2-(propyloxy)ethanol

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1998

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The study methodology followed was equivalent or similar to OECD TG 417 and was conducted in accordance with the Principles of GLP and the report contains sufficient information to permit a meaningful evaluation of study results

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1998

Report date:

1998

Materials and methods

Objective of study:

toxicokinetics

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

Some procedures and activities were not fully documented.Some animal room daily environmental records were not located.The animal records(receipt, environmental and lighting) had a significant number of write-overs and other inappropriate corrections to t

Principles of method if other than guideline:

The current studies were undertaken to determine the rate and extent of metabolism of Ethylene glycol mono propyl ether [14C]-EGPE following either oral, nose-only inhalation, or dermal exposures, and to determine blood kinetic parameters for EGPE and Propoxy acetic acid (PAA) following exposures by these routes as well as following intravenous administration.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

2-(propyloxy)ethanol

EC Number:

220-548-6

EC Name:

2-(propyloxy)ethanol

Cas Number:

2807-30-9

Molecular formula:

C5H12O2

IUPAC Name:

2-(propyloxy)ethanol

Details on test material:

- Name of test material (as cited in study report): Ethylene glycol mono-propyl ether (EGPE)
- Physical state: liquid
- Analytical purity: 99.9% pure EGPE by capillary gas chromatography.
- Impurities (identity and concentrations): not specified
- Lot/batch No.: not specified
- Radiochemical purity (if radiolabelling): The radiochemical purities for both of these preparations were determined initially to be 97.9 % by packed-column gas chromatography with radiochemical flow detection
- Specific activity (if radiolabelling): Two samples of 2-[ethylene-l ,2-I4C]EGPE ([14C]-EGPE) were obtained from Wizard Laboratories (Davis, CA) wii h specific radioactivities of 8.7 mCi/mmole and 15.3 mCi/mmole.
- Locations of the label (if radiolabelling): not specified
- Expiration date of radiochemical substance (if radiolabelling): not specified
- Stability under test conditions: not specified
- Storage condition of test material: not specified
- Other: Unlabeled Propxyacetic acid (PAA) and Butoxyacetic acid (BAA), required as GC standards, were prepared by reaction of the corresponding sodium salts of n-propanol and n-butanol, respectively, with sodium monochloroacetate. The 14C-labeled acid, [1-14C]propoxyacetic acid, was prepared in a manner similar to that described for the unlabeled acids. The labeled starting material, [1-14C]chloroacetic acid (Sigma Chemical Co., St. Louis, MO), was added along with a large excess of solid sodium monochloroacetate to an excess of the sodium propoxide in anhydrous propanol. The final [14C]-PAA had a specific activity of 8.9 µCi/g and was characterized by capillary-column GC/MS. All other chemicals: were of reagent-grade purity.

Radiolabelling:

yes

Remarks:

Two samples of 2-[ethylene-l ,2-I4C]EGPE ([14C]-EGPE) were obtained from Wizard Laboratories (Davis, CA) with specific radioactivities of 8.7 mCi/mmole and 15.3 mCi/mmole.

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River
- Age at study initiation: 6-7 weeks of age
- Weight at study initiation: 193-225 g
- Fasting period before study: Feed was withheld for a period of approximately 6-8 hr before and 4 hr after the oral gavage administration.
- Housing: individually housed
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 8 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72 ± 4°F
- Humidity (%): 50 ± 20%
- Air changes (per hr): not specified
- Photoperiod (hrs dark / hrs light): 12 hours light/dark cycle

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Oral doses were formulated with distilled, deionized water at a concentration such that the nominal doses of 15 mg/kg and 150 mg/kg of EGPE and 100 µCi/kg and were delivered in a volume of 5 ml/kg.

Duration and frequency of treatment / exposure:

single

Doses / concentrations

Remarks:

Doses / Concentrations:
15 mg/kg and 150 mg/kg

No. of animals per sex per dose / concentration:

5-10 animals

Control animals:

no

Positive control reference chemical:

not applicable

Details on study design:

- Dose selection rationale: based on literature and previous studies
- Rationale for animal assignment: randomly assigned

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: expired air, urine, faeces, blood, spleen, liver and kidneys, carcass and cage washes
- Time and frequency of sampling: as described below

METABOLITE CHARACTERISATION STUDIES
- as described below

Statistics:

Metabolism data and blood concentrations were summarized using descriptive statistics including calculations of means and standard deviations.
Pharmacokinetic analyses. All compartmental pharmacokinetic parameters were determined using SAS NLIN (Version 6, SAS Institute Inc., Cary, NC). The concentrations of EGPE and PAA in blood, determined, were analyzed for individual rats at each collection time. Model parameters for individual animals were averaged within studies. Estimates for the area under the blood concentration-time curve, blood half-life, rate of clearance, and rate constants for absorption and elimination were determined following the selection and optimization of an appropriate model. Reported Cmax values for EGPE and PAA following iv or oral administrations are simply the highest measured values for all sampling points. All calculated half-lives are based on simple first-order elimination using calculated elimination rate constants (T1/2 = 0.693/λel).

