Chris Tikellis

ACE2 deficiency modifies renoprotection afforded by ACE inhibition in experimental diabetes

OBJECTIVE— The degradation of angiotensin (Ang) II by ACE2, leading to the formation of Ang 1–7, is an important step in the renin-angiotensin system (RAS) and one that is significantly altered in the diabetic kidney. This study examines the role of ACE2 in early renal changes associated with diabetes and the influence of ACE2 deficiency on ACE inhibitor–mediated renoprotection. RESEARCH DESIGN AND METHODS— Diabetes was induced by streptozotocin in male c57bl6 mice and ACE2 knockout (KO) mice. After 5 weeks of study, animals were randomized to receive the ACE inhibitor perindopril (2 mg · kg−1 · day−1). Wild-type mice were further randomized to receive the selective ACE2 inhibitor MLN-4760 (10 mg · kg−1 · day−1) and followed for an additional 5 weeks. Markers of renal function and injury were then assessed. RESULTS— Induction of diabetes in wild-type mice was associated with a reduction in renal ACE2 expression and decreased Ang 1–7. In diabetic mice receiving MLN-4760 and in ACE2 KO mice, diabetes-associated albuminuria was enhanced, associated with an increase in blood pressure. However, renal hypertrophy and fibrogenesis were reduced in diabetic mice with ACE2 deficiency, and hyperfiltration was attenuated. Diabetic wild-type mice treated with an ACE inhibitor experienced a reduction in albuminuria and blood pressure. These responses were attenuated in both diabetic ACE2 KO mice and diabetic mice receiving MLN-4760. However, other renoprotective and antifibrotic actions of ACE inhibition in diabetes were preserved in ACE2-deficient mice. CONCLUSIONS— The expression of ACE2 is significantly modified by diabetes, which impacts both pathogenesis of kidney disease and responsiveness to RAS blockade. These data indicate that ACE2 is a complex and site-specific modulator of diabetic kidney disease.

Genetic Ace2 deficiency accentuates vascular inflammation and atherosclerosis in the ApoE knockout mouse.

Rationale: Angiotensin-converting enzyme (ACE)2 opposes the actions of angiotensin (Ang) II by degrading it to Ang 1-7. Objective: Given the important role of Ang II/Ang 1-7 in atherogenesis, we investigated the impact of ACE2 deficiency on the development of atherosclerosis. Methods and Results: C57Bl6, Ace2 knockout (KO), apolipoprotein E (ApoE) KO and ApoE/Ace2 double KO mice were followed until 30 weeks of age. Plaque accumulation was increased in ApoE/Ace2 double KO mice when compared to ApoE KO mice. This was associated with increased expression of adhesion molecules and inflammatory cytokines, including interleukin-6, monocyte chemoattractant protein-1, and vascular cell adhesion molecule-1, and an early increase in white cell adhesion across the whole aortae on dynamic flow assay. In the absence of a proatherosclerotic (ApoE KO) genotype, ACE2 deficiency was also associated with increased expression of these markers, suggesting that these differences were not an epiphenomenon. ACE inhibition prevented increases of these markers and atherogenesis in ApoE/ACE2 double KO mice. Bone marrow macrophages isolated from Ace2 KO mice showed increased proinflammatory responsiveness to lipopolysaccharide and Ang II when compared to macrophages isolated from C57Bl6 mice. Endothelial cells isolated from Ace2 KO mice also showed increased basal activation and elevated inflammatory responsiveness to TNF-&agr;. Similarly, selective inhibition of ACE2 with MLN-4760 also resulted in a proinflammatory phenotype with a physiological response similar to that observed with exogenous Ang II (10−7 mol/L). Conclusions: Genetic Ace2 deficiency is associated with upregulation of putative mediators of atherogenesis and enhances responsiveness to proinflammatory stimuli. In atherosclerosis-prone ApoE KO mice, these changes potentially contribute to increased plaque accumulation. These findings emphasize the potential utility of ACE2 repletion as a strategy to reduce atherosclerosis.

