The Experts below are selected from a list of 26967 Experts worldwide ranked by ideXlab platform
Wolfgang Schwack - One of the best experts on this subject based on the ideXlab platform.
-
effect of bromine oxidation on high performance thin layer chromatography multi Enzyme Inhibition Assay detection of organophosphates and carbamate insecticides
Journal of Chromatography A, 2011Co-Authors: Rami Akkad, Wolfgang SchwackAbstract:Abstract Following high-performance thin-layer chromatography, thiophosphate pesticides, which inhibit choline esterases, are detectable using a multi-Enzyme Inhibition Assay (HPTLC-EI) based on rabbit liver esterase (RLE), Bacillus subtilis (BS2) esterase, or cutinase (from Fusarium solani pisi ). Because choline esterase Inhibition is more effective after conversion of thiophosphate thions into their corresponding oxons, a pre-oxidation step was added to the HPTLC-EI Assay. Bromine vapour was found to be more effective than iodine or UV irradiation for oxidation. Following oxidation, the inhibitory strength of parathion, parathion-methyl, chlorpyrifos, chlorpyrifos-methyl, and malathion, expressed as HPTLC Enzyme Inhibition factors ( f i ), increased by approximately 2 orders of magnitude. In contrast, bromine oxidation of organophosphate and carbamate insecticides resulted in a slight reduction in their Inhibition factors, due to partial bromination and degradation of the parent compounds, while bromine oxidation increased the Inhibition factors for demeton-S-methyl and propoxur. Apple juice and water samples spiked with paraoxon (0.001 mg/L), parathion (0.05 mg/L), and chlorpyrifos (0.5 mg/L) were used to test the HPTLC-EI system, resulting in mean recoveries of 95–106% and 91–102% for RLE and cutinase, respectively.
-
multi Enzyme Inhibition Assay for detection of insecticidal organophosphates and carbamates by high performance thin layer chromatography 1 basics of method development
Jpc-journal of Planar Chromatography-modern Tlc, 2008Co-Authors: Rami Akkad, Wolfgang SchwackAbstract:A recently introduced microtiter-plate multiEnzyme-Inhibition Assay using rabbit liver esterase (RLE), Bacillus subtilis (BS2) esterase, and cutinase from Fusarium solani pizi has been successfully transferred to high-performance thin-layer chromatography. Paraoxon, malaoxon, and carbofuran as esterase inhibitors with high, medium, and low inhibitory activity, respectively, were used to optimize method performance with regard to Enzyme concentration, incubation time, and time of immersion in α-naphthyl acetate-fast blue salt B substrate. For paraoxon as strongest inhibitor, limits of detection (LOD) of 1.3, 1.2, and 540 pg per band were determined using RLE, BS2, and cutinase, respectively. Respective LODs were 7.9, 7.4, and 760 ng per band for malaoxon, and 33, 54, and 1420 ng per band for carbofuran. With regard to the LODs of strong, medium, and weak inhibitors, the detectability range is favorably reduced for the low-sensitivity cutinase (0.54–1420 ng per band) whereas it was approximately 3 × 10 4 an...
-
Multi-Enzyme Inhibition Assay for Detection of Insecticidal Organophosphates and Carbamates by High-Performance Thin-Layer Chromatography. 1. Basics of Method Development
JPC – Journal of Planar Chromatography – Modern TLC, 2008Co-Authors: Rami Akkad, Wolfgang SchwackAbstract:A recently introduced microtiter-plate multiEnzyme-Inhibition Assay using rabbit liver esterase (RLE), Bacillus subtilis (BS2) esterase, and cutinase from Fusarium solani pizi has been successfully transferred to high-performance thin-layer chromatography. Paraoxon, malaoxon, and carbofuran as esterase inhibitors with high, medium, and low inhibitory activity, respectively, were used to optimize method performance with regard to Enzyme concentration, incubation time, and time of immersion in a-naphthyl acetate-fast blue salt B substrate. For paraoxon as strongest inhibitor, limits of detection (LOD) of 1.3, 1.2, and 540 pg per band were determined using RLE, BS2, and cutinase, respectively. Respective LODs were 7.9, 7.4, and 760 ng per band for malaoxon, and 33, 54, and 1420 ng per band for carbofuran. With regard to the LODs of strong, medium, and weak inhibitors, the detectability range is favorably reduced for the low-sensitivity cutinase (0.54–1420 ng per band) whereas it was approximately 3 × 10^4 and 5 × 10^4 for RLE and BS2, respectively.
Qun Fang - One of the best experts on this subject based on the ideXlab platform.
