title: Aggregation of PEGylated liposomes driven by hydrophobic forces.
abstract: Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from -71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences.
authors: Department of Biophysics and Radiation Biology, Semmelweis University, 1094 Budapest, Tűzoltó Str. 37-47, Hungary. Electronic address: bozo.tamas@med.semmelweis-univ.hu.
authors: Tamás
authors: T
authors: Bozó
authors: Nanomedicine Research and Education Center, Semmelweis University, 1089 Budapest, Nagyvárad Square 4, Hungary; SeroScience Ltd., 1089 Budapest, Nagyvárad Square 4, Hungary. Electronic address: tmeszaros@seroscience.com.
authors: Tamás
authors: T
authors: Mészáros
authors: Biological Nanochemistry Research Group, Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Magyar tudósok körútja 2, Hungary. Electronic address: mihaly.judith@ttk.mta.hu.
authors: Judith
authors: J
authors: Mihály
authors: Biological Nanochemistry Research Group, Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Magyar tudósok körútja 2, Hungary. Electronic address: bota.attila@ttk.mta.hu.
authors: Attila
authors: A
authors: Bóta
authors: Department of Biophysics and Radiation Biology, Semmelweis University, 1094 Budapest, Tűzoltó Str. 37-47, Hungary; MTA-SE Molecular Biophysics Research Group, Semmelweis University, 1094 Budapest, Tűzoltó Str. 37-47, Hungary. Electronic address: miklos.kellermayer@med.semmelweis-univ.hu.
authors: Miklós S Z
authors: MSZ
authors: Kellermayer
authors: Nanomedicine Research and Education Center, Semmelweis University, 1089 Budapest, Nagyvárad Square 4, Hungary; SeroScience Ltd., 1089 Budapest, Nagyvárad Square 4, Hungary. Electronic address: jszebeni2@gmail.com.
authors: János
authors: J
authors: Szebeni
authors: Nanomedicine Research and Education Center, Semmelweis University, 1089 Budapest, Nagyvárad Square 4, Hungary.
authors: Benedek
authors: B
authors: Kálmán
mesh_terms: D000645:Ammonium Sulfate / Q000737:chemistry*; D055592:Biophysical Phenomena; D057927:Hydrophobic and Hydrophilic Interactions; D008081:Liposomes / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D012492:Salts / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D008081:Liposomes; D011108:Polymers; D012492:Salts; D011092:Polyethylene Glycols; D000645:Ammonium Sulfate
keywords: Aggregation; Ammonium sulfate; Fusion; Hydrophobic effect; Kosmotropic salt; Liposome; PEG