Figure 1.

Effect of freeze drying and cryoprotecting additives on superoxide dismutase (SOD) activity of SOD NP conjugates and shelf-life study for SOD liposomes. (A) Activity of freshly prepared conjugates before freeze drying was considered to be 100%. Sucrose is preferred cryoprotector because its use leads to the highest activity retention for all types of conjugates. All conjugates here are lacking the antibody. Cryoprotector control (black); sucrose (light gray) and trehalose (dark gray). (B) For samples with sucrose and trehalose cryoprotectors, ∼80% of activity is retained after 120 days of accelerated aging at 37°C, which corresponds to ∼1 year shelf-life on storage at room temperature. SOD activity immediately after freeze drying was considered to be 100%. All conjugates here are lacking the antibody. SOD liposomes without any cryoprotector (square); SOD liposomes with sucrose (circle) and trehalose (triangle). *P<0.01, **P<0.05, ***P<0.001. PLGA, poly(lactide-co-glycolide).