Tamiru et al. BMC Complementary and Alternative Medicine 2012, 12:151
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RESEARCH ARTICLE
Open Access
Evaluation of the effects of 80% methanolic leaf
extract of Caylusea abyssinica (fresen.) fisch. &
Mey. on glucose handling in normal, glucose
loaded and diabetic rodents
Wondmagegn Tamiru1, Ephrem Engidawork1* and Kaleab Asres2
Abstract
Background: The leaves of Caylusea abyssinica (fresen.) Fisch. & Mey. (Resedaceae), a plant widely distributed in East
African countries, have been used for management of diabetes mellitus in Ethiopian folklore medicine. However, its
use has not been scientifically validated. The present study was undertaken to investigate antidiabetic effects of the
hydroalcoholic leaf extract of C. abyssinica extract in rodents.
Materials and method: Male Animals were randomly divided into five groups for each diabetic, normoglycemic
and oral glucose tolerance test (OGTT) studies. Group 1 served as controls and administered 2% Tween-80 in
distilled water, (TW80); Group 2 received 5 mg/kg glibenclamide (GL5); Groups 3, 4 and 5 were given 100 (CA100),
200 (CA200) and 300 (CA300) mg/kg, respectively, of the hydroalcoholic extract of C. abyssinica. Blood samples were
then collected at different time points to determine blood glucose levels (BGL). Data were analyzed using one way
ANOVA followed by Dunnet’s post hoc test and p < 0.05was considered as statistically significant.
Results: In normal mice, CA200 and GL5 induced hypoglycemia starting from the 2nd h but the hypoglycemic
effect of CA300 was delayed and appeared at the 4th h (p < 0.05 in all cases). In diabetic mice, BGL was significantly
reduced by CA100 (p < 0.05) and CA300 (p < 0.01) starting from the 3rd h, whereas CA200 (p < 0.001) and GL5
(p < 0.05) attained this effect as early as the 2nd h. In OGTT, TW80 (p < 0.01) and CA100 (p < 0.01) brought down BGL
significantly at 120 min, while CA200 (p < 0.001) and GL5 (p < 0.001) achieved this effect at 60 min indicating the
oral glucose load improving activity of the extract. By contrast, CA300 was observed to have no effect on OGTT.
Acute toxicity study revealed the safety of the extract even at a dose of 2000 mg/kg. Preliminary phytochemical
study demonstrated the presence of various secondary metabolites, including, among others, saponins, flavonoids
and alkaloids.
Conclusion: The results indicate that C. abyssinica is endowed with antidiabetic and oral glucose tolerance
improving actions, particularly at the dose of 200 mg/kg in experimental animals. These activities of the plant
extract may be related to the presence of secondary metabolites implicated in antidiabetic activities of plant
extracts via different hepatic and extra-hepatic mechanisms. These results thus support the traditional use of the
leaf extract for the management of diabetes mellitus.
Keywords: Caylusea abyssinica, Diabetes, Hypoglycemic effect
* Correspondence: ephrem.engidawork@aau.edu.et
1
Department of Pharmacology and Therapeutics, School of Pharmacy, Addis
Ababa University, P.O, Box 1176, Addis Ababa, Ethiopia
Full list of author information is available at the end of the article
© 2012 Tamiru et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Tamiru et al. BMC Complementary and Alternative Medicine 2012, 12:151
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Background
Diabetes mellitus (DM) is a group of metabolic disorders
characterized by the presence of a chronic hyperglycemia
due to defective insulin secretion and/or insulin action. It
is also associated with dysfunctions in carbohydrate, fat
and protein metabolism [1,2]. Chronic hyperglycemia can
lead to long-term complications and tissue damages such
as retinopathy, nephropathy and/or neuropathy, often
associated with serious diseases, which are devastating to
the individual and very expensive to the health care services [3]. The worldwide prevalence of DM has risen dramatically over the past two decades at alarming rates. The
global prevalence for 2010 was 6.4% and predicted to rise
to 7.1% by the year 2030 [3,4]. Several treatment strategies
are currently used for managing DM and early intervention is needed in order to minimize the risk of macrovascular disease such as cardiovascular disorders [5]. Insulin
and oral hypoglycemic agents as well as diet and exercise
may be used in the management of DM. In spite of the
introduction of hypoglycemic agents, diabetes and the
related complications continue to be a major health problem worldwide [6].
