Serotype b of Aggregatibacter actinomycetemcomitans triggers pro-inflammatory responses and amyloid beta secretion in hippocampal cells: a novel link between periodontitis and Alzheimer´s disease?

Sialic acid metabolism of oral bacteria and its potential role in colorectal cancer and Alzheimer's disease

Sialic acid metabolism in oral bacteria is a complex process involving nutrient acquisition, immune evasion, cell surface modification, and the production of metabolites that contribute to bacterial persistence and virulence in the oral cavity. In addition to causing various periodontal diseases, certain oral pathogenic bacteria, such as Porphyromonas gingivalis, Tannerella forsythia, and Fusobacterium nucleatum, can induce inflammatory reactions and influence the immunity of host cells. These associations with host cells are linked to various diseases, particularly colorectal cancer and Alzheimer's disease. Sialic acid can be found in the host oral mucosa, saliva, or food residues in the oral cavity, and it may promote the colonization of oral bacteria and contribute to disease development. This review aims to summarize the role of sialic acid metabolism in oral bacteria and discuss its effect on the pathogenesis of colorectal cancer and Alzheimer's disease.

Smoking Impacts Alzheimer's Disease Progression Through Oral Microbiota Modulation

Alzheimer's disease (AD) is an important public health challenge with a limited understanding of its pathogenesis. Smoking is a significant modifiable risk factor for AD progression, and its specific mechanism is often interpreted from a toxicological perspective. However, microbial infections also contribute to AD, with oral microbiota playing a crucial role in its progression. Notably, smoking alters the ecological structure and pathogenicity of the oral microbiota. Currently, there is no systematic review or summary of the relationship between these three factors; thus, understanding this association can help in the development of new treatments. This review summarizes the connections between smoking, AD, and oral microbiota from existing research. It also explores how smoking affects the occurrence and development of AD through oral microbiota, and examines treatments for oral microbiota that delay the progression of AD. Furthermore, this review emphasizes the potential of the oral microbiota to act as a biomarker for AD. Finally, it considers the feasibility of probiotics and oral antibacterial therapy to expand treatment methods for AD.

Recent Aspects of Periodontitis and Alzheimer's Disease-A Narrative Review

Periodontitis is an inflammatory condition affecting the supporting structures of the teeth. Periodontal conditions may increase the susceptibility of individuals to various systemic illnesses, including Alzheimer's disease. Alzheimer's disease is a neurodegenerative condition characterized by a gradual onset and progressive deterioration, making it the primary cause of dementia, although the exact cause of the disease remains elusive. Both Alzheimer's disease and periodontitis share risk factors and clinical studies comparing the associations and occurrence of periodontitis among individuals with Alzheimer's disease have suggested a potential correlation between these conditions. Brains of individuals with Alzheimer's disease have substantiated the existence of microorganisms related to periodontitis, especially Porphyromonas gingivalis, which produces neurotoxic gingipains and may present the capability to breach the blood-brain barrier. Treponema denticola may induce tau hyperphosphorylation and lead to neuronal apoptosis. Lipopolysaccharides-components of bacterial cell membranes and mediators of inflammation-also have an impact on brain function. Further research could unveil therapeutic approaches targeting periodontal pathogens to potentially alleviate AD progression.

The oral-brain axis: can periodontal pathogens trigger the onset and progression of Alzheimer's disease?

Alzheimer's disease (AD) is the most prevalent form of dementia, characterized by a progressive cognitive decline. Sporadic AD, accounting for more than 95% of cases, may arise due to the influence of environmental factors. It was reported that periodontitis, a common oral ailment, shares several risk factors with AD, including advanced age, smoking, diabetes, and hypertension, among others. Periodontitis is an inflammatory disease triggered by dysbiosis of oral microorganisms, whereas Alzheimer's disease is characterized by neuroinflammation. Many studies have indicated that chronic inflammation can instigate brain AD-related pathologies, including amyloid-β plaques, Tau protein hyperphosphorylation, neuroinflammation, and neurodegeneration. The potential involvement of periodontal pathogens and/or their virulence factors in the onset and progression of AD by the oral-brain axis has garnered significant attention among researchers with ongoing investigations. This review has updated the periodontal pathogens potentially associated with AD, elucidating their impact on the central nervous system, immune response, and related pathological processes in the brain to provide valuable insights for future research on the oral-brain axis.

Oral Microbiome and Alzheimer's Disease

The accumulation of amyloid-beta plaques in the brain is a central pathological feature of Alzheimer's disease. It is believed that amyloid responses may be a result of the host immune response to pathogens in both the central nervous system and peripheral systems. Oral microbial dysbiosis is a chronic condition affecting more than 50% of older adults. Recent studies have linked oral microbial dysbiosis to a higher brain Aβ load and the development of Alzheimer's disease in humans. Moreover, the presence of an oral-derived and predominant microbiome has been identified in the brains of patients with Alzheimer's disease and other neurodegenerative diseases. Therefore, in this opinion article, we aim to provide a summary of studies on oral microbiomes that may contribute to the pathogenesis of the central nervous system in Alzheimer's disease.

The role of periodontitis-associated bacteria in Alzheimer's disease: A narrative review

Alzheimer's disease causes memory loss and dementia in older adults through a neurodegenerative mechanism. Despite the pathophysiological clarification of this cognitive disorder, novel molecular and cellular pathways should be identified to determine its exact mechanism. Alzheimer's disease (AD) is pathologically characterized by senile plaques comprising beta-amyloid and neurofibrillary tangles (NFTs) formed by hyperphosphorylated tau as a microtubule-associated protein with a key role in the pathogenesis of AD. Periodontitis through inflammatory pathways is a risk factor for deteriorating cognitive impairment in AD patients. Poor oral hygiene coupled with immunocompromised status in older adults causes periodontal diseases and chronic inflammations through an oral bacterial imbalance. Toxic bacterial products, including bacteria themselves, can reach the central nervous system through the bloodstream and evoke inflammatory responses. The present review was conducted to investigate relationships between AD and periodontitis-involved bacteria as a risk factor.

