Angiotensin I converting enzyme and chymase in cardiovascular tissues

Recent studies have provided evidence that the human cardiovascular tissues contain components of the renin-angiotensin system: angiotensinogen, renin, angiotensin I converting enzyme (ACE), chymase and angiotensin II (Ang II) receptors. In addition to ACE, a cardiac Ang II forming serine proteinase, human heart chymase, has been identified in the human left ventricle. Unlike rat heart, only a minor (approximately 11%) component of Ang II forming activity in the human left ventricle was due to ACE, since the majority (approximately 80%) of activity was due to chymase. Human heart chymase has been purified to homogeneity and characterized. Recently, the cDNA and gene for this enzyme have been cloned. Biochemical characterization revealed that heart chymase is the most efficient and specific Ang II forming enzyme described thus far. The different cellular and regional distribution of ACE and heart chymase in the heart as well as in blood vessels implies distinct pathophysiological roles for these two Ang II forming enzymes. Several reports indicate that ACE-independent Ang II formation appears to take place in hypoxic or ischemic heart or blood vessel in vivo and to be involved in vascular remodeling after balloon injury. Therefore, it is very important to clarify the detailed mechanisms of the tissue Ang II formation in humans and its contribution to the pathophysiological changes in cardiovascular disease. In this review, we review the pathophysiological roles of the two main Ang II forming enzymes, ACE and chymase, in cardiovascular homeostasis.