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See detailDoes the new water-soluble form of curcumin(NDS27) inhibit the oxidant response of stimulated neutrophils and HL-60 cells?
Derochette, Sandrine ULg; Franck, Thierry ULg; Deby-Dupont, Ginette et al

Poster (2012, September 07)

Neutrophils (PMNs) are involved in host defense against infections through the production of reactive oxygen species (ROS) and the release of an oxidant enzyme, myeloperoxidase (MPO), to kill pathologic ... [more ▼]

Neutrophils (PMNs) are involved in host defense against infections through the production of reactive oxygen species (ROS) and the release of an oxidant enzyme, myeloperoxidase (MPO), to kill pathologic agents. But, an excessive stimulation of PMNs is associated with development of inflammatory diseases. Neutrophils are prime targets to control inflammatory events and the therapeutic use of polyphenols is proposed to lower oxidative stress. The aim of this work was to study antioxidant effect of NDS27, a water-soluble form of curcumin, on stimulated equine PMNs and human promyelocytic leukemia cells (HL-60) which are less differenciated. 2',7'-Dichlorofluorescin diacetate and lucigenin were used to measure ROS production by activated HL-60 cells or PMNs. NDS27 (10-6 to 10-4 M) was pre-incubated with cells and eliminated before their activation to study its intracellular effects on ROS production. The effect of NDS27 on MPO activity released by the cells was determined by SIEFED. Likewise, the ability of NDS27 to enter into the cells was checked by HPLC on the cellular extracts.NDS27 significantly and dose-dependently inhibited the ROS production in both cell types without affecting their viability. Its intracellular effect showed higher efficiency for PMNs while its interaction with HL-60 cells remained better. The activity of MPO released by PMNs and HL-60 cells was decreased by NDS27 with a more efficient effect for PMNs. Our findings suggest that the greater efficiency of NDS27 in mature PMNs is not due to a better membrane permeability or a better interaction between membrane and NDS27, but rather to an inhibitory effect on the ROS production by the more mature cells, probably by targeting the enzymes implied in respiratory burst like MPO and NADPH oxidase. The modulatory effect of NDS27 towards oxidant activity of cells involved in immune and inflammatory response opens therapeutic perspectives to control pathologies with excessive inflammatory reactions. [less ▲]

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See detailA confocal microscopic study of mitochondrial alterations of renal HK-2 cells exposed to an endotoxic stress
Quoilin, Caroline ULg; Mouithys-Mickalad, Ange ULg; Fontaine-Aupart, Marie-Pierre et al

Poster (2012, September)

Sepsis has a profound deleterious effect on kidney functions through complex mechanisms, which involve the immune response, inflammatory pathways, intracellular dysfunction and hemodynamic instability ... [more ▼]

