Identification of PPARgamma partial agonists of natural origin (II): in silico prediction in natural extracts with known antidiabetic activity

Exploring antidiabetic potential of a polyherbal formulation Madhurakshak Activ: An in vitro and in silico study

Madhurakshak Activ (MA), a commercial polyherbal antidiabetic preparation is known to manage diabetes mellitus (DM) by reducing blood glucose levels. However, lacks systematic mechanistic evaluation for their molecular and cellular mode of actions. In the present study, hydro-alcoholic and aqueous extract of MA were evaluated for their effects on glucose adsorption, diffusion, amylolysis kinetics and transport across the yeast cells using in vitro techniques. Bioactive compounds identified from MA by LC-MS/MS were assessed for their binding potential against DPP-IV and PPARγ via an in silico approach. Our results revealed that the adsorption of glucose increased dose dependently (5 mM -100 mM). Both extracts exhibited linear glucose uptake into the yeast cells (5 mM - 25 mM), whereas glucose diffusion was directly proportional to time (30-180 min). Pharmacokinetic analysis revealed drug-like properties and low toxicity levels for all the selected compounds. Among the tested compounds, 6-hydroxyluteolin (-8.9 against DPP-IV and PPARγ) and glycyrrhetaldehyde (DPP-IV -9.7 and PPARγ -8.5) have exhibited higher binding affinity compared to the positive control. Therefore, the above compounds were further considered for molecular dynamics simulation which showed stability of the docked complexes. Hence, studied mode of actions might produce a concerted role of MA in increasing the rate of glucose absorption and uptake followed by the in silico studies which suggest that the compounds identified from MA may inhibit DPP-IV and PPARγ phosphorylation.

Identification of human phosphoglycerate mutase 1 (PGAM1) inhibitors using hybrid virtual screening approaches

PGAM1 plays a critical role in cancer cell metabolism through glycolysis and different biosynthesis pathways to promote cancer. It is generally known as a crucial target for treating pancreatic ductal adenocarcinoma, the deadliest known malignancy worldwide. In recent years different studies have been reported that strived to find inhibitory agents to target PGAM1, however, no validated inhibitor has been reported so far, and only a small number of different inhibitors have been reported with limited potency at the molecular level. Our in silico studies aimed to identify potential new PGAM1 inhibitors that could bind at the allosteric sites. At first, shape and feature-based models were generated and optimized by performing receiver operating characteristic (ROC) based enrichment studies. The best query model was then employed for performing shape, color, and electrostatics complementarity-based virtual screening of the ChemDiv database. The top two hundred and thirteen hits with greater than 1.2 TanimotoCombo score were selected and then subjected to structure-based molecular docking studies. The hits yielded better docking scores than reported compounds, were selected for subsequent structural similarity-based clustering analysis to select the best hits from each cluster. Molecular dynamics simulations and binding free energy calculations were performed to validate their plausible binding modes and their binding affinities with the PGAM1 enzyme. The results showed that these compounds were binding in the reported allosteric site of the enzyme and can serve as a good starting point to design better active selective scaffolds against PGAM1enzyme.

Bioactivity-Guided Fractionation and Identification of Antidiabetic Compound of Syzygium polyanthum (Wight.)'s Leaf Extract in Streptozotocin-Induced Diabetic Rat Model

(1) Background: An earlier study on the hypoglycemic activity of S. polyanthum (Wight.) leaf methanol extract identified squalene as the major chemical compound. The present study was conducted to assess the hypoglycemic effect of fractions and subfractions of the methanol extract of S. polyanthum compared to the squalene using a bioassay-guided in vivo study. (2) Methods: The methanol extract was fractionated using the liquid−liquid fractionation method. Streptozotocin-induced type 1 diabetic rat was used to study the hypoglycemic effect. (3) Results: The findings showed that chloroform fraction significantly (p < 0.05) lowered blood glucose levels of diabetic rats as compared to the control. Further fractionation of chloroform fraction yielded subfraction-1 and -2, whereby subfraction-1 exhibited a higher blood-glucose-lowering effect. The lipid profile test showed that the total cholesterol level of subfraction-1 and squalene-treated groups decreased significantly (p < 0.05). An immunohistochemistry study revealed that none of the treatments regenerated pancreatic β-cells. Gas chromatography−mass spectrophotometer analysis identified the presence of squalene in the active methanol extract, chloroform fraction, and subfraction-1. In silico analysis revealed a higher affinity of squalene against protein receptors that control lipid metabolism than metformin. (4) Conclusions: Data obtained from the present work suggested the crude methanol extract exerted the highest hypoglycemic effect compared to fraction, subfraction, and squalene, confirming synergistic effect may be responsible for the hypoglycemic activity of S. polyanthum.

