Protective layer

Liposomes have been recognized as excellent drug delivery systems, but when they come in direct contact with different blood components they may trigger an immediate activation of the innate immune system. The aim of this was to produce long-circulating, blood-compatible liposomes by developing a construct of liposomes covered by a novel unique Corline© heparin complex (CHC; 70 heparin moleculesper complex) to avoid recognition by the innate immune system. Unilamellar, cationic liposomes were produced by extrusion through a 100-nm polycarbonate membrane. Coating of liposomes with the macromolecular CHC was accomplished by electrostatic interactions. Dynamic light scattering as well as quartz crystal microbalance with dissipation (QCM-D) measurements were used to verify the electrostatic deposition of the negatively charged CHC to cationic liposomes. The CHC-coated liposomes did not aggregate when in contact with lepirudin anti-coagulated plasma. Unlike previous attempts to coat liposomes with heparin, this technique produced freely moveable heparin strands sticking out from the liposome surface, which exposed anti-thrombin (AT) binding sites reflecting the anticoagulant potentials of the liposomes. In experiments using lepirudin-anticoagulated plasma, CHC-coated liposomes, in contrast to non-coated control liposomes, did not activate the complement system, as evidenced by low C3a and sC5b-9 generation and reduced leakage from the liposomes. In conclusion, we show that liposomes can be successfully coated with the biopolymer CHC, resulting in biocompatible and stable liposomes that have significant application potential.