A prediction model using 2-propanol and 2-butanone in urine distinguishes breast cancer.

Safe and noninvasive methods for breast cancer screening with improved accuracy are urgently needed. Volatile organic compounds (VOCs) in biological samples such as breath and blood have been investigated as noninvasive novel markers of cancer. We investigated volatile organic compounds in urine to assess their potential for the detection of breast cancer. One hundred and ten women with biopsy-proven breast cancer and 177 healthy volunteers were enrolled. The subjects were divided into two groups: a training set and an external validation set. Urine samples were collected and analyzed by gas chromatography and mass spectrometry. A predictive model was constructed by multivariate analysis, and the sensitivity and specificity of the model were confirmed using both a training set and an external set with reproducibility tests. The training set included 60 breast cancer patients (age 34-88 years, mean 60.3) and 60 healthy controls (age 34-81 years, mean 58.7). The external validation set included 50 breast cancer patients (age 35-85 years, mean 58.8) and 117 healthy controls (age 18-84 years, mean 51.2). One hundred and ninety-one compounds detected in at least 80% of the samples from the training set were used for further analysis. The predictive model that best-detected breast cancer at various clinical stages was constructed using a combination of two of the compounds, 2-propanol and 2-butanone. The sensitivity and specificity in the training set were 93.3% and 83.3%, respectively. Triplicated reproducibility tests were performed by randomly choosing ten samples from each group, and the results showed a matching rate of 100% for the breast cancer patient group and 90% for the healthy control group. Our prediction model using two VOCs is a useful complement to the current diagnostic tools. Further studies inclusive of benign tumors and non-breast malignancies are warranted.

Chemoselective and Highly Sensitive Quantification of Gut Microbiome and Human Metabolites.

The microbiome has a fundamental impact on the human host's physiology through the production of highly reactive compounds that can lead to disease development. One class of such compounds are carbonyl-containing metabolites, which are involved in diverse biochemical processes. Mass spectrometry is the method of choice for analysis of metabolites but carbonyls are analytically challenging. Herein, we have developed a new chemical biology tool using chemoselective modification to overcome analytical limitations. Two isotopic probes allow for the simultaneous and semi-quantitative analysis at the femtomole level as well as qualitative analysis at attomole quantities that allows for detection of more than 200 metabolites in human fecal, urine and plasma samples. This comprehensive mass spectrometric analysis enhances the scope of metabolomics-driven biomarker discovery. We anticipate that our chemical biology tool will be of general use in metabolomics analysis to obtain a better understanding of microbial interactions with the human host and disease development.

Resolution and Quantitation of Mercapturic Acids Derived from Crotonaldehyde, Methacrolein, and Methyl Vinyl Ketone in the Urine of Smokers and Nonsmokers.

Using improved HPLC analysis conditions, we report the separation of three isomers of mercapturic acid conjugates previously assigned in the literature only to 3-hydroxy-1-methylpropylmercapturic acid (HMPMA-1), a human urinary metabolite of crotonaldehyde. The new conditions, employing a biphenyl column cooled to 5 °C and eluted with a gradient of formic acid, acetonitrile, and methanol, allow the analysis of human urinary mercapturic acids derived not only from crotonaldehyde but also from its isomers methacrolein (3-hydroxy-2-methylpropyl mercapturic acid, HMPMA-2) and methyl vinyl ketone (3-hydroxy-3-methylpropyl mercapturic acid, HMPMA-3). The mercapturic acids were detected and quantified by LC-ESI-MS/MS using the corresponding stable isotope labeled mercapturic acids as internal standards. The analysis was validated for accuracy and precision and applied to urine samples collected from cigarette smokers and nonsmokers. Smokers had significantly higher levels of all three mercapturic acids than did nonsmokers. The results demonstrated that HMPMA-3 from methyl vinyl ketone comprised the major portion of the peaks previously ascribed in multiple studies to HMPMA-1. HMPMA-1 had concentrations intermediate between those of HMPMA-2 and HMPMA-3 in both smokers and nonsmokers. This study reports the first quantitation of HMPMA-2 and HMPMA-3 in human urine. The observation of higher levels of HMPMA-3 than in the other two mercapturic acids suggests a previously unrecognized potential significance of methyl vinyl ketone as a toxicant in smokers and nonsmokers.

Metabolism of inhaled methylethylketone in rats.

