Evaluation of the Effect of Onosma Bracteatum Wall (Boraginaceae) On Bronchial Hyperreactivity in Sensitized Guinea Pigs

Asthma is a chronic inflammatory disorder of the airways. The available treatment options have major limitations owing to low efficacy, associated adverse events and compliance issues. Therefore, the health burden of bronchial asthma is increasing globally at an alarming rate, providing a strong impetus for the development of new therapeutics. Onosma bracteatum ( O. bracteatum ) is known traditionally in Ayurveda to possess anti-asthmatic activity. Hence, the present investigation was undertaken to evaluate the effect of aerial parts of O. bracteatum on bronchial hyperreactivity by various in vivo and in vitro experimental models. Experimental models studied were total and differential cell estimation in bronchoalveolar lavage fluid (BALF) , estimation of histamine release from lungs, in vitro studies on tracheal strip and histopathological studies of egg albumin-sensitized guinea pigs. Treatment with ethanolic extract of O. bracteatum (5 mg/kg, p.o., for 15 days) significantly decreased the total and differential leukocyte count in bronchoalveolar lavage fluid (BALF), and also blocked histamine release from chopped lung tissues of sensitized guinea pigs.   Ethanolic extract of O. bracteatum (5 mg/kg, p.o., for 15 days) prevented the potentiation of the responses of histamine and acetylcholine which resulted in a significant decrease in pD 2 value of histamine and acetylcholine in guinea pig tracheal strip. Histopathological changes induced by egg albumin were also significantly reduced by the treatment with ethanolic extract of O. bracteatum (5 mg/kg, p.o., for 15 days) . These results suggest that O. bracteatum decreases bronchial hyperresponsiveness by decreasing the infiltration of inflammatory mediators like eosinophils, neutrophils in BALF, inhibiting histamine release from lungs of sensitized guinea pigs and by decreasing airway inflammation.