Fig. 3.

Effect of ascorbic acid on the stability of quercetin, luteolin and their O-methylated metabolites in the culture medium (A) and cell viability in the presence of flavonols (B). (A) Flavonoids were added to cell-free culture medium without (gray) or with (black) 500 μM ascorbic acid at a final concentration of 10 μM and incubated for 24 h. Values are calculated as percent of zero time-treated control. (B) Cells were treated for 24 h with 10 or 50 μM quercetin or isorhamnetin without (gray) or with (black) 500 μM ascorbic acid. Cell viability was measured as described in the Materials and methods section using Cell Proliferation Reagent WST-1. Values are calculated as the percentage of vehicle-treated (gray bar) or ascorbic acid-treated (black bar) controls and are the mean ± SD from five independent determinations. Significant differences from controls were evaluated by the Student's t-test (*p < 0.05).