Mechanisms of protective effects induced by blockade of the renin-angiotensin system: novel role of the pancreatic islet angiotensin-generating system in Type 2 diabetes

EGCG-derived polymeric oxidation products enhance insulin sensitivity in db/db mice

The present study investigated the influence of epigallocatechin-3-gallate (EGCG) and its autoxidation products on insulin sensitivity in db/db mice. Compared to EGCG, autoxidation products of EGCG alleviated diabetic symptoms by suppressing the deleterious renal axis of the renin-angiotensin system (RAS), activating the beneficial hepatic axis of RAS, and downregulating hepatic and renal SELENOP and TXNIP. A molecular weight fraction study demonstrated that polymeric oxidation products were of essential importance. The mechanism of action involved coating polymeric oxidation products on the cell surface to protect against cholesterol loading, which induces abnormal RAS. Moreover, polymeric oxidation products could regulate RAS and SELENOP at doses that were far below cytotoxicity. The proof-of-principal demonstrations of EGCG-derived polymeric oxidation products open a new avenue for discovering highly active polymeric oxidation products based on the oxidation of naturally occurring polyphenols to manage diabetes and other diseases involving abnormal RAS.

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EGCG autoxidation forms polymeric oxidation products.

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The polymeric oxidation products are coated on the surface of cells or tissues.

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The surface coating regulates RAS, SELENOP, and TXNIP in db/db mice.

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The surface coating increases insulin sensitivity in db/db mice.

Angiotensin(1-7) Improves Islet Function in Diabetes Through Reducing JNK/Caspase-3 Signaling

The aim of this study is to investigate whether Angiotensin (1-7), the physiological antagonist of Angiotensin II (AngII), has antidiabetic activity and the possible mechanism. Male Wistar rats were randomly divided into 3 groups: control group fed the normal diet, DM group fed high-fat diet and injected with STZ, and Angiotensin (1-7) group receiving injection of STZ followed by Angiotensin (1-7) treatment. Serum Ang II, fasting blood glucose, insulin, HOMA-IR, and HOMA-beta were determined in control, diabetes and Angiotensin (1-7) groups. The increased AngII and insulin resistance in diabetes group were accompanied by changes in islet histopathology. However, Angiotensin (1-7) improved the islet function and histopathology in diabetes without affecting the level of AngII. Western blot confirmed that Angiotensin (1-7) decreased the cleaved caspase 3 levels in pancreas of DM. The increased expression of JNK, Bax, and Bcl2 genes under diabetic conditions were partially reversed after Angiotensin (1-7) administration in pancreas. Immunofluorescence analysis showed that p-JNK was markedly increased in islet of DM rats, which was markedly alleviated after Angiotensin (1-7) treatment. Furthermore, Angiotensin (1-7) reversed high glucose(HG) induced mitochondrial apoptosis augments. Finally, Angiotensin (1-7) attenuated the apoptosis of INS-1 cells through reducing JNK activation in diabetes, which was blocked by anisomycin (a potent agonist of JNK). Our findings provide supporting evidence that Angiotensin (1-7) improved the islet beta-cells apoptosis by JNK-mediated mitochondrial dysfunction, which might be a novel target for the treatment and prevention of beta-cells dysfunction in DM.

Diabetes and Renin-Angiotensin-Aldosterone System: Pathophysiology and Genetics

Diabetes mellitus (DM) is a metabolic disorder and characterized by hyperglycemia. Being a concern of both the developed and developing world, diabetes is a global health burden and is a major cause of mortality world-wide. The most common is the type 2 diabetes mellitus (T2DM), which is mainly caused by resistance to insulin. Long-term complications of diabetes cause microvascular related problems (eg. nephropathy, neuropathy and retinopathy) along with macrovascular complications (eg. cardiovascular diseases, ischemic heart disease, peripheral vascular disease). Renin-angiotensin-aldosterone system (RAAS) regulates homeostasis of body fluid that in turn, maintains blood pressure. Thus, RAAS plays pivotal role in the pathogenesis of long-term DM complications like cardiovascular diseases and chronic kidney diseases. T2DM is a polygenic disease, and the roles of RAAS components in insulin signaling pathway and insulin resistance have been well documented. Hyperglycemia has been found to be associated with the increased plasma renin activity, arterial pressure and renal vascular resistance. Several studies have reported involvement of single variants within particular genes in initiation and development of T2D using different approaches. This chapter aims to investigate and discuss potential genetic polymorphisms underlying T2D identified through candidate gene studies, genetic linkage studies, genome wide association studies.

