GQ-16, a novel peroxisome proliferator-activated receptor γ (PPARγ) ligand, promotes insulin sensitization without weight gain

Novel thiazolidin-4-one benzenesulfonamide hybrids as PPARγ agonists: Design, synthesis and in vivo anti-diabetic evaluation

In the current study, two series of novel thiazolidin-4-one benzenesulfonamide arylidene hybrids 9a-l and 10a-f were designed, synthesized and tested in vitro for their PPARɣ agonistic activity. The phenethyl thiazolidin-4-one sulphonamide 9l showed the highest PPARɣ activation % by 41.7%. Whereas, the 3-methoxy- and 4-methyl-4-benzyloxy thiazolidin-4-one sulphonamides 9i, and 9k revealed moderate PPARɣ activation % of 31.7, and 32.8%, respectively, in addition, the 3-methoxy-3-benzyloxy thiazolidin-4-one sulphonamide 10d showed PPARɣ activation % of 33.7% compared to pioglitazone. Compounds 9b, 9i, 9k, 9l, and 10d revealed higher selectivity to PPARɣ over the PPARδ, and PPARα isoforms. An immunohistochemical study was performed in HepG-2 cells to confirm the PPARɣ protein expression for the most active compounds. Compounds 9i, 9k, and 10d showed higher PPARɣ expression than that of pioglitazone. Pharmacological studies were also performed to determine the anti-diabetic activity in rats at a dose of 36 mg/kg, and it was revealed that compounds 9i and 10d improved insulin secretion as well as anti-diabetic effects. The 3-methoxy-4-benzyloxy thiazolidin-4-one sulphonamide 9i showed a better anti-diabetic activity than pioglitazone. Moreover, it showed a rise in blood insulin by 4-folds and C-peptide levels by 48.8%, as well as improved insulin sensitivity. Moreover, compound 9i improved diabetic complications as evidenced by decreasing liver serum enzymes, restoration of total protein and kidney functions. Besides, it combated oxidative stress status and exerted anti-hyperlipidemic effect. Compound 9i showed a superior activity by normalizing some parameters and amelioration of pancreatic, hepatic, and renal histopathological alterations caused by STZ-induction of diabetes. Molecular docking studies, molecular dynamic simulations, and protein ligand interaction analysis were also performed for the newly synthesized compounds to investigate their predicted binding pattern and energies in PPARɣ binding site.

PPARγ partial agonist LPSF/GQ-16 prevents dermal and pulmonary fibrosis in HOCl-induced systemic sclerosis (SSc) and modulates cytokine production in PBMC of SSc patients

Thiazolidinediones (TZD) are synthetic molecules that have a range of biological effects, including antifibrotic and anti-inflammatory, and they may represent a promising therapeutic strategy for systemic sclerosis (SSc). The aim of this study was to investigate the immunomodulatory and antifibrotic properties of LPSF/GQ-16, a TZD derivative, in peripheral blood mononuclear cells (PBMC) from SSc patients and in a murine model of SSc HOCl-induced. The PBMC of 20 SSc patients were stimulated with phytohemagglutinin (PHA) and treated with LPSF/GQ-16 for 48 h, later cytokines in the culture supernatants were quantified by sandwich enzyme-linked immunosorbent assay (ELISA) or cytometric bead array (CBA). Experimental SSc was induced by intradermal injections of hypochlorous acid (HOCl) for 6 weeks. HOCl-induced SSc mice received daily treatment with LPSF/GQ-16 (30 mg/kg) through intraperitoneal injections during the same period. Immunological parameters were evaluated by flow cytometry and ELISA, and dermal and pulmonary fibrosis were evaluated by RT-qPCR, hydroxyproline dosage and histopathological analysis. In PBMC cultures, it was possible to observe that LPSF/GQ-16 modulated the secretion of cytokines IL-2 (p < 0.001), IL-4 (p < 0.001), IL-6 (p < 0.001), IL-17A (p = 0.006), TNF (p < 0.001) and IFN-γ (p < 0.001). In addition, treatment with LPSF/GQ-16 in HOCl-induced SSc mice promoted a significant reduction in dermal thickening (p < 0.001), in the accumulation of collagen in the skin (p < 0.001), down-regulated the expression of fibrosis markers in the skin (Col1a1, α-Sma and Tgfβ1, p < 0.001 for all) and lungs (Il4 and Il13, p < 0.001 for both), as well as reduced activation of CD4 + T cells (p < 0.001), B cells (p < 0.001) and M2 macrophages (p < 0.001). In conclusion, LPSF/GQ-16 showed immunomodulatory and antifibrotic properties, demonstrating the therapeutic potential of this molecule for SSc.

Rational design of thiazolidine-4-one-gallic acid hybrid derivatives as selective partial PPARγ modulators: an in-silico approach for type 2 diabetes treatment

Type 2 diabetes mellitus is a bipolar metabolic disorder characterized by abnormalities in insulin production from β-cells and insulin resistance. Thiazolidinediones are potent anti-diabetic agents that act through the modulation of the peroxisome proliferator-activated receptor γ (PPARγ), a nuclear receptor. However, their full agonistic activity leads to severe side effects by stabilizing Helix12 through strong hydrogen bonding with the TYR473 residue. Partial and selective PPARγ modulators (GW0072, GQ16, VSP-51, MRL-20, MBX-213, INT131) have demonstrated superior results compared to full agonists without causing adverse effects, as reported in existing data. To address this uncertainty and advance therapeutic options, we identified and designed a novel class of compounds (A1-A23) based on a hybrid structure combining phenolic and Thiazolidine-4-one's moieties. Our rational drug design strategy incorporated structural-activity relationship principle, and validated the docking studies through calculated the root mean square deviation. Additionally, we conducted molecular docking, binding energy, molecular dynamics simulations, and post-molecular dynamics calculations to evaluate the dynamics behavior between the ligands and protein. The selected ligands demonstrated highly favorable docking scores and binding energies, comparable to the co-crystal (rosiglitazone) such as A12 (-13.9 kcal/mol and -86.2 kcal/mol), A1 (-11.1 kcal/mol and -79.5 kcal/mol), A13 (-11.3 kcal/mol and -91.4 kcal/mol), and the co-crystal itself (-9.8 kcal/mol and -76 kcal/mol), respectively. Finally, the MD revealed that, the selected ligands were equally contributed for stabilization of Helix12 and β-sheets. It was concluded, the designed ligands (A12, A1, and A13) exhibited weaker hydrogen-bond interactions with specific residue TYR473 which partially modulated the PPARγ protein.Communicated by Ramaswamy H. Sarma.

Genistein enhances NAD+ biosynthesis by upregulating nicotinamide phosphoribosyltransferase in adipocytes

A decrease in the NAD+ level in adipocytes causes adipose-tissue dysfunction, leading to systemic glucose, and lipid metabolism failure. Therefore, it is necessary to develop small molecules and nutraceuticals that can increase NAD+ levels in adipocytes. Genistein, a nutraceutical derived from soybeans, has various physiological activities and improves glucose and lipid metabolism. In this study, we aimed to unravel the effects of genistein on the NAD+ level in adipocytes and the underlying molecular mechanisms. Genistein enhanced NAD+ biosynthesis by increasing the expression of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in NAD+ biosynthesis. A pull-down assay using genistein-immobilized beads revealed prohibitin 1 (PHB1) as a target protein of genistein. The knockdown of Phb1 suppressed the genistein-induced increase in NAMPT expression and NAD+ level in adipocytes. Genistein-bound PHB1 contributed to the stabilization of the transcription factor CCAAT/enhancer-binding protein β through the activation of extracellular signal-regulated kinase, resulting in increased NAMPT expression at the transcriptional level. Genistein induced the dephosphorylation of peroxisome proliferator-activated receptor at serine 273 and increased the level of the insulin-sensitizing adipokine adiponectin in adipocytes, whereas the knockdown of Nampt and Phb1 abolished these genistein-mediated effects. Our results proved the potential efficacy of genistein in increasing the NAD+ level and restoring metabolic function in adipocytes. Furthermore, we identified PHB1, localized to the plasma membrane, as a novel candidate target protein for increased expression of NAMPT in adipocytes. Overall, these findings will assist in developing NAD+-boosting nutraceuticals to alleviate metabolic dysfunctions in adipose tissues.

