Molecular Mechanisms Underlying Cell Death Research Articles

Involvement of the Mitochondrial Death Pathway in Chemopreventive Benzyl Isothiocyanate-induced Apoptosis

In the present study, we studied the molecular mechanism underlying cell death induced by a cancer chemoprotective compound benzyl isothiocyanate (BITC). The cytotoxic effect of BITC was examined in rat liver epithelial RL34 cells. Apoptosis was induced when the cells were treated with 20 mum BITC, characterized by the appearance of phosphatidylserine on the outer surface of the plasma membrane and caspase-3 activation, whereas no caspase activation and propidium iodide incorporation into cell were detected with 50 mum BITC that induced necrosis. The mitochondrial death pathway was suggested to be involved in BITC-induced apoptosis because the treatment of cells with BITC-induced caspase-9-dependent apoptosis and mitochondrial transmembrane potential (Delta Psi m) alteration. We demonstrated here for the first time that BITC directly modifies mitochondrial functions, including inhibition of respiration, mitochondrial swelling, and release of cytochrome c. Moreover, glutathione depletion by diethyl maleate significantly accelerated BITC-triggered apoptosis, suggesting the involvement of a redox-dependent mechanism. This was also implicated by the observations that intracellular accumulation of reactive oxygen species, including superoxide (O(2)) and hydroperoxides (HPOs), was indeed detected in the cells treated with BITC and that the intracellular HPO level was significantly attenuated by pretreatment with N-acetylcysteine. The treatment with a pharmacological scavenger of O(2), Tiron, also diminished the HPO formation by approximately 80%, suggesting that most of the HPOs were H(2)O(2) derived from the dismutation of O(2). These results suggest that BITC induces apoptosis through a mitochondrial redox-sensitive mechanism.

Cell death: Current difficulties in discriminating apoptosis from necrosis in the context of pathological processes in vivo

The term apoptosis was proposed to define a type of cell death morphologically, biochemically, and molecularly distinct from necrosis, which plays a fundamental regulatory function in the control of the overall size of cell populations, being complementary but opposite to cell proliferation [Kerr et al. (1972): Br J Cancer 26:239-257]. This view has led to the appreciation that apoptosis is an integral part of normal biological processes and may impact on disease states. Introduction of the concept of apoptosis has raised great interest and many studies have been aimed to the identification of genes responsible for the induction of cell death. Indeed, over the past few years, many genes whose expression is associated with cell death have been described, and the molecular mechanisms underlying cell death have been, in some circumstances, clearly established. However, it is now evident that extension of the conclusions achieved by studies performed with highly selected in vitro systems (simple systems), to in vivo conditions (complex systems), has generated a certain degree of confusion. This is in part due to the indiscriminate use of the term apoptosis and to the uncertainty whether apoptosis is always different from necrosis, and, if this is the case, to the lack of well established criteria to discriminate the two processes; in addition, it still remains to be established whether both types of cell death, although different, could be induced simultaneously by the same agent, depending on the cell type and the experimental condition used. The distinction between apoptosis and necrosis, is not simply a problem of terminology; if necrosis and apoptosis are different from a mechanistic point of view, and if necrosis is merely the passive result of cellular injury (still to be shown), it becomes critical to discriminate between the two processes, in order to understand how to modulate apoptosis in view of its potential therapeutic use. This review will summarize existing informations and discuss some of the conflicting issues related to cell death in the liver.