Allergenicity and cross-reactivity of naphthenic acid and its metallic salts in experimental animals.

ABSTRACT

The allergenicity and the cross-reactivity of naphthenic acid (NA) and its metallic salts were evaluated in experimental animals. In the guinea pig maximization test, sensitizing skin reactions were observed with cobalt naphthenate (CoN), zinc naphthenate (ZnN) and NA, but not with copper naphthenate, with CoN being the most potent sensitizer. Animals sensitized with 1 naphthenic compound cross-reacted to the other 3 as well. Furthermore, animals in the CoN-sensitized group reacted to the relevant metallic salt cobalt chloride (CoCl2). A dose-response study using the CoN-sensitized group showed that the concentration of CoCl2 required to elicit a skin reaction of similar extent in comparison with CoN was more than 10 times higher, when skin-reaction scores were compared on the basis of cobalt content. In the local lymph node assay, significant increases in stimulation index values without skin irritation were observed with CoN and ZnN, where the former was more potent than the latter. Although CoN is a reported skin sensitizer, this study showed that skin allergenicity of naphthenic compounds is not restricted solely to CoN. In addition, the results suggest the main antigenic determinant of naphthenic compounds to be the structure of NA, even though metal moieties modulate their allergenicity.