Characteristics of the case and control participants.

<p>Total IgE levels were logarithmically transformed before statistical testing to meet the assumption of a normal distribution.</p

Associations between asthma, betel chewing, plasma markers and respiratory function in male participants (n = 147).

<p>Arecoline, arecaidine, IgE, hs-CRP, leptin, TGF-β1 and eotaxin-1 levels were logarithmically transformed before statistical testing to meet the assumption of a normal distribution.</p>a<p>Least significant difference (LSD) multiple comparisons were performed to compare plasma markers and pulmonary function between current and non-current betel chewing in males with asthma and controls, respectively.</p>b<p>General linear regression was used to assess the associations between plasma markers and the four groups of male cases and controls with and without betel chewing by adjusting for age, BMI and smoking.</p

In cultured gingival fibroblast cells, the levels of eotaxin-1 were measured by ELISA in supernatants from cells treated with different levels of arecoline (0, 10, 25, 100, and 200 μg/ml for 24 h).

<p>The levels of eotaxin-1 (mean±SD) were analyzed by one-way ANOVA and Bonferroni multiple correction tests in which the P values are adjusted by multiplying by 10. * p = 0.03301 for the pretreatment of arecoline at 100 μg/ml induced significant elevation of eotaxin-1 levels (1489±78 pg/ml) compared with the pretreatment of arecoline at 0 μg/ml (1044±95 pg/ml) under TNF-alpha and IL-4 stimulation. Arecoline, at a concentration of 200 μg/ml, increased cytotoxicity by more than 45% <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091889#pone.0091889-Chiang1" target="_blank">[22]</a>. The stimulated groups indicate that the fibroblast cells were treated with IL-4 (50 ng/ml) and TNF-alpha (100 ng/ml) for 72 hours. The baseline groups are fibroblast cells that were treated with arecoline alone, not stimulated with IL-4 and TNF-alpha. Arecoline alone at any tested concentrations from 0 to 200 μg/ml cannot induce detectable eotaxin-1 release (0±0 pg/ml for any tested dose of arecoline).</p

Logistic regression analyses of the adjusted associations between betel chewing and asthma.

1<p>Logistic regression adjusted for age, gender, BMI and smoking.</p>2<p>Logistic regression adjusted for age, gender, BMI, smoking and log eotaxin-1 levels (345 cases and 389 controls were randomly selected to measure eotaxin-1 levels).</p>3<p>The mediation effect of eotaxin-1 was 50.5% of the total effect of betel chewing on asthma being mediated through this pathway.</p

In cultured dermal fibroblast cells, the levels of eotaxin-1 were measured by ELISA in supernatants from cells treated with different levels of arecoline (0, 10, 25, 100, and 200 μg/ml for 24 h).

<p>The levels of eotaxin-1 (mean±SD) were analyzed by one-way ANOVA and Bonferroni multiple correction tests in which the P values are adjusted by multiplying by 10. * p = 0.01035 for the pretreatment of arecoline at 100 μg/ml induced significant elevation of eotaxin-1 levels (2700±98 pg/ml) compared with the pretreatment of arecoline at 0 μg/ml (1850±142 pg/ml) under the TNF-alpha and IL-4 stimulations. Arecoline increased cytotoxicity with more than 45% at a concentration of 200 μg/ml <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091889#pone.0091889-Chiang1" target="_blank">[22]</a>. The stimulated groups indicate that the fibroblast cells were treated with IL-4 (50 ng/ml) and TNF-alpha (100 ng/ml) for 72 hours. The baseline groups are fibroblast cells that were treated with arecoline alone, not stimulated with IL-4 and TNF-alpha.</p

The associations of the duration, amount and total life time consumption of betel chewing and asthma.

<p>Total life time exposure of betel chewing:one chewed pack corresponds to 10 betel quids.</p