Potential Metabolic Biomarkers in Adult Asthmatics

An integrated metabo-lipidomics profile of induced sputum for the identification of novel biomarkers in the differential diagnosis of asthma and COPD

BACKGROUND

Due to their complexity and to the presence of common clinical features, differentiation between asthma and chronic obstructive pulmonary disease (COPD) can be a challenging task, complicated in such cases also by asthma-COPD overlap syndrome. The distinct immune/inflammatory and structural substrates of COPD and asthma are responsible for significant differences in the responses to standard pharmacologic treatments. Therefore, an accurate diagnosis is of central relevance to assure the appropriate therapeutic intervention in order to achieve safe and effective patient care. Induced sputum (IS) accurately mirrors inflammation in the airways, providing a more direct picture of lung cell metabolism in comparison to those specimen that reflect analytes in the systemic circulation.

METHODS

An integrated untargeted metabolomics and lipidomics analysis was performed in IS of asthmatic (n = 15) and COPD (n = 22) patients based on Ultra-High-Pressure Liquid Chromatography-Mass Spectrometry (UHPLC-MS) and UHPLC-tandem MS (UHPLC-MS/MS). Partial Least Squares-Discriminant Analysis (PLS-DA) was applied to resulting dataset. The analysis of main enriched metabolic pathways and the association of the preliminary metabolites/lipids pattern identified to clinical parameters of asthma/COPD differentiation were explored. Multivariate ROC analysis was performed in order to determine the discriminatory power and the reliability of the putative biomarkers for diagnosis between COPD and asthma.

RESULTS

PLS-DA indicated a clear separation between COPD and asthmatic patients. Among the 15 selected candidate biomarkers based on Variable Importance in Projection scores, putrescine showed the highest score. A differential IS bio-signature of 22 metabolites and lipids was found, which showed statistically significant variations between asthma and COPD. Of these 22 compounds, 18 were decreased and 4 increased in COPD compared to asthmatic patients. The IS levels of Phosphatidylethanolamine (PE) (34:1), Phosphatidylglycerol (PG) (18:1;18:2) and spermine were significantly higher in asthmatic subjects compared to COPD.

CONCLUSIONS

This is the first pilot study to analyse the IS metabolomics/lipidomics signatures relevant in discriminating asthma vs COPD. The role of polyamines, of 6-Hydroxykynurenic acid and of D-rhamnose as well as of other important players related to the alteration of glycerophospholipid, aminoacid/biotin and energy metabolism provided the construction of a diagnostic model that, if validated on a larger prospective cohort, might be used to rapidly and accurately discriminate asthma from COPD.

Lipid species profiling of bronchoalveolar lavage fluid cells of horses housed on two different bedding materials

The lipidome of equine BALF cells has not been described. The objectives of this prospective repeated-measures study were to explore the BALF cells' lipidome in horses and to identify lipids associated with progression or resolution of airway inflammation. BALF cells from 22 horses exposed to two bedding materials (Peat 1-Wood shavings [WS]-Peat 2) were studied by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The effects of bedding on lipid class and species compositions were tested with rmANOVA. Correlations between lipids and cell counts were examined. The BALF cells' lipidome showed bedding-related differences for molar percentage (mol%) of 60 species. Whole phosphatidylcholine (PC) class and its species PC 32:0 (main molecular species 16:0_16:0) had higher mol% after Peat 2 compared with WS. Phosphatidylinositol 38:4 (main molecular species 18:0_20:4) was higher after WS compared with both peat periods. BALF cell count correlated positively with mol% of the lipid classes phosphatidylserine, sphingomyelin, ceramide, hexosylceramide, and triacylglycerol but negatively with PC. BALF cell count correlated positively with phosphatidylinositol 38:4 mol%. In conclusion, equine BALF cells' lipid profiles explored with MS-based lipidomics indicated subclinical inflammatory changes after WS. Inflammatory reactions in the cellular lipid species composition were detected although cytological responses indicating inflammation were weak.

