Advances in Oral Mucosal Immunity and the Microbiome

Standardized studies of the oral microbiome: From technology-driven to hypothesis-driven

The microbiome is in a symbiotic relationship with the host. Among the microbial consortia in the human body, that in the oral cavity is complex. Instead of repeatedly confirming biomarkers of oral and systemic diseases, recent studies have focused on a unified clinical diagnostic standard in microbiology that reduces the heterogeneity caused by individual discrepancies. Research has also been conducted on other topics of greater clinical importance, including bacterial pathogenesis, and the effects of drugs and treatments. In this review, we divide existing research into technology-driven and hypothesis-driven, according to whether there is a clear research hypothesis. This classification allows the demonstration of shifts in the direction of oral microbiology research. Based on the shifts, we suggested that establishing clear hypotheses may be the solution to major research challenges.

Frontiers in Oral Mucosal Immunity and the Microbiome

The 2nd International Conference on Oral Mucosal Immunity and the Microbiome (OMIM) took place at the Grecotel Kos Imperial Hotel, Kos, Greece, between 25th and 30th September 2021, under the auspices of the Aegean Conferences. This has only been the second Aegean Conference of this thematic, the first one having taken place in 2018 in Crete, during the same period of the year. Given the hardships in travel and heightened infection transmission risks amid the COVID-19 pandemic, the Conference was well attended by 29 international speakers across the world. For many of the participants, this was the first conference travel in the post-pandemic era, and quite significant that it has taken place on the island of Hippocrates. Stringent regional health and safety regulations had to be followed to accomplish for this in-person Conference to take place. Frontiers in Oral Health has hosted papers from presentations of the Conference, whereas the present article serves as the proceedings of the Conference with summaries of the presentations.

Access to dental care and blood pressure profiles in adults with high socioeconomic status

Background

Reduced access to dental care may increase cardiovascular risk; however, socioeconomic factors are believed to confound the associations. We hypothesized that the relation persists despite economic wellness and high education, with reduced access to dental care affecting cardiovascular risk at least in part through its effect on blood pressure (BP), possibly mediated by systemic inflammation.

Methods

We first assessed the sociodemographic and clinical characteristics related to last dental visit timing (≤ or >6 months; self‐reported) using national representative cross‐sectional data. Then, the association of last dental visit timing with clinic BP was selectively investigated in highly educated, high income participants, further matched for residual demographic and clinical confounders using propensity score matching (PSM). The mediating effect of systemic inflammation was formally tested. Machine learning was implemented to investigate the added value of dental visits in predicting high BP over the variables included in the Framingham Hypertension Risk Score among individuals without an established diagnosis of hypertension.

Results

Of 27,725 participants included in the population analysis, 46% attended a dental visit ≤6 months. In the PSM cohort (n = 2350), last dental visit attendance >6 months was consistently associated with 2 mmHg higher systolic BP (P = 0.001) and with 23 to 35% higher odds of high/uncontrolled BP compared with attendance ≤6 months. Inflammation mildly mediated the association. Access to dental care improved the prediction of high BP by 2%.

Conclusions

Dental care use impacts on BP profiles independent of socioeconomic confounders, possibly through systemic inflammation. Regular dental visits may contribute to preventive medicine.

The psychobiological links between chronic stress-related diseases, periodontal/peri-implant diseases, and wound healing

Chronic stress is a relevant disease to periodontal practice, encompassing 25%-28% of the US population (American Psychological Association 2015). While it is well established that chronic psychologic stress can have significant deleterious systemic effects, only in recent decades have we begun to explore the biochemical, microbial, and physiologic impacts of chronic stress diseases on oral tissues. Currently, chronic stress is classified as a "risk indicator" for periodontal disease. However, as the evidence in this field matures with additional clinically controlled trials, more homogeneous data collection methods, and a better grasp of the biologic underpinnings of stress-mediated dysbiosis, emerging evidence suggests that chronic stress and related diseases (depression, anxiety) may be significant contributing factors in periodontal/peri-implant disease progression and inconsistent wound healing following periodontal-related therapeutics. Ideal solutions for these patients include classification of the disease process and de-escalation of chronic stress conditions through coping strategies. This paper also summarizes periodontal/implant-related therapeutic approaches to ensure predictable results for this specific patient subpopulation.

