Suppressive Effect of a Hot Water Extract of Adzuki Beans (Vigna angularis) on Hyperglycemia after Sucrose Loading in Mice and Diabetic Rats

Potential anti-obesity effect of saponin metabolites from adzuki beans: A computational approach

In contrast to its widespread traditional and popular culinary use to reduce weight, Vigna angularis (adzuki beans) was not subjected to sufficient scientific scrutiny. Particularly, its saponins whose role was never investigated before to unveil the beans' antidiabetic and anti-obesity effects. Four vital pancreatic and intestinal carbohydrate enzymes were selected to assess the potency of the triterpenoidal saponins of V. angularis to bind and activate these proteins through high-precision molecular modeling and dynamics mechanisms with accurate molecular mechanics Generalized Born Surface Area (MMGBSA) energy calculations; thus, recognizing their anti-obesity potential. Our results showed that adzukisaponin VI and adzukisaponin IV were the best compounds in the α-amylase and α-glucosidase enzymatic grooves, respectively. Adzukisaponin VI and angulasaponin C were the best fitting in the N-termini of sucrase-isomaltose (SI) enzyme, and angulasaponin C was the best scoring compound in maltase-glucoamylase C-termini. All of them outperformed the standard drug acarbose. These compounds in their protein complexes were selected to undergo molecular simulations of the drug-bound protein compared to the apo-protein through 100 ns, which confirmed the consistency of binding to the key amino acid residues in the four enzyme pockets with the least propensity of unfolding. Detailed analysis is given of the different polar and hydrophobic binding interactions of docked compounds. While maltase-adzukisaponin VI complex scored the lowest MMGBSA free energy of -67.77 Kcal/mol, α-amylase complex with angulasaponin B revealed the free binding energy of -74.18 Kcal/mol with a dominance of van der Waals energy (ΔEVDW) and the least change from the start to the end of the simulation time. This study will direct researchers to the significance of isolating the pure adzuki saponin components to conduct future in vitro and in vivo experimental works and even clinical trials.

Chromosome-level reference genome and resequencing of 322 accessions reveal evolution, genomic imprint and key agronomic traits in adzuki bean

Adzuki bean (Vigna angularis) is an important legume crop cultivated in over 30 countries worldwide. We developed a high-quality chromosome-level reference genome of adzuki bean cultivar Jingnong6 by combining PacBio Sequel long-read sequencing with short-read and Hi-C technologies. The assembled genome covers 97.8% of the adzuki bean genome with a contig N50 of approximately 16 Mb and a total of 32 738 protein-coding genes. We also generated a comprehensive genome variation map of adzuki bean by whole-genome resequencing (WGRS) of 322 diverse adzuki beans accessions including both wild and cultivated. Furthermore, we have conducted comparative genomics and a genome-wide association study (GWAS) on key agricultural traits to investigate the evolution and domestication. GWAS identified several candidate genes, including VaCycA3;1, VaHB15, VaANR1 and VaBm, that exhibited significant associations with domestication traits. Furthermore, we conducted functional analyses on the roles of VaANR1 and VaBm in regulating seed coat colour. We provided evidence for the highest genetic diversity of wild adzuki (Vigna angularis var. nipponensis) in China with the presence of the most original wild adzuki bean, and the occurrence of domestication process facilitating transition from wild to cultigen. The present study elucidates the genetic basis of adzuki bean domestication traits and provides crucial genomic resources to support future breeding efforts in adzuki bean.

The Potential of the Adzuki Bean (Vigna angularis) and Its Bioactive Compounds in Managing Type 2 Diabetes and Glucose Metabolism: A Narrative Review

Type 2 diabetes (T2D) is a common noncommunicable disease. In the United States alone, 37 million Americans had diabetes in 2017. The adzuki bean (Vigna angularis), a legume, has been reported to possess antidiabetic benefits. However, the extent and specific mechanisms through which adzuki bean consumption may contribute to T2D prevention and management remain unclear. Therefore, the aim of this narrative review is to analyze current evidence supporting the utilization of adzuki beans in the diet as a strategy for preventing and managing T2D. Animal studies have demonstrated a positive impact of adzuki beans on managing T2D. However, supporting data from humans are limited. Conversely, the potential of adzuki bean consumption in preventing T2D via modulating two T2D risk factors (obesity and dyslipidemia) also lacks conclusive evidence. Animal studies have suggested an inconsistent and even contradictory relationship between adzuki bean consumption and the management of obesity and dyslipidemia, in which both positive and negative relationships are reported. In sum, based on the existing scientific literature, this review found that the effects of adzuki bean consumption on preventing and managing T2D in humans remain undetermined. Consequently, human randomized controlled trials are needed to elucidate the potential benefits of the adzuki bean and its bioactive components in the prevention and management of T2D.

