Airway Bacterial Biodiversity in Exhaled Breath Condensates of Asthmatic Children-Does It Differ from the Healthy Ones?

The Role of Exhaled Breath Condensate in Chronic Inflammatory and Neoplastic Diseases of the Respiratory Tract

Asthma and chronic obstructive pulmonary disease (COPD) are among the most common chronic respiratory diseases. Chronic inflammation of the airways leads to an increased production of inflammatory markers by the effector cells of the respiratory tract and lung tissue. These biomarkers allow the assessment of physiological and pathological processes and responses to therapeutic interventions. Lung cancer, which is characterized by high mortality, is one of the most frequently diagnosed cancers worldwide. Current screening methods and tissue biopsies have limitations that highlight the need for rapid diagnosis, patient differentiation, and effective management and monitoring. One promising non-invasive diagnostic method for respiratory diseases is the assessment of exhaled breath condensate (EBC). EBC contains a mixture of volatile and non-volatile biomarkers such as cytokines, leukotrienes, oxidative stress markers, and molecular biomarkers, providing significant information about inflammatory and neoplastic states in the lungs. This article summarizes the research on the application and development of EBC assessment in diagnosing and monitoring respiratory diseases, focusing on asthma, COPD, and lung cancer. The process of collecting condensate, potential issues, and selected groups of markers for detailed disease assessment in the future are discussed. Further research may contribute to the development of more precise and personalized diagnostic and treatment methods.

The Role of Biodiversity in the Development of Asthma and Allergic Sensitization: A State-of-the-Science Review

BACKGROUND

Changes in land use and climate change have been reported to reduce biodiversity of both the environment and human microbiota. These reductions in biodiversity may lead to inadequate and unbalanced stimulation of immunoregulatory circuits and, ultimately, to clinical diseases, such as asthma and allergies.

OBJECTIVE

We summarized available empirical evidence on the role of inner (gut, skin, and airways) and outer (air, soil, natural waters, plants, and animals) layers of biodiversity in the development of asthma, wheezing, and allergic sensitization.

METHODS

We conducted a systematic search in SciVerse Scopus, PubMed MEDLINE, and Web of Science up to 5 March 2024 to identify relevant human studies assessing the relationships between inner and outer layers of biodiversity and the risk of asthma, wheezing, or allergic sensitization. The protocol was registered in PROSPERO (CRD42022381725).

RESULTS

A total of 2,419 studies were screened and, after exclusions and a full-text review of 447 studies, 82 studies were included in the comprehensive, final review. Twenty-nine studies reported a protective effect of outer layer biodiversity in the development of asthma, wheezing, or allergic sensitization. There were also 16 studies suggesting an effect of outer layer biodiversity on increasing asthma, wheezing, or allergic sensitization. However, there was no clear evidence on the role of inner layer biodiversity in the development of asthma, wheezing, and allergic sensitization (13 studies reported a protective effect and 15 reported evidence of an increased risk).

CONCLUSIONS

Based on the reviewed literature, a future systematic review could focus more specifically on outer layer biodiversity and asthma. It is unlikely that association with inner layer biodiversity would have enough evidence for systematic review. Based on this comprehensive review, there is a need for population-based longitudinal studies to identify critical periods of exposure in the life course into adulthood and to better understand mechanisms linking environmental exposures and changes in microbiome composition, diversity, and/or function to development of asthma and allergic sensitization. https://doi.org/10.1289/EHP13948.

First Exploration of the Altered Microbial Gut-Lung Axis in the Pathogenesis of Human Refractory Chronic Cough

PURPOSE

Cough represents a natural mechanism that plays an important defensive role in the respiratory tract, but in some conditions, it may become persistent, nonproductive, and harmful. In general, refractory chronic cough (RCC) occurs in about 20% of individuals; hence, we aimed to assess the presence of altered gut-lung communication in RCC patients through a compositional and functional characterization of both gut (GM) and oral microbiota (OM).

METHODS

16S rRNA sequencing was used to characterize both GM and OM composition of RCC patients and healthy controls (HC). PICRUST2 assessed functional changes in microbial communities while gas chromatography was used to evaluate fecal short-chain fatty acid levels and serum-free fatty acid (FFA) abundances.

