A unique PPARgamma ligand with potent insulin-sensitizing yet weak adipogenic activity

Design, synthesis, and biological evaluation of deuterated indolepropionic acid derivatives as novel long-acting pan PPARα/γ/δ agonists

Metabolic syndrome is a complex disease with diverse symptoms, but current pharmacological interventions have limited efficacy. Indeglitazar, a pan-agonist targeting the three-peroxisome proliferator activated receptors (PPAR), exhibits significant therapeutic effects on both diabetic and fatty liver animal models. However, its short half-life limits the in vivo efficacy, which might be attributed to the β-oxidation of indolepropionic acid at Indeglitazar. To overcome this metabolic instability, two deuterium atoms were introduced to the α-position of indolepropionic acid to block the β-oxidation. In this study, several deuterated derivatives were found to sustain PPARs activity and extend the half-life of liver microsomes. In oral glucose tolerance tests, I-1 exhibited the strongest glucose-lowering effect on ob/ob mice in this series. In db/db mice, I-1 reduced lipid levels, liver steatosis and promoted UCP1 expression in white adipose tissue. Mechanistic studies further revealed that I-1 exerts stronger effects than Indeglitazar on the regulation of genes related to lipid metabolism, mitochondrial function, and oxidative stress. Furthermore, I-1 significantly reduced liver steatosis, hepatocellular ballooning, inflammation, and fibrosis in NASH model induced by HFD + CCl4, and even exerted better therapeutic effect than that of Indeglitazar. With the above attractive efficacy, deuterated derivative I-1 is considered as a promising treatment for metabolic syndrome.

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

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

Understanding PPARγ and Its Agonists on Trophoblast Differentiation and Invasion: Potential Therapeutic Targets for Gestational Diabetes Mellitus and Preeclampsia

The increasing incidence of pregnancy complications, particularly gestational diabetes mellitus (GDM) and preeclampsia (PE), is a cause for concern, as they can result in serious health consequences for both mothers and infants. The pathogenesis of these complications is still not fully understood, although it is known that the pathologic placenta plays a crucial role. Studies have shown that PPARγ, a transcription factor involved in glucose and lipid metabolism, may have a critical role in the etiology of these complications. While PPARγ agonists are FDA-approved drugs for Type 2 Diabetes Mellitus, their safety during pregnancy is not yet established. Nevertheless, there is growing evidence for the therapeutic potential of PPARγ in the treatment of PE using mouse models and in cell cultures. This review aims to summarize the current understanding of the mechanism of PPARγ in placental pathophysiology and to explore the possibility of using PPARγ ligands as a treatment option for pregnancy complications. Overall, this topic is of great significance for improving maternal and fetal health outcomes and warrants further investigation.

The Activation of PPARγ by (2Z,4E,6E)-2-methoxyocta-2,4,6-trienoic Acid Counteracts the Epithelial–Mesenchymal Transition Process in Skin Carcinogenesis

Cutaneous squamous cell carcinoma (cSCC) is the most common UV-induced keratinocyte-derived cancer, and its progression is characterized by the epithelial–mesenchymal transition (EMT) process. We previously demonstrated that PPARγ activation by 2,4,6-octatrienoic acid (Octa) prevents cutaneous UV damage. We investigated the possible role of the PPARγ activators Octa and the new compound (2Z,4E,6E)-2-methoxyocta-2,4,6-trienoic acid (A02) in targeting keratinocyte-derived skin cancer. Like Octa, A02 exerted a protective effect against UVB-induced oxidative stress and DNA damage in NHKs. In the squamous cell carcinoma A431 cells, A02 inhibited cell proliferation and increased differentiation markers’ expression. Moreover, Octa and even more A02 counteracted the TGF-β1-dependent increase in mesenchymal markers, intracellular ROS, the activation of EMT-related signal transduction pathways, and cells’ migratory capacity. Both compounds, especially A02, counterbalanced the TGF-β1-induced cell membrane lipid remodeling and the release of bioactive lipids involved in EMT. In vivo experiments on a murine model useful to study cell proliferation in adult animals showed the reduction of areas characterized by active cell proliferation in response to A02 topical treatment. In conclusion, targeting PPARγ may be useful for the prevention and treatment of keratinocyte-derived skin cancer.

A New Insight into an Alternative Therapeutic Approach to Restore Redox Homeostasis and Functional Mitochondria in Neurodegenerative Diseases

Neurodegenerative diseases are accompanied by oxidative stress and mitochondrial dysfunction, leading to a progressive loss of neuronal cells, formation of protein aggregates, and a decrease in cognitive or motor functions. Mitochondrial dysfunction occurs at the early stage of neurodegenerative diseases. Protein aggregates containing oxidatively damaged biomolecules and other misfolded proteins and neuroinflammation have been identified in animal models and patients with neurodegenerative diseases. A variety of neurodegenerative diseases commonly exhibits decreased activity of antioxidant enzymes, lower amounts of antioxidants, and altered cellular signalling. Although several molecules have been approved clinically, there is no known cure for neurodegenerative diseases, though some drugs are focused on improving mitochondrial function. Mitochondrial dysfunction is caused by oxidative damage and impaired cellular signalling, including that of peroxisome proliferator-activated receptor gamma coactivator 1α. Mitochondrial function can also be modulated by mitochondrial biogenesis and the mitochondrial fusion/fission cycle. Mitochondrial biogenesis is regulated mainly by sirtuin 1, NAD⁺, AMP-activated protein kinase, mammalian target of rapamycin, and peroxisome proliferator-activated receptor γ. Altered mitochondrial dynamics, such as increased fission proteins and decreased fusion products, are shown in neurodegenerative diseases. Due to the restrictions of a target-based approach, a phenotype-based approach has been performed to find novel proteins or pathways. Alternatively, plasma membrane redox enzymes improve mitochondrial function without the further production of reactive oxygen species. In addition, inducers of antioxidant response elements can be useful to induce a series of detoxifying enzymes. Thus, redox homeostasis and metabolic regulation can be important therapeutic targets for delaying the progression of neurodegenerative diseases.

