Protective Effect of the Ethyl Acetate Fraction of Sargassum muticum Against Ultraviolet B–Irradiated Damage in Human Keratinocytes

The aim of this study was to investigate the cytoprotective properties of the ethyl acetate fraction of Sargassum muticum (SME) against ultraviolet B (UVB)-induced cell damage in human keratinocytes (HaCaT cells). SME exhibited scavenging activity toward the 1,1-diphenyl-2-picrylhydrazyl radicals and hydrogen peroxide (H2O2) and UVB-induced intracellular reactive oxygen species (ROS). SME also scavenged the hydroxyl radicals generated by the Fenton reaction (FeSO4 + H2O2), which was detected using electron spin resonance spectrometry. In addition, SME decreased the level of lipid peroxidation that was increased by UVB radiation, and restored the level of protein expression and the activities of antioxidant enzymes that were decreased by UVB radiation. Furthermore, SME reduced UVB-induced apoptosis as shown by decreased DNA fragmentation and numbers of apoptotic bodies. These results suggest that SME protects human keratinocytes against UVB-induced oxidative stress by enhancing antioxidant activity in cells, thereby inhibiting apoptosis

Peroxiredoxin 6 phospholipid hydroperoxidase activity in the repair of peroxidized cell membranes

Although lipid peroxidation associated with oxidative stress can result in cellular death, sub-lethal lipid peroxidation can gradually resolve with return to the pre-exposure state. We have shown that resolution of lipid peroxidation is greatly delayed in lungs or cells that are null for peroxiredoxin 6 (Prdx6) and that both the phospholipase A2 and the GSH peroxidase activities of Prdx6 are required for a maximal rate of recovery. Like other peroxiredoxins, Prdx6 can reduce H2O2 and short chain hydroperoxides, but in addition can directly reduce phospholipid hydroperoxides. This study evaluated the relative role of these two different peroxidase activities of Prdx6 in the repair of peroxidized cell membranes. The His26 residue in Prdx6 is an important component of the binding site for phospholipids. Thus, we evaluated the lungs from H26A-Prdx6 expressing mice and generated H26A-Prdx6 expressing pulmonary microvascular endothelial cells (PMVEC) by lentiviral infection of Prdx6 null cells to compare with wild type in the repair of lipid peroxidation. Isolated lungs and PMVEC were exposed to tert-butyl hydroperoxide and mice were exposed to hyperoxia (> 95% O2). Assays for lipid peroxidation in wild type control and mutant lungs and cells showed ~4-fold increase at end-exposure. Control lungs and cells showed gradual resolution during a post-exposure recovery period. However, there was no recovery from lipid peroxidation by H26A-Prdx6 lungs or PMVEC. These studies confirm an important role for Prdx6 in recovery from membrane lipid peroxidation and indicate that reduction of H2O2 or short chain hydroperoxides does not play a role in the recovery process. Keywords: Lipid peroxidation, Oxidant stress, Hyperoxia, Endothelial cells, Perfused lung, Histidine mutatio