In vivo and in vitro Activities of Medicinal Plants on Haemic and Humoral Trypanosomes: A Review
Reports on the in vivo and in vitro activities of medicinal plants on haemic and humoral trypanosomes showed that several medicinal plants, worldwide, possessed trypanocidal or trypanostatic activity. The choice of specific plants by researchers were based on their trypanocidal claims as documented in ancient pharmacopoeia, knowledge from traditional healers, herdsmen, village elders and feeding habits of large primates. The plants were subjected to various methods of extraction. The choice of extraction method depended largely on the part of the plan to be tested and often, fractionated through thin layer chromatography, infrared spectroscopy, mass spectroscopy, nuclear magnetic resonance spectroscopy to yield bioactive components. This was with a view of elucidating structural components and possible synthesis of new trypanocides. The commonly encountered active principles in the extracts were saponins, terepins, phenolics, flavonoids, tannins, glycosides, anthraquinones, columbins, neolignan, quinines, phlobatanin, resins and alkaloids. These fractions, produced efficacy ether singly or synergistically at dosages (<800 mg kg-1) in vivo, leading to the elimination of parasitaemia, modulating declined red cell indices and the alleviation of clinical signs of trypanosomosis. Most of the extracts however, produced effect in vitro within minutes of application in a graded dose manner. The extracts in most cases produced signs of acute toxicity (in vivo) at dosages (>800 mg kg-1) leading to degenerative changes in vital organs. Signs of cytotoxicity were also encountered in vitro on various cell lines. Therefore, the folkloric medicinal applications of plants for the treatment of trypanosomosis have a pharmacological basis. This may therefore, lead to the synthesis of new, cheap and easily available trypanocides of less toxicity.
October 10, 2010; Accepted: October 19, 2010;
Published: November 16, 2010
Over 250, 000 undiscovered flowering plants with medicinal properties exist
worldwide (Madureira, 2008). In spite of a rapidly expanding
literature on phytochemistry, only a small percentage of the total plant species
have been examined chemically and it is still a vast field for research (Gyang,
2001). Several medicinal plants are the most ancient source for the treatment
of human and animal trypanosomosis. The use of decoctions from medicinal plants
for the treatment of trypanosomosis dates as far back as ancient Egypt, Greece,
Mediterranean, India, Assyria and China (Trease and Evans,
1989). Indeed, the discoveries of medicinal plants for the treatment of
trypanosomosis have been associated with the study of traditional pharmacopia,
wisdom from village elders and traditional healers (Onuaguluchi,
1966; Nwude and Ibrahim, 1980; Aliu
and Nwude, 1982; Ibrahim et al., 1983). Similarly,
the natural instinct and progression of wild primates to utilize medicinal plants
in the wild, have often led to the discovery of medicinal plants with antitrypanosomal
efficacy (Clayton and Wolf, 1993).
However, in spite of the possible role of medicinal plants as trypanocides
(Asuzu and Chineme, 1990; Nok, 2002;
Mbaya et al., 2007, 2009a,
2010), some of the secondary metabolites in the extracts
are toxic in nature (Mbaya et al., 2007). Meanwhile,
the trypanocidal and trypanostatic efficacy of plant extracts are associated
with the presence of one or more biologically active principles (Atawodi
et al., 2002; Nok, 2002; Mbaya
et al., 2007). Phytochemical assays have also shown that the antitrypanosomal
activity is due to minor components or synergistic interaction of all, or some
of the active components. Many advances in the field of ethnopharmacology in
general, led the World Health Organization (WHO) to develop an international
programme, which reviews available scientific data relating to the efficacy
of medicinal plants for synthesizing forms that are more effective. This can
however, be possible through extraction, separation, isolation, characterization,
investigation into the biosynthetic pathways, quantitative evolutions and elucidation
of structural formulae of the active ingredients through infra-red spectroscopy,
mass spectroscopy, nuclear magnetic resonance spectroscopy (Sofowara,
1982). This may lead to the development of cheap, less toxic and available
trypanocides, which will eliminate the problem of drug resistance and relapse
(Soerjato, 1996; Cragg et al.,
1997; Mbaya et al., 2009a). In spite of the
fact that several plants with trypanocidal efficacy exists, no new, safe and
reliable trypanocides have been introduced for the past thirty years, this review
was therefore, undertaken to collate reports on in vivo and in vitro
activities of medicinal plants on haemic and humoral trypanosomes as basis for
future manufacturing of new trypanocidal drugs.
