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4-Hydroxynonenal
Malondialdehyde (MDA) is the formula CH2(CHO)2. The structure of this species is more complex than this formula suggests. This reactive species occurs naturally and is a marker for oxidative stress.
Malondialdehyde mainly exists in the enol form:[2]
In organic solvents, the cis-isomer is favored, whereas in water the trans-isomer predominates.
Malondialdehyde is a highly reactive compound that is not typically observed in pure form. In the laboratory it can be generated in situ by hydrolysis of 1,1,3,3-tetramethoxypropane, which is commercially available.[2] It is easily deprotonated to give the sodium salt of the enolate (m.p. 245 °C).
Malondialdehyde results from lipid peroxidation of polyunsaturated fatty acids.[3] It is a prominent product in Thromboxane A2 synthesis wherein cyclooxygenase 1 or cycloxygenase 2 metabolizes arachidonic acid to prostaglandin H2 by platelets and a wide array of other cell types and tissues. This product is further metabolized by Thromboxane synthase to Thromboxane A2, 12-Hydroxyheptadecatrienoic acid, and malonyldialdehyde.[4][5] Alternatively, it may rearrange non-enzymatically to a mixture of 8-cis and 8-trans isomers of 12-hydroxyeicosaheptaenoic acid plus malonyldialdehyde (see 12-Hydroxyheptadecatrienoic acid).[6] The degree of lipid peroxidation can be estimated by the amount of malondialdehyde in tissues.[3]
Corneas of patients suffering from keratoconus and bullous keratopathy have increased levels of malondialdehyde, according to one study.[15] MDA also can be found in tissue sections of joints from patients with osteoarthritis.[16]
Malondialdehyde is reactive and potentially mutagenic.[13] It has been found in heated edible oils such as sunflower and palm oils.[14]
Malondialdehyde and other thiobarbituric reactive substances (TBARS) condense with two equivalents of thiobarbituric acid to give a fluorescent red derivative that can be assayed spectrophotometrically.[2][12] 1-Methyl-2-phenylindole is an alternative more selective reagent.[2]
Human ALDH1A1 aldehyde dehydrogenase is capable of oxidizing malondialdehyde.
Malondialdehyde reacts with deoxyadenosine and deoxyguanosine in DNA, forming DNA adducts, the primary one being M1G, which is mutagenic.[11] The guanidine group of arginine residues condense with malondialdehyde to give 2-aminopyrimidines.
[10][9]
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