Methylethylketone (MEK) is widely used in industry, often in combination with other compounds. Although nontoxic, it can make other chemicals harmful. This study investigates the fate of MEK in rat blood, brain and urine as well as its hepatic metabolism following inhalation over 1 month (at 20, 200 or 1400 ppm). MEK did not significantly accumulate in the organism: blood concentrations were similar after six-hour or 1-month inhalation periods, and brain concentrations only increased slightly after 1 month's exposure. Urinary excretion, based on the major metabolites, 2,3-butanediols (± and meso forms), accounted for less than 2.4% of the amount inhaled. 2-Butanol, 3-hydroxy-2-butanone and MEK itself were only detectable in urine in the highest concentration conditions investigated, when metabolic saturation occurred. Although MEK exposure did not alter the total cytochrome P450 concentration, it induced activation of both CYP1A2 and CYP2E1 enzymes. In addition, the liver glutathione concentration (reduced and oxidized forms) decreased, as did glutathione S-transferase (GST) activity (at exposure levels over 200 ppm). These metabolic data could be useful for pharmacokinetic model development and/or verification and suggest the ability of MEK to influence the metabolism (and potentiate the toxicity) of other substances.

Toluene and methylethylketone: effect of combined exposure on their metabolism in rat.

1. Multiple exposures are ubiquitous in industrial environments. In this article, we highlight the risks faced by workers and complete the data available on the metabolic impact of a common mixture: toluene (TOL) and methylethylketone (MEK). 2. Rats were exposed by inhalation under controlled conditions either to each solvent individually, or to mixtures of the two. How the interaction between the two solvents affected their fate in the blood and brain, their main relevant urinary metabolites (o-cresol, benzylmercapturic acid for TOL and 2,3-butanediols for MEK) and their hepatic metabolism were investigated. 3. Although the cytochrome P450 concentration was unchanged, and the activities of CYP1A2 and CYP2E1 isoforms were not additively or synergistically induced by co-exposure, TOL metabolism was inhibited by the presence of MEK (and vice versa). Depending on the relative proportions of each compound in the mixture, this sometimes resulted in a large increase in blood and brain concentrations. Apart from extreme cases (unbalanced mixtures), the amount of o-cresol and benzylmercapturic acid (and to a lesser extent 2,3-butanediols) excreted were proportional to the blood solvent concentrations. 4. In a co-exposure context, ortho-cresol and benzylmercapturic acid can be used as urinary biomarkers in biomonitoring for employees to relatively accurately assess TOL exposure.

Vortex-assisted surfactant-enhanced emulsification microextraction based on solidification of floating organic drop combined with high performance liquid chromatography for determination of naproxen and nabumetone.

A novel, rapid, simple and green vortex-assisted surfactant-enhanced emulsification microextraction method based on solidification of floating organic drop was developed for simultaneous separation/preconcentration and determination of ultra trace amounts of naproxen and nabumetone with high performance liquid chromatography-fluorescence detection. Some parameters influencing the extraction efficiency of analytes such as type and volume of extractant, type and concentration of surfactant, sample pH, KCl concentration, sample volume, and vortex time were investigated and optimized. Under optimal conditions, the calibration graph exhibited linearity in the range of 3.0-300.0ngL(-1) for naproxen and 7.0-300.0ngL(-1) for nabumetone with a good coefficient of determination (R(2)>0.999). The limits of detection were 0.9 and 2.1ngL(-1). The relative standard deviations for inter- and intra-day assays were in the range of 5.8-10.1% and 3.8-6.1%, respectively. The method was applied to the determination of naproxen and nabumetone in urine, water, wastewater and milk samples and the accuracy was evaluated through recovery experiments.

High throughput HPLC-ESI(-)-MS/MS methodology for mercapturic acid metabolites of 1,3-butadiene: Biomarkers of exposure and bioactivation.