Since time immemorial, plant extracts have been used
to treat patients with DM in various parts of the world.
Currently, especially in developing countries, many
plants were listed to be used for the management of diabetes [7-10]. A large number of these plants or their
preparation have been evaluated and confirmed to have
hypoglycemic effects in animal models [11,12]. Some
have also been evaluated in human beings [13-15]. Most
of these plants contain glycosides, alkaloids, terpenoids,
flavonoids, polysaccharides, and saponins, which are frequently implicated to having anti-diabetic effect [16,17].
However, much is not known about the specific mechanism of action of these plants, although insulinomimetic
activity has been proposed for some [18].
The practice of using plants for management of diabetes
is also documented in Ethiopia just like other ailments.
The leaves of Caylusea abyssinica (fresen.) Fisch. & Mey.
(family, Resedaceae) have been used in the treatment of
DM in Ethiopian folk-medicine without any scientific
proof for safety and efficacy [19]. Thus, investigating the
safety and efficacy of this plant in animal model could give
valuable information to the public at large and also serves
as baseline data for researchers engaged in search of medicinal plants with antidiabetic activity. The World Health
Organization Expert Committee on diabetes recommended that traditional medicinal herbs be further investigated as they are frequently considered to be less toxic
and free from side effects [20]. Therefore, search for safe
and more effective agents has continued to be an important area of active research. The present study was therefore undertaken to investigate antidiabetic effects of the
80% methanolic leaf extract of C. abyssinica in rodents.
Page 2 of 7
Method
Drugs and chemicals
The following drugs and chemicals were used in the
experiment: Streptozocin (Chengdu Yuyang High-tech
Developing Co.,Ltd, China), glucose standard strip/kits
(GLAB, Germany), glibenclamide (Sanofi-Aventis, USA),
one touch glucometer (GLAB, Germany), Tween-80
(BDH Laboratory supplies Ltd, England), methanol absolute acetone free (ReAgent Chemical Services Ltd, UK),
hydrochloric acid (BDH Ltd, England,) chloroform
(ACS, ISO, Merck), sulfuric acid (Farm Italia Carrloerba,
Italy), acetic anhydride (Techno Pharmchem, India), ferric chloride (FISHER Scientific Company, New Jersey),
potassium ferrocyanide (BDH Ltd, England), ferric
sulfate (BDH Ltd, England), lead acetate (BDH Ltd,
England), and ethyl acetate (ACS, Merck).
Plant material
C. abyssinica (fresen.) Fisch. & Mey, was collected from
Dirre, 55 km away from Addis Ababa (10 km on the
roadway from Bishoftu to Ziquala) in November 2010.
Taxonomic identification was done and a voucher specimen was deposited (voucher specimen number WT/
001) at the National Herbarium, College of Natural
Sciences, Addis Ababa University.
Experimental animals
Healthy Male Swiss albino mice (weighing 20–30 g and
age of 8–12 weeks) and Wistar rats (weighing 150–200 g
and age of 3 months) were obtained from the animal
house of Ethiopian Health and Nutrition Research Institute and School of Pharmacy, Addis Ababa University.
Animals were housed in polypropylene cages (6–10 animals per cage), maintained under standard condition
(12 h light and 12 h dark cycle; 25-30°C) and allowed
free access to pellet diet and water ad libtum. After randomized grouping and before initiation of the experiment, animals were acclimatized to the laboratory
conditions. All procedures complied with The Guide for
the Care and Use of Laboratory Animals [21] and
approved by the Institutional Review Board of the
School of Pharmacy, Addis Ababa University.
Extraction
Leaves of the plant material was thoroughly washed with
distilled water to remove dirt and soil, and dried under
shade and optimal ventilation. The plant material was
then pulverized and the powdered plant material was
macerated in 80% methanol for 72 h in three successive
volumes. The resultant hydro-alcoholic extract was dried
under reduced pressure. The dried extract was kept in a
refrigerator until use.
