An immunological method for the detection of captopril-protein conjugate

To clarify the mechanism of cytotoxicity induced by captopril (Cp), interactions between tissue protein and Cp were studied by the enzyme-linked immunosorbent assay (ELISA) method. The amide-linked adducts [hemocyanin from keyhole limpet-Cp adduct (KLH-Cp) and poly-L-Lys-Cp adduct (pLys-Cp)] using carbodiimide, and a disulfide-linked adduct [ovalbumin-Cp adduct (OVA-Cp)] were prepared. To determine the formation of the protein-Cp adduct, rabbit antisera against KLH-Cp was employed. The immunoreactivities with pLys-Cp and OVA-Cp against anti KLH-Cp sera were elevated when compared with the unmodified protein. With the inhibition ELISA, this antisera was useful for detecting the Cp disulfide-linked conjugate. In kidney cytosol, a high level of immunoreactivity was observed. Plasma and liver cytosol reactivities were similar, and approximately 40% against kidney cytosol. Thus, a method for the detection of the Cp-protein adduct using ELISA has been established. Formation of the Cp-protein adduct was observed in rat plasma and in liver and kidney cytosol. These findings suggest the possibility that the formation of Cp-protein adduct is partially related to cytotoxicity in liver.