The association between missing teeth and non-alcoholic fatty liver disease in adults

Multifunctional role of oral bacteria in the progression of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver disorders of varying severity, ultimately leading to fibrosis. This spectrum primarily consists of NAFL and non-alcoholic steatohepatitis. The pathogenesis of NAFLD is closely associated with disturbances in the gut microbiota and impairment of the intestinal barrier. Non-gut commensal flora, particularly bacteria, play a pivotal role in the progression of NAFLD. Notably, Porphyromonas gingivalis, a principal bacterium involved in periodontitis, is known to facilitate lipid accumulation, augment immune responses, and induce insulin resistance, thereby exacerbating fibrosis in cases of periodontitis-associated NAFLD. The influence of oral microbiota on NAFLD via the "oral-gut-liver" axis is gaining recognition, offering a novel perspective for NAFLD management through microbial imbalance correction. This review endeavors to encapsulate the intricate roles of oral bacteria in NAFLD and explore underlying mechanisms, emphasizing microbial control strategies as a viable therapeutic avenue for NAFLD.

Identifying MS4A6A+ macrophages as potential contributors to the pathogenesis of nonalcoholic fatty liver disease, periodontitis, and type 2 diabetes mellitus

Purpose

Concrete epidemiological evidence has suggested the mutually-contributing effect respectively between nonalcoholic fatty liver disease (NAFLD), type 2 diabetes mellitus (T2DM), and periodontitis (PD); however, their shared crosstalk mechanism remains an open issue.

Method

The NAFLD, PD, and T2DM-related datasets were obtained from the NCBI GEO repository. Their common differentially expressed genes (DEGs) were identified and the functional enrichment analysis performed by the DAVID platform determined relevant biological processes and pathways. Then, the STRING database established a PPI network of such DEGs and topological analysis through Cytoscape 3.7.1 software along with the machine-learning analysis by the least absolute shrinkage and selection operator (LASSO) algorithm screened out hub characteristic genes. Their efficacy was validated by external datasets using the receiver operating characteristic (ROC) curve, and gene expression and location of the most robust one was determined using single-cell sequencing and immunohistochemical staining. Finally, the promising drugs were predicted through the CTD database, and the CB-DOCK 2 and Pymol platform mimicked molecular docking.

Result

Intersection of differentially expressed genes from three datasets identified 25 shared DEGs of the three diseases, which were enriched in MHC II-mediated antigen presenting process. PPI network and LASSO machine-learning analysis determined 4 feature genes, of which the MS4A6A gene mainly expressed by macrophages was the hub gene and key immune cell type. Molecular docking simulation chosen fenretinide as the most promising medicant for MS4A6A+ macrophages.

Conclusion

MS4A6A+ macrophages were suggested to be important immune-related mediators in the progression of NAFLD, PD, and T2DM pathologies.

Nisin lantibiotic prevents NAFLD liver steatosis and mitochondrial oxidative stress following periodontal disease by abrogating oral, gut and liver dysbiosis

Oral microbiome dysbiosis mediates chronic periodontal disease, gut microbial dysbiosis, and mucosal barrier disfunction that leads to steatohepatitis via the enterohepatic circulation. Improving this dysbiosis towards health may improve liver disease. Treatment with antibiotics and probiotics have been used to modulate the microbial, immunological, and clinical landscape of periodontal disease with some success. The aim of the present investigation was to evaluate the potential for nisin, an antimicrobial peptide produced by Lactococcus lactis, to counteract the periodontitis-associated gut dysbiosis and to modulate the glycolipid-metabolism and inflammation in the liver. Periodontal pathogens, namely Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia and Fusobacterium nucleatum, were administrated topically onto the oral cavity to establish polymicrobial periodontal disease in mice. In the context of disease, nisin treatment significantly shifted the microbiome towards a new composition, commensurate with health while preventing the harmful inflammation in the small intestine concomitant with decreased villi structural integrity, and heightened hepatic exposure to bacteria and lipid and malondialdehyde accumulation in the liver. Validation with RNA Seq analyses, confirmed the significant infection-related alteration of several genes involved in mitochondrial dysregulation, oxidative phosphorylation, and metal/iron binding and their restitution following nisin treatment. In support of these in vivo findings indicating that periodontopathogens induce gastrointestinal and liver distant organ lesions, human autopsy specimens demonstrated a correlation between tooth loss and severity of liver disease. Nisin's ability to shift the gut and liver microbiome towards a new state commensurate with health while mitigating enteritis, represents a novel approach to treating NAFLD-steatohepatitis-associated periodontal disease.

