L-Glutamate Enhances Barrier and Antioxidative Functions in Intestinal Porcine Epithelial Cells.

BACKGROUND L-Glutamate (Glu) is a major amino acid in milk and postweaning diets for mammals (including pigs and human infants). However, effects of Glu on intestinal mucosal barrier and antioxidative functions are unknown. OBJECTIVE This study tested the hypothesis that Glu may enhance the barrier function of intestinal porcine epithelial cell line 1 (IPEC-1) cells by upregulating the expression of tight junction proteins. METHODS IPEC-1 cells were cultured with or without Glu in the presence or absence of 1 mmol/L diquat (an oxidant) for indicated time points. Cell numbers, transepithelial electrical resistance (TEER), mRNA, and protein abundance of glutamate transporter, the release of lactate dehydrogenase (LDH), and the abundance of tight junction proteins were determined. RESULTS Compared with 0 mmol/L Glu, 0.5-, 1-, and 2 mmol/L Glu stimulated (P < 0.05) cell growth by 13-37% at 24 h and 12-34% at 48 h, respectively. In addition, 0.5 mmol/L Glu increased (P < 0.05) TEER (by 58% at 24 h and by 98% at 48 h, respectively). These effects of Glu were associated with increased mRNA abundance of Glu transporter solute carrier family 1 member 1 (SLC1A1) by 30-130% and protein abundance of excitatory amino acid transporter 3 (encoded by SLC1A1) by 19-34%, respectively. In a cell model of oxidative stress induced by 1 mmol/L diquat, 0.5 mmol/L Glu enhanced cell viability, TEER, and membrane integrity (as indicated by the reduced release of LDH) in IPEC-1 cells by increasing the abundance of the tight junction proteins occludin, claudin-3, zonula occludens (ZO)-2, and ZO-3. CONCLUSION These findings indicate that Glu plays an important role in mucosal barrier function by enhancing cell growth and maintaining membrane integrity in response to oxidative stress.