Results and discussion

Preliminary studies:

not applicable

Toxicokinetic / pharmacokinetic studies

Details on absorption:

as described below

Details on distribution in tissues:

as described below

Details on excretion:

as described below

Toxicokinetic parameters

Toxicokinetic parameters 1

Test no.:

#1

Toxicokinetic parameters:

Cmax: 6.9 ± 3.4 µg/ml (15 mg/kg, oral)

Toxicokinetic parameters 2

Test no.:

#2

Toxicokinetic parameters:

AUC: 2.0 ± 1.4 mg-hr/kg (15 mg/kg, oral)

Toxicokinetic parameters 3

Test no.:

#3

Toxicokinetic parameters:

half-life 1st: 0.13 ± 0.01 hr (15 mg/kg, oral)

Toxicokinetic parameters 4

Test no.:

#4

Toxicokinetic parameters:

other: Clearance Clb: 1.3 ± 1.2 kg/hr (15 mg/kg, oral)

Toxicokinetic parameters 5

Test no.:

#5

Toxicokinetic parameters:

other: Apparent volume of distribution Vd: 0.24 ± 0.24 (15 mg/kg, oral)

Toxicokinetic parameters 6

Test no.:

#6

Toxicokinetic parameters:

Cmax: 34.5 ± 7.0 µg/ml (150 mg/kg, oral)

Toxicokinetic parameters 7

Test no.:

#7

Toxicokinetic parameters:

AUC: Not calculated (150 mg/kg, oral)

Toxicokinetic parameters 8

Test no.:

#8

Toxicokinetic parameters:

half-life 1st: 0.20 ± 0.03 hr (150 mg/kg, oral)

Toxicokinetic parameters 9

Test no.:

#9

Toxicokinetic parameters:

other: Clearance Clb: Not calculated (150 mg/kg, oral)

Toxicokinetic parameters 10

Test no.:

#10

Toxicokinetic parameters:

other: Apparent volume of distribution Vd: Not calculated (150 mg/kg, oral)

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

as described below

Any other information on results incl. tables

Oral Administration of [Ethylene-UL- 14C]-EGPE 15 mg/kg:

Recovery of radioactivity: Male rats received an average dose of 14.14 ± 0.49 mg of EGPE/kg body weight. Based on the amount and the specific activity of the [Ethylene-UL-14C]-EGPE administered (20.509 µCi/g), this corresponded to a mean administered activity of 18.360 ± 1.045 µCi/rat.

 

At the final collection period, mean cumulative recovered radioactivity amounted to 97.0% of the administered dose. The majority of the recovered radioactivity was present in the urine. Elimination was rapid by this route, with 72.2% of the administered dose recovered in urine and cage wash samples by 12 hr and a total of 74.7% by 72 hr. A minor but significant portion of the administered dose was eliminated as 14CO2.

 

Elimination as 14CO2 was rapid and accounted for 12.0% of the dose by 72 hr. Most of the radioactivity eliminated as 14CO2, was recovered during the first 12-hr collection period (9.5 %). An additional 1.3 % of the administered dose was recovered from feces and 0.1 % as volatile organics.

 

Tissue distribution of residual radioactivity: The distribution of residual radioactivity found in selected tissues and carcasses of rats at 72 hr following oral administration of 15 mg/kg of [14C]-EGPE. Recovery values are expressed as both concentration (nrnol/g tissue) or as a percentage of the administered dose. The carcasses contained the greatest amounts (percentages) of total residual radioactivity, accounting for 7.1 % of the administered dose. Lesser amounts of radiolabel were found in the kidneys, livers, and spleens and represented 0.07%, 1.4%, and 0.03%, respectively, for these samples. The livers contained the highest concentration of residual radioactivity, 33.4 nmole/g, with lower concentrations in the carcasses (9.3 nmole/g), kidneys (12.4 nmole/g), and spleens (12.8 nmole/g).

