Determination of 5-hydroxy-N-methylpyrrolidone and 2-hydroxy-N-methylsuccinimide in human urine

Quantification of six potential unspecific human biomarkers of 1-vinyl-2-pyrrolidone exposure in Sprague-Dawley rat urine using gas chromatography coupled with triple mass spectrometry

RATIONALE

The monomer 1-vinyl-2-pyrrolidone (VP) is a substance with excellent solvent features. It is used in a wide variety of pharmaceutical, cosmetic, food industrial or technical applications and produced on an industrial scale. Since VP has caused adenocarcinoma of the nasal cavity and liver cell carcinoma in long-term experiments with rats, a human biomarker would be appreciated for risk assessment.

METHODS

A sensitive analytical electron ionization gas chromatography/tandem mass spectrometry (GC/MS/MS) method for the determination of six possible biomarkers for VP in urine was established and validated. Two isotope-labeled internal standards (ISTD) were used for quantification. A simple and easy to use freeze-drying step was performed prior to derivatization with N-tert-butyldimethylsilyl-N-methyltrifluoracetamide (MTBSTFA) and following sample extraction for cleanup purposes.

RESULTS

A calibration curve with six calibration standards ranging from 50 μg/L to 2000 μg/L (10-fold higher for H-OPAA) in urine was prepared. Validation results were satisfactory with recoveries ranging from 88.2 to 110.2 % with two exceptions for the lowest quality control for two substances without ISTD (126.4 % and 139.3 %). Three of the substances could be identified as VP metabolites in an exposure study with Sprague-Dawley (SD) rats.

CONCLUSIONS

A quick and easy to use method has been established for six target molecules investigated for a better understanding of the metabolism of VP. Two of three substances identified as metabolites of VP could serve as a nonspecific human biomarker for VP exposure as shown with an excerpt of an exposure study performed in SD rats.

Isotope-dilution method for the determination of 1-vinyl-2-pyrrolidone-mercapturic acid as a potential human biomarker for 1-vinyl-2-pyrrolidone via online SPE ESI-LC/MS/MS in negative ionization mode

We established and validated a specific and sensitive analytical method for the determination of 1-vinyl-2-pyrrolidone (VP) as 1-vinyl-2-pyrrolidone-mercapturic acid (VPMA) in urine using an electrospray liquid chromatography tandem mass spectrometry (ESI-LC/MS/MS) column switching method. An online solid phase extraction (SPE) for sample cleanup was performed by column switching to a restricted access material and back-flushing to the analytical column. A Phenomenex Luna C8 column was used for sample separation (150mm; ID 4,6mm; 3μm). D4-VPMA served as an isotope labeled internal standard and was detected in negative multiple-reaction monitoring (MRM) mode. The Limit of quantification (LOQ) for VPMA was 1.5μg/L, the intra-day precision of three concentrations (2μg/L, 75μg/L and 400μg/L) of spiked urine samples ranged from 2.7 to 7.3%, the inter-day precision from 3.4 to 14.4%. The accuracy ranged from 6.2 to 9.0%, for the intra-day experiments and from 0.3 to 6.9% for the inter-day experiments. The method was applied to urines of Sprague-Dawley rats exposed to VP as a proof of principle of VPMA as a potential biomarker.

Determination of N-methyl-2-pyrrolidone and its metabolites in urine by micellar electrokinetic chromatography

A fast and accurate micellar electrokinetic capillary chromatography (MEKC) method was developed for monitoring N-methyl-2-pyrrolidone (NMP) exposure. Baseline separation of NMP and its main metabolites: 5-hydroxy-N-methyl-2-pyrrolidone (5HNMP), N-methylsuccinimide (MSI), 2-hydroxy-N-methylsuccinimide (2HMSI), and 2-pyrrolidone (2P) was obtained within 6 min in an uncoated fused silica capillary using 5 mM phosphate buffer and 140 mM sodium dodecyl sulfate (pH 7.1) as background electrolyte (BGE). On-line UV-detection was performed at 200 nm and the applied electric field was 400 V cm−1. Possible interference of BGE-induced system peaks on separation was investigated by computer simulation and no such interference was observed. The developed MEKC method combined with solid phase extraction for sample preparation was successfully applied to the analysis of urine of rats exposed to NMP. The urinary excretion was determined in 0–6 h and 6–24 h specimens collected after an intragastic administration of 308 mg NMP / kg rat body weight. The results of NMP disposition kinetics in rat urine are reported for NMP and metabolites.

