Prevention of angiotensin II-mediated renal oxidative stress, inflammation, and fibrosis by angiotensin-converting enzyme 2

New and old agents in the management of diabetic nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy is a long-standing complication of diabetes mellitus and is responsible for more than 40% of end-stage renal disease cases in developed countries. Unfortunately, conventional renin-angiotensin-aldosterone system (RAAS) inhibitor medications only partially protect against the development and progression of diabetic nephropathy. Moreover, RAAS inhibitors have failed as primary prevention therapy in type 1 diabetes. Thus, agents targeting alternative pathogenic mechanisms leading to diabetic nephropathy have been intensively investigated, which is the topic of this review.

RECENT FINDINGS

Promising emerging agents have targeted neurohormonal activation (alternative components of the RAAS and neprilysin inhibition), tubuloglomerular feedback mechanisms (sodium glucose cotransporter 2 inhibition and incretin-based therapy) and renal inflammation/fibrosis.

SUMMARY

Evidence demonstrating the potential of these agents to protect and prevent progression of diabetic nephropathy is summarized in this review. There are dedicated clinical trials ongoing with these therapies, which have the potential to change the clinical practice.

Angiotensin-converting enzyme 2 ameliorates renal fibrosis by blocking the activation of mTOR/ERK signaling in apolipoprotein E-deficient mice

Angiotensin-converting enzyme 2 (ACE2) has been shown to prevent atherosclerotic lesions and renal inflammation. However, little was elucidated upon the effects and mechanisms of ACE2 in atherosclerotic kidney fibrosis progression. Here, we examined regulatory roles of ACE2 in renal fibrosis in the apolipoprotein E (ApoE) knockout (KO) mice. The ApoEKO mice were randomized to daily deliver either angiotensin (Ang) II (1.5mg/kg) and/or human recombinant ACE2 (rhACE2; 2mg/kg) for 2 weeks. Downregulation of ACE2 and upregulation of phosphorylated Akt, mTOR and ERK1/2 levels were observed in ApoEKO kidneys. Ang II infusion led to increased tubulointerstitial fibrosis in the ApoEKO mice with greater activation of the mTOR/ERK1/2 signaling. The Ang II-mediated renal fibrosis and structural injury were strikingly rescued by rhACE2 supplementation, associated with reduced mRNA expression of TGF-β1 and collagen I and elevated renal Ang-(1-7) levels. In cultured mouse kidney fibroblasts, exposure with Ang II (100nmolL(-1)) resulted in obvious elevations in superoxide generation, phosphorylated levels of mTOR and ERK1/2 as well as mRNA levels of TGF-β1, collagen I and fibronectin 1, which were dramatically prevented by rhACE2 (1mgmL(-1)) or mTOR inhibitor rapamycin (10μmolL(-1)). These protective effects of rhACE2 were eradicated by the Ang-(1-7)/Mas receptor antagonist A779 (1μmolL(-1)). Our results demonstrate the importance of ACE2 in amelioration of kidney fibrosis and renal injury in the ApoE-mutant mice via modulation of the mTOR/ERK signaling and renal Ang-(1-7)/Ang II balance, thus indicating potential therapeutic strategies by enhancing ACE2 action for preventing atherosclerosis and fibrosis-associated kidney disorders.

RELATIONSHIP OF OXIDATIVE STRESS TO URINARY ANGIOTENSIN CONVERTING ENZYME 2 IN TYPE 2 DIABETES MELLITUS PATIENTS

CONTEXT

Angiotensin converting enzyme 2 (ACE2) is highly expressed in the kidney and cleaves angiotensin II to Angiotensin (1-7), annihilating the deleterious effects of angiotensin II which is known to be a strong activator of oxidative stress.

OBJECTIVE

We aimed to evaluate the relationship of oxidative stress to urinary ACE2 (uACE2) in type 2 diabetes mellitus (T2DM) patients.

DESIGN

We included consecutive normo or microalbuminuric T2DM patients in an observational transversal study. Routine laboratory investigations, plasma malondialdehyde (MDA, fluorimetric thiobarbituric method) as a marker of prooxidant capacity and superoxide dismutase (SOD, cytochrome reduction method) and catalase (CAT) activity (in erythrocyte lysate by the modification of absorbance method) as two measures of serum antioxidant capacity and uACE2 (ELISA method) were assessed.

RESULTS

MDA showed a negative correlation with SOD (r=-0.44, p=0.001), CAT (r=-0.37, p=0.006), uACE2 (r=-0.33, p=0.016) and a positive correlation with glycated haemoglobin (HbA1c) (r=0.49, p<0.001) and associated cardiovascular disease (r=0.42, p=0.001). CAT as also positively correlated to uACE2 (r=0.29, p=0.037). SOD was also negatively correlated with glycemia (r=-0.71, p<0.001) and HbA1c (r=-0.53, p<0.001). Patients with lower MDA (when divided according to median value of 3.88 nmol/mL) had higher uACE2 57.15(40.3-71.2) pg/mL compared to 38.5(31.8-45.95) pg/mL in patients with higher MDA (p<0.001). In multivariate logistic regression uACE2 was the only predictor for MDA above or below its median (OR=0.94, 95%CI[0.90-0.98], p=0.002).

CONCLUSION

Increased prooxidant serum capacity is associated with lower uACE2 levels in T2DM patients.

FGF23 from bench to bedside

There is a strong association between elevated circulating fibroblast growth factor-23 (FGF23) levels and adverse outcomes in patients with chronic kidney disease (CKD) of all stages. Initially discovered as a regulator of phosphate and vitamin D homeostasis, FGF23 has now been implicated in several pathophysiological mechanisms that may negatively impact the cardiovascular and renal systems. FGF23 is purported to have direct (off-target) effects in the myocardium, as well as canonical effects on FGF receptor/α-klotho receptor complexes in the kidney to activate the renin-angiotensin-aldosterone system, modulate soluble α-klotho levels, and increase sodium retention, to cause left ventricular hypertrophy (LVH). Conversely, FGF23 could be an innocent bystander produced in response to chronic inflammation or other processes associated with CKD that cause LVH and adverse cardiovascular outcomes. Further exploration of these complex mechanisms is needed before modulation of FGF23 can become a legitimate clinical target in CKD.

Novel Epidermal Growth Factor Receptor Inhibitor Attenuates Angiotensin II-Induced Kidney Fibrosis

Chronic activation of renin-angiotensin system (RAS) greatly contributes to renal fibrosis and accelerates the progression of chronic kidney disease; however, the underlying molecular mechanism is poorly understood. Angiotensin II (Ang II), the central component of RAS, is a key regulator of renal fibrogenic destruction. Here we show that epidermal growth factor receptor (EGFR) plays an important role in Ang II-induced renal fibrosis. Inhibition of EGFR activation by novel small molecules or by short hairpin RNA knockdown in Ang II-treated SV40 mesangial cells in vitro suppresses protein kinase B and extracellular signal-related kinase signaling pathways and transforming growth factor-β/Sma- and Mad-related protein activation, and abolishes the accumulation of fibrotic markers such as connective tissue growth factor, collagen IV. The transactivation of EGFR by Ang II in SV40 cells depends on the phosphorylation of proto-oncogene tyrosine-protein kinase Src (c-Src) kinase. Further validation in vivo demonstrates that EGFR small molecule inhibitor successfully attenuates renal fibrosis and kidney dysfunction in a mouse model induced by Ang II infusion. These findings indicate a crucial role of EGFR in Ang II-dependent renal deterioration, and reveal EGFR inhibition as a new therapeutic strategy for preventing progression of chronic renal diseases.

Effects of telmisartan and linagliptin when used in combination on blood pressure and oxidative stress in rats with 2-kidney-1-clip hypertension

OBJECTIVE

To investigate the effects of linagliptin alone and in combination with the angiotensin II receptor blocker (ARB), telmisartan on blood pressure (BP), kidney function, heart morphology and oxidative stress in rats with renovascular hypertension.

METHODS

Fifty-seven male Wistar rats underwent unilateral surgical stenosis of the renal artery [2-kidney-1-clip (2k1c) method]. Animals were randomly divided into four treatment groups (n = 14-18 per group) receiving: telmisartan (10 mg/kg per day in drinking water), linagliptin (89 ppm in chow), combination (linagliptin 89 ppm + telmisartan 10 mg/kg per day) or placebo. An additional group of 12 rats underwent sham surgery. BP was measured one week after surgery. Hypertensive animals entered a 16-week dosing period. BP was measured 2, 4, 8, 12 and 16 weeks after the initiation of treatment. Blood and urine were tested for assessment of kidney function and oxidative stress 6, 10, 14 and 18 weeks after surgery. Blood and urine sampling and organ harvesting were finally performed.