Microglial cell response to experimental periodontal disease

OBJECTIVES

Microglial activation is critical for modulating the neuroinflammatory process and the pathological progression of neurodegenerative diseases, such as Alzheimer's disease (AD). Microglia are involved in forming barriers around extracellular neuritic plaques and the phagocytosis of β-amyloid peptide (Aβ). In this study, we tested the hypothesis that periodontal disease (PD) as a source of infection alters inflammatory activation and Aβ phagocytosis by the microglial cells.

METHODS

Experimental PD was induced using ligatures in C57BL/6 mice for 1, 10, 20, and 30 days to assess the progression of PD. Animals without ligatures were used as controls. Maxillary bone loss and local periodontal tissue inflammation associated with the development of PD were confirmed by morphometric bone analysis and cytokine expression, respectively. The frequency and the total number of activated microglia (CD45+ CD11b+ MHCII+) in the brain were analyzed by flow cytometry. Mouse microglial cells (1 × 105) were incubated with heat-inactivated bacterial biofilm isolated from the ligatures retrieved from the teeth or with Klebsiella variicola, a relevant PD-associated bacteria in mice. Expression of pro-inflammatory cytokines, toll-like receptors (TLR), and receptors for phagocytosis was measured by quantitative PCR. The phagocytic capacity of microglia to uptake β-amyloid was analyzed by flow cytometry.

RESULTS

Ligature placement caused progressive periodontal disease and bone resorption that was already significant on day 1 post-ligation (p < 0.05) and continued to increase until day 30 (p < 0.0001). The severity of periodontal disease increased the frequency of activated microglia in the brains on day 30 by 36%. In parallel, heat-inactivated PD-associated total bacteria and Klebsiella variicola increased the expression of TNFα, IL-1β, IL-6, TLR2, and TLR9 in microglial cells (1.6-, 83-, 3.2-, 1.5-, 1.5-fold, respectively p < 0.01). Incubation of microglia with Klebsiella variicola increased the Aβ-phagocytosis by 394% and the expression of the phagocytic receptor MSR1 by 33-fold compared to the non-activated cells (p < 0.0001).

CONCLUSIONS

We showed that inducing PD in mice results in microglia activation in vivo and that PD-associated bacteria directly promote a pro-inflammatory and phagocytic phenotype in microglia. These results support a direct role of PD-associated pathogens in neuroinflammation.

Persister Cell Formation and Elevated lsrA and lsrC Gene Expression upon Hydrogen Peroxide Exposure in a Periodontal Pathogen Aggregatibacter actinomycetemcomitans

The effect of hydrogen peroxide, an antiseptic dental treatment, on Aggregatibacter actinomycetemcomitans, the main causative agent of localized invasive periodontitis, was investigated. Hydrogen peroxide treatment (0.06%, 4× minimum inhibitory concentration) resulted in the persistence and survival of approximately 0.5% of the bacterial population. The surviving bacteria did not genetically acquire hydrogen peroxide resistance but exhibited a known persister behavior. Sterilization with mitomycin C significantly reduced the number of A. actinomycetemcomitans persister survivors. RNA sequencing of hydrogen peroxide-treated A. actinomycetemcomitans showed elevated expression of Lsr family members, suggesting a strong involvement of autoinducer uptake. In this study, we found a risk of A. actinomycetemcomitans persister residual from hydrogen peroxide treatment and hypothesized associated genetic mechanisms of persister from RNA sequencing.

Antibodies against Periodontal Microorganisms and Cognition in Older Adults

INTRODUCTION

Markers of poor oral health are associated with impaired cognition and higher risk of Alzheimer disease (AD) and thus may help predict AD.

OBJECTIVES

The aim of this study was to evaluate the cross-sectional association between empirically derived groups of 19 IgG antibodies against periodontal microorganisms and cognition in middle-aged and older adults.

METHODS

The study population consisted of participants of the third National Health and Nutrition Examination Survey (NHANES III) (1988 to 1994), who were 60 y and older, among whom cognition and IgG antibodies against 19 periodontal microorganisms were measured (N = 5,162).

RESULTS

In multivariable quantile regression analyses, the Orange-Red (Prevotella melaninogenica, Prevotella intermedia, Prevotella nigrescens, Porphyromonas gingivalis) and Yellow-Orange (Staphylococcus intermedius, Streptococcus oralis, Streptococcus mutans, Fusobacterium nucleatum, Peptostreptococcus micros, Capnocytophaga ochracea) cluster scores were negatively associated with cognition. A 1-unit higher cluster score for the Orange-Red cluster was associated on average with a lower cognitive score (β for 30th quantile = -0.2640; 95% confidence interval [CI], -0.3431 to -0.1848). Similarly, a 1-unit higher score for the Yellow-Orange cluster was associated with a lower cognitive score (β for 30th quantile = -0.2445; 95% CI, -0.3517 to -0.1372).

CONCLUSION

Groups of IgG antibodies against periodontal microorganisms were associated with lower cognition among free living adults 60 years and older, who were previously undiagnosed with cognitive impairment. Though poor oral health precedes the development of dementia and AD, oral health information is currently not used, to our knowledge, to predict dementia or AD risk. Combining our findings with current algorithms may improve risk prediction for dementia and AD.

KNOWLEDGE TRANSLATION STATEMENT

IgG antibodies against periodontal microorganisms were associated with lower cognition among adults 60 years and older previously undiagnosed with cognitive impairment. Periodontal disease may predict cognition among older adults.

