The Role of the Oral Microbiota in the Etiopathogenesis of Oral Squamous Cell Carcinoma

Identification of Aerobic Salivary Microorganisms in Patients With Oral Squamous Cell Carcinoma Using MALDI-TOF MS: Preliminary Findings From a Pilot Study

RATIONALE

Oral squamous cell carcinoma (OSCC) is a multifactorial disease, and emerging evidence links the oral microbiome to its development. Rapid, noninvasive identification of salivary microorganisms may offer novel diagnostic and prognostic insights into oral cancer.

METHODS

Salivary microbiota from OSCC patients and healthy individuals were analyzed using MALDI Biotyper. Saliva samples were cultured, and microbial identification was performed based on protein spectral profiles using an UltrafleXtreme MALDI-TOF mass spectrometer.

RESULTS

Thirteen OSCC patients (mean age 55 ± 11 years; 69% male) and nineteen healthy controls (mean age 55 ± 10 years; 79% male) were analyzed. Distinct microbial profiles were observed in OSCC patients, including pathogenic species previously associated with carcinogenesis, suggesting potential biomarkers for oral cancer.

CONCLUSIONS

The MALDI Biotyper is an effective, noninvasive tool for identifying salivary microbiota. Its application may support early diagnosis and prognosis of OSCC, reinforcing the significance of the oral microbiome in cancer etiology.

Asarum sieboldii, a Potential Ethnomedicinal Herb in Dentistry and Oral Health

Asarum sieboldii, a species of wild ginger native to East Asia, has long been recognised as an important herb in Asian traditional medicine. It has been applied in the treatment of toothache, cough, asthma, and sinusitis. A. sieboldii has gained global interest because it offers solutions to multiple health concerns. The plant is renowned for its anti-inflammatory, analgesic, antimicrobial, antifungal, and antioxidant properties. Its roots exhibit a wide range of biological and pharmacological effects. The plant contains several chemical constituents, including methyleugenol, 3,4,5-trimethoxytoluene, and safrole, which contribute to its medicinal benefits. Whereas literature search highlights the potential application of A. sieboldii in herbal medicine, to date its application in dentistry remains largely unexplored, with the existing literature vastly fragmented in various sources. This review therefore, provides a comprehensive overview of the potential application of A. sieboldii in dentistry and oral health. The plant shows considerable promise and appears to be effective for managing common oral diseases such as tooth decay, periodontal diseases, toothache, oral cancer, oral ulcers, and gingivitis. Its ability to inhibit nitric oxide release, along with its neuroprotective effects, further enhances its potential for relieving pain and inflammation. With these therapeutic benefits, A. sieboldii presents a promising natural alternative or a complementary option to conventional dental treatments, capable of addressing a wide range of oral health conditions. The findings from this review could serve as a solid foundation for future research, supporting the development of high-quality, safe, and effective A. sieboldii-based products in dentistry and oral health.

An Overview of the Etiopathogenic Mechanisms Involved in the Expression of the Oral Microbiota

Background/Objectives: The diversity of the oral microbiota exerts its effects in maintaining dental and overall health. The unique genetic profile of each individual influences the composition of the oral microbiota, determining susceptibility to certain diseases. The aim is to observe its role by highlighting the pathogenic mechanisms involved in oral dysbiosis and identify genetic determinism's influence in maintaining balance. Methods: This study was designed as a narrative review of the oral microbiota, utilizing some of the principles and guidelines of systematic review to increase methodological rigor. We examined 121 articles such as reviews, meta-analyses, editorials, and observational studies, which met the inclusion and exclusion criteria. The inclusion criteria for studies were as follows: (1) studies that evaluated the impact of the microbiota in oral or/and systemic diseases; (2) studies that observed pathogenic mechanisms in the oral microbiota; (3) studies that evaluated the interaction of the microbiota with the immune system (4); studies that evaluated genetic implications in the microbiota. Results: Host genes regulate inflammatory and immunological reactions that play a role in microbiological balance. This explains the increased resistance of some to diseases, including gingivitis or periodontitis. Also, the implications of oral dysbiosis are reflected not only locally, but also generally, being associated with various systemic conditions. Conclusions: Understanding the pathogenic mechanisms and genetic determinants involved in oral dysbiosis may help create individualized therapies for preventing and managing oral and systemic disorders. A healthy lifestyle and adequate oral hygiene can facilitate a diverse and balanced microbiome, crucial for overall health.

Pathophysiological Responses of Oral Keratinocytes After Exposure to Flavored E-Cigarette Liquids

BACKGROUND

Electronic cigarettes (ECIGs) have grown in popularity, particularly among adolescents and young adults. Flavored ECIG-liquids (E-liquids) are aerosolized by these ECIGs and inhaled into the respiratory system. Several studies have shown detrimental effects of E-liquids in airway tissues, revealing that flavoring agents may be the most irritating component. However, research on the effects of E-liquids on biological processes of the oral cavity, which is the first site of aerosol contact, is limited. Hence, this study focuses on the effects of E-liquid flavors on oral epithelial cells using the OKF6/TERT-2 cell line model.

METHODOLOGY

E-liquid was prepared with and without flavors (tobacco, menthol, cinnamon, and strawberry). OKF6/TERT-2 oral epithelial cells, cultured at 37 °C and 5% CO2, were exposed to 1% E-liquid ± flavors for 24 h. Outcomes determined include cell morphology, media pH, wound healing capability, oxidative stress, expression of mucin and tight junction genes, glycoprotein release, and levels of inflammatory cytokines (TNFα, IL-6, and IL-8).

RESULTS

Exposure to 1% flavored E-liquids negatively affect cellular confluency, adherence, and morphology. E-liquids ± flavors, particularly cinnamon, increase oxidative stress and production of IL-8, curtail wound healing recovery, and decrease glycoprotein release. Gene expression of muc5b is downregulated after exposure to E-liquids. In contrast, E-liquids upregulate occludin and claudin-1.

CONCLUSIONS

This study suggests that ECIG use is not without risk. Flavored E-liquids, particularly cinnamon, result in pathophysiological responses of OKF6/TERT-2 cells. The dysregulation of inflammatory responses and cellular biology induced by E-liquids may contribute to various oral pathologies.

[Prophyromonas gingivalis Promotes the Formation of Immunosuppressive Microenvironment in Oral Squamous Cell Carcinoma by CCR6+ Regulatory T Cells: A Study of the Mechanisms Invovled]

Objective

To investigate the mechanisms by which Porphyromonas gingivalis (P. gingivalis) promotes the malignant progression of oral squamous cell carcinoma (OSCC) through the recruitment of chemokine receptor 6-positive (CCR6+) regulatory T cells (Treg) in the tumor microenvironment (TME).

