Peroxynitrite-mediated α-tocopherol oxidation in low-density lipoprotein: a mechanistic approach

• Published in: Free radical biology & medicine Vol. 36; no. 2; pp. 152 - 162
• Main Authors: Botti, Horacio, Batthyány, Carlos, Trostchansky, Andrés, Radi, Rafael, Freeman, Bruce A., Rubbo, Homero
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.01.2004
• Subjects: alpha-Tocopherol - metabolism; Antioxidant; Ascorbate; Ascorbic Acid - pharmacology; Carbon Dioxide - pharmacology; Carbonate radical; Free radical; gamma-Tocopherol - metabolism; Humans; Kinetics; Lipid Peroxidation - drug effects; Lipoproteins, LDL - metabolism; Low-density lipoprotein oxidation; Nitric oxide; Nitric Oxide - pharmacology; Oxidation-Reduction - drug effects; Peroxynitrite; Peroxynitrous Acid - administration & dosage; Peroxynitrous Acid - antagonists & inhibitors; Peroxynitrous Acid - pharmacology; α-Tcopherol; γ-Tcopherol; NO; DETA NONOate; Ascorbate; Low-density lipoprotein oxidation; α-TOH; Free radical; Carbonate radical; ONOOH; LDL; OH; ONOO; CL-OOH; O 2; DTPA; Peroxynitrite; α-Tcopherol; γ-TOH; γ-Tcopherol; Antioxidant; LOO; apo B-100; Nitric oxide; NO 2; α-TQ; SIN; NOC-12
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2003.10.006

Previous reports proposed that peroxynitrite (ONOO −) oxidizes α-tocopherol (α-TOH) through a two-electron concerted mechanism. In contrast, ONOO − oxidizes phenols via free radicals arising from peroxo bond homolysis. To understand the kinetics and mechanism of α-TOH and γ-tocopherol (γ-TOH) oxidation in low-density lipoprotein (LDL) (direct vs. radical), we exposed LDL to ONOO − added as a bolus or an infusion. Nitric oxide (·NO), ascorbate and CO 2 were used as key biologically relevant modulators of ONOO − reactivity. Although ∼80% α-TOH and γ-TOH depletion occurred within 5 min of incubation of 0.8 μM LDL with a 60 μM bolus of ONOO −, an equimolar infusion of ONOO − over 60 min caused total consumption of both antioxidants. γ-Tocopherol was preserved relative to α-TOH, probably due to γ-tocopheroxyl radical recycling by α-TOH. α-TOH oxidation in LDL was first order in ONOO − with ∼12% of ONOO − maximally available. Physiological concentrations of ·NO and ascorbate spared both α-TOH and γ-TOH through independent and additive mechanisms. High concentrations of ·NO and ascorbate abolished α-TOH and γ-TOH oxidation. Nitric oxide protection was more efficient for α-TOH in LDL than for ascorbate in solution, evidencing the kinetically highly favored reaction of lipid peroxyl radicals with ·NO than with α-TOH as assessed by computer-assisted simulations. In addition, CO 2 (1.2 mM) inhibited both α-TOH and lipid oxidation. These results demonstrate that ONOO − induces α-TOH oxidation in LDL through a one-electron free radical mechanism; thus the inhibitory actions of ·NO and ascorbate may determine low α-tocopheryl quinone accumulation in tissues despite increased ONOO − generation.