title: Apple extract induces increased epithelial resistance and claudin 4 expression in Caco-2 cells.
abstract: BACKGROUND
  The small intestinal epithelium functions both to absorb nutrients, and to provide a barrier between the outside, luminal, world and the human body. One of the passageways across the intestinal epithelium is paracellular diffusion, which is controlled by the properties of tight junction complexes. We used a differentiated Caco-2 monolayer as a model for small intestinal epithelium to study the effect of crude apple extracts on paracellular permeability.
  
  
  RESULTS
  Exposure of crude apple homogenate to the differentiated Caco-2 cells increased the paracellular resistance, determined as trans-epithelial electrical resistance (TEER). This increase was linearly related to the concentration of apple present. The TEER-enhancing effect of apple extract was due to factors mainly present in the cortex, and the induction was not inhibited by protein kinase inhibitors. Apple-induced resistance was accompanied by increased expression of several tight junction related genes, including claudin 4 (CLDN4).
  
  
  CONCLUSIONS
  Crude apple extract induces a higher paracellular resistance in differentiated Caco-2 cells. Future research will determine whether these results can be extrapolated to human small intestinal epithelia.
authors.affiliation: Wageningen University and Research Centre, Food & Biobased Research, Wageningen, The Netherlands. ram_vreeburg@hotmail.com
authors.forename: Robert A M
authors.initials: RA
authors.lastname: Vreeburg
authors.forename: Esther E
authors.initials: EE
authors.lastname: van Wezel
authors.forename: Francisco
authors.initials: F
authors.lastname: Ocaña-Calahorro
authors.forename: Jurriaan J
authors.initials: JJ
authors.lastname: Mes
mesh_terms: D018938:Caco-2 Cells; D062506:Claudin-4; D057167:Claudins / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects*; D005638:Fruit / Q000737:chemistry; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D027845:Malus / Q000737:chemistry*; D010936:Plant Extracts / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D019108:Tight Junctions / Q000502:physiology
chemical_list: C568157:CLDN4 protein, human; D062506:Claudin-4; D057167:Claudins; D010936:Plant Extracts