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

Abstract

Metabolism by peptidases plays an important rôle 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. To characterise the extracellular hydrolysis of CGRP as a mechanism for the selective inactivation of this neuropeptide in GCF from periodontitis sites. Samples of GCF from periodontitis patients and periodontally-healthy subjects were incubated with synthetic human SP, NKA or CGRP. Reaction between the GCF constituents and synthetic peptides was allowed to progress from 0-180 min. Results of neuropeptide metabolism at each time were analysed by matrix-assisted laser desorption/ionisation mass spectrometry. There was no evidence of metabolism of SP, NKA or CGRP by constituents of healthy GCF. Metabolism of synthetic SP and NKA was minimal even after extensive incubation with periodontitis GCF. However, loss of carboxy-terminal amino acids was evident after only 1 min incubation with periodontitis GCF. The pattern of CGRP metabolism, which proceeded from the C-terminus, indicated that the neuropeptide was degraded by a carboxypeptidase. After 180 min, there was extensive carboxypeptidase degradation of CGRP to an 11 amino acid peptide. It is concluded that carboxypeptidase activity in GCF from periodontitis patients is responsible for rapid breakdown of CGRP but not SP or NKA. The rapid action of this carboxypeptidase on the anti-inflammatory neuropeptide CGRP is suggestive of a pathophysiological rôle for the enzyme in selectively degrading CGRP, thereby potentiating periodontal inflammation.