Steviol glycoside safety: are highly purified steviol glycoside sweeteners food allergens?

Effect of steviol glycosides as natural sweeteners on glucose metabolism in adult participants

Steviol glycosides (SGs) are recognized as safe natural sweeteners; however, evidence from randomized controlled trials (RCTs) showed an inconclusive effect of SGs on glucose metabolism in adult participants. We aimed to conduct a systematic review and meta-analysis of RCTs to assess the effect of SGs on glucose metabolism. We systematically searched PubMed, Web of Science and EMBASE to include eligible RCTs. Our primary outcomes were differences between SGs and the control group with respect to changes in blood glucose from the baseline to the end of intervention (including fasting blood glucose [FBG], and HbA1c measurements). A random-effects meta-analysis was conducted for data synthesis to calculate the pooled mean difference (MD). There were twelve RCTs included for analyses with a total of 871 participants (48% females). A significant effect of SGs on FBG (MD = -4.10 mg dl-1, 95% CI -6.55 to -1.65) was found, while no significant difference in HbA1c (MD = 0.01%, 95% CI -0.12% to 0.13%) was observed between SGs and controls. The whole quality of evidence was rated as low. Subgroup analyses demonstrated favorable effects of SGs on FBG in participants aged ≤50 years, those without diabetes mellitus (DM) or hypertension at the baseline, and overweight and obese adults. Sensitivity analyses yielded results largely similar to the main findings. To conclude, SGs are found to produce significant improvement in glucose metabolism in adult participants when compared with the control. More evidence is required to further clarify and support the benefit of SGs as a sugar substitute for glucose metabolism.

The Natural Sweetener Stevia: An Updated Review on its Phytochemistry, Health Benefits, and Anti-diabetic Study

Stevia rebaudiana Bertoni is one of the significant high qualities of non-caloric sugar substitute sweetener plants against diabetes disease. Diabetes mellitus is one of the most common metabolic diseases caused by insulin secretion defects, insulin resistance in peripheral tissues, or both. Stevia rebaudiana is a perennial shrub of the Compositae family that is grown in several places around the world. It contains a plethora of different bioactive constituents which are responsible for several activities and sweetness. This sweetness is due to the presence of steviol glycosides which is 100-300 times sweeter than sucrose. Furthermore, stevia reduces oxidative stress, lowering the risk of diabetes. Its leaves have been used to control and treat diabetes and a variety of other metabolic diseases. This review summarizes the history, bioactive constituents of S. rebaudiana extract, pharmacology, anti-diabetic activity, and its application, especially in food supplements.

Recent Advances in the Biosynthesis of Natural Sugar Substitutes in Yeast

Natural sugar substitutes are safe, stable, and nearly calorie-free. Thus, they are gradually replacing the traditional high-calorie and artificial sweeteners in the food industry. Currently, the majority of natural sugar substitutes are extracted from plants, which often requires high levels of energy and causes environmental pollution. Recently, biosynthesis via engineered microbial cell factories has emerged as a green alternative for producing natural sugar substitutes. In this review, recent advances in the biosynthesis of natural sugar substitutes in yeasts are summarized. The metabolic engineering approaches reported for the biosynthesis of oligosaccharides, sugar alcohols, glycosides, and rare monosaccharides in various yeast strains are described. Meanwhile, some unresolved challenges in the bioproduction of natural sugar substitutes in yeast are discussed to offer guidance for future engineering.

Stevia (Stevia rebaudiana) extract ameliorates insulin resistance by regulating mitochondrial function and oxidative stress in the skeletal muscle of db/db mice

BACKGROUND

Type 2 diabetes mellitus (T2DM), a growing health problem worldwide, is a metabolic disorder characterized by hyperglycemia due to insulin resistance and defective insulin secretion by pancreatic β-cells. The skeletal muscle is a central organ that consumes most of the insulin-stimulated glucose in the body, and insulin resistance can damage muscles in T2DM. Based on a strong correlation between diabetes and muscles, we investigated the effects of stevia extract (SE) and stevioside (SV) on the skeletal muscle of diabetic db/db mice.

