Registration Dossier

Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
30 September 2005 to 16 January 2006
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to generally and/or internationally accepted testing guidelines.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2006
Report Date:
2006

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Qualifier:
according to
Guideline:
other: In Vitro Dermal Absorption Rate Testing of Certain Chemicals of Interest to the Occupational Safety and Health Administration. Feberal Register: April 26, 2004 (Volume 69, No. 80)
Principles of method if other than guideline:
The objective of the current testing was to determine a 10 and 60 minute short-term absorption rate using human cadaver skin mounted in an in vitro diffusion cell model.
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report):dipropylene glycol methyl ether (DPGME)
- Physical state: liquid
- Analytical purity: 100% (COA)
- Impurities (identity and concentrations): none identified
- Isomers composition: 2,2-DPGME [1-(2-methoxy-propoxy)-2-propanol, CAS No. 13429-07-7], 54.45%; 2,1-DPGME [2-(2-methoxy-propoxy)-1-propanol, CAS No. 13588-28-8], 2.83%; 1,2-DPGME [1-(2-methoxy-methylethoxy)-2-propanol, CAS No. 20324-32-7], 40.20%; and 1,1 [2-(2-methoxy-methylethoxy)-1-propanol, CAS No. 55956-21-3], 2.52%
- Purity test date: 14 October 2005 (last date of analysis)
- Lot/batch No.: H27215
- Stability under test conditions: the test substance appeared to be stable under the conditions of the study; no evidence of instability observed
Radiolabelling:
no

Test animals

Species:
human
Strain:
other: not applicable
Sex:
male
Details on test animals and environmental conditions:
Not applicable

Administration / exposure

Type of coverage:
other: static in vitro diffusion cells
Vehicle:
unchanged (no vehicle)
Duration of exposure:
10 and 60 minutes
Doses:
30 microliters/cm^2
No. of animals per group:
Duplicate skin membranes from each of 3 donors
Details on study design:
Dose Formulations and Applications

These studies were designed to measure short-term absorption rates at 10 and 60 min. DPGME was applied neat to all skin surfaces at a constant dose volume of 30 microliters/cm^2; this required a volume of 19.2 microliters based in the exposure area of 0.64 cm^2. Following dose applications, donor chamber openings were occluded with Parafilm. Three groups of in vitro cells were prepared with 4 replicate skin samples in each group. A total of 6 replicate chambers were terminated at each time point.

Terminal Washing Procedure

At termination, either 10 or 60 min, the receptor fluid was removed and placed in glass containers. With donor chambers clamped in-place, the surface of each skin replicate was washed with a 2% solution of Ivory Soap in deionized water followed by a deionized water rinse. The soap wash and rinse for each replicate was collected in glass vials. After washing, the receptor and donor chambers were filled with saline and final membrane integrity measurement using EI was determined. The skin membranes were then removed, placed into glass vials, minced with scissors, and extracted with water.

Gas Chromatic Analysis

Samples of receptor solution, skin wash and rinse samples and skin extracts were analyzed by gas chromatography with flame ionization detection (GC-FID). Aliquots (2 microliter) were analyzed using a Hewlett Packard Model 6890 gas chromatograph equipped with a HP Wax, 30 m x 0.53 mm x 1.0 micrometer (film thickness) column. Helium was used as the carrier gas. The following instrumental parameters were employed: injector temperature, 250°C; detector temperature, 260°C; oven temperature, 120°C (isothermal); and carrier gas flow, 35 ml/min.

The amount of DPGME applied to each skin replicate was determined by GC-FID analysis of triplicate 19.2 microliter aliquots (representing the actual volume applied to each replicate). Standard solutions of DPGME in saline were prepared ranging in concentration from 0.05 microgram/ml to 0.5 microgram/ml. In this concentration range, detector response was linear. The limit of quantitation (LOQ) for this method was equivalent to the lowest standard, 0.05 microgram/ml. Based on the analysis of quality control samples, method precision was 56-132% and accuracy was 82-133%.
Details on in vitro test system (if applicable):
Human Skin Samples

Samples of human abdominal cadaver skin from 3 donors, collected within 24 h of death, were obtained from the National Disease Research Interchange (NDRI, Philadelphia, PA, USA) and upon receipt were stored frozen at approximately -20°C until prepared for use. In preparation for use, skin samples were thawed at room temperature, the full thickness skin was immersed in 60°C water for approximately 45 s to 2 min, and the epidermis peeled from the dermis. The thickness of representative membranes, containing an intact stratum corneum and epidermis, were measured with a digital micrometer (Mahr Federal Inc., Providence, RI, USA) and ranged from 46 to 63 micrometers. The resulting epidermal skin samples from this procedure were then stored under refrigeration at 1 to 10 °C until readied for use.

