Role of angiotensin-converting enzyme 2 in cardiac hypertrophy induced by nitric oxide synthase inhibition

Limonin ameliorates cardiovascular dysfunction and remodeling in hypertensive rats

AIMS

Limonin is a tetracyclic triterpenoid isolated from citrus fruits. Here, the effects of limonin on cardiovascular abnormalities in nitric oxide-deficient rats induced by N^ω-Nitrol-arginine methyl ester (L-NAME) were explored.

MAIN METHODS

Male Sprague Dawley rats were given L-NAME (40 mg/kg, drinking water) for 3 weeks and then treated daily with polyethylene glycol (vehicle), limonin (50 or 100 mg/kg) or telmisartan (10 mg/kg) for two weeks.

KEY FINDINGS

Limonin (100 mg/kg) markedly reduced L-NAME-induced hypertension, cardiovascular dysfunction and remodeling in rats (P < 0.05). Increases in systemic angiotensin-converting enzyme (ACE) activity and angiotensin II (Ang II) and a reduction in circulating ACE2 were restored in hypertensive rats treated with limonin (P < 0.05). Reductions in antioxidant enzymes and nitric oxide metabolites (NOx) and increases in oxidative stress components induced by L-NAME were relieved by limonin treatment (P < 0.05). Limonin suppressed the increased expression of tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 in cardiac tissue and circulating TNF-α in rats that received L-NAME (P < 0.05). Changes in Ang II receptor type I (AT1R), Mas receptor (MasR), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-ĸB) and NADPH oxidase subunit 2 (gp91^phox) protein expression in cardiac and aortic tissue were normalized by limonin (P < 0.05).

SIGNIFICANCE

In conclusion, limonin ameliorated L-NAME-induced hypertension, cardiovascular dysfunction and remodeling in rats. These effects were relevant to restorations of the renin-angiotensin system, oxidative stress and inflammation in NO-deficient rats. The molecular mechanisms are associated with the modulation of AT1R, MasR, NF-ĸB and gp91^phox protein expression in cardiac and aortic tissue.

Overexpression of angiotensin-converting enzyme 2 by renin-angiotensin system inhibitors. Truth or myth? A systematic review of animal studies

Angiotensin-converting enzyme 2 (ACE2) protects against organ damage in hypertension and cardiovascular diseases by counter regulating the renin-angiotensin system (RAS). ACE2 is also the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Based on the claim that RAS inhibitors (RASIs) cause ACE2 overexpression in some animal experiments, concerns have arisen that RASIs may aggravate SARS-CoV-2 infection and coronavirus disease-2019 severity in RASI-treated patients. To achieve a comprehensive review, a systematic search of MEDLINE/PubMed was conducted regarding the effects of RASIs on tissue ACE2 mRNA/protein expression in healthy animals and animal models of human diseases. We identified 88 eligible articles involving 168 experiments in the heart, kidneys, lungs, and other organs. Three of 38 experiments involving healthy animals showed ACE2 expression greater than twice that of the control (overexpression). Among 102 disease models (130 experiments), baseline ACE2 was overexpressed in 16 models (18 experiments) and less than half the control level (repression) in 28 models (40 experiments). In 72 experiments, RASIs did not change ACE2 levels from the baseline levels of disease models. RASIs caused ACE2 overexpression compared to control levels in seven experiments, some of which were unsupported by other experiments under similar conditions. In 36 experiments, RASIs reversed or prevented disease-induced ACE2 repression, yielding no or marginal changes. Therefore, ACE2 overexpression appears to be a rare rather than common consequence of RASI treatment in healthy animals and disease models. Future studies should clarify the pathophysiological significance of RASI-induced reversal or prevention of ACE2 repression in disease models.

