PPARα Ligand-Binding Domain Structures with Endogenous Fatty Acids and Fibrates

N-Tosyl Hydrazone Benzopyran, a New Ligand of PPARα Obtained from Mapping the Conformational Space of Its Active Site

We report here a new ligand for the peroxisome-proliferator-activated receptor type α (PPARα), an N-tosyl hydrazone benzopyran that was designed throughout the mapping of the polar zone of the binding site of PPARα; such a compound displays a strong activity on this receptor that is comparable to that of the reference compound WY-14643. For the design of the N-tosyl hydrazone benzopyran, we have carried out an exhaustive conformational study of WY-14643 and a previously reported hydrazine benzopyran derivative using conformational potential energy surfaces (PES). This study allowed us to map in a systematic way the entire binding site of the PPARα. PESs allowed us to evaluate all of the critical points on the surface (minimum, transition states, and maxima) and determine the different conformational interconversion paths. Once the geometries of the different complexes were determined, we carried out the study of the different molecular interactions that stabilize these complexes through the use of QTAIM calculations. We report here for the first time the molecular behavior of WY-14643 and two compounds synthesized in our lab interacting in the active site of the PPARα providing all of the details about the different interactions that stabilize the formation of these complexes. On the basis of such information, we were able to design and synthesize a new N-tosyl hydrazone benzopyran possessing a strong agonist effect on PPARα. The information provided by this study is very useful to get a better understanding of the behavior with this type of ligand on the PPARα, giving also interesting information as a guide for the design of new ligands for this receptor.

Mammalian hydroxylation of microbiome-derived obesogen, delta-valerobetaine, to homocarnitine, a 5-carbon carnitine analogue

The recently discovered microbiome-generated obesogen, δ-valerobetaine (5-(trimethylammonio)pentanoate), is a 5-carbon structural analogue of the carnitine precursor, γ-butyrobetaine. Here, we report that δ-valerobetaine is enzymatically hydroxylated by mammalian γ-butyrobetaine dioxygenase (BBOX) to form 3-hydroxy-5-(trimethylammonio)pentanoate, a 5-carbon analogue of carnitine, which we term homocarnitine. Homocarnitine production by human liver extracts depends upon the required BBOX cofactors, 2-oxoglutarate, Fe2+, and ascorbate. Molecular dynamics simulations show successful docking of δ-valerobetaine and homocarnitine to BBOX, pharmacological inhibition of BBOX prevents homocarnitine production, and transfection of a liver cell line with BBOX substantially increases production. Furthermore, an in vivo isotope tracer study shows the conversion of 13C3-trimethyllysine to 13C3-δ-valerobetaine then 13C3-homocarnitine in mice, confirming the in vivo production of homocarnitine. Functional assays show that carnitine palmitoyltransferase acylates homocarnitine to acyl-homocarnitine, analogous to the reactions for the carnitine shuttle. Studies of mouse tissues and human plasma show widespread distribution of homocarnitine and fatty acyl-homocarnitines. The respective structural similarities of homocarnitine and acyl-homocarnitines to carnitine and acyl-carnitines indicate that homocarnitine could impact multiple sites of carnitine distribution and activity, potentially mediating microbiome-associated obesity and metabolic disorders.

Computational dissection through network pharmacology and structure-based analysis unravels mechanistic actions of bioactive compounds in a hepatoprotective herb, Picrorhiza kurroa for the treatment of NAFLD and NASH

Non-Alcoholic fatty liver disease has become a silent pandemic worldwide with no authorized medicine available. Picrorhiza kurroa is a traditional hepatoprotective herb wherein extracts provide therapeutic efficacy but not the individual compounds. Hence, the aim of the study is exploration of active molecules in P. kurroa extracts and identification of mechanistic actions to pinpoint potential leads towards drug development. We employed network pharmacology to identify the significance of combinatorial effect of compounds on multiple targets. The NAFLD/NASH associated genes encoding protein targets overlapped with the predicted protein targets of P. kurroa compounds. Then, overlapping targets were considered further to capture the interactive targets from Protein-Protein-Interaction network of NAFLD and NASH. The networks were generated to capture the role of proteins in different signaling pathways, diseases, and effective compounds as therapeutics. Furthermore, structural, and biophysical analysis was performed for significant complexes. We observed that the compounds like astragalin, Picroside-I, Vernicoside, Rutin, Quercetin, Kaempferol, Gallic acid, Ellagic acid in P. kurroa acted synergistically by enhancing the bioavailability of active compounds and affecting various morbidities of NAFLD through involvement in different signaling and disease pathways such as oxidative phosphorylation, FoxO signaling, inflammation, several cancerous and diabetic pathways. The network pharmacology revealed the interactive behavior of proteins involved in NAFLD treated by P. kurroa compounds. Furthermore, molecular docking and molecular dynamic simulation study showed potential candidates in therapeutics. Overall, the study suggested multi-target drug discovery for treating complex diseases by providing leads in herbal extracts as potential therapeutic botanicals.

How PPAR-alpha mediated inflammation may affect the pathophysiology of chronic kidney disease

Chronic kidney disease (CKD) is a major risk factor for death in adults. Inflammation plays a role in the pathogenesis of CKD, but the mechanisms are poorly understood. Peroxisome proliferator-activated receptor alpha (PPAR-α) is a nuclear receptor and one of the three members (PPARα, PPARβ/δ, and PPARγ) of the PPARs that plays an important role in ameliorating pathological processes that accelerate acute and chronic kidney disease. Although other PPARs members are well studied, the role of PPAR-α is not well described and its role in inflammation-mediated chronic disease is not clear. Herein, we review the role of PPAR-α in chronic kidney disease with implications for the immune system.

A new ciprofibrate calcium salt with improved solubility and intrinsic dissolution rate

Ciprofibrate (CIP) is an active pharmaceutical ingredient (API) classified as class II on the basis of biopharmaceutical classification system (BCS), what indicates that it has low solubility in aqueous solvents. The use of API salts has attracted attention due to their improvements in solubility, tolerability, higher rate and extent of absorption, and faster onset of the therapeutic effect. In this work, a new crystalline CIP monohydrated calcium salt (Ca(CIP)2.H2O) was successfully obtained and its crystal structure determined by single crystal X-ray diffraction analysis (SCXRD). Additionally, Ca(CIP)2.H2O was widely characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and submitted to solubility, intrinsic dissolution and accelerated stability studies. Ca(CIP)2.H2O exhibited higher solubility and dissolution rate than CIP-free form and was stable up to 6 months at 40 °C (75 %RH). Therefore, Ca(CIP)2.H2O may be a viable alternative for use in solid dosage forms.

A chemical modification of a peroxisome proliferator-activated receptor pan agonist produced a shift to a new dual alpha/gamma partial agonist endowed with mitochondrial pyruvate carrier inhibition and antidiabetic properties

New analogs of the PPAR pan agonist AL29-26 encompassed ligand (S)-7 showing potent activation of PPARα and -γ subtypes as a partial agonist. In vitro experiments and docking studies in the presence of PPAR antagonists were performed to help interpretation of biological data and investigate the main interactions at the binding sites. Further in vitro experiments showed that (S)-7 induced anti-steatotic effects and enhancement of the glucose uptake. This latter effect could be partially ascribed to a significant inhibition of the mitochondrial pyruvate carrier demonstrating that (S)-7 also acted through insulin-independent mechanisms. In vivo experiments showed that this compound reduced blood glucose and lipid levels in a diabetic mice model displaying no toxicity on bone, kidney, and liver. To our knowledge, this is the first example of dual PPARα/γ partial agonist showing these combined effects representing, therefore, the potential lead of new drugs for treatment of dyslipidemic type 2 diabetes.

Limitations in mitochondrial programming restrain the differentiation and maturation of human stem cell-derived β cells

Pluripotent stem cell (SC)-derived islets offer hope as a renewable source for β cell replacement for type 1 diabetes (T1D), yet functional and metabolic immaturity may limit their long-term therapeutic potential. Here, we show that limitations in mitochondrial transcriptional programming impede the formation and maturation of SC-derived β (SC-β) cells. Utilizing transcriptomic profiling, assessments of chromatin accessibility, mitochondrial phenotyping, and lipidomics analyses, we observed that SC-β cells exhibit reduced oxidative and mitochondrial fatty acid metabolism compared to primary human islets that are related to limitations in key mitochondrial transcriptional networks. Surprisingly, we found that reductions in glucose- stimulated mitochondrial respiration in SC-islets were not associated with alterations in mitochondrial mass, structure, or genome integrity. In contrast, SC-islets show limited expression of targets of PPARIZ and PPARγ, which regulate mitochondrial programming, yet whose functions in β cell differentiation are unknown. Importantly, treatment with WY14643, a potent PPARIZ agonist, induced expression of mitochondrial targets, improved insulin secretion, and increased the formation and maturation of SC-β cells both in vitro and following transplantation. Thus, mitochondrial programming promotes the differentiation and maturation of SC-β cells and may be a promising target to improve β cell replacement efforts for T1D.

