The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform
M. Porcel - One of the best experts on this subject based on the ideXlab platform.
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Kinetic–spectrophotometric determination of theophylline, Dyphylline, and proxyphylline by use of partial least-squares regression
Analytical and Bioanalytical Chemistry, 2002Co-Authors: H. Iturriaga, J. Coello, S. Maspoch, M. PorcelAbstract:A kinetic–spectrophotometric method for the determination of theophylline, Dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5–13 µg mL^–1 Dyphylline and proxyphylline, and 2–9 µg mL^–1 theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for Dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.
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kinetic spectrophotometric determination of theophylline Dyphylline and proxyphylline by use of partial least squares regression
Analytical and Bioanalytical Chemistry, 2002Co-Authors: H. Iturriaga, J. Coello, S. Maspoch, M. PorcelAbstract:A kinetic–spectrophotometric method for the determination of theophylline, Dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5–13 µg mL–1 Dyphylline and proxyphylline, and 2–9 µg mL–1 theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for Dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.
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"Multi component kinetic-spectrophotometric analysis. Selection of wavelength and time ranges."
The Analyst, 2001Co-Authors: H. Iturriaga, S. Maspoch, Jordi Coello, M. PorcelAbstract:An empirical method for the selection of the best wavelength and time ranges which can be used in the quantification of binary mixtures, in a kinetic–spectrophotometric system, is proposed. It is based on finding those ranges which provide the least correlation between the kinetic profiles and the spectra of the products of reaction. The method was applied to the analysis of binary mixtures using simulated data with different rate constant ratios and in the presence of an interference that shows spectral overlap with the analytes. Subsequently, the proposed method was applied to the resolution of Dyphylline and proxyphylline mixtures. The system studied was characterized by an elevated similarity in the kinetic behavior of the analytes under pseudo-first-order conditions and an elevated degree of spectral overlap of the products of reaction. In spite of this, satisfactory results were obtained in the quantification of the two analytes. The standard error of prediction (SEP) and the standard deviation between replicates (SDBR) did not show significant differences, being of the order of 4 and of 3% for Dyphylline and proxyphylline, respectively.
Su-hwei Chen - One of the best experts on this subject based on the ideXlab platform.
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Rapid determination of acyclovir in plasma and cerebrospinal fluid by micellar electrokinetic chromatography with direct sample injection and its clinical application.
Electrophoresis, 2006Co-Authors: Hsin-hua Yeh, Yuan-han Yang, Su-hwei ChenAbstract:A simple MEKC with UV detection at 254 nm for analysis of acyclovir in plasma and in cerebrospinal fluid (CSF) by direct injection without any sample pretreatment is described. The separation of acyclovir from biological matrix was performed at 25 degrees C using a BGE consisting of Tris buffer with SDS as the electrolyte solution. Several parameters affecting the separation of the drug from biological matrix were studied, including the pH and concentrations of the Tris buffer and SDS. Using Dyphylline as an internal standard, the linear ranges of the method for the determination of acyclovir in plasma and in CSF all exceeded the range of 2-50 microg/mL; the detection limit of the drug in plasma and in CSF (S/N = 3; injection 3.45 kPa, 5 s) was 1.0 microg/mL. The applicability of the proposed method for determination of acyclovir in plasma and CSF collected at 8 h after intravenous administration of 500 mg acyclovir (Zovirax) in two patients with herpes simplex encephalitis was demonstrated.
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Simultaneous determination of theophylline and Dyphylline by micellar electrokinetic chromatography and application in drug formulations
Journal of chromatography. B Analytical technologies in the biomedical and life sciences, 2003Co-Authors: Wei-shan Huang, Shun-jin Lin, Su-hwei ChenAbstract:Abstract A simple micellar electrokinetic chromatography is described for well resolution of theophylline, Dyphylline and caffeine. The separation was performed at 25 °C using a background electrolyte consisting of 10 mM borate buffer at pH 9 and 40 mM sodium dodecyl sulfate (SDS) as running buffer. Under this condition, good separation with high efficiency and short analyses time required is achieved. Several parameters affecting the separation of the drugs were studied, including the pH and concentrations of the borate buffer and sodium dodecyl sulfate. Using caffeine as an internal standard (I.S.), the linear range of the method for the determination of theophylline and Dyphylline was over 0.03–1 μmol ml−1; the detection limit (signal-to-noise ratio 3; injection 0.3 psi, 3 s) was 0.01 and 0.02 μmol ml−1, respectively.
