Growth inhibitory activities of oxyprenylated and non-prenylated naturally occurring phenylpropanoids in cancer cell lines

Novel procedures for olive leaves extracts processing: Selective isolation of oleuropein and elenolic acid

Several processes have been developed in the past to selectively extract oleuropein and its aglycones from olive derived materials. In the present manuscript, we outline a novel approach for processing olive leaves aqueous extracts. This allowed first to select microwave irradiation as the methodology able to provide a large enrichment in oleuropein. Subsequently, the use of lamellar solids led to the selective and high yield concentration of the same. Adsorption on solids also largely contributed to the long term chemical stability of oleuropein. Finally, an eco-friendly, readily available, and reusable catalyst like H2SO4 supported on silica was applied for the hydrolysis of oleuropein into hydroxytyrosol and elenolic acid. This latter was in turn selectively isolated by an acid-base work-up providing its monoaldehydic dihydropyran form (7.8 % extractive yield), that was unequivocally characterized by GC-MS. The isolation of elenolic acid in pure form is described herein for the first time.

Novel insights into the biomolecular mechanism of action of 4'-geranyloxyferulic acid, a colon cancer chemopreventive agent

In this manuscript the biomolecular mechanism of action of the natural colon cancer chemopreventive agent 4'-geranyloxyferulic acid in cultured Caco-2 cells has been investigated. It was first demonstrated how the application of this phytochemical led to a time- and dose-dependent decrease of cell viability and in parallel to a massive generation of reactive oxygen species and induction of caspases 3 and 9, finally providing apoptosis. This event is accompanied by deep modifications in key pro-apoptotic targets like CD95, DR4 and 5, cytochrome c, Apaf-1, Bcl-2, and Bax. Such effects can explain the large apoptosis recorded in Caco-2 cells treated with 4'-geranyloxyferulic acid.

FXR agonists for colorectal and liver cancers, as a stand-alone or in combination therapy

Farnesoid X receptor (FXR, NR1H4) is generally considered as a tumor suppressor of colorectal and liver cancers. The interaction between FXR, bile acids (BAs) and gut microbiota is closely associated with an increased risk of colorectal and liver cancers. Increasing evidence shows that FXR agonists may be potential therapeutic agents for colorectal and liver cancers. However, FXR agonists alone do not produce the desired results due to the complicated pathogenesis and single therapeutic mechanism, which suggests that effective treatments will require a multimodal approach. Based on the principle of improvingefficacy andreducingside effects, combination therapy is currently receiving considerable attention. In this review, colorectal and liver cancers are grouped together to discuss the effects of FXR agonists alone or in combination for combating the two cancers. We hope that this review will provide a theoretical basis for the clinical application of novel FXR agonists or combination with FXR agonists against colorectal and liver cancers.

Therapeutic Effects of Coumarins with Different Substitution Patterns

The use of derivatives of natural and synthetic origin has gained attention because of their therapeutic effects against human diseases. Coumarins are one of the most common organic molecules and are used in medicine for their pharmacological and biological effects, such as anti-inflammatory, anticoagulant, antihypertensive, anticonvulsant, antioxidant, antimicrobial, and neuroprotective, among others. In addition, coumarin derivates can modulate signaling pathways that impact several cell processes. The objective of this review is to provide a narrative overview of the use of coumarin-derived compounds as potential therapeutic agents, as it has been shown that substituents on the basic core of coumarin have therapeutic effects against several human diseases and types of cancer, including breast, lung, colorectal, liver, and kidney cancer. In published studies, molecular docking has represented a powerful tool to evaluate and explain how these compounds selectively bind to proteins involved in various cellular processes, leading to specific interactions with a beneficial impact on human health. We also included studies that evaluated molecular interactions to identify potential biological targets with beneficial effects against human diseases.

