Antioxidant Activity of African Medicinal Plants

Antioxidant Activity of African Medicinal Plants

21 Antioxidant Activity of African Medicinal Plants Mikhail Olugbemiro Nafiua, Musa Oyewole Salawua and Mutiu Idowu Kazeemb a Department of Biochemis...

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21 Antioxidant Activity of African Medicinal Plants Mikhail Olugbemiro Nafiua, Musa Oyewole Salawua and Mutiu Idowu Kazeemb a

Department of Biochemistry, University of Ilorin, Ilorin, Nigeria, Department of Biochemistry, Lagos State University, Ojo, Nigeria

b

21.1

Introduction

Antioxidants are powerful free radical scavengers in the body, while free radicals are highly reactive chemical substances such as superoxide, hydroxyl radical, or singlet oxygen [1] that travel around in the body and cause damage to body cells. Free radical damage is one of the most prominent causes of devastating diseases that are responsible for killing many people in the world, such as cardiovascular disease, which can manifest as heart attacks, and cancer [2]. The aging process has been linked by some researchers to free radical damage in the body [3]. Free radicals naturally occur in the body as a result of chemical reactions during normal cellular processes. They can also be formed in response to environmental factors such as excess pollution, excessive UV rays, and exposure to cigarette smoke, automobile exhaust, and pesticides. Inadequate rest or sleep, inability to manage stress responses, and unhealthy eating habits can also cause free radical damage [35]. In chronic infections and inflammation, as well as in other disorders, release of leukocytes and other phagocytic cells readily defends the organism from further injury. The cells do this by releasing free oxidant radicals, and these by-products are generally reactive oxygen species (ROS) such as superoxide anion, hydroxyl radical, nitric oxide, and hydrogen peroxide, which result from cellular redox processes [6,7]. At low or moderate concentrations, ROS exert beneficial effects on cellular responses and immune function [7,8]. At high levels, however, free radicals and oxidants generate oxidative stress, a deleterious process that can damage cell structures, including lipids, proteins, and DNA [9]. Oxidative stress plays a major role in the development of chronic and degenerative ailments such as cancer, autoimmune disorders, rheumatoid arthritis, cataracts, aging, cardiovascular, and neurodegenerative diseases [9,10].

Medicinal Plant Research in Africa. DOI: http://dx.doi.org/10.1016/B978-0-12-405927-6.00021-7 © 2013 Elsevier Inc. All rights reserved.

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Sources of Antioxidants

An array of intracellular and extracellular antioxidant mechanisms are essential to scavenge any oxidant “reactive intermediates,” which are continuously generated in almost all aerobic cells; otherwise, tissue damage occurs [11,12]. An antioxidant is any substance which, when present at low concentrations compared with those of an oxidizable substrate, significantly delays or prevents oxidation of substrate. The term “oxidizable substrate” includes almost everything found in living cells, including proteins, lipids, DNA, and carbohydrates [13]. Antioxidants are compounds that protect biological systems against the potentially harmful effects of processes or reactions that can cause excessive oxidation [14,15]. They act as free radical scavengers by preventing and repairing damage caused by ROS and, therefore, can enhance the immune defense and lower the risk of cancer and degenerative diseases [6,12]. The human body is equipped with an antioxidant defense system that deactivates these highly reactive free radicals [16]. Antioxidant enzymes (made in the body) and antioxidant molecules (found in plants) soak up all the excess energy that these free radicals have, turning them into harmless particles or waste products that we can then get rid of [3]. The adverse effects of oxidative stress on human health have become a serious issue. One solution to the problem is to supplement the diet with antioxidant compounds that are contained in natural plant sources [17]. The World Health Organization (WHO) has estimated that 80% of earth’s inhabitants rely on traditional medicine for their primary health care needs, and most of this therapy involves the use of plant extracts and their active components [18]. These natural plant antioxidants can therefore serve as a type of preventive medicine. Recent reports indicate that there is an inverse relationship between the dietary intake of antioxidant-rich foods and the incidence of human disease [19]. However, synthetic antioxidants, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), have been widely used as antioxidants in the food industry and may be responsible for liver damage and carcinogenesis [20,21]. For this reason, interest in the use of natural antioxidants has increased. Plants have been the basis of traditional medicines throughout the world for thousands of years and continue to provide new remedies to humankind; a great deal of effort has therefore focused on using available experimental techniques to identify natural antioxidants from plants.

