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Skin sensitisation

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Administrative data

Endpoint:
skin sensitisation: in vivo (LLNA)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2012
Report date:
2012

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)
Deviations:
yes
Remarks:
See further explanation in "Principles of method if orther than guideline" below.
Principles of method if other than guideline:
The study was performed according to OECD 429, however not employing the use of radioactive labelling to measure cell proliferation, as the radioactive method proposed by the OECD guideline led to problems in various EU laboratories: such as (i) practical difficulties/complexity of the test, in particular the radiochemical steps, which sometimes resulted in loss of specimen/activity; this in turn led to variability in the results and to a poor reproducibility and (ii) radiation protection issues. However, the OECD guideline allows other endpoints for assessment of proliferation in form of lymph node cell counts and lymph node weights if justification and appropriate scientific support exist showing the validity of this method.
The alternative method used for the study employing the lymph node weight and lymph node cell count to assess proliferation has been established by an European interlaboratory validation exercise, as described in the two publications by Ehling et al. 2005a and 2005b. This method has the advantage of (i) more simplistic experimental work, (ii) less variability, (iii) better reproducibility, (iv) faster results, (v) reduced costs.
In addition, the acute inflammatory skin reaction is measured by ear weight determination of circular biopsies of the ears and ear thickness measurements on test day 1 and test day 4 to identify skin irritation properties of the test item. It is important to determine if a positive test result is due to the skin irritation potential of the test item or due to its sensitising properties.
Stimulation indices were calculated for the lymph node cell count, lymph node weight, ear weight and ear thickness by dividing the average values per group of the test item treated animals by the vehicle treated ones.
Values above 1.4 (lymph node cell count to identify sensitisation) or 1.1 (ear weight to identify irritation) are considered positive (these values were fixed empirically during the inter-laboratory validation of this method (Ehling et al. 2005a and Ehling et al. 2005b)).
Ehling et al. 2005a: Ehling, G., M. Hecht, A. Heusener, J. Huesler, A. O. Gamer, H. van Loveren, T. Maurer, K. Riecke, L. Ullmann, P. Ulrich, R. Vandebriel, H.-W. Vohr: An European inter-laboratory validation of alternative endpoints of the murine local lymph node assay: First round; Toxicology 212, 60-68 (2005a);
Ehling et al. 2005b: Ehling, G., M. Hecht, A. Heusener, J. Huesler, A. O. Gamer, H. van Loveren, T. Maurer, K. Riecke, L. Ullmann, P. Ulrich, R. Vandebriel, H.-W. Vohr: An European inter-laboratory validation of alternative endpoints of the murine local lymph node assay: 2nd round; Toxicology 212, 69-79 (2005b).

GLP compliance:
yes (incl. QA statement)
Type of study:
mouse local lymph node assay (LLNA)

Test material

Constituent 1
Chemical structure
Reference substance name:
O-isopropyl ethylthiocarbamate
EC Number:
205-517-7
EC Name:
O-isopropyl ethylthiocarbamate
Cas Number:
141-98-0
Molecular formula:
C6H13NOS
IUPAC Name:
N-ethyl(propan-2-yloxy)carbothioamide
Test material form:
other: Liquid
Details on test material:
- Name of test material (as cited in study report): IPETC
- Physical state: Liquid
- Stability under test conditions: Stable
- Storage condition of test material: ambient

In vivo test system

Test animals

Species:
mouse
Strain:
NMRI
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories,Research Models and Services, Germany GmbH, Sandhofer Weg 7, 97633 Sulzfeld, Germany
- Age at study initiation: 9 weeks
- Weight at study initiation: 26-32 g
- Housing: kept individually in MAKROLON cages (type III)
- Diet (e.g. ad libitum): Commercial ssniff® R/M-H V1534 (ssniff Spezialdiäten GmbH, 59494 Soest, Germany; served as food ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: At least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22°C ± 3°C
- Humidity (%): 55% ± 15%
- Air changes (per hr): 12-18 times per hour
- Photoperiod (hrs dark / hrs light): 12 hours light / 12 hours dark

Study design: in vivo (LLNA)

Vehicle:
acetone/olive oil (4:1 v/v)
Remarks:
(3+1 v/v used instead)
Concentration:
5 % active substance
10 % active substance
25 % active substance
No. of animals per dose:
6 animals per dose
Details on study design:
RANGE FINDING TESTS:
- Compound solubility: soluable
- Irritation: not observed
- Lymph node proliferation response:

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method:
- Criteria used to consider a positive response: Stimulation indices were calculated for the lymph node cell count, lymph node weight, ear weight and ear thickness by dividing the average values per group of the test item treated animals by the vehicle treated ones.
Values above 1.4 (lymph node cell count to identify sensitisation) or 1.1 (ear weight to identify irritation) are considered positive (these values were fixed empirically during the inter-laboratory validation of this method (Ehling et al. 2005a and Ehling et al. 2005b)

Ehling et al. 2005a: Ehling, G., M. Hecht, A. Heusener, J. Huesler, A. O. Gamer, H. van Loveren, T. Maurer, K. Riecke, L. Ullmann, P. Ulrich, R. Vandebriel, H.-W. Vohr: An European inter-laboratory validation of alternative endpoints of the murine local lymph node assay: First round; Toxicology 212, 60-68 (2005a);
Ehling et al. 2005b: Ehling, G., M. Hecht, A. Heusener, J. Huesler, A. O. Gamer, H. van Loveren, T. Maurer, K. Riecke, L. Ullmann, P. Ulrich, R. Vandebriel, H.-W. Vohr: An European inter-laboratory validation of alternative endpoints of the murine local lymph node assay: 2nd round; Toxicology 212, 69-79 (2005b).


TREATMENT PREPARATION AND ADMINISTRATION:
Positive control substance(s):
hexyl cinnamic aldehyde (CAS No 101-86-0)
Statistics:
For lymph node weight significance at p ≤ 0.01 is considered positive (U-test according to MANN and WHITNEY). A possible concentration-response-relationship for the lymph node weight in order to determine a possible irritating potential was examined by linear regression analysis employing PEARSON's correlation coefficient. Outliers would have been determined according to the Nalimov test.

Results and discussion

Positive control results:
The positive control group caused the expected increases in lymph node cell count and lymph node weight (statistically significant at p ≤ 0.01). Therefore, the study can be regarded as valid.

In vivo (LLNA)

Results
Key result
Parameter:
SI
Remarks on result:
other: see "Any other information on results incl. tables"

Any other information on results incl. tables

Stimulation indices (SI):

Parameter

Group 1, negative control

Group 2,

5%

Group 3, 10%

Group 4, 25%

Group 5,

positive control

Lymph node cell count

1.000

0.971

1.067

1.139

1.838

Lymph node weight

1.000

0.948

1.172

1.103

1.431

Ear weight

1.000

1.006

1.043

0.933

1.171

Difference of

ear thickness

1.000

1.009

0.966

0.974

1.265

____ significantly different from control at p ≤ 0.01

Applicant's summary and conclusion

Interpretation of results:
not sensitising
Remarks:
Migrated information Criteria used for interpretation of results: EU
Conclusions:
In conclusion, under the present test conditions, IPETC at concentrations of 5%, 10% or 25% (w/w) in acetone/olive oil (3+1, v/v) did not reveal any sensitising properties in the local lymph node assay.