RESULTS

Renal stenosis caused an increase in mean ± SD systolic BP as compared with the sham group (157.7 ± 29.3 vs. 106.2 ± 20.5 mmHg, respectively; P < 0.001). Telmisartan alone and in combination with linagliptin, normalized SBP (111.1 ± 24.3 mmHg and 100.4 ± 13.9 mmHg, respectively; P < 0.001 vs. placebo). Telmisartan alone and in combination with linagliptin significantly prevented cardiac hypertrophy, measured by heart weight and myocyte diameter. Renal function measured by cystatin C was not affected by 2k1c surgery. Telmisartan significantly increased plasma concentration of cystatin C. 2k1c surgery initiated fibrosis in both kidneys. Telmisartan promoted further fibrotic changes in the clipped kidney, as measured by protein expression of Col1a1 and histology for interstitial fibrosis and glomerulosclerosis. In non-clipped kidneys, telmisartan demonstrated antifibrotic properties, reducing Col1a1 protein expression. Plasma levels of oxidized low-density lipoprotein were higher in the placebo-treated 2k1c rats as compared to sham-operated animals. The increase was abolished by linagliptin alone (P = 0.03 vs. placebo) and in combination with telmisartan (P = 0.02 vs. placebo). Combination therapy also significantly reduced plasma concentration of carbonyl proteins (P = 0.04 vs. placebo).

CONCLUSION

Inhibition of type 4 dipeptidyl peptidase with linagliptin did not counter BP-lowering effects of ARB in 2k1c rats. Linagliptin reduced lipid and protein oxidation in 2k1c rats, and this effect was BP-independent.

Deletion of angiotensin-converting enzyme 2 exacerbates renal inflammation and injury in apolipoprotein E-deficient mice through modulation of the nephrin and TNF-alpha-TNFRSF1A signaling

Background

The renin-angiotensin system (RAS) has been implicated in atherosclerotic lesions and progression to chronic kidney diseases. We examined regulatory roles of angiotensin-converting enzyme 2 (ACE2) in the apolipoprotein E (ApoE) knockout (KO) kidneys.

Methods

The 3-month-old wild-type, ApoEKO, ACE2KO and ApoE/ACE2 double-KO (DKO) mice in a C57BL/6 background were used. The ApoEKO mice were randomized to daily deliver either Ang II (1.5 mg/kg) and/or human recombinant ACE2 (rhACE2; 2 mg/kg) for 2 weeks. We examined changes in pro-inflammatory cytokines, renal ultrastructure, and pathological signaling in mouse kidneys.

Results

Downregulation of ACE2 and nephrin levels was observed in ApoEKO kidneys. Genetic ACE2 deletion resulted in modest elevations in systolic blood pressure levels and Ang II type 1 receptor expression and reduced nephrin expression in kidneys of the ApoE/ACE2 DKO mice with a decrease in renal Ang-(1-7) levels. These changes were linked with marked increases in renal superoxide generation, NADPH oxidase (NOX) 4 and proinflammatory factors levels, including interleukin (IL)-1beta, IL-6, IL-17A, RANTES, ICAM-1, Tumor necrosis factor-alpha (TNF-alpha) and TNFRSF1A. Renal dysfunction and ultrastructure injury were aggravated in the ApoE/ACE2 DKO mice and Ang II-infused ApoEKO mice with increased plasma levels of creatinine, blood urea nitrogen and enhanced levels of Ang II in plasma and kidneys. The Ang II-mediated reductions of renal ACE2 and nephrin levels in ApoEKO mice were remarkably rescued by rhACE2 supplementation, along with augmentation of renal Ang-(1-7) levels. More importantly, rhACE2 treatment significantly reversed Ang II-induced renal inflammation, superoxide generation, kidney dysfunction and adverse renal injury in ApoEKO mice with suppression of the NOX4 and TNF-alpha-TNFRSF1A signaling. However, rhACE2 had no effect on renal NOX2 and TNFRSF1B expression and circulating lipid levels.

Conclusions

ACE2 deficiency exacerbates kidney inflammation, oxidative stress and adverse renal injury in the ApoE-mutant mice through modulation of the nephrin, NOX4 and TNF-alpha-TNFRSF1A signaling. While rhACE2 supplementation alleviates inflammation, renal dysfunction and glomerulus injury in the ApoE-mutant mice associated with upregulations of Ang-(1-7) levels and nephrin expression and suppression of the TNF-alpha-TNFRSF1A signaling. Strategies aimed at enhancing the ACE2/Ang-(1-7) actions may have important therapeutic potential for atherosclerotic renal injury and kidney diseases.

Immunization with an ApoB-100 Related Peptide Vaccine Attenuates Angiotensin-II Induced Hypertension and Renal Fibrosis in Mice

Recent studies suggest the potential involvement of CD8+ T cells in the pathogenesis of murine hypertension. We recently reported that immunization with apoB-100 related peptide, p210, modified CD8+ T cell function in angiotensin II (AngII)-infused apoE (-/-) mice. In this study, we hypothesized that p210 vaccine modulates blood pressure in AngII-infused apoE (-/-) mice. Male apoE (-/-) mice were immunized with p210 vaccine and compared to unimmunized controls. At 10 weeks of age, mice were subcutaneously implanted with an osmotic pump which released AngII for 4 weeks. At 13 weeks of age, p210 immunized mice showed significantly lower blood pressure response to AngII compared to controls. CD8+ T cells from p210 immunized mice displayed a different phenotype compared to CD8+ T cells from unimmunized controls. Serum creatinine and urine albumin to creatinine ratio were significantly decreased in p210 immunized mice suggesting that p210 vaccine had renal protective effect. At euthanasia, inflammatory genes IL-6, TNF-α, and MCP-1 in renal tissue were down-regulated by p210 vaccine. Renal fibrosis and pro-fibrotic gene expression were also significantly reduced in p210 immunized mice. To assess the role of CD8+ T cells in these beneficial effects of p210 vaccine, CD8+ T cells were depleted by CD8 depleting antibody in p210 immunized mice. p210 immunized mice with CD8+ T cell depletion developed higher blood pressure compared to mice receiving isotype control. Depletion of CD8+ T cells also increased renal fibrotic gene expression compared to controls. We conclude that immunization with p210 vaccine attenuated AngII-induced hypertension and renal fibrosis. CD8+ T cells modulated by p210 vaccine could play an important role in the anti-hypertensive, anti-fibrotic and renal-protective effect of p210 vaccine.

Angiotensin-(1-7) prevents systemic hypertension, attenuates oxidative stress and tubulointerstitial fibrosis, and normalizes renal angiotensin-converting enzyme 2 and Mas receptor expression in diabetic mice

We investigated the relationship between Ang-(1-7) [angiotensin-(1-7)] action, sHTN (systolic hypertension), oxidative stress, kidney injury, ACE2 (angiotensin-converting enzyme-2) and MasR [Ang-(1-7) receptor] expression in Type 1 diabetic Akita mice. Ang-(1-7) was administered daily [500 μg/kg of BW (body weight) per day, subcutaneously] to male Akita mice from 14 weeks of age with or without co-administration of an antagonist of the MasR, A779 (10 mg/kg of BW per day). The animals were killed at 20 weeks of age. Age-matched WT (wild-type) mice served as controls. Ang-(1-7) administration prevented sHTN and attenuated kidney injury (reduced urinary albumin/creatinine ratio, glomerular hyperfiltration, renal hypertrophy and fibrosis, and tubular apoptosis) without affecting blood glucose levels in Akita mice. Ang-(1-7) also attenuated renal oxidative stress and the expression of oxidative stress-inducible proteins (NADPH oxidase 4, nuclear factor erythroid 2-related factor 2, haem oxygenase 1), pro-hypertensive proteins (angiotensinogen, angiotensin-converting enzyme, sodium/hydrogen exchanger 3) and profibrotic proteins (transforming growth factor-β1 and collagen IV), and increased the expression of anti-hypertensive proteins (ACE2 and MasR) in Akita mouse kidneys. These effects were reversed by A779. Our data suggest that Ang-(1-7) plays a protective role in sHTN and RPTC (renal proximal tubular cell) injury in diabetes, at least in part, through decreasing renal oxidative stress-mediated signalling and normalizing ACE2 and MasR expression.

Functional and molecular evidence for expression of the renin angiotensin system and ADAM17-mediated ACE2 shedding in COS7 cells

The renin angiotensin system (RAS) plays a vital role in the regulation of the cardiovascular and renal functions. COS7 is a robust and easily transfectable cell line derived from the kidney of the African green monkey, Cercopithecus aethiops. The aims of this study were to 1) demonstrate the presence of an endogenous and functional RAS in COS7, and 2) investigate the role of a disintegrin and metalloproteinase-17 (ADAM17) in the ectodomain shedding of angiotensin converting enzyme-2 (ACE2). Reverse transcription coupled to gene-specific polymerase chain reaction demonstrated expression of ACE, ACE2, angiotensin II type 1 receptor (AT1R), and renin at the transcript levels in total RNA cell extracts. Western blot and immunohistochemistry identified ACE (60 kDa), ACE2 (75 kDa), AT1R (43 kDa), renin (41 kDa), and ADAM17 (130 kDa) in COS7. At the functional level, a sensitive and selective mass spectrometric approach detected endogenous renin, ACE, and ACE2 activities. ANG-(1-7) formation (m/z 899) from the natural substrate ANG II (m/z 1,046) was detected in lysates and media. COS7 cells stably expressing shRNA constructs directed against endogenous ADAM17 showed reduced ACE2 shedding into the media. This is the first study demonstrating endogenous expression of the RAS and ADAM17 in the widely used COS7 cell line and its utility to study ectodomain shedding of ACE2 mediated by ADAM17 in vitro. The transfectable nature of this cell line makes it an attractive cell model for studying the molecular, functional, and pharmacological properties of the renal RAS.

