Angiotensin-(1–7) attenuates diabetic nephropathy in Zucker diabetic fatty rats

Molecular regulation of the renin-angiotensin system in haemodialysis patients

BACKGROUND

Blockade of the renin-angiotensin system (RAS) exerts beneficial effects in patients with mild-to-moderate chronic kidney disease, yet evidence suggesting a similar benefit in haemodialysis (HD) patients is not available. Furthermore, knowledge of the effects of RAS blockade on systemic RAS components in HD patients is limited. Analysis of the quantity and dynamics of all known peripheral constituents of the RAS may yield important pathomechanistic information of a widespread therapeutic measure in HD patients.

METHODS

Fifty-two HD patients from the following groups were analysed cross-sectionally: patients without RAS blockade (n = 16), angiotensin-converting enzyme inhibitor (ACEi) users (n = 8), angiotensin receptor blocker (ARB) users (n = 11), patients on ACEi plus ARB (dual blockade, n = 8) and anephric patients (n = 9). Ten healthy volunteers served as controls. Angiotensin metabolites were quantified by mass spectrometry.

RESULTS

In general, HD patients showed a broad variability of RAS activity. Patients without RAS blockade displayed angiotensin metabolite patterns similar to healthy controls. ACEi therapy increased plasma Ang 1-10 and Ang 1-7 concentrations, whereas ARB treatment increased both Ang 1-8 and Ang 1-5, while suppressing Ang 1-7 to minimal levels. Dual RAS blockade resulted in high levels of Ang 1-10 and suppressed levels of other angiotensins. Anephric patients were completely devoid of detectable levels of circulating angiotensins.

CONCLUSION

In HD patients, the activity status of the systemic RAS is highly distorted with the emergence of crucial angiotensin metabolites upon distinct RAS blockade. The characterization of molecular RAS patterns associated with specific RAS interfering therapies may help to individualize future clinical studies and therapies.

The renin-angiotensin system and aging in the kidney

Aging is associated with progressive functional deterioration and structural changes in the kidney. Changes in the activity or responsiveness of the renin-angiotensin system (RAS) occur with aging. RAS changes predispose the elderly to various fluid and electrolyte imbalances as well as acute kidney injury and chronic kidney disease. Among the multiple pathways involved in renal aging, the RAS plays a central role. This review summarizes the association of the RAS with structural and functional changes in the aging kidney and age-related renal injury, and describes the underlying mechanisms of RAS-related renal aging. An improved understanding of the renal aging process may lead to better individualized care of the elderly and improved renal survival in age-related diseases.

Angiotensin-converting enzyme 2 and angiotensin 1-7: novel therapeutic targets

Angiotensin-converting enzyme (ACE) 2 and its product angiotensin 1–7 are thought to have effects that counteract the adverse actions of other, better-known renin–angiotensin system (RAS) components

Numerous experimental studies have suggested that ACE2 and angiotensin 1–7 have notable protective effects in the heart and blood vessels

ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the functional importance and signalling mechanisms of angiotensin-1–7-induced actions remain unclear

New pharmacological interventions targeting ACE2 are expected to be useful in clinical treatment of cardiovascular disease, especially those associated with overactivation of the conventional RAS

More studies, especially randomized controlled clinical trials, are needed to clearly delineate the benefits of therapies targeting angiotensin 1–7 actions

Angiotensin-converting enzyme 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of the better-known members of the renin–angiotensin system and might, therefore, be useful therapeutic targets in patients with cardiovascular disease. Professor Jiang and colleagues review the evidence for the potential roles of these proteins in various cardiovascular conditions, including hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes.

The renin–angiotensin system (RAS) has pivotal roles in the regulation of normal physiology and the pathogenesis of cardiovascular disease. Angiotensin-converting enzyme (ACE) 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of other, better known and understood, members of the RAS. The physiological and pathological importance of ACE2 and angiotensin 1–7 in the cardiovascular system are not completely understood, but numerous experimental studies have indicated that these components have protective effects in the heart and blood vessels. Here, we provide an overview on the basic properties of ACE2 and angiotensin 1–7 and a summary of the evidence from experimental and clinical studies of various pathological conditions, such as hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes mellitus. ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the relevant functions and signalling mechanisms of actions induced by angiotensin 1–7 have not been conclusively determined. The ACE2–angiotensin 1–7 pathway, however, might provide a useful therapeutic target for the treatment of cardiovascular disease, especially in patients with overactive RAS.