Historical perspective: Historically, man did not require the modern
methods of investigation to collect a material medica of plants, which he often
used in conjunction with magical and other ritual practices for the treatment
of trypanosomosis. The use of folk medicine is based on knowledge of treatments
of ailments based on traditional beliefs, which are common to a group of rural
people (Sofowara, 1982). Before the 18th century, only
slow progress was made in phytochemistry where compounds of cane sugar, starch,
camphor and benzoic acid were virtually used for the treatment of all forms
of diseases as a result, hundreds of plants were burnt to yield ashes, which
were soaked and used for various therapies (Gyang, 2001).
This method, however, led to several disappointments to earlier researchers.
In the 19th century, progress became more rapid and in 1903, alkaloids were
isolated (Trease and Evans, 1989). This active ingredient
among others was found to be trypanocidal (Grand, 1989;
Atawodi et al., 2003; Abubakar
et al., 2005; Mbaya et al., 2007).
In the 20th century, several plants with trypanocidal activity were discovered
worldwide (Igweh and Onabanjo, 1989; Sepulveda-Boza
and Cassele, 1996; Freiburghaus et al., 1996,
1997, 1998, Muellas-Serrano
et al., 2000; Weniger et al., 2001;
Nok, 2002; Mbaya et al.,
2007, 2009a; 2010). However,
in South Americas aboriginal societies, ethnobotanists are currently fighting
a battle against time to record such information before such vital knowledge
is lost (Trease and Evans, 1989).
Methods of extraction of trypanocidal plants: The extraction of bioactive
agents from plant materials is one of the most intensive of natural products
research today and yet the field is far from being exhausted (Gyang,
2001). The choice of a specific method or solvent depends largely on the
nature of the plant material and the component to be isolated. Dried materials
were often pulverized into fine particles before exhaustive extraction, whereas,
fresh leaves and succulent portions were homogenized and extracted using a suitable
solvent (Mittal et al., 1981; Sofowara,
1982; Gyang, 2001).
In most situations, where air dried materials were powdered into small particles,
extraction was most productive with 100% methanol or ethanol (Kaltungo,
1977; Rabo et al., 2000; Fabiola
et al., 2002; Atawodi et al., 2003;
Samia et al., 2006; Mbaya
et al., 2007; Mikail, 2009). In other cases,
ethanol and water were used (Fabiola et al., 2002;
Kamanzi et al., 2004; Wurochekke
and Nok, 2004; Wurochekke et al., 2004; Sara
et al., 2004; Ndjakou et al., 2007;
Shuaibu et al., 2008; Ogbunugafor
et al., 2008; Nibret et al., 2009).
In situations where succulent leaves such as aloe vera or fruits were extracted
to obtain pulp (Nok et al., 1996; Abubakar
et al., 2005), small pieces were obtained, before extraction. When
seeds were involved, separation from the pulp using a wire mesh was necessary.
Chloroform was used as solvent in some cases (Samia et
al., 2006). In aqueous extraction, water was used until a good yield
(v/v) was obtained (Rabo et al., 2000; Igweh
et al., 2002; Patricia et al., 2005;
Nwodo et al., 2007).
In vivo and in vitro toxicity of crude plant extracts:
Although, immense traditional knowledge exists in the ethnopharmacology of trypanosomosis,
accidental poisonings due to over dosages have been reported (Daziel,
1973; Nwude and Ibrahim, 1980; Rabo,
et al., 2000). Hence, scientific evaluation of toxicities by determining
lethal dosages (LD50) or lethal concentrations (LC50)
usually preceded in vivo trypanocidal efficacy trials (Mbaya
et al., 2007, 2009a, 2010).
During in vitro studies, cytotoxicity in mammalian cell cultures has
been documented (Camacho et al., 2003; Sara
et al., 2004; Patricia et al., 2005).