Identification of Potential Drug Targets of Calix[4]arene by Reverse Docking

Calixarenes are displaying great potential for the development of new drug delivery systems, diagnostic imaging, biosensing devices and inhibitors of biological processes. In particular, calixarene derivatives are able to interact with many different enzymes and function as inhibitors. By screening of the potential drug target database (PDTD) with a reverse docking procedure, we identify and discuss a selection of 100 proteins that interact strongly with calix[4]arene. We also discover that leucine (23.5 %), isoleucine (11.3 %), phenylalanines (11.3 %) and valine (9.5 %) are the most frequent binding residues followed by hydrophobic cysteines and methionines and aromatic histidines, tyrosines and tryptophanes. Top binders are peroxisome proliferator-activated receptors that already are targeted by commercial drugs, demonstrating the practical interest in calix[4]arene. Nuclear receptors, potassium channel, several carrier proteins, a variety of cancer-related proteins and viral proteins are prominent in the list. It is concluded that calix[4]arene, which is characterized by facile access, well-defined conformational characteristics, and ease of functionalization at both the lower and higher rims, could be a potential lead compound for the development of enzyme inhibitors and theranostic platforms.

Modulation of host lipid metabolism by virus infection leads to exoskeleton damage in shrimp

The arthropod exoskeleton provides protection and support and is vital for survival and adaption. The integrity and mechanical properties of the exoskeleton are often impaired after pathogenic infection; however, the detailed mechanism by which infection affects the exoskeleton remains largely unknown. Here, we report that the damage to the shrimp exoskeleton is caused by modulation of host lipid profiles after infection with white spot syndrome virus (WSSV). WSSV infection disrupts the mechanical performance of the exoskeleton by inducing the expression of a chitinase (Chi2) in the sub-cuticle epidermis and decreasing the cuticle chitin content. The induction of Chi2 expression is mediated by a nuclear receptor that can be activated by certain enriched long-chain saturated fatty acids after infection. The damage to the exoskeleton, an aftereffect of the induction of host lipogenesis by WSSV, significantly impairs the motor ability of shrimp. Blocking the WSSV-caused lipogenesis restored the mechanical performance of the cuticle and improved the motor ability of infected shrimp. Therefore, this study reveals a mechanism by which WSSV infection modulates shrimp internal metabolism resulting in phenotypic impairment, and provides new insights into the interactions between the arthropod host and virus.

Hypoglycemic Activity of Rice Resistant-Starch Metabolites: A Mechanistic Network Pharmacology and In Vitro Approach

Rice (Oryza sativa L.) is one of the primary sources of energy and nutrients needed by the body, and rice resistant starch (RRS) has been found to have hypoglycemic effects. However, its biological activity and specific mechanisms still need to be further elucidated. In the present study, 52 RRS differential metabolites were obtained from mouse liver, rat serum, canine feces, and human urine, and 246 potential targets were identified through a literature review and database analysis. A total of 151 common targets were identified by intersecting them with the targets of type 2 diabetes mellitus (T2DM). After network pharmacology analysis, 11 core metabolites were identified, including linolenic acid, chenodeoxycholic acid, ursodeoxycholic acid, deoxycholic acid, lithocholic acid, lithocholylglycine, glycoursodeoxycholic acid, phenylalanine, norepinephrine, cholic acid, and L-glutamic acid, and 16 core targets were identified, including MAPK3, MAPK1, EGFR, ESR1, PRKCA, FYN, LCK, DLG4, ITGB1, IL6, PTPN11, RARA, NR3C1, PTPN6, PPARA, and ITGAV. The core pathways included the neuroactive ligand-receptor interaction, cancer, and arachidonic acid metabolism pathways. The molecular docking results showed that bile acids such as glycoursodeoxycholic acid, chenodeoxycholic acid, ursodeoxycholic acid, lithocholic acid, deoxycholic acid, and cholic acid exhibited strong docking effects with EGFR, ITGAV, ITGB1, MAPK3, NR3C1, α-glucosidase, and α-amylase. In vitro hypoglycemic experiments further suggested that bile acids showed significant inhibitory effects on α-glucosidase and α-amylase, with CDCA and UDCA having the most prominent inhibitory effect. In summary, this study reveals a possible hypoglycemic pathway of RRS metabolites and provides new research perspectives to further explore the therapeutic mechanism of bile acids in T2DM.

Different Coactivator Recruitment to Human PPARα/δ/γ Ligand-Binding Domains by Eight PPAR Agonists to Treat Nonalcoholic Fatty Liver Disease

Three peroxisome proliferator-activated receptor subtypes, PPARα, PPAR(ß/)δ, and PPARγ, exert ligand-dependent transcriptional control in concert with retinoid X receptors (RXRs) on various gene sets harboring PPAR response elements (PPREs) in their promoter regions. Ligand-bound PPAR/RXR complexes do not directly regulate transcription; instead, they recruit multiprotein coactivator complexes to specific genomic regulatory loci to cooperatively activate gene transcription. Several coactivators are expressed in a single cell; however, a ligand-bound PPAR can be associated with only one coactivator through a consensus LXXLL motif. Therefore, altered gene transcription induced by PPAR subtypes/agonists may be attributed to the recruitment of various coactivator species. Using a time-resolved fluorescence resonance energy transfer assay, we analyzed the recruitment of four coactivator peptides (PGC1α, CBP, SRC1, and TRAP220) to human PPARα/δ/γ-ligand-binding domains (LBDs) using eight PPAR dual/pan agonists (bezafibrate, fenofibric acid, pemafibrate, pioglitazone, elafibranor, lanifibranor, saroglitazar, and seladelpar) that are/were anticipated to treat nonalcoholic fatty liver disease. These agonists all recruited four coactivators to PPARα/γ-LBD with varying potencies and efficacy. Only five agonists (bezafibrate, pemafibrate, elafibranor, lanifibranor, and seladelpar) recruited all four coactivators to PPARδ-LBD, and their concentration-dependent responses differed from those of PPARα/γ-LBD. These results indicate that altered gene expression through consensus PPREs by different PPAR subtypes/agonists may be caused, in part, by different coactivators, which may be responsible for the unique pharmacological properties of these PPAR agonists.

A pan-PPAR agonist E17241 ameliorates hyperglycemia and diabetic dyslipidemia in KKAy mice via up-regulating ABCA1 in islet, liver, and white adipose tissue

OBJECTIVE

Type 2 diabetes mellitus (T2DM) is a common chronic metabolic disease. Peroxisome proliferator-activated receptors (PPARs) play crucial roles in regulating glucolipid metabolism. Previous studies showed that E17241 could ameliorate atherosclerosis and lower fasting blood glucose levels in ApoE-/- mice. In this work, we investigated the role of E17241 in glycolipid metabolism in diabetic KKAy mice.

APPROACH AND RESULTS

We confirmed that E17241 is a powerful pan-PPAR agonist with a potent agonistic activity on PPARγ, a high activity on PPARα, and a moderate activity on PPARδ. E17241 also significantly increased the protein expression of ATP-binding cassette transporter 1 (ABCA1), a crucial downstream target gene for PPARs. E17241 clearly lowered plasma glucose levels, improved OGTT and ITT, decreased islet cholesterol content, improved β-cell function, and promoted insulin secretion in KKAy mice. Moreover, E17241 could significantly lower plasma total cholesterol and triglyceride levels, reduce liver lipid deposition, and improve the adipocyte hypertrophy and the inflammatory response in epididymal white adipose tissue. Further mechanistic studies indicated that E17241 boosts cholesterol efflux and insulin secretion in an ABCA1 dependent manner. RNA-seq and qRT-PCR analysis demonstrated that E17241 induced different expression of PPAR target genes in liver and adipose tissue differently from the PPARγ agonist rosiglitazone. In addition, E17241 treatment was also demonstrated to have an exhilarating cardiorenal benefits.

CONCLUSIONS

Our results demonstrate that E17241 regulates glucolipid metabolism in KKAy diabetic mice while having cardiorenal benefits without inducing weight gain. It is a promising drug candidate for the treatment of T2DM.

