Phytochemical Screening and Antioxidant Activities of Some Selected Medicinal Plants Used for Malaria Therapy in Southwestern Nigeria

Abstract

Purpose: Oxidative stress has been shown to play an important role in the development of anaemia in malaria. Indeed, increase in total antioxidant status has been shown to be important in recovery from malaria. The antioxidant activities of four medicinal plants traditionally used in the treatment of malaria in southwestern Nigeria were determined. Methods: The ethanolic extracts of the leaves of Carica papaya Linn. [Caricaceae] , stem bark of Magnifera indica Linn. [Anacardiaceae], leaves of Psidium guajava Linn. [Myrtaceae] and the leaves of Vernonia amygdalina Del. [Compositae], were used in the present study. The plant parts commonly used in the locality in malaria therapy were employed in this study. The plants were screened for the presence of phytochemicals and, their effect on 2,2-Diphenyl-1-picryl-hydrazyl radical (DPPH) was used
to determine their free radical scavenging activity. Results: Phytochemical screening of the plants showed the presence of flavonoids, terpenoids, saponins, tannins and reducing sugars. M. indica did not contain cardiac glycosides and alkaloids while, P. guajava also showed the absence of alkaloids and anthraquinones. Anthraquinones was similarly
absent from V. amygdalina. Concentrations of the plant extracts required for 50% inhibition of DPPH radical scavenging effect (IC50) were recorded as 0.04 mg/ml, 0.313 mg/ml, 0.58 mg/ml, 2.30 mg/ml and 0.054 mg/ml for P. guajava, M. Indica, C. papaya, V. amygdalina and Vitamin C, respectively. Conclusion: All the plants showed potent inhibition of DPPH radical scavenging activity, P. guajava being the most potent. The free radical scavenging (antioxidant) activities of these plants probably contribute to the effectiveness of the above plants in malaria therapy.

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Adisa et al
Trop J Pharm Res, September 2008; 7 (3)
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Tropical Journal of Pharmaceutical Research, September 2008; 7 (3): 1019-1024
© Pharmacotherapy Group,
Faculty of Pharmacy, University of Benin,
Benin City, 300001 Nigeria.
All rights reserved.
Available online at http://www.tjpr.org
Research Article
Phytochemical Screening and Antioxidant Activities
of Some Selected Medicinal Plants Used for Malaria
Therapy in Southwestern Nigeria
GA Ayoola1*, HAB Coker1, SA Adesegun2, AA Adepoju-Bello1,
K Obaweya1, EC Ezennia1, TO Atangbayila1
1Department of Pharmaceutical Chemistry, 2Department of Pharmacognosy, Faculty of Pharmacy, University of
Lagos, Lagos, Nigeria
Abstract
Purpose: Oxidative stress has been shown to play an important role in the development of anaemia in
malaria. Indeed, increase in total antioxidant status has been shown to be important in recovery from
malaria. The antioxidant activities of four medicinal plants traditionally used in the treatment of malaria
in southwestern Nigeria were determined.
Methods: The ethanolic extracts of the leaves of Carica papaya Linn. [Caricaceae] , stem bark of
Magnifera indica Linn. [Anacardiaceae], leaves of Psidium guajava Linn. [Myrtaceae] and the leaves of
Vernonia amygdalina Del. [Compositae], were used in the present study. The plant parts commonly
used in the locality in malaria therapy were employed in this study. The plants were screened for the
presence of phytochemicals and, their effect on 2,2-Diphenyl-1-picryl-hydrazyl radical (DPPH) was used
to determine their free radical scavenging activity.
Results: Phytochemical screening of the plants showed the presence of flavonoids, terpenoids,
saponins, tannins and reducing sugars. M. indica did not contain cardiac glycosides and alkaloids while,
P. guajava also showed the absence of alkaloids and anthraquinones. Anthraquinones was similarly
absent from V. amygdalina. Concentrations of the plant extracts required for 50% inhibition of DPPH
radical scavenging effect (IC50) were recorded as 0.04 mg/ml, 0.313 mg/ml, 0.58 mg/ml, 2.30 mg/ml and
0.054 mg/ml for P. guajava, M. Indica, C. papaya, V. amygdalina and Vitamin C, respectively.
Conclusion: All the plants showed potent inhibition of DPPH radical scavenging activity, P. guajava
being the most potent. The free radical scavenging (antioxidant) activities of these plants probably
contribute to the effectiveness of the above plants in malaria therapy.
Key words: Carica papaya, Magnifera indica, Psidium guajava, Vernonia amygdalina, Antioxidants,
Malaria, DPPH, Oxidative stress.
*Corresponding author: E-mail:oyetayo68@yahoo.com; Tel: +234-1-8940442

