t-BuOOH induces ferroptosis in human and murine cell lines.

Reactive oxygen species (ROS)-induced apoptosis has been extensively studied. Increasing evidence suggests that ROS, for instance, induced by hydrogen peroxide (HO), might also trigger regulated necrotic cell death pathways. Almost nothing is known about the cell death pathways triggered by tertiary-butyl hydroperoxide (t-BuOOH), a widely used inducer of oxidative stress. The lipid peroxidation products induced by t-BuOOH are involved in the pathophysiology of many diseases, such as cancer, cardiovascular diseases, or diabetes. In this study, we exposed murine fibroblasts (NIH3T3) or human keratinocytes (HaCaT) to t-BuOOH (50 or 200 μM, respectively) which induced a rapid necrotic cell death. Well-established regulators of cell death, i.e., p53, poly(ADP)ribose polymerase-1 (PARP-1), the stress kinases p38 and c-Jun N-terminal-kinases 1/2 (JNK1/2), or receptor-interacting serine/threonine protein kinase 1 (RIPK1) and 3 (RIPK3), were not required for t-BuOOH-mediated cell death. Using the selective inhibitors ferrostatin-1 (1 μM) and liproxstatin-1 (1 μM), we identified ferroptosis, a recently discovered cell death mechanism dependent on iron and lipid peroxidation, as the main cell death pathway. Accordingly, t-BuOOH exposure resulted in a ferrostatin-1- and liproxstatin-1-sensitive increase in lipid peroxidation and cytosolic ROS. Ferroptosis was executed independently from other t-BuOOH-mediated cellular damages, i.e., loss of mitochondrial membrane potential, DNA double-strand breaks, or replication block. HO did not cause ferroptosis at equitoxic concentrations (300 μM) and induced a (1) lower and (2) ferrostatin-1- or liproxstatin-1-insensitive increase in lipid peroxidation. We identify that t-BuOOH and HO produce a different pattern of lipid peroxidation, thereby leading to different cell death pathways and present t-BuOOH as a novel inducer of ferroptosis.