Solanum (PROSEA Medicinal plants)

Plant Resources of South-East Asia Introduction

List of species

Solanum L.

Protologue: Sp. pl. 1: 184 (1753); Gen. pl. ed. 5: 85 (1754).

Family: Solanaceae

Chromosome number: x= 12; S. capsicoides: 2n= 24, S. erianthum: 2n= 24, S. mammosum:n= 11, 12, S. nigrum: 2n= 72, S. trilobatum: 2n= 24

• Solanum erianthum D. Don,
• S. nigrum L.

• Solanum, nightshade (En)
• Solanum, morelle (Fr).

Estimates differ greatly, but Solanum probably comprises some 1000-1100 species. It is cosmopolitan, except in boreal, alpine and aquatic habitats. The principal centre of diversity is located in Central and South America, with secondary centres in Africa and Australia. With a total of 60 wild and cultivated species, New Guinea is probably the area in Malesia with the most species; by comparison, Peninsular Malaysia has about 15 species and Java and the Philippines about 25 species each.

Solanum is used to cure digestive and intestinal problems, including stomach-ache, diarrhoea, piles and dysentery, and for various skin problems such as sores, boils, cuts, wounds and bruises. Many species are also employed to treat fever and malaria, headache and rheumatism. Some are considered to be stimulants whereas others have sedative properties. Furthermore, Solanum is frequently used for various diseases of the respiratory tract, such as coughs, sore throat, bronchitis and asthma. Finally, many species are applied to treat urinary problems.

Solanum shows insecticidal and fungicidal properties. The leaves and stems of many species are often cooked or steamed and eaten as a vegetable. The unripe fruits are eaten in curries, whereas the ripe ones of some Solanum species are edible either cooked or raw. Caution must be taken when eating Solanum, as several species are poisonous.

The fruits of S. sanitwongsei are on sale in Bangkok markets, and have been cultivated commercially in Manila.

The steroidal alkaloids of the Solanaceae occur as glycosides (hence glycoalkaloids). The known steroidal alkaloids are based on a C₂₇ cholestane skeleton and can be divided into 5 groups: solanidanes, spirosolanes, 22,26-epiminocholestane, α-epiminocyclohemiketal and 3-aminospirostane. The first 2 groups have attracted the most research. The solanidanes, with important alkaloids such as solanidine, leptidine and demissidine, are characterized by an indolizidine moiety. Important spirosolane alkaloids include solasodine, tomatidine and tomatidenol. The spirosolanes are structurally similar to saponins of the diosgenin type, except that the oxygen in the spiro-alketal pattern has been replaced by nitrogen.

Solanidine is present in S. capsicoides, whereas solasodine is found in S. erianthum, S. nigrum and S. trilobatum. The total alkaloid content of air-dried leaves and fruits is respectively 0.26% and 0.14% for S. capsicoides, 0.37% and 0.39% for S. erianthum, 0.43% and 0.10% for S. nigrum and 0.36% and 0.96% for S. trilobatum. The solasodine content in Solanum fruits from Indian samples is 0.01-0.70% in S. erianthum and 0-0.28% in S. nigrum, whereas the total glycoalkaloid content in fruits of S. trilobatum has been found to be 3.5%. Leaf samples of S. erianthum from Vietnam contained 0.26% solasodine, 0.05% tomatidine and 0.01% solaverbascine. S. erianthum also has steroidal saponins and free genins. As well as solasodine, S. nigrum contains the sapogenins diosgenin and tigogenin. The unripe berries have 0.68% solasodine, 0.19% diosgenin and 0.15% tigogenin, whereas leaves contain 1.28% tigogenin.

