IMMUNOCHEMICAL DETECTION AND IDENTIFICATION OF PROTEIN ADDUCTS OF DICLOFENAC IN THE SMALL-INTESTINE OF RATS - POSSIBLE ROLE IN ALLERGIC REACTIONS

Idiosyncratic adverse drug reactions are unpredictable, target multipl e organ systems, and often become life-threatening events. Although th e causes of idiosyncratic adverse drug reactions are not known in most cases, evidence suggests that they may be mediated through immunologi cal mechanisms, It is generally thought that for a drug to lead to an immune response, it must first become covalently bound to a carrier pr otein. Since most drugs are unreactive, it is usually a reactive metab olite that is expected to form covalent adducts, However, it is not cl ear why more people do not develop immune reactions against drug-prote in adducts. One possible explanation is that orally administered drugs may lead to oral tolerance in most individuals through mechanisms sim ilar to that found with orally administered antigens. However, very li ttle is known regarding the interaction of drugs with gut-associated l ymphoid tissue of the small intestine, where oral tolerance call devel op. As an initial step to test this hypothesis, we have investigated w hether diclofenac, a commonly used nonsteroidal antiinflammatory drug, call lead to protein adducts in rat small intestine. Diclofenac was a dministered to rats by gastric gavage. Immunoblot analysis of small in testine homogenates and isolated enterocyte subcellular fractions with drug-specific antiserum revealed 142-, 130-, 110-, and 55-kDa protein adducts of diclofenac. The 142- and 130-kDa adducts of diclofenac wer e identified as aminopeptidase N (CD13) and sucrase-isomaltase, respec tively, by amino acid sequence analyses and by their reactions with pr otein-specific antibodies. The adducts were localized by immunohistoch emistry and found primarily in the mid-villus and villus-tip enterocyt es and also in the dome overlying Peyer's patches. Similar adducts wer e detected immunochemically in villus-tip enterocytes of animals treat ed with halothane or acetaminophen. These results show that intestinal protein adducts of drugs can be formed in gut-associated lymphoid tis sue where they may lead to the down-regulation of drug-induced allergi c reactions in many individuals.