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Tibetan medicinal plants have been used for more than 2 000 years. In order to find their differences in antioxidant activity, total phenolics and total flavonoids between "hot-nature" and "cold-nature" herbs, we investigated the antioxidant activities of 40 Tibetan herbs from Qinghai plateau, with 20 herbs in cold-nature and 20 herbs in hot-nature. Antioxidant capacities were evaluated by the following methods: scavenging ABTS•(+) (2, 2'azinobis-(3-ethylbenz-thiazoline-6-sulfonic acid), scavenging O2•(-), and Ferric-reducing antioxidant power (FRAP). The effects on inhibition of mitochondrion lipid peroxidation were determined by measuring the formation of TBARS (Thiobarbituric acid reactive substrates). Total phenolics and flavonoids were estimated by Folin-Ciocalteu and NaNO2-Al(NO3)3-NaOH colorimetric methods. Interestingly, the cold-nature herbs displayed higher antioxidant activities than the hot-nature ones, corresponding to nearly three-fold higher total phenolic contents in the cold-nature herbs. Moreover, the antioxidant activities correlated linearly with the levels of total phenolics for both cold-nature and hot-nature herbs, but only with the levels of total flavonoids for the hot-nature herbs. The results suggested that the phenolic compounds, but not the flavonoids, play the major role in antioxidant capacities of the cold-nature herbs. These findings could shed new lights on the study the theory of Tibetan medicine.

<i>Potentilla parvifolia </i>Fisch. (Rosaceae) is a traditional medicinal plant in P. R. China. In this study, seven flavonoids, ayanin (<b>1</b>), tricin (<b>2</b>), quercetin (<b>3</b>), tiliroside (<b>4</b>), miquelianin (<b>5</b>), isoquercitrin (<b>6</b>), and astragalin (<b>7</b>), were separated and purified from ethyl acetate extractive fractions from ethanol extracts of <i>P. parvifolia</i> using a combination of sevaral chromatographic methods. The human neuroblastoma SH-SY5Y cells were differentiated with all trans-retinoic acid and treated with okadaic acid to induce tau protein phosphorylation and synaptic atrophy, which could establish an Alzheimer's disease cell model. The neuroprotective effects of these flavonoids in cellular were evaluated <i>in vitro</i> by this cell model. Results from the Western blot and morphology analysis suggested that compounds <b>3</b> and <b>4</b> had the better neuroprotective effects.