Scutellaria (PROSEA)
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Introduction |
Scutellaria L.
- Protologue: Sp. pl. 2: 598 (1753); Gen. pl. ed. 5: 260 (1754).
- Family: Labiatae
- Chromosome number: x= unknown; S. discolor: 2n= 24, 26
Major species
- Scutellaria javanica Jungh.
Vernacular names
- Skullcap (En).
- Scutellaire (Fr)
- Vietnam: thuẫn.
Origin and geographic distribution
Scutellaria , with 360 species, is almost cosmopolitan. Originally it was absent only from the Amazon Basin, lowland tropical Africa, South Africa, deserts of Central Asia, most of the Pacific Islands and New Zealand, and north of the Arctic circle. The centres of diversity are found in the mountain regions of Central Asia and China, which are also considered to be the regions where Scutellaria originated; only 3 species are native in Malesia.
Uses
A multitude of Scutellaria species are used internally in the form of infusions and decoctions to alleviate stomach complaints and as a diuretic and antipyretic. Various species are used externally as a decoction or poultice to treat fungal skin infections as well as boils or scabies.
Outside the Malesian region S. baicalensis Georgi is an important medicinal plant, cultivated extensively for its roots in China, Korea and Japan. The roots are used in traditional Vietnamese medicine as a general tonic to balance the body, to treat bacterial infections of the respiratory and gastro-intestinal tracts, and this species has been successfully grown in northern Vietnam.
Properties
Scutellaria species, like many other Labiatae, contain an essential oil. The constituents of this oil are referred to as belonging to the monoterpenoids, sesquiterpenoids, phenylpropane derivatives or iridoid glycosides without further specification. Scutellaria species are also reported to contain diterpenes (in aerial parts e.g. of the neoclerodane type), large amounts of triterpenes, phytosterols and phenolic constituents (e.g. caffeic acid, flavonoids).
The presence and biological activities of flavonoids in Scutellaria have been particularly well studied. The aerial parts of S. discolor were found to contain chrysin, chrysin-7-O-glucuronide, apigenin, luteolin, wogonin, 5,7-dihydroxy-8,2'-dimethoxyflavone, 5,7,8-trihydroxyflavone-8-O-βD-glucuronide, 5,7,2',6'-tetrahydroxy-8-methoxyflavone-2'-O-βD-(2-O-caffeoyl)-glucoside, 5,7-dihydroxy-8,2'6'-trimethoxyflavone and 5,7,4'-trihydroxy-8-methoxyflavone. The latter two compounds are also present in the roots of S. discolor, together with pinocembrin, wogonin, wogonin-7-O-glucuronide, norwogonin, norwogonin-7-O-glucuronide, 7-hydroxy-5,8-dimethoxyflavone, 7-hydroxy-5,8,2'-trimethoxyflavone, 5,7-dihydroxy-8,2'-dimethoxyflavone, 5,7,2'-trihydroxy-8-methoxyflavone, 5,7,2'-trihydroxy-8,6'-dimethoxyflavone, 2(S)-5,7-dihydroxy-8,2'-dimethoxyflavanone, 2(S)-7-hydroxy-5,8,2'-trimethoxyflavanone, 5,2'-dihydroxy-7,8,6'-trimethoxyflavanone, 5,2'-dihydroxy-6,8,6'-trimethoxyflavanone and 2'4'-dihydroxy-2,3',6'-trimethoxy-chalcone.
The flavonoids scutellarin, found in S. baicalensis and S. javanica, and baicalein (= 5,6,7-trihydroxyflavone) inhibit the activity of partially purified rat brain protein kinase C. Various flavonoids present in S. baicalensis also show inhibitory effects against a considerable number of viruses: e.g. baicalin (= 5,6-dihydroxyflavone-7-O-βD-glucuronide) against the human T cell leukaemia virus type 1 and the human immunodeficiency virus (HIV-1), 5,7,2'-trihydroxy- and 5,7,2',3'-tetrahydroxyflavone against the Epstein-Barr virus, and 5,7,4'-trihydroxy-8-methoxyflavone against A-H3N2 subtype and B-subtype of the influenza virus. 2(S)-5,7,2',6'-Tetrahydroxyflavanone showed a remarkable antibacterial activity against e.g. Escherichia coli, Bacillus subtilis and Staphylococcus aureus.
Furthermore, baicalein shows antiproliferative activity in cultured rabbit vascular muscle cells, and lipoxygenase-inhibitory activity. It may be useful as a template for the development of drugs to prevent the pathological changes of atherosclerosis and restenosis. The pharmacological action of baicalein may be partially attributed to its free radical scavenging activity. Other pharmacological activities of the flavonoids include: anti-inflammatory activity of baicalein in the rat adjuvant arthritis model, inhibition of LPS-induced IL-1 production by baicalin, baicalein and wogonin, and inhibition by baicalein of leukotriene C-4 biosynthesis by rat resident peritoneal macrophages. Another effect of the flavanoids is the inhibition of the release of slow reacting substances of anaphylaxis (SRS-A) from sensitized guinea- pig lungs after antigen challenge.
