The renin angiotensin system as a therapeutic target to prevent diabetes and its complications

Perspectives on the Potential Benefits of Antihypertensive Peptides towards Metabolic Syndrome

In addition to the regulation of blood pressure, the renin-angiotensin system (RAS) also plays a key role in the onset and development of insulin resistance, which is central to metabolic syndrome (MetS). Due to the interplay between RAS and insulin resistance, antihypertensive compounds may exert beneficial effects in the management of MetS. Food-derived bioactive peptides with RAS blocking properties can potentially improve adipose tissue dysfunction, glucose intolerance, and insulin resistance involved in the pathogenesis of MetS. This review discusses the pathophysiology of hypertension and the association between RAS and pathogenesis of the MetS. The effects of bioactive peptides with RAS modulating effects on other components of the MetS are discussed. While the in vivo reports on the effectiveness of antihypertensive peptides against MetS are encouraging, the exact mechanism by which these peptides infer their effects on glucose and lipid handling is mostly unknown. Therefore, careful design of experiments along with standardized physiological models to study the effect of antihypertensive peptides on insulin resistance and obesity could help to clarify this relationship.

Is chronic kidney disease associated with diabetic retinopathy in Asian adults?

BACKGROUND

Diabetic nephropathy (DN) is commonly associated with diabetic retinopathy (DR). Few studies have demonstrated that chronic kidney disease (CKD) is associated with DR. However, it is not clear if CKD in the absence of albuminuria is associated with DR.

METHODS

We included 301 participants with diabetes (Chinese, Malay and Indian ethnicity aged ≥24 years who participated in the Singapore Prospective Study Program (2003-2007). Retinal photographs taken from both eyes were graded for DR using the modified Airlie House Classification. We examined the association of CKD defined by low estimated glomerular filtration rate (eGFR) (<60 mL/min per 1.73 m(2) , n = 54), and albuminuria (urinary albumin-to-creatinine ratio ≥30, n = 116) with any-DR (n = 99) in logistic regression models. We replicated this analysis in another independent population-based sample of Malay adults (n = 265) with similar methodology in Singapore.

RESULTS

41% of those with low-eGFR had normoalbuminuria. In separate models, while albuminuria was significantly associated with any-DR, low-eGFR was not significantly associated with any-DR. In a model combining both markers, compared to the referent group (normal-eGFR+normoalbuminuria), the odds ratio (OR) (95% confidence interval [CI]) of any-DR were: 2.33 (1.27-4.27) for normal-eGFR+albuminuria, 1.38 (0.49-3.91) for low-eGFR + normoalbuminuria, and 2.64 (1.05-6.63) for low-eGFR+albuminuria. Similar findings for any-DR were observed in the replication cohort of Malay persons (3.56 [1.49-8.54] for normal-eGFR+albuminuria, 1.69 (0.52-5.55) for low-eGFR+normoalbuminuria, 4.34 [1.68-11.24] for low-eGFR+albuminuria.

CONCLUSION

We demonstrated that CKD is associated with DR only in the presence of albuminuria suggesting that CKD is more likely related to diabetes in the presence of albuminuria.

Renin-Angiotensin-aldosterone system in diabetes and hypertension

Activation of the renin-angiotensin-aldosterone system (RAAS) is the primary etiologic event in the development of hypertension in people with diabetes mellitus. Modulation of the RAAS has been shown to slow the progression and even cause regression of the microvascular and macrovascular complications associated with diabetes mellitus. Early pharmacotherapy with agents that decrease RAAS activation in the adipose tissue have had a dramatic impact on the prevalence of diabetes related complications. Recent data show that preventing the development of "angry fat" can prevent not just hypertension but also type 2 diabetes mellitus and its associated complications. This review updates what is known about angry fat and the role of RAAS inhibition in preventing the metabolic sequelae of local RAAS activation.

