A novel partial agonist of peroxisome proliferator-activated receptor-gamma (PPARgamma) recruits PPARgamma-coactivator-1alpha, prevents triglyceride accumulation, and potentiates insulin signaling in vitro

Chemogenomics for NR1 nuclear hormone receptors

Nuclear receptors (NRs) regulate transcription in response to ligand binding and NR modulation allows pharmacological control of gene expression. Although some NRs are relevant as drug targets, the NR1 family, which comprises 19 NRs binding to hormones, vitamins, and lipid metabolites, has only been partially explored from a translational perspective. To enable systematic target identification and validation for this protein family in phenotypic settings, we present an NR1 chemogenomic (CG) compound set optimized for complementary activity/selectivity profiles and chemical diversity. Based on broad profiling of candidates for specificity, toxicity, and off-target liabilities, sixty-nine comprehensively annotated NR1 agonists, antagonists and inverse agonists covering all members of the NR1 family and meeting potency and selectivity standards are included in the final NR1 CG set. Proof-of-concept application of this set reveals effects of NR1 members in autophagy, neuroinflammation and cancer cell death, and confirms the suitability of the set for target identification and validation.

Myotubularin-related-protein-7 inhibits mutant (G12V) K-RAS by direct interaction

Inhibition of K-RAS effectors like B-RAF or MEK1/2 is accompanied by treatment resistance in cancer patients via re-activation of PI3K and Wnt signaling. We hypothesized that myotubularin-related-protein-7 (MTMR7), which inhibits PI3K and ERK1/2 signaling downstream of RAS, directly targets RAS and thereby prevents resistance. Using cell and structural biology combined with animal studies, we show that MTMR7 binds and inhibits RAS at cellular membranes. Overexpression of MTMR7 reduced RAS GTPase activities and protein levels, ERK1/2 phosphorylation, c-FOS transcription and cancer cell proliferation in vitro. We located the RAS-inhibitory activity of MTMR7 to its charged coiled coil (CC) region and demonstrate direct interaction with the gastrointestinal cancer-relevant K-RASG12V mutant, favouring its GDP-bound state. In mouse models of gastric and intestinal cancer, a cell-permeable MTMR7-CC mimicry peptide decreased tumour growth, Ki67 proliferation index and ERK1/2 nuclear positivity. Thus, MTMR7 mimicry peptide(s) could provide a novel strategy for targeting mutant K-RAS in cancers.

Binding of Per- and Polyfluoroalkyl Substances (PFAS) to the PPARγ/RXRα-DNA Complex

Nuclear receptors are the fundamental building blocks of gene expression regulation and the focus of many drug targets. While binding to DNA, nuclear receptors act as transcription factors, governing a multitude of functions in the human body. Peroxisome proliferator-activator receptor γ (PPARγ) and the retinoid X receptor α (RXRα) form heterodimers with unique properties and have a primordial role in insulin sensitization. This PPARγ/RXRα heterodimer has been shown to be impacted by per- and polyfluoroalkyl substances (PFAS) and linked to a variety of significant health conditions in humans. Herein, a selection of the most common PFAS (legacy and emerging) was studied utilizing molecular dynamics simulations for PPARγ/RXRα. The local and global structural effects of PFAS binding on the known ligand binding pockets of PPARγ and RXRα as well as the DNA binding domain (DBD) of RXRα were inspected. The binding free energies were predicted computationally and were compared between the different binding pockets. In addition, two electronic structure approaches were utilized to model the interaction of PFAS within the DNA binding domain, density functional theory (DFT) and domain-based pair natural orbital coupled cluster with perturbative triples (DLPNO-CCSD(T)) approaches, with implicit solvation. Residue decomposition and hydrogen-bonding analysis were also performed, detailing the role of prominent residues in molecular recognition. The role of l-carnitine is explored as a potential in vivo remediation strategy for PFAS interaction with the PPARγ/RXRα heterodimer. In this work, it was found that PFAS can bind and act as agonists for all of the investigated pockets. For the first time in the literature, PFAS are postulated to bind to the DNA binding domain in a nonspecific manner. In addition, for the PPARγ ligand binding domain, l-carnitine shows promise in replacing smaller PFAS from the pocket.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Partial Activation of PPAR-γ by Synthesized Quercetin Derivatives Modulates TGF-β1-Induced EMT in Lung Cancer Cells

Non-small cell lung cancer (NSCLC) has a very low survival rate due to poor response to chemotherapy and late detection. Epithelial to mesenchymal transition (EMT) is regarded as a major contributor to drive metastasis during NSCLC progression. Towards this, transforming growth factor-beta 1 (TGF-β1) is the key driver that endows cancer cells with increased aggressiveness. Recently, this group synthesized a series of Schiff base quercetin derivatives (QDs) and ascertained their effectiveness on EMT markers of A549 cell line. This study evidenced that the EMT process is counteracted via the partial activation of a nuclear hormone receptor, Peroxisome proliferator-activated receptor (PPAR)-γ through QDs. Here, that work is extended to investigate the interplay between PPAR-γ partial activation and TGF-β1-induced EMT in human lung cancer A549 cells. The results reveal that TGF-β1 plays a critical role in suppressing PPAR-γ, which is markedly reversed and increased by partial agonists: QUE2FH and QUESH at both protein and transcriptional levels. The partial agonists not only stimulate PPAR-γ in a balanced manner but also prevent the loss of E-cadherin and acquisition of TGF-β1-induced mesenchymal markers (Snail, Slug, Vimentin, and Zeb-1). Subsequently, the effects are accompanied by attenuation of TGF-β1-induced migratory ability of A549 cells.

Identification of Selective PPAR-γ Modulators by Combining Pharmacophore Modeling, Molecular Docking, and Adipogenesis Assay

The clinically used glitazones (rosiglitazone and pioglitazone) for type 2 diabetes mellitus therapy have been linked to serious side effects such as fluid retention, congestive heart failure, weight gain, bone loss, and an increased risk of bladder cancer. The complete activation of PPAR-γ receptors in target tissues is linked to these effects. Many studies have demonstrated that partial PPAR-γ activators (GW0072, PAT5A, GQ16) give equivalent therapeutic benefits to full PPAR-γ agonists without the associated side effects. These breakthroughs cleared the path for the development of partial agonists or selective PPAR-γ modulators (SPPARγMs). This study combined pharmacophore modeling, molecular docking, and an adipogenesis experiment to identify thiazolidine analogs as SPPARMs/partial agonists. A custom library of 220 molecules was created and virtual screened to discover 90 compounds as SPPARγMs/ partial agonists. The chosen eight compounds were synthesized and tested for adipogenesis using 3T3L1 cell lines. These compounds' partial agonistic activity was evaluated in 3T3L1 cell lines by comparing their capacity to stimulate PPAR-γ mediated adipogenesis to that of a full agonist, rosiglitazone. The findings of the adipogenesis experiment demonstrate that all eight compounds examined had a partial potential to stimulate adipogenesis when compared to the full agonist, rosiglitazone. The current investigation identified eight possible PPAR-γ partial agonists or SPPARγMs that may be effective in the treatment of type 2 diabetes mellitus.

