Aliskiren prevents cardiovascular complications and pancreatic injury in a mouse model of obesity and type 2 diabetes

Reactive Oxygen Species in the Aorta and Perivascular Adipose Tissue Precedes Endothelial Dysfunction in the Aorta of Mice with a High-Fat High-Sucrose Diet and Additional Factors

Metabolic syndrome (Mets) is the major contributor to the onset of metabolic complications, such as hypertension, type 2 diabetes mellitus (DM), dyslipidemia, and non-alcoholic fatty liver disease, resulting in cardiovascular diseases. C57BL/6 mice on a high-fat and high-sucrose diet (HFHSD) are a well-established model of Mets but have minor endothelial dysfunction in isolated aortas without perivascular adipose tissue (PVAT). The purpose of this study was to evaluate the effects of additional factors such as DM, dyslipidemia, and steatohepatitis on endothelial dysfunction in aortas without PVAT. Here, we employed eight-week-old male C57BL/6 mice fed with a normal diet (ND), HFHSD, steatohepatitis choline-deficient HFHSD (HFHSD-SH), and HFHSD containing 1% cholesterol and 0.1% deoxycholic acid (HFHSD-Chol) for 16 weeks. At week 20, some HFHSD-fed mice were treated with streptozocin to develop diabetes (HFHSD-DM). In PVAT-free aortas, the endothelial-dependent relaxation (EDR) did not differ between ND and HFHSD (p = 0.25), but in aortas with PVAT, the EDR of HFHSD-fed mice was impaired compared with ND-fed mice (p = 0.005). HFHSD-DM, HFHSD-SH, and HFHSD-Chol impaired the EDR in aortas without PVAT (p < 0.001, p = 0.019, and p = 0.009 vs. ND, respectively). Furthermore, tempol rescued the EDR in those models. In the Mets model, the EDR is compromised by PVAT, but with the addition of DM, dyslipidemia, and SH, the vessels themselves may result in impaired EDR.

Endothelial Extracellular Signal-Regulated Kinase/Thromboxane A2/Prostanoid Receptor Pathway Aggravates Endothelial Dysfunction and Insulin Resistance in a Mouse Model of Metabolic Syndrome

Background Metabolic syndrome is characterized by insulin resistance, which impairs intracellular signaling pathways and endothelial NO bioactivity, leading to cardiovascular complications. Extracellular signal-regulated kinase (ERK) is a major component of insulin signaling cascades that can be activated by many vasoactive peptides, hormones, and cytokines that are elevated in metabolic syndrome. The aim of this study was to clarify the role of endothelial ERK2 in vivo on NO bioactivity and insulin resistance in a mouse model of metabolic syndrome. Methods and Results Control and endothelial-specific ERK2 knockout mice were fed a high-fat/high-sucrose diet (HFHSD) for 24 weeks. Systolic blood pressure, endothelial function, and glucose metabolism were investigated. Systolic blood pressure was lowered with increased NO products and decreased thromboxane A2/prostanoid (TP) products in HFHSD-fed ERK2 knockout mice, and Nω-nitro-l-arginine methyl ester (L-NAME) increased it to the levels observed in HFHSD-fed controls. Acetylcholine-induced relaxation of aortic rings was increased, and aortic superoxide level was lowered in HFHSD-fed ERK2 knockout mice. S18886, an antagonist of the TP receptor, improved endothelial function and decreased superoxide level only in the rings from HFHSD-fed controls. Glucose intolerance and the impaired insulin sensitivity were blunted in HFHSD-fed ERK2 knockout mice without changes in body weight. In vivo, S18886 improved endothelial dysfunction, systolic blood pressure, fasting serum glucose and insulin levels, and suppressed nonalcoholic fatty liver disease scores only in HFHSD-fed controls. Conclusions Endothelial ERK2 increased superoxide level and decreased NO bioactivity, resulting in the deterioration of endothelial function, insulin resistance, and steatohepatitis, which were improved by a TP receptor antagonist, in a mouse model of metabolic syndrome.

Insight into the hepatoprotective, hypolipidemic, and antidiabetic impacts of aliskiren in streptozotocin-induced diabetic liver disease in mice

BACKGROUND

Diabetic hepatopathy is a serious complication of poorly controlled diabetes mellitus. An efficient antidiabetic drug which keeps normal liver tissues is not available. The renin-angiotensin system has been reported to be involved in both diabetic state and liver function. Aliskiren is a direct renin inhibitor and a recently antihypertensive drug with poly-pharmacological properties. The aim of the current study is to explore the possible hepatoprotective effects and mechanisms of action of aliskiren against streptozotocin (STZ) induced liver toxicity.

METHODS

Mice were distributed to 3 groups; first: the normal control group, second: the diabetic control group, third: the diabetic group which received aliskiren (25 mg/kg; oral) for 4 weeks. At the end of the treatment period, plasma glucose, insulin, lipid profile, oxidative stress, and liver function tests were evaluated spectrophotometrically. ELISA technique was used to measure the expression levels of TNF-α and adiponectin. Furthermore, a Histopathological examination of liver samples was done.

RESULTS

It was shown that aliskiren treatment ameliorated the STZ-induced oxidative stress and elevated inflammatory biomarkers, hypercholesterolemia, serum aminotransferases and alkaline phosphatase levels in diabetic mice. In addition, hepatocellular necrosis, and fibrosis were improved by aliskiren treatment.

CONCLUSION

aliskiren protects against the liver damage caused by STZ-induced diabetes. This can be explained by its ability to block angiotensin-II, and its anti-diabetic, hypocholesterolemic, antioxidant and anti-inflammatory effects. Aliskiren could be a novel therapeutic strategy to prevent liver diseases associated with hypertension and diabetes mellitus.

The emerging role of leptin in obesity-associated cardiac fibrosis: evidence and mechanism

Cardiac fibrosis is a hallmark of various cardiovascular diseases, which is quite commonly found in obesity, and may contribute to the increased incidence of heart failure arrhythmias, and sudden cardiac death in obese populations. As an endogenous regulator of adiposity metabolism, body mass, and energy balance, obesity, characterized by increased circulating levels of the adipocyte-derived hormone leptin, is a critical contributor to the pathogenesis of cardiac fibrosis. Although there are some gaps in our knowledge linking leptin and cardiac fibrosis, this review will focus on the interplay between leptin and major effectors involved in the pathogenesis underlying cardiac fibrosis at both cellular and molecular levels based on the current reports. The profibrotic effect of leptin is predominantly mediated by activated cardiac fibroblasts but may also involve cardiomyocytes, endothelial cells, and immune cells. Moreover, a series of molecular signals with a known profibrotic property is closely involved in leptin-induced fibrotic events. A more comprehensive understanding of the underlying mechanisms through which leptin contributes to the pathogenesis of cardiac fibrosis may open up a new avenue for the rapid emergence of a novel therapy for preventing or even reversing obesity-associated cardiac fibrosis.

Metabolic Remodeling with Hepatosteatosis Induced Vascular Oxidative Stress in Hepatic ERK2 Deficiency Mice with High Fat Diets

We previously demonstrated the marked hepatosteatosis and endothelial dysfunction in hepatocyte-specific ERK2 knockout mice (LE2KO) with a high-fat/high-sucrose diet (HFHSD), but detailed metabolic changes and the characteristics in insulin-sensitive organs were not tested. This study aimed to characterize metabolic remodeling with changes in insulin-sensitive organs, which could induce endothelial dysfunction in HFHSD-LE2KO. The serum glucose and fatty acid (FA) were modestly higher in HFHSD-LE2KO than HFHSD-Control. FA synthesis genes were up-regulated, which was associated with the decreased phosphorylation of AMPK and ACC, and with the up-regulation of SREBP-1 in the liver from HFHSD-LE2KO. In FA and amino acids fraction analysis, arachidonic acid/eicosapentaenoic acid ratio, L-ornithine/arginine ratio, asymmetric dimethylarginine and homocysteine levels were elevated in HFHSD-LE2KO. Insulin-induced phosphorylation of AKT was blunted in skeletal muscle. Serum leptin and IL-1β were elevated, and serum adiponectin was decreased with the enlargement of epididymal adipocytes. Finally, the enhanced superoxide levels in the aorta, which were blunted with CCCP, apocynin, and tempol, were observed in HFHSD-LE2KO. A pre-incubation of aortic rings with tempol improved endothelial dysfunction in HFHSD-LE2KO. HFHSD-LE2KO revealed an acceleration of FA synthesis in the liver leading to insulin resistance in skeletal muscle and the enlargement of visceral adipocytes. Global metabolic remodeling such as changes in arginine metabolism, ω3/ω6 ratio, and adipocytokines, could affect the vascular oxidative stress and endothelial dysfunction in HFHSD-LE2KO.

