Secretory leukocyte protease inhibitor and its potential interactions with elastase and cathepsin B in gingival crevicular fluid and saliva from patients with chronic periodontitis.

BACKGROUND AND OBJECTIVE: Elastase is carried into the oral cavity by gingival crevicular fluid (GCF) from periodontal lesions. Our study investigated the regulation of elastase activity by secretory leukocyte protease inhibitor (SLPI) and the possible action of another GCF protease on this protective salivary component. MATERIAL AND METHODS: Whole-mouth saliva (WMS), parotid saliva (PS) and GCF were obtained from 19 patients with periodontitis. The concentrations of active elastase and cathepsin B were determined using peptide substrates. SLPI and alpha1-proteinase inhibitor (alpha1PI) concentrations were determined using enzyme-linked immunosorbent assays (ELISAs). The molecular forms of SLPI were examined by immunoblotting. RESULTS: The molar concentrations of elastase, cathepsin B and alpha1PI were higher in GCF than in WMS and especially PS (p <0.0002). The GCF SLPI concentrations were also higher than the WMS SLPI concentrations (p <0.05). All WMS components increased with GCF content, significantly for elastase and SLPI (p <0.002). In GCF, the concentration of alpha1PI was higher than the concentration of SLPI (p <0.0002), while there was no significant difference for WMS. SLPI and elastase levels in GCF and WMS were inversely related (p <0.005). In SLPI immunoblots, PS contained only the intact 14-kDa molecule of SLPI, while WMS also contained an 8-kDa fragment. For WMS there was a positive correlation between SLPI degradation and cathepsin B (p <0.002). Incubation of WMS alone or of PS with GCF in the presence of cysteine proteinase activators caused SLPI immunoreactivity to shift to 8 kDa. CONCLUSION: For GCF, serum-derived alpha1PI is the major elastase inhibitor, but in WMS SLPI probably reduces activity. The inflamed gingivae can be an additional source of SLPI in the oral cavity, but here the molecule is apparently cleaved by GCF cysteine proteinases, such as cathepsin B.