Methods

The Cancer Genome Atlas (TCGA) database was used to analyze the correlation between chemokine ligand 20 (CCL20), CCR6, and Treg. The Treg enrichment index and the expression levels of interleukin (IL)-10 and tumor necrosis factor β1 (TGF-β1) were assessed in the high CCR6 expression group of OSCC patients. C57BL/6 mice were randomly assigned to a control group and an experimental group (n = 6 in each group). The control group received a single injection of 100 μL SCC7, a mice head and neck squamous carcinoma cell line, while the experimental group received a single injection of 100 μL mixture of SCC7 cells and P. gingivalis in the cheek. After two weeks, the mice were sacrificed, and immunohistochemistry was performed to assess the expression levels of CCR6 and forkhead box protein 3 (FOXP3) in OSCC. Flow cytometry was performed to analyze the effects of P. gingivalis on OSCC malignant biological behavior, CCR6+ Treg cells, and the immune microenvironment.

Results

Bioinformatics analysis revealed a correlation between CCL20, CCR6, and Treg (r = 0.373, P < 0.000 1). OSCC patients with high CCR6 expression showed higher Treg enrichment scores and increased IL-10 expression. Animal experiments showed that P. gingivalis promoted the increase in the tumor volume (mm3) (0.294 ± 0.105 in the control group and 0.526 ± 0.101 in the experimental group, P < 0.01) and mass (mg) (206.200 ± 53.950 in the control group and 376.000 ± 119.200 in the experimental group, P < 0.01) in mice with OSCC. Immunohistochemistry confirmed a correlation between CCR6 and FOXP3 (r = 0.659, P < 0.05), and P. gingivalis promoted the expression of CCR6 and FOXP3. Flow cytometry analysis showed that P. gingivalis increased the proportion of CCR6+ Treg (%) (13.780 ± 1.506 in the control group and 18.260 ± 2.257 in the experimental group, P < 0.01) and decreased the proportion of CD8+ T cells (%) (27.120 ± 1.647 in the control group and 21.060 ± 3.148 in the experimental group, P < 0.01) in OSCC, thereby promoting the formation of a immunosuppressive microenvironment.

Conclusion

P. gingivalis promotes the malignant progression of OSCC by recruiting CCR6+ Treg cells to form an immunosuppressive TME.

Current Review on Nanophytomedicines in the Treatment of Oral Cancer: Recent Trends and Treatment Prospects

Cancer is one of the major life-threatening diseases in the world and oral cancer is the 8th most common type of deadly cancers in Asian countries. Despite many causes, tobacco is the main causative agent as 90% of oral cancer cases were due to daily consumption of tobacco and its products. The major drawback of the conventional therapies for oral cancer including chemotherapy, surgery and radiotherapy or combination of these is the dose limiting toxicity. Developments in technology and research led to new innovative discoveries in cancer treatments. In the past few decades, increased attention has been given to researches in alternative cancer treatment strategies using plants and plant products. Recently many anticancer drugs from natural products or phytochemicals were approved internationally. Due to the low bioavailability and poor solubility of phytochemicals, various research works on nano-carrier based drug delivery systems were exploited in the recent past to make them as promising anticancer agents. In the current review, an overview of oral cancer and its treatment, risk factors, missing links of conventional therapies, contribution of nanotechnology in cancer treatment and research on phytochemical based drug treatment and different polymeric nanoparticles were discussed briefly. The future prospects for the use of various types of polymeric nanoparticles applied in the diagnosis and treatment of oral cancer were also mentioned. The major concern of this review is to give the reader a better understanding on various types of treatment for oral cancer.

Fusobacterium nucleatum in tumors: from tumorigenesis to tumor metastasis and tumor resistance

Fusobacterium nucleatum, an anaerobic Gram-negative bacterium primarily residing in the oral cavity, has garnered significant attention for its emerging role in cancer progression and prognosis. While extensive research has revealed mechanistic links between Fusobacterium nucleatum and colorectal cancer, a comprehensive review spanning its presence and metastatic implications in cancers beyond colorectal origin is conspicuously absent. This paper broadens our perspective from colorectal cancer to various malignancies associated with Fusobacterium nucleatum, including oral, pancreatic, esophageal, breast, and gastric cancers. Our central focus is to unravel the mechanisms governing Fusobacterium nucleatum colonization, initiation, and promotion of metastasis across diverse cancer types. Additionally, we explore Fusobacterium nucleatum's adverse impacts on cancer therapies, particularly within the domains of immunotherapy and chemotherapy. Furthermore, this paper underscores the clinical research significance of Fusobacterium nucleatum as a potential tumor biomarker and therapeutic target, offering a novel outlook on its applicability in cancer detection and prognostic assessment.

Oral Microbiome Research in Biopsy Samples of Oral Potentially Malignant Disorders and Oral Squamous Cell Carcinoma and Its Challenges

This study aims to evaluate the potential benefits and challenges of integrating oral microbiome research into the clinical management of oral potentially malignant disorders (OPMD) and oral squamous cell carcinoma (OSCC). The oral microbiome has gained significant attention for its role in the pathogenesis and progression of these conditions, with emerging evidence suggesting its value as a diagnostic and prognostic tool. By critically analyzing current evidence and methodological considerations, this manuscript examines whether microbiome analysis in biopsy samples can aid in the early detection, prognosis, and management of OPMD and OSCC. The complexity and dynamic nature of the oral microbiome require a multifaceted approach to fully understand its clinical utility. Based on this review, we conclude that studying the oral microbiome in this context holds significant promise but also faces notable challenges, including methodological variability and the need for standardization. Ultimately, this manuscript addresses the question, “Should such research be undertaken, given the intricate interactions of various factors and the inherent obstacles involved?”, and also emphasizes the importance of further research to optimize clinical applications and improve patient outcomes.

Clinical relationships between the intratumoral microbiome and risk factors for head and neck cancer

A bioinformatic analysis is a promising approach to understand the relationship between the vast tumor microbiome and cancer development. In the present study, we studied the relationships between the intratumoral microbiome and classical clinical risk factors using bioinformatics analysis of the Cancer Genome Atlas (TCGA) and the Cancer Microbiome Atlas (TCMA) datasets. We used TCMA database and investigated the abundance of microbes at the genus level in solid normal tissue (n = 22) and the primary tumors of patients with head and neck squamous cell carcinoma (HNSCC) (n = 154) and identified three major tumor microbiomes, Fusobacterium, Prevotella, and Streptococcus. The tissue level of Fusobacterium was higher in primary tumors than in solid normal tissue. However, univariate and multivariate analyses of these 3 microbes showed no significant effects on patient survival. We then extracted 43, 55, or 59 genes that were differentially expressed between the over and under the median groups for Fusobacterium, Prevotella, or Streptococcus using the criteria of >2.5, >1.5, or >2.0 fold and p < 0.05 in the Mann-Whitney U test. The results of a pathway analysis revealed the association of Fusobacterium- and Streptococcus-related genes with the IL-17 signaling pathway and Staphylococcus aureus infection, while Prevotella-associated pathways were not extracted. A protein-protein interaction analysis revealed a dense network in the order of Fusobacterium, Streptococcus, and Prevotella. An investigation of the relationships between the intratumoral microbiome and classical clinical risk factors showed that high levels of Fusobacterium were associated with a good prognosis in the absence of alcohol consumption and smoking, while high levels of Streptococcus were associated with a poor prognosis in the absence of alcohol consumption. In conclusion, intratumoral Fusobacterium and Streptococcus may affect the prognosis of patients with HNSCC, and their effects on HNSCC are modulated by the impact of drinking and smoking.