Role of non-classical renin-angiotensin system axis in renal fibrosis

The renin–angiotensin system (RAS) is a major regulator of renal fibrosis. Besides the classical renin/Angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/AT1 and AT2 axis, multiple new axes have been recently described. The new members have added new dimensions to RAS, including the ACE2/Ang(1–7)/Mas receptor axis, the prorenin/(pro)renin receptor(PRR)/intracelluar pathway axis, and the Angiotensin A (Ang A), alamandine-Mas-related G protein coupled receptor D(MrgD) axis. This review summarized recent studies regarding role of the non-classical RAS axis in renal fibrosis, and its possible implications to the intervention of progression of chronic kidney disease.

Antagonism of angiotensin 1-7 prevents the therapeutic effects of recombinant human ACE2

Activation of the angiotensin 1-7/Mas receptor (MasR) axis counteracts angiotensin II (Ang II)-mediated cardiovascular disease. Recombinant human angiotensin-converting enzyme 2 (rhACE2) generates Ang 1-7 from Ang II. We hypothesized that the therapeutic effects of rhACE2 are dependent on Ang 1-7 action. Wild type male C57BL/6 mice (10-12 weeks old) were infused with Ang II (1.5 mg/kg/d) and treated with rhACE2 (2 mg/kg/d). The Ang 1-7 antagonist, A779 (200 ng/kg/min), was administered to a parallel group of mice. rhACE2 prevented Ang II-induced hypertrophy and diastolic dysfunction while A779 prevented these beneficial effects and precipitated systolic dysfunction. rhACE2 effectively antagonized Ang II-mediated myocardial fibrosis which was dependent on the action of Ang 1-7. Myocardial oxidative stress and matrix metalloproteinase 2 activity was further increased by Ang 1-7 inhibition even in the presence of rhACE2. Activation of Akt and endothelial nitric oxide synthase (eNOS) by rhACE2 were suppressed by the antagonism of Ang 1-7 while the activation of pathological signaling pathways was maintained. Blocking Ang 1-7 action prevents the therapeutic effects of rhACE2 in the setting of elevated Ang II culminating in systolic dysfunction. These results highlight a key cardioprotective role of Ang 1-7, and increased Ang 1-7 action represents a potential therapeutic strategy for cardiovascular diseases.

KEY MESSAGES

Activation of the renin-angiotensin system (RAS) plays a key pathogenic role in cardiovascular disease. ACE2, a monocarboxypeptidase, negatively regulates pathological effects of Ang II. Antagonizing Ang 1-7 prevents the therapeutic effects of recombinant human ACE2. Our results highlight a key protective role of Ang 1-7 in cardiovascular disease.

Short-term treatment with diminazene aceturate ameliorates the reduction in kidney ACE2 activity in rats with subtotal nephrectomy

Angiotensin converting enzyme (ACE) 2 is an important modulator of the renin angiotensin system (RAS) through its role to degrade angiotensin (Ang) II. Depletion of kidney ACE2 occurs following kidney injury due to renal mass reduction and may contribute to progressive kidney disease. This study assessed the effect of diminazine aceturate (DIZE), which has been described as an ACE2 activator, on kidney ACE2 mRNA and activity in rats with kidney injury due to subtotal nephrectomy (STNx). Sprague Dawley rats were divided into Control groups or underwent STNx; rats then received vehicle or the DIZE (s.c. 15 mg/kg/day) for 2 weeks. STNx led to hypertension (P<0.01), kidney hypertrophy (P<0.001) and impaired kidney function (P<0.001) compared to Control rats. STNx was associated with increased kidney cortical ACE activity, and reduced ACE2 mRNA in the cortex (P<0.01), with reduced cortical and medullary ACE2 activity (P<0.05), and increased urinary ACE2 excretion (P<0.05) compared to Control rats. Urinary ACE2 activity correlated positively with urinary protein excretion (P<0.001), and negatively with creatinine clearance (P=0.04). In STNx rats, DIZE had no effect on blood pressure or kidney function, but was associated with reduced cortical ACE activity (P<0.01), increased cortical ACE2 mRNA (P<0.05) and increased cortical and medullary ACE2 activity (P<0.05). The precise in vivo mechanism of action of DIZE is not clear, and its effects to increase ACE2 activity may be secondary to an increase in ACE2 mRNA abundance. In ex vivo studies, DIZE did not increase ACE2 activity in either Control or STNx kidney cortical membranes. It is not yet known if chronic administration of DIZE has long-term benefits to slow the progression of kidney disease.

Loss of prolyl carboxypeptidase in two-kidney, one-clip goldblatt hypertensive mice

It is well documented that angiotensin (Ang) II contributes to kidney disease progression. The protease prolyl carboxypeptidase (PRCP) is highly expressed in the kidney and may be renoprotective by degrading Ang II to Ang-(1-7). The aim of the study was to investigate whether renal PRCP protein expression and activity are altered in two-kidney, one-clip (2K1C) Goldblatt hypertensive mice. Left renal artery was constricted by using 0.12 mm silver clips. Blood pressure was measured using telemetry over the eleven weeks of study period and revealed an immediate increase in 2K1C animals during the first week of clip placement which was followed by a gradual decrease to baseline blood pressure. Similarly, urinary albumin excretion was significantly increased one week after 2K1C and returned to baseline levels during the following weeks. At 2 weeks and at the end of the study, renal pathologies were exacerbated in the 2K1C model as revealed by a significant increase in mesangial expansion and renal fibrosis. Renal PRCP expression and activity were significantly reduced in clipped kidneys. Immunofluorescence revealed the loss of renal tubular PRCP but not glomerular PRCP. In contrast, expression of prolyl endopeptidase, another enzyme capable of converting Ang II into Ang-(1-7), was not affected, while angiotensin converting enzyme was elevated in unclipped kidneys and renin was increased in clipped kidneys. Results suggest that PRCP is suppressed in 2K1C and that this downregulation may attenuate renoprotective effects via impaired Ang II degradation by PRCP.

Simvastatin attenuates angiotensin II‑induced inflammation and oxidative stress in human mesangial cells

Chronic kidney disease (CKD) is an intractable disease in which inflammation and oxidative stress are important. In the present study, the effect of simvastatin on inflammation and oxidative stress induced by angiotensin II (Ang II) in human mesangial cells (HMCs) and its corresponding mechanism was examined. In the in vitro experiment, HMCs were pretreated either without additives (control group) or with simvastatin at different concentrations (0, 0.1, 1 or 10 µM) for 1 h and were then stimulated by Ang II (1 µM) for 24 h. Following stimulation, the cells were collected for analysis using quantitative polymerase chain reaction, western blotting and dihydroethidium staining. The supernatant of the cells was collected and analyzed using an enzyme‑linked immunosorbent assay. The results demonstrated that simvastatin suppressed the increased mRNA expression of monocyte chemoattractant protein‑1, tumor necrosis factor‑α, interleukin (IL)‑1β and IL‑6 and the content of reactive oxygen species induced by Ang II in a dose‑dependent manner. In addition, simvastatin decreased the protein expression of cyclooxygenase‑2 (COX‑2), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and protein kinase C (PKC) as well as the content of prostaglandin E2 and the phosphorylation level of nuclear factor‑κB (NF‑κB) p65 in a dose‑dependent manner. Furthermore, simvastatin significantly increased the protein expression of peroxisome proliferator‑activated receptor γ (PPARγ). Therefore, simvastatin suppressed inflammation and oxidative stress in Ang II‑stimulated HMCs via COX‑2, PPARγ, NF‑κB, NADPH oxidase and PKCs, thereby exerting a protective effect on CKD.

Role of microRNA-29b in angiotensin II-induced epithelial-mesenchymal transition in renal tubular epithelial cells

Angiotensin II (Ang II) has been proven to induce epithelial-mesenchymal transition (EMT). The aim of the present study was to determine the role of microRNA-29b (miR-29b) during Ang II-induced EMT. For this purpose, we used spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rats. The levels of Ang II and its receptor in the kidneys of the SHRs are significantly higher than those in the age-matched WKY rats. As shown by RT-qPCR, the expression of miR-29b in the renal cortex was lower in the SHRs than in the WKY rats. For in vitro experiments, NRK-52E renal tubular epithelial cells were treated with 10(-7) M Ang II; we found that the expression of miR-29b was decreased in the cells treated with Ang II. In addition, transfection of the NRK-52E cells with miR-29b inhibitor led to the downregulation of miR-29b in these cells, and increased the expression of transforming growth factor (TGF)-β, α-smooth muscle actin (α-SMA) and collagen I (Col I). Similar results were observed with the induction of Ang II expression in the NRK-52E cells. By contrast, the upregulation of miR-29b by transfection with miR-29b mimics inhibited the overexpression of these genes induced by Ang II. These results suggest that miR-29b plays an important role in Ang II-induced EMT.

