Derivatization-free determination of short-chain volatile amines in human plasma and urine by headspace gas chromatography-mass spectrometry.

BACKGROUND: Short-chain volatile amines (SCVA) are an interesting compound class playing crucial roles in physiological and toxicological human settings. Dimethylamine (DMA), trimethylamine (TMA), diethylamine (DEA), and triethylamine (TEA) were investigated in detail. METHODS: Headspace gas chromatography coupled to mass spectrometry (HS-GC-MS) was used for the simultaneous qualitative and quantitative determination of four SCVA in different human body fluids. Four hundred microliters of Li-heparin plasma and urine were analyzed after liberation of volatile amines under heated conditions in an aqueous alkaline and saline environment. Target analytes were separated on a volatile amine column and detected on a Thermo DSQ II mass spectrometer scheduled in single ion monitoring mode. RESULTS: Chromatographic separation of selected SCVA was done within 7.5 minutes. The method was developed and validated with respect to accuracy, precision, recovery and stability. Accuracy and precision criteria were below 12% for all target analytes at low and high levels. The selected extraction procedure provided recoveries of more than 92% from both matrices for TMA, DEA and TEA. The recovery of DMA from Li-heparin plasma was lower but still in the acceptable range (>75%). The newly validated method was successfully applied to plasma and urine samples from healthy volunteers. Detected concentrations of endogenous metabolites DMA and TMA are comparable to already known reference ranges. CONCLUSION: Herein, we describe the successful development and validation of a reliable and broadly applicable HS-GC-MS procedure for the simultaneous and quantitative determination of SCVA in human plasma and urine without relying on derivatization chemistry.

Longitudinal urinary metabolomic profiling reveals metabolites for asthma development in early childhood.

BACKGROUND: Several metabolites and altered metabolic pathways have been reported to be associated with asthma. However, longitudinal analysis of the dynamics of metabolites contributing to the development of asthma has not yet been fully clarified. METHODS: We sought to identify the metabolic mechanisms underlying asthma development in early childhood. Thirty children with asthma and paired healthy controls from a prospective birth cohort were enrolled. Time series analysis of urinary metabolites collected at ages 1, 2, 3, and 4 years was assessed using 1 H nuclear magnetic resonance (NMR) spectroscopy coupled with partial least squares discriminant analysis (PLS-DA). Metabolites identified were studied in relation to changes over time in a linear mixed model for repeated measures. RESULTS: A total of 172 urine samples collected from the enrolled children were analyzed. Urinary metabolomics identified four metabolites significantly associated with childhood asthma development, with longitudinal analysis. Among them, dimethylamine, a metabolite produced by intestinal bacteria, appeared to shift from higher to lower level during asthma development. A persistent lower level of 1-methylnicotinamide and allantoin was found in children with asthma, with a peak difference at age 3 years (P = .032 and P = .021, respectively). Furthermore, a significant inverse correlation was found between allantoin and house dust mite sensitization (Spearman's r = -.297 P = .035). CONCLUSIONS: Longitudinal urinary metabolomic profiling provides a link of microbe-environment interactions in the development of childhood asthma. 1-Methylnicotinamide and allantoin may participate in allergic reactions in response to allergen exposure, potentially serving as specific biomarkers for asthma.

Metabolic influence of acute cyadox exposure on Kunming mice.

Cyadox is an antibiotic drug and has the potential to be used as a feedstuff additive in promoting the growth of animals. However, the toxicity of cyadox should be fully assessed before application, and this has prompted the current investigation on the metabolic responses of mice to cyadox exposure, using a metabonomic technique. Three groups of Kunming mice were respectively given a single dose of cyadox at three different concentrations (100, 650, and 4000 mg/kg body weight) via gavage. We present here the metabolic alterations of urine, plasma, liver, and renal medulla extracts induced by cyadox exposure. The metabolic alterations induced by cyadox exposure are dose-dependent, and metabolic recovery is achieved only for low and moderate levels of cyadox exposure during the experimental period. Cyadox exposure resulted in a disturbance of gut microbiota, which is manifested in depleted levels of urinary hippurate, trimethylamine-N-oxide (TMAO), dimethylamine (DMA), and trimethylamine (TMA). In addition, mice exposed to cyadox at high levels caused accumulations of amino acids and depletions of nucleotides in the liver. Furthermore, marked elevations of nucleotides and a range of organic osmolytes, such as myo-inositol, choline, and glycerophosphocholine (GPC), and decreased levels of amino acids are observed in the renal medulla of cyadox-exposed mice. These results suggest that cyadox exposure causes inhibition of amino acid metabolism in the liver and disturbance of gut microbiota community, influencing osmolytic homeostasis and nucleic acids synthesis in both the liver and the kidney. Our work provides a comprehensive view of the toxicological effects of cyadox, which is important in animal and human food safety.