Autoantibody against angiotensin II type I receptor induces pancreatic β-cell apoptosis via enhancing autophagy

Autoantibody against the angiotensin II type I receptor (AT1-AA) has been found in the serum of patients with diabetes mellitus (DM). However, it remains unclear whether AT1-AA induces β-cell apoptosis and participates in the development of DM. In this study, an AT1-AA-positive rat model was set up by active immunization, and AT1-AA IgG was purified. INS-1 cells were treated with AT1-AA, and cell viability, apoptosis, and autophagy-related proteins were detected by Cell Counting Kit-8 assay, flow cytometry, and western blot analysis, respectively. Results showed that existence of AT1-AA impaired the islet function and increased the apoptosis of pancreatic islet cells in rats, and the autophagy level in rat pancreatic islet tissues tended to increase gradually with the prolongation of immunization time. AT1-AA markedly reduced INS-1 cell viability, promoted cell apoptosis, and decreased insulin secretion in vitro. In addition, the autophagy level was gradually increased along with the prolongation of AT1-AA treatment time. Meanwhile, it was determined that treatment with autophagy inhibitor 3-methyladenine and angiotensin II type 1 receptor (AT1R) blocker telmisartan could improve insulin secretion and apoptosis in vitro and in vivo. In conclusion, it is deduced that upregulation of autophagy contributed to the AT1-AA-induced β-cell apoptosis and islet dysfunction, and AT1R mediated the signal transduction.

Angiotensin-converting enzyme as a new immunologic target for the new SARS-CoV-2

The coronavirus disease 2019 (COVID-19) pandemic has affected the daily lives of millions of people worldwide and had caused significant mortality; hence, the assessment of therapeutic options is of great interest. The leading cause of death among COVID-19 patients is acute respiratory distress syndrome caused by hyperinflammation secondary to cytokine release syndrome (CRS). Cytokines, such as tumor necrosis factor-α, interleukin-6, interferon-γ and interleukin-10, are the main mediators of CRS. Based on recent evidence, the angiotensin-converting enzyme (ACE) II is known to be the target of the COVID-19 spike protein, which enables the virus to penetrate human cells. ACE II also possesses an anti-inflammatory role in many pathologies such as cardiovascular disease, hypertension, diabetes mellitus and other conditions, which are the main risk factors of poor prognosis in COVID-19 infection. Changes in tissue ACE II levels are associated with many diseases and hyperinflammatory states, and it is assumed that elevated levels of ACE II could aggravate the course of COVID-19 infection. Therefore, the use of renin-angiotensin-aldosterone system inhibitors (RASis) in COVID-19 patients could be hypothetically considered, though sufficient evidence is not presented by the scientific community. In this work, based on the most recent pieces of evidence, the roles of RAS and RASi in immunologic interactions are addressed. Furthermore, the molecular and immunologic aspects of RASi and their potential significance in COVID-19 are discussed.

Chronic Intermittent Hypoxia Triggers a Senescence-like Phenotype in Human White Preadipocytes

Obstructive sleep apnea (OSA) is a common sleep disorder associated with obesity. Emerging evidence suggest that OSA increases the risk of cardiovascular morbidity and mortality partly via accelerating the process of cellular aging. Thus, we sought to examine the effects of intermittent hypoxia (IH), a hallmark of OSA, on senescence in human white preadipocytes. We demonstrate that chronic IH is associated with an increased generation of mitochondrial reactive oxygen species along with increased prevalence of cells with nuclear localization of γH2AX & p16. A higher prevalence of cells positive for senescence-associated β-galactosidase activity was also evident with chronic IH exposure. Intervention with aspirin, atorvastatin or renin-angiotensin system (RAS) inhibitors effectively attenuated IH-mediated senescence-like phenotype. Importantly, the validity of in vitro findings was confirmed by examination of the subcutaneous abdominal adipose tissue which showed that OSA patients had a significantly higher percentage of cells with nuclear localization of γH2AX & p16 than non-OSA individuals (20.1 ± 10.8% vs. 10.3 ± 2.7%, Padjusted < 0.001). Furthermore, the frequency of dual positive γH2AX & p16 nuclei in adipose tissue of OSA patients receiving statin, aspirin, and/or RAS inhibitors was comparable to non-OSA individuals. This study identifies chronic IH as a trigger of senescence-like phenotype in preadipocytes. Together, our data suggest that OSA may be considered as a senescence-related disorder.

