Cobalt induces oxidative stress in isolated liver mitochondria responsible for permeability transition and intrinsic apoptosis in hepatocyte primary cultures

Abstract

a b s t r a c tIt is well established that cobalt mediates the occurrence of oxidative stress which contributes to cell toxicity and death. However, the mechanisms of these effects are not fully understood. This investigation aimed at establishing if cobalt acts as an inducer of mitochondrial-mediated apoptosis and at clarifying the mechanism of this process.Cobalt, in the ionized species Co 2+ , is able to induce the phenomenon of mitochondrial permeability transition (MPT) in rat liver mitochondria (RLM) with the opening of the transition pore. In fact, Co 2+ induces mitochondrial swelling, which is prevented by cyclosporin A and other typical MPT inhibitors such as Ca 2+ transport inhibitors and bongkrekic acid, as well as anti-oxidant agents. In parallel with mitochondrial swelling, Co 2+ also induces the collapse of electrical membrane potential. However in this case, cyclosporine A and the other MPT inhibitors (except ruthenium red and EGTA) only partially prevent « drop, suggesting that Co 2+ also has a proton leakage effect on the inner mitochondrial membrane. MPT induction is due to oxidative stress, as a result of generation by Co 2+ of the highly damaging hydroxyl radical, with the oxidation of sulfhydryl groups, glutathione and pyridine nucleotides. Co 2+ also induces the release of the pro-apoptotic factors, cytochrome c and AIF. Incubation of rat hepatocyte primary cultures with Co 2+ results in apoptosis induction with caspase activation and increased level of expression of HIF-1␣.All these observations allow us to state that, in the presence of calcium, Co 2+ is an inducer of apoptosis triggered by mitochondrial oxidative stress.

The cell death response to the ROS inducer, cobalt chloride, in neuroblastoma cell lines according to p53 status

“…AIF was discovered as a mitochondrial proapoptotic factor, which is translocated first to the cytosol and to the nucleus, and induces cell death signaling (19). CoCl 2 has been reported to induce a ∆Ψ mt loss, followed by AIF release (2). In SHSY5Y cells, we did not observe any AIF release from the mitochondria to nuclei at different times during CoCl 2 treatment.…”

“…It is well known that CoCl 2 , the commonly used hypoxia mimetic agent, induces cell death through oxidative stress by increasing ROS generation (2,31). A part of its effect was mediated by stabilizing of HIF1α and the activation of downstream signaling.…”

“…At millimolar doses, cobalt chloride (CoCl 2 ) can mimic at least partially the effects of hypoxic agents, as it interacts with HIF-1α, and prevents its degradation by prolyl hydroxylase (1,2). In addition, it generates reactive oxygen species (ROS) (3) through various mechanisms.…”

“…The involvement of the apoptosis inducing factor (AIF) in mitochondrial downstream pathways, in the absence of caspase activation has been investigated extensively (19). The involvement of AIF has been described in numerous models of cell death including metals, such as As203 (20) or CoCl 2 (2,6). Moreover, data have suggested that caspase-independent cell death can also correspond to an autophagic process (21).…”

Silver nanoparticles inhibit the function of hypoxia-inducible factor-1 and target genes: insight into the cytotoxicity and antiangiogenesis

“…CoCl 2 artificially induces hypoxia, a process also known as "pseudohypoxia", by blocking the degradation of HIF-1α, which leads to a accumulation of HIF-1α in the cell. 45,46 Many reports have indicated that both CoCl 2 and hypoxia regulate a similar group of genes on a global gene expression level. 47 In order to confirm the findings obtained under hypoxic conditions, we also investigated the effects of AgNPs on the transcriptional activity of HIF under pseudohypoxia conditions induced by CoCl 2 .…”