Glutamine Reduces TNF-α by Enhancing Glutathione Synthesis in Lipopolysaccharide-Stimulated Alveolar Epithelial Cells of Rats

To investigate the role of glutathione (GSH) synthesis in the regulation on nuclear factor (NF)-kappa B activity and tumor necrosis factor-alpha (TNF-alpha) release by glutamine (GLN) in lipopolysaccharide (LPS)-stimulated alveolar type II (AT-II) epithelial cells of rat lungs. Primary cultured AT-II cells were pre-treated with various doses of GLN for 2, 8, 16, 24 h. At the 8 h time point before LPS stimulation, various doses of L-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH synthesis, were added with 10 mM GLN. Then the cells were stimulated with 1 mu g/ml LPS for 24 h. The cells were obtained for GSH measurement. TNF-alpha level in the supernatant was determined by enzyme-linked immunosorbent assay. NF-kappa B activity was assessed by electrophoretic mobility shift assay. Eight hours before LPS exposure was the best time point for GLN's enhancing GSH synthesis. LPS could significantly decrease the GSH level, increase NF-kappa B activation and TNF-alpha release in AT-II cells. Supplementation of GLN could increase the GSH level and attenuate the release of TNF-alpha in LPS-stimulated AT-II cells in a dose-dependant manner. And NF-kappa B activation also could be prevented by GLN. BSO could block the effect of GLN. As a precursor of GSH, glutamine could prevent the NF-kappa B activation and attenuate the release of TNF-alpha in LPS-stimulated AT-II cells and the effect may be mediated via GSH synthesis.