1,3-Butadiene (BD) is an important industrial and environmental carcinogen present in cigarette smoke, automobile exhaust, and urban air. The major urinary metabolites of BD in humans are 2-(N-acetyl-L-cystein-S-yl)-1-hydroxybut-3-ene/1-(N-acetyl-L-cystein-S-yl)-2-hydroxybut-3-ene (MHBMA), 4-(N-acetyl-L-cystein-S-yl)-1,2-dihydroxybutane (DHBMA), and 4-(N-acetyl-L-cystein-S-yl)-1,2,3-trihydroxybutyl mercapturic acid (THBMA), which are formed from the electrophilic metabolites of BD, 3,4-epoxy-1-butene (EB), hydroxymethyl vinyl ketone (HMVK), and 3,4-epoxy-1,2-diol (EBD), respectively. In the present work, a sensitive high-throughput HPLC-ESI(-)-MS/MS method was developed for simultaneous quantification of MHBMA and DHBMA in small volumes of human urine (200 µl). The method employs a 96 well Oasis HLB SPE enrichment step, followed by isotope dilution HPLC-ESI(-)-MS/MS analysis on a triple quadrupole mass spectrometer. The validated method was used to quantify MHBMA and DHBMA in urine of workers from a BD monomer and styrene-butadiene rubber production facility (40 controls and 32 occupationally exposed to BD). Urinary THBMA concentrations were also determined in the same samples. The concentrations of all three BD-mercapturic acids and the metabolic ratio (MHBMA/(MHBMA+DHBMA+THBMA)) were significantly higher in the occupationally exposed group as compared to controls and correlated with BD exposure, with each other, and with BD-hemoglobin biomarkers. This improved high throughput methodology for MHBMA and DHBMA will be useful for future epidemiological studies in smokers and occupationally exposed workers.

NMR-based urinalysis for beta-ketothiolase deficiency.

BACKGROUND: Beta-ketothiolase deficiency is a rare inborn errors of metabolism (IEM) affecting the catabolism of isoleucine, characterized by severe ketoacidosis in children of 6 to 24months old. A prompt diagnosis is of paramount importance as the metabolic decompensation can be effectively reverted by glucose infusion and health outcomes are improved on a protein-restricted diet. Currently, majority of the laboratory diagnosis were made based on mass-spectrometry and molecular genetics while little is mentioned on the advancement of nuclear magnetic resonance (NMR) spectroscopy for the diagnosis of this condition. CASE: We report a case of beta-ketothiolase deficiency in a 1-y-old Chinese boy who presented with repeated vomiting, impaired consciousness and severe ketoacidosis. NMR urinalysis detected excessive amount of butanone (a disease specific marker of beta-ketothiolase deficiency), tiglylglycine, (intermediate of isoleucine catabolism) and ketones. Diagnosis of beta-ketothiolase deficiency was further established by molecular genetic studies of ACAT1 gene of the proband. CONCLUSIONS: This case illustrated that NMR-based urinalysis is complementary to organic acid analysis for diagnosis of beta-ketothiolase deficiency. The operation of NMR is simple and fast; sample preparation is a two-step procedure while the NMR acquisition is automatic and usually takes <15min. We envisage that NMR analysis will become more available in clinical laboratories and will play an important role in acute pediatric care.

Identification of combined conjugation of nabumetone phase I metabolites with glucuronic acid and glycine in minipig biotransformation using coupling high-performance liquid chromatography with electrospray ionization mass spectrometry.

High-performance liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry (ESI-MS) was applied for the analysis of nabumetone metabolites during the biotransformation in minipigs. In addition to known phase I metabolites, the identification of phase II metabolites was achieved on the basis of their full-scan mass spectra and subsequent MS(n) analysis using both positive-ion and negative-ion ESI mode. Some phase I metabolites are conjugated with both glucuronide acid and glycine, which is quite unusual type of phase II metabolite not presented so far for nabumetone. These metabolites were found in small intestine content, but they were absent in minipigs urine.

Sex differences in urinary levels of several biological indicators of exposure: a simulation study using a compartmental-based toxicokinetic model.

Toxicokinetic modeling is a useful tool to describe or predict the behavior of a chemical agent in the human or animal organism. A general model based on four compartments was developed in a previous study to quantify the effect of human variability on a wide range of biological exposure indicators. The aim of this study was to adapt this existing general toxicokinetic model to three organic solvents--methyl ethyl ketone, 1-methoxy-2-propanol, and 1,1,1,-trichloroethane--and to take into account sex differences. In a previous human volunteer study we assessed the impact of sex on different biomarkers of exposure corresponding to the three organic solvents mentioned above. Results from that study suggested that not only physiological differences between men and women but also differences due to sex hormones levels could influence the toxicokinetics of the solvents. In fact the use of hormonal contraceptive had an effect on the urinary levels of several biomarkers, suggesting that exogenous sex hormones could influence CYP2E1 enzyme activity. These experimental data were used to calibrate the toxicokinetic models developed in this study. Our results showed that it was possible to use an existing general toxicokinetic model for other compounds. In fact, most of the simulation results showed good agreement with the experimental data obtained for the studied solvents, with a percentage of model predictions that lies within the 95% confidence interval varying from 44.4 to 90%. Results pointed out that for same exposure conditions, men and women can show important differences in urinary levels of biological indicators of exposure. Moreover, when running the models by simulating industrial working conditions, these differences could be even more pronounced. A general and simple toxicokinetic model, adapted for three well-known organic solvents, allowed us to show that metabolic parameters can have an important impact on the urinary levels of the corresponding biomarkers. These observations give evidence of an interindividual variability, an aspect that should have its place in the approaches for setting limits of occupational exposure.

