Arsenic trioxide (As2O3) induced calcium signals and cytotoxicity in two human cell lines: SY-5Y neuroblastoma and 293 embryonic kidney (HEK)

Arsenic trioxide (As2O3) has anticancer properties; however, its use also leads to neuro-, hepato- or nephro-toxicity, and therefore, it is important to understand the mechanism of As2O3 toxicity. We studied As2O3 influence on intracellular calcium ([Ca2+]i) homeostasis of human neuroblastoma SY-5Y and embryonic kidney cells (HEK 293).We also relate the As2O3 induced [Ca2+]i modifications with cytotoxicity.We used Ca2+ sensitive dyes (fluo-4 and rhod-2) combined with laser scanning microscopy or fluorescence activated cell sorting to measure Ca2+ changes during the application of As2O3 and we approach evaluation of cytotoxicity.As2O3 (1 μM) increased [Ca2+]i in SY-5Y and HEK 293 cells. Three forms of [Ca2+]i-elevations were found: (1) steady-state increases, (2) transient [Ca2+]i-elevations and (3) Ca2+-spikes. [Ca2+]i modifications were independent from extracellular Ca2+ but dependent on internal calcium stores. The effect was not reversible. Inositol triphosphate (IP3) and ryanodine (Ry) receptors are involved in regulation of signals induced by As2O3. 2-APB and dantrolene significantly reduced the [Ca2+]i-rise (p < 0.001, t-test) but did not completely abolish [Ca2+]i-elevation or spiking. This indicates that other Ca2+ regulating mechanisms are involved. In cytotoxicity tests As2O3 significantly reduced cell viability in both cell types. Staining with Hoechst 33342 showed occurrence of apoptosis and DNA damage.Our data suggest that [Ca2+]i is an important messenger in As2O3 induced cell death.