Analysis of creatine, creatinine, creatine-d3 and creatinine-d3 in urine, plasma, and red blood cells by HPLC and GC–MS to follow the fate of ingested creatine-d3

Studies on the Reaction of Dietary Methylglyoxal and Creatine during Simulated Gastrointestinal Digestion and in Human Volunteers

The reactive 1,2-dicarbonyl compound methylglyoxal (MGO) is consumed with food and its concentrations decrease during digestion. In the present paper, the reaction of MGO with creatine, arginine, and lysine during simulated digestion, and its reaction with creatine during the digestion in human volunteers, was studied. Therefore, simulated digestion experiments with a gastric and an intestinal phase were performed. Additionally, an intervention study with 12 subjects consuming MGO-containing Manuka honey and creatine simultaneously or separately was conducted. Derivatization with o-phenylenediamine and HPLC–UV was used to measure MGO, while creatine and glycated amino compounds were analyzed via HPLC–MS/MS. We show that MGO quickly reacts with creatine and arginine, but not lysine, during simulated digestion. Creatine reacts with 56% of MGO to form the hydroimidazolone MG-HCr, and arginine reacted with 4% of MGO to form the hydroimidazolone MG-H1. In the intervention study, urinary MG-HCr excretion is higher in subjects who consumed MGO and creatine simultaneously compared to subjects who ingested the substances separately. This demonstrates that the 1,2-dicarbonyl compound MGO reacts with amino compounds during human digestion, and glycated adducts are formed. These contribute to dietary glycation products consumed, and should be considered in studies investigating their physiological consequences.

An LC-MS/MS method for creatine and creatinine analysis in paraquat-intoxicated patients

A sudden increase in serum creatinine after paraquat intoxication has been reported in several clinical studies. However, this dramatic change of creatinine may be possibly due to an interconversion of creatine-creatinine in relation to paraquat toxicity. In order to investigate the creatine-creatinine relationship, a liquid chromatography tandem mass spectrometry in combination with electrospray ionization was developed and validated for simultaneous determination of creatine and creatinine in the serum. The chromatographic separation was achieved on a Gemini® C₆-Phenyl column with a gradient elution consisting of 0.1% formic acid in ultrapure water and methanol as the mobile phase. The method yielded suitable levels of specificity and selectivity, and calibration curves of creatine and creatinine in serum were linear over the concentration range of 0.5-200 µg mL^-1. The limit of quantification of both compounds was 0.5 µg mL^-1, and the method was accurate within the recovery range of 96.23-102.75%, indicating the robustness of the method. The method was successfully applied to toxicological samples from paraquat-intoxicated patients, and the concentrations of creatine and creatinine were quantified. High creatine concentrations in serum samples were observed which may lead to high serum creatinine despite normal kidney function as creatine is converted to creatinine in proportion to its concentration.

Hydrophilic interaction chromatography coupled to tandem mass spectrometry as a method for simultaneous determination of guanidinoacetate and creatine

The biosynthesis of creatine (Cr) is closely related to the bioavailability of guanidinoacetate (GAA). The lack of one or the other may compromise their role in the energy transport and cell signaling. A reliable estimate of their levels in biological samples is imperative since they are important markers of many metabolic disorders. Therefore, a new LC-MS/MS method for simultaneous determination and quantification of GAA and Cr by multiple reaction monitoring (MRM) mode was developed based on the hydrophilic interaction chromatography (HILIC) and response surface methodology (RSM) for the optimization of chromatographic parameters. The optimized parameters ensured good separation of these similar, very polar molecules (chromatographic resolution > 1.5) without prior derivatization step in a short analysis run (6 min). The developed method was validated to ensure accurate (R, 75.1-101.6%), precise (RSD < 20%) and low quantification (LOQ of 0.025 μg mL^-1 for GAA and 0.006 μg mL^-1 for Cr) of the tested analytes and the use of matrix-matched calibration eliminated variable effects of complex matrices such as human plasma and urine. Therefore, this method can be implemented in medical laboratories as a tool for the diagnostics of creatine deficiencies and monitoring of guanidinoacetate and creatine supplementation regimes in biological samples.