Assessment of Prognostic Factors, Clinical Features Including the Microbiome, and Treatment Outcomes in Patients with Cancer of Unknown Primary Site

INTRODUCTIONS

cancer of unknown primary site (CUP) is a heterogeneous group of cancers in which metastases are found, and the primary tumor is not detected with available diagnostic methods. CUP is a disease that has not been fully researched, and its biology is unclear. The clinical characteristics of CUP are variable, but the prognosis of patients is usually unfavorable, and the possibilities of radical treatment are limited. The microbiome is the genes and gene products of microorganisms residing in a human body. In recent years, thanks to the use of next-generation sequencing, it is possible to assess the impact of the microbiome on human body functions. Head and neck cancers, due to the rich microbiome of this area, are influenced by it, and dysbiosis may be a risk factor for the development of cancer. Objective of this work: the aim of this study was to evaluate prognostic factors, clinical features including the microbiome, and treatment outcomes in patients with cancer of unknown primary site.

RESULTS

in the study group, increased numbers of bacteria of the phyla Bacteroides, Fusobacteria, Bacillota, Actinomycetota, Actinobacteria, and Candidatus were detected, while Firmicutes and Proteobacteria were detected in smaller numbers. Independent predictors of CUP occurrence were the following: leukocyte count of at most 6.49 × 103/mm, bacteria from the Proteobacteria phylum in the microbiome below 11.6%, Firmicutes below 22.1%, and Actinobacteria at least 11.0%. Increased numbers of Porphyromonas and Fusobacterium bacteria were associated with the risk of radiotherapy complications and shortened survival rate.

CONCLUSIONS

clinical diagnosis and treatment of patients with CUP is complicated and difficult due to the lack of consensus on this issue. Treatment and prognosis of patients with CUP is unsatisfactory. The clinical value of the influence of the microbiome on the development, course, and treatment of cancer is becoming increasingly important. The microbiome may become a marker of response to anticancer treatment and the risk of its complications. Immunity modulation with the microbiome provides opportunities for further research on improving the effectiveness of oncological treatment. Fusobacterium and Porphyromonas seem to be the bacteria most important for the development of cancer, also worsening the prognosis of patients by increasing the risk of complications of radiotherapy and shortening the survival rate of patients. Streptococcus and Lactobacillus seem to be bacteria that reduce the risk of cancer, reduce the risk of complications, and improve the prognosis of patients. Total protein deficiency and elevated inflammatory markers are also important predictors of cancer risk.

Biological biomarkers of oral cancer

The oral squamous cell carcinoma (OSCC) 5 year survival rate of 41% has marginally improved in the last few years, with less than a 1% improvement per year from 2005 to 2017, with higher survival rates when detected at early stages. Based on histopathological grading of oral dysplasia, it is estimated that severe dysplasia has a malignant transformation rate of 7%-50%. Despite these numbers, oral dysplasia grading does not reliably predict its clinical behavior. Thus, more accurate markers predicting oral dysplasia progression to cancer would enable better targeting of these lesions for closer follow-up, especially in the early stages of the disease. In this context, molecular biomarkers derived from genetics, proteins, and metabolites play key roles in clinical oncology. These molecular signatures can help predict the likelihood of OSCC development and/or progression and have the potential to detect the disease at an early stage and, support treatment decision-making and predict treatment responsiveness. Also, identifying reliable biomarkers for OSCC detection that can be obtained non-invasively would enhance management of OSCC. This review will discuss biomarkers for OSCC that have emerged from different biological areas, including genomics, transcriptomics, proteomics, metabolomics, immunomics, and microbiomics.

The Impact of Oral Microbiome Dysbiosis on the Aetiology, Pathogenesis, and Development of Oral Cancer

Oral squamous cell carcinoma (OSCC) is the most common head and neck cancer. Although the oral cavity is an easily accessible area for visual examination, the OSCC is more often detected at an advanced stage. The global prevalence of OSCC is around 6%, with increasing trends posing a significant health problem due to the increase in morbidity and mortality. The oral cavity microbiome has been the target of numerous studies, with findings highlighting the significant role of dysbiosis in developing OSCC. Dysbiosis can significantly increase pathobionts (bacteria, viruses, fungi, and parasites) that trigger inflammation through their virulence and pathogenicity factors. In contrast, chronic bacterial inflammation contributes to the development of OSCC. Pathobionts also have other effects, such as the impact on the immune system, which can alter immune responses and contribute to a pro-inflammatory environment. Poor oral hygiene and carbohydrate-rich foods can also increase the risk of developing oral cancer. The risk factors and mechanisms of OSCC development are not yet fully understood and remain a frequent research topic. For this reason, this narrative review concentrates on the issue of dysbiosis as the potential cause of OSCC, as well as the underlying mechanisms involved.

Oral microbiota and metabolites: key players in oral health and disorder, and microbiota-based therapies

The review aimed to investigate the diversity of oral microbiota and its influencing factors, as well as the association of oral microbiota with oral health and the possible effects of dysbiosis and oral disorder. The oral cavity harbors a substantial microbial burden, which is particularly notable compared to other organs within the human body. In usual situations, the microbiota exists in a state of equilibrium; however, when this balance is disturbed, a multitude of complications arise. Dental caries, a prevalent issue in the oral cavity, is primarily caused by the colonization and activity of bacteria, particularly streptococci. Furthermore, this environment also houses other pathogenic bacteria that are associated with the onset of gingival, periapical, and periodontal diseases, as well as oral cancer. Various strategies have been employed to prevent, control, and treat these disorders. Recently, techniques utilizing microbiota, like probiotics, microbiota transplantation, and the replacement of oral pathogens, have caught the eye. This extensive examination seeks to offer a general view of the oral microbiota and their metabolites concerning oral health and disease, and also the resilience of the microbiota, and the techniques used for the prevention, control, and treatment of disorders in this specific area.

Oral microbiome and its relationship with oral cancer

ABSTRACT

As the initial point for digestion, the balance of oral microorganisms plays an important role in maintaining local and systemic health. Oral dysbiosis, or an imbalance in the oral microbial community, may lead to the onset of various diseases. The presence or abnormal increase of microbes in the oral cavity has attracted significant attention due to its complicated relationship with oral cancer. Oral cancer can remodel microbial profiles by creating a more beneficial microenvironment for its progression. On the other hand, altered microbial profiles can promote tumorigenesis by evoking a complex inflammatory response and affecting host immunity. This review analyzes the oncogenic potential of oral microbiome alterations as a driver and biomarker. Additionally, a potentially therapeutic strategy via the reversal of the oral microbiome dysbiosis in oral cancers has been discussed.

The potential value of oral microbial signatures for prediction of oral squamous cell carcinoma based on machine learning algorithms

OBJECTIVE

This study aimed to explore the potential predictive value of oral microbial signatures for oral squamous cell carcinoma (OSCC) risk based on machine learning algorithms.

METHODS

The oral microbiome signatures were assessed in the unstimulated saliva samples of 80 OSCC patients and 179 healthy individuals using 16S rRNA gene sequencing. Four different machine learning classifiers were used to develop prediction models.

