N-(2-Benzoylphenyl)-L-tyrosine PPARgamma agonists. 3. Structure-activity relationship and optimization of the N-aryl substituent

Synthesis of Tetrahydrofuro[2,3-d]oxazoles and Oxazoles by Hypervalent Iodine (III)-Promoted [2 + 2 + 1] Annulation

Reaction of a hypervalent iodine reagent with bistriflimide efficiently promotes three-component regioselective cyclization of tetrahydrofuro[2,3-d]oxazoles and oxazoles from homopropargyl alcohols bearing a phenyl group, with different substituents on the aryl alkyne compounds affecting the selectivity of the resulting product. Utilizing the hydroxyethyl oxazole derivatives obtained in this research could aid in the development of various peroxisome proliferator-activated receptor agonist derivatives.

Cyclooxygenase-2 Inhibitor Parecoxib Was Disclosed as a PPAR-γ Agonist by In Silico and In Vitro Assay

In a search for effective PPAR-γ agonists, 110 clinical drugs were screened via molecular docking, and 9 drugs, including parecoxib, were selected for subsequent biological evaluation. Molecular docking of parecoxib to the ligand-binding domain of PPAR-γ showed high binding affinity and relevant binding conformation compared with the PPAR-γ ligand/antidiabetic drug rosiglitazone. Per the docking result, parecoxib showed the best PPAR-γ transactivation in Ac2F rat liver cells. Further docking simulation and a luciferase assay suggested parecoxib would be a selective (and partial) PPAR-γ agonist. PPAR-γ activation by parecoxib induced adipocyte differentiation in 3T3-L1 murine preadipocytes. Parecoxib promoted adipogenesis in a dose-dependent manner and enhanced the expression of adipogenesis transcription factors PPAR-γ, C/EBPα, and C/EBPβ. These data indicated that parecoxib might be utilized as a partial PPAR-γ agonist for drug repositioning study.

Targeting Nuclear Receptors in Neurodegeneration and Neuroinflammation

Nuclear receptors, also known as ligand-activated transcription factors, regulate gene expression upon ligand signals and present as attractive therapeutic targets especially in chronic diseases. Despite the therapeutic relevance of some nuclear receptors in various pathologies, their potential in neurodegeneration and neuroinflammation is insufficiently established. This perspective gathers preclinical and clinical data for a potential role of individual nuclear receptors as future targets in Alzheimer's disease, Parkinson's disease, and multiple sclerosis, and concomitantly evaluates the level of medicinal chemistry targeting these proteins. Considerable evidence suggests the high promise of ligand-activated transcription factors to counteract neurodegenerative diseases with a particularly high potential of several orphan nuclear receptors. However, potent tools are lacking for orphan receptors, and limited central nervous system exposure or insufficient selectivity also compromises the suitability of well-studied nuclear receptor ligands for functional studies. Medicinal chemistry efforts are needed to develop dedicated high-quality tool compounds for the therapeutic validation of nuclear receptors in neurodegenerative pathologies.

Induction of peroxisome proliferator activated receptor γ (PPARγ) mediated gene expression and inhibition of induced nitric oxide production by Maerua subcordata (Gilg) DeWolf

BACKGROUND

The health benefits of botanicals is linked to their phytochemicals that often exert pleiotropic effects via targeting multiple molecular signaling pathways such as the peroxisome proliferator-activated receptors (PPARs) and the nuclear factor kappaB (NFκB). The PPARs are transcription factors that control metabolic homeostasis and inflammation while the NF-κB is a master regulator of inflammatory genes such as the inducible nitric-oxide synthase that result in nitric oxide (NO) overproduction.

METHODS

Extracts of Maerua subcordata (MS) and selected candidate constituents thereof, identified by liquid chromatography coupled to mass spectroscopy, were tested for their ability to induce PPARγ mediated gene expression in U2OS-PPARγ cells using luciferase reporter gene assay and also for their ability to inhibit lipopolysaccharide (LPS) induced NO production in RAW264.7 macrophages. While measuring the effect of test samples on PPARγ mediated gene expression, a counter assay that used U2OS-Cytotox cells was performed to monitor cytotoxicity or any non-specific changes in luciferase activity.

RESULTS

The results revealed that the fruit, root, and seed extracts were non-cytotoxic up to a concentration of 30 g dry weight per litre (gDW/L) and induced PPARγ mediated gene expression but the leaf extract showed some cytotoxicity and exhibited minimal induction. Instead, all extracts showed concentration (1-15 gDW/L) dependent inhibition of LPS induced NO production. The root extract showed weaker inhibition. Among the candidate constituents, agmatine, stachydrine, trigonelline, indole-3-carboxyaldehyde, plus ethyl-, isobutyl-, isopropyl, and methyl-isothiocyanates showed similar inhibition, and most showed increased inhibition with increasing concentration (1-100 μM) although to a lesser potency than the positive control, aminoguanidine.

CONCLUSION

The present study demonstrated for the first time the induction of PPARγ mediated gene expression by MS fruit, root, and seed extracts and the inhibition of LPS induced NO production by MS fruit, leaf, root, and seed extracts and some candidate constituents thereof.

Characterization of the metabolites of GW1929 in rat by liquid chromatography coupled with electrospray ionization tandem mass spectrometry

RATIONALE

GW1929 is a potent PPAR-γ activator. To fully understand its mechanism of action, it is necessary to study the in vitro and in vivo metabolism.

