Browsing by Subject "Short chain fatty acids"

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Einfluss kurzkettiger Fettsäuren und mikrobieller Fermentationsprodukte neuartiger Oligosaccharide auf Cytotoxizität, Proliferation und Apoptose von humanen Coloncarcinom-Zelllinien
(2006) Roser, Silvia; Rechkemmer, Gerhard
Colon cancer is the second most common cancer in Germany. The role of dietary fibre in the prevention of colon cancer is still controversial: Promising results from in vitro and animal studies are contradictory to inconsistent results from epidemiological stu-dies. Functional carbohydrates as constituents of prebiotic food can modify the colonic microflora for the benefit of short chain fatty acid (SCFA)-producing microbial strains. The SCFA-concentrations should also be increased in the distal part of the colon where most colon carcinomas are developing. SCFA are considered to be preventive against colon cancer. For this study, three different new functional oligosaccharides (OS, made of Isomaltulose and resistant starch) were produced from the Südzucker company and fermented in vitro with human feces of healthy test subjects. The resulting fermentation supernatants (FS) were tested in a cell culture system, using colon carcinoma cell lines of various degrees of differentiation (HT29, HT29 Clone 19A, T84). Cytotoxicity, proliferation, the induction of apoptosis, influences on the cell cycle and electrophysiological parameters were measured. Spectral photometric and flow cytometric methods were performed, as well as measurements in vertical diffusion chambers (Ussing chambers). The parallel testing of SCFA-mixtures with the same SCFA-concentrations as in the FS was included, as well as the testing of a FS ?Control? which was produced without OS-fermentation. Several independent fermentations revealed reproducible results regarding the SCFA-concentrations of the FS. After OS-fermentation, the ratio of the three major SCFA in the FS, acetate, propionate, and butyrate, was similar to that observed in vivo. The FS and SCFA-mixtures tested had a cytotoxic effect on all cell lines at the con-centration of 50 %. A dose dependent decrease in cell proliferation could be found, as well as the induction of apoptosis at a concentration of 50 %. Parallel testing of the analogous SCFA-mixtures showed that cytotoxic and proliferation inhibiting effects of the FS could be primarily attributed to their SCFA-content. This could not be confirmed for apoptosis induction: the SCFA-mixtures were mostly able to induce a higher apoptosis rate than the FS. Similarly, the effects of FS and SCFA-mixtures on the cell cycle were different: The SCFA-mixtures showed more potent inhibition of DNA-synthesis than the analogous FS, which generally led to an arrest in the G2-phase of the cell cycle. Neither FS nor SCFA-mixtures had an impact on transepithelial resistance or short circuit current of differentiated cell monolayers in Ussing chambers. The difference in the fermentation patterns of the various FS and the SCFA-concentrations of the SCFA-mixtures was not great enough to achieve significantly different results in the test systems used. Also, the various differentiation grades of the cell lines showed inconsistent results after treatment with FS and their SCFA-mixtures, so that no correlation could be found between degree of differentiation and test compound action. This study shows that the in vitro fermentation of OS with human feces results in reproducible SCFA-patterns in the FS, similar to the in vivo situation. For the screening of FS and their SCFA-mixtures, respectively, a spectrum of methods was established for the incubation with colon carcinoma cell lines of various differentiation states and of all stages of growth (exponential, subconfluent, confluent, fully differentiated monolayer). Indeed, the effects measured after incubation with FS could only in part been ascribed to their SCFA content. Other FS components than SCFA that play a role, especially regarding to their apoptosis inhibiting and cell cycle influencing effects, remain to be identified. Also, this study allows no conclusions to be drawn, which of the fermented OS is more promising in it?s beneficial influence on colon cancer preventing factors, e.g. the induction of apoptosis, than the other. Future studies should investigate FS with greater differences in their SCFA-concentrations. The same OS which were used for the in vitro fermentation, should also be tested in animal studies and human intervention studies to elucidate their fermentation patterns in vivo.