Differential Virulence of Aggregatibacter actinomycetemcomitans Serotypes Explained by Exoproteome Heterogeneity

Aggregatibacter actinomycetemcomitans (Aa) is a Gram-negative bacterial pathogen associated with periodontitis and nonoral diseases like rheumatoid arthritis and Alzheimer´s disease. Aa isolates with the serotypes a, b, and c are globally most prevalent. Importantly, isolates displaying these serotypes have different clinical presentations. While serotype b isolates are predominant in severe periodontitis, serotypes a and c are generally encountered in mild periodontitis or healthy individuals. It is currently unknown how these differences are reflected in the overall secretion of virulence factors. Therefore, this study was aimed at a comparative analysis of exoproteomes from different clinical Aa isolates with serotypes a, b, or c by mass spectrometry, and a subsequent correlation of the recorded exoproteome profiles with virulence. Overall, we identified 425 extracellular proteins. Significant differences in the exoproteome composition of isolates with different serotypes were observed in terms of protein identification and abundance. In particular, serotype a isolates presented more extracellular proteins than serotype b or c isolates. These differences are mirrored in their virulence in infection models based on human salivary gland epithelial cells and neutrophils. Remarkably, serotype a isolates displayed stronger adhesive capabilities and induced more lysis of epithelial cells and neutrophils than serotype b or c isolates. Conversely, serotype c isolates showed relatively low leukotoxicity, while provoking NETosis to similar extents as serotype a and b isolates. Altogether, we conclude that the differential virulence presentation by Aa isolates with the dominant serotypes a, b, or c can be explained by their exoproteome heterogeneity. IMPORTANCE Periodontitis is an inflammatory disease that causes progressive destruction of alveolar bone and supporting tissues around the teeth, ultimately resulting in tooth loss. The bacterium Aggregatibacter actinomycetemcomitans (Aa) is a prevalent causative agent of periodontitis, but this oral pathogen is also associated with serious extraoral diseases like rheumatoid arthritis and Alzheimer's disease. Clinical Aa isolates are usually distinguished by serotyping, because of known serotype-specific differences in virulence. Aa with serotype b is associated with aggressive forms of periodontitis, while isolates with serotypes a or c are usually encountered in cases of mild periodontitis or healthy individuals. The molecular basis for these differences in virulence was so far unknown. In the present study, we pinpoint serotype-specific differences in virulence factor production by clinical Aa isolates. We consider these findings important, because they provide new leads for future preventive or therapeutic approaches to fight periodontitis and associated morbidities.

Oral microbiome in older adults with mild cognitive impairment

The association between the oral microbiome and mild cognitive impairment (MCI) remains unclear. This study aimed to investigate such an association among Chinese older adults. Participants without dementia were recruited from the community. A battery of neuropsychological tests was administered to evaluate the cognitive function. The diagnosis of MCI was based on Peterson's criteria. The non-stimulated saliva was collected to extract sequences of the oral microbiome. Forty-seven MCI and 47 cognitively normal participants were included. There was significant difference in alpha diversity and insignificant difference in beta diversity between the two groups of participants. Compared with the cognitively normal group, Gemella haemolysans and Streptococcus gordonii were two significantly decreased species while Veillonella unclassified_Veillonella and Fusobacterium sp._HMT_203 were two significantly increased species in the MCI group. The richness of Gemella haemolysans presented the best discriminate value for MCI with the AUC (Area Under Curve) of 0.707, a cut-off value of 0.008 for relative abundance, the sensitivity of 63.8% and specificity of 70.2%. The dysbiosis of oral microbiome and relative abundance of Gemella haemolysans was significantly associated with MCI. Further studies were needed to develop new treatment strategies targeting the oral microbiome for cognitive impairment.

Potential mechanisms between periodontitis and Alzheimer's disease: a scoping review

Background

Research has suggested 2 potential mechanisms by which the periodontal inflammatory response may communicate to distant organs: 1) direct translocation of periodontal bacteria from the oral cavity to another organ system; and 2) inflammation as a result of metastatic periodontal inflammation. The purpose of this scoping review is to explore these mechanisms as potential mediators between periodontitis and Alzheimer's disease.

Methods

A reiterative literature search of peer-reviewed articles was performed in the PubMed and Scopus databases using keywords or combinations such as Alzheimer's disease AND periodontitis OR periodontal disease AND inflammation.

Results

A total of 777 articles were identified. After eliminating duplicates and reviewing titles and abstracts, 84 articles were selected for full-text review. Following full-text review, 19 articles met the eligibility criteria for the study.

Discussion

The review of the literature highlights how periodontitis may contribute to neuroinflammation by the introduction of periodontal bacteria and/or proinflammatory cytokines locally produced at the periodontium.

Conclusion

Inflammation is an important mechanism in the onset and progression of both periodontitis and Alzheimer's disease. Nevertheless, further studies are necessary to better understand the multifactorial pathogenesis of Alzheimer's disease.

Association Between Oral Bacteria and Alzheimer's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Pre-clinical evidence implicates oral bacteria in the pathogenesis of Alzheimer's disease (AD), while clinical studies show diverse results.

OBJECTIVE

To comprehensively assess the association between oral bacteria and AD with clinical evidence.

METHODS

Studies investigating the association between oral bacteria and AD were identified through a systematic search of six databases PubMed, Embase, Cochrane Central Library, Scopus, ScienceDirect, and Web of Science. Methodological quality ratings of the included studies were performed. A best evidence synthesis was employed to integrate the results. When applicable, a meta-analysis was conducted using a random-effect model.

RESULTS

Of the 16 studies included, ten investigated periodontal pathobionts and six were microbiome-wide association studies. Samples from the brain, serum, and oral cavity were tested. We found over a ten-fold and six-fold increased risk of AD when there were oral bacteria (OR = 10.68 95% CI: 4.48-25.43; p < 0.00001, I2 = 0%) and Porphyromonas gingivalis (OR = 6.84 95% CI: 2.70-17.31; p < 0.0001, I2 = 0%) respectively in the brain. While AD patients exhibited lower alpha diversity of oral microbiota than healthy controls, the findings of bacterial communities were inconsistent among studies. The best evidence synthesis suggested a moderate level of evidence for an overall association between oral bacteria and AD and for oral bacteria being a risk factor for AD.

