Studies on the inhibitory effect of vitamin E against secondary reaction of lipid peroxidation

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Oxidative cleavage of unsaturated lipids during peroxidation gives rise to cytotoxic and genotoxic a,β-unsaturated aldehydes, such as 4-hydroxy-2-nonenal (HNE) and 4-oxo-2-nonenal (ONE). We have studied the reactivity of vitamin E with HNE or ONE to clarify the role of vitamin E on the detoxification of α,β-unsaturated aldehydes. Α-Tocopherol (α-TH), the most active vitamin E, did not react with these aldehydes, whereas y- and δ- THs could react with ONE or HNE under the acidic conditions. ONE is known to be the most reactive aldehyde among the secondary of lipid peroxidation products. Therefore, the reaction products of y-TH with ONE have been investigated. When y-TH was reacted with ONE at 37℃ in the presence of HC1, product peaks 1-3 were detected by reversed-phase HPLC. Compounds 1-3 were isolated and their structures were determined by NMR. Compound 1 was determined to be 5- (1- (furan-2-yl) pentyl) -y-tocopherol, the addition product of y-TH with ONE. Compound 2 was also the addition product of y-TH with ONE where the C-5 position and 6-hydroxyl group of y-TH were bound to the C-5 and C-4 positions of ONE. Compound 3 was the addition product of γ-TH with two ONE molecules where the C-1 position of ONE residue in compound 2 was bound to the C-5 position of another ONE molecule. S-TH could also react with ONE to form some addition products although their structures were still unknown. The results indicate that y- and 8-THs which possess nucleophilic character in the chroman ring can act as scavengers of lipophilic electrophiles such as ONE.y-TH is the major form of vitamin E in plant seeds and consequently in our diet. Thus, γ-TH may trap the membrane-soluble α,β-unsaturated aldehydes to form unreactive carbon-centered adducts before they can damage important biological molecules.