Jeppesen PB, Gregersen S, Alstrup KK, Hermansen K.
 

Extracts of leaves from the plant Stevia rebaudiana Bertoni have been used in the traditional treatment of diabetes in Paraguay and Brazil. Recently, we demonstrated a direct insulinotropic effect in isolated mouse islets and the clonal beta cell line INS-1 of the glycoside stevioside that is present in large quantity in these leaves. Type 2 diabetes is a chronic metabolic disorder that results from defects in both insulin and glucagon secretion as well as insulin action. In the present study we wanted to unravel if stevioside in vivo exerts an antihyperglycaemic effect in a nonobese animal model of type 2 diabetes. An i.v. glucose tolerance test (IVGT) was carried out with and without stevioside in the type 2 diabetic Goto-Kakizaki (GK) rat, as well as in the normal Wistar rat. Stevioside (0.2 g/kg BW) and D-glucose (2.0 g/kg BW) were administered as i.v. bolus injections in anaesthetized rats. Stevioside significantly suppressed the glucose response to the IVGT in GK rats (incremental area under the curve (IAUC): 648 +/- 50 (stevioside) vs 958 +/- 85 mM x 120 min (control); P < 0.05) and concomitantly increased the insulin response (IAUC: 51116 +/- 10967 (stevioside) vs 21548 +/- 3101 microU x 120 min (control); P < 0.05). Interestingly, the glucagon level was suppressed by stevioside during the IVGT, (total area under the curve (TAUC): 5720 +/- 922 (stevioside) vs 8713 +/- 901 pg/ml x 120 min (control); P < 0.05). In the normal Wistar rat stevioside enhanced insulin levels above basal during the IVGT (IAUC: 79913 +/- 3107 (stevioside) vs 17347 +/- 2882 microU x 120 min (control); P < 0.001), however, without altering the blood glucose response (IAUC: 416 +/- 43 (stevioside) vs 417 +/- 47 mM x 120 min (control)) or the glucagon levels (TAUC: 5493 +/- 527 (stevioside) vs 5033 +/- 264 pg/ml x 120 min (control)). In conclusion, stevioside exerts antihyperglycaemic, insulinotropic, and glucagonostatic actions in the type 2 diabetic GK rat, and may have the potential of becoming a new antidiabetic drug for use in type 2 diabetes. 
 

Chan P, Tomlinson B, Chen YJ, Liu JC, Hsieh MH, Cheng JT.
 

AIMS: Stevioside is a natural plant glycoside isolated from the plant Stevia rebaudiana which has been commercialized as a sweetener in Japan for more than 20 years. Previous animal studies have shown that stevioside has an antihypertensive effect. This study was to designed to evaluate the effect of stevioside in human hypertension. METHODS: A multicentre, randomized, double-blind, placebo-controlled study was undertaken. This study group consisted of 106 Chinese hypertensive subjects with diastolic blood pressure between 95 and 110 mmHg and ages ranging from 28 to 75 years with 60 subjects (men 34, women 26; mean +/- s.d., 54.1+/-3.8 years) allocated to active treatment and 46 (men 19, women 27; mean +/- s.d., 53.7+/-4.1 years) to placebo treatment. Each subject was given capsules containing stevioside (250 mg) or placebo thrice daily and followed-up at monthly intervals for 1 year.RESULTS: After 3 months, the systolic and diastolic blood pressure of the stevioside group decreased significantly (systolic: 166.0+/-9.4-152.6+/-6.8 mmHg; diastolic: 104.7 +/- 5.2-90.3+/-3.6 mmHg, P<0.05), and the effect persisted during the whole year. Blood biochemistry parameters including lipid and glucose showed no significant changes. No significant adverse effect was observed and quality of life assessment showed no deterioration.CONCLUSIONS: This study shows that oral stevioside is a well tolerated and effective modality that may be considered as an alternative or supplementary therapy for patients with hypertension.
 

Hsu YH, Liu JC, Kao PF, Lee CN, Chen YJ, Hsieh MH, Chan P.
 