The Molecular Mechanisms of Hypoglycemic Properties and Safety Profiles of Swietenia Macrophylla Seeds Extract: A Review

BACKGROUND: Insulin resistance (IR) is known as the root cause of type 2 diabetes; hence, it is a substantial therapeutic target. Nowadays, studies have shifted the focus to natural ingredients that have been utilized as a traditional diabetes treatment, including Swietenia macrophylla. Accumulating evidence supports the hypoglycemic activities of S. macrophylla seeds extract, although its molecular mechanisms have yet to be well-established. AIM: This review focuses on the hypoglycemic molecular mechanisms of S. macrophylla seeds extract and its safety profiles. METHODS: An extensive search of the latest literature was conducted from four main databases (PubMed, Scopus, Science Direct, and Google Scholar) using several keywords: “swietenia macrophylla, seeds, and diabetes;” “swietenia macrophylla, seeds, and oxidative stress;” “swietenia macrophylla, seeds, and inflammation;” “swietenia macrophylla, seeds, and GLUT4;” and “swietenia macrophylla, seeds, and toxicities.” RESULTS: The hypoglycemic activities occur through modulating several pathways associated with IR and T2D pathogenesis. The seeds extract of S. macrophylla modulates oxidative stress by decreasing malondialdehyde (MDA), oxidized low-density lipoprotein, and thiobarbituric acid-reactive substances while increasing antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and catalase). Another propose mechanism is the modulating of the inflammatory pathway by attenuating nuclear factor kappa β, tumor necrosis factor α, inducible nitric oxide synthase, and cyclooxygenase 2. Some studies have shown that the extract can also control phosphatidylinositol-3-kinase/ Akt (PI3K/Akt) pathway by inducing glucose transporter 4, while suppressing phosphoenolpyruvate carboxykinase. Moreover, in vitro cytotoxicity and in vivo toxicity studies supported the safety profile of S. macrophylla seeds extract with the LD50 higher than 2000 mg/kg. CONCLUSION: The potential of S. macrophylla seeds as antidiabetic candidate is supported by many studies that have documented their non-toxic and hypoglycemic effects, which involve several molecular pathways.

Research progress of indole compounds with potential antidiabetic activity

New types of antidiabetic agents are continually needed with diabetes becoming the epidemic in the world. Indole alkaloids play an important role in natural products owing to their variable structures and versatile biological activities like anticonvulsant, anti-inflammatory, antidiabetic, antimicrobial, and anticancer activities, which are a promising source of novel antidiabetic drugs discovery. The synthesized indole derivatives possess similar properties to natural indole alkaloids. In the last two decades, more and more indole derivatives have been designed and synthesized for searching their bioactivities. This present review describes comprehensive structures of indole compounds with the potential antidiabetic activity including natural indole alkaloids and the synthetic indole derivatives based on the structure classification, summarizes their approaches isolated from natural sources or by synthetic methods, and discusses the antidiabetic effects and the mechanisms of action. Furthermore, this review also provides briefly synthetic procedures of some important indole derivatives.

