il\VOLVEMENT OF RETII\OIC ACID II{ - MSpace at the University of ...

of a large array of cellular abnormalities (Mukai and Goldstein 1976; Shamberger et al.
1974;Teebor et al. 1988).
II.c. Antioxidant reserve
Every living form is constantly attacked by the exogenous and endogenously
generated free radicals. However, physiological systems are in place to ensure the
protection against these damaging molecules. This is achieved by the activity of several
enzymatic and nonenzymatic intracellular antioxidant protective systems (Freeman and
Crapo 1982). Three intracellular enzymes play a crucial role in the endogenous
antioxidant enzl'rnatic protection: superoxide dismutase (SOD), glutathione peroxidase
(GSHPx) and catalase. This battery of endogenous antioxidants, also known as
antioxidant reserve, ensure the maintenance of optimal milieu for the functioning of
essential physiological processes (Singal and Kirshenbaum 1990). Another group of
intracellular antioxidants are nonenzymatíc compounds such as tocopherol (vitamin E),
carotenoids (provitamin A compounds), retinol (vitamin A), melatonin, ubiquinol,
ascorbic acid (vitamin C) and glutathione (Kaul et al. 1993; Palace et al. 1999). Despite
the differences between their mechanisms of action, one general mechanism of
antioxidant protection is proposed. Antioxidative protection is achieved by the
nonenzSrmatic antioxidant's ability to quench potentialiy damaging free radicals and
prevent the propagation of free-radical induced cellular damage. This reactive oxidant is
then converted into a new non-reactive product (Halliwell and Gutteridge i990; Palace et
aL 1999; Tesoriere et al. 1 993).
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