Objective: Adenoviral gene transfer to the arrested heart during cardiopulmonary bypass (CPB) is a novel method of allowing prolonged vector contact with the myocardium. In this model we investigated the importance of temperature, duration of arrest and cardioplegia on transgene expression.
Methods: First-generation adenoviral vector (1 x 10(12) total viral particles) containing the transgene for the human beta2-adrenoceptor (Adeno-beta(2)AR) or beta-galactosidase (Adeno-beta(gal)) was delivered to neonatal piglets via the proximal aorta, during simulated cardiac surgery, and allowed to dwell for the cross-clamp duration. Four treatment groups received Adeno-beta(2)AR. Groups A (n=4) and B (n=6) underwent cold crystalloid cardioplegia arrest for 10 and 30 min, respectively, Group C (n=5) underwent warm crystalloid cardioplegia arrest for 10 min, and Group D (n=5) underwent warm fibrillatory arrest for 10 min. Group E (n=6) received Adeno-beta(gal) and underwent cold crystalloid cardioplegia arrest (30 min). Animals were weaned off CPB and recovered for 2 days. Receptor density was assessed in membrane fractions using radioligand binding and compared using the Mann-Whitney U-test.
Results: Left ventricular transgene overexpression, as evidenced by elevated betaAR density, following Adeno-beta(2)AR treatment was greatest with cold cardioplegia (Group A 588+/-288.8 fmol/mg; P=0.002 and Group B 520+/-250.9 fmol/mg; P=0.01) versus control (Group E 109+/-8.4 fmol/mg). Overexpression also occurred with warm cardioplegia (Group C 274+/-69.5 fmol/mg; P=0.05) and ventricular fibrillation (Group D 215+/-48.4 fmol/mg; P=0.02) versus control. Comparison of the combined cold cardioplegia groups versus those treated with warm conditions showed a trend towards increased expression with cold conditions (P=0.1). Receptor density was also significantly increased in the right ventricle of animals in Group B (165+/-18.1 fmol/mg; P=0.03) and Group D (181+/-23.4 fmol/mg; P=0.02) versus control (Group E 118+/-5.8 fmol/mg).
Conclusions: Cold crystalloid cardioplegia is not detrimental to gene transfer in vivo. In fact, there was a trend towards increased left ventricular transgene expression when the adenoviral vector was delivered following cold versus warm cardioplegia. Shorter periods of contact with the vector may reduce transgene overexpression. Therefore, gene transfer is possible during cardiac surgery with clinically used myocardial protection techniques.