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INTRODUCTION
Malaria is a global disease prevalent in the
tropics caused by Plasmodium species. It is
one of the oldest and greatest health
challenges affecting 40% of the world’s
population. It affects 300-500 million people
and kills 1.5-2.7 million people annually1.
High mortality rate is reported in children and
pregnant women, also the disease has a
negative impact on the economy of prevalent
countries2. In Nigeria, malaria is endemic
throughout the country. World health
Organization (WHO) has estimated malaria
mortality rate for children under five in Nigeria
at 729 per 100,0003 Nigeria’s Ministry of
Health reported in April 2004 that malaria is
responsible for one out of ten deaths in
pregnant women and costs the Federal
Government of Nigeria over one billion naira
annually3.
One of the major reasons for the development
of anaemia in malaria seems to be oxidative
stress4-6. The immune system of the body is
activated by infections, including malaria,
thereby causing the release of reactive
oxygen species. In addition to this, the
malaria parasite also stimulates certain cells
to produce reactive oxygen species thereby
resulting in haemoglobin degradation5,7.
Indeed, depressed level of plasma
antioxidants has been shown in Plasmodium
falciparum-infected children and it has been
suggested as a possible contributor to the
morbidity and mortality of malaria1.
Increased resistance of malaria parasites to
the commonly used antimalarial drugs have
been reported, and hence the need to
intensify research in the area of development
of new antimalarial drugs especially from
medicinal plants. A review of the medicinal
plants used in the southwestern part of
Nigeria for the treatment of malaria indicates
that a rich flora diversity exists in Nigeria8.
The present study aims to investigate the free
radical scavenging activities of some of the
commonly used medicinal plants in
southwestern Nigeria. The following plants
were selected for investigation: C. papaya, P.
guajava, V. amygdalina, and M. indica. The
decoctions of the leaves of C. papaya, P.
guajava, V. amygdalina and a decoction of the
stem bark of M. indica are commonly used in
the traditional treatment of malaria in
southwestern Nigeria.
MATERIALS AND METHODS
Collection and identification of plant
materials
Fresh leaves of C. papaya, P. guajava, V.
amygdalina and the stem bark M. indica were
collected from the premises of Lagos
University Teaching Hospital, Lagos, Nigeria
in January 2007. The plants were identified
by Dr S.A. Adesegun of the Department of
Pharmacognosy, Faculty of Pharmacy,
University of Lagos, Lagos, Nigeria.
Extraction of plant materials
The plant materials (leaves of C. papaya, P.
guajava, V. amygdalina and the stem bark of
M. indica) were air-dried at room temperature
(26˚C) for 2 weeks, after which it was grinded
to a uniform powder. The ethanol extracts
were prepared by soaking 100 g each of the
dry powdered plant materials in 1 L of ethanol
at room temperature for 48 h. The extracts
were filtered after 48 h, first through a
Whatmann filter paper No. 42 (125mm) and
then through cotton wool. The extracts were
concentrated using a rotary evaporator with
the water bath set at 40˚C. The percentage
yield of extracts ranged from 7–19%w/w.
Phytochemical screening
Phytochemical screening were perfomed
using standard procedures9-10.
Test for reducing sugars (Fehling’s test)
The aqueous ethanol extract (0.5 g in 5 ml of
water) was added to boiling Fehling’s solution
(A and B) in a test tube. The solution was
observed for a colour reaction.
Test for anthraquinones
0.5 g of the extract was boiled with 10 ml of
sulphuric acid (H2SO4) and filtered while hot.
The filtrate was shaken with 5 ml of
chloroform. The chloroform layer was pipette
into another test tube and 1 ml of dilute

