Multifunctional polymer-modified liposomes that capture and neutralize toxic protein, histones

Poly-N-isopropylacrylamide (pNIPAm) based polymer nanoparticles (NPs) with the capacity to recognize, capture and neutralize the target toxic peptide melittin in vivo by multiple weak interactions are of significant interest... [ view full abstract ]

Poly-N-isopropylacrylamide (pNIPAm) based polymer nanoparticles (NPs) with the capacity to recognize, capture and neutralize the target toxic peptide melittin in vivo by multiple weak interactions are of significant interest as “plastic antidotes”. The multipoint interactions are generated by N-tert-butylacrylamide (TBAm, a hydrophobic monomer) and acrylic acid (AAc, a negatively charged monomer). However, the NPs have low biocompatibilities and short circulation time. To improve these problems, we focused on modification of linear polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization of NIPAm, TBAm and AAc onto liposomal surface. Histones, major mediators of sepsis, were chosen as target proteins. The linear polymer library was prepared by changing the AAc ratio and polymer length. Liposomal sizes and zeta-potentials were not significantly different between before and after polymer modification onto the liposomal surface even in the increasing of AAc ratio and polymer length. The modification rates of polymers depend on AAc ratio and polymer length. The circulation times of polymer-modified liposomes were far longer than linear polymers. Interactions between polymer-modified liposomes and histones were monitored by quartz crystal microbalance (QCM). As a result, polymers including higher density of AAc enhanced affinity of liposomes to the histones. In addition, there is an optimal length to induce high affinity to the histones. We next demonstrated toxin neutralization effect of polymer-modified liposomes using mouse endothelial 2H-11 cells. The optimized polymer-modified liposomes inhibited histones cytotoxicity in vitro. These results indicate that the liposomes bound and neutralized target protein, histones. To confirm whether polymer-modified liposomes neutralize histones in vivo, optimized polymer-modified liposomes were intravenously injected into mice after the lethal injection of histones via tail vein. The polymer-modified liposomes improved survival rate of mice exposed to lethal dose of histones. Namely, polymer-modified liposomes neutralized histones in the bloodstream. The functional liposomes capable of capturing and neutralizing the target biomacromolecules can be used as new antidotes.