A single direct injection into the left ventricular wall of an adeno-associated virus 9 (AAV9) vector expressing extracellular superoxide dismutase from the cardiac troponin-T promoter protects mice against myocardial infarction.

BACKGROUND: Localized administration of a highly efficient gene delivery system in combination with a cardiac-selective promoter may provide a favorable biosafety profile in clinical applications such as coronary artery bypass graft surgery, where regions of myocardium can be readily injected to protect them against the potential threat of future ischemic events.
METHODS: Adeno-associated virus (AAV) vectors expressing luciferase or enhanced green fluorescent protein (eGFP) packaged into AAV serotypes 1, 2, 6, 8 and 9 were injected into the left ventricular (LV) wall of adult mice to determine the time course, magnitude and distribution of gene expression. An AAV9 vector expressing extracellular superoxide dismutase (EcSOD) from the cardiac troponin T (cTnT) promoter was then directly injected into the LV wall of adult mice. Myocardial infarction was induced 4 weeks after injection and infarct size was determined by triphenyltetrazolium chloride and phthalo blue staining.
RESULTS: Serotypes AAV 9, 8, 1 and 6 provided early onset of gene expression in the heart with minimal extra-cardiac gene expression. AAV9 provided the highest magnitude of gene expression. Immunostaining for eGFP showed expression spanning the anterior to posterior walls from the mid ventricle to the apex. A single direct injection of the AAV9 vector bearing EcSOD ( n  = 5) decreased the mean infarct size by 50% compared to the eGFP control group (n = 8) (44 ± 7% versus 22 ± 5%; p = 0.04).
CONCLUSIONS: AAV serotype 9 is highly efficient for cardiac gene delivery, as evidenced by early onset and high-level gene expression. AAV9-mediated, cardiac selective overexpression of EcSOD from the cTnT promoter significantly reduced infarct size in mice.