Blood glucose-lowering activity of protocatechuic acid is mediated by inhibiting a-glucosidase

α-Glucosidase inhibitors are effective in controlling postprandial hyperglycemia,which play crucial roles in the management of type 2 diabetes.Protocatechuic acid(PCA)is one of phenolic acids existing not only in various plant foods but also as a major microbial metabolite of dietary anthocyanins in the large colon.The present study investigated the inhibitory mechanism of PCA on a-glucosidase in vitro and examined its effect on postprandial blood glucose levels in vivo.Results from in vitro experiments demonstrated that PCA was a mix-type inhibitor of a-glucosidase.Driven by hydrogen bonds and van der Waals interactions,PCA reversibly bound withα-glucosidase to form a stable a-glucosidase-PCA complex in a spontaneous manner.The computational simulation found that PCA could insert into the active cavity of a-glucosidase and establish hydrogen bonds with catalytic amino acid residues.PCA binding aroused the steric hindrance for substrates to enter active sites and caused the structural changes of interacted catalytic amino acid residues.PCA also exhibited postprandial hypoglycemic capacity in diabetic mice.This study may provide the theoretical basis for the application of PCA as an active ingredient of functional foods in dietary management of diabetes.

Investigating the cellular functions of β-Glucosidases for synthesis of lignocellulose-degrading enzymes in Trichoderma reesei

β-glucosidases play an important role in the synthesis of cellulase in fungi,but their molecular functions and mechanisms remain unknown.We found that the 10 putativeβ-glucosidases investigated in Trichoderma ree-sei facilitate cellulase production,with cel3j being the most crucial.Transcriptional analysis revealed that the most affected biological processes in△cel3j strain were cellulase synthesis,ribosome biogenesis,and RNA poly-merases.Moreover,CEL3J was unconventionally transported through the endoplasmic reticulum,bypassing the Golgi apparatus,whereas cel3j overexpression altered cellulase secretion from conventional to unconventional,likely owing to the activated unconventional protein secretion pathway(UPS),as indicated by the upregulation of genes related to UPS.The mTORC1-GRASP55 signaling axis may modulate the unconventional secretion of CEL3J and cellulase.The transcriptional levels of genes associated with DNA replication,the cell cycle,and meiosis were noticeably affected by overexpressing cel3j.These data give new clues for exploring the roles ofβ-glucosidases and the molecular mechanisms of their unconventional secretion in fungi.

Antioxidant,antimicrobial,and α-glucosidase inhibitory activities of saponin extracts from walnut(Juglans regia L.) leaves

Objective:To investigate the relationship between triterpenoid saponin content and antioxidant,antimicrobial,and α-glucosidase inhibitory activities of 70%ethanolic,butanolic,aqueous,supernate and precipitate extracts of Juglans regia leaves.Methods:Triterpenoid saponins of different Juglans regia leaf extracts were measured by the vanillin method.Antioxidant activity was evaluated against DPPH and ABTS free radicals.We also assessed α-glucosidase inhibitory and antimicrobial activities of the leaf extracts.Pearson’s correlation coefficient was evaluated to determine the correlation between the saponin content and biological activities.Results:The butanolic extract was most effective against DPPH with an IC50of 6.63μg/mL,while the aqueous extract showed the highest scavenging activity against ABTS free radical with an IC50of 42.27μg/mL.Pearson’s correlation analysis indicated a strong negative correlation (r=-0.956) between DPPH radical scavenging activity (IC50) and the saponin content in the samples examined.In addition,the aqueous extract showed the best α-glucosidase inhibitory activity compared with other extracts.All the extracts had fair antibacterial activity against Bacillus subtilis,Escherichia coli,and Klebsiella pneumoniae except for the aqueous extract.Conclusions:Juglans regia extracts show potent antioxidant,antimicrobial,and α-glucosidase inhibitory activities.There is a correlation between saponin levels in Juglans regia leaf extracts and the studied activities.However,additional research is required to establish these relationships by identifying the specific saponin molecules responsible for these activities and elucidating their mechanisms of action.

