Exploring the causal relationship between periodontitis and gut microbiome: Unveiling the oral-gut and gut-oral axes through bidirectional Mendelian randomization

Differences in oral microbiota between elderly and adults: A systematic review

OBJECTIVE

The aging process may significantly impact bacteria in the oral cavity (oral microbiome), leading to notable changes in its diversity and composition, potentially influencing systemic health. This systematic review aimed to compare the oral microbiota of elderly individuals (≥60 years) with that of younger adults.

DESIGN

A comprehensive search of PubMed, Medline, EMBASE and CINAHL identified 794 studies published between 2005 and May 2023. Studies were included if the investigators compared the oral microbiome of elderly with younger adults using 16S rRNA sequencing. The JBI Critical Appraisal Checklist for Analytical Cross-Sectional Studies was employed to evaluate risk of bias. Ten full-text articles met the criteria for inclusion.

RESULTS

The included studies revealed inconsistent results regarding alpha and beta diversity and the abundance of bacterial phyla with aging. Some studies reported increased diversity or abundance, others showed decreases, and several found no significant differences. However, this review identified a consistent decline in the abundance of Haemophilus, Granulicatella, and Veillonella, alongside an increase in Comamonas, in elderly populations across multiple studies. These genera may play critical roles in maintaining oral health and microbial stability in elderly populations, highlighting the need for further investigation.

CONCLUSIONS

The variability in microbial diversity and abudance suggests that confounding factors such as oral hygiene, systemic health, medication use, and lifestyle may complicate interpretation of results. In conclusion, future research should employ longitudinal designs with standardized methodologies and address confounding factors to better understand the aging oral microbiome and its implications for healthspan and quality of life.

Association between clonal hematopoiesis and periodontitis: a two-sample mendelian randomization study

Clonal hematopoiesis (CH) is an age-associated phenomenon characterized by the proliferation of blood cells carrying somatic mutations. Recent studies suggest a potential link between CH and periodontitis, but the causal relationship remains unclear. A two-sample Mendelian randomization (MR) analysis was implemented, examining whether CH phenotypes are causally associated with periodontitis. CH phenotypes included overall clonal hematopoiesis (CH-overall), CH with a DNMT3A mutation (CH-DNMT3A), CH with a TET2 mutation (CH-TET2), large clones (CH-large), and small clones (CH-small). Genetic instruments were derived from genome-wide association studies, and the inverse-variance weighted (IVW) method was the primary analytical approach. Sensitivity analyses and reverse MR were also performed to ensure robustness. MR analysis demonstrated a significant association between CH-DNMT3A and periodontitis (odds ratio: 0.084, 95% CI: 0.007-0.972, P = 0.047), suggesting a protective role. No significant associations were found for other CH phenotypes. Reverse MR analyses showed no statistical evidence of a bidirectional relationship between periodontitis and any CH phenotype. Additionally, the analyses showed no signs of pleiotropy or heterogeneity that could confound the results. Our findings suggest a novel protective role for DNMT3A-mutated CH in periodontitis. Further research is warranted to explore the mechanisms underlying this association.

Unraveling the mechanisms underlying air pollution-induced dysfunction of the oral-gut-brain axis: implications for human health and well-being

Air pollution exposure has become an international health issue that poses many risks to life and health. The bidirectional regulatory network, known as the oral-gut-brain axis connects the oral cavity, intestine, and central nervous system, as well as its influence on health outcomes from exposure to air pollution is receiving increased attention. This article systematically details the epidemiological evidence linking air pollutants to diseases affecting the oral, respiratory, intestinal, and nervous systems, while also explaining the route of air pollutants via the oral-gut-brain axis. The oral-gut-brain axis anomalies resulting from air pollution and their underlying molecular processes are also covered. The study provides a fresh viewpoint on how exposure to air pollution affects health and investigates cutting-edge preventative and therapeutic techniques.

