Allergenic components in modified and unmodified rosin. Chemical characterization and studies of allergenic activity.

Gäfvert, E. 1994. Allergenic components in modified and unmodified rosin. Chemical characterization and studies of allergenic activity. Acta Dermato-Venereologica. Suppl. 184. 36pp. Uppsala. Unmodified rosin (colophony) is a well-known cause of contact allergy (delayed type hypersensitivity). Rosin is obtained from coniferous trees and consists mainly of diterpenoid resin acids. Most rosin used in technical products is chemically modified. In the common modification of rosin with maleic anhydride, the major product formed is maleopimaric acid (MPA). MPA was identified in experimental sensitization studies as a potent contact allergen. MPA is also formed when rosin is modified with fumaric acid at high temperature and with prolonged heating. The amounts of MPA in technical quality rosins modified with maleic anhydride or fumaric acid might be enough to sensitize individuals handling these rosins. The major product of the modification of rosin with fumaric acid, fumaropimaric acid (FPA), did not elicit any reactions in the animals tested. In another common rosin modification, glycerol esterification, the major product formed was identified as glyceryl triabietate (GTA). In an experimental sensitization study none of the animals reacted to GTA. However, a minor product formed, glyceryl 1-monoabietate (GMA) showed sensitizing capacity. The presence of new contact allergens due to the modification, together with remaining unmodified material, contributes to the risk of developing allergy from contact with these types of rosin. A new main contact allergen in unmodified rosin was identified; 13,14(beta)-epoxyabietic acid. The allergenicity of this epoxide was comparable to that of an earlier identified rosin allergen, 15-hydroperoxyabietic acid (15-HPA). The allergens were detected as their methyl esters. Experimental sensitization and cross-reactivity of oxidation products of resin acids were studied. A pattern of cross-reactivity was observed which indicates that the hydroperoxide of abietic acid (15-HPA) may react to form a complete antigen via two different routes. One route seems to be via the formation of epoxides which then react with skin protein to form the complete antigen, and the other, via radical formation due to cleavage of the peroxide bond. The radical formed may then react with skin protein, so producing the complete antigen. Few other studies have shown results indicating the formation of several antigens from one hapten.