Protection of coumarins against linoleic acid hydroperoxide-induced cytotoxicity

Antioxidant and anti‑inflammatory effects of esculin and esculetin (Review)

Fraxinus chinensis Roxb is a deciduous tree, which is distributed worldwide and has important medicinal value. In Asia, the bark of Fraxinus chinensis Roxb is a commonly used traditional Chinese medicine called Qinpi. Esculetin is a coumarin compound derived from the bark of Fraxinus chinensis Roxb and its glycoside form is called esculin. The aim of the present study was to systematically review relevant literature on the antioxidant and anti-inflammatory effects of esculetin and esculin. Esculetin and esculin can promote the expression of various endogenous antioxidant proteins, such as superoxide dismutase, glutathione peroxidase and glutathione reductase. This is associated with the activation of the nuclear factor erythroid-derived factor 2-related factor 2 signaling pathway. The anti-inflammatory effects of esculetin and esculin are associated with the inhibition of the nuclear factor κ-B and mitogen-activated protein kinase inflammatory signaling pathways. In various inflammatory models, esculetin and esculin can reduce the expression levels of various proinflammatory factors such as tumor necrosis factor-α, interleukin (IL)-1β and IL-6, thereby inhibiting the development of inflammation. In summary, esculetin and esculin may be promising candidates for the treatment of numerous diseases associated with inflammation and oxidative stress, such as ulcerative colitis, acute lung and kidney injury, lung cancer, acute kidney injury.

Esculetin Provides Neuroprotection against Mutant Huntingtin-Induced Toxicity in Huntington's Disease Models

Huntington’s disease (HD) is a neurodegenerative disorder caused by an abnormal CAG trinucleotide repeat expansion within exon 1 of the huntingtin (HTT) gene. This mutation leads to the production of mutant HTT (mHTT) protein which triggers neuronal death through several mechanisms. Here, we investigated the neuroprotective effects of esculetin (ESC), a bioactive phenolic compound, in an inducible PC12 model and a transgenic Drosophila melanogaster model of HD, both of which express mHTT fragments. ESC partially inhibited the progression of mHTT aggregation and reduced neuronal death through its ability to counteract the oxidative stress and mitochondria impairment elicited by mHTT in the PC12 model. The ability of ESC to counteract neuronal death was also confirmed in the transgenic Drosophila model. Although ESC did not modify the lifespan of the transgenic Drosophila, it still seemed to have a positive impact on the HD phenotype of this model. Based on our findings, ESC may be further studied as a potential neuroprotective agent in a rodent transgenic model of HD.

Partition and stability of folic acid and caffeic acid in hollow zein particles coated with chitosan

The carriers for hydrophobic bioactives have been extensively studied, while those for hydrophilic bioactives are still challenging. The partition of bioactives in the particles depends greatly on their solubility, interaction with carrier materials, as well as structure of carriers. In this study, chitosan-coated hollow zein particles using calcium phosphate as a sacrificing template (CS-HZ) were fabricated to co-encapsulate folic acid (FA) and caffeic acid (CA). Partition, photostability, and antioxidant capacity of bioactive compounds were also studied. The size, polydispersity index and ζ-potential of optimized CS-HZ were 176.3 nm, 0.14 and +39.3 mV, respectively, indicating their small and uniform dimension with excellent colloidal stability. FA interacted with chitosan to form complexes and then coated on the zein particles where CA was encapsulated. After co-encapsulation in CS-HZ, the photostability of both FA and CA was improved in comparison with encapsulation of single compound, with 85% of FA remaining after 240 min of UVA irradiation, and 90% of CA remaining after 80 min. Antioxidant activity of CA decreased upon encapsulation, but significantly increased after irradiation. Findings in this study shed some light on the design of carriers for co-delivery of hydrophilic compounds in acidic condition.

Esculetin as a Bifunctional Antioxidant Prevents and Counteracts the Oxidative Stress and Neuronal Death Induced by Amyloid Protein in SH-SY5Y Cells

Oxidative stress (OS) appears to be an important determinant during the different stages of progression of Alzheimer’s Disease (AD). In particular, impaired antioxidant defense mechanisms, such as the decrease of glutathione (GSH) and nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2), a master regulator of antioxidant genes, including those for GSH, are associated with OS in the human AD brain. Among the neuropathological hallmarks of AD, the soluble oligomers of amyloid beta (Aβ) peptides seem to promote neuronal death through mitochondrial dysfunction and OS. In this regard, bifunctional antioxidants can exert a dual neuroprotective role by scavenging reactive oxygen species (ROS) directly and concomitant induction of antioxidant genes. In this study, among natural coumarins (esculetin, scopoletin, fraxetin and daphnetin), we demonstrated the ability of esculetin (ESC) to prevent and counteract ROS formation in neuronal SH-SY5Y cells, suggesting its profile as a bifunctional antioxidant. In particular, ESC increased the resistance of the SH-SY5Y cells against OS through the activation of Nrf2 and increase of GSH. In similar experimental conditions, ESC could also protect the SH-SY5Y cells from the OS and neuronal death evoked by oligomers of Aβ_1–42 peptides. Further, the use of the inhibitors PD98059 and LY294002 also showed that Erk1/2 and Akt signaling pathways were involved in the neuroprotection mediated by ESC. These results encourage further research in AD models to explore the efficacy and safety profile of ESC as a novel neuroprotective agent.

