title: Mechanisms of membrane transport of poorly soluble drugs: role of micelles in oral absorption processes.
abstract: Micelles formed in the GI tract by bile acid and lecithin play an important role in oral absorption of poorly soluble drugs. In this situation, the drug molecules are present in equilibrium between the free and micellar states. In this study, the relationship between the free drug concentration and the membrane permeability of poorly soluble drugs was examined. Permeability across a Caco-2 monolayer and a dialysis membrane were measured in a side-by-side chamber system. The concentrations of sodium taurocholate (NaTC) and lecithin were varied to allow measurement of membrane permeability at different concentrations of free drugs. For troglitazone, hexylparaben, and heptylparaben, an increase in the NaTC and lecithin concentrations caused the permeability across the Caco-2 monolayer to decrease slightly, whereas the permeability across the dialysis membrane decreased markedly. In contrast, the changes in permeability of griseofulvin with an increased micelle concentration were similar for the Caco-2 monolayer and the dialysis membrane. Assuming that the permeability for the dialysis membrane reflects the free drug concentration in the medium, these results suggest that troglitazone and alkylparabens, but not griseofulvin, can partition directly from micelles to Caco-2 monolayers. This mechanism may contribute to oral absorption of drugs that are poorly soluble in water.
authors.affiliation: Ono Pharmaceutical Co., Ltd, 3-1-1 Sakurai Shimamoto-Cho Mishima-Gun, Osaka 618-8585, Japan. k.yano@ono.co.jp
authors.forename: Koji
authors.initials: K
authors.lastname: Yano
authors.forename: Yoshie
authors.initials: Y
authors.lastname: Masaoka
authors.forename: Makoto
authors.initials: M
authors.lastname: Kataoka
authors.forename: Shinji
authors.initials: S
authors.lastname: Sakuma
authors.forename: Shinji
authors.initials: S
authors.lastname: Yamashita
mesh_terms: D000284:Administration, Oral; D018938:Caco-2 Cells; D002463:Cell Membrane Permeability; D055598:Chemical Phenomena; D002839:Chromans / Q000493:pharmacokinetics; D003956:Dialysis / Q000379:methods; D006118:Griseofulvin / Q000493:pharmacokinetics; D006801:Humans; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D054709:Lecithins / Q000737:chemistry; D008823:Micelles; D010226:Parabens / Q000493:pharmacokinetics; D012995:Solubility; D013656:Taurocholic Acid / Q000737:chemistry; D013806:Theophylline / Q000493:pharmacokinetics; D045162:Thiazolidinediones / Q000493:pharmacokinetics; D000077288:Troglitazone
chemical_list: D002839:Chromans; D054709:Lecithins; D008823:Micelles; D010226:Parabens; D045162:Thiazolidinediones; D006118:Griseofulvin; D013656:Taurocholic Acid; D013806:Theophylline; D000077288:Troglitazone