Mendelian randomization analysis reveals causal effects of migraine and its subtypes on early-onset ischemic stroke risk

Previous observational studies have suggested at a potential link between migraine, particularly migraine with aura, and the susceptibility to early-onset ischemic stroke. We aimed to investigate the causal effects of genetically determined migraine and its subtypes on the risk of early-onset ischemic stroke using the two-sample Mendelian randomization method. Genetic instrumental variables associated with migraine and its subtypes were acquired from two sources with the largest sample sizes available. Summary data for early-onset ischemic stroke was acquired from a study encompassing individuals aged 18-59 years, comprising 16,730 cases and 599,237 non-stroke controls. The random-effects inverse variance weighted method was used as the primary analysis approach. Additionally, linkage disequilibrium score regression analysis was used to evaluate the genetic correlation. The Mendelian randomization analysis revealed no association between overall migraine and migraine without aura with the risk of early-onset ischemic stroke. However, migraine with aura showed a suggestive association with an elevated risk of early-onset ischemic stroke, with odds ratios of 1.114 (95% confidence interval = 1.005 to 1.236, p-value = 0.040) and 1.062 (95% confidence interval = 1.002 to 1.126, p-value = 0.042) based on instruments from two independent sources. The odds ratio was 1.074 (95% confidence interval = 1.022 to 1.130, p-value = 0.005) based on instruments from both two sources. No evidence of heterogeneity or horizontal pleiotropy was found. By contrast, migraine with aura was not related to ischemic stroke in all adults. Furthermore, a significant positive genetic correlation was found between migraine with aura and early-onset ischemic stroke (genetic correlation = 0.208, 95% confidence interval = 0.038 to 0.377, p-value = 0.016). This study provides evidence of a causal relationship between migraine with aura and the risk of early-onset ischemic stroke, as well as a positive genetic correlation between them.

Butyrate Metabolism-Related Gene Signature in Tumor Immune Microenvironment in Lung Adenocarcinoma: A Comprehensive Bioinformatics Study

BACKGROUND

Experimental results have verified the suppressive impact of butyrate on tumor formation. Nevertheless, there is a limited understanding of the hidden function of butyrate metabolism within the tumor immune microenvironment (TIME) of lung adenocarcinoma (LUAD). This research aimed at digging the association between genes related to butyrate metabolism (butyrate metabolism-related genes [BMRGs) and immune infiltrates in LUAD patients.

METHODS

Through analyzing The Cancer Genome Atlas dataset (TCGA), the identification of 38 differentially expressed BMRGs was made between LUAD and normal samples. Later, a prognostic signature made up of nine BMRGs was made to evaluate the risk score of LUAD subjects. Notably, high-risk scores emerged as negative prognostic indicators for overall survival in LUAD subjects. Additionally, BMRGs displayed associations with immunocyte infiltration levels, immune pathway activities, and pivotal prognostic hub BMRGs.

RESULTS

One key prognostic BMRG, PTGDS, exhibited a robust correlation with T cells, the chemokine-related pathway, and the TCR signaling pathway. This study suggests that investigating the interplay between butyrate metabolism and T cells could present a promising novel approach to cancer treatment. OncoPredict analysis further unveiled distinct sensitivities of nine medicine in high- and low-risk groups, facilitating the selection of optimal treatment strategies for individual LUAD patients.

CONCLUSIONS

The study establishes that the BMRG signature serves as a sensitive predictive biomarker, providing profound insights into the crucial effect of butyrate metabolism in the context of LUAD TIME.

The role of circulating cytokines in heart failure: a bidirectional, two-sample Mendelian randomization study

Background

Cytokines play a pivotal role in the progression of heart failure (HF) by modulating inflammatory responses, promoting vasoconstriction, and facilitating endothelial injury. However, it is now difficult to distinguish the causal relationship between HF and cytokines in observational studies. Mendelian randomization (MR) analyses of cytokines probably could enhance our comprehension to the underlying biological processes of HF.

