Prenylated Coumarins of the Genus Citrus: An Overview of the 2006- 2016 Literature Data

O-Prenyl coumarins (3,3-dimethylallyl, geranyl-, farnesyl- and related biosynthetic derivatives) represent a class of rarely occurring natural products. In the last two decades, such secondary metabolites have been found to possess promising and effective pharmacological properties, mainly in terms of anti-cancer and anti-inflammatory properties. To date, about 160 oxyprenylated coumarins have been extracted from plants, fungi, and bacteria. The genus Citrus has been demonstrated to be among the richest source of the title products. The aim of this comprehensive review is to make a survey of the so far reported literature citations about the main O-prenyl coumarins found in this genus from phytochemical and pharmacological point of views and for which no surveys of the in so far reported literature have been made.

Oxyprenylated Phenylpropanoids Bind to MT1 Melatonin Receptors and Inhibit Breast Cancer Cell Proliferation and Migration

Oxyprenylated compounds (i.e., ferulic acid and coumarin derivatives) demonstrate neuroprotection and anticancer properties as reported in previous studies. We have tested the affinity of oxyprenylated ferulic acid (1-4) and umbelliferone derivatives (5-11) to melatonin receptors as well as their antiproliferation and antimigratory properties against breast cancer (BC) cell lines. All the compounds except for ferulic acid, boropinic acid, and umbelliferone had binding affinities to melatonin receptors in the nM to μM range, and both auraptene and umbellinprenin reduced BC cell proliferation and migration in phenotypically diverse BC including triple negative.

A green deep eutectic solvent dispersive liquid-liquid micro-extraction (DES-DLLME) for the UHPLC-PDA determination of oxyprenylated phenylpropanoids in olive, soy, peanuts, corn, and sunflower oil

A green dispersive liquid-liquid microextraction (DLLME) using deep eutectic solvent (DES) as the extracting solvent has been developed and applied for the simultaneous quantification of ferulic acid, umbelliferone, boropinic acid, 7-isopentenyloxycoumarin, 4'-geranyloxyferulic acid (GOFA), and auraptene in some vegetable oils using ultra high performance liquid chromatography (UHPLC) with photodiode array detection (PDA). All parameters in the extraction step, including selection and loading of both extracting and dispersing solvents, amount of both extractant and disperser solvent were investigated and optimized. PhAA/TMG DES achieved higher recovery and enrichment factor compared to other DESs. The validated method showed good linearity with correlation coefficients, r²>0.9990 for all the analytes. Furthermore, this is the first time that eco-friendly solvents are used for the extraction of oxyprenylated phenylpropanoids and the corresponding extract analyzed with ultra high performance liquid chromatography with photodiode array detection.

Characterization of the Degradation Profile of Umbelliprenin, a Bioactive Prenylated Coumarin of a Ferulago Species

Umbelliprenin is a secondary plant metabolite that displays promising chemopreventive, anti-inflammatory, and antigenotoxic properties. It possesses potential for applications to human welfare notably to prevent the emergence of cancer. For this purpose, stability studies are needed to define proper storage conditions and adapted formulations for this drug candidate. The identification of degradative products is a major concern for the preclinical development of umbelliprenin, providing also interesting information related to potential original phytochemicals formed in plants exposed to stressors. The stability profile of umbelliprenin under various stress conditions including exposure to heat, light, oxidation, and hydrolytic medium was assessed via HPLC/UV data. The data support that umbelliprenin undergoes inter- and intramolecular [2+2] cycloaddition under light exposure, leading respectively to a cyclobutane-umbelliprenin dimer and a 16-membered macrocycle. Their structures were characterized via MS and NMR data. It was shown that UV-A filters prevent this process, whereas UV-B filters and antioxidants are not or weakly effective. The study provides useful information for the preclinical development of umbelliprenin as an original chemopreventive agent.

