Effect of resveratrol and modulation of cytokine production on human periodontal ligament cells

Abstract

Periodontitis is a multifactorial polymicrobial infection characterized by a destructive inflammatory process. Porphyromonas gingivalis, a Gram-negative anaerobic black-pigmented rod, which produces several virulence factors that stimulate human periodontal ligament cells (HPLCs) to produce various inflammatory mediators, has been implicated as a crucial etiologic agent in the initiation and progression of periodontitis. Since natural polyphenols such as resveratrol have growth-inhibitory effects on some bacterial pathogens and have shown chemo-preventive, anti-inflammatory and antioxidant activity, in the present study we used an HPLC model stimulated with lipopolysaccharide (LPS) of P. gingivalis to simulate the in vivo conditions such as those found in diseased periodontal sites. To determine whether resveratrol interferes with P. gingivalis LPS-activity and reduces the production of pro-inflammatory molecules, we investigated its effect on the cytokines IL-1β, IL-6, IL-8, IL-12 and TNF-α and NO production of HPLCs.

The results showed that resveratrol treatment decreased in a dose- and time-dependent manner the NO expression induced by P. gingivalis LPS, correlated to an increased viability of infected HPLCs, and decreased the production of pro-inflammatory cytokines in HPLCs stimulated by P. gingivalis LPS. These results suggest that the ability of resveratrol to determine immunomodulatory effects could provide possible therapeutic applications for the treatment of periodontitis.

Introduction

Periodontitis is an infectious inflammatory disease induced by an imbalance between bacterial virulence and the host defences. Periodontopathogens in subgingival sites induce host cellular and humoral responses [1]. The host response, in most cases resulting from bacterial infection, targets the elimination or control of periodontopathogens and prevents the progression of periodontal diseases and related inflammatory processes [2]. In other cases, the continuous challenge on host immune and resident cells by periodontopathogens and their virulence factors results in enhanced and uncontrolled secretion of cytokines [1], [2], [3]. A major objective of periodontal therapy is the regeneration of destroyed periodontal connective tissues by enhancing the formation of cementum and bone and the attachment of connective tissue fibers [4]. Bacteria of the subgingival plaque can invade the dento-periodontal attachment and move to deeper tissues such as the periodontal ligament and the alveolar bone. It has been suggested that human periodontal ligament cells (HPLCs) can play an active role in the local immune responses that may initiate periodontitis [5], [6].

Porphyromonas gingivalis, a Gram-negative anaerobic black-pigmented rod, has been implicated as a crucial etiologic agent in the initiation and progression of periodontitis [7], [8]. This pathogen produces several virulence factors that stimulate HPLCs to produce inflammatory mediators, such as prostaglandin E2, matrix metalloproteinases (MMPs) and proinflammatory cytokines [6]. These mediators further activate the periodontal cells to mount excessive host inflammatory responses, resulting in disease progression and periodontal destruction. A variety of substances and biological factors have been suggested to reduce bacterial infection and promote periodontal healing and regeneration [9], [10], [11]. For instance, a recent study suggested that adverse periodontal conditions can be stabilized by anti-inflammatory drugs and inhibitors of MMPs and proinflammatory cytokines [12]. Antibiotics are largely used to manage periodontal diseases, but their excessive use has led to the development of antibiotic-resistant mutants.

As an alternative to synthetic compounds, natural products are receiving considerable attention for use in medical therapy. Plant-derived dietary constituents, like polyphenols of various foods and herbs, are beneficial to human health and play an important role in the prevention of disease [13], [14].

Resveratrol (trans-3,4′,-5-trihydroxystilbene), a dietary antioxidant polyphenol found in various plants, including grapes, red wine, berries, and peanuts [15], [16], has been studied for its chemopreventive, anti-inflammatory and antioxidant activity. Resveratrol was demonstrated to inhibit cellular processes associated with tumor initiation, promotion, and progression [17].

To account for the diverse effects of resveratrol, it has been suggested that the biological activities involve the downregulation of the expression of various markers, including inducible nitric oxide (NO) and NO synthase [18]. Although NO has been demonstrated to have a beneficial effect on host defense mechanisms against various pathogenic bacteria [19], [20], the uncontrolled release of these cytotoxic substances [21] and proinflammatory mediators including cytokines [22], [23] by the migrating cells may damage the host tissues. Because the immunomodulatory effects of resveratrol may influence the degree of the local response to infection, knowledge of their intrinsic influence on the HPLC inflammatory response appears to be significant. HPLCs have a share in the immune response in the oral cavity and can produce cytokines that increase the inflammatory response and that supply for normal communication. Considering that natural polyphenols such as resveratrol are reported to have bactericidal properties against pathogenic bacteria [24], [25] and since the potential therapeutic effects of resveratrol have not been studied extensively, in the present work, we evaluated whether this compound exerts a modulatory effect on the expression of inflammatory cytokines and NO production by P. gingivalis LPS in HPLCs.