Identification of Picrasidine C as a Subtype-Selective PPARα Agonist

Identification of phytochemicals as putative ligands for the targeted modulation of peroxisome proliferator-activated receptor α (PPARα) in animals

The PPAR family of transcription factors are ligand-activated and regulate diverse functions including metabolic, neurological, and inflammatory diseases, neurodegenerative disorders, fertility or reproduction in the body. Specifically, PPARα is known to play a role in reducing the levels of circulating triglycerides and regulating energy homeostasis in livestock animals. This study aimed to identify phytochemicals that could serve as ligands for modulation of the bovine nuclear peroxisome proliferator-activated receptor alpha (PPARα) using molecular docking studies. Therefore, we investigated 1000 flavonoids belonging to different groups for their ability to bind to PPARα using molecular docking. Out of 1000, 6 top lead compounds with maximum binding affinity, evaluated through molecular docking, were further analysed for physicochemical properties and drug-likeness attributes. The results revealed that two flavonoids, Quercetin-3-o-rhamnoside and (-)- epicatechingallate, which are known fatty acid synthase inhibitors, demonstrated high docking scores with PPARα (-8.66 kcal/mol and -8.49 kcal/mol, respectively) and low RMSD values with PPARα (1.61 kcal/mol and 1.28 kcal/mol, respectively) as compared to PPARα agonist (synthetic), fenofibrate (-6.24 kcal/mol and 2.19 kcal/mol) and thus analyzed further for prediction of stability of docked complexes through MD simulations. MD simulation studies predicted the stability of complexes and the complex of Quercetin-3-o-rhamnoside and (-)- epicatechingallate were found to be stable at 100 ns based on RSMD value and RMSF residue index. Through computational analysis, the screened compounds showed good pharmacokinetic parameters, including non-toxicity, non-carcinogenic, high gastrointestinal absorption and thus can serve as potential drug candidates. Finally, the findings suggest that these phytochemicals have the potential to act as potent PPARα pharmacological agonists to prevent disease mechanisms and their related complications, providing insights into the role of phytochemicals as feed additives in animals for modulating PPARα functions.Communicated by Ramaswamy H. Sarma.

Picrasidine J, a Dimeric β-Carboline-Type Alkaloid from Picrasma quassioides, Inhibits Metastasis of Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) are associated with recurrence, distant metastasis, and poor overall survival. This highlights the need for identifying potential therapeutics with minimal side-effects. The present study was designed to investigate the anticancer effects of picrasidine J, a dimeric β-carboline-type alkaloid isolated from the southern Asian plant Picrasma quassioides. The results showed that picrasidine J significantly inhibits HNSCC cell motility, migration, and invasion. Specifically, picrasidine J inhibited the EMT process by upregulating E-cadherin and ZO-1 and downregulating beta-catenin and Snail. Moreover, picrasidine J reduced the expression of the serine protease KLK-10. At the signaling level, the compound reduced the phosphorylation of ERK. All these factors collectively facilitated the inhibition of HNSCC metastasis with picrasidine J. Taken together, the study identifies picrasidine J as a potential anticancer compound of plant origin that might be used clinically to prevent the distant metastasis and progression of HNSCC.

Targeting PPARs for therapy of atherosclerosis: A review

Atherosclerosis, a chief pathogenic factor of cardiovascular disease, is associated with many factors including inflammation, dyslipidemia, and oxidative stress. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and are widely expressed with tissue- and cell-specificity. They control multiple genes that are involved in lipid metabolism, inflammatory response, and redox homeostasis. Given the diverse biological functions of PPARs, they have been extensively studied since their discovery in 1990s. Although controversies exist, accumulating evidence have demonstrated that PPAR activation attenuates atherosclerosis. Recent advances are valuable for understanding the mechanisms of action of PPAR activation. This article reviews the recent findings, mainly from the year of 2018 to present, including endogenous molecules in regulation of PPARs, roles of PPARs in atherosclerosis by focusing on lipid metabolism, inflammation, and oxidative stress, and synthesized PPAR modulators. This article provides information valuable for researchers in the field of basic cardiovascular research, for pharmacologists that are interested in developing novel PPAR agonists and antagonists with lower side effects as well as for clinicians.

