title: Anionic PAMAM dendrimers rapidly cross adult rat intestine in vitro: a potential oral delivery system?
abstract: OBJECTIVE
  To investigate systematically the effect of polyamidoamine (PAMAM) dendrimer size, charge, and concentration on uptake and transport across the adult rat intestine in vitro using the everted rat intestinal sac system.
  
  
  METHODS
  Cationic PAMAM dendrimers (generations 3 and 4) and anionic PAMAM dendrimers (generations 2.5, 3.5, and 5.5) that were modified to include on average a single pendant amino group were radioiodinated using the Bolton and Hunter Reagent. 125I-Labelled dendrimers were incubated with everted sacs in vitro and the transfer of radioactivity into the tissue and serosal fluid was followed with time.
  
  
  RESULTS
  The serosal transfer rates seen for all anionic generations were extremely high with Endocytic Indices (EI) in the range 3.4-4.4 microL/mg protein/h. The concentration-dependence of serosal transfer was linear over the dendrimer concentration range 10-100 microg/mL. For 125I-labelled generation 5.5 the rate of tissue uptake was higher (EI = 2.48+/-0.51 microL/mg protein/h) than seen for 125I-labelled generations 2.5 and 3.5 (0.6-0.7 microL/mg protein/h) (p < 0.05). The 125I-labelled cationic PAMAM dendrimers (generations 3 and 4) displayed a tissue uptake (EI = 3.3-4.8 microL/mg protein/h) which was higher (p < 0.05) than the rate of serosal transfer (EI = 2.3-2.7 microL/mg protein/h), probably due to nonspecific adsorption of cationic dendrimer to the mucosal surface.
  
  
  CONCLUSIONS
  As the anionic PAMAM dendrimers displayed serosal transfer rates that were faster than observed for other synthetic and natural macromolecules (including tomato lectin) studied in the everted sac system, these interesting nanoscale structures may have potential for further development as oral drug delivery systems.
authors.affiliation: Centre for Polymer Therapeutics, The School of Pharmacy, London, UK.
authors.forename: R
authors.initials: R
authors.lastname: Wiwattanapatapee
authors.forename: B
authors.initials: B
authors.lastname: Carreño-Gómez
authors.forename: N
authors.initials: N
authors.lastname: Malik
authors.forename: R
authors.initials: R
authors.lastname: Duncan
mesh_terms: D000818:Animals; D002850:Chromatography, Gel; D050091:Dendrimers; D004337:Drug Carriers; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007408:Intestinal Absorption / Q000187:drug effects*; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D008297:Male; D010316:Particle Size; D011073:Polyamines / Q000737:chemistry / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D050091:Dendrimers; D004337:Drug Carriers; D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; C104700:PAMAM Starburst; D011073:Polyamines