Cyclopentenediones, inhibitors of farnesyl protein transferase and anti-tumor compounds, isolated from the fruit of Lindera erythrocarpa Makino

Methyl lucidone inhibits airway inflammatory response by reducing TAK1 activity in human bronchial epithelial NCI-H292 cells

Background

Methyl lucidone (ML), a methyl derivative of lucidone, has anti-inflammatory properties. However, the molecular mechanisms that reduce the inflammatory effect of ML in human lung epithelial cells remain unkown. This study aimed to elucidate the molecular mechanisms underlying the anti-inflammatory effect of ML.

Methods

Four compounds (ML, methyl linderone, kanakugiol, and linderone) from Lindera erythrocarpa Makino were evaluated for their ability to reduce MUC5AC secretion levels in phorbol-12-myristate-13-acetate (PMA)-stimulated NCI-H292 cells using ELISA. The expression and secretion levels of inflammatory response-related proteins were analyzed using quantitative reverse transcription-PCR, ELISA, and western blotting. To determine whether ML directly regulates TGF-β-activated kinase 1 (TAK1), we performed an in vitro kinase assay.

Results

ML treatment effectively reduced the levels of inflammatory cytokines, including interleukin-1β and TNF-α, increased by stimulation. Furthermore, ML downregulated the pathway cascade of both IκB kinase (IKK)/NF-κB and p38 mitogen-activated protein (MAP) kinase/CREB by inhibiting the upstream kinase TAK1. An in vitro kinase analysis confirmed that ML treatment significantly reduced the kinase activity of TAK1.

Conclusion

ML pretreatment repressed the PMA-stimulated inflammation reaction by reducing the TAK1-mediated IKK/NF-κB and p38 MAP kinase/CREB signaling. These findings suggest that ML may improve respiratory health and can be used as a dietary supplement or functional food to prevent inflammatory lung diseases.

Lucidone inhibits autophagy and MDR1 via HMGB1/RAGE/PI3K/Akt signaling pathway in pancreatic cancer cells

Gemcitabine (GEM) drug resistance remains a difficult challenge in pancreatic ductal adenocarcinoma (PDAC) treatment. Therefore, identifying a safe and effective treatment strategy for PDAC is urgent. Lucidone is a natural compound extracted from the fruits of Lindera erythrocarpa Makino. However, the role of lucidone in PDAC inhibition remains unclear. In addition, high-mobility group box 1 (HMGB1) and receptor for advanced glycation end products (RAGE) are involved in multidrug resistance protein 1 (MDR1) regulation and GEM resistance. Thus, this study aimed to explore the function of lucidone in tumor cytotoxicity and chemosensitivity through the suppression of RAGE-initiated signaling in PDAC cells. The data showed that lucidone significantly promoted apoptotic cell death and inhibited the expression of autophagic proteins (Atg5, Beclin-1, LC3-II, and Vps34) and MDR1 by inhibiting the HMGB1/RAGE/PI3K/Akt axis in both MIA Paca-2 cells and MIA Paca-2GEMR cells (GEM-resistant cells). Notably, convincing data were also obtained in experiments involving RAGE-specific siRNA transfection. In addition, remarkable cell proliferation was observed after treatment with lucidone combined with GEM, particularly in MIA Paca-2GEMR cells, indicating that lucidone treatment enhanced chemosensitivity. Collectively, this study provided the underlying mechanism by which lucidone treatment inhibited HMGB1/RAGE-initiated PI3K/Akt/MDR1 signaling and consequently enhanced chemosensitivity in PDAC.

