Inhibition of nitric-oxide-mediated apoptosis in Jurkat leukemia cells despite cytochrome c release

We have recently shown that nitric-oxide (NO)-induced apoptosis in Jurkat h uman leukemia cells requires degradation of mitochondria phospholipid cardi olipin, cytochrome c release, and activation of caspase-9 and caspase-3. Mo reover, an inhibitor of lipid peroxidation, Trolox, suppressed apoptosis in Jurkat cells induced by NO donor glycerol trinitrate. Here we demonstrate that this antiapoptotic effect of Trolox occurred despite massive release o f the mitochondrial protein cytochrome c into the cytosol and mitochondrial damage. Incubation with Trolox caused a profound reduction of intracellula r ATP concentration in Jurkat cells treated by NO. Trolox prevented cardiol ipin degradation and caused its accumulation in Jurkat cells. Furthermore, Trolox markedly down-regulated the NO-mediated activation of caspase-9 and caspase-3. Caspase-9 is known 60 be activated by released cytochrome c and together with caspase-3 is considered the most proximal to mitochondria. Ou r results suggest that the targets of the antiapoptotic effect of Trolox ar e located downstream of the mitochondria and that caspase activation and su bsequent apoptosis could be blocked even in the presence of cytochrome c re leased from the mitochondria. (C) 2001 Academic Press.