Endogenous product of lipid peroxidation and prostaglandin biosynthesis in mammals; also formed by oxidation of polyunsaturated fatty acids in foods. Reacts with functional groups of a variety of cellular compounds including DNA and amino acids, forming genotoxic adducts and crosslinks. Associated with detrimental protein modifications and decreased nutritional value in foods. Prepn: L. Claisen, Ber. 36, 3664 (1903); R. Hüttel, ibid. 74, 1825 (1941). Chemistry and reactions with amino acids: V. Nair et al., J. Am. Chem. Soc. 103, 3030 (1981). NMR spectroscopy: S. H. Bertz, G. Dabbagh, J. Org. Chem. 55, 5161 (1990). Determn methods using thiobarbituric acid: H. H. Draper et al., Free Radical Biol. Med. 15, 353 (1993). HPLC determn in foods: P. Bergamo et al., J. Agric. Food Chem. 46, 2171 (1998); in biological samples: R. Mateos et al., J. Chromatogr. B 827, 76 (2005). Acute toxicity study: D. L. Crawford et al., Toxicol. Appl. Pharmacol. 7, 826 (1965). Clinical use as biomarker in neurodegenerative disease: M. Dib et al., J. Neurol. 249, 367 (2002); in coronary artery disease: H. H. Jung et al., Am. J. Nephrol. 24, 537 (2004). Review of metabolism: H. H. Draper, M. Hadley, Xenobiotica 20, 901-907 (1990); of biochemistry: H. Esterbauer et al., Free Radical Biol. Med. 11, 81-128 (1991). Review of carcinogenic risk: IARC Monographs 71, Part 3, 1037-1047 (1999); of toxicity of DNA adducts: L. J. Marnett, IARC Sci. Publ. 150, 17-27 (1999); and pathological significance: D. Del Rio et al., Nutr. Metab. Cardiovasc. Dis. 15, 316-328 (2005).