Asymmetric dimethylarginine in children with homocystinuria or phenylketonuria.

Plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis from L-arginine and a cardiovascular risk factor, was found to be elevated in plasma of homocysteinemic adults. Enhanced cardiovascular risk due to homocystinuria and impaired renal function has been found in patients with phenylketonuria (PKU) on protein-restricted diet. However, it is still unknown whether ADMA synthesis is also elevated in children with homocystinuria due to cystathionine beta-synthase deficiency (classical homocystinuria), and whether ADMA may play a role in phenylketonuria in childhood. In the present study, we investigated the status of the L-arginine/NO pathway in six young patients with homocystinuria, in 52 young phenylketonuria patients on natural protein-restricted diet, and in age- and gender-matched healthy children serving as controls. ADMA in plasma and urine was determined by GC-MS/MS. The NO metabolites nitrate and nitrite in plasma and urine, and urinary dimethylamine (DMA), the dimethylarginine dimethylaminohydrolase (DDAH) metabolite of ADMA, were measured by GC-MS. Unlike urine ADMA excretion, plasma ADMA concentration in patients with homocystinuria was significantly higher than in controls (660±158 vs. 475±77 nM, P=0.035). DMA excretion rate was considerably higher in children with homocystinuria as compared to controls (62.2±24.5 vs. 6.5±2.9 µmol/mmol creatinine, P=0.068), indicating enhanced DDAH activity in this disease. In contrast and unexpectedly, phenylketonuria patients had significantly lower ADMA plasma concentrations compared to controls (512±136 vs. 585±125 nM, P=0.009). Phenylketonuria patients and controls had similar L-arginine/ADMA molar ratios in plasma. Urinary nitrite excretion was significantly higher in phenylketonuria as compared to healthy controls (1.7±1.7 vs. 0.7±1.2 µmol/mmol creatinine, P=0.003). Our study shows that the L-arginine/NO pathway is differently altered in children with phenylketonuria and homocystinuria. Analogous to hyperhomocysteinemic adults, elevated ADMA plasma concentrations could be a cardiovascular risk factor in children with homocystinuria. In phenylketonuria, the L-arginine/NO pathway seems not be altered. Delineation of the role of ADMA in childhood phenylketonuria and homocystinuria demands further investigation.

Plasma dimethylarginines during the acute inflammatory response.

INTRODUCTION: Asymmetric dimethylarginine (ADMA) concentrations are increased in critically ill patients and may play a role in multiple organ failure. However, plasma ADMA concentrations during the development of the inflammatory response have not been documented. We measured plasma ADMA, as well as urinary excretion of its major metabolite dimethylamine, and nitrate as a marker of nitric oxide synthase (NOS) activity, in a cohort of patients undergoing elective knee arthroplasty that is known to provoke a significant inflammatory response. METHODS: Thirty-eight patients were recruited. Fasting venous blood samples were obtained pre-operatively and at 12h and daily until the fifth post-operative day. ADMA and symmetric dimethylarginine (SDMA) were measured by high-performance liquid chromatography (HPLC). Urinary dimethylamine and nitrate were measured pre-operatively and on each of the post-operative mornings using HPLC and expressed as a ratio to creatinine. RESULTS: Plasma ADMA fell by a median of 31% during the post-operative period, reaching a nadir on day 2, and recovering to baseline by the end of the study. SDMA showed no significant changes. No increase in urinary dimethylamine excretion was noted until day 5 post-op, whereupon it doubled. Urinary nitrate showed a small, but nonsignificant decrease on day 2, suggesting no major activation of NOS activity. CONCLUSIONS: Plasma ADMA concentration decreases rapidly and transiently during the first 48h of acute inflammation. This appears not be caused by increased catabolism and may reflect increased cellular partitioning. This may serve to regulate NOS activity and prevent harmful increases in inducible NOS in situations where it is not appropriate.

A metabonomic comparison of urinary changes in Zucker and GK rats.