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

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

LMO3 reprograms visceral adipocyte metabolism during obesity

Abstract

Obesity and body fat distribution are important risk factors for the development of type 2 diabetes and metabolic syndrome. Evidence has accumulated that this risk is related to intrinsic differences in behavior of adipocytes in different fat depots. We recently identified LIM domain only 3 (LMO3) in human mature visceral adipocytes; however, its function in these cells is currently unknown. The aim of this study was to determine the potential involvement of LMO3-dependent pathways in the modulation of key functions of mature adipocytes during obesity. Based on a recently engineered hybrid rAAV serotype Rec2 shown to efficiently transduce both brown adipose tissue (BAT) and white adipose tissue (WAT), we delivered YFP or Lmo3 to epididymal WAT (eWAT) of C57Bl6/J mice on a high-fat diet (HFD). The effects of eWAT transduction on metabolic parameters were evaluated 10 weeks later. To further define the role of LMO3 in insulin-stimulated glucose uptake, insulin signaling, adipocyte bioenergetics, as well as endocrine function, experiments were conducted in 3T3-L1 adipocytes and newly differentiated human primary mature adipocytes, engineered for transient gain or loss of LMO3 expression, respectively. AAV transduction of eWAT results in strong and stable Lmo3 expression specifically in the adipocyte fraction over a course of 10 weeks with HFD feeding. LMO3 expression in eWAT significantly improved insulin sensitivity and healthy visceral adipose tissue expansion in diet-induced obesity, paralleled by increased serum adiponectin. In vitro, LMO3 expression in 3T3-L1 adipocytes increased PPARγ transcriptional activity, insulin-stimulated GLUT4 translocation and glucose uptake, as well as mitochondrial oxidative capacity in addition to fatty acid oxidation. Mechanistically, LMO3 induced the PPARγ coregulator Ncoa1, which was required for LMO3 to enhance glucose uptake and mitochondrial oxidative gene expression. In human mature adipocytes, LMO3 overexpression promoted, while silencing of LMO3 suppressed mitochondrial oxidative capacity. LMO3 expression in visceral adipose tissue regulates multiple genes that preserve adipose tissue functionality during obesity, such as glucose metabolism, insulin sensitivity, mitochondrial function, and adiponectin secretion. Together with increased PPARγ activity and Ncoa1 expression, these gene expression changes promote insulin-induced GLUT4 translocation, glucose uptake in addition to increased mitochondrial oxidative capacity, limiting HFD-induced adipose dysfunction. These data add LMO3 as a novel regulator improving visceral adipose tissue function during obesity.

Key messages

LMO3 increases beneficial visceral adipose tissue expansion and insulin sensitivity in vivo.

LMO3 increases glucose uptake and oxidative mitochondrial activity in adipocytes.

LMO3 increases nuclear coactivator 1 (Ncoa1).

LMO3-enhanced glucose uptake and mitochondrial gene expression requires Ncoa1.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-021-02089-9.

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

The Role of PPARγ Ligands in Breast Cancer: From Basic Research to Clinical Studies

Peroxisome proliferator-activated receptor gamma (PPARγ), belonging to the nuclear receptor superfamily, is a ligand-dependent transcription factor involved in a variety of pathophysiological conditions such as inflammation, metabolic disorders, cardiovascular disease, and cancers. In this latter context, PPARγ is expressed in many tumors including breast cancer, and its function upon binding of ligands has been linked to the tumor development, progression, and metastasis. Over the last decade, much research has focused on the potential of natural agonists for PPARγ including fatty acids and prostanoids that act as weak ligands compared to the strong and synthetic PPARγ agonists such as thiazolidinedione drugs. Both natural and synthetic compounds have been implicated in the negative regulation of breast cancer growth and progression. The aim of the present review is to summarize the role of PPARγ activation in breast cancer focusing on the underlying cellular and molecular mechanisms involved in the regulation of cell proliferation, cell cycle, and cell death, in the modulation of motility and invasion as well as in the cross-talk with other different signaling pathways. Besides, we also provide an overview of the in vivo breast cancer models and clinical studies. The therapeutic effects of natural and synthetic PPARγ ligands, as antineoplastic agents, represent a fascinating and clinically a potential translatable area of research with regards to the battle against cancer.

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

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

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.

The Effect of Biotinylated PAMAM G3 Dendrimers Conjugated with COX-2 Inhibitor (celecoxib) and PPARγ Agonist (Fmoc-L-Leucine) on Human Normal Fibroblasts, Immortalized Keratinocytes and Glioma Cells in Vitro

Glioblastoma multiforme (GBM) is the most malignant type of central nervous system tumor that is resistant to all currently used forms of therapy. Thus, more effective GBM treatment strategies are being investigated, including combined therapies with drugs that may cross the blood brain barrier (BBB). Another important issue considers the decrease of deleterious side effects of therapy. It has been shown that nanocarrier conjugates with biotin can penetrate BBB. In this study, biotinylated PAMAM G3 dendrimers substituted with the recognized anticancer agents cyclooxygenase-2 (COX-2) inhibitor celecoxib and peroxisome proliferator-activated receptor γ (PPARγ) agonist Fmoc-L-Leucine (G3-BCL) were tested in vitro on human cell lines with different p53 status: glioblastoma (U-118 MG), normal fibroblasts (BJ) and immortalized keratinocytes (HaCaT). G3-BCL penetrated efficiently into the lysosomal and mitochondrial compartments of U-118 MG cells and induced death of U-118 MG cells via apoptosis and inhibited proliferation and migration at low IC₅₀ = 1.25 µM concentration, considerably lower than either drug applied alone. Comparison of the effects of G3-BCL on expression of COX-2 and PPARγ protein and PGE₂ production of three different investigated cell line phenotypes revealed that the anti-glioma effect of the conjugate was realized by other mechanisms other than influencing PPAR-γ expression and regardless of p53 cell status, it was dependent on COX-2 protein level and high PGE₂ production. Similar G3-BCL cytotoxicity was seen in normal fibroblasts (IC₅₀ = 1.29 µM) and higher resistance in HaCaT cells (IC₅₀ = 4.49 µM). Thus, G3-BCL might be a good candidate for the targeted, local glioma therapy with limited site effects.

