Oral bacteria as determinants for respiratory health

Project Information

BRuSH

Grant agreement ID: 804199

DOI

10.3030/804199

Project closed

EC signature date 29 November 2018

Start date 1 January 2019

End date 28 February 2025

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 938,00

EU contribution

€ 1 499 938,00

Coordinated by

UNIVERSITETET I BERGEN
Norway

Periodic Reporting for period 4 - BRuSH (Oral bacteria as determinants for respiratory health)

Reporting period: 2023-07-01 to 2025-02-28

Summary of the context and overall objectives of the project

The oral cavity is the gateway to the lower respiratory tract, and oral bacteria have an important part to play for lung health. This may be the case for pathogens as well as commensal bacteria and the balance between species. The oral bacterial community of patients with periodontitis is dominated by gram-negative bacteria and a higher lipopolysaccharide (LPS) activity than in healthy microbiota. Furthermore, bacteria with especially potent pro-inflammatory LPS have been shown to be more common in the lungs of asthmatic than in healthy individuals. The working hypothesis of BRuSH is that microbiome communities dominated by LPSproducing bacteria which induce a particularly strong pro-inflammatory immune response in the host, will have a negative effect on respiratory health. The hypothesis will be tested in two longitudinally designed population-based lung health studies. BRuSH aim to identify whether specific bacterial composition and types of LPS producing bacteria in oral and dust samples predict lung function and respiratory health over time; and if the different types of LPS-producing bacteria affect LPS in saliva and dust. BRuSH will apply functional genome annotation that can assign biological significance to raw bacterial DNA sequences. With this bioinformatics tool we will cluster microbiome data into various LPS-producers: bacteria with LPS with strong inflammatory effects and others with weak- or antagonistic effects. The epidemiological studies will be supported by mice-models of asthma and cell assays of human bronchial epithelial cells, by exposing mice and bronchial cells to chemically synthesized Lipid A (the component that drive the LPS-induced immune responses) of various potency.

The 2010 Global Burden of Disease has estimated that 3.9 billon people worldwide have poor dental health. According to the WHO, 300 million people have asthma. The prevalence of COPD and asthma is expected to increase because of increasing life expectancy and an aging population. Both periodontal diseases and chronic lung diseases will increase in the coming years due to increasing life expectancy and an aging population. Both disease conditions occur more often in groups with low socio-economic status, and lead to poorer quality of life for those affected. Periodontitis are the most common cause of lost teeth during the lifetime. Symptoms of periodontitis could be bleeding when brushing teeth and during dental flossing, redness, and edema of the gums. Periodontitis are heritable but are also affected by age and lifestyle. Early diagnostics and treatment are important to prevent the disease from developing into more severe forms. The decline in use of dental care is most pronounced among individuals of low social status, and social inequalities in dental health and use of dental care services are evident among elderly in Norway as well as in other European countries. The goal of BRuSH is to prove a causal relationship between oral microbiome and lung health, and gain knowledge that will enable us to make oral health a feasible target for intervention programs aimed at optimizing lung health and preventing respiratory disease.

The objective of BRuSH is first to explore whether the relative abundance of hexa-, penta-, and tetra-acylated LPS-producing bacteria in gingival and dust samples are associated with asthma severity, changes in lung function and respiratory diseases status over time. Secondly, to investigate whether the levels of LPS in oral and dust samples are associated with those outcomes; and whether the contribution of hexa-, penta-, and tetra-acylated LPS-producing bacteria influences these LPS levels. Third, to apply synthetized lipid As in mice models of experimental asthma and in vitro models of human bronchial epithelial cells. To reach these goals, BRuSH will use data and biobank material from two large population-based studies; the RHINESSA generation study (Respiratory Health In Northern Europe, Spain and Australia; www.RHINESSA.net) and the ECRHS study (European Community Respiratory Health Survey; www.ecrhs.org) and in addition in vitro and in vivo models to test how different lipid As influence lung health.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In a general study population, RHINESSA, with mostly healthy participants, we found that self-reported gum bleeding (when brushing teeth) was associated with higher abundance of bacteria associated with periodontal disease, and lower diversity in those applying frequent dental hygiene measures. The microbiome data was further grouped by which type of lipid A the gram-negative bacteria can produce, which tells us about how potent the bacteria are in inducing inflammation in the host. The results showed that the majority of the gram-negative bacteria were penta-acylated bacteria (40%) whereas only 3% were hexa-acylated bacteria (more potent). LPS concentration in saliva corresponded with penta-acylated lipid A producing bacteria. Furthermore, the bacterial diversity was lower in adults with allergy and some types of bacteria was associated with lower lung function.

With longitudinal data and follow-up every 10th year, we can also establish that reporting often or always to bleed from the gums during toothbrushing are a strong predictor for reporting periodontitis 10 years later. With a multi-center design, we can also establish that there are differences between the Nordic countries and some of these difference are most likely due to cost and access of dental care.

Indoor air particle were sampled in homes of 1200 participants in the ECRHS study from five cites in Northern Europe. The samples were analyzed for bacteria and endotoxin. Proteobacteria were more abundant in Aarhus and Tartu, while Actinobacteria were more abundant in Bergen and Reykjavik than in other Nordic cities. Tartu showed the highest bacterial richness and Bergen the lowest. The same pattern was evident for endotoxin. We find that 54%of the bacteria were penta-acylated lipid A producing bacteria and only 3% were the potent hexa-acylated lipid A producing bacteria, and 30% gram-positive bacteria. The protocol for for the EDCs that were used to collect the airborne particles indoors were optimized to extract sufficient biomass to allow for both endotoxin and microbiome analyses. Climatic factors such as precipitation, wind and temperature were the most important determinants for explaining the differences in indoor bacterial composition between the five Nordic cities. Other factors that were important determinants were keeping a dog, sleeping with the window open, the age of the person living in the house and the number of persons in the homes, in addition to cleaning frequency.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

To establish the link between oral inflammatory bacteria and lung inflammation, we are investigating if treatment of periodontitis (gum disease) in a relatively young and healthy population can improve lung function, with lung function measured at several time points before and after treatment of periodontitis. The results of the oral health intervention study (BORALIS) are now ready and published in Respiratory Research. We found that 12 months after treatment the airway resistance had improved compared to baseline. This shows how important oral health is for systemic health and inflammation. It is the first study to explore this in a population with lung-healthy participants.

Linking oral microbiome to lung health. Illustrator: Joana C. Carvalho