To further investigate pathogenesis and pathogenic process of type 2 diabetes mellitus (T2DM), we compared the urinary metabolic profiling of Zucker obese and Goto-kakizaki (GK) rats by NMR-based metabonomics. Principal component analysis (PCA) on urine samples of both models rats indicates markedly elevated levels of creatine/creatinine, dimethylamine, and acetoacetate, with concomitantly declined levels of citrate, 2-ketoglurarate, lactate, hippurate, and succinate compared with control rats, respectively. Simultaneously, compared with Zucker obese rats, the GK rats show decreased levels of trimethylamine, acetate, and choline, as well as increased levels of creatine/creatinine, acetoacetate, alanine, citrate, 2-ketoglutarate, succinate, lactate, and hippurate. This study demonstrates metabolic similarities between the two stages of T2DM, including reduced tricarboxylic acid (TCA) cycle and increased ketone bodies production. In addition, compared with Zucker obese rats, the GK rats have enhanced concentration of energy metabolites, which indicates energy metabolic changes produced in hyperglycemia stage more than in insulin resistance stage.

The Relationship between Fish Intake and Urinary Trimethylamine-N-Oxide.

SCOPE: Fish intake is reported to be associated with certain health benefits; however, accurate assessment of fish intake is still problematic. The objective of this study is to identify fish intake biomarkers and examine relationships with health parameters in a free-living population. METHODS AND RESULTS: In the NutriTech study, ten participants randomized into the fish group consume increasing quantities of fish for 3 days per week for 3 weeks. Urine is analyzed by NMR spectroscopy. Trimethylamine-N-oxide (TMAO), dimethylamine, and dimethyl sulfone are identified and display significant dose-response with intake (p < 0.05). Fish consumption yields a greater increase in urinary TMAO compared to red meat. Biomarker-derived fish intake is calculated in the National Adult Nutrition Survey cross-sectional study. However, the correlation between fish intake and TMAO (r = 0.148, p < 0.01) and that between fish intake and calculated fish intake (r = 0.142, p < 0.01) are poor. In addition, TMAO shows significantly positive correlation with serum insulin and insulin resistance in males and the relationship is more pronounced for males with high dietary fat intake. CONCLUSION: Urinary TMAO displays a strong dose-response relationship with fish intake; however, use of TMAO alone is insufficient to determine fish intake in a free-living population.

The L-arginine/NO pathway in end-stage liver disease and during orthotopic liver and kidney transplantation: biological and analytical ramifications.

The L-arginine/nitric oxide (L-Arg/NO) pathway is altered in liver and kidney diseases. However, the status of the L-Arg/NO pathway during and after orthotopic transplantation is insufficiently investigated and findings are uncertain because of analytical shortcomings. Also, most human studies have focused on individual members of the L-Arg/NO pathway such as nitrate or asymmetric dimethylarginine (ADMA). In the present article we report on a pilot study investigating extensively the status of the L-Arg/NO pathway before and during orthotopic liver transplantation (OLT). By using fully validated, highly sensitive and specific GC-MS and GC-MS/MS methods nitrite, nitrate, ADMA and its hydrolysis product dimethylamine (DMA), L-arginine and L-ornithine were measured in blood and urine. Our study gives strong evidence of the exceptional importance of hepatic dimethylarginine dimethylaminohydrolase (DDAH) activity for the elimination of systemic ADMA. In end-stage liver disease the synthesis of NO and ADMA as well as the DDAH activity are elevated. However, increase in DDAH activity is insufficient to efficiently eliminate overproduced ADMA. The transplanted liver graft is capable of clearing ADMA in a rapid and sufficient manner. In contrast to studies from other groups, our study shows that in OLT as well as in living donor kidney transplantation, the second study reported here, reperfusion of the graft does not cause drastic alterations to the L-Arg/NO pathway with regard to NO synthesis. In the OLT study the concentration of circulating L-arginine fell temporally dramatically, while L-ornithine levels increased diametrically, most likely due to elevation of arginase activity. However, the relatively long-lasting decrease in plasmatic L-arginine in OLT seems not to have affected NO synthesis after reperfusion. Our OLT study suggests that liver reperfusion is associated with greatly elevated activity of proteolytic and hydrolytic enzymes including DDAH and arginase. Suppression of proteolytic and hydrolytic activity in transplantation could be a useful measure to improve outcome and remains to be investigated in further studies on larger patient collectives. The importance of analytical chemistry in this area of research is also discussed in this article.

A faster and simpler UPLC-MS/MS method for the simultaneous determination of trimethylamine N-oxide, trimethylamine and dimethylamine in different types of biological samples.