Glycoalkaloids are toxic to animals when injected. Like saponins, they are surface-active and haemolytic, and possess antifungal and cytostatic properties. Solanum steroidal glycoalkaloids affect the body mainly in two ways: the intact glycoalkaloid is an irritant, whereas the steroidal alkamine affects the nervous system. The pharmacological effects of these compounds may possibly be attributable to the ability of the steroidal glycoalkaloids to impair the functioning of membranes of strategic muscle and nerve cells in mammals. Evidence to support this is the toxicity of alkaloids to plants and fungi where complexation has been demonstrated with membrane sterols; it has been shown that the alkaloid sensitivity in Pythium and Phytophthora increases when these fungi are grown on a medium containing sterol and incorporate the sterol into their membranes. However, aglycones also have a still unexplained deleterious effect on certain tissues and organisms, and other mechanisms may be involved in the toxicity of Solanum alkaloids. Furthermore, the toxicity of the alkaloids is highly pH-dependent: lower pH levels greatly reduce toxicity.

The physiological and pathological effects of steroidal glycoalkaloids on mammals are numerous. Solanine has been observed to depress the central nervous system in rabbits; solanine, chacoine and tomatine have been observed to induce tachycardia in rabbits and rats; chacoine, tomatine and solanine have been observed to induce tachypnea or bradypnea in rabbits. Other reported effects are hypotension induced by tomatine in rats and rabbits, positive inotropic (cardiotonic) action by tomatine, chacoine, solanine, demissine, commersonine and solanidine in frogs, hyperglycaemia induced by solanine in rats, haemolysis and haemorrhage induced by tomatine in rats, inhibition of plasma cholinesterase by solanine, solanidine, tomatine and demissidine in humans and embryotoxicity induced by solanine in rats and mice.

The powdered aerial parts of S. nigrum and its methanolic extract significantly reduced gastric ulcer formation in rats. The activity may be due to inhibition of acid and pepsin secretions and/or their in vitro ability to bind these; inhibition of the acid production alone by cimetidine did not decrease ulcer formation. "Sobatum" is the partially purified component of S. trilobatum obtained from the 75:25 petroleum ether/ethyl acetate extract. It has been found to be cytotoxic in Dalton's Lymphoma ascites, Ehrlich ascites cell lines and tissue culture cells (L929 and Vero). "Sobatum" significantly inhibited peritoneal tumours induced by Dalton's Lymphoma ascites and Ehrlich ascites tumour cells. It was also found to reduce solid tumour growth in mice, when given either simultaneously or prophylactically, and is more active in simultaneous administration in Ehrlich ascites cell lines. It was found that "Sobatum" was more active against Ehrlich ascites-induced solid tumour than Dalton's Lymphoma ascites-induced solid tumours. It has been experimentally proven that "Sobatum" has the ability to retard the development of solid tumours and 7,12-dimethylbenz(a)anthracene-induced carcinogenesis. In another experiment with mice, "Sobatum" was administered intraperitoneally. It failed to influence the induction of micronuclei in bone marrow erythrocytes of mice 24 hours and 72 hours after the second administration, thereby demonstrating that "Sobatum" has no cytogenic toxic potential. The rare sterol carpesterol isolated from S. trilobatum (also found in S. torvum Swartz) has anti-inflammatory activity on carrageenin-induced mouse paw oedema; it proved as effective as hydrocortisone and withaferin A (from Withania somnifera (L.) Dunal). The alcoholic extract of S. nigrum berries (100-400 mg/kg) showed significant inhibition of carrageenin-induced oedema in albino rats. The aqueous leaf extract of S. erianthum did not produce any significant suppression of Plasmodium berghei infection in mice.

A large number of fungi are inhibited in growth and development by steroidal alkaloids such as tomatine, solanine, and chaconine. An alcoholic extract of leaves of S. nigrum is active against Staphylococcus aureus and Escherichia coli. Leaf extracts of S. nigrum inhibited lesion production in leaves in response to the tobacco mosaic virus. The flavonoid-rich extract of S. erianthum possesses antibacterial and antifungal activity. Gram-positive bacteria are inhibited, but gram-negative ones are not, whereas the flavonoids have been found to be toxic to the fungi Aspergillus flavus and Candida albicans. Some other pharmacological activities of Solanum include antispasmodic, hypotensive, hypocholesterolaemic and anti-HIV-1 activity induced by S. nigrum in mammals, and insecticidal and molluscicidal activity of S. nigrum and of S. mammosum L.

