Journal of Ethnopharmacology ∎ (∎∎∎∎) ∎∎∎–∎∎∎

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Journal of Ethnopharmacology journal homepage: www.elsevier.com/locate/jep

Medicinal plants used as excipients in the history in Ghanaian herbal medicine Sara Holm Freiesleben a, Jens Soelberg a,b, Anna K Jäger a,n a b

Department of Drug Design and Pharmacology, Universitetsparken 2, 2100 Copenhagen, Denmark Museum of Natural Medicine, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark

art ic l e i nf o

a b s t r a c t

Article history: Received 14 January 2015 Received in revised form 1 March 2015 Accepted 3 March 2015

Ethnopharmacological relevance: The present study was carried out to investigate the traditional use, pharmacology and active compounds of four plants commonly used as excipients in herbal medicine in Ghana. Materials and methods: A comprehensive literature search was conducted to gain knowledge about the traditional use, pharmacology and active compounds of the four plant excipients. The broth dilution antibacterial assay and the DPPH radical scavenging antioxidant assay were used to evaluate the antibacterial and antioxidant activity of the plants, respectively. Ethanol, warm water and cold water extracts were prepared from the dried seeds/fruits of Aframomum melegueta, Piper guineense, Xylopia aethiopica and Monodora myristica, and tested in the assays. Results: A. melegueta and P. guineense seemed to act as pharmacoenhancers, since they have been shown to inhibit specific CYP-enzymes. A. melegueta could act as an antioxidant to preserve herbal preparations. None of the plant excipients had antibacterial activity against the bacteria tested in this study. Compounds with an aromatic or pungent smell had been identified in all the plant excipients. An explanation for the use of the plants as excipients could rely on their taste properties. Conclusion: The present study suggests that there may be more than one simple explanation for the use of these four plants as excipients. Plausible explanations have been proven to be: (1) a way to increase the effect of the medicine, (2) a way to make the medicine more palatable or (3) a way to preserve the activity of the medicinal preparation over time. & 2015 Published by Elsevier Ireland Ltd.

Keywords: Plant excipients Antioxidant Aframomum melegueta Piper guineense Xylopia aethiopica Monodora myristica

1. Introduction It has been described how plant medicine in Ghana is administered together with other herbal ingredients (Abbiw, 1990; Schumacher, 1827; Soelberg et al., 2015). These ingredients include Aframomum melegueta, Piper guineense, Xylopia aethiopica and Monodora myristica (Abbiw, 1990). In a comprehensive research of historical and contemporary medicinal plant uses in Ghana, which included interviews with local traditional doctors and herbalists, respondents explained the use of plant excipients in four different ways: (1) as a way to increase the effect of the medicine, (2) as a way to make the medicine more palatable, (3) as a way to preserve the activity of the medicinal preparation over time or (4) as a way to increase the susceptibility of the body to the medicine (Soelberg et al., 2015).

n

Corresponding author. Tel.: þ 45 35336339; fax: þ45 35336041. E-mail address: [email protected] (A. Jäger).

The present study aimed to find an explanation for the use of these herbal ingredients as excipients in herbal medicine, as part of a larger research collaboration, which aims to examine historical and contemporary medicinal plants in Ghana (Soelberg et al., 2015). This was achieved by investigating the traditional use, pharmacology and active compounds of the four plant excipients. Furthermore the plants were tested for antimicrobial and antioxidant activity.

2. Literature review In the following section each of the plants A. melegueta, P. guineense, X. aethiopica and M. myristica are described, and their traditional uses and known chemical constituents are accounted. The databases EMBASE, PubMed and SciFinder were used as well as books such as the comprehensive survey of economically important plants grown in West Tropical Africa “Useful plants of West Tropical Africa” revised by Burkill (1985, 1997, 2000).

http://dx.doi.org/10.1016/j.jep.2015.03.005 0378-8741/& 2015 Published by Elsevier Ireland Ltd.

