal creatinine regime for increasing brain creatinine levels is essential for maintaining brain health and treating neurodegeneration.

Key transcriptional effectors of the pancreatic acinar phenotype and oncogenic transformation

Proper maintenance of mature cellular phenotypes is essential for stable physiology, suppression of disease states, and resistance to oncogenic transformation. We describe the transcriptional regulatory roles of four key DNA-binding transcription factors (Ptf1a, Nr5a2, Foxa2 and Gata4) that sit at the top of a regulatory hierarchy controlling all aspects of a highly differentiated cell-type-the mature pancreatic acinar cell (PAC). Selective inactivation of Ptf1a, Nr5a2, Foxa2 and Gata4 individually in mouse adult PACs rapidly altered the transcriptome and differentiation status of PACs. The changes most emphatically included transcription of the genes for the secretory digestive enzymes (which conscript more than 90% of acinar cell protein synthesis), a potent anabolic metabolism that provides the energy and materials for protein synthesis, suppressed and properly balanced cellular replication, and susceptibility to transformation by oncogenic KrasG12D. The simultaneous inactivation of Foxa2 and Gata4 caused a greater-than-additive disruption of gene expression and uncovered their collaboration to maintain Ptf1a expression and control PAC replication. A measure of PAC dedifferentiation ranked the effects of the conditional knockouts as Foxa2+Gata4 > Ptf1a > Nr5a2 > Foxa2 > Gata4. Whereas the loss of Ptf1a or Nr5a2 greatly accelerated Kras-mediated transformation of mature acinar cells in vivo, the absence of Foxa2, Gata4, or Foxa2+Gata4 together blocked transformation completely, despite extensive dedifferentiation. A lack of correlation between PAC dedifferentiation and sensitivity to oncogenic KrasG12D negates the simple proposition that the level of differentiation determines acinar cell resistance to transformation.

Metformin May Alter the Metabolic Reprogramming in Cancer Cells by Disrupting the L-Arginine Metabolism: A Preliminary Computational Study

Metabolic reprogramming in cancer is considered to be one of the most important hallmarks to drive proliferation, angiogenesis, and invasion. AMP-activated protein kinase activation is one of the established mechanisms for metformin’s anti-cancer actions. However, it has been suggested that metformin may exert antitumoral effects by the modulation of other master regulators of cellular energy. Here, based on structural and physicochemical criteria, we tested the hypothesis that metformin may act as an antagonist of L-arginine metabolism and other related metabolic pathways. First, we created a database containing different L-arginine-related metabolites and biguanides. After that, comparisons of structural and physicochemical properties were performed employing different cheminformatic tools. Finally, we performed molecular docking simulations using AutoDock 4.2 to compare the affinities and binding modes of biguanides and L-arginine-related metabolites against their corresponding targets. Our results showed that biguanides, especially metformin and buformin, exhibited a moderate-to-high similarity to the metabolites belonging to the urea cycle, polyamine metabolism, and creatine biosynthesis. The predicted affinities and binding modes for biguanides displayed good concordance with those obtained for some L-arginine-related metabolites, including L-arginine and creatine. In conclusion, metabolic reprogramming in cancer cells by metformin and biguanides may be also driven by metabolic disruption of L-arginine and structurally related compounds.

Determination of equilibria constants of arginine:glycine amidinotransferase (AGAT)-catalyzed reactions using concentrations of circulating amino acids

Arginine:glycine amidinotransferase (AGAT) catalyzes mainly two reactions that generate 1) L-homoarginine (hArg) from L-arginine and L-lysine (K_harg) and 2) guanidinoacetate (GAA) and L-ornithine from L-arginine and glycine (K_gaa). Previously, we found that pharmacological treatment of Becker muscular dystrophy (BMD) patients with metformin or L-citrulline resulted in antidromic effects on serum hArg and GAA concentrations, seemingly acting as an inhibitor and effector of AGAT activity, respectively. Here, we used data of this study as a model to determine K_harg and K_gaa values by using the concentrations of the participating amino acids measured in serum samples of the BMD patients. The study aimed to prove the general utility of this approach to investigate effects of amino acids and drugs on AGAT-catalyzed reactions in vivo in humans.

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.

