Unconjugated bilirubin is associated with protection from early-life wheeze and childhood asthma

Update on asthma biology

This is an exciting time to be conducting asthma research. The recent development of targeted asthma biologics has validated the power of basic research to discover new molecules amenable to therapeutic intervention. Advances in high-throughput sequencing are providing a wealth of "omics" data about genetic and epigenetic underpinnings of asthma, as well as about new cellular interacting networks and potential endotypes in asthma. Airway epithelial cells have emerged not only as key sensors of the outside environment but also as central drivers of dysregulated mucosal immune responses in asthma. Emerging data suggest that the airway epithelium in asthma remembers prior encounters with environmental exposures, resulting in potentially long-lasting changes in structure and metabolism that render asthmatic individuals susceptible to subsequent exposures. Here we summarize recent insights into asthma biology, focusing on studies using human cells or tissue that were published in the past 2 years. The studies are organized thematically into 6 content areas to draw connections and spur future research (on genetics and epigenetics, prenatal and early-life origins, microbiome, immune and inflammatory pathways, asthma endotypes and biomarkers, and lung structural alterations). We highlight recent studies of airway epithelial dysfunction and response to viral infections and conclude with a framework for considering how bidirectional interactions between alterations in airway structure and mucosal immunity can lead to sustained lung dysfunction in asthma.

The association of infant urinary adrenal steroids with the risk of childhood asthma development

BACKGROUND

Adrenal steroids play important roles in early-life development. However, our understanding of the effects of perinatal adrenal steroids on the development of childhood asthma is incomplete.

OBJECTIVE

To evaluate the associations between early-life adrenal steroid levels and childhood asthma.

METHODS

Participants included the Infant Susceptibility to Pulmonary Infections and Asthma following Respiratory Syncytial Virus Exposure birth cohort children with untargeted urinary metabolomics data measured during early infancy (n = 264) and nasal immune mediator data measured concurrently at age 2 to 6 months (n = 76). A total of 11 adrenal steroid compounds were identified using untargeted metabolomics and 6 asthma-relevant nasal immune mediators from multiplex assays were a priori selected. Current asthma at ages 5 and 6 years was ascertained using validated questionnaires. Associations were tested using logistic and linear regression with confounders adjustment.

RESULTS

Pregnenetriol disulfate (adjusted odds ratio [aOR] = 0.20, 95% CI = 0.06-0.68) and 3a,21-dihydroxy-5b-pregnane-11,20-dione-21-glucuronide (aOR = 0.34, 95% CI = 0.14-0.75) were inversely associated with childhood asthma at 5 and 6 years after multiple testing adjustment. There was a significant interaction effect of pregnanediol-3-glucuronide by biological sex assigned at birth (aOR = 0.11, 95% CI = 0.02-0.51, for those with female sex) on childhood asthma. Pregnenetriol disulfate was inversely associated with granulocyte-macrophage colony-stimulating factor (β = -0.45, q-value = 0.05). 3a,21-dihydroxy-5b-pregnane-11,20-dione 21-glucuronide was inversely associated with interleukin [IL]-4 (β = -0.29, q-value = 0.02), IL-5 (β = -0.35, q-value = 0.006), IL-13 (β = -0.26, q-value = 0.02), granulocyte-macrophage colony-stimulating factor (β = -0.35, q-value = 0.006), and fibroblast growth factor-β (β = -0.24, q-value = 0.01) after multiple testing adjustment.

CONCLUSION

The inverse association between adrenal steroids downstream of progesterone and 17-hydroxypregnenolone and the odds of childhood asthma and nasopharyngeal type 2 immune biomarkers suggest that increased early-life adrenal steroids may suppress type 2 inflammation and protect against the development of childhood asthma.