Structural characterizations andα-glucosidase inhibitory activities of four Lepidium meyenii polysaccharides with different molecular weights

Four polysaccharides(MCPa,MCPb,MCPc,MCPd)were obtained from Lepidium meyenii Walp.Their structures were characterized by chemical and instrumental methods including total sugar,uronic acid and protein content determi-nation,UV,IR and NMR spectroscopy,as well as monosaccharide composition determination and methylation analy-ses.Four polysaccharides were a group of glucans with different molecular weights ranging from 3.12 to 14.4 kDa,and shared a similar backbone chain consisting of(1→4)-glucose linkages with branches attached to C-3 and C-6.Furthermore,bioactivity assay showed that MCPs had concentration-dependent inhibitory activity onα-glucosidase.MCPb(Mw=10.1 kDa)and MCPc(Mw=5.62 kDa)with moderate molecular weights exhibited higher inhibitory activ-ity compared with MCPa and MCPd.

Ethanol extract of Annona muricata Linn fruit perform antidiabetic effect on type 2 diabetic mice through α-glucosidase inhibition

Objective:To explore the anti-diabetic effects and its underlying mechanism of Annona muricata Linn fruit ethanol extract(AME).Methods:Streptozotocin-induced type 2 diabetic(T2DM)mouse model was constructed.Those diabetic mice were randomly grouped and given 50 mg/kg acarbose or AME(200 mg/kg,100 mg/kg or 50 mg/kg)for four weeks.The body weight,postprandial blood glucose and glycosylated hemoglobin levels were measured during the administration.After the administration,a glucose tolerance test was performed,and the levels of triglycerides,cholesterol and low-density lipoproteins in mice were detected by biochemical test kits.The inhibitory activity of AME onα-glucosidase in vivo and in vitro was determined by enzyme inhibition tests.Results:AME significantly reduced weight gain,postprandial blood glucose,glycosylated hemoglobin and low-density lipoprotein levels in T2DM mice;enhanced glucose tolerance and pancreaticβ-cell function of T2DM mice;inhibitedα-glucosidase activity in mouse intestine in an noncompetitive manner.Conclusion:AME may noncompetitive inhibitα-glucosidase activity and reduce postprandial glucose intake to achieve a therapeutic and regulatory effect on type 2 diabetes.

α-Glucosidase Inhibitors from Glycyrrhiza uralensis Fisch.

Aim To screen for α-glucosidase inhibitor from Glyeyrrhiza uralensis Fisch.. Methods Glycyrrhizic acid, glycyrrhetinic acid, flavonoids of glycyrrhiza, alkaloids of glycyrrhiza, and glycyrrhiza polysaccharides were isolated from the root of Glycyrrhiza uralensis Fisch. respectively. Three compounds were isolated from the flavonoids of glycyrrhiza as guided by the α-glucosidase inhibitory test in vitro. Moreover, the characteristics of inhibitory kinetics of glycyrol and glycyrrhetinic acid were investi- gated. Results The flavonoids of glycyrrhiza and glycyrrhetinic acid had the strongest α-glucosidase inhibitory activity. Glycyrol,β-sitosterol and liquifitin were isolated and identified. Glycyrol was a fast- binding, reversible, noncompetitive α-glucosidase inhibitor, showing IC50 at 0.26 μg·mL^-1 Glycyrrhetinic acid was a fast-binding, irreversible α-glucosidase inhibitor, showing IC50 at 102.4 μg·mL^-1. Conclusion Glycyrol is an effective α-glucosidase inhibitor.

