Fish oil nano-emulsion kills macrophage: Ferroptosis triggered by catalase-catalysed superoxide eruption

•Catalase-induced vigorous superoxide production in fish oil nano-emulsion.•The resulting superoxide caused fatal oxidative damages in murine macrophage.•The fish oil induced cell death can be inhibited by a catalase-specific inhibitor.•The cell death involves ferroptosis but not apoptosis.•A hidden health risk of the fish oil nano-emulsion was discovered.