Oral delivery of Angiotensin-converting enzyme 2 and Angiotensin-(1-7) bioencapsulated in plant cells attenuates pulmonary hypertension

Emerging evidences indicate that diminished activity of the vasoprotective axis of the renin-angiotensin system, constituting angiotensin-converting enzyme 2 (ACE2) and its enzymatic product, angiotensin-(1-7) [Ang-(1-7)] contribute to the pathogenesis of pulmonary hypertension (PH). However, long-term repetitive delivery of ACE2 or Ang-(1-7) would require enhanced protein stability and ease of administration to improve patient compliance. Chloroplast expression of therapeutic proteins enables their bioencapsulation within plant cells to protect against gastric enzymatic degradation and facilitates long-term storage at room temperature. Besides, fusion to a transmucosal carrier helps effective systemic absorption from the intestine on oral delivery. We hypothesized that bioencapsulating ACE2 or Ang-(1-7) fused to the cholera nontoxin B subunit would enable development of an oral delivery system that is effective in treating PH. PH was induced in male Sprague Dawley rats by monocrotaline administration. Subset of animals was simultaneously treated with bioencapsulaed ACE2 or Ang-(1-7) (prevention protocol). In a separate set of experiments, drug treatment was initiated after 2 weeks of PH induction (reversal protocol). Oral feeding of rats with bioencapsulated ACE2 or Ang-(1-7) prevented the development of monocrotaline-induced PH and improved associated cardiopulmonary pathophysiology. Furthermore, in the reversal protocol, oral ACE2 or Ang-(1-7) treatment significantly arrested disease progression, along with improvement in right heart function, and decrease in pulmonary vessel wall thickness. In addition, a combination therapy with ACE2 and Ang-(1-7) augmented the beneficial effects against monocrotaline-induced lung injury. Our study provides proof-of-concept for a novel low-cost oral ACE2 or Ang-(1-7) delivery system using transplastomic technology for pulmonary disease therapeutics.

P300-dependent STAT3 acetylation is necessary for angiotensin II-induced pro-fibrotic responses in renal tubular epithelial cells

AIM

To explore the signal transducer and activator of transcription 3 (STAT3) signaling pathway, especially STAT3 acetylation, in angiotensin II (Ang II)-induced pro-fibrotic responses in renal tubular epithelial cells.

METHODS

Rat renal tubular epithelial cell line (NRK-52E) was used. STAT3 acetylation and phosphorylation, as well as the expression of fibronectin, collagen IV and transforming growth factor-β1 (TGF-β1) were examined using Western blotting. The level and localization of STAT3 phosphorylation on Tyr705 were detected with fluorescence immunocytochemistry. The cells were transfected with a plasmid vector carrying p300 gene or siRNA targeting p300 to regulate p300 expression.

RESULTS

Overexpression of p300 significantly increased STAT3 acetylation on Lys685, STAT3 phosphorylation on Tyr705, and the expression of TGF-β1, collagen IV and fibronectin in the cells. Treatment of the cells with Ang II (1 μmol/L) significantly increased STAT3 phosphorylation on Tyr705 through JAK2 activation, and dose-dependently increased the expression of fibronectin, collagen IV and TGF-β1. Pretreatment with curcumin, an inhibitor of JAK2 and p300, blocked Ang II-induced effects. Knockdown of p300 significantly decreased STAT3 acetylation on Lys685, and abolished Ang II-stimulated STAT3 phosphorylation on Tyr705, whereas pretreatment of the cells with C646, a selective inhibitor of p300, inhibited Ang II-induced STAT3 nuclear translocation and the expression of TGF-β1, collagen IV and fibronectin. Pretreatment of the cells with AG490, a JAK2 inhibitor, markedly inhibited Ang II-induced STAT3 phosphorylation on Tyr705 and fibronectin expression.

CONCLUSION

p300-dependent STAT3 acetylation is necessary for Ang II-induced STAT3 phosphorylation and the consequent pro-fibrotic responses in renal tubular epithelial cells in vitro.

Inhibition of STAT3 acetylation is associated with angiotesin renal fibrosis in the obstructed kidney

AIM

To explore the relationship between the signal transducer and activator of transcription 3 (STAT3) signaling and renal fibrosis.

METHODS

Rat renal tubular epithelial NRK-52E cells were treated with angiotesin II (Ang II), nicotinamide (an inhibitor of NAD+-dependent class III protein deacetylases, SIRT1-7), or resveratrol (an activator of SIRT1). Mice underwent unilateral ureteral obstruction (UUO) were used for in vivo studies. Renal interstitial fibrosis was observed with HE and Masson's trichrome staining. STAT3 acetylation and phosphorylation, fibronectin, collagen I, collagen IV, and α-smooth muscle actin (α-SMA) levels were examined using Western blotting.

RESULTS

Nicotinamide (0.625-10 mmol/L) dose-dependently increased STAT3 acetylation on Lys685 and phosphorylation on Tyr705 in NRK-52E cells, accompanied by accumulation of fibronectin and collagen IV. Ang II increased STAT3 phosphorylation on Tyr705 and the expression of fibronectin, collagen IV and α-SMA in the cells. Pretreatment with resveratrol (12.5 μmol/L) blocked Ang II-induced effects in the cells. UUO induced marked STAT3 phosphorylation, fibronectin, collagen IV and α-SMA accumulation, and renal interstitial fibrosis in the obstructed kidneys, which were significantly attenuated by daily administration of resveratrol (100 mg/kg).

CONCLUSION

STAT3 acetylation plays an important role in activation of STAT3 signaling pathway and consequent renal fibrosis.

From gene to protein-experimental and clinical studies of ACE2 in blood pressure control and arterial hypertension

Hypertension is a major risk factor for stroke, coronary events, heart and renal failure, and the renin-angiotensin system (RAS) plays a major role in its pathogenesis. Within the RAS, angiotensin converting enzyme (ACE) converts angiotensin (Ang) I into the vasoconstrictor Ang II. An “alternate” arm of the RAS now exists in which ACE2 counterbalances the effects of the classic RAS through degradation of Ang II, and generation of the vasodilator Ang 1-7. ACE2 is highly expressed in the heart, blood vessels, and kidney. The catalytically active ectodomain of ACE2 undergoes shedding, resulting in ACE2 in the circulation. The ACE2 gene maps to a quantitative trait locus on the X chromosome in three strains of genetically hypertensive rats, suggesting that ACE2 may be a candidate gene for hypertension. It is hypothesized that disruption of tissue ACE/ACE2 balance results in changes in blood pressure, with increased ACE2 expression protecting against increased blood pressure, and ACE2 deficiency contributing to hypertension. Experimental hypertension studies have measured ACE2 in either the heart or kidney and/or plasma, and have reported that deletion or inhibition of ACE2 leads to hypertension, whilst enhancing ACE2 protects against the development of hypertension, hence increasing ACE2 may be a therapeutic option for the management of high blood pressure in man. There have been relatively few studies of ACE2, either at the gene or the circulating level in patients with hypertension. Plasma ACE2 activity is low in healthy subjects, but elevated in patients with cardiovascular risk factors or cardiovascular disease. Genetic studies have investigated ACE2 gene polymorphisms with either hypertension or blood pressure, and have produced largely inconsistent findings. This review discusses the evidence regarding ACE2 in experimental hypertension models and the association between circulating ACE2 activity and ACE2 polymorphisms with blood pressure and arterial hypertension in man.

Increasing serum soluble angiotensin-converting enzyme 2 activity after intensive medical therapy is associated with better prognosis in acute decompensated heart failure

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2) is an endogenous counterregulator of the renin-angiotensin system that has been recently identified in circulating form. We aimed to investigate the relationship among changes in soluble ACE2 (sACE2) activity, myocardial performance, and long-term clinical outcomes in patients with acute decompensated heart failure (ADHF). We hypothesized that increasing sACE2 activity levels during intensive medical treatment are associated with improved myocardial performance and long-term clinical outcomes.

METHODS AND RESULTS

In 70 patients admitted to the intensive care unit with ADHF, serum sACE2 activity levels, echocardiographic data, and hemodynamic variables were collected within 12 hours of admission (n = 70) and 48-72 hours after intensive medical treatment (n = 57). The median [interquartile range] baseline and 48-72-hour serum sACE2 activity levels were 32 [23-43] ng/mL and 40 [28-60] ng/mL, respectively. Baseline serum sACE2 activity levels correlated with surrogate measures of right ventricular diastolic dysfunction, including right atrial volume index (RAVi; r = 0.31; P = .010), tricuspid E/A ratio (r = 0.39; P = .007), and B-type natriuretic peptide (r = 0.32; P = .008). However, there were no correlations between serum sACE2 and left ventricular systolic or diastolic dysfunction. After intensive medical therapy, a 50% increase in baseline serum sACE2 levels predicted a significant reduction in risk of death, cardiac transplantation, or ADHF rehospitalization, including after adjustment for baseline age, RAVi, and BNP levels (hazard ratio 0.35, 95% confidence interval 0.12-0.84; P = .018).

CONCLUSIONS

In patients admitted with ADHF, increasing serum sACE2 activity levels during intensive medical therapy predict improved outcomes independently from underlying cardiac indices.