A Hypothesis From Metabolomics Analysis of Diabetic Retinopathy: Arginine-Creatine Metabolic Pathway May Be a New Treatment Strategy for Diabetic Retinopathy

Diabetic retinopathy is one of the serious complications of diabetes, which the leading causes of blindness worldwide, and its irreversibility renders the existing treatment methods unsatisfactory. Early detection and timely intervention can effectively reduce the damage caused by diabetic retinopathy. Metabolomics is a branch of systems biology and a powerful tool for studying pathophysiological processes, which can help identify the characteristic metabolic changes marking the progression of diabetic retinopathy, discover potential biomarkers to inform clinical diagnosis and treatment. This review provides an update on the known metabolomics biomarkers of diabetic retinopathy. Through comprehensive analysis of biomarkers, we found that the arginine biosynthesis is closely related to diabetic retinopathy. Meanwhile, creatine, a metabolite with arginine as a precursor, has attracted our attention due to its important correlation with diabetic retinopathy. We discuss the possibility of the arginine-creatine metabolic pathway as a therapeutic strategy for diabetic retinopathy.

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.

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.

Chronic Dialysis Patients Are Depleted of Creatine: Review and Rationale for Intradialytic Creatine Supplementation

There is great need for the identification of new, potentially modifiable risk factors for the poor health-related quality of life (HRQoL) and of the excess risk of mortality in dialysis-dependent chronic kidney disease patients. Creatine is an essential contributor to cellular energy homeostasis, yet, on a daily basis, 1.6–1.7% of the total creatine pool is non-enzymatically degraded to creatinine and subsequently lost via urinary excretion, thereby necessitating a continuous supply of new creatine in order to remain in steady-state. Because of an insufficient ability to synthesize creatine, unopposed losses to the dialysis fluid, and insufficient intake due to dietary recommendations that are increasingly steered towards more plant-based diets, hemodialysis patients are prone to creatine deficiency, and may benefit from creatine supplementation. To avoid problems with compliance and fluid balance, and, furthermore, to prevent intradialytic losses of creatine to the dialysate, we aim to investigate the potential of intradialytic creatine supplementation in improving outcomes. Given the known physiological effects of creatine, intradialytic creatine supplementation may help to maintain creatine homeostasis among dialysis-dependent chronic kidney disease patients, and consequently improve muscle status, nutritional status, neurocognitive status, HRQoL. Additionally, we describe the rationale and design for a block-randomized, double-blind, placebo-controlled pilot study. The aim of the pilot study is to explore the creatine uptake in the circulation and tissues following different creatine supplementation dosages.

Creatine in T Cell Antitumor Immunity and Cancer Immunotherapy

Creatine is a broadly used dietary supplement that has been extensively studied for its benefit on the musculoskeletal system. Yet, there is limited knowledge regarding the metabolic regulation of creatine in cells beyond the muscle. New insights concerning various regulatory functions for creatine in other physiological systems are developing. Here, we highlight the latest advances in understanding creatine regulation of T cell antitumor immunity, a topic that has previously gained little attention in the creatine research field. Creatine has been identified as an important metabolic regulator conserving bioenergy to power CD8 T cell antitumor reactivity in a tumor microenvironment; creatine supplementation has been shown to enhance antitumor T cell immunity in multiple preclinical mouse tumor models and, importantly, to synergize with other cancer immunotherapy modalities, such as the PD-1/PD-L1 blockade therapy, to improve antitumor efficacy. The potential application of creatine supplementation for cancer immunotherapy and the relevant considerations are discussed.

Expeller-Pressed Canola (Brassica napus) Meal Modulates the Structure and Function of the Cecal Microbiota, and Alters the Metabolome of the Pancreas, Liver, and Breast Muscle of Broiler Chickens

The inoculation of one-day-old broiler chicks with the cecal contents from a mature broiler breeder resulted in a highly diverse and uniform cecal bacterial community. CM did not affect feed consumption, weight gain, nor the richness, evenness, or diversity of the cecal bacterial community. However, the structure of the bacterial community was altered in birds fed the CM diet. Although the CM diet was formulated to contain equivalent metabolizable energy to the control diet, it contained more dietary fiber. The abundance of bacterial families, including those that are known to contain species able to metabolize fiber was altered (e.g., bacteria within the families, Methanobacteriaceae, Atopobiaceae, Prevotellaceae, Clostridiales Family XIII, Peptostreptococcaceae, and Succinivibrionaceae), and concentrations of SCFAs were higher in the ceca of birds fed the CM diet. Moreover, concentrations of isoleucine, isobutyrate, glutamate, and 2-oxoglutarate were higher, whereas concentrations of phenyllactic acid, indole, glucose, 3-phenylpropionate, and 2-oxobutyrate were lower in the digesta of chickens that were fed CM. The metabolic profiles of pancreas, liver, and breast muscle tissues of birds fed the CM diet differed from control birds. Metabolites that were associated with energy production, protection against oxidative stress, and pathways of amino acid and glycerophospholipid metabolism had altered concentrations in these tissues. Some of the observed changes in metabolite levels may indicate an increased disease risk in birds fed the CM diet (e.g., pancreatitis), and others suggested that birds mounted metabolic response to offset the adverse impacts of CM (e.g., oxidative stress in the liver).

