Alstonia (PROSEA Medicinal plants)

Plant Resources of South-East Asia Introduction

List of species

Alstonia R.Br.

Protologue: On Asclepiad.: 64 (1810).

Family: Apocynaceae

Chromosome number: x= 11, 20, 21; A. macrophylla: 2n= 22, A. scholaris: 2n= 22, 44

• Alstonia macrophylla Wallich ex G. Don,
• A. scholaris (L.) R.Br.

• Pulai (trade name, (very) lightweight hardwood species), white cheesewood, white pine, milkwood (En); hard alstonia (trade name, medium-heavy hardwood), hard milkwood (En).

Alstonia consists of 43 species and has a pantropical distribution. It ranges from Central America, tropical Africa to the Marquesas in the far eastern Pacific, and from the Himalayas and China in the north to New South Wales in the south. One species is native in Central America, 2 in tropical Africa, 6 in Australia, 16 in the Pacific region, 18 in the Malesian region and the rest occur in continental Asia. A. scholaris is the most widespread species and occurs from India and Sri Lanka through Indo-China and southern China towards Malesia, south to Queensland and east to the Solomon Islands. Several species have been planted outside their natural area of distribution.

The bark, the latex from the bark or other plant parts of Alstonia are widely used in traditional medicine throughout South-East Asia. The bitter taste may explain its popularity as a tonic and febrifuge, and it is further credited with astringent and anthelmintic properties. It is employed in liver and intestinal troubles, heart diseases, asthma, various skin diseases, fever and as a vulnerary, as well as an emmenagogue.

The latex or an extract from the bark of A. costata (J.G. Forster) R.Br. (syn. A. vitiensis Seem.) is used as an eye lotion in Fiji and the Solomon Islands. In southern Vietnam, an infusion of the roots or leaves of A. annamensis (Monach.) Sidiyasa (syn. A. angustifolia var. annamensis Monach.) is employed to treat respiratory afflictions. The fruits of A. venenata R.Br. from India, posses tonic and anthelmintic properties, and are used as a remedy for impure blood, syphilis, insanity and epilepsy. Alstonia includes economically important timbers. The timber of pulai species (A. angustiloba, A. iwahigensis, A. scholaris and A. spatulata) is used for pencil manufacture, matches, tea chests, crates, plywood, pulp, carpentry and carving. The timber of hard alstonia species (A. angustifolia, A. macrophylla and A. spectabilis) is used for construction purposes, furniture and flooring. The latex of A. scholaris is used for chewing gum. Outside Malesia other species are used for this purpose too. Some species of Alstonia are planted as ornamental trees because of their pagoda-like crown.

The bark of Alstonia is stocked by local drugstores, while the latex is tapped and used on a local scale. Mention is made of A. scholaris bark being traded as "dita bark".

Thirty-one monoterpenoid indole-alkaloids have been isolated from the leaves and stem bark of A. angustifolia from Malaysia. Several of them are known compounds; these include for instance yohimbine, O-acetyl-yohimbine, tubotaiwine and (derivatives of) echitamine, akuammicine, alstonisine, alstonerine and carpamine. Examples of the new alkaloids include N-oxide-, methoxy- and dehydro-derivatives of yohimbine, villalstonine, macrocarpamine and akuammicine.

In addition, a crude root alkaloidal extract displayed an IC₅₀ of 0.35 μg/ml against Plasmodium falciparum K1. Furthermore, yohimbine is a well-known α₂-adrenergic receptor antagonist.

From A. angustiloba, a series of vallesamine-type alkaloids were isolated, which included: vallesamine, O-acetylvallesamineangustilobine A, 15-hydroxyangustilobine A, angustilobine B, 4,6-secoangustilobinal, 6,7-seco-19,20-epoxyangustilobine B, 6,7-seco-6-cyanostemmadenine, 6,7- secoangustilobine B, and nor-6,7-secoangustilobine A.

Series of monomeric and bisindole and oxindole alkaloids have been isolated from several parts of A. macrophylla. These include 2 new bisindole alkaloids, alstomacrophylline and alstomacroline, which have been isolated from the root bark, along with 6 known alkaloids: alstonerine, alstophylline, macrocarpamine, alstoumerine, 20-epi-antirhine and villastonine-N-oxide. New oxindole alkaloids such as N-b-demethylalstophyllal oxindola nd alstonal, together with three known alkaloids, N-b-demethylalstophylline oxindole, alstonisine and talcarpine, have been isolated from the bark. In addition, new alkaloids from the leaves include (-)-strictaminolamine, 19-hydroxyvincamajine, alstonamide, demethoxyalstonamide alstoumerine and macroxine. The known indole alkaloids alstonisine, alstonerine, alstophylline, macralstonine, anhydromacralstonine, (-)1,2-dihydro-N-methylstrictamine, talcarpine, vincamajine, vincorine, cabucraline and quebrachidine, were also isolated and identified from the bark and leaves. Furthermore, rare alkaloids such as N(4)-oxides of cathafoline and 11-methoxyakuammicine, vincamajine 17-O-veratrate and vincamajine N(1)-tri-O-methylgallate were isolated from the leaves of A. macrophylla.