Evidence that methylglyoxal and receptor for advanced glycation end products are implicated in bladder dysfunction of obese diabetic ob/ob mice

Glycolytic overload in diabetes causes large accumulation of the highly reactive dicarbonyl compound methylglyoxal (MGO) and overproduction of advanced glycation end products (AGEs), which interact with their receptors (RAGE), leading to diabetes-associated macrovascular complications. The bladder is an organ that stays most in contact with dicarbonyl species, but little is known about the importance of the MGO-AGEs-RAGE pathway to diabetes-associated bladder dysfunction. Here, we aimed to investigate the role of the MGO-AGEs-RAGE pathway in bladder dysfunction of diabetic male and female ob/ob mice compared with wild-type (WT) lean mice. Diabetic ob/ob mice were treated with the AGE breaker alagebrium (ALT-711, 1 mg/kg) for 8 wk in drinking water. Compared with WT animals, male and female ob/ob mice showed marked hyperglycemia and insulin resistance, whereas fluid intake remained unaltered. Levels of total AGEs, MGO-derived hydroimidazolone 1, and RAGE in bladder tissues, as well as fluorescent AGEs in serum, were significantly elevated in ob/ob mice of either sex. Collagen content was also markedly elevated in the bladders of ob/ob mice. Void spot assays in filter paper in conscious mice revealed significant increases in total void volume and volume per void in ob/ob mice with no alterations of spot number. Treatment with ALT-711 significantly reduced the levels of MGO, AGEs, RAGE, and collagen content in ob/ob mice. In addition, ALT-711 treatment normalized the volume per void and increased the number of spots in ob/ob mice. Activation of AGEs-RAGE pathways by MGO in the bladder wall may contribute to the pathogenesis of diabetes-associated bladder dysfunction.NEW & NOTEWORTHY The involvement of methylglyoxal (MGO) and advanced glycation end products (AGEs) in bladder dysfunction of diabetic ob/ob mice treated with the AGE breaker ALT-711 was investigated here. Diabetic mice exhibited high levels of MGO, AGEs, receptor for AGEs (RAGE), and collagen in serum and/or bladder tissues along with increased volume per void, all of which were reduced by ALT-711. Activation of the MGO-AGEs-RAGE pathway in the bladder wall contributes to the pathogenesis of diabetes-associated bladder dysfunction.

Hachimijiogan, a traditional herbal medicine, modulates adipose cell function and ameliorates diet-induced obesity and insulin resistance in mice

Hachimijiogan (HJG) has originally been used to ameliorate a variety of symptoms associated with low ambient temperatures. However, its pharmacological action in metabolic organs remains unclear. We hypothesized that HJG may modulate metabolic function and have a potential therapeutic application to metabolic diseases. To test this hypothesis, we investigated metabolic action of HJG in mice. Male C57BL/6J mice chronically administered with HJG showed a reduction in adipocyte size with increased transcription of beige adipocyte-related genes in subcutaneous white adipose tissue. HJG-mixed high-fat diet (HFD)-fed mice showed alleviation of HFD-induced weight gain, adipocyte hypertrophy, liver steatosis with a significant reduction in circulating leptin and Fibroblast growth factor 21 despite no changes in food intake or oxygen consumption. Feeding an HJG-mixed HFD following 4-weeks of HFD feeding, while a limited effect on body weight, improved insulin sensitivity with a reversal of decreased circulating adiponectin. In addition, HJG improved insulin sensitivity in the leptin-deficient mice without significant effects on body weight. Treatment with n-butanol soluble extracts of HJG potentiated transcription of Uncoupling protein 1 mediated by β3-adrenergic agonism in 3T3L1 adipocytes. These findings provide evidence that HJG modulates adipocyte function and may exert preventive or therapeutic effects against obesity and insulin resistance.

Biological Screening and Crystallographic Studies of Hydroxy γ-Lactone Derivatives to Investigate PPARγ Phosphorylation Inhibition

PPARγ represents a key target for the treatment of type 2 diabetes and metabolic syndrome. To avoid serious adverse effects related to the PPARγ agonism profile of traditional antidiabetic drugs, a new opportunity is represented by the development of molecules acting as inhibitors of PPARγ phosphorylation by the cyclin-dependent kinase 5 (CDK5). Their mechanism of action is mediated by the stabilization of the PPARγ β-sheet containing Ser273 (Ser245 in PPARγ isoform 1 nomenclature). In this paper, we report the identification of new γ-hydroxy-lactone-based PPARγ binders from the screening of an in-house library. These compounds exhibit a non-agonist profile towards PPARγ, and one of them prevents Ser245 PPARγ phosphorylation by acting mainly on PPARγ stabilization and exerting a weak CDK5 inhibitory effect.

AM-879, a PPARy non-agonist and Ser273 phosphorylation blocker, promotes insulin sensitivity without adverse effects in mice

Obesity is one of the main risk factors for type 2 diabetes, and peroxisome proliferator-activated receptor γ (PPARγ) is considered a promising pathway on insulin sensitivity and adipose tissue metabolism. The search for molecules acting as insulin sensitizers have increased, especially for molecules that block PPARγ-Ser273 phosphorylation, without reaching full agonism. We evaluated the in vivo effects of AM-879, a PPARγ non-agonist, and found that AM-879 exerts different effects in mice depending on the dose. At lower doses, this ligand decreased BAT, increased leptin and Crh expression. However, at a higher dose, it promoted improvement on insulin sensitivity, ameliorates expression of metabolism-related genes, decreased the expression of genes related to liver toxicity, maintaining body weight and adipocyte size. These results present a new lead molecule to ameliorates insulin resistance and confirm AM-879 as a PPARγ non-agonist which blocks Ser273 phosphorylation as a good strategy to modulate insulin sensitivity without developing the adverse effects promoted by PPARγ full agonists.

Citrus nutraceutical eriocitrin and its metabolites are partial agonists of peroxisome proliferator-activated receptor gamma (PPARγ): a molecular docking and molecular dynamics study

Peroxisome proliferator-activated receptor gamma (PPARγ) agonists are potent insulin sensitizers in treating type 2 diabetes. Despite being very effective in the fight against diabetes-mediated complications, PPARγ agonists are accompanied by severe side effects leading to complicated health problems, making the discovery of novel safe ligands highly pertinent. A significant intense research effort is in progress to explore the PPARγ activating potential of a wide range of natural compounds. Lemon (Citrus limon) contains various bioactive flavonoids, and eriocitrin is the major flavonoid. It possesses substantial antioxidant and anticancer, lipid-lowering activities and prevents obesity-associated metabolic diseases. Eriocitrin is metabolized to eriodictyol in the intestine, and the absorbed eriodictyol undergoes conversion to numerous metabolites in vivo. It is unclear if eriocitrin or its metabolites are responsible for their beneficial effects. We have used molecular docking, ADMET properties, drug-likeness score and molecular dynamics simulation study to find if eriocitrin and its metabolites are potent binders for PPARγ. Docking studies revealed that eriocitrin binds to PPARγ with the highest binding energy, but ADMET properties and in vivo studies show that the bioavailability of eriocitrin is very poor. Molecular dynamics studies were carried out to validate the docking results, and multiple parameters like RMSD, RMSF, Radius of gyration, SASA, hydrogen bond analysis, interaction energy, principal component analysis, Gibbs free energy and MM-PBSA were calculated. Based on our studies, eriodictyol, eriodictyol 7-O-glucuronide, eriodictyol 3'-O-glucuronide, homoeriodictyol and homoeriodictyol 7-O-glucuronide which are metabolites of eriocitrin appear to be potent partial agonists of PPARγ under physiological conditions.Communicated by Ramaswamy H. Sarma.

