Asteraceae (formerly Compositae) Bidens pilosa L.

B. pilosa (common names: hairy beggarticks, cobbler’s pegs, farmer’s friend, stick-tights,

Review of African Medicinal and Food Plants 53

pitch-forks, burr marigold) occurs widely in the tropical and subtropical areas of the world, where an infusion of the plant is trad- itionally used as an antidote for venomous insects and food poisoning. The flowers are administered for pulmonary diseases, and the leaf is used for the treatment of haemor- rhoids and liver and nasopharyngeal afflic- tions (Burkill, 1985; Abarjo et al., 2004).

Pharmacological studies on the plant dem- onstrated its anti-inflammatory, antihyper- tensive, anti-ulcerogenic, hepatoprotective, immunosuppressive, anti-leukaemic, antimal- arial and antimicrobial properties, while spec- troscopic analyses of the butanol fraction of the ethanol extract of the whole plant revealed the presence of heptanyl-2-O-β xylofuranosyl- (1→6)-β-glucopyranoside and eight phenolic compounds, namely, quercetin 3-O-rabinobi- oside, quercetin-3-O-rutinoside, chlorogenic acid, 3,4-di-O-caffeoylquinic acid, 3,5-di-O- caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, jacein and centaurein (Chiang et al., 2004; Deba et al., 2008).

Evaluation of the chemopreventive activ- ities of crude and fractionated extracts of the plant showed that the ethyl acetate and bu- tanolic fractions partitioned from the ethanolic extract exhibited significant free radical scav- enging activity (IC₅₀ = 14–17 μg/ml) compar- able to that of α-tocopherol (Chiang et  al., 2004). Analysis of the essential oils from the leaves and flowers by GC-MS revealed the presence of 44 components, with β-caryophyl- lene and τ-cadinene being the main compounds in the leaves and flowers, respectively. With the DPPH assay, the essential oils from the leaves and flowers, with IC₅₀ values of 47.5 and 49.7 μg/ml, respectively, were superior in antioxidant properties to the aqueous ex- tracts tested; all of the extracts and essential oils seemed to inhibit the oxidation of linoleic acid in the β-carotene bleaching assay (Deba et al., 2008).

In a further study of the antioxidant properties, Cortés-Rojas et al. (2012) reported that the leaf/flower extracts of B. pilosa had a higher antioxidant activity (IC₅₀ 35.35 μg/ml) than the stem extract, which had the least anti- oxidant activity (IC₅₀ 117.2 μg/ml); the anti- oxidant activity was directly correlated with the total flavonoid (TFC) and total polyphenol

(TPC) contents. The highest antioxidant activ- ity was obtained by dynamic maceration, and this was also statistically different from the antioxidant activity presented by other extract- ive methods. Using the DPPH and ABTS rad- ical scavenging tests and the FRAP assay, Wu et al. (2013) demonstrated that the ethyl acet- ate extract of B. pilosa var. radiata Sch. Bip. had higher antioxidant activity than other extracts and also a remarkable antiproliferative effect against different tumour cell lines; these ac- tivities were highly correlated with TPC and TFC, respectively, and the active ingredients were identified as 5,7,4′-trihydroxy-3,3′-di- methylflavonol.

Chromolaena odorata (L.) R. King & H. Robinson

C. odorata (formerly Eupatorium odoratum L. and E. conyzoides Vahl.) has the common names of Armstrong’s weed, baby tea, bitter bush, butterfly weed, Christmas bush, chromolaena, devil weed, eupatorium, Jack-in-the-bush, kingweed, paraffinbush, paraffinweed, Siam weed, turpentine weed and triffid weed. It is a diffuse, scrambling shrub that occurs mainly as a weed of plantation crops and pastures of southern Asia and western Africa. It is also known as ‘Elizabeth’, ‘Independence leaf’ and ‘Awolowo’ among the Igbos of south- eastern Nigeria. The leaves are widely used across West African countries as a vegetable for soup preparation.

The plant has been demonstrated to exhibit a dose-dependent ability to scavenge nitric oxide radicals in vitro in a way similar to the standard antioxidant phenolic compound, quercetin (Alisi and Onyeze, 2008), and the phenolic compounds isolated from the plant have been shown to protect cultured skin cells from oxidative damage (Phan et al., 2001). Owoyele et al (2008) associated the observed analgesic, antipyretic and anti-inflamatory activities of the plant to the antioxidant fla- vonoids present.

