Influence of glutamine on cytokine production by human gut in vitro.

Background: glutamine modulates cytokine production by immune cells in vitro and protects the gut from experimental enterocolitis, but data on the effect of glutamine on cytokine production in human gut are lacking. Aim: to assess the effect of glutamine pre-treatment in vivo and in vitro on cytokine production by intestinal mucosa. Methods: nine fasted volunteers received either enteral glutamine or saline over 6h in a cross-over design. Duodenal biopsies were cultured for 24h with or without glutamine. Cytokine content of culture media was analysed by ELISA, and the expression of cytokine mRNA in biopsies was assessed by semi-quantitative RT-PCR. Results: glutamine given in vivo and in vitro significantly decreased IL-6 [1.4 (0.8–8.5) vs 8.9 (1.0–43.9)] and IL-8 production [5.8 (0–51.4) vs 53.0 (2.5–114.6), pg/mg wet tissue], median (range), both P≤0.01, in comparison to no glutamine experiments. Glutamine did not influence IL-4 production. IL-1β, IL-10 and TNF-α were not detectable in culture media. The expression of any cytokine mRNA was not influenced by glutamine. Conclusions: glutamine reduces pro-inflammatory cytokine production by human intestinal mucosa, probably by a post-transcriptional pathway. Glutamine could be useful to modulate inflammatory conditions with imbalanced cytokine production.