Infant Bronchiolitis Endotypes and the Risk of Developing Childhood Asthma: Lessons From Cohort Studies

Severe bronchiolitis (i.e., bronchiolitis requiring hospitalization) during infancy is a heterogeneous condition associated with a high risk of developing childhood asthma. Yet, the exact mechanisms underlying the bronchiolitis-asthma link remain uncertain. Birth cohort studies have reported this association at the population level, including only small groups of patients with a history of bronchiolitis, and have attempted to identify the underlying biological mechanisms. Although this evidence has provided valuable insights, there are still unanswered questions regarding severe bronchiolitis-asthma pathogenesis. Recently, a few bronchiolitis cohort studies have attempted to answer these questions by applying unbiased analytical approaches to biological data. These cohort studies have identified novel bronchiolitis subtypes (i.e., endotypes) at high risk for asthma development, representing essential and enlightening evidence. For example, one distinct severe respiratory syncytial virus (RSV) bronchiolitis endotype is characterized by the presence of Moraxella catarrhalis and Streptococcus pneumoniae, higher levels of type I/II IFN expression, and changes in carbohydrate metabolism in nasal airway samples, and is associated with a high risk for childhood asthma development. Although these findings hold significance for the design of future studies that focus on childhood asthma prevention, they require validation. However, this scoping review puts the above findings into clinical context and emphasizes the significance of future research in this area aiming to offer new bronchiolitis treatments and contribute to asthma prevention.

Metabolomic profiles during early childhood and risk of food allergies and asthma in multiethnic children from a prospective birth cohort

BACKGROUND

There are increasing numbers of metabolomic studies in food allergy (FA) and asthma, which, however, are predominantly limited by cross-sectional designs, small sample size, and being conducted in European populations.

OBJECTIVE

We sought to identify metabolites unique to and shared by children with FA and/or asthma in a racially diverse prospective birth cohort, the Boston Birth Cohort.

METHODS

Mass spectrometry-based untargeted metabolomic profiling was performed using venous plasma collected in early childhood (n = 811). FA was diagnosed according to clinical symptoms consistent with an acute hypersensitivity reaction at food ingestion and food specific-IgE > 0.35 kU/L. Asthma was defined on the basis of physician diagnosis. Generalized estimating equations were applied to analyze metabolomic associations with FA and asthma, adjusting for potential confounders.

RESULTS

During a mean ± standard deviation follow-up of 11.8 ± 5.2 years from birth, 78 children developed FA and 171 developed asthma. Androgenic and pregnenolone steroids were significantly associated with a lower risk of FA, especially for egg allergy. N,N,N-trimethyl-5-aminovalerate (odds ratio [OR] = 0.65, 95% confidence interval [CI] = 0.48-0.87), and 1-oleoyl-2-arachidonoyl-sn-glycero-3-phosphoinositol (OR = 0.77; 95% CI = 0.66-0.90) were inversely associated with FA risk. Orotidine (OR = 4.73; 95% CI = 2.2-10.2) and 4-cholesten-3-one (OR = 0.52; 95% CI = 0.35-0.77) were the top 2 metabolites associated with risk of asthma, although they had no association with FA. In comparison, children with both FA and asthma exhibited an altered metabolomic profile that aligned with that of FA, including altered levels of lipids and steroids.

CONCLUSION

In this US multiethnic prospective birth cohort, unique and shared alterations in plasma metabolites during early childhood were associated with risk of developing FA and/or asthma. These findings await further validation.

Revealing polygenic pleiotropy using genetic risk scores for asthma

In this study we examined how genetic risk for asthma associates with different features of the disease and with other medical conditions and traits. Using summary statistics from two multi-ancestry genome-wide association studies of asthma, we modeled polygenic risk scores (PRSs) and validated their predictive performance in the UK Biobank. We then performed phenome-wide association studies of the asthma PRSs with 371 heritable traits in the UK Biobank. We identified 228 total significant associations across a variety of organ systems, including associations that varied by PRS model, sex, age of asthma onset, ancestry, and human leukocyte antigen region alleles. Our results highlight pervasive pleiotropy between asthma and numerous other traits and conditions and elucidate pathways that contribute to asthma and its comorbidities.

