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R X Tan

Publications and source records attributed to R X Tan.

At least 19 recordsLinked to original sources
PubMed2006

Antifungal and new metabolites of Myrothecium sp. Z16, a fungus associated with white croaker Argyrosomus argentatus.

AIMS: Fungal infection is still a life-threatening risk for the immunocompromised population such as AIDS patients and those who receive treatments with immunosuppressors and/or frequent administrations of wide-spectrum antibiotics, which inevitably lead to the drug resistance and unbalanced microflora populations. The present work was accordingly performed to characterize more potent antifungal metabolites from various cultures of marine fungi residing in white croaker Argyrosomus argentatus. METHODS AND RESULTS: The three most common opportunistic human pathogens Candida albicans (CCCCM ID 00148), Aspergillus niger (CCCCM ACCC 30005) and Trichophyton rubrum (CCCCM ID 00001) were selected as test fungi. A total of 16 cultivable fungal strains were isolated from the variant tissues of Ar. argentatus collected from the Yellow Sea, followed by preliminary antifungal screenings of the EtOAc extracts of the corresponding cultures. As a result, the inhibition of the three target fungi, plus being allergic to isolators' skin, were discerned with the EtOAc extract of the fungus under the isolation number Z16 that was identified subsequently as Myrothecium sp. by a combination of morphological and 18S rDNA finger-typing characteristics. A follow-up bioassay fractionation of the EtOAc extract, in conjunction with spectral analyses [MS, (1)H-NMR, (13)C-NMR, distortionless enhancement by polarization transfer (DEPT), heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond resonance (HMBC)] wherever required, afforded eventually the characterization of a new acid (compound 1: 4,5-ditridecyl-octanedioic acid), three macrocyclic trichothecenes including roridin A (compound 2), verrucarin A (compound 3) and 8beta-acetoxy-roridin H (compound 4), (22E,24R)-cerevisterol (compound 5) and N-phenyl-beta-amino-naphthalene (compound 6). In vitro antifungal tests showed that the three trichothecenes were active against A. niger, T. rubrum and C. albicans with MICs of 31.25, 62.5 and 125 microg ml(-1) for compound 2, 250, 125 and 31.25 microg ml(-1) for compound 3 as well as 125, 62.5 and 125 microg ml(-1) for compound 4 respectively. The MICs of ketoconazole (co-assayed herewith as a positive reference) against A. niger, T. rubrum and C. albicans were 31.25, 250, 31.25 microg ml(-1) respectively. A preliminary structure-activity relationship of the antifungal trichothecenes was highlighted in brief. CONCLUSIONS: The present investigation demonstrated that marine fungus Myrothecium sp. Z16 associated with white croaker (Ar. argentatus), was an efficient producer of a new acid and antifungal trichothecenes, the latter presumably being also the allergic substances in the culture. SIGNIFICANCE AND IMPACT OF THE STUDY: The title marine fungus was investigated to be a resource of new aliphatic acid, and trichothecenes with potent antifungal and dermal toxic actions.

Animals↗
PubMed2005

Repellent and insecticidal activities of essential oils from Artemisia princeps and Cinnamomum camphora and their effect on seed germination of wheat and broad bean.

Repellent and insecticidal activities of essential oils extracted from leaves of Artemisia princeps Pamp and seeds of Cinnamomum camphora (L.) Presl. against storage pests Sitophillus oryzae L. and Bruchus rugimanus Bohem were investigated. Results showed that the two individual oils displayed good, but their mixture (1:1) exhibited much better repellent activities at concentrations from 250 to 1000 microg g(-1) and insecticidal actions at concentrations 1000 microg g(-1) against the test beetles S. oryzae and B. rugimanus. Oils from A. princeps and C. camphora applied individually were significantly toxic to seed germination of wheat at 500 microg ml(-1). However, no toxic effects were found when the two oils were mixed (1:1 w/w) at the same concentration. These observations indicated that the mixture of the two plant-derived oils had a synergic effect and could be used in the control of storage pests.

Animals↗
PubMed2005

Sulfation of a polysaccharide produced by a marine filamentous fungus Phoma herbarum YS4108 alters its antioxidant properties in vitro.

