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Catechins are naturally occurring polyphenols, which are supposed to have antioxidative effects on foods and living cells. We examined the antioxidative effects of (+)-catechin and 3-O-acyl derivatives of (+)-catechin in combination with copper(II) [Cu(II)] ions on the formation of carbonyl groups in bovine serum albumin (BSA) at pH 7.4 by incubating in vitro for 90 min at 37°C. In the presence of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), a free radical generator, the formation of carbonyl groups in BSA, which increased time-dependently, was significantly (p<0.05) attenuated by the addition of (+)-catechin and 3-O-acyl-(+)-catechins. However, Cu(II) ions, but not Zn(II) ions, blocked the antioxidative effects of (+)-catechin and 3-O-octanoyl-(+)-catechin on the oxidative modification of BSA induced by AAPH. On the other hand, Cu(II) ions had no influence on the scavenging activity of (+)-catechin for 2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonate) cation radicals. Furthermore, in the absence of AAPH, coexistence of Cu(II) ions with (+)-catechin greatly accelerated the formation of carbonyl groups in BSA, being dependent on the concentrations of Cu(II) ions and (+)-catechin. These results suggest that Cu(II) ions could convert (+)-catechin from an antioxidant to a prooxidant in protein oxidation.

Copper(II) Ions Convert Catechins from Antioxidants to Prooxidants in Protein Carbonyl Formation