NLRP3 inflammasome mediates angiotensin II-induced islet β cell apoptosis

Elevation of angiotensin II (Ang II) in the serum of patients with diabetes is known to promote apoptosis of islet β cells, but the underlying mechanism remains unclear. The aim of the present study was to explore the role of Nod-like receptor protein 3 (NLRP3) inflammasome in Ang II-induced apoptosis of pancreatic islet β cells and investigate the possible underlying mechanism. The effect of Ang II on INS-1 cell (a rat insulinoma cell line) viability was detected by CCK-8 method. The cell apoptosis was detected by flow cytometry and western blot analysis. The effect of Ang II on the expressions of thioredoxin-interacting protein (TXNIP) and NLRP3 protein was detected by western blot analysis. The expression of TXNIP mRNA was detected by real-time polymerase chain reaction. The results showed that Ang II was able to reduce INS-1 cell viability and promote apoptosis and at the same time up-regulate the expressions of TXNIP and NLRP3 components. Ang II-induced apoptosis was inhibited after administration of the NLRP3 inhibitor MCC950, and TXNIP silencing could reduce the NLRP3 expression and apoptosis, while both effects of Ang II on TXNIP-NLRP3 and its apoptosis-inducing effect were inhibited by angiotensin II type I receptor (AT1R) blocker Telmisartan. Our results demonstrated that the TXNIP-NLRP3 inflammasome pathway mediated Ang II-induced INS-1 cell apoptosis and might hopefully become a novel target for the treatment of diabetes mellitus.

Effects of Irbesartan Pretreatment on Pancreatic β-Cell Apoptosis in STZ-Induced Acute Prediabetic Mice

The current study was performed to investigate the effects and potential effects of irbesartan pretreatment on pancreatic β-cell apoptosis in a streptozotocin- (STZ-) induced acute mouse model of prediabetes. Twenty-four male BALB/C mice (18–22 g) were randomly divided into three groups: normal control group (NC, n = 6), STZ group (STZ, n = 8), and irbesartan + STZ group (IRB + STZ, n = 10). In the IRB + STZ group, mice were administered irbesartan (300 mg/kg per day) by gavage for one week. The STZ group and IRB + STZ group received STZ (80 mg/kg by intraperitoneal (IP) injection once). The NC group received normal saline (80 mg/kg by IP injection once). Fasting blood glucose prior to STZ injection and presacrifice was analysed using samples withdrawn from the caudal vein to confirm the induction of prediabetes. Haematoxylin and eosin staining, immunohistochemical detection of insulin, and apoptosis analysis were performed. Reverse transcription-quantitative polymerase chain reaction was used to detect angiotensin II type 1 receptor (AT1R), caspase-3, and p38 mitogen-activated protein kinase (MAPK) mRNA expression. Blood glucose was significantly higher in the STZ group (9.01 ± 1.1089 vs 4.78 ± 0.7026) and IRB + STZ group (7.86 ± 1.1811 vs 4.78 ± 0.7026) compared with the NC group (P < 0.05). In comparison to the STZ group, the islet cell damage was marginally improved in the IRB + STZ group, and the IRB + STZ group had a significantly lower apoptotic rate than the STZ group (22.42 ± 8.3675 vs 50.86 ± 5.3395, P < 0.001). AT1R expression in the IRB + STZ group was lower than that in the STZ group (1.56 ± 1.2207 vs 3.92 ± 2.4392, P < 0.05). The mRNA expression of caspase-3 in pancreatic tissue was significantly lower in the IRB + STZ group than in the STZ group (0.90 ± 0.7272 vs 1.88 ± 1.0572, P < 0.05). Similarly, the IRB + STZ group also had lower p38MAPK levels than the STZ group (1.16 ± 1.0642 vs 2.55 ± 1.7925, P > 0.05). In conclusion, irbesartan pretreatment improved glucose levels and insulin secretion and decreased islet β-cell apoptosis to protect islet β cells in an STZ-induced acute prediabetic mouse model.