Bacterial Extracellular Vesicles: A Candidate Molecule for the Diagnosis and Treatment of Allergic Diseases

Extracellular vesicles (EVs) are an end product released from almost all living cells such as eukaryotic cells and bacteria. These membrane vesicles containing proteins, lipids, and nucleic acids are mainly involved in intracellular communications through the transfer of their components from donor to acceptor cells. Moreover, EVs have been implicated in many functions in response to environmental changes, contributing to health and disease; bacterial EVs depending on their specific parental bacterium have diverse effects on immune responses to play a beneficial or pathogenic role in patients with various allergic and immunologic diseases. As bacterial EVs are a completely new area of investigation in this field, we highlight our current understanding of bacterial EVs and discuss their diagnostic and therapeutic potentials (as immunomodulators) for targeting asthma and atopic dermatitis.

Association of eosinophil‐derived neurotoxin levels with asthma control status in patients with aspirin‐exacerbated respiratory disease

Background

The long‐term goals of asthma treatment are to achieve well control of symptoms and to minimize the future risk of asthma exacerbation. Identifying biomarkers for uncontrolled asthma is important for improving the asthma outcome. This study aimed to investigate the association of the levels of eosinophil‐derived neurotoxin (EDN) with asthma control status in specific asthma phenotype, aspirin‐exacerbated respiratory disease (AERD), and aspirin‐tolerant asthma (ATA).

Methods

A total of 136 adult asthmatics, including 47 asthmatics with AERD and 89 asthmatics with ATA, were enrolled. Plasma, sputum, and urine were collected at enrollment and the levels of EDN were measured by the K‐EDN ELISA kit. Urinary leukotriene E4 (LTE₄) level was measured using liquid chromatography–mass spectrometry (LC‐MS)/MS methods. Asthma control status was evaluated according to the GINA guideline, asthma control test and asthma control questionnaire scores.

Results

In the total study subjects, sputum levels of EDN as well as of urine and plasma EDN showed significantly higher levels in patients with uncontrolled asthma than in those with well‐controlled or partly‐controlled asthma (ANOVA, p < 0.001); in patients with AERD, the sputum EDN levels showed significant correlations with ACT, ACQ, and AQLQ scores (p = 0.010, r = −0.536, p = 0.001, r = 0.665, and p < 0.001, r = −0.691, respectively), while no differences were noted in patients with ATA. Sputum EDN level was the only significant factor for ACT, ACQ, and AQLQ scores in patients with AERD (p = 0.001, p < 0.001, and p < 0.001, respectively) in the multivariate analysis adjusting for age, sex, peripheral eosinophil count, and urine LTE₄. The ROC curve analysis demonstrated that sputum EDN can predict uncontrolled asthma with 80% sensitivity and 88.2% specificity for ACT ≤ 19 (area under the ROC curve [AUC] = 0.824, p = 0.019); 71.4% sensitivity and 86.7% specificity for ACQ ≥ 1.5 (AUC = 0.752, p = 0.049) only in AERD patients.

Conclusion

The level of sputum EDN may be a potential biomarker for identifying the asthma control status in patients with AERD.

Immunologic Basis of Type 2 Biologics for Severe Asthma

Asthma is a chronic airway inflammatory disease characterized by reversible airway obstruction and airway hyperreactivity to various environmental stimuli, leading to recurrent cough, dyspnea, and wheezing episodes. Regarding inflammatory mechanisms, type 2/eosinophilic inflammation along with activated mast cells is the major one; however, diverse mechanisms, including structural cells-derived and non-type 2/neutrophilic inflammations are involved, presenting heterogenous phenotypes. Although most asthmatic patients could be properly controlled by the guided treatment, patients with severe asthma (SA; classified as a treatment-refractory group) suffer from uncontrolled symptoms with frequent asthma exacerbations even on regular anti-inflammatory medications, raising needs for additional controllers, including biologics that target specific molecules found in asthmatic airway, and achieving the precision medicine for asthma. This review summarizes the immunologic basis of airway inflammatory mechanisms and current biologics for SA in order to address unmet needs for future targets.

