Fionnuala T. Lundy
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osteoclasts and has a key role in degrading bone matrix molecules. Cathepsin K levels have
been shown to be increased in GCF from periodontitis patients (Mogi and Otogoto, 2007)
however cathepsin-K was not associated significantly with clinical measurements of disease
severity or inflammation indicating that more research on this important cathepsin is required
to clarify its biomarker potential. GCF cathepsin G levels (determined by ELISA) showed
significant correlation with measured clinical parameters of disease such as GCF volume,
gingival index and probing depth, although cathepsin G activity in GCF did not correlate in
the same way (Kunimatsu et al., 1995).
MMPs
Matrix metalloproteinases (MMPs) are zinc-dependent host endoproteinases derived
predominantly from PMNs during acute stages of periodontal disease. MMPs are responsible
for both tissue degradation and remodelling. As periodontal disease progresses gingival and
periodontal ligament collagens are degraded by host cell-derived MMPs. MMP-8, also
referred to as collagenase-2 is the most prevalent MMP in diseased periodontal tissue and
GCF and has a key role in degrading the triple helical structures of types I, II, and III
collagens found in alveolar bone (Birkedal-Hansen, 1993). In addition to release from PMNs,
mesenchymal cells, such as human gingival and periodontal ligament fibroblasts and
chondrocytes produce MMP-8 (Chubinskaya et al., 1996). Opinion is divided in terms of the
potential usefulness of MMP-8 as a biomarker of disease. Elevated MMP-8 levels have been
observed in GCF (Ingman et al., 1996) and saliva (Ingman et al., 1996; Rai et al., 2008) of
periodontitis patients. However no significant differences in GCF MMP-8 levels between
healthy and periodontitis subjects were observed using a checkerboard immunoblotting
technique (Teles et al., 2009b). Further studies are required to evaluate MMP-8 either alone
or in conjunction with other biomarkers to predict the risk of future disease occurrence and to
monitor treatment interventions. Of the other family members, MMP-2, MMP-3 and MMP-9,
have also been determined in saliva of periodontitis patients (Ingman et al., 1996). However
given the abundance of MMP-8, less emphasis has been placed on the other MMP family
members as potential biomarkers of disease.
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