-
coupling liquid chromatography mass spectrometry detection with microfluidic droplet array for label free Enzyme Inhibition Assay
Analyst, 2014Co-Authors: Xiu-li Wang, Ying Zhu, Qun FangAbstract:In this work, the combination of droplet-based microfluidics with liquid chromatography/mass spectrometry (LC/MS) was achieved, for providing a fast separation and high-information-content detection method for the analysis of nanoliter-scale droplets with complex compositions. A novel interface method was developed using an oil-covered droplet array chip to couple with an LC/MS system via a capillary sampling probe and a 4 nL injection valve without the need of a droplet extraction device. The present system can perform multistep operations including parallel Enzyme Inhibition reactions in nanoliter droplets, 4 nL sample injection, fast separation with capillary LC, and label-free detection with ESI-MS, and has significant flexibility in the accurate addressing and sampling of droplets of interest on demand. The system performance was evaluated using angiotensin I and angiotensin II as model samples, and the repeatabilities of peak area for angiotensin I and angiotensin II were 2.7% and 7.5% (RSD, n = 4), respectively. The present system was further applied to the screening for inhibitors of cytochrome P450 (CYP1A2) and measurement of the IC50 value of the inhibitor. The sample consumption for each droplet Assay was 100 nL, which is reduced 10–100 times compared with conventional 384-multi-well plate systems usually used in high-throughput drug screening.
-
Coupling liquid chromatography/mass spectrometry detection with microfluidic droplet array for label-free Enzyme Inhibition Assay
The Analyst, 2014Co-Authors: Xiu-li Wang, Ying Zhu, Qun FangAbstract:In this work, the combination of droplet-based microfluidics with liquid chromatography/mass spectrometry (LC/MS) was achieved, for providing a fast separation and high-information-content detection method for the analysis of nanoliter-scale droplets with complex compositions. A novel interface method was developed using an oil-covered droplet array chip to couple with an LC/MS system via a capillary sampling probe and a 4 nL injection valve without the need of a droplet extraction device. The present system can perform multistep operations including parallel Enzyme Inhibition reactions in nanoliter droplets, 4 nL sample injection, fast separation with capillary LC, and label-free detection with ESI-MS, and has significant flexibility in the accurate addressing and sampling of droplets of interest on demand. The system performance was evaluated using angiotensin I and angiotensin II as model samples, and the repeatabilities of peak area for angiotensin I and angiotensin II were 2.7% and 7.5% (RSD, n = 4), respectively. The present system was further applied to the screening for inhibitors of cytochrome P450 (CYP1A2) and measurement of the IC50 value of the inhibitor. The sample consumption for each droplet Assay was 100 nL, which is reduced 10–100 times compared with conventional 384-multi-well plate systems usually used in high-throughput drug screening.
-
droplet based microfluidic flow injection system with large scale concentration gradient by a single nanoliter scale injection for Enzyme Inhibition Assay
Analytical Chemistry, 2012Co-Authors: Longfei Cai, Ying Zhu, Qun FangAbstract:We described a microfluidic chip-based system capable of generating droplet array with a large scale concentration gradient by coupling flow injection gradient technique with droplet-based microfluidics. Multiple modules including sample injection, sample dispersion, gradient generation, droplet formation, mixing of sample and reagents, and online reaction within the droplets were integrated into the microchip. In the system, nanoliter-scale sample solution was automatically injected into the chip under valveless flow injection analysis mode. The sample zone was first dispersed in the microchannel to form a concentration gradient along the axial direction of the microchannel and then segmented into a linear array of droplets by immiscible oil phase. With the segmentation and protection of the oil phase, the concentration gradient profile of the sample was preserved in the droplet array with high fidelity. With a single injection of 16 nL of sample solution, an array of droplets with concentration gradient...
N. Gopakumar - One of the best experts on this subject based on the ideXlab platform.
-
Anti-inflammatory activity of Red and White Lotus seeds (Nelumbo nucifera) in Albino Rats
Veterinary World, 2010Co-Authors: P. V. Chakravarthi, N. GopakumarAbstract:The present study was carried out to evaluate the anti-inflammatory activity of red and white lotus seeds in albino rats. The Carrageenin induced paw edema model was used for studying the antiinflammatory activity. The cyclooxygenase-2 (COX-2) Enzyme Inhibition Assay was carried out in spectrophotometer to identify the specific mode of action. Forty eight adult Sprague-Dawley rats were used in this experiment. They were divided into six groups of eight each and maintained under ideal laboratory conditions. Group I was taken as control and group II treated with the standard drug diclofenac potassium @ 3mg/kg/celecoxib @ 10mg/kg (in case of COX–2 Assay) on 7th day of study. The methanolic extract of Nelumbo nucifera seeds of red and white varieties @ 400mg/kg and 600mg/kg were fed to group III, IV, V and VI respectively, for 7 days. All groups of lotus seed extracts were revealed anti-inflammatory activity in Carragenin induced inflammation as well as in COX-2 Enzyme Inhibition Assay. While comparing all groups, the higher dose group of white lotus seed extracts, exhibited more pronounced Inhibition than other groups.