CONCLUSION

Current evidence moderately supports the association between oral bacteria and AD, while the association was strong when oral bacteria were detectable in the brain. Further evidence is needed to clarify the interrelationship between both individual species and bacterial communities and the development of AD.

Antibodies against HSV-1 and Curli Show the Highest Correlation in Parkinson's Disease Patients in Comparison to Healthy Controls

Parkinson’s disease (PD) is a neurodegenerative disorder involving the accumulation of alpha-synuclein (α-syn)/Lewy bodies in the brain and -enteric nervous system. The etiology of the disease is not well understood, but bacterial and viral infections may contribute to the pathogenesis of PD. It has been suggested that the gastrointestinal (GI) complications observed in PD patients may arise from bacterial dysbiosis, leading to curli/α-syn deposits in the enteric nervous system. Enteric bacteria secrete curli, a functional amyloid peptide involved in adhesion to surfaces, cell invasion, and biofilm formation. However, these bacterial amyloids can initiate additional α-syn deposits through immune system activation and cross-seeding. In this study, we investigate the humoral response against α-syn, curli peptides, and various bacterial and viral immunogen peptides in PD patients, and compare them with those in healthy controls (HCs). Polyclonal IgG antibodies (Abs) were detected against peptides derived from α-syn (α-syn100−114), curli (Curli133−141), Porphyromonas gingivalis Pg (RgpA800−812, Kpg328−339), Aggregatibacter actinomycetemcomitans (LtxA1429−445, LtxA264−80), Mycobacterium avium subsp. paratuberculosis (MAP3865c125−133, MAP1,4-a-gbp157−173 and MAP_402718−32), Epstein−Barr virus (EBNA1400−413, BOLF1305−320), and Herpes Simplex virus 1 (UI4222−36), as investigated by indirect ELISA of 51 serum samples from PD and 58 sex and age-matched HCs. Significant differences in OD (optical density) values and Abs positivity between PD patients and HCs were observed for Kpg (82.3% vs. 10.3%), followed by RgpA (60.7% vs. 24.1%), curli (51% vs. 22.4%), and UI42 (43.1% vs. 25.8%) in PD, compared to HCs sera (p < 0.001). No significant difference was found in the ODs obtained from other tested peptides in PD patients, compared to HCs. Significant positive correlations between OD values obtained by ELISA were observed for UI42 and curli (r = 0.811, p < 0.0001), Kpg and RgpA (r = 0.659, p < 0.0001), followed by LtxA1 and LtxA2 (r = 0.653, p < 0.0001). The correlation between the HY scale (Hoehn and Yahr Scale) and LtxA1 (r = 0.306, p < 0.028) and HY and Kpg (r = 0.290, p < 0.038) were significantly positive. This study reports a significantly increased humoral response against curli, Pg, and HSV-1 in PD patients, implying that they could be important factors in the pathogenesis of the disease. In addition, the high positive correlation between UI42 and curli may suggest the involvement of HSV-1 in GI dysbiosis. Therefore, the role of each individual pathogen and curli in PD needs to be further investigated.

Correlation study of periodontitis with cognitive impairment

OBJECTIVES

This study aimed to determine the association of periodontitis with cognitive impairment by evaluating periodontal conditions in middle-aged and elderly people of normal cognition and cognitive impairment.

METHODS

Forty patients with cognitive impairment and thirty-five healthy controls were included in this study. Mini-mental state examination (MMSE) was used to evaluate the level of cognitive function in all patients and controls. Periodontal conditions including severity of periodontitis, number of remaining teeth, percentage of bleeding on probing, probing depth (PD), and attachment level (AL) were examined. Periodontal conditions were compared between patients and controls, and the correlation between periodontal conditions and cognitive-function level was analyzed. Statistical analysis was performed with SPSS 26.0.

RESULTS

The distribution of severity of periodontitis significantly differed between patients and controls (χ2=13.309 and P=0.001). The proportion of severe periodontitis in the cognitive-impairment group was significantly higher than that in the healthy controls (P<0.05). The percentage of sites with PD≥6 mm and AL≥5 mm in the cognitive-impairment group was higher than that in the controls, whereas the percentage of sites with PD=1-3 mm and AL=0-2 mm was higher in the controls (P<0.05). No significant difference in percentage of bleeding on probing was found in the two groups (P>0.05). Patients with cognitive impairment had fewer teeth than the controls (P<0.05). The level of cognitive function, assessed by MMSE, was positively correlated with the number of teeth and the percentage of sites with AL=0-2 mm, and it was negatively correlated with the percentage of sites with AL≥5 mm (P<0.05).

CONCLUSIONS

A correlation existed between periodontitis and cognitive impairment. Further study is essential to explore the specific relationship and related mechanism between periodontitis and cognitive impairment.

Implications of Microorganisms in Alzheimer's Disease

Alzheimer’s disease (AD) is a deadly brain degenerative disorder that leads to brain shrinkage and dementia. AD is manifested with hyperphosphorylated tau protein levels and amyloid beta (Aβ) peptide buildup in the hippocampus and cortex regions of the brain. The nervous tissue of AD patients also contains fungal proteins and DNA which are linked to bacterial infections, suggesting that polymicrobial infections also occur in the brains of those with AD. Both immunohistochemistry and next-generation sequencing (NGS) techniques were employed to assess fungal and bacterial infections in the brain tissue of AD patients and non-AD controls, with the most prevalent fungus genera detected in AD patients being Alternaria, Botrytis, Candida, and Malassezia. Interestingly, Fusarium was the most common genus detected in the control group. Both AD patients and controls were also detectable for Proteobacteria, followed by Firmicutes, Actinobacteria, and Bacteroides for bacterial infection. At the family level, Burkholderiaceae and Staphylococcaceae exhibited higher levels in the brains of those with AD than the brains of the control group. Accordingly, there is thought to be a viscous cycle of uncontrolled neuroinflammation and neurodegeneration in the brain, caused by agents such as the herpes simplex virus type 1 (HSV1), Chlamydophilapneumonia, and Spirochetes, and the presence of apolipoprotein E4 (APOE4), which is associated with an increased proinflammatory response in the immune system. Systemic proinflammatory cytokines are produced by microorganisms such as Cytomegalovirus, Helicobacter pylori, and those related to periodontal infections. These can then cross the blood–brain barrier (BBB) and lead to the onset of dementia. Here, we reviewed the relationship between the etiology of AD and microorganisms (such as bacterial pathogens, Herpesviridae viruses, and periodontal pathogens) according to the evidence available to understand the pathogenesis of AD. These findings might guide a targeted anti-inflammatory therapeutic approach to AD.