METHODS

For in vitro metabolism, GW1929 was incubated with rat hepatocytes at 37°C for 2 h. For in vivo metabolism, rats were orally administered with GW1929 at a single dose of 10 mg/kg and plasma, urinary and fecal samples were collected at defined time points. All the samples were analyzed by the developed ultra-high-performance liquid chromatography combined with tandem mass spectrometry. The structures of metabolites were proposed according to their accurate masses and product ions.

RESULTS

A total of 17 metabolites, including seven glucuronide conjugates, were detected and structurally identified. M4 (hydroxylation), M13 (demethylation) and M14 (hydroxylation) were the most abundant metabolites. The metabolic pathways of GW1929 referred to hydroxylation, demethylation, deamination and glucuronidation.

CONCLUSIONS

The present study provided new information on the in vitro and in vivo metabolic profiles of GW1929 which will be helpful for a better understanding of the mechanism of the elimination of GW1929.

Synthesis and evaluation of new designed multiple ligands directed towards both peroxisome proliferator-activated receptor-γ and angiotensin II type 1 receptor

Because of the complex biological networks, many pathologic disorders fail to be treated with a molecule directed towards a single target. Thus, combination therapies are often necessary, but they have many drawbacks. An alternative consists in building molecules intended to interact with multiple targets, called designed multiple ligands. We followed such a strategy in order to treat metabolic syndrome, by setting up molecules directed towards both type 1 angiotensin II (AT₁) receptor and peroxisome proliferator-activated receptor-γ (PPAR-γ). For this purpose, many molecules were prepared by merging both pharmacophores following three different strategies. Their ability to activate PPAR-γ and to block AT₁ receptors were evaluated in vitro. This strategy led to the preparation of many new PPAR-γ activating and AT₁ blocking molecules. Among them, some exhibited both activities, highlighting the convenience of this approach.

Design, synthesis, and evaluation of novel l-phenylglycine derivatives as potential PPARγ lead compounds

In accordance with the structural characteristics of thiazolidinedione drugs and highly bioactive tyrosine derivatives, we tentatively designed the l-phenylglycine derivatives TM1 and TM2 based on basic principles of drug design and then synthesized them. The in vitro screening of peroxisome proliferator-activated receptor gamma (PPARγ) activated activity, α-glucosidase inhibitory and dipeptidyl peptidase-4 inhibitory activities showed that the novel molecule M5 had efficient PPAR response element (PPRE) activated activity (PPRE relative activity 105.04% at 10 μg·mL^-1 compared with the positive control pioglitazone, with 100% activity). Therefore, M5 was selected as the hit compound from which the TM3 and TM4 series of compounds were further designed and synthesized. Based on the PPRE relative activities of TM3 and TM4, we discovered another new molecule, TM4h, which had the strongest PPRE relative activity (120.42% at 10 μg·mL^-1). In addition, the concentration-dependent activity of the highly active compounds was determined by assaying their half-maximal effective concentration (EC₅₀) values. The molecular physical parameter calculation and the molecular toxicity prediction were used to theoretically evaluate the lead-likeness and safety of the active compounds. In conclusion, we identified a potential PPARγ lead molecule and developed a tangible strategy for antidiabetic drug development.

Effect of Hexadecyl Azelaoyl Phosphatidylcholine on Cardiomyocyte Apoptosis in Myocardial Ischemia-Reperfusion Injury: A Hypothesis

Reperfusion after myocardial ischemia can induce cardiomyocyte death, known as myocardial reperfusion injury. The pathophysiology of the process of reperfusion suggests the confluence multiple pathways. Recent studies have focused on the inflammatory response, which is considered to be the main mechanism during the process of myocardial ischemia-reperfusion injury and can cause cardiomyocyte apoptosis. Peroxisome proliferator-activated receptors gamma activated by endogenous ligands and exogenous ligand can decrease the inflammatory response in cardiomyocytes. Thiazolidinediones are synthetic, high-affinity, selective ligands for peroxisome proliferator-activated receptors gamma, and can inhibit the inflammatory response, decrease myocardial infarct size, and protect cardiac function. However, thiazolidinediones, including rosiglitazone and pioglitazone, can also contribute to adverse cardiovascular events such as congestive heart failure. Therefore, there are some limitations to the use of thiazolidinediones. Most endogenous ligands were of low affinity until hexadecyl azelaoyl phosphatidylcholine was identified as a high-affinity ligand and agonist for peroxisome proliferator-activated receptors gamma. Hexadecyl azelaoyl phosphatidylcholine binds recombinant peroxisome proliferator-activated receptors with an affinity (Kd(app) ≈40 nM) which is equivalent to rosiglitazone. Therefore, hexadecyl azelaoyl phosphatidylcholine is a specific peroxisome proliferator-activated receptors gamma agonist. Given these findings, we hypothesized that the use of hexadecyl azelaoyl phosphatidylcholine can activate the peroxisome proliferator-activated receptors gamma signal pathways and prevent the inflammatory response process of myocardial ischemia-reperfusion injury, with reduced cardiomyocyte apoptosis and death.