Angiotensin 1–7 mediates renoprotection against diabetic nephropathy by reducing oxidative stress, inflammation, and lipotoxicity

The renin-angiotensin system, especially angiotensin II (ANG II), plays a key role in the development and progression of diabetic nephropathy. ANG 1–7 has counteracting effects on ANG II and is known to exert beneficial effects on diabetic nephropathy. We studied the mechanism of ANG 1–7-induced beneficial effects on diabetic nephropathy in db/db mice. We administered ANG 1–7 (0.5 mg·kg−1·day−1) or saline to 5-mo-old db/db mice for 28 days via implanted micro-osmotic pumps. ANG 1–7 treatment reduced kidney weight and ameliorated mesangial expansion and increased urinary albumin excretion, characteristic features of diabetic nephropathy, in db/db mice. ANG 1–7 decreased renal fibrosis in db/db mice, which correlated with dephosphorylation of the signal transducer and activator of transcription 3 (STAT3) pathway. ANG 1–7 treatment also suppressed the production of reactive oxygen species via attenuation of NADPH oxidase activity and reduced inflammation in perirenal adipose tissue. Furthermore, ANG 1–7 treatment decreased lipid accumulation in db/db kidneys, accompanied by increased expressions of renal adipose triglyceride lipase (ATGL). Alterations in ATGL expression correlated with increased SIRT1 expression and deacetylation of FOXO1. The upregulation of angiotensin-converting enzyme 2 levels in diabetic nephropathy was normalized by ANG 1–7. ANG 1–7 treatment exerts renoprotective effects on diabetic nephropathy, associated with reduction of oxidative stress, inflammation, fibrosis, and lipotoxicity. ANG 1–7 can represent a promising therapy for diabetic nephropathy.

Heterozygote loss of ACE2 is sufficient to increase the susceptibility to heart disease

Angiotensin-converting enzyme 2 (ACE2) metabolizes Ang II into Ang 1-7 thereby negatively regulating the renin-angiotensin system. However, heart disease in humans and in animal models is associated with only a partial loss of ACE2. ACE2 is an X-linked gene; and as such, we tested the clinical relevance of a partial loss of ACE2 by using female ACE2(+/+) (wildtype) and ACE2(+/-) (heterozygote) mice. Pressure overload in ACE2(+/-) mice resulted in greater LV dilation and worsening systolic and diastolic dysfunction. These changes were associated with increased myocardial fibrosis, hypertrophy, and upregulation of pathological gene expression. In response to Ang II infusion, there was increased NADPH oxidase activity and myocardial fibrosis resulting in the worsening of Ang II-induced diastolic dysfunction with a preserved systolic function. Ang II-mediated cellular effects in cultured adult ACE2(+/-) cardiomyocytes and cardiofibroblasts were exacerbated. Ang II-mediated pathological signaling worsened in ACE2(+/-) hearts characterized by an increase in the phosphorylation of ERK1/2 and JNK1/2 and STAT-3 pathways. The ACE2(+/-) mice showed an exacerbated pressor response with increased vascular fibrosis and stiffness. Vascular superoxide and nitrotyrosine levels were increased in ACE2(+/-) vessels consistent with increased vascular oxidative stress. These changes occurred with increased renal fibrosis and superoxide production. Partial heterozygote loss of ACE2 is sufficient to increase the susceptibility to heart disease secondary to pressure overload and Ang II infusion.

KEY MESSAGE

Heart disease in humans with idiopathic dilated cardiomyopathy is associated with a partial loss of ACE2. Heterozygote female ACE2 mutant mice showed enhanced susceptibility to pressure overload-induced heart disease. Heterozygote female ACE2 mutant mice showed enhanced susceptibility to Ang II-induced heart and vascular diseases. Partial loss of ACE2 is sufficient to enhance the susceptibility to heart disease.

The Renin-Angiotensin-aldosterone system in vascular inflammation and remodeling

The RAAS through its physiological effectors plays a key role in promoting and maintaining inflammation. Inflammation is an important mechanism in the development and progression of CVD such as hypertension and atherosclerosis. In addition to its main role in regulating blood pressure and its role in hypertension, RAAS has proinflammatory and profibrotic effects at cellular and molecular levels. Blocking RAAS provides beneficial effects for the treatment of cardiovascular and renal diseases. Evidence shows that inhibition of RAAS positively influences vascular remodeling thus improving CVD outcomes. The beneficial vascular effects of RAAS inhibition are likely due to decreasing vascular inflammation, oxidative stress, endothelial dysfunction, and positive effects on regeneration of endothelial progenitor cells. Inflammatory factors such as ICAM-1, VCAM-1, TNFα, IL-6, and CRP have key roles in mediating vascular inflammation and blocking RAAS negatively modulates the levels of these inflammatory molecules. Some of these inflammatory markers are clinically associated with CVD events. More studies are required to establish long-term effects of RAAS inhibition on vascular inflammation, vascular cells regeneration, and CVD clinical outcomes. This review presents important information on RAAS's role on vascular inflammation, vascular cells responses to RAAS, and inhibition of RAAS signaling in the context of vascular inflammation, vascular remodeling, and vascular inflammation-associated CVD. Nevertheless, the review also equates the need to rethink and rediscover new RAAS inhibitors.

ACE2 deficiency increases NADPH-mediated oxidative stress in the kidney

Abstract Angiotensin-converting enzyme 2 (ACE2) is highly expressed in the kidney and hydrolyzes angiotensin II (Ang II) to Ang(1-7). Since Ang II is a strong activator of oxidative stress, we reasoned that ACE2 could be involved in the regulation of renal oxidative stress by governing the levels of Ang II. We, therefore, assessed levels of oxidative stress in kidney cortex of ACE2 knockout and wild-type littermate mice under baseline conditions. We found multiple markers of increased oxidative stress in ACE2KO mice. NADPH oxidase activity was increased in kidney cortex from ACE2KO mice as compared to WT (227 ± 24% vs.100 ± 19%, P < 0.001). However, kidney catalase and superoxide dismutase activities were not different between groups. Exogenous Ang II was degraded less efficiently by kidneys from ACE2KO mice than WT mice, and administration of an AT1R blocker (losartan 30 mg/kg/day) resulted in normalization of NADPH oxidase activity in the ACE2KO. These findings suggest that an AT1R-dependent mechanism contributes to increased ROS observed in the ACE2KO. This study demonstrates that genetic deficiency of ACE2 activity in mice fosters oxidative stress in the kidney in the absence of overt hypertension and is associated with reduced kidney capacity to hydrolyze Ang II. ACE2KO mice serve as a novel in vivo model to examine the role of overactivity of NADPH oxidase in kidney function.

ACE2: angiotensin II/angiotensin-(1-7) balance in cardiac and renal injury

Our current recognition of the renin-angiotensin system is more convoluted than originally thought due to the discovery of multiple novel enzymes, peptides, and receptors inherent in this interactive biochemical cascade. Over the last decade, angiotensin-converting enzyme 2 (ACE2) has emerged as a key player in the pathophysiology of hypertension and cardiovascular and renal disease due to its pivotal role in metabolizing vasoconstrictive/hypertrophic/proliferative angiotensin II into favorable angiotensin-(1-7). This review addresses the considerable advancement in research on the role of tissue ACE2 in the development and progression of hypertension and cardiac and renal injury. We summarize the results from recent clinical and experimental studies suggesting that serum or urine soluble ACE2 may serve as a novel biomarker or independent risk factor relevant for diagnosis and prognosis of cardiorenal disease. We also review recent proceedings on novel therapeutic approaches to enhance ACE2/angiotensin-(1-7) axis.

Modulation of angiotensin II-induced inflammatory cytokines by the Epac1-Rap1A-NHE3 pathway: implications in renal tubular pathobiology

Besides the glomerulus, the tubulointerstitium is often concomitantly affected in certain diseases, e.g., diabetic nephropathy, and activation of the renin-angiotensin system, to a certain extent, worsens its outcome because of perturbations in hemodynamics and possibly tubuloglomerular feedback. Certain studies suggest that pathobiology of the tubulointerstitium is influenced by small GTPases, e.g., Rap1. We investigated the effect of ANG II on inflammatory cytokines, while at the same time focusing on upstream effector of Rap1, i.e., Epac1, and some of the downstream tubular transport molecules, i.e., Na/H exchanger 3 (NHE3). ANG II treatment of LLC-PK1 cells decreased Rap1a GTPase activity in a time- and dose-dependent manner. ANG II treatment led to an increased membrane translocation of NHE3, which was reduced with Epac1 and PKA activators. ANG II-induced NHE3 translocation was notably reduced with the transfection of Rap1a dominant positive mutants, i.e., Rap1a-G12V or Rap1a-T35A. Transfection of cells with dominant negative Rap1a mutants, i.e., Rap1a-S17A, or Epac1 mutant, i.e., EPAC-ΔcAMP, normalized ANG II-induced translocation of NHE3. In addition, ANG II treatment led to an increased expression of inflammatory cytokines, i.e., IL-1β, IL-6, IL-8, and TNF-α, which was reduced with Rap1a-G12V or Rap1a-T35A transfection, while it reverted to previous comparable levels following transfection of Rap1a-S17A or EPAC-ΔcAMP. ANG II-induced expression of cytokines was reduced with the treatment with NHE3 inhibitor S3226 or with Epac1 and PKA activators. These data suggest that this novel Epac1-Rap1a-NHE3 pathway conceivably modulates ANG II-induced expression of inflammatory cytokines, and this information may yield the impetus for developing strategies to reduce tubulointertstitial inflammation in various renal diseases.

Manipulating angiotensin metabolism with angiotensin converting enzyme 2 (ACE2) in heart failure

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Heart failure is increasing in prevalence associated with a huge economic burden.

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ACE2 is a negative regulator of the renin–angiotensin system.

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Elevated ACE2 activity is a biomarker in heart failure.

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Enhancing ACE2 action may have unique therapeutic effects in patients with heart failure.