Solanum steroidal alkaloids are useful in industry as steroid precursors. Solasodine is a nitrogen analogue of diosgenin, a compound often used as raw material for the production of medicinal steroids. The synthetic steroids have three main applications in medicine: as anti-inflammatory corticosteroids, as contraceptive sex steroids and as anabolic steroids.

Steroidal alkaloids (e.g. diosgenin and tigogenin) are also found in Dioscorea and Smilax species; these are also used as starting material for steroid hormone semisynthesis.

• Annual or perennial, erect or ascending, unarmed or spiny herbs, shrubs or rarely small trees, with simple, branched, stellate or glandular hairs.
• Leaves alternate or rarely subopposite, simple and entire to lobed, pinnatisect or imparipinnate, petiolate, exstipulate.
• Inflorescence a terminal cyme but usually appearing lateral by growth of a lateral bud and extra-axillary cyme, appearing racemose, umbellate or paniculate or rarely reduced to a solitary flower.
• Flowers regular, bisexual or rarely andromonoecious; calyx campanulate, rotate or cupular, (4-)5(-10)-lobed; corolla stellate, rotate or campanulate, (4-)5(-10)-lobed, white, violet, purple or blue; stamens (4-)5, inserted on the corolla throat, alternating with the corolla lobes, anthers often connivent, opening by terminal pores or slits; ovary superior, 2(-4)-locular with many ovules in each cell, style simple, stigma capitate or bifid.
• Fruit a usually globose berry, with a persistent and sometimes enlarged calyx, few to many-seeded.
• Seeds orbicular to subreniform, compressed, often minutely pitted or reticulate.
• Seedling with epigeal germination; cotyledons emergent, ovate to linear-lanceolate; first leaves usually entire.

Most Solanum species flower and fruit almost throughout the year. Flowers are pollinated by insects. Fruit maturation takes about 2-3 months. The fruits are eaten by birds and mammals which disperse the seeds.

Solanum has been subdivided into 7 subgenera and numerous sections and series. S. nigrum, being the type-species of the genus, belongs to subgenus Solanum, S. erianthum to subgenus Brevantherum and the other four species treated below to subgenus Leptostemon which also includes S. melongena L. and S. mammosum L., species well-known for their fruits. It is in South-East Asia that the taxonomy of Solanum is least known: a thorough taxonomic revision is urgently needed. Adding to the taxonomic confusion is the fact that S. erianthum has been extensively referred to as S. verbascifolium L., which actually proved to be identical with a South American species. Moreover, in South-East Asian literature, S. capsicoides has often been misinterpreted as S. aculeatissimum Jacq. Furthermore, S. nigrum belongs to a complex of very similar species (including e.g. S. americanum Miller and S. villosum Miller), which are sometimes regarded as mere forms of a single variable species. S. nigrum arose from hybridization of the diploid S. americanum and the tetraploid S. villosum. S. villosum is distinguished by its yellow, orange or red berries. S. americanum and S. nigrum are much more difficult to distinguish. The former has usually umbellate inflorescences, anthers 1.0-2.0 mm long, a glossy, purplish-black berry with generally 50-80 seeds and an enlarged calyx with reflexed lobes in fruit. For the latter, see below. S. mammosum, originally from Central and South America but introduced in the Malesian region for its decorative fruits, has poisonous fruits which are occasionally used as an insecticide against cockroaches and caterpillars. S. procumbens Lour., S. spirale Roxb. and S. surattense Burm.f. (synonym: S. xanthocarpum Schrad. & J.C. Wendl.) are used in folk medicine in Indo-China. S. aviculare J.G. Forster, S. laciniatum Aiton and S. khasianum C.B. Clarke are a reputed rich source of solasodine. Originating from outside the Malesian region, they have received special attention in breeding programmes for cultivation at higher elevation in Java. In particular S. khasianum merrits further research.

Most medicinal species of Solanum are weeds of gardens, fields and waste places, occurring in sunny or slightly shaded sites at low to medium altitudes, but S. nigrum is found up to 3100 m.

Those Solanum cultivated as vegetables in South-East Asia can be propagated by seed, shoot cuttings and by division of rooted shoots.