Crude extracts of the bark and leaves of A. macrophylla possessed hypotensive action in animals. In addition, in a test with the multidrug-resistant K1 strain of Plasmodium falciparum cultured in human erythrocytes, pronounced antiplasmodial activity was exhibited by the methanol extract of the root bark of A. macrophylla with an IC₅₀ value of 5.7 μg/ml. Subsequently, 13 indole alkaloids were isolated from the active extract. These alkaloids and a semisynthetic bisindole O-acetylmacralstonine were furthermore tested against the K1 strain of P. falciparum. Pronounced antiplasmodial activity was observed mainly among the bisindole alkaloids, particularly villalstonine and macrocarpamine with IC₅₀ values of 0.27 and 0.36 μM, respectively. The potent alkaloids were also tested against T9-96, a chloroquine-sensitive strain of P. falciparum. It has been observed that the active alkaloids, in contrast to chloroquine, have significantly higher affinity to the K1 strain than to the T9-96 strain.

The same alkaloids have also been assessed for cytotoxic activity against two human lung cancer cell lines, MOR-P (adenocarcinoma) and COR-L23 (large cell carcinoma), using the SRB assay. Pronounced cytotoxic activity was exhibited by the bisindoles on both cell lines. This suggests that, in comparison with the corresponding monomeric indoles, at least part of both the ring systems present in the bisindoles is essential for cytotoxic activity. The potent alkaloids were additionally tested against a human normal cell line (breast fibroblasts) and other human cancer cell lines including StMI1 1a (melanoma), Caki-2 (renal cell carcinoma), MCF7 (breast adenocarcinoma), and LS174T (colon adenocarcinoma). The bisindoles O-acetylmacralstonine, villalstonine and macrocarpamine were found to possess pronounced activity against cancer cell lines with IC₅₀ values in the range of 2-10 μM, with no discernible cell-type selectivity. However, O-acetylmacralstonine displayed discernibly less toxicity against the normal breast fibroblasts.

A whole range of monoterpenoid, monomeric and bisindole and oxindole alkaloids have been isolated from several parts of A. scholaris, e.g. roots, root bark, stems and leaves. The derivatives belong to several structural types, derived from akummicine, akuammidine, echitamine, nareline, picralinaline, picrinine, strictamine, tetrahydroalstonine, angustilobine, tubotaiwine and lagunamine (= 19-hydroxytubotaiwine).

Several of these compounds display pharmacological activity; e.g. strictamine was found to be a mono-amino oxidase inhibitor in vitro. Echitaminechloride has been examined for its anticancer effects on methylcholanthrene induced fibrosarcoma. Echitaminechloride dissolved in saline (10 mg/kg body weight) and injected subcutaneously for 20 days in fibrosarcoma rats has exhibited significant regression in tumour growth. The altered activities of plasma and liver transaminases andγ-glutamyl transpeptidase and lipid peroxidation in fibrosarcoma have been corrected to near normal after this treatment. The decreased liver glutathione content and the lowered activities of glutathione peroxidase, superoxide dismutase and catalase have also been reversed to near normal after echitaminechloride treatment. Furthermore, the cytotoxic effect of echitaminechloride is enhanced by adding vitamin A. In addition, malignant tumours are known to exhibit high rates of glycolytic activity leading to high production of lactic acid. Hence, neoplastic cells have elevated activity of enzymes responsible for glycolysis. Therefore, the effect of echitamine chloride on energy metabolism of S-180 cells was investigated to gain a better understanding of its mode of action, including its effect on the mitochondrial and cellular respiration of S-180 cells, and the effects on glucose utilization, pyruvate utilization and lactate formation (studied in whole S-180 cells and S-180 cell-free homogenate). The levels of glycolytic enzymes such as hexokinase and lactate dehydrogenase were estimated, with particular emphasis placed on hexokinase which occurs both in cytosolic and particulate forms in neoplastic cells. In conclusion, echitamine chloride was found to affect both cellular and mitochondrial respiration, leading to reduction of the cellular energy pool and thereby resulting in the loss of viability of S-180 cells.

