BackgroundGrowing evidence exists for soluble Angiotensin Converting Enzyme-2 (sACE2) as a biomarker in definitive heart failure (HF), but there is little information about changes in sACE2 activity in hypertension with imminent heart failure and in reverse remodeling.Methods, FindingsPatients with systolic HF (NYHAII-IV, enrolled for cardiac resynchronisation therapy, CRT, n = 100) were compared to hypertensive patients (n = 239) and to a healthy cohort (n = 45) with preserved ejection fraction (EF>50%) in a single center prospective clinical study. The status of the heart failure patients were checked before and after CRT. Biochemical (ACE and sACE2 activity, ACE concentration) and echocardiographic parameters (EF, left ventricular end-diastolic (EDD) and end-systolic diameter (ESD) and dP/dt) were measured.sACE2 activity negatively correlated with EF and positively with ESD and EDD in all patient's populations, while it was independent in the healthy cohort. sACE2 activity was already increased in the hypertensive group, where signs for imminent heart failure (slightly decreased EF and barely increased NT-proBNP levels) were detected. sACE2 activities further increased in patients with definitive heart failure (EF<50%), while sACE2 activities decreased with the improvement of the heart failure after CRT (reverse remodeling). Serum angiotensin converting enzyme (ACE) concentrations were lower in the diseased populations, but did not show a strong correlation with the echocardiographic parameters.ConclusionsSoluble ACE2 activity appears to be biomarker in heart failure, and in hypertension, where heart failure may be imminent. Our data suggest that sACE2 is involved in the pathomechanism of hypertension and HF.

It was shown recently that angiotensin-converting enzyme activity is limited by endogenous inhibition in vivo, highlighting the importance of angiotensin II (ACE2) elimination. The potential contribution of the ACE2 to cardiovascular disease progression was addressed. Serum ACE2 activities were measured in different clinical states (healthy, n=45; hypertensive, n=239; heart failure (HF) with reduced ejection fraction (HFrEF) n=141 and HF with preserved ejection fraction (HFpEF) n=47). ACE2 activity was significantly higher in hypertensive patients (24.8±0.8 U/ml) than that in healthy volunteers (16.2±0.8 U/ml, p=0.01). ACE2 activity further increased in HFrEF patients (43.9±2.1 U/ml, p=0.001) but not in HFpEF patients (24.6±1.9 U/ml) when compared with hypertensive patients. Serum ACE2 activity negatively correlated with left ventricular systolic function in HFrEF, but not in hypertensive, HFpEF or healthy populations. Serum ACE2 activity had a fair diagnostic value to differentiate HFpEF from HFrEF patients in this study. Serum ACE2 activity correlates with cardiovascular disease development: it increases when hypertension develops and further increases when the cardiovascular disease further progresses to systolic dysfunction, suggesting that ACE2 metabolism plays a role in these processes. In contrast, serum ACE2 activity does not change when hypertension progresses to HFpEF, suggesting a different pathomechanism for HFpEF, and proposing a biomarker-based identification of these HF forms.

Endothelial cells express surface angiotensin-converting enzyme 2 (ACE2), the main receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that promotes the infection of endothelial cells showing activation and damage. Bronchoalveolar lavage fluid from coronavirus disease-2019 (COVID-19) subjects showed a critical imbalance in the renin-angiotensin-aldosterone system with the upregulated expression of ACE2. Recently, intravenous recombinant ACE2 was reported as an effective therapy in severe COVID-19 by blocking the viral entry to target cells. Here, we present a case of a critically ill COVID-19 patient with acute respiratory distress syndrome where circulating ACE2 was first measured to monitor disease prognosis. ACE2 activity increased about 40-fold over the normal range and showed a distinct time course as compared to 2-3-fold higher levels of endothelium biomarkers. Although the level of soluble E-selectin followed the clinical status of our patient similar to ferritin and IL-6 levels, the dramatic rise in serum ACE2 activity may act as an endogenous nonspecific protective mechanism against SARS-CoV-2 infection that preceded the recovery of our patient.

About 8% of the adult population is taking angiotensin-converting enzyme (ACE) inhibitors to treat cardiovascular disease including hypertension, myocardial infarction and heart failure. These drugs decrease mortality by up to one-fifth in these patients. We and others have reported previously that endogenous inhibitory substances suppress serum ACE activity, in vivo, similarly to the ACE inhibitor drugs. Here we have made an effort to identify this endogenous ACE inhibitor substance. ACE was crosslinked with interacting proteins in human sera. The crosslinked products were immunoprecipitated and subjected to Western blot. One of the crosslinked products was recognized by both anti-ACE and anti-HSA (human serum albumin) antibodies. Direct ACE-HSA interaction was confirmed by binding assays using purified ACE and HSA. HSA inhibited human purified (circulating) and human recombinant ACE with potencies (IC50) of 5.7±0.7 and 9.5±1.1 mg/mL, respectively. Effects of HSA on the tissue bound native ACE were tested on human saphenous vein samples. Angiotensin I evoked vasoconstriction was inhibited by HSA in this vascular tissue (maximal force with HSA: 6.14±1.34 mN, without HSA: 13.54±2.63 mN), while HSA was without effects on angiotensin II mediated constrictions (maximal force with HSA: 18.73±2.17 mN, without HSA: 19.22±3.50 mN). The main finding of this study is that HSA was identified as a potent physiological inhibitor of the ACE. The enzymatic activity of ACE appears to be almost completely suppressed by HSA when it is present in its physiological concentration. These data suggest that angiotensin I conversion is limited by low physiological ACE activities, in vivo.

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