METHODS

The mice were administered saline, metformin  (200 mg/kg/day), SE (200 and 500 mg/kg/day), and SV (40 mg/kg/day) for 35 days. During administration, we checked the levels of fasting blood glucose twice a week and conducted the oral glucose tolerance test (OGTT) and insulin tolerance test (ITT). After administration, we analyzed serum biochemical parameters, triglyceride (TG), total cholesterol (TC), insulin and antioxidant enzymes, and the cross-sectional area of skeletal muscle fibers of db/db mice. Western blots were conducted using the skeletal muscle of mice to examine the effect of SE and SV on protein expression of insulin signaling, mitochondrial function, and oxidative stress.

RESULTS

SE and SV administration lowered the levels of fasting blood glucose, OGTT, and ITT in db/db mice. The administration also decreased serum levels of TG, TC, and insulin while increasing those of superoxide dismutase (SOD) and glutathione peroxidase (GPx). Interestingly, muscle fiber size was significantly increased in db/db mice treated with SE500 and SV. In the skeletal muscle of db/db mice, SE and SV administration activated insulin signaling by increasing the protein expression of insulin receptor substrate, Akt, and glucose transporter type 4. Furthermore, SE500 administration markedly increased the protein expression of AMP-activated protein kinase-α, sirtuin-1, and peroxisome proliferator-activated receptor-γ coactivator-1α. SV administration significantly reduced oxidative stress by down-regulating the protein expression of 4-hydroxynonenal, heme oxygenase-1, SOD, and GPx. In addition, SE500 and SV administration suppressed the expression of apoptosis-related proteins in the skeletal muscle of db/db mice.

CONCLUSION

SE and SV administration attenuated hyperglycemia in diabetic mice. Moreover, the administration ameliorated insulin resistance by regulating mitochondrial function and oxidative stress, increasing muscle fiber size. Overall, this study suggests that SE and SV administration may serve as a potential strategy for the treatment of diabetic muscles.

Steviol Glycosides from Stevia rebaudiana: An Updated Overview of Their Sweetening Activity, Pharmacological Properties, and Safety Aspects

This literature-based review synthesizes the available scientific information about steviol glycosides as natural sweeteners and molecules with therapeutic potential. In addition, it discusses the safety concerns regarding human consumption. Steviol glycosides exhibit a superior sweetener proficiency to that of sucrose and are noncaloric, noncariogenic, and nonfermentative. Scientific evidence encourages stevioside and rebaudioside A as sweetener alternatives to sucrose and supports their use based on their absences of harmful effects on human health. Moreover, these active compounds isolated from Stevia rebaudiana possess interesting medicinal activities, including antidiabetic, antihypertensive, anti-inflammatory, antioxidant, anticancer, and antidiarrheal activity. The described bioactivities of steviol glycosides deserve special attention based on their dose dependence and specific pathological situations. Further clinical research is needed to understand underlying mechanisms of action, therapeutic indexes, and pharmacological applications.

Natural and low-caloric rebaudioside A as a substitute for dietary sugars: A comprehensive review

For health and safety concerns, traditional high-calorie sweeteners and artificial sweeteners are gradually replaced in food industries by natural and low-calorie sweeteners. As a natural and high-quality sugar substitute, steviol glycosides (SvGls) are continually scrutinized regarding their safety and application. Recently, the cultivation of organic stevia has been increasing in many parts of Europe and Asia, and it is obvious that there is a vast market for sugar substitutes in the future. Rebaudioside A, the main component of SvGls, is gradually accepted by consumers due to its safe, zero calories, clear, and sweet taste with no significant undesirable characteristics. Hence, it can be used in various foods or dietary supplements as a sweetener. In addition, rebaudioside A has been demonstrated to have many physiological functions, such as antihypertension, anti-diabetes, and anticaries. But so far, there are few comprehensive reviews of rebaudioside A. In this review article, we discuss the physicochemical properties, metabolic process, safety, regulatory, health benefits, and biosynthetic pathway of rebaudioside A and summarize the modification methods and state-of-the-art production and purification techniques of rebaudioside A. Furthermore, the current problems hindering the future production and application of rebaudioside A are analyzed, and suggestions are provided.

