Cameroonian Medicinal Plants: Pharmacology and Derived Natural Products

Review Article published: 25 October 2010 doi: 10.3389/fphar.2010.00123 Cameroonian medicinal plants: pharmacology and derived natural products

Victor Kuete1,2 and Thomas Efferth 2*

1 Department of Biochemistry, Faculty of Science, University of Dschang, Dschang, Cameroon 2 Department of Pharmaceutical Biology, Institute of Pharmacy, University of Mainz, Mainz, Germany

Edited by: Many developing countries including Cameroon have mortality patterns that reflect high levels of Leslie Gunatilaka, University of Arizona, infectious diseases and the risk of death during pregnancy and childbirth, in addition to cancers, USA cardiovascular diseases and chronic respiratory diseases that account for most deaths in the Reviwed by: Apollinaire Tsopmo, Carleton developed world. Several medicinal plants are used traditionally for their treatment. In this review, University, Canada plants used in Cameroonian traditional medicine with evidence for the activities of their crude Dhammika Nanayakkara, University of extracts and/or derived products have been discussed. A considerable number of plant extracts Mississippi, USA and isolated compounds possess significant antimicrobial, anti-parasitic including antimalarial, *Correspondence: anti-proliferative, anti-inflammatory, anti-diabetes, and antioxidant effects. Most of the biologically Thomas Efferth, Department of Pharmaceutical Biology, Institute of active compounds belong to terpenoids, phenolics, and alkaloids. Terpenoids from Cameroonian Pharmacy and Biochemistry, University plants showed best activities as anti-parasitic, but rather poor antimicrobial effects. The best of Mainz, Staudinger Weg 5, 55128 antimicrobial, anti-proliferative, and antioxidant compounds were phenolics. In conclusion, many Mainz, Germany. medicinal plants traditionally used in Cameroon to treat various ailments displayed good activities e-mail: [email protected] in vitro. This explains the endeavor of Cameroonian research institutes in drug discovery from indigenous medicinal plants. However, much work is still to be done to standardize methodologies and to study the mechanisms of action of isolated natural products.

Keywords: medicinal plants, ethnopharmacology, Africa

Public health concern and diseases in Cameroon typhi infections). In the Cameroonian population, the lifetime Health care is a basic service essential in any effort to combat pov- risk of developing active tuberculosis once infected, in absence of erty, and is often promoted with public funds in Africa to achieve HIV infection, is about 10%, meanwhile this increases tenfold in this aim (Castro-Leal et al., 2000). Nevertheless, curative health HIV infected individuals (Noeske et al., 2004). Malaria remains the spending is not always well targeted to the poorest, representing leading cause of morbidity in Cameroon, and among the top five about 50.5% of Cameroonian (Edmondson, 2001). Many devel- causes of mortality. Malaria represents approximately 45–50% of oping countries including Cameroon have mortality patterns that health consultations, and 23% of admissions (Edmondson, 2001). reflect high levels of infectious diseases and the risk of death during The unsatisfactory management of all diseases throughout the pregnancy and childbirth, in addition to cancers, cardiovascular continent as well as in Cameroon, which allows partially treated diseases and chronic respiratory diseases that account for most and relapsed patients to become sequentially resistant, may play deaths in the developed world (WHO, 2009). In Cameroon, 3 out a significant role in the development of resistance for infectious of 20 patients are able to buy prescribed drugs in hospitals and one diseases (Jones et al., 2008; McGaw et al., 2008). Effective treat- out of every 1000 patients are able to see a specialist. Health care ment of diseases is challenging for various reasons, including lack activities are coordinated by the Ministry of Public Health which of accessibility and elevated expense of drugs and low adherence receives the second highest budgetary allocation per ministry each owing to toxicity of second-line drugs. It is all too likely that the year (Speak Clear Association of Cameroon, 2004). Health facilities emergence of resistance will be experienced in the future, exhaust- are either run as government services or private services managed ing the current arsenal of chemical defenses at our disposal. For this by the various churches and other private individuals. There are also purpose, new drugs are urgently needed, and research programs traditional doctors that play a great role as far as the provisions of into alternative therapeutics including medicinal plants investiga- health care services are concerned. The major diseases associated tions should be encouraged. with high degree of risk within the population include food or waterborne diseases (bacterial and protozoal diarrhea, hepatitis A Biodiversity and protected area in Cameroon and E, and typhoid fever), vector borne diseases (malaria and yellow The biodiversity of Cameroon in term of protected land area, fever), water contact diseases (schistosomiasis), respiratory diseases number of plant and some animals groups with threatened spe- (meningococcal meningitis), and animal contact diseases (rabies) cies are summarized in Table 1 and Figure 1. (Index mundi, 2008). Very often, there is a coexistence of many Cameroon has a rich biodiversity, with about 8,620 plants species infectious diseases. Ammah et al. (1999) demonstrated that high and several animal groups (EarthTrends, 2003), encountered in both proportion of patients (33%) had malaria coexisting with typhoid protected (about 8 %), and unprotected areas. About 155 plant spe- (Salmonella typhimurium, Salmonella paratyphi, and Salmonella cies are classified by the International Union for the Conservation

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Table 1 | Biodiversity and protected area in Cameroon, Sub-Saharan of Nature and Natural Resources (IUCN) as threatened species. Africa, and the World (Source: EarthTrends, 2003). Threatened species used as medicinal plants include Thecacoris annobonae Pax & K. Hoffm (Euphorbiaceae) (Cheek, 2004), Pausinystalia Cameroon Sub-Saharan World johimbe (K. Schum) (Rubiaceae) (Ngo Mpeck et al., 2004), Prunus afri- Africa cana (Hook. f.) Kalkm (Rosaceae) (Focho et al., 2009). Ancistrocladus korupensis D. W. Thomas & Gereau (Ancistrocladaceae), Carpolobia Total land areas 47,544 2,429,241 13,328,979 lutea G.Don (Polygalaceae), Dacryodes edulis (G. Don) H. J. Lam. Protected area (000 ha) (Burseraceae), Enantia chlorantha Oliv (Annonaceae), Garcinia man- Extent of protected areas by IUCN Category (000 ha), 2003 nii Oliv. (Clusiaceae), Garcinia cola Heckel (Clusiaceae), Gnetum afri- Total protected area 3,741 264,390 1,457,674 canum Welw. (Gnetaceae), Invingia gabonensis Baill. (Irvingiaceae), (Categories I–V) Massularia acuminata (G. Don) Bullock (Rubiaceae), Pentaclethra Marine and Littoral 389 − 417,970 macrophylla Benth. (Leguminosae), Baillonella toxisperma Pierre protected areasa var. obovata Aubrév. & Pellegr. (Sapotaceae), Calamus deeratus Protected areas as a 8.0% 10.9% 10.8% Mann & Wendl. (Palmae), Cola acuminata (P.Beauv.) Schoot et percent of total land area Endl. (Sterculiaceae), Eremospatha macrocarpa (Mann & Wendl.) Biosphere reserves in 2002 Wendl. (Palmae), Raphia regalis Becc. (Palmae), Raphia vinifera Number of sites 3 46 408 P.Beauv. (Palmae) and Ricinodendron heudelotti (Baill.) Pierre Total area (000 ha) 876 − 439,000 (Euphorbiaceae) (Koné, 1997). Protected zones include both land Number and status of species (3,741 ha) and marine areas (389 ha) (EarthTrends, 2003). Higher plants Ethnobotanical uses of medicinal plants in Total known species 8,260 – – Cameroon (number) Traditional healing plays an integral role in black African culture Number of threatened 155 – 5,714 as it provides primary health care needs for a large majority (about species 80%) of the population (WHO, 2002). In Cameroon, there is a rich Mammals tradition in the use of herbal medicine for the treatment of several Total known species 409 − – ailments. Unfortunately, the integration of traditional medicine (number) in the health system is not yet effective, due to its disorganization Number of threatened 40 − 1,137 (Nkongmeneck et al., 2007). However, the government strategies of species health envisage the organization of traditional medicine in order Breeding birds to provide the main trends for the development and its integration Total known species 165 − – (Anonymous, 2006). Adjanohoun et al. (1996) provided a useful (number) review of the traditional use of medicinal plants in Cameroon, Number of threatened 15 − 1,192 although much work remains to be done regarding the documen- specie tation of existing ethnobotanical knowledge. Jiofack et al. (2010) Reptiles also documented the traditional use of 289 plants species belonging Number of total 210 − – to 89 families against 220 pathologies. Sixty eight percent of the known species documented plants are used to treat more than twenty important Number of threatened 1 − 293 diseases. They are used as decoction, infusion, maceration, powder, species powder mixtures, plaster, calcinations, and squeeze in water, boil- Amphibians ing, cooking with young cock or sheep meat or groundnut paste, Number of total 171 − – direct eating, juice, fumigation, and sitz bath (Jiofack et al., 2010). known species The most recurrent diseases or disorders treated are typhoid, male Number of threatened 1 − 157 sexual disorders, malaria, gonorrhea, gastritis, rheumatism, fever, species dysentery, diarrhea, dermatitis, boils, cough, wounds, syphilis, steril- Fish ity, sexually transmitted diseases, ovarian cysts, and amoebiasis, with Number of total 138 − – more than two hundred plants being used to cure these diseases or known species disorders (Jiofack et al., 2010). Number of threatened 27 − 74 2 species Investigation of the pharmacological potential of medicinal plants of Cameroon IUCN, International Union for the Conservation of Nature and Natural Resources; Antimicrobial activity Categories I, Nature Reserves, Wilderness, Areas; Categories II, National Parks; Category III, Natural monument; Category IV, Habitat/species management area; Plants are widely used traditionally for the treatment of microbial infec- Category V, Protected landscape/seascape. tions. A review of the antimicrobial potential of Cameroon medicinal aMarine and littoral protected areas are not included in the “Total area protected” plants (Kuete, 2010a) reported more than 58 species in vitro active above; bIncludes IUCN categories I–V, marine and littoral protected areas are excluded from these totals. extracts or isolated compounds. Cut-off points for activity in term of (–): data not available. IC50-values were set to 100 μg/ml for extract and 25 μM for compounds