Simultaneous determination of nabumetone and its principal metabolite in medicines and human urine by time-resolved fluorescence.

A simple fluorescent methodology for the simultaneous determination of nabumetone and its main metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA), in pharmaceutical preparations and human urine is proposed. Due to the strong overlapping between the fluorescence spectra of both analytes, the use of fluorescence decay curves to resolve their mixture is proposed, since these curves are more selective. Values of dependent instrumental variables affecting the signal-to-noise ratio were fixed using a simplex optimization procedure. A factorial design with three levels per factor coupled to a central composite design was selected to obtain a calibration matrix of thirteen standards plus one blank sample that was processed using a partial least-squares (PLS) analysis. In order to assess the goodness of the proposed method, a prediction set of ten synthetic samples was analyzed, obtaining recovery percentages between 97 and 105%. Limits of detection, calculated by means of a new criterion, were 0.96 µg L(-1) and 0.88 µg L(-1) for nabumetone and 6-MNA, respectively. The method was also tested in the pharmaceutical preparation Relif, which contains nabumetone, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both analytes in human urine samples was successfully carried out by the PLS-analysis of a matrix of fifteen standards plus four analyte blanks and the use of the standard addition technique. Although urine shows native fluorescence, no extraction method or prior separation of the analytes was needed.

Sex differences in urinary levels of several biological indicators of exposure: a human volunteer study.

The aim of the study was to quantify the variability on biological indicators of exposure between men and women for three well known solvents: methyl ethyl ketone, 1-methoxy-2-propanol and 1,1,1-trichloroethane. Another purpose was to explore the effect of selected CYP2E1 polymorphisms on the toxicokinetic profile. Controlled human exposures were carried out in a 12 m³ exposure chamber for each solvent separately, during 6h and at half of the threshold limit value. The human volunteers groups were composed of ten young men and fifteen young women, including ten women using hormonal contraceptive. An analysis of variance mainly showed an effect on the urinary levels of several biomarkers of exposure among women due to the use of hormonal contraceptive, with an increase of more than 50% in metabolites concentrations and a decrease of up to 50% in unchanged substances concentrations, suggesting an increase in their metabolism rate. The results also showed a difference due to the genotype CYP2E1*6, when exposed to methyl ethyl ketone, with a tendency to increase CYP2E1 activity when volunteers were carriers of the mutant allele. Our study suggests that not only physiological differences between men and women but also differences due to sex hormones levels can have an impact on urinary concentrations of several biomarkers of exposure. The observed variability due to sex among biological exposure indices can lead to misinterpretation of biomonitoring results. This aspect should have its place in the approaches for setting limits of occupational exposure.

Differential exposure biomarker levels among cigarette smokers and smokeless tobacco consumers in the National Health and Nutrition Examination Survey 1999-2008.

Assessment of biomarkers is an appropriate way to estimate exposure to cigarette mainstream smoke and smokeless tobacco (SLT) constituents in tobacco consumers. Using the US National Health and Nutrition Examination Survey (NHANES, 1999-2008), biomarkers of volatile organic compounds, halogenated aromatic hydrocarbons (HAHs), polycyclic aromatic hydrocarbons (PAHs), acrylamide, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and metals were evaluated. In general, biomarker levels in SLT consumers were significantly lower than in smokers (excluding NNK and some HAHs) and were not significantly different compared with nonconsumers (excluding NNK and some PAHs). These results provide useful information for science-based risk assessment and regulation of tobacco products.

Acetone, butanone, pentanone, hexanone and heptanone in the headspace of aqueous solution and urine studied by selected ion flow tube mass spectrometry.

