Japanese study reveals protective effect of nasal microbiome on eosinophilic chronic sinusitis

As in other countries around the world, the prevalence of chronic rhinosinusitis (CRS) has been alarmingly increasing in Japan over the past decade. CRS is an inflammatory disease that lasts for at least 12 weeks and can cause nasal congestion, runny nose, difficulty breathing through the nose, facial pain, and even loss of smell. Unfortunately, treating CRS is complex because the disease manifests itself in many forms. CRS can be divided into eosinophilic (ECRS) or non-eosinophilic (non-ECRS) types. In ECRS, there is an increase in eosinophils, a type of white blood cell that releases inflammatory compounds, in the tissues of the nasal cavity and sinuses.

The increase in the prevalence of CRS is largely driven by environmental factors, which in turn are influenced by lifestyle changes. Among various environmental factors, microorganisms present in the nasal cavities and passages are known to significantly affect our health. However, it is unclear whether the nasal microbiome contributes to the development of ECRS.

To address this knowledge gap, a Japanese research team led by Assistant Professor Masanori Kidoguchi, School of Medical Sciences, University of Fukui, Japan, recently conducted a study of chronic sinusitis in the Japanese population, focusing on the nasal microbiome.Their paper was also co-authored by Professor Shigeharu Fujieda from the University of Fukui and Professor Emiko Noguchi from the University of Tsukuba and was published in Journal of Allergy and Clinical Immunology September 25, 2023. Dr. Kidoguchi said: “We conducted this study because the pathological functions of bacteria and their metabolites in the development of ECRS remain unclear.“

First, the researchers collected nasal swabs from 143 subjects, 65 with ECRS, 45 with non-ECRS, and 33 healthy control subjects. They then compared the microbiome diversity between the CRS and control groups in these samples and found significant differences, suggesting that the nasal microbiome is indeed related to (or affected by) the disease.

More importantly, there were significant differences in microbiome composition between the ECRS and non-ECRS groups.Through chemical and genetic testing, the team discovered that the bacterium Fusobacterium nucleatum (Fusarium nucleatum) were found to be lower in ECRS patients. Furthermore, metagenomic analysis showed that lipopolysaccharide (LPS) synthesis was higher in non-ECRS patients than in ECRS patients.

Based on these results, Dr. Kidoguchi speculates: “Fusobacterium nucleatum is known to cause inflammation through the production of LPS. Some studies have shown that lipopolysaccharides have different structures and functions depending on the bacterial species. Therefore, we hypothesized that LPS derived from F. nucleatum may be involved in the pathogenesis of ECRS and non-ECRS.“

To test this hypothesis, the research team investigated whether LPS derived from Fusarium nucleatum Effects on the expression of specific cytokines in human bronchial epithelial cell cultures.Their experiments showed that LPS is derived exclusively from Fusarium nucleatum inhibited expression Aluminum oxide 15an enzyme that plays a key role in the development of nasal polyps and eosinophil-related inflammation.

Taken together, the results of this study suggest that disruption of the nasal microbiota may play a key role in ECRS. This finding could be used to develop more effective strategies to deal with this troublesome situation. “The microbiome may strongly influence treatment resistance in chronic sinusitis and may also have an impact on other allergic diseases,” Dr. Kidoguchi commented, “Future research is expected to promote the development of probiotics and lifestyle changes to prevent refractory chronic sinusitis.“

Let’s hope that a deeper understanding of these inflammatory conditions will pave the way for therapeutic and preventive strategies to improve the quality of life of ECRS patients.