Flavonoids from the Genus Astragalus: Phytochemistry and Biological Activity.

Flavonoids, the most common plant polyphenols are widely distributed in every species and possess a broad range of pharmacological activities. The genus Astragalus is the largest in the Fabaceae family with more than 2,500 species spread. They are known to contain different metabolites such as flavonoids, saponins, and polysaccharides. Plants from the genus have been used in the traditional medicine of many countries for centuries. This paper is focused on the large group of flavonoid compounds. Details on structure as well as information about the pharmacological properties of flavonoids, isolated from Astragalus species have been discussed. This review is based on publications until the first half of 2014 and includes also the results from our phytochemical investigations of the genus.

Flavoalkaloids and Flavonoids from Astragalus monspessulanus.

A new flavonol tetraglycoside, quercetin-3-O-[α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→6)]-ß-D-galactopyranosyl]-7-O-ß-D-glucopyranoside (1), and two new flavonol alkaloids, N-(8-methylquercetin-3-O-[α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→6)]-ß-D-galactopyranosyl])-3-hydroxypiperidin-2-one (2) and N-(8-methylkaempferol-3-O-[α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→6)]-ß-D-galactopyranosyl])-3-hydroxypiperidin-2-one (3), were isolated from the aerial parts of Astragalus monspessulanus ssp. monspessulanus. Two rare flavonoids with an unusual 3-hydroxy-3-methylglutaric acid moiety, quercetin-3-O-α-L-rhamnopyranosyl-(1→2)-[6-O-(3-hydroxy-3-methylglutaryl)-ß-D-galactopyranoside (4) and kaempferol-3-O-α-L-rhamnopyranosyl-(1→2)-[6-O-(3-hydroxy-3-methylglutaryl)-ß-D-galactopyranoside (5), were isolated from the aerial parts of A. monspessulanus ssp. illyricus. In addition, the eight known flavonoids alangiflavoside (6), alcesefoliside (7), mauritianin (8), quercetin-3-ß-robinobioside (9), cosmosine (10), apigenin-4'-O-glucoside (11), trifolin (12), and rutin (13) were isolated from aerial parts of A. monspessulanus ssp. monspessulanus. Their structures were elucidated via NMR and HRESIMS data. In a model that tested t-BuOOH-induced oxidative stress on isolated rat hepatocytes, flavonoids 1-13 had statistically significant cytoprotective activity similar to that of silymarin, tested at 60 µg/mL. The most prominent effects were observed for flavonoids 1, 4, 7, and 12.

Experimental liver protection of n-butanolic extract of Astragalus monspessulanus L. on carbon tetrachloride model of toxicity in rat.

OBJECTIVE: To investigate the hepatoprotective potential of n-butanolic extract of Astragalus monspessulanus L. (EAM) against in-vitro/in-vivo carbon tetrachloride (CCl4)-induced liver damage in rats. Silymarin was used as a positive control. METHODS AND RESULTS: The in-vitro experiments were carried out in primary isolated rat hepatocytes first incubated with CCl4 (86 µmol/l). Hepatic injury was discerned by a decrease in cell viability and cell glutathione (GSH) levels, an increase in lactate dehydrogenase leakage into the medium, and an elevation in malondialdehyde (MDA) quantity. Cell pre-incubation with EAM (1 µg/ml and 10 µg/ml) significantly ameliorated the CCl4-induced liver damage. In-vivo rats were challenged orally with CCl4 (10% solution in olive oil) alone and after 7 days pre-treatment with EAM (100 mg/kg body weight per day, oral gavage). CCl4 damage was judged by an increased production of MDA, depletion of cell GSH, and a decrease in cell antioxidant defense system. EAM pre-treatment normalizes the activities of the antioxidant enzymes and the levels of GSH and MDA. These data are supported by the histopathological examination. CONCLUSION: These results indicate that EAM has a similar significant protective effect, in vitro and in vivo, against CCl4 induced hepatotoxicity in rat as silymarin.This may be due to its antioxidant and membrane stabilizing properties.