A Comparative Effects of Some Selected Medicinal Plants on Blood Sugar Level, Lipid Profile and Oral Glucose Tolerance Test in Normal and Alloxan-Induced Diabetic Rats

Abstract

Diabetes mellitus (DM) is a common and serious metabolic disorder throughout the world. Despite the availabilities of hypoglycemic agents from natural and synthetic sources, diabetes and its complications continued to be a major health care problem. The management of diabetes without any side effects is still a challenge; therefore plants continue to play an important role in the discovery of new compounds for the treatment of this disease. The study was undertaken to evaluate the comparative effects of some selected medicinal plants on blood sugar level, lipid profile and oral glucose tolerance test in alloxan-induced diabetic rats. The dried coarse powders from plants were exhaustively extracted with ethanol by cold extraction. An effort was made to investigate the acute toxicity (LD50) of the extracts. Diabetes was induced in Norwegian Long Evans rats by a single intra-peritoneal administration of alloxan monohydrate (110mg/kg). Preliminary hypoglycemic properties were investigated at 30, 60 and 90 mins after the oral administration of extracts in fasting rats. The qualitative presence of phytoconstituents in the extracts was also determined by standard methods. On the basis of preliminary screening the plant Grewia asiatica (GAE), Alpinia nigra (ANE) and Urginea indica (UIE) extracts with demonstrable hypoglycemic activity were further evaluated for their safety and efficacy in alloxan-induced diabetic rats. After induction of diabetes the rats were divided into several groups for oral administration of GAE (200, 400mg/kg), ANE (50, 100, 200 mg/kg) and UIE (12, 25 mg/kg) once daily for a period of 15 days. Metformin (150mg/kg) was used as standard drug. The survival rate, time course of changes in blood sugar levels (FBS) and body weights were measured after the treatment. We have also estimated serum triglycerides (TG), total cholesterol (TC) and high density lipoprotein (HDL), serum glutamic-oxaloacetic transaminase (SGOT) and creatine kinase-myocardium type (CK-MB). To compare the effects of GAE200, ANE100 and UIE25 in diabetic rats, we have examined OGTT, lipid profiles, liver glycogen and histopathology. A comparative in-vitro antioxidant activity including flavonoid content, phenolic content, total antioxidant activity, reducing power capacity and 1,1-diphenyl-2- picryl-hydrazyl (DPPH) free radical scavenging activity were also carried out. Finally, the bioactive principles from UIE were isolated and identified through bio-assay guided fractionations using chromatographic techniques and spectral analysis respectively. Our results demonstrated that ethanol extracts from plants were non-toxic in rats. All the plants possessed hypoglycemic activities of which GAE (200mg/kg), ANE (100mg/kg) and UIE (25mg/kg) showed remarkable efficacy. Preliminary phytochemical analysis of GAE, ANE and UIE revealed the presence of triterpenoid, flavonoid, steroid, glycoside, saponin and tannin. The 15 days survival rate among the treatment groups was 100% (p<0.001 vs DC). Oral administration of GAE, ANE and UIE significantly lowered the fasting blood sugar levels and the effects were dose-dependent. Oral ingestion of GAE, ANE and UIE significantly improved body weight and organ weight and reduced the levels SGOT and CK-MB. The data revealed that the level HDL increased and the level of TC and TG were significantly decreased with GAE, ANE and UIE at all dose levels. Also the increment of LDL, VLDL and LDL/HDL ratio were significantly attenuated after the treatment. Diabetic rats treated with GAE, ANE and UIE, showed significant improvement in oral glucose tolerance and restored the liver glycogen content. All the extracts have favorable effects on the preservation pancreatic morphology as evidenced by increase number of viable β-cells of the pancreas. Among the treatment groups UIE25 showed most significant reduction in blood sugar level, lipid profile, and restoration of liver glycogen and normalization of pancreatic β-cells architecture. The free radical scavenging activity of extracts GAE, ANE and UIE showed considerable total antioxidant activity with IC50 of 76.45±0.21μg/ml, 43.25±0.15μg/ml and 27.50±0.021 μg/ml, respectively in DPPH scavenging assay. Among the three plant extracts the UIE showed the highest iron reducing capacity (absorbance 1.31 at 200μg/ml vs ascorbic acid standard 1.55 at 200 μg/ml), total phenol content (87.74mg of GAE/g dried extract), total flavonoid (67.72mg of quercetin/g dried extract) and total antioxidant (307.25 mg of ascorbic acid/g dried extract). Two compounds UC-1 and UC-3 were isolated from chloroform fractions of UIE and were identified as 5,7-dihydroxy-2-methyl-4H-chromen-4-one and 5-hydroxy-7-methoxy-2- methyl-4H-chromen-4-one, respectively. These compounds were the first report of isolation from the plant Urginea indica. Further, rats treated with UC-1 and UC-3 showed a significant improvement in glucose tolerance, attenuated blood sugar levels and lipid profiles; and restored liver glycogen content. Oral ingestion of UC-1 and UC-3 significantly reduced the levels of SGOT and CK-MB as well as improvement in pancreatic β-cell architectures. We concluded that the plant bark of Grewia asiatica (Phalsa), rhizome of Alpinia nigra (Jangli Ada) and bulb of Urginea indica (Bon Pianj) as well as isolated compounds UC-1 and UC-3 exhibited significant effects on the fasting blood glucose level, improvement in liver glycogen content, serum SGOT, CK-MB levels as well as organ protection. The beneficial effects of extracts as well as isolated compounds can be partially explained by the preservation of pancreatic β-cell structure through the suppression of oxidative stress. However, the exact mechanism by which UC-1 and UC-3 exerted its beneficial effects in alloxan-induced diabetic rats remained to be elucidated.