(202a) Prediction of Nitric Oxide Concentrations During Inflammation and Carcinogenesis

Nitric oxide (NO) production in the colon has been linked to inflammatory bowel disease (IBD) and increased risk for colon cancer. However, measurements of NO concentration in the inflamed colon are difficult and it remains unknown what NO levels are pathophysiological. A computational model, based on anatomical length scales, was used to predict spatially varying NO concentrations within a colonic crypt under inflammatory conditions. Critical parameters in the colonic crypt model include rates of NO formation and consumption by macrophages and epithelial cells; for epithelial cells, in particular, these quantities are not well known. Primary macrophages, a macrophage cell line, and an epithelial cell line were subjected to simulated inflammatory conditions in vitro and rates of NO synthesis and consumption were determined by fitting concentration data to a detailed kinetic model. Using the experimentally measured NO kinetic rates in our colonic crypt model, NO concentration profiles in an inflamed crypt were generated for a variety of scenarios, including different spatial distributions of macrophages based on immunohistochemical data taken from mice infected with Citrobacter rodentium. Simulations showed that macrophages arranged in a monolayer configuration at the base of the crypt elicited maximum NO concentrations and that putative stem cells, which remain at or near the base of the crypt, are exposed to the highest concentrations of NO. In contrast to migrating epithelial cells, any oncogenic mutations in the stem cell population could accumulate and persist over time. These results highlight how NO concentration predictions should facilitate efforts to elucidate the underlying mechanisms that link NO exposure and carcinogenesis in IBD. In ongoing work, we are using similar methods to estimate NO levels in cutaneous melanomas.