Characterization of an Agarophyton chilense Oleoresin Containing PPARγ Natural Ligands with Insulin-Sensitizing Effects in a C57Bl/6J Mouse Model of Diet-Induced Obesity and Antioxidant Activity in Caenorhabditis elegans

The biomedical potential of the edible red seaweed Agarophyton chilense (formerly Gracilaria chilensis) has not been explored. Red seaweeds are enriched in polyunsaturated fatty acids and eicosanoids, which are known natural ligands of the PPARγ nuclear receptor. PPARγ is the molecular target of thiazolidinediones (TZDs), drugs used as insulin sensitizers to treat type 2 diabetes mellitus. Medical use of TZDs is limited due to undesired side effects, a problem that has triggered the search for selective PPARγ modulators (SPPARMs) without the TZD side effects. We produced Agarophyton chilense oleoresin (Gracilex®), which induces PPARγ activation without inducing adipocyte differentiation, similar to SPPARMs. In a diet-induced obesity model of male mice, we showed that treatment with Gracilex® improves insulin sensitivity by normalizing altered glucose and insulin parameters. Gracilex® is enriched in palmitic acid, arachidonic acid, oleic acid, and lipophilic antioxidants such as tocopherols and β-carotene. Accordingly, Gracilex® possesses antioxidant activity in vitro and increased antioxidant capacity in vivo in Caenorhabditis elegans. These findings support the idea that Gracilex® represents a good source of natural PPARγ ligands and antioxidants with the potential to mitigate metabolic disorders. Thus, its nutraceutical value in humans warrants further investigation.

Andrographis paniculata and Its Main Bioactive Ingredient Andrographolide Decrease Alcohol Drinking and Seeking in Rats Through Activation of Nuclear PPARγ Pathway

BACKGROUND AND AIMS

Andrographis paniculata is an annual herbaceous plant which belongs to the Acanthaceae family. Extracts from this plant have shown hepatoprotective, anti-inflammatory and antidiabetic properties, at least in part, through activation of the nuclear receptor Peroxisome Proliferator-Activated Receptor-gamma (PPAR γ). Recent evidence has demonstrated that activation of PPARγ reduces alcohol drinking and seeking in Marchigian Sardinian (msP) alcohol-preferring rats.

METHODS

The present study evaluated whether A. paniculata reduces alcohol drinking and relapse in msP rats by activating PPARγ.

RESULTS

Oral administration of an A. paniculata dried extract (0, 15, 150 mg/kg) lowered voluntary alcohol consumption in a dose-dependent manner and achieved ~65% reduction at the dose of 450 mg/kg. Water and food consumption were not affected by the treatment. Administration of Andrographolide (5 and 10 mg/kg), the main active component of A. paniculata, also reduced alcohol drinking. This effect was suppressed by the selective PPARγ antagonist GW9662. Subsequently, we showed that oral administration of A. paniculata (0, 150, 450 mg/kg) prevented yohimbine- but not cues-induced reinstatement of alcohol seeking.

CONCLUSIONS

Results point to A. paniculata-mediated PPARγactivation as a possible therapeutic strategy to treat alcohol use disorder.

In silico analysis of a potential antidiabetic phytochemical erythrin against therapeutic targets of diabetes

Diabetes mellitus is a multifactorial disorder characterized by a chronic elevation in blood glucose levels. Currently, antidiabetic drugs are available to counteract the associated pathologies. Their concomitant effects necessitate the investigation for an effective and safe drug aimed to diminish blood glucose levels with fewer side effects. Several researchers are taking new initiatives to explore plant sources as they are known to contain a wide variety of active agents. Hence, the present study was undertaken to study the role of natural products using in silico interaction studies. Erythrin a compound present in lichens was selected as a potential anti-diabetic agent. Molecular docking studies were carried out with 14 target proteins to evaluate its antidiabetic potential. Molecular docking analysis resulted in favourable binding energy of interaction ranging as low as - 119.676 to - 92.9545 kcal/mol for erythrin, Analogue showed the highest interactions with 3C45 (- 119.676 kcal/mol) followed by 2Q5S (- 118.398 kcal/mol), 1XU7 (- 117.341 kcal/mol), 3K35 (- 114.267 kcal/mol). Erythrin was found to fare better than the three clinically used antidiabetic compounds, metformin, repaglinide and sitagliptin. Further, the molecular interactions between erythrin and the diabetes related target proteins was established by analysing the interactions with associated amino acids. In silico pharmacokinetics and toxicity profile of erythrin using admetSAR software predicted erythrin as non-carcinogenic and non-mutagenic. The drug-likeliness was calculated using molsoft software respecting Lipinski's rule of five. The compound was found to comply with Lipinksi rules violating only one filter criterion. The study suggested that erythrin could be a potential anti-diabetic agent.

