The Potential for Emerging Microbiome-Mediated Therapeutics in Asthma

The Role of the Microbiome in the Pathogenesis and Treatment of Asthma

The role of the microbiome in the pathogenesis and treatment of asthma is significant. The purpose of this article is to show the interplay between asthma and the microbiome, and main areas that require further research are also highlighted. The literature search was conducted using the PubMed database. After a screening process of studies published before May 2023, a total of 128 articles were selected in our paper. The pre-treatment bronchial microbiome in asthmatic patients plays a role in their responsiveness to treatment. Gut microbiota and its dysbiosis can contribute to immune system modulation and the development of asthma. The association between the microbiome and asthma is complex. Further research is necessary to clarify which factors might moderate that relationship. An appropriate gut microbiome and its intestinal metabolites are a protective factor for asthma development. Prebiotics and certain dietary strategies may have a prophylactic or therapeutic effect, but more research is needed to establish final conclusions. Although the evidence regarding probiotics is ambiguous, and most meta-analyses do not support the use of probiotic intake to reduce asthma, several of the most recent studies have provided promising effects. Further studies should focus on the investigation of specific strains and the examination of their mechanistic and genetic aspects.

Novel potential treatable traits in asthma: Where is the research taking us?

Asthma is a complex, heterogeneous disease in which the underlying mechanisms are not fully understood. Patients are often grouped into phenotypes (based on clinical, biologic, and physiologic characteristics) and endotypes (based on distinct genetic or molecular mechanisms). Recently, patients with asthma have been broadly split into 2 phenotypes based on their levels of type 2 inflammation: type 2 and non-type 2 asthma. However, this approach is likely oversimplified, and our understanding of the non-type 2 mechanisms in asthma remains extremely limited. A better understanding of asthma phenotypes and endotypes may assist in development of drugs for new therapeutic targets in asthma. One approach is to identify "treatable traits," which are specific patient characteristics related to phenotypes and endotypes that can be targeted by therapies. This review will focus on emerging treatable traits in asthma and aim to describe novel patient subgroups and endotypes that may represent the next step in the search for new therapeutic approaches.

Microbiota - The Unseen Players in Adult Asthmatic Airways

Modulation of human lung airway physiology by commensal microbiota has become one of the key mechanisms involved in the pathogenesis of adult asthma. Recent evidence suggests that the composition of respiratory microbiota plays a significant role in the manifestation of adult asthma; however, scientific evidence about the relationship between airway microbial diversity and phenotypes of adult asthma is limited. Further research is needed to understand the interactions between the airway microbiota and host immune response to develop microbiota-based strategies in management of adult asthma. This study reviews the advances in culture-independent methods for detection of airway microbiome, the current data about airway microbiota in healthy individuals and in adult patients with asthma with a focus on bacterial communities, and the future research directions in airway microbiome.

Gut Microbiota and Lung Injury

Gut microbiota are known to impact multiple organs including the lung. The cross talk between gut microbes and lungs, termed as the "gut-lung axis," is vital for immune response and homeostasis in the airways. In this chapter, we summarized the coordinated development of microorganisms in the gut and lung, exogenous and endogenous factors related to the cross talk, the mechanisms of the gut-lung axis and their dysbiosis in lung diseases. Although the current understanding of the gut-lung axis is in its infancy, several gut microbiota-associated strategies have been designed to treat and prevent lung diseases.

The short-chain free fatty acid receptor FFAR3 is expressed and potentiates contraction in human airway smooth muscle

