Sensitizing potency of epoxy resin components in the local lymph node assay (LLNA)

Status:

completed 12/2006

Aims:

Owing to their technical properties, epoxy resins are used for a variety of purposes, for example in the construction, metal, turbine, automotive and paints industries. The processing of epoxy resins is increasingly causing cases of allergic contact eczema; both the resins themselves, and reactive thinners and curing components have a sensitizing effect. The EPOX-2002 study conducted by the IVDK (the German Information Network of Departments of Dermatology) systematically examined the incidence of reactions to relevant epoxy resin system components in the skin test on exposed sufferers, i.e. patients with a positive reaction to epoxy resin. Valid findings concerning the sensitizing potency of the individual components are required in order to support manufacturing industry in its search for suitable components with the lowest possible sensitizing potency. Diagnostic surveys on human subjects are of only limited benefit here, since relatively high sensitization quotas may also be caused by the particularly widespread use or high exposure concentrations of the substance concerned.
The local lymph node assay (LLNA) on the mouse constitutes a validated animal model which, in comparison with the older sensitization tests on guinea pigs, permits more objective conclusions regarding the strength of effect. Based upon practical experience, the following twelve common epoxy resin system components were selected for the LLNA: bisphenol A and bisphenol F resin, 1,6-hexanediol diglycidyl ether, p-tert-butyl-phenyl-glycidyl ether, trimethylolpropane triglycidyl ether, alkyl C12-C14 glycidyl ether, m-xylylene diamine and isophorone diamine, dipropylenetriamine, trimethylhexane-1,6-diamine, aminoethylethanolamine and 1,2-diaminocyclohexane.
A further important aspect of the project was the validation of a special variant of the LLNA, which is now in widespread use. The variant presents a lower health risk to the laboratory staff conducting the assay, since it requires no radioactive chemicals.

Activities/Methods:

Prior to the experimental part of the study, data from animal experiments were surveyed and assessed with regard to the acute toxicity, skin irritation and skin sensitizing potential of the substances to be tested. The purpose of these data was to avoid duplicate testing and to facilitate selection of the concentration for the LLNA. Suitable solvents, the suitability for application and the skin irritation potential of the test substance formulations were determined in preliminary tests, and the selected concentration adjusted if appropriate.
Each of the epoxy resin system components was tested in the LLNA at three different concentrations, acetone being employed as the solvent. The test substance formulations were analyzed by gas chromatography and mass spectrometry, and their stability and the correctness of the concentration monitored by a gas-chromatographic analysis over the duration of application. The tests were conducted in accordance with OECD test guideline No. 429 in observance of the OECD good laboratory practice regulations. The OECD test guideline describes the incorporation of radioactively marked thymidine into the lymph node cells as a basis for assessment of the skin-sensitizing potency. At the same time, the parameters of a non-radioactive test variant were determined. In this test variant, the number of cells in the ear lymph nodes was determined.

Results:

The LLNA revealed no pronounced differences in sensitizing potency between the twelve substances tested. All exhibited a moderate to strong sensitizing potency. Indications suggested however that the solvent has a stronger influence upon the test results than was previously supposed. In a follow-up project, tests were therefore conducted with different solvents in order to investigate the extent to which the solvent used may actually be regarded as a disturbance factor.
The results obtained by the "cold" (non-radioactive) and "hot" (radioactive) methods exhibited close correlation, and were forwarded to the European Centre for the Validation of Alternative Methods in Ispra (Italy).

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