Different roles of Nrf2 and NFKB in the antioxidant imbalance produced by esculetin or quercetin on NB4 leukemia cells.

Esculetin (6,7-dihydrocoumarin) and the flavonoid quercetin (3,5,7,3',4' pentahydroxyflavone) are compounds that could change the balance of redox homeostasis. NB4 leukemia cells were treated with 25 µM quercetin for 24 h and with esculetin at either 100 or 500 µM for different times. Quercetin increased the levels of pro-inflammatory NFkB p65 in the nucleus correspondingly reducing them in the cytosol. The levels of NFkB p65 decreased in the nucleus at high esculetin concentration treatments for long times (19 h), concomitantly increasing the levels of anti-inflammatory NFkB p50 in the nucleus. This could suggest formation of inhibitory p50 homodimers possibly related with anti-inflammatory response. Lipoxygenase expression was reduced either by esculetin or quercetin. A significant increase of Nrf2 in the nucleus of NB4 cells treated with 100 µM esculetin for 19 h was observed. Quercetin increased the levels of Nrf2 in the cytosol reducing them in the nucleus. Superoxide dismutase expression increased in NB4 cells treated with esculetin in contrast with quercetin. All these data support a relevant differential role for NFkB and Nrf2 in anti-inflammatory and redox response when apoptosis was induced by esculetin or quercetin in human leukemia NB4 cells.

Esculetin Neutralises Cytotoxicity of t-BHP but Not of H2O2 on Human Leukaemia NB4 Cells.

The coumarin esculetin shows antioxidant action on some cell types, both by scavenging ROS and by decreasing ROS production. We have previously demonstrated the induction of apoptosis by esculetin on NB4 human leukaemia cells by an ill-defined mechanism related to ROS levels. In this work, we analyze the effect of the simultaneous treatment with esculetin and two oxidants to observe the early events in the mechanism of esculetin-induced apoptosis. Our results show that, from the early time of 15 min, esculetin acts synergistically with H2O2 to decrease cell viability and metabolic activity and to increase apoptosis in NB4 cells. In contrast, the early oxidative effects of t-BHP are neutralised by esculetin, protecting human leukaemia NB4 cells from apoptosis. Esculetin seems to restrict the increase in peroxides caused by H2O2 or t-BHP in the time interval analyzed. These results contribute to a better understanding of the cytotoxic effect caused by esculetin on NB4 cells. At the same time, the early neutralisation of exogenous oxidants could be of interest to prevent diseases related to oxidative stress imbalance.

Dequalinium induces cytotoxicity in human leukemia NB4 cells by downregulation of Raf/MEK/ERK and PI3K/Akt signaling pathways and potentiation of specific inhibitors of these pathways.

Delocalized lipophilic cation dequalinium (DQA) selectively accumulates in mitochondria and displays anticancer activity in different malignancies. Our previous studies indicate a DQA-induced cytotoxicity in human acute promyelocytic leukemia NB4 cells by early disturbance in mitochondrial function and oxidative stress. This study shows the ability of DQA to downregulate Raf/MEK/ERK1/2 and PI3K/Akt signaling pathways in NB4 cells which leads to cell death by apoptosis and/or necrosis. Moreover, DQA potentiates the action of specific inhibitors of these pathways. These DQA effects could be mediated by redox regulation of Akt. Our results contribute to a better understanding of the cytotoxic DQA mechanism on leukemia cells and encourage the performance of further studies in combination with other agents such as kinase inhibitors for improving the efficacy of therapies against acute promyelocytic leukemia.

Dequalinium induces human leukemia cell death by affecting the redox balance.

Dequalinium, an amphiphilic quinolinium derivative, selectively accumulates in mitochondria and displays anticancer activity in cells from different malignancies. Previous studies indicate a differential DQA-induced cytotoxicity in NB4 and K562 human leukemia cells as a consequence of an early disturbance in mitochondrial function. Results in this paper show that DQA induces a concentration-dependent oxidative stress by decreasing GSH level and increasing ROS in a cell type specific way. Inhibitors of the JNK and p38 stress regulated kinases potentiate DQA-induced NB4 cell death suggesting a protective function for these enzymes. K562 cells with relatively high GSH levels remained resistant to DQA action.