Rh-Catalyzed Intermolecular Reactions of α-Alkyl-α-Diazo Carbonyl Compounds with Selectivity over β-Hydride Migration

Rh-carbenes derived from α-diazocarbonyl compounds have found broad utility across a remarkable range of reactivity, including cyclopropanation, cyclopropenation, C-H insertions, heteroatom-hydrogen insertions, and ylide forming reactions. However, in contrast to α-aryl or α-vinyl-α-diazocarbonyl compounds, the utility of α-alkyl-α-diazocarbonyl compounds had been moderated by the propensity of such compounds to undergo intramolecular β-hydride migration to give alkene products. Especially challenging had been intermolecular reactions involving α-alkyl-α-diazocarbonyl compounds. This Account discusses the historical context and prior limitations of Rh-catalyzed reactions involving α-alkyl-α-diazocarbonyl compounds. Early studies demonstrated that ligand and temperature effects could influence chemoselectivity over β-hydride migration. However, effects were modest and conflicting conclusions had been drawn about the influence of sterically demanding ligands on β-hydride migration. More recent advances have led to a more detailed understanding of the reaction conditions that can promote intermolecular reactivity in preference to β-hydride migration. In particular, the use of bulky carboxylate ligands and low reaction temperatures have been key to enabling intermolecular cyclopropenation, cyclopropanation, carbonyl ylide formation/dipolar cycloaddition, indole C-H functionalization, and intramolecular bicyclobutanation with high chemoselectivity over β-hydride migration. Cyclic α-diazocarbonyl compounds have been shown to be particularly resilient toward β-hydride migration and are the first class of compounds that can engage in intermolecular reactivity in the presence of tertiary β-hydrogens. DFT calculations were used to propose that for cyclic α-diazocarbonyl compounds, ring constraints relieve steric interaction for intermolecular reactions and thereby accelerate the rate of intermolecular reactivity relative to intramolecular β-hydride migration. Enantioselective reactions of α-alkyl-α-diazocarbonyl compounds have been developed using bimetallic N-imido-tert-leucinate-derived complexes. The most effective complexes were found by computation and X-ray crystallography to adopt a "chiral crown" conformation in which all of the imido groups are presented on one face of the paddlewheel complex in a chiral arrangement. Insight from computational studies guided the design and synthesis of a mixed ligand paddlewheel complex, Rh2(S-PTTL)3TPA, the structure of which bears similarity to the chiral crown complex Rh2(S-PTTL)4. Rh2(S-PTTL)3TPA engages substrate classes (aliphatic alkynes, silylacetylenes, α-olefins) that are especially challenging in intermolecular reactions of α-alkyl-α-diazoesters and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C-H functionalization with yields and enantioselectivities that are comparable or superior to Rh2(S-PTTL)4. The work detailed in this Account describes progress toward enabling a more general utility for α-alkyl-α-diazo compounds in Rh-catalyzed carbene reactions. Further studies on ligand design and synthesis will continue to broaden the scope of their selective reactions.

Hierarchical control of coherent gene clusters defines the molecular mechanisms of glioblastoma

Glioblastoma is a highly-aggressive and rapidly-lethal tumor characterized by resistance to therapy. Although data on multiple genes, proteins, and pathways are available, the key challenge is deciphering this information and identifying central molecular targets. Therapeutically targeting individual molecules is often unsuccessful due to the presence of compensatory and redundant pathways, and crosstalk. A systems biology approach that involves a hierarchical gene group networks analysis can delineate the coherent functions of different disease mediators. Here, we report an integrative networks-based analysis to identify a system of coherent gene modules in primary and secondary glioblastoma. Our study revealed a hierarchical transcriptional control of genes in these modules. We elucidated those modules responsible for conversion of the glioma-associated microglia/macrophages into glioma-supportive, immunosuppressive cells. Further, we identified clusters comprising mediators of angiogenesis, proliferation, and cell death for both primary and secondary glioblastomas. Data obtained for these clusters point to a possible role of transcription regulators that function as the gene modules mediators in glioblastoma pathogenesis. We elucidated a set of possible transcription regulators that can be targeted to affect the selected gene clusters at specific levels for glioblastoma. Our innovative approach to construct informative disease models may hold the key to successful management of complex diseases including glioblastoma and other cancers.

Synthesis of PPAR-γ activators inspired by the marine natural product, paecilocin A

A series of N-substituted phthalimide derivatives were synthesized based on a pharmacophore study of paecilocin A (a natural PPAR-γ agonist) and synthetic leads. The introduction of hydrophilic and hydrophobic groups to the phthalimide skeleton yielded compounds 3-14. Compound 7 showed significant PPAR-γ activation in a luciferase assay using rat liver Ac2F cells. Docking simulations showed that a free hydroxyl group on the phthalimide head and a suitable hydrophilic tail, including a phenyl linker, were beneficial for PPAR-γ activation. Compound 7 and rosiglitazone concentration-dependently activated PPAR-γ with EC50 values of 0.67 μM and 0.028 μM, respectively. These phthalimide derivatives could be further investigated as a new class of PPAR-γ ligands.

Recent pharmacological developments on rhodanines and 2,4-thiazolidinediones

Thiazolidines are five-member heterocyclic having sulfur, nitrogen, and oxygen atoms in their ring structure and exhibiting potent as well as wide range of pharmacological activities. In this minireview, recent updates on synthesis and pharmacological evaluations of molecules based on 2,4-thiazolidine and rhodanine are discussed.

