Role of Surface Charge of Nanoscale Ultrasound Contrast Agents in Complement Activation and Phagocytosis

PURPOSE: To prepare nanoscale ultrasound contrast agents (Nano-UCAs) and examine the role of their surface charge in complement activation and phagocytosis. MATERIALS AND METHODS: We analyzed serum proteins present in the corona formed on Nano-UCAs and evaluated two important protein markers of complement activation (C3 and SC5b-9). The effect of surface charge on phagocytosis was further assessed using THP-1 macrophages. RESULTS: When Nano-UCAs were incubated with human serum, they were opsonized by various blood proteins, especially C3. Highly charged Nano-UCAs, whether positive or negative, were favorably opsonized by complement proteins and phagocytized by macrophages. CONCLUSION: Charged Nano-UCAs show a higher tendency to activated complement system, and are efficiently engulfed by macrophages. The present results provide meaningful insights into the role of the surface charge of nanoparticles in the activation of the innate immune system, which is important not only for the design of targeted Nano-UCAs, but also for the effectiveness and safety of other theranostic agents.