Obesity Animal Models for Acupuncture and Related Therapy Research Studies

Obesity and related diseases are considered as pandemic representing a worldwide threat for health. Animal models are critical to validate the effects and understand the mechanisms related to classical or innovative preventive and therapeutic strategies. It is, therefore, important to identify the best animal models for translational research, using different evaluation criteria such as the face, construct, and predictive validity. Because the pharmacological treatments and surgical interventions currently used for treating obesity often present many undesirable side effects, relatively high relapse probabilities, acupuncture, electroacupuncture (EA), and related therapies have gained more popularity and attention. Many kinds of experimental animal models have been used for obesity research studies, but in the context of acupuncture, most of the studies were performed in rodent obesity models. Though, are these obesity rodent models really the best for acupuncture or related therapies research studies? In this study, we review different obesity animal models that have been used over the past 10 years for acupuncture and EA research studies. We present their respective advantages, disadvantages, and specific constraints. With the development of research on acupuncture and EA and the increasing interest regarding these approaches, proper animal models are critical for preclinical studies aiming at developing future clinical trials in the human. The aim of the present study is to provide researchers with information and guidance related to the preclinical models that are currently available to investigate the outcomes of acupuncture and related therapies.

Therapeutic Renin Inhibition in Diabetic Nephropathy-A Review of the Physiological Evidence

The purpose of this systematic review was to investigate the scientific evidence to support the use of direct renin inhibitors (DRIs) in diabetic nephropathy (DN). MEDLINE was searched for articles reported until 2018. A standardized dataset was extracted from articles describing the effects of DRIs on plasma renin activity (PRA) in DN. A total of three clinical articles studying PRA as an outcome measure for DRIs use in DN were identified. These clinical studies were randomized controlled trials (RCTs): one double-blind crossover, one post hoc of a double-blind and placebo-controlled study, and one open-label and parallel-controlled study. Two studies reported a significant decrease of albuminuria associated with PRA reduction. One study had a DRI as monotherapy compared with placebo, and two studies had DRI as add-in to an angiotensin II (Ang II) receptor blocker (ARB). Of 10,393 patients with DN enrolled in five studies with DRI, 370 (3.6%) patients had PRA measured. Only one preclinical study was identified that determined PRA when investigating the effects of aliskiren in DN. Moreover, most of observational preclinical and clinical studies identified report on a low PRA or hyporeninemic hypoaldosteronism in DM. Renin inhibition has been suggested for DN, but proof-of-concept studies for this are scant. A small number of clinical and preclinical studies assessed the PRA effects of DRIs in DN. For a more successful translational research for DRIs, specific patient population responsive to the treatment should be identified, and PRA may remain a biomarker of choice for patient stratification.

The Vascular Consequences of Metabolic Syndrome: Rodent Models, Endothelial Dysfunction, and Current Therapies

Metabolic syndrome is characterized by visceral obesity, dyslipidemia, hyperglycemia and hypertension, and affects over one billion people. Independently, the components of metabolic syndrome each have the potential to affect the endothelium to cause vascular dysfunction and disrupt vascular homeostasis. Rodent models of metabolic syndrome have significantly advanced our understanding of this multifactorial condition. In this mini-review we compare the currently available rodent models of metabolic syndrome and consider their limitations. We also discuss the numerous mechanisms by which metabolic abnormalities cause endothelial dysfunction and highlight some common pathophysiologies including reduced nitric oxide production, increased reactive oxygen species and increased production of vasoconstrictors. Additionally, we explore some of the current therapeutics for the comorbidities of metabolic syndrome and consider how these benefit the vasculature.

The use of aliskiren as an antifibrotic drug in experimental models: A systematic review

Aliskiren is an oral antihypertensive medication that acts by directly inhibiting renin. High levels of circulating renin and prorenin activate the pathological signaling pathway of fibrosis. This drug also reduces oxidative stress. Thus, the aim of this systematic review is to analyze experimental studies that show the actions of aliskiren on fibrosis. PubMed and LILACS databases were consulted using the keywords aliskiren and fibrosis within the period between 2005 and 2017. Fifty-three articles were analyzed. In the heart, aliskiren attenuated remodeling, hypertrophy, inflammatory cytokines, collagen deposition, and oxidative stress. In the kidneys, there was a reduction in interstitial fibrosis, the infiltration of inflammatory cells, apoptosis, proteinuria, and in the recruitment of macrophages. In diabetic models, an improvement in the albumin/creatinine relationship and in the insulin pathway in skeletal muscles was observed; aliskiren was beneficial to pancreatic function and glucose tolerance. In the liver, aliskiren reduced fibrosis, steatosis, inflammatory cytokines, and collagen deposition. In the lung and peritoneal tissues, there was a reduction in fibrosis. Many studies have reported on the beneficial effects of aliskiren on endothelial function and arterial rigidity. A reduction in fibrosis in different organs is cited by many authors, which complies with the results found in this review. However, studies diverge on the use of the drug in diabetic patients. Aliskiren has antifibrotic potential in several experimental models, interfering with the levels of fibrogenic cytokines and oxidative stress. Therefore, its use in diseases in which fibrosis plays an important pathophysiological role is suggested.

The renin-angiotensin system as a target to solve the riddle of endocrine pancreas homeostasis

Local renin-angiotensin system (RAS) in the pancreas is linked to the modulation of glucose-stimulated insulin secretion (GSIS) in beta cells and insulin sensitivity in target tissues, emerging as a promising tool in the prevention and/or treatment of obesity, diabetes, and systemic arterial hypertension. Insulin resistance alters pancreatic islet cell distribution and morphology and hypertrophied islets exhibit upregulated angiotensin II type 1 receptor, which drives oxidative stress, apoptosis, and fibrosis, configuring beta cell dysfunction and diminishing islet lifespan. Pharmacological modulation of RAS has shown beneficial effects in diet-induced obesity model, mainly related to the translational potential that angiotensin receptor blockers and ECA2/ANG (1-7)/MAS receptor axis modulation have when it comes to islet preservation and type 2 diabetes prevention and/or treatment. This review describes the existing evidence for different approaches to blocking RAS elements in the management of insulin resistance and diabetes and focuses on islet remodeling and GSIS in rodents and humans.

Telmisartan is effective to ameliorate metabolic syndrome in rat model - a preclinical report

BACKGROUND

Metabolic syndrome (MS) is known to be associated with hypertension, insulin resistance, and dyslipidemia, and it raises the risk for cardiovascular diseases and diabetes mellitus. Telmisartan is used in clinic as an angiotensin II receptor blocker and it is also identified as activating peroxisome proliferator-activated receptors δ (PPARδ). Activation of PPARδ produced beneficial effects on fatty acid metabolism and glucose metabolism. This study aims to investigate the effects of telmisartan on the modulation of MS in rats fed a high-fat/high-sodium diet.

METHODS

Rats were fed with a high-fat/high-sodium diet and received injections of streptozotocin at low dose to induce MS. Then, rats with MS were treated with telmisartan. The weight, glucose tolerance, and insulin sensitivity were measured. The lipid profiles were also obtained. The weights of retroperitoneal and epididymal fat pads were determined. The role of PPARδ in telmisartan treatment was identified in rats pretreated with the specific antagonist GSK0660.

