Flavonoids and urate antioxidant interplay in plasma oxidative stress

Flavonoids are naturally occurring plant compounds with antioxidant propert ies. Their consumption has been associated with the protective effects of c ertain diets against some of the complications of atherosclerosis. Low-dens ity lipoprotein (LDL) oxidative modification is currently thought to be a s ignificant event in the atherogenic process. Most of the experiments concer ning the inhibition of LDL oxidation used isolated LDL. We used diluted hum an whole plasma to study the influence of flavonoids on lipid peroxidation (LPO) promoted by copper, and their interaction with uric acid, one of the most important plasma antioxidants. Lipid peroxidation was evaluated by the formation of thiobarbituric acid reactive substances (TBARS) and of free m alondialdehyde (MDA). The comparative capability of the assayed flavonoids on copper (II) reduction was tested using the neocuproine colorimetric test . In our assay system, urate disappears and free MDA and TBARS formation in crease during the incubation of plasma with copper. Most of the tested flav onoids inhibited copper-induced LPO. The inhibition of LPO by flavonoids co rrelated positively with their capability to reduce copper (II). The urate consumption during the incubation of plasma with copper was inhibited by my ricetin, quercetin and kaempferol. The inhibition of urate degradation by f lavonoids correlated positively with the inhibition of LPO. Urate inhibited the copper-induced LPO in a concentration-dependent mode. Luteolin, rutin, catechin, quercetin had an antioxidant synergy with urate. Our results sho w that some flavonoids could protect endogenous urate from oxidative degrad ation, and demonstrate an antioxidant synergy between urate and some of the flavonoids.