RESULTS

In comparison with HC, RCC patients reported increased saliva alpha-diversity and statistically significant beta-diversity in both GM and OM. Also, a, respectively, significant increased or reduced Firmicutes/Bacteroidota ratio in stool and saliva samples of RCC patients has been shown, in addition to a modification of the abundances of several taxa in both GM and OM. Moreover, a potential fecal over-expression of lipopolysaccharide biosynthesis and lipoic acid metabolism pathways and several differences in serum FFA levels have been reported in RCC patients than in HC.

CONCLUSION

Since differences in both GM and OM of RCC patients have been documented, these findings could provide new information about RCC pathogenesis and also pave the way for the development of novel nutritional or pharmacological interventions for the management of RCC through the restoration of eubiotic gut-lung communication.

Nerolidol attenuates airway inflammation and airway remodeling and alters gut microbes in ovalbumin-induced asthmatic mice

Asthma is a common respiratory disease associated with airway inflammation. Nerolidol is an acyclic sesquiterpenoid with anti-inflammatory properties. BALB/C mice were sensitized with ovalbumin (OVA) to induce asthma symptoms and given different doses of Nerolidol. We found that Nerolidol reduced OVA-induced inflammatory cell infiltration, the number of goblet cells and collagen deposition in lung tissue. Nerolidol reduced the OVA-specific IgE levels in serum and alveolar lavage fluid in an asthma model. Immunohistochemical staining of α-SMA (the marker of airway smooth muscle) showed that Nerolidol caused bronchial basement membrane thinning in asthmatic mice. The hyperplasia of airway smooth muscle cells (ASMCs) is an important feature of airway remodeling in asthma. ASMCs were treated with 10 ng/mL TGF-β to simulate the pathological environment of asthma in vitro and then treated with different doses of Nerolidol. Nerolidol inhibited the activity of TGF-β/Smad signaling pathway both in the lung tissue of OVA-induced mouse and TGF-β-stimulated ASMCs. 16s rRNA sequencing was performed on feces of normal mice, the changes of intestinal flora in OVA-induced asthmatic mice and Nerolidol-treated asthmatic mice were studied. The results showed that Nerolidol reversed the reduced gut microbial alpha diversity in asthmatic mice. Nerolidol changed the relative abundance of gut bacteria at different taxonomic levels. At the phylum level, the dominant bacteria were Bacteroidota, Firmicutes, and Proteobacteria. At the genus level, the dominant bacteria were Lactobacillus, Muribaculaceae, Bacteroides, and Lachnospiraceae. We conclude that Nerolidol attenuates OVA-induced airway inflammation and alters gut microbes in mice with asthma via TGF-β/Smad signaling.

The respiratory microbiome in childhood asthma

Asthma is the most prevalent noncommunicable disease in childhood, characterized by reversible airway constriction and inflammation of the lower airways. The respiratory tract consists of the upper and lower airways, which are lined with a diverse community of microbes. The composition and density of the respiratory microbiome differs across the respiratory tract, with microbes adapting to the gradually changing physiology of the environment. Over the past decade, both the upper and lower respiratory microbiomes have been implicated in the etiology and disease course of asthma, as well as in its severity and phenotype. We have reviewed the literature on the role of the respiratory microbiome in asthma, making a careful distinction between the relationship of the microbiome with development of childhood asthma and its relationship with the disease course, while accounting for age and the microbial niches studied. Furthermore, we have assessed the literature regarding the underlying asthma endotypes and the impact of the microbiome on the host immune response. We have identified distinct microbial signatures across the respiratory tract associated with asthma development, stability, and severity. These data suggest that the respiratory microbiome may be important for asthma development and severity and may therefore be a potential target for future microbiome-based preventive and treatment strategies.

Bacterial Microbiota of Asthmatic Children and Preschool Wheezers' Airways-What Do We Know?

Asthma is the most chronic pulmonary disease in pediatric population, and its etiopathology still remains unclear. Both viruses and bacteria are suspected factors of disease development and are responsible for its exacerbation. Since the launch of The Human Microbiome Project, there has been an explosion of research on microbiota and its connection with various diseases. In our review, we have collected recent data about both upper- and lower-airway bacterial microbiota of asthmatic children. We have also included studies regarding preschool wheezers, since asthma diagnosis in children under 5 years of age remains challenging due to the lack of an objective tool. This paper indicates the need for further studies of microbiome and asthma, as in today's knowledge, there is no particular bacterium that discriminates the asthmatics from the healthy peers and can be used as a potential biological factor in the disease prevalence and treatment.