Heliotropium (PROSEA)
Introduction |
Heliotropium L.
- Protologue: Sp. pl. 1: 130 (1753); Gen. pl. ed. 5: 164 (1754).
- Family: Boraginaceae
- Chromosome number: x= 7, 8, 9, 11, 13; H. curassavicum: 2n= 26, 52, H. indicum: 2n= 22, H. ovalifolium: 2n= 22
Major species
- Heliotropium indicum L.
Vernacular names
- Heliotrope (En). Héliotrope (Fr).
Origin and geographic distribution
Heliotropium consists of about 250 species, and is distributed in tropical, subtropical and warm temperate regions of all continents. A total of 11 species are recorded for the Malesian region: 7 species can be considered indigenous and 1 naturalized; 3 species are known solely from cultivation, though they occasionally occur as a weed.
Uses
The leaves of various Heliotropium species are generally applied in poultices throughout the Malesian region, and in other parts of the world. They are used to cure ulcers, wounds and local inflammations. A decoction of the leaves of H. indicum is reported to be applied in the treatment of urticaria. A decoction of various parts of the plants is used as an emmenagogue or even abortifacient in Indo-China and the Philippines. H. arborescens L. (synonym: H. peruvianum L.) is widely cultivated as an ornamental in tropical (e.g. Java), subtropical and temperate countries.
Properties
Pyrrolizidine alkaloids are common constituents of various genera belonging to the Boraginaceae and Compositae and to the papilionoid genus Crotalaria. Biosynthetically, these alkaloids are derived from two molecules of the amino acid ornithine, which are utilized in the formation of the bicyclic pyrrolizidine skeleton (necine moiety). This basic skeleton seldom occurs in its free form, but is generally found as an ester with rare monobasic or dibasic acids: the necic acids.
The interest in these compounds is mainly focused on their toxic effects in animals, livestock and sporadically in humans. Many pyrrolizidine alkaloids exhibit a pronounced hepatic toxicity. Toxic structures must have an 1,2-unsaturation in the pyrrolizidine ring, and an ester function on the side chain. Mammalian liver oxidases transform typical alkaloids into reactive pyrrole structures, which are potent alkylating agents and react with suitable cell nucleophiles, e.g. nucleic acids and proteins. Although the toxic effects of these metabolites are usually primarily seen in the liver, lung and/or other tissues may also be affected. In addition to the cytotoxic effects mentioned, mutagenic and carcinogenic activities of pyrrolizidine alkaloids have been reported in literature.
In general, animals will avoid eating plants containing pyrrolizidine alkaloids. However, in times of scarcity, and when fodder is contaminated, accidental consumption can lead to acute or chronic intoxication. In humans, generally only symptoms of chronic intoxication are observed, as a result of a prolonged use of herbal medicines consisting of plants containing pyrrolizidine alkaloids (e.g. Senecio and Symphytum species).
Indicine, indicine-N-oxide, acetyl-indicine, indicinine, heleurine, heliotrine, supinine, supinidine and lindelofidine are pyrrolizidine alkaloids isolated from H. indicum, that are all hepatotoxic. Furthermore, the literature contains reports of the presence of trachelanthamidine and retronecine in H. indicum. H. curassavicum contains trachelanthamidine, supinidine and retronecine. In all organs at all developmental stages, supinidine was the minor necine; trachelanthamidine was the dominant base in H. curassavicum, whereas retronecine was dominant in H. indicum. A larger proportion (17-65%) of retronecine has been found in the roots and generative parts of H. curassavicum than in the leaves and stems.
Indicine-N-oxide has shown significant activity against W-256 carcinoma in rats, and leukaemia L-121 in mice. The compound has also been administered as a brief infusion over 15 minutes to patients with solid tumours who had received prior chemotherapy. Dose-limiting effects were leukopenia and thrombocytopaenia, and the toxicity was cumulative with repeated doses. In general, the undesirable hepatotoxicity prevented any further development. In addition, anti-inflammatory and wound healing properties are reported.
Furthermore, phytochemical investigations have revealed the presence of the biogenic amines putrescine, spermidine and spermine in leaves and inflorescence of H. indicum, and the sterols diosgenin, tigogenin, lanosterol and β-sitosterol in H. scabrum.
Description
- Annual or perennial herbs or subshrubs.
- Leaves alternate, simple, petiolate or sessile, stipules absent.