Angiotensin converting enzyme 2 (ACE2), is a monocarboxypeptidase which metabolizes several peptides including the degradation of Ang II, a peptide with vasoconstrictive/proliferative/effects, to generate Ang 1–7, which acting through its receptor Mas exerts vasodilatory/anti-proliferative actions. The classical pathway of the RAS involving the ACE-Ang II-AT₁ receptor axis is antagonized by the second arm constituted by the ACE2-Ang 1–7/Mas receptor axis. Loss of ACE2 enhances the adverse pathological remodeling susceptibility to pressure-overload and myocardial infarction. Human recombinant ACE2 is also a negative regulator of Ang II-induced myocardial hypertrophy, fibrosis and diastolic dysfunction and suppresses pressure-overload induced heart failure. Due to its characteristics, the ACE2-Ang 1–7/Mas axis may represent new possibilities for developing novel therapeutic strategies for the treatment of heart failure. Human recombinant ACE2 has been safely administered to healthy human volunteers intravenously resulting in sustained lowering of plasma Ang II levels. In this review, we will summarize the beneficial effects of ACE2 in heart disease and the potential use of human recombinant ACE2 as a novel therapy for heart failure.

Low serum sodium is associated with protein energy wasting and increased interdialytic weight gain in haemodialysis patients

Background

Low serum sodium (Na) has been associated with decreased body mass index and increased cardiovascular mortality in haemodialysis (HD) patients. We examined the relationship between serum Na and selected nutritional parameters of protein energy wasting that are not affected from the hydration status in a cohort of HD patients.

Methods

Triceps skinfold thickness (TSF), mid-arm circumference (MAC), mid-arm muscle circumference (MAMC), handgrip strength (HGS) and subjective global assessment (SGA) were assessed in maintenance HD patients using standard techniques. MAMC was calculated with the formula MAMC (cm) = MAC (cm) −3.142 × TSF cm. Pre-dialysis serum Na values from routine monthly laboratory measurements were averaged for the last 6 months prior to the nutritional assessment.

Results

Altogether 172 patients with anthropometric data were included in the final analysis. Mean age was 66 ± 14, females 62 (36%) and diabetics 48 (28.9%). Patients with pre-dialysis serum Na below the mean value (136.2 mEq/L) had lower MAMC, HGS, SGA scores and albumin levels (23.50 ± 3.16 cm versus 24.58 ± 3.71 cm, P = 0.048; 21.7 ± 13.6 kg versus 28.0 ± 12.4 kg, P = 0.030; 5.1 ± 1.2 versus 5.7 ± 1.0, P = 0.012 and 31.65 ± 4.73 mg/L versus 32.25 ± 3.91 mg/L, P = 0.022, respectively) and higher interdialytic weight gains. Pre-dialysis serum Na correlated positively with MAMC, handgrip and SGA (Pearson's correlation r = 0.165, P = 0.031, r = 0.237, P = 0.022 and r = 0.195, P = 0.011, respectively).

Conclusion

This study demonstrates that low serum sodium is associated with protein energy wasting and increased interdialytic weight gain in HD patients.

Angiotensin-converting enzyme (ACE and ACE2) imbalance correlates with the severity of cerulein-induced acute pancreatitis in mice

Angiotensin-converting enzyme (ACE) and its effector peptide angiotensin II (Ang II) have been implicated in the pathogenesis of pancreatitis. Angiotensin-converting enzyme 2 (ACE2) degrades Ang II to angiotensin-(1-7) [Ang-(1-7)] and has recently been described to have an antagonistic effect on ACE signalling. However, the specific underlying role of ACE2 in the pathogenesis of severe acute pancreatitis (SAP) is unclear. In the present study, the local imbalance of ACE and ACE2, as well as Ang II and Ang-(1-7) expression, was compared in wild-type (WT) and ACE2 knock-out (KO) or ACE2 transgenic (TG) mice subjected to cerulein-induced SAP. Serum amylase, tumour necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-10 levels and histological morphometry were used to determine the severity of pancreatitis. In WT mice, pancreatic ACE and Ang II and serum Ang II expression increased (P < 0.05), while pancreatic ACE2 and Ang-(1-7) and serum Ang-(1-7) levels were also significantly elevated (P < 0.05) from 2 to 72 h after the onset of SAP. However, the ratio of pancreatic ACE2 to ACE expression was significantly reduced (from 1.46 ± 0.09 to 0.27 ± 0.05, P < 0.001) and paralleled the severity of pancreatitis. The Ace2 KO mice exhibited increased levels of tumour necrosis factor-α, IL-1β, IL-6, multifocal coagulative necrosis and inflammatory infiltrate, and lower levels of serum IL-10 and pancreatic Ang-(1-7) (4.70 ± 2.13 versus 10.87 ± 2.51, P < 0.001) compared with cerulein-treated WT mice at the same time point. Conversely, Ace2 TG mice with normal ACE expression were more resistant to SAP challenge as evidenced by a decreased inflammatory response, attenuated pathological changes and increased survival rates. These data suggest that the ACE2-ACE imbalance plays an important role in the pathogenesis of SAP and that pancreatic ACE2 is an important factor in determining the severity of SAP.

Update on the Angiotensin converting enzyme 2-Angiotensin (1-7)-MAS receptor axis: fetal programing, sex differences, and intracellular pathways

The renin-angiotensin-system (RAS) constitutes an important hormonal system in the physiological regulation of blood pressure. Indeed, dysregulation of the RAS may lead to the development of cardiovascular pathologies including kidney injury. Moreover, the blockade of this system by the inhibition of angiotensin converting enzyme (ACE) or antagonism of the angiotensin type 1 receptor (AT1R) constitutes an effective therapeutic regimen. It is now apparent with the identification of multiple components of the RAS that the system is comprised of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS can be defined as the ACE-Ang II-AT1R axis that promotes vasoconstriction, sodium retention, and other mechanisms to maintain blood pressure, as well as increased oxidative stress, fibrosis, cellular growth, and inflammation in pathological conditions. In contrast, the non-classical RAS composed of the ACE2-Ang-(1-7)-Mas receptor axis generally opposes the actions of a stimulated Ang II-AT1R axis through an increase in nitric oxide and prostaglandins and mediates vasodilation, natriuresis, diuresis, and oxidative stress. Thus, a reduced tone of the Ang-(1-7) system may contribute to these pathologies as well. Moreover, the non-classical RAS components may contribute to the effects of therapeutic blockade of the classical system to reduce blood pressure and attenuate various indices of renal injury. The review considers recent studies on the ACE2-Ang-(1-7)-Mas receptor axis regarding the precursor for Ang-(1-7), the intracellular expression and sex differences of this system, as well as an emerging role of the Ang1-(1-7) pathway in fetal programing events and cardiovascular dysfunction.

The cooperative roles of inflammation and oxidative stress in the pathogenesis of hypertension

SIGNIFICANCE

Innate and adaptive immunity play fundamental roles in the development of hypertension and its complications. As effectors of the cell-mediated immune response, myeloid cells and T lymphocytes protect the host organism from infection by attacking foreign intruders with bursts of reactive oxygen species (ROS).

RECENT ADVANCES

While these ROS may help to preserve the vascular tone and thereby protect against circulatory collapse in the face of overwhelming infection, aberrant elaboration of ROS triggered by immune cells in the absence of a hemodynamic insult can lead to pathologic increases in blood pressure. Conversely, misdirected oxidative stress in cardiovascular control organs, including the vasculature, the kidney, and the nervous system potentiates inflammatory responses, augmenting blood pressure elevation and inciting target organ damage.

CRITICAL ISSUES

Inflammation and oxidative stress thereby act as cooperative and synergistic partners in the pathogenesis of hypertension.

FUTURE DIRECTIONS

Pharmacologic interventions for hypertensive patients will need to exploit this robust bidirectional relationship between ROS generation and immune activation in cardiovascular control organs to maximize therapeutic benefit, while limiting off-target side effects.

The role of renin-angiotensin system in cellular differentiation: implications in pancreatic islet cell development and islet transplantation

In addition to the well-characterized circulating renin-angiotensin system (RAS), local RAS has been identified recently in diverse tissues and organs. The presence of key components of the RAS in local tissues is important for our understanding of the patho-physiological mechanism(s) of several metabolic diseases, and may serve as a major therapeutic target for cardiometabolic syndromes. Locally generated and physiologically active RAS components have functions that are distinct from the classical vasoconstriction and fluid homeostasis actions of systemic RAS and cater specifically for local tissues. Local RAS can affect islet-cell function and structure in the adult pancreas as well as proliferation and differentiation of pancreatic stem/progenitor cells during development. Differentiation of stem/progenitor cells into insulin-expressing cells suitable for therapeutic transplantation offers a desperately needed new approach for replacement of glucose-responsive insulin producing cells in diabetic patients. Given that the generation of functional and transplantable islet cells has proven to be difficult, elucidation of RAS involvement in cellular regeneration and differentiation may propel pancreatic stem/progenitor cell development and thus β-cell regeneration forward. This review provides a critical appraisal of current research progress on the role of the RAS, including the newly characterized ACE2/Ang-(1-7)/Mas axis in the proliferation, differentiation, and maturation of pancreatic stem/progenitor cells. It is thus plausible to propose that the AT1 stimulation could be a repair mechanism involving the AT2R as well as the ACE2/Ang-(1-7)/Mas axis in directing β-cell development in diabetic patients using genetic and pharmaceutical manipulation of the RAS.

