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Endogenous Materials (endogenous + material)
Selected AbstractsEffectiveness of an ultrafiltration device for use with the enzyme-hydrolysed protein method for determining endogenous ileal nitrogen and amino acid excretion in the pigJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2001Suzanne M Hodgkinson Abstract The aim of the work was to perform an in vitro study to determine the effectiveness of Centriprep-10 concentrator devices for use with the enzyme-hydrolysed protein method for the determination of endogenous ileal nitrogen and amino acid flows. Different amounts of enzyme-hydrolysed casein (EHC) were added to tubes containing digesta collected from pigs that had received a protein-free diet for 5,8 days. The samples were centrifuged and then ultrafiltered using Centriprep-10 concentrators. The precipitate from the centrifugation step was added to the retentate from the ultrafiltration, and this material was analysed for nitrogen and amino acids. The ultrafiltrates were also analysed for nitrogen. The amount of nitrogen that was deemed to have originated from the EHC and remained in the precipitate plus retentate fraction of digesta after processing, expressed as a percentage of the total amount of nitrogen added to the tubes as EHC, ranged from 1.0 to 5.0%. The overall mean amounts of amino acid in the precipitate plus retentate fractions originating from the EHC, expressed as a percentage of the amino acids added to the tubes as EHC, ranged from 2.4 to 5.8%. The results demonstrate that with Centriprep-10 concentrators there is a less than complete separation of nitrogen and amino acids originating from EHC from endogenous material in digesta, but for most amino acids this is unlikely to be due to binding of the amino acids to digesta. The incomplete separation of EHC from the endogenous fraction of digesta by Centriprep-10 concentrators may lead to a small overestimation (approximately 2%) of endogenous ileal nitrogen and amino acid flows. © 2001 Society of Chemical Industry [source] Analytical strategies for identifying drug metabolitesMASS SPECTROMETRY REVIEWS, Issue 3 2007Chandra Prakash Abstract With the dramatic increase in the number of new chemical entities (NCEs) arising from combinatorial chemistry and modern high-throughput bioassays, novel bioanalytical techniques are required for the rapid determination of the metabolic stability and metabolites of these NCEs. Knowledge of the metabolic site(s) of the NCEs in early drug discovery is essential for selecting compounds with favorable pharmacokinetic credentials and aiding medicinal chemists in modifying metabolic "soft spots". In development, elucidation of biotransformation pathways of a drug candidate by identifying its circulatory and excretory metabolites is vitally important to understand its physiological effects. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) have played an invaluable role in the structural characterization and quantification of drug metabolites. Indeed, liquid chromatography (LC) coupled with atmospheric pressure ionization (API) MS has now become the most powerful tool for the rapid detection, structure elucidation, and quantification of drug-derived material within various biological fluids. Often, however, MS alone is insufficient to identify the exact position of oxidation, to differentiate isomers, or to provide the precise structure of unusual and/or unstable metabolites. In addition, an excess of endogenous material in biological samples often suppress the ionization of drug-related material complicating metabolite identification by MS. In these cases, multiple analytical and wet chemistry techniques, such as LC-NMR, enzymatic hydrolysis, chemical derivatization, and hydrogen/deuterium-exchange (H/D-exchange) combined with MS are used to characterize the novel and isomeric metabolites of drug candidates. This review describes sample preparation and introduction strategies to minimize ion suppression by biological matrices for metabolite identification studies, the application of various LC-tandem MS (LC-MS/MS) techniques for the rapid quantification and identification of drug metabolites, and future trends in this field. © 2007 Wiley Periodicals, Inc., Mass Spec Rev [source] Determination of the disulfide bond pattern of the endogenous and recombinant angiogenesis inhibitor endostatin by mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2001Harald