The α-amylase and α-glucosidase inhibitory effects of Irish seaweed extracts

To date, numerous studies have reported on the antidiabetic properties of various plant extracts through inhibition of carbohydrate-hydrolysing enzymes. The objective of this research was to evaluate extracts of seaweeds for α-amylase and α-glucosidase inhibitory effects. Cold water and ethanol extracts of 15 seaweeds were initially screened and from this, five brown seaweed species were chosen. The cold water and ethanol extracts of Ascophyllum nodosum had the strongest α-amylase inhibitory effect with IC₅₀ values of 53.6 and 44.7 μg/ml, respectively. Moreover, the extracts of Fucus vesiculosus Linnaeus were found to be potent inhibitors of α-glucosidase with IC₅₀ values of 0.32 and 0.49 μg/ml. The observed effects were associated with the phenolic content and antioxidant activity of the extracts, and the concentrations used were below cytotoxic levels. Overall, our findings suggest that brown seaweed extracts may limit the release of simple sugars from the gut and thereby alleviate postprandial hyperglycaemia.     

Antimutagenic and α-glucosidase inhibitory effects of constituents from Kaempferia parviflora

The dichloromethane extract and ethyl acetate soluble fraction of Kaempferia parviflora showed antimutagenicity and α-glucosidase inhibitory activity. 7-Methoxyflavones were the major constituents of both extracts and demonstrated antimutagenic activity. In particular, 5,7-dimethoxyflavone (IC₅₀ = 0.40 nmol/plate), 5,3′-dihydroxy-3,7,4′-trimethoxyflavone (0.40 nmol/plate), 3,5,7-trimethoxyflavone (0.42 nmol/plate) and 5-hydroxy-7-methoxyflavone (0.47 nmol/plate) showed potent antimutagenic activity. The results of structure–activity relationship studies suggest that methylation of the 5-hydroxy group enhanced activity. On the other hand, increasing the number of methoxy groups on the B ring caused a reduction in activity. In the case of an α-glucosidase inhibitory effect, 5,7,3′,4′-tetramethoxyflavone exhibited the highest activity (IC₅₀ = 20.4 μM), followed by 5,7,4′-trimethoxyflavone (54.3 μM) and 3,5,7,3′,4′-pentamethoxyflavone (64.3 μM). The results suggest that the α-glucosidase inhibitory activity was enhanced by the methoxy groups at the 5-, 3′- and 4′-position and was reduced by the methoxy group at the 3-position.     

Metabolite profiling and inhibitory properties of leaf extracts of Ficus benjamina towards α-glucosidase and α-amylase

The use of antioxidant-rich medicinal plants having the potential to reduce oxidative stress and postprandial hyperglycemic pressure is one of the most promising option for the management of diabetes. This study presents information on metabolite profiling and in vitro anti-diabetic effects of leaf extracts of Ficus benjamina. The DPPH (2, 2-diphenyl-1-picrylhydrazyl radicals) assay was performed to determine the in vitro antioxidant potential of the plant extracts. The anti-diabetic effects were investigated by evaluating inhibitory properties of F. benjamina leaf extracts towards carbohydrate hydrolyzing enzymes, i.e., α-glucosidase and α-amylase, whereas ¹H NMR and UHPLC-QTOF-MS/MS analytical methods were employed for metabolite profiling of F. benjamina leaf extracts. Among 40, 60, 80, and 100% ethanolic leaf extracts of F. benjamina, 80% ethanolic extract exhibited the highest antioxidant activity based upon its DPPH radical scavenging ability (IC₅₀ value: 63.71 ± 2.66 µg/mL). The 80% ethanolic leaf extract of F. benjamina also proved to be the most efficient α-glucosidase and α-amylase inhibitor with IC₅₀ values of 9.65 ± 1.04 µg/mL and 13.08 ± 1.06 µg/mL, respectively; these values were even better than acarbose with α-glucosidase inhibition activity (IC₅₀ = 116.01 ± 3.83 µg/mL) and α-amylase inhibition activity (IC₅₀ = 152.66 ± 7.32 µg/mL). Moreover, a total of 31 metabolites were identified in F. benjamina leaf extract, which may have the potential to contribute to its antioxidant and inhibitory properties against carbohydrate hydrolyzing enzymes. The findings of this study depict F. benjamina leaf extracts as a promising α-glucosidase and α-amylase inhibitor, and therefore, can be utilized for the development of anti-diabetic functional diets/nutra-pharmaceuticals.     

