UC Irvine

A preponderance of carcinogenesis studies in rodents and epidemiologic studies in humans suggests a potential role of dietary fiber in the prevention of colorectal cancer. Recently, wheat bran fiber used as a dietary supplement has been shown to decrease the growth of rectal adenomatous polyps in patients with familial polyposis; however, few studies of high-risk human populations have been attempted to determine the effects of dietary fiber supplementation on markers of carcinogenesis in the colon or rectum. We have designed a one-arm study to evaluate the effects of dietary supplementation with wheat bran fiber [i.e., 13.5 g/day for 8 wk; after 1 mo, 2 g/day (compliance evaluation period)] on [3H]thymidine rectal mucosa cell labeling (i.e., percent of epithelial cells incorporating [3H]thymidine into DNA in intact rectal crypt cells over a 90-min exposure as well as in minced rectal biopsy tissue over a 24-hr exposure) in rectal biopsy specimens. The biopsy specimens were obtained at sigmoidoscopy in 17 compliant patients with a history of resected colon or rectal cancer. We categorized patients as having initially low or initially high [3H]thymidine-labeling indices (i.e., percent of mucosa cells that incorporate [3H]thymidine into DNA during 1.5- or 24-hour in vitro incubations) by using the median baseline labeling index as a cutoff between high and low values. On the basis of a chi-square test used to identify patients with a statistically significant (P less than .001) change, six of the eight patients who initially had high 24-hour outgrowth labeling indices showed a significant decrease in the rectal mucosa biopsy specimens obtained after treatment. An overall 22% decrease was observed in rectal mucosa cell biopsy specimens obtained at study termination (P less than .001). Of the eight patients with initially high total [3H]thymidine-labeling indices in crypt organ culture, four had a significant (P less than .001) decrease from baseline values, one had a significant increase, and three showed no change following the fiber intervention. The wheat bran fiber dietary supplement of 13.5 g/day was well tolerated by this group of older (54-70 yr) patients. Although the [3H]-thymidine labeling index data suggest that the wheat bran fiber supplement can inhibit DNA synthesis and rectal mucosa cell proliferation in high-risk patients, the results of this small pilot study should not be overinterpreted vis à vis the potential role of wheat bran fiber as a chemopreventive agent for colorectal cancer.(ABSTRACT TRUNCATED AT 400 WORDS)