Does hydrogen bonding contribute to lipoperoxidation-dependent membrane fluidity variation? An EPR-spin labeling study

Assessing Photosensitized Membrane Damage: Available Tools and Comprehensive Mechanisms

Lipids are important targets of the photosensitized oxidation reactions, forming important signaling molecules, disorganizing and permeabilizing membranes, and consequently inducing a variety of biological responses. Although the initial steps of the photosensitized oxidative damage in lipids are known to occur by both Type I and Type II mechanisms, the progression of the peroxidation reaction, which leads to important end-point biological responses, is poorly known. There are many experimental tools used to study the products of lipid oxidation, but neither the methods nor their resulting observations were critically compared. In this article, we will review the tools most frequently used and the key concepts raised by them in order to rationalize a comprehensive model for the initiation and the progression steps of the photoinduced lipid oxidation.

Lipid Hydroperoxide Compromises the Membrane Structure Organization and Softens Bending Rigidity

Lipid hydroperoxides are key mediators of diseases and cell death. In this work, the structural and dynamic perturbations induced by the hydroperoxidized POPC lipid (POPC-OOH) in fluid POPC membranes, at both 23 and 37 °C, were addressed using advanced small-angle X-ray scattering (SAXS) and fluorescence methodologies. Notably, SAXS reveals that the hydroperoxide group decreases the lipid bilayer bending rigidity. This alteration disfavors the bilayer stacking and increases the swelling in-between stacked bilayers. We further investigated the changes in the apolar/polar interface of hydroperoxide-containing membranes through time-resolved fluorescence/anisotropy experiments of the probe TMA-DPH and time-dependent fluorescence shifts of Laurdan. A shorter mean fluorescence lifetime for TMA-DPH was obtained in enriched POPC-OOH membranes, revealing a higher degree of hydration near the membrane interface. Moreover, a higher microviscosity near TMA-DPH and lower order are predicted for these oxidized membranes, at variance with the usual trend of variation of these two parameters. Finally, the complex relaxation process of Laurdan in pure POPC-OOH membranes also indicates a higher membrane hydration and viscosity in the close vicinity of the -OOH moiety. Altogether, our combined approach reveals that the hydroperoxide group promotes alterations in the membrane structure organization, namely, at the level of membrane order, viscosity, and bending rigidity.

Free radicals and polyphenols: The redox chemistry of neurodegenerative diseases

The oxidation of bioorganic materials by air and, particularly, the oxidative stress involved in the cell loss and other pathologies associated with neurodegenerative diseases (NDs) are of enormous social and economic importance. NDs generally involve free radical reactions, beginning with the formation of an initiating radical by some redox, thermal or photochemical process, causing nucleic acid, protein and lipid oxidations and the production of harmful oxidative products. Physically, persons afflicted by NDs suffer progressive loss of memory and thinking ability, mood swings, personality changes, and loss of independence. Therefore, the development of antioxidant strategies to retard or minimize the oxidative degradation of bioorganic materials has been, and still is, of paramount importance. While we are aware of the importance of investigating the biological and medical aspects of the diseases, elucidation of the associated chemistry is crucial to understanding their progression, heading to intelligent chemical intervention to find more efficient therapies to prevent or delay the onset of the diseases. Accordingly, this review aims to provide the reader with a chemical base to understand the behavior and properties of the reactive oxygen species involved and of typical radical scavengers such as polyphenolic antioxidants. Some discussion on the structures of the various species, their formation, chemical reactivities and lifetimes is included. The ultimate goal is to understand how, when and where they form, how far they travel prior to react, which molecules are their targets, and how we can, eventually, control their activity to minimize their impact by means of chemical methods. Recent strategies explore chemical modifications of the hydrophobicity of potent, natural antioxidants to improve their efficiency by fine-tuning their concentrations at the reaction site.