Proliferative activity in the proximal and distal colon of the rat after fasting and refeeding

Trefoil peptide expression and goblet cell number in rat intestine: effects of KGF and fasting-refeeding

The trefoil factor family peptides TFF1, TFF2, and TFF3 are important for gut mucosal protection and restitution. Keratinocyte growth factor (KGF) stimulates proliferation and differentiation of epithelial cells with potent effects on goblet cells. To investigate interactions between food intake and KGF, rats were fed ad libitum (control), fasted for 72 h, or fasted for 72 h and then refed for 72 h with or without KGF (3 mg. kg(-1). day(-1)). With fasting, goblet cell number in duodenum increased, TFF3 mRNA in duodenum and jejunum decreased, and TFF3 protein did not change or increased. KGF during fasting stimulated colonic growth, normalized TFF3 mRNA in duodenum and jejunum, and broadly upregulated gut goblet cell number and TFF3 protein expression. With fasting-refeeding, KGF increased small bowel and colonic mucosal growth, goblet cell number, and TFF3 protein but had variable effects on TFF3 mRNA. KGF induced TFF2 mRNA and protein in duodenum and jejunum with both nutritional regimens. We conclude that nutrient availability modifies rat intestinal goblet cell number, TFF3 mRNA, and the gut-trophic effects of KGF in a region-specific manner. KGF enhances TFF2 expression in proximal small bowel and increases goblet cell number and TFF3 protein content throughout the intestine independent of food intake.

The effect of protein kinase C activation on colonic epithelial cellular integrity

We have investigated whether activation of protein kinase C has a direct cytotoxic effect on colonic mucosal epithelial cells and whether oxidant-induced damage to colonocytes is mediated by activation of cellular protein kinase C. Incubation of freshly harvested cells from rat colon with the protein kinase C activator, phorbol 12-myristate, resulted in a concentration-dependent increase in the extent of cell injury. Phorbol 12-myristate acetate (0.1-10 microM) also increased cellular protein kinase C activity and this was reduced significantly by treating cells with the antagonists staurosporine or 2-[1-(3-dimethylaminopropyl)-indol-3-yl]3-(-indol-3-yl)maleimide (GF 109203X; 10 microM). Phorbol 12-myristate acetate treatment also resulted in increased translocation of proteins for protein kinase C isoforms alpha, delta and epsilon from cytosol to membrane particulate fractions. The antagonists reduced the extent of cell damage in response to phorbol 12-myristate acetate. Furthermore, cell injury in response to the phorbol acetate was also inhibited by the addition of the oxidant scavengers, superoxide dismutase or catalase to the cell suspension. Addition of H(2)O(2) to the incubation medium (0.1-100 microM) resulted in an increase in cellular protein kinase C activity, an increase in the expression of the alpha, beta and zeta isoforms and a reduction in cell integrity. The cellular damaging actions of H(2)O(2) were significantly reduced by the protein kinase C antagonists, staurosporine or 2-[1-(3-dimethylaminopropyl)-indol-3-yl]-3-(-indol-3-yl)maleimide (GF 109203X). These findings suggest that protein kinase C activation results in colonic cellular injury and this damage is mediated, at least in part, by release of reactive oxidants. Furthermore, oxidant-mediated damage to these cells also involves protein kinase C activation.

The involvement of protein kinase C in nitric oxide-induced damage to rat isolated colonic mucosal cells

1 The role of protein kinase C (PKC) in colonic cellular injury in response to high concentrations of nitric oxide (NO) released from the donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP) was investigated. 2 Addition of SNAP (0.1-1000 microM) to the cellular suspension resulted in a dose-dependent increase in the extent of damage to isolated colonic mucosal cells as assessed by Trypan blue dye uptake and release of the lysosmal enzyme, N-acetyl-beta-glucosaminidase. SNAP treatment also resulted in an increase in cellular total PKC activity. These increases were reduced or eliminated by pretreatment of the cells with the PKC antagonists staurosporine or GF 109203X or the NO scavenger, phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). 3 PKC-alpha, PKC-delta, PKC-epsilon and PKC-zeta were detected in colonic cellular lysates by immunoblotting. However, only PKC-epsilon protein was increased in response to SNAP treatment. Furthermore, SNAP treatment resulted in activation of PKC-epsilon by causing translocation of the enzyme from the cytosolic to membrane fraction of the cell. This effect was eliminated if cells were preincubated with the NO scavenger, PTIO. 4 The extent of cellular damage in response to addition of SNAP to the incubation medium was enhanced by coincubation with the PKC activator, phorbol 12-myristate 13-acetate (PMA; 1 and 10 microM). 5 PKC activity and the extent of cell damage in response to SNAP were reduced by preincubation of the cells with the peroxyl scavenger, ebselen (0.01-10 microM). 6 These data suggest that the PKC-epsilon isoform of the enzyme mediates NO-induced damage to colonic mucosal cells. This response may occur, at least in part, due to peroxynitrite formation.

