Pharmacological and Clinical Studies of Medicinal Plants That Inhibit Dipeptidyl Peptidase-IV.

Dipeptidyl peptidase IV (DPP-IV) is an enzyme responsible for the degradation of the incretin hormone glucagon-like peptide-1 (GLP-1). DPP-IV plays a significant role in regulating blood glucose levels by modulating the activity of GLP-1. In the context of diabetes, DPP-IV inhibitors effectively block the activity of DPP-IV, hence mitigating the degradation of GLP-1. This, in turn, leads to an extension of GLP-1's duration of action, prolongs gastric emptying, enhances insulin sensitivity, and ultimately results in the reduction of blood glucose levels. Nonetheless, reported adverse events of DPP-IV inhibitors on T2DM patients make it essential to understand the activity and mechanism of these drugs, particularly viewed from the perspective of finding the effective and safe add-on medicinal plants, to be implemented in clinical practice. This review is intended to bring forth a thorough overview of plants that work by reducing DPP-IV activity, from computational technique, enzymatic study, animal experiments, and studies in humans. The articles were searched on PubMed using "Plants", "DPP-IV", "DPP-IV inhibitor", "GLP-1", "Type 2 diabetes", "diabetes", "in silico", "in vitro", "in vivo", "studies in human", "clinical study" as the query words, and filtered for ten years of publication period. Eighteen plants showed inhibition against DPP-IV as proven by in silico, in vitro, and in vivo studies; however, only ten plants were reported for efficacy in clinical studies. Several plant-based DPP-IV inhibitors, eg, Allium sativum, Morus Alba, Curcuma longa, Pterocarpus marsupium, and Taraxacum officinale, have established their functional role in inhibiting DPP-IV and have proven their effectiveness through studies in humans earning them a prominent place in therapeutic discovery.

Discovery of anthraquinones as DPP-IV inhibitors: Structure-activity relationships and inhibitory mechanism.

Dipeptidyl peptidase IV (DPP-IV) is an integrated type II transmembrane protein that reduces endogenous insulin contents and increases plasma glucose levels by hydrolyzing glucagon-like peptide-1 (GLP-1). Inhibition of DPP-IV regulates and maintains glucose homeostasis, making it an attractive drug target for the treatment of diabetes II. Natural compounds have tremendous potential to regulate glucose metabolism. In this study, we examined the DPP-IV inhibitory activity of a series of natural anthraquinones and synthetic structural analogues on DPP-IV using fluorescence-based biochemical assays. The inhibitory efficiency differed among anthraquinone compounds with different structures. Alizarin (7), aloe emodin (11), emodin (13) emerged the outstanding inhibitory potential for DPP-IV with IC50 values lower than 5 µM. To clarifying the inhibitory mechanism, inhibitory kinetics were performed, which showed that alizarin red S (8) and 13 were effective non-competitive inhibitors of DPP-IV, while alizarin complexone (9), rhein (12), and anthraquinone-2-carboxylic acid (23) were mixed inhibitors. Emodin was determined as inhibitor with the strongest DPP-IV-binding affinity determined via molecular docking. Structure-activity relationship (SAR) demonstrated that hydroxyl group at C-1 and C-8 sites and hydroxyl, hydroxymethyl or carboxyl group at the C-2 or C-3 site were very essential for DPP-IV inhibition, replacement of hydroxyl group with amino group at C-1 could led to an increase of the inhibitory potential. Further fluorescence imaging showed that both compounds 7 and 13 significantly inhibited DPP-IV activity in RTPEC cells. Overall, the results indicated that anthraquinones would be a natural functional ingredient for inhibiting DPP-IV and provided new ideas for searching and developing potential antidiabetic compounds.

Green tea extract exhibits antidiabetic effects partly through regulating dipeptidyl peptidase-4 expression in adipose tissue.

