Mo1913 Influence of a Dipeptidyl Peptidase-4 Inhibitor on Intestinal Neoplasia Formation in APC MIN/+ Mice Fed a High Fat Diet

Abstract

Background: The association between type 2 diabetes mellitus and intestinal neoplasia has been shown epidemiologically. It is also well known that a high fat diet (HFD) promotes insulin resistance which is a risk factor for intestinal neoplasia. Dipeptidyl peptidase-4 (DPP4) inhibitors are used clinically in diabetes therapy to prolong the effects of glucagon-like peptide-1 (GLP-1). However, because another derivative from proglucagon, the intestinotrophic hormone GLP-2, is also a substrate for DPP-4, DPP-4 inhibitionmay enhance intestinal carcinogenesis by increasing endogenous active GLP-2. We therefore conducted this study to investigate the influence of a DPP-4 inhibitor on intestinal tumorigenesis in Apc Min/+ mice fed a HFD. Material and Methods: Segmental differences in DPP-4, 8, and 9 mRNA expression and DPP enzyme activity were determined in the mice. The DPP-4 inhibitor, sitagliptin (0.3, 1 or 3 mg/kg), was given orally. Mucosal DPP activity and GLP concentrations were measured 24 hr after administration. Six-week-old male Apc Min/+ mice were randomized to either a HFD (60 kcal fat) group or control diet (10 kcal fat) group for 9 weeks. Each group was divided into two groups, which were either treated or not treated with sitagliptin (3 mg/kg/day, i.g.). The mice were sacrificed 9 weeks after the initiation of treatment. The small intestine was coiled up into a Swiss roll, which was used to determine the number, size, and localization of tumors. Results: DPP-4 mRNA was expressed at high levels in the jejunum and ileum, with high DPP-4 activity also being detected. Oral sitagliptin caused a dose-dependent suppression in mucosal DPP-4 activity. Although the mucosal concentration of total GLP-2 was not affected, the concentration of GLP-1(7-36) was significantly elevated in the mucosa of the ileum. From seven to eight weeks after the initiation of sitagliptin treatment, bloody and inconsistent stools were observed mainly in the control diet and sitagliptin-treated mice. These mice also showed significantly lower body weight gains. In the control diet group, daily treatment with sitagliptin caused a significant increase in the number of intestinal tumors compared with mice not treated with sitagliptin. Daily treatment with sitagliptin suppressed the number of intestinal tumors in the HFD group, although this change was not statistically significant. Conclusion: This study demonstrated that chronic treatment with sitagliptin increased endogenous mucosal GLPs in the intestine and promoted intestinal tumorigenesis in lean mice, whereas sitagliptin treatment tended to suppress tumorigenesis in mice fed a HFD. Because a HFD promotes insulin resistance and intestinal neoplasia, DPP-4 inhibition may also be useful as an agent for preventing cancer in obese or diabetic patients.