Renin inhibition attenuates insulin resistance, oxidative stress, and pancreatic remodeling in the transgenic Ren2 rat

Incorporation of Oxidized Phenylalanine Derivatives into Insulin Signaling Relevant Proteins May Link Oxidative Stress to Signaling Conditions Underlying Chronic Insulin Resistance

A link between oxidative stress and insulin resistance has been suggested. Hydroxyl free radicals are known to be able to convert phenylalanine (Phe) into the non-physiological tyrosine isoforms ortho- and meta-tyrosine (o-Tyr, m-Tyr). The aim of our study was to examine the role of o-Tyr and m-Tyr in the development of insulin resistance. We found that insulin-induced uptake of glucose was blunted in cultures of 3T3-L1 grown on media containing o- or m-Tyr. We show that these modified amino acids are incorporated into cellular proteins. We focused on insulin receptor substrate 1 (IRS-1), which plays a role in insulin signaling. The activating phosphorylation of IRS-1 was increased by insulin, the effect of which was abolished in cells grown in m-Tyr or o-Tyr media. We found that phosphorylation of m- or o-Tyr containing IRS-1 segments by insulin receptor (IR) kinase was greatly reduced, PTP-1B phosphatase was incapable of dephosphorylating phosphorylated m- or o-Tyr IRS-1 peptides, and the SH2 domains of phosphoinositide 3-kinase (PI3K) bound the o-Tyr IRS-1 peptides with greatly reduced affinity. According to our data, m- or o-Tyr incorporation into IRS-1 modifies its protein–protein interactions with regulating enzymes and effectors, thus IRS-1 eventually loses its capacity to play its role in insulin signaling, leading to insulin resistance.

Screening and Identification of Key Genes for Activation of Islet Stellate Cell

Background

It has been demonstrated that activated islet stellate cells (ISCs) play a critical role in islet fibrogenesis and significantly contribute to the progression of type 2 diabetes mellitus. However, the key molecules responsible for ISCs activation have not yet been determined. This study aimed to identify the potential key genes involved in diabetes-induced activation of ISCs.

Method

Stellate cells were isolated from three 10-week-old healthy male Wistar rats and three Goto-Kakizaki (GK) rats. Cells from each rat were primary cultured under the same condition. A Genome-wide transcriptional sequence of stellate cells was generated using the Hiseq3000 platform. The identified differentially expressed genes were validated using quantitative real-time PCR and western blotting in GK rats, high fat diet (HFD) rats, and their controls.

Results

A total of 204 differentially expressed genes (DEGs) between GK. ISCs and Wistar ISCs (W.ISCs) were identified, accounting for 0.58% of all the 35,362 genes detected. After the Gene Ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses, the mRNA levels of these genes were further confirmed by real-time PCR in cultured ISCs. We then selected Fos, Pdpn, Bad as the potential key genes for diabetes-induced activation of ISCs. Finally, we confirmed the protein expression levels of FOS, podoplanin, and Bad by western blotting and immunofluorescence in GK rats, HFD rats, and their controls. The results showed that the expression level of FOS was significantly decreased, while podoplanin and Bad were significantly increased in GK.ISCs and HFD rats compared with controls, which were consistent with the expression of α-smooth muscle actin.

Conclusions

A total of 204 DEGs were found between the GK.ISCs and W.ISCs. After validating the expression of potential key genes from GK rats and HFD rats, Fos, Pdpn, and Bad might be potential key genes involved in diabetes-induced activation of ISCs.

Epigenetic modifications of the renin-angiotensin system in cardiometabolic diseases

Cardiometabolic diseases (CMDs) are among the most prevalent and the highest mortality diseases. Single disease etiology such as gene mutation, polymorphisms, or environmental exposure has failed to explain the origin of CMD. This can be evident in the discrepancies in disease susceptibility among individuals exposed to the same environmental insult or who acquire the same genetic variation. Epigenetics is the intertwining of genetic and environmental factors that results in diversity in the disease course, severity, and prognosis among individuals. Environmental exposures modify the epigenome and thus provide a link for translating environmental impact on changes in gene expression and precipitation to pathological conditions. Renin-angiotensin system (RAS) is comprising genes responsible for the regulation of cardiovascular, metabolic, and glycemic functions. Epigenetic modifications of RAS genes can lead to overactivity of the system, increased sympathetic activity and autonomic dysfunction ultimately contributing to the development of CMD. In this review, we describe the three common epigenetic modulations targeting RAS components and their impact on the susceptibility to cardiometabolic dysfunction. Additionally, we highlight the therapeutic efforts of targeting these epigenetic imprints to the RAS and its effects.

An Immediate and Long-Term Complication of COVID-19 May Be Type 2 Diabetes Mellitus: The Central Role of β-Cell Dysfunction, Apoptosis and Exploration of Possible Mechanisms

The novel coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was declared a pandemic by the WHO on 19 March 2020. This pandemic is associated with markedly elevated blood glucose levels and a remarkable degree of insulin resistance, which suggests pancreatic islet β-cell dysfunction or apoptosis and insulin's inability to dispose of glucose into cellular tissues. Diabetes is known to be one of the top pre-existing co-morbidities associated with the severity of COVID-19 along with hypertension, cardiocerebrovascular disease, advanced age, male gender, and recently obesity. This review focuses on how COVID-19 may be responsible for the accelerated development of type 2 diabetes mellitus (T2DM) as one of its acute and suspected long-term complications. These observations implicate an active role of metabolic syndrome, systemic and tissue islet renin-angiotensin-aldosterone system, redox stress, inflammation, islet fibrosis, amyloid deposition along with β-cell dysfunction and apoptosis in those who develop T2DM. Utilizing light and electron microscopy in preclinical rodent models and human islets may help to better understand how COVID-19 accelerates islet and β-cell injury and remodeling to result in the long-term complications of T2DM.

Decades-old renin inhibitors are still struggling to find a niche in antihypertensive therapy. A fleeting look at the old and the promising new molecules

Hypertension is a diverse illness interlinked with cerebral, cardiovascular (CVS) and renal abnormalities. Presently, the malady is being treated by focusing on Renin- angiotensin system (RAS), voltage-gated calcium channels, peripheral vasodilators, renal and sympathetic nervous systems. Cardiovascular and renal abnormalities are associated with the overactivation of RAS, which can be constrained by angiotensin- converting enzyme inhibitors (ACEIs), angiotensin II (Ang-II) -AT1 receptor blockers (ARBs) and renin inhibitors. The latter is a new player in the old system. The renin catalyzes the conversion of angiotensinogen to Angiotensin I (Ang-I). This can be overcome by inhibiting renin, a preliminary step, eventually hinders the occurrence of the cascade of events in the RAS. Various peptidomimetics, the first-generation renin inhibitors developed six decades ago have limited drug-like properties as they suffered from poor intestinal absorption, high liver first-pass metabolism and low oral bioavailability. The development of chemically diverse molecules from peptides to nonpeptides expanded the horizon to achieving direct renin inhibition. Aliskiren, a blockbuster drug that emerged as a clinical candidate and got approved by the US FDA in 2007 was developed by molecular modeling studies. Aliskiren indicated superior to average efficacy and with minor adverse effects relative to other RAS inhibitors. However, its therapeutic use is limited by poor oral bioavailability of less than 2% that is similar to first-generation peptidic compounds. In this review, we present the development of direct renin inhibitors (DRIs) from peptidic to nonpeptidics that lead to the birth of aliskiren, its place in the treatment of cardiovascular diseases and its limitations.

