Zinc supplementation modifies tight junctions and alters barrier function of CACO-2 human intestinal epithelial layers.
BACKGROUND
Zinc deficiency is known to result in epithelial barrier leak in the GI tract. Precise effects of zinc on epithelial tight junctions (TJs) are only beginning to be described and understood. Along with nutritional regimens like methionine-restriction and compounds such as berberine, quercetin, indole, glutamine and rapamycin, zinc has the potential to function as a TJ modifier and selective enhancer of epithelial barrier function.


OBJECTIVE
The purpose of this study was to determine the effects of zinc-supplementation on the TJs of a well-studied in vitro GI model, CACO-2 cells.


METHODS
Barrier function was assessed electrophysiologically by measuring transepithelial electrical resistance (Rt), and radiochemically, by measuring transepithelial (paracellular) diffusion of 14C-D-mannitol and 14C-polyethyleneglycol. TJ composition was studied by Western immunoblot analyses of occludin, tricellulin and claudins-1 to -5 and -7.


RESULTS
Fifty- and 100-μM zinc concentrations (control medium is 2 μM) significantly increase Rt but simultaneously increase paracellular leak to D-mannitol. Claudins 2 and 7 are downregulated in total cell lysates, while occludin, tricellulin and claudins-1, -3, -4 and -5 are unchanged. Claudins-2 and -7 as well as tricellulin exhibit decreased cytosolic content as a result of zinc supplementation.


CONCLUSIONS
Zinc alters CACO-2 TJ composition and modifies TJ barrier function selectively. Zinc is one of a growing number of "nutraceutical" substances capable of enhancing epithelial barrier function, and may find use in countering TJ leakiness induced in various disease states.
Lankenau Institute for Medical Research, 100 W Lancaster Ave, Wynnewood, PA 19096, USA.
Xuexuan
X
Wang
Mary Carmen
MC
Valenzano
Joanna M
JM
Mercado
E Peter
EP
Zurbach
James M
JM
Mullin
D015153:Blotting, Western; D018938:Caco-2 Cells; D002470:Cell Survival / Q000187:drug effects; D057167:Claudins / Q000235:genetics / Q000378:metabolism; D003470:Culture Media; D004247:DNA / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects*; D062794:MARVEL Domain Containing 2 Protein / Q000235:genetics / Q000378:metabolism; D062793:Occludin / Q000235:genetics / Q000378:metabolism; D019108:Tight Junctions / Q000187:drug effects*; D015032:Zinc / Q000494:pharmacology*
D057167:Claudins; D003470:Culture Media; D062794:MARVEL Domain Containing 2 Protein; D062793:Occludin; D004247:DNA; D015032:Zinc