An edible fungi Pleurotus ostreatus inhibits adipogenesis via suppressing expression of PPAR γ and C/EBP α in 3T3-L1 cells: In vitro validation of gene knock out of RNAs in PPAR γ using CRISPR spcas9

OBJECTIVE

Obesity is now well recognized as a disorder, one that is essentially preventable through changes in lifestyle. Obesity is also a main concern associated with expanded morbidity and mortality from many noncommunicable illnesses (NCDs). The study aimed to determine the antiobesity effect of Pleurotus ostreatus (PO) and its bioactive anthraquinone (AQ). The overall promoter genes CEBPα (CCAAT enhancer binding protein α) and PPARγ (Peroxisome proliferator activated receptor γ) in controlling the homeostasis of glucose was analysed using 3T3-L1 cell line. Finally, an insilico study was carried out using CRISPR software to identify the RNA's involved in adipogenesis especially of the control gene PPARγ.

MATERIALS AND METHODS

Preliminary screening of the edible fungi and their bio actives led to the marvellous discovery of side effect free agonists for treating obesity (adipogenesis). An edible fungi Pleurotus ostreatus (PO) were analysed in a screening platform with different series of tests for adipocyte differentiation, triglyceride analysis, lipolysis determination, glucose uptake assay, cytotoxicity assay and lipase activity followed by specific gene expression analysis. The gene knockout mechanism was also elucidated by CRISPR spcas 9 tool.

RESULTS

The antiadipogenic (antiobesity) activity of DMSO extract of PO were found to stimulate the insulin dependent uptake of glucose. The extract also decreased the levels of triglycerides and glycerol accumulation in differentiated adipocyte cells. The binding FABP4 (Fatty acid binding protein) and transport protein FATP1 (Fatty acid transport protein) along with the fat breaking LPL (lipoprotein lipase) was found to be inhibited after the PO treatment at varying concentration (0-300 μg/ml). CRISPR spcas9 genome editing software was used as an insilico approach in validating the efficiency of mouse embryonic and human adipogenic cell line (3T3-L1). These tool analysed and found 4 RNAs gene knock out possibilities in PPARγ and their efficiency for further treating obesity.

CONCLUSION

These novel finding contribute to the confirmation that edible fungi PO and it's bioactive AQ is an adequate supplement for constraining the lipid and triglycerides in differentiated mature adipocytes by reversing the fat deposition. Thereby, forbidding the enzymes linked with fat absorption. Besides, the CRISPR tool identified gene knock out possibilities of control gene PPARγ, will pave a way in further research for treating obesity.

Biotinylated PAMAM G3 dendrimer conjugated with celecoxib and/or Fmoc-l-Leucine and its cytotoxicity for normal and cancer human cell lines

Tumors still remain one of the main causes of mortality due to the lack of effective anti-cancer therapy. Recently it has been shown, that overexpression of inducible cyclooxygenase-2 (COX-2) and decrease of peroxisome proliferator-activated receptor γ (PPARγ) expression accompany many malignances, therefore, it has been proposed, that COX-2 inhibitors and PPARγ agonists are potential candidates for anticancer therapy and their synergistic, antineoplastic action has been described. In the present study a COX-2 inhibitor (celecoxib) and/or PPARγ agonist (Fmoc-l-Leucine) were conjugated with the biotinylated G3 PAMAM dendrimer to form a three different constructs targeted to cells with increased biotin uptake. All conjugates were characterized by the NMR spectroscopy. Investigation of three types of human cells: normal skin fibroblasts (BJ), immortalized keratinocytes (HaCaT) and cancer lines: glioblastoma (U-118 MG) and squamous cell carcinoma (SCC-15) revealed similar biotin labeled ATTO590 accumulation (after 24 h), except for SCC-15 with significantly lower loading. Constitutive expression of COX-2 protein was confirmed in all tested cells with significantly higher levels (2-2.5 times) in both cancer lines. Comparison of cytotoxicity of the new synthetized dendrimers clearly documented the highest cytotoxicity of the G3^1B16C15L dendrimer conjugated with both drugs (1: 1) as compared with drugs alone and single conjugates. Additive effects of construct with both compounds were shown for fibroblasts and both cancer cell lines in the order BJ > U-118 MG > SCC-15 with IC₅₀ in the range: 0.69, 1.44 and 2.22 μM, respectively and lowest cytotoxicity in HaCaT cells (IC₅₀ = 2.88). Our results showed, that biotinylated G3 PAMAM dendrimers substituted with COX-2 inhibitor, celecoxib, and PPARγ agonist, Fmoc-l-Leucine (1:1) may be a good candidate for local therapy of glioblastoma but not a skin cancer. Since the effect of PPARγ agonists on COX-2 expression vary depending upon the cell type, specificity of used agonist and the presence of other environmental factors, it is necessary to carefully evaluate the response of chosen drugs on the target cells.

Hispidulin inhibits hepatocellular carcinoma growth and metastasis through AMPK and ERK signaling mediated activation of PPARγ

Hispidulin, a phenolic flavonoid, exerts potent cytotoxicity towards a variety of human cancers. However, the effects of hispidulin on hepatocellular carcinoma (HCC) and underlying molecular mechanisms of its action remain elusive. The present study investigated the effect of hispidulin on HCC in experimental models, including tumor cell lines and mouse tumor xenograft. Results demonstrated that hispidulin was cytotoxic and anti-proliferative to HCC cell lines (SMMC7721 and Bel7402). Hispidulin activated caspase-3 and triggered apoptosis in HCC cells. Moreover, hispidulin inhibited cell migration and invasion by inhibiting the expression of matrix metalloproteinases (MMP-2, MMP-9) and by inducing tissue inhibitor of metalloproteinase-3 (TIMP-3) expression. Hispidulin activated peroxisome proliferator-activated receptor γ (PPARγ) signaling which mainly contributed to its cytotoxicity in HCC cells. Remarkably, GW9662 (a PPARγ inhibitor) or PPARγ targeting siRNA significantly abrogated the anti-proliferative, pro-apoptotic, and anti-metastatic effects of hispidulin in HCC cells. Furthermore, hispidulin induced activation of PPARγ which was associated with increased phosphorylation of AMPK, ERK, JNK in HCC cells. Compound C (an AMPK inhibitor) or PD98059 (a MEK inhibitor) partly reversed the effects of hispidulin on PPARγ signaling in HCC cells. In contrast, no significant changes in PPARγ signaling were observed in HCC cells pretreated with SP600125 (a JNK inhibitor), while SP6000125 significantly inhibited the anti-cancer effects of hispidulin in HCC cells. Hispidulin administration effectively suppressed Bel7402 xenograft tumor growth and lung metastasis in vivo. Our findings indicate that PPARγ activation by hispidulin effectively suppressed HCC cell growth and metastasis both in vitro and in vivo.