Partial Substitution of Alfalfa Hay by Stevia (Stevia rebaudiana) Hay Can Improve Lactation Performance, Rumen Fermentation, and Nitrogen Utilization of Dairy Cows

The objective of this study was to determine the effect of replacing isonitrogenous and isoenergetic basis alfalfa hay (AH) with stevia (Stevia rebaudiana) hay in dairy cow diets on nutrient digestion, milk performance, rumen fermentation, and nitrogen (N) utilization. In this study, 24 healthy Holstein lactating dairy cattle with a similar milk yield of 33.70 ± 2.75 (mean ± SD) kg, days in milk 95.98 ± 23.59 (mean ± SD) days, and body weight 587.75 ± 66.97 (mean ± SD) kg were selected and randomly allocated into three groups. The constituents of the three treatments were (1) 30.0% AH, and 0% stevia hay (SH) for the AH group; (2) 24.0% AH, and 6% SH for the 6% SH group; (3) 18.0% AH, and 12% SH for the 12% SH group. The substitution of AH with SH did not affect dry matter intake (DMI), gross energy (GE), and other nutrients intake but increased the digestibility of neutral detergent fiber (NDF) and acid detergent fiber (ADF). Compared with the AH diet, the cows fed the 6% SH diet had a higher milk yield and concentration of milk fat. Fecal and urinary nitrogen (N) were lower in cows fed a 6% SH diet than in cows fed the AH diet. Milk N secretion and milk N as a percentage of N intake were higher in cows fed a 6% SH diet than in cows fed AH diets. The concentration of ruminal volatile fatty acids, acetic acid, and ammonia-N were higher in cows fed a 6% SH diet than in cows fed an AH diet. By comparison, the 12% SH group did not affect milk yield, milk composition, N utilization, and rumen fermentation compared with the AH and 6% SH groups. In conclusion, it appears that feeding 6% SH, replacing a portion of AH, may improve lactation performance and N utilization for lactating dairy cows.

Case of a 6-year-old boy with anaphylaxis induced by erythritol with positive skin prick test and negative basophil activation test

Erythritol is widely used as an additive in foods and pharmaceuticals. We present the case of a 6-year-old boy who developed an allergy to erythritol. He showed a positive skin prick test result and a negative basophil activation test result. In cases involving allergens with low molecular weights, the test results should be carefully interpreted.

Natural sweetener Stevia rebaudiana: Functionalities, health benefits and potential risks

Stevia rebaudiana is a South American plant, the cultivation of which is increasing worldwide due to its high content of sweet compounds. Stevia sweetness is mainly due to steviol glycosides, that are ~250-300 times sweeter than sucrose. Many studies have suggested the benefits of Stevia extract over sugar and artificial sweeteners, but it is still not a very popular sugar substitute. This review summarizes current data on the biological activities of S. rebaudiana extract and its individual glycosides, including anti-hypertensive, anti-obesity, anti-diabetic, antioxidant, anti-cancer, anti-inflammatory, and antimicrobial effects and improvement of kidney function. Possible side effects and toxicity of Stevia extract are also discussed.

In Vitro Modulatory Effect of Stevioside, as a Partial Sugar Replacer in Sweeteners, on Human Child Microbiota

The effect of stevioside on human health is still insufficiently highlighted by recent research. The total or partial replacement of sugar with sweeteners influences the general state of health, especially the human microbiota's response as a determining factor in the onset of type 2 diabetes. The present study aimed to present the long-term (one-year) in vitro effect that regular stevioside consumption had on children's pattern microbiota. A metabolomic response was established by determining the synthesis of organic acids and a correlation with antioxidant status. An increase in the number of bacterial strains and the variation of amount of butyrate and propionate to the detriment of lactic acid was observed. The effect was evidenced by the progressive pH increasing, the reduction of acetic acid, and the proliferation of Escherichia coli strains during the simulations. Synthesis of the main short-chain fatty acids (SCFAs) was interpreted as a response (adaptation) of the microbiota to the stevioside, without a corresponding increase in antioxidant status. This study demonstrated the modulatory role of stevioside on the human microbiota and on the fermentation processes that determine the essential SCFA synthesis in maintaining homeostasis. The protection of the microbiota against oxidative stress was also an essential aspect of reducing microbial diversity.

