Influences of crude extract of tea leaves, Camellia sinensis, on streptozotocin diabetic male albino mice
ABSTRACT Natural remedies from medicinal plants are considered to be effective and safe alternative treatment for diabetes mellitus. The aim of the present study was to investigate the hypoglycemic activity of the crude tea leaves extract on streptozotocin (STZ)-induced diabetic mice. The average body weight of animals with diabetes and their percentage changes of body weight gain after 15 and 30 days were significantly lower than that of the normal control mice. In diabetic mice, supplementation with tea leaves extract decreased the loss of body weight. After 15 and 30 days, significant increases in the levels of serum glucose, triglycerides, cholesterol, creatinine, urea, uric acid, glutamic pyruvic acid transaminase (GPT) and glutamic oxaloacetic acid transaminase (GOT) were noted in STZ-diabetic mice fed with normal diet. Also, the values of total protein in this group were statistically declined after 15 and 30 days. The levels of serum glucose and GPT were significantly elevated after 15 and 30 days in diabetic mice supplemented with tea leaves extract. Moreover, the level of serum GOT was notably increased after 30 days. Insignificant alterations were observed in the levels of serum triglycerides, cholesterol, total protein, creatinine, urea and uric acid in diabetic mice supplemented with tea leaves extract. Thus, the present results have shown that tea leaves extract has the antihyperglycemic, antihyperlipidemic, and antihyperproteinemic effects and consequently may alleviate liver and kidney damage associated with STZ-induced diabetes in mice.
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ABSTRACT: Tea is one of the most widely consumed beverages in the world, next to water. It can be categorized into three major types, depending on the level of fermentation, i.e., green and white (unfermented), oolong (partially fermented) and black (fermented) tea. Each type of tea has a distinct composition, dependent on how the leaves are processed, as well as maturation, geographical location and agricultural practices. White tea (WT), the least processed tea, is one of the less studied and is ascribed to have the highest content of phenolic compounds. Tea polyphenols, especially catechin derivatives, are potent antioxidant agents, with positive effects on human health. Antioxidant components have aroused great interest because of their ability to scavenge free radicals, thereby inhibiting oxidative stress. During the past years, oxidative damage induced by reactive species has been linked to the development of several human diseases such as cardiovascular diseases, diabetes mellitus, neurodegenerative disorders and certain types of cancer. Therefore, tea antioxidants may be of great value in preventing the onset and/or the progression of oxidative stress mediated diseases, when endogenous defences are insufficient against reactive species. The possible beneficial health effects of WT are being investigated and have received considerable attention in recent years. In this review, we aim to explore the new findings concerning WT effects on health.International Journal of Food Science, Nutrition and Dietetics. 01/2013; 2:1-15.
Influences of crude extract of tea leaves, Camellia
sinensis, on streptozotocin diabetic male albino mice
Atef M. Al-Attara,*, Talal A. Zarib
aDepartment of Biological Sciences, Faculty of Sciences, King Abdul Aziz University,P.O. Box 139109, Jeddah 21323, Saudi Arabia
bDepartment of Biological Sciences, Faculty of Sciences, King Abdul Aziz University,P.O. Box 80203, Jeddah 21589, Saudi Arabia
Received 8 May 2010; revised 18 May 2010; accepted 18 May 2010
Available online 26 May 2010
treatment for diabetes mellitus. The aim of the present study was to investigate the hypoglycemic
activity of the crude tea leaves extract on streptozotocin (STZ)-induced diabetic mice. The average
body weight of animals with diabetes and their percentage changes of body weight gain after 15 and
30 days were significantly lower than that of the normal control mice. In diabetic mice, supplemen-
tation with tea leaves extract decreased the loss of body weight. After 15 and 30 days, significant
increases in the levels of serum glucose, triglycerides, cholesterol, creatinine, urea, uric acid, glutamic
pyruvic acid transaminase (GPT) and glutamic oxaloacetic acid transaminase (GOT) were noted in
STZ-diabetic mice fed with normal diet. Also, the values of total protein in this group were statisti-
cally declined after 15 and 30 days. The levels of serum glucose and GPT were significantly elevated
after 15 and 30 days in diabetic mice supplemented with tea leaves extract. Moreover, the level of
serum GOT was notably increased after 30 days. Insignificant alterations were observed in the levels
of serum triglycerides, cholesterol, total protein, creatinine, urea and uric acid in diabetic mice sup-
plemented with tea leaves extract. Thus, the present results have shown that tea leaves extract has the
antihyperglycemic, antihyperlipidemic, and antihyperproteinemic effects and consequently may alle-
viate liver and kidney damage associated with STZ-induced diabetes in mice.
