Indoor metabolites may indicate childhood asthma, allergic rhinitis risks
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Key takeaways:
- Homes of children who did not have disease were enriched with environmental microbes and metabolites.
- Homes of children with disease were enriched with mycotoxins and synthetic chemicals.
Indoor metabolites and chemicals may be more accurate indicators of risks for childhood asthma and allergic rhinitis than the indoor microbiome, according to a study published in Eco-Environment and Health.
Interventions that target these metabolites and chemicals may help prevent or mitigate these diseases, Yu Sun, PhD, College of Life Sciences, South China Agricultural University, Guangzhou, China, and colleagues wrote.
The case-control study involved 32 children with asthma, 37 children with allergic rhinitis, 28 with both and 52 healthy controls from middle schools in three geographically distinct regions of Malaysia.
Microbiome, genetic diversity
Using dust samples, the researchers identified 6,247 microbial species in the homes of these children, including 5,975 bacteria, 140 eukaryotes, 38 archaea and 94 viruses.
Human skin commensals and environmental commensals were the most abundant indoor bacteria, the researchers said, along with a few opportunistic pathogens.
Fungal species such as common indoor molds and human skin fungi were the most abundant eukaryotes, and bacterial phage and human herpesvirus mainly constituted the low abundance (< 0.01%) of indoor archaeal and viral species.
There was a small but significant variation in indoor microbial diversity between the homes of the children with asthma, children with both asthma and allergic rhinitis, and healthy children (permutational multivariate analysis of variance, R2 = 0.03; P = .005), the researchers continued.
The homes of the healthy children were enriched with a higher number of outdoor species as well, compared with the homes of the children with disease. However, only a few species were enriched in the homes of the children with disease.
Although the researchers annotated 2.76 functional genes against the KEGG database, including half that were metabolic genes, there were no statistical differences in the overall composition of functional genes in the children with asthma, allergic rhinitis and both or in the healthy children.
Starch and sucrose metabolism, galactose metabolism and secondary bile acid biosynthesis pathways were enriched in the homes of healthy children.
Also, there was a correlation between species diversity and functional pathway diversity (R = 0.48; P < .0001), the researchers said, suggesting that diverse microbial exposure leads to diverse functional gene exposure. Further, there was no enriched functional pathway in the homes of children with asthma or allergic rhinitis.
Metabolites and chemicals
The dust samples from homes included 1,442 metabolites and chemicals, including derivatives of keto acids, indoles, pyridines and flavonoids that were exclusively enriched in the homes of healthy children but not in the homes of children with disease (fold change > 1.5; P < .01; false discovery rate < 0.05).
The researchers characterized the enriched keto acids, indoles and pyridines in the homes of the healthy children as closely involved in producing potentially protective indoor microorganisms. Also, the researchers said, the flavonoids came from a class of secondary metabolites that are derived from multiple plants.
A literature search revealed interconnections between the class of keto acid and the class of indoles and their derivatives, whereas the compounds in the flavonoids were independent of each other, suggesting different sources.
The homes of the children with asthma, allergic rhinitis and both were exclusively enriched with mycotoxins, which are toxic secondary metabolites that are produced by fungi, and synthetic chemicals.
Further, there were significantly higher abundances of Fusarium graminearum and Alternaria alternata in the homes of children with asthma compared with the homes of healthy children (P < .05, Wilcoxon test).
These abundances are consistent with the enrichment of metabolites in children with asthma, the researchers said, adding that these mycotoxins have been classified as hazardous chemicals with fatal or toxic effects.
The synthetic chemicals primarily included herbicide, insecticide and food and cosmetic additives, which also have been classified as hazardous, with effects including skin and eye irritation, gastrointestinal diseases and inflammation.
Prediction models
By using seven indole derivatives, 15 flavonoids and four mycotoxins as marker metabolites, the researchers achieved an average of 74.9% accuracy in differentiating between schools with high prevalence and low prevalence of asthma.
However, adding keto acids, pyridines and synthetic chemicals into the model slightly decreased accuracy (area under the curve = 62.2%-71.4%). Characteristic microbial genera from a dataset from Shanghai produced a 51% classification accuracy.
The classification results for allergic rhinitis were similar, the researchers continued, with 77.1% accuracy from using indole, flavonoids and mycotoxins as marker metabolites; 70.7% with keto acids, pyridines and synthetic chemicals; and 59.5% with the Shanghai dataset.
These findings led the researchers to conclude that indoor microorganisms had less power in differentiating schools based on their asthma prevalence, but that indoor metabolites have potential for environmental assessments and in health outcome classifications for asthma and allergic rhinitis.
Noting that they hope to enlarge their sample size and research other regions as they retest their current findings, the researchers also said they think the metabolome may be a more universal and reliable classified and environmental risk assessment index for asthma and allergic rhinitis in the future.
As physicians test whether rooms are “metabolite healthy,” the researchers said, interventions may include altering the indoor microbiome or curbing specific chemical exposures.
Perspective
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It is important that people approach asthma from different angles: finding the right inhaler for their body and making sure their dwelling is allergy and asthma friendly. This study has shown the importance of living in an asthma-safe environment and how those who do not can be harmed in their own home.
Doctors can keep increasing doses of inhalers, but that will not help when patients are living in dwellings where their lungs are constantly irritated by chemicals, pet urine, cigarette smoke, mildew, mold, incense and other irritants. Patients are often nose blind to various scents and asthma triggers. Asthma home visiting programs can detect problems and provide resources to fix the environmental triggers.
Most of these programs are free and grant-funded through the CDC. Asthma home visiting programs can offer incentives such as dry and wet mops, low-odor cleaning supplies, air purifiers, vacuums, trash cans or mouse traps. The CDC funds 24 sites throughout the United States. Physicians and patients can find nearby programs online.
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