Registration Dossier

Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable publication/thesis which meets basic scientific principles

Data source

Reference
Reference Type:
other: Ph.D. thesis
Title:
The Cutaneous Disposition of the Sensitizing Chemicals Hydroxycitronellal and Dinitrochlorobenzene
Author:
Tonge, R. P.
Year:
1995
Bibliographic source:
Thesis submitted for Degree of Philosophy in the University of London

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
Investigation of the absorption and distribution of Hydroxycitronellal through different layers of rat skin using an in vitro flow-though diffusion cell system.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
not specified
Details on test material:
HC:
- Name of test material (as cited in study report): 7-Hydroxycitronellal, Hydroxycitronellal or HC
- Provided by Bush Boake Allen Ltd., London, U.K.
- Purity: 98% ('Pure 55' grade)

[14C]HC:
- Specific activity: 200 kBq/mg, 34 Mbq/mmol (5.4 µCi/mg, 930 µCi/mmol)
- Locations of the label: 3,7-Dimethyl-7-hydroxy[7-14C]ocanal
- Purity: 95.3%
- Purchased from Amersham international, Buckinghamshire, England, U.K.
- Storage condition: -20°C
Radiolabelling:
yes
Remarks:
[14C]HC (hydroxycitronellal)

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Harlan Olac (Oxford, U.K.)
- Weight at study initiation: ca. 200 g
- Diet and Water: ad libitum

Administration / exposure

Type of coverage:
occlusive
Vehicle:
other: no vehicle or ethanol or ethanol:DEP (75:25)
Duration of exposure:
Absorption of HC through rat skin: up to 72 h
Distribution of HC between the different layers of rat skin: up to 6 h
Doses:
4 µL neat HC, 20 µL 20% HC in ethanol or 20 µL 20% HC in ethanol:DEP (mixture of unlabelled and [14C]-labelled HC, each dose contained 1 µCi of radioactivity).
HC neat: 12 mg/cm2
HC 20% in EtOH: 11.16 mg/cm2
HC 20% in EtOH/DEP: 12.59 mg/cm2

No. of animals per group:
see "Any other information on materials and methods incl. tables"
Details on study design:
DOSE PREPARATION
- Method for preparation of dose suspensions: the stock vial of [14C]HC was diluted appropriately with unlabelled HC and the dose solutions were prepared with or without vehicle.
Details on in vitro test system (if applicable):
SKIN PREPARATION
- Type of skin: dorsal region of male F344 rats
- Preparative technique: After shaving with animal clippers, the dorsal skin was cut out with dissecting scissors. The skin was placed uppermost on a plastic dissecting board and circles of skin 1.7 cm in diameter cut using a circular steel wad punch. Excess subcutaneous tissue was removed with scissors
- Storage conditions: The skin circles (0.32 cm2) were kept in a petridish on ice for a few minutes until required.

PRINCIPLES OF ASSAY
- Diffusion cell: 6 -14 teflon diffusion cell system with an extra large conical flask, a fraction collector and a peristaltic pump
- Receptor fluid: HEPES buffered Hank's balanced salt solution (HHBSS), pH 7.4
- Flow-through system: yes; Skin circles were placed epidermis side uppermost in the teflon cells and clamped into the cell with the threaded neck. peristaltic pump primed on maximum speed for approximately 3 - 5 min; after this time the pump was set to 1.5 mL/h for the duration of the experiment.
- Test temperature: The skin surface was maintained at 32°C

Results and discussion

Any other information on results incl. tables

1) The absorption of neat HC through full-thickness rat skin and the effect of the vehicle on the absorption:

