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Biomedical subjects

C E Olsen

Publications and source records attributed to C E Olsen.

At least 55 records · Page 3Linked to original sources
PubMed1999

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 4: hyperbolic activation of rat liver microsomal NADPH-cytochrome C reductase by the novel acetylator 7,8-diacetoxy-4-methylcoumarin.

The effect of 7,8-diacetoxy-4-methylcoumarin (DAMC) has been studied on hepatic NADPH cytochrome C reductase-- an enzyme participating in the microsomal electron transport. The preincubation of liver microsomes with DAMC resulted in a time-dependent activation of NADPH cytochrome C reductase. The catalytic activity of the enzyme enhanced nearly 600% by 25 microM concentration of DAMC after 10 min of preincubation. The action of DAMC on the reductase resulted in enhanced v(max) while Km remained constant. A plot of 1/v(max) as a function of DAMC concentration resulted in a non-linear, but rectangular hyperbola indicative of hyperbolic activation. DAMC was also proved to be effective in significantly enhancing the activity of NADPH cytochrome C reductase in vivo. 7,8-Dihydroxy-4-methylcoumarin (DHMC), the deacetylated product of DAMC failed to irreversibly activate the enzyme. The activation effect of DAMC upon the enzyme was abolished by p-hydroxymercury benzoate. The role of a transacetylase in transferring the acetyl group of DAMC to the amino acid(s) of the active site of NADPH cytochrome C reductase causing irreversible enzyme activation is enunciated.

Acetylation↗
PubMed1999

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 5: Pulse radiolysis studies on the antioxidant action of 7,8-diacetoxy-4-methylcoumarin.

7,8-Dihydroxy-4-methylcoumarin (1, DHMC) and 7,8-diacetoxy-4-methylcoumarin (2, DAMC) were shown to possess radical scavenging property and strongly inhibit membrane lipid peroxidation. Although free polyphenolic compounds are known to be antioxidants, the antioxidant action of the acetoxy compound DAMC was intriguing. Hence, pulse radiolysis studies were undertaken to explain the antioxidant action of DAMC. Accordingly, DAMC and DHMC were separately reacted with the system generating azide radicals and the resulting transient spectra were recorded. The spectra so obtained in both the cases demonstrated peak at 410 nm, characteristic of phenoxyl radical. The rate constants for the formation of phenoxyl radical from DHMC and DAMC were 34 x 10(8) M(-1) s(-1) and 6.2 x 10(8) M(-1) s(-1), respectively. We propose that the free radical mediated oxidation of DAMC initially produces a radical cation that loses an acetyl carbocation to yield the phenoxyl radical. It is possible to conclude that the mechanism of the antioxidant action of DAMC follows the pathway similar to that of DHMC involving the formation of a stable phenoxyl radical.

Antioxidants↗
PubMed1999

Spectrofluorometric characterization of beta-lactoglobulin B covalently labeled with 2-(4'-maleimidylanilino)naphthalene-6-sulfonate.

Bovine beta-lactoglobulin, genetic variant B, has been labeled with 2-(4'-maleimidylanilino)naphthalene-6-sulfonic acid through covalent attachment through the Cys-121 thiol group for the study of stepwise pressure denaturation of this whey protein by fluorescence spectroscopy. The labeling was performed under nondenaturing conditions with a factor of 5 excess of the fluorophore in dimethylformamide/water (1:10) to yield the whey protein highly labeled after chromatographic separation. MALDI-TOF mass spectroscopy confirmed labeling. The emission from the fluorophore, which is sensitive to the microenvironment, has been characterized for the labeled protein (aqueous pH 7.4 solution, 25 degrees C) and has a lambda(em,max) = 410 nm (lambda(ex,max) = 318 nm) with a fluorescence lifetime of 6.1 +/- 0.2 ns. Fluorescence anisotropy increases and fluorescence quantum yield (Phi(f) = 0.103 at 320 nm) decreases with increasing excitation wavelength. For increasing hydrostatic pressure, fluorescence quantum yield showed a minimum at approximately 50 MPa, corresponding to the pre-denatured "pressure-melted" state in which thiol reactivity previously was found to increase prior to reversible protein unfolding.

Anilino Naphthalenesulfonates↗
PubMed1999

Metabolic engineering of p-hydroxybenzylglucosinolate in Arabidopsis by expression of the cyanogenic CYP79A1 from Sorghum bicolor.