Hippeastrum stapfianum (Kraenzl.) R.S.Oliveira & Dutilh (Amaryllidaceae) Ethanol Extract Activity on Acetylcholinesterase and PPAR-α/γ Receptors

Hippeastrum stapfianum (Kraenzl.) R.S.Oliveira & Dutilh (Amaryllidaceae) is an endemic plant species from the Brazilian savannah with biological and pharmacological potential. This study evaluated the effects of ethanol extract from H. stapfianum leaves on acetylcholinesterase enzyme activity and the action on nuclear receptors PPAR-α and PPAR-γ. A gene reporter assay was performed to assess the PPAR agonist or antagonist activity with a non-toxic dose of H. stapfianum ethanol extract. The antioxidant capacity was investigated using DPPH^• scavenging and fosfomolybdenium reduction assays. The identification of H. stapfianum's chemical composition was performed by gas chromatography-mass spectrometry (GC-MS) and HPLC. The ethanol extract of H. stapfianum activated PPAR-α and PPAR-γ selectively, inhibited the acetylcholinesterase enzyme, and presented antioxidant activity in an in vitro assay. The major compounds identified were lycorine, 7-demethoxy-9-O-methylhostasine, and rutin. Therefore, H. stapfianum is a potential source of drugs for Alzheimer's disease due to its ability to activate PPAR receptors, acetylcholinesterase inhibition activity, and antioxidant attributes.

Alternatively Spliced Landscape of PPARγ mRNA in Podocytes Is Distinct from Adipose Tissue

Podocytes are highly differentiated epithelial cells, and their structural and functional integrity is compromised in a majority of glomerular and renal diseases, leading to proteinuria, chronic kidney disease, and kidney failure. Traditional agonists (e.g., pioglitazone) and selective modulators (e.g., GQ-16) of peroxisome-proliferator-activated-receptor-γ (PPARγ) reduce proteinuria in animal models of glomerular disease and protect podocytes from injury via PPARγ activation. This indicates a pivotal role for PPARγ in maintaining glomerular function through preservation of podocytes distinct from its well-understood role in driving insulin sensitivity and adipogenesis. While its transcriptional role in activating adipokines and adipogenic genes is well-established in adipose tissue, liver and muscle, understanding of podocyte PPARγ signaling remains limited. We performed a comprehensive analysis of PPARγ mRNA variants due to alternative splicing, in human podocytes and compared with adipose tissue. We found that podocytes express the ubiquitous PPARγ Var 1 (encoding γ1) and not Var2 (encoding γ2), which is mostly restricted to adipose tissue and liver. Additionally, we detected expression at very low level of Var4, and barely detectable levels of other variants, Var3, Var11, VartORF4 and Var9, in podocytes. Furthermore, a distinct podocyte vs. adipocyte PPAR-promoter-response-element containing gene expression, enrichment and pathway signature was observed, suggesting differential regulation by podocyte specific PPARγ1 variant, distinct from the adipocyte-specific γ2 variant. In summary, podocytes and glomeruli express several PPARγ variants, including Var1 (γ1) and excluding adipocyte-specific Var2 (γ2), which may have implications in podocyte specific signaling and pathophysiology. This suggests that that new selective PPARγ modulators can be potentially developed that will be able to distinguish between the two forms, γ1 and γ2, thus forming a basis of novel targeted therapeutic avenues.

Identification of a novel PPARγ modulator with good anti-diabetic therapeutic index via structure-based screening, optimization and biological validation

PPARγ is well-known as the target receptor of TZD anti-diabetic drugs. However, recently the therapeutic benefits of these TZD drugs have been compromised by many severe side effects because of their full PPARγ agonistic action to lock the AF-2 helix. Herein, we conducted a virtual screening in the combination with structure-based design, synthesis and biological evaluation both in vitro and in vivo, leading to the identification of a potent candidate YG-C-20 as the SPPARγM with improved and safer anti-diabetic therapeutics. Mechanistically, this compound presented such desired pharmacological profiles (e.g., preferable anti-diabetic efficiencies and minimized side effects) mainly via selectively inhibiting the CDK5-mediated phosphorylation of PPARγ-Ser273 and up-regulating the expression of insulin-sensitive genes Adiponectin and Glut4, yet lacking the classical full agonism to induce the adipogenesis and the expression of key adipogenic genes including PPARγ, aP2, CD36, LPL, C/EBPα and FASN. Further validation led to the final recognition of its (R)-configured isomer as the potential conformational form. Subsequent molecular docking studies revealed a unique hydrogen-bonding network of (R)-YG-C-20 with three full PPARγ agonism-unrelated residues, especially with PPARγ-Ser273 phosphorylation-associated site Ser342, which not only gives a clear verification for our structure-based design but also provides a proof of concept for the abovementioned molecular mechanism.

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.

Selective modulator of nuclear receptor PPARγ with reduced adipogenic potential ameliorates experimental nephrotic syndrome

Glomerular disease manifests as nephrotic syndrome (NS) with high proteinuria and comorbidities, and is frequently refractory to standard treatments. We hypothesized that a selective modulator of PPARγ, GQ-16, will provide therapeutic advantage over traditional PPARγ agonists for NS treatment. We demonstrate in a pre-clinical NS model that proteinuria is reduced with pioglitazone to 64%, and robustly with GQ-16 to 81% of nephrosis, comparable to controls. Although both GQ-16 and pioglitazone restore glomerular-Nphs1, hepatic-Pcsk9 and serum-cholesterol, only GQ-16 restores glomerular-Nrf2, and reduces hypoalbuminemia and hypercoagulopathy. GQ-16 and pioglitazone restore common and distinct glomerular gene expression analyzed by RNA-seq and induce insulin sensitizing adipokines to various degrees. Pioglitazone but not GQ-16 induces more lipid accumulation and aP2 in adipocytes and white adipose tissue. We conclude that selective modulation of PPARγ by a partial agonist, GQ-16, is more advantageous than pioglitazone in reducing proteinuria, NS associated comorbidities, and adipogenic side effects of full PPARγ agonists.

Discovery by Virtual Screening of an Inhibitor of CDK5-Mediated PPARγ Phosphorylation

Thiazolidinedione PPARγ agonists such as rosiglitazone and pioglitazone are effective antidiabetic drugs, but side effects have limited their use. It has been posited that their positive antidiabetic effects are mainly mediated by the inhibition of the CDK5-mediated Ser273 phosphorylation of PPARγ, whereas the side effects are linked to classical PPARγ agonism. Thus compounds that inhibit PPARγ Ser273 phosphorylation but lack classical PPARγ agonism have been sought as safer antidiabetic therapies. Herein we report the discovery by virtual screening of 10, which is a potent PPARγ binder and in vitro inhibitor of the CDK5-mediated phosphorylation of PPARγ Ser273 and displays negligible PPARγ agonism in a reporter gene assay. The pharmacokinetic properties of 10 are compatible with oral dosing, enabling preclinical in vivo testing, and a 7 day treatment demonstrated an improvement in insulin sensitivity in the ob/ob diabetic mouse model.