-
Anti-inflammatory activity of red and white lotus seeds Nelumbo nucifera in albino rats
Veterinary World, 2010Co-Authors: P. V. Chakravarthi, N. GopakumarAbstract:The present study was carried out to evaluate the anti-inflammatory activity of red and white lotus seeds in albino rats. The Carrageenin induced paw edema model was used for studying the anti-inflammatory activity. The cyclooxygenase-2 (COX-2) Enzyme Inhibition Assay was carried out in spectrophotometer to identify the specific mode of action. Forty eight adult Sprague-Dawley rats were used in this experiment. They were divided into six groups of eight each and maintained under ideal laboratory conditions. Group I was taken as control and group II treated with the standard drug diclofenac potassium @ 3mg/kg/celecoxib @ 10mg/kg (in case of COX–2 Assay) on 7th day of study. The methanolic extract of Nelumbo nucifera seeds of red and white varieties @ 400mg/kg and 600mg/kg were fed to group III, IV, V and VI respectively, for 7 days. All groups of lotus seed extracts were revealed anti-inflammatory activity in Carragenin induced inflammation as well as in COX-2 Enzyme Inhibition Assay. While comparing all groups, the higher dose group of white lotus seed extracts, exhibited more pronounced Inhibition than other groups. [Vet World 2010; 3(4.000): 157-159
Rami Akkad - One of the best experts on this subject based on the ideXlab platform.
-
effect of bromine oxidation on high performance thin layer chromatography multi Enzyme Inhibition Assay detection of organophosphates and carbamate insecticides
Journal of Chromatography A, 2011Co-Authors: Rami Akkad, Wolfgang SchwackAbstract:Abstract Following high-performance thin-layer chromatography, thiophosphate pesticides, which inhibit choline esterases, are detectable using a multi-Enzyme Inhibition Assay (HPTLC-EI) based on rabbit liver esterase (RLE), Bacillus subtilis (BS2) esterase, or cutinase (from Fusarium solani pisi ). Because choline esterase Inhibition is more effective after conversion of thiophosphate thions into their corresponding oxons, a pre-oxidation step was added to the HPTLC-EI Assay. Bromine vapour was found to be more effective than iodine or UV irradiation for oxidation. Following oxidation, the inhibitory strength of parathion, parathion-methyl, chlorpyrifos, chlorpyrifos-methyl, and malathion, expressed as HPTLC Enzyme Inhibition factors ( f i ), increased by approximately 2 orders of magnitude. In contrast, bromine oxidation of organophosphate and carbamate insecticides resulted in a slight reduction in their Inhibition factors, due to partial bromination and degradation of the parent compounds, while bromine oxidation increased the Inhibition factors for demeton-S-methyl and propoxur. Apple juice and water samples spiked with paraoxon (0.001 mg/L), parathion (0.05 mg/L), and chlorpyrifos (0.5 mg/L) were used to test the HPTLC-EI system, resulting in mean recoveries of 95–106% and 91–102% for RLE and cutinase, respectively.
-
multi Enzyme Inhibition Assay for detection of insecticidal organophosphates and carbamates by high performance thin layer chromatography 1 basics of method development
Jpc-journal of Planar Chromatography-modern Tlc, 2008Co-Authors: Rami Akkad, Wolfgang SchwackAbstract:A recently introduced microtiter-plate multiEnzyme-Inhibition Assay using rabbit liver esterase (RLE), Bacillus subtilis (BS2) esterase, and cutinase from Fusarium solani pizi has been successfully transferred to high-performance thin-layer chromatography. Paraoxon, malaoxon, and carbofuran as esterase inhibitors with high, medium, and low inhibitory activity, respectively, were used to optimize method performance with regard to Enzyme concentration, incubation time, and time of immersion in α-naphthyl acetate-fast blue salt B substrate. For paraoxon as strongest inhibitor, limits of detection (LOD) of 1.3, 1.2, and 540 pg per band were determined using RLE, BS2, and cutinase, respectively. Respective LODs were 7.9, 7.4, and 760 ng per band for malaoxon, and 33, 54, and 1420 ng per band for carbofuran. With regard to the LODs of strong, medium, and weak inhibitors, the detectability range is favorably reduced for the low-sensitivity cutinase (0.54–1420 ng per band) whereas it was approximately 3 × 10 4 an...