Free radicals and other reactive oxygen species (ROS) are generated by all aerobic cells and are widely believed to play a significant role in aging as well as a number of degenerative or pathological diseases. This study compared the free radical-scavenging properties and antioxidant activity of YCP, a polysaccharide from the mycelium of a marine filamentous fungus Phoma herbarum YS 4108 and its two chemically sulfated derivatives YCP-S1 and YCP-S2. Sulfation, which masks hydroxyl groups of YCP polysaccharide molecule, could introduce new antioxidant activity, such as superoxide and hydroxyl radicals scavenging activity, metal chelating action, lipid peroxidation and linoleic acid oxidation inhibition capability. Furthermore, sulfated YCP was more potent than YCP at protecting erythrocytes against oxidative damage hemolysis. The current data suggest for the first time that sulfation of polysaccharide significantly increases its antioxidant activity and the chemical modification of polysaccharides may allow the preparation of derivatives with new properties and a variety of applications.

Animals↗
PubMed2005

Laccase production by Monotospora sp., an endophytic fungus in Cynodon dactylon.

The effects of the carbon and nitrogen sources, initial pH and incubation temperature on laccase production by the endophytic fungus Monotospora sp. were evaluated. The optimal temperature and initial pH for laccase production by Monotospora sp. in submerged culture were found to be 30 degrees C and 8.5, respectively. Maltose (2 g l(-1)) and ammonium tartrate (10 g l(-1)) were the most suitable carbon and nitrogen source for laccase production. Under optimal culture medium, the maximum laccase activity was determined to be 13.55 U ml(-1), which was approximately four times higher than that in basal medium. This is the first report on laccase production by an endophytic fungus.

Ascomycota↗
PubMed2005

Purification, characterization and enzymatic degradation of YCP, a polysaccharide from marine filamentous fungus Phoma herbarum YS4108.

YCP, a mitogenic polysaccharide with its molecular weight (MW) of 2.4 x 10(3) kDa, was isolated from the mycelium of the marine filamentous fungus Phoma herbarum YS4108 by a combination of ion-exchange chromatography on DEAE-32 and gel permeation over Sephacryl S-400. The detailed compositional, spectroscopic and methylation analyses of the polysaccharide demonstrated that its backbone possessed most likely a linear alpha-(1 --> 4) bonded glucopyranoside main chain co-bearing through side alpha-(1 --> 6)-linkage. The alpha-(1 --> 4) bondage of the glucopyranoside building blocks in YCP was confirmed by the observation that it could be hydrolyzed by the alpha-amylase produced by Bacillus licheniformis. A reliable concentration monitoring experimentation highlighted that the reducing sugars released continuously from YCP during its incubation with the enzyme, and the MW of the main resulting fragment weighed 0.8 x 10(4) Da with approximately 10% of YCP converted to maltose, maltotriose and glucose after a 120-min enzymatic degradation. Finally, YCP was found to be able to increase phagocytic activity of mice in vitro and in vivo, indicating that it may be looked up as a potent immunomodulator that could activate macrophages.

Animals↗
PubMed2005

Protection of PC12 cells from hydrogen peroxide-induced injury by EPS2, an exopolysaccharide from a marine filamentous fungus Keissleriella sp. YS4108.

A number of studies indicate that free radicals are involved in the neurodegeneration in Parkinson's and Alzheimer's diseases. EPS2, an exopolysaccharide with a mean molecular weight of 1.3 x 10(5) Da, was isolated by ion-exchange and sizing chromatography from the culture of Keissleriella sp. YS4108, a marine filamentous fungus. Compositionally, it is composed of galactose, glucose, rhamnose, mannose and glucuronic acid in an approximate proportion of 50:8:1:1:0.4. The protective effects of EPS2 on peroxide hydrogen (H2O2)-induced cell lesion, level of lipid peroxidation, antioxidant enzyme activities were investigated in the rat pheochromocytoma line PC12 cells. Following a 1-h exposure of the cells to H2O2, a significant reduction in cell survival and activities of glutathione peroxidase (GSH-Px) and catalase (CAT), as well as increased levels in malondialdehyde (MDA) production and lactate dehydrogenase (LDH) release were observed. However, preincubation of the cells with EPS2 prior to H2O2 exposure elevated the cell survival and GSH-Px and CAT activities, and decreased the level of MDA and LDH activity in a dose-dependent manner. In conclusion, EPS2 possesses pronounced protective effects against H2O2-induced cell toxicity. The finding is of a higher value in searching for new therapeutic agent for treating oxidative damage-derived neurodegenerative disorders.

Animals↗
PubMed2005

New and cytotoxic anthraquinones from Pleospora sp. IFB-E006, an endophytic fungus in Imperata cylindrical.

