Antidiabetic Activity of Some Indian Medicinal Plants

Abstract

The effect of aqueous extracts of Syzygium cumini. Linn., Gymnema sylvestre. (Retz.) Schult., and Portulaca olearacea. Linn. were investigated in fasting normal and streptozotocin (STZ)-induced diabetic rats. The effects of extracts on oral glucose tolerance in normal fasting rats were also studied. The aqueous extracts of S. cumini. (200 mg/kg) and G. sylvestre. (200 mg/kg) decreased the blood glucose in normal rats significantly at 2 and 4 h of extract administration (p < 0.05, p < 0.01). The S. cumini. and G. sylvestre. extracts decreased the increase of glucose levels significantly (p < 0.05) at 90 and 180 min after the glucose load in glucose tolerance test. In STZ diabetic animals, the aqueous extracts of S. cumini. and G. sylvestre. decreased the blood glucose significantly (p < 0.05) at 4 h. The aqueous extract of P. olearacea. did not show any hypoglycemic activity.

Keywords:

• Aqueous extracts
• Gymnema sylvestre
• Portulaca olearacea
• Streptozotocin-induced diabetic rats
• Syzygium cumini

Introduction

Indian systems of medicine use herbal remedies extensively for the treatment of diabetes. In the international scenario, there is a renewed interest in herbal medicines, as they are considered safer. In Unani medicine, diabetes is treated with formulations containing different plant materials. Here we studied the antidiabetic activity of some medicinal plants mentioned in the Unani formulation Qurs ziabitus (Hakim, 1997).

Syzygium cumini. Linn. (Myrtaceae) is a large evergreen tree attaining 30 m in height and found throughout India up to an altitude of 1800 m. The seeds are used in the Ayurveda and Unani systems of traditional medicine as an antidiabetic. The seed contains tannins (19%), ellagic acid, gallic acid (1–2%), a glycoside (jamboline), starch, and small quantity of essential oil (Anonymous, 1998). Seeds are also reported to contain corilagin, 3,6-hexahydroxydipenoylglucose, 1-galloylglucose, 3-galloylglucose, and quercetin (Rastogi & Mehrotra, 1991). Seed extracts showed hypoglycemic activity on oral administration to normal rabbits (Rastogi & Mehrotra, 1990). Seed extracts reduced tissue damage in diabetic rat brain on oral administration for 6 weeks (Prince et al., 2003). Water-soluble gummy fiber from seeds of S. cumini. skeels reduced blood glucose levels and improved oral glucose tolerance (Pandey & Khan, 2002).

Gymnema sylvestre. (Retz.) Schult. (Asclepiadaceae) is a large woody climber running over the tops of high trees. It is distributed in Konkan, western ghats, and southern India. It is also found in Sri Lanka and tropical parts of Africa (Kirtikar & Basu, 2000a). The plant is used as bitter, and in eye complaints, biliousness, bronchitis, and asthma in the Indian traditional medicine (Ayurveda). The fresh leaves are chewed to reduce glycosuria (Kirtikar & Basu, 2000a). The leaves contain gymnemic acids III, IV, V, VIII, and IX. A hypoglycemic component conduritol A was isolated from the leaves (Rastogi & Mehrotra, 1995). New flavonol glycosides, namely kaempferol 3-O.-β.-D-glucopyranosyl-(1,6)-β.-D-galactopyranoside was isolated from aerial parts of G. sylvestre. (Liu et al., 2004). The ethanol extract of leaves produced antimicrobial activity against Bacillus pumilis., B. subtilis., Pseudomonas aeruginosa., and Staphylococcus aureus. (Satdive et al., 2003). Extracts of G. sylvestre. leaves improved serum cholesterol and triglyceride levels in rats fed on high-fat diet (Shigematsu et al., 2001). Three new saponins isolated from ethanol extract of leaves were identified as 21 β.-O.-benzoylsitakisogenin 3-O.-β.-D-glucopyranosyl (1 → 3)-β.-D-glucuronopyranoside (I), the potassium salt of longispinogenin 3-O.-β.-D-glucopyranosyl (1 → 3)-β.-D-glucuronopyranoside (II), and the potassium salt of 29-hydroxylongispinogenin 3-O.-β.-D-glucuronopyranosyl (1 → 3)-β.-D-glucuronopyranoside (III). The saponin I exhibited antisweet activity (Ye et al., 2001).

Portulaca olearacea. Linn. (Portulacaceae) is an annual succulent prostrate herb. It is distributed all over India and in the Himalayas up to an altitude of 1700 m. It grows in all warm countries. In Ayurveda, its leaves are used to treat tumors, inflammation, asthma, diarrhea, dysentery, and piles. In Unani medicine, it is used to allay thirst, headache, low fevers, stomatitis, piles, and burns (Kirtikar & Basu 2000b). The seeds contain noradrenaline, 4-(2-aminoethyl) pyrocatechol, 3-(3, 4-dihydroxyphenyl) alanine, and catechol (Rastogi & Mehrotra, 1999).