Mechanism for Inhibition of Folic Acid Photodecomposition by Various Antioxidants

Folic acid, a synthetic form of folate, is a water-soluble vitamin that is essential during periods of rapid cell division and growth. However, it decomposes upon ultraviolet irradiation to form inactive photoproducts. In this study, the protective effect and mechanisms of antioxidants, including cinnamic acids, flavonoids, catechol and its derivatives, stilbenes, p-benzoquinone and its derivatives, isoprenoids, curcumin, oleic acid, and linoleic acid, against folic acid photodecomposition were investigated by using fluorescence and absorbance spectroscopy, high-performance liquid chromatography, and antioxidant assay. It was found that antioxidants could inhibit or delay the folic acid decomposition in varying degrees, among which caffeic acid was the most effective. The increase in its remarkable antioxidant efficiency and absorbance in the UVA region during irradiation contributed to its effective protection. This finding could be useful for the protection of photolabile components in food and other uses.

Topology-Dependent Dissociation Mode of the O-H Bond in Monohydroxycoumarins

All possible monohydroxycoumarin derivatives are modeled using density functional theory computations in order to investigate the role of the hydroxyl group position for the radical-scavenging and antioxidant activity of these compounds. Geometry optimization is performed using the B3LYP functional with the 6-311++G(d,p) basis set. The enthalpy changes are assessed in gas phase and in implicit water using the polarized continuum model. Structure-reactivity patterns are delineated. The most reactive isomers as well as the most probable mechanism of interaction between monohydroxycoumarins and free radicals are outlined.

Synthesis of 4-aryl-1,2,3-triazolyl appended natural coumarin-related compounds with antiproliferative and radical scavenging activities and intracellular ROS production modification

Diverse natural coumarin-based compounds linked to aryl via a 1,2,3-triazole spacer with antiproliferative activity against K562 cells, radical scavenging activity and a decrease of ROS production were provided.

Comprehensive investigation of the enzymatic oligomerization of esculin by laccase in ethanol : water mixtures

The oligomerization of esculin by laccase in aqueous medium resulted in a precipitate fraction with excellent antioxidant properties.

Influence of coumarin and some coumarin derivatives on serum lipid profiles in carbontetrachloride-exposed rats

In the present study, coumarin and some coumarin derivatives (esculetin, scoparone, and 4-methylumbelliferone) were investigated for their lipid-lowering effect in rats. Male Sprague–Dawley rats (150–200 g) were divided into six groups and each group comprised of five rats. Hepatic injury-dependent hyperlipidemia was induced by carbon tetrachloride (CCl4, 1.25 ml/kg). Coumarin and coumarin derivatives esculetin (35 mg/kg), scoparone (35 mg/kg), 4-methylumbelliferone (35 mg/kg), or coumarin (30 mg/kg) were administered to experimental groups at 12-h intervals. Animals received the derivatives esculetin, scoparone or 4-methylumbelliferone prior to the administration of a single toxic dose of CCl4. Serum total cholesterol (TC), triglyceride (TG), very low-density lipoprotein cholesterol (VLDL-C), and low-density lipoprotein cholesterol (LDL-C) levels significantly increased in CCl4-treated group ( p < 0.05, p < 0.01, p < 0.01, and p < 0.05, respectively), while levels of serum high-density lipoprotein cholesterol (HDL-C) decreased ( p < 0.01). 4-Methylumbelliferone had no recovery effects on serum TC levels, however, significantly prevented CCl4-induced hyperlipidemia by reducing TG and VLDL-C levels ( p < 0.05 and p < 0.05, respectively). In addition, coumarin had no recovery effect on any of the serum lipid parameters against CCl4-induced hyperlipidemia. Among the coumarin derivatives only esculetin and scoparone significantly prevented serum HDL-C in CCl4-induced dyslipidemia. The results from this study indicate that the chemical structure of coumarins plays an important role on the regulation of serum lipid profiles.

