CHAPTER 3 PLANTS OF THE GENUS SYZYGIUM (MYRTACEAE): A REVIEW ON ETHNOBOTANY, MEDICINAL PROPERTIES AND PHYTOCHEMISTRY IAN EDWIN COCK and MATTHEW CHEESMAN CONTENTS 3.1 Introduction .................................................................................... 35 3.2 Ethnopharmacology ....................................................................... 37 3.3 Phytochemistry and Antioxidant Properties ................................... 44 3.4 Antimicrobial Activity ................................................................... 45 3.5 Anticancer Activity ........................................................................ 54 3.6 Anti-Inflammatory Activity and Immunomodulation .................... 59 3.7 Antidiabetic Activity ...................................................................... 63 Author Copy 3.8 Conclusions .................................................................................... 66 3.9 Summary ........................................................................................ 68 Keywords ................................................................................................ 69 References ............................................................................................... 70 Apple Academic Press 3.1 INTRODUCTION Plants have been used as therapeutic agents since the start of civilization. In many developing countries, herbal medicinal systems remain important in the treatment of many ailments. Ayuvedic medicine is still commonly For Non-Commercial Use 36 Bioactive Compounds of Medicinal Plants practiced within India with an estimated 85% of Indians still using crude plant preparations for the treatment of wide variety of diseases and ail- ments [79]. Traditional Chinese medicine (TCM) and African medicinal systems also account for major portion of healthcare in their populations. Even in countries where allopathic/Western medicine is dominant, medici- nal plants still make significant contributions. Furthermore, many people are returning to herbal medicine systems due to the perception that natural medicines are often a safer alternative than allopathic drugs. Individuals are also seeking treatments for diseases, which have not yet been remedied by modern medicine. Many of the prescription drugs currently marketed for a wide variety of ailments were originally isolated from plants and/or are semi-synthetic analogues of phytochemicals. It has been estimated that approximately 25% of all prescription drugs currently in use are of plant origin [122, 194]. Furthermore, 75% of new anticancer drugs marketed between 1981 and 2006 were derived from plant compounds [122]. Traditional plant- based medicines are generally used as crude formulations (e.g., infusions, tinctures and extracts, essential oils, powders, poultices, and other herbal preparations). Modern natural product drug discovery generally focuses on isolating and characterizing the individual phytochemical compo- nents with the aim of producing an analogue with increased bioactivity/ bioavailability. Such studies have given rise to many useful drugs such as quinine (from Cinchona spp.), digoxin (from Digitalis spp.) as well as the anticancer drug paclitaxel (from Taxus brevifolia Nutt.) and vin- cristine and vinblastine (from Vinca rosea). However, the bioactivities Author Copy observed for crude extracts are often much enhanced or even entirely dif- ferent to those seen for the individual components [32, 81]. Crude plant extracts may contain hundreds, or even thousands, of different chemical constituents that interact in complex ways. Often it is not known how an extract works, even when its therapeutic benefit is well established. Thus, phytochemical and mechanistic studies of traditional medicines may be Apple Academic Press complex, and it is often difficult to assign single compound/bioactivity relationship. The genus Syzygium (Family Myrtaceae) is the largest genus of flow- ering plants globally, comprising approximately 1200–1800 species [174]. The genusFor has Non-Commercial a wide range, occurring naturally Use in subtropical and Plants of the Genus Syzygium (Myrtaceae) 37 tropical regions of Africa and Madagascar, Asia, and throughout Ocea- nia and the Pacific region. The greatest diversity occurs in Australia and Southeast Asia. It is believed that many species in this region have not yet been correctly categorized taxonomically, and it is likely that new species will be categorized in the future [174]. Most Syzygium species range from medium to large evergreen trees and shrubs, many of which have a history of usage in traditional medicinal systems. Some species have culinary uses and are commercially produced for their edible fruits (e.g., Syzygium jambos, commonly known as rose