Protection of Mitochondrial Potential and Activity by Oxyprenylated Phenylpropanoids

A series of five naturally occurring oxyprenylated phenylpropanoids, namely, the coumarins auraptene (7-geranyloxycoumarin) 1 and 7-isopentenyloxycoumarin 2, and the coumaric acid and ferulic acid derivatives, 4'-isopentenyloxycoumaric acid 3, boropinic acid 4, and 4'-geranyloxyferulic acid 5 were tested for their effects on mitochondrial functionality using the organophosphate pesticides glyphosate and chlorpyrifos, and resveratrol, as the reference. While not showing an appreciable in vitro antioxidant activity, and virtually no or a little effect on the viability of non-cancer cell lines BEAS-2B and SHSY-5Y, all phytochemicals exhibited a marked protective effect on mitochondrial potential and activity, with values that were comparable to resveratrol. Auraptene 1 and 7-isopentenyloxycoumarin 2 were seen to be the most effective secondary metabolite to this concern, in particular in being able to completely abolish the decrease of mitochondrial potential induced by increasing concentration of both glyphosate and chlorpyrifos. All the compounds tested also exhibited a protective effect on mitochondrial activity. The potency displayed will shed more light on the molecular basis of the beneficial effects of auraptene, 7-isopentenyloxycoumarin, and structurally related oxyprenylated phenylpropanoids reported to date in the literature.

Natural Products Targeting Liver X Receptors or Farnesoid X Receptor

Nuclear receptors (NRs) are a superfamily of transcription factors induced by ligands and also function as integrators of hormonal and nutritional signals. Among NRs, the liver X receptors (LXRs) and farnesoid X receptor (FXR) have been of significance as targets for the treatment of metabolic syndrome-related diseases. In recent years, natural products targeting LXRs and FXR have received remarkable interests as a valuable source of novel ligands encompassing diverse chemical structures and bioactive properties. This review aims to survey natural products, originating from terrestrial plants and microorganisms, marine organisms, and marine-derived microorganisms, which could influence LXRs and FXR. In the recent two decades (2000-2020), 261 natural products were discovered from natural resources such as LXRs/FXR modulators, 109 agonists and 38 antagonists targeting LXRs, and 72 agonists and 55 antagonists targeting FXR. The docking evaluation of desired natural products targeted LXRs/FXR is finally discussed. This comprehensive overview will provide a reference for future study of novel LXRs and FXR agonists and antagonists to target human diseases, and attract an increasing number of professional scholars majoring in pharmacy and biology with more in-depth discussion.

Screening of in vitro and in silico α-amylase, α-glucosidase, and lipase inhibitory activity of oxyprenylated natural compounds and semisynthetic derivatives

Metabolic syndrome has several characteristic manifestations, including insulin resistance and dyslipidaemia, that demand therapeutic approaches, such as the inhibition of enzymes involved in nutrient absorption and digestion.This study aimed to evaluate the potential pharmacological use of natural compounds widespread in the plant kingdom and their semisynthetic compounds against target enzymes. Twenty-three oxyprenylated natural compoundswere investigated for their ability to inhibit α-amylase, α-glucosidase, and pancreatic lipase enzymes by in vitro assays. Moreover, in silico molecular docking was performed to analyse their binding capabilities into 3D structures. Farnesyloxyferulic acid, geranyloxyvanillic acid, nelumal A, and geranyloxyferulic acid showed the highest inhibition activity in all three in vitro enzyme assays. Moreover, in silico molecular docking of these four compounds was used to analyse their possible binding in 3D structures of the investigated enzymes. The results indicate that these compounds have considerable therapeutic potential for the treatment of metabolic syndrome, and further studies are warranted for their pharmacological development.

Novel FXR agonist nelumal A suppresses colitis and inflammation-related colorectal carcinogenesis

FXR is a member of the nuclear receptor superfamily and bile acids are endogenous ligands of FXR. FXR activation has recently been reported to inhibit intestinal inflammation and tumour development. This study aimed to investigate whether the novel FXR agonist nelumal A, the active compound of the plant Ligularia nelumbifolia, can prevent colitis and colorectal carcinogenesis. In a mouse colitis model, dextran sodium sulfate-induced colonic mucosal ulcer and the inflammation grade in the colon significantly reduced in mice fed diets containing nelumal A. In an azoxymethane/dextran sodium sulfate-induced mouse inflammation-related colorectal carcinogenesis model, the mice showed decreased incidence of colonic mucosal ulcers and adenocarcinomas in nelumal A-treated group. Administration of nelumal A also induced tight junctions, antioxidant enzymes, and FXR target gene expression in the intestine, while it decreased the gene expression of bile acid synthesis in the liver. These findings suggest that nelumal A effectively attenuates colonic inflammation and suppresses colitis-related carcinogenesis, presumably through reduction of bile acid synthesis and oxidative damage. This agent may be potentially useful for treatment of inflammatory bowel diseases as well as their related colorectal cancer chemoprevention.