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.

Sex differences in the metabolic effects of the renin-angiotensin system

Obesity is a global epidemic that greatly increases risk for developing cardiovascular disease and type II diabetes. Sex differences in the obese phenotype are well established in experimental animal models and clinical populations. While having higher adiposity and obesity prevalence, females are generally protected from obesity-related metabolic and cardiovascular complications. This protection is, at least in part, attributed to sex differences in metabolic effects of hormonal mediators such as the renin-angiotensin system (RAS). Previous literature has predominantly focused on the vasoconstrictor arm of the RAS and shown that, in contrast to male rodent models of obesity and diabetes, females are protected from metabolic and cardiovascular derangements produced by angiotensinogen, renin, and angiotensin II. A vasodilator arm of the RAS has more recently emerged which includes angiotensin-(1-7), angiotensin-converting enzyme 2 (ACE2), mas receptors, and alamandine. While accumulating evidence suggests that activation of components of this counter-regulatory axis produces positive effects on glucose homeostasis, lipid metabolism, and energy balance in male animal models, female comparison studies and clinical data related to metabolic outcomes are lacking. This review will summarize current knowledge of sex differences in metabolic effects of the RAS, focusing on interactions with gonadal hormones and potential clinical implications.

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.

Chronic AT1 blockade improves glucose homeostasis in obese OLETF rats

Obesity is associated with the inappropriate activation of the renin-angiotensin system (RAS), which increases arterial pressure, impairs insulin secretion and decreases peripheral tissue insulin sensitivity. RAS blockade reverses these detriments; however, it is not clear whether the disease state of the organism and treatment duration determine the beneficial effects of RAS inhibition on insulin secretion and insulin sensitivity. Therefore, the objective of this study was to compare the benefits of acute vs chronic angiotensin receptor type 1 (AT₁) blockade started after the onset of obesity, hyperglycemia and hypertension on pancreatic function and peripheral insulin resistance. We assessed adipocyte morphology, glucose intolerance, pancreatic redox balance and insulin secretion after 2 and 11 weeks of AT₁ blockade in the following groups of rats: (1) untreated Long-Evans Tokushima Otsuka (lean control; n = 10), (2) untreated Otsuka Long-Evans Tokushima Fatty (OLETF; n = 12) and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/day by oral gavage; n = 12). Regardless of treatment duration, AT₁ blockade decreased systolic blood pressure and fasting plasma triglycerides, whereas chronic AT₁ blockade decreased fasting plasma glucose, glucose intolerance and the relative abundance of large adipocytes by 22, 36 and 70%, respectively. AT₁ blockade, however, did not improve pancreatic oxidative stress or reverse impaired insulin secretion. Collectively, these data show that AT₁ blockade after the onset of obesity, hyperglycemia and hypertension improves peripheral tissue insulin sensitivity, but cannot completely reverse the metabolic derangement characterized by impaired insulin secretion once it has been compromised.

Depletion of ubiA prenyltransferase domain containing 1 expression promotes angiotensin II‑induced hypertrophic response in AC16 human myocardial cells via modulating the expression levels of coenzyme Q10 and endothelial nitric oxide synthase

UbiA prenyltransferase domain containing 1 (UBIAD1) is closely associated with cardiovascular diseases. However, at the cellular level, little is known about how UBIAD1 is expressed and functions in cardiomyocyte hypertrophy. The aim of the present study was to investigate the expression and role of UBIAD1 in angiotensin II (Ang II)‑induced hypertrophy in AC16 cardiomyoblast cells. The loss‑of‑function approach was used to knock down UBIAD1 in vehicle‑ and Ang II‑stimulated AC16 cells. The levels of atrial natriuretic factor (ANF) and caspase-3 were measured and compared between vehicle‑ and Ang II‑treated AC16 cells pretreated with control siRNA or siRNA against UBIAD1. In addition, the levels of coenzyme Q10 (CoQ10) and endothelial nitric oxide synthase (eNOS) were evaluated and compared between these groups. Ang II induced hypertrophy and apoptosis in AC16 cells, accompanied by increased expression of ANF and caspase-3, and decreased expression of UBIAD1. These effects were potentiated by UBIAD1 knockdown. In addition, Ang II treatment suppressed the expression of CoQ10 and eNOS, as well as the production of NO, and these inhibitory effects were also enhanced by UBIAD1 knockdown. Thus, silencing of UBIAD1 expression promotes a myocardial hypertrophic response to Ang II stimulation, in part, by suppressing the expression of CoQ10 and eNOS.

Renin inhibition improves metabolic syndrome, and reduces angiotensin II levels and oxidative stress in visceral fat tissues in fructose-fed rats

Renin–angiotensin system in visceral fat plays a crucial role in the pathogenesis of metabolic syndrome in fructose-fed rats. However, the effects of renin inhibition on visceral adiposity in metabolic syndrome are not fully investigated. We investigated the effects of renin inhibition on visceral adiposity in fructose-fed rats. Male Wistar–Kyoto rats were divided into 4 groups for 8-week experiments: Group Con (standard chow diet), Group Fru (high-fructose diet; 60% fructose), Group FruA (high-fructose diet and concurrent aliskiren treatment; 100 mg/kg body weight [BW] per day), and Group FruB (high-fructose diet and subsequent, i.e. 4 weeks after initiating high-fructose feeding, aliskiren treatment; 100 mg/kg BW per day). The high-fructose diet induced metabolic syndrome, increased visceral fat weights and adipocyte sizes, and augmented angiotensin II (Ang II), NADPH oxidase (NOX) isoforms expressions, oxidative stress, and dysregulated production of adipocytokines from visceral adipose tissues. Concurrent and subsequent aliskiren administration ameliorated metabolic syndrome, dysregulated adipocytokines, and visceral adiposity in high fructose-fed hypertensive rats, and was associated with reducing Ang II levels, NOX isoforms expressions and oxidative stress in visceral fat tissues. Therefore, this study demonstrates renin inhibition could improve metabolic syndrome, and reduce Ang II levels and oxidative stress in visceral fat tissue in fructose-fed rats, and suggests that visceral adipose Ang II plays a crucial role in the pathogenesis of metabolic syndrome in fructose-fed rats.

Systemic and tissue-specific effects of aliskiren on the RAAS and carbohydrate/lipid metabolism in obese patients with hypertension

Aliskiren penetrates adipose and skeletal muscle in hypertensive patients with abdominal obesity and reduces renin-angiotensin-aldosterone system activity. After discontinuation, blood pressure-lowering effects are observed possibly through drug-tissue binding. We performed microdialysis evaluation of adipose tissue and skeletal muscle before and during an insulin-modified frequently sampled intravenous glucose tolerance test (IM-FSIGT). Aliskiren 300 mg (n = 8) or amlodipine 5 mg (n = 8) once daily were administered during a 12-week randomized treatment period. Aliskiren elicited variable changes in median interstitial angiotensin II (Ang II) in adipose (2.60-1.30 fmol/mL) and skeletal muscle (2.23-0.68 fmol/mL); amlodipine tended to increase adipose and skeletal muscle Ang II (P = .066 for skeletal muscle treatment difference). Glucose/insulin increased median plasma Ang II 1 hour after glucose injection (1.04-2.50 fmol/mL; P = .001), which was markedly attenuated by aliskiren but not amlodipine. Aliskiren increased glucose disposition index (P = .012) and tended to increase acute insulin response to glucose (P = .067). Fasting adipose glycerol (-17%; P = .064) and fasting muscle glucose dialysate (-17%; P = .025) were decreased by aliskiren but not amlodipine. In summary, aliskiren decreased Ang II production in response to glucose/insulin stimulus and elicited metabolic effects in adipose and skeletal muscle suggestive of increased whole-body glucose utilization.