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Figure 1 | Portion of land area protected (A) by IUCN Category (2003) and threatened species (B) (2002–2003) in Cameroon (Source: EarthTrends, 2003). IUCN, International Union for the Conservation of Nature and Natural Resources; Categories I, nature reserves, wilderness, areas; Categories II, national parks; Category III, natural monument; Category IV, habitat/species management area; Category V, protected landscape/seascape.

(Cos et al., 2006). However, in the case of antimicrobial evaluation to bioactive compounds isolated from Cameroonian medicinal plants of extracts and compounds, determination of IC50 is not the optimal have shown that efflux by AcrAB-TolC pumps was one of the likely parameter for significance, most of the reported data being given as mechanisms of defense of Gram-negative bacteria to compounds 23 MIC values. Kuete (2010a) also set the bar as follows for extract: signif- and 47 (Kuete et al., 2010c). icant (MIC < 100 μg/ml), moderate (100 < CMI ≤ 625 μg/ml) or weak (CMI > 625 μg/ml). For compounds, this stringent endpoints criteria Antimalarial activity were: significant (MIC < 10 μg/ml), moderate (10 < MIC ≤ 100 μg/ml), In Cameroon, several plant species are used to treat malaria. A review and low or negligible (MIC > 100 μg/ml) (Kuete, 2010a). More than on traditionally used plants reported up to 217 species (Titanji et al., 50 microorganisms were found to be sensitive to such extracts and 2008). Some of these plants were screened in vitro for their activity significant activity with minimally inhibiting concentrations (MIC) against P. falciparum and more than 100 bioactive compounds were of less than 100 μg/ml (Kuete, 2010a). Some of the extracts includ- isolated (Titanji et al., 2008), most of which, however, showed only ing those from Bersama engleriana, Dorstenia angusticornis, Dorstenia low or modest antimalarial activities. In the present review, we focus barteri, Diospyros canaliculata, Diospyros crassiflora, Newbouldia laevis, only on plant extract and compounds that exhibited considerably and Ficus cordata exhibited a wide range of activity on both bacteria high activities. The proposed cut-off points for in vitro activity of and fungi (Kuete, 2010a). antimalarial extracts based on their IC50 values can be categorized as

Some of the bioactive compounds such as diospyrone (23), crassi- follows: IC50 < 0.1 μg/ml (very good); 0.1–1 μg/ml (good); 1.1–10 μg/ florone 24( ), newbouldiaquinone (25), newbouldiaquinone A (26), ml (good to moderate); 11–25 μg/ml (weak), 26–50 (very weak), laurentixanthone A (30), laurentixanthone B (31), smeathxanthone >100 μg/ml (inactive) (Willcox et al., 2004a). The following inhibi- B (32), cheffouxanthone (33), bangangxanthone A (34), globulixan- tion percentages were proposed for in vivo activity of antimalarial thone C (35), D (36) and E (37), moracin T (43), and U (44), nkolbi- extracts at a fixed dose of 250 mg/kg/day: 100–90% (very good sine (59), norerythrosuaveolide (60), were isolated and characterized activity); 90–50% (good to moderate); 50–10% (moderate to weak); for the first time from Cameroonian medicinal plants Kuete,( 2010a). 0% (inactive) (Willcox et al., 2004a). Several plant extracts from Other compounds such as plumbagin (27), lapachol (28) (found to Cameroonian medicinal plants were reported for their antimalarial be inactive in vivo in some cases), isobavachalcone (47), 4-hydrox- activities (Table 2), the most active (IC50 < 1 μg/ml) being that from ylonchocarpin (48), kanzonol C (49) exhibited interesting activities Enantia chlorantha (Boyom et al., 2009). and were suggested as potential candidates for new antimicrobial Some isolated compounds were also reported for their antimalar- drug (Kuete, 2010a). Though compound 28 is known to possess good ial activities (Table 2). An IC50 of 1.5 μM was chosen as cut-off point antimicrobial activity in vitro, it will be necessary to assess its in vivo for several compounds (Calas et al., 1997). The threshold for in vitro efficacy. However this compounds was activein vitro against intracel- chloroquine resistance has been defined as IC50 > 100 nM (Ringwald lular amastigotes of Leishmania braziliensis and inactive in vivo using et al., 1996). According to Mahmoudi et al. (2006), compounds with hamster infected model (Lima et al., 2004). Thecacoris cf. annobonae IC50 > 5 μM were considered as inactive against parasite develop-

Pax & K. Hoffm (Euphorbiaceae) exhibited significant antimicrobial ment, compounds with IC50 between 0.06 and 5 μM being active,

(MIC < 10 μg/ml) activities against Mycobacterium tuberculosis H37Rv, and values of IC50 < 0.06 μM implying the drugs to be very toward

Bacillus cereus and Pseudomonas aeruginosa (Kuete et al., 2010b). The P. falciparum. We will take into consideration up to IC50 < 20 μg/ extract from T. annobonae was reported to induce E. coli death through ml to report on the activity of antimalarial compounds isolated the inhibition of H+-ATPase-mediated proton pumping (Kuete et al., from Cameroonian medicinal plants. So far, active compounds iso- 2010b). Investigations the mode of resistance of the microorganisms lated belong to three main groups of secondary metabolites, terpe-

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Table 2 | Plants used in Cameroon to treat malaria, with evidence of their activities.

Family Speciesa Traditional treatment Plant part Bioactive (or potentially Screened activity used active) compoundsb

Acanthaceae Thomandersia Malaria, diarrhea, colitis, Bark, leaves, Not identified IC50 < 30 μg/ml reported for hensii De Wild furuncles, abscesses, pulp, sap, hexane extract from the stem and Th. Dur (LB Th syphilis, ulcers, urogenital roots bark on P. falciparum W2 0301) disorders, intestinal parasites, (Indochina I/CDC) chloroquine- debility, tiredness, edema, resistant strain (Bickii et al., rheumatism, eye 2007b) inflammations (Letouzey, 1985; Ngadjui et al., 1994).