In vivo toxicity studies: The toxicity of the decoction from
the stem bark of Butyrospermum paradoxum (Sapotaceae) sub. sp. Parkii
(G. Don) Hepper used in Nrtheastern Nigeria for the treatment of trypanosomosis
was evaluated in vivo in rabbits (Rabo, 1998; Rabo
et al., 2000) and in rats (Mbaya et al.,
2007). Following the intra-peritoneal administration of the methanolic extract
of the stem bark, doses (>80 mg kg-1) produced behavioural changes,
morbidity and mortality in the rodents. The symptoms, which were dose dependent,
included anorexia, dehydration, depression, prostration, coma and death and
at necropsy, congestion with oedema of the lungs, bronchi, bronchioles, kidneys,
hepatomegally, with focal necrosis of hepatocytes. Similarly, Mbaya
et al. (2009a) observed similar but transient signs of toxicity in
rats administered derivatives of Artemisia annua. The root extract of
Mitragyna ciliata at dosages (>800 mg kg-1) produced acute
signs of toxity in mice (Ogbunugafor et al., 2008).
Signs of toxicity for most extracts were observed generally above 800 mg kg-1
(Rabo, 1998; Rabo et al., 2000;
Mbaya et al., 2007; Ogbunugafor
et al., 2008). On the other hand, dosages (<800 mg kg-1)
of Annona senegalensis Pers. leaf did not lead to fatality in mice (Ogbadoyi
et al., 2007). Similarly, the crude extracts or dihydrochelerythrine
derivatives from Garcina lucida produced little toxicity in vivo
(Jean et al., 2007).
Cytotoxicity (in vitro) studies: An in vitro evaluation
of the efficacy of Holarrhena africana fractions on Trypanosoma brucei
rhodesiense, showed that one fraction designated as HaF (5) showed no overt
cytotoxicity against L-6 cells (Nwodo et al., 2007).
Meanwhile, evaluation of cytotoxicity of trypanocidal Beninese plants showed
that Hymenocardia acida, Trichilia emetica leaves, were cytotoxic
to mammalian cells at higher IC50S but with the exception of
methylene chloride leaf extract of Strychnos spinosa (Sara
et al., 2004). Ndjakou et al. (2007)
evaluated the cytotoxic effects of some selected Cameroonian plants with efficacy
against T. cruzi and T. b. rhodesiense. Cytotoxicity and selectivity
index (SI (b) = 22.5) was higher with the methanolic stem bark extract of Albizia
zygia. Meanwhile, methylene extracts of Anogeissus leiocarpus and
Terminalia avicennoides on fibroblast did not reveal serious toxicity
at moderate concentrations but was toxic to the cells at higher concentrations
(Shuaibu et al., 2008).
It was also observed by Patricia et al. (2005),
that extracts of Brazilian medicinal plants with trypanocidal activities, such
as Bacharis trimera, Cymbopogon citratus, Matricaria chamomilla,
Mikania glomerata, Ocimum gratissimum, Piper regnellii,
Prunus domestica, Psidium guajava, Sambucus canadensis,
Stryphnodendron adstringens, Tanacetum parthenium and Tanacetum vulgare
showed no toxic effect on sheep erythrocytes, in vitro. A methanolic
and aqueous extraction of 43 plant species, selected from ethnopharmacological
and chemical taxonomic data with possible antitrypanosomal properties showed
efficacy against T. brucei, however, Annona purpurea was the most
toxic to KB cells (Camacho et al., 2003).