Exogenous thyroxine improves glucose intolerance in insulin-resistant rats

Both hypothyroidism and hyperthyroidism are associated with glucose intolerance, calling into question the contribution of thyroid hormones (TH) on glucose regulation. TH analogues and derivatives may be effective treatment options for glucose intolerance and insulin resistance (IR), but their potential glucoregulatory effects during conditions of impaired metabolism are not well described. To assess the effects of thyroxine (T4) on glucose intolerance in a model of insulin resistance, an oral glucose tolerance test (oGTT) was performed on three groups of rats (n = 8): (1) lean, Long Evans Tokushima Otsuka (LETO), (2) obese, Otsuka Long Evans Tokushima Fatty (OLETF) and (3) OLETF + T4 (8.0 µg/100 g BM/day × 5 weeks). T4 attenuated glucose intolerance by 15% and decreased IR index (IRI) by 34% in T4-treated OLETF compared to untreated OLETF despite a 31% decrease in muscle Glut4 mRNA expression. T4 increased the mRNA expressions of muscle monocarboxylate transporter 10 (Mct10), deiodinase type 2 (Di2), sirtuin 1 (Sirt1) and uncoupling protein 2 (Ucp2) by 1.8-, 2.2-, 2.7- and 1.4-fold, respectively, compared to OLETF. Activation of AMP-activated protein kinase (AMPK) and insulin receptor were not significantly altered suggesting that the improvements in glucose intolerance and IR were independent of enhanced insulin-mediated signaling. The results suggest that T4 treatment increased the influx of T4 in skeletal muscle and, with an increase of DI2, increased the availability of the biologically active T3 to upregulate key factors such SIRT1 and UCP2 involved in cellular metabolism and glucose homeostasis.

Anti-diabetic and renoprotective effects of aliskiren in streptozotocin-induced diabetic nephropathy in female rats

Since chronic kidney disease due to diabetic nephropathy (DN) is becoming an ever larger health burden worldwide, more effective therapies are desperately needed. In the present study, the anti-diabetic and renoprotective effects of aliskiren have been evaluated in streptozotocin (STZ)-induced DN in rats. DN was induced by a single intraperitoneal injection of STZ (65 mg/kg). Three weeks after STZ, rats were divided into four groups; normal, diabetic, diabetic treated with gliclazide (10 mg/kg/day) for 1 month, and diabetic treated with aliskiren (50 mg/kg/day) for 1 month. At the end of the experiment, mean arterial blood pressure and heart rate were recorded. Rats were then euthanized and serum was separated for determination of glucose, insulin, kidney function tests, superoxide dismutase activity (SOD), adiponectin, and tumor necrosis factor-alpha (TNF-α). One kidney was used for estimation of malondialdehyde (MDA), reduced glutathione (GSH), and nitric oxide (NO) contents. Other kidney was used for histopathological study and immunohistochemical measurement of caspase-3 and transforming growth factor beta (TGF-β). In addition, islets of Langerhans were isolated from normal rats by collagenase digestion technique for in vitro study. Aliskiren normalized STZ-induced hyperglycemia, increased insulin level both in vivo and in vitro, normalized kidney function tests and blood pressure, and alleviated STZ-induced kidney histopathological changes. This could be related to the ability of aliskiren toward preserving hemodynamic changes and alleviating oxidative stress and inflammatory and apoptotic markers induced by STZ in rats. However, aliskiren was more effective than gliclazide in relieving STZ-induced DN. These findings support the beneficial effect of aliskiren treatment in DN which could be attributed to its anti-diabetic, renoprotective, antioxidant, anti-inflammatory, and anti-apoptotic effects. Moreover, clinical studies are required to establish the effectiveness of aliskiren treatment in patients suffering from hypertension and diabetes.

Cardiometabolic crosstalk in obesity-associated arterial hypertension

Abdominal obesity and elevated blood pressure commonly occur in the same patient and are key components of the metabolic syndrome. However, the association between obesity and increased blood pressure is variable. We review mechanisms linking cardiovascular and metabolic disease in such patients including altered systemic and regional hemodynamic control, neurohumoral activation, and relative natriuretic peptide deficiency. Moreover, we discuss recent results using omics techniques providing insight in molecular pathways linking adiposity, metabolic disease, and arterial hypertension. Recognition of the mechanisms orchestrating the crosstalk between cardiovascular and metabolic regulation in individual patients may lead to better and more precise treatments. It is reassuring that recently developed cardiovascular and metabolic medications may in fact ameliorate, both, cardiovascular and metabolic risks.

Aliskiren Reduces Hepatic steatosis and Epididymal Fat Mass and Increases Skeletal Muscle Insulin Sensitivity in High-Fat Diet-Fed Mice

Aliskiren has been found to reduce chronic injury and steatosis in the liver of methionine-choline-deficient (MCD) diet-fed mice. This study investigated whether aliskiren has an anti-steatotic effect in HFD-fed mice, which are more relevant to human patients with non-alcoholic fatty liver disease than MCD mice. Mice fed with 4-week normal chow or HFD randomly received aliskiren (50 mg/kg/day) or vehicle via osmotic minipumps for further 4 weeks. Aliskiren reduced systemic insulin resistance, hepatic steatosis, epididymal fat mass and increased gastrocnemius muscle glucose transporter type 4 levels with lower tissue angiotensin II levels in the HFD-fed mice. In addition, aliskiren lowered nuclear peroxisome proliferator-activated receptor gamma and its down-signaling molecules and increased cytochrome P450 4A14 and carnitine palmitoyltransferase 1A (CPT1a) in liver. In epididymal fat, aliskiren inhibited expressions of lipogenic genes, leading to decrease in fat mass, body weight, and serum levels of leptin and free fatty acid. Notably, in the gastrocnemius muscle, aliskiren increased phosphorylation of insulin receptor substrate 1 and Akt. Based on these beneficial effects on liver, peripheral fat and skeletal muscle, aliskiren is a promising therapeutic agent for patients with NAFLD.

Comparative effects of Aliskiren and Telmisartan in high fructose diet-induced metabolic syndrome in rats

Fructose is a commonly used sweetener associated with diets that increase the prevalence of metabolic syndrome (MS). Inhibition of the renin-angiotensin system (RAS) has been consistently demonstrated to reduce MS. However, there has been no direct comparison among different pharmacological modes of inhibiting the RAS concerning their effects on MS. This study investigated the effect of aliskiren, a direct renin inhibitor, versus telmisartan, an angiotensin II-receptor blocker, in the treatment of fructose-induced MS in rats. MS was induced by high fructose (FRC) diet feeding for 12 weeks. Oral administrations of telmisartan (TEL, 5 mg/kg), aliskiren (ALS, 30 mg/kg) or vehicle were started in the last 4 weeks. Results showed that administration of either TEL or ALS with FRC diet equally ameliorated the metabolic parameters (glucose level, oral glucose tolerance test, insulin resistance and serum lipids profile), systolic blood pressure and oxidative stress markers (malondialdehyde, nitric oxide, reduced glutathione levels and catalase activity). Additionally, the effects of TEL and ALS were associated with a decrease in body composition index and attenuation of liver index, serum liver enzyme activities and hepatic expressions of inflammatory and fibrotic markers (tumor necrosis factor-α, nuclear factor kappa-B and transforming growth factor-β) with a significant increase in hepatic glucose transporter-2 and peroxisome proliferator-activated receptors-alpha and gamma expressions. The results suggested that, at indicated dosage, ALS has ameliorative effect equal to that of TEL against FRC-induced metabolic and hepatic disorders; implying that drugs which inhibit the RAS, by different mode of inhibition, profoundly affect fructose-induced MS in rats.