Steam explosion improves extractability,antioxidant activity and α-glucosidase inhibitory activity of the constituents of Java tea (Clerodendranthus spicatus)

In this work, the steam explosion (SE) technology was exploited to extract valuable phytochemicals from Java tea (Clerodendranthus spicatus). Modification effects of SE on apparent morphology and physicochemical properties of Java tea were investigated to confirm that SE destroyed the cell wall structure and enhanced pore space, which facilitated the dissolution of ingredients. After SE pretreatment, the contents of phenolics, triterpenes, and sterols of Java tea extracts were maximally increased by 40.68%, 25.69%, and 40.11% in the leaves group, and increased by 147.09%, 204.50%, and 115.24% in the stems group, respectively. The antioxidant and α-glucosidase inhibition capacity of extracts were also obviously enhanced. Multivariate analysis indicated that phenolics and triterpenes were the main active substances in the extracts, and the leaves treated at 1.0 MPa and stems treated at 2.4 MPa showed higher comprehensive score. This study provided a promising method for Java tea pretreatment for improving extractability and bioactivity.     

Identification and characterization of novel α-amylase and α-glucosidase inhibitory peptides from camel whey proteins

This study explores the inhibitory properties of camel whey protein hydrolysates (CWPH) toward α-amylase (AAM) and α-glucosidase (AG). A general full factorial design (3 × 3) was applied to study the effect of temperature (30, 37, and 45°C), time (120, 240, and 360 min), and enzyme (pepsin) concentration (E%; 0.5, 1, and 2%). The results showed that maximum degree of hydrolysis was obtained when hydrolysis was carried out at higher temperature (45°C; P < 0.05), compared with lower temperatures of 30 and 37°C. Electrophoretic pattern displays degradation of all protein bands upon hydrolysis by pepsin at various hydrolysis conditions applied. All the 27 CWPH generated showed significant AAM and AG inhibitory potential as indicated by their lower IC₅₀ values (mg/mL) compared with intact whey proteins. In total 196 peptides were identified from selected hydrolysates and 15 potential peptides (PepSite score > 0.8; http://pepsite2.russelllab.org/) were explored via in silico approach. Novel peptides PAGNFLMNGLMHR, PAVACCLPPLPCHM, MLPLMLPFTMGY, and PAGNFLPPVAAAPVM were identified as potential inhibitors for both AAM and AG due to their high number of binding sites and highest binding probability toward the target enzymes. CCGM and MFE, as well as FCCLGPVPP were identified as AG and AAM inhibitory peptides, respectively. This is the first study that reports novel AG and AAM inhibitory peptides from camel whey proteins. The future direction for this research involves synthesis of these potential AG and AAM inhibitory peptides in a pure form and investigate their antidiabetic properties in the in vitro, as well as in vivo models. Thus, CWPH can be considered for potential applications in glycaemic regulation.     

Purification and characterisation of α-glucosidase inhibitory peptides from defatted camellia seed cake

Enzymatically derived peptides from different proteins have displayed the potential to provide health benefits. Present research aims to obtain the functional peptides and improve the economic value of camellia seed cake via enzymatic hydrolysis. Camellia seed cake protein hydrolysates (CSCPH) prepared with alcalase demonstrated higher α-glucosidase inhibitory activity. After ultrafiltration, the α-glucosidase inhibitory activity of different components was compared. The component (CSCPH-IV) with the highest activity was selected for further separation and purification. The peptides were purified using reverse-phase high-performance liquid chromatography (RP-HPLC) twice and identified as GHSLESIK, GLTSLDRYK and SPGYYDGR by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Subsequently, the preliminarily inhibitory effect of these peptides on α-glucosidase activity was demonstrated by the molecular docking model. These results showed that three novel peptides isolated from the hydrolysates of camellia seed cake have the potential to be used as anti-diabetic compounds for the development of functional foods.     

