Cimetidine Reduces Alveolar Bone Loss in Induced Periodontitis in Rat Molars

Reduction of osteoclast formation and survival following suppression of cytokines by diacerein in periodontitis

Periodontitis causes an increase in several bioactive agents such as interleukins (IL), tumor necrosis factor (TNF)-α and receptor activator of NF-kB ligand (RANKL), which induce the osteoclast formation and activity. Since diacerein exerts anti-TNF-α and anti-IL-1 effects, alleviating bone destruction in osteoarthritis, we investigated whether this drug inhibits the formation and survival of osteoclast in the periodontitis. Rats were distributed into 3 groups: 1) group with periodontitis treated with 100 mg/kg diacerein (PDG), 2) group with periodontitis treated with saline (PSG) and group control (CG) without any treatment. After 7, 15 and 30 days, the maxillae were collected for light and transmission electron microscopy analyses. Gingiva samples were collected to evaluate the mRNA levels for Tnf, Il1b, Tnfsf11 and Tnfrsf11b by RT-qPCR. In PDG, the expression of Tnf and Il1b genes reduced significantly compared to PSG, except for Tnf expression at 7 days. The number of osteoclasts reduced significantly in the PDG in comparison with PSG at 7 and 15 days. In all periods, the IL-6 immunoexpression, RANKL/OPG immunoexpression and mRNA levels of Tnfsf11/Tnfrsf11b ratio were significantly lower in PDG than in PSG. PDG exhibited significantly higher frequency of TUNEL-positive osteoclasts than in PSG and CG at all time points. Osteoclasts with caspase-3-immunolabelled cytoplasm and nuclei with masses of condensed chromatin were observed in PDG, confirming osteoclast apoptosis. Diacerein inhibits osteoclastogenesis by decreasing Tnf and Il1b mRNA levels, resulting in decreased RANKL/OPG ratio, and induces apoptosis in osteoclasts of alveolar process of rat molars with periodontitis.

Effects of the DL76 Antagonist/Inverse Agonist of Histamine H3 Receptors on Experimental Periodontitis in Rats: Morphological Studies

BACKGROUND

Periodontitis preceded by gingivitis is the most common form of periodontal disease and occurs due to the interaction of microorganisms present in the complex bacterial aggregates of dental plaque biofilm and their metabolism products with periodontal tissues. Histamine is a heterocyclic biogenic amine acting via four types of receptors. Histamine H3 receptors act as presynaptic auto/heteroreceptors to regulate the release of histamine and other neurotransmitters.

AIM

Since the nervous system is able to regulate the progression of the inflammatory process and bone metabolism, the aim of this study was to investigate the effects of DL76, which acts as an antagonist/inverse agonist of H3 receptors, on the course of experimental periodontitis.

MATERIALS AND METHODS

This study was conducted in 24 mature male Wistar rats weighing 245-360 g, aged 6-8 weeks. A silk ligature was placed on the second maxillary molar of the right maxilla under general anesthesia. From the day of ligating, DL76 and 0.9% NaCl solutions were administered subcutaneously for 28 days in the experimental and control groups, respectively. After the experiment, histopathological, immunohistochemical and radiological examinations were performed.

RESULTS

Ligation led to the development of the inflammatory process with lymphocytic infiltration, increased epithelial RANKL and OPG expression as well as bone resorption. DL76 evoked a reduction in (1) lymphocytic infiltration, (2) RANKL and OPG expression as well as (3) bone resorption since the medians of the mesial and distal interdental spaces in the molars with induced periodontitis were 3.56-fold and 10-fold lower compared to the corresponding values in saline-treated animals with periodontitis.

CONCLUSION

DL76 is able to inhibit the progression of experimental periodontitis in rats, as demonstrated by a reduction in the inflammatory cell infiltration, a decrease in the RANKL/RANK OPG pathway expression and a reduction in the alveolar bone resorption.