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.

Modulation of the action of insulin by angiotensin-(1-7)

The prevalence of Type 2 diabetes mellitus is predicted to increase dramatically over the coming years and the clinical implications and healthcare costs from this disease are overwhelming. In many cases, this pathological condition is linked to a cluster of metabolic disorders, such as obesity, systemic hypertension and dyslipidaemia, defined as the metabolic syndrome. Insulin resistance has been proposed as the key mediator of all of these features and contributes to the associated high cardiovascular morbidity and mortality. Although the molecular mechanisms behind insulin resistance are not completely understood, a negative cross-talk between AngII (angiotensin II) and the insulin signalling pathway has been the focus of great interest in the last decade. Indeed, substantial evidence has shown that anti-hypertensive drugs that block the RAS (renin-angiotensin system) may also act to prevent diabetes. Despite its long history, new components within the RAS continue to be discovered. Among them, Ang-(1-7) [angiotensin-(1-7)] has gained special attention as a counter-regulatory hormone opposing many of the AngII-related deleterious effects. Specifically, we and others have demonstrated that Ang-(1-7) improves the action of insulin and opposes the negative effect that AngII exerts at this level. In the present review, we provide evidence showing that insulin and Ang-(1-7) share a common intracellular signalling pathway. We also address the molecular mechanisms behind the beneficial effects of Ang-(1-7) on AngII-mediated insulin resistance. Finally, we discuss potential therapeutic approaches leading to modulation of the ACE2 (angiotensin-converting enzyme 2)/Ang-(1-7)/Mas receptor axis as a very attractive strategy in the therapy of the metabolic syndrome and diabetes-associated diseases.

Intrarenal distributions and changes of Angiotensin-converting enzyme and Angiotensin-converting enzyme 2 in feline and canine chronic kidney disease

Angiotensin-converting enzyme (ACE) is a key enzyme in the renin-angiotensin system (RAS). ACE2 is a newly identified member of the RAS. The present immunohistochemical study focused on changes in intrarenal ACE and ACE2 immunoreactivity in feline and canine chronic kidney disease (CKD). ACE immunoreactivity was predominantly observed in the brush border of the proximal tubules in dogs and cats. ACE immunoreactivity was lower in CKD kidneys than in normal kidneys, and quantitative analysis demonstrated negative correlations between ACE and renal tissue damage in dogs. ACE2 immunoreactivity was also detected in the proximal tubules; it increased or decreased with CKD in dogs, depending on the renal region assessed. The changes in ACE and ACE2 in CKD were associated with the plasma creatinine concentration in dogs. Findings from dogs with glomerulonephritis were similar to those from dogs with non-glomerulonephritis. The present study suggests that changes in the intrarenal expression of ACE and ACE2 contribute to the pathological mechanisms of canine CKD, but not to the mechanisms of feline CKD.

Oral formulation of angiotensin-(1-7) improves lipid metabolism and prevents high-fat diet-induced hepatic steatosis and inflammation in mice