Glucosinolates are natural products in cruciferous plants, including Arabidopsis thaliana. CYP79A1 is the cytochrome P450 catalysing the conversion of tyrosine to p-hydroxyphenylacetaldoxime in the biosynthesis of the cyanogenic glucoside dhurrin in sorghum. Both glucosinolates and cyanogenic glucosides have oximes as intermediates. Expression of CYP79A1 in A. thaliana results in the production of high levels of the tyrosine-derived glucosinolate p-hydroxybenzylglucosinolate, which is not a natural constituent of A. thaliana. This provides further evidence that the enzymes have low substrate specificity with respect to the side chain. The ability of the cyanogenic CYP79A1 to integrate itself into the glucosinolate pathway has important implications for an evolutionary relationship between cyanogenic glucosides and glucosinolates, and for the possibility of genetic engineering of novel glucosinolates.

Arabidopsis↗
PubMed1999

Evaluation of oligonucleotides containing two novel 2'-O-methyl modified nucleotide monomers: a 3'-C-allyl and a 2'-O,3'-C-linked bicyclic derivative.

The two ribo-configured nucleosides 1-(3-C-allyl-2-O-methyl-beta-D-ribo-pentofuranosyl)thymine 3 and (1S,5R,6R,8R)-5-hydroxy-6-(hydroxymethyl)-1-methoxy-8-(thymin-1-yl )- 2,7-dioxabicyclo[3.3.0]octane 6 have been transformed into their corresponding phosphoramidites, 5 and 8 respectively, and used as building blocks for the synthesis of modified oligonucleotides. The oligonucleotides were shown to hybridize with decreased binding affinity towards complementary single stranded DNA and RNA.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed1998

The eight-amino acid internal loop of PSI-C mediates association of low molecular mass iron-sulfur proteins with the P700-FX core in photosystem I.

The PSI-C subunit of photosystem I (PS I) shows similarity to soluble 2[4Fe-4S] ferredoxins. PSI-C contains an eight residue internal loop and a 15 residue C-terminal extension which are absent in the ferredoxins. The eight-residue loop has been shown to interact with PSI-A/PSI-B (Naver, H., Scott, M. P., Golbeck, J. H., Moller, B. L., and Scheller, H. V. (1996) J. Biol. Chem. 271, 8996-9001). Four mutant proteins were constructed. Two were modified barley PSI-C proteins, one lacking the loop and the C terminus (PSI-Ccore) and one where the loop replace the C-terminal extension (PSI-CcoreLc-term). Two were modified Clostridium pasteurianum ferredoxins, one with the loop of barley PSI-C and one with both the loop and the C terminus of PSI-C. Wild-type proteins and the mutants were used to reconstitute barley P700-FX cores lacking PSI-C, -D, and-E. Western blotting showed that PSI-CcoreLc-term binds to PS I, whereas PSI-Ccore does not. Without PSI-D the PSI-CcoreLc-term mutant accepts electrons from FX in contrast to PSI-C mutants without the loop. Flash photolysis of P700-FX cores reconstituted with C. pasteurianum ferredoxin showed that only the ferredoxin mutants with the loop accepted electrons from FX. From this, it is concluded that the loop of PSI-C is necessary and sufficient for the association between PS I and PSI-C, and that the loop is functional as an interaction domain even when positioned at the C terminus of PSI-C or on a low molecular mass, soluble ferredoxin.

Amino Acid Sequence↗
PubMed1998

Kaempferol tetraglucosides from cabbage leaves.

Four flavonol glycosides were isolated from a leaf extract of cabbage and characterized by chemical and spectroscopic methods including 1H and 13C NMR and negative ion FAB-MS. The common structure of the four compounds was kaempferol 3-O-beta-D-[beta-D-glucopyranosyl(1-->2)glucopyranoside]-7- O-beta-D-[beta-D-glucopyranosyl(1-->4)glucopyranoside]. This compound was found unmodified or acylated at C-2"' (outer glucose in sophorosyl moiety) with either sinapic acid, ferulic acid or caffeic acid. The possible role of diversity in glycosylation and acylation patterns of flavonol glycosides for plant defences against herbivores is discussed.

Brassica↗
PubMed1998

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part I: Dioxygenated 4-methyl coumarins as superb antioxidant and radical scavenging agents.

Twenty-three 4-methylcoumarins bearing different functionalities have been examined for the first time for their effect on NADPH-catalysed liver-microsomal lipid peroxidation with a view to establish structure-activity relationship. Dihydroxy- and diacetoxy-4-methylcoumarins produced dramatic inhibition of lipid peroxidation. 7,8-Diacetoxy-4-methylcoumarin and 7,8-dihydroxy-4-methylcoumarin were found to possess superb antioxidant and radical scavenging activities.

Animals↗
PubMed1998

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part II: Mechanism-based inhibition of rat liver microsome-mediated aflatoxin B1-DNA binding by the candidate antimutagen 7,8-diacetoxy-4-methylcoumarin.