Please cite this article as: Freiesleben, S.H., et al., Medicinal plants used as excipients in the history in Ghanaian herbal medicine. Journal of Ethnopharmacology (2015), http://dx.doi.org/10.1016/j.jep.2015.03.005i

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Fig. 1. Seeds of (A) Aframomum melegueta, K. Schum., (B) Piper guineense, Schumach., (C) Xylopia aethiopica, A. Rich. and (D) Monodora myristica Dunal.

2.1. Botanical description and use as spices in Europe of the four plant excipients A. melegueta K. Schum. is a species in the family Zingiberaceae (Burkill, 2000) (Fig. 1). It is an herbaceous plant with leafy stems that grow to 1½ m with pink or white inflorescences at the base. Seeds from this plant are also known as Grains of paradise, Alligator pepper, Melegueta pepper, Guinea grains or Guinea pepper (Burkill, 2000). The plant is native to West Africa where the seeds are commonly used as a spice and as a general medicinal panacea (“wonder drug”) (Abbiw, 1990; Burkill, 2000). Earlier, the spice was also commercially traded in Europe, but it was later replaced by black pepper (Piper nigrum) when imports from India became common (Ekanem et al., 2007). P. guineense Schumach. is a species in the family Piperaceae (Burkill, 1997) (Fig. 1). The plant is a climber, which can grow to 10 m or more in length. The plant has black berries or peppercorns. The peppercorns are also called West African black pepper, Ashanti pepper, Benin pepper, Guinea cubebs or bush pepper (Burkill, 1997). X. aethiopica A. Rich. is a species in the family Annonaceae (Burkill, 1985; Obiri and Osafo, 2013) (Fig. 1). The plant is a tropical evergreen tree that can grow as high as 20 m (Burkill, 1985; Obiri and Osafo, 2013). It has short prop roots and smooth gray bark (Burkill, 1985). It is largely found in West, Central and Southern Africa (Somova et al., 2001). The most important part of this plant is the fruits, which are commonly used as a spice and are also known as African pepper, Guinea pepper or Ethiopian pepper (Burkill, 1985; Obiri and Osafo, 2013). M. myristica Dunal is a species in the family Annonaceae (Burkill, 1985) (Fig. 1). It is an edible plant that grows wild in evergreen West African forests (Ekeanyanwu and Etienajirhevwe, 2012), and it grows as high as 35 m (Burkill, 1985). The seeds are usually embedded in a white sweet smelling pulp (Burkill, 1985; Ekeanyanwu and Etienajirhevwe, 2012). The seeds are aromatic

and are used in food resembling the taste of nutmeg. The seeds are also known as African nutmeg, false nutmeg, calabash nutmeg and calabar nutmeg (Burkill, 1985). 2.2. Traditional uses of the four plant excipients In Ghana seeds/fruits of A. melegueta, P. guineense, X. aethiopica and M. myristica are used as spices for flavoring food, but they are also used in medicine especially as an excipient to many other medicines (Abbiw, 1990; Adetutu et al., 2011; Agbonon et al., 2010; Asase et al., 2012; Burkill, 1985, 1997, 2000; Schumacher, 1827; Udoh, 1999). In the 19th century A. melegueta was described as an ingredient in herbal mixtures, often used along with lemon juice together with various other plants. These other plants include: macerated root bark of Senna occidentalis (L.) Link. made into an ointment for ringworm; macerated root of Clausena anisata (Willd.) Hook.f. ex Benth. smeared over the face for facial swellings; macerated root of Lantana camara L. rubbed on the whole body in case of snake bites; crushed leafs of Cissus quadrangularis L. rubbed into the whole body to treat an illness called Anasarea (a kind of dropsy) (Schumacher, 1827). Dropsy is also treated with other mixtures containing A. melegueta; seeds are finely ground together with the root of Ipomoea mauritiana Jacq. and mixed with water for drinking and rubbed over the whole body; seeds are crushed along with Phyllanthus amarus Schumach. and Thonn. and rubbed over the whole body (Schumacher, 1827). Other mixtures of A. melegueta are: seeds are finely grated along with root bark of Zanthoxylum zanthoxyloides (Lam.) Zepern. and Timler. and rubbed on the painful place in gout-pains; seeds are pounded with leaves of Solanum americanum Mill. and used as an ointment for rheumatic pains; seeds are chewed together with leaves of Byrsocarpus coccineus Schumach. and applied to a poisonous snakebite; seeds in a decoction together with leaves