Natural remedies from medicinal plants are considered to be effective and safe alternative
ª 2010 King Saud University. All rights reserved.
Diabetes mellitus is an increasingly common, potentially devas-
tating, expensive, treatable but incurable life long disease.
Globally, the estimated incidence of diabetes mellitus and
projection for year 2010, as given by International Diabetes
Federation is 239 million (Gandhi, 2001). Diabetes mellitus is
a chronic metabolic disorder of multiple aetiologies, character-
ized by a state of insulin deficiency that leads to a rise in
glycemia (Gupta et al., 2005), initially involving changes in car-
bohydrate metabolism and secondarily of lipids and proteins
*Corresponding author. Tel.: +966 504629915.
E-mail addresses: email@example.com (A.M. Al-Attar), talzari@
yahoo.com (T.A. Zari).
1319-562X ª 2010 King Saud University. All rights reserved. Peer-
review under responsibility of King Saud University.
Production and hosting by Elsevier
Saudi Journal of Biological Sciences (2010) 17, 295–301
King Saud University
Saudi Journal of Biological Sciences
(Fontes, 2002; Negri, 2005). The most common symptoms ob-
served in type I diabetes patients are polydipsia, polyuria, gly-
cosuria, weakness with no apparent cause, and slow healing of
wounds (Fontes, 2002). The levels of glycemia and insulinemia
must be controlled in order to avoid later complications of dia-
betes, such as atherosclerosis, hypertension, hypertriglyceride-
mia, hypercholesterolemia, myocardial infarction, ischemic
attacks, impotence, retinopathy and nephropathy (Stadler
et al., 2003). As yet there are no effective therapies to cure dia-
betes (Maiti et al., 2004). Many hypoglycemiant agents, such as
the biguanides and sulfonylureas, are used alone or together
with insulin to treat this disease. However, these medications
can cause serious side effects (Hwang et al., 2005), motivating
a search for safer, more efficacious agents to control diabetes.
In recent years, interest has increased in using natural prod-
are effective in reducing glycemia, causing fewer side effects and
with lower cost than the usual antidiabetic agents (Pushparaj
et al., 2000; Gupta et al., 2005; Lee and Sohn, 2009; Sohn
et al., 2010). The majority of the plants that are used in popular
medicine for treatment of diabetes have been shown to possess
biologically active chemical constituents (alkaloids, carbohy-
drates, cumarins, flavonoids, terpenoids, phenolic substances,
and other constituents) that can be used as new hypoglycemiant
agents (Marles and Fansworth, 1995; Gupta et al., 2005; Negri,
2005). Tea is one of the most widely consumed beverages in the
world, second only to water, and its medicinal properties have
ber of theTheaceae family, andblack, oolong, andgreentea are
grow to heights of 30 feet, but is usually pruned to 2–5 feet for
cultivation. The leaves are dark green, alternate and oval, with
in clusters or singly. Unlike black and oolong tea,green tea pro-
duction does not involve oxidation of young tea leaves. Black
tea, however, undergoes fermentation, while green tea does
not (Hamilton-miller, 1995). Green tea is producedfrom steam-
ing fresh leaves at high temperatures, thereby inactivating the
oxidizing enzymes and leaving the polyphenol content intact.
