Increasing sample throughput in pharmacological studies by using dual-column liquid chromatography with tandem mass spectrometry

Quantification of fatty acid oxidation products using online high-performance liquid chromatography tandem mass spectrometry

Oxidized fatty acids formed via lipid peroxidation are implicated in pathological processes such as inflammation and atherosclerosis. A number of methods may be used to detect specific oxidized fatty acids containing a single or multiple combinations of epoxide, hydroxyl, ketone, and hydroperoxide moieties on varying carbon chain lengths from C8 up to C30. Some of these methods are nonspecific and their use in biological systems is fraught with difficulty. Measures of specific oxidized fatty acid derivatives help in identifying oxidation pathways in pathological processes. We used liquid chromatography coupled with electrospray ionization tandem mass spectrometry as an efficient, selective, and sensitive method for identifying and analyzing multiple specific fatty acid peroxidation products in human plasma and other biological matrices. We then distilled the essential components of a number of these analyses to provide an efficient protocol by which fatty acid oxidation products and their parent compounds can be determined. In this protocol, addition of a synthetic internal standard to the sample, followed by base hydrolysis at elevated temperature and liquid-liquid phase sample extraction with lighter-than-water solvents, facilitates isolation of the oxidized fatty acid species. These species can be identified and accurately quantified using stable-isotope dilution and multiple-reaction monitoring. Use of a coupled multiplexed gradient HPLC system on the front end enables high-throughput chromatography and more efficient use of mass spectrometer time.

Rapid determination of losartan and losartan acid in human plasma by multiplexed LC-MS/MS

A rapid LC-MS/MS method has been developed and validated for the determination of losartan (LOS) and its metabolite losartan acid (LA) (EXP-3174) in human plasma using multiplexing technique (two HPLC units connected to one MS/MS). LOS and LA were extracted from human plasma by SPE technique using Oasis HLB cartridge without evaporation and reconstitution steps. Hydroflumethiazide (HFTZ) was used as an internal standard (IS). The analytes were separated on Zorbax SB C-18 column. The mass transition [M-H] ions used for detection were m/z 421.0 --> 127.0 for LOS, m/z 435.0 --> 157.0 for LA, and m/z 330.0 --> 239.0 for HFTZ. The proposed method was validated over the concentration range of 2.5-2000 ng/mL for LOS and 5.0-3000 ng/mL for LA with correlation coefficient > or = 0.9993. The overall recoveries for LOS, LA, and IS were 96.53, 99.86, and 94.16%, respectively. Total MS run time was 2.0 min/sample. The validated method has been successfully used to analyze human plasma samples for applications in 100 mg fasted and fed pharmacokinetic studies.

Sensitive column-switching high-performance liquid chromatography method for determination of propiverine in human plasma

A sensitive column-switching high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection was developed for the determination of propiverine in human plasma. Propiverine and internal standard, oxybutynin, were extracted from human plasma that had been made basic with 5N sodium hydroxide into methyl tert-butyl ether. The extracted plasma sample was injected onto the HPLC system consisting of a pretreatment column, a concentrating column, and an analytical column, which were connected with a six-port switching valve. The assay was linear in concentration ranges of 2-200 ng/ml for propiverine in human plasma. This method showed excellent sensitivity (a limit of detection of 0.5 ng/ml), good precision and accuracy. This method is suitable for bioequivalence studies following single dose in healthy volunteers.

Interaction between simvastatin and metoprolol with respect to cardiac beta-adrenoceptor density, catecholamine levels and perioperative catecholamine requirements in cardiac surgery patients