RESULTS

The results showed that telmisartan, but not losartan, significantly reduced plasma glucose and plasma insulin, and improved insulin resistance in rats with MS. Telmisartan also decreased blood pressure and lipids more significantly than losartan. Moreover, GSK0660 effectively reversed the effects of telmisartan in the MS rats. In the MS group, telmisartan activated PPARδ to enhance the levels of phosphorylated GLUT4 in muscle or the expression of phosphoenolpyruvate carboxykinase (PEPCK) in the liver, which was also abolished by GSK0660. Telmisartan is useful to ameliorate hypertension and insulin resistance in rats with MS. Telmisartan improves the insulin resistance through increased expression of GLUT4 and down-regulation of PEPCK via PPARδ-dependent mechanisms.

CONCLUSION

Telmisartan has been proven to ameliorate MS, particularly in the prediabetes state. Therefore, telmisartan is suitable to develop for the management of MS in clinics.

Animal models of metabolic syndrome: a review

Metabolic syndrome (MetS) consists of several medical conditions that collectively predict the risk for cardiovascular disease better than the sum of individual conditions. The risk of developing MetS in human depends on synergy of both genetic and environmental factors. Being a multifactorial condition with alarming rate of prevalence nowadays, establishment of appropriate experimental animal models mimicking the disease state in humans is crucial in order to solve the difficulties in evaluating the pathophysiology of MetS in human. This review aims to summarize the underlying mechanisms involved in the pathophysiology of dietary, genetic, and pharmacological models of MetS. Furthermore, we will discuss the usefulness, suitability, pros and cons of these animal models. Even though numerous animal models of MetS have been established, further investigations on the invention of new animal model and clarification of plausible mechanisms are still necessary to confer a better understanding to researchers on the selection of animal models for their studies.

DPP-4 inhibition with linagliptin ameliorates cognitive impairment and brain atrophy induced by transient cerebral ischemia in type 2 diabetic mice

Background

It is unclear whether dipeptidylpeptidase-4 (DPP-4) inhibition can counteract the impairment of cognitive function and brain injury caused by transient cerebral ischemia in type 2 diabetes. The present study was undertaken to test our hypothesis that linagliptin, a DPP-4 inhibitor, administration following transient cerebral ischemia can ameliorate cognitive impairment and brain injury in diabetic mice.

Methods

db/db mice, a model of obese type 2 diabetes, were subjected to transient cerebral ischemia by 17 min of bilateral common carotid artery occlusion (BCCAO), and were administered (1) vehicle or (2) linagliptin for 8 weeks or 1 week. For the long-term experiment on 8 weeks of linagliptin treatment, cognitive function, and volume and neuronal cell number of hippocampus and cortex were estimated in each group of mice. For the short-term experiment on 1 week of linagliptin treatment, cerebral IgG extravasation, Iba-1 positive cell number (reactive microglia), oxidative stress, and claudin-5 and gp91phox protein levels were measured in each group of mice.

Results

Linagliptin administration almost completely suppressed the circulating DPP-4 activity in db/db mice, but did not significantly reduce blood glucose or ameliorate glucose intolerance in db/db mice. Linagliptin administration following transient cerebral ischemia significantly counteracted cognitive impairment in diabetic mice, as estimated by water maze test and passive avoidance test. Linagliptin administration ameliorated the decrease in cerebral volume and neuronal cell number in hippocampus and cortex of diabetic mice. Linagliptin administration significantly reduced the increase in cerebral IgG extravasation and the increase in reactive microglia caused by transient cerebral ischemia in diabetic mice. Furthermore, linagliptin significantly suppressed the increase in cerebral oxidative stress in transient cerebral ischemia-subjected diabetic mice. Furthermore, linagliptin significantly increased cerebral claudin-5 and significantly decreased gp91phox in diabetic mice subjected to transient cerebral ischemia.

Conclusions

DPP-4 inhibition with linagliptin counteracted cognitive impairment and brain atrophy induced by transient cerebral ischemia in diabetic mice, independently of blood glucose lowering effect. This cerebroprotective effect of linagliptin was associated with the suppression of blood-brain barrier disruption and the attenuation of cerebral oxidative stress. Thus, our present work highlights DPP-4 inhibition as a promising therapeutic strategy for cognitive impairment and cerebral vascular complications in type 2 diabetes.

Glycemic control with empagliflozin, a novel selective SGLT2 inhibitor, ameliorates cardiovascular injury and cognitive dysfunction in obese and type 2 diabetic mice

Background

There has been uncertainty regarding the benefit of glycemic control with antidiabetic agents in prevention of diabetic macrovascular disease. Further development of novel antidiabetic agents is essential for overcoming the burden of diabetic macrovascular disease. The renal sodium glucose co-transporter 2 (SGLT2) inhibitor is a novel antihyperglycemic agent for treatment of type 2 diabetes. This work was performed to determine whether empagliflozin, a novel SGLT2 inhibitor, can ameliorate cardiovascular injury and cognitive decline in db/db mouse, a model of obesity and type 2 diabetes.

Methods

(1) Short-term experiment: The first experiment was performed to examine the effect of 7 days of empagliflozin treatment on urinary glucose excretion and urinary electrolyte excretion in db/db mice. (2) Long-term experiment: The second experiment was undertaken to examine the effect of 10 weeks of empagliflozin treatment on cardiovascular injury, vascular dysfunction, cognitive decline, and renal injury in db/db mice.

Results

(1) Short-term experiment: Empagliflozin administration significantly increased urinary glucose excretion, urine volume, and urinary sodium excretion in db/db mice on day 1, but did not increase these parameters from day 2. However, blood glucose levels in db/db mice were continuously decreased by empagliflozin throughout 7 days of the treatment. (2) Long-term experiment: Empagliflozin treatment caused sustained decrease in blood glucose in db/db mice throughout 10 weeks of the treatment and significantly slowed the progression of type 2 diabetes. Empagliflozin significantly ameliorated cardiac interstitial fibrosis, pericoronary arterial fibrosis, coronary arterial thickening, cardiac macrophage infiltration, and the impairment of vascular dilating function in db/db mice, and these beneficial effects of empagliflozin were associated with attenuation of oxidative stress in cardiovascular tissue of db/db mice. Furthermore, empagliflozin significantly prevented the impairment of cognitive function in db/db mice, which was associated with the attenuation of cerebral oxidative stress and the increase in cerebral brain-derived neurotrophic factor. Empagliflozin ameliorated albuminuria, and glomerular injury in db/db mice.

Conclusions

Glycemic control with empagliflozin significantly ameliorated cardiovascular injury and remodeling, vascular dysfunction, and cognitive decline in obese and type 2 diabetic mice. Thus, empagliflozin seems to be potentially a promising therapeutic agent for diabetic macrovascular disease and cognitive decline.

Approach to assessing determinants of glucose homeostasis in the conscious mouse

Obesity and type 2 diabetes lessen the quality of life of those afflicted and place considerable burden on the healthcare system. Furthermore, the detrimental impact of these pathologies is expected to persist or even worsen. Diabetes is characterized by impaired insulin action and glucose homeostasis. This has led to a rapid increase in the number of mouse models of metabolic disease being used in the basic sciences to assist in facilitating a greater understanding of the metabolic dysregulation associated with obesity and diabetes, the identification of therapeutic targets, and the discovery of effective treatments. This review briefly describes the most frequently utilized models of metabolic disease. A presentation of standard methods and technologies on the horizon for assessing metabolic phenotypes in mice, with particular emphasis on glucose handling and energy balance, is provided. The article also addresses issues related to study design, selection and execution of metabolic tests of glucose metabolism, the presentation of data, and interpretation of results.

Protective effects of aliskiren, a direct renin inhibitor, in rats with acute pancreatitis

AIM: To investigate the inhibitory effects of aliskiren on the renin angiotensin system (RAS) in rats with acute pancreatitis (AP) and to explore the mechanisms involved.

