In Vitro Studies on Alpha Glucosidase Inhibitory Activity of Some Indigenous Plants- Juniper Publishers
Juniper Publishers- Journal of complementary medicine
Diabetes mellitus is a common and very prevalent
disease affecting the citizens of both developed and developing
countries. The deficiency or insensitivity of insulin in diabetes
mellitus causes glucose to accumulate in the blood, leading to various
complications. Currently available pharmacotherapies for the treatment
of diabetes mellitus include oral hypoglycemic agents and insulin. One
of therapeutic approach to treat diabetes is to decrease postprandial
hyperglycemia in patients with type II diabetes that can be achieved by
the inhibition of carbohydrate hydrolyzing enzymes like α-amylase and
α-glucosidase. These enzyme inhibitors which are currently used in the
clinical practice for management of diabetes also exhibit certain
gastrointestinal side effects. Thus, there is an urgent need to identify
and explore such enzyme inhibitors, especially from the natural sources
having fewer side effects. In the present study, aqueous extracts of
selected plants namely Catharanthus roseus, Caesalpinia bonducella and Mucuna pruriens
which are used in the Ayurvedic traditional system of medicine to treat
diabetes were tested for their inhibitory effect on α-glucosidase. The
results of the study revealed that the extract of C.roseus was found to
be more effective in inhibition of the enzyme α-glucosidase as compared
to C.bonducella and M.pruriens, whereas Acarbose exhibited maximum
α-glucosidase inhibitory activity with 4.5mm as the diameter of the
inhibitory ring. Further studies are necessary for use of the extracts
of C.roseus, C. bonducella and M.pruriens as chemotherapeutic agents for clinic use in the treatment of diabetes and obesity. .
Keywords: Antidiabetic; α-glucosidase; Inhibitory effects; Indigenous plantsIntroduction
Diabetes mellitus is a common and very prevalent
disease affecting the citizens of both developed and developing
countries and has become a major source of ill health worldwide [1,2].
It has been predicted that by 2030, India, China and the United States
will have the largest number of people with diabetes [3]. Diabetes
mellitus is characterized by hyperglycaemia, lipidaemia and oxidative
stress and predisposes affected individuals to long-term complications
afflicting the eyes, skin, kidneys, nerves and blood vessels [4]. One of
the therapeutic approaches to treat diabetes is to decrease
postprandial hyperglycemia in patients with type II diabetes. It can be
effectively achieved by the inhibition of carbohydrate hydrolyzing
enzymes like α-amylase and α-glucosidase. However, such inhibitors which
are currently used in the clinical practice for management of diabetes
are known to exhibit various gastrointestinal side effects. Thus, there
is an urgent need to identify and explore inhibitors of carbohydrate
hydrolyzing enzymes from natural sources having fewer side effects.
Plant and plant products are being used as a source of medicine since
long. Traditional herbal medicines form an important part of healthcare
system in India [5]. Ayurveda and other ancient Indian literature have
mentioned several herbal plants and their preparations useful in the
treatment of various diseases and disorders [6,7]. Ethanopharmacological
surveys
have shown that more than 1200 plants have been mentioned in traditional
medicine for their alleged hypoglycemic activity [8]. Numerous plants
and their products have been widely prescribed and used for diabetic
treatment all around the world with less known mechanistic basis of
their functioning. The present study was therefore undertaken to make a
comparative study for the ability of the selected plants to inhibit
α-glucosidase activity.
Catharanthus roseus a traditionally known medicinal plant, which belongs to the family Apocynaceae,
is an erected procumbent herb or under shrub containing latex. It has
been known to possess antibacterial, antimicrobial, antifungal,
antioxidant, anticancer and antiviral activities. The organic extracts
of C. roseus has been used in the folklore for the treatment of
diabetes, malaria, leukemia wasp stings, sore throat, eye irritation,
infections and to stop bleeding. It is also used a as an astringent,
diuretic and expectorant [9,10].
Caesalpinia bonducella (Family:
Caesalpiniaceae) is prickly shrub claimed to have multiple therapeutic
properties. All parts of the plant have medicinal properties, so it is a
very valuable medicinal plant which is utilized in traditional system
of medicine. The plant has been reported to possess anxiolytic,
antinociceptive, antidiarrhoeal, antidiabetic, adaptogenic,
anthelmintic, anti inflammatory, antimalarial, antimicrobial,
antipyretic, analgesic,
antibacterial, antispasmodic, antioxidant, antiproliferative,
antipsoriatic, antitumor, larvacidal, muscle contractile,
hepatoprotective, anticonvulsant and antifilarial activities [11,12].
Mucuna pruriens (Fabaceae) is one of the popular drugs in
the Ayurvedic system of medicine. Various preparations from the
seeds of this plant are used for the management of several free
radical mediated diseases such as ageing, rheumatoid arthritis,
diabetes, atherosclerosis, male infertility and nervous disorders
[13,14].
The present study thus aimed to make a comparative study
for the ability of the extracts of selected plants to inhibit in-vitro
α-glucosidase activity.
Materials and methods
Chemicals and reagents
All the chemicals used during the experimental work were
of analytical grade obtained from S.D. Fine Chemicals Pvt. Ltd.,
Mumbai, Sigma chemical company, USA and Loba chemicals,
Mumbai.
