Gene Transfer with Echo-enhanced Contrast Agents: Comparison between Albunex, Optison, and Levovist in Mice—Initial Results

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Abstract
To determine if commercially available echo-enhanced microbubble contrast agents could be used to increase gene transfection efficiency by means of relatively low-intensity ultrasound-mediated microbubble destruction in skeletal muscles. Three types of ultrasound microbubble contrast agents (0.01 mL of albumin [Albunex] and human albumin [Optison] and 10 mg/mL of SH U 508A [Levovist]) were each separately mixed with the reporter plasmid DNA (25 microg) encoding green fluorescent protein (GFP) prior to intramuscular injection into the quadriceps muscle of a mouse thigh bilaterally (seven mice per contrast agent). One of the muscle sites that was injected with plasmid DNA was irradiated with low-intensity therapeutic ultrasound (1 MHz) at an intensity of 2.0 W/cm2 for 2 minutes. Mice were sacrificed 7 days after ultrasound treatment for gene expression assay. The number of GFP-expressing muscle fibers was counted. Statistical significance was determined with a two-tailed Student t test. P <.05 was considered to indicate statistically significant difference. Muscle tissue exposed to ultrasound with air-filled Albunex or Levovist microbubbles revealed no difference in the number of GFP-expressing muscle fibers compared with the control non-ultrasound-exposed muscle. Albumin-coated octafluoropropane gas-filled Optison microbubbles showed a 10-fold increase in the number of GFP-expressing fibers (P <.05). Low-intensity ultrasound with echo-enhanced Optison induced efficient gene transfer unlike that with Albunex or Levovist.