Ultrasound assisted synthesis and cytotoxicity evaluation of known 2',4'-dihydroxychalcone derivatives against cancer cell lines

This work reports on the development of an efficient and ecofriendly ultrasound assisted method for the high yield synthesis (70.0-94.0%) of eighteen oxyalkylated derivatives of 2',4'-dihydroxychalcone. Synthesized compounds were subjected to in vitro biological assays against HT-29 (colorectal), MCF-7 (breast), and PC-3 (prostate) human tumor cell lines, these cell lines are among the ten most aggressive malignancies diagnosed in the world. Cytotoxicity evaluations showed that four of the synthesized compounds exhibited moderate to very high toxic activity against MCF-7 (IC₅₀ = 8.4-34.3 μM) and PC-3 (IC₅₀ = 9.3-29.4 μM) - comparable to 5-fluorouracil (IC₅₀ 16.4-22.3 μM). The same compounds only showed moderate activity against HT-29 (IC₅₀ 15.3-36.3 μM), closer to daunorubicin (IC₅₀ 15.1 μM). Next, although selectivity index (SI) of compounds was weak, compound 18 exhibited a remarkable and selective cytotoxic activity (5.8-10.57) against cancer cells. Outside of these, most compounds significantly reduced cell survival, increased reactive oxygen species (ROS) and caspase activity, and decreased mitochondrial membrane permeability. In this sense, a portion of anti-proliferative activity is due to apoptosis. Notwithstanding, due to its remarkable response, chalcone 18 may be a potential alternative as a chemotherapeutic anti-carcinogen.

7-Isopentenyloxycoumarin: What Is New across the Last Decade

7-Isopentenyloxycoumarin is among the most widespread naturally occurring prenyloxy umbelliferone derivatives. This secondary metabolite of mixed biosynthetic origin has been typically isolated from plants belonging to several genera of the Rutaceae and Apiaceae families, comprising widely used medicinal plants and in general plants with beneficial effects on human welfare, as well as edible fruits and vegetables. Although known for quite a long time (more than 50 years), only in the last two decades has this natural compound been revealed to exert powerful and promising pharmacological properties, such as active cancer chemopreventive, antibacterial, antiprotozoal, antifungal, anti-inflammatory, neuroprotective, and antioxidant properties, among the activities best outlined in the recent literature. The aim of this comprehensive miniature review article is to detail the novel natural sources and the effects described during the last decade for 7-isopentenyloxycoumarin and what has been reported on the mechanisms of action underlying the observed biological activities of this oxyprenylated secondary metabolite. In view of the herein described data, suggestions on how to address future research on the abovementioned natural product and structurally related derivatives in the best ways according to the authors will be also provided.

Biologically Active Compounds of Plants: Structure-Related Antioxidant, Microbiological and Cytotoxic Activity of Selected Carboxylic Acids

Natural carboxylic acids are plant-derived compounds that are known to possess biological activity. The aim of this review was to compare the effect of structural differences of the selected carboxylic acids (benzoic acid (BA), cinnamic acid (CinA), p-coumaric acid (p-CA), caffeic acid (CFA), rosmarinic acid (RA), and chicoric acid (ChA)) on the antioxidant, antimicrobial, and cytotoxic activity. The studied compounds were arranged in a logic sequence of increasing number of hydroxyl groups and conjugated bonds in order to investigate the correlations between the structure and bioactivity. A review of the literature revealed that RA exhibited the highest antioxidant activity and this property decreased in the following order: RA > CFA ~ ChA > p-CA > CinA > BA. In the case of antimicrobial properties, structure-activity relationships were not easy to observe as they depended on the microbial strain and the experimental conditions. The highest antimicrobial activity was found for CFA and CinA, while the lowest for RA. Taking into account anti-cancer properties of studied NCA, it seems that the presence of hydroxyl groups had an influence on intermolecular interactions and the cytotoxic potential of the molecules, whereas the carboxyl group participated in the chelation of endogenous transition metal ions.

