Uptake of the colon carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by different segments of the rat gastrointestinal tract: Its implication in colorectal carcinogenesis

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a colon carcinogen in rats. In the present study the absorption of PhIP in the small and large intestine of Fischer 344 rats was determined, and the relevance of the differences in the degree of absorption of PhIP along the gastrointestinal axis for the PhIP-mediated colon carcinogenesis process is discussed. PhIP uptake was low in the different gut sections of Fischer 344 rats, the PhIP tissue levels varying in the following order: proximal jejunum > distal jejunum > proximal colon > distal colon = rectum. Furthermore, abcc2 was mainly expressed in the proximal parts of the small intestine, in particular in the proximal jejunum. Extremely low expression levels were observed in distal jejunum, ileum, caecum and proximal colon, whereas abcc2 was almost not detected in distal colon and rectum. These data, together with previously published results, lend support to the hypothesis that PhIP is taken up in the proximal segments of the small intestine and after being metabolically activated in the liver reaches the stem cell compartment of the colonic crypts via the blood circulation, the crypt cells in the distal colon and rectum being particularly at risk, since these almost do not express abcc2.     

Prä- und probiotische Kosmetik

The human skin provides a habitat for a variety of microorganisms, the skin microflora. There is a complex network of interactions between the microbes and cells of the epidermis. Modern analytical methods in molecular biology have revealed new insights into this complex diversity of partially unculturable microbial organisms. Most of the resident microbes on healthy skin can be regarded as being harmless or even beneficial to skin. In the case of diseases with some imbalance in microorganisms, such as impure skin/mild acne or dry skin/mild atopic dermatitis, pre- and probiotic concepts represent an effective alternative to strictly antibacterial products. Prebiotic actives rebalance the skin microflora while probiotic approaches predominantly consist of applying an inactivated microbial biomass of beneficial bacteria. Several examples of successful in vivo studies illustrate this new principle for gentle cosmetics derived from the food sector.     

Application of the colon-simulation technique for studying the effects of Saccharomyces boulardii on basic parameters of porcine cecal microbial metabolism disturbed by clindamycin

AIMS: The present study analyzed the effects of Saccharomyces boulardii on the biochemical parameters of microbial hindgut metabolism disturbed by clindamycin. METHODS: The experiments were carried out under in vitro conditions using the semicontinuous colon-simulation technique. This technique is standardized for quantitatively measuring parameters of microbial hindgut metabolism. The fluid and particle phase of pig hindgut contents were used for the in vitro incubations. The 5-day control period was followed by clindamycin exposure alone (312.5 mg/day for 5 days) or by a combined treatment of clindamycin and S. boulardii (400 mg/day for 5 days). RESULTS: Clindamycin resulted in significant decreases in production rates of short-chain fatty acids (SCFAs) which were associated with substantial changes in molar SCFA proportions at the expense of butyrate. These effects could at least partly be compensated for by S. boulardii, in particular by enhancements of acetate and propionate fermentation to control levels. In contrast, butyrate fermentation could not be reconstituted. In a second experiment the potential use of S. boulardii as a substrate for hindgut microbial metabolism was studied by comparing living and autoclaved yeast. Propionate and butyrate fermentation rates were unaffected whereas acetate fermentation tended to be higher in the presence of living yeast. CONCLUSIONS: S. boulardii can be effective to compensate for changes in microbial fermentation in response to antibiotic treatment. Despite the lack of statistical significance it might be concluded that the increase in fermentation end products can only partly be explained by the utilization of the yeast as a substrate for microbial metabolism.     

Reactions of N-quaternary 1-phenyl-3,4-dihydroisoquinolinium compounds with nucleophiles--products and their isomerism--part 2

A series of substituted 1-phenyl-3,4-dihydroisoquinolinium compounds was treated with O-, C- and N-nucleophilic agents in order to study ring-chain isomerism of the products. With methanolate carbinolamine ethers and with cyanide pseudocyanides as cyclic species resulted from these iminium salts. Electronic and steric differently substituted dihydroisoquinoline compounds reacted with hydroxylamine under ring opening generally to amine oximes predominantly in their Z-configuration. A cyclic isomer substituted with a hydroxylamine group--also in equilibrium in solution--could be excluded. With O-methylhydroxylamine a similar reaction gave rise to amine oxime methyl ethers only. 4-Phenylsemicarbazide and 4-nitrophenylhydrazine in pyridine produced the ring opened hydrazone derivatives.     

