Biochemical and Histopathological Effects of Aflatoxin on ...

4.3 The Lipid Peroxidation process
Cellular biomolecules like lipids are the most susceptible to oxidative
damage. Reaction <strong>of</strong> ROS with lipids leads to the highly damaging reaction,
lipid peroxidation. Singlet oxygen reacts with unsaturated fatty acids, forms
lipid hydroperoxides that breaks down to several products <strong>of</strong> lipid
peroxidation. (Thomas et al, 2002). The reaction sequence starts with a radical
(eg. 'OH) which removes one proton from the hydrocarbon tail <strong>of</strong> the fatty
acid leaving the radical <strong>of</strong> the acid. This radical undergoes isomerization <strong>and</strong>
oxidation with molecular oxygen yielding a peroxy radical <strong>of</strong> the fatty acid.
Peroxy radical removes protons from other molecules <strong>and</strong> become
hydroperoxide. Since this proton may originate from another fatty acid, a new
cycle is started <strong>and</strong> lipid peroxidation proceeds via a chain reaction, until the
chain is interrupted by either the dimerisation <strong>of</strong> two radicals or until the
proton is removed from a substance which forms relatively stable radicals
with low reactivity (radical scavengers). Through this chain reaction, one
initiating radical may lead to the peroxidation <strong>of</strong> hundreds <strong>of</strong> fatty acids. The
resulting hydroperoxides are unstable <strong>and</strong> decomposed by chain cleavage to a
very complex mixture <strong>of</strong> aldehydes, ketones, alkanes, carboxylic acids <strong>and</strong>
polymerization products ( Esterbauer et al , 1982). Hydroperoxides <strong>and</strong>
decomposition products are toxic <strong>and</strong> may form fluorescent adducts with
DNA (Fujimoto et al , 1984). The only mechanism, which produces
malondialdehyde III biological systems, IS lipid peroxidation.
Malondialdehyde is not the major product <strong>of</strong> lipid peroxidation, but a typical
degradation product.
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