Natural Products Attenuating Biosynthesis, Processing, and Activity of Ras Oncoproteins: State of the Art and Future Perspectives

RAS genes encode signaling proteins, which, in mammalian cells, act as molecular switches regulating critical cellular processes as proliferation, growth, differentiation, survival, motility, and metabolism in response to specific stimuli. Deregulation of Ras functions has a high impact on human health: gain-of-function point mutations in RAS genes are found in some developmental disorders and thirty percent of all human cancers, including the deadliest. For this reason, the pathogenic Ras variants represent important clinical targets against which to develop novel, effective, and possibly selective pharmacological inhibitors. Natural products represent a virtually unlimited resource of structurally different compounds from which one could draw on for this purpose, given the improvements in isolation and screening of active molecules from complex sources. After a summary of Ras proteins molecular and regulatory features and Ras-dependent pathways relevant for drug development, we point out the most promising inhibitory approaches, the known druggable sites of wild-type and oncogenic Ras mutants, and describe the known natural compounds capable of attenuating Ras signaling. Finally, we highlight critical issues and perspectives for the future selection of potential Ras inhibitors from natural sources.

Methyl Linderone Suppresses TPA-Stimulated IL-8 and MMP-9 Expression Via the ERK/STAT3 Pathway in MCF-7 Breast Cancer Cells

Methyl linderone (ML), a cyclo-pentenedione, was isolated from the fruit of Lindera erythrocarpa Makino (family Lauraceae). This plant has well-known anti-inflammatory effects; however, the anti-cancer effects of ML have not yet been reported. Thus, in the present study we investigated the effects of ML on the metastasis of human breast cancer cells. We used 12-O-tetradecanoyl phorbol-13-acetate (TPA)-stimulated MCF-7 cells as the cell model to study the effects of ML on invasion and migration. ML was found to reduce the invasion and migration rate of TPA-stimulated MCF-7 cells. Moreover, it inhibited two metastasis-related factors, matrix metalloproteinase-9 (MMP-9) and interleukin-8 (IL-8), at the mRNA and protein expression levels, in TPA-treated MCF-7 cells. The mechanism by which ML exerted these effects was through the inhibition of translocation of activator protein-1 (AP-1) and signal transducer and activator of transcription-3 (STAT3), mediated via phosphorylation of extracellular signal-regulated kinase (ERK). Taken together, our findings indicated that ML attenuated the TPA-stimulated invasion and migration of MCF-7 cells by suppressing the phosphorylation of ERK and its downstream factors, AP-1 and STAT3. Therefore, ML is a potential agent for the treatment of breast cancer metastasis.

New Anti-inflammatory Flavonol Glycosides from Lindera akoensis Hayata

Inflammation is related to many diseases. Lindera akoensis Hayata was often used in folktherapy in Taiwan for inflammation. In this study, three new flavonol acyl glycosides, namelykaempferol-3-O--D-4",6"-di-(E)-p-coumaroylglucoside (1), 3"-(E)-p-coumaroylafzelin (2) and 40-Omethyl-2",4"-di-(E)-p-coumaroylquercitrin (3), and three components, 3-dodecyl-4-hydroxy-5-methyldihydrofuran-2-one (4), 2-acetoxyclovan-9-ol (5), (1,4,6)-trihydroxyeudesmane(6) that were isolated from the natural product for the first time were obtained along with 25 knowncompounds from L. akoensis. Their structures were determined by comprehensive spectroscopicanalyses (1D and 2D NMR, EI-, ESI- and HRESI-MS). The ability of 1 to decrease the LPS-stimulatedproduction of nitrite in RAW264.7 cell was evaluated, showing an IC50 value of 36.3 ± 3.2 μM.This result supports the value of L. akoensis as a traditional medicine resource.

