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.

Protocatechuic acid and quercetin attenuate ETEC-caused IPEC-1 cell inflammation and injury associated with inhibition of necroptosis and pyroptosis signaling pathways

Background:Necroptosis and pyroptosis are newly identified forms of programmed cell death,which play a vital role in development of many gastrointestinal disorders.Although plant polyphenols have been reported to protect intestinal health,it is still unclear whether there is a beneficial role of plant polyphenols in modulating necroptosis and pyroptosis in intestinal porcine epithelial cell line(IPEC-1)infected with enterotoxigenic Escherichia coli(ETEC)K88.This research was conducted to explore whether plant polyphenols including protocatechuic acid(PCA)and quercetin(Que),attenuated inflammation and injury of IPEC-1 caused by ETEC K88 through regulating necroptosis and pyroptosis signaling pathways.Methods:IPEC-1 cells were treated with PCA(40μmol/L)or Que(10μmol/L)in the presence or absence of ETEC K88.Results:PCA and Que decreased ETEC K88 adhesion and endotoxin level(P<0.05)in cell supernatant.PCA and Que increased cell number(P<0.001)and decreased lactate dehydrogenases(LDH)activity(P<0.05)in cell supernatant after ETEC infection.PCA and Que improved transepithelial electrical resistance(TEER)(P<0.001)and reduced fluorescein isothiocyanate-labeled dextran(FD4)flux(P<0.001),and enhanced membrane protein abundance of occludin,claudin-1 and ZO-1(P<0.05),and rescued distribution of these tight junction proteins(P<0.05)after ETEC infection.PCA and Que also declined cell necrosis ratio(P<0.05).PCA and Que reduced mRNA abundance and concentration of tumor necrosis factor-α(TNF-α),interleukin(IL)-6 and IL-8(P<0.001),and down-regulated gene expression of toll-like receptors 4(TLR4)and its downstream signals(P<0.001)after ETEC infection.PCA and Que down-regulated protein abundance of total receptor interacting protein kinase 1(t-RIP1),phosphorylated-RIP1(p-RIP1),p-RIP1/t-RIP1,t-RIP3,p-RIP3,mixed lineage kinase domain-like protein(MLKL),p-MLKL,dynamin-related protein 1(DRP1),phosphoglycerate mutase 5(PGAM5)and high mobility group box 1(HMGB1)(P<0.05)after ETEC infection.Moreover,PCA and Que reduced protein abundance of nod-like receptor protein 3(NLRP3),nod-like receptors family CARD domain-containing protein 4(NLRC4),apoptosis-associated speck-like protein containing a CARD(ASC),gasdermin D(GSDMD)and caspase-1(P<0.05)after ETEC infection.Conclusions:In general,our data suggest that PCA and Que are capable of attenuating ETEC-caused intestinal inflammation and damage via inhibiting necroptosis and pyroptosis signaling pathways.

Beneficial effects of protocatechuic acid on diabetic retinopathy in streptozocin-induced diabetic rats

·AIM:To determine the effects of protocatechuic acid(PCA)on streptozocin-induced diabetic retinopathy(DR)in rats.·METHODS:Wistar rats were given a 50 mg/kg intraperitoneal injection of streptozocin to induce diabetes.Animals were assigned randomly one of four groups(8 rats per group):control,diabetic,diabetic plus PCA(25 mg/kg·d),and diabetic plus PCA(50 mg/kg·d).After inducing diabetes,treatments were started one week later and continued for eight weeks.After the experiment,the rats were sacrificed,and their retinas were taken for biochemical and molecular analysis.·RESULTS:PCA administration diminished the blood glucose and glycated haemoglobin levels relative to the diabetic group.In diabetic rats,PCA lowered elevated levels of advanced glycosylated end products(AGEs)and receptor for AGEs(RAGE).In the retina of diabetic rats,PCA effectively decreased inflammatory cytokine,nuclear factor-κB,tumour necrosis factor-α,interleukin-1β,and vascular endothelial growth factor,and increased antioxidant markers glutathione,superoxide dismutase,and catalase.·CONCLUSION:The protective benefits of PCA against DR may be attributable to its suppression of the AGEs and RAGE and its antioxidant and anti-inflammatory properties.

Dietary protocatechuic acid ameliorates inflammation and up-regulates intestinal tight junction proteins by modulating gut microbiota in LPS-challenged piglets