Role of Plant Derived Products Through Exhilarating Peroxisome Proliferator Activated Receptor-γ (ppar-γ) in the Amelioration of Obesity Induced Insulin Resistance

Abstract:

Insulin resistance is an elemental facet of the etiology of diabetes mellitus and the principal relating factor between obesity and diabetes. Oxidative stress, lipotoxicity, inflammation and receptor dysfunction are the underlying determinants of insulin resistance commencement in metabolic illnesses. ppar-γ is a nuclear transcription factor whose activation or inhibition directly influences insulin resistance and controls glucose and lipid homeostasis by modulating gene expression. Synthetic ligands of ppar-γ are therapeutically employed to counter the hyper-glycaemia associated with obesity and type 2 diabetes, but they possess severe side effects. In the modern era, bioactive phytochemicals have been employed in the drug development process and a considerable investigation has recently been initiated to analyze the ppar-γ activating ability of diverse phytochemicals. In this review, we outlined the role of phytochemicals in insulin resistance treatment through ppar-γ activation.

Discovery of the first-in-class dual PPARδ/γ partial agonist for the treatment of metabolic syndrome

The peroxisome proliferator-activated receptors (PPARs) exert vital function in the regulation of energy metabolism, which were considered as promising targets of metabolic syndrome. Until now, PPARδ/γ dual agonist is rarely reported, and thereby the pharmacologic action of PPARδ/γ dual agonist is still unclear. In this study, we identified a dual PPARδ/γ partial agonist 6 (ZLY06) based on the cyclization strategy of PPARα/δ dual agonist GFT505. ZLY06 revealed excellent pharmacokinetic profiles suitable for oral medication. Moreover, ZLY06 markedly improved glucolipid metabolism without weight gain, and alleviated fatty liver by promoting the β-oxidation of fatty acid and inhibiting hepatic lipogenesis. In contrast, weight gain and hepatic steatosis were observed in Rosiglitazone, a widely used PPARγ full agonist. All of these results indicated that ZLY06 exhibits potential benefits on metabolic syndrome, while no adverse effects related to PPARγ full agonist.

Synthesis and biological evaluation of cajanonic acid A derivatives as potential PPARγ antagonists

Four series of cajanonic acid A (CAA) derivatives have been designed and synthesized. The newly prepared compounds have been screened for glucose consumption activity in HepG2 cell lines and PPARγ antagonistic activity in HEK293 cell lines. Compound 26g bearing a tetrahydroisoquinolinone scaffold showed the most potent PPARγ antagonistic and hypoglycemic activities. An oral glucose tolerance test (OGTT) was performed and the results further confirmed that 26g was a potent hypoglycemic agent. In addition, the possible binding modes for compound 26g in the PPARγ protein have been investigated in this study.

Evaluation of the action of LPSF/GQ-16 on cytokines and PPAR-γ gene expression after in vitro irradiation of peripheral blood mononuclear cells

PURPOSE

Patients submitted to radiotherapy (RT) may present in their healthy tissues surrounding the treated tumor, some typical acute inflammatory reactions induced by ionizing radiation (IR). The manifestation of inflammatory processes is a result of exacerbation of the immune system, as a response to radiation exposure, and this can be a limiting factor for RT protocols. To counteract this, some thiazolidinediones, such as LPSF/GQ-16, may be useful for modulating the patient's radioinduced inflammatory response in normal tissues. In this context, the present work aims to evaluate the activity of LPSF/GQ-16 on the levels of cytokines and the expression of the gene PPARγ in mononuclear cells irradiated in vitro, to analyze the immunomodulatory activity of the molecule and its action on radiomitigation.

MATERIALS AND METHODS

For this, blood samples from eight donors were collected and irradiated with 2 Gy, then the PBMC (peripheral blood mononuclear cells) were cultured and treated with LPSF/GQ-16. The levels of cytokines TNF-α, IFN-γ, IL-2 and IL-4 were quantified by CBA, while the genes of TNF-α, IFN-γ and PPARγ were analyzed by RT-PCR.

RESULTS

LPSF/GQ-16 significantly reduced the expression of proinflammatory cytokines (IFN-γ and TNF-α) in irradiated and nonirradiated groups. There was no significant reduction of anti-inflammatory cytokines (IL-2 and IL-4) by LPSF/GQ-16. The mRNA expression of PPAR-γ, IFN-γ and TNF-α in the presence of LPSF/GQ-16 was higher in the nonirradiated sample.

CONCLUSION

LPSF/GQ-16 showed effective activity after irradiation, with an important immunomodulatory activity in irradiated PBMCs.

Insights into Dynamic Mechanism of Ligand Binding to Peroxisome Proliferator-Activated Receptor γ toward Potential Pharmacological Applications

Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the nuclear receptor superfamily, which regulates the transcription of a variety of genes involved in lipid and glucose metabolism, inflammation, and cell proliferation. These functions correlate with the onset of type-2 diabetes, obesity, and immune disorders, which makes PPARγ a promising target for drug development. The majority of PPARγ functions are regulated by binding of small molecule ligands, which cause conformational changes of PPARγ followed by coregulator recruitment. The ligand-binding domain (LBD) of PPARγ contains a large Y-shaped cavity that can be occupied by various classes of compounds such as full agonists, partial agonists, natural lipids, and in some cases, a combination of multiple molecules. Several crystal structure studies have revealed the binding modes of these compounds in the LBD and insight into the resulting conformational changes. Notably, the apo form of the PPARγ LBD contains a highly mobile region that can be stabilized by ligand binding. Furthermore, recent biophysical investigations have shed light on the dynamic mechanism of how ligands induce conformational changes in PPARγ and result in functional output. This information may be useful for the design of new and repurposed structures of ligands that serve a different function from original compounds and more potent pharmacological effects with less undesirable clinical outcomes. This review provides an overview of the peculiar characteristics of the PPARγ LBD by examining a series of structural studies focused on the dynamic mechanism of binding and the potential applications of strategies for ligand screening and chemical labeling.

Identification of the anti-fungal drug fenticonazole nitrate as a novel PPARγ-modulating ligand with good therapeutic index: Structure-based screening and biological validation

In this study, SB-VHTS of the old drug library was conducted to seek for novel PPARγ ligand. In the end, an antifungal drug, FN, was identified in vitro and in vivo as a new and potent PPARγ-modulating ligand to demonstrate significantly anti-diabetic and anti-NAFLD efficacies with minimized side effects induced by PPARγ full agonists TZDs drugs. Further mechanistic investigations revealed that FN showed such desired pharmacological properties mainly through selectively activating the expressions of Adiponectin and GLUT4, effectively promoting the Akt Ser473 phosphorylation, inhibiting the expressions of proinflammatory genes including TNF-α, IL-1β and IL-6 and blocking the PPARγ Ser273 phosphorylation mediated by CDK5 without leading to adipogenesis and increasing the expressions of key adipogenic genes CD36, AP2, LPL, C/EBPα, FASN and PPARγ. Subsequently, a molecular docking study revealed an interesting binding mode between FN and PPARγ LBD including the hydrogen-bonding network among oxygen atom, sulfur atom and nitrogen atom in FN respectively with the PPARγ residues Cys285, Tyr327 and Ser342, which gave proof of concept for the above anti-diabetic action mechanism. Taken together, our findings not only suggest that FN can serve as the new, safe and highly efficacious anti-diabetic and anti-NAFLD agents for clinical use, they can also provide a molecular basis for the future development of PPARγ modulators with a high therapeutic index and the possibility to explore new uses of old drugs for immediate drug discovery.

Structural Biology-Based Exploration of Subtype-Selective Agonists for Peroxisome Proliferator-Activated Receptors

Progress in understanding peroxisome proliferator-activated receptor (PPAR) subtypes as nuclear receptors that have pleiotropic effects on biological responses has enabled the exploration of new subtype-selective PPAR ligands. Such ligands are useful chemical biology/pharmacological tools to investigate the functions of PPARs and are also candidate drugs for the treatment of PPAR-mediated diseases, such as metabolic syndrome, inflammation and cancer. This review summarizes our medicinal chemistry research of more than 20 years on the design, synthesis, and pharmacological evaluation of subtype-selective PPAR agonists, which has been based on two working hypotheses, the ligand superfamily concept and the helix 12 (H12) holding induction concept. X-ray crystallographic analyses of our agonists complexed with each PPAR subtype validate our working hypotheses.

