Effects of yam dioscorin interventions on improvements of the metabolic syndrome in high-fat diet-induced obese rats

Vitisin B, a resveratrol tetramer from Vitis thunbergii var. taiwaniana, ameliorates impaired glucose regulations in nicotinamide/streptozotocin-induced type 2 diabetic mice

Background and aim

In Taiwan, Vitis thunbergii var. taiwaniana (VTT) is used in traditional medicine and as a local tea. VTT rich in resveratrol and resveratrol oligomers have been reported to exhibit anti-obesity and anti-hypertensive activities in animal models; however, no studies have investigated type 2 diabetes mellitus (T2DM) treatments. This study aimed to investigate the anti-T2DM effects of resveratrol tetramers isolated from the VTT in nicotinamide/streptozotocin (STZ)-induced Institute of Cancer Research (ICR) mice.

Experimental procedure

The oral glucose tolerance test (OGTT) was used to imitate postprandial blood glucose (BG) regulations in mice by pre-treatment with VTT extracts, resveratrol tetramers of vitisin A, vitisin B, and hopeaphenol 30 min before glucose loads. Vitisin B (50 mg/kg) was administered to treat T2DM-ICR mice once daily for 28 days to investigate its hypoglycemic activity.

Results and conclusion

Mice pre-treated with VTT-S-95EE, or vitisin B (100 mg/kg) 30-min before glucose loading showed significant reductions (P < 0.001) in the area under the curve at 120-min (BG-AUC0-120) than those without pre-treatment with VTT-S-95 E E or vitisin B. Vitisin B-treated T2DM mice showed hypoglycemic activities via a reduction in plasma dipeptidyl peptidase (DPP)-IV activities to maintain insulin actions and differed significantly than those of untreated T2DM mice (P < 0.05), and also reduced BG-AUC0-120 and insulin-AUC0-120 in the OGTT.These in vivo results showed that VTT containing vitisin B would be beneficial for developing nutraceuticals and/or functional foods for glycemic control in patients with T2DM, which should be investigated further.

Could consumption of yam (Dioscorea) or its extract be beneficial in controlling glycaemia: a systematic review

Yam (Dioscorea spp.) and its associated extracts have been shown to possess a variety of biological activities and identified as beneficial in the control of glycaemia in patients with type II diabetes mellitus (T2DM). The objective was to conduct a systematic search of the literature to investigate whether yam and its extract can improve glycaemia and whether the consumption of yam could be beneficial for managing T2DM. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and the Population, Invention, Comparison and Outcome framework, three databases (PubMed, Scopus and Web of Science) were searched using a key term strategy. Strict inclusion criteria were employed to identify all relevant and available studies. The quality of these studies was assessed using SYRCLE's Risk of Bias tool. Ten studies were included, and all studies consisted of findings from rodent models of diabetes, including animals consuming high fat diets or genetic models of diabetes. All ten studies showed that the consumption of yam and/or its extracts (containing dioscin, dioscorin, diosgenin, DA-9801/02 or Chinese yam polysaccharides) improved glycaemia. These included improvements in fasting blood glucose and reductions in glucose and increase in insulin levels following a glucose tolerance test. Furthermore, significant changes in body weight and adiposity were observed in nine studies, these included improvements in lipid biomarkers in four and reductions in inflammatory markers in one. The current work indicates that the consumption of yam or its extracts can be beneficial for improving blood glucose; however, the molecular mechanism for these effects remains largely unknown. Future trials on human subjects are warranted.

Additional Benefit of Chinese Medicine Formulae Including Dioscoreae rhizome (Shanyao) for Diabetes Mellitus: Current State of Evidence

Background

Chinese medicine has been used to treat diabetes symptoms for thousands of years. Dioscoreae rhizome or Shanyao is a Chinese medicinal herb that is routinely used in the treatment of diabetes mellitus (DM).

Objective

The purpose of this study is to evaluate the evidence of the added benefits and safety of herbal formulae containing Shanyao in clinical studies and the possible mechanisms of Shanyao in the prevention and treatment of DM in experimental studies.

Methods

We searched nine databases for randomized controlled trials (RCTs) that included Shanyao in the formulae in the treatment of type 2 DM. Furthermore, experimental studies on the prevention and treatment of DM by Shanyao in English- and Chinese-language databases were identified.

Results

Fifty-three moderate quality RCTs with herbal formulae containing Shanyao were identified. Results from meta-analysis indicated that Shanyao alone or formulae containing Shanyao in addition to conventional treatments could benefit people with type 2 DM in lowering blood glucose, blood lipids and reducing insulin resistance. Moreover, adverse events were significantly lower in the CHM plus conventional group than those in the conventional group. Shanyao may exert the benefit through various mechanisms including inhibition of α-glucosidase and DPP-IV activity, increase of endogenous GLP-1 and immune regulating activities.

