Urinary Creatine Excretion Research Articles

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.

Effect of guanidinoacetic acid supplementation on nitrogen retention and methionine methyl group flux in growing steers fed corn-based diets.

Six ruminally cannulated Holstein steers (256 ± 14 kg) were used in a 6 × 6 Latin square design to assess effects of guanidinoacetic acid (GAA) supplementation on N retention and methionine (Met) methyl group flux in growing cattle fed corn-based diets. Factorial treatments were two levels of Met (0 or 5 g/d) and three levels of GAA (0, 7.5, or 15 g/d) delivered by continuous abomasal infusion. Periods were 10 d in length and included 6 d of treatment adaptation, 3 d for total fecal and urine collections, and 1 d for blood sampling and flux measurements. Urinary N linearly increased (P < 0.01) with GAA supplementation and decreased (P < 0.05) with Met supplementation. Fecal N excretion was unaffected (P ≥ 0.42) by treatment. Retained N was not affected by GAA supplementation, but it was increased (P < 0.01) by Met supplementation. Use of methionine for transmethylation reactions, as well remethylation of homocysteine, was not affected by GAA supplementation when Met was not supplemented, but tended to be linearly increased by GAA supplementation when Met was supplemented (GAA-linear × Met interaction; P = 0.07), with the increases matching the amount of GAA provided. This response suggests that methylation reactions for compounds other than GAA were reduced by GAA supplementation when Met supply was deficient. Plasma concentrations and urinary excretion of creatine increased linearly (P = 0.03 and P = 0.06, respectively) when GAA was supplemented. There was a linear increase (P < 0.01) in urinary GAA excretion with GAA supplementation. Neither plasma concentration nor urinary excretion of creatinine was affected (P ≥ 0.17) by treatment. No treatment differences (P ≥ 0.13) were observed for plasma haptoglobin concentrations. Plasma urea-N linearly increased (P < 0.05) with GAA supplementation. Concentrations of Met and taurine increased (P < 0.05) when Met was supplemented. Plasma arginine was greatest at the intermediate level of supplemental GAA (quadratic, P < 0.05). The increase in N retention when Met was supplemented demonstrates Met was limiting in the corn-based diet. Supplementation of GAA alone or with Met as a methyl donor did not increase N retention in growing steers, perhaps because creatine production was favored over protein deposition as a use for Met.

Urine metabolic phenotyping in children with nocturnal enuresis and comorbid neurobehavioral disorders

Nocturnal enuresis (NE) is a common problem among 10% school-aged children. The etiologies underlying childhood NE is complex and not fully understood nowadays. Nevertheless, increasing evidence suggests a potential link between neurobehavioral disorders and enuresis in children. In this study, we aimed to explore novel metabolomic insights into the pathophysiology of NE and also, its association with pediatric psychiatric problems. Urine collected from 41 bedwetting children and 27 healthy control children was analyzed by using 1H-nuclear magnetic resonance spectroscopy from August 2017 to December 2018. At regular follow-up, there were 14 children with refractory NE having a diagnosis of attention deficient hyperactivity disorder (ADHD) or anxiety. Eventually, we identified eight significantly differential urinary metabolites and particularly increased urinary excretion of betaine, creatine and guanidinoacetate linked to glycine, serine and threonine metabolism were associated with a comorbidity of neurobehavioral disorders in refractory bedwetting children. Notably, based on physiological functions of betaine acting as a renal osmolyte and methyl group donor, we speculated its potential role in modulation of renal and/or central circadian clock systems, becoming a useful urinary metabolic marker in diagnosis of treatment-resistant NE in children affected by these two disorders.

Effects of guanidinoacetic acid supplementation on nitrogen retention and methionine flux in cattle.