Rh-catalyzed intermolecular reactions of cyclic α-diazocarbonyl compounds with selectivity over tertiary C-H bond migration

Intermolecular Rh-catalyzed reactions of cyclic α-diazocarbonyl compounds with chemoselectivity over β-hydride elimination are described. These methods represent the first general intermolecular reactions of Rh-carbenoids that are selective over tertiary β-C-H bond migration. Successful transformations include cyclopropanation, cyclopropenation, and various X-H insertion reactions with a broad scope of substrates. We propose that the intermolecular approach of substrates to carbenes from acyclic diazo precursors may be relatively slow due to a steric interaction with the ester function, which is perpendicular to the π-system of the carbene. For carbenes derived from five- and six-membered cyclic α-diazocarbonyls, it is proposed that the carbene is constrained to be more conjugated with the carbonyl, thereby relieving the steric interaction for intermolecular reactions, and accelerating the rate of intermolecular reactivity relative to intramolecular β-hydride migration. However, attempts to use α-diazo-β-ethylcaprolactone in intermolecular cyclopropanation with styrene were unsuccessful. It is proposed that the conformational flexibility of the seven-membered ring allows the carbonyl to be oriented perpendicular to Rh-carbene. The significant intermolecular interaction between the carbonyl and approaching substrate is in agreement with the poor ability of α-diazo-β-ethylcaprolactone to participate in intermolecular cyclopropanation reactions. DFT calculations provide support for the mechanistic proposals that are described.

Design and synthesis of marine fungal phthalide derivatives as PPAR-γ agonists

On the basis of a marine fungal phthalide (paecilocin A) skeleton, we synthesized 20 analogs and evaluated them for peroxisome proliferator-activated receptor gamma (PPAR-γ) binding and activation. Among these analogs, 6 and 7 had significant PPAR-γ binding activity, and 7 showed further PPAR-γ activation in rat liver Ac2F cells. In docking simulation, 7 formed H bonds with key amino acid residues of the PPAR-γ binding domain, and the overall positioning was similar to rosiglitazone. This new phthalide derivative is considered an interesting new molecular class of PPAR-γ ligands.

Frontal affinity chromatography with MS detection of the ligand binding domain of PPARγ receptor: ligand affinity screening and stereoselective ligand-macromolecule interaction

In this study we report the development of new chromatographic tools for binding studies based on the gamma isoform ligand binding domain (LBD) of peroxisome proliferator-activated receptor (PPARγ) belonging to the nuclear receptor superfamily of ligand-activated transcription factors. PPARγ subtype plays important roles in the functions of adipocytes, muscles, and macrophages with a direct impact on type 2 diabetes, dyslipidemia, atherosclerosis, and cardiovascular disease. In order to set up a suitable immobilization chemistry, the LBD of PPARγ receptor was first covalently immobilized onto the surface of aminopropyl silica particles to create a PPARγ-Silica column for zonal elution experiments and then onto the surface of open tubular (OT) capillaries to create PPARγ-OT capillaries following different immobilization conditions. The capillaries were used in frontal affinity chromatography coupled to mass spectrometry (FAC-MS) experiments to determine the relative binding affinities of a series of chiral fibrates. The relative affinity orders obtained for these derivatives were consistent with the EC(50) values reported in literature. The optimized PPARγ-OT capillary was validated by determining the K(d) values of two selected compounds. Known the role of stereoselectivity in the binding of chiral fibrates, for the first time a detailed study was carried out by analysing two enantioselective couples on the LBD-PPARγ capillary by FAC and a characteristic two-stairs frontal profile was derived as the result of the two saturation events. All the obtained data indicate that the immobilized form of PPARγ-LBD retained the ability to specifically bind ligands.

PPAR Gamma Activators: Off-Target Against Glioma Cell Migration and Brain Invasion

Today, there is increasing evidence that PPARγ agonists, including thiazolidinediones (TDZs) and nonthiazolidinediones, block the motility and invasiveness of glioma cells and other highly migratory tumor entities. However, the mechanism(s) by which PPARγ activators mediate their antimigratory and anti-invasive properties remains elusive. This letter gives a short review on the debate and adds to the current knowledge by applying a PPARγ inactive derivative of the TDZ troglitazone (Rezulin) which potently counteracts experimental glioma progression in a PPARγ independent manner.

Cross-Talk between PPARs and the Partners of RXR: A Molecular Perspective

The PPARs are integral parts of the RXR-dependent signaling networks. Many other nuclear receptor subfamily 1 members also require RXR as their obligatory heterodimerization partner and they are often co-expressed in any given tissue. Therefore, the PPARs often complete with other RXR-dependent nuclear receptors and this competition has important biological implications. Thorough understanding of this cross-talk at the molecular level is crucial to determine the detailed functional roles of the PPARs. At the level of DNA binding, most RXR heterodimers bind selectively to the well-known “DR1 to 5” DNA response elements. As a result, many heterodimers share the same DR element and must complete with each other for DNA binding. At the level of heterodimerization, the partners of RXR share the same RXR dimerization interface. As a result, individual nuclear receptors must complete with each other for RXR to form functional heterodimers. Cross-talk through DNA binding and RXR heterodimerization present challenges to the study of these nuclear receptors that cannot be adequately addressed by current experimental approaches. Novel tools, such as engineered nuclear receptors with altered dimerization properties, are currently being developed. These tools will enable future studies to dissect specific RXR heterodimers and their signaling pathways.

Fluorine-18 labeling and biodistribution studies on peroxisome proliferator-activated receptor-gamma ligands: potential positron emission tomography imaging agents

INTRODUCTION

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is an important regulator of lipid metabolism; it controls the differentiation of preadipocytes and is also found at high levels in small metastatic tumors. In this report, we describe the radiochemical synthesis and evaluation of two (18)F-labeled analogs of the potent and selective PPARgamma agonist farglitazar.