Emerging evidence suggests that gut microbiota-derived short-chain fatty acids (SCFAs; acetate, propionate, and butyrate) are important modulators of the inflammatory state in diseases such as asthma. However, the functional expression of the G_i protein-coupled free fatty acid receptors (FFAR2/GPR43 and FFAR3/GPR41) has not been identified on airway smooth muscle (ASM). Classically, acute activation of G_i-coupled receptors inhibits cyclic AMP (cAMP) synthesis, which impairs ASM relaxation and can also induce crosstalk between G_i- and G_q-signaling pathways, potentiating increases in intracellular Ca²⁺ concentration ([Ca²⁺]_i), favoring ASM contraction. In contrast, chronic activation of G_i-coupled receptors can sensitize adenylyl cyclase resulting in increased cAMP synthesis favoring relaxation. We questioned whether the G_i-coupled FFAR2 or FFAR3 is expressed in human ASM, whether they modulate cAMP and [Ca²⁺]_i, and whether SCFAs modulate human ASM tone. We detected the protein expression of FFAR3 but not FFAR2 in native human ASM and primary cultured human airway smooth muscle (HASM) cells. In HASM cells, acute activation of FFAR3 with SCFAs inhibited forskolin-stimulated cAMP accumulation, but chronic activation did not sensitize cAMP synthesis. SCFAs induced [Ca²⁺]_i increases that were attenuated by pertussis toxin, gallein, U73122, or xestospongin C. Acute treatment with SCFAs potentiated acetylcholine-stimulated [Ca²⁺]_i increases and stress fiber formation in cells and contraction of ex vivo human airway tissues. In contrast, chronic pretreatment of human ASM with propionate did not potentiate airway relaxation. Together, these findings demonstrate that FFAR3 is expressed in human ASM and contributes to ASM contraction via reduced cAMP and increased [Ca²⁺]_i.

Impact of Human Microbiome on Health

The human genome in the recent years, by the advent of technological advancements, has emerged as a major prolocutor for reciprocity between the human body and the food consumed. As known, microbiome comprises all the genetic materials within a microbiota and can thereby be also referred to as metagenome of the microbiota. Contemporary researches have revealed the influence of microbiome not only on human mind and health status, but also in wide range of disease switching, ranging from cardio-metabolic diseases, allergies and obesities to life-threatening diseases such as cancer. Though the complete mechanism of many diseases is yet unclear, research works have revealed that the metabolites, nutrients and microbes can be regarded as the key players for such physiological state. The major approach of this chapter is to enlighten the interrelationship of the microbiome on the human health either in a synergistic or in an antagonistic manner.

The current state of omics technologies in the clinical management of asthma and allergic diseases

OBJECTIVE

To review the state of omics science specific to asthma and allergic diseases and discuss the current and potential applicability of omics in clinical disease prediction, treatment, and management.

DATA SOURCES

Studies and reviews focused on the use of omics technologies in asthma and allergic disease research and clinical management were identified using PubMed.

STUDY SELECTIONS

Publications were included based on relevance, with emphasis placed on the most recent findings.

RESULTS

Omics-based research is increasingly being used to differentiate asthma and allergic disease subtypes, identify biomarkers and pathological mediators, predict patient responsiveness to specific therapies, and monitor disease control. Although most studies have focused on genomics and transcriptomics approaches, increasing attention is being placed on omics technologies that assess the effect of environmental exposures on disease initiation and progression. Studies using omics data to identify biological targets and pathways involved in asthma and allergic disease pathogenesis have primarily focused on a specific omics subtype, providing only a partial view of the disease process.

CONCLUSION

Although omics technologies have advanced our understanding of the molecular mechanisms underlying asthma and allergic disease pathology, omics testing for these diseases are not standard of care at this point. Several important factors need to be addressed before these technologies can be used effectively in clinical practice. Use of clinical decision support systems and integration of these systems within electronic medical records will become increasingly important as omics technologies become more widely used in the clinical setting.

The Role of the Microbiome in Asthma: The Gut⁻Lung Axis

Asthma is one of the most common chronic respiratory diseases worldwide. It affects all ages but frequently begins in childhood. Initiation and exacerbations may depend on individual susceptibility, viral infections, allergen exposure, tobacco smoke exposure, and outdoor air pollution. The aim of this review was to analyze the role of the gut⁻lung axis in asthma development, considering all asthma phenotypes, and to evaluate whether microbe-based therapies may be used for asthma prevention. Several studies have confirmed the role of microbiota in the regulation of immune function and the development of atopy and asthma. These clinical conditions have apparent roots in an insufficiency of early life exposure to the diverse environmental microbiota necessary to ensure colonization of the gastrointestinal and/or respiratory tracts. Commensal microbes are necessary for the induction of a balanced, tolerogenic immune system. The identification of commensal bacteria in both the gastroenteric and respiratory tracts could be an innovative and important issue. In conclusion, the function of microbiota in healthy immune response is generally acknowledged, and gut dysbacteriosis might result in chronic inflammatory respiratory disorders, particularly asthma. Further investigations are needed to improve our understanding of the role of the microbiome in inflammation and its influence on important risk factors for asthma, including tobacco smoke and host genetic features.

Does lung microbiome play a causal or casual role in asthma?

