Journal of Experimental Pharmacology
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ORIGINAL RESEARCH
Evaluation of hypoglycemic, antihyperglycemic and
antihyperlipidemic activities of 80% methanolic
seed extract of Calpurnia aurea (Ait.) Benth.
(Fabaceae) in mice
This article was published in the following Dove Press journal:
Journal of Experimental Pharmacology
Yaschilal Muche Belayneh 1
Eshetie Melese Birru 2
Digambar Ambikar 2
1
Department of Pharmacy, College of
Medicine and Health Sciences, Wollo
University, Dessie, Ethiopia; 2Department
of Pharmacology, College of Medicine and
Health Sciences, University of Gondar,
Gondar, Ethiopia
Background: Diabetes mellitus is one of the most common chronic health problems in the
world. As currently available antidiabetic medications have limitations in terms of safety,
efficacy, and cost, it is an important research area to investigate medicinal plants for new
antidiabetic compounds that can lead to effective, safe and less costly pharmacotherapy. The
present study was done to evaluate the antidiabetic and antidyslipidemic activities of 80%
methanolic seed extract of Calpurnia aurea (Ait.) Benth. (Fabaceae) in mice.
Methods: Blood glucose lowering activity of three doses (2.75 mg/kg, 5.5 mg/kg and 11
mg/kg) of the hydromethanolic seed extract of Calpurnia aurea was studied in three animal
models: normoglycemic mice, oral glucose-loaded mice, and streptozotocin-induced diabetic
mice. Additionally, the effect of the seed extract on body weight and serum lipid profile was
studied in the streptozotocin-induced diabetic mice. Glibenclamide (5 mg/kg) was used as a
standard drug in all animal models of the study. Blood glucose level was measured using a
glucose meter, whereas serum lipid level was measured using an automated chemistry
analyzer. Data were analyzed using one-way analysis of variance followed by Tukey’s post
hoc multiple comparison test.
Results: Hydromethanolic extract of C. aurea seeds showed blood glucose lowering activity
in all animal models, and it improved body weight loss and diabetic dyslipidemia in diabetic
mice after 14 days of treatment.
Conclusion: This study revealed that hydromethanolic extract of Calpurnia aurea seeds has
significant hypoglycemic, antihyperglycemic and antihyperlipidemic activities.
Keywords: diabetes mellitus, calpurnia aurea, streptozotocin, seed, mice
Background
Correspondence: Yaschilal Muche
Belayneh
Department of Pharmacy, College of
Medicine and Health Sciences, Wollo
University, PO Box 1145, Dessie, Ethiopia
Tel +251 91 809 2466
Email yaschilal.muche19@gmail.com
Diabetes mellitus (DM) is one of four priority non-communicable public health
problems targeted for action by WHO.1 Diabetes directly affects lipid levels in the
blood, resulting in diabetic dyslipidemia.2 Diabetic patients are likely to have lower
serum levels of high-density lipoprotein cholesterol (HDL-C), higher serum levels
of triglyceride (TG), and similar serum values for low-density lipoprotein cholesterol (LDL-C) but with higher levels of small dense LDL when compared with nondiabetic patients.3,4
Currently available medications for DM are often limited in efficacy, carry the risk of
adverse effects, and are often too costly, especially for the developing world.5 Therefore,
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Journal of Experimental Pharmacology 2019:11 73–83
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http://doi.org/10.2147/JEP.S212206
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Belayneh et al
searching for plant-derived antidiabetic compounds which are
accessible and do not require intensive and costly pharmaceutical processing is an attractive research area. It was estimated
that more than 1,000 plant species are traditionally being used
for the treatment of DM.5 The families of plants with the most
potent antidiabetic activities include Leguminosae (Fabaceae),
Asteraceae, Moraceae, Lamiaceae, Liliaceae, Cucurbitaceae,
Rosaceae, Euphorbiaceae, and Araliaceae.6
Calpurnia aurea (Ait.) Benth. (Fabaceae) is a yellowflowered, multi-stemmed, 3–4 m tall small tree or shrub
widely distributed in Africa, ranging from the Cape
Province to Eritrea, and it also occurs in southern India.7,8
There are two subspecies of C. aurea, subsp. aureu which is
found in Ethiopia and other parts of Africa and subsp.
indica which occurs in India.9
C. aurea (Ait.) Benth. (Fabaceae) is traditionally used
for the treatment of DM in parts of Ethiopia. An ethnobotanical survey of Shenasha, Agew-awi, and Amhara peoples
of northwest Ethiopia reported that the seed, as well as the
leaf of the plant, is used orally for the treatment of DM.10
Another survey in Nekemtae town (east Wollega, Ethiopia)
reported that a leaf decoction of the plant is taken orally to
treat DM.11 However, the antidiabetic activity of this medicinal plant has not been scientifically studied.