The antidiabetic effects of green tea have been demonstrated in clinical trials and epidemiological studies. This study investigated the antidiabetic effects of green tea extract (GTE) and its underlying molecular mechanisms using a leptin receptor-deficient db/db mouse model (Leprdb/db). Treatment with GTE for 2 weeks improved glucose tolerance and insulin sensitivity in Leprdb/db mice. In addition, GTE treatment reduced the body weight and adiposity of Leprdb/db mice. Furthermore, GTE treatment reduced pro-inflammatory gene expression, including nuclear factor kappa B (NF-κB) in white adipose tissue (WAT), and also reduced dipeptidyl peptidase-4 (DPP4) expression levels in WAT as well as in the serum. The promoter region of Dpp4 contains the NF-κB binding site, and DPP4 was found to be a direct target of NF-κB. Consistently, in vitro treatment of cells with GTE or its main constituent epigallocatechin gallate reduced lipopolysaccharide-induced NF-κB/DPP4 expression in 3T3-L1 adipocytes and RAW264.7 cells. Overall, our data demonstrated that GTE exerts an anti-diabetic effect by regulating the expression levels of NF-κB and DPP4 in WAT.

Protective effects and mechanisms of Lizhong decoction against non-alcoholic fatty liver disease in a rat model.

OBJECTIVE: To investigate the protective effects and molecular mechanisms of Lizhong decoction (, LZD) against non-alcoholic fatty liver disease (NAFLD). METHODS: Male Wistar rats were fed a high-fat diet for four weeks to induce NAFLD, and were administered LZD by gavage for four weeks. Potential therapeutic targets for NAFLD were analyzed using network pharmacology. Liver pathology was evaluated using Oil Red O and hematoxylin-eosin staining. Furthermore, mitochondrial function, lipid metabolism, oxidative stress, and inflammatory response were examined. RESULTS: Rats with NAFLD exhibited high levels of hepatic damage and cholesterol deposition. Moreover, apoptosis was increased, superoxide dismutase and glutathione content were reduced, malondialdehyde content was increased, and the protein expression of inflammatory cytokines and p-c-Jun N-terminal kinase was increased. The LZD treatment ameliorated mitochondrial dysfunction, reduced liver damage, inhibited oxidative stress and inflammatory response, upregulated peroxisome proliferator-activated receptor (PPAR)-γ expression, and suppressed dipeptidyl peptidase 4 (DPP4) expression in the liver. CONCLUSION: It was found that LZD alleviates NAFLD by activating PPAR-γ and inhibiting DPP4.

Hypoglycemic peptide-enriched hydrolysates of Corbicula fluminea and Chlorella sorokiniana possess synergistic hypoglycemic activity through inhibiting α-glucosidase and dipeptidyl peptidase-4 activity.

BACKGROUND: The prevalence of diabetes mellitus worldwide has increased in recent decades. Maintaining the level of blood glucose is the most basic and important issue for diabetics. This study aimed to investigate the hypoglycemic activity of a combination of hypoglycemic peptide-enriched hydrolysates of Corbicula fluminea (ACH) and Chlorella sorokiniana (PCH). RESULTS: Combined supplementation of ACH and PCH synergistically inhibited α-glucosidase and DPP4 activities in vitro. After 4 weeks of treatment with ACH and/or PCH, the plasma glucose concentration and insulin, homeostasis model assessment-estimated insulin resistance (HOMA-IR), total cholesterol (TC) and triglyceride (TG) levels significantly decreased. The hypoglycemic peptides in ACH and PCH were purified and assayed for α-glucosidase and DPP4 activity. The hypoglycemic peptides in ACH and PCH effectively decreased α-glucosidase and DPP4 activities. In silico assays showed that these two peptide types have different docking poses, which determined their inhibitory effect against α-glucosidase and DPP4 activity. CONCLUSION: Combined treatment with hypoglycemic peptide-enriched ACH and PCH could modulate blood glucose by synergistically inhibiting α-glucosidase and DPP4 activities. © 2021 Society of Chemical Industry.

Virtual screening of dipeptidyl peptidase-4 inhibitors using quantitative structure-activity relationship-based artificial intelligence and molecular docking of hit compounds.

Dipeptidyl peptidase-4 (DPP-4) inhibitors are becoming an essential drug in the treatment of type 2 diabetes mellitus; however, some classes of these drugs exert side effects, including joint pain and pancreatitis. Studies suggest that these side effects might be related to secondary inhibition of DPP-8 and DPP-9. In this study, we identified DPP-4-inhibitor hit compounds selective against DPP-8 and DPP-9. We built a virtual screening workflow using a quantitative structure-activity relationship (QSAR) strategy based on artificial intelligence to allow faster screening of millions of molecules for the DPP-4 target relative to other screening methods. Five regression machine learning algorithms and four classification machine learning algorithms were applied to build virtual screening workflows, with the QSAR model applied using support vector regression (R2pred 0.78) and the classification QSAR model using the random forest algorithm with 92.2% accuracy. Virtual screening results of > 10 million molecules obtained 2 716 hits compounds with a pIC50 value of > 7.5. Additionally, molecular docking results of several potential hit compounds for DPP-4, DPP-8, and DPP-9 identified CH0002 as showing high inhibitory potential against DPP-4 and low inhibitory potential for DPP-8 and DPP-9 enzymes. These results demonstrated the effectiveness of this technique for identifying DPP-4-inhibitor hit compounds selective for DPP-4 and against DPP-8 and DPP-9 and suggest its potential efficacy for applications to discover hit compounds of other targets.

