QUANTITATIVE STRUCTURE-ACTIVITY-RELATIONSHIPS FOR SKIN SENSITIZATION POTENTIAL OF URUSHIOL ANALOGS

The relative alkylation index (RAI), a theoretically derived parameter intended to quantify the relative extent of carrier haptenation resul ting from a given dose of a given sensitizer, has previously been succ essfully applied to the analysis of relative sensitization potential a nd dose-response data for a variety of contact allergens which are dir ectly electrophilic. Here the RAI concept is applied to analysis of da ta on compounds related to urushiol (i.e., 3-substituted catechols), t he naturally occurring mixture of allergens responsible for contact al lergy to poison ivy and poison oak. These allergens are believed to ac t as pro-electrophiles, being oxidized to electrophilic orthoquinones in vivo. It is found that the various types of urushiol derivatives fi t the same sort of RAI-sensitization relationships as expected theoret ically and as found previously with direct acting electrophiles. There is evidence that in many cases, the test conditions were such that ov erload effects, whereby the degree of sensitization induced decreases with increasing carrier haptenation, applied. It is also concluded tha t the question as to the relative sensitization potencies of the natur ally occurring urushiols remains open. The commonly held view that wit h these materials, sensitization potential increases with increasing u nsaturation in the 3-hydrocarbyl chain of the 3-hydrocarbyl catechols, is based on evidence that is capable of alternative interpretation.