The hepatoprotective effect of A. scholaris on liver injuries induced by carbon tetrachloride (CCl₄), β-D-galactosamine, acetaminophen (paracetamol) and ethanol was investigated by means of serum-biochemical and histopathological examinations. Treatment with A. scholaris following induction reduced, dose-dependently, the elevation of serum transaminases levels and histopathological changes such as cell necrosis, inflammatory cell infiltration, which were e.g. caused by the single administration of 32 μl/kg CCl₄ or 600 mg/kg acetaminophen in mice. A. scholaris significantly lowered 288 mg/kg β-D-galactosamine induced serum transaminases elevation in rats. A tendency was also shown to inhibit cell necrosis and inflammatory cell infiltration caused by β-D-galactosamine upon histopathological examination of the animals.

Antifertility effects of an ethanolic leaf extract of A. scholaris were observed in male albino rats after oral administration (100 mg/kg/day per animal) for 21 days. The extract did not interfere with spermatogenesis but females mated by males treated with the extract showed significant luteolytic and anti-implantational effect. In addition, an ether extract from A. scholaris bark injected in immature female mice at a dose equivalent to 2 g of crude plant material for 5 days showed significant increase of mammary gland measured on whole mount preparation and simultaneous increase of utero-ovarian structure, suggesting that the active principles may be natural oestrogenic substances.

The effectiveness of Alstonia in the treatment of malaria is controversial. The antiplasmodial effect of echinatine, one of the major alkaloids, is very limited. However, despite the absence of antimalarial activity a dose-dependent improvement of the condition combined with delayed mortality was noticed amongst mice infected with Plasmodium berghei receiving a methanol extract of A. scholaris bark.

Finally, a crude extract of the bark of A. spatulata was found to contain the triterpene lupeol, as well as its benzoyl- and acetyl-derivatives. The latter 2 showed remarkable hypoglycaemic effects upon oral administration to glucose fed rabbits.

• Shrubs or small to large, evergreen or deciduous, laticiferous trees up to 60 m tall; bole straight, generally coarsely fluted at the base and up to 200 cm in diameter; bark surface generally tessellated with small scales or shallowly fissured, appearing smooth at a distance, variable in colour, generally pale or purplish-black, outer bark granular, inner bark cream, soft, frequently conspicuously exuding sticky white latex; branches verticillate, mostly 4-5 together, distant.
• Leaves in verticils of 3-8, or sometimes opposite, simple, entire, with very variable shape (even in the same tree), from lanceolate to obovate and obtuse to acute or acuminate, glabrous or sometimes hairy, generally fleshy but papery when dry; venation pinnate, with many parallel secondary veins often linked near the margin by a hardly looped intramarginal vein; petiole generally short, with or without intrapetiolar stipules.
• Inflorescence terminal, cymose, compound, frequently in whorls or umbellate, few- to many-flowered, pedunculate.
• Flowers actinomorphic, bisexual, protandrous, generally small and fragrant; calyx 5-lobed, united at base into a short tube; corolla white, yellow or red, with 5 rotate, contorted, imbricate and spreading lobes, tube long, cylindrical, widening around the anthers, thickened at the throat, rather densely pubescent inside just below the stamens and on the lobes; stamens included, inserted on the corolla tube, filaments short but distinct, anthers basifixed, introrse, triangular to narrowly triangular, apices touching each other above the stigma in bud; disk annular, entire or lobed, free or adnate to the ovary, often indistinct; ovary superior, with 2 carpels, apocarpous or syncarpous, with 2 placentas per locule, ovules numerous, in 2-many rows, style 1, filiform to very short, glabrous, pistil head with minute, narrow or robust wide cleft stigmoid apex.
• Fruit composed of 2 follicles, free or connate at the base (sometimes united into a single capsule), woody, long and slender, dehiscent along an adaxial suture, inconspicuously striate outside, containing many seeds.
• Seed with endosperm, thin, flattened, minutely foveolate, glabrous or (often dorsally) pubescent, ciliate at both ends, sometimes winged.
• Seedling with epigeal germination; hypocotyl erect; cotyledons leaf-like, thin, oblong or ovate-oblong with an obtuse top and rounded base; leaves decussate, exstipulate.

Seedlings are vigorous and hardy, and young trees demand full light in order to grow vigorously. Under favourable conditions they are undoubtedly fast growers, although no data are available on growth rates. Young trees of most species have a pagoda-like crown with a monopodial appearance (according to Prévost's architectural tree model). The growth of branches is intermittent. However, crowns of A. angustifolia and A. macrophylla, belonging to section Monuraspermum Monach., are of normal sympodial structure, even when young (Koriba's architectural tree model).

The trees are often deciduous at irregular intervals. They do not flower at every leaf-change, but only after marked periods of dry weather. The large branches of big trees provide favourable nesting sites for wild bees.

Pollination is by insects; when flowering, trees are often surrounded by butterflies and bees. The fruits open on the tree and the seeds, which have a tuft of silky hairs at each end, are dispersed by wind.

