Glutamine preferentially inhibits T-helper type 2 cell-mediated airway inflammation and late airway hyperresponsiveness through the inhibition of cytosolic phospholipase A2 activity in a murine asthma model

Summary Background The non‐essential amino acid, l‐glutamine (Gln), is abundant in the human body. Gln exhibits beneficial effects on endotoxic shock through the inhibition of cytosolic phospholipase A2 (cPLA2) activity. cPLA2 has been reported to be implicated in the pathogenesis of asthma, but the effects of Gln on asthma have not yet been defined. Objective To investigate the effects of Gln on allergic bronchial inflammation and airway hyperresponsiveness (AHR), and to determine the possible action mechanisms of Gln in a murine model of asthma. Methods cPLA2 phosphorylation was assessed by immunoprecipitation and Western blotting. Smears of bronchoalveolar lavage cells were stained with Diff‐Quik solution for differential cell counting. Airway levels of the proteins [T‐helper type‐1 (Th1) and Th2 cytokines, and mucin] were measured by ELISA. mRNA expression of cytokines was assessed by real‐time RT‐PCR. AHR was assessed as a change in airway resistance (RL). Histological studies were performed to assess the levels of mucin and pulmonary inflammation. Results Systemic Gln administration inhibited cPLA2 phosphorylation and its enzymatic activity in the lungs. Additionally, Gln effectively suppressed the key features of Th2‐dependent asthmatic features, such as airway eosinophilia, mucus formation, and airway type 2 cytokine production, as well as late AHR. Conclusion Gln was found to be effective in the suppression of Th2‐dependent phenotypes and late AHR, and this effect of Gln appeared to be at least partially attributable to its ability to suppress cLPA2 activity in the airway. Our results suggest that clinical use of Gln for patients with asthma may be beneficial.