Study on the bioavailability of stevioside-encapsulized lutein and its mechanism

This study aims to develop novel lutein nanoparticles encapsulized by stevioside (LUT-STE, 165 ± 2 nm average particles size) and systematically evaluate its bioavailability. Multiple spectroscopy and NMR analyses showed lutein and stevioside could interact through hydrogen bonds, CHπ interaction and van der Waals forces. Molecular docking simulation showed lutein was well distributed in the hydrophobic cavity of stevioside. Analyzed by Caco-2 cellular models, the transported amount of LUT-STE was 2.39 times that of lutein in 120 min with a P_app (B → A)/P_app (A → B) value of 0.63 ± 0.04. Nystatin and dynasore significantly reduced the cellular uptake of LUT-STE by 41.3% and 57.7%, respectively. Compared with free lutein, LUT-STE increased the C_max in mice plasma by 5.01-fold and promoted the accumulation in multiple organs. LUT-STE promoted the protein expressions of CD36, NPC1L1 and PPARγ in both cell and animal models. In conclusion, stevioside entrapment significantly promote the bioavailability of lutein through multiple transmembrane pathways.

Production of rebaudioside D from stevioside using a UGTSL2 Asn358Phe mutant in a multi-enzyme system

Rebaudioside D is a sweetener from Stevia rebaudiana with superior sweetness and organoleptic properties, but its production is limited by its minute abundance in S. rebaudiana leaves. In this study, we established a multi-enzyme reaction system with S. rebaudiana UDP-glycosyltransferases UGT76G1, Solanum lycopersicum UGTSL2 and Solanum tuberosum sucrose synthase StSUS1, achieving a two-step glycosylation of stevioside to produce rebaudioside D. However, an increase in the accumulation of rebaudioside D required the optimization of UGTSL2 catalytic activity towards glucosylation of rebaudioside A and reducing the formation of the side-product rebaudioside M2. On the basis of homology modelling and structural analysis, Asn358 in UGTSL2 was subjected to saturating mutagenesis, and the Asn358Phe mutant was used instead of wild-type UGTSL2 for bioconversion. The established multi-enzyme reaction system employing the Asn358Phe mutant produced 14.4 g l-1 (1.6 times of wild-type UGTSL2) rebaudioside D from 20 g l-1 stevioside after reaction for 24 h. This system is useful for large-scale rebaudioside D production and expands our understanding of the pathways involved in its synthesis.

Stevia as a Natural Sweetener: A Review

Stevia rebaudiana of the Asteraceae family is a perennial shrub. It is a sweetener herb also known as sweet weed, sweet leaf, sweet herbs and honey leaf, native to Argentina, Brazil and Paraguay. The leaves of stevia are sweeter than sucrose with zero calories. Steviol, a diterpenoid glycoside derivative identified from this plant, is sweeter than sucrose and is safe when used as a sweetening agent. Diabetic and obese people with hyperglycemia who are in a condition to follow a strict diet can use stevioside as an alternative sweetener. In addition to its hypoglycemic property, the plant also exhibits antibacterial, anti-inflammatory, hypotensive, antiseptic, diuretic, anti-fertility and cardiotonic properties. It has also been documented to show good effects on treating skin diseases such as dermatitis, acne, eczema etc. The leaves of stevia with enriched phytoconstituents could be an alternative natural sweetener for children, adults and old age persons who have a craze to drink beverages and eat sweetened food products in their habitual life.

