Phytochemical Screening and Antidiabetic Activity of Aqueous, Ethanolic and Methanolic Extracts of Stevia Rebaudiana and Catharanthus Roseus in Streptozotocin Induced Diabetic Rats

1. INTRODUCTION

Diabetes is a serious, long-term condition that occurs when the body cannot produce any or enough insulin or cannot effectively use the insulin it produces. According to WHO estimates, 422 million people worldwide are diabetic and 1.6 million deaths were directly caused by diabetes in 2016. Diabetes could become the 7th leading cause of death worldwide by 2030. The increase in the number of deaths is due to a rich diet, obesity and sedentary population [12]. Diabetes is a complex disease both in its physiopathological mechanisms and in the genesis of its complications. People with diabetes are at increased risk of cardiovascular, peripheral vascular and cerebrovascular disease [39]. Two major classes of diabetes mellitus, IDDM or Type 1or Juvenile onset Diabetes which is caused by destruction of β- cells of pancreatic Islets, and NIDDM or Type 2 or maturity onset diabetes caused by abnormality in gluco-receptor, reduced sensitivity of peripheral tissues to insulin, excess of hyperglycemic hormones like glucagons [23]. Type 2 diabetes is a major public health issue in India, more likely to develop Diabetes at younger ages at lower body mass indices [21] India has the highest number of diabetes cases worldwide (40 million) [39]. Another 30 million Indians have pre-diabetes and are at high risk of developing T2DM. T2DM prevention is a priority in Indian populations. Diabetes is a chronic disorder of carbohydrate, fat and protein metabolism characterized by increased fasting and postprandial blood sugar levels [27]. Diabetes mellitus is a complex metabolic disorder resulting from either insulin insufficiency or insulin dysfunction. Type I diabetes (insulin dependent) is caused due to insulin insufficiency because of lack