2,2',4,4'-Tetrabromodiphenyl Ether (PBDE 47) Selectively Stimulates Proatherogenic PPARγ Signatures in Human THP-1 Macrophages to Contribute to Foam Cell Formation

2,2',4,4'-Tetrabromodiphenyl ether (PBDE 47) is one of the most prominent PBDE congeners detected in the human body, suggesting that the potential health risks of PBDE 47 should be thoroughly considered. However, the cardiovascular toxicity of PBDE 47 remains poorly understood. Here, toxic outcomes of PBDE 47 in human THP-1 macrophages concerning foam cell formation, which play crucial roles in the occurrence and development of atherosclerosis, were elucidated. First, our results indicated that PBDE 47 affected the PPARγ pathway most efficiently in THP-1 macrophages by transcriptomic analysis. Second, the PPARγ target genes CD36 and FABP4, responsible for lipid uptake and accumulation in macrophages, were consistently upregulated both at transcriptional and translational levels in THP-1 macrophages upon PBDE 47. Unexpectedly, PBDE 47 failed to activate the PPARγ target gene LXRα and PPARγ-LXRα-ABCA1/G1 cascade, which is activated by the PPARγ full agonist rosiglitazone and enables cholesterol efflux in macrophages. Thus, coincident with the selective upregulation of the PPARγ target genes CD36 and FABP4, PBDE 47, distinct from rosiglitazone, functionally resulted in more lipid accumulation and oxLDL uptake in THP-1 macrophages through high-content analysis (HCA). Moreover, these effects were markedly abrogated by the addition of the PPARγ antagonist T0070907. Mechanistically, the structural basis of selective activation of PPARγ by PBDE 47 was explored by molecular docking and dynamics simulation, which indicated that PBDE 47 interacted with the PPARγ ligand binding domain (PPARγ-LBD) distinctively from that of rosiglitazone. PBDE 47 was revealed to interact with helix 3 and helix 5 but not helix 12 in the PPARγ-LBD. Collectively, these results unraveled the potential cardiovascular toxicity of PBDE 47 by selective activation of PPARγ to facilitate foam cell formation for the first time.

Hepatokine ERAP1 Disturbs Skeletal Muscle Insulin Sensitivity Via Inhibiting USP33-Mediated ADRB2 Deubiquitination

Chronic inflammation in liver induces insulin resistance systemically and in other tissues, including the skeletal muscle (SM); however, the underlying mechanisms remain largely unknown. RNA sequencing of primary hepatocytes from wild-type mice fed long-term high-fat diet (HFD), which have severe chronic inflammation and insulin resistance revealed that the expression of hepatokine endoplasmic reticulum aminopeptidase 1 (ERAP1) was upregulated by a HFD. Increased ERAP1 levels were also observed in interferon-γ-treated primary hepatocytes. Furthermore, hepatic ERAP1 overexpression attenuated systemic and SM insulin sensitivity, whereas hepatic ERAP1 knockdown had the opposite effects, with corresponding changes in serum ERAP1 levels. Mechanistically, ERAP1 functions as an antagonist-like factor, which interacts with β2 adrenergic receptor (ADRB2) and reduces its expression by decreasing ubiquitin-specific peptidase 33-mediated deubiquitination and thereby interrupts ADRB2-stimulated insulin signaling in the SM. The findings of this study indicate ERAP1 is an inflammation-induced hepatokine that impairs SM insulin sensitivity. Its inhibition may provide a therapeutic strategy for insulin resistance-related diseases, such as type 2 diabetes.

A New Fungal Triterpene from the Fungus Aspergillus flavus Stimulates Glucose Uptake without Fat Accumulation

Through activity-guided fractionation, a new triterpene (asperflagin, 1) was isolated as a PPAR-γ agonist from the jellyfish-derived fungus Aspergillus flavus. Asperflagin displayed selective and moderate transactivation effects on PPAR-γ in Ac2F rat liver cells. Based on further biological evaluation and molecular docking analysis, we postulated that asperflagin might function as a PPAR-γ partial agonist. This compound was calculated to display a typical PPAR-γ ligand–receptor interaction that is distinct from that of full agonistic antidiabetics such as rosiglitazone, and may retain the antidiabetic effect without accompanying weight gain. Weight gain and obesity are typical side effects of the PPAR-γ full agonist rosiglitazone, and lead to suboptimal outcomes in diabetic patients. Compared to rosiglitazone, asperflagin showed higher glucose uptake in HepG2 human liver cells at concentrations of 20 and 40 μM but induced markedly lower adipogenesis and lipid accumulation in 3T3-L1 preadipocytes. These results suggest that asperflagin may be utilized for further study on advanced antidiabetic leads.

The Synbiotic Combination of Akkermansia muciniphila and Quercetin Ameliorates Early Obesity and NAFLD through Gut Microbiota Reshaping and Bile Acid Metabolism Modulation

Gut microbiota plays a key role in obesity and non-alcoholic fatty liver disease (NAFLD), so synbiotics could be a therapeutic alternative. We aim to evaluate a nutritional intervention together with the administration of the bacteria Akkermansia muciniphila and the antioxidant quercetin in an in vivo model of early obesity and NAFLD. 21-day-old rats were fed with control or high-fat diet for six weeks. Then, all animals received control diet supplemented with/without quercetin and/or A. muciniphila for three weeks. Gut microbiota, NAFLD-related parameters, circulating bile acids (BAs) and liver gene expression were analyzed. The colonization with A. muciniphila was associated with less body fat, while synbiotic treatment caused a steatosis remission, linked to hepatic lipogenesis modulation. The synbiotic promoted higher abundance of Cyanobacteria and Oscillospira, and lower levels of Actinobacteria, Lactococcus, Lactobacillus and Roseburia. Moreover, it favored elevated unconjugated hydrophilic BAs plasma levels and enhanced hepatic expression of BA synthesis and transport genes. A. muciniphila correlated with circulating BAs and liver lipid and BA metabolism genes, suggesting a role of this bacterium in BA signaling. Beneficial effects of A. muciniphila and quercetin combination are driven by gut microbiota modulation, the shift in BAs and the gut-liver bile flow enhancement.

The pleiotropic peroxisome proliferator activated receptors: Regulation and therapeutics

The Peroxisome proliferator-activated receptors (PPARs) are key regulators of metabolic events in our body. Owing to their implication in maintenance of homeostasis, both PPAR agonists and antagonists assume therapeutic significance. Understanding the molecular mechanisms of each of the PPAR isotypes in the healthy body and during disease is crucial to exploiting their full therapeutic potential. This article is an attempt to present a rational analysis of the multifaceted therapeutic effects and underlying mechanisms of isotype-specific PPAR agonists, dual PPAR agonists, pan PPAR agonists as well as PPAR antagonists. A holistic understanding of the mechanistic dimensions of these key metabolic regulators will guide future efforts to identify novel molecules in the realm of metabolic, inflammatory and immunotherapeutic diseases.