There is considerable evidence that induction of oxidative stress is a key process in the pathogenesis of DM and
diabetic complications.12–14 The role of antioxidants in
treating diabetes and its complications through prevention
of oxidative stress has been explained.13–15 C. aurea (Ait.)
Benth. leaves and seeds have strong in vitro antioxidant
activities.7,16
The antidiabetic activity of medicinal plants is mainly
due to the presence of alkaloids, phenolic compounds,
flavonoids, and terpenoids.5,6,17–19 A previous preliminary
phytochemical study has shown that the hydromethanolic
extract of C. aurea seeds also contains these secondary
metabolites, which are known to have blood glucose lowering activity.20
The present study was therefore undertaken to investigate the antidiabetic and antidyslipidemic effects of an
80% methanolic seed extract of C. aurea (Ait.) Benth.
(Fabaceae) using in vivo models. The findings of this
study may serve as baseline information for the scientific
community to further investigate the plant C. aurea by
initiating advanced studies on molecular mechanisms
with identification of the active phytochemicals which
may serve as lead compounds for the development of
new antidiabetic drugs.
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Materials and methods
Collection of plant materials
Fresh matured seeds of C. aurea were collected from the
compound of the University of Gondar, Gondar town
(located in the Central Gondar zone of Amhara region,
northwest Ethiopia) in January 2017. Taxonomic identification of the plant was done by a botanist, and a specimen
of the plant material was preserved in the Herbarium of the
Biology Department, University of Gondar with a voucher
number YM001 for future reference.
Drugs, chemicals, and instruments
The following drugs, chemicals, and instruments were
used during the study. Streptozotocin (STZ; Sigma
Aldrich Co., St Louis, MO, USA), glibenclamide (GLC;
Julphar Pharmaceuticals, Ras Al Khaimah, United Arab
Emirates), citric acid monohydrate (Lab Tech Chemicals,
India), tri-sodium citrate dihydrate (Blulux Laboratories,
Faridabad, India), methanol absolute (Nice Chemicals
Private Limited, Ernakulam, India), 40% glucose solution
(Reyoung Pharmaceuticals, Shandong, China), sterilized
water for injections (Nirma Ltd, Ahmedabad, India), analytical balance, pH meter, i-QARE DS-W® blood glucose
meter and strips (Alliance International, Taiwan), distilled
water (DW), automated chemistry analyzer (Shenzhen
Mindray Bio-medical Electronics Co., Ltd, Shenzhen,
China). All chemicals used were of analytical grade.
Preparation of plant crude extracts
The seeds of the plant were thoroughly washed with DW
to remove dirt and then dried under shade with optimal
ventilation. Then, the dried seeds were pulverized. The
coarse-powdered seeds (1 kg) were macerated in 80%
methanol for 72 h and then the extracts were filtered
using Whatman filter paper No.1. The marc was remacerated two times with fresh solvent, each for 72 h, and the
filtrates obtained from the successive maceration were
dried in an oven at 40°C.
Experimental animals
Healthy male Swiss albino mice (weighing 25–30 g and
aged 8–12 weeks) were used in all experiments except for
the acute oral toxicity tests. The mice were obtained from
the Ethiopian Public Health Institute (EPHI) and they were
kept in the animal house of the Department of
Pharmacology, University of Gondar. The animals were
fed with a standard pellet diet and water ad libitum.
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Animals were acclimatized to the laboratory conditions for
a week before the initiation of the experiment. Fasting
animals were kept in raised mesh bottom cages to prevent
coprophagy.
Acute toxicity study
The acute oral toxicity test of the hydromethanolic seed
extract was done based on the limit and main test recommendations of OECD No 425 Guideline.21 On the first day
of the test, one female Swiss albino mouse fasted for 3 h
was given 2,000 mg/kg of the extract orally. As mortality
was observed in the first mouse that received 2,000 mg/kg
of the seed extract, the main test was conducted in order to
determine the LD50. In the main test single female mice
were dosed in sequence at 48 h intervals using a starting
dose of 175 mg/kg and a dose progression factor of 3.2.
The dosing was stopped after testing six consecutive animals because five reversals (response, which is the death
of the mouse, was observed at one dose, and a nonresponse is observed at the next dose tested) occurred.
Animals were observed individually at least once during
the first 30 min after dosing, periodically during the first
24 h with special attention given during the first 4 h, and
daily thereafter, for a total of 14 days.
Grouping and dosing of animals
Male animals were used for normoglycemic, oral glucose
loaded, and diabetic mice models because female mice are
less sensitive to streptozotocin,22,23 and they are also less
sensitive to insulin compared to male animals.24
In the normoglycemic, oral glucose loaded and single
dose treated diabetic animal models, mice were randomly
divided into five groups (each group containing six mice).
