Stevioside from Stevia rebaudiana Bertoni Increases Insulin Sensitivity in 3T3-L1 Adipocytes

Potential of Diterpenes as Antidiabetic Agents: Evidence from Clinical and Pre-Clinical Studies

Diterpenes are a diverse group of structurally complex natural products with a wide spectrum of biological activities, including antidiabetic potential. In the last 25 years, numerous diterpenes have been investigated for antidiabetic activity, with some of them reaching the stage of clinical trials. However, these studies have not been comprehensively reviewed in any previous publication. Herein, we critically discussed the literature on the potential of diterpenes as antidiabetic agents, published from 1995 to September, 2021. In the period under review, 427 diterpenes were reported to have varying degrees of antidiabetic activity. Steviol glycosides, stevioside (1) and rebaudioside A (2), were the most investigated diterpenes with promising antidiabetic property using in vitro and in vivo models, as well as human subjects. All the tested pimaranes consistently showed good activity in preclinical evaluations against diabetes. Inhibitions of α-glucosidase and protein tyrosine phosphatase 1B (PTP 1B) activities and peroxisome proliferator-activated receptors gamma (PPAR-γ) agonistic property, were the most frequently used assays for studying the antidiabetic activity of diterpenes. The molecular mechanisms of action of the diterpenes include increased GLUT4 translocation, and activation of phosphoinositide 3-kinase (PI3K) and AMP-activated protein kinase (AMPK)-dependent signaling pathways. Our data revealed that diterpenes hold promising antidiabetic potential. Stevioside (1) and rebaudioside A (2) are the only diterpenes that were advanced to the clinical trial stage of the drug discovery pipeline. Diterpenes belonging to the abietane, labdane, pimarane and kaurane class have shown promising activity in in vitro and in vivo models of diabetes and should be further investigated.

Steviol Represses Glucose Metabolism and Translation Initiation in Pancreatic Cancer Cells

Pancreatic cancer has the worst prognosis and lowest survival rate among all cancers. Pancreatic cancer cells are highly metabolically active and typically reprogrammed for aberrant glucose metabolism; thus they respond poorly to therapeutic modalities. It is highly imperative to understand mechanisms that are responsible for high glucose metabolism and identify natural/synthetic agents that can repress glucose metabolic machinery in pancreatic cancer cells, to improve the therapeutic outcomes/management of pancreatic cancer patients. We have identified a glycoside, steviol that effectively represses glucose consumption in pancreatic cancer cells via the inhibition of the translation initiation machinery of the molecular components. Herein, we report that steviol effectively inhibits the glucose uptake and lactate production in pancreatic cancer cells (AsPC1 and HPAF-II). The growth, colonization, and invasion characteristics of pancreatic cancer cells were also determined by in vitro functional assay. Steviol treatment also inhibited the tumorigenic and metastatic potential of human pancreatic cancer cells by inducing apoptosis and cell cycle arrest in the G1/M phase. The metabolic shift by steviol was mediated through the repression of the phosphorylation of mTOR and translation initiation proteins (4E-BP1, eIF4e, eIF4B, and eIF4G). Overall, the results of this study suggest that steviol can effectively suppress the glucose metabolism and translation initiation in pancreatic cancer cells to mitigate their aggressiveness. This study might help in the design of newer combination therapeutic strategies for pancreatic cancer treatment.

Molecular mechanism of down-regulating adipogenic transcription factors in 3T3-L1 adipocyte cells by bioactive anti-adipogenic compounds

Obesity is growing at an alarming rate, which is characterized by increased adipose tissue. It increases the probability of many health complications, such as diabetes, arthritis, cardiac disease, and cancer. In modern society, with a growing population of obese patients, several individuals have increased insulin resistance. Herbal medicines are known as the oldest method of health care treatment for obesity-related secondary health issues. Several traditional medicinal plants and their effective phytoconstituents have shown anti-diabetic and anti-adipogenic activity. Adipose tissue is a major site for lipid accumulation as well as the whole-body insulin sensitivity region. 3T3-L1 cell line model can achieve adipogenesis. Adipocyte characteristics features such as expression of adipocyte markers and aggregation of lipids are chemically induced in the 3T3-L1 fibroblast cell line. Differentiation of 3T3-L1 is an efficient and convenient way to obtain adipocyte like cells in experimental studies. Peroxisome proliferation activated receptor γ (PPARγ) and Cytosine-Cytosine-Adenosine-Adenosine-Thymidine/Enhancer-binding protein α (CCAAT/Enhancer-binding protein α or C/EBPα) are considered to be regulating adipogenesis at the early stage, while adiponectin and fatty acid synthase (FAS) is responsible for the mature adipocyte formation. Excess accumulation of these adipose tissues and lipids leads to obesity. Thus, investigating adipose tissue development and the underlying molecular mechanism is important in the therapeutical approach. This review describes the cellular mechanism of 3T3-L1 fibroblast cells on potential anti-adipogenic herbal bioactive compounds.