Effects of α-glucosidase Inhibitors on the Function of Mulberry Leaf Extract as an Additive in Feedstuff

The mulberry juice contains high concentrations of α-glucosidase inhibitors that affect glycometabolism and cause diarrhea in animals, thereby affecting the de-velopment and application of mulberry （Morus alba L.） as feedstuff resources. ln this study, the effects of mulberry leaf extract with and without removal of mulberry juice on starch metabolism were analyzed and compared. The results showed that mul-berry leaf extract with removal of mulberry juice exhibited significantly lower inhibi-tion rate on starch metabolism compared with mulberry leaf extract without removal of mulberry juice. ln animal feeding trials, piglet feedstuff was added with 10% mul-berry leaf powder; compared with mulberry leaf powder without removal of mulberry juice, experimental piglets fed with mulberry leaf powder with removal of mulberry juice exhibited significantly improved weight gain and significantyl reduced diarrhea rate.

Historical tillage promotes grass-legume mixtures establishment and accelerates soil microbial activity and organic carbon decomposition

Perennial grass-legume mixtures have been extensively used to restore degraded grasslands,increasing grassland productivity and forage quality.Tillage is crucial for seedbed preparation and sustainable weed management for the establishment of grass-legume mixtures.However,a common concern is that intensive tillage may alter soil characteristics,leading to losses in soil organic carbon(SOC).We investigated the plant community composition,SOC,soil microbial biomass carbon(MBC),soil enzyme activities,and soil properties in long-term perennial grass-legume mixtures under two different tillage intensities(once and twice)as well as in a fenced grassland(FG).The establishment of grass-legume mixtures increased plant species diversity and plant community coverage,compared with FG.Compared with once tilled grassland(OTG),twice tilled grassland(TTG)enhanced the coverage of high-quality leguminous forage species by 380.3%.Grass-legume mixtures with historical tillage decreased SOC and dissolved organic carbon(DOC)concentrations,whereas soil MBC concentrations in OTG and TTG increased by 16.0%and 16.4%,respectively,compared with FG.TTG significantly decreased the activity of N-acetyl-β-D-glucosaminidase(NAG)by 72.3%,whereas soil enzymeβ-glucosidase(βG)in OTG and TTG increased by 55.9%and 27.3%,respectively,compared with FG.Correlation analysis indicated a close association of the increase in MBC andβG activities with the rapid decline in SOC.This result suggested that MBC was a key driving factor in soil carbon storage dynamics,potentially accelerating soil carbon cycling and facilitating biogeochemical cycling.The establishment of grass-legume mixtures effectively improves forage quality and boosts plant diversity,thereby facilitating the restoration of degraded grasslands.Although tillage assists in establishing legume-grass mixtures by controlling weeds,it accelerates microbial activity and organic carbon decomposition.Our findings provide a foundation for understanding the process and effectiveness of restoration management in degraded grasslands.

Inhibitory activities of microalgal fucoxanthin againstα-amylase,α-glucosidase, and glucose oxidase in 3T3-L1cells linked to type 2 diabetes

Postprandial hyperglycemia is an early indication of type 2 diabetes and the target of many anti-diabetic and anti-obesity studies.α-Glucosidase and α-amylase are the crucial factors in regulating starch digestion and glucose absorption,making them key targets for many studies to treat postprandial hyperglycemia.We studied the inhibitory activities of microalgal fucoxanthin against rat-intestinalα-glucosidase and pancreaticα-amylase along with the antidiabetic eff ect to induce diff erentiation in 3T3-L1 pre-adipocytes using Oil Red-O staining.Fucoxanthin displayed strong hindrance activities towardα-amylase in a concentration-dependent manner,with an IC50 value of 0.68mmol/L,whereas weak inhibitory activity against α-glucosidase,with an IC 50 value of 4.75 mmol/L.Fucoxanthin also considerably elevated glucose oxidase activity in 3T3-L1 cells by 31.3%at 5μmol/L.During adipocyte differentiation,fucoxanthin showed lipid accumulation in 3T3-L1 cells with no cytotoxicity up to 20μmol/L.However,fucoxanthin had no inhibitory activity on glucose-6-phosphate dehydrogenase.These results suggest that fucoxanthin might be useful for the prevention of obesity or diabetes by inhibiting carbohydrate-hydrolyzing enzymes and lipid accumulation and be utilized as an ingredient for a functional food or dietary supplement.

