HAPTEN DESIGN AND DEVELOPMENT OF AN ELISA (ENZYME-LINKED-IMMUNOSORBENT-ASSAY) FOR THE DETECTION OF THE MERCAPTURIC ACID CONJUGATES OF NAPHTHALENE

Measurement of urinary metabolites constitutes a noninvasive method to assess toxic exposure. Naphthalene is a common environmental contaminant showing selective pulmonary toxicity in mice and presumably is involved in development of lung disease in man (Buckpitt, A.R.; Franklin, R.B. Pharmacol. Ther. 1989, 41, 339). A glutathione-based detoxification pathway leads to the formation of the mercapturic acid conjugates [NaphMA 1, (R)-N-acetyl-S-[(1R*,2R*)-1,2-dihydro-1-hydroxy-2-naphthyl]cysteine] and (R)-N-acetyl-S-[(1R*,2R*)-1,2-dihydro-2-hydroxy-1-naphthyl]cysteine] which are excreted in urine. Herein we report the development of an immunoassay for the specific detection of these urinary metabolites. This study confirms the importance of appropriate hapten design and synthesis in controlling the specificity and sensitivity of the immunoassay. Our strategy was to prepare haptens that allow covalent attachment to a carrier protein at a site opposite to the N-acetylcysteine moiety. The antibodies obtained by immunizing six rabbits with these NaphMA derivatives (haptens 13 and 14) have been used for the development of an ELISA (enzyme-linked immunosorbent assay) which detects NaphMA 1 in the range between 100 and 6 pg/mL with an I50 of 29 pg/mL. Its ability to detect these important naphthalene metabolites in human urine is demonstrated.