The most abundant polyphenol of soy leaves,coumestrol, displays potent α-glucosidase inhibitory activity

The leaves of soybean (Glycine max) were extracted into four different polar solvents: ethylacetate, butanol, ethanol and water. The ethylacetate extract (EE) showed the lowest IC₅₀ value against α-glucosidase (70.1 μg/ml). To investigate the compounds responsible for this effect, activity guided fractionation of soybean leaves by chromatography yielded seven phenolic compounds which were identified as formononetin (1), afromosin (2), coumestrol (3), isotrifoliol (4), phaseol (5), glyceofuran (6) and a new compound, glyceollin V (7). Importantly, coumestrol 3 was not only the most potent component with IC₅₀ = 6.0 μM, but also the most abundant polyphenol in soybean leaves. There was shown to be an increasing inhibition across the developmental stage of the plant, which correlated strongly with an increase in compound 3 in the leaves. In fact, we have shown it can comprise up to 65% of the polyphenols in the leaves by HPLC analysis.     

Anti-diabetic activity peptides from albumin against α-glucosidase and α-amylase

The objectives of this study were to identify novel peptides from albumin, and to evaluate and validate the anti-diabetic activity of peptides against α-glucosidase and α-amylase. In the research, albumin hydrolysate was purified and identified, tandem MS was adapted to characterise the amino acid sequences of peptides from the hydrolysate. In addition, anti-diabetic effects of the peptides with α-glucosidase and α-amylase inhibitory activity have been performed. The present work found eight novel peptides from albumin. Results also suggested that peptide KLPGF had α-glucosidase inhibitory activity with an IC(50) of 59.5±5.7μmoll(-1) and α-amylase inhibitory activity with an IC(50) of 120.0±4.0μmoll(-1). In conclusion, the results revealed that the peptide KLPGF was a potential anti-diabetic inhibitor.     

Antioxidant and α-glucosidase inhibitory phenolics isolated from highbush blueberry flowers

Blueberries have been extensively researched, but there are limited studies on other parts of the plant. Here we report the first phytochemical examination of highbush blueberry (Vaccinium corymbosum) flowers, which yielded 21 phenolics. The compounds were identified from extensive NMR and mass spectral analyses and included five caffeic acid (1-5), three coumaric acid (6-8), and two cinnamyl alcohol (9-10) derivatives, eight flavonol glycosides (11-18), and three phenylpropanoid-substituted catechins (19-21). The isolates were evaluated for antioxidant and α-glucosidase inhibitory activities. Overall, the flavonol glycosides and phenylpropanoid-substituted catechins showed superior antioxidant activities compared to the positive controls, vitamin C (IC(50)=63μM) and butylated hydroxytoluene (IC(50)=1548μM). Similarly, these phenolic sub-classes were more potent α-glucosidase inhibitors than the clinical drug, acarbose (IC(50)=200μM). Thus, non-consumed parts of food plants may be exploited as sources of bioactive compounds beyond their edible parts alone for nutraceutical and functional food applications.     

Phenolic content,antioxidant capacity,and α-amylase and α-glucosidase inhibitory activities of Dimocarpus longan Lour.

Food Science and Biotechnology - The aim of this study was to compare the phenolic compound profiles and antioxidant capacities of eight varieties of longan (Dimocarpus longan Lour.) planted in the...     

Differential biochemical and kinetic properties of α-amylases from Rhyzopertha dominica (F.) progenies reared on wheat varieties differing in α-amylase inhibitory activity

