Protection of intestinal cells against reactive oxygen species by amino acids

We have investigated the ability of specific amino acids to inhibit the formation of reactive oxygen species (ROS) in cultured human intestinal cells. ROS are significant in the initiation and progression of a number of intestinal diseases, including ulcerative colitis and Crohn's disease. Specific amino acids, such as glycine, have been shown to alleviate intestinal injury and prevent damage in cultured intestinal cells exposed to oxidising agents. To determine if these effects are due to reduced ROS generation we incubated confluent monolayers of Caco‐2 cells with amino acids for 4 hours prior to exposure to the oxidising agent tert‐butyl hydroperoxide (tBOOH). ROS were quantified with the fluorescent probe 5‐(and‐6)‐carboxy‐2′, 7′‐dichlorohydrofluorescein diacetate. Treatment with glycine, L‐cysteine, L‐glutamic acid or N‐acetylcysteine (all 5mM) significantly reduced intracellular ROS concentration (p<0.01‐p<0.001). Glycine treatment resulted in the greatest reduction. Treatment with combinations of amino acids conferred no advantage over individual amino acids. L‐alanine had no beneficial effect. Glycine uptake was significantly increased in cells treated with glycine (p<0.05). This is consistent with earlier work showing that glycine protection in Caco‐2 cells was dependent on uptake. The spectrum of amino acids able to reduce ROS generation is suggestive of a mechanism involving increased production of the antioxidant glutathione, required for normal intestinal function and composed of the amino acids glycine, glutamic acid and cysteine. Sponsored by Newcastle University