Effect of dietary resistant starch on inhibition of preneoplasia in azoxymethane-induced rodent models

Diet choices can play a role in disease incidence, especially diseases associated with the digestive system, such as Irritable Bowel Syndrome, Crohn\u27s disease, and colorectal cancer. Starch is a large component of the the human diet and the non-digestible portion, referred to as dietary fiber, has been implicated as a factor that decreases the risk for colorectal cancer. Modified or naturally occurring resistant starches share similar digestion resistant properties as dietary fiber and may produce similar protective effects. Two different animal models, F344 rats and A/J mice, were used to compare preneoplasia inhibition when fed one of three resistant starch diets or a control cornstarch (CS). The resistant starches used included a native high amylose starch (HA7), a high-amylose chemically modified with octenyl succinic anhydride (OS-HA7), and a high-amylose complexed with stearic acid (SA-HA7). Two common preneoplasia are aberrant crypt foci (ACF) and mucin-depleted foci (MDF). Azoxymethane (AOM), a chemical carcinogen, was used to induce the preneoplasia in the rodent models by means of weekly intraperitoneal injections; rats received two weekly injections of 15mg AOM/kg body weight, mice received four weekly injections of 7.5mg AOM/kg body weight. Saline injections were used as a control. Experimental diets were fed for ten weeks following the last carcinogen injection. Antibiotics were also administered to a few of the rats to determine the potential effects on preneoplasia inhibition when fed resistant starch diets. In both animal studies, the animals treated with AOM and fed the SA-HA7 diet developed the greatest number of ACF. While the SA-HA7 diet had the greatest number of ACF, it subsequently had the fewest MDF present. The animals fed the resistant starch diets that developed the fewest ACF were different between the two animal studies; OS-HA7 fed rats and HA7 fed mice. Analysis by two and three-way ANOVAs determined that there was no diet effect experienced in either study for ACF. The MDF results suggest that MDF may not be a reliable or relevant biomarker for colorectal cancer as the greatest number of MDF were observed in rats fed the CS diet and treated with saline and administered antibiotics. General conclusions from this study recommend further studies to identify a reliable biomarker and to determine the long term effects of resistant starch intake on the inhibition of colon tumors