Determination of an in vivo metabolite of a human immunodeficiency virus protease-inhibitor in human plasma by high-performance liquid chromatography with tandem mass spectrometry

Targeted mass spectrometry approaches for protein biomarker verification

The search for protein biomarkers has been a highly pursued topic in the proteomics community in the last decade. This relentless search is due to the constant need for validated biomarkers that could facilitate disease risk stratification, disease diagnosis, prognosis, monitoring as well as drug development, which ultimately would improve our quality of life. The recent development of proteomic technologies including the advancement of mass spectrometers with high sensitivity and speed has greatly advanced the discovery of potential biomarkers. One of the bottlenecks lies in the development of well-established verification assays to screen the biomarker candidates identified in the discovery stage. Recently, absolute quantitation using multiple-reaction monitoring mass spectrometry (MRM-MS) in combination with isotope-labeled internal standards has been extensively investigated as a tool for high-throughput protein biomarker verification. In this review, we describe and discuss recent developments and applications of MRM-MS methods for biomarker verification.

Suppression of cerebrospinal fluid HIV burden in antiretroviral naive patients on a potent four-drug antiretroviral regimen

OBJECTIVE

To determine the longitudinal response of HIV in the cerebrospinal fluid (CSF) to highly active antiretroviral therapy (HAART) and to investigate the levels of indinavir penetrating into the CSF.

DESIGN

Open study of HIV-infected subjects naive to therapy with protease inhibitors.

SETTING

Tertiary care referral center.

SUBJECTS

Twenty-five participants were begun on indinavir, nevirapine, zidovudine, and lamivudine.

INTERVENTIONS

Lumbar punctures were performed prior to therapy and 2 and 6 months after beginning therapy. Plasma and CSF were assayed for routine cell counts, chemistries, HIV load and indinavir levels.

RESULTS

Twenty-two subjects had CSF HIV RNA level data available at all three time points, three others at baseline and 2 months. At month 2 of therapy, nine of 25 (36%) subjects had CSF HIV RNA levels > 50 HIV RNA copies/ml. By 6 months, all 22 subjects had CSF HIV RNA levels < 50 HIV RNA copies/ml. CSF white blood cell counts fell from a baseline mean of 5.3 x 10(6)/l to 1.9 x 10(6)/l (P = 0.013) at 6 months. Plasma indinavir levels declined rapidly while CSF levels remained stable throughout the 8-h dosing interval. The median CSF indinavir level was 71 ng/ml, approximating the upper limit of the 95% inhibitory concentration for indinavir against HIV-1.

CONCLUSIONS

CSF HIV RNA levels cannot be expected to fall below 50 HIV RNA copies/ml even after 2 months of therapy on HAART. Prolonged therapy may be required to suppress HIV levels within the central nervous system.

Determination of rofecoxib (MK-0966), a cyclooxygenase-2 inhibitor, in human plasma by high-performance liquid chromatography with tandem mass spectrometric detection

A method for the determination of 4-(4-methanesulfonylphenyl)-3-phenyl-5H-furan-2-one (Rofecoxib, Vioxx, MK-0966, I) a cyclooxygenase-2 inhibitor, in human plasma has been developed. The method is based on high-performance liquid chromatography (HPLC) with atmospheric pressure chemical ionization tandem mass spectrometric (APCI-MS-MS) detection in negative ionization mode using a heated nebulizer interface. Drug and internal standard (II) were isolated from basified plasma using liquid-liquid extraction. The organic extracts were dried, reconstituted in mobile phase and injected into the HPLC-MS-MS system. Compounds I and II were chromatographed on a narrow bore (100 mm x 3.0 mm) C18 analytical column, with mobile phase consisting of acetonitrile:water (1:1, v/v) at a flow-rate of 0.4 ml/min. The MS-MS detection was performed on a PE-Sciex API III Plus tandem mass spectrometer operated in selected reaction monitoring mode. The parent-->product ion combinations of m/z 313-->257 and 327-->271 were used to quantify I and II, respectively, after chromatographic separation of the analytes. The assay was validated in the concentration range of 0.1 to 100 ng/ml of plasma. The precision of the assay (expressed as coefficient of variation) was less than 10% at all concentrations within the standard curve range, with adequate assay accuracy. The effect of HPLC mobile phase components on the ionization efficiency and sensitivity of detection in the positive and negative ionization modes, and the detailed description of all necessary steps involved in the assay for I in plasma are presented.

