Expanding Mn2+ loading capacity of BSA via mild non-thermal denaturing and cross-linking as a tool to maximize the relaxivity of water protons

Abstract

Development of nanoparticles (NPs) serving as contrast enhancing agents in MRI requires a combination of high contrasting effect with the biosafety and hemocompatibility. This work demonstrates that bovine serum albumin (BSA) molecules bound to paramagnetic Mn²⁺ ions are promising building blocks of such NPs. The desolvation-induced denaturation of BSA bound with Mn²⁺ ions followed by the glutaraldehyde-facilitated cross-linking provides the uniform in size 102.0 ± 0.7 nm BSA-based nanoparticles (BSA-NPs) loaded with Mn²⁺ ions, which are manifested in aqueous solutions as negatively charged spheres with high colloid stability. The optimal loading of Mn²⁺ ions into BSA-NPs provides maximum values of longitudinal and transverse relaxivity at 98.9 and 133.6 mM^-1 s^-1, respectively, which are among the best known from the literature. The spin trap EPR method indicates that Mn²⁺ ions bound to BSA-NPs exhibit poor catalytic activity in the Fenton-like reaction. On the contrary, the presence of BSA-NPs has an antioxidant effect by preventing the accumulation of hydroxyl radicals produced by H₂O₂. The NPs exhibit remarkably low hemolytic activity and hemagglutination can be avoided at concentrations lower than 110 μM. Thus, BSA-NPs bound with Mn²⁺ ions are promising candidates for combining high contrast effect with biosafety and hemocompatibility.

Keywords: Albumin; Cross-linking; Nanoparticle.