Nitrite–glucose–glucose oxidase system directly induces rat heart homogenate oxidation and tyrosine nitration: Effects of some flavonoids

Protein tyrosine nitration is a common post-translational modification occurring under conditions of nitrative/oxidative stress in a number of diseases. It has been found that in the presence of nitrite and hydrogen peroxide, hemoprotein catalyzes protein tyrosine nitration. In this paper, it was found that in heart homogenate, protein nitration and oxidation could be induced by a nitrite–glucose–glucose oxidase system without addition of exogenous heme or hemoprotein. Several structural diversity flavonoids (quercetin, rutin, baicalein, baicalin, apigenin, puerarin, and (+)-catechin) could, more or less, protect rat heart homogenate from oxidative and nitrative injury induced by nitrite–glucose–glucose oxidase in vitro. The inhibitory effects of flavonoids on protein nitration and lipid peroxidation were consistent with their antioxidant activities, whereas the inhibitory effects on protein oxidation were almost contrary to their antioxidant activities. These results mean that nitrite–glucose–glucose oxidase system can cause heart homogenate protein nitration and protein oxidation in different pathways, and those flavonoids with strong antioxidant activities may contribute their protective effect partly through inhibiting protein nitration.