Anti-Migratory Effects of 4'-Geranyloxyferulic Acid on LPS-Stimulated U937 and HCT116 Cells via MMP-9 Down-Regulation: Involvement of ROS/ERK Signaling Pathway

Matrix metalloproteinases (MMPs) play a crucial role in tumor angiogenesis, and metastasis. 4'-geranyloxyferulic acid (GOFA) has anti-tumor and anti-inflammatory proprieties. Herein, we aimed to determine whether this compound affects cell survival, invasion, and migration through reactive oxygen species (ROS)-mediated MMPs activation of extracellular signal-regulated kinases (ERKs) and p38 signaling in lymphocytic histiocytoma (U937) and colorectal cancer (HCT116) cells. We observed that lipopolysaccharide (LPS) stimulated U937 and HCT116 cells presented abnormal cell proliferation and increased metalloproteinase (MMP-9) activity and expression. Non-cytotoxic doses of GOFA blunted matrix invasive potential by reducing LPS-induced MMP-9 expression and cell migration via inhibiting ROS/ ERK pathway. GOFA also attenuated apoptosis and cell senescence. Our findings indicate that GOFA, inhibiting cancer cell proliferation and migration, could be therapeutically beneficial to prevent tumor metastasis.

Modulation of CAT-2B-Mediated l-Arginine Uptake and Nitric Oxide Biosynthesis in HCT116 Cell Line Through Biological Activity of 4'-Geranyloxyferulic Acid Extract from Quinoa Seeds

Chenopodium quinoa Wild is a “pseudocereal” grain which attracts a lot of attention in the scientific community as it has a positive effect on health. Here, we investigate the presence of biologically active O-prenylated phenylpropanoids in the ethanol extract of commercially available quinoa seeds. We claim that 4′-Geranyloxyferulic acid (GOFA) was the only phytochemical product found that belongs to quinoa’s group secondary metabolites. We studied the changes in the oxidative and inflammatory status of the cellular environment in HCT 116 cell line processed with quinoa extract and its component GOFA; the implementation was done through the analysis of the antioxidant enzymes (SOD and CAT), the pro-inflammatory components (iNOS, IL-6 and TNF-α), and the products of intermediary metabolism (ONOO⁻, O₂⁻). Moreover, the l-arginine uptake was proposed as a target of the tested compounds. We demonstrated that the GOFA, through a decrease of the CAT-2B expression, leads to a reduction of the l-arginine uptake, downregulating the harmful iNOS and restoring the altered redox state. These results propose a new molecular target involved in the reduction of the critical inflammatory process responsible for the cancer progression.

HPLC Analysis and Skin Whitening Effects of Umbelliprenin-containing Extracts of Anethum Graveolens, Pimpinella Anisum, and Ferulago Campestris

Umbelliprenin has recently been shown to have great potential as a skin whitening agent. Wishing to investigate the same effect in plant species known to biosynthesize this coumarin, three plants belonging to the Apiaceae family, namely Anethum graveolens L. (dill), Pimpinella anisum L. (anise), and Ferulago campestris (Besser) Grecescu (field ferula) were screened by HPLC analysis for their respective content of umbelliprenin in extracts obtained with different solvent mixtures and by maceration and ultrasound-assisted processes. EtOH was shown to be the best solvent, providing umbelliprenin yields ranging from 1.7% to 14.4% (with respect to the total amount of extract obtained). Extracts with the highest content of this farnesyloxycoumarin were then assayed as modulators of melanogenesis in cultured murine Melan A cells employing the same umbelliprenin obtained by chemical synthesis as the reference. A parallelism between the content of the coumarin and the recorded depigmenting effect (60% for the EtOH extract of F. campestris as the best value) was revealed for all plants extracts when applied at a dose of 100 μg/mL. Our results demonstrate that the same potential of umbelliprenin can be ascribed also to umbelliprenin-enriched plant extracts which reinforces enforce the widespread use of phyto-preparations for cosmetic purposes (e.g., A. graveolens).

Biomolecular Targets of Oxyprenylated Phenylpropanoids and Polyketides

Oxyprenylated secondary metabolites (e.g. phenylpropanoids and polyketides) represent a rare class of natural compounds. Over the past two decades, this group of phytochemicals has become a topic of intense research activity by several teams worldwide due to their in vitro and in vivo pharmacological activities, and to their great therapeutic and nutraceutical potential for the chemoprevention of acute and chronic diseases affecting humans. Such investigations have provided evidence that oxyprenylated secondary metabolites are able to interact with several biological targets at different levels accounting for their observed anticarcinogenic, anti-inflammatory, neuroprotective, immunomodulatory, antihypertensive, and metabolic effects. The aim of the present contribution is to provide a detailed survey of the so far reported data on the capacities of selected oxyprenylated phenylpropanoids and polyketides to trigger receptors, enzymes, and other types of cellular factors for which they exhibit a high degree of affinity and therefore evoke specific responses. With respect to the rather small amounts of these compounds available from natural sources, their chemical synthesis is also highlighted.