Air pollution, metabolites and respiratory health across the life-course

Previous studies have explored the relationships of air pollution and metabolic profiles with lung function. However, the metabolites linking air pollution and lung function and the associated mechanisms have not been reviewed from a life-course perspective. Here, we provide a narrative review summarising recent evidence on the associations of metabolic profiles with air pollution exposure and lung function in children and adults. Twenty-six studies identified through a systematic PubMed search were included with 10 studies analysing air pollution-related metabolic profiles and 16 studies analysing lung function-related metabolic profiles. A wide range of metabolites were associated with short- and long-term exposure, partly overlapping with those linked to lung function in the general population and with respiratory diseases such as asthma and COPD. The existing studies show that metabolomics offers the potential to identify biomarkers linked to both environmental exposures and respiratory outcomes, but many studies suffer from small sample sizes, cross-sectional designs, a preponderance on adult lung function, heterogeneity in exposure assessment, lack of confounding control and omics integration. The ongoing EXposome Powered tools for healthy living in urbAN Settings (EXPANSE) project aims to address some of these shortcomings by combining biospecimens from large European cohorts and harmonised air pollution exposure and exposome data.

Extracellular Traps: A Novel Therapeutic Target for Severe Asthma

Asthma is a complicated disease defined by a combination of clinical symptoms and physiological characteristics. Typically, asthma is diagnosed by the presence of episodic cough, wheezing, or dyspnea triggered by variable environmental factors (allergens and respiratory infections), and reversible airflow obstruction. To date, the majority of asthmatic patients have been adequately controlled by anti-inflammatory/bronchodilating agents, but those with severe asthma (SA) have not been sufficiently controlled by high-dose inhaled corticosteroids-long-acting beta-agonists plus additional controllers including leukotriene modifiers. Accordingly, these uncontrolled patients provoke a special issue, because they consume high healthcare resources, requiring innovative precision medicine solutions. Recently, phenotyping based on biomarkers of airway inflammation has led to elucidating the pathophysiological mechanism of SA, where emerging evidence has highlighted the significance of eosinophil or neutrophil extracellular traps contributing to the development of SA. Here, we aimed to provide current findings about extracellular traps as a novel therapeutic target for asthma to address medical unmet needs.

Asthma and the Missing Heritability Problem: Necessity for Multiomics Approaches in Determining Accurate Risk Profiles

Asthma is ranked among the most common chronic conditions and has become a significant public health issue due to the recent and rapid increase in its prevalence. Investigations into the underlying genetic factors predict a heritable component for its incidence, estimated between 35% and 90% of causation. Despite the application of large-scale genome-wide association studies (GWAS) and admixture mapping approaches, the proportion of variants identified accounts for less than 15% of the observed heritability of the disease. The discrepancy between the predicted heritable component of disease and the proportion of heritability mapped to the currently identified susceptibility loci has been termed the ‘missing heritability problem.’ Here, we examine recent studies involving both the analysis of genetically encoded features that contribute to asthma and also the role of non-encoded heritable characteristics, including epigenetic, environmental, and developmental aspects of disease. The importance of vertical maternal microbiome transfer and the influence of maternal immune factors on fetal conditioning in the inheritance of disease are also discussed. In order to highlight the broad array of biological inputs that contribute to the sum of heritable risk factors associated with allergic disease incidence that, together, contribute to the induction of a pro-atopic state. Currently, there is a need to develop in-depth models of asthma risk factors to overcome the limitations encountered in the interpretation of GWAS results in isolation, which have resulted in the missing heritability problem. Hence, multiomics analyses need to be established considering genetic, epigenetic, and functional data to create a true systems biology-based approach for analyzing the regulatory pathways that underlie the inheritance of asthma and to develop accurate risk profiles for disease.