Role of aldosterone and angiotensin II in insulin resistance: an update

The role of the Renin-Angiotensin-Aldosterone system (RAAS) on the development of insulin resistance and cardiovascular disease is an area of growing interest. Most of the deleterious actions of the RAAS on insulin sensitivity appear to be mediated through activation of the Angiotensin II (Ang II) Receptor type 1 (AT(1)R) and increased production of mineralocorticoids. The underlying mechanisms leading to impaired insulin sensitivity remain to be fully elucidated, but involve increased production of reactive oxygen species and oxidative stress. Both experimental and clinical studies also implicate aldosterone in the development of insulin resistance, hypertension, endothelial dysfunction, cardiovascular tissue fibrosis, remodelling, inflammation and oxidative stress. There is abundant evidence linking aldosterone, through non-genomic actions, to defective intracellular insulin signalling, impaired glucose homeostasis and systemic insulin resistance not only in skeletal muscle and liver but also in cardiovascular tissue. Blockade of the different components of the RAAS, in particular Ang II and AT(1)R, results in attenuation of insulin resistance, glucose homeostasis, as well as decreased cardiovascular disease morbidity and mortality. These beneficial effects go beyond to those expected with isolated control of hypertension. This review focuses on the role of Ang II and aldosterone in the pathogenesis of insulin resistance, as well as in clinical relevance of RAAS blockade in the prevention and treatment of the metabolic syndrome and cardiovascular disease.

Production and in vitro characterization of lisinopril-loaded nanoparticles for the treatment of restenosis in stented coronary arteries

Lisinopril, an angiotensin converting enzyme (ACE) inhibitor drug, was encapsulated in poly(lactide-co-glicolide) (PLGA) nanoparticles (NP) for site-specific delivery by catheters in prevention of restenosis. NP were prepared by emulsification-diffusion method. The PLGA type, stabilizing agent type and its concentration were studied as process variables. The z-average particle size varied between 265-412 nm. The highest zeta potential was seen in NP prepared with Pluronic F-68. None of the studied variables or their interactions had a significant effect on the particle size while all had main effect on the zeta potential. The highest entrapment efficiency was 93% and all studied variables and their interactions except PLGA type and its interaction with the stabilizer type had significant effects on the loading. Baker-Lonsdale model was the most appropriate model for release of lisinopril from NP. Five per cent PLGA 75:25 and 5% Pluronic F-68 showed promising results for 21 days release of lisinopril as an anti-restenotic agent.

Evidence for benefits of angiotensin receptor blockade beyond blood pressure control

Elevated levels of angiotensin II result in oxidative stress and endothelial dysfunction, which initiate atherogenic pathologic processes that are important in cardiovascular disease development. Angiotensin II induces its deleterious effects primarily through the type 1 receptor; these effects are inhibited by angiotensin II receptor blockers (ARBs) directly at the receptor level. Angiotensin II may potentiate protective mechanisms through stimulation of the type 2 receptor, which is not blocked by ARBs. Accumulating data suggest that blockade of angiotensin II production or activity provides vascular and cardioprotective benefits, such as reduction of atrial fibrillation, acute myocardial infarction, and heart failure events. Moreover, blockade of the renin-angiotensin system has been shown to offer renal protection in subjects with and without diabetes mellitus and to reduce the risk of new-onset diabetes.

Attenuation of vascular/neural dysfunction in Zucker rats treated with enalapril or rosuvastatin

OBJECTIVE

Obese Zucker rats, animal model for the metabolic syndrome, develop a diabetes-like neuropathy that is independent of hyperglycemia. The purpose of this study was to determine whether drugs used to treat cardiovascular dysfunction in metabolic syndrome also protect nerve function.

METHODS AND PROCEDURES

Obese Zucker rats at 20 weeks of age were treated for 12 weeks with enalapril or rosuvastatin. Lean rats were used as controls. Vasodilation in epineurial arterioles was measured by videomicroscopy. Endoneurial blood flow (EBF) was measured by hydrogen clearance and nerve conduction velocity was measured following electrical stimulation of motor or sensory nerves.

RESULTS

Enalapril treatment decreased serum angiotensin-converting enzyme (ACE) activity and both drugs reduced serum cholesterol levels. In obese Zucker rats at 32 weeks of age superoxide levels were elevated in the aortas and epineurial arterioles, which were reduced by treatment with either drug. Nitrotyrosine levels were increased in epineurial arterioles and reduced with enalapril treatment. EBF was decreased and corrected by treatment with either drug. Motor nerve conduction velocity was decreased and significantly improved with enalapril treatment. Obese Zucker rats were hypoalgesic in response to a thermal stimulus and this was significantly improved with either treatment. Treatment with either enalapril or rosuvastatin significantly reversed the decrease in acetylcholine-mediated vascular relaxation of epineurial arterioles in obese Zucker rats.

DISCUSSION

Even though obese Zucker rats have normal glycemia vascular and neural dysfunctions develop with age and can be improved by treatment with either enalapril or rosuvastatin.