Cardiac protective effects of irbesartan via the PPAR-gamma signaling pathway in angiotensin-converting enzyme 2-deficient mice

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2), a monocarboxypeptidase which metabolizes angiotensin II (Ang II) to generate Ang-(1-7), has been shown to prevent cardiac hypertrophy and injury but the mechanism remains elusive. Irbesartan has the dual actions of angiotensin receptor blockade and peroxisome proliferator-activated receptor-γ (PPARγ) activation. We hypothesized that irbesartan would exert its protective effects on ACE2 deficiency-mediated myocardial fibrosis and cardiac injury via the PPARγ signaling.

METHODS

10-week-old ACE2 knockout (ACE2KO; Ace2(-/y)) mice received daily with irbesartan (50 mg/kg) or saline for 2 weeks. The wild-type mice (Ace2(+/y)) were used to the normal controls. We examined changes in myocardial ultrastructure, fibrosis-related genes and pathological signaling by real-time PCR gene array, Western blotting, Masson trichrome staining and transmission electron microscope analyses, respectively.

RESULTS

Compared with the Ace2(+/y) mice, cardiac expression of PPARα and PPARγ were reduced in Ace2(-/y) mice and the myocardial collagen volume fraction (CVF) and expression of fibrosis-related genes were increased, including transforming growth factor-β1 (TGFβ1), connective tissue growth factor (CTGF), collagen I and collagen III. Moreover, ACE2 deficiency triggered cardiac hypertrophy, increased myocardial fibrosis and adverse ultrastructure injury in ACE2KO hearts with higher levels of atrial natriuretic factor (ANF) and phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), without affecting cardiac systolic function. Intriguingly, treatment with irbesartan significantly reversed ACE2 deficiency-mediated pathological hypertrophy and myocardial fibrosis in Ace2(-/y) mice linked with enhancement of plasma Ang-(1-7) level and downregulation of AT1 receptor in heart. Consistent with attenuation of myocardial fibrosis and ultrastructure injury, the myocardial CVF and levels of ANF, TGFβ1, CTGF, collagen I, collagen III and phosphorylated ERK1/2 were lower, and expression of PPARγ was higher in ACE2KO mice in response to irbesartan treatment, without affecting cardiac expression of PPARα, PPARδ, β-myosin heavy chain, TGFβ2 and fibronectin.

CONCLUSIONS

We conclude that irbesartan prevents ACE2 deficiency-mediated pathological hypertrophy and myocardial fibrosis in ACE2 mutant mice via activation of the PPARγ signaling and suppression of the TGFβ-CTGF-ERK signaling, resulting in attenuation of myocardial injury. Drugs targeting ACE2 and PPARγ represent potential candidates to prevent and treat myocardial injury and related cardiac disorders.

Pharmacokinetics and pharmacodynamics of recombinant human angiotensin-converting enzyme 2 in healthy human subjects

BACKGROUND AND OBJECTIVES

Angiotensin-converting enzyme 2 (ACE2) converts angiotensin II (Ang1-8) to angiotensin 1-7 (Ang1-7), a functional antagonist of Ang1-8, with vasodilatory, antiproliferative, antiangiogenic, and anti-inflammatory properties. In conditions with an unbalanced renin-angiotensin-aldosterone system with elevated Ang1-8, administration of ACE2 has shown promising effects in a variety of animal models. Enhancing ACE2 activity by exogenous administration of ACE2 might also be beneficial in human diseases with pathologically elevated Ang1-8. As a first step we performed a first-in-man study to determine pharmacokinetics, pharmacodynamics, safety, and tolerability of recombinant ACE2 in healthy volunteers.

METHODS

Recombinant human ACE2 (rhACE2) was administered intravenously to healthy human subjects in a randomized, double-blind, placebo-controlled, single-dose, dose-escalation study followed by an open-label multiple-dose study. ACE2 concentrations were determined by quantifying ACE2 activity and ACE2 content in plasma samples. Concentrations of the angiotensin system effector peptides Ang1-8, Ang1-7, and Ang1-5 were determined using a liquid chromatography-tandem mass spectrometry method.

RESULTS

Single rhACE2 doses of 100-1,200 μg/kg caused a dose-dependent increase of systemic exposure with biphasic elimination and a dose-independent terminal half-life of 10 h. In all single-dose cohorts, Ang1-8 decreased within 30 min postinfusion, angiotensin 1-7 (Ang1-7) either increased (100 and 200 μg/kg doses), decreased, or remained unchanged (400-1,200 μg/kg doses), whereas angiotensin 1-5 (Ang1-5) transiently increased for all doses investigated. With the exception of the lowest rhACE2 dose, the decrease in Ang1-8 levels lasted for at least 24 h. Repeated dosing (400 μg/kg for 3 or 6 days) caused only minimal accumulation of ACE2, and Ang1-8 levels were suppressed over the whole application period.

CONCLUSIONS

Administration of rhACE2 was well tolerated by healthy human subjects. Exposure was dose dependent with a dose-independent terminal elimination half-life in the range of 10 h. Despite marked changes in angiotensin system peptide concentrations, cardiovascular effects were absent, suggesting the presence of effective compensatory mechanisms in healthy volunteers.

ACE2, angiotensin-(1–7), and Mas: the other side of the coin

The renin–angiotensin system (RAS) has recently been extended by the addition of a novel axis consisting of the angiotensin-converting enzyme 2 (ACE2), the heptapeptide angiotensin (1–7) (Ang-(1–7)), and the G protein-coupled receptor Mas. ACE2 converts the vasoconstrictive and pro-oxidative peptide angiotensin II (Ang II) into Ang-(1–7) which exerts vasodilatory and antioxidative effects via its receptor Mas. Thereby, ACE2 regulates the local actions of the RAS in cardiovascular tissues and the ACE2/Ang-(1–7)/Mas axis exerts protective actions in hypertension, diabetes, and other cardiovascular disorders. Consequently, this novel RAS axis represents a promising therapeutic target for cardiovascular and metabolic diseases.

TIMP3 is the primary TIMP to regulate agonist-induced vascular remodelling and hypertension

AIMS

Hypertension is accompanied by structural remodelling of vascular extracellular matrix (ECM). Tissue inhibitor of metalloproteinases (TIMPs) inhibits matrix metalloproteinases (MMPs) that degrade the matrix structural proteins. In response to a hypertensive stimulus, the balance between MMPs and TIMPs is altered. We examined the role of TIMPs in agonist-induced hypertension.

METHODS AND RESULTS

We subjected TIMP-knockout mice to angiotensin II (Ang II) infusion, and found that Ang-II-induced hypertension in TIMP1(-/-), TIMP2(-/-), and TIMP4(-/-) mice was comparable to wild-type (WT) mice, but significantly suppressed in TIMP3(-/-) mice. Ex vivo pressure myography analyses on carotid and mesenteric arteries revealed that Ang-II-infused TIMP3(-/-) arteries were more distensible with impaired elastic recoil compared with the WT group. The acute response to vasoconstriction and vasodilation was intact in TIMP3(-/-) mesenteric and carotid arteries. Mesenteric arteries from TIMP3(-/-)-Ang II mice exhibited a reduced media-to-lumen ratio, suppressed collagen and elastin levels, elevated elastase and gelatinase proteolytic activities compared with WT-Ang II. TIMP3(-/-)-Ang II carotid arteries also showed adverse structural remodelling. Treatment of mice with doxycycline, a matrix metalloproteinase inhibitor, improved matrix integrity in mesenteric and carotid arteries in TIMP3(-/-)-Ang II and differentially regulated elastin and collagen levels in WT-Ang II vs. TIMP3(-/-)-Ang II.

CONCLUSION

Our study demonstrates a critical role for TIMP3, among all TIMPs, is preserving arterial ECM in response to Ang II. It is critical to acknowledge that the suppressed Ang-II-induced hypertension in TIMP3(-/-) mice is not a protective mechanism but owing to adverse remodelling in arterial matrix.

Angiotensin-converting enzyme 2 activation improves endothelial function

Diminished release and function of endothelium-derived nitric oxide coupled with increases in reactive oxygen species production is critical in endothelial dysfunction. Recent evidences have shown that activation of the protective axis of the renin-angiotensin system composed by angiotensin-converting enzyme 2, angiotensin-(1-7), and Mas receptor promotes many beneficial vascular effects. This has led us to postulate that activation of intrinsic angiotensin-converting enzyme 2 would improve endothelial function by decreasing the reactive oxygen species production. In the present study, we tested 1-[[2-(dimetilamino)etil]amino]-4-(hidroximetil)-7-[[(4-metilfenil)sulfonil]oxi]-9H-xantona-9 (XNT), a small molecule angiotensin-converting enzyme 2 activator, on endothelial function to validate this hypothesis. In vivo treatment with XNT (1 mg/kg per day for 4 weeks) improved the endothelial function of spontaneously hypertensive rats and of streptozotocin-induced diabetic rats when evaluated through the vasorelaxant responses to acetylcholine/sodium nitroprusside. Acute in vitro incubation with XNT caused endothelial-dependent vasorelaxation in aortic rings of rats. This vasorelaxation effect was attenuated by the Mas antagonist D-pro7-Ang-(1-7), and it was reduced in Mas knockout mice. These effects were associated with reduction in reactive oxygen species production. In addition, Ang II-induced reactive oxygen species production in human aortic endothelial cells was attenuated by preincubation with XNT. These results showed that chronic XNT administration improves the endothelial function of hypertensive and diabetic rat vessels by attenuation of the oxidative stress. Moreover, XNT elicits an endothelial-dependent vasorelaxation response, which was mediated by Mas. Thus, this study indicated that angiotensin-converting enzyme 2 activation promotes beneficial effects on the endothelial function and it is a potential target for treating cardiovascular disease.

