title: Chitosans as absorption enhancers for poorly absorbable drugs 2: mechanism of absorption enhancement.
abstract: OBJECTIVE
  It has recently been shown that the absorption enhancing and toxic effects of chitosans are dependent on their chemical composition. In this study, the mechanisms underlying these effects were investigated at the cellular level.
  
  
  METHODS
  The effects on epithelial cells of chitosans with different chemical composition, absorption enhancing properties and toxicities were studied in Caco-2 monolayers. Chitosan C( 1:31) has a low degree of acetylation (DA) (1%) and a low m.w. (31 kD), and displays dose-dependent absorption enhancement and cytotoxicity; chitosan C(35:170) has a higher DA (35%) and a higher m.w. (170 kD), is less dose-dependent in absorption enhancement, and is not cytotoxic. A third non-toxic chitosan C(49:22) with a high DA (49%), a low m.w. (22 kD), and no influence on epithelial permeability was used as control.
  
  
  RESULTS
  C(1:31) and C(35:170) bound tightly to the epithelium. Cellular uptake of the chitosans was not observed. Both chitosans increased apical but not basolateral cell membrane permeability and induced a redistribution of cytoskeletal F-actin and the tight junction protein ZO-1. This resulted in increased paracellular permeability of hydrophilic marker molecules of different molecular weights. Addition of negatively charged heparin inhibited the cellular and the absorption enhancing effects of the chitosans, indicating that these effects are mediated via their positive charges. The onset of the effects of C(35:170) on apical membrane permeability and tight junction structure was much faster than that of C(1:31). C(49:22) did not influence any of the properties of the Caco-2 cell monolayers studied.
  
  
  CONCLUSIONS
  The binding and absorption enhancing effects of chitosans on epithelial cells are mediated through their positive charges. The interaction of chitosans with the cell membrane results in a structural reorganisation of tight junction-associated proteins which is followed by enhanced transport through the paracellular pathway.
authors.affiliation: Department of Pharmaceutics, Uppsala University, Biomedical Center, Sweden. Nicolaas.Schipper@eu.pnu.com
authors.forename: N G
authors.initials: NG
authors.lastname: Schipper
authors.forename: S
authors.initials: S
authors.lastname: Olsson
authors.forename: J A
authors.initials: JA
authors.lastname: Hoogstraate
authors.forename: A G
authors.initials: AG
authors.lastname: deBoer
authors.forename: K M
authors.initials: KM
authors.lastname: Vårum
authors.forename: P
authors.initials: P
authors.lastname: Artursson
mesh_terms: D015415:Biomarkers; D002460:Cell Line; D002686:Chitin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D048271:Chitosan; D007408:Intestinal Absorption / Q000187:drug effects*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism; D010539:Permeability
chemical_list: D015415:Biomarkers; D002686:Chitin; D048271:Chitosan