Blood-Based Biomarkers for Eosinophilic Esophagitis and Concomitant Atopic Diseases: A Look into the Potential of Extracellular Vesicles

Eosinophilic esophagitis (EoE) is a chronic, Th2-inflammatory disease of the esophagus that can severely affect food intake. Currently, diagnosis and assessing response to treatment of EoE is highly invasive and requires endoscopy with esophageal biopsies. Finding non-invasive and accurate biomarkers is important for improving patient well-being. Unfortunately, EoE is usually accompanied by other atopies, which make it difficult to identify specific biomarkers. Providing an update of circulating EoE biomarkers and concomitant atopies is therefore timely. This review summarizes the current knowledge in EoE blood biomarkers and two of its most common comorbidities, bronchial asthma (BA) and atopic dermatitis (AD), focusing on dysregulated proteins, metabolites, and RNAs. It also revises the current knowledge on extracellular vesicles (EVs) as non-invasive biomarkers for BA and AD, and concludes with the potential use of EVs as biomarkers in EoE.

Early-life fecal metabolomics of food allergy

BACKGROUND

Intestinal microenvironmental perturbations may increase food allergy risk. We hypothesize that children with clinical food allergy, those with food sensitization, and healthy children can be differentiated by intestinal metabolites in the first years of life.

METHODS

In this ancillary analysis of the Vitamin D Antenatal Asthma Reduction Trial (VDAART), we performed untargeted metabolomic profiling in 824 stool samples collected at ages 3-6 months, 1 year and 3 years. Subjects included 23 with clinical food allergy at age 3 and/or 6 years, 151 with food sensitization but no clinical food allergy, and 220 controls. We identified modules of correlated, functionally related metabolites and sought associations of metabolite modules and individual metabolites with food allergy/sensitization using regression models.

RESULTS

Several modules of functionally related intestinal metabolites were reduced among subjects with food allergy, including bile acids at ages 3-6 months and 1 year, amino acids at age 3-6 months, steroid hormones at 1 year, and sphingolipids at age 3 years. One module primarily containing diacylglycerols was increased in those with food allergy at age 3-6 months. Fecal caffeine metabolites at age 3-6 months, likely derived from breast milk, were increased in those with food allergy and/or sensitization (beta = 5.9, 95% CI 1.0-10.8, p = .02) and were inversely correlated with fecal bile acids and bilirubin metabolites, though maternal plasma caffeine levels were not associated with food allergy and/or sensitization.

CONCLUSIONS

Several classes of bioactive fecal metabolites are associated with food allergy and/or sensitization including bile acids, steroid hormones, sphingolipids, and caffeine metabolites.

Nasopharyngeal lipidomic endotypes of infants with bronchiolitis and risk of childhood asthma: a multicentre prospective study

BACKGROUND

Bronchiolitis is the leading cause of hospitalisation of US infants and an important risk factor for childhood asthma. Recent evidence suggests that bronchiolitis is clinically heterogeneous. We sought to derive bronchiolitis endotypes by integrating clinical, virus and lipidomics data and to examine their relationship with subsequent asthma risk.

METHODS

This is a multicentre prospective cohort study of infants (age <12 months) hospitalised for bronchiolitis. We identified endotypes by applying clustering approaches to clinical, virus and nasopharyngeal airway lipidomic data measured at hospitalisation. We then determined their longitudinal association with the risk for developing asthma by age 6 years by fitting a mixed-effects logistic regression model. To account for multiple comparisons of the lipidomics data, we computed the false discovery rate (FDR). To understand the underlying biological mechanism of the endotypes, we also applied pathway analyses to the lipidomics data.

RESULTS

Of 917 infants with bronchiolitis (median age, 3 months), we identified clinically and biologically meaningful lipidomic endotypes: (A) cinicalclassiclipidmixed (n=263), (B) clinicalseverelipidsphingolipids-high (n=281), (C) clinicalmoderatelipidphospholipids-high (n=212) and (D) clinicalatopiclipidsphingolipids-low (n=161). Endotype A infants were characterised by 'classic' clinical presentation of bronchiolitis. Profile D infants were characterised by a higher proportion of parental asthma, IgE sensitisation and rhinovirus infection and low sphingolipids (eg, sphingomyelins, ceramides). Compared with endotype A, profile D infants had a significantly higher risk of asthma (22% vs 50%; unadjusted OR, 3.60; 95% CI 2.31 to 5.62; p<0.001). Additionally, endotype D had a significantly lower abundance of polyunsaturated fatty acids (eg, docosahexaenoic acid; FDR=0.01). The pathway analysis revealed that sphingolipid metabolism pathway was differentially expressed in endotype D (FDR=0.048).

