Analysis of alpha2u-globulin in rat urine and kidneys by liquid chromatography-electrospray ionization mass spectrometry

Multiple Reaction Monitoring for Direct Quantitation of Intact Proteins Using a Triple Quadrupole Mass Spectrometer

Methods that can efficiently and effectively quantify proteins are needed to support increasing demand in many bioanalytical fields. Triple quadrupole mass spectrometry (QQQ-MS) is sensitive and specific, and it is routinely used to quantify small molecules. However, low resolution fragmentation-dependent MS detection can pose inherent difficulties for intact proteins. In this research, we investigated variables that affect protein and fragment ion signals to enable protein quantitation using QQQ-MS. Collision induced dissociation gas pressure and collision energy were found to be the most crucial variables for optimization. Multiple reaction monitoring (MRM) transitions for seven standard proteins, including lysozyme, ubiquitin, cytochrome c from both equine and bovine, lactalbumin, myoglobin, and prostate-specific antigen (PSA) were determined. Assuming the eventual goal of applying such methodology is to analyze protein in biological fluids, a liquid chromatography method was developed. Calibration curves of six standard proteins (excluding PSA) were obtained to show the feasibility of intact protein quantification using QQQ-MS. Linearity (2-3 orders), limits of detection (0.5-50 μg/mL), accuracy (<5% error), and precision (1%-12% CV) were determined for each model protein. Sensitivities for different proteins varied considerably. Biological fluids, including human urine, equine plasma, and bovine plasma were used to demonstrate the specificity of the approach. The purpose of this model study was to identify, study, and demonstrate the advantages and challenges for QQQ-MS-based intact protein quantitation, a largely underutilized approach to date.

The vomeronasal organ mediates interspecies defensive behaviors through detection of protein pheromone homologs

Potential predators emit uncharacterized chemosignals that warn receiving species of danger. Neurons that sense these stimuli remain unknown. Here we show that detection and processing of fear-evoking odors emitted from cat, rat, and snake require the function of sensory neurons in the vomeronasal organ. To investigate the molecular nature of the sensory cues emitted by predators, we isolated the salient ligands from two species using a combination of innate behavioral assays in naive receiving animals, calcium imaging, and c-Fos induction. Surprisingly, the defensive behavior-promoting activity released by other animals is encoded by species-specific ligands belonging to the major urinary protein (Mup) family, homologs of aggression-promoting mouse pheromones. We show that recombinant Mup proteins are sufficient to activate sensory neurons and initiate defensive behavior similarly to native odors. This co-option of existing sensory mechanisms provides a molecular solution to the difficult problem of evolving a variety of species-specific molecular detectors.

A sample preparation process for LC–MS/MS analysis of total protein drug concentrations in monkey plasma samples with antibody

The determination of protein concentrations in plasma samples often provides essential information in biomedical research, clinical diagnostics, and pharmaceutical discovery and development. Binding assays such as ELISA determine meaningful free analyte concentrations by using specific antigen or antibody reagents. Concurrently, mass spectrometric technology is becoming a promising complementary method to traditional binding assays. Mass spectrometric assays generally provide measurements of the total protein analyte concentration. However, it was found that antibodies may bind strongly with the protein analyte such that total concentrations cannot be determined. Thus, a sample preparation process was developed which included a novel "denaturing" step to dissociate binding between antibodies and the protein analyte prior to solid phase extraction of plasma samples and LC-MS/MS analysis. In so doing, the total protein analyte concentrations can be obtained. This sample preparation process was further studied by LC-MS analysis with a full mass range scan. It was found that the protein of interest and other plasma peptides were pre-concentrated, while plasma albumin was depleted in the extracts. This capability of the sample preparation process could provide additional advantages in proteomic research for biomarker discovery and validation. The performance of the assay with the novel denaturing step was further evaluated. The linear dynamic range was between 100.9ng/mL and 53920.0ng/mL with a coefficient of determination (r(2)) ranging from 0.9979 and 0.9997. For LLOQ and ULOQ samples, the inter-assay CV was 12.6% and 2.7% and inter-assay mean accuracies were 103.7% and 99.5% of theoretical concentrations, respectively. For QC samples, the inter-assay CV was between 2.1% and 4.9%, and inter-assay mean accuracies were between 104.1% and 110.0% of theoretical concentrations.