Modulation of glucose metabolism by the renin-angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is an enzymatic cascade functioning in a paracrine and autocrine fashion. In animals and humans, RAAS intrinsic to tissues modulates food intake, metabolic rate, adiposity, insulin sensitivity, and insulin secretion. A large array of observations shows that dysregulation of RAAS in the metabolic syndrome favors type 2 diabetes. Remarkably, angiotensin-converting enzyme inhibitors, suppressing the synthesis of angiotensin II (ANG II), and angiotensin receptor blockers, targeting the ANG II type 1 receptor, prevent diabetes in patients with hypertensive or ischemic cardiopathy. These drugs interrupt the negative feedback loop of ANG II on the RAAS cascade, which results in increased production of angiotensins. In addition, they change the tissue expression of RAAS components. Therefore, the concept of a dual axis of RAAS regarding glucose homeostasis has emerged. The RAAS deleterious axis increases the production of inflammatory cytokines and raises oxidative stress, exacerbating the insulin resistance and decreasing insulin secretion. The beneficial axis promotes adipogenesis, blocks the production of inflammatory cytokines, and lowers oxidative stress, thereby improving insulin sensitivity and secretion. Currently, drugs targeting RAAS are not given for the purpose of preventing diabetes in humans. However, we anticipate that in the near future the discovery of novel means to modulate the RAAS beneficial axis will result in a decisive therapeutic breakthrough.

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 attenuates steatohepatitis and increases turnover of hepatic fat in mice fed with a methionine and choline deficient diet

Background & Aims

Activation of the renin-angiotensin-system is known to play a role in nonalcoholic steatohepatitis. Renin knockout mice manifest decreased hepatic steatosis. Aliskiren is the first direct renin inhibitor to be approved for clinical use. Our study aims to evaluate the possible therapeutic effects and mechanism of the chronic administration of aliskiren in a dietary steatohepatitis murine model.

Methods

Male C57BL/6 mice were fed with a methionine and choline-deficient (MCD) diet to induce steatohepatitis. After 8 weeks of feeding, the injured mice were randomly assigned to receive aliskiren (50 mg_·kg^-1 per day) or vehicle administration for 4 weeks. Normal controls were also administered aliskiren (50 mg_·kg^-1 per day) or a vehicle for 4 weeks.

Results

In the MCD mice, aliskiren attenuated hepatic steatosis, inflammation and fibrosis. Aliskiren did not change expression of lipogenic genes but increase turnover of hepatic fat by up-regulating peroxisome proliferator-activated receptor α, carnitine palmitoyltransferase 1a, cytochrome P450-4A14 and phosphorylated AMP-activated protein kinase. Furthermore, aliskiren decreased the hepatic expression of angiotensin II and nuclear factor κB. The levels of oxidative stress, hepatocyte apoptosis, activation of Kupffer cells and hepatic stellate cells, and pro-fibrotic markers were also reduced in the livers of the MCD mice receiving aliskiren.

Conclusions

Aliskiren attenuates steatohepatitis and fibrosis in mice fed with a MCD diet. Thus, the noted therapeutic effects might come from not only the reduction of angiotensin II but also the up-regulation of fatty acid oxidation-related genes.

The role of the renin-angiotensin system in the development of insulin resistance in skeletal muscle

The canonical renin-angiotensin system (RAS) involves the initial action of renin to cleave angiotensinogen to angiotensin I (ANG I), which is then converted to ANG II by the angiotensin converting enzyme (ACE). ANG II plays a critical role in numerous physiological functions, and RAS overactivity underlies many conditions of cardiovascular dysregulation. In addition, ANG II, by acting on both endothelial and myocellular AT1 receptors, can induce insulin resistance by increasing cellular oxidative stress, leading to impaired insulin signaling and insulin-stimulated glucose transport activity. This insulin resistance associated with RAS overactivity, when coupled with progressive ß-cell dysfunction, eventually leads to the development of type 2 diabetes. Interventions that target RAS overactivity, including ACE inhibitors, ANG II receptor blockers, and, most recently, renin inhibitors, are effective both in reducing hypertension and in improving whole-body and skeletal muscle insulin action, due at least in part to enhanced Akt-dependent insulin signaling and insulin-dependent glucose transport activity. ANG-(1-7), which is produced from ANG II by the action of ACE2 and acts via Mas receptors, can counterbalance the deleterious actions of the ACE/ANG II/AT1 receptor axis on the insulin-dependent glucose transport system in skeletal muscle. This beneficial effect of the ACE2/ANG-(1-7)/Mas receptor axis appears to depend on the activation of Akt. Collectively, these findings underscore the importance of RAS overactivity in the multifactorial etiology of insulin resistance in skeletal muscle, and provide support for interventions that target the RAS to ameliorate both cardiovascular dysfunctions and insulin resistance in skeletal muscle tissue.

(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.

Acute regulation of pancreatic islet microcirculation and glycaemia by telmisartan and ramipril: discordant effects between normal and Type 2 diabetic rats

Diabetic patients are often treated with an ACEi (angiotensin-converting enzyme inhibitor) or angiotensin receptor antagonist against hypertension or albuminuria. These drugs also have a positive impact on glucose tolerance, but the mechanism for this remains elusive. Hypothesizing a positive non-additive effect, we studied whether the angiotensin receptor antagonist telmisartan or the ACEi ramipril acutely influence insulin secretion and glycaemia in vivo in healthy and Type 2 diabetic rats through effects on islet blood perfusion. Telmisartan and ramipril were injected intravenously into anaesthetized non-diabetic Wistar rats or Type 2 diabetic GK (Goto–Kakizaki) rats. In non-diabetic Wistar rats, neither whole PBF (pancreatic blood flow) nor IBF (islet blood flow) were significantly influenced by telmisartan and ramipril, alone or in combination. Renal blood flow was enhanced significantly by telmisartan and ramipril when used in combination, whereas ABF (adrenal blood flow) was not affected by any of the drugs. Telmisartan and ramipril both significantly increased serum insulin levels, but did not influence glycaemia. In Type 2 diabetic GK rats, both whole PBF and IBF were significantly decreased by telmisartan and ramipril, but only when used in combination. Renal blood flow was enhanced significantly by telmisartan and ramipril alone, but not when used in combination, whereas ABF was not affected by any of the drugs. Telmisartan and ramipril both significantly decreased serum insulin levels, and non-additively elevated blood glucose levels. In conclusion, the present study suggests that a local pancreatic RAS (renin–angiotensin system), sensitive to acute administration of telmisartan and ramipril, controls pancreatic IBF and insulin secretion and thereby has an impact on glucose tolerance. Our findings indicate unexpected significant differences in the effects of these agents on islet microcirculation, in vivo insulin secretion and glycaemia between healthy and Type 2 diabetic rats.

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.

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.

