Acute Toxicity of Aqueous and Ethanolic Extracts of Strophanthus hispidus Stem Bark

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*Corresponding author: E-mail: mosibemhe@fudutsinma.edu.ng;
International Journal of Biochemistry Research
& Review
9(1): 1-5, 2016, Article no.IJBcRR.22036
ISSN: 2231-086X, NLM ID: 101654445
SCIENCEDOMAIN international
www.sciencedomain.org
Acute Toxicity of Aqueous and Ethanolic Extracts of
Strophanthus hispidus Stem Bark
M. Osibemhe
1*
, B. O. Abdulrahman
1
and I. O. Onoagbe
2
1
Department of Biochemistry and Molecular Biology, Faculty of Science and Education, Federal
University Dutsin-Ma, Katsina State, Nigeria.
2
Department of Biochemistry, Faculty of Life Sciences, University of Benin, Benin City, Edo State,
Nigeria.
Authors’ contributions
This work was carried out in collaboration between all authors. Author IOO designed the study, wrote
the protocol and supervised the work. Authors MO and BOA carried out all laboratories work and
performed the statistical analysis. Author MO wrote the first draft of the manuscript, managed the
literature searches and edited the manuscript. All authors read and approved the final manuscript.
Article Information
DOI: 10.9734/IJBCRR/2016/22036
Editor(s):
(1) Dileep G. Nair, Ministry of Higher Education, Sultanate of Oman.
Reviewers:
(1) Abdullahi M. Nuhu, Kaduna Polytechnic, Kaduna, Nigeria.
(2)
Begum Rokeya, Bangladesh University of Health Sciences, Bangladesh.
Complete Peer review History:
http://sciencedomain.org/review-history/12209
Received 14
th
September 2015
Accepted 13
th
October 2015
Published 9
th
November 2015
ABSTRACT
The aim of this study was to determine the median lethal dose (LD
50
) of the extracts (aqueous and
ethanol) of S. hispidus stem bark. A modified Lorke’s (1983) method was used in this study. Varying
doses of the extracts were administered orally to male albino rats. Treatment-related signs of toxicity
and mortality were monitored for 24 hrs and continued for 72 hrs. Treatment-related mortality was
observed at the dose of 1000 mg/kg body weight and above in the ethanolic extract and 1600 mg/kg
body weight in the aqueous extract. Signs of sedation, exophthalmos, decreased locomotion and
appetite in the aqueous or ethanolic treated animals were observed in the early stages of
experimentation. However, these signs were not sustained in surviving animals. The LD
50
was 2154
and 2039 mg/kg body weight for aqueous and ethanolic extracts of S. hispidus stem bark
respectively. The results showed that 1000 mg/kg body weight and above of S. hispidus stem bark
may be slightly toxic. Therefore, moderate dosage is advised for purposes of medication.
Original Research Article

Osibemhe et al.; IJBcRR, 9(1): 1-5, 2016; Article no.IJBcRR.22036
2
Keywords: Medication; exophthalmos; mortality; experimentation.
1. INTRODUCTION
Plants produce a great diversity of substances
that can have therapeutic significance for
maintaining human health and improving the
quality of human life, thus justifying their use in
traditional medicine [1]. According to their
traditional use, natural compounds are often
assumed to be safe. However, several studies
have reported that a great number of plant
species used as food ingredients or in traditional
medicine present mutagenic, carcinogenic or
toxic properties [2-4]. Drug toxicity can occur on
many different time-scales. Acute toxicity results
from a single exposure to a drug, with adverse
effects resulting in minutes to hours [5]. A
fundamental goal of toxicology is to determine
safe levels of exposure to potentially poisonous
substances for human and the environment [5].
The scientific exploitation of herbs used ethno-
medically for pain relief, wound healing and
abolishing fevers has resulted in the identification
of a wide range of compounds that have been
developed as new therapies for several ailments
including diabetes [6].
A few of these herbal products have scientific
data on their toxic levels in literatures. Acute
toxicity testing can provide a guide to selection
of doses of herbal medicines, in order to avoid
potential harmful effects when used.
Strophanthus hispidus is an African shrub that
belongs to the genus; Strophanthus, the family of
Apocynaceae. Its popularity in folklore medicine
for the treatment of diabetes, ulcer, gonorrhea as
well as its bitter taste may not be unconnected
with the presence of important phytochemicals
such as saponins, alkaloids, phenols, flavonoids
and tannins [7]. This work is therefore aimed at
providing scientific records as to the amount of S.
hispidus that may constitute potential risk in
animal model.
