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

•PAM induced cell death in human neuroblastoma SH-SY5Y cells.•PAM triggered Zn2+ liberation from intracellular Zn2+ stores.•TPEN, a cell-permeable Zn2+ chelator, protected against PAM-induced cell death.•Liberated Zn2+ elicited ROS generation, PARP-1 activation, and NAD+ and ATP loss.•Conversion of PAM stimulus to Zn2+ signal is critical for PAM cytotoxicity.

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 (Zn2+) from intracellular Zn2+ stores and to provoke Zn2+-dependent cell death. In this study, we thus examined whether Zn2+ 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 Zn2+ chelator N,N,N′,N′-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN) protected against PAM-induced cell death. Zn2+ imaging using the fluorescent Zn2+ probe FluoZin-3 revealed that PAM elicited a rise of intracellular free Zn2+. 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 Zn2+ released from intracellular Zn2+ stores serves as a key mediator of PAM-induced cell death in SH-SY5Y cells.