动物造模,药效评价,IBD动物模型 z-bio 2024-08-01 445

　　The chemical induction method started early and has become the most mature and commonly used method for preparing IBD models since the 1960s. There are many types of chemical irritants, including acetic acid, sodium dextran sulfate, sodium peroxynitrite, carrageenan, etc. There are also some small molecule haptens such as 2,4-dinitrochlorobenzenes (DNCB), 2,4,6-trinitrobenzenesulfonic acid (TNBS), 2,4-dinitrophenylbenzenesulfonate (DNBS), etc., which are often included in the category of chemical stimulation modeling. Therefore, it is necessary to clarify a concept: the mechanism of chemical stimulation modeling is that the intestinal mucosa is first directly stimulated by a certain chemical substance, leading to cell damage, increased vascular permeability, activation of certain inflammatory factors, etc. During this process, an immune response is inevitable. But this reaction process is fundamentally different from intestinal immune reactive enteritis (as described later). When DNCB, TNBS, etc. are directly applied to the intestine alone (or in combination with ethanol, acetic acid, etc.) without sensitization, especially when enteritis occurs after only one use, it can be considered as chemical stimulation modeling.

　　1. Acetic acid model

　　[Modeling mechanism] Acetic acid directly stimulates the intestinal mucosa, causing epithelial necrosis, vascular damage, and increasing vascular permeability; Acetic acid can activate kinins, promote fibrinolysis, interfere with coagulation, and initiate inflammation by activating the cyclooxygenase and lipoxygenase pathways.

　　【 Modeling Method 】 Wistar rats were lightly anesthetized with ether. A polyethylene catheter with an outer diameter of 2mm was inserted into the colon 8cm from the anus, and 2ml of 3% acetic acid was slowly injected. The injection was completed after 10 seconds, and then rinsed twice with 5ml of physiological saline. The rats were kept supine with their heads low and feet high for 30 seconds to prevent fluid from flowing out of the colon. After 5 days, animal diarrhea, bloody stools, weight loss, mucosal bleeding, epithelial necrosis, submucosal edema, neutrophil infiltration, etc. can be seen. Inflammation can gradually extend to the lamina propria, submucosal layer, and even muscular layer.

　　The model features temporary, non-specific mucosal damage and acute inflammation. Strong self-healing ability. Its inflammatory mediators are similar to those of acute enteritis in humans. The drawback is that it cannot accurately reflect the immunological changes of human UC and cannot reflect the chronic and recurrent characteristics of human UC.

　　This model is simple and easy to implement, with low cost, short cycle, good repeatability, and high success rate. Suitable for studying the acute phase of human UC, the inflammatory mechanisms of inflammatory mediators, and drug treatment mechanisms, but not suitable for studying immune mechanisms. The key to successful model induction is the concentration and duration of action of acetic acid, which is suitable for producing diffuse inflammation without perforation.

　　2. Sodium dextran sulfate model

　　Dextran sulfate sodium (DSS) is a sulfated polysaccharide synthesized from sucrose, which has the same anti hemostatic and anti coagulation effects as heparin. The mechanism of DSS induced ulcerative colitis may be related to its impact on DNA synthesis, inhibition of epithelial cell proliferation, and disruption of the intestinal mucosal barrier, leading to the migration of gut microbiota to the mucosal lamina propria, which in turn triggers macrophage overactivation and Th1/Th2/Th17 cell dysfunction.

　　[Modeling Method] BALB/c mice, half male and half female, 8-9 weeks, 16-18g, 5% DSS prepared with distilled water. Option 1: After freely drinking 5% DSS for 7 days, mice were switched to freely drinking distilled water for 10 days, forming one cycle, which is the acute UC model. Option 2: Mice complete 4 cycles according to option 1, which transforms them into a chronic UC model. Animals were euthanized 7 days after the end of either the first cycle (acute phase) or the fourth cycle (chronic phase). The results showed that in the acute phase, mice developed diarrhea on the 4th to 5th day after the start of modeling, with positive occult blood test results. On the 5th to 7th day, there was visible bloody stool, which lasted until the 8th to 9th day. The lesion develops continuously from the anus to the mouth, with the rectum being the most severe. The affected area has mucosal congestion and edema, with scattered erosions or ulcers visible. The mucosa and submucosa are mainly infiltrated by neutrophils. Chronic mice not only experience diarrhea and bloody stools at the same time as the acute phase, but also show bloody stools and diarrhea 5-6 days after discontinuing DSS, as well as colon granulation tissue proliferation, mucosal structure loss, glandular deformation and atrophy, and intestinal shortening. The mucosa and submucosa are mainly infiltrated by lymphocytes, plasma cells, and macrophages.

　　The model features are consistent with the clinical characteristics of human IBD, including both chronic phase and acute exacerbation of chronic disease. Can be used to study the pathological features of acute and remission phases of human IBD.

　　Colonic mucosal lesions are mainly found on the left side and can lead to atrophy and underdevelopment of the colonic epithelium, thereby increasing the risk of cancer. This is similar to the fact that human UC can become cancerous.

　　Model Evaluation and Application: IBD occurs when animals freely consume DSS, minimizing the interference of human factors during modeling. The method is simple, easy to implement, has good repeatability, and can be used for both acute and remission phases of UC. If the amount of DSS consumed by animals can be accurately controlled, it will further reduce the differences in model lesions. This model is commonly used to screen for preventive and therapeutic drugs for UC associated colorectal cancer.