21.3

African Medicinal Plants with Antioxidant Potential

21.3.1 Diospyros abyssinica Hiern Diospyros abyssinica (also known as kˆoforonto and baforonto) is a species of trees in the Ebenaceae family that grows in the southern part of Africa, particularly in Mali. It can also be found in Angola, Guinea, Eritrea, and Ethiopia [22].

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The trees have been used in many traditional medical systems around the world, including traditional Ayurvedic, African, and Chinese medicine. Nearly every part of these plants has been used as a medicine in some way, for example, as an astringent and to cure biliousness [22]. In Zimbabwe, a juice made from the bark and leaves of D. abyssinica combined with the root juice of Albizia lebbeck is used as a remedy for snakebites. The most frequently isolated compounds from D. abyssinica are the triterpenoids betulin, betulinic acid (1), and lupeol [23]. All of these compounds are well-known antiinflammatory compounds. This species has a significant medicinal value, as demonstrated by its use in traditional medicine (Figure 21.1). The root bark from D. abyssinica has been tested for antioxidant activity [24]. It was extracted with a series of solvents, including petroleum ether, dichloromethane, chloroform, 80% aqueous ethanol, and water (at 50 C and 100 C). It was determined that the root bark of D. abyssinica is the richest source of extracted

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Figure 21.1 Chemical structures of selected antioxidant compounds identified in African plants: betulinic acid (1); gallic acid (2); 1,2,3,4,6-pentagalloyl glucose (3); centaurin (4); centaureidin (5); momordicoside (6); p-methoxybenzoic acid (7); oleoside (8); oleuropein (9).

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compounds—36.7% of the weight of the plant material is composed of antioxidants. D. abyssinica exhibited the greatest radical scavenging activity with the 80% ethanol and methanol extracts. Thus, this plant appears to be an excellent source of antioxidants (Table 21.1) [24].

21.3.2 Pistacia lentiscus L. P. lentiscus is extensively used in folk medicine by rural populations in Algeria, Morocco, and Egypt. P. lentiscus is important because of its medicinal value. The aerial parts have traditionally been used as a stimulant, for their diuretic properties, and to treat hypertension, coughs, sore throats, eczema, stomach aches, kidney stones, and jaundice [25,26]. The reducing power and radical scavenging activity of the extracts from the leaves of P. lentiscus in solvents such as ethanol, ethyl acetate, aqueous/ethyl acetate, hexane, aqueous/hexane, chloroform, and aqueous/chloroform have been studied in vitro [28]. Using the diphenylpicryhydrazyl (DPPH) scavenging activity assay, it was found that all of the P. lentiscus extracts, except for the chloroform extract, have a high radical scavenging activity (90%), equivalent to that of the standard, BHA (89%). The ethanolic and aqueous fractions from the ethyl acetate extract have high scavenging activities, with values of 78% and 90.29%, respectively. Overall, P. lentiscus exhibited outstanding reducing power, good radical scavenging activity against DPPH and H2O2, slow inhibition of lipid peroxidation, and richness in tannins; however, it also showed a lack of flavonoids [28]. In vitro antioxidant and antimutagenic activities of two polyphenols isolated from the fruits of P. lentiscus have been investigated. These polyphenols are gallic acid (2) and 1,2,3,4,6-pentagalloyl glucose (3) [27].