Selective recognition of creatinine - Development of a colorimetric sensor

The present report describes a simple and cost effective protocol for colourimetric determination of creatinine (CR), L-cysteine stabilized copper nanoparticles (L-cys-CuNPs) exhibited selective and sensitive interaction with CR. Utilizing this interaction, a colourimetric sensor has been developed based on the reduction in LSPR intensity as monitored by a UV-visible spectrophotometer. The developed sensor exhibited a linear dynamic range of 5.33 × 10^-6 to 3.33 × 10^-7 M. Proposed sensor is simple and cost - effective compared to methods based on noble metal nanoparticles and the sensitivity to determine CR was as low as 4.54 × 10^-10 M. The sensor was successfully applied for quantification of CR in artificial serum and urine samples. Sensor developed in this work has a high potential for rapid and on-site determination of CR in physiological and clinical samples.

A clinical biomarker assay for the quantification of d3-creatinine and creatinine using LC-MS/MS

BACKGROUND

Current methods to measure skeletal muscle mass are not practical in a clinical setting. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods that measure the amount of urinary d3-creatinine enrichment after a single tracer dose of d3-creatine was developed.

RESULTS

The biomarkers d3-creatinine and creatinine were detected in human urine using LC-MS/MS. In this assay a surrogate analyte, d3-creatinine, was used to quantify endogenous creatinine. However, since endogenous concentrations of creatinine were orders of magnitude higher than d3-creatinine, the peak area of a less intense isotope of creatinine was acquired. A response factor is used to correct for using a less intense isotope multiple reaction monitoring transition.

CONCLUSION

Novel LC-MS/MS assays were developed that quantify the biomarkers d3-creatinine, creatinine and d3-creatine in urine. This method allows the estimation of total body creatine pool size and subsequent calculation of muscle mass. This assay was originally validated as fit-for-purpose and was followed by full validation.

Stability of creatine derivatives during simulated digestion in an in vitro model

Newly developed forms of creatine are often claimed to exhibit improved bioavailability and efficacy. They are of great interest for sports nutrition and therapeutic uses. However, for most newer creatine forms stability after ingestion under physiological conditions is insufficiently documented, relevant data are inconsistent or even missing. Therefore, we developed a controlled simulated digestion system for testing different creatine derivatives in specific simulated parts of the human digestive system. All derivatives showed high stability with negligible formation of creatinine.

Creatine and guanidinoacetate content of human milk and infant formulas: implications for creatine deficiency syndromes and amino acid metabolism

Creatine is essential for normal neural development; children with inborn errors of creatine synthesis or transport exhibit neurological symptoms such as mental retardation, speech delay and epilepsy. Creatine accretion may occur through dietary intake or de novo creatine synthesis. The objective of the present study was to determine how much creatine an infant must synthesise de novo. We have calculated how much creatine an infant needs to account for urinary creatinine excretion (creatine's breakdown product) and new muscle lay-down. To measure an infant's dietary creatine intake, we measured creatine in mother's milk and in various commercially available infant formulas. Knowing the amount of milk/formula ingested, we calculated the amount of creatine ingested. We have found that a breast-fed infant receives about 9 % of the creatine needed in the diet and that infants fed cows' milk-based formula receive up to 36 % of the creatine needed. However, infants fed a soya-based infant formula receive negligible dietary creatine and must rely solely on de novo creatine synthesis. This is the first time that it has been shown that neonatal creatine accretion is largely due to de novo synthesis and not through dietary intake of creatine. This has important implications both for infants suffering from creatine deficiency syndromes and for neonatal amino acid metabolism.

The metabolic burden of creatine synthesis

Creatine synthesis is required in adult animals to replace creatine that is spontaneously converted to creatinine and excreted in the urine. Additionally, in growing animals it is necessary to provide creatine to the expanding tissue mass. Creatine synthesis requires three amino acids: glycine, methionine and arginine, and three enzymes: L-arginine:glycine amidinotransferase (AGAT), methionine adenosyltransferase (MAT) and guanidinoacetate methyltransferase (GAMT). The entire glycine molecule is consumed in creatine synthesis but only the methyl and amidino groups, respectively, from methionine and arginine. Creatinine loss averages approximately 2 g (14.6 mmol) for 70 kg males in the 20- to 39-year age group. Creatinine loss is lower in females and in older age groups because of lower muscle mass. Approximately half of this creatine lost to creatinine can be replaced, in omnivorous individuals, by dietary creatine. However, since dietary creatine is only provided in animal products, principally in meat and fish, virtually all of the creatine loss in vegetarians must be replaced via endogenous synthesis. Creatine synthesis does not appear to place a major burden on glycine metabolism in adults since this amino acid is readily synthesized. However, creatine synthesis does account for approximately 40% of all of the labile methyl groups provided by S-adenosylmethionine (SAM) and, as such, places an appreciable burden on the provision of such methyl groups, either from the diet or via de novo methylneogenesis. Creatine synthesis consumes some 20-30% of arginine's amidino groups, whether provided in the diet or synthesized within the body. Creatine synthesis is, therefore, a quantitatively major pathway in amino acid metabolism and imposes an appreciable burden on the metabolism of methionine and of arginine.