Ectopic Overexpression of PPARγ2 in the Heart Determines Differences in Hypertrophic Cardiomyopathy After Treatment With Different Thiazolidinediones in a Mouse Model of Diabetes

The clinical controversy of rosiglitazone as a hypoglycemic agent is potentially associated with heart failure, mainly due to its potent activation of peroxisome proliferator-activated receptor γ (PPARγ). PPARγ partial agonists showed superior pharmacological profiles to rosiglitazone. This study compared differences in cardiac morphology and function of the PPARγ partial agonist CMHX008 with rosiglitazone. High-fat diet (HFD) induced obese mice, ob/ob mice and cardiomyocytes overexpressing PPARγ2 were treated with CMHX008 or rosiglitazone. Heart function, myocardial morphology, and hypertrophy-related gene expression were examined. Clinical information from patients with type 2 diabetes mellitus (T2DM) who had taken rosiglitazone and undergone Doppler echocardiography was collected. HFD and ob/ob mice significantly developed cardiac contractile dysfunction, with upregulated PPARγ2 protein levels in heart tissues. Cardiomyocytes of HFD and ob/ob mice were disorderly arranged, the cell areas expanded, and collagen accumulated. In vitro cardiomyocytes overexpressing PPARγ2 displayed obvious structural abnormalities and high mRNA levels of ANP and BNP, critical cardiac hypertrophy-related genes. HFD-fed mice treated with rosiglitazone or CMHX008 had significantly improved cardiac function, but rosiglitazone induced higher expression of ANP and βMHC and hypertrophic cardiomyopathy, while CMHX008 did not. Patients with T2DM taking rosiglitazone exhibited increased thickness of the posterior wall and the ventricular septum, suggesting cardiac hypertrophy. Our findings show that diabetic cardiomyopathy was associated with ectopic overexpression of PPARγ2. The full agonist rosiglitazone prevents cardiac dysfunction at the expense of compensatory hypertrophy, while the partial agonist CMHX008 shared a comparable protective effect without altering the structure of cardiomyocytes.

A Data-Driven Transcriptional Taxonomy of Adipogenic Chemicals to Identify White and Brite Adipogens

BACKGROUND

Chemicals in disparate structural classes activate specific subsets of the transcriptional programs of peroxisome proliferator-activated receptor-γ (PPARγ) to generate adipocytes with distinct phenotypes.

OBJECTIVES

Our objectives were to a) establish a novel classification method to predict PPARγ ligands and modifying chemicals; and b) create a taxonomy to group chemicals on the basis of their effects on PPARγ's transcriptome and downstream metabolic functions. We tested the hypothesis that environmental adipogens highly ranked by the taxonomy, but segregated from therapeutic PPARγ ligands, would induce white but not brite adipogenesis.

METHODS

3T3-L1 cells were differentiated in the presence of 76 chemicals (negative controls, nuclear receptor ligands known to influence adipocyte biology, potential environmental PPARγ ligands). Differentiation was assessed by measuring lipid accumulation. mRNA expression was determined by RNA-sequencing (RNA-Seq) and validated by reverse transcription-quantitative polymerase chain reaction. A novel classification model was developed using an amended random forest procedure. A subset of environmental contaminants identified as strong PPARγ agonists were analyzed by their effects on lipid handling, mitochondrial biogenesis, and cellular respiration in 3T3-L1 cells and human preadipocytes.

RESULTS

We used lipid accumulation and RNA-Seq data to develop a classification system that a) identified PPARγ agonists; and b) sorted chemicals into likely white or brite adipogens. Expression of Cidec was the most efficacious indicator of strong PPARγ activation. 3T3-L1 cells treated with two known environmental PPARγ ligands, tetrabromobisphenol A and triphenyl phosphate, which sorted distinctly from therapeutic ligands, had higher expression of white adipocyte genes but no difference in Pgc1a and Ucp1 expression, and higher fatty acid uptake but not mitochondrial biogenesis. Moreover, cells treated with two chemicals identified as highly ranked PPARγ agonists, tonalide and quinoxyfen, induced white adipogenesis without the concomitant health-promoting characteristics of brite adipocytes in mouse and human preadipocytes.

DISCUSSION

A novel classification procedure accurately identified environmental chemicals as PPARγ ligands distinct from known PPARγ-activating therapeutics.

CONCLUSION

The computational and experimental framework has general applicability to the classification of as-yet uncharacterized chemicals. https://doi.org/10.1289/EHP6886.

Thiazolidinedione "Magic Bullets" Simultaneously Targeting PPARγ and HDACs: Design, Synthesis, and Investigations of their In Vitro and In Vivo Antitumor Effects

Monotargeting anticancer agents suffer from resistance and target nonspecificity concerns, which can be tackled with a multitargeting approach. The combined treatment with HDAC inhibitors and PPARγ agonists has displayed potential antitumor effects. Based on these observations, this work involves design and synthesis of molecules that can simultaneously target PPARγ and HDAC. Several out of 25 compounds inhibited HDAC4, and six compounds acted as dual-targeting agents. Compound 7i was the most potent, with activity toward PPARγ EC50 = 0.245 μM and HDAC4 IC50 = 1.1 μM. Additionally, compounds 7c and 7i were cytotoxic to CCRF-CEM cells (CC50 = 2.8 and 9.6 μM, respectively), induced apoptosis, and caused DNA fragmentation. Furthermore, compound 7c modulated the expression of c-Myc, cleaved caspase-3, and caused in vivo tumor regression in CCRF-CEM tumor xenografts. Thus, this study provides a basis for the rational design of dual/multitargeting agents that could be developed further as anticancer therapeutics.

Nelfinavir and Its Active Metabolite M8 Are Partial Agonists and Competitive Antagonists of the Human Pregnane X Receptor

The HIV protease inhibitor nelfinavir is currently being analyzed for repurposing as an anticancer drug for many different cancers because it exerts manifold off-target protein interactions, finally resulting in cancer cell death. Xenosensing pregnane X receptor (PXR), which also participates in the control of cancer cell proliferation and apoptosis, was previously shown to be activated by nelfinavir; however, the exact molecular mechanism is still unknown. The present study addresses the effects of nelfinavir and its major and pharmacologically active metabolite nelfinavir hydroxy-tert-butylamide (M8) on PXR to elucidate the underlying molecular mechanism. Molecular docking suggested direct binding to the PXR ligand-binding domain, which was confirmed experimentally by limited proteolytic digestion and competitive ligand-binding assays. Concentration-response analyses using cellular transactivation assays identified nelfinavir and M8 as partial agonists with EC₅₀ values of 0.9 and 7.3 µM and competitive antagonists of rifampin-dependent induction with IC₅₀ values of 7.5 and 25.3 µM, respectively. Antagonism exclusively resulted from binding into the PXR ligand-binding pocket. Impaired coactivator recruitment by nelfinavir as compared with the full agonist rifampin proved to be the underlying mechanism of both effects on PXR. Physiologic relevance of nelfinavir-dependent modulation of PXR activity was investigated in respectively treated primary human hepatocytes, which showed differential induction of PXR target genes and antagonism of rifampin-induced ABCB1 and CYP3A4 gene expression. In conclusion, we elucidate here the molecular mechanism of nelfinavir interaction with PXR. It is hypothesized that modulation of PXR activity may impact the anticancer effects of nelfinavir. SIGNIFICANCE STATEMENT: Nelfinavir, which is being investigated for repurposing as an anticancer medication, is shown here to directly bind to human pregnane X receptor (PXR) and thereby act as a partial agonist and competitive antagonist. Its major metabolite nelfinavir hydroxy-tert-butylamide exerts the same effects, which are based on impaired coactivator recruitment. Nelfinavir anticancer activity may involve modulation of PXR, which itself is discussed as a therapeutic target in cancer therapy and for the reversal of chemoresistance.