Antioxidant activity of fraxetin and its regeneration in aqueous media. A density functional theory study

Fraxetin is an excellent and versatile antioxidant in aqueous media. In addition it regenerates, scavenging two radical equivalents per cycle.

Photoproducts of 7-Hydroxycoumarins in Aqueous Solution

Near-UV irradiation of aqueous solutions of 7-hydroxy-6-methoxycoumarin (scopoletin) and 6,7-dihydroxycoumarin (esculetin) resulted in the formation of dimers. Substantially greater amounts of the 7-hydroxy-6-methoxycoumarin photodimer were produced compared with that of 6,7-dihydroxycoumarin. Fluorescence spectra indicated that the initial photolytic reaction involves the excited state of the phenolate form of the monomeric coumarin. The electro-spray ionization (ESI) mass spectrum suggested that the major product (with a sodiated quasimolecular ion at m/z 405) from the photolysis of scopoletin in water had formed by oxidative dimerisation and possibly had a 3,3′-bond. A second dimer (with a sodiated quasimolecular ion at m/z 407) was probably a 2 + 2 cyclodimer. This work concluded that photolysis of coumarins in water results in oxidative dimerisation whereas photolysis in the solid state or in organic solvents results in cyclodimerisation. Minor monomeric photoproducts were a dihydroxy-6-methoxycoumarin from 7-hydroxy-6-methoxycoumarin and a trihydroxycoumarin from 6,7-dihydroxycoumarin. During ESI-mass spectrometry (ESI-MS), sodiated quasimolecular ions of the photodimer formed more readily than protonated quasimolecular ions and the sodiated ions did not fragment readily. Protonated quasimolecular ions of the monomeric coumarins formed more readily than their sodiated counterparts and the protonated ions fragmented to create daughter ion spectra that were useful for chemical structural assignment.

Formation of biopolymers owing to the oxidation of esculetine by Cu(II) ions in a Ca-polygalacturonate network

Pectic acids participate in the transport of heavy metal ions in the root apoplasm by establishing interactions that can lead to their partial or total immobilization. The ions accumulated can be mobilized by phenolic compounds and organic acids of the root exudates. In this context, we tested, in aqueous phase, the ability of malic acid and esculetine (ESC) to mobilize the Cu(II) ions accumulated in a Ca-polygalacturonate matrix (Ca-PGA) used as a model of the root apoplasm. The results show that at pH 5.0 and 6.0 malic acid mobilizes about 22% and 34% of the Cu(II) accumulated, respectively, whereas ESC about 12% and 25%. ESC was found to cause the reduction of Cu(II) to Cu(I) with formation of ESC oxidation products. The study of the Cu(II)-ESC binary system evidenced that one molecule of ESC reduces one Cu(II) ion with formation of semiquinonic radicals that couple to form two dimers. The Cu(II) reduction by ESC was found faster in the presence of malic acid.

Filtrate of Phellinus linteus Broth Culture Reduces Infarct Size Significantly in a Rat Model of Permanent Focal Cerebral Ischemia

Phellinus linteus, a natural growing mushroom, has been known to exhibit anti-tumor, anti-inflammatory, anti-allergic and anti-oxidant effects. Aiming to exploit the neuroprotective effects of P. linteus, we evaluated its effects on infarct volume reduction in a rat model of focal cerebral ischemia. Male Sprague-Dawley rats were subjected to right middle cerebral artery occlusion. Filtrate of P. linteus broth culture (various doses), fractionated filtrate (based on molecular weight) or control medium was administered intraperitoneally to rats before or after ischemia induction. Rats were killed at 24 h after the stroke surgery. Cortical and caudoputaminal infarct volumes were determined separately using an image analysis program following staining with 2,3,5-triphenyltetrazolium chloride. Significant cortical infarct volume reductions were found in the pre-treatment groups (30 and 60 minutes before onset of cerebral ischemia) compared with the control group, showing dose dependence. Posttreatment (30 minutes after ischemic onset) also significantly reduced cortical infarct volume. Furthermore, the higher molecular weight (≥12 000) fraction of the culture filtrate was more effective compared with the lower molecular weight fraction. The present findings suggest that P. linteus may be a new promising approach for the treatment of focal cerebral ischemia, with the additional benefit of a wide therapeutic time window since significant infarct volume reduction is obtained by administration even after the ischemic event. Our finding that the higher molecular weight fraction of the P. linteus culture filtrate demonstrated more prominent effect may provide a clue to identify the neuroprotective substances and mechanisms.

