Development of a multi-matrix LC-MS/MS method for urea quantitation and its application in human respiratory disease studies

Rapid quantification of polymyxin B in human pulmonary epithelial lining fluid by LC-MS/MS and its clinical application

Pulmonary epithelial lining fluid (ELF) was commonly used for the pharmacokinetic study in lower respiratory tract infections. To characterize the intrapulmonary pharmacokinetic properties of polymyxin B following aerosol delivery, we developed and fully validated a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for quantifying polymyxin B in human bronchoalveolar lavage fluid (BALF). The ELF concentrations were calculated by the BALF values of polymyxin B using urea as a volume normalizer. Chromatographic separation was achieved on a Phonomenex Kinetex XB-C18 column(100 mm × 2.1 mm I.D., 2.6 μm)in acetonitrile and water both containing 0.2 % formic acid. The flow rate was set as 0.4 mL/min for a 3.5 min running time. Protein precipitation was used in preparing BALF samples with polymyxin E1 as an internal standard. Polymyxin B was detected under multiple reaction monitoring conditions using the electrospray ionization interface running in the positive ionization mode. The assay showed a good linear relationship over the tested concentration ranges of 0.0300/0.00306---10.0/1.02 mg/L for polymyxin B1/B2 in bronchoalveolar lavage fluid (R2 > 0.99). The inter- and inter-day precisions (RSD, %) were < 12.2 %(15.2 % for LLOQ samples)and the accuracies (%) were within the range of 94.3 ∼ 110.4 %. This reliable LC-MS/MS method for detection of polymyxin B was successfully applied to conduct a pulmonary penetration study in patients following aerosol administration.

A novel urease-assisted ratiometric fluorescence sensing platform based on pH-modulated copper-quenched near-infrared carbon dots and methyl red-quenched red carbon dots for selective urea monitoring

A novel and sensitive fluorescence ratiometric method is developed for urea detection based  on the pH-sensitive response of two fluorescent carbon dot (CD) systems: R-CDs/methyl red (MR) and NIR-CDs/Cu2+. The sensing mechanism involves breaking down urea using the enzyme urease, releasing ammonia and increasing pH. At higher pH, the fluorescence of NIR-CDs is quenched due to the enhanced interaction with Cu2+, while the fluorescence of R-CDs is restored as the acidic MR converts to its basic form, removing the inner filter effect. The ratiometric signal (F608/F750) of the R-CDs/MR and NIR-CDs/Cu2+ intensities changed in response to the pH induced by urea hydrolysis, enabling selective and sensitive urea detection. Detailed spectroscopic and morphological investigations confirmed the fluorescence probe design and elucidated the sensing mechanism. The method exhibited excellent sensitivity (0.00028 mM LOD) and linearity range (0.001 - 8.0 mM) for urea detection, with successful application in milk samples for monitoring adulteration, demonstrating negligible interference and high recovery levels (96.5% to 101.0%). This ratiometric fluorescence approach offers a robust strategy for selective urea sensing in complicated matrices.

A universal surrogate matrix assay for urea measurement in clinical pharmacokinetic studies of respiratory diseases

In pharmacokinetic studies for respiratory diseases, urea is a commonly used dilution marker for volume normalization of various biological matrices, owing to the fact that urea diffuses freely throughout the body and is minimally affected by disease states. In this study, we developed a convenient liquid chromatography-tandem mass spectrometry (LC-MS/MS) surrogate matrix assay for accurate urea quantitation in plasma, serum and epithelial lining fluid. Different mass spectrometer platforms and ionization modes were compared in parallel. The LC method and mass spectrometer parameters were comprehensively optimized to reduce interferences, to smooth the baseline and to maximize the signal-to-noise ratio. Saline was selected as the surrogate matrix, and its suitability was confirmed by good parallelism and accurate quality control sample measurements. Reliable and robust assay performance was demonstrated by precision and accuracy, dilution integrity, sensitivity, recovery and stability, all of which met bioanalysis requirements to support clinical studies. The assay performance was also verified and better understood by comparing it with a colorimetric assay and to a surrogate analyte assay. The newly developed surrogate matrix assay has the potential to be further expanded for urea quantitation in numerous physiological matrices.