Sepsis has a profound deleterious effect on kidney functions through complex mechanisms, which involve the immune response, inflammatory pathways, intracellular dysfunction and hemodynamic instability. Those factors are difficult to discriminate in vivo. To get a better understanding of renal respiratory dysfunction, we developed an in vitro model of sepsis-induced acute kidney injury using proximal tubular epithelial cell lines (HK-2) exposed to a bacterial endotoxin (lipopolysaccharide, LPS). Using this model, our first work has demonstrated that the basal respiration of renal HK-2 cells subjected to endotoxins was altered and presented a strong decrease in the oxygen consumption rates. Our working hypothesis of the pathophysiology of sepsis-induced AKI is based on a change in mitochondrial function that has been termed cytopathic hypoxia. A consequence of mitochondrial function alterations is an inability of the cell to use molecular oxygen for ATP production. The oxidative phosphorylation within mitochondria is interrupted because of the inhibition of cytochrome oxidase. The present investigation was carried out to establish whether mitochondrial alterations might be a mechanism of renal tubular epithelial injury during sepsis. To reach this goal the mitochondrial alterations of renal HK-2 cells exposed to an endotoxic stress was studied by confocal laser-scanning microscope. Confocal microscope allowed observation of the evoked phenomena at the single cell level and in real time. More particulary, mitochondrial morphology, mitochondrial membrane potential (ΔΨm) and generation of reactive oxygen species were recorded using specific vital fluorescent probes and quantified by image processing and analysis. Mitochondrial membrane potential is generated by the mitochondrial electron transport chain. This gradient is critical for the formation of ATP, and a fall in membrane potential is an indicator of mitochondrial dysfunction. ΔΨm was measured using the lipophilic cationic probe TMRE and it was shown that LPS produced a decrease in ΔΨm. In parallel, superoxide generation was measured by using MitoSOX which is selectively targeted to the mitochondria. There was a significant increase in mitochondrial superoxide-specific oxidation of MitoSOX when HK-2 cells were submitted to LPS. Overall, the model of HK-2 cells exposed to LPS displays some key features of sepsis-induced acute kidney injury. The confocal microscopy study has suggested a mechanism of toxicity dependent on mitochondrial oxidant generation and mitochondrial dysfunction. Indeed, the exposure to LPS has resulted in an increased generation of superoxide and a loss of mitochondrial function probably initiated by a fall in mitochondrial potential. [less ▲]

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See detailEndotoxin-induced basal respiration alterations of renal HK-2 cells: A sign of pathologic metabolism down-regulation
Quoilin, Caroline ULg; Mouithys-Mickalad, Ange ULg; Duranteau, Jacques et al

in Biochemical and Biophysical Research Communications (2012), 423(2), 350-354

To study the mechanism of oxygen regulation in inflammation-induced acute kidney injury, we investigate the effects of a bacterial endotoxin (lipopolysaccharide, LPS) on the basal respiration of proximal ... [more ▼]

To study the mechanism of oxygen regulation in inflammation-induced acute kidney injury, we investigate the effects of a bacterial endotoxin (lipopolysaccharide, LPS) on the basal respiration of proximal tubular epithelial cells (HK-2) both by high-resolution respirometry and electron spin resonance spectroscopy. These two complementary methods have shown that HK-2 cells exhibit a decreased oxygen consumption rate when treated with LPS. Surprisingly, this cellular respiration alteration persists even after the stress factor was removed. We suggested that this irreversible decrease in renal oxygen consumption after LPS challenge is related to a pathologic metabolic down-regulation such as a lack of oxygen utilization by cells. [less ▲]

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See detailPhysical Fitness and Mitochondrial Respiratory Capacity in Horse Skeletal Muscle
Votion, Dominique ULg; Gnaiger, Erich; Lemieux, Hélène et al

in PLoS ONE (2012), 7(4), 1-12

We applied high-resolution respirometry and multiple substrate-uncoupler-inhibitor titration protocols to study mitochondrial physiology in small (1.0–2.5 mg) permeabilized muscle fibres sampled from ... [more ▼]

We applied high-resolution respirometry and multiple substrate-uncoupler-inhibitor titration protocols to study mitochondrial physiology in small (1.0–2.5 mg) permeabilized muscle fibres sampled from triceps brachii of healthy horses. The present investigation on horse skeletal muscle has tested the methodology used to study mitochondrial function in muscle microbiopsies by high-resolution respirometry to define reference protocols for horses (from sampling procedure to data analysis). [less ▲]

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See detailPossible intracellular effect of the new water-soluble form of curcumin (NDS27) on the oxidant response of stimulated neutrophils
Derochette, Sandrine ULg; Mouithys-Mickalad, Ange ULg; Deby-Dupont, Ginette et al

Poster (2012, April 18)

Neutrophils (PMNs) are involved in host defense against infections through the production of reactive oxygen species (ROS) to kill pathologic agents. But, an excessive ROS production, called “oxidative ... [more ▼]