Protease Inhibitors Purified from the Canola Meal Extracts of Two Genetically Diverse Genotypes Exhibit Antidiabetic and Antihypertension Properties.

Valorization of vegetable oil waste residues is gaining importance due to their high protein and polyphenol contents. Protease inhibitors (PIs), proteins from these abundantly available waste residues, have recently gained importance in treating chronic diseases. This research aimed to use canola meal of genetically diverse Brassica napus genotypes, BLN-3347 and Rivette, to identify PIs with diverse functionalities in therapeutic and pharmacological applications. The canola meal PI purification steps involved: native PAGE and trypsin inhibition activity, followed by ammonium sulfate fractionation, anion exchange, gel filtration, and reverse-phase chromatography. The purified PI preparations were characterized using SDS-PAGE, isoelectric focusing (IEF), and N terminal sequencing. SDS-PAGE analysis of PI preparations under native reducing and nonreducing conditions revealed three polymorphic PIs in each genotype. The corresponding IEF of the genotype BLN-3347, exhibited three acidic isoforms with isoelectric points (pI) of 4.6, 4.0, and 3.9, while Rivette possessed three isoforms, exhibiting two basic forms of pI 8.65 and 9.9, and one acidic of pI 6.55. Purified PI preparations from both the genotypes displayed dipeptidyl peptidase-IV (DPP-IV) and angiotensin-converting enzyme (ACE) inhibition activities; the BLN-3347 PI preparation exhibited a strong inhibitory effect with lower IC50 values (DPP-IV 37.42 µg/mL; ACE 129 µg/mL) than that from Rivette (DPP-IV 67.97 µg/mL; ACE 376.2 µg/mL). In addition to potential human therapy, these highly polymorphic PIs, which can inhibit damaging serine proteases secreted by canola plant pathogens, have the potential to be used by canola plant breeders to seek qualitative trait locus (QTLs) linked to genes conferring resistance to canola diseases.

Anti-insulin resistance effect of constituents from Senna siamea on zebrafish model, its molecular docking, and structure-activity relationships.

Senna siamea has been used as an antidiabetic drug since antiquity. With regard to traditional Thai medicine, the use of S. siamea was described for diabetes therapy. To understand the molecular mechanism regarding insulin resistance. Pure compounds were isolated from wood extract. We studied their biological activities on insulin-resistance using an in vivo zebrafish model. We also performed an in silico study; molecular docking, and in vitro study by taking advantage of the enzyme inhibitory activities of α-glucosidase, PTP1B, and DPP-IV. Based on the preliminary investigation that ethyl acetate and ethanol extracts have potent effects against insulin resistance on zebrafish larvae, five compounds were isolated from two fractions following: resveratrol, piceatannol, dihydropiceatannol, chrysophanol, and emodin. All of the isolated compounds had anti-insulin resistance effects on zebrafish larvae. Resveratrol, piceatannol, and dihydropiceatannol also demonstrated inhibitory effects against α-glucosidase. Chrysophanol and emodin inhibited PTP1B activity, while resveratrol showed a DPP-IV inhibition effect via the molecular docking. The results of enzyme assay were similar. In conclusions, S. siamea components demonstrated effects against insulin resistance. The chemical structure displayed identical biological activity to that of the compounds. Therefore, S. siamea wood extract and their components are potential therapeutic options in the treatment of diabetes.