The therapeutic potential of inhibiting PPARγ phosphorylation to treat type 2 diabetes

A promising approach for treating type 2 diabetes mellitus (T2DM) is to target the Peroxisome Proliferator-Activated Receptor γ (PPARγ) transcription factor, which regulates the expression of proteins critical for T2DM. Mechanisms involved in PPARγ signaling are poorly understood, yet globally increasing T2DM prevalence demands improvements in drug design. Synthetic, nonactivating PPARγ ligands can abolish the phosphorylation of PPARγ at Ser273, a posttranslational modification correlated with obesity and insulin resistance. It is not understood how these ligands prevent phosphorylation, and the lack of experimental mechanistic information can be attributed to previous ambiguity in the field as well as to limitations in experimental approaches; in silico modeling currently provides the only insight into how ligands block Ser273 phosphorylation. The future availability of experimental evidence is critical for clarifying the mechanism by which ligands prevent phosphorylation and should be the priority of future T2DM-focused research. Following this, the properties of ligands that enable them to block phosphorylation can be improved upon to generate ligands tailored for blocking phosphorylation and therefore restoring insulin sensitivity. This would represent a significant step forward for treating T2DM. This review summarizes current knowledge of the roles of PPARγ in T2DM as well as the effects of synthetic ligands on the modulation of these roles. We hypothesize potential factors that contribute to the reduction in recent developments and summarize what has currently been done to shed light on this critical field of research.

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.

Tetrazoles as PPARγ ligands: A structural and computational investigation

Diabetes is an important chronic disease affecting about 10% of the adult population in the US and over 420 million people worldwide, resulting in 1.6 million deaths every year, according to the World Health Organization. The most common type of the disease, type 2 diabetes, can be pharmacologically managed using oral hypoglycemic agents or thiazolidinediones (TZDs), such as pioglitazone, which act by activating the Peroxisome Proliferated-Activated Receptor γ. Despite their beneficial effects in diabetes treatment, TZDs like rosiglitazone and troglitazone were withdrawn due to safety reasons, creating a void in the pharmacological options for the treatment of this important disease. Here, we explored a structure-based approach in the screening for new chemical probes for a deeper investigation of the effects of PPARγ activation. A class of tetrazole compounds was identified and the compounds named T1, T2 and T3 were purchased and evaluated for their ability to interact with the PPARγ ligand binding domain (LBD). The compounds were binders with micromolar range affinity, as determined by their IC₅₀ values. A Monte Carlo simulation of the compound T2 revealed that the tetrazole ring makes favorable interaction with the polar arm of the receptor binding pocket. Finally, the crystal structure of the PPARγ-LBD-T2 complex was solved at 2.3 Å, confirming the binding mode for this compound. The structure also revealed that, when the helix H12 is mispositioned, an alternative binding conformation is observed for the ligand suggesting an H12-dependent binding conformation for the tetrazole compound.

Concise perspectives on some synthetic thiazolidine-2,4-dione derivatives and their specific pharmacodynamic aspects

Glitazones are synthetic derivatives of thiazolidinedione, and are designated as oral anti-diabetic agents, primarily acting on peroxisome proliferator-activated receptor-gamma (PPAR-γ) receptors and driving some crucial metabolic pathways linked to glucose and lipid metabolism at transcriptional level. Despite presenting adverse effects, including weight gain, fluid retention, prostate hyperplasia, hyperinsulinemia, and myocardial infarction, they are still preferred in clinical settings due to their utmost efficacy and selectivity. However, these complications kept glitazones restrained for long-term usage. The present review briefly highlights some important synthetic derivatives of thiazolidine2,4-dione and emphasizes the influence of various structural manipulations on their bio-efficacy.

Hypoglycemic and Hypolipidemic Swords: Synthesis and In-vivo Biological Assessment of 5-benzylidene-2,4-thiazolidinediones

Thiazolidinedione (TZD), being a privileged scaffold, has been known as a significant structural moiety of antidiabetic drugs. TZD has been known to improve glycaemic control in type 2 diabetes mellitus (T2DM) by increasing insulin sensitivity in the body. A novel series of 5-benzylidene 2,4-thiazolidinedione derivatives were designed, synthesized (V1-V28), and structurally confirmed by different spectroscopic techniques such as FTIR, ¹H NMR, ¹³C NMR, and Mass spectrometry. Upon the safety assessment of the synthesized molecules in non-transformed hepatocytes by MTT reduction assay, these were found non-toxic. These derivatives were then further evaluated for their antihyperglycemic and antihyperlipidemic properties in a high-fat diet and low dose of streptozotocin-induced diabetic rats. Altogether, seven biochemical parameters were analyzed, namely blood glucose, triglycerides, cholesterol, creatinine, blood urea nitrogen, HDL-cholesterol, and glycosylated hemoglobin in serum by standard methods. Four synthetic molecules (V2, V4, V5, and V20) possessed significant hypoglycaemic and hypolipidemic activity as compared to the positive control pioglitazone. Moreover, the histopathological studies of the heart and liver revealed no significant toxicity. Two representative compounds V2 and V4, were evaluated for their PPARγ activation potential, demonstrating that they were partial PPARγ agonists, thus confirming our designing hypothesis. Based on the results obtained, we assume that these compounds have the potential to be developed as future antidiabetic agents.

PPARγ S273 Phosphorylation Modifies the Dynamics of Coregulator Proteins Recruitment

The nuclear receptor PPARγ is essential to maintain whole-body glucose homeostasis and insulin sensitivity, acting as a master regulator of adipogenesis, lipid, and glucose metabolism. Its activation through natural or synthetic ligands induces the recruitment of coactivators, leading to transcription of target genes such as cytokines and hormones. More recently, post translational modifications, such as PPARγ phosphorylation at Ser273 by CDK5 in adipose tissue, have been linked to insulin resistance trough the dysregulation of expression of a specific subset of genes. Here, we investigate how this phosphorylation may disturb the interaction between PPARγ and some coregulator proteins as a new mechanism that may leads to insulin resistance. Through cellular and in vitro assays, we show that PPARγ phosphorylation inhibition increased the activation of the receptor, therefore the increased recruitment of PGC1-α and TIF2 coactivators, whilst decreases the interaction with SMRT and NCoR corepressors. Moreover, our results show a shift in the coregulators interaction domains preferences, suggesting additional interaction interfaces formed between the phosphorylated PPARγ and some coregulator proteins. Also, we observed that the CDK5 presence disturb the PPARγ-coregulator's synergy, decreasing interaction with PGC1-α, TIF2, and NCoR, but increasing coupling of SMRT. Finally, we conclude that the insulin resistance provoked by PPARγ phosphorylation is linked to a differential coregulators recruitment, which may promote dysregulation in gene expression.

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.

Obesity-Linked PPARγ S273 Phosphorylation Promotes Insulin Resistance through Growth Differentiation Factor 3

The thiazolidinediones (TZDs) are ligands of PPARγ that improve insulin sensitivity, but their use is limited by significant side effects. Recently, we demonstrated a mechanism wherein TZDs improve insulin sensitivity distinct from receptor agonism and adipogenesis: reversal of obesity-linked phosphorylation of PPARγ at serine 273. However, the role of this modification hasn't been tested genetically. Here we demonstrate that mice encoding an allele of PPARγ that cannot be phosphorylated at S273 are protected from insulin resistance, without exhibiting differences in body weight or TZD-associated side effects. Indeed, hyperinsulinemic-euglycemic clamp experiments confirm insulin sensitivity. RNA-seq in these mice reveals reduced expression of Gdf3, a BMP family member. Ectopic expression of Gdf3 is sufficient to induce insulin resistance in lean, healthy mice. We find Gdf3 inhibits BMP signaling and insulin signaling in vitro. Together, these results highlight the diabetogenic role of PPARγ S273 phosphorylation and focus attention on a putative target, Gdf3.