Stevioside, a diterpenoid glycoside, shows anti-inflammatory property against Dextran Sulphate Sodium-induced ulcerative colitis in mice

Inflammatory bowel disease is an umbrella-term used to describe a set of chronic inflammatory conditions that affect the gastro-intestinal tract. Since most of the inflammatory medications in current use have several undesirable side-effects, stevioside, a naturally occurring, high-intensity sweetener was assessed in our study for its anti-inflammatory properties by in-vitro and in-vivo experiments. Stevioside was observed to significantly inhibit the levels of LPS induced elevation of cytokines, TNF-α (P < 0.05) and IL-6 (P < 0.001) as well as the production of reactive oxygen species (P < 0.01) and nitrites (P < 0.001) in RAW264.7 cells. Stevioside has also been evaluated for its anti-inflammatory effect by using dextran sulfate sodium (DSS)-induced ulcerative colitis model in mice. Stevioside significantly reduced the disease activity index (DAI) score, ameliorated the inflammatory symptoms induced by DSS in mice and exhibited intact colon histo-architecture. Stevioside treatment significantly inhibited the levels of pro-inflammatory cytokines, TNF-α and IL-6, and the protein expressions of pro-inflammatory mediators, COX-2 (P < 0.01) and iNOS (P < 0.01) and restored the levels of endogenous anti-oxidants such as superoxide dismutase (P < 0.01), catalase (P < 0.001), glutathione s-transferase (P < 0.001) and reduced glutathione (P < 0.001) level in colon tissues. It was also observed that stevioside significantly suppressed NF-κB (p65) activation by abrogating IκB phosphorylation and attenuated the phosphorylation of p38, ERK and JNK proteins in colon tissues. The findings of the present study suggest that stevioside exhibits anti-inflammatory property by inhibiting NF-κB (p65) and MAPK pathways and can be employed as an adjunct in nutraceuticals to treat IBD.

Comparative metabolic and ionomic profiling of two cultivars of Stevia rebaudiana Bert. (Bertoni) grown under salinity stress

This study provides a comprehensive investigation on the impact of increasing NaCl concentrations on hydroponically grown Stevia rebaudiana cultivars (Shoutian-2 and Fengtian). Growth parameters including plant height, biomass and physiological responses including osmotic potential were measured. In addition, the levels of steviol glycosides, elements and primary metabolites were measured and statistically evaluated. The cultivar Fengtian grew faster, accumulated less Na⁺ and compatible organic solutes, and more K⁺ in the leaves, as compared to the cv. Shoutian-2. Metabolite analysis identified 81 differentially accumulated metabolites, indicating an alteration in the metabolite phenotype of both cultivars upon exposure to salinity A general increase in many amino acids, amines, sugars and sugar phosphates with a concurrent decrease in most organic acids; including tricarboxylic acid (TCA) cycle intermediates, was observed. In the more salt tolerant cv. Fengtian, the levels of hexose phosphates and metabolites involved in cellular protection increased in response to salinity. These metabolites remained unchanged in the sensitive cv. Shoutian-2. Interestingly, salt treatment notably increased the rebaudioside A concentration by 53% while at the same time stevioside decreased by 38% in Fengtian which has important implications for controlling the relative amounts of reboudioside A and stevioside. The findings of this study leads to the conclusion that mild salinity stress can increase the yield of sweetener compounds, which is dependent on the cultivar and the level of salinity stress.

Stevia rebaudiana Bertoni and Its Effects in Human Disease: Emphasizing Its Role in Inflammation, Atherosclerosis and Metabolic Syndrome

PURPOSE OF REVIEW

Stevia rebaudiana Bertoni is a perennial shrub with zero calorie content that has been increasing in popularity for its potential use as an adjuvant in the treatment of obesity. The level of evidence supporting general benefits to human health is insufficient. We conducted a review of the literature summarizing the current knowledge and role in human disease.