In all three animal models, Group I (negative control) was
treated with 10 mL/kg DW; Groups II, III, and IV were
treated with 2.75 mg/kg, 5.5 mg/kg, and 11 mg/kg hydromethanolic seed extract, respectively; and Group V (positive control) was treated with the standard drug, 5 mg/
kg GLC.
In the repeated dose treated diabetic mice, animals
were randomly divided into six groups (five groups of
diabetic mice and one additional group of normal mice,
each group containing six mice). Group I was treated with
10 mL/kg DW and served as a diabetic control; Groups II,
III, and IV were treated with 2.75 mg/kg, 5.5 mg/kg, and
11 mg/kg hydromethanolic seed extract, respectively;
Group V was treated with 5 mg/kg GLC and served as a
diabetic positive control; and Group VI (a group of
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Belayneh et al
normoglycemic mice) was treated with 10 mL/kg DW
and served as a normal control.
The three different doses of hydromethanolic C. aurea
seed extract (CASE) for this study were selected based on
the result of the acute oral toxicity test. GLC (5 mg/kg) was
selected as a standard drug for this study based on reports of
earlier studies.25–27 The study was conducted using the oral
route of administration because people traditionally use the
plant via the oral route.10,11 All the doses were administered at
a volume not greater than 10 mL/kg body weight of mice.21
Measurement of blood glucose level
In all cases, blood samples for blood glucose measurement
were withdrawn from the tail vein of each animal by
cutting the tip of the tail aseptically. Blood glucose level
(BGL) was measured using a DS-W® blood glucose meter.
Measurement of the BGL was done in triplicate and the
average value was taken.
Induction of experimental diabetes
Experimental diabetes was induced using STZ. The drug
was dissolved in 0.1 M cold citrate buffer (pH=4.5). The
freshly prepared solution was then administered intraperitoneally at 150 mg/kg dose to mice28 which were fasted
overnight for 16 h prior to administration. Thirty minutes
after the administration of STZ, animals were allowed to
have free access to food and water. Additionally, animals
were allowed to drink 5% sucrose solution 6 h after the
administration of STZ for the next 24 h to prevent death
secondary to hypoglycemic shock. Then, animals were
screened for the induction of diabetes four days after
STZ injection. Mice which showed fasting BGL>200
mg/dL were included in the study as diabetic mice.26,29
Diabetic mice were randomly divided into different groups
just after the screening to perform the experimental studies. The bedding of the cages was changed every day
after STZ injection to maintain dryness of cages for polyuric diabetic animals.
Assessing hypoglycemic activity in
normoglycemic mice
Mice, which were fasted overnight for 16 h, were randomly divided into five different groups (six animals per
group). Then, the animals were treated according to their
respective groupings as mentioned above. BGL of each
mouse was measured just before treatment (at 0 h) as a
baseline, and then at 1, 2, 4 and 6 h post-treatment.
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Belayneh et al
Assessing the antihyperglycemic activity
of the seed extract in oral glucose-loaded
mice
Mice were used to evaluate the effect of the plant extract on
oral glucose tolerance because overnight fasting increases
their insulin sensitivity.30,31 Thus, the model can be more
sensitive to screen anti-hyperglycemic activity of the plant
extract. Overnight fasted (for 16 h) mice were randomly
divided into five groups (six mice per group). Then, mice
were treated with DW, hydromethanolic seed extract and
GLC according to their respective groupings. Thirty minutes after the treatments,25,32 2.5 g/kg of glucose solution
were administered to each animal orally.25 BGLs were
measured for each animal just before treatment (at 0 min)
as a baseline, and then at 30, 60 and 120 min following oral
glucose administration.25,33
Assessing the effect of a single dose of the
seed extract on blood glucose of diabetic
mice
After overnight fasting for 16 h, STZ-induced diabetic
mice were assigned randomly into five groups and treated
with DW, plant extract and GLC according to their respective groupings as explained above. BGL was measured
just before treatment (at 0 h) as a baseline, and then at 2,
4, 6 and 8 h post-treatment.
Assessing the effects of repeated doses of
the seed extract on blood glucose, body
weight and serum lipid level of diabetic
mice
Overnight fasted (for 16 h) diabetic mice and normal mice
were randomly divided into six groups and treated with
DW, seed extract and GLC once daily in the morning for
14 days according to their respective groupings as
explained above. BGL and body weight of diabetic mice
were measured just before starting treatment on the first
day as a baseline, and then on the seventh and 14th day of
treatment following overnight fasting for 16 h.34
On the 15th day, overnight fasted mice were euthanized by sodium pentobarbitone (150 mg/kg IP) anesthesia
and blood samples were collected via cardiac puncture
from each mouse. The blood samples were kept at room
temperature for 2 h to allow coagulation and then centrifuged at 2,000 rpm for 10 min. Then, serum samples were
prepared from supernatant of the centrifuged blood
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samples to measure the level of serum TG, TC, and
HDL-C using an automated chemistry analyzer.