The polyphenols found in tea are more commonly known as
flavonols or catechins, and comprise 30–40 percent of the
extractable solids of dried green tea leaves. The main catechins
in green tea are epicatechin, epicatechin-3-gallate, epigallocate-
chin, and epigallocatechin-3-gallate (EGCG), with the latter
being the highest in concentration. Green tea polyphenols have
demonstrated significant antioxidant, anticarcinogenic, anti-
inflammatory, thermogenic, probiotic, and antimicrobial prop-
1992; Alschuler, 1998). Therefore, the present study was under-
taken to evaluate the effectiveness of the crude leaves extract of
Camellia sinensis as antihyperglycemic agents in streptozotocin
(STZ)-induced diabetic mice.
2. Materials and methods
2.1. Collection of tea leaves and preparation of the extract
Fresh tea leaves were directly collected from the tea plantation
farms in Cameron Highlands, Malaysia. The leaves were air-
dried at room temperature and stored in dry plastic container
until use for extract preparation. The leaves extract was pre-
pared every three days. The dried leaves (5 g) were powdered
in an electric blender, put in one liter boiling water for 5 min
and the mixture then left to cool to room temperature. The
mixture was filtered and the resulting extract was kept in
refrigerator until use in the experiment.
2.2. Animals and experimental protocol
Male albino mice of MF1 strain, weighing 26.4–32.2 g were
used in this study. The experimental animals were obtained
from the Experimental Animal Unit of King Fahd Medical
Research Center, King Abdul Aziz University, Jeddah, Saudi
Arabia. The experimental animals were housed in standard
plastic cages and maintained under controlled laboratory con-
ditions of humidity (65%), temperature (20 ± 1 ?C) and
12:12 h light: dark cycle. Mice were fed ad libitum on normal
commercial chow and had free access to water. For the exper-
imental induction of diabetes, STZ (Sigma–Aldrich Corp, St.
Louis, MO, USA) was freshly prepared by dissolving in
0.9% NaCl before administration. A single dose of 60 mg/kg
STZ was injected intraperitoneally to mice. Five days after
STZ injection, only mice with blood glucose concentration
higher than 310 mg/dL (at fasting state) were considered as
diabetic and included in the present study. A total of 60 mice
were categorized into 4 groups, each group consisting of 15
mice. Group 1 was normal healthy control, intraperitoneally
received saline solution. Group 2 was diabetic control. Group
3 was diabetic mice, administered orally with tea leaves extract
at a dose of 0.5 mL/day. Group 4 was non diabetic mice, intra-
peritoneally received saline solution and treated with tea leaves
extract at the same dose given to group 3. The body weights of
mice were measured at the start of the experimental period,
after 15 and 30 days, using a digital balance. These weights
were determined at the same time during the morning. After
15 and 30 days of treatment, mice were anaesthetized with
diethyl ether, the blood samples were collected from orbital ve-
nous plexus after overnight fasting and it was used for separat-
ing the serum for analyzing the biochemical parameters. Serum
glucose, triglycerides, cholesterol, creatinine, urea, uric acid,
glutamic pyruvic acid transaminase (GPT) and glutamic oxalo-
acetic acid transaminase (GOT) were measured using an auto-
matic analyzer (Reflotron? Plus System, Roche, Germany).
Serum total protein was estimated using Automated Clinical
Chemistry Analysis System, Dimension? type RXL Max
(Dade Behring Delaware, DE 19714, USA).
2.3. Statistical analysis
Statistical analysis was performed by one way analysis of var-
iance (ANOVA) followed by Duncan’s Multiple Range Tests
(DMRT). All values were expressed as mean with their stan-
dard deviation (SD). P values <0.05 were considered as
The body weights in all experimental groups are represented in
Fig. 1. The percentage changes of body weight gain in control
mice were 12.7% after 15 days and 27.0% after 30 days
296A.M. Al-Attar, T.A. Zari
(Fig. 2). Likewise, the changes of body weight gain were 12.5%
and 28.9% in fourth group after 15 and 30 days respectively.
