Unconjugated bilirubin modulates the intestinal epithelial barrier function in a human-derived in vitro model.
Unconjugated bilirubin promotes intestinal secretion without affecting nutrient digestion or absorption. In the current study, the effects of unconjugated bilirubin (UCB) on the barrier function of the intestinal epithelium were investigated. The apical side of human intestinal cell line Caco-2 monolayers was challenged with purified UCB. Transepithelial electrical resistance and paracellular fluxes of 10 kD Cascade blue conjugate dextran were measured. Cell monolayer viability was studied using LDH release and trypan blue exclusion tests. Redistribution of enterocyte tight junction occludin was studied by confocal microscopy. Bilirubin induced a dose-dependent decrease of transepithelial electrical resistance (TEER). This effect was maximal at 6 h and tended to be reversed at 48 h. Oxidated bilirubin was ineffective. Bilirubin significantly increased fluorescent dextran paracellular passage. Cell viability was not affected by UCB over the 5-200 nmol/L concentration range. Finally, bilirubin triggered a reversible redistribution of tight junctional occludin. UCB increases the permeability of intestinal epithelium. This effect is reversible, dependent on the redox status of the molecule and the rearrangement of the tight junction. These data attribute to bilirubin a novel role of functional modulator of intestinal paracellular permeability in vitro.
Raimondi
Francesco
F
Department of Pediatrics, Università Federico II, Naples, Italy. raimondi@unina.it
Crivaro
Valeria
V
Capasso
Letizia
L
Maiuri
Luigi
L
Santoro
Pasquale
P
Tucci
Maria
M
Barone
Maria Vittoria
MV
Pappacoda
Serena
S
Paludetto
Roberto
R
D001663:Bilirubin / Q000502:physiology*; D018938:Caco-2 Cells; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D003911:Dextrans / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D017097:Electric Impedance; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins / Q000032:analysis; D062793:Occludin; D009942:Organometallic Compounds / Q000493:pharmacokinetics; D009943:Organophosphorus Compounds / Q000493:pharmacokinetics; D010084:Oxidation-Reduction; D010539:Permeability; D019108:Tight Junctions / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
D003911:Dextrans; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; D009942:Organometallic Compounds; D009943:Organophosphorus Compounds; C066850:Cascade Blue; D001663:Bilirubin