title: The effect of two novel cholesterol-lowering agents, disodium ascorbyl phytostanol phosphate (DAPP) and nanostructured aluminosilicate (NSAS) on the expression and activity of P-glycoprotein within Caco-2 cells.
abstract: BACKGROUND
  Many drugs are substrates for P-glycoprotein (P-gp) and interactions involving P-gp may be relevant to clinical practice. Co-administration with P-gp inhibitors or inducers changes the absorption profile as well as the risk for drug toxicity, therefore it is important to evaluate possible P-gp alterations. The purpose of this study was to investigate the effect of two novel cholesterol-lowering agents, disodium ascorbyl phytostanol phosphate (DAPP) and nanostructured aluminium silicate (NSAS), a protonated montmorillonite clay, on mdr-1 gene expression and its protein, P-glycoprotein (P-gp) within Caco-2 cells.
  
  
  METHODS
  The effects of DAPP and NSAS on the regulation of mdr-1 gene, P-gp protein expression and activity within Caco-2 cells, were determined using cell viability and cytotoxicity tests, RT-PCR, Western Blot analysis and bi-directional transport studies.
  
  
  RESULTS
  We observed a significant down-regulation of mdr-1 mRNA (e.g. 38.5 ± 17% decrease vs. control at 5 μM DAPP and 61.2 ± 25% versus control at 10 μM DAPP; n = 6, P* < 0.05) within Caco-2 cells. Western Blot analysis of P-gp expression showed that changes in mdr-1 gene expression lead to correlating changes in P-gp protein expression. This down-regulation of P-glycoprotein also resulted in decreased activity of P-glycoprotein compared to untreated control. In contrast, when Caco-2 cells were treated with NSAS, no changes in mdr-1 gene expression, P-gp protein expression nor P-gp activity were observed.
  
  
  CONCLUSIONS
  DAPP but not NSAS decreases P-gp mediated drug efflux through decreased mdr-1 gene expression and consequently decreased P-gp protein expression. These findings have to be taken into consideration when DAPP is concurrently given with other drugs that are substrates for P-gp since drug-drug interactions harbour a safety issue and alter bioavailability profiles.NSAS does not have any P-gp altering properties and therefore might not affect drug-drug interactions. We conclude from this study that NSAS might make a safer drug candidate compared to DAPP for lowering LDL-cholesterol.
authors.forename: Kristina
authors.initials: K
authors.lastname: Sachs-Barrable
authors.forename: Jerald W
authors.initials: JW
authors.lastname: Darlington
authors.affiliation: Division of Pharmaceutics and Biopharmaceutics, Faculty of Pharmaceutical Sciences, The University of British Columbia, 2405 Wesbrook Mall, Vancouver, V6T 1Z3, British Columbia, Canada. Kishor.Wasan@usask.ca.
authors.forename: Kishor M
authors.initials: KM
authors.lastname: Wasan
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000538:Aluminum Silicates / Q000494:pharmacology* / Q000633:toxicity; D000924:Anticholesteremic Agents / Q000494:pharmacology* / Q000633:toxicity; D001692:Biological Transport; D018938:Caco-2 Cells; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D005456:Fluorescent Dyes / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D049329:Nanostructures / Q000633:toxicity; D010840:Phytosterols / Q000494:pharmacology* / Q000633:toxicity; D020112:Rhodamine 123 / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000538:Aluminum Silicates; D000924:Anticholesteremic Agents; C445524:FM-VP4 compound; D005456:Fluorescent Dyes; D010840:Phytosterols; D020112:Rhodamine 123; C049037:aluminosilicate