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.

Reconstitution of the Ornithine Cycle with Arginine:Glycine Amidinotransferase to Engineer Escherichia coli into an Efficient Whole-Cell Catalyst of Guanidinoacetate

Guanidino compounds can be synthesized by transamidination reactions using arginine as a guanidine group donor. The efficiency of guanidino biosynthesis is often affected by the supply of arginine and the inhibition of the coproduct ornithine. To alleviate this shortcoming, we designed a reconstituted ornithine cycle in Escherichia coli to engineer an efficient whole-cell catalyst for guanidinoacetate (GAA) production by introducing a heterogeneous arginine:glycine amidinotransferase (AGAT). To alleviate the inhibition of ornithine, a citrulline synthetic module was constructed and optimized by introducing a glutamine self-sufficient system. Then, to improve the pathway from citrulline to arginine, an aspartate self-sufficient system was introduced into the arginine synthetic module. By combining these modules (GAA, citrulline, and arginine synthetic modules), a reconstituted ornithine cycle was developed, which significantly improved the biocatalyst efficiency (3.9-fold increase). In the system, arginine was regenerated efficiently through the reconstituted ornithine cycle, which converted arginine from a substrate to a cofactor for the transamidination reaction, thereby relieving the ornithine inhibition. Moreover, the amidino group of GAA in this system was mainly supplied by carbon and nitrogen assimilation. After the engineering process, 8.61 g/L GAA (73.56 mM) with a productivity of 0.39 g/L/h was achieved in a 22 h bioconversion. To the best of our knowledge, this is the first time that GAA has been produced in E. coli. This reconstructed ornithine cycle could be used as a transamidination platform for amidino group supply and has potential applications in the biosynthesis of other guanidino compounds.

Creatine metabolism: energy homeostasis, immunity and cancer biology

Perturbations in metabolic processes are associated with diseases such as obesity, type 2 diabetes mellitus, certain infections and some cancers. A resurgence of interest in creatine biology is developing, with new insights into a diverse set of regulatory functions for creatine. This resurgence is primarily driven by technological advances in genetic engineering and metabolism as well as by the realization that this metabolite has key roles in cells beyond the muscle and brain. Herein, we highlight the latest advances in creatine biology in tissues and cell types that have historically received little attention in the field. In adipose tissue, creatine controls thermogenic respiration and loss of this metabolite impairs whole-body energy expenditure, leading to obesity. We also cover the various roles that creatine metabolism has in cancer cell survival and the function of the immune system. Renewed interest in this area has begun to showcase the therapeutic potential that lies in understanding how changes in creatine metabolism lead to metabolic disease.

Repeated Administration of Clinical Doses of Tramadol and Tapentadol Causes Hepato- and Nephrotoxic Effects in Wistar Rats

Tramadol and tapentadol are fully synthetic and extensively used analgesic opioids, presenting enhanced therapeutic and safety profiles as compared with their peers. However, reports of adverse reactions, intoxications and fatalities have been increasing. Information regarding the molecular, biochemical, and histological alterations underlying their toxicological potential is missing, particularly for tapentadol, owing to its more recent market authorization. Considering the paramount importance of liver and kidney for the metabolism and excretion of both opioids, these organs are especially susceptible to toxicological damage. In the present study, we aimed to characterize the putative hepatic and renal deleterious effects of repeated exposure to therapeutic doses of tramadol and tapentadol, using an in vivo animal model. Male Wistar rats were randomly divided into six experimental groups, composed of six animals each, which received daily single intraperitoneal injections of 10, 25 or 50 mg/kg tramadol or tapentadol (a low, standard analgesic dose, an intermediate dose and the maximum recommended daily dose, respectively). An additional control group was injected with normal saline. Following 14 consecutive days of administration, serum, urine and liver and kidney tissue samples were processed for biochemical, metabolic and histological analysis. Repeated administration of therapeutic doses of both opioids led to: (i) increased lipid and protein oxidation in liver and kidney, as well as to decreased total liver antioxidant capacity; (ii) decreased serum albumin, urea, butyrylcholinesterase and complement C3 and C4 levels, denoting liver synthesis impairment; (iii) elevated serum activity of liver enzymes, such as alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and γ-glutamyl transpeptidase, as well as lipid profile alterations, also reflecting hepatobiliary commitment; (iv) derangement of iron metabolism, as shown through increases in serum iron, ferritin, haptoglobin and heme oxygenase-1 levels. In turn, elevated serum cystatin C, decreased urine creatinine output and increased urine microalbumin levels were detected upon exposure to tapentadol only, while increased serum amylase and urine N-acetyl-β-D-glucosaminidase activities were observed for both opioids. Collectively, these results are compatible with kidney injury. Changes were also found in the expression levels of liver- and kidney-specific toxicity biomarker genes, upon exposure to tramadol and tapentadol, correlating well with alterations in lipid profile, iron metabolism and glomerular and tubular function. Histopathological analysis evidenced sinusoidal dilatation, microsteatosis, mononuclear cell infiltrates, glomerular and tubular disorganization, and increased Bowman's spaces. Although some findings are more pronounced upon tapentadol exposure, our study shows that, when compared with acute exposure, prolonged administration of both opioids smooths the differences between their toxicological effects, and that these occur at lower doses within the therapeutic range.