Annonaceae Uvariopsis Malaria (Boyom et al., 2009) Bark, leaves Not identified, but plants of IC50 < 5 μg/ml reported for the congolana (De this family were reported to crude extract from the leaves and Wild) Fries contain acetogeninsc bark on P. falciparum strain W2 (37016/HNC) (Boyom et al., 2009)

Polyalthia oliveri Malaria (Boyom et al., 2009) Bark IC50 < 5 μg/ml reported for the Engl. (19416 SRF/ crude extract from the bark on P. Cam) falciparum strain W2 (Boyom et al., 2009)

Enantia Malaria (Boyom et al., 2009) Bark, leaves Not identified IC50 < 1 μg/ml reported with the chlorantha Oliv. crude extract from the leaves and (32065/SRF/Cam) bark on P. falciparum strain W2 (Boyom et al., 2009)

Apocynaceae Picralima nitida Malaria, diarrhoea, intestinal Bark, roots, Not identified IC50 < 30 μg/ml reported for the Stapf (LB Pn worms, gonorrhoea, seeds; fruits methanol and dichloromethane– 0301) inflammation (Letouzey, methanol 1:1 extracts from the 1985; Ezeamuzie et al., 1994; seeds and bark on P. falciparum Fakeye et al., 2000) W2 (Indochina I/CDC) chloroquine- resistant strain (Bickii et al., 2007b)

Euphorbiaceae Croton Malaria (Boyom et al., 2009) Bark Not identified IC50 < 10 μg/ml reported for the zambesicus crude extract from the bark on P. Muell. Arg. (8204/ falciparum strain W2 (Boyom SRFCam) et al., 2009)

Neoboutonia Malaria (Boyom et al., 2009) Bark, leaves Not identified IC50 < 10 μg/ml reported for the glabrescens Müll. crude extract from the leaves and Arg. Prain (7433/ bark on P. falciparum strain W2 SRFCam) (Boyom et al., 2009)

Guttiferae Symphonia Stomach and skin aches, Bark Gaboxanthone (38); IC50 <20 μM on P. falciparum globulifera Linn f. laxative for pregnant women, symphonin (39); globuliferin reported for compounds 38–40 (50788/HNC) general tonic, Malaria (40); guttiferone A (50) and 50 (Ngouela et al., 2006). (Aubreville, 1950; Irvine, (Ngouela et al., 2006). 1961; Ngouela et al., 2006).

Lauraceae Beilschmiedia Not reported Bark 5-Hydroxy-7,8- IC50 <5 μM on chloroquine- zenkeri Engl. dimethoxyflavone; resistant P. falciparum reported for pipyahyine; betulinic acid pipyahyine (Lenta et al., 2009) (Lenta et al., 2009)

Meliaceae Entandrophragma Malaria (Bickii et al., 2007a) Bbark 22-Hydroxyhopan-3-one; IC50 < 20 μg/ml on P. falciparum angolense 24-methylenecycloartenol W2 strain reported for Welwitsch C.D.C. (8); tricosanoic acid; compounds 8–10. The (29933/HNC) methylangolensate; dichloromethane – methanol (1:1) 7α-acetoxydihydronomilin extract of the stem bark of that

(9); 7α-obacunylacetate (10) plant exhibited IC50 of 18.8 μg/ml (Bickii et al., 2007a) (Bickii et al., 2007a)

(Continued)

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Table 2 | Continued

Family Speciesa Traditional treatment Plant part Bioactive (or potentially Screened activity used active) compoundsb

Khaya Malaria (Obih et al., 1985; Bark and Methylangolensate (1); IC50 < 20 μg/ml on P. falciparum grandifoliola Bray et al., 1990; Weenen seeds 6-methylhydroxyangolensate W2 strain reported for bark and C.D.C. (PM et al., 1990). (2); gedunin (3); catechin; seeds extracts; compounds 1–7. 098/95/HNC) 7-deacetylkhivorin (4); Compound 3 exhibited an additive 1-deacetylkhivorin (5); effect when combined with swietenolide (6); chloroquine (Bickii et al., 2000) 6-acetylswietenolide (7) (Bickii et al., 2000) Turreanthus Malaria and other fevers Bark, seeds, 16-oxolabda-8 (17), None of the active compounds

africanus (Zhou et al., 1997) leaves 12(E)-dien-15-oic acid; exhibited IC50 < 20 μg/ml on P. methyl-14, 15-epoxylabda-8 falciparum F 32, chloroquine (17), 12(E)-diene-16-oate; sensitive strain (Ngemenya et al., turreanin A (Ngemenya et al., 2006) 2006)

Moraceae Artocarpus Malaria (Boyom et al., 2009) Bark, leaves Not identified IC50 < 10 μg/ml reported for the communis J.R. & crude extract from the leaves and G. Forst (43982 bark on P. falciparum strain W2 HNC) (Boyom et al., 2009)

Dorstenia Malaria (Boyom et al., 2009) Twigs Not identified IC50 < 10 μg/ml reported with the convexa De Wild crude extract from the twigs on P. (53450 HNC) falciparum strain W2 (Boyom et al., 2009)

Zingiberaceae Aframomum Malaria (Kenmogne et al., Seeds Aulacocarpin A (11); IC50 < 20 μM on P. falciparum zambesiacum 2006) aulacocarpin B; reported for compounds 11–14 (Baker) K. Schum 3-deoxyaulacocarpin A (12); (Kenmogne et al., 2006) (37737HNY) methyl-14n,15-epoxy-3b- hydroxy-8(17),12-elabdadien- 16-oate; galanolactone; zambesiacolactone A (13); zambesiacolactone B (14); aframodial (Kenmogne et al., 2006)

Reneilmia Malaria (Tchuendem et al., Fruits Oplodiol (17); 5E,10(14)- IC50 < 5 μM reported on P. cincinnata (K. 1999) Germacradien-1β,4β-diol falciparum D6 and W2 strains for Schum.) Bak. (16); 1(10)E,5E- compounds 15–17 on P. germacradien-4β-ol (15) falciparum D6 strain (Tchuendem (Tchuendem et al., 1999) et al., 1999 aHNC or SRFK: Cameroon National herbarium code; LB, Laboratory of Botany, Yaoundé. bCompounds characterized for the first time in Cameroonian medicinal plant are underlined. cAnnonaceous acetogenins are inhibitors of complex I (NADH: ubiquinone oxidoreductase) in mitochondrial electron transport systems (Lewis et al., 1993), and NADH oxidase of plasma membranes (Morré et al., 1995), two enzymes found in Plasmodium falciparum. noids (Figure 2), phenolics (Figure 3), and alkaloids (Figure 4). (12); zambesiacolactone A (13), and B (14) (Kenmogne et al., 2006); Antimalarial terpenoids including sesqui-, di-, and triterpenoids 1(10)E,5E-germacradien-4β-ol (15); 5E,10(14)-germacradien- are the most frequently isolated compounds from Cameroonian 1β,4β-diol (16); oplodiol (17) (Tchuendem et al., 1999); IC50 < 5 μg/ plants. Several natural products were reported as being active against ml were obtained for compounds 3 (1.25 μg/ml), and 10 (2 μg/ml)

Plasmodium falciparum, with IC50 values below 20 μg/ml, including (Bickii et al., 2000, 2007a), while values below 5 μM were recorded methylangolensate (1); 6-methylhydroxyangolensate (2); gedunin for compounds 12 (4.97 μM) (Kenmogne et al., 2006), 15 (1.54 μM); (3); 7-deacetylkhivorin (4); 1-deacetylkhivorin (5); swietenolide (6); 16 (1.63 μM) and 17 (4.17 μM) (Tchuendem et al., 1999). 6-acetylswietenolide (7) (Bickii et al., 2000); 24-methylenecycloar- Phenolic compounds (Figure 3) such as gaboxanthone (38); tenol (8); 7α-acetoxydihydronomilin (9); 7α-obacunylacetate (10) symphonin (39); globuliferin (40); guttiferone A (50) (Ngouela (Bickii et al., 2007a); aulacocarpin A (11); 3-deoxyaulacocarpin A et al., 2006) also exhibited antimalarial activities when tested on

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Figure 2 | Bioactive terpenoids. Activity [(a) antimalarial, (b) anti-inflammatory, (c) antitrypanosomal]; Glc, glucosyl group; Ac, acetyl group.

