ELECTRON TRANSPORT-MEDIATED WASTEFUL CONSUMPTION OF NADH PROMOTES THELETHAL RESPONSE OF U937 CELLS TO TERT-BUTYLHYDROPEROXIDE

The toxicity of a short-term exposure to tert-butylhydroperoxide in U9 37 cells was markedly reduced by chemically or experimentally induced respiratory deficiency. Rotenone mitigated the lethal effects of the h ydroperoxide over the same concentration-range in which the complex I inhibitor inhibited oxygen utilization. U937 cells that were made resp iration deficient by growing them in the presence of either chloramphe nicol or ethidium bromide, were in both circumstances highly resistant to tert-butylhydroperoxide. The improved survival was not a direct co nsequence of the absence of electron transport, but rather was attribu table to the large amounts of NADH which accumulate in the mitochondri a of chemically hypoxic or respiration-deficient cells. Indeed, the to xicity elicited by tert-butylhydroperoxide was also abolished by suppl ementation with either of two different NADH-linked substrates, namely pyruvate or P-hydroxybutyrate. Accumulation of intramitochondrial NAD H, and the resulting cytoprotective effects, was associated with preve ntion of the loss of nonprotein sulphydryls and mitochondrial membrane potential. Neither rotenone nor pyruvate reduced the toxicity of tert -butylhydroperoxide in thiol-depleted cells. Taken together, these res ults indicate that depletion of mitochondrial NADH is a critical event in the cytotoxic response to tert-butylhydroperoxide since this pyrid ine nucleotide prevents mitochondrial dysfunction and cell death cause d by the hydroperoxide. As a consequence, in hydroperoxide-treated cel ls electron transport is highly detrimental since it consumes mitochon drial NADH.