Adzuki Bean MY59 Extract Reduces Insulin Resistance and Hepatic Steatosis in High-Fat-Fed Mice via the Downregulation of Lipocalin-2

Adzuki bean is well known as a potential functional food that improves metabolic complications from obesity and diabetes. Lipocalin-2 (LCN2) has been implicated to have an important role in obesity and diabetes. However, the protective roles of adzuki bean MY59 extract (ABE) on insulin resistance and hepatic steatosis are not fully understood. In the present study, we investigated the effects of ABE on LCN2 expression in high-fat diet (HFD)-fed mice. ABE reduced HFD-induced fat mass and improved insulin resistance. In addition to hepatic steatosis, HFD-fed mice showed many apoptotic cells and neutrophils in the epididymal fat pads. However, these findings were significantly reduced by ABE supplementation. In particular, we found that increased LCN2 proteins from serum, epididymal fat pads, and liver in HFD-fed mice are significantly reduced by ABE. Furthermore, ABE reduced increased heme oxygenase-1 and superoxide dismutase-1 expressions in adipose tissue and liver in HFD-fed mice. We found that hepatic nuclear factor-kappa B (NF-κB) p65 expression in HFD-fed mice was also reduced by ABE. Thus, these findings indicate that ABE feeding could improve insulin resistance and hepatic steatosis by decreasing LCN2-mediated inflammation and oxidative stress in HFD-fed mice.

VaSDC1 Is Involved in Modulation of Flavonoid Metabolic Pathways in Black and Red Seed Coats in Adzuki Bean (Vigna angularis L.)

Seed coat colour is an important nutritional quality trait. Variations in anthocyanins and flavonoids induce the diversity of seed coat colour in adzuki bean (Vigna angularis L.). Red seed coat and black seed coat are important adzuki bean cultivars. Insights into the differences of flavonoid metabolic pathways between black and red adzuki bean are significant. In this study, we explored that the difference in seed coat colour between the red (Jingnong6) and the black (AG118) is caused by the accumulation of anthocyanins. The RNA-sequencing (RNA-Seq) and real-time reverse transcription (qRT)-PCR results showed that the Vigna angularis L. seed coat color (VaSDC1) gene, an R2R3-MYB transcription factor, should be the key gene to regulate the black and red seed coat colours. In three different colouring staes of seed development, VaSDC1 was specifically expressed in the black seed coat (AG118) landrace, which activates the structural genes of flavonoid metabolic pathways. As a result, this caused a substantial accumulation of anthocyanins and created a dark blue-black colour. In the red (Jingnong6) seed coat variety, low expression levels of VaSDC1 resulted in a lower accumulation of anthocyanins than in AG118. In addition, VaSDC1 was genetically mapped in the interval between simple-sequence repeat (SSR) markers Sca326-12, Sca326-4, and BAgs007 on chromosome 3 using an F₄ segregating population derived from the cross between Jingnong6 and AG118. These results will facilitate the improvement of nutritional quality breeding in adzuki beans.

Alpha-amylase as molecular target for treatment of diabetes mellitus: A comprehensive review

The alpha (α)-amylase is a calcium metalloenzyme that aids digestion by breaking down polysaccharide molecules into smaller ones such as glucose and maltose. In addition, the enzyme causes postprandial hyperglycaemia and blood glucose levels to rise. α-Amylase is a well-known therapeutic target for the treatment and maintenance of postprandial blood glucose elevations. Various enzymatic inhibitors, such as acarbose, miglitol and voglibose, have been found to be effective in targeting this enzyme, prompting researchers to express an interest in developing potent alpha-amylase inhibitor molecules. The review mainly focused on designing different derivatives of drug molecules such as benzofuran hydrazone, indole hydrazone, spiroindolone, benzotriazoles, 1,3-diaryl-3-(arylamino) propan-1-one, oxadiazole and flavonoids along with their target-receptor interactions, IC₅₀ values and other biological activities.

Protective effects of medicinal plant against diabetes induced cardiac disorder: A review

ETHNOPHARMACOLOGY RELEVANCE

Nowadays, there is an increase in global tendency to use medicinal plants as preventive and therapeutic agents to manage diabetes and its long-term complications such as cardiovascular disorders owing to their availability and valuable traditional background.

AIM OF STUDY

This review aims to introduce common medicinal plants, which have been demonstrated to have cardioprotective effects on diabetes and their mechanisms of action.

MATERIALS AND METHODS

Online literature databases, including Web of Sciences, PubMed, Science Direct, Scopus and Google Scholar were searched without date limitation by May 2020. The following keywords (natural products or medicinal plants or herbal medicine or herb or extract) and (diabetes or antidiabetic or hyperglycemic) and (cardiomyopathy or heart or cardioprotective or cardiac or cardio) were used, and after excluding non-relevant articles, 81 original English articles were selected.

RESULTS

The surveyed medicinal plants induced cardioprotective effects mostly through increasing antioxidant effects leading to attenuating ROS production as well as by inhibiting inflammatory signaling pathways and related cytokines. Moreover, they ameliorated the Na+/K + ATPase pump, the L-type Ca₂⁺ channel current, and the intracellular ATP. They also reduced cardiac remodeling and myocardial cell apoptosis through degradation of caspase-3, Bax, P53 protein, enhancement of Bcl-2 protein expression as well as downregulation of TGFβ1 and TNFα expression. In addition, the extracts improved cardiac function through increasing EF% and FS% as well as restoring hemodynamic parameters.

CONCLUSIONS

The reviewed medicinal plants demonstrated cardioprotective manifestations in diabetes through intervention with mechanisms involved in the diabetic heart to restore cardiovascular complications.

