The study of the mechanism of arsenite toxicity in respiration-deficient cells reveals that NADPH oxidase-derived superoxide promotes the same downstream events mediated by mitochondrial superoxide in respiration-proficient cells

摘要

We herein report the results from a comparative study of arsenite toxicity in respiration-proficient (RP) and - deficient (RD) U937 cells. An initial characterization of these cells led to the demonstration that the respiration-deficient phenotype is not associated with apparent changes in mitochondrial mass and membrane potential. In addition, similar levels of superoxide (O-2(center dot-)) were generated by RP and RD cells in response to stimuli specifically triggering respiratory chain-independent mitochondrial mechanisms or extramitochondrial, NADPH-oxidase dependent, mechanisms. At the concentration of 2.5 mu M, arsenite elicited selective formation of O-2(center dot-) in the respiratory chain of RP cells, with hardly any contribution of the above mechanisms. Under these conditions, O-2(center dot-) triggered downstream events leading to endoplasmic reticulum (ER) stress, autophagy and apoptosis. RD cells challenged with similar levels of arsenite failed to generate O-2(center dot-) because of the lack of a functional respiratory chain and were therefore resistant to the toxic effects mediated by the metalloid. Their resistance, however, was lost after exposure to four fold greater concentrations of arsenite, coincidentally with the release of O-2(center dot-) mediated by NADPH oxidase. Interestingly, extramitochondrial O-2(center dot-) triggered the same downstream events and an identical mode of death previously observed in RP cells.