The present study was accomplished to gain insights into the biochemical and kinetic properties of Rhyzopertha dominica’s α-amylase isoforms (named RdA70, RdA79, and RdA90) expressed in progenies reared in wheat varieties differing in α-amylase inhibitory activity. An inverse relationship was observed between the progenies’ amylase activity and the wheat inhibitory activity. Wheat samples with a high and low infestation (named HI-Borlaug and LI-Villa Juarez, respectively) were chosen to simplify the study. The progenies amylases were isolated by hydrophobic interaction chromatography, while the wheat samples were analyzed in α-amylase inhibitory activity by size exclusion chromatography. The isoforms RdA70 and RdA90 from LI-Villa Juarez progeny showed higher enzyme activities (73.8 and 43.4%, respectively) than those from HI-Borlaug. When the amylase isoforms were tested in susceptibility to inhibition by the inhibitory albumins, those from LI-Villa Juarez were more susceptible than those of the HI-Borlaug. Determination of the kinetic parameters revealed that RdA70 from the HI-Borlaug progeny showed 3.0-fold less starch affinity than that from the LI-Villa Juarez (K_m of 12.3 ± 1.8 versus 4.0 ± 0.3). The rest of the α-amylases did not show the same pattern as RdA70 in the HI-Bourlag as that their starch affinity was further reduced (RdA79 K_m = 23.1 ± 4.3, RdA90 K_m = 17.1 ± 2.9). Estimation of IC₅₀ values confirmed the high sensitivity of the three α-amylases of the LI-Villa Juarez progeny to wheat α-amylase inhibitors. The inhibitor constant K_i was the lowest for RdA70 in the LI-Villa Juarez progeny indicating the inhibitor’ tight binding to that isoenzyme. These results suggest that R. dominica uses RdA70 to bind large amounts of wheat α-amylase inhibitors than RdA79 and RdA90 as a physiological defense mechanism.     

The inhibitory effects of ethanol extracts from sorghum,foxtail millet and proso millet on α-glucosidase and α-amylase activities

Cereal crops have recently experienced increased interest due to their potential health benefits. It has been suggested that the intake of whole grain foods is beneficial to the prevention and management of diabetes mellitus. In this study, we investigated the inhibitory effect of 70% EtOH extracts from different cultivars of sorghum, foxtail millet and proso millet on α-glucosidase and α-amylase. Among the six sorghum cultivars, Mongdang-susu(SS-1), Me-susu(SS-2), Susongsaengi-susu(SS-3) and Sikyung-susu(SS-4) extracts exhibited higher inhibitory activities against α-glucosidase (IC₅₀ = 1.1–1.4 μg/ml) than acarbose, reference inhibitor (IC₅₀ = 2.1 μg/ml). In addition, these extracts strongly inhibited degradation of starch by pancreatic and salivary α-amylase, whereas extracts from foxtail and proso millets exhibited no visible or detectible inhibitory effect on α-amylase or on α-glucosidase activity. These in vitro studies indicate the potential of sorghum in the development of effective anti-diabetic agents.     

Flavan-3-ol contents,anti-oxidative and α-glucosidase inhibitory activities of Cynomorium songaricum

Flavan-3-ol oligomers from the stems of Cynomorium songaricum were found to show potent SOD-like activity with one of the dimers being most potent. The flavan-3-ols also showed inhibitory activity on α-glucosidase, implying the beneficial effects of this herb on diabetes patients. The total (extractable and non-extractable) tannin content of this herb was found to be as high as 18.3%. The contents of catechin, flavan-3-ol oligomers and extractable tannins using 70% acetone, methanol or water were analysed. It was found that 70% acetone was the most efficient extract solvent amongst these three solvents, especially for higher flavan-3-ol oligomers.     

Isolation and characterisation of an α-glucosidase inhibitory substance from fructose–tyrosine Maillard reaction products

An α-glucosidase inhibitory substance was isolated and characterised from fructose–tyrosine Maillard reaction products (MRPs) and the inhibition mode of the active substance determined. The ethyl acetate fraction of fructose–tyrosine MRPs showed strong α-glucosidase inhibitory activity; this fraction was isolated and purified using silica gel column chromatography and semi-preparative RP-HPLC. The structure of the purified compound was determined using spectroscopic methods. The isolated compound was identified as 2,4-bis (p-hydroxyphenyl)-2-butenal (C₁₆H₁₄O₃, HPB242). This is the first report of baker’s yeast α-glucosidase inhibitory activity of HPB242 isolated from fructose–tyrosine MRPs. The IC₅₀ value of HPB242 on α-glucosidase inhibition was 4.00 ± 0.09 μg/ml. Kinetic data revealed that HPB242 inhibits the p-NPG hydrolysing activity of baker’s yeast α-glucosidase noncompetitively with a K_i value of 0.870 mM.