Lipid peroxidation

Mechanism of lipid peroxidation. R stands for the unbranched alkyl radical of the fatty acid.

Under lipid peroxidation refers to the oxidative degradation of lipids . During this process, a lipid donates electrons to reactive radicals . The radical chain reaction set in motion can lead to cell damage in the case of lipids in the cell membrane. In the case of low-density lipoprotein (a lipoprotein that transports lipids in the blood), oxidative modifications occur, which lead to arteriosclerosis via the formation of foam cells . Lipid peroxidation is also responsible for the spoilage of animal and vegetable oils and fats (" becoming rancid "). Mostly polyunsaturated fatty acids are affected because they contain numerous double bonds between which there are particularly reactive methylene groups .

Start reaction (initiation)

The reaction of a fatty acid (LH) with a radical creates a reactive fatty acid radical (L *), to which O _{2 is} added in the next step of radical substitution and a lipid peroxyl radical (LOO *) is generated, which then leads to a chain reaction. There are numerous initiators in biological systems - often they are reactive oxygen species . Enzymes such as lipoxygenases , peroxidases with H ₂ O ₂ , myeloperoxidase with H ₂ O ₂ / Cl ^- or hemoglobin with H ₂ O ₂ as well as macrophages can generate radicals that trigger lipid peroxidation.

Follow-up reaction (prolongation)

The resulting fatty acid peroxyl radical can now transfer its radical function through hydrogen abstraction to other unsaturated fatty acids , which in turn add O ₂ and thus keep the chain reaction going, or with a molecule with antioxidant properties (e.g. α-tocopherol or γ-tocopherol ) respond. In the latter case, the chain reaction is interrupted. The radical chain reaction usually only gets fully underway as soon as all antioxidants have been completely consumed (lag time).

Termination reaction

The chain reaction is only interrupted when:

1. a stable non-radical is created by the reaction of two radicals.
2. the unsaturated fatty acids are used up.
3. Antioxidants scavenge all radicals.

There are numerous natural fat-soluble antioxidants. In the human low-density lipoprotein, there are on average 7 molecules of α-tocopherol per particle, which prevent biological units from being completely oxidized in living organisms.

literature

• U. Martens: The effects of hydrogen peroxide-induced lipid peroxidation on the fatty acid composition of erythrocyte phospholipids. Fragment of a dissertation at the University of Heidelberg, published on August 25, 1999, pdf
• Joachim Rassow , Karin heim, Roland Netzker, Rainer Deutzmann: Dual Series - Biochemistry. 1st edition. Thieme, 2006, ISBN 3-13-125351-7 .

Individual evidence

1. ↑ H. Esterbauer, SP Gieseg, A. Giessauf, O. Ziouzenkova, P. Ramos: Role of natural antioxidants in-inhibiting Cu ⁺⁺ -mediated oxidation of LDL. In: G. Bellomo, G. Finardi, E. Maggi, C. Rice-Evans (Eds.): Free Radicals Lipoprotein Oxidation and Atherosclerosis-Biological and Clinical Aspects. Richelieu Press, 1995, ISBN 0-903840-10-3 , pp. 11-26.
2. ↑ H. Esterbauer, SP Gieseg, A. Giessauf, O. Ziouzenkova, P. Ramos: Role of natural antioxidants in-inhibiting Cu ⁺⁺ -mediated oxidation of LDL. In: G. Bellomo, G. Finardi, E. Maggi, C. Rice-Evans (Eds.): Free Radicals Lipoprotein Oxidation and Atherosclerosis-Biological and Clinical Aspects. Richelieu Press, 1995, ISBN 0-903840-10-3 , p. 13.
3. ↑ H. Esterbauer, J. Gebicki, H. Puhl, G. Jürgens: The role of lipid peroxidation and antioxidants in oxidative modification of LDL. In: Free Rad. Biol. Med. 13, 1992, pp. 341-390. (English).