Differentiation of Caco-2 cells requires both transcriptional and post-translational down-regulation of Myc.

Caco-2 cancer cell line is widely used to reproduce in vitro the differentiation of absorptive enterocytes of human intestinal epithelium. This cell line, when cultured over confluence for 21 days, spontaneously undergoes cell cycle arrest and differentiates with the formation of a polarized enterocyte-like monolayer. During this process, Myc protein is completely down-regulated, as occurs in normal enterocytes. Caco-2 cells differ from normal enterocytes for mutations of APC and ß-catenin genes, factors known to be involved in the transcriptional control of MYC gene during enterocyte differentiation. In this paper, we investigated how Myc regulation could be achieved during Caco-2 differentiative process, notwithstanding the APC and ß-catenin mutations. We highlighted the post translational regulation of Myc protein as one of the essential mechanisms that allows the exit from cell cycle and onset of differentiation of Caco-2 cells. Moreover, we found a strong correlation between Myc protein downregulation and the expression of the transcription factor Cdx2, suggesting the existence of a regulative link between these two proteins.

Cell growing density affects the structural and functional properties of Caco-2 differentiated monolayer.

The human intestinal Caco-2 cell line has been extensively used as a model of the intestinal barrier. However, it is widely reported in literature that culture-related conditions, as well as the different Caco-2 cell lines utilized in different laboratories, often lead to problems of reproducibility making difficult to compare results. We developed a new cell-maintenance protocol in which Caco-2 cells were subcultured at 50% of confluence instead of 80% of confluence, as usually suggested. Using this new protocol, Caco-2 cells retained a higher proliferation potential resulting in a cell population, which, on reaching confluence, was able to differentiate almost synchronously, forming a more homogeneous and polarized cell monolayer, as compared to that obtained using a high cell growing density. This comparison has been done by analyzing the gene expression and the structural characteristics of the 21-days differentiated monolayers by microarrays hybridization and by confocal microscopy. We then investigated if these differences could also modify the effects of toxicants on 21-days-differentiated cells. We analyzed the 2 h-acute toxicity of CuCl(2) in terms of actin depolymerization and metallothionein 2A (MT2A) and heat shock protein 70 (HSPA1A) genes induction. Copper treatment resulted in different levels of actin depolymerization and gene expression induction in relationship with culture protocol, the low-density growing cells showing a more homogeneous and stronger response. Our results suggest that cell growing density could influence a number of morphological and physiological properties of differentiated Caco-2 cells and these effects must be taken in account when these cells are used as intestinal model.

Toxicological profile of cereulide, the Bacillus cereus emetic toxin, in functional assays with human, animal and bacterial cells.

Some strains of the endospore-forming bacterium Bacillus cereus produce a heat-stable ionophoric peptide, cereulide, of high human toxicity. We assessed cell toxicity of cereulide by measuring the toxicities of crude extracts of cereulide producing and non-producing strains of B. cereus, and of pure cereulide, using cells of human, animal and bacterial origins. Hepatic cell lines and boar sperm, with cytotoxicity and sperm motility, respectively, as the end points, were inhibited by 1 nM of cereulide present as B. cereus extract. RNA synthesis and cell proliferation in HepG2 cells was inhibited by 2 nM of cereulide. These toxic effects were explainable by the action of cereulide as a high-affinity mobile K+ carrier. Exposure to cereulide containing extracts of B. cereus caused neither activation of CYP1A1 nor genotoxicity (comet assay, micronucleus test) at concentrations below those that were cytotoxic (0.6 nM cereulide). Salmonella typhimurium reverse mutation (Ames) test was negative. Exposure of Vibrio fischeri to extracts of B. cereus caused stimulated luminescence up to 600%, independent on the presence of cereulide, but purified cereulide inhibited the luminescence with an IC(50% (30 min)) of 170 nM. Thus the luminescence-stimulating B. cereus substance(s) masked the toxicity of cereulide in B. cereus extracts to V. fischeri.

An inter-laboratory study to evaluate the effects of medium composition on the differentiation and barrier function of Caco-2 cell lines.