Please cite this article as: Freiesleben, S.H., et al., Medicinal plants used as excipients in the history in Ghanaian herbal medicine. Journal of Ethnopharmacology (2015), http://dx.doi.org/10.1016/j.jep.2015.03.005i

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of Vernonia colorata (Willd.) Drake. are used for drinking when the blood flux (dysentery) is not too serious (Schumacher, 1827). Many of these traditional uses from the 19th century of A. melegueta, as an excipient in herbal mixtures, are still in use today (Soelberg et al., 2015). Leaves and stem bark of A. melegueta are mixed with Erythrophleum ivorense, Anopyxis klaineana, Cocos nucifera, Turraeanthus africanus, Alstonia boonei and the root of Annona muricata and the mixture smeared on the body for use against malaria (Asase et al., 2012). P. guineense is a component in the herbal medicine called Niprisan, which are used for sickle cell anemia. Niprisan is prepared from seeds of P. guineense, flower buds of Eugenia caryophyllata, stem of Pterocarpus osun, leaves of Sorghum bicolor and “trona” (Obodozie et al., 2010). The spicy preparation called Yaji used in soup as an aphrodisiac is prepared from fruits of P. guineense, the rhizome of Zingiber officinale, flower buds of Eugenia aromatica, seeds of Pargia biglobosa and fruits of Solanum sp. (Ibrahim et al., 2010). A powdered mixture of plant products used by some Nigerian traditional medical practitioners for treatment of epilepsy is prepared from dried fruits of P. guineense, Sacroblottis gabonensis, Elaeis guineensis and Musa paradisiaca (Abila et al., 1993). Fruits of X. aethiopica are used in different mixtures to treat hypertension. The fruits are mixed with seeds of Sida acuta; leaves of Tapinanthus species; seeds of Syzygium aromaticum and Zingiber officinale rhizome (Gbolade, 2012). Seeds of M. myristica are used as an aromatic and stimulating addition to medicines (Burkill, 1985).

2.3. Pharmacological activities of the four plant excipients The four plant excipients, A. melegueta, P. guineense, X. aethiopica and M. myristica, have been tested for various pharmacological activities. Pharmacological activities of seeds of A. melegueta reported in the literature are: analgesic (Umukoro and Ashorobi, 2007b), repellant (Ukeh et al., 2009), gastro-protective (Rafatullah et al., 1995), central nervous system depressant activity (Umukoro and Ashorobi, 2005b), sexual stimulant (Kamtchouing et al., 2002; Mbongue et al., 2012), antibacterial (Doherty et al., 2010; Konning et al., 2004; Sonibare et al., 2011), antifungal (Konning et al., 2004), anti-estrogenic (El-Halawany et al., 2011), reducing cell proliferation and cell growth of tumor cells (Gismondi et al., 2013), antioxidant (Adefegha and Oboh, 2012a; Kazeem et al., 2012), weight gain reduction (Inegbenebor et al., 2009; Sugita et al., 2013; Suzuki et al., 2009), efflux pump inhibition in mycobacteria (Groblacher et al., 2012), antimycobacterial (Galal, 1996) antidiabetic (Ilic et al., 2010), inhibition of CYP3A4, 3A5 and 3A7 (Agbonon et al., 2010), anti-hypertensive (Lawal et al., 2007) and antidiarrheal (Umukoro and Ashorobi, 2005a). Pharmacological activities of fruits of P. guineense reported in the literature are: anticonvulsive (Abila et al., 1993), antifungal (Konning et al., 2004), antioxidant (Adefegha and Oboh, 2012b, c; Agbor et al., 2007), mosquito-repellant (Adewoyin et al., 2006), increase of penile erection and ejaculatory latency (Kamtchouing et al., 2002), inhibition of CYP3A4, CYP3A5 and CYP3A7 (Agbonon et al., 2010), inhibition of α-amylase and α-glucosidase, SNPinduced lipid peroxidation (Adefegha and Oboh, 2012c) and depolarization of neuromuscular blocking action (Udoh et al., 1999). Pharmacological activities of fruit essential oil are: antibacterial (Oyedeji et al., 2005), sedative when inhaled (Tankam and Ito, 2013) and insecticidal activity against Sitophilus zeamais (Francois et al., 2009). The herbal medicine Niprisan, in which P. guineense is a component, has been shown to exhibit antisickling activity (Obodozie et al., 2010).