Conclusion

Evidence from this review suggested that there appeared to be added clinical benefits associated with the use of Shanyao for DM, whether as a food supplement or as a CHM combined with hypoglycemic agents with a good safety profile.

The perceptions of natural compounds against dipeptidyl peptidase 4 in diabetes: from in silico to in vivo

Dipeptidyl peptidase IV (DPP-4), an incretin glucagon-like peptide-1 (GLP-1) degrading enzyme, contains two forms and it can exert various physiological functions particular in controlling blood glucose through the action of GLP-1. In diabetic use, the DPP-4 inhibitor can block the DDP-4 to attenuate GLP-1 degradation and prolong GLP-1 its action and sensitize insulin activity for the purpose of lowering blood glucose. Nonetheless the adverse effects of DPP-4 inhibitors severely hinder their clinical applications, and notably there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis, herbs, and plants with fewer side effects. In this review, we highlight various strategies, namely computational biology (in silico), in vitro enzymatic and cell assays, and in vivo animal tests, for seeking natural DPP-4 inhibitors from botanic sources including herbs and plants. The pros and cons of all approaches for new inhibitor candidates or hits will be under discussion.

Development of Yam Dioscorin-Loaded Nanoparticles for Paracellular Transport Across Human Intestinal Caco-2 Cell Monolayers

Dioscorins, the major storage proteins of yam tubers, exert immunomodulatory activities. To improve oral bioavailability of dioscorins in the intestine, recombinant dioscorin (rDioscorin) was coated with N,N,N-trimethyl chitosan (TMC) and tripolyphosphate (TPP), resulting in the formation of TMC-rDio-TPP nanoparticles (NPs). The loading capacity and entrapment efficiency of rDioscorin in the NPs were 26 ± 0.7% and 61 ± 1.4%, respectively. The NPs demonstrated a substantial release profile in the pH environment of the jejunum. The rDioscorin released from the NPs stimulated proliferation and phagocytosis of the macrophage RAW264.7 and activated the gene expression of IL-1β and IL-6. Incubation of the NPs in the Caco-2 cell monolayer led to a 5.2-fold increase of P_app compared with rDioscorin alone, suggesting that rDioscorin, with the assistance of TMC, can be promptly transported across the intestinal epithelia. These results demonstrate that the TMC-rDio-TPP NPs can be utilized for elucidating the immunopharmacological effects of dioscorins through oral delivery.

135-Day Interventions of Yam Dioscorin and the Dipeptide Asn-Trp (NW) To Reduce Weight Gains and Improve Impaired Glucose Tolerances in High-Fat Diet-Induced C57BL/6 Mice

The C57BL/6J mice were fed a 135-day normal diet or a high-fat diet (HFD) without, or concurrent with, a single yam dioscorin (80 mg/kg) or dipeptide NW (40 mg/kg) intervention every day. The final body weights (g) of mice were 26.1 ± 1.4, 34.97 ± 2.1, 31.75 ± 2.6, and 31.66 ± 3.1, respectively, for normal diet-fed, HFD-fed, dioscorin-intervened, and NW-intervened group. The mice in both intervened groups showed similar less weight gains and had significant differences (P < 0.05) compared to those in the HFD group under the same cumulative HFD intakes. The blood biochemical index of mice with dioscorin interventions showed significantly lower contents in total cholesterol and low-density lipoprotein, and NW interventions showed significantly lower total triglyceride contents compared to those of the HFD group (P < 0.05). Both intervened mice exhibited similar reductions in total visceral lipid contents and have significant differences compared to those of the HFD group (P < 0.05). The dioscorin intervention was better than NW interventions in lowering blood glucose levels by oral glucose tolerance tests and both showed significant differences (P < 0.05) compared to those in the HFD group. Yam dioscorin or dipeptide NW will potentially be used for preventive functional foods of less body weight gains and impaired glucose tolerance controls, which require further clinical trial investigations.

Hot-Water Extracts from Roots of Vitis thunbergii var. taiwaniana and Identified ε-Viniferin Improve Obesity in High-Fat Diet-Induced Mice

In this study, hot-water extracts (HW) from roots of Vitis thunbergii var. taiwaniana (VTT-R) were shown to lower levels of lipid accumulation significantly (P < 0.01 or 0.001) compared to the control in 3T3-L1 adipocytes. The VTT-R-HW (40 mg/kg) interventions concurrent with a high-fat (HF) diet in C57BL/6 mice over a 5 eek period were shown to reduce body weights significantly (P < 0.05) compared to those of mice fed a HF diet under the same food-intake regimen. The (+)-ε-viniferin isolated from VTT-R-HW was shown to reduce the size of lipid deposits significantly compared to the control (P < 0.05 or 0.001) in 3T3-L1 adipocytes, and dose-dependent 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitions showed that the 50% inhibitory concentration was calculated to be 96 μM. The two-stage (+)-ε-viniferin interventions (10 mg/kg, day 1 to day 38; 25 mg/kg, day 39 to day 58) were shown to lower mice body weights significantly (P < 0.05 or 0.001), the weight ratio of mesenteric fat, blood glucose, total cholesterol, and low-density lipoprotein compared to that of the HF group under the same food-intake regimen but without concurrent VTT-R-HW interventions. It might be possible to use VTT-R-HW or (+)-ε-viniferin as an ingredient in the development of functional foods for weight management, and this will need to be investigated further.