P. falciparum. IC50 values below 5 μg/ml were reported with com- 2005). It is estimated that about 200 million people worldwide are pounds 38 (3.53 μM); 39 (1.29 μM); 40 (3.86 μM) and 50 (3.17 μM) currently affected by schistosomiasis, a disease caused by flatworms (Ngouela et al., 2006). Few alkaloids from Cameroonian medicinal belonging to the genus Schistosoma. The disease is usually chronic plants (Figure 4) were characterized. For example, pipyahyine (61) and debilitating, with severe consequences on the urinary tract exhibited good activity (IC50 < 5 μM) toward chloroquine-resistant where S. haematobium is the organism involved and major dam- P. falciparum (Lenta et al., 2009). age to the intestinal tract where S. mansoni, S. intercalatum or S. Studies dealing with the mechanisms of action of antimalarial japonicum are involved (Jatsa et al., 2009). In humans, Toxoplasma compounds are still limited. However, some of the extracts from infections are widespread and lead to severe diseases in individu- Cameroonian medicinal plants such as those from Annonaceae als with immature or suppressed immune system. Consequently, species were suggested to exert their antiplasmodial activity by toxoplasmosis became one of the major opportunistic infections the inhibition of vital parasitic enzymes such as cysteine proteases of the AIDS epidemic (Luft and Remington, 1992). Toxoplasmosis (Boyom et al., 2009). also affects T. gondii-negative women during pregnancy and is a serious threat for embryos. Despite the huge impact of these para- Other anti-parasitic activities sitic diseases, the drugs used for their treatment are often toxic, Parasitic trypanosomatids cause a number of important diseases, marginally effective, administered by injection only, expensive, including human African trypanosomiasis, Chagas disease, and and/or compromised by the development of resistance (Ouellette leishmaniasis. More than 60 million people living in 36 sub-Saharan et al., 2004; Croft et al., 2005). Only few researchers in Cameroon Africa countries are at risk of contracting sleeping sickness, caused focused on antitrypanosomal and antileishmanial compounds by Trypanosoma brucei gambiense and T. b. rhodesience (WHO, from medicinal plants. Available published data on traditionally 2007). It is estimated that currently 300,000–500,000 people were used medicinal plants are compiled in Table 3. Herein, similar infected in 2001, with 50,000 deaths annually (Fairlamb, 2003; cut-off points as indicated above for antimalarials have been WHO, 2007). Leishmania species cause a spectrum of disease rang- considered for activities against trypanosomal, leishmanial and ing from self-healing cutaneous lesions to life-threatening visceral schistosomal pathogens. Compounds with good antileishmanial infections, with 2 million new cases occurring annually (WHO, activities were isolated from Garcinia lucida (Clusiaceae), with IC50

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Anti-proliferative activity Screenings of medicinal plants used as anticancer drugs has provided modern medicine with effective cytotoxic pharmaceuticals. More than 60% of the approved anticancer drugs in United State of America (from 1983 to 1994) were from natural origin (Stévigny et al., 2005; Newman and Cragg, 2007). The diversity of the biosyn- thetic pathways in plants has provided a variety of lead structures that have been used in drug development. In this last decade, investigations on natural compounds have been particularly successful in the field of anticancer drug research. Early examples of anticancer agents developed from higher plants are the antileukemic alkaloids (vinblastine and vincristine), which were both obtained from the Madagascar periwinkle (Catharanthus roseus) (Voss et al., 2005). The development of the highly automated bioassay screening based on colorimetric methods that quantified the proliferation of cell culture (Mosmann, 1983) of a huge number of plants extracts have permitted to find that many plant families (Guittiferae, Rubiaceae, Apocynaceae, Euphorbiaceae, Solanaceae, etc.) exhibited a great potential of anti-proliferative activity (Hostettmann et al., 2000; Whelan and Ryan, 2003). A large number of plant extracts have shown the in vitro and in vivo antitumor activities (Hostettmann et al., 2000). In the US NCI plant screening program, a crude extract

is generally considered to have in vitro cytotoxic activity if the IC50 value following incubation between 48 and 72 h, is less than 20 μg/ ml, while it is less than 4 μg/ml for pure compounds (Boik, 2001). This cut-off point for good cytotoxic compound has also been defined as 10 μM (Brahemi et al., 2010). Despite the exceptional biodiversity of Africa, few scientific studies have been carried out in the continent regarding the anti-proliferative properties of medicinal plants. However, some Cameroonian plants and derived natural products were tested for their anti-proliferative effects. Five medicinal plants widely used in cancer treatment, Sida acuta, Sida cordifolia, Sida rhombilifolia, Urena lobata, Viscum album, were recently screened for their cytoxicity against Hep G2 hepatocarcinoma cells rather showed moderate anti-proliferative effects (Pieme et al., 2010). However, studies based on the inhibition of Crown Gall tumors revealed pronounced tumor reducing activity of extracts from the roots and leaves from Bersama engleriana (Kuete et al.,

2008). An IC50 of 27.16 μg/ml was reported for Antiaris africana

in DU-145 prostate cancer cells, while even better activity (IC50 of 13.84 μg/ml) was recorded in Hep G2 hepatocarcinoma cells (Kuete et al., 2009). One of the most active compounds isolated from Figure 3 | Bioactive phenolics [quinones (23–29), xanthones (30–42), A. africana, 3,39-dimethoxy-49-O-β-d-xylopyronosylellagic acid arylbenzofurans (43–46)]. Activity [(a) antimicrobial, (b) anti-inflammatory, (c) (58) (Figure 3) exhibited considerable anti-proliferative activities antimalarial, (d) anti-proliferative, (e) antioxidant]. [Chalcones (47–49), benzophenone (50), flavone (51–52), isoflavones (53–56), pterocarpene (57), toward HepG2 (IC50 of 3.84 μg/ml) and DU-145 (IC50 of 6.24 μg/ ellagic acid derivative (58)]. Activity [(a) antimicrobial, (b) anti-inflammatory, ml) cells (Kuete et al., 2009). Compound 28, the main constituent of (c) antimalarial, (d) anti-proliferative, (e) antioxidant]. a Cameroonian medicinal plant, Newbouldia leavis (Bignoniaceae)

was found to be very active against DU-145 cells with an IC50 of 64.59 nM (Eyong et al., 2008). Wighteone (53) and alpinumiso- values of 2.0 and 6.6 μg/ml, respectively, for dihydrochelerythrine flavone 54( ) isolated from Erythrina indica (Leguminosae) were (62) and 6-acetonyldihydrochelerythrine (63) against L. dono- reported to be cytotoxic (effective dose of 0.78 and 4.13 μg/ml, vani (Fotie et al., 2007). Significant antitrypanosomal activities respectively) when tested against KB nasopharyngeal cancer cells were also reported for stigmastane derivatives, vernoguinosterol (Nkengfack et al., 2001). Globulixanthones A (41) and B (42) (21) and vernoguinoside (22) (Figure 2) isolated from Vernonia isolated for the first time in the Cameroonian medicinal plant, guineensis (Asteraceae), against bloodstream trypomastigotes of Symphonia globulifera L. f. (Clusiaceae), showed good anti-prolif-

Trypanosoma brucei rhodesiense with IC50 values ranging from 3 erative activities against human KB cells, with IC50 values of 2.15 to 5 μg/ml (Tchinda et al., 2002). and 1.78 μg/ml, respectively (Nkengfack et al., 2002). Compound

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Figure 4 | Bioactive alkaloids. Activity [(a) antimicrobial, (b) antimalarial, (c) antileishmanial].

47 isolated from Dorstenia barteri (Ngameni et al., 2007) and D. can be an important source of safer drugs for the treatment of pain turbinata (Ngameni et al., 2009) was cytotoxic toward a wide spec- and inflammation. Several medicinal plants and derived products trum of tumor cell lines, including ovarian carcinoma OVCAR-8 were screened for their anti-inflammatory and analgesic proper- cells, prostate carcinoma PC3 cells, breast carcinoma MCF-7 cells, ties (Table 4). Bark extract as well as terpenoids from Combretum and lung carcinoma A549 cells (Jing et al., 2010). Compound 47 molle (Combretaceae), β-d-glucopyranosyl 2α,3β,6β-trihydroxy- significantly ablated Akt phosphorylation at Ser-473 and Akt kinase 23-galloylolean-12-en-28-oate (18); combregenin (19); arjungenin activity in cells, which subsequently led to inhibition of Akt down- (20) (Figure 2) showed good activities against carrageenan-induced stream substrates and evoked significant levels the mitochondrial paw edema in rat (Ponou et al., 2008). A naphthoquinone, 2-acetyl- pathway of apoptosis (Jing et al., 2010). Nishimura et al. (2007) 7-methoxynaphthol[2,3-b]furan-4,9-quinone (29), isolated from demonstrated that compound 47 induced apoptotic cell death with the anti-inflammatory crude extract of Millettia versicolor inhib- caspase-3 and -9 activation and Bax upregulation in neuroblastoma ited 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced acute cell lines. Compound 47 inhibited MMP-2 secretion from U87 ear edema and phospholipase A2 (PLA2) acute mouse paw edema glioblastoma cells (Ngameni et al., 2007). Compounds 48 and 49 (Fotsing et al., 2003). Isoflavones, griffonianone D (55) (Figure 3) also isolated from Dorstenia turbinata (Moraceae), inhibited the isolated from Millettia griffoniana (Yankep et al., 2003), warangalone matrix metalloproteinase (MMP)-2 secretion from brain tumor- (56) isolated from the bark of Erythrina addisoniae (Talla et al., derived glioblastoma cells (Ngameni et al., 2006). 2003), and erycristagallin (57) isolated from the root of Erythrina mildbraedii (Njamen et al., 2003), showed marked effectiveness as