Tamiru et al. BMC Complementary and Alternative Medicine 2012, 12:151
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Preliminary phytochemical screening
Hypoglycemic test in normal mice
Standard screening tests of the extract were carried out
for various plant constituents. The crude extract was
screened for the presence or absence of secondary metabolites such as reducing sugars, alkaloids, steroidal compounds, phenolic compounds, tannins, saponins,
flavonoids, cardiac glycosides, and anthraquinones using
standard procedures [22,23].
Mice were fasted for 4–6 h, but water was allowed ad
libtum, and then randomly divided into five different
groups (6 animals per group). The animals were treated
according to their respective grouping. Using aseptic conditions, blood sample was then collected from tail veins of
each animal to determine BGL at 0, 1, 2, 3 and 4 h posttreatment. BGL was determined using GLAB strips and
GLAB one-touch glucometer. Measurement of BGL was
done in triplicate and the average value was taken.
Acute toxicity test
Acute toxicity test was done based on the limit test
recommendations of OECD 425 Guideline [24]. On day
one, Swiss albino mouse fasted for 3–4 h was given
2000 mg/kg of the extract orally. The mouse was then
kept under strict observation for physical or behavioral
changes for 24 h, with special attention during the first
4 h. Following the results from the first mouse, other
four mice were recruited and fasted for 3–4 h and administered a single dose of 2000 mg/kg and was observed
in the same manner. These observations continued for
further 14 days for any signs of overt toxicity.
Grouping and dosing of animals
Male animals were used for the hypoglycemic and antidiabetic studies based on the results of preliminary study
which demonstrated a better percent induction of diabetes by streptozotocin in males than females. Besides,
published reports indicate streptozotocin induces severe
diabetes in females, with diminished survival rates and
they are also less sensitive to insulin compared to male
animals [25]. For oral glucose tolerance tests (OGTT),
rats were used since they are preferable in such studies
[26]. In all cases, group I received 2% Tween-80 in distilled water (TW80) and served as controls; Group II
received a standard, 5 mg/kg of glibenclamide, (GL5);
Group III-V received 100 mg/kg (CA 100), 200 mg/kg
(CA 200) and 300 mg/kg (CA 300). of C. abyssinica
extract, respectively.
The doses were selected based on the acute toxicity
study. The middle dose was one tenth of the limit dose
which was 200 mg/kg. Higher dose was calculated as
twice the middle dose, which should have been 400 mg/
kg. However; the data from preliminary study revealed
that 400 mg/kg tended to raise blood glucose level
(BGL) and CA 300 was thus taken as a higher dose level.
The lower dose level was calculated by taking half of the
middle dose, i.e. 100 mg/kg. Volume administered was
determined based on OECD guideline that states 2 mL/
100 g of body weight of the animal [24]. For the positive
control, 5 mg/kg was selected based on earlier reports
[27,28]. As people traditionally use the preparations of
the plant extract via oral route, the study was conducted
using oral route of administration [19].
Assessing antidiabetic activity
Diabetes was induced using streptozocin. The drug was
dissolved in 0.1 M citrate buffer (pH = 4.5). The solution
was then administered intraperitonially at 150 mg/kg
dose to mice that were fasted for 4–6 h prior to administration. Seventy-two hours later, animals were screened
for diabetes. Mice which showed fasting BGL > 200 mg/
dL were included in the study [29]. Diabetic mice were
kept for overnight, each group in a separate cage and
were fasted for 4–6 h. The animals were then randomly
divided into five groups (n = 9/group) and treated with
the extract according to their respective group. Blood
samples were collected from the tails of the animals to
determine BGL at 0, 1, 2, 3 and 4 h post-treatment.
Oral glucose tolerance test
Rats were fasted overnight for 12–14 h and assigned
randomly into 5 groups (n = 6/group), each group in
separate cage and baseline BGL was determined. Thirty
minutes before extract treatment, all of the rats were
loaded with 2 g/kg glucose solution and then orally treated according to their respective grouping. Blood samples were then collected to determine BGL prior to
treatment and after 30, 60 and 120 min of treatment as
described above.
Statistical analysis
All data were expressed as mean ± SEM and percent
changes. Between and within group analysis was carried
out using one way ANOVA followed by Dunnet’s post
hoc test and level of significance was set at p < 0.05. For
data processing, SPSS data analysis software Version
19.0 was used.