A comprehensive guide to the pharmacologic regulation of angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 entry receptor

The recent emergence of coronavirus disease-2019 (COVID-19) as a global pandemic has prompted scientists to address an urgent need for defining mechanisms of disease pathology and treatment. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19, employs angiotensin converting enzyme 2 (ACE2) as its primary target for cell surface attachment and likely entry into the host cell. Thus, understanding factors that may regulate the expression and function of ACE2 in the healthy and diseased body is critical for clinical intervention. Over 66% of all adults in the United States are currently using a prescription drug and while earlier findings have focused on possible upregulation of ACE2 expression through the use of renin angiotensin system (RAS) inhibitors, mounting evidence suggests that various other widely administered drugs used in the treatment of hypertension, heart failure, diabetes mellitus, hyperlipidemias, coagulation disorders, and pulmonary disease may also present a varied risk for COVID-19. Specifically, we summarize mechanisms on how heparin, statins, steroids and phytochemicals, besides their established therapeutic effects, may also interfere with SARS-CoV-2 viral entry into cells. We also describe evidence on the effect of several vitamins, phytochemicals, and naturally occurring compounds on ACE2 expression and activity in various tissues and disease models. This comprehensive review aims to provide a timely compendium on the potential impact of commonly prescribed drugs and pharmacologically active compounds on COVID-19 pathology and risk through regulation of ACE2 and RAS signaling.

A Low-Sodium Diet Boosts Ang (1-7) Production and NO-cGMP Bioavailability to Reduce Edema and Enhance Survival in Experimental Heart Failure

Sodium restriction is often recommended in heart failure (HF) to block symptomatic edema, despite limited evidence for benefit. However, a low-sodium diet (LSD) activates the classical renin-angiotensin-aldosterone system (RAAS), which may adversely affect HF progression and mortality in patients with dilated cardiomyopathy (DCM). We performed a randomized, blinded pre-clinical trial to compare the effects of a normal (human-equivalent) sodium diet and a LSD on HF progression in a normotensive model of DCM in mice that has translational relevance to human HF. The LSD reduced HF progression by suppressing the development of pleural effusions (p < 0.01), blocking pathological increases in systemic extracellular water (p < 0.001) and prolonging median survival (15%, p < 0.01). The LSD activated the classical RAAS by increasing plasma renin activity, angiotensin II and aldosterone levels. However, the LSD also significantly up-elevated the counter-regulatory RAAS by boosting plasma angiotensin converting enzyme 2 (ACE2) and angiotensin (1-7) levels, promoting nitric oxide bioavailability and stimulating 3'-5'-cyclic guanosine monophosphate (cGMP) production. Plasma HF biomarkers associated with poor outcomes, such as B-type natriuretic peptide and neprilysin were decreased by a LSD. Cardiac systolic function, blood pressure and renal function were not affected. Although a LSD activates the classical RAAS system, we conclude that the LSD delayed HF progression and mortality in experimental DCM, in part through protective stimulation of the counter-regulatory RAAS to increase plasma ACE2 and angiotensin (1-7) levels, nitric oxide bioavailability and cGMP production.

Targeting the renin-angiotensin-aldosterone system in fibrosis

Fibrosis is characterized by excessive deposition of extracellular matrix components such as collagen in tissues or organs. Fibrosis can develop in the heart, kidneys, liver, skin or any other body organ in response to injury or maladaptive reparative processes, reducing overall function and leading eventually to organ failure. A variety of cellular and molecular signaling mechanisms are involved in the pathogenesis of fibrosis. The renin-angiotensin-aldosterone system (RAAS) interacts with the potent Transforming Growth Factor β (TGFβ) pro-fibrotic pathway to mediate fibrosis in many cell and tissue types. RAAS consists of both classical and alternative pathways, which act to potentiate or antagonize fibrotic signaling mechanisms, respectively. This review provides an overview of recent literature describing the roles of RAAS in the pathogenesis of fibrosis, particularly in the liver, heart, kidney and skin, and with a focus on RAAS interactions with TGFβ signaling. Targeting RAAS to combat fibrosis represents a promising therapeutic approach, particularly given the lack of strategies for treating fibrosis as its own entity, thus animal and clinical studies to examine the impact of natural and synthetic substances to alter RAAS signaling as a means to treat fibrosis are reviewed as well.