Phytochemical screening of various trypanocidal plants used in the folkloric
treatment of trypanosomosis: Earlier workers (Bisset
and Phillipson, 1971; Kerharo and Adam, 1974; Oguakwa
et al., 1980; Ohiri et al., 1983;
Grand, 1989; Nok et al.,
1996; Rabo, 1998) isolated active components from
plant materials used in the treatment of trypanosomosis. In recent years, workers
(Ohiri et al., 1983; Copp
et al., 2003; Atawodi et al., 2003;
Sara et al., 2004; Patricia
et al., 2005; Nok et al., 2005;
Abubakar et al., 2005; Jean
et al., 2007; Nwodo et al., 2007;
Ogbadoyi et al., 2007; Ogbunugafor
et al., 2008; Shuaibu et al., 2008;
Nyasse et al., 2004; Nibret
et al., 2009; Mbaya et al., 2007 2009a,
2010) have isolated various compounds with trypanocidal
The immense chemical constituents and range of biodiversity of plants may in
the future, lead to the development of hundreds of pharmacological agents with
trypanocidal activities. The active components in the stem bark of Anogeissus
leiocarpus and Terminalia avicennoides were hydrolysable tannins
(Shuaibu et al., 2008). Most of the Nigerian
Savannah plants such as Khaya senegalensis, Piliostigma reticulatum, Securidaca
longependunculata and Terminalia avicennoides contain mainly alkaloids,
flavonoids, phenolics and terepins (Grand, 1989; Atawodi
et al., 2003). Grand (1989) also encountered
similar biological components in the leaves of Piliostigma reticulatum.
Nok et al. (1996), reported that Allium sativum
(Liliaeceae) produced four fractions; ethyl acetate/methanol, ethyl acetate/ethanol,
benzene/ methanol and acetic acid/methanol. Among these fractions, the acetic
acid/methanol fraction retained the trypanocidal feature of the crude extract.
Crude methanolic and dichloromethane extracts from the flowers of Solanecio
angulatus yielded alkaloids (Nibret et al., 2009).
The authors also observed that the dichloromethane extract of Crotalaria
phillipsiae twigs yielded Senecionine. Nok et al.
(2005) demonstrated that the plant Aristolochia albidia yielded dipterpenoid
furanolactone (columbin), a potent trypanocide, while Ogbadoyi
et al. (2007) showed that Annona senegalensis leaf extract
contained mainly tannins, phlobatanins and saponins. Similarly, the ethanolic
extract of the stem bark of Butryrospermum paradoxum (Sapoataceae) was
found to contain tannins and alkaloids (Rabo, 1998; Mbaya
et al., 2007).
One fraction designated as HaF (5) was obtained from the aqueous extract of
young leaves of Holarrhena africana, a plant used in Nigerian traditional
medicine (Nwodo et al., 2007). Mbaya
et al. (2010) also showed that the ethanolic extract of the stem
bark of Azadirachta indica contained salanin, melzantriol, nimbin, cardiac
glycosides, tannins, alkaloids and saponins produced a remarkable trypanocidal
activity in vivo and in vitro. Similarly, Abe
et al. (2002) isolated Eupomatenoid-7 (neolignan) and fragransin
(lignan) from crude leaves and flower extract of Aristolochia taliscana,
a potent anti T. cruzi derivative. In a bid to evaluate the phytochemical
components of the fresh pulp of some trypanocidal Nigerian plants, Aloe vera
showed heavy presence of tannins, resins and alkaloids (Abubakar
et al., 2005). In the same study, Mamordica balsamina had
more of glycosides while Annona senegalensis leaves had more of tannins
followed by glycosides and less of flavonoids and saponins (Abubakar
et al., 2005). Similarly, the authors also reported that Securidaca
longipendunculata root and root barks had high concentrations of alkaloids,
flavonoids and saponins.
Three benzo [c] phenanthridine alkaloids were isolated from the stem bark of
Garcinia lucida and proven to be trypanocidal at the same time, its new
derivative , (S) 1-(9,10-dihydro-7, 8-dimethoxy-10-methyl-1-1, 2-benzophen anthridine-9-yl)
propan-2-one (lucidamine A) (S) was produced semi synthetically. The crude extract
as well as the synthetic derivatives produced excellent antitrypanosomal activity
(Jean et al., 2007). Sara
et al. (2004) analysed the crude methylene chloride leaf extracts
from potential trypanocidal plants from Benin such as Hymenocardia acida,
Strychnos spinosa, Cassia sieberiana and Trichilia emetica.
Tannins, flavonoids and quinones were the active principles encountered. Tannins
have equally been identified decades ago in the leaves of all species of S.
spinosa (Watt and Breyer-Brandwijk, 1962; Persinos
and Quimby, 1967; Doquenois and Anton, 1968; Kerharo
and Adam, 1974).