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Trop J Pharm Res September 2008; 7 (3)
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ammonia was added. The resulting solution
was observed for colour changes.
Test for terpenoids (Salkowski test)
To 0.5 g each of the extract was added 2 ml of
chloroform. Concentrated H2S04 (3 ml) was
carefully added to form a layer. A reddish
brown colouration of the interface indicates
the presence of terpenoids.
Test for flavonoids
Three methods were used to test for
flavonoids. First, dilute ammonia (5 ml) was
added to a portion of an aqueous filtrate of the
extract. Concentrated sulphuric acid (1 ml)
was added. A yellow colouration that
disappear on standing indicates the presence
of flavonoids. Second, a few drops of 1%
aluminium solution were added to a portion of
the filtrate. A yellow colouration indicates the
presence of flavonoids. Third, a portion of the
extract was heated with 10 ml of ethyl acetate
over a steam bath for 3 min. The mixture was
filtered and 4 ml of the filtrate was shaken with
1 ml of dilute ammonia solution. A yellow
colouration indicates the presence of
flavonoids.
Test for saponins
To 0.5 g of extract was added 5 ml of distilled
water in a test tube. The solution was shaken
vigourously.and observed for a stable
persistent froth. The frothing was mixed with
3 drops of olive oil and shaken vigourously
after which it was observed for the formation
of an emulsion.
Test for tannins
About 0.5 g of the extract was boiled in 10 ml
of water in a test tube and then filtered. A few
drops of 0.1% ferric chloride was added and
observed for brownish green or a blue-black
colouration
Test for alkaloids
0.5 g of extract was diluted to 10 ml with acid
alcohol, boiled and filtered. To 5 ml of the
filtrate was added 2 ml of dilute ammonia. 5
ml of chloroform was added and shaken
gently to extract the alkaloidal base. The
chloroform layer was extracted with 10 ml of
acetic acid. This was divided into two
portions. Mayer’s reagent was added to one
portion and Draggendorff’s reagent to the
other. The formation of a cream (with Mayer’s
reagent) or reddish brown precipitate (with
Draggendorff’s reagent) was regarded as
positive for the presence of alkaloids.
Test for cardiac glycosides (Keller-Killiani
test)
To 0.5 g of extract diluted to 5 ml in water was
added 2 ml of glacial acetic acid containing
one drop of ferric chloride solution. This was
underlayed with 1 ml of concentrated
sulphuric acid. A brown ring at the interface
indicated the presence of a deoxysugar
characteristic of cardenolides. A violet ring
may appear below the brown ring, while in the
acetic acid layer a greenish ring may form just
above the brown ring and gradually spread
throughout this layer.
Determination of antioxidant activity
The radical scavenging activities of the plant
extracts against 2,2-Diphenyl-1-picryl hydrazyl
radical (Sigma-Aldrich) were determined by
UV spectrophotometry at 517 nm. Radical
scavenging activity was measured by a
slightly modified method previously
described12,13. The following concentrations
of the extracts were prepared, 0.05, 0.1, 0.5,
1.0, 2.0 and 5 mg/ml in methanol (Analar
grade). Vitamins C was used as the
antioxidant standard at concentrations of 0.02,
0.05, 0.1, 0.2, 0.5 and 0.75 mg/ml. I ml of the
extract was placed in a test tube, and 3 ml of
methanol was added followed by 0.5 ml of 1
mM DPPH in methanol. A blank solution was
prepared containing the same amount of
methanol and DPPH. The radical scavenging
activity was calculated using the following
formula:
% inhibition = {[Ab-Aa]/Ab} x 100 ……(1)
where Ab is the absorption of the blank
sample and Aa is the absorption of the extract