Antioxidant and α-glucosidase inhibitor activities of natural compounds isolated from Quercus gilva Blume leaves

Objective: To isolate and investigate antioxidant and α-glucosidase inhibitor compounds in the leaves of Quercus gilva Blume(Q. gilva).Methods: Dry leaves of Q. gilva were extracted with methanol and the methanolic extract was further separated by silica gel column chromatography using several solvents with increasing polarity. The antioxidant activities of the isolated compounds were evaluated using various in vitro assays: 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, hydrogen peroxide radical scavenging activity, β-carotene bleaching assay, and reducing power assay. The α-glucosidase inhibitory assay was conducted against α-glucosidase from Saccharomyces cerevisiae.Results: Three compounds were isolated and their structures were identii ed as catechin(1), epicatechin(2), and tiliroside(3) using an instrumental analysis. Compound 2 had higher antioxidant activity with inhibitory concentrations(IC50) of(22.55 ± 2.23) μmol/L than that of quercetin, which was used as the standard, with an IC50 of(28.08 ± 2.39) μmol/L, followed by compound 1 with IC50 of(40.86 ± 3.45) μmol/L. On the other hand, compound 3 had the lowest antioxidant activity with an IC50 of(160.24 ± 8.15) μmol/L. However, compound 3 had the highest α-glucosidase inhibitory activity with an IC50 of(28.36 ± 0.11) μmol/L, followed by compounds 1 and 2 with(168.60 ± 5.15) and(920.60 ± 10.10) μmol/L, respectively.Conclusions: The results obtained for the antioxidant activities and α-glucosidase inhibitory activities in a methanolic extract from the leaves of Q. gilva coni rmed the potential of this plant as a source of natural antioxidants and antidiabetic medicine.

α-Glucosidase Inhibitory Activities of Lutein and Zeaxanthin Purified from Green Alga Chlorella ellipsoidea

α-Glucosidase inhibitors are used therapeutically to treat type-2 diabetes mellitus. Through a bioassay-guided fractionation technique, three carotenoids,(all-E)-lutein,(all-E)-zeaxanthin and(9-Z)-zeaxanthin, were purified from the green alga Chlorella ellipsoidea, in which(all-E)-lutein and(9-Z)-zeaxanthin had potent α-glucosidase inhibitory activity. IC_(50) values of(all-E)-lutein and(9-Z)-zeaxanthin were 70 and 53.5 μmol L^(-1) against Saccharomyces cerevisiae α-glucosidase, respectively, with non-competitive inhibition. In addition, IC_(50) values of(9-Z)-zeaxanthin against Bacillus stearothermophilus and rat-intestinal α-glucosidase were 805.1 and 671.2 μmol L^(-1), respectively. The K_i values of(all-E)-lutein and(9-Z)-zeaxanthin against S. cerevisiae α-glucosidase were 78.1 and 16.5 μmol L^(-1), respectively. Therefore, C. ellipsoidea carotenoids might be utilized as a novel candidate to prevent type-2 diabetes mellitus related disorders in food and medical industry.

Screening ofα-glucosidase inhibitors in large-leaf yellow tea by offline bioassay coupled with liquid chromatography tandem mass spectrometry

Larger-leaf yellow tea(LYT)is a characteristic type of Chinese tea produced in Huoshan County,Anhui Province,which is made by mature leaves with stems.According to recent report,LYT showed competitive effects in anti-hyperglycemia in comparison to other teas such as green or black tea.However,the bioactive compounds of LYT are still undiscovered so far.For this purpose,5 fractions of LYT were prepared by sequential extraction.The in vitro bioassay results indicated that the ethyl acetate fraction of LYT had the strongest inhibitory effects onα-glucosidase andα-amylase.Fluorescence-quenching analysis and proteinbinding test revealed that the compounds of ethyl acetate fraction could inhibitα-glucosidase andα-amylase activities through binding to enzymes or other mechanisms.All chromatographic peaks of high-performance liquid chromatography(HPLC)of ethyl acetate fraction were separated and collected.The purified compounds were identified by liquid chromatography-mass spectrometry(LC-MS),and subsequently screened by calculating their inhibition ratio onα-glucosidase at the real concentration in LYT infusion.The results showed that(-)-epigallocatechin gallate,(-)-gallocatechin gallate,caffeine,N-ethyl-2-pyrrolidone-substituted flavan-3-ols were effective inhibitors forα-glucosidase.

