The dialdehyde of malonic acid.
Used as an indicator of fatty acid and lipid peroxidation, and oxidative changes in foods MDA and other 'thiobarbituric reactive substances' (TBARS) condense with two equivalents of thiobarbituric acid to give a fluorescent red derivative that can be assayed spectrophotometrically. 1-Methyl-2-phenylindole is an alternative more selective reagent.; Malondialdehyde (MDA) is the dialdehyde of malonic acid and a biomarker of oxidative damage to lipids caused by smoking.; Oxidized lipids are able to produce MDA as a decomposition product. The mechanism is thought to involve formation of prostaglandin-like endoperoxides from polyunsaturated fatty acids with two or more double bonds. An alternative mechanism is based on successive hydroperoxide formation and β-cleavage of polyunsaturated fatty acids. MDA is then directly formed by β-scission of a 3-hydroperoxyaldehyde or by reaction between acrolein and hydroxyl radicals. While oxidation of polyunsaturated fatty acids is the major source of MDA in vivo, other minor sources exists such as byproducts of free radical generation by ionizing radiation and of the biosynthesis of prostaglandins. Aldehydes are generally reactive species capable of forming adducts and complexes in biological systems and MDA is no exception although the main species at physiological pH is the enolate ion which is of relative low reactivity. Consistent evidence is available for the reaction between MDA and cellular macromolecules such as proteins, RNA and DNA. MDA reacts with DNA to form adducts to deoxyguanosine and deoxyadenosine which may be mutagenic and these can be quantified in several human tissues. Oxidative stress is an imbalance between oxidants and antioxidants on a cellular or individual level. Oxidative damage is one result of such an imbalance and includes oxidative modification of cellular macromolecules, induction of cell death by apoptosis or necrosis, as well as structural tissue damage. Chemically speaking, oxidants are compounds capable of oxidizing target molecules. This can take place in three ways: abstraction of hydrogen, abstraction of electrons or addition of oxygen. All cells living under aerobic conditions are continuously exposed to a large numbers of oxidants derived from various endogenous and exogenous sources. The endogenous sources of oxidants are several and include the respiratory chain in the mitochondria, immune reactions, enzymes such as xanthine oxidase and nitric oxide synthase and transition metal mediated oxidation. Various exogenous sources of ROS also contribute directly or indirectly to the total oxidant load. These include effects of ionizing and non-ionizing radiation, air pollution and natural toxic gases such as ozone, and chemicals and toxins including oxidizing disinfectants. A poor diet containing inadequate amounts of nutrients may also indirectly result in oxidative stress by impairing cellular defense mechanisms. The cellular macromolecules, in particular lipids, proteins and DNA, are natural targets of oxidation. Oxidants are capable of initiating lipid oxidation by abstraction of an allylic proton from a polyunsaturated fatty acid. This process, by multiple stages leading to the formation of lipid hydroperoxides, is a known contributor to the development of atherosclerosis. (PMID: 17336279); 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. It is easily deprotonated to give the sodium salt of the enolate (m.p. 245 °C).; Malondialdehyde is the organic compound with 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.; Reactive oxygen species degrade polyunsaturated lipids, forming malondialdehyde. This compound is a reactive aldehyde and is one of the many reactive electrophile species that cause toxic stress in cells and form covalent protein adducts which are referred to as advanced lipoxidation end products (ALE), in analogy to advanced glycation end-products (AGE). The production of this aldehyde is used as a biomarker to measure the level of oxidative stress in an organism.