Structural insights into the heterodimeric complex of the nuclear receptors FXR and RXR

Farnesoid X receptor (FXR) is a member of the family of ligand-activated nuclear receptors. FXR plays critical roles in maintaining many metabolic pathways, including bile acid regulation and glucose and lipid homeostasis, and forms a heterodimeric complex with the retinoid X receptor (RXR). Despite the important roles of the FXR/RXR heterodimerization in human physiology, the molecular basis underlying the FXR/RXR interaction is still uncertain in the absence of a complex structure. Here, we report the heterodimeric structure of FXR and RXR in the presence of an FXR agonist (WAY-362450), RXR agonist (9-cis-retinoic acid), and a peptide derived from a steroid receptor coactivator (SRC2), revealing both unique and conserved modes for FXR heterodimerization. We found that the dimerization with RXR induced allosteric conformational changes on the coactivator-binding site of FXR. These changes enhanced the transcriptional activity of FXR by promoting the coactivator binding, thus suggesting a structural basis for the functional permissiveness of the FXR/RXR heterodimer complex. Furthermore, sequence analyses together with functional mutagenesis studies indicated that the helix H10 largely responsible for the dimerization is highly conserved and also critical for the FXR transcriptional activity. Our findings highlight the important roles of RXR heterodimerization in the nuclear receptor signaling, providing a potential framework to develop pharmaceutical agents in treating FXR/RXR-related diseases.

The natural compound, formononetin, extracted from Astragalus membranaceus increases adipocyte thermogenesis by modulating PPARγ activity

BACKGROUND AND PURPOSE

Increasing energy expenditure through adipocyte thermogenesis is generally accepted as a promising strategy to mitigate obesity and its related diseases. However, few clinically effective and safe agents are known to promote adipocyte thermogenesis. In this study, 20 traditional Chinese herbal medicines were screened to examine whether they induced adipocyte thermogenesis.

EXPERIMENTAL APPROACH

The effects of Chinese herbal medicines or components isolated from extracts of A. membranaceus, on adipocyte thermogenesis were analysed by assessing expression of uncoupling protein 1 (UCP1) by qPCR. Eight-week-old C57BL6/J male mice were fed a high-fat diet for 8 weeks and then randomized to two groups treated with vehicle or formononetin for another 8 weeks. Glucose tolerance tests and staining of adipose tissue with haematoxylin and eosin were carried out. Whole-body oxygen consumption was measured with an open-circuit indirect calorimetry system.

KEY RESULTS

Extracts of A. membranaceus increased expression of Ucp1 in primary cultures of mouse adipocytes. Formononetin was the only known component of A. membranaceus extracts to increase adipocyte Ucp1 expression. Diet-induced obese mice treated with formononetin gained less weight and showed higher energy expenditure than untreated mice. In addition, formononetin binds directly with PPARγ.

CONCLUSIONS AND IMPLICATION

Taken together, our study demonstrates that the Chinese herbal medicine from A. membranaceus and its constituent formononetin have the potential to reduce obesity and associated metabolic disorders. Our results suggest that formononetin regulates adipocyte thermogenesis as a non-classical PPARγ agonist.

BCAA Metabolism and Insulin Sensitivity - Dysregulated by Metabolic Status?

Branched-chain amino acids (BCAAs) appear to influence several synthetic and catabolic cellular signaling cascades leading to altered phenotypes in mammals. BCAAs are most notably known to increase protein synthesis through modulating protein translation, explaining their appeal to resistance and endurance athletes for muscle hypertrophy, expedited recovery, and preservation of lean body mass. In addition to anabolic effects, BCAAs may increase mitochondrial content in skeletal muscle and adipocytes, possibly enhancing oxidative capacity. However, elevated circulating BCAA levels have been correlated with severity of insulin resistance. It is hypothesized that elevated circulating BCAAs observed in insulin resistance may result from dysregulated BCAA degradation. This review summarizes original reports that investigated the ability of BCAAs to alter glucose uptake in consequential cell types and experimental models. The review also discusses the interplay of BCAAs with other metabolic factors, and the role of excess lipid (and possibly energy excess) in the dysregulation of BCAA catabolism. Lastly, this article provides a working hypothesis of the mechanism(s) by which lipids may contribute to altered BCAA catabolism, which often accompanies metabolic disease.

Activation of PPARγ mediates icaritin-induced cell cycle arrest and apoptosis in glioblastoma multiforme

BACKGROUND

Glioblastoma multiforme (GBM) is the most prevalent primary malignancy of the brain. This study was designed to investigate whether icaritin exerts anti-neoplastic activity against GBM in vitro.

MATERIALS AND METHODS

Cell Counting Kit-8 (CCK-8) assay was utilized to examine the viability of GBM cells. The apoptotic cell population was measured by flow cytometry analysis. Cell cycle distribution was detected by flow cytometry as well. Western blot analysis was performed to examine the level of biomarker proteins in GBM cells. Levels of PPARγ mRNA and protein were detected by qPCR and western blot analysis, respectively. To examine the role of PPARγ in the anti-neoplastic activity of icaritin, PPARγ antagonist GW9662 or PPARγ siRNA was used. The activity of PPARγ was determined by DNA binding and luciferase assays.