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Rapid Simultaneous Determination of Three Methylxanthines in Human Plasma by Capillary Electrophoresis
Journal of Liquid Chromatography & Related Technologies, 2003Co-Authors: Chia-hsien Feng, Shun-jin Lin, Su-hwei ChenAbstract:Abstract A simple capillary electrophoresis method is described for simultaneous determination of three methylxanthines, theophylline, Dyphylline, and caffeine in human plasma. Plasma proteins are precipitated by acetonitrile and the supernatant was performed in Tris buffer (20 mM; pH 9) with sodium dodecyl sulfate (SDS) (150 mM) as an anionic surfactant. Several parameters affecting the separation of the drugs were studied, including the pH and concentrations of the Tris buffer and SDS. Application of the proposed method to the determination of theophylline and Dyphylline in human plasma proved to be feasible. The practicability of the proposed method is demonstrated on a healthy volunteer.
H. Iturriaga - One of the best experts on this subject based on the ideXlab platform.
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Kinetic–spectrophotometric determination of theophylline, Dyphylline, and proxyphylline by use of partial least-squares regression
Analytical and Bioanalytical Chemistry, 2002Co-Authors: H. Iturriaga, J. Coello, S. Maspoch, M. PorcelAbstract:A kinetic–spectrophotometric method for the determination of theophylline, Dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5–13 µg mL^–1 Dyphylline and proxyphylline, and 2–9 µg mL^–1 theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for Dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.
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kinetic spectrophotometric determination of theophylline Dyphylline and proxyphylline by use of partial least squares regression
Analytical and Bioanalytical Chemistry, 2002Co-Authors: H. Iturriaga, J. Coello, S. Maspoch, M. PorcelAbstract:A kinetic–spectrophotometric method for the determination of theophylline, Dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5–13 µg mL–1 Dyphylline and proxyphylline, and 2–9 µg mL–1 theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for Dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.
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"Multi component kinetic-spectrophotometric analysis. Selection of wavelength and time ranges."
The Analyst, 2001Co-Authors: H. Iturriaga, S. Maspoch, Jordi Coello, M. PorcelAbstract:An empirical method for the selection of the best wavelength and time ranges which can be used in the quantification of binary mixtures, in a kinetic–spectrophotometric system, is proposed. It is based on finding those ranges which provide the least correlation between the kinetic profiles and the spectra of the products of reaction. The method was applied to the analysis of binary mixtures using simulated data with different rate constant ratios and in the presence of an interference that shows spectral overlap with the analytes. Subsequently, the proposed method was applied to the resolution of Dyphylline and proxyphylline mixtures. The system studied was characterized by an elevated similarity in the kinetic behavior of the analytes under pseudo-first-order conditions and an elevated degree of spectral overlap of the products of reaction. In spite of this, satisfactory results were obtained in the quantification of the two analytes. The standard error of prediction (SEP) and the standard deviation between replicates (SDBR) did not show significant differences, being of the order of 4 and of 3% for Dyphylline and proxyphylline, respectively.
S. Maspoch - One of the best experts on this subject based on the ideXlab platform.
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Kinetic–spectrophotometric determination of theophylline, Dyphylline, and proxyphylline by use of partial least-squares regression
Analytical and Bioanalytical Chemistry, 2002Co-Authors: H. Iturriaga, J. Coello, S. Maspoch, M. PorcelAbstract:A kinetic–spectrophotometric method for the determination of theophylline, Dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5–13 µg mL^–1 Dyphylline and proxyphylline, and 2–9 µg mL^–1 theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for Dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.