Host mRNA Analysis of Periodontal Disease Patients Positive for Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans and Tannerella forsythia

Periodontal disease is a frequent pathology worldwide, with a constantly increasing prevalence. For the optimal management of periodontal disease, there is a need to take advantage of actual technology to understand the bacterial etiology correlated with the pathogenic mechanisms, risk factors and treatment protocols. We analyzed the scientific literature published in the last 5 years regarding the recent applications of mRNA analysis in periodontal disease for the main known bacterial species considered to be the etiological agents: Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans and Tannerella forsythia. We identified new pathogenic mechanisms, therapeutic target genes and possible pathways to prevent periodontal disease. The mRNA analysis, as well as the important technological progress in recent years, supports its implementation in the routine management of periodontal disease patients.

HIF-1α drives the transcription of NOG to inhibit osteogenic differentiation of periodontal ligament stem cells in response to hypoxia

Osteogenic differentiation of periodontal ligament stem cells (PDLSCs) is limited in hypoxia, and HIF-1α is key to the response to hypoxia. However, its mechanisms remain largely unknown. This study discovered an osteogenesis-related gene sensitive to hypoxia in PDLSCs, and investigated the molecular mechanisms between HIF-1α and the gene. NOG, a gene that negatively regulates osteogenesis, was discovered by RNA-seq. Under normoxic conditions, HIF-1α overexpression led to enhanced expression of NOG/Noggin and inhibited the expression of osteogenesis-related genes, while inhibition of HIF-1α reversed this effect. The expression of HIF-1α, NOG/Noggin and the osteogenesis-related genes were detected by qRT-PCR or Western blot. Mechanistically, we verified that HIF-1α binds to the hypoxia response element (-1505 to -1502) in the promotor of NOG to enhance secretion of Noggin by chromatin immunoprecipitation and a dual-luciferase reporter assay. IHC staining findings in an animal model verified that Noggin-associated osteogenic differentiation was inhibited in hypoxia. NOG displayed a concordant relationship with HIF-1α, and secreted more with increasing of HIF-1α. Hypoxia stabilized HIF-1α, which bound to the HRE (-1505 to -1502) of the NOG promotor to enhance NOG transcription resulted in inhibiting osteogenic differentiation of PDLSCs. This study offers a promising therapy for periodontitis.

Inflammation—Cause or consequence of late onset Alzheimer’s disease or both? A review of the evidence

Accumulating evidence suggests that inflammation is involved in the development of late onset Alzheimer’s disease (LOAD). However, it is not clear whether inflammation is a cause or consequence, or both. The aim of this paper is to review the relationship between inflammation and LOAD. We also review the effect of anti-inflammation on the risk of LOAD to further elucidate the relationship between inflammation and LOAD.

Periodontal microorganisms and Alzheimer disease - A causative relationship?

In the initiation or exacerbation of Alzheimer disease, the dissemination of oral microorganisms into the brain tissue or the low‐level systemic inflammation have been speculated to play a role. However, the impact of oral microorganisms, such as Porphyromonas gingivalis, on the pathogenesis of Alzheimer disease and the potential causative relationship is still unclear. The present review has critically reviewed the literature by examining the following aspects: (a) the oral microbiome and the immune response in the elderly population, (b) human studies on the association between periodontal and gut microorganisms and Alzheimer disease, (c) animal and in vitro studies on microorganisms and Alzheimer disease, and (d) preventive and therapeutic approaches. Factors contributing to microbial dysbiosis seem to be aging, local inflammation, systemic diseases, wearing of dentures, living in nursing homes and no access to adequate oral hygiene measures. Porphyromonas gingivalis was detectable in post‐mortem brain samples. Microbiome analyses of saliva samples or oral biofilms showed a decreased microbial diversity and a different composition in Alzheimer disease compared to cognitively healthy subjects. Many in‐vitro and animal studies underline the potential of P gingivalis to induce Alzheimer disease‐related alterations. In animal models, recurring applications of P gingivalis or its components increased pro‐inflammatory mediators and β‐amyloid in the brain and deteriorated the animals' cognitive performance. Since periodontitis is the result of a disturbed microbial homoeostasis, an effect of periodontal therapy on the oral microbiome and host response related to cognitive parameters may be suggested and should be elucidated in further clinical trials.

Oral biosciences: The annual review 2021

BACKGROUND

The Journal of Oral Biosciences is devoted to advancing and disseminating fundamental knowledge concerning every aspect of oral biosciences.

HIGHLIGHT

This review features review articles in the fields of "Extracellular Vesicles," "Propolis," "Odontogenic Tumors," "Periodontitis," "Periodontium," "Flavonoids," "Lactoferrin," "Dental Plaque," "Anatomy," "Induced Pluripotent Stem Cells," "Bone Cell Biology," "Dysgeusia," "Dental Caries," and "Dental Pulp Cavity," in addition to the review article by the winners of the "Lion Award" ("Sox9 function in salivary gland development") presented by the Japanese Association for Oral Biology.