Oral renin inhibitors in clinical practice: a perspective review

Hypertension is an important risk factor for cardiovascular morbidity and mortality. The importance of the renin-angiotensin-aldosterone system (RAAS) in cardiovascular and renal diseases has long been recognized: for this reason the conventional therapies, such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), β-blockers, and aldosterone antagonists represent the backbone of current antihypertensive therapy. Aliskiren is the first direct renin inhibitor (DRI) suitable for oral administration. By achieving more complete renin-angiotensin system inhibition, direct renin inhibitors may afford greater protection from hypertensive complications. Present evidence indicates that aliskiren reduces baseline systolic and diastolic blood pressure greater than placebo and that it is as effective as other first-line antihypertensive agents. Extra advantages can be reached when it is used in combination therapy. Clinical trials and in vitro studies also suggest that aliskiren has several cardioprotective and renoprotective effects. Therapy with aliskiren is well tolerated, but recently some concerns have arisen because of the early termination of the ALTITUDE study due to an increased incidence of adverse effects.

Angiotensin receptor blockade recovers hepatic UCP2 expression and aconitase and SDH activities and ameliorates hepatic oxidative damage in insulin resistant rats

Metabolic syndrome (MetS) is commonly associated with elevated renin-angiotensin system, oxidative stress, and steatohepatitis with down-regulation of uncoupling proteins (UCPs). However, the mechanisms linking renin-angiotensin system, steatosis, and UCP2 to hepatic oxidative damage during insulin resistance are not described. To test the hypothesis that angiotensin receptor activation contributes to decreased hepatic UCP2 expression and aconitase activity and to increased oxidative damage after increased glucose intake in a model of MetS, lean and obese Long Evans rats (n = 10/group) were randomly assigned to the following groups: 1) untreated Long Evans Tokushima Otsuka (lean, strain control), 2) untreated Otsuka Long Evans Tokushima Fatty (OLETF) (MetS model), 3) OLETF + angiotensin receptor blocker (ARB) (10 mg olmesartan/kg·d × 6 wk), 4) OLETF + high glucose (HG) (5% in drinking water × 6 wk), and 5) OLETF + ARB + HG (ARB/HG × 6 wk). HG increased body mass (37%), plasma triglycerides (TGs) (35%), plasma glycerol (87%), plasma free fatty acids (28%), and hepatic nitrotyrosine (74%). ARB treatment in HG decreased body mass (12%), plasma TG (15%), plasma glycerol (23%), plasma free fatty acids (14%), and hepatic TG content (42%), suggesting that angiotensin receptor type 1 (AT1) activation and increased adiposity contribute to the development of obesity-related dyslipidemia. ARB in HG also decreased hepatic nitrotyrosine and increased hepatic UCP2 expression (59%) and aconitase activity (40%), as well as antioxidant enzyme activities (50-120%), suggesting that AT1 activation also contributes to protein oxidation, impaired lipid metabolism, and antioxidant metabolism in the liver. Thus, in addition to promoting obesity-related hypertension, AT1 activation may also impair lipid metabolism and antioxidant capacity, resulting in steatosis via decreased UCP2 and tricarboxylic acid cycle activity.

Transcriptional and translational regulation of cytokine signaling in inflammatory β-cell dysfunction and apoptosis

Disease is conventionally viewed as the chaotic inappropriate outcome of deranged tissue function resulting from aberrancies in cellular processes. Yet the patho-biology of cellular dysfunction and death encompasses a coordinated network no less sophisticated and regulated than maintenance of homeostatic balance. Cellular demise is far from passive subordination to stress but requires controlled coordination of energy-requiring activities including gene transcription and protein translation that determine the graded transition between defensive mechanisms, cell cycle regulation, dedifferentiation and ultimately to the activation of death programmes. In fact, most stressors stimulate both homeostasis and regeneration on one hand and impairment and destruction on the other, depending on the ambient circumstances. Here we illustrate this bimodal ambiguity in cell response by reviewing recent progress in our understanding of how the pancreatic β cell copes with inflammatory stress by changing gene transcription and protein translation by the differential and interconnected action of reactive oxygen and nitric oxide species, microRNAs and posttranslational protein modifications.

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.

Oxidative stress in the cardiorenal metabolic syndrome

Excess visceral adiposity contributes to inappropriate activation of the renin-angiotensin-aldosterone system despite a state of volume expansion and of salt retention that contributes to subclinical elevations of pro-oxidant mechanisms. These adverse effects are mediated by excess generation of reactive oxygen species (ROS) and diminished antioxidant defense mechanisms. Excess tissue (i.e., skeletal muscle, liver, heart) free oxygen radicals contribute to impairments in the insulin-dependent metabolic signaling pathways that regulate glucose utilization/disposal and systemic insulin sensitivity. The generation of ROS is required for normal cell signaling and physiological responses. It is a loss of redox homeostasis that results in a proinflammatory/profibrotic milieu that promotes impairments in insulin metabolic signaling, reduced endothelial-mediated vasorelaxation, and associated cardiovascular and renal structural and functional abnormalities. These maladaptive processes are increasingly recognized as important in the progression of hypertension in the cardiorenal metabolic phenotype. There is increasing evidence to support a critical role for Ang II signaling through the AT(1)R and aldosterone actions through the MR in conjunction with an altered redox-mediating impaired endothelial, cardiac and renal function in this metabolic phenotype. There are emerging clinical data that indicate that therapies that target the renin angiotensin-aldosterone system (RAAS) also attenuate oxidative stress, and improve endothelial, cardiac and renal functions, which collectively contribute to reductions in hypertension.

Aliskiren improves insulin resistance and ameliorates diabetic renal vascular complications in STZ-induced diabetic rats

Aliskiren, a direct renin inhibitor (DRI), has therapeutic effects in patients with hypertension and associated complications, but its potential mechanism in diabetic nephropathy is lacking. The effects of aliskiren in Streptozotocin (STZ)-induced renal complication in diabetic rats were investigated. Aliskiren treatment for eight weeks at the dose of 10 mg/kg/day, via osmotic mini-pump, induced improvement in blood glucose levels, systolic blood pressure (BP) and serum creatinine. Improvement of insulin resistance by aliskiren was confirmed by increased glucose translocation in liver and muscle and hence insulin levels. The treated group also showed improvement in glomerulosclerosis and tubulointerstitial injury. Aliskiren treatment also improved albumin levels in plasma, suppressed profibrotic and proinflammatory cytokine synthesis viz TNF-α and TGF-β and angiogenesis by a decrease in VEGF. In addition, the level of total proteins and GFR via cystatin c and beta-2microglobulin along with adiponectin and erythropoietin were also improved. These results suggest that the beneficial organ protective effect of aliskiren is mediated by improvement in insulin resistance as well as a direct anti-fibrotic effect in the target organ in STZ-induced diabetic rats with a slight effect on blood pressure. Aliskiren may be a useful therapeutic agent in the treatment of type 2 diabetes and diabetic nephropathy.

Aliskiren penetrates adipose and skeletal muscle tissue and reduces renin-angiotensin system activity in obese hypertensive patients

OBJECTIVE

In animals, the direct renin inhibitor aliskiren showed extensive tissue binding in the kidney and long-lasting renal effects. Aliskiren provides prolonged blood pressure-lowering effects following treatment discontinuation in patients. Therefore, we investigated whether aliskiren attains tissue concentrations sufficient to inhibit local renin-angiotensin system (RAS) activity in patients.

METHODS

We included 10 hypertensive patients with abdominal adiposity in an open-label study. Following 1-2 weeks washout, patients received 2 weeks placebo, then 4 weeks aliskiren 300 mg once daily, followed by 4 weeks washout, and then 4 weeks amlodipine 5 mg once daily. Drug concentrations and RAS biomarkers were measured in interstitial fluid using microdialysis and in biopsies from abdominal subcutaneous adipose and skeletal muscle.