SPE–GC/FTD determination of N-methyl-2-pyrrolidone and its metabolites in urine

An analytical method using a combination of solid-phase extraction (SPE) and gas chromatography with a flame thermionic detector (GC/FTD) was developed for determination of N-methyl-2-pyrrolidone (NMP), N-methylsuccinimide (MSI), and 2-hydroxy-N-methylsuccinimide (2-HMSI) in human urine. The SPE cartridge of poly(divinylbenzene/hydroxymethacrylate) used was directly loaded with urine sample, followed by elution with methyl isobutyl ketone (MIBK) and subsequent centrifugation, and the supernatant was injected into the capillary GC using a DB1701. This method allowed efficient separation of NMP, MSI, and 2-HMSI, which were nearly free of interference by other GC peaks arising from urine. Recoveries of NMP, MSI, and 2-HMSI from the SPE cartridge were about 98, 101, and 67%, respectively, with limits of detection of 0.04, 0.02, and 0.06 mg/L, respectively, which met the regulatory requirements. The present method was used for assay in biological monitoring of workers exposed to NMP in their occupational environment.

Human experimental exposure study on the uptake and urinary elimination of N-methyl-2-pyrrolidone (NMP) during simulated workplace conditions

A human experimental study was carried out with 16 volunteers to examine the elimination of N-methyl-2-pyrrolidone (NMP) after exposure to the solvent under simulated workplace conditions. The NMP concentrations were 10, 40 and 80 mg/m(3) for 2 x 4 h with an exposure-free interval of 30 min. Additionally, a peak exposure scenario (25 mg/m(3) baseline, 160 mg/m(3) peaks for 4 x 15 min, time-weighted average: 72 mg/m(3)) was tested. The influence of physical activity on the uptake and elimination of NMP was studied under otherwise identical exposure conditions but involving moderate workload on a bicycle ergometer (75 W for 6 x 10 min). The peak times and biological half-lives of urinary NMP and its main metabolites 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI) in urine were analysed as well as the interrelationships between exposure and biomarkers. All analytes showed a close correlation between their post-shift peak concentrations and airborne NMP. An exposure to the current German workplace limit value of 80 mg/m(3) under resting conditions resulted in urinary peak concentrations of 2,400 microg/L NMP, 117 mg/g creatinine 5-HNMP and 32 mg/g creatinine 2-HMSI (workload conditions: 3,400 microg/L NMP, 150 mg/g creatinine 5-HNMP, 44 mg/g creatinine 2-HMSI). Moderate workload enhanced the total uptake of NMP by approximately one third. Differences between the estimated and the observed total amount of urinary metabolites point to a significant contribution of dermal absorption on the uptake of NMP. This aspect, together with the influence of physical workload, should be considered for the evaluation of a biological limit value for NMP.

Human volunteer study on the influence of exposure duration and dilution of dermally applied N-methyl-2-pyrrolidone (NMP) on the urinary elimination of NMP metabolites

OBJECTIVES

N-Methyl-2-pyrrolidone (NMP) is a versatile solvent used in various industrial processes and applications. Apart from its mildly irritating effects on the eyes, the mucous membranes and the skin, NMP has revealed prenatal toxicity in animal experiments after the oral administration of high doses. The dermal absorption of NMP and the urinary elimination of its main metabolites were investigated within an experimental exposure study.

METHODS

Four male volunteers were exposed to liquid NMP under occlusive conditions on the back of one hand with varying exposure times and solvent concentrations. Urine was collected before, during and after the exposure and analysed for the main NMP metabolites 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI).