Anti-inflammatory and analgesic activities an anti-inflammatory on PLA2-induced paw edema and on TPA- Pain is one common health problem with substantial socioeconomic induced ear edema in mice (Njamen et al., 2003; Talla et al., 2003). impact because of its high incidence. It is a symptom of many dis- Flavonoids sigmoidin A (51) and B (52) (Figure 3) isolated from eases and it is estimated that 80–100% of the population experience Erithrina sigmoidea, and compound 57 were also effective against back pain at least once in the life time (Jain et al., 2002). The treat- TPA-induced ear edema (Njamen et al., 2003, 2004). ment of pain requires analgesics including inflammatory products. Hence, most of the non-steroidal anti-inflammatory agents also Anti-diabetic activity have analgesic activity. The inhibition of prostaglandin E2 (PGE2) Diabetes mellitus is a group of metabolic disorders with one com- and nitric oxide (NO) production has been proposed as a potential mon manifestation, hyperglycemia (WHO, 1980, 1985). Chronic therapy for different inflammatory disorders (Nowakowska, 2007). hyperglycemia causes damage to eyes, kidneys, nerves, heart, and Although, many analgesics and anti-inflammatory agents are present blood vessels (Mayfield, 1998). It is caused by inherited and/or on the market, modern drug therapy is associated with some adverse acquired deficiency in insulin production of the pancreas, or by effects like gastrointestinal irritation (Jain et al., 2002; Osadebe and unresponsiveness toward insulin. It results either from inadequate Okoye, 2003), fluid retention, bronchospasm, and prolongation of secretion of hormone insulin, an inadequate response of target cells bleeding time. Therefore, it is necessary to search for new drugs to insulin, or a combination of these factors (Malviya et al., 2010). with less adverse effects. Medicinal plants have been used for the Diabetes is projected to become one of the world’s main disablers development of new drugs and continue to play an invaluable role and killers within the next 25 years (Malviya et al., 2010). The man- for the progress of drug discovery (Raza et al., 2001). Plant extracts agement of diabetes is a global problem and a successful treatment

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Table 3 | Plants used in Cameroon to treat some parasitic infections with evidence of their activities.

Family Speciesa Traditional treatment Plant part Bioactive (or potentially Screened activityC used active) compoundsb Annonaceae Polyalthia Rheumatic pains (Surville, Not Polyveoline; 3-O-acetyl Antitrypanosomal activity: weak

p o ly s i n suaveolens Engl. 1955) specified greenwayodendrin; ; activity for polyveoline (IC50: & Diels (1227/ greenwayodendrin-3-one 32 μM); 3-O-acetyl

SRFK) (Ngantchou et al., 2010) greenwayodendrin (IC50: 54 μM); mixture of polysin and

greenwayodendrin-3-one (IC50: 18 μM) against T. brucei (Ngantchou et al., 2010) Asteraceae Vernonia Anthelmintic, anti-poison, Leaves Vernoguinosterol (21); Antitrypanosomal activity: guineensis Benth. malaria, jaundice (Iwu, 1993) vernoguinoside (22) (Tchinda significant for compounds22 (BUD 301) et al., 2002) and 23 against four strains of bloodstream trypomastigotes T.

b. rhodesiense with IC50 values in the range 3–5 mg/ml (Tchinda et al., 2002) Guttiferae Garcinia lucida Gastric infections, anti-poison Bark Dihydrochelerythrine (62); Antileishmanial activity: Vesque (5768/ (Nyemba et al., 1990) 6-acetonyldihydrochelerythrine Significant activity for HNC) (63); lucidamine A (Fotie et al., compounds 62 and 63 and 2007) moderate for lucidamine A against L. donovani. Also, 100% Inhibition of promastigote at 100 μg/ml were reported for all the above compounds (Fotie et al., 2007) Meliaceae Turraeanthus Asthma, stomachache, Aerial parts, Turraeanthin C; sesamin Antitoxoplamal activity: africanus (Welw. intestinal worms, and roots (Vardamides et al., 2008) Moderate activity for ex C.D.C.) Pellegr inflammatory diseases turraeanthin C and low activity (8233/HNC) (Ekwalla and Tongo, 2003) for crude bark extract and sasamin. Inhibition of parasite growth at 10 μg/ml was found to be 55% for turraeanthin C, 20% for sesamin and 40% for crude extract (Vardamides et al., 2008) Verbenaceae Clerodendrum Epilepsy, headache, intestinal Not Not identified but, flavonoids, Antischistosomal activity: umbellatum Poir helminthiasis, irregular specified saponins, saponosides, 100 % reduction rate reported (7405/HNC) menstruation, infective tannins, and triterpenes were for mice infected with S. dermatitis, asthma, detected in the leaves mansoni when treated with metaphysical powers, aqueous extract (Jatsa et al., 160 mg/kg body weight of whitlow, vulvovaginitis 2009) aqueous leaves extract (Jatsa (Adjanohoun et al., 1996; Jatsa et al., 2009) et al., 2009) aHNC or SRFK: Cameroon National herbarium code; BUD, Herbarium of the Botany Department of the University of Dschang, Cameroon). bCompounds characterized for the first time in Cameroonian medicinal plant are underlined. cScreened activity: Leishmania donovani (L. donovani); Schistosoma mansoni (S. mansoni); Toxoplasma gondii (T. gondii); Trypanosoma brucei rhodesiense (T. b. rhodesiense); Trypanosoma brucei (T. brucei). has not yet been discovered. The total number of persons affected The annual mortality linked to diabetes worldwide is estimated globally is projected to rise from 246 million in 2007 to 380 mil- to be above one million. In Cameroon, the prevalence of diabetes lion in 2025, if prevention measures will not be scaled up (Bennett, increased from 2% in 1998 (in a study supported by the World 2007). In Africa, the number of diabetic patients in 2006 was Diabetes Foundation, WDF) to 5% in 2003 and 6.5% in 2007 (in 10.4 million, and it is expected to increase to 18.7 million in 2025. another WDF study, Walgate, 2008). Medicinal plants have been

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Table 4 | Plants used in Cameroon as anti-inflammatory and analgesic agents, with evidence of their activities. Table 4 | Continued

Family Speciesa Traditional treatment Plant part Bioactive (or Screened activityc Family Speciesa Traditional treatment Plant part Bioactive (or Screened activityc used potentially active) used potentially active) compoundsb compoundsb