Current Insights on the Impact of Proteomics in Respiratory Allergies

Respiratory allergies affect humans worldwide, causing extensive morbidity and mortality. They include allergic rhinitis (AR), asthma, pollen food allergy syndrome (PFAS), aspirin-exacerbated respiratory disease (AERD), and nasal polyps (NPs). The study of respiratory allergic diseases requires new technologies for early and accurate diagnosis and treatment. Omics technologies provide the tools required to investigate DNA, RNA, proteins, and other molecular determinants. These technologies include genomics, transcriptomics, proteomics, and metabolomics. However, proteomics is one of the main approaches to studying allergic disorders' pathophysiology. Proteins are used to indicate normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. In this field, the principal goal of proteomics has been to discover new proteins and use them in precision medicine. Multiple technologies have been applied to proteomics, but that most used for identifying, quantifying, and profiling proteins is mass spectrometry (MS). Over the last few years, proteomics has enabled the establishment of several proteins for diagnosing and treating respiratory allergic diseases.

Metabolomic Associations of Asthma in the Hispanic Community Health Study/Study of Latinos

Asthma disproportionally affects Hispanic and/or Latino backgrounds; however, the relation between circulating metabolites and asthma remains unclear. We conducted a cross-sectional study associating 640 individual serum metabolites, as well as twelve metabolite modules, with asthma in 3347 Hispanic/Latino background participants (514 asthmatics, 15.36%) from the Hispanic/Latino Community Health Study/Study of Latinos. Using survey logistic regression, per standard deviation (SD) increase in 1-arachidonoyl-GPA (20:4) was significantly associated with 32% high odds of asthma after accounting for clinical risk factors (p = 6.27 × 10−5), and per SD of the green module, constructed using weighted gene co-expression network, was suggestively associated with 25% high odds of asthma (p = 0.006). In the stratified analyses by sex and Hispanic and/or Latino backgrounds, the effect of 1-arachidonoyl-GPA (20:4) and the green module was predominantly observed in women (OR = 1.24 and 1.37, p < 0.001) and people of Cuban and Puerto-Rican backgrounds (OR = 1.25 and 1.27, p < 0.01). Mutations in Fatty Acid Desaturase 2 (FADS2) affected the levels of 1-arachidonoyl-GPA (20:4), and Mendelian Randomization analyses revealed that high genetically regulated 1-arachidonoyl-GPA (20:4) levels were associated with increased odds of asthma (p < 0.001). The findings reinforce a molecular basis for asthma etiology, and the potential causal effect of 1-arachidonoyl-GPA (20:4) on asthma provides an opportunity for future intervention.

Immunoregulatory effects of Lactococcus lactis-derived extracellular vesicles in allergic asthma

Background

Probiotics have been shown to prevent various allergic diseases by producing extracellular vesicles (EVs). However, the role of EVs in allergic asthma has not yet been completely determined.

Methods

Gut microbial composition, mainly genera related to probiotics, was investigated in allergic asthmatic mice. Moreover, EVs were isolated from Lactococcus lactis (L. lactis, a selected bacterium) and EV proteins were identified by peptide mass fingerprinting. EV functions in immune responses were evaluated in vivo or ex vivo. Furthermore, the levels of specific IgG antibodies (an alternative marker for EV quantification) to L. lactis‐EVs were measured by ELISA in the sera of 27 asthmatic patients and 26 healthy controls.