Valerenic acid attenuates pathological myocardial hypertrophy by promoting the utilization of multiple substrates in the mitochondrial energy metabolism

INTRODUCTION

Valerenic acid (VA) is a unique and biologically active component in Valeriana officinalis L., which has been reported to have a regulatory effect on the cardiovascular system. However, its therapeutic effects on pathological myocardial hypertrophy (PMH) and the underlying mechanisms are undefined.

OBJECTIVES

Our study aims to elucidate how VA improves PMH, and preliminarily discuss its mechanism.

METHODS

The efficacy of VA on PMH was confirmed by in vivo and in vitro experiments and the underlying mechanism was investigated by molecular dynamics (MD) simulations and specific siRNA interference.

RESULTS

VA enhanced cardiomyocyte fatty acid oxidation (FAO), inhibited hyper-activated glycolysis, and improved the unbalanced pyruvate-lactate axis. VA could significantly improve impaired mitochondrial function and reduce the triglyceride (TG) in the hypertrophic myocardium while reducing the lactate (LD) content. Molecular mechanistic studies showed that VA up-regulated the expression of peroxisome proliferator-activated receptor-α (PPARα) and downstream FAO-related genes including CD36, CPT1A, EHHADH, and MCAD. VA reduced the expression of ENO1 and PDK4, the key enzymes in glycolysis. Meanwhile, VA improved the pyruvate-lactate axis and promoted the aerobic oxidation of pyruvate by inhibiting LDAH and MCT4. MD simulations confirmed that VA can bind with the F273 site of PPARα, which proposes VA as a potential activator of the PPARα.

CONCLUSION

Our results demonstrated that VA might be a potent activator for the PPARα-mediated pathway. VA directly targets the PPARα and subsequently promotes energy metabolism to attenuate PMH, which can be applied as a potentially effective drug for the treatment of HF.

Lanhuashen stimulates the positive cross-regulation mediated by the S1P axis to ameliorate the disorder of glucolipid metabolism induced by the high sucrose diet in Drosophila melanogaster

ETHNOPHARMACOLOGICAL RELEVANCE

Herba Wanlenbergiae, named 'Lanhuashen' (LHS) in Chinese, is derived from the dried herba of Wahlenbergia marginata (Thunb.) A.DC. It is an abundant resource that has been used in traditional Chinese medicine (TCM) for over 600 years. LHS has the effects of enriching consumptive disease and relieving deficient heat, consistent with the therapy for type 2 diabetes mellitus (T2DM) in TCM. As the basic remedy of Yulan Jiangtang capsules, a listed Chinese medicine specifically for treating T2DM, LHS is a potential candidate for an anti-T2DM drug. However, due to the lack of pharmacodynamic studies and chemical component analysis, the application and development of LHS as a treatment for T2DM have been hindered.

AIM OF THE STUDY

To evaluate the regulation of the disorder of glucolipid metabolism using LHS extracts and its therapeutic potential in T2DM.

MATERIALS AND METHODS

Chemical components in LHS extracts were analysed using UPLC-Q Exactive-Orbitrap-MS. Subsequently, high sucrose diet (HSD)-induced Drosophila melanogaster were used as suitable models for T2DM in vivo. Behavioural and biochemical tests were performed to evaluate the regulation of the disorder of glucolipid metabolism using LHS in T2DM flies. Furthermore, integrative metabolomic and transcriptomic analysis was applied to reveal the specific effects of LHS extracts on metabolites and genes. Meanwhile, bioinformatic analysis was carried out to predict the targeted transcription factors (TFs) and potentially effective components of LHS extracts.

RESULTS

We redefined the chemical profile of LHS with 76 identified chemical components, including 65 chemical components for the first time. As indicated by decreased trehalose, glucose and triglyceride levels and increased total protein levels, LHS extracts were perceived to alleviate the disorder of glucolipid metabolism in HSD-induced T2DM fruit flies. Integrative metabolomic and transcriptomic analysis revealed that LHS extracts eliminated the accumulation of sphingolipids and subsequently stimulated the positive cross-regulation mediated by the sphingosine 1-phosphate (S1P) axis, resulting in the activation of the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) signalling pathway and inhibition of lysosome-mediated apoptosis. Bioinformatic analysis revealed that the upstream TFs, transcriptional enhancer factor TEF-5 (TEAD3) and peroxisome proliferator-activated receptor alpha (PPARA), were the potential targets of atractylenolide III, dihydrokaempferol and syringaldehyde, the potentially effective components of LHS extracts. Therefore, this TF network was plausibly the basis for the efficacy.

CONCLUSIONS

LHS extracts broadly modulated TF-dependent gene expression and subsequently stimulated the positive cross-regulation mediated by the S1P axis to ameliorate the disorder of glucolipid metabolism. Our study provides critical evidence considering LHS as a potential drug candidate for T2DM, inspiring the discovery and development of innovative therapeutic agents based on the cross-regulation mediated by the S1P axis for treating T2DM and related complications.

Design and Synthesis of Novel Indole Ethylamine Derivatives as a Lipid Metabolism Regulator Targeting PPARα/CPT1 in AML12 Cells

Peroxisome proliferator-activated receptor alpha (PPARα) and carnitine palmitoyltransferase 1 (CPT1) are important targets of lipid metabolism regulation for nonalcoholic fatty liver disease (NAFLD) therapy. In the present study, a set of novel indole ethylamine derivatives (4, 5, 8, 9) were designed and synthesized. The target product (compound 9) can effectively activate PPARα and CPT1a. Consistently, in vitro assays demonstrated its impact on the lipid accumulation of oleic acid (OA)-induced AML12 cells. Compared with AML12 cells treated only with OA, supplementation with 5, 10, and 20 μM of compound 9 reduced the levels of intracellular triglyceride (by 28.07%, 37.55%, and 51.33%) with greater inhibitory activity relative to the commercial PPARα agonist fenofibrate. Moreover, the compound 9 supplementations upregulated the expression of hormone-sensitive triglyceride lipase (HSL) and adipose triglyceride lipase (ATGL) and upregulated the phosphorylation of acetyl-CoA carboxylase (ACC) related to fatty acid oxidation and lipogenesis. This dual-target compound with lipid metabolism regulatory efficacy may represent a promising type of drug lead for NAFLD therapy.

Herpetrione, a New Type of PPARα Ligand as a Therapeutic Strategy Against Nonalcoholic Steatohepatitis

Non-alcoholic fatty liver disease, especially nonalcoholic steatohepatitis (NASH), is a leading cause of cirrhosis and liver cancer worldwide; nevertheless, there are no Food and Drug Administration-approved drugs for treating NASH until now. Peroxisome proliferator-activated receptor alpha (PPARα) is an interesting therapeutic target for treating metabolic disorders in the clinic, including NASH. Herpetrione, a natural lignan compound isolated from Tibetan medicine Herpetospermum caudigerum, exerts various hepatoprotective effects, but its efficacy and molecular mechanism in treating NASH have not yet been elucidated. Here, we discovered that herpetrione lessened lipid accumulation and inflammation in hepatocytes stimulated with oleic acid and lipopolysaccharide, and effectively alleviated NASH caused by a high-fat diet or methionine-choline-deficient diet by regulating glucolipid metabolism, insulin resistance, and inflammation. Mechanistically, RNA-sequencing analyses further showed that herpetrione activated PPAR signaling, which was validated by protein expression. Furthermore, the analysis of molecular interactions illustrated that herpetrione bound directly to the PPARα protein, with binding sites extending to the Arm III domain. PPARα deficiency also abrogated the protective effects of herpetrione against NASH, suggesting that herpetrione protects against hepatic steatosis and inflammation by activation of PPARα signaling, thereby alleviating NASH. Our findings shed light on the efficacy of a natural product for treating NASH, as well as the broader prospects for NASH treatment by targeting PPARα.

Current Clinical Trial Status and Future Prospects of PPAR-Targeted Drugs for Treating Nonalcoholic Fatty Liver Disease

The number of patients with nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) is increasing globally and is raising serious concerns regarding the increasing medical and economic burden incurred for their treatment. The progression of NASH to more severe conditions such as cirrhosis and hepatocellular carcinoma requires liver transplantation to avoid death. Therefore, therapeutic intervention is required in the NASH stage, although no therapeutic drugs are currently available for this. Several anti-NASH candidate drugs have been developed that enable treatment via the modulation of distinct signaling cascades and include a series of drugs targeting peroxisome proliferator-activated receptor (PPAR) subtypes (PPARα/δ/γ) that are considered to be attractive because they can regulate both systemic lipid metabolism and inflammation. Multiple PPAR dual/pan agonists have been developed but only a few of them have been evaluated in clinical trials for NAFLD/NASH. Herein, we review the current clinical trial status and future prospects of PPAR-targeted drugs for treating NAFLD/NASH. In addition, we summarize our recent findings on the binding modes and the potencies/efficacies of several candidate PPAR dual/pan agonists to estimate their therapeutic potentials against NASH. Considering that the development of numerous PPAR dual/pan agonists has been abandoned because of their serious side effects, we also propose a repositioning of the already approved, safety-proven PPAR-targeted drugs against NAFLD/NASH.