CONCLUSIONS

In this multicentre prospective cohort study of infants with bronchiolitis, integrated clustering of clinical, virus and lipidomic data identified clinically and biologically distinct endotypes that have a significantly differential risk for developing asthma.Delete.

Prenatal and Postnatal Exposure to Ambient Air Pollution and Preschool Asthma in Neonatal Jaundice Infants

Purpose

Both air pollutant exposure and neonatal jaundice (NJ) have known effects on childhood asthma, but a higher total serum bilirubin (TSB) level has been associated with lung protection. This study aimed to assess whether prenatal/postnatal exposure to ambient air pollutants is related to the development of asthma in infants with NJ.

Patients and Methods

A nested case–control retrospective study was performed using the data of infants with NJ in the Kaohsiung Medical University Hospital Research Database. Data on average ambient air pollution concentrations within six months, the first year and second year after birth, and in the first, second and third prenatal trimesters were collected. NJ was defined as TSB levels ≥ 2 mg/dl with the diagnosis less than one-month-old. Asthma was defined as a diagnosis with medication use. We constructed conditional logistic regression models to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs).

Results

Exposure to NO and SO₂ at all six time points in the study was significantly associated with an increased risk of preschool asthma in infants with NJ. The overall peak OR (95% CI) of SO₂, PM_2.5, PM₁₀, NO, NO₂, and NO_X were 1.277 (1.129–1.444), 1.057 (1.023–1.092), 1.035 (1.011–1.059), 1.272 (1.111–1.455), 1.168 (1.083–1.259) and 1.104 (1.051–1.161), respectively. Fetuses in the first and second trimester were most vulnerable to ambient air pollutant exposure such as SO₂ PM_2.5, NO, NO₂ and NO_X during the prenatal period. Exposure to all six ambient air pollutants during the first and second years after birth significantly affected preschool asthma in NJ infants.

Conclusion

In different time windows, prenatal and postnatal exposure to SO₂, PM_2.5, PM₁₀, NO, NO₂, and NO_X were associated with preschool asthma in NJ infants. The relatively high impact of NO and SO₂ exposure in infants with NJ requires further studies and prevention measures.

Biliverdin/Bilirubin Redox Pair Protects Lens Epithelial Cells against Oxidative Stress in Age-Related Cataract by Regulating NF-κB/iNOS and Nrf2/HO-1 Pathways

Age-related cataract (ARC) is the leading cause of vision impairment globally. It has been widely accepted that excessive reactive oxygen species (ROS) accumulation in lens epithelial cells (LECs) is a critical risk factor for ARC formation. Biliverdin (BV)/bilirubin (BR) redox pair is the active by-product of heme degradation with robust antioxidative stress and antiapoptotic effects. Thus, we purpose that BV and BR may have a therapeutic effect on ARC. In the present study, we determine the expression levels of enzymes regulating BV and BR generation in human lens anterior capsule samples. The therapeutic effect of BV/BR redox pair on ARC was assessed in hydrogen peroxide (H₂O₂)-damaged mouse LECs in vitro. The NF-κB/inducible nitric oxide synthase (iNOS) and nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathways were evaluated to illustrate the molecular mechanism. The results revealed that the mRNA expressions of Nrf2, HO-1, and biliverdin reductase A (BVRA) were all decreased in human samples of age-related nuclear cataract. BV/BR redox pair pretreatment protected LECs against H₂O₂ damage by prohibiting NF-κB p65 nuclear trafficking, ameliorating iNOS expression, reducing intracellular and mitochondrial ROS levels, and restoring glutathione (GSH) and superoxide dismutase (SOD) levels. BV and BR pretreatment also regulated the expression of apoptotic molecules (Bax, Bcl-2, and cleaved caspase-3), thus decreasing the apoptosis of LECs. In addition, BV/BR pair promoted Nrf2 nuclear accumulation and HO-1 induction, whereas the knockdown of BVRA counteracted the effect of BV on activating Nrf2/HO-1 pathway and antiapoptosis. These findings implicated that BV/BR redox pair protects LECs against H₂O₂-induced apoptosis by regulating NF-κB/iNOS and Nrf2/HO-1 pathways. Moreover, BVRA is responsible for BV-mediated cytoprotection by reductive conversion of BV to BR. This trial is registered with ChiCTR2000036059.

