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Inhibition of protein oxidation by the macrophage-synthesised antioxidant 7,8-dihydroneopterin

Protein is the pivotal component involved in most cellular activities. As the most abundant cellular molecule, it is the most likely target of any reactive oxygen species (ROS).1 Often considered to be a passive target during free radical exposure, there is now considerable evidence showing ROS damage to proteins leads to the formation of reactive protein bound DOPA2 and protein hydroperoxides.3 Both these reactive protein products of free radical damage to proteins can form secondary radical products, causing further free radical damage. DOPA has been shown to enhance Fenton reactions by reducing transition metals causing oxidation of DNA.4,5 Protein hydroperoxides consume ascorbate and thiol groups,3 crosslink DNA6 and damage cellular systems.7 Cells should have evolved mechanisms to limit or inhibit the formation of these reactive products of free radical damage. We would expect immune cells, which are exposed to extreme concentrations of ROS in sites of inflammation, to have some type of additional protective mechanism. We have investigated the macrophage-synthesised antioxidant 7,8-dihydroneopterin (7,8-NP) as a possible inhibitor of protein oxidation using a number of cellular and non-cellular systems. 7,8-NP is a potent peroxyl radical scavenger capable of inhibiting low density lipoprotein oxidation8 and iron mediated lipid peroxidation of cellular membranes.9 Micromolar concentrations of 7,8NP suppress dityrosine formation in hydrogen peroxide treated red blood cell ghosts.10 We report here the 7,8-NP mediated inhibition of protein hydroperoxide formation on bovine serum albumin (BSA) exposed to peroxyl radicals and hydroxyl radicals.