Methods

This study was to explore the correlation between 41 cytokines with HF at the genetic level by MR analysis. We selected a HF dataset from the Heart Failure Molecular Epidemiology for Therapeutic Targets (HERMES) 2018 and a cytokine dataset from a meta-analysis of cytokine levels in Finns. Two-sample, bidirectional MR analyses were performed using Inverse Variance Weighted (IVW), Weighted Median and MR- egger, and the results were tested for heterogeneity and pleiotropy, followed by sensitivity analysis.

Results

Genetic prediction of high levels of circulating Macrophage inflammatory pro-tein-1β(MIP-1β) (P = 0.0389), Interferon gamma induced protein 10(IP-10) (P = 0.0029), and Regu-lated on activation, normal T cell expressed and secreted(RANTES) (P = 0.0120) expression was associated with an elevated risk of HF. HF was associated with the increased levels of circulating Interleukin-2 receptor, alpha subunit(IL-2ra) (P = 0.0296), Beta nerve growth fac-tor(β-NGF) (P = 0.0446), Interleukin-17(IL-17) (P = 0.0360), Basic fibroblast growth factor(FGF-basic) (P = 0.0220), Platelet derived growth factor BB(PDGF-BB) (P = 0.0466), and Interferon-gamma(IFN-γ) (P = 0.0222); and with decreased levels of Eotaxin (P = 0.0133). The heterogeneity and pleiotropy of the cytokines were acceptable, except for minor heterogeneity of FGF-basic and IL-17.

Conclusion

These findings provide compelling evidence for a genetically predictive relationship between cytokines and HF, emphasizing a great potential of targeted modulation of cytokines in slowing the progression of HF. This study draws further conclusions at the genetic level, providing a basis for future large-scale clinical trials.

Intestinal homeostasis disrupted by Periodontitis exacerbates Alzheimer's Disease in APP/PS1 mice

Periodontitis exacerbates Alzheimer's disease (AD) through multiple pathways. Both periodontitis and AD are intricately correlated to intestinal homeostasis, yet there is still a lack of direct evidence regarding whether periodontitis can regulate the progression of AD by modulating intestinal homeostasis. The current study induced experimental periodontitis in AD mice by bilaterally ligating the maxillary second molars with silk and administering Pg-LPS injections in APPswe/PS1ΔE9 (APP/PS1) mice. Behavioral tests and histological analyses of brain tissue were conducted after 8 weeks. Gut microbiota was analyzed and colon tissue were also evaluated. Then, fecal microbiota from mice with periodontitis was transplanted into antibiotic-treated mice to confirm the effects of periodontitis on AD and the potential mechanism was explored. The results indicated periodontitis exacerbated cognitive impairment and anxious behaviour in APP/PS1 mice, with increased Aβ deposition, microglial overactivation and neuroinflammation in brain. Moreover, the intestinal homeostasis of AD mice was altered by periodontitis, including affecting gut microbiota composition, causing colon inflammation and destroyed intestinal epithelial barrier. Furthermore, AD mice that underwent fecal transplantation from mice with periodontitis exhibited worsened AD progression and disrupted intestinal homeostasis. It also impaired intestinal barrier function, elevated peripheral inflammation, damaged blood-brain barrier (BBB) and caused neuroinflammation and synapses impairment. Taken together, the current study demonstrated that periodontitis could disrupt intestinal homeostasis to exacerbate AD progression potential via causing gut microbial dysbiosis, intestinal inflammation and intestinal barrier impairment to induce peripheral inflammation and damage BBB, ultimately leading to neuroinflammation and synapse impairment. It underscores the importance of maintaining both periodontal health and intestinal homeostasis to reduce the risk of AD.

Mendelian randomization suggests causal correlations between inflammatory cytokines and immune cells with mastitis

Objectives

Previous studies have reported that immunoinflammatory responses have associations with mastitis. Here, we aimed to further figure out whether circulating inflammatory cytokines and immune cells causally impact mastitis liability.

