Abstract
Gallic acid (GA) is widely used as a dietary supplement due to several health-promoting effects, although its effects on intestinal-epithelial-cell integrity and transport remain mostly unknown. The present study aims to clarify the effects of GA on tight junctions and intestinal nutrient uptake through in vitro and ex vivo models. Both intestinal porcine enterocyte cell line-J2 cells and porcine middle-jejunum segments were treated with 5 (T5), 25 (T25) and 50 (T50) µm GA and mounted in Ussing chambers to determine transepithelial resistance (TEER), claudin-1 (CLDN1), occludin (OCLN), zonula occludens-1 (ZO-1) protein (in tissues and cells) and mRNA (in cells) expression. In addition, uptake of l-glutamate (l-Glut), l-arginine (l-Arg), l-lysine (l-Lys) and l-methionine (l-Meth) together with cationic-amino-acid transporter-1 (CAT-1) and excitatory-amino-acid transporter-3 (EAAT3) expression was evaluated. No apoptosis was observed in GA-treated cells, but TEER and CLDN1 protein abundance was lower with T50 compared with untreated cells. l-Arg and l-Lys uptake was greater with T5 than with T25 and T50. Ex vivo, T50 decreased the TEER values and the protein levels of CLDN1, OCLN and ZO-1, whereas T5 and T25 only decreased CLDN1 protein expression compared with untreated tissues. Moreover, T25 increased l-Glut and l-Arg uptake, the latter confirmed by an increased protein expression of CAT-1. GA influences intestinal uptake of the tested cationic amino acids at low concentrations and decreases the intestinal-cell barrier function at high concentrations. Similarities were observed between in vitro and ex vivo, but different treatment times and structures must be considered.
Highlights
Gallic acid (GA) is widely used as a dietary supplement due to several health-promoting effects, its effects on intestinal-epithelial-cell integrity and transport remain mostly unknown
Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling staining revealed that gallic acid-treated intestinal porcine enterocyte cell line-J2 cells may not undergo apoptosis
The transepithelial resistance (TEER) value of intestinal porcine enterocyte cell line (IPEC)-J2 cells decreased (−36 %, P = 0·03) when cells were incubated with T50 (Fig. 1) compared with T0
Summary
Gallic acid (GA) is widely used as a dietary supplement due to several health-promoting effects, its effects on intestinal-epithelial-cell integrity and transport remain mostly unknown. The present study aims to clarify the effects of GA on tight junctions and intestinal nutrient uptake through in vitro and ex vivo models Both intestinal porcine enterocyte cell line-J2 cells and porcine middle-jejunum segments were treated with 5 (T5), 25 (T25) and 50 (T50) μM GA and mounted in Ussing chambers to determine transepithelial resistance (TEER), claudin (CLDN1), occludin (OCLN), zonula occludens-1 (ZO-1) protein (in tissues and cells) and mRNA (in cells) expression. Together with other extracellular stimuli, can modulate both tight-junction proteins and AA transporter expression[6,7,8] This latter property is of great interest for human and animal well-being, considering that AA are effectors of epithelial cell function[9].
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