MDCK cell systems

The in vitro system we have been using to study the transepithelial transport is cultured Madin-Darby canine kidney (MDCK) epithelial cells (11). When cultured on microporous polycarbonate filters (Transwell, Costar, Cambridge, MA), MDCK cells will develop into monolayers mimicking the mucosal epithelium (11). When these cells reach confluence, tight junctions will be established between the cells, and free diffusion of solutes across the cell monolayer will be markedly inhibited. Tight junction formation can be monitored by measuring the transepithelial electrical resistance (TEER) across the cell monolayers. In Figure 1, MDCK cells were seeded at 2 X 104 cells per well in Transwells (0.4 p pore size) as described previously. TEER and 14C-sucrose transport were measured daily. To determine 14C-sucrose... 

Figure 32 Disappearance and appearance kinetics of transcellular flux of the lipophilic antioxidant PNU-78,517 (pKa 6.5) across MDCK cell monolayers in Transwell systems at 37°C. Donor solutions contained 3% bovine serum albumin (BSA), and receiver solutions contained 0.5-5% BSA at pH 7.4. [Redrawn from Raub et al. (1993) with permission from the publisher.]... 

Cell lines, such as the Caco-2 and MDCK cells [27, 35, 47, 49, 57, 67, 128-133], have been used frequently to study different transporters in the GI tract. These cell lines have been evaluated for transport both in absorptive and secretory direction and in addition also been transfected with specified transporter systems of interests to yield new clones [23, 31, 72, 79, 80, 134] or co-cultures [135], Some of the uptake transporters belonging to the organic cation transporter (OCT) family have also been identified in cell lines such as the pig kidney cell line LLC-PK1, and MDCK [67, 136]. In fact, its presence in Caco-2 cells needs to be further elucidated as reports have shown both the absence and presence of transporters from this family of transporters [136-138],... 

Amide 39 is a potent and selective inhibitor of GlyT-1 both in vitro (Ki = 1.79 nM) and in vivo (CSF-glycine ED2oo 3.9 mg/kg, rat, p.o.) but with limited permeability across Madin-Darby canine kidney (MDCK) cell membranes [78]. Optimization led to fused [3.1.0] and [3.3.0] azabi-cyclic analogs 40 (PF-3463275) [78] and 41 [79], respectively. Analogs of both systems demonstrated excellent potency (fC = 1.7-95 nM), and improved permeability, PK, and in vivo efficacy. Spatial working memory... 

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]. 

While Caco-2 cells typically require 21 days to become suitable for use, the Madin-Darby Canine Kidney (MDCK) cell line, derived from the dog kidney, typically only requires 3 days. This cell-line may prove to be a useful alternative, as the two cell lines show many common features. More investigation is required into how comparable the two systems are. 

Despite the high social relevance of infectious diseases and widespread use of animal cell lines in vaccine production, the application of even unstructured models for quantitative analysis and parameter estimation has not been common practice in bioprocess optimization. So far, research concerning influenza vaccine production in MDCK cell cultures has focused on the characterization of metabolism, growth of different cell lines and virus yields in various production systems [1,2]. 

As already outlined above, P-glycoprotein is constitutively expressed in several organs, such as kidney, liver, intestine, and also at the blood-brain barrier. P-gp substrates therefore show poor oral absorption, enhanced renal and biliary excretion, and usually do not enter the brain [28]. This spurred the development of medium- and high-throughput systems addressing the P-gp substrate properties of compounds of interest. These systems mostly rely on transport studies through a monolayer of P-gp expressing Caco-2 [29] or MDCK cells [30]. In parallel, in silico methods have also... 

With the difficulties associated with accurate estimation of permeability based only on physicochemical properties, a variety of methods of measuring permeability have been developed and used, among which are (l)cul-tured monolayer cell systems, such as Caco-2 or MDCK ( 2 diffusion cell systems that use small sections of intestinal mucosa between two chambers (3) in situ intestinal perfusion experiments performed in anesthetized animals such as rats and (4)intestinal perfusion studies performed in humans (40,54-62). All of these methods offer opportunities to study transport of drug across biological membranes under well-controlledconditions. Caco-2 mono-layer systems in particular have become increasingly commonly used in recent years and human intestinal perfusion methods are also becoming more commonly available. Correlations between Caco-2 permeability and absorption in humans have been developed in several laboratories (63-72). As shown in Fig. 

In this experimental system, the addition of an antibody that binds to E-cadherin, preventing Its homophilic Interactions, blocks the Ca " -dependent attachment of suspended MDCK cells to a substrate and the subsequent formation of intercellular adherens junctions. 

The Importance of Ca to the formation and integrity of tight junctions has been demonstrated In studies with MDCK cells In the experimental system described previously (see Figure 6-7). If the growth medium In the chamber contains very low concentrations of Ca, MDCK cells form a mono-layer In which the cells are not connected by tight junctions. As a result, fluids and salts flow freely across the cell layer. When sufficient Ca " is added to the medium, tight junctions form within an hour, and the cell layer becomes Impermeable... 

Figure 8.4 Palmostatin B specifically inhibits depalmitoylation. (a) Schematic illustration of the Cy3-labeled semisynthetic lipoproteins (Cy3 is a fluorescent label). The two differentially lipid-modified carboxyterminal N-Ras heptapeptides were coupled via a maleimido-caproyl linker to the carboxyterminal cysteine of recombinant expressed N-Ras (1 -181). GalT-CFP is a marker for the Golgi system. Citrine-N-Ras is a fluorescently labeled N-Ras construct, (b) Confocal time-lapse images of MDCK cells expressing the Golgi marker GalT-CFP and Citrine-N-Ras before and after microinjection of CysFar (i) or PalFar (ii). Cells were incubated for 80 min with 1 [iM palmostatin B before the experiment, (c) Quantitative ratiometric...

The LLC-PKl and MDCK cell lines are pig and dog kidney epithelial cells, respectively, that require shorter culture (4-A days) periods for monolayer formation in the transwell system. These two cell lines present their own set of challenges for data interpretation. LLC-PKl cells have endogenous BCRP activity (Jonker et al., 2000). MDCKI cells have high endogenous P-gp activity (Raggers et al., 2002 Goh et al., 2002). 

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