Methods

The two-sample Mendelian randomization made use of genetic variances of 91 inflammatory cytokines from a large publicly available genome-wide association study (GWAS) containing 14,824 participants, 731 immunophenotypes data from 3,757 individuals as exposures separately, and mastitis from a GWAS summary (1880 cases and 211699 controls of European ancestry) as outcome. The primary analysis applied the inverse-variance weighted (IVW) method to estimate causal influences, with MR-Egger, weighted median, weighted mode and simple mode as supplementary approaches. Heterogeneity and pleiotropy were evaluated by the Cochrane Q test, MR-Egger intercept test, and MR-PRESSO global test.

Results

The results indicated that CX3CL1 may be suggestively relevant to the risk of mastitis (odds ratio, OR = 1.434, 95% CI = 1.142~1.800, p = 0.002). Moreover, three immunophenotypes were identified as having a potential causal link to mastitis (p < 0.05). Significantly, CD28- CD8dim %CD8dim (OR = 1.058, 95% CI = 1.024 ~ 1.093, p = 0.0006) and CD45 on CD33br HLA DR+ (OR = 1.097, 95% CI = 1.039 ~ 1.157, p = 0.0008) were found to induce mastitis possibly. Conversely, CD39+ secreting Treg AC (OR = 0.929, 95% CI = 0.884~ 0.978, p = 0.005) pertained to protective factors of mastitis. Cochran's Q test and MR-Egger intercept test indicated no significant heterogeneity (p > 0.05) or pleiotropy (p > 0.05), supporting the robustness and reliability of our findings.

Conclusion

Our study adds to current knowledge on the causal roles of inflammatory cytokines and immune cells on mastitis by genetic means, thus guiding future clinical research.

Causal roles of skin and gut microbiota in skin appendage disorders suggested by genetic study

OBJECTIVES

There is evidence from observational studies that human microbiota is linked to skin appendage Disorders (SADs). Nevertheless, the causal association between microbiota and SADs is yet to be fully clarified.

METHODS

A comprehensive two-sample Mendelian randomization (MR) was first performed to determine the causal effect of skin and gut microbiota on SADs. A total of 294 skin taxa and 211 gut taxa based on phylum, class, order, family, genus, and ASV level information were identified. Summary data of SADs and eight subtypes (acne vulgaris, hidradenitis suppurativa, alopecia areata, rogenic alopecia, rosacea, rhinophyma, seborrhoeic dermatitis, and pilonidal cyst) were obtained from the FinnGen consortium. We performed bidirectional MR to determine whether the skin and gut microbiota are causally associated with multiple SADs. Furthermore, sensitivity analysis was conducted to examine horizontal pleiotropy and heterogeneity.

RESULTS

A total of 65 and 161 causal relationships between genetic liability in the skin and gut microbiota with SADs were identified, respectively. Among these, we separately found 5 and 11 strong causal associations that passed Bonferroni correction in the skin and gut microbiota with SADs. Several skin bacteria, such as Staphylococcus, Streptococcus, and Propionibacterium, were considered associated with multiple SADs. As gut probiotics, Bifidobacteria and Lactobacilli were associated with a protective effect on SAD risk. There was no significant heterogeneity in instrumental variables or horizontal pleiotropy.

CONCLUSIONS

Our MR analysis unveiled bidirectional causal relationships between SADs and the gut and skin microbiota, and had the potential to offer novel perspectives on the mechanistic of microbiota-facilitated dermatosis.

Leveraging genetics to investigate causal effects of immune cell phenotypes in periodontitis: a mendelian randomization study

Introduction

Immune cells are dynamic in the inflammatory environment and play a key role in eradicating periodontal pathogens, modulating immune responses, and instigating tissue destruction. Identifying specific immune cell phenotypes associated with periodontitis risk is essential for targeted immunotherapeutic interventions. However, the role of certain specific immune cell phenotypes in the development of periodontitis is unknown. Mendelian randomization offers a novel approach to reveal causality and address potential confounding factors through genetic instruments.

Methods

This two-sample Mendelian randomization study assessed the causal relationship between 731 immune cell phenotypes and periodontitis using the inverse variance weighting method with the GWAS catalog genetic database. Methodological robustness was ensured through Cochran's Q test, MR-Egger regression, MR-PRESSO, and Leave-One-Out analysis.