Involvement of Periodontal Disease in the Pathogenesis and Exacerbation of Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis: A Review

The increasing incidence of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH), along with global lifestyle changes, requires further in-depth research to elucidate the mechanisms and develop new treatment strategies. In addition, the number of patients with periodontal disease has increased recently, suggesting that periodontal disease is sometimes associated with systemic conditions. In this review, we summarize recent studies linking periodontal disease and NAFLD, the concept of the mouth-gut-liver axis, oral and intestinal microbiota, and liver disease. We suggest new research directions toward a detailed mechanistic understanding and novel targets for treatment and prevention. Forty years have passed since the concepts of NAFLD and NASH were first proposed. however, no effective prevention or treatment has been established. We also found that the pathogenesis of NAFLD/NASH is not limited to liver-related diseases but has been reported to be associated with various systemic diseases and an increasing number of causes of death. In addition, changes in the intestinal microbiota have been shown to be a risk factor for periodontal diseases, such as atherosclerosis, diabetes, rheumatoid arthritis, nonalcoholic fatty liver disease, and obesity.

The Triangle of Nonalcoholic Fatty Liver Disease, Metabolic Dysfunction, and Periodontitis: Analysis of the Dental, Oral, Medical and Epidemiological (DOME) Records-Based Nationwide Research

This study aimed to analyze the associations of nonalcoholic fatty liver disease (NAFLD) with dental parameters, while controlling for socio-demographics, health-related habits, and each of the metabolic syndrome (MetS) components, consequences, and related conditions among a nationally representative sample of young and middle-aged adults. To that end, we analyzed data from the dental, oral, medical epidemiological (DOME) cross-sectional records-based study that combined comprehensive socio-demographic, medical, and dental databases of a nationally representative sample of military personnel. Included were 132,529 subjects aged 18-50 who attended military dental clinics for one year. The prevalence of NAFLD in the study population was 0.7% (938/132,529). The following parameters maintained a statistically positive association with NAFLD in the multivariate analysis (from highest to lowest OR): male sex (OR = 3.91 (2.29-6.66)), hyperlipidemia (OR = 3.69 (2.75-4.95)), diabetes Type 2 (OR = 3.14 (2.21-4.46)), hypertension (OR = 1.67 (1.30-2.14)), periodontitis (OR = 1.42 (1.06-1.89)), body mass index (BMI) (OR = 1.15 (1.13-1.18)), and age (OR = 1.08 (1.06-1.09)). The multivariate analysis established a profile of the "patient vulnerable to NAFLD", including older age, male sex, and other MetS components, including diabetes type 2, hypertension, hyperlipidemia, BMI, and periodontitis. This profile aligns with the current new definition of metabolic dysfunction-associated fatty liver disease (MAFLD). We also analyzed the associations of the sum of the standard dental unit (SDU) scores of planned (SDU-P) and delivered (SDU-D) dental procedures per patient with NAFLD using receiver operating characteristic (ROC) analysis. The SDU-P (planned) score exhibited excellent discrimination for NAFLD (area under the curve (AUC) = 0.718 (0.703-0.734)). Overall, the results confirmed the hypothesis of this research, i.e., that NAFLD is associated with dental morbidity, particularly with periodontitis.