Methyllucidone inhibits STAT3 activity by regulating the expression of the protein tyrosine phosphatase MEG2 in DU145 prostate carcinoma cells

During the search for signal transducer and activator of transcription 3 (STAT3) inhibitors from natural products, methyllucidone, isolated from Lindera species (Lauraceae), was identified as a STAT3 inhibitor. Methyllucidone inhibited STAT3 phosphorylation at tyrosine 705 in a dose- and time dependent manner in DU145 prostate cancer cells and suppressed IL-6-induced STAT3 phosphorylation at Tyr-705 in LNCaP cells. Methyllucidone decreased the expression levels of STAT3 target genes, such as cyclin D1, cyclin A, Bcl-2, Mcl-1, and survivin. Methyllucidone inhibited DU145 cell growth and induced apoptosis by arresting the cell cycle at G1 phase. Notably, knockdown of the MEG2 gene by small interfering RNA suppressed the ability of methyllucidone to inhibit STAT3 activation. Methyllucidone regulates STAT3 activity by modulating MEG2 expression, and our results suggest that this compound is a novel inhibitor of the STAT3 pathway and may be a useful lead molecule for the development of a therapeutic STAT3 inhibitor.

Anti-inflammatory effect and mechanism of action of Lindera erythrocarpa essential oil in lipopolysaccharide-stimulated RAW264.7 cells

The aim of this study was to investigate the chemical constituents of Lindera erythrocarpa essential oil (LEO) by gas chromatography-mass spectrometry and evaluate their inhibitory effect on the expression of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Fifteen compounds, accounting for 63.7 % of the composition of LEO, were identified. The main compounds were nerolidol (18.73 %), caryophyllene (14.41 %), α-humulene (7.73 %), germacrene-D (4.82 %), and α-pinene (4.47 %). LEO significantly inhibited the expression of inducible nitric oxide (NO) synthase and cyclooxygenase-2, and subsequent production of NO and prostaglandin E₂. In addition, it reduced the release of pro-inflammatory cytokines in LPS-activated RAW264.7 cells. The molecular mechanism underlying the effect of LEO was associated with inhibition of the phosphorylation of mitogen-activated protein kinase (MAPK). Furthermore, LEO inhibited LPS-induced phosphorylation and degradation of inhibitor of kappa B-α, which is required for the activation of the p50 and p65 nuclear factor (NF)-κB subunits in RAW264.7 cells. Taken together, these data suggest that LEO exerted its anti-inflammatory effect by downregulating LPS-induced production of pro-inflammatory mediators through the inhibition of NF-κB and MAPK signaling in RAW264.7 cells.

Covalent Modifiers: A Chemical Perspective on the Reactivity of α,β-Unsaturated Carbonyls with Thiols via Hetero-Michael Addition Reactions

Although Michael acceptors display a potent and broad spectrum of bioactivity, they have largely been ignored in drug discovery because of their presumed indiscriminate reactivity. As such, a dearth of information exists relevant to the thiol reactivity of natural products and their analogues possessing this moiety. In the midst of recently approved acrylamide-containing drugs, it is clear that a good understanding of the hetero-Michael addition reaction and the relative reactivities of biological thiols with Michael acceptors under physiological conditions is needed for the design and use of these compounds as biological tools and potential therapeutics. This Perspective provides information that will contribute to this understanding, such as kinetics of thiol addition reactions, bioactivities, as well as steric and electronic factors that influence the electrophilicity and reversibility of Michael acceptors. This Perspective is focused on α,β-unsaturated carbonyls given their preponderance in bioactive natural products.

Lucidone protects human skin keratinocytes against free radical-induced oxidative damage and inflammation through the up-regulation of HO-1/Nrf2 antioxidant genes and down-regulation of NF-κB signaling pathway

