title: Preactivated thiolated pullulan as a versatile excipient for mucosal drug targeting.
abstract: OBJECTIVE
  The purpose of the present study was to generate a novel mucoadhesive thiolated pullulan with protected thiol moieties and to evaluate its suitability as mucosal drug delivery system.
  
  
  METHODS
  Two different synthetic pathways: bromination-nucleophilic substitution and reductive amination including periodate cleavage were utilized to synthesize such thiolated pullulans. The thiomer (pullulan-cysteamine) with the highest amount of free thiol groups was further enrolled in a reaction with 6-mercaptonicotinamide and its presence in pullulan structure was confirmed via NMR analysis. Furthermore, unmodified, thiolated and preactivated thiolated pullulan were investigated in terms of mucoadhesion via rotating cylinder studies and rheological synergism method as well as their toxicity potential over Caco-2 cells.
  
  
  RESULTS
  Comparing both methods the reductive amination seems to be the method of choice resulting in comparatively higher coupling rates. Using this procedure pullulan-cysteamine conjugate displayed 1522±158μmol immobilized thiol groups and 280±70μmol free thiol groups per gram polymer. Furthermore, 82% of free thiol groups on this conjugate were linked with 6-mercaptonicotinamide (6-MNA). The adhesion time on the rotating cylinder was up to 46-fold prolonged in case of the thiolated polymer and up to 75-fold in case of the preactivated polymer. Rheological measurements of modified pullulan samples showed 98-fold and 160-fold increase in dynamic viscosity upon the addition of mucus within 60min, whereas unmodified pullulan did not show an increase in viscosity at all. Both conjugates had a minor effect on Caco-2 cell viability.
  
  
  CONCLUSIONS
  Because of these features preactivated thiolated pullulan seems to represent a promising type of mucoadhesive polymers for the development of various mucosal drug delivery systems.
authors.affiliation: Department of Pharmaceutical Technology, Institute of Pharmacy, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria.
authors.forename: Gintare
authors.initials: G
authors.lastname: Leonaviciute
authors.affiliation: Department of Pharmaceutical Technology, Institute of Pharmacy, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria.
authors.forename: Wongsakorn
authors.initials: W
authors.lastname: Suchaoin
authors.affiliation: Department of Pharmaceutical Chemistry, Institute of Pharmacy, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Matuszczak
authors.affiliation: Department of Pharmaceutical Technology, Institute of Pharmacy, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria.
authors.forename: Hung Thanh
authors.initials: HT
authors.lastname: Lam
authors.affiliation: Department of Pharmaceutical Technology, Institute of Pharmacy, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria.
authors.forename: Arshad
authors.initials: A
authors.lastname: Mahmood
authors.affiliation: Department of Pharmaceutical Technology, Institute of Pharmacy, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria. Electronic address: andreas.bernkop@uibk.ac.at.
authors.forename: Andreas
authors.initials: A
authors.lastname: Bernkop-Schnürch
mesh_terms: D000268:Adhesiveness; D018938:Caco-2 Cells; D002470:Cell Survival / Q000187:drug effects; D004337:Drug Carriers / Q000737:chemistry* / Q000633:toxicity; D005079:Excipients / Q000737:chemistry*; D005936:Glucans / Q000737:chemistry*; D006801:Humans; D009093:Mucus / Q000378:metabolism*; D012212:Rheology; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D004337:Drug Carriers; D005079:Excipients; D005936:Glucans; D013438:Sulfhydryl Compounds; C009109:pullulan
keywords: 5,5′-Dithiobis(2-nitro-benzoic acid) (Ellman’s reagent) (PubChem CID: 62549); Cysteamine (PubChem CID: 6058); Mucoadhesion; N-Bromosuccinimide (PubChem CID: 67184); Preactivation; Pullulan; Rheology; Sodium cyanoborohydride (PubChem CID: 20587905); Sodium periodate (PubChem CID: 23667635); Thiolation; Thiomer; Thiourea (PubChem CID: 2723790); Trinitrobenzenesulfonic acid (PubChem CID: 11045); Triphenylphosphine (PubChem CID: 11776)