Quercetin modifies reactive oxygen levels but exerts only partial protection against oxidative stress within HL-60 cells

Quercetin may contribute to the protection afforded by fruit- and vegetable-rich diets against diseases for which excess production of reactive oxygen species (ROS) has been implicated as a causal or contributory factor. We examine the effect of short term (90 min) quercetin (1-100 muM) exposure on the progress of menadione induced oxidative stress within HL-60 cells. 2 ' ,7 ' -dichlorofluorescein and rhodamine-123 fluorescence, resulting from oxidation of the ROS-sensitive dyes dichlorodihydrofluorescein and dihydrorhodamine-123 respectively, were utilised as indicators of general ROS levels. Ethidium fluorescence, resulting from oxidation of dihydroethidium, was used as a potentially more specific indicator of O(2)(-). Exposure to quercetin alone induced a decrease in DCF and rhodamine fluorescence. Conversely, ethidium. fluorescence was enhanced by treatment with greater than or equal to 40 muM quercetin. Incubation with 1-100 pM quercetin reduced the extent of menadione-induced increase in DCF and rhodamine fluorescence but the menadione-induced increase in ethidium fluorescence was further elevated for cells treated with greater than or equal to 25 muM quercetin. Exposure to greater than or equal to 10 muM quercetin abrogated menadione-induced DNA single-strand breaks but, paradoxically, quercetin exacerbated membrane damage and failed to enhance the viability of menadione-challenged cells. In conclusion, quercetin exerts only site-specific protection against oxidative stress. (C) 2001 Elsevier Science B.V. All rights reserved.