Results

14 immune cell phenotypes showed potential positive causal associations with periodontitis risk (p < 0.05), suggesting an increased risk, while 11 immune cell phenotypes exhibited potential negative causal associations (p < 0.05), indicating a reduced risk. No significant heterogeneity or pleiotropy was observed.

Conclusion

This study underscores certain immune cell types as potential periodontitis risk biomarkers, laying a theoretical foundation for future individualized treatment and precision medicine development.

The association between diets and periodontitis: a bidirectional two-sample Mendelian randomization study

Background

Periodontitis, a complex inflammatory condition, has been associated with dietary habits and antioxidants. While the association between certain dietary patterns and periodontitis has been documented, the bidirectional relationship remains unclear. This study utilizes Mendelian randomization (MR) analysis to investigate the bidirectional associations between dietary factors comprising dietary antioxidants, and periodontitis.

Methods

Employing a two-sample MR approach, this study analyzed genome-wide association study (GWAS) data on diets and periodontitis from large databases and published literature. Instrumental variables (IVs) were selected and filtered based on genetic variants associated with dietary factors and periodontitis, respectively. Various MR methods, including Inverse Variance Weighted, MR-Egger, Weighted Median, Weighted Mode, and Simple Mode were applied to assess the bidirectional associations. Sensitivity analyses were conducted to validate the robustness of the findings.

Results

Our analysis revealed significant associations between certain dietary factors and the risk of periodontitis. Specifically, higher intake of filtered coffee, low-calorie drinks, and other cereals, as well as increased metabolic circulating levels of gamma-tocopherol, were associated with an elevated risk of periodontitis. Conversely, consumption of cheese, white rice, chocolate bars, unsalted peanuts, and higher absolute circulating levels of vitamin C were linked to a reduced risk. Additionally, the study suggests that periodontitis may influence dietary habits, indicating a bidirectional relationship.

Conclusion

This study provides additional evidence of a bidirectional association between dietary factors and periodontitis. It highlights the importance of dietary interventions in the prevention and management of periodontitis. The findings underscore the need for incorporating dietary counseling into periodontal disease management protocols and suggest the potential of personalized dietary strategies for periodontitis patients. Further research is warranted to explore the mechanisms underlying these associations and to confirm these findings in diverse populations.

Associations of inflammatory cytokines with palmoplantar pustulosis: a bidirectional Mendelian randomization study

Background

Variations in circulatory cytokine levels have been observed during the onset and course of palmoplantar pustulosis (PPP); however, whether these changes are due to etiological or secondary factors is unclear. To clarify the causal relationship, we conducted a summarized-level bidirectional Mendelian randomization (MR) analysis in this study.

Methods

A FinnGen biobank genome-wide association study (GWAS) of 212,766 individuals (524 PPP patients and 212,242 controls) provided summary data for PPP, whereas genetic instrumental variables (IVs) linked to circulation cytokine levels were gathered from a GWAS of 14,824 European individuals. The inverse-variance weighted (IVW), weighted median (WME), simple mode, and MR-Egger methods were used to ascertain the changes in PPP pathogenic cytokine taxa. Sensitivity analysis, which included horizontal pleiotropy analysis, was then conducted. The reliability of the results was assessed using the leave-one-out approach and the MR Steiger test, which evaluated the strength of a causal relationship. To evaluate the reverse causality between PPP and circulating cytokine levels, a reverse MR analysis was carried out.

Results

Our study demonstrated positive associations between C-X-C motif chemokine 6 (CXCL6) and PPP (odds ratio, OR 1.257, 95%CI: 1.001-1.570, p = 0.043). C-C motif chemokine 19 (CCL19) and interleukin-6 (IL-6) were suggested to be protectively associated with the development of PPP (OR: 0.698,95% CI: 0.516-0.944, p = 0.020; OR: 0.656, 95%CI:0.437-0.985, p = 0.042). The results were steady after sensitivity and heterogeneity analyses.