Synthesized Peptides from Yam Dioscorin Hydrolysis in Silico Exhibit Dipeptidyl Peptidase-IV Inhibitory Activities and Oral Glucose Tolerance Improvements in Normal Mice

RRDY, RL, and DPF were the top 3 of 21 peptides for inhibitions against dipeptidyl peptidase-IV (DPP-IV) from the pepsin hydrolysis of yam dioscorin in silico and were further investigated in a proof-of-concept study in normal ICR mice for regulating glucose metabolism by the oral glucose tolerance test (OGTT). The sample or sitagliptin (positive control) was orally administered by a feeding gauge; 30 min later, the glucose loads (2.5 g/kg) were performed. RRDY, yam dioscorin, or sitagliptin preload, but not DPF, lowered the area under the curve (AUC0-120) of blood glucose and DPP-IV activity and elevated the AUC0-120 of blood insulin, which showed significant differences compared to control (P < 0.05 or 0.001). These results suggested that RRDY and yam dioscorin might be beneficial in glycemic control in normal mice and need further investigations in diabetic animal models.

Vitis thunbergii var. taiwaniana Extracts and Purified Compounds Ameliorate Obesity in High-Fat Diet-Induced Obese Mice

The increasing prevalence of obesity continues to gain more attention worldwide. In this study, diet-induced obese mice were used to evaluate the antiobesity effects of extracts, fractions, and purified compounds from Vitis thunbergii var. taiwaniana (VTT). The C57BL/6J mice were fed a 5-week high-fat diet (HF) concurrently with ethanol extracts (Et-ext, 80 mg/kg) from roots (R), stems (S), and leaves (L) by oral gavage daily. Only R-Et-ext interventions showed significant weight reduction in mice compared with those in the HF group; however, mouse plasma contents of total cholesterols (TC), total triglycerides (TG) and low-density lipoproteins (LDL) of all three Et-ext intervened groups showed significant reductions compared with those in the HF group. Furthermore, intervention with the ethyl acetate-partitioned fraction (EA-fra, 60 mg/kg) from R-Et-ext but not the n-butanol-partitioned fraction or water fraction from R-Et-ext showed significant weight reduction in mice compared with those in the HF group. The same molecular weights of three resveratrol tetramers, (+)-hopeaphenol, (+)-vitisin A, and (-)-vitisin B, were isolated from the EA-fra of VTT-R. The (+)-vitisin A and fenofibrate (25 mg/kg) but not the (+)-hopeaphenol and (-)-vitisin B interventions showed significant weight reduction in mice compared with those in the HF group. The total feed intake among the HF groups with or without interventions showed no significant differences. The mouse plasma contents of TC, TG, LDL, free fatty acid, and plasma lipase activity of the three resveratrol tetramer-intervened groups showed reductions in the mice compared with those in the HF group. It was proposed that the lipase inhibitory activities of VTT extracts and purified resveratrol tetramers might contribute in part to the antiobesity effect, and these results suggested that VTT may be developed as functional food for achieving antiobesity objectives and requires further investigation.

Anti-α-glucosidase and Anti-dipeptidyl Peptidase-IV Activities of Extracts and Purified Compounds from Vitis thunbergii var. taiwaniana

Ethanol extracts (Et) from the stem (S) and leaf (L) of Vitis thunbergii var. taiwaniana (VTT) were used to investigate yeast α-glucosidase and porcine kidney dipeptidyl peptidase-IV (DPP-IV) inhibitory activities. Both VTT-Et showed complete α-glucosidase inhibition at 0.1 mg/mL; VTT-S-Et and VTT-L-Et showed 26 and 11% DPP-IV inhibition, respectively, at 0.5 mg/mL. The VTT-Et interventions (20 and 50 mg/kg) resulted in improvements in impaired glucose tolerance of diet-induced obese rats. (+)-Hopeaphenol, (+)-vitisin A, and (-)-vitisin B were isolated from the ethyl acetate fractions of S-Et and showed yeast α-glucosidase inhibition (IC50 = 18.30, 1.22, and 1.02 μM) and porcine kidney DPP-IV inhibition (IC50 = 401, 90.75, and 15.3 μM) compared to acarbose (6.39 mM) and sitagliptin (47.35 nM), respectively. Both (+)-vitisin A and (-)-vitisin B showed mixed noncompetitive inhibition against yeast α-glucosidase and porcine kidney DPP-IV, respectively. These results proposed that VTT extracts might through inhibitions against α-glucosidase and DPP-IV improve the impaired glucose tolerance in diet-induced obese rats.