Functional and Structural Insights into the Human PPARα/δ/γ Targeting Preferences of Anti-NASH Investigational Drugs, Lanifibranor, Seladelpar, and Elafibranor

No therapeutic drugs are currently available for nonalcoholic steatohepatitis (NASH) that progresses from nonalcoholic fatty liver via oxidative stress-involved pathways. Three cognate peroxisome proliferator-activated receptor (PPAR) subtypes (PPARα/δ/γ) are considered as attractive targets. Although lanifibranor (PPARα/δ/γ pan agonist) and saroglitazar (PPARα/γ dual agonist) are currently under investigation in clinical trials for NASH, the development of seladelpar (PPARδ-selective agonist), elafibranor (PPARα/δ dual agonist), and many other dual/pan agonists has been discontinued due to serious side effects or little/no efficacies. This study aimed to obtain functional and structural insights into the potency, efficacy, and selectivity against PPARα/δ/γ of three current and past anti-NASH investigational drugs: lanifibranor, seladelpar, and elafibranor. Ligand activities were evaluated by three assays to detect different facets of the PPAR activation: transactivation assay, coactivator recruitment assay, and thermal stability assay. Seven high-resolution cocrystal structures (namely, those of the PPARα/δ/γ-ligand-binding domain (LBD)-lanifibranor, PPARα/δ/γ-LBD-seladelpar, and PPARα-LBD-elafibranor) were obtained through X-ray diffraction analyses, six of which represent the first deposit in the Protein Data Bank. Lanifibranor and seladelpar were found to bind to different regions of the PPARα/δ/γ-ligand-binding pockets and activated all PPAR subtypes with different potencies and efficacies in the three assays. In contrast, elafibranor induced transactivation and coactivator recruitment (not thermal stability) of all PPAR subtypes, but the PPARδ/γ-LBD-elafibranor cocrystals were not obtained. These results illustrate the highly variable PPARα/δ/γ activation profiles and binding modes of these PPAR ligands that define their pharmacological actions.

Peroxisome proliferator-activated receptor-α activation facilitates contextual fear extinction and modulates intrinsic excitability of dentate gyrus neurons

The dentate gyrus (DG) of the hippocampus encodes contextual information associated with fear, and cell activity in the DG is required for acquisition and extinction of contextual fear. However, the underlying molecular mechanisms are not fully understood. Here we show that mice deficient for peroxisome proliferator-activated receptor-α (PPARα) exhibited a slower rate of contextual fear extinction. Furthermore, selective deletion of PPARα in the DG attenuated, while activation of PPARα in the DG by local infusion of aspirin facilitated extinction of contextual fear. The intrinsic excitability of DG granule neurons was reduced by PPARα deficiency but increased by activation of PPARα with aspirin. Using RNA-Seq transcriptome we found that the transcription level of neuropeptide S receptor 1 (Npsr1) was tightly correlated with PPARα activation. Our results provide evidence that PPARα plays an important role in regulating DG neuronal excitability and contextual fear extinction.

Oleic acid stimulates cell proliferation and BRD4-L-MYC-dependent glucose transporter transcription through PPARα activation in ovarian cancer cells

Fatty acids (FAs) play important roles in cell membrane structure maintenance, energy production via β-oxidation, and as extracellular signaling molecules. Prior studies have demonstrated that exposure of cancer cells to FAs affects cell survival, cell proliferation, and cell motility. Oleic acid (OA) has somewhat controversial effects in cancer cells, with both pro- and anti-cancer effects, depending on cell type. Our prior findings suggested that OA enhances cell survival in serum starved HNOA ovarian cancer cells by activating glycolysis, but not β-oxidation. Here, we pharmacologically examined the cellular mechanisms by which OA stimulates glycolysis in HNOA cells. OA induced cell cycle progression, leading to increase in cell number through peroxisome proliferator activated receptor (PPAR) α activation. OA-induced glycolysis was mediated by increased GLUT expression, and increases in GLUT expression were mediated by increased L-MYC expression. Furthermore, L-MYC expression was due to BRD4 activation. These findings suggested involvement of the BRD4-L-MYC-GLUT axis in OA-stimulated glycolysis. These results suggested that OA could activate PPARα to stimulate two pathways: glycolysis and cell cycle progression, and provided insight into the role of OA in ovarian cancer cell growth.

Downregulation of miRNA-155-5p contributes to the adipogenic activity of 2-ethylhexyl diphenyl phosphate in 3T3-L1 preadipocytes

2-Ethylhexyl diphenyl phosphate (EHDPP) is a commonly used organophosphorus flame retardant and food packaging material. Because of its high lipophilic and bioaccumulative properties, adipocytes are the primary target of EHDPP. However, the toxicity of EHDPP on preadipocytes and the potential mechanism have not been fully elucidated. MicroRNAs (miRNAs) are thought to be an important mediator that contribute to the toxicity of environmental contaminants. To identify the miRNAs specifically responsible for EHDPP exposure and their role in EGDPP's toxicity in preadipocytes, the adipogenic effects and miRNA expression profiling were performed on 3T3-L1 preadipocytes exposed to EHDPP. EHDPP at concentrations of 1-10 μM promoted adipocyte differentiation, as evidenced by lipid staining, triglyceride content, and expression of adipogenesis markers. MiRNA-seq analysis revealed that 7 differentially expressed miRNAs were recognized under EHDPP exposure, with miR-155-5p being the top down-regulated miRNA. Quantitative reverse transcription PCR (RT-qPCR) analysis showed that miR-155-5p level fell sharply during the first 2 days and continued to fall dose-dependently throughout the EHDPP exposure period. MiR-155-5p inhibition promotes adipocyte differentiation, whereas its overexpression counteracted EHDPP-induced adipogenesis. Luciferase reporter assay identified CCAAT/enhancer-binding protein beta (C/EBPβ) as a target of miR-155-5p in 3T3-L1 preadipocytes in response to EHDPP. Taken together, EHDPP exposure down-regulated miR-155-5p, which then increased C/EBPβ and peroxisome proliferator-activated receptor γ (PPARγ) expression and promoted adipogenesis in preadipocytes.

Low-carbohydrate diets containing plant-derived fat but not animal-derived fat ameliorate heart failure

Cardiovascular disease (CVD) is a global health burden in the world. Although low-carbohydrate diets (LCDs) have beneficial effects on CVD risk, their preventive effects remain elusive. We investigated whether LCDs ameliorate heart failure (HF) using a murine model of pressure overload. LCD with plant-derived fat (LCD-P) ameliorated HF progression, whereas LCD with animal-derived fat (LCD-A) aggravated inflammation and cardiac dysfunction. In the hearts of LCD-P-fed mice but not LCD-A, fatty acid oxidation-related genes were highly expressed, and peroxisome proliferator-activated receptor α (PPARα), which regulates lipid metabolism and inflammation, was activated. Loss- and gain-of-function experiments indicated the critical roles of PPARα in preventing HF progression. Stearic acid, which was more abundant in the serum and heart of LCD-P-fed mice, activated PPARα in cultured cardiomyocytes. We highlight the importance of fat sources substituted for reduced carbohydrates in LCDs and suggest that the LCD-P-stearic acid-PPARα pathway as a therapeutic target for HF.

Peroxisome Proliferator-Activated Receptor-Targeted Therapies: Challenges upon Infectious Diseases

Peroxisome proliferator-activated receptors (PPARs) α, β, and γ are nuclear receptors that orchestrate the transcriptional regulation of genes involved in a variety of biological responses, such as energy metabolism and homeostasis, regulation of inflammation, cellular development, and differentiation. The many roles played by the PPAR signaling pathways indicate that PPARs may be useful targets for various human diseases, including metabolic and inflammatory conditions and tumors. Accumulating evidence suggests that each PPAR plays prominent but different roles in viral, bacterial, and parasitic infectious disease development. In this review, we discuss recent PPAR research works that are focused on how PPARs control various infections and immune responses. In addition, we describe the current and potential therapeutic uses of PPAR agonists/antagonists in the context of infectious diseases. A more comprehensive understanding of the roles played by PPARs in terms of host-pathogen interactions will yield potential adjunctive personalized therapies employing PPAR-modulating agents.