Pilot genome-wide association study identifying novel risk loci for type 2 diabetes in a Maya population

Type 2 diabetes mellitus (T2D) is one of the two leading causes of mortality in Mexico. However, most studies have focused on Caucasians or Asians, and there are a small number of studies investigating Maya populations. Furthermore, to the best of our knowledge, there is no information on isolated Maya communities with T2D frequencies of 20% that are primarily attributed to ethnicity. Consequently, this study focused on assessing which genetic risk variants could be involved in the high rates of T2D in 92 individuals with Maya ancestry; 47 were diagnosed with T2D, and 45 were classified as healthy individuals. A pilot genome-wide association study was performed using the Affymetrix Axiom Genome-wide LAT1 array. The population structure was determined with the ADMIXTURE software using 1289 Latin American selected polymorphisms, and 39 polymorphisms associated with T2D were included for replication. Association tests were performed using the Statistical Analysis System (SAS) using the allelic, genotype and Armitage trend tests. The results indicated that population structure analysis displayed no differences between T2D patients and healthy individuals; 24 loci located were identified for probable association with T2D (p > 1.288 × 10^-7 and p < 1.348 × 10^-4); the polymorphism AGTR2 rs1914711 in chromosome X was identified by the allele test (OR = 6.824; p = 1.448 × 10^-9) as a candidate gene for association with T2D; and ARL15 rs4311394 was associated as a T2D protector by genotype and the Armitage trend test (OR = 0.318; p = 0.001). In conclusion, this study proposes 24 candidate SNPs associated with T2D for replication studies and one for protective association with T2D.

Re-analysis of public genetic data reveals a rare X-chromosomal variant associated with type 2 diabetes

The reanalysis of existing GWAS data represents a powerful and cost-effective opportunity to gain insights into the genetics of complex diseases. By reanalyzing publicly available type 2 diabetes (T2D) genome-wide association studies (GWAS) data for 70,127 subjects, we identify seven novel associated regions, five driven by common variants (LYPLAL1, NEUROG3, CAMKK2, ABO, and GIP genes), one by a low-frequency (EHMT2), and one driven by a rare variant in chromosome Xq23, rs146662075, associated with a twofold increased risk for T2D in males. rs146662075 is located within an active enhancer associated with the expression of Angiotensin II Receptor type 2 gene (AGTR2), a modulator of insulin sensitivity, and exhibits allelic specific activity in muscle cells. Beyond providing insights into the genetics and pathophysiology of T2D, these results also underscore the value of reanalyzing publicly available data using novel genetic resources and analytical approaches.

Genome-wide association studies have uncovered several loci associated with diabetes risk. Here, the authors reanalyse public type 2 diabetes GWAS data to fine map 50 known loci and identify seven new ones, including one near ATGR2 on the X-chromosome that doubles the risk of diabetes in men.

Effects of β(3)-adrenoceptor activation on expression of pancreatic adrenoceptors and angiotensin II receptors in ApoE(-/-) mice

Hyperlipidemia can be harmful to the pancreas and β3-adrenoceptor agonist can improve lipid metabolism disorder. We aimed to study the effects of β3-adrenoceptor activation on glucose, insulin and the expression of pancreatic adrenoceptors and angiotensin II receptors. Ten C57BL/6J mice at the age of 10 weeks served as normal control, and forty age-matched apolipoprotein E knockout (ApoE(-/-)) mice were randomly divided into hyperlipidaemia model group, low-dose and high-dose β3-adrenoceptor agonist group and β3-adrenoceptor antagonist group. After 26 weeks of high-fat diet, treatments were given for 12 weeks. Serum glucose and insulin levels in 48 weeks old mice were measured using an automatic biochemical detector. Quantitative rt-PCR and Western blot were used to analyze the mRNA and protein expression of α1A-, α2A-, β2-, β3-adrenoceptors and angiotensin II type 1 and type 2 receptors in pancreas. We found that β3-adrenoceptor agonist could decrease serum glucose and insulin levels in aged ApoE(-/-) mice (P<0.01) and down-regulate the expression of α1A-adrenoceptor and angiotensin II type 1 receptor which were significantly increased in model mice (P<0.05, P<0.01). Compared with the model mice, α2A-, β2-, β3-adrenoceptor and angiotensin II type 2 receptor expression were up-regulated in β3-adrenoceptor agonist treat mice (P<0.05, P<0.01). These results suggest that chronic β3-adrenoceptor activation regulated the expression of adrenoceptors and angiontensin II receptors towards contrary direction, which indicates that there are interactions between β3-adrenoceptor and subtypes of adrenoceptor and angiotensin II receptor, and these interactions may play a protective role in pancreas and improve glucose metabolism disorders.

Ang(1-7) treatment attenuates β-cell dysfunction by improving pancreatic microcirculation in a rat model of Type 2 diabetes

AIMS

Pancreatic microcirculation plays a pivotal role in the physiological function and survival of β-cells. Ang(1- 7) is a novel component of the renin angiotensin system (RAS) that has beneficial effects on microcirculation. In the present study, we investigated the effects of systemic Ang(1-7) administration (with or without its receptor Mas antagonist A- 779) on pancreatic microcirculation and β-cell function.

