Analysis of exhaled eicosanoid species for differentiating asthma from normal controls
In the discovery phase of the study, in addition to those previously reported11, including LTB4, the level of 15-HETE, but not TXB2, in EBCs of subjects with asthma (N=60) was significantly lower than that noted in the control group (N=20) (Data not shown). To confirm the validity of these eicosanoid species in differentiating asthma patients from normal subjects, a total of 415 children were included in the validation phase, which consisted of 318 stable asthmatic and 97 healthy subjects. The demographics of these asthmatic children and healthy children are summarized in Table 1. Significant differences were noted for age, gender, serum total IgE, FEV1 and FeNO between the subjects in the asthmatic and the control groups (all had p<0.001 except for age and gender with p<0.05 and p<0.01, respectively; Table 1). No significant difference was found for BMI. In the expanded case-control design, the levels of exhaled 15-HETE were significantly lower for asthmatic subjects than for healthy subjects (p<0.0001; Table 2), while the level of TXB2 was similar between the two groups. Correlation analysis revealed that in asthmatic children, there was a significant positive correlation between the levels of TXB2 and those of LTB4 and PGE2 (Supplementary Figs. S1A and S1B) in the exhaled condensate. Moreover, among the asthmatic subjects, negative correlations were found for TXB2 and FEV1, and also for 15-HETE and LTB4, (r=-0.13, p<0.05; r=-0.11, p<0.05, respectively; Supplemental Figs. S1C and S1D).
When the asthmatic population was stratified into different severity groups (Table 2), it was noted that in comparison to the mild group, the moderate group was characterized with lower levels of exhaled 15-HETE, and the severe group exhibited even lower levels. The difference in 15-HETE levels between healthy subjects and all three asthmatic severity groups was significant, but no significant difference was found between groups for TXB2. Further, as 15-HETE is known to exert inhibitory effect on 5-LOX–derived pro-inflammatory leukotrienes, the ratios of exhaled 15-HETE/LTB4 were calculated, and the results showed that the ratio of 15-HETE/LTB4 was significantly lower in subjects with severe asthma (p<0.01; Table 2). We then utilized the data of Table 2 to generate the ROC curves and calculated the AUC values for each eicosanoid species. Figure 1 shows the ROC curves and the AUC values of the analyzed eicosanoids in differentiating asthma from healthy controls. Results showed a similar discriminating power for exhaled 15-HETE, FEV1 and FeNO (Fig. 1).