Relative reactivity of vitamin A versus a mixture of beta-carotene geometric isomers with electrochemically generated superoxide and hydroperoxyl radicals

The present study comprises a kinetic comparison of the reactivity of elect rochemically generated superoxide, O-2(.-), and hydroperoxyl, HO2., radical s toward a mixture of beta -carotene geometric isomers versus all-trans-ret inol (vitamin A). Rate constants were determined by computer simulation of experimental cyclic voltammetric data. It is reported that all-trans-retino l reacts more readily with both O-2(.-) and HO2. than a mixture of geometri c beta -carotene isomers. Specifically, the latter is unreactive at less th an or equal to 25 mM with O-2(.-) within the timescale of cyclic voltammetr y, while it reacts with HO2. at least an order of magnitude slower than all -trans-retinol. Our results indicate that all-trans-retinol is a better rad ical scavenger than a mixture of geometric beta -carotene isomers and paral lel the results of a recent epidemiological study which has shown that vita min A may be a better anticarcinogenic agent than beta -carotene. (C) 2001 Elsevier Science Ltd. All rights reserved.