Caco-2 cell system model

There are several cell monolayer models that are frequently used for the evaluation of drug permeability and absorption potential (Table 18.1). For a more detailed discussion, please refer to Chap. 8. Caco-2 cells (adenocarcinoma cells derived from colon) are the most extensively characterized and frequently used of the available cell lines [5-9], A unique feature of Caco-2 cells is that they undergo spontaneous enterocyte differentiation in cell culture. Unlike intestinal enterocytes, Caco-2 cells are immortalized and replicate rapidly into confluent monolayers. When the cells reach confluency during culture on a semi-porous membrane, they start to polarize and form tight junctions, creating an ideal system for permeability and transport studies. During the past decade, use of... 

The known variability associated to the behavior of Caco-2 cell lines, together with the need to find a more robust and easy to grow type of culture led the pharmaceutical industry to substitute this system by, for example, MDCK cell cultures. So in silico modelers have also turned towards this new kind of in vitro cell data, although to a lesser extent than with Caco-2 systems. Perhaps the only notable example of the use of MDCK data is Refsgaard s categorical model, where a dataset of Caco-2 permeability values was enriched with MDCK permeability data [99]. 

Caco-2 cells and isolated small intestine are models of basic nutrition that contributed to the understanding of resveratrol absorption and bioavailability. While the Caco-2 absorption model is a well-defined cellular in vitro system based on a human colonic adenocarcinoma cell line, the isolated small intestine model is nearer to in vivo conditions and is also simpler to handle. It also avoids the methodological problems of in vivo perfusion models [Barthe et al., 1998, 1999]. 

However, this systems need further evaluation. For an industrial environment coculture systems need to be robust and reliable being at the same time easy to handle. On the other hand, convincing advantages have to be shown to change the monolayer system to a coculture model or to change the cell system used. In many companies CACO-2 cells are used since many years and an immense data base is available. 

Meaney CM, O Driscoll CM. Comparison of the permeation enhancement potential of simple bile salt and mixed bile salt fatty acid micellar systems using the Caco-2 cell culture model. Int J Pharm 2000 207(10) 21-30. 

Given the role of specific transporters for which prediction models are not (yet) available, the measurement of partitioning is necessary in many cases. For a number of situations systems are available to measure transport. One well-defined model for estimating the parameters for oral uptake is the Caco-2 cell system [30, 31]. Other systems exist for the blood-brain barrier [32] and the blood-placenta barrier [33]. 

Among these testing methods, the small animal GI model and the Caco-2 cell culture model have shown the best correlation with oral absorption in vivo. The Caco-2 culture system consists of a monolayer of human intestinal epithelial cells grown on semipermeable supports such as polycarbonate membranes. Because the cells are human in origin, they exhibit many characteristics of the human small intestinal epithelium. The permeability coefficients relative to the extents of human drug absorption are listed here ... 

PAMPA-biomimetic-Caco-2-comparison Several in vitro assays have been developed to evaluate the Gl absorption of compounds. Our aim was to compare three of these methods (/) the BAMPA method, which offers a HT, noncellular approach to the measurement of passive transport ( ) the traditional Caco-2 cell assay, the use of which as a HT tool is limited by the long cell differentiation time (21 days) and (// ) The BioCoat HTS Caco-2 assay system, which reduces Caco-2 cell differentiation to three days. The transport of known compounds (such as cephalexin, propranolol, or chlorothiazide) was studied at pH 7.4 and 6.5 in BAMPA and both Caco-2 cell models. Permeability data obtained was correlated to known values of human absorption. Best correlations (f= 0.9) were obtained at pH 6.5 for BAMPA and at pH 7.4 for the Caco-2 cells grown for 21 days. The Caco-2 BioCoat HTS Caco-2 assay system does not seem to be adequate for the prediction of absorption. The overall results indicate that BAMPA and the 21 -day Caco-2 system can be complementary for an accurate prediction of human intestinal absorption. 

A number of in vitro systems to model absorption have been developed and have gained widespread use through their successful prediction of human absorption. These include the Caco-2 cell monolayer model, Ussing chambers... 

Cell permeability, which is measured byPapp, as used herein refers to the ability of a compound to traverse an intact cell monolayer unchanged in an in vitro system. Note that this definition differs from what many chemists think of as cell permeability, the ability to get inside but not necessarily pass through a cell. This too is a useful definition in the right context, but when discussing results in cell monolayer models like the Caco-2 one described later, the through a cell monolayer definition needs to be used. 

Caco-2Ceiis Brush Border Membrane Vesicles Epithelial Cell Model Isolated Intestinal Cells Non-Intestinal Cell Systems To determine mechanism an rate of drug passage arxl transport. 

The most commonly used cell culture model today is the 21-day Caco-2 human colonic cell line derived from a human adenocarcinoma. They can be cultured in special transwell cell culture plates (Figure 9) that enable the investigation of passive diffusion (apical to basolateral side) and active transport (basolateral to apical side). Although the system has its limitations, for many compounds it can give a good indication of likely in vivo absorption. An alternative cell culture, which has been shown to correlate well with absorption in vivo and permeability in Caco-2 cultures, is the 3-day Madin-Darby canine kidney cell line. Also, the expression of transporter proteins in cell cultures has led to new screens being established for identifying transporter substrates. 

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