Results
Extraction
The percentage yield of 80% methanolic extract of
the dried leaves of C. abyssinica was found to be 18.5%
(w/w). The extract was dark-brown semisolid at room
temperature and solidified when stored in a refrigerator.
Extract returned to semisolid state on re-exposure to
room temperature.
Tamiru et al. BMC Complementary and Alternative Medicine 2012, 12:151
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Preliminary phytochemical screening
Phytochemical screening of the crude extract of C. abyssinica revealed the presence of various secondary metabolites (Table 1). Alkaloids, cardiac glycosides, reducing
sugars, steroidal compounds and phenolic compounds,
tannins, saponins and flavonoids were detected in the
crude extract.
Acute toxicity study
Acute toxicity study of the hydroalcoholic extract of C.
abyssinica did not reveal any behavioral, neurological,
autonomic or physical changes such as alertness, motor
activity, restlessness, convulsions, coma, diarrhea and
lacrimation. Besides, the extract did not cause mortality
in the animals at a dose of 2000 mg/kg during the observation time. Thus, the median lethal dose (LD50) of the
plant extract is said to be greater than 2000 mg/kg, indicating a good safety margin.
Effects on normoglycemic mice
Results of the effect of C. abyssinica on BGL of normal
mice are presented in Table 2. Within group analysis
revealed that TW80 treated animals did not show significant reduction in BGL across all time points compared to
the fasting (initial or baseline) level, although percent reduction tended to be higher at the 3rd (30.9%) and 4th
(23.8%) h. Similarly, CA100 failed to show significant
hypoglycemic effect at all-time points, though percent reduction appeared to be higher at the 3rd (42.5%) and 4th
(42.1%) h. By contrast, CA200 produced a significant
(p < 0.05) reduction in BGL at the 2nd (47%), 3rd (49.4%)
and 4th (44%) h post treatment compared to the initial
level. Likewise, GL5 brought about significant reduction at
the 2nd (p < 0.05), 3rd (p < 0.01) and 4th h (p < 0.05), by
about 37.3%, 42.8% and 29.9%, respectively. However,
Table 1 Phytochemical screening results of the 80%
methanolic extract of the leaves of Caylusea abyssinica
TEST
RESULT
Page 4 of 7
CA300 was noted to produce significant reduction
(p < 0.05, 53.5%) of BGL only at the 4th h.
Between groups analysis, on the other hand, did not
produce any significant difference in fasting BGL across
groups. Significant hypoglycemia was, however, recorded
for CA200 and GL5 at the 2nd h (p < 0.05 in both cases)
when the groups were compared with TW80. Interestingly, no apparent difference was noted when the different doses of the extract were compared with each other
as well as with the positive control at all-time points.
Effects on streptozocin-induced diabetic mice
Seventy five mice were injected streptoztocin and 50 of
them found to be diabetic, with a success rate of 66.7%.
Out of the fifty mice, two died before the start of administration of the extract and all the rest survived until the
end of the experiment. The effects of C. abyssinica on
streptozotocin-induced diabetes are shown in Table 3.
Intra-group analysis demonstrated that TW80 had no effect on BGL at all-time points compared to the initial
level. By contrast, treatment with the extract and glibenclamide did produce alterations in BGL compared to initial values. Accordingly, whilst CA100 (p < 0.05 in both
cases) and CA300 (p < 0.01 in both cases) produced a
significant reduction at the 3rd and 4th h; CA200
(p < 0.001 in all instances) and GL5 (p < 0.05, p < 0.01,
and p < 0.001, for the time points, respectively) did show
a significant reduction at the 2nd, 3rd and 4th h. Maximum reduction was attained at the 4th h, with percent
reduction for CA100, C200, C300, GL5 being 52.2%,
62.3%, 52.8%, and 63%, respectively.
In inter-group analysis, no detectable changes were
noted between the fasting BGL of all groups. Subsequent
analysis showed that CA100 (p < 0.05 in all cases) and
CA200 (p < 0.05 at the 1st h and p < 0.01 for the rest) significantly decreased BGL at all-time points compared to
TW80 animals. Likewise, GL5 produced a similar pattern, with p-values becoming very significant (p < 0.01 or
p < 0.001) from the 2nd h onwards. On the other hand,
CA300 was capable of reducing BGL significantly
(p < 0.05) only at the 2nd and 3rd h (p < 0.05 in both
cases). No detectable changes in BGL were observed
either amongst the extract or when extracts were
compared with the positive control.
