Effect of Functionalized Magnetic MnFe 2 O 4 Nanoparticles on Fibrillation of Human Serum Albumin Shubhatam Sen, † Suraj Konar, § Amita Pathak, § Swagata Dasgupta,* ,§ and Sunando DasGupta* ,‡ † Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur 721302, India ‡ Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India § Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, India * S Supporting Information ABSTRACT: Pathogenesis of amyloid-related diseases is related to nonnative folding of proteins with the formation of insoluble deposits in the extracellular space of various tissues. Having the unique properties of small size, large surface area, biodegradability, and relative nontoxicity, magnetic nanoparticles have drawn a lot of attention in biomedical applications. Herein, we demonstrate the effect of bare and differently functionalized magnetic MnFe 2 O 4 nanoparticles on fibrillation of human serum albumin in vitro. The process has been monitored using Thioflavin T fluorescence, Congo red binding assay, circular dichroism, fluorescence microscopy, and transmission electron microscopy. From our experimental results, amine functionalized MnFe 2 O 4 nanoparticles are found to inhibit formation of fibrils more effectively than bare ones, while carboxylated nanoparticles do not have a significant effect on fibrillation. This study has explored the prospects of using specific magnetic nanoparticles with appropriate modification to control self-assembly of proteins and may act as a precursor in therapeutic applications. 1. INTRODUCTION Aggregation of protein resulting into amyloid fibrils is the central reason behind many human diseases like Parkinson’s, Huntington’s, and prion diseases and Alzheimer’s disease. 1-3 In these types of diseases, normally soluble proteins get transformed into toxic amyloid fibrils with high cross β-sheet content, the perpendicular arrangement of strands to fibrillar axis. 4 The deposited fibrils in extracellular spaces of various tissues cause cellular damages. 5 Human serum albumin (HSA), the most abundant plasma protein, may be considered as an amyloidogenic model protein due to its tendency to aggregate in vitro. 6,7 HSA is a natively α-helical (>60%) globular protein consisting of 585 amino acid residues. HSA consists of three domains, each with two subdomains and 17 disulfide bridges. 8,9 HSA plays a crucial role in the transportation of fatty acids, metal ions, and physiologically important compounds. Lacking any predisposition to form amyloid fibrils, HSA requires necessary solution conditions, such as low pH, high temper- ature, presence of chemical denaturant, metal ions, etc. that will favor partial destabilization of HSA molecules to form amyloid- like fibrils. 10 In the literature, various factors have been reported to affect HSA aggregation. The influence of pH, ionic strength, and electrostatic interactions on the fibrillation process of HSA has previously been reported. 11,12 The effect of solvation on the conformational change of HSA in aqueous ethanol solvent has been observed. 13 Aggregation of HSA has also been studied in the presence of metal ions, sugars, surfactants, etc. for promoting, inhibiting, or disintegrating purposes. 14-17 Literature indicates use of nanosized materials in various biomedical applications. 18,19 Owing to their small size, nanoparticles pass through the blood-brain barrier freely. 20 Nanoparticles also have enhanced surface to volume ratio which can be utilized to modify their surface properties physically or chemically thus controlling the interaction of protein with nanoparticles. Linse et al. have shown that nanoparticles such as copolymer particles, cerium oxide particles, quantum dots, and carbon nanotubes significantly enhance the rate of formation of fibrils. 21 While gold nanoparticles have been reported to induce formation of protein aggregates, 22 photothermal ablation of amyloid aggregates by gold nanoparticles has also been reported. 23 Rocha et al. have reported that fibrillation of amyloid-β (Aβ) peptide can be significantly prevented by fluorinated nano- particles. 24 Studies also indicate the effect of DHLA-capped quantum dots and Au nanoparticles on the fibrillation pathway of HSA under varying experimental conditions. 25,26 Magnetic nanoparticles (MNP) are finding increased use in biorelated applications due to their magnetic properties, biocompatibility, and relative nontoxicity. The application of Received: August 5, 2014 Revised: September 18, 2014 Published: September 23, 2014 Article pubs.acs.org/JPCB © 2014 American Chemical Society 11667 dx.doi.org/10.1021/jp507902y | J. Phys. Chem. B 2014, 118, 11667-11676