Isolation and Characterization of Antihyperglycemic Compounds from Vigna angularis Extracts

Functional foods that inhibit α-amylase and α-glucosidase activity are effective for regulating the blood glucose level and preventing hyperglycemia. Extracts of adzuki beans (ABs, Vigna angularis), widely eaten in East Asia, can inhibit α-amylase and α-glucosidase activity. In this study, we identified and evaluated the components in an AB water extract (ABWE) after boiling, which is an essential process for cooking ABs. The ABWE before boiling inhibited α-amylase and α-glucosidase activity and the boiled ABWE showed slightly stronger inhibitory effects. High-performance liquid chromatography, liquid chromatography-mass spectrometry, and nuclear magnetic resonance analyses identified (+)-catechin 7-O-β-d-glucopyranoside (C7G), (+)-epicatechin 7-O-β-d-glucopyranoside (E7G), and (+)-catechin as the bioactive components in boiled ABWE. Interestingly, the quantity of E7G significantly increased after boiling (from 0% to 17.1 ± 1.3%). E7G showed stronger inhibition of α-amylase and α-glucosidase than C7G; the IC₅₀ values for α-amylase were 0.74 ± 0.04 mg/mL (C7G) and 0.40 ± 0.09 mg/mL (E7G), and for α-glucosidase the IC₅₀ values were 0.085 ± 0.032 mg/mL (C7G) and 0.051 ± 0.007 mg/mL (E7G). Our findings suggest that C7G and E7G are the main active components in ABWE as they inhibit α-amylase and α-glucosidase and their inhibitory effect is not lost after boiling. These results support the effectiveness of boiled ABs in the promotion of health. PRACTICAL APPLICATION: We identified (+)-catechin 7-O-β-d-glucopyranoside (C7G), (+)-epicatechin 7-O-β-d-glucopyranoside (E7G), and (+)-catechin in adzuki bean extracts and commercially available boiled adzuki bean products. Interestingly, the E7G content was increased by boiling, and this compound showed strong inhibitory activity toward α-amylase and α-glucosidase. These results support the consumption of boiled adzuki beans to prevent acute rises in blood glucose level.

Quality Characteristics and Antioxidant Activities of Rice/Adzuki Bean Mixtures Cooked Using Two Different Methods

This study explored the optimal preparation and the antioxidant levels of rice/adzuki bean mixtures. We compared the quality and physicochemical characteristics of cooked mixtures of rice and adzuki beans prepared using normal and high-pressure rice cookers, with and without the addition of alcohol (15%, v/v). The water-binding capacity and swelling power decreased upon addition of adzuki beans, but water solubility increased. The peak, trough, final, and setback viscosities decreased, but the breakdown viscosity increased. The total polyphenol and flavonoid contents increased after addition of adzuki beans. Total polyphenol contents in cooked rice/20% (w/w) Arari and Geomguseul bean mixtures in a normal cooker with addition of alcohol were 3.00 and 3.09 times higher than plain rice. The flavonoid contents were 10.33 and 8.90 times higher than plain rice. The predominant phenolic acids in cooked rice/Arari bean mixtures were p-coumaric acid and trans-3-hydroxycinnamic acid, and in cooked rice/Geomguseul bean mixtures, they were syringic acid and trans-3-hydroxycinnamic acid. Overall, phenolic acid levels were higher in mixtures cooked in plain water. The DPPH- and ABTS-radical-scavenging activities increased upon addition of adzuki beans. DPPH radical-scavenging activities in cooked rice/20% (w/w) Arari and Geomguseul bean mixtures in a normal cooker with addition of alcohol were 9.09 and 9.22 times higher than plain rice. ABTS radical-scavenging activities were 8.74 and 9.01 times higher than plain rice. Moreover, rice/adzuki bean mixtures prepared in a normal cooker, with addition of alcohol, exhibited higher antioxidant levels than other samples. We present the antioxidative properties of rice/adzuki bean mixtures prepared in different ways; these data will aid manufacturers.

Antidiabetic Effects of Vigna nakashimae Extract in Humans: A Preliminary Study

BACKGROUND

Vigna nakashimae (VN) extract has been shown to have antidiabetic and antiobesity effects in various animal studies; however, to our knowledge, no data on such effects exist in humans.

METHODS

We performed a randomized placebo-controlled study to investigate the antidiabetic effects of VN extract treatment for 12 weeks in humans. A total of 18 Korean patients with type 2 diabetes were enrolled in this study and were allocated randomly to either the VN extract group (1 g thrice daily) or control group (placebo tablets) for 12 weeks. We investigated blood glucose levels, body weight, lipid profiles, and adverse events after 12 weeks of treatment. Fifteen subjects were included in the final analysis.

RESULTS

There was no difference in age, sex, fasting glucose levels, or lipid profiles between the VN extract and control groups at baseline. However, the baseline glycosylated hemoglobin (HbA_1c) levels of the control group were lower than those of the VN extract group. After treatment with VN extract for 12 weeks, the body weight and lipid profile of the VN extract group remained unchanged; however, the HbA_1C levels decreased by 0.36% ± 0.33% (p = 0.027). In contrast, the HbA_1C levels of the control group did not change after 12 weeks (p = 0.228). During the 12-week treatment with VN extract, no serious adverse events were reported.

CONCLUSION

Our data indicate that VN extract has implications for glucose lowering in type 2 diabetic patients.

