The nitrite/collagen reaction: Non-enzymatic nitration as a model system for age-related damage

The effects of age seen in long-lived connective tissue proteins are though t to be the result of post-translational modifications by reactive molecule s. One such molecule is the nitrite ion. Human nitrite exposure results pre dominately from endogenous production of nitric oxide as well as inhalation of cigarette smoke and ingestion of cured meats. Although nitrite reaction s with various proteins have been studied previously with regard to carcino genesis, the specific reaction with collagen and its role in age-related da mage has never been examined. We describe the reaction of nitrite with type I collagen at neutral pH and body temperature. The incubation of collagen with nitrite results in an increase in cross-linking, the accumulation of a yellow chromophore, and a depletion of tyrosine residues. Similar changes also are found in aged human collagen. In addition, 3-nitro-tyrosine, which has recently been used as a marker for peroxynitrite mediated damage, is p roduced from this reaction. Thus, we propose non-enzymatic nitration as an in vitro model system for human collagen age-related damage.