Marine Natural and Nature-Inspired Compounds Targeting Peroxisome Proliferator Activated Receptors (PPARs)

Peroxisome proliferator-activated receptors α, γ and β/δ (PPARα, PPARγ, and PPARβ/δ) are a family of ligand-activated transcriptional factors belonging to the superfamily of nuclear receptors regulating the expression of genes involved in lipid and carbohydrate metabolism, energy homeostasis, inflammation, and the immune response. For this reason, they represent attractive targets for the treatment of a variety of metabolic diseases and, more recently, for neurodegenerative disorders due to their emerging neuroprotective effects. The degree of activation, from partial to full, along with the selectivity toward the different isoforms, greatly affect the therapeutic efficacy and the safety profile of PPAR agonists. Thus, there is a high interest toward novel scaffolds with proper combinations of activity and selectivity. This review intends to provide an overview of the discovery, optimization, and structure-activity relationship studies on PPAR modulators from marine sources, along with the structural and computational studies that led to their identification and/or elucidation, and rationalization of their mechanisms of action.

The Effect of Citrus aurantium on Non-Small-Cell Lung Cancer: A Research Based on Network and Experimental Pharmacology

Purpose

To screen the main active components of Citrus aurantium through a network pharmacology approach, construct a component-disease target network, explore its molecular mechanism for the treatment of non-small-cell lung cancer (NSCLC), and validate it experimentally.

Methods

The active ingredients in Citrus aurantium and the targets of Citrus aurantium and NSCLC were collected through the Traditional Chinese Medicine Systematic Pharmacology Database and Analysis Platform (TCMSP), GeneCards, and OMIM databases. The protein interaction network was constructed using the STRING database, and the component-disease relationship network graph was analyzed using Cytoscape 3.9.1. The Metascape database can be used for GO and KEGG enrichment analyses. The Kaplan-Meier plotter was applied for overall survival analysis of key targets of Citrus aurantium in the treatment of NSCLC. Real-time PCR (RT-PCR) and Western blotting were used to determine the mRNA and protein levels of key targets of Citrus aurantium for the treatment of NSCLC.

Results

Five active ingredients of Citrus aurantium were screened, and 54 potential targets for the treatment of NSCLC were found, of which the key ingredient was nobiletin and the key targets are TP53, CXCL8, ESR1, PPAR-α, and MMP9. GO and KEGG enrichment analyses indicated that the mechanism of nobiletin in treating NSCLC may be related to the regulation of cancer signaling pathway, phosphatidylinositol-3 kinase (PI3K)/protein kinase B (Akt) signaling pathway, lipid and atherosclerosis signaling pathway, and neurodegenerative signaling pathway. The experimental results showed that nobiletin could inhibit the proliferation of NSCLC cells and upregulate the levels of P53 and PPAR-α and suppress the expression of MMP9 (P < 0.05).

Conclusion

Citrus aurantium can participate in the treatment of NSCLC through multiple targets and pathways.

New IMB16-4 Hot-Melt Extrusion Preparation Improved Oral Bioavailability and Enhanced Anti-Cholestatic Effect on Rats

Background

Cholestasis is challenging to treat due to lacked effective drugs. N-(3,4,5-trichlorophenyl)-2 (3-nitrobenzenesulfonamido) benzamide, abbreviated as IMB16-4, which may be effective for the treatment of cholestasis. However, its poor solubility and bioavailability seriously obstruct the research programs.

Methods

A hot-melt extrusion (HME) preparation was first applied to increase the bioavailability of IMB16-4, the oral bioavailability, anti-cholestatic effect and vitro cytotoxicity of IMB16-4 and IMB16-4-HME were evaluated. Meanwhile, the molecular docking and qRT-PCR were used to validate the mechanism behind.

Results

The oral bioavailability of IMB16-4-HME improved 65-fold compared with that of pure IMB16-4. Pharmacodynamics results demonstrated that IMB16-4-HME prominently decreased the serum levels of total bile acid (TBA) and alkaline phosphatase (ALP), but elevated the level of total bilirubin (TBIL) and direct bilirubin (DBIL). Histopathology revealed that IMB16-4-HME at lower dose exhibited stronger anti-cholestatic effect compared with pure IMB16-4. In addition, molecular docking demonstrated that IMB16-4 has great affinity with PPARα, and qRT-PCR results revealed that IMB16-4-HME significantly elevated the mRNA expression level of PPARα, but decreased the mRNA level of CYP7A1. Cytotoxicity assays demonstrated that the hepatotoxicity of IMB16-4-HME was absolutely attributed to IMB16-4, and the excipients of IMB16-4-HME may increase the drug load within HepG2 cells.

Conclusion

The HME preparation significantly increased the oral bioavailability and anti-cholestatic effect of pure IMB16-4, but caused liver injury at high dose, which require a dose balance between the curative effect and safety in the future research.

Peptide Helix-Y12 as Potential Effector for Peroxisome Proliferator-Activated Receptors

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors involved in the regulation of lipids and glucose metabolism, and immune response. Therefore, they have been considered pharmacological targets for treating metabolic diseases, such as dyslipidemia, atherosclerosis, and non-alcoholic fatty liver disease. However, the available synthetic ligands of PPARs have mild to significant side effects, generating the necessity to identify new molecules that are selective PPAR ligands with specific biological responses. This study aimed to evaluate some components of the atheroprotective and hepatoprotective HB-ATV-8 nanoparticles [the amphipathic peptide Helix-Y¹², thermozeaxanthin, thermozeaxanthin-13, thermozeaxanthin-15, and a set of glycolipids], as possible ligands of PPARs through blind molecular docking. According to the change in free energy upon protein-ligand binding, ∆G _b, thermozeaxanthins show a more favorable interaction with PPARs, followed by Helix-Y¹². Moreover, Helix-Y¹² interacts with most parts of the Y-shaped ligand-binding domain (LBD), surrounding helix 3 of PPARs, and reaching helix 12 of PPARα and PPARγ. As previously reported for other ligands, Tyr314 and Tyr464 of PPARα interact with Helix-Y¹² through hydrogen bonds. Several PPARα's amino acids are involved in the ligand binding by hydrophobic interactions. Furthermore, we identified additional PPARs' amino acids interacting with Helix-Y¹² through hydrogen bonds still not reported for known ligands. Our results show that, from the studied ligand set, the Helix-Y¹² peptide and Tzeaxs have the most significant probability of binding to the PPARs' LBD, suggesting novel ligands for PPARs.

Targeting peroxisomal fatty acid oxidation improves hepatic steatosis and insulin resistance in obese mice

Obesity and diabetes normally cause mitochondrial dysfunction and hepatic lipid accumulation, while fatty acid synthesis is suppressed and malonyl-CoA is depleted in the liver of severe obese or diabetic animals. Therefore, a negative regulatory mechanism might work for the control of mitochondrial fatty acid metabolism that is independent of malonyl-CoA in the diabetic animals. As mitochondrial β-oxidation is controlled by the acetyl-CoA/CoA ratio, and the acetyl-CoA generated in peroxisomal β-oxidation could be transported into mitochondria via carnitine shuttles, we hypothesize that peroxisomal β-oxidation might play a role in regulating mitochondrial fatty acid oxidation and inducing hepatic steatosis under the condition of obesity or diabetes. This study reveals a novel mechanism by which peroxisomal β-oxidation controls mitochondrial fatty acid oxidation in diabetic animals. We determined that excessive oxidation of fatty acids by peroxisomes generates considerable acetyl-carnitine in the liver of diabetic mice, which significantly elevates the mitochondrial acetyl-CoA/CoA ratio and causes feedback suppression of mitochondrial β-oxidation. Additionally, we found that specific suppression of peroxisomal β-oxidation enhances mitochondrial fatty acid oxidation by reducing acetyl-carnitine formation in the liver of obese mice. In conclusion, we suggest that induction of peroxisomal fatty acid oxidation serves as a mechanism for diabetes-induced hepatic lipid accumulation. Targeting peroxisomal β-oxidation might be a promising pathway in improving hepatic steatosis and insulin resistance as induced by obesity or diabetes.

A novel nuclear receptor subfamily enlightens the origin of heterodimerization

BACKGROUND

Nuclear receptors are transcription factors of central importance in human biology and associated diseases. Much of the knowledge related to their major functions, such as ligand and DNA binding or dimerization, derives from functional studies undertaken in classical model animals. It has become evident, however, that a deeper understanding of these molecular functions requires uncovering how these characteristics originated and diversified during evolution, by looking at more species. In particular, the comprehension of how dimerization evolved from ancestral homodimers to a more sophisticated state of heterodimers has been missing, due to a too narrow phylogenetic sampling. Here, we experimentally and phylogenetically define the evolutionary trajectory of nuclear receptor dimerization by analyzing a novel NR7 subgroup, present in various metazoan groups, including cnidarians, annelids, mollusks, sea urchins, and amphioxus, but lost in vertebrates, arthropods, and nematodes.