Background: Weaning is one of the major factors that cause stress and intestinal disease in piglets. Protocatechuic acid(PCA) is an active plant phenolic acid which exists in Chinese herb, Duzhong(Eucommia ulmoides Oliver), and is also considered as the main bioactive metabolite of polyphenol against oxidative stress and inflammation. This study aimed to investigate the effect of PCA on growth performance, intestinal barrier function, and gut microbiota in a weaned piglet model challenged with lipopolysaccharide(LPS).Methods: Thirty-six piglets(Pig Improvement Company line 337 × C48, 28 d of age, 8.87 kg ± 0.11 kg BW) were randomly allocated into 3 treatments and fed with a basal diet(CTL), a diet added 50 mg/kg of aureomycin(AUR), or a diet supplemented with 4000 mg/kg of PCA, respectively. The piglets were challenged with LPS(10 μg/kg BW) on d 14 and d 21 by intraperitoneal injection during the 21-d experiment. Animals(n = 6 from each group) were sacrificed after being anesthetized by sodium pentobarbital at 2 h after the last injection of LPS. The serum was collected for antioxidant indices and inflammatory cytokines analysis, the ileum was harvested for detecting mRNA and protein levels of tight junction proteins by PCR and immunohistochemical staining, and the cecum chyme was collected for intestinal flora analysis using 16 S rRNA gene sequencing.Results: Dietary supplementation of PCA or AUR significantly increased the expression of tight junction proteins including ZO-1 and claudin-1 in intestinal mucosa, and decreased the serum levels of thiobarbituric acid reactive substances(TBARS) and IL-6, as compared with CTL group. In addition, PCA also decreased the serum levels of IL-2 and TNF-α(P < 0.05). Analysis of gut microbiota indicated that PCA increased the Firmicutes/Bacteroidetes ratio(P < 0.05). Spearman's correlation analysis at the genus level revealed that PCA reduced the relative abundance of Prevotella 9, Prevotella 2, Holdemanella, and Ruminococcus torques group(P < 0.05), and increased the relative abundance of Roseburia and Desulfovibrio(P < 0.05), whereas AUR had no significant effect on these bacteria.Conclusions: These results demonstrated that both PCA and AUR had protective effect on oxidative stress, inflammation and intestinal barrier function in piglets challenged with LPS, and PCA potentially exerted the protective function by modulating intestinal flora in a way different from AUR.

Optimization of the Ultrasonic-assisted Extraction Process for Protocatechuic Acid from Emilia sonchifolia DC by Response Surface Methodology

[Objectives] This study was conducted to optimize the extraction process of protocatechuic acid from Emilia sonchifolia DC. [Methods] The optimal extraction conditions were determined by single factor,response surface analysis and variance analysis,and the content of protocatechuic acid was determined by HPLC. [Results] The protocatechuic acid standard curve equation was: y = 1 435 x + 8 403,R^2= 0. 999 8,indicating a good linear relationship. The optimal extraction conditions were as follows: a temperature at 80 ℃,an extraction time of 1 h,a material-to-liquid ratio at 1:10 and an ultrasonic power of 600 W,and the content of protocatechuic acid extracted was 1. 93 mg/g. The method showed a RSD of 0. 41%,less than 2%,and the detection limit was 0. 0000047261 g/ml.The experimental sample X1 was the low-level 0. 1 mg/ml standard solution,which showed recovery of protocatechuic acid between 100.8% and 105.2%,with a RSD of 0. 013%;and the sample X2 was the high-level 1. 0 mg/ml standard solution,which exhibited recovery between 100. 6% and 102. 2%,with a RSD of 0.076%. Thus,the recovery was high,and the requirements of the performance index were met. [Conclusions] The detection method is stable and reliable and can produce satisfactory results.

Caffeic acid and protocatechuic acid modulate Nrf2 and inhibit Ehrlich ascites carcinomas in mice

Objective:To assess the nuclear factor-erythroid 2-related factor-2(Nrf2)modulatory effect of caffeic acid and protocatechuic acid and determine the anti-tumor activity of these phenolic compounds against Ehrlich ascites carcinoma growth in mice.Methods:Antioxidant activity of protocatechuic acid and caffeic acid was assessed using ferric reducing antioxidant power(FRAP)and 2,2-diphenyl-1-picrylhydrazyl(DPPH).Nrf2 activation potential of phenolic compounds was tested by quantitative realtime polymerase chain reaction,and luciferase complementation reporter assays.In vivo efficacy was tested using the Ehrlich ascites carcinoma model.Results:FRAP and DPPH radical scavenging assays showed that caffeic acid and protocatechuic acid were more potent compared with cinnamic acid and benzoic acid.Luciferase complementation reporter assays identified caffeic acid and protocatechuic acid as the activators of Nrf2.Both caffeic acid and protocatechuic acid upregulated the expression of Nrf2 target genes heme oxygenase-1(HO-1),glutamate-cysteine ligase catalytic subunit(GCLC),and glutamate-cysteine ligase modifier subunit(GCLM)and the activity of NAD(P)H:quinone oxidoreductase 1(NQO1)when tested on HCT-116 cells using a cell-based assay system at 9 h.In addition,intraperitoneal administration of caffeic acid and protocatechuic acid to Ehrlich ascites carcinoma bearing mice suppressed tumor growth and angiogenesis.Conclusions:Caffeic acid and protocatechuic acid can modulate Nrf2 and inhibit Ehrlich ascites carcinoma cells.