Recent acquisitions on oxyprenylated secondary metabolites as anti-inflammatory agents

Oxyprenylated secondary metabolites from plants, fungi, and bacteria, and their semisynthetic derivatives have been subject of growing interest during the last decade. Such natural products in fact have been discovered as potentially novel lead compounds for a series of pharmacological activities, mainly in terms of anti-cancer and anti-inflammatory ones. Especially during the last 5 years, a wider panel of prenyloxy secondary metabolites have been investigated from chemical and biological points of view and these include benzoic acids, alcohols, aldehydes, chalcones, anthraquinones, 1,4-naphthoquinones, other than the well known oxyprenylated ferulic acid and coumarin derivatives. The aim of this comprehensive review is to focus on the anti-inflammatory properties and related mechanisms of action of selected classes of oxyprenylated naturally occurring compounds and their semisynthetic analogues covering the literature period from 2011 to 2017. In vitro and in vivo data on their pharmacological activity triggering different pathways of the overall inflammatory machinery as well as structure activity relationship acquisitions will be summarized in order to make a detailed survey of the most recent reports on the potential of the title compounds as a novel class of anti-inflammatory agents.

The interaction of auraptene and other oxyprenylated phenylpropanoids with glucose transporter type 4

BACKGROUND

Glucose transporter 4 (GLUT4) is firmly established to play a pivotal role in glucose metabolism and in particular in modulating the insulin-stimulated glucose transport in several tissues, such as skeletal muscle and adipose tissue. Stimulation of GLUT4 by insulin results in its translocation to the plasma membrane, activation of several kinases, and finally in a large glucose influx into cells.

PURPOSE

In this study we investigated the modulating properties of four biologically active oxyprenylated ferulic acid and umbelliferone derivatives and of their unprenylated parent compounds on GLUT-4 mediated glucose uptake and translocation.

METHODS

Oxyprenylated phenylpropanoids have been synthesized in high yields and purity by already reported methodologies. All the synthesized chemicals were tested for their capacity to modulate GLUT4 mediated glucose uptake and GLUT4 translocation in L6 rat skeletal myoblasts in the concentration range 0.1 - 10 µM. Insulin (0.1 µM) was used as positive control. Western blot analysis was employed to assess if GLUT4 translocation occurred prior to increase of glucose uptake. Statistical analyses were carried out by the Dunnett multiple comparison test.

RESULTS

4'-Geranyloxyferulic acid (GOFA), 7-isopentenyloxycoumarin, and auraptene (7-geranyloxycoumarin) increased glucose uptake in a concentration-dependent manner, and significant increases were observed at 0.1 µM for GOFA, and 10 µM for 7-isopentenyloxycoumarin, and auraptene. These products also were able to significantly promote the translocation of GLUT4 to the plasma membrane of L6 myotubes. After treatment with compounds for 15 min, the incorporated amounts of GOFA, 7-isopentenyloxucoumarin, and auraptene were 0.15, 0.32, and 1.77 nmols/60-mm culture dish, respectively. A sample of raw Italian propolis, found to be rich in GOFA and auraptene, was also seen to mimic insulin-effect in the concentration range 0.01 - 1.0 mg/ml.

CONCLUSIONS

Among the compounds assayed, auraptene showed to possess potentialities to be a potent activator of both translocation of GLUT4 and glucose influx into skeletal muscle cells with the highest bioavailability among effective compounds. Its capacity to modulate sugar metabolism, coupled to its presence in edible Citrus fruits, can be regarded as an additional reason to account for the already known stimulating properties of some vegetable (e.g. bitter orange).

Interaction of 7-Alkoxycoumarins with the Aryl Hydrocarbon Receptor

The aryl hydrocarbon receptor (AhR) is a transcription factor activated by a vast array of natural and synthetic ligands. It plays a pivotal role in numerous physiological and pathological responses, such as cell proliferation and differentiation, induction of xenobiotic metabolizing enzymes, response to environmental toxins, and several others. In this study, we investigated the ability of some natural compounds (oxyprenylated ferulic acid and umbelliferone derivatives) and their semisynthetic analogues (e.g., differently substituted 7-alkoxycoumarins) to activate AhR, using a reporter luciferase assay. Among them, we found that 7-isopentenyloxycoumarin was the best AhR activator. Boropinic acid, 7-but-2'-enyloxycoumarin, 7-(2',2'-dimethyl-n-propyloxy)coumarin, 7-benzyloxycoumarin, and 7-(3'-hydroxymethyl-3'-methylallyloxy)coumarin were also active, although to a lesser extent. All the compounds were also analyzed for their ability to inhibit AhR activation, using a reference ligand, 6-formylindolo[3,2-b]carbazole. Data recorded in the present investigation pointed out the importance of a 3,3-dimethylallyloxy side chain attached to the coumarin ring core as a key moiety for AhR activation.

