Plasma-activated medium-induced intracellular zinc liberation causes death of SH-SY5Y cells

Plasma is an ionized gas consisting of ions, electrons, free radicals, neutral particles, and photons. Plasma-activated medium (PAM), which is prepared by the irradiation of cell-free medium with non-thermal atmospheric pressure plasma, induces cell death in various types of cancer cell. Since PAM contains reactive oxygen species (ROS), its anti-cancer effects are thought to be attributable to oxidative stress. Meanwhile, oxidative stress has been shown to induce the liberation of zinc (Zn(2+)) from intracellular Zn(2+) stores and to provoke Zn(2+)-dependent cell death. In this study, we thus examined whether Zn(2+) is involved in PAM-induced cell death using human neuroblastoma SH-SY5Y cells. Exposure to PAM triggered cell death in SH-SY5Y cells. The cell-permeable Zn(2+) chelator N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN) protected against PAM-induced cell death. Zn(2+) imaging using the fluorescent Zn(2+) probe FluoZin-3 revealed that PAM elicited a rise of intracellular free Zn(2+). In addition, PAM stimulated PARP-1 activation, mitochondrial ROS generation, and the depletion of intracellular NAD(+) and ATP. These findings suggest that PAM-induced PARP-1 activation causes energy supply exhaustion. Moreover, TPEN suppressed all of these events elicited by PAM. Taken together, we demonstrated here that Zn(2+) released from intracellular Zn(2+) stores serves as a key mediator of PAM-induced cell death in SH-SY5Y cells.