  Neat HC 20% HC in Ethanol 20% HC in Ethanol:DEP
  mean % +/- SD mean % +/- SD mean % +/- SD
Mean culmulative % dose absorbed (receptor fluid) 30,34 7,18 28,81 5,36 33,38 4,05
Mean % dose skin (dermis/epidermis/stratum corneum) 33,89 9,47 31,58 5,04 27,67 8,37
Mean % dose swabbed off skin surface 23,2 10,09 15,65 4,91 19,39 9,70
Mean % dose tape-stripped off skin surface 3,65 1,09 3,08 1,22 1,73 0,57
Mean % dose on cell body and cell cap 15,15 5,71 11,78 5,89 7,69 1,42
Mean % dose total recovery 99,41 8,30 87,12 4,52 89,17 3,34
Sum of % dose receptor fluid + skin   64   60   61  
Calculated dose bioavailable* 53   50   52  

Values are from 3 individual experiments with skin from 3 different animals (n=12). skin from a single animal was used for each experiment.

*excluding estimated amount in stratum corneum acc. to ratio of experiment 4:

Mean % dose in receptor fluid + (mean % dose skin *2/3)

For all vehicles examined, no significant differences in the absorption of HC though rat skin were observed.

2) The effect of stratum corneum removal on the absorption of HC through rat skin:

20% HC in Ethanol 20% HC in Ethanol
Full thickness skin Tape-stripped skin
mean % +/- SD mean % +/- SD
Mean culmulative % dose absorbed (receptor fluid) 22,4 12,44 64,34 10,17
Mean % dose skin (dermis/epidermis/stratum corneum) 10,69 4,72 10,39 2,06
Mean % dose swabbed off skin surface 42,3 10,21 21,34 9,98
Mean % dose tape-stripped off skin surface 1,09 0,21 0,45 0,12
Mean % dose on cell body and cell cap 11,05 7,00 4,29 2,37
Mean % dose total recovery 87,5 3,62 100,78 11,89
Sum of % dose receptor fluid + skin   33   75  
Calculated dose bioavailable* 30   n.a.  

Values are from a single experiment with skin from 1 animal (n=3).

*excluding estimated amount in stratum corneum acc. to ratio of experiment 4:

Mean % dose in receptor fluid + (mean % dose skin *2/3)

Compared to full-thickness skin, removal of the stratum corneum resulted in a 3-fold increase in the total amount of HC traversing the skin in 72 hours.

3) The effect of stratum corneum and epidermis removal on the absorption of HC through rat skin:

20% HC in Ethanol 20% HC in Ethanol
  Full thickness skin Dermatomed skin
  mean % +/- SD mean % +/- SD
Mean culmulative % dose absorbed (receptor fluid) 21,56 8,21 80,48 9,79
Mean % dose skin (dermis/epidermis/stratum corneum) 15,46 6,60 9,51 5,96
Mean % dose swabbed off skin surface 41,01 5,90 0,96 0,21
Mean % dose tape-stripped off skin surface 1,5 0,33 0,06 0,02
Mean % dose on cell body and cell cap 7,57 2,75 1 0,57
Mean % dose total recovery 87,53 1,28 92,01 3,13
Sum of % dose receptor fluid + skin   37   90  
Calculated dose bioavailable* 32   n.a.  

Values are from a single experiment with skin from 1 animal (n=3).

*excluding estimated amount in stratum corneum acc. to ratio of experiment 4:

Mean % dose in receptor fluid + (mean % dose skin *2/3)

Compared to full-thickness skin, dermatomed skin (removal of the stratum corneum and epidermis) resulted in a statistically significant 4-fold increase in the total amount of HC traversing the skin in 72 hours.

4) Distribution of HC between different layers of rat skin:

HC in the stratum corneum rised to a max. level of 5.82 +/- 2.12% at 1h after application and remained approximately constant up to 5.63 +/-1.34% of applied dose at 6h (mean +/-SD, n=12).

HC in remaining skin (dermis/epidermis) rised to a max. level of 7.8 +/- 2.06% at 1h after application and remained approximately constant up to 10.78 +/-4.26% of applied dose at 6h (mean +/-SD, n=12).

No data were given for the amounts HC found in other compartments.

According to these data 1/3 of the amounts HC found in skin are estimated to be located in the SC and 2/3 in epidermis and dermis.

Applicant's summary and conclusion