Ethical considerations
The experiment was conducted in accordance with the
Guide for the Care and Use of Laboratory Animals,35
and the proposal of the study was submitted and approved
by the ethical review committee of the School of
Pharmacy, University of Gondar before the commencement of the study.
Statistical analysis
Data were expressed as mean ± standard error of the mean.
Means of all parameters among groups and within a group
were compared using one-way ANOVA followed by
Tukey’s post hoc multiple comparison test. Values of
p<0.05 were considered statistically significant. SPSS
Version 20 software (IBM Corporation, Armonk, NY,
USA) was used for statistical analysis.
Result
Percentage yield of the hydromethanolic
seed extract of C. aurea
A total of 136 g of dried yellowish brown gummy seed
extract was harvested at the end of the extraction process
from 1 kg of dried powdered seeds (percentage yield,
13.60% (w/w)).
Acute oral toxicity study
The acute oral toxicity study revealed that the median
lethal dose (LD50) of CASE is between 55 mg/kg and
175 mg/kg based on the main test recommendations of
OECD guideline no 425 (Table 1).
Hypoglycemic activity of 80% methanolic
seed extract of C. aurea in
normoglycemic mice
The effect of hydromethanolic seed extract of C. aurea on
fasting BGL of normoglycemic mice is summarized in
Table 2. Between-groups analysis revealed no significant
difference in baseline fasting BGL across groups. CASE
11 mg/kg significantly reduced the BGL at the fourth and
sixth hours (p<0.05) compared to the negative control.
Similarly, BGL was significantly reduced by 5 mg/kg
GLC at the second (p<0.05), fourth (p<0.01) and sixth
(p<0.05) hour compared to the negative control. A statistically significant difference in BGL was not observed
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Table 1 Acute oral toxicity study of the 80% methanolic seed extract of Calpurnia aurea
Test sequence
Mouse ID
Dose (mg/kg)
Outcome
Remark
1
2
1
2
175
55
Dead
Survived
Convulsion was followed by death within 10 mins after dosing
No death and sign of toxicity was observed
3
3
175
Dead
Convulsion was followed by death within 10 mins after dosing
4
5
4
5
55
175
Survived
Dead
No death and sign of toxicity was observed
Convulsion was followed by death within 10 mins after dosing
6
6
55
Survived
No death and sign of toxicity was observed
Table 2 Hypoglycemic activity of hydromethanolic Calpurnia aurea seed extract in normoglycemic mice
Group
Blood glucose level (mg/dL)
0h
1h
2h
4h
6h
DW 10 ml/kg
68.17±7.97
70.22±7.90
72.33±8.09
73.5±7.33
68.06±7.99
CASE 2.75 mg/kg
CASE 5.5 mg/kg
69.00±2.52
74.61±3.81
72.17±9.64
74.00±3.13
62.56±8.34
72.28±2.41
60.56±10.17
61.89±1.90
58.11±10.47
59.39±5.14β1
CASE 11 mg/kg
70.11±3.71
62.50±4.40
59.39±2.73
47.17±3.59a1,
GLC 5 mg/kg
70.56±5.86
54.00±5.34
47.72±5.03
c1, β1
41.89±2.73
β2
a2, β3
37.78±3.80a1,
37.67±2.4
β3
a1, β3
Notes: Each value represents mean ± SEM, n=6 for each treatment. aCompared to the negative control, ccompared to CASE 5.5 mg/kg, βcompared to the baseline blood
glucose level. 1p<0.05, 2p<0.01 and 3p<0.001.
Abbreviations: CASE, C. aurea seed extract; DW, distilled water; GLC, glibenclamide.
when groups treated with different doses of the seed
extract compared with each other and compared with the
positive control at all time points.
Within-group analysis showed that treatment with 5.5
mg/kg CASE significantly reduced the BGL at the sixth
hour (p<0.05) compared to the baseline level with a percentage reduction of 20.39%. Similarly, a significant
reduction in BGL was induced with 11 mg/kg CASE at
the fourth (p<0.01) and sixth (p<0.001) hour compared to
the baseline level with percentage reduction in BGL,
32.72% and 46.11%, respectively. In addition, the standard
drug (GLC) reduced the BGL significantly at the second,
fourth and sixth hours compared to the baseline level with
percentage reductions of 32.37%, 40.63%, and 46.61%,
respectively.