Determination of indinavir, a HIV-1 protease inhibitor, in human plasma using ion-pair reversed-phase high-performance liquid chromatography

Indinavir is widely prescribed as a component of potent antiretroviral therapy for the treatment of HIV-1 infection. Because virologic failure of therapy can result from subtherapeutic drug levels, monitoring of indinavir levels may be important in clinical management. We have developed a simple, accurate, and precise high-performance liquid chromatographic (HPLC) assay for measurement of indinavir concentration in human plasma. In our method, indinavir was extracted from plasma with dichloromethane at pH 10.4, which resulted in quantitative recovery of indinavir and the internal standard (IS), methyl-indinavir (86% and 80%-97%, respectively). Chromatographic separation was accomplished using a Luna C18 (2) (Phenomenex) analytic column with a mobile phase composed of acetonitrile:phosphate buffer (25 mM) and 0.2% triethylamine pH 7.0 (34.5:65.5, v/v). Ion-paired reagent triethylamine was necessary to ensure an appropriate retention time for indinavir and differentiate it from other protease inhibitors that were coextracted. Quantification was performed at 210 nm. The standard curves were linear (r2>0.999) over the concentration range 25-5,000 ng/mL, when 1-mL aliquots of plasma were extracted. Inter- and intraday coefficients of variation were acceptable. The assay was used to determine trough and peak levels of in plasma from 12 subjects who received indinavir 1200 mg every 12 hours, 1000 mg every 12 hours, or 800 mg every 8 hours. The concentrations of indinavir found in this study (trough 26-768 ng/mL; peak at 1 hr 3,309-17,568 ng/mL) has a wider range than defined previously (trough 50-300 ng/mL; peak 6,000-12,000 ng/mL). This study illustrates three potential uses of indinavir monitoring: to assess individual dosing regimen, to assess patient compliance, and to monitor unusual indinavir levels caused by changed drug clearance.

Determination of indinavir, potassium sorbate, methylparaben, and propylparaben in aqueous pediatric suspensions

A gradient, reversed phase, HPLC method was developed for simultaneous analysis of potassium sorbate, methylparaben, propylparaben, and indinavir in aqueous suspensions that contain a proprietary orange flavoring and Magnasweet sweetener enhancer (MacSanrews and Forbes Company, Magnasweet product brochure). The chromatographic separation is performed on an Eclipse XDB-C8 column using a gradient run with an analysis time of 35 min. The mobile phase consists of acetonitrile and acetonitrile:citrate buffer, pH 4.0 (20:80 v/v). The method successfully separates the three preservatives, indinavir (active ingredient), the orange flavoring, the Magnasweet species, and the indinavir lactone degradate. Recovery, linearity, and precision results for the three preservatives and indinavir are described. The method applies to two types of formulations: Xanthan Gum suspension and NanoSystems suspension.

Simultaneous determination of omeprazole and 5'-hydroxyomeprazole in human plasma by liquid chromatography-tandem mass spectrometry

A method for the simultaneous determination of omeprazole and 5'-hydroxyomeprazole in human plasma is described. Isolation of the analytes from plasma was achieved via solid-phase extraction using a polymeric sorbent based cartridge. The analytes were chromatographed under reversed-phase conditions on a Zorbax XDB-C8 column (50 x 4.6 mm). The HPLC mobile phase consisted of a mixture of acetonitrile-water (21:79, v/v) containing 10 mM ammonium hydroxide. The apparent pH of the mobile phase was adjusted to 8.5 with formic acid prior to use. A Sciex API III+ tandem mass spectrometer equipped with a heated nebulizer atmospheric pressure chemical ionization interface was used as a detector and was operated in the positive ion mode. Multiple reaction monitoring using the precursor-->product ion combinations of m/z 362-->214, 346-->198 and 316-->147 was used to detect 5'-hydroxyomeprazole, omeprazole and internal standard, respectively. The method was validated in the concentration range of 10-500 ng/ml plasma with adequate assay precision and accuracy. The assay was used to determine the cytochrome P450 2C19 phenotype of subjects participating in clinical trials of compounds under development.