Results

Allergic asthmatic mice showed a lower proportion of Lactococcus compared to healthy mice. L. lactis was cultured and its EVs abundantly contained pyruvate kinase. When allergic asthmatic mice were intranasally treated with EVs, airway hyperresponsiveness, eosinophil number, cytokine secretion, and mucus production were significantly decreased. Moreover, L. lactis‐EV treatment shifted immune responses from Th2 to Th1 by stimulating dendritic cells to produce IL‐12. In addition, significantly lower levels of serum specific IgG4 (but not IgG1) to L. lactis‐EVs were noted in asthmatic patients than in healthy controls. A positive correlation between the levels of EV‐specific IgG4 and FEV₁ (%), but a negative correlation between the levels of EV‐specific IgG4 and IL‐13 were observed.

Conclusion

These findings suggest that L. lactis‐EVs may have immune‐regulating effects on airway inflammation mediated by dendritic cell activation, providing a potential benefit for allergic asthma.

Airway Microbiome and Serum Metabolomics Analysis Identify Differential Candidate Biomarkers in Allergic Rhinitis

Allergic rhinitis (AR) is a common heterogeneous chronic disease with a high prevalence and a complex pathogenesis influenced by numerous factors, involving a combination of genetic and environmental factors. To gain insight into the pathogenesis of AR and to identity diagnostic biomarkers, we combined systems biology approach to analyze microbiome and serum composition. We collected inferior turbinate swabs and serum samples to study the microbiome and serum metabolome of 28 patients with allergic rhinitis and 15 healthy individuals. We sequenced the V3 and V4 regions of the 16S rDNA gene from the upper respiratory samples. Metabolomics was used to examine serum samples. Finally, we combined differential microbiota and differential metabolites to find potential biomarkers. We found no significant differences in diversity between the disease and control groups, but changes in the structure of the microbiota. Compared to the HC group, the AR group showed a significantly higher abundance of 1 phylum (Actinobacteria) and 7 genera (Klebsiella, Prevotella and Staphylococcus, etc.) and a significantly lower abundance of 1 genus (Pelomonas). Serum metabolomics revealed 26 different metabolites (Prostaglandin D2, 20-Hydroxy-leukotriene B4 and Linoleic acid, etc.) and 16 disrupted metabolic pathways (Linoleic acid metabolism, Arachidonic acid metabolism and Tryptophan metabolism, etc.). The combined respiratory microbiome and serum metabolomics datasets showed a degree of correlation reflecting the influence of the microbiome on metabolic activity. Our results show that microbiome and metabolomics analyses provide important candidate biomarkers, and in particular, differential genera in the microbiome have also been validated by random forest prediction models. Differential microbes and differential metabolites have the potential to be used as biomarkers for the diagnosis of allergic rhinitis.

Inside the Alterations of Circulating Metabolome in Antarctica: The Adaptation to Chronic Hypoxia

Although the human body may dynamically adapt to mild and brief oxygen shortages, there is a growing interest in understanding how the metabolic pathways are modified during sustained exposure to chronic hypoxia. Located at an equivalent altitude of approximately 3,800 m asl, the Concordia Station in Antarctica represents an opportunity to study the course of human adaption to mild hypoxia with reduced impact of potentially disturbing variables else than oxygen deprivation. We recruited seven healthy subjects who spent 10 months in the Concordia Station, and collected plasma samples at sea level before departure, and 90 days, 6 months, and 10 months during hypoxia. Samples were analyzed by untargeted liquid chromatography high resolution mass spectrometry to unravel how the non-polar and polar metabolomes are affected. Statistical analyses were performed by clustering the subjects into four groups according to the duration of hypoxia exposure. The non-polar metabolome revealed a modest decrease in the concentration of all the major lipid classes. By contrast, the polar metabolome showed marked alterations in several metabolic pathways, especially those related to amino acids metabolism, with a particular concern of arginine, glutamine, phenylalanine, tryptophan, and tyrosine. Remarkably, all the changes were evident since the first time point and remained unaffected by hypoxia duration (with the exception of a slight return of the non-polar metabolome after 6 months), highlighting a relative inability of the body to compensate them. Finally, we identified a few metabolic pathways that emerged as the main targets of chronic hypoxia.