Absorption - in vitro Tests - Cell Based

The present chapter will focus on one part of early ADME (Adsorption, Distribution, Metabolism, Excretion) strategy the absorption and efflux screening. 

Since many projects focus on the most accepted route of administration - the oral one - assessment of oral bioavailability potential for a compound is a very important part in early ADME screening. 

Absorption of compounds in the gastrointestinal tract occurs mainly in the small intestine with 3 different regions (duodenum, jejunum and ileum) and in the large intestine (colon). In the small intestine the uptake surface is increased by folds (3-times), villi (30-times) and microvilli (600-times). In the colon folds and villi are absent (Daugherty and Mrsny 1999). 

The major physiological role of the GI, namely to provide a protection against pathogens and allow at the same time the permeation of nutrients and 

Peyers patches are covered by epithelial cells which can differentiate into M cells. M cells play an important role in the immunologic surveillance of the gut and are involved in specific functions like transport of particles, antigens, macromolecules. M cells seem to be involve in the absorption of intact proteins (Walker and Sanderson 1992). Peyers patches have been studied for uptake of macromolecules. Their proximal vicinity to immunocompetent cells is another hurdle for industrial use as a preferred uptake route (Daugherty and Mrsny 1999 Neutra 1998). M cells have been used to study uptake of lectins (for overview, see Daugherty and Mrsny 1999). However both cell types - Peyers patches and M cells - clearly are limited in their use as a preferred uptake route due to a small surface area they are covering and the limited capacity of absorbed molecules. 

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Chapter II.D Absorption - in vitro Tests - Cell Based... 

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