Preventive effect of mesenchymal stem cell culture supernatant on luminal stricture after endoscopic submucosal dissection in the rectum of pigs

Background Mesenchymal stem cells (MSCs) are valuable in regenerative medicine, and MSC culture supernatant (MSC-CS) reportedly inhibits inflammation and fibrosis. We investigated whether colorectal luminal stricture develops after circumferential endoscopic submucosal dissection (ESD) in the colorectum, and whether the development of luminal stricture could be prevented by using MSC-CS enema. Methods In the first experiment, we performed circumferential ESD in the rectums or distal colons of pigs (n=4 in each group). We sacrificed the pigs on Day22 and measured the degree of luminal stricture. In the second experiment, we performed circumferential ESD in the rectums of pigs and administered an MSC-CS gel or a control gel enema after ESD for 4days. We sacrificed the pigs on Day8 (n=3 in each group) or 22 (n=3 in each group) to measure the degree of luminal stricture, and performed histological analysis. Results Severe luminal stricture was observed in the rectum but not in the distal colon. Moreover, fiber accumulation in the submucosa and hypertrophy of the muscularis propria were observed in the rectum but not in the distal colon. The degree of luminal stricture in the rectum was significantly lower in the MSC-CS group than in the control group.Furthermore, MSC-CS attenuated myofibroblast activation and hypertrophy of the muscularis propria on Day22, and reduced inflammatory cell infiltration on Day8. Conclusions Luminal stricture after ESD developed only in the rectum because of the difference in myofibroblast activation and fiber accumulation. In addition, MSC-CS enema prevented luminal stricture after ESD, possibly by inhibiting the inflammatory reaction and fibrosis.