Initial State and Transition State Contributions to Reactivity Trends of Base-Catalyzed Hydrolysis of Some Nitro Chromen-2-One Derivatives

Base-catalyzed hydrolysis of 6-nitro-2H-chromen-2-one (NC) and 6-nitro-2H-chromen-2-one-3-carboxylic acid (NCC) in binary water/methanol and water/acetone mixtures were studied kinetically at 298 K. The changes in the activation barrier of the investigated compounds from water to water/methanol and water/acetone mixtures were estimated from the kinetic data. Solvent effects on the reactivity trends were analyzed into initial state and transition state components. These were determined from the transfer chemical potentials of the reactants and the kinetic data. The transfer chemical potentials δ m μ θ for NC were derived from its solubilities in water/methanol and water/acetone mixtures, and the transfer chemical potentials for NCC− anion were derived from solubility data for its calcium, cerium and lanthanum salts. Base-catalyzed hydrolysis of NC and NCC in water/methanol and water/acetone mixtures follow a rate law with k obs=k 2·c(HO−) and k obs=k 1+k2·c(HO−), respectively. The decrease in the rate constants of base-catalyzed hydrolysis of NC as methanol% or acetone% increases is dominated by the initial state (IS), while the decrease in the rate constants of base-catalyzed hydrolysis of NCC as methanol% or acetone% increases is dominated by the transition state (TS).

Protective effects of coumarin and coumarin derivatives against carbon tetrachloride-induced acute hepatotoxicity in rats

The comparison of the antioxidant activity of some coumarins with their molecular structure is well determined. However, the protective function of coumarins with various chemical structures against liver toxicity has not yet been well established. Therefore, the aim of this study was to evaluate the possible cytoprotective properties of coumarin and some coumarin derivatives against CCl(4) (carbon tetrachloride)-induced hepatotoxicity. Coumarin (1,2-benzopyrone) and coumarin derivatives esculetin (6,7-dihydroxycoumarin), scoparone (6,7-dimethoxycoumarin) and 4-methylumbelliferone (7-hyroxy-4-methyl) were examined for their protective effect against CCl(4)-induced hepatotoxicity in Male Sprague-Dawley rats. A single toxic dose of CCl(4) (1.25 ml kg(-1), orally) produced liver damage in rats, seen histologically as centrilobular necrosis. Administration of CCl(4) increased serum enzyme levels of aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP). Pre-treatment of rats with esculetin (31.15 mg kg(-1), orally) and scoparone (35 mg kg(-1), orally) significantly prevented CCl(4)-induced increase in serum enzymes, whereas 4-methylumbelliferone (35 mg kg(-1)) and coumarin (30 mg kg(-1)) had no effect against CCl(4)-induced rise in serum enzymes. Morphological findings were consistent with the plasma transaminase observations. Among the coumarin analogs, esculetin, which possesses orthodihydroxy coumarins, showed the strongest protective effect against CCl(4)-induced liver damage, followed by scoparone, 4-methylumbelliferone and coumarin, respectively. The results of this study indicate that the chemical structures of coumarins play an important role in the prevention of liver toxicity.

Coumarin derivatives protection against ROS production in cellular models of Aβtoxicities

The role of oxidative stress and free radicals in the development of Alzheimer's disease (AD) has been the focus of many recent studies. The role of hydrogen peroxide (H(2)O(2)) in AD is thought to be associated with Abeta (amyloid - beta) damage in cells. A number of coumarin derivatives were previously found to be potent anti-inflammatory and antioxidant agents. Herein, these coumarin derivatives were tested as H(2)O(2) scavengers with the DCF assay using two types of neuronal cells: (a) wild type (N2a) neuroblastoma cells and (b) APP/PS1 transgenic cell line expressing Abeta. Their scavenging activity was varied between the types of cell cultures and it was found to be concentration and time dependent in the mutant cells. Their protective role against cell death further supports this notion. These results suggest that these compounds could be used as a template in the design of new molecules with a possible role in AD.

The crystal structure of Aquifex aeolicus prephenate dehydrogenase reveals the mode of tyrosine inhibition

TyrA proteins belong to a family of dehydrogenases that are dedicated to l-tyrosine biosynthesis. The three TyrA subclasses are distinguished by their substrate specificities, namely the prephenate dehydrogenases, the arogenate dehydrogenases, and the cyclohexadienyl dehydrogenases, which utilize prephenate, l-arogenate, or both substrates, respectively. The molecular mechanism responsible for TyrA substrate selectivity and regulation is unknown. To further our understanding of TyrA-catalyzed reactions, we have determined the crystal structures of Aquifex aeolicus prephenate dehydrogenase bound with NAD(+) plus either 4-hydroxyphenylpyuvate, 4-hydroxyphenylpropionate, or l-tyrosine and have used these structures as guides to target active site residues for site-directed mutagenesis. From a combination of mutational and structural analyses, we have demonstrated that His-147 and Arg-250 are key catalytic and binding groups, respectively, and Ser-126 participates in both catalysis and substrate binding through the ligand 4-hydroxyl group. The crystal structure revealed that tyrosine, a known inhibitor, binds directly to the active site of the enzyme and not to an allosteric site. The most interesting finding though, is that mutating His-217 relieved the inhibitory effect of tyrosine on A. aeolicus prephenate dehydrogenase. The identification of a tyrosine-insensitive mutant provides a novel avenue for designing an unregulated enzyme for application in metabolic engineering.

