Wild Garlic) from Southern Africa
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ETHNOPHARMACOLOGICAL AND PHYTOCHEMICAL REVIEW OF ALLIUM SPECIES (SWEET GARLIC) AND TULBAGHIA SPECIES (WILD GARLIC) FROM SOUTHERN AFRICA SL Lyantagaye Department of Molecular Biology and Biotechnology, College of Natural and Applied Sciences, University of Dar es Salaam, P.O. Box 35179, Dar es Salaam, Tanzania. E-mail: [email protected], [email protected], Phone: +255-787537030 ABSTRACT Tulbaghia (wild Garlic) is a plant genus most closely related to the genus Allium both in the family Alliaceae and is entirely indigenous to Southern Africa. Indigenous people use several species of the genus as food and medicine, and few species are commonly grown as ornamentals. Biological and pharmacological research on Tulbaghia species and their relationship with Allium sativum (sweet Garlic) are presented and critically evaluated. Informations from studies on the treatment of microbes-caused diseases as well as of cancer have been presented in ethnobotanical reports. Moreover, recent scientific studies have been performed on crude extracts for certain Tulbaghia species as reviewed in this article. This article gives a critical assessment of the literature to date and aims to show that the pharmaceutical potential of the members of the genus Tulbaghia is comparable to that of its close relative A. sativum but has been underestimated and deserves closer attention. Keywords: Allium sativum, Ethnobotany, Ethnopharmacology, Medicinal, Phytochemical, Southern Africa, Tulbaghia INTRODUCTION species of Tulbaghia have been reported in Tulbaghia (wild Garlic) is a plant genus scientific literature as ethnobotanically used belonging to the family Alliaceae and is a or phytochemically investigated. However, small plant genus of about 30 species all significant information on chemical profile indigenous to the Southern Africa region is available only for one species, Tulbaghia (Williamson 1955, Vosa 1975, Tredgold violaceae, and has been found to be rich in 1986, van Wyk and Gericke 2000, Figure 1) sulfur–containing compounds; the and is very interesting from both biological compounds in most cases account for the and chemical perspective. Some member characteristic odours and the medicinal species have been able to adopt foreign properties of both the Tulbaghia and Allium environmental conditions as they are being species. This review will focus mainly on grown in as far as Europe and America the genus Tulbaghia and its (Benham 1993). Most of its member species ethnopharmacological relationship with are closely related to Allium sativum (sweet Allium. Garlic) and hence commonly known as wild garlic. There are many chemical constituents The Alliaceae family that have been identified in the Alliaceae Alliaceae is a family of herbaceous perennial family. The strong onion or garlic smells are flowering plants, which are monocots in the found in the Tulbaghia and Allium genera, order Asparagales. The family has been while steroidal saponins are found in most widely but not universally recognized, in the of the species (Dahlgren et al. 1985). The past, the plants involved were often treated medicinal uses of the Allium plants have as belonging to the family Liliaceae. The been widely studied and recorded (Ross Angiosperm Phylogeny Group II system 2003). Only 3 of the 30 distinguished (APG II system) of 2003 recognizes the Tanz. J. Sci. Vol. 37 2011 family and places it in the order Asparagales in the clade monocots. Figure 1: A map showing countries (Southern Africa) where Tulbaghia plants are indigenous. The Alliaceae family has about 600 species Genetical relationship between the genera in 30 genera and is a widely distributed Tulbaghia and Allium family (APG 2003). The major places of The physical ends of eukaryotic distribution for the whole family are chromosomes are protected from being Mediterranean Europe, Asia, North and recognised and processed as DNA breaks by South America and Sub-Saharan Africa telomeres. Tandemly repeated short (APG 1998, APG 2003). The Sub-Saharan minisatellite motif of DNA is usually found Africa genera are Allium, Tulbaghia and in the telomeres and is called telomeric Agapanthus (Dahlgren et al. 1985). DNA repeats. Telomere repeats are Probably the most popular genus is Allium, remarkably conserved among eukaryotes, which includes several important food and sequence variation among most of the plants, including garlic (A. sativum and A. major taxonomic groups does not exceed scordoprasum), onions (Allium cepa), one or two nucleotides (Li et al. 2000). In chives (A. schoenoprasum), and leeks (A. plants this particular motif (5’-TTTAGGG- porrum). A strong "oniony" odour is 3’) was first characterised in Arabidopsis characteristic of the whole genus Allium, but thaliana (Richards and Ausubel, 1988) and not all members are equally flavorful has since been found in the majority of plant (Kourounakis and Rekka 1991). A. sativum species (Cox et al. 1993) and is now refered and Allium cepa are worldwide known for to as the Arabidopsis cap. their medicinal use (Ross 2003). However, not all plants