Submitted to: North Dakota Academy of Science Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/25/2002
Publication Date: 4/25/2002
Citation: Fox, E., Davis, C.D., Johnson, W.T. 2002. Dietary copper but not dietary zinc decreases protein kinase C alpha expression and dimethylhydrazine-induced aberrant crypt foci formation in the rat colon [abstract]. Proceedings of the North Dakota Academy of Science. 56:45.
Technical Abstract: Worldwide, colon cancer is the fourth greatest cause of cancer death. In the United States, it is the second leading cause of cancer mortality. It is believed that diet is the single largest factor to bring about colon cancer and may account for 35-45% of the disease. It has been shown that copper (Cu) deficiency increases the incidence of chemically-induced colon cancer in rats. A recent study has also shown that changes in protein kinase C (PKC) isoform protein concentration may correlate with the increased susceptibility of Cu-deficient rats to colon cancer. However, the effect of dietary zinc (Zn) on colon cancer susceptibility and PKC expression is unknown even though PKC is a zinc-containing protein. The purpose of this study was to determine what, if any, effect dietary Zn has on colon cancer susceptibility and PKC expression. One hundred eight weanling, male Fischer-344 rats were fed diets containing 1 ug Cu/g or 6 ug Cu/g diet and 5 ug Zn/g diet or 35 ug Zn/g diet in an AIN-93 based diet. The experimental diets continued for 24 days after which 21 rats/diet were injected with dimethylhydrazine (DMH) (25 mg/kg body weight) dissolved in saline with 1 mmol/L EDTA, adjusted to pH 7.4 with NaOH. They were given an additional similar dose 7 days later. Six other rats/diet received a comparable injection of saline with 1 mmol/L EDTA only. Two weeks after the last carcinogen dose the rats used for PKC analysis (6 carcinogen and 6 control per diet) were sacrificed. Six weeks later the remaining 15 animals per diet were sacrificed for aberrant crypt analysis. Samples from rats used for PKC analysis were obtained by removing the colon and rectum and flushing with cold saline. The colonic mucosa was scraped and processed. PKC was determined by immunoblotting. Crypt analysis was done by fixing the entire colon and rectum between a paper towel in 70% ethanol. The samples were stained with 1 g/L methylene blue in 0.1 mol/L sodium phosphate buffer (pH 7.4). The total number of aberrant crypts (AC) and aberrant crypt foci (ACF) were evaluated by means of a dissecting microscope to visualize the ACF and AC. This study lends support to previous studies showing that rats fed Cu-deficient diets has decreased PKC alpha protein expression and increased DMH-induced aberrant crypt formation. The Western blots indicate that dietary copper deficiency significantly reduced PKC alpha protein in both the homogenate (p<0.009 and cytosolic (p<0.04) fractions; however, the varying levels of dietary zinc did not affect PKC alpha protein expression. The rats fed the Cu-deficient diet had 30% more total aberrant crypts (p<0.003) and 22% more aberrant crypt foci (p<0.003) than did animals fed the Cu-adequate diet. Therefore, while dietary copper did appear to affect the rat susceptibility to colon cancer, dietary zinc did not appear to have any effect. Zinc is needed for normal growth. Therefore, the lack of an effect of dietary zinc may affect normal development, but not the abnormal development of cancer. Within this study, the rats fed the zinc deficient diet weighed less than the rats fed the zinc adequate diet.