- Inflorescence usually a unilateral, scorpioid cyme, sometimes 2 cymes close together on dichotomous branches, or even numerous short cymes crowded together in a head-like manner, with or without bracts.
- Flowers actinomorphic, bisexual, 5-merous; calyx lobes almost free, unequal; corolla tubular, funnel-shaped or hypocrateriform, white, yellow or purple; stamens included in corolla tube, with very short filaments; ovary superior, 4-locular.
- Fruit undivided with 4 locules or by reduction 1 fertile locule, or separating in 2 bilocular pyrenes, most often these pyrenes again separating into 2 unilocular nutlets; nutlets smooth or sculptured.
- Seedling with epigeal germination; cotyledons leafy, glabrous, with rounded apex; hypocotyl elongated, densely hairy, epicotyl very short.
Growth and development
H. indicum may flower throughout the year. The flowering season is very long, and new flowers develop apically within a cyme while mature nutlets are already present at the base of the inflorescence.
Other botanical information
Heliotropium belongs to the subfamily Heliotropioideae, which also includes Tournefortia. Infrageneric classification suffers from the absence of a recent taxonomic revision covering Old World and New World species. The Malesian Heliotropium species belong to several sections.
Ecology
Heliotropium occurs in very diverse habitats, though drier places are preferred in general. Some species are weeds, often introduced from the New World at an early date and now widespread in the palaeotropics.
Harvesting
Plants of Heliotropium are harvested when fully grown, and can be used fresh or dried.
Yield
H. curassavicum and H. indicum grown under greenhouse conditions showed the greatest accumulation of alkaloids after the beginning of flowering. Young leaves, young inflorescences and seedlings showed very high alkaloid levels. With ageing, the content of alkaloids in leaves decreased 20-fold. In both species the highest alkaloid content was found in the roots and inflorescence. These parts also exhibited the highest relative amounts of N-oxides ranging from 60-90% of the total alkaloid content. No significant age-dependent differences in N-oxides were found.
Genetic resources and breeding
Most Heliotropium species are widespread and common weeds. Therefore the risk of genetic erosion seems slight. No breeding programmes are known to exist.
Prospects
The possible applications in cancer therapy are limited by the toxic effects, in particular the hepatotoxic effects, of the pyrrolizidine alkaloids.
Literature
- Birecka, H., Di Nolfo, T.E., Martin, W.B. & Frohlich, M.W., 1984. Polyamines and leaf senescence in pyrrolizidine alkaloid bearing Heliotropium plants. Phytochemistry 23: 991-997.
- Bruneton, J., 1995. Pharmacognosy, phytochemistry, medicinal plants. Technique & Documentation Lavoisier, Paris, France. pp. 675-680.
- Catalfamo, J.L., Martin, W.B. & Birecka, H., 1982. Accumulation of alkaloids and their necines in Heliotropium curassavicum, H. spathulatum and H. indicum. Phytochemistry 21(11): 2669-2675.
- Dewick, P.M. (Editor), 1997. Medicinal natural products. John Wiley & Sons, Chichester, United Kingdom. pp. 283-285.
- Gutierrez, H.G., 1982. An illustrated manual of Philippine materia medica. Vol. 2. National Research Council of the Philippines, Tagig, Metro Manila, the Philippines. pp. 442-444.
- Holm, L.G., Plucknett, D.L., Pancho, J.V. & Herberger, J.P., 1977. The world's worst weeds. Distribution and biology. East-West Center. The University Press of Hawaii, Honolulu, United States. pp. 291-294.
- Kugelman, M., Liu, W.C., Axelrod, M., McBride, T.J. & Rao, K.V., 1976. Indicine-N-oxide: the anti-tumor principle of Heliotropium indicum. Lloydia 39(2/3): 125-128.
- Ohnuma, T., Sridhar, K.S., Ratner, L.H. & Holland, J.F., 1982. Phase I study of indicine N-oxide in patients with advanced cancer. Cancer Treatment Report 66(7): 1509-1515.
- Riedl, H., 1997. Boraginaceae. In: Kalkman, C. et al. (Editors): Flora Malesiana. Series 1, Vol. 13. Rijksherbarium/Hortus Botanicus, Leiden, the Netherlands. pp. 43-144.
- Van den Dungen, F.M., 1993. Symphytum officinale L. PhD-thesis Universiteit Utrecht, the Netherlands. 191 pp.
Selection of species
Authors
- Wongsatit Chuakul, Noppamas Soonthornchareonnon & Promjit Saralamp