[A new method for determination of renin inhibitors]

To determine the concentration of renin inhibitors in plasma or other biological fluids, we developed an original approach to the already existing methods, such as HPLC or radio-inhibitor binding and enzyme inhibitor assays. We made an antigen-antibody complex by linking human renin (0.8 nM) to a specific monoclonal antibody fixed to magnetic spheres (3E8-magnogel). A binding technique with 3H-43845 (4 nM) was applied to this preparation to assess the association and dissociation kinetics of SR 43845, a highly potent and specific renin inhibitor. Standard curves were built and CI50 was 0.53 +/- 0.07 nM (n = 5). One of the application of this method is the biochemical characterization of renin inhibitors. We close several various chemical structure renin inhibitors having the inhibiting activity of 0.01 to 10,000 nM (CI50 human PRA). Preliminary results show a good correlation (r = 0.97; n = 12) with those obtained in plasma. In other respects, this new assay was applied to determine SR 43845 plasma concentrations in human pharmacokinetic studies and in primate pharmacological studies. The limit of detection was 0.09 ng/ml. Finally, it is now possible to perform a relationship between plasma concentrations of renin inhibitor and blood pressure changes or other biochemical parameters changes to allow a better understanding to the renin-angiotension system.