diabetes (insulin independent) are unable to respond to insulin and can be treated with dietary changes, exercise and medication. Type II diabetes is the more common form of diabetes constituting 70-80% of the diabetic population. Symptoms for both diabetic conditions may include: (i) high levels of sugar in the blood; (ii) unusual thirst; (iii) frequent urination; (iv)extreme hunger and loss of weight; (v) blurred vision; (vi) nausea and vomiting; (vii) extreme weakness and tiredness; (viii) irritability, mood changes etc. Though patho physiology of diabetes remains to be fully understood, experimental evidences suggest the involvement of free radicals in the pathogenesis of diabetes [30] and more importantly in the development of diabetic complications [4, 26]. Free radicals are capable of damaging cellular molecules, DNA, proteins and lipids leading to altered cellular functions. Many recent studies reveal that antioxidants capable of neutralizing free radicals are effective in preventing experimentally induced diabetes in animal models [24, 29] as well as reducing the severity of diabetic complications [15]. For the development of diabetic complications, the abnormalities produced in lipids and proteins are the major etiologic factors. In diabetic patients, extra-cellular and long lived proteins, such as elastin, laminin, collagen are the major targets of free radicals. These proteins are modified to form glycolproteins due to hyperglycemia. The modification of these proteins present in tissues such as lens, vascular wall and basement membranes are associated with the development of complications of diabetes such as cataracts, micro-angiopathy, therosclerosis and nephropathy [7]. During diabetes, lipoproteins are oxidized by free radicals. There are also multiple abnormalities of lipoprotein metabolism in very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL) in diabetes. Lipid peroxidation is enhanced due to increased oxidative stress in diabetic condition. Apart from this, advanced glycation end products (AGEs) are formed byz non- enzymatic glycosylation of proteins. AGEs tend to accumulate on long-lived molecules in tissues and generate abnormalities in cell and tissue functions [10, 11]. Although several therapies are in use for treatment, there are certain limitations due to high cost and side effects such as development of hypoglycemia, weight gain, gastrointestinal disturbances, liver toxicity etc [37]. Based on recent advances and involvement of oxidative stress in complicating diabetes mellitus, efforts are on to find suitable antidiabetic and antioxidant therapy. Medicinal plants are being looked up once again for the treatment of diabetes. Many conventional drugs have been derived from prototypic molecules in medicinal plants. To date, over 400 traditional plant treatments for diabetes have been reported, although only a small number of these have received scientific and medical evaluation to assess DM is based on oral hypoglycemic agents and insulin. However, DM is also treated in Indian traditional medicine using anti-diabetic medicinal plants [9, 36]. The oral hypoglycemic agents currently used in clinical practice have characteristic profiles of serious side effects [19]. Hence, there is a need to search for newer anti-diabetic agents that retain therapeutic efficacy and are devoid of side effects that could be important sources of such agents. Stevia rebaudiana is a herbaceous perennial shrub belonging to the sunflower family Asteraceae indigenous to Brazil and Paraguay [1]. It is commonly known as honey leaf, which is estimated to be 300 times sweeter than sugar cane [8]. The leaves of Stevia contain a natural complex mixture of eight zero caloric sweet diterpene glycosides, such as isosteviol, stevioside, rebaudiosides (A, B, C, D, E, F), steviolbioside and dulcoside A. Stevioside is degraded to steviol, by intestinal bacterial micro flora of human being, it does not have neurological or renal side effects associated with some of the artificial sweeteners [16]. The medicinal value of plants lies in some chemical substances that produce a definite physiological action on the human body. The most important bioactive compounds of plants are alkaloids, flavanoids, tannins and phenolic compounds [34]. Stevia possesses anti-hyperglycaemic, anti-hypertensive, anti-oxidant, anti-tumor, anti-diarrheal, diuretic, gastro and renal-protective, immunomodulatory [13], anti-bacterial, anti-fungal, anti-inflammatory, anti-microbial, anti-viral, anti-yeast, cardio-tonic, and vasodilator properties [16]. Hence, stevia leaves have been extensively used as a non-caloric sugar substitute in many kinds of foods, medicine, beverage, cosmetics, wine making, household chemical industry and other food industries [35]. The anti-hyperglycemic effect of S. rebaudiana was investigated in both rats and humans [22, 40]. They mentioned that stevioside demonstrates a positive effect on hyperglycemia through decreasing the absorption of glucose in duodenum, glycogenolysis and gluconeogenesis. Vinca rosea (C. roseus) Linn. (Apocynaceae) is an herbaceous sub shrub also known as Madagascar periwinkle, Vinca rosea, or Lchnera rosea worldwide. It is cultivated mainly for its alkaloids, which are having anticancer activities.The two classes of active compounds in Vinca are alkaloids and tannins. Catharanthus roseus produces more than 100 monoterpenoids indole alkaloids (TIA) in different organs. The leaves and stems are the sources of dimeric alkaloids, vinacristine and vinblastine that are indispensable cancer drugs, while roots have antihypertensive, ajmalicine and serpentine. The leaves have been known to contain 150 useful alkaloids among other pharmacologically active compounds. Significant antihyperglycemic and hypotensive activity of the leaf extracts have been reported in laboratory synthetic drugs used for the treatment of diabetes result in many complications. Hence the use of natural sources such as the leaves of Stevia rebaudiana and Catharanthus roseus for the treatment of diabetes is safe and non-carcinogenic [5, 25]. Hence the present study was designed to evaluate the anti-diabetic activity of aqueous, ethanolic and methanolic extracts of the Stevia rebaudiana and Catharanthus roseus leaves against STZ-induced diabetic rats. The effect of the extracts of Stevia rebaudiana and Catharanthus roseus was compared to Glibenclamide, used as a standard drug against Diabetes Mellitus.

Аll the сhemiсаls рrосured fоr this wоrk were оf аnаlytiсаl grаde, chloroform, ethanol, methanol, Hydrochloric acid (HCL), Sulphuric acid (H2SO4) and α- naphthol were рrосured frоm S.D. Fine Chem. Ltd, Mumbаi, Indiа.

Leaves of Stevia rebaudiana collected from Hosnagar taluk and Catharanthus roseus from Ayanur Kote village of Shivamogga District were tentatively identified by Dr. T. Parameshwara Naik a renowned botanist in Shivamogga.