RESULTS

We focused on NR7 of the cephalochordate amphioxus B. lanceolatum. We present a complementary set of functional, structural, and evolutionary analyses that establish that NR7 lies at a pivotal point in the evolutionary trajectory from homodimerizing to heterodimerizing nuclear receptors. The crystal structure of the NR7 ligand-binding domain suggests that the isolated domain is not capable of dimerizing with the ubiquitous dimerization partner RXR. In contrast, the full-length NR7 dimerizes with RXR in a DNA-dependent manner and acts as a constitutively active receptor. The phylogenetic and sequence analyses position NR7 at a pivotal point, just between the basal class I nuclear receptors that form monomers or homodimers on DNA and the derived class II nuclear receptors that exhibit the classical DNA-independent RXR heterodimers.

CONCLUSIONS

Our data suggest that NR7 represents the "missing link" in the transition between class I and class II nuclear receptors and that the DNA independency of heterodimer formation is a feature that was acquired during evolution. Our studies define a novel paradigm of nuclear receptor dimerization that evolved from DNA-dependent to DNA-independent requirements. This new concept emphasizes the importance of DNA in the dimerization of nuclear receptors, such as the glucocorticoid receptor and other members of this pharmacologically important oxosteroid receptor subfamily. Our studies further underline the importance of studying emerging model organisms for supporting cutting-edge research.

Medicinal Chemistry and Chemical Biology of Nurr1 Modulators: An Emerging Strategy in Neurodegeneration

Nuclear receptor related 1 (Nurr1) is a transcription factor with neuroprotective and antineuroinflammatory properties. Observations from genetic studies and human patients support potential of Nurr1 as a therapeutic target in neurodegeneration, but due to a lack of high-quality chemical tools for pharmacological control of Nurr1, its target validation is pending. Nevertheless, considerable progress has recently been made in elucidating structural and functional characteristics of Nurr1, and several ligand scaffolds have been discovered. Here, we analyze Nurr1's structure and mechanisms compared to other nuclear receptors, summarize the known small molecule Nurr1 ligands, and discuss the available evidence for the therapeutic potential of Nurr1 in neurodegeneration.

The omega-3 hydroxy fatty acid 7(S)-HDHA is a high-affinity PPARα ligand that regulates brain neuronal morphology

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARα) is emerging as an important target in the brain for the treatment or prevention of cognitive disorders. The identification of high-affinity ligands for brain PPARα may reveal the mechanisms underlying the synaptic effects of this receptor and facilitate drug development. Here, using an affinity purification-untargeted mass spectrometry (AP-UMS) approach, we identified an endogenous, selective PPARα ligand, 7(S)-hydroxy-docosahexaenoic acid [7(S)-HDHA]. Results from mass spectrometric detection of 7(S)-HDHA in mouse and rat brain tissues, time-resolved FRET analyses, and thermal shift assays collectively revealed that 7(S)-HDHA potently activated PPARα with an affinity greater than that of other ligands identified to date. We also found that 7(S)-HDHA activation of PPARα in cultured mouse cortical neurons stimulated neuronal growth and arborization, as well as the expression of genes associated with synaptic plasticity. The findings suggest that this DHA derivative supports and enhances neuronal synaptic capacity in the brain.

Lipid Messenger Phosphatidylinositol-4,5-Bisphosphate Is Increased by Both PPARα Activators and Inhibitors: Relevance for Intestinal Cell Differentiation

Simple Summary

Fibrates, such as fenofibrate, are widely used drugs for dyslipidaemia treatment. It is known that they activate peroxisome proliferator-activated receptor α (PPARα) which serves as a lipid sensor in the organism. This article addresses how activators and inhibitor of the PPARα could affect differentiation of intestinal cells. Carcinogenesis is a disruption of normal differentiation process and colorectal carcinoma is the third most common cancer in terms of incidence, but the secondp in terms of mortality. One of the important signalling pathways in intestinal cell differentiation as well as carcinogenesis is PI3K/Akt/PTEN. We showed that PPARα activators as well as inhibitor affected the levels of one member of this pathway called phosphatidylinositol-4,5-bisphosphate. This molecule is important for formation of microvilli, the essential structures of fully differentiated intestinal cells.

Abstract

We investigated the effects of PPARα activators fenofibrate and WY-14643 as well as the PPARα inhibitor GW6471 on the PI3K/Akt/PTEN pathway of intestinal cell differentiation. Our previous study showed that all these compounds increased the expression of villin, a specific marker of intestinal cell differentiation in HT-29 and Caco2 cells. Our current results confirmed the central role of lipid messenger phosphatidylinositol-4,5-bisphosphate (PIP2), a known player in brush border formation, in mediating the effects of tested PPARα ligands. Although all tested compounds increased its levels, surprisingly, each of them affected different PIP2-metabolizing enzymes, especially the levels of PIP5K1C and PTEN. Moreover, we found a positive relationship between the expression of PPARα itself and PIP2 as well as PIP5K1C. By contrast, PPARα was negatively correlated with PTEN. However, the expression of antigens of interest was independent of PPARα subcellular localization, suggesting that it is not directly involved in their regulation. In colorectal carcinoma tissues we found a decrease in PTEN expression, which was accompanied by a change in its subcellular localization. This change was also observed for the regulatory subunit of PI3K. Taken together, our data revealed that fenofibrate, WY-14643, and GW6471 affected different members of the PI3K/Akt/PTEN pathway. However, these effects were PPARα-independent.

OLHA (Nα-oleoylhistamine) modulates activity of mouse brain histaminergic neurons

Histaminergic (HA) neurons are located in the tuberomamillary nucleus (TMN) of the posterior hypothalamus, from where they project throughout the whole brain to control wakefulness. We examined the effects of N^α-oleoylhistamine (OLHA), a non-enzymatic condensation product of oleic acid (OLA) and histamine, on activity of mouse HA neurons in brain slices. OLHA bidirectionally modulated the firing of HA neurons. At 10 nM OLHA inhibited or had no action, whereas at 1 μM it evoked excitatory and inhibitory responses. Inhibition was not seen in presence of the histamine receptor H3 (H₃R) antagonist clobenpropit and in calcium-free medium. Pre-incubation with a histamine-reuptake blocker prevented the decrease in firing by OLHA. OLHA-evoked increase in firing (EC₅₀ ∼44 nM) was insensitive to blockers of cannabinoid 1 and 2 receptors and of the capsaicin receptor, but was significantly impaired by the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) antagonist MK886, which suppressed also the rise in intracellular calcium level caused by OLHA. The OLHA-evoked excitation was mimicked by synthetic PPAR-alpha agonists (gemfibrozil and GW7647) and was abolished by the PKA inhibitor H-89. The H₃R affinity (Ki) for histamine, measured in HEK293 cells with stable expression of human H₃R, was higher than for OLHA (Ki: 42 vs 310 nM, respectively). Expression of PPAR-alpha was not different between TMN regions of males and females, responses to OLHA did not differ. Molecular modelling of PPAR-alpha bound to either OLHA or OEA showed similar binding energies. These findings shed light on a novel biotransformation product of histamine which may play a role in health and disease.

Arylalkynyl amide-type peroxisome proliferator-activated receptor γ (PPARγ)-selective antagonists covalently bind to the PPARγ ligand binding domain with a unique binding mode

Peroxisome proliferator-activated receptor γ (PPARγ) antagonists are drug candidates for the treatment of type 2 diabetes, obesity, and osteoporosis. Previously, we have designed and synthesized a series of substituted phenylalkynyl amide-type PPARγ antagonists. The representative compound, MMT-160, exhibited nanomolar-order PPARγ antagonistic activity. To understand the antagonistic mode of action of MMT-160, mass spectrometric and X-ray crystallographic analysis of MMT-160 in the presence of the PPARγ ligand binding domain (LBD) were performed. The mass spectrometry results clearly indicated that alkynyl amide-type PPARγ antagonists were covalently bound to the PPARγ LBD. The X-ray crystallographic analysis indicated that MMT-160 acted as a Michael acceptor and covalently bound to the PPARγ LBD via Cys285. In addition, MMT-160 bound to the PPARγ LBD with a binding mode that was different from the binding modes observed for PPARγ agonists and partial agonists.

