Protein and thiol oxidation in cells exposed to peroxyl radicals is inhibited by the macrophage synthesised pterin 7,8-dihydroneopterin

Abstract

Monocyte cells are exposed to a range of reactive oxygen species (ROS) when they are recruited to a site of inflammation. In this study, we have examined the damage caused to the monocyte-like cell line U937 by peroxyl radicals and characterised the protective effect of the macrophage synthesised compound 7,8-dihydroneopterin. Exposure of U937 cells to peroxyl radicals, generated by the thermolytic breakdown of 2,2'-azobis(amidinopropane) dihydrochloride (AAPH), resulted in the loss of cell viability as measured by thiazolyl blue (MTT) reduction, and lactate dehydrogenase (LDH) leakage. The major form of cellular damage observed was cellular thiol loss and the formation of reactive protein hydroperoxides. Peroxyl radical oxidation of the cells only caused a small increase in cellular lipid oxidation measured. Supplementation of the media with increasing concentrations of 7,8-dihydroneopterin significantly reduced the cellular thiol loss and inhibited the formation of the protein hydroperoxides. High performance liquid chromatography (HPLC) analysis showed 7,8-dihydroneopterin was oxidised by both peroxyl radicals and preformed protein hydroperoxides to predominately 7,8-dihydroxanthopterin. The possibility that 7,8-dihydroneopterin is a cellular antioxidant protecting macrophage proteins during inflammation is discussed.

Structural and functional properties of rice bran protein oxidized by peroxyl radicals

“…Peroxyl radicals are both major initiating factors of lipid peroxidation chain reactions and an ROS for broad protein oxidation. [21,22] Peroxyl radical further reacting with HO 2 • leads to the generation of an alkoxyl radical and its hydroxyl derivative. Among all the free radicals generated during lipid peroxidation propagation, peroxyl radicals are the key chain-propagating species, and the reaction of peroxyl radicals continues the propagation process in protein chain oxidation reactions by abstracting hydrogen atoms from protein.…”

Effects of oxidative modification on thermal aggregation and gel properties of soy protein by peroxyl radicals

“…Recent studies about lipid peroxidation product-mediated soy protein oxidation have confirmed that lipid peroxidation-derived free radicals, lipid hydroperoxides and reactive aldehydes could covalently modify soy protein and change structural characteristics of soy protein (Wu et al, 2009a(Wu et al, ,b,c, 2010. Intermediate free radicals generated during propagation of lipid peroxidation include lipid radicals, peroxyl radicals and alkoxyl radicals, in which peroxyl radicals are key chain-propagating species and reaction of peroxyl radicals constitutes propagation process in protein chain oxidation reactions (Duggan et al, 2002). Peroxyl radical-mediated protein oxidation was generally studied to investigate the roles of lipid peroxidationderived free radicals in protein oxidation (Kang et al, 2001).…”

Modulation of Free Radical Formation by Pterin Derivatives

“…Formation of protein hydroperoxides by peroxyl radicals was inhibited (30) in accordance with earlier reported scavenging of peroxyl radicals by dihydroneopterin (25). Loss of thiol groups in cells exposed to peroxyl radicals was also reduced by dihydroneopterin (31). While there was an inhibition of the loss of cell viability of monocyte-like U937 cells mediated by ferrous ions as well as hypochlorite, the effect of dihydroneopterin on hydrogen peroxide induced loss of Pteridines/Vol.…”