Rice Bran Extract Protected against LPS-Induced Neuroinflammation in Mice through Targeting PPAR-γ Nuclear Receptor

PPAR-γ anti-inflammatory functions have received significant attention since its agonists have been shown to exert a wide range of protective effects in many experimental models of neurologic diseases. Rice bran is very rich in polyunsaturated fatty acids, which are reported to act as PPAR-γ partial agonists. Herein, the anti-inflammatory effect of rice bran extract (RBE) through PPAR-γ activation was evaluated in LPS-induced neuroinflammatory mouse model in comparison to pioglitazone (PG) using 80 Swiss albino mice. RBE (100 mg/kg) and PG (30 mg/kg) were given orally for 21 days and LPS (0.25 mg/kg) was injected intraperitoneally for the last 7 days. TNF-α and COX-2 brain contents were evaluated by real-time PCR and immunohistochemical analysis. In addition, NFκB binding to its response element was evaluated alongside with the effect of treatments on IκB gene expression. Furthermore, PPAR-γ sumoylation was also studied. Finally, histopathological examination was performed for different brain areas. RBE administration was found to protect against the LPS-induced inflammatory effects by decreasing the inflammatory mediator expression in mice brains. It also decreased PPAR-γ sumoylation without significant effect on IκB expression or NFκB binding to its response element. The majority of the effects were attenuated in presence of PPAR-γ antagonist (GW9662). Level of significance was set to P < 0.05. Such findings highlight the agonistic effect of RBE component(s) on PPAR-γ and support the hypothesis of involvement of PPAR-γ activation in its neuroprotective effect.

Anti-Diabetic Effect of Telmisartan Through its Partial PPARγ-Agonistic Activity

Telmisartan is an angiotensin II receptor antagonist, which selectively inhibits the angiotensin II type 1 receptor. Thus, it is widely used for hypertension management. Nowadays, telmisartan's effect on peroxisome proliferator-activated receptors (PPARs) is gaining wider attention. PPARs are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. Telmisartan is reported to have a partial PPARγ-agonistic effect while avoiding the safety concerns found with full PPARγ agonists (thiazolidinediones). Telmisartan could be an alternative treatment option, with dual benefit for diabetes mellitus (DM) and hypertension. This review summarizes the anti-diabetic activity of telmisartan via its partial PPARγ-agonistic activity.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Myotubularin-related protein 7 activates peroxisome proliferator-activated receptor-gamma

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a transcription factor drugable by agonists approved for treatment of type 2 diabetes, but also inhibits carcinogenesis and cell proliferation in vivo. Activating mutations in the Kirsten rat sarcoma viral oncogene homologue (KRAS) gene mitigate these beneficial effects by promoting a negative feedback-loop comprising extracellular signal-regulated kinase 1/2 (ERK1/2) and mitogen-activated kinase kinase 1/2 (MEK1/2)-dependent inactivation of PPARγ. To overcome this inhibitory mechanism, we searched for novel post-translational regulators of PPARγ. Phosphoinositide phosphatase Myotubularin-Related-Protein-7 (MTMR7) was identified as cytosolic interaction partner of PPARγ. Synthetic peptides were designed resembling the regulatory coiled-coil (CC) domain of MTMR7, and their activities studied in human cancer cell lines and C57BL6/J mice. MTMR7 formed a complex with PPARγ and increased its transcriptional activity by inhibiting ERK1/2-dependent phosphorylation of PPARγ. MTMR7-CC peptides mimicked PPARγ-activation in vitro and in vivo due to LXXLL motifs in the CC domain. Molecular dynamics simulations and docking predicted that peptides interact with the steroid receptor coactivator 1 (SRC1)-binding site of PPARγ. Thus, MTMR7 is a positive regulator of PPARγ, and its mimicry by synthetic peptides overcomes inhibitory mechanisms active in cancer cells possibly contributing to the failure of clinical studies targeting PPARγ.

To Probe Full and Partial Activation of Human Peroxisome Proliferator-Activated Receptors by Pan-Agonist Chiglitazar Using Molecular Dynamics Simulations

Chiglitazar is a promising new-generation insulin sensitizer with low reverse effects for the treatment of type II diabetes mellitus (T2DM) and has shown activity as a nonselective pan-agonist to the human peroxisome proliferator-activated receptors (PPARs) (i.e., full activation of PPARγ and a partial activation of PPARα and PPARβ/δ). Yet, it has no high-resolution complex structure with PPARs and its detailed interactions and activation mechanism remain unclear. In this study, we docked chiglitazar into three experimentally resolved crystal structures of hPPAR subtypes, PPARα, PPARβ/δ, and PPARγ, followed by 3 μs molecular dynamics simulations for each system. Our MM-GBSA binding energy calculation revealed that chiglitazar most favorably bound to hPPARγ (-144.6 kcal/mol), followed by hPPARα (-138.0 kcal/mol) and hPPARβ (-135.9 kcal/mol), and the order is consistent with the experimental data. Through the decomposition of the MM-GBSA binding energy by residue and the use of two-dimensional interaction diagrams, key residues involved in the binding of chiglitazar were identified and characterized for each complex system. Additionally, our detailed dynamics analyses support that the conformation and dynamics of helix 12 play a critical role in determining the activities of the different types of ligands (e.g., full agonist vs. partial agonist). Rather than being bent fully in the direction of the agonist versus antagonist conformation, a partial agonist can adopt a more linear conformation and have a lower degree of flexibility. Our finding may aid in further development of this new generation of medication.

Selective peroxisome proliferator-activated receptor-gamma modulator, INT131 exhibits anti-inflammatory effects in an EcoHIV mouse model

Despite the use of antiretroviral therapy for the treatment of HIV-1 infection, cognitive impairments, that is, HIV-1-associated neurocognitive disorders remain prevalent potentially due to persistent viral replication, production of viral proteins, associated brain inflammation or in certain instances, antiretroviral neurotoxicity. Cellular targets in the brain include microglia which in response to infection release inflammatory markers and viral proteins. Evidence suggests that PPARγ agonists exert anti-inflammatory properties in neurological disorders. However, these agonists namely, thiazolidinediones have limited use in the clinic due to reported adverse side effects. INT131 is a novel non-thiazolidinedione compound that belongs to a new class of drugs known as selective PPARγ modulators. INT131 is considered to have a safer profile; however, its neuroprotective role in vivo is not known.The goal of this study was to examine the effect of INT131 in the context of EcoHIV-induced inflammation in vitro, in primary cultures of mouse glial cells and in vivo, in a mouse model of EcoHIV-associated brain inflammation, as well as characterize its pharmacokinetic properties and brain penetration. In primary cultures of glial cells and in the in vivo mouse model, EcoHIV exposure resulted in a significant elevation of inflammatory markers such as TNFα, IL-1β, CCL3, and C3 which were attenuated with INT131 treatment. Pharmacokinetic analyses revealed that INT131 penetrates into the brain with a brain to blood partition ratio Kp value of 8.5%. Overall, this is the first report to demonstrate that INT131 could be a potential candidate for the treatment of HIV-1-associated brain inflammation.

(-)-O-Methylcubebin from Vitex trifolia Enhanced Adipogenesis in 3T3-L1 Cells via the Inhibition of ERK1/2 and p38MAPK Phosphorylation

In this study, for the purpose of elucidation for antidiabetic components, we isolated and identified compounds that could become lead compounds for the development of antidiabetic agents from the herbal medicine Vitex trifolia, which is used for liver protection in Myanmar. Three kinds of lignan, (-)-O-methylcubebin (MC), (-)-hinokinin, and (-)-cubebin, were isolated from the ethyl acetate extract of the leaves of V. trifolia, using various chromatography. Among the three isolated compounds, MC showed the strongest effects to increase intracellular lipid accumulation in 3T3-L1 cells. From the results of the elucidation of the MC’s effects on the adipogenesis of 3T3-L1 cells, the downsizing of adipocytes and the promotion of the expression of adipogenesis-related proteins, as well as adiponectin, were observed. On the other hand, since the activity of MC was inhibited by antagonists of PPARγ and improved by inhibitors of the classical mitogen-activated protein kinase (MAPK) pathway and p38MAPK pathway, MC was considered to be an agonist of PPARγ, and furthermore promoted adipogenesis via the inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38MAPK phosphorylation. Although MC showed similar effects to those of rosiglitazone (RO) used as a positive control, RO promoted the migration of GLUT4 from the cytoplasm to the cell membrane, whereas MC did not show such an effect. From the abovementioned results, it was considered that MC could be a lead compound for the development of antidiabetic drugs that does not show weight gain, which is a side effect of RO.