Description
- Perennial or rarely annual herbs or small shrubs; stems prostrate to erect, often 4-angled.
- Leaves opposite, simple, margin entire to pinnatifid, petiolate to subsessile, exstipulate.
- Flowers solitary, opposite or in small false whorls, in the axil of leaves or bracts, in terminal or axillary, 1-sided or all-sided racemes or spikes; calyx with a short tube, 2-lipped, the lips entire, upper lip deciduous, with a large shield- or pouch-like appendage or rarely both lips expanded to form a bladder-like structure; corolla 2-lipped, with a usually long tube which is bent upwards at base or bent distally or both, upper lip hooded, entire or notched, lower lip 3-lobed; stamens 4, inserted on the corolla tube, didynamous, anterior pair longest, anthers of the anterior pair 1-celled, those of the posterior pair 2-celled; disk tubular; ovary superior, on a short gynophore, 2-carpellate but 4-locular with a single ovule in each cell, style with a 2-fid stigma.
- Fruit consisting of 4 dry, ovoid to globose nutlets.
- Seeds without endosperm.
- Seedling with epigeal germination; cotyledons free, leafy; hypocotyl elongated; all leaves opposite.
Growth and development
Malesian Scutellaria species have been found flowering throughout the year. In Taiwan S. indica has been observed flowering and fruiting from September to May. Pollination is by insects, mainly bees. The nutlets are simply shed when the wind tosses the inflorescence to and fro, without a distinct dispersal mechanism.
Other botanical information
Scutellaria takes a rather isolated position within the Labiatae, being the only genus of the subfamily Scutellarioideae. Its subdivision into subgenera and sections has been subject to much debate, but the most recent view recognizes 2 subgenera, Scutellaria and Apeltanthus, and 7 sections. All Malesian species belong to the subgenus Scutellaria and section Scutellaria which harbours about 240 species.
Ecology
Scutellaria species generally occur on grassy plains, along forest tracks and streams, in forest edges, but also in open primary forest and savanna forest, in Malesia from the lowland up to 2400(-3300) m altitude.
In vitro production of active compounds
Research on in vitro production of flavonoids in Scuttelaria is restricted to S. baicalensis. Cell suspension culture as well as stem callus culture yielded a range of flavonoids, with the major constituents being baicalin and wogonin-7-0-glucuronic acid.
Harvesting
Scuttelaria plants are uprooted to collect the roots.
Handling after harvest
The roots are washed and dried before being stored.
Prospects
The flavonoids isolated from various Scutellaria species show a broad range of interesting pharmacological effects that merit further research, e.g. the inhibition of several pathological viruses, activities on the immune system (including inhibition of immune factors) and free radical scavenging activity.
Literature
- Cantino, P.D. & Sanders, R.W., 1986. Subfamilial classification of Labiatae. Systematic Botany 11: 163-185.
- Hamada, H., Hiramatsu, M., Edamatsu, R. & Mori, A., 1993. Free radical scavenging action of baicalein. Archives of Biochemistry and Biophysics 306(1): 261-266.
- Huang, H.C., Wang, H.R. & Hsieh, L.M., 1994. Antiproliferative effect of baicalein, a flavonoid from a Chinese herb, on vascular smooth muscle cell. European Journal of Pharmacology 251(1): 91-93.
- Keng, H., 1978. Labiatae. In: van Steenis, C.G.G.J. (General editor): Flora Malesiana. Series 1, Vol. 8. Sijthoff & Noordhoff International Publishers, Alphen aan den Rijn, the Netherlands. pp. 323-326.
- Konoshima, T. et al., 1992. Studies on inhibitors of skin tumor promotion XI. Inhibitory effects of flavonoids from Scutellaria baicalensis on Epstein-Barr virus activation and their anti-tumor-promoting activities. Chemical and Pharmaceutical Bulletin 40(2): 531-533.
- Nguyen Van Duong, 1993. Medicinal plants of Vietnam, Cambodia and Laos. Mekong Printing, Santa Ana, California, United States. pp. 215-216.
- Paton, A., 1990. A global taxonomic investigation of Scutellaria (Labiatae). Kew Bulletin 45: 399-450.
- Perry, L.M., 1980. Medicinal plants of East and Southeast Asia. Attributed properties and uses. The MIT Press, Cambridge, Massachusetts, United States & London, United Kingdom. p. 194.
- Tomimori, T., Miyaichi, Y., Imoto, Y., Kiu, H. & Namba, T., 1988. Studies on the Nepalese crude drugs XI. On the flavonoid constituents of the aerial parts of Scutellaria discolor Colebr. Chemical and Pharmaceutical Bulletin (Tokyo) 36(9): 3654-3658.
- Xu, G., Zhang, L.P., Shen, H.F. & Hu, C.Q., 1993. Inhibition of protein kinase C by scutellarein and its analogues. Acta Academiae Medicinae Shanghai 20(3): 187-191.
Selection of species
Authors
- H.P. Hernandez