21.3.3 Urtica dioica L. Stinging nettle or common nettle, U. dioica, is a herbaceous perennial flowering plant native to Europe, Asia, northern Africa, and North America, and is the bestknown member of the nettle genus Urtica. U. dioica L. (Urticaceae) leaves have been used in Libya in the form of a medicinal tea or decoction as diuretic and antidiabetic therapies and to treat stomach disorders [29]. The antioxidant capacity of this plant was evaluated using several in vitro methods such as superoxide anion scavenging (SAS) and 2,2-diphenylpicryhydrazyl methods. The SAS method determined that the antioxidant activity of U. dioica at an acidic pH was 0.013 μg/mL resorcinol equivalents (Re eq.); the DPPH method in methanolic solution determined that the antioxidant activity was 419 μg/mL. The total phenolic content was found to be 0.35 mg/l gallic acid equivalent (GAE) [64]. Concentrations of U. dioica L. extract of 50, 100, and 250 μg/mL showed 39%, 66%, and 98% inhibition, respectively, of the peroxidation of a linoleic acid emulsion. By contrast, α-tocopherol, the positive control, at 60 μg/mL, exhibited only 30% inhibition [30]. It can be concluded that U. dioica L. has powerful antioxidant activities.

Table 21.1 Hit African Medicinal Plants with Antioxidant Potential Plant and Family

Traditional Uses

Countries of the Studies

Potentially Active Compounds

Reported Activities

D. abyssinica (Ebenaceae) Pistacia lentiscus (Anacardiaceae) Urtica dioica (Urticaceae) Bidens pilosa (Asteraceae) Momordica charantia (Cucurbitaceae) Dorstenia picta (Moraceae) Eucalyptus camaldulensis (Myrtaceae) Olea europaea (Oleaceae)

Snake bite [23], astringent [22]

Mali, Guinea

Anti-inflammatory [22]

Stimulant, diuretic, hypertension [25], cough, kidney stones, jaundice [26] Diuretic, antidiabetic [29]

Algeria, Morocco, Egypt Libya

Betulinic acid [23], lupeol [24] Gallic acid, 1,2,3,4,6pentagalloyl glucose [27] Not identified

Antioxidant [30]

Anti-inflammatory, antiseptic, antidiabetic [24], anticancer [31,32] Antidiabetic [35]

Nigeria

Centaurin, centaureidin [33]

Antihypertensive [34]

Morocco, Egypt

Antioxidant [37]

Antidiabetic, hypertension [38], cough, headache analgesic [34] Antibacterial, expectorant [41], antidiarrhea [42] Dysentery, fever, piles, and fistula [45], anti-inflammatory, antibacterial, antihypertensive, antidiabetics [46] Gastroenteritis, hemorrhage, kidney disorder [57] Vaginal infection, abdominal pain [59], diarrhea, diabetes [60] Anemia, pneumonia, aphrodisiac, antimalarial [61], inflammation [62]

Cameroon

Momordicoside, methoxy benzoic acid [36] Quercitrin, 6,8-dipreny leridictyol [39] 1,8-cineole [43]

Pelargonium reniforme (Geraniaceae) Sacoglottis gabonensis (Humiriaceae) Mallotus oppositifolius (Euphorbiaceae)

Antioxidant, antimutagenic [27,28]

Tunisia

Oleuropein, oleside, ligstroside [47]

South Africa

Not identified

Antihypertensive, antioxidant, antiinflammatory, antinociceptive [40] Antimicrobial, analgesic, inflammation, antioxidant [44] Antimicrobial [48,49], gastroprotective [50], antioxidant [51,52], antiatherosclerotic [53], antiviral [54], antitumor [55,56] Antioxidant [58]

Gambia, Angola, Senegal Nigeria

Bergenin [60]

Antioxidants [60]

Not identified

Anti-inflammatory [62], antimicrobial effects [63]