Alkaloids
+
Tannins
+
Saponins
+
Anthraquinone glycosides
-
O-anthraquinones
-
Effect on oral glucose tolerance test in rats
Cardiac glycosides
+
Flavonoids
+
Reducing sugars
+
Phlabotannins
-
Steroidal compounds
+
Phenolic compounds
+
Effects of the extract of C. abyssinica on OGTT are shown
in Table 4. BGL of all groups prior to extract administration
(0 min) showed no apparent difference compared to each
other. All groups, however, showed significant increase by
20-40% (p < 0.05 or p < 0.01) in BGL 30 min following
extract administration (one hour after oral glucose loading),
confirming the induction of hyperglycemia. Hyperglycemia
with glucose challenge was not significantly brought down
+ : present, – : absent.
Tamiru et al. BMC Complementary and Alternative Medicine 2012, 12:151
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Table 2 Hypoglycemic effects of 80% methanolic leaf extract of Caylusea abyssinica on blood glucose levels in normal
mice
Blood glucose level in mg/dL
Group
0h
1h
TW80
72.00 ± 9.77
66.00 ± 6.51
GL5
85.33 ± 11.61
68.83 ± 9.22
CA100
79.17 ± 25.33
53.5 ± 3.82
2h
3h
81.67 ± 10.83
53.5 ± 5.47a1,b1
58.67 ± 7.42
a1,b1
CA200
83.33 ± 16.76
54.17 ± 8.53
44.33 ± 6.38
CA300
96.33 ± 21.44
75.00 ± 16.21
57.17 ± 5.91
4h
50.33 ± 1.67
54.83 ± 2.97
48.83 ± 2.44a2
56.83 ± 6.2a1
45.5 ± 3.21
45.83 ± 4.43
a1
46.83 ± 3.05a1
42.17 ± 3.4
44.83 ± 3.12a1
50.5 ± 7.11
n = 6; CA100 = C. abyssinica extract 100 mg/kg, CA200 = C. abyssinica extract 200 mg/kg, CA300 = C. abyssinica extract 300 mg/kg, TW80 = 2%Tween-80,
GL5 = Glibenclamide 5 mg/kg; a compared with fasting blood glucose level (t = 0 h), b compared with negative control group; 1p < 0.05, 2 p < 0.01.
with TW80 at 60 min but significant difference was
achieved at 120 min (p < 0.01, 35.6%). Although CA100
failed to produce detectable changes at 60 min, it brought
down glucose level by 45.4% (p < 0.01) at 120 min compared to peak hyperglycemia. CA200, however, significantly
improved oral glucose loading at 60 (p < 0.001, 31.8%) and
120 min (p < 0.001, 37.4%), respectively. Likewise, GL5 produced significant improvement of hyperglycemia at 60
(p < 0.001, 40.6%) and 120 min (p < 0.001, 42%). By contrast,
CA300 failed to produce significant improvement in BGL
following glucose challenge at all-time points.
Inter-group analysis, on the other hand, showed that
GL5 and CA 200 were capable of reducing BGL significantly (p < 0.001and p < 0.01, respectively) at 60 min
compared with TW80. However, BGL was not significantly different between GL5, CA200 and TW80 at
120 min. None of the three doses showed significant
difference amongst each other at all-time points. In contrast, GL5 treated groups exhibited significant improvement (p < 0.001) at 60 min compared to CA100.
Discussion
Developing agents for management of DM that are devoid
of adverse effects are still a challenge to the medical care
system. Thus, research is increasingly done on medicinal
plants with the hope of developing a relatively safe antidiabetic plant-based product alone or in combination with
other agents [29]. In this study, no detectable changes
were observed in baseline BGL across groups in both
normal (Table 2) as well as diabetic animals (Table 3),
however, significant reductions started to appear when the
hydroalcoholic extract and the standard drug were administered, indicating that changes produced were attributed
to treatments received. Therefore, the results of this study
indicated that hydroalcoholic extract of C. abyssinica
reduces BGL level in normal and diabetic mice as well as
in glucose induced hyperglycemic rats.