CONCLUSION

These reviews in the Journal of Oral Biosciences have inspired its readers to broaden their knowledge regarding various aspects of oral biosciences. The current editorial review introduces these exciting review articles.

The pathogenic mechanism of oral bacteria and treatment with inhibitors

OBJECTIVES

The objective of this study was to introduce the evidence obtained through extensive research that periodontitis increases risk of many systemic diseases.

METHOD

Analysis of some oral bacteria (P. gingivalis, T. denticola, T. forsythia, A. actinomycetemcomitans, and F. nucleatum) and its related treatments and mediators by the specific methods (western blot, ELISA, etc).

RESULTS

This article reviews in detail the evidence obtained through extensive research that periodontitis increases risk of many systemic diseases, including cardiovascular disease, rheumatoid arthritis, and Alzheimer's disease. These diseases are known to be associated with some certain specific gram-negative bacteria as periodontal pathogens, which induce inflammation and related diseases through TLR receptors, kinases, transcriptional factors and other cytokines. We also reviewed the latest research for inhibitors against inflammation and related diseases that have potential to be further applied clinically. In addition, based on a large amount of research evidence, we draw two tables about the mechanism of disease caused by periodontal bacteria, so that readers can easily search and analyze these research results.

DISCUSSION

This review details how the periodontal bacteria and their virulence factors can trigger host immune defense and induce many systemic diseases via inflammation and invasion. This Review also addressed the latest research around inhibitors against inflammation.

Prioritising NHS dental treatments: a mixed-methods study

Objectives To determine the priorities of patients and dental professionals concerning NHS dental treatments, the factors influencing prioritisation and the willingness to contribute towards the cost of NHS dental treatments.Methods Focus groups and interviews involving patients and practitioners informed the development of a piloted questionnaire concerning the priorities for NHS dental treatments. Patients attending three purposively selected dental settings in London and Kent, as well as dental professionals working within a large London dental hospital were recruited to participate in this initial qualitative phase. Qualitative interviews were audiotaped, transcribed verbatim and analysed using the framework approach. Subsequently, another sample of patients and dental professionals within the three dental settings and dental hospital completed a questionnaire. Regression models were used to determine the predictors of perceived priorities and willingness to contribute to NHS dental costs based on the questionnaire data.Results Three focus groups (n = 9) and one semi-structured interview with patients and one focus group of dental professionals (four general dental practitioners and two dental nurses) were conducted. Participants prioritised NHS dental treatments that improve quality of life and social wellbeing. Factors influencing the prioritisation of NHS dental treatments included: individual responsibility for oral health care; concerns about self-esteem and confidence; age-related issues; and the role of treatment in prevention of future dental and general health problems, with financial concerns underpinning these themes. Out of the 455 questionnaires completed, 414 (383 patients and 31 general dental practitioners) were included in the analysis. The provision of emergency dental treatment for children was afforded the highest priority among both patients (59%) and dentists (74.2%). Both groups of participants felt that full funding for most NHS dental treatments should be prioritised for children (<18 years old) rather than adults (p <0.05).Conclusion Participants prioritised NHS dental treatments that would improve social wellbeing and quality of life, with an emphasis on full coverage for NHS treatment for children and young people. Policy makers should account for these preferences in the planning of NHS dental services.

Periodontal bacteria in the brain-Implication for Alzheimer's disease: A systematic review

Periodontitis is a chronic non-communicable disease caused by a dysbiotic microbiota. Pathogens can spread to the bloodstream, colonize other tissues or organs, and favor the onset of other pathologies, such as Alzheimer's disease (AD). Pathogens could permanently or transiently colonize the brain and induce an immune response. Thus, we analyzed the evidence combining oral bacteria's detection in the brain, both in animals and humans affected with AD. This systematic review was carried out following the PRISMA guideline. Studies that detected oral bacteria at the brain level were selected. The search was carried out in the Medline, Latindex, SciELO, and Cochrane Library databases. SYRCLE tool and Newcastle-Ottawa Scale were used for the risk of bias assessment. 23 studies were selected according to the eligibility criteria. Infection with oral pathogens in animals was related to developing neuropathological characteristics of AD and bacteria detection in the brain. In patients with AD, oral bacteria were detected in brain tissues, and increased levels of pro-inflammatory cytokines were also detected. There is evidence of a microbiological susceptibility to develop AD when the most dysbiosis-associated oral bacteria are present. The presence of bacteria in the brain is related to AD's pathological characteristics, suggesting an etiological oral-brain axis.

The Association of Periodontitis and Alzheimer's Disease: How to Hit Two Birds with One Stone

Alzheimer's disease (AD) is the leading cause of cognitive impairment in the elderly. Recent evidence suggests that preventive interventional trials could significantly reduce the risk for development of dementia. Periodontitis is the most common dental disease characterized by chronic inflammation and loss of alveolar bone and perialveolar attachment of teeth. Growing number of studies propose a potential link between periodontitis and neurodegeneration. In the first part of the paper, we overview case-control studies analyzing the prevalence of periodontitis among AD patients and healthy controls. Second, we survey observational libraries and cross-sectional studies investigating the risk of cognitive decline in patients with periodontitis. Next, we describe the current view on the mechanism of periodontitis linked neural damage, highlighting bacterial invasion of neural tissue from dental plaques, and periodontitis induced systemic inflammation resulting in a neuroinflammatory process. Later, we summarize reports connecting the four most common periodontal pathogens to AD pathology. Finally, we provide a practical guide for further prevalence and interventional studies on the management of cognitively high-risk patients with and without periodontitis. In this section, we highlight strategies for risk control, patient information, dental evaluation, reporting protocol and dental procedures in the clinical management of patients with a risk for periodontitis and with diagnosed periodontitis. In conclusion, our review summarizes the current view on the association between AD and periodontitis and provides a research and intervention strategy for harmonized interventional trials and for further case-control or cross-sectional studies.