In Silico Design, Synthesis and Evaluation of Novel Series of Benzothiazole- Based Pyrazolidinediones as Potent Hypoglycemic Agents

Background:

The discovery of novel ligand binding domain (LBD) of peroxisome proliferator- activated receptor γ (PPARγ) has recently attracted attention to few research groups in order to develop more potent and safer antidiabetic agents.

Objective:

This study is focused on docking-based design and synthesis of novel compounds combining benzothiazole and pyrazolidinedione scaffold as potential antidiabetic agents.

Methods:

Several benzothiazole-pyrazolidinedione hybrids were synthesized and tested for their in vivo anti-hyperglycemic activity. Interactions profile of title compounds against PPARγ was examined through molecular modelling approach.

Results:

All tested compounds exhibited anti-hyperglycemic activity similar or superior to the reference drug Rosiglitazone. Introducing chlorine atom and alkyl group at position-6 and -5 respectively on benzothiazole core resulted in enhancing the anti-hyperglycemic effect. Docking study revealed that such groups demonstrated favorable hydrophobic interactions with novel LBD Ω- pocket of PPARγ protein.

Conclusion:

Among the tested compounds, N-(6-chloro-5-methylbenzo[d]thiazol-2-yl-4-(4((3,5- dioxopyrazolidin-4-ylidene)methyl)phenoxy)butanamide 5b was found to be the most potent compound and provided valuable insights to further develop novel hybrids as anti-hyperglycemic agents.

The PPAR Ω Pocket: Renewed Opportunities for Drug Development

The past decade of PPARγ research has dramatically improved our understanding of the structural and mechanistic bases for the diverging physiological effects of different classes of PPARγ ligands. The discoveries that lie at the heart of these developments have enabled the design of a new class of PPARγ ligands, capable of isolating central therapeutic effects of PPARγ modulation, while displaying markedly lower toxicities than previous generations of PPARγ ligands. This review examines the emerging framework around the design of these ligands and seeks to unite its principles with the development of new classes of ligands for PPARα and PPARβ/δ. The focus is on the relationships between the binding modes of ligands, their influence on PPAR posttranslational modifications, and gene expression patterns. Specifically, we encourage the design and study of ligands that primarily bind to the Ω pockets of PPARα and PPARβ/δ. In support of this development, we highlight already reported ligands that if studied in the context of this new framework may further our understanding of the gene programs regulated by PPARα and PPARβ/δ. Moreover, recently developed pharmacological tools that can be utilized in the search for ligands with new binding modes are also presented.

GQ-130, a novel analogue of thiazolidinedione, improves obesity-induced metabolic alterations in rats: Evidence for the involvement of PPARβ/δ pathway

The present investigation aimed to characterize the effect of a short-time treatment with a new thiazolidinedione (TZD) derivative, GQ-130, on metabolic alterations in rats fed a high-fat diet (HFD). We investigated whether metabolic alterations induced by GQ-130 were mediated though a mechanism that involves PPARβ/δ transactivation. Potential binding and transactivation of PPARα, PPARβ/δ or PPARγ by GQ-130 were examined through cell transactivation, 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence quenching assays and thermal shift assay. For in vivo experiments, male 8-week-old Wistar rats were divided into three groups fed for 6 weeks with: (a) a standard rat chow (14% fat) (control group), (b) a HFD (57.8% fat) alone (HFD group), or (c) a HFD associated with an oral treatment with GQ-130 (10 mg/kg/d) during the last week (HFD-GQ group). In 293T cells, unlike rosiglitazone, GQ-130 did not cause significant transactivation of PPARγ but was able to activate PPARβ/δ by 153.9 folds in comparison with control values (DMSO). Surprisingly, ANS fluorescence quenching assay reveals that GQ-130 does not bind directly to PPARβ/δ binding site, a finding that was further corroborated by thermal shift assay which evaluates the thermal stability of PPARβ/δ in the presence of GQ-130. Compared to the control group, rats of the HFD group showed obesity, increased systolic blood pressure (SBP), insulin resistance, impaired glucose intolerance, hyperglycaemia, and dyslipidaemia. GQ-130 treatment abolished the increased SBP and improved all metabolic dysfunctions observed in the HFD group. Oral treatment with GQ-130 was effective in improving HFD-induced metabolic alterations probably through a mechanism that involves PPARβ/δ activation.

Redox Biology of Peroxisome Proliferator-Activated Receptor-γ in Pulmonary Hypertension

Significance: Peroxisome proliferator-activated receptor-gamma (PPARγ) maintains pulmonary vascular health through coordination of antioxidant defense systems, inflammation, and cellular metabolism. Insufficient PPARγ contributes to pulmonary hypertension (PH) pathogenesis, whereas therapeutic restoration of PPARγ activity attenuates PH in preclinical models. Recent Advances: Numerous studies in the past decade have elucidated the complex mechanisms by which PPARγ in the pulmonary vasculature and right ventricle (RV) protects against PH. The scope of PPARγ-interconnected pathways continues to expand and includes induction of antioxidant genes, transrepression of inflammatory signaling, regulation of mitochondrial biogenesis and bioenergetic integrity, control of cell cycle and proliferation, and regulation of vascular tone through interactions with nitric oxide and endogenous vasoactive molecules. Furthermore, PPARγ interacts with an extensive regulatory network of transcription factors and microRNAs leading to broad impact on cell signaling. Critical Issues: Abundant evidence suggests that targeting PPARγ exerts diverse salutary effects in PH and represents a novel and potentially translatable therapeutic strategy. However, progress has been slowed by an incomplete understanding of how specific PPARγ pathways are critically disrupted across PH disease subtypes and lack of optimal pharmacological ligands. Future Directions: Recent studies indicate that ligand-induced post-translational modifications of the PPARγ receptor differentially induce therapeutic benefits versus adverse side effects of PPARγ receptor activation. Strategies to selectively target PPARγ activity in diseased cells of pulmonary circulation and RV, coupled with development of ligands designed to specifically regulate post-translational PPARγ modifications, may unlock the full therapeutic potential of this versatile master transcriptional and metabolic regulator in PH.

Design, synthesis, and evaluation of potent novel peroxisome proliferator-activated receptor γ indole partial agonists

Peroxisome Proliferator-Activated Receptor γ (PPARγ) is a nuclear receptor important for glucose homeostasis and insulin sensitivity. The anti-diabetic drugs thiazolidinediones improve insulin sensitivity by blocking PPARγ phosphorylation at S273; however, their full agonism on PPARγ also causes significant unwanted side effects. The indole derivative UHC1 displays insulin-sensitizing effect by acting as a partial agonist through the inhibition of PPARγ S273 phosphorylation, but without full agonist-associated side effects; however, its potency leaves much to be desired. Herein we report the design and synthesis of potent indole analogs as partial PPARγ agonists via the structure-activity relationship studies. Our studies revealed that vanillylamine and piperonyl benzylamine at Site 1 are favored to bind PPARγ with either biphenyl or 3-trifluoromethyl benzyl group at Site 2. In particular, compound WO91A with vanillylamine at Site 1 displays highly potent PPARγ binding affinity (IC₅₀ = 16.7 nM), over 30-fold more potent than the parental compound UHC1, yet with less side effect-associated transactivation activity.

