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Biochemical, Molecular, and Genetic Mechanisms

Glutamine Pretreatment Reduces IL-8 Production in Human Intestinal Epithelial Cells by Limiting IB Ubiquitination

Aurélie Hubert-Buron^*, Jonathan Leblond^*, Arnaud Jacquot^*, Philippe Ducrotté^*,, Pierre Déchelotte^*,,1 and Moïse Coëffier^*,

^* Appareil Digestif Environnement et Nutrition (ADEN EA-3234), Institut Fédératif de Recherches Multidisciplinaires sur les Peptides, Medical Faculty, 76183 Rouen, France and Rouen University Hospital, Rouen, France

¹ To whom correspondence should be addressed. E-mail: pierre.dechelotte{at}chu-rouen.fr.

Glutamine, the most abundant amino acid in the human body, plays several important roles in the intestine. Recent studies showed that glutamine regulates protein metabolism and intestinal inflammation among other mechanisms by reducing proinflammatory cytokine release. Because regulation of the inflammatory response was shown to be linked to proteolysis regulation, we hypothesized that glutamine pretreatment could act on IL-8 production in human intestinal epithelial cells through the regulation of inhibitor B (IB) ubiquitination. The HCT-8 cells were pretreated for 24 h with 0.6, 2, or 10 mmol/L glutamine. IL-8 concentration and IB (free and ubiquitinated) expressions were assessed by ELISA and immunoblotting, respectively. A pretreatment with 10 mmol/L glutamine decreased IL-8 production under both basal and proinflammatory conditions (both P < 0.05). In the presence of a proteasome inhibitor (MG132), the ubiquitin-IB complex expression was not significantly modified by glutamine under basal conditions but decreased significantly under proinflammatory conditions (P < 0.05). After the addition of 10 mmol/L of glutamine, the free IB expression increased under basal and stimulated conditions (both P < 0.05). A glutamine pretreatment of 10 mmol/L did not affect ubiquitin expression or proteasome activity. This study indicates that glutamine pretreatment may reduce the intestinal inflammatory response by limiting the proteolysis of IB.

KEY WORDS: • glutamine • cytokine • IB • ubiquitin • intestine

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