Prophylactic supplement with melatonin successfully suppresses the pathogenesis of periodontitis through normalizing RANKL/OPG ratio and depressing the TLR4/MyD88 signaling pathway

Abstract

Periodontitis (PD) is an inflammatory disease characterized by gingival inflammation and resorption of alveolar bone. Impaired receptor activator of nuclear factor-kappa B ligand/osteoprotegerin (RANKL/OPG) signaling caused by enhanced production of pro-inflammatory cytokines plays an essential role in the pathogenesis of PD. Considering melatonin possesses significant anti-inflammatory property, this study aimed to determine whether prophylactic treatment with melatonin would effectively normalize RANKL/OPG signaling, depress toll-like receptor 4/myeloid differentiation factor 88 (TLR4/MyD88)-mediated pro-inflammatory cytokine activation, and successfully suppress the pathogenesis of PD. PD was induced in adult rats by placing the ligature at molar subgingival regions. Fourteen days before PD induction, 10, 50, or 100 mg/kg of melatonin was intraperitoneally injected for consecutive 28 days. Biochemical and enzyme-linked immunosorbent assay were used to detect TLR4/MyD88 activity, RANKL, OPG, interleukin 1β, interleukin 6, and tumor necrosis factor-α levels, respectively. The extent of bone loss, bone mineral intensity, and calcium intensity was further evaluated by scanning electron microscopy, micro-computed tomography, and energy-dispersive X-ray spectroscopy. Results indicated that high RANKL/OPG ratio, TLR4/MyD88 activity, and pro-inflammatory cytokine levels were detected following PD. Impaired biochemical findings paralleled well with severe bone loss and reduced calcium intensity. However, in rats pretreated with melatonin, all above parameters were successfully returned to nearly normal levels with maximal change observed in rats receiving 100 mg/kg. As prophylactic treatment with melatonin effectively normalizes RANKL/OPG signaling by depressing TLR4/MyD88-mediated pro-inflammatory cytokine production, dietary supplement with melatonin may serve as an advanced strategy to strengthen oral health to counteract PD-induced destructive damage.

Melatonin and inflammation—Story of a double‐edged blade

“…As the proinflammatory actions of TLR4 are frequently also associated with NF‐κB activation and prooxidant effects, inhibitory actions of melatonin on TLR4 are of particular mechanistic interest for the understanding of reducing inflammation. This mode of action by melatonin was repeatedly demonstrated and sometimes shown to be associated with inhibitions of NF‐κB and of inflammasome activation as well as upregulation of Nrf2 . These findings were obtained in different organs and models, under various conditions, from endotoxemia, ischemia/reperfusion and other forms of brain injury to chemically induced inflammation.…”

Melatonin controls microbiota in colitis by goblet cell differentiation and antimicrobial peptide production through Toll-like receptor 4 signalling

“…Given normal physiologic conditions, the colon does not express Reg3β and α-defensin but these AMPs are induced in colitis 55 , suggesting that TLR4 signalling www.nature.com/scientificreports www.nature.com/scientificreports/ also plays a role in Reg3β regulation by melatonin. Although melatonin has been reported to inhibit TLR4/NF-κB signalling 56,57 , TLR4 signalling appears to link pathogen sensing and AMP production is thought to play protective role in melatonin function. Experiments with TLR4 KO mice and TLR4 inhibitor revealed the anti-colitic effects of melatonin on goblet cell differentiation and induction of melatonin receptor.…”

Melatonin: Another avenue for treating osteoporosis?

“…The results indicated that the RANKL/osteoprotegerin ratio, Toll‐like receptor (TLR)4/MyD88 activity, and pro‐inflammatory cytokine levels were imbalanced following periodontitis. However, in melatonin‐pretreated rats, all of these parameters were successfully restored to nearly normal levels with the maximal dose (100 mg/kg), which suggests that melatonin may counteract periodontitis‐induced destructive bone damage . Melatonin treatment reduces serum levels of terminal C telopeptide of collagen Type I (CTX), RANKL, and osteoclast activity but increases bone ALP in an experimental periodontitis rat model.…”

“…However, in melatonin-pretreated rats, all of these parameters were successfully restored to nearly normal levels with the maximal dose (100 mg/kg), which suggests that melatonin may counteract periodontitis-induced destructive bone damage. 133 Melatonin treatment reduces serum levels of terminal C telopeptide of collagen Type I (CTX), RANKL, and osteoclast activity but increases bone ALP in an experimental periodontitis rat model. The results revealed that melatonin treatment significantly inhibits regional resorption of alveolar bone and contributes to periodontal healing in this experimental periodontitis rat model.…”