Can Porphyromonas gingivalis Contribute to Alzheimer's Disease Already at the Stage of Gingivitis?

Alzheimer's disease (AD) has been associated with periodontitis, which starts as gingivitis. Similar to periodontitis, gingivitis bacteria, bacterial products, and inflammatory mediators can travel to the brain via the blood stream and promote brain inflammation. Periodontal pathogens such as Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, both associated with AD, have been found in dental plaque of children already at the age of 3. It is suggested that these bacteria during long-term exposure may drive microglia (brain resident macrophage cells) into a pro-inflammatory M1 phase where they contribute to AD rather than protect against it. This notion comes from studies in mice showing that microglia actually can "remember" previous inflammatory challenge and become "trained" or "tolerant" to toxins like lipopolysaccharide. If gingivitis has an impact on AD, which should be verified, AD prophylaxis should start already at this pre-periodontitis stage with removal of supragingival plaque.

Clinical, inflammatory and microbiological outcomes of full-mouth scaling with adjunctive glycine powder air-polishing: A randomized trial

AIM

To determine the effects of glycine powder air-polishing (GPAP) as an adjunct to full-mouth scaling and root planing (SRP) on clinical, inflammatory and microbiological outcomes in patients with untreated periodontitis.

MATERIALS AND METHODS

Forty-one patients were randomly assigned to the control group A (SRP) and test groups B1 (subgingival GPAP right after SRP) and B2 (subgingival GPAP right before SRP). Clinical examinations and sample collections (saliva, subgingival plaque, serum and gingival crevicular fluid) were performed at assessment visits and before therapies at clinical visits of baseline, 6-week and 3-month. C-reactive protein, IL-6 and TNF-α were assessed in serum and gingival crevicular fluid, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum were measured in saliva and subgingival plaque.

RESULTS

Patients in control and test groups did not significantly differ by age, sex and disease severity at baseline. Participants in control and intervention groups had similar improvements in clinical parameters (PD, BOP, PLI and BI). All groups had a similar percentage of sites showing PD reduction of ≥2 mm between baseline and follow-up visits, with a few exceptions. Reduced C-reactive protein, IL-6 and TNF-α in serum were found after treatments.

CONCLUSION

Full-mouth SRP with and without GPAP resulted in largely similar clinical, inflammatory and microbiological outcomes in the care of untreated periodontitis.

U.S. state correlations between oral health metrics and Alzheimer's disease mortality, prevalence and subjective cognitive decline prevalence

Given the association between periodontal disease (PdD) and Alzheimer’s disease (AD), we examined correlations between states’ age-adjusted AD mortality rates, AD prevalence, subjective cognitive decline (SCD) prevalence, and oral health data. Data sources include the Centers for Disease Control and Prevention, scientific literature, and oral health rankings formulated by WalletHub.com and Toothbrush.org. Pearson (r) or Spearman (r_s) correlation coefficients were generated and evaluated. AD mortality rates correlate with dental visits (r = − 0.50, p = 0.0003), partial (r = 0.39, p = 0.005) or total (r = 0.44, p = 0.001) edentulism, WalletHub.com (r_s = 0.30, p = 0.03) and Toothbrush.org (r_s = 0.35, p = 0.01) rankings. AD prevalence correlates with dental visits (r = − 0.30, p = 0.03), partial (r = 0.55, p = 0.00003) or total (r = 0.46, p = 0.0009) edentulism, prevalence of any (r = 0.38, p = 0.006) or severe-stage (r = 0.46, p = 0.0009) PdD, and WalletHub.com (r_s = 0.38, p = 0.006) rankings. SCD prevalence in adults aged ≥ 45 years correlates with dental visits (r = − 0.69, p < 0.00001), partial (r = 0.33, p = 0.02) or total (r = 0.37, p = 0.008) edentulism, prevalence of any (r = 0.53, p = 0.0001) or severe-stage (r = 0.57, p = 0.00002) PdD, WalletHub.com (r_s = 0.53, p = 0.00008) and Toothbrush.org (r_s = 0.60, p < 0.00001) rankings. State metrics indicative of compromised oral health correlate with AD mortality rates, AD prevalence and SCD prevalence.

Delivery of Periodontopathogenic Extracellular Vesicles to Brain Monocytes and Microglial IL-6 Promotion by RNA Cargo

Gram-negative bacterial extracellular vesicles (EVs), also known as outer membrane vesicles (OMVs), are secreted from bacterial cells and have attracted research attention due to their role in cell-to-cell communication. During OMV secretion, a variety of cargo such as extracellular RNA (exRNA) is loaded into the OMV. The involvement of exRNAs from a range of bacteria has been identified in several diseases, however, their mechanism of action has not been elucidated. We have recently demonstrated that OMVs secreted by the periodontopathogen Aggregatibacter actinomycetemcomitans can cross the blood-brain barrier (BBB) and that its exRNA cargo could promote the secretion of proinflammatory cytokines in the brain. However, it was unclear whether the brain immune cells could actually take up bacterial OMVs, which originate outside of the brain, in an appropriate immune response. In the present study, using monocyte-specific live CX3CR1-GFP mice, we visualized OMV-colocalized meningeal macrophages and microglial cells into which bacterial OMVs had been loaded and intravenously injected through tail veins. Our results suggested that meningeal macrophages uptake BBB-crossed OMVs earlier than do cortex microglia. BV2 cells (a murine microglia cell line) and exRNAs were also visualized after OMV treatment and their proinflammatory cytokine levels were observed. Interleukin (IL)-6 and NF-κB of BV2 cells were activated by A. actinomycetemcomitans exRNAs but not by OMV DNA cargo. Altogether, these findings indicate that OMVs can successfully deliver exRNAs into brain monocyte/microglial cells and cause neuroinflammation, implicating a novel pathogenic mechanism in neuroinflammatory diseases.