The genus Alstonia is divided into 5 sections, mainly on the basis of seed morphological characteristics. The sections Alstonia and Monuraspermum occur in Malesia. They mainly differ from each other by the number of secondary veins, direction of the contortion of the corolla lobes, shape of the seed and architecture. Alstonia trees often resemble jelutong (Dyera costulata (Miq.) Hook.f.) trees, but they can be distinguished by their usually tall buttresses and typically fluted stems. Within South-East Asia Alstonia can also be confused with the genera Ochrosia, Rauvolfia and Tabernaemontana which all have verticillate leaves, but Alstonia can be distinguished by its slender fruits and ciliate seeds. The name Alstonia R.Br. is conserved as a later homonym of Alstonia Scop. which is a synonym of Pacouria (Apocynaceae). Giant stomata have been observed in A. macrophylla.

Alstonia grows in both primary and secondary lowland evergreen to deciduous rain forest. They occur on humus-rich clayey soils but also on sandy or even limestone soils and in locations which are periodically inundated and carry swamp or peat-swamp forest, to comparatively dry areas with savanna woodlands. They occur from sea-level to up to about 3000 m altitude, in areas with 0-3 dry months per year.

Seeds of Alstonia are difficult to collect, as the fruits open while still on the trees. The weight of 1000 seeds is about 1.5-2 g. The germination rate of fresh seeds is high, nearly 100%. Seeds can be stored in closed tins for 2 months, maintaining a germination rate of 90%. Seeds of A. angustiloba germinate in 2-8 weeks after sowing. In Indonesia, seedlings are planted into the field when they are 15-25 cm tall, with a spacing of 1 m × 2 m and interplanted with Leucaena leucocephala (Lamk) de Wit. In planting experiments in Peninsular Malaysia 3-4-month-old seedlings are used at spacings of 3 m × 3 m and 5 m × 2 m, respectively. Trials in secondary forest, denuded sites and open sites with top soil retained, showed similar early survival of about 75% after 23 months.

A. scholaris has been grafted. Cleft grafting and inverted T-grafting have been found to be most appropriate.

There is hardly any experience with silviculture of Alstonia. Young Alstonia trees coppice well.

The bark of Alstonia is simply removed in slices from the trunk and major branches, no mention is made of percentage of bark that needs to remain to guarantee survival of the tree. The latex is harvested by making incisions in the bark.

Data on yield of Alstonia for pharmaceutical applications are scarce. The trunk and major branches of a 25-year-old A. scholaris tree yielded 19 kg of dry bark.

The bark of Alstonia can be dried for storage and future use.

Most Alstonia are common and widely distributed, although they occur scattered, and do not seem immediately liable to genetic erosion, largely because they often invade severely disturbed locations. However, stands are heavily depleted locally as a result of deforestation caused by logging and shifting cultivation (e.g. in the Philippines) and the remaining stands need protection.

Alstonia contains a vast array of indole-alkaloids, of which several, as isolated compounds, display pharmacological activity. These are especially in the field of anti-plasmodial activity and cytotoxicity, both in vitro and in vivo. More research, however, will be needed to fully investigate their potential, when for instance in the case of a new anti-malarial lead, a generally low cytotoxicity has to be combined with a high anti-plasmodial activity.

• Keawpradub, N., Eno-Amooquaye, E., Burke, P.J. & Houghton, P.J., 1999. Cytotoxic activity of indole alkaloids from Alstonia macrophylla. Planta Medica 65(4): 311-315.
• Keawpradub, N., Kirby, G.C., Steele, J.C. & Houghton, P.J., 1999. Antiplasmodial activity of extracts and alkaloids of three Alstonia species from Thailand. Planta Medica 65(8): 690-694.
• Lin, S.C., Lin, C.C., Lin, Y.H., Supriyatna, S. & Pan, S.L., 1996. The protective effect of Alstonia scholaris R.Br. on hepatotoxin-induced acute liver damage. American Journal of Chinese Medicine 24(2): 153-164.
• Said, I.M., Din, L.B., Yusoff, N.I., Wright, C.W., Cai, Y. & Phillipson, J.D., 1992. A new alkaloid from the roots of Alstonia angustifolia. Journal of Natural Products 55(9): 1323-1324.
• Saraswathi, V., Ramamoorthy, N., Subramaniam, S., Mathuram, V., Gunasekaran, P. & Govindasamy, S., 1998. Inhibition of glycolysis and respiration of sarcoma-180 cells by echitamine chloride. Chemotherapy 44(3): 198-205.
• Sidiyasa, K., 1998. Taxonomy, phylogeny, and wood anatomy of Alstonia (Apocynaceae). Blumea supplement 11. 230 pp.

• Alstonia angustifolia
• Alstonia angustiloba
• Alstonia iwahigensis
• Alstonia macrophylla
• Alstonia scholaris
• Alstonia spatulata
• Alstonia spectabilis

• Stephen P. Teo