The Kidneys Are Quantitatively More Important than Pancreas and Gut as a Source of Guanidinoacetic Acid for Hepatic Creatine Synthesis in Sow-Reared Yucatan Miniature Piglets

BACKGROUND

Arginine:glycine amidinotransferase, necessary for the conversion of arginine (Arg) to guanidinoacetic acid (GAA), is expressed mainly in kidney and pancreas. The methylation of GAA to creatine (Cre) primarily occurs in the liver. The role of the gut in Cre homeostasis has not been characterized.

OBJECTIVE

We aimed to quantify the contribution of kidney, pancreas, and gut as sources of GAA for Cre synthesis.

METHODS

Sow-reared, feed-deprived Yucatan miniature piglets (17-21 d old) were randomly assigned to acute intravenous treatments (expressed in μmol/kg/min) of: 1) Arg (4.8) + methionine (1.4) (Arg/Met), 2) Cre (0.6) with Arg/Met (Cre/Arg/Met), 3) citrulline (4.8) + methionine (1.4) (Cit/Met), or 4) alanine (6.2) (Ala). Suckling piglets were also studied.

RESULTS

Renal GAA release was higher during Cit/Met compared with all other treatments (53-360% higher; P < 0.01), suggesting that Cit is a better precursor than Arg for renal GAA synthesis. Kidneys contributed higher (P < 0.01) proportions of the total GAA with Cit/Met (89%) and Arg/Met (68%) treatments compared with pancreas and gut. In the suckling pigs, kidneys contributed 88% of the GAA, with the remainder released by pancreas. None of the treatments resulted in a net flux of Cre across the kidney or pancreas. In the gut, Arg/Met and Cre/Arg/Met, but not Cit/Met, resulted in a net release of Cre. Cre/Arg/Met resulted in a higher net GAA release from the gut (P < 0.0001) and pancreas (P < 0.001) (68% of total GAA produced) compared with all other treatments (<19% from both organs), perhaps because GAA not needed for creatine synthesis was subsequently released.

CONCLUSIONS

Cit is a better precursor than Arg for renal GAA synthesis, and kidney is the major source of GAA for Cre synthesis in neonatal piglets, but the gut also has the capacity to synthesize GAA and Cre when Arg and Met are available.

Creatine as a Neuroprotector: an Actor that Can Play Many Parts

Creatine is a nitrogenous organic acid that plays a central role as an energy buffer in high energy demanding systems, including the muscular and the central nervous system. It can be acquired from diet or synthesized endogenously, and its main destination is the system creatine/phosphocreatine that strengthens cellular energetics via a temporal and spatial energy buffer that can restore cellular ATP without a reliance on oxygen. This compound has been proposed to possess secondary roles, such as direct and indirect antioxidant, immunomodulatory agent, and possible neuromodulator. However, these effects may be associated with its bioenergetic role in the mitochondria. Given the fundamental roles that creatine plays in the CNS, several preclinical and clinical studies have tested the potential that creatine has to treat degenerative disorders. However, although in vitro and in vivo animal models are highly encouraging, most clinical trials fail to reproduce positive results suggesting that the prophylactic use for neuroprotection in at-risk populations or patients is the most promising field. Nonetheless, the only clearly positive data of the creatine supplementation in human beings are related to the (rare) creatine deficiency syndromes. It seems critical that future studies must establish the best dosage regime to increase brain creatine in a way that can relate to animal studies, provide new ways for creatine to reach the brain, and seek larger experimental groups with biomarkers for prediction of efficacy.