Saponins and Flavonoids from Adzuki Bean (Vigna angularis L.) Ameliorate High-Fat Diet-Induced Obesity in ICR Mice

Background and purpose: As an herbal medicine, adzuki bean has been practiced since the Tang Dynasty of China to maintain health and control weight; this practice is still very popular in China nowadays. However, it is still lack of sufficient scientific basis to explain scientific principle of this popular civil practice in weight control using adzuki bean. The purpose of this study was to verify and explain the anti-obesity effects of adzuki bean through in vitro enzymatic assays, in vitro lipolysis and in vivo study of obese mice model.

Methods: Inhibitory effects of flavonoids and saponins from adzuki bean (Vigna angularis) on pancreatic lipase, α-glucosidase activities, and noradrenaline-induced lipolysis were assessed. High-fat diet-induced obesity model was created to study anti-obesity effects of adzuki bean. Both serum and liver lipid parameters were determined after 8 weeks intervention.

Results: Adzuki bean extracts enhanced lipolysis. Compared to the final body weight of high-fat diet group, oral administration of adzuki bean significantly (p < 0.05) reduced the final body weight of mice and adipose tissue accumulation. The adzuki bean intervention also significantly reduced the levels of serum triglyceride, total cholesterol, low density lipoprotein-cholesterol, and liver lipid.

Conclusion: Adzuki bean demonstrated the anti-obesity effects on mice, such effects may mediated through the inhibitory effects of flavonoids and saponins from adzuki bean on α-glucosidase and pancreatic lipase activities, and lipolysis enhancement effect of active components from adzuki bean.

Characterization and quantification of flavonoids and saponins in adzuki bean (Vigna angularis L.) by HPLC-DAD-ESI-MSn analysis

BACKGROUND

Bioactive activities of adzuki bean have been widely reported, however, the phytochemical information of adzuki bean is incomplete. The aim of this study was to characterize and quantify flavonoids and saponins in adzuki bean. High performance liquid chromatography with diode array detection and electro spray ionization-tandem multi-stage mass spectrometry (HPLC-DAD-ESI-MSⁿ) were applied to do qualitative and quantitative analyses.

RESULTS

A total of 15 compounds from adzuki bean were identified by HPLC-DAD-ESI-MSⁿ. Among 15 compounds identified, four flavonoids (catechin, vitexin-4″-O-glucoside, quercetin-3-O-glucoside, and quercetin-3-O-rutinoside) and six saponins (azukisaponin I, II, III, IV, V, and VI) in adzuki bean were further quantified by external calibration method using HPLC-MS with the program of time segment and extract ion chromatogram (EIC) analysis.

CONCLUSIONS

Current qualitative and quantitative method based on HPLC and MS technique provides a scientific basis for in vitro and in vivo pharmacological study in the future. Graphical abstract Isolation and characterization of flavonoids and saponins from adzuki bean.

Bioactivities, isolation and purification methods of polysaccharides from natural products: A review

Polysaccharides play multiple roles and have extensive bioactivities in life process and an immense potential in healthcare, food and cosmetic industries, due to their therapeutic effects and relatively low toxicity. This review describes their major functions involved in antitumor, anti-virus, and anti-inflammatory bioactivities. Due to their enormous structural heterogeneity, the approaches for isolation and purification of polysaccharides are distinct from that of the other macromolecules such as proteins, etc. Yet, to achieve the homogeneity is the initial step for studies of polysaccharide structure, pharmacology, and its structure-activity relationships. According to the experiences accumulated by our lab and the published literatures, this review also introduces the methods widely used in isolation and purification of polysaccharides.

Targeting glucose metabolism for healthy aging

Advancing age is the greatest single risk factor for numerous chronic diseases. Thus, the ability to target the aging process can facilitate improved healthspan and potentially lifespan. Lack of adequate glucoregulatory control remains a recurrent theme accompanying aging and chronic disease, while numerous longevity interventions result in maintenance of glucoregulatory control. In this review, we propose targeting glucose metabolism to enhance regulatory control as a means to ameliorate the aging process. We highlight that calorie restriction improves glucoregulatory control and extends both lifespan and healthspan in model organisms, but we also indicate more practical interventions (i.e., calorie restriction mimetics) are desirable for clinical application in humans. Of the calorie restriction mimetics being investigated, we focus on the type 2 diabetes drug acarbose, an α-glucosidase inhibitor that when taken with a meal, results in reduced enzymatic degradation and absorption of glucose from complex carbohydrates. We discuss alternatives to acarbose that yield similar physiologic effects and describe dietary sources (e.g., sweet potatoes, legumes, and berries) of bioactive compounds with α-glucosidase inhibitory activity. We indicate future research should include exploration of how non-caloric compounds like α-glucosidase inhibitors modify macronutrient metabolism prior to disease onset, which may guide nutritional/lifestyle interventions to support health and reduce age-related disease risk.

