Streblus (PROSEA Medicinal plants)

Plant Resources of South-East Asia Introduction

List of species

Streblus Lour.

Protologue: Fl. cochinch.: 615 (1790).

Family: Moraceae

Chromosome number: x= 13, 14; S. asper: 2n= 26

Streblus asper Lour.

• Thailand: khoi (general)
• Vietnam: ru·ªëi.

Streblus comprises 22 species and occurs in Africa and Madagascar, and from Nepal, India and Sri Lanka to Indo-China, southern China, Thailand, throughout the Malesian region towards the Solomon Islands, Australia, New Zealand and the Pacific Islands, east to Fiji, Samoa and the Cook Islands, and north to Hawaii. Only 7 species occur within Malesia.

S. asper is a well-known medicinal plant, also in South-East Asia. Its bark is traded as a medicine used to treat leprosy, piles, diarrhoea, dysentery and elephantiasis, and it shows anti-cancer and anti-malaria activities. In Ayurvedic medicine it is used for cardiac disorders, epilepsy and oedema. In India, the latex is put on sore heels and chapped hands, and on glandular swellings; it is credited with antiseptic and astringent properties. In Thailand and Indo-China the latex is employed as a sedative. A paste of the leaves is applied to swellings. A poultice of the roots is applied to ulcers, boils and inflamed swellings. The powdered root is prescribed in dysentery. A decoction of the roots is given in syphilis, and that of the bark in fevers, dysentery and diarrhoea; externally it is applied as a wound disinfectant. Seeds are used in nosebleed, haemorrhoids, diarrhoea and as a carminative; externally a paste is applied in leucoderma.

In Malaysia, an extract of the leaves of S. asper is used to make milk coagulate with a texture similar to that of yoghurt. Old leaves have been applied for polishing ivory and cooking utensils. In Thailand, the bark is also used to manufacture paper; elsewhere in Indo-China it is also used to make rope and for rough clothing. Ripe fruits of S. asper can be eaten raw or boiled. Young leaves are fed to cattle and goats in India and Indo-China. In the Philippines it is planted as an ornamental; in Indonesia it has been grown as a cover crop in forest plantations. The wood is hard with a fine grain but can only be used for small objects.

Although mention is made of the trade in bark of S. asper as well as plantings for this purpose, no trade statistics are available. Most likely bark and other parts of Streblus are traded on a local scale only.

Preliminary pharmacological investigations showed stem- and root bark extracts of S. asper to have a definite action on the isolated rabbit myocardium, or a pronounced action on smooth musculature including cardioactivity in general. Subsequent phytochemical investigations of the stem bark revealed the presence of about 0.03% of cardiac glycosides (cardenolides): 10 were isolated from the ether and chloroform extracts and 21 from the water soluble portion. In addition, the main components, i.e. strebloside, asperoside and mansonin, as well as various extracts showed a wide range of defined pharmacological activities.

Strebloside and mansonin displayed significant cytotoxic activity in the KB cell system. The methanol extract of S. asper can be classified as an antibiotic with a cytotoxicity at 200μg/ml. It also shows complete in vitro inhibition of herpes simplex virus at 50μg/ml, complete inhibition of the Sindbis virus at 100μg/ml in the dark, and partial inhibition at 50μg/ml, and partial inhibition of polio virus at 50μg/ml.

The antimalarial activity was evaluated in Balb/c mice infected with Plasmodium berghei (strain NK 65), which were treated intraperitoneally with 100μl of a diluted bark extract every 48 hours from day 7 after infection. The extract significantly suppressed parastaemia. All mice in the control group died within 18 days, but none of the treated mice. 70% of treated mice died 25-32 days after infection, but the remaining 30% cleared the parasites completely from their blood and recovered. This group when rechallenged with P. berghei also resisted the infection.

The in vitro antifilarial effects of asperoside and strebloside isolated from S. asper were studied on females of the bovine filarial parasite Setaria cervi . Both compounds caused death of the worms within 2-3 hours at concentrations of 10μg/ml (1.7 pmoles) and were also found to inhibit motility and glucose uptake of the parasites at lower concentrations (0.1μg/ml; 0.17 pmoles). Parasites preincubated with either asperoside or strebloside also had lowered profiles of glucokinase, malate dehydrogenase and succinate dehydrogenase activities, suggesting that their lethal effects were due to effects on glucose metabolism. Both glycosides were subsequently shown to interfere with the glutathione metabolism of the adult filarial parasites, which disturbed various vital activities, ultimately resulting in death of the parasites.

Macrofilaricidal activity of the crude extract of the stem bark of S. asper , asperoside and strebloside were studied in infected rodents: Litomosoides carinii -infected Sigmodon hispidus , Brugia malayi -infected Mastomys natalensis and Acanthocheilonema viteae -infected M. natalensis . Both asperoside and strebloside showed antifilarial activity, of which asperoside was the more effective. It was found to be active at 50 mg/kg orally against L. carinii (90%), B. malayi (70%) and A. viteae (70%).

A 10% solution of the crude extract of S. asper also exhibited a 100% mortality rate of Boophilus microplus cattle ticks after 48 hours using the dipping method. The larvae left in contact with a dry film of plant extract (1.11 mg/m²) showed a relatively high mortality of 71-85%.