Angiotensin (Ang)-(1-7) has been described as an important tool on treating and preventing metabolic disorders. In this study, we aimed to evaluate the effect of an oral formulation of Ang-(1-7) included in hydroxypropylβ-cyclodextrin (HPβCD/Ang-[1-7]) on hepatic function, steatosis, and on liver inflammatory markers expression in mice treated with a high-fat diet. Male FVB/N mice were divided into 4 groups and fed for 60 days, with each group receiving 1 of the following diets: standard diet+HPβCD, standard diet+Ang-(1-7)/HPβCD, high-fat diet+HPβCD, or high-fat diet+Ang-[1-7]/HPβCD. Body weight, food intake, and blood parameters, such as total cholesterol, triglyceride, alaninetransaminases, and aspartate transaminases, were evaluated. Immunohistochemical analyses were performed for inflammatory markers tumor necrosis factor-α and interleukin-6. Expression of angiotensin converting enzyme, angiotensin-converting enzyme-2, interleukin-1β, tumor necrosis factor-α, interleukin-6, transforming growth factor-β, acetyl-CoA carboxylase, carbohydrate-responsive element-binding protein, peroxisome proliferator-activated receptor-γ, and sterol regulatory element-binding proteins-1c was evaluated by quantitative real-time polymerase chain reaction. The major findings of our study included reduced liver fat mass and weight, decreased plasma total cholesterol, triglyceride, and alaninetransaminase enzyme levels in the oral Ang-(1-7)-treated groups compared with the control groups. These results were accompanied by a significant reduction in tumor necrosis factor-α and interleukin-6 mRNA expression in the liver. Analyses of liver adipogenesis-related genes by quantitative real-time polymerase chain reaction showed that acetyl-CoA carboxylase, peroxisome proliferator-activated receptor-γ, and sterol regulatory element-binding proteins-1c mRNA expression were significantly suppressed. In conclusion, we observed that treatment with Ang-(1-7) improved metabolism and decreased proinflammatory profile and fat deposition in liver of mice.

Apelin retards the progression of diabetic nephropathy

Apelin and its receptor APJ have pleiotropic effects in mice and humans and play a protective role in cardiovascular diseases at least partially by inhibiting oxidative stress. Our objective was to study the effect of apelin on the progression of kidney disease in mice with established type 1 diabetes. Ove26 mice with type 1 diabetes received daily subcutaneous injections of apelin for 2 or 14 wk. APJ localizes in the glomeruli and blood vessels of kidneys. Renal APJ expression was reduced in diabetic mice but increased after treatment with apelin. Apelin treatment did not affect glycemia, body weight, or blood pressure in diabetic mice. Whole kidney and glomerular hypertrophy, as well as renal inflammation, including monocyte chemoattractant protein 1 and vascular cell adhesion molecule 1 expression, NF-κB activation, and monocyte infiltration, was inhibited after short and long treatment with apelin. Apelin administration significantly reduced albuminuria at 6 mo. Short treatment with apelin was sufficient to reverse the downregulation of the antioxidant enzyme catalase. Expression of angiotensin II and angiotensin type 1 receptor (AT1) in kidneys from diabetic mice treated was not affected by apelin. These findings show for the first time that apelin exerts a protective effect on the diabetic kidney. Short administration is sufficient to reduce kidney and glomerular hypertrophy as well as renal inflammation, but prolonged treatment is required to improve albuminuria. This effect was independent of the activation of the renin angiotensin system but correlated with upregulation of the antioxidant catalase. Apelin may represent a novel tool to treat diabetic nephropathy.

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.

Angiotensin-converting enzyme 2, angiotensin-(1-7) and Mas: new players of the renin-angiotensin system

Angiotensin (Ang)-(1-7) is now recognized as a biologically active component of the renin-angiotensin system (RAS). Ang-(1-7) appears to play a central role in the RAS because it exerts a vast array of actions, many of them opposite to those attributed to the main effector peptide of the RAS, Ang II. The discovery of the Ang-converting enzyme (ACE) homolog ACE2 brought to light an important metabolic pathway responsible for Ang-(1-7) synthesis. This enzyme can form Ang-(1-7) from Ang II or less efficiently through hydrolysis of Ang I to Ang-(1-9) with subsequent Ang-(1-7) formation by ACE. In addition, it is now well established that the G protein-coupled receptor Mas is a functional binding site for Ang-(1-7). Thus, the axis formed by ACE2/Ang-(1-7)/Mas appears to represent an endogenous counterregulatory pathway within the RAS, the actions of which are in opposition to the vasoconstrictor/proliferative arm of the RAS consisting of ACE, Ang II, and AT(1) receptor. In this brief review, we will discuss recent findings related to the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular and renal systems, as well as in metabolism. In addition, we will highlight the potential interactions of Ang-(1-7) and Mas with AT(1) and AT(2) receptors.