Phytochemical distribution in hull and cotyledon of adzuki bean (Vigna angularis L.) and mung bean (Vigna radiate L.), and their contribution to antioxidant, anti-inflammatory and anti-diabetic activities

Total saponin content, total phenolics content, total flavonoids content, condensed tannin content in hull, cotyledon and whole grain of both adzuki bean and mung bean were determined by colorimetric methods. Vitexin and isovitexin contents in mung bean were determined by HPLC. Antioxidant effects were evaluated with DPPH scavenging activity and ferric reducing antioxidant power assay. In vitro anti-inflammatory and anti-diabetic effects of beans were evaluated by protease and aldose reductase inhibitory assays, respectively. The results indicated that the bean hulls were the most abundant in phytochemicals and largely contributed antioxidant activities, anti-inflammatory effects and anti-diabetic effects of whole grains. The result showed that mung bean hull was the most abundant with vitexin at 37.43 mg/g and isovitexin at 47.18 mg/g, respectively. Most of the phytochemicals and bioactivities were most predominantly contributed by the bean hulls with exception for condensed tannin of mung bean; which was more abundant in the cotyledon than its hull.

α-Glucosidase inhibitory activity of protein-rich extracts from extruded adzuki bean in diabetic KK-Ay mice

An extrusion process has been widely used for the development of many functional foods. The aim of this study was to assess the effect of the extrusion process on the α-glucosidase inhibitory properties of adzuki bean protein in type 2 diabetes model KK-A(y) mice. The extruded adzuki bean protein (EA) was prepared by adding 1% and 2% into the diet for 42 days. It was found that the fasting blood glucose concentration was significantly decreased with the EA-2 group compared with the control diabetic mice group. In addition, there was a significant decrease in serum triglyceride, blood urea nitrogen levels and increased high density lipoprotein (HDL)-cholesterol. Meanwhile, hepatic lipids were improved and the content of α-dicarbonyl compounds in the kidney were reduced in mice fed with EA. These results suggest that the intake of EA could moderate type 2 diabetes and diabetic complications.

Constituents of Vigna angularis and their in vitro anti-inflammatory activity

Nine non-phenolic compounds, including four furanylmethyl glycosides, angularides A-D, one ent-kaurane diterpene glycoside, angularin A, and four triterpenoid saponins, angulasaponins A-D, were isolated from seeds of Vigna angularis, together with eight known compounds. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic analysis as well as chemical methods. Angularin A, angulasaponins A-C, and azukisaponins III and VI showed inhibition of nitric oxide production in LPS-activated RAW264.7 macrophages, with IC50 values ranging from 13μM to 24μM.

Antidiabetic potential of commonly consumed legumes: a review

Over the last few decades, lifestyle changes have resulted in a drastic increase in the incidence of diabetes all over the world, especially in the developing countries. Oral hypoglycemic agents and insulin form the mainstay in controlling diabetes, but they have prominent side effects and fail to significantly alter the course of diabetic complications. Appropriate diet and exercise programs that form a part of lifestyle modifications have proven to be greatly effective in the management of this disease. Dietary therapy is showing a bright future in the prevention and treatment of diabetes. Legumes, owing to their high nutritive value, are increasingly being used in dietetic formulations in the treatment and prevention of diabetes on account of their antidiabetic potential. Given this background, this paper reviews the glucose- and lipid-lowering action possessed by various commonly consumed legumes through several animal and human studies. It is concluded that the various legumes not only have varying degrees of antidiabetic potential but are also beneficial in decreasing the risk factors for cardiovascular and renal disease.

Inhibition of Increases in Blood Glucose and Serum Neutral Fat byMomordica charantiaSaponin Fraction

Focusing on a functional component of Momordica charantia, saponin, we investigated its effects on serum glucose and neutral fat levels. Saponin was extracted as a butanol-soluble fraction (saponin fraction) from hot blast-dried Momordica charantia powder. The disaccharidase-inhibitory activity and the pancreatic lipase-inhibitory activity of the saponin fraction were measured, and in vivo sugar- and lipid-loading tests were performed. The saponin fraction inhibited disaccharidase activity and elevation of the blood glucose level after sucrose loading. The fraction also markedly inhibited pancreatic lipase activity and elevation of the serum neutral fat level after corn oil loading. Based on these findings, the main active component related to the anti-diabetic effect of Momordica charantia is present in the butanol fraction, and it may be saponin. The blood glucose and serum neutral fat-lowering effects of Momordica charantia were closely associated with its inhibitory activity against disaccharidase and pancreatic lipase.

Regulation of the differentiation of osteoblasts and osteoclasts by a hot-water extract of adzuki beans (Vigna angularis)

Osteoporosis is a global public health problem thought to be caused by an imbalance in bone metabolism. We examined in this study the 40% ethanol fraction of HP-20 resin in combination with a hot-water adzuki extract (EtEx.40) for its effect on osteoblast and osteoclast differentiation. EtEx.40-treated murine preosteoblast MC3T3-E1 cells exhibited significantly elevated alkaline phosphatase activity and mineralization. EtEx.40 facilitated osteoblast differentiation by up-regulating such osteoblast differentiation-related molecules as runt-related transcription factor 2, distal-less homeobox 5, and osterix via p38 mitogen-activated protein kinase. EtEx.40 also suppressed the formation of large tartrate-resistant acid phosphatase-positive multinucleated cells in RAW264.7 cells that had been stimulated with the receptor activator of the nuclear factor κB ligand/macrophage colony-stimulating factor. EtEx.40 significantly inhibited NF-κB activation, thus reducing the expression of such downstream molecules as c-Fos and NFATc1. Our findings suggest that EtEx.40 could be used to maintain bone mass.