RESULTS

Compared with control participants, OSCC patients had a higher microbial dysbiosis index (MDI, p < 0.001). Among four machine learning classifiers, random forest (RF) provided the best predictive performance, followed by the support vector machines, artificial neural networks and naive Bayes. After controlling the potential confounders using propensity score matching, the optimal RF model was further developed incorporating a minimal set of 20 bacteria genera, exhibiting better predictive performance than the MDI (AUC: 0.992 vs. 0.775, p < 0.001).

CONCLUSIONS

The novel MDI and RF model developed in this study based on oral microbiome signatures may serve as noninvasive tools for predicting OSCC risk.

Insights into the oral microbiota in human systemic cancers

The oral cavity stands as one of the pivotal interfaces facilitating the intricate interaction between the human body and the external environment. The impact of diverse oral microorganisms on the emergence and progression of various systemic cancers, typified by oral cancer, has garnered increasing attention. The potential pathogenicity of oral bacteria, notably the anaerobic Porphyromonas gingivalis and Fusobacterium nucleatum, has been extensively studied and exhibits obvious correlation with different carcinoma types. Furthermore, oral fungi and viruses are closely linked to oropharyngeal carcinoma. Multiple potential mechanisms of oral microbiota-induced carcinogenesis have been investigated, including heightened inflammatory responses, suppression of the host immune system, influence on the tumor microenvironment, anti-apoptotic activity, and promotion of malignant transformation. The disturbance of microbial equilibrium and the migration of oral microbiota play a pivotal role in facilitating oncogenic functions. This review aims to comprehensively outline the pathogenic mechanisms by which oral microbiota participate in carcinogenesis. Additionally, this review delves into their potential applications in cancer prevention, screening, and treatment. It proves to be a valuable resource for researchers investigating the intricate connection between oral microbiota and systemic cancers.

Differential analysis of serum immunology and gut microbiota in patients with gastrointestinal diseases

Objective

Gastric and intestinal diseases possess distinct characteristics although they are interconnected. The primary objective of this study was to investigate the pathogenesis of gastrointestinal diseases through different analyses of clinical characteristics, serum immunology, and gut microbiota in patients with gastrointestinal diseases.

Methods

We collected serum samples from 89 patients with gastrointestinal diseases and 9 healthy controls for immunological assessment, stool samples for DNA extraction, library construction, sequencing, as well as clinical data for subsequent analysis.

Results

Regarding clinical characteristics, there were significant differences between the disease group and the healthy control (HC) group, particularly in terms of age, cancer antigen 125 (CA125), cancer antigen 199 (CA199), alpha-fetoprotein (AFP), total bilirubin (TBIL) and indirect bilirubin (IBIL). The intestinal disease (ID) group exhibited the highest IL-6 level, which significantly differed from the stomach disease (SD) group (p < 0.05). In comparing the HC with the ID groups, significant differences in abundance were detected across 46 species. The HC group displayed a greater abundance of Clostridiales, Clostridia, Firmicutes, Bifidobacterium, Bifidobacteriaceae, Bifidobacteriales, Actinobacteria, Veillonellaceae, Longum, Copri, Megamonas and Callidus than other species. Similarly, when comparing the HC with the SD groups, significant differences in abundance were identified among 49 species, with only one species that the Lachnospiraceae in the HC group exhibited a higher abundance than others. Furthermore, certain clinical characteristics, such as CA125, CA199, glucose (Glu), creatine kinase-MB (CKMB) and interleukin-22 (IL-22), displayed positive correlations with enriched gut species in the ID and SD groups, while exhibiting a negative correlation with the HC group.

Conclusion

The disturbance in human gut microbiota is intimately associated with the development and progression of gastrointestinal diseases. Moreover, the gut microbiota in the HC group was found more diverse than that in the ID and SD groups, and there were significant differences in microbial species among the three groups at different classification levels. Notably, a correlation was identified between specific clinical characteristics (e.g., CA125, CA199, Glu, CKMB and IL-22) and gut microbiota among patients with gastrointestinal diseases.

Comparative analysis of microbial composition and functional characteristics in dental plaque and saliva of oral cancer patients

BACKGROUND

The oral cavity is home to various ecological niches, each with its own unique microbial composition. Understanding the microbial communities and gene composition in different ecological niches within the oral cavity of oral cancer (OC) patients is crucial for determining how these microbial populations contribute to disease progression.

METHODS

In this study, saliva and dental plaque samples were collected from patients with OC. Metagenomic sequencing was employed to analyze the microbial community classification and functional composition of the different sample groups.

RESULTS

The results of the study revealed significant differences in both the function and classification of microbial communities between saliva and dental plaque samples. The diversity of microbial species in saliva was found to be higher compared to  that in plaque samples. Notably, Actinobacteria were enriched in the dental plaque of OC patients. Furthermore, the study identified several inter-group differential marker species, including Prevotella intermedia, Haemophilus parahaemolyticus, Actinomyces radius, Corynebacterium matruchitii, and Veillonella atypica. Additionally, 1,353 differential genes were annotated into 23 functional pathways. Interestingly, a significant correlation was observed between differentially labeled species and Herpes simplex virus 1 (HSV-1) infection, which may be related to the occurrence and development of cancer.

CONCLUSIONS

Significant differences in the microbial and genetic composition of saliva and dental plaque samples were observed in OC patients. Furthermore, pathogenic bacteria associated with oral diseases were predominantly enriched in saliva. The identification of inter-group differential biomarkers and pathways provide insights into the relationship between oral microbiota and the occurrence and development of OC.

Oral microbiota and oral squamous cell carcinoma: a review of their relation and carcinogenic mechanisms

Oral Squamous Cell Carcinoma (OSCC) is the most common type of head and neck cancer worldwide. Emerging research suggests a strong association between OSCC and the oral microbiota, a diverse community of bacteria, fungi, viruses, and archaea. Pathogenic bacteria, in particular Porphyromonas gingivalis and Fusobacterium nucleatum, have been closely linked to OSCC. Moreover, certain oral fungi, such as Candida albicans, and viruses, like the human papillomavirus, have also been implicated in OSCC. Despite these findings, the precise mechanisms through which the oral microbiota influences OSCC development remain unclear and necessitate further research. This paper provides a comprehensive overview of the oral microbiota and its relationship with OSCC and discusses potential carcinogenic pathways that the oral microbiota may activate or modulate are also discussed.

Drug delivery systems for enhanced tumour treatment by eliminating intra-tumoral bacteria

Cancer remains one of the serious threats to human health. The relationship between bacteria and various tumours has been widely reported in recent years, and studies on intra-tumoral bacteria have become important as intra-tumoral bacteria directly affect the tumorigenesis, progression, immunity and metastatic processes. Therefore, eliminating these commensal intra-tumoral bacteria while treating tumour is expected to be a potential strategy to further enhance the clinical outcome of tumour therapy. Drug delivery systems (DDSs) are widely used to deliver antibiotics and chemotherapeutic drugs for antibacterial and anticancer applications, respectively. Thus, this review firstly provides a comprehensive summary of the association between intra-tumoral bacteria and a host of tumours, followed by a description of advanced DDSs for improving the therapeutic efficacy of cancer treatment through the elimination of intra-tumoral bacteria. It is hoped that this review will provide guidelines for the therapeutic and "synergistic antimicrobial and antitumour" drug delivery strategy.

