Dietary heme induces acute oxidative stress, but delayed cytotoxicity and compensatory hyperproliferation in mouse colon.

Red meat consumption is associated with an increased colon cancer risk. Heme, present in red meat, injures the colon surface epithelium by generating cytotoxic and oxidative stress. Recently, we found that this surface injury is compensated by hyperproliferation and hyperplasia of crypt cells, which was induced by a changed surface to crypt signaling. It is unknown whether this changed signaling is caused by cytotoxic stress and/or oxidative stress, as these processes were never studied separately. The aim of this study was to determine the possible differential effects of dietary heme on these luminal stressors and their impact on the colonic mucosa after 2, 4, 7 and 14 days of heme feeding. Mice received a purified, humanized, control diet or the diet supplemented with 0.2 µmol heme/g. Oxidative and cytotoxic stress were measured in fecal water. Proliferation was determined by Ki67-immunohistochemistry and mucosal responses by whole-genome transcriptomics. After heme ingestion, there was an acute increase in reactive oxygen species (ROS) leading to increased levels of lipid peroxidation products. Mucosal gene expression showed an acute antioxidant response, but no change in cell turnover. After day 4, cytotoxicity of the colonic contents was increased and this coincided with differential signaling and hyperproliferation, indicating that cytotoxicity was the causal factor. Simultaneously, several oncogenes were activated, whereas the tumor suppressor p53 was inhibited. In conclusion, luminal cytotoxicity, but not ROS, caused differential surface to crypt signaling resulting in mucosal hyperproliferation and the differential expression of oncogenes and tumor suppressor genes.

Dietary haem stimulates epithelial cell turnover by downregulating feedback inhibitors of proliferation in murine colon.

OBJECTIVE: Colon cancer is a leading cause of cancer deaths in Western countries and is associated with diets high in red meat. Haem, the iron-porphyrin pigment of red meat, induces cytotoxicity of gut contents and damages the colon surface epithelium. Compensatory hyperproliferation leads to epithelial hyperplasia which increases the risk of colon cancer. The aim of this study was to identify molecules signalling from the surface epithelium to the crypt to initiate hyperproliferation upon stress induced by haem. METHODS: C57Bl6/J mice (n=9/group) received a 'westernised' control diet (40 en% fat) with or without 0.5 µmol/g haem for 14 days. Colon mucosa was used to quantify cell proliferation and for microarray transcriptome analysis. Gene expression profiles of surface and crypt cells were compared using laser capture microdissection. Protein levels of potential signalling molecules were quantified. RESULTS: Haem-fed mice showed epithelial hyperproliferation and decreased apoptosis, resulting in hyperplasia. Microarray analysis of the colon mucosa showed 3710 differentially expressed genes (false discovery rate (q) <0.01), with many involved in the cell cycle. Expression levels of haem- and stress-related genes showed that haem affected surface cells but did not directly affect crypt cells. Injured surface cells should therefore signal to crypt cells to induce compensatory hyperproliferation. Haem downregulated the inhibitors of proliferation, Wnt inhibitory factor 1, Indian Hedgehog and bone morphogenetic protein 2. Interleukin-15 was also downregulated. Haem upregulated amphiregulin, epiregulin and cyclo-oxygenase-2 mRNA in surface cells. Their protein/metabolite levels were, however, not increased as haem induced surface-specific inhibition of translation by increasing 4E-BP1. CONCLUSIONS: Haem induces colonic hyperproliferation and hyperplasia by inhibiting the surface to crypt signalling of feedback inhibitors of proliferation.