[The Role of Nrf2 Pathway Activation in Hippocampal Neuron Injury of Neonatal Rats with Bilirubin Encephalopathy]

OBJECTIVE

To explore the effect of nuclear factor-erythroid 2-related factor (Nrf2) pathway activation on hippocampal neuron damage in neonatal rats with bilirubin encephalopathy.

METHODS

Neonatal rats were randomly assigned to a control group (Control), a model group (Model) and an Nrf2 activator TBHQ (tert-Butylhydroquinone) group (TBHQ), with 20 rats in each group. Bilirubin solution was injected through the cerebellomedullary cistern to establish the neonatal rat model of bilirubin encephalopathy. Neurobehavioral changes were observed in rats and the water content of the brain tissue was measured. Nissl staining was done to observe the damage of hippocampal neurons. TUNEL staining was used to observe the apoptosis of hippocampal neurons. Colorimetric analysis was done to determine the Caspase-3 activity in the hippocampus. The content of malondialdehyde (MDA) and reduced glutathione (GSH) and the activity of superoxide dismutase (SOD) in the hippocampus were examined by chemical analysis. qRT-PCR and Western blot were done to measure the expression of Nrf2 and heme oxygenase-l (HO-1) mRNA and proteins in the hippocampus.

RESULTS

After injection of bilirubin into the cerebellomedullary cistern, the young rats in the Model group and the TBHQ group showed different degrees of neurological abnormalities, while those in the control group showed no significant neurobehavioral abnormalities. Compared with the Control group, the Model group had severe neuronal damage, and the water content of brain tissue, the apoptosis of hippocampal neurons, the activity of Caspase-3 and the content of MDA content significantly increased ( P<0.01), while the SOD activity, GSH content, the expression of Nrf2 and HO-1 mRNA and proteins significantly decreased ( P<0.05). Compared with the Model group, neuronal damage was improved in the TBHQ group, and the water content of brain tissue, apoptosis of hippocampal neurons, activity of Caspase-3 and MDA content were all significantly reduced ( P<0.01), while SOD activity, GSH content and the expression of Nrf2 and HO-1 mRNA and proteins were significantly increased ( P<0.05).

CONCLUSION

Activation of the Nrf2 pathway can improve hippocampal neuronal damage in neonatal rats with bilirubin encephalopathy and inhibit neuronal apoptosis and the oxidation reaction.

Research Progress of Metabolomics in Asthma

Asthma is a highly heterogeneous disease, but the pathogenesis of asthma is still unclear. It is well known that the airway inflammatory immune response is the pathological basis of asthma. Metabolomics is a systems biology method to analyze the difference of low molecular weight metabolites (<1.5 kDa) and explore the relationship between metabolic small molecules and pathophysiological changes of the organisms. The functional interdependence between immune response and metabolic regulation is one of the cores of the body's steady-state regulation, and its dysfunction will lead to a series of metabolic disorders. The signal transduction effect of specific metabolites may affect the occurrence of the airway inflammatory immune response, which may be closely related to the pathogenesis of asthma. Emerging metabolomic analysis may provide insights into the pathogenesis and diagnosis of asthma. The review aims to analyze the changes of metabolites in blood/serum/plasma, urine, lung tissue, and exhaled breath condensate (EBC) samples, and further reveals the potential pathogenesis of asthma according to the disordered metabolic pathways.