Rho kinase inhibition protects kidneys from diabetic nephropathy without reducing blood pressure

Rho-associated kinases (ROCK) are activated in the kidney as well as in cultured cells of diabetic models and have been implicated in renal pathophysiology. To explore whether inhibition of ROCK is protective, we studied its role in a model of accelerated diabetic nephropathy where uninephrectomized rats were made diabetic by streptozotocin. After establishing diabetes, rats were treated with the ROCK inhibitor fasudil continuously or for the final 6 weeks of an 18-week experimental period. The results were compared to similar rats given losartan, an established treatment of clinical and experimental diabetic nephropathy, or a combination of both agents. Vehicle-treated diabetic and non-diabetic uninephrectomized rats served as controls. Diabetes resulted in a rapid development of albuminuria, higher glomerulosclerosis and interstitial fibrosis scores, lower glomerular filtration rates, and increased expression of several molecular markers of diabetic nephropathy. Eighteen weeks of fasudil treatment reduced renal ROCK activity, and ameliorated diabetes-induced structural changes in the kidney and expression of the molecular markers in association with a modest anti-proteinuric effect but no change in blood pressure. Late intervention with fasudil reduced glomerulosclerosis, but did not influence proteinuria. Most effects of fasudil were comparable to those of losartan, although losartan lowered blood pressure and further lowered proteinuria. The combination of both treatments was no different than losartan alone. Thus, ROCK inhibition protected the kidney from diabetic nephropathy even though it did not reduce the blood pressure.

Angiotensin-converting enzyme 2 is a key modulator of the renin–angiotensin system in cardiovascular and renal disease

Purpose of reviewAngiotensin-converting enzyme 2 (ACE2) has recently emerged as a key regulator of the renin–angiotensin system in both health and disease. Recent findingsACE2 deficiency is associated with elevated tissue and circulating levels of angiotensin II and reduced levels of angiotensin 1–7. Phenotypically, this results in a modest elevation in systolic blood pressure and left ventricular hypertrophy. In atherosclerosis-prone apolipoprotein E knockout mice, ACE2 deficiency results in augmented vascular inflammation and an inflammatory response that contributes to increased atherosclerotic plaque formation. In the kidney, ACE2 deficiency is associated with progressive glomerulosclerosis. Interventions such as ACE2 replenishment or augmentation of its actions have proven successful in reducing hypertension, plaque accumulation, and renal and cardiac damage in a range of different models. Although promising, the balance of the renin–angiotensin system remains complicated, with some evidence that overexpression of ACE2 may have adverse cardiac effects, and ACE2 and its metabolic products may promote epithelial-to-mesenchymal transition. SummaryRepletion of ACE2s activities offers a new strategy to complement current clinical interventions in treating hypertension, renal and cardiovascular disease. In particular conditions where ACE inhibition and angiotensin receptor blockade are partially effective, the adjunctive actions of ACE2 may not only reduce clinical escape but also augment the efficacy of interventions.

Dicarbonyl stress in the absence of hyperglycemia increases endothelial inflammation and atherogenesis similar to that observed in diabetes.

The deleterious effects of high glucose levels and enhanced metabolic flux on the vasculature are thought to be mediated by the generation of toxic metabolites, including reactive dicarbonyls like methylglyoxal (MG). In this article, we demonstrate that increasing plasma MG to levels observed in diabetic mice either using an exogenous source (1% in drinking water) or generated following inhibition, its primary clearance enzyme, glyoxalase-1 (with 50 mg/kg IP bromobenzyl-glutathione cyclopentyl diester every second day), was able to increase vascular adhesion and augment atherogenesis in euglycemic apolipoprotein E knockout mice to a similar magnitude as that observed in hyperglycemic mice with diabetes. The effects of MG appear partly mediated by activation of the receptor for advanced glycation end products (RAGE), as deletion of RAGE was able to reduce inflammation and atherogenesis associated with MG exposure. However, RAGE deletion did not completely prevent inflammation or vascular damage, possibly because the induction of mitochondrial oxidative stress by dicarbonyls also contributes to inflammation and atherogenesis. Such data would suggest that a synergistic combination of RAGE antagonism and antioxidants may offer the greatest utility for the prevention and management of diabetic vascular complications.

