Biocidal Mechanisms of Metallic Copper Surfaces - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 124

Fig. 6.13 Schematic representing the three steps that characterize lipid oxidation

membrane lipids leading to their oxidation (lipid peroxidation) and degradation
(products measured by the TBARS assay), we have to look at how lipid oxidation
events occur.

6.3.3.3 Lipid Oxidation Chemistry

Lipid oxidation is a series of oxidative chain reactions that leads to the degradation
of lipids and starts with electron transfer from lipids to radicals by free radical chain
reaction mechanism. These events are known to happen ubiquitously in biological
systems [ 78 ], however mechanisms underlying such processes in vivo are not fully
understood. Lipid (L) oxidation was shown to follow in three steps: initiation,
propagation, and termination (Fig. 6.13 )[ 31 , 78 ].
Polyunsaturated fatty acids are more prone to the electron transfer process than
saturated fatty acids due to the presence of the double bond, which stabilize allylic
(C

C-C ￿ ) radicals formed in oxidation process. Initiation of lipid oxidation starts
by removal of a hydrogen from a lipid (unsaturated/saturated), leaving an unpaired
electron on the carbon (lipid radical (L￿)), which can then react with molecular
oxygen to form a peroxyl radical (LOO￿) (Fig. 6.13 ). After that, the peroxyl radical
is capable of removing a hydrogen from another lipid, thus propagating the lipid
oxidation (Fig. 6.13 )[ 38 ]. Oxidized lipids rapidly oxidize other lipids leading to
further lipid oxidation until non-radical monomers are formed (termination)
(Fig. 6.13 ). Once started, this process is self-propagating and self-accelerating,
being designated as autocatalytic. A single initiating-event can lead to about 200-
300 chain reactions, showing how effective one initiation -event is [ 13 , 41 ]. Never-
theless, biological systems developed counter measures antioxidants, capable to
control lipid oxidation. When the initiation of lipid oxidation is at higher than
normal rates, lipid oxidation can result in irreversible membrane damage and,
consequently, cell death.
Lipid oxidation is not a spontaneous reaction but can be triggered very easily.
Thermodynamically, direct damage to biomolecules by molecular oxygen is not
possible due to different electron spin states, however in the presence of catalysts

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