Role of ferroptosis in periodontitis: An animal study in rats

OBJECTIVE

This study aimed to investigate (1) the temporal pattern of ferroptosis, an iron-dependent cell death, in ligation-induced rat periodontitis and (2) the effect of ferrostatin-1, a ferroptosis inhibitor, on the model.

BACKGROUND

Ferroptosis may contribute to various diseases. However, the role of ferroptosis in periodontitis is still fully understood.

METHODS

In the first experiment, 25 rats with ligation-induced periodontitis were sacrificed on days 0, 1, 2, 7, and 10. Gingivae were obtained to determine tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and ferroptotic biomarkers, including solute carrier family 3 member 2 (SLC3A2) and solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (Gpx4), via immunoblotting. Using microcomputed tomography (μCT) and histology, the periodontal soft and hard tissue lesions, including dental alveolar bone crest level, bony characteristics of the surrounding alveolus, periodontal tissue inflammation, and periodontal tissue losses, were evaluated. In study two, 16 rats with induced periodontitis were grouped according to ferrostatin-1 treatment. The rats were intraperitoneally injected with solvent or ferrostatin-1 (1.5 mg/kg/day) 1 day before ligation and sacrificed on days 7 and 10. Gingival protein changes and periodontal tissue damage were also examined.

RESULTS

In study one, SLC3A2/SLC7A11 and Gpx4 decreased since day 1; however, TNF-α/IL-1β increased on days 7 and 10. Moreover, the μCT/histology revealed resorptive bony characteristics, inflamed gingival tissue, and periodontal attachment loss. In study two, ferrostatin-1-injected rats exhibited significantly increased SLC3A2/SLC7A11 and Gpx4 but decreased TNF-α/IL-1β than vehicle rats. They also revealed lessened bone resorption, tissue inflammation, and attachment loss.

CONCLUSION

This study highlights the role of ferroptosis, via the system Xc/Gpx4 pathway, in experimental periodontitis and may serve as a regulatory strategy.

Histamine deficiency deteriorates LPS-induced periodontal diseases in a murine model via NLRP3/Caspase-1 pathway

Histamine is a versatile biogenic amine, generated by the unique enzyme histidine decarboxylase (Hdc). Accumulating evidence has proven that histamine plays important roles in numerous biological and pathophysiological processes. However, the role and mechanism of Hdc/Histamine signaling in periodontal diseases remain unclear. In our current study, the concentration of histamine increased in the serum, and Hdc gene expression was upregulated in the gingiva of WT mice with LPS-induced periodontal inflammation. With Hdc-GFP mice, we identified that Hdc/GFP in the periodontium was expressed in CD11b⁺ myeloid cells, rather than in tryptase-positive mast cells. Hdc-expressing CD11b⁺Gr-1⁺ neutrophils significantly increased in the peripheral blood of Hdc-GFP mice one day after LPS injection. Lack of histamine in Hdc^-/- mice not only promoted the activation and infiltration of more CD11b⁺ cells into the peripheral blood but also upregulated mRNA expression levels of IL-1β, IL-6, MCP-1and MMP9 in the gingiva compared to WT mice one day after LPS stimulation. 28 days after LPS treatment, we observed that Hdc^-/- mice exhibited more alveolar bone loss and more osteoclasts than WT mice, which was slightly ameliorated by the administration of exogenous histamine. In vivo and in vitro mechanistic studies revealed that the mRNA expression levels of proinflammatory cytokines and protein levels of NLRP3, Caspase-1, and cleaved-Caspase-1 were upregulated after blocking histamine receptor 1 and 2, especially histamine receptor 1. Taken together, CD11b⁺Gr-1⁺ neutrophils are the predominant Hdc-expressing sites in periodontal inflammation, and deficiency of endogenous histamine in Hdc^-/- mice exacerbates the destruction of the periodontium. Disruption of the histamine/H₁R/H₂R axis aggravates the inflammatory immune response via NLRP3/Casapse-1 pathway.