Ghana, Togo

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21.3.4 Bidens pilosa Linn. B. pilosa Linn. (Asteraceae) is widely distributed in subtropical and tropical regions. It is 30100 cm in height with yellow flowers and is commonly known as “hairy beggar ticks,” “sticks tights,” and “Spanish needles.” The plant is used in various folk medicines for its anti-inflammatory, antiseptic, liver-protective, bloodpressure lowering, and hypoglycemic effects [34]. The plant has been widely used in Nigeria as a traditional medicine and as a major ingredient of an herbal tea that is believed to prevent inflammation and cancer [31,32]. Phenylpropanoid glucosides, polyacetylenes, diterpenes, flavonoids, and flavone glycosides have been identified as the bioactive components of this plant and are thought to be involved in its antioxidant activity [33]. The methanol extract of B. pilosa was shown to prevent the onset of hypertension and to reduce blood pressure in rats [34]. In addition, the fresh leaves and flowers of B. pilosa were subjected to steam distillation, and colorless and yellowish essential oils were obtained in amounts of 0.08% and 0.06% (w/w), respectively. Gas chromatographymass spectrometry analysis of these essential oils resulted in the identification of 44 compounds. Chang et al. [65] also isolated two compounds, centaurin (4) and centaureidin (5), from the butanol fraction of the plant.

21.3.5 Momordica charantia L. The bitter gourd (Momordica charantia L.) belongs to the family Cucurbitaceae and has long been used in foods and medicines [66]. The bitter gourd is known by different names, such as balsam pear and karela, and it grows in tropical and subtropical regions of India, Malaysia, China, Africa, the Middle East, the United States, and Thailand [66]. It is common in the North African countries such as Morocco and Egypt. The bitter gourd can be used to treat diabetes mellitus and appears to be a safe alternative to reduce blood glucose [35]. In the DPPH radical scavenging assay, the activity of the positive control, ascorbic acid, was the highest (200 mg/mL), followed by the leaf, the green fruit, the stem, and the ripe fruit fractions of the bitter gourd. The IC50 values were lowest in the leaf fraction (9.72 mg/mL), followed by the green fruit fraction (11.00 mg/mL), the stem fraction (17.8 mg/mL), and the ripe fruit fraction (27.6 mg/mL). In the hydroxyl radical scavenging assay, the activity of the leaf fraction was greater than that of the other fractions but lower than that of ascorbic acid. The green fruit had the highest IC50 value (119 mg/mL), followed by the leaf (167 mg/mL), the stem (267 mg/mL), and the ripe fruit (173 mg/mL) [37]. Bio-guided fractionation of the methanol extract of M. charantia dried gourds led to the isolation of 11 compounds. These include momordicoside (6) and p-methoxybenzoic acid (7) [36].

21.3.6 Dorstenia picta L. D. picta (Moraceae) is an herbaceous plant used in southern Cameroon as an antidiabetic and antihypertensive drug. Other traditional uses of the genus Dorstenia are

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against headaches and abdominal pain [38]. It has been reported that Dorstenia psilurus, Dorstenia cilianta, and Dorstenia barteri have antihypertensive, antioxidant, anti-inflammatory, and antinociceptive activity, respectively [40]. Many antioxidant compounds have been isolated from this plant. They include quercitrin, 6,8-diprenyleridictyol, bartericin A, and 6-prenylapigenin [39]. A decoction from the leaves of the D. psilurus is used to treat cough, headache, and stomach pain in Cameroon. In Panama and Mexico, D. contrajerva leaves are used to fight against fever and snake venom [34]. Aside from their medicinal uses, Dorstenia plants are also used in the preparation of food, as in the case of D. foetida, whose tubers are cooked and eaten in Oman, and D. psilurus, whose rhizomes are used as spices for the preparation of na’a poh in Cameroon [67].