We investigated the protective effects of lucidone, a naturally occurring cyclopentenedione isolated from the fruits of Lindera erythrocarpa Makino, against free-radical and inflammation stimulator 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidative stress in human keratinocyte (HaCaT) cells, with the aim of revealing the possible mechanisms underlying the protective efficacy. Lucidone pretreatment (0.5-10 μg/mL) markedly increased HaCaT cell viability and suppressed AAPH-induced reactive oxygen species (ROS) generation, lipid peroxidation, and DNA damage. Notably, the antioxidant potential of lucidone was directly correlated with the increased expression of an antioxidant gene, heme oxygenase 1 (HO-1), which was followed by the augmentation of the nuclear translocation and transcriptional activation of NF-E2-related factor-2 (Nrf2), with or without AAPH. Nrf2 knockdown diminished the protective effects of lucidone. We also observed that lucidone pretreatment inhibited AAPH-induced inflammatory chemokine prostaglandin E₂ (PGE₂) production and the expression of cyclooxygenase-2 (COX-2) in HaCaT cells. Lucidone treatment also significantly inhibited AAPH-induced nuclear factor-κB (NF-κB) activation and suppressing the degradation of inhibitor-κB (I-κB). Furthermore, lucidone significantly diminished AAPH-induced COX-2 expression through the down-regulation of the extracellular signal-regulated kinase (ERK) and p38 MAPK signaling pathways. Therefore, lucidone may possess antioxidant and anti-inflammatory properties and may be useful for the prevention of free radical-induced skin damage.

Lucidone suppresses hepatitis C virus replication by Nrf2-mediated heme oxygenase-1 induction

Upon screening of plant-derived natural products against hepatitis C virus (HCV) in the replicon system, we demonstrate that lucidone, a phytocompound, isolated from the fruits of Lindera erythrocarpa Makino, significantly suppressed HCV RNA levels with 50% effective concentrations of 15 ± 0.5 μM and 20 ± 1.1 μM in HCV replicon and JFH-1 infectious assays, respectively. There was no significant cytotoxicity observed at high concentrations, with a 50% cytotoxic concentration of 620 ± 5 μM. In addition, lucidone significantly induced heme oxygenase-1 (HO-1) production and led to the increase of its product biliverdin for inducing antiviral interferon response and inhibiting HCV NS3/4A protease activity. Conversely, the anti-HCV activity of lucidone was abrogated by blocking HO-1 activity or silencing gene expression of HO-1 or NF-E2-related factor 2 (Nrf2) in the presence of lucidone, indicating that the anti-HCV action of lucidone was due to the stimulation of Nrf-2-mediated HO-1 expression. Moreover, the combination of lucidone and alpha interferon, the protease inhibitor telaprevir, the NS5A inhibitor BMS-790052, or the NS5B polymerase inhibitor PSI-7977, synergistically suppressed HCV RNA replication. These findings suggest that lucidone could be a potential lead or supplement for the development of new anti-HCV agent in the future.

Hepatoprotective effect of lucidone against alcohol-induced oxidative stress in human hepatic HepG2 cells through the up-regulation of HO-1/Nrf-2 antioxidant genes

Lucidone was previously reported to exhibit anti-inflammatory activity in vitro and in vivo. In the present study, we characterized the mechanisms underlying the hepatoprotective effect of lucidone against alcohol-induced oxidative stress in vitro. Human hepatoma (HepG2) cells were pretreated with lucidone (1-10μg/mL) and then hepatotoxicity was stimulated by the addition ethanol (100mM). With response to ethanol-challenge, increased amount of alanine aminotransferase (ALT) and aspirate aminotransferase (AST) release were observed, whereas lucidone pretreatment significantly inhibited the leakage of AST and ALT in HepG2 cells without appreciable cytotoxic effects. We also found that lucidone pretreatment significantly decreased ethanol-induced nitric oxide (NO), tumor necrosis factor-α (TNF-α), malondialdehyde (MDA), reactive oxygen species (ROS) and glutathione (GSH) depletion in HepG2 cells. Furthermore, Western blot and quantitative-PCR analyses showed that ethanol-exposure apparently down-regulated endogenous anti-oxidant hemoxygenase-1 (HO-1) expression, whereas pretreatment with lucidone significantly up-regulates HO-1 expression followed by the transcriptional activation of NF-E2 related factor-2 (Nrf-2). Interestingly, the profound up-regulation of HO-1 and Nrf-2 were observed in only ethanol-challenged cells, which evidenced that lucidone-induced induction of HO-/Nrf-2 were specific with oxidative stress. Thus, we concluded that lucidone-mediated up-regulation of phase-II enzymes and HO-1 via Nrf-2 signaling pathway may provide a pivotal mechanism for its hepatoprotective action.