Creatine stores high-energy phosphate bonds in muscle and is synthesized in the liver through methylation of guanidinoacetic acid (GAA). Supplementation of GAA may therefore increase methyl group requirements, and this may affect methyl group utilization. Our experiment evaluated the metabolic responses of growing cattle to postruminal supplementation of GAA, in a model where methionine (Met) was deficient, with and without Met supplementation. Seven ruminally cannulated Holstein steers (161 kg initial body weight [BW]) were limit-fed a soybean hull-based diet (2.7 kg/d dry matter) and received continuous abomasal infusions of an essential amino acid (AA) mixture devoid of Met to ensure that no AA besides Met limited animal performance. To provide energy without increasing the microbial protein supply, all steers received ruminal infusions of 200 g/d acetic acid, 200 g/d propionic acid, and 50 g/d butyric acid, as well as abomasal infusions of 300 g/d glucose. Treatments, provided abomasally, were arranged as a 2 × 3 factorial in a split-plot design, and included 0 or 6 g/d of l-Met and 0, 7.5, and 15 g/d of GAA. The experiment included six 10-d periods. Whole body Met flux was measured using continuous jugular infusion of 1-13C-l-Met and methyl-2H3-l-Met. Nitrogen retention was elevated by Met supplementation (P < 0.01). Supplementation with GAA tended to increase N retention when it was supplemented along with Met, but not when it was supplemented without Met. Supplementing GAA linearly increased plasma concentrations of GAA and creatine (P < 0.001), but treatments did not affect urinary excretion of GAA, creatine, or creatinine. Supplementation with Met decreased plasma homocysteine (P < 0.01). Supplementation of GAA tended (P = 0.10) to increase plasma homocysteine when no Met was supplemented, but not when 6 g/d Met was provided. Protein synthesis and protein degradation were both increased by GAA supplementation when no Met was supplemented, but decreased by GAA supplementation when 6 g/d Met were provided. Loss of Met through transsulfuration was increased by Met supplementation, whereas synthesis of Met from remethylation of homocysteine was decreased by Met supplementation. No differences in transmethylation, transsulfuration, or remethylation reactions were observed in response to GAA supplementation. The administration of GAA, when methyl groups are not limiting, has the potential to improve lean tissue deposition and cattle growth.

208 Effects of supplemental guanidinoacetic acid, creatine, and choline on protein deposition and methyl group metabolites in growing steers

Abstract Methyl group donors (e.g., methionine, choline) can improve performance in transition dairy cows. Our objective was to determine how modulation of methyl group status would affect protein deposition and plasma and urine metabolites associated with methyl group metabolism. Six ruminally cannulated Holstein steers (200 kg) were used in a 6×6 Latin square design with 10-d periods. Factorial treatments, which were continuously infused abomasally, included 3 methyl group modulators (MGM: control; 15 g/d guanidinoacetic acid [GAA]; or 16.8 g/d creatine) and 2 levels of choline (0 or 5 g/d choline ion). Providing GAA or creatine increases body creatine supply; however, GAA consumes methyl groups to synthesize creatine, whereas supplemental creatine directly spares methyl groups that would be used for its synthesis. Steers received 4 kg/d of a corn-based diet. Total collection of urine and feces occurred from d 7 to 9 to measure N retention. Jugular blood was collected on d 10. No interactions between MGM and choline were observed. GAA increased N retention (P = 0.04), whereas creatine did not. Urinary creatine excretion was increased by GAA and creatine supplementation (P &amp;lt; 0.0001). Urinary GAA output was greater for GAA than creatine and control (P &amp;lt; 0.0001). Plasma creatine concentration was increased by GAA and creatine supplementation (P ≤0.01), with GAA leading to a larger increase. Plasma GAA concentration increased with GAA provision (P &amp;lt; 0.0001) but tended to be decreased by creatine (P = 0.09). Plasma urea-N and urinary urea-N output were not affected by MGM (P ≥ 0.25). Choline did not affect N retention (P = 0.69) or urinary GAA or creatine excretions (P ≥ 0.14). Choline increased plasma creatine (P = 0.04), but not plasma GAA. Choline did not affect plasma urea-N or urinary urea-N output (P ≥ 0.68). These data demonstrate that GAA has potential to improve protein deposition in growing cattle. Additionally, choline provision may allow for greater creatine synthesis in the body.