New Peroxisome Proliferator-Activated Receptor Agonist (GQ-11) Improves Wound Healing in Diabetic Mice

Objective: Chronic wounds associated with diabetes are an important public health problem demanding new treatments to improve wound healing and decrease amputations. Monocytes/macrophages play a key role in sustained inflammation associated with impaired healing and local administration of peroxisome proliferator-activated receptor (PPAR)γ agonists may modulate macrophage, improving healing. In this study, we investigated the effects of GQ-11, a partial/dual PPARα/γ agonist, on macrophage function and wound healing in diabetes. Approach: Wounds were surgically induced at the dorsum of C57BL/6J and BKS.Cg-Dock7^m +/+ Lepr^db/J (db/db) mice and treated with hydrogel (vehicle), pioglitazone or GQ-11, for 7 or 10 days, respectively. After treatment, wounds were analyzed histologically and by quantitative PCR (qPCR). In addition, bone marrow-derived macrophages (BMDM) were cultured from C57BL/6J mice and treated with vehicle, pioglitazone, or GQ-11, after challenge with lipopolysaccharide or interleukin-4 to be analyzed by qPCR and flow cytometry. Results: GQ-11 treatment upregulated anti-inflammatory/pro-healing factors and downregulated pro-inflammatory factors both in wounds of db/db mice and in BMDM. Innovation: Wounds of db/db mice treated with GQ-11 exhibited faster wound closure and re-epithelization, increased collagen deposition, and less Mac-3 staining compared with vehicle, providing a new approach to treatment of diabetic wound healing to prevent complications. Conclusion: GQ-11 improves wound healing in db/db mice, regulating the expression of pro- and anti-inflammatory cytokines and wound growth factors, leading to increased re-epithelization and collagen deposition.

Microbiota determines insulin sensitivity in TLR2-KO mice

INTRODUCTION

Environmental factors have a key role in the control of gut microbiota and obesity. TLR2 knockout (TLR2^-/-) mice in some housing conditions are protected from diet-induced insulin resistance. However, in our housing conditions these animals are not protected from diet-induced insulin-resistance.

AIM

The aim of the present study was to investigate the influence of our animal housing conditions on the gut microbiota, glucose tolerance and insulin sensitivity in TLR2^-/- mice.

MATERIAL AND METHODS

The microbiota was investigated by metagenomics, associated with hyperinsulinemic euglycemic clamp and GTT associated with insulin signaling through immunoblotting.

RESULTS

The results showed that TLR2^-/- mice in our housing conditions presented a phenotype of metabolic syndrome characterized by insulin resistance, glucose intolerance and increase in body weight. This phenotype was associated with differences in microbiota in TLR2^-/- mice that showed a decrease in the Proteobacteria and Bacteroidetes phyla and an increase in the Firmicutesphylum, associated with and in increase in the Oscillospira and Ruminococcus genera. Furthermore there is also an increase in circulating LPS and subclinical inflammation in TLR2^-/-. The molecular mechanism that account for insulin resistance was an activation of TLR4, associated with ER stress and JNK activation. The phenotype and metabolic behavior was reversed by antibiotic treatment and reproduced in WT mice by microbiota transplantation.

CONCLUSIONS

Our data show, for the first time, that the intestinal microbiota can induce insulin resistance and obesity in an animal model that is genetically protected from these processes.

[Role of PPARγ, a transcription factor in cardiovascular disease]

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand activated transcription factor known to regulate fatty acid metabolism. Thiazolidinediones (TZDs), PPARγ synthetic agonists, currently used to treat patients with type 2 diabetes, have been shown to lower the blood pressure and protect against vascular diseases such as atherosclerosis. In line with these findings, it has been reported that individuals with loss-of-function mutations of PPARγ developed sever early-onset hypertension in addition to metabolic abnormalities. Accumulating evidences suggest PPARγ in the vasculature has protective effects on cardiovascular disease despite unclear mechanism. Because of ubiquitous expression of PPARγ, TZDs are well-known to be associated with serious side effects such as weight gain, fluid retention, and bone fractures. Thus identification of mechanisms on tissue-specific PPARγ activity may lead to the development of targeted treatment which is characterized by no deleterious effects. This review discusses role of PPARγ in cardiovascular disease.

Exploring the mechanism of PPARγ phosphorylation mediated by CDK5

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor with a key role in metabolic processes and is target of CDK5 kinase phosphorylation at S245 (S273 in PPARγ isoform 2), thereby inducing insulin resistance. A remarkable effort has been addressed to find PPARγ ligands that inhibit S245 phosphorylation, but the poor understanding in this field challenges the design of such ligands. Here, through computational and biophysical methods, we explored an experimentally validated model of PPARγ-CDK5 complex, and we presented K261, K263 or K265, which are conserved in mammals, as important anchor residues for this interaction. In addition, we observed, from structural data analysis, that PPARγ ligands that inhibit S245 phosphorylation are not in direct contact with these residues; but induce structural modifications in PPARγ:CDK5/p25 interface. In summary, our PPARγ and CDK5/p25 interaction analyses open new possibilities for the rational design of novel inhibitors that impair S245 phosphorylation.

Importance of the Proximity and Orientation of Ligand-Linkage to the Design of Cinnamate-GW9662 Hybrid Compounds as Covalent PPARγ Agonists

Covalent agonists of PPARγ cause unique receptor conformational changes and behave as selective PPARγ modulators, whereas there are few covalent agonists other than endogenous unsaturated fatty acids metabolites. Previously, we established a cell-based strategy to identify new PPARγ ligands and synthesized a new-type of covalent agonist that possesses the hybrid structure of a plant-derived cinnamic acid derivative and GW9662, a covalent antagonist. Herein, we report six analogues that differ in how the two fragments are linked together. Compounds with a simplified linker showed potent agonistic activity with improved EC₅₀ values (less than 5 nM), indicating that close proximity between the two fragments improves binding affinity. When the position of cinnamic acid moiety was placed at 4′ carbon of aniline ring, PPARγ agonist activity was completely abolished. Docking studies suggested that the activation profile likely depends on interaction with the cavity around helix 3, β-sheet, and Ω-loop region in the ligand-binding domain. Furthermore, a cell-based assay revealed that agonist-type compounds activate PPARγ transcription in a manner dependent on covalent linkage with the Cys285 residue leading to prolonged transactivation. This activation feature reflects pharmacological benefits of covalent drugs, suggesting that these hybrid compounds may serve as potential leads for a new-class of covalent PPARγ ligands.

Evidence that peroxisome proliferator-activated receptor γ suppresses squamous carcinogenesis through anti-inflammatory signaling and regulation of the immune response

A variety of evidence suggests that peroxisome proliferator-activated receptor (PPAR)γ agonists may represent a potential pharmacologic target in the prevention or treatment of skin cancer. In particular, recent reports suggest that PPARγ activation may exert at least some of its anti-neoplastic effects through the suppression of tumor promoting chronic inflammation as well as by strengthening antitumor immune responses. This activity is thought to occur through a distinct mode of ligand interaction with PPARγ that causes transrepression of transcription factors that are involved in inflammatory and immunomodulatory signaling. However, current thiazolidinedione (TZD)-type PPARγ agonists have significant safety concerns that limit their usefulness as a preventive or therapeutic option. Due to the relatively large ligand binding pocket of PPARγ, a diverse group of ligands can be seen to interact with distinct modes of binding to PPARγ, leading to the phenomenon of partial agonist activity and selective PPARγ modulators (SPPARγM). This has led to the development of ligands that are tailored to deliver desired pharmacologic activity, but lack some of the negative side effects associated with full agonists, such as the currently utilized TZD-type PPARγ agonists. In addition, there is evidence that a number of phytochemicals that are currently being touted as antineoplastic nutraceuticals also possess PPARγ activity that may partially explain their pharmacologic activity. We propose that one or more of these partial agonists, SPPARγMs, or putative phytochemical PPARγ ligands could presumably be used as a starting point to design more efficacious anti-neoplastic PPARγ ligands that lack adverse pharmacological effects.

