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Toxicological information

Basic toxicokinetics

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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:
2017
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 butoxyacetic 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 and single concentration over a 48 hour elimination period with two analytical periods (0-24 and 24-48hrs).
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Specific details on test material used for the study:
Source: TCI Europe nv
Purity: 99.8%.
Batch number GK02
Radiolabelling:
no

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals 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, Plexiglass metabolism cages.
- 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
- air changes per hour: 10

IN-LIFE DATES: From: 9/5/17 To: 11/5/17

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
water
Duration and frequency of treatment / exposure:
Single dose. Volume given 10mL/kgbw.
Doses / concentrations
Dose / conc.:
1 000 mg/kg bw (total dose)
Remarks:
Single dose was used based on an earlier study using 2-(2-methoxyethoxy)ethanol at multiple doses which confirmed no significant difference in metabolite patterns with dose
No. of animals per sex per dose:
4
Control animals:
no
Positive control:
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: Lower limit of quantification 0.1ug/mL for all metabolites.
Statistics:
Mean and standard deviation calculated

Results and discussion

Main ADME resultsopen allclose all
Type:
metabolism
Type:
excretion

Toxicokinetic / pharmacokinetic studies

Details on excretion:
Recovery of dose material was 85% using BEEAA calibration curve as the reference substance for those metabolites detected that did not have reference substances available. (The latter is considered closest in terms of functional groups and molecular size). The laboratory consider recovery above 80% to be essentially complete.

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
The results described here are the for the total metabolites collected over the 48 hour observation period. Most of the expected metabolites were seen, although the acetic acid derivative of TEGBE was the main one. Unchanged TEGBE was only 0.2%. No conjugates were seen. A substantial number of metabolites were seen that can be attributed to oxidation of the butyl chain; collectively, these account for 5-15% of the total metabolites. A summary of the main metabolite percentages (those expected) is:

- BEEAA: 43.2 % (4.1)
- BEAA: 4.7% (0.3)
- TEG: 7.8% (0.8)
- DEG: 2.6 % (0.2)
- BAA: 4.3 % (0.5)
- TEGBE: 0.2% (0.1)

SD shown in brackets.
>98% was excreted in the first 24 hours.

The following metabolites were also detected. The figures shown were based on the calibration curve for BEEAA:

- HEEAA: 2.7% (0.2).
- HEAA: 5.5% (0.5)
- OTEGBE: 0.8% (0.1)
- OBEEAA: 4.8% (1.2)
- HBEEAA: 6.6% (1.4)
- HTEGBE: 1.8% (0.4)
- CMEHNA: 0.3% (0.1%)

For the assignment of the structures to the abbreviations, see the attachments to this record. Abbreviations are as follows:

HEAA: 2-(2-hydroxyethoxy)acetic acid
HEEAA: 2-(2-(2-hydroxyethoxy)ethoxy)acetic acid
HEAA: 2-(2-hydroxyethoxy)acetic acid
CMEHBA: 4-(2-(carboxymethoxy)ethoxy)-2-hydroxybutanoic acid
OTEGBE: 4-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)buta-2-one
OBEEAA: 2-(2-(2-(3-oxobutoxy)ethoxy)ethoxy)acetic acid
HBEEAA: 2-(2-(2-(3-hydroxybutoxy)ethoxy)ethoxy)acetic acid
HTEGBE: 4-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)buta-2-ol

Any other information on results incl. tables

Results for 0 -24 and 24 -48 hour collection periods combined.

The tables below show the amounts collected over the two different time periods (average of three animals). The figures for the substances for which calibration curves were not available are based on the lower figures from using TEGBE as the reference substance:

Time period

0 – 24hr

24 – 48hr

BEEAA

42.3%

1.0%

BAA

4.2%

0.1%

DEG

2.5%

0.1%

HEEAA

2.7%

0.1%

TEGBE

0.2%

n.d.

 TEG  7.7%  0.1%
 BEAA  4.6%  0.1%
 OTEGBE  0.8%  <0.1%
 OBEEAA  4.8%  0.1%
 HTEGBE  1.8%  0.04%
 Sulphate  <0.1%  n.d.
 HEAA  5.5%  0.1%
 CMEHBA  0.6%  0.1%

n.d.=not detected

Applicant's summary and conclusion

Conclusions:
TEGBE is eliminated >98% within 24 hours in the urine with metabolism to produce 2-(2-(2-butoxyethoxy)ethoxy)acetic acid accounting for 50-60% of the excreted metabolites (either as the metabolite itself or further metabolites of it.) About 4% of the dose is metabolised to butoxyacetic acid. Metabolites are also produced through cleavage of the ether backbone and also through oxidation of the terminal butyl chain.
Executive summary:

In a study to examine the metabolism 2 -(2 -butoxyethoxy)ethanol, SD rats were given a single oral dose of 1000mg/kgbw and the urine collected over two 24 hour periods for analysis for a number of expected metabolites. The main metabolite was 2 -(2 -(2 -butoxyethoxy)ethoxy)acetic acid (BEEAA), which accounted for 43% of the original dose. The metabolite butoxyacetic acid was found, the amount accounting for ~4% of the dose of 2 -(2 -(2 -butoxyethoxy)ethoxy)ethanol given. This demonstrates that oxidation of the hydroxyl function is the main metabolic pathway but lesser amounts of the substance are metabolised by cleavage of the ether linkages and also through oxidation of the butyl chain, although metabolites from the latter route could also be due to further oxidation of BEEAA as the secondary metabolites from these two routes are the same. The study also showed that >98% of the dose of 2 -(2 -(2 -butoxyethoxy)ethoxy)ethanol was eliminated within 24 hours demonstrating rapid metabolism (half life ~4 -5 hours) and no potential for bioaccumulation. Around 85% of the dose was collected in the urine within 48 hours, which is considered within the boundaries of what can be considered complete recovery.