Carbohydrate Polymers 117 (2015) 577–584 Contents lists available at ScienceDirect Carbohydrate Polymers j ourna l ho me page: www.elsevier.com/locate/carbpol Thiolated nanocarriers for oral delivery of hydrophilic macromolecular drugs S. Dünnhaupt a , J. Barthelmes a , S. Köllner a , D. Sakloetsakun b , G. Shahnaz c , A. Düregger d , A. Bernkop-Schnürch a,∗ a University of Innsbruck, Institute of Pharmacy/Pharmaceutical Technology, CCB—Centrum of Chemistry and Biomedicine, Innrain 80-82, 6020 Innsbruck, Austria b Faculty of Pharmaceutical Sciences, Khon Kaen University, Khon Kaen 40002, Thailand c Department of Pharmacy, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad 54320, Pakistan d Medical University of Innsbruck, Department of Experimental Urology, Anichstrasse 35, 6020 Innsbruck, Austria a r t i c l e i n f o Article history: Received 27 January 2014 Received in revised form 22 September 2014 Accepted 22 September 2014 Available online 7 October 2014 Keywords: Polymer synthesis Nanoparticles Permeation enhancement Adhesion Cytotoxic effects Chemical compounds studied in this article: Chitosan (PubChem CID: CID 21896651) Thioglycolic acid (PubChem CID: 1133) l-Cysteine hydrochloride (PubChem CID: 60960) Dithionitrobenzoic acid (PubChem CID: 6254) Thiazolyl blue tetrazolium bromide (MTT) (PubChem CID: 64965) Sodium borohydride (PubChem CID: 22959485) a b s t r a c t It was the aim of this study to investigate the effect of unmodified as well as thiolated anionic poly(acrylic acid) (PAA) and cationic chitosan (CS) utilized in free-soluble form and as nanoparticulate system on the absorption of the hydrophilic compound FD 4 across intestinal epithelial cell layer with and without a mucus layer. Modifications of these polymers were achieved by conjugation with cysteine to PAA (PAA- Cys) and thioglycolic acid to CS (CS-TGA). Particles were prepared via ionic gelation and characterized based on their amount of thiol groups, particle size and zeta potential. Effects on the cell layer concerning absorption enhancement, transepithelial electrical resistance (TEER) and cytotoxicity were investigated. Permeation enhancement was evaluated with respect to in vitro transport of FD 4 across Caco-2 cells, while mucoadhesion was indirectly examined in terms of adsorption behaviour when cells were covered with a mucus layer. Lyophilized particles displayed around 1000 mol/g of free thiol groups, particle sizes of less than 300 nm and a zeta potential of 18 mV (CS-TGA) and -14 mV (PAA-Cys). Cytotoxicity stud- ies confirmed that all polymer samples were used at nontoxic concentrations (0.5% m/v). Permeation studies revealed that all thiolated formulations had pronounced effects on the paracellular permeability of mucus-free Caco-2 layers and enhanced the permeation of FD 4 3.0- to 5.3-fold. Moreover, polymers administered as particles showed a higher permeation enhancement than their corresponding solu- tions. However, the absorption-enhancing effect of each thiolated formulation was significantly (p < 0.05) reduced when cells were covered with mucus layer. In addition, all formulations were able to decrease the TEER of the cell layer significantly (p < 0.05). Therefore, both thiolated polymers as nanoparticulate delivery systems represent a promising tool for the oral administration of hydrophilic macromolecules. © 2014 Published by Elsevier Ltd. 1. Introduction Based on their hydrophilic nature and molecular mass, macro- molecular drugs exhibit a poor permeability across mucosal membranes resulting in overall insufficient bioavailability. Accord- ingly, at present most of these drugs are primarily administered via the parenteral route as just a limited portion of the dose reaches the plasma to generate its pharmacological effect when administered orally (Aungst, 2000). The design of a suitable drug ∗ Corresponding author. Tel.: +43 512 507 58600; fax: +43 512 507 58699. E-mail address: Andreas.Bernkop@uibk.ac.at (A. Bernkop-Schnürch). delivery system for oral administration of macromolecular drugs and their absorption to therapeutic levels is therefore a major aim. Promising systems may comprise of excipients providing the drug entire to the specific site of absorption, prolonging its resi- dence time and increasing the permeability for an easier transport to the systemic circulation. Therefore, reversible modifications of epithelial barrier structure by permeation enhancers are required. Low molecular weight enhancers generally have physicochemical characteristics favouring their own absorption, whereas polymeric enhancers are not absorbed, whereby the risk of systemic toxicity is minimized. One example for a suitable polymeric enhancer are thi- olated polymer or designed thiomers, which have been developed as a category of mucoadhesive polymers with reactive thiol groups http://dx.doi.org/10.1016/j.carbpol.2014.09.078 0144-8617/© 2014 Published by Elsevier Ltd.