Alleviation of diabetes mellitus through the restoration of ß-cell function and lipid metabolism by Aloe vera (L.) Burm. f. extract in obesogenic WNIN/GR-Ob rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Aloe vera (L.) Burm. f. extract has been medicinally used for over 5000 years in different cultures for its curative and therapeutic properties ranging from dermatitis to diabetes. It has been demonstrated to alleviate diabetes through its protective effects on pancreatic islets and by improving insulin secretion. AIM OF THE STUDY: To investigate the simultaneous effect of ethanolic A. vera gel extract on diabetes and obesogenic milieu in Streptozotocin-induced WNIN/GR-Ob mutant obese rats. MATERIALS AND METHODS: A total of 30 rats were grouped equally into WNIN/GR-Ob control (received water as a vehicle), WNIN/GR-Ob Diabetic rats (Streptozotocin-35 mg/kg bw), WNIN/GR-Ob Diabetic rats + Sitagliptin (10 mg/kg bw), WNIN/GR-Ob Diabetic rats + A. vera (300 mg/kg bw) and GR-Ob control + A. vera (300 mg/kg bw). After 4 weeks of treatment, fasting blood glucose, serum insulin, Homeostatic Model Assessment - Insulin Resistance and ß-cell function, glucose-stimulated insulin secretion, Dipeptidyl peptidase-IV activity, and lipid profiles were studied. In addition, ultrastructural analysis of isolated islets and dual-energy X-ray absorptiometry analysis for body composition were also carried out. RESULTS: The A. vera treated group showed a significant reduction (p < 0.05) in triglyceride, Very low-density lipoprotein levels, Triglyceride to High-density lipoprotein ratio as well as fasting blood glucose levels and DPP-IV activity with a concomitant increase in the serum insulin levels. The increase in IR was observed in both WNIN/GR-Ob control and diabetic rats with a significant decrease in ß-cell function in the diabetic rats as per Homeostatic Model Assessment values. Oral administration of A. vera was effective in both reducing Homeostatic Model Assessment-Insulin Resistance and increasing Homeostatic Model Assessment-ß values. Also, the treated group demonstrated preservation of islets and a significant increase (p < 0.05) in the diameter of ß-cell as evident through Scanning electron microscope analysis. The increase in lean body mass was manifested in the treated group with a reduction in Fat percent in comparison with other groups. CONCLUSION: The beneficial effects of A. vera in WNIN/GR-Ob strain may be attributed to its ability to lower lipid profile thus improve insulin sensitivity and/or modulating ß-cell function. Thus, it has great therapeutic potential as an herbal remedy for the treatment of diabetes and associated adverse effects such as obesity. The exact mechanism underlying the observation needs to be investigated further to explore the anti-obesity and anti-diabetic properties of A. vera and advocate its potential application as alternative medicine.

Magnetic ligand fishing using immobilized DPP-IV for identification of antidiabetic ligands in lingonberry extract.

In this work, a new magnetic ligand fishing probe for discovery of DPP-IV inhibitory ligands was developed and it was tested as a proof of concept on the fruit extract of Vaccinium vitis-idaea (lingonberry). The ligands were shown to have appreciable dipeptidyl peptidase IV (DPP-IV) inhibitory activity (IC50: 31.8 µg mL-1).) Inhibition of DPP-IV is a well-known therapeutic approach for management of type 2 diabetes (T2D). DPP-IV was successfully immobilized onto magnetic beads and was shown to retain its catalytic activity and selectivity over a model mixture. A total of four ligands were successfully fished out and identified as cyanidin-3-galactoside (2), cyanidin-3-arabinoside (3), proanthocynidin A (4), and 10-carboxyl-pyranopeonidin 3-O-(6″-O-p-coumaroyl)-glucoside (5) using HPLC/HRMS.

Role of zonulin and GLP-1/DPP-IV in alleviation of diabetes mellitus by peptide/polypeptide fraction of Aloe vera in streptozotocin- induced diabetic wistar rats.

