Perioceutics: Matrix metalloproteinase inhibitors as an adjunctive therapy for inflammatory periodontal disease

Matrix Metalloproteinases in Oral Health-Special Attention on MMP-8

Matrix metalloproteinases (MMPs) are a large family of Ca²⁺ and Zn²⁺ dependent proteolytic enzymes, able to cleave the various components of the extracellular matrix (ECM), as well as a range of other regulatory molecules. Several reports have proven the important role of both MMPs and their endogenous inhibitors, TIPMs, in oral health, the initial development of the tooth, and during enamel maturation. In this mini-review, we aim to summarize the literature information about the functions of MMPs, paying more attention to MMP-8 (collagenase-2 or neutrophil collagenase) in the development and progression of periodontitis, peri-implantitis, and carious lesions. We also emphasize the role of particular gene variants in MMP8 as predisposing factors for some oral diseases.

The Role of Matrix Metalloproteinases (MMP-8, MMP-9, MMP-13) in Periodontal and Peri-Implant Pathological Processes

Severe periodontitis, a destructive inflammatory disease of the supporting tissues of the teeth, ranks sixth in terms of global spread, affecting about 11% of the population. Metalloproteinases (MMPs) are extracellular matrix (ECM) macromolecules that are important in cellular development and morphogenesis, and they are capable of activating growth factors in their proximity, cell surface receptors, and adhesion molecules. MMPs are part of a major family of zinc-dependent endopeptidases, and their activity is modulated and regulated by certain inhibitors known as tissue metalloproteinase inhibitors (TIMPs). Because type I collagen is the major component of the periodontal extracellular matrix, special attention has been paid to the role of collagenases, especially MMP-8 and MMP-13 and gelatinases, MMP-2 and MMP-9, in periodontal diseases. In fact, MMP-8 (or collagenase 2) is currently one of the most promising biomarkers for periodontitis in oral fluids. Among them, salivary MMP-9 has been shown to be a more sensitive marker for periodontal inflammation during orthodontic treatment, which opens new perspectives in reducing periodontal hazards during such treatments. Both MMP-8 and MMP-9 are extremely valuable diagnostic tools in treating periodontitis, and future studies and healthcare policies should focus on implementing more accessible methods of chairside testing in order to reduce the prevalence of this disease.

Identification of single nucleotide pleomorphisms associated with periodontal disease in head and neck cancer irradiation patients by exome sequencing

OBJECTIVE

Periodontal disease (PD) is a common oral complication in patients with head and neck cancer (HNC) undergoing radiation therapy (RT). Our objective was to identify candidate single nucleotide polymorphisms (SNPs) associated with PD in radiation-treated patients with HNC.

STUDY DESIGN

DNA was extracted from the saliva of patients with HNC (n = 69) before RT. Clinical attachment loss (CAL) increment greater than 0.2 mm over 24 months after RT was used to define PD progression. After exome sequencing, SNPs associated with post-RT PD progression were identified by using logistic regression and homozygosity analyses. The web tools STRING, the Database for Annotation, Visualization and Integrated Discovery (DAVID), GeneCodis, and Ensembl Variant Effect Predictor were used for functional analysis.

RESULTS

Of the 48 patients with HNC with post-RT PD progression, 24 had no tooth with 5 mm or greater pocket depth before RT, whereas of the 21 patients with HNC without progression, 11 had PD initially. A total of 330 SNPs (249 genes) with over-represented homozygous genotype (98.5% variant allele) were found to be associated with post-RT PD. Sixty of these corresponded to PD-related pathways, including previously identified genes. In patients with HNC with post-RT PD progression, SNPs were found in genes (n = 10) in contrast to those without progression (n = 7).

CONCLUSIONS

The SNPs of collagen genes were identified, potentially defining susceptibility to PD in patients with HNC, and this could be further investigated to characterize PD drug targets.

The Photomodulation Activity of Metformin Against Oral Microbiome

Periodontitis is one of the most common inflammatory diseases of the periodontium, which results in the inflammatory destruction of supporting structures around teeth and is closely associated with the development of systemic disease. Due to a wide variety of antibiotic resistance periodontopathic bacteria, photodynamic therapy (PDT) is a non-invasive adjunctive therapeutic modality that is capable of destroying the whole range of microbes. Metformin (Metf) is an antidiabetic drug, and recent studies suggest that cancer patients who receive Metf and are exposed to radiotherapy and chemotherapy show better outcomes. Our surveys in this review introduce Metf as a potent stimulus in increasing the efficacy of PDT in the induction of destruction in microbial cells.

Zoledronate Impairs Socket Healing after Extraction of Teeth with Experimental Periodontitis

Osteonecrosis of the jaws (ONJ) is a rare but severe complication of antiresorptive medications, such as bisphosphonates, used in the treatment of bone malignancy or osteoporosis. Tooth extraction and dental disease have been strongly associated with ONJ development. Here, we investigated molecular and cellular markers of socket healing after extraction of healthy or teeth with experimental periodontitis (EP) in Wistar-Han rats treated with zoledronic acid (ZA). We included 4 experimental groups: vehicle-treated animals with extraction of healthy teeth or teeth with ligature-induced EP and ZA-treated animals with extraction of healthy teeth or teeth with EP. Animals were pretreated with vehicle or ZA for a week, and EP was induced. Four weeks later, the second maxillary molars were extracted; sockets were allowed to heal for 4 wk; animals were euthanized; and maxillae were isolated. Radiographically, extraction sockets in groups 1, 2, and 3 demonstrated normal healing. Contrary incomplete socket healing was noted after extraction of teeth with EP in ZA-treated rats of group 4. Histologically, persistent inflammation and extensive osteonecrosis were seen in group 4. Disorganization of the collagen network, collagen type III predominance, and lack of collagen fiber insertion in the necrotic bone were associated with impaired socket healing. Cells positive for MMP-9, MMP-13, and α-SMA expression were present at the areas of epithelial invagination and adjacent to osteonecrotic bone. Importantly, human biopsies from patients with ONJ showed similar findings. Our data emphasize the importance of dental disease and tooth extraction in ONJ pathogenesis and help delineate an altered profile in wound-healing markers during ONJ development.