apple). These are eaten fresh or used to produce jams and preserves. Other species are used as spices and flavoring agents. For the economically most important spe- cies Syzygium aromaticum (clove), the unopened flower bud is used as a spice. This plant has also been used as traditional medicine because of its antimicrobial and anesthetic properties [25]. The antimicrobial activity of S. aromaticum is well known, and numerous studies have reported on the antibacterial [8] and antifungal [126] activities of oils and extracts from clove. Other Syzygium species from Southeast Asia (S. jambos) [113] and India (Syzygium lineare and Syzygium cumini) [50] have also been shown to have antimicrobial activity. Most information available on anti- microbial activities of Australian Syzygium species has been anecdotal, although Australian Aborigines are known to have used them as medici- nal agents [36]. This chapter summarizes recent research on the medicinal properties, phytochemistry, and therapeutic mechanisms of Syzygium species and also highlights future areas of research on the medicinal activities of Syzygium Author Copy species. 3.2 ETHNOPHARMACOLOGY Members of genus Syzygium have been used for a broad range of medici- Apple Academic Press nal purposes by traditional healers from a wide variety of ethnic and cul- tural groups (Table 3.1). The best documented of these are the species used in traditional Indian medicinal systems, particularly the Ayurveda. Ayurvedic practitioners employ various species of Syzygium for a wide variety of medicinal purposes including coughs and colds, diarrhea and For Non-Commercial Use TABLE 3.1 38 Summary of Origin, Medicinal Properties, and Phytochemical Constituents (where known) for Selected Syzygium Species Worldwide Species Common name Origin Medicinal properties Known constituents Ref. Syzygium alliiligneum Mission Beach North The fruit is mainly used Unknown. [36] Hyland satinash, onionwood, eastern as a nutritious, high anti- puddenwood Australia oxidant food. Syzygium anisatum Ringwood, anise Australia Potent broad spectrum Contains a diversity of [23, 36, (Vicfkery) Craven & Biffen myrtle, aniseed tree antibacterial activity terpenoids. Has especially 197] high levels of monoter- penoids. Essential oils produced from the leaves are high in anethole and chavicol. Bioactive Compounds of MedicinalPlants Bioactive Compoundsof Syzygium aqueum Alston Water cherry, watery Indonesia Has high antioxidant Author Copy High antioxidant capacity [105, 106, rose apple, laulau and Malay- capacity. Has antihyper- Contains relatively high 125, 200] sia glycemic effects so is levels of terpenoids and useful for the treatment of flavonoids. diabetes. Syzygium aromaticum (L.) Clove Native to Used as an analgesic and High levels of terpenoids. [47, 97, Merrill & Perry Indonesia, anodyne for toothache. Especially high in eugenol. 130] but natural- Also used as a carmina- Has a high antioxidant Apple Academic Press ized widely tive, a digestive aid and capacity. throughout as an antihelmintic. It Asia has good antimicrobial properties. Possible anti- diabetes use. For Non-Commercial Use Plants oftheGenus Species Common name Origin Medicinal properties Known constituents Ref. Syzygium australe (H.L. Brush cherry, scrub Eastern Both leaves and fruit have High antioxidant capaci- [26, 34, Wendl. Ex Link) B .Hyland cherry, creek lilly- Australia broad spectrum antibacte- ties with particularly high 75, 88, pilly, creek satinash, rial properties. Inhibits ascorbic acid levels. 152, 201] watergum anthrax. Inhibits cancer cell proliferation. Syzygium Syzygium cordatum Waterbessie, Water Southern Used to treat respiratory Phenolic compounds, [38-40, (Hochst.) berry, undoni, Africa ailments, tuberculous, triterpenoids. 188] umSwi, umJoni, and includ- stomach complaints, diar- hute ing South rhoea and diabetes. Has (Myrtaceae) Africa, antibacterial activity. Zimbabwe, Mozam- bique Author Copy Syzygium Francisii (F.M. Giant water gum, Eastern Antiseptic properties High Antioxidant capacity. [26] Bailey) L.A.S. Johnson rose satinash, Francis Australia Contains relatively high water gum levels of terpenoids and Flavonoids. Syzygium grande (Wight) Sea apple South East Antiseptic properties The flavonoid xyloside [150] Walp. Asia and the triterpenoid rham- noside have been reported in leaf extracts. Apple Academic Press Syzygium cumini (L.) Jambul, jambolan, Indian sub- Antibacterial antidiabetic High antioxidant capac- [13, 16, Skeels. jamblang jamun, Java continent (antihyperglycemic), anti- ity Rich in anthocyanins, 117, 155] plum inflammatory properties ellagic acid, isoquercetin kaemferol and myrecetin. For Non-Commercial Use 39 40 TABLE 3.1 (Continued) Species Common name Origin Medicinal properties Known