The antioxidants esculetin and quercetin modulate differently redox balance in human NB4 leukemia cells

The aim is to study the involvement of reactive oxygen species on redox homeostasis of acute promyelocytic leukemia cells using two antioxidants as models for tentative leukemia therapies. The NB4 leukemia cell line has increased reactive oxygen species (ROS) levels. Esculetin and quercetin are antioxidants that alter redox equilibrium, diminishing cell viability and inducing cell death in some cancer cells. The analysis of the role of reactive oxygen species on redox balance and apoptosis in NB4 leukemia cells was addressed by modulating redox balance with oxidants hydrogen peroxide (H2O2) and tert-butylhydroperoxide (t-BHP) and antioxidant compounds (esculetin and quercetin). Cell viability of NB4 cells was measured by flow cytometry using propidium iodide (PI). Colorimetric MTT (3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) gave an index of cell metabolism. Apoptosis was measured using Annexin V-FITC (fluorescein isothiocyanate coupled to annexin V). Intracellular ROS levels were detected using the fluorescent probes H2DCFDA (2, 7-dichloro-dihydrofluorescein diacetate) and DHE (dihydro-ethidine). Pre-treatment with quercetin prevented early loss of cell viability induced by either H2O2 or t-BHP. It reduced apoptosis produced by H2O2 and prevented that induced by t-BHP. Pre-treatment with esculetin, in contrast, increased apoptosis induced by H2O2 but reduced that produced by t-BHP. The superoxide anion content increased after incubation with either H2O2 or t-BHP, mainly in esculetin pretreatment. Esculetin, but not quercetin, prevented peroxide production by either H2O2 or t-BHP. Therefore, esculetin and quercetin regulate differentially redox balance in human NB4 human leukemia cells, presumably via different redox mechanisms, which opens up potential applications in antileukemia therapy.