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kinetic spectrophotometric determination of theophylline Dyphylline and proxyphylline by use of partial least squares regression
Analytical and Bioanalytical Chemistry, 2002Co-Authors: H. Iturriaga, J. Coello, S. Maspoch, M. PorcelAbstract:A kinetic–spectrophotometric method for the determination of theophylline, Dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5–13 µg mL–1 Dyphylline and proxyphylline, and 2–9 µg mL–1 theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for Dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.
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"Multi component kinetic-spectrophotometric analysis. Selection of wavelength and time ranges."
The Analyst, 2001Co-Authors: H. Iturriaga, S. Maspoch, Jordi Coello, M. PorcelAbstract:An empirical method for the selection of the best wavelength and time ranges which can be used in the quantification of binary mixtures, in a kinetic–spectrophotometric system, is proposed. It is based on finding those ranges which provide the least correlation between the kinetic profiles and the spectra of the products of reaction. The method was applied to the analysis of binary mixtures using simulated data with different rate constant ratios and in the presence of an interference that shows spectral overlap with the analytes. Subsequently, the proposed method was applied to the resolution of Dyphylline and proxyphylline mixtures. The system studied was characterized by an elevated similarity in the kinetic behavior of the analytes under pseudo-first-order conditions and an elevated degree of spectral overlap of the products of reaction. In spite of this, satisfactory results were obtained in the quantification of the two analytes. The standard error of prediction (SEP) and the standard deviation between replicates (SDBR) did not show significant differences, being of the order of 4 and of 3% for Dyphylline and proxyphylline, respectively.
Kathleen W Scotto - One of the best experts on this subject based on the ideXlab platform.
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abstract 992 regulation of abcg2 lysosomal degradation by xanthines role of the pi3k akt pathway
Cancer Research, 2013Co-Authors: Rui Ding, Barton A Kamen, Jia Shi, Kathleen W ScottoAbstract:ABCG2 confers multidrug resistance to a wide range of structurally unrelated chemotherapeutic drugs, often resulting in the failure of cancer chemotherapy. Accordingly, the downregulation of ABCG2 expression and/or function has been proposed as part of a regimen to improve cancer therapeutic efficacy. Previously, we have reported that a group of xanthines including caffeine, theophylline and Dyphylline can dramatically decrease ABCG2 protein in drug resistant cells, causing a significant increase in the intracellular retention of ABCG2 substrates and sensitization of the cells to chemotherapeutic agents (Ding et al., Mol Pharmacol 81:328-337, 2012). This downregulation of ABCG2 is due to a selective acceleration of its lysosomal degradation by xanthines. We now show that xanthines induce the endocytosis and subsequent degradation of ABCG2. In addition, PI3K/AKT/mTORC1 signaling was found to be involved in mediating the effect of xanthines on ABCG2, since both caffeine and theophylline strongly inhibited activation of AKT and mTORC1, and inhibition of both AKT and mTORC1 mimicked the effect of xanthines on ABCG2. Furthermore, adenosine, a nucleoside vital for purine metabolism and energy homeostasis, fully reversed the downregulation effect of caffeine on ABCG2. Interestingly, this adenosine-mediated effect occurs intracellularly and independent of adenosine receptor signalling, identifying a novel mechanism whereby the xanthine-degradation of ABCG2 is influenced by intracellular levels of adenosine. Importantly, adenosine also blocked the lysosomal degradation of ABCG2 that was induced by PI3K/AKT inhibition, indicating that the adenosine-mediated intracellular events cross-talk with the PI3K/AKT pathway in regulating ABCG2 degradation. This study enhances our understanding of the regulation of ABCG2 internalization and degradation, and identifies new targets for the development of ABCG2 expression/function modulating agents for chemosensitization. Citation Format: Rui Ding, Barton A. Kamen, Jia Shi, Kathleen W. Scotto. Regulation of ABCG2 lysosomal degradation by xanthines: Role of the PI3K/AKT pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 992. doi:10.1158/1538-7445.AM2013-992
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Abstract 992: Regulation of ABCG2 lysosomal degradation by xanthines: Role of the PI3K/AKT pathway.
