An in vivo microdialysis coupled with liquid chromatography/tandem mass spectrometry study of cortisol metabolism in monkey adipose tissue.

It is postulated that elevated tissue concentrations of cortisol may be associated with the development of metabolic syndrome, obesity, and type 2 diabetes. The 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) enzyme regenerates cortisol from inactive cortisone in tissues such as liver and adipose. To better understand the pivotal role of 11beta-HSD1 in disease development, an in vivo microdialysis assay coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis using stable isotope-labeled (SIL) cortisone as a substrate was developed.

An in vitro microdialysis methodology to study 11beta-hydroxysteroid dehydrogenase type 1 enzyme activity in liver microsomes.

Microdialysis sampling coupled with liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS/MS) was used to observe in vitro 11beta-hydroxysteroid dehydrogenase type 1 (HSD1) enzyme-catalyzed conversion of stable-isotope-labeled cortisone to cortisol in liver microsomes from dog, monkey, and human. Experimental conditions that would affect the microdialysis sampling approach including probe length, perfusion fluid flow rate, extraction efficiency (E(d)), substrate concentration, and enzyme reaction conditions were evaluated. Dialysates containing high salt concentrations (>150 mM) were directly assayed using LC/MS/MS without additional sample cleanup.

Automated enzyme inhibition assay method for the determination of atorvastatin-derived HMG-CoA reductase inhibitors in human plasma using radioactivity detection.

Introduction: A Tecan-based enzyme inhibition assay has been developed for the determination of atorvastatin-derived 'active' and 'total' (active inhibitors plus atorvastatin lactone and other potential inhibitors following base hydrolysis) 3-hydroxy-3-methylglutaryl-Coenzyme A (HMG-CoA) reductase inhibitor concentrations in human plasma. Atorvastatin is an inhibitor of HMG-CoA reductase, which is a key rate-limiting enzyme in the cholesterol biosynthesis. Previously, atorvastatin-derived HMG-CoA reductase inhibitors were measured via enzyme inhibition assays by manual operation.

Quantitation of geometric isomers of a phosphodiesterase inhibitor in rat and monkey plasma using liquid chromatography-tandem mass spectrometry.

Quantitation of geometric isomers of a phosphodiesterase inhibitor was required to determine the extent of interconversion following dosing of a single isomer in preclinical pharmacokinetic studies. Assays were developed for the simultaneous determination of Compound A (Fig. 1), 6-[1-methyl-1-(methylsulfonyl)ethyl-8(3-{(E)-2-(3-methyl-1,2,4-oxadiazol-5-yl)-2-[4-(methylsulfonyl)phenyl]ethenyl}phenyl)quinoline] and its geometric Z-isomer, Compound B, in plasma using liquid chromatography-tandem mass spectrometry.

Determination of M+4 stable isotope labeled cortisone and cortisol in human plasma by microElution solid-phase extraction and liquid chromatography/tandem mass spectrometry.

A sensitive microElution solid-phase extraction (SPE) liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the determination of M+4 stable isotope labeled cortisone and cortisol in human plasma. In this method, M+4 cortisone and M+4 cortisol were extracted from 0.3 mL of human plasma samples using a Waters Oasis HLB 96-well microElution SPE plate using 70 microL methanol as the elution solvent, and chromatographed on a Waters Symmetry C18 column (4.

Application of a novel ultra-low elution volume 96-well solid-phase extraction method to the LC/MS/MS determination of simvastatin and simvastatin acid in human plasma.

A novel extraction method has been utilized in the LC/MS/MS determination of simvastatin and simvastatin acid in human plasma. In this method, 300 microl of plasma sample was loaded onto a Waters Oasis 96-well HLB microElution plate, the stationary phase was washed using 2 x 400 microl of 5% methanol in water, and the analytes were eluted using 35 microl of 95/5 acetonitrile/H(2)O twice. The sample extracts were diluted with 40 microl of methyl ammonium acetate (1mM, pH 4.

Pharmacokinetics of montelukast in asthmatic patients 6 to 24 months old.

Montelukast is a cysteinyl leukotriene receptor antagonist approved for the treatment of asthma for those ages 1 year old to adult. The purpose of this study was to evaluate the pharmacokinetic comparability of a 4-mg dose of montelukast oral granules in patients > or = 6 to < 24 months old to the 10-mg approved dose in adults. This was an open-label study in 32 patients.

Quantitative analysis of simvastatin and its beta-hydroxy acid in human plasma using automated liquid-liquid extraction based on 96-well plate format and liquid chromatography-tandem mass spectrometry.

An assay based on automated liquid-liquid extraction (LLE) and liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been developed and validated for the quantitative analysis of simvastatin (SV) and its beta-hydroxy acid (SVA) in human plasma. A Packard MultiProbe II workstation was used to convert human plasma samples collected following administration of simvastatin and quality control (QC) samples from individual tubes into 96-well plate format. The workstation was also used to prepare calibration standards and spike internal standards.

Determination of simvastatin-derived HMG-CoA reductase inhibitors in biomatrices using an automated enzyme inhibition assay with radioactivity detection.

A robust, automated enzyme inhibition assay method was developed and validated for the determination of HMG-CoA reductase inhibitory activities in plasma and urine samples following simvastatin (SV) administration. The assay was performed on Tecan Genesis 150 and 200 systems equipped with 8-probe and 96-well plates. Plasma samples containing HMG-CoA reductase inhibitors were treated with acetonitrile for protein precipitation before being incubated with HMG-CoA reductase, [14C]-HMG-CoA, and NADPH for a fixed length of time at a fixed temperature.

Sensitive method for the quantitative determination of gemfibrozil in dog plasma by liquid-liquid cartridge extraction and liquid chromatography-tandem mass spectrometry.

A sensitive LC-MS/MS assay for the quantitative determination of gemfibrozil in dog plasma has been developed and validated and is described in this work. The assay involved the extraction of the analyte from 0.5-ml aliquots of dog plasma using Chem Elut cartridges and methyl tert.

Robotic inhibition assay for determination of HMG-CoA reductase inhibitors in human plasma.

The cholesterol-lowering drug simvastatin (SIMV, Zocor reduced heart attacks by 42% in patients who had high cholesterol levels and suffered from heart disease. Upon oral administration, SIMV is quickly hydrolyzed to its beta-hydroxyacid and other acid metabolites, which are potent inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase. A Tecan-based enzyme inhibition assay has been developed to improve the existing Zymark-based assay for the determination of both active and total concentrations of HMG-CoA reductase inhibitors in human plasma.

Mechanistic studies on metabolic interactions between gemfibrozil and statins.

A series of studies were conducted to explore the mechanism of the pharmacokinetic interaction between simvastatin (SV) and gemfibrozil (GFZ) reported recently in human subjects. After administration of a single dose of SV (4 mg/kg p.o.

Effects of liquid chromatography mobile phase buffer contents on the ionization and fragmentation of analytes in liquid chromatographic/ionspray tandem mass spectrometric determination.

The effects of liquid chromatography mobile phase buffer contents on the ionization and fragmentation of drug molecules in liquid chromatographic/ionspray tandem mass spectrometric (LC/MS/MS) determination were evaluated for simvastatin (SV) and its hydroxy acid (SVA). The objective was to improve further the sensitivity for SV by overcoming the unfavorable condition caused by the formation of multiple major adduct ions and multiple major fragment ions when using ammonium as LC mobile phase buffer. Mobile phases (70:30 acetonitrile-buffer, 2 mM, pH 4.