Relevance of oxidative stress for heme iron-triggered toxicity in intestinal cells and cellular defense mechanisms

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Dietary heme is an important iron source in human nutrition and occurs abundantly in red meat, whose excessive consumption is associated with an increased risk for colorectal cancer formation. Heme plays a central role in this process and promotes tumorigenesis via different mechanisms. It is known that heme iron causes oxidative stress and cytotoxicity in intestinal cells, while non-heme iron such as iron chloride exhibits only moderate effects. Using genetic and pharmacological approaches, we previously identified heme oxygenase-1 as an important factor in intestinal cells that confers protection against heme iron. However, the precise chemical nature of the reactive oxygen species (ROS) formed in intestinal cells as well as their spatio-temporal generation on the subcellular level is only little understood. Furthermore, it is unclear whether the antioxidant enzymes katalase (KAT), superoxide dismutase (SOD)-1 and SOD2 as well as perioxiredoxin-1 (PRDX1) are involved in the protection of intestinal cells against heme iron. The objective of this study is to investigate the fate of heme iron in intestinal cells, the spatio-temporal ROS generation and their relevance for gastrointestinal toxicity. In addition, the impact of potentially relevant antioxidant enzymes (KAT, SOD1, SOD2 and PRDX1) on these events will be studied. To this end, hemin (Fe3+-protoporphyrine) as well as inorganic iron(III)chloride and iron (II)sulfate as non-heme iron sources should be tested. Non-malignantly transformed human colonic epithelial cells and colorectal cancer cells should be used as cell models. Additionally, murine intestinal oragnoids and tumorids will be used. Based on our preliminary work, we would like to address the following issues: 1.) how is the fate of heme iron versus non-heme iron in intestinal cells and how the global proteome is affected by these iron species, 2.) in which cell compartment and kinetics arise which ROS upon exposure of intestinal cells to heme iron versus non-heme iron, and 3.) what is the impact of the antioxidant enzymes KAT, SOD1, SOD2 and PRDX1 in intestinal cells following treatment with heme iron and non-heme iron and how does their deficiency affect oxidative stress, toxicity and the global proteome in intestinal cells.