 

Oral Administration of [Ethylene-UL- 14C]-EGPE 150 mg/kg

Recovery of radioactivity. Male rats received an average dose of 143.1 ± 3.6 mg of EGPE/kg body weight. Based on the amount and the specific activity of the [14C]-EGPE administered (20.755 µCi/g), this corresponded to a mean administered activity of

19.30 ± 0.51 µCi/rat.

 

At the final collection period, mean cumulative recovered radioactivity amounted to 95.5 % of the administered dose. The majority of the recovered radioactivity was present in the urine. Elimination was rapid by this route, with 75.8% of the administered dose recovered in urine and cage wash samples by 12 hr and a total of 80.8% by 72 hr. A minor but significant portion of the administered dose was eliminated as 14CO2. 14CO2 accounted for 7.9% of the dose by 72 hr. Elimination as 14CO2 was rapid, as most of the radioactivity eliminated as 14CO2, was recovered during the first 12-hr collection period (6.1 %). An additional 1.1 % of the administered dose was recovered from feces and 0.2% as volatile organics.

Tissue distribution of residual radioactivity: The distribution of residual radiolabel found in selected tissues and carcasses of rats at 72 hr following oral administration of 150 mg/kg of [14C]-EGPE. Recovery values are expressed as either a concentration (nmol/g tissue) or as a percentage of the administered dose. The highest level of total residual radioactivity was found in carcasses and represented 4.4% of the administered dose. Lesser total amounts of radioactivity were found in the kidneys, livers, and spleens and represented 0.07 %, 0.9%, and 0.02%, respectively, for these samples. The livers contained the highest residual concentrations of radioactivity, 207.7 nmol/g, with lesser concentrations in the carcasses (57.8 nmol/g), kidneys (83.9 nmol/g), and spleens (84.1 nmol/g).

Identification and Quantitation of Metabolites:

 

A number of fractions (4 to 6) were isolated by preparative HPLC analysis of urine from rats treated with [14C]-EGPE. A component eluting at approximately 7 min under the preparative chromatographic conditions was presumed to be ethylene glycol (EG). The presence of this metabolite was confirmed by conversion to the dibenzoyl derivative followed by GC/MS quantitation. The acid, PAA, eluted at approximately 20 min and its structure was confirmed by extraction followed by GC/MS analysis. The glycine conjugate of PAA (N-propoxyscetyl glycine) eluted at approximately 29 min and its structure confirmed by conversion to the methyl ester followed by GC/MS analysis. In addition, components intermediate in retention times between that of the acid and the glycine conjugate were tentatively identified as the glucuronide and sulfate conjugates of EGPE by thermospray liquid chromatography/mass spectrometry.

 

Further characterization of urinary metabolites was obtained by chemical and enzymatic treatment of 12-hr, composite urine samples followed by analytical HPLC analysis. Treatment with P-glucuronidase resulted in the complete or nearly complete loss of a component having a retention time of 9.2 to 9.5 min. Comparable increases in levels of EGPE, seen following this β-glucuronidase treatment, confirmed the identity of this component as the glucuronic acid conjugate of EGPE. Treatment with arylsulfatase resulted in a consistent but small reduction in the amount of the glucuronic acid conjugate, presumably due to the presence of β-glucuronidase activity in the arylsulfatase. Thus, the presence of a sulfate conjugate based on sulfatase treatment could not be confirmed by enzymatic treatment. Treatment with 3 N HCl nearly eliminated the glycine conjugate peak (retention time of 9.8 to 10.6 min) with the production of a comparable amount of the acid, PAA. In addition, acid treatment caused the apparent loss of an unidentified component from some samples. This unknown component, present at levels as high as 3.2 % in buffer-treated samples, may be an acid-labile conjugate of either EGPE or PAA.

As many as 7 components were quantified by analytical HPLC analysis of 12-hr urine samples. The acid, PAA, accounted for the majority of the urinary radioactivity (41.6 % to 60.5 %) in these samples. The glycine conjugate accounted for 23.5 % to 37.6% of the radioactivity in urine samples. Lesser amounts of several other metabolites were also quantitated: ethylene glycol accounted for 6.0% to 14.4% of the radioactivity; EGPE –glucuronide accounted for 2.3% to 6.3% of the radioactivity; and EGPE itself was present at levels of 1.67 % to 4.55 % . The parent compound, EGPE, although detected was not consistently present in urine from all animals within any given dose group. In addition, two other unidentified components (Unknowns 1 and 2) were also present at levels of from 1.3 % to 5.0% of the urinary radioactivity.

 

HPLC analysis of 24-hr urine samples: The acid, PAA, and the glycine conjugate were detected in all samples and these accounted for the majority of radioactivity in the urine samples. A component eluting at the retention time of ethylene glycol was also observed in all urine samples except those from rats dosed orally at 150 mg/kg.

