Pharmacologic modulation of ACE2 expression

Cardioprotective Angiotensin-(1-7) Peptide Acts as a Natural-Biased Ligand at the Angiotensin II Type 1 Receptor

Hyperactivity of the renin-angiotensin-aldosterone system through the angiotensin II (Ang II)/Ang II type 1 receptor (AT1-R) axis constitutes a hallmark of hypertension. Recent findings indicate that only a subset of AT1-R signaling pathways is cardiodeleterious, and their selective inhibition by biased ligands promotes therapeutic benefit. To date, only synthetic biased ligands have been described, and whether natural renin-angiotensin-aldosterone system peptides exhibit functional selectivity at AT1-R remains unknown. In this study, we systematically determined efficacy and potency of Ang II, Ang III, Ang IV, and Ang-(1-7) in AT1-R-expressing HEK293T cells on the activation of cardiodeleterious G-proteins and cardioprotective β-arrestin2. Ang III and Ang IV fully activate similar G-proteins than Ang II, the prototypical AT1-R agonist, despite weaker potency of Ang IV. Interestingly, Ang-(1-7) that binds AT1-R fails to promote G-protein activation but behaves as a competitive antagonist for Ang II/Gi and Ang II/Gq pathways. Conversely, all renin-angiotensin-aldosterone system peptides act as agonists on the AT1-R/β-arrestin2 axis but display biased activities relative to Ang II as indicated by their differences in potency and AT1-R/β-arrestin2 intracellular routing. Importantly, we reveal Ang-(1-7) a known Mas receptor-specific ligand, as an AT1-R-biased agonist, selectively promoting β-arrestin activation while blocking the detrimental Ang II/AT1-R/Gq axis. This original pharmacological profile of Ang-(1-7) at AT1-R, similar to that of synthetic AT1-R-biased agonists, could, in part, contribute to its cardiovascular benefits. Accordingly, in vivo, Ang-(1-7) counteracts the phenylephrine-induced aorta contraction, which was blunted in AT1-R knockout mice. Collectively, these data suggest that Ang-(1-7) natural-biased agonism at AT1-R could fine-tune the physiology of the renin-angiotensin-aldosterone system.

Circulating angiotensin-converting enzyme 2 activity in kidney transplantation: a longitudinal pilot study

BACKGROUND/AIMS

Angiotensin-converting enzyme 2 (ACE2) is the only known active homologue of ACE, and degrades angiotensin (Ang) II and Ang I to Ang(1-7) and Ang(1-9), respectively. The role of ACE2 in kidney transplant (KT) is unknown. Our objective was to investigate circulating ACE2 activity in KT patients, and the relationship between serum ACE2 activity and age, gender, graft function and cardiovascular risk markers in KT patients.

METHODS

113 KT patients with stable graft function were included in this cross-sectional study. Circulating ACE2 activity was assessed using a fluorescent assay.

RESULTS

Circulating ACE2 activity was detectable in KT patients and was increased in KT with ischemic heart disease as compared to KT without ischemic heart disease (105.9 ± 8.7 vs. 97.1 ± 7.05 relative fluorescence units (RFU)/µl/h, p < 0.05). ACE2 activity was increased in male KT as compared to females (105.2 ± 9.1 vs. 84.7 ± 6.9 RFU/µl/h, p = 0.05). ACE2 activity correlated positively with serum creatinine (r = 0.27), serum urea (r = 0.29), age (r = 0.24), aspartate transaminase (r = 0.39), alanine transaminase (r = 0.48), γ-glutamyl transferase (γ-GT) (r = 0.52), age (r = 0.24), and glycosylated hemoglobin (r = 0.19) (p < 0.05). By multiple regression analysis, age, serum creatinine, and serum γ-GT were independent predictors of serum ACE2 activity (r = 0.66, p < 0.001).

CONCLUSIONS

Circulating ACE2 activity is measurable in KT patients and directly correlates with age, renal allograft and liver function parameters. These findings suggest that measurement of serum ACE2 may be used as a non-invasive marker to understand the role of the renin-angiotensin system in KT patients.

Abnormalities of angiotensin regulation in postural tachycardia syndrome

BACKGROUND

Postural tachycardia syndrome (POTS) is a disorder characterized by excessive orthostatic tachycardia and significant functional disability. We previously reported that POTS patients have low blood volume and inappropriately low plasma renin activity (PRA) and aldosterone. In this study, we sought to more fully characterize the renin-angiotensin-aldosterone system (RAAS) to gain a better understanding of the pathophysiology of POTS.

OBJECTIVE

The purpose of this study was to prospectively assess the plasma levels of angiotensin (Ang) peptides and their relationship to other RAAS components in patients with POTS compared with healthy controls.

METHODS

Heart rate, PRA, Ang I, Ang II, Ang (1-7), and aldosterone were measured in POTS patients (n = 38) and healthy controls (n = 13) while they were consuming a sodium-controlled diet.

