MINIREVIEW
The Role of Carbon
Dioxide in Free Radical Reactions
of the Organism
A.
VESELÁ, J. WILHELM
Department of Medical Chemistry and Biochemistry,
Second Faculty of Medicine, Charles University,
Center for Experimental Cardiovascular Research,
Prague, Czech Republic
Received August 6, 2001
Accepted November 22, 2001
Summary
Carbon dioxide interacts both with
reactive nitrogen species and reactive oxygen
species. In the presence of superoxide, NO reacts
to form peroxynitrite that reacts with CO2 to
give nitrosoperoxycarbonate. This compound
rearranges to nitrocarbonate which is prone to
further reactions. In an aqueous environment, the
most probable reaction is hydrolysis producing
carbonate and nitrate. Thus the net effect of CO2
is scavenging of peroxynitrite and prevention of
nitration and oxidative damage. However, in a
nonpolar environment of membranes, nitrocarbonate
undergoes other reactions leading to nitration of
proteins and oxidative damage. When NO reacts
with oxygen in the absence of superoxide, a
nitrating species N2O3 is formed. CO2 interacts
with N2O3 to produce a nitrosyl compound that,
under physiological pH, is hydrolyzed to nitrous
and carbonic acid. In this way, CO2 also prevents
nitration reactions. CO2 protects superoxide
dismutase against oxidative damage induced by
hydrogen peroxide. However, in this reaction
carbonate radicals are formed which can propagate
the oxidative damage. It was found that
hypercapnia in vivo protects against the damaging
effects of ischemia or hypoxia. Several
mechanisms have been suggested to explain the
protective role of CO2 in vivo. The most
significant appears to be stabilization of the
iron-transferrin complex which prevents the
involvement of iron ions in the initiation of
free radical reactions.
Key
words
CO2
· peroxynitrite · Free radicals · Oxidative
damage · Hypercapnia
Reprint
requests
Doc. Dr. J. Wilhelm, Department of Medical
Chemistry and Biochemistry, Second Faculty of
Medicine, Charles University, Plzeňská 221, 150
00 Prague 5, Czech Republic. E-mail:
jiri.wilhelm@lfmotol.cuni.cz
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