RECENT FINDINGS

Despite stevia's minimal systemic absorption, studies have been promising regarding its potential benefits against inflammation, carcinogenesis, atherosclerosis glucose control, and hypertension. On the other hand, the growing popularity of artificial sweeteners does not correlate with improved trends in obesity. An increased intake of artificial non-caloric sweeteners may not be associated with decreased intake of traditional sugar-sweetened beverages and foods. The effects of Stevia on weight change have been linked to bacteria in the intestinal microbiome, mainly by affecting Clostridium and Bacteroides sp.

POPULATIONS

A growing body of evidence indicates that Stevia rebaudiana Bertoni is protective against malignant conversion by inhibition of DNA replication in human cancer cell growth in vitro. Consumption of Stevia has demonstrated to be generally safe in most reports. Further clinical studies are warranted to determine if regular consumption brings sustained benefits for human health.

Stevia Leaf to Stevia Sweetener: Exploring Its Science, Benefits, and Future Potential

Steviol glycoside sweeteners are extracted and purified from the Stevia rebaudiana Bertoni plant, a member of the Asteraceae (Compositae) family that is native to South America, where it has been used for its sweet properties for hundreds of years. With continued increasing rates of obesity, diabetes, and other related comorbidities, in conjunction with global public policies calling for reductions in sugar intake as a means to help curb these issues, low- and no-calorie sweeteners (LNCSs, also known as high-potency sweeteners) such as stevia are gaining interest among consumers and food manufacturers. This appeal is related to stevia being plant-based, zero calorie and with a sweet taste that is 50-350 times sweeter than sugar, making it an excellent choice for use in sugar- and calorie-reduced food and beverage products. Despite the fact that the safety of stevia has been affirmed by several food regulatory and safety authorities around the world, insufficient education about stevia's safety and benefits, including continuing concern with regard to the safety of LNCSs in general, deters health professionals and consumers from recommending or using stevia. Therefore, the aim of this review and the stevia symposium that preceded this review at the ASN's annual conference in 2017 was to examine, in a comprehensive manner, the state of the science for stevia, its safety and potential health benefits, and future research and application. Topics covered included metabolism, safety and acceptable intake, dietary exposure, impact on blood glucose and insulin concentrations, energy intake and weight management, blood pressure, dental caries, naturality and processing, taste and sensory properties, regulatory status, consumer insights, and market trends. Data for stevia are limited in the case of energy intake and weight management as well as for the gut microbiome; therefore, the broader literature on LNCSs was reviewed at the symposium and therefore is also included in this review.

A fusion protein strategy for soluble expression of Stevia glycosyltransferase UGT76G1 in Escherichia coli

The UDP-glucosyltransferase UGT76G1 from Stevia rebaudiana converts stevioside to rebaudioside A via a one-step glycosylation reaction, which increases the amount of sweet-tasting rebaudioside A and decreases the amount of stevioside that has a bitter aftertaste. This enzyme could, therefore, conceivably be used to improve the organoleptic properties of steviol glycosides and offer a cost-effective preparation of high-purity rebaudioside A. Producing soluble enzymes by overexpression is a prerequisite for large-scale biocatalysis. However, most of the UGT76G1 overexpressed in Escherichia coli is in inclusion bodies. In this study, three N-terminal fusion partners, 3'-phosphoadenosine-5'-phosphatase (CysQ), 2-keto-3-deoxy-6-phosphogluconate aldolase (EDA) and N-utilisation substance A (NusA), were tested to improve UGT76G1 expression and solubility in E. coli. Compared with the fusion-free protein, the solubility of UGT76G1 was increased 40% by fusion with CysQ, and the glucosyltransferase activity of the crude extract was increased 82%. This successful CysQ fusion strategy could be applied to enhance the expression and solubility of other plant-derived glucosyltransferases and presumably other unrelated proteins in the popular, convenient and cost-effective E. coli host.

Health outcomes of non-nutritive sweeteners: analysis of the research landscape

BACKGROUND

Food products containing non-nutritive sweeteners (NNSs) instead of sugar have become increasingly popular in the last decades. Their appeal is obviously related to their calorie-free sweet taste. However, with the dramatic increase in their consumption, it is reasonable and timely to evaluate their potential health benefits and, more importantly, potential adverse effects. The main aim of this scoping review was to map the evidence about health outcomes possibly associated with regular NNS consumption by examining the extent, range, and nature of research activity in this area.