Evolutionary expression differences of creatine synthesis-related genes: Implications for skeletal muscle metabolism in fish

The creatine/phosphocreatine system is the principal energy buffer in mammals, but is scarcely documented in fish. We measured the gene expression of major enzymes of this system, glycine amidinotransferase (GATM), guanidinoacetate N-methyltransferase (GAMT) and muscle-type creatine kinase (CKM) in kidney, liver, and muscle tissues of fish and mammals. CKM was expressed strongly in the muscles of all examined species. In contrast, GATM and GAMT were strongly expressed in the muscle tissue of fish, but not of mammals. This indicates that creatine synthesis and usage are spatially separated in mammals, but not in fish, which is supported by RNA-Seq data of 25 species. Differences in amino acid metabolism along with methionine adenosyltransferase gene expression in muscle from fishes but not mammals further support a central metabolic role of muscle in fish, and hence different organization of the creatine/phosphocreatine biosynthesis system in higher and lower vertebrates.

Mechanisms underlying UCP1 dependent and independent adipocyte thermogenesis

The growing focus on brown adipocytes has spurred an interest in their potential benefits for metabolic diseases. Brown and beige (or brite) adipocytes express high levels of uncoupling protein 1 (Ucp1) to dissipate heat instead of generating ATP. Ucp1 induction by stimuli including cold, exercise, and diet increases nonshivering thermogenesis, leading to increased energy expenditure and prevention of obesity. Recently, studies in adipocytes have indicated the existence of functional Ucp1-independent thermogenic regulators. Furthermore, substrate cycling involving creatine metabolites, cold-induced N-acyl amino acids, and oxidized lipids in white adipocytes can increase energy expenditure in the absence of Ucp1. These studies emphasize the need for a better understanding of the mechanisms governing energy expenditure in adipocytes and their potential applications in the prevention of human obesity and metabolic diseases.

Creatine Monohydrate and Guanidinoacetic Acid Supplementation Affects the Growth Performance, Meat Quality, and Creatine Metabolism of Finishing Pigs

This study aimed to investigate the effects of creatine monohydrate (CMH) and guanidinoacetic acid (GAA) supplementation on the growth performance, meat quality, and creatine metabolism of finishing pigs. The pigs were randomly allocated to three treatment groups: the control group, CMH group, and GAA group. In comparison to the control group, CMH treatment increased average daily feed intake and GAA treatment increased average daily feed intake and average daily gain of pigs. In addition, CMH and GAA treatment increased pH_45 min, myofibrillar protein solubility, and calpain 1 mRNA expression level and decreased the drip loss and shear force value in longissimus dorsi or semitendinosus muscle. Moreover, CMH and GAA supplementation increased the concentrations of creatine and phosphocreatine and the mRNA expressions of guanidinoacetate N-methyltransferase and creatine transporter in longissimus dorsi muscle, semitendinosus muscle, liver, or kidneys and decreased the mRNA expressions of arginine:glycine amidinotransferase in kidneys. In conclusion, CMH and GAA supplementation could improve the growth performance and meat quality and alter creatine metabolism of finishing pigs.

Effects of single and combined metformin and L-citrulline supplementation on L-arginine-related pathways in Becker muscular dystrophy patients: possible biochemical and clinical implications

The L-arginine/nitric oxide synthase (NOS) pathway is considered to be altered in muscular dystrophy such as Becker muscular dystrophy (BMD). We investigated two pharmacological options aimed to increase nitric oxide (NO) synthesis in 20 male BMD patients (age range 21-44 years): (1) supplementation with L-citrulline (3 × 5 g/d), the precursor of L-arginine which is the substrate of neuronal NO synthase (nNOS); and (2) treatment with the antidiabetic drug metformin (3 × 500 mg/d) which activates nNOS in human skeletal muscle. We also investigated the combined use of L-citrulline (3 × 5 g/d) and metformin (3 × 500 mg/d). Before and after treatment, we measured in serum and urine samples the concentration of amino acids and metabolites of L-arginine-related pathways and the oxidative stress biomarker malondialdehyde (MDA). Compared to healthy subjects, BMD patients have altered NOS, arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT) pathways. Metformin treatment resulted in concentration decrease of arginine and MDA in serum, and of homoarginine (hArg) and guanidinoacetate (GAA) in serum and urine. L-Citrulline supplementation resulted in considerable increase of the concentrations of amino acids and creatinine in the serum, and in their urinary excretion rates. Combined use of metformin and L-citrulline attenuated the effects obtained from their single administrations. Metformin, L-citrulline or their combination did not alter serum nitrite and nitrate concentrations and their urinary excretion rates. In conclusion, metformin or L-citrulline supplementation to BMD patients results in remarkable antidromic changes of the AGAT and GAMT pathways. In combination, metformin and L-citrulline at the doses used in the present study seem to abolish the biochemical effects of the single drugs in slight favor of L-citrulline.

