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Voacanga africana Stapf

Protologue
Journ. Linn. Soc., Bot. 30: 87 (1894).
Family
Apocynaceae
Chromosome number
2n = 22
Synonyms
Voacanga angolensis Stapf ex Hiern (1898).
Vernacular names
Small-fruit wild frangipani (En). Voacanga d’Afrique (Fr). Cata grande (Po).
Origin and geographic distribution
Voacanga africana is widespread in mainland tropical Africa, from Senegal east to Kenya and south to Angola, Zimbabwe and Mozambique.
Uses
Different plant parts of Voacanga africana are used medicinally throughout its distribution area. The latex or decoctions or infusions of the stem bark, leaves or roots are put on wounds, boils and sores, and used to treat gonorrhoea, eczema, fungal infections and scabies. They are also taken to treat heart problems, hypertension and rheumatic afflictions. The latex is put in teeth to treat caries or dripped in the eye to cure ophthalmia.
In Senegal a leaf decoction is drunk as a tonic and against fatigue. A root decoction is drunk three times daily to treat post-partum pains and hernia. In Côte d’Ivoire a decoction of the leaves is applied as a wash against diarrhoea, put into a bath against oedema, and is used as a friction and in a drink in the treatment of leprosy. Pulp from the leaves or stem bark is applied to soothe convulsions in children and the juice is put in the nostrils as a tranquilizer. In Cameroon the fruit is used in infusion to treat peptic ulcers. In DR Congo the bark in decoction is taken against intestinal worms, but this is considered a dangerous remedy. An infusion of the twigs is applied in bronchitis. A paste of the roots is applied to the head to kill lice. The dried and powdered roots without the outer bark are mixed with porridge and taken against kidney troubles and menstruation problems in women. In Tanzania the fruit and seeds are extracted with cold water and the extract taken against internal sores. The seeds are also used to treat high blood pressure. The root bark of Voacanga species is generally ingested to combat fatigue and increase endurance of drummers and hunters and, in higher doses, also for magic and religious purposes.
Pharmaceutical companies in Europe extract tabersonine from the seeds, which is readily converted into vincamine, a compound widely used in medicines for geriatric patients. Seed extracts are also used in medicines to treat heart diseases, to lower blood pressure and to treat cancer.
In Senegal the fruits are considered edible. In West Africa the copious latex has been used for adulterating Hevea rubber and children use it to make balls to play with. As it is sticky, it is used to catch birds. In Zambia and Ghana wood is burnt to obtain salt. Voacanga africana supplies poles for building purposes but the wood is considered inferior. Arrows and knife sheaths are made from the branches. In DR Congo, the wood is used to make musical instruments. The wood is also used for firewood. Good fibre can be obtained from the bark and is made into rope. In Nigeria, a yarn is made, which is mixed with cotton or other fibres to make mats. In Tanzania Voacanga africana is planted for ornamental purposes because of its sweet-scented white flowers.
Production and international trade
There is a steady market for Voacanga seeds since the 1980s. Several hundred tonnes of seeds of Voacanga africana and some other Voacanga species, e.g. Voacanga thouarsii Roem. & Schult., are exported from Côte d’Ivoire, Ghana, Cameroon and DR Congo to pharmaceutical companies in France and Germany.
Export prices from Cameroon in 2004 were (per kg): stem bark US$ 14, stem bark powder US$ 18, roots US$ 14, root powder US$ 18, root bark US$ 47, root bark powder US$ 51, seeds US$ 6. In the United States, prices of seed or root bark taken from the internet in 2005 were: 30 g seed US$ 20, 30 g root bark US$ 24, 115 g root bark US$ 80, 450 g root bark US$ 280, 1 kg root bark US$ 400.
Properties