RESULTS

The urinary concentration of the metabolites upon exposure to undiluted NMP for 2 h increased rapidly with 5-HNMP reaching a maximum at 4-5 h and 2-HMSI after 26-29 h. The application of aqueous NMP solutions resulted in a delay of the peak time for 5-HNMP of approximately 6 h as compared with the undiluted solvent. An average dermal absorption of 5.4+/-1.5 mg NMP cm(-2) h(-1) was calculated for a 2 h exposure to undiluted NMP (6.5+/-2.0 mg NMP cm(-2) h(-1) for a 30 min exposure). Aqueous dilution of NMP to 50% was followed by a decrease of the absorption to 0.9+/-0.5 mg NMP cm(-2) h(-1). NMP metabolite concentrations in the range of the detection limits were found only in isolated urine samples after exposure to 10% NMP in aqueous dilution.

CONCLUSIONS

NMP is rapidly absorbed across the skin and the dermal route may contribute significantly to the uptake of the solvent. Therefore, a biomonitoring of NMP exposed workers is essential for occupational-medical surveillance. Both urinary metabolites reflect the internal dose after a dermal absorption of NMP and thus qualify as suitable biomarkers for NMP exposure.

Ambient monitoring and biomonitoring of workers exposed to N-methyl-2-pyrrolidone in an industrial facility

OBJECTIVES

The exposure of seven workers and three on-site study examiners to N-methyl-2-pyrrolidone (NMP) was studied in an adhesive bonding compound and glue production facility.

METHODS

Airborne NMP was analysed by personal and stationary sampling on activated charcoal tubes. NMP and its main metabolites, 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI), were analysed in pre-shift and post-shift spot urine samples by gas chromatography-mass spectrometry. The workers were examined with respect to irritation of the eyes, the mucous membranes and the skin, and health complaints before and after the work-shift were recorded.

RESULTS

The time-weighted average concentration of NMP in most work areas varied between 0.2 and 3.0 mg/m3. During the manual cleaning of stirring vessels, valves and tools, 8-h TWA exposures of up to 15.5 mg/m3 and single peak exposures of up to 85 mg/m3) were observed. NMP and its metabolites were detected in two pre-shift urine specimens. NMP and 5-HNMP concentrations in post-shift urine samples of five workers and three on-site study examiners were below 125 microg/g creatinine and 15 mg/g creatinine, respectively, while two vessel-cleaning workers showed significantly higher urinary NMP concentrations of 472 and 711 microg/g creatinine and 5-HNMP concentrations of 33.5 and 124 mg/g creatinine. 2-HMSI was detectable in four post-shift samples (range: 1.6-14.7 mg/g creatinine). The vessel cleaner with the highest NMP exposure reported irritation of the eyes, the upper respiratory tract and headaches.

CONCLUSIONS

The results of this study indicate a relatively low overall exposure to NMP in the facility. An increased uptake of NMP occurred only during extensive manual vessel cleaning. Health complaints associated with NMP exposure were recorded in one case and might be related to an excessive dermal exposure due to infrequent and inadequate use of personal protective equipment.

Human experimental exposure to N-methyl-2-pyrrolidone (NMP): toxicokinetics of NMP, 5-hydroxy- N-methyl-2-pyrrolidone, N-methylsuccinimide and 2-hydroxy- N-methylsuccinimide (2-HMSI), and biological monitoring using 2-HMSI as a biomarker

OBJECTIVE

N-methyl-2-pyrrolidone (NMP) is a strong and selective organic solvent with an extensive and increasing use. It has been reported to be a compound that is toxic to the reproductive system. The aim of this study was to evaluate toxicokinetics parameters for NMP and its metabolites, 5-hydroxy- N-methyl-2- pyrrolidone (5-HNMP), N-methylsuccinimide (MSI) and 2-hydroxy- N-methylsuccinimide (2-HMSI), and to develop a method for biological monitoring of NMP exposure that uses 2-HMSI as a biomarker.