Differences between Holstein dairy cows in renal clearance rate of urea affect milk urea concentration and the relationship between milk urea and urinary nitrogen excretion

Urine and fecal excretions from cattle contribute to global nitrogen (N) emissions. The milk urea nitrogen (MUN) concentration in dairy cows is positively correlated with urinary urea N (UUN) emissions, and both decline with the reduction in crude protein intake. However, MUN concentration may differ between individual cows despite feeding the same ration. Thus, we hypothesized that due to differences in endogenous N utilization cows with high MUN concentration excrete more UUN than cows with a low MUN concentration. The objective of the present study was to elucidate N partitioning and urea metabolism in dairy cows with divergent MUN concentrations fed two planes of crude protein. Twenty Holstein dairy cows with high (HMU; n = 10) and low (LMU; n = 10) milk urea concentrations were fed two isocaloric diets with a low (LP) and normal (NP) crude protein level. Methane and ammonia emissions were recorded in respiration chambers. Feed intake, feces and urine excretions and milk yield were recorded for four days and subsamples were analyzed for total N and N-metabolites. A carbon-13 labeled urea bolus was administered intravenously followed by a series of plasma samplings. Total N and UUN excretions and ammonia emissions from excreta were lower on the LP diet, however, methane emissions, urinary N excretions and ammonia emissions were comparable between groups. Although plasma and salivary urea concentrations, urea pool size and urea turnover were higher, HMU cows had lower renal urea clearance rates. Additionally, HMU cows had lower renal clearance rates for creatinine, uric acid and creatine and excreted less uric acid (on the LP diet only) and creatine with urine. In conclusion, contrary to our hypothesis, HMU cows did not excrete more UUN than LMU cows. The lower urinary creatine excretion of HMU cows suggests that these animals have a lower environmental nitrogen footprint.

Impact of Dietary Protein intake, Lean Body Mass percentage, Body Mass Index, Physical activity on Urinary Creatine and Urinary Creatinine excretion in a TeamSport

Background: Creatine and Creatinine plays a role in muscle function. Urinary creatine and urinary creatinine concentration was measured in order to see significance in monitoring athlete and athlete’s performance. Objective: Evaluate association of dietary protein intake, Lean Body Mass (LBM) percentage, Body Mass Index (BMI) and physical activity on urinary creatine, urinary creatinine concentration in different team sports [cricket players (C), basketball players (B) and football players (F)]. Methodology: A total of 62 players from different team sports - C (n-20), B (n-17) and F (n-25) age of 18-30 years participated. Post training urine samples was analyzed. Using Jaffe's reaction, urinary creatinine was obtained and Urinary creatine is obtained by difference in the creatinine present before and after heating with acid solution. 24 hour dietary recall was taken to find athletes protein intake. LBM were taken using Body Impedence Analysis (BIA machine). Data were analysed using SPSS (Statistical Package for Social Sciences Version 16.0). Findings: Pearson bivariate correlation (2-tailed) was used to find the relationship between BMI, LBM, total dietary protein intake per day, dietary protein, duration of practice with urine creatinine and creatine level. Positive correlation between urinary creatine and total dietary protein intake per day, dietary protein according to body weight per day was found (p&lt;0.001), (p&lt;0.005) respectively. Negative correlation between urinary creatinine and dietary protein according to body weight per day and duration of practice per day was found (p&lt;0.001), (p&lt;0.005) respectively. Urinary creatine mean (SD) values- C group 78.63 ± 27.17, B group 102.65 ± 38 and F group 169.60±41.58. Urinary creatinine mean (SD) values- C group 46.60 ± 37.23,B group 84.88 ± 48.27 and F group 70.40±44.083. Conclusion &amp; Significance: Significant increase was seen in urinary creatine excretion with respect to dietary protein per day, dietary protein according to body weight per day. Urinary creatine excretion is more in football players followed by basketball players. Significant decline was seen in urinary creatinine excretion with respect to increase dietary protein according to body weight per day and increase duration of practice. Urinary Creatine excretion is more in basketball players followed by football players Urinary creatine and urinary creatinine excretion depends on sports-type, duration of sports and protein consumption.

A Retrospective Study of the Relationship Between Testicular Damage and Urinary Creatine Excretion: Possible Markers of Testicular Toxicity Induced by Drugs

