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.


CONCLUSIONS
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.
State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
Ning
N
Jiao
State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and bio2046@hotmail.com.
Zhenlong
Z
Wu
State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
Yun
Y
Ji
State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
Bin
B
Wang
State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
Zhaolai
Z
Dai
State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and Department of Animal Science, Texas A&M University, College Station, TX.
Guoyao
G
Wu
D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D019587:Dietary Supplements; D004178:Diquat / Q000037:antagonists & inhibitors / Q000633:toxicity; D017097:Electric Impedance; D050580:Excitatory Amino Acid Transporter 3 / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D018698:Glutamic Acid / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D009994:Osmolar Concentration; D016877:Oxidants / Q000037:antagonists & inhibitors / Q000633:toxicity; D018384:Oxidative Stress; D012333:RNA, Messenger / Q000378:metabolism; D034421:Sus scrofa; D062725:Tight Junction Proteins / Q000819:agonists* / Q000378:metabolism
D000975:Antioxidants; D050580:Excitatory Amino Acid Transporter 3; D016877:Oxidants; D012333:RNA, Messenger; D062725:Tight Junction Proteins; D018698:Glutamic Acid; D004178:Diquat
antioxidative function; glutamate; intestinal epithelial cell; intestinal–mucosal barrier; oxidative stress