Osteoimmunological mechanisms involved in orthodontically and bacterially induced periodontal stress

Advancing oral immunology for improving oral health

Although substantial progress has been made in dentistry in terms of diagnosis and therapy, current treatment methods in periodontology, orthodontics, endodontics, and oral and maxillofacial surgery, nevertheless, suffer from numerous limitations, some of which are associated with a dramatic reduction in the quality of life. Many general mechanisms of inflammation and immunity also apply to the oral cavity and oral diseases. Nonetheless, there are special features here that are attributable, on the one hand, to developmental biology and, on the other hand, to the specific anatomical situation, which is characterized by a close spatial relationship of soft and hard tissues, exposure to oral microbiota, and to a rapid changing external environment. Currently, a comprehensive and overarching understanding is lacking about how the immune system functions in oral tissues (oral immunology) and how oral immune responses contribute to oral health and disease. Since advances in translational immunology have created a game-changing shift in therapy in rheumatology, allergic diseases, inflammatory bowel disease, and oncology in recent years, it is reasonable to assume that a better understanding of oral immunology might lead to practice-changing diagnostic procedures and therapies in dentistry and thereby also profoundly improve oral health in general.

In vivo and In vitro Identification of Endocannabinoid Signaling in Periodontal Tissues and Their Potential Role in Local Pathophysiology

The endocannabinoid system (ECS) with its binding receptors CB1 and CB2 impacts multiple pathophysiologies not only limited to neuronal psychoactivity. CB1 is assigned to cerebral neuron action, whereas CB2 is mainly expressed in different non-neuronal tissues and associated with immunosuppressive effects. Based on these tissue-selective CB receptor roles, it was the aim of this study to analyze potential expression in periodontal tissues under physiological conditions and inflammatory states. In vivo, CB receptor expression was investigated on human periodontal biopsies with or without bacterial inflammation and on rat maxillae with or without sterile inflammation. In vitro analyses were performed on human periodontal ligament (PDL) cells at rest or under mechanical strain via qRT-PCR, Western blot, and immunocytochemistry. P < 0.05 was set statistical significant. In vivo, CB1 expression was significantly higher in healthy PDL structures compared to CB2 (13.5% ± 1.3 of PDL tissues positively stained; 7.1% ± 0.9). Bacterial inflammation effected decrease in CB1 (9.7% ± 2.4), but increase in CB2 (14.7% ± 2.5). In contrast, sterile inflammation caused extensive CB1 (40% ± 1.9) and CB2 (41.7% ± 2.2) accumulations evenly distributed in the tooth surrounding PDL. In vitro, CB2 was ubiquitously expressed on gene and protein level. CB1 was constitutively expressed on transcriptional level (0.41% ± 0.09), even higher than CB2 (0.29% ± 0.06), but undetectable on protein level. Analyses further revealed expression changes of both receptors in mechanically loaded PDL cells. CB1 and CB2 are varyingly expressed in periodontal tissues, both adjusted by different entities of periodontal inflammation and by mechanical stress. This indicates potential ECS function as regulatory tool in controlling of periodontal pathophysiology.

Verification of γ-Amino-Butyric Acid (GABA) Signaling System Components in Periodontal Ligament Cells In Vivo and In Vitro

CNS key neurotransmitter γ-amino-butyric acid (GABA) and its signaling components are likewise detectable in non-neuronal tissues displaying inter alia immunomodulatory functions. This study aimed at identifying potential glutamate decarboxylase (GAD)65 and GABA receptor expression in periodontal ligament (PDL) cells in vivo and in vitro, with particular regard to inflammation and mechanical loading. Gene expression was analyzed in human PDL cells at rest or in response to IL-1ß (5 ng/ml) or TNFα (5 ng/ml) challenge via qRT-PCR. Western blot determined constitutive receptor expression, and confocal laser scanning fluorescence microscopy visualized expression changes induced by inflammation. ELISA quantified GAD65 release. Immunocytochemistry was performed for GABA component detection in vitro on mechanically loaded PDL cells, and in vivo on rat upper jaw biopsies with mechanically induced root resorptions. Statistical significance was set at p < 0.05. GABA_B1, GABA_B2, GABA_A1, and GABA_A3 were ubiquitously expressed both on gene and protein level. GABA_A2 and GAD65 were undetectable in resting cells, but induced by inflammation. GABA_B1 exhibited the highest basal gene expression (6.97 % ± 0.16). IL-1ß markedly increased GABA_B2 on a transcriptional (57.28-fold ± 12.40) and protein level seen via fluorescence microscopy. TNFα-stimulated PDL cells released GAD65 (3.68 pg/ml ± 0.17 after 24 h, 5.77 pg/ml ± 0.65 after 48 h). Immunocytochemistry revealed GAD65 expression in mechanically loaded PDL cells. In vivo, GABA components were varyingly expressed in an inflammatory periodontal environment. PDL cells differentially express GABA signaling components and secrete GAD65. Inflammation and mechanical loading regulate these neurotransmitter molecules, which are also detectable in vivo and are potentially involved in periodontal pathophysiology.