Bilateral sympathetic stellate ganglionectomy attenuates myocardial remodelling and fibrosis in a rat model of chronic volume overload

Reducing sympathetic neurohormone expression is a key therapeutic option in attenuating cardiac remodelling. Present study tested the feasibility of attenuating cardiac remodelling through reducing sympathetic neurohormone level by partial cardiac sympathetic denervation in a rat model of chronic volume overload. Male Sprague‐Dawley rats were randomized into sham group (S, n = 7), aortocaval fistula group (AV, n = 7), and aortocaval fistula with bilateral sympathetic stellate ganglionectomy group (AD, n = 8). After 12 weeks, myocardial protein expression of sympathetic neurohormones, including tyrosine hydroxylase, neuropeptide Y, growth associated protein 43, and protein gene product 9.5, were significantly up‐regulated in AV group compared to S group, and down‐regulated in AD group. Cardiac remodelling was aggravated in AV group compared to S group and attenuated in AD group. The myocardial deposition of extracellular matrix, including collagen I and III, was enhanced in AV group, which was reduced in AD group. Myocardial angiotensin II and aldosterone expressions were significantly up‐regulated in AV group and down‐regulated in AD group. Our results show that bilateral sympathetic stellate ganglionectomy could attenuate cardiac remodelling and fibrosis by down‐regulating sympathetic neurohormones expression in this rat model of chronic volume overload.

Inhibition on angiotensin-converting enzyme exerts beneficial effects on trabecular bone in orchidectomized mice

BACKGROUND

This study aimed to study the osteo-preservative effects of captopril, an inhibitor on angiotensin-converting enzyme (ACE), on bone mass, micro-architecture and histomorphology as well as the modulation of captopril on skeletal renin-angiotensin system (RAS) and regulators for bone metabolism in mice with bilateral orchidectomy.

METHODS

The orchidectomized (ORX) mice were orally administered with vehicle or captopril at low dose (10mg/kg) and high dose (50mg/kg) for six weeks. The distal femoral end, the proximal tibial head and the lumbar vertebra (LV) were stained by hematoxylin and eosin, Safranin O/Fast Green and masson-trichrome. Micro-computed tomography was performed to measure bone mineral density (BMD).

RESULTS

Treatment with captopril increased trabecular bone area at distal metaphysis of femur, proximal metaphysis of tibia and LV-4, moreover, high dose of captopril significantly elevated trabecular BMD of LV-2 and LV-5. The mRNA expressions of renin receptor, angiotensinogen, carbonic anhydrase II, matrix metalloproteinase-9, and tumor necrosis factor-alpha were significantly decreased in tibia of ORX mice following treatment with captopril. The administration with captopril enhanced the ratio of OPG/RANKL mRNA expression, the mRNA expression of transforming growth factor-beta and the protein expression of bradykinin receptor-1.

CONCLUSIONS

The inhibition on ACE by captopril exerts beneficial effects on trabecular bone of ORX mice. The therapeutic efficacy may be attributed to the regulation of captopril on local RAS and cytokines in bone.

Renin-angiotensin system inhibitors and risk of fractures: a prospective cohort study and meta-analysis of published observational cohort studies

The renin-angiotensin system (RAS) represents an important target of antihypertensive medications. Angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II receptor blockers (ARB), which are widely-used RAS inhibiting drugs, have been suggested to have beneficial effects on bone tissue. We aimed to assess the associations of use of ACEIs and/or ARBs with the risk of fractures using a population-based prospective cohort and a meta-analysis of published prospective cohort studies. Information on antihypertensive medication use (including both ACEIs and ARBs) were assessed in 1743 men and women of the Kuopio Ischemic Heart Disease prospective cohort study. Hazard ratios (HRs) [95% confidence intervals (CI)] of ACEIs or ARBs use with incident fractures were calculated. A total of 203 composite (hip, humeral, and wrist) fractures occurred during a median follow-up of 14.8 years. In multivariate adjusted analysis, the HR for composite fractures comparing users of ACEIs or ARBs with non-users was 1.00 (0.59-1.69). The corresponding adjusted HR for hip fractures comparing users versus non-users of ACEIs or ARBs was 0.89 (0.32-2.47). Including the current study, a total of 11 observational cohort studies involving 3526,319 participants and >323,355 fractures were included in a meta-analysis. Comparing ACEI users with non-users and ARB users with non-users, the HRs for composite fractures were 1.09 (0.89-1.33) and 0.87 (0.76-1.01) respectively. The corresponding HRs for hip fractures were 0.91 (0.86-0.95) and 0.80 (0.75-0.85) respectively. Use of RAS inhibitors was not associated with long-term risk of composite fractures in both primary and pooled analyses. Pooled evidence however suggests a beneficial effect of RAS blockers on hip fracture risk.