Effect of stevia on the gut microbiota and glucose tolerance in a murine model of diet-induced obesity

Artificial sweeteners have been shown to induce glucose intolerance by altering the gut microbiota; however, little is known about the effect of stevia. Here, we investigate whether stevia supplementation induces glucose intolerance by altering the gut microbiota in mice, hypothesizing that stevia would correct high fat diet-induced glucose intolerance and alter the gut microbiota. Mice were split into four treatment groups: low fat, high fat, high fat + saccharin and high fat + stevia. After 10 weeks of treatment, mice consuming a high fat diet (60% kcal from fat) developed glucose intolerance and gained more weight than mice consuming a low fat diet. Stevia supplementation did not impact body weight or glucose intolerance. Differences in species richness and relative abundances of several phyla were observed in low fat groups compared to high fat, stevia and saccharin. We identified two operational taxonomic groups that contributed to differences in beta-diversity between the stevia and saccharin groups: Lactococcus and Akkermansia in females and Lactococcus in males. Our results demonstrate that stevia does not rescue high fat diet-induced changes in glucose tolerance or the microbiota, and that stevia results in similar alterations to the gut microbiota as saccharin when administered in concordance with a high fat diet.

Stevia rebaudiana Bertoni bioactive effects: From in vivo to clinical trials towards future therapeutic approaches

Stevia rebaudiana Bertoni, a plant from South America and indigenous of Paraguay, has shown several biological effects and healthy properties, although it is especially used in South America and some Asiatic regions. In addition, it is a natural sweetener, almost 300 times sweeter than sucrose, being attributed to its phytoconstituents prominent antioxidant, antimicrobial, antidiabetic (antihyperglycemic, insulinotropic, and glucagonostatic), antiplatelet, anticariogenic, and antitumor effects. In this sense, this work aims to provide an extensive overview on the historical practices of stevia and its effects in human health based on its chemical composition and applications for both food and pharmaceutical industries.

Effect of steviol, steviol glycosides and stevia extract on glucocorticoid receptor signaling in normal and cancer blood cells

The use of steviol glycosides as non-caloric sweeteners has proven to be beneficial for patients with type 2 diabetes mellitus (T2D), obesity, and metabolic syndrome. However, recent data demonstrate that steviol and stevioside might act as glucocorticoid receptor (GR) agonists and thus correlate with adverse effects on metabolism. Herein, we evaluated the impact of steviol, steviol glycosides, and a Greek-derived stevia extract on a number of key steps of GR signaling cascade in peripheral blood mononuclear cells (PBMCs) and in Jurkat leukemia cells. Our results revealed that none of the tested compounds altered the expression of primary GR-target genes (GILZ, FKPB5), GR protein levels or GR subcellular localization in PBMCs; those compounds increased GILZ and FKPB5 mRNA levels as well as GRE-mediated luciferase activity, inducing in parallel GR nuclear translocation in Jurkat cells. The GR-modulatory activity demonstrated by stevia-compounds in Jurkat cells but not in PBMCs may be due to a cell-type specific effect.

Glycosides from Stevia rebaudiana Bertoni Possess Insulin-Mimetic and Antioxidant Activities in Rat Cardiac Fibroblasts

Stevia rebaudiana Bertoni is a shrub having a high content of sweet diterpenoid glycosides in its leaves, mainly stevioside and rebaudioside A, which are used as noncaloric, natural sweeteners. The aim of this study was to deepen the knowledge about the insulin-mimetic effect exerted by four different mixtures of steviol glycosides, rich in stevioside and rebaudioside A, in neonatal rat cardiac fibroblasts. The potential antioxidant activity of these steviol glycosides was also assessed, as oxidative stress is associated with diabetes. Likewise the insulin effect, steviol glycosides caused an increase in glucose uptake into rat fibroblasts by activating the PI3K/Akt pathway, thus inducing Glut4 translocation to the plasma membrane. The presence of S961, an insulin antagonist, completely abolished these effects, allowing to hypothesize that steviol glycosides could act as ligands of the same receptor engaged by insulin. Moreover, steviol glycosides counteracted oxidative stress by increasing reduced glutathione intracellular levels and upregulating expression and activity of the two antioxidant enzymes superoxide dismutase and catalase. The present work unravels the insulin-mimetic effect and the antioxidant property exerted by steviol glycosides, suggesting their potential beneficial role in the cotreatment of diabetes and in health maintenance.