-
Multi-Enzyme Inhibition Assay for Detection of Insecticidal Organophosphates and Carbamates by High-Performance Thin-Layer Chromatography. 1. Basics of Method Development
JPC – Journal of Planar Chromatography – Modern TLC, 2008Co-Authors: Rami Akkad, Wolfgang SchwackAbstract:A recently introduced microtiter-plate multiEnzyme-Inhibition Assay using rabbit liver esterase (RLE), Bacillus subtilis (BS2) esterase, and cutinase from Fusarium solani pizi has been successfully transferred to high-performance thin-layer chromatography. Paraoxon, malaoxon, and carbofuran as esterase inhibitors with high, medium, and low inhibitory activity, respectively, were used to optimize method performance with regard to Enzyme concentration, incubation time, and time of immersion in a-naphthyl acetate-fast blue salt B substrate. For paraoxon as strongest inhibitor, limits of detection (LOD) of 1.3, 1.2, and 540 pg per band were determined using RLE, BS2, and cutinase, respectively. Respective LODs were 7.9, 7.4, and 760 ng per band for malaoxon, and 33, 54, and 1420 ng per band for carbofuran. With regard to the LODs of strong, medium, and weak inhibitors, the detectability range is favorably reduced for the low-sensitivity cutinase (0.54–1420 ng per band) whereas it was approximately 3 × 10^4 and 5 × 10^4 for RLE and BS2, respectively.
Robert G. Webster - One of the best experts on this subject based on the ideXlab platform.
-
susceptibility of avian influenza viruses of the n6 subtype to the neuraminidase inhibitor oseltamivir
Antiviral Research, 2012Co-Authors: Terri D Stoner, Jasmine Turner, Nicholas J Negovetich, Elena A Govorkova, Sharon Frase, David E Stallknecht, Patrick Seiler, Scott Krauss, Robert G. WebsterAbstract:Abstract Avian influenza viruses are a source of genetic material that can be transmitted to humans through direct introduction or reassortment. Although there is a wealth of information concerning global monitoring for antiviral resistance among human viruses of the N1 and N2 neuraminidase (NA) subtypes, information concerning avian viruses of these and other NA subtypes is limited. We undertook a surveillance study to investigate the antiviral susceptibility of avian influenza N6 NA viruses, the predominant subtype among wild waterfowl. We evaluated 73 viruses from North American ducks and shorebirds for susceptibility to the NA inhibitor oseltamivir in a fluorescence-based NA Enzyme Inhibition Assay. Most (90%) had mean IC50 values ranging from 50.0 nM. Susceptibility to oseltamivir remained stable among all isolates collected over approximately three decades (P ⩽ 0.74). Two isolates with I222V NA substitution had moderately reduced susceptibility to oseltamivir in vitro (IC50, 30.0 and 40.0 nM). One field sample was a mixed population containing an avian paramyxovirus (APMV) and H4N6 influenza virus, as revealed by electron microscopy and hemagglutination Inhibition Assays with a panel of anti-APMV antisera. This highlights the importance of awareness and careful examination of non-influenza pathogens in field samples from avian sources. This study showed that oseltamivir-resistant N6 NA avian influenza viruses are rare, and must be tested both phenotypically and genotypically to confirm resistance.
-
detection of influenza virus resistance to neuraminidase inhibitors by an Enzyme Inhibition Assay
Antiviral Research, 2002Co-Authors: Larisa V Gubareva, Robert G. Webster, Frederick G HaydenAbstract:Abstract We previously characterized influenza viruses whose selection in the presence of neuraminidase (NA) inhibitors resulted in a substituted residue (position 119, 152, 274, or 292) in the NA active center. To identify the most favorable conditions for detecting NA inhibitor-resistant viruses we compared the results of four modifications of the NA Inhibition Assay utilizing a fluorogenic substrate. The IC50 values were highly dependent upon Assay conditions, and most mutant Enzymes were more sensitive to changes in Assay conditions (e.g. addition of PO43−, Ca2+, DMSO, or EDTA) than wild-type Enzymes or a mutant NA with an Arg292 → Lys substitution. Although the levels of resistance to zanamivir, oseltamivir carboxylate, and BCX-1812 (RWJ-270201) for each mutant varied among Assays, mutants with substitutions at framework residues 119 or 274 exhibited sensitivity to at least one inhibitor. Viruses with substitutions at catalytic residues 152 or 292 were resistant to each inhibitor in all Assays. Monitoring resistance in a clinical setting will require a panel of resistant viruses to ensure that Assay conditions are favorable for detecting variants with substituted residues in the NA active center. Because variants selected in the presence of one NA inhibitor could be variably resistant to other inhibitors, all three inhibitors should be used in drug susceptibility testing.