A Mouse Model of Creatine Transporter Deficiency Reveals Impaired Motor Function and Muscle Energy Metabolism

Creatine serves as fast energy buffer in organs of high-energy demand such as brain and skeletal muscle. L-Arginine:glycine amidinotransferase (AGAT) and guanidinoacetate N-methyltransferase are responsible for endogenous creatine synthesis. Subsequent uptake into target organs like skeletal muscle, heart and brain is mediated by the creatine transporter (CT1, SLC6A8). Creatine deficiency syndromes are caused by defects of endogenous creatine synthesis or transport and are mainly characterized by intellectual disability, behavioral abnormalities, poorly developed muscle mass, and in some cases also muscle weakness. CT1-deficiency is estimated to be among the most common causes of X-linked intellectual disability and therefore the brain phenotype was the main focus of recent research. Unfortunately, very limited data concerning muscle creatine levels and functions are available from patients with CT1 deficiency. Furthermore, different CT1-deficient mouse models yielded conflicting results and detailed analyses of their muscular phenotype are lacking. Here, we report the generation of a novel CT1-deficient mouse model and characterized the effects of creatine depletion in skeletal muscle. HPLC-analysis showed strongly reduced total creatine levels in skeletal muscle and heart. MR-spectroscopy revealed an almost complete absence of phosphocreatine in skeletal muscle. Increased AGAT expression in skeletal muscle was not sufficient to compensate for insufficient creatine transport. CT1-deficient mice displayed profound impairment of skeletal muscle function and morphology (i.e., reduced strength, reduced endurance, and muscle atrophy). Furthermore, severely altered energy homeostasis was evident on magnetic resonance spectroscopy. Strongly reduced phosphocreatine resulted in decreased ATP/Pi levels despite an increased inorganic phosphate to ATP flux. Concerning glucose metabolism, we show increased glucose transporter type 4 expression in muscle and improved glucose clearance in CT1-deficient mice. These metabolic changes were associated with activation of AMP-activated protein kinase – a central regulator of energy homeostasis. In summary, creatine transporter deficiency resulted in a severe muscle weakness and atrophy despite different compensatory mechanisms.

Creatine supplementation to total parenteral nutrition improves creatine status and supports greater liver and kidney protein synthesis in neonatal piglets

BackgroundCreatine is not included in commercial pediatric parenteral products; the entire creatine requirement must be met by de novo synthesis from arginine during parenteral nutrition (PN). Poor arginine status is common during PN in neonates, which may compromise creatine accretion. We hypothesized that creatine supplementation will improve creatine status and spare arginine in PN-fed piglets.MethodsPiglets (3-5-day (d) old) were provided PN with or without creatine for 14 d. Tissue concentrations of creatine metabolites and activities of creatine-synthesizing enzymes, as well as tissue protein synthesis rates and liver lipid parameters, were measured.ResultsCreatine provision lowered kidney and pancreas L-arginine:glycine amidinotransferase (AGAT, EC number 2.1.4.1) activities and plasma guanidinoacetic acid (GAA) concentration, suggesting the downregulation of de novo creatine synthesis. Creatine increased plasma creatine concentrations to sow-fed reference levels and increased the creatine concentrations in most tissues, but not in the brain. PN creatine resulted in greater protein synthesis in the liver and the kidney, but not in the pancreas, skeletal muscle, or gut. Creatine supplementation also reduced liver cholesterol concentrations, but not triglyceride or total fat.ConclusionThe addition of creatine to PN may optimize the accretion of creatine and reduce the metabolic burden of creatine synthesis in rapidly growing neonates.

Dietary creatine supplementation lowers hepatic triacylglycerol by increasing lipoprotein secretion in rats fed high-fat diet

Recent studies have shown that dietary creatine supplementation can prevent lipid accumulation in the liver. Creatine is a small molecule that plays a large role in energy metabolism, but since the enzyme creatine kinase is not present in the liver, the classical role in energy metabolism does not hold in this tissue. Fat accumulation in the liver can lead to the development of nonalcoholic fatty liver disease (NAFLD), a progressive disease that is prevalent in humans. We have previously reported that creatine can directly influence lipid metabolism in cell culture to promote lipid secretion and oxidation. Our goal in the current study was to determine whether similar mechanisms that occur in cell culture were present in vivo. We also sought to determine whether dietary creatine supplementation could be effective in reversing steatosis. Sprague-Dawley rats were fed a high-fat diet or a high-fat diet supplemented with creatine for 5 weeks. We found that rats supplemented with creatine had significantly improved rates of lipoprotein secretion and alterations in mitochondrial function that were consistent with greater oxidative capacity. We also find that introducing creatine into a high-fat diet halted hepatic lipid accumulation in rats with fatty liver. Our results support our previous report that liver cells in culture with creatine secrete and oxidize more oleic acid, demonstrating that dietary creatine can effectively change hepatic lipid metabolism by increasing lipoprotein secretion and oxidation in vivo. Our data suggest that creatine might be an effective therapy for NAFLD.