The Structure Basis of Phytochemicals as Metabolic Signals for Combating Obesity

The consumption of phytochemicals, bioactive compounds in fruits and vegetables, has been demonstrated to ameliorate obesity and related metabolic symptoms by regulating specific metabolic pathways. This review summarizes the progress made in our understanding of the potential of phytochemicals as metabolic signals: we discuss herein selected molecular mechanisms which are involved in the occurrence of obesity that may be regulated by phytochemicals. The focus of our review highlights the regulation of transcription factors toll like receptor 4 (TLR4), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), the peroxisome proliferator-activated receptors (PPARs), fat mass and obesity-associated protein (FTO) and regulation of microRNAs (miRNA). In this review, the effect of phytochemicals on signaling pathways involved in obesity were discussed on the basis of their chemical structure, suggesting molecular mechanisms for how phytochemicals may impact these signaling pathways. For example, compounds with an isothiocyanate group or an α, β-unsaturated carbonyl group may interact with the TLR4 signaling pathway. Regarding Nrf2, we examine compounds possessing an α, β-unsaturated carbonyl group which binds covalently with the cysteine thiols of Keap1. Additionally, phytochemical activation of PPARs, FTO and miRNAs were summarized. This information may be of value to better understand how specific phytochemicals interact with specific signaling pathways and help guide the development of new drugs to combat obesity and related metabolic diseases.

Picrasidine I Triggers Heme Oxygenase-1-Induced Apoptosis in Nasopharyngeal Carcinoma Cells via ERK and Akt Signaling Pathways

Nasopharyngeal carcinoma (NPC) has a higher incidence in Taiwan than worldwide. Although it is a radiosensitive malignancy, cancer recurrence is still high in the advanced stages because of its ability to induce lymph node metastasis. Picrasidine I from Picrasma quassioides has been reported as a potential drug for targeting multiple signaling pathways. The present study aimed to explore the role of picrasidine I in the apoptosis of NPC cells. Our results show that picrasidine I induced cytotoxic effects in NPC cells and caused cell cycle arrest in the sub-G1, S, and G2/M phases. Western blot analysis further demonstrated that the modulation of apoptosis through the extrinsic and intrinsic pathways was involved in picrasidine I-induced cell death. Downregulation of the ERK1/2 and Akt signaling pathways was also found in picrasidine I-induced apoptosis. Additionally, the apoptosis array showed that picrasidine I significantly increased heme oxygenase-1 (HO-1) expression, which could act as a critical molecule in picrasidine I-induced apoptosis in NPC cells. The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets also revealed that the HMOX1 mRNA level (HO-1) is lower in patients with head and neck squamous carcinoma (HNSCC) and NPC than in patients without cancer. Our study indicated that picrasidine I exerts anticancer effects in NPC by modulating HO-1 via the ERK and Akt signaling pathways.

Anticancer effects of picrasidine I on oral squamous cell carcinoma

Picrasidine I is a dimeric alkaloid derived from a Southern Asian plant Picrasma quassioides and demonstrated to possess pharmacological activities, such as anti-inflammatory and anti-osteoclastogenic effects. However, its potential anticancer effect remains unclear. In the present study, anticancer activity of picrasidine I was assessed by treating oral squamous cell carcinoma cells with different concentrations of picrasidine I (20, 30, and 40 μM) for 24, 48, and 72 h. The findings revealed that picrasidine I reduced the cell viability in a dose-dependent manner. Picrasidine I exerted its cytotoxic effect through arresting cell cycle at G2/M phase by downregulating cyclin A, cyclin B, CDK4, and CDK6, and inducing apoptosis in oral cancer cells. The induction of apoptosis was evidenced by increasing expression of death receptors, disruption of mitochondrial membrane potential, increased activation of PARP and caspases 3, 8, and 9, enhanced expression of proapoptotic mediators (Bak and Bim L/S), and reduced expression of antiapoptotic mediators (Bcl-2 and Bcl-xL). Moreover, analysis of MAPK signaling pathway revealed that picrasidine I-mediated proapoptotic activities by downregulating JNK phosphorylation. Taken together, the study identifies picrasidine I as a potent anticancer agent that can be used as a therapeutic intervention against oral squamous cell carcinoma.

Alkaloids from Picrasma quassioides: An overview of their NMR data, biosynthetic pathways and pharmacological effects

Picrasma quassioides, a member of the Simaroubaceae family, is the subject of research in numerous pharmacological and chemical studies. This plant mainly contains alkaloids, quassinoids and terpenoids. These molecules exhibit various pharmacological benefits, such as anti-inflammatory, anticancer, and anti-viral effects, on the cardiovascular system. Alkaloids make up the majority of these molecules. This review describes 127 alkaloid substances from P. quassioides. These alkaloids can be divided into the following classes: β-carbolines, canthinones and alkaloid dimers. A compilation of their nuclear magnetic resonance spectroscopy data and possible biosynthetic pathways of these compounds and the pharmacological effects of P. quassioides are also included.