The active role of leguminous plant components in type 2 diabetes

Diabetes appears to be one of the most frequent noncommunicable diseases in the world. A permanent growth in the incidence of diabetes can be observed and according to the International Diabetes Federation (IDF) the year 2030 will mark the increase in the number of diabetics to 439 mln worldwide. Type 2 diabetes accounts for about 90% of all diabetes incidence. Nutrition model modification not only features the basic element in type 2 diabetes treatment but also constitutes the fundamental factor influencing a morbidity rate decrease. Leguminous plants are a key factor in the diabetic diet; plants such as pulses or soybeans are nutritious products valued highly in nutrition. These legumes are high in the content of wholesome protein and contain large amounts of soluble alimentary fiber fractions, polyunsaturated fatty acids, vitamins and minerals, and bioactive substances with antioxidant, anti-inflammatory, and anticancer activity. They are distinguished by the high amount of bioactive compounds that may interfere with the metabolism of glucose. The most significant bioactive compounds displaying antidiabetic activity in leguminous plants are as follows: genistein and daidzein, alpha-amylase inhibitors, and alpha-glucosidase inhibitors. In vitro research using leguminous plant extracts has confirmed their antidiabetic properties. Leguminous plants should be employed in the promotion of healthy lifestyles in terms of functional food.

Oleanolic acid acetate inhibits osteoclast differentiation by downregulating PLCγ2-Ca(2+)-NFATc1 signaling, and suppresses bone loss in mice

Owing to their potential pharmacological activities in human disease, natural plant-derived compounds have recently become the focus of increased research interest. In this study, we first isolated oleanolic acid acetate (OAA), a triterpenoid compound, from Vigna angularis (azuki bean) to discover anti-bone resorptive agents. Many studies have identified and described the various medicinal effects of V. angularis extract. However, the pharmacological effect of OAA-derived V. angularis extract, particularly the effect on osteoclastogenesis, is not known. Therefore, we investigated the effect and mechanism of OAA in receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. OAA inhibited RANKL-induced osteoclast differentiation in bone marrow macrophages (BMMs) without any evidence of cytotoxicity. Interestingly, OAA significantly inhibited Btk phosphorylation, phospholipase Cγ2 (PLCγ2) phosphorylation, calcium ion (Ca(2+)) oscillation, and nuclear factor of activated T cell c1 (NFATc1) expression in RANKL-stimulated BMMs, but did not affect RANKL-induced mitogen-activated protein kinase. OAA also inhibited the bone-resorbing activity of mature osteoclasts. Furthermore, mice treated with OAA demonstrated marked attenuation of lipopolysaccharide-induced bone erosion based on micro-computed tomography and histologic analysis of femurs. Taken together, the results suggested that OAA inhibited RANKL-mediated osteoclastogenesis via PLCγ2-Ca(2+)-NFATc1 signaling in vitro and suppressed inflammatory bone loss in vivo.

Constituents from Vigna vexillata and their anti-inflammatory activity

The seeds of Vigna genus are important food resources and there have already been many reports regarding their bioactivities. In our preliminary bioassay, the chloroform layer of methanol extracts of V. vexillata demonstrated significant anti-inflammatory bioactivity. Therefore, the present research is aimed to purify and identify the anti-inflammatory principles of V. vexillata. One new sterol (1) and two new isoflavones (2,3) were reported from the natural sources for the first time and their chemical structures were determined by the spectroscopic and mass spectrometric analyses. In addition, 37 known compounds were identified by comparison of their physical and spectroscopic data with those reported in the literature. Among the isolates, daidzein (23), abscisic acid (25), and quercetin (40) displayed the most significant inhibition of superoxide anion generation and elastase release.

Anti-diabetic effects of lactic acid bacteria in normal and type 2 diabetic mice

The antidiabetic effects of lactic acid bacteria were investigated using mice. In Experiment 1, normal ICR mice were loaded with sucrose or starch with or without viable Lactobacillus rhamnosus GG cells. GG significantly inhibited postprandial blood glucose levels when administered with sucrose or starch. In Experiment 2, KK-A^y mice, a model of genetic type 2 diabetes, were given a basal diet containing viable GG cells or viable Lactobacillus delbrueckii subsp. bulgaricus cells for 6 weeks. Viable GG cells significantly inhibited fasting blood glucose, postprandial blood glucose in a glucose tolerance test and HbA1c. Such effects were not shown by viable L. bulgaricus cells. In Experiment 3, the KK-A^y mice were given a basal diet containing viable GG cells or heat-treated GG cells for 3 weeks. The viable GG cells significantly suppressed fasting blood glucose and impaired glucose tolerance, but the heat-treated GG showed no effects. These results demonstrated that GG decreased the postprandial blood glucose in ICR mice, and that the antidiabetic activity of lactic acid bacteria on the KK-A^y mice differed depending on the bacterial strain and whether the bacterium is viable when it arrives in the intestine. In the present study, we conclude that the antidiabetic activity may result from continuous inhibition of the postprandial blood glucose through suppression of glucose absorption from the intestine. These findings indicate that specific strains of lactic acid bacterium can be expected to be beneficial for the management of type 2 diabetes.