Differential response of bone and kidney to ACEI in db/db mice: A potential effect of captopril on accelerating bone loss

The components of renin-angiotensin system (RAS) are expressed in the kidney and bone. Kidney disease and bone injury are common complications associated with diabetes. This study aimed to investigate the effects of an angiotensin-converting enzyme inhibitor, captopril, on the kidney and bone of db/db mice. The db/db mice were orally administered by gavage with captopril for 8weeks with db/+ mice as the non-diabetic control. Serum and urine biochemistries were determined by standard colorimetric methods or ELISA. Histological measurements were performed on the kidney by periodic acid-schiff staining and on the tibial proximal metaphysis by safranin O and masson-trichrome staining. Trabecular bone mass and bone quality were analyzed by microcomputed tomography. Quantitative polymerase chain reaction and immunoblotting were applied for molecular analysis on mRNA and protein expression. Captopril significantly improved albuminuria and glomerulosclerosis in db/db mice, and these effects might be attributed to the down-regulation of angiotensin II expression and the expression of its down-stream profibrotic factors in the kidney, like connective tissue growth factor and vascular endothelial growth factor. Urinary excretion of calcium and phosphorus markedly increased in db/db mice in response to captopril. Treatment with captopril induced a decrease in bone mineral density and deterioration of trabecular bone at proximal metaphysis of tibia in db/db mice, as shown in the histological and reconstructed 3-dimensional images. Even though captopril effectively reversed the diabetes-induced changes in calcium-binding protein 28-k and vitamin D receptor expression in the kidney as well as the expression of RAS components and bradykinin receptor-2 in bone tissue, treatment with captopril increased the osteoclast-covered bone surface, reduced the osteoblast-covered bone surface, down-regulated the expression of type 1 collagen and transcription factor runt-related transcription factor 2 (markers for osteoblastic functions), and up-regulated the expression of carbonic anhydrase II (marker for bone resorption). Captopril exerted therapeutic effects on renal injuries associated with type 2 diabetes but worsened the deteriorations of trabecular bone in db/db mice; the latter of which was at least in part due to the stimulation of osteoclastogenesis and the suppression of osteogenesis by captopril.

Effects of losartan treatment on the physicochemical properties of diabetic rat bone

Inhibitors of the renin-angiotensin system used to treat several diseases have also been shown to be effective on bone tissue, suggesting that angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may reduce fracture risk. The present study investigated the effects of losartan on the physicochemical and biomechanical properties of diabetic rat bone. Losartan (5 mg/kg/day) was administered via oral gavage for 12 weeks. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Whole femurs were tested under tension to evaluate the biomechanical properties of bone. The physicochemical properties of bone were analyzed by Fourier transform infrared spectroscopy. Although losartan did not recover decreases in the BMD of diabetic bone, it recovered the physicochemical (mineral and collagen matrix) properties of diabetic rat bone. Furthermore, losartan also recovered ultimate tensile strength of diabetic rat femurs. Losartan, an angiotensin II type 1 receptor blocker, has a therapeutic effect on the physicochemical properties of diabetic bone resulting in improvement of bone strength at the material level. Therefore, specific inhibition of this pathway at the receptor level shows potential as a therapeutic target for diabetic patients suffering from bone diseases such as osteopenia.

