The marine toxin palytoxin induces necrotic death in HaCaT cells through a rapid mitochondrial damage

Palytoxin (PLTX) is one of the most toxic algal biotoxin known so far. It transforms the Na⁺/K⁺-ATPase into a cationic channel inducing a massive intracellular Na⁺ influx. However, from a mechanistic point of view, the features and the intracellular pathways leading to PLTX-induced cell death are still not completely characterized. This study on skin HaCaT keratinocytes demonstrates that PLTX induces necrosis since propidium iodide uptake was observed already after 1 h toxin exposure, an effect that was not lowered by toxin removal. Furthermore, necrotic-like morphological alterations were evidenced by confocal microscopy. Apoptosis occurrence was excluded since no caspases 3/7, caspase 8, and caspase 9 activation as well as no apoptotic bodies formation were recorded. Necrosis was preceded by a very early mitochondrial damage as indicated by JC-1 fluorescence shift, recorded already after 5 min toxin exposure. This shift was totally abolished when Na⁺ and Ca²⁺ ions were withdrawn from culture medium, whereas cyclosporine-A was ineffective, excluding the occurrence of a controlled biochemical response.