Altered growth and attachment of rabbit crypt colonocytes isolated from different developmental stages

Development and characterization of 2-dimensional culture for buffalo intestinal cells

Small intestinal epithelial cells (IEC) play a major role in the absorption of nutrients and toxins. Due to the similarity of genome-wide single copy protein orthologues between cattle and human, establishment of ruminant's primary small IEC culture could be a valuable tool for toxicity studies. Therefore, the current study focused on the development and characterization of buffalo IEC culture, as cattle slaughter is banned in India. The buffalo jejunum fragments were washed consecutively several times in saline, warm phosphate buffered saline (PBS), PBS with 5 mM dithiothreitol, digesting solution and 2% sorbitol in PBS. The cells were cultured on 17 µg/cm² collagen coated plates and transwell plates with serum (2% Fetal bovine serum (FBS) and 10% FBS) and serum-free culture conditions. The cells were differentiated into typical epithelial cobblestone morphology from day 5 onwards in 50% successful cultures. The cultured IEC were characterized by gene expression of epithelial cell markers, cytokeratin and vimentin, and enterocyte markers like villin, zonula occluden (ZO1), fatty acid binding protein 2 (FABP2) and small intestinal peptidase (IP). Based on the morphology and gene expression profile, 10% FBS has been recommended for culturing primary buffalo IEC on collagen coated plates for 10 days. However, 50% of the successful cultures could not show epithelial phenotype on 10% FBS culture conditions even on collagen coated plates. Interestingly, undifferentiated IEC showed an increasing expression of FABP2, IP and ZO1 transcripts compared to differentiated intestinal cells with 10% FBS on collagen plates. Therefore, future studies are needed to understand the role of FABP2, IP and ZO1 in differentiation of buffalo IEC.

The use of cultured primary bovine colon epithelial cells as a screening model to detect genotoxic effects of heterocyclic aromatic amines in the comet assay

Isolated epithelial cells from the bovine colon were maintained in dividing monolayer cultures and used as a model system for colon tissue in in vitro toxicological studies. The cytotoxic effects of the heterocyclic aromatic amines 2-amino-3-methylimidazo [4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhiP) were investigated in these cells and IC(50) values were determined by inhibition of neutral red uptake into the cultured cells. Although PhiP was not cytotoxic up to concentrations of 500 microM, IQ was cytotoxic above 300 microM. The induction of DNA strand breaks in cultured bovine epithelial colon cells was determined using the alkaline single-cell gel electrophoresis (Comet assay) technique, and subsequently, the DNA damage was used as a determinant of genotoxic effects of the heterocyclic aromatic amines in order to establish this system for detection of adverse effects of chemicals in a model system for the colon. In the absence of an external enzymatic metabolizing system (S9 mix) both amines did not induce DNA strand breaks. When S9 mix was used, PhiP induced DNA strand breaks above 10 microM whereas IQ did not show any significant effect at 300 microM. This cell culture system was found to be a useful screening system for testing of compounds that are considered to affect colonic tissue.

Role of protein kinase C-delta in the age-dependent secretagogue action of bile acids in mammalian colon

The role of specific PKC isoforms in the regulation of epithelial Cl(-) secretion by Ca(2+)-dependent secretagogues remains controversial. In the developing rabbit distal colon, the bile acid taurodeoxycholate (TDC) acts via intracellular calcium to stimulate Cl(-) transport in adult, but not in young, animals, whereas the PKC activator phorbol dibutyrate (PDB) stimulates Cl(-) transport at all ages. We tested the hypothesis that specific PKC isoforms account for the age-specific effects of TDC. The effects of conventional (cPKC) and novel (nPKC) PKC-specific inhibitors on TDC- and PDB-stimulated Cl(-) transport in adult and weanling colonocytes were assessed by using 6-methoxy-quinolyl acetoethyl ester. In adult colonocytes, the cPKC inhibitor Gö-6976 inhibited PDB action but not TDC action, whereas the cPKC and nPKC inhibitor Gö-6850 blocked both TDC and PDB actions. Additionally, rottlerin and the PKC-delta-specific inhibitor peptide (deltaV1-1) inhibited TDC- and PDB-stimulated Cl(-) transport in adult colonocytes. Rottlerin also decreased TDC-stimulated short-circuit current in intact colonic epithelia. Only Gö-6976, but neither rottlerin nor deltaV1-1, inhibited PDB-stimulated transport in weanling colonocytes. Colonic lysates express PKC-alpha, -lambda, and -iota protein equally at all ages, but they do not express PKC-gamma or -theta at any age. Expression of PKC-beta and PKC-epsilon protein was newborn>adult>weanling, whereas PKC-delta was expressed in adult but not in weanling or newborn colonocytes. TDC (1.6-fold) and PDB (2.0-fold) stimulated PKC-delta enzymatic activity in adult colonocytes but failed to do so in weanling colonocytes. PKC-delta mRNA expression showed age dependence. Thus PKC-delta appears critical for the action of TDC in the adult colon, and its low expression in young animals may account for their inability to secrete in response to bile acids.

