Comparative study of cyclosporine and tacrolimus vs newer Immunosuppressants mycophenolate mofetil and rapamycin on coronary endothelial function

Background: Endothelial dysfunction contributes to the development of intimal hyperplasia in transplanted hearts by decreasing the protective effects of endothelial-derived nitric oxide. Immunosuppressive drugs may increase the dysfunction caused by rejection and further accelerate the development of graft coronary vasculopathy. This study compares the effect of cyclosporine and tacrolimus vs two newer immunosuppressive drugs, mycophenolate mofetil and rapamycin, on coronary endothelial function. Methods: An in vitro model of drug incubation in Krebs-bicarbonate solution (4degreesC, 48 hours) using porcine epicardial coronary arteries was developed. Coronary endothelial function studies were performed in organ chamber experiments after incubation with cyclosporine (10(-4), 10(-7) mol/liter), tacrolimus (10(-4), 10(-7) mol/liter), mycophenolate Mofetil (10(-4), 10(-7) mol/liter), rapamycin (10(-7), 10(-11) mol/liter), and their vehicles to assess effects on G-protein-mediated vasorelaxations leading to the release of nitric oxide. Results: Exposure to cyclosporine and mycophenolate mofetil was associated with a dose-dependent decrease in endothelium-dependent relaxations to serotonin (an agonist that binds to 5-HT1D receptors coupled to Gi-protein) but no impairment of relaxations to bradykinin (an agonist that binds to B-2 receptors coupled to Gq-proteins). Exposure to tacrolimus and rapamycin caused severe impairment of relaxations to serotonin and a lesser one to bradykinin. We observed alterations of relaxations to the calcium ionophore A23187 after exposure to mycophenolate mofetil and rapamycin. Exposure to rapamycin and mycophenolate mofetil vehicles impaired relaxation to all agonists. Conclusions: These results suggest that cyclosporine and mycophenolate mofetil induce a dysfunction of the vasorelaxing properties of the endothelium that may lead to a decrease in the protective effects of nitric oxide on the vascular wall but that these drugs still have a more favorable vascular profile than do tacrolimus and rapamycin. Decreased endothelial function after mycophenolate mofetil and rapamycin exposure could be caused by their vehicles.