15-keto-prostaglandin E2 activates host peroxisome proliferator-activated receptor gamma (PPAR-γ) to promote Cryptococcus neoformans growth during infection

Cryptococcus neoformans is one of the leading causes of invasive fungal infection in humans worldwide. C. neoformans uses macrophages as a proliferative niche to increase infective burden and avoid immune surveillance. However, the specific mechanisms by which C. neoformans manipulates host immunity to promote its growth during infection remain ill-defined. Here we demonstrate that eicosanoid lipid mediators manipulated and/or produced by C. neoformans play a key role in regulating pathogenesis. C. neoformans is known to secrete several eicosanoids that are highly similar to those found in vertebrate hosts. Using eicosanoid deficient cryptococcal mutants Δplb1 and Δlac1, we demonstrate that prostaglandin E₂ is required by C. neoformans for proliferation within macrophages and in vivo during infection. Genetic and pharmacological disruption of host PGE₂ synthesis is not required for promotion of cryptococcal growth by eicosanoid production. We find that PGE₂ must be dehydrogenated into 15-keto-PGE₂ to promote fungal growth, a finding that implicated the host nuclear receptor PPAR-γ. C. neoformans infection of macrophages activates host PPAR-γ and its inhibition is sufficient to abrogate the effect of 15-keto-PGE₂ in promoting fungal growth during infection. Thus, we describe the first mechanism of reliance on pathogen-derived eicosanoids in fungal pathogenesis and the specific role of 15-keto-PGE₂ and host PPAR-γ in cryptococcosis.

Cryptococcus neoformans is an opportunistic fungal pathogen that is responsible for significant numbers of deaths in the immunocompromised population worldwide. Here we address whether eicosanoids produced by C. neoformans manipulate host innate immune cells during infection. Cryptococcus neoformans produces several eicosanoids that are notable for their similarity to vertebrate eicosanoids, it is therefore possible that fungal-derived eicosanoids may provoke physiological effects in the host. Using a combination of in vitro and in vivo infection models we identify a specific eicosanoid species—prostaglandin E2 –that is required by C. neoformans for growth during infection. We subsequently show that prostaglandin E₂ must be converted to 15-keto-prostaglandin E₂ within the host before it has these effects. Furthermore, we find that prostaglandin E₂/15-keto-prostaglandin E₂ mediated virulence is via activation of host PPAR-γ –an intracellular eicosanoid receptor known to interact with 15-keto-PGE₂.

Peptides and Peptidomimetics as Potential Antiobesity Agents: Overview of Current Status

There is a high occurrence of obesity worldwide without many new medications being approved for its treatment. Therefore, there is an urgent need to introduce new approaches for treating obesity. Bioactive peptides have been used to treat metabolic disorders- such as type-2 diabetes and obesity; while also possessing anti-oxidant, anti-inflammatory, anti-microbial, and anti-viral properties. However, the development of these peptides has taken backstage due to their size, reduced stability, poor delivery and bioavailability, fast rate of degradation etc. But with the emergence of newer techniques for multifunctional peptides, mimetics, peptide analogs, and aptamers, there is a sudden revival in this therapeutic field. An increased attention is required for development of the natural peptides from food and marine sources which can mimic the function of mediators involved in weight management to avoid obesity. Herein, the search for the structures of anti-obesity peptides was carried out in order to establish their potential for drug development in future. An extensive search for the current status of endogenous, food and marine peptides, with reference to novel and interesting experimental approaches based on peptidomimetics for controlling obesity, was performed. Apolipoprotein A-I (apoA-I), melanocortin-4 receptor (MC4R)-specific agonist, GLP-1 dual and triple agonists, neuropeptides and prolactin-releasing peptide mimetics were specifically examined for their anti-obesity role. Novel peptides, mimetics, and synthesis interventions are transpiring and might offer safer alternatives for otherwise scarcely available safe antiobesity drug. A deeper understanding of peptides and their chemistry through the use of peptide engineering can be useful to overcome the disadvantages and select best mimetics and analogs for treatment in future.

Polyherbal dietary supplementation for prediabetic adults: study protocol for a randomized controlled trial

Background

Prediabetes describes a state of hyperglycemia outside of normal limits that does not meet the criteria for diabetes diagnosis, is generally symptomless, and affects an estimated 38% of adults in the United States. Prediabetes typically precedes the diagnosis of type 2 diabetes, which accounts for increased morbidity and mortality. Although the use of dietary and herbal supplements is popular worldwide, and a variety of single herbal medicines have been examined for glycemic management, the potential of increasingly common polyherbal formulations to return glycemic parameters to normal ranges among adults with prediabetes remains largely unexplored. The purpose of this study is to evaluate the efficacy of a commercially available, polyherbal dietary supplement on glycemic and lipid parameters in prediabetic individuals.

Methods

In this multi-site, double-blinded, randomized controlled clinical trial, 40 participants with prediabetes will be randomized to either a daily oral polyherbal dietary supplement (GlucoSupreme™ Herbal; Designs for Health®, Suffield, CT, USA; containing cinnamon bark (Cinnamomum cassia), banaba leaf (Lagerstroemia speciosa standardized to 1% corosolic acid), kudzu root (Pueraria lobata standardized to 40% isoflavones), fenugreek seed (Trigonella foenum-graceum standardized to 60% saponins), gymnema leaf (Gymnema sylvestre standardized to 25% gymnemic acid), American ginseng root (Panax quinquefolius standardized to 5% ginsenosides), and berberine HCl derived from bark (Berberis aristata)) or placebo for 12 weeks. Short-, medium-, and comparatively long-term markers of glycemic control (blood glucose and fasting insulin, fructosamine, and glycated hemoglobin/A1c, respectively), and other glycemic parameters (GlycoMark, β-cell function, and insulin sensitivity/resistance) will be obtained. Lipid profile (total cholesterol, LDL, HDL, and triglycerides), inflammation (hs-CRP), progression to type 2 diabetes mellitus, as well as safety indices (ALT, AST) will be obtained. An intention-to-treat analysis will be used to assess changes in study outcomes.

Discussion

Treatment options for adults with prediabetes are currently limited. This study aims to evaluate the safety and efficacy of a commercially available dietary supplement in the popular, but as yet insufficiently studied, category of polyherbal formulas for the management of glycemic parameters and other biomarkers associated with prediabetes.

Trial registration

ClinicalTrials.gov, ID: NCT03388762. Retrospectively registered on 4 January 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-3032-6) contains supplementary material, which is available to authorized users.