The air-dried plant material, leaves of Stevia rebaudiana and Catharanthus roseus (50-100 g) was washed thoroughly to remove the dirt and impurities, air dried under shade at room temperature and finely grinded with the help of mixer grinder. Extraction of the bioactive compounds was carried out in water, methanol and ethanol. Distilled water was added to the crushed material in a ratio of 1:4 (w/v) and kept at 300C for 24 hrs. The organic solvents were added in a ratio of 1:45 (w/v) shaken properly with the residue for 3hrs at their respective boiling temperatures. The extracts were filtered through whatman filter paper and stored at -200C for further use. 2.4. Phytochemical Screening The leaf extracts of Stevia rebaudiana and Catharanthus roseus were analyzed for the presence of alkaloids, glycosides, triterpenoids, steroids, saponins, flavonoids, tannins and carbohydrates according to standard methods [18]. 2.4.1. Tests for alkaloid: Test solution was prepared by tritrating 40 to 50 mg extract with dilute acid (10 % acetic acid or 1 to 5 % hydrochloric acid). Mayer’s test Mayer‟s reagent (Solution I: Dissolve 1.36 g HgCl2 in 60 mL water; Solution II: Dissolve 5 g potassium iodide in 10 mL water. Combine these two solutions and add water up to 100 mL). Test solution (0.5 to 1 mL) was added with 1 to 2 mL of Mayer‟s reagent and development of white or buff colour precipitates indicates the presence of alkaloid. 2.4.2. Test for flavonoid Test solution was prepared by dissolving 50 to 100 mg extract in 10 mL methanol/water. Shinoda test: Test solution (1 to 2 mL) was added with a pinch of magnesium metal powder and a few drops of concentrated hydrochloric acid. Development of orange, pink, red to purple colours indicated the presence of flavones, flavonols or xanthones. Sulfuric acid test: Test solution (1 to 2 mL) was added with few drops of concentrated sulfuric acid from the side wall of test tubes. Flavones and flavonols dissolve into concentrated H2SO4, producing a deep yellow coloured solution. Flavanones give orange to red colour. 2.4.3. Test for Triterpenoids: About 5 ml of extract was mixed in 2 ml of chloroform; 2 ml of acetic anhydride and a few drops of conc. H2SO4 was added. Reddish violet colour indicated the presence of triterpenoids.

2.4.5. Test for Saponin: Take 0.1 to 0.2 g of extract and add 10 mL distilled water, and shake vigorously. The appearance of froth that stabilizes for 10 to 15 minutes indicates the presence of saponin. 2.4.6. Test for Glycoside Salkowaski’s test: To the crude extract (about 50 to 100 mg) taken add 2 mL of chloroform, shake well and then add 2 mL of concentrated H2SO4 along the side of the test tube. The development of reddish brown colour at the interface indicates the presence of sterol. 2.4.7. Test for Carbohydrates Molisch’s Test : Molisch‟s reagent (Dissolve 1 g of α- naphthol in 10 mL of methanol or isopropyl

concentrated sulphuric acid from the side of the inclined test tube. Appearance of red brown/violet ring at the interface of acid and aqueous solution indicates the presence of sugars. 2.4.8. Test for Tannins Ferric Chloride Test: Prepare 5 % solution of ferric chloride in 90 % methanol. Test solution (1 to 2 mL) was added with few drops of ferric chloride solution and development of dark green or deep blue colour indicates the presence of tannins.

GROUP-I: Normal (Rats injected with normal saline is considered as vehicle control). GROUP-II: Diabetic control (was administered with 20% Glucose Soln. for 14 days) GROUP-III: STZ induced diabetic Wistar rats were administered with standard drug (Glibenclamide) 5 mg/kg for 14 days, served as positive control. GROUPS-IV to IX: STZ induced diabetic Wistar rats were administered with Aqueous, ethanolic and methanolic extracts of Stevia rebaudiana and Catharanthus roseus at the dose of 300 mg/kg rat body weight respectively. On day 14 all animals were deprived of food, and water was given ad libitum. On day 15 blood glucose levels were measured using Glucometer (Accu-chek) by tail pinching method. Data was analyzed using one way ANOVA followed by suitable post-hoc test. clothing‟s and slippers to ensure adequate personal health and safety and to avoid inhalation and skin contact with the test items.

Following the guidelines of OECD (Organization for Economic Co-operation and Development), the acute oral toxicity [32], was performed on the adult Wistar rats. The rats were kept fasting for overnight providing only water, after which the extracts (aqueous, ethanol, and methanol) were administered orally at the dose level of 5 mg/kg. The animals were observed continuously for 3 hours for general behaviour, neurological and autonomic profiles and then every 30 minutes for next 3 hours and finally for mortality after 24 hours till 7 days. If mortality was observed in one animal, then the same dose was repeated again to confirm the toxic dose. If mortality was not observed, the procedure was repeated for further higher dose such as 100, 200, and 300 mg/kg body weight.