 

Pharmacokinetic Analysis:

 

Following iv administration, the parent alcohol was rapidly removed from blood with a calculated first-order elimination rate constant (λel) of 5.57 hr-1 and corresponding half-life of 0.124 hr. The concentration of the acid, PAA, rose rapidly through a peak value at 0.5 hr of 21.5 µg/g (182 nmole/g) and was subsequently eliminated with a first-order rate constant of 0.924 hr-1, corresponding to a half-life in blood of 0.750 hr.

 

Similar to the results obtained in the iv study, a first-order elimination rate constant of 5.17 hr-1 and calculated half-life of 0.134 hr were obtained for EGPE following oral administration of 15 mg/kg. In addition, a rapid uptake phase was seen at this dose level with a calculated λel, of 24.73 hr-1. At the higher dose of 150 mg/kg, uptake and elimination of the parent alcohol was again rapid.

 

A single-compartment elimination rate constant for EGPE of 3.46 hr-1 was calculated, yielding an elimination half-life of 0.20 hr. The less rapid elimination at the higher oral dose level suggests more prolonged absorption or saturation of metabolism and/or elimination. In the case of the acid, PAA, formation and elimination kinetics following oral administration at 15 mg/kg were similar to those found in the iv study. Thus, the acid was eliminated with a first-order rate constant of 0.527 hr-1, corresponding to a half-life of the acid in blood of 1.32 hr. At the higher dose of 150 mg/kg, elimination of the acid appeared saturated. Analyzed concentrations of the acid reached 145 µg/g (1228 nmole/g) at the 2-hr sampling point. It was not possible to fit early (< 6 hr) blood concentrations of the acid in the 150 mg/kg oral study to an exponential uptake and elimination model. However, blood concentrations of the acid obtained following 6 hr were fitted to a single exponential function yielding an elimination rate constant of 0.293 hr-1 and corresponding half-life of 2.37 hr. This elevated half-life may represent saturation of metabolism or renal elimination of the acid.

 

Concentrations of the alcohol in blood increased during the 6-hr exposure reaching a peak level of 1.14 µg/g (10.9 nmole/g) at the 6-hr collection point. Following removal of excess test material at 6 hr, EGPE blood concentrations were too low to afford quantitation. PAA concentrations also rose steadily during the 6-hr exposure reaching a maximum level of 17.0 µg/g (144 nmole/g) at the 6-hr collection. Following the 6-hr exposure, blood concentrations of the acid declined with a first-order elimination rate constant of 0.45 hr-l, corresponding to a half-life of 1.54 hr.

 

In both studies, blood concentrations of the parent alcohol remained low but relatively constant over the duration of the 6-hr exposures. Curve-fitting analysis of EGPE concentrations during the exposures yielded steady-state (blood concentrations (Css) of 0.45 and 3.42 µg/g for the 25 and 175 ppm exposures, respectively. Following the cessation of exposure at 25 ppm, EGPE blood concentrations were too low to afford quantitation. Following the 6-hr exposure at 175 ppm, EGPE blood concentrations declined with a first order elimination rate constant of 5.20 hr-1, corresponding to a half-life of 0.133 hr. Concentrations of PAA increased steadily during the 6-hr exposures. The acid declined in concentration in blood subsequent to exposures with first-order rate constants for the elimination of 0.757 hr-1 and 0.479 hr-1 for the low and high concentrations, respectively. These values correspond to elimination half-lives of 0.92 and 1.45 hr, respectively.

 

Radioactivity in blood of rats dosed with [14C]-EGPE: The majority of 14C-activity is accounted for as EGPE and PAA prior to 2 hr. In later samples of blood, 14C-activity is present which cannot be accounted for as parent compound or acid metabolite. This residual blood activity presumably represents incorporation of label into normal metabolic intermediates, thus leading to complete metabolism to 14CO2. Activity in blood persisted through the end of the study. Similar results were obtained following oral, dermal, or inhalation exposures to [14C]-EGPE

 

Dermal Absorption Rate: A mean dermal absorption rate of 0.73 mg/cm2/hr was calculated based on recovered radioactivity from the dermal absorption and pharmacokinetics study. This yielded a value of 0.792 x 10^-3cm/hr for the permeability coefficient (Kp).

