Lipid Peroxidation Mechanisms and Their Contribution to Ferroptosis

Abstract

The attack of reactive oxygen species (ROS) on reactive lipids leads to free radical chain reactions with molecular oxygen, a process termed lipid peroxidation. Increased lipid peroxidation is associated with many human diseases, including cancer, diabetes, neurodegenerative diseases, and, more recently, cell death. The rate-determining step in lipid peroxidation reactions is usually the propagation step in which the peroxyl radical can undergo either hydrogen(H)-atom transfer or peroxyl-radical addition reaction. The rate constants of the H-atom transfer process for several reactive lipids and sterols have been measured using the peroxyl radical clock method. However, no method was available to study the peroxyl-radical addition reaction. In this dissertation, I aim to elucidate lipid peroxidation mechanisms and their relevance in ferroptosis, a form of regulated cell death driven by lipid peroxidation of polyunsaturated fatty acids (PUFAs). In this work, I modified the original linoleate-based peroxyl radical clock to enable the measurement of both the H-atom transfer and peroxyl-radical addition reactions in the propagation step. The new probe was then applied to study lipid peroxidation mechanism and kinetics for a variety of biologically important lipids, including conjugated fatty acids, sterols, coenzyme Q10, and lipophilic vitamins, such as vitamin D3 and A, for the first time. Next, I elucidated the effects of various unsaturated lipids in sensitizing ferroptosis. I then sought to elucidate the mechanism underlying the potency of the different ferroptosis-inducing conjugated and nonconjugated PUFAs. Next, I investigated the relevance of ER stress and unfolded protein response in ferroptosis execution. Finally, I summarize all the findings of this collective work and propose how research in this area can continue to expand.