Diabetes was induced in the adult Wistar rats by injecting intra-peritoneally with a single dose of 50 mg/kg streptozotocin after dissolving it in freshly prepared ice-cold citrate buffer (0.1M, pH 4.5) after 18 hrs of fasting. After the injection, they had free access to feed and water and were given 20% glucose solution for 24 hrs to prevent initial drug induced hypoglycemic shock or mortality [33]. The normal control rats received only distilled water and standard diet. Development of diabetes mellitus in the rats were confirmed by testing fasting blood glucose level (FBGL) using Accu-chek Glucometer, after 48 hrs of STZ injection. The rats with FBSL higher than 200 mg/dL were considered diabetic and were selected for the study [3] [Table-1]. 2.8. Drug Administration: The group-I control rats received normal saline and fed on normal diet. The group-II was diabetic control. The group-III rats received a standard anti-diabetic drug Glibenclamide of 5 mg/kg orally dissolved in normal saline solution. The Stevia rebaudiana and Catharanthus roseus leaf extract at the dose of 100, 200, and 300 mg/kg body weight was given orally to the groups IV to IX respectively. Then blood glucose levels were estimated on every 1st, 7th, and 15th day.

The phytochemical analysis of aqueous, methanolic, and ethanolic extracts of Stevia rebaudiana and Catharanthus roseus leaf powder revealed the presence of alkaloids, flavonoids, triterpenoids, steroids, saponins, glycosides, carbohydrates and tannins. Alkaloids were abundantly present in aqueous extract than in methanol and ethanol. Flavanoids were abundantly present in both aqueous and methanol extract, than in ethanol. Triterpenoids was totally absent in aqueous, present in methanol and moderately present in ethanol extract. Steroids were abundantly present in all the three extracts. Saponins were abundantly present in aqueous, just present in methanol and ethanol extracts. Glycoside was abundantly present in all the three extracts. Carbohydrates were absent in the water extract, just present in methanol and ethanol extracts. Tannins were abundantly present in aqueous extract, just present in methanol and ethanol extract. The aqueous extract did not show the presence of Triterpenoids and Carbohydrates Stevia rebaudiana. Alkaloids were abundantly present in the ethanolic extract, moderately in methanolic extract, merely present in aqueous extract. Flavanoids were abundantly present in ethanolic and methanolic extract but absent in aqueous extract. Triterpenoids were moderately present in ethanolic and methanolic extracts, absent in aqueous extract. Steroids were present only in the ethanolic extracts. Saponins were abundantly present in the ethanolic and methanolic extracts, just present in the aqueous extract. Glycosides were merely present in all the three extracts. Carbohydrates were present only in the ethanolic and methanolic extracts. Tannins were abundantly present in the ethanolic, moderately present in methanolic and just present in the aqueous extracts in Catharanthus roseus (Table-1).

mg/kg body weight. So, the extracts were safe for long term administration.

The blood glucose levels measured in normal and experimental rats in initial and at the 1st 7th and 15th days of treatment are given in (Table-2). Streptozotocin-induced diabetic rats showed significant increase in the levels on blood glucose as compared to normal rats. Oral administration of aqueous, ethanolic and methanolic extracts (300 mg/kg) showed significant decrease (p<0.05) in blood glucose level. The ethanolic and methanolic extract significantly showed reduction (p<0.05) in blood glucose level than the aqueous extract in Stevia rebaudiana. Similarly oral administration of methanolic and aqueous extracts (300 mg/kg) showed significant decrease (p<0.05) in blood glucose level than the ethanolic extract in Catharanthus roseus. The standard drug, Glibenclamide decreased blood glucose level in 15 days treatment.

