Angiotensin II formation from ACE and chymase in human and animal hearts: methods and species considerations

TLDR

The study examined how angiotensin‑converting enzyme and chymase contribute to angiotensin II production in left ventricular membranes of humans, dogs, rabbits, rats, and mice, hypothesizing that ACE localizes to high‑detergent preparations while chymase localizes to low‑detergent preparations. ACE and chymase activities were quantified in membrane fractions isolated with low‑detergent (LD) and high‑detergent (HD) extractions. Human hearts showed a 16‑fold higher ACE activity in HD versus LD preparations and a 15‑fold higher chymase activity in LD versus HD, leading to the highest total angiotensin II production among species, whereas mouse hearts had the greatest ACE‑driven ANG II, highlighting species‑specific differences with chymase predominating in human hearts.

Abstract

The current study examined the contributions of angiotensin-converting enzyme (ACE) vs. chymase to angiotensin II (ANG II) generation in membrane preparations from left ventricles of humans, dogs, rabbits, and rats and from total heart of mice. ACE and chymase activity were measured in membrane preparations extracted with low or high detergent (LD and HD, respectively) concentrations. We hypothesized that ACE, which is membrane bound in vivo, would be preferentially localized to the HD preparation, whereas chymase, which is localized to the cytoplasm and cardiac interstitium, would be localized to the LD preparation. In human heart, ACE activity was 16-fold higher in the HD than in the LD preparation, whereas chymase activity was 15-fold higher in the LD than in the HD preparation. Total ANG II formation was greater in human heart [15.8 ± 3.4 (SE) μmol ANG II ⋅ g −1 ⋅ min −1 ] than in dog, rat, rabbit, and mouse hearts (3.90 ± 0.35, 0.41 ± 0.02, 0.61 ± 0.07, and 1.16 ± 0.08 μmol ANG II ⋅ g −1 ⋅ min −1 , respectively, P < 0.05, by analysis of variance). ANG II formation from ACE was higher in mouse heart (1.09 ± 0.05 μmol ANG II ⋅ g −1 ⋅ min −1 , P < 0.001) than in rabbit, human, dog, and rat hearts (0.55 ± 0.06, 0.34 ± 0.01, 0.32 ± 0.06, and 0.31 ± 0.02 μmol ANG II ⋅ g −1 ⋅ min −1 , respectively). In contrast, chymase activity was higher in human heart (15.3 ± 3.4 μmol ANG II ⋅ g −1 ⋅ min −1 ) than in dog, rat, rabbit, and mouse hearts (3.59 ± 0.29, 0.10 ± 0.01, 0.06 ± 0.01, and 0.07 ± 0.01 μmol ANG II ⋅ g −1 ⋅ min −1 , respectively). Our results demonstrate important species differences in the pathways of intracardiac ANG II generation. Chymase predominated over ACE activity in human heart, accounting for extremely high total ANG II formation in human heart compared with dog, rat, rabbit, and mouse hearts.