Rubiaceae

1.5.1. Rubiaceae

Rubiaceae (coffee family) is a big family of about 500 genera and 6000 species with a mostly pantropical and subtropical distribution; in East Africa 109 genera and 740 species (Lye et al.

2008). The family is recognised by simple leaves, prominent interpetiolar stipules, inferior ovaries and gamopetalous flowers. It is known for a large diversity of natural products, including iridoids, alkaloids, methylxanthines (caffeine, theobromine and theophylline) and anthranoids (Heinrich et al. 2004). Evidences from molecular phylogenies (Bremer 1996,

Razafimandimbison & Bremer 2002) suggest that the family can be divided into three

subfamilies (Cinchonoideae, Ixoroideae, and Rubioideae). The previously most commonly used malaria medicine, chloroquine, is derived from the bark of Cinchona officinalis L. and related species. The genus Cinchona belongs to tribe Cinchoneae in subfamily Cinchonoideae.

Naucleeae has been widely accepted as a separate tribe within the subfamily Cinchonoideae. We have selected to work with two species from the Naucleeae tribe: Sarcocephalus latifolius and Mitragyna rubrostipulata.

1.5.1.1. Sarcocephalus latifolius (Sm.) E.A.Bruce

Nauclea latifolia is the basionym of S. latifolius. Both names are used in the literature about this medicinal plant. However the work of Razafimandimbison and Bremer (2002) and Bridson &

Verdcourt (1988) in Flora of Tropical East Africa retain the status of Sarcocephalus as a separate genus and we follow their advice.

S. latifolius is a shrub or small tree growing in woodland savannas in tropical Africa (Fig. 3). The fruits are edible, but nowadays mainly used as fodder, even though it has been found to have high content of vitamin C and iron (Amoo & Lajide, 1999). Leaves, stem bark, roots and root bark are used as medicine to treat a wide range of ailments (Lye et al. 2008) like hernia, backache, uterine fibroids, diarrhoea, stomach ache, tuberculosis, gastrointestinal, helminths in man and animals, diabetes, hypertension, and urethritis (Okoli & Iroegbu, 2004). However the most common use is against malaria and effects are well documented (Benoit-Vical et al. 1998;

Traore et al. 2000; Asase et al. 2005; Zirihi et al. 2005; Abbah et al. 2010). The pharmacological

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activities of the plant on uncomplicated malaria are now investigated to develop an effective therapy (Abbah et al. 2010).

S. latifolius is one of the traditionally used plants that have undergone rather extensive phytochemical screening, which have revealed monoterpene, triterpene and indole alkaloids, (Shellard & Lala 1978; Hotellier et al. 1980; Abreu & Pereira 1998 and 2001; Ngnokam et al.

2003; Hideyuki et al. 2003), saponins (Okoli & Iroegbu 2004), sugar fractions in the bark (Abreu et al. 2001), and proanthocyanidins (Fakae et al. 2000). However extracts with high

Fig. 3. Sarcocephalus latifolius, drawing from Bridson & Vercourt 1988. Right: Fruit (above) and tree harvested for roots (below). Photos: T. Stangeland

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concentration of alkaloids have also demonstrated a significant genotoxicity in human cells, and it is recommended that it should be used with caution (Traore-Keita et al. 2000). An aqueous root bark extract has demonstrated neuropharmacological effect on rodents, indicating psychoactive substances (Amos et al. 2005). A recent similar study of the same extract suggests the presence of biologically active compounds with anti-nociceptive, anti-inflammatory and anti-pyretic activities that justify the use to treat malaria (Abbah et al. 2010). Since bioactivity and chemistry is so well documented for S. latifolius and the fact that it is becoming locally scarce (Tabuti 2007, Okello & Ssegawa 2007), our research focuses on germination and growing experiments for this species.

1.5.1.2. Mitragyna rubrostipulata (Schum.) Hav

We have in our recent papers (Stangeland et al. 2007, Stangeland et al. 2010) applied the name Hallea for one of our major plants studied (Hallea rubrostipulata J.-F. Leroy). However, recently this name was found to be a homonym of Hallea G. B. Mathews (Deng 2007). The genus Hallea J.-F. Leroy can therefore not be used, and Deng (2007) replaced it with a new name, viz. Fleroya Y.F. Deng. However Razafimandimbison and Bremer (2002) had some years earlier re-included Hallea J.-F. Leroy in Mitragyna Korth. This latter treatment is probably the most acceptable one.