A literature survey indicated that several flavonoids have antitrypanosomal
activity (Raz, 1998; Camacho et
al., 2000; Tarus et al., 2002). C.
sieberiana have been shown to contain anthracenic derivatives (Doquenois
and Anton, 1968; Nok, 2002). Ogbunugafor
et al. (2008) during a chemical analysis of the active fraction of
Mitragyna ciliata and Pelleger (Rubiaceae) showed that, ethanolic
root extracts of the plants yielded alkaloids.
In vivo effect of medicinal plants on humoral trypanosomes: Table
1 shows the various medicinal plants reported to have in vivo anti
trypanosomal activity against humoral trypanosomes. Trypanosoma brucei
group of trypanosomes such as T. brucei brucei, T. evansi, T. b. rhodesiense
and T. brucei gambiense were classified as humoral (Losos
and Ikede, 1972; Mbaya et al., 2009b). For
T. cruzi, however, it exists in two forms, trypamastigote in the blood
(haemic) and amastigote (humoral) intracellularly in the tissues (Losos
and Ikede, 1972). However, T. cruzi along with the T. brucei
group are humoral due to their preference for solid tissues, particularly in
loose connective tissue stroma and fluids of body cavities. They are able to
elicit both humoral and cell mediated immune response. In the extra vascular
sites, the organisms elicit cellular infiltrations and degenerative changes.
Morinda lucida was reported to posses a remarkable effect trypano-suppressive
property on T. brucei in vivo (Asuzu and Chineme,
|| Plants with in vivo antitrypanosomal effects against
Root extract of Securidaca longependunculata (Polygalacea), leaf
extract of Guiera senegalensis (Combretaceae) (Aderbauer
et al., 2008a), flowers of Solanecio angulatus and twigs of
Crotalaria phillipsiae (Nibret et al., 2009)
showed moderate antitrypanosomal activity against T. brucei in vivo.
Similarly, Nwodo et al. (2007) reported that
aqueous young leaf extract of Holarrhena africana caused complete disappearance
of T. brucei in vivo, without relapse. Jean et
al. (2007) also, showed that extract of stem bark of Garcinia lucida
displayed attractive activity against T. brucei in vivo. The pulp of
several Nigerian plants such as Mamordica balsamina, Aloe vera
and Annona senegalensis leaves prolonged the survival period of T.
brucei infected rats (Abubakar et al., 2005).
The therapeutic effect of Aristolachia bacteolata showed remarkable
activity in vivo against T. evansi (Samia
et al., 2006). An in vivo analysis of the diterpenoid furanolactone
(columbin) from Aristolachia albida in T. brucei infected mice
revealed that 25 mg kg-1 administered for three consecutive days,
cleared the parasites from circulation (Nok et al.,
2005). The only set back according to the authors, was that columbin could
not clear parasites in the cerebrospinal fluid. Nok et
al. (1996) showed that the oily extracts of Allium sativum (Liliacea)
at one point it completely suppressed the ability of T. b. brucei to
infect mice and at another, it cured mice in 4 days at 120 mg/kg/day. After
fractionization by column chromatography, the acetic acid/methanol fraction
retained trypanocidal features of the crude extract. The authors reported that
the extract-contained diallyl-disulfide (DAD) which, interfered with the parasites
ability to synthesize membrane lipids. Ogbadoyi et al.
(2007) evaluated the chemotherapeutic effects of crude and partially purified
aqueous extracts of leaves, whole root and stem bark of Annona senegalensis.
The extracts at a dosage of 200 mg/kg/day completely cured mice of T. brucei.