Antioxidant andα-glucosidase inhibitiory activity of Cercis chinensis flowers

Antioxidant andα-glucosidase inhibitiory active compounds of Cercis chinensis flowers were investigated with bio-assay guiding method.Ethyl acetate fraction(CLEa)and n-butanol fraction(CLBu)exhibited antioxidant andα-glucosidase inhibitiory activity in vitro,and the corresponding active fractions,EaFr.3,EaFr.5 and BuFr.1,exhibited higher antioxidant andα-glucosidase inhibitiory activity than those of other fractions.Eight compounds,ethyl gallate(1),stearic acid(2),docosanoic acid(3),5α-stigmast-9(11)-en-3β-ol(4),kaempferol-3-O-α-rhamnopyranoside(5),vanillic acid(6),fisetin(7),andβ-sitosterol(8),were isolated and identified from CLEa and CLBu.Ethyl gallate shown the highest antioxidant activity by scavenging DPPH radical and reducing ferric compared.Docosanoic acid and vanillic acid shown strongerα-glucosidase inhibitory activity than that of acarbose.

α-Glucosidase inhibitors isolated from medicinal plants

Objective:α-Glucosidase inhibitors can be used as a new class of antidiabetic drug.By competitively inhibiting glycosidase activity,these inhibitors help to prevent the fast breakdown of sugars and thereby control the blood sugar level.This study provides a wealth of information aboutα-glucosidase inhibitors isolated from medicinal plants;this knowledge will be useful in finding more potent antidiabetic candidates from the natural resources for the clinical development of antidiabetic therapeutics.Results:411 compounds exhibitingα-glucosidase inhibitory activity were summarized and isolated them from medicinal plants.The compound classes isolated include:terpenes(61)from 14 genus,alkaloids(37)from 11 genus,quinines(49)from 4 genus,flavonoids(103)from 24 genus,phenols(37)from 9 genus,phenylpropanoids(73)from 20 genus,sterides(8)from 5 genus,and other types of compounds(43).Conclusion:Compounds withα-glucosidase inhibitory activity are abundant in nature and can be obtained from several sources.They have highα-glucosidase inhibitory potential,and can be clinically developed for treating diabetes mellitus.

Chemical Constituents from Turnip and Their Effects on α-Glucosidase

Brassica rapa var.rapa(turnip)is an important crop in Qinghai-Tibet Plateau(QTP)with anti-hypoxic effect.Turnip is rich in glucosinolates,isothiocyanates and phenolic compounds with diverse biological activities,involving anti-oxidant,anti-tumor,anti-diabetic,anti-inflammatory,anti-microbial,hypolipidemic,cardioprotective,hepatoprotective,nephroprotective and analgesic properties.In this study,the ethyl acetate(EtOAc)and butanol parts of Brassica rapa were first revealed with inhibitory effects onα-glucosidase,whereas the water part was inactive.Subsequent bioassay-guided isolation on the EtOAc and butanol parts yielded 12 compounds,involving three indole derivatives,indole-3-acetonitrile(1)4-methoxyindole-3-acetonitrile(2)and indole-3-aldehyde(3)two flavonoids,liquiritin(4)and licochalcone A(5)two phenylpropanoids,sinapic acid(6)and caffeic acid(7)two phenylethanol glycosides,2-phenylethylβ-glucopyranoside(8)and salidroside(9)and three other compounds,syringic acid(10)adenosine(11)and(3β,20E)-ergosta-5,20(22)-dien-3-ol(12)Licochalcone A(5)and caffeic acid(7)showedα-glucosidase inhibitory activity with IC 50 values of 62.4±8.0μM and 162.6±3.2μM,comparable to the positive control,acarbose(IC 50=142±0.02μM).Docking study suggested that licochalcone A(5)could well align in the active site ofα-glucosidase(docking score=-52.88)by forming hydrogen bonds(Gln1372,Asp1420,Gln1372,Arg1510),hydrophobic effects(Tyr1251,Tyr1251,Trp1355,Phe1560,Ile1587,Trp1355,Phe1559,Phe1559)andπ-πstacking interaction(Trp1355).This study provides valuable information for turnip as a new resource in searching anti-diabetic candidates.

