(-)-Steviol

The herbs of Stevia rebaudiana

Synthesis of rebaudioside D, using glycosyltransferase UGTSL2 and in situ UDP-glucose regeneration.[Pubmed:29680056]

Food Chem. 2018 Sep 1;259:286-291.

Steviol glycosides from Stevia rebaudiana leaves are used in stevia-based sweeteners for their intense sweetness and low calories. Rebaudioside D is present in leaves in minute quantities ( approximately 0.4-0.5% w/w total dry weight), but it is approximately 350 times sweeter than sucrose, and sweeter than the more abundant rebaudioside A and stevioside. In the present study, pathways for rebaudioside D synthesis and UDP-glucose recycling were developed by coupling recombinant UDP-glucosyltransferase UGTSL2 from Solanum lycopersicum and sucrose synthase StSUS1 from Solanum tuberosum. Reaction parameters, including substrate ratio, sucrose concentration, temperature, crude extract concentration, and reaction time, were evaluated, and 17.4g/l of rebaudioside D (yield=74.6%) was obtained from 20g/l of rebaudioside A after 20h, using UDP or UDP-glucose in recombinant cell crude extracts. Extending the reaction time generated rebaudioside M2 from further glycosylation of rebaudioside D. Km values for UGTSL2 indicated a higher affinity for rebaudioside D than for rebaudioside A.

Steviol slows renal cyst growth by reducing AQP2 expression and promoting AQP2 degradation.[Pubmed:29524884]

Biomed Pharmacother. 2018 May;101:754-762.

Overexpression of aquaporin 2 (AQP2) was observed and suggested to be involved in fluid secretion leading to cyst enlargement in polycystic kidney disease (PKD). The cyst expansion deteriorates the renal function and, therefore, therapies targeting cyst enlargement are of clinical interest. Of note, inhibition of vasopressin function using vasopressin 2 receptor (V2R) antagonist which decreased cAMP production along with AQP2 production and function can slow cyst growth in ADPKD. This finding supports the role of AQP2 in cyst enlargement. Steviol, a major metabolite of the sweetening compound stevioside, was reported to retard MDCK cyst growth and enlargement by inhibiting CFTR activity. Interestingly, its efficacy was found to be higher than that of CFTRinh-172. Since steviol was also found to produce diuresis in rodent, it is likely that steviol might have an additional effect in retarding cyst progression, such as inhibition of AQP2 expression and function. Here, we investigated the effect of steviol on AQP2 function and on cyst growth using an in vitro cyst model (MDCK and Pkd1(-/-) cells). We found that steviol could markedly inhibit cyst growth by reducing AQP2 expression in both Pkd1(-/-) and MDCK cells. Real-time PCR also revealed that steviol decreased AQP2 mRNA expression level as well. Moreover, a proteasome inhibitor, MG-132, and the lysosomotropic agent, hydroxychloroquine (HCQ) were found to abolish the inhibitory effect of steviol in Pkd1(-/-) cells. Increased lysosomal enzyme marker (LAMP2) expression following steviol treatment clearly confirmed the involvement of lysosomes in steviol action. In conclusion, our finding showed for the first time that steviol slowed cyst growth, in part, by reducing AQP2 transcription, promoted proteasome, and lysosome-mediated AQP2 degradation. Due to its multiple actions, steviol is a promising compound for further development in the treatment of PKD.

[Method of Quantitative Analysis Using Enzymatic Hydrolysis of alpha-Glucosyltransferase-Treated Stevia in Foods].[Pubmed:29743465]

Shokuhin Eiseigaku Zasshi. 2018;59(1):30-35.

A quantitative analysis by HPLC of alpha-glucosyltransferase-treated stevia in foods was considered. This analysis is the way which hydrolyzed alpha-glucosyltransferase-treated stevia in the stevioside (SS) and the rebaudioside A (RS) using a glucoamylase. Recovery (%) of alpha-glucosyltransferase-treated stevia, spiked at 200 mg/kg in various foods, were more than 80% and the relative standard deviations were less than 5.0% as SS and RS for the rate of collection. A qualitative analysis by LC-MS/MS was performed 36 products of commercial foods containing stevia. We quantified of 11 products in which alpha-glucosyltransferase-treated stevia was detected. Quantitative value was at most 180 mg/kg as SS, at most 70 mg/kg as RS.