MATERIALS AND METHODS

The isomeric aromatic fluorine-substituted target compounds [(2S)-(2-benzoylphenylamino)-3-(4-(2-[2-(4-[(18)F]fluorophenyl)-5-methyloxazol-4-yl]ethoxy)-phenyl)propionic acid ([(18)F]-1) and (2S)-[2-(4-fluorobenzoyl)phenylamino]-3-(4-[2-(5-methyl-2-phenyloxazol-4-yl)ethoxy]-phenyl)propionic acid ([(18)F]-2)] were prepared in fluorine-18-labeled form, respectively, by radiofluorination of an iodonium salt precursor or by Ullmann-type condensation with 2-iodo-4'-[(18)F]fluorobenzophenone after nucleophilic aromatic substitution with [(18)F]fluoride ion. Each compound was obtained in high specific activity and good radiochemical yield.

RESULTS AND DISCUSSION

(18)F-1 and (18)F-2 have high and selective PPARgamma binding affinities comparable to that of the parent molecule farglitazar, and they were found to have good metabolic stability. Tissue biodistribution studies of (18)F-1 and (18)F-2 were conducted, but PPARgamma-mediated uptake of both agents was minimal.

CONCLUSION

This study completes our first look at an important class of PPARgamma ligands as potential positron emission tomography (PET) imaging agents for breast cancer and vascular disease. Although (18)F-1 and (18)F-2 have high affinities for PPARgamma and good metabolic stability, their poor target-tissue distribution properties, which likely reflect their high lipophilicity combined with the low titer of PPARgamma in target tissues, indicate that they have limited potential as PPARgamma PET imaging agents.

Selective, potent PPARgamma agonists with cyclopentenone core structure

A series of analogues of the PPARgamma ligand 15-deoxy-Delta(12,14)-PGJ(2) have been synthesized by functionalization of a 5-alkyl-4-hydroxycyclopentenone core structure obtained by Piancatelli rearrangement of precursor furylcarbinol. Transient transactivation assays indicate that analogues 18 and 20 are selective nanomolar agonists of PPARgamma. This subtype selectivity is lost in derivatives (23, 24) with an alkynyl (oct-1-yn) chain at the C3 position, although the cyclopentenone derivative with cis relative configuration (23) showed greater affinity for PPARalpha.

Retinol saturase promotes adipogenesis and is downregulated in obesity

Adipocyte differentiation is controlled by many transcription factors, but few known downstream targets of these factors are necessary for adipogenesis. Here we report that retinol saturase (RetSat), which is an enzyme implicated in the generation of dihydroretinoid metabolites, is induced during adipogenesis and is directly regulated by the transcription factor peroxisome proliferator activated receptor gamma (PPARgamma). Ablation of RetSat dramatically inhibited adipogenesis but, surprisingly, this block was not overcome by the putative product of RetSat enzymatic activity. On the other hand, ectopic RetSat with an intact, but not a mutated, FAD/NAD dinucleotide-binding motif increased endogenous PPARgamma transcriptional activity and promoted adipogenesis. Indeed, RetSat was not required for adipogenesis when cells were provided with exogenous PPARgamma ligands. In adipose tissue, RetSat is expressed in adipocytes but is unexpectedly downregulated in obesity, most likely owing to infiltration of macrophages that we demonstrate to repress RetSat expression. Thiazolidinedione treatment reversed low RetSat expression in adipose tissue of obese mice. Thus, RetSat plays an important role in the biology of adipocytes, where it favors normal differentiation, yet is reduced in the obese state. RetSat is thus a novel target for therapeutic intervention in metabolic disease.

Thiazolidinediones and the preservation of beta-cell function, cellular proliferation and apoptosis

The thiazolidinediones (TZDs) or glitazones are pharmaceutical agents that have profound effects on energy expenditure and conservation. They also exert significant anti-inflammatory effects and influence cell proliferation and cell death. The drugs are primarily used in clinical practice in the treatment of patients with type 2 diabetes mellitus, a disorder of insulin resistance that occurs when the pancreatic beta-cells are unable to produce adequate amounts of insulin to maintain euglycaemia. Loss of pancreatic beta-cell function in type 2 diabetes is progressive and often precedes overt diabetes by 10 years or more, as was shown by the United Kingdom Prospective Diabetes Study. Any therapeutic or preventive approach that would limit or reverse loss of beta-cell function in diabetes would have profound effects on the morbidity associated with this widespread disease. Evidence suggesting a potential role of TZDs in preserving beta-cell function in type 2 diabetes as well as the ability of these agents to exert anti-inflammatory and proapoptotic anticancer effects, and their ability to promote cellular proliferation in various organs is reviewed.

