Expression of endomyocardial nitric oxide synthase and coronary endothelial function in human cardiac allografts

Background-Inducible nitric oxide synthase (iNOS) is expressed and is funct ionally active in the presence of transplant arteriosclerosis. However, the early involvement of iNOS in alterations of microvascular endothelial func tion in the absence of preexisting lesions remains unclear; this informatio n would be of prognostic value. We studied the course of iNOS mRNA expressi on, transcardiac nitric oxide production, and their potential association w ith microvascular coronary endothelial dysfunction in human cardiac allogra fts. Methods and Results-A total of 42 patients were studied at 1, 6, and 12 mon ths after heart transplantation. Microvascular coronary flow velocity reser ve (CFVR) was tested in an endothelium-dependent (acetylcholine) and -indep endent manner (adenosine) using a Doppler flow wire. Endomyocardial iNOS ex pression was determined by reverse transcription polymerase chain reaction. iNOS protein and nitrotyrosine levels were detected by immunohistochemistr y. Transcardiac plasma nitrite/nitrate (NOx) levels were measured by the Gr iess reaction. CFVR was impaired in 26.1% of patients (n=11) at I month and in 31% of patients (n=13) at 12 months after heart transplantation. Patien ts who developed impaired CFVR in the first year showed a significant incre ase in iNOS gene expression. Patients with impairment of CFVR I month after heart transplantation had higher levels of iNOS mRNA than patients with a normal CFVR. Patients with an initial impairment of CFVR who did not improv e over time presented with significantly higher iNOS mRNA levels. iNOS prot ein and nitrotyrosine were expressed in the endomyocardial vessels of patie nts with impaired CFVR. Transcardiac NOx release was higher in patients wit h impaired CFVR. Conclusions-In human cardiac allografts, microvascular endothelial dysfunct ion is associated with an enhanced endomyocardial iNOS mRNA expression and higher transcardiac NOx production and is accompanied by the expression of nitrotyrosine protein, suggesting peroxynitrite plays a role in the disease process. The data from the present study suggest an important role for the iNOS/nitric oxide pathway in the regulation of microvascular function in t he absence of preexisting atherosclerotic lesions.