2-(2-methoxyethoxy)ethanol

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2017

Materials and methods

Objective of study:

excretion

metabolism

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The urinary route is known to account for virtually all of the metabolites of the E series glycol ethers. This study was primarily to look for the presence of methoxyacetic acid as an indicator of the route of metabolism and the relevance of this metabolite when considering potential toxicity. A non radiolabelled analytical approach was developed to look for the expected metabolites in urine following a single dose over a 48 hour elimination period.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

2-(2-methoxyethoxy)ethanol

EC Number:

203-906-6

EC Name:

2-(2-methoxyethoxy)ethanol

Cas Number:

111-77-3

Molecular formula:

C5H12O3

IUPAC Name:

2-(2-methoxyethoxy)ethanol

Specific details on test material used for the study:

Source: INEOS nv, Antwerp, Belgium
Purity: 99.8%.

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Germany
- Age at study initiation: 9-10 weeks
- Weight at study initiation: All animals within +/-20% of each other
- Individual metabolism cages: yes
- Diet (ad libitum): Special Diet Services, Witham, UK
- Water (ad libitum): Human grade, Vitens
- Acclimation period: 5 days total including 1 day in metabolism cage. Animals also subject to quarantine period when microbiological status of a random sample of the batch of animals checked.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 45-65
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 20/12/16 To: 22/12/16

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Duration and frequency of treatment / exposure:

Single dose. Volume given 10mL.kgbw.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

500 mg/kg bw (total dose)

Doses / concentrations 2

Dose / conc.:

1 000 mg/kg bw (total dose)

Doses / concentrations 3

Dose / conc.:

2 000 mg/kg bw (total dose)

No. of animals per sex per dose / concentration:

4

Control animals:

no

Positive control reference chemical:

no

Details on dosing and sampling:

- Tissues and body fluids sampled: urine
- Time and frequency of sampling: Collection periods 0-24hrs, 24-48hrs
- From how many animals: (samples pooled or not): measurements of individual animals
- Method type(s) for identification: See 'any other information for details of method"
- Limits of detection and quantification: To be confirmed in final report but all key metabolites well above LOD/LOQ.

Statistics:

Mean and standard deviation calculated

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on excretion:

Recovery of dose material exceeded 95% at all dose levels leading to conclusion that almost all the substance is excreted by this route.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

All of the expected metabolites were seen, although the acetic acid derivative of DEGME dominated. Additionally, trace amounts of four other metabolites were seen. One was identified as the sulphate conjugate. A second was identified as a metabolite of DEG; the other two were not identified but one contained nitrogen. Since the unknowns were no more than ~0.1%, it was not considered necessary to identify them. A summary of the main metabolite percentages (those expected) across the three dose levels is:
- MEAA: 87 - 95%
- DEGME: 3.5 - 5%
- DEG: 2 - 2.5%
- MAA: 1-1.5%
- DEGME-G: 0.5 - 1%

Nearly all of the MEAA was excreted in the first 24 hours, showing it has a relatively short half life.

The following metabolites were also detected:

- DEGME-sulphate conjugate ~0.02%
- Glycolic acid (metabolite of DEG) (0.3 - 0.5%)
- Unknown metabolite containing nitrogen) up to 0.1%
- Unknown metabolite 0.01 - 0.02%

Any other information on results incl. tables

Results for 0 -24 and 24 -48 hour collection periods combined. Note that the figure for DEG also includes the amount detected as glycolic acid, since this is a known metabolite of DEG:

Dose	500mg/kg (SD)	1000mg/kg (SD)	2000mg/kg (SD)
MEAA	94.5% (7.5)	90.9% (8.5)	87.2% (4.5)
MAA	1.4% (0.1)	1.1% (0.1)	0.8% (0.1)
DEG	2.9% (0.4)	2.3% (0.8)	2.2% (0.4)
Glucoronide	1.0% (0.1)	0.8% (0.1)	0.7% (0.1)
DEGME	3.4% (0.4)	3.6% (0.7)	4.9% (0.7)
TOTAL RECOVERED (48hr)	103.3% (7.1)	98.7% (7.3)	95.9% (3.8)

The tables below show the amounts collected over the two different time periods for the three different doses:

Time period Dose 500mg/kg	0 – 24hr	24 – 48hr
MEAA	93.2%	1.4%
MAA	1.1%	0.3%
DEG	2.9%	0.0%
Glucoronide	1.0%	0.0%
DEGME	3.4%	0.0%

Time period Dose 1000mg/kg	0 – 24hr	24 – 48hr
MEAA	89.7%	1.2%
MAA	0.7%	0.3%
DEG	2.3%	0.0%
Glucoronide	0.8%	0.0%
DEGME	3.6%	0.0%

Time period Dose 2000mg/kg	0 – 24hr	24 – 48hr
MEAA	86.2%	1.0%
MAA	0.5%	0.3%
DEG	2.2%	0.0%
Glucoronide	0.7%	0.0%
DEGME	4.9%	0.0%

Applicant's summary and conclusion

Conclusions:

DEGME is eliminated >95% within 24 hours in the urine primarily in the form of the acid metabolite 2-(2-methoxyethoxy)acetic acid. About 1% of the dose is metabolised to methoxyacetic acid. Small amounts of diethylene glycol, DEGME itself and its glucoronide conjugate are also found in the urine.

Executive summary:

In a study to examine the metabolism 2 -(2 -methoxyethoxy)ethanol, SD rats were given single oral doses of 500, 1000 and 2000mg/kg and the urine collected over two 24 hour periods for analysis for a number of expected metabolites. The dominant metabolite was 2 -(2 -methoxyethoxy)acetic acid, which accounted for 87 -95% of the original dose. Unmetabolised 2 -(2 -methoxyethoxy)ethanol, the glucoronide conjugate and diethylene glycol were also found in small quantities. In addition, the metabolite methoxyacetic acid was found, the amount accounting for 0.8 -1.4% of the dose of 2 -(2 -methoxyethoxy)ethanol given, with the amount seeming to decline with increasing dose. This demonstrates that oxidation of the hydroxyl function is the dominant metabolic pathway but small amounts of the substance are metabolised by cleavage of the ether linkage. The study also showed that around 98% of the dose of 2 -(2 -methoxyethoxy)ethanol is eliminated within 24 hours and that MAA half life increases significantly at very high dose, which could explain the reproductive effects seen at very high dose through build up of concentration.