Neutrophils (PMNs) are involved in host defense against infections through the production of reactive oxygen species (ROS) to kill pathologic agents. But, an excessive ROS production, called “oxidative stress” is associated with tissue damages and development of chronic or acute inflammatory diseases. PMNs are prime therapeutic targets to control inflammatory events associated to ROS production. Nowadays, there is a growing interest for the use of polyphenolic molecules to modulate the inflammatory response. The aim of this work was to study the antioxidant effect of NDS27 (1), a new highly water-soluble form of the polyphenolic molecule curcumin, on in vitro stimulated equine PMNs. NDS27 (10-6 to 10-4 M) was pre-incubated with cells and eliminated before their activation. The ability of NDS27 to enter into the cells was checked by HPLC from the cellular extracts. The intracellular ROS production by phorbol myristate acetate (PMA) stimulated PMNs was measured by fluorescence using 2’,7’-dichlorofluorescin diacetate. Lucigenin dependent chemiluminescence was used to measure extracellular ROS production. Additionally, the effect of NDS27 was tested on the activity of myeloperoxidase (MPO), a hemic enzyme contributing to the oxidant response of neutrophils. The activity of the released MPO by cytochalazine B (CB) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) stimulated PMNs was measured by SIEFED (“Specific Immunologic Extraction Followed by Enzymatic Detection”) (2). The HPLC results showed that NDS27 enters into PMNs and interacts with their membrane. NDS27 significantly and dose-dependently inhibited the ROS production in neutrophils without affecting their viability. Likewise, the activity of MPO released by PMNs was lowered by NDS27. Overall, our findings demonstrate that the membrane of neutrophils is permeable to NDS27 or interacts with the drug, suggesting that its inhibitory effect on ROS production is mainly associated to an intracellular effect probably by acting on the enzymes implied in respiratory burst like NADPH oxidase and MPO. The modulatory effect of NDS27 towards the oxidant activity of cells involved in immune and inflammatory response open therapeutic perspectives to control equine or human pathologies with excessive inflammatory reactions. 1. Neven et al. 2011, Patent Application Publication: US2011/0257126 A1 2. Serteyn et al. 2005, European Patent Specification : EP1711817 B1 [less ▲]

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See detailAssessment of reactive oxygen species production in cultured equine skeletal myoblasts in response to conditions of anoxia followed by reoxygenation with or without exposure to peroxidases.
Ceusters, Justine ULg; Mouithys-Mickalad, Ange ULg; de la Rebière de Pouyade, Geoffroy ULg et al

in American Journal of Veterinary Research (2012), 73(3), 426-434

Objective—To culture equine myoblasts from muscle microbiopsy specimens, examine myoblast production of reactive oxygen species (ROS) in conditions of anoxia followed by reoxygenation, and assess the ... [more ▼]

Objective—To culture equine myoblasts from muscle microbiopsy specimens, examine myoblast production of reactive oxygen species (ROS) in conditions of anoxia followed by reoxygenation, and assess the effects of horseradish peroxidase (HRP) and myeloperoxidase (MPO) on ROS production. Animals—5 healthy horses (5 to 15 years old). Procedures—Equine skeletal myoblast cultures were derived from 1 or 2 microbiopsy specimens obtained from a triceps brachii muscle of each horse. Cultured myoblasts were exposed to conditions of anoxia followed by reoxygenation or to conditions of normoxia (control cells). Cell production of ROS in the presence or absence of HRP or MPO was assessed by use of a gas chromatography method, after which cells were treated with a 3,3′-diaminobenzidine chromogen solution to detect peroxidase binding. Results—Equine skeletal myoblasts were successfully cultured from microbiopsy specimens. In response to anoxia and reoxygenation, ROS production of myoblasts increased by 71%, compared with that of control cells. When experiments were performed in the presence of HRP or MPO, ROS production in myoblasts exposed to anoxia and reoxygenation was increased by 228% and 183%, respectively, compared with findings for control cells. Chromogen reaction revealed a close adherence of peroxidases to cells, even after several washes. Conclusions and Clinical Relevance—Results indicated that equine skeletal myoblast cultures can be generated from muscle microbiopsy specimens. Anoxia-reoxygenation– treated myoblasts produced ROS, and production was enhanced in the presence of peroxidases. This experimental model could be used to study the damaging effect of exercise on muscles in athletic horses. [less ▲]

