Development of a Quantitative SPE LC-MS/MS Assay for Bradykinin in Human Plasma

Significance of the Topic

Bradykinin is a physiologically active peptide that regulates vasodilation, vascular permeability, and inflammatory responses. Precise quantification of its low plasma concentrations is crucial for investigating cardiovascular function and monitoring disease progression or therapeutic effects.

Objectives and Overview of the Study

This work aimed to develop and validate a rapid, sensitive, and specific solid-phase extraction (SPE) LC-MS/MS assay for bradykinin in human plasma. Key goals included achieving a broad dynamic range (5–10000 pg/mL), minimizing artifactual peptide formation, and ensuring robust performance for clinical and pharmacokinetic applications.

Methodology

Sample Preparation:

• Spiking of 200 µL plasma with a [Lys-des-Arg9]-bradykinin internal standard, followed by dilution with 5% NH₄OH.
• Mixed-mode SPE using Oasis WCX µElution plates: conditioning, sample loading, sequential washes (5% NH₄OH and 10% ACN), and elution with 1% TFA in 75:25 ACN:H₂O.
• Elimination of evaporation steps to reduce peptide loss and streamline the workflow.

Chromatography and Detection:

• UPLC on a CORTECS UPLC C18 column (2.1 × 50 mm, 1.6 µm) with a 3.5-minute gradient (0.1% formic acid in water/acetonitrile) at 35 °C.
• MS/MS detection on a Xevo TQ-S in positive ESI mode, monitoring 3+ precursors and high m/z b/y fragments for enhanced selectivity.

Used Instrumentation

• ACQUITY UPLC System
• Xevo TQ-S Mass Spectrometer
• CORTECS UPLC C18 Column (2.1 × 50 mm, 1.6 µm)
• Oasis WCX 96-well µElution Plate
• Waters ACQUITY Collection Plate

Main Results and Discussion

The assay delivered sharp chromatographic peaks (2.5–3.0 s width) and improved sensitivity using solid-core UPLC particles. Optimized basic pretreatment and wash conditions in SPE achieved full recovery of bradykinin and <10% matrix effects. Calibration curves (5–10000 pg/mL) were linear (R² > 0.99). QC samples (25–5000 pg/mL) showed accuracies of 99.8–106.8% and CVs ≤ 5.5%. The inclusion of protease inhibitors during blood collection prevented ex vivo peptide formation, underscoring the importance of pre-analytical control.

Benefits and Practical Applications

• High sensitivity and specificity for low-level bradykinin measurement in clinical and pharmacokinetic studies.
• Rapid sample preparation (<30 min) and short run time (3.5 min per injection) for increased throughput.
• Robust quantification suitable for multiplex assays and differentiation of related peptides.

Future Trends and Applications

Advances in SPE chemistries and high-resolution mass spectrometry are expected to enhance peptide bioanalysis further. Automation and microfluidic sample handling may increase throughput and reproducibility. The workflow can be adapted to quantify other low-abundance biomarkers in translational research.

Conclusion

A validated SPE LC-MS/MS method for bradykinin in human plasma was established, combining mixed-mode extraction, solid-core UPLC separation, and targeted MS/MS detection. The assay offers rapid, accurate, and precise quantification, making it well-suited for clinical and pharmacokinetic applications.

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