Bromodeoxyuridine: a diagnostic tool in biology and medicine, Part III. Proliferation in normal, injured and diseased tissue, growth factors, differentiation, DNA replication sites and in situ hybridization

This paper is a continuation of parts I (history, methods and cell kinetics) and II (clinical applications and carcinogenesis) published previously (Dolbeare, 1995 Histochem. J. 27, 339, 923). Incorporation of bromodeoxyuridine (BrdUrd) into DNA is used to measure proliferation in normal, diseased and injured tissue and to follow the effect of growth factors. Immunochemical detection of BrdUrd can be used to determine proliferative characteristics of differentiating tissues and to obtain birth dates for actual differentiation events. Studies are also described in which BrdUrd is used to follow the order of DNA replication in specific chromosomes, DNA replication sites in the nucleus and to monitor DNA repair. BrdUrd incorporation has been used as a tool for in situ hybridization experiments.

Effect of dehydroepiandrosterone on pentose phosphate pathway activity in the rat colon

1. The effects of fasting and fasting followed by refeeding on the activities of the oxidative pentose pathway (OPP) and the non-oxidative pentose pathway (NOPP) were estimated by the rate of production of 14CO2 from [1-14C] glucose in isolated rat colonocytes, and the production of hexose 6-phosphates from ribose 5-phosphate in rat colonic cytosols, respectively. 2. The OPP activity in colonocytes from rats in the fasted state was 50% lower when compared to colonocytes from rats refed after a fast. This indicated induction of the rate-limiting enzyme of the OPP, glucose 6-P dehydrogenase (G6-PDH) in the latter instance. No effect on the maximal catalytic activity of the enzymes of the NOPP was seen in colonocytes from rats refed after a fast compared with colonocytes from rats in the fasted state. 3. Isolated colonocytes obtained from the distal colon of rats refed after a fast, showed a significant decrease (30%) in OPP activity when incubated with 50 microM dehydroepiandrosterone (DHEA). A similar degree of inhibition was seen with 10 mM butyrate (P < 0.05). In contrast, using colonic cytosols, both DHEA and butyrate had no effect on the maximal catalytic activity of the NOPP. 4. Intraperitoneal injection (i.p.) of DHEA in rats refed after a fast showed a significant increase in the maximal catalytic activity of the NOPP in the distal colon (46%; P < 0.05). A similar elevation in the maximal catalytic activity of the NOPP was seen in the distal colon of DHEA treated pair-fed rats (43%; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Mouse and human micronucleus models for assessing genotoxicity of whole foods in intervention studies

There is an emerging need to apply classical genotoxicity assays to assess, in vivo, the carcinogenic or anti-carcinogenic potential of traditional and novel foods. The micronucleus techniques in peripheral blood erythrocytes and lymphocytes are two of the methods that have been used for assessing chromosome-damaging effects following and during dietary interventions with whole foods. The advantage of this approach stems from the practicality of the methods and the possibility of using these techniques in both human and rodent models. The potential application of these methods is illustrated by comparison of recent examples in the literature and from ongoing research.

Glucose metabolism in proliferating epithelial cells from the rat colon

1. The effects of fasting and fasting followed by refeeding on the activities of the oxidative pentose pathway (OPP) and the tricarboxylic acid cycle (TCA) in isolated rat colonocytes were estimated by the rate of production of 14CO2 from [1-14C]glucose and [6-14C]glucose, respectively. 2. Refeeding after a fast induced a 2-3-fold increase in glucose flux through the OPP and TCA cycle and the degree of change was similar in colonocytes from the proximal and distal colon. 3. Butyrate at a concentration of 40 mM inhibited the OPP by 20-30% (P less than 0.05) but had no effect on the activity of the TCA cycle. Glutamine at a concentration of 2 mM decreased the glucose flux through both the OPP and the TCA cycle by 30-50% (P less than 0.05). 4. Production of 14CO2 from the oxidation of butyrate or glucose indicated that the former was 5-7 times more active in colonocytes from fasted rats. After refeeding, however, butyrate utilization was similar to fasting values in the proximal colon but significantly lower (P less than 0.05) in the distal colon.

Pyruvate sparing by butyrate and propionate in proliferating colonic epithelium

1. The effects of fasting and fasting followed by refeeding on the relative activities of the pyruvate dehydrogenase (PDH) complex and the tricarboxylic acid (TCA) cycle in isolated rat colonocytes were estimated by the rate of production of 14CO2 from [1-14C]pyruvate and [3-14C]pyruvate, respectively. 2. Decarboxylation of pyruvate by the PDH complex exceeded that by the TCA cycle in both fasted and fasted/refed colonocytes, was higher in distal than in proximal colon, and was stimulated by refeeding following a fast. 3. Oxidation of pyruvate by both the PDH complex and the TCA cycle was inhibited by butyrate. 4. Propionate alone had no effect, but synergized with butyrate to further reduce pyruvate decarboxylation by the TCA cycle. 5. Preferential utilization of butyrate by proliferating colonic epithelial cells is postulated to maximize the energy yield and spare pyruvate and its precursors for alternative synthetic roles necessary for active cell division.

Zinc deficiency is associated with suppression of colonocyte proliferation in the distal large bowel of rats

As zinc status may influence susceptibility to colon cancer, we examined the effect of dietary zinc deficiency on the proliferation of epithelial cells (colonocytes) in the large bowel of rats. When compared to feed-restricted rats, those with zinc deficiency showed a significant reduction in proliferation in the distal colon as assessed by accumulated metaphase arrest and crypt cell production rates in vivo. Zinc deficiency had no apparent effect on thymidine kinase activity in colonocytes but was accompanied by minor changes in fecal mass and fecal pH. In rats, zinc deficiency is associated with a reduction in the rate of proliferation of colonocytes in the distal colon.