Bullet for periodontal disease in future: Chemically modified tetracyclines

Chronic periodontitis is nowadays popularly regarded as Dysbiosis, [1] which causes destruction of tissues rich in collagen like periodontal ligament, alveolar bone and gingival connective tissue. The oral biofilm comprises many periodontal pathogens better regarded as ‘triggers’ in causing chronic periodontitis. Since, not everyone will be affected in the same manner due to periodontal pathogens. Some might not elicit a host response while, the others might have exaggerated response. So, host modulation therapy came into existence to counteract the exaggerated host response. The chemically modified tetracyclines (CMTs) have emerged to inhibit the inflammatory response or to reduce the collagenolytic activity of host. Though a derivative of tetracyclines, it still lacks an antimicrobial action and hence, can be used for periodontitis for longer duration with no adverse effects of gastrointestinal toxicity which parent tetracyclines have.

Role of Chemically Modified Tetracyclines in the Management of Periodontal Diseases: A Review

Researchers have found that Chemically Modified Tetracyclines (CMTs) act through multiple mechanisms, affecting several parameters of osteoclast function and consequently inhibit bone resorption by altering intracellular calcium concentration and interacting with the putative calcium receptor; decreasing ruffled border area; diminishing acid production; diminishing the secretion of lysosomal cysteine proteinases (cathepsins); inducing cell retraction by affecting podosomes; inhibiting osteoclast gelatinase activity; selectively inhibiting osteoclast ontogeny or development; and inducing apoptosis or programmed cell death of osteoclasts. Thus TCs/CMTs, as anti-resorptive drugs, may act similarly to bisphosphonates and primarily affect osteoclast function. Researchers have evaluated the influence of various chemically modified tetracyclines from CMT-1 to CMT-10 on collagenases and gelatinases through in vitro or animal studies and concluded that all the CMTs except CMT-5 inhibited periodontal breakdown through MMP inhibition in the following order of efficacy: CMT-8>CMT-1>CMT-3>CMT-4>CMT-7. Thus the non-antimicrobial actions of the chemically modified analogues of tetracyclines have shown remarkably better mechanisms to those of agents with established anti-inflammatory/antioxidant potential. These findings clarify the multi-faceted actions of tetracyclines which are unique amongst antimicrobials, with therapeutic applications in periodontal and metabolic diseases. Hence, the present review describes the role of chemically modified tetracyclines in the management of periodontal diseases.

Hypothesis

The hypothesis that matrix metalloproteinase (MMP) inhibitors reduce risks of cardiovascular disease in humans is plausible, unproven, and difficult to test, due, in part, to differences in specificity and route of administration. Endogenous tissue inhibitors of metalloproteinases (TIMPs) are tight-binding, protein inhibitors that function in vivo and can be engineered to enhance specificity for desired targets. Nonetheless, TIMPs have been difficult to test, in part, because their secondary functions, including cell growth promotion and angiogenesis, raise concerns about side effects and they cannot be delivered orally. In contrast, doxycycline and other chemically modified tetracyclines are broad-spectrum, reversible MMP inhibitors with lower affinity but can be taken orally and have US Food and Drug Administration approval. The completed phase 2 randomized trials in humans of MMP inhibitors have methodologic limitations but generally show no significant benefits with adverse effects. At present, the principal research challenge is to achieve a better understanding of the complexities of biological functions of MMPs and subsequently to conduct large-scale phase 3 trials.

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.