Increased levels of homocysteine (Hcy), recognized as hyperhomocysteinemia (HHcy), were associated with cardiovascular diseases. There was controversy regarding the detrimental versus cardio protective role of inducible nitric oxide synthase (iNOS) in ischemic heart disease. The aim of this study was to test the hypothesis that the Hcy generated nitrotyrosine by inducing the endothelial nitric oxide synthase, causing endothelial-myocyte (E-M) coupling. To differentiate the role of iNOS versus constitutive nitric oxide synthase (eNOS and nNOS) in Hcy-mediated nitrotyrosine generation and matrix remodeling in cardiac dysfunction, left ventricular (LV) tissue was analyzed from cystathionine beta synthase (CBS) heterozygote knockout, iNOS homozygote knockout, CBS-/+/iNOS-/- double knockout, and wild-type (WT) mice. The levels of nitrotyrosine, MMP-2 and -9 (zymographic analysis), and fibrosis (by trichrome stain) were measured. The endothelial-myocyte function was determined in cardiac rings. In CBS-/+ mice, homocysteine was elevated and in iNOS-/- mice, nitric oxide was significantly reduced. The nitrotyrosine and matrix metalloproteinase-9 (MMP-9) levels were elevated in double knockout and CBS-/+ as compared to WT mice. Although MMP-2 levels were similar in CBS-/+, iNOS-/-, and CBS-/+/iNOS-/-, the levels were three- to fourfold higher than WT. The levels of collagen were similar in CBS-/+ and iNOS-/-, but they were threefold higher than WT. Interesting, the levels of collagen increased sixfold in double knockouts, compared to WT, suggesting synergism between high Hcy and lack of iNOS. Left ventricular hypertrophy was exaggerated in the iNOS-/- and double knockout, and mildly increased in the CBS-/+, compared to WT mice. The endothelial-dependent relaxation was attenuated to the same extent in the CBS-/+ and iNOS-/-, compared to WT, but it was robustly blunted in double knockouts. The results concluded that homocysteine generated nitrotyrosine in the vicinity of endothelium, caused MMP activation and endothelium-myocyte uncoupling. The generation of nitrotyrosine was independent of iNOS.
2008 Wiley-Liss, Inc.