RESULTS

Our findings revealed that icaritin markedly suppresses cell growth in a dose-dependent and time-dependent fashion. The cell population at the G0/G1 phase of the cell cycle was significantly increased following icaritin treatment. Meanwhile, icaritin promoted apoptotic cell death in T98G and U87MG cells. Further investigation showed upregulation of PPARγ played a key role in the anti-neoplastic activities of icaritin. Moreover, our result demonstrated activation of AMPK signaling by icaritin mediated the modulatory effect of icaritin on PPARγ.

CONCLUSION

Our results suggest the PPARγ may mediate anti-neoplastic activities against GBM.

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

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

The α-melanocyte stimulating hormone/peroxisome proliferator activated receptor-γ pathway down-regulates proliferation in melanoma cell lines

Background

The α-Melanocyte Stimulating Hormone (αMSH)/Melanocortin-1 receptor (MC1R) interaction promotes melanogenesis through the cAMP/PKA pathway. The direct induction of this pathway by Forskolin (FSK) is also known to enhance melanocyte proliferation. αMSH acts as a mitogenic agent in melanocytes and its effect on proliferation of melanoma cells is less known. We previously identified the αMSH/Peroxisome Proliferator Activated Receptor (PPARγ) pathway as a new pathway on the B16-F10 mouse melanoma cell line. αMSH induced the translocation of PPARγ into the nucleus as an active transcription factor. This effect was independent of the cAMP/PKA pathway and was mediated by the activation of the PI(4,5)P2/PLC pathway, a pathway which we have described to be triggered by the αMSH-dependent MC1R stimulation. Moreover, in the same study, preliminary experiments showed that mouse melanoma cells responded to αMSH by reducing proliferation and that PPARγ was involved in this effect. Due to its key role in the control of cell proliferation, PPARγ agonists are used in therapeutic models for different forms of cancer, including melanoma. The purpose of this study was: (a) to confirm the different proliferative behavior in response to αMSH in healthy and in melanoma condition; (b) to verify whether the cAMP/PKA pathway and the PLC/PPARγ pathway could exert an antagonistic function in the control of proliferation; (c) to deepen the knowledge of the molecular basis responsible for the down-proliferative response of melanoma cells after exposure to αMSH.

Methods

We employed B16-F10 cell line, a human melanoma cell line (Mel 13) and two primary cultures of human melanocytes (NHM 1 and NHM 2, respectively), all expressing a wild type MC1R and responding to the αMSH in terms of pigmentation. We evaluated cell proliferation through: a) cell counting, b) cell cycle analysis c) protein expression of proliferation modulators (p27, p21, cyclin D1 and cyclin E).

Results

The αMSH acted as a mitogenic agent in primary cultures of human melanocytes, whereas it determined a slow down of proliferation in melanoma cell lines. FSK, as an inducer of the cAMP/PKA pathway, reproduced the αMSH mediated effect on proliferation in NHMs but it did not mimic the αMSH effect on proliferation in B16-F10 and Mel 13 melanoma cell lines. Meanwhile, 3 M3-FBS (3 M3), as an inducer of PI(4,5)P2/PLC pathway, reproduced the αMSH proliferative effect. Further experiments, treating melanoma cell lines with αMSH in the presence/absence of GW9662, as an inhibitor of PPARγ, confirmed the key role of this transcription factor in decreasing cell proliferation in response to the hormone exposure.

Conclusions

In both melanoma cell lines, αMSH determined the reduction of proliferation through the PI(4,5)P2/PLC pathway, employing PPARγ as an effector element. These evidence could offer perspectives for new therapeutic approaches for melanoma.

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0611-4) contains supplementary material, which is available to authorized users.

Repairing Mitochondrial Dysfunction in Disease

Mitochondria are essential organelles for many aspects of cellular homeostasis, including energy harvesting through oxidative phosphorylation. Alterations of mitochondrial function not only impact on cellular metabolism but also critically influence whole-body metabolism, health, and life span. Diseases defined by mitochondrial dysfunction have expanded from rare monogenic disorders in a strict sense to now also include many common polygenic diseases, including metabolic, cardiovascular, neurodegenerative, and neuromuscular diseases. This has led to an intensive search for new therapeutic and preventive strategies aimed at invigorating mitochondrial function by exploiting key components of mitochondrial biogenesis, redox metabolism, dynamics, mitophagy, and the mitochondrial unfolded protein response. As such, new findings linking mitochondrial function to the progression or outcome of this ever-increasing list of diseases has stimulated the discovery and development of the first true mitochondrial drugs, which are now entering the clinic and are discussed in this review.

The activation of PPARγ by 2,4,6-Octatrienoic acid protects human keratinocytes from UVR-induced damages

Increasing attention is addressed to identify products able to enhance skin photoprotection and to prevent skin carcinogenesis. Several studies have demonstrated that the α-melanocyte stimulating hormone (αMSH), acting on a functional MC1R, provides a photoprotective effect by inducing pigmentation, antioxidants and DNA repair. We discovered a link between αMSH and the nuclear receptor Peroxisome Proliferator-Activated Receptor-γ (PPARγ), suggesting that some of the αMSH protective effects may be dependent on PPARγ transcriptional activity. Moreover, we demonstrated that the activation of PPARγ by the parrodiene 2,4,6-octatrienoic acid (Octa) induces melanogenesis and antioxidant defence in human melanocytes and counteracts senescence-like phenotype in human fibroblasts. In this study, we demonstrate that the activation of PPARγ by Octa exerts a protective effect against UVA- and UVB-induced damage on normal human keratinocytes (NHKs), the major target cells of UV radiation. Octa promotes the antioxidant defence, augments DNA repair and reduces the induction of proteins involved in UV-induced DNA damage response. Our results contribute to deepen the analysis of the αMSH/PPARγ connection and suggest perspectives for the development of new molecules and formulations able to prevent cutaneous UV damage by acting on the different skin cell populations through PPARγ activation.

