ASSESSMENT OF THE SKIN SENSITIZATION POTENTIAL OF TOPICAL MEDICAMENTSUSING THE LOCAL LYMPH-NODE ASSAY - AN INTERLABORATORY EVALUATION

The murine local lymph node assay (LLNA) is a method for the predictiv e identification of chemicals that have a potential to cause skin sens itization. Activity is measured as a function of lymph node cell (LNC) proliferative responses stimulated by topical application of test che micals. Those chemicals that induce a threefold or greater increase in LNC proliferation compared with concurrent vehicle controls are class ified as skin sensitizers. In the present investigations we have evalu ated further the reliability and accuracy of the LLNA. In the context of an international interlaboratory trial the sensitization potentials of six materials with a history of use in topical medicaments have be en evaluated: benzoyl peroxide, hydroquinone, penicillin G, streptomyc in sulfate, ethylenediamine dihydrochloride, and methyl salicylate. Ea ch chemical was analyzed in the LLNA by all five laboratories. Either the standard LLNA protocol or minor modifications of it were used Benz oyl peroxide and hydroquinone, both human contact allergens, elicited strong LLNA responses in each laboratory. Penicillin G, another materi al shown previously to cause allergic contact dermatitis in humans, wa s also positive in all laboratories. Streptomycin sulfate induced equi vocal responses, in that this material provoked a positive LLNA respon se in only one of the five laboratories, and then only at the highest concentration tested. Ethylenediamine dihydrochloride dissolved in a 3 :1 mixture of acetone with water, or in 4:1 acetone:olive oil (one lab oratory), was uniformly negative. However, limited further testing wit h the free base of ethylene diamine yielded a positive LLNA response w hen applied in acetone:olive oil (AOO). Finally, methyl salicylate, a nonsensitizing skin irritant, was negative at all test concentrations in each laboratory. Collectively these data serve to confirm that the local lymph node assay is sufficiently robust to yield equivalent resu lts when performed independently in separate laboratories and indicate also that the LLNA is oi value in assessing the skin sensitization po tential of topical medicaments.