Ogbunugafor et al. (2008) showed that butanolic
root extract of Mitragyna ciliata (Rubiaceae) possessed trypanocidal
activity. They observed a correlation between calcium concentration and parasitaemia,
suggesting that the active agent had effect on the calcium metabolism in the
rodents, which was deleterious to the organism. Wurochekke
et al. (2004) reported that the crude methanolic extract of Lawsonia
inermis had trypanocidal effect against T. brucei in vivo. A concentration
of 8.3 mg mL-1 ameliorated clinical signs but did not affect the
level of parasitaemia and packed cell volume in mice even when an adjuvant (glycerol)
was added. The crude methanolic extract of the plant Butyrospermum paradoxum
(Sapotacea) found in the Nigerian savannah, produced a remarkable trypanocidal
effect, through complete suppression or delay in parasite stablishment with
a reduction in the level of parasitaemia and severity of clinical signs as well
as enhanced the survival of rats infected with T. brucei (Rabo,
1998; Mbaya et al., 2007). Similarly, Nok
et al. (1993) and Mbaya et al. (2010)
showed that Azadirachta indica possesses remarkable trypanocidal effect
with a reduction in the level of T. brucei parasitaemia in vitro
and in vivo respectively.
In vitro effect of medicinal plants on humoral trypanosomes:
Table 2 shows various medicinal plants with in vitro
antitrypanosomal activity against humoral trypanosomes. In this method, trypanosomes
were propagated in specialized media assayed with crude extracts of medicinal
plant materials at various concentrations (Nok et al.,
1993; Atawodi et al., 2002, 2003;
Igweh et al., 2002; Mbaya
et al., 2010). This was followed by incubation at 37°C and parasitaemia
determination (Kamanzi et al., 2004; Wurochekke
and Nok, 2004; Patricia et al., 2005; Nwodo
et al., 2007; Ndjakou et al., 2007; Shuaibu
et al., 2008; Aderbauer et al., 2008b;
The methanolic extracts of various parts of the plants; Securidaca longependunculata,
Khaya senegalensis, Piliostigma reticulatum and Terminalia
avicennoides harvested from the Savannah vegetation belt of Nigeria, exhibited
strong trypanocidal activity against T. brucei while Lawsoni inermis
roots, Prosopis africana and Sterculia setigera slightly reduced
motility in vitro (Atawodi et al., 2003).
Similarly, an in vitro trypanicidal activity of 13 medicinal plants used
by local herdsmen in Northern Nigeria for the treatment of trypanosomosis, showed
that the aqueous root bark extract of Khaya senegalensis had the highest
activity, Tamarindus indica was less effective while the stem bark of
Albizia lebbeck was not (Wurochekke and Nok, 2004).
Seven selected Cameroonian medicinal plants, traditionally used to treat malaria,
showed that the methanolic extract of Albizia zygia (Fabaceae) stem bark
was effective against T. b. rhodesiense and T. cruzi (Ndjakou
et al., 2007). Meanwhile, in Côte d Ivoire, the in
vitro antitrypanosomal activity of crude ethanolic extract of 101 medicinal
plants in that region, showed that T. b. rhodesiense was most sensitive
to Enantia polycarpa (Annonaceae) and Trichilia emetica (Meliaceae)
(Kamanzi et al., 2004). Similarly, the trypanocidal
activity of petroleum ether extracts of the root bark of a Tanzanian medicinal
plant; Cussonia zimmermanii was found to be effective against T. b.
rhodesiense and T. cruzi (Martin et al.,
2007). The antitrypanosomal activity of the methanolic extracts of Anogeissus
leiocarpus and Terminalia avicennoides were evaluated in vitro
against T. brucei among other trypanosomes.
||Plants with in vitro antitrypanosomal effects against
The extracts were found to be effective with Minimum Inhibitory Concentration
(MIC) value range of 12.5-50 mg mL-1 (Shuaibu
et al., 2008). Following earlier reports on the trypanocidal activity
of Khaya senegalensis Atawodi et al. (2003),
Wurochekke and Nok, 2004) and Mikail
(2009) demonstrated similar activity with Khaya senegalensis among
others (Sclerocarya birrea and Commiphora kerstingii) against
T. brucei in vitro at concentrations of 2 and 4 mg mL-1, respectively.
The aqueous young leaf extract of Holarrhena africana, a plant used in
the Nigerian traditional medicine system, exhibited a good activity against
T. brucei in vitro. On fraction designated as HaF (5) showed an in
vitro activity against T. b. rhodesiense (Nwodo
et al., 2007).