Natural products as modulators of the nuclear receptors and metabolic sensors LXR, FXR and RXR

Nuclear receptors (NRs) represent attractive targets for the treatment of metabolic syndrome-related diseases. In addition, natural products are an interesting pool of potential ligands since they have been refined under evolutionary pressure to interact with proteins or other biological targets. This review aims to briefly summarize current basic knowledge regarding the liver X (LXR) and farnesoid X receptors (FXR) that form permissive heterodimers with retinoid X receptors (RXR). Natural product-based ligands for these receptors are summarized and the potential of LXR, FXR and RXR as targets in precision medicine is discussed.

Chemical characterization and cytotoxic, genotoxic, and mutagenic properties of Baccharis trinervis (Lam, Persoon) from Colombia and Brazil

PHARMACOLOGY RELEVANCE

Baccharis trinervis (Lam, Persoon) leaves are used in the traditional medicine for the treatment of high fevers, edema, inflammation, sores and muscle cramps, snakebites and as antiseptic.

AIM OF THE STUDY

To investigate the cytotoxic, genotoxic, and mutagenic effects of extracts and fractions of B. trinervis from Brazil and Colombia in Chinese Hamster Ovary (CHO) cells, and to examine the mutagenic activity in Salmonella typhimurium.

MATERIAL AND METHODS

Aqueous extracts (AE) of aerial parts of B. trinervis from Brazil (B) and Colombia (C) were fractioned in ethyl acetate fraction (EAF), butanol extract (BF), and aqueous residue fraction (ARF). Qualitative chemical screening and determination of total flavonoid content were made. Identification of chemical constituents was performed by High Performance Liquid Chromatography (HPLC) and High Resolution Mass Spectrometry (HRMS). For the in vitro tests, CHO cells were treated for 3h with extracts and fractions. The cytotoxic activity was evaluated by clonal survival and 3-(4.5-dimethylthiazole-2-yl)-2.5-biphenyl tetrazolium bromide reduction assay (MTT). Genotoxic and mutagenic effects were evaluated by the alkaline comet assay and Cytokinesis-blockage micronucleus test (CBMN), respectively. Additionally, Salmonella/microsome assay was carried out to determinate the mutagenic effects in EAF from Brazil and Colombia.

RESULTS

Phytochemical analyses indicated the presence of saponins and flavonoids. AE and EAF were the samples with the highest quantity of total flavonoids. HPLC showed the presence of luteolin only in AEC, and caffeic acid, ellagic acid, rosmarinic acid, and rutin were identified in AEB and AEC (AEC>AEB). The HRMS in positive mode of EAFB and EAFC showed presence of two carboxylic acids, coumarin, and two terpenoids. In addition, were identified one terpenoid and two carboxylic acids in AE, BF and ARF of B. trinervis from both countries in negative mode. Dose-dependent cytotoxic effects were observed in CHO cells treated with B. trinervis extracts and fractions by using clonal survival and MTT at concentrations higher than 0.05mg/mL. All the extracts and fractions induced DNA strand breaks in CHO cells with dose-dependent response, mostly EAFB and EAFC. The EAF from Brazil and Colombia showed mutagenic effect at 0.5mg/mL, while the other fractions did not show a significant difference in relation to the control. No mutagenic effects were found in EAF from both countries by the Salmonella/microsome assay.

CONCLUSIONS

Cytotoxic and genotoxic effects were demonstrated in all extracts and fractions used, although only EAF showed mutagenic effects by CBMN, but not by Salmonella/microsome assay. Our results suggest that flavonoids, phenylpropanoids, coumarins, and diterpenes may be responsible for the cytotoxic, genotoxic and mutagenic effects observed.

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.

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.

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.

