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

Endoplasmic reticulum homeostasis: a potential target for diabetic nephropathy

The endoplasmic reticulum (ER) is the most vigorous organelle in intracellular metabolism and is involved in physiological processes such as protein and lipid synthesis and calcium ion transport. Recently, the abnormal function of the ER has also been reported to be involved in the progression of kidney disease, especially in diabetic nephropathy (DN). Here, we reviewed the function of the ER and summarized the regulation of homeostasis through the UPR and ER-phagy. Then, we also reviewed the role of abnormal ER homeostasis in residential renal cells in DN. Finally, some ER stress activators and inhibitors were also summarized, and the possibility of maintaining ER homeostasis as a potential therapeutic target for DN was discussed.

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.

Aliskiren effect on non-alcoholic steatohepatitis in metabolic syndrome

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is highly associated with metabolic syndrome, a major cause of morbidity in the globalized society. The renin-angiotensin system (RAS) influences hepatic fatty acid metabolism, inflammation and fibrosis. Thus, in the present study, we aimed to evaluate the effect of aliskiren, a direct renin inhibitor, on metabolic syndrome-related NASH.

METHODS

C57BL/6 male mice (n = 45) were divided into three groups: controls; animals inoculated with streptozotocin (STZ) (40 mg/kg/day) for 5 days and fed with high fat diet (HFD) for 8 weeks; and animals inoculated with STZ for 5 days, fed with HFD for 8 weeks and treated with aliskiren (100 mg/kg/day) for the final 2 weeks. Glycemic and insulin levels, hepatic lipid profile, histological parameters and inflammatory protein expression were analyzed.

RESULTS

Aliskiren normalized plasma glucose and insulin levels, reduced cholesterol, triglycerides and total fat accumulation in liver and diminished hepatic injury, steatosis and fibrosis. These results could be explained by the ability of aliskiren to block angiotensin-II, lowering oxidative stress and inflammation in liver. Also, it exhibited a beneficial effect in increasing insulin sensitivity.

CONCLUSION

These findings support the use of aliskiren in the treatment of metabolic syndrome underlying conditions. However, clinical studies are indispensable to test its effectiveness in the treatment of patients with metabolic syndrome.

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.

Aliskiren directly improves endothelial progenitor cell function from Type II diabetic patients

BACKGROUND

Endothelial progenitor cell (EPC) functions are impaired in the presence of diabetes mellitus. Aliskiren is a direct renin inhibitor, which is expected to modify proangiogenic cells. This study aimed to investigate whether and how aliskiren could improve the function of EPCs from patients with type II diabetes (T2DM).

MATERIALS AND METHODS

Endothelial progenitor cells fibronectin adhesion assay, chamber assay and in vitro tube formation assay were used to estimate the degree of EPC adhesion, migration and tube formation abilities. EPC protein and mRNA expressions were evaluated by Western blot and quantitative RT-PCR, respectively. EPC vascular endothelial growth factor (VEGF) and (pro)renin receptor ((P)RR) expression was knocked down by VEGF and (P)RR siRNA.

RESULTS

Aliskiren (0·1 or 10 μM) dose-dependently improved functions and increased both VEGF and stromal cell-derived factor-1α (SDF-1α) expression of EPCs from patients with T2DM or EPCs from healthy volunteers and treated with high glucose. Transfection with VEGF siRNA significantly reduced the aliskiren-induced SDF-1α expression. Furthermore, (P)RR siRNA transfection impaired the aliskiren-induced VEGF and SDF-1 expression.

CONCLUSIONS

The results show that aliskiren improved EPC function from patients with T2DM in a dose-dependent manner probably via the (P)RR and VEGF/SDF-1α-related mechanisms.

Feasibility of fluorescence energy transfer system for imaging the renoprotective effects of aliskiren in diabetic mice

Introduction:

We investigated the feasibility of using a fluorescence resonance energy transfer system to image enzymatic activity in order to evaluate the effects of aliskiren (a direct renin inhibitor) on diabetic nephropathy.

Materials and methods:

First, we induced diabetes in C57BL/6J mice using streptozotocin, then treated them with either aliskiren (25 mg/kg/day) or the angiotensin type 1 receptor blocker valsartan (15 mg/kg/day) for four weeks. Finally, we utilized renin fluorescence resonance energy transfer substrate to assess renin activity.

Results:

Renin activity was much higher in the kidneys of diabetic mice compared to those of the non-diabetic control mice. While aliskiren inhibited this activity, valsartan did not. We noted that production of reactive oxygen species intensified and the bioavailability of nitric oxide diminished in the glomeruli of diabetic mice. Aliskiren and valsartan significantly ameliorated these effects. They suppressed glomerular production of reactive oxygen species and urinary albumin excretion. In fact, urinary albumin excretion in diabetic mice treated with aliskiren or valsartan was lower than that in untreated diabetic mice. Furthermore, aliskiren and valsartan significantly reduced glomerular permeability by maintaining the glomerular endothelial surface layer.

Conclusion:

Fluorescence resonance energy transfer could provide a new tool for evaluating tissue and plasma enzymatic activity.

Renin inhibitor aliskiren exerts beneficial effect on trabecular bone by regulating skeletal renin-angiotensin system and kallikrein-kinin system in ovariectomized mice

SUMMARY

The skeletal renin-angiotensin system contributes to the development of osteoporosis. The renin inhibitor aliskiren exhibited beneficial effects on trabecular bone of osteoporotic mice, and this action might be mediated through angiotensin and bradykinin receptor pathways. This study implies the potential application of renin inhibitor in the management for postmenopausal osteoporosis.