The average of body weight of animals with diabetes (group
2) and their body weight gain (8.7% and 16.1%) after 15
and 30 days were significantly lower than that of the normal
control mice (Figs. 1 and 2). In diabetic mice, supplementation
of tea leaves extract decreased the body weight loss. The
changes of body weight gain were 10.4% and 22.7% after 15
and 30 days respectively in third group (Fig. 2).
After 15 and 30 days, significant increases in the levels of
serum glucose (336.3% and 453.5%), triglycerides (38.6%
and 45.4%), cholesterol (33.4% and 55.4%), creatinine
(55.0% and 81.6%), urea (23.2% and 46.5%), uric acid
(16.8% and 58.6%), GPT (29.6% and 58.6%) and GOT
(38.7% and 82.6%) were noted in STZ-diabetic mice fed with
normal diet (Tables 1 and 2). Also, the values of total protein
in this group were statistically declined after 15 (8.4%) and
30 days (18.6%). In third group, the levels of serum glucose
(249.5% and 282.6%) and GPT (19.5% and 23.8%) were sig-
nificantly elevated after 15 and 30 days. The level of serum
GOT was notably increased (15.3%) after 30 days in diabetic
mice supplemented with tea leaves extract. Insignificant altera-
tions were observed in the levels of serum triglycerides, choles-
terol, total protein, creatinine, urea and uric acid in diabetic
mice supplemented with tea leaves extract. The values of all
serum biochemical parameters were remarkably unchanged
in normal mice supplemented with tea leaves extract.
Diabetes mellitus is associated with several complications such
as atherosclerosis, myocardial infarction, nephropathy, etc.
(Pushparaj et al., 2007). These complications are usually re-
lated to chronically elevated blood glucose level. Strepotozot-
ocin has been used as a diabetogenic agent in experimental
animals. The present investigation demonstrated that STZ in-
duced significant decreases in body weight gain of mice after 15
and 30 days. Similar observations were detected in many
experimental studies (Satav and Katyare, 2004; Kavalali
et al., 2007; Sridevi et al., 2007; Zari and Al-attar, 2007; Sub-
ash-Babu et al., 2008; Sellamuthu et al., 2009; Salahuddin
et al., 2010). One of the parameters to consider the ameliora-
tion of the diabetic state is to ascertain the effect of treatment
on the body weight. An increase in body weight implies that
anabolic effects have overridden the catabolic ones. No varia-
tion means protection against weight loss. Decrease in body
weight would mean that catabolism has persisted. Effects of
certain plant/plant products in body weight gain in diabetic
state have been reported by Stanley et al. (2000). In the present
study, mice group treated with tea leaves extract was effective
Body weight (g)
ControlSTZSTZ plus leaves extract Leaves extract
Body weights (mean ± SD) at 0, 15 and 30 days in groups 1 (control), 2 (STZ), 3 (STZ plus tea leaves extract) and 4 (tea leaves
Body weight change (%)
ControlSTZ STZ plus leaves extract Leaves extract
Percentage changes of body weight at 15 and 30 days in groups 1 (control), 2 (STZ), 3 (STZ plus tea leaves extract) and 4 (tea
Influences of crude extract of tea leaves, Camellia sinensis, on streptozotocin diabetic male albino mice 297
in exerting protection against body weight loss. Insulin is a ma-
jor anabolic hormone in the body. Its deficiency not only af-
fects glucose metabolism but
metabolism. Unopposed actions of the counter-regulatory hor-
mones also play an important role in metabolic derangements.
With deficiency of insulin the scale swings from insulin pro-
moted anabolism to catabolism of proteins and fats. Proteoly-
sis follows and gluconeogenic amino acids are removed by liver
and used as building blocks for glucose. The catabolism of
proteins and fat tends to induce negative nitrogen balance.
alsoprotein and fat
This results in increased appetite (polyphagia). The combina-
tion of polyphagia coupled with weight loss is paradoxical
and always raises the suspicion of diabetes (Crowford and Co-
tran, 2000). Disturbance in the metabolisms results in wasting
of muscles and early fatigability. Either a protection against
weight loss alone or an increase of body weight has their
own distinctive role to play. The normalization of carbohy-
drate, protein and fat metabolisms would alleviate the diabetic
symptoms like loss of weight and fatigability. This would cer-
tainly improve the quality of life of the individual. From the
after 15 and 30 days.