Epidermal growth factor stimulates chloride transport in primary cultures of weanling and adult rabbit colonocytes

OBJECTIVES

We have shown that Ca2+-dependent regulation of Cl- secretion in the mammalian colon exhibits age dependence. Because epidermal growth factor (EGF) has a well-established role in growth and can increase intracellular calcium [Ca2+]i, it is conceivable that its developmental influence may extend to the regulation of intestinal ion transport. In this study, we examined the role of EGF in the regulation of Cl- transport in the developing rabbit distal colon.

MATERIALS AND METHODS

Because serum contains growth factors, which could have confounded our studies, we first established an optimal milieu for testing EGF in primary cultures of adult rabbit distal colonocytes by culturing them for 24 h in media containing 0%, 1%, 5%, and 20% serum. Chloride transport (millimoles per second) and [Ca2+]i were measured with use of the fluorescent indicator N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE) and Fura-2AM, respectively.

RESULTS

Serum depletion had no effect on cell number, DNA content, or basal Cl- transport, but it significantly affected cell viability. In media with 0%, 1%, or 20% serum, bethanechol, 8BrcAMP, taurodeoxycholate, and EGF stimulated Cl- transport to a similar extent. EGF maximally stimulated Cl- transport at 16.3 nmol/L and 20 minutes. Bethanechol, but not EGF, increased [Ca2+]i. EGF did not alter bethanechol-stimulated Cl- transport or [Ca2+]i. EGF acts via an EGF-receptor and mitogen activated protein kinase (MAPK) signaling pathway, since stimulation of Cl- transport was abolished by genistein, AG1478, and PD98059. Weanling and adult colonocytes, cultured in 1% serum, showed similar basal and EGF-stimulated Cl- transport.

CONCLUSIONS

EGF stimulates rabbit colonic Cl- transport via a Ca2+-independent, tyrosine kinase- and MAPK-dependent pathway, and its effects are not age dependent.

Immunochemical, biomolecular and biochemical characterization of bovine epithelial intestinal primocultures

BACKGROUND

Cultures of enterocytes and colonocytes represent valuable tools to study growth and differentiation of epithelial cells. In vitro models may be used to evaluate passage or toxicity of drugs, interactions of enteropathogenes bacteria strains with intestinal epithelium and other physiologic or pathologic phenomenon involving the digestive tract.

RESULTS

Cultures of bovine colonocytes and jejunocytes were obtained from organoid-enriched preparations, using a combination of enzymatic and mechanical disruption of the intestine epithelium, followed by an isopicnic centrifugation discarding most single cells. Confluent cell monolayers arising from plated organoids exhibited epithelium typical features, such as the pavement-like structure, the presence of apical microvilli and tight junctions. Accordingly, cells expressed several markers of enterocyte brush border (i.e. maltase, alkaline phosphatase and fatty acid binding protein) as well as an epithelial cytoskeleton component (cytokeratin 18). However, enterocyte primocultures were also positive for the vimentin immunostaining (mesenchyme marker). Vimentin expression studies showed that this gene is constitutively expressed in bovine enterocytes. Comparison of the vimentin expression profile with the pattern of brush border enzymes activities, suggested that the decrease of cell differentiation level observed during the enterocyte isolation procedure and early passages of the primoculture could result from a post-transcriptional de-repression of vimentin synthesis. The low differentiation level of bovine enterocytes in vitro could partly be counteracted adding butyrate (1-2 mM) or using a glucose-deprived culture medium.

CONCLUSION

The present study describes several complementary approaches to characterize bovine primary cultures of intestinal cells. Cultured cells kept their morphologic and functional characteristics during several generations.

Growth and characterisation of primary bovine colon epithelial cells in vitro

Epithelial crypts from the bovine colon were obtained by using a combined mechanical and enzymatic isolation method, followed by differential D-sorbitol gradient centrifugation. By using this isolation technique, a pure fraction of epithelial crypts with minimal mesenchymal contamination was obtained. The crypts were seeded in collagen-coated plastic flasks. The attached epithelial cells proliferated and formed a confluent monolayer after 6 days in culture. Under low-serum culture conditions (1% fetal calf serum), the cells had a population doubling time of 21-22 hours. During the culture period, the colonocytes were characterised morphologically and enzymatically. The morphology of the cultured cells was confirmed by scanning electron microscopy and transmission electron microscopy. The presence of microvilli, tight junctions and desmosomes demonstrated the ability of the cultured cells to restore an epithelial-like cell monolayer. The epithelial origin of the cells was demonstrated by labelling the cells with antibodies against epithelial-specific cytokeratins 7 and 13. The functional integrity of the cells was evaluated by measuring various marker enzymes (gamma-glutamyltranspeptidase, acid phosphatase, alkaline phosphatase, NADH-dehydrogenase) and membrane-associated Na+-K+-ATPase activity. Membrane integrity was determined by measuring the leakage of lactate dehydrogenase into the culture medium. This new culture system for bovine colon epithelial cells could be used as an in vitro model of the colon epithelium in physiological and toxicological studies.