Oral tumor heterogeneity, its implications for patient monitoring and designing anti-cancer strategies

Oral cancer tumors occur in the mouth and are mainly derived from oral mucosa linings. It is one of the most common and fatal malignant diseases worldwide. The intratumor heterogeneity (ITH) of oral cancerous tumor is vast, so it is challenging to study and interpret. Due to environmental selection pressures, ITH arises through diverse genetic, epigenetic, and metabolic alterations. The ITH also talks about peri-tumoral vascular/ lymphatic growth, perineural permeation, tumor necrosis, invasion, and clonal expansion/ the coexistence of multiple subclones in a single tumor. The heterogeneity offers tumors the adaptability to survive, induce growth/ metastasis, and, most importantly, escape antitumor therapy. Unfortunately, the ITH is prioritized less in determining disease pathology than the traditional TNM classifications or tumor grade. Understanding ITH is challenging, but with the advancement of technology, this ITH can be decoded. Tumor genomics, proteomics, metabolomics, and other modern analyses can provide vast information. This information in clinics can assist in understanding a tumor's severity and be used for diagnostic, prognostic, and therapeutic decision-making. Lastly, the oral tumor ITH can lead to individualized, targeted therapy strategies fighting against OC.

Alcohol consumption modulates Candida albicans-induced oral carcinogenesis and progression

OBJECTIVES

This study aimed to determine the impact of low levels of alcohol consumption on the interaction of the oral cavity with Candida albicans, a species that is commonly found at higher levels in the oral cavities of regular alcohol consumers, patients with pre-malignant diseases, and patients with existing oral cancer (OC).

METHODS

The gingival squamous cell carcinoma cell line, Ca9-22, was subjected to low-level ethanol exposure before co-culture with heat-inactivated C. albicans (HICA). We performed cell viability assays, measured reactive oxygen species, and used Western blot analysis for cell death markers to examine the effect of ethanol and HICA on cells. Scratch assays and anchorage-independent growth assays were used to determine cell behavioral changes.

RESULTS

The results showed that ethanol in combination with HICA exacerbated cell death and cell cycle disruption, delayed NF-κB signaling, increased TIMP-2 secretion, and subsequently decreased MMP-2 secretion when compared to exposure to HICA alone. Conversely, both ethanol and HICA independently increased proliferation of Ca9-22 cells in scratch assays, and in combination, increased their capacity for anchorage-independent growth.

CONCLUSION

Low levels of ethanol may provide protective effects against Candida-induced inflammatory oral carcinogenesis or OC progression.

Oral Bacteria, Virus and Fungi in Saliva and Tissue Samples from Adult Subjects with Oral Squamous Cell Carcinoma: An Umbrella Review

Oral squamous cell carcinoma (OSCC) is the most common oral cavity malignancy associated with multiple risk factors. In the last 14 years, oral dysbiosis has attracted the scientific community's attention as a potential oncogenic factor, in parallel with the development of omics technologies that have revolutionized microbiological research. The present umbrella review aimed to investigate the oral microbiological content (bacilli, viruses, and fungi) of tissue and saliva samples from adult (>18 years) patients with OSCC. The secondary objective was to compare the oral microbiome of OSCC subjects with non-OSCC subjects. The study protocol was under the PRISMA statement and registered on PROSPERO (CRD42023448153). Data from 32 systematic reviews were extracted, qualitatively summarized, and analyzed using AMSTAR-2. An increase in oral bacteria of the phylum Fusobacteria, Proteobacteria, and Bacteroidetes and a decrease in Firmicutes and Actinobacteria were observed in OSCC patients. The increased bacterial genera were periodontopathogens. The most common viruses were EBV and HPV, especially the high-risk genotypes. Candida was the most studied oral fungus and was always increased in OSCC subjects. Further studies should investigate the possible carcinogenic mechanisms of oral microorganisms found increased in tissue samples and saliva from adult subjects with OSCC.

The Mechanisms of Probiotics, Prebiotics, Synbiotics, and Postbiotics in Oral Cancer Management

Oral carcinogenesis is preceded by oral diseases associated with inflammation such as periodontitis and oral candidiasis, which are contributed by chronic alcoholism, smoking, poor oral hygiene, and microbial infections. Dysbiosis is an imbalance of microbial composition due to oral infection, which has been reported to contribute to oral carcinogenesis. Therefore, in this review, we summarised the role of probiotics, prebiotics, synbiotics, and postbiotics in promoting a balanced oral microbiome, which may prevent oral carcinogenesis due to oral infections. Probiotics have been shown to produce biofilm, which possesses antibacterial activity against oral pathogens. Meanwhile, prebiotics can support growth and increase the benefit of probiotics. In addition, postbiotics possess antibacterial, anticariogenic, and anticancer properties that potentially aid in oral cancer prevention and treatment. The use of probiotics, prebiotics, synbiotics, and postbiotics for oral cancer management is still limited despite their vast potential, thus, discovering their prospects could herald a novel approach to disease prevention and treatment while participating in combating antimicrobial resistance.

Hypoxia-induced tumor exosomes promote angiogenesis through miR-1825/TSC2/mTOR axis in oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) is characterized by enhanced angiogenesis resulting in poor prognosis despite improvements in diagnostic/therapeutic techniques. Here, we aimed at investigating potential roles of miR-1825 enclosed in OSCC-derived exosomes on angiogenesis under hypoxic conditions.

METHODS

Effects of miR-1825 mimic/inhibitor as well as hypoxia-induced tumor derived exosomes on human umbilical vein endothelial cells (HUVECs) were evaluated using cell viability, migration/invasion, tube formation, and spheroid-based 3D angiogenesis assays.

RESULTS

Hypoxic conditions caused significant increase in miR-1825 levels in OSCC cells and hiTDEs. miR-1825 alone and within hiTDEs promoted endothelial cell viability, migration, invasion, and angiogenic potential, which is reversed via inhibition of miR-1825 expression. miR-1825 within hiTDEs altered the angiogenesis potential of HUVEC cells via deregulation of TSC2/mTOR axis.

CONCLUSIONS

We showed that hypoxia led to OSCC-derived exosome mediated transfer of miR-1825 to HUVECs and enhanced angiogenesis in OSCC in vitro.

Oral Potentially Malignant Disorders and Candida in Oral Tongue Squamous Cell Carcinoma Patients

This retrospective study addressed the role of oral potentially malignant disorders and the presence of intraepithelial Candida hyphae in the carcinogenesis of the oral tongue squamous cell carcinoma and its association with smoking, alcohol consumption, and oral inflammatory burden. The medical records of 183 subjects diagnosed with oral tongue squamous cell carcinoma at the Helsinki University Hospital were investigated. Preceding oral lichen planus, lichenoid reaction, and leukoplakia diagnosis were recorded. Further, the data on Candida hyphae in histological samples as an indicator of oral candidiasis, oral inflammatory burden, smoking, and alcohol consumption were recorded and analyzed. The histopathological diagnosis of oral lichen planus/lichenoid reaction (p < 0.001) and the presence of Candida hyphae (p = 0.005) were associated significantly with female gender. Oral lichen planus/lichenoid reaction patients were less often smokers than patients without these lesions. Candida hyphae were more often recorded in patients without alcohol use (p = 0.012). Oral lichen planus/lichenoid reaction and Candida hyphae in histological samples were associated with female gender and lower levels of typical risk factors, such as alcohol use and smoking, in oral tongue squamous cell carcinoma patients. Therefore, these patients should be well monitored despite a potential lack of the classical risk factors of oral carcinoma.