2. MATERIALS AND METHODS
2.1 Animals
Male rats (Wistar strain) obtained from the
Department of Anatomy, University of Benin,
Benin City, Nigeria were used. The rats weighing
between 100-232 g were maintained under
standard animal house condition and were
allowed free access to food (growers mash
produced by Bendel Feed and flour Mill, Ewu
Edo State) and water for two weeks to
acclimatize to the new environment. All animals
were handled with proper care and humanely
treated according to our Institutional Animal
Ethics Committee guidelines as well as the
internationally accepted practices for use and
care of laboratory animals as contained in US
guidelines [8].
2.2 Medicinal Plant
The stems of S. hispidus were collected from
Galadimawa, in Giwa Local Government,
Kaduna State, Nigeria. They were identified by
Mr. U. S. Gallah of the Department of Biological
Science, Ahmadu Bello University, Zaria, Nigeria
where a specimen with voucher number (no:
2714) was deposited.
2.3 Preparation and Extraction of Plant
Materials
A modified method of Onoagbe et al. [9] was
used. The stems of S. hispidus were thoroughly
washed with clean water and the barks were
peeled off by incision. They were then dried
under shade for two weeks and then pulverized
into fine powder with the aid of a mechanical
pulverizer. Measured quantities of the powdered
sample were extracted separately in aqueous
and 99% ethanol for 72 hrs followed by periodic
stirring and they were kept in a refrigerator to
avoid any microbial growth. The extracts were
filtered using cheese-cloth and the filtrate re-
filtered using Whatman No. 42 (125 mm) filter
paper. The filtrates collected were lyophilized
using a freeze-dryer and stored in an airtight
container for further analysis.
2.4 Acute Toxicity Study
The method of Lorke, (1983) [10] for the
determination of lethal dose (LD
50
) with little
modification was used in this experiment. A total
of 26 male rats were used. The rats were
randomly selected into two major groups of 13
rats each and were kept in standard cage. The
groups were labeled 1 and 2. The experiment
was carried out in two phases. In the phase one,
rats in group 1 were again selected randomly into
three sub-groups of three rats each and were
administered orally with the aid of a gavage,
doses of 10, 100, and 1000 mg/kg body weight

Osibemhe et al.; IJBcRR, 9(1): 1-5, 2016; Article no.IJBcRR.22036
3
aqueous extract respectively. Similarly, the
second group (2) which was also randomly
selected into three sub-groups of three rats each
was administered respective doses of ethanolic
extract. Both groups were monitored frequently
during working hours for signs of toxicity and
mortality and subsequently for 24 hours.
Observations were continued for 72 hours for
any late sign of toxicity. In the second phase,
four rats in group 1 were made into four groups
of one rat each and were administered doses of
1000, 1600, 2900 and 5000 mg/kg body weight
aqueous extract respectively. In a similar
manner, four rats were also selected from group
2 into four groups of one rat each. They were
administered ethanolic extract at the doses of
800, 1600, 2600 and 3600 mg/kg body weight
respectively. Again, both groups were monitored
for signs of toxicity and mortality as in the phase
one. The second phase was used in the
calculation of the median lethal dose (LD
50
).
3. RESULTS
The results for the acute toxicity study of both
extracts of S. hispidus stem bark are presented
in Tables 1-2. 1000 mg/kg body weight and
above in the ethanolic extract (Table 2) and 1600
mg/kg body weight and above in the aqueous
extract (Table 1) resulted in mortality. The LD
50
was beyond 2000 mg/kg for both extracts.
(Tables 1-2).
4. DISCUSSION
Diabetes mellitus is a disease that is increasingly
affecting millions of people all over the world.
And this disease has no known cure in spite of its
age long existence. Currently there are over 150
millions diabetics worldwide and this is likely to
increase to 300 million or more by 2025 [11].
