Human studies related to protein oxidation: Protein carbonyl content as a marker of damage

Proteins constitute the major 'working force' for all forms of biological w ork. Their exact conformation and pattern of folding are tightly connected to their activity and function. Reactive oxygen and nitrogen species (ROS a nd RNS) are formed during normal metabolism and in higher fluxes under path ological conditions. They cause cellular damage, an important part of which is the oxidation of amino acid residues on proteins, forming protein carbo nyls. Other direct modifications of protein side chains, such as o-tyrosine , chloro-, nitrotyrosine, and dityrosine, have been identified. In addition , carbohydrate and lipid derivatives can react with proteins Co form adduct s that can be analyzed. Protein carbonyl content (PCC) is the most widely used marker of oxidative modification of proteins. There are several methodologies for the quantitat ion of PCC; in all of them 2,4-dinitrophenyl hydrazine is allowed to react with the protein carbonyls to form the corresponding hydrazone, which can b e analyzed optically by radioactive counting or immunohistochemically. Usin g PCC as a marker, it could be demonstrated that oxidative damage to protei ns correlates well with aging and the severity of some diseases. A critical evaluation of PCC and other markers of protein oxidation is presented, tog ether with examples of protein oxidation in diabetes, neurodegenerative dis eases, and aging.