Crystal Structure,Stability and Dissolution of a Drug-drug Molecular Salt Hydrate of Berberine with Protocatechuic Acid

A drug-drug molecular salt hydrate of berberine and protocatechuic acid has been prepared.Protocatechuic acid lost its carboxylic proton and turned to be protocatechuic anion to form a 1：1：1 organic salt hydrate with berberine,[C（20）H（18）NO4]＋[C7H5O4]^-·H2O（1）.Compound1 crystallizes in the triclinic system,space group P1 with a = 7.9849（5）,b =10.5437（5）,c = 14.3621（5）？,α = 77.983（4）,β = 82.900（4）,γ = 78.024（4）o,V = 1152.82（10） A^3,Mr= 507.48,Dc= 1.462 g/cm^3,μ = 0.929 mm^-1,F（000） = 532,Z = 2,the final R = 0.0488 and w R = 0.1322 for 3993 reflectionswith I 〉 2σ（I）.The hydrate exhibited good solid state stability against humidity,which may result from strong hydrogen-bonding interactions between water molecules and carboxylate groups.The hydrate also exhibited acceptable solubility and dissolution rate.

Protective and therapeutic effect of protocatechuic acid in assessment of letrozole- induced polycystic ovary syndrome in rats

Objective:To investigate the potential activity of protocatechuic acid in female Wistar rats with letrozole-induced polycystic ovary syndrome(PCOS).Methods:Thirty rats were divided into five groups of six each.Group 1 received 0.5%carboxy methyl cellulose orally and served as the normal control group;group 2 was treated orally with 1 mg/kg of letrozole daily for 21 days and served as the PCOS induced group;group 3 was orally administered with letrozole of 1 mg/kg for 21 days and further administered with standard drug of clomiphene citrate at a dose of 1 mg/kg body weight in 0.5%carboxy methyl cellulose per oral and served as the standard group;groups 4 and 5 were administered with letrozole of 1 mg/kg for 21 days and further treated with protocatechuic acid orally at low dose of 5 mg/kg body weight and high dose of 15 mg/kg body weight respectively for 15 days.At the end of the study period,rats were subjected for the estimation of invasive blood pressure and heart rate,biochemical estimations and antioxidant assay.In addition,ovarian histomorphology was examined.Results:The PCOS was confirmed in the letrozole induced rats with increased concentration of androgen,abnormal lipid levels,glucose,glycosylated haemoglobin and also depletion of antioxidants.After protocatechuic acid treatment,the increased levels of testosterone due to induction of PCOS were restored to normal levels.Additionally,there was a consistent decrease in luteinizing hormone and follicle stimulating hormone levels in the treatment groups,followed by decrease in the number of cysts after treatment with protocatechuic acid.Histopathological observations showed a remarkable recovery of the ovarian tissue and the presence of normalized structure of antral follicle.Protocatechuic acid treatment restored all the parameters to normalcy and abolished cysts formation in ovaries of female rats.Conclusions:Protocatechuic acid shows potential protective effects in letrozole-induced PCOS rats.The protective effect is comparable to that of clomiphene citrate and thus shows its potential in the treatment of PCOS.

Study on the effect of Danbei Yifei formula on pulmonary fibrosis based on network pharmacology and molecular docking technology

Objective:To determine the pharmacodynamic material basis and mechanism of Danbei Yifei formula on pulmonary fibrosis.Methods:Starting with the clear absorbed components of Danbei Yifei formula or the potential effective components in line with the five rules of Ribinsky,the network pharmacology method and technology of traditional Chinese medicine were used to predict and analyze the action targets of Danbei Yifei formula in vivo,such as Salvia miltiorrhiza,PINBEI,Taoren,etc.On the basis of enrichment analysis,the core pathway of Danbei Yifei formula in the treatment of pulmonary fibrosis was identified,and the binding energy of drug ligand and protein target was determined through molecular docking technology simulation and verification,and its affinity and stability were evaluated.To clarify the material basis and mechanism of Danbei Yifei formula in the treatment of pulmonary fibrosis.Result:The results of network pharmacology prediction of traditional Chinese medicine showed that Danbei Yifei formula contained 72 potential pharmacodynamic components and 26 corresponding targets,including CHRM1、MAPK14、CCL2、ADRB1、PTGS1、PPARG、ALOX5、Pde3a、CHRM2、Adrb2、TNF、JUN、Adora2a、LTA4H、CYP1A2、OPRD1、CHRM3、DRD2、OPRM1、ARG1、EDNRA、Il6st、TACR1、MMP1、MMP8、Ptgs2,which were related to pulmonary fibrosis and pulmonary fibrosis Lung related diseases are highly correlated.There were 26 Go items(P<0.05)in go functional enrichment analysis,including 22 biological process(BP),9 cellular component(CC)and 3 molecular function(MF)categories.The results of network pharmacology showed that many components,such as protocatechuic acid and aminosuccinic acid,had direct effects on known targets of pulmonary fibrosis.Conclusion:Danbei Yifei formula contains many effective components which have inhibitory effect on pulmonary fibrosis,and it may play its role through the mechanism of multi-component and multi-target synergistic effect.