Present study was designed to evaluate hypoglycemic and hypolipidemic effects of flavonoids from tatary buckwheat (TBF) in type 2 diabetic rats induced by combination of high-fat diet and streptozotocin injection. After induction of type 2 diabetes, diabetic rats were randomly divided into five groups: diabetic control group, low-dose TBF treated group, middle-dose TBF treated group, high -dose TBF treated group, and glibenclamide treated group, with normal rats used as the control group. After treatment for 28 days, body weight, fasting blood glucose (FBG), serum insulin, total cholesterol (TC), triglyceride (TG), high-density lipoprotein-cholesterol (HDL-C), and low-density lipoprotein-cholesterol (LDL-C) levels were measured and oral glucose toler ance test (OGTT) was performed. The results showed that TBF significantly decreased FBG and serum insulin levels, increased body weights and improved glucose intolerance in diabetic rats. Furthermore, it decreased TC, TG, and LDL-C levels and increased HDL-C levels in these rats. These evidences indicated that TBF possesses hypoglycemic and hypolipidemic effects in type 2 diabetic rats and suggested that TBF has the potential to be a candidate for investigation as an anti-diabetic agent in humans.
Keywords
Hypoglycemic, Hypolipidemic, Type 2 diabetes, Flavonoids from tatary buckwheat, Rats.
Introduction
Diabetes mellitus is a hereditary, chronic disorder in the endocrine system that constitutes a major public health problem throughout the world [1]. It is characterized by absolute or relative deficiencies in insulin secretion and/ or insulin action associated with chronic hyperglycemia and disturbances of carbohydrate, lipid and protein metabolism [2,3]. As a consequence of the metabolic derangements in diabetes, many complications develop including hyperlipidemia, hyperinsulinemia, hypertension, and atherosclerosis [4]. Diabetes mellitus is classified into two major categories: type 1 diabetes (formerly known as insulin dependent diabetes mellitus or IDDM) and type 2 diabetes (formerly known as non-insulin dependent diabetes mellitus or NIDDM) [5]. A worldwide survey has reported that 143 million people in the world live with diabetes and this number will probably double by the year 2030 [6]. Over 90% percent of diabetic patients are diagnosed with type 2 diabetes [7]. Type 2 diabetes, often associated with obesity, high blood glucose, blood lipid abnormalities, mainly increase levels of TC, TG, LDL-C, serum insulin and decrease levels of HDL-C, which lead to a series of complications. Different types of oral hypoglycaemic agents such as biguanides and sulphonylurea are available along with insulin for the treatment of diabetes mellitus but have side effects associated with their uses [8]. Therefore, there is an urgent need to search for the drugs of a natural origin with fewer side effects. Flavonoids, a class of natural drugs with high biological activity are abundant in plants. They are reported to have protective effects against the development of diabetes as well as a mitigation effect of diabetes consequences [9].
Buckwheat, also called triangle wheat, belongs to the family Polygonaceae, genus Fagopyrum Meisn [10]. There are 15 kinds of species in the Fagopyrum family and only common buckwheat (Fagopyrum esculentum) and tartary buckwheat (Fagopyrum tataricum) are cultured species. Tartary buckwheat originated in eastern Tibet or northwestern Yunnan in China and is grown only in Asia, Europe and North America [11]. As an important functional food material, tartary buckwheat grain contains proteins with high biological value and balanced amino acid composition, relatively high crude fiber and vitamins B1, B2, and B6 and more flavonoids than common buckwheat [12]. The flavonoids content was 40 mg/g in tartary buckwheat seeds while it was 10 mg/g in common buckwheat seeds [13]. Flavonoids from tatary buckwheat (TBF) mainly include rutin, quercetin, orienin, vitexin, isovitexin, isoorientin, protocatechuic acid, and hyperin [14]. It has been reported that TBF exhibit multiple pharmacological activities such as antihypertensive, antioxidant, anti-hypercholesterolemia, anti-cancer and neuroprotection functions [10]. However, few studies have examined the therapeutic effects of TBF on diabetes mellitus. The present investigation was aimed at evaluating the hypoglycemic and hypolipidemic effects of TBF in diabetic rats induced by combination of high-fat diet and streptozotocin injection.
Materials and Methods
Plant Material
The air-dried tartary buckwheat grains were purchased from Liangshan agricultural institution (Sichuan, China) and identified by Professor Zhong Zhang, Xichang College (XiChang, China). Voucher specimens were deposited at the herbarium of Xichang College. The plant materials were ground into a coarse powder with the help of a suitable grinder. The powder was stored in an airtight container and kept in a cool, dark and dry place before experiment.
Chemicals and Reagents
Streptozotocin (STZ) was purchased from Sigma Chemical Co. (St. Louis, Mo, USA). Glibenclamide was purchased from Shandong Boshan Pharmaceutical Co., Ltd. (Zibo, China). The kits for triglycerides (TG), total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C) were purchased from the Nanjing Jiancheng Bioengineering Institute (Nanjing, China). Insulin ELISA kits were purchased from Pumai Biotechnology Co., Ltd. (Shanghai, China). Glucose analyzer and strips were purchased from Roche Diagnostics (Shanghai) Co., Ltd. (Shanghai, China). All of the other chemicals and reagents were standard commercially available biochemical quality. Triple distilled water was used in all experiments.
Animals and Breeding Conditions
Male Sprague Dawley rats, weighing 180-220 g were obtained the Experimental Animal Center of Sichuan University (Chengdu, China). The animals were housed in a room kept under controlled conditions with temperature maintained at 22°C to 25°C on a 12 h light: 12-h dark cycle, diet and water were supplied ad libitum. All experiments and protocols described in present study were approved by the Institutional Animal Ethics Committee of XiChang College.
Preparations of Flavonoids from Tatary Buckwheat
The flavonoids from tatary buckwheat (TBF) were prepared as previously described [10,15] with a few modifications. Briefly about 10.0 g of the ground powder was mixed with 400 ml ethanol-water (60:40, v/v) in a sealed vessel and then placed in a microwave extraction apparatus (WF-4000C, PreeKem Scientific Instruments Co., Ltd., Shanghai, China). The extraction temperature was 70°C, extraction time was 20 min and microwave power was 600 W. After that, the extract was centrifuged at 1,509 Ã