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Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
01/2011-03/2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP-study with well described method.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2011

Materials and methods

Objective of study:
metabolism
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
This study was designed to investigate the rate of in vitro hydrolysis of dipropylene glycol methyl ether acetate (DPMA) in rat whole blood and rat liver S9 fraction under physiological conditions and compared with its shorter-chain analog, propylene glycol methyl ether (PMA). Additionally, tissue:plasma partition coefficients of the plasma protein unbound DPMA and its possible metabolite dipropylene glycol methyl ether (DPM) and a shorter-chain analog (PMA) were predicted using quantitative structure activity relationship (QSAR) prediction software for a series of tissues (i.e., brain, heart, lung, muscle, skin, intestine, spleen and bone).
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Details on test material:
- Name of test material (as cited in study report): Dipropylene Glycol Methyl Ether Acetate (DPMA) (CASRN 88917-22-0 for mixture of isomers)
- Physical state: liquid
- Analytical purity: 99.8% by weight :
- Purity test date:
- Lot/batch No.:
Radiolabelling:
no

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals or test system and environmental conditions:
Rat (male Fischer 344) liver S9 fraction was purchased from XenoTech, LLC (Lenexa, KS). Blood from control male Fischer 344 rats was collected at TERC. All related animal handling and sample collection guidelines were followed.

Administration / exposure

Details on exposure:
not applicable
Duration and frequency of treatment / exposure:
not applicable
Doses / concentrations
Remarks:
Doses / Concentrations:
in vitro: 38 and 380 µM
No. of animals per sex per dose / concentration:
not applicable
Positive control reference chemical:
not applicable
Details on study design:
see below
Details on dosing and sampling:
see below
Statistics:
Descriptive statistics (i.e., mean ± standard deviation) are reported. All calculations in the database were conducted using Microsoft Excel (Microsoft Corporation, Redmond, Washington) spreadsheets and databases in full precision mode (15 digits of accuracy). The rate of hydrolysis was determined using first-order disappearance of DPMA and PMA from the incubation mixtures using Microsoft Excel spreadsheets based kinetic program (PKSolver).

Results and discussion

Preliminary studies:
not applicable

Any other information on results incl. tables

In Vitro Hydrolysis of propylene glycol methyl ether acetate (PMA) and dipropylene glycol methyl ether acetate (DPMA)

 

The time-course of disappearance of PMA and DPMA from rat whole blood and rat liver S9 are shown in Figures 1 and 2. The data of the individual incubations are presented in Tables 1 and 2. Hydrolysis of PMA was very rapid, both from the rat whole blood and rat liver S9 fraction, as expected from earlier data (Dow 2001). The rate of disappearance was same for the low (5 ppm) and high (50 ppm) concentrations in both matrices (Tables 1 and 2). The first-order rate constants of disappearance of PMA was 0.04 min-1 at the low and between 0.05-0.06 min-1 at the high concentration. The half life was between 11 and 18 min (Tables 1 and 2; Figures 1 and 2).

 

Hydrolysis of both of the major isomers of DPMA (isomers A and B*) was very rapid in whole blood; in almost all cases faster than the hydrolysis of PMA (only one out of the total of twelve incubations was slower than PMA) (Table 1, Figure 1). The first-order rate constant of disappearance of DPMA-A and DPMA-B from rat whole blood was 0.06-0.07 min-1 (t½ = 10-12 min) and 0.04-0.05 min-1 (t½ = 13-17 min), respectively without any dose dependency (Table 1, Figure 1). This was consistent with the hypothesis that the rate of hydrolysis increases with the increase in the length of the aliphatic chain of glycol acetate. Disappearance of DPMA from the rat liver S9 fractions, however, was slower than the disappearance of PMA (Table 2, Figure 2). The rate constant of disappearance of PMA from the rat liver S9 was 0.04-0.06 min-1 (t½ = 11-18 min) and of both of the DPMA isomers was 0.01-0.02 min-1 (t½ = 40-50 min for DPMA-A and 58-82 min for DPMA-B) (Table 2, Figure 2). The hydrolysis of DPMA in the rat liver S9 fraction was 3- to 5-fold slower than that of PMA. The hydrolysis of PMA was consistent with the earlier report (Dow 2001) in both blood and S9. Hydrolysis of DPMA was comparable with PMA only in the whole blood.