Indole alkaloids are by far the most important compounds of Voacanga spp. Voacanga africana has been studied most extensively. The total amount of alkaloids in root bark is 5–10%, in trunk bark 4–5%, in leaves 0.3–0.45% and in seeds 1.5–3.5%. The main alkaloids of the root bark are corynanthean-ibogan class dimers, chiefly voacamine, voacamidine and voacorine; vobtusine (a rare plumeran-plumeran class dimer) has also been isolated. Among the monomers found, the ibogan class voacangine and voacristine (= voacangarine) are the most important constituents; the plumeran class tabersonine has also been found. In the stem bark, voacamine and congeners predominate; vobtusine has also been identified. The leaves contain mainly dimeric alkaloids of both the voacamine and vobtusine groups; but the monomeric plumeran class voaphylline is the main alkaloid. The alkaloid composition of the seeds is very different, and consists almost exclusively of tabersonine.
The alkaloids show a vast range of pharmacological activities. Tabersonine is only slightly toxic. It has about a quarter of the hypotensive activity of reserpine (which is commonly used to treat high blood pressure), and a spasmolytic effect on the smooth muscle of the intestine. It has no tumour-inhibiting activity. High doses of voacangine bring about convulsions and asphyxia, but in lower doses voacangine exhibits mostly rather moderate central nervous sytem-stimulant activity. It exhibits some cataleptic activity. In regular doses, it has anticonvulsant activity, increases hexobarbital sleeping time in mice and decreases body temperature. In addition, it has local analgesic activity, hypotensive properties and causes bradycardia. The hydrochloride salt of voacangine has significant diuretic activity.
Most of the pharmacological work on voacamine and voacorine has focused on their cardiotonic properties. Voacamine shows little tendency to accumulate, and is less toxic than cardiac glycosides such as digitoxin. Voacamine sulphate resembles cardiac glycosides. When tried clinically on patients with chronic cardiac insufficiencies of various origins, it caused considerable improvement in their clinical status and in haemodynamic parameters, while there was little effect on the heart rate. The alkaloid was effective both orally and intravenously. In high doses both voacamine and voacorine are hypertensive, due largely to peripheral vasoconstriction. These compounds also have parasympatholytic and sympatholytic properties, bringing about contraction of smooth muscle fibres, and they are also central nervous system depressants. Voacamine, voacorine and voacamidine are all cytotoxic in the P-388 cell culture assay. In experiments with rats and mice, parenteral and oral administration of these compounds slowed the growth of transplanted and primary induced neoplasms. Vobtusine causes hypotension as a result of peripheral vasodilatation and a direct depressant action on the heart. In moderate doses initial agitation is followed by a sedative effect; high doses may bring about convulsions and death. Vobtusine is of no clinical interest.
Tabersonine, the major alkaloid from the seeds, is readily converted to vincamine and vincamine derivatives. Vincamine shows protective activity and improves performance in animal models of cognitive dysfunction produced experimentally by cerebral ischaemia, and by amnesia producing agents. Subsequently, vincamine was shown to increase cerebral blood flow as a result of cerebral vasodilatation and may also enhance cellular respiration. It has become very popular in Europe especially for geriatric patients and for patients suffering from cerebral arteriosclerosis; there is improvement in the EEG and clinical status, it ameliorates disturbances of attention, memory and mood.
The aqueous extract of the root bark showed antibacterial activity, anti-amoebic activity against Entamoeba histolytica and antispasmodic activity on the guinea-pig ileum. This triple action may well explain its traditional use as an antidiarrhoeal. The fruit extract contains a compound with cytoprotective and ulcer-healing properties. Finally, the stem bark was tested for molluscicidal activity on the freshwater snail Bulinus globulus, but was found to be only moderately effective.
Leaf-cell suspension cultures of Voacanga africana, grown for 20 days under standard conditions, yielded 6 alkaloids. Tabersonine, lochnericine and minovincinine were the major ones. Voafrine A and B, dimers of the plumeran-plumeran class not previously detected from nature, were also produced. These compounds are of pharmacological interest because of they are related to vincaleucoblastine (vinblastine).