RESULTS

We detected aliskiren in all compartments. After 4 weeks of treatment, microdialysate aliskiren concentrations (ng/ml) were 2.4 ± 2.1 (adipose) and 7.1 ± 4.2 (skeletal muscle), similar to plasma concentrations (8.4 ± 4.4); tissue concentrations (ng/g) were 29.0 ± 16.7 (adipose) and 107.3 ± 68.6 (skeletal muscle). Eight weeks after discontinuation, aliskiren was measurable in tissue biopsies but not in plasma or in interstitial fluid. Pooled microdialysate samples from two sets of four patients suggested reduction in tissue angiotensin II with aliskiren but not with amlodipine.

CONCLUSION

In obese hypertensive patients, aliskiren penetrates adipose and skeletal muscle tissue at levels that are apparently sufficient to reduce tissue RAS activity. Furthermore, tissue binding may contribute to aliskiren's prolonged blood pressure-lowering effect following discontinuation.

Angiotensin receptor blockade increases pancreatic insulin secretion and decreases glucose intolerance during glucose supplementation in a model of metabolic syndrome

Renin-angiotensin system blockade improves glucose intolerance and insulin resistance, which contribute to the development of metabolic syndrome. However, the contribution of impaired insulin secretion to the pathogenesis of metabolic syndrome is not well defined. To assess the contributions of angiotensin receptor type 1 (AT₁) activation and high glucose intake on pancreatic function and their effects on insulin signaling in skeletal muscle and adipose tissue, an oral glucose tolerance test (oGTT) was performed in five groups (n = 10/group) of rats: 1) lean strain-control 2) obese Otsuka Long-Evans Tokushima Fatty (OLETF), 3) OLETF + angiotensin receptor blocker (ARB; 10 mg/kg · d olmesartan for 6 wk; OLETF ARB), 4) OLETF + 5% glucose water (HG) for 6 wk (OLETF HG), and 5) OLETF + HG + ARB (OLETF HG/ARB). The glucose response to the oGTT increased 58% in OLETF compared with lean-strain control, whereas glucose supplementation increased it an additional 26%. Blockade of angiotensin receptor reduced the oGTT response 19% in the ARB-treated groups and increased pancreatic insulin secretion 64 and 113% in OLETF ARB and OLETF HG/ARB, respectively. ARB treatment in OLETF ARB and OLETF HG/ARB did not have an effect on insulin signaling proteins in skeletal muscle; however, it reduced pancreatic AT₁ protein expression 20 and 27%, increased pancreatic glucagon-like peptide-1 (GLP-1) receptor protein expression 41 and 88%, respectively, and increased fasting plasma GLP-1 approximately 2.5-fold in OLETF ARB. The results suggest that improvement of glucose intolerance is independent of an improvement in muscle insulin signaling, but rather by improved glucose-stimulated insulin secretion associated with decreased pancreatic AT₁ activation and increased GLP-1 signaling.

Beneficial effects of pioglitazone against cardiovascular injury are enhanced by combination with aliskiren in a rat model of diabetic nephropathy

OBJECTIVES

Aliskiren is the first in a new class of orally active direct renin inhibitors, approved for the treatment of hypertension. However, the efficacy of aliskiren in diabetic cardiovascular complications remains to be defined. This study aimed to test the hypothesis that aliskiren may enhance the beneficial effects of pioglitazone against cardiovascular injury associated with diabetic nephropathy.

METHODS

Diabetic nephropathy was induced in rats by unilateral nephrectomy followed by streptozotocin injection. Diabetic nephropathic rats were orally given vehicle, pioglitazone, aliskiren, or combined pioglitazone and aliskiren for four weeks to compare their effects on cardiovascular injury, particularly myocardial fibrosis.

KEY FINDINGS

Pioglitazone treatment significantly attenuated cardiac lipid peroxidation, oxidative injury and myocardial fibrosis in diabetic nephropathic rats. This was associated with up-regulation of transforming growth factor-β1 and matrix metalloproteinase-2 genes, along with down-regulation of tissue inhibitor of metalloproteinase-2 gene in cardiac tissue. The combination of aliskiren with pioglitazone exerted greater beneficial effect than monotherapy with either drug, on all the aforementioned parameters.

CONCLUSIONS

Our findings suggested that aliskiren enhanced the protective effects of pioglitazone against myocardial fibrosis, in experimental diabetic nephropathy. Thus, the combination of aliskiren and pioglitazone may be a potential therapeutic strategy for cardiovascular injury associated with diabetic nephropathy.

Ultrastructure Study of Transgenic Ren2 Rat Aorta - Part 1: Endothelium and Intima

BACKGROUND: The renin-angiotensin-aldosterone system plays an important role in the development and progression of hypertension and accelerated atherosclerosis (atheroscleropathy) associated with the cardiorenal metabolic syndrome and type 2 diabetes mellitus. Additionally, the renin-angiotensin-aldosterone system plays an important role in vascular-endothelial-intimal cellular and extracellular remodeling. METHODS: Thoracic aortas of young male transgenic heterozygous (mRen2)27 (Ren2) rats were utilized for this ultrastructural study. This lean model of hypertension, insulin resistance and oxidative stress harbors the mouse renin gene with increased local tissue (aortic) levels of angiotensin II and angiotensin type 1 receptors and elevated plasma aldosterone levels. RESULTS: The ultrastructural observations included marked endothelial cell retraction, separation, terminal nuclear lifting, adjacent duplication, apoptosis and a suggestion of endothelial progenitor cell attachment. The endothelium demonstrated increased caveolae, microparticles, depletion of Weibel-Palade bodies, loss of cell-cell and basal adhesion hemidesmosome-like structures, platelet adhesion and genesis of subendothelial neointima. CONCLUSION: These observational ultrastructural studies of the transgenic Ren2 vasculature provide an in-depth evaluation of early abnormal remodeling changes within conduit-elastic arteries under conditions of increased local levels of angiotensin II, oxidative stress, insulin resistance and hypertension.

Partial restoration of cardio-vascular defects in a rescued severe model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a leading genetic cause of infantile death. Loss of a gene called Survival Motor Neuron 1 (SMN1) and, as a result, reduced levels of the Survival Motor Neuron (SMN) protein leads to SMA development. SMA is characterized by the loss of functional motor neurons in the spinal cord. However, accumulating evidence suggests the contribution of other organs to the composite SMA phenotype and disease progression. A growing number of congenital heart defects have been identified in severe SMA patients. Consistent with the clinical cases, we have recently identified developmental and functional heart defects in two SMA mouse models, occurring at embryonic stage in a severe SMA model and shortly after birth in a less severe model (SMN∆7). Our goal was to examine the late stage cardiac abnormalities in untreated SMN∆7 mice and to determine whether gene replacement therapy restores cardiac structure/function in rescued SMN∆7 model. To reveal the extent of the cardiac structural/functional repair in the rescued mice, we analyzed the heart of untreated and treated SMN∆7 model using self-complementary Adeno-associated virus (serotype 9) expressing the full-length SMN cDNA. We examined the characteristics of the heart failure such as remodeling, fibrosis, oxidative stress, and vascular integrity in both groups. Our results clearly indicate that fibrosis, oxidative stress activation, vascular remodeling, and a significant decrease in the number of capillaries exist in the SMA heart. The cardiac structural defects were improved drastically in the rescued animals, however, the level of impairment was still significant compared to the age-matched wildtype littermates. Furthermore, functional analysis by in vivo cardiac magnetic resonance imaging (MRI) revealed that the heart of the treated SMA mice still exhibits functional defects. In conclusion, cardiac abnormalities are only partially rescued in post-birth treated SMA animals and these abnormalities may contribute to the premature death of vector-treated SMA animals with seemingly rescued motor function but an average life span of less than 70 days as reported in several studies.