Gut microbiota-dependent metabolites trimethylamine N-oxide (TMAO), trimethylamine (TMA) and dimethylamine (DMA) from dietary methylamines have recently gained much attention due to their high association with chronic kidney disease risk. Hence a simpler and faster performance liquid chromatography-tandem mass spectrometry method was developed and validated. The quantitative analysis was achieved within 6 min by using Agilent 6460C UPLC-MS/MS with 10% methyl alcohol isocratic elution and was more simple, convenient and rapid than that of previously reported methods. Furthermore, method verification results showed that the method correlation coefficient was 0.99978293, 0.99997514 and 0.98784721, and the detection limit was 0.121, 8.063 and 0.797 µg L-1, and the precision of the retention time and peak area of analytes was less than 0.331 and 3.280, respectively. The method was applied to simultaneously determine TMAO, TMA and DMA in the urine and serum from mice treated with normal, high l-carnitine, or high choline diet. Quantitative recoveries of TMAO, TMA and DMA were in the range of 94.2%-101.0%, and the RSD values were lower than 5.17%. The proposed UPLC-MS/MS-based assay should be of value for further evaluating TMAO as a risk marker and for examining the effect of dietary factors on TMAO metabolism.

Time-Course Changes in Urine Metabolic Profiles of Rats Following 90-Day Exposure to Propoxur.

As a major kind of carbamate insecticide, propoxur plays an important role in agriculture, veterinary medicine, and public health. The acute toxicity of propoxur is mainly neurotoxicity due to the inhibition of cholinesterase. However, little is known regarding the toxicity of propoxur upon long-term exposure at low dose. In this study, Wistar rats were orally administrated with low dose (4.25 mg/kg body weight/day) for consecutive 90 days. And the urine samples in rats treated with propoxur for 30, 60, and 90 days were collected and analyzed by employing 1H NMR-based metabolomics approach. We found that propoxur caused significant changes in the urine metabolites, including taurine, creatinine, citrate, succinate, dimethylamine, and trimethylamine-N-oxide. And the alteration of the metabolites was getting more difference compared with that of the control as the exposure time extending. The present study not only indicated that the changed metabolites could be used as biomarkers of propoxur-induced toxicity but also suggested that the time-course alteration of the urine metabolomic profiles could reflect the progressive development of the toxicity following propoxur exposure.

Dimethylamine and diet.

Forty-six different foods eaten by six healthy male volunteers were investigated as potential sources of the aliphatic secondary amine, dimethylamine. None that were representatives from the fruit and vegetable, meat, dairy and grain produce categories afforded any measurable elevation in urinary dimethylamine output following ingestion. All of the statistically significant increases occurred after consumption of fish and seafoods. However, within this category a wide variation was observed. The highest values were obtained for coley, squid and whiting with cod, haddock, sardine, skate and swordfish also producing substantial increases. Freshwater trout, plaice and prawns gave no discernable effect. It seems that not all fish and seafoods may be treated equally with regards to human dimethylamine exposure and that the situation is more complicated than at first appears.

Short-chain aliphatic amines in human urine: a mathematical examination of metabolic interrelationships.

The relationships between several small molecular weight aliphatic amines (methylamine, dimethylamine, trimethylamine, and ethylamine) and an associated N-oxide (trimethylamine N-oxide) quantified in human urine collected from 203 healthy volunteers have been assessed mathematically. Principal component analysis highlighted a female subgroup with raised trimethylamine levels and the possibility of hormonal influence on the N-oxidation of trimethylamine has been proposed. A second subgroup of men, who ate a large meal of fish before the study, displayed raised levels of all compounds except ethylamine. In all cases, ethylamine was least significantly correlated with the other urinary components and appeared metabolically unrelated.

Accurate quantification of dimethylamine (DMA) in human urine by gas chromatography-mass spectrometry as pentafluorobenzamide derivative: evaluation of the relationship between DMA and its precursor asymmetric dimethylarginine (ADMA) in health and disease.