Alzheimer's Disease-Like Pathology Triggered by Porphyromonas gingivalis in Wild Type Rats Is Serotype Dependent

Periodontal disease is a disease of tooth-supporting tissues. It is a chronic disease with inflammatory nature and infectious etiology produced by a dysbiotic subgingival microbiota that colonizes the gingivodental sulcus. Among several periodontal bacteria, Porphyromonas gingivalis (P. gingivalis) highlights as a keystone pathogen. Previous reports have implied that chronic inflammatory response and measurable bone resorption are observed in young mice, even after a short period of periodontal infection with P. gingivalis, which has been considered as a suitable model of experimental periodontitis. Also, encapsulated P. gingivalis strains are more virulent than capsular-defective mutants, causing an increased immune response, augmented osteoclastic activity, and accrued alveolar bone resorption in these rodent experimental models of periodontitis. Recently, P. gingivalis has been associated with Alzheimer’s disease (AD) pathogenesis, either by worsening brain pathology in AD-transgenic mice or by inducing memory impairment and age-dependent neuroinflammation middle-aged wild type animals. We hypothesized here that the more virulent encapsulated P. gingivalis strains could trigger the appearance of brain AD-markers, neuroinflammation, and cognitive decline even in young rats subjected to a short periodontal infection exposure, due to their higher capacity of activating brain inflammatory responses. To test this hypothesis, we periodontally inoculated 4-week-old male Sprague-Dawley rats with K1, K2, or K4 P. gingivalis serotypes and the K1-isogenic non-encapsulated mutant (GPA), used as a control. 45-days after periodontal inoculations with P. gingivalis serotypes, rat´s spatial memory was evaluated for six consecutive days in the Oasis maze task. Following functional testing, the animals were sacrificed, and various tissues were removed to analyze alveolar bone resorption, cytokine production, and detect AD-specific biomarkers. Strikingly, only K1 or K2 P. gingivalis-infected rats displayed memory deficits, increased alveolar bone resorption, pro-inflammatory cytokine production, changes in astrocytic morphology, increased Aβ1-42 levels, and Tau hyperphosphorylation in the hippocampus. None of these effects were observed in rats infected with the non-encapsulated bacterial strains. Based on these results, we propose that the bacterial virulence factors constituted by capsular polysaccharides play a central role in activating innate immunity and inflammation in the AD-like pathology triggered by P. gingivalis in young rats subjected to an acute experimental infection episode.

Potential Bidirectional Relationship Between Periodontitis and Alzheimer's Disease

Alzheimer’s disease (AD) is the most prevalent form of dementia in the elderly population, representing a global public health priority. Despite a large improvement in understanding the pathogenesis of AD, the etiology of this disorder remains still unclear, and no current treatment is able to prevent, slow, or stop its progression. Thus, there is a keen interest in the identification and modification of the risk factors and novel molecular mechanisms associated with the development and progression of AD. In this context, it is worth noting that several findings support the existence of a direct link between neuronal and non-neuronal inflammation/infection and AD progression. Importantly, recent studies are now supporting the existence of a direct relationship between periodontitis, a chronic inflammatory oral disease, and AD. The mechanisms underlying the association remain to be fully elucidated, however, it is generally accepted, although not confirmed, that oral pathogens can penetrate the bloodstream, inducing a low-grade systemic inflammation that negatively affects brain function. Indeed, a recent report demonstrated that oral pathogens and their toxic proteins infect the brain of AD patients. For instance, when AD progresses from the early to the more advanced stages, patients could no longer be able to adequately adhere to proper oral hygiene practices, thus leading to oral dysbiosis that, in turn, fuels infection, such as periodontitis. Therefore, in this review, we will provide an update on the emerging (preclinical and clinical) evidence that supports the relationship existing between periodontitis and AD. More in detail, we will discuss data attesting that periodontitis and AD share common risk factors and a similar hyper-inflammatory phenotype.

The Role of Periodontitis and Periodontal Bacteria in the Onset and Progression of Alzheimer's Disease: A Systematic Review

The evidence of a connection between the peripheral inflammatory processes and neurodegenerative diseases of the central nervous system is becoming more apparent. This review of the related literature highlights the most recent clinical, epidemiological, and in vitro studies trying to investigate possible connections between periodontal bacteria and the onset and progression of Alzheimer's disease. This review was conducted by searching databases such as PubMed and Scopus using keywords or combinations such as Alzheimer's Disease AND periodontal or dementia AND periodontitis OR periodontal. After eliminating overlaps and screening the articles not related to these issues, we identified 1088 records and proceeded to the selection of articles for an evaluation of the associative assumptions. The hypothesis suggested by the authors and confirmed by the literature is that the bacterial load and the inflammatory process linked to periodontal disease can intensify inflammation at the level of the central nervous system, favoring the occurrence of the disease. The analysis of the literature highlights how periodontal disease can directly contribute to the peripheral inflammatory environment by the introduction of periodontal or indirect pathogenic bacteria and proinflammatory cytokines locally produced at the periodontal level following bacterial colonization of periodontal defects.

Tools of Aggregatibacter actinomycetemcomitans to Evade the Host Response

Periodontitis is an infection-induced inflammatory disease that affects the tooth supporting tissues, i.e., bone and connective tissues. The initiation and progression of this disease depend on dysbiotic ecological changes in the oral microbiome, thereby affecting the severity of disease through multiple immune-inflammatory responses. Aggregatibacter actinomycetemcomitans is a facultative anaerobic Gram-negative bacterium associated with such cellular and molecular mechanisms associated with the pathogenesis of periodontitis. In the present review, we outline virulence mechanisms that help the bacterium to escape the host response. These properties include invasiveness, secretion of exotoxins, serum resistance, and release of outer membrane vesicles. Virulence properties of A. actinomycetemcomitans that can contribute to treatment resistance in the infected individuals and upon translocation to the circulation, also induce pathogenic mechanisms associated with several systemic diseases.