METHODS

These effects were studied in vivo using a rat model of Type 2 diabetes (T2DM). Pancreatic microcirculation and islet microvessel density were measured; and β-cell function, insulin content, and the apoptosis of islet cells were assessed, respectively. Additionally, we evaluated endothelial nitric oxide synthase (eNOS) expression and nitric oxide (NO) concentration in islets.

RESULTS

After Ang(1-7) intervention, pancreatic microcirculation and intra-islet microvessel density were significantly improved (p<0.05), and more importantly, first-phase insulin secretion of β-cells as well as relative insulin content in islets were increased, and the amount of apoptotic islet cells was decreased (p<0.05). And eNOS expression and NO release were up-regulated in pancreatic islets by Ang(1-7) administration (p<0.05). These positive effects of Ang(1-7) were prevented by the addition of A-779 (p<0.05).

CONCLUSIONS

Our findings suggest that systemic Ang(1-7) treatment could attenuate β-cell dysfunction and ameliorate islet cell apoptosis in T2DM rats by improving pancreatic microcirculation, perhaps through the mechanism of endothelial vasodilation.

Effects of combination therapy with vildagliptin and valsartan in a mouse model of type 2 diabetes

Background

Dipeptidyl peptidase-4 (DPP-4) inhibitors modulate incretin hormones and exert anti-diabetic effects in type 2 diabetes mellitus. Treatment with angiotensin II type 1 receptor blockers (ARB) is a proven successful intervention for hypertension with type 2 diabetes. The present study investigated the combined effects of the DPP-4 inhibitor vildagliptin and the ARB valsartan in a mouse model of type 2 diabetes.

Methods

C57BL/6 J mice fed with high-fat diet (HFD) or db/db mice were treated with placebo, phloridzin (PHZ), vildagliptin alone (ViL), valsartan alone (VaL) or ViL with VaL (ViLVaL) for 8 weeks.

Results

Glucose metabolism was improved in response to PHZ, ViL and ViLVaL in both HFD and db/db mice. Upon glucose challenge, ViLVaL showed the greatest suppression of blood glucose excursions, with increased insulin secretion, in db/db mice. ViLVaL treatment also showed an improvement of insulin sensitivity in db/db mice. Serum inflammatory cytokines were significantly decreased, and adiponectin was highest, in the ViLVaL group. ViLVaL improved insulin signaling and attenuated stress signaling in liver with amelioration of hepatic steatosis due to activated fatty acid oxidation in db/db mice. Furthermore, immunohistochemical analysis of the pancreas revealed that the combination treatment resulted in an increased expression of insulin and PDX-1, and increased insulin content.

Conclusions

The combination therapy of ViL and VaL improves both pancreatic beta-cell function and insulin sensitivity, with a reduction of the inflammatory and cell stress milieu in mouse models of T2DM. Our results suggest that this combination therapy exerts additive or even synergistic benefits to treat T2DM.

The renin angiotensin aldosterone system and insulin resistance in humans

Alterations in the renin angiotensin aldosterone system (RAAS) contribute to the underlying pathophysiology of insulin resistance in humans; however, individual differences in the treatment response of insulin resistance to RAAS blockade persist. Thus, understanding inter-individual differences in the relationship between the RAAS and insulin resistance may provide insights into improved personalized treatments and improved outcomes. The effects of the systemic RAAS on blood pressure regulation and glucose metabolism have been studied extensively; however, recent discoveries on the influence of local tissue RAAS in the skeletal muscle, heart, vasculature, adipocytes, and pancreas have led to an improved understanding of how activated tissue RAAS influences the development of insulin resistance and diabetes in humans. Angiotensin II (ANGII) is the predominant RAAS component contributing to insulin resistance; however, other players such as aldosterone, renin, and ACE2 are also involved. This review examines the role of local ANGII activity on insulin resistance development in skeletal muscle, adipocytes, and pancreas, followed by a discussion of the other RAAS components implicated in insulin resistance, including ACE2, Ang1-7, renin, and aldosterone.

