Effect of subacute ibuprofen dosing on rectal mucosal prostaglandin E2 levels in healthy subjects with a history of resected polyps.

Nonsteroidal antiinflammatory drugs are among the most promising chemopreventive agents for colorectal cancer. Although the mechanism by which nonsteroidal antiinflammatory drugs exert such effects remains to be further characterized, their best known pharmacological effect is inhibition of prostaglandin synthetase, which leads to decreases in tissue prostaglandin levels. We conducted a randomized, double-blind, controlled study to examine the effect of daily ibuprofen treatment on the rectal mucosal prostaglandin E2 (PGE2) levels in healthy subjects with a history of resected polyps. Study participants (n = 27) completed a 2-week run-in period and were then randomized to take a single, daily dose of ibuprofen (300 or 600 mg) or of a placebo for 4 weeks. Rectal biopsy specimens were taken before and after the run-in period and at 2 and 4 weeks after the ibuprofen/placebo treatment. Notably large between- and within-subject variability in the rectal mucosal PGE2 content was seen. The changes in PGE2 levels after ibuprofen/placebo treatment correlated with the baseline PGE2 content. After adjustment of the baseline values, 2 weeks of 300 mg/day of ibuprofen treatment resulted in significantly more suppression of PGE2 levels than that observed after the placebo treatment (55% versus 22% suppression from baseline; P = 0.033). Although other ibuprofen treatment schedules and doses appeared to result in suppression in the PGE2 levels, the suppression was not statistically significant because of the large variability in this measurement. Because lower doses are associated with fewer adverse effects, a dose of 300 mg of ibuprofen/day should be considered for future Phase II chemoprevention studies. Stratifying study participants, based on their baseline PGE2 levels and inclusion of a larger number of study subjects, are recommended for future trials where the rectal mucosal PGE2 level is to be used as a surrogate end point biomarker.

Lack of effect of a high-fiber cereal supplement on the recurrence of colorectal adenomas. Phoenix Colon Cancer Prevention Physicians' Network.

BACKGROUND: The risks of colorectal cancer and adenoma, the precursor lesion, are believed to be influenced by dietary factors. Epidemiologic evidence that cereal fiber protects against colorectal cancer is equivocal. We conducted a randomized trial to determine whether dietary supplementation with wheat-bran fiber reduces the rate of recurrence of colorectal adenomas. METHODS: We randomly assigned 1429 men and women who were 40 to 80 years of age and who had had one or more histologically confirmed colorectal adenomas removed within three months before recruitment began to a supervised program of dietary supplementation with either high amounts (13.5 g per day) or low amounts (2 g per day) of wheat-bran fiber. The primary end point was the presence or absence of new adenomas at the time of follow-up colonoscopy. Subjects and physicians, including colonoscopists, were unaware of the group assignments. RESULTS: Of the 1303 subjects who completed the study, 719 had been randomly assigned to the high-fiber group and 584 to the low-fiber group. The median times from randomization to the last follow-up colonoscopy were 34 months in the high-fiber group and 36 months in the low-fiber group. By the time of the last follow-up colonoscopy, at least one adenoma had been identified in 338 subjects in the high-fiber group (47.0 percent) and in 299 subjects in the low-fiber group (51.2 percent). The multivariate adjusted odds ratio for recurrent adenoma in tile high-fiber group, as compared with the low-fiber group, was 0.88 (95 percent confidence interval, 0.70 to 1.11; P=0.28), and the relative risk of recurrence according to the number of adenomas, in the high-fiber group as compared with the low-fiber group, was 0.99 (95 percent confidence interval, 0.71 to 1.36; P=0.93). CONCLUSIONS: As used in this study, a dietary supplement of wheat-bran fiber does not protect against recurrent colorectal adenomas.

APC-dependent changes in expression of genes influencing polyamine metabolism, and consequences for gastrointestinal carcinogenesis, in the Min mouse.

The colorectal mucosa of pre-symptomatic individuals with familial adenomatous polyposis (FAP) contains elevated levels of the proliferation-associated polyamines. The Min mouse, like humans with FAP, expresses an abnormal genotype for the APC tumor suppressor gene. In order to determine how APC mutation influences intestinal tissue polyamine content, we measured steady-state RNA levels of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, antizyme (AZ), a protein which negatively regulates ODC, and the spermidine/spermine N(1)-acetyltransferase (SSAT), the first enzyme in polyamine catabolism. RNA content was increased 6- to 8-fold in both the small intestine and colon for ODC, decreased significantly in the small intestine but not the colon for AZ and was not statistically different in either intestinal tissue for SSAT in Min mice compared with normal littermates. Consistent with the changes in ODC and AZ gene expression, small intestinal, but not colonic, polyamine content was elevated in Min mice compared with normal littermates. Treatment of Min mice with the specific ODC inhibitor difluoromethylornithine (DFMO) suppressed small intestinal, but not colonic, polyamine content and tumor number. These data indicate that small intestinal tissue polyamine content is elevated in Min mice by a mechanism involving APC-dependent changes in ODC and AZ RNA. Further, ODC enzyme activity, which is influenced by both ODC and AZ RNA levels and inhibited by DFMO, is consequential for small intestinal tumorigenesis in this model. In the FAP population, DFMO may be of value in the chemoprevention of small intestinal adenocarcinoma that remains a risk following colectomy.