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Title: Intestinal absorption barriers as modelled by p-glycoprotein and cytochrome P450 3A4 in Caco-2 cells
Author: Tran, Christine Diem-Chau Huynh
Awarding Body: University of Aston in Birmingham
Current Institution: Aston University
Date of Award: 1999
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The passage number and origin of two populations of Caco-2 cells influence their enterocyte-like characteristics. Caco-2 cells of passage number >90 from Novartis pharmaceutical company possess higher levels of expression of alkaline phosphatase and P-glycoprotein and a greater cellular uptake of Gly-L-Pro than those ofpassage number <40 from the American Type Tissue Culture collection. High P-gp expressing Caco-2 cells have been developed through stepwise selection of the cells with doxorubicin. This newly-developed cell line (hereafter referred to as Type I) possesses approximately twice as much P-gp protein than non-exposed cells, restricts the transepithelialtransport of vincristine in the apicalto- basolateral direction whilst facilitating its transport in the reverse direction and accumulates less vincristine than non-exposed cells. There is no apparent evidence of the co-existence of the multidrug resistance protein (MRP) in Type I cells to account for the above-listed observations. Stopping the exposure for more than 28 days decreases the P-gp protein expression in previously doxorubicinexposed Type I Caco-2 cells and reduces the magnitude of vincristine transepithelial fluxes in both directions to the levels that are almost similar to those ofnon-exposed cells. Exposing Caco-2 cells to 0.25 ~ la., 25-dihydroxyvitamin D3 induces their expression of cytochrome P450 3A4 protein to the level that is equivalent to that from isolated human jejunal cells. Under the same treatment, doxorubicinexposed (Type I) cells metabolise midazolam poorly and less extensively compared to non-exposed cells, suggesting that there is no such co-regulation of P-gp and CYP3A4 in Caco-2 cells. However, there is evidence which suggests CYP3A metabolises midazolam into 1- and 4-hydroxymidazolam, the latter may possibly be a P-gp substrate and is transported extracellularly by P-gp, supporting the hypothesis of P-gp-CYP3A4 synergistic roles in keeping xenobiotics out of the body. Doxorubicin-exposed (Type I) cells are less effective in translocating L-proline and glycyl-L-proline across the cell monolayers. Caco-2, P-glycoprotein (P-gp), Vincristine sulphate, Cytochrome P450 3A4 (CYP3A4), Midazolam, L-Proline, Glycyl-L-proline.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Pharmacology & pharmacy & pharmaceutical chemistry Pharmacology