Characterization of lipid-encapsulated microbubbles for delivery of nitric oxide

Abstract

Nitric oxide (NO) is a potent bioactive gas capable of inducing vasodilatory, anti-inflammatory, and bactericidal effects. The short half-life, high reactivity, and rapid diffusivity of NO make therapeutic delivery challenging. The goal of this work was to develop a technique to sequester NO within lipid-shelled microbubbles. Microbubbles loaded with either NO alone (NO-MB) or with NO and octafluoropropane (NO-OFP-MB) were synthesized by high-shear mixing of 1 mL lipids with either 1 mL of NO, or a mixture of 0.9 mL NO and 0.1 mL OFP. The size distribution and attenuation coefficient of NO-MB and NO-OFP-MB were measured using a Coulter counter and a broadband acoustic attenuation spectroscopy system, respectively. The payload of NO in the microbubbles was assessed using an amperometric micro-electrode sensor. Co-encapsulation of NO with OFP increased the number density, attenuation coefficient, and temporal stability of lipid-shelled microbubbles. However, the amount of NO loaded in NO-MB and NO-OFP-MB was similar (0.91 ± 0.03 μM and 0.93 ± 0.1 μM, respectively). These results suggest that NO can be encapsulated within lipid-shelled microbubbles. However, co-encapsulation of OFP does not enhance the NO payload or the temporal stability, despite an increase in attenuation and number density of lipid-shelled microbubbles. Nitric oxide (NO) is a potent bioactive gas capable of inducing vasodilatory, anti-inflammatory, and bactericidal effects. The short half-life, high reactivity, and rapid diffusivity of NO make therapeutic delivery challenging. The goal of this work was to develop a technique to sequester NO within lipid-shelled microbubbles. Microbubbles loaded with either NO alone (NO-MB) or with NO and octafluoropropane (NO-OFP-MB) were synthesized by high-shear mixing of 1 mL lipids with either 1 mL of NO, or a mixture of 0.9 mL NO and 0.1 mL OFP. The size distribution and attenuation coefficient of NO-MB and NO-OFP-MB were measured using a Coulter counter and a broadband acoustic attenuation spectroscopy system, respectively. The payload of NO in the microbubbles was assessed using an amperometric micro-electrode sensor. Co-encapsulation of NO with OFP increased the number density, attenuation coefficient, and temporal stability of lipid-shelled microbubbles. However, the amount of NO loaded in NO-MB and NO-OFP-MB wa...