A statistically significant difference in BGL was not
observed at all time points when the GLC treated group
was compared with seed extract treated groups. Similarly,
a statistically significant difference in BGL was not
observed at all time points when all the seed extract treated
groups were compared with one another.
Within-group analysis showed that oral glucose administration to mice caused a statistically significant (p<0.001)
increment in BGL after 30 min in all groups regardless of
the treatments given. Additionally, 60 min after oral glucose loading significant hyperglycemia was observed in all
groups except the GLC treated group as compared to the
respective baseline BGL. The BGL reduced to normal or
the baseline level in all groups at the second hour post oral
glucose load.
Antihyperglycemic activity of the seed
extract in oral glucose-loaded mice
Antihyperglycemic activity of single dose
of C. aurea seed extract in STZ-induced
diabetic mice
There was no significant difference in baseline BGL across
groups just before the administration of DW, plant extract
and GLC (Table 3). Between-groups analysis showed that
5.5 mg/kg and 11 mg/kg CASE significantly reduced the
hyperglycemia (p<0.05 in both cases) at the second hour
compared to the negative control. Similarly, 5 mg/kg GLC
reduced the BGL significantly at 60 and 120 min post oral
glucose administration compared to the DW treated group.
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A total of 69 male Swiss albino mice were injected with
STZ and 52 of them were found to be diabetic (fasting
BGL>200 mg/dL) four days after STZ injection, with a
success rate of 75.36%. Among the 52 diabetic mice, one
died before the administration of the test substances and
all the remaining animals survived until the end of the
experiment.
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Table 3 Effect of the hydromethanolic Calpurnia aurea seed extract on oral glucose tolerance in normoglycemic mice
Group
Blood glucose level (mg/dL)
0 min
DW 10 ml/kg
30 min
87.06±8.25
CASE 2.75 mg/kg
CASE 5.5 mg/kg
60 min
β3
120 min
β1, µ1
112.45±13.29µ3
β2, µ3
84.28±3.30µ3
80.94±2.40a1,
142.17±15.66
202.95±15.84
β3
88.67±4.30
84.11±7.65
210.83±9.65
172.83±13.61β3
132.61±12.07
128.44±11.39β2,
CASE 11 mg/kg
76.50±2.69
β3
202.56±17.12
130.22±11.38
GLC 5 mg/kg
81.44±1.24
180.72±8.75β3
82.83±5.43a1,
µ1
β2, µ3
76.45±2.96
µ3
61.78±8.59a3,
µ3
a1 µ3
c1, µ3
Notes: Each value represents mean ± SEM, n=6 for each treatment. aCompared to the negative control, βcompared to the baseline blood glucose level, µcompared to the
blood glucose level at 30 min. 1p<0.05, 2p<0.01 and 3p<0.001. Time refers to the time after oral glucose administration.
Abbreviations: CASE, C. aurea seed extract; DW, distilled water; GLC, glibenclamide.
Antihyperglycemic activity of a single dose of the
extracts was studied in STZ-induced diabetic mice. As
shown in Table 4, between- and within-group comparisons
were performed to analyze BGL differences across the
various groups and time points, respectively. The
between-group analysis indicated no significant difference
in baseline fasting BGL across all groups. Similarly, a
significant difference in BGL was not observed across all
groups at the second hour post-treatment. Compared to the
negative control, a significant BGL reduction was observed
at sixth and eighth hour in 5.5 mg/kg and 11 mg/kg CASE
treated groups; and at fourth, sixth, and eighth hours in the 5
mg/kg GLC treated group. There was no statistically significant difference in BGL at all time points when groups
treated with the seed extract were compared to each other,
and compared to the GLC treated group.
Within-group comparison indicated that significant
BGL reduction was not observed in CASE 2.75 mg/kg,
CASE 5.5 mg/kg and DW treated groups at all time points
compared to the baseline fasting BGL. However, the percent reduction in BGL was recorded as 27.47% in the
CASE 2.75 mg/kg treated group and 50.15% in the
CASE 5.5 mg/kg treated group at the eighth hour compared to the respective baseline fasting BGL. CASE 11
mg/kg was able to decrease the BGL significantly at the
sixth and eighth (p<0.05) hour compared to the initial
value with percentage reductions of 46.36% and 51.47%,
respectively. The standard drug, GLC, also produced a
significant BGL reduction at the fourth, sixth and eighth
(p<0.001) hour compared to the baseline level.
Antihyperglycemic activity of the
repeated doses of C. aurea seed extract in
STZ-induced diabetic mice
Between-group comparisons indicated that the baseline
BGL of the diabetic groups was significantly higher than
the baseline BGL of the normal control, but no statistically
significant difference was observed in baseline BGL across
diabetic groups (Table 5). Groups treated with 2.75 mg/kg,
5.5 mg/kg and 11 mg/kg CASE and 5 mg/kg GLC showed
a significant reduction in BGL on the seventh and 14th day
of treatment compared to the diabetic control. There was
no statistically significant difference in BGL at all time
points when groups treated with the different doses of
CASE compared with each other. Similarly, the GLC
treated group showed no significant difference in BGL at
all time points when compared to CASE treated groups.
