MTT Reduction by Flavonoids in the Absence of Cells: Influence of Medium Type and Serum

The MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) assay is widely accepted as a simple and reproducible method for determining cell proliferation or cytotoxicity in vitro. In this study, we show that the flavonoids quercetin, rutin and luteolin but not apigenin can reduce MTT in the absence of live cells in the following order: quercetin >> rutin > luteolin > apigenin. The final concentrations of the flavonoids used were 200, 100, 50, 25 and 12.5 µg/ml. Results further show that MTT reduction in Dulbecco’s Modified Eagle’s Medium (DMEM) is statistically higher than those in RPMI 1640 and F12 media, which are generally similar. Particularly for luteolin, MTT reduction is considerably higher with serum than without serum. In the case of quercetin at 50 µg/ml, a serum concentration of even only 0.01% is sufficient to significantly enhance MTT reduction versus that at 0% (P < 0.05, Student’s T-test). The authors hypothesize that flavonoid structure, nutrient concentration in the culture medium as well as serum components directly affect MTT reduction by flavonoids in the absence of cells.