AOM/DSS model and mouse endoscopy

Ten-week-old mice (n=10 per group) with a body weight of >20 g were injected intraperitoneally with AOM (10 mg per kg body weight). Experimental groups were similar with regard to age and sex ratio.

The mutagenic agent AOM (Sigma) initiates intestinal tumor formation, which is promoted by three cycles of the pro-inflammatory reagent DSS (MP Biomedicals, Santa Ana, CA, USA) in the drinking water (2% w/v). Each cycle lasted 7 days with 14 days of recovery in between (Figure 3a). For evaluation of diarrhea severity, the following score was used: (0) no diarrhea: solid stool with no sign of soiling around the anus. (1) Mild diarrhea: formed stool that appears moist on the outside. Some signs of soiling around anus. (2) Diarrhea: unformed stool with a mucous-like appearance. Considerable soiling around the anus. (3) Severe diarrhea: mostly clear or mucous-like liquid stool with very minimal solid present and considerable soiling around anus. (4) Bloody diarrhea: severe diarrhea with bloody contingent and considerable soiling around anus.

High-resolution mouse endoscopy was performed as described²⁸ with a Mainz COLOVIEW endoscopic system (Karl Storz, Tuttlingen, Germany). In all, 5% isoflurane in oxygen was administered for anesthesia initiation and then decreased to 2% in oxygen for anesthesia maintenance. Eighty days after injection, mice were killed by cervical dislocation and bowel cavity was opened. The colon was removed, rinsed with PBS and opened longitudinally. Colorectal tumors were counted and tumor diameters were measured with a sliding caliper. Some tumors were taken for immunohistochemical analyses, whereas others were used for protein isolation as described.