Asthma is the most common chronic disease in childhood. The pathogenesis of asthma is multifactorial and is thought to include environmental factors interacting with genetics during pregnancy and in the first years of life. In the last decades, a possible role of gut microbiota in allergic disease pathogenesis has been demonstrated. Next generation sequencing techniques have allowed the identification of a distinct microbiome in the healthy lungs. The lung microbiome is characterized by the prevalence of bacteria belonging to the phylum Bacteroidetes (mostly Prevotella and Veilonella spp) in healthy subjects and to the phylum Proteobacteria in asthmatics (mostly Haemophilus, Moraxella, and Neisseria spp). In asthma, as well as in other diseases, the lung microbiome composition changes due to a disruption of the delicate balance between immigration and elimination of bacteria. The lung microbiome can interact with the immune system, thus influencing inflammation. Early infections with viruses, such as respiratory syncytial virus, may alter lung microbiome composition favoring the emergence of Proteobacteria, a phylum which is also linked to severity of asthma and bronchial hyperreactivity. Lastly, antibiotics may alter the gut and lung microbiota and potentially disturb the relationship between microbiota and host. Therefore, antibiotics should be prescribed with increasing awareness of their potential harmful effect on the microbiota in young children with and without asthma. The potential effects of probiotics and prebiotics on lung microbiome are unknown.

Evidence establishing a link between prenatal and early-life stress and asthma development

PURPOSE OF REVIEW

The objective of this review is to provide an update on our evolving understanding of the effects of stress in pregnancy and during early development on the onset of asthma-related phenotypes across childhood, adolescence, and into early adulthood.

RECENT FINDINGS

Accumulating evidence over the past 2 decades has established that prenatal and early-life psychological stress and stress correlates (e.g., maternal anxiety or depression) increase the risk for childhood respiratory disorders. Recent systematic reviews and meta-analyses including numerous prospective epidemiological and case-control studies substantiate a significant effect of prenatal stress and stress in early childhood on the development of wheeze, asthma, and other atopic-related disorders (eczema and allergic rhinitis), with many studies showing an exposure-response relationship. Offspring of both sexes are susceptible to perinatal stress, but effects differ. The impact of stress on child wheeze/asthma can also be modified by exposure timing. Moreover, coexposure to prenatal stress can enhance the effect of chemical stressors, such as prenatal traffic-related air pollution, on childhood respiratory disease risk. Understanding complex interactions among exposure dose, timing, child sex, and concurrent environmental exposures promises to more fully characterize stress effects and identify susceptible subgroups. Although the link between perinatal stress and childhood asthma-related phenotypes is now well established, pathways by which stress predisposes children to chronic respiratory disorders are not as well delineated. Mechanisms central to the pathophysiology of wheeze/asthma and lung growth and development overlap and involve a cascade of events that include disrupted immune, neuroendocrine, and autonomic function as well as oxidative stress. Altered homeostatic functioning of these integrated systems during development can enhance vulnerability to asthma and altered lung development.

SUMMARY

Mechanistic studies that more comprehensively assess biomarkers reflecting alterations across interrelated stress response systems and associated regulatory processes, in both pregnant women and young children, could be highly informative. Leveraging high-throughput systems-wide technologies to include epigenomics (e.g., DNA methylation, microRNAs), transcriptomics, and microbiomics as well as integrated multiomics are needed to advance this field of science. Understanding stress-induced physiological changes occurring during vulnerable life periods that contribute to chronic respiratory disease risk could lead to the development of preventive strategies and novel therapeutic interventions.

Microbiome and asthma

The mucosal immune system is in constant communication with the vast diversity of microbes present on body surfaces. The discovery of novel molecular mechanisms, which mediate host-microbe communication, have highlighted the important roles played by microbes in influencing mucosal immune responses. Dendritic cells, epithelial cells, ILCs, T regulatory cells, effector lymphocytes, NKT cells and B cells can all be influenced by the microbiome. Many of the mechanisms being described are bacterial strain- or metabolite-specific. Microbial dysbiosis in the gut and the lung is increasingly being associated with the incidence and severity of asthma. More accurate endotyping of patients with asthma may be assisted by further analysis of the composition and metabolic activity of an individual’s microbiome. In addition, the efficacy of specific therapeutics may be influenced by the microbiome and novel bacterial-based therapeutics should be considered in future clinical studies.