Study On The Bioactivities Of Scutellaria Barbata And The Relevant Constituents

Scutellaria barbata D.Don (SB) , a herb belonging to the Lamiaceae family, is widely distributed in China. This herb is known in traditional Chinese Medicine as Ban-Zhi- Lian and has been used as an anti-inflammatory and antitumor agent and as a diuretic. However, active constituents and the mechanism underlying the activity were unclear. In this study, we used the bioassayed-guided fractionation of Scutellaria barbata to find active fractions for antitumor, antioxidant and antimicrobial activity and then try to elucidate active constituents. Our research will be beneficial to develop new drug from SB. 1 Antitumor activityEthanolic extract of SB was dissolved in water and fractionated sequentially with n-hexane, chloroform, ethylacetate and n-butanol. The fractions were concentrated under reduced pressure to yieled a n-hexane fraction (HE-SB), chloroform fraction (CE-SB), ethylacetate fraction (EE-SB), n-butanol fraction (BE-SB) and remainder of water fraction (WE-SB). Antitumor activity of each fraction was evaluated by the MTT assay using human cancer cell lines. CE-SB showed the greatest antitumor activity in vitro. We further studied the antitumor mechanism of CE-SB and evaluated its antitumor activity in vivo.Bel-7402 cells apoptosis induced by CE-SB was examined by using several methods. The results showed that morphology of Bel-7402 cells treated with CE-SB changed. Compared to untrated cells, numerous CE-SB-trated cells became flat and shrunken. Disorganization of the nucleus with chromatin changes induced by CE-SBin Bel-7402 cells were characterized using Hoechst 33258 staining, cells cultured with CE-SB had numerous cells with condensation of chromatin and fragmentation of nuclei. Bel-7402 cells treated with CE-SB also had the specific biochemical change , the agarose gel electrophoresis of extracted genomic DNA from CE-SB-trated cells generated " ladder" patter of discontinuous DNA fragments. In addition, the analysis by flow cytometry showed the sub-Gi peaks, the proportion of apoptotic cells in cell population increased with the increase of CE-SB dose. Cell cycle modulation of Bel-7402 cells treated with CE-SB was also analyzed. CE-SB dose-dependently decreased S phase content.Cytotoxicity of SB on normal cells was also evaluated, SB exerted small cytotoxin effect on normal liver cell line L-02 when compared with a chemotherapeutic anticancer drug, mitomycin C (MMC).In vivo experiments, effects of CE-SB on the growth of Si go solid tumor and on the life span of ascites tumor bearing mice were studied. At 60 mg/kg.d, CE-SB treatment significantly inhibited the solid tumor proliferation and increased life span of ascites tumor bearing mice (P<0.01) .CE-SB was separated to yield five fractions (A~E) by chromatography on silica gel, each fraction was tested for cytotoxicity in Bel-7402 cells, fraction A and B showed stronger cytotoxicity. Two active fractions was further chromatographed on silica gel , Sephadex LH-20 and preparative HPLC to yield seven monomers, four compounds showed significant cytotoxic effect to Bel-7402 cell lines. Six monomers were identified as sitosterol, phytol, wogonin, luteolin, Scuterivulactone C\ and 7,4'-dihydroxy-5,8-dimethoxy flavone. 2 Antioxidant activityThe free radical-scavenging effects of the fractions were evaluated in the flavins system. The results showed that four fractions had scavenging activities of superoxide radical with the except of HE-SB. EE-SB and BE-SB showed stronger scavenging effects than other fractions. The free radical-scavenging effect was closely related to the content of flavonoids. Total flavone fraction (TF-SB) was extracted from SB and refined. With the increase of content of total flavones, free radical-scavenging effect of TF-SB became more evident. The antioxidant activity of TF-SB was furtherevaluated in terms of the inhibition effects on lipid peroxidation of erythrocyte membrane in three radicals generation systems. The results showed that TF-SB dose-dependently inhibited the increases of lipid peroxidation content when the membrane exposed to xanthine-xanthine oxidase system, H2O2 or UV light. The results suggest that TF-SB may protect erythrocyte membrane from the lipid peroxidation damage induced by radicals.3 Antimicrobial activityThe extracts of SB were screened for antibacterial activities by using disc diffusion method against three reference strains. The results showed that essential oil exert the strongest antibacterial activity. Antimicrobial activity of essential oil was further investigated by using disc diffusion and broth microdilution methods against 17 microorganisms, including 16 MRS A strains. The results showed that the oil displayed a broad spectrum and exert a more stronger antibacterial effect against gram-positive bacteria than gram-negative bacteria and yeasts. Among the microorganisms tested, only S. paratyphi-h was resistant to the oil. MRS A was also sensitive to the oil. In addition, in the most case the MIC was equivalent to the MBC, indicating a bactericidal activity of the oil.4 Essential oil analysisEssential oil was analyzed by GC-MS and GC-FID. The analyses were carried out by using three different polar fused-silica capillary columns. Constituents were identified by comparison of their mass spectra with those in the NIST 98 GC-MS library and those in the literature, as well as by comparison of their retention indices with literature data. Retention indices of the components were determined relative to the retention times of a series n-alkanes with linear interpolation. Quantitative results were obtained by GC-FID. Forty-one compounds, representing 85.6% of the oil, were identified. The essential oil consisted mainly of oxygenated monoterpenes and sesqui-terpenes. Menthol (7.7%), linalool (6.7%), a -terpieol (1.5%) and thymol (1.4%) were the main oxygenated monoterpenes, whereas (z)- a -trans-bergamotol (5.1%) and globulol (4.2% ) were the main oxygenated sesquiterpenes. The levels of several sesquiterpene hydrocarbons, such as 3 -bourbonene(2.8%) and 3 -himachalene (1.5%), were also significant. Among other compounds, considerable amounts ofhexahydrofarnesylacetone (11.0%), 3,7,11,15-tetramethyl-2-hexadecen-l-ol (7.8%), l-octen-3-ol (7.1%) and methyleugenol (5.6%) were detected.The oil complexity demanded independent analyses on dissimilar stationary phase columns. By using apolar column, low-polarity column and polar column, separation of some unresolved components in a column is achieved in other columns and many more components could be found. The MS search routine used linear retention indices as a post-search filter and the identification of the unknowns was made more reliable. 5 Interaction of flavonoids from SB with proteinsFlavonoids, comprising an important group of polyphenolics in SB, possed antitumor and antioxidative effects. A number of biochemical and molecular biological investigations have revealed that proteins are frequently the 'targets' for therapeutically active flavonoids. However, very little is known about the mode of interactions of these compounds with their respective target proteins at the molecular level. The research of interaction of flavonoids with proteins will be helpful to reveal the mechanism that flavonoids exert pharmacological effects in vivo. In our experiment, interaction of scutellarin and scutellarein with human serum albumin (HSA) and calthymus histone Hi were investigated by absorption and fluorescence measurement. It is proved that the mechanism of fluorescence quenching of two kinds of protein by two compounds belongs to static quenching. The binding constant and the number of binding sites of two compounds with HSA were measured at different pH by fluorescence quenching method. The binding distance and transfer efficiency between two compounds with HSA were obtained according to FGrster theory of non-radiation energy transfer. The binding constant and the number of binding sites of two compounds with histone Hi were also obtained at pH 7.4. The binding constants of two compounds with two kinds of protein were K>104. The results suggest that two compounds could bind strongly to two kinds of proteins.