Functional and Structural Insights into Human PPARα/δ/γ Subtype Selectivity of Bezafibrate, Fenofibric Acid, and Pemafibrate

Among the agonists against three peroxisome proliferator-activated receptor (PPAR) subtypes, those against PPARα (fibrates) and PPARγ (glitazones) are currently used to treat dyslipidemia and type 2 diabetes, respectively, whereas PPARδ agonists are expected to be the next-generation metabolic disease drug. In addition, some dual/pan PPAR agonists are currently being investigated via clinical trials as one of the first curative drugs against nonalcoholic fatty liver disease (NAFLD). Because PPARα/δ/γ share considerable amino acid identity and three-dimensional structures, especially in ligand-binding domains (LBDs), clinically approved fibrates, such as bezafibrate, fenofibric acid, and pemafibrate, could also act on PPARδ/γ when used as anti-NAFLD drugs. Therefore, this study examined their PPARα/δ/γ selectivity using three independent assays—a dual luciferase-based GAL4 transactivation assay for COS-7 cells, time-resolved fluorescence resonance energy transfer-based coactivator recruitment assay, and circular dichroism spectroscopy-based thermostability assay. Although the efficacy and efficiency highly varied between agonists, assay types, and PPAR subtypes, the three fibrates, except fenofibric acid that did not affect PPARδ-mediated transactivation and coactivator recruitment, activated all PPAR subtypes in those assays. Furthermore, we aimed to obtain cocrystal structures of PPARδ/γ-LBD and the three fibrates via X-ray diffraction and versatile crystallization methods, which we recently used to obtain 34 structures of PPARα-LBD cocrystallized with 17 ligands, including the fibrates. We herein reveal five novel high-resolution structures of PPARδ/γ–bezafibrate, PPARγ–fenofibric acid, and PPARδ/γ–pemafibrate, thereby providing the molecular basis for their application beyond dyslipidemia treatment.

Gene repression through epigenetic modulation by PPARA enhances hepatocellular proliferation

Peroxisome proliferator-activated receptor α (PPARA) is a key mediator of lipid metabolism and inflammation. Activation of PPARA in rodents causes hepatocyte proliferation, but the underlying mechanism is poorly understood. This study focused on genes repressed by PPARA and analyzed the mechanism by which PPARA promotes hepatocyte proliferation in mice. Activation of PPARA by agonist treatment was autoregulated, and induced expression of the epigenetic regulator UHRF1 via activation of the newly described PPARA target gene E2f8, which, in turn, regulates Uhrf1. UHRF1 strongly repressed the expression of CDH1 via methylation of the Cdh1 promoter marked with H3K9me3. Repression of CDH1 by PPARA activation was reversed by PPARA deficiency or knockdown of E2F8 or UHRF1. Furthermore, a forced expression of CDH1 inhibited expression of the Wnt signaling target genes such as Myc after PPARA activation, and suppressed hepatocyte hyperproliferation. These results demonstrate that the PPARA-E2F8-UHRF1-CDH1 axis causes epigenetic regulation of hepatocyte proliferation.

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PPARA activation induces the UHRF1 expression via novel PPARA target gene E2f8

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Induction of UHRF1 by PPARA activation represses Cdh1 gene marked with H3K9me3

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CDH1 suppresses hepatocyte proliferation after PPARA activation

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Autoinduction of PPARA by agonist enhances cell proliferation via E2F8-UHRF1-CDH1

Exploring Compounds to be used as Cosmetic Agents that Activate Peroxisome Proliferator-Activated Receptor Alpha

OBJECTIVE

The human epidermis is formed by the proliferation and differentiation of keratinocytes adjacent to the basement membrane. The outermost layer, the stratum corneum, is equipped with a barrier function that prevents water evaporation, and intercellular lipids play an important role in this barrier function. When the barrier is functioning normally, evaporation is prevented; however, when barrier function is impaired, moisture evaporates, resulting in dry and rough skin. Therefore, maintenance of normal barrier function is critical for maintaining normal skin function. Peroxisome proliferator-activated receptor α (PPARα) is mainly involved in lipid metabolism in the liver but is also expressed in the epidermis and is involved in inducing keratinocyte differentiation, promoting lipid production, maintaining barrier function, and suppressing skin inflammation. Hence, compounds that activate PPARα are expected to control skin function. Therefore, we identified PPARα activators from among extracts of natural resources that have been approved for use in humans and analyzed the effects of these extracts on skin function.

METHODS

First, extracts of 474 natural resources were screened using a PPARα activator screening cell line independently constructed in our laboratory. Next, reporter assays were performed using the Gal4-chimera system to evaluate whether these extracts act as ligands for PPARα. We then analyzed their effect on primary normal human epidermal keratinocyte cells by using real-time RT-PCR. Finally, we evaluated PPARα activation effect by the combination of these extracts.

RESULTS

We identified 36 extracts having the effect of activating PPARα. In particular, #419, a Typha angustifolia spike extract, showed concentration-dependent transcriptional activation through PPARα-LBD and was considered to be likely to contain a compound that is a ligand of PPARα. #419 increased the expression of PPARα target genes as well as genes related to skin function in primary cultured human epidermal keratinocytes. Finally, the use of #419 in combination with nine extracts increased PPAR activity more than twice as much as #419 alone treatment.

CONCLUSIONS

These results showed that the reporter cell line could be useful for discovering extracts of natural resources and that the identified Typha angustifolia spike extract could be used in cosmetics that activate PPARα, which expected to improve skin function.

Phenolic Lipids Derived from Cashew Nut Shell Liquid to Treat Metabolic Diseases

Metabolic diseases are increasing at staggering rates globally. The peroxisome proliferator-activated receptors (PPARα/γ/δ) are fatty acid sensors that help mitigate imbalances between energy uptake and utilization. Herein, we report compounds derived from phenolic lipids present in cashew nut shell liquid (CNSL), an abundant waste byproduct, in an effort to create effective, accessible, and sustainable drugs. Derivatives of anacardic acid and cardanol were tested for PPAR activity in HEK293 cell co-transfection assays, primary hepatocytes, and 3T3-L1 adipocytes. In vivo studies using PPAR-expressing zebrafish embryos identified CNSL derivatives with varying tissue-specific activities. LDT409 (23) is an analogue of cardanol with partial agonist activity for PPARα and PPARγ. Pharmacokinetic profiling showed that 23 is orally bioavailable with a half-life of 4 h in mice. CNSL derivatives represent a sustainable source of selective PPAR modulators with balanced intermediate affinities (EC₅₀ ∼ 100 nM to 10 μM) that provide distinct and favorable gene activation profiles for the treatment of diabetes and obesity.

Structural overview and perspectives of the nuclear receptors, a major family as the direct targets for small-molecule drugs

The nuclear receptors (NRs) are an evolutionarily related family of transcription factors, which share certain common structural characteristics and regulate the expressions of various genes by recognizing different response elements. NRs play important roles in cell differentiation, proliferation, survival and apoptosis, rendering them indispensable in many physiological activities including growth and metabolism. As a result, dysfunctions of NRs are closely related to a variety of diseases, such as diabetes, obesity, infertility, inflammation, the Alzheimer's disease, cardiovascular diseases, prostate and breast cancers. Meanwhile, small-molecule drugs directly targeting NRs have been widely used in the treatment of above diseases. Here we summarize recent progress in the structural biology studies of NR family proteins. Compared with the dozens of structures of isolated DNA-binding domains (DBDs) and the striking more than a thousand of structures of isolated ligand-binding domains (LBDs) accumulated in the Protein Data Bank (PDB) over thirty years, by now there are only a small number of multi-domain NR complex structures, which reveal the integration of different NR domains capable of the allosteric signal transduction, or the detailed interactions between NR and various coregulator proteins. On the other hand, the structural information about several orphan NRs is still totally unavailable, hindering the further understanding of their functions. The fast development of new technologies in structural biology will certainly help us gain more comprehensive information of NR structures, inspiring the discovery of novel NR-targeting drugs with a new binding site beyond the classic LBD pockets and/or a new mechanism of action.

[PPARα-Ligand Binding Modes Revealed by X-ray Crystallography]

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptor-type transcription factors that consist of three subtypes (α, γ, and β/δ) with distinct physiological functions and ligand recognition. PPARs regulate energy metabolism and therefore become therapeutic targets for various metabolic diseases. While PPARα agonists are used as anti-dyslipidemia drugs and PPARγ agonists as anti-type 2 diabetes drugs, PPAR dual/pan agonists (that acts on two or three subtypes) are expected to treat non-alcoholic steatohepatitis (NASH), pulmonary fibrosis, etc. Structural analyses of PPAR-ligand-binding domain (LBD)-ligand co-crystals using X-ray crystallography have been done mainly on PPARγ, in which ligand-free apocrystals were prepared; however, the information on PPARα-LBD and PPARδ-LBD is limited. Recently, we succeeded to obtain 34 novel co-crystal structures of PPARα-LBD and various PPARα ligands (including fibrates) using various co-crystallization techniques. This procedure is applicable to preparation of PPARδ-LBD co-crystals, and contributes to molecular design of new PPAR targeted drugs based on all three PPAR-LBD structures.