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See detailAntioxidant and anti-inflammatory like properties of benzoic acid analogs on the oxidant response of neutrophils: structure/redox potential relationship study.
Franck, Thierry ULg; Mouithys-Mickalad, Ange ULg; Robert, Thierry ULg et al

in Free Radical Biology & Medicine (2012), 53(supplement 1),

We investigated the antioxidant capacity of phenolic acid derivatives by measuring their capacity to prevent ABTS oxidation and evaluating their anti-inflammatory like-properties on the oxidant response ... [more ▼]

We investigated the antioxidant capacity of phenolic acid derivatives by measuring their capacity to prevent ABTS oxidation and evaluating their anti-inflammatory like-properties on the oxidant response of neutrophils, especially on superoxide anion production and the activity of myeloperoxidase (MPO), an oxidant enzyme present and released by the primary granules of neutrophils. The superoxide anion production by PMA-stimulated neutrophils was measured by lucigenin-enhanced chimiluminescence (CL) and the activity of MPO by SIEFED to study the potential interaction of a molecule with the enzyme without interferences due to medium. The antioxidant and anti-inflammatory activities of the phenolic compounds were correlated to their redox potentials measured by voltammetry method, and discussed in relation to their molecular structure. The ability of the phenolic molecules to decrease ABTS oxidation and CL production was inversely correlated to their redox potential increasing as follows: propyl gallate > gallic acid > caffeic acid > 3,4-dihydroxybenzoic acid > ferulic acid > syringic acid > 2,6-dihydroxybenzoic acid > salicylic acid > benzoic acid. The number of hydroxyl groups (3) and their position (catechol) were essential for the efficacy of the molecules as stoichiometric antioxidants or scavengers. On MPO activity, the inhibitory capacity of the molecules was not really correlated with their redox potential and increased as follows: gallic acid > caffeic acid > 2,6-dihydroxybenzoic acid > propyl gallate > ferulic acid = syringic acid > 3,4-dihydroxybenzoic acid = salicylic acid > benzoic acid. The number of OH groups and the elongation of the carboxyl group were essential for the inhibition of MPO activity, probably by facilitating the interaction with the MPO active site or structure. The redox potential measurement seems to be a good technique to select stoichiometric antioxidants, but not anti-catalytic ones. [less ▲]

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See detailPolyphenol Content and Modulatory Activities of Some Tropical Dietary Plant Extracts on the Oxidant Activities of Neutrophils and Myeloperoxidase
Tsumbu, César Ndele ULg; Deby-Dupont, Ginette; Tits, Monique ULg et al

in International Journal of Molecular Sciences (2012), 13(1), 628-650

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See detailAntioxidant and Antiradical Activities of Manihot esculenta Crantz (Euphorbiaceae) Leaves and Other Selected Tropical Green Vegetables Investigated on Lipoperoxidation and Phorbol-12-myristate-13-acetate (PMA) Activated Monocytes
Tsumbu, César Ndele ULg; Deby-Dupont, Ginette; Tits, Monique ULg et al

in Nutrients (2011), 3(9), 818-838

Abelmoschus esculentus (Malvaceae), Hibiscus acetosella (Malvaceae), Manihot esculenta Crantz (Euphorbiaceae) and Pteridium aquilinum (Dennstaedtiaceae) leaves are currently consumed as vegetables by ... [more ▼]

