Induction of mitochondrial manganese superoxide dismutase confers resistance to apoptosis in acute myeloblastic leukaemia cells exposed to etoposide

Abstract

Summary.We investigated the possible roles of mitochondrial manganese superoxide dismutase (MnSOD) and bcl-2 in etoposide-induced cell death in acute myeloblastic leukaemia (AML) using two subclones of the OCI/AML-2 cell line, the etoposide-sensitive (ES) and the etoposide-resistant (ER), as models. Cell death after 24 h exposure to 10 mmol/l etoposide was about 60% and 70% in the ES subclone and about 20% and 25% in the ER subclone, when analysed by trypan blue and annexin V respectively. Cytochrome c ef¯ux from mitochondria to cytosol was observed after 4 h of exposure in both subclones, whereas the activation of caspase-3 was not detectable until after 12 h of exposure in the ES subclone and 24 h of exposure in the ER subclone, using Western blotting. The decrease in mitochondrial membrane potential, when analysed by the JC-1 probe¯uorocytometrically, also appeared to take place later in the ER than in the ES subclone. Both subclones showed evident basal expression of MnSOD and bcl-2 by Western blotting. Etoposide caused a potent induction of MnSOD, more than 400% at 12 h, in the ER but not in the ES subclone. No signi®cant change in bcl-2 expression could be observed in either of the subclones during exposure to etoposide when analysed by Western blotting or¯ow cytometry. In conclusion, we suggest that MnSOD might have a special role in the protection of AML cells against etoposide-induced cell death. Although unable to in¯uence the cytochrome c ef¯ux to cytosol, MnSOD might prevent the disruption of mitochondrial membrane potential, which evidently leads to cell death by releasing various activators of apoptosis.

Thiol protecting agents and antioxidants inhibit the mitochondrial permeability transition promoted by etoposide: implications in the prevention of etoposide-induced apoptosis

“…Since the compounds that prevent the VP-16-induced MPT do not affect the mitochondrial functional activities, our data, taken together with those on the oxidative stress effects of VP-16 in cells undergoing apoptosis [7,14,16] and on VP-16-induced oxidation of protein thiol groups [28], suggest that MPT promoted by VP-16 is related to oxidative stress caused by oxidant species generated by this drug [2,3], leading to changes in the redox status of mitochondrial NAD(P)H, GSH and protein thiol groups oxidation.…”

“…Moreover, different studies confirm that cells treated with MPT inducers alone undergo apoptosis and that, at least in most models of apoptosis, the induction of MPT and mitochondrial cytochrome c release are essential components of the apoptotic pathway [11 -13]. On the other hand, cells undergoing VP-16-induced apoptosis, which is prevented by glutathione (GSH) and N-acetylcysteine (NAC) [7], also evidence a significant increase in the generation of ROS [14], mitochondrial NO production [15] and induction of MnSOD [16]. Furthermore, VP-16 induces peroxide formation and depletion of GSH in cells during the apoptotic process [17], suggesting the occurrence of GSH oxidation or cleavage of the catalytic subunit of g-glutamilcysteine synthetase [17], probably due to the intermediate formation of hydroxyl and phenoxyl radicals [2,3].…”

Starvation-dependent differential stress resistance protects normal but not cancer cells against high-dose chemotherapy

“…We examined whether STS could also enhance resistance of mice against etoposide, a widely used chemotherapy drug that damages DNA by multiple mechanisms and displays a generalized toxicity profile ranging from myelosuppression to liver and neurologic damage (22)(23)(24). Furthermore, etoposide has been reported to increase the production of ROS in human glioblastoma cells, leading to cellular apoptosis possibly mediated by p53 (25), and to increase the production of ROS and MnSOD expression in myeloid leukemia cells (26). We administered an unusually high dose of etoposide (80 mg/kg) to A/J mice that had been starved for 48 h. In humans, one-third of this concentration of etoposide (30-45 mg/kg) is considered to be a high dose and therefore in the maximum allowable range (27).…”

Millimeter wave treatment inhibits the mitochondrion-dependent apoptosis pathway in chondrocytes

“…This structure, in turn, recruits and activates caspase-9. Activated caspase-9 cleaves and activates executioner caspases, such as caspase-3, and eventually results in apoptosis (22,23,26). Therefore, to evaluate the effect on MW on the mitochondrion-dependent apoptosis pathway, we evaluated the release of cytochrome c and the activation of caspase-9 and caspase-3.…”

“…It is an early event preceding phosphatidylserine externalization and coincides with caspase activation (22,23). We used a JC-1 dye-based assay to evaluate mitochondrial membrane potential.…”