Table 4 Antihyperglycemic activity of single dose of Calpurnia aurea seed extract in streptozotocin-induced diabetic mice
Group
Blood glucose level (mg/dL)
0h
2h
4h
DW 10 mL/kg
394.11±31.03
383.06±27.65
396.39±26.71
397.45±18.52
399.61±22.00
CASE 2.75 mg/kg
369.45±33.27
307.00±62.98
255.00±49.74
245.50±57.01
235.11±49.68
CASE 5.5 mg/kg
CASE 11 mg/kg
395.39±53.55
341.89±50.75
308.78±61.45
267.06±45.23
232.06±60.77
194.78±30.46
193.83±45.04a1
183.39±27.12a1,
GLC 5 mg/kg
368.50±43.02
283.39±39.09
a
176.61±14.01
6h
a1, β3
171.72±18.27
8h
β1
a1, β3
197.11±54.32a1
157.83±19.81a2,
β1
a2, β3
155.72±13.59
Notes: Each value represents mean ± SEM, n=6 for each treatment. Compared to the negative control, compared to the baseline blood glucose level. 1p<0.05, 2p<0.01,
3
p<0.001.
Abbreviations: CASE, C. aurea seed extract; DW, distilled water; GLC, glibenclamide.
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β
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Belayneh et al
Table 5 Antihyperglycemic effect of repeated doses of Calpurnia aurea seed extract in Streptozotocin-induced diabetic mice
Group
Fasting blood glucose level (BGL; mg/dL)
Baseline
7th day
n3
14th day
n3
n3
383.67±45.83
387.00±47.77
Diabetic control
394.11±31.0
CASE 2.75 mg/kg
CASE 5.5 mg/kg
369.45±33.27n3
395.39±53.55n3
222.17±34.81a1,
195.83±24.23a2,
β1
CASE 11 mg/kg
341.89±50.75n3
154.39±23.19a3,
β2
GLC 5 mg/kg
Normal control
n3
368.50±43.02
76.83±2.51
Percent reduction in baseline BGL
β2
a3, β3
145.56±26.72
77.67±2.50
7th day
14th day
2.6%
1.8%
39.86%
50.47%
40.73%
51.65%
218.95±34.59a1,
191.17±23.91a2,
β1
148.22±23.22a3,
β2
54.84%
56.65%
a3, β3
60.49%
−1.09%
62.91%
−2.4%
β2
136.67±26.41
78.67±2.75
Notes: Each value represents mean ± SEM, n=6 for each group. aCompared to the diabetic control, ncompared to the normal control, βcompared to baseline blood glucose
level. 1p<0.05, 2p<0.01, 3p<0.001.
Abbreviations: CASE, C. aurea seed extract; GLC, glibenclamide.
Within-group analysis revealed that all the CASE treated groups and the GLC treated group showed a significant
reduction in BGL at the seventh and 14th day of treatment
compared to the baseline level. But a significant change in
BGL was not observed in the diabetic and normal control
groups at all time points compared to the baseline level
(Table 5).
extract and the GLC treated group did not show a significant body weight change at all time points compared to the
respective baseline body weight.
Effect of the repeated doses of C. aurea
seed extract on body weight of STZinduced diabetic mice
There was a significant elevation (p<0.001) of serum total
cholesterol, triglycerides, and a significant reduction
(p<0.001) of HDL cholesterol in the diabetic control
compared to the normal control (Table 7). The administration of 5.5 mg/kg and 11 mg/kg C. aurea seed extract
for 14 days significantly reduced (p<0.05) the levels of
serum total cholesterol while significantly increasing
(p<0.05) the HDL cholesterol level. Similarly, all three
doses of CASE significantly reduced the serum triglyceride level. The standard drug GLC also significantly
reduced (p<0.001) TC and TG level while increasing
(p<0.01) the HDL-C. Additionally, a significant difference in the level of serum TC, TG and HDL-C was not
observed when groups treated with CASE compared with
each other.
STZ-induced diabetes caused a statistically significant
body weight loss in the diabetic control at the seventh
and 14th day of treatment compared to the normal control
group (Table 6). All the three doses of CASE (2.75, 5.5
and 11 mg/kg) and GLC significantly improved the body
weight of diabetic mice at the 14th day of treatment
compared to the DW treated diabetic control.