Transgenic maize in the presence of ampicillin modifies the metabolic profile and microbial population structure of bovine rumen fluid in vitro

Recently, transgenic crops have been considered as possible donors of transgenes that could be taken up by micro-organisms under appropriate conditions. In an in vitro rumen simulation system, effects of ampicillin on microbial communities growing either on rumen contents with transgenic maize carrying a gene that confers resistance to ampicillin or its isogenic counterpart as substrates were examined continuously over 13 d. Rate of production of SCFA was measured to determine functional changes in the rumen model and single-strand conformational polymorphism was used to detect alterations in structure of the microbial community. Rumen contents treated with ampicillin displayed a marked decrease in the rate of production of SCFA and diversity of the microbial community was reduced severely. In the presence of transgenic maize, however, the patterns of change of rumen micro-organisms and their metabolic profiles were different from that of rumen fluid incorporating maize bred conventionally. Recovery of propionate production was observed both in the rumen fluid fed transgenic and conventional maize after a delay of several days but recovery occurred earlier in fermenters fed transgenic maize. Alterations in the microbial population structures resulting from the ampicillin challenge were not reversed during the experimental run although there was evidence of adaptation of the microbial communities over time in the presence of the antibiotic, showing that populations with different microbial structures could resume a pre-challenge metabolic profile following the introduction of ampicillin, irrespective of the source of the plant material in the growth medium.     

Regulation of growth hormone (GH) receptor (GHR1 and GHR2) mRNA level by GH and metabolic hormones in primary cultured tilapia hepatocytes

Growth hormone (GH) regulates essential physiological functions in teleost fishes, including growth, metabolism, and osmoregulation. Recent studies have identified two clades of putative receptors for GH (GHR1 clade and GHR2 clade) in fishes, both of which are highly expressed in the liver. Moreover, the liver is an important target for the anabolic effects of GH via endocrine IGFs, and liver sensitivity to GH is modulated by metabolic hormones. We investigated the effects of GH, insulin, glucagon, cortisol and triiodothyronine on GHR1 and GHR2 mRNA levels in primary cultured tilapia hepatocytes. Physiological concentrations of GH strongly stimulated GHR2 mRNA level (0.5-50×10(-9)M), but did not affect GHR1 mRNA level. Insulin suppressed stimulation of GHR2 mRNA level by GH (10(-8)-10(-6)M). Insulin increased basal GHR1 mRNA level (10(-8)-10(-6)M). Cortisol increased basal GHR2 mRNA level (10(-7)-10(-6)M), but did not consistently affect GH-stimulated GHR2 mRNA level. Cortisol increased basal GHR1 mRNA level (10(-9)-10(-6)M). Glucagon suppressed GH-stimulated GHR2 mRNA level and increased basal GHR1 mRNA level at a supraphysiological concentration (10(-6)M). A single injection of GH (5μg/g) increased liver GHR2 mRNA level, and insulin injection (5μg/g) decreased both basal and GH-stimulated GHR2 mRNA levels after 6h. In contrast, insulin and GH injection had little effect on liver GHR1 mRNA level. This study shows that GHR1 and GHR2 gene expression are differentially regulated by physiological levels of GH and insulin in tilapia primary hepatocytes.     

Differential regulation of Igf1 and Igf2 mRNA levels in tilapia hepatocytes: effects of insulin and cortisol on GH sensitivity

Igf1 and Igf2 stimulate growth and development of vertebrates. In mammals, liver-derived endocrine Igf1 mediates the growth promoting effects of GH during postnatal life, whereas Igf2 stimulates placental and fetal growth and is not regulated by GH. Insulin enhances Igf1 production by the mammalian liver directly, and by increasing hepatocyte sensitivity to GH. We examined the regulation of igf1 and igf2 mRNA levels by GH, insulin, and cortisol, and the effects of insulin and cortisol on GH sensitivity in primary cultured hepatocytes of tilapia, a cichlid teleost. GH increased mRNA levels of both igf1 and igf2 in a concentration-related and biphasic manner over the physiological range, with a greater effect on igf2 mRNA level. Insulin increased basal igf2 mRNA level, and strongly increased GH-stimulated igf2 mRNA level, but slightly reduced basal igf1 mRNA level and did not affect GH-stimulated igf1 mRNA level. Cortisol inhibited GH stimulation of igf1, but increased GH stimulation of igf2 mRNA level. The synergistic effect of insulin and GH on igf2 mRNA level was confirmed in vivo. These results indicate that insulin and cortisol differentially modulate the response of igf1 and igf2 mRNA to GH in tilapia hepatocytes, and suggest that the regulation of liver Igf2 production differs between fish and mammals. Regulation of liver Igf2 production in fish appears to be similar to regulation of liver Igf1 production in mammals.