Membrane curvature enhances oxidation within lipid bilayers in a composition-dependent manner.

Excessive production of reactive oxygen species (ROS) in cells results in oxidative stress, which can promote lipid oxidation in cellular membranes. This oxidation of membrane lipids accompanies various diseases and can even result in cell death through processes such as ferroptosis. The complex compositions and diverse morphologies of cellular membranes make understanding the mechanisms of lipid oxidation challenging, especially when attempting to investigate membrane composition and curvature simultaneously. Here, we utilize reconstituted lipid membranes and the fluorescent oxidation probe C11-BODIPY to quantify oxidation in lipid bilayers as functions of both lipid composition and membrane curvature. By tethering synthetic lipid vesicles to glass substrates, we were able to monitor oxidation of the fluorescent probe on a per vesicle basis using fluorescence microscopy. Our results demonstrate that highly curved membranes markedly increase both the rate and extent of oxidation across diverse membrane compositions. This effect arises from greater exposure of lipid tails to the aqueous environment, which allows more efficient transport of ROS into the hydrophobic core of the bilayer. Compositional effects on oxidation are most pronounced in membranes with low curvature (i.e., greater than 100 nm diameter) and become progressively weaker as curvature increases. We found that low to moderate cholesterol levels (i.e., 10-25 mol%) suppress curvature-dependent oxidation by tightening lipid packing, whereas high cholesterol content (i.e., 50 mol%) restores curvature sensitivity by influencing lateral lipid mobility. Together, these findings establish membrane curvature and lipid composition as interdependent determinants of oxidative susceptibility, offering new insight into how cells regulate or resist oxidative stress.