Urine is commonly analysed in clinical practice by a variety of liquid-phase techniques to check for excessive ketone bodies, proteins and salts to name just a few compounds. However, little work has been carried out to measure the volatile compounds emitted by urine since these do not yet have an established role in clinical diagnosis. There is, however, a growing body of evidence that these volatile compounds can be indicators of adverse physiological conditions and disease and with the advent of sensitive gas-phase analytical methods they can be quickly quantified in urine headspace and potentially provide valuable support for clinical diagnosis. Thus, we are developing selected ion flow tube mass spectrometry, SIFT-MS, for the real-time analysis of urine headspace, ultimately to support rapid diagnosis in the clinical environment. In this paper we focus on volatile ketones in the headspace of aqueous solutions and urine donated by three healthy volunteers. Using SIFT-MS, we have unambiguously quantified in urine headspace acetone, by far the most abundant ketone, butanone, pentanone, hexanone and heptanone using NO(+) precursor ions. Further to this, we have determined the Henry's Law coefficients, HLC, for these ketones in aqueous solution to allow the liquid-phase concentrations in urine to be estimated from headspace levels of their vapours. In addition, the influence of the addition of physiological amounts of dissolved urea, sodium chloride and hydrochloric acid on the partitioning of these ketones between the aqueous phase and gas phase has been investigated and found to be small, which gives greater credence to the use of the HLC obtained using aqueous solutions for the estimation of ketone concentrations in urine. Finally, parallel measurements of the levels of acetone in exhaled breath and urine headspace have been obtained and shown to be very similar, which gives support to the previous deduction from breath analysis that acetone is a truly systemic compound.

Analysis of ingested material and urine by GC-MS and 1H NMR spectroscopy: poisoning of an adult with adulterated soda.

The purpose of this work is to characterize chemical compounds added to an ingested soda by (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy and by gas chromatography-mass spectrometry in the electron impact mode. A second point was to highlight possible metabolic disturbances by considering urinary profile. Without any pretreatment, dimethylphtalate, 2-butanone, and 2,2,4-trimethylpentanediol diisobutyrate were found in the adulterated soda. Quantitative analysis was performed by relative integration of peak areas. Huge quantities of 2,2,4-trimethylpentanediol diisobutyrate and dimethylphtalate were found in the oily layer. 2-Butanone, which is miscible in water, was found in the two phases as well as small quantities of dimethylphtalate. The urine sample was collected on hospital admission and was also analyzed by (1)H NMR spectroscopy. The major abnormal compound found was 1,2-propanediol. Other disturbances concerned endogenous metabolites such as 2-ketoglutaric acid, lactic acid, and betaine.

The effects of host physiology on the attraction of tsetse (Diptera: Glossinidae) and Stomoxys (Diptera: Muscidae) to cattle.

In Zimbabwe, studies were made of the numbers of tsetse (Glossina spp.) and stable flies (Stomoxys spp.) attracted to cattle of different nutritional status, age and sex. Host odours were analysed to determine the physiological basis of these differences and improved methods are described for measuring rates of production of kairomones. Seasonal fluctuations in host weight, related to changes in pasture quality, had no significant effect on attraction of tsetse or Stomoxys. However, both attraction to different individuals and carbon dioxide production by these individuals were strongly correlated with weight, suggesting a possible link. Attraction to the odour from different types of cattle decreased in the order ox>cow>heifer>calf, and oxen were twice as attractive as calves of less than 12 months old. Lactation did not alter the relative attractiveness of cows. Calves less than six months old produced lower levels of carbon dioxide, acetone, octenol and phenols than oxen, but for older calves and cows, levels of production of known kairomones and repellents were similar to those of an ox. Carbon dioxide produced by cattle varied according to time of day and the animal's weight; cattle weighing 500 kg produced carbon dioxide at a mean rate of 2.0 l min(-1) in the morning and 2.8 l min(-1) in the afternoon compared to respective rates of 1.1 and 1.9 l min(-1) for cattle weighing 250 kg. Artificially adjusting the doses of carbon dioxide produced by individual cattle to make them equivalent did not remove significant differences in attractiveness for tsetse but did for Stomoxys. Increasing the dose of carbon dioxide from 1 to 4 l min(-1) in a synthetic blend of identified kairomones simulating those produced by a single ox, increased attractiveness to tsetse but not to the level of an ox. The results suggest that the main sources of differences in the attractiveness of individual cattle are likely to be variation in the production of carbon dioxide and, for tsetse, other unidentified kairomone(s). The biological and practical implications of these findings are discussed.

Identification and determination of phase II nabumetone metabolites by high-performance liquid chromatography with photodiode array and mass spectrometric detection.

