Peroxidation of lipids in membranes and lipoproteins proceeds through
the classical free radical sequence encompassing initiation, propagati
on, and termination phases which are expressed by a lag phase in which
Little oxidation occurs, followed by a rapid increase in autocatalysi
s by chain-propagating intermediates and, finally, a decrease in the r
ate of oxidation. The lag phase is lengthened by preventive or chain-b
reaking antioxidants, which scavenge the initiation reaction or interc
ept the chain-carrying species. Hence, the lag phase in lipid peroxida
tion processes reflects the antioxidant status of membranes and lipopr
oteins and, as a corollary, their resistance to oxidation. A large num
ber of lipid peroxidation studies with different membranes attest to t
he complex free radical network underlying this process. The type of i
nitiator and the steady-state level of oxygen are important factors th
at affect differently the rates of the individual steps of peroxidatio
n. Equally complex are the factors that influence the lag phase preced
ing the oxidation of LDL. Lipid peroxyl radicals play a key role in th
e dynamics of lipid peroxidation: on the one hand, the lag phase is be
st defined for chain-breaking compounds able to reduce peroxyl radical
s; on the other hand, the overall time course of lipid peroxidation is
largely influenced by the rate constants for propagation reactions an
d termination involving peroxyl radical recombination.