Activation of the Renin-Angiotensin System Mediates the Effects of Dietary Salt Intake on Atherogenesis in the Apolipoprotein E Knockout Mouse

Dietary salt intake is a major determinant of the activation state of renin-angiotensin-aldosterone system. Given the important role of the renin-angiotensin-aldosterone system in plaque accumulation, we investigated its role in the development of atherogenesis associated with sodium intake in apolipoprotein E knockout mice. Six-weeks of a low-salt diet (containing 0.03% sodium) resulted in a 4-fold increase in plaque accumulation in apolipoprotein E knockout mice when compared with mice receiving normal chow (containing 0.30% sodium). This was associated with activation of the renin-angiotensin-aldosterone system, increased vascular expression of adhesion molecules and inflammatory cytokines, and increased adhesion of labeled leukocytes across the whole aorta on a dynamic flow assay. These changes were blocked with the angiotensin-converting enzyme inhibitor perindopril (2 mg/kg per day). A high-salt diet (containing 3% sodium) attenuated vascular inflammation and atherogenesis, associated with suppression of the renin-angiotensin-aldosterone system, although systolic blood pressure levels were modestly increased (5±1 mmHg). Constitutive activation of the renin-angiotensin-aldosterone system in angiotensin-converting enzyme 2 apolipoprotein E knockout mice was also associated with increased atherosclerosis and vascular adhesion, and this was attenuated by a high-salt diet associated with suppression of the renin-angiotensin-aldosterone system. By contrast, a low-salt diet failed to further activate the renin-angiotensin-aldosterone system or to increase atherosclerosis in angiotensin-converting enzyme 2 apolipoprotein E knockout mice. Together, these data validate a relationship between salt-mediated renin-angiotensin-aldosterone system activation and atherogenesis, which may partly explain the inconclusive or paradoxical findings of recent observational studies, despite clear effects on blood pressure.

Preventing diabetes in patients with hypertension : one more reason to block the renin-angiotensin system

Patients with essential hypertension are at increased risk of type 2 (non-insulin-dependent) diabetes. Recent large studies have been unable to delineate any superiority in one class of antihypertensive drug over another, independent of their effects in reducing blood pressure; however, in the longer term, antihypertensive agents that are able to reduce the risk of diabetes may have a theoretical advantage. To this end, the findings of several recent clinical trials have suggested that blockade of the renin–angiotensin system (RAS) may protect against the development of de-novo diabetes in ‘at risk’ patients. This beneficial effect appears to outweigh both the adverse metabolic effects of agents used in the control arm of these studies and the control of blood pressure achieved. Furthermore, recent evidence suggests that the RAS may have a direct role in the pathogenesis of diabetes. Angiotensin-mediated increases in oxidative stress, inflammation, and free fatty acids concentrations potentially contribute to β-cell dysfunction in diabetes. In addition, activation of the RAS appears to potentiate the action of other pathogenic pathways, including glucotoxicity, lipotoxicity, and advanced glycation. In experimental models of type 2 diabetes, blockade of the RAS with angiotensin-converting enzyme inhibitors or angiotensin receptor antagonists also results in the improvement of islet structure and function. At least three large controlled trials are currently under way to study the utility of blockade of the RAS in the development of diabetes, including studies of combination therapy. It is hoped that these studies will demonstrate the true potential of blockade of the RAS for the prevention of diabetes.