Galinsoga parviflora Cav.

G. parviflora, commonly called potato weed, gallant-soldiers and small flowered galin- soga, is native to Mexico and South America

54 S.E. Atawodi et al.

but has become naturalized in Africa and also occurs widely as a weed in different parts of the world. It is traditionally used in the treatment of dermatitis in some countries (Derwin´ska et al., 2006).

Extracts and fractions of the plant have a dose-dependent free radical scavenging abil- ity against DPPH and superoxide radicals as well as inhibitory effects on linoleic acid per- oxidation in a manner comparable to that of gallic acid (Bazylko et al., 2012). Derwin´ska et al. (2006) studied the antioxidant activity of water-methanol (50:50) extracts of G. parviflora that were fractionated successively by SPE (solid-phase extraction) columns with water, 20% methanol, 50% methanol, 70% methanol and pure methanol. Using DPPH, xanthine oxidase and linoleic acid peroxidation assays, they showed that the 50% and 20% methanolic fractions, which were rich in flavonoids, had significant antioxidant effects compared with the 70% methanol and pure methanol fractions.

The flavonoids detected in G. parviflora include patulitrin, quercimeritrin, quercitaget- rin and caffeoyl derivatives (Bazyllko et  al., 2012). The flavanones galinsoside A and B, 7,3′,4′-trihydroxyflavone and 3,5,7,3′,4-pen- tahydroxyflavanone have also been iso- lated from an ethyl acetate-soluble fraction of G. parviflora; these two compounds have been shown to possess significant and moder- ate antioxidant and urease inhibitory activ- ity, respectively (Ferheen et al., 2009).

Tridax procumbens L.

T. procumbens, commonly called Tridax daisy is a herb that is widely distributed in the trop- ics, where a cold infusion of the whole plant is taken orally as a traditional treatment of fever or applied as a wash for the treatment of eye infections; the decoction is prescribed for treatment of typhoid fever. The species is also used in the treatment of coughs, asthma, epi- lepsy and diarrhoea (Mann et al., 2003).

An in vitro antioxidant assay utilizing the DPPH radical scavenging assay showed that the ethanolic extract of the plant scavenged free radicals at a rate of 96.7% at concentra- tion of 250 μg/ml – more than the ascorbic (94.81%) and gallic acid (92.92%) standards; it also had a relatively high reducing potential

as measured by the reduction of potassium ferricyanide measured at 900 nm (absorbance 0.89) compared with the gallic acid standard (absorbance 0.99), suggesting that the plant has redox properties that allow it to act as a reducing agent, hydrogen donor or oxygen quencher. The total phenolic content of the extract, at 12 mg/g GAE, showed a good cor- relation with the antioxidant activity of the plant (Habila et al., 2010).

In another study, the effect of the chloro- form insoluble fraction of an ethanolic extract of T. procumbens was assessed against d-galac- tosamine/lipopolysaccharide (d-GalN/LPS)- induced hepatitis in rats. The results showed a marked normalization of the activities of enzymic antioxidants such as SOD, CAT, GPx, glutathione S-transferase and the levels of non-enzymic antioxidants (GSH, vitamins C and E), and of malondialdehyde (MDA), which had been distorted by administration of d-GalN/LPS. This suggests that the plant is very effective in alleviating the d-GalN/ LPS-induced oxidative stress and, hence, has antioxidant properties (Ravikumar et al., 2005).

Vernonia amygdalina Del.

Vernonia amygdalina Del., popularly known as bitter leaf, is a 2–5 m tall shrub with petiolate green leaves of about 6 mm diameter. The leaves are characteristically bitter but this can be abated by boiling them or by soaking in several changes of clean water. The stem and root divested of the bark are used as chewing sticks in Nigeria. More importantly, the leaves are a very popular soup vegetable and have even been reported to be consumed by tribes in some parts of Nigeria (Abosi and Raseroka, 2003). Pharmacological studies have shown that the leaf extract has both hypoglycaemic and hypolipidaemic properties in experimen- tal animals and so could be used in managing diabetes mellitus (Ojiako and Nwanjo, 2006).

3.2.8 Bignoniaceae