Chromatographic analyses play an important role in the identification and determination of phase I and phase II drug metabolites. While the chemical standards of phase I metabolites are usually available from commercial sources or by various synthetic, degradation or isolation methods, the phase II drug metabolites have usually more complicated structures, their standards are in general inaccessible and their identification and determination require a comprehensive analytical approach involving the use of xenobiochemical methods and the employment of hyphenated analytical techniques. In this work, various high-performance liquid chromatography (HPLC) methods were employed in the evaluation of xenobiochemical experiments leading to the identification and determination of phase II nabumetone metabolites. Optimal conditions for the quantitative enzymatic deconjugation of phase II metabolites were found for the samples of minipig bile, small intestine contents and urine. Comparative HPLC analyses of the samples of above-mentioned biomatrices and of the same biomatrices after their enzymatic treatment using beta-glucuronidase and arylsulfatase afforded the qualitative and quantitative information about phase II nabumetone metabolites. Hereby, three principal phase II nabumetone metabolites (ether glucuronides) were discovered in minipig's body fluids and their structures were confirmed using liquid chromatography (LC)-electrospray ionization mass spectrometric (MS) analyses.

Detection of carboxylic acids and inhibition of hippuric acid formation in rats treated with 3-butene-1,2-diol, a major metabolite of 1,3-butadiene.

Epidemiological studies have indicated that 1,3-butadiene exposure is associated with an increased risk of leukemia. In human liver microsomes, 1,3-butadiene is rapidly oxidized to butadiene monoxide, which can then be hydrolyzed to 3-butene-1,2-diol (BDD). In this study, BDD and several potential metabolites were characterized in the urine of male B6C3F1 mice and Sprague-Dawley rats after BDD administration (i.p.). Rats given 1420 micromol kg(-1) BDD excreted significantly greater amounts of BDD relative to rats administered 710 micromol kg(-1) BDD. Rats administered 1420 or 2840 micromol kg(-1) BDD excreted significantly greater amounts of BDD per kilogram of body weight than mice given an equivalent dose. Trace amounts of 1-hydroxy-2-butanone and the carboxylic acid metabolites, crotonic acid, propionic acid, and 2-ketobutyric acid, were detected in mouse and rat urine after BDD administration. Because of the identification of the carboxylic acid metabolites and because of the known ability of carboxylic acids to conjugate coenzyme A, which is critical for hippuric acid formation, the effect of BDD treatment on hippuric acid concentrations was investigated. Rats given 1420 or 2272 micromol kg(-1) BDD had significantly elevated ratios of benzoic acid to hippuric acid in the urine after treatment compared with control urine. However, this effect was not observed in mice administered 1420 or 2840 micromol kg(-1) BDD. Collectively, the results demonstrate species differences in the urinary excretion of BDD and show that BDD administration in rats inhibits hippuric acid formation. The detection of 1-hydroxy-2-butanone and the carboxylic acids also provides insight regarding pathways of BDD metabolism in vivo.

The effects of co-exposure to methyl ethyl ketone on the biological monitoring of occupational exposure to N,N-dimethylformamide.

OBJECTIVES: (1) To assess whether urinary N,N-dimethylformamide (U-DMF) is suitable as a biomarker when co-exposure to methyl ethyl ketone (MEK) exists, and to evaluate whether it is suitable as an exposure biomarker of DMF. (2) To examine whether the co-exposure to MEK affects the characteristics of U-NMF and U-DMF. (3) To investigate if the difference in creatinine-adjusted and non-adjusted measurements of urinary biomarkers of DMF exposure is substantial. METHODS: Personal exposure monitoring of N,N-dimethylformamide (DMF) and MEK on 11 synthetic-leather workers was performed for 5 consecutive days. Daily post-shift urine for each individual was collected and was analyzed for urinary N-methylformamide (U-NMF) and U-DMF levels on both non-adjusted and creatinine-adjusted bases. RESULTS: Both U-NMF and U-DMF showed significant associations with airborne DMF. Positive and significant associations between U-NMF and U-DMF on either a non-adjusted basis or a creatinine-adjusted basis were found. Satisfactory linear associations ( P<0.01) between all kinds of urinary biomarkers and DMF exposure were found. The co-exposure to MEK exerted more effect on the relationship of airborne DMF to U-DMF than to U-NMF. CONCLUSIONS: U-DMF is detectable when occupational DMF exposure is near or below the occupational exposure limit of 10 ppm. In view of the performance of sensitivity, specificity, and positive predictive value, U-NMF, in general, is superior to U-DMF. However, on a par with other findings in this and previous studies, U-DMF might be considered as a complimentary biomarker of exposure to DMF in addition to U-NMF. No distinction between creatinine-adjustment or non-adjustment for urine specimens was found in the biological monitoring of DMF exposure. Further exploration of the influence of co-exposure to MEK at higher exposure is warranted.