A Novel Chemically-Modied Curcumin 2.24: Short-term Systemic Treatment for Natural Periodontitis in Dogs

Chronic periodontitis, a severe periodontal inammatory disease, is initiated by the anaerobic microbial biolm, however the tissue-breakdown is predominantly mediated by the host-response. The pathogenesis mediated by the latter is characterized by the generation of inammatory mediators (e.g., cytokines), and the production of collagenolytic and tissue-destructive enzymes (especially the matrix metalloproteinases, MMPs) causing connective tissue and bone destruction. These biochemical changes, such as over-production of MMP-9, might be detected in the very-early stage of this disease/inammatory process, even before apparent clinical manifestations. Interestingly, our pilot study of a short-term/1-month therapy of CMC2.24 (a novel chemically-modied curcumin) in the beagle dogs with naturally-occurring periodontitis indicated that, it did appear to signicantly reduce both pro- and activated-MMP-9 in peripheral blood, compared to placebo group at early stage (1 month), prior to apparent clinical improvement at late stage (3 months). And therefore, MMP-9 may serve as an early and sensitive biomarker that can precede and predict future clinical changes in disease severity and response to treatment which we observed in our long-term study in this dog model of natural periodontitis.

improvement at late stage (3 months). And therefore, MMP-9 may serve as an early and sensitive biomarker that can precede and predict future clinical changes in disease severity and response to treatment which we observed in our long-term study in this dog model of natural periodontitis.

Main Text
Deng et al (1) recently proposed a newer therapeutic strategy to treat naturally-occurring periodontitis (NOP) in beagle dogs, involving oral/systemic administration of a novel chemically-modi ed curcumin (CMC2.24; a phenylaminocarbonyl curcumin), for 3-months, as a host-response modulator. This pleiotropic therapy, based on a well-known natural product, was designed to reduce pathologic in ammatory/collagenolysis in oral and other diseases, and includes enhanced resolution of in ammation and inhibition of bone loss. In the current study, we determined whether shorter-term therapy with this novel compound, for 1-month, as an adjunct to mechanical debridement, could be effective in reducing NOP in beagles, an animal model with characteristics similar to human periodontitis.
We also determined whether biochemical changes, in in ammatory mediators and tissue-destructive matrix metalloproteinases (MMPs), are affected by CMC2.24 treatment before clinical changes become apparent.
Interestingly, our results indicated that a short-term/1-month protocol, although it did not result in obvious clinical improvement at early stage, did appear to reduce both pro-and activated-MMP-9 in peripheral blood, which might serve as early and sensitive biomarkers that precede and predict future clinical changes in oral (and other) in ammatory diseases.
In brief, although a 1-month CMC2.24 treatment produced no detectable effect on in ammatory cytokines [e.g., Interleukin-1 beta (IL-1β), Interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α): which were affected with longer-term/3-momth therapy (1)) in the GCF and circulation of these dogs with NOP, an signi cant effect of CMC2.24 on both pro-and activated-MMP-9 was observed in the peripheral blood ( Fig. 1). At baseline, the level of activated-MMP-9 in CMC2.24-treated group was 100% greater/higher (p < 0.05) than in the placebo-group. However, after 1-month therapy, although the activated-MMP-9 in the placebo-group remained unchanged, the dogs treated with CMC2.24 showed a signi cant (p < 0.05) 50% reduction of activated-MMP-9 down to the unchanged levels in placebo-group. In addition, the total-and pro-MMP-9 values in the CMC2.24-treated group were also signi cantly reduced; in contrast, their baseline values were identical to placebo. These data suggest a possible protection by this novel curcuminoid, early-on in the disease/in ammatory process. The reduction of activated-MMP-9 can be partially due to the decreased levels of total-MMP-9, or this compound promotes the EXCESSIVE degradation of pro-MMP-9 by proteinases (e.g., trypsin), during the activation process, resulting in enzymatically-inactive small molecular weight fragments. In fact, this mechanism had been proposed previously by us to explain the loss of collagenolytic activity when pro-collagenase (pro-MMP-8) and pro-gelatinase (pro-MMP-9) were activated by pre-incubation with trypsin in the presence of doxycycline (due to Ca 2+ /Zn 2+ binding by this tetracycline).(2) This novel mechanism was also described by Smith et al (3,4) who stated that "doxycycline disrupts the hemopexin-like or catalytic domain of collagenase, and alters the conformation of pro-collagenase or collagenase by binding enzyme-associated Ca 2+ , resulting in the MMPs becoming more susceptible to proteolysis and leading to irreversible loss of enzyme protein." Since CMC2.24 has a cation-binding site similar to (and more potent than) the tetracyclines, a polyenolic assembly, it may exhibit a similar mechanism of disrupting the conformation of MMP-9, thus rendering this MMP susceptible to degradation to small-inactive fragments. Future experiments are needed to validate this proposed mechanism.
It's worth noting that studies have indicated that MMP-9 helps mediate connective tissue breakdown and alveolar bone loss during periodontitis.(5-8) Thus, treatment with MMP-inhibitors may effectively suppress tissue breakdown, and decrease severity of periodontitis, as well as other chronic in ammatory diseases such as diabetes, rheumatoid arthritis and osteoporosis.(2) Previously, we mentioned that MMPs have been found to degrade the insulin receptor which would be expected to suppress normal glucose metabolism/control. (5,(9)(10)(11)(12)(13) Another possible mechanism of action of MMP-inhibitors is pHdependent. During the MMP-8 activation process either with APMA or trypsin, when doxycycline was added, the activated-MMP-8 was excessively degraded into smaller-molecular weight inactive fragments (< 30 kDa). (2,14) Thus, the reduced level of activated-MMP-9 in this 1-month study by CMC2.24 could be explained (at least in part) by this fragmentation theory; longer-term therapy with CMC2.24 could then result in additional biochemical as well as clinical improvements.

Summary
In conclusion, this preliminary 1-month study indicates that orally-administered CMC2.24 is a rapidly effective and potent inhibitor of host-derived MMPs and that this early effect, with longer periods of

Consent for publication
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Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.