The Experts below are selected from a list of 711 Experts worldwide ranked by ideXlab platform
Jos H. Beijnen - One of the best experts on this subject based on the ideXlab platform.
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development and validation of a high performance liquid chromatography tandem mass spectrometry assay for the quantification of dexamphetamine in human plasma
Journal of Pharmaceutical and Biomedical Analysis, 2018Co-Authors: Maikel Herbrink, Bastiaan Nuijen, Bas Thijssen, Michel J.x. Hillebrand, Jan H.m. Schellens, Jos H. BeijnenAbstract:Abstract Dexamphetamine is registered for the treatment of attention deficit hyperactivity disorder and narcolepsy. Current research has highlighted the possible application of dexamphetamine in the treatment of cocaine addiction. To support clinical pharmacologic trials a new simple, fast, and sensitive assay for the quantification of dexamphetamine in human plasma using liquid chromatography tandem mass spectrometry (LC–MS/MS) was developed. Additionally, it is the first reported LC–MS assay with these advantages to be fully validated according to current US FDA and EMA guidelines. Human plasma samples were collected on an outpatient basis and stored at nominally −20 °C. The analyte and the internal standard (stable isotopically labeled dexamphetamine) were extracted using double liquid–liquid extraction (plasma-organic and organic-water) combined with Snap-Freezing. The aqueous extract was filtered and 2 μL was injected on a C18-column with isocratic elution and analyzed with triple quadrupole mass spectrometry in positive ion mode. The validated concentration range was from 2.5–250 ng/mL and the calibration model was linear. A weighting factor of 1 over the squared concentration was applied and correlation coefficients of 0.997 or better were obtained. At all concentrations the bias was within ±15% of the nominal concentrations and imprecision was ≤15%. All results were within the acceptance criteria of the latest US FDA guidance and EMA guidelines on method validation. In conclusion, the developed method to quantify dexamphetamine in human plasma was fit to support a clinical study with slow-release dexamphetamine.
Bruno G Frenguelli - One of the best experts on this subject based on the ideXlab platform.
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an ion pair reversed phase hplc method for determination of fresh tissue adenine nucleotides avoiding freeze thaw degradation of atp
Analytical Biochemistry, 2009Co-Authors: Stephanie Zur Nedden, Robert Eason, Alex S F Doney, Bruno G FrenguelliAbstract:Knowledge of the energetic state of tissue is required in a wide range of experimental studies, particularly those investigating the decline and recovery of cellular metabolism after metabolic stress. Such information can be obtained from high-performance liquid chromatography (HPLC) determination of tissue levels of adenine nucleotides (ATP, ADP, and AMP) and their interrelationship in the tissue energy charge (EC). Accordingly, a large range of techniques with which to measure these molecules and their downstream metabolites have been reported. However, the accurate determination of the tissue EC also depends on the nucleotide extraction procedure given that changes in adenine nucleotide levels take place very quickly when ATPases are not inactivated immediately. In this article, we describe an ion-pair reversed-phase HPLC method by which separation of adenine nucleotides can be performed rapidly, allowing multiple analyses in 1 day, with both high sensitivity and extraction efficiency and using fresh samples, thereby avoiding freeze-thaw degradation of nucleotides. We applied this method to hippocampal brain slice extracts and show that same-day extraction and analysis results in a more accurate determination of the in situ energetic state than does the commonly used Snap-Freezing in liquid nitrogen.
Franklyn A Howe - One of the best experts on this subject based on the ideXlab platform.