M. rubrostipulata is a tree up to 25 m high, indigenous to East Africa (Fig. 4). It grows in wet forests from Rwanda to Ethiopia and further south to Malawi, and is common in swamp forests along Lake Victoria. In the Sango Bay area in Uganda the bark of the tree is one of the most commonly used drugs to treat malaria.

During the last decades little attention has been paid on the use and bioactivity of M.

rubrostipulata, except for one study on anti-plasmodial activity in Rwanda (Muganga et al.

2010), and a few studies on its use in Uganda (Ssegawa & Kasenene 2007a; Kamatenesi &

Oryem-Origa 2005). However from the beginning of the 1900 century the genus Mitragyna gained considerable attention after Ridley in 1897 reported the leaves and bark of Mitragyna

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speciosa Korth. as a cure for opium addiction. The leaves of M. speciosa (“Kratum”) were chewed for many years in Thailand as an opium substitute, but are now forbidden. The first alkaloid was isolated from M. speciosa by Hooper in 1907 and was later called mitragynine (Shellard 1974). Mitragynine was later found to have pain-threshold elevating and antitussative properties comparable to codeine, and no addictive properties (Macko et al. 1972). Another alkaloid found in M. speciosa, viz. 7-hydroxymitragynine was found to have a more potent antinociceptive activity than morphine (Matsumoto et al. 2004). Both antinociceptive and anti-inflammatory activity of methanol extract was demonstrated on rodents (Shaik Mossadeq et al.

2009). Presently the use of Kratum has gained considerable interest and increased use as self treatment of Opioid withdrawal (Boyer et al. 2007).

Fig. 4. Mitragyna (Hallea) rubrostipulata, drawing from Bridson & Vercourt 1988. Right:

Flowers (above) and stem harvested for bark (below). Photos: T. Stangeland

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In West Africa Mitragyna inermis (Willd.) K.Schum. is commonly used to treat malaria. Traore-Keita et al. (2000) demonstrated that total alkaloids obtained by chloroform extraction had potent antiproliferate action (counteracting the process of cell division) on two P. falciparum strains, while aqueous extract did not show significant activity, which indicate that the pharmacological activity of Rubiaceae are mostly due to alkaloids.

The first alkaloid from the bark of M. rubrostipulata: mitraphylline was isolated by Michiels &

Leroux in 1925 but the structure was not determined until 1958 by Seaton et al. (1958). Later Shellard (1978) isolated the alkaloids hirsutine, hirsuteine, rhynchophylline, isorhynchophylline, rotundifoline, isomitraphylline, rhynchophylline N-oxide and anti rotundifoline in addition to mitraphylline. All alkaloids were present in the root bark, but hirsutine and hirsuteine were not found in the leaves and stem bark. In Uganda the stem bark of M. rubrostipulata is used against malaria (Ssegawa &Kasenene 2007a) and to treat erectile dysfunction (Kamatenesi-Mugisha &

Oryem-Origa 2005). We have not found any reports on in vitro or in vivo tests on activity, and if effect can be demonstrated, we do not know what kind of compounds cause the effect. However cat’s claw (Uncaria tomentosa DC.) is a very popular and widely used medicinal plant from the Amazon used as an immunomodelatory, anti-inflammatory and anti-cancer remedy (Pilarski et al. 2007). U. tomentosa belongs to the same subfamily as the tribes Sarcocephalus and

Mitragyna: Cinchonoideae. Two of the active ingredients are common with M. rubrostipulata:

mitraphylline and isomitraphylline. Currently the standardisation of commercial formulation of cat’s claw is based on the alkaloid content, but still there is some controversy whether the effect is caused by the alkaloids. Sandoval et al. (2002) argue that anti-inflammatory and antioxidant effect must be caused by some other active principle than alkaloids, while Garcia Prado et al.

(2007) demonstrated promising antiproliferative effect of mitraphylline on human glioma and neuroblastoma cell lines, and Pilarski et al. (2007) indicate that isomitraphylline and pteropodine are the most suitable substances for standardisation of cat’s claw preparations. It is well known that the alkaloid content show large variation according to time of year of harvesting and growing conditions for different Mitragyna species (Shellard 1974) as well as for Uncaria (Pilarski et al. 2007).

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