# Reactive oxygen species and peroxynitrite in acetaminophen-induced liver injury: Lipid peroxidation and ferroptosis-like cell death

## TL;DR

This paper reviews how acetaminophen overdose causes liver injury and compares it to a type of cell death called ferroptosis.

## Contribution

The paper clarifies the distinction between APAP-induced necrosis and ferroptosis, highlighting conditions under which the latter may occur.

## Key findings

- APAP-induced liver injury involves glutathione depletion and peroxynitrite formation but not impaired GPX4 activity.
- Ferrous iron can trigger lipid peroxidation and switch APAP-induced cell death to a ferroptosis-like mode.
- Under normal conditions, APAP hepatotoxicity does not involve ferroptosis.

## Abstract

Acetaminophen (APAP) overdose is a clinically relevant model of drug hepatotoxicity and acute liver failure. After decades of research, many aspects of the mechanism of APAP-induced liver injury are well established. These include the cytochrome P450 2E1-mediated formation of a reactive metabolite, hepatic glutathione depletion, mitochondrial protein adduct formation with oxidant stress and peroxynitrite formation, iron-catalyzed protein nitration in mitochondria, the opening of the mitochondrial permeability transition pore, and release of mitochondrial intermembrane proteins including endonuclease G, which translocate to the nucleus and cause DNA fragmentation, the final step of cell necrosis signaling. However, the mode of cell death remains controversial, as there are many overlaps with apoptosis, necroptosis, and pyroptosis. More recently, ferroptosis has come into focus as a popular cell death mode, creating a new controversial topic. The current review addresses some of the similarities and differences between ferroptosis and APAP-induced necrosis. For example, there is extensive glutathione depletion, but glutathione peroxidase 4 activity is not impaired; there is oxidant stress, but superoxide is used to form peroxynitrite; and there is evidence for an important role of ferrous iron as a catalyst for protein nitration. Moreover, lipid peroxidation is very limited, and excess Vitamin E does not protect. However, cotreatment of an APAP overdose with exogenous ferrous iron can induce extensive lipid peroxidation and switch the mode of cell death. Thus, APAP hepatotoxicity does not involve ferroptosis under normal, clinically relevant conditions, but a change in co-ingested supplements can trigger a switch to ferroptosis-like cell death.