NADH oxidation by peroxynitrite. II Effects of flavonoids.

ALVAREZ S; VALDEZ L; SCHÖPFER F; PODEROSO JJ; BOVERIS A

Santa Bárbara, EEUU

Congreso; World Congress “Oxidant and antioxidants in Biology"; 1999

Oxygen Club of California

Peroxynitrite (ONOO­-) is a powerful oxidant (E (ONOO-­/·NO2) = +1.4 V) formed in a diffusion-controlled termination reaction of the free radicals nitric oxide (·NO) and superoxide anion (O2·­). Some flavonoids have been reported to posess biological activities, as free radical scavenging. The aim of the present work is to compare the reducing activities of several favonoids ((+) catechin, (-) epicatechin, caffeic acid, and chlorogenic acid) in their reactions with ONOO-­. Ginkgo biloba and grape seeds extracts, that contain flavonoids among the active compounds, were also tested for ONOO-­ scavenging activity. We used a model of simple competition that involves the participation of ONOO-­, NADH, and the flavonoids as competitive reductants for ONOO­. An indirect fluorometric technique was used to estimate the IC50 of the flavonoids tested. The reaction of ONOO-­ with NADH was followed at 37°C, using 340 and 463 nm as excitation and emission wavelengths, respectively. The reaction medium consisted of 50 mM phosphate buffer, 0.1 mM DTPA, pH 7.0, 100 µM NADH and 100-700 µM ONOO-­. The IC50 calculated were: 275 ± 23 µM for (+) catechin, 313 ± 23 µM for (-) epicatechin, 144 ± 29 µM for caffeic acid, and 173 ± 36 µM for chlorogenic acid. The IC50 calculated for the extracts were: 85 ± 11 µg/ml for Ginkgo biloba and 118 ± 16 µg/ml for grape seed extract. Among the number of flavonoids tested the following order of potency was observed: caffeic acid > chlorogenic acid > (+) catechin > (-) epicatechin, and Ginkgo biloba extract > grape seed extract.