ETHNO-PHARMACOLOGICAL RELEVANCE: The genus Aloe has a long history of usage in medicine. Aloe barbadensis Miller, commonly known as Aloe vera, is said to possess anti-diabetic, anti-inflammatory, anti-cancer, anti-microbial, immunomodulation, wound healing properties. AIM OF THE STUDY: In diabetes mellitus, loss in intestinal permeability is observed with high levels of zonulin and low levels of glucagon-like peptide-1 (GLP-1) leading to hyperglycemia. The aim of the study was to understand the role of peptide/polypeptide fraction (PPF) of Aloe vera in the alleviation of diabetes through maintaining the intestinal permeability by regulating the zonulin and GLP-1 levels. MATERIALS AND METHODS: The PPF of Aloe vera was obtained through trichloroacetic acid precipitation. The anti-diabetic potential of the PPF was tested through DPP-IV inhibition, glucose diffusion assay, and by using Rin-m5F cells. The anti-diabetic potential of the PPF was tested at a dose of 0.450 mg/kg bw in vivo using streptozotocin-induced diabetic Wistar rats. The effect of PPF on fasting plasma glucose, insulin, glucagon, Zonulin, GLP-1, DPP-IV, levels were studied in diabetic rats. The histopathological studies of the pancreas, small intestine, and liver were carried out for organ-specific effects. RESULTS: PPF has the ability to reduce fasting plasma glucose levels with concomitant increase in insulin levels in streptozotocin-induced diabetic rats. It was also observed that increase in GLP-1 levels with a decrease in DPP-IV and zonulin levels thereby mitigating the loss of intestinal permeability. These findings correlate with the small intestine's histopathological observation where the excessive proliferation of epithelium in the small intestine of diabetic rats was reduced after PPF treatment. CONCLUSION: These results suggest that the PPF of Aloe vera alleviates diabetes through islet cell rejuvenation via GLP-1/DPP-IV pathway and thereby suggesting the usage of PPF as an alternate medicine for diabetes mellitus with the possibility to reduce the intestinal permeability and zonulin levels.

Rosa canina L. Can Restore Endoplasmic Reticulum Alterations, Protein Trafficking and Membrane Integrity in a Dextran Sulfate Sodium-Induced Inflammatory Bowel Disease Phenotype.

Rosa canina L. is a natural polyphenol-rich medicinal plant that exhibits antioxidant and anti-inflammatory activities. Recent in vivo studies have demonstrated that a methanol extract of Rosa canina L. (RCME) has reversed an inflammatory bowel disease (IBD)-like phenotype that has been triggered by dextran sulfate sodium (DSS) in mice. In the current study, we investigated the effects of RCME on perturbations of cellular mechanisms induced by DSS-treatment of intestinal Caco-2 cells, including stress response in the endoplasmic reticulum (ER), protein trafficking and sorting as well as lipid rafts integrity and functional capacities of an intestinal enzyme. 6 days post-confluent cells were treated for 24 h with DSS (3%) or simultaneously with DSS (3%) and RCME (100 µg/mL) or exclusively with RCME (100 µg/mL) or not treated. The results obtained demonstrate the ability of RCME to counteract the substantial increase in the expression levels of several ER stress markers in DSS-treated cells. Concomitantly, the delayed trafficking of intestinal membrane glycoproteins sucrase-isomaltase (SI) and dipeptidyl peptidase 4 (DPP4) induced by DSS between the ER and the Golgi has been compromised by RCME. Furthermore, RCME restored the partially impaired polarized sorting of SI and DPP4 to the brush border membrane. An efficient sorting mechanism of SI and DPP4 is tightly associated with intact lipid rafts structures in the trans-Golgi network (TGN), which have been distorted by DSS and normalized by RCME. Finally, the enzymatic activities of SI are enhanced in the presence of RCME. Altogether, DSS treatment has triggered ER stress, impaired trafficking and function of membrane glycoproteins and distorted lipid rafts, all of which can be compromised by RCME. These findings indicate that the antioxidants in RCME act at two major sites in Caco-2 cells, the ER and the TGN and are thus capable of maintaining the membrane integrity by correcting the sorting of membrane-associated proteins.

Effects of 22 traditional anti-diabetic medicinal plants on DPP-IV enzyme activity and glucose homeostasis in high-fat fed obese diabetic rats.