METHODS

Six healthy, male volunteers were exposed to NMP in an exposure chamber for 8 h at concentrations of 10, 25 and 50 mg/m(3). In addition, three of the subjects were exposed a second time at 50 mg/m(3). Air levels were monitored by Amberlite XAD-7 sampling and gas chromatography (GC) analysis. Levels of NMP and the metabolites in plasma and urine were analysed by GC or GC with mass spectrometry detection.

RESULTS

The concentration of 2-HMSI in plasma and urine rose during exposure and reached a peak approximately 15 h after the end of exposure. It then decayed according to a one-compartment model with a half-time of about 18 h. There were very close correlations between the NMP air levels, on the one hand, and concentrations of 2-HMSI in plasma (r=0.98) and creatinine-adjusted urinary 2-HMSI levels (r=0.96), on the other. The renal clearances were 0.13, 1.4, 0.12 and 1.2 l/h for NMP, 5-HNMP, MSI and 2-HMSI, respectively. The total clearances were 11.4, 3.2, 8.5 and 1.1 l/h for NMP, 5-HNMP, MSI and 2-HMSI, respectively. The apparent volumes of distribution were 41, 28, 120 and 28 l for NMP, 5-HNMP, MSI and 2-HMSI, respectively.

CONCLUSIONS

Toxicokinetics parameters for NMP, 5-HNMP, MSI and 2-HMSI have been estimated. Furthermore, 2-HMSI is applicable as a biomarker of exposure to NMP, and the levels in plasma and urine may be used to indicate an exposure over three days.

Toxicokinetics and metabolism of N-[14C]methylpyrrolidone in male Sprague-Dawley rats. A saturable NMP elimination process

This study evaluated the toxicokinetics of N-[(14)C]methylpyrrolidone ([(14)C]NMP) after intravenous administration (0.1, 1, 10, 100, and 500 mg/kg, in saline solution) or topical application (20 and 40 micro l/cm(2); 10 cm(2), neat) in haired male Sprague-Dawley rats. Whatever the dose, unchanged NMP was intensively distributed into the body with a volume of distribution of 69% of body weight. After this phase, unchanged NMP declined almost linearly with time for 3 to 4 h after administration and then followed a mono-exponential function (t1/2 = 0.8 h) for the three lowest doses. The maximal plasma level of 5-hydroxy-N-methylpyrrolidone (5-HNMP), the main metabolite, was reached 4 to 6 h later for the three lowest doses and 8 to 24 h later for the highest doses. These findings indicate that the elimination of NMP is governed by a saturable metabolism process. The Michaelis-Menten parameters estimated from plasma levels of unchanged NMP were 2 mM and 3.8 mg/h, respectively. Between 4 and 10% of the administered doses were excreted in the urine as unchanged NMP. Urinary clearance of NMP (0.03 to 0.07 ml/min) indicates intensive tubular reabsorption. 5-HNMP was the main urinary metabolite and accounted for 42 to 55% of the administered doses. Its maximal urinary excretion occurred between 4 and 6 h after administration of the three lowest doses and between 8 and 24 h for the two highest doses. Urinary clearance (0.9 to 1.3 ml/min) was compatible with renal elimination by simple glomerular filtration.

Quantitative determination of 5-hydroxy-N-methylpyrrolidone in urine for biological monitoring of N-methylpyrrolidone exposure

The aim of this work was to validate a sensitive method for quantitative analysis of 5-hydroxy-N-methylpyrrolidone (5-HNMP) in urine. This compound has been recommended as a marker for biological monitoring of N-methylpyrrolidone (NMP) exposure. Different solvents and alternative methods of extraction including liquid-liquid extraction (LLE) on Chem Elut and solid-phase extraction (SPE) on Oasis HLB columns were tested. The most efficient extraction of 5-HNMP in urine was LLE with Chem Elut columns and dichloromethane as a solvent (consistently 22% of recovery). The urinary extracts were derivatized by bis(trimethylsilyl)trifluoroacetamide and analysed by gas chromatography-mass spectrometry (GC-MS) with tetradeutered 5-HNMP as an internal standard. The detection limit of this method is 0.017 mg/l urine with an intraassay precision of 1.6-2.6%. The proposed method of extraction is simple and reproducible. Four different m/z signal ratios of TMS-5-HNMP and tetralabelled TMS-5-HNMP have been validated and could be indifferently used in case of unexpected impurities from urine matrix.