The phytochemical plumbagin reciprocally modulates osteoblasts and osteoclasts

Bone metabolism is essential for maintaining bone mineral density and bone strength through a balance between bone formation and bone resorption. Bone formation is associated with osteoblast activity whereas bone resorption is linked to osteoclast differentiation. Osteoblast progenitors give rise to the formation of mature osteoblasts whereas monocytes are the precursors for multi-nucleated osteoclasts. Chronic inflammation, auto-inflammation, hormonal changes or adiposity have the potential to disturb the balance between bone formation and bone loss. Several plant-derived components are described to modulate bone metabolism and alleviate osteoporosis by enhancing bone formation and inhibiting bone resorption. The plant-derived naphthoquinone plumbagin is a bioactive compound that can be isolated from the roots of the Plumbago genus. It has been used as traditional medicine for treating infectious diseases, rheumatoid arthritis and dermatological diseases. Reportedly, plumbagin exerts its biological activities primarily through induction of reactive oxygen species and triggers osteoblast-mediated bone formation. It is plausible that plumbagin's reciprocal actions - inhibiting or inducing death in osteoclasts but promoting survival or growth of osteoblasts - are a function of the synergy with bone-metabolizing hormones calcitonin, Parathormone and vitamin D. Herein, we develop a framework for plausible molecular modus operandi of plumbagin in bone metabolism.

Cyanidin-3-O-glucoside downregulates ligation-activated endoplasmic reticulum stress and alleviates induced periodontal destruction in rats

OBJECTIVE

Cyanidin-3-O-glucoside (C3G), a dietary anthocyanin, possesses various biological properties, including alleviating endoplasmic reticulum (ER) stress. This study examined the effect of C3G on periodontitis via ER stress in rats.

DESIGN

Periodontitis was induced by placing silk sutures around maxillary second molars. C3G (0, 3, or 9 mg/kg) was fed on the day before ligation (10 rats/group). Further, 10 non-ligation control rats received deionized water. On day 8, gingivae were obtained to determine CCAAT/enhancer-binding protein homologous protein (CHOP), c-Jun N-terminal kinase (JNK), phospho-JNK (p-JNK), and nuclear factor-κB (NF-κB) by immunoblotting. Periodontal destruction was evaluated using micro-computed tomography (μCT) and histology.

RESULTS

Gingival expression of CHOP, p-JNK/JNK, and NF-κB significantly increased in ligation rats (0 mg/kg C3G) than that in controls. However, protein expression in ligation groups presented a negative association with C3G concentration. By μCT, the distance of cemento-enamel junction to bone significantly increased in ligation groups; however, distances showed a negative association with C3G concentration. In the region of interest, bone volume and trabecular thickness and number significantly decreased in ligation groups but they were positively associated with C3G concentration. In terms of trabecular separation, opposite results were found. Histologically, infiltrated connective tissue (ICT) and periodontal destructions increased in ligation groups; however, they were negatively associated with C3G concentration. Moreover, ICT area is positively correlated with μCT- and histologically measured destructions and protein expression of CHOP, p-JNK/JNK, or NF-κB.

CONCLUSION

C3G promotes favorable modulation of ER stress and alleviates destruction of periodontitis, which may imply a new strategy.