Cytotoxicity and Pro-Apoptotic Activity of 2,2´-Bis[4,5-bis(4-hydroxybenzyl)-2-(4-hydroxyphenyl)cyclopent-4-en-1,3-dione], a Phenolic Cyclopentenedione Isolated from the Cyanobacterium Strain Nostoc sp. str. Lukešová 27/97

The cytotoxicity of the polyphenol 2,2´-bis[4,5-bis(4-hydroxybenzyl)-2-(4-hydroxyphenyl)cyclopent-4-en-1,3-dione], nostotrebin 6 (NOS-6), was tested under in vitro conditions using mouse fibroblasts (BALB/c cells). Identification of NOS-6 and its uptake into fibroblasts was examined by multi-stage mass spectrometry analysis with the following fragmentation pattern: MS (m/z) [M+H]⁺ 799.1 → MS² 399.1 → MS³ 305.1 → MS⁴ 277.1. Using several cell viability assays, the IC₅₀ of NOS-6 after 24 h incubation was found to be 8.48 ± 0.16/12.15 ± 1.96 µM (neutral red/MTT assay) which was higher than that of doxorubicin. It was found that NOS-6 is capable of inducing both types of cell death, apoptosis and necrosis in a dose-dependent manner. The biological activities of the cyclopentenediones and preliminary data on NOS-6 cytotoxicity are discussed.

Protective effect of components isolated from Lindera erythrocarpa against oxidative stress-induced apoptosis of H9c2 cardiomyocytes

Eight compounds were isolated from the methanol fraction of Lindera erythrocarpa and assessed for their ability to protect H9c2 cardiomyocytes against oxidative stress-induced cell death. Three of the compounds significantly reduced the release of lactate dehydrogenase from H9c2 cardiomyocytes treated with buthionine-[S,R]-sulfoximine and reduced the uptake of propidium iodide by these cells. These effects were concentration-dependent. The three inhibitory compounds were identified as (-)-epicatechin, avicularin and quercitrin by spectroscopic techniques including one- and two-dimensional NMR and mass spectroscopy.

Lucidone, a novel melanin inhibitor from the fruit of Lindera erythrocarpa Makino

The effects of lucidone on tyrosinase and antimelanogenic activity were investigated. Initially, we found that lucidone strongly inhibits the activity of mushroom tyrosinase. The effects of lucidone on tyrosinase were further examined in alpha-MSH-induced B16 melanoma cells. Lucidone significantly inhibits tyrosinase activity and leads to decreased melanin content in cultured B16 melanoma cells. Lucidone also attenuates the expression of tyrosinase and MITF (Microphthalmia-associated Transcription Factor) protein in a concentration-dependent manner, as shown by western blot. Quantitative real-time reverse-transcription polymerase chain reaction (RT-PCR) confirmed that lucidone inhibits the expression of tyrosinase mRNA. Accordingly, the effects of lucidone on the ERK signaling pathway were also investigated, but lucidone was not found to play major role in the induction of ERK activation. Our data indicate that the antimelanogenic activity of lucidone is probably due to its inhibition of tyrosinase activity and the suppression of tyrosinase and MITF expression.

Nostotrebin 6, a bis(cyclopentenedione) with cholinesterase inhibitory activity isolated from Nostoc sp. str. Lukesová 27/97

Nostotrebin 6, a new polyphenolic compound with a fully substituted 2,2'-bis(cyclopent-4-en-1,3-dione) skeleton, was isolated from a methanolic extract of the cyanobacterial strain Nostoc sp. str. Lukesová 27/97. The structure of this compound was determined using X-ray crystallography and further supported by NMR, IR spectroscopy, and MS. Nostotrebin 6 is an S-parabolic I-parabolic noncompetitive inhibitor of acetylcholinesterase (IC(50) = 5.5 microM) and an S-parabolic I-parabolic mixed inhibitor of butyrylcholinesterase (IC(50) = 6.1-7.5 microM). The inhibitory potency of nostotrebin 6 was compared with that of tacrine and galanthamine.