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Pharmacological activities of fruits of X. aethiopica reported in the literature are: antimicrobial (Ikeyi et al., 2013; Sonibare et al., 2011), anthelminthic (Ekeanyanwu and Etienajirhevwe, 2012), antifungal (Konning et al., 2004), antioxidant (Adefegha and Oboh, 2012b), anti-anaphylactic, anti-inflammatory (Obiri and Osafo, 2013), antiparasitic (Fall et al., 2003), analgesic (Woode et al., 2012), mosquito-repellant (Adewoyin et al., 2006), antiplasmodial (Fekam Boyom et al., 2003), hypotensive and diuretic (Somova et al., 2001). Pharmacological activities of seeds of M. myristica reported in the literature are: anthelminthic (Ekeanyanwu and Etienajirhevwe, 2012; Okpekon et al., 2004), antibacterial (Mbosso et al., 2010) and active against mites (Okpekon et al., 2004). The stem exhibits moderate antiplasmodial activity (Lekana-Douki et al., 2011). 2.4. Chemical constituents and their pharmacological activities in the four plant excipients The seeds of A. melegueta have been tested for chemical constituents in a phytochemical screening and the presence of alkaloids and saponins have been determined, as well as the absence of tannins, cyanogenetic glycosides, cardiac glycosides and anthraquinones (Sonibare et al., 2011). Some active compounds of the seeds are hydrophenolalkanones such as paradol, shogaol, zingerone and gingerol (Galal, 1996; Umukoro and Ashorobi, 2007a). These compounds account for the pungent and peppery taste of A. melegueta seeds (Iwami et al., 2011; Sugita et al., 2013; Vriens et al., 2008). The structures of these compounds are shown in Fig. 2. Paradol has been shown to have thermogenesis activity, increasing the temperature of brown adipose tissue in rats (Iwami et al., 2011). This effect of paradol is similar to the effect of other pungent compounds such as capsaicin in chili, allyl isothiocyanate in mustard, cinnamaldehyde in cinnamon, piperine in pepper and gingerols and shogaols in ginger (Iwami et al., 2011). It is therefore reasonable to suggest that the three other pungent compounds in A. melegueta, shogaol, zingerone and gingerol could have this thermogenesis activity as well. P. guineense has been tested for its chemical constituents in several studies. The fruits contain alkaloids including piperine, which is the major alkaloid responsible for its pungent smell (Adosraku et al., 2013). The alkaloids wisanine and wisanidine have been isolated from the roots of P. guineense (Addae-Mensah et al., 1976, 1977). Wisanine possess sedative, tranquillizing and some anticonvulsant properties (Ayitey-Smith and Addae-Mensah, 1977) as well as an antipsychotic effect (Ayitey-Smith and Addae-Mensah, 1983). The content of the essential oils of different parts of the plant have been investigated (Amvam Zollo et al., 1998; Francois et al., 2009; Oyedeji et al., 2005; Tankam and Ito, 2013). The monoterpene limonene has been identified in fruitleaf- and liana/stem essential oils (Francois et al., 2009; Oyedeji et al., 2005). The phenylpropanoid myristicin has been identified in fruit- and leaf essential oils (Amvam Zollo et al., 1998; Oyedeji et al., 2005). Furthermore the fruit essential oil contained a phenolic derivative 3,5-dimethoxytoluene (Tankam and Ito, 2013), the monoterpenes linalool (Francois et al., 2009; Oyedeji et al., 2005; Tankam and Ito, 2013), β-pinene (Amvam Zollo et al., 1998; Francois et al., 2009; Oyedeji et al., 2005; Tankam and Ito, 2013), α-pinene (Amvam Zollo et al., 1998; Francois et al., 2009) and cis-β-ocimene (Oyedeji et al., 2005), the sesquiterpenes βcaryophyllene (Francois et al., 2009; Oyedeji et al., 2005), ishwarane, β-elemene, bicyclogermacrene and α-humulene (Oyedeji et al., 2005) and the phenylpropanoid sarisan (Oyedeji et al., 2005). The leaf essential oil contained the sesquiterpenes germacrene (Francois et al., 2009) and E-β-farnesene (Amvam Zollo et al., 1998). The liana/stem essential oil contained the sesquiterpene (Z,E)-α-Farsenene (Francois et al., 2009). The activity of some of