21.3.7 Eucalyptus camaldulensis Dehnh. E. camaldulensis is an important ethnomedicinal plant belonging to the family Myrtaceae. It is used as a remedy for sore throat and other bacterial infections of the respiratory and urinary tracts. Essential oils of the leaves are used in the treatment of lung diseases, while the volatile oils are used as expectorants [41]. Topical ointments containing eucalyptus oil have also been used in traditional Aboriginal medicines to heal wounds and fungal infections. Eucalyptus oil obtained by steam distillation and rectification of the fresh leaves has eucalyptol (1,8-cineole) as its active ingredient, and this is responsible for its various pharmacological actions [43]. Antimicrobial activity of the methanolic extracts of E. camaldulensis has also been reported [68,69]. The tree is widely used in traditional medicine to treat a variety of disease conditions including cold, asthma, cough, diarrhea and dysentery, hemorrhage, laryngalgia, laryngitis, sore throat, spasm, trachea, and vermifuge [42]. Some studies have demonstrated that leaf extract and essential oil of Eucalyptus sp. have antifungal, repellent, antibacterial, analgesic, and anti-inflammatory activities [44]. It has been determined that essential oil of eucalyptus possesses hydroxyl radical scavenging activity greater than BHT and curcumin, which were used as positive controls in the study, and also possessed the greatest capacity to scavenge superoxide radicals [44]. Abd El-Mageed et al. [70] also determined and published the chemical composition of the essential oil from E. camaldulensis.

21.3.8 Olea europaea L. O. europaea L., belonging to the family Oleaceae, is a small evergreen tree, from 12 to 20 ft high, with hoary, rigid branches and a grayish bark. In many countries, extract of O. europaea is used in the treatment of migraines, insomnia, diarrhea, dysentery, fever, piles, and fistula [45]. O. europaea is abundantly found in Tunisia, with more than 50 different cultivars. There has been increasing interest in olive products and by-products of the olive tree, and especially the olive leaves, due to their various bioactivities. Historically, olive leaves have been used as a remedy for fever and other diseases

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such as malaria [71]. According to Tunisian folk medicine, olive leaves are recommended in a wide range of ailments, including inflammatory disorders, bacterial infections, hypertension, and diabetes, but modes of preparation and administration vary: earache is cured by using olive leaves in hot olive oil with salt [46]. Olive leaf juice, despite its irritation, is recommended for curing trachoma. When chewed, this plant organ is used to relieve tooth pain and to treat lip irritation. A decoction of the leaves, used as a liquid mouthwash, is used for treating aphthous, gingivitis, and glossitis [72,73]. Previous studies have demonstrated that olive leaves are used for their antimicrobial [48,49], gastroprotective [50], antioxidant [51,52], hypotensive [74], hypoglycemic [75], antiatherosclerotic [53], antiviral [54], antitumor [55,56], and antiinflammatory properties [76]. The pharmacological properties of olive oil, the olive fruit, and its leaves have been recognized as important components of medicine and a healthy diet because of their phenolic content [77]. Phenolic compounds are found in all parts of the olive plant, but their nature and concentration varies greatly among the various tissues. In O. europaea, oleuropein, demethyl-oleuropein, ligstroside, and oleoside (8) represent the predominant phenolic oleosides [47], whereas verbascoside [78] is the main hydroxycinnamic derivative of the olive fruit. [79] Oleuropein (9) is generally the most prominent phenolic compound in olive cultivars. Oleuropein possesses good antioxidant properties. It potently and dose dependently inhibits copper sulfate-induced oxidation of low-density lipoproteins (LDL) [80,81]. Oleuropein has the ability both to scavenge nitric oxide and to cause an increase in inducible nitric oxide synthase (iNOS) expression in the cell. A scavenging effect of oleuropein was also demonstrated with respect to hypochlorous acid (HOCl) [80].

21.3.9 Pelargonium reniforme Curt. P. reniformeA, belonging to the family Geraniaceae, is native to the coastal regions of South Africa [82]. The plant is notable for its narrow, deep-red flowers and its large, heart-shaped leaves. Along with other closely related species, the root has been used for centuries as a traditional herbal remedy in South Africa [83]. Pelargonium species are widely used by traditional healers in areas of southern Africa by Sotho, Xhosa, Khoi-San, and Zulus for its curative and palliative effects in the treatment of diarrhea, dysentery, fever, respiratory tract infections, liver complaints, wounds, gastroenteritis, hemorrhage, and kidney and bladder disorders [57,84,85]. Both the rhizome and the herb have been used for different purposes since ancient times to treat malaria, inflammation, and abdominal and uterine disorders. The root extracts have been shown to have antibacterial, antifungal, and antitubercular activities; this may justify its use by the people of South Africa in the treatment of cough and tuberculosis [86]. The leaves were used to treat wounds and abscesses and were used externally to treat neuralgia, throat infections, and a wide range of skin diseases such as