The role of dietary creatine

The daily requirement of a 70-kg male for creatine is about 2 g; up to half of this may be obtained from a typical omnivorous diet, with the remainder being synthesized in the body Creatine is a carninutrient, which means that it is only available to adults via animal foodstuffs, principally skeletal muscle, or via supplements. Infants receive creatine in mother's milk or in milk-based formulas. Vegans and infants fed on soy-based formulas receive no dietary creatine. Plasma and muscle creatine levels are usually somewhat lower in vegetarians than in omnivores. Human intake of creatine was probably much higher in Paleolithic times than today; some groups with extreme diets, such as Greenland and Alaskan Inuit, ingest much more than is currently typical. Creatine is synthesized from three amino acids: arginine, glycine and methionine (as S-adenosylmethionine). Humans can synthesize sufficient creatine for normal function unless they have an inborn error in a creatine-synthetic enzyme or a problem with the supply of substrate amino acids. Carnivorous animals, such as lions and wolves, ingest much larger amounts of creatine than humans would. The gastrointestinal tract and the liver are exposed to dietary creatine in higher concentrations before it is assimilated by other tissues. In this regard, our observations that creatine supplementation can prevent hepatic steatosis (Deminice et al. J Nutr 141:1799-1804, 2011) in a rodent model may be a function of the route of dietary assimilation. Creatine supplementation has also been reported to improve the intestinal barrier function of the rodent suffering from inflammatory bowel disease.

Low-Dose Creatine Supplementation Lowers Plasma Guanidinoacetate, but Not Plasma Homocysteine, in a Double-Blind, Randomized, Placebo-Controlled Trial

BACKGROUND

Creatine synthesis from guanidinoacetate consumes ~50% of s-adenosylmethionine (SAM)-derived methyl groups, accounting for an equivalent proportion of s-adenosylhomocysteine (SAH) and total homocysteine (tHcys) synthesis. Dietary creatine inhibits the synthesis of guanidinoacetate, thereby lowering plasma tHcys in rats.

OBJECTIVE

We tested the hypotheses that creatine supplementation lowers plasma guanidinoacetate, increases blood SAM, lowers blood SAH, and lowers plasma tHcys.

METHODS

Bangladeshi adults were randomly assigned to receive 1 of 4 treatments for 12 wk: placebo (n = 101), 3 g/d creatine (Cr; n = 101), 400 μg/d folic acid (FA; n = 153), or 3 g/d creatine plus 400 μg/d folic acid (Cr+FA; n = 103). The outcomes of plasma guanidinoacetate and tHcys, as well as whole blood SAM and SAH, were analyzed at baseline and week 12 by HPLC. Treatment effects of creatine supplementation were examined with the use of the group comparisons of Cr vs. placebo and Cr+FA vs. FA.

RESULTS

Plasma guanidinoacetate declined by 10.6% (95% CI: 4.9, 15.9) in the Cr group while increasing nonsignificantly in the placebo group (3.7%; 95% CI: -0.8, 8.5) (Pgroup difference = 0.0002). Similarly, plasma guanidinoacetate declined by 9.0% (95% CI: 3.4, 14.2) in the Cr+FA group while increasing in the FA group (7.0%; 95% CI: 2.0, 12.2) (Pgroup difference < 0.0001). Plasma tHcys declined by 23.4% (95% CI: 19.5, 27.1) and 21.0% (95% CI: 16.4, 25.2) in the FA and Cr+FA groups, respectively (Pgroup difference = 0.41), with no significant changes in the placebo or Cr groups (Pgroup difference = 0.35). A decrease in guanidinoacetate over time was associated with a decrease in tHcys over time in the Cr+FA group (β = 0.30; 95% CI: 0.17, 0.43; P < 0.0001).

CONCLUSIONS

Our findings indicate that whereas creatine supplementation downregulates endogenous creatine synthesis, this may not on average lower plasma tHcys in humans. However, tHcys did decrease in those participants who experienced a decline in plasma guanidinoacetate while receiving creatine plus folic acid supplementation. This trial was registered at clinicaltrials.gov as NCT01050556.