Among the various doses of the extract, maximum
activity was observed with CA200 in all tests. It is interesting to note that CA200 was capable of bringing down
streptozocin-induced hyperglycemia close to TW80 and
GL-5 values (Table 3). The extract also brought the
hyperglycemic state in OGTT down within 60 min in
the same manner to that of glybenclamide (Table 4).
Thus, it is plausible to assume that the plant extract and
glibenclamide might produce hypoglycemic and antidiabetic effects by a similar mechanism (i.e. by enhancing
insulin release or insulin-like effect). Extracts of other
plants, including Cassia italic [30] and Vinca rosea [27]
have been reported to have similar mode of action with
that of glibenclamide, lending evidence to this assertion.
It was observed that the extract exerted its action in a
non-dose dependent manner, particularly the higher
dose produced less activity. CA300 did produce a
delayed but significant hypoglycemia and antidiabetic action, although it did not improve oral glucose tolerance.
Table 3 Antidiabetic effects of 80% methanolic leaf extract of Caylusea abyssinica on blood glucose levels in
streptozotocin induced mice
Blood glucose level in mg/dL
Group
0h
1h
TW80
376.56 ± 39.02
432. 78 ± 33.87
338.33 ± 24.22
GL5
342.44 ± 36.97
306.00 ± 40.97
223.78 ± 31.27a1,
CA100
CA200
CA300
335.33 ± 48.12
326.44 ± 43.78
352.11 ± 38.52
2h
b1
269.56 ± 43.34
b1
268.33 ± 18.28
318.556 ± 40.49
3h
b1
b1
215.11 ± 37.27
a3, b2
167.89 ± 18.01
b1
229.22 ± 30.78
4h
331.45 ± 47.53
272.00 ± 38.58
161.22 ± 27.69a2,
b2
126.56 ± 22.64a 3,
a1, b1
160.33 ± 36.98
a3, b2
123.00 ± 15.52 a3,
179.89 ± 39.39
147. 78 ± 19.61
187.44 ± 36.39
a2, b1
b2
a1, b1
a2
166.22 ± 34.29
n = 9-10; CA100 = C. abyssinica extract 100 mg/kg, CA200 = C. abyssinica extract 200 mg/kg, CA300 = C. abyssinica extract 300 mg/kg, TW80 = 2%Tween-80,
GL5 = Glibenclamide 5 mg/kg; a compared with fasting blood glucose level (t = 0 h), b compared with negative control group; 1p < 0.05, 2 p < 0.01, and 3p < 0.001.
b2
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Table 4 The effects of 80% methanolic leaf extract of Caylusea abyssinica on Oral Glucose Tolerance Test in rats
Blood glucose level in mg/dl
Group
0 min
30 min
TW80
102.33 ± 3.20
140.50 ± 16.76a1
60 min
GL5
101.83 ± 6.29
125.17 ± 11.47 a2
CA100
116.83 ± 4.19
158.67 ± 15.34 a2
a1
CA200
104.00 ± 1.98
131.50 ± 8.68
CA300
103.50 ± 9.21
127.17 ± 13.34a1
120 min
126.83 ± 6.55d3
74.33 ± 8.72b3,c3
145.83 ± 7.03d3
b3,c2
89.67 ± 4.90
117.33 ± 9.06d3
90.50 ± 1.96 b2
72.67 ± 8.79b3
86.67 ± 5.82b3
82.33 ± 4.45b3,e2
100.00 ± 12.03
n = 6; CA100 = C. abyssinica extract 100 mg/kg, CA200 = C. abyssinica extract 200 mg/kg, CA300 = C. abyssinica extract 300 mg/kg, TW80 = 2%Tween-80,
GL5 = Glibenclamide 5 mg/kg; a compared to blood glucose levels (BGL) at 0 min, b compared with BGL after 30 min, c compared with the negative control,
compared with the positive control; 1p < 0.05, 2 p < 0.01 and 3 p < 0.001. Time refers to time after extract administration.
The highest dose determined was 400 mg/kg, however,
this dose produced an increase in BGL during the preliminary analysis that led to its exclusion from the study.
This observation suggests that activity might decrease
with dose. BGL reduction, probably, is the net effect of
the interplay between various constituents of the extract.
