Thiol protecting agents and antioxidants inhibit the mitochondrial permeability...

• Author(s): Custódio, José B. A. ; Cardoso, Carla M. P. ; Almeida, Leonor M.
• Date: 2002
• Persistent ID: http://hdl.handle.net/10316/5792
• Origin: Estudo Geral - Universidade de Coimbra
• Subject(s): Etoposide; Anticancer; Apoptosis; Mitochondrial permeability transition; Antioxidants; Oxidative stress
• Document Type: Article
• Language: English

Description

Etoposide (VP-16) is known to promote cell apoptosis either in cancer or in normal cells as a side effect. This fact is preceded by the induction of several mitochondrial events, including increase in Bax/Bcl-2 ratio followed by cytochrome c release and consequent activation of caspase-9 and -3, reduction of ATP levels, depolarization of membrane potential ([Delta][Psi]) and rupture of the outer membrane. These events are apoptotic factors essentially associated with the induction of the mitochondrial permeability transition (MPT). VP-16 has been shown to stimulate the Ca2+-dependent MPT induction similarly to prooxidants and to promote apoptosis by oxidative stress mechanisms, which is prevented by glutathione (GSH) and N-acetylcysteine (NAC). Therefore, the aim of this work was to study the effects of antioxidants and thiol protecting agents on MPT promoted by VP-16, attempting to identify the underlying mechanisms on VP-16-induced apoptosis. The increased sensitivity of isolated mitochondria to Ca2+-induced swelling, Ca2+ release, depolarization of [Delta][Psi] and uncoupling of respiration promoted by VP-16, which are prevented by cyclosporine A proving that VP-16 induces the MPT, are also efficiently prevented by ascorbate, the primary reductant of the phenoxyl radicals produced by VP-16. The thiol reagents GSH, dithiothreitol and N-ethylmaleimide, which have been reported to prevent the MPT induction, also protect this event promoted by VP-16. The inhibition of the VP-16-induced MPT by antioxidants agrees with the prevention of etoposide-induced apoptosis by GSH and NAC and suggests the generation of oxidant species as a potential mechanism underlying the MPT that may trigger the release of mitochondrial apoptogenic factors responsible for apoptotic cascade activation. http://www.sciencedirect.com/science/article/B6T56-45MDTK0-1/1/8c058bbb86c4e2aa262e5705ce08671f