Glycemic Effects of Rebaudioside A and Erythritol in People with Glucose Intolerance

BACKGROUND

Rebaudioside A and erythritol are nonnutritive sweeteners. There have been several studies of their glycemic effects, but the outcomes remain controversial. The purpose of this study was to evaluate the glycemic effects of rebaudioside A and erythritol as a sweetener in people with glucose intolerance.

METHODS

This trial evaluated the glycemic effect after 2 weeks of consumption of rebaudioside A and erythritol as sweeteners in a pre-diabetic population. The patients were evaluated for fructosamine, fasting plasma glucose, C-peptide, insulin, and 2-hour plasma glucose before and after consumption of sweetener. The primary outcome was a change in fructosamine levels from the baseline to the end of treatment. Secondary outcomes were the changes in levels of fasting plasma glucose and 2-hour plasma glucose.

RESULTS

From the baseline to the end of experiment, the changes in fructosamine levels after consumption of rebaudioside A and erythritol, did not differ significantly (244.00±19.57 vs. 241.68±23.39 μmol/L, P=0.366). The change in levels from the baseline to end of the study for rebaudioside A and erythritol were fasting plasma glucose (102.56±10.72 vs. 101.32±9.20 mg/dL), 2-hour plasma glucose (154.92±54.53 vs. 141.92±42.22 mg/dL), insulin (7.56±4.29 vs. 7.20±5.12 IU/mL), and C-peptide (2.92±1.61 vs. 2.73±1.31 ng/mL), respectively, and also did not differ significantly (P>0.05 for all).

CONCLUSION

Our study suggests that consumption of rebaudioside A and erythritol does not alter the glucose homeostasis in people with glucose intolerance.

Molecular evidence of insulinomimetic property exhibited by steviol and stevioside in diabetes induced L6 and 3T3L1 cells

BACKGROUND

The defective responsiveness of body tissues to insulin involves the insulin receptors of cell membranes. The binding of insulin to its receptor induce an increase of high affinity glucose transporter molecules in target cell surface that enhance the uptake of glucose in to these cells. The WHO expert committee recommended the importance to investigate the hypoglycemic agents from plant origin, which are used in traditional medicine for the treatment of diabetes. Stevioside, a natural sweetener and a diterpene glycoside extracted from Stevia rebaudiana (Bertoni) has been used as an anti-hyperglycemic agent for the treatment of diabetes for decades.

HYPOTHESIS

To reveal the molecular mechanism underlying the insulinomimetic activity of stevioside and its aglycone metabolite, steviol using cell line models.

STUDY DESIGN

Efficacy of stevioside and steviol in inducing glucose absorption was studied at transcript level, protein level and by measuring glucose absorption in the cell using in-vitro cell line studies.

METHOD

Quantification of glucose transporter (GLUT4) transcript was done in 3T3-L1 adipocytes and L6 myotubes by qPCR using RPL23 as the internal control. GLUT4 protein was quantified using anti GLUT4 antibody by ELISA and radioactive glucose uptake studies were done to measure the rate of glucose absorption.

RESULTS

The absolute and relative quantitation of GLUT4 gene by qPCR showed the activation of GLUT4 transcript at lower concentration of steviol (1 µM) and higher concentration of stevioside (100 µM) in both L6 myotubes and 3T3-L1 adipocytes. The increased level of glut4 protein and the glucose uptake in both the cell lines using the same concentration of steviol and stevioside further supports the qPCR data. The copy number and the expression level of GLUT4 gene, the amount of GLUT4 protein and the glucose uptake efficacy support the insulinomimetic effect of steviol and stevioside.

CONCLUSION

The results of the study clearly demonstrate the functional similarity of steviol and stevioside with that of insulin in controlling the level of glucose in both the cell lines. In other words, the insulinomimetic property of stevioside and steviol was evident from the data.