dependent on RNA quality. Therefore, for subsequent statistical analysis we excluded 11 samples with an RNA quality score less than 7 (see Methods). The remaining 28 microarrays included 8 samples each from the controls and the cohort with severe asthma exacerbation and 6 samples from both the cohort with moderate asthma exacerbation and the no-exacerbation cohort. With use of stringent statistical analysis in which the probability of a false positive was restricted to 1%, comparison of the group with severe asthma exacerbation and the control group revealed that microRNA miR-582-5p is significantly induced (;24-fold) in the cohort of those with severe asthma exacerbation (Fig 1). The expression level of miR-582-5p in the group with moderate exacerbation and the group with no exacerbation is intermediate compared with that in the control group and the group with severe asthma exacerbation (see Fig E1 in in this article's Online Repository at www.jacionline.org). Interestingly, miR-582-5p has been found to be upregulated in sputum of subjects exposed to ozone, altering their respiratory immune response. 5 We investigated whether the increase in miR-582-5p expression might be due to alterations in cell populations. Using a set of mi-croRNAs characteristic for lymphocytes, red blood cells, immune cells, and epithelial cells, we compared expression between the group with severe asthma exacerbation and the control group. No significant differences were observed (see Fig E2 and the Methods section in this article's Online Repository at www. jacionline.org). Our study demonstrated that it is feasible to obtain adequate quantities of high-quality microRNAs by using a noninvasive approach and conduct complex genomic studies of pediatric asthma in the ED. Although the use of blood and/or bronchial epithelial cells has been a preferred method of obtaining the ''ideal'' tissue sample for biomarker studies in the past, this approach is not always practical, especially in the pediatric population. Here, we show that nasal epithelium can be used as a bronchial epithelium surrogate obtained via a substantially less invasive method compared with endobronchial lavage. There are several limitations to our study. The first is the small cohort size. Although prior research revealed that significant differences in gene expression are detectable in small sample sizes (N < _ 30), 6 our findings warrant further validation. However, our statistical analysis showed that significant changes in micro-RNA expression could be detected in nasal epithelia with a low false-positive rate, even in a limited cohort. We found that high-quality RNAs are important to obtain robust results. Further improvements in the collection protocol may provide improved consistency in RNA quality. Second, the majority of enrolled patients were African American, reflecting the demographics of our ED population. A multicenter study with a diverse population would be the optimal setting to validate our results. In conclusion, it is feasible to obtain high-quality micr...
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