Ajulemic acid, a synthetic nonpsychoactive cannabinoid acid, bound to the ligand binding domain of the human peroxisome proliferator-activated receptor gamma

Ajulemic acid (AJA) is a synthetic analog of THC-11-oic acid, a metabolite of tetrahydrocannabinol (THC), the major active ingredient of the recreational drug marijuana derived from the plant Cannabis sativa. AJA has potent analgesic and anti-inflammatory activity in vivo, but without the psychotropic action of THC. However, its precise mechanism of action remains unknown. Biochemical studies indicate that AJA binds directly and selectively to the isotype gamma of the peroxisome proliferator-activated receptor (PPARgamma) suggesting that this may be a pharmacologically relevant receptor for this compound and a potential target for drug development in the treatment of pain and inflammation. Here, we report the crystal structure of the ligand binding domain of the gamma isotype of human PPAR in complex with ajulemic acid, determined at 2.8-A resolution. Our results show a binding mode that is compatible with other known partial agonists of PPAR, explaining their moderate activation of the receptor, as well as the structural basis for isotype selectivity, as observed previously in vitro. The structure also provides clues to the understanding of partial agonism itself, suggesting a rational approach to the design of molecules capable of activating the receptor at levels that avoid undesirable side effects.

Synthesis and evaluation of N-acetyl-l-tyrosine based compounds as PPARα selective activators

The development of type 2 diabetes in obese individuals is linked to lipid accumulation in non-adipose tissues. A series of N-acetyl-L-tyrosine derivatives were synthesized and evaluated for PPAR transactivation. Compounds 4d and 4f were found to show better PPARalpha transactivation as compared to PPARgamma. Molecular docking analysis was carried out to study their important interactions with the active site of PPARalpha.

International Union of Pharmacology. LXI. Peroxisome proliferator-activated receptors

The three peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors of the nuclear hormone receptor superfamily. They share a high degree of structural homology with all members of the superfamily, particularly in the DNA-binding domain and ligand- and cofactor-binding domain. Many cellular and systemic roles have been attributed to these receptors, reaching far beyond the stimulation of peroxisome proliferation in rodents after which they were initially named. PPARs exhibit broad, isotype-specific tissue expression patterns. PPARalpha is expressed at high levels in organs with significant catabolism of fatty acids. PPARbeta/delta has the broadest expression pattern, and the levels of expression in certain tissues depend on the extent of cell proliferation and differentiation. PPARgamma is expressed as two isoforms, of which PPARgamma2 is found at high levels in the adipose tissues, whereas PPARgamma1 has a broader expression pattern. Transcriptional regulation by PPARs requires heterodimerization with the retinoid X receptor (RXR). When activated by a ligand, the dimer modulates transcription via binding to a specific DNA sequence element called a peroxisome proliferator response element (PPRE) in the promoter region of target genes. A wide variety of natural or synthetic compounds was identified as PPAR ligands. Among the synthetic ligands, the lipid-lowering drugs, fibrates, and the insulin sensitizers, thiazolidinediones, are PPARalpha and PPARgamma agonists, respectively, which underscores the important role of PPARs as therapeutic targets. Transcriptional control by PPAR/RXR heterodimers also requires interaction with coregulator complexes. Thus, selective action of PPARs in vivo results from the interplay at a given time point between expression levels of each of the three PPAR and RXR isotypes, affinity for a specific promoter PPRE, and ligand and cofactor availabilities.

Synthesis and evaluation of aminomethyl dihydrocinnamates as a new class of PPAR ligands

PPAR ligands with varied subtype selectivity have been synthesized using an achiral aminomethyl dihydrocinnamate template. Several compounds in this series have demonstrated potent plasma glucose and triglyceride lowering capability in rodent models of type 2 diabetes.

Thiazolidinediones: potential as therapeutics for psoriasis and perhaps other hyperproliferative skin disease

The thiazolidinediones constitute a family of synthetic compounds that act as high-affinity ligands for persoxisome proliferator-activated receptor-gamma (PPAR-gamma), a member of the nuclear hormone receptor family. Although originally developed to facilitate glucose control in patients with Type 2 diabetes, a number of studies showed that these agents effectively inhibited epithelial cell proliferation and tissue inflammation. Many of the initial cell growth inhibition studies were conducted with malignant epithelial cells from various sites; however, in addition to malignant epithelial cells, other studies showed that rapidly proliferating epidermal keratinoctyes in culture were also sensitive to the growth-inhibiting action of these moieties. Additional studies subsequently demonstrated that some patients with plaque psoriasis responded to treatment with one or another member of the thiazolidinedione family. Due to the potential therapeutic benefit of these compounds in diseases such as psoriasis, studies have been conducted to elucidate mechanisms by which growth inhibition is achieved. Interference with a number of growth-influencing signalling pathways has been demonstrated. Of interest, some of the growth-inhibiting effects are seen under conditions in which PPAR-gamma activation may not be responsible for the activity. Based on therapeutic potential, additional ongoing studies are aimed at developing novel thiazolidinediones that may have better efficacy than the currently available agents. Other studies are aimed at identifying optimal ways to use these agents in the treatment of hyperplastic skin diseases such as psoriasis.

2D QSAR of PPARγ agonist binding and transactivation

Multilinear QSAR models are developed for the largest and most diverse set of PPARgamma agonists treated hitherto. Binding of these small molecules to the human nuclear receptor PPARgamma is described by models that are built on simple 2D molecular descriptors and nevertheless are of good quality and predictive power (e.g., 144 compounds, 10 descriptors, r2=0.79, r2(cv)=0.76). The models presented are thoroughly validated by crossvalidation, randomization experiments, bootstrapping, and training set/test set partitioning. They may therefore be helpful in the design of new antidiabetic drug candidates. For gene transactivation, the functional activity of the agonists, a corresponding model for a similarly diverse compound set is of somewhat lower statistical quality.

