Nitric oxide scavenging rates of solubilized resveratrol and flavonoids.
Relative nitric oxide scavenging rates of water-insoluble lipophilic antioxidants, such as resveratrol and flavonoids were determined using a β-cyclodextrin analog, DM-β-CD (heptakis(2,6-di-O-methyl)-β-cyclodextrin) as a solubilizer. Antioxidant-mediated decrease of NO concentration was measured with the electron spin resonance-based PTIO (2-phenyl-4,4,5,5-methylimidazoline-1-oxyl 3-oxide) method, from which scavenging rates were calculated. Because both the antioxidant and PTIO form inclusion complex with DM-β-CD, a kinetic treatment was necessary to calculate the scavenging rates. Resveratrol showed the highest NO scavenging rate among the tested antioxidants. The magnitudes of scavenging rates were in the order of: resveratrol>catechin≈myricetin>epicatechin>epigallocatechin gallate>kaempferol. This order is not in agreement with the oxygen radical scavenging rates: i.e., myricetin>epigallocatechin gallate>catechin≈epicatechin>resveratrol>kaempferol. The tested antioxidants showed lower scavenging rates than hydrophilic antioxidants such as uric acid and caffeic acids. Previous redox potential measurement of antioxidants revealed that NO scavenging occurs through non-free radical mechanism, indicating that the scavenging capacity is dependent on the nature of the scavenging reaction.