The effects of different angiotensin II type 1 receptor blockers on the regulation of the ACE-AngII-AT1 and ACE2-Ang(1-7)-Mas axes in pressure overload-induced cardiac remodeling in male mice

Angiotensin II (AngII) type 1 receptor blockers (ARBs) have been effectively used in hypertension and cardiac remodeling. However, the differences among them are still unclear. We designed this study to examine and compare the effects of several ARBs widely used in clinics, including Olmesartan, Candesartan, Telmisartan, Losartan, Valsartan and Irbesartan, on the ACE-AngII-AT1 axis and the ACE2-Ang(1-7)-Mas axis during the development of cardiac remodeling after pressure overload. Although all of the six ARBs, attenuated the development of cardiac hypertrophy and heart failure induced by transverse aortic constriction (TAC) for 2 or 4weeks in the wild-type mice evaluated by echocardiography and hemodynamic measurements, the degree of attenuation by Olmesartan, Candesartan and Losartan tended to be larger than that of the other three drugs tested. Additionally, the degree of downregulation of the ACE-AngII-AT1 axis and upregulation of the ACE2-Ang(1-7)-Mas axis was higher in response to Olmesartan, Candesartan and Losartan administration in vivo and in vitro. Moreover, in angiotensinogen-knockdown mice, TAC-induced cardiac hypertrophy and heart failure were inhibited by Olmesartan, Candesartan and Losartan but not by Telmisartan, Valsartan and Irbesartan administration. Furthermore, only Olmesartan and Candesartan could downregulate the ACE-AngII-AT1 axis and upregulate the ACE2-Ang(1-7)-Mas axis in vitro. Our data suggest that Olmesartan, Candesartan and Losartan could effectively inhibit pressure overload-induced cardiac remodeling even when with knockdown of Ang II, possibly through upregulation of the expression of the ACE2-Ang(1-7)-Mas axis and downregulation of the expression of the ACE-AngII-AT1 axis. In contrast, Telmisartan, Valsartan and Irbesartan only played a role in the presence of AngII, and Losartan had no effect in the presence of AngII in vitro.

Renin inhibitor aliskiren exerts beneficial effect on trabecular bone by regulating skeletal renin-angiotensin system and kallikrein-kinin system in ovariectomized mice

SUMMARY

The skeletal renin-angiotensin system contributes to the development of osteoporosis. The renin inhibitor aliskiren exhibited beneficial effects on trabecular bone of osteoporotic mice, and this action might be mediated through angiotensin and bradykinin receptor pathways. This study implies the potential application of renin inhibitor in the management for postmenopausal osteoporosis.

INTRODUCTION

The skeletal renin-angiotensin system plays key role in the pathological process of osteoporosis. The present study is designed to elucidate the effect of renin inhibitor aliskiren on trabecular bone and its potential action mechanism in ovariectomized (OVX) mice.

METHODS

The OVX mice were treated with low dose (5 mg/kg) or high dose (25 mg/kg) of aliskiren or its vehicle for 8 weeks. The bone turnover markers were measured by ELISA. The structural parameters of trabecular bone at lumbar vertebra (LV) and distal femoral metaphysis were measured by micro-CT. The expression of messenger RNA (mRNA) and protein was studied by RT-PCR and immunoblotting, respectively.

RESULTS

Aliskiren treatment reduced urinary excretion of calcium and serum level of tartrate-resistant acid phosphatase in OVX mice. The treatment with aliskiren significantly increased bone volume (BV/TV) and connectivity density (Conn.D) of trabecular bone at LV-2 and LV-5 as well as dramatically enhanced BV/TV, Conn.D, bone mineral density (BMD/BV) and decreased bone surface (BS/BV) at the distal femoral end. Aliskiren significantly down-regulated the expression of angiotensinogen, angiotensin II (Ang II), Ang II type 1 receptor, bradykinin receptor (BR)-1, and osteocytic-specific gene sclerostin as well as the osteoclast-specific genes, including carbonic anhydrase II, matrix metalloproteinase-9, and cathepsin K.