Signaling Mechanisms of Selective PPARγ Modulators in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease characterized by abnormal protein accumulation, synaptic dysfunction, and cognitive impairment. The continuous increase in the incidence of AD with the aged population and mortality rate indicates the urgent need for establishing novel molecular targets for therapeutic potential. Peroxisome proliferator-activated receptor gamma (PPARγ) agonists such as rosiglitazone and pioglitazone reduce amyloid and tau pathologies, inhibit neuroinflammation, and improve memory impairments in several rodent models and in humans with mild-to-moderate AD. However, these agonists display poor blood brain barrier permeability resulting in inadequate bioavailability in the brain and thus requiring high dosing with chronic time frames. Furthermore, these dosing levels are associated with several adverse effects including increased incidence of weight gain, liver abnormalities, and heart failure. Therefore, there is a need for identifying novel compounds which target PPARγ more selectively in the brain and could provide therapeutic benefits without a high incidence of adverse effects. This review focuses on how PPARγ agonists influence various pathologies in AD with emphasis on development of novel selective PPARγ modulators.

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.

FAM3A mediates PPARγ's protection in liver ischemia-reperfusion injury by activating Akt survival pathway and repressing inflammation and oxidative stress

FAM3A is a novel mitochondrial protein, and its biological function remains largely unknown. This study determined the role and mechanism of FAM3A in liver ischemia-reperfusion injury (IRI). In mouse liver after IRI, FAM3A expression was increased. FAM3A-deficient mice exhibited exaggerated liver damage with increased serum levels of AST, ALT, MPO, MDA and oxidative stress when compared with WT mice after liver IRI. FAM3A-deficient mouse livers had a decrease in ATP content, Akt activity and anti-apoptotic protein expression with an increase in apoptotic protein expression, inflammation and oxidative stress when compared WT mouse livers after IRI. Rosiglitazone pretreatment protected against liver IRI in wild type mice but not in FAM3A-deficient mice. In cultured hepatocytes, FAM3A overexpression protected against, whereas FAM3A deficiency exaggerated oxidative stress-induced cell death. FAM3A upregulation or FAM3A overexpression inhibited hypoxia/reoxygenation-induced activation of apoptotic gene and hepatocyte death in P2 receptor-dependent manner. FAM3A deficiency blunted rosiglitazone's beneficial effects on Akt activation and cell survival in cultured hepatocytes. Collectively, FAM3A protects against liver IRI by activating Akt survival pathways, repressing inflammation and attenuating oxidative stress. Moreover, the protective effects of PPARγ agonist(s) on liver IRI are dependent on FAM3A-ATP-Akt pathway.

Raffinose from Costus speciosus attenuates lipid synthesis through modulation of PPARs/SREBP1c and improves insulin sensitivity through PI3K/AKT

Among several metabolic disorders, the pathogenesis of insulin resistance is considered to be multifactorial. Raffinose, an oligosaccharide isolated from the rhizome of Costus speciosus showed ≤50% inhibition of lipid accumulation in differentiated HepG2 and 3T3-L1 cells through exhibiting partial agonism to PPARγ, and, an enhanced secretion of adiponectin in 3T3-L1 adipocytes. Raffinose was also observed to attenuate the expression of SREBP1c, ACC and FAS which are involved in the fatty acid synthesis. A corresponding upregulation of PPARα and ACO involved in fatty acid oxidation was observed in steatotic HepG2 hepatocytes and 3T3-L1 adipocytes. In vitro evaluation of its anti-diabetic potential showed a dose dependent enhancement of glucose uptake. Investigation of the insulin sensitizing efficacy of Raffinose revealed an increase in Glut4 translocation via phosphorylation of IRβ/PI3K/Akt in differentiated L6 myocytes and 3T3-L1 preadipocytes. In addition, Raffinose was potentially involved in glycogen synthesis by inhibiting the activation of GSK3β. Hence, Raffinose could be a useful therapeutic agent for metabolic maladies.

5-aminosalicylic acid improves lipid profile in mice fed a high-fat cholesterol diet through its dual effects on intestinal PPARγ and PPARα

Obesity is associated with a series of metabolic complications, including dyslipidemia and insulin resistance (IR) that lack effective therapies. In recent years, intestinal inflammation has been suggested to contribute to obesity related metabolic syndrome and targeting gut inflammation with 5-ASA improves diet induced IR, however, its role in dyslipidemia is unknown and has never been explored. In the present study, we reported for the first time that administration of 5-ASA for 12 weeks significantly improved lipid profile by repressing plasma triglycerides and free cholesterol levels in mice fed high-fat cholesterol diet (HFC). In addition, liver lipids were significantly reduced by 5-ASA treatment in HFC-fed mice. Mechanistically, anti-inflammatory genes peroxisome proliferator-activated receptor-γ (Pparγ) and M2 marker, such as Mrc1 and Ym1, were remarkably upregulated, while pro-inflammation gene monocyte chemoattractant protein-1 (Mcp-1) were downregulated in small intestine of mice treated by 5-ASA. Further, 5-ASA improved gastrointestinal barrier by increasing the expression of the tight junction marker ZO-1. 5-ASA also enhanced cholesterol translocation by elevating genes expression of Npc1l1 and Abcg5/8. Moreover, mice fed HFC 5-ASA expressed increased Pparα in small intestinal and its target genes function in lipid oxidation and hydrolysis were remarkable elevated. Taken together, we reported a novel role of 5-ASA which may serve as a therapy target intestinal inflammation induced dyslipidemia.

Novel Benzylidene Thiazolidinedione Derivatives as Partial PPARγ Agonists and their Antidiabetic Effects on Type 2 Diabetes

Peroxisome proliferator-activated receptor γ (PPARγ) has received significant attention as a key regulator of glucose and lipid homeostasis. In this study, we synthesized and tested a library of novel 5-benzylidene-thiazolidin-2,4-dione (BTZD) derivatives bearing a substituent on nitrogen of TZD nucleus (compounds 1a-1k, 2i-10i, 3a, 6a, and 8a-10a). Three compounds (1a, 1i, and 3a) exhibited selectivity towards PPARγ and were found to be weak to moderate partial agonists. Surface Plasmon Resonance (SPR) results demonstrated binding affinity of 1a, 1i and 3a towards PPARγ. Furthermore, docking experiments revealed that BTZDs interact with PPARγ through a distinct binding mode, forming primarily hydrophobic contacts with the ligand-binding pocket (LBD) without direct H-bonding interactions to key residues in H12 that are characteristic of full agonists. In addition, 1a, 1i and 3a significantly improved hyperglycemia and hyperlipidaemia in streptozotocin-nicotinamide (STZ-NA)-induced diabetic rats at a dose of 36 mg/kg/day administered orally for 15 days. Histopathological investigations revealed that microscopic architecture of pancreatic and hepatic cells improved in BTZDs-treated diabetic rats. These findings suggested that 1a, 1i and 3a are very promising pharmacological agents by selectively targeting PPARγ for further development in the clinical treatment of type 2 diabetes mellitus.

Polypharmacology of N6-(3-Iodobenzyl)adenosine-5'-N-methyluronamide (IB-MECA) and Related A3 Adenosine Receptor Ligands: Peroxisome Proliferator Activated Receptor (PPAR) γ Partial Agonist and PPARδ Antagonist Activity Suggests Their Antidiabetic Potential

A3 adenosine receptor (AR) ligands including A3 AR agonist, N6-(3-iodobenzyl)adenosine-5'-N-methyluronamide (1a, IB-MECA) were examined for adiponectin production in human bone marrow mesenchymal stem cells (hBM-MSCs). In this model, 1a significantly increased adiponectin production, which is associated with improved insulin sensitivity. However, A3 AR antagonists also promoted adiponectin production in hBM-MSCs, indicating that the A3 AR pathway may not be directly involved in the adiponectin promoting activity. In a target deconvolution study, their adiponectin-promoting activity was significantly correlated to their binding activity to both peroxisome proliferator activated receptor (PPAR) γ and PPARδ. They functioned as both PPARγ partial agonists and PPARδ antagonists. In the diabetic mouse model, 1a and its structural analogues A3 AR antagonists significantly decreased the serum levels of glucose and triglyceride, supporting their antidiabetic potential. These findings indicate that the polypharmacophore of these compounds may provide therapeutic insight into their multipotent efficacy against various human diseases.