METHODS: Seventy-two SD rats were randomly divided into a sham operation group, an acute AP model group, and an aliskiren therapy group. AP was induced by retrograde injection of 3.5% sodium taurocholate (0.1 mL/100 g) into the biliopancreatic duct. Aliskiren solution was administered in rats of the aliskiren therapy group by gavage at a dose of 20 mg/kg, and equivalent volume of normal saline (NS) was given in the other two groups. Rats in each group were further divided into three subgroups for taking inferior vena cava blood samples at 6, 12 and 24 h, respectively. The rats were then killed to observe pancreatic pathological changes and measure serum amylase (AMY), tumor necrosis factor-α (TNF-α), angiotensin Ⅱ (Ang Ⅱ), and plasma renin activity (PRA). The expression of nuclear factor kappa-B (NF-kB) and angiotensin Ⅱ type 1 receptor (AT1R) in the pancreas was determined by immunohistochemistry．

RESULTS: Compared with the AP group, pancreatic histopathological score (7.25 ± 0.80, 9.57 ± 1.54, 12.75 ± 1.22), AMY (2230.87 U/L ± 224.71 U/L, 2137.41 U/L ± 193.31 U/L, 2457.01 U/L ± 188.81 U/L), TNF-α (26.28 ng/L ± 2.45 ng/L, 27.51 ng/L ± 1.91 ng/L, 27.17 ng/L ± 2.02 ng/L), PRA [7.31 ng/(mL•h) ± 1.94 ng/(mL•h), 8.69 ng/(mL•h) ± 1.78 ng/(mL•h), 9.04 ng/(mL•h) ± 1.78 ng/(mL•h)], Ang Ⅱ (755.47 ng/L ± 121.33 ng/L, 871.17 ng/L ± 129.43 ng/L, 878.39 ng/L ± 81.29 ng/L), positive rates of AT1R (48.60 ± 6.28, 49.62 ± 7.19, 51.20 ± 7.04) and NF-κB (65.66 ± 4.93, 68.66 ± 5.23, 68.13 ± 7.14) at each time point (6, 12, 24 h) were decreased significantly (P < 0.05 for all) in the aliskiren therapy group.

CONCLUSION: Aliskiren can protect from pancreatic inflammation and injury in AP rats.

Aliskiren-attenuated myocardium apoptosis via regulation of autophagy and connexin-43 in aged spontaneously hypertensive rats

There are controversies about the mechanism of myocardium apoptosis in hypertensive heart disease. The aim of this study was to investigate the relationship among autophagy, Cx43 and apoptosis in aged spontaneously hypertensive rats (SHRs) and establish whether Aliskiren is effective or not for the treatment of myocardium apoptosis. Twenty-one SHRs aged 52 weeks were randomly divided into three groups, the first two receiving Aliskiren at a dose of 10 and 25 mg/kg/day respectively; the third, placebo for comparison with seven Wistar-Kyoto (WKY) as controls. After a 2-month treatment, systolic blood pressure (SBP), heart to bw ratios (HW/BW%) and angiotensin II (AngII) concentration were significantly enhanced in SHRs respectively. Apoptotic cardiomyocytes detected with TUNEL and immunofluorescent labelling for active caspase-3 increased nearly fourfolds in SHRs, with a decline in the expression of survivin and AKT activation, and an increase in caspase-3 activation and the ratio of Bax/Bcl-2. Myocardium autophagy, detected with immunofluorescent labelling for LC3-II, increased nearly threefolds in SHRs, with the up-regulation of Atg5, Atg16L1, Beclin-1 and LC3-II. The expression of Cx43 plaque was found to be down-regulated in SHRs. Aliskiren significantly reduced SBP, HW/BW%, AngII concentration and the expression of AT(1)R. Thus, Aliskiren protects myocardium against apoptosis by decreasing autophagy, up-regulating Cx43. These effects showed a dose-dependent tendency, but no significance. In conclusion, the myocardium apoptosis developed during the hypertensive end-stage of SHRs could be ameliorated by Aliskiren via the regulation of myocardium autophagy and maladaptive remodelling of Cx43.

Deterioration of kidney function by the (pro)renin receptor blocker handle region peptide in aliskiren-treated diabetic transgenic (mRen2)27 rats

Dual renin-angiotensin system (RAS) blockade in diabetic nephropathy is no longer feasible because of the profit/side effect imbalance. (Pro)renin receptor [(P)RR] blockade with handle region peptide (HRP) has been reported to exert beneficial effects in various diabetic models in a RAS-independent manner. To what degree (P)RR blockade adds benefits on top of RAS blockade is still unknown. In the present study, we treated diabetic TGR(mREN2)27 rats, a well-established nephropathy model with high prorenin levels [allowing continuous (P)RR stimulation in vivo], with HRP on top of renin inhibition with aliskiren. Aliskiren alone lowered blood pressure and exerted renoprotective effects, as evidenced by reduced glomerulosclerosis, diuresis, proteinuria, albuminuria, and urinary aldosterone levels as well as diminished renal (P)RR and ANG II type 1 receptor expression. It also suppressed plasma and tissue RAS activity and suppressed cardiac atrial natriuretic peptide and brain natriuretic peptide expression. HRP, when given on top of aliskiren, did not alter the effects of renin inhibition on blood pressure, RAS activity, or aldosterone. However, it counteracted the beneficial effects of aliskiren in the kidney, induced hyperkalemia, and increased plasma plasminogen activator-inhibitor 1, renal cyclooxygenase-2, and cardiac collagen content. All these effects have been linked to (P)RR stimulation, suggesting that HRP might, in fact, act as a partial agonist. Therefore, the use of HRP on top of RAS blockade in diabetic nephropathy is not advisable.

Aliskiren limits abdominal aortic aneurysm, ventricular hypertrophy and atherosclerosis in an apolipoprotein-E-deficient mouse model

In the present study, the efficacy of aliskiren in limiting the progression of abdominal aortic aneurysm, ventricular hypertrophy and atherosclerosis were examined in a mouse model. Aliskiren limited the progression of these pathologies, suggesting the potential of this medication for cardiovascular-protective protection.

Direct renin inhibition with aliskiren protects against myocardial ischemia/reperfusion injury by activating nitric oxide synthase signaling in spontaneously hypertensive rats

BACKGROUND

We tested the hypothesis that direct renin inhibition with aliskiren protects against myocardial ischemia/reperfusion (I/R) injury in spontaneously hypertensive rats (SHR), and examined the mechanism by which this occurs.

METHODS AND RESULTS

Male SHR were treated (orally, 4 weeks) with saline or aliskiren (30 or 60 mg kg(-1) day(-1)) and subjected to 30 minutes of left anterior descending coronary artery occlusion followed by 6 or 24 hours of reperfusion. Only the higher dose significantly lowered systolic blood pressure, the lower dose causing a smaller apparent lowering that was nonsignificant. Despite this difference in blood pressure-lowering effect, both doses increased the ejection fraction and fractional shortening and reduced myocardial infarct size equally. I/R decreased cardiac expression of phosphatidylinositol 3-kinase (PI3K), phospho-Akt and phospho-endothelial nitric oxide synthase (phospho-eNOS), but increased expression of inducible nitric oxide synthase (iNOS); these changes were all abrogated by aliskiren. Moreover, aliskiren decreased superoxide anion generation and increased cyclic guanosine-3',5'-monophosphate, an index of bioactive nitric oxide, in myocardium. It also decreased the expression of myocardial matrix metalloproteinase-2, matrix metalloproteinase-9, and tissue inhibitor of metalloproteinases-1 (TIMP-1) following I/R. In a Langendorff heart preparation, the detrimental cardiac effects of I/R were abrogated by aliskiren, and these protective effects were abolished by NOS or PI3K inhibition. In a parallel study, although specific iNOS inhibition reduced plasma malondialdehyde and myocardial superoxide anion generation, it did not affect the deleterious effects of I/R on myocardial structure and function.

CONCLUSIONS

Direct renin inhibition protects against myocardial I/R injury through activation of the PI3K-Akt-eNOS pathway.

