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Article

Dietary Soy Protein Is Associated with Reduced Intestinal Mucosal Polyamine Concentration in Male Wistar Rats¹

Weiqun Wang ^*,2 and Carl M. Higuchi^**

^* Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011; Cancer Research Center of Hawaii, University of Hawaii, Honolulu, HI 96813; and ^** John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96822

²To whom correspondence should be addressed.

Quantitation of polyamine levels has been correlated with biomarkers of proliferation in the colon mucosa where dysregulated epithelial hyperproliferation is associated with colorectal cancer risk. This study was performed to assess the response of polyamine measurements to dietary factors in an animal model. Male Wistar rats were fed purified diet or diets substituted by 20% lard fat, 20% beet fiber and 20% soy protein. After 2 wk, mucosal polyamines were measured along intestinal tracts by HPLC. In rats fed the control diet (n = 10), mucosal polyamines were found at high levels in the duodenum, jejunum and ileum but at low levels in the cecum, colon and rectum. Compared with rats fed the control diet, those fed the 20% lard diet showed greater polyamine levels in the large intestine (P < 0.05, n = 10), but those fed the 20% fiber diet exhibited lower polyamine levels in the small intestine (P < 0.05, n = 9). However, rats fed the 20% soy protein diet had lower polyamine levels in both small and large intestines (P < 0.05, n = 15). Significant linear correlations were observed between rectal polyamine levels and the dietary energy intakes in these four diet groups (r = 0.972–0.991, P < 0.001). Supplementation of 0.1% soy isoflavones to the basal diet or 0.3% DL-methionine to the 20% soy protein diet for 4 wk did not affect polyamine levels. The results indicate that soy protein reduced mucosal polyamine levels, at least in part, through reduction of energy intakes. Further studies are warranted to verify that polyamine levels in intestinal mucosa are useful as an intermediate endpoint of the dietary risk factors.

KEY WORDS: • polyamines • soy proteins • biomarker • colorectal cancer • rats