Gas chromatography/atmospheric pressure chemical ionization-time of flight mass spectrometry: analytical validation and applicability to metabolic profiling

Gas Chromatography (GC)-Mass Spectrometry (MS) with Atmospheric Pressure (AP) interface was introduced more than 30 years ago but never became a mainstream technique, mainly because of technical difficulties and cost of instrumentation. A recently introduced multipurpose AP source created the opportunity to reconsider the importance of AP ionization for GC. Here, we present an analytical evaluation of GC/APCI-MS showing the benefits of soft atmospheric pressure chemical ionization for GC in combination with a Time of Flight (TOF) mass analyzer. During this study, the complete analytical procedure was optimized and evaluated with respect to characteristic analytical parameters, such as repeatability, reproducibility, linearity, and detection limits. Limits of detection (LOD) were found within the range from 11.8 to 72.5 nM depending on the type of compound. The intraday and interday repeatability tests demonstrate relative standard deviations (RSDs) of peak areas between 0.7%-2.1% and 3.8%-6.4% correspondingly. Finally, we applied the developed method to the analysis of human cerebrospinal fluid (CSF) samples to check the potential of this new analytical combination for metabolic profiling.

Creatine metabolism and the urea cycle

Because creatine and creatine phosphate are irreversibly converted to creatinine, there is a continuous need for their replacement. This occurs by means of diet and de novo synthesis. Dietary creatine is provided in animal products and can amount to about half of the required amount. Synthesis provides the remainder. Creatine synthesis is a major component of arginine metabolism, amounting to more than 20% of the dietary intake of this amino acid. Creatine metabolism is of importance to patients with urea cycle disorders in two ways, both related to arginine levels. In patients with arginase deficiency, markedly elevated arginine levels may result in higher concentrations of guanidinoacetate and higher rates of creatine synthesis. This is of concern because it is thought that elevated levels of guanidinoacetate may exert neurotoxic effects. In the case of the other urea cycle disorders, arginine levels are markedly decreased unless the patients are supplemented with this amino acid. Decreased levels of arginine may result in decreased rates of creatine synthesis. This may be compounded by the fact that such patients, maintained on low protein diets, will also have lower dietary creatine intakes. There is some evidence that this may decrease brain creatine levels which may contribute to the neurological symptoms exhibited by these patients. It is clear that patients with urea cycle disorders also have altered creatine metabolism. Whether this contributes in a significant way to their neurological symptoms remains an open question.

Creatine synthesis is a major metabolic process in neonatal piglets and has important implications for amino acid metabolism and methyl balance

Our objectives in this study were as follows: 1) to determine the rate of creatine accretion by the neonatal piglet; 2) identify the sources of this creatine; 3) measure the activities of the enzymes of creatine synthesis; and 4) to estimate the burden that endogenous creatine synthesis places on the metabolism of the 3 amino acids required for this synthesis: glycine, arginine, and methionine. We found that piglets acquire 12.5 mmol of total creatine (creatine plus creatine phosphate) between 4 and 11 d of age. As much as one-quarter of creatine accretion in neonatal piglets may be provided by sow milk and three-quarters by de novo synthesis by piglets. This rate of creatine synthesis makes very large demands on arginine and methionine metabolism, although the magnitude of the demand depends on the rate of remethylation of homocysteine and of reamidination of ornithine. Of the 2 enzymes of creatine synthesis, we found high activity of l-arginine:glycine amidinotransferase in piglet kidneys and pancreas and of guanidinoacetate methyltransferase in piglet livers. Piglet livers also had appreciable activities of methionine adenosyltransferase, which synthesizes S-adenosylmethionine, and of betaine:homocysteine methyltransferase, methionine synthase, and methylene tetrahydrofolate reductase, which are required for the remethylation of homocysteine to methionine. Creatine synthesis is a quantitatively major metabolic process in piglets.