Hematobiochemical values (mean ± SD) of control, STZ, STZ plus tea leaves extract and tea leaves extract treated mice
Parameters Periods (days)Treatments
ControlSTZSTZ + leaves extractLeaves extract
77.86 ± 3.89
76.14 ± 4.85
122.57 ± 8.62
129.71 ± 4.89
83.43 ± 5.03
81.06 ± 1.03
6.69 ± 0.50
7.17 ± 0.26
0.40 ± 0.04
0.38 ± 0.02
18.24 ± 1.05
17.09 ± 0.94
3.46 ± 0.34
3.89 ± 0.37
22.71 ± 2.29
20.50 ± 0.91
43.57 ± 3.21
45.26 ± 2.60
339.71 ± 34.30a,b
421.43 ± 15.13a,b
169.86 ± 13.31a,b
188.57 ± 13.39a,b
111.29 ± 9.12a,b
125.94 ± 5.45a,b
6.13 ± 0.21a,b
5.84 ± 0.14a,b
0.62 ± 0.05a,b
0.69 ± 0.03a,b
22.47 ± 1.61a,b
25.04 ± 5.33a
4.04 ± 0.37a,b
4.59 ± 0.47a,b
29.43 ± 3.82a,b
32.51 ± 1.47a,b
60.43 ± 5.00a,b
82.63 ± 4.18a,b
272.14 ± 32.42a,c
291.29 ± 14.85a,c
128.86 ± 5.31
134.29 ± 12.66
85.86 ± 9.37
80.27 ± 2.46
6.51 ± 0.31
7.20 ± 0.256
0.38 ± 0.06
0.38 ± 0.03
18.06 ± 1.05
18.27 ± 1.58
3.36 ± 0.34
3.86 ± 0.39
27.14 ± 2.6a,c
25.37 ± 0.93a,c
41.43 ± 2.57
52.19 ± 6.11a,c
75.29 ± 4.61
76.28 ± 2.75
126.71 ± 6.42
132.29 ± 3.55
81.43 ± 4.79
79.87 ± 2.24
6.60 ± 0.27
7.06 ± 0.31
0.41 ± 0.03
0.36 ± 0.05
17.50 ± 1.51
17.20 ± 0.95
3.45 ± 0.20
3.74 ± 0.40
23.14 ± 2.19
21.19 ± 2.07
40.29 ± 2.81
44.14 ± 2.38
Total protein (g/dL)
Uric acid (mg/dL)
aIndicates a significant difference between control and treated groups.
bIndicates a significant difference between mice exposed to STZ and STZ plus tea leaves extract or tea leaves extract.
cIndicates a significant difference between mice exposed to STZ plus tea leaves extract and tea leaves extract.
15 and 30 days compared with control values.
Percentage changes of hematobiochemical values of STZ, STZ plus tea leaves extract and tea leaves extract treated mice after
Parameters Periods (days)Treatments
STZ STZ + leaves extract Leaves extract
298A.M. Al-Attar, T.A. Zari
present study it can be concluded that tea leaves extract is
obviously effective not only in preventing body weight loss
but also in helping to gain weight. STZ induced highly signifi-
cant increases in the levels of serum glucose, triglycerides, cho-
lesterol, creatinine, urea, uric acid, GPT and GOT. These
findings are generally in agreement with previous experimental
diabetes studies (Ene et al., 2006; Al-Attar and Zari, 2007; Jas-
mine and Daisy, 2007; Subash-Babu et al., 2008; Andallu et al.,
2009; Farswan et al., 2009; Sellamuthu et al., 2009; Salahuddin
et al., 2010). Kasetti et al. (2010) reported that STZ induced sig-
nificant increases in the levels of serum glucose, triglycerides,
cholesterol, low density lipoprotein cholesterol (LDL-C), very
low density lipoprotein cholesterol (VLDL-C), creatinine, urea,
GPT, GOT and alkaline phosphatase (ALP) in male rats. Also,
they demonstrated that the levels of serum insulin and high
density lipoprotein cholesterol (HDL-C) were statistically de-
creased in diabetic rats. The present decline of serum total pro-
tein in diabetic rats is clearly associated with reduction of body
weight. The decrease in body weight in diabetic rats clearly
shows a loss or degradation of structural proteins due to diabe-
tes. The structural proteins are known to contribute for the
body weight (Rajkumar and Govindarajulu, 1991). Protein
synthesis may be decreased in all tissues due to absolute or rel-
ative deficiency of insulin in STZ-induced diabetic rats. Addi-
tionally, several studies showed that the levels of serum total
protein were declined in diabetic animals (Surana et al., 2008;
Yokozawa et al., 2008; Gupta and Gupta, 2009).