Angiotensin-Converting Enzyme 2 Deficiency Aggravates Glucose Intolerance via Impairment of Islet Microvascular Density in Mice with High-Fat Diet

The aim of this study was to evaluate the effects of angiotensin-converting enzyme 2 (ACE2) on glucose homeostasis and islet function in mice. Male wildtype (WT) and ACE2 knockout (ACE2 KO) mice were divided into chow diet group and long-term high-fat diet (HFD) group. After 16 weeks of feeding, the islet function of the animals was evaluated by intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin releasing test (IPIRT). The pancreas was immunohistochemically stained to analyze the relative content of insulin (IRC), vascular endothelial growth factor (VEGF), and microvessel density (MVD) in islets. There was no difference of body weight, area under curve of glucose (AUCG), area under curve of insulin from 0 to 5 min (AUGI0-5), MVD, and RVC (relative content of VEGF) between WT and ACE2 KO mice with regular chow diet. Under the condition of long-term HFD, the AUCG of ACE2 KO mice was increased obviously in comparison with the WT mice, with decreased IRC, MVD, AUGI0-5, AUCI0-30, and RVC (all P < 0.05). In conclusion, these results show that ACE2 deficiency deteriorates islet function of mice with long-term HFD via impairment of islet microvasculature.

Valsartan improves adipose tissue function in humans with impaired glucose metabolism: a randomized placebo-controlled double-blind trial

BACKGROUND

Blockade of the renin-angiotensin system (RAS) reduces the incidence of type 2 diabetes mellitus. In rodents, it has been demonstrated that RAS blockade improved adipose tissue (AT) function and glucose homeostasis. However, the effects of long-term RAS blockade on AT function have not been investigated in humans. Therefore, we examined whether 26-wks treatment with the angiotensin II type 1 receptor blocker valsartan affects AT function in humans with impaired glucose metabolism (IGM).

METHODOLOGY/PRINCIPAL FINDINGS

We performed a randomized, double-blind, placebo-controlled parallel-group study, in which 38 subjects with IGM were treated with valsartan (VAL, 320 mg/d) or placebo (PLB) for 26 weeks. Before and after treatment, an abdominal subcutaneous AT biopsy was collected for measurement of adipocyte size and AT gene/protein expression of angiogenesis/capillarization, adipogenesis, lipolytic and inflammatory cell markers. Furthermore, we evaluated fasting and postprandial AT blood flow (ATBF) ((133)Xe wash-out), systemic inflammation and insulin sensitivity (hyperinsulinemic-euglycemic clamp). VAL treatment markedly reduced adipocyte size (P<0.001), with a shift toward a higher proportion of small adipocytes. In addition, fasting (P = 0.043) and postprandial ATBF (P = 0.049) were increased, whereas gene expression of angiogenesis/capillarization, adipogenesis and macrophage infiltration markers in AT was significantly decreased after VAL compared with PLB treatment. Interestingly, the change in adipocyte size was associated with alterations in insulin sensitivity and reduced AT gene expression of macrophage infiltration markers. VAL did not alter plasma monocyte-chemoattractant protein (MCP)-1, TNF-α, adiponectin and leptin concentrations.

CONCLUSIONS/SIGNIFICANCE

26-wks VAL treatment markedly reduced abdominal subcutaneous adipocyte size and AT macrophage infiltration markers, and increased ATBF in IGM subjects. The VAL-induced decrease in adipocyte size was associated with reduced expression of macrophage infiltration markers in AT. Our findings suggest that interventions targeting the RAS may improve AT function, thereby contributing to a reduced risk of developing cardiovascular disease and type 2 diabetes.

TRIAL REGISTRATION

Trialregister.nl NTR721 (ISRCTN Registry: ISRCTN42786336).

Angiotensin II type 2 receptor is critical for the development of human fetal pancreatic progenitor cells into islet-like cell clusters and their potential for transplantation

Local renin-angiotensin systems (RASs) regulate the differentiation of tissue progenitors. However, it is not known whether such systems can regulate the development of pancreatic progenitor cells (PPCs). To address this issue, we characterized the expression profile of major RAS components in human fetal PPC preparations and examined their effects on the differentiation of PPCs into functional islet-like cell clusters (ICCs). We found that expression of RAS components was highly regulated throughout PPC differentiation and that locally generated angiotensin II (Ang II) maintained PPC growth and differentiation via Ang II type 1 and type 2 (AT(1) and AT(2)) receptors. In addition, we observed colocalization of AT(2) receptors with critical β-cell phenotype markers in PPCs/ICCs, as well as AT(2) receptor upregulation during differentiation, suggesting that these receptors may regulate β-cell development. In fact, we found that AT(2) , but