ABSTRACT
Protein binding to lipid-coated nanoparticles has been pursued quantitatively by using fluorescence correlation spectroscopy. The binding of three important plasma proteins to lipid-enwrapped quantum dots (QDs) shows very low affinity, with an apparent dissociation coefficient in the range of several hundred micromolar. Thus, the tendency to adsorb is orders of magnitude weaker than for QDs coated with dihydrolipoic acid.
Subject(s)
Blood Proteins/metabolism , Lysophosphatidylcholines/metabolism , Quantum Dots/metabolism , Spectrometry, Fluorescence/methods , Blood Proteins/chemistry , Humans , Hydrodynamics , Lysophosphatidylcholines/chemistry , Models, Molecular , Protein Binding , Quantum Dots/chemistryABSTRACT
Liposomes are becoming increasingly important as drug delivery systems, to target a drug to specific cells and tissues and thereby protecting the recipient from toxic effects of the contained drug. Liposome preparations have been described to activate complement. In this study, we have investigated complement activation triggered by neutral dimyristoyl-phosphocholine (DMPC) liposomes in human plasma and whole-blood systems. Incubation in plasma led to the generation of complement activation products (C3a and sC5b-9). Unexpectedly, investigations of surface-bound C3 revealed contact activated, conformationally changed C3 molecules on the liposomes. These changes were characterized by Western blotting with C3 monoclonal antibodies, and by incubating liposomes with purified native C3 and factors I and H. Quartz crystal microbalance analysis confirmed binding of C3 to planar DMPC surfaces. In addition, we demonstrated that DMPC liposomes bound to or were phagocytized by granulocytes in a complement-dependent manner, as evidenced by the use of complement inhibitors. In summary, we have shown that C3 is activated both by convertase-dependent cleavage, preferentially in the fluid phase, by mechanisms which are not well elucidated, and also by contact activation into C3(H2O) on the DMPC surface. In particular, this contact activation has implications for the therapeutic regulation of complement activation during liposome treatment.
Subject(s)
Complement Activation/drug effects , Complement C3/metabolism , Liposomes/metabolism , Phospholipids/pharmacology , Adsorption , Computer Systems , Dimyristoylphosphatidylcholine/pharmacology , Electrophoresis, Polyacrylamide Gel , Flow Cytometry , Humans , Models, Biological , Phagocytosis/drug effects , Protein Binding/drug effects , Proteolysis/drug effects , Quartz Crystal Microbalance TechniquesABSTRACT
Supported lipid bilayers (SLBs) were prepared on glass and silicon slides grafted with polyethylene glycol (PEG) and covalently bound cholesteryl anchors to fix the lipid bilayer on the surface. Phospholipid bilayers and bilayers modified by addition of covalently bound PEG were investigated. Using contact angle measurements, the surface energy components of bilayer surfaces were analyzed using van Oss' and Owens-Wendt's methods. A quantitative correlation between the polar proton acceptor component of the surface energies and the respective hydration densities was proven for SLBs of pure lipids. We could show that the presence of PEG in the SLB produces a significant change of the proton acceptor component. Regarding the correlation between the surface energies and the hydration densities of SLBs with PEG, we were able to show a dependency on the PEG conformation.
