1-ethylpyrrolidin-2-one

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Study period:

2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

Metabolism and elimination of N‑ethyl‑2‑pyrrolidone (NEP) in human males after oral dosage

Author:

H. M. Koch, M. Bader, T. Weiss, S. Koslitz, A. Schütze, H.-U. Käfferlein, T. Brüning

Year:

2013

Bibliographic source:

Arch Toxicol, DOI 10.1007/s00204-013-1150-1, published online 14 Nov. 2013

Materials and methods

Objective of study:

metabolism

toxicokinetics

Test guideline

Qualifier:

no guideline followed

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Test material form:

liquid

Details on test material:

N-Ethyl-2-pyrrolidone (NEP), chemical purity 98 % was purchased from Sigma-Aldrich (Seelze, Germany).

Radiolabelling:

no

Test animals

Species:

other: human

Details on species / strain selection:

The volunteers for this study were three healthy Caucasian males between 40 and 43 years of age and between 83 and 95 kg in weight, born and living in Germany. The volunteers had no known occupational exposure to NEP.

Sex:

male

Administration / exposure

Route of administration:

oral: unspecified

Vehicle:

other: decaffeinated coffee

Details on exposure:

The dose was taken orally during breakfast, with NEP dissolved in decaffeinated coffee served in an edible cup to ensure the complete dose was ingested.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

20.9 other: mg

Doses / concentrations 2

Dose / conc.:

0.22 mg/kg bw/day (nominal)

No. of animals per sex per dose / concentration:

3 human volunteers

Control animals:

no

Details on dosing and sampling:

Each volunteer collected all urine voids of 4 days (96 h) in 250 mL polypropylene (PP) specimen collection containers following dosing of NEP. The volunteers recorded the time of the void of each sample. The urine volume of each individual sample was determined as the difference between the weight of the filled and the empty container. In the event a volunteer provided more than one container per void, the total volume was calculated per void and the total volume was combined and mixed in a 1 L PP container. Aliquots of the individual samples were stored in 15 mL polypropylene/polyethylene vessels and frozen at −18 °C within 12 h after collection, the latest.

Results and discussion

Main ADME results

Type:

metabolism

Results:

By orally dosing NEP to three male volunteers the major kinetic and metabolic parameters for the two urinary metabolites 5-HNEP and 2-HESI.were determined.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

The two postulated NEP metabolites 5-hydroxy-N-ethyl-2-pyrrolidone (5-HNEP) and 2-hydroxy-N-ethylsuccinimide (2-HESI) have been detected in urine samples from the general population. In samples of NEP exposed human volunteersthe above postulated NEP metabolites 5-HNEP and 2-HESI were indetified and quantified and their urinary elimination kinetics were determined.

Any other information on results incl. tables

As described previously by Schindler et al. (2012) trace levels of both 5-HNEP and 2-HESI could already be detected in the pre-dose sample of volunteer 1 originating from a suspected background exposure of the general population to NEP. However, these pre-dose levels of 5-HNEP (0.070 mg/L) and 2-HESI (0.077 mg/L) were considerably lower than the levels observed after the controlled dosage of this study. The pre-dose metabolite levels of volunteers 2 and 3 were below the LOD of the analytical method. Thus, the background exposure to NEP did not interfere with the study design to investigate elimination kinetics and metabolic conversion factors.

While on day 3 after the dosing 5-HNEP concentrations already dropped to levels close to the LOD and/or the possible background exposure, 2-HESI levels remains still rather high. The three volunteers provided 119 urine voids over the course of the study.

Regarding the elimination, the fast rise of urinary 5-HNEP concentration after the dose within hours is followed by a steady decline to levels around the LOD on day 3 post dose. The urinary peak concentrations of 2 -HESI are observed much later, around 24 h post dose, give or take several hours, depending upon the individual and the dimensions. While creatinine correction had a smoothing effect on the time course of elimination for 5-HNEP for all three individuals, the effect was opposite for 2-HESI with a smoother elimination characteristic and a better concordance between the individuals for the mg/L values. In all cases elimination of 2 -HESI was still going on 4 days after the dose.

