Dixon, Anne E.

Abstract RATIONALE: 4G4G/4G5G SERPINE1 genotypes produce high concentrations of plasminogen activator inhibitor-1 and are associated with worse asthma outcomes. A secondary analysis of the American Lung Association (ALA) SOYA trial showed that soy isoflavones significantly reduced asthma exacerbations versus placebo among patients with 4G4G/4G5G SERPINE1 genotypes. We hypothesized that baseline characteristics predict optimal responders to soy isoflavones among this subgroup. METHODS: ALA-SOYA was a randomized controlled trial that tested the efficacy of soy isoflavones vs. placebo for reducing asthma exacerbations among adolescents and adults with symptomatic asthma. In this responder analysis among participants with 4G4G/4G5G SERPINE1 genotypes, baseline demographic and clinical characteristics were tested for effect modification of the treatment assignment (soy/placebo) on the primary outcome of annualized number of asthma exacerbations using interaction terms in negative binomial regression models, with a significance threshold of p-interaction=0.15. RESULTS: Data were available for n=168 participants. Soy reduced the annualized number of asthma exacerbations relative to placebo among patients with 4G4G/4G5G SERPINE1 genotypes (incident rate ratio (IRR)=0.37, 95% confidence interval (CI): 0.15-0.90, p=0.028). Self-reported adherence to baseline controller therapy was the only significant effect modifier of this association (interaction p=0.115), with those using inhaled corticosteroid (ICS)/long-acting beta-agonist (LABA) controller therapy at least twice weekly experiencing reductions in asthma exacerbations with soy versus placebo (IRR = 0.25, 95% CI: 0.09-0.69; p= 0.007) but not among those using ICS/LABA controller therapy less frequently (IRR = 1.33, 95% CI: 0.22-8.02; p= 0.757). CONCLUSION: Soy isoflavones reduce asthma exacerbations among patients with the 4G4G/4G5G SERPINE1 genotypes and are most effective in those with greater adherence to asthma controller therapy regimens.