METHODS

We systematically searched Ovid MEDLINE, EMBASE and the Cochrane CENTRAL databases for studies on NNSs (artificial sweeteners or natural, non-caloric sweeteners, either used individually or in combination) using text terms with appropriate truncation and relevant indexing terms. All human studies investigating any health outcomes of a NNS intervention or exposure were eligible for inclusion. No studies were excluded based on language, study design or methodological quality. Data for each health outcome were summarized in tabular form and were discussed narratively.

RESULTS

Finally, we included 372 studies in our scoping review, comprising 15 systematic reviews, 155 randomized controlled trials (RCTs), 23 non-randomized controlled trials, 57 cohort studies, 52 case-control studies, 28 cross sectional studies and 42 case series/case reports. In healthy subjects, appetite and short term food intake, risk of cancer, risk of diabetes, risk of dental caries, weight gain and risk of obesity are the most investigated health outcomes. Overall there is no conclusive evidence for beneficial and harmful effects on those outcomes. Numerous health outcomes including headaches, depression, behavioral and cognitive effects, neurological effects, risk of preterm delivery, cardiovascular effects or risk of chronic kidney disease were investigated in fewer studies and further research is needed. In subjects with diabetes and hypertension, the evidence regarding health outcomes of NNS use is also inconsistent.

CONCLUSIONS

This scoping review identifies the needs for future research to address the numerous evidence gaps related to health effects of NNSs use.It also specifies the research questions and areas where a systematic review with meta-analyses is required for the proper evaluation of health outcomes associated to regular NNSs consumption.

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.

Stevia Glycosides: Chemical and Enzymatic Modifications of Their Carbohydrate Moieties to Improve the Sweet-Tasting Quality

Stevia glycosides, extracted from the leaves of the plant Stevia rebaudiana Bertoni, display an amazing high degree of sweetness. As processed plant products, they are considered as excellent bio-alternatives for sucrose and artificial sweeteners. Being noncaloric and having beneficial properties for human health, they are the subject of an increasing number of studies for applications in food and pharmacy. However, one of the main obstacles for the successful commercialization of Stevia sweeteners, especially in food, is their slight bitter aftertaste and astringency. These undesirable properties may be reduced or eliminated by modifying the carbohydrate moieties of the steviol glycosides. A promising procedure is to subject steviol glycosides to enzymatic glycosylation, thereby introducing additional monosaccharide residues into the molecules. Depending on the number and positions of the monosaccharide units, the taste quality and sweetness potency of the compounds will vary. Many studies have been performed already, and this review summarizes the structures of native steviol glycosides and the recent data of modifications of the carbohydrate moieties that have been published to provide an overview of the current progress.

Transmembrane transport of steviol glucuronide and its potential interaction with selected drugs and natural compounds

Steviol glucuronide (SVG) is the major metabolite derived from steviol, the aglycone of stevioside and rebaudioside A. After the ingestion of stevioside and rebaudioside A, SVG is formed and excreted into the urine in humans. In the present study, transporter mediated efflux and uptake of SVG was investigated in order to understand molecular mechanisms underlying its renal clearance. Results showed that SVG was not a substrate of efflux transporters BCRP, MRP2, MATE1 or P-gp. In contrast, OAT3 played a predominant role in the uptake of SVG in comparison to OATP1B1, OATP1B3, or OATP2B1. Quercetin, telmisartan, diclofenac, and mulberrin displayed a relatively strong inhibition against OAT3 mediated uptake of SVG with IC50 values of 1.8, 2.9, 8.0, and 10.0 μM, respectively. Because OAT3 is a major uptake transporter in the kidney, inhibition of OAT3 activity may alter SVG's renal clearance by drugs and natural compounds that are used concomitantly with stevia leaf extracts.