Effects of inhibition of poly(adenosine diphosphate-ribose) synthase on acute cardiac allograft rejection

Background. Nitric oxide synthase (NOS)-2 is expressed during acute cardiac allograft rejection in association with death of heart muscle cells. The nuclear enzyme poly(adenosine cliphosphate [ADP]-ribose) synthase (PARS) is activated by agonists such as NO and peroxynitrite, which cause single-strand DNA breaks; PARS, in turn can promote both necrosis and apoptosis. To investigate the hypothesis that NO produced by NOS-2 in cardiornyocytes activates PARS and contributes to heart muscle cell death by apoptosis, experiments were performed using a heterotopic rat abdominal heart transplant model and cytokine-stimulated heart muscle cells in tissue culture. Methods. Cardiac allografts were treated after transplantation with either the PARS inhibitor 5-aminoisoquinolinone at 3 mg/kg subcutaneously daily or with vehicle. Isolated purified adult rat cardiomyocytes incubated with cytokines to induce NOS-2 were treated in vitro with another PARS inhibitor, 3-aminobenzamide (3AB). Results. PARS inhibition increased cardiac-allograft survival from 6 +/- 2 to 10 +/- 3 days (n=6, n=6, P<0.05). The inflammatory infiltrate, NOS-2-positive macrophages, myocyte apoptosis, and myocyte content of nitrotyrosine and poly(ADP-ribose) were significantly decreased in PARS inhibited aflografts at day 5 posuransplantation. Similarly, apoptosis and PARS activity were diminished in cytokine- stimulated adult rat cardiomyocytes when either 3AB or L-NMMA were applied. Conclusions. The data indicate that PARS activation occurs during acute cardiac- allograft rejection and contributes significantlyto the inflammatory response and to the death of cardiac muscle cells byapoptosis. Theysuggest that PARS inhibition combined with immunosuppression might enhance salvage of heart-muscle cells during acute cardiacallograft rejection.