Overexpression of catalase prevents hypertension and tubulointerstitial fibrosis and normalization of renal angiotensin-converting enzyme-2 expression in Akita mice

We investigated the relationship among oxidative stress, hypertension, renal injury, and angiotensin-converting enzyme-2 (ACE2) expression in type 1 diabetic Akita mice. Blood glucose, blood pressure, and albuminuria were monitored for up to 5 mo in adult male Akita and Akita catalase (Cat) transgenic (Tg) mice specifically overexpressing Cat, a key antioxidant enzyme in their renal proximal tubular cells (RPTCs). Same-age non-Akita littermates and Cat-Tg mice served as controls. In separate studies, adult male Akita mice (14 wk) were treated with ANG 1-7 (500 μg·kg⁻¹·day⁻¹ sc) ± A-779, an antagonist of the Mas receptor (10 mg·kg⁻¹·day⁻¹ sc), and euthanized at the age of 18 wk. The left kidneys were processed for histology and apoptosis studies. Renal proximal tubules were isolated from the right kidneys to assess protein and gene expression. Urinary angiotensinogen (AGT), angiotensin II (ANG II), and ANG 1-7 were quantified by specific ELISAs. Overexpression of Cat attenuated renal oxidative stress; prevented hypertension; normalized RPTC ACE2 expression and urinary ANG 1-7 levels (both were low in Akita mice); ameliorated glomerular filtration rate, albuminuria, kidney hypertrophy, tubulointerstitial fibrosis, and tubular apoptosis; and suppressed profibrotic and proapoptotic gene expression in RPTCs of Akita Cat-Tg mice compared with Akita mice. Furthermore, daily administration of ANG 1-7 normalized systemic hypertension in Akita mice, which was reversed by A-779. These data demonstrate that Cat overexpression prevents hypertension and progression of nephropathy and highlight the importance of intrarenal oxidative stress and ACE2 expression contributing to hypertension and renal injury in diabetes.

Adiponectin attenuates angiotensin II-induced oxidative stress in renal tubular cells through AMPK and cAMP-Epac signal transduction pathways

Obesity is a risk factor for chronic kidney disease (CKD) progression. Circulating levels of adiponectin, an adipokine, decrease with obesity and play a protective role in the cardiovascular system. We hypothesized that adiponectin might also protect the kidney. Because activation of the renin-angiotensin system (RAS) is a contributor to CKD progression, we tested our hypothesis by studying the interactions between adiponectin and angiotensin II (ANG II) in renal tubular cells. Primary human renal proximal tubule cells expressed both adiponectin receptor 1 and 2 (adipoR1 and R2). ANG II-induced NADPH oxidase activation and oxidative stress were attenuated by adiponectin and dependent on adipoR1. Activation of AMPK with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) mimicked, while inhibition of AMPK with compound C abrogated, the effect of adiponectin on ANG II-induced activation of NADPH oxidase. Similarly, the effect of adiponectin was recapitulated by the stable cAMP analogs 4-chlorophenylthio (pCPT)-cAMP and dibutyryl (db)-cAMP and blocked by the adenylate cyclase inhibitor SQ22536. Adiponectin did not activate PKA in renal tubular cells, and the specific PKA inhibitor myristoylated PKI (14-22) amide failed to block the inhibitory effect of adiponectin on ANG II-induced NADPH oxidase activation. In contrast, the specific Epac activator 8-(4-chlorophenylthio)-2'-O-methyl (8-CPT-2-O-Me)-cAMP blocked ANG II-induced activation of NADPH oxidase, an effect that was reversed by coincubation with the AMPK inhibitor compound C. Finally, adiponectin attenuated ANG II-induced NF-κB activation and fibronectin protein expression. These in vitro findings support the hypothesis that adiponectin may attenuate the deleterious effects of ANG II in the kidney and play a protective role in CKD.

Effects of felodipine combined with puerarin on ACE2-Ang (1-7)-Mas axis in renovascular hypertensive rat

This study aimed to investigate the effect of combination of felodipine+puerarin on ACE2-Ang (1-7)-Mas axis, and to explore the protective effect of the combination against kidney in renovascular hypertensive rats. Goldblatt rats were randomly divided into 5 groups as follows: 4 groups which were treated with felodipine (Felo), puerarin (Pue), Felo+Pue, and Felo+captopril (Cap), respectively, and a control group of animals that were administrated with distilled water. Contents of Ang II and Ang (1-7) in renal tissues were determined by ELISA kit. The mRNA expression of ACE2/Mas and ACE/AT1 in kidneys was analyzed by RT-PCR. After 8weeks of treatment, compared with Goldblatt group, Felo+Pue reduced SBP, DBP and HR (p<0.01 or p<0.05), ameliorated renal interstitial fibrosis, decreased the level of Ang II and increased that of Ang (1-7), upregulated mRNA expression of ACE2 and Mas, decreased that of ACE and AT1, and downregulated protein expression of TGF-β1 in kidneys (p<0.01). Compared with Felo group, Felo+Pue decreased DBP and HR more markedly, attenuated fibrosis, decreased Ang II levels and increased those of Ang (1-7), upregulated mRNA expression of ACE2 in bilateral kidneys and that of Mas in ischemic kidney, downregulated that of ACE in bilateral kidneys and that of AT1 in ischemic kidney, and decreased expression of TGF-β1 protein significantly. In a word, a combination of Felo+Pue has a more efficient therapeutic effect on DBP and HR, and contributes to a better protection against renal interstitial fibrosis.

Identification of prolyl carboxypeptidase as an alternative enzyme for processing of renal angiotensin II using mass spectrometry

Angiotensin-converting enzyme 2 (ACE2) catalyzes conversion of ANG II to ANG-(1-7). The present study uses newly established proteomic approaches and genetic mouse models to examine the contribution of alternative renal peptidases to ACE2-independent formation of ANG-(1-7). In situ and in vitro mass spectrometric characterization showed that substrate concentration and pH control renal ANG II processing. At pH ≥6, ANG-(1-7) formation was significantly reduced in ACE2 knockout (KO) mice. However, at pH <6, formation of ANG-(1-7) in ACE2 KO mice was similar to that in wild-type (WT) mice, suggesting alternative peptidases for renal ANG II processing. Furthermore, the dual prolyl carboxypeptidase (PCP)-prolyl endopeptidase (PEP) inhibitor Z-prolyl-prolinal reduced ANG-(1-7) formation in ACE2 KO mice, while the ACE2 inhibitor MLN-4760 had no effect. Unlike the ACE2 KO mice, ANG-(1-7) formation from ANG II in PEP KO mice was not different from that in WT mice at any tested pH. However, at pH 5, this reaction was significantly reduced in kidneys and urine of PCP-depleted mice. In conclusion, results suggest that ACE2 metabolizes ANG II in the kidney at neutral and basic pH, while PCP catalyzes the same reaction at acidic pH. This is the first report demonstrating that renal ANG-(1-7) formation from ANG II is independent of ACE2. Elucidation of ACE2-independent ANG-(1-7) production pathways may have clinically important implications in patients with metabolic and renal disease.

Interaction between TGF-β and ACE2-Ang-(1-7)-Mas pathway in high glucose-cultured NRK-52E cells

Transforming growth factor-β (TGF-β) is pivotal in diabetic nephropathy (DN). Angiotensin converting enzyme-2 (ACE2) converts angiotensin II (Ang II) to angiotensin 1-7 (Ang-(1-7)), which binds to Mas. Proximal tubular ACE2 is decreased in DN. ACE2 deficiency exacerbates whereas ACE2 overexpression attenuates DN. Thus, we investigated the mechanism of high glucose-decreased ACE2 in terms of the interaction between TGF-β and ACE2-Ang-(1-7)-Mas in NRK-52E cells. We found that high glucose increased TGF-β1. SB431542 attenuated high glucose-inhibited ACE2 and Mas and Ang-(1-7) conversion from Ang II while attenuating high glucose-induced fibronectin. TGF-β1 also decreased ACE2 and Mas and Ang-(1-7) conversion from Ang II. A779 attenuated Ang-(1-7)-decreased TGF-β1 and Ang-(1-7)-activated JAK2-STAT3. Moreover, A779, LY294002 and AG490 attenuated Ang-(1-7)-inhibited TGF-β1. The combination of Ang-(1-7) and Mas attenuated TGF-β1 (but not high glucose)-induced fibronectin. Thus, high glucose decreases ACE2 via TGF-βR in NRK-52E cells. Additionally, there is a negative feedback function between TGF-β and ACE2, and the combined inhibition of TGF-β and activation of the ACE2-Ang-(1-7)-Mas may be useful for treating diabetic renal fibrosis.