Pharmacological effects of Picrasma quassioides (D. Don) Benn for inflammation, cancer and neuroprotection (Review)

Picrasma quassioides (D. Don) Benn is an Asian shrub with a considerable history of traditional medicinal use. P. quassioides and its extracts exhibit good therapeutic properties against several diseases, including anti-inflammatory, antibacterial and anticancer effects. However, the composition of compounds contained in P. quassioides is complex; although various studies have examined mixtures or individual compounds extracted from it, studies on the application of P. quassioides extracts remain limited. In the present review, the structures and functions of the compounds identified from P. quassioides and their utility in anti-inflammatory, anticancer and neuroprotectant therapies was discussed. The present review provided up-to-date information on pharmacological activities and clinical applications for P. quassioides extracts.

Evolution of a 4-Benzyloxy-benzylamino Chemotype to Provide Efficacious, Potent, and Isoform Selective PPARα Agonists as Leads for Retinal Disorders

Peroxisome proliferator-activated receptor alpha (PPARα) is expressed in retinal Müller cells, endothelial cells, and in retinal pigment epithelium; agonism of PPARα with genetic or pharmacological tools ameliorates inflammation, vascular leakage, neurodegeneration, and neovascularization associated with retinal diseases in animal models. As such, PPARα is a promising drug target for diabetic retinopathy and age-related macular degeneration. Herein, we report proof-of-concept in vivo efficacy in an streptozotocin-induced vascular leakage model (rat) and preliminary pharmacokinetic assessment of a first-generation lead 4a (A91). Additionally, we present the design, synthesis, and evaluation of second-generation analogues, which led to the discovery of 4u and related compounds that reach cellular potencies <50 nM and exhibit >2,700-fold selectivity for PPARα over other PPAR isoforms. These studies identify a pipeline of candidates positioned for detailed PK/PD and pre-clinical evaluation.

Computational investigation reveals Picrasidine C as selective PPARα lead: binding pattern, selectivity mechanism and ADME/tox profile

Natural products and their derivatives have been recognized as an important source of therapeutic agents for many years. Previously we isolated a dimeric β-carboline-type alkaloid Picrasidine C from the root of Picrasma quassioides as subtype-selective peroxisome proliferator-activated receptor α (PPARα) agonist. In order to modify this natural product for better affinity and druggability, we investigated a series of properties exhibited by Picrasidine C, such as its binding mode with PPARα, the selectivity mechanism over PPARγ, as well as ADME/Tox profile through computational methods including sequence alignment, molecular docking, pharmacophore modeling and molecular dynamics simulations. The detailed information of binding pattern and affinity for Picrasidine C elucidated here will be valuable for chemical modification. Besides, the steric hindrance of residue Phe363 in PPARγ pocket was speculated as the main isoform selectivity mechanism for Picrasidine C, which would be helpful for the design of selective derivatives. ADME/Tox prediction was conducted to avoid potential undesirable pharmacokinetic properties for reducing the risk of failure. Finally, novel skeletons were derived from lead compound by core hopping method, validated through molecular dynamic simulations and MM-GBSA calculation. In short, the information obtained from computational strategy would be valuable for us to find more potent, safe and selective PPARα agonists during structural optimization.

A novel cathepsin L inhibitor prevents the progression of idiopathic pulmonary fibrosis

In previous work, the target of asperphenamate as a natural product was successfully determined as cathepsin by the natural product consensus pharmacophore strategy. In order to develop accurate SAR (structure-activity relationship) of asperphenamate-type cathepsin inhibitor, we chose several novel analogs with heterocyclic moiety to perform further study. The molecular simulation showed that 4-pyridyl derivative 3 with the greatest cathepsin inhibitory activity presented new interaction modes with protein utilizing its B-ring moiety. And then molecular dynamics (MD) simulation further revealed that 3 and cathepsin kept stable interaction in the binding site, which validated the molecular docking results. In view that cathepsins play an important role in fibrosis and some cathepsin inhibitors display the therapeutic ability for fibrosis, we investigated the anti-fibrotic effect of 3in vitro and in vivo. The results indicated that 3 displayed the strongest inhibitory effect on the formation of α-SMA and collagen I as the protein markers of fibrosis among all tested derivatives. Further in vivo assay confirmed that 3 indeed showed significant inhibitory ability against pulmonary fibrosis by the method of H&E and Masson staining as well as immunohistochemical staining for characteristic α-SMA proteins.