Metallothionein deficiency exacerbates diabetic nephropathy in streptozotocin-induced diabetic mice

Oxidative stress and inflammation play important roles in diabetic complications, including diabetic nephropathy. Metallothionein (MT) is induced in proximal tubular epithelial cells as an antioxidant in the diabetic kidney; however, the role of MT in renal function remains unclear. We therefore investigated whether MT deficiency accelerates diabetic nephropathy through oxidative stress and inflammation. Diabetes was induced by streptozotocin injection in MT-deficient (MT−/−) and MT+/+ mice. Urinary albumin excretion, histological changes, markers for reactive oxygen species (ROS), and kidney inflammation were measured. Murine proximal tubular epithelial (mProx24) cells were used to further elucidate the role of MT under high-glucose conditions. Parameters of diabetic nephropathy and markers of ROS and inflammation were accelerated in diabetic MT−/− mice compared with diabetic MT+/+ mice, despite equivalent levels of hyperglycemia. MT deficiency accelerated interstitial fibrosis and macrophage infiltration into the interstitium in the diabetic kidney. Electron microscopy revealed abnormal mitochondrial morphology in proximal tubular epithelial cells in diabetic MT−/− mice. In vitro studies demonstrated that knockdown of MT by small interfering RNA enhanced mitochondrial ROS generation and inflammation-related gene expression in mProx24 cells cultured under high-glucose conditions. The results of this study suggest that MT may play a key role in protecting the kidney against high glucose-induced ROS and subsequent inflammation in diabetic nephropathy.

(Pro)renin receptor and insulin resistance: possible roles of angiotensin II-dependent and -independent pathways

A growing body of evidence has suggested the potential role of (pro)renin receptor [(P)RR] in the pathogenesis of cardiovascular and renal injuries during the development of hypertension and diabetes. However, there is very little information on the contribution of (P)RR to the pathophysiology of insulin resistance. In this regard, our preliminary data showed that the development of insulin resistance was associated with nonproteolytic activation of prorenin as well as local angiotensin II generation in skeletal muscle and adipose tissues of obese Otsuka Long-Evans Tokushima Fatty rats. In fructose-fed rats, insulin resistance was also associated with nonproteolytic activation of prorenin and skeletal muscle angiotensin II generation. Furthermore, inhibition of (P)RR with handle region decoy peptide (HRP) improved the development of fructose-induced insulin resistance. However, in other animal model, such as transgenic rats overexpressing the human renin gene, HRP failed to ameliorate glucose intolerance. In this review, we will summarized the current knowledge regarding the possible contribution of (P)RR to the pathophysiology of insulin resistance.

Coronary endothelial dysfunction and mitochondrial reactive oxygen species in type 2 diabetic mice

Endothelial cell (EC) dysfunction is implicated in cardiovascular diseases, including diabetes. The decrease in nitric oxide (NO) bioavailability is the hallmark of endothelial dysfunction, and it leads to attenuated vascular relaxation and atherosclerosis followed by a decrease in blood flow. In the heart, decreased coronary blood flow is responsible for insufficient oxygen supply to cardiomyocytes and, subsequently, increases the incidence of cardiac ischemia. In this study we investigate whether and how reactive oxygen species (ROS) in mitochondria contribute to coronary endothelial dysfunction in type 2 diabetic (T2D) mice. T2D was induced in mice by a high-fat diet combined with a single injection of low-dose streptozotocin. ACh-induced vascular relaxation was significantly attenuated in coronary arteries (CAs) from T2D mice compared with controls. The pharmacological approach reveals that NO-dependent, but not hyperpolarization- or prostacyclin-dependent, relaxation was decreased in CAs from T2D mice. Attenuated ACh-induced relaxation in CAs from T2D mice was restored toward control level by treatment with mitoTempol (a mitochondria-specific O2(-) scavenger). Coronary ECs isolated from T2D mice exhibited a significant increase in mitochondrial ROS concentration and decrease in SOD2 protein expression compared with coronary ECs isolated from control mice. Furthermore, protein ubiquitination of SOD2 was significantly increased in coronary ECs isolated from T2D mice. These results suggest that augmented SOD2 ubiquitination leads to the increase in mitochondrial ROS concentration in coronary ECs from T2D mice and attenuates coronary vascular relaxation in T2D mice.

Myocardial tissue remodeling in adolescent obesity

BACKGROUND

Childhood obesity is a significant risk factor for cardiovascular disease in adulthood. Although ventricular remodeling has been reported in obese youth, early tissue-level markers within the myocardium that precede organ-level alterations have not been described.

METHODS AND RESULTS

We studied 21 obese adolescents (mean age, 17.7±2.6 years; mean body mass index [BMI], 41.9±9.5 kg/m(2), including 11 patients with type 2 diabetes [T2D]) and 12 healthy volunteers (age, 15.1±4.5 years; BMI, 20.1±3.5 kg/m(2)) using biomarkers of cardiometabolic risk and cardiac magnetic resonance imaging (CMR) to phenotype cardiac structure, function, and interstitial matrix remodeling by standard techniques. Although left ventricular ejection fraction and left atrial volumes were similar in healthy volunteers and obese patients (and within normal body size-adjusted limits), interstitial matrix expansion by CMR extracellular volume fraction (ECV) was significantly different between healthy volunteers (median, 0.264; interquartile range [IQR], 0.253 to 0.271), obese adolescents without T2D (median, 0.328; IQR, 0.278 to 0.345), and obese adolescents with T2D (median, 0.376; IQR, 0.336 to 0.407; P=0.0001). ECV was associated with BMI for the entire population (r=0.58, P<0.001) and with high-sensitivity C-reactive protein (r=0.47, P<0.05), serum triglycerides (r=0.51, P<0.05), and hemoglobin A1c (r=0.76, P<0.0001) in the obese stratum.

CONCLUSIONS

Obese adolescents (particularly those with T2D) have subclinical alterations in myocardial tissue architecture associated with inflammation and insulin resistance. These alterations precede significant left ventricular hypertrophy or decreased cardiac function.

Hepatic extracellular signal-regulated kinase 2 suppresses endoplasmic reticulum stress and protects from oxidative stress and endothelial dysfunction

Background

Insulin signaling comprises 2 major cascades: the insulin receptor substrate/phosphatidylinositol 3′‐kinase/protein kinase B and Ras/Raf/mitogen‐activated protein kinase/kinase/ERK pathways. While many studies on the tissue‐specific effects of the insulin receptor substrate/phosphatidylinositol 3′ ‐kinase/protein kinase B pathway have been conducted, the role of the other cascade in tissue‐specific insulin resistance has not been investigated. High glucose/fatty acid toxicity, inflammation, and oxidative stress, all of which are associated with insulin resistance, can activate ERK. The liver plays a central role in metabolism, and hepatosteatosis is associated with vascular diseases. The aim of study was to elucidate the role of hepatic ERK2 in hepatosteatosis, metabolic remodeling, and endothelial dysfunction.

Methods and Results

We created liver‐specific ERK2 knockout mice and fed them with a high‐fat/high‐sucrose diet for 20 weeks. The high‐fat/high‐sucrose diet–fed liver‐specific ERK2 knockout mice exhibited a marked deterioration in hepatosteatosis and metabolic remodeling represented by impairment of glucose tolerance and decreased insulin sensitivity without changes in body weight, blood pressure, and serum cholesterol/triglyceride levels. In the mice, endoplasmic reticulum stress was induced together with decreased mRNA and protein expressions of hepatic sarco/endoplasmic reticulum Ca²⁺‐ATPase 2. In a hepatoma cell line, inhibition of ERK activation– induced endoplasmic reticulum stress only in the presence of palmitate. Vascular reactive oxygen species were elevated with upregulation of nicotinamide adenine dinucleotide phosphate oxidase1 (Nox1) and Nox4 and decreased phosphorylation of endothelial nitric oxide synthase, which resulted in the remarkable endothelial dysfunction in high‐fat/high‐sucrose diet–fed liver‐specific ERK2 knockout mice.

Conclusions

Hepatic ERK2 suppresses endoplasmic reticulum stress and hepatosteatosis in vivo, which results in protection from vascular oxidative stress and endothelial dysfunction. These findings demonstrate a novel role of hepatic ERK2 in obese‐induced insulin resistance in the protection from hepatovascular metabolic remodeling and vascular diseases.