RESULTS

POTS patients had larger orthostatic increases in heart rate than did controls (52 ± 3 [mean ± SEM] bpm vs 27 ± 6 bpm, P = .001). Plasma Ang II was significantly higher in POTS patients (43 ± 3 pg/mL vs 28 ± 3 pg/mL, P = .006), whereas plasma Ang I and angiotensin 1-7 [Ang-(1-7)] were similar between groups. Despite the twofold increase of Ang II, POTS patients trended to lower PRA levels than did controls (0.9 ± 0.1 ng/mL/h vs 1.6 ± 0.5 ng/mL/h, P = .268) and lower aldosterone levels (4.6 ± 0.8 pg/mL vs 10.0 ± 3.0 pg/mL, P = .111). Estimated angiotensin-converting enzyme-2 (ACE2) activity was significantly lower in POTS patients than in controls (0.25 ± 0.02 vs 0.33 ± 0.03, P = .038).

CONCLUSION

Some patients with POTS have inappropriately high plasma Ang II levels, with low estimated ACE2 activity. We propose that these abnormalities in Ang regulation may play a key role in the pathophysiology of POTS in some patients.

ACE2, a promising therapeutic target for pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a chronic lung disease with poor diagnosis and limited therapeutic options. The currently available therapies are ineffective in improving the quality of life and reducing mortality rates. There exists a clear unmet medical need to treat this disease, which necessitates the discovery of novel therapeutic targets/agents for safe and successful therapy. An altered renin–angiotensin system (RAS) has been implicated as a causative factor in the pathogenesis of PAH. Angiotensin II (Ang II), a key effector peptide of the RAS, can exert deleterious effects on the pulmonary vasculature resulting in vasoconstriction, proliferation, and inflammation, all of which contribute to PAH development. Recently, a new member of the RAS, angiotensin converting enzyme 2 (ACE2), was discovered. This enzyme functions as a negative regulator of the angiotensin system by metabolizing Ang II to a putative protective peptide, angiotensin-(1–7). ACE2 is abundantly expressed in the lung tissue and emerging evidence suggests a beneficial role for this enzyme against lung diseases. In this review, we focus on ACE2 in relation to pulmonary hypertension and provide proof of principle for its therapeutic role in PAH.

Human recombinant ACE2 reduces the progression of diabetic nephropathy

OBJECTIVE

Diabetic nephropathy is one of the most common causes of end-stage renal failure. Inhibition of ACE2 function accelerates diabetic kidney injury, whereas renal ACE2 is downregulated in diabetic nephropathy. We examined the ability of human recombinant ACE2 (hrACE2) to slow the progression of diabetic kidney injury.

RESEARCH DESIGN AND METHODS

Male 12-week-old diabetic Akita mice (Ins2(WT/C96Y)) and control C57BL/6J mice (Ins2(WT/WT)) were injected daily with placebo or with rhACE2 (2 mg/kg, i.p.) for 4 weeks. Albumin excretion, gene expression, histomorphometry, NADPH oxidase activity, and peptide levels were examined. The effect of hrACE2 on high glucose and angiotensin II (ANG II)-induced changes was also examined in cultured mesangial cells.

RESULTS

Treatment with hrACE2 increased plasma ACE2 activity, normalized blood pressure, and reduced the urinary albumin excretion in Akita Ins2(WT/C96Y) mice in association with a decreased glomerular mesangial matrix expansion and normalization of increased alpha-smooth muscle actin and collagen III expression. Human recombinant ACE2 increased ANG 1-7 levels, lowered ANG II levels, and reduced NADPH oxidase activity. mRNA levels for p47(phox) and NOX2 and protein levels for protein kinase Calpha (PKCalpha) and PKCbeta1 were also normalized by treatment with hrACE2. In vitro, hrACE2 attenuated both high glucose and ANG II-induced oxidative stress and NADPH oxidase activity.

CONCLUSIONS

Treatment with hrACE2 attenuates diabetic kidney injury in the Akita mouse in association with a reduction in blood pressure and a decrease in NADPH oxidase activity. In vitro studies show that the protective effect of hrACE2 is due to reduction in ANG II and an increase in ANG 1-7 signaling.

Angiotensin-converting enzyme 2: implications for blood pressure and kidney disease

PURPOSE OF REVIEW

Angiotensin-converting enzyme 2 (ACE 2), the main product of which is Ang 1-7, which binds to its receptor, Mas, is an important member of the renin-angiotensin system.

RECENT FINDINGS

A substantial body of research indicates that ACE2 is cardioprotective and renoprotective. ACE2 participates in a pathway that is counterregulatory to the effects of angiotensin II (Ang II). The mechanisms by which the protective effects of ACE2 occur are just beginning to be elucidated.

SUMMARY

As ACE2 appears to exert protective effects within the kidney and vasculature, recent data indicate that how it is expressed, what regulates it, and how it interacts with other biological systems may ultimately have clinical implications.