The pathogenesis and management of hypertension in diabetic kidney disease

Hypertension commonly coexists with diabetes, and its prevalence is even higher in the presence of diabetic kidney disease. The pathogenesis of hypertension in this population stems from increased extracellular volume and increased vasoconstriction that results from mechanisms that may be attributed to both diabetes and the eventual impairment of renal function. Antihypertensive therapy aimed at reducing blood pressure remains a primary goal in preventing the incidence of diabetic kidney and slowing its progression. Initial therapy should consist of an ACE inhibitor or ARB titrated to the maximally tolerated dose. Using combination RAAS therapy further reduces proteinuria, but the benefits of this strategy compared with the potential risks of hyperkalemia and acute deterioration of renal function are still unknown. Endothelin receptor antagonists also lower proteinuria, but these can be associated with volume overload and edema with no clear long-term benefit on renal function yet identified. Further large clinical trials are needed to better understand how progression to ESRD can be slowed or halted in patients with diabetic kidney disease.

Brain renin-angiotensin system in the nexus of hypertension and aging

Aging is associated with an imbalance in sympathetic and parasympathetic outflow to cardiovascular effector organs. This autonomic imbalance contributes to the decline in cardiovagal baroreceptor reflex function during aging, which allows for unrestrained activation of the sympathetic nervous system to negatively impact resting systolic blood pressure and its variability. Further, impaired baroreflex function can contribute to the development of insulin resistance and other features of the metabolic syndrome during aging through overlap in autonomic neural pathways that regulate both cardiovascular and metabolic functions. Increasing evidence supports a widespread influence of the renin-angiotensin system (RAS) on both sympathetic and parasympathetic activity through receptors distributed to peripheral and central sites of action. Indeed, therapeutic interventions to block the RAS are well established for the treatment of hypertension in elderly patients, and reduce the incidence of new-onset diabetes in clinical trials. Further, RAS blockade increases lifespan and improves numerous age-related pathologies in rodents, often independent of blood pressure. The beneficial effects of these interventions are at least in part attributed to suppression of angiotensin II formed locally within the brain. In particular, recent insights from transgenic rodents provide evidence that long-term alteration in the brain RAS modulates the balance between angiotensin II and angiotensin-(1-7), and related intracellular signaling pathways, to influence cardiovascular and metabolic function in the context of hypertension and aging.

Actions of polypeptides at the neuromuscular junction

The effects of several polypeptides, e.g. angiotensin II, substance P, oxytocin and vasopressin, on the isolated frog gastrocnemius, chick biventer cervicis and rat hemodiaphragm preparations were studied using electrophysiological and neurochemical techniques. The effects of angiotensin II, substance P, oxytocin and vasopressin on neuromuscular transmission and muscle contraction were investigated by studying the following parameters: the directly and indirectly-elicited twitch and tetanic contractions, nerve compound action potential, uptake of 3H-methylcholine into nerve-muscle preparations, the contractures produced by depolarizing drugs, e.g. ACh or TEA. The results showed that angiotensin II (10(-10)-10(-6) M) and substance P (10(-7)-10(-6) M) enhanced neuromuscular transmission and muscle contraction by increasing the amplitudes of the indirectly-elicited twitch and tetanic contractions. Oxytocin and vasopressin (1-100 mU/ml-1) both depressed neuromuscular transmission by reducing the contractile and electrical response in the frog, chick and rat skeletal muscle. It was concluded that, like their effects on ganglionic transmission, the peptides can modify neuromuscular transmission. The mechanism by which these peptides produce their effects may be dependent on external calcium concentration. These peptides may affect both pre- and postjunctional mechanisms; prejunctionally by increasing/decreasing the release of ACh, and postjunctionally by affecting the sensitivity of the postjunctional membrane to depolarizing drugs and/or producing a contracture in the skeletal muscle.