Neuroprotective effect of prenyloxycoumarins from edible vegetables

The present study is designed to investigate the effect of some natural prenyloxyphenylpropanoids as neuroprotective agents against NMDA-induced toxicity in mixed cortical cell cultures containing both neurons and astrocytes. Excitotoxicity was induced by exposure of cultures to NMDA (100microM) at room temperature in a HEPES-buffered salt solution followed by incubation at 37 degrees C for the following 24h in MEM-Eagle's supplemented with 15.8mM NaHCO(3) and 25mM glucose. Tested compounds were mixed with NMDA. Neuronal injury was measured in all experiments by examination of cultures with phase-contrast microscopy at 20x, 18-20h after the insult while neuronal damage was quantitatively assessed by counting dead neurons stained with trypan blue and by measuring lactate dehydrogenase (LDH) released in the medium. Results showed that only natural prenyloxyphenylpropanoids containing a coumarin nucleus, namely 7-isopentenyloxycoumarin and auraptene, both found in nature from plants belonging to the genus Citrus and other of the family of Rutaceae, including edible ones, exerted a good dose-dependent manner protective effect against NMDA-induced neurotoxicity in particular at concentrations ranging from 1 to 10microM.

Neuroprotective coumarins from the root of Angelica gigas: structure-activity relationships

An n-butanol-soluble fraction of the root of Angelica gigas Nakai (Umbelliferae) exhibited significant protection against glutamate-induced toxicity in primary cultured rat cortical cells. Using neuroprotective activity-guided fractionation, nine coumarins; marmesinin (1), nodakenin (2), columbianetin-O-beta-D-glucopyranoside (3), (S)-peucedanol-7-O-beta-D-glucopyranoside (4), (S)-peucedanol-3'-O-beta-D-glucopyranoside (5), skimmin (6), apiosylskimmin (7), isoapiosylskimmin (8) and magnolioside (9), were isolated from the n-butanol fraction. Of these nine coumarins, three dihydrofuranocoumarins; 1, 2 and 3, exhibited significant neuroprotective activities against glutamate-induced toxicity, exhibiting cell viabilities of about 50% at concentrations ranging from 0.1 to 10 microM. To explore the structure-activity relationships of coumarins, sixteen previously isolated compounds; 10-25, were simultaneously evaluated in the same system. Our results revealed that cyclization of the isoprenyl group, such as dihydropyran or dihydrofuran, or the furan ring at the C-6 position of coumarin, as well as lipophilicity played an important role in the neuroprotective activity of coumarins.

Inhibitory effect of natural coumarin compounds, esculetin and esculin, on oxidative DNA damage and formation of aberrant crypt foci and tumors induced by 1,2-dimethylhydrazine in rat colons

The effects of esculetin (6,7-dihydroxycoumarin) and its 6-glycoside, esculin, on 8-oxo-2'-deoxyguanosine (8-oxodG) formation and carcinogenesis induced by a chemical carcinogen, 1,2-dimethylhydrazine (DMH), were examined in the colons of male Fischer 344 rats. Animals were given water containing esculetin or esculin for 7 d before subcutaneous injection of DMH (20 mg/kg body wt), killed 24 h after DMH treatment, and the levels of thiobarbituric acid reactive substances (TBARS) and 8-oxodG in the colons were determined. Both esculetin and esculin suppressed significantly the DMH-induced increases in 8-oxodG and TBARS in rat colon mucosa. We further investigated the modifying effect of esculin intake on the development of DMH-induced colonic aberrant crypt foci (ACF). Animals were given DMH once a week for 4 weeks to induce ACF. They then received water containing esculin ad libitum for 5 weeks (initiation phase) or 11 weeks after DMH treatment (post-initiation phase). Animals in the positive control group received tap water throughout the experiment. At the end of the experiment (16 weeks), the ingestion of esculin during the initiation phase significantly reduced the incidence of gross tumors, the number of ACF per rat and the mean number of AC per focus, while the esculin treatment during the post-initiation phase significantly decreased only the number of ACF per rat. These results suggest that esculin intake has an inhibitory effect on DMH-induced oxidative DNA damage and carcinogenesis in rat colons.

