Figure 2.

MDA generation cycle: (1) the high reactivity of polyunsaturated fatty acids to oxidizing agents is promoted by the methylene groups positioned between the cis double bonds along the chain. The removal of the hydrogen atoms leads to unsaturated lipid carbon-centered radicals (2) that are vulnerable to oxidizing and conversion into highly unstable peroxyl radicals (3). Depending on the position of the peroxyl radical in the carbon chain, two pathways are possible: terminal position at one of the two ends of the double bond system will result in reduction to conjugated diene hydroperoxides (4), while internal position will result in multiple products by mono- and/or bi-cyclizations, coupling to O2 or reductions. The fragmentation of a bicyclic peroxide compound (5) structurally analogous to the prostaglandin endoperoxide generates the malondialdehyde (6), *: free electron.