Human matters in asthma: Considering the microbiome in pulmonary health

[Recent research on the relationship between pulmonary microbiome and asthma endotypes in children]

Bronchial asthma is not considered a singular disease, but rather a collection of syndromes with multiple phenotypes and mechanisms that involve various signaling pathways. It typically emerges during the preschool years, and its etiology is intricate and diverse. In recent years, the advancement of high-throughput sequencing technology has revealed that early alterations in lung microbiota may be associated with asthma incidence and progression. Moreover, significant variations in lung microbiota have been observed among different airway inflammation profiles, known as asthma endotypes. Hence, a comprehensive understanding of the characteristics of lung microbiota in children with asthma can aid in managing disease progression and improving long-term prognosis. Additionally, such insights may spark novel approaches to diagnosing and treating childhood asthma.

Effects of early postnatal hyperoxia exposure combined with early ovalbumin sensitization on lung inflammation and bacterial flora in a juvenile mouse model of asthma

Objective

The aim of this study is to explore the effects of early postnatal hyperoxia exposure combined with early ovalbumin (OVA) sensitization on lung inflammation and bacterial flora in neonatal mice on a juvenile mouse model of asthma.

Methods

Thirty-two newborn female C57BL/6 J mice were randomly divided into four groups, which including room air+phosphate-buffered saline (PBS) group, hyperoxia+PBS group, room air+OVA group, and hyperoxia+OVA group, according to the hyperoxia exposure and/or OVA induction. Mice were exposed to either 95% O₂ or room air for 7 days after birth; after 7 days, they were exposed to air and received an intraperitoneal injection of OVA suspension or PBS solution on postnatal days 21 (P21) and 28 (P28). From P36 to P42, the mice were allowed to inhale of 1% OVA or 0.9% NaCl solution. The mice were observed after the last excitation. HE staining was performed to observe the pathological changes in lung tissues. Wright-Giemsa staining was used to perform bronchoalveolar lavage fluid (BALF) leukocyte sorting. Enzyme-linked immunosorbent assay was used to determined the cytokines levels of interleukin (IL)-2, IL-5, IL-13, IL-17A, and IL-10 and serum IgE levels in BALF. Additionally, 16S rRNA sequencing was used to analyze the characteristics of lung microbiota.

Results

Mice in the hyperoxia+OVA group showed asthma-like symptoms. HE staining results revealed a significant thickening of the airway wall and airway inflammation. BALF analysis of cellular components showed significant increases in total leukocyte and eosinophil counts and the levels of cytokines related to Th2 (IL-5 and IL-13) and Th17 (IL-17A); 16S rRNA sequencing revealed that the main members of the pulmonary microflora were Actinobacteriota, Proteobacteria, Firmicutes, and Bacteroidota at the phylum level. In addition, the bacteria with a major role were Acinetobacter and Moraxellaceae in the O₂ + OVA group.

Conclusion

The mouse suffering from postnatal hyperoxia exposure and early OVA sensitization, changes in symptoms, pathology, leukocyte and eosinophil counts, and levels of different T-cell cytokines in BALF and lung microbiota, which may provide a basis for the establishment of a juvenile mouse model of asthma.

Lung microbiota and potential treatment of respiratory diseases

The unique microbiome found in the lungs has been studied and shown to be associated with both pulmonary homeostasis and lung diseases. The lung microbiome has the potential to produce metabolites that modulate host-microbe interactions. Specifically, short-chain fatty acids (SCFAs) produced by certain strains of the lung microbiota have been shown to regulate immune function and maintain gut mucosal health. In response, this review described the distribution and composition of the microbiota in lung diseases and discussed the impact of the lung microbiota on health and lung disease. In addition, the review further elaborated on the mechanism of microbial metabolites in microbial-host interaction and their application in the treatment of lung diseases. A better understanding of the interaction between the microbiota, metabolites, and host will provide potential strategies for the development of novel methods for the treatment of pulmonary microbial induced lung diseases.

The Impact of Smoking on Microbiota: A Narrative Review

Cigarette smoke is a classic risk factor for many diseases. The microbiota has been recently indicated as a new, major player in human health. Its deregulation-dysbiosis-is considered a new risk factor for several illnesses. Some studies highlight a cross-interaction between these two risk factors-smoke and dysbiosis-that may explain the pathogenesis of some diseases. We searched the keywords "smoking OR smoke AND microbiota" in the title of articles on PubMed^®, UptoDate^®, and Cochrane^®. We included articles published in English over the last 25 years. We collected approximately 70 articles, grouped into four topics: oral cavity, airways, gut, and other organs. Smoke may impair microbiota homeostasis through the same harmful mechanisms exerted on the host cells. Surprisingly, dysbiosis and its consequences affect not only those organs that are in direct contact with the smoke, such as the oral cavity or the airways, but also involve distant organs, such as the gut, heart, vessels, and genitourinary tract. These observations yield a deeper insight into the mechanisms implicated in the pathogenesis of smoke-related diseases, suggesting a role of dysbiosis. We speculate that modulation of the microbiota may help prevent and treat some of these illnesses.