Structural Basis for PPARs Activation by The Dual PPARα/γ Agonist Sanguinarine: A Unique Mode of Ligand Recognition

Peroxisome proliferator-activated receptors (PPARs) play crucial roles in glucose and lipid metabolism and inflammation. Sanguinarine is a natural product that is isolated from Sanguinaria Canadensis, a potential therapeutic agent for intervention in chronic diseases. In this study, biochemical and cell-based promoter-reporter gene assays revealed that sanguinarine activated both PPARα and PPARγ, and enhanced their transcriptional activity; thus, sanguinarine was identified as a dual agonist of PPARα/γ. Similar to fenofibrate, sanguinarine upregulates the expression of PPARα-target genes in hepatocytes. Sanguinarine also modulates the expression of key PPARγ-target genes and promotes adipocyte differentiation, but with a lower adipogenic activity compared with rosiglitazone. We report the crystal structure of sanguinarine bound to PPARα, which reveals a unique ligand-binding mode of sanguinarine, dissimilar to the classic Y-shaped binding pocket, which may represent a new pharmacophore that can be optimized for selectively targeting PPARα. Further structural and functional studies uncover the molecular basis for the selectivity of sanguinarine toward PPARα/γ among all three PPARs. In summary, our study identifies a PPARα/γ dual agonist with a unique ligand-binding mode, and provides a promising and viable novel template for the design of dual-targeting PPARs ligands.

The Role of PPAR Alpha in the Modulation of Innate Immunity

Peroxisome proliferator-activated receptor α is a potent regulator of systemic and cellular metabolism and energy homeostasis, but it also suppresses various inflammatory reactions. In this review, we focus on its role in the regulation of innate immunity; in particular, we discuss the PPARα interplay with inflammatory transcription factor signaling, pattern-recognition receptor signaling, and the endocannabinoid system. We also present examples of the PPARα-specific immunomodulatory functions during parasitic, bacterial, and viral infections, as well as approach several issues associated with innate immunity processes, such as the production of reactive nitrogen and oxygen species, phagocytosis, and the effector functions of macrophages, innate lymphoid cells, and mast cells. The described phenomena encourage the application of endogenous and pharmacological PPARα agonists to alleviate the disorders of immunological background and the development of new solutions that engage PPARα activation or suppression.

Crystal Structures of the Human Peroxisome Proliferator-Activated Receptor (PPAR)α Ligand-Binding Domain in Complexes with a Series of Phenylpropanoic Acid Derivatives Generated by a Ligand-Exchange Soaking Method

Peroxisome proliferator-activated receptor (PPAR)α, a member of the nuclear receptor family, is a transcription factor that regulates the expression of genes related to lipid metabolism in a ligand-dependent manner, and has attracted attention as a target for hypolipidemic drugs. We have been developing phenylpropaonic acid derivatives as PPARα-targeted drug candidates for the treatment of metabolic diseases. Recently, we have developed the "ligand-exchange soaking method," which crystallizes the recombinant PPARα ligand-binding domain (LBD) as a complex with intrinsic fatty acids derived from an expression host Escherichia (E.) coli and thereafter replaces them with other higher-affinity ligands by soaking. Here we applied this method for preparation of cocrystals of PPARα LBD with its ligands that have not been obtained with the conventional cocrystallization method. We revealed the high-resolution structures of the cocrystals of PPARα LBD and the three synthetic phenylpropaonic acid derivatives: TIPP-703, APHM19, and YN4pai, the latter two of which are the first observations. The overall structures of cocrystals obtained from the two methods are identical and illustrate the close interaction between these ligands and the surrounding amino acid residues of PPARα LBD. This ligand-exchange soaking method could be applicable to high throughput preparations of co-crystals with another subtype PPARδ LBD for high resolution X-ray crystallography, because it also crystallizes in complex with intrinsic fatty acid(s) while not in the apo-form.

Structural Basis for Anti-non-alcoholic Fatty Liver Disease and Diabetic Dyslipidemia Drug Saroglitazar as a PPAR α/γ Dual Agonist

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptor-type transcription factors that consist of three subtypes (α, γ, and β/δ) with distinct functions and PPAR dual/pan agonists are expected to be the next generation of drugs for metabolic diseases. Saroglitazar is the first clinically approved PPARα/γ dual agonist for treatment of diabetic dyslipidemia and is currently in clinical trials to treat non-alcoholic fatty liver disease (NAFLD); however, the structural information of its interaction with PPARα/γ remains unknown. We recently revealed the high-resolution co-crystal structure of saroglitazar and the PPARα-ligand binding domain (LBD) through X-ray crystallography, and in this study, we report the structure of saroglitazar and the PPARγ-LBD. Saroglitazar was located at the center of "Y"-shaped PPARγ-ligand-binding pocket (LBP), just as it was in the respective region of PPARα-LBP. Its carboxylic acid was attached to four amino acids (Ser289/His323/His449/Thr473), which contributes to the stabilization of Activating Function-2 helix 12, and its phenylpyrrole moiety was rotated 121.8 degrees in PPARγ-LBD from that in PPARα-LBD to interact with Phe264. PPARδ-LBD has the consensus four amino acids (Thr253/His287/His413/Tyr437) towards the carboxylic acids of its ligands, but it seems to lack sufficient space to accept saroglitazar because of the steric hindrance between the Trp228 or Arg248 residue of PPARδ-LBD and its methylthiophenyl moiety. Accordingly, in a coactivator recruitment assay, saroglitazar activated PPARα-LBD and PPARγ-LBD but not PPARδ-LBD, whereas glycine substitution of either Trp228, Arg248, or both of PPARδ-LBD conferred saroglitazar concentration-dependent activation. Our findings may be valuable in the molecular design of PPARα/γ dual or PPARα/γ/δ pan agonists.

Mechanisms Mediating the Regulation of Peroxisomal Fatty Acid Beta-Oxidation by PPARα

In mammalian cells, two cellular organelles, mitochondria and peroxisomes, share the ability to degrade fatty acid chains. Although each organelle harbors its own fatty acid β-oxidation pathway, a distinct mitochondrial system feeds the oxidative phosphorylation pathway for ATP synthesis. At the same time, the peroxisomal β-oxidation pathway participates in cellular thermogenesis. A scientific milestone in 1965 helped discover the hepatomegaly effect in rat liver by clofibrate, subsequently identified as a peroxisome proliferator in rodents and an activator of the peroxisomal fatty acid β-oxidation pathway. These peroxisome proliferators were later identified as activating ligands of Peroxisome Proliferator-Activated Receptor α (PPARα), cloned in 1990. The ligand-activated heterodimer PPARα/RXRα recognizes a DNA sequence, called PPRE (Peroxisome Proliferator Response Element), corresponding to two half-consensus hexanucleotide motifs, AGGTCA, separated by one nucleotide. Accordingly, the assembled complex containing PPRE/PPARα/RXRα/ligands/Coregulators controls the expression of the genes involved in liver peroxisomal fatty acid β-oxidation. This review mobilizes a considerable number of findings that discuss miscellaneous axes, covering the detailed expression pattern of PPARα in species and tissues, the lessons from several PPARα KO mouse models and the modulation of PPARα function by dietary micronutrients.

Preparation of co-crystals of human PPAR-LBD and ligand for high-resolution X-ray crystallography

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptor-type transcription factors with three subtypes (α, δ, and γ) that regulate cell differentiation and metabolism. Co-crystals of human PPARα-ligand-binding domain (LBD)-PPARα ligand for X-ray crystallography have been difficult to obtain. Recombinant human PPARα-LBD proteins contain intrinsic fatty acids (iFAs of Escherichia coli origin) and may be unstable without ligands during crystallization. To circumvent these limitations, we have successfully applied various crystallization techniques, including co-crystallization, cross-seeding, soaking, delipidation, and coactivator peptide supplementation.

For complete details on the use and execution of this protocol, please refer to Kamata et al. (2020).

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Protocols for recombinant PPARα ligand-binding domain protein purification

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Techniques to prepare PPARα-ligand co-crystals for high-resolution X-ray crystallography

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Strategy to obtain PPARα co-crystals with low-affinity PPARα ligands