A Novel Class of Natural FXR Modulators with a Unique Mode of Selective Co-regulator Assembly

The farnesoid X receptor (FXR) is an important target for drug discovery. Small molecules induce a conformational change in FXR that modulates its binding to co-regulators, thus resulting in distinct FXR functional profiles. However, the mechanisms for selectively recruiting co-regulators by FXR remain elusive, partly because of the lack of FXR-selective modulators. We report the identification of two natural terpenoids, tschimgine and feroline, as novel FXR modulators. Remarkably, their crystal structures uncovered a secondary binding pocket important for ligand binding. Further, tschimgine or feroline induced dynamic conformational changes in the activation function 2 (AF-2) surface, thus leading to differential co-regulator recruiting profiles, modulated by both hydrophobic and selective hydrogen-bond interactions unique to specific co-regulators. Our findings thus provide a novel structure template for optimization for FXR-selective modulators of clinical value.

Visualization and Quantification of Browning Using a Ucp1-2A-Luciferase Knock-in Mouse Model

Both mammals and adult humans possess classic brown adipocytes and beige adipocytes, and the amount and activity of these adipocytes are considered key factors in combating obesity and its associated metabolic diseases. Uncoupling protein 1 (Ucp1) is the functional marker of both brown and beige adipocytes. To facilitate a reliable, easy, and sensitive measurement of Ucp1 expression both in vivo and in vitro, we generated a Ucp1-2A-luciferase knock-in mouse by deleting the stop codon for the mouse Ucp1 gene and replacing it with a 2A peptide. This peptide was followed by the luciferase coding sequence to recapitulate the expression of the Ucp1 gene at the transcriptional and translational levels. With this mouse, we discovered a cold-sensitive brown/beige adipose depot underneath the skin of the ears, which we named uBAT. Because of the sensitivity and high dynamic range of luciferase activity, the Ucp1-2A-luciferase mouse is useful for both in vitro quantitative determination and in vivo visualization of nonshivering thermogenesis. With the use of this model, we identified and characterized axitinib, an oral small-molecule tyrosine kinase inhibitor, as an effective browning agent.

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

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

Review: Vascular protective effects of peroxisome proliferator-activated receptor agonists

ardiovascular disease is significantly increased in patients with the metabolic syndrome and type 2 diabetes. A clustering of risk factors, including dyslipidaemia, insulin resistance, hypertension, inflammation and coagulation disorders are acting in concert to promote cardiovascular events in these patients. Peroxisome proliferator-activated receptors (PPARs) are transcription factors that influence vascular function by altering gene expression in vascular tissue and indirectly via effects on other tissues. Indeed, PPAR activation displays beneficial effects on glucose homeostasis and lipid metabolism, and also on endothelial function and vessel wall inflammation. Clinically used PPARα agonists, such as fibrates, and PPARγ agonists, such as insulin-sensitising thiazolidinediones, may consequently alter the process of atherosclerosis, especially in subjects with the metabolic syndrome and type 2 diabetes. The present review highlights emerging evidence for beneficial effects of PPAR α and PPARγ in the prevention and treatment of atherosclerosis in such high-risk patients.

Licarin B from Myristica fragrans improves insulin sensitivity via PPARγ and activation of GLUT4 in the IRS-1/PI3K/AKT pathway in 3T3-L1 adipocytes

Licarin B, a major bioactive compound isolated fromMyristica fragransmace improves glucose uptakeviaPPARγ and GLUT4 translocation in IRS-1/PI3K/AKT pathway in adipocytes

Synergistic activation of human pregnane X receptor by binary cocktails of pharmaceutical and environmental compounds

Humans are chronically exposed to multiple exogenous substances, including environmental pollutants, drugs and dietary components. Many of these compounds are suspected to impact human health, and their combination in complex mixtures could exacerbate their harmful effects. Here we demonstrate that a pharmaceutical oestrogen and a persistent organochlorine pesticide, both exhibiting low efficacy when studied separately, cooperatively bind to the pregnane X receptor, leading to synergistic activation. Biophysical analysis shows that each ligand enhances the binding affinity of the other, so the binary mixture induces a substantial biological response at doses at which each chemical individually is inactive. High-resolution crystal structures reveal the structural basis for the observed cooperativity. Our results suggest that the formation of ‘supramolecular ligands' within the ligand-binding pocket of nuclear receptors contributes to the synergistic toxic effect of chemical mixtures, which may have broad implications for the fields of endocrine disruption, toxicology and chemical risk assessment.

Endocrine-disrupting chemicals act on nuclear hormone receptors, such as PXR. Here, Delfosse et al. show how two such chemicals interact with each other in the PXR ligand-binding pocket, forming a so-called supramolecular ligand that is a more potent PXR activator than each of the two chemicals alone.

Pharmacological repression of PPARγ promotes osteogenesis

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is the master regulator of adipogenesis and the pharmacological target of the thiazolidinedione (TZD) class of insulin sensitizers. Activation of PPARγ by TZDs promotes adipogenesis at the expense of osteoblast formation, contributing to their associated adverse effects on bone. Recently we reported the development of PPARγ antagonist SR1664, designed to block the obesity induced phosphorylation of serine 273 (S273) in the absence of classical agonism, to derive insulin sensitizing efficacy with improved therapeutic index. Here we identify the structural mechanism by which SR1664 actively antagonizes PPARγ, and extend these findings to develop the inverse agonist SR2595. Treatment of isolated bone marrow derived mesenchymal stem cells (MSCs) with SR2595 promotes induction of osteogenic differentiation. Together these results identify the structural determinants of ligand mediated PPARγ repression, and suggest a therapeutic approach to promote bone formation.

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

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

Antiallergic Function of KR62980, a Peroxisome Proliferator-Activated Receptor-γ Agonist, in a Mouse Allergic Rhinitis Model

PURPOSE

Peroxisome proliferator-activated receptor γ (PPAR-γ) has been shown to play an important role in the control of inflammatory responses acting on macrophages, mast cells, T cells and eosinophils. A novel PPAR-γ ligand, KR62980 have been recently focused on due to the lower undesirable effects than other PPAR-γ ligands such as rosiglitazone and pioglitazone. The present study was aimed to investigate the effects of KR62980 on nasal symptoms and immunopathological profiles in allergic nasal mucosa in murine allergic rhinitis model.

METHODS

BALB/c mice were sensitized and challenged intranasally with ovalbumin (OVA). KR62980 was administered intraperitoneally or orally 3 hours before each intranasal OVA challenge.

