Browsing by Subject "Colonmucosa"

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Erhöhung der Butyratbildung durch Fütterung von Resistenter Stärke beim Schwein: Konsequenzen für die Mitose und Apoptoseregulation der Colonmucosa
(2004) Mentschel, Joachim; Claus, Rolf
Effects of nutrition on health status were examined in numerous studies for human as well as animal species. The interest is mainly focused on those components which are known to exert a beneficial effect on health. Specifically prae- and probiotic substances are discussed to decrease the use of antibiotics in animal nutrition. Moreover epidemiological studies suggest that a higher fiber content reduces the risk for carcinogenesis. The effects seem to be mediated by short chain fatty acids (SCFA). SCFA are major products of microbial fermentation of fiber in the hindgut and are essential for normal colonic function. Butyrate has been shown to have the most significant effects on colonic epithelium. For example colonic recovery after mucosal atrophy is improved due to butyrate supply. To examine the principles of the butyrate dependent effects, in numerous studies the effects of butyrate on mitosis, cell differentiation, and apoptosis of epithelial cells were determined. It has been shown that butyrate increases proliferation of normal cells both in vitro and in vivo, but decreases proliferation in neoplastic cells in vitro. In addition the incubation of adenoma and tumour cell lines with butyrate induced apoptosis whereas the absence of butyrate from the incubation medium triggered apoptosis in guinea pig colonic mucosa. This antiapoptotic function of butyrate has been confirmed in the bovine ruminal epithelium. The reasons for these contradicting results and the regulation of butyrate mediated apoptosis have not been examined so far. In the present study, therefore, the effects of butyrate on colonic epithelium were investigated by feeding resistant potato starch. Effects were verified by determining immunocytochemical parameters. The experiments were performed with 18 castrated male pigs (German Landrace x Pietrain). They were divided into the control group, the resistant starch group (RS), and the realimentation group (RE). At the end of the feeding period the pigs were killed and tissue samples for immunocytochemical studies were obtained. The controls were fed during the whole treatment period (19d) with a ration containing pregelatinized starch with a high ileal digestibility (14,13 MJME and 173,5g XP / kg DM). The RS group received the same diet for 10 days. Thereafter a ration with a lower ileal digestibility containing raw potato starch (11,28 MJME and 138,5g XP/ kg DM) was fed for 5 days in the adaptation period and for 19 d in the treatment period. The pigs of the RE group were fed identically, however after the control diet a starvation period of 3 days was included. Due to the lower energy content of resistant starch compared to pregelatinized starch the average energy and protein content differed between the two rations. To ensure an equal energy and protein supply the RS and RE group received a higher amount of the resistant starch ration. For later analytical determination of pH and SCFA, representative amounts of fresh faeces were collected every morning. They were stored deep frozen (-20°C). At the end of the experimental period pigs were killed and colonic tissue samples were taken for histological and immunocytochemical analysis. Feeding of resistant starch led to a 2.2-fold increase of butyrate in faeces. The morphological results revealed a significant increase of crypt depth (20%) in the resistant starch groups. This difference, however, can not be explained by a different mitotic rate which was nearly identical in both groups. Thus the morphological difference has to be attributed to the differences in the apoptotic activity which was significantly lower (40%) in the groups fed with resistant starch. This decrease of apoptosis was paralleled by an increase of the mucus area of goblet cells which were shown to contain EGF (epidermal growth factor). The difference was about 50%. The results indicate a link between apoptosis and EGF in the colonic epithelium. A reduction of apoptosis by 40% and no change of mitotic rate should lead to higher differences in epithelial development. The low increase of crypt depth can be explained by the shift of apoptosis along the crypt axis. In the group with high butyrate levels 39% of the apoptotic cells were located in the basal compartment of the crypts, in the control-group, however, only 17%. This higher incidence of apoptosis in the stem-cell compartment led to an decrease of average lifespan of colonocytes and consequently to the relative low increase of epithelium. The compartmental distribution of apoptosis is regulated by pro- and antiapoptotic members of the bcl-2 family. Compared to the control group the higher apoptotic rate in the basal compartment of the butyrate group was paralleled by the higher expression (3,5- fold) of the proapoptotic protein Bak. In addition the expression of the antiapoptotic protein Bcl-2 was increased in the luminal compartment by 55%. The results of the RS and RE group did not differ significantly. Due to the treatment-period of 19 days and the high turnover-rate in the colon the effects of starvation seem to be compensated. In conclusion the results demonstrate that under in vivo conditions in the pig butyrate is an inhibitor of apoptosis, but additional mechanisms ensure that the resulting proliferation is limited.