| Chronic inflammation is strongly associated with an increased risk of cancer. DNA damage is proposed to be one important mechanism for carcinogenesis. Phagocytes, which accumulate at sites of inflammation, might be sources of oxidants that promote DNA damage via a pathway involving myeloperoxidase, a heme protein present in neutrophils and monocytes that generates the powerful oxidant hypochlorous acid (HOCI). Oxidative stress and genetic instability has also been suggested to contribute to the development of atherosclerosis, another chronic inflammatory disorder. Clinical, biochemical and epidemiologic studies suggest that myeloperoxidase is associated with cancer risk and atherosclerosis, indicating a possible role for myeloperoxidase in the pathogenesis of the two diseases.;While the potential role of DNA damage in cancer and atherosclerosis is clearly important, the sources and molecular mechanisms of such damage remain poorly understood. For example, little is known about the pathways that promote in vivo oxidation of nucleobases, nucleosides, and nucleic acids. It is known, however, that HOCI converts nucleobases into various oxygenated and chlorinated species in vitro..;To determine if halogenated nucleobases are generated in vivo, we used isotope dilution mass spectrometry to quantify halogenated uracil levels in human inflammatory tissue. We demonstrated the presence of two products of myeloperoxidase, 5-chlorouracil and 5-bromouracil, in inflamed tissue, but not in normal human plasma, urine or mouse liver tissue. These observations provide the first direct evidence that myeloperoxidase targets nucleobases for oxidative damage in vivo, and that myeloperoxidase-derived oxidants might be pathophysiologically relevant sources of DNA damage.;We also found elevated levels of 5-chlorouracil in human atherosclerotic lesions. Furthermore, we established the ability of human macrophages, one of the cellular hallmarks of atherosclerosis, to chlorinate uracil in vitro. While chlorination of nucleic acids has primarily been examined using highly reactive HOCI, we found uracil to also be chlorinated by long-lived N-chloramines---the reaction products of HOCI with free amine groups on free amino acids, peptides and proteins.;Our studies demonstrate that halogenation of uracil occurs during inflammation in humans. The production of these mutagenic nucleobases by macrophages in the atherosclerotic lesion may play a role in atherogenesis and other chronic inflammatory diseases. |
