New Markers of Oxidative Damage to Macromolecules
The presence of free radicals in biological material has been discovered some 50 years ago. In physiological conditions, free radicals, in the first place the ones of oxygen and nitrogen, are continuously synthesized and involved in the regulation of a series of physiological processes. The excess of free radicals is efficiently eliminated from the body in order to prevent their toxic effects. Toxic effects of free radicals may be classified into three groups: a) change of intracellular redox potential, b) oxidative modification of lipids, proteins and DNA, and c) gene activation. Lipid peroxidation involving cell membranes, lipoproteins and other molecules leads to the production of primary high-reactive intermediaries (alkyl radicals, conjugated dienes, peroxy- and alkoxyl radicals and lipid hydroperoxide), whose further breakdown generates the secondary products of lipid peroxidation: short-chain evaporable hydrocarbons, aldehydes and final products of lipid peroxidation: isoprostanes, MDA, 4-hydroxy-2, 3-transnonenal and 4,5-dihydroxydecenal which are important mediators of atherosclerosis, coronary disease, acute myocardial infarction, rheumatoid arthritis, systemic sclerosis and lupus erythematodes. Oxidative modification of proteins is manifested by changes in their primary, secondary and tertiary structures. Proteins have a specific biological function, and therefore their modification results in unique functional consequences. The nature of protein modification may provide valid information on the type of oxidants causing the damage. Chlorotyrosyl is a specific marker of oxidative damage to tyrosine caused by HOCl action, which most commonly reflects the involvement of neutrophils and monocytes in oxidative stress, while nitrotyrosyl indicates the presence of higher peroxy-nitrite synthesis. Methyonin and cysteine are the amino acids most sensitive to oxidative stress, carbonyl groups are markers of severe damage caused by free radicals, and di-tyrosyl is the most significant and sensitive marker of oxidative modification made by γ rays. >Carbonyl stress< is an important form of the secondary oxidation of proteins, where reducing sugars non-enzymatically react with amino groups of proteins and lipids and give rise to the production of covalent compounds known as advanced glycosylated end products (AGE-products). A hydroxyl radical damages the DNA, leading to a loss of base and the formation of abasic sites (AP sites), break of DNA chain and sugar modification. Final lipid peroxidation products (MDA) may covalently bind to DNA, producing the >DNA radicals< which are responsible for mutations. Measurement of an adequate oxidative stress biomarker may not only point to an early onset of disease, its progression and assessment of therapy effectiveness, but can also help in the clarification of the pathophysiological mechanisms of tissue damage caused by oxidative stress, prediction of disease prognosis and choice of appropriate treatment in the early stages of disease.
Lipid Peroxidation