Mechanism and effects of artesunate on the liver function of rats with type 1 diabetic periodontitis

Periodontitis is an inflammatory disease of the gums. Periodontitis in patients with diabetes can aggravate insulin resistance, but its molecular and biological mechanism remains unclear. This study aimed to explore the effects of diabetic periodontitis on liver function and determine the mechanism by which artesunate improves liver function. Rats with streptozotocin-induced diabetes were divided into five groups, i.e., normal control group (NC group), diabetic periodontitis group (DM+PD group), artesunate intervention group (ART group), insulin intervention group (INS group), and combined medication intervention group (ART+INS group). Drug interventions were then administered to the rats in each group as follows: 50 mg/kg artesunate to the ART group, 6 U/kg insulin to the INS group, and 50 mg/kg artesunate + 6 U/kg insulin to the ART+INS group. Blood samples, liver tissues, and the maxillary alveolar bone were collected post-sacrifice. ART was found to significantly ameliorate hyperglycemia, blood lipid levels, and liver function. The levels of inflammatory factors reduced; the effect was more pronounced in the ART+INS group. Artesunate presumably inhibits the TLR4/NF-κB signaling pathway and expression of downstream inflammatory factors, thereby exerting a protective effect on diabetes-related liver function. This offers a fresh approach to treat diabetes mellitus.

Periodontitis, chronic liver diseases, and the emerging oral-gut-liver axis

The liver carries out a wide range of functions ranging from the control of metabolites, nutrient storage, and detoxification to immunosurveillance. While inflammation is essential for the tissue remodeling and maintenance of homeostasis and normal liver physiology, constant exposure to dietary and microbial products creates a niche for potentially prolonged immune activation and unresolved inflammation in susceptible host. Failure to restrain inflammation can lead to development of chronic liver diseases characterized by fibrosis, cirrhosis and eventually liver failure. The liver maintains close interactions with numerous organs which can influence its metabolism and physiology. It is also known that oral cavity microenvironment can influence the physiological conditions of other organs and emerging evidence implicates that this could be true for the liver as well. Presence of chronic inflammation and dysbiotic microbiota is a common feature leading to clinical pathology both in periodontitis and chronic liver diseases (CLDs). In fact, known CLDs appear to have some relationship with periodontitis, which impacts the onset or progression of these conditions in a bidirectional crosstalk. In this review, we explore the emerging association between oral‐gut‐liver axis focusing on periodontitis and common CLDs including nonalcoholic fatty liver disease, chronic viral hepatitis, liver cirrhosis, and hepatocellular cancer. We highlight the immune pathways and oral microbiome interactions which can link oral cavity and liver health and offer perspectives for future research.

Deciphering the toxicological role of Porphyromonas gingivalis derived endotoxins in liver diseases

Periodontitis is a most prevalent and infectious multifactorial inflammatory disease and is characterized by the progressive destruction of the tooth-supporting tissues. Porphyromonas gingivalis, a Gram‑negative oral anaerobe, mainly causes periodontitis and it is one of the most important risk factors responsible for aggravation of existing systemic diseases. Several experimental and clinical studies have shown the positive association between periodontitis and different forms of liver disease. Periodontal diseases increase the prevalence of non-alcoholic fatty liver diseases and cirrhosis. Infected periodontium and pathogens in the periodontal microenvironments release pathogen-associated molecular patterns such as peptidoglycan, lipopolysaccharides, gingipain, fimbria, bacterial DNA, etc, and damage-associated molecular patterns such as interleukins-1α, β, - 8, and galectin-3, etc. These virulence factors and cytokines enter the bloodstream, disseminate into the whole body, and induce a variety of systemic pathological effects, including liver diseases (steatosis and fibrosis). Maintaining oral hygiene by scaling and root planning significantly improves liver damage in patients with periodontitis. Dentists and physicians should have more awareness in understanding the bidirectional nature of the relationship between oral and systemic diseases. Importantly, periodontitis condition aggravates simple fatty liver into fibrotic disease and therefore, the aim of this review is to understand the possible link between periodontitis and liver diseases.