Materials and Methods

Plant material

Syzygium cumini. seeds, Gymnema sylvestre. leaves, and Portulaca olearacea. seeds obtained from a local market in Delhi were identified and authenticated by Dr. M.P. Sharma, Taxonomist, Department of Botany, Jamia Hamdard (New Delhi, India). Voucher specimens were deposited in the Phytochemistry Research Laboratory, Department of Pharmacognosy and Phytochemistry, Faculty of Pharmacy, Jamia Hamdard (New Delhi, India).

Preparation of the extract

Air-dried, powdered plant material of about 100 g was boiled with 250 ml water for 1 h and filtered. The filtrate was dried and stored in a refrigerator for further studies. The dried extracts were suspended in 1% Tween 80 in water for the animal studies. The dose of 200 mg/kg was selected in correlation with the dose of the plant drugs used in the Unani formulation Qurs ziabitus (Hakim, 1997).

Chemicals

All chemicals and reagents used were of analytical grade and obtained from Sigma Chemical Company (St. Louis, MO, USA). The one-touch strips for the estimation of glucose were purchased from Lifescan Inc. (USA).

Animal treatment

Wistar albino rats (150–200 g) obtained from Central Animal Facility, Jamia Hamdard University, were maintained on 12-h light/dark cycle and allowed food and water ad libitum.. All the extracts were administered orally. The institutional animal ethics committee approved the experimental procedures.

Effect of extracts on the blood glucose of normal fasted rats

Animals were divided into five groups. Group I served as control and received the vehicle. Group II received the reference drug glibenclamide (3 mg/kg), and groups III, IV, and V received the S. cumini., G. sylvestre., and P. oleracea. extracts (200 mg/kg), respectively. The blood glucose levels were measured just prior to and after 2 and 4 h of extract administration.

Effect of extracts on the glucose tolerance of normal fasted rats

Animals were divided into five groups. All the animals were given 1.5 g glucose/kg orally (dissolved in water for injection). Animals were given drugs immediately after the glucose administration. Group I served as control and received the vehicle. Group II received the reference drug glibenclamide (3 mg/kg), and groups III, IV, and V received the S. cumini., G. sylvestre., and P. oleracea. extracts (200 mg/kg), respectively. Blood glucose level was measured just prior to and after 30, 90, and 180 min of glucose administration.

Effect of extracts on the blood glucose of streptozotocin-induced diabetic rats

Diabetes was induced in animals by single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg) freshly prepared in citrate buffer (pH 4.5). Control rats received only buffer. Diabetes was confirmed by checking the blood glucose levels after 48 h of streptozotocin injection. Animals showing blood glucose level above 250 mg/dl were selected for the study. Diabetic animals were randomly assigned from group II to VI. Group I contained normal animals only and served as normal control. Group II served as diabetic control. Groups I and II received vehicle during the experiments; group III received the reference standard drug glibenclamide (3 mg/kg); groups IV, V, and VI received the S. cumini., G. sylvestre., and P. oleracea. extracts (200 mg/kg), respectively. Blood glucose level was measured just prior to and after 2 and 4 h of extracts administration.

Estimation of blood glucose

The blood glucose level was estimated with the glucometer One Touch Basic Plus (Lifescan Inc.) using the strips (glucose oxidase method).

Statistical analysis

Values are expressed as mean ± standard error of the mean. Statistical significance was calculated by using one-way analysis of variance followed by Dunnets t.-test. The values were considered significantly different when the p < 0.05.

Results

The aqueous extracts of S. cumini. and G. sylvestre. decreased the blood glucose level in normal animals significantly (p < 0.01) at 2 and 4 h (Table 1). The aqueous extracts of S. cumini. and G. sylvestre. decreased the blood glucose level significantly (p < 0.01, p < 0.05) at 90 and 180 min after glucose load. They decreased the peak rise in glucose after 30 min but not significantly (Table 2). The aqueous extracts of S. cumini. and G. sylvestre. decreased the blood glucose level in STZ diabetic animals significantly (p < 0.05) at 4 h (Table 3). The aqueous extract of P. olearacea. did not produce antidiabetic effect in any of the models studied.

Table 1 Effect of aqueous extract of drugs on the blood glucose level of normal fasted rats.

		Blood glucose level mg/100 ml
Groups	Treatment	Initial	2 h	4 h
I	Control	86.16 ± 3.10	83.83 ± 3.54	84.11 ± 3.42
II	Glibenclamide (3 mg/kg)	84.83 ± 2.85	46.83 ± 4.57^a.	48.5 ± 4.64^a.
III	Syzygium cumini. (200 mg/kg)	84.66 ± 3.15	54.12 ± 4.02^a.	55.63 ± 3.72^a.
IV	Gymnema slyvestre. (200 mg/kg)	79.33 ± 2.81	58.33 ± 4.86^a.	63.16 ± 3.75^a.
V	Portulaca olearacea. (200 mg/kg)	79.66 ± 3.04	82.31 ± 3.05	84.16 ± 3.54

All values are mean±SEM.