The seed oil is a by-product of the commercial extraction of tabersonine for vincamine synthesis. The main fatty acids are palmitic (15–20%), stearic (7–16%), oleic (49–60%) and linoleic (15–20%) acid. The oil has cosmetic and nutritional value.
Adulterations and substitutes
Plants producing alkaloids of the ibogan and bisindole type occur in several other Apocynaceae genera, e.g. Catharanthus, Hunteria, Picralima, Rauvolfia, Tabernaemontana and Tabernanthe. Vincamine is commercially extracted from Vinca major L.
Description
Shrub or small tree up to 10(–25) m tall, repeatedly dichotomously branched, glabrous to hairy in all parts; trunk up to 30(–40) cm in diameter; bark pale grey-brown, smooth or shallowly fissured, with some white latex. Leaves opposite, simple and entire; stipules absent; petiole 0–2 cm long with a short ocrea at base; blade elliptical or narrowly elliptical, 7–42 cm × 3–20 cm, base cuneate or decurrent into the petiole, apex acuminate, pinnately veined with 8–22 pairs of lateral veins. Inflorescence a fairly lax cyme, 2 together in the forks of branches, usually many-flowered; peduncle 6–25 cm long, slender; bracts as long as the calyx, ovate, obtuse, deciduous, leaving a conspicuous scar. Flowers bisexual, regular, 5-merous, with bad smell; pedicel 3–20 mm long; calyx campanulate, tube 3.5–9 mm long, twisted, lobes broadly ovate to oblong, 3.5–8 mm long, with rounded to truncate or emarginate apex, usually partly recurved, imbricate in bud, pale green, deciduous; corolla tube almost cylindrical, 7–15 mm long, twisted, lobes obovate, narrowly obovate or elliptical, 12–37 mm × 7–16 mm, rounded, spreading and often recurved later, creamy, greenish-creamy, yellow or less often white; stamens inserted 2–3 mm below the corolla mouth, slightly exserted, anthers sessile, narrowly triangular, 4–5 mm long, base sagittate; ovary superior, consisting of 2 carpels connate at base, surrounded by a ring-shaped disk, style narrowly obconical, split, twisted and curled at the base, pistil head 1–1.5 mm long, with a thin ring at base and 5 short lobes, coherent with the anthers. Fruit consisting of 2 separate globose follicles, but often only one developing, 3–8 cm in diameter, green with numerous whitish spots, yellow when mature, 2-valved, many-seeded. Seeds obliquely ellipsoid, 7–10 mm long, laterally with 5 grooves, rough, minutely warty, dark brown, aril yellow or orange, pulpy. Seedling with epigeal germination.
Other botanical information
Voacanga is an Old World genus comprising 12 species, 7 in Africa and 5 in Asia. It is closely related to Tabernaemontana. The seeds of Tabernaemontana are difficult to distinguish from those of Voacanga but are usually larger.
Voacanga bracteata Stapf occurs in rainforest from Sierra Leone to DR Congo. The pulped root, latex and juice are used in frictions to cure rheumatism. In Gabon the bark is taken in decoction in magic and religious rituals. In DR Congo the fruit is considered edible. The root bark and stem bark have an alkaloid composition similar to that of Voacanga africana, but lack alkaloids of the plumeran class. The seeds, however, contain tabersonine. The abundant latex was formerly used in Liberia as an adulterant of Hevea rubber. Voacanga chalotiana Pierre ex Stapf occurs in Congo, DR Congo and Angola. It enters in a preparation to cure hernia in Congo. The stem bark has antifungal properties against pathogens affecting humans and plants.
Growth and development
Voacanga africana plants develop according to the architectural growth model of Leeuwenberg determined by a monopodial orthotropic trunk, which ends in a terminal inflorescence. After flowering the 2 uppermost axillary buds develop into branches, so that the growth is sympodial. The infructescence seems to be axillary. Voacanga africana flowers mainly at the end of the dry season.
Ecology
Voacanga africana occurs in the understorey of open forest, often secondary forest, and in gallery forest in savanna areas. It is often gregarious in coastal forest. It occurs from sea-level to 1100 m altitude.
Propagation and planting