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Trop J Pharm Res September 2008; 7 (3)
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RESULTS
Phytochemical screening of plant
materials
The phytochemical screening of the plants
studied showed the presence of flavonoids
terpenoids, saponins and tannins (Table 1),
M. indica, V. amygdalina and P. guajava
showed the absence of anthraquinones. M.
indica and P. guajava tested negative for the
presence of alkaloids and only M. indica
tested negative for the presence of cardiac
glycosides (Table 1).
Radical scavenging (antioxidant) activity
IC50 of 0.04, 0.31, 0.58, 2.30 and 0.054 mg/ml
were recorded for P. guajava, M. indica, C.
papaya, V. amygdalina and Vitamin C,
respectively (Figure 1).
DISCUSSION
Phytochemical screening of the plants
revealed some differences in the constituents
of the four plants tested. C. papaya tested
positive for all the phytochemicals tested; M.
indica showed the absence of
anthraquinones, alkaloids and cardiac
glycosides; V. amygdalina tested positive for
all except anthraquinones while P. guajava
tested positive for all except Anthraquinones
and alkaloids. All the plants exhibited potent
antioxidant activity. The presence of
flavonoids and tannins in all the plants is likely
to be responsible for the free radical
scavenging effects observed. Flavonoids and
tannins are phenolic compounds and plant
phenolics are a major group of compounds
that act as primary antioxidants or free radical
scavengers14.
The DPPH test provides information on the
reactivity of the test compounds with a stable
free radical. DPPH gives a strong absorption
band at 517nm in visible region. When the
odd electron becomes paired off in the
presence of a free radical scavenger, the
absorption reduces and the DPPH solution is
decolourised as the colour changes from deep
violet to light yellow. The degree of reduction
in absorbance measurement is indicative of
the radical scavenging (antioxidant) power of
the extract. The crude extract of P. guajava
appeared to be as potent as Vitamin C with a
maximum inhibition of 91% at 0.5mg/ml which
is comparable to 95% for vitamin C at the
Table 1: Phytochemical constituents of C. papaya, M. indica, V. amygdalina and P. guajava
Test C. Papaya M. indica V. amygdalina P. guajava
Reducing sugar + + + +
Anthraquinone + - - -
Terpenoids + + + +
Flavonoids + + + +
Saponins + + + +
Tannins + + + +
Alkaloids + - + -
Cardiac
glycosides
+ - + +

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Trop J Pharm Res September 2008; 7 (3)
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same concentration. M. indica was six times
less potent than the standard with a maximum
inhibition of 91% at 1 mg/ml, followed by C.
Papaya which was eleven times less potent
(than vitamin C) with a maximum inhibition of
83.8% at 5mg/ml. V. amygdalina was the
least potent (42 times less potent than the
standard) showing a maximum inhibition of
77.7% at 5 mg/ml. This study suggests that
these plants possess antioxidant activities
which can counteract the oxidative damage
induced by the malaria parasite. This may be
one of their mode of action in malaria therapy.
CONCLUSION
Extracts from C. papaya, M. Indica, V.
amygdalina and P. guajava showed varying
antioxidant (free radical scavenging) activities
when compared to vitamin C in the following
order: V. amygdalina < C. papaya < M. indica
< Vitamin C ≤ P. guajava. The results
suggest that the antioxidant activity of these
plants may contribute to their claimed
antimalarial property.
ACKNOWLEGEMENT
We thank Mr P. Ojobor of the Central
Research Laboratory; Mr T.I. Adeleke of the
Pharmacognosy Department; Mrs.Y.A.
Bashorun, Mr Olatunji and Mr Olajide of
Pharmaceutical Chemistry Department, all of
the University of Lagos, for technical support.
We also thank Ms J.O. Ashamu for assistance
in the preparation of this manuscript.
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0
10
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0.05 0.1 0.5 1 2 5
Concentration mg/ml
% Inhibition of DPPH
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Figure 1: Inhibition of DPPH by the ethanolic extracts of C. papaya, M. indica, P. Guajava
and V. Amygdalina, respectively.

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