Abelmoschus esculentus (Malvaceae), Hibiscus acetosella (Malvaceae), Manihot esculenta Crantz (Euphorbiaceae) and Pteridium aquilinum (Dennstaedtiaceae) leaves are currently consumed as vegetables by migrants from sub-Saharan Africa living in Western Europe and by the people in the origin countries, where these plants are also used in the folk medicine. Manihot leaves are also eaten in Latin America and some Asian countries. This work investigated the capacity of aqueous extracts prepared from those vegetables to inhibit the peroxidation of a linoleic acid emulsion. Short chain, volatile C-compounds as markers of advanced lipid peroxidation were measured by gas chromatography by following the ethylene production. The generation of lipid hydroperoxides, was monitored by spectroscopy using N-N′-dimethyl-p-phenylene-diamine (DMPD). The formation of intermediate peroxyl, and other free radicals, at the initiation of the lipid peroxidation was investigated by electron spin resonance, using α-(4-pyridyl-1-oxide)-N-tert-butylnitrone as spin trap agent. The ability of the extracts to decrease the cellular production of reactive oxygen species (ROS) in “inflammation like” conditions was studied by fluorescence technique using 2′,7′-dichlorofluorescine-diacetate as fluorogenic probe, in a cell model of human monocytes (HL-60 cells) activated with phorbol ester. Overall the extracts displayed efficient concentration-dependent inhibitory effects. Their total polyphenol and flavonoid content was determined by classic colorimetric methods. An HPLC-UV/DAD analysis has clearly identified the presence of some polyphenolic compounds, which explains at least partially the inhibitions observed in our models. The role of these plants in the folk medicine by sub-Saharan peoples as well as in the prevention of oxidative stress and ROS related diseases requires further consideration. [less ▲]

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See detailSpecific Immuno Extraction Followed by Enzymatic Detection (SIEFED), a new tool to measure active myeloperoxidase in complex media and to screen potential inhibitors of this enzyme.
Serteyn, Didier ULg; Mouithys-Mickalad, Ange ULg; Deby-Dupont, Ginette et al

in The 7th International Human Peroxidase Meeting, 22-25 May 2011, Brussels (2011, May 25)

A method called SIEFED (“Specific Immuno Extraction Followed by Enzymatic Detection”) was developed for the specific measurement of myeloperoxidase (MPO) activity without interference of the sample medium ... [more ▼]

A method called SIEFED (“Specific Immuno Extraction Followed by Enzymatic Detection”) was developed for the specific measurement of myeloperoxidase (MPO) activity without interference of the sample medium. In this method, MPO is first extracted out of aqueous or biological samples by its capture by immobilized anti-MPO antibodies. A washing step then allows to eliminate the solution or biological fluid with interfering materials (proteins, lipids, reducing or oxidizing molecules, ...) and in a last step the activity of MPO bound to its antibodies is measured by using a sensitive detection system containing a fluorogenic substrate, hydrogen peroxide and nitrite as reaction enhancer. SIEFED is a method of choice to measure easily, quantitatively, and specifically the active part of MPO present in biological samples or complex media. Results obtained with this technique applied to biological samples emphasize the importance to distinguish the total MPO concentration of a sample obtained by ELISA from the active part of MPO, which is the real witness of the oxidant potential of the enzyme. SIEFED is also a powerful tool to study compounds or natural extracts that could have an inhibitory effect on the activity of MPO. Since the potential inhibitor is first incubated with the enzyme solution, and further eliminated by washing after the immunocapture of MPO, the tested compound or extract cannot interfere with the chromogenic substrate used to measure the activity of MPO or with products derived from the enzyme activity. Thus, an inhibitory effect could only be attributed to a direct interaction of the tested compound with the enzyme, either on the active site or another key position of the structure. In conclusion, the SIEFED technique opens new perspectives to study pathologies in which the release of active MPO is relevant and to select interesting compounds or extracts able to modulate the MPO activity. [less ▲]

