Diabetes promotes DMH-induced colorectal cancer by increasing the activity of glycolytic enzymes in rats

Abstract

The objective of the present study was to investigate the association between diabetes mellitus and colorectal carcinogenesis as well as the possible mechanism involved in this interaction. Diabetes rat models were induced with a low dose of STZ followed by a low dose of DMH to induce colorectal cancer. The formation of ACF in the colon and the incidence, number and size of tumors were measured. The activity of glycolytic enzymes in colonic tissues was also measured. The results demonstrated that both the total number of ACF and the number of foci that contain a different number of crypts were increased in diabetic rats. At the end of the experimental treatment, the incidence, number and size of tumors were also increased in diabetic rats. Overall, these data indicated that diabetes increased the risk of colorectal cancer. The activity of HK and PK in colonic tissues was increased in diabetic rats, whereas the activity of PDH was decreased. In addition, the activities of these enzymes in intratumor were higher than that of in peritumor. These data indicated that the high rate of glycolysis may play a role in colorectal carcinogenesis in diabetic rats.

Figure 1. Time course of the experiment and the animal treatment procedures.

STZ was administered as 35 mg/kg, i.p. and DMH was administered as 25 mg/kg/week, i.p. The abbreviations denote STZ: Streptozotocin; DMH: 1,2-dimethylhydrazine; ACF: Aberrant crypt foci.

Figure 2. Body weight of rats throughout the entire experiment.

Values are expressed as mean ± S.E.M. and analyzed using unpaired student’s T test at P<0.05. At the conclusion of the experiment, *P<0.05 vs. Control group. ^#P<0.05 vs. DMH group.

Figure 3. Formation of ACF induced by DMH in the rat colon.

Fig. 3A: normal crypt foci (100×). Fig. 3B: Crypt enlargement and deformation (40×). Fig. 3C: ACF formed by 2 aberrant crypts (40×). Fig. 3D: ACF formed by 3 aberrant crypts (40×). Fig. 3E: ACF formed by ≥3 aberrant crypts (40×). Fig. 3F: tumor-like tissue (40×).

Figure 4. Tumor tissues obtained from DMH-induced rats.

Fig. 4A: The largest tumor obtained from the STZ+DMH group. Fig. 4B: Several small tumors together isolated from the DMH group. Fig. 4C: Several tumors collected from one rat in the STZ+DMH group. Fig. 4D: Tumor growth in the intestinal lumen interfering with bowel movements, resulting in difficult defecation and building of gas in the intestine in some rats.

Figure 5. A bar chart demonstrating the proliferation index (PI) of colorectal tumor cells in DMH-induced colon tissues (DMH group and STZ+DMH group).

The PI was expressed as the percentage of PCNA-positive nuclei among the total number of cells counted. Values are expressed as mean ± S.E.M. and analyzed using unpaired student’s T test at P<0.05. *P<0.05 vs. DMH group.

Figure 6. Bar charts demonstrating the enzyme activities in colon tissues.

No tumor formation was detected in the Control group and STZ group, so dissect the samples at random. Samples were collected from the intratumoral and the peritumoral regions respectively in the DMH group and STZ+DMH group. The activities of hexokinase (HK), pyruvate kinase (PK) and pyruvate dehydrogenase (PDH) in colonic tissues were measured. Values are expressed as mean ± S.E.M. and analyzed using unpaired student’s T test at P<0.05. Fig. 6A: Analysis of HK. *P<0.05 vs. Control group. ^#P<0.05 vs. Peritumor respectively. ^$P<0.05 vs. DMH group respectively; Fig. 6B: Analysis of PK. *P<0.05 vs. Control group. ^#P<0.05 vs. Peritumor respectively; Fig. 6C: Analysis of PDH. *P<0.05 vs. Control group. ^#P<0.05 vs. Peritumor respectively. ^$P<0.05 vs. DMH group respectively. Fig. 6D: Analysis of HK, PK and PDH activities at different time course in the STZ+DMH group. *P<0.05 vs. Start point respectively. ^#P<0.05 vs. STZ injection respectively.