Experimental and Molecular Therapeutics, 2013Co-Authors: Rui Ding, Barton A Kamen, Jia Shi, Kathleen W ScottoAbstract:ABCG2 confers multidrug resistance to a wide range of structurally unrelated chemotherapeutic drugs, often resulting in the failure of cancer chemotherapy. Accordingly, the downregulation of ABCG2 expression and/or function has been proposed as part of a regimen to improve cancer therapeutic efficacy. Previously, we have reported that a group of xanthines including caffeine, theophylline and Dyphylline can dramatically decrease ABCG2 protein in drug resistant cells, causing a significant increase in the intracellular retention of ABCG2 substrates and sensitization of the cells to chemotherapeutic agents (Ding et al., Mol Pharmacol 81:328-337, 2012). This downregulation of ABCG2 is due to a selective acceleration of its lysosomal degradation by xanthines. We now show that xanthines induce the endocytosis and subsequent degradation of ABCG2. In addition, PI3K/AKT/mTORC1 signaling was found to be involved in mediating the effect of xanthines on ABCG2, since both caffeine and theophylline strongly inhibited activation of AKT and mTORC1, and inhibition of both AKT and mTORC1 mimicked the effect of xanthines on ABCG2. Furthermore, adenosine, a nucleoside vital for purine metabolism and energy homeostasis, fully reversed the downregulation effect of caffeine on ABCG2. Interestingly, this adenosine-mediated effect occurs intracellularly and independent of adenosine receptor signalling, identifying a novel mechanism whereby the xanthine-degradation of ABCG2 is influenced by intracellular levels of adenosine. Importantly, adenosine also blocked the lysosomal degradation of ABCG2 that was induced by PI3K/AKT inhibition, indicating that the adenosine-mediated intracellular events cross-talk with the PI3K/AKT pathway in regulating ABCG2 degradation. This study enhances our understanding of the regulation of ABCG2 internalization and degradation, and identifies new targets for the development of ABCG2 expression/function modulating agents for chemosensitization. Citation Format: Rui Ding, Barton A. Kamen, Jia Shi, Kathleen W. Scotto. Regulation of ABCG2 lysosomal degradation by xanthines: Role of the PI3K/AKT pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 992. doi:10.1158/1538-7445.AM2013-992
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xanthines down regulate the drug transporter abcg2 and reverse multidrug resistance
Molecular Pharmacology, 2012Co-Authors: Rui Ding, Jia Shi, Kirk Pabon, Kathleen W ScottoAbstract:ABCG2 is an ATP-binding-cassette (ABC) transporter that confers multidrug resistance (MDR) to tumor cells by extruding a broad variety of chemotherapeutic agents, ultimately leading to failure of cancer therapy. Thus, the down-regulation of ABCG2 expression and/or function has been proposed as part of a regimen to improve cancer therapeutic efficacy. In this study, we found that a group of xanthines including caffeine, theophylline, and Dyphylline can dramatically decrease ABCG2 protein in cells that have either moderate (BeWo, a placental choriocarcinoma cell line) or high (MCF-7/MX100, a breast cancer drug-resistant cell subline) levels of ABCG2 expression. This down-regulation is time-dependent, dose-dependent, and reversible. Using lysosomal inhibitors, we found that xanthines decreased ABCG2 by inducing its rapid internalization and lysosome-mediated degradation. As a consequence, caffeine treatment significantly increased the retention of an established ABCG2 substrate in MCF-7/MX100 cells but not in parental MCF-7 cells and sensitized the MDR cells to the chemotherapeutic agent mitoxantrone (MX); combination treatment with MX and caffeine decreased the IC50 of MX ∼10-fold and induced a greater degree of apoptotic cell death than MX treatment alone. Taken together, our results describe a novel function for this large class of therapeutically relevant compounds and suggest that a subset of xanthines could be developed as combination therapy to improve the efficacy of anticancer drugs that are ABCG2 substrates.