In Mali and Burkina Faso, trypanocidal effects of lipophilic extracts of medicinal
plants showed that the root bark of Securidaca longependunculata (Polygalaceae)
and the leaf extract of Guiera senegalensis (Combretaceae) reduced parasitaemia
in vitro (Aderbauer et al., 2008a, b).
In Brazil, extracts obtained from 19 species of plants, used traditionally for
the treatment of various ailments, were tested against epimastigote forms of
T. cruzi in vitro. The results showed that Bacharis trimera, Cymbopogon
citratus, Matricaria chamomilla, Mikania glomerata, Ocimum
gratissimum, Piper regnellii, Prunus domestica, Psidium guajava, Sambucus
canadensis, Stryphnodendron adstringens, Tanacetum parthenium and Tanacetum
vulgare had significant effect against T. cruzi in vitro (Patricia
et al., 2005).
The in vitro effects of crude methanol and dichloromethane extracts
of 19 Ethiopian plants and 4 pure pyrrolizidine alkaloids on T. brucei was
evaluated (Nibret et al., 2009). The most active
extract was the dichloromethane extract of Solanecio angulatus flowers,
where the reduced alkaloid extract prepared from S. angulatus
flowers followed by an acid base extraction, showed more antitrypanosomal activity
than the unreduced alkaloid extract. The authors also reported that the second
most active extract was the dichloromethane extract of Crotalaria phillipsiae
twigs while others, showed moderate activity. The diterpenoid furanolactone
(columbin) isolated from Aristolochia albida inhibited culture forms
of T. brucei (Nok et al., 2005). in
vitro analysis of columbin at 5-250 μg mL-1 showed complete
lysis of the parasite within 10-20 min post-incubation.
In Maringá, Parana, Brazil, the efficacy of crude extracts or essential
oils of 15 medicinal plants such as Ocimum gratissimum, Lippia alba, Piper
regnellii, Stryphnodendron adstringens and Tanacetum vulgare showed severe
anti trypanosomal activity (Fabiola et al., 2002).
However, they observed, that Psidium guajava and Punica granatum
produced a lower activity as against Achillea millefolium, Eugenia
uniflora, Mikania glomerata, Plantago major while Spilanthes acmella
had no effect on T. cruzi in vitro.
The in vitro efficacy of the crude methanolic leaf extract of Lawsonia
inermis against T. brucei at a concentration of 48.3 mg mL-1
showed that the extract had in vitro activity in a graded dose manner
(Wurochekke et al., 2004). An in vitro
investigation of the trypanocidal effect on butanolic extract of the root bark
of Mitragyna ciliata revealed that it had low antioxidative property
and the active fraction (alkaloids) may be responsible for its trypanocidal
activity (Ogbunugafor et al., 2008).
The in vitro antitrypanosomal activity of methylene chloride, methanol
and aqueous extracts of the leaves and twigs of Cassia sieberiana (Caesalpiniacea),
Hymenocardia acida (Hymenocardiaceae), Pericopsis laxiflora (Papilionaceae),
Trichilia emetica (Meliaceae) and Strychnos spinosa (Loganiaceae)
used traditionally in Benin for the treatment of human sleeping sickness were
evaluated against T.b. brucei (Sara et al.,
2004). The results showed that Hymenocardia acida twig and Strychnos
spinosa leaf and methanolic chloride extracts of Trichilia emetica
leaf were most active with MIC values <19 μg mL-1. The authors
also reported that the determination of the IC50 values of the methylene
chloride leaf extracts on T. b. brucei and T. b. rhodesiense on
two mammalian cell lines showed that all the extracts possessed some antitrypanosomal
activity. Igweh et al. (2002) demonstrated that
aqueous extract of Brassica oleracea effectively immobilized T. b.
brucei within a 3-hour incubation period, which rendered the organism none
infective to mice.
Atindehou et al. (2004) also evaluated the activity of 101 crude ethanolic
extracts derived from 88 medicinal plants from Côte d Ivoire through
in vitro studies using T. b. rhodesiense. They observed that extracts
from Enantia polycarpa (Annonaceae) and Trichilia emetica (Meliaceae)
were the most promising ones. Their IC50 values were 0.5 and 0.04
mg mL-1 with selective indexes of 616 and 209 respectively. Camacho
et al. (2003) observed that the methanolic and aqueous extracts derived
from 43 plant species, showed varied in vitro activities. They observed
that Annona purpurea and Alstonia macrophylla had IC50
values below 10 mg mL-1, which produced a high activity against T.