Beta-blockade is a standard cardiovascular therapy known to induce the up-regulation of beta-adrenoceptor density. Upon ligand-binding, beta-adrenoceptors are normally internalised via the arrestin pathway, and after dissociation they are re-inserted into the membrane. This means that at high catecholamine levels the adrenoceptor density is low and under beta-blockade it is high. The insertion of receptors into the membrane is often dependent on farnesylation processes that can be inhibited by statins. We carried out a prospective, controlled, observational study to determine whether beta-blockade-induced up-regulation of beta-adrenoceptor density is attenuated by statin therapy and whether this would subsequently affect catecholamine consumption during surgery. We obtained pre-operative blood samples and intra-operative biopsies of the right atrial appendage from 39 patients (age: 65+/-5 years; BMI: 28+/-1) undergoing coronary bypass surgery with or without simvastatin (20 mg/day) therapy and with or without concomitant metoprolol therapy (50 mg/day). The atrial tissue was used for radioligand-binding studies with (-)-[125I]-iodocyanopindolol (ICYP) and for assessment of the beta-adrenoceptor subtype distribution following standard protocols. In the blood samples, plasma adrenaline and noradrenaline concentrations were determined using HPLC. In all tissue samples, we found a total beta-adrenoceptor density of 38+/-4 fmol/mg protein in untreated controls; this which was up-regulated to 55+/-5 fmol/mg protein in patients receiving metoprolol. This increase in receptor number was nearly prevented completely by simvastatin therapy (42+/-5 fmol/mg protein). The up-regulation could be attributed to increases in the beta1-adrenoceptor subtype. In contrast, simvastatin alone had no effect on beta-adrenoceptor density. Pre-operative adrenaline levels were slightly reduced in all drug therapy groups (nonsignificant differences), while the levels noradrenaline were not significantly different among the groups. With respect to the perioperative catecholamine requirements, patients on metoprolol needed significantly less dopamine than control patients, while patients undergoing simvastatin/metoprolol therapy needed as much as the controls. The post-operative total catecholamine requirements were not different among the four groups of patients. There were no differences in plasma metoprolol concentration between patients receiving metoprolol alone and those receiving a combination of metoprolol and simvastatin.

IN CONCLUSION

Simvastatin therapy seems to counter-regulate the up-regulation of beta-adrenoceptor density. In the up-regulated state induced by metoprolol therapy, the patients seemed to need less catecholamines during cardiac surgery, which may be due to the higher number of beta-adrenoceptors. Additional simvastatin therapy did not reduce post-operative catecholamine consumption.

Quantification of propiverine by liquid chromatography/electrospray tandem mass spectrometry: Application to a bioequivalence study of two formulations in healthy subjects

Here we report on the development and validation of a sensitive and rapid reversed-phase liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitative determination of propiverine in human plasma. After adding an internal standard (oxybutynin chloride) to human plasma, samples were extracted using n-hexane/ethylacetate (8:2, v/v). Compounds extracted were analyzed by reversed-phase high-performance liquid chromatography (HPLC) with multiple reaction monitoring (MRM) mode for analyte detection. This method for determination of propiverine proved accurate and reproducible, with a limit of quantitation of 0.5 ng/ml in human plasma. The standard calibration curve for propiverine was linear (r2=0.9988) over the concentration range 0.5-1000.0 ng/ml in human plasma. The intra- and inter-day precision over this concentration range was lower than 8.66% (relative standard deviation, %R.S.D.), and accuracy was between 99.46 and 109.41%, respectively. This method was successfully applied to a bioequivalence study of two propiverine hydrochloride tablet formulations (20 mg) in 24 healthy subjects after a single administration.

Description and Validation of a Four-Channel Staggered LC−MS/MS System for High-Throughput in Vitro Screens

A parallel four-channel LC-MS/MS system for quantitative high-throughput in vitro screens is described. The system comprises four pumps, a four-valve autosampler equipped with a nine-port stream selector valve, and a triple quadrupole mass spectrometer. Staggered injections across the sample list are performed by four injector valves onto separate columns in such a manner that the chromatographic window of interest is always eluting from one of the columns into the mass spectrometer. To demonstrate the applicability of the system, three different compounds (verapamil, propanolol, dextromethorphan) were analyzed. The results showed that the sample throughput could be increased more than three times in comparison with a conventional single-column LC-MS/MS system. Validation results for the three compounds showed an accuracy of 85.0-108%, a precision (given as relative standard deviation) of 2.60-10.7%, and a carryover of less than 0.1%.

Determination of neomycin by LC–tandem mass spectrometry using hydrophilic interaction chromatography

A specific, and automated method was developed to quantitate neomycin in human serum. Samples were prepared with an automated solid phase extraction (SPE). The hydrophilic interaction chromatography (HILIC) was used for additional sample cleanup and baseline separation. The analyte neomycin was detected with electrospray ionisation tandem mass spectrometry (ESI-MS-MS). Using a volume of 500 microl biological sample the lower limit of quantification was 100 ng/ml. The described HILIC-MS-MS method is suitable for clinical and pharmcokinetical investigations of neomycin.