Spatio-temporal immunolocalization of VEGF-A, Runx2, and osterix during the early steps of intramembranous ossification of the alveolar process in rat embryos

Vascular endothelial growth factor A (VEGF-A) is expressed by several cell types and is a crucial factor for angiogenic-osteogenic coupling. However, the immunolocalization of VEGF-A during the early stages of the alveolar process formation remains underexplored. Thus, we analyzed the spatio-temporal immunolocalization of VEGF-A and its relationship with Runt-related transcription factor 2 (Runx2) and osterix (Osx) during the early steps of intramembranous ossification of the alveolar process in rat embryos. Embryo heads (E) of 16, 18 and 20-day-old rats were processed for paraffin embedding. Histomorphometry and immunohistochemistry to detect VEGF-A, Runx2, and Osx (osteoblast differentiation markers) were performed. The volume density of bone tissue including bone cells and blood vessels increased significantly in E18 and E20. Cells showing high VEGF-A immunoreactivity were initially observed within a perivascular niche in the ectomesenchyme; afterwards, these cells were diffusely located near bone formation sites. Runx2-and Osx-immunopositive cells were observed in corresponded regions of cells showing strong VEGF-A immunoreactivity. Although these immunostained cells were observed in all specimens, this immunolocalization pattern was more evident in E16 specimens and gradually decreased in E18 and E20 specimens. Double immunofluorescence labelling showed intracellular co-localization of Osx and VEGF-A in cells surrounding the developing alveolar process, indicating a crucial role of VEGF-A in osteoblast differentiation. Our results showed VEGF-A immunoexpression in osteoblasts and its precursors during the maxillary alveolar process formation of rat embryos. Moreover, the VEGF-A-positive cells located within a perivascular niche at the early stages of the alveolar process development suggest a crosstalk between endothelium and ectomesenchymal cells, reinforcing the angiogenic-osteogenic coupling in this process.

Histomorphometric and immunohistochemical study shows that tricalcium silicate cement associated with zirconium oxide or niobium oxide is a promising material in the periodontal tissue repair of rat molars with perforated pulp chamber floors

AIM

To evaluate the periodontium response to tricalcium silicate (TCS) with zirconium oxide (ZrO₂ ) or niobium oxide (Nb₂ O₅ ) used in the sealing of perforated pulp chamber floors in rat maxillary molars.

METHODOLOGY

In eighty rats, the perforations in right maxillary molars were filled with either TCS + ZrO₂ , TCS + Nb₂ O₅ , White MTA (used as a gold standard material) or no repair material was placed (Sham Group, SG); the left molars of SG, were used as controls (CG). Sections of maxillary fragments following 7, 15, 30 and 60 days were used to evaluate the volume densities of inflammatory cells (VvIC) and fibroblasts (VvFb), width of the periodontal space, amount of collagen, number of osteoclasts and number of IL-6-immunostained cells. The data were subjected to two-way ANOVA followed by Tukey's test (P ≤ 0.05).

RESULTS

At all periods, significant differences in VvIC were not detected among TCS + ZrO_2, TCS + Nb₂ O₅ and MTA groups, which had values significantly lower (P < 0.05) than the SG. Significant differences in the number of IL-6-immunolabelled cells were not observed among TCS + ZrO₂ , TCS + Nb₂ O₅ and MTA groups (P > 0.05) at 15, 30 and 60 days. At 7, 15 and 30 days, the number of osteoclast was significantly greater in TCS + ZrO_2, TCS + Nb₂ O₅ and MTA (P < 0.05) than in the CG; no significant difference was detected after 60 days (P > 0.05). The width of the periodontal space and amount of collagen in TCS + ZrO₂ and TCS + Nb₂ O₅ groups were similar to the CG at 30 and 60 days while SG specimens had a significant reduction (P < 0.05) in the amount of collagen and significant increase (P < 0.05) in the width of the periodontal space.

CONCLUSIONS

TCS + ZrO₂ and TCS + Nb₂ O₅ were associated with periodontium repair since these materials allowed the reestablishment of periodontal space width and collagen formation when used in the filling of uninfected perforations in the pulp chamber floor of maxillary rat molars. Furthermore, the significant reduction in the periodontal space of TCS + ZrO₂ and TCS + Nb₂ O₅ specimens after 60 days confirmed that the experimental materials were associated with a more rapid recovery of the injured tissues than MTA.

