Differential antioxidant protection against oxidants by esculetin or quercetin in human leukemia NB4 cells

Esculetin (6,7-dihydrocoumarin) and the flavonoid quercetin (3,5,7,3',4' pentahydroxyflavone) show different pharmacological properties probably related to effects on redox homeostasis. Human leukemia NB4 cells were preincubated for 30 min or 2 h with either 100 μM esculetin or 25 μM quercetin. The cells were then treated with 1 mM H 2 O 2 or 250 μM tert-butyl hydroperoxide (t-BHP) for 1 h. Pretreatments with quercetin prevented loss of cell viability (impermeability to PI) induced by H 2 O 2 or t-BHP. Treatment with 1 mM H 2 O 2 for 1 h produced lower apoptotic cells (26%) than 250 μM t-BHP (38%). Pretreatments with esculetin increased the apoptosis induced by H 2 O 2 but reduced significantly the apoptosis produced by t-BHP. Quercetin reduced apoptosis produced by H 2 O 2 and wholly protects against apoptosis induced by t-BHP. Superoxide was increased by treatment with H 2 O 2 or t-BHP. Esculetin or quercetin increased the levels of superoxide in cells treated with H 2 O 2 but reduced them in cells treated with t-BHP. Esculetin but not quercetin almost prevented peroxide production by H 2 O 2 . Our results show different effects of antioxidant treatment on leukemia cells and possible differential applications for antitumor therapy with either of those antioxidant compounds used.