Shrubs or herbs of Hypericum L. species are distributed throughout the world. They are found in the Mediterranean region, Portugal, Spain, Canary Islands [Spain], Africa, Turkey, Australia, Tasmania, New Zealand, New Caledonia, Papua New Guinea, parts of South-East Asia, Sri Lanka, and from North to South America. Etymologically, the name Hypericum L. was first used by Linnaeus. It comes from hyper (over) and eikon (image), on account of the image that appears on the petals. According to other botanists, the name comes from hypo and ereikn or erikn meaning “plant that grows under heathers”; it could also come from hyper and eikon meaning “plant resembling a ghost’s image or plant with an air of mystery”.
Many authors reported on the chemical composition and the variability of the main components in different species of Hypericum L.. However, the chemical study of this genus began with Hypericum perforatum L. in 1830 with the pioneering isolation of hypericin by Bruchner, who named the compound “hypericum red”. About one century later, in 1911, the compound was identified and renamed hypericin by Cerny, who also isolated other similar constituents without a proven structure determination, because the correct structure of hypericin was established in 1953 by Brockman and Sanne. Hypericin [4, 5, 7, 4′, 5′, 7′-hexahydro-2,2′-dimethyl-mes-o-naphthodianthrone] is a natural photosensitizing polycyclic aromatic dione which can be extracted from certain plants of the Hypericum L. genus. It is a photodynamic dark-red pigment and was the target of all the analytical methods reported in the literature. Moreover, the structural variation among such miscellaneous plant quinones was reviewed in 1979 by Thomson.
Medicinal Importance of Hypericum L.
Species of the genus Hypericum L. are used as medicinal remedies throughout the world. Hypericum L. species are an abundant source of pharmaceutical products and a significant interest has been concentrated on the activity, among others, of the naphthodianthrones hypericin and its derivatives. From current information it is clear that hypericin is only found in certain species belonging to the genus Hypericum L.. This photodynamic pigment is considered to be one of the most important compounds from a pharmacological point of view. It displays considerable antiviral activity against several viruses, including the human immunodeficiency virus type I. Thus, it is now considered to be a potentially valuable agent for the photodynamic therapy of cancer and other diseases. On the other hand, other authors reported that hypericin has antidepressant effects which were determined by inhibition of monoamino oxidase (MAO) in vitro. Since hypericin is considered to be an inhibitor of both types A and B of MAO, this result would confirm the supposition that it is the active constituent in Hypericum L. extract.
Hypericum canariense L.
Hypericum canariense L. is a shrub species endemic to the Canary Islands, Spain, and belongs to the Hypericaceae family. This very interesting medicinal plant is widely distributed in these islands [Gran Canaria, Tenerife, Gomera, Hierro and La Palma]. In our islands, it is common and even abundant in moist, sunny areas of the Laurisilva (Laurel forest), and/or Fayal-Brezal and/or Thermophile Forest. Hypericum canariense L. is a widely used medicinal plant, known as Hiperico or Granadillo in Canary Islands folk medicine. This shrub species is glabrous or sometimes glaucescent. It flowers in spring and summer and reproduces from seeds with a low rate of viability. This species is abundantly branched and grows to between 1 and 3 m in height. The stems are erect, branched at the top and 20-90cm long. The leaves are smooth, simple, opposite, lanceolate or elliptic-lanceolate, 1-3 cm long and decussate. Its large, very beautiful golden yellow flowers grow in groups of not very thick terminal inflorescences. Each flower has five lanceolated petals some 2 cm in length, with numerous stamens which form a crown around an overdeveloped pistil. The ovary is ovoid. The capsules are oval-shaped, hard and reddish-brown and contain a large number of very tiny seeds.
Importance of Hypericum canariense L.
Hypericum canariense L. is considered an important source of pharmaceutical compounds which are contained in the aerial parts of this plant. Hypericum canariense L. extracts used in folk therapy today are prepared by extracting the aerial parts of this species with mixtures of ethanol and water. This folk medicine has been recognised by the scientific, medical and commercial communities. This has resulted in attempts to isolate the medicinally active agents and determine their range of application. Obviously, further investigation into alternative methods to obtain hypericin is needed. In vitro culture of Hypericum canariense L. is considered a very promising approach towards providing a long-term source of this valuable compound.
Hypericum canariense L.: Future Prospects
Primary metabolism in plants is essential for growth and development of cells, tissue and organs. Until recently, secondary metabolism was generally regarded as a non-essential process that produced by-products or plant wastes. However, there is evidence that secondary metabolites such as phenols, terpenoids and alkaloids may contribute to plant defence against attacks by herbivores and pathogenic micro-organisms. In addition, the cytotoxic nature of some secondary metabolites has made them medicinally important. Examples included the naphthodianthrone hypericin and its derivatives which have especially been used, due to their antiviral and anticancer activities. A general increase in interest in use of Hypericaceae medicinal plants as natural products for pharmaceutical applications has swept the world over the past years. As the demand for hypericin products expands, the efforts of plant collectors have sought other alternatives. For this purpose, plant cell and tissue culture techniques have developed into a branch of biotechnology with attractive prospects for agriculture as well as for the chemical and pharmaceutical industries. Due to the presence of the therapeutically valuable cytotoxic and antidepressant naphthodianthrones hypericin and derivatives in some Hypericum L. species, these medicinal plants became one of the major fields of interest in modern plant cell biotechnology. The high demand for these chemical compounds was one of the major motives to study the possibilities for their production by tissue culture techniques. In the last 10 years, perspectives have changed and considerable progress has been achieved in the therapeutic approach with hypericin extracts. On the other hand, the production of hypericin is still far from being economically feasible. However, considerable improvement in the efficiency of plant cell and tissue culture may be expected. To the best of our knowledge, no patents have been registered for the commercial production of hypericin. Furthermore, more experience with large-scale culturing of in situ and in vitro plant material is needed for this purpose.
Hypericum canariense L.: Conclusion
An overview is given of some aspects of the history, principles and applications of this medicinal plant endemic to the Canary Islands. The main applications discussed in the review are related to micropropagation, in vitro plant breeding and production of hypericin. In spite of the fact that in vitro propagation of mature Hypericum canariense L. often proved difficult, satisfactory micropropagation was achieved. Thus, the cultivation of this endemic medicinal species is discussed with reference to other Hypericum L. species. In conclusion, as described above, shoot multiplication and rooting of Hypericum canariense L., a very interesting medicinal plant, was achieved in vitro using shoot tips and nodal segments as explants for the purpose of obtaining the chemical product hypericin. The possibility to increase the concentration of this compound by tissue culture is presently being considered.
Selections from the book: “Medicinal and Aromatic Plants XII” (2002).