Chymase mediates angiotensin-(1-12) metabolism in normal human hearts

Abstract

Background Identification of angiotensin-(1-12) [Ang-(1-12)] in forming Ang II by a non-renin dependent mechanism has increased knowledge on the paracrine/autocrine mechanisms regulating cardiac expression of Ang peptides. This study now describes in humans the identity of the enzyme accounting for Ang-(1-12) metabolism in the left ventricular (LV) tissue of normal subjects. Methods and Results Reverse phase HPLC characterized the products of 125I-Ang-(1-12) metabolism in plasma membranes (PMs) from human LV in the absence and presence of inhibitors for chymase (chymostatin), angiotensin converting enzyme (ACE) 1 (lisinopril) and 2 (MLN-4760) and neprilysin (SHC39370). In the presence of the inhibitor cocktail ≥ 98 ± 2% of cardiac 125I-Ang-(1-12) remained intact, whereas exclusion of chymostatin from the inhibitor cocktail led to significant conversion of Ang-(1-12) into angiotensin II. In addition, chymase-mediated hydrolysis of 125I-Ang I was higher compared to Ang-(1-12). Negligible Ang-(1-12) hydrolysis occurred by ACE, ACE2, and neprilysin. A high chymase activity was detected for both 125I-Ang-(1-12) and 125I-Ang I substrates. Conclusions Chymase accounts for the conversion of Ang-(1-12) and Ang I to Ang II in normal human LV. These novel findings expand knowledge of the alternate mechanism by which Ang-(1-12) contributes to the production of cardiac angiotensin peptides.

RETRACTED: Differential expression of the angiotensin-(1-12)/chymase axis in human atrial tissue

“…Through a series of publications we showed: 1)- increased expression and content of Ang-(1-12) in the hypertrophied heart of SHR (Jessup et al, 2008); 2)- the production of Ang II from Ang-(1-12) to be independent of renin in the isolated heart of two rat hypertensive strains and three normotensive control rats (Trask et al, 2008), the heart of anephric WKY rats (Ferrario et al, 2009), and rats fed a low salt diet (Nagata et al, 2010); and 3)- a contribution of chymase in Ang-(1-12) metabolism in the heart of SHR (Ahmad et al, 2011b) while ACE accounts for the degradation of Ang-(1-12) in the circulation of both WKY and SHR (Moniwa et al, 2013). In extending these experimental findings to the human heart we identified Ang-(1-12) and chymase in left atria specimens from patients undergoing heart surgery (Ahmad et al, 2011a) and left ventricle of normal subjects (Ahmad et al, 2013). …”

Newly Discovered Components and Actions of the Renin–Angiotensin System

“…This concept has been recently challenged by the discovery of angiotensin (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) [Ang (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)], a peptide containing a 2-amino-acid (Leu 11 -Tyr 12 ) C-terminal extension of Ang I. 3 Initially isolated and identified from the rat small intestine, Ang (1-12) is present in high concentrations (comparable with those of Ang I and II) in other peripheral tissues, such as the aorta, heart, and kidneys, although its circulating levels are substantially lower than those of Ang I and II.…”

“…3,4 Tissue levels of Ang (1-12) were unchanged after bilateral nephrectomy, renin inhibition, and Na + loading, which markedly reduced the circulating and tissue levels of Ang I and II and Na + restriction, which increased Ang I and II levels. [4][5][6] The relatively higher tissue level of Ang (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and its lack of change in response to systemic manipulation has suggested a possible physiological and pathophysiologic role in tissues, independently of the systemic circulation. 3,4 Initially, Ang (1-12) was found to induce a vasoconstrictor response in rat aorta that could be blocked either with an ACE inhibitor or AT 1 R blocker, suggesting that Ang (1-12) might be a peptide precursor of Ang II.…”

“…[7][8][9] Studies have indicated that in tissues, such as heart, instead of ACE, chymase seems to be the major Ang (1-12)-metabolizing enzyme. [7][8][9] However, a recent study shows a different result for Ang (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) metabolism in the systemic circulation of normotensive and hypertensive rats, where ACE was shown to cleave the Leu 10 -Leu 11 bond of Ang (1-12) to generate Ang I. 10 Chymase, a chymotrypsin-like enzyme expressed in the secretory granules of mast cells, is generally accepted as the major catalyst for Ang I to II conversion in the heart and in the vasculature.…”

“…Ang (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) has the potential to be a major source of Ang II, both via conversion to Ang I and directly to Ang II via chymase in the heart and possibly other tissues. Ang (1-12) is likely to be more important at the tissue than the systemic level.…”