CONCLUSIONS

This study revealed that renin inhibitor aliskiren exhibited the beneficial effects on trabecular bone of ovariectomy-induced osteoporotic mice, and the underlying mechanism for this action might be mediated through Ang II and BR signaling pathways in bone.

Involvement of Renin-Angiotensin System in Damage of Angiotensin-Converting Enzyme Inhibitor Captopril on Bone of Normal Mice

This study was performed to investigate the effect of angiotensin-converting enzyme inhibitor, captopril, on bone metabolism and histology, and the action of captopril on the components of the skeletal renin-angiotensin system (RAS) and bradykinin receptor in normal male mice. The mice were orally administered captopril (10 mg/kg) for 4 weeks with vehicle-treated mice as normal control. The histology of trabecular bone at the distal femoral end was determined by hematoxylin & eosin, Safranin O and Masson-Trichrome staining. The captopril-treated mice showed a decreased level of testosterone (p<0.05) and procollagen type I N-terminal propeptide (p<0.05) in serum as compared to those in the control group. Captopril has detrimental effects on trabecular bone as demonstrated by the loss of cancellous bone mass and network connections as well as changes to the chondrocytes zone. The expression of angiotensin-converting enzyme (p<0.05), renin receptor (p<0.01), angiotensin II (p<0.05) and bradykinin receptor 2 (p<0.05) was significantly up-regulated following the captopril treatment. Thus, the potential underlying mechanism of the damage of captopril on bone can be attributed the increased activity of local bone RAS and the activation of bradykinin receptor.

Impairing effects of angiotensin-converting enzyme inhibitor Captopril on bone of normal mice

There are contradicting results about the effects of angiotensin-converting enzyme inhibitors (ACEIs) on bones. This study was aimed to investigate the effect of ACEI, Captopril, on bone metabolism and histology as well as the action of Captopril on skeletal renin-angiotensin system (RAS) and bradykinin receptor pathway in normal male mice. The urine, serum, tibias and femurs from normal control mice and Captopril-treated (10mg/kg) mice were collected for biochemical, histological and molecular analyses after drug administration for eight weeks. The mice after the treatment with Captopril had a significant decrease of serum testosterone level. The histological measurements showed the loss of trabecular bone mass and trabecular bone number, and the breakage of trabecular bone network as well as the changes of chondrocyte zone at epiphyseal plate in Captopril-treated mice. The defect of Captopril on trabecular bone was reflected by the quantitative bio-parameters from micro-CT. The expression of renin receptor and bradykinin B2 receptor (B2R) was significantly up-regulated in tibia of mice upon to the Captopril treatment, which decreased the ratio of OPG/RANKL and the expression of osteoblastic factor RUNX2. Furthermore, Captopril treatment resulted in the increase of pAkt/Akt and pNFκB expression in tibia. The present study revealed the impairing effects of Captopril on bone via interfering with the circulating sex hormone level and B2R pathway, which suggests that the bone metabolism of patients need to be carefully monitored when being prescribed for ACEIs.

Renin inhibition improves ovariectomy-induced osteoporosis of lumbar vertebra in mice

The skeletal renin–angiotensin system (RAS) is involved in the progression of osteoporosis and the active peptide within the RAS, angiotensin II (ANG II), has deleterious effects on bones. This study was performed to investigate whether suppression of the rate-limiting step of the RAS cascade by the renin inhibitor aliskiren has a benefit on trabecular bone in osteoporotic mice. A postmenopausal osteoporosis model was induced by bilateral ovariectomy. The ovariectomized (OVX) mice were treated with a low (5 mg/kg) or high (25 mg/kg) dose of aliskiren for 6 weeks. Micro-computed tomography was performed to detect trabecular bone parameters of lumbar vertebra and to obtain 3-dimensional (3D) images. Treatment with aliskiren markedly increased bone volume over total volume (p<0.05), trabecular bone number (p<0.05), connectivity density (p<0.05), and bone mineral density (p<0.05) and reduced trabecular bone separation (p<0.05) compared to vehicle-treated OVX mice. Similarly, the 3D images were consistent with the quantitative data that showed aliskiren could markedly reverse the ovariectomy-induced pathological changes of trabecular bone. Thus, this study indicated that the treatment of estrogen-deficient mice with aliskiren could markedly increase bone mass and improve trabecular bone structure, suggesting its potential application in treating postmenopausal osteoporosis.

