INHIBITION OF THE OXIDATIVE MODIFICATION OF LDL BY NITECAPONE

We studied in vitro the ability of nitecapone, hydroxy-5-nitrophenyl)m ethylene]-2,4-pentanedione, a novel water-soluble compound with antiox idative properties, to inhibit the LDL oxidation promoted by copper io ns, the aqueous free radical generator 2,2'-azobis(2-amidinopropane) h ydrochloride (AAPH), and mouse peritoneal macrophages. In these three oxidation systems, the extent of LDL oxidation was determined by measu ring the formation of conjugated dienes, the formation of thiobarbitur ic acid-reactive substances, the change in the electrophoretic mobilit y of LDL, and the uptake of LDL by macrophages. When LDL oxidation was promoted by copper ions, the reaction was found to be inhibited by ni tecapone added in a three- to five-molar excess of the concentration o f copper ions. The mechanism by which nitecapone exerted its antioxida tive effect in copper-mediated LDL oxidation depended on binding and r edox inactivation of the copper ions. Moreover, nitecapone released LD L-bound copper ions and so rendered the LDL particles more resistant t o oxidation. In contrast to a water-soluble alpha-tocopherol analogue that was rapidly consumed during the oxidative process, nitecapone ret ained its inhibitory effect for at least 2 days. Using immobilized met al ion affinity chromatography, we showed that nitecapone binds both c opper and iron ions, whereas its affinity for zinc ions is low. Niteca pone also inhibited LDL oxidation in the free radical-mediated oxidati on system (AAPH). In this system, nitecapone showed synergistic antiox idative action with ascorbic acid. Finally, nitecapone inhibited macro phage-mediated LDL oxidation. Accordingly, nitecapone appears to have a unique antioxidative profile in that it both selectively chelates pr o-oxidative transition metals and scavenges free radicals. Moreover, n itecapone has the potential of protecting LDL from oxidation in more c omplex biological in vitro systems in which multiple modes of oxidativ e stress act simultaneously, suggesting that this new compound, alread y tested in humans for its ability to inhibit catechol-O-methyltransfe rase activity, could potentially be used as an antioxidant drug.