Abstract
An acylated flavonol glycoside, helichrysoside, at a dose of 10 mg/kg/day per os for 14 days, improved the glucose tolerance in mice without affecting the food intake, visceral fat weight, liver weight, and other plasma parameters. In this study, using hepatoblastoma-derived HepG2 cells, helichrysoside, trans-tiliroside, and kaempferol 3-O-β-d-glucopyranoside enhanced glucose consumption from the medium, but their aglycones and p-coumaric acid did not show this activity. In addition, several acylated flavonol glycosides were synthesized to clarify the structural requirements for lipid metabolism using HepG2 cells. The results showed that helichrysoside and related analogs significantly inhibited triglyceride (TG) accumulation in these cells. The inhibition by helichrysoside was more potent than that by other acylated flavonol glycosides, related flavonol glycosides, and organic acids. As for the TG metabolism-promoting activity in high glucose-pretreated HepG2 cells, helichrysoside, related analogs, and their aglycones were found to significantly reduce the TG contents in HepG2 cells. However, the desacyl flavonol glycosides and organic acids derived from the acyl groups did not exhibit an inhibitory impact on the TG contents in HepG2 cells. These results suggest that the existence of the acyl moiety at the 6′′ position in the D-glucopyranosyl part is essential for glucose and lipid metabolism-promoting activities.
Highlights
Flavonoids are one of the most abundant classes of secondary plant metabolites
This paper deals with the practical synthesis and glucose tolerance-improving activity of helichrysoside (1 = quercetin 3-O-(6 -O-trans-p-coumaroyl)-β-d-glucopyranoside), isolated from Helichrysum kraussii and H. stoechas [24,25] by other research groups
We have reported that several anti-diabetogenic therapeutic candidates obtained from natural resources, such as acylated flavonol glycosides from Sinocrassula indica [39]; saponins from Borassus flabellifer [40]; and thiosugars from Salacia reticulata, S. oblonga, and S. chinensis [41,42,43,44,45,46], showed the inhibition of postprandial hyperglycemia and/or improvement of glucose tolerance in sugar-loaded animal models
Summary
Flavonoids are one of the most abundant classes of secondary plant metabolites. Flavonoids are biosynthesized by the shikimate and acetate-malonate pathways and are comprised of compounds that possess a common C6-C3-C6 skeleton, where two aromatic rings (named ring A and B) are linked via a heterocyclic 4H-pyrane ring (ring C). Modification of the 15-carbon skeleton through different oxidation levels and substituents to ring C gives rise to different classes of flavonoids, such as flavones, flavonols, flavanones, chalcones, dihydroflavonols (flavanonols), isoflavones, aurones, anthocyanidins, leucoanthocyanidines (flavan-3,4-diols), and flavan-3-ols. They naturally occur in aglycone forms, and as glycosylated and/or acylated derivatives and oligomeric and polymeric structures, such as the flavan-3-ol-derived condensed tannins and proanthocyanidins [1,2,3,4,5]. The structures of 1 and 16 are similar: the former has a p-coumaroyl ester at the 6-position in the β-D-glucopyranosyl moiety of quercetin 3-O-β-d-glucopyranoside (isoquercitrin, 17), while the latter has the common acyl group at the same position of kaempferol 3-O-β-d-glucopyranoside (18)
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