John Endostatin, a C-terminal fragment of collagen XVIII, is a promising protein drug which is in development for cancer therapy due to its anti-angiogenic activity. Although several endogenous molecular forms of human endostatin differing in their N-terminal length and their post-translational modifications (18.5,22,kDa) have been discovered, only one recombinant form of 20,kDa is used in clinical trials. This protein, recombinantly expressed in Pichia pastoris, contains four cysteines forming two disulfide bonds (Cys1-Cys4 and Cys2-Cys3). In contrast, there are conflicting data about the disulfide pattern of endogenous material. This report presents the disulfide analyses of both the endogenous circulating endostatins isolated from human hemofiltrate and the recombinant protein. The determination of the disulfide pattern was performed by Edman degradation, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and electrospray ionization ion trap mass spectrometry (ESI-ITMS) performed in the off-line nanospray mode. All native and recombinant endostatins exhibited a Cys1-Cys4 (Cys162 -Cys302) and Cys2-Cys3 (Cys264 -Cys294) linkage. For a clear discussion of fragmented disulfide-bridged peptide chains obtained from MSn experiments, a modified general nomenclature is proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] A simplified protein precipitation/mixed-mode cation-exchange solid-phase extraction, followed by high-speed liquid chromatography/mass spectrometry, for the determination of a basic drug in human plasmaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2006Y.-J. Xue A simplified protein precipitation/mixed-mode cation-exchange solid-phase extraction (PPT/SPE) procedure has been investigated. A mixture of acetonitrile and methanol along with formic acid was used to precipitate plasma proteins prior to selectively extracting the basic drug. After vortexing and centrifugation, the supernatants were directly loaded onto an unconditioned Oasis® MCX µElution 96-well extraction plate, where the protonated drug was retained on the negatively charged sorbent while interfering neutral lipids, steroids or other endogenous materials were washed away. Normal wash steps were deemed unnecessary and not used before sample elution. The sample extracts were analyzed under both conventional and high-speed liquid chromatography/tandem mass spectrometry (LC/MS/MS) conditions to examine the feasibility of the PPT/SPE procedure for human plasma sample clean-up. For the conventional LC/MS/MS method, chromatographic separation was achieved on a C18, 2.1,×,50,mm column with gradient elution (k,,=,5.5). The mobile phase contained 0.1% formic acid in water and 0.1% formic acid in acetonitrile. For the high-speed LC/MS/MS method, chromatographic separation was achieved on a C18, 2.1,×,10,mm guard column with gradient elution (k,,=,2.2, Rt,=,0.26,min). The mobile phase contained 0.1% formic acid in water and 0.001% trifluoroacetic acid in acetonitrile. Detection for both conventional and high-speed LC/MS/MS methods was by positive ion electrospray tandem mass spectrometry on a ThermoElectron Finnigan TSQ Quantum Ultra, where enhanced resolution (RP 2000; 0.2,amu) was used for high-speed LC/MS/MS. The standard curve, ranging from 0.5 to 100,ng/mL, was fitted to a 1/x weighted quadratic regression model. This combined PPT/SPE procedure effectively eliminated time-consuming sorbent conditioning and wash steps, which are essential for a conventional mixed-mode SPE procedure, but retained the advantages of both PPT (removal of plasma proteins) and mixed-mode SPE (analyte selectivity). The validation results demonstrated that this PPT/SPE procedure was well suited for both conventional and high-speed LC/MS/MS analyses. In comparison with a conventional mixed-mode SPE procedure, the simplified PPT/SPE process provided comparable sample extract purity. This simple sample clean-up procedure can be applied to other basic compounds with minor modifications of PPT solvents. Copyright © 2006 John Wiley & Sons, Ltd. [source] Development of a liquid chromatography/tandem mass spectrometry assay for the quantification of PM02734, a novel antineoplastic agent, in dog plasmaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2006Jianming Yin A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay was developed and validated to quantify a novel antineoplastic agent, PM02734, in dog plasma. The method was validated to demonstrate the