Intra-group analysis revealed that the diabetic control
showed significant (p<0.01) body weight loss at the 14th
day of treatment compared to the baseline body weight,
but the normal control, groups treated with the plant
Effect of the repeated doses of C. aurea
seed extract on serum lipid level of STZinduced diabetic mice
Table 6 Effect of the repeated doses of CASE on body weight of streptozotocin-induced diabetic mice
Group
Body weight (g)
Before induction of diabetes
Diabetic control
28.67±0.95
Baseline
7th day of treatment
26.77±0.89
23.88±1.24
14th day of treatment
n2
20.88±1.15n3,
CASE 2.75 mg/kg
28.58±0.99
27.92±1.40
26.93±1.72
27.00±1.75
CASE 5.5 mg/kg
CASE 11 mg/kg
28.50±0.75
28.92±0.72
27.50±0.82
27.58±1.01
26.68±0.90
27.18±1.01
26.95±0.89a2
27.67±0.98a3
GLC 5 mg/kg
28.75±0.48
26.07±0.73
25.95±0.71
26.53±0.72a2
Normal control
29.00±0.47
29.45±0.36
a
30.03±0.53
n
β2
a2
30.70±0.59
β
Notes: Each value represents mean ± SEM, n=6 for each group. Compared to the diabetic control, compared to the normal control, compared to baseline body weight.
1
p<0.05, 2p<0.01, 3p<0.001.
Abbreviations: CASE, Calpurnia aurea seed extract; GLC, glibenclamide.
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Belayneh et al
Table 7 Effect of repeated doses of Calpurnia aurea seed extract on serum lipid level of streptozotocin-induced diabetic mice
Groups
Serum lipid level (mg/dL)
TC
Diabetic control
TG
191.33±4.07
n3
157.67±10.60
150.33±10.60a1,
CASE 11 mg/kg
149.67±4.06a1,
99.50±8.27
83.83±5.36
22.17±3.05n3
a1, n3
33.00±2.88
36.50±2.64a1
164.83±13.49
n3
CASE 2.75 mg/kg
CASE 5.5 mg/kg
GLC 5 mg/kg
Normal control
HDL-C
n3
n3
n3
a3, b3, c2, d2
128.50±6.21
127.50±6.73a1,
119.50±4.22a2,
77.50±5.55
73.50±7.26
n3
n2
37.00±0.58a1
a3, b3, c3, d2
38.50±2.68a2
41.17±4.88
Notes: Each value represents mean ± SEM, n=6 for each group. aCompared to the diabetic control, bcompared to CASE 2.75 mg/kg, ccompared to CASE 5.5 mg/kg,
d
compared to CASE 11 mg/kg, ncompared to the normal control. 1p<0.05, 2p<0.01, 3p<0.001.
Abbreviations: CASE, C. aurea seed extract; GLC, glibenclamide; TC, total cholesterol; TG, triglyceride; HDL-C, high density lipoprotein cholesterol.
Discussion
DM is one of the largest global health problems of the
twenty-first century.36 There is a need for safer and more
effective drug therapy because currently available medications for DM have definite limitations. Investigating plantderived compounds, which are easily accessible and do not
require intensive pharmaceutical processing, for the treatment of DM is an important research area.5,34
There was no previous acute oral toxicity study on the
hydromethanolic seed extract of C. aurea. This study
revealed that the median lethal dose of the hydromethanolic seed extract is between 55 mg/kg and 175 mg/kg,
showing the toxic nature of the seeds.
In the present study, experimental diabetes in mice was
induced using STZ [2-deoxy-2-(3-methyl-3-nitrosourea)-1D-glucopyranose]. STZ-induced DM is well documented
and a commonly used model of experimental diabetes in
mice.37 Previous studies showed that single intraperitoneal
injection of 150 mg/kg STZ can produce sustained hyperglycemia in mice at least for 8 weeks.38 Similarly, the present
study revealed that STZ-induced persistent hyperglycemia
without significant change in BGL during the study period of
two weeks as observed in the diabetic control mice. STZ is a
better diabetogenic agent than alloxan with wider species
effectiveness and greater reproducibility, and this could be
attributed to the fact that STZ is more stable in solution
before and after injection in animals than alloxan.39 The
three major mechanisms associated with pancreatic β cell
death secondary to STZ exposure are DNA methylation,
nitric oxide, and reactive oxygen species production.39 STZ
toxicity to β cells is short-lived and further impairment of the
surviving β cell function is due to hyperglycemic toxicity.40
In this study, there were no detectable differences in
baseline BGL across groups in each animal model;
80
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additionally, the vehicle treated groups did not show significant reduction of BGL compared to the baseline level.
However, significant reductions in BGL were observed in
all models after the administration of the hydroalcoholic
seed extract and standard drug, indicating changes induced
on BGL were attributed to treatments received.