Oral Microbiome in Health and Disease: Maintaining a Healthy, Balanced Ecosystem and Reversing Dysbiosis

The oral microbiome is a complex and dynamic assemblage of microorganisms that normally exist within the mouth, contributing to host health via a number of mechanisms, including exclusion of harmful microbes and immune optimization [...].

Cross-kingdom Microbial Interactions Within the Oral Cavity and Their Implications for Oral Disease

Purpose of Review

This review serves to highlight the cross-kingdom interactions that can occur within the human oral cavity between fungus Candida albicans and oral bacteria, and their impact on the delicate balance between oral health and disease.

Recent Findings

A growing number of physical, chemical, and metabolic networks have been identified that underpin these cross-kingdom interactions. Moreover, these partnerships are often synergistic and can modulate microbial burden or virulence. This, in turn, can drive the onset or progression of oral diseases such as dental caries, periodontitis, denture-associated stomatitis, and oral cancer.

Summary

The impact of cross-kingdom interactions on the cellular, biochemical, and communal composition of oral microbial biofilms is increasingly clear. With growing insight into these processes at the molecular level, so this knowledge can be used to better inform the development of novel strategies to manipulate the oral microbiota to promote oral health and combat oral disease.

Oral dysbiosis in the onset and carcinogenesis of oral epithelial dysplasia: A systematic review

OBJECTIVE

This systematic review aims to investigate possible connections between the oral microbiome and the onset and carcinogenesis of oral epithelial dysplasia (OED).

METHODS

A systematic search was performed on PubMed, Embase, Cochrane Database, and SCOPUS by two authors independently, addressing the focused question- "Has oral microbiome dysbiosis been involved in the onset and carcinogenesis of oral epithelial dysplasia?" We used the Newcastle-Ottawa scale to assess the quality of studies included in the review.

RESULTS

Out of 580 references screened, ten studies were found eligible for inclusion. All studies were case-control studies, and only qualitative analysis was conducted due to heterogeneous characteristics. The overall risk of bias in the eligible studies was considered as high. Microbiome diversity indices showed inconsistent evidence among studies. A significant increase of phylum Bacteroidetes in OED patients was reported in five studies. Five studies reported an increase of genus Fusobacterium in both the OED and oral squamous cell carcinoma (OSCC) patients and six different studies respectively reported a reduction of genus Streptococcus in both the OED and OSCC groups when compared to normal controls. Other predominant bacteria that were specific to different patient groups varied in each study.

CONCLUSIONS

The results of the included studies showed that the composition of the oral microbiome in patients with OED compared to healthy controls and OSCC patients was inconsistent. However, all ten studies showed non-negligible heterogeneity in the type and size of the sample, and the comparability between groups, which strongly limited the external validity of results. Further studies are strongly recommended.

Microbial dysbiosis in oral squamous cell carcinoma: A systematic review and meta-analysis

OBJECTIVE

The aim of this study was to summarize previously published data and assess the alterations in the composition of the oral microbiome in OSCC using a systematic review and meta-analysis.

DESIGN

Electronic databases were systematically searched for studies on the oral microbiome in OSCC published before December 2021. Qualitative assessments of compositional variations at the phylum level were performed. The meta-analysis on abundance changes of bacteria genera was performed via a random-effects model.

RESULTS

A total of 18 studies involving 1056 participants were included. They consisted of two categories of studies: 1) case-control studies (n = 9); 2) nine studies that compared the oral microbiome between cancerous tissues and paired paracancerous tissues. At the phylum level, enrichment of Fusobacteria but depletion in Actinobacteria and Firmicutes in the oral microbiome was demonstrated in both categories of studies. At the genus level, Fusobacterium showed an increased abundance in OSCC patients (SMD = 0.65, 95% CI: 0.43-0.87, Z = 5.809, P = 0.000) and in cancerous tissues (SMD = 0.54, 95% CI: 0.36-0.72, Z = 5.785, P = 0.000). The abundance of Streptococcus was decreased in OSCC (SMD = -0.46, 95% CI: -0.88-0.04, Z = -2.146, P = 0.032) and in cancerous tissues (SMD = -0.45, 95% CI: -0.78-0.13, Z = -2.726, P = 0.006).

CONCLUSIONS

Disturbances in the interactions between enriched Fusobacterium and depleted Streptococcus may participate in or prompt the occurrence and development of OSCC and could be potential biomarkers for detection of OSCC.

F. nucleatum facilitates oral squamous cell carcinoma progression via GLUT1-driven lactate production

BACKGROUND

Tumor-resident microbiota has been documented for various cancer types. Oral squamous cell carcinoma (OSCC) is also enriched with microbiota, while the significance of microbiota in shaping the OSCC microenvironment remains elusive.

METHODS

We used bioinformatics and clinical sample analysis to explore relationship between F. nucleatum and OSCC progression. Xenograft tumor model, metabolic screening and RNA sequencing were performed to elucidate mechanisms of pro-tumor role of F. nucleatum.

FINDINGS

We show that a major protumorigenic bacterium, F. nucleatum, accumulates in invasive margins of OSCC tissues and drives tumor-associated macrophages (TAMs) formation. The mechanistic dissection shows that OSCC-resident F. nucleatum triggers the GalNAc-Autophagy-TBC1D5 signaling, leading to GLUT1 aggregation in the plasma membrane and the deposition of extracellular lactate. Simultaneous functional inhibition of GalNAc and GLUT1 efficiently reduces TAMs formation and restrains OSCC progression.

INTERPRETATION

These findings suggest that tumor-resident microbiota affects the immunomodulatory and protumorigenic microenvironment via modulating glycolysis and extracellular lactate deposition. The targeted intervention of this process could provide a distinct clinical strategy for patients with advanced OSCC.

FUNDING

This work was supported by the National Natural Science Foundation of China for Key Program Projects (82030070, to LC) and Distinguished Young Scholars (31725011, to LC), as well as Innovation Team Project of Hubei Province (2020CFA014, to LC).

Oral Microbial Signatures of Tobacco Chewers and Oral Cancer Patients in India

Dysbiosis of the oral microbiome has been found to play a key role in the genesis and progression of oral cancer (OC). Tobacco chewing, a risk factor for oral cancer, is also associated with oral dysbiosis. Since tobacco chewing is a lifestyle habit in the South Asian subcontinent, including India, and contributes to one-third of the global oral cancer burden; we aimed to identify the oral bacterial diversity of Indian oral cancer patients and tobacco chewers. We used 16S rRNA amplicon sequencing to study the composition of oral microbiota in OC patients and tobacco chewers in India and compared it with healthy controls. The abundance of predominant phyla, Firmicutes, and Bacteroidetes varied between the study groups. Our study identified Leptotrichia, Treponema, Lautropia, and Cardiobacterium as significantly enriched in tobacco chewers, whereas genera Pseudomonas, Capnocytophaga, and Mycoplasma were enriched in oral cancer, which could be potential biomarkers for the Indian population. Furthermore, the functional prediction revealed that genes involved in lipid biosynthesis and fatty acid elongation were upregulated in the oral cancer group, whereas those for the reductive TCA cycle were upregulated in the tobacco group. As the role of bacteria in oral cancer is becoming more evident, identification of bacterial diversity and biomarkers for tobacco chewers and OC patients can aid in the early diagnosis of OC in high-risk individuals.