The present study investigated the effects of hot water extracts of 22 medicinal plants used traditionally to treat diabetes on Dipeptidyl peptidase-IV (DPP-IV) activity both in vitro and in vivo in high-fat fed (HFF) obese-diabetic rats. Fluorometric assay was employed to determine the DPP-IV activity. For in vivo studies, HFF obese-diabetic rats were fasted for 6 h and blood was sampled at different times before and after the oral administration of the glucose alone (18 mmol/kg body weight) or with either of the four most active plant extracts (250 mg/5 ml/kg, body weight) or established DPP-IV inhibitors (10 µmol/5 ml/kg). DPP-IV inhibitors: sitagliptin, vildagliptin and diprotin A, decreased enzyme activity by a maximum of 95-99% (P<0.001). Among the 22 natural anti-diabetic plants tested, AnogeissusLatifolia exhibited the most significant (P<0.001) inhibitory activity (96 ± 1%) with IC50 and IC25 values of 754 and 590 µg/ml. Maximum inhibitory effects of other extracts: Aegle marmelos, Mangifera indica, Chloropsis cochinchinensis, Trigonella foenum-graecum and Azadirachta indica were (44 ±7%; 38 ± 4%; 31±1%; 28±2%; 27±2%, respectively). A maximum of 45% inhibition was observed with >25 µM concentrations of selected phytochemicals (rutin). A.latifolia, A. marmelos, T. foenum-graecum and M. indica extracts improved glucose tolerance, insulin release, reduced DPP-IV activity and increased circulating active GLP-1 in HFF obese-diabetic rats (P<0.05-0.001). These results suggest that ingestion of selected natural anti-diabetic plants, in particular A. latifolia, A. marmelos, T. foenum-graecum and M. indica can substantially inhibit DPP-IV and improve glucose homeostasis, thereby providing a useful therapeutic approach for the treatment of T2DM.

Synthesis, Biological Evaluation, and QPLD Studies of Piperazine Derivatives as Potential DPP-IV Inhibitors.

BACKGROUND: Diabetes mellitus is a serious global health issue, currently affecting 425 million people and is set to affect over 690 million people by 2045. It is a chronic disease characterized by hyperglycemia due to relative or absolute insulin hormone deficiency. Dipeptidyl peptidase- IV (DPP-IV) inhibitors are hypoglycemic agents augmenting the action of the incretin hormones that stimulate insulin secretion from the pancreatic beta cells. OBJECTIVE: In this study, synthesis and biological evaluation of seven piperazine derivatives 3a-g was carried out. METHODS: The synthesized molecules were characterized using proton-nuclear magnetic resonance, carbon-nuclear magnetic resonance, infrared spectroscopy and mass spectrometry. RESULTS: In vitro biological evaluation study showed comparable DPP-IV inhibitory activity for the targeted compounds ranging from 19%-30% at 100 µM concentration. Furthermore, the in vivo hypoglycemic activity of 3d was evaluated using streptozotocin-induced diabetic mice. It was found that compound 3d significantly decreased the blood glucose level when the diabetic group treated with 3d was compared to the control diabetic group. Quantum-Polarized Ligand Docking (QPLD) studies demonstrate that 3a-g fit the binding site of DPP-IV enzyme and form H-bonding with the backbones of R125, E205, E206, K554, W629, Y631, Y662, R669, and Y752. CONCLUSION: Piperazine derivatives were successfully found to be new scaffolds as potential DPP-IV inhibitors.

Anti-hyperglycaemic and insulin-releasing effects of Camellia sinensis leaves and isolation and characterisation of active compounds.

Anti-diabetic actions of Camellia sinensis leaves, used traditionally for type 2 diabetes (T2DM) treatment, have been determined. Insulin release, membrane potential and intra-cellular Ca were studied using the pancreatic ß-cell line, BRIN-BD11 and primary mouse pancreatic islets. Cellular glucose-uptake/insulin action by 3T3-L1 adipocytes, starch digestion, glucose diffusion, dipeptidyl peptidase-4 (DPP-IV) activity and glycation were determined together with in vivo studies assessing glucose homoeostasis in high-fat-fed (HFF) rats. Active phytoconstituents with insulinotropic activity were isolated using reversed-phase HPLC, LCMS and NMR. A hot water extract of C. sinensis increased insulin secretion in a concentration-dependent manner. Insulinotropic effects were significantly reduced by diazoxide, verapamil and under Ca-free conditions, being associated with membrane depolarisation and increased intra-cellular Ca2+. Insulin-releasing effects were observed in the presence of KCl, tolbutamide and isobutylmethylxanthine, indicating actions beyond K+ and Ca2+ channels. The extract also increased glucose uptake/insulin action in 3T3L1 adipocyte cells and inhibited protein glycation, DPP-IV enzyme activity, starch digestion and glucose diffusion. Oral administration of the extract enhanced glucose tolerance and insulin release in HFF rats. Extended treatment (250 mg/5 ml per kg orally) for 9 d led to improvements of body weight, energy intake, plasma and pancreatic insulin, and corrections of both islet size and ß-cell mass. These effects were accompanied by lower glycaemia and significant reduction of plasma DPP-IV activity. Compounds isolated by HPLC/LCMS, isoquercitrin and rutin (464·2 Da and 610·3 Da), stimulated insulin release and improved glucose tolerance. These data indicate that C. sinensis leaves warrant further evaluation as an effective adjunctive therapy for T2DM and source of bioactive compounds.

