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Skin sensitisation

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Administrative data

skin sensitisation: in vivo (LLNA)
Type of information:
experimental study
Adequacy of study:
weight of evidence
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well documented publication which meets basic scientific principles.

Data source

Reference Type:
Identification of Metal Allergens in the Local Lymph Node Assay
Basketter, D.A., Lea, L.J., Cooper, K.J., Ryan, C.A., Gerberick, G.F., Dearman, R.J., Kimber, I.
Bibliographic source:
American Journal of Contact Dermatitis, Vol 10, No 4 (December), 1999: pp 207-212

Materials and methods

Test guideline
according to guideline
OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)
GLP compliance:
not specified
Type of study:
mouse local lymph node assay (LLNA)

Test material

Constituent 1
Chemical structure
Reference substance name:
Copper dichloride
EC Number:
EC Name:
Copper dichloride
Cas Number:
Molecular formula:
copper(2+) dichloride
Constituent 2
Reference substance name:
Copper (II) chloride
Copper (II) chloride
Details on test material:
- Name of test material (as cited in study report): Copper (II) chloride
- Substance type: inorganic salt
- Physical state: aqueous solution
- Analytical purity: > 99% (Aldrich, Gillingham, UK)

In vivo test system

Test animals

not specified
Details on test animals and environmental conditions:
- Source: Harlan Olac, Bicester, United Kingdom
- Age at study initiation: 7-12 weeks

Study design: in vivo (LLNA)

dimethyl sulphoxide
1.0, 2.5 and 5.0%
No. of animals per dose:
Positive control substance(s):
other: In these investigations, the LLNA was used to determine the skin sensitization potential of 13 metal salts, 8 of which were considered to possess a significant ability to sensitize man, whereas the remaining 5 were judged to lack such potential.
A substance was regarded as a skin sensitizer if, at any test concentration, the proliferation in treated lymph nodes was threefold or greater than that in the concurrent vehicle treated controls.

Results and discussion

Positive control results:
Of the 13 metals considered here, 8 (Au, Be, Co, Cr, Hg, Ni, Pt, and Sn) were judged to possess significant ability to cause ACD. Nickel showed evidence of a positive dose-response trend, but could not be tested at higher application concentrations to determine whether it might reach a threshold positive level. In the LLNA, 7 of these 8 sensitizing metals were identified correctly, with nickel being the only allergen that was missed. At first sight, this might seem to be an important predictive error, because, as mentioned above, nickel is a very frequent cause of ACD in humans.

In vivo (LLNA)

Remarks on result:
other: see Remark
Copper was found, at 1 or more test concentrations, to stimulate lymph node cell proliferation at least threefold greater than that observed in concurrent vehicle-treated control, although in this series of experiments the substance was not found to display convincing dose-responses. Stimulation index (SI) was as follows: 1 % : 8.1; 2.5 %: 13.8; 5.0 %: 13.6% Copper elicited a marked proliferative response (SI > 5). However, it caused substantial local adverse effects, with necrosis at the higher test concentrations. Therefore, Copper was not considered to possess significant ability to sensitize the skin. When compared with the classification that was based on substantial human experience, the LLNA result for copper in this test was considered to be false positive.

Applicant's summary and conclusion

Interpretation of results:
not sensitising
Cu was not considered to possess, to any significant degree, the ability to cause skin sensitization in humans, and, thus, would not be classified and labeled as sensitizer.
Executive summary:

Among the metals tested, 5 metals evaluated (Al, Cu, Mn, Pb, and Zn) were not considered to possess, to any significant degree, the ability to cause skin sensitization in humans, and, thus, would not be classified and labeled as sensitizers. In the present LLNA, 4 of the 5 were correctly identified, the false positive being Cu. This material is a very rare human skin sensitizer, and it would not be expected to yield positive results in a hazard identification method such as the LLNA. However, it was noted that at the concentrations used, the copper (II) chloride salt in dimethyl sulfoxide (DMSO) was extremely irritant, and this may have contributed to relatively high stimulation indices observed. Although it is clear that, in this case, Cu is a true false positive (the stimulation indices obtained are higher than seen with the significant skin irritant, sodium dodecyl sulfate, which at most are typically in the range of 4 to 5) the data obtained nevertheless emphasize the need for scientific evaluation of the results of skin sensitization testing rather than prescriptive evaluation in terms of a simple regulatory model.

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