Susceptibility of plasma to ferrous iron/hydrogen peroxide-mediated oxidation: Demonstration of a possible Fenton reaction

The aim of our study was to evaluate a model system by using iron in the peroxidation of plasma. Lipid peroxidation was monitored by fluorometric measurement of lipid peroxides (LPO). Plasma coincubated with Fe²⁺ and H₂O₂ had a 268% increase in plasma LPO after 1 h. The optimum concentrations were 0.42 mmol/L Fe²⁺ and 0.73 mol/L H₂O₂. Coincubation of plasma with these concentrations of Fe²⁺ and H₂O₂ separately resulted in no increase in plasma LPO. The increase in plasma LPO after oxidation with Fe²⁺/H₂O₂ was paralleled by a decrease in plasma polyunsaturated fatty acids, an increase in the relative electrophoretic mobility of low-density lipoprotein (LDL), and decreases in apolipoprotein (apo) B-100 and apo A-I immunoreactivity. In vitro oxidation of LDL and high-density lipoprotein separately with this system produced increases of LPO of 246% and 128%, respectively. LPO formation in plasma was inhibited by catalase, desferrioxamine, and mannitol, but not by superoxide dismutase. Hydroxyl radical generation with Fe²⁺/H₂O₂ was evidenced by fragmentation of deoxyribose. We conclude that the Fe²⁺/H₂O₂ system, possibly by a Fenton reaction mechanism, resulted in significant plasma oxidation. This model system may be useful for examining lipid peroxidation in clinical investigations.