Voacanga africana is readily propagated by seed; vegetative propagation using cuttings is possible but success rates are generally low. It is not frost resistant, but plants will survive if protected for the first 3 years. Dry seeds store well under cool conditions. Seed storage behaviour is orthodox; viability is maintained for more than 3 years in airtight storage at ambient temperature with 11–15% humidity. Seeds are pressed into seedling trays filled with pure river sand, covered with a shallow layer of sand or compost and kept moist. Germination starts within 10–25 days. Soaking the seed overnight may hasten germination. Germination is generally good but slow, reaching 50% after 4 weeks and 90% after 7 weeks.
Management
The fruits, bark and roots of Voacanga africana are mainly collected from the wild. In south-western Cameroon enrichment planting has been done in a 60 ha plot, and a plantation of 100 ha was established in 1992.
Harvesting
Fruits of Voacanga africana are picked from the tree when mature. The follicles are opened by hand to release the pulp with the seeds. The pulp is gently squashed in water to release the seeds, which are dried in the sun. Bark should preferably be collected at the end of the growing season in view of the higher alkaloid content. Roots are simply cleaned to obtain the root bark. Careless harvesting, even of fruits, often leads to the destruction of the tree.
Handling after harvest
Dried seeds are pulverized and the powdered material is usually subjected to extraction for alkaloids by standard methods. Other more sophisticated methods have been patented. A kg of seed yields 25–30 g tabersonine. Trunk bark, after being removed in strips, is dried. Patented extraction procedures have been developed to obtain cardioactive components from the bark.
Genetic resources
Destructive harvesting methods for the international pharmaceutical market cause concern as the species is rapidly becoming endangered. The extensive collection of fruits to obtain the seeds limits regeneration. The apparent tolerance of Voacanga africana to disturbed habitats and its quick regeneration ability lowers the risk of genetic erosion. Except for some occasional representations in botanical gardens no germplasm collections or breeding programmes are known to exist.
Prospects
Many of the indole alkaloids found in Voacanga africana and related species display very distinct and interesting pharmacological activities. Some of them have potential as candidates for lead compounds in the development of future medicines. Much research has been done already, but much more will be needed in future to fully exploit their possibilities.
The extensive harvesting of fruits and the cutting of trees to gather fruits to fulfil the demand for seeds of large pharmaceutical companies are causing rapid disappearance of Voacanga africana from the wild in many regions. Investigation to develop methods of sustainable production (e.g. plantations) is needed to counteract this development. In the meantime, local authorities should be vigilant in stopping the destructive harvesting to preserve the species for the future.
Major references
• Bisset, N.G., 1985. Phytochemistry and pharmacology of Voacanga species. In: Leeuwenberg, A.J.M. (Editor). Series of revisions of Apocynaceae 15. Agricultural University Wageningen Papers 85–3. Wageningen Agricultural University, Wageningen, Netherlands. pp. 81–113.
• Bisset, N.G., 1985. Uses of Voacanga species. In: Leeuwenberg, A.J.M. (Editor). Series of revisions of Apocynaceae 15. Wageningen Agricultural University Papers 85–3. Wageningen Agricultural University, Wageningen, Netherlands. pp. 115–122.
• Burkill, H.M., 1985. The useful plants of West Tropical Africa. 2nd Edition. Volume 1, Families A–D. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 960 pp.
• Hendrian, R., 2001. Voacanga Thou. In: van Valkenburg, J.L.C.H. & Bunyapraphatsara, N. (Editors). Plant Resources of South-East Asia No 12(2): Medicinal and poisonous plants 2. Backhuys Publishers, Leiden, Netherlands. pp. 582–585.
• Leeuwenberg, A.J.M., 1985. Voacanga Thou. In: Leeuwenberg, A.J.M. (Editor). Series of revisions of Apocynaceae 15. Wageningen Agricultural University Papers 85–3. Wageningen Agricultural University, Wageningen, Netherlands. pp. 5–80.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Tona, L., Kambu, K., Mesia, K., Cimanga, K., Apers, S., De Bruyne, T., Pieters, L., Totte, J. & Vlietinck, A.J., 1999. Biological screening of traditional preparations from some medicinal plants used as antidiarrhoeal in Kinshasa, Congo. Phytomedicine 6(1): 59–66.
