Nitrogen Oxides and Their Roles in Cancer Etiology

Purpose of Review The term “nitrogen oxides” refers to a group of molecules composed of nitrogen and oxygen. Sources of human exposure are varied ranging from environmental (acid rain), occupational (combustion of fossil fuels), and dietary to endogenously generated. Nitrogen oxides have a long association with human diseases including cancer. The goal of this review is to give a brief overview of the biological sources, relevant biological reactions, and the associations with cancer of several biologically relevant nitrogen oxides categorized based on the oxidation state of the nitrogen. Recent Findings The chemical reactivity of nitrogen oxides as well as their cellular distribution and microenvironmental characteristics determine the downstream biological or pathobiological effects of nitrogen oxides. Some species may react directly at the site of exposure or production, while others can be transported systemically and become metabolized to more reactive species at distant locations. The roles of nitrogen oxides in cancer biology are often contradictory due to the complexity and diversity of their biological effects. Summary Nitrogen oxides can participate in both causative and curative mechanisms of tumor biology. The appreciation of the high complexity and diversity of the biological effects of these reactive species in biological system will prompt our fundamental understanding of their roles in cancer and our search for improved and novel therapeutic strategies.