Carboxypeptidase-mediated metabolism of calcitonin gene-related peptide inhuman gingival crevicular fluid - a role in periodontal inflammation?

Background: Metabolism by peptidases plays an important role in modulating the levels of biologically-active neuropeptides. The metabolism of the anti -inflammatory neuropeptide calcitonin gene-related peptide (GCRP), but not the pro-inflammatory neuropeptides substance P (SP) and neurokinin A (NKA) by components of the gingival crevicular fluid (GCF), could potentiate the inflammatory process in periodontitis. Aims: To characterise the extracellular hydrolysis of CGRP as a mechanism f or the selective inactivation of this neuropeptide in GCF from periodontiti s sites. Methods: Samples of GCF from periodontitis patients and periodontally-healt hy subjects were incubated with synthetic human SP, NKA or CGRP. Reaction b etween the GCF constituents and synthetic peptides was allowed to progress from 0-180 min. Results of neuropeptide metabolism at each time were analys ed by matrix-assisted laser desorption/ionisation mass spectrometry. Results: There was no evidence of metabolism of SP, NKA or CGRP by constitu ents of healthy GCE Metabolism of synthetic SP and NKA was minimal even aft er extensive incubation with periodontitis GCE However, loss of carboxy-ter minal amino acids was evident after only 1 min incubation with periodontiti s CCE The pattern of CGRP metabolism, which proceeded from the C-terminus, indicated that the neuropeptide was degraded by a carboxypeptidase. After 1 80 min, there was extensive carboxypeptidase degradation of CGRP to an 11 a mino acid peptide. Conclusions: It is concluded that carboxypeptidase activity in GCF from per iodontitis patients is responsible for rapid breakdown of CGRP but not SP o r NKA. The rapid action of this carboxypeptidase on the anti-inflammatory n europeptide CGRP is suggestive of a pathophysiological role for the enzyme in selectively degrading CGRP, thereby potentiating periodontal inflammatio n.