Real-time monitoring of polymyxin B-sodium deoxycholate sulfate binding with immobilized human serum albumin by surface plasmon resonance

Abstract

Polymyxin B (PMB) has a high protein binding capacity with human serum albumin (HSA), which is the dominant plasma protein. This study aims to evaluate the kinetic parameters to understand the binding of PMB and PMB-based sodium deoxycholate sulfate (SDCS) formulations with HSA by surface plasmon resonance. The kinetics of PMB presented the best fit with a two-state reaction model, wherein the conformational change occurred after binding. PMB interacted with HSA in a temperature and formulation-dependent manner. PMB-SDCS formulations provided lower HSA binding than PMB in all experiments. Circular dichroism spectra confirmed the secondary structure of HSA changes in a decreased α-helical content in PMB formulations. UV–visible spectra revealed the microenvironment of tryptophan-214 changes after incubation with PMB formulations. Also, three-dimensional fluorescence demonstrated that the maximum intensity of tryptophan-214 decreased and shifted. The vibrational frequency of Fourier-transform infrared spectroscopy confirmed the conformational changes in the secondary structure of HSA. Therefore, PMB formulated with SDCS affected the PMB binding to HSA. A lower protein binding with HSA from PMB-SDCS formulations was a result of shielding the positive charge of PMB by SDCS therefore higher unbound PMB is available at the target sites. From this work, the modification PMB binding with HSA would help in PMB formulation design and perhaps dose adjustment of PMB for suitable drug availability in clinical setting.