Identification of α-glucosidase inhibitors from Clinacanthus nutans leaf extract using liquid chromatography-mass spectrometry-based metabolomics and protein-ligand interaction with molecular docking

The present study used in vitro and in silico techniques, as well as the metabolomics approach to characterise α-glucosidase inhibitors from different fractions of Clinacanthus nutans. C. nutans is a medicinal plant belonging to the Acanthaceae family, and is traditionally used to treat diabetes in Malaysia. nHexane, n-hexane: ethyl acetate(1:1, v/v), ethyl acetate, ethyl acetate: methanol(1:1, v/v), and methanol fractions were obtained via partitioning of the 80% methanolic crude extract. The in vitro α-glucosidase inhibitory activity was analyzed using all the fractions collected, followed by profiling of the metabolites using liquid chromatography combined with mass spectrometry. The partial least square(PLS) statistical model was developed using the SIMCA P^+14.0 software and the following four inhibitors were obtained:(1) 4,6,8-Megastigmatrien-3-one;(2) N-Isobutyl-2-nonen-6,8-diynamide;(3) 1′,2′-bis(acetyloxy)-3′,4′-didehydro-2′-hydro-β, ψ-carotene; and(4) 22-acetate-3-hydroxy-21-(6-methyl-2,4-octadienoate)-olean-12-en-28-oic acid. The in silico study performed via molecular docking with the crystal structure of yeast isomaltase(PDB code: 3 A4 A) involved a hydrogen bond and some hydrophobic interactions between the inhibitors and protein. The residues that interacted include ASN259, HID295, LYS156, ARG335,and GLY209 with a hydrogen bond, while TRP15, TYR158, VAL232, HIE280, ALA292, PRO312, LEU313,VAL313, PHE314, ARG315, TYR316, VAL319, and TRP343 with other forms of bonding.

Selection of Yeast Strains Containing β-Glucosidase for Improving Wine Aroma

Aroma is an important component for characteristic of wine. β-glucosidase is an enzyme for enhancing wine aroma during fermentation and aging. The aim of this study was to evaluate β-glucosidase activities from 17 yeast strains. It was found that strain 71 B-1122 exhibited highest activity of β-glucosidase. The purified enzyme of this strain was characterized. The purified enzyme was added in Muscat must before wine making process. The must and wine were determined for volatile compounds by headspace-SPME/GC-MS and found that the hexyl acetate, linalool, phenethyl, nerol and geraniol compounds were significantly increased after treated with the enzyme. Sensory evaluation of the combined alcoholic fermentation and flavour enrichment of Muscat juice by adding of purified β-glucosidase enzyme showed well oenological properties especially aroma. Therefore, in producing wine, yeast strain selection and addition of β-glucosidase enzyme should be considered because they were important factors affecting wine aroma.

Effects of Hibiscus sabdariffa Linn. fruit extracts on α-glucosidase enzyme,glucose diffusion and wound healing activities

