Biomarkers of Periodontal Disease: Past, Present and Future Challenges
101
inflammation (Waddington et al., 1998) or by down-regulated decorin expression by
fibroblasts. Degradation products originating from the active destruction of the alveolar bone
could prove to be effective biomarkers for active destruction of alveolar bone if robust assays
could be developed for their determination.
Further work on ECM degradation products has been possible as a result of increasingly
sophisticated ‗omic‘ technologies. Metabolomics, the systematic study of the unique chemical
fingerprints that specific cellular processes leave behind, is a powerful tool for biomarker
discovery in bodily fluids including GCF. It represents an unbiased approach to studying the
cellular metabolites of the host pathogen interaction in periodontal disease. Metabolomic
profiling of GCF has yielded over 200 metabolites with altered levels associated with
periodontal disease status (Barnes et al., 2009). Some of these metabolites, including
representatives of the purine degradation pathway (a major biochemical source for reactive
oxygen species production), were significantly accelerated at disease sites and responded to a
triclosan-containing dentifrice in a 6-week clinical study (Barnes et al., 2010). Four of the
markers, inosine, lysine, putrescine, and xanthine, could be very sensitive indicators for
periodontal status and should be investigated further as putative biomarkers.
Biomarkers
of Bone Turnover
Alveolar bone loss is a key discriminator between gingivitis and periodontitis and
remains an important area for biomarker discovery.
Alkaline Phosphatise (ALP)
ALP is released from PMNs during the inflammatory response (McCulloch, 1994), from
osteoblasts during bone formation (Christenson, 1997) and from periodontal ligament
fibroblastsduring periodontal regeneration (Groenveld et al., 1997). ALP activity in GCF is
thought to reflect periodontal recurrent inflammation or healing phases in chronic
periodontitis patients (Chapple et al., 1999). GCF ALP activity has been
proposed as a marker
of successful treatment in chronic periodontitis since this activity was shown to decrease as
early as 15 days following scaling and root planning and (Perinetti et al., 2008).
Osteocalcin
Osteocalcin is a small, noncollagenous, highly conserved, secreted protein that is
associated with the mineralized matrix of bone. Elevated serum levels of osteocalcin have
been found during periods of rapid bone turnover, such as during fracture repair. Studies have
shown that GCF osteocalcin levels alone are unable to discriminate between active and
inactive sites (Nakashima et al., 1996).
Osteopontin
Osteopontin is a single-chain polypeptide with a molecular weight of approximately
32,600 daltons. It is produced by both osteoblasts and osteoclasts, and as a result has a role in
both bone maturation/mineralization as well as bone resorption. Osteopontin has been shown
to correlate with clinical measures of disease (Kido et al., 2001). Further research should be
directed to determining osteopontin‘s potential as a biomarker of disease progression.
Fionnuala T. Lundy
102
Osteonectin
Osteonectin is a 32,000 dalton bone-specific protein that binds selectively to both
hydroxyapatite and collagen, and has been implicated in the early phases of tissue
mineralization. In a cross-sectional study of osteonectin in GCF, osteonectin levels appeared
to be a sensitive marker for detection of periodontal disease status (Bowers et al., 1989).
Pyridinoline Cross-Linked Carboxyterminal Telopeptide of Type I Collagen
(ICTP)
Following the synthesis of procollagen and its release into the ECM, collagen fibrils
undergo a series of posttranslational modifications some of which result in cross-link
formation between the telopeptide regions of type I collagen. Pyridinoline cross-linked
carboxyterminal telopeptide of type I collagen (ICTP) is derived from the carboxyterminal
telopeptide regions of type I collagen cross-linked via pyridinoline or deoxypyridinoline
(Risteli et al., 1993). These ICTP cross links are essential for providing mechanical stability
to the ECM and more importantly are specific to bone and cartilage. ICTP levels in GCF have
been shown to be significantly elevated in periodontitiscompared to gingivitis or
periodontally healthy subjects (Palys et al., 1998). ICTP levels correlated with clinical
parameters and putative periodontal pathogens, demonstrating significant reductions after
periodontal therapy (Palys et al., 1998). Given the specificity of ICTP measurement for bone
resorptionfurther work should be undertaken to develop ICTP measurements as putative
biomarkers for periodontal disease.
Combinations
of Biomarkers
The use of multiple biomarkers has been employed for many years to improve the
diagnostic or prognostic potential of individual markers. Combination of osteocalcin,
collagenase, PGE
2
, alpha-2 macroglobulin, elastase and alkaline phosphatase was shown to
increase diagnostic sensitivity and specificity values to 80 and 91%, respectively
(Offenbacher et al., 1986). With advancements in novel technologies the ease of multiple
biomarker measurements has improved. Multiple combinations of salivary biomarkers
(MMP-8, MMP-9 and osteoprotegerin) combined with red-complex anaerobic periodontal
pathogens (such as
Porphyromonas gingivalis
or
Treponema denticola
) provided highly
accurate predictions of periodontal disease category (Ramseier et al., 2009).
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