Differentiated human intestinal Caco-2 cells are frequently used in toxicology and pharmacology as in vitro models for studies on intestinal barrier functions. Since several discrepancies exist among the different lines and clones of Caco-2 cells, comparison of the results obtained and optimisation of models for use for regulatory purposes are particularly difficult, especially with respect to culture conditions and morphological and biochemical parameters. An inter-laboratory study has been performed on the parental cell line and on three clonal Caco-2 cell lines, with the aim of standardising the culture conditions and identifying the best cell line with respect to parameters relevant to barrier integrity, namely, trans-epithelial electrical resistance (TEER) and mannitol passage, and of epithelial differentiation (alkaline phosphatase activity). Comparison of the cell lines maintained in traditional serum-supplemented culture medium or in defined medium, containing insulin, transferrin, selenium and lipids, showed that parameter performance was better and more reproducible with the traditional medium. The maintenance of the cell lines for 15 days in culture was found to be sufficient for the development of barrier properties, but not for full epithelial differentiation. Caco-2/TC7 cells performed better than the other three cell lines, both in terms of reproducibility and performance, exhibiting low TEER and mannitol passage, and high alkaline phosphatase activity.

Two in vitro models for gas-phase exposure to volatile compounds.

Two experimental models suitable for the screening of volatile compounds were set up. The first consisted of a glass-chamber slide with eight wells, one carrying the test compound, and the others carrying cells in monolayers. In the second model, the cells were cultured in a glass Petri dish, and the test compound was poured onto a filter lying on a glass cover-slip, supported by a metal ring. Four plant volatiles [carvacrol, S-(+)- carvone, thymol and decanal] and one essential oil (caraway oil) were chosen as test compounds. The toxicity rankings obtained with the two models were compared with that obtained in a previous study performed with the same compounds under conventional culture conditions. Differences in the toxicity ranking were observed between the conventional culture conditions and the gas-phase models, confirming the importance of correct exposure conditions for the evaluation of toxicity. Both models have advantages that make them suitable as a preliminary step in the toxicity screening of volatile compounds, or for use in a test battery when combined with conventional approaches.

Cytostatic properties of a novel compound derived from Penicillium pinophilum: an in vitro study.

3-O-Methylfunicone (OMF), a secondary metabolite produced by Penicillium pinophilum, inhibits the in vitro growth of plant pathogenic fungi. This specific property suggested that the compound could be used against other fungal pathogenic activities, including dermatological ones. However, for such applications, toxicological side-effects should be taken into account, in order to prevent other types of risk to mammalian cells. Therefore, investigations were made of the basic toxicity of OMF toward a human tumour cell line. The compound was found to have a cytostatic effect, which represents a counter-indication to its use as a therapeutic agent in dermatology, but suggests that it may have potential as an anti-tumour agent. This study confirmed the validity of in vitro systems for preliminary assays on new compounds, in order to avoid the use of animals in toxicological studies.

The '3Rs' model and the concept of alternatives in animal research: a questionnaire survey.

It has been 45 years since Russell and Burch first proposed the concept of the '3Rs', yet it remains unclear how those individuals involved in animal research view and implement these concepts. The authors used a questionnaire survey to determine how well-known experts judged issues related to the 3Rs.

Good Caco-2 cell culture practices.

The human Caco-2 cells differentiate spontaneously in culture forming monolayers of mature intestinal enterocytes which have been used as a model of the intestinal barrier for in vitro toxicology studies. Reproducibility problems often reported in literature have been generally ascribed to different culture-related conditions, such as the type of animal serum used, the supplements added to the culture media, the passage number and the source of cell clones. The Caco-2 cell culture protocol here described has been recently optimized in our laboratory, producing a homogeneous and highly polarized monolayer of cells which display many of the characteristics of the intestinal enterocytes. This protocol differs from standard protocols mainly because Caco-2 cells are subcultured when they reach just 50% of confluence, instead of 80%, retaining a high proliferation potential. When this cell population is seeded at high density on filter inserts differentiates almost synchronously and much more homogenously.