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See detailEffect of benzoic acid analogs on myeloperoxidase activity measured by a new technique to study their direct interaction with the enzyme.
Franck, Thierry ULg; Mazloum, Ali; Mouithys-Mickalad, Ange ULg et al

Poster (2011, May)

Myeloperoxidase (MPO) plays a key role in inflammatory response and constitutes a target for new drug development. The effects of some benzoic acid analogs were studied on the specific activity of human ... [more ▼]

Myeloperoxidase (MPO) plays a key role in inflammatory response and constitutes a target for new drug development. The effects of some benzoic acid analogs were studied on the specific activity of human MPO measured by SIEFED (“Specific Immunologic Extraction Followed by Enzymatic Detection”), an original method that consists of incubation of the compound with MPO, followed by capture of the enzyme by specific antibodies, washing (elimination of the compounds) and enzymatic detection of the immunocaptured enzyme. The compounds tested at 10-4, 10-5 and 10-6 M were studied in terms of structure activity relationship. Gallic acid (3,4,5-trihydroxybenzoic acid) with 3 hydroxyl groups had an important dose dependent inhibitory effect on MPO activity. Other molecules with less or without hydroxyl groups [3,4-dihydroxybenzoic acid, 2-hydroxybenzoic acid (salicylic acid) and benzoic acid] had rather an activator effect at 10-5 and 10-6 M. 2,4,6-Trihydroxybenzoic acid, with two hydroxyl groups adjacent to the carboxyl group, had a less efficient inhibitory effect. Caffeic acid (3,4-dihydroxycinnamic acid) with a propenoic acid group presented a dose dependent inhibitory effect on MPO activity contrary to its analog 3,4-dihydroxybenzoic acid. The esterification of the carboxyl group of gallic acid to obtain propyl gallate induced an activation of MPO at 10-5 and 10-6 M. Finally, the substitution of one or two hydroxyl groups by methoxyl ones (ferulic and syringic acids) decreased the efficiency of the molecules on the enzyme inhibition. The SIEFED technique appears as an innovative pharmacological tool to study the direct interaction of compounds with MPO. Number and position of hydroxyl groups and the extension of the carboxyl group of benzoic acid play a crucial role in the inhibition of MPO activity probably by facilitating the interaction with the active site or another elements of the enzyme structure. [less ▲]

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See detailModulating effects of acepromazine on the reactive oxygen species production by stimulated equine neutrophils
Sandersen, Charlotte ULg; Mouithys-Mickalad, Ange ULg; de la Rebière de Pouyade, Geoffroy ULg et al

in Veterinary Anaesthesia & Analgesia (2011), 38

To investigate the effect of acepromazine (ACP) on reactive oxygen species (ROS) production by stimulated equine neutrophils.

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See detailProduction of free radicals and oxygen consumption by primary equine endothelial cells during anoxia-reoxygenation.
de la Rebière de Pouyade, Geoffroy ULg; Salciccia, Alexandra ULg; Ceusters, Justine ULg et al

in Open Biochemistry Journal (The) (2011), 5

The endothelium plays an active role in ischemia/reperfusion injuries. Herein, we report the effect of a single or successive cycles of anoxia/reoxygenation (A/R) on the mitochondrial respiratory function ... [more ▼]

The endothelium plays an active role in ischemia/reperfusion injuries. Herein, we report the effect of a single or successive cycles of anoxia/reoxygenation (A/R) on the mitochondrial respiratory function of equine endothelial cells (cultured from carotids) monitored by high resolution oxymetry, and on their production of reactive oxygen species (ROS). ROS were measured by electron paramagnetic resonance (ESR) using POBN and DMPO spin traps, and by gas chromatography (GC) of ethylene released by ROS-induced alpha-keto-gamma-(methylthio)butyric acid (KMB) oxidation. The oxygen consumption significantly decreased with the number of A/R cycles, and POBN-ESR spectra were specific of adducts formed in the cells from superoxide anion. After a one-hour A/R cycle, high intensity DMPO-ESR spectra were observed and assigned to superoxide anion trapping; the GC results confirmed an important production of ROS compared to normoxic cells. These results show that A/R induces mitochondrial alterations in endothelial cells, and strongly stimulates their oxidative activity as demonstrated by ESR and GC methods. [less ▲]