In addition to 7-methoxy-2-methyl-3,4,5-trihydroxyanthraquinone (1), physcion (2), macrosporin (3), deoxybostrycin (4), altersolanol B (5) and dactylariol (6), a new hexahydroanthraquinone named pleospdione (7) was isolated from the culture of Pleospora sp . IFB-E006, an endophytic fungus residing in the normal stem of Imperata cylindrical (Gramineae). Structure determination of pleospdione was accomplished using IR, HR-ESI-MS, 1D and 2D NMR spectral analysis. Compounds 4 - 6 exhibited significant cytotoxic activity against human colon cancer (SW1116) and leukemia (K562) cell lines while compounds 1, 2 and 7 were only weakly or moderately active.

Anthraquinones↗
PubMed2004

Regioselective sonochemical synthesis of genistein derivatives.

Differential functionalization of the phenolic groups in genistein was carried out in excellent yields under ultrasonic irradiation. The isoflavone ring had proved to be unstable under stirring at 60 degrees C and phenyl benzyl ketone was unexpectedly isolated instead of the genistein derivative.

Genistein↗
PubMed2004

Endophytic naphthopyrone metabolites are co-inhibitors of xanthine oxidase, SW1116 cell and some microbial growths.

Fractionation of the extract of Aspergillus niger. IFB-E003, an endophyte in Cyndon dactylon, gave four known compounds naphtho-gamma-pyrones rubrofusarin B, fonsecinone A, asperpyrone B and aurasperone A, which were further investigated biologically. Rubrofusarin B was shown to be cytotoxic to the colon cancer cell line SW1116 (IC50: 4.5 microgml-1), and aurasperone A inhibitory on XO (xanthine oxidase) (IC50: 10.9 micromoll-1). Moreover, the four naphtho-gamma-pyrones exhibited growth inhibitions against the five test microbes with MICs ranging in between 1.9 and 31.2 microgml(-1). The present recognition of rubrofusarin B and aurasperone A as strong co-inhibitors on XO, colon cancer cell and some microbial pathogens is of significance for the imperative discovery of new relevant therapeutic agents.

Anti-Infective Agents↗
PubMed2004

Aspergillus fumigatus CY018, an endophytic fungus in Cynodon dactylon as a versatile producer of new and bioactive metabolites.

Aspergillus fumigatus CY018 was recognized as an endophytic fungus for the first time in the leaf of Cynodon dactylon. By bioassay-guided fractionation, the EtOAc extract of a solid-matrix steady culture of this fungus afforded two new metabolites, named asperfumoid (1) and asperfumin (2), together with six known bioactive compounds including monomethylsulochrin, fumigaclavine C, fumitremorgin C, physcion, helvolic acid and 5alpha,8alpha-epidioxy-ergosta-6,22-diene-3beta-ol as well as other four known compounds ergosta-4,22-diene-3beta-ol, ergosterol, cyclo(Ala-Leu) and cyclo(Ala-Ile). Through detailed spectroscopic analyses including HRESI-MS, homo- and hetero-nuclear correlation NMR experiments (HMQC, COSY, NOESY and HMBC), the structures of asperfumoid and asperfumin were established to be spiro-(3-hydroxyl-2,6-dimethoxyl-2,5-diene-4-cyclohexone-(1,3')-5'-methoxyl-7'-methyl-(1'H, 2'H, 4'H)-quinoline-2',4'-dione) and 5-hydroxyl-2-(6-hydroxyl-2-methoxyl-4-methylbenzoyl)-3,6-dimethoxyl-benzoic methyl ester, respectively. All of the 12 isolates were subjected to in vitro bioactive assays against three human pathogenic fungi Candida albicans, Tricophyton rubrum and Aspergillus niger. As a result, asperfumoid, fumigaclavine C, fumitremorgin C, physcion and helvolic acid were shown to inhibit C. albicans with MICs of 75.0, 31.5, 62.5, 125.0 and 31.5 microg/mL, respectively.

Antifungal Agents↗
PubMed2004

Antibacterial and xanthine oxidase inhibitory cerebrosides from Fusarium sp. IFB-121, an endophytic fungus in Quercus variabilis.