Major phenolic compounds, antioxidant capacity and antidiabetic potential of rice bean (Vigna umbellata L.) in China

Interest in edible beans as nutraceuticals is increasing. In the present study, the individual phenolic acids, the total phenolic content (TPC), the total flavonoid content (TFC), and the antioxidant and antidiabetic potential of 13 varieties of rice beans from China were investigated. Eight phenolic compounds (catechin, epicatechin, p-coumaric acid, ferulic acid, vitexin, isovitexin, sinapic acid, quercetin) were analyzed on an ultra-performance liquid chromatography (UPLC) mass spectrometry (MS) system. The rice bean varieties had significant differences in total phenolic compounds (ranging from 123.09 ± 10.35 to 843.75 ± 30.15 μg/g), in TPC (ranging from 3.27 ± 0.04 to 6.43 ± 0.25 mg gallic acid equivalents (GAE)/g), in TFC (ranging from 55.95 ± 11.16 to 320.39 ± 31.77 mg catechin (CE)/g), in antioxidant activity (ranging from 39.87 ± 1.37 to 46.40 ± 2.18 μM·TE/g), in α-glucosidase inhibition activity (ranging from 44.32 ± 2.12 to 68.71 ± 2.19) and in advanced glycation end products formation inhibition activity (ranging from 34.11 ± 0.59 to 75.75 ± 0.33). This study is the first report on phytochemistry and biological activities in rice beans.

Antidiabetic effects of natural plant extracts via inhibition of carbohydrate hydrolysis enzymes with emphasis on pancreatic alpha amylase

INTRODUCTION

The increasing prevalence of type 2 diabetes mellitus and the negative clinical outcomes observed with the commercially available anti-diabetic drugs have led to the investigation of new therapeutic approaches focused on controlling postprandrial glucose levels. The use of carbohydrate digestive enzyme inhibitors from natural resources could be a possible strategy to block dietary carbohydrate absorption with less adverse effects than synthetic drugs.

AREAS COVERED

This review covers the latest evidence regarding in vitro and in vivo studies in relation to pancreatic alpha-amylase inhibitors of plant origin, and presents bioactive compounds of phenolic nature that exhibit anti-amylase activity.

EXPERT OPINION

Pancreatic alpha-amylase inhibitors from traditional plant extracts are a promising tool for diabetes treatment. Many studies have confirmed the alpha-amylase inhibitory activity of plants and their bioactive compounds in vitro, but few studies corroborate these findings in rodents and very few in humans. Thus, despite some encouraging results, more research is required for developing a valuable anti-diabetic therapy using pancreatic alpha-amylase inhibitors of plant origin.

Biological potential of sixteen legumes in China

Phenolic acids have been identified in a variety of legumes including lima bean, broad bean, common bean, pea, jack bean, goa bean, adzuki bean, hyacinth bean, chicking vetch, garbanzo bean, dral, cow bean, rice bean, mung bean and soybean. The present study was carried out with the following aims: (1) to identify and quantify the individual phenolic acid and determine the total phenolic content (TPC); (2) to assess their antioxidant activity, inhibition activities of α-glucosidase, tyrosinase, and formation of advanced glycation endproducts; and (3) to investigate correlations among the phytochemicals and biological activity. Common bean possesses the highest antioxidant activity and advanced glycation endproducts formation inhibition activity. Adzuki bean has the highest α-glucosidase inhibition activity, and mung bean has the highest tyrosinase inhibition activity. There are significant differences in phytochemical content and functional activities among the bean species investigated. Selecting beans can help treat diseases such as dermatological hyperpigmentation illness, type 2 diabetes and associated cardiovascular diseases.

A determination of potential α-glucosidase inhibitors from Azuki Beans (Vigna angularis)

A 70% ethanol extract from azuki beans (Vigna angularis) was extracted further with CH₂Cl₂, EtOAc and n-BuOH to afford four fractions: CH₂Cl₂-soluble, EtOAc-soluble, n-BuOH-soluble and residual extract fractions. The EtOAc-soluble fractions showed the highest α-glucosidase inhibitory activity. Two pure flavonoid compounds, vitexin and isovitexin, were isolated (using the enzyme assay-guide fractionation method) from the EtOAc-soluble fractions. We further evaluated the interaction between the flavonoid compounds and α-glucosidase by fluorescence spectroscopy. Vitexin and isovitexin showed high inhibitory activities, with IC₅₀ values of 0.4 mg·mL⁻¹ and 4.8 mg·mL⁻¹, respectively. This is the first study of the active compositions of azuki beans against α-glucosidase.

Influence of altitudinal variation on the antioxidant and antidiabetic potential of azuki bean (Vigna angularis)

The individual phenolic acids, total phenolic content, total flavonoid content and antioxidant activity of azuki bean (Vigna angularis) varieties from 13 provinces of China were investigated. Eight phenolic compounds were analysed on an ultra-performance liquid chromatography-mass spectrometry system. The results obtained suggest that the azuki beans can be considered as a good source of phenolic compounds, and growing the azuki beans at high altitude may be an effective way to enhance the antioxidant and antidiabetic potential of the beans.