share the typical plant telomere sequence and recently the 59 Lyantagaye – Ethnopharmacological and phytochemical review of Allium and Tulbaghia … presence of this or its variation has been sulfides, propionthiol and vinyl disulfide in used to show genetic similarity. Allium, their essential oils (Dahlgren et al. 1985). Tulbaghia and Nothoscordum (family Alliaceae) are devoid of the Arabidopsis- A. sativum and its extracts have been widely type telomeres (Fay and Chase 1996). Aloe recognized worldwide as agents for (Asphodelaceae) and Hyacinthella prevention and treatment of cardiovascular (Hyacinthaceae), both belonging to and other metabolic diseases, Asparagales, possess human/vertebrate-type atherosclerosis, hyperlipidemia, thrombosis, sequences (5’-TTAGGG-3’) at their hypertension, microbial infections, asthma, chromosome termini (Puizina et al. 2003, and diabetes (Reuter 1995, Reuter et al. Weiss and Scherthan 2002). As all these 1996). The therapeutic properties of A. genera are petaloid monocots in the sativum have been through review in the Asparagales, it suggests that an absence of book called Medicinal Plants of the World Arabidopsis-type telomeres may be (Humana) by Ross (2003). characteristic of this related group of plants (Adams et al. 2000, Weiss-Schneeweiss et The chemistry of Allium species al. 2004). The only other plant genera so far The active components of A. sativum reported without such telomeres are Cestrum include antioxidants such as organosulfur and closely related genera Vestia and Sessea compounds, free radicals scavenger (Solanaceae) (Sykorova et al. 2003). A. cepa flavonoids such as allixin, trace elements (Alliaceae) lacks both Arabidopsis-type and such as germanium (normalizer and human-type telomeres; it possesses an immunostimulant), selenium (for optimal unknown type of telomere. (Sykorova et al. function of the antioxidant enzyme 2006). However, there exist significant glutathione peroxidase), volatile oil differences between members of Allium and containing sulfur compounds, amino acids that of Tulbaghia. For example, A. sativum and other bio-active compounds (Ross has 2n = 3x = 24 and T. violacea has a non- 2003). Garlic chemistry is complex, and a bimodal karyotype (2n = 12) (Fay and number of other compounds are also Chase 1996), which is not suprising for produced in the plant by the aging process. different species. As simply stated, organosulfur compounds are organic molecules that contain the Therapeutics of Allium species element sulfur. Depending on structure, the The genus Allium has about 1250 species, presence of sulfur in an organic molecule is making it one of the largest plant genera in often indicated by a distinctive and the world (Dahlgren et al. 1985). The plants oftentimes unpleasant and ‘loud’ odour. can vary in height between 5 cm and 150 However, organosulfur compounds can also cm. The flowers form an umbel at the top of confer pleasant odour characteristics, as is a leafless stalk. A. sativum is indigenous to observed in garlic and onions. The aroma Asia and probably the most widely used and flavor molecules in garlic and onions are herb in the world (Hyams 1971), but it has derived from precursor compounds that are been grown in most of tropical and derivatives of the amino acid cysteine. subtropical region. A. sativum has linear sheathing leaves, globose umbels of white A. sativum and A. cepa (onion) both contain or reddish flowers. The bulbs are composed 1-5% dry weight of cysteine derivatives in of “cloves”, which are wrapped in a shared which the proton at sulfur in cysteine is whitish papery coat. The odour is weak replaced with an alkyl or alkenyl when the plant is intact, when damaged the substituent, and the sulfur atom is itself smell grows strong. They are perennial oxidized to the sulfoxide. The cysteine bulbous plants containing mostly sulfoxide derivatives found in onions and organosulfur compounds, such as allyl garlic are indicated in (Figure 2, Scheme 1). 60 Tanz. J. Sci. Vol. 37 2011 Onions contain propiin, isoalliin and Hornícková et al. 2010). Alliin exhibits methiin, whereas garlic contains isoalliin, considerable biological activity methiin and alliin (Ichikawam et al. 2006, (Kourounakis and Rekka 1991). O O S OH S OH O NH2 O NH2 Methiin Alliin O O S OH S OH O NH2 O NH2 Isoalliin Propiin Figure 2: Cysteine sulfoxide (organosulfur) derivatives found in onions and garlic. O O O O OH O OH O OH S OH S OH S OH O HN O HN O HN NH2 NH2 NH2 O O O !-L-Glutamyl-S-(2-propenyl)-L-cysteine (GSAC) !-L-Glutamyl-S-(trans-1-propenyl)-L-cysteine (GSPC) !-L-Glutamyl-S-methyl-L-cysteine (GSMC) !-Glutamyl transpeptidase !-Glutamyl transpeptidase !-Glutamyl transpeptidase Oxidase Oxidase Oxidase O O O S OH S OH S OH O NH2 O NH2 O NH2 (+)-S-(2-propenyl)-L-cysteine sulfoxide (Alliin) (+)-S-(trans-1-propenyl)-L-cysteine sulfoxide (Isoalliin) (+)"S-Methyl-L-cysteine sulfoxide (Methiin) Scheme 1: Biosynthetic pathway of organosulfer compounds in garlic (Ichikawam et al. 2006). The distinct flavors of garlic and onion sulfoxide derivatives are contained in the reflect varying amounts of cysteine cytoplasm of the plant cells.