Please cite this article as: Freiesleben, S.H., et al., Medicinal plants used as excipients in the history in Ghanaian herbal medicine. Journal of Ethnopharmacology (2015), http://dx.doi.org/10.1016/j.jep.2015.03.005i

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α-phellandrene

Kaurenoic acid

p-cymene

ent-15-oxo-kaur-16-en-19-oic acid

α-pinene

Fig. 2. Structures of some active constituents of (A) Aframomum melegueta seeds, (B) Piper guineense seeds (C) Xylopia aethiopica and (D) seed essential oil of Monodora myristica.

the compounds in the essential oils have been identified: when inhaled 3,5-dimethoxytoluene and linalool (Tankam and Ito, 2013) had sedative activity and linalool had possibly insecticidal and antifungal activity (Amvam Zollo et al., 1998; Francois et al., 2009); β-pinene had possibly sedative and insecticidal activity (Francois et al., 2009; Tankam and Ito, 2013); α-pinene and limonene had possibly insecticidal activity (Francois et al., 2009). Structures of some active compounds of P. guineense are shown in Fig. 2.

The fruit essential oil of X. aethiopica contains a variety of mono- and sesquiterpenes, the main compounds varying depending on the place of collection (Karioti et al., 2004). Many studies of the fruits of X. aethiopica have been performed (Karioti et al., 2004). In these studies it was confirmed that dried fruits collected in Egypt, Benin and Mali all had high contents of the monoterpenes β-pinene and 1,8-cineole (Karioti et al., 2004). Dried fruits collected in Benin have been shown to contain mainly sabinene (monoterpene), while fruits from Egypt were rich in 4-

Please cite this article as: Freiesleben, S.H., et al., Medicinal plants used as excipients in the history in Ghanaian herbal medicine. Journal of Ethnopharmacology (2015), http://dx.doi.org/10.1016/j.jep.2015.03.005i

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terpineol (monoterpene) (Karioti et al., 2004). Despite mono- and sesquiterpenes other studies have also reported a content of diterpenes such as 13-epimanoyl oxide, kaur-16-ene (Elhassan et al., 2010) and xylopic acid (Woode et al., 2012). Some bioactive compounds of X. aethiopica have been identified. Phenolics and alkaloids have been identified as the main compounds responsible for the antimicrobial activity (Ikeyi et al., 2013). Xylopic acid, kaurenoic acid and ent-15-oxokaur-16-en-19-oic acid have been identified as the main compounds responsible for a diuretic effect, and xylopic acid specifically for a hypotensive effect. The structures of these compounds are shown in Fig. 2. The seed essential oil of M. myristica contains mainly monoterpenoids (93.2 %) (Koudou et al., 2007). The major constituents are α-phellandrene (34.3 to 37.8 %) (Cimanga et al., 2002; Koudou et al., 2007), p-cymene (19.3 to 22.2 %) (Cimanga et al., 2002; Koudou et al., 2007) and α-pinene (6.3 to 10.2 %) (Cimanga et al., 2002; Koudou et al., 2007). The structures of these compounds are shown in Fig. 2.