Anti-oxidative and photo-protective effects of coumarins isolated from Fraxinus chinensis

Free radicals and reactive oxygen species (ROS), which are generated by UV irradiation, may cause serious injury to skin cell membranes, DNA and functional proteins. In addition, these agents stimulate the expressions of matrix metalloproteinases (MMPs), which can degrade most components of the extracellular matrix (ECM), including collagen. In order to develop new anti-photoaging agents, five major components from the extract of Fraxinus chinensis extract (FCE) were identified. Two of the major components of FCE were found to be esculin (11.2%) and esculetin (1.9%). FCE (IC50: 50.0 microg/mL 1, 1-diphenyl-2-picrylhydrazyl (DPPH); 19.8 microg/mL, superoxide anion radical) and esculetin (IC50: 2.1 microg/mL DPPH; 0.6 microg/mL, superoxide anion radical) showed strong antioxidative activities. Of the compounds tested, esculetin showed the strongest scavenging activity against DPPH radicals, followed by superoxide anions from the xanthine/xanthine oxidase system. The intracellular ROS scavenging activity showed that oxidation of 5-(6-)-chloromethyl-2', 7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA) was effectively inhibited by esculetin, with potent free radical scavenging activity was also shown in UVB-irradiated human dermal fibroblasts (HDFs). Moreover, treatment of UVA-irradiated HDFs with esculetin resulted in dose-dependent decreases in the expression levels of MMP-1 mRNA and protein. From these results, FCE and one of its components, esculetin, were predicted to be potentially useful as ingredients in cosmetics for protecting against photoaging.

Morroniside prevents peroxide-induced apoptosis by induction of endogenous glutathione in human neuroblastoma cells

(1) Morroniside belongs to an extensive group of natural iridorid glycosides. In the present study, using human neuroblastoma SH-SY5Y cells, we have investigated the protective effects of this compound on modifications in endogenous reduced glutathione (GSH), intracellular oxygen species (ROS) and apoptotic death on H(2)O(2)-mediated cytoxicity. (2) Incubation of cells with morroniside led to a significant dose-dependent elevation of cellular GSH accompanied by a marked protection against H(2)O(2)-mediated toxicity. Morroniside at 1-100 microM inhibited the formation of ROS and the activation of caspase-3 and 9, and the upregulation of Bcl-2, whereas no significant change occurred in Bax levels. (3) The results indicated that the anti-oxidative and anti-apoptotic properties render this natural compound potentially protective against H(2)O(2)-induced cytotoxicity. (4) This study suggested that intracellular GSH appeared to be an important factor in morroniside-mediated cytoprotection against H(2)O(2)-toxicity in SH-SY5Y cells.

Fraxetin prevents rotenone-induced apoptosis by induction of endogenous glutathione in human neuroblastoma cells

Fraxetin belongs to an extensive group of natural phenolic anti-oxidants. In the present study, using a human neuroblastoma SH-SY5Y cells, we have investigated the protective effects of this compound on modifications in endogenous reduced glutathione (GSH), intracellular oxygen species (ROS) and apoptotic death on rotenone-mediated cytoxicity. Incubation of cells with the fraxetin led to a significant elevation dose-dependent of cellular GSH and this was accompanied by a marked protection against rotenone-mediated toxicity, which was also significantly reversed in the cells with buthionine sulfoximine (BSO) co-treatment. Taken together, this study suggested that intracellular GSH appeared to be an important factor in fraxetin-mediated cytoprotection against rotenone-toxicity in SH-SY5Y cells. Fraxetin at 10-100 muM inhibited the formation of ROS, cytochrome c release, activation of caspase-3 and 9, and suppressed the up-regulation of Bax, whereas no significant change occurred in Bcl-2 levels. Our results indicated that the anti-oxidative and anti-apoptotic properties render this natural compound potentially protective against rotenone-induced cytotoxicity.

Suppression of 8-oxo-2'-deoxyguanosine formation and carcinogenesis induced by N-nitrosobis (2-oxopropyl)amine in hamsters by esculetin and esculin

Effects of esculetin (6,7-dihydroxycoumarin) and its glycoside, esculin, on 8-oxo-2'-deoxyguanosine (8-oxodG) formation and carcinogenesis induced by a chemical carcinogen, N-nitrosobis(2-oxopropyl)amine (BOP), were examined in the pancreas of female Syrian golden hamsters. Animals were administered esculetin by gastric intubation into the stomach 30 min before BOP administration or ingestion of a diet containing esculin for 7 days before BOP administration, and killed 1 or 4h after BOP treatment, and the contents of thiobarbituric acid-reacting substrates (TBARS) and 8-oxodG in the pancreas were determined. Both compounds suppressed significantly the BOP-induced increases in 8-oxodG and TBARS contents in hamster pancreas. We further investigated the effect of esculin on pancreatic carcinogenesis by the rapid production model induced by augmentation pressure with a choline-deficient diet, ethionine, methionine and BOP. Esculin was given ad libitum as a 0.05% aqueous solution in either the initiation or promotion phases. The incidence of invasive tumors in animals given esculin during the initiation phase was significantly smaller than in the control group, while esculin given during the promotion phase showed no apparent effects. These results suggest that the intake of esculin has an inhibitory effect on BOP-induced oxidative DNA damage and carcinogenesis in hamster pancreas.