Characterization of Mesenchymal Stem Cells Derived from Bisphosphonate-Related Osteonecrosis of the Jaw Patients' Gingiva

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a clinical condition that specifically occurs in the oral cavity, characterized by retarded wound healing in oral mucosa accelerating the exposure of bone. Moreover, the pathological mechanism remains poorly understood. Gingival mesenchymal stem cells (GMSCs) play a critical role in gingival healing and soft tissue regeneration. Although previous studies have showed that bisphosphonates (BPs) are highly toxic to healthy GMSC, there is overall lack of direct evidence demonstrating the characterization of GMSCs derived from BRONJ patients. In present study, we isolated GMSCs for the first time from the central area of BRONJ patients' gingiva (center-BRONJ GMSCs) and the peripheral area (peri-BRONJ GMSCs), and found that they exhibited decreased proliferation, adhesion, migration capacities and underwent early apoptosis in vitro compared control GMSCs. Notably, the central and peripheral BRONJ GMSCs transplantation in a mice excisional skin model also displayed lower cell survival rate and poor healing effects than that of controls. Mechanistically, TGF-β1 signaling pathway was suppressed not only in BRONJ patients' gingival lesions but also in BRONJ GMSCs transplantation animal model. The results above suggested that under the microenvironment of BRONJ patients, the dysfunction of GMSCs and the suppressed TGF-β1 signaling pathway may be the vital factors in impaired gingival healing, thus contributing to persistent exposure of underlying bone and development of BRONJ. This study provides new insights into the prevention for BRONJ by improving the functions of GMSCs and upregulating TGF-β1 in accelerating gingival wound healing. Schematic illustration of the dysfunction of BRONJ GMSCs in vitro and BRONJ GMSCs transplantation in a mice skin model delaying cutaneous wound healing mainly via suppressing TGF-β1 signaling pathway.

Treatment challenges and delivery systems in immunomodulation and probiotic therapies for periodontitis

Introduction: Periodontitis is a widespread illness that arises due to disrupted interplay between the oral microbiota and the host immune response. In some cases, conventional therapies can provide temporary remission, although this is often followed by disease relapse. Recent studies of periodontitis pathology have promoted the development of new therapeutics to improve treatment options, together with local application using advanced drug delivery systems.Areas covered: This paper provides a critical review of the status of current treatment approaches to periodontitis, with a focus on promising immunomodulation and probiotic therapies. These are based on delivery of small molecules, peptides, proteins, DNA or RNA, and probiotics. The key findings on novel treatment strategies and formulation of advanced delivery systems, such as nanoparticles and nanofibers, are highlighted.Expert opinion: Multitarget therapy based on antimicrobial, immunomodulatory, and probiotic active ingredients incorporated into advanced delivery systems for application to the periodontal pocket can improve periodontitis treatment outcomes. Translation of such adjuvant therapy from laboratory to patient is expected in the future.

Microbiota in viral infection and disease in humans and farm animals

The influence of the microbiota on viral infection susceptibility and disease outcome is undisputable although varies among viruses. The purpose of understanding the interactions between microbiota, virus, and host is to identify practical, effective, and safe approaches that target microbiota for the prevention and treatment of viral diseases in humans and animals, as currently there are few effective and reliable antiviral therapies available. The initial step for achieving this goal is to gather clinical evidences, focusing on the viral pathogens-from human and animal studies-that have already been shown to interact with microbiota. The subsequent step is to identify mechanisms, through experimental evidences, to support the development of translational applications that target microbiota. In this chapter, we review evidences of virus infections altering microbiota and of microbiota enhancing or suppressing infectivity, altering host susceptibility to certain viral diseases, and influencing vaccine immunogenicity in humans and farm animals.