Method development for the concentration determination of a protein in human plasma utilizing 96-well solid-phase extraction and liquid chromatography/tandem mass spectrometric detection

Although liquid chromatography/tandem mass spectrometry (LC/MS/MS) technology has been widely used for quantitative analysis of small organic molecules, it has been a challenging task to quantitatively analyze protein samples utilizing this technology in biological matrices for pre-clinical and clinical studies. Here we present our initial results in method development for the quantitative determination of rK5 protein concentrations in human plasma samples utilizing LC/MS/MS technology. A protein similar in structure to rK5, but with a slightly reduced molecular weight, was used as internal standard. A 96-well solid-phase extraction procedure was developed to effectively extract protein analytes from plasma samples. Quantitative analysis was obtained by a novel approach of protein monitoring that employed selective reaction monitoring (SRM). Even though mass spectrometry of the internal standard protein gave no fragment ions, SRM monitoring greatly reduced background interference. Using samples prepared in human plasma with sodium EDTA as anticoagulant, a correlation coefficient (r(2)) of 0.9940 was obtained by producing a single standard curve with the injection of six rows of standards with a concentration range from 100 ng/mL to 10 microg/mL. The mean analytical recovery for these standards ranged from 91.5 to 103.6%. The CVs for individual standard levels ranged from 3.7 to 20.9%. The experiment was also repeated using samples prepared in human plasma with sodium heparin as anticoagulant, which produced a correlation coefficient (r(2)) of 0.9952 obtained from a single standard curve with the injection of four rows of standards with a concentration range from 50 ng/mL to 10 microg/mL. The mean analytical recovery for the standards ranged from 96.2 to 104.6%. The CVs for individual standard levels ranged from 2.6 to 15.6%.

Electrospray LC-MS/MS quantitation, stability, and preliminary pharmacokinetics of bradykinin antagonist polypeptide B201 (NSC 710295) in the mouse

B201 (NSC 710295), [SUIM-(Darg-Arg-Pro-Hyp-Gly-Igl-Ser-Digl-Oic-Arg)(2)], a third generation of bradykinin (BK) antagonist, has been found to possess high potency. We report the development of a highly sensitive electrospray LC-MS/MS assay method for the analysis of B201 in plasma for the first time, using an ion-trap mass spectrometer. Human or mouse plasma (0.2 ml) was spiked with B201 and the internal standard, substance P. The compounds were extracted with a preconditioned C-18 reversed-phase column and analyzed by LC-MS/MS. The analytes were separated on a 50 x 2 mm (i.d.) BetaBasic C8 column, using a gradient elution. The positive ion selected reaction monitor mode was used monitoring the transitions of ions at m/z 938.9(3+)-->816.0(2+) for B201 and 674.3(2+)-->665.7(2+) for substance P. Assay validation was performed, and the limit of quantitation (LOQ) for B201 was found to be 1 ng/ml for human plasma and 2.5 ng/ml for mouse plasma. The recovery was 78% for B201 and 88% for substance P. The assay was linear from 2.5 to 1500 ng/ml for mouse plasma monitored. Using a 0.2 ml plasma, the within-day CVs were 9.3% at 2.5 ng/ml, 6.5% at 100 ng/ml, and 3.8% at 1000 ng/ml for human plasma (n=6). For mouse plasma, the respective within-day CVs were 17.6, 9.6, and 6.2% (n=6). The between-day CVs for human plasma were 8.2, 10.9, and 2.4%, respectively, (n=3) and the respective values for mouse plasma were 11.9, 8.6 and 6.5% (n=6). Pharmacokinetics of B201 in the mouse was studied following i.v. administration at 5 mg/kg and found to conform to a two-compartment model with an initial half-life of 14 min and a terminal half-life of 44 h. Plasma B201 peak level was detected at microg/ml range and the levels were detectable for a least 24 h. Preliminary oral bioavailability was found to be about 1%. This method demonstrates that an ion trap mass spectrometer can be a powerful tool to quantify large peptides at low nanogram per milliliter with a non-isotopically labeled internal standard.