A consensus statement for the clinical use of the renal sodium-glucose co-transporter-2 inhibitor dapagliflozin in patients with type 2 diabetes mellitus

INTRODUCTION

The present review developed a clinical consensus based on a Delphi method on Dapagliflozin, a selective inhibitor of the renal sodium-glucose co-transporter-2 (SGLT2-I) in the treatment of patients with Type 2 diabetes mellitus. Areas covered: Panel members, using a 5-point scale, were asked to rate 9 statements on pharmakodinamic, mode of action on glycaemic and extra-glycaemic effects, and safety of dapaglifozin, Members also aimed to identify the patient most susceptible to the treatment with dapagliflozin . Expert commentary: Dapagliflozin is effective in lowering the plasma glucose concentration with a good safety profile. Dapagliflozin can be utilized in combination with all other antihyperglycaemic agents at all stages of the disease: however, a reduced GFR limits its efficacy. As for the other drugs of the class, Dapagliflozin positively modifies other risk factors for CV disease: these effects will be tested in the so far largest cardiovascular outcome trial for the SGLT2 inhibitors so far, the DECLARE trial, which will communicate whether this class of drugs will be disease-modifier in patients with type 2 diabetes also in primary prevention.

Acronychiabaueri Analogue Derivative-Loaded Ultradeformable Vesicles: Physicochemical Characterization and Potential Applications

Elastic and ultradeformable liposomes were synthesized and physicochemically characterized to make suitable topical formulations for delivering the anti-inflammatory and anticancer compound 3-(4'-geranyloxy-3'-methoxyphenyl)-2-trans-propenoic acid. The average sizes of elastic and ultradeformable liposomes are below 300 nm, while the size distribution and Z-potential are below 0.3 and - 25 mV, respectively. The presence of 3-(4'-geranyloxy-3'-methoxyphenyl)-2-trans-propenoic acid does not affect the physicochemical parameters of nanovesicles. Elastic and ultradeformable liposomes show a zero order release kinetic and are stable at room temperature for a long time with or without 3-(4'-geranyloxy-3'-methoxyphenyl)-2-trans-propenoic acid. The ultradeformable liposomes are more deformable than elastic liposomes. These differences may depend on sodium cholate derivatives making nanoformulations. The 3-(4'-geranyloxy-3'-methoxyphenyl)-2-trans-propenoic acid-loaded elastic and ultradeformable liposomes can provide innovative nanotherapeutics-based natural compounds for the potential treatment of cutanous inflammation.

Madagascine Induces Vasodilatation via Activation of AMPK

Madagascine (3-isopentenyloxyemodin) can be chemically synthesized or purified from several Rhamnus species, and it is found to have more potent biological activities than the parent compound emodin. The aim of this study is to characterize the vasodilatory effect of madagascine on vasoconstriction and sphingosylphosphorylcholine induced vasospasm in ex vivo and reveal the potential mechanisms in vitro. The effects of madagascine on vasoconstriction of rat mesenteric resistance arteries (MRAs) induced by K⁺, methoxamine, and endothelin-1 were, respectively, studied. The cholesterol-enriched porcine coronary vascular smooth muscle (VSM) strips were used to investigate the effects of madagascine on abnormal constriction induced by sphingosylphosphorylcholine (SPC) which has a pivotal role in vasospasm. The vasodilatory effect was induced by madagascine (0.3-100 μM) in isolated rat MRAs and the vasodilatory effect was blocked by NO synthase inhibitor L-NAME and AMPK inhibitor compound C. Madagascine (10 μM) also significantly relaxed the abnormal constriction in porcine VSM induced by SPC and the effect was abolished by compound C. Madagascine significantly increased the phosphorylation of endothelial nitric oxide synthase (eNOS) in endothelial cells while decreasing the phosphorylation of myosin phosphatase target subunit 1 (MYPT1) in VSM cells. Madagascine-induced vasodilatation was abrogated using small interfering RNA knockdown of AMPK. In summary, madagascine exerted vasodilatation through activating AMPK, leading to the activation of eNOS in endothelium and inhibition of ROCK/MYPT1 in VSM. This study suggests the potential value of madagascine in amelioration of vasospasm related cardiovascular diseases.

