Mechanisms and anticarcinogenic effects of diet-related apoptosis in the intestinal mucosa.

There is now ample epidemiological evidence to show that the wide international variations in the incidence of both adenomatous polyps and colo-rectal cancer are linked to diet, but the mechanisms through which particular dietary constituents influence the onset of neoplasia are poorly understood. The crypt epithelial cells of the human gastrointestinal mucosa are amongst the most rapidly proliferating tissues in the body, and those of the colorectum are particularly vulnerable to neoplasia. Within the crypt, continuous division of basally localized stem cells gives rise to daughter cells that may divide once or twice again, before differentiating and migrating to the mucosal surface. The majority of nascent crypt epithelial cells differentiate, become senescent and are shed into the gut lumen, but a small proportion die by apoptosis soon after cell division. Various lines of evidence suggest that these pathways of programmed cell death provide a protective mechanism against induction of neoplasia by removing genetically damaged stem cells before they can divide further and give rise to precancerous lesions. There is evidence that the short-chain fatty acid butyrate and several different classes of food constituents, including some polyunsaturated fatty acids, flavonoids and glucosinolate breakdown products, can regulate the processes of cell proliferation and death in vitro, and in colorectal crypts in vivo. All three classes of food components suppress the emergence of aberrant crypt foci in animal models of carcinogenesis. The cellular mechanisms underlying these phenomena, and their possible significance for human health, are discussed.