title: Probing peptide amphiphile self-assembly in blood serum.
abstract: There has been recent interest in designing smart diagnostic or therapeutic self-assembling peptide or polymeric materials that can selectively undergo morphological transitions to accumulate at a disease site in response to specific stimuli. Developing approaches to probe these self-assembly transitions in environments that accurately amalgamate the diverse plethora of proteins, biomolecules, and salts of blood is essential for creating systems that function in vivo. Here, we have developed a fluorescence anisotropy approach to probe the pH-dependent self-assembly transition of peptide amphiphile (PA) molecules that transform from spherical micelles at pH 7.4 to nanofibers under more acidic pH's in blood serum. By mixing small concentrations of a Ru(bipy)3(2+)-tagged PA with a Gd(DO3A)-tagged PA having the same lipid-peptide sequence, we showed that the pH dependence of self-assembly is minimally affected and can be monitored in mouse blood serum. These PA vehicles can be designed to transition from spherical micelles to nanofibers in the pH range 7.0-7.4 in pure serum. In contrast to the typical notion of serum albumin absorbing isolated surfactant molecules and disrupting self-assembly, our experiments showed that albumin does not bind these anionic PAs and instead promotes nanofibers due to a molecular crowding effect. Finally, we created a medium that replicates the transition pH in serum to within 0.08 pH units and allows probing self-assembly behavior using conventional spectroscopic techniques without conflicting protein signals, thus simplifying the development pathway from test tube to in vivo experimentation for stimuli-responsive materials.
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Radiology, Wright Center for Innovation in Biomolecular Imaging, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Arijit
authors.initials: A
authors.lastname: Ghosh
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Buettner
authors.forename: Aaron A
authors.initials: AA
authors.lastname: Manos
authors.forename: Ashley J
authors.initials: AJ
authors.lastname: Wallace
authors.forename: Michael F
authors.initials: MF
authors.lastname: Tweedle
authors.forename: Joshua E
authors.initials: JE
authors.lastname: Goldberger
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D005454:Fluorescence Polarization; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D057139:Nanofibers / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D044967:Serum / Q000737:chemistry*; D012709:Serum Albumin / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D008823:Micelles; D010455:Peptides; D012709:Serum Albumin; D014867:Water; D011092:Polyethylene Glycols