Two antibacterial and xanthine oxidase inhibitory cerebrosides, one of which is chemically new, were characterized from the chloroform-methanol (1:1) extract of Fusarium sp. IFB-121, an endophytic fungus in Quercus variabilis. By means of chemical and spectral methods [IR, electrospray ionization MS (ESI-MS), tandem ESI-MS, 1H and 13C NMR, distortionless enhancement by polarization transfer, COSY, heteronuclear multiple-quantum coherence, heteronuclear multiple-bond correlation, and 2-D nuclear Overhauser effect correlation spectroscopy], the structure of the new metabolite named fusaruside was established as (2S,2'R,3R,3'E,4E,8E,10E)-1-O-beta-D-glucopyranosyl-2-N-(2'-hydroxy-3'-octadecenoyl)-3-hydroxy-9-methyl-4,8,10-sphingatrienine, and the structure of the other was identified as (2S,2'R,3R,3'E,4E,8E)-1-O-beta-D-glucopyranosyl-2-N-(2'-hydroxy-3'-octadecenoyl)-3-hydroxy-9-methyl-4,8-sphingadienine. Both new and known cerebrosides, although inactive to Trichophyton rubrum and Candida albicans, showed strong antibacterial activities against Bacillus subtilis, Escherichia coli, and Pseudomonas fluorescens, with their minimum inhibitory concentrations being 3.9, 3.9, and 1.9 microg/mL, and 7.8, 3.9, and 7.8 microg/mL, respectively. Furthermore, both metabolites were inhibitory to xanthine oxidase, with the IC50 value of fusaruside being 43.8 +/- 3.6 microM and the known cerebroside being 55.5 +/- 1.8 microM.

Anti-Bacterial Agents↗
PubMed2004

Anti-Helicobacter pylori metabolites from Rhizoctonia sp. Cy064, an endophytic fungus in Cynodon dactylon.

A new benzophenone, named rhizoctonic acid (1), together with three known compounds monomethylsulochrin (2), ergosterol (3) and 3beta,5alpha,6beta-trihydroxyergosta-7,22-diene (4) were isolated through bioassay-guided fractionations from the culture of Rhizoctonia sp. (Cy064), an endophytic fungus in the leaf of Cynodon dactylon. The structure of the new acid 1 was elucidated to be 5-hydroxy-2-(2-hydroxy-6-methoxy-4-methylbenzoyl)-3-methoxybenzoic acid by a combination of spectral analyses. Furthermore, the structure of monomethylsulochrin 2 was confirmed by 13C-NMR analysis. All four metabolites were subjected to a more detailed in vitro assessment of their antibacterial action against five clinically isolated and one reference (ATCC 43504) Helicobacter pylori strains.

Anti-Infective Agents↗
PubMed2004

Inhibition of MAO A and B by some plant-derived alkaloids, phenols and anthraquinones.

A total of seventeen phytochemicals including seven alkaloids (piperine, strychnine, brucine, stachydrine, tetrandrine, frangchinoline and sinomenine), four phenols (paeonol, honokiol, magnolol and eugenol) and six anthraquinones (emodin, rhein, chrysorphanol, aloe-emodin, physcion and 1,8-dihydroxyanthraquinone) was examined for inhibitory activity of monoamine oxidase (MAO) A and B from rat brain mitochondrial. Among these compounds, piperine and paeonol were found to be inhibitory against MAO A in a dose-dependent manner with IC(50) values of 49.3 and 54.6 microM, respectively. Piperine, paeonol and emodin were shown to inhibit MAO B in a dose-dependent manner with the IC(50) data of 91.3, 42.5 and 35.4 microM, respectively. Lineweaver-Burk transformation of the inhibition data indicated that the inhibitory action of piperine on MAO A was of mixed type, and that of paeonol on the same type of the enzyme was of non-competitive type. For piperine, the K(i) and K(I) were determined to be 35.8 and 25.7microM, respectively. For paeonol, the K(i) was estimated to be 51.1 microM. The inhibition of piperine and paeonol on MAO B was of competitive type with K(i) values of 79.9 and 38.2 microM, respectively. The inhibition of emodin on MAO B was of mixed type with the K(i) and K(I) data of 15.1 and 22.9 microM, respectively. The present investigation showed that the phytochemicals piperine, paeonol and emodin are potent MAO inhibitors whereas other compounds were inactive against any type of MAO at 100 microM in the present assay.

Alkaloids↗
PubMed2004

Inhibitory effects of flavonoids from Hypericum perforatum on nitric oxide synthase.