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ringworm, ulcers, and rashes [87]. In folk medicine, Pelargonium was used internally as a styptic for metrorrhagia, menorrhagia, hematuria, hemorrhoids, syphilis, and peptic and duodenal ulcers. Paracelsus described it as having cardiotonic and antidepressive activity and suggested it for leucorrhea as a mouthwash. It is commonly used for childhood ailments such as chicken pox, measles, and mumps [88]. Methanol and water extracts assessed by three established in vitro methods, namely, 2,20 -azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and ferric ion reducing power, showed that P. reniforme extract possessed strong scavenging and antioxidant activities and moderate reducing power, thus validating its traditional use in the treatment of liver diseases. Flavonoids and hydrolyzable tannins of P. reniforme showed marked antioxidant effects using a DPPH radical generating system and a luminol-dependent chemiluminescence assay [58].

21.3.10 Sacoglottis gabonensis Baill. S. gabonensis Baill. is a perennial tree that grows across Africa, from Senegal and Gambia east to the Central African Republic and south to Angola. Decoctions of S. gabonensis stem bark are used to treat illnesses such as abdominal pains, fever, gonorrhea, and diarrhea, and are sometimes used to treat hypertension and diabetes in various parts of Africa. In Senegal and Congo, a stem bark decoction is mixed with other plants and added to bath water to treat ovarian troubles, vaginal infections, and children with fever. The stem bark of this plant is also used as a palm wine additive, as it is claimed to prolong the shelf life of the wine, add potency, reduce foaming, and impart a bitter taste [89,90]. It is also reported to have aphrodisiac properties. The main active ingredient in the stem bark decoction of S. gabonensis is bergenin, an isocoumarin. The stem bark extract has been reported to have hepatoprotective properties and antilipid peroxidation activity in vivo in rats [91]. Bergenin has been reported to protect against 2,4-dinitrophenylhydrazine (DNPH)-induced hepatotoxicity and toxicity to red blood cells in rats. The stem bark extract of S. gabonensis and its main isolated compound bergenin have been reported to have antioxidant properties [59]. However, more research is needed to evaluate its potential as a lead drug. The effect of the bark extract on 2,4DNPH experimental lipid peroxidation and the side effects of 2,4-DNPH and ethanol on natural antioxidant enzymes and vitamins were studied. The bark extract, like bergenin, exerted a protective action on brain tissue, though to a lesser extent, as against oxidant 2,4-DNPH. The inhibitory effect is dependent on dose and on activity per unit weight basis. The extract appears a more powerful inhibitor than vitamins E and C [60,92]. This suggests that the pharmacologic action of the bark extract as an anticancer agent may possibly be due to the antioxidant potentials of the extract and bergenin, which is believed to be the active substance in the S. gabonensis stem bark extract.

