Overcoming Peptide Instability in Blood: Development and Validation of a Stabilized LC-MS/MS Method for a 15-mer...

Peptide therapeutics pose significant analytical challenges in pharmacokinetic studies due to rapid degradation in biological matrices, particularly whole blood, where proteolytic activity can lead to substantial ex vivo loss. These challenges are amplified in small-animal studies that rely on microliter-scale sampling, where plasma separation is impractical, and whole blood must be directly analyzed. Despite existing stabilization strategies, their effectiveness in whole blood remains insufficiently understood.

In this study, we performed a systematic evaluation of multiple stabilization approaches for the 15-mer peptide B4-007 in mouse whole blood and identified limitations of commonly used methods, including incomplete protection by protease inhibitors and instability following organic solvent treatment without matrix removal. Based on these findings, we developed an integrated stabilization workflow involving immediate acidification with a relatively high concentration of formic acid (10%), followed by acetonitrile-mediated protein precipitation and matrix cleanup. This combined strategy effectively suppressed enzymatic degradation and preserved peptide integrity. The optimized workflow was coupled with LC-MS/MS analysis and validated over a range of 1-1000 ng/mL using only 5 μL of whole blood, meeting the U.S. Food and Drug Administration bioanalytical validation criteria. The method was successfully applied to a preliminary pharmacokinetic study in mice.

This work provides a systematic assessment of peptide stabilization strategies in whole blood and demonstrates that combining rapid acidification with organic solvent quenching and matrix removal can overcome limitations of existing approaches. The study offers practical methodological insights and a robust workflow as a starting point for developing stabilization strategies for other labile peptides in low-volume whole blood samples.