Potency values from the local lymph node assay: application to classification, labelling and risk assessment.

Hundreds of chemicals are contact allergens but there remains a need to identify and characterise accurately skin sensitising hazards. The purpose of this review was fourfold. First, when using the local lymph node assay (LLNA), consider whether an exposure concentration (EC3 value) lower than 100% can be defined and used as a threshold criterion for classification and labelling. Second, is there any reason to revise the recommendation of a previous ECETOC Task Force regarding specific EC3 values used for sub-categorisation of substances based upon potency? Third, what recommendations can be made regarding classification and labelling of preparations under GHS? Finally, consider how to integrate LLNA data into risk assessment and provide a rationale for using concentration responses and corresponding no-effect concentrations. Although skin sensitising chemicals having high EC3 values may represent only relatively low risks to humans, it is not possible currently to define an EC3 value below 100% that would serve as an appropriate threshold for classification and labelling. The conclusion drawn from reviewing the use of distinct categories for characterising contact allergens was that the most appropriate, science-based classification of contact allergens according to potency is one in which four sub-categories are identified: 'extreme', 'strong', 'moderate' and 'weak'. Since draining lymph node cell proliferation is related causally and quantitatively to potency, LLNA EC3 values are recommended for determination of a no expected sensitisation induction level that represents the first step in quantitative risk assessment.

Assessment of the skin sensitization potential of topical medicaments using the local lymph node assay: an interlaboratory evaluation.

The murine local lymph node assay (LLNA) is a method for the predictive identification of chemicals that have a potential to cause skin sensitization. Activity is measured as a function of lymph node cell (LNC) proliferative responses stimulated by topical application of test chemicals. Those chemicals that induce a threefold or greater increase in LNC proliferation compared with concurrent vehicle controls are classified as skin sensitizers. In the present investigations we have evaluated 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 been evaluated: benzoyl peroxide, hydroquinone, penicillin G, streptomycin sulfate, ethylenediamine dihydrochloride, and methyl salicylate. Each chemical was analyzed in the LLNA by all five laboratories. Either the standard LLNA protocol or minor modifications of it were used. Benzoyl peroxide and hydroquinone, both human contact allergens, elicited strong LLNA responses in each laboratory. Penicillin G, another material shown previously to cause allergic contact dermatitis in humans, was also positive in all laboratories. Streptomycin sulfate induced equivocal responses, in that this material provoked a positive LLNA response 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 laboratory), was uniformly negative. However, limited further testing with the free base of ethylene diamine yielded a positive LLNA response when 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 results when performed independently in separate laboratories and indicate also that the LLNA is of value in assessing the skin sensitization potential of topical medicaments.

Pathology considerations for, and subsequent risk assessment of, chemicals identified as immunosuppressive in routine toxicology.

Several proposals have been made with the aim of assisting in the early identification of chemicals with immunotoxic potential. The Organisation for Economic Cooperation and Development is now likely to incorporate enhanced immunopathology into the test guideline for the 28-day rat study, which may be regarded as a Tier I investigation. However, no guidelines have yet been proposed either for how the new data generated will be evaluated, or for how a subsequent risk assessment will be made. In this paper, considerations for the immunopathological assessment of the thymus, spleen, lymph nodes and bone marrow are described, together with comments on haematological and organ weight changes that may be associated with immunotoxicity. Their interpretation will depend on the doses at which changes are manifest, the quantity and quality of the effects observed and the presence and severity of other forms of toxicity. Lastly, risk assessment and the approach to Tier II testing in immunotoxicity is discussed. It is concluded that much of this work must be on a case-by-case basis, but should not in principle differ from the approach adopted for any other type of toxicity identified ina 28-day study.

Respiratory allergy: hazard identification and risk assessment.

Various chemicals and proteins of industrial importance are known to cause respiratory allergy, with occupational asthma being the most important manifestation of the disease. This paper describes clinical syndromes, mechanisms associated with occupational respiratory hypersensitivity, and methods available currently for the prospective identification of potential respiratory allergens. Certain classes of chemicals are commonly associated with occupational respiratory allergy. There is insufficient information, however, to predict respiratory sensitization potential from analysis of structure alone, although reactivity with proteins is likely to be relevant. As yet there exist no fully validated or widely applied predictive methods or internationally harmonized guidelines. The most promising predictive animal methods are the mouse IgE test and guinea pig models. Work in mice has focused upon events occurring during the induction phase of sensitization following primary encounter with the test chemical. In contrast, guinea pig models have been used primarily to identify respiratory allergens (chemicals or proteins) as a function of elicitation reactions induced in previously sensitized animals. Given the possible serious health manifestations of respiratory allergy, early identification of respiratory sensitizers is urgently required. The two methods should, as a priority, be developed further and the production of a detailed protocol for these methods be undertaken to facilitate further validation. Together, this information will allow for two types of risk assessment associated with respiratory allergy: the risk that exposure to a material will (1) induce sensitization in an individual and (2) elicit allergic reactions in a previously sensitized individual.