Anti-Inflammatory Saponins From an Edible Aquatic Plant Nymphoides hydrophylla

Introduction: The present investigation of Nymphoides hydrophylla is a Taiwan indigenous edible aquatic plant, belongs to the Menyanthaceae family, and has been used as a traditional food with potential medicinal values against fever, insect bites, ulcer, and skin diseases. Interestingly, we found that the plant extract showed a significant anti-inflammatory effect. Objectives: The aim is isolation, structure elucidation, and anti-inflammatory evaluation of secondary metabolites from N. hydrophylla. Material and Methods: This study involves the bioactive isolation and structural studies of the pure compounds determined by NMR, UV, IR spectroscopies, and HRMS. The anti-inflammatory activity of the pure compounds was evaluated in vitro. In addition, isolates showed remarkable anti-inflammatory activities to regulate superoxide anion generation and elastase release in fMLF/CB-induced human neutrophils. Results: This study conducted 10 oleanane-type saponins with oligoglycoside linkage, including two new (1 and 2) identified from the butanol extract of N. hydrophylla. As a result, Compounds 1 and 2, representing new triterpene saponins, have not been previously reported. In vitro anti-inflammatory tests revealed that Compounds 1, 5–7, 9, and 10 showed significant anti-inflammatory effects by inhibiting superoxide anion generation with IC₅₀ values of 1.62, 0.92, 0.28, 2.69, 0.29, and 0.15 μM, respectively, whereas compounds 1, 5, 6, 9, and 10 showed potential inhibition on elastase release in human neutrophils, with IC₅₀ values of 0.19, 1.12, 0.70, 0.68, and 0.51 μM, respectively. Conclusion: Our findings suggested that the components of N. hydrophylla have the potential to develop anti-inflammatory agents.