Dimethylamine [DMA, (CH(3))(2)NH)] is abundantly present in human urine. Main sources of urinary DMA have been reported to include trimethylamine N-oxide, a common food component, and asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis. ADMA is excreted in the urine in part unmetabolized and in part after hydrolysis to DMA by dimethylarginine dimethylaminohydrolase (DDAH). Here we describe a GC-MS method for the accurate and rapid quantification of DMA in human urine. The method involves use of (CD(3))(2)NH as internal standard, simultaneous derivatization with pentafluorobenzoyl chloride and extraction in toluene, and selected-ion monitoring of m/z 239 for DMA and m/z 245 for (CD(3))(2)NH in the electron ionization mode. GC-MS analysis of urine samples from 10 healthy volunteers revealed a DMA concentration of 264+/-173 microM equivalent to 10.1+/-1.64 micromol/mmol creatinine. GC-tandem MS analysis of the same urine samples revealed an ADMA concentration of 27.3+/-15.3 microM corresponding to 1.35+/-1.2 micromol/mmol creatinine. In these volunteers, a positive correlation (R=0.83919, P=0.0024) was found between urinary DMA and ADMA, with the DMA/ADMA molar ratio being 10.8+/-6.2. Elevated excretion rates of DMA (52.9+/-18.5 micromol/mmol creatinine) and ADMA (3.85+/-1.65 micromol/mmol creatinine) were found by the method in 49 patients suffering from coronary artery disease, with the DMA/ADMA molar ratio also being elevated (16.8+/-12.8). In 12 patients suffering from end-stage liver disease, excretion rates of DMA (47.8+/-19.7 micromol/mmol creatinine) and ADMA (5.6+/-1.5 micromol/mmol creatinine) were found to be elevated, with the DMA/ADMA molar ratio (9.17+/-4.2) being insignificantly lower (P=0.46). Between urinary DMA and ADMA there was a positive correlation (R=0.6655, P<0.0001) in coronary artery disease, but no correlation (R=0.27339) was found in end-stage liver disease.

Effect of pistachio consumption on the modulation of urinary gut microbiota-related metabolites in prediabetic subjects.

The specific nutritional composition of nuts could affect different metabolic pathways involved in a broad range of metabolic diseases. We therefore investigated whether chronic consumption of pistachio nuts modifies the urine metabolome in prediabetic subjects. We designed a randomized crossover clinical trial in 39 prediabetic subjects. They consumed a pistachio-supplemented diet (PD, 50% carbohydrates, 33% fat, including 57 g/d of pistachios daily) and a control diet (CD, 55% carbohydrates, 30% fat) for 4 months each, separated by a 2-week wash-out. Nuclear magnetic resonance (NRM) was performed to determine changes in 24-h urine metabolites. Significant changes in urine metabolites according to the different intervention periods were found in uni- and multivariate analysis. Score plot of the first two components of the multilevel partial least squares discriminant analysis (ML-PLS-DA) showed a clear separation of the intervention periods. Three metabolites related with gut microbiota metabolism (i.e., hippurate, p-cresol sulfate and dimethylamine) were found decreased in PD compared with CD (P<.05). Moreover, cis-aconitate [intermediate of the tricarboxylic acid (TCA)] was also found decreased following PD compared with CD. Intragroup analysis showed that creatinine levels were significantly increased in PD (P=.023), whereas trimethylamine N-oxide (TMAO) was found significantly reduced following PD (P=.034). Our results suggest that chronic pistachio consumption may modulate some urinary metabolites related to gut microbiota metabolism and the TCA cycle; all associated with metabolic derangements associated with insulin resistance and Type 2 diabetes.

Nuclear magnetic resonance studies of blood plasma and urine from subjects with chronic renal failure: identification of trimethylamine-N-oxide.

We have used 1H-, 13C- and 14N-NMR spectroscopy to investigate the constituents of plasma and urine in 16 patients with chronic renal failure (CRF). Resonances not previously observed in spectra of plasma from healthy volunteers were seen in CRF plasma, including those for trimethylamine-N-oxide (TMAO) and dimethylamine (DMA). A possible analogy with the plasma of elasmobranch fishes, in which TMAO stabilizes proteins in the presence of very high urea concentrations, is noted. The intensity of the TMAO resonance for CRF subjects was correlated with the plasma concentration of urea (R = 0.55) and creatinine (R = 0.74), suggesting that the presence of TMAO is closely related to the degree of renal failure. When normal subjects ate a meal of TMAO-containing fish, TMAO appeared rapidly in the plasma and in the urine. Thus TMAO is efficiently cleared by the healthy kidney. Differences in the interaction of lactate with plasma proteins were detected by NMR, suggesting that uraemia impairs their transport roles.

Investigations into biochemical changes of genetic hypertensive rats using 1H nuclear magnetic resonance-based metabonomics.

