Enteral glutamine differentially regulates Nrf 2 along the villus-crypt axis of the intestine to enhance glutathione levels.

BACKGROUND AND AIM Glutamine is an important energy source for the intestinal epithelium, and its supplementation protects intestinal epithelial cells by induction of glutathione. However, mechanisms of glutathione induction in cells at various stages of differentiation along the crypt to villus axis are not well understood. This study examined induction of glutathione in response to glutamine along the intestinal villus-crypt axis and evaluated regulatory mediators involved in the process. METHODS Animals were administered 4% glutamine in feed for 7 days, following which enterocytes at various stages of differentiation were isolated and glutathione levels and signaling mediators involved in its regulation were studied. RESULTS In control animals, glutathione levels were higher in the intestinal crypt than in the villus or middle region. This was accompanied by elevated expression of the modifier subunit of glutathione synthetase (GCLM) and the transcription factor Nrf2 when compared with cells from the villus and middle regions. These levels were further enhanced by glutamine throughout the intestine, although the effects were more dramatic in the crypt. In parallel to glutathione induction, glutamine supplementation also altered actin dynamics and proliferation in cells of the crypt. CONCLUSIONS These results suggest that the variation of glutathione levels along the villus-crypt axis in the intestine is due to gradients in expression of mediators such as glutamate cysteine ligase modifier subunit and Nrf2. The protective effects of glutamine supplementation seem to be most pronounced in the crypt, where it upregulates proliferation, glutathione levels and alters actin dynamics.