The present investigation indicates the ameliorative of body
weight changes, serum hypoglycemic, hypolipidemic, hyper-
proteinemic, protective of kidney serum markers (creatinine,
urea and uric acid) and attenuation of liver serum enzymes
(GPT and GOT) effects of crude tea leaves extract in STZ-dia-
betic mice. Anandh Babu et al. (2006) showed that the admin-
istration of green tea extract to diabetic rats resulted in
significant recovery in body weight, heart weight: body weight
ratio and blood glucose levels. The administration of green tea
extract reduced cholesterol, triglyceride, free fatty acid and
LDL-C levels, and increased HDL-C levels, in the serum of
diabetic rats. In addition, green tea extracts decreased choles-
terol, triglyceride, free fatty acids levels and lipoprotein lipase
activity in the myocardium of diabetic rats. Also, they reported
that these beneficial effects of green tea extract are ascribed to
its antihyperglycemic and hypolipidemic activity. According to
Jus´kiewicz et al. (2008), supplementation of a diet with green
tea extract had no influence on elevated food intake, body
weight loss, increased glucose concentration, or declined anti-
oxidant capacity of water-soluble substances in plasma in the
diabetic rats. In cases of intestinal maltase activity, attenuation
of liver and kidney hypertrophy, triacylglycerol concentration,
and aspartate aminotransferase activity in the serum, both die-
tary treatments normalized metabolic disorders caused by STZ
injection to a similar extent. Unlike the green tea low dose
(0.01%) group, the green tea high dose (0.2%) treatment sig-
nificantly ameliorated development of diabetes-induced abnor-
mal values for small intestinal saccharase and lactase activities,
renal microalbuminuria, thiobarbituric acid-reactive substance
content in kidney tissue, as well as total antioxidant status in
the serum of rats. The green tea high dose group was also char-
acterized by higher antioxidant capacity of lipid-soluble sub-
stances in plasma and superoxide dismutase activity in the
serum. Although the higher dose of green tea extract did not
completely protect against STZ-induced hyperglycemia and
oxidative stress in experimental rats, this study suggests that
green tea extract ingested at high amounts may prove to be
a useful therapeutic option in the reversal of diabetic dysfunc-
tion (Jus´kiewicz et al., 2008). Renno et al. (2008) demonstrated
that green tea extract provides a beneficial effect on long-term
diabetic nephropathy via suppressing hyperglycemia and pre-
venting glycogen accumulation in the proximal tubules. The
therapeutic property of green tea seems propitious in improv-
ing kidney nephropathy by significantly improving serum and
urine parameters. They showed that these findings support the
importance of controlling blood glucose levels and may be
slowing or even reversing some of the early pathologies of dia-
betic nephropathy. Additionally, Ramadan et al. (2009) com-
pared the modulatory effects of two different doses of black
tea aqueous extract and green tea aqueous extract on experi-
mentally induced hyperglycemia, hyperlipidemia and liver dys-
function by alloxan (which destroys pancreatic b-cells and
induces type 1 diabetes) and a cholesterol-rich diet (which in-
duces obesity and type 2 diabetes) in male Wistar albino rats.