Acanthaceae Acanthus Cough, hypertension, skin Leaves Not identified Leave extract showed analgesic Guttiferae Allanblackia Amoebic dysentery, diarrhea, Bark Betulinic acid, lupeol, Crude extract from the bark, montanus infection, boil, witches, and anti-inflammatory properties monticola indigestion, pulmonary and amangostin lupeol, betulinic acid, and (Nees) T. dysmenorrhoea, pain, epilepsy, and the proposed mechanism Staner L.C. infections, skin diseases, (Nguemfo et al., 2009) a-mangostin inhibited paw Anderson miscarriages, heart troubles, was the inhibition of the (61168/HNC) headache, inflammation, and carrageenan-induced edema rat (1652/ rheumatic pain, syphilis (Burkill, prostaglandins pathway at generalized pain (Raponda- (Nguemfo et al., 2007, 2009) SRF61CAM) 1985; Adjanohoun et al., 1996; 200 mg/kg in rats. Also, this Waker and Sillans, 1961) Babu et al., 2001; Noumi and extract at 200 mg/kg body weight Leguminosae Erythrina Dysentery, asthma, venereal Bark Warangalone (56) (Talla Bark extract and compound 56 Fozi, 2003; Igoli et al., 2005; in rats reduced carrageenan- addisoniae diseases, boils, and leprosy et al., 2003) showed an anti-inflammatory on Nana et al., 2008) induced edema, and formalin- Hutchinson & (Talla et al., 2003) the PLA2-induced paw edema and induced pain (Asongalem et al., Dalziel (41617/ 12-O-tetradecanoylphorbol 2004). HNC) 13-acetate-induced ear edema in Anacardiaceae Sclerocarya Boils and blood circulation Bark Not identified Bark extract inhibited albumin- mice (Talla et al., 2003) birrea (A. Rich.) problems, rheumatism, induced paw edema (Ojewole, Erythrina Dysentery, stomach pains, Bark, Erycristagallin (57) Root bark extract inhibited the Hochst (7770/ infectious diseases, 2004), Formalin- or Freund’s mildbraedii venereal diseases, asthma, roots (Njamen et al., 2003) carrageenan-induced mouse paw HNC) inflammation (Mojeremane and adjuvant (CFA)-carrageenan-, Harms (50452/ female sterility, ulcers, boils whilst compound 57 inhibited the Tshwenyane, 2004; Fotio et al., histamine, or serotonin-induced HNC) and various types of PLA -induced mouse paw edema 2009) paw edema (Fotio et al., 2009) in 2 inflammations (Oliver-Bever, and mouse ear edema induced by rats 1986) 2-O-tetradecanoylphorbol Caesalpiniaceae Erythrophleum Anti-poison, dermatitis, Bark Not identified Extract from the bark and 13-acetate (Njamen et al., 2003) suaveolens, infectious disease, convulsion, fractions at 19.2 μg/ml showed Erythrina Female infertility, stomach pain, Bark Sigmoidin A (51) and B Compound 51 inhibited Guillemin & inflammation due to snake bite, inhibition of carrageenin-induced sigmoidea Hua and gonorrhea (Giner-Larza (52) (Njamen et al., PLA -induced paw edema in Perrottet cardiac problems, headaches, paw edema in rats; Hexane 2 et al., 2001) 2004) mice, while both compounds 51 (HN001AD) migraines edema, rheumatism, fraction inhibited the and 52 were found to be effective asthma (Dalziel, 1937; 5-lipoxygenase activity (Dongmo 12-O-tetradecanoylphorbol Bouquet, 1969; Leiderer, 1982; et al., 2001) 13-acetate-induced ear edema Neuwinger, 1998) (Njamen et al., 2004) Combretaceae Combretum Fever, abdominal pains, Bark β-d-glucopyranosyl 2α,3 Bark extract, compounds 18–20

molle R.Br. ex convulsion, worm infections, β,6β-trihydroxy-23- showed good activity against Millettia Intestine parasitosis, Not 2-acetyl-7- CH2Cl2 fraction from methanol G.Don (6518/ AIDS (Bessong et al., 2004) galloylolean-12-en-28- carrageenan-induced paw edema versicolor rheumatism, pain, infertility specified methoxynaphthol[2,3-b] crude bark extract inhibited SRF/CAM) oate (18); combregenin in rat (Ponou et al., 2008) Welw. (32315/ (Adjanohoun et al., 1988; furan-4,9-quinone (29) carrageenan-induced paw edema (19); arjungenin (20), HNC) Bouquet, 1969) (Fotsing et al., 2003) and TPA-induced acute ear edema arjunglucoside I, in mouse as well as compound 29 combreglucoside (Ponou (Fotsing et al., 2003) et al., 2008) Millettia Boils, insects bits, Bark, griffonianone D (55) Extract of the root bark and Crassulaceae Kalanchoe Earache, smallpox, headache, Not Not identified n-Butanol fraction inhibited griffoniana Baill. inflammatory affections like roots (Yankep et al., 2003) compound 55 showed anti- crenata Andr. inflammation, pain, asthma, specified carrageenani-, histamine-, (32315/SRF/ pneumonia, and asthma, inflammatory effects via inhibition

(50103/YA/HNC) palpitation, convulsion, general serotonin-, and formalin-induced HNC) infertility, amenorrhea, of PLA2-induced mouse paw debility (Dimo et al., 2006) paw edema in rats (Dimo et al., menopausal disorders edema and TPA-induced acute 2006) (Sandberg and Cronlund, 1977) mouse ear edema (Yankep et al., Euphorbiaceae Bridelia Abdominal pain, contortion, Bark, Not identified Crude bark extract showed 2003) scleroneura arthritis, inflammation (Watt roots peripheral and central analgesic Solanaceae Solanum Fever, wounds, tooth decay, Leaves Not identified Crude extract from the leaves (42088/HNC) and Breyer-Brandwijk, 1962; and anti-inflammatory activity torvum Swartz. haemostatic properties, pain, inhibits both acetic acid- and Théophile et al., 2006) against acute inflammation (21103/HNC) anti-inflammation (Henty, 1973; pressure-induced pain at 300 mg/ processes in rats (Théophile et al., Ndebia et al., 2007) kg body weight of rats, and also 2006) anti-inflammatory activity on Euphorbiaceae Uapaca Fever, inflammation, pain, skin Not Not identified Bark crude extract showed carrageenan-induced paw edema guineensis diseases, and sexual specified analgesic activity, and inhibited (Ndebia et al., 2007 (41501/HNC) dysfunction (Vivien and Faure, carrageenan-induced 1996) inflammation in rats (Nkeh- aHNC or SRFK: Cameroon National herbarium code. b Chungag et al., 2009) Compounds characterized for the first time in Cameroonian medicinal plant are underlined. c Screened activity: TPA (2-O-tetradecanoylphorbol 13-acetate); PLA2 (phospholipase A2). (Continued)

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Table 4 | Plants used in Cameroon as anti-inflammatory and analgesic agents, with evidence of their activities. Table 4 | Continued

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reported to be useful in diabetes worldwide and have empirically a considerable number showing good activities (Agbor et al., been used as anti-diabetic and anti-hyperlipidemic remedies. Anti- 2007). Many of them exhibited high inhibition percentages on hyperglycemic effects of these plants were attributed to their ability the basis of Folin, Ferric reducing antioxidant power (FRAP), to restore the function of pancreatic tissues by increasing insulin and DPPH (1,1-diphenyl-2-picrylhydrazyl) assays. Plants with output, inhibiting the intestinal absorption of glucose, or enhancing good activities included Alchornea cordifolia (Euphorbiaceae), metabolism of insulin-dependent processes. Several plant prepara- Dacryodes edulis (Burseraceae), Ocimum basilicum (Lamiaceae), tions were traditionally used in Cameroon to treat diabetes. Some Harungana madagascariensis (Hypericaceae), Cylicodiscus gabun- of them were screened for their bioactivity, but most of the studies ensis (Mimosaceae), Coleus coprosifolius (Lamiaceae) (Agbor et al., were not pursued until the isolation of active principles. Plants 2007). Arylbenzofurans isolated from the bark of Morus mesozygia with hypoglycaemic activities include Anacardium occidentale, (Moraceae), moracin T (43), moracin U (44), moracin S (45); Sclerocarya birrea, Ageratum conyzoides, Ceiba pentandra, Kalanchoe moracin R (46) also showed strong DPPH scavenging capability crenata, Bridelia ndellensis, Irvingia gabonensis, Bersama engleriana with IC50 values of 4.12, 5.06, 6.08, and 7.17 μg/ml, respectively and Morinda lucida (Table 5). (Kapche et al., 2009). The activity of the crude extract of this plant