Short-term heat pre-treatment modulates the release of HMGB1 and pro-inflammatory cytokines in hPDL cells following mechanical loading and affects monocyte behavior

OBJECTIVE

Heat shock proteins (HSP) act as cell-protective molecules that are upregulated upon thermal insult, hypoxia, and ischemia. Such ischemic conditions can be found during tissue remodeling associated with orthodontic tooth movement or trauma when compression forces lead to cell necrosis and subsequent clearance of cellular debris by immune competent cells. Host immune overreaction can result in undesired side effects such as tooth root resorption. Here, we analyzed whether heat pre-treatment would affect the initially catabolic host immune response induced by mechanical loading of human periodontal ligament (hPDL) cells, which represent major constituents of the tooth supporting apparatus involved in the regulation of periodontal remodeling.

MATERIALS AND METHODS

Fifth passage hPDL cells were exposed to an elevated temperature of 43° for 1 h prior to mechanical loading. Cell morphology, high mobility group box protein 1 (HMGB1), interleukin (IL)-6, and IL-8 expression were analyzed microscopically and by ELISA. The physiological relevance for monocyte behavior was tested in monocyte adhesion and osteoclast differentiation assays.

RESULTS

Short-term heat pre-treatment did not show any visible effect on hPDL cell morphology, but resulted in a significant downregulation of pro-inflammatory cytokines when being additionally loaded mechanically. Supernatants of heat-exposed hPDL cell cultures demonstrated a reduced impact on monocyte adhesion and osteoclastic differentiation.

CONCLUSIONS

Heat pre-treatment of hPDL cells induces cell-protective mechanisms towards mechanical stress and favors the reduction of cell stress associated effects on monocyte/macrophage physiology.

CLINICAL RELEVANCE

These data present the induction of heat shock proteins as a promising treatment option to limit undesired side effects of periodontal remodeling.

Histopathological Verification of Osteoimmunological Mediators in Peri-Implantitis and Correlation to Bone Loss and Implant Functional Period

Peri-implantitis (PI) is characterized by inflammation and bone resorption eventually leading to implant failure, but the characteristic pathologic determinants are undefined to date. This study aims to elucidate the parameters involved in PI pathogenesis, including intraoral implant retention time, extent of bone loss, smoking history, and identification of osteoimmunological markers for inflammation and bone loss. Peri-implant tissues (n = 21) displaying clinically diagnosed PI from patients with vertical bone loss ranging from 0-12 mm and implant function period between 1 and 60 months were evaluated by histochemistry and immunohistochemistry for TRAP, CD3, RANK, RANKL, OPG, and TNF-α. Statistical analyses were performed with the Welch test and correlation coefficients were calculated. Most bone resorption occurred during the first 12 months of implant function and correlated with the extent of inflammation, although histological signs of inflammation strongly varied between samples from minimal appearance of inflammatory cells to extended infiltrates. Implant function period and smoking history did not significantly affect the degree of inflammation. Higher RANK levels emerged in the first 12 months of implant function compared to longer retention times and were negatively correlated to the occurrence of RANKL. Additionally, histological signs of inflammation were about two-fold higher in specimens with bone resorption up from 5 mm compared to under 5 mm. CD3(+) cells were more prevalent in extensive inflammatory infiltrates and samples derived from smokers. Our analyses proved that PI-induced bone loss is differentially influenced by the parameters evaluated in this study, but a distinct interconnection between disease severity and implant retention time can be established.