Coumarin derivatives as potential antitumor agents: Growth inhibition, apoptosis induction and multidrug resistance reverting activity

A small library of coumarins, carrying butynyl-amino chains, was synthesized continuing our studies in the field of MDR reverting ageEnts and in order to obtain multipotent agents to combat malignancies. In particular, the reported anticancer and chemopreventive natural product 7-isopentenyloxycoumarin was linked to different terminal amines, selected on the basis of our previously reported results. The anticancer behaviour and the MDR reverting ability of the new compounds were evaluated on human colon cancer cells, particularly prone to develop the MDR phenotype. Some of the new derivatives showed promising effects, directly acting as cytotoxic compounds and/or counteracting MDR phenomenon. Compound 1e emerged as the most interesting of this series, showing a multipotent biological profile and suggesting that conjugation of an appropriate coumarin core with a properly selected butynyl-amino chain allows to obtain novel hybrid molecules endowed with improved in vitro antitumor activity.

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.

Synthesis and Evaluation of Novel Oxyalkylated Derivatives of 2',4'-Dihydroxychalcone as Anti-Oomycete Agents against Bronopol Resistant Strains of Saprolegnia sp

A series of novel oxyalkylchalcones substituted with alkyl groups were designed and synthesized, and the antioomycete activity of the series was evaluated in vitro against Saprolegnia strains. All tested O-alkylchalcones were synthesized by means of nucleophilic substitution from the natural compound 2′,4′-dihydroxychalcone (1) and the respective alkyl bromide. The natural chalcone (1) and 10 synthetic oxyalkylchalcones (2–11) were tested against Saprolegnia parasitica and Saprolegnia australis. Among synthetic analogs, 2-hydroxy,4-farnesyloxychalcone (11) showed the most potent activity against Saprolegnia sp., with MIC and MOC values of 125 µg/mL (similar to bronopol at 150 µg/mL) and 175 µg/mL, respectively; however, 2′,4′-dihydroxychalcone (1) was the strongest and most active molecule, with MIC and MOC values of 6.25 µg/mL and 12.5 µg/mL.

Plumbagin, Juglone, and Boropinal as Novel TRPA1 Agonists

A series of seven oxyprenylated phenylpropanoids and naphthoquinones were tested regarding their ability to activate transient receptor potential ankyrin subtype 1 channel (TRPA1). Three of the assayed compounds, namely, boropinal (3), juglone (5), and plumbagin (7), acted as strong modulators of TRPA1 channels with EC50 values of 9.8, 1.7, and 0.5 μM, respectively, as assessed by Ca(2+) assays. Moreover, the compounds elicited TRPA1 currents in electrophysiological whole cell recordings. We additionally provide evidence that plumbagin activated TRPA1-positive neurons isolated from mouse dorsal root ganglion neurons but did not affect sensory neurons from TRPA1-deficient mice. The high potencies of plumbagin and juglone to activate TRPA1 channels may explain the molecular basis of the mucosal irritant properties of these compounds as well as of related naphthoquinones and phytopreparations, as widely reported in the literature.

Cytotoxic Activity of Lomatiol and 7-(3′-Hydroxymethyl-3′-methylallyloxy)coumarin

7-(3′-Hydroxymethyl-3′-methylallyloxy)coumarin, bearing a 3′-hydroxy-3′-methylallyl group as the O-side chain, and lomatiol, a lapachol derivative sharing the same structural feature, were tested for their in vitro growth inhibitory activities on six cancer cell lines using the MTT colorimetric assay, along with the respective 3′,3′-dimethylallyl derivatives and unprenylated products used for comparison. Data revealed that lomatiol displayed the strongest growth inhibitory activities in vitro although not as efficient as the parent compound lapachol. The oxidized O-prenylcoumarin recorded better growth inhibitory capacities than the prenylated and unprenylated parent products.

Cytotoxic Evaluation against Breast Cancer Cells of Isoliquiritigenin Analogues from Spatholobus suberectus and Their Synthetic Derivatives

Five isoliquiritigenin analogues, including a new methylene-bridged bischalcone (1), were isolated from Spatholobus suberectus. Cytotoxicity screening of these isolates and several synthetic derivatives indicated that the introduction, removal, position modification, or glycosylation of hydroxy groups in isoliquiritigenin did not improve the resultant cytotoxicity against the MCF-7 and MDA-MB-231 human breast cancer cell lines. In addition, cyclization of OH-2' chalcones or reduction of the α,β-unsaturated carbonyl double bond decreased such cytotoxicity substantially. However, methylation of hydroxy groups resulted in a marked increase in such cytotoxic activity. Among these active isoliquiritigenin analogues, 3',4',5',4″-tetramethoxychalcone (3h) was obtained as a compound with promising cytotoxic activity.

