Topical Area: Diet and Cancer
Objectives : Colon Cancer is the second deadliest cancerous disease worldwide among men and women. It has been estimated that more than half of colon cancers may be preventable by dietary intervention. A disturbance of the homeostasis between cellular proliferation and apoptosis is associated with colon cancer development. Watermelon (Citrullus lanatus) is rich in L-citrulline, a precursor of L-arginine. It has been shown that L-arginine may have anti-inflammatory roles and serves as a substrate for synthesis of nitric oxide, which in turn exerts wide-ranging physiological effects including tumoricidal effects via modification of cell kinetics. Our research examined if colon cancer can be prevented with the supplementation of watermelon powder by lowering cellular proliferation but enhancing apoptosis.
Methods : In order to test the hypothesis, 21-days old 32 Sprague Dawley rats were allocated to three groups; control, L- arginine (0.36% L-arginine) and watermelon powder (0.5%, w/w). Carcinogen azoxymethane was injected at week 4 and 5, and colon tissues were harvested at 5 week after the 2nd carcinogen injection. Cell proliferation and apoptosis were enumerated using a quantitative immunohistochemical analysis of Ki-67 antibody and TUNEL assay, respectively.
Results : Cell proliferation was mainly located bottom of colonic crypt (P < 0.05). Apoptotic cells were mostly located in the upper part of crypt (P < 0.05). L-arginine and watermelon fed rats lowered cell proliferation index and proliferative zone (P < 0.05). However, no difference was found on apoptosis among the three groups.
Conclusions : These results suggest that watermelon powder supplementation may reduce the risk of colon cancer by reducing cell proliferation rather than alteration of apoptosis. Further study will follow to determine the mechanism of anti-proliferative effect of watermelon supplementation.
Funding Sources : National Watermelon Promotion Board; SDSU/UCSD Cancer Center Partnership Scholars Program