Differences in Ca(2+) signaling underlie age-specific effects of secretagogues on colonic Cl(-) transport

Taurodeoxycholic acid (TDC) stimulates Cl(-) transport in adult (AD), but not weanling (WN) and newborn (NB), rabbit colonic epithelial cells (colonocytes). The present study demonstrates that stimuli like neurotensin (NT) are also age specific and identifies the age-dependent signaling step. Bile acid actions are segment and bile acid specific. Thus although TDC and taurochenodeoxycholate stimulate Cl(-) transport in AD distal but not proximal colon, taurocholate has no effect in either segment. TDC increases intracellular Ca(2+) concentration ([Ca(2+)](i)) in AD, but not in WN and NB, colonocytes. In AD cells, TDC (5 min) action on Cl(-) transport needs intra- but not extracellular Ca(2+). NT, histamine, and bethanechol increase Cl(-) transport and [Ca(2+)](i) in AD, but not WN, distal colonocytes. However, A-23187 increased [Ca(2+)](i) and Cl(-) transport in all age groups, suggesting that Ca(2+)-sensitive Cl(-) transport is present from birth. Study of the proximal steps in Ca(2+) signaling revealed that NT, but not TDC, activates a GTP-binding protein, Galpha(q), in AD and WN cells. In addition, although WN and AD colonocytes had similar levels of phosphatidylinositol 4,5-bisphosphate, NT and TDC increased 1,4,5-inositol trisphosphate content only in AD cells. Nonresponsiveness of WN cells to Ca(2+)-dependent stimuli, therefore, is due to the absence of measurable phospholipase C activity. Thus delays in Ca(2+) signaling afford a crucial protective mechanism to meet the changing demands of the developing colon.

Ion transport during growth and differentiation

The major function of the adult colon is to reabsorb fluid from the chyme. This ability to conserve salt and water is especially important in newborns, where reserves are small and diarrhea is frequent. Although much is known about regulation of Cl- transport in the adult colon, postnatal changes in electrolyte transport are not well characterized. We have established an in vitro model to study colonic epithelial cells (colonocytes) at different stages of development. Primary cultures were isolated from newborn, weanling, and adult rabbit colon and properties such as growth and Cl- transport characterized. The isolation procedure yielded a crypt-enriched population of cells, and the cell yield per gram mucosa increased with age. The colonocytes also showed an age-related decrease in attachment to extracellular matrix, with maximum attachment seen with Matrigel and collagen IV. The crypt enrichment was confirmed by demonstrating that the cell population was capable of transporting Cl-, which was stimulated by agents such as forskolin and phorbol esters at all ages. Agents that increased intracellular cGMP, however, did not increase Cl- transport at any age. It was interesting to observe that the secondary bile acid, taurodeoxycholate, stimulated Cl- transport only in the adult but not newborn or weanling distal colonocytes. We have demonstrated that rabbit distal colonocytes can be kept viable in culture and transport Cl- at all ages. However, the regulation of Cl- transport changes during ontogeny and depends on the signaling pathway.

Primary cell cultures of bovine colon epithelium: isolation and cell culture of colonocytes

Epithelial cells from bovine colon were isolated by mechanical preparation combined with an enzymatic digestion from colon specimens derived from freshly slaughtered animals. After digestion with collagenase I, the isolated tissue was centrifuged on a 2% D-sorbitol gradient to separate epithelial crypts which were seeded in collagen I-coated culture flasks. By using colon crypts and omitting the seeding of single cells a contamination by fibroblasts was prevented. The cells proliferated under the chosen culture conditions and formed monolayer cultures which were maintained for several weeks, including subcultivation steps. A population doubling time of about 21 hr was estimated in the log phase of the corresponding growth curve. During the culture period the cells were characterized morphologically and enzymatically. By using antibodies against cytokeratine 7 and 13 the isolated cells were identified as cells of epithelial origin. Antibodies against vimentin served as negative control. Morphological features such as microvilli, desmosomes and tight junctions, which demonstrated the ability of the cultured cells to restore an epithelial like monolayer, were shown by ultrastructural investigations. The preservation of the secretory function of the cultured cells was demonstrated by mucine cytochemistry with alcian blue staining. A stable expression of enzyme activities over a period of 6 days in culture occurred for gamma-glutamyltranspeptidase, acid phosphatase and NADH-dehydrogenase activity under the chosen culture conditions. Activity of alkaline phosphatase decreased to about 50% of basal value after 6 days in culture. Preliminary estimations of the metabolic competence of these cells revealed cytochrome P450 1A1-associated EROD activity in freshly isolated cells which was stable over 5 days in cultured cells. Then activity decreased completely. This culture system with primary epithelial cells from the colon will be used further as a model for the colon epithelium in toxicological studies in vitro.