Inhibitory characteristics of flavonol-3-O-glycosides from Polygonum aviculare L. (common knotgrass) against porcine pancreatic lipase

Abstract

Pancreatic lipase (PL) is an enzyme that plays an essential role in the digestion of dietary lipids and is a suitable target for an anti-obesity dietary supplement. The objective of this study was to find a novel source of PL inhibitors from Korean medicinal plants and investigate the PL-inhibitory properties of the active constituents. From among 34 kinds of methanolic crude extracts, Polygonum aviculare L. showed the highest PL-inhibitory activity (63.97 ± 0.05% of inhibition). Solvent fractionation and liquid chromatography/mass spectrometry (LC/MS) analysis identified flavonol-3-O-glycosides, flavonol-3-O-(2″-galloyl)-glycosides, and flavonol aglycones as active constituents. Furthermore, the inhibitory characteristics of the major compounds were investigated in terms of enzyme kinetics and fluorescence quenching. The results suggested that the inhibitory activity of the major compounds is closely related to the tertiary structural change in PL, and that differences in inhibitory activity occurred due to slight discrepancies in their chemical structure.

Figure 1

Comparison of the pancreatic lipase (PL)-inhibitory activities of Polygonum aviculare L. crude extract and its n-hexane/ethyl acetate (EtOAc) fractions. The concentration of all samples was 0.25 mg/mL. The PL-inhibitory activity of the EtOAc fraction was significantly stronger than that of the other fractions. Error bars indicate standard error of the mean. Asterisks between bars denote significant differences in PL-inhibitory activity (p < 0.01, Duncan’s multiple range test on ANOVA). NS, not significantly different (p > 0.01).

Figure 2

Ultra-performance liquid chromatography coupled with electrospray ionization mass spectrometry (UPLC-ESI-MS) analysis of Polygonum aviculare L. crude extract and its ethyl acetate (EtOAc) fraction. (a) UPLC chromatogram of crude extract. (b) UPLC chromatogram of EtOAc fraction. (c) Chemical structures of annotated compounds in the EtOAc fraction. The EtOAc fraction was mostly composed of 10 kinds of flavonoids (1–10) and also contained several fatty acids (*).

Figure 3

Lineweaver-Burk plots for the determination of inhibition type of the major compounds and flavonol aglycones against pancreatic lipase. (a) Quercetin. (b) Kaempferol. (c) Myricitrin. (d) Quercitrin. (e) Avicularin. The experiments were conducted under the concentrations of compounds at 50 μM and 100 μM together with blank.

Figure 4

Fluorescence emission spectra of pancreatic lipase in the presence of the major compounds and flavonol aglycones. (a) Quercetin. (b) Kaempferol. (c) Myricitrin. (d) Quercitrin. (e) Avicularin. The solid line shows the fluorescence emission spectra in the absence of compounds.