Insights into modeling streptozotocin-induced diabetes in ICR mice

Streptozotocin (STZ)-induced diabetes in ICR mice is often used to model diabetes mellitus and its complications, as well as other pathologies. In studies of diabetes progression and effects of newly developed treatments, experimental results may be difficult to interpret because blood glucose levels (BGLs) of untreated diabetic control animals tend to decline substantially during typical experimental time spans of 8-11 h. To address this problem, the authors examined several experimental conditions that might affect BGL stability, including STZ dose, initial mouse weight, fasting regimen and light:dark cycle. The authors found that diabetes severity was dependent on initial mouse weight and that weight loss after diabetes induction was less severe in heavier mice. Furthermore, a dose of 150 mg STZ per kg body weight was sufficient to induce stabilized acute diabetes without causing many complications. Finally, BGL could be stabilized in diabetic mice that were not treated with insulin by avoiding pre-fasting before an 8-h experiment and by allowing mice limited access to food during the experiment.

Hypoglycemic effect of hot-water extract of adzuki (Vigna angularis) in spontaneously diabetic KK-A(y) mice

OBJECTIVE

Recently, we reported that 40% ethanol fraction of hot-water extracts of adzuki (Vigna angularis; EtEx.40) suppressed the postprandial blood glucose level and serum insulin level in normal mice and streptozotocin-induced type 1 diabetic rats. The present study examined the hypoglycemic effect of EtEx.40 on blood glucose, insulin concentrations, organ weight, serum composition, and hepatic lipid content in spontaneously diabetic KK-A(y)/Ta Jcl mice, a model for type 2 diabetes.

METHODS

To investigate the prevention of type 2 diabetes by EtEx.40 ingestion, 4-wk-old non-diabetic KK-A(y) mice were fed an AIN-76 diet containing 5000 mg of EtEx.40/kg of body weight per day (EtEx.40) or an AIN-76 diet without EtEx.40 for 8 wk. Furthermore, to investigate the improvement of type 2 diabetes, 7-wk-old diabetic KK-A(y) mice were fed EtEx.40 for 4 wk.

RESULTS

Compared with the control group, EtEx.40 supplementation had a significant effect in lowering blood glucose levels, water intake, serum insulin levels, urinary glucose, urinary microalbumin/creatinine ratio, liver triacylglycerol, and total cholesterol levels. Similar results were observed in 7-wk-old diabetic KK-A(y) mice fed EtEx.40 for 4 wk. These effects were also found after short-term administration of EtEx40. Overall, EtEx.40 improved several diabetic symptoms in KK-A(y) mice.

CONCLUSION

EtEx.40 obtained from hot-water adzuki extracts showed preventive and ameliorative effects on the progression of diabetes in genetically diabetic KK-A(y) mice. In the present study, we conclude that the preventive and ameliorative effects by EtEx.40 were due to the modulation of blood glucose levels and the protective effect against oxidative damage in diabetes mellitus.

Extracts of Momordica charantia suppress postprandial hyperglycemia in rats

Momordica charantia (bitter melon) is commonly known as vegetable insulin, but the mechanisms underlying its hypoglycemic effect remain unclear. To address this issue, the effects of bitter melon extracts on postprandial glycemic responses have been investigated in rats. An aqueous extract (AE), methanol fraction (MF) and methanol insoluble fraction (MIF) were prepared from bitter melon. An oral sucrose tolerance test revealed that administration of AE, MF or MIF each significantly suppressed plasma glucose levels at 30 min as compared with the control. In addition, the plasma insulin level at 30 min was also significantly lower after MF administration than in the control in the oral sucrose tolerance test. By contrast, these effects of bitter melon extracts were not observed in the oral glucose tolerance test. In terms of mechanism, bitter melon extracts dose-dependently inhibited the sucrase activity of intestinal mucosa with IC(50) values of 8.3, 3.7 and 12.0 mg/mL for AE, MF and MIF, respectively. The fraction with a molecular weight of less than 1,300 (LT 1,300) obtained from MF inhibited the sucrase activity most strongly in an uncompetitive manner with an IC(50) value of 2.6 mg/mL. Taken together, these results demonstrated that bitter melon suppressed postprandial hyperglycemia by inhibition of alpha-glucosidase activity and that the most beneficial component is present in the LT 1,300 fraction obtained from MF.

The nutraceutical role of thePhaseolus vulgarisα-amylase inhibitor

The present review assesses the potential of thePhaseolus vulgarisα-amylase inhibitor isoform 1 (α-AI1) starch blockers as a widely used remedy against obesity and diabetes. Consumption of the α-amylase inhibitor causes marginal intraluminal α-amylase activity facilitated by the inhibitor's appropriate structural, physico-chemical and functional properties. As a result there is decreased postprandial plasma hyperglycaemia and insulin levels, increased resistance of starch to digestion and increased activity of colorectal bacteria. The efficacy and safety of the amylase inhibitor extracts, however, depend on the processing and extraction techniques used. The extracts are potential ingredients in foods for increased carbohydrate tolerance in diabetics, decreased energy intake for reducing obesity and for increased resistant starch. Research developments in the distribution and biosynthesis of the α-amylase inhibitor, relevant physico-chemical properties, the molecular starch-blocking mechanism, anti-obesity and anti-diabetes effects, safety of extracts and the need for research into their potential anti-colorectal cancer effect are discussed.