INTRODUCTION

The skeletal renin-angiotensin system plays key role in the pathological process of osteoporosis. The present study is designed to elucidate the effect of renin inhibitor aliskiren on trabecular bone and its potential action mechanism in ovariectomized (OVX) mice.

METHODS

The OVX mice were treated with low dose (5 mg/kg) or high dose (25 mg/kg) of aliskiren or its vehicle for 8 weeks. The bone turnover markers were measured by ELISA. The structural parameters of trabecular bone at lumbar vertebra (LV) and distal femoral metaphysis were measured by micro-CT. The expression of messenger RNA (mRNA) and protein was studied by RT-PCR and immunoblotting, respectively.

RESULTS

Aliskiren treatment reduced urinary excretion of calcium and serum level of tartrate-resistant acid phosphatase in OVX mice. The treatment with aliskiren significantly increased bone volume (BV/TV) and connectivity density (Conn.D) of trabecular bone at LV-2 and LV-5 as well as dramatically enhanced BV/TV, Conn.D, bone mineral density (BMD/BV) and decreased bone surface (BS/BV) at the distal femoral end. Aliskiren significantly down-regulated the expression of angiotensinogen, angiotensin II (Ang II), Ang II type 1 receptor, bradykinin receptor (BR)-1, and osteocytic-specific gene sclerostin as well as the osteoclast-specific genes, including carbonic anhydrase II, matrix metalloproteinase-9, and cathepsin K.

CONCLUSIONS

This study revealed that renin inhibitor aliskiren exhibited the beneficial effects on trabecular bone of ovariectomy-induced osteoporotic mice, and the underlying mechanism for this action might be mediated through Ang II and BR signaling pathways in bone.

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.

Renin inhibition improves ovariectomy-induced osteoporosis of lumbar vertebra in mice

The skeletal renin–angiotensin system (RAS) is involved in the progression of osteoporosis and the active peptide within the RAS, angiotensin II (ANG II), has deleterious effects on bones. This study was performed to investigate whether suppression of the rate-limiting step of the RAS cascade by the renin inhibitor aliskiren has a benefit on trabecular bone in osteoporotic mice. A postmenopausal osteoporosis model was induced by bilateral ovariectomy. The ovariectomized (OVX) mice were treated with a low (5 mg/kg) or high (25 mg/kg) dose of aliskiren for 6 weeks. Micro-computed tomography was performed to detect trabecular bone parameters of lumbar vertebra and to obtain 3-dimensional (3D) images. Treatment with aliskiren markedly increased bone volume over total volume (p<0.05), trabecular bone number (p<0.05), connectivity density (p<0.05), and bone mineral density (p<0.05) and reduced trabecular bone separation (p<0.05) compared to vehicle-treated OVX mice. Similarly, the 3D images were consistent with the quantitative data that showed aliskiren could markedly reverse the ovariectomy-induced pathological changes of trabecular bone. Thus, this study indicated that the treatment of estrogen-deficient mice with aliskiren could markedly increase bone mass and improve trabecular bone structure, suggesting its potential application in treating postmenopausal osteoporosis.

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.

Correlation between type 1 diabetic nephropathy and insulin resistance

AIM: To perform a quantitative test for urinary protein and different renal function indexes and explore the expression and phosphorylation of relevant proteins in the insulin signal pathway.

METHODS: Controls and cases at a ratio of 1:1 were included in this prospective randomized controlled clinical study. There were 40 patients with diabetic nephropathy (DN) and 40 normal cases with comparable age. Plasma samples were collected from the subjects to detect the protein expression of insulin receptor substrate (IRS)-2, p-IRS-2, AKT, and p-AKT by Western blot. The correlations of the quantity of urinary protein, RBF and GFR with homeostasis model assessment-insulin resistance (HOMA-IR), homeostasis model assessment-insulin sensitive index (HOMA-ISI) and homeostasis model assessment-pancreatic beta-cell function (HOMA-β%) were analyzed.

RESULTS: The ratios of p-IRS-2/IRS-2 and p-AKT/AKT decreased significantly in the DN group compared with the normal group (P < 0.05). There was a positive correlation between the quantity of urinary protein and HOMA-IR (P < 0.05) and a negative correlation between the quantity of urinary protein and HOMA-ISI (P < 0.05).

CONCLUSION: The ratios of p-IRS-2/IRS-2 and p-AKT/AKT decrease in DN patients. There exist correlations between the quantity of urinary protein and HOMA-IR and HOMA-ISI. These results indicate that the decrease of HOMA-ISI, the increase of HOMA-IR and the blockage of the insulin signal pathway may be key factors that cause DN.

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.

Inflammation in the pathogenesis of microvascular complications in diabetes

Diabetes and hyperglycemia create a proinflammatory microenvironment that progresses to microvascular complications such as nephropathy, retinopathy, and neuropathy. Diet-induced insulin resistance is a potential initiator of this change in type 2 diabetes which can increase adipokines and generate a chronic low-grade inflammatory state. Advanced glycation end-products and its receptor, glycation end-products AGE receptor axis, reactive oxygen species, and hypoxia can also interact to worsen complications. Numerous efforts have gained way to understanding the mechanisms of these modulators and attenuation of the inflammatory response, however, effective treatments have still not emerged. The complexity of inflammatory signaling may suggest a need for multi-targeted therapy. This review presents recent findings aimed at new treatment strategies.