L-Glutamine Attenuates Apoptosis in Porcine Enterocytes by Regulating Glutathione-Related Redox Homeostasis

Background: Programmed cell death plays a fundamental role in intestinal development and mucosal homeostasis. Dysregulation of these processes is associated with an impaired intestinal-mucosal barrier, reduced nutrient absorption, and initiation and progression of intestinal diseases. 4-Hydroxy-2-nonenal (4-HNE), a product of lipid peroxidation, is commonly used to induce oxidative stress in cells. L-Glutamine is known to protect cells from apoptosis. However, the underlying mechanisms are largely unknown. Objective: This study was conducted to test the hypothesis that L-glutamine attenuates 4-HNE-induced apoptosis by modulating glutathione (GSH) and thioredoxin (TXN) antioxidant systems and the expression of genes involved in 4-HNE metabolism in enterocytes. Methods: Intestinal porcine epithelial cell line 1 (IPEC-1) cells were cultured with or without 4-HNE (30 mu mol/L) in the presence of 0.05 or 0.25 mmol L-glutamine/L (a physiological concentration in the lumen of the small intestine) for indicated time periods. Cell viability, abundances of apoptotic proteins, mitochondrial membrane depolarization, production of reactive oxygen species (ROS) and GSH, and expression of genes involved in the biosynthesis of GSH, thioredoxin, and 4-HNE metabolism were determined. Results: Compared with basal medium containing 0.05 mmol L-glutamine/L, 4-HNE enhanced apoptosis by 19.6% (P < 0.05) in a caspase-3-dependent manner. This effect was accompanied by elevated intracellular ROS production (39.5% and 85.3% for 2-and 4-h treatment, respectively), increasedmitochondrial depolarization by 80%, and decreased intracellular GSH concentrations by 17.7%. These effects of 4-HNE were reduced by 0.25 mmol L-glutamine/L. Further study showed that the protective effect of L-glutamine was associated with the enhanced expression of genes involved in GSH production (including GCLC, GCLM, GSR, CBS, and CTH) by 3.9-14-fold, as well as genes involved in 4-HNE metabolism [e.g., glutathione S-transferase A (GSTA) 1 and GSTA4] by 1.9-7.2-fold. The mRNA levels for ADH5, AKR1C1, AKR1A1, and TXNRD1 were enhanced 1.4-8.8-fold by 4-HNE but were not changed in cells co-treated with 4-HNE and L-glutamine. Conclusion: These findings indicate that L-glutamine attenuates 4-HNE-induced apoptosis by regulating GSH-related redox homeostasis and enhancing GSTA-mediated metabolism in enterocytes.