Quantitative profiling of 4'-geranyloxyferulic acid and its conjugate with l-nitroarginine methyl ester in mononuclear cells by high-performance liquid chromatography with fluorescence detection

Oxyprenylated natural products were shown to exert in vitro and in vivo remarkable anti-cancer and anti-inflammatory effects. This paper describes a rapid, selective, and sensitive HPLC method with fluorescence detection for determination of 4'-geranyloxyferulic acid (GOFA) and its conjugate with l-nitroarginine methyl ester (GOFA-L-NAME) in mononuclear cells. Analytes were extracted from cells using methanol and eluted on a GraceSmart RP₁₈ analytical column (250×4.6mm i.d., 5μm particle size) kept at 25°C. A mixture of formic acid 1% in water (A) and methanol (B) were used as mobile phase, at a flow-rate of 1.2mL/min in gradient elution. A fluorescence detector (excitation/emission wavelength of 319/398nm for GOFA and GOFA-L-NAME), was used for the two analytes. Calibration curves of GOFA and GOFA-L-NAME were linear over the concentration range of 1.0-50μg/mL, with correlation coefficients (r²)≥0.9995. Intra- and inter-assay precision do not exceed 6.8%. The accuracy was from 94% to 105% for quality control samples (2.0, 25.0 and 40μg/mL). The mean (RSD%) extraction recoveries (n=5) for GOFA and GOFA-L-NAME from spiked cells at 2.0, 25.0 and 40.0μg/mL were 92.4±1.5%, 94.7±0.9% and 93.8±1.1%, for GOFA and 95.3±1.2%, 94.8±1.0% and 93.9±1.3%, for GOFA-L-NAME. The limits of detection and quantification were 0.3μg/mL and 1.0μg/mL for GOFA and GOFA-L-NAME. This method was successfully applied to measure GOFA and GOFA-L-NAME concentrations in a mononuclear cells.

Auraptene and Other Prenyloxyphenylpropanoids Suppress Microglial Activation and Dopaminergic Neuronal Cell Death in a Lipopolysaccharide-Induced Model of Parkinson's Disease

In patients with Parkinson’s disease (PD), hyperactivated inflammation in the brain, particularly microglial hyperactivation in the substantia nigra (SN), is reported to be one of the triggers for the delayed loss of dopaminergic neurons and sequential motor functional impairments. We previously reported that (1) auraptene (AUR), a natural prenyloxycoumain, suppressed inflammatory responses including the hyperactivation of microglia in the ischemic brain and inflamed brain, thereby inhibiting neuronal cell death; (2) 7-isopentenyloxycoumarin (7-IP), another natural prenyloxycoumain, exerted anti-inflammatory and neuroprotective effects against excitotoxicity; and (3) 4′-geranyloxyferulic acid (GOFA), a natural prenyloxycinnamic acid, also exerted anti-inflammatory effects. In the present study, using an intranigral lipopolysaccharide (LPS)-induced PD-like mouse model, we investigated whether AUR, 7-IP, and GOFA suppress microglial activation and protect against dopaminergic neuronal cell death in the SN. We successfully showed that these prenyloxyphenylpropanoids exhibited these prospective abilities, suggesting the potential of these compounds as neuroprotective agents for patients with PD.

