Tissues are continually exposed to reactive oxygen species (ROS) that are produced in tissues from metabolism processes or the inflammatory response of leukocytes or macrophages. It is estimated that as much as 1 % of consumed oxygen may be converted to ROS, which can cause damage to various cellular components. Proteins are one of the cellular components most vulnerable to oxidative damage by ROS, which results in an increase in protein carbonyl content. This oxidative modification of proteins can lead to cross-linking, peptide fragmentation, modified residues and the conversion of one amino group to another. If sufficient protein damage accumulates, cell death will occur.