Solid-phase extraction of esculetin from the ash bark of Chinese traditional medicine by using molecularly imprinted polymers

A molecularly imprinted polymer solid-phase extraction method is used to extract esculetin from the ash bark of Chinese traditional medicine. Ratio of ethanol and water as washing solution were investigated. Data of accumulative adsorption on molecularly imprinted polymers from the continuous loading experiment suggests that there are two different kinds of recognition sites in molecularly imprinted polymers. By selecting the washing and eluting solution a scheme was designed to separate esculetin and its analogues including esculin, coumarin, 7-methoxylcoumarin and daphnetin. Finally, by applying the revised scheme esculetin was extracted from the ash bark of Chinese traditional medicine that was purchased from two big drugstores, respectively, with both molecularly imprinted polymers and non-molecularly imprinted polymers.

Inhibitory Effect of Coumarins from Weigela subsessilis on Low Density Lipoprotein Oxidation

Oxidation of low density lipoprotein (LDL) is thought to be a major factor in the pathophysiology of atherosclerosis. In the present study, we found that coumarins isolated from Weigela subsessilis (Caprifoliaceae) inhibited LDL oxidation mediated by either catalytic copper ions (Cu2+) or free radicals generated with the azo compound 2,2'-azobis-(2-amidinopropane)dihydrochloride (AAPH). Of the coumarins tested, scopoletin (1) and cleomiscosin A (2) increased the lag time of conjugated diene formation and inhibited the generation of thiobarbituric acid reactive substances (TBARS) in a dose-dependent manner. In addition, it was found that compounds 1 and 2 had the capacity to protect the fragmentation of apolipoprotein B-100 (apoB-100). These results suggest that W. subsessilis and its active coumarins, 1 and 2, may have a role to play in preventing the LDL oxidation involved in atherogenesis.

Antioxidant properties of 3-hydroxycoumarin derivatives

A series of hydroxylated 3-hydroxycoumarins was synthesised by the reaction of 3-aryl-2-hydroxypropenoic derivatives with boron tribromide. They were evaluated for their ability to scavenge the 2,2-diphenyl-1-picrylhydrazyl radical, the superoxide anion radical, the hydroxyl radical and the peroxynitrite anion and to inhibit copper-induced human LDL peroxidation. The physicochemical results were in accordance to establish the compounds hydroxylated on C-6 and C-7 positions as the most active of the series with antioxidant potencies comparable to those of quercetin and vitamin C. These compounds form o- and p-quinonoid derivatives upon radical scavenging and may serve as new lead compounds for pharmacological investigations.

Neuroprotective effect of fraxetin and myricetin against rotenone-induced apoptosis in neuroblastoma cells

Rotenone-induced apoptosis is considered to contribute to the etiology of Parkinson's disease (PD). We try to prevent the apoptosis induced by rotenone toxicity with 50 microM myricetin, 100 microM fraxetin and 100 microM N-acetylcysteine (NAC) that protect against reactive oxygen species (ROS), on SH-SY5Y human neuroblastoma cell line. Morphological changes induced by rotenone and intracellular ROS were assessed in live SH-SY5Y dopaminergic cells by confocal microscopy using the fluorescent dyes, dihydroethidium and 2',7'-dichlorofluorescein diacetate (DCFH-DA). DNA fragmentation was assayed as index of apoptosis. We also investigated oxidative stress parameters such as the glutathione redox status and lipid peroxidation. The exposure of the SH-SY5Y cells to rotenone 5 microM for 16 h produced severe morphological changes, DNA fragmentation and significative increases in the levels of hydrogen peroxide and superoxide anion. These increases were reduced by a 30-min pretreatment with fraxetin 100 microM or NAC 100 microM. DNA laddering produced by rotenone treatment was also inhibited by fraxetin and NAC. Treatment with 5 microM rotenone induced loss of reduced glutathione (GSH) and increased cellular levels of oxidized glutathione (GSSG). Fraxetin and NAC treatments restored glutathione redox ratio diminished after rotenone challenge and decreased the levels of lipid peroxidation. These results suggest that the natural antioxidants, such as fraxetin, may prevent the apoptotic death of dopaminergic cells induced by rotenone and mediated by oxidative stress.