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an assessment of the effects of sample ischaemia and spinning time on the metabolic profile of brain tumour biopsy specimens as determined by high resolution magic angle spinning 1h nmr
NMR in Biomedicine, 2008Co-Authors: Kirstie S Opstad, Anthony B Bell, John R Griffiths, Franklyn A HoweAbstract:High-resolution magic angle spinning (HRMAS) 1H NMR of biopsy tissue provides a biochemical profile that has potential diagnostic and prognostic value, and can aid interpretation of the lower-resolution 1H-NMR spectra obtained in vivo. However, the biochemical profile obtained may be affected by experimental factors such as a period of ischaemia before Snap-Freezing of the biopsy tissue for subsequent analysis and the mechanical stress of the spinning procedure of HRMAS itself. We have used normal rat brain cortex as a ‘gold standard’, either funnel-frozen or deliberately allowed to become ischaemic for set periods of time before Snap-Freezing, to quantitatively investigate these two effects. In addition, we have compared biochemical changes that occur in normal rat brain during HRMAS (spun continuously at 5 kHz for 4 h at 4°C as could be required for a two-dimensional acquisition) with those that occur in biopsy samples from low-grade and high-grade adult human astrocytomas, during the same HRMAS procedure. Significant changes due to delayed initial sample Freezing were noted in metabolites associated with glycolysis (alanine, glucose and lactate), as expected. However, for the funnel-frozen rat tissue at 4°C, there were even more significant changes, which appear to be the result of extended spinning at 5 kHz. In particular, the 18% total creatine increase observed is unlikely to be de novo synthesis of creatine. More likely, the asymptotic exponential increase in creatine suggests an exponential release of an NMR-invisible bound creatine store as a result of tissue damage from mechanical stress of sample spinning. Overall, it appears that tissue ischaemia during biopsy excision and delays in Snap-Freezing may have less significant effects on metabolite profile than the prolonged spinning times required for two-dimensional HRMAS, and this must be accounted for when results are being interpreted. Copyright © 2008 John Wiley & Sons, Ltd.
Stephanie Zur Nedden - One of the best experts on this subject based on the ideXlab platform.
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an ion pair reversed phase hplc method for determination of fresh tissue adenine nucleotides avoiding freeze thaw degradation of atp
Analytical Biochemistry, 2009Co-Authors: Stephanie Zur Nedden, Robert Eason, Alex S F Doney, Bruno G FrenguelliAbstract:Knowledge of the energetic state of tissue is required in a wide range of experimental studies, particularly those investigating the decline and recovery of cellular metabolism after metabolic stress. Such information can be obtained from high-performance liquid chromatography (HPLC) determination of tissue levels of adenine nucleotides (ATP, ADP, and AMP) and their interrelationship in the tissue energy charge (EC). Accordingly, a large range of techniques with which to measure these molecules and their downstream metabolites have been reported. However, the accurate determination of the tissue EC also depends on the nucleotide extraction procedure given that changes in adenine nucleotide levels take place very quickly when ATPases are not inactivated immediately. In this article, we describe an ion-pair reversed-phase HPLC method by which separation of adenine nucleotides can be performed rapidly, allowing multiple analyses in 1 day, with both high sensitivity and extraction efficiency and using fresh samples, thereby avoiding freeze-thaw degradation of nucleotides. We applied this method to hippocampal brain slice extracts and show that same-day extraction and analysis results in a more accurate determination of the in situ energetic state than does the commonly used Snap-Freezing in liquid nitrogen.
Jan H.m. Schellens - One of the best experts on this subject based on the ideXlab platform.
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development and validation of a high performance liquid chromatography tandem mass spectrometry assay for the quantification of dexamphetamine in human plasma
Journal of Pharmaceutical and Biomedical Analysis, 2018Co-Authors: Maikel Herbrink, Bastiaan Nuijen, Bas Thijssen, Michel J.x. Hillebrand, Jan H.m. Schellens, Jos H. BeijnenAbstract:Abstract Dexamphetamine is registered for the treatment of attention deficit hyperactivity disorder and narcolepsy. Current research has highlighted the possible application of dexamphetamine in the treatment of cocaine addiction. To support clinical pharmacologic trials a new simple, fast, and sensitive assay for the quantification of dexamphetamine in human plasma using liquid chromatography tandem mass spectrometry (LC–MS/MS) was developed. Additionally, it is the first reported LC–MS assay with these advantages to be fully validated according to current US FDA and EMA guidelines. Human plasma samples were collected on an outpatient basis and stored at nominally −20 °C. The analyte and the internal standard (stable isotopically labeled dexamphetamine) were extracted using double liquid–liquid extraction (plasma-organic and organic-water) combined with Snap-Freezing. The aqueous extract was filtered and 2 μL was injected on a C18-column with isocratic elution and analyzed with triple quadrupole mass spectrometry in positive ion mode. The validated concentration range was from 2.5–250 ng/mL and the calibration model was linear. A weighting factor of 1 over the squared concentration was applied and correlation coefficients of 0.997 or better were obtained. At all concentrations the bias was within ±15% of the nominal concentrations and imprecision was ≤15%. All results were within the acceptance criteria of the latest US FDA guidance and EMA guidelines on method validation. In conclusion, the developed method to quantify dexamphetamine in human plasma was fit to support a clinical study with slow-release dexamphetamine.