Abstract
In this study, the inhibitory potential of bacterial neuraminidase (NA) was observed on the leaves of Epimedium koreanum Nakai, which is a popular ingredient in traditional herbal medicine. This study attempted to isolate the relevant, responsible metabolites and elucidate their inhibition mechanism. The methanol extraction process yielded eight flavonoids (1–8), of which compounds 7 and 8 were new compounds named koreanoside F and koreanoside G, respectively. All the compounds (1–8) showed a significant inhibition to bacterial NA with IC50 values of 0.17–106.3 µM. In particular, the prenyl group on the flavonoids played a critical role in bacterial NA inhibition. Epimedokoreanin B (compound 1, IC50 = 0.17 µM) with two prenyl groups on C8 and C5′ of luteolin was 500 times more effective than luteolin (IC50 = 85.6 µM). A similar trend was observed on compound 2 (IC50 = 0.68 µM) versus dihydrokaempferol (IC50 = 500.4 µM) and compound 3 (IC50 = 12.6 µM) versus apigenin (IC50 = 107.5 µM). Kinetic parameters (Km, Vmax, and Kik/Kiv) evaluated that all the compounds apart from compound 5 showed noncompetitive inhibition. Compound 5 was proven to be a mixed type inhibitor. In an enzyme binding affinity experiment using fluorescence, affinity constants (KSV) were tightly related to inhibitory activities.
Highlights
The neuraminidases (EC 3.2.1.18) are enzymes that catalyze the hydrolysis of terminal neuraminic acid from a variety of glycoproteins and gangliosides
We have undertaken a thorough investigation of bacterial neuraminidase inhibition by E. koreanum Nakai, an important medicinal plant
The principal components were identified as prenylated flavonoids, including two new ones, named koreanoside F and koreanoside G
Summary
The neuraminidases (EC 3.2.1.18) are enzymes that catalyze the hydrolysis of terminal neuraminic acid from a variety of glycoproteins and gangliosides. Aboveground parts of E. koreanum Nakai (leaves and stem) have been used as a medicinal herb for a. The aboveground parts of E. koreanum Nakai (leaves and stem) have been used as a medicinal herb for general tonic against infertility, as well as against inflammatory diseases including cardiovascular a general tonic against infertility, as well as against inflammatory diseases including cardiovascular diseases and arthritis [11,12]. Species continues to be a rich source of phenolic metabolites, of which prenylated flavonoids are the. Its species continues to be a rich source of phenolic metabolites, of which prenylated flavonoids major constituents. Inthe particular, observed were a critical role of for thebacterial prenyl group on the flavonoids in enzyme. Particular, we observed a critical role of the prenyl group on the flavonoids in enzyme inhibition
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