was also reported as significant (IC50: 5.92 μg/ml), by means of Antioxidant activities the DPPH scavenging assay (Kapche et al., 2009). The common link between oxidants and inflammatory reactions, infections, cancer, and other disorders has been well established Other activities (Mongelli et al., 1997; Wang et al., 1999). However, this may not Other studies involving Cameroon medicinal plants include their really be of therapeutic relevance, but more of a preventive medi- action on human fertility and enzymatic activities. However, few cine. In chronic infections and inflammation as well as in other studies have focused on these activities, explaining the scarcity of disorders, release of leukocytes and other phagocytic cells readily published data. defends the organism from further injury. The cells do this by Some plants with positive effects on the reproductive system releasing free oxidant radicals, and these by-products are gener- based on studies using experimental rats have been reported. They ally reactive oxygen species (ROS) such as super oxide anion, include Aloe buettneri (Liliaceae), Justicia insularis and Dicliptera hydroxyl radical, nitric oxide, and hydrogen peroxide that result verticillata (Acanthaceae) and Hibiscus macranthus (Malvaceae), from cellular redox processes (Ames et al., 1993; Mongelli et al., locally used to regulate the menstrual cycle and to treat dys- 1997). At low or moderate concentrations, ROS exert beneficial menorrhea or infertility in women (Telefo et al., 1998); Basella effects on cellular responses and immune function. At high levels, alba (Basellaceae) (Moundipa et al., 2005), and Mondia whitei however, free radicals and oxidants generate oxidative stress, a (Periplocaceae) traditionally claimed to increase libido (Watcho deleterious process that can damage cell structures, including et al., 2001). lipids, proteins, and DNA (Pham-Huy et al., 2008). Oxidative Some compounds from Cameroonian plants were investigated stress plays a major role in the development of chronic and for the ability to interfere with the activity of some enzymes such degenerative ailments such as cancer, autoimmune disorders, as xanthine oxidase, phosphodiesterase I, or prolyl endopeptidase. rheumatoid arthritis, cataract, aging, cardiovascular, and neu- Xanthine oxidase catalyzes the oxidative hydroxylation of hypox- rodegenerative diseases (Willcox et al., 2004b; Pham-Huy et al., anthine or xanthine using oxygen as a cofactor, and the result- •− 2008). Antioxidants act as free radical scavengers by prevent- ing end products are superoxide anion (O2 ) and uric acid. The ing and repairing damages caused by ROS and, therefore, can inhibitors of xanthine oxidase enzyme can prevent the generation enhance the immune defense and lower the risk of cancer and of excess superoxide anions (Chung et al., 1997). Phosphodiesterase degenerative diseases (Ames et al., 1993; Pham-Huy et al., 2008). I successively hydrolyzes 5′-mononucleotides from 3′-hydroxyl- In recent years, there is an increasing interest in finding antioxi- terminated ribo- and deoxyribo-oligonucleotides. The enzyme has dant phytochemicals, because they can inhibit the propagation of been widely utilized as a tool for structural and sequential studies free radical reactions, and thereby protect the human body from of nucleic acids. The 5′-nucleotide phosphodiesterase isozyme-V diseases (Terao and Piskula, 1997). Several medicinal plants of test is useful in detecting liver metastatis in breast, gastrointestinal, Cameroon were screened for their antioxidant properties and a lung, and various other forms of cancers (Lei-Injo et al., 1980). number of bioactive compounds was isolated (Table 6). Omisore Prolyl endopeptidase catalyzes the hydrolysis of peptide bonds at et al. (2005) considered the cut-off point for antioxidant activ- the l-proline carboxy terminal and, thus, plays an important role in ity as 50 μg/ml. Samples with IC50 > 50 μg/ml were classified as the biological regulation of proline-containing neuropeptides and being moderately active, while samples with IC50 < 50 μg/ml were peptide hormones, which are recognized to be involved in learning judged as having high antioxidant capacity. In the present paper, and memory (Szeltner et al., 2000). The stilbene glycosides isolated samples will be considered to have high or significant antioxidant from Boswellia papyrifera (Del.) Hochst (Burseraceae), trans-4′,5‑ capacity with IC50 < 50 μg/ml (extract) or IC50 < 10 μg/ml (com- dihydroxy-3-methoxystilbene-5-O-{α-l-rhamnopyranosyl-(1-2)- pounds), moderate antioxidant capacity with 50 < IC50 < 100 μg/ [α-l-rhamnopyranosyl-(1-6)]-β-d-glucopyranoside and trans-4′, ml (extract) or 10 < IC50 < 20 μg/ml (compounds) and low anti- 5-dihydroxy-3-methoxystilbene-5-O-[α-l-rhamnopyranosyl- oxidant capacity with IC50 > 100 μg/ml (extract) or IC50 > 20 μg/ (1-6)]-β-d-glucopyranoside exhibited significant inhibition of ml (compounds). Extracts from 42 medicinal plants of Cameroon phosphodiesterase I and xanthine oxidase (Atta-ur-Rahman used for the treatment of anemia, diabetes, AIDS, malaria, and et al., 2005). Triterpenes such as 3-α-acetoxy-27-hydroxylup- obesity were recently screened for antioxidant properties, with 20(29)-en-24-oic acid, 11-keto-β-boswellic acid, β-elemonic

Frontiers in Pharmacology | Ethnopharmacology October 2010 | Volume 1 | Article 123 | 12 Kuete and Efferth Cameroonian medicinal plants al., ) Kamanyi Kamanyi Njike et Njike al., 2009 al., al., 1998; 1998; al., et ï Ojewole, 2003; 2003; Ojewole, ) ) in rats in ) ), acting directly on on directly acting ), Nyuna al., 2010 al., ) al., 2009 al., ) al., 2008 al., Kamtchouing et Kamtchouing al., 2008 al., ) al., 2005 al., Ndifossap et Ndifossap Dzeufiet et Dzeufiet b ) al., 2006 al., Kamgang et Kamgang et Sokeng ) al., 2007 al., al., 2007; Gondwe et Gondwe 2007; al., ) Dzeufiet et Dzeufiet al., 1994 al., Screened activity Screened throughactivity anti-diabetes showed extract Leaves and STZ of action diabetogenic the against role protective ( rats in effects hypoglycemic et Sokeng in hypoglycemic exert to reported been have extracts Bark ( treatments chronic and acute following rats et Dimo ( cells insulin-secreting anti-hyperglycemic and hypoglycemic showed extract Leaves ( rats diabetic STZ-induced in activities diabetic STZ-induced in hyperglycemia reduced extract Roots ( rats possess to found was plant whole the of extract Ethanol lowering by rats normal in effect hypoglycemic significant by effect anti-hyperglycemic and levels glucose blood in levels normal at glycemia maintaining and lowering ( rats diabetic of fractions and extracts dichloromethane and acetate Ethyl 2 type in levels glucose blood lowered significantly bark the ( rats diabetic diabetes on effect modulatory showed extract Seeds ( dyslipidemia induced ( properties hypoglycemic showed extract Leaves 2005 both in effects hypoglycemic potent showed extract Root ( mice diabetic alloxan-induced and normoglycemic et al., ) Kamgang et Kamgang al., 2008 al., ) Kuete et Kuete Bioactive (or potentially potentially (or Bioactive compounds active) identified Not identified Not identified Not terpenoids, but identified Not polysaccharides, tannins, and flavonoids saponins, from identified were alkaloids ( leaves the 2008 identified Not identified Not flavonoids, but identified Not saponins, triterpenes, phenols, were anthraquinones and plan the of parts all in detected ( identified Not Not identified identified Not Whole Whole plant fruits, Bark, leaves, roots Plant part part Plant used Leaves Leaves, roots bark, Bark, leaves, roots Whole plant Not specified Leaves, bark, Stem roots Not specified ) ) al., al.,

al., al., al., al.,

al., 1994 al., al., 2008 al., Watt and Watt al., 1996; 1996; al.,

) Addae- Ngondi et Ngondi Kamanyi et Kamanyi al., 1998 al., Kamgang et Kamgang al., 1999; Ngounou et Ngounou 1999; al.,

) ra, 1989; Tsabang et Tsabang 1989; ra, é ) ) Noumi et Noumi al., 2007 al., ) Kamtchouing et Kamtchouing al., 2008 al., al., 2002 al., Lavergne and V and Lavergne al., 2005 al., Watcho et Watcho ) ) Traditional treatment Traditional ( mellitus Diabetes rectitis, gangrenous dysentery, diarrhea, Diabetes, ( eyes sore ulcers, disorders, stomach fevers, et Gelfand 1966; Bryant, 1962; Breyer-Brandwijk, et Dieye 1985; to due bleeding diabetes, disease, skin fever, Cough, carbuncle, eczema, furuncle, wounds, external ( headaches 2001 dizziness, headache, hypertension, diabetes, Diuretic, ulcer, peptic fever, trouble, mental constipation, ( leprosy rheumatism, Tchakonang, and Noumi 2000; Dibakto, and Noumi 2000; et Ueda 2001; ( diabetes Inflammatory diseases, ( diabetes and diarrhea, rheumatism, fever, et Onunkwo 1985; Achenbach, and Mensah et Sokeng disorders, hepatic and gastrointestinal Gonorrhea, ( analgesis diabetes, infection, wounds 2005 infertility, male diseases, infectious spasms, Cancer, ( diabetes necessarily not diuresis of cases adult Uncontrolled body general to linked but diabetes with associated ( weight of loss rapid and weakness

L. (Aubry (Aubry L. Gurke Gurke a Species Anacardium occidentale (41935/HNC) birrea Sclerocarya Hochst] Rich.) [(A. (7770/HNC) Ageratum conyzoides pentandra Ceiba Gaertner (L) (43623/HNC) crenata Kalanchoe (50103/ (WEKC) YA/HNC) ndellensis Bridelia (9676/HNC) Beille Irvingia gabonensis ex Lecomte Baill. O’Rorke) (28054/HNC) Bersama engleriana lucida Morinda Benth (19050/SFR/Cam) (24725/HNC) 5 | Plants used in Cameroon to treat diabetes, with evidence of their activities. their of evidence with diabetes, treat to Cameroon in used Plants | 5 Screened activity:(STZ). streptozotocin HNC or SRFK: Cameroon National herbarium code. a b Table Family Anacardiaceae Asteraceae Bombacaceae Crassulaceae Euphorbiaceae Irvingiaceae Melianthaceae Rubiaceae

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Table 6 | Plants used in Cameroon with evidence of their as antioxidant activities.

