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< 0.051 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 mmoVL 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 Glir plays an important role in mucosal barrier function by enhancing cell growth and maintaining membrane integrity in response to oxidative stress.