Complexes of Lapachol and Lawsone with Lanthanides

Naturally occurring 2-hydroxy-1,4-naphthoquinones are well known to form readily stable complexes with transition metals. In this short communication we describe for the first time the synthesis and preliminary data about structural characterization of complexes between two naturally widespread 2-hydroxy-1,4-naphthoquinones, namely lapachol (1) and lawsone (2), with selected lanthanides like lanthanum, gadolinium, and ytterbium. When tested as cytotoxic compounds, such complexes exhibited an activity that was either higher or equal to that of the parent naphthoquinone.

Inhibition of Soybean 15-Lipoxygenase by Naturally Occurring Acetophenones and Derricidin

Three selected naturally occurring oxyprenylated secondary metabolites, namely 2-hydroxy4-isopentenyloxyacetophenone (1), 4-geranyloxy-2-hydroxyacetophenone (2), 4-farnesyloxyacetophenone (3), and derricidin (4) were synthesized and their inhibitory potency against soybean 15-lipoxygenase evaluated. Compounds 1 and 4 showed the most potent inhibitory activity with IC50 values of 2.5 μM and 0.6 μM.

Screening for novel plant sources of prenyloxyanthraquinones: Senna alexandrina Mill. and Aloe vera (L.) Burm. F

As a continuation of our ongoing studies aimed to reveal the presence of oxyprenylated anthraquinones in plants claimed to have a laxative effect, in this article, we describe the extraction and HPLC separation of madagascin (3-isopentenyloxyemodin) and 3-geranyloxyemodine from dried leaves and fruits of Senna alexandrina Mill. (Leguminosae) and leaves and gel of Aloe vera (L.) Burm. F. (Xanthorrhoeaceae). Both compounds are described herein for the first time as components of extracts of the title plants.

Antibacterial Activities of Oxyprenylated Chalcones and Napthtoquinone against Helicobacter pylori

In this study, we synthesized and characterized the antibacterial activity of three naturally occurring oxyprenylated chalcones {xinjiachalcone A (1), (2 E)-1-{2,6-dihydroxy-4-[(3-methylbut-2-enyl)oxy]phenyl}-3-(4-hydroxyphenyl)prop-2-en-1-one (2), (2 E)-1-{2,6-dihydroxy-4-[(3-methylbut-2-enyl)oxy]phenyl}-3-phenylprop-2-en-1-one (3), and lawsone 2-isopentenyl ether (4)}. Using several strains of Helicobacter pylori, including clinical ones, minimum inhibitory concentration (MIC) values and bactericidal activities of these compounds were determined. Xinjiachalcone A (1), active principle of Glycyrrhiza inflata Batalin, was the most effective compound, showing both a low MIC and a strong bactericidal activity against H. pylori. This study suggests that these compounds represent potential natural molecules for the prevention and treatment of H. pylori associated diseases.

Synthesis and anti-cancer activity of naturally occurring 2,5-diketopiperazines

Three naturally occurring oxyprenylated diketopiperazines were synthesized and preliminarily tested as growth inhibitory agents in vitro against various cancer cell lines. The compounds were tested on six human cancer cell lines with different sensitivity to proapoptotic stimuli using the MTT colorimetric assay. The data revealed that of the chemicals under study only deoxymicelianamide (11) displayed the highest activity, recording mean IC50 growth inhibitory values ranging from 2 to 23 μM. A comparative study with the non-geranylated saturated derivative of (11) revealed the importance of the presence of the geranyloxy side chain and the exocyclic 2,5-DPK double bond moiety for the observed activity.

The cytotoxic activities of 7-isopentenyloxycoumarin on 5637 cells via induction of apoptosis and cell cycle arrest in G2/M stage

BACKGROUND

Bladder cancer is the second common malignancy of genitourinary tract, and transitional cell carcinomas (TCCs) account for 90% of all bladder cancers. Due to acquired resistance of TCC cells to a wide range of chemotherapeutic agents, there is always a need for search on new compounds for treatment of these cancers. Coumarins represent a group of natural compounds, which some of them have exerted valuable anti-tumor activities. The current study was designed to evaluate anti-tumor properties and mechanism of action of 7-isopentenyloxycoumarin, a prenyloxycoumarin, on 5637 cells (a TCC cell line).