^a.p < 0.01 when compared with control.

Table 2 Effect of aqueous extract of drugs on the oral glucose tolerance test of normal fasted rats.

		Blood glucose level mg/100 ml
Groups	Treatment	Initial	30 m	90 m	180 m
I	Control	82.18 ± 2.32	128.43 ± 3.35	120.61 ± 3.67	111.23 ± 3.94
II	Glibenclamide (3 mg/kg)	84.32 ± 2.12	108.15 ± 3.36	96.34 ± 2.62^a.	89.45 ± 2.81^a.
III	Syzygium cumini. (200 mg/kg)	86.83 ± 1.86	110.5 ± 2.33	100.83 ± 2.15^a.	91.33 ± 3.46^a.
IV	Gymnema slyvestre. (200 mg/kg)	82.16 ± 1.42	108.16 ± 3.19	98.52 ± 2.81^a.	88.34 ± 2.3^a.
V	Portulaca olearacea. (200 mg/kg)	82.5 ± 2.36	123.4 ± 4.33	112.33 ± 3.98	102.33 ± 3.71

All values are mean±SEM.

^a.p < 0.01 when compared with control.

Table 3 Effect of aqueous extract of drugs on the glucose level of diabetic rats.

		Blood glucose level mg/100 ml
Groups	Treatment	Initial	2 h	4 h
I	Control (normal)	82.24 ± 3.64	81.63 ± 2.84	82.47 ± 2.35
II	Diabetic control	281.56 ± 8.25^a.	276.36 ± 7.58^a.	280.12 ± 8.64^a.
III	Glibenclamide (3 mg/kg)	283.85 ± 8.75	244.38 ± 10.21^c.	218.15 ± 12.64^b.
IV	Syzygium cumini. (200 mg/kg)	282.42 ± 9.12	251.37 ± 11.68	238.29 ± 13.67^c.
V	Gymnema slyvestre. (200 mg/kg)	288.44 ± 10.12	255.71 ± 13.45	234.86 ± 13.25^c.
VI	Portulaca olearaceae. (200 mg/kg)	285.54 ± 8.64	282.26 ± 9.52	286.73 ± 9.24

All values are mean±SEM.

^a.p < 0.001 when compared with normal control (group I).

^b.p < 0.01 when compared with diabetic control (group II).

^c.p < 0.05 when compared with diabetic control (group II).

Discussion

The results indicate that the aqueous extracts of S. cumini. and G. sylvestre. decreased the blood glucose level in normal animals. In spite of the counterregulatory factors such as glucagons, catecholamines, and cortisol, which control the balance of blood glucose levels during normal physiology (Gerich, 1988), hypoglycemia was maintained for 4 h during the experiments. The hypoglycemic effect observed in normal rats suggests these extracts possess the pharmacological effect. These plants may contain some hypoglycemic principles that probably act by initiating the release of insulin from the pancreatic β.-cells of normal animals (sulfonylurea-like effect) (Akhtar et al., 1984).

In the oral glucose tolerance test (GTT), the blood glucose in control animals rose to a peak value around 120–130 mg/100 ml after 30 min. The aqueous extracts of S. cumini. and G. sylvestre. lowered the peak values at 30 min of glucose load indicating more pronounced hypoglycemic action of the extracts. The probable mechanism may be through the stimulation of release of insulin from β.-cells of islets of Langerhans in the presence of increased glucose (Kar et al., 1999).

STZ administration at a dosage of 50 mg/kg to normal rats significantly elevated the blood glucose levels compared with rats injected with citrate buffer alone as reported for albino rats (El-Fiky et al., 1996). The results indicate that aqueous extracts of S. cumini. and G. sylvestre. decrease the blood glucose levels in STZ diabetic rats. Administration of STZ selectively destroys the β.-cells of the islets of Langerhans (Elsner et al., 2000). The destruction of β.-cells cause the marked decrease in insulin levels (Gilman et al., 2001). The hypoglycemic action of the extract in diabetic rats may be possible through the insulinomimetic action or by other mechanisms such as stimulation of glucose uptake by peripheral tissues, inhibition of endogenous glucose production, or activation of gluconeogenesis in liver and muscles, as similar mechanisms have been reported for plant extracts with antidiabetic activity (Burcelain et al., 1995). Further investigations are required to determine the exact cellular and molecular mechanisms of the antidiabetic activity of the extracts.

In conclusion, our study indicates that the aqueous extracts of S. cumini. and G. sylvestre. exhibited activity both in normal and streptozotocin-induced diabetic rats and also increased the tolerance of animals on oral glucose tolerance test.

Acknowledgment

We would like to express our gratitude for the financial assistance provided by the Department of Biotechnology, Government of India, New Delhi, India, to carry out this project.