Both tea extracts significantly alleviated most signs of the met-
abolic syndrome including hyperglycemia (resulting from type
1 and 2 diabetes), dyslipidemia and impairment of liver func-
tions induced by alloxan or the cholesterol-rich diet in the ani-
mals. Also, the tea extracts significantly modulated both the
severe decrease and increase in body weight induced by alloxan
and the high-cholesterol diet, respectively. Moreover, they
showed that these modulatory effects were partial or complete,
but significant and dose dependent, and slightly more in green
tea in most cases. Also, they reported that the study supports
the hypothesis that both black and green teas may have bene-
ficial effects against the risks of the metabolic syndrome and
cardiovascular complications as shown in rat models of human
obesity and diabetes.
Diabetic animal’s models exhibit high oxidative stress due
to persistent and chronic hyperglycemia, which depletes the
activity of antioxidative defense system and thus promotes free
radical generation (Ihara et al., 1999; Coskun et al., 2005). Be-
cause the expression levels of antioxidant enzymes such as
superoxide dismutase, catalase and glutathione peroxidase
are known to be very low in the islets of Langerhans compared
with other tissues (Tiedge et al., 1997), b-cells may be particu-
larly susceptible to oxidative stress (Kaneto et al., 2001). The
hyperglycemic in STZ-treated animals leads to the formation
of hydrogen peroxide, which subsequently generates free radi-
cals such as O2?and OH?. These reactive compounds can
cause peroxidation of lipids, resulting in the formation of
hydroperoxy fatty acids and endoperoxides (Pushparaj et al.,
2000). In the present investigation, the mechanism by which
supplementation of crude tea leaves extract could be exert a
hypoglycemic role may be by antioxidant effect. The tradi-
tional tea (Camellia sinensis) infusion is characterized by a high
content of flavonoids. Flavonoids are a large group of phenolic
products of plant metabolism with a variety of phenolic struc-
tures that have unique biological properties and may be
responsible for many of the health benefits attributed to tea.
Tea is an important source of flavonoids in the diet and the
flavonoids found in tea are known to be strong antioxidants
(Rietveld and Wiseman, 2003). Cai et al. (2002) studied the
antioxidative effects of the principal polyphenolic components
extracted from green tea leaves and they showed that the ki-
netic analysis of the antioxidation process demonstrates that
these green tea polyphenols are good antioxidants for liver
Influences of crude extract of tea leaves, Camellia sinensis, on streptozotocin diabetic male albino mice299
microsomal peroxidation. An another possible mechanism by
which crude tea leaves extract mediates a hypoglycemic effect
may be by reduction of glucose absorption in small intestine
and the serum insulin effect, either the pancreatic secretion
of insulin from b-cells or its release from restrict insulin. Wu
et al. (2004) demonstrated that insulin-stimulated glucose up-
take of, and insulin binding to, adipocytes were significantly
increased in Sprague–Dawley rats supplemented with green
tea. Also, they showed that green tea increases insulin sensitiv-
ity in rats and that green tea polyphenol is one of the active
In summary, in spite of the previous studies focused on the
effect of green or black tea leaves extract in diabetic models,
this is the first study to investigate the effects of crude extract
of tea leaves in STZ-diabetic mice. Also, the present study pro-
vided evidence indicating that the crude extract of tea leaves
significantly reduces the levels of serum glucose in diabetic
mice. In addition, treatment with the extract causes the protec-
tive role and recovery of certain altered hematobiochemical
parameters and of the body weight of diabetic mice. Addition-
ally, the present results justify the development of additional
physiological, pharmacological and biochemical researches in
order to clarify the nature of the substances responsible for
the effect and the exact mechanisms action of active substances
of fresh tea leaves. Finally, further experimental studies are
needed to explore the influence of different doses of fresh crude
tea leaves extract on diabetic models.
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Influences of crude extract of tea leaves, Camellia sinensis, on streptozotocin diabetic male albino mice301