Efficient transmural cardiac gene transfer by intrapericardial injection in neonatal mice

An efficient cardiac gene transfer technique in murine models would greatly facilitate the elucidation of the pathophysiology of cardiomyopathies and the development of genetic therapies. Direct myocardial injection or catheter-based intracoronary infusion is not easily achievable in mice and resultant transgene expression is often limited in distribution. A replication-defective, recombinant adenovirus encoding luciferase (5x10(9)pfu) or lacZ (4-5x10(10)particles/animal) was injected percutaneously into the pericardial cavity of 4-5 day old mice. Chemiluminescence assay for luciferase activity at 3 days post-injection revealed the highest activity in the heart (heart=288+/-110, lungs=19+/-5, liver=11+/-5 ng/gm tissue, n=11). X-gal staining of cryostat sections demonstrated widespread transmural lacZ expression in the left ventricle, interventricular septum, right ventricle, and atrial appendages, and the average fractional area of X-gal staining in a left ventricle was 66+/-16% (range 40-92%, n=21 sections). However, the long-term survival of these mice was compromised. Reduction in the injectate volume by 50% significantly improved survival but concurrently reduced lacZ expression. Significant lacZ expression was observed in the right ventricle and interventricular septum but left ventricular expression was predominantly epicardial, with variable myocardial penetration. At 2 months post-injection, lacZ expression persisted only in atrial tissues, pulmonary veins, and great vessels. Despite lack of persistent transgene expression in ventricular tissues, the high degree of transgene expression achieved may be sufficient to allow evaluation of short-term effects of specific genetic manipulations in the heart.