It is likely that higher doses may activate non-specifically
both BGL lowering and rising mechanisms. Indeed, it
has been reported that the presence of interfering substances in plant extracts may diminish hypoglycemic
effect [12,31-35]. It is also likely that bigger doses could
cause some toxic effect [35] to specific targets of glucose
lowering mechanisms, which could have been the target
for hypoglycemic agents.
On the other hand, the lower dose (100 mg/kg) of the
extract appeared to be ineffective in reducing BGL in
normal (Table 2) and glucose loaded animals (Table 4).
This could be attributed to inability of the dose to overcome counter-regulatory physiological mechanisms [36],
lesser concentration of the active principles to induce
hypoglycemia or the small sample size employed that
precluded statistical significance. On the other hand,
CA100 produced antidiabetic action in streptozocininduced mice, which might imply that the hypoglycemic
nature of the lower dose would be apparent when there
is an alteration in normal blood glucose regulatory
systems by diabetes.
The results also showed that antidiabetic activity of
the extract increased with time, as maximal effect was
achieved at the 4th h (Table 3). This could mean that the
active principles in the extract need time to reach sufficient concentration at the target site, as a similar pattern
was observed with other plants displaying anti-diabetic
activity [37]. The plant extract showed relatively faster
antidiabetic onset of action than the standard drug.
However, the doses of C. abyssinica extract exhibited a
varied onset of action, which probably resulted from
interference of other principles, particularly at higher
doses. Constituents such as reducing sugars that have a
higher glycemic index could give rise to free glucose
after digestion and they may tend to raise BGL following
d
absorption. The appearance of such an effect in the face
of the hypoglycemic actions by the active agents could
lead to a delay in appearance of the action, especially at
higher doses where the extract may result in higher
concentrations of such molecules.
Interestingly, in OGTT the hydroalcolic extract
showed significant reduction in BGL from 60 min onwards except for the higher dose. This suggests that the
extract is endowed with the ability to enhance glucose
regulatory mechanisms, reflecting a potential advantage
of the extract in minimizing hyperglycemia related complications of diabetes. This is true provided that the
extract happens to demonstrate a similar action with
repeated administration.
Preliminary phytochemical screening of the hydroalcoholic extract of C. abyssinica demonstrated the presence
of secondary metabolites (Table 1), which are known to
produce hypoglycemic effects in other plants by various
mechanisms [18,38,39]. No previous phytochemical
reports could be found in the literature concerning the
genus Caylusea. However, other members of the family
Resedaceae such as Reseda muricata and Randonia africana have been reported to contain flavonoids, phenolic
compounds, glycosides and alkaloids [40], which are in
line with the current findings. Thus, the antidiabetic,
hypoglycemic and enhanced glucose utilization effect of
the hydroalcoholic extract of C. abyssinica may be associated with the presence of these different secondary
metabolites that act individually or synergistically.
Conclusion
Taken together, the present study demonstrated that the
80% methanolic extract of C. abyssinica exhibited a significant antidiabetic effect in rodents, providing evidence
for the traditional claim. The effective dose of the extract
was found to be 200 mg/kg, although this dose was associated with the risk of hypoglycemia. Besides, the plant
was found to have a greater safety margin, which is
coupled with its activity making it a potential herb to
develop plant-based products after further investigation.
Tamiru et al. BMC Complementary and Alternative Medicine 2012, 12:151
http://www.biomedcentral.com/1472-6882/12/151
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
All authors involved in the design and write up of the study, and WT
-conducted the actual study and the statistical analysis. All authors approved
the submitted version of the manuscript.
Acknowledgements
We are grateful to Addis Ababa University for funding this study.
Author details
1
Department of Pharmacology and Therapeutics, School of Pharmacy, Addis
Ababa University, P.O, Box 1176, Addis Ababa, Ethiopia. 2Department of
Pharmacognosy and Pharmaceutical Chemistry, School of Pharmacy, Addis
Ababa University, Addis Ababa, Ethiopia.
Received: 19 March 2012 Accepted: 8 September 2012
Published: 11 September 2012
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Cite this article as: Tamiru et al.: Evaluation of the effects of 80%
methanolic leaf extract of Caylusea abyssinica (fresen.) fisch. & Mey. on
glucose handling in normal, glucose loaded and diabetic rodents. BMC
Complementary and Alternative Medicine 2012 12:151.