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21.3.11 Mallotus oppositifolius Lour. M. oppositifolius is a shrub of the family Euphorbiaceae that grows in many parts of Africa. It is used in folk medicine and herbal preparations for the treatment of dysentery, worms, and malaria. It is also used traditionally for the treatment of convulsion, epilepsy, parasitic eye and kidney infections, as a diuretic and painkiller, and in treatment of paralysis, spasm, headache, and swelling. A decoction of the root is used for anemia, pneumonia, and as an aphrodisiac, and the stick is chewed for oral hygiene and teeth cleaning [61]. Anti-inflammatory [62] and antimicrobial effects [63,93] of the plant have also been reported. M. oppositifolius extracts were found to contain alkaloids, cardiac glycosides, and phenolic compounds, with higher concentrations residing in the leaves than in the roots [62,63]. Antioxidant and anti-inflammatory activities of the crude extracts in hexane and methanol were evaluated by the β-carotene linoleate model system and the carrageenan-induced rat paw edema animal model [62]. The root methanolic and ethanolic extracts showed antioxidant activity. Thin-layer chromatographic analyses of the extracts showed the presence of phenolic compounds in the crude extracts, two of which were flavonoids. The anti-inflammatory activity of the crude extracts therefore could be due to those compounds. In a recent study, the antioxidant properties of the methanolic extract of the leaves of M. oppositifolius, in comparison with BHA as a standard antioxidant, using three free radical generators, namely, hydrophilic radical generator 2,2-azobis (2-amidino propane) dihydrochloride (AAPH), hydrophobic radical generator 2,2azobis(2,4-dimethylvaleronitrile) (AMVN), and hydroxyl radical and nonspecific radical generator Fe21/ascorbate system in an in vitro, in vivo, and ex vivo model systems, were performed. In vitro study indicated that the methanolic extract of M. oppositifolius (MEMO) leaves failed to inhibit lipid peroxidation induced by AAPH, while BHA offered 55.5% inhibition [62]. In addition, while AMVNinduced lipid peroxidation was inhibited by 17.7% and 29.4% by MEMO and BHA, respectively, Fe21/ascorbate system-induced lipid peroxidation was inhibited by 57.9% and 78.9% by MEMO and BHA, respectively. Ex vivo studies showed that MEMO at 100 mg/kg body weight reduced malondialdehyde and protein carbonyl levels by 34.5% and 12.0%, respectively, compared with the control. In vivo, MEMO increased (p , 0.05) superoxide dismutase and catalase activities by 408.0% and 295.0%, respectively. Therefore, this study demonstrates that MEMO exhibits antioxidant and radical scavenging activity, as well as enhancement of enzymatic antioxidant capacity, and as such could intervene in toxicological processes mediated by free radical mechanisms [62].

21.3.12 Thonningia sanguinea Vahl. Thonningia sanguinea Vahl. (Balanophoraceae), also called “kulla” by the Hausa of Nigeria, is a plant devoid of chlorophylls with bright red-colored flowers that grows as parasite on Hevea brasiliensis (rubber tree), Phoenix dactylifera (oil palm), and Theobroma cacao (cocoa trees) [94,95]. The flowers and rhizomes of

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the plant are used in herbal medicine as vermifuge, astringent, and treatment for dysentery, diarrhea, leprosy, cutaneous infections, abscesses, dental caries, gingivitis, hemorrhoids, and fever [96]. T. sanguinea extracts have also been reported to possess antibacterial activity, including against multidrug-resistant strains [97]. The flowers of T. sanguinea are widely used in Ivory Coast in the treatment of microbial diseases, mainly the salmonellae diseases [98]. In Africa, multidrugresistant nontyphoidal salmonellae (NTS) are one of the leading causes of morbidity and high mortality in children under 5 years of age [99]. T. sanguinea is also known to possess antioxidant activity [100,101]. N’Guessan et al. [102] successfully isolated two phenolic antioxidant compounds from this plant. These are brevifolin carboxylic acid and gallic acid.

21.4

Conclusions

This review discussed medicinally significant plant species selected from Africa with high antioxidant activities when compared to synthetic antioxidants. It focuses on plants belonging to several different families from around Africa to understand their therapeutic uses and their potential antioxidant activities. Different antioxidant chemical compounds isolated from some of these plants were also discussed in order to know the active constituents responsible for the antioxidant potential of the plants. However, it is worthy of note that most scientific studies on the antioxidant potential of these medicinal plants were conducted in vitro using different methods such as DPPH radical scavenging activity and SAS assay. The results obtained from these in vitro assays may not necessarily imply that the same effect will be produced when performed in the living organism. Therefore, there is need for in vivo studies before these plants can be validated for use in medicine.

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