Objective:To provide in vitro evidence for antidiabetic activity through potential inhibition of α-glucosidase enzyme,glucose diffusion and enhancement in the wound healing using methanolic extract and fractions from Hibiscus sabdariffa Linn.fruit.Methods:The inhibitory action of methanolic extract and fractions of such fruit on aglucosidase enzyme and glucose movement through in vitro assay assessment was reported.Their activities on wound healing were tested using the scratch assay.Results:Ethyl acetate fraction at 50 mg/m L concentration exhibited significant aglucosidase inhibition(95.79 mg/m L) with P < 0.05.At the same concentration,the methanolic extract as well as other fractions revealed lower α-glucosidase inhibition and higher glucose diffusion retardation across the dialysis tube than the control.Ethyl acetate and butanol fractions displayed notably higher glucose diffusion inhibitory activity of 5.21 mmol/L and 5.2 mmol/L,respectively as compared to methanolic extract and n-hexane fraction of 6.58 mmol/L and 6.49 mmol/L,respectively.Conversely,compared to other fractions the methanolic extract and ethyl acetate fraction manifested proliferative effect at the incubation time of 6 h during the wound healing study.Conclusions:It is established that methanolic extract and fractions from H.sabdariffa Linn.fruit can inhibit the α-glucosidase enzyme and glucose movement as well as influence the wound healing activity positively.

Evaluation of bioactive flavonoids in Citri Reticulatae Pericarpium from different regions and its association with antioxidant andα-glucosidase inhibitory activities

Background:To explore the differences of 14 batches of Citri Reticulatae Pericarpium from different regions.Methods:The main aim of this study was to develop a high-performance liquid chromatography method-photodiode array detection for determining the contents of five flavonoids and the chromatographic fingerprints of Citri Reticulatae Pericarpium from different regions.Theα-glucosidase inhibitory activities and antioxidant properties of Citri Reticulatae Pericarpium,based on free-radical scavenging assays against 1,1-diphenyl-2-picrylhydrazyl,2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid),and hydroxyl radicals,were estimated and compared.Results:Among the tested compounds,the content of hesperidin(13.386-68.235 mg/g)was the highest and that of hesperitin(0.045-0.277 mg/g)was the lowest.In comparing different sources of Citri Reticulatae Pericarpium,the contents of narirutin in Citri Reticulatae Pericarpium from Guangdong(0.824-0.851 mg/g)and Sichuan(1.069-1.204 mg/g)provinces of China were lower than in other provinces.In contrast,nobiletin(8.429-12.237 mg/g)and tangeretin(3.947-4.613 mg/g)were most abundant in Guangdong sources of Citri Reticulatae Pericarpium,followed by samples from Sichuan Province(nobiletin:6.761-7.658 mg/g;tangeretin:3.422-3.933 mg/g).Correlation analysis showed that nobiletin and tangeretin were the main contributors to the antioxidant capacity,and narirutin was the main active component inhibiting theα-glucosidase activity of Citri Reticulatae Pericarpium.Conclusion:This work revealed that the intrinsic quality of Citri Reticulatae Pericarpium was affected by different growing regions,which provides a scientific basis for controlling the quality of Citri Reticulatae Pericarpium and rationally developing and utilizing Citri Reticulatae Pericarpium.

Bioactive constituents from the leaves of Quercus phillyraeoides A.Gray for-glucosidase inhibitor activity with concurrent antioxidant activity

Severalα-glucosidase inhibitory constituents were isolated from the methanolic extract of the leaves of Quercus phillyraeoides A.Gray(Q.phillyraeoides)using a bioassay-guided fractionation technique.Further separation and purification of the methanol-soluble fraction led to the isolation of constituents with moderate and strong inhibitory activities againstα-glucosidase:α-sitosterol-d-glucoside(1)and condensed tannin fractions(2,3,4,5,and 6).Compound 1 and fractions 2-6 had inhibitory concentration(IC50)values againstm-glucosidase from Saccharomyces cerevisiae of 118.8,2.79,2.78,3.10,2.60,and 3.14μg/mL,respectively,while quercetin as the standard had an IC50 value of 4.80mg/mL.Furthermore,the significant antioxidant activities were evaluated using several assays,such as the DPPH radical scavenging,hydrogen peroxide radical scavenging,reducing power,andβ-carotene-linoleate bleaching assays,and the results suggested that the isolated constituents showed their possible application for treating the hyperglycemia-induced oxidative stress.The results of the present study showed the potential of Q.phillyraeoides as a rich source of natural antidiabetic medicine.