RESULTS

Administration of KR62980 significantly decreased the number of nasal rubbing, nasal sneezing, ova-specific IgE and total IgE in serum, secretion of Interleukin (IL)-4, IL-5, and IL-17 from the spleen and eosinophilic infiltration in the nasal mucosa. KR62980 decreased the expression of IL-4, IL-5 and IL-10 mRNAs in the nasal mucosal tissue, while, it elevated the level of IL-10 and IFN-γ in splenocyte culture. KR62980 seemed to decrease IL-17 level in local and systemic level even though it did not reach to statistical significance. The anti-inflammatory effect was more definite when the KR62980 was administered intraorally than intraperitoneally.

CONCLUSIONS

A novel PPAR-γ ligand, KR62980 can attenuate OVA-induced allergic inflammation in mice mainly through modulation of Th2 cytokines. This finding suggests that PPAR-γ might have a role in the treatment of allergic rhinitis.

Botanical compounds and their regulation of nuclear receptor action: the case of traditional Chinese medicine

Nuclear receptors (NRs) are major pharmacological targets that allow an access to the mechanisms controlling gene regulation. As such, some NRs were identified as biological targets of active compounds contained in herbal remedies found in traditional medicines. We aim here to review this expanding literature by focusing on the informative articles regarding the mechanisms of action of traditional Chinese medicines (TCMs). We exemplified well-characterized TCM action mediated by NR such as steroid receptors (ER, GR, AR), metabolic receptors (PPAR, LXR, FXR, PXR, CAR) and RXR. We also provided, when possible, examples from other traditional medicines. From these, we draw a parallel between TCMs and phytoestrogens or endocrine disrupting chemicals also acting via NR. We define common principle of action and highlight the potential and limits of those compounds. TCMs, by finely tuning physiological reactions in positive and negative manners, could act, in a subtle but efficient way, on NR sensors and their transcriptional network.

On the metabolically active form of metaglidasen: improved synthesis and investigation of its peculiar activity on peroxisome proliferator-activated receptors and skeletal muscles

Metaglidasen is a fibrate-like drug reported as a selective modulator of peroxisome proliferator-activated receptor γ (PPARγ), able to lower plasma glucose levels in the absence of the side effects typically observed with thiazolidinedione antidiabetic agents in current use. Herein we report an improved synthesis of metaglidasen's metabolically active form halofenic acid (R)-2 and that of its enantiomer (S)-2. The activity of the two stereoisomers was carefully examined on PPARα and PPARγ subtypes. As expected, both showed partial agonist activity toward PPARγ; the investigation of PPARα activity, however, led to unexpected results. In particular, (S)-2 was found to act as a partial agonist, whereas (R)-2 behaved as an antagonist. X-ray crystallographic studies with PPARγ were carried out to gain more insight on the molecular-level interactions and to propose a binding mode. Given the adverse effects provoked by fibrate drugs on skeletal muscle function, we also investigated the capacity of (R)-2 and (S)-2 to block conductance of the skeletal muscle membrane chloride channel. The results showed a more beneficial profile for (R)-2, the activity of which on skeletal muscle function, however, should not be overlooked in the ongoing clinical trials studying its long-term effects.

The Concise Guide to PHARMACOLOGY 2013/14: nuclear hormone receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full.

Nuclear hormone receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets.

It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Screening for bioactive metabolites in plant extracts modulating glucose uptake and fat accumulation

Dichloromethane and methanol extracts of seven different food and medicinal plants were tested in a screening platform for identification of extracts with potential bioactivity related to insulin-dependent glucose uptake and fat accumulation. The screening platform included a series of in vitro bioassays, peroxisome proliferator-activated receptor (PPAR) γ-mediated transactivation, adipocyte differentiation of 3T3-L1 cell cultures, and glucose uptake in both 3T3-L1 adipocytes and primary porcine myotubes, as well as one in vivo bioassay, fat accumulation in the nematode Caenorhabditis elegans. We found that dichloromethane extracts of aerial parts of golden root (Rhodiola rosea) and common elder (Sambucus nigra) as well as the dichloromethane extracts of thyme (Thymus vulgaris) and carrot (Daucus carota) were able to stimulate insulin-dependent glucose uptake in both adipocytes and myotubes while weekly activating PPARγ without promoting adipocyte differentiation. In addition, these extracts were able to decrease fat accumulation in C. elegans. Methanol extracts of summer savory (Satureja hortensis), common elder, and broccoli (Brassica oleracea) enhanced glucose uptake in myotubes but were not able to activate PPARγ, indicating a PPARγ-independent effect on glucose uptake.

Modulation of PPARγ provides new insights in a stress induced premature senescence model

Peroxisome proliferator-activated receptor gamma (PPARγ) may be involved in a key mechanism of the skin aging process, influencing several aspects related to the age-related degeneration of skin cells, including antioxidant unbalance. Therefore, we investigated whether the up-modulation of this nuclear receptor exerts a protective effect in a stress-induced premature senescence (SIPS) model based on a single exposure of human dermal fibroblasts to 8-methoxypsoralen plus + ultraviolet-A-irradiation (PUVA). Among possible PPARγ modulators, we selected 2,4,6-octatrienoic acid (Octa), a member of the parrodiene family, previously reported to promote melanogenesis and antioxidant defense in normal human melanocytes through a mechanism involving PPARγ activation. Exposure to PUVA induced an early and significant decrease in PPARγ expression and activity. PPARγ up-modulation counteracted the antioxidant imbalance induced by PUVA and reduced the expression of stress response genes with a synergistic increase of different components of the cell antioxidant network, such as catalase and reduced glutathione. PUVA-treated fibroblasts grown in the presence of Octa are partially but significantly rescued from the features of the cellular senescence-like phenotype, such as cytoplasmic enlargement, the expression of senescence-associated-β-galactosidase, matrix-metalloproteinase-1, and cell cycle proteins. Moreover, the alterations in the cell membrane lipids, such as the decrease in the polyunsaturated fatty acid content of phospholipids and the increase in cholesterol levels, which are typical features of cell aging, were prevented. Our data suggest that PPARγ is one of the targets of PUVA-SIPS and that its pharmacological up-modulation may represent a novel therapeutic approach for the photooxidative skin damage.

