Evans Mary E, Jones Dean P, Ziegler Thomas R
Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA.
J Nutr. 2003 Oct;133(10):3065-71. doi: 10.1093/jn/133.10.3065.
Epithelial cell apoptosis is an important regulator of normal gut mucosal turnover; however, excessive apoptosis may inhibit mucosal restitution during pathophysiologic states. Apoptosis is induced by oxidative stress and cytokines, but regulation by specific nutrients has been infrequently studied under these conditions. Glutamine (Gln) is an important metabolic fuel for intestinal epithelial cells and a precursor to the antioxidant glutathione (GSH), which has antiapoptotic effects. In cultured intestinal epithelial cells, Gln depletion increases oxidant-induced apoptosis. This study examined whether Gln protects against apoptosis induced by the cytokine tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) in the human colon carcinoma cell line, HT-29. TRAIL-induced apoptosis in HT-29 cells was characterized by an increase in the percentage of cells in the sub-G1 fraction by flow cytometry, nuclear condensation and the activation of caspase-8 and caspase-3. TRAIL-induced apoptosis was completely prevented by Gln, but not inhibited by other amino acids, including the GSH constituents, glutamate, cysteine and glycine. Similar antiapoptotic effects of Gln occurred when apoptosis was induced by a combination of tumor necrosis factor-alpha and interferon-gamma. Cellular GSH was oxidized during TRAIL-induced apoptosis. This effect was completely blocked by Gln, however, inhibition of GSH synthesis with buthionine sulfoximine did not alter Gln antiapoptotic effects. Furthermore, glutamate prevented GSH oxidation in response to TRAIL but did not protect against TRAIL-induced apoptosis. These results show that Gln specifically protects intestinal epithelial cells against cytokine-induced apoptosis, and that this occurs by a mechanism that is distinct from the protection against oxidative stress mediated by cellular GSH.
上皮细胞凋亡是正常肠道黏膜更新的重要调节因子；然而，在病理生理状态下，过度凋亡可能会抑制黏膜修复。氧化应激和细胞因子可诱导凋亡，但在这些情况下，特定营养素的调节作用鲜有研究。谷氨酰胺（Gln）是肠上皮细胞重要的代谢燃料，也是具有抗凋亡作用的抗氧化剂谷胱甘肽（GSH）的前体。在培养的肠上皮细胞中，Gln缺乏会增加氧化剂诱导的凋亡。本研究检测了Gln是否能保护人结肠癌细胞系HT-29免受细胞因子肿瘤坏死因子-α相关凋亡诱导配体（TRAIL）诱导的凋亡。TRAIL诱导HT-29细胞凋亡的特征为，通过流式细胞术检测发现亚G1期细胞百分比增加、细胞核固缩以及半胱天冬酶-8和半胱天冬酶-3激活。Gln可完全阻止TRAIL诱导的凋亡，但其他氨基酸，包括GSH的组成成分谷氨酸、半胱氨酸和甘氨酸则不能抑制。当肿瘤坏死因子-α和干扰素-γ联合诱导凋亡时，Gln也具有类似的抗凋亡作用。在TRAIL诱导的凋亡过程中，细胞内GSH被氧化。然而，Gln可完全阻断这种作用，用丁硫氨酸亚砜胺抑制GSH合成并未改变Gln的抗凋亡作用。此外，谷氨酸可防止TRAIL诱导的GSH氧化，但不能保护细胞免受TRAIL诱导的凋亡。这些结果表明，Gln可特异性保护肠上皮细胞免受细胞因子诱导的凋亡，且其作用机制不同于细胞内GSH介导的抗氧化应激保护机制。
