FR and FR-S reduce DENV and ZIKV NS1-induced endothelial dysfunction. (A, B) HPMEC monolayers were incubated with or without 10 μg/mL of DENV-2 NS1 and then treated with FR (A) or FR-S (B) at three different concentrations, as indicated. (C, D) HBMEC monolayers were incubated with or without 10 μg/mL of ZIKV NS1 and then treated with FR (C) or FR-S (D) at three different concentrations, as indicated. TEER was measured 2–10 h post-treatment. The area under the curve (AUC) of each treatment was compared to treatment with NS1 alone via one-way ANOVA + Dunnett’s multiple comparisons test. Asterisks indicate statistically significant differences, with *, p < 0.05; **, p < 0.005; ***, p < 0.001; or ****, p < 0.0001.