3.3. Antioxidant assay—reduction of the stable radical 2,2-diphenol1-picrylhydrazyl (DPPH) The dry ethanolic plant extracts were dissolved in DMSO. The water extracts were dissolved in water to reach a concentration of 0.4 mg/mL. The DPPH assay was adjusted to 96-well microtiter plates. 50 mL of the test solutions were added to the wells. Serial 4-fold dilutions of the extracts were made resulting in 6 final concentrations (0.0977–100 mg/mL). 150 mL of 0.1 mM DPPH was added to all wells, except the blanks. Ascorbic acid was used as positive control in the concentrations 0.05–200 mM. The plates were left for 30 min at room temperature and the absorbances in the wells were read at 517 nm. The assay was performed in triplicate. The free radical scavenging activity was calculated as percent inhibition with respect to the reference, which contained all the reagents without the test samples, according to the following equation: percent inhibition ¼

3. Materials and methods

5

Absreference  Abssample U 100 % Absreference

Percent inhibition was plotted against the logarithmic concentration of the samples.

3.1. Plant extracts 4. Results and discussion Dried seeds/fruits of A. melegueta (voucher: JS 224), P. guineense (voucher: JS 302), X. aethiopica (voucher: JS 303) and M. myristica (voucher: JS 304) were purchased from herbal markets in Ghana in January 2014 by Jens Soelberg. Vouchers are deposited at Museum of Natural Medicine, University of Copenhagen. The plant materials were grinded and extracted with water or ethanol. Warm water extracts were made as a decoction under reflux for 30 min and the cold water extracts were sonicated for 30 min. Ethanol extracts were also sonicated for 30 min. After decoction or sonication the extracts were filtered and taken to dryness in a speed vac.

3.2. Antimicrobial assay The dry ethanolic plant extracts were dissolved in 3 % DMSO and Mueller-Hinton buillon (MHB) was added to reach a concentration of 3.2 mg/mL. The water extracts were dissolved in MHB at 3.2 mg/mL. A standard broth-microdilution method utilizing 96-well microtiter plates were used to estimate the MIC values. To each well was added 50 mL of MHB and 50 mL of the test solutions. The plant extracts were tested in 2-fold dilutions in final concentrations of 25–800 mg/mL. To each well was added 50 mL of 24 h old bacteria cultures that were adjusted according to the Mc. Farland standard 0.67 and then diluted 100 times to reach a concentration of 2E6 cfu/mL. The microorganisms Escherichia coli ATCC 1229, Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 9027 and Bacillus subtilits ATCC 6633 were used as test organisms. A sterility control was made by adding 100 mL of MHB and a growth control was made by adding 50 mL MHB and 50 mL bacteria culture. The absorbance in the wells was read at 600 nm before the plates were incubated at 37 1C. After 24 h of incubation the absorbance in the wells was read again at 600 nm. The assay was performed in triplicate. Streptomycin was used as control. The growth was calculated in percent compared to the growth control. % growth ¼