Values are expressed as mean ± SEM; n=9 *p= 0.05 statistically significant Vehicle control versus Diabetic control/ Treatment groups (G4-G9) #p 0.05= statistically significant Vehicle control versus Diabetic control/ Treated groups (G4-G9)

The phytochemical analysis of Stevia rebaudiana and Catharanthus roseus leaves revealed the presence of alkaloids, flavonoids, triterpenoids, steroids, saponins, glycosides, carbohydrates and tannins (Table-1). The results showed that Stevia rebaudiana and Catharanthus roseus leaves extract caused a significant (P<0.05) reduction in

comparison to the ethanolic and methanolic extracts in Stevia rebaudiana. Similarly oral administration of methanolic and aqueous extracts (300 mg/kg) showed significant decrease (p<0.05) in blood glucose level than the ethanolic extract of Catharanthus roseus in diabetic rats. But, the anti-Diabetic activity may be due to the presence of steviosides a bioactive compound in Stevia rebaudiana and bioactive compounds like alkaloids such as (catharanthine, vindoline, vindolidine, vindolicine, vindolinine, vinblastine, vincristine, leurosine, and lochnerine), glycosides, tannins, triterpenoids, steroids, saponins, carbohydrates and flavanoids in Catharanthus roseus . This was almost similar to results obtained with reference drug glibenclamide (341.60- 132.66 mg/dL). These results confirmed the use of Stevia rebaudiana and Catharanthus roseus leaves in the Indian traditional practice as an anti-diabetic agent [2]. The Stevioside in Stevia rebaudiana and alkaloids such as (catharanthine, vindoline, vindolidine, vindolicine, vindolinine, vinblastine, vincristine, leurosine, and lochnerine) in Catharanthus roseus may be responsible to bring about a decrease in blood glucose level by potentiation of the insulin effect of plasma by increasing the pancreatic secretion of insulin from β-cells of the islets of Langerhans. Previous study showed that stevioside was able to regulate blood glucose levels by enhancing not only insulin secretion and sensitivity but also insulin utilization in insulin deficient rats [14]. According to studies carried out, stevia extract may contain some biomolecules that may sensitize the insulin receptor to insulin or stimulates the β-cells of islets of langerhans to release insulin which may finally lead to improvement of carbohydrate metabolizing enzymes towards the reestablishment of normal blood glucose level [20]. Number of plants has been used traditionally in treatment of diabetes and some have been proven scientifically to have hypoglycemic activity. These plant extract contain compound like polysaccharides, flavonoids, terpenoids and tannins, steroid, polypeptides and alkaloids, responsible for the antidiabetic activity. Higher blood glucose levels are expected in streptozotocin induced diabetic rats, since streptozotocin causes a massive reduction in insulin release, by the destruction of the β-cells of the islets of Langerhans and inducing hyperglycemia [29]. A number of other plants have been reported to exert hypoglycemic activity through insulin release-stimulatory effects [17]. Pepato et al. (2005) reported that the therapeutic potential of Eugenia jambolana is related to the geographic region in which the plant was grown and to the part of the plant used [38, 31]. However, the possible mechanism by which the drug brings about its hypoglycemic actions may be by competitively inhibiting the glucose receptors at intestinal level, either by increasing the pancreatic secretions of Insulin from the cells of Islets of Langerhans or its release from bound insulin. The of three doses 100, 200, and 300 mg/kg. The dose 300 mg/kg showed more significant reduction of blood glucose levels when compared with that of standard. (Table-2) The aim of the present study was to evaluate the antidiabetic effect of aqueous, ethanolic and methanolic extracts of Stevia rebaudiana and Catharanthus roseus against streptozotocin-induced diabetic rats (Figure-1). The standard drug, Glibenclamide has been used for many years to treat diabetes, to stimulate insulin secretion from pancreatic β-cells [41]. The possible mechanism by which leaves brings about a decrease in blood glucose level may be by potentiation of the insulin effect of plasma by increasing the pancreatic secretion of insulin from β-cells of the islets of Langerhans. But, the Stevia rebaudiana and Catharanthus roseus leaves which were collected from Hosnagar taluk and Ayanur Kote village in Shivamogga district of Karnataka state, India have anti-diabetic properties. These results confirmed the use of Stevia rebaudiana and Catharanthus roseus leaves in traditional system of medicine to treat diabetes in India. Further comprehensive chemical and pharmacological investigations are needed to elucidate the exact mechanism of the hypoglycemic effect of Stevia rebaudiana and Catharanthus roseus leaves.

The authors thank Department of Microbiology, Jain University, Bangalore. Dr. T. Parmeshwara Naik, Dept., of Botany and Seed Technology, the faculty members and research scholars of Department of Biotechnology, Sahyadri Science College, Kuvempu Univeristy, Shivamogga for extending their laboratory facility in carrying out this work.

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PG Department of Microbiology, CPGS, Jain University, Jayanagar 3rd Block, Bangalor, India rkmurthy07@gmail.com