A compound-based proteomic approach discloses 15-ketoatractyligenin methyl ester as a new PPARγ partial agonist with anti-proliferative ability

Proteomics based approaches are emerging as useful tools to identify the targets of bioactive compounds and elucidate their molecular mechanisms of action. Here, we applied a chemical proteomic strategy to identify the peroxisome proliferator-activated receptor γ (PPARγ) as a molecular target of the pro-apoptotic agent 15-ketoatractyligenin methyl ester (compound 1). We demonstrated that compound 1 interacts with PPARγ, forms a covalent bond with the thiol group of C285 and occupies the sub-pocket between helix H3 and the β-sheet of the ligand-binding domain (LBD) of the receptor by Surface Plasmon Resonance (SPR), mass spectrometry-based studies and docking experiments. 1 displayed partial agonism of PPARγ in cell-based transactivation assays and was found to inhibit the AKT pathway, as well as its downstream targets. Consistently, a selective PPARγ antagonist (GW9662) greatly reduced the anti-proliferative and pro-apoptotic effects of 1, providing the molecular basis of its action. Collectively, we identified 1 as a novel PPARγ partial agonist and elucidated its mode of action, paving the way for therapeutic strategies aimed at tailoring novel PPARγ ligands with reduced undesired harmful side effects.

Highly Flexible Protein-Peptide Docking Using CABS-Dock

Protein-peptide molecular docking is a difficult modeling problem. It is even more challenging when significant conformational changes that may occur during the binding process need to be predicted. In this chapter, we demonstrate the capabilities and features of the CABS-dock server for flexible protein-peptide docking. CABS-dock allows highly efficient modeling of full peptide flexibility and significant flexibility of a protein receptor. During CABS-dock docking, the peptide folding and binding process is explicitly simulated and no information about the peptide binding site or its structure is used. This chapter presents a successful CABS-dock use for docking a potentially therapeutic peptide to a protein target. Moreover, simulation contact maps, a new CABS-dock feature, are described and applied to the docking test case. Finally, a tutorial for running CABS-dock from the command line or command line scripts is provided. The CABS-dock web server is available from http://biocomp.chem.uw.edu.pl/CABSdock/ .

Novel Podophyllotoxin Derivatives as Partial PPARγ Agonists and their Effects on Insulin Resistance and Type 2 Diabetes

Peroxisome proliferator-activated receptor γ (PPARγ) is recognized as a key regulator of insulin resistance. In this study, we searched for novel PPARγ agonists in a library of structurally diverse organic compounds and determined that podophyllotoxin exhibits partial agonist activity toward PPARγ. Eight novel podophyllotoxin-like derivatives were synthesized and assayed for toxicity and functional activity toward PPARγ to reduce the possible systemic toxic effects of podophyllotoxin and to maintain partial agonist activity toward PPARγ. Cell-based transactivation assays showed that compounds (E)-3-(hydroxy(3,4,5-trimethoxyphenyl)methyl)-4-(4(trifluoromethyl)styryl)dihydrofuran-2(3H)-one (3a) and (E)-4-(3-acetylstyryl)-3-(hydroxyl (3,4,5-trimethoxyphenyl)methyl)dihydrofuran-2(3H)-one (3f) exhibited partial agonist activity. An experiment using human hepatocarcinoma cells (HepG2) that were induced to become an insulin-resistant model showed that compounds 3a and 3f improved insulin sensitivity and glucose consumption. In addition, compounds 3a and 3f significantly improved hyperglycemia and insulin resistance in high-fat diet-fed streptozotocin (HFD-STZ)-induced type 2 diabetic rats at a dose of 15 mg/kg/day administered orally for 45 days, without significant weight gain. Cell toxicity testing also showed that compounds 3a and 3f exhibited weaker toxicity than pioglitazone. These findings suggested that compounds 3a and 3f improved insulin resistance in vivo and in vitro and that the compounds exhibited potential for the treatment of type 2 diabetes mellitus.

Thyroid-stimulating hormone improves insulin sensitivity in skeletal muscle cells via cAMP/PKA/CREB pathway-dependent upregulation of insulin receptor substrate-1 expression

Thyroid-stimulating hormone (TSH) receptor is expressed in extrathyroidal tissues such as hepatocytes, adipocytes, and skeletal muscle, which suggests a possible novel role of TSH in various metabolic processes in extrathyroidal tissues independent of thyroid hormones. We investigated whether TSH has any effects on glucose tolerance and insulin sensitivity in the skeletal muscle using diet-induced obesity (DIO) mouse models and rodent skeletal muscle cells. TSH improved glucose tolerance in DIO mice and this was associated with an improvement of skeletal muscle insulin sensitivity resulting from the increased expression of insulin receptor substrate (IRS)-1 protein and mRNA therein. TSH significantly increased both basal and insulin-stimulated glucose transport in rat L6 myotubes and increased the expression of IRS-1 protein and mRNA in these cells as well. TSH also stimulated Irs1 promoter activation; this stimulation was abolished by protein kinase A (PKA) inhibition using H89 or by mutation of the cAMP-response element site located at -1155 to -875 bp of the Irs1 promoter region, supporting a novel role of TSH activated-cAMP/PKA/CREB signaling in the regulation of Irs1 expression. In conclusion, TSH improves insulin sensitivity in skeletal muscle by increasing Irs1 gene expression. This regulatory effect is mediated by a PKA-CREB-dependent pathway.

Allosteric Pathways in the PPARγ-RXRα nuclear receptor complex

Understanding the nature of allostery in DNA-nuclear receptor (NR) complexes is of fundamental importance for drug development since NRs regulate the transcription of a myriad of genes in humans and other metazoans. Here, we investigate allostery in the peroxisome proliferator-activated/retinoid X receptor heterodimer. This important NR complex is a target for antidiabetic drugs since it binds to DNA and functions as a transcription factor essential for insulin sensitization and lipid metabolism. We find evidence of interdependent motions of Ω-loops and PPARγ-DNA binding domain with contacts susceptible to conformational changes and mutations, critical for regulating transcriptional functions in response to sequence-dependent DNA dynamics. Statistical network analysis of the correlated motions, observed in molecular dynamics simulations, shows preferential allosteric pathways with convergence centers comprised of polar amino acid residues. These findings are particularly relevant for the design of allosteric modulators of ligand-dependent transcription factors.

SR2067 Reveals a Unique Kinetic and Structural Signature for PPARγ Partial Agonism

Synthetic full agonists of PPARγ have been prescribed for the treatment of diabetes due to their ability to regulate glucose homeostasis and insulin sensitization. While the use of full agonists of PPARγ has been hampered due to severe side effects, partial agonists have shown promise due to their decreased incidence of such side effects in preclinical models. No kinetic information has been forthcoming in regard to the mechanism of full versus partial agonism of PPARγ to date. Here, we describe the discovery of a partial agonist, SR2067. A co-crystal structure obtained at 2.2 Å resolution demonstrates that interactions with the β-sheet are driven exclusively via hydrophobic interactions mediated through a naphthalene group, an observation that is unique from other partial agonists. Surface plasmon resonance revealed that SR2067 binds to the receptor with higher affinity (KD = 513 nM) as compared to that of full agonist rosiglitazone, yet it has a much slower off rate compared to that of rosiglitazone.