Research to provide scientific data for plants with
acclaimed hypoglycemic and anti-diabetic
properties are on the increase. This became
more apparent following WHO (1994) [12]
recommendations regarding the need to develop
and evaluate better pharmacological agents for
improving insulin secretion, enhancing insulin
sensitivity, preventing beta-cell destruction,
promoting beta-cell regeneration or repair and
interrupting pathways leading to the various
Table 1. LD
50
determination on aqueous extract
Phase one
Doses (mg/kg)
Number of rats/
Group
Ratio of dead rats
10 3 0/3
*
100 3 0/3
1000 3 0/3
Phase two
Doses (mg/kg)
Number of rats/
Group
Ratio of dead rats
1000 1 0/1
1600 1 0/1
2900 1 1/1
5000 1 1/1
*
Number of dead animals/ number of animals used, LD
50
=√ × . (Where a= highest non-lethal dose, b= least
lethal dose) within 24 hours of extract administration, LD
50
=√1600 × 2900 =√4640000 = 2154 mg/kg (oral)
Table 2. LD
50
determination on ethanolic extract
Phase one
Doses (mg/kg)
Number of rats/
Group
Ratio of dead rats
10 3 0/3
*
100 3 0/3
1000 3 1/3
Phase two
Doses (mg/kg)
Number of rats/
Group
Ratio of dead rats
800 1 0/1
1600 1 0/1
2600 1 1/1
3600 1 1/1
*
Number of dead animals/ number of animals used, LD
50
=√ × . (Where a= highest non-lethal dose, b= least
lethal dose). Within 24 hours of extract administration, LD
50
=√1600 × 2600 =√4160000 = 2039 mg/kg (oral)

Osibemhe et al.; IJBcRR, 9(1): 1-5, 2016; Article no.IJBcRR.22036
4
complications of diabetes. The major contributory
factors to this growing interest include these
recommendations, the cost and side effects of
most orthodox hypoglycaemic agents, low
therapeutic index of synthetic compounds and
growing incidences of drug resistance [13,14].
Ojiako and Igwe, [15] has reported the use of S.
hispidus for the treatment of diabetes by the
ethnic tribal people of Africa. The major
hindrance to the use of traditional herbal
preparations is the lack of scientific and clinical
data in support of better understanding of the
efficacy and safety of the drugs [16]. In screening
drugs, determination of LD
50
is usually an initial
step in the assessment and evaluation of the
toxic characteristics of a substance. The oral
LD
50
of aqueous and ethanolic extracts of S.
hispidus stem bark were found to be 2154 and
2039 mg/kg body weight (Tables 1 and 2)
respectively in the present study. Treatment-
related mortality (Tables 1 and 2) and signs of
sedation, exophthalmos, decreased locomotion
and appetite in the aqueous or ethanolic treated
animals were observed in the early stages of
experimentation at the dose of 1000 mg/kg body
weight and above in the ethanolic extract and
1600 mg/kg body weight and above in the
aqueous extract. According to [17], any
substance with oral LD
50
above 1000 mg/kg body
weight in rats is regarded as being of low toxicity
or relatively safe. Based on Hodge and Sterner
scale [18], a test drug administered orally is
considered extremely toxic at≤ 1 mg kg
-1
, highly
toxic at 1-50 mg kg
-1
, moderately toxic at 50-500
mg kg
-1
, slightly toxic at 500-5000 mg kg
-1
,
practically non toxic at 5000-15,000 mg kg
-1
and
relatively harmless at≥15,00 mg kg
-1
. Agbaje et
al. [19] has reported LD
50
for both intraperitoneal
and oral routes of Syzigium aromaticum (L.) in
rodents as 265 and 2500 mg/kg body weight.
The oral (rat) LD50 of ethanol extract of Vitex
leucoxylon leaf (>3000 mg/kg), cold water
infusion extract of the same plant (1050 mg/kg),
ethanolic extracts of Ailanthus excelsa (1000
mg/kg), Toddalia asiatica (350 mg/kg) and
Araucaria bidwilli (250 mg/kg) have been
reported [20]. The scarcity of scientific data to
validate local claims on the use of S. hispidus for
the treatment of diabetes as well as lack of data
about its tolerable dosage hinders meaningful
comparison.
5. CONCLUSION
The findings from this study indicated that S.
hispidus stem bark extracts may be slightly toxic
at high doses. S. hispidus may also be
considered to be relatively safe since the
qualitative and quantitative acute toxicity in
animals only has little relevance to human acute
toxicity in special cases and after many years of
usage. The results also showed that ethanolic
extract has lower acute toxicity than aqueous
extract of S. hispidus. Despite these justifications
that S. hispidus stem bark extracts may be
relatively safe, moderate dosage is advised for
purposes of medication. Also, studies to
establish safer and therapeutic doses of S
hispidus stem bark for specific ailments as well
as research on its cytotoxic effect on animal
model are recommended in order to ascertain its
true toxic level.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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