specificity, limit of quantification (LOQ), accuracy, and precision of measurements. The calibration range for PM02734 was established using PM02734 standards from 0.05 to 100,ng/mL in blank plasma. The dominating ions were doubly charged molecular ions [M+2H]2+ at m/z 740.0 instead of singly charged ones at m/z 1478.4. The selected reaction monitoring (SRM), based on the m/z 740.0,,,212.2 transition, was specific for PM02734, and that based on the m/z 743.8,,,212.2 transition was specific for deuterated PM02734 (the internal standard, IS); no endogenous materials interfered with the analysis of PM02734 and IS from blank plasma. The assay was linear over the concentration range 0.05,100,ng/mL. In terms of sensitivity of assay 0.05,ng/mL is a very low LLOQ, especially considering PM02734 is a peptide. The correlation coefficients for the calibration curves ranged from 0.9990 to 0.9999. The mean intraday and interday accuracies for all calibration standards (n,=,9) ranged from 93 to 111% (,11% bias) in dog plasma, and the mean interday precision for all calibration standards was less than 6.4%. The mean intra- and interday assay accuracy for all quality control replicates in dog plasma (n,=,9), determined at each QC level throughout the validated runs, ranged from 85,111% (,15% bias) and from 99,109% (,9% bias), respectively. The mean intra- and interday assay precision was less than 12.1 and 13.3% for all QC levels, respectively. The assay has been used to support preclinical pharmacokinetic (PK) and toxicokinetic studies. The results showed that preclinical samples could be monitored for PM02734 up to 168,h after dosing, which allowed us to identify multiple elimination phases and accurately estimate PK information. Copyright © 2006 John Wiley & Sons, Ltd. [source] Development of a liquid chromatography/tandem mass spectrometry assay for the quantification of rabeprazole in human plasmaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2005Jinchang Huang A simple and sensitive liquid chromatography/tandem mass spectrometry method, employing electrospray ionization, has been developed and validated to quantify rabeprazole in human plasma using omeprazole as the internal standard. The method was validated to demonstrate the specificity, lower limit of quantification, accuracy, and precision of measurements. Selected reaction monitoring was specific for rabeprazole and omeprazole (the internal standard, IS); no endogenous materials interfered with the analysis of rabeprazole and IS from blank plasma. The assay was linear over the concentration range 0.2,200,ng/mL using a 2,µL aliquot of plasma. The correlation coefficients for the calibration curves ranged from 0.9988,0.9994. The intra- and inter-day precision, calculated from quality control samples, were less than 6.65%. A mixture of methanol and water (50:50) was used as the isocratic mobile phase, with 0.1% of formic acid in water, that did not affect the stability of rabeprazole or IS. A simple sample preparation method of protein precipitation with methanol was chosen. The method was employed in a pharmacokinetic study after oral administration of 20,mg rabeprazole to 24 healthy volunteers. Copyright © 2005 John Wiley & Sons, Ltd. [source] Determination of bisphenol A in human breast milk by HPLC with column-switching and ,uorescence detectionBIOMEDICAL CHROMATOGRAPHY, Issue 8 2004Yen Sun Abstract A highly sensitive HPLC method was developed for the determination of xenoestrogenic compound, bisphenol A (BPA) in human breast milk samples. After a two-step liquid,liquid extraction, BPA was derivatized with ,uorescent labeling reagent, 4-(4,5-diphenyl-1H -imidazol-2-yl)benzoyl chloride (DIB-Cl). The excess ,uorescent reagent could be removed effectively using a column-switching system. The separation of DIB-BPA from endogenous materials in milk was carried out on two C18 columns and ,uorescence intensity was monitored at 475 nm with the excitation of 350 nm. A good linearity (r = 0.994) was observed of BPA in the concentration range of 0.2,5.0 ng mL,1 in breast milk, and the detection limit was 0.11 ng mL,1 at a signal-to-noise ratio of 3. Intra- and inter-day precision (RSD, %) were less than 8.7 and 10.4, respectively. Twenty-three breast milk samples of healthy lactating women were analyzed for the BPA concentration; the mean value was 0.61 ± 0.20 ng mL,1, with no correlation to the lipid content of milk samples. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||