Cooperative cobinding of synthetic and natural ligands to the nuclear receptor PPARγ

Crystal structures of peroxisome proliferator-activated receptor gamma (PPARγ) have revealed overlapping binding modes for synthetic and natural/endogenous ligands, indicating competition for the orthosteric pocket. Here we show that cobinding of a synthetic ligand to the orthosteric pocket can push natural and endogenous PPARγ ligands (fatty acids) out of the orthosteric pocket towards an alternate ligand-binding site near the functionally important omega (Ω)-loop. X-ray crystallography, NMR spectroscopy, all-atom molecular dynamics simulations, and mutagenesis coupled to quantitative biochemical functional and cellular assays reveal that synthetic ligand and fatty acid cobinding can form a 'ligand link' to the Ω-loop and synergistically affect the structure and function of PPARγ. These findings contribute to a growing body of evidence indicating ligand binding to nuclear receptors can be more complex than the classical one-for-one orthosteric exchange of a natural or endogenous ligand with a synthetic ligand.

Role of an indole-thiazolidiene PPAR pan ligand on actions elicited by G-protein coupled receptor activated neutrophils

Neutrophils are the first line of defence during inflammatory processes; nevertheless, exacerbated influx and actions of neutrophils in terms of uncontrolled inflammation are harmful to the host. Hence, neutrophil activity is the target of drugs seeking to address undesired inflammation. Here, we investigated the mechanisms of action of a ligand of the three isoforms of peroxisome proliferator-activated receptors (PPAR; (5Z)-5-[(5-bromo-1H-indole-3-yl)methylene]-3-(4-chlorobenzyl)-thiazolidine-2,4-dione), dubbed LYSO-7, on neutrophils activated by N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLP), an agonist of G-protein coupled receptors (GPCRs) that binds to membrane-formylated peptide and activates intracellular inflammation pathways. Neutrophils were collected from the peritoneal cavity of male Wistar rats four hours after oyster glycogen injection. Afterwards, the neutrophils were incubated with saline or LYSO-7 (1 or 10 μM, 30 min), washed and stimulated with fMLP (10^-7 μM, 1 h). LYSO-7 treatment inhibited gene and protein expression of adhesion molecules, CD62 L and CD18, abolished adhesion of neutrophils to endothelial cells, impaired chemotaxis, blocked the enhancement of intracellular calcium levels, induced the expression of PPARγ as well as PPARβδ and reduced nuclear translocation of nuclear factor κB (NF-κB). Moreover, topical application of LYSO-7 (10 mM) prior to local application of fMLP (10^-7 μM) diminished the in vivo leukocyte-endothelial interactions in the mesentery microcirculation of rats. Together, our data highlight the effectiveness of anti-inflammatory actions of LYSO-7 on neutrophils activated by GPCRs, depending, at least in part, on impaired of NF-κB activation and induction of PPAR expression.

Functional Regulation of PPARs through Post-Translational Modifications

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor superfamily and they are essential regulators of cell differentiation, tissue development, and energy metabolism. Given their central roles in sensing the cellular metabolic state and controlling metabolic homeostasis, PPARs became important targets of drug development for the management of metabolic disorders. The function of PPARs is mainly regulated through ligand binding, which induces structural changes, further affecting the interactions with co-activators or co-repressors to stimulate or inhibit their functions. In addition, PPAR functions are also regulated by various Post-translational modifications (PTMs). These PTMs include phosphorylation, SUMOylation, ubiquitination, acetylation, and O-GlcNAcylation, which are found at numerous modification sites. The addition of these PTMs has a wide spectrum of consequences on protein stability, transactivation function, and co-factor interaction. Moreover, certain PTMs in PPAR proteins have been associated with the status of metabolic diseases. In this review, we summarize the PTMs found on the three PPAR isoforms PPARα, PPARβ/δ, and PPARγ, and their corresponding modifying enzymes. We also discuss the functional roles of these PTMs in regulating metabolic homeostasis and provide a perspective for future research in this intriguing field.

CMHX008, a PPARγ partial agonist, enhances insulin sensitivity with minor influences on bone loss

Traditional thiazolidinediones (TZDs), such as rosiglitazone, are peroxisome proliferator-activated receptor γ (PPARγ) potent agonists that can be used to treat type 2 diabetes but carry unwanted effects, including increased risk for fracture. The present work aimed to compare the insulin-sensitizing efficacies and bone-loss side effects of CMHX008, a novel TZDs-like PPARγ partial agonist, with those of rosiglitazone. A TR-FRET PPARγ competitive binding assay was used to compare the binding affinity between CMHX008 and rosiglitazone. Mice were administered vehicle, CMHX008 or rosiglitazone for 16 weeks. Mesenchymal stem cells (MSCs) were used to examine differences in differentiation into osteoblasts after compounds treatment. TR-FRET showed lower affinity to PPARγ by CMHX008 compared with rosiglitazone. Mice treated with CMHX008 showed insulin sensitization similar to that of mice treated with rosiglitazone, which was related to the significant inhibition of PPARγ Ser273 phosphorylation and improved insulin sensitivity by facilitating the phosphorylation of insulin receptor and Akt in adipose tissues. Micro-CT and histomorphometric analyses demonstrated that the degree of trabecular bone loss after treatment with CMHX008 was weaker than that observed with rosiglitazone, as evidenced by consistent changes in BV/TV, Tb.N, Tb.Th, Tb.Sp, and the mineral apposition rate. MSCs treated with CMHX008 showed higher ALP activity and mRNA levels of bone formation markers than did cells treated with rosiglitazone in the osteoblast differentiation test. Thus, CMHX008 showed insulin-sensitizing effects similar to those of rosiglitazone with a lower risk of bone loss, suggesting that PPARγ sparing eliminates the skeletal side effects of TZDs while maintaining their insulin-sensitizing properties.

GQ-11: A new PPAR agonist improves obesity-induced metabolic alterations in LDLr-/- mice

BACKGROUND

Obesity and insulin resistance/diabetes are important risk factors for cardiovascular diseases and demand safe and efficacious therapeutics.

OBJECTIVE

To assess the effects of a new thiazolidine compound-GQ-11-on obesity and insulin resistance induced by a diabetogenic diet in LDL receptor-deficient (LDLr^-/-) mice.

METHODS

Molecular docking simulations of GQ-11, PPARα and PPARγ structures were performed. Male C57BL/6J LDLr^-/- mice fed a diabetogenic diet for 24 weeks were treated with vehicle, GQ-11 or pioglitazone or (20 mg/kg/day) for 28 days by oral gavage. Glucose tolerance test, insulin, HOMA-IR, adipokines (leptin, adiponectin) and the lipid profile were assessed after treatment. Adipose tissue was analysed by X-ray analysis and morphometry; gene and protein expression were evaluated by real-time PCR and western blot, respectively.

RESULTS

GQ-11 showed partial agonism to PPARγ and PPARα. In vivo, treatment with GQ-11 ameliorated insulin sensitivity and did not modify subcutaneous adipose tissue and body weight gain. In addition, GQ-11 restored adipokine imbalance induced by a diabetogenic diet and enhanced Glut-4 expression in the adipose tissue. Improved insulin sensitivity was also associated with lower levels of MCP-1 and higher levels of IL-10. Furthermore, GQ-11 reduced triglycerides and VLDL cholesterol and increased HDL-cholesterol by upregulation of Apoa1 and Abca1 gene expression in the liver.

CONCLUSION

GQ-11 is a partial/dual PPARα/γ agonist that demonstrates anti-diabetic effects. Additionally, it improves the lipid profile and ameliorates chronic inflammation associated with obesity in atherosclerosis-prone mice.