Radical-scavenging and iron-chelating properties of carvedilol, an antihypertensive drug with antioxidative activity

Carvedilol, an antihypertensive agent, has been in clinical use for several years. In addition to its function as a β-blocker, carvedilol has been shown to act as an antioxidant. However, there is some controversy as to how carvedilol achieves its antioxidative ability: by radical scavenging or ion chelation? We therefore used a method of radical generation independent of metal ions to investigate the antioxidative properties of carvedilol. We showed that carvedilol decreased low-density lipoprotein (LDL) oxidation induced by a peroxyl radical-generating system [2,2′-azobis(2-amidinopropane)hydrochloride]. Formation of thiobarbituric acid-reactive substances, lipid hydroperoxides, and newly generated epitopes on oxidised LDL was used to monitor LDL oxidation. We further showed that carvedilol was consumed during reaction with peroxyl radicals. However, carvedilol showed no reaction with nitrogen-centered radicals (1,1-diphenyl-2-picrylhydrazyl and 2,2′-azino-di-[3-ethylbenzthiazoline sulphonate]), which are often used in assays for determining antioxidative properties. On the other hand, we found that carvedilol acted as a chelator of ferric ions. Using mass spectrometry and NMR spectroscopy, we observed complex formation with free and acetylacetonate-complexed ferric ions. The binding constant with Fe 3+ was in the range of 10 5 L/mol. From our data, we concluded that carvedilol acts as both a metal chelator and a radical scavenger in vitro. However, it is selective in reacting with different radicals and is not an electron-donating radical scavenger as is α-tocopherol. Therefore, taking into account the low physiological concentration, the antioxidative properties reported earlier may not solely be explained by its radical-scavenging activity.