Porphyromonas gingivalis promotes the progression of oral squamous cell carcinoma by activating the neutrophil chemotaxis in the tumour microenvironment

BACKGROUND

We aimed to determine the significance of Porphyromonas gingivalis (P. gingivalis) in promoting tumour progression in the tumour microenvironment (TME) of oral squamous cell carcinoma (OSCC).

METHODS

The Gene Expression Omnibus (GEO) was used to screen out the differentially expressed genes from the two datasets of GEO138206 and GSE87539. Immunohistochemistry and immunofluorescence analysis of samples, cell biological behaviour experiments, and tumour-bearing animal experiments were used to verify the results in vivo and in vitro. The mechanism was revealed at the molecular level, and rescue experiments were carried out by using inhibitors and lentiviruses.

RESULTS

CXCL2 was selected by bioinformatics analysis and was found to be related to a poor prognosis in OSCC patients. Samples with P. gingivalis infection in the TME of OSCC had the strongest cell invasion and proliferation and the largest tumour volume in tumour-bearing animal experiments and exhibited JAK1/STAT3 signalling pathway activation and epithelial-mesenchymal transition (EMT). The expression of P. gingivalis, CXCL2 and TANs were independent risk factors for poor prognosis in OSCC patients. A CXCL2/CXCR2 signalling axis inhibitor significantly decreased the invasion and proliferation ability of cells and the tumour volume in mice. When lentivirus was used to block the CXCL2/CXCR2 signalling axis, the activity of the JAK1/STAT3 signalling pathway was decreased, and the phenotype of EMT was reversed.

CONCLUSION

Porphyromonas gingivalis promotes OSCC progression by recruiting TANs via activation of the CXCL2/CXCR2 axis in the TME of OSCC.

Oral Microflora in the Background of Oral Cancer: A Review

Oral cancer exhibits a multifactorial etiology. Microorganisms residing within the oral cavity as normal commensals have long been studied in terms of their role in the process of carcinogenesis. Other factors such as tobacco and alcohol consumption have also been implicated in carcinogenesis as the primary risk factors. Poor oral hygiene, dietary abnormalities, and betel nut chewing can also act as contributory factors in the process of carcinogenesis. Multiple research works have been carried out in the past to shed some light on the role of exogenous bacterial species in the development of cancers. Studies conducted were to assess changes in the oral microflora in patients suffering from oral carcinoma and to evaluate and compare pre-operative and post-operative changes in oral microbiota. For this review, multiple articles were studied and evaluated. Appropriate conclusions were drawn and are presented in the review. A definitive link between cancer and microflora is yet to be established. In the present article, a review of the studies done on the contribution of microbial flora present within the oral cavity and their role in oral cancer is done and its nature and extent are evaluated. A variety of microbiological agents can contribute to the progression of carcinogenesis in the presence of definitive risk factors such as alcoholism and smoking.

Cross-kingdom interaction between Candida albicans and oral bacteria

Candida albicans is a symbiotic fungus that commonly colonizes on oral mucosal surfaces and mainly affects immuno-compromised individuals. Polymicrobial interactions between C. albicans and oral microbes influence the cellular and biochemical composition of the biofilm, contributing to change clinically relevant outcomes of biofilm-related oral diseases, such as pathogenesis, virulence, and drug-resistance. Notably, the symbiotic relationships between C. albicans and oral bacteria have been well-documented in dental caries, oral mucositis, endodontic and periodontal diseases, implant-related infections, and oral cancer. C. albicans interacts with co-existing oral bacteria through physical attachment, extracellular signals, and metabolic cross-feeding. This review discusses the bacterial-fungal interactions between C. albicans and different oral bacteria, with a particular focus on the underlying mechanism and its relevance to the development and clinical management of oral diseases.

Microbiome landscape of lesions and adjacent normal mucosal areas in oral lichen planus patient

The pathogenesis of oral lichen planus (OLP) remains unclear, and microbial dysbiosis has been proposed to play a role in the pathogenesis of OLP. Oral mucosal swabs from 77 OLP patients and 76 healthy subjects were collected. The bacterial community among the OLP lesion, the adjacent normal mucosal, and the oral mucosal surface in healthy people were analyzed by 16S sequencing. The factor of gender and age that may affect the flora distribution of OLP patients were explored. Results indicate no significant difference in microbiota between OLP and the adjacent group. Compared with the healthy group, Neisseria, Haemophilus, Fusobacterium, Porphyromonas, Rothia, Actinomyces, and Capnocytophaga significantly increased in the OLP group. Actinomyces increased in male OLP patients, and the other six bacteria increased in female OLP patients. In female OLP patients, Lautropia and Dialister were positively correlated with age. While in male OLP patients, Moraxella, Porphyromonas, and Fusobacterium were positively correlated with age. Functional enrichment analysis suggested that abnormal energy metabolism related to ATP synthases, abnormal transport and metabolism of glycans, amino acids, and vitamins, and disorders of the local immune microenvironment might exist in OLP lesion.

Strategies to Combat Caries by Maintaining the Integrity of Biofilm and Homeostasis during the Rapid Phase of Supragingival Plaque Formation

Bacteria in the oral cavity, including commensals and opportunistic pathogens, are organized into highly specialized sessile communities, coexisting in homeostasis with the host under healthy conditions. A dysbiotic environment during biofilm evolution, however, allows opportunistic pathogens to become the dominant species at caries-affected sites at the expense of health-associated taxa. Combining tooth brushing with dentifrices or rinses combat the onset of caries by partially removes plaque, but resulting in the biofilm remaining in an immature state with undesirables’ consequences on homeostasis and oral ecosystem. This leads to the need for therapeutic pathways that focus on preserving balance in the oral microbiota and applying strategies to combat caries by maintaining biofilm integrity and homeostasis during the rapid phase of supragingival plaque formation. Adhesion, nutrition, and communication are fundamental in this phase in which the bacteria that have survived these adverse conditions rebuild and reorganize the biofilm, and are considered targets for designing preventive strategies to guide the biofilm towards a composition compatible with health. The present review summarizes the most important advances and future prospects for therapies based on the maintenance of biofilm integrity and homeostasis as a preventive measure of dysbiosis focused on these three key factors during the rapid phase of plaque formation.