The influence of alkaloids on oxidative stress and related signaling pathways

Alkaloids have always attracted scientific interest due to either their positive or negative effects on human beings. This review aims to summarize their antioxidant effects by both classical in vitro scavenging assay and at the cellular level. Since most in vitro studies used the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assay, the results from those studies are summed up in the first part of the article. In the second part, available data on the effect of alkaloids on NADPH-oxidase, the key enzyme for reactive oxygen species production, at the cellular level, are summarized. More than 130 alkaloids were tested by DPPH assay. However, due to methodological differences, a direct comparison is hardly possible. It can be at least concluded that some of them were either similar to or even more active than standard antioxidants and the number of aromatic hydroxyl groups seems to be the major determinant for the activity. The data on inhibition of NADPH-oxidase activity by alkaloids demonstrated that there is little relationship to the DPPH assay. The mechanism seems to be based on inhibition of synthesis, activation or translocation of NADPH-oxidase subunits. In some alkaloids, activation of the nuclear factor Nrf2 pathway was documented to be the grounds for inhibition of NADPH-oxidase. Interestingly, many alkaloids can behave both as anti-oxidants and pro-oxidants depending on conditions and pro-oxidation might be the reason for activation of Nrf2. Available data on other "antioxidant" transcription factors FOXOs and PPARs are also mentioned.

FGFR2 regulation by picrasidine Q inhibits the cell growth and induces apoptosis in esophageal squamous cell carcinoma

Fibroblast growth factor receptor (FGFR) 2 and its downstream signaling cascades, PI3 K/AKT/mTOR is playing an important role in cell survival and proliferations. In this study, we firstly found that picrasidine Q (PQ), an alkaloid component extracted from Angelica keiskei species, has the capacity of anti-cell transformation and anti-cancer. After ligand shape similarity approach of PQ, we found that PQ targeted FGFR 2 and verified by FGFR2 kinase assay as well as computational docking model. FGFR2 highly expressed in esophageal cancer tissues and PQ inhibited fibroblast growth factor (FGF)-induced cell transformation. Furthermore, PQ inhibited cell proliferation and induced cell cycle arrest and apoptosis in KYSE30, KYSE410, and KYSE450 esophageal squamous cell carcinoma (ESCC) cells. It was confirmed by detecting of biological markers such as cyclinD1, cyclinD3 and cyclinB1 for cell cycle or cleaved caspase-7, caspase-3, and PARP for apoptosis. PQ targeting of FGFR2 kinase activities suppressed downstream target proteins including phosphorylation of AKT and mTOR but not MEK/ERK signaling pathways. Taken together, our results are the first to identify that PQ might be a chemopreventive and chemotherapeutic agent by direct targeting FGFR2 and inhibiting cell proliferation of ESCC cells.

The potential of natural products for targeting PPARα

Peroxisome proliferator activated receptors (PPARs) α, -γ and -β/δ are ligand-activated transcription factors and members of the superfamily of nuclear hormone receptor. These receptors play key roles in maintaining glucose and lipid homeostasis by modulating gene expression. PPARs constitute a recognized druggable target and indeed several classes of drugs used in the treatment of metabolic disease symptoms, such as dyslipidemia (fibrates, e.g. fenofibrate and gemfibrozil) and diabetes (thiazolidinediones, e.g. rosiglitazone and pioglitazone) are ligands for the various PPAR isoforms. More precisely, antidiabetic thiazolidinediones act on PPARγ, while PPARα is the main molecular target of antidyslipidemic fibrates. Over the past few years, our understanding of the mechanism underlying the PPAR modulation of gene expression has greatly increased. This review presents a survey on terrestrial and marine natural products modulating the PPARα system with the objective of highlighting how the incredible chemodiversity of natural products can provide innovative leads for this "hot" target.

Radix Stellariae extract prevents high-fat-diet-induced obesity in C57BL/6 mice by accelerating energy metabolism

Stellaria dichotoma L. is widely distributed in Ningxia and surrounding areas in northwestern China. Its root, Radix Stellariae (RS), has been used in herbal formulae for treating asthenic-fever, infection, malaria, dyspepsia in children and several other symptoms. This study investigated whether the RS extract (RSE) alleviates metabolic disorders. The results indicated that RSE significantly inhibited body weight gain in high-fat (HF)-diet-fed C57BL/6 mice, reduced fasting glucose levels, and improved insulin tolerance. Moreover, RSE increased the body temperature of the mice and the expression of uncoupling proteins and peroxisome proliferator-activated receptors in the white adipose tissue. Thus, RSE alleviated metabolic disorders in HF-diet-fed C57BL/6 mice by potentially activating UCP and PPAR signaling.