Oral Administration of l-Arginine Potentiates Allergen-Induced Airway Inflammation and Expression of Interleukin-5 in Mice

Abstract

The role of nitric oxide in the airway hyperresponsiveness and inflammation of bronchial asthma has not yet been established. However,l-arginine, the substrate for nitric oxide synthases, reportedly alleviates airway hyperresponsiveness caused by parainfluenza virus and reduces granulocytic inflammation induced by ischemia-reperfusion. We investigated the effects ofl-arginine on a murine model of allergic asthma that included airway hyperresponsiveness, eosinophilic inflammation and expression of interleukin (IL)-5 in the lung. The mice received drinking water with or without l-arginine for 9 weeks. Histologic evaluation and cellular profiles in bronchoalveolar lavage fluid showed that p.o. administration of l-arginine (72 μmol/kg/day) significantly enhanced eosinophilic airway inflammation and goblet cell proliferation that were associated with intratracheal instillation of ovalbumin. l-Arginine also increased protein levels of IL-5 and IL-2 in supernatants from the lung exposed to ovalbumin. The number of eosinophils in bronchoalveolar lavage fluid correlated significantly with the expression of IL-5.l-Arginine did not reverse ovalbumin-associated airway hyperresponsiveness to inhaled ACh. These results suggest that p.o. administration of l-arginine aggravates allergen-induced eosinophilic airway inflammation via expression of IL-5, and in this model it does not show therapeutic efficacy against airway hyperresponsiveness associated with allergen exposure. Oral administration of l-arginine, the precursor of nitric oxide, may not be an effective intervention in allergic asthma.