In vitro effects of rebaudioside A, stevioside and steviol on porcine cytochrome p450 expression and activity.[Pubmed:29655729]

Food Chem. 2018 Aug 30;258:245-253.

The physiological effects of the Stevia-derived compounds, rebaudioside A, stevioside and steviol have been the focus of several studies due to their use as sweeteners in food. Despite that, little is known about their potential food-drug interactions. In the present study, IPEC-J2 cells and primary hepatocytes were used to investigate the effect of rebaudioside A, stevioside and steviol on cytochrome p450 (CYP) mRNA expression. Moreover, hepatic microsomes were used to investigate direct interactions between the compounds and specific CYP activity. In IPEC-J2 no changes in mRNA expression of CYP1A1 or CYP3A29 were observed with the Stevia-derived compounds. In primary hepatocytes all three tested compounds induced a significant increase in CYP3A29 expression. The tested compounds had no direct effect on specific CYP activity. In conclusion, rebaudioside A, stevioside and steviol induce only minor or no changes to the CYP expression and activity, and are not likely to cause food-drug interactions.

Centella asiatica ameliorates diabetes-induced stress in rat tissues via influences on antioxidants and inflammatory cytokines.[Pubmed:29501767]

Biomed Pharmacother. 2018 May;101:447-457.

Centella asiatica (L.) Urban (Family: Apiaceae) is a perennial herb that has been used to elevate mood, improve memory, treat wounds and manage kidney-related ailments in African traditional medicine practice. This study evaluated the potential benefits of C. asiatica (CA) on diabetes-induced stress in kidney and brain of rats. Following the induction of diabetes mellitus (DM), rats were orally treated with vehicle, CA or Metformin daily for 14 days. After treatment, renal and brain levels of inflammatory cytokines, TNF-alpha, IFN-gamma, IL-4, and IL-10 were assessed. Oxidant and antioxidant biomarkers were also evaluated. Phyto-compounds in the crude methanol extract of CA were analyzed by Gas Chromatography-Mass Spectroscopy. Diabetes increased malondialdehyde (MDA) concentration by 39%; elevated levels of TNF-alpha (44%) and IFN-gamma (20%); and reduced the antioxidant status in the kidney in comparison to normal control rats. In the brain, diabetic control rats had significantly greater levels of MDA, TNF-alpha, and IFN-gamma (182%, 40%, and 20%, respectively) in addition to the lowered antioxidant status when compared to normal control rats. However, treatment with CA significantly reduced the renal levels of MDA (33%), TNF-alpha (78%), and IFN-gamma (42%) while that of IL-10 increased by 18% when compared to diabetic control rats. In the brain, CA treatment elicited significant reductions in MDA (37%), TNF-alpha (30%), and IFN-gamma (37%) levels while those of IL-4 and IL-10 increased by 94% and 20% respectively. In addition, the renal and brain antioxidant status was significantly boosted by CA treatment. Several medicinal compounds including ascorbic acid, asiatic acid, oleanolic acid, stevioside, stigmasterol, and alpha-humulene were identified in the crude extract of CA. Findings from this study suggest CA may protect diabetic tissues from stress via antioxidant and anti-inflammatory mechanisms that can be useful in the management of diabetic complications.

Development of pure certified reference material of stevioside.[Pubmed:29571500]

Food Chem. 2018 Jul 30;255:75-80.

Pure stevioside was extracted from leaves of Stevia rebaudiana (Bertoni) to be used as a reference material in the instrument calibration or method validation process. The mass fraction was determined by comparison between the mass balance method and quantitative nuclear magnetic resonance (qNMR) spectroscopy. The impurities in the sample were analyzed by Karl Fischer titration for moisture content and thermogravimetric analysis for inorganic residue. Homogeneity, together with short term and long term stability, were also studied and the uncertainty was reported. The certified value of this mass fraction is 0.986+/-0.0019 (k=2) with 1year stability.

Steviol is a major metabolite of the sweetening compound stevioside. Steviol slows renal cyst growth by reducing AQP2 expression and promoting AQP2 degradation.

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