Calcitriol suppresses lipopolysaccharide-induced alveolar bone damage in rats by regulating T helper cell subset polarization

BACKGROUND

Although the immunomodulatory properties of calcitriol in bone metabolism have been documented for decades, its therapeutic role in the management of periodontitis remains largely unexplored. In this study, we hypothesized that calcitriol suppresses lipopolysaccharide (LPS)-induced alveolar bone loss by regulating T helper (Th) cell subset polarization.

METHODS

To test this hypothesis, we determined the effect of calcitriol intervention on the development of LPS-induced periodontitis in rats in terms of bone loss (micro-CT analysis), local inflammatory infiltration levels, the number of osteoclasts (hematoxylin and eosin staining) and the level of osteoclastogenesis (tartrate-resistant acid phosphatase method). Furthermore, immunohistochemistry was used to assess the expression levels of the receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) as well as the cytokine levels of interferon-γ (IFN-γ), interleukin-4 (IL-4), IL-17, and IL-10 throughout the LPS-injected region. Finally, the polarization potential of Th cells in peripheral blood was analyzed using flow cytometry.

RESULTS

Calcitriol intervention decreased alveolar bone loss in response to LPS injection and inflammatory cell infiltration. Analysis of osteoclast number and RANKL and OPG expression showed that bone resorption activity was largely suppressed in response to calcitriol administration, along with decreased IL-17 levels but increased IL-4 and IL-10 levels in periodontal tissues (the LPS-injected region). Similarly, the percentages of Th2 and Treg cells in peripheral blood increased, but the percentages of Th1 and Th17 cells decreased in rats receiving calcitriol.

CONCLUSION

Our findings suggest that calcitriol can be used to inhibit bone loss in experimental periodontitis, likely via the regulation of local and systemic Th cell polarization.

Immunomodulatory properties of cimetidine: Its therapeutic potentials for treatment of immune-related diseases

Histamine exerts potent modulatory impacts on the cells of innate- [including neutrophils, monocytes, macrophages, dendritic cells (DCs), natural killer (NK) cells and NKT cells] and adaptive immunity (such as Th1-, Th2-, Th17-, regulatory T-, CD8⁺ cytotoxic T cells, and B cells) through binding to histamine receptor 2 (H2R). Cimetidine, as an H2R antagonist, reverses the histamine-mediated immunosuppression, as it has powerful stimulatory effects on the effector functions of neutrophils, monocytes, macrophages, DCs, NK cells, NKT cells, Th1-, Th2-, Th17-, and CD8⁺ cytotoxic T cells. However, cimetidine reduces the regulatory/suppressor T cell-mediated immunosuppression. Experimentally, cimetidine potentiate some immunologic activities in vitro and in vivo. The therapeutic potentials of cimetidine as an immunomodulatory agent were also investigated in a number of human diseases (such as cancers, viral warts, allergic disorders, burn, and bone resorption) and vaccination. This review aimed to provide a concise summary regarding the impacts of cimetidine on the immune system and highlight the cellular mechanisms of action and the immunomodulatory effects of this drug in various diseases to give novel insights regarding the therapeutic potentials of this drug for treatment of immune-related disorders. The review encourages more investigations to consider the immunomodulatory characteristic of cimetidine for managing of immune-related disorders.

Eosinophil cationic protein and histamine production by neutrophils from patients with periodontitis

BACKGROUND

Periodontitis develops through an inflammatory process caused by an infection at the microbial biofilm, followed by tissue destruction mediated by leukocytes, which cause clinically significant destruction of connective tissue and bone. Several elements derived from the bacteria cause the inflammatory response and the release of mediators involved in destruction of the periodontium. There are number of inflammatory mediators released by leukocytes, mainly neutrophils, upon bacterial challenge. Neutrophils produce and release eosinophil cationic protein (ECP) and histamine, two important inflammatory mediators; however, their role has not been characterized in periodontal inflammation. Thus, the purpose of this study is to investigate whether neutrophils from patients with periodontitis can produce ECP and histamine in response to lipopolysaccharides (LPSs).