Pharmacological properties of tanshinones, the natural products from Salvia miltiorrhiza

Danshen (Cai, et al. 2016) is the dry root and rhizome of the herbaceous plant Salvia miltiorrhiza Bge. of family labiatae, a perennial plant that is native to China and Japan. The primary modern clinical applications of Danshen are for heart disease, chronic hepatitis, early cirrhosis, cerebral ischemia and pulmonary heart disease. Emerging evidence from cellular, animal, and clinical studies has begun to illuminate the pharmacological attributes of the primary lipophilic tanshinones from Danshen, which include tanshinone I, tanshinone II, cryptotanshinone and dihydrotanshinone, etc. Tanshinones offer the properties of anti-oxidation, anti-inflammation, antitumor, phytoestrogenic activity, vasodilation, neuroprotection, regulate metabolic function and other pharmacological advances. This chapter will review the discovery of the pharmacodynamic mechanism and pharmacokinetic studies of tanshinones and Danshen for further clinical applications.

Synthesis and Cytotoxicities of Royleanone Derivatives

Carnosic acid was used as starting material to synthesize royleanone derivatives featured C11-C14 para quinone. The importance of C-20 group of royleanone derivatives was verified by the cytotoxicity assay of royleanonic acid, miltionone I and deoxyneocrptotanshinone. Following our synthetic route, 15 amide derivatives were synthesized and 8 compounds exhibited moderate cytotoxic activities against three human cancer lines in vitro.

Development of an In Vitro Screening Platform for the Identification of Partial PPARγ Agonists as a Source for Antidiabetic Lead Compounds

Type 2 diabetes (T2D) is a metabolic disorder where insulin-sensitive tissues show reduced sensitivity towards insulin and a decreased glucose uptake (GU), which leads to hyperglycaemia. Peroxisome proliferator-activated receptor (PPAR)γ plays an important role in lipid and glucose homeostasis and is one of the targets in the discovery of drugs against T2D. Activation of PPARγ by agonists leads to a conformational change in the ligand-binding domain, a process that alters the transcription of several target genes involved in glucose and lipid metabolism. Depending on the ligands, they can induce different sets of genes that depends of their recruitment of coactivators. The activation of PPARγ by full agonists such as the thiazolidinediones leads to improved insulin sensitivity but also to severe side effects probably due to their behavior as full agonists. Partial PPARγ agonists are compounds with diminished agonist efficacy compared to full agonist that may exhibit the same antidiabetic effect as full agonists without inducing the same magnitude of side effects. In this review, we describe a screening platform for the identification of partial PPARγ agonists from plant extracts that could be promising lead compounds for the development of antidiabetic drugs. The screening platform includes a series of in vitro bioassays, such as GU in adipocytes, PPARγ-mediated transactivation, adipocyte differentiation and gene expression as well as in silico docking for partial PPARγ agonism.

In vitro and in silico perspectives on estrogenicity of tanshinones from Salvia miltiorrhiza

This work aims to investigate the structure-activity relationship for binding and activation of human estrogen receptor α ligand binding domain (hERα-LBD) with tanshinones by a combination of in vitro and in silico approaches. The recombinant hERα-LBD was expressed in E. coli strain. The direct binding interactions of tanshinones with hERα-LBD and their ERα agonistic potency were investigated by fluorescence polarization (FP) and reporter gene assays, respectively. FP assay suggested that the tested tanshinones can bind to hERα-LBD as affinity ligands. Tanshinones acted as agonists of hERα as demonstrated by transactivation of estrogen response element (ERE) in transiently transfected MCF-7 cells and by molecular docking of these compounds into the hydrophobic binding pocket of hERα-LBD. Interestingly, comparison of the calculated binding energies versus Connolly solvent-excluded volume and experimental binding affinities showed a good correlation. This work may provide insight into chemical and pharmacological characterization of novel bioactive compounds from Salvia miltiorrhiza.

