APOPTOSIS AND INCREASED EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASEIN HUMAN ALLOGRAFT-REJECTION

Background. The mechanisms of myocyte death during cardiac allograft r ejection are incompletely understood, In a previous study using a rat heterotopic cardiac allograft model, we showed that cardiac myocyte ap optosis, inducible nitric oxide synthase (iNOS) mRNA, protein and enzy me activity, and nitrotyrosine increased simultaneously during cardiac allograft rejection, This study was designed to investigate whether a poptosis and expression of iNOS occur in human cardiac allograft rejec tion, Methods. Right ventricular endomyocardial biopsies from 30 cases of allograft rejection (International Society of Heart and Lung Trans plantation grade 3A/B) were compared with 12 biopsies with no rejectio n (International Society of Heart and Lung Transplantation grade 0), S amples were co-labeled for apoptosis and muscle actin, Serial sections were stained for iNOS, nitrotyrosine, and the leukocyte markers CD3, CD4, CD8, and CD68 to identify T-cell subpopulations and macrophages, Results, Biopsies with cardiac allograft rejection showed a 30-fold in crease of apoptotic cells when compared with controls, Most apoptotic cardiac myocytes were found in proximity to macrophage (CD68(+))-rich inflammatory infiltrates, iNOS immunoreactivity was strongest in macro phages and adjacent myocytes, which also showed high levels of nitroty rosine, representing damage by peroxynitrite, Conclusions, Apoptosis i s a major form of myocyte death during human cardiac allograft rejecti on, Cardiac myocyte apoptosis is closely associated with expression of iNOS in macrophages and myocytes and with nitration of myocyte protei ns by peroxynitrite.