Plant material
The seeds of M.pruriens, and C. bonducella were collected from
local areas of Kasegaon, District Sangli, (MS), India, whereas the
roots of C.roseus were collected from local areas of Karad, District
Satara, (MS), India. The plant material was further identified and
authenticated by the Department of Botany, YC College of Science,
Karad. The plant material was cleaned thoroughly, dried in a hot
air oven (50 °C) separately powdered, passed through 60 mesh
sieve (BS) and thereafter stored in an airtight container at 4 °C till
further use.
Preparation of plant extracts
Aqueous extracts were prepared by extracting the powders of
the plant materials with hot water (70 °C) in a mechanical shaker
(24 h), filtered and freeze dried.
Alpha glucosidase inhibition [15]
The plant extracts were spotted on the plate (diameters≤
2mm). Agar solution containing 1.6% starch was poured on the
plate. Enzyme (2mg/ml) in 0.1 mol/l acetate buffer (pH 4.5) was
impregnated on to the paper. After the substrate solution gelled,
the paper was overlaid on the substrate agar layer. The plate
was incubated for 1.5h at 55 0C, 0.05 mmol/l iodine solution was
poured on the surface after the paper was peeled off. Excess iodine
was removed by rinsing the sheet with water. A purple ring would
appear around a sample spot that contained inhibitors.
Statistical analysis
All the analyses were carried out in triplicate and the results
were expressed in mean ± SD.
Results and Discussion
One of the therapeutic approaches to treat diabetes is to
decrease postprandial hyperglycemia in patients with type II
diabetes that can be achieved by the inhibition of carbohydrate
hydrolyzing enzymes like α-amylase and α-glucosidase.
Pancreatic α -amylase is a key enzyme in the digestive system
and catalyses the initial step in hydrolysis of starch to a mixture
of smaller oligosaccharides consisting of maltose, maltotriose,
and a number of α-(l-6) and α-(1-4) oligoglucans. These are then
acted on by α -glucosidases and further degraded to glucose
which on absorption enters the blood-stream. Degradation of this
dietary starch proceeds rapidly and leads to elevated PPHG (postprandial
hyperglycemia). It has been shown that activity of HPA
(human pancreatic α -amylase) in the small intestine correlates
to an increase in post-prandial glucose levels, the control of which
is therefore an important aspect in treatment of type 2 diabetes
[16,17].
Inhibitors of pancreatic α -amylase delay carbohydrate
digestion causing a reduction in the rate of glucose absorption and
lowering the post-prandial serum glucose levels. Some inhibitors
currently in clinical use are Acarbose, Miglitol and Voglibose have
their own limitations. They are non-specific, produce serious side
effects and fail to elevate diabetic complications. Acarbose which
has strong α-amylase inhibitory activity produces digestive tract
disorder such as abdominal distention, bloating, flatulence, and
possibly diarrhea [18].
Therefore, natural inhibitors from dietary plants are useful
as they have lower inhibitory activity against α-amylase and a
stronger inhibitory activity against α- glucosidase and can be
used as effective therapy for postprandial hyperglycemia with
minimal side effects. Many phytoconstituents have been reported
to possess α-amylase and α-glucosidase inhibitors. Some phenolic
compounds in sweet potato, strawberry, Raspbery, Olive oil, pears,
coca and Lentils are reported to be effective human α-amylase
inhibitors. Flavonoids and anthocyacin are also reported to have
inhibitory activity against α-amylase [19]. Natural polyphenols
have been described to have potential to hinder the activity
of carbohydrate hydrolyzing enzymes like α-amylase and
α-glucosidase [20].
In the present study α-glucosidase inhibitory activity of the
plant extracts was studied by TLC plate method. It is a rapid and
possesses high capacity; about 25 samples can be performed in
one TLC plate of 36cm2 area with results in just 2 hours. The doses
of plant extracts were spotted on the plate and the inhibitory
ring of Acarbose and the plant extracts was determined after its
treatment with starch. The diameter of the inhibitory ring for the
selected plant extracts and Acarbose are given in Table 1.
Acarbose, the standard used exhibited maximum α-glucosidase
inhibitory activity with 4.5mm as the diameter of the inhibitory
ring whereas it was observed as 3.8mm, 3.5mm and 2.9mm for
C.roseus, C.bonducella and M.pruriens respectively. Diameter of
inhibitory ring (mm) obtained with different plant extracts is
shown in Figure 1.
The results revealed that C.roseus, C.bonducella and M.pruriens
showed α-glucosidase inhibitory activity and can thus reduce
the rate of digestion and absorption of carbohydrates. The
α-glucosidase inhibitory activity exhibited by the selected
plant extracts may be attributed to the presence of various
phytoconstituents in these extracts.
Conclusion
The results of the present study indicate that the selected plant
extracts exhibited maximum α-glucosidase inhibitory activity and
thus, will prove to be beneficial to reduce the rate of digestion and
absorption of carbohydrates. The plant extracts may essentially
contain herbal bioactive compounds inhibiting α-glucosidase
enzyme activity. Further studies have to be carried out in order
to identify the bioactive constituents for use of the extracts of
C.roseus, C.bonducella and M.pruriens as chemotherapeutic agents
in clinic use for the treatment of diabetes and obesity.
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