Early co-expression of cyclooxygenase-2 and renin in the rat kidney cortex contributes to the development of N(G)-nitro-L-arginine methyl ester induced hypertension

We investigated the involvement of cyclooxygenase-2 (COX-2) and the renin-angiotensin system in N(G)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension. Male Wistar rats were treated with L-NAME (75.0 mg·(kg body mass)(-1)·day(-1), in their drinking water) for different durations (1-33 days). COX-2 and renin mRNA were measured using real-time PCR in the renal cortex, and prostanoids were assessed in the renal perfusate, whereas angiotensin II (Ang II) and Ang (1-7) were quantified in plasma. In some rats, nitric oxide synthase inhibition was carried out in conjunction with oral administration of captopril (30.0 mg·kg(-1)·day(-1)) or celecoxib (1.0 mg·kg(-1)·day(-1)) for 2 or 19 days. We found a parallel increase in renocortical COX-2 and renin mRNA starting at day 2 of treatment with L-NAME, and both peaked at 19-25 days. In addition, L-NAME increased renal 6-Keto-PGF(1α) (prostacyclin (PGI2) metabolite) and plasma Ang II from day 2, but reduced plasma Ang (1-7) at day 19. Captopril prevented the increase in blood pressure, which was associated with lower plasma Ang II and increased COX-2-derived 6-Keto-PGF(1α) at day 2 and plasma Ang (1-7) at day 19. Celecoxib partially prevented the increase in blood pressure; this effect was associated with a reduction in plasma Ang II. These findings indicate that renal COX-2 expression increased in parallel with renin expression, renal PGI2 synthesis, and plasma Ang II in L-NAME-induced hypertension.

Urinary angiotensin-converting enzyme 2 in hypertensive patients may be increased by olmesartan, an angiotensin II receptor blocker

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2) is highly expressed in the kidney and converts angiotensin (Ang) II to Ang-(1-7), a renoprotective peptide. Urinary ACE2 has been shown to be elevated in patients with chronic kidney disease. However, the effects of antihypertensive agents on urinary ACE2 remain unclear.

METHODS

Of participants in the Tanno-Sobetsu cohort study in 2011 (n = 617), subjects on no medication (n = 101) and hypertensive patients treated with antihypertensive agents, including the calcium channel blockers amlodipine and long-acting nifedipine; the ACE inhibitor enalapril; and the Ang II receptor blockers losartan, candesartan, valsartan, telmisartan, and olmesartan, for more than 1 year (n = 100) were enrolled, and urinary ACE2 level was measured.

RESULTS

Glucose and hemoglobin A1c were significantly higher in patients treated with enalapril, telmisartan or olmesartan than in the control subjects. Urinary albumin-to-creatinine ratio (UACR) was significantly higher in patients treated with enalapril than in the control subjects. Urinary ACE2 level was higher in the olmesartan-treated group, but not the other treatment groups, than in the control group. Urinary ACE2 level was positively correlated with systolic blood pressure (r = 0.211; P = 0.003), UACR (r = 0.367; P < 0.001), and estimated salt intake (r = 0.260; P < 0.001). Multivariable regression analysis after adjustment of age, sex, and the correlated indices showed that the use of olmesartan was an independent predictor of urinary ACE2 level.

CONCLUSIONS

In contrast with other antihypertensive drugs, olmesartan may uniquely increase urinary ACE2 level, which could potentially offer additional renoprotective effects.