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See detailModulatory activities of Agelanthus dodoneifolius (Loranthaceae) extracts on stimulated equine neutrophils and myeloperoxidase activity
Boly, Rainatou; Dessy, Stephanie; Kohnen, Stephan et al

in International Journal of Molecular Medicine (2011), 28

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See detailESR technique for non invasive way to quantify cyclodextrins effect on cell membranes
Grammenos, Angeliki ULg; Mouithys-Mickalad, Ange ULg; Guelluy, Pierre-Henri ULg et al

in Biochemical and Biophysical Research Communications (2010)

A new way to study the action of cyclodextrin was developed to quantify the damage caused on cell membrane and lipid bilayer. The Electron Spin Resonance (ESR) spectroscopy was used to study the action of ... [more ▼]

A new way to study the action of cyclodextrin was developed to quantify the damage caused on cell membrane and lipid bilayer. The Electron Spin Resonance (ESR) spectroscopy was used to study the action of Randomly methylated-beta-cyclodextrin (Rameb) on living cells (HCT-116). The relative anisotropy observed in ESR spectrum of nitroxide spin probe (5-DSA and cholestane) is directly related to the rotational mobility of the probe,which can be further correlated with themicroviscosity. The use of ESR probes clearly shows a close correlation between cholesterol contained in cells and cellular membrane microviscosity. This study also demonstrates the Rameb ability to extract cholesterol and phospholipids in time- and dose-dependent ways. In addition, ESR spectra enabled to establish that cholesterol is extracted from lipid rafts to form stable aggregates. The present work supports that ESR is an easy, reproducible and noninvasive technique to study the effect of cyclodextrins on cell membranes. [less ▲]

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See detailSynthesis of poly(vinyl alcohol)/C60 and poly(N-vinylpyrrolidone)/C60 nanohybrids as potential photodynamic cancer therapy agents
Hurtgen, Marie ULg; Debuigne, Antoine ULg; Mouithys-Mickalad, Ange ULg et al

in Chemistry : An Asian Journal (2010), 5(4), 859-868

Well-defined poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone)-co-poly(vinyl acetate) (PNVPco-PVAc) chains end-capped by Co-(acac)2 (acac=acetylacetonate) and prepared by cobalt-mediated radical ... [more ▼]

Well-defined poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone)-co-poly(vinyl acetate) (PNVPco-PVAc) chains end-capped by Co-(acac)2 (acac=acetylacetonate) and prepared by cobalt-mediated radical polymerization (CMRP) are grafted onto a fullerene. Homolytic Co-C bond cleavage of the polymer chain ends at 30°C releases the polymeric radicals that add onto C60, thereby leading to the corresponding PVAc/C60 and PNVP-co-PVAc/C60 nanohybrids. The [polymer–Co(acac)2]/[C60] molar ratio was varied to adjust the structure of the nanohybrids, and more particularly the number of grafted arms. Finally, the potential of the hydrosoluble PVOH/C60 nanohybrids, which result from the methanolysis of the ester groups of PVAc/C60, and of the PNVP-co-PVAc/C60 nanohybrids as photosensitizers for photodynamic therapy (PDT), was approached. First, photobleaching tests demonstrated the ability of these nanohybrids to produce singlet oxygen upon irradiation, which can play a role in cell damage. Second, cell viability assays demonstrated that both types of nanohybrids are deprived of intrinsic cytotoxicity in the dark, whereas they promoted significant cell mortality when subjected to light treatment. The selective response of these materials to irradiation makes them promising compounds for PDT. [less ▲]

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