In vivo and in vitro effect of medicinal plants on haemic
trypanosomes: Table 3 shows the various medicinal plant
reported to have either in vivo or in vitro antitrypanosomal activity
against haemic trypanosomes. Trypanosoma congolense and Trypanosoma
vivax are the haemic trypanosomes, with effects presented mostly in the
cardiovascular system (Losos and Ikede, 1972). In acute
T. congolense and T. vivax infections, petechial haemorrhages
occur on serosal surfaces, which are related to disseminate intravascular coagulation.
The ability of T. congolense to sequester in small vessels and capillaries
of the brain, heart, skeletal and other tissues often leads to prolonged pre-patent
period (Losos and Ikede, 1972; Maxie
and Losos, 1977; Mbaya et al., 2007).
In vivo approach: The acclaimed Butyrospermum paradoxum
(Sapotaceae) stem bark and Azadirachta indica are commonly used for the
treatment of human and animal trypanosomosis, in northeastern Nigeria.
|| Plants with in vivo and in vitro antitrypanosomal
effects against haemic trypanosomes
Under scientific trials, the former, produced antitrypanosomal effect by completely
preventing the establishment of T. congolense infection when administered
simultaneously with infection (Mbaya et al., 2007)
and the later, in T. brucei infected rats (Mbaya
et al., 2010). The extracts produced remarkable antitrypanosomal
effects through complete suppression with reduction in the level of parasitaemia
and the severity of the attendant disease. Similarly, the oily extract from
the pulp of Allium sativum (Liliaceae) cured experimental T. vivax
and T. congolense infection in mice at 120 mg/kg/day (Nok
et al., 1996). They also reported that Allium sativum inhibited
phospholipidase from the organisms and that column chromatography fractionization
produced acetic acid/methanol with trypanocidal feature of the crude extract.
In vitro approach: Atawodi et al. (2003)
reported that extracts from 23 plants harvested from the Savannah vegetation
belt of Nigeria, had trypanocidal activity against T. congolense at concentrations
of 4, 0.4 and 0.04 mg mL-1. They observed that, extracts of Khaya
senegalensis, Piliostigma reticulatum, Securidaca longependunculata and
Terminalia avicennoides were strongly trypanocidal to T. congolense
within 60 min of application, while, extracts of Anchomanes difformis, Cassytha
spp, Lannea kerstingii, Prosopis africana were trypanocidal to T.
congolense. The extracts from the stem bark of Anogeissus leiocarpus
and Terminalia avicennoides possessed remarkable trypanocidal activity
(Shuaibu et al., 2008).
Future prospects: The understanding of the mechanisms of action of chemical
compound and their host parasite relationship have led to the development of
several new agents with trypanocidal properties (Bacchi
et al., 1980; Bitonti et al., 1986;
Fairlamb, 1989). However, drug resistance and relapse
parasitaemia are common with all standard trypanocides and in recent years,
no new and effective trypanocide have been produced (Onyeyili
and Egwu, 1995). Moreover, the associated toxicity, cost and unavailability
of the standard trypanocides have been a source of concern. In view of these,
ethnopharmacology may lead to the manufacturing of cheap, easily available and
less toxic trypanocides (Rabo, 1998; Mbaya
et al., 2007, 2009a, 2010).
This may be possible when the mechanisms of action of natural products are
obtained through isolation, identification and evaluation of bioactive substances
(Trease and Evans, 1989). This can therefore, lead to
structural modification and synthesis to reduce toxicities, prolong their activity
and increase their potency.
Given the large number (250,000-500, 000) of plant species of which, only 5-15% have been investigated for the presence of bioactive compounds there is need to elaborate an efficient strategy for successful screening. Beside traditional means of flora investigation, ethnomedicine, chemotaxonomy and systemic screening of apes feeding behaviour could be a complementary source of information for targeting plants with trypanocidal properties.
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