Development of an Orally Bioavailable Isoliquiritigenin Self-Nanoemulsifying Drug Delivery System to Effectively Treat Ovalbumin-Induced Asthma

Purpose: Isoliquiritigenin (ILQ), an important component of Anti-Asthma Herbal Medicine Intervention (ASHMI), had shown potent anti-asthma effect in vitro in our previous study. However, poor solubility and low bioavailability hindered in vivo application to treat asthma. This study was to develop a novel ILQ loaded self-nanoemulsifying drug delivery system (ILQ-SMEDDS) with enhanced bioavailability. Methods: The optimized SMEDDS formulation was composed of ethyl oleate (oil phase), Tween 80 (surfactant) and PEG400 (co-surfactant) at a mass ratio of 3:6:1. The physiochemical properties of ILQ-SMEDDS, including drug content, globule size, zeta potential, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, were characterized. And the in vitro release profile, in situ intestinal absorption, in vivo pharmacokinetic parameters and the anti-asthma effect of ILQ suspension and ILQ-SMEDDS were evaluated. Results: The ILQ-SMEDDS had an average globule size of 20.63 +/- 1.95 nm with a polydispersity index (PDI) of 0.11 +/- 0.03, and its zeta potential was - 12.64 +/- 2.12 mV. The cumulative release rate of ILQ from ILQ-SMEDDS to the simulated gastrointestinal tract was significantly higher than that of free ILQ suspension. And area under curve with ILQ-SMEDDS was found to be 3.95 times higher than that of ILQ suspension indicating improved bioavailability by SMEDDS. Although ILQ-SMEDDS showed a slight less effective inhibitory effect on eotaxin-1 in human lung fibroblast (HFL-1) cells than free ILQ, in an ovalbumin-induced asthma model, ILQ-SMEDDS exhibited more efficacy than ILQ suspension in improving asthma-associated inflammation, including eosinophil production, ovalbumin-specific immunoglobulin E (OVA-sIgE), interleukin 4 (IL 4), interleukin 5 (IL 5) and interferon-gamma (IFN-gamma). Even the low dose of ILQ-SMEDDS group (10 mg/kg) showed better anti-asthma effect than that of the ILQ suspension group (20 mg/kg). Conclusion: Compared with ILQ suspension, ILQ-SMEDDS showed significantly improved bioavailability and anti-asthma effect, revealing its potential as a favorable pharmaceutical agent for treating asthma.