Radiolabeled Selective Matrix Metalloproteinase 13 (MMP-13) Inhibitors: (Radio)Syntheses and in Vitro and First in Vivo Evaluation

The noninvasive imaging of MMP activity in vivo could have a high impact in basic research as well as in clinical applications. This approach can be established using radiolabeled MMP inhibitors (MMPIs) as tracers for the detection of activated MMPs by means of PET. However, the complexity of diseases associated with dysregulated MMP expression necessitates the imaging of distinct MMPs or MMP subgroups to distinguish their individual role in specific diseases. To this end, selective and potent MMP-13 inhibitors based on a N,N'-bis(benzyl)pyrimidine-4,6-dicarboxamide core have been synthesized and successfully radiolabeled with carbon-11, fluorine-18, and gallium-68. Selected radiolabeled candidates were evaluated in vitro and in vivo regarding their pharmacokinetic properties and metabolic stability.

Host modulation therapy: An indispensable part of perioceutics

Traditionally, only antimicrobials have been used as the chemotherapeutic modality for the treatment of periodontitis. Though bacteria are the primary etiologic factors of periodontal diseases, yet the extent and severity of tissue destruction seen in periodontitis is determined by the host immuno-inflammatory response to these bacteria. This increasing awareness and knowledge of the host-microbial interaction in periodontal pathogenesis has presented the opportunity for exploring new therapeutic strategies for periodontitis by means of targeting host response via host-modulating agents. This has lead to the emergence of the field of "Perioceutics" i.e. the use of parmacotherapeutic agents including antimicrobial therapy as well as host modulatory therapy for the management of periodontitis. These host-modulating agents used as an adjunct tip the balance between periodontal health and disease progression in the direction of a healing response. In this article the host-modulating role of various systemically and locally delivered perioceutic agents will be reviewed.

Anti-inflammatory Actions of Adjunctive Tetracyclines and Other Agents in Periodontitis and Associated Comorbidities

The non-antimicrobial properties of tetracyclines such as anti-inflammatory, proanabolic and anti-catabolic actions make them effective pharmaceuticals for the adjunctive management of chronic inflammatory diseases. An over-exuberant inflammatory response to an antigenic trigger in periodontitis and other chronic inflammatory diseases could contribute to an autoimmune element in disease progression. Their adjunctive use in managing periodontitis could have beneficial effects in curbing excessive inflammatory loading from commonly associated comorbidities such as CHD, DM and arthritis. Actions of tetracyclines and their derivatives include interactions with MMPs, tissue inhibitors of MMPs, growth factors and cytokines. They affect the sequence of inflammation with implications on immunomodulation, cell proliferation and angiogenesis; these actions enhance their scope, in treating a range of disease entities. Non-antimicrobial chemically modified tetracyclines (CMTs) sustain their diverse actions in organ systems which include anti-inflammatory, anti-apoptotic, anti-proteolytic actions, inhibition of angiogenesis and tumor metastasis. A spectrum of biological actions in dermatitis, periodontitis, atherosclerosis, diabetes, arthritis, inflammatory bowel disease, malignancy and prevention of bone resorption is particularly relevant to minocycline. Experimental models of ischemia indicate their specific beneficial effects. Parallel molecules with similar functions, improved Zn binding and solubility have been developed for reducing excessive MMP activity. Curbing excessive MMP activity is particularly relevant to periodontitis, and comorbidities addressed here, where specificity is paramount. Unique actions of tetracyclines in a milieu of excessive inflammatory stimuli make them effective therapeutic adjuncts in the management of chronic inflammatory disorders. These beneficial actions of tetracyclines are relevant to the adjunctive management of periodontitis subjects presenting with commonly prevalent comorbidities addressed here.

Matrix metalloproteinases and periodontal diseases

Periodontitis is a chronic inflammatory disorder characterized a complex interaction between periodontopathic bacteria and the host inflammatory response resulting in release of pro-inflammatory cytokines leading to the destruction of periodontal tissues and alveolar bone. One of the important host factors involved in periodontal diseases is matrix metalloproteinases (MMPs), which is responsible for collagen and extracellular matrix (ECM) degradation of the periodontal tissues. MMPs comprise a family of around 25 members broadly categorized into six groups, which are involved in various physiological and pathological conditions. The activities of MMP are generally balanced by endogenous inhibitors such as tissue inhibitors of metalloproteinase (TIMP), and any imbalance between MMP and TIMP levels plays an important role in the disease progression. Assessment of MMP in tissues, GCF, and saliva may serve as an important biomarker in diagnosis of periodontal diseases and also for prognostic follow-up. Targeted therapy aimed at reducing effects of MMP may serve as a useful adjunct for treatment of periodontitis. This review provides an overview of MMP and its role in various physiological and pathological conditions with emphasis on its association with periodontal diseases. A note on its inhibitors and therapeutic importance is also provided.