The inhibitory effects of six flavonoids from Hypericum perforatum were assessed spectrophotometrically using nitric oxide synthase (NOS) in blood and cerebral homogenate of rats. Of the assayed compounds, quercetin and hyperoside showed concentration-dependent enzyme inhibitory actions. The IC50 values of quercetin for inhibiting NOS in rat cerebral homogenate and blood were 63.06 and 57.54 microM, and those of hyperoside 56.23 and 158.49 microM, respectively. The competitive patterns were discerned with the inhibition of the two flavonoids on NOS in serum and cerebral homogenate (except a mixed type inhibition was observed with quercetin in inhibiting cerebral NOS). Furthermore, similar inhibitions were found for quercetin upon NOS in cerebral homogenate and blood. However, a stronger inhibitory effect of hyperoside on the enzyme was discerned in cerebrum than in blood. These results suggested that the galactose moiety in hyperoside may be associated with the selectivity of the NOS inhibition.

Animals↗
PubMed2004

A potent feed preservative candidate produced by Calcarisporium sp., an endophyte residing in stargrass (Cynodon dactylon).

AIMS: The cultures of an endophytic fungus Calcarisporium sp. were screened for inhibitors on the growth of feed-associated moulds and on the aflatoxin biosynthesis to find a safe and effective feed preservative. METHODS AND RESULTS: Eight test fungi were isolated from the spoiled poultry feed. The endophytic fungus Calcarisporium sp. was separated from the Chinese coastal grass Cynodon dactylon. The antifungal action concerning the endophytic culture extract (ECE) was performed with propionic acid (PPA) as the corresponding reference. The ECE had a similar antifungal efficacy to PPA in a concentration-dependent manner. The susceptibility order of the ECE to the test fungi was found to be Fusarium sp. > Aspergillus spp. > Penicillium spp. Furthermore, the application of the ECE in pelleted-layer duck feed as a preservative was carried out at a humidity of 10, 15 and 20%. It has been discerned that mould growth and aflatoxin biosynthesis could be co-inhibited almost completely by ECE at concentrations higher than 1.0% (w/w). The LD50 of the ECE on mice was shown to be higher than 28 g kg-1. CONCLUSIONS: The ECE can be selected as an inhibitor to preserve poultry feed on inhibiting the growth of mould and aflatoxin biosynthesis during feed storage. SIGNIFICANCE AND IMPACT OF THE STUDY: The ECE may be an effective and biosafe antifungal ingredient for poultry feed and holds a potential market prospect in feed industry.

Aflatoxins↗
PubMed2003

High-performance liquid chromatographic analysis of bioactive triterpenes in Perilla frutescens.

Perilla frutescens (L.) Britt. (Lamiaceae), a famous traditional Chinese medicine, has been used for the treatment of various diseases. To evaluate the quality of P. frutescens, a simple, rapid and accurate high-performance liquid chromatography (HPLC) method was developed for the assessment of three bioactive triterpene acids: tormentic acid (TA), oleanolic acid (OA) and ursolic acid (UA). The HPLC system used an Spherisob octadecylsilyl silica (ODS) column with acetonitrile and aqueous H(3)PO(4) as the mobile phase and detection at 206 nm. The method was precise with relative standard deviations for these three constituents that ranged between 0.6-1.5% (intraday) and 0.7-2.6% (interday). The content of these three phytochemicals in the leaves of P. frutescens growing at eight different locations of China was determined to establish the effectiveness of the method.

Chromatography, High Pressure Liquid↗
PubMed2003

Pinelloside, an antimicrobial cerebroside from Pinellia ternata.

An antimicrobial cerebroside, pinelloside, was isolated from the air-dried tubers of Pinellia ternata (Thunb.) Breit. Its structure was determined as 1-O-beta-D-glucopyranosyl-(2S,3R,4E,11E)-2-(2'R-hydroxyhexadecenoylamino)-4,11-octadecadiene-1,3-diol by chemical transformation and extensive spectroscopic analyses (IR, MS, 1H and 13C NMR, DEPT as well as 2D NMR techniques HMBC, HMQC, 1H-1H COSY and NOESY). The antimicrobial assay showed that this compound was inhibitory to the growth of Bacillus subtilis, Staphylococcus aureus, Aspergillus niger and Candida albicans, with minimum inhibitory concentrations (MICs) of 20, 50, 30 and 10 microg/ml, respectively. The MICs of penicillin G against bacteria B. subtilis, S. aureus, E. coli, P. fluorescens and H. pylori were 0.80, 0.34, 0.56, 1.34 and 0.92, and those of ketoconazole against fungi A. niger, C. albicans and T. rubrum 0.90, 0.65 and 1.0 microg/ml, respectively.

Anti-Infective Agents↗