• Tona, L., Kambu, K., Ngimbi, N., Cimanga, K. & Vlietinck, A.J., 1998. Antiamoebic and phytochemical screening of some Congolese medicinal plants. Journal of Ethnopharmacology 61(1): 57–65.
Other references
• Adjanohoun, E.J. & Aké Assi, L., 1979. Contribution au recensement des plantes médicinales de Côte d’Ivoire. Centre National de Floristique, Abidjan, Côte d’Ivoire. 358 pp.
• Adjanohoun, E.J., Adjakidjè, V., Ahyi, M.R.A., Aké Assi, L., Akoègninou, A., d’Almeida, J., Apovo, F., Boukef, K., Chadare, M., Cusset, G., Dramane, K., Eyme, J., Gassita, J.N., Gbaguidi, N., Goudote, E., Guinko, S., Houngnon, P., Lo, I., Keita, A., Kiniffo, H.V., Kone-Bamba, D., Musampa Nseyya, A., Saadou, M., Sodogandji, T., De Souza, S., Tchabi, A., Zinsou Dossa, C. & Zohoun, T., 1989. Contribution aux études ethnobotaniques et floristiques en République Populaire du Bénin. Agence de Coopération Culturelle et Technique, Paris, France. 895 pp.
• Arbonnier, M., 2002. Arbres, arbustes et lianes des zones sèches d’Afrique de l’Ouest. CIRAD, MNHN, UICN. 573 pp.
• Cunningham, A.B., 1997. An Africa-wide overview of medicinal plant harvesting, conservation and health care. In: Bodeker, G. & Vantomme, P. (Editors). Medicinal plants for forest conservation and health care. Non-Wood Forest Products 11, FAO, Rome, Italy. 158 pp.
• Hedberg, I., Hedberg, O., Madati, P.J., Mshigeni, K.E., Mshiu, E.N. & Samuelsson, G., 1982. Inventory of plants used in traditional medicine in Tanzania. I. Plants of the families Acanthaceae-Cucurbitaceae. Journal of Ethnopharmacology 6(1): 29–60.
• Kuster-Laine, I., 1985. Contribution à l’étude de trois phanérogames congolaises douées de propriétés antifongiques : Crossopteryx febrifuga (Afzel. ex G. Don) Benth., Rubiacées, Cathormion altissimum (Hook. f.) Hutch et Dandy, Légumineuses-Mimosacées, Voacanga chalotiana Pierre, Apocynacées. Thèse de Doctorat d'Etat, Département de Pharmacie, Université de Besançon, Besançon, France. 64 pp.
• Latham, P., 2004. Useful plants of Bas-Congo province, Democratic Republic of the Congo. DFID, London, United Kingdom. 320 pp.
• Rafidison, P., Baillet, A., Baylocq, D. & Pellerin, F., 1987. Study of Voacanga africana seed oil: Etude de l’huile des graines de Voacanga africana. Oleagineux 42(7): 299–302.
• Tan, P.V. & Nyasse, B., 2002. Anti-ulcer compound from Voacanga africana with possible histamine H12 receptor blocking activity. Phytomedicine 7(6): 509–515.
• Lovett, J.C., Ruffo, C.K. & Gereau, R.E., 2003. Field guide to the moist forest trees of Tanzania. [Internet] Centre for Ecology Law and Policy, Environment Department, University of York, York, United Kingdom. http://www.york.ac.uk/ res/celp/webpages/projects/ecology/ tree%20guide/guide.htm. Accessed June 2005.
Sources of illustration
• Leeuwenberg, A.J.M., 1985. Voacanga Thou. In: Leeuwenberg, A.J.M. (Editor). Series of revisions of Apocynaceae 15. Wageningen Agricultural University Papers 85–3. Wageningen Agricultural University, Wageningen, Netherlands. pp. 5–80.
Author(s)
A. Maroyi
Department of Biological Sciences, Bindura University of Science Education, P.O. Bag 1020, Bindura, Zimbabwe


Editors
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
A. Gurib-Fakim
Faculty of Science, University of Mauritius, Réduit, Mauritius
Associate editors
C.H. Bosch
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
M.S.J. Simmonds
Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom
R. Arroo
Leicester School of Pharmacy, Natural Products Research, De Montfort University, The Gateway, Leicester LE1 9BH, United Kingdom
A. de Ruijter
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Photo editor
A. de Ruijter
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Maroyi, A., 2006. Voacanga africana Stapf. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
Distribution Map wild


1, leafy branch; 2, inflorescence; 3, fruit; 4, seeds.
Redrawn and adapted by Iskak Syamsudin



inflorescences


flowers in bud


flowers


fruiting branch


fruiting branch


dried root bark