Evaluation of the Antihyperglycemic Effect of Minor Steviol Glycosides in Normoglycemic and Induced-Diabetic Wistar Rats

Stevioside Ameliorates Palmitic Acid-Induced Abnormal Glucose Uptake via the PDK4/AMPK/TBC1D1 Pathway in C2C12 Myotubes

BACKGROUND

Stevioside (SV) with minimal calories is widely used as a natural sweetener in beverages due to its high sweetness and safety. However, the effects of SV on glucose uptake and the pyruvate dehydrogenase kinase isoenzyme (PDK4) as an important protein in the regulation of glucose metabolism, remain largely unexplored. In this study, we used C2C12 skeletal muscle cells that was induced by palmitic acid (PA) to assess the effects and mechanisms of SV on glucose uptake and PDK4.

METHODS

The glucose uptake of C2C12 cells was determined by 2-NBDG; expression of the Pdk4 gene was measured by quantitative real-time PCR; and expression of the proteins PDK4, p-AMPK, TBC1D1 and GLUT4 was assessed by Western blotting.

RESULTS

In PA-induced C2C12 myotubes, SV could significantly promote cellular glucose uptake by decreasing PDK4 levels and increasing p-AMPK and TBC1D1 levels. SV could promote the translocation of GLUT4 from the cytoplasm to the cell membrane in cells. Moreover, in Pdk4-overexpressing C2C12 myotubes, SV decreased the level of PDK4 and increased the levels of p-AMPK and TBC1D1.

CONCLUSION

SV was found to ameliorate PA-induced abnormal glucose uptake via the PDK4/AMPK/TBC1D1 pathway in C2C12 myotubes. Although these results warranted further investigation for validation, they may provide some evidence of SV as a safe natural sweetener for its use in sugar-free beverages to prevent and control T2DM.

Biological activity and structural modification of isosteviol over the past 15 years

Isosteviol is a tetracyclic diterpenoid obtained by hydrolysis of stevioside. Due to its unique molecular skeleton and extensive pharmacological activities, isosteviol has attracted more and more attention from researchers. This review summarized the structural modification, pharmacological activity and microbial transformation of isosteviol from 04/2008 to 10/2023. In addition, the research history, structural characterization, and pharmacokinetics of isosteviol were also briefly reviewed. This review aims to provide useful literature resources and inspirations for the exploration of diterpenoid drugs.

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.

The anti-diabetic activities of natural sweetener plant Stevia: an updated review

Diabetes mellitus is one of the key metabolic diseases cause due to defects in the secretion of insulin, insulin resistance in peripheral tissues, or both. Plants remained an important source of nutrition as well as medicine. Stevia rebaudiana Bertoni is one of the important high qualities non-caloric sugar substitute sweetener plants against diabetes disease. The compounds like steviol, rebaudioside A, stevioside, etc. can lower the sugar level many fold. In addition, it decreases oxidative stress, hence reduces the risk of diabetes. Its leaves have been used for the control and treatment of diabetes and many other metabolic diseases. In animal model experiments it reduces blood sugar level and promotes liver and kidney functions. In this review, we highlighted the most recent literature on the safe use of Stevia for the treatment of diabetes, its use as a functional food, and its mode of therapeutic action in different animal model experiments. However, keeping Stevia as a model plant; detailed investigations are needed for the identification of new metabolites and its use against diabetes and related diseases.

Safety of a proposed amendment of the specifications for steviol glycosides (E 960) as a food additive: to expand the list of steviol glycosides to all those identified in the leaves of Stevia Rebaudiana Bertoni

The EFSA Panel on Food Additives and Flavourings (FAF) provides a scientific opinion on the safety of the proposed amendment of the specifications for steviol glycosides (E 960) as a food additive, in particular to expand the list of steviol glycosides to 60 steviol glycosides identified in the leaves of Stevia Rebaudiana Bertoni. With the existing specifications, the food additive must be comprised of not less than 95% of the 11 named steviol glycosides. The proposed change is to include all 60 steviol glycosides in the same limit value of 95% and this would allow the presence of up to 5% of impurities. FAF Panel considered that all steviol glycosides share the same metabolic fate, and therefore, the safety of 60 identified steviol glycosides can be based on read-across from toxicological data previously evaluated by EFSA and the acceptable daily intake (ADI) of 4 mg/kg body weight (bw) per day will apply to all those steviol glycosides. However, according to the proposed change in specifications, there remains a small but not insignificant fraction of the additive that would be undefined and therefore cannot be evaluated by the Panel. The Panel concluded that the inclusion of the 60 steviol glycosides in the proposed specifications for steviol glycoside (E960) would not be of safety concern. However, the Panel cannot conclude on the safety of the proposed amendment to the specifications of steviol glycosides (E 960) as food additive if the purity assay value of not less than 95% for the total content of steviol glycosides is maintained.

Natural Alternative Sweeteners and Diabetes Management

PURPOSE OF REVIEW

The goal of this review is to discuss the data on natural alternative sweeteners and their effects on glucose homeostasis and other metabolic parameters within the past five years. We sought to answer whether common natural alternative sweeteners have a positive or negative effect on glucose control in both human and animal models, and whether the data supports their widespread use as a tool to help reduce the prevalence of diabetes and associated comorbid conditions.

RECENT FINDINGS

Recent studies suggest that natural alternative sweeteners may reduce hyperglycemia, improve lipid metabolism, and have antioxidant effects particularly in those that have baseline diabetes. Diabetes and metabolic syndrome have become a global healthcare crisis and the sugar overconsumption plays a major role. The use of artificial sweeteners has become more prevalent to improve insulin resistance in those with diabetes, obesity, and metabolic syndrome, although the evidence does not support this result. There are however some promising data to suggest that natural alternative sweeteners may be a better alternative to sugar and artificial sweeteners.

Liraglutide Enhances Autophagy and Promotes Pancreatic β Cell Proliferation to Ameliorate Type 2 Diabetes in High-Fat-Fed and Streptozotocin-Treated Mice

Background

Clinical and experimental studies have revealed that liraglutide has multiple anti-diabetes biological effects. However, little is known about its role in autophagy and pancreatic β cell proliferation. This study aimed to assessed the effects of liraglutide on pancreatic β cell proliferation and autophagy in a mouse model of type 2 diabetes.

Material/Methods

The effect of liraglutide on autophagy and proliferation in pancreatic β cells was investigated using a high-fat-fed and streptozotocin-induced mouse model of type 2 diabetes.

Results

Liraglutide significantly improved the symptoms of high-fat-fed (HFD) and streptozotocin (STZ)-induced type 2 diabetic mice, as indicated by body weight gain, reduction of blood glucose and plasma insulin, and enhanced sensitivity to insulin. The results of quantitative real-time polymerase chain reaction and Western blot analysis showed that liraglutide upregulated AGT5 expression and promoted the conversion of LC3-I to LC3-II, thus improving the defective autophagy. In addition, we observed that both mRNA and protein expressions of PCNA and Ki-67 were upregulated by liraglutide treatment. Immunocytochemical staining results showed that the number of PCNA- or Ki-67-positive cells in pancreatic islet tissues in the HFD + STZ + liraglutide group were increased compared with the HFD + STZ group.

Conclusions

These results strongly suggest that liraglutide is able to enhance autophagy and promote pancreatic β cell proliferation. This study improves our insights into the mechanism by which liraglutide treatment relieves diabetes, and provides experimental evidence for clinical utilization of liraglutide in type 2 diabetes treatment.