The arterial depressor response to chronic low-dose angiotensin II infusion in female rats is estrogen dependent

The complex role of the renin-angiotensin-system (RAS) in arterial pressure regulation has been well documented. Recently, we demonstrated that chronic low-dose angiotensin II (ANG II) infusion decreases arterial pressure in female rats via an AT(2)R-mediated mechanism. Estrogen can differentially regulate components of the RAS and is known to influence arterial pressure regulation. We hypothesized that AT(2)R-mediated depressor effects evident in females were estrogen dependent and thus would be abolished by ovariectomy and restored by estrogen replacement. Female Sprague-Dawley rats underwent ovariectomy or sham surgery and were treated with 17β-estradiol or placebo. Mean arterial pressure (MAP) was measured via telemetry in response to a 2-wk infusion of ANG II (50 ng·kg(-1)·min(-1) sc) or saline. MAP significantly decreased in females treated with ANG II (-10 ± 2 mmHg), a response that was abolished by ovariectomy (+4 ± 2 mmHg) and restored with estrogen replacement (-6 ± 2 mmHg). Cardiac and renal gene expression of components of the RAS was differentially regulated by estrogen, such that overall, estrogen shifted the balance of the RAS toward the vasodilatory axis. In conclusion, estrogen-dependent mechanisms offset the vasopressor actions of ANG II by enhancing RAS vasodilator pathways in females. This highlights the potential for these vasodilator pathways as therapeutic targets, particularly in women.

Angiotensin converting enzyme 2 and atherosclerosis.

Angiotensin converting enzyme 2 (ACE2) is a homolog of angiotensin converting enzyme (ACE) which generates angiotensin II from angiotensin I. ACE, its product angiotensin II and the downstream angiotensin type I receptor are important components of the renin-angiotensin system (RAS). Angiotensin II, the most important component of the RAS, promotes the development of atherosclerosis. The identification of ACE2 in 2000 opened a new chapter of research on the regulation of the RAS. ACE2 degrades pro-atherosclerotic angiotensin II and generates anti-atherosclerotic angiotensin 1-7. In this review, we explored the importance of ACE2 in protecting experimental animals from developing atherosclerosis and its involvement in human atherosclerosis. We also examined the published evidence assessing the importance of ACE2 in different cell types relevant to atherosclerosis and putative underlying cellular and molecular mechanisms linking ACE2 with protection from atherosclerosis. ACE2 shifts the balance from angiotensin II to angiotensin 1-7 inhibiting the progression of atherosclerosis in animal models.

Expression analysis of the epigenetic methyltransferases and methyl-CpG binding protein families in the normal B-cell and B-cell chronic lymphocytic leukemia (CLL).

The importance of epigenetic modifications in carcinogenesis has been a source of controversy for some time. There is little doubt that changes in genomic hypermethylation contribute to the silencing of tumour suppressor genes. Furthermore, recent studies have also identified the significance of genomic hypomethylation associated with chromosomal instability and tumourigenesis. One of the most perplexing questions regarding epigenetic modifications and leukemogenesis is the relationship with DNA methyltransferases (DNMT’s). The primary function of the DNMT enzymes is to methylate genomic DNA, whereas the methyl-CpG binding domain proteins (MBD) interpret this methylation signal and regulate gene expression and chromatin behaviour. In this study we analyse these gene families by quantitative real-time PCR to investigate whether expression levels and the B-cell chronic lymphocytic leukemia (B-CLL) phenotype are associated. Furthermore, given the epigenetic crosstalk between genome stability and the histone chromatin code we have analysed eukaryotic histone methyltransferase (Eu-HMTaseI). Surprisingly, we did not observe significant changes in DNMT1 expression in B-CLL cases when compared to normal lymphocytes, regardless of whether we normalise against GAPDH or PCNA as reference standards. Indeed, expression of the maintenance and de novo methylases were independently regulated. Of particular note was the significant down regulation of DNMT3b. Furthermore, we observed a positive correlation between HMTaseI expression levels and stage of leukemia suggesting that changes in the methylation patterns in B-CLL may represent deregulation of the epigenetic repertoire that also include the methylation dependent binding proteins, MBD2 and MeCP2. We envisage changes in the epigenetic program are multifactorial in nature and postulate that the prevalent genomic methylases just one component of a larger epigenetic repertoire.