Family Speciesa Traditional treatment Plant part Bioactive (or potentially Screened activityc used active) compoundsb Ebenaceae Diospyros Epilepsy, paralysis, Leaves 11-O-p- DPPH scavenging activity: sanza-minika A. convulsions, spasm, pains hydroxybenzoylnorbergenin; significant for 4-O- Chevalier (9649/ (Burkill, 1985) 4-O-(30-methylgalloyl) galloylnorbergenin, moderate for SRFCam) norbergenin; 4-O- norbergenin, 11-O-p- syringoylnorbergenin; Hydroxybenzoylnorbergenin, norbergenin; 4-O- 4-O-(30-Methylgalloyl)norbergenin galloylnorbergenin; quercitol and 4-O-Syringoylnorbergenin (Tangmouo et al., 2009) (Tangmouo et al., 2009) Guttiferae Garcinia Dressing for wounds Sap Bangangxanthone A; DPPH scavenging activity: polyantha Oliv (Bouquet, 1969) bangangxanthone B; bangangxanthone A isolated from (1337/SRF/Cam) 2-hydroxy-1,7- the bark showed the best activity

dimethoxyxanthone; with an IC50 = 87.0 μM while the 1,5-dihydroxyxanthone standard value for BHA was

(Lannang et al., 2005) IC50 = 42.0 μM (Lannang et al., 2005) Garcinia afzelii Bacterial infections, dental Leaves; Afzeliixanthones A; DPPH scavenging activity: Engl. caries (Adu-Tutu et al., flowers afzeliixanthones B (Waffo Significant for the crude extract and 1979; Waffo et al., 2006) et al., 2006) moderate for Afzelii xanthones A and B (Waffo et al., 2006)

Hypericaceae Harungana Diarrhea, dysentery, Not Harunmadagascarins A and DPPH scavenging activity: IC50 of madagascariensis indigestion, poor specified Harunmadagascarins B, 60.97; 64.76 were recorded with Lam. (32358/ pancreatic function harunganol B and harungin harunmadagascarin and harunganol HNC) (Berhaut, 1975; Prajapati anthrone (Kouam et al., 2005) B respectively (Kouam et al., 2005) et al., 2003) Meliaceae Carapa grandiflora Arthritis, general fatigue, Seeds Quercitrin (Omisore et al., DPPH scavenging activity: low for sprsgue skin diseases and as 2005) quercetin (Omisore et al., 2005) febrifuge (Ayafor et al., 1994) Mimosaceae Entada rheedii Jaundice (Nzowa et al., Seeds Rheediinoside A; rheediinoside ABTS·+ scavenging activity: Spreng (19966/ 2010) B (Nzowa et al., 2010) moderate for rheediinoside B; low SRI/CAM) for rheediinoside A; DPPH scavenging activity: low activity for rheediinoside A and rheediinoside B (Nzowa et al., 2010) Moraceae Dorstenia Malaria (Boyom et al., Twigs Bartericins A; stigmasterol; DPPH scavenging activity: low convexa De Wild 2009) isobavachalcone (Omisore bartericin A and isobavachalcone (53450 HNC) et al., 2005) and stigmasterol (Omisore et al., 2005) Dorstenia barteri Snakebite, rheumatic, Whole Bartericins A, and B; DPPH scavenging activity: Bureau (44016/ infectious diseases, plant stigmasterol; isobavachalcone; significant for twigs extract HNC) arthritis (Tsopmo et al., 4-hydroxylonchocarpin (Omisore et al., 2005) 1999) (Omisore et al., 2005) Dorstenia mannii Rheumatism, stomach Leaves Dorsmanin F; 6,8- DPPH scavenging activity: low for Hook. f. (2135/ disorders (Bouquet, 1969) diprenyleridictyol (Omisore 6,8-diprenyleriodictyol, and HNC) et al., 2005) dosrmanin F (Omisore et al., 2005) Morus mesozygia Arthritis, rheumatism, Bark Moracin R (46); moracin S (45); DPPH scavenging activity: Stapf. (4228/ malnutrition, debility, moracin T (43); moracin U (44) significant for bark crude extract, SRFK) pain-killers, stomach (Kapche et al., 2009) compounds 43–46 (Kapche et al., disorders, wound 2009) infections, gastroenteritis, peptic ulcer, infectious diseases (Burkill, 1985; Noumi and Dibakto, 2002) (Continued)

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Table 6 | Continued Family Speciesa Traditional treatment Plant part Bioactive (or potentially Screened activityc used active) compoundsb Piperaceae Piper umbellatum Poisoning, pitting edema, Whole Piperumbellactams A; DPPH scavenging activity: Linn (6516/SRF/ fetal malpresentation, plant piperumbellactams B; Moderate activity reported for CAM) filariasis, rheumatism, piperumbellactams C; piperumbellactams A and low hemorrhoids, N-p-coumaroyl tyramine activities for piperumbellactams B; dysmenorrheal, general (Tabopda et al., 2008) C; N-p-coumaroyl tyramine pains (Tabopda et al., (Tabopda et al., 2008) 2008) aHNC or SRFK: Cameroon National herbarium code. bCompounds characterized for the first time in Cameroonian medicinal plant are underlined. CScreened activity: DPPH or 1,1-diphenyl-2-picryl hydrazyl radical assay (evaluates the ability of antioxidants to scavenge free radicals; Hydrogen-donating ability is an index of the primary antioxidants; these antioxidants donate hydrogen to free radicals, leading to non-toxic species and therefore to inhibition of the propagation phase of lipid oxidation [Lugasi et al., 1998]); ABTS·+: 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium radical cation; BHA: 3-t-butyl-4-hydroxya- nisole; Significant activity (IC50 < 50 μg/ml), moderate activity (50 < IC50 < 100 μg/ml), low activity (IC50 > 100 μg/ml). acid, 3 α-acetoxy-11‑keto-β-boswellic acid, and β-boswellic acid to standardize methods and cut-off points for describing their also exhibited prolyl endopeptidase inhibitory activities (Atta-ur- bioactivities. Other recommendations include parallel screenings Rahman et al., 2005). by using cytotoxicity tests to preclude non-specific cytotoxicity from being interpreted as efficient following in vitro screening. Conclusion The elucidation of the mechanisms of action of biologically active The present review presents an overview of medicinal plants extracts and compounds should be strengthened and given prior- research in Cameroon and is intended to serve as scientific base- ity in future investigations as already shown for natural products line information for the documented plants as well as a starting from other parts of the world (Kong et al., 2009; Youns et al., 2010; point for future studies. The paper draws attention on some active Konkimalla and Efferth, 2010). metabolites and plant extracts, with the potential for new drugs or improved plant medicines. The review inevitably shows the richness Acknowledgments of the Cameroon flora as medicinal resource and demonstrates the Authors are grateful to Dr. H.M. Poumale (Faculty of Science, effectiveness of numerous traditionally used plants. Presently, there University of Yaoundé I) for his support. Victor Kuete is also thank- is an urgent necessity for standardization of plant-derived drugs, ful to the Deutscher Akademische Austausch Dienst (DAAD) for the as their use is still empirical. There is also an urgent requirement postdoctoral fellowship at the University of Mainz, Germany.

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