Diffusion Cells

Static Franz-type diffusion cells (PermeGear, Inc., Bethlehem, PA, USA) were used for the current study as first described by Franz (1975). Epidermal skin samples were removed from refrigeration and hydrated in 0.9% saline for approximately 15 min. Following hydration, skin membranes were mounted onto the tops of the receptor chambers with the stratum corneum uppermost. Receptor and donor chambers were filled with saline and in vitro cells were clamped in place and heated using a re-circulating water bath to a receptor fluid temperature of 32ºC. The membranes were allowed to equilibrate for 30 min after which the integrity of each membrane was assessed by measurement of electrical impedance (EI) prior to the application of test material. Membranes with measured EI values of >/= 17 k-ohms were considered intact and were retained for use in the study. Saline in the donor and receptor chambers was removed prior to dosing, and the receptor chamber filled with fresh 0.9% saline.

Results and discussion

Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Absorption in different matrices:
Cumulative absorption and absorption rate data are summarized in Table 1. Following the 10-min and 60-min applications, mean values of 1.66 micrograms and 40.6 micrograms of DPGME, respectively, were present in receptor fluids. Significantly more test material was present in the skin samples (stratum corneum plus epidermis), with mean values for the 10-min and 60-min applications of 70.0 micrograms and 105.7 micrograms, respectively. The short-term absorption rates determined in the current study were 658.6 micrograms/cm^2/h and 228.5 micrograms/cm^2/h, respectively, for the 10-min and 60-min exposures. These were calculated based on the total absorbed test material (sum of DPGME in receptor fluid and skin), and normalized to exposure times and exposed skin area (Table1).
Total recovery:
Summarized in Table 2 are total recovery values for DPGME from the 10-min and 60-min exposures. Based on the analysis of replicate aliquots, 29,306 micrograms of DPGME was applied to each skin replicate (based on analysis of replicate mock doses of 19.2 microliters) and total recovery of DPGME was 87.7% ± 17.6% and 88.6% ± 19.3%, respectively, for the 10- and 60-min exposures. As a percentage of applied dose, negligible amounts of DPGME were present in receptor fluids at 10 min (<0.01%). At 60 min, only 0.14% of the applied dose was found in the receptor fluid. The majority of recovered DPGME was found in skin washes, with 87.4% ± 17.5% and 88.1% ± 19.3%, respectively, at the 10-min and 60-min exposures. Skin samples contained 0.24% ± 0.10% and 0.36% ± 0.31% of the applied dose, respectively, at the 10-min and 60-min exposures.

Any other information on results incl. tables

Table 1: Levels of DPGME in receptor fluid and skin, total absorbed DPGME, and calculated absorption rates

Exposure Time

DPGME

in RF

(micrograms)

DPGME

in Skin

(micrograms)

Total Absorbed

RF + Skin

(micrograms)

Absorption Rate

(micrograms/cm2/h)

(min)

Mean

SD

Mean

SD

Mean

SD

Mean

SD

10

1.66

1.52

70.0

28.1

71.7

27.8

658.6

255.9

60

40.6

27.5

105.7

88.3

146.2

77.2

228.5

120.6

Table 2: Recovery of DPGME as a percentage of the applied dose

10 Min

60 Min

Mean

SD

Mean

SD

Receptor Fluid

<0.01

<0.01

0.14

0.09

Skin Wash

87.4

17.5

88.1

19.3

Skin

0.24

0.10

0.36

0.31

Total Recovery

87.7

17.6

88.6

19.3

Applicant's summary and conclusion

Conclusions:
Following a 10-minute exposure to a finite application of DPGME, 1.66 micrograms and 70.0 micrograms of DPGME were detected in the receptor fluid and skin, respectively. This corresponds to a 10-minute absorption rate of 658.6 micrograms/cm^2/h.

Following a 60-minute exposure to a finite application of DPGME, 40.6 and 105.7 micrograms of DPGME were detected in the receptor fluid and skin, respectively. This corresponds to a 60-minute absorption rate of 228.5 micrograms/cm^2/h.