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Ussing Chamber

Ussing chambers were initially developed to measure the transport of ions, nutrients, and drugs across various epithelial tissues (Ussing and Zerhan 1951, see Chap. 23). With the Ussing chamber technique, the intestinal segment is mounted in an Ussing chamber where one side will be exposed to buffer with the compound of interest (apical or lumen side) and the other side to buffer without the compound of interest (basolateral or mucosal side). The major advantage of this system is that different parts of the intestine (from duodenum to colon) can be used (Smith et al. 1992). However the method is laborious and has a relatively low-throughput, and shortterm survival in culture. Recently, TNO described a more high throughput system, InTESTine™ which allow up to 96 incubations simultaneously (Roeselers et al. 2013, see Chap. 24).

Isolated and Perfused Intestinal Segments

Isolated and perfused intestinal segments were first described by Baker et al. (1968) who prepared these segments from dog ileum. During the last decade, a wide range of isolated organ systems, either from whole organs or resected intestinal tissue, have been developed for biomedical and pharmaceutical research. For this system a part of the intestine including the vascular bed is isolated and both ends of the intestine is sealed before the tissue is mounted in to the perfusion system, where the artery is perfused with a well-defined buffer. The compound of interest can be administered as a bolus injection into the gut lumen and samples can be withdrawn at several times points form the recirculating perfusate (Wei et al. 2009). A major advantage of the system is that the model displays a normal morphology, histology and physiology. However, the difficulty of obtaining sufficient quality and quantity of organs and the limited duration of experiments are a major drawback.

-D Culture Systems

The development of 3D cell culture models have been increased in the past few years (Salerno-Goncalves et al. 2011; Yu et al. 2012). 3-D culture systems are prepared from cell lines, primary cells and/or organ cultures using various methods, including spontaneous aggregation in a suspension culture, implantation onto 3D scaffolds (e.g. collagen or synthetic materials) and culture in Transwell® systems or in rotating culture bioreactors (Schmeichel and Bissell 2003). These systems range in complexity and carry distinct advantages and disadvantages including experimental costs, level of expertise, optimization, reproducibility and validation.

The power of 3-D culture systems is that they permit cells to change shape and form cell–cell connections that are prohibited on rigid conventional culture substrates. The models can be applied for instance to study cell attachment, migration and proliferation. One example of a 3-D intestinal system is the gut organoid. Organoids are cultured from adult intestinal stem cells and have self-renewing capacity. Their structure and hierarchy highly resemble the in vivo intestinal epithelium. The major advantage of the gut organoid system over other GI models is the long-term culturing, next to the broad range host species and GIT compartments (stomach, ileum, colon) and gene manipulation possibilities (Koo et al. 2012). So far, development and application of the intestinal organoid system focused mainly towards the use of organoids for regenerative medicine purposes. However, further expansion of this system will lead to broader application range and expansion of the read out possibilities.

Most ex vivo intestinal tissue models make use of tissue obtained from different animal species (e.g. rabbit, piglets or rats), since the availability of healthy human intestinal tissue is limited. The disadvantage of using animal tissue, is the interspecies differences in anatomy, physiology, metabolism, diet and micro-biota, which complicates the extrapolation of data to humans (Nejdfors et al. 2000; Deferme et al. 2008). Pigs share more physiological and immunological similarities to humans than rodents, and the use of (mini)pigs is becoming increasingly common in nutritional research (Patterson et al. 2008, see Chap. 24).

The majority of the in vitro intestinal tissue models are used for absorption studies using drug or food compounds. Since intestinal tissue consist of multiple cell types (e.g. immune cells, enteroendocrine cells) it can be envisioned that these models could also be applicable to study innate immune responses or satiety. Unfortunately hardly any evidence was found to use these models to study the effect of food on innate immune response, this is most likely due to viability issues. Intestinal tissue is viable for approx. 2 h due to intestinal oedema and disruption of the villi (Plumb et al. 1987). Two hours is too short to measure the production of excreted compounds like cytokines or chemokines. Efforts to elongate viability of tissue incubations are on-going and promising (Tsilingiri et al. 2012). However measurements of these compounds on mRNA level should be possible. Recently, intestinal segments were used to study the effect of sugars, proteins and fatty acids on the release of satiety hormones (Voortman et al. 2012, see Chap. 23). The advantage of this model is that the hormone release can be studied in different parts of the intestine. This is very important, since it has been shown that the secretion of satiety hormones is site specific. A novel method to study effects of foods and drug compounds on intestinal tissue is the organoid model (see Chap. 22). This is a promising model, since the lifetime of this, from stem cells derived tissue, is much longer than excised intestinal tissue. However the model is still being in its infancy and the wide applicability still has to be proven.

In the following chapters we will focus more in depth on the applicability of three intestinal models namely, Ussing chamber, intestinal segments and organoids.

 
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