Antihyperglycaemic activity of ethylacetate extract of Chlorophytum alismifolium in type 2 diabetes: The involvement of peroxisome proliferator-activated receptor-γ and dipeptidyl peptidase-4.

OBJECTIVE: This research is to investigate the antihyperglycaemic activity and the underlying mechanisms of action of the ethylacetate extract of Chlorophytum alismifolium (EACA) tubers in a type 2 diabetes model. METHODS: The tubers were processed and sequentially extracted in hexane followed by ethylacetate, using a Soxhlet apparatus, and subjected to gas chromatography-mass spectrometry (GC-MS). The acute toxicity of EACA was investigated in albino Wistar rats. An antihyperglycaemic study was carried out using high-fat diet (pelletized diet and margarine in the ratio of 10:1 and 20% fructose solution) and streptozotocin-induced hyperglycaemic Wistar rats. The effects of the extract (150, 300 and 600 mg/kg) on blood glucose level, insulin, peroxisome proliferator-activated receptor-γ (PPAR-γ) and dipeptidyl peptidase-4 (DPP-4) were evaluated using enzyme-linked immunosorbent assay. RESULTS: The oral median lethal dose in Wistar rats was estimated to be > 5000 mg/kg. Treatment with EACA at all doses significantly reduced the fasting blood glucose levels, compared to the hyperglycaemic control, and over time. Administration of EACA increased the serum insulin and PPAR-γ levels while decreasing DPP-4 levels. GC-MS analysis revealed the presence of 13 compounds, with isothiazole and isoxazolidine covering total area of 24.6% and 22.69%, respectively. CONCLUSION: The findings from this study showed that EACA has important compounds with beneficial effect in type 2 diabetes and acts by increasing insulin secretion and PPAR-γ level and decreasing DPP-4 activity.

Inhibitory evaluation of Curculigo latifolia on α-glucosidase, DPP (IV) and in vitro studies in antidiabetic with molecular docking relevance to type 2 diabetes mellitus.

The inhibition of α-glucosidase and DPP enzymes capable of effectively reducing blood glucose level in the management of type 2 diabetes. The purpose of the present study is to evaluate the inhibitory potential of α-glucosidase and DPP (IV) activity including with the 2-NBDG uptake assay and insulin secretion activities through in vitro studies. The selected of active compounds obtained from the screening of compounds by LC-MS were docked with the targeted enzyme that involved in the mechanism of T2DM. From the results, root extracts displayed a better promising outcome in α-glucosidase (IC50 2.72 ± 0.32) as compared with the fruit extracts (IC50 3.87 ± 0.32). Besides, root extracts also displayed a better activity in the inhibition of DPP (IV), enhance insulin secretion and glucose uptake activity. Molecular docking results revealing that phlorizin binds strongly with α-glucosidase, DPP (IV) and Insulin receptor (IR) enzymes with achieving the lowest binding energy value. The present work suggests several of the compounds have the potential that contribute towards inhibiting α-glucosidase and DPP (IV) and thus effective in lowering post-prandial hyperglycaemia.

Identification and Comparison of Peptides from Chickpea Protein Hydrolysates Using Either Bromelain or Gastrointestinal Enzymes and Their Relationship with Markers of Type 2 Diabetes and Bitterness.

The chickpea (Cicer arietinum L.) is one of the most important pulses worldwide. The objective was to identify, compare and evaluate peptides from chickpea hydrolysates produced by two enzymatic treatments. The antidiabetic potential and bitterness of the peptides and induction of bitter receptors were identified in silico. Proteins were isolated from the Kabuli variety. Peptides were produced from the proteins using a simulated digestive system (pepsin/pancreatin, 1:50 Enzyme/Protein, E/P), and these peptides were compared with those produced via bromelain hydrolysis (1:50 E/P). The protein profiles, sequences and characteristics of the peptides were evaluated. The biochemical inhibition and molecular docking of dipeptidyl peptidase-IV (DPP-IV), α-amylase and α-glucosidase were also studied. The molecular docking identified peptides from enzymatic hydrolysis as inhibitors of DPP-IV. The high hydrophobicity of the peptides indicated the potential for bitterness. There was no correlation between peptide length and DPP-IV binding. Peptides sequenced from the pepsin/pancreatin hydrolysates, PHPATSGGGL and YVDGSGTPLT, had greater affinity for the DPP-IV catalytic site than the peptides from the bromelain hydrolysates. These results are in agreement with their biochemical inhibition, when considering the inhibition of sitagliptin (54.3 µg/mL) as a standard. The bitter receptors hTAS2R38, hTAS2R5, hTAS2R7 and hTAS2R14 were stimulated by most sequences, which could be beneficial in the treatment of type 2 diabetes. Chickpea hydrolysates could be utilized as functional ingredients to be included in the diet for the prevention of diabetes.

