In this work, we measured the effects of pharmacological concentrations of cisplatin (cis-diaminedichloroplatinum II) on mitochondrial function, cell viability, and DNA fragmentation in Jurkat cells. The exposure of cells to 0-25 μM cisplatin for 3 h had no immediate effect on cellular mitochondrial oxygen consumption, measured using a palladium-porphyrin oxygen sensing phosphor. Similarly, the cell viability as measured by trypan blue staining was unchanged immediately following exposure to the drug, and no small DNA fragments, characteristic of drug-induced apoptosis, appeared. At 24 h after exposure to cisplatin, cellular respiration and viability decreased relative to controls and the amount of small DNA fragments, measured using quantitative agarose gel electrophoresis, was proportional to the concentration of cisplatin present during the drug exposure period. The small DNA fragments showed the banding pattern (with a spacing of ∼300 bp) characteristic of drug-induced cell death by apoptosis. The changes in respiration and DNA fragmentation correlated linearly with the amount of platinum bound to DNA, determined by atomic absorption spectroscopy immediately following drug exposure. The oxygen consumption by beef heart mitochondria was not affected 0-24 h after exposure to 25 μM cisplatin or to solutions containing the monoaquated form of the drug, suggesting that the drug does not attack the mitochondrial respiratory chain directly. Cells exposed to the peptide benzyloxycarbonyl-val-ala-asp- fluoromethyl ketone, which blocks apoptosis by the caspase pathway, showed a decrease in cisplatin-induced DNA fragmentation but not in the impairment of cellular respiration. Thus, although apoptosis is caspase-dependent, the impairment of cellular respiration is independent of the caspase system. Collectively, these results suggest that alteration in mitochondrial function is a secondary effect of cisplatin cytotoxicity in Jurkat cells.
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