ðOD t 24  OD t 0 Þtest U100% ðOD t 24  OD t 0 Þgrowth control

Traditional doctors and herbalists in Ghana explained that the four excipients were used: (1) as a way to increase the effect of the medicine, (2) as a way to make the medicine more palatable, (3) as a way to preserve the activity of the medicinal preparation over time or (4) as a way to increase the susceptibility of the body to the medicine (Soelberg et al., 2015). The literature study of the four plant excipients revealed several bioactivities of the plants in herbal mixtures as well as alone. A. melegueta and P. guineense had been shown to inhibit specific CYP-enzymes (Agbonon et al., 2010). Inhibition of these enzymes can result in enhancement of drugs, which is enzymatically degraded by the enzymes, thereby increasing the effect of the medicine. A. melegueta has also been reported to inhibit an efflux pump in mycobacteria. This could mean that the plant can be used together with antibiotics to avoid resistance (Groblacher et al., 2012). A. melegueta, P. guineense, X. aethiopica and M. myristica all contain odour-rich compounds, some of which have a pungent smell (Adosraku et al., 2013; Cimanga et al., 2002; Iwami et al., 2011; Sugita et al., 2013; Tairu et al., 1999; Vriens et al., 2008). These strong smells and tastes could mask unpleasant tastes in other medicines and in this way make the medicine more palatable. In the present study, the antioxidant and antibacterial activity of the four excipients were tested to evaluate if they possessed the ability to preserve a medicinal preparation. One study performed the DPPH free radical scavenging assay on water extracts of all four plant excipients, finding IC50 values for A. melegueta, P. guineense, X. aethiopica and M. myristica between 16.77–17.38 mg/mL (Adefegha and Oboh, 2012c), which was considered as non-active. In other studies A. melegueta, P. guineense and X. aethiopica showed antioxidant activity with IC50 values of 110 mg/mL, 500 mg/mL and 300 mg/mL, respectively (Adefegha and Oboh, 2012b; Kazeem et al., 2012). In this study extracts of A. melegueta resulted in inhibition curves with maximal inhibition near 100% (Fig. 3). The ethanolic extract of A. melegueta showed the highest antioxidant activity, with and IC50 of 1.0270.08 mg/mL, compared to the IC50 of ascorbic acid of

Please cite this article as: Freiesleben, S.H., et al., Medicinal plants used as excipients in the history in Ghanaian herbal medicine. Journal of Ethnopharmacology (2015), http://dx.doi.org/10.1016/j.jep.2015.03.005i

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% inhibition

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[ascorbic acid] µg/mL Fig. 3. Antioxidant MIC curves for ( ) ethanol, ( ) warm water and ( ) cold water extracts of (A) Aframomum melegueta, (B) Piper guineense, (C) Xylopia aethiopica and (D) Monodora myristica, (E) Positive control ( ) Ascorbic acid (mg/mL).

4.2070.30 mg/mL, which is remarkably good activity for a raw extract. The warm and cold water extracts of A. melegueta had slightly lower activity than ascorbic acid, 11.8873.86 mg/mL and 14.1770.99 mg/mL, respectively. The extracts of the three other species were not considered to possess antioxidant activity.

All four plants have been claimed to have antibacterial activity (Doherty et al., 2010; Ikeyi et al., 2013; Konning et al., 2004; Mbosso et al., 2010; Oyedeji et al., 2005; Sonibare et al., 2011), but the plants have been tested on different microbes and with different assays. Most studies used the disc diffusion assay and

Please cite this article as: Freiesleben, S.H., et al., Medicinal plants used as excipients in the history in Ghanaian herbal medicine. Journal of Ethnopharmacology (2015), http://dx.doi.org/10.1016/j.jep.2015.03.005i

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the extracts were active at concentrations between 10–50 mg/mL (Doherty et al., 2010; Konning et al., 2004; Sonibare et al., 2011). Because the extracts were only active in such high concentrations they cannot be considered as antimicrobial. This was also confirmed in this study, in which none of the extracts showed 100% inhibition at any of the concentrations tested, indicating that the MIC is higher than 800 mg/mL. No studies have investigated the changes in bioavailability of other plant medicines the four excipients might affect. It is therefore not possible at this point in time to verify the traditional doctors and herbalists' claim that the excipients increase the susceptibility of the body to the medicine.

5. Conclusion From the results of the present study three out of the four explanations for addition of excipients, claimed by traditional doctors and herbalists in Ghana, have been shown to be plausible. The CYP-enzyme inhibition of A. melegueta and P. guineense and the mycobacterial efflux pump inhibition of A. melegueta could increase the effect of the medicine. The odour-rich compounds of A. melegueta, P. guineense, X. aethiopica and M. myristica could most likely make the medicine more palatable. The antioxidative activity of A. melegueta could preserve the activity of the medicinal preparation over time.

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