Inhibitory effect of esculin on oxidative DNA damage and carcinogenesis induced by N-nitrosobis(2-oxopropyl)amine in hamster pancreas

The effects of esculin, a natural coumarin compound, on the formation of 8-oxo-2'-deoxyguanosine (8-oxodG) and carcinogenesis induced by a chemical carcinogen, N-nitrosobis(2-oxopropyl)amine (BOP), were examined in the pancreas of female Syrian golden hamsters. Animals were given a diet containing esculin for 7 days, and killed 4~h after BOP treatment, and the contents of 8-oxodG were measured in the nuclear DNA of the pancreas. Esculin suppressed significantly the increase in the 8-oxodG content of hamster pancreas induced by BOP. Furthermore, the effect of esculin on the rapid production model experiment for pancreatic carcinogenesis using BOP was investigated. Esculin was given ad libitum as a 0.05% aqueous solution during either the initiation or promotion phases. The incidence of invasive tumors in animals given esculin during the initiation phase was significantly lower than in the control group, while the incidence in animals given esculin during the promotion phase showed no significant change. These results suggest that the intake of esculin has an inhibitory effect on BOP-induced oxidative DNA damage and carcinogenesis in hamster pancreas.

Effect of fraxetin and myricetin on rotenone-induced cytotoxicity in SH-SY5Y cells: comparison with N-acetylcysteine

The purpose of this study was to investigate the potential neuroprotective effects of myricetin (flavonoid) and fraxetin (coumarin) on rotenone-induced apoptosis in SH-SY5Y cells, and the possible signal pathway involved in a neuronal cell model of Parkinson's disease. These two compounds were compared to N-acetylcysteine. The viability of cells was assessed by 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and cytotoxicity was assayed by lactate dehydrogenase (LDH) released into the culture medium. Parameters related to apoptosis, such as caspase-3 activity, the cleavage of poly(ADP-ribose) polymerase and the levels of reactive oxygen species were also determined. Rotenone caused a time- and dose-dependent decrease in cell viability and the degree of LDH release was proportionally to the effects on cell viability. Cells were pretreated with fraxetin, myricetin and N-acetylcysteine at different concentrations for 30 min before exposure to rotenone. Cytotoxicity of rotenone (5 microM) for 16 h was significantly diminished as well as the release of LDH into the medium, by the effect of fraxetin, myricetin and N-acetylcysteine, with fraxetin (100 microM) and N-acetylcysteine (100 microM) being more effective than myricetin (50 microM). Rotenone-induced apoptosis in SH-SY5Y cells was detected by an increase in caspase-3 activity and in the cleavage of poly(ADP-ribose) polymerase. After exposing these cells to rotenone, a significant increase in reactive oxygen species preceded apoptotic events. Fraxetin (100 microM) and N-acetylcysteine (100 microM) not only reduced rotenone-induced reactive oxygen species formation, but also attenuated caspase-3 activity and poly(ADP-ribose) polymerase cleavage at 16 h against rotenone-induced apoptosis. The effect of fraxetin in both experiments was similar to that of N-acetylcysteine. These results demonstrated the protective action of fraxetin and suggest that it can reduce apoptosis, possibly by decreasing free radical generation in SH-SY5Y cells. Myricetin at 100 microM was without any preventive effect.

Suppression of lipid hydroperoxide-induced oxidative damage to cellular DNA by esculetin

Linoleic acid hydroperoxide (LOOH) has been reported to cause an increase in the content of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a typical oxidation product of DNA bases, in cultured cells due to coexisting iron(III) ion. We examined whether coumarins are able to suppress the formation of 8-oxodG in the DNA of human diploid fibroblasts, TIG-7 cells, treated with LOOH and iron(III) ion. Cotreatment of TIG-7 cells with esculetin (6,7-dihydroxycoumarin) significantly suppressed the increase in 8-oxodG content induced by LOOH and iron(III) ion. Pretreatment of cells with esculetin for 24 h was also effective in protecting cellular DNA against oxidative damage induced by subsequent treatment with LOOH and iron(III) ion. Pretreatment with esculin, the 6-glucoside of esculetin, was effective, but to a lesser extent. Furthermore, the free radical-scavenging activities of coumarins and hydroxycinnamic acids were examined by measuring the inhibition of spin-adduct formation of hydroxyl radicals with 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Compounds bearing an ortho-catechol moiety, such as esculetin, fraxetin, and caffeic acid, significantly reduced the ESR signal intensities of the DMPO-OH spin adduct. These results indicate that esculetin is effective in protecting cells against DNA damage induced by oxidative stress and that the presence of an ortho-catechol moiety is important for antioxidant activities against reactive oxygen species.