The dipeptide H-Trp-Glu-OH shows highly antagonistic activity against PPARgamma: bioassay with molecular modeling simulation

The peroxisome proliferator-activated receptor gamma (PPARgamma) is an important therapeutic drug target for several conditions, including diabetes, inflammation, dyslipidemia, hypertension, and cancer. It is shown that an antagonist or partial agonist of PPARgamma has attractive potential applications in the discovery of novel antidiabetic agents that may retain efficacious insulin-sensitizing properties and minimize potential side effects. In this work, the dipeptide H-Trp-Glu-OH (G3335) was discovered to be a novel PPARgamma antagonist. Biacore 3000 results based on the surface plasmon resonance (SPR) technique showed that G3335 exhibits a highly specific binding affinity against PPARgamma (K(D) = 8.34 microM) and is able to block rosiglitazone, a potent PPARgamma agonist, in the stimulation of the interaction between the PPARgamma ligand-binding domain (LBD) and RXRalpha-LBD. Yeast two-hybrid assays demonstrated that G3335 exhibits strong antagonistic activity (IC50 = 8.67 microM) in perturbing rosiglitazone in the promotion of the PPARgamma-LBD-CBP interaction. Moreover, in transactivation assays, G3335 was further confirmed as an antagonist of PPARgamma in that G3335 could competitively bind to PPARgamma against 0.1 microM rosiglitazone to repress reporter-gene expression with an IC50 value of 31.9 muM. In addition, homology modeling and molecular-docking analyses were performed to investigate the binding mode of PPARgamma-LBD with G3335 at the atomic level. The results suggested that residues Cys285, Arg288, Ser289, and His449 in PPARgamma play vital roles in PPARgamma-LBD-G3335 binding. The significance of Cys285 for PPARgamma-LBD-G3335 interaction was further demonstrated by PPARgamma point mutation (PPARgamma-LBD-Cys285Ala). It is hoped our current work will provide a powerful approach for the discovery of PPARgamma antagonists, and that G3335 might be developed as a possible lead compound in diabetes research.

PPAR-gamma: a nuclear receptor with affinity for cannabinoids

An increasing number of cannabinoid actions are being reported that do not appear to be mediated by either CB1 or CB2, the known cannabinoid receptors. One such example is the synthetic analog ajulemic acid (AJA), which shows potent analgesic and anti-inflammatory effects in rodents and humans. AJA binds weakly to CB1 only at concentrations many fold higher than its therapeutic range, and is, therefore, completely free of psychotropic effects in both normal subjects and pain patients suggesting the involvement of a target site other than CB1. AJA as well as several other cannabinoids appear to have profound effects on cellular lipid metabolism as evidenced by their ability to transform fibroblasts into adipocytes where the accumulation of lipid droplets can be readily observed. Such transformations can be mediated by the activation of the nuclear receptor PPAR-gamma. A variety of small molecule ligands including AJA have been shown to induce the activation of PPAR-gamma and, in some cases this has led to the introduction of clinically useful agents. It is suggested that PPAR-gamma may serve a receptor function for certain actions of some cannabinoids.

Inflammatory modulation of PPAR gamma expression and activity

Nitric oxide (NO) production increases with age in the lupus-prone MRL/lpr mouse, paralleling disease activity. One mechanism for excess NO production in MRL/lpr mice may be a defect in down-regulatory mechanisms of the iNOS pathway. A potential modulator of NO is the nuclear hormone receptor peroxisome proliferation activated receptor gamma (PPARgamma). We demonstrate that renal PPARgamma protein expression was altered as disease progressed in MRL/lpr mice, which paralleled increased iNOS protein expression. Additionally, MRL/lpr-derived primary mesangial cells expressed less PPARgamma than BALB/c mesangial cells and produced more NO in response to LPS and IFNgamma. Furthermore, PPARgamma activity was reduced in mesangial cells following exposure to inflammatory mediators. This activity was restored with the addition of a NOS enzyme inhibitor. These results indicate that the activation of inflammatory pathways may lead to reduced activity and expression of PPARgamma, further exacerbating the disease state.

A yeast two-hybrid technology-based system for the discovery of PPARgamma agonist and antagonist

Peroxisome proliferator-activated receptor gamma (PPARgamma) is an important therapeutic drug target against several diseases such as diabetes, inflammation, dyslipidemia, hypertension, and cancer. Ligand binding to PPARgamma is responsible for controlling the biological functions, and developing new technology to measure ligand-PPARgamma binding is significant for both the function study of the receptor and ligand discovery. In this study, we exploited an efficient approach for the discovery of PPARgamma agonist and antagonist via a yeast two-hybrid system based on the fact that PPARgamma interacts with the coactivator CBP (CREP-binding protein) ligand-dependently. We employed the MEL1 reporter gene instead of the traditionally used LacZ gene to evaluate the protein-protein interactions by conducting a convenient alpha-galactosidase assay in the yeast strain AH109 with genes of PPARgamma-LBD (ligand-binding domain) and CBP N terminus introduced. With this built screening platform, the EC(50) values of the PPARgamma agonists rosiglitazone, troglitazone, pioglitazone, indomethacin, 15-deoxy-Delta12,14-prostaglandin J(2) (15d-PGJ(2)), and GI262570 were investigated, and the quantitatively antagonistic effect by IC(50) of the PPARgamma typical antagonist GW9662 on the rosiglitazone agonistic activity was fully examined. The reliability of this presented system evaluated by the comparable agreement of EC(50) and IC(50) values for the test compounds with the reported ones indicated that this yeast two-hybrid-based approach is powerful for PPARgamma agonist and antagonist screening. In addition, because this screening system is designed for use in a microtiter plate format where numerous chemicals could be readily screened, it is hoped that this yeast two-hybrid screening approach may be adaptable for high-throughput settings.