Molecular determinants of PPARγ partial agonism and related in silico/in vivo studies of natural saponins as potential type 2 diabetes modulators

The metabolic syndrome, which includes hypertension, type 2 diabetes (T2D) and obesity, has reached an epidemic-like scale. Saponins and sapogenins are considered as valuable natural products for ameliorating this pathology, possibly through the nuclear receptor PPARγ activation. The aims of this study were: to look for in vivo antidiabetic effects of a purified saponins' mixture (PSM) from Astragalus corniculatus Bieb; to reveal by in silico methods the molecular determinants of PPARγ partial agonism, and to investigate the potential PPARγ participation in the PSM effects. In the in vivo experiments spontaneously hypertensive rats (SHRs) with induced T2D were treated with PSM or pioglitazone as a referent PPARγ full agonist, and pathology-relevant biochemical markers were analysed. The results provided details on the PSM modulation of the glucose homeostasis and its potential mechanism. The in silico studies focused on analysis of the protein-ligand interactions in crystal structures of human PPARγ-partial agonist complexes, pharmacophore modelling and molecular docking. They outlined key pharmacophoric features, typical for the PPARγ partial agonists, which were used for pharmacophore-based docking of the main PSM sapogenin. The in silico studies, strongly suggest possible involvement of PPARγ-mediated mechanisms in the in vivo antidiabetic and antioxidant effects of PSM from A. corniculatus.

O-prenylated flavonoid, an antidiabetes constituent in Melicope lunu-ankenda

ETHNOPHARMACOLOGICAL RELEVANCE

Melicope lunu-ankenda leaves are used to treat diabetes in folklore medicinal practices in India and Malaysia. Here we report the isolation of an O-prenylated flavonoid (3,5,4'-trihydroxy-8,3'-dimethoxy-7-(3-methylbut-2-enoxy)flavone; OPF) from the leaves of M. lunu-ankenda and its antidiabetes activity against type-2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

OPF was isolated from M. lunu-ankenda leaves by extraction and repeated column chromatography and its structure was elucidated by IR, UV-vis, 1D-, 2D-NMR and mass spectral analyses. Blood glucose lowering activity of OPF was tested in normal rats by oral glucose tolerance test and its efficacy was tested in STZ-induced type-2 diabetic rats. SGOT, SGPT, ALP, serum urea, total triglycerides, total cholesterol and reduction in HDLC, protein and serum insulin levels in normal rats and STZ-induced type-2 diabetic rats were measured. Acute toxicity of OPF was tested at 500 mg/kg dose. Mechanism of antidiabetes action of OPF was elucidated by insulin release from RIN 5F cells.

RESULTS

OPF isolated from M. lunu-ankenda showed significant blood glucose lowering activity in oral glucose tolerance test on overnight fasted, glucose loaded normal rats and the optimum activity was observed at a dose of 10mg/kg body weight. In neonatal streptozotocin (STZ) induced diabetic rats, the OPF treatment for 20 days significantly ameliorated the derailed blood glucose levels, liver glycogen and serum biological parameters including insulin to normal levels. OPF on acute toxicity evaluation did not show any conspicuous toxic symptoms even at a higher dose of 500 mg/kg body weight in mice. On evaluating the mechanism of antidiabetes action, it was observed that, OPF induced insulin release from cultured RIN 5F cells in vitro from which it was evident that the OPF acts on pancreatic β-cells for insulin release thereby correcting the derailed blood glucose levels, serum biochemical parameters and ameliorate various diabetic complications in STZ-induced diabetic rats.

CONCLUSIONS

This study shows the potent antidiabetes activity of OPF and describes its mechanism of action. OPF is a promising candidate for the development of new generation anti-DM drugs. Isolation of the O-prenylated flavonoid justifies the use of M. lunu-ankenda for diabetic treatments in folklore practices.

