Metformin prevents hormonal and metabolic disturbances and 1,2-dimethylhydrazine-induced colon carcinogenesis in non-diabetic rats

Objective: The morphology and functions of the proximal and distal large intestine are not the same. The incidence of colorectal cancer in these regions is also different, as tumors more often appear in the descending colon than in the ascending colon. Inflammatory bowel disease and colorectal cancer can increase transepithelial permeability, which is a sign of reduced intestinal barrier function. However, there is not enough evidence to establish a connection between the difference in colorectal cancer incidence in the proximal and distal colon and intestinal permeability or the effects of carcinogenesis on the barrier properties in various areas of the colon. The aim of the study was to assess the permeability of different segments of the large intestine according to a developed mapping methodology in healthy rats and rats with 1,2-dimethylhydrazine (DMH)-induced colon adenocarcinoma. Methods: The short circuit current, the transepithelial electrical resistance and the paracellular permeability to fluorescein of large intestine wall of male Wistar rats were examined in the Ussing chambers. The optical density of the solution from the serosa side to assess the concentration of the diffused fluorescein from mucosa to serosa was analyzed by spectrophotometry. The morphometric and histological studies were performed by optical microscopy. Results: Rats with DMH-induced colon adenocarcinomas showed elevated transepithelial electrical resistance in the areas of neoplasm development. In contrast, there was no change in the electrophysiological properties of tumor adjacent areas, however, the paracellular permeability of these areas to fluorescein was increased compared to the control rats and was characterized by sharply reduced barrier function. Conclusions: The barrier properties of the colon vary depending on tumor location. The tumors were less permeable than the intact intestinal wall and probably have a negative influence on tumor-adjacent tissues by disrupting their barrier function.

It has been shown that metformin dose-dependently inhibits the development of colon tumors induced by 1,2-dimethylhydrazine (DMH) in rats. The metformin effect manifested itself as a decrease in the amount and average size of tumors, increased degree of their differentiation, and reduction of invasion depth, which was more pronounced in the group of animals that received metformin at a dose of 100 mg/kg of body weight as compared with rats treated with metformin at a dose of 300 mg/kg.

Colon cancer is accompanied by a decrease of epithelial barrier properties, which are determined by tight junction (TJ) proteins between adjacent epithelial cells. The aim of the current study was to analyze the expression of TJ proteins in a rat model of 1,2-dimethylhydrazine (DMH)-induced colorectal cancer, as well as the barrier properties and TJ protein expression of IPEC-J2 cell monolayers after incubation with DMH. Transepithelial electrical resistance and paracellular permeability for sodium fluorescein of IPEC-J2 were examined by an epithelial volt/ohm meter and spectrophotometry. The expression and localization of TJ proteins were analyzed by immunoblotting and immunohistochemistry. In the colonic tumors of rats with DMH-induced carcinogenesis, the expression of claudin-3 and -4 was significantly increased compared to controls. The transepithelial electrical resistance of IPEC-J2 cells increased, while paracellular permeability for sodium fluorescein decreased, accompanied by an increased expression of claudin-4. The increase of claudin-4 in rat colon after chronic DMH exposure was consistent with the acute effect of DMH on IPEC-J2 cells, which may indicate an essential role of this protein in colorectal cancer development.

Recently it has been reported that the tumor adjacent colon tissues of 1,2-dymethylhydrazine induced (DMH)-rats revealed a high paracellular permeability. We hypothesized that the changes might be induced by cytokines. Colorectal cancer is accompanied by an increase in tumor necrosis factor alpha (TNFα) and interleukin 10 (IL10) that exert opposite regulatory effects on barrier properties of the colon, which is characterized by morphological and functional segmental heterogeneity. The aim of this study was to analyze the level of TNFα and IL10 in the colon segments of DMH-rats and to investigate their effects on barrier properties of the proximal and distal parts of the colon in healthy rats. Enzyme immunoassay analysis showed decreased TNFα in tumors in the distal part of the colon and increased IL10 in proximal tumors and in non-tumor tissues. Four-hour intraluminal exposure of the colon of healthy rats with cytokines showed reduced colon barrier function dependent on the cytokine: TNFα decreased it mainly in the distal part of the colon, whereas IL10 decreased it only in the proximal part. Western blot analysis revealed a more pronounced influence of IL10 on tight junction (TJ) proteins expression by down-regulation of the TJ proteins claudin-1, -2 and -4, and up-regulation of occludin only in the proximal part of the colon. These data may indicate a selective role of the cytokines in regulation of the barrier properties of the colon and a prominent role of IL10 in carcinogenesis in its proximal part.

The incidence of colorectal cancer in different parts of the large intestine is not the same, as tumors more often appear in the distal part of the colon compared to the proximal one. The purpose of this study was to investigate heterogeneity of the barrier properties of the colon and clarify the effects of Prostaglandin E2 and interleukin-1beta on its different parts. An in-depth analysis of short circuit current, transepithelial electrical resistance and paracellular permeability for sodium fluorescein in Ussing chambers showed that the proximal part of the colon was less permeable compared to the distal one and the substances had different effects on the parameters of permeability in different parts of the colon. We suppose that heterogeneity of the barrier properties of the colon and various effects of their regulation by local molecular agents may determine different incidence of pathologies in the colon.