Mechanisms by which butter fat may be protective against colon carcinogenesis

Abstract

Of all the cancers, colon cancer appears to be the most affected by diet, especially high intake of fat. Although the mechanisms by which dietary fats affect colon carcinogenesis are still unknown, they may involve the modulation of cell proliferation, fatty acid composition of membrane phospholipids and prostaglandin synthesis. The purpose of this study was to determine the effect of different types (butter fat, palm oil and corn oil) and amounts (5%, 7.5% and 15% by weight) of dietary fat on 1) colonic cell proliferation; 2) fatty acid composition of membrane phospholipids; 3) prostaglandin (PGE2and PGI2) synthetic capacity of colonocytes and relate changes in fatty acid composition in cell membrane phospholipids and prostaglandin synthetic capacity to changes in colonic cell proliferation. Ninety male Sprague Dawley rats were randomly assigned to one of nine experimental diet groups (3 different types of fat x 3 different amounts of fat). Two way analysis of variance was used to determine the effect of type of fat, amount of fat and the interaction. The P values were less than 0.05 for the effects of the type of fat or the amount of fat but not for the interaction. Total means of the type of fat groups or the amount of fat groups were separated by Duncan's Multiple Range Test. Butter fat resulted in a lower labeling index (P<O. 000 1) and a lower proliferative zone (P<O. 00 1 8) than either palm oil or corn oil in both proximal and distal colon. The type of fat had a significant effect on fatty 'd composition of phospholipids in both the proximal and distal colon. The butter fat diet which is high in saturated fatty acid did not result in higher levels of saturated fatty acids of mucosal phospholipids, whereas the corn oil diet which is high in linoleic acid (I 8:2n-6) resulted in higher levels of n-6 fatty acids of mucosal phospholipids. The significant effect of type of fats on prostaglandin synthesis was shown with PGE2only in the proximal colon (P<0.0387). Butter fat resulted in lower level of PGE2 production than either palm or corn oil. There were significant effects of amount of fats on PGE2 synthesis in the proximal (P<0.0239) and distal colon (P<0.0008). The significant effect of amount of fats on PGI2 synthesis was only in the distal colon (P<0.0027). The consistent pattern was observed with PGE2 synthesis in both proximal and distal colon and PGI2 synthesis in the distal colon.; The greater the amount of fat in the diet, the lower the production of prostaglandins. The data suggest that butter fat may be protective against experimentally induced colon carcinogenesis by decreasing precursors for prostaglandin synthesis thus decreasing synthesis of PGE2and decreasing cell proliferation.