Diosgenin and solasodine have been isolated from 6-month-old callus of S. erianthum; the undifferentiated callus tissue was established from sterilized seeds on Murashige and Skoog's revised medium. Blue light stimulated solasodine synthesis and green light stimulated diosgenin synthesis in the callus. Optimal growth was reached after 6 weeks when the dry weight of the tissue had increased 6.6-fold. After 6 weeks only about 147 μg diosgenin and 47 μg solasodine had been produced per g of dry-weight tissue; this is very little.

In West Java S. nigrum grown as a leaf vegetable is fairly free from diseases and pests.

Leaves, stems, berries and roots of Solanum are harvested for medicinal use. When used as a vegetable, leaves and young shoots of S. nigrum are hand-picked.

In many species the steroidal alkaloid and sapogenin content decline as the fruit ripens. Leaf alkaloid and sapogenin content also decline with age. In India a method has been developed to estimate solasodine content in S. nigrum leaves 3 months after sowing by estimating their N content. At this stage of growth a top dressing or foliar sprays may be applied to increase solasodine yield.

In general, Solanum fruits are used fresh. The other harvested parts are dried and can be stored in sealed containers, preferably in a cool well-aerated room.

S. capsicoides is resistant to Pseudomonas and is a non-host for potato cyst nematodes. There are no records of medicinally important Solanum in germplasm collections. In view of their weedy nature the risk of genetic erosion seems to be rather limited. The great variation in alkaloid content within species may offer possibilities for selection. However, the alkaloid content also varies substantially as a result of ecological conditions, drying and storage.

Several Solanum species containing the spirosolane alkaloids solasodine and tomatidenol are considered promising as alternatives to Dioscorea species as a source of raw material for steroid production, including 16 dehydropregnelone acetate. Hormonal derivatives of this steroid are used as active ingredients of the oral contraceptive pill. The ability of S. trilobatum components to retard the development of solid tumours and to act as anti-inflammatory deserves further research.

• Akhtar, M.S. & Munir, M., 1989. Evaluation of the gastric antiulcerogenic effect of Solanum nigrum, Brassica oleracea and Ocimum basilicum in rats. Journal of Ethnopharmacology 27(1-2): 163-176.
• Bhattacharya, T.K., Ghosh, M.N. & Subramanian, S.S., 1980. A note on anti-inflammatory activity of carpesterol. Fitoterapia 51(5): 265-268.
• Blomqvist, M.M., 1997. Taxonomy and uses of medicinally important species in the genera Datura L. and Solanum L. (Solanaceae) in South-East Asia. Unpublished MSc. thesis, Department of Plant Taxonomy, Wageningen Agricultural University, the Netherlands. 132 pp.
• Council of Scientific and Industrial Research, 1972. The wealth of India: a dictionary of Indian raw materials and industrial products. Vol. 9. Publications and Information Directorate, New Delhi, India. pp. 378-429.
• Mohanan, P.V. & Devi, K.S., 1997. Effect of Sobatum on tumour development and chemically induced carcinogenesis. Cancer Letter 112(2): 219-223.
• Mohanan, P.V., Rathinam, K. & Devi, K.S., 1996. Lack of micronucleus induction by 'Sobatum' in bone marrow erythrocytes of Swiss mice. Mutation Research 361(1): 23-27.
• 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. pp. 394-396.
• Roddick, J.G., 1986. Steroidal alkaloids of the Solanaceae. In: d'Arcy, W.G. (Editor): Solanaceae: biology and systematics. Columbia University Press, New York, United States. pp. 201-222.
• Roddick, J.G., 1991. The importance of the Solanaceae in medicine and drug therapy. In: Hawkes, J.G., Lester, R.N., Nee, M. & Estrada, N. (Editors): Solanaceae III: taxonomy, chemistry, evolution. Royal Botanic Gardens Kew and Linnean Society of London, United Kingdom. pp. 7-23.
• Siemonsma, J.S. & Kasem Piluek (Editors), 1993. Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, the Netherlands. pp. 249-260.

• Solanum capsicoides
• Solanum erianthum
• Solanum nigrum
• Solanum sanitwongsei
• Solanum sarmentosum
• Solanum trilobatum

• M.M. Blomqvist & Nguyen Tien Ban