ObjectivesCreatine and creatine phosphate act as a buffer system for the regeneration of ATP in tissues with high and fluctuating energy demands. Total creatine content of the rat testis is high compared to all other tissues except skeletal muscle and creatine excretion in rat urine has been shown to increase following testicular damage caused by toxicants. Because the use of biomarkers in toxicology is becoming increasingly important, we investigated whether urinary creatine might be a useful marker for testicular damage in human.MethodsIn a retrospective study, the records of 22 male patients with urological malignancies treated with cisplatin, leuprorelin or goserelin at 4‐week intervals between October 2005 and October 2015 were evaluated. Urinary creatine and serum follicle‐stimulating hormone (FSH), luteinizing hormone (LH) and testosterone levels were assessed in all patients. Single‐voided urine samples were collected to determine urinary creatine‐to‐creatinine ratios. Blood sample collection was done in the morning when serum testosterone levels are around their peak: such morning time sampling for testosterone measurements is recommended in the clinical setting and routinely used in epidemiological studies.ResultsSeven patients with urothelial carcinoma treated with cisplatin based chemotherapy (mean age, 64.1 years) showed no significant changes in urine creatine/creatinine ratio during treatment and had a significant increase in FSH and LH levels and a significant decrease in testosterone levels compared to those at baseline. Similarly, no significant changes in urine creatine/creatinine ratio occurred in patients with prostatic carcinoma treated with leuprorelin (n=8; mean age, 70.0 years) or goserelin (n=7; mean age, 70.4 years), both of whom had castrate levels of testosterone (≤0.5 ng/mL) and suppressed levels of FSH and LH during treatment.ConclusionsOur data demonstrate that testicular damage could not be detected by urinary creatine in patients treated with drugs showing testicular toxicity. Two major testicular functions, i.e., the production of testosterone and formation of haploid germ cells, are generally considered to be regulated by pituitary gonadotrophins, with LH acting on the testosterone‐producing Leydig cells located in the interstitium and FSH affecting Sertoli cells in the seminiferous tubules. Thus, our hormonal data may indicate the presence of cisplatin‐induced Sertoli cell dysfunction and inhibition of Leydig cell function by LH‐RH analogues.Support or Funding InformationNoneThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Dietary creatine supplementation during pregnancy: a study on the effects of creatine supplementation on creatine homeostasis and renal excretory function in spiny mice.

Recent evidence obtained from a rodent model of birth asphyxia shows that supplementation of the maternal diet with creatine during pregnancy protects the neonate from multi-organ damage. However, the effect of increasing creatine intake on creatine homeostasis and biosynthesis in females, particularly during pregnancy, is unknown. This study assessed the impact of creatine supplementation on creatine homeostasis, body composition, capacity for de novo creatine synthesis and renal excretory function in non-pregnant and pregnant spiny mice. Mid-gestation pregnant and virgin spiny mice were fed normal chow or chow supplemented with 5% w/w creatine for 18days. Weight gain, urinary creatine and electrolyte excretion were assessed during supplementation. At post mortem, body composition was assessed by Dual-energy X-ray absorptiometry, or tissues were collected to assess creatine content and mRNA expression of the creatine synthesising enzymes arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT) and the creatine transporter (CrT1). Protein expression of AGAT and GAMT was also assessed by Western blot. Key findings of this study include no changes in body weight or composition with creatine supplementation; increased urinary creatine excretion in supplemented spiny mice, with increased sodium (P<0.001) and chloride (P<0.05) excretion in pregnant dams after 3days of supplementation; lowered renal AGAT mRNA (P<0.001) and protein (P<0.001) expressions, and lowered CrT1 mRNA expression in the kidney (P<0.01) and brain (P<0.001). Creatine supplementation had minimal impact on creatine homeostasis in either non-pregnant or pregnant spiny mice. Increasing maternal dietary creatine consumption could be a useful treatment for birth asphyxia.

Impact of maternal obesity on the metabolic profiles of pregnant women and their offspring at birth

Obesity is currently an increasing public health problem. The intra-uterine environment plays a critical role in foetal development. The objective of this study is to investigate the association of obesity with modifications in the metabolic profiles of pregnant women, and their new-borns. Based on the PELAGIE cohort (Brittany, France), a sample of 321 pregnant women was divided into three groups according to their body mass index (BMI) (normal, over-weight and obese). Nuclear magnetic resonance-based metabolomics analyses were performed on maternal urine and cord-blood samples. Partial least squares regression-discriminant analysis (PLS-DA), polytomous and logistic regressions were used to differentiate the metabolic profiles of the three BMI groups after adjusting for potential confounders. Specific profiles were observed for the overweight and obese women (BMI > 25) compared to the normal-weight women: they had a decrease in urinary hippurate excretion associated with a decrease in phenylalanine and an increase in creatinine. We also showed an increase in the urinary excretion of lactate, citrate, acetate, creatine, and lysine only in obese women (BMI > 30) compared to the normal-weight women. The PLS-DA modelling did not reveal any significant difference between the cord-blood metabolic profiles of newborns according to maternal BMI—although infants born of obese women had a higher birth weight and a lower Apgar score. Our results confirmed the potential link between obesity and gut microbiota disruption (changes in urinary acids), as well as energy and amino-acid metabolism but did not reveal any disruption among newborns.

