Quantification of des-Arg-bradykinin using a chemiluminescence enzyme immunoassay: application to its kinetic profile during plasma activation

There is a renewed interest in the kininase I pathway of kinin metabolism, because des-Arg⁹-bradykinin (des-Arg⁹-BK) and des-Arg¹⁰-Lys-BK are selective and potent agonists of the B₁ receptors, that are apparently upregulated by tissue injury. We have developed a polyclonal rabbit antiserum against des-Arg¹⁰-Lys-BK. In a radioimmunoassay for des-Arg¹⁰-Lys-BK, this antiserum exhibited high specificity. Notably, native kinins with the C-terminal Arg residue, bradykinin (BK) and Lys-BK, did not cross-react to a significant extent, whereas des-Arg⁹-BK and digoxygenin (DIG)-des-Arg⁹-BK exhibited a complete cross-reactivity. The antibodies were used to set up a sensitive chemiluminescence enzyme immunoassay (CLEIA) using the DIG-anti-DIG system as intermediate for the revelation of the immune complexes. The detection limit and the half-maximal saturation concentration for des-Arg⁹-BK were 27 and 1530 fmol/ml respectively. This assay, as well as another for BK quantification, have been applied in vitro to rabbit plasma activated by kaolin. The conversion of BK into des-Arg⁹-BK was generally efficient, and the persistence and concentration of both peptides were increased in the presence of enalaprilat an inhibitor of the angiotensin converting enzyme (ACEI). Rabbits treated with bacterial lipopolysaccharide exhibited and increase of plasma immunoreactive des-Arg⁹-BK that was potentiated in animals also treated with ACEI. This CLEIA for des-Arg⁹-BK is a new analytical tool applicable to analyze of the kininase I metabolites of kinins in vitro and in vivo. Measurements of des-Arg⁹-BK may be useful indicators of the kallikrein-kinin system activation.