Expression of metallothionein in dimethylhydrazine-induced colonic precancerous and cancerous model in rat.

Aim: Metallothionein (MT) is a small protein with a high affinity for divalent heavy metals and has a function in zinc homeostasis. The purpose of this study was to assess the MT mRNA gene expression as well as the MT protein content by immunohistochemistry and radioimmunoassay (RIA) in 1,2-dimethylhydrazine (DMH)-induced precancerous and cancerous colonic tissue in rats.

Materials And Methods: Six-week-old rats were given subcutaneous injections of DMH twice a week for 3 months and sacrificed at 4 months (precancerous model) and 6 months (cancerous model). We determined MT mRNA expression by reverse transcription polymerase chain reaction and MT protein content by both immunohistochemical expression and cadmium-109 RIA.

Results: MT mRNA expression in the large intestine showed statistically significant decrease in the precancerous (P < 0.01) and the cancerous (P < 0.001) model as compared with controls. Immunohistochemical expression of MT showed statistically significant decrease (P < 0.05) in the colonic cancerous tissue. MT content in the large intestine showed statistically significant decrease in precancerous (P < 0.005) and cancerous (P < 0.001) model as compared with controls.

Conclusion: This study suggests that a decrease in the colonic MT mRNA expression, MT protein expression, and content in DMH-induced colonic cancer model is associated with the development of preneoplastic lesions and further progression to carcinoma in the colon results in a greater reduction in the levels of each of these parameters.