Maryam Mahmoudi, Reidar Lund, Thomas Daniel Vogelaar, Hanne Røberg-Larsen
Section of Chemical Life Science, Department of Chemistry, University of Oslo, Norway 1
Email: maryam.mahmoudi@kjemi.uio.no
Infections caused by resistant bacterial strains represent a major threat to human health, and antimicrobial peptides (AMPs) such as colistin remain among the few last-resort treatment options. [1, 2] Despite its clinical relevance, colistin use is limited by severe toxicity, and encapsulation in polymer-based nanocarriers has been explored to improve stability and reduce side effects. [3] A key challenge is to quantify colistin reliably under physiologically relevant conditions to better understand its release from nanocarriers.
In this study, hydrophilic interaction liquid chromatography (HILIC) and reversed phase chromatography (RP) with ultraviolet detection (LC-UV) were investigated for colistin analysis. Optimization efforts included adjusting detection wavelength, mobile phase composition, and chromatographic conditions. However, both approaches faced substantial limitations: HILIC-LC-UV showed poor retention and low resolution due to colistin’s strong polarity, while reversed-phase LC-UV produced inconsistent signals with high noise and vague peaks. These difficulties stem from colistin’s large molecular size, high polarity, and partial charges, which challenge the chromatographic separation and ultimately compromise UV detection.
Although robust quantification was not achieved with LC-UV methods, the findings provide valuable insights into the analytical difficulties of large polar antimicrobial peptides. Importantly, colistin can be more reliably detected using mass spectrometry, which benefits from its ease of ionization and the higher sensitivity and specificity of MS-based detection. However, this will not solve the challenge with poor peak shape in HILIC and limited retention in RP. This highlights the need for advanced techniques to achieve accurate and reproducible quantification of colistin in drug delivery research. [4]
References
[1] «Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis,» (in eng), Lancet, vol. 399, no. 10325, pp. 629-655, Feb 12 2022, doi: 10.1016/s0140-6736(21)02724-0.
[2] A. Moretta et al., «Antimicrobial Peptides: A New Hope in Biomedical and Pharmaceutical Fields,» (in eng), Front Cell Infect Microbiol, vol. 11, p. 668632, 2021, doi: 10.3389/fcimb.2021.668632.
[3] T. D. Vogelaar, A. E. Agger, J. E. Reseland, D. Linke, H. Jenssen, and R. Lund, «Crafting Stable Antibiotic Nanoparticles via Complex Coacervation of Colistin with Block Copolymers,» (in eng), Biomacromolecules, vol. 25, no. 7, pp. 4267-4280, Jul 8 2024, doi: 10.1021/acs.biomac.4c00337.
[4] K.-Y. Kim, B.-H. Kim, W. G. Kwack, H.-J. Kwon, S.-H. Cho, and C.-W. Kim, «Simple and robust LC–MS/MS method for quantification of colistin methanesulfonate and colistin in human plasma for therapeutic drug monitoring,» Journal of Pharmaceutical and Biomedical Analysis, vol. 236, p. 115734, 2023.