Dermal exposure to aqueous solutions of N-methyl pyrrolidone

N-methyl pyrrolidone (NMP) is a substance widely used for its strong and selective solvent capacity. The strong potential NMP has for skin absorption makes biological monitoring ideal for exposure assessment. This study looked at brief exposures to NMP in aqueous solutions over a range of concentrations. Two volunteers placed one hand in NMP solutions ranging from 5 to 25% for as long as 15 min followed by urine collection for 48 h. The analyte of interest (analysed by GC-MS) was the NMP metabolite 5-hydroxy-N-methyl pyrrolidone (5-HNMP). Excretion of 5-HNMP was plotted against time and this showed that urine concentrations were at a maximum after about 10 h and 5-HNMP excretion continued for 48 h after exposure. The half-life of excretion was found to be approximately 11 h. The mean correlation between exposure (as a measure of exposure duration and solution concentration) and total 5-HNMP excreted was 0.9297.

Determination of 5-hydroxy-N-methyl-2-pyrrolidone and 2-hydroxy-N-methylsuccinimide in human plasma and urine using liquid chromatography-electrospray tandem mass spectrometry

A method for simultaneous determination of 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI) was developed. These compounds are metabolites from N-methyl-2-pyrrolidone (NMP), a powerful and widely used organic solvent. 5-HNMP and 2-HMSI were purified from plasma and urine by solid-phase extraction using Isolute ENV+ columns, and analysed by liquid chromatography coupled to a mass spectrometer fitted with an atmospheric pressure turbo ion spray ionisation interface in the positive ion mode. The method was validated for plasma and urine concentrations from 0.12 to 25 microg/ml. The recoveries for 5-HNMP and 2-HMSI in plasma were 99 and 98%, respectively, and in urine 111 and 106%, respectively. For 5-HNMP and 2-HMSI, the within-day precision in plasma was 1-4 and 3-6%, respectively, and in urine 2-12 and 3-10%, respectively. The corresponding data for the between-day precision was 5 and 3-6%, respectively, and 4-6 and 7-8%, respectively. The detection limit for 5-HNMP was 4 ng/ml in plasma and 120 ng/ml in urine. For 2-HMSI, it was 5 ng/ml in plasma and 85 ng/ml in urine. The method is applicable for analysis of plasma and urine samples from workers exposed to NMP.

Determination of N-methylsuccinimide and 2-hydroxy-N-methylsuccinimide in human urine and plasma

A method for determination of N-methylsuccinimide (MSI) and 2-hydroxy-N-methylsuccinimide (2-HMSI) in human urine and of MSI in human plasma was developed. MSI and 2-HMSI are metabolites of the widely used organic solvent N-methyl-2-pyrrolidone (NMP). MSI and 2-HMSI were purified from urine and plasma by C8 solid-phase extraction and analysed by gas chromatography-mass spectrometry in the negative-ion chemical ionisation mode. The intra-day precisions in urine were 2-6% for MSI (50 and 400 ng/ml) and 3-5% for 2-HMSI (1000 and 8000 ng/ml). For MSI in plasma it was 2% (60 and 1200 ng/ml). The between-day precisions in urine were 3-4% for MSI (100 and 1000 ng/ml) and 2-4% for 2-HMSI (10,000 and 18,000 ng/ml) and 3-4% for MSI in plasma (100 and 900 ng/ml). The recoveries from urine were 109-117% for MSI (50 and 400 ng/ml) and 81-89% for 2-HMSI (1000 and 8000 ng/ml). The recovery of MSI from plasma was 91-101% (50 and 500 ng/ml). The detection limits for MSI were 3 ng/ml in urine and 1 ng/ml in plasma and that of 2-HMSI in urine was 200 ng/ml. The method is applicable for analysis of urine and plasma samples from workers exposed to NMP.