Effect of angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers on the rate of new-onset diabetes mellitus: a review and pooled analysis

The rising prevalence and health burden of diabetes mellitus require that new approaches for prevention among high-risk populations be evaluated. Emerging evidence from the prospective evaluations of secondary and tertiary outcomes and from retrospective evaluations in randomized controlled trials suggests that angiotensin-converting enzyme (ACE) inhibitors and angiotensin II type 1 receptor blockers (ARBs) may reduce the occurrence of new-onset diabetes. Therefore, we each independently searched MEDLINE for randomized controlled trials from January 1966-October 2005 that used an ACE inhibitor or ARB as a primary intervention versus a control group not receiving an ACE inhibitor or ARB and that reported the occurrence of diabetes. Thirteen trials were identified. In each of the 13 studies, the frequency of diabetes in the ACE inhibitor or ARB groups was lower than that in the control groups. In addition, it was consistent in that no study significantly excluded any benefit from ACE inhibitors or ARBs on the rate of new-onset diabetes. The combined occurrence of new-onset diabetes in all 13 studies was 2249 cases among 31,283 patients (7.2%) in the ACE inhibitor or ARB group versus 3230 cases among 35,988 patients (9.0%) in the control group. The combined relative risk of diabetes was 0.80, with a 95% confidence interval of 0.76-0.84, based on a two-sided alpha of 0.05, in favor of ACE inhibitors and ARBs. This observation needs to be confirmed by randomized controlled trials with the frequency of diabetes as the primary prospective end point.

Diabetes prevention: is there more to it than lifestyle changes?

Over the past years, there has been an explosive increase in the prevalence of type 2 diabetes (T2DM) and this is expected to continue, entailing associated morbidity and mortality. An increasing number of studies explore the different ways T2DM could be prevented. On-going lifestyle modifications need to be addressed. High-risk patients should be given counselling on weight loss, possibly using a low glycaemic index diet, with a target of around 7-10% over 6-12 months, as well as instruction for increasing physical activity to around 150 min of physical exercise weekly (NNT = 4-8). Moderate alcohol consumption and coffee consumption may also be of benefit (NNT = 89 and 66, respectively). Metformin (NNT = 14), acarbose (NNT = 11) and troglitazone (NNT = 6) have been shown to prevent/delay T2DM and angiotensin-converting enzyme (ACE) inhibitors and statins appear to have an adjunctive role (NNT = 42 and 112, respectively). Trials with orlistat and bariatric surgery have also prevented T2DM (NNT = 36 and 6, respectively), and forthcoming treatment with GLP1 mimetics appears promising. Diabetes prevention studies should help create well-defined strategies for screening and treating high-risk populations in the real world, as prevention is our only chance to alleviate the ever growing burden of diabetes mellitus in the world.

ACE inhibitor or angiotensin II receptor antagonist attenuates diabetic neuropathy in streptozotocin-induced diabetic rats

ACE inhibition and/or blocking of the angiotensin II receptor are recognized as first-line treatment for nephropathy and cardiovascular disease in diabetic patients. However, little information is available about the potential benefits of these drugs on diabetic neuropathy. We examined vascular and neural activity in streptozotocin-induced diabetic rats that were treated for 12 weeks with enalapril, an ACE inhibitor, or L-158809, an angiotensin II receptor blocker. A prevention protocol (group 1) as well as three intervention protocols (treatment was initiated after 4, 8, or 12 weeks of diabetes [groups 2, 3, and 4, respectively]) were used. Endoneurial blood flow and motor nerve conduction velocity (MNCV) were impaired in all groups of untreated diabetic rats. In group 1, treatment of diabetic rats with enalapril or L-158809 partially prevented the diabetes-induced decrease in endoneurial blood flow and MNCV. In groups 2-4, intervention with enalapril was more effective in reversing the diabetes-induced impairment in endoneurial blood flow and MNCV than L-158809. The superoxide level in the aorta and epineurial arterioles of diabetic rats was increased. Treatment of diabetic rats with enalapril or L-158809 reduced the superoxide level in the aorta in all groups but was less effective in epineurial arterioles. Acetylcholine and calcitonin gene-related peptide (CGRP) cause vasodilation in epineurial arterioles of the sciatic nerve, which was impaired by diabetes. Treatment of diabetic rats (all groups) with enalapril or L-158809 completely prevented/reversed the diabetes-induced impairment in CGRP-mediated vascular relaxation. Treatment with enalapril or L-158809 was also effective in improving impaired acetylcholine-mediated vasodilation, but the efficacy was diminished from groups 1 to 4. These studies suggest that ACE inhibitors and/or angiotensin II receptor blockers may be effective treatments for diabetes and vascular and neural dysfunction. However, the efficacy of these treatments may be dependent on when the treatment is initiated.