Effects of chymostatin, a chymase inhibitor, on blood pressure, plasma and tissue angiotensin II, renal haemodynamics and renal excretion in two models of hypertension in the rat : Effect of chymase inhibition in hypertensive rats

Although angiotensin II (Ang II)-forming enzymatic activity in the human left cardiac ventricle is minimally inhibited by angiotensin I (Ang I) converting enzyme inhibitors, over 75% of this activity is inhibited by serine proteinase inhibitors (Urata, H., Healy, B., Stewart, R. W., Bumpus, F. M., and Husain, A. (1990) Circ. Res. 66, 883-890). We now report the identification and characterization of the major Ang II-forming, neutral serine proteinase, from left ventricular tissues of the human heart. A 115,150-fold purification from human cardiac membranes yielded a purified protein with an Mr of 30,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Based upon its amino-terminal sequence, the major human cardiac Ang II-forming proteinase appears to be a novel member of the chymase subfamily of chymotrypsin-like serine proteinases. Human heart chymase was completely inhibited by the serine proteinase inhibitors, soybean trypsin inhibitor, phenylmethylsulfonyl fluoride, and chymostatin. It was partially inhibited by p-tosyl-L-phenylalanine chloromethyl ketone, but was not inhibited by p-tosyl-L-lysine chloromethyl ketone, and aprotinin. Also, human heart chymase was not inhibited by inhibitors of the other three classes of proteinases. Human heart chymase has a high specificity for the conversion of Ang I to Ang II and the Ang I-carboxyl-terminal dipeptide His-Leu (Km = 60 microM; Kcat = 11,900 min-1; Kcat/Km = 198 min-1 microM-1). Human heart chymase did not degrade several peptide hormones, including Ang II, bradykinin, and vasoactive intestinal peptide, nor did it form Ang II from angiotensinogen. The high substrate specificity of human heart chymase for Ang I distinguishes it from other Ang II-forming enzymes including Ang I converting enzyme, tonin, kallikrein, cathepsin G, and other known chymases.

Reduced preload and afterload to the heart are important effects of angiotensin converting enzyme (ACE) inhibitors in the treatment of congestive heart failure. However, since angiotensin II (Ang II) directly increases the strength of myocardial contraction, suppression of Ang II formation by ACE inhibitors could potentially reduce the beneficial effects of Ang II on the failing heart. To study how ACE inhibition suppresses cardiac Ang II formation in man, we characterized ACE-dependent and ACE-independent Ang II-forming pathways in eight normal and 24 failing human hearts obtained at cardiac transplantation. Ang II-forming activity in left ventricular (LV) membrane preparations was assessed by measuring the conversion of [125I]angiotensin I (Ang I) to [125I]Ang II. LV [125I]Ang II-forming activity in normal hearts (35.5 +/- 2.7 fmol/min/mg, n = 8) was not different from that in hearts from patients with ischemic cardiomyopathy (25.5 +/- 2.9 fmol/min/mg, n = 9) and was 48% lower (p less than 0.001) in hearts from patients with idiopathic cardiomyopathy (18.5 +/- 1.9 fmol/min/mg, n = 15).(ABSTRACT TRUNCATED AT 250 WORDS)