Maximum concentrations (mean of the three individuals) for 5-HNEP occurred approximately 7 h and for 2-HESI approximately 18 h post dose (based upon mg/L values). Elimination half-times, determined mathematically from the mg/L and creatinine-adjusted concentrations over time via the rate constant k (halftime = ln(2)/k) were approximately 7 h for 5-HNEP and between 22 and 27 h for 2-HESI, depending on whether mg/L or creatinine-adjusted concentrations were used for calculation. While the range of elimination half-times for 5-HNEP (5.5–8.5 h) was rather small both between the individuals and the underlying concentration dimension the range for 2-HESI was considerably larger (17.4–29.9 h).

In general, these elimination half times are in rather good accordance to the known elimination half times of the analogous NMP metabolites determined from three individuals after oral exposure to 100 mg NMP of ~4 h for 5 -HNMP and of ~17 h for 2 -HMSI (Åkesson and Jönsson 1997). The primary hydroxylated metabolites of both N-alkyl pyrrolidones are eliminated much faster than the later-stage succinimide metabolites. However, the data on NEP compared to the previously published data on NMP indicate that the elimination half times of the NEP metabolites seem to be somewhat longer than elimination half times of the NMP metabolites. Within the first 24 h after exposure, 33.3 % of the oral NEP dose was excreted as the two metabolites (26.4 % as 5 -HNEP and 6.9 % as 2 -HMSI) in the urine. On day two, another 10.5 % of the dose was excreted. On day two, 2-HESI was the major metabolite (8.2 %) with 5-HNEP representing only a minor share (2.3 %). After day two, NEP was almost exclusively eliminated as 2-HESI. In total, within 4 days 50.7 % of the dose were recovered as these two metabolites in urine (28.9 % as 5-HNEP and 21.6 % as 2-HESI). For 2-HESI, the elimination was not finished on day four.

The individual variation between the three volunteers with respect to the amount of NEP excreted as the primary metabolite 5-HNEP was rather small, with excreted fractions in a tight range between 27.8 and 30.1 %. The individual variation for 2-HESI was much more pronounced, accounting for between 17.2 and 26.9 % of the dose. Possibly, the reason for this observation lies in the fact that 2-HESI is the third successive metabolite of the oxidativepathway of NEP (with much more factors influencing its individual metabolism) and that its elimination occursmuch slower than the elimination of the primary metabolite 5-HESI.

Applicant's summary and conclusion

Executive summary:

Abstract:

N-Ethyl-2-pyrrolidone (NEP) is an industrial solvent that has been increasingly used to substitute N-methyl-2-pyrrolidone. The two postulated NEP metabolites 5-hydroxy-N-ethyl-2-pyrrolidone (5 -HNEP) and 2 -hydroxy-N-ethylsuccinimide (2-HESI) have recently been detected in urine samples from the general population. Thus, the toxicokinetic characterization of these biomarkers of NEP exposure in humans is of relevance both in the occupational as well as the environmental field. 20.9 mg NEP was dosed to three male volunteers. These volunteers collected all their urine samples over a period of 4 days post dose. In these samples the above postulated NEP metabolites 5 -HNEP and 2 -HESI were identified and quantified.

After 4 days 50.7 % of the dose was recovered as these two metabolites in urine, 29.1 % as 5 -HNEP and 21.6 % as 2-HESI. The largest share of 5-HNEP was excreted within 24 h post dose, while the major share of 2-HESI was excreted on day 2 post dose. An elimination half-time for 5 -HNEP of approx. 7 h was estimated and for 2-HESI of approx. 22–27 h. While the elimination of 5-HNEP was basically finished 72 h post dose, significant amounts of 2-HESI were still eliminated after 96 h. According to the authors, both biomarkers can be used in human biomonitoring studies to extrapolate from urinary measurements to the NEP dose taken up and thus to evaluate the risk caused by exposure to this chemical.