An ethnobotanical survey and inhibitory effects on NLRP3 inflammasomes/Caspase-1 of herbal recipes' extracts traditionally used in Rwanda for asthma treatment

Ethnopharmacological relevance: Respiratory diseases and asthma, in particular, are nowadays a global health problem. In Rwanda, some traditional healers claim to treat asthma with plant-based recipes, though there is no scientific proof so far. Aim of the study: Our study aimed at evaluating the toxicity and the anti-inflammatory effect of plant recipes used in Rwanda against asthma in order to select potential candidates for further characterization of the active compounds. Materials and methods: Water (aqueous) and methanol-dichloromethane (organic) extracts from selected folkloric recipes were submitted for toxicity test on THP-1 derived macrophages using CellTiter-Glo Luminescent Cell Viability Assay. The evaluation of the anti-inflammatory effect of the plant extracts was carried out using the Caspase-Glo 1 Inflammasome assay on THP-1-derived macrophages. Results: Most of both organic and aqueous extract showed more than 95% of cell viability up to 200 mu g/ml, except for RO3Cn organic extract that inhibited 25% of the cell viability. Plant extracts inhibited caspase-1 activation in THP-1 derived macrophages in a dose-dependent manner. Four extracts (RO3Cn and RO7Kn aqueous extracts, R1OMK and R19Sz organic extracts) strongly downregulated the activation of caspase-1 (more than 70% at 50 mu g/ml). In general, organic extracts exhibited better caspase-1 inhibitory effects than their aqueous counterparts. Conclusions: The inhibition of inflammasome/caspase-1 is one of key mechanisms of action in asthma. Some traditional recipes are active on this mechanism and are thus strong candidates for the treatment of asthma and other inflammasome-mediated diseases. Further investigations are needed to characterize active molecules.