Cxc. Santos et al., Uric acid oxidation by peroxynitrite: Multiple reactions, free radical formation, and amplification of lipid oxidation, ARCH BIOCH, 372(2), 1999, pp. 285-294
Uric acid has been considered to be an efficient scavenger of peroxynitrite
but the reaction between urate and peroxynitrite has been only partially c
haracterized. Also, previous studies have indicated that urate may increase
peroxynitrite-mediated oxidation of low density lipoprotein (LDL). Here, w
e examined the reaction between urate and peroxynitrite by combining kineti
c, oxygen consumption, spin trapping, and product identification studies; i
n parallel, are tested the effect of urate upon peroxynitrite-mediated lipi
d oxidation. Our results demonstrated that urate reacts with peroxynitrite
with an apparent second order rate constant of 4.8 x 10(2) M-1.s(-1) in a c
omplex process, which is accompanied by oxygen consumption and formation of
allantoin, alloxan, and urate-derived radicals. The main radical was ident
ified as the aminocarbonyl radical by the electrospray mass spectra of its
5,5-dimethyl-l-pyrroline N-oxide adduct. Mechanistic studies suggested that
urate reacts with peroxynitrous acid and with the radicals generated from
its decomposition to form products that can further react with peroxynitrit
e anion. These many reactions may explain the reported efficiency of urate
in inhibiting some peroxynitrite-mediated processes. Production of the amin
ocarbonyl radical, however, may propagate oxidative reactions. We demonstra
ted that this radical is likely to be the species responsible for the effec
ts of urate in amplifying peroxynitrite-mediated oxidation of liposomes and
LDL, which was monitored by the formation of lipid peroxides and thiobarbi
turic acid-reactive substances. The aminocarbonyl radical was not detectabl
e during urate attack by other oxidants and consequently it is unlikely to
be responsible for all previously described prooxidant effects of uric acid
. (C) 1999 Academic Press.