7,8-Diacetoxy-4-methylcoumarin (DAMC), with no prerequisite for oxidative biotransformation has been reported to produce suicide inactivation of microsomal cytochrome P-450-catalysed formation of aflatoxin B1-8,9-oxide that binds to DNA. Parenteral administration of DAMC to rats caused significant inhibition of AFB1 binding to hepatic DNA in vivo as well as AFB1-induced micronuclei formation in bone marrow cells. These results highlight the antimutagenic potential of DAMC.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1998

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 3: A novel mechanism for the inhibition of biological membrane lipid peroxidation by dioxygenated 4-methylcoumarins mediated by the formation of a stable ADP-Fe-inhibitor mixed ligand complex.

7,8-Dihydroxy-4-methylcoumarin (DHMC) and 7,8-diacetoxy-4-methylcoumarin (DAMC) have been reported to effectively inhibit in-vivo lipid peroxidation in rat tissues induced by CCl4 and paraquat. DHMC was found to readily impart green colour to the lipid peroxidation incubation mixture containing ADP and Fe3+, whereas DAMC formed green complex only upon incubation with liver microsomes, confirming our earlier observation that liver microsomal deacetylase hydrolyses DAMC to DHMC. Sensitive pH metric technique revealed the formation of ADP-Fe-DHMC ternary complex with highest stability, while Fe-DHMC and ADP-DHMC had negligible stabilities concluding that ADP-perferryl ion formation is prevented by DHMC resulting in the production of stable ternary mixed ligand complex (ADP-Fe-DHMC), thereby inhibiting the formation of O2-, and eventually other reactive oxygen species (ROS) responsible for membrane lipid peroxidation.

Adenosine Diphosphate↗
PubMed1998

A flavonoid 7-O-methyltransferase is expressed in barley leaves in response to pathogen attack.

We have shown previously that transcripts corresponding to the cDNA clone pBH72-F1, with similarities to O-methyltransferases (OMT), accumulated in barley leaves in response to attack by the pathogenic fungus Blumeria graminis (Plant Mol Biol 26 (1994) 1797). To investigate the accumulation pattern in the defence response and the organ localization of the pBH72-F1-encoded polypeptide (F1-OMT), an antiserum was raised against Escherichia coli expressed F1-OMT. The 43 kDa protein was absent in normal leaves but accumulated strongly in response to pathogen attack. The F1-OMT protein accumulated faster in barley lines inoculated with an avirulent B. graminis isolates compared to a virulent isolate. Additionally, F1-OMT related proteins were detected in developing kernels. F1-OMT was expressed as a functional enzyme in E. coli and the substrate specificity was investigated. The enzyme exhibited OMT activity towards flavonoid aglycones with the highest activity against apigenin (4',5,7-trihydroxyflavone). In contrast, caffeic acid did not serve as substrate for F1-OMT. The product of F1-OMT was analyzed by HPLC and GC-MS and found to be genkwanin (4',5-dihydroxy-7-methoxyflavone). Initial velocity data were best represented by a sequential bi-bi mechanism, and kinetic parameters of KSAM = 10.9 microM, Kapigenin = 4.6 microM and a specific activity of 0.45 mukat/g were obtained. Barley F1-OMT, apigenin 7-O-methyltransferase, is suggested to be involved in the production of a methylated flavonoid phytoalexin.

Ascomycota↗
PubMed1998

Alkamides from Phyllanthus fraternus.

Two alkamides E,E-2,4-octadienamide and E,Z-2,4-decadienamide have been isolated from Phyllanthus fraternus, a plant used in Ghanaian traditional medicine to treat malaria. The compounds possess an alpha, beta, gamma, delta-unsaturated conjugated amide, a feature believed to enhance antiplasmodial activity. By means of an in vitro assay the two alkamides have been shown to possess moderate antiplasmodial activity.

Amides↗
PubMed1998

Angiotensin converting enzyme (ACE) inhibitors from Jasminum azoricum and Jasminum grandiflorum.

Bioactivity-guided fractionation of extracts of the aerial parts of Jasminum azoricum var. travancorense, using an in vitro ACE inhibition assay, led to isolation of three oligomeric, iridoid-type compounds, which were named sambacein I-III. Their structures are based on spectroscopic and chemical evidence. Similarly, fractionation of extracts of aerial parts of J. grandiflorum resulted in the isolation of the previously reported ACE inhibitor, oleacein. The IC50 values of purified ACE inhibitors were 26-36 microM. Moreover, 2-(3,4-dihydroxyphenyl)-ethanol, isoquercitrin and ursolic acid were isolated from J. grandiflorum. Sambaceins and oleacein are formed from genuine iridoid glucosides during processing of the plant material. NMR spectroscopy was used to measure the level of the ACE inhibitors in the traditional medicines prepared in Kerala from these Jasminum species.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Cladobotryal: a fungal metabolite with a novel ring system.