Inhibition of the human ether-a-go-go-related gene (HERG) K+ channels by Lindera erythrocarpa

Lindera erythrocarpa Makino (Lauraceae) is used as a traditional medicine for analgesic, antidote, and antibacterial purposes and shows anti-tumor activity. We studied the effects of Lindera erythrocarpa on the human ether-a-go-go-related gene (HERG) channel, which appears of importance in favoring cancer progression in vivo and determining cardiac action potential duration. Application of MeOH extract of Lindera erythrocarpa showed a dose-dependent decrease in the amplitudes of the outward currents measured at the end of the pulse (I(HERG)) and the tail currents of HERG (I(tail)). When the BuOH fraction and H(2)O fraction of Lindera erythrocarpa were added to the perfusate, both I(HERG) and I(tail) were suppressed, while the hexane fraction, CHCl(3) fraction, and EtOAc fraction did not inhibit either I(HERG) or I(tail). The potential required for half-maximal activation caused by EtOAc fraction, BuOH fraction, and H(2)O fraction shifted significantly. The BuOH fraction and H(2)O fraction (100 microg/mL) decreased g(max) by 59.6% and 52.9%, respectively. The H(2)O fraction- and BuOH fraction-induced blockades of I(tail) progressively decreased with increasing depolarization, showing the voltage-dependent block. Our findings suggest that Lindera erythrocarpa, a traditional medicine, blocks HERG channel, which could contribute to its anticancer and cardiac arrhythmogenic effect.

Antiinflammatory activity of Lindera erythrocarpa fruits

In this study, in vitro and in vivo antiinflammatory activities of fruits from Lindera erythrocarpa Makino were evaluated. The ethyl acetate soluble fraction derived from the ethanol extract of L. erythrocarpa fruits inhibited significantly nitric oxide (NO) production in lipopolysaccharide (LPS) induced NO in the murine macrophage cell line (RAW264.7) assay, the EC(50) being 16.35 microg/mL. Four compounds, including lucidone (1), cis/trans-methylludicone (2), methyl linderone (3) and linderone (4) were identified from the active fraction based on the bioactivity-guided fractionation procedure. Of these lucidone possessed the strongest NO inhibitory activity with an EC(50) value of 4.22 microg/mL. Furthermore, results from the protein expression assay demonstrated that lucidone suppressed iNOS and COX-2 protein expression in a dose-dependent manner. Lucidone also provided antiinflammatory activity in the croton oil-induced ear edema assay. When it was applied topically at a dosage of 0.5 and 1 mg per ear, the percent edema reduction in treated mice was 44% and 25%, respectively. The results obtained in this study indicated that lucidone has a good potential to be developed as an antiinflammation agent.

Inhibitory effect of obovatal on the migration and invasion of HT1080 cells via the inhibition of MMP-2

Because the activation of matrix metalloproteinases (MMP) is a key factor in the metastatic process, compounds with the ability to inhibit MMP activity have a potential in the treatment of tumor. From the examination of 2000 plant extracts, obovatal isolated from the extract of the leaves of Magnolia obovata THUNB was a potent inhibitor of MMP-2 enzyme in vitro. In human fibrosarcoma cells (HT1080) activated with MMP-2, obovatal inhibited MMP-2 enzyme activity and expression. In addition, the compound blocked migration and invasion of the cells. This study demonstrates that obovatal exerts its anticancer effects through blocking migration and invasion by inhibition of MMP-2 expression and activity, and also will be a good lead molecule for the development of anti-tumor drug.