Nitrotyrosine was found to be dependent on the severity of myxomatous mitral valve disease (MMVD). However, a correlation of serum nitrotyrosine concentration in dogs with MMVD and the progression of the disease has not been investigated. This study compared changes in serum nitrotyrosine concentration with the progression of MMVD. Nine client-owned dogs were recruited for the study. Dogs were classified by measuring the amount of regurgitation using echocardiography into mild, moderate, or severe MMVD groups. Serum nitrotyrosine concentration was measured by an enzyme-linked immunosorbent assay test. Serum nitrotyrosine concentration was significantly higher at 180 days than at 0 day (P < 0.05). However, serum nitrotyrosine concentration at 360 days was lower than that at 180 days (P < 0.05). Serum nitrotyrosine concentration at 540 days was lower than at 180 days (P < 0.05). There was no correlation between serum nitrotyrosine and left atrial to aortic root diameter ratio (LA/Ao ratio) (n = 33, $R^2=0.003$, P = 0.759). Also, there was no correlation between serum nitrotyrosine and vertebral heart score (VHS) (n = 33, $R^2=0.026$, P = 0.368) and left ventricular end-diastolic diameter, normalized for body weight by the formula (LVEDDN) (n = 33, $R^2=0.053$, P = 0.196). The results of the study suggest that the progression of MMVD is correlated with changes in serum nitrotyrosine concentration, which shows potential for use as a cardiac biomarker which can be used to analyze the progression of disease in MMVD.

Keywords: MMVD, nitrotyrosine, iNOS, peroxynitrite, LVEDDN, canine