METHODS

ECP and histamine production in response to LPSs was analyzed by enzyme-linked immunosorbent assay. Expression of the histidine decarboxylase and ECP was also analyzed by flow cytometry and fluorescence microscopy in neutrophils from patients with periodontitis in response to LPS.

RESULTS

It was found that neutrophils from patients with periodontitis express higher levels of histidine decarboxylase and ECP than those from healthy volunteers, and they also release higher levels of histamine.

CONCLUSION

Findings described could represent new knowledge indicating neutrophils as a source of histamine and ECP in the progression of periodontitis.

Cimetidine Reduces Interleukin-6, Matrix Metalloproteinases-1 and -9 Immunoexpression in the Gingival Mucosa of Rat Molars With Induced Periodontal Disease

BACKGROUND

Histamine seems to act, via H₂ receptor, on inflammatory processes by stimulating interleukin (IL)-6 and matrix metalloproteinase (MMP) release. As cimetidine is an H₂ receptor antagonist, the authors hypothesize that this antiulcer drug reduces IL-6, MMP-1, and MMP-9 immunoexpression in gingiva with induced periodontal disease (PD). To confirm a possible modulatory role of IL-6 on MMPs, the relationship between IL-6/MMP-1 and IL-6/MMP-9 immunoexpression was evaluated.

METHODS

Forty-six male rats were distributed into the cimetidine group (CimG: received daily intraperitoneal injections of 100 mg/kg of body weight of cimetidine) or the saline group (SG). PD was induced by cotton ligature around the maxillary left first molars (PDSG and PDCimG). The right molars were used as controls (SG and CimG). After 7, 15, 30, and 50 days, maxillary fragments were processed for paraffin embedding or for transmission electron microscopy. Tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in the alveolar process surface and number of IL-6, MMP-1, and MMP-9-immunolabeled cells in the gingival mucosa were quantified. Statistical analyses were performed (P ≤0.05).

RESULTS

In PDSG and PDCimG, gingival mucosa exhibited few collagen fibers among numerous inflammatory cells. In PDCimG, the number of TRAP-positive osteoclasts and IL-6, MMP-1, and MMP-9-immunolabeled cells was significantly lower than in PDSG at all periods. A positive correlation between IL-6/MMP-1 and IL-6/MMP-9 was detected in PDSG and PDCimG.

CONCLUSION

Cimetidine decreases bone loss through reduction of osteoclast number and induces reduction of IL-6, MMP-1, and MMP-9 immunoexpression, reinforcing the idea that the beneficial effect of cimetidine in PD may be due to reduction of IL-6 immunolabeling in the inflamed gingival mucosa.

Influences of Fucoxanthin on Alveolar Bone Resorption in Induced Periodontitis in Rat Molars

The aim of this study was to evaluate the effects of systemic fucoxanthin treatment on alveolar bone resorption in rats with periodontitis. Thirty rats were divided into control, experimental periodontitis (EP), and experimental periodontitis-fucoxanthin (EP-FUCO) groups. Periodontitis was induced by ligature for four weeks. After removal of the ligature, the rats in the EP-FUCO group were treated with a single dose of fucoxanthin (200 mg/kg bw) per day for 28 consecutive days. At the end of the study, all of the rats were euthanized and intracardiac blood and mandible tissue samples were obtained for biochemical, immunohistochemical, and histometric analyses. Fucoxanthin treatment resulted in a slight decrease in tumor necrosis factor-α, interleukin-1β, and interleukin-6 levels and a significant decrease in oxidative stress index. It was observed that fucoxanthin caused a significant reduction in receptor activator of nuclear factor kappa-β ligand (RANKL) levels and a statistically non-significant elevation in osteoprotegerin and bone-alkaline phosphatase levels. There were no significant differences in alveolar bone loss levels between the EP and EP-FUCO groups. This experimental study revealed that fucoxanthin provides a limited reduction in alveolar bone resorption in rats with periodontitis. One of the mechanisms underlying the mentioned limited effect might be related to the ability of fucoxanthin to inhibit oxidative stress-related RANKL-mediated osteoclastogenesis.