A mechanistic PK/PD model to enable dose selection of the potent anti-tryptase antibody (MTPS9579A) in patients with moderate-to-severe asthma

Tryptase, a protease implicated in asthma pathology, is secreted from mast cells upon activation during an inflammatory allergic response. MTPS9579A is a novel monoclonal antibody that inhibits tryptase activity by irreversibly dissociating the active tetramer into inactive monomers. This study assessed the relationship between MTPS9579A concentrations in healthy subjects and tryptase levels in serum and nasal mucosal lining fluid from healthy subjects and patients with moderate-to-severe asthma. These data were used to develop a mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model that quantitatively inter-relates MTPS9579A exposure and inhibition of active tryptase in the airway of patients with asthma. From initial estimates of airway tryptase levels and drug partitioning, the PK/PD model predicted almost complete neutralization of active tryptase in the airway of patients with asthma with MTPS9579A doses of 900 mg and greater, administered intravenously (i.v.) once every 4 weeks (q4w). Suppression of active tryptase during an asthma exacerbation event was also evaluated using the model by simulating the administration of MTPS9579A during a 100-fold increase in tryptase secretion in the local tissue. The PK/PD model predicted that 1800 mg MTPS9579A i.v. q4w results in 95.7% suppression of active tryptase at the steady-state trough concentration. Understanding how the exposure-response relationship of MTPS9579A in healthy subjects translates to patients with asthma is critical for future clinical studies assessing tryptase inhibition in the airway of patients with moderate-to-severe asthma.

Multiplex Hybrid Antigen-Capture LC-MRM Quantification in Sera and Nasal Lining Fluid of AZD7442, a SARS-CoV-2-Targeting Antibody Combination

AZD7442 (tixagevimab [AZD8895]/cilgavimab [AZD1061]) is a monoclonal antibody (mAb) combination in development for the prevention and treatment of coronavirus disease 2019. Traditionally, bioanalysis of mAbs is performed using ligand binding assays (LBAs), which offer sensitivity, robustness, and ease of implementation. However, LBAs frequently require generation of critical reagents that typically take several months. Instead, we developed a highly sensitive (5 ng/mL limit of quantification) method using a hybrid LBA-liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) approach for quantification of the two codosed antibodies in serum and nasal lining fluid (NLF), a rare matrix. The method was optimized by careful selection of multiple reaction monitoring, capture reagents, magnetic beads, chromatographic conditions, evaluations of selectivity, and matrix effect. The final assay used viral spike protein receptor-binding domain as capture reagent and signature proteotypic peptides from the complementarity-determining region of each mAb for detection. In contrast to other methods of similar/superior sensitivity, our approach did not require multidimensional separations and can be operated in an analytical flow regime, ensuring high throughput and robustness required for clinical analysis at scale. The sensitivity of this method significantly exceeds typical sensitivity of ∼100 ng/mL for analytical flow 1D LBA-LC-MS/MS methods for large macromolecules, such as antibodies. Furthermore, infection and vaccination status did not impact method performance, ensuring method robustness and applicability to a broad patient population. This report demonstrated the general applicability of the hybrid LBA-LC-MS/MS approach to platform quantification of antibodies with high sensitivity and reproducibility, with specialized extension to matrices of increasing interest, such as NLF.