In order to determine the antimicrobial effectiveness of a mouthwash containing S. asper leaf extract on Streptococcus mutans and total salivary bacteria, a single blind clinical study was conducted in 30 humans. At each experimental session, a pretest saliva sample was taken. After giving the pretest samples, the subjects rinsed with S. asper leaf extract or distilled water control for 60 seconds, then the post-test saliva samples were collected at 0, 0.5, 1, 3, 5 and 6 h. The results indicated that S. asper leaf extract significantly reduced S. mutans counts compared to the placebo, although there were no significant differences in total salivary bacterial counts between the groups. It was concluded that mouthwash containing S. asper leaf extract can reduce S. mutans without changing the oral ecology.

The crude extract of the leaves of S. asper was found to coagulate milk. There was no significant change in the milk pH after coagulation by the extract. The milk coagulating activity of the crude extract remained stable upon heating up to 70°C, above which activity was lost. Coagulation at 28°C occurred within 1-2 h, at 70°C within a few minutes. The extract was also stable when prepared in media with a pH ranging from 5.5-9.0. Furthermore, the addition of calcium chloride did not affect coagulating activity of the extract.

• Evergreen, monoecious or dioecious, armed or unarmed, shrubs or small to medium-sized trees up to 30 m tall; bole often irregular and fluted, branchless for up to 15 m, up to 60(-75) cm in diameter, without distinct buttresses; bark surface smooth, becoming finely and irregularly cracked or fissured, grey, inner bark yellowish or whitish, with or without milky latex; crown compact, dense.
• Leaves distichous or sometimes arranged spirally, simple, entire to toothed; stipules free or connate, lateral to completely amplexicaul.
• Inflorescence axillary, bisexual or unisexual, solitary or paired, racemose, spicate or subcapitate, sometimes the female flower solitary. Flowers unisexual; male flowers 3-5-merous; tepals imbricate or valvate in bud; stamens bending outward at anthesis; pistillode present; female flowers 4-merous; tepals free or almost free, variably unequal; ovary superior, free, 1-locular with a single ovule, stigmas 2 or 4.
• Fruit drupaceous or a dehiscent or indehiscent capsule; fruiting tepals enlarged or not, not to slightly fleshy.
• Seedling with hypogeal germination; cotyledons unequal, the larger not emergent, the smaller emergent; hypocotyl not elongated; first few leaves scale-like, lower leaves arranged spirally, subsequent ones distichous.

Seedlings of S. asper may develop into creeping shrubs that only later develop an upright branch that becomes the trunk. The seeds of S. asper are often dispersed by white ants which drag them into their nests, where they often germinate. In Java, S. taxoides flowers and fruits throughout the year, whereas flowering and fruiting of S. asper is confined to June-September.

Streblus is a variable genus divided into 5 sections, and includes the former genera Phyllochlamys , Sloetia and Taxotrophis . It is very closely related to Trophis , from which it mainly differs by the free tepals.

Streblus is mostly found in lowland and hill forest up to 900 m altitude. S. asper is a characteristic element of monsoon forest; it also occurs in areas disturbed by man.

S. asper has been propagated by cuttings to establish a cover crop in forest plantations. Semi-hardwood cuttings treated with indole butyric acid at 10 000 ppm showed good rooting ability when propagated in a mist box using sand and rice husk charcoal in a 1:1 ratio as a rooting medium.

S. asper responds well to coppicing.

Leaves of Streblus are plucked or branches are simply cut. Likewise, strips of bark are obtained and sap is collected by making incisions in the bark. Roots are dug up and fruits are collected when mature.

Plant parts of Streblus are used fresh or dried for future use.

S. asper and S. taxoides are both widespread and common in monsoon areas throughout South-East Asia, and therefore certainly not endangered. There are no known breeding programmes of Streblus .

Extracts and isolated cardenolides from Streblus show interesting activities. The in vivo antifilarial activity of cardenolides opens up possibilities for generating new leads. The extract of S. asper leaf shows some potential as a natural oral hygiene product against dental caries in human. More information is however needed in the field of toxicology in order to fully evaluate this potential.

• Das, M.K. & Beuria, M.K., 1991. Anti-malarial property of an extract of the plant Streblus asper in murine malaria. Transactions of the Royal Society of Tropical Medicine and Hygiene 85(1): 40-41.
• Datta, S.K. & Datta, P.C., 1984. Pharmacognosy of Streblus bark drug. International Journal of Crude Drug Research 22(2): 61-71.
• Nguyen Ba, 1998. Streblus Lour. In: Sosef, M.S.M., Hong, L.T. & Prawirohatmodjo, S. (Editors): Plant Resources of South-East Asia No 5(3). Timber trees: Lesser-known timbers. Backhuys Publishers, Leiden, the Netherlands. pp. 537-539.
• Singh, S.N., Raina, D., Chatterjee, R.K. & Srivastava, A.K., 1998. Antifilarial glycosides of Streblus asper: effect on metabolism of adult Setaria cervi females. Helminthologia 35(4): 173-177.
• Taylor, R.S.L., Hudson, J.B., Manandhar, N.P. & Towers, G.H.N., 1996. Antiviral activities of medicinal plants of southern Nepal. Journal of Ethnopharmacology 53(2): 97-104.
• Taweechaisupapong, S., Wongkham, S., Chareonsuk, S., Suparee, S., Srilalai, P. & Chaiyarak, S., 2000. Selective activity of Streblus asper on Mutans streptococci. Journal of Ethnopharmacology 70(1): 73-79.

Titi Kalima