Biosynthesis of homoarginine (hArg) and asymmetric dimethylarginine (ADMA) from acutely and chronically administered free L-arginine in humans

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis, whereas L-arginine (Arg) and L-homoarginine (hArg) serve as substrates for NO synthesis. ADMA and other methylated arginines are generally believed to exclusively derive from guanidine (N (G))-methylated arginine residues in proteins by protein arginine methyltransferases (PRMTs) that use S-adenosylmethionine (SAM) as the methyl donor. L-Lysine is known for decades as a precursor for hArg, but only recent studies indicate that arginine:glycine amidinotransferase (AGAT) is responsible for the synthesis of hArg. AGAT catalyzes the formation of guanidinoacetate (GAA) that is methylated to creatine by guanidinoacetate methyltransferase (GAMT) which also uses SAM. The aim of the present study was to learn more about the mechanisms of ADMA and hArg formation in humans. Especially, we hypothesized that ADMA is produced by N (G)-methylation of free Arg in addition to the known PRMTs-involving mechanism. In knockout mouse models of AGAT- and GAMT-deficiency, we investigated the contribution of these enzymes to hArg synthesis. Arg infusion (0.5 g/kg, 30 min) in children (n = 11) and ingestion of high-fat protein meals by overweight men (n = 10) were used to study acute effects on ADMA and hArg synthesis. Daily Arg ingestion (10 g) or placebo for 3 or 6 months by patients suffering from peripheral arterial occlusive disease (PAOD, n = 20) or coronary artery disease (CAD, n = 30) was used to study chronic effects of Arg on ADMA synthesis. Mass spectrometric methods were used to measure all biochemical parameters in plasma and urine samples. In mice, AGAT but not GAMT was found to contribute to plasma hArg, while ADMA synthesis was independent of AGAT and GAMT. Arg infusion acutely increased plasma Arg, hArg and ADMA concentrations, but decreased the plasma hArg/ADMA ratio. High-fat protein meals acutely increased plasma Arg, hArg, ADMA concentrations, as well as the plasma hArg/ADMA ratio. In the PAOD and CAD studies, plasma Arg concentration increased in the verum compared to the placebo groups. Plasma ADMA concentration increased only in the PAOD patients who received Arg. Our study suggests that in humans a minor fraction of free Arg is rapidly metabolized to ADMA and hArg. In mice, GAMT and N (G)-methyltransferases contribute to ADMA and hArg synthesis from Arg, whereas AGAT is involved in the synthesis of hArg but not of ADMA. The underlying biochemical mechanisms remain still elusive.

Maternal creatine homeostasis is altered during gestation in the spiny mouse: is this a metabolic adaptation to pregnancy?

BACKGROUND

Pregnancy induces adaptations in maternal metabolism to meet the increased need for nutrients by the placenta and fetus. Creatine is an important intracellular metabolite obtained from the diet and also synthesised endogenously. Experimental evidence suggests that the fetus relies on a maternal supply of creatine for much of gestation. However, the impact of pregnancy on maternal creatine homeostasis is unclear. We hypothesise that alteration of maternal creatine homeostasis occurs during pregnancy to ensure adequate levels of this essential substrate are available for maternal tissues, the placenta and fetus. This study aimed to describe maternal creatine homeostasis from mid to late gestation in the precocial spiny mouse.

METHODS

Plasma creatine concentration and urinary excretion were measured from mid to late gestation in pregnant (n = 8) and age-matched virgin female spiny mice (n = 6). At term, body composition and organ weights were assessed and tissue total creatine content determined. mRNA expression of the creatine synthesising enzymes arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT), and the creatine transporter (CrT1) were assessed by RT-qPCR. Protein expression of AGAT and GAMT was also assessed by western blot analysis.

RESULTS

Plasma creatine and renal creatine excretion decreased significantly from mid to late gestation (P < 0.001, P < 0.05, respectively). Pregnancy resulted in increased lean tissue (P < 0.01), kidney (P < 0.01), liver (P < 0.01) and heart (P < 0.05) mass at term. CrT1 expression was increased in the heart (P < 0.05) and skeletal muscle (P < 0.05) at term compared to non-pregnant tissues, and creatine content of the heart (P < 0.05) and kidney (P < 0.001) were also increased at this time. CrT1 mRNA expression was down-regulated in the liver (<0.01) and brain (<0.01) of pregnant spiny mice at term. Renal AGAT mRNA (P < 0.01) and protein (P < 0.05) expression were both significantly up-regulated at term, with decreased expression of AGAT mRNA (<0.01) and GAMT protein (<0.05) observed in the term pregnant heart. Brain AGAT (<0.01) and GAMT (<0.001) mRNA expression were also decreased at term.

CONCLUSION

Change of maternal creatine status (increased creatine synthesis and reduced creatine excretion) may be a necessary adjustment of maternal physiology to pregnancy to meet the metabolic demands of maternal tissues, the placenta and developing fetus.