Activation of mTOR/p70S6 kinase by ANG II inhibits insulin-stimulated endothelial nitric oxide synthase and vasodilation

Elevated tissue levels of angiotensin II (ANG II) are associated with impairment of insulin actions in metabolic and cardiovascular tissues. ANG II-stimulated activation of mammalian target of rapamycin (mTOR)/p70 S6 kinase (p70S6K) in cardiovascular tissues is implicated in cardiac hypertrophy and vascular remodeling. However, the role of ANG II-stimulated mTOR/p70S6K in vascular endothelium is poorly understood. In the present study, we observed that ANG II stimulated p70S6K in bovine aortic endothelial cells. ANG II increased phosphorylation of insulin receptor substrate-1 (IRS-1) at Ser(636/639) and inhibited the insulin-stimulated phosphorylation of endothelial nitric oxide synthase (eNOS). An inhibitor of mTOR, rapamycin, attenuated the ANG II-stimulated phosphorylation of p70S6K and phosphorylation of IRS-1 (Ser(636/639)) and blocked the ability of ANG II to impair insulin-stimulated phosphorylation of eNOS, nitric oxide production, and mesenteric-arteriole vasodilation. Moreover, point mutations of IRS-1 at Ser(636/639) to Ala prevented the ANG II-mediated inhibition of insulin signaling. From these results, we conclude that activation of mTOR/p70S6K by ANG II in vascular endothelium may contribute to impairment of insulin-stimulated vasodilation through phosphorylation of IRS-1 at Ser(636/639). This ANG II-mediated impairment of vascular actions of insulin may help explain the role of ANG II as a link between insulin resistance and hypertension.

Restoration of the blood pressure circadian rhythm by direct renin inhibition and blockade of angiotensin II receptors in mRen2.Lewis hypertensive rats

BACKGROUND

Alterations in the circadian arterial pressure rhythm predict cardiovascular mortality. We examined the circadian arterial pressure rhythm and the effect of renin-angiotensin system blockade in congenic mRen2.Lewis hypertensive rats, a renin-dependent model of hypertension derived from the backcross of transgenic hypertensive [mRen-2]27 rats with Lewis normotensive ones.

METHODS

Twenty-nine mRen2.Lewis hypertensive rats were randomly assigned to drink tap water (vehicle; n = 9), valsartan (30 mg/kg/day; n = 10), or valsartan (30 mg/kg/day) combined with aliskiren given subcutaneously (50 mg/kg/day; n = 10) for 2 weeks. Arterial pressure, heart rate, and locomotive activity were recorded with chronically implanted radiotelemetry probes. The awake/asleep ratio was calculated as [awake mean arterial pressure (MAP) mean - asleep MAP mean)] / (awake MAP mean) x 100. Plasma renin activity (PRA) and concentration (PRC), and plasma and kidney angiotensin II (Ang II) were measured by radioimmunoassay (RIAs).

RESULTS

Untreated hypertensive rats showed an inverse arterial pressure rhythm, higher at day and lower at night, accompanied by normal rhythms of heart rate and locomotive activity. Treatment with valsartan or aliskiren and valsartan normalized the elevated arterial pressure and the arterial pressure rhythm, with the combination therapy being more effective in reducing MAP and in restoring the awake/asleep ratio. While PRA and PRC increased with the treatments, the addition of aliskiren to valsartan partially reversed the increases in plasma Ang II levels. Valsartan and the aliskiren and valsartan combination markedly reduced the renal cortical content of Ang II.

CONCLUSION

The altered circadian arterial pressure rhythm in this renin-dependent hypertension model uncovers a significant role of Ang II in the desynchronization of the circadian rhythm of arterial pressure, heart rate, and locomotive activity.

Aliskiren as a novel therapeutic agent for hypertension and cardio-renal diseases

Objectives

High blood pressure (BP) is a major risk factor for cardiovascular and renal complications. A majority of treated hypertensive patients still complain of high BP. The renin-angiotensin aldosterone system (RAAS) has been a centre-stage target for all the cardiovascular and cardio-renal complications. Aliskiren, is the first direct renin inhibitor (DRI) to be approved by the US FDA. Renin controls the rate-limiting step in the RAAS cascade and hence is the most favorable target for RAAS suppression.

Key findings

This review article strives to summarize the pharmacokinetic, preclinical and clinical studies done so far pertaining to the efficacy of aliskiren. Further, the pharmacology of aliskiren has been comprehensively dealt with to enhance understanding so as to further research in this unfathomed area in the multitude of cardiovascular disorders and renal diseases.

Summary

Aliskiren has been shown to have comparable BP-lowering effects to other RAAS inhibitors. Recent clinical trials have indicated that it might contribute significantly in combination with other agents for the protection of end-organ diseases.

Chronic renin inhibition with aliskiren improves glucose tolerance, insulin sensitivity, and skeletal muscle glucose transport activity in obese Zucker rats

We have demonstrated previously that overactivity of the renin-angiotensin system (RAS) is associated with whole body and skeletal muscle insulin resistance in obese Zucker (fa/fa) rats. Moreover, this obesity-associated insulin resistance is reduced by treatment with angiotensin-converting enzyme inhibitors or angiotensin receptor (type 1) blockers. However, it is currently unknown whether specific inhibition of renin itself, the rate-limiting step in RAS functionality, improves insulin action in obesity-associated insulin resistance. Therefore, the present study assessed the effect of chronic, selective renin inhibition using aliskiren on glucose tolerance, whole body insulin sensitivity, and insulin action on the glucose transport system in skeletal muscle of obese Zucker rats. Obese Zucker rats were treated for 21 days with either vehicle or aliskiren (50 mg/kg body wt ip). Renin inhibition was associated with a significant lowering (10%, P < 0.05) of resting systolic blood pressure and induced reductions in fasting plasma glucose (11%) and free fatty acids (46%) and homeostatic model assessment for insulin resistance (13%). Glucose tolerance (glucose area under the curve) and whole body insulin sensitivity (inverse of the glucose-insulin index) during an oral glucose tolerance test were improved by 15% and 16%, respectively, following chronic renin inhibition. Moreover, insulin-stimulated glucose transport activity in isolated soleus muscle of renin inhibitor-treated animals was increased by 36% and was associated with a 2.2-fold greater Akt Ser(473) phosphorylation. These data provide evidence that chronic selective inhibition of renin activity leads to improvements in glucose tolerance and whole body insulin sensitivity in the insulin-resistant obese Zucker rat. Importantly, chronic renin inhibition is associated with upregulation of insulin action on skeletal muscle glucose transport, and it may involve improved Akt signaling. These data support the strategy of targeting the RAS to improve both blood pressure regulation and insulin action in conditions of insulin resistance.

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.