Creatine: Endogenous Metabolite, Dietary, and Therapeutic Supplement

Creatine and phosphocreatine serve not only as an intracellular buffer for adenosine triphosphate, but also as an energy shuttle for the movement of high-energy phosphates from mitochondrial sites of production to cytoplasmic sites of utilization. The spontaneous loss of creatine and of phosphocreatine to creatinine requires that creatine be continuously replaced; this occurs by a combination of diet and endogenous synthesis. Vegetarians obtain almost no dietary creatine. Creatine synthesis makes major demands on the metabolism of glycine, arginine, and methionine. Large doses of creatine monohydrate are widely taken, particularly by athletes, as an ergogenic supplement; creatine supplements are also taken by patients suffering from gyrate atrophy, muscular dystrophy, and neurodegenerative diseases. Children with inborn errors of creatine synthesis or transport present with severe neurological symptoms and a profound depletion of brain creatine. It is evident that creatine plays a critical, though underappreciated, role in brain function.

Methyl balance and transmethylation fluxes in humans

Various questions have been raised about labile methyl balance and total transmethylation fluxes, and further discussion has been encouraged. This report reviews and discusses some of the relevant evidence now available. The fact that, if needed, labile methyl balance is maintained by methylneogenesis appears to be established, but several aspects of transmethylation remain uncertain: definitive measurements of the rate of total transmethylation in humans of both sexes on various diets and at various ages; the extent to which synthesis of phosphatidylcholine has been underestimated; and the relative contributions of the 2 pathways for the formation of sarcosine (ie, N-methylglycine). The available evidence indicates that the quantitatively most important pathways for S-adenosylmethionine-dependent transmethylation in mammals are the syntheses of creatine by guanidinoacetate methyltransferase, of phosphatidylcholine by phosphatidylethanolamine methyltransferase, and of sarcosine by glycine N-methyltransferase. Data presented in this report show that S-adenosylmethionine and methionine accumulate abnormally in the plasma of humans with glycine N-methyltransferase deficiency but not of those with guanidinoacetate N-methyltransferase deficiency or in the plasma or livers of mice devoid of phosphatidylethanolamine N-methyltransferase activity. The absence of such accumulations in the latter 2 conditions may be due to removal of S-adenosylmethionine by synthesis of sarcosine. Steps that may help clarify the remaining issues include the determination of the relative rates of synthesis of sarcosine, creatine, and phosphatidylcholine by rapid measurement of the rates of radiolabel incorporation into these compounds from L-[methyl-3H]methionine administered intraportally to an experimental animal; clarification of the intracellular hepatic isotope enrichment value during stable-isotope infusion studies to enhance the certainty of methyl flux estimates during such studies; and definitive measurement of the dietary betaine intake from various diets.

Molecularly imprinted solid-phase extraction combined with molecularly imprinted polymer-sensor: a diagnostic tool applicable to creatine deficiency syndrome

Primary creatine deficiency syndromes (CDS) are a new group of disorders caused by guanidinoacetate methyltransferase (GAMT) deficiency, which affects endogenous creatine biosynthesis with depletion of body creatine. A deficiency in creatine can be corrected by treatment with oral creatine supplementation and this necessitates a simple and sensitive screening method for early detection of creatine in dilute physiologic fluids. In this work an artificial receptor, molecularly imprinted polymer (MIP), for creatine was used both as a material for solid-phase extraction (SPE) and as a sensing element in a voltammetric sensor. Using the combination of molecularly imprinted solid-phase extraction (MISPE) with a complementary MIP sensor, the minimum detectable amount was found to be 0.0015 ng mL(-1) (RSD = 1.3%, S/N = 3). The MISPE-MIP sensor combination provided up to 60-fold preconcentration, which was more than sufficient for achieving the required quantification limit 50 ng mL(-1) (or 0.0025 ng mL(-1) after 2 x 10(4)-fold dilution) for creatine in human blood serum.