 

In order to better understand the behavior of DPMA in a biological system, tissue to plasma partition coefficients were determined in situ (Table 3) using a modification of the method described by Poulin and Theil (2000). For comparison, the same parameters were also determined for its expected metabolites, DPM and a shorter-chain analog, PMA. The model used log Kow of DPMA, DPM and PMA (which was between 0.05 and 0.6 for all three) and their unbound fraction in the plasma. The Kow of the three compounds was obtained from the Material Safety Data Sheets and plasma binding was estimated in situ using ADME Suite. Consistent with the physicochemical properties of glycol ether and acetate (high water soluble neutral molecules), most of the parent compounds remained free (unbound) in the plasma; plasma protein binding of the three test materials was between 7 and 21% (Table 3). The tissue:plasma partition coefficient of DPMA was ≤0.80 in all tissues (adipose, brain, heart, lung, muscle, skin, spleen) estimated, which was similar to that estimated for DPM and PMA (Table 3). On the basis of the tissue:plasma partition coefficient, DPMA is expected to have short residence time in tissues and no accumulation, similar to the estimated low volume of distribution (Vd = 1.0-1.2 L/kg) of the three compounds in humans (Table 3).

 

On the basis of these results, DPMA is expected to rapidly hydrolyze once absorbed. Higher hydrolysis is expected prior to absorption in cases of oral exposure. The overall rate of hydrolysis of DPMA in biological systems is expected to be similar to that of PMA, which is supported by the similarities in log Kow, predicted plasma protein binding, estimated tissue:plasma partition coefficients and volume of distribution. Although, DPMA was slowly hydrolyzed by the liver S9, the overall impact of this slow hydrolysis will likely be limited due to its low tissue partition coefficient and restriction of the absorbed DPMA mostly to the blood, where it is rapidly hydrolyzed.

 

*DPMA isomer A: 2-(2-methoxy-1-methylethoxy)-1-methylethyl acetate

*DPMA isomer B: 2-(2-methoxypropoxy)-1-methylethyl acetate

Applicant's summary and conclusion

Conclusions:
On the basis of these results, DPMA is expected to rapidly hydrolyze once absorbed. The overall rate of hydrolysis of DPMA in biological systems is expected to be similar to that of PMA, which is supported by the similarities in log Kow, plasma protein binding, tissue:plasma partition coefficients and volume of distribution. Although, DPMA was slowly hydrolyzed by the liver S9, the overall impact of this slow hydrolysis will likely be limited due to its low tissue partition coefficient and restriction of the absorbed DPMA mostly to the blood, where it is rapidly hydrolyzed.
Executive summary:

This study was designed to determine the rate of in vitro hydrolysis of dipropylene glycol methyl ether acetate (DPMA) in rat whole blood and rat liver S9 fraction under physiological conditions and compared with its shorter-chain analog, propylene glycol methyl ether acetate (PMA). Additionally, tissue:plasma partition coefficients of the plasma protein unbound DPMA and its possible metabolite dipropylene glycol methyl ether (DPM) and PMA were estimated in situ for comparison. Two concentrations (38 and 380 µM) of DPMA and PMA were incubated separately with rat whole blood or rat liver S9 fraction under physiological conditions. The rate of hydrolysis was determined by sequential sampling and analysis of the incubation mixture at 0, 1, 2, 5, 10, 15, 30, and 60 minutes for the disappearance of the two major isomers of DPMA or PMA by GC/MS. Tissue to plasma partition coefficient of the unbound fraction of DPMA and PMA was estimated in situ using their physiochemical properties.

 

Hydrolysis of PMA was very rapid, both from the rat whole blood and rat liver S9 fraction without any dose dependency. The first-order rate constants of disappearance of PMA in both matrices was 0.04 min-1 at the low and between 0.05-0.06 min-1 at the high concentration resulting in its disappearance t½ to be between 11 and 18 min. Hydrolysis of both of the major isomers of DPMA was faster (t½ DPMA-A = 10-12 min; DPMA-B = 13-17 min) than PMA in whole blood. However, hydrolysis of DPMA from the rat liver S9 fractions was 3- to 5-fold slower (t½ DPMA-A = 40-50; DPMA-B = 58-82 min) than that of PMA.

 

Consistent with the physiochemical properties of glycol ether and acetate (high water soluble neutral molecules), plasma binding was estimated to be only 7-21%, which resulted in the tissue:plasma partition coefficient of ≤0.80 in all tissues for DPMA, DPM and PMA. Similarly, all three test materials had low volume of distribution (Vd = 1.0-1.2 L/kg).

On the basis of these results, DPMA is expected to rapidly hydrolyze once absorbed. The overall rate of hydrolysis of DPMA in biological systems is expected to be similar to that of PMA, which is supported by the similarities in log Kow, plasma protein binding, tissue:plasma partition coefficients and volume of distribution. Although, DPMA was slowly hydrolyzed by the liver S9, the overall impact of this slow hydrolysis will likely be limited due to its low tissue partition coefficient and restriction of the absorbed DPMA mostly to the blood, where it is rapidly hydrolyzed.