Transcriptional coregulators: fine-tuning metabolism

Metabolic homeostasis requires that cellular energy levels are adapted to environmental cues. This adaptation is largely regulated at the transcriptional level, through the interaction between transcription factors, coregulators, and the basal transcriptional machinery. Coregulators, which function as both metabolic sensors and transcriptional effectors, are ideally positioned to synchronize metabolic pathways to environmental stimuli. The balance between inhibitory actions of corepressors and stimulatory effects of coactivators enables the fine-tuning of metabolic processes. This tight regulation opens therapeutic opportunities to manage metabolic dysfunction by directing the activity of cofactors toward specific transcription factors, pathways, or cells/tissues, thereby restoring whole-body metabolic homeostasis.

Characterization of telmisartan-derived PPARγ agonists: importance of moiety shift from position 6 to 5 on potency, efficacy and cofactor recruitment

Selective modulation of the peroxisome proliferator-activated receptor gamma (PPARγ) by direct binding of small molecules demonstrates a promising tool for treatment of insulin resistance and type 2 diabetes mellitus. Besides its blood pressure-lowering properties, the AT1-receptor blocker telmisartan has been shown to be a partial agonist of PPARγ with beneficial metabolic effects in vitro and in mice. In our previous work, comprehensive structure-activity relationship (SAR) studies discussed the different parts of the telmisartan structure and various moieties. Based on these findings, we designed and synthesized new PPARγ ligands with a benzimidazole (agonists 4-5 and 4-6), benzothiophene (agonists 5-5 and 5-6) or benzofuran (agonists 6-5 and 6-6) moiety either at position 5 or 6 of the benzimidazole core structure. Lipophilicity and EC50 values were improved for all new compounds compared with telmisartan. Regarding PPARγ activation, the compounds were characterized by a differentiation assay using 3T3-L1 cells and a luciferase assay with COS-7 cells transiently transfected with pGal4-hPPARgDEF, pGal5-TK-pGL3 and pRL-CMV. A decrease in both potency and efficacy was observed after the shift of either the benzothiophene or the benzofuran moiety from position 6 to position 5. Selective recruitment of the coactivators TRAP220, SRC-1 and PGC-1α, and release of corepressor NCoR1 determined by time-resolved fluorescence resonance energy transfer (TR-FRET) was detected depending on residues in position 5 or 6.

The therapeutic potential of nuclear receptor modulators for treatment of metabolic disorders: PPARγ, RORs, and Rev-erbs

Nuclear receptors (NRs) play central roles in metabolic syndrome, making them attractive drug targets despite the challenge of achieving functional selectivity. For instance, members of the thiazolidinedione class of insulin sensitizers offer robust efficacy but have been limited due to adverse effects linked to activation of genes not involved in insulin sensitization. Studies reviewed here provide strategies for targeting subsets of PPARγ target genes, enabling development of next-generation modulators with improved therapeutic index. Additionally, emerging evidence suggests that targeting the NRs ROR and Rev-erb holds promise for treating metabolic syndrome based on their involvement in circadian rhythm and metabolism.

Bixin and norbixin have opposite effects on glycemia, lipidemia, and oxidative stress in streptozotocin-induced diabetic rats

The present study investigated the effects of oral administration of annatto carotenoids (bixin (BIX) and norbixin (NBIX)) on glucose levels, lipid profiles, and oxidative stress parameters in streptozotocin (STZ)-induced diabetic rats. Animals were treated for 30 days in the following groups: nondiabetic control, diabetic vehicle, diabetic 10 mg/kg BIX, diabetic 100 mg/kg BIX, diabetic 10 mg/kg NBIX, diabetic 100 mg/kg NBIX, diabetic metformin, and diabetic insulin. Blood glucose, LDL cholesterol, and triglyceride levels were reduced in the diabetic rats treated with BIX. BIX treatment prevented protein oxidation and nitric oxide production and restored superoxide dismutase activity. NBIX treatment did not change most parameters assessed, and at the highest dose, it increased LDL cholesterol and triglycerides levels and showed prooxidant action (increased protein oxidation and nitric oxide levels). These findings suggested that BIX could have an antihyperglycemic effect, improve lipid profiles, and protect against damage induced by oxidative stress in the diabetic state. Because NBIX is a water-soluble analog of BIX, we propose that lipophilicity is crucial for the protective effect of annatto carotenoids against streptozotocin-induced diabetes.

Regulation of selective PPARγ modulators in the differentiation of osteoclasts

Diabetes is the most common chronic disease in the world and causes complications with many diseases, such as heart disease and osteoporosis. Osteoporosis is a systemic bone disease characterized by imbalance in bone resorption and bone formation. Osteoclast is type of bone cell that functions in bone resorption and plays a critical role in bone remodeling. Rosiglitazone and pioglitazone, which belong to Thiazolidinediones(TZDs), are commonly used antidiabetic drugs. As PPARγ full agonists, they can activate PPARγ in a ligand-dependent way. Recent studies indicate that these PPARγ full agonists have some side effects, such as weight gain and bone loss, which may increase the risk of osteoporosis. In contrast, selective PPARγ Modulators (SPPARγMs) are novel PPARγ ligands that can activate PPARγ in different ways and lead to distinct downstream genes. Mice bone marrow cells were stimulated with recombinant mouse RANKL and M-CSF to generate osteoclasts. To determine the effect on osteoclasts formation, PPARγ ligands (Rosiglitazone, Fmoc-L-Leu, and Telmisartan) were added at the beginning of the culture. Rosiglitazone significantly increased the differentiation of multinucleated osteoclasts, while osteoclasts formation triggered by SPPARγMs was much less than that displayed by rosiglitazone. We found that the enhancement of PPARγ ligands may be associated with TRAF6 and downstream ERK signal pathway. We also demonstrated osteoclasts show characteristic M2 phenotype and can be further promoted by PPARγ ligands, especially rosiglitazone. In conclusion, reduced osteoclasts differentiation characteristic of SPPARγMs highlights SPPARγMs potential as therapeutic targets in diabetes, versus traditional antidiabetic drugs.