INDUCIBLE NITRIC-OXIDE SYNTHASE EXPRESSION IN SMOOTH-MUSCLE CELLS ANDMACROPHAGES OF HUMAN TRANSPLANT CORONARY-ARTERY DISEASE

Background-The inducible isoform of the nitric oxide synthase (iNOS) p roduces large amounts of nitric oxide in response to cytokine stimulat ion. Previous investigations have demonstrated iNOS expression in the setting of acute and chronic rejection in experimental cardiac transpl ant models. The goal of this study was to Investigate whether iNOS is upregulated in human transplant coronary artery disease (TCAD), a majo r cause of late mortality after cardiac transplantation. Methods and R esults-We studied 15 patients with TCAD and 10 with normal coronary ar teries. In situ hybridization and immunohistochemistry were used in ti ssue sections to localize iNOS mRNA and protein, respectively. The pre sence of peroxynitrite was indirectly assessed by immunostaining with an anti-nitrotyrosine antibody. Normal coronary arteries had no eviden ce of iNOS expression. In contrast, 30 of 36 coronary artery segments with TCAD (83%) were immunostained by the iNOS antibody. The presence of iNOS mRNA was demonstrated in these vessels by in situ hybridizatio n. Specific cell markers identified iNOS-positive cells as neointimal macrophages and smooth muscle cells. Nitrotyrosine immunoreactivity co localized with iNOS expression in arteries with TCAD, distributed in m acrophages and smooth muscle cells. Conclusions-iNOS mRNA and protein are expressed in human arteries with TCAD, where they are associated w ith extensive nitration of protein tyrosines. These findings indicate that the high-output nitric oxide pathway and possibly the oxidant per oxynitrite might be involved in the process leading to the development of TCAD.