Impact of Saharan Dust and SERPINA1 Gene Variants on Bacterial/Fungal Balance in Asthma Patients

Abstract

The Canary Islands, a region with high asthma prevalence, are frequently exposed to Saharan Dust Intrusions (SDIs), as are a wide range of countries in Europe. Alpha-1 antitrypsin (SERPINA1 gene) regulates the airway's inflammatory response. This study analyzed the combined effect of SDI exposure and SERPINA1 variants on bacterial/fungal DNA concentrations in saliva and pharyngeal samples from asthmatic patients. Bacterial and fungal DNAs were quantified by qPCR in 211 asthmatic patients (GEMAS study), grouped based on their exposure to daily PM₁₀ concentrations. Associations between SDI exposure, microbial DNA concentrations, and nine variants in SERPINA1 were tested using linear regression models adjusted for confounders. The ratio between bacterial and fungal DNA was similar in saliva and pharyngeal samples. SDI exposure for 1-3 days was enough to observe significant microbial DNA change. Increased bacterial DNA concentration was detected when SDI exposure occurred 4-10 days prior to sampling, while exposure between days 1 and 3 led to a reduction in the fungal DNA concentration. The T-allele of SERPINA1 SNV rs2854254 prevented the increase in the bacterial/fungal DNA ratio in pharyngeal samples after SDI exposure. The bacterial/fungal DNA ratio represents a potential tool to monitor changes in the microbiome of asthmatic patients.

Keywords: 16S rRNA; 18S rRNA; SERPINA1; SNV; Saharan dust intrusions; asthma; microbial DNA concentration.

Figure 1

Bacterial, fungal, and ratio of bacterial/fungal DNA concentrations in saliva and pharyngeal samples. DNA purified from saliva (blue) or pharyngeal (green) samples was used for real-time qPCR measurement of DNA concentrations of (a) bacteria, (b) fungi, or (c) the bacterial/fungal ratio. In all cases, median and interquartile ranges are shown. The number of samples, after removal of outliers, is indicated below each plot. Differences were evaluated using the Mann–Whitney U test. Statistically significant p-values (<0.05) are highlighted in bold.

Figure 2

Effect of SDI exposure on bacterial, fungal, and ratio of bacterial/fungal DNA concentrations. Patients were subdivided considering whether they were exposed (Yes) or not (No) to an SDI in the 10-day period prior to sampling. (a) Bacterial DNA concentration in saliva (blue) or pharyngeal (green) samples. (b) Results for fungal DNA concentration. (c) Results for the ratio of bacterial/fungal DNA concentrations. In all cases, the Mann–Whitney U test was used to test differences between groups. Significant p-values (<0.05) are highlighted in bold. The sample numbers after the removal of outliers are shown below each plot.

Figure 3

Non-accumulative effect of SDI exposure over bacterial, fungal, and ratio of bacterial/fungal DNA concentrations. (a) Bacterial DNA concentration was measured in saliva (blue) or pharyngeal (green) samples. Patients were distributed as Not-exposed (0 out of 10 days prior to sampling; light), Low-exposed (1–3 days; medium), or High-exposed (4–6 days; dark). (b) Results obtained as in A, but for the fungal 18S rRNA gene copy number. (c) Results obtained as in A, but for the ratio of bacterial/fungal DNA concentrations. In all cases, the Mann–Whitney U test was used to evaluate all possible pairwise comparisons between DNA concentrations. Significant p-values (<0.05) are highlighted in bold, and the sample size after outlier removal from each group is shown below each plot.

Figure 4

Time-course effect of SDI exposure over bacterial, fungal, and ratio of bacterial/fungal DNA concentrations. (a) Bacterial DNA concentration was measured in saliva (blue) or pharyngeal (green) samples. Patients were distributed as Not-exposed (0 out of 10 days prior to sampling; light), Early-exposed (exposed between days 1 and 3 prior to sampling; medium), or Late-exposed (exposed between days 4 and 10 prior to sampling; dark). (b) Results obtained as in A, but for fungal 18S rRNA gene copy number per nanogram of purified DNA. (c) Results obtained as in A, but for the ratio of bacterial/fungal DNA concentrations. In all cases, the Mann–Whitney U test was used to compare with the Not-exposed group. Significant p-values (<0.05) are highlighted in bold, and the sample size after outlier removal from each group is shown below each plot.

Figure 5

Effect of SNV rs2854254 and SDI exposure over the ratio of bacterial/fungal DNA concentrations in pharyngeal samples. (a) Patients were distributed considering their rs2854254 genotype, and the pharyngeal ratio of bacterial/fungal DNA concentrations was compared. (b) The pharyngeal ratio of bacterial/fungal DNA concentrations was compared between exposed and not-exposed individuals inside each genotype group. (c) The pharyngeal ratio of bacterial/fungal DNA concentrations was compared between genotypes inside each exposure group. In all cases, the Mann–Whitney U test was used. Significant p-values (<0.05) are highlighted in bold, and the sample size after outlier removal from each group is shown below each plot.