BACKGROUND: Stevioside is a natural sweet-tasting glycoside isolated from the herb Stevia rebaudiana, composed of stevia, a diterpenic carboxylic alcohol with three glucose molecules, mainly used commercially as sugar substitute. Previous study has shown that it can lower blood pressure in anesthetized spontaneously hypertensive rats (SHR). This study was undertaken to evaluate the antihypertensive effect of stevioside in different strains of hypertensive rats and to observe whether there is difference in blood pressure lowering effect. METHODS: Noninvasive tail-cuff method was employed to measure blood pressure. Stevioside at the concentrations of 50, 100 and 200 mg/kg were administered intraperitoneally (ip) to normotensive Wistar-Kyoto rats (NTR), SHR, deoxycorticosterone acetate-salt (DOCA-NaCl) sensitive hypertensive rats (DHR) and renal hypertensive rats (RHR). RESULTS: Significant hypotensive effect of stevioside administered ip was noted in different strains of rats at the dose of 50 mg/kg. When stevioside was increased to the concentrations of 100 and 200 mg/kg, ip, it also caused slow and persistent lowering of blood pressure in SHR and NTR. Data also showed that stevioside given at the concentrations of 100, 200 and 400 mg/kg ip resulted in lowering of blood pressure in SHR dose-dependently. Blood pressure returned to previous levels after the drug was discontinued for 2-3 days. Drinking of 0.1% stevioside solution in mature SHR could have antihypertensive effect and also prevented hypertension in immature SHR. CONCLUSIONS: This study reconfirmed stevioside has hypotensive effect and the effect is more prominent in hypertensive rats.
 

Lee CN, Wong KL, Liu JC, Chen YJ, Cheng JT, Chan P.
 

Stevioside is a sweet-tasting glycoside occurring abundantly in the leaves of Stevia rebaudiana (Compositae). It has been used popularly in Japan and Brazil as a sugar substitute for decades. Previous study has shown that it lowered blood pressure in spontaneously hypertensive rats (SHRs) when administered intravenously. This study shows that intraperitoneal injection of stevioside 25 mg/kg also has antihypertensive effect in SHRs. In isolated aortic rings from normal rats, stevioside could dose-dependently relax the vasopressin-induced vasoconstriction in both the presence and absence of endothelium. However, stevioside had no effect on phenylephrine- and KCl-induced phasic vasoconstriction. In addition, stevioside lost its influence on vasopressin-induced vasoconstriction in Ca(2+)-free medium. The results indicate that stevioside caused vasorelaxation via an inhibition of Ca(2+) influx into the blood vessel. This phenomenon was further confirmed in cultured aortic smooth muscle cells (A7r5). Using 10(-5) M methylene blue for 15 min, stevioside could still relax 10(-8) M vasopressin-induced vasoconstriction in isolated rat aortic rings, showing that this vasorelaxation effect was not related to nitric oxide. The present data show that the vasorelexation effect of stevioside was mediated mainly through Ca(2+) influx inhibition.
 

Takahashi K, Matsuda M, Ohashi K, Taniguchi K, Nakagomi O, Abe Y, Mori S, Sato N, Okutani K, Shigeta S.
 

Anti-human rotavirus (HRV) activity of hot water extracts from Stevia rebaudiana (SE) was examined. SE inhibited the replication of all four serotypes of HRV in vitro. This inhibitory effect of SE was not reduced on the prior exposure of SE to HCl for 30 min at pH 2. Binding assay with radiolabeled purified viruses indicated that the inhibitory mechanism of SE is the blockade of virus binding. The SE inhibited the binding of anti-VP7 monoclonal antibody to HRV-infected MA104 cells. The inhibitory components of SE were found to be heterogeneous anionic polysaccharides with different ion charges. The component analyses suggested that the purified fraction named as Stevian with the highest inhibitory activity consists of the anionic polysaccharide with molecular weight of 9800, and contains Ser and Ala as amino acids. Analyses of sugar residues suggest uronic acid(s) as sugar components. It did not contain amino and neutral sugars and sulfate residues. These findings suggest that SE may bind to 37 kD VP7 and interfere with the binding of VP7 to the cellular receptors by steric hindrance, which results in the blockade of the virus attachment to cells.