50 Years Ago in The Journal of Pediatrics: Interrelationships in the Urinary Excretion of Creatine, Creatinine, Free Alpha Amino Acid Nitrogen, and Total Nitrogen in Premature Infants

50 Years Ago in The Journal of Pediatrics: Interrelationships in the Urinary Excretion of Creatine, Creatinine, Free Alpha Amino Acid Nitrogen, and Total Nitrogen in Premature Infants

Optimization of insulin-mediated creatine retention during creatine feeding in humans

The aim of this study was to determine whether creatine ingested in combination with relatively small quantities of essential amino acids, simple sugars, and protein would stimulate insulin release and augment whole-body creatine retention to the same extent as a large bolus of simple sugars. Seven young, healthy males underwent three randomized, 3-day experimental trials. Each day, 24-h urine collections were made, and on the second day participants received 5 g creatine + water (creatine trial), 5 g creatine + ∼95 g dextrose (creatine + carbohydrate) or 5 g creatine + 14 g protein hydrolysate, 7 g leucine, 7 g phenylalanine, and 57 g dextrose (creatine + protein, amino acids, and carbohydrate) via naso-gastric tube at three equally spaced intervals. Blood samples were collected at predetermined intervals after the first and third naso-gastric bolus. After administration of the first and third bolus, serum insulin concentration was increased by 15 min (P < 0.05) in the creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate trials compared with creatine alone, and plasma creatine increased more following creatine alone (15 min, P < 0.05) than in the creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate trials. Urinary creatine excretion was greater with creatine alone (P < 0.05) than with creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate. Administration of creatine + protein, amino acids, and carbohydrate can stimulate insulin release and augment whole-body creatine retention to the same extent as when larger quantities of simple sugars are ingested.

Supplemented Creatine Induces Changes in Human Metabolism of Thiocompounds and One- and Two-Carbon Units

The administration of creatine (5 g/day for one month) to 11 young active sportsmen affected their urinary excretion of creatine, creatinine, and thiodiglycolic acid (TDGA) as well as blood levels of homocysteine, vitamin B12 and folates. The probands were divided into four groups, according to the amount of creatine found in urine, and of folates and vitamin B12 determined in blood. The changes of folates and vitamin B12 were mutually reciprocal. Each group utilized CR as donor of one- and two-carbon (1C and 2C) units by means of homocysteine (HoCySH), folates, and vitamin B12, in different metabolic pathways. In 10 men the creatine administration was accompanied by an increase of HoCySH level in blood, while in the last man, with accidentally discovered hyperhomocysteinemia, the HoCySH level dropped by 50%. Differences between initial and terminal TDGA levels indicate that creatine affects equilibria of redox processes. Creatinine excretion into urine changed in the dependence on the extent of metabolic disturbances.

Urinary creatine and methylamine excretion following 4 × 5 g · day−1 or 20 × 1 g · day−1 of creatine monohydrate for 5 days

In this study, we examined the effect of two creatine monohydrate supplementation regimes on 24-h urinary creatine and methylamine excretion. Nine male participants completed two trials, separated by 6 weeks. Participants ingested 4 × 5 g · day−1 creatine monohydrate for 5 days in one trial and 20 × 1 g · day−1 for 5 days in the other. We collected 24-h urine samples on 2 baseline days (days 1–2), during 5 days of supplementation (days 3–7), and for 2 days post-supplementation (days 8–9). Urine was assayed for creatine using high-performance liquid chromatography and methylamine using gas chromatography. Less creatine was excreted following the 20 × 1 g · day−1 regime (49.25 ± 10.53 g) than the 4 × 5 g · day−1 regime (62.32 ± 9.36 g) (mean ± s; P < 0.05). Mean total excretion of methylamine (n = 6) over days 3–7 was 8.61 ± 7.58 mg and 24.81 ± 25.76 mg on the 20 × 1 g · day−1 and 4 × 5 g · day−1 regimes, respectively (P < 0.05). The lower excretion of creatine using 20 × 1 g · day−1 doses suggests a greater retention in the body and most probably in the muscle. Lower and more frequent doses of creatine monohydrate appear to further attenuate formation of methylamine.

