Use of fecal water as a biomarker in dietary intervention studies

In epidemiologic studies investigating associations between nutritional factors and cancer, the observed study end point generally is the clinical diagnosis of tumor occurrence. In experimental studies, however, it is desirable to develop biomarkers linked to the early stages of carcinogenesis. In particular, such efforts have been made in colonic carcinogenesis in which the molecular details of the different stages are well characterized. The types of biomarkers necessary in dietary intervention studies are biomarkers of exposure, effect and susceptibility. The rapid advancement of genetic testing, determination of genetic polymorphisms and link of genetic disposition to dietary effects on carcinogenesis is of great scientific interest and importance. Biomarkers of exposure are usually measured in blood plasma, and dose-dependent changes in plasma concentration are studied to evaluate the bioavailability of dietary components. However, in colonic carcinogenesis, it is also important to determine the exposure biomarkers directly in the intestinal lumen or feces and the exposed epithelial cells. In dietary intervention studies with healthy volunteers, the effects of consuming carotenoid-containing foods (carrot and tomato juice) on the carotenoid concentration in fecal water was investigated. Carotenoid concentrations up to 50-60 [micro]mol/L were measured. These values are at least 10 times higher than the maximal concentrations that would be achieved in the plasma after prolonged consumption of carotenoid-rich foods with high bioavailability or using dietary supplements. Investigating the biological effects of carotenoids at concentrations present in fecal water on human colon carcinoma cell lines (HT29) revealed that the high concentrations induced apoptosis in growing cells (50% inhibitory concentration: ~15 [micro]mol/L for [beta]-carotene). Fecal water itself not only induces apoptosis but also markedly reduces the proliferation of colon carcinoma cells. Fecal water (diluted 1:100) caused an inhibition of cell growth by ~50%, indicating a pronounced antiproliferative potential. Intervention with carotenoid-rich foods did not significantly alter the antiproliferative effect of fecal water. In summary, the development and validation of suitable biomarkers is of great importance in dietary intervention studies investigating the link between dietary factors and various molecular and cellular processes of carcinogenesis.