Biology of Bone Tissue: Structure, Function, and Factors That Influence Bone Cells

Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.

Tumor necrosis factor-α antagonist infliximab inhibits osteoclast formation of peripheral blood mononuclear cells but does not affect periodontal ligament fibroblast-mediated osteoclast formation

BACKGROUND AND OBJECTIVE

The inflammatory cytokine tumor necrosis factor-alpha (TNF-α) is elevated in inflamed periodontal tissues and may contribute to periodontitis progression. TNF-α stimulates formation and activity of osteoclasts, the cells that are recruited in periodontitis, that cause alveolar bone degradation and subsequent tooth loss. We previously showed that TNF-α is elevated in co-cultures of periodontal ligament fibroblast (PDLF) and peripheral blood mononuclear cells (PBMC). Hence, TNF-α could be a determining factor in osteoclast formation in these cultures, as osteoclasts are formed despite the fact that prototypical osteoclast differentiation factor receptor activator of nuclear factor kappa-B ligand is outnumbered at least 100-fold by its inhibitor osteoprotegerin in these cultures.

MATERIAL AND METHODS

To assess the role of TNF-α in periodontitis-associated osteoclast formation in vitro, osteoclast formation was analyzed in the presence of the anti-TNF-α therapeutic agent infliximab in two culture systems: (i) PBMC in co-culture with PDLFs from controls and patients with periodontitis, or (ii) with PBMC only. PDLFs from control and patients with periodontitis were exposed to infliximab, PBMCs were added and the formation of osteoclast-like cells was assessed.

RESULTS

TNF-α was highest levels in supernatants at 7 d in co-cultures and declined at 14 and 21 d. TNF-α was undetectable in cultures that received infliximab. The formation and activity of osteoclasts in co-cultures was not affected by infliximab. In contrast, infliximab in cultures of only PBMC significantly reduced the formation of osteoclasts. This reduction was accompanied by a decreased number and size of cell clusters, a step that precedes the formation of osteoclasts. TNF-α was again undetectable in the supernatant of infliximab-treated cultures, but was detectable at similar levels in cell lysates of control and infliximab-treated PBMC cultures.

CONCLUSION

Our study shows that the contribution of TNF-α to osteoclast formation is cell system dependent. It contributes to PBMC-induced osteoclast formation, possibly by establishing stronger cell-cell interactions that precede osteoclast formation.

Effect of Cimetidine on Nitro-Oxidative Stress in a Rat Model of Periodontitis

Background and aims

Periodontitis is a chronic inflammation that involves nitro-oxidative stress with damaging periodontal structural effects. We aimed to evaluate the consequences of low-dose cimetidine on nitro-oxidative stress in periodontitis.

Methods

A rat model of ligature-induced periodontitis was used. After two weeks, the periodontitis groups were treated with cimetidine, aminoguanidine, N-nitro-L-arginine methyl ester and trolox for one week. On day 21, blood was drawn and the serum analyzed for measurement of total nitrites and nitrates, total oxidative status, total antioxidant response, and oxidative stress index.

Results

Cimetidine had an inhibitory effect on the synthesis of nitric oxide (p=0.001), total oxidative status (p=0.01) and oxidative stress index (p=0.01). Total antioxidant reactivity was increased by cimetidine (p=0.01). The effects of cimetidine were almost like those of aminoguanidine, NG-nitro-L-arginine methyl ester, and trolox.

Conclusions

Low-dose cimetidine can be used as adjunctive host modulatory therapy in chronic periodontitis because it reduces nitro-oxidative stress.