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
In conclusion, EGPE is rapidly absorbed and excreted following either oral or inhalation exposure with a majority of administered dose eliminated within 12 h. Following administration of either 15 or 150 mg/kg [14C]-EGPE 97% and 96%, respectively, of the administered doses were recovered by 72 hr. The majority of activity eliminated (75 or 81 % respectively) was present in urine. The acid metabolite, 2-propoxyacetic acid (PAA), and its glycine conjugate, N-(2-propoxyacetyl)glycine, were the principle urinary metabolites identified regardless of route of administration. The relatively high amounts of residual radioactivity remaining in carcasses after 72 hr, as well as the appearance of significant amounts of radiolabeled CO2 suggests complete conversion of absorbed EGPE to components of intermediary metabolism.

The similar absorption and elimination pharmacokinetics determined for EGPE and its metabolite, PAA, suggest that observed differences in the toxicities of EGPE and EGBE may be due to inherent differences in the acid metabolites. Glycine conjugation offers an additional, alternative elimination pathway in the rat and provides an explanation for the increased elimination rate observed for PAA versus that for BAA. This latter fact may contribute to a decreased toxicity of the acid metabolite observed in the rat. Only in the case of the 150 mg/kg oral dose of EGPE was elimination of the acid, PAA, apparently saturated. In this latter case, blood concentrations of the acid were in excess of 1200 nmole/g. Thus, it is apparent that saturation of urinary elimination of the acid occur between 600 and 1200 nmole/g blood concentrations.

Executive summary:

The absorption, distribution, elimination, metabolism, and pharmacokinetics of ethylene glycol mono-n-propyl ether (EGPE) were determined following either intravenous, oral, dermal, or inhalation exposures of male Sprague-Dawley rats to 2-[ethylene-1,2-14C]-EGPE ([14C]-EGPE).

 

Regardless of the route of administration, absorbed radioactivity was eliminated rapidly with the majority present in 12-hr sample collections. Following oral administration of either 15 or 150 mg/kg [14C]-EGPE, 97% and 96%, respectively, of the administered doses were recovered by 72 hr. In this case, urinary elimination accounted for 75 % to 81 % of the activity recovered. Inhalation exposures at either 25 ppm or 175 ppm [14C]-EGPE resulted in similar patterns of elimination: 80% of the estimated administered dose being eliminated in the urine at 25 ppm and 79% eliminated in the urine at 175 ppm. Less than 27% of dermally administered radioactivity was absorbed during a 6-hr exposure period. The majority (74%) of the administered radioactivity was recovered either as unabsorbed liquid or in washings of the application sites. The acid metabolite, 2-propoxyacetic acid (PAA), and its glycine conjugate, N-(2-propoxyacetyl)glycine, were the principal urinary metabolites identified regardless of route of administration. In the case of 12-h urinary metabolites (oral, dermal, or inhalation exposures), PAA accounted for 42% to 61 % of the total urinary radioactivity and the glycine conjugate an additional 24% to 38%. The formation of ethylene glycol as a urinary metabolite was confirmed by conversion to the dibenzoyl derivative and separate analysis by GC/MS. Ethylene glycol accounted for up to 14% of the radioactivity present in urine regardless of route of administration. Glucuronidase treatment of urine (all routes of administration) revealed the presence of the glucuronide of EGPE at levels of 2% to 6 % of the recovered radioactivity. The half-lives for the first-order elimination of EGPE and PAA from rat blood were 0.12 and 0.75 hr, respectively (iv administration). The apparent volume of distribution and clearance rat(for EGPE were 98.7 % and 1.3 kg/hr, respectively, following iv administration. Oral administration of EGPE at 15 mg/kg yielded similar pharmacokinetic parameters. At an oral dose of 150 mg/kg, the parent alcohol had an elimination half-life of 0.20 hr, suggesting saturation of metabolism or excretion processes. Elimination of the acid, PAA, was less rapid than that of the parent alcohol but displayed first-order elimination kinetics in all cases except following the high oral dose. In this latter case, elimination of the acid appeared to be saturated. Feedback inhibition of metabolism by the acid is a possible explanation for the effects seen at the high oral dose. Given the similarity of pharmacokinetic parameters for EGPE compared with EGBE, differences in the rodent toxicities of these two materials may reflect inherent differences in toxicity of the primary metabolites, PAA and BAA. However, increased elimination of PAA as the glycine conjugate may provide an alternative explanation for thr: observed differences. In conclusion, as with other similar glycol ethers, EGPE is rapidly absorbed and eliminated in the male rat following either iv, oral, or inhalation exposures Similar patterns of metabolite excretion are observed regardless of route of administration. Dermal absorption of EGPE is moderately rapid with subsequent elimination by this route displaying a pattern of metabolites similar to other routes of administration.