Conclusion

At the genetic prediction level, we identified causally connected inflammation-related variables that contributed to the onset and development of PPP. The therapeutic options for some refractory PPP have expanded due to tailored cytokine therapy, generating fresh concepts for PPP diagnostics and mechanism investigation.

Association between migraine and venous thromboembolism: a Mendelian randomization and genetic correlation study

Objective

Previous observational studies have reported an increased risk of venous thromboembolism (VTE) among individuals with migraine. This study aimed to investigate the causal effect of migraine on the development of VTE, as well as explore the genetic correlation between them.

Methods

We conducted a two-sample Mendelian randomization (MR) study using publicly available summary statistics from large-scale genome-wide association studies for migraine and VTE. Linkage disequilibrium score regression analysis was performed to estimate the genetic correlation between migraine and VTE.

Results

There were several shared risk variants (p-value < 5 × 10-8) between migraine and VTE. Linkage disequilibrium score regression analysis found a significant positive genetic correlation between migraine and VTE. The genetic correlations based on two migraine datasets were 0.208 (se = 0.031, p-value = 2.91 × 10-11) and 0.264 (se = 0.040, p-value = 4.82 × 10-11), respectively. Although main MR analysis showed that migraine was associated with an increased risk of VTE (odds ratio = 1.069, 95% confidence interval = 1.022-1.118, p-value = 0.004), the association attenuated to non-significance when using several other MR methods and using another set of genetic instruments. In addition, evidence of heterogeneity was found. Reverse MR analysis showed VTE was associated with increased risk of migraine with aura (odds ratio = 1.137, 95% confidence interval = 1.062-1.218, p-value = 2.47 × 10-4) with no evidence of pleiotropy and heterogeneity.

Conclusion

We showed suggestive evidence indicating an association between migraine and increased risk of VTE. Additionally, we found robust evidence suggesting that VTE is associated with an increased risk of migraine. The positive genetic correlation indicates that migraine and VTE has shared genetic basis. Further investigations will be necessary to address potential sex-specific effects in the analysis.

Inflammatory cytokines and oral lichen planus: a Mendelian randomization study

Background

Inflammatory cytokines have long been considered closely related to the development of oral lichen planus (OLP), and we further explored the causal relationship between the two by Mendelian randomization (MR) method.

Methods

We performed bidirectional MR analyses by large genome-wide association studies (GWAS). The data included a large-scale OLP dataset, as well as datasets of 41 inflammatory cytokines. All data were obtained from the University of Bristol database, which includes 41 inflammatory cytokines, and the GWAS Catalog database, which includes 91 inflammatory cytokines. OLP data were obtained from the Finngen database, which includes 6411 cases and 405770 healthy controls. We used the inverse variance weighted (IVW) method, MR-Egger method, weighted median method, simple mode method and weighted mode method to analyze the causal relationship between inflammatory cytokines and OLP, and we also combined with sensitivity analysis to further verify the robustness of the results. We performed a meta-analysis of positive or potentially positive results for the same genes to confirm the reliability of the final results.

Results

We primarily used the IVW analysis method, corrected using the Benjamin Hochberg (BH) method. When p<0.00038 (0.05/132), the results are significantly causal; when 0.00038

Conclusion

There is a causal association between OLP and some inflammatory cytokines, which may play an important role in the pathogenesis of OLP and require further attention.

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Key Words

• Mendelian randomization
• immunity
• inflammation
• inflammatory cytokines
• oral lichen planus

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MESH Headings

• Humans
• Cytokines/genetics
• Genome-Wide Association Study
• Lichen Planus, Oral/genetics
• Mendelian Randomization Analysis
• Reproducibility of Results

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Affiliation(s)

Xin Chen Department of Oral and Maxillofacial Surgery, Jiangyin People's Hospital Affiliated to Nantong University, Wuxi, Jiangsu, China
Simin Zhang Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of General Dentistry, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
Xiao Wu Endodontic Department, School of Stomatology, Nanjing Medical University, Nanjing, Jiangsu, China
Yuxi Lei Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of Emergency Room, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
Bing Lei Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of General Dentistry, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
Zhibai Zhao Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of General Dentistry, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China

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