The Arginine-Creatine Pathway is Disturbed in Children and Adolescents With Renal Transplants

Cardiovascular disease is an important cause of morbidity in recipients of renal transplants. The aim of the present study was to analyze the status of the arginine-creatine pathway in such patients, given the relationship between the arginine metabolism and both renal function and the methionine-homocysteine cycle. Twenty-nine children and adolescents (median age 13, range 6-18 years), who had received a renal allograft 14.5-82.0 months before, were recruited for the study. On immunosuppressive therapy, all patients evidenced an adequate level of renal function. Plasma concentrations of homocysteine and glycine were significantly higher, whereas urinary excretions of guanidinoacetate and creatine were significantly lower than controls. Urinary excretions of guanidinoacetate and creatine correlated positively with creatinine clearance. Urinary excretion of creatine was negatively correlated with plasma concentration of homocysteine. The demonstration of disturbances in the arginine-creatine pathway in patients with well-functioning renal transplants and in absence of chronic renal failure represents a novel finding. We speculate that the low urinary excretion of guanidinoacetate and creatine is probably related to the nephrotoxic effect of immunosuppressive therapy and to defective methylation associated with the presence of hyperhomocysteinemia.

An NMR-based metabonomic investigation on effects of milk and meat protein diets given to 8-year-old boys

The objective of the study was to investigate the ability of an NMR-based metabonomic approach, applied to biofluids, to explore and identify overall exogenous and endogenous biochemical effects of a short-time high intake of milk protein or meat protein given to prepubertal children, the aim being to compare relative differences and not an absolute quantification. A total of twenty-four 8-year-old boys were asked to take 53 g protein as milk (n 12) or meat daily (n 12). At baseline and after 7 d, urine and serum samples were collected and high-resolution 1H NMR spectra were acquired on these using a 800 MHz spectrometer. The milk diet reduced the urinary excretion of hippurate, while the meat diet increased the urinary excretion of creatine, histidine and urea. The NMR measurements on serum revealed minor changes in the lipid profile, which most probably should be ascribed to an increase in the content of SCFA in the blood after consumption of the milk diet. The meat diet had no effect on the metabolic profile of serum. The study for the first time demonstrates the capability of proton NMR-based metabonomics to identify the overall biochemical effects of consumption of different animal proteins. The urine metabolite profile is more susceptible to perturbations as a result of short diet interventions than the serum metabolite profile. The milk diet-induced reduction in urinary excretion of hippurate suggests alterations in gut microflora, which may be useful information for further studies elucidating the effects of bioactive components in milk.

The creatine content of Creatine Serum™ and the change in the plasma concentration with ingestion of a single dose

Three samples of Creatine Serum™ ATP Advantage from Muscle Marketing USA, Inc. were assayed for creatine by two different techniques by four independent laboratories, and for creatinine by two different techniques by two laboratories. A further sample was assayed for phosphorylcreatine. Dry weight and total nitrogen were also analysed. Six male volunteers ingested in random order, over 3 weeks: (A) water; (B) 2.5 g creatine monohydrate (Cr · H2O) in solution; and (C) 5 ml Creatine Serum™ (reportedly containing an equivalent amount of Cr · H2O). Blood samples were collected before and up to 8 h after each treatment and plasma was analysed for creatine and creatinine. Eight-hour urine samples were analysed for creatine. Ingestion of 2.5 g creatine monohydrate in solution resulted in a significant increase in plasma creatine (from 59.1±11.8 μmol · l−1 to 245.3±74.6 μM μmol · l−1; mean±s) and urinary creatine excretion. No increase in plasma or urinary creatine or creatinine was found on ingestion of Creatine Serum™ or water. Analysis showed 5 ml of Creatine Serum™ to contain <10 mg Cr · H2O and approximately 90 mg creatinine. Phosphorylcreatine was not detectable and only a trace amount of phosphorous was present. Total nitrogen analysis ruled out significant amounts of other forms of creatine. We conclude that the trace amounts of creatine in the product would be too little to affect the muscle content even with multiple dosing.