The study on normoglycemic mice revealed that the 80%
methanolic seed extract of C. aurea at the dose of 5.5 mg/kg
and 11 mg/kg showed significant hypoglycemic activity.
Similarly, the extract at the dose of 5.5 mg/kg and 11 mg/
kg showed significant antihyperglycemic activity after
administration of single dose of the extract in oral glucose
loaded mice as well as in STZ induced diabetic mice.
Additionally, all three doses of CASE showed significant
antihyperglycemic activity and improvement in body weight
after administration of repeated doses of the extract in diabetic mice. The hypoglycemic and antihyperglycemic activities of CASE were dose-dependent. In all cases, a higher
reduction in BGL was observed with 11mg/kg CASE.
The antidiabetic activity of medicinal plants is due to the
presence of phytochemicals like alkaloids, phenolic compounds, flavonoids, and terpenoids.5,6,17–19 Flavonoids are
known to have insulinogenic and pancreatic beta cell regenerating activities.6,17 Thus, the blood glucose lowering effect
of the hydromethanolic extract may be due to the presence of
these different secondary metabolites known to have antidiabetic activity with possible additive or synergistic effects.
The antidiabetic activity of CASE may be due to the
induction of insulin secretion from beta cells of the pancreas or enhancement of glucose uptake in the peripheral
tissue.41 However, detailed pharmacological and biochemical studies are required to identify the exact mechanism
for the hypoglycemic and antihyperglycemic effects
observed in the study.
Journal of Experimental Pharmacology 2019:11
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The extract showed a relatively delayed onset of blood
glucose lowering action compared to the standard drug. This
might be due to the presence of compounds with a higher
glycemic index that could lead to increased BGL following
absorption. The presence of such an effect in the face of the
blood glucose lowering actions by the active compounds
could lead to a delay in the action of the plant extract.26
STZ-induced diabetes is associated with significant
body weight loss.22,27 Mice with severe STZ-induced
hyperglycemia tend to lose a large percentage of their
body weight.22,38 Similarly, the present study revealed
that STZ caused significant body weight loss in the diabetic control mice. STZ-induced diabetes leads to body
weight loss due to increased wasting of fat stores,42 muscle
and tissue proteins.43,44 Hence, the weight gain after
repeated administration of the hydromethanolic C. aurea
seed extract in STZ-induced diabetic mice suggests the
antihyperglycemic activity of the extract.
One of the complications of DM is a disturbance in
serum lipid level which is manifested mainly by high
serum TG, TC, and low HDL-C.4,27 This lipid abnormality
is due to activation of hormone-sensitive lipase that leads
to increased lipolysis and increased secretion of VLDL
from the liver.3,4 Insulin deficiency also causes decreased
activity of lipoprotein lipase which leads to decreased
clearance of VLDL and chylomicrons.45 Additionally, an
increased triglyceride level can stimulate the enzymatic
activity of cholesteryl ester transfer protein, resulting in
increased triglyceride content of HDL and LDL.
Triglyceride-enriched HDL particles are subjected to
increased catabolism, whereas triglyceride-enriched LDL
particles undergo subsequent hydrolysis via lipoprotein
lipase or hepatic lipase, resulting in LDL particle size.4
In this study, the diabetic control showed significantly
increased serum TG, TC, and decreased HDL-cholesterol
as expected. Administration of CASE for 2 weeks significantly reduced serum TG, TC, and increased HDL-C in a
dose-dependant manner, but it is not known whether the
seed extract had a direct effect on lipid metabolism or the
antidyslipidemic activity is achieved only due to the controlled hyperglycemia.
Conclusion
Methanolic extract of C. aurea seeds showed significant
hypoglycemic, antihyperglycemic and antihyperlipidemic
activities, justifying the traditional use of the plant for the
treatment of DM. However, further phytochemical investigations are required to isolate and identify the active
Journal of Experimental Pharmacology 2019:11
Belayneh et al
compounds responsible for the antidiabetic activity of the
plant.
Abbreviations list
CASE, Calpurnia aurea seed extract; IP, intraperitoneal;
LD50, Median lethal dose; OECD, Organization for
Economic Cooperation and Development.
Availability of data and materials
All the datasets used and analyzed during the current study
are available from the corresponding author on reasonable
request.
Ethics approval
Ethical approval was obtained from the Ethical Review
Committee of the School of Pharmacy, University of
Gondar, before conducting the experiment.
Acknowledgments
We are grateful to the University of Gondar for funding
this study.
An abstract of this paper was presented at the 29th Annual
Conference of EPHA (Ethiopian Public Health Association) as
a poster presentation and conference talk. The poster’s abstract
was published in “Poster Abstracts” and is available at: http://
www.etpha.org/conference/index.php/29thConference/
29thConference/paper/view/1007.
Disclosure
The authors declare that they have no competing interests.
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