Periodontal disease-related nonalcoholic fatty liver disease and nonalcoholic steatohepatitis: An emerging concept of oral-liver axis

Periodontal disease, a chronic inflammatory disease of the periodontal tissues, is not only a major cause of tooth loss, but it is also known to exacerbate/be associated with various metabolic disorders, such as obesity, diabetes, dyslipidemia, and cardiovascular disease. Recently, growing evidence has suggested that periodontal disease has adverse effects on the pathophysiology of liver disease. In particular, nonalcoholic fatty liver disease, a hepatic manifestation of metabolic syndrome, has been associated with periodontal disease. Nonalcoholic fatty liver disease is characterized by hepatic fat deposition in the absence of a habitual drinking history, viral infections, or autoimmune diseases. A subset of nonalcoholic fatty liver diseases can develop into more severe and progressive forms, namely nonalcoholic steatohepatitis. The latter can lead to cirrhosis and hepatocellular carcinoma, which are end‐stage liver diseases. Extensive research has provided plausible mechanisms to explain how periodontal disease can negatively affect nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, namely via hematogenous or enteral routes. During periodontitis, the liver is under constant exposure to various pathogenic factors that diffuse systemically from the oral cavity, such as bacteria and their by‐products, inflammatory cytokines, and reactive oxygen species, and these can be involved in disease promotion of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. Also, gut microbiome dysbiosis induced by enteral translocation of periodontopathic bacteria may impair gut wall barrier function and promote the transfer of hepatotoxins and enterobacteria to the liver through the enterohepatic circulation. Moreover, in a population with metabolic syndrome, the interaction between periodontitis and systemic conditions related to insulin resistance further strengthens the association with nonalcoholic fatty liver disease. However, most of the pathologic links between periodontitis and nonalcoholic fatty liver disease in humans are provided by epidemiologic observational studies, with the causal relationship not yet being established. Several systematic and meta‐analysis studies also show conflicting results. In addition, the effect of periodontal treatment on nonalcoholic fatty liver disease has hardly been studied. Despite these limitations, the global burden of periodontal disease combined with the recent nonalcoholic fatty liver disease epidemic has important clinical and public health implications. Emerging evidence suggests an association between periodontal disease and liver diseases, and thus we propose the term periodontal disease–related nonalcoholic fatty liver disease or periodontal disease–related nonalcoholic steatohepatitis. Continued efforts in this area will pave the way for new diagnostic and therapeutic approaches based on a periodontologic viewpoint to address this life‐threatening liver disease.

Relationship between NAFLD and Periodontal Disease from the View of Clinical and Basic Research, and Immunological Response

Periodontal disease is an inflammatory disease caused by pathogenic oral microorganisms that leads to the destruction of alveolar bone and connective tissues around the teeth. Although many studies have shown that periodontal disease is a risk factor for systemic diseases, such as type 2 diabetes and cardiovascular diseases, the relationship between nonalcoholic fatty liver disease (NAFLD) and periodontal disease has not yet been clarified. Thus, the purpose of this review was to reveal the relationship between NAFLD and periodontal disease based on epidemiological studies, basic research, and immunology. Many cross-sectional and prospective epidemiological studies have indicated that periodontal disease is a risk factor for NAFLD. An in vivo animal model revealed that infection with periodontopathic bacteria accelerates the progression of NAFLD accompanied by enhanced steatosis. Moreover, the detection of periodontopathic bacteria in the liver may demonstrate that the bacteria have a direct impact on NAFLD. Furthermore, Porphyromonas gingivalis lipopolysaccharide induces inflammation and accumulation of intracellular lipids in hepatocytes. Th17 may be a key molecule for explaining the relationship between periodontal disease and NAFLD. In this review, we attempted to establish that oral health is essential for systemic health, especially in patients with NAFLD.

