Drug absorption colon role

Shameem, M., Katori, N., Aoyagi, N., and Kojima, S. Oral solid controlled release dosage forms Role of Gl-mechanical destructive forces and colonic release in drug absorption under fasted and fed conditions in humans. Pharm. Res. 12(7) 1049—1054, 1995. 

The apical localized sodium-dependent bile add transporter (ASBT) is expressed in the human duodenum and ileum and is barely detectable in colon [16]. ASBT transports bile adds such as glycodeoxycholate and chenodeoxycholic add (XX) [49, 50]. Few examples exist where the bile acid scaffold has been used as a promoiety for a prodrug approach. ASBT has micromolar affinities for the natural substrates, and the studies on ASBT are too few to make a general statement on the potential and role of this transporter in drug absorption [49, 50]. 

Three major cell models obtained from human colon cancers have been used HT-29, and T84, and Caco-2. HT-29 is a cell line capable of secreting mucin it has been used to study the effect of mucin on drug absorption. The T84 cell line does not express biochemical differentiation markers and is not particularly useful for studying drug transport. However, the T84 ceU line does express P-glycoprotein and can be used to study the role of this efflux pump. ... 

Measurements of absolute solubility and dissolution are routinely performed during drug development, but knowledge of phytochemicals is limited. As described above, liberation of phytochemicals from the food matrix and subsequent dissolution into gastrointestinal fluids are both affected by a number of parameters. Thus, the bioaccessibility (i.e., the fraction of a substance available for absorption by an organism) of a compound in the small intestine may vary considerably, and a substantial proportion of food-derived phytochemicals may not be absorbed in the small intestine and reach the colon. In this case, colonic microflora will mainly contribute to their hydrolysis, but the precise nature and role of microbial hydrolysis remains controversial for many phytochemicals [10]. 

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