BACKGROUND: Angiotensin (Ang) II, which plays a crucial role in the cardiac remodeling process, is generated via angiotensin-converting enzyme (ACE); however, an alternative generation pathway, chymase, which is stored in the mast cells, also exists in the heart. Cardiac chymase is insensitive to ACE inhibitors (ACEIs), and heart chymase promotes interstitial fibrosis by affecting collagen metabolism via transforming growth factor-beta in vitro. Therefore, selective chymase blockade seems to be an important strategy in the prevention of cardiac remodeling METHODS AND RESULTS: We evaluated the effects of a specific chymase inhibitor, SUNC8257 (Chy I; 10 mg/kg twice a day; n=7), on changes in cardiac structures, Ang II levels, and gene expressions, which are characterized as molecular markers for fibrosis, in dogs with tachycardia induced heart failure (HF). In HF, the number of chymase enzyme-positive mast cells increased in the left ventricle (LV) compared with the normal group; however, Chy I significantly decreased the mast cell density and cardiac Ang II levels. Despite no significant differences in LV systolic function compared with the vehicle group, Chy I decreased LV end-diastolic pressure and shortened the prolongation of tau. Chy I suppressed collagen-type I and III and transforming growth factor-beta mRNA levels and decreased fibrosis in the LV compared with the vehicle. CONCLUSIONS: The chymase pathway may be critical for cardiac diastolic dysfunction accompanied with fibrosis. Chronic chymase inhibition may therefore become an important strategy in the prevention of cardiac remodeling in HF.
BACKGROUND: Angiotensin (Ang) II, which plays a crucial role in the cardiac remodeling process, is generated via angiotensin-converting enzyme (ACE); however, an alternative generation pathway, chymase, which is stored in the mast cells, also exists in the heart. Cardiac chymase is insensitive to ACE inhibitors (ACEIs), and heart chymase promotes interstitial fibrosis by affecting collagen metabolism via transforming growth factor-beta in vitro. Therefore, selective chymase blockade seems to be an important strategy in the prevention of cardiac remodeling METHODS AND RESULTS: We evaluated the effects of a specific chymase inhibitor, SUNC8257 (Chy I; 10 mg/kg twice a day; n=7), on changes in cardiac structures, Ang II levels, and gene expressions, which are characterized as molecular markers for fibrosis, in dogs with tachycardia induced heart failure (HF). In HF, the number of chymase enzyme-positive mast cells increased in the left ventricle (LV) compared with the normal group; however, Chy I significantly decreased the mast cell density and cardiac Ang II levels. Despite no significant differences in LV systolic function compared with the vehicle group, Chy I decreased LV end-diastolic pressure and shortened the prolongation of tau. Chy I suppressed collagen-type I and III and transforming growth factor-beta mRNA levels and decreased fibrosis in the LV compared with the vehicle. CONCLUSIONS: The chymase pathway may be critical for cardiac diastolic dysfunction accompanied with fibrosis. Chronic chymase inhibition may therefore become an important strategy in the prevention of cardiac remodeling in HF.