Quantitative analysis of urea in serum by synchronous modulation and demodulation fluorescence spectroscopy

High-precision spectral data is a necessary prerequisite for quantitative analysis of complex solution components. In order to improve the accuracy of spectral data, this paper proposes a method of synchronous modulation and demodulation. This article also combines the "M + N" theory, cleverly uses the excitation fluorescence of the components in the serum and its self-absorption phenomenon, collects the fluorescence spectrum of the serum sample, and then uses the partial least squares (PLS) method and the cubic optimization model method to establish a model to analyze the urea concentration of serum. At the same time, in order to verify the effectiveness of synchronous modulation and demodulation method, the unmodulated fluorescence spectrum is used to establish the regression model of urea concentration. Compared with the unmodulated fluorescence spectrum modeling results, the fluorescence spectrum modeling results after modulation and demodulation have been significantly improved. In the modeling results of fluorescence spectrum after synchronous modulation and demodulation, the Rc is 0.916753, the RMSEC is 2.05848 mmol/L, the Rp is 0.79663, and the RMSEP is 3.16812 mmol/L, the Rp-all is 0.88879, and the RMSEP-all is 2.32114 mmol/L. The results show that the method of synchronous modulation and demodulation proposed in this paper not only reduces the influence of dark current, ambient light and background noise on the signal-to-noise ratio of the spectral data, but also effectively avoids the error caused by the non-synchronization of the chopper and the spectrometer. Therefore, the method used in this paper not only improves the signal-to-noise ratio and accuracy of spectral data, but also improves the accuracy of spectral quantitative analysis of complex solutions.

Current developments in LC-MS for pharmaceutical analysis

Liquid chromatography (LC) based techniques in combination with mass spectrometry (MS) detection have had a large impact on the development of new pharmaceuticals in the past decades.

Passive sweat collection and colorimetric analysis of biomarkers relevant to kidney disorders using a soft microfluidic system

The rich range of biomarkers in sweat and the ability to collect sweat in a non-invasive manner create interest in the use of this biofluid for assessments of health and physiological status, with potential applications that range from sports and fitness to clinical medicine. This paper introduces two important advances in recently reported classes of soft, skin-interfaced microfluidic systems for sweat capture and analysis: (1) a simple, broadly applicable means for collection of sweat that bypasses requirements for physical/mental exertion or pharmacological stimulation and (2) a set of enzymatic chemistries and colorimetric readout approaches for determining the concentrations of creatinine and urea in sweat, throughout ranges that are physiologically relevant. The results allow for routine, non-pharmacological capture of sweat for patient populations, such as infants and the elderly, that cannot be expected to sweat through exercise, and they create potential opportunities in the use of sweat for kidney disease screening/monitoring. Studies on human subjects demonstrate these essential capabilities, with quantitative comparisons to standard methods. The results expand the range of options available in microfluidic sampling and sensing of sweat for disease diagnostics and health monitoring.

Development, validation and comparison of surrogate matrix and surrogate analyte approaches with UHPLC-MS/MS to simultaneously quantify dopamine, serotonin and γ-aminobutyric acid in four rat brain regions

As biomarkers, endogenous neurotransmitters play critical roles in the process of neuropsychiatric diseases, and neurotransmitter levels in different brain regions can contribute to neurological disease diagnosis and treatment. Due to the lack of a blank matrix for endogenous neurotransmitters, surrogate-matrix and surrogate-analyte approaches have been used for the determination of neurotransmitters to solve this problem. In this study, we capitalised on the high accuracy, precision, and throughput of UHPLC-MS/MS and developed new methods based on the two approaches. Both approaches satisfied FDA and EMA validation criterias after an appropriate parallelism assessment, and they were used to further quantify the three endogenous neurotransmitters, including dopamine (DA), serotonin (5-HT) and γ-aminobutyric acid (GABA) in rat brain four regions (cortex, striatum, hypothalamus and hippocampus) which represent the catecholamines, indolamines, and amino acids, respectively. Comparison of the results in the same rats (n = 10) showed there was no significant difference in DA, 5-HT, or GABA levels between the two approaches (P > 0.05). The concentrations of DA and GABA were highest in striatum and hypothalamus, respectively, and the levels of 5-HT were paralleled in striatum and hippocampus almost 2-fold higher than other regions. This is the first study to compare these two approaches in the determination of endogenous neurotransmitter content in the rat brain, and the surrogate-matrix approach proved to be simple, rapid, and reliable, considering cost, matrix similarity, and practicality.