Current Status, Opportunities, and Challenges of Exosomes in Oral Cancer Diagnosis and Treatment

Oral cancer is one of the most common cancers in the world, with more than 300,000 cases diagnosed each year, of which oral squamous cell carcinoma accounts for more than 90%, with a 5-year survival rate of only 40–60%, and poor prognosis. Exploring new strategies for the early diagnosis and treatment of oral cancer is key to improving the survival rate. Exosomes are nanoscale lipid bilayer membrane vesicles that are secreted by almost all cell types. During the development of oral cancer, exosomes can transport their contents (DNA, RNA, proteins, etc) to target cells and promote or inhibit the proliferation, invasion, and metastasis of oral cancer cells by influencing the host immune response, drug-resistant metastasis, and tumour angiogenesis. Therefore, exosomes have great potential and advantages as biomarkers for oral cancer diagnosis, and as drug delivery vehicles or targets for oral cancer therapy. In this review, we first describe the biogenesis, biological functions, and isolation methods of exosomes, followed by their relationship with oral cancer. Here, we focused on the potential of exosomes as oral cancer biomarkers, drug carriers, and therapeutic targets. Finally, we provide an insightful discussion of the opportunities and challenges of exosome application in oral cancer diagnosis and treatment, intending to offer new ideas for the clinical management of oral cancer.

Microbiota in health and diseases

The role of microbiota in health and diseases is being highlighted by numerous studies since its discovery. Depending on the localized regions, microbiota can be classified into gut, oral, respiratory, and skin microbiota. The microbial communities are in symbiosis with the host, contributing to homeostasis and regulating immune function. However, microbiota dysbiosis can lead to dysregulation of bodily functions and diseases including cardiovascular diseases (CVDs), cancers, respiratory diseases, etc. In this review, we discuss the current knowledge of how microbiota links to host health or pathogenesis. We first summarize the research of microbiota in healthy conditions, including the gut-brain axis, colonization resistance and immune modulation. Then, we highlight the pathogenesis of microbiota dysbiosis in disease development and progression, primarily associated with dysregulation of community composition, modulation of host immune response, and induction of chronic inflammation. Finally, we introduce the clinical approaches that utilize microbiota for disease treatment, such as microbiota modulation and fecal microbial transplantation.

MicroRNA-21 Expression as a Prognostic Biomarker in Oral Cancer: Systematic Review and Meta-Analysis

Oral carcinoma represents one of the main carcinomas of the head and neck region, with a 5-year survival rate of less than 50%. Smoking and tobacco use are recognized risk factors. Prognostic survival biomarkers can be a valid tool for assessing a patient’s life expectancy and directing therapy towards specific targets. Among the biomarkers, the alteration of miR-21 expression in tumor tissues is increasingly reported as a valid prognostic biomarker of survival for oral cancer. The purpose of this meta-analysis was, therefore, to investigate and summarize the results in the literature concerning the potential prognostic expression of tissue miR-21 in patients with OSCC. Methods: The systematic review was conducted following the PRISMA guidelines using electronic databases, such as PubMed, Scopus, and the Cochrane Central Register of Controlled Trials, with the use of combinations of keywords, such as miR-21 AND oral cancer, microRNA AND oral cancer, and miR-21. The meta-analysis was performed using the RevMan 5.41 software. Results: At the end of the article-selection process, 10 studies were included in the meta-analysis, and the result for the main outcome was a pooled HR per overall survival (OS) of 1.29 (1.16–1.44) between high and low expression of miR-21. Conclusions: The data in the literature and the results emerging from the systematic review indicate that miR-21 can provide a prognostic indication in oral cancer.

Oral microbiota in human systematic diseases

Oral bacteria directly affect the disease status of dental caries and periodontal diseases. The dynamic oral microbiota cooperates with the host to reflect the information and status of immunity and metabolism through two-way communication along the oral cavity and the systemic organs. The oral cavity is one of the most important interaction windows between the human body and the environment. The microenvironment at different sites in the oral cavity has different microbial compositions and is regulated by complex signaling, hosts, and external environmental factors. These processes may affect or reflect human health because certain health states seem to be related to the composition of oral bacteria, and the destruction of the microbial community is related to systemic diseases. In this review, we discussed emerging and exciting evidence of complex and important connections between the oral microbes and multiple human systemic diseases, and the possible contribution of the oral microorganisms to systemic diseases. This review aims to enhance the interest to oral microbes on the whole human body, and also improve clinician’s understanding of the role of oral microbes in systemic diseases. Microbial research in dentistry potentially enhances our knowledge of the pathogenic mechanisms of oral diseases, and at the same time, continuous advances in this frontier field may lead to a tangible impact on human health.

Porphyromonas gingivalis in oral squamous cell carcinoma: A review

Oral cancer contributes significantly to the global cancer burden. Oral bacteria play an important role in the spread of oral cancer, according to mounting evidence. The most proven instance is the carcinogenic implications of Porphyromonas gingivalis, a key pathogen in chronic periodontitis. It is imperative to understand the pathogenesis of P. gingivalis in OSCC. This review aims to gather and assess scientific shreds of evidence on the involvement of Porphyromonas gingivalis in the molecular mechanism of oral squamous cell carcinoma.

Association Between Oral Microbiota and Human Brain Glioma Grade: A Case-Control Study

Gliomas are the most prevalent form of primary malignant brain tumor, which currently have no effective treatments. Evidence from human studies has indicated that oral microbiota is closely related to cancers; however, whether oral microbiota plays a role in glioma malignancy remains unclear. The present study aimed to investigate the association between oral microbiota and grade of glioma and examine the relationship between malignancy-related oral microbial features and the isocitrate dehydrogenase 1 (IDH1) mutation in glioma. High-grade glioma (HGG; n=23) patients, low-grade glioma (LGG; n=12) patients, and healthy control (HCs; n=24) participants were recruited for this case-control study. Saliva samples were collected and analyzed for 16S ribosomal RNA (rRNA) sequencing. We found that the shift in oral microbiota β-diversity was associated with high-grade glioma (p=0.01). The phylum Patescibacteria was inversely associated with glioma grade (LGG and HC: p=0.035; HGG and HC: p<0.01). The genera Capnocytophaga (LGG and HC: p=0.043; HGG and HC: p<0.01) and Leptotrichia (LGG and HC: p=0.044; HGG and HC: p<0.01) were inversely associated with glioma grades. The genera Bergeyella and Capnocytophaga were significantly more positively correlated with the IDH1 mutation in gliomas when compared with the IDH1-wild-type group. We further identified five oral microbial features (Capnocytophaga Porphyromonas, Haemophilus, Leptotrichia, and TM7x) that accurately discriminated HGG from LGG (area under the curve [AUC]: 0.63, 95% confidence interval [CI]: 0.44-0.83) and HCs (AUC: 0.79, 95% CI: 0.68-0.92). The functional prediction analysis of oral bacterial communities showed that genes involved in cell adhesion molecules (p<0.001), extracellular matrix molecule-receptor interaction (p<0.001), focal adhesion (p<0.001), and regulation of actin cytoskeleton (p<0.001) were associated with glioma grades, and some microbial gene functions involving lipid metabolism and the adenosine 5'-monophosphate-activated protein kinase signaling pathway were significantly more enriched in IDH1 mutant gliomas than compared with the IDH1-wild-type gliomas. In conclusion, our work revealed oral microbiota features and gene functions that were associated with glioma malignancy and the IDH1 mutation in glioma.