In screening for antifungal metabolites a novel compound, cladobotryal, was isolated from the mycoparasitic fungus Cladobotryum varium. Its structure was established as (+)-(2R*,3R*)-2-[(Z)-2-buten-2-yl]-3, 7-dihydro-3-formyl-3-methyl-5-phenylfuro[2,3-b]pyridin-4(2H)-one on the basis of spectroscopic evidence and single crystal X-ray analysis of its methyl hemiacetal. The fused furo[2,3-b]pyridinone skeleton of cladobotryal seems unprecedented within the chemical literature.

Antifungal Agents↗
PubMed1998

Aflatoxin B1-induced micronuclei and cell cycle alterations in lung and bone marrow cells and their modulation by Piper argyrophyllum extract.

Aflatoxin B, (AFB1) is a clastogen that causes cellular damage by covalent modification of nucleic acids. In this investigation, male rats were injected i.p. with AFB1 (8 mg/kg b.w.) in DMSO and the same dose of AFB1 was also administered intratracheally (i.t.) to the animals separately. The animals were killed after 26 h of the carcinogen treatment, femur bone was removed, and bone marrow cells were isolated and stained with Mayer's hematoxylin and eosin. Micronuclei (Mn) were scored by using light microscopy. Bronchoalveolar lavage (BAL) was prepared from rats administered AFB1 i.t. A part of BAL was fixed with 70% ethanol, stained with the fluorochrome DAPI, and analysed for cell cycle variations; the other part of the lavage was used for making slides to record Mn with a fluorescent microscope. A significantly greater proportion of lung cells were found to enter cell cycle with extended S-phase due to AFB1 treatment. Mn were induced in polychromatic erythrocytes (PCE) as compared to normochromatic erythrocytes (NCE) in the bone marrow of AFB1-treated rats, where there was nearly a three-fold increase in the number of Mn of bone marrow cells. The administration of AFB1 resulted in a two-fold rise in the Mn in the lung cells. The effect of BSO, DEM, and PB, the modulators of AFB1 metabolism, was studied on AFB1-induced Mn formation. A significant increase in the Mn score in PCEs of BSO- and DEM-treated rats was noted, while a slight reduction in the Mn score was noted in the case of PB-treated rats. The administration of the methanol extract of the leaves of Piper argyrophyllum (taken up in DMSO) to rats for a week exhibited normalising effect on AFB1-induced Mn in bone marrow cells. These observations record the induction of Mn in lung cells due to AFB1 for the first time. We propose the utility of AFB1-induced Mn as a model for screening plant extracts as inhibitors of genotoxicity. Prevention of genotoxic changes described above by phytochemicals is being pursued in our Laboratories.

Aflatoxin B1↗
PubMed1997

Anti-invasive activity of alkaloids and polyphenolics in vitro.

Invasiveness, the ability of certain tumour cells to migrate beyond their natural tissue boundaries, often leads to metastasis, and usually determines the fatal outcome of cancer. The need for anti-invasive agents has led us to search for possibly active compounds among alkaloids and polyphenolics. One hundred compounds were screened in an assay based on the confrontation of invasive human MCF-7/6 mammary carcinoma cells with fragments of normal embryonic chick heart in vitro. Anti-invasive activity was frequently found among chalcones having a prenyl group. Six compounds were found to inhibit invasion when added to the culture medium at concentrations as low as 1 microM. For at least three of them the anti-invasive effect could be associated with a cytotoxic effect on the MCF-7/6 cells, but not on the heart tissue. This selective cytotoxicity was substantiated by different methods, such as histology and growth assays (volume measurements, cell counts, MTT and sulforhodamine B assays). The anti-invasive effects of the compounds could neither be ascribed to induction of apoptosis nor to the promotion of cell-cell adhesion. Our data indicate that among the alkaloids and polyphenolics a number of molecules can inhibit growth and invasion of human mammary cancer cells via selective cytotoxicity.

Alkaloids↗
PubMed1997

Oxysporidinone: a novel, antifungal N-methyl-4-hydroxy-2-pyridone from Fusarium oxysporum.

Oxysporidinone (1), a novel 3,5-disubstituted N-methyl-4-hydroxy-2-pyridone, was isolated from fermentations of Fusarium oxysporum (CBS 330.95) by counter-current chromatography. The structure was determined by spectroscopic methods including NMR, MS, IR, and UV analysis. Oxysporidinone exhibited growth inhibitory activity against several common plant pathogenic fungi.

Antifungal Agents↗