Black Adzuki Bean (Vigna angularis) Extract Protects Pancreatic β Cells and Improves Glucose Tolerance in C57BL/6J Mice Fed a High-Fat Diet

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.

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.

Blended extract of oat, sorghum, adzuki bean, finger millet, and proso millet improved hyperglycemia and insulin resistance in the streptozotocin-nicotinamide-induced diabetic rats

Grains contain bioactive components that potentially have protective effects on chronic diseases such as diabetes. The anti-diabetic effects of blended grain ethanol extract (BGE) were evaluated in streptozotocin-nicotinamide (STZ-NA)-induced diabetic rats. BGE was prepared by mixing oat, sorghum, adzuki bean, finger millet, and proso millet (30:30:15:15:10). The rats were assigned into four groups, normal control, diabetic model control (DM), STZ-NA rats administered 200 mg/kg body weight (bw) of metformin, and STZ-NA rats administered 500 mg/kg bw of BGE (BGE). After 6 weeks of administration, the homeostatic model assessment of insulin resistance (12%) in BGE decreased compared to DM. Strikingly, the fasting blood glucose (23%) and oral glucose tolerance test (15%) were improved in BGE compared to DM. BGE also increased insulin immunoreactivities in pancreatic β-cells. In sum, BGE exhibits anti-hyperglycemic effects by improving fasting glucose levels and insulin secretion from pancreatic β-cells in the STZ-NA-induced diabetic rats.

Nutritional Composition, Efficacy, and Processing of Vigna angularis (Adzuki Bean) for the Human Diet: An Overview

Adzuki beans are grown in several countries around the world and are widely popular in Asia, where they are often prepared in various food forms. Adzuki beans are rich in starch, and their proteins contain a balanced variety of amino acids with high lysine content, making up for the lack of protein content of cereals in the daily diet. Therefore, the research on adzuki beans and the development of their products have broad prospects for development. The starch, protein, fat, polysaccharide, and polyphenol contents and compositions of adzuki beans vary greatly among different varieties. The processing characteristic components of adzuki beans, such as starch, isolated protein, and heated flavor, are reported with a view to further promote the processing and development of adzuki bean foods. In addition to favorable edibility, the human health benefits of adzuki beans include antioxidant, antibacterial, and anti-inflammatory properties. Furtherly, adzuki beans and extracts have positive effects on the prevention and treatment of diseases, including diabetes, diabetes-induced kidney disease or kidney damage, obesity, and high-fat-induced cognitive decline. This also makes a case for the dual use of adzuki beans for food and medicine and contributes to the promotion of adzuki beans as a healthy, edible legume.

Comparison of the Effects of a Bean-Based and a White Rice-Based Breakfast Diet on Postprandial Glucose and Insulin Levels in Chinese Patients with Type 2 Diabetes

BACKGROUND This study compared the effects of a bean-based and a white rice-based breakfast diet on postprandial glucose and insulin levels in Chinese patients with type 2 diabetes mellitus (T2DM). MATERIAL AND METHODS We recruited 63 patients with T2DM. The patients participated in the randomized 2×2 crossover trial. The bean-based diet group and white rice control group were matched for 50 g of available carbohydrate at breakfast. The patients followed the diets for 3 days. Vein blood samples were collected at 0, 30, 60, 120, and 180 min after eating. Data were analyzed using a repeated-measures analysis of variance. The results are expressed as the mean±standard error of mean (SEM) or as the median with interquartile range values. RESULTS Compared with the white rice control, postprandial glucose was significantly lower with the bean-based diet treatments at 60 min (P=0.004), 120 min (P=0.000), and 180 min (P=0.000). The insulin levels of the bean-based diet group were significantly higher at 60 min (P=0.013). The C-peptide levels of the bean-based diet group were significantly higher at 30 min (P=0.042) and 60 min (P=0.005) postprandial. The glucose area under the curve (AUC) showed a similar trend (P=0.000). There were no statistically significant differences in the AUC of insulin and C-peptide, except C-peptide AUC at 0 to 60 min (P=0.027). CONCLUSIONS Compared with a white rice-based breakfast, a bean-based diet significantly reduced postprandial glucose levels and promoted insulin secretion. These results support a dietary approach to reduce postprandial hyperglycemia.

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.