International Journal of Pharmaceutics 429 (2012) 22–30 Contents lists available at SciVerse ScienceDirect International Journal of Pharmaceutics jou rn al h om epa ge: www.elsevier.com/locate/ijpharm Bio-relevant media to assess drug permeability: Sodium taurocholate and lecithin combination or crude bile? Katja Berginc ∗ , Jurij Trontelj, Albin Kristl Faculty of Pharmacy, University of Ljubljana, Aˇ skerˇ ceva 7, 1000 Ljubljana, Slovenia a r t i c l e i n f o Article history: Received 10 October 2011 Received in revised form 21 February 2012 Accepted 6 March 2012 Available online 17 March 2012 Keywords: Bio-relevant conditions Taurocholate Lecithin Bile Permeability Drug binding a b s t r a c t The assessment of in vivo drug absorption with in vitro permeability models demands the use of transport media with surface acting compounds. With the aim to establish their influence on in vitro permeability of 30 drugs through Caco-2 monolayers, cell vitality/integrity and micellar drug entrapment, tauro- cholate/lecithin (NaTC/Leci) and pig crude bile were applied. Drug permeabilities were correlated to fraction of drugs absorbed and appropriate NaTC/Leci and bile concentrations were proposed to simu- late fasted/fed conditions in vitro (bile in the concentration range 1–5 v/v% or 0.2/0.05 mM NaTC/Leci for fasted; 10 v/v% bile or 3/0.75 mM NaTC/Leci for fed conditions) without detrimental effects on mono- layer integrity/vitality (NaTC/Leci was more toxic than bile). Surfactants exerted different affinities for drugs; free drug concentration (c free ) of some was significantly lowered only by bile, while for the others NaTC/Leci and bile significantly diminished c free . For some substances NaTC/Leci and bile significantly increased their permeabilities (i.e. more than 3-times) in spite of profound c free decrease indicating the existence of an alternative absorption mechanism. Based on these data, the impact of bile on in vitro drug permeability and micellar drug entrapment cannot be adequately simulated by NaTC/Leci, because their effects on drug absorption differ. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Efficient and effective drug discovery, achieved with combi- natorial chemistry and high-through put screenings, generates numerous lead compounds entering drug/pharmaceutical devel- opment processes, where optimal candidates progress through different stages depending on data generated with in vitro solubil- ity, permeability, and receptor assays (Stegemann et al., 2007). The failure of in vitro models to adequately predict drug/product in vivo performance can thus wrongfully terminate further development or it can significantly add to the delays and costs before actual drug marketing. Therefore, it is of outmost importance to mimic bio- relevant conditions in the in vitro environment to obtain a correct insight into the actual in vivo drug behavior. Furthermore, such an understanding is crucial for the development and interpretation of Abbreviations: Ap, apical; Papp, apparent permeability coefficient; Bl, basolateral; BL, bile; BCS, Biopharmaceutical Classification System; DMEM, Dulbecco’s modified Eagle medium; FaSSIF, fasted state simulated intestinal fluid; FeSSIF, fed state sim- ulated intestinal fluid; F abs , fraction of drug absorbed in humans; c free , free drug concentration; LDH, lactate dehydrogenase; Leci, lecithin; RSE, relative standard error; NaTC, taurocholate; TEER, transepithelial electrical resistance. ∗ Corresponding author. Tel.: +386 1 4769536; fax: +386 1 4258031. E-mail address: katja.berginc@ffa.uni-lj.si (K. Berginc). dissolution tests in generic pharmaceutical drug development prior to entering the bioequivalence trials. The dissolution methods have attempted to reproduce the envi- ronment in the gastrointestinal tract by introducing variations of fasted state simulated intestinal fluid (FaSSIF), and fed state sim- ulated intestinal fluid (FeSSIF) instead of simple water buffers (Vertzoni et al., 2004; Zoeller and Klein, 2007; Jantratid et al., 2008). Sodium taurocholate and lecithin (3 mM taurocholate and 0.75 mM lecithin in FaSSIF; 15 mM taurocholate and 3 mM lecithin in FeSSIF) have been chosen and attempts have been made to replace them by other non-physiological surface acting compounds owing to high cost of pure taurocholate and lecithin and time- consuming buffer preparation process (Zoeller and Klein, 2007). The need for bio-relevant experimental conditions has also been addressed in the in vitro permeability measurements. Thus, tau- rocholate, lecithin and its lipolytic products were included into buffers for permeability experiments (Aungst, 2000; Kataoka et al., 2006; Lind et al., 2007; Patel et al., 2006). Unfortunately, the toxi- city of taurocholate towards Caco-2 cell monolayers and rat small intestine was very high (Kataoka et al., 2006; Patel et al., 2006). Caco-2 monolayers lost their integrity and vitality at 10 (Ingels et al., 2002) or at 15 mM (Patel et al., 2006) taurocholate and at 3 mM lecithin (Ingels et al., 2002), while the sensitivity of rat small intestine towards taurocholate was even more pronounced (Patel et al., 2006). Furthermore, it was established that simple ionic 0378-5173/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ijpharm.2012.03.015