Effects of angiotensin-converting enzyme inhibitor, captopril, on bone of mice with streptozotocin-induced type 1 diabetes

There are contradictory results about the effect of angiotensin-converting enzyme inhibitors (ACEIs) on bone. This study was performed to address the skeletal renin-angiotensin system (RAS) activity and the effects of the ACEI, captopril, on the bone of streptozotocin-induced type 1 diabetic mice. Histochemical assessment on bone paraffin sections was conducted by Safranin O staining and tartrate-resistant acid phosphatase staining. Micro-computed tomography was performed to analyze bone biological parameters. Gene and protein expression were determined by real-time polymerase chain reaction and immunoblotting, respectively. Type 1 diabetic mice displayed osteopenia phenotype and captopril treatment showed no osteoprotective effects in diabetic mice as shown by the reduction of bone mineral density, trabecular thickness and bone volume/total volume. The mRNA expression of ACE and renin receptor, and the protein expression of renin and angiotensin II were markedly up-regulated in the bone of vehicle-treated diabetic mice compared to those of non-diabetic mice, and these molecular changes of skeletal RAS components were effectively inhibited by treatment with captopril. However, treatment with captopril significantly elevated serum tartrate-resistant acid phosphatase 5b levels, reduced the ratio of osteoprotegerin/receptor activator of nuclear factor-κB ligand expression, increased carbonic anhydrase II mRNA expression and the number of matured osteoclasts and decreased transforming growth factor-β and osteocalcin mRNA expression in the tibia compared to those of diabetic mice. The present study demonstrated that the use of the ACEI, captopril, has no beneficial effect on the skeletal biological properties of diabetic mice. However, this could be attributed, at least partially, to its suppression of osteogenesis and stimulation of osteoclastogenesis, even though it could effectively inhibit high activity of local RAS in the bone of diabetic mice.

Angiotensin-(1-7) and angiotensin-(1-9): function in cardiac and vascular remodelling

The RAS (renin-angiotensin system) is integral to cardiovascular physiology; however, dysregulation of this system largely contributes to the pathophysiology of CVD (cardiovascular disease). It is well established that AngII (angiotensin II), the main effector of the RAS, engages the AT1R (angiotensin type 1 receptor) and promotes cell growth, proliferation, migration and oxidative stress, all processes which contribute to remodelling of the heart and vasculature, ultimately leading to the development and progression of various CVDs, including heart failure and atherosclerosis. The counter-regulatory axis of the RAS, which is centred on the actions of ACE2 (angiotensin-converting enzyme 2) and the resultant production of Ang-(1-7) [angiotensin-(1-7)] from AngII, antagonizes the actions of AngII via the receptor Mas, thereby providing a protective role in CVD. More recently, another ACE2 metabolite, Ang-(1-9) [angiotensin-(1-9)], has been reported to be a biologically active peptide within the counter-regulatory axis of the RAS. The present review will discuss the role of the counter-regulatory RAS peptides Ang-(1-7) and Ang-(1-9) in the cardiovascular system, with a focus on their effects in remodelling of the heart and vasculature.

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.

Angiotensin II receptor antagonists in acute coronary syndromes

BACKGROUND

It is well known that inappropriate or exaggerated activity of the renin-angiotensin system might contribute to the development of systemic hypertension with consequent organ injury and associated increased risk of acute cardiovascular (CV) diseases. This review will discuss evidence form basic research and clinical studies, investigating the efficacy of angiotensin II receptor blockers (ARBs) in the management of acute coronary syndromes (ACS).

MATERIALS AND METHODS

This narrative review is based on the material found on MEDLINE and PubMed up to June 2013. We looked for the terms 'angiotensin, AT1 receptor, ACE inhibitors' in combination with 'acute coronary syndromes, acute myocardial infarction, pathophysiology'.

RESULTS

Preclinical studies showed relevant protective effects of ARBs to reduce adverse cardiac remodelling in animal models of acute cardiac ischaemia. However, although recommended in Consensus guidelines as a good alternative to angiotensin-converting enzyme inhibitors (ACEIs), clinical studies did not confirm a superior efficacy of the ARBs as compared to ACEIs. As a matter of fact for some authors, these drugs might potentially have deleterious effects increasing the CV risk.

CONCLUSIONS

Emerging evidence from clinical trials suggests that the use of ARBs in ACS might be controversial, and caution should be used for their clinical use to replace ACEIs in ACS.