Protective effects of Angelica sinensis polysaccharide against hyperglycemia and liver injury in multiple low-dose streptozotocin-induced type 2 diabetic BALB/c mice

Angelica sinensis polysaccharide (ASP), one of the major active ingredients isolated from the roots of Angelica sinensis (Oliv.) Diels, possesses antidiabetic bioactivity.

Computational study of the binding orientation and affinity of PPARγ agonists: inclusion of ligand-induced fit by cross-docking

A cross-docking study for describing differential binding energies of PPARγ and agonists was successful after the inclusion of protein flexibility through the use of several crystal receptor conformations.

Erythropoietin alleviates hepatic insulin resistance via PPARγ-dependent AKT activation

Erythropoietin (EPO) has beneficial effects on glucose metabolism and insulin resistance. However, the mechanism underlying these effects has not yet been elucidated. This study aimed to investigate how EPO affects hepatic glucose metabolism. Here, we report that EPO administration promoted phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation in palmitic acid (PA)-treated HepG2 cells and in the liver of high-fat diet (HFD)-fed mice, whereas adenovirus-mediated silencing of the erythropoietin receptor (EPOR) blocked EPO-induced AKT signalling in HepG2 cells. Importantly, a peroxisome proliferator-activated receptor γ (PPARγ) antagonist and PPARγ small interfering RNA (siRNA) abrogated the EPO-induced increase in p-AKT in HepG2 cells. Lentiviral vector-mediated hepatic PPARγ silencing in HFD-fed C57BL/6 mice impaired EPO-mediated increases in glucose tolerance, insulin sensitivity and hepatic AKT activation. Furthermore, EPO activated the AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1) signalling pathway, and AMPKα and SIRT1 knockdown each attenuated the EPO-induced PPARγ expression and deacetylation and PPARγ-dependent AKT activation in HepG2 cells. In summary, these findings suggest that PPARγ is involved in EPO/EPOR-induced AKT activation, and targeting the PPARγ/AKT pathway via EPO may have therapeutic implications for hepatic insulin resistance and type 2 diabetes.

Review of the Structural and Dynamic Mechanisms of PPARγ Partial Agonism

PPARγ (peroxisome proliferator activated receptor γ) is a ligand activated transcription factor of the nuclear receptor superfamily that controls the expression of a variety of genes involved in fatty acid metabolism, adipogenesis, and insulin sensitivity. While endogenous ligands of PPARγ include fatty acids and eicosanoids, synthetic full agonists of the receptor, including members of the thiazolidinedione (TZD) class, have been widely prescribed for the treatment of type II diabetes mellitus (T2DM). Unfortunately, the use of full agonists has been hampered by harsh side effects with some removed from the market in many countries. In contrast, partial agonists of PPARγ have been shown to retain favourable insulin sensitizing effects while exhibiting little to no side effects and thus represent a new potential class of therapeutics for the treatment of T2DM. Partial agonists have been found to not only display differences in transcriptional and cellular outcomes, but also act through distinct structural and dynamic mechanisms within the ligand binding cavity compared to full agonists.

Pharmacophore modeling improves virtual screening for novel peroxisome proliferator-activated receptor-gamma ligands

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a nuclear hormone receptor involved in regulating various metabolic and immune processes. The PPAR family of receptors possesses a large binding cavity that imparts promiscuity of ligand binding not common to other nuclear receptors. This feature increases the challenge of using computational methods to identify PPAR ligands that will dock favorably into a structural model. Utilizing both ligand- and structure-based pharmacophore methods, we sought to improve agonist prediction by grouping ligands according to pharmacophore features, and pairing models derived from these features with receptor structures for docking. For 22 of the 33 receptor structures evaluated we observed an increase in true positive rate (TPR) when screening was restricted to compounds sharing molecular features found in rosiglitazone. A combination of structure models used for docking resulted in a higher TPR (40 %) when compared to docking with a single structure model (<20 %). Prediction was also improved when specific protein-ligand interactions between the docked ligands and structure models were given greater weight than the calculated free energy of binding. A large-scale screen of compounds using a marketed drug database verified the predictive ability of the selected structure models. This study highlights the steps necessary to improve screening for PPARγ ligands using multiple structure models, ligand-based pharmacophore data, evaluation of protein-ligand interactions, and comparison of docking datasets. The unique combination of methods presented here holds potential for more efficient screening of compounds with unknown affinity for PPARγ that could serve as candidates for therapeutic development.

A Novel Partial Agonist of Peroxisome Proliferator-Activated Receptor γ with Excellent Effect on Insulin Resistance and Type 2 Diabetes

Partial agonists of peroxisome proliferator-activated receptor γ (PPARγ) reportedly reverse insulin resistance in patients with type 2 diabetes mellitus. In this work, a novel non-thiazolidinedione-partial PPARγ ligand, MDCCCL1636 [N-(4-hydroxyphenethyl)-3-mercapto-2-methylpropanamide], was investigated. The compound displayed partial agonist activity in biochemical and cell-based transactivation assays and reversed insulin resistance. MDCCCL1636 showed a potential antidiabetic effect on an insulin-resistance model of human hepatocarcinoma cells (HepG2). High-fat diet-fed streptozotocin-induced diabetic rats treated with MDCCCL1636 for 56 days displayed reduced fasting serum glucose and reversed dyslipidemia and pancreatic damage without significant weight gain. Furthermore, MDCCCL1636 had lower toxicity in vivo and in vitro than pioglitazone. MDCCCL1636 also potentiated glucose consumption and inhibited the impairment in insulin signaling targets, such as AKT, glycogen synthase kinase 3β, and glycogen synthase, in HepG2 human hepatoma cells. Overall, our results suggest that MDCCCL1636 is a promising candidate for the prevention and treatment of type 2 diabetes mellitus.

Identification of a novel selective agonist of PPARγ with no promotion of adipogenesis and less inhibition of osteoblastogenesis

Nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) plays an important role in the regulation of glucose homeostasis and lipid metabolism. However, current PPARγ-targeting drugs such as thiazolidinediones (TZDs) are associated with undesirable side effects. We identified a small molecular compound, F12016, as a selective PPARγ agonist by virtual screening, which showed moderate PPARγ agonistic activity and binding ability for PPARγ. F12016 did not activate other PPAR subtypes at 30 μM and selectively modulated PPARγ target gene expression. In diabetic KKAy mice, F12016 had insulin-sensitizing and glucose-lowering properties, and suppressed weight gain. In vitro, F12016 effectively increased glucose uptake and blocked cyclin-dependent kinase 5-mediated phosphorylation of PPARγ at Ser273, but slightly triggered adipogenesis and less inhibited osteoblastogenesis than rosiglitazone. Moreover, compared with the full agonist rosiglitazone, F12016 had a distinct group of coregulators and a different predicted binding mode for the PPARγ ligand-binding domain. A site mutation assay confirmed the key epitopes, especially Tyr473 in AF-2. In summary, our study shows that F12016 is a non-TZD, novel selective PPARγ agonist without the classical lipogenic side effects, which may provide a new structural strategy for designing PPARγ ligands with advantages over TZDs.