Design, synthesis and evaluation of carbazole derivatives as PPAR alpha/gamma dual agonists and antioxidants

A series of hydroxycarbazole derivatives were synthesized and evaluated for PPAR alpha/gamma dual agonist as well as antioxidant activities. While most compounds showed good antioxidant activity, some compounds were identified as potential PPAR alpha/gamma dual agonists as well. Compounds 10a and 16 were found to be active in animal studies.

The Nonthiazolidinedione Tyrosine-Based Peroxisome Proliferator-Activated Receptor γ Ligand GW7845 Induces Apoptosis and Limits Migration and Invasion of Rat and Human Glioma Cells

Despite new approaches, treatment options for malignant gliomas are still limited, calling for further development of therapeutic strategies. The peroxisome proliferator-activated receptor (PPAR)gamma, a member of the nuclear hormone receptor family, represents a possible new target for neoplastic therapies. Synthetic PPARgamma agonists were developed and are already in clinical use for the treatment of type II diabetes, since PPARgamma plays a crucial role in lipid metabolism and regulation of insulin sensitivity. Beyond these metabolic effects, PPARgamma agonists exhibit antineoplastic effects in various malignant tumor cells. Here, we investigated the antineoplastic effects of the nonthiazolidinedione tyrosine-based PPARgamma ligand (S)-2-(1-carboxy-2-{4-[2-(5-methyl-2-phenyloxazol-4-yl)ethoxy]phenyl}ethylamino)benzoic acid methyl ester (GW7845) in rat and human glioma cells. GW7845 reduced cellular viability of rat C6 glioma and human glioma cells in a time-dependent manner. Analysis of GW7845-treated tumor cells revealed induction of apoptotic cell death as determined by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and cleaved caspase-3 activation. Furthermore, GW7845 reduced proliferation of C6 glioma cells as measured by Ki-67 immunore-activity. There was also a reduction of migration and invasion, assessed by Boyden chamber and spheroid experiments. Together, these data indicate that the PPARgamma agonist GW7845 may be of potential use in treatment of malignant gliomas.

2-Alkoxydihydrocinnamates as PPAR agonists. Activity modulation by the incorporation of phenoxy substituents

Herein we describe a series of potent and selective PPARgamma agonists with moderate PPARalpha affinity and little to no affinity for other nuclear receptors. In vivo studies in a NIDDM animal model (ZDF rat) showed that these compounds are efficacious at low doses in glucose normalization and plasma triglyceride reduction. Compound 1b (LY519818) was selected from our SAR studies to be advanced to clinical evaluation for the treatment of type II diabetes.

Reduced serum dipeptidyl peptidase-IV after metformin and pioglitazone treatments

Dipeptidyl peptidase-IV (DPP-IV) regulates metabolism by degrading incretins involved in nutritional regulation. Metformin and pioglitazone improve insulin sensitivity whereas glyburide promotes insulin secretion. Zucker diabetic rats were treated with these antidiabetic agents for 2 weeks and DPP-IV activity and expression were determined. Serum DPP-IV activity increased whereas tissue activity decreased as the rats aged. Treatment of rats with metformin, pioglitazone, and glyburide did not alter DPP-IV mRNA expression in liver or kidney. Metformin and pioglitazone significantly (P<0.05) reduced serum DPP-IV activity and glycosylated hemoglobin. Glyburide did not lower DPP-IV activity or glycosylated hemoglobin. Regression analysis showed serum DPP-IV activity correlated with glycosylated hemoglobin (r=0.92) and glucagon-like peptide-1 levels (r=-0.49). Metformin, pioglitazone, and glyburide had no effect on serum DPP-IV activity in vitro, indicating these are not competitive DPP-IV inhibitors. We propose the in vivo inhibitory effects observed with metformin and pioglitazone on serum DPP-IV activity results from reduced DPP-IV secretion.

Novel PPARγ Agonists GI 262570, GW 7845, GW 1929, and Pioglitazone Decrease Calcium Channel Function and Myogenic Tone in Rat Mesenteric Arteries

Novel non-thiazolidinedione, tyrosine-derived peroxisome proliferator-activated receptor gamma agonists, GI 262570, GW 7845, GW 1929, developed by GlaxoSmithKline (GSK) along with pioglitazone and nisoldipine, were studied on currents through L-type voltage-dependent calcium channels (VDCC) in freshly isolated smooth muscle cells from mesenteric arteries, and on the diameter of pressurized mesenteric arteries in vitro. Using Ba2+ (10 mmol/l) as the charge carrier through VDCC, the half-inhibition constants (IC50) for GI 262570, GW 7845, GW 1929, and pioglitazone were 2.0 +/- 0.5, 3.0 +/- 0.5, 5.0 +/- 0.7, and 10.0 +/- 0.8 mumol/l, respectively. For arterial diameter measurements the IC50 values for GI 262570, GW 7845, GW 1929, and pioglitazone were 2.4, 4.1, 6.3, and 13.9 mumol/l, respectively. Each GSK compound and pioglitazone was effective at inhibiting VDCC and relaxing pressurized arteries, suggesting that the vasodilation of resistance arteries could be explained by the inhibition of calcium entry through VDCC.