Genetically hypertensive rats provide a simple and accessible model for studying essential hypertension, which is a polygenic, heterogenous and multifactorial disease. Their genetic and metabolic features are of great interest because they may provide insight into the pathophysiological processes underlying essential hypertension. We have investigated the genetic influence on metabolic balance and metabolite excretion patterns in stroke-prone spontaneously hypertensive rats (SHRSP) with established hypertension using 1H NMR-based metabonomics. Urinary metabolite profiles for SHRSP and their age-matched normotensive controls, Wistar Kyoto rats, were acquired using 1H NMR spectroscopy. Principal components analysis was applied to these complex NMR data to facilitate differentiation and determine metabolic differences between urine samples collected from the hypertensive and normotensive rats. Consequently, it was possible to distinguish urine samples between the two strains in the principal components scores plot. The loadings plot showed that taurine, creatine and some unidentified metabolites resonating at around delta 2.48, 3.10 and 3.58 predominantly contributed to the separation. In SHRSP, the urinary levels of taurine and creatine were found to be higher and the intensities of the unknown signals much lower than those in the Wistar Kyoto rats. Although the pathophysiological significance of these components remains to be elucidated, this study suggests that 1H NMR-based metabonomics is a promising approach to provide new information on metabolic changes related to the pathophysiological processes of the genetically hypertensive rats.

H nuclear magnetic resonance spectroscopic investigation of urine for diagnostic and clinical assessment of methanol intoxication.

Occasional or suicidal methanol intoxications are a permanent problem for most Poisoning Centers around the World. Therefore it is important to look for new diagnostic and clinical prognostic methods. In the present paper 5 cases of methanol intoxication were analyzed. At first the methanol concentrations in blood and urine were estimated with headspace gas chromatography technique. Next the urine samples were examined with 1H NMR spectroscopy, then the levels of ethanol, methanol and its metabolite, formate, lactate and trimethylamine-N-oxide with dimethylamine were evaluated. The concentrations of the above compounds were correlated with the patient's clinical status, the level of ethanol and methanol and biochemical parameters. The results indicate the correlation between clinical course of intoxication, prognostication and lactate level. There were no significant parallels for formate level as acidosis causing metabolite and initial methanol levels. In the urine samples of intoxicated patients the increased trimethyl-N-oxide and dimethylamine levels were observed, which may indicate renal cortex damage. Contrary to the opinion of some clinicians, methanol intoxication may be connected with renal functional disturbances. 1H NMR examination of urine appears to be an excellent tool to evaluate the clinical course of methanol intoxication.

Diurnal rhythms in the human urine metabolome during sleep and total sleep deprivation.

Understanding how metabolite levels change over the 24 hour day is of crucial importance for clinical and epidemiological studies. Additionally, the association between sleep deprivation and metabolic disorders such as diabetes and obesity requires investigation into the links between sleep and metabolism. Here, we characterise time-of-day variation and the effects of sleep deprivation on urinary metabolite profiles. Healthy male participants (n = 15) completed an in-laboratory study comprising one 24 h sleep/wake cycle prior to 24 h of continual wakefulness under highly controlled environmental conditions. Urine samples were collected over set 2-8 h intervals and analysed by (1)H NMR spectroscopy. Significant changes were observed with respect to both time of day and sleep deprivation. Of 32 identified metabolites, 7 (22%) exhibited cosine rhythmicity over at least one 24 h period; 5 exhibiting a cosine rhythm on both days. Eight metabolites significantly increased during sleep deprivation compared with sleep (taurine, formate, citrate, 3-indoxyl sulfate, carnitine, 3-hydroxyisobutyrate, TMAO and acetate) and 8 significantly decreased (dimethylamine, 4-DTA, creatinine, ascorbate, 2-hydroxyisobutyrate, allantoin, 4-DEA, 4-hydroxyphenylacetate). These data indicate that sampling time, the presence or absence of sleep and the response to sleep deprivation are highly relevant when identifying biomarkers in urinary metabolic profiling studies.

Dimethylamine formation in man.

Trimethylamine N-oxide, a common food component, has been identified as a major source of urinary dimethylamine in man. The potential pathophysiological consequences of exposure to dietary derived dimethylamine are raised.

Dimethylamine in human urine.

The urinary excretion of dimethylamine has been measured in 203 unrelated healthy volunteers (102 male) who maintained their normal diets. The results for female volunteers are the first reported in the literature. The average daily output was 17.43 +/- 11.80 mg (mean +/- S.D.) (21.21 +/- 14.78 male; 13.74 +/- 5.65 female) with values for the majority of the population lying within the 0.68-35.72 mg range. Four male outliers excreted up to 109.2 mg; these large amounts of dimethylamine were presumed to be of dietary origin. The literature pertaining to urinary levels of dimethylamine has been summarised and integrated with the present observations.