Association between periodontal disease, tooth loss and liver diseases risk

AIM

The purpose of this study is to assess the associations between periodontal disease, tooth loss and liver diseases.

MATERIALS AND METHODS

PubMed and Embase databases were utilized to search eligible studies. Odds ratio (OR) with 95% confidence interval (CI) was used as effect size to assess the associations between periodontal disease, tooth loss and liver diseases risk.

RESULTS

Our results indicated positive associations between periodontal disease and non-alcoholic fatty liver disease (NAFLD) (OR = 1.19, 95% CI = 1.06-1.33), liver cirrhosis (OR = 2.28, 95% CI = 1.50-3.48) and elevated transaminase level risk (OR = 1.08, 95% CI = 1.02-1.15). Moreover, tooth loss could increase NAFLD (OR = 1.33, 95% CI = 1.12- 1.56) and liver cancer risk (OR = 1.34, 95% CI = 1.04-1.74), and every five increment in tooth loss was associated with 5% increased liver cancer risk (OR = 1.05, 95% CI = 1.01 - 1.10) with a linear relationship. In addition, tooth loss had a positive tendency towards liver cirrhosis risk (OR = 2.03, 95% CI = 0.85-4.85) although there was no statistical significance.

CONCLUSION

Periodontal disease and tooth loss are positively associated with liver diseases including NAFLD, elevated transaminase level, liver cirrhosis and liver cancer.

Oral Diseases Associated with Nonalcoholic Fatty Liver Disease in the United States

The US prevalence of nonalcoholic fatty liver disease (NAFLD) is 30.6% and increasing. NAFLD shares some risk factors with periodontitis and dental caries. We explored the association between NAFLD and several oral conditions among US adults, using data from the cross-sectional, nationally representative National Health and Nutrition Examination Survey (NHANES), 1988 to 1994. NAFLD was assessed with ultrasonography (USON), the screening gold standard not available in the more recent NHANES, and the noninvasive Fibrosis Score (FS), Fatty Liver Index (FLI), and US Fatty Liver Index (US-FLI) as other screening alternatives. There were 5,421 eligible dentate adults aged 21 to 74 y with complete relevant data, with transferrin levels ≤50%, without hepatitis B or C, who were not heavy drinkers. Multivariable models were developed to examine the independent effects of moderate-severe periodontitis, untreated dental caries, caries experience, and tooth loss (<20 teeth) on NAFLD while controlling for clinical, biological, and sociodemographic factors. Weighted estimates for odds ratios (ORs) and 95% CIs were calculated with logistic regression. Between 17% and 24% of adults had NAFLD depending on the classification criteria. In adjusted models, as compared with those with better oral health, adults with <20 teeth were more likely to have NAFLD depending on the measure (USON: OR = 1.50, 95% CI = 1.11 to 2.02; FS: OR = 4.36, 95% CI = 3.47 to 5.49; FLI: OR = 1.99, 95% CI = 1.52 to 2.59; US-FLI: OR = 2.32, 95% CI = 1.79 to 3.01). People with moderate-severe periodontitis were more likely to have NAFLD (USON: OR = 1.54, 95% CI = 1.06 to 2.24; FS: OR = 3.10, 95% CI = 2.31 to 4.17; FLI: OR = 1.61, 95% CI = 1.13 to 2.28; US-FLI: OR = 2.21, 95% CI = 1.64 to 2.98). People with any untreated caries were more likely to have NAFLD (USON: OR = 1.51, 95% CI = 1.20 to 1.90; FLI: OR = 1.80, 95% CI = 1.33 to 2.44). NAFLD was associated with tooth loss, periodontitis, and, for some NAFLD measures, untreated dental caries but not overall caries experience after controlling for several key sociodemographic and behavioral factors. Results suggest that further evaluation is needed to better understand this health-oral health interrelationship and potential opportunities for medical-dental integration.