Age related reference values for urine creatine and guanidinoacetic acid concentration in children and adolescents by gas chromatography–mass spectrometry

A new gas chromatography–mass spectrometry method for routine quantification of urine creatine and guanidinoacetic acid (GAA) has been developed to provide a fast, reliable and inexpensive metabolic screening. Our method uses a two-step derivatization procedure which involves a reaction with hexafluoroacetylacetone followed by a reaction with mono-trimethylsilyltrifluoroacetamide. The standard curves showed linearity over a range of 43–4269 μmol/l for GAA and 38–7325 μmol/l for creatine, which covers the range of GAA and creatine normally found in urine. The lower detection limit is 1.54 μmol/l for GAA and 1.22 μmol/l for creatine, whereas the lower quantification limit is 5.04 μmol/l for GAA and 4.19 μmol/l for creatine. This method was also employed to establish reference values for GAA and creatine in healthy infants, children and adolescents based on the analysis of 169 urine samples. Although no sex differences were observed, normal GAA urinary levels and creatine excretion are distinct in age-related subgroups. We identified a statistically significant age difference in two major groups for GAA (children under 4 years, 18–159 μmol/mmol creatinine; and subjects of 5–16 years, 18–130 μmol/mmol creatinine) whereas three groups were discriminated for creatine (children under 4 years, 0.04–1.51 mmol/mmol creatinine; subjects of 5–11 years, 0.04–1.07 mmol/mmol creatinine; and subjects of 12–16 years, 0.04–0.56 mmol/mmol creatinine).

An hypothesis for a mechanism underlying hepatotoxin-induced hypercreatinuria.

As part of a wider metabonomic investigation into the early detection and discrimination of site-specific hepatotoxicity, male Sprague-Dawley rats were dosed with the model hepatotoxins allyl formate, ethionine and alpha-naphthylisothiocyanate (ANIT). Urine samples collected pre- and post-dose were examined by (1)H nuclear magnetic resonance (NMR) spectroscopy and the toxin-induced changes in urinary taurine and creatine excretion were quantified. Hypertaurinuria and hypercreatinuria were observed following allyl formate dosing, hypertaurinuria with no change in creatine excretion was observed after ethionine dosing, and hypotaurinuria and hypercreatinuria were observed after ANIT dosing. These changes are indicative of different effects on liver and it has been previously suggested that some hepatotoxin-induced changes in urinary taurine excretion may be due to altered hepatic cysteine utilisation. A related hypothesis is now presented that would explain the selective hypercreatinuria in terms of increased cysteine synthesis.

NMR and pattern recognition studies on the time-related metabolic effects of alpha-naphthylisothiocyanate on liver, urine, and plasma in the rat: an integrative metabonomic approach.

We present here a novel integrative metabonomic approach to probe toxic effects of drugs in experimental animals using alpha-naphthylisothiocyanate (ANIT) as a model hepatotoxicant. Male Han-Wistar rats were dosed with ANIT (150 mg/kg, n = 25), and plasma and liver samples were collected for NMR and magic-angle spinning (MAS) NMR spectroscopy at 3, 7, 24, 31, and 168 h postdosing. Urine was collected continuously for 3 days prior to dosing and up to 168 h postdose. Histopathology and plasma clinical chemistry was also performed at all time points. Liver samples were analyzed either intact by 600 MHz 1H MAS NMR techniques or using high resolution (liquid state) 1H NMR of water-acetonitrile extracts. These data were related to sequential 1H NMR measurements in urine and plasma using pattern recognition methods. 1D 1H NMR spectra were data-reduced and analyzed using principal components analysis (PCA) to show the time-dependent biochemical variations induced by ANIT toxicity. From the eigenvector loadings of the PCA, those regions of the 1H NMR spectra and hence the combinations of endogenous metabolites marking the main phase of the toxic episode were identified. The ANIT-induced biochemical manifestations included a hepatic lipidosis associated with hyperlipidaemia; hyperglycaemia and glycosuria; increased urinary excretion of taurine and creatine; a shift in energy metabolism characterized by increased plasma ketone bodies with reduced urinary excretion of tricarboxylic acid cycle intermediates and raised hepatic bile acids leading to bile aciduria. The integration of metabolic data derived from several sources gives a holistic approach to the study of time-related toxic effects in the intact system and enables the characterization of key metabolic effects during the development and recovery from a toxic lesion.