The Prophylactic Effects of Isosteviol Aerosol Inhalation on Bronchial Asthma in Mice

The diterpenoid isosteviol is one of the stevia derivatives that have reported various activities. In mice inhaling isosteviol, OVA- and ACh-induced bronchial asthma showed a dose-dependent improvement of a decline in the expression of inflammatory cytokines and the infiltration of basophils. Compared with inhalation of budesonide 0.6 mg/kg, sensitized mice inhaling 1.0 mg/kg dosage of isosteviol performed a higher tolerate against the ACh stimulation. In behavior tests, the 1.0 mg/kg isosteviol nebulization reached almost 80% of the level of budesonide with regard to the ameliorative effects on depression-like behavior and improvement in sport ability. In addition, lung and systemic inflammation were markedly prevented by isosteviol with a dosage of more than 0.6 mg/kg, which exhibited limited expression of IL-1β and TNF-α, less infiltration of basophils in lung tissues, and a low level of systemic immunocytes, which showed in hematoxylin and eosin staining, RT-PCR, and ELISA results. On the other hand, none of the abnormal pathology was found in both peripheral and central organs of all the administration groups. Generally, this study implicated that the mechanism could involve effects of isosteviol inhalation on the suppression of IL-1β and TNF-α to restrict a systemic upsurge of immunocytes and infiltration into the lung that prevents the occurrence of depression-like behavior and hypokinesia.