The protective effects of nine
flavonoids, including
apigenin,
eriodictyol,
3-hydroxyflavone, kaempherol,
luteolin,
quercetin,
rutin, and
taxifolin (Table 1), on the cytotoxicity of
linoleic acid hydroperoxide (LOOH) toward rat
pheochromocytoma PC12 cells were examined. The cytotoxicity was assessed by the
trypan blue exclusion test and so-called MTT assay. When cells were preincubated with each
flavonoid prior to LOOH exposure,
quercetin,
3-hydroxyflavone, or
luteolin decreased LOOH cytotoxicity toward undifferentiated cells, while only
luteolin decreased efficiently LOOH cytotoxicity toward differentiated cells. On the other hand, when cells were coincubated with each
flavonoid and LOOH, kaempherol,
eriodictyol,
quercetin,
3-hydroxyflavone,
luteolin, or
taxifolin decreased LOOH cytotoxicity toward undifferentiated and differentiated cells. On both preincubation prior to LOOH exposure and coincubation with LOOH,
luteolin acted as the most efficiently
protective agent against LOOH cytotoxicity. Further, these
flavonoids showed protective effects on coincubation rather than preincubation. Flow cytometry using the fluorescence probe
2',7'-dichlorofluorescin diacetate revealed that LOOH increases the intracellular level of
reactive oxygen species in undifferentiated cells in a dose-dependent manner, and that
desferrioxamine mesylate suppresses the LOOH-induced increase in the level. These
flavonoids suppress the LOOH-induced increase. Further, the protective effect of
flavonoids on LOOH cytotoxicity correlates with the suppression of the LOOH-induced increase. These results suggest that such
flavonoids are beneficial for neuronal cells under oxidative stress.