Randomized, double-blind, placebo-controlled trial to evaluate the effect of Helicobacter pylori eradication on glucose homeostasis in type 2 diabetic patients

BACKGROUND AND AIMS

Literature data suggest an association between Helicobacter pylori infection and glucose homeostasis. However, a causative link between them has not been demonstrated yet. The aim of this study is to investigate the effect of H. pylori eradication on glucose homeostasis in patients with type 2 diabetes.

METHODS AND RESULTS

A randomized, double-blind, placebo-controlled trial was conducted to investigate the effect of H. pylori eradication on glucose homeostasis in 154 patients with type 2 diabetes and who tested positive for H. pylori infection (mean age (SD), 63.1 (8.1) years). Subjects were assigned to H. pylori eradication treatment or placebo. Metabolic and inflammatory parameters were measured in all subjects at baseline and 4 weeks after the treatment. H. pylori eradication led to an improvement in glucose homeostasis, measured by HOMA-IR (p < 0.001) and KITT (0 = 0.041), due to the decrease in fasting insulin levels (p = 0.004). The results also showed that lower levels of inflammatory parameters were present after eradication.

CONCLUSION

To our knowledge this is the first randomized, double blind, controlled study where the effect of H. pylori eradication on glucose homeostasis in subjects with type 2 diabetes has been investigated. Our findings demonstrate that H. pylori eradication improves glucose homeostasis in patients with type 2 diabetes through a decrease in pro-inflammatory factors.

TRIAL REGISTRATION NUMBER

ACTRN12609000255280 (https://www.anzctr.org.au/).

Recent developments in the pharmacology of prenylated xanthones

Prenylated xanthones are secondary metabolites that are particularly common in plants belonging to the Clusiaceae family. Such compounds have been the focus intensive research because of their potential as biologically active agents. Here, we survey data published over the past decade relating to the properties of prenylated xanthones to provide a more detailed view of the potential of these naturally occurring compounds as therapeutic agents.

Extracellular microRNAs and endothelial hyperglycaemic memory: a therapeutic opportunity?

Type 2 diabetes mellitus (T2DM) is a major cause of cardiovascular (CV) disease. Several large clinical trials have shown that the risk for patients with diabetes of developing CV complications is only partially reduced by early, intensive glycaemic control and lifestyle interventions, and that such complications result from changes in complex, not fully explored networks that contribute to the maintenance of endothelial function. The accumulation of senescent cells and the low-grade, systemic, inflammatory status that accompanies aging (inflammaging) are involved in the development of endothelial dysfunction. Such phenomena are modulated by epigenetic mechanisms, including microRNAs (miRNAs). MiRNAs can modulate virtually all gene transcripts. They can be secreted by living cells and taken up in active form by recipient cells, providing a new communication tool between tissues and organs. MiRNA deregulation has been associated with the development and progression of a number of age-related diseases, including the enduring gene expression changes seen in patients with diabetes. We review recent evidence on miRNA changes in T2DM, focusing on the ability of diabetes-associated miRNAs to modulate endothelial function, inflammaging and cellular senescence. We also discuss the hypothesis that miRNA-containing extracellular vesicles (i.e. exosomes and microvesicles) could be harnessed to restore a 'physiological' signature capable of preventing or delaying the harmful systemic effects of T2DM.

A Novel Class of Emerging Anticancer Compounds: Oxyprenylated Secondary Metabolites from Plants and Fungi

O-Prenyl secondary metabolites (3,3-dimethylallyl, geranyl-, farnesyl- and related biosynthetic derivatives) represent a class of rarely occurring natural products. In the last two decades such compounds have been found to exert promising and effective pharmacological activities, mainly in terms of anti-cancer properties. To date about 350 oxyprenylated secondary metabolites, the most part of which having a phenylpropanoid or a polyketide core, have been extracted from plants mainly belonging to the Rutaceae, Apiaceae, and Fabaceae families, and from fungi and bacteria. The aim of this comprehensive review is to make a survey of the in so far reported literature citations about O-prenyl secondary metabolites exhibiting in vitro and in vivo anti-cancer properties from phytochemical and pharmacological point of views.