Renin-angiotensin system blockers protect pancreatic islets against diet-induced obesity and insulin resistance in mice

Background

The associations between obesity, hypertension and diabetes are well established, and the renin-angiotensin system (RAS) may provide a link among them. The effect of RAS inhibition on type 2 diabetes is still unclear; however, RAS seems to play an important role in the regulation of the pancreas and glucose intolerance of mice fed high-fat (HF) diet.

Methods

C57BL/6 mice fed a HF diet (8 weeks) were treated with aliskiren (50 mg/kg/day), enalapril (30 mg/kg/day) or losartan (10 mg/kg/day) for 6 weeks, and the protective effects were extensively compared among groups by morphometry, stereological tools, immunostaining, Western blotting and hormonal analysis.

Results

All RAS inhibitors significantly attenuated the increased blood pressure in mice fed a HF diet. Treatment with enalapril, but not aliskiren or losartan, significantly attenuated body mass (BM) gain, glucose intolerance and insulin resistance, improved the alpha and beta cell mass and prevented the reduction of plasma adiponectin. Furthermore, enalapril treatment improved the protein expression of the pancreatic islet Pdx1, GLUT2, ACE2 and Mas receptors. Losartan treatment showed the greatest AT2R expression.

Conclusion

Our findings indicate that ACE inhibition with enalapril attenuated several of the deleterious effects of the HF diet. In summary, enalapril appears to be responsible for the normalization of islet morphology and function, of alpha and beta cell mass and of Pdx1 and GLUT2 expression. These protective effects of enalapril were attributed, primarily, to the reduction in body mass gain and food intake and the enhancement of the ACE2/Ang (1-7) /Mas receptor axis and adiponectin levels.

Aliskiren improves vascular smooth muscle function in the skin microcirculation of type 2 diabetic patients with normal renal function

OBJECTIVE

The objective of this paper is to study the effect of aliskiren on metabolic parameters and micro- and macrovascular reactivity in individuals diagnosed with or at high risk for developing type 2 diabetes mellitus (T2DM).

RESEARCH DESIGN AND METHODS

We studied 47 T2DM and 41 at-risk individuals in a randomized, double-blinded, placebo-controlled trial. All subjects were treated with 150 mg aliskiren or placebo daily for 12 weeks. Twenty-six (55%) of T2DM and four (8%) at-risk subjects were also treated with angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers.

RESULTS

Aliskiren treatment was associated with improvement in systolic and diastolic blood pressure and endothelium-independent vasodilation at the skin microcirculation in those with T2DM but not in those at risk. There were no incidences of hypotension and no significant changes in serum potassium or creatinine levels with aliskiren treatment in either study group.

CONCLUSIONS

Aliskiren improves blood pressure and vascular smooth muscle function in the skin microcirculation of T2DM patients.

The direct renin inhibitor aliskiren improves vascular remodelling in transgenic rats harbouring human renin and angiotensinogen genes

In the present study, we tested the hypothesis that chronic treatment with the direct rennin inhibitor aliskiren improves the remodelling of resistance arteries in dTGR (double-transgenic rats). dTGR (5 weeks) were treated with aliskiren (3 mg/kg of body mass per day) or ramipril (1 mg/kg of body mass per day) for 14 days and compared with age-matched vehicle-treated dTGR. BP (blood pressure) was similarly reduced in both aliskiren-treated and ramipril-treated rats compared with control dTGR (167±1 and 169±2 mmHg compared with 197±4 mmHg respectively; P<0.05). The M/L (media-to-lumen) ratio assessed on pressurized preparations was equally reduced in aliskiren-treated and ramipril-treated rats compared with controls (6.3±0.5 and 6.4±0.2% compared with 9.8±0.4% respectively; P<0.05). Endothelium-dependent and -independent relaxations were similar among the groups. L-NAME (NG-nitro-L-arginine methyl ester) significantly reduced acetylcholine-induced dilation in drug-treated dTGR. This effect was significantly more prominent in aliskiren-treated rats. eNOS (endothelial NO synthase) expression showed a 2-fold increase only in aliskiren-treated dTGR as compared with controls (P<0.01) and ramipril-treated dTGR (P<0.05). Plasma nitrite, as an index of NO production, was significantly increased in dTGR treated with either aliskiren or ramipril compared with controls. Only aliskiren induced a 2-fold increase in plasma nitrite, which was significantly greater than that induced by ramipril (P<0.05). gp91phox expression and ROS (reactive oxygen species) production in aorta were significantly and similarly reduced by both drugs. In conclusion, equieffective hypotensive doses of aliskiren or ramipril reduced the M/L ratio of mesenteric arteries and improved oxidative stress in dTGR. However, only aliskiren increased further NO production in the vasculature. Hence, in dTGR, direct renin inhibition induces favourable effects similar to that induced by ACE (angiotensin-converting enzyme) inhibition in improving vascular remodelling through different mechanisms.

TRPV1-mediated UCP2 upregulation ameliorates hyperglycemia-induced endothelial dysfunction

Background

Diabetic cardiovascular complications are characterised by oxidative stress-induced endothelial dysfunction. Uncoupling protein 2 (UCP2) is a regulator of mitochondrial reactive oxygen species (ROS) generation and can antagonise oxidative stress, but approaches that enhance the activity of UCP2 to inhibit ROS are scarce. Our previous studies show that activation of transient receptor potential vanilloid 1 (TRPV1) by capsaicin can prevent cardiometabolic disorders. In this study, we conducted experiments in vitro and in vivo to investigate the effect of capsaicin treatment on endothelial UCP2 and oxidative stress. We hypothesised that TRPV1 activation by capsaicin attenuates hyperglycemia-induced endothelial dysfunction through a UCP2-mediated antioxidant effect.

Methods

TRPV1^-/-, UCP2 ^-/- and db/db mice, as well as matched wild type (WT) control mice, were included in this study. Some mice were subjected to dietary capsaicin for 14 weeks. Arteries isolated from mice and endothelial cells were cultured. Endothelial function was examined, and immunohistological and molecular analyses were performed.

Results

Under high-glucose conditions, TRPV1 expression and protein kinase A (PKA) phosphorylation were found to be decreased in the cultured endothelial cells, and the effects of high-glucose on these molecules were reversed by the administration of capsaicin. Furthermore, high-glucose exposure increased ROS production and reduced nitric oxide (NO) levels both in endothelial cells and in arteries that were evaluated respectively by dihydroethidium (DHE) and DAF-2 DA fluorescence. Capsaicin administration decreased the production of ROS, restored high-glucose-induced endothelial dysfunction through the activation of TRPV1 and acted in a UCP2-dependent manner in vivo. Administration of dietary capsaicin for 14 weeks increased the levels of PKA phosphorylation and UCP2 expression, ameliorated the vascular oxidative stress and increased NO levels observed in diabetic mice. Prolonged dietary administration of capsaicin promoted endothelium-dependent relaxation in diabetic mice. However, the beneficial effect of capsaicin on vasorelaxation was absent in the aortas of UCP2 ^-/- mice exposed to high-glucose levels.

Conclusion

TRPV1 activation by capsaicin might protect against hyperglycemia-induced endothelial dysfunction through a mechanism involving the PKA/UCP2 pathway.

Direct renin inhibition modulates insulin resistance in caveolin-1-deficient mice

OBJECTIVE

To test the hypothesis that aliskiren improves the metabolic phenotype in a genetic mouse model of the metabolic syndrome (the caveolin-1 (cav-1) knock out (KO) mouse).

MATERIALS/METHODS

Eleven-week-old cav-1 KO and genetically matched wild-type (WT) mice were randomized to three treatment groups: placebo (n=8/group), amlodipine (6 mg/kg/day, n=18/ group), and aliskiren (50 mg/kg/day, n=18/ group). After three weeks of treatment, all treatment groups were assessed for several measures of insulin resistance (fasting insulin and glucose, HOMA-IR, and the response to an intraperitoneal glucose tolerance test (ipGTT)) as well as for triglyceride levels and the blood pressure response to treatment.

RESULTS

Treatment with aliskiren did not affect the ipGTT response but significantly lowered the HOMA-IR and insulin levels in cav-1 KO mice. However, treatment with amlodipine significantly degraded the ipGTT response, as well as the HOMA-IR and insulin levels in the cav-1 KO mice. Aliskiren also significantly lowered triglyceride levels in the cav-1 KO but not in the WT mice. Moreover, aliskiren treatment had a significantly greater effect on blood pressure readings in the cav-1 KO vs. WT mice, and was marginally more effective than amlodipine.

CONCLUSIONS

Our results support the hypothesis that aliskiren reduces insulin resistance as indicated by improved HOMA-IR in cav-1 KO mice whereas amlodipine treatment resulted in changes consistent with increased insulin resistance. In addition, aliskiren was substantially more effective in lowering blood pressure in the cav-1 KO mouse model than in WT mice and marginally more effective than amlodipine.

Telmisartan attenuates diabetic nephropathy by suppressing oxidative stress in db/db mice

BACKGROUND/AIMS

Telmisartan, an angiotensin II type 1 receptor blocker, is widely used to treat hypertension and kidney diseases, including diabetic nephropathy, because of its renoprotective effects. However, the mechanism by which telmisartan prevents proteinuria and renal dysfunction in diabetic nephropathy is still unclear. In this study, we examined the effects of telmisartan against diabetic nephropathy in db/db mice.

METHODS

Telmisartan was administered at a dose of 5 mg/kg/day for 3 weeks to db/db (diabetic) and db/m (control) mice. Urinary albumin excretion, renal histology, and the gene expression of oxidative stress and inflammatory markers in renal tissue were determined. To evaluate the effects of telmisartan on reactive oxygen species (ROS) production, superoxide was detected by dihydroethidium (DHE) staining in vivo and in vitro.

RESULTS

Telmisartan reduced albuminuria, mesangial matrix expansion, macrophage infiltration, and the expression of ROS markers (NADPH oxidase 4- and 8-hydroxydeoxyguanosine) and inflammatory cytokines (monocyte chemoattractant protein-1, osteopontin, and transforming growth factor-β) in the kidney. DHE staining showed that telmisartan decreased ROS generation in the kidney and in cultured mesangial and proximal tubular epithelial cells.

CONCLUSIONS

Taken together, these findings indicate that telmisartan protects against diabetic nephropathy by reducing diabetes-induced oxidative stress.

Cardiovascular changes in animal models of metabolic syndrome

Metabolic syndrome has been defined as a group of risk factors that directly contribute to the development of cardiovascular disease and/or type 2 diabetes. Insulin resistance seems to have a fundamental role in the genesis of this syndrome. Over the past years to the present day, basic and translational research has used small animal models to explore the pathophysiology of metabolic syndrome and to develop novel therapies that might slow the progression of this prevalent condition. In this paper we discuss the animal models used for the study of metabolic syndrome, with particular focus on cardiovascular changes, since they are the main cause of death associated with the condition in humans.

Nitric oxide: orchestrator of endothelium-dependent responses

The present review first summarizes the complex chain of events, in endothelial and vascular smooth muscle cells, that leads to endothelium-dependent relaxations (vasodilatations) due to the generation of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS) and how therapeutic interventions may improve the bioavailability of NO and thus prevent/cure endothelial dysfunction. Then, the role of other endothelium-derived mediators (endothelium-derived hyperpolarizing (EDHF) and contracting (EDCF) factors, endothelin-1) and signals (myoendothelial coupling) is summarized also, with special emphasis on their interaction(s) with the NO pathway, which make the latter not only a major mediator but also a key regulator of endothelium-dependent responses.

Direct renin inhibitor prevents and ameliorates insulin resistance, aortic endothelial dysfunction and vascular remodeling in fructose-fed hypertensive rats

Angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers can improve insulin resistance and vascular dysfunction in insulin-resistant rats; however, there are few reports on the effects of direct renin inhibitors on these conditions. We investigated the effects of a direct renin inhibitor, aliskiren, on insulin resistance, aortic endothelial dysfunction and vascular remodeling in fructose-fed hypertensive rats. Male Wistar-Kyoto rats were divided into four groups (n=6 per group) and studied for 8 weeks: Group Con: standard chow diet; group Fru: high-fructose diet (60% fructose); Group FruA: high-fructose diet with concurrent aliskiren treatment (100 mg kg(-1) per day); and Group FruB: high-fructose diet with subsequent aliskiren treatment 4 weeks later. Blood was collected for biochemical assays, and isolated rings of the thoracic aorta were obtained for analysis of vascular reactivity, vascular structure and lipid peroxide. Rats fed with high-fructose diets developed significant systolic hypertension, decreased plasma nitrite (NO(2); nitric oxide metabolite) levels and increased plasma glucose, insulin, triglyceride, total cholesterol and aortic lipid peroxide levels, and aortic wall thickness compared with control rats. Aliskiren treatment, either concurrent or subsequent, elevated plasma NO(2) levels and reduced systolic hypertension, insulin resistance, dyslipidemia, aortic lipid peroxide levels and aortic wall hypertrophy in FHR. The peak endothelium-dependent aortic relaxations were significantly higher in rats that received aliskiren treatment than in those that did not. In conclusion, our findings suggest that aliskiren prevents and ameliorates insulin resistance, aortic endothelial dysfunction and oxidative vascular remodeling in fructose-fed hypertensive rats.

Amlodipine enhances amelioration of vascular insulin resistance, oxidative stress, and metabolic disorders by candesartan in metabolic syndrome rats

BACKGROUND

The pharmacological advantage of combination of an angiotensin receptor blocker (ARB) and a calcium-channel blocker (CCB) is not fully defined. This study was undertaken to elucidate the potential benefit of their combination in metabolic syndrome.

METHODS

SHR/NDmcr-cp (SHRcp), a rat model of human metabolic syndrome, were divided into four groups, and were administered (i) vehicle, (ii) candesartan (an ARB) 0.3 mg/kg/day, (iii) amlodipine (a CCB) 3 mg/kg/day, and (iv) candesartan 0.3 mg/kg/day plus amlodipine 3 mg/kg/day, for 4 weeks.

RESULTS

Candesartan, amlodipine, or their combination significantly ameliorated the impairment of vascular endothelium-dependent relaxation with acetylcholine in SHRcp. However, the impairment of insulin-induced vasodilation in SHRcp was partially improved by candesartan alone, but not by amlodipine alone. Interestingly, amlodipine added to candesartan synergistically enhanced the improvement of impaired insulin-induced vasodilation by candesartan, indicating the synergistic improvement of vascular insulin resistance by the combination of these drugs. Candesartan alone, but not amlodipine alone, significantly attenuated vascular superoxide and NADPH oxidase subunit p22phox in SHRcp. Amlodipine added to candesartan synergistically enhanced the reduction of vascular p22phox levels and superoxide by candesartan in SHRcp, suggesting the association of vascular insulin resistance with oxidative stress. Furthermore, the combination of candesartan with amlodipine synergistically decreased the increase in visceral adipocyte size, serum free-fatty acid, and tumor necrosis factor-α in SHRcp.

CONCLUSIONS

ARB and CCB combination synergistically ameliorated vascular insulin resistance in metabolic syndrome, being associated with the synergistic attenuation of vascular oxidative stress and metabolic disorders.

The role of renin inhibition in treating the hypertensive patient with diabetes: a summary of preclinical and clinical evidence

Comorbid hypertension and diabetes is common and associated with substantially greater cardiovascular and renal risk relative to hypertension alone. Tissue renin-angiotensin system (RAS) overactivity is a hallmark of diabetes and contributes to target organ damage. Treatment guidelines recommend angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) for reducing cardiorenal risk in patients with hypertension plus diabetes. However, these agents only partially prevent cardiovascular and renal morbidity/mortality. Further attempts to improve clinical outcomes have focused on the use of an ACE inhibitor plus an ARB, but this combination has not demonstrated a favorable risk-benefit profile. Direct renin inhibitors provide a more comprehensive blockade of the RAS compared with ACE inhibitors or ARBs, and may be of particular benefit in counteracting tissue RAS overactivity. In this article, the role of the RAS in diabetic hypertension and the preclinical and clinical effects of direct renin inhibitor therapy on target organs are reviewed.

Effects of renin-angiotensin-aldosterone system blockade on chlorhexidine gluconate-induced sclerosing encapsulated peritonitis in rats

Sclerosing encapsulated peritonitis (SEP) is a rare complication of long term peritoneal dialysis. Renin-angiotensin-aldosterone system (RAAS) may play a role in the development of peritoneal fibrosis in CAPD patients. We aimed to evaluate the effect of aliskiren, valsartan, and aliskiren + valsartan therapy on SEP. The study included 30 Wistar albino rats which were divided into five groups: I (Control) SF solution i.p.; II (CG group) chlorhexidine gluconate i.p.; III aliskiren oral plus CG i.p.; IV valsartan oral plus CG i.p.; and V aliskiren oral, valsartan oral and CG i.p. On the twenty-first day, all of the rats were sacrificed. All of the groups were analyzed in terms of peritoneal thickness, degree of inflammation, vasculopathy, neovascularization and fibrosis. Also, the parietal peritoneal tissue samples were evaluated for matrix metalloproteinase 2 (MMP-2) using the ELISA method. Peritoneal thickness and fibrosis scores were lower in the valsartan group compared to the CG group (P < 0.05). Peritoneal fibrosis scores were lower in the aliskiren group compared to CG group (P < 0.05) but no difference was observed between the peritoneal thickness scores of the two groups (P > 0.05). Tissue MMP-2 levels were significantly higher in the CG group compared other groups (P < 0.05). There were no statistically significant differences between the aliskiren, valsartan and aliskiren + valsartan groups according to the tissue MMP-2 levels. Due to the antifibrotic properties of valsartan, it is thought to be a possible choice to prevent SEP development. We found no positive impact of aliskiren or aliskiren + valsartan combination compared to valsartan alone.

Effects of aliskiren on QT duration and dispersion in hypertensive patients with type 2 diabetes mellitus

AIM

To evaluate the effect of aliskiren compared to amlodipine on QT duration and dispersion in hypertensive patients with type 2 diabetes.

METHODS

A total of 170 outpatients aged 50-75 years with mild to moderate hypertension (SBP >130 and <180 mmHg and DBP >80 and <100 mmHg) and type 2 diabetes were randomly treated with aliskiren 300 mg or amlodipine 10 mg, both given once daily for 24 weeks, according to a prospective, open label, blinded-end point, parallel group design. At the end of the placebo run-in, and after 12, and 24 weeks of treatment blood pressure (BP) measurements (by mercury sphygmomanometer, Korotkoff I and V), plasma biochemistry and a standard 12-lead surface ECG were evaluated.

RESULTS

Both aliskiren and amlodipine significantly reduced systolic blood pressure (SBP)/diastolic blood pressure (DBP) values (-27.2/-14.3 mmHg, p < 0.001 vs. placebo and -27.8/-14.2 mmHg, p < 0.001 vs. placebo, respectively), with no statistical difference between the two drugs. Aliskiren, but not amlodipine, significantly reduced maximum QT interval (QTmax) (-14 ms at 12 weeks and -17 ms at 24 weeks, both p < 0.05 vs. placebo) and corrected QT max (QTc max) (-26 ms and -31 ms, p < 0.01) as well as the dispersion of both QT (-11 ms and -13 ms, p < 0.01) and QTc (-18 ms and -19 ms, p < 0.01).

CONCLUSIONS

Despite similar BP lowering effect, aliskiren, but not amlodipine, reduced QT duration and dispersion, which might be related to the ability of aliskiren to interfere with mechanisms underlying myocardial electrical instability in the heart of diabetic hypertensive patients.

Multidisciplinary pharmacotherapeutic options for nonalcoholic Fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are multidisciplinary liver diseases that often accompany type 2 diabetes or metabolic syndrome, which are characterized by insulin resistance. Therefore, effective treatment of type 2 diabetes and metabolic syndrome should target not only the cardiometabolic abnormalities, but also the associated liver disorders. In the last decade, it has been shown that metformin, thiazolidinediones, vitamin E, ezetimibe, n-3 polyunsaturated fatty acids, renin-angiotensin system (RAS) blockers, and antiobesity drugs may improve hepatic pathophysiological disorders as well as clinical parameters. Accordingly, insulin sensitizers, antioxidative agents, Niemann-Pick C1-like 1 (NPC1L1) inhibitors, RAS blockers, and drugs that target the central nervous system may represent candidate pharmacotherapies for NAFLD and possibly NASH. However, the efficacy, safety, and tolerability of long-term treatment (potentially for many years) with these drugs have not been fully established. Furthermore, clinical trials have not comprehensively examined the efficacy of lipid-lowering drugs (i.e., statins, fibrates, and NPC1L1 inhibitors) for the treatment of NAFLD. Although clinical evidence for RAS blockers and incretin-based agents (GLP-1 analogs and dipeptidyl peptidase-4 inhibitors) is also lacking, these agents are promising in terms of their insulin-sensitizing and anti-inflammatory effects without causing weight gain.

Aliskiren reduced renal fibrosis in mice with chronic ischemic kidney injury--beyond the direct renin inhibition

Chronic renal ischemia leads to renal fibrosis and atrophy. Activation of the renin-angiotensin-aldosterone system is one of the main mechanisms driving chronic renal ischemic injury. The aim of the present study was to define the effect of aliskiren in chronic ischemia of the kidney. Two-kidney, one-clip mice were used to study chronic renal ischemia. Aliskiren significantly lowered the blood pressure in mice with renal artery constriction (92.1±1.1 vs. 81.0±1.8 mm Hg, P<0.05). Renin expression was significantly increased in ischemic kidneys when treated with aliskiren. In addition, (Pro)renin receptor expression was decreased by aliskiren in ischemic kidneys. Aliskiren treatment significantly increased klotho expression and reduced the expression of fibrogenic cystokines, caspase-3 and Bax in ischemic kidneys. Histological examination revealed that aliskiren significantly reduced the nephrosclerosis score (4.5±1.9 vs. 7.3±0.4, P<0.05). Immunofluorescence staining also showed that aliskiren decreased the deposition of interstitial collagen I in ischemic kidneys. In conclusion, direct renin inhibition significantly reduced renal fibrosis and apoptosis following chronic renal ischemia.

Aliskiren prevents and ameliorates metabolic syndrome in fructose-fed rats

INTRODUCTION

The renin-angiotensin system plays a major role in the pathogenesis of metabolic syndrome. The objective of this study was to examine the effects of aliskiren, a direct renin inhibitor, on the metabolic syndrome of fructose-fed rats.

MATERIAL AND METHODS

Male Sprague-Dawley rats were divided into 4 groups (n = 6 for each group). Group Con: rats were fed a standard chow diet for 8 weeks, group Fru: rats were fed a high fructose diet (60% fructose) for 8 weeks, group FruA: rats were fed a high fructose diet and were co-infused with aliskiren (100 mg/kg/day), and group FruB: rats were treated as group Fru, but aliskiren was administered 4 weeks later. Systolic blood pressure (SBP), homeostasis model assessment-insulin resistance (HOMA-IR), and blood profiles were measured.

RESULTS

By the end of week 4 and 8 of a high fructose diet, SBP had increased significantly from 111 ±5 to 142 ±4 and 139 ±5 mmHg (p < 0.05), respectively. A high fructose diet significantly increased HOMA-IR from baseline (6.15 ±1.59) to 21.25 ±2.08 and 21.28 ±3.1 (p < 0.05) at week 4 and 8, respectively, and significantly induced metabolic syndrome. Concurrent aliskiren treatment prevented the development of hypertension and metabolic syndrome in fructose-fed rats. When fructose-induced hypertension was established, subsequent aliskiren treatment for 4 weeks reversed the elevated SBP and ameliorated metabolic syndrome. There were no significant differences in food, water intake, urine flow or body weight gain among groups.

CONCLUSIONS

Aliskiren not only prevents but also ameliorates metabolic syndrome in fructose-fed rats.