Labeled substance P as a neuropeptide reporter substance for enzyme activity.

Recently, we developed a bradykinin reporter assay and demonstrated the differing protease activity in Complex Regional Pain Syndrome patients vs. controls. In order to further characterize CRPS pathophysiology, the neuropeptide substance P was evaluated as possible reporter substance, here. It was labeled with a chromophore at the lysine residue and generated two major fragments following incubation with serum (amino acid residues 3-8 and 3-11) which were reproducibly separated by thin-layer chromatography. Dabsylated substance P was shown to be a substrate of angiotensin-converting enzyme. The combination of both bradykinin and substance P reporter substances with specific enzyme inhibitors will shed more light on biochemical pathways in inflammatory processes and pain. Comparative clinical studies are now needed to define the application range of both assays in more detail.