RESULTS

MTT results revealed that the cytotoxic effects of 7-isopentenyloxycoumarin on 5637 cancerous cells were more prominent in comparison to HDF-1 normal cells. This coumarin increased the amount of chromatin condensation and DNA damage in 5637 cells by 58 and 33%, respectively. The results also indicated that it can induce apoptosis most probably via activation of caspase-3 in these cells. Moreover, propidium iodide staining revealed that 7-isopentenyloxycoumarin induced cell cycle arrest at G2/M stage, after 24 h of treatment.

CONCLUSION

Our results indicated that 7-isopentenyloxycoumarin had selective toxic effects on this bladder cancer cell line and promoted its effects by apoptosis induction and cell cycle arrest. This coumarin can be considered for further studies to reveal its exact mechanism of action and also its anti-cancer effects in vivo.

In Vitro Anti-proliferative Effect of Naturally Occurring Oxyprenylated Chalcones

As a continuation of our ongoing studies aimed to depict the effects and mechanism of action of naturally occurring oxyprenylated phenylpropanoids and polyketides, in this paper we describe the synthesis and in vitro anti-proliferative effects of selected compounds belonging to the above cited classes of secondary metabolites on six cancer cell lines using the MTT colorimetric assay. Our study revealed that among the natural products tested, only oxyprenylated chalcones exhibited an appreciable effect (mean IC50 = 32 - 64 μM), while substituted alcohols, phenylpropenes, naphthoquinones, and aminoacid derivatives were by far less active or inactive.

Anti-Helicobacter Pylori Activities of Natural Isopentenyloxycinnamyl Derivatives from Boronia Pinnata

In this study we investigated the anti- Helicobacter pylori activity of four isopentenyloxycinnamyl derivatives from the Australian shrub Boronia pinnata Sm. (Rutaceae), structurally related to boropinic acid: ( E)-3-(4-(3-methylbut-2-enyloxy)-3,5-dimethoxyphenyl)acrylaldehyde (1), boropinol C (2), boropinal (3) and boropinol A (4). In vitro growth of H. pylori strains 26695 and B128 was analyzed in liquid culture with increasing doses of these compounds. Bacterial morphology was visualized by scanning electron microscopy. The in vivo effects of the two most efficient molecules that reduced bacterial growth in vitro, compounds 3 and 4, were investigated on H. pylori gastric colonization in the mouse model. The presence of these compounds in the bacterial cultures led to alterations of bacterial surface and flagella. In vivo, both compounds 3 and 4 at 250 μM reduced significantly the ability of H. pylori to colonize the gastric mucosa of mice, compared with untreated ones. These data indicate that these natural isopentenyloxycinnamyl derivatives related to boropinic acid can be considered as novel antibacterial agents with anti- H. pylori activity.

Re-investigation of the Anthraquinone Pool of Rhamnus spp.: Madagascin from the Fruits of Rhamnus cathartica and R. intermedia

As a continuation of our ongoing studies aimed at revealing the presence of oxyprenylated anthraquinones in plants belonging to the genus Rhamnus, in this paper we describe the extraction and HPLC separation of madagascin (3-isopentenyloxyemodin) from the fruits of R. cathartica L. and R. intermedia Steud. & Hochst. The title compound is described herein for the first time as a component of fruit extracts of Rhamnus species.

Synthesis and antimicrobial activity of geranyloxy- and farnesyloxy-acetophenone derivatives against oral pathogens

The compounds 2',6'-dihydroxy-4'-geranyloxyacetophenone (1) and 2',6'-dihydroxy-4'-farnesyloxy-acetophenone (2) are oxyprenylated secondary metabolites extracted from plants belonging to the Rutaceae family. In this study, 1 and 2 were synthesized and tested for their antimicrobial activity toward major oral pathogens. Compounds 1 and 2 were synthesized by selective prenylation of 2,4,6-trihydroxyacetophenone at the 4' position with geranyl and farnesyl bromide, respectively. Compound 1 showed stronger antimicrobial activity than 2 against major oral pathogens, including Gram positive bacteria (Streptococcus mutans, Streptococcus sobrinus), Gram negative bacteria (Prevotella intermedia, Porphyromonas gingivalis) and Candida albicans. Evidences were obtained that the mode of action of 1 and 2 may be related to their iron-chelating property. This study suggests that 1 and 2 may represent potential natural molecules for the prevention/treatment of common oral infections, including dental caries, periodontal disease, and candidiasis.