| BackgroundBecause of the rapid developing in economy and changing food habits, there was an increasing trend yearly at colorectal cancer incidence in our country.It has become a threat to people's physical and mental health. It is an effectively preventive method to tumor by ingesting natural food that has anticancer effect. At present, the relationship of resistant starch (RS) and colon cancer is being paid close attention at home and abroad. A number of food, such as cereals, legumes, tubers, green banana have been shown to contain various amounts of RS. Few animal experiments is reported about RS preventing colorectal cancer, especially concerning the effect of RS on the precancerous leisions of colorectal cancer.ObjectivesWe use the model of AOM-induced colorectal cancer in Wistar rat. This study was designed to determine the potential inhibitory influence of RS at different doses through the observation of the rat growth test, the small intestine movement test and metabolic test. And it was also designed to investigate the influence of a premalignant lesion by testing the number of ACF, one of the early landmarks of colorectal cancer, and some other biomarkers, such as PCNA, AgNORs, Bcl-2 and Bax. The results will provide evidence for early diagnosis and treatment of colorectal cancer, and be of great importance for guiding Chinese diets and early preventing colorectal cancer. Methods1. The determination of the resistant starch content of potatoThe contents of resistant starch and total starch were determined by a method that mimicked gastrointestinal conditions, and used to prepared for animals'meals.2. Effects of resistant starch on intestine function of AOM-induced colorectal cancer in ratsMale Wistar rats were randomly divided into 5 groups:negative control group, positive control group and three different resistant starch (RS) added groups with the ratio of 7.6%,15.2% and 22.8%(n= 10 each group). For inducing colonic tumorigenesis, rats received chemical carcinogen (AOM) injections by intraperitoneal once a week for two consecutive weeks. Animals in different RS added groups received the corresponding doses of RS while rats in the positive control group and the negative control group received ordinary feed during the whole study. This study was designed to determine the protective effect on intestine of RS at different doses through the observation of the small intestine movement test and metabolic test. Fecal pH and fecal output were measured in the 5th weekend and the intestinal transit time measurement was carried out in the7th weekend.Then comparing them among groups. And it was also designed to investigate the influence of weight by testing the rat growth.3. The study of prophylactic effect of resistant starch on precancerous lesions of AOM-induced colorectal cancer in ratsMale Wistar rats were randomly divided into 5 groups:negative control group, positive control group and three different resistant starch (RS) added groups with the ratio of 7.6%,15.2% and 22.8%.For inducing colonic tumorigenesis, rats received chemical carcinogen (AOM) injections by intraperitoneal once a week for two consecutive weeks. Animals in different RS added groups received the corresponding doses of RS while rats in the positive control group and the negative control group received ordinary feed during the whole study. At 13 weeks after the first injection, all of the rats were killed. Colons of rats were removed and the total numbers of ACF as well as the number of crypts per focus were scored using a light microscope at low magnification after staining with 0.5% methylene blue solution. Some other biomarkers (such as PCNA, AgNORs, Bcl-2 and Bax) were also determined by immunohistochemical method and compared among groups to investigate the effect of RS on the precancerous lesion of colon cancer.Results1. The contents of total starch of 100g potato starch was (98.90±4.84)g, and the contents of resistant starch of 100g TS was (79.27±9.06)g.2. Body weight alteration of rat:During the whole study, each group of rats grew well and weight was increasing. The body weights of rats in RS groups were lower than control and there was a dose-dependent in lower weight and high RS level. Compared with the positive control group,the body weights of rats in the high dose group was significantly decreased (P<0.05).3. The fecal excreting habit:Addition of RS to the diet significantly increased fecal output and water content. In the three groups RS fed rats, further increase in fecal output and water content were seen with the concentration of RS. The intestinal transit time was shortened by addition of RS and high-RS group had a more markedly effect.4. Intestinal tract pH:Fecal pH in the three RS added groups were significantly decreased than the positive control group (P< 0.05).5. The number of colonic ACF:ACF were discovered in both of the positive control group and in RS groups. But the negative control was no ACF formation. Compared with the positive control group, the number of ACF and AC in the three RS added groups were both significantly reduced (P< 0.01).6. Colonic PCNA-LI and the number of AgNORs:The number of AgNORs and the PCNA-LI in the positive control group were more than the negative control group. Compared with the positive control group, the number of AgNORs and the PCNA-LI in the three RS added groups were both reduced and high-RS group had a more markedly effect.7. Expression of colonic Bcl-2 and Bax protein:There was a low expression of Bcl-2 and Bax in the negative control group. In addition, RS inhibited the expression of Bcl-2 and enhanced the expression of Bax.Conclusions1. Dietary RS retarded the body weight gain to rat. Therefore it may be an effective natural approach to the treatment of obesity.2. Dietary RS shorten the GTT and increase the fecal output and moisture. These effects on excreting habit might be beneficial for eliminating toxic substrates timely. It also decreased intestinal tract pH. All these findings showed that RS favourably influence the colonic luminal environment.3. ACF may be a valuable middle point instead of cancer incidence for colorectal cancer research of chemical prevention.4. The application of some biomarkers (such as PCNA, AgNORs, Bcl-2 and Bax) will provide evidence for early diagnosis and treatment of colorectal cancer, and be of great importance for guiding Chinese diets and early preventing colorectal cancer. Therefore it can be used for the clinical early diagnosis.5. Pre-cancerous model has many advantages such as shorter period, less investment, simple and reliable method and so on. It can be used for reference by other experiments.
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