Formation of Lipid-Protein Adducts in Low-Density Lipoprotein by Fluxes of Peroxynitrite and Its Inhibition by Nitric Oxide

Abstract

Peroxynitrite (PN), the product of the diffusion-limited reaction between nitric oxide (•NO) and superoxide (O•−2), represents a relevant mediator of oxidative modifications in low-density lipoprotein (LDL). This work shows for the first time the simultaneous action of low-controlled fluxes of PN and •NO on LDL oxidation in terms of lipid and protein modifications as well as oxidized lipid-protein adduct formation. Fluxes of PN (e.g., 1 μM min−1) initiated lipid oxidation in LDL as measured by conjugated dienes and cholesteryl ester hydroperoxides formation. Oxidized-LDL exhibited a characteristic fluorescent emission spectra (λexc = 365 nm, λmax = 417 nm) in parallel with changes in both the free amino groups content and the relative electrophoretic mobility of the particle. Physiologically relevant fluxes of •NO (80–300 nM min−1) potently inhibited these PN-dependent oxidative processes. These results are consistent with PN-induced adduct formation between lipid oxidation products and free amino groups of LDL in a process prevented by the simultaneous presence of •NO. The balance between rates of PN and •NO production in the vascular wall will critically determine the final extent of LDL oxidative modifications leading or not to scavenger receptor-mediated LDL uptake and foam cell formation.