A number of studies have been conducted to elucidate the chemical constituents and pharmacological activities of the aerial parts of Epimedium herb. Several methods such as column chromatography, liquid chromatography, pulse polarography, coulometric titration, and fluorometry have been used to study the flavonoids from Epimedium species (8). The main constituents in Epimedium plants are the prenylflavone glycosides. Among the important active constituents isolated from the aerial parts of these herbs are the flavonol glycosides (such as icariin and baohuoside I, Fig. 1) and flavonoids.
The glycoside icariin was first isolated from E. macranthum (9). The isolation of icariin from E. brevicornum (10-12), E. koreanum (11,12), E. acuminatum (13,14), E.fargesii (15), E. wushanense (16), E. hunanense (2), and E. sagittatum (3) was reported. The presence of icariin in Epimedium herb can be detected by thin-layer chromatography. However, content of other fla-vones might vary in different species (17).
Other compounds isolated from Epimedium herb include phenooxy-chromones, flavanoids, chrysoeriol, quercetin, apigenin, apigenin 7,4'-di-methyl ether, kempferol, tricin, luteolin, thalictoside, and brevicornin (8). Luteolin, a flavone, was found to have estrogenic activity with a relative potency of 58% compared to genistein (18). Apigenin and quercetin are also estrogenic. Other flavanoids and flavanol glycosides described in Epimedium include epimedokoreanoside I, icariside I, icaritin, epimedoside A, epimedins
A, B, and C, p-anhydroicaritin, tricin, korepimedoside A and B, sagittato-sides A, B, and C, sagittatins A and B, diphylloside A and B, baohuosides I-VII, and baohuosu (16,19-21). Some of these flavonol glycosides, e.g., baohuoside I (2), were reported to have immunomodulatory activity. The herb also contains ceryl alcohol linolenic acid, oleic acid, palmitic acid, sterols, benzene, tannins, fats, saponins, vitamin E, zinc, and some essential oils.
The quantitative changes of flavonoids in E. koreanum in different collecting periods were determined by HPLC and UV spectrophotometry. The result shows that the highest content of flavonoids is found in the flowering period (May) (22).
The seasonal fluctuation of flavonol glycosides in the leaves of E. gran-diflorum var. thunbergianum, E. cremeum, and E. sempervirens (Berberida-ceae) was also investigated (23). The total content of glycosides was greatest at flowering time, and as the leaves mature it became less fluctuating with a little decrease. The ideal period for the harvest of Epimedium leaves was 2 or 3 months after flowering.
By means of RP-HPLC, nine major flavonoids in different parts of five Epimedium plants listed in the Chinese Pharmacopoeia were analyzed and the total contents of nine flavonoids in the four species were found to be highest in the rhizome and roots, followed by leaves and stems (24). The composition of the main constituents and relative contents in the five species were similar in leaves and stems, but different from the rhizome and roots. These differences may affect their pharmaceutical properties.
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