Abelmoschus esculentus subfractions attenuate Aß and tau by regulating DPP-4 and insulin resistance signals.

BACKGROUND: Insulin resistance could be associated with the development of Alzheimer disease (AD). The neuropathological hallmarks of AD are beta amyloid (Aß) produced from sequential cleavage initiated by ß-secretase and degraded by insulin degradation enzyme (IDE), as well as hyperphosphorylation of tau (p-tau). Insulin action involves the cascades of insulin receptor substrates (IRS) and phosphatidylinositol 3-kinase (PI3K), while phosphorylation of IRS-1 at ser307 (p-ser307IRS-1) hinders the response. Our previous report suggested dipeptidyl peptidase-4 (DPP-4) is crucial to insulin resistance, and the subfractions of Abelmoschus esculentus (AE), F1 and F2, attenuate the signaling. Here we aim to investigate whether AE works to reduce Aß generation via regulating DPP4 and insulin resistance. METHODS: The subfractions F1 and F2 were prepared according to a succession of procedures. F1 was composed by quercetin glycosides and triterpene ester, and F2 contained a large amount of polysaccharides. The in vitro insulin resistance model was established by SK-N-MC cell line treated with palmitate. MTT was used to define the dose range, and thereby Western blot, ELISA, and the activity assay were used to detect the putative markers. One-way ANOVA was performed for the statistical analysis. RESULTS: Treatment of palmitate induced the level of p-ser307IRS-1. Both F1 and F2 effectively decrease p-ser307IRS-1, and recover the expression of p-PI3K. However, the expression of total IRS plunged with 25 µg/mL of F1, while descended steadily with 5 µg/mL of F2. As palmitate increased the levels of Aß40 and Aß42, both AE subfractions were effective to reduce Aß generation of and ß-secretase activity, but IDE was not altered in any treatment conditions. The expression of DPP4 was also accompanied with insulin resistance signals. Inhibition of DPP4 attenuated the activity of ß-secretase and production of Aß. Moreover, the present data revealed that both AE subfractions significantly decrease the level of p-Tau. CONCLUSIONS: In conclusion, we demonstrated that AE would be a potential adjuvant to prevent insulin resistance and the associated pathogenesis of AD, and F2 seems more feasible to be developed.

Grape seed procyanidins suppress the apoptosis and senescence of chondrocytes and ameliorates osteoarthritis via the DPP4-Sirt1 pathway.

Osteoarthritis (OA) is a complicated pathological condition affecting thousands of people around world, many with substantial unmet medical care needs and without any effective therapies. Previous study has indicated that glucagon-like peptide-1 (GLP-1) is involved in the pathological progress of osteoarthritis; however, the role of dipeptidase-4 (DPP4), which regulates the degradation of GLP-1, still remains unclear in osteoarthritis. Herein, after comparing normal mouse cartilage tissues with OA mouse cartilage tissues by histological analysis, we found out that DPP4 was highly expressed in OA cartilage tissues. To investigate the role of DPP4 in osteoarthritis, the apoptosis and senescence of chondrocytes were found to be decreased in vitro when DPP4 was downregulated by siRNA in chondrocytes. Further study showed that the inhibition of DPP4 by procyanidins, a grape seed extract, attenuated apoptosis and senescence of chondrocytes in vitro. Furthermore, the results showed that DPP4 inhibition protects cartilage by activating Sirt1, which has been reported to be associated with many pathophysiological processes, particularly in age-related diseases, such as neurodegenerative disorders and osteoarthritis. In addition, animal experiment results demonstrated that procyanidins were capable of ameliorating the progression of osteoarthritis through the inhibition of DPP4. This study provides a competitive target for the therapeutic treatment of osteoarthritis, and procyanidins were shown to be a potential medicine for the restoration of the effects of osteoarthritis.