Identification of novel multitargeted PPARα/γ/δ pan agonists by core hopping of rosiglitazone

The thiazolidinedione class peroxisome proliferator-activated receptor gamma (PPARγ) agonists are restricted in clinical use as antidiabetic agents because of side effects such as edema, weight gain, and heart failure. The single and selective agonism of PPARγ is the main cause of these side effects. Multitargeted PPARα/γ/δ pan agonist development is the hot topic in the antidiabetic drug research field. In order to identify PPARα/γ/δ pan agonists, a compound database was established by core hopping of rosiglitazone, which was then docked into a PPARα/γ/δ active site to screen out a number of candidate compounds with a higher docking score and better interaction with the active site. Further, absorption, distribution, metabolism, excretion, and toxicity prediction was done to give eight compounds. Molecular dynamics simulation of the representative Cpd#1 showed more favorable binding conformation for PPARs receptor than the original ligand. Cpd#1 could act as a PPARα/γ/δ pan agonist for novel antidiabetic drug research.

An in vitro study reveals the nutraceutical potential of punicic acid relevant to diabetes via enhanced GLUT4 expression and adiponectin secretion

The prevalence of diabetes and heart diseases is increasing in the world. Nutraceuticals of natural origin are gaining importance as an alternative to modern drugs for the management of metabolic syndrome. In the present study, punicic acid (PA), a major bioactive found in pomegranate seed, was subjected for biological characterization with respect to peroxisome proliferator-activated receptor gamma (PPARγ) agonist property in an in vitro system (3T3-L1 adipocytes). We evaluated the adipogenic potential of various concentrations (5, 10 and 30 μM) of PA by studying triglyceride accumulation and glycerol-3-phosphate dehydrogenase (GPDH) activity in adipocytes, which were found to be increased moderately compared with the positive control, i.e. rosiglitazone (RG). Glucose uptake activity (↑225.93% ± 2.55% for 30 μM of PA), and the prevention of reactive oxygen species (ROS) generation (↓57 ± 1.83% for 30 μM of PA) in adipocytes with PA were also evaluated. We also found that PA increased adiponectin secretion and upregulated GLUT4 expression and translocation in adipocytes. Molecular modelling studies revealed a high binding affinity of PA to the PPARγ ligand binding domain. An in vitro ligand binding assay based on time-resolved fluorescence resonance energy transfer (TR-FRET) also proved PA as a PPARγ agonist. Finally, we conclude that PA is a potential nutraceutical and should be encouraged for use both as a prophylactic and therapeutic agent.

Modulation of liver function, antioxidant responses, insulin resistance and glucose transport by Oroxylum indicum stem bark in STZ induced diabetic rats

A decoction of stem bark of Oroxylum indicum Vent. (OI) is taken (2-3 times/day) by the tribal people of Sikkim, India to treat diabetes but scientific validation of its overall potential is lacking. Present study was aimed to assess in vitro antihyperglycemic activity of standardized OI extract using inhibition of α-glucosidase, BSA glycation and enhancement of insulin sensitivity. Antidiabetic and antioxidant modulatory effects of OI extract along with the blood biomarkers of toxic response were studied in streptozotocin (STZ) induced diabetic rats. In vitro analysis showed strong antioxidant capacity of OI -and potential to inhibit BSA glycation and α-glucosidase activity which was comparable to standard counterparts. Extract also improved insulin sensitivity in mature 3T3-L1 adipocytes. In vivo effects of OI extract (oral 250 mg/kg b.wt.) on STZ induced type II diabetic rats normalized the antioxidant status (p≤0.01). Analysis of blood biomarkers of toxic response indicated its safety. Lowering of total cholesterol and HDL levels (p≤0.05) and restoration of glycated Hb (p≤0.01) were also found in OI treated diabetic rats. HOMA-IR, QUICKI analysis along with area under the curve analysis showed the capacity of OI extract to enhance the insulin sensitivity significantly (p≤0.01) which was confirmed by increased GLUT-4 translocation in skeletal muscles.