Possible Mechanisms of Local Tissue Renin-Angiotensin System Activation in the Cardiorenal Metabolic Syndrome and Type 2 Diabetes Mellitus

The role of local tissue renin-angiotensin system (tRAS) activation in the cardiorenal metabolic syndrome (CRS) and type 2 diabetes mellitus (T2DM) is not well understood. To this point, we posit that early redox stress-mediated injury to tissues and organs via accumulation of excessive reactive oxygen species (ROS) and associated wound healing responses might serve as a paradigm to better understand how tRAS is involved. There are at least five common categories responsible for generating ROS that may result in a positive feedback ROS-tRAS axis. These mechanisms include metabolic substrate excess, hormonal excess, hypoxia-ischemia/reperfusion, trauma, and inflammation. Because ROS are toxic to proteins, lipids, and nucleic acids they may be the primary instigator, serving as the injury nidus to initiate the wound healing process. Insulin resistance is central to the development of the CRS and T2DM, and there are now thought to be four major organ systems important in their development. In states of overnutrition and tRAS activation, adipose tissue, skeletal muscle (SkM), islet tissues, and liver (the quadrumvirate) are individually and synergistically related to the development of insulin resistance, CRS, and T2DM. The obesity epidemic is thought to be the driving force behind the CRS and T2DM, which results in the impairment of multiple end-organs, including the cardiovascular system, pancreas, kidney, retina, liver, adipose tissue, SkM, and nervous system. A better understanding of the complex mechanisms leading to local tRAS activation and increases in tissue ROS may lead to new therapies emphasizing global risk reduction of ROS resulting in decreased morbidity and mortality.

Renin and cardiovascular disease: Worn-out path, or new direction

Inhibition of the renin angiotensin system has beneficial effects in cardiovascular prevention and treatment. The advent of orally active direct renin inhibitors adds a novel approach to antagonism of the renin-angiotensin system. Inhibition of the first and rate-limiting step of the renin angiotensin cascade offers theoretical advantages over downstream blockade. However, the recent discovery of the (pro)renin receptor which binds both renin and prorenin, and which can not only augment catalytic activity of both renin and prorenin in converting angiotensinogen to angiotensin I, but also signal intracellularly via various pathways to modulate gene expression, adds a significant level of complexity to the field. In this review, we will examine the basic and clinical data on renin and its inhibition in the context of cardiovascular pathophysiology.

Aliskiren improves insulin resistance and ameliorates diabetic vascular complications in db/db mice

BACKGROUND

Aliskiren is a direct renin inhibitor (DRI) and provides an organ-protective effect in human and animal experiments. However, there is no current evidence of the effect of DRI on insulin resistance and metabolic abnormalities in type 2 diabetic animals. Methods. We investigated the effects and molecular mechanism of aliskiren in db/db mice and cultured mesangial cells (MCs).

RESULTS

Aliskiren treatment for 3 months at a dose of 25 mg/kg/day via an osmotic mini-pump did not induce significant changes in blood glucose levels, systolic blood pressure, serum creatinine and electrolyte levels. However, aliskiren treatment improved insulin resistance confirmed by insulin tolerance test and various biomarkers including homeostasis model assessment index levels and lipid abnormalities. The treated group also exhibited significant improvement in cardiac functional and morphological abnormalities including left ventricular hypertrophy, and induced phenotypic changes in adipose tissue. Aliskiren treatment also markedly decreased urinary albumin excretion, glomerulosclerosis and suppressed profibrotic and proinflammatory cytokine synthesis and improved renal lipid metabolism. In cultured MCs, high glucose stimulation increased MC renin concentration. Furthermore, renin treatment directly up-regulates synthesis of proinflammatory and profibrotic cytokines, which were abolished by prior treatment with aliskiren and angiotensin receptor (AT1) antagonist. These results suggest that the beneficial effect of aliskiren is mediated by an angiotensin-dependent mechanism.

CONCLUSIONS

Together, these results imply that aliskiren provides an organ-protective effect through improvement in insulin resistance and lipid abnormality, as well as direct anti-fibrotic effect in target organ in db/db mice. Aliskiren may be a useful new therapeutic agent in the treatment of type 2 diabetes mellitus and diabetic nephropathy.

Pericytopathy: oxidative stress and impaired cellular longevity in the pancreas and skeletal muscle in metabolic syndrome and type 2 diabetes

The pericyte's role has been extensively studied in retinal tissues of diabetic retinopathy; however, little is known regarding its role in such tissues as the pancreas and skeletal muscle. This supportive microvascular mural cell plays an important and novel role in cellular and extracellular matrix remodeling in the pancreas and skeletal muscle of young rodent models representing the metabolic syndrome and type 2 diabetes mellitus (T2DM). Transmission electron microscopy can be used to evaluate these tissues from young rodent models of insulin resistance and T2DM, including the transgenic Ren2 rat, db/db obese insulin resistantߞT2DM mouse, and human islet amyloid polypeptide (HIP) rat model of T2DM. With this method, the earliest pancreatic remodeling change was widening of the islet exocrine interface and pericyte hypercellularity, followed by pericyte differentiation into islet and pancreatic stellate cells with early fibrosis involving the islet exocrine interface and interlobular interstitium. In skeletal muscle there was a unique endothelial capillary connectivity via elongated longitudinal pericyte processes in addition to pericyte to pericyte and pericyte to myocyte cellcell connections allowing for paracrine communication. Initial pericyte activation due to moderate oxidative stress signaling may be followed by hyperplasia, migration and differentiation into adult mesenchymal cells. Continued robust oxidative stress may induce pericyte apoptosis and impaired cellular longevity. Circulating antipericyte autoantibodies have recently been characterized, and may provide a screening method to detect those patients who are developing pericyte loss and are at greater risk for the development of complications of T2DM due to pericytopathy and rarefaction. Once detected, these patients may be offered more aggressive treatment strategies such as early pharmacotherapy in addition to lifestyle changes targeted to maintaining pericyte integrity. In conclusion, we have provided a review of current knowledge regarding the pericyte and novel ultrastructural findings regarding its role in metabolic syndrome and T2DM.

Angiotensin receptor blocker/diuretic combination preserves insulin responses in obese hypertensives

BACKGROUND

Thiazide diuretics can impair glucose metabolism and increase new-onset diabetes. Adding an angiotensin receptor blocker to diuretics may protect against these metabolic effects; however, the mechanism of this protection is unclear.

METHOD

To explore potential mechanisms, a 16-week multicenter trial was conducted to ascertain the relative glucose metabolism effects of combined hydrochlorothiazide and angiotensin receptor blocker (valsartan) therapy compared with hydrochlorothiazide and calcium channel blocker (amlodipine) treatment in 412 centrally obese hypertensive individuals (BMI = 35 +/- 7 kg/m, seated BP = 159 +/- 8/94 +/- 8 mmHg, and mean age 56 years). Individuals were randomized to valsartan/hydrochlorothiazide, with force-titration to 320/25 mg or hydrochlorothiazide, with titration to hydrochlorothiazide 25 mg and amlodipine 10 mg, respectively. Changes from baseline to week 16 in fasting and 2-h postprandial glucose and insulin levels after an oral glucose load were measured.

RESULTS

At week 16, clinic blood pressure reductions were similar (P > 0.05) in both groups. Fasting and 2-h glucose levels increased (P < 0.05) with the amlodipine combination but not with the valsartan combination. In concert with these glucose responses, postprandial insulin increases from baseline were substantially greater with valsartan than with amlodipine plus hydrochlorothiazide group (P = 0.001). The glucose responses were inversely related to insulin responses at the study conclusion.

CONCLUSION

The novel observation of this investigation was that the combination of valsartan and hydrochlorothiazide was associated with greater glucose-stimulated insulin secretory and lesser glycemic excursion responses than the amlodipine combination group. Thus, this data suggests that adding an angiotensin receptor blocker attenuates the negative effects of thiazides on pancreatic beta-cell glucose-induced insulin secretion.