Mechanism of ziram-induced apoptosis in human natural killer cells.

We previously found that ziram, a dithiocarbamate fungicide, significantly inhibited natural killer (NK) activity in a dose-dependent manner. To explore the mechanism of this inhibition, we investigated ziram-induced apoptosis in human NK cells. Human NK-92MI cells were treated with ziram at 0.0625-4 µM for 2-64 h. Apoptosis was determined by FITC-Annexin-V/PI staining. To explore the mechanism of apoptosis, intracellular levels of active caspases 3, 3/7, 8, and 9 and pan-caspase and mitochondrial cytochrome-c release were determined by flow cytometry. Disruption to mitochondrial transmembrane potential was determined with a MitoLight? Apoptosis Detection Kit. It was found that ziram induced apoptosis in a dose- and time-dependent manner in human NK cells. Ziram increased the intracellular levels of active caspases 3, 3/7, 8, and 9 and pan-caspase in a dose-dependent manner, and a caspase-3 inhibitor, Z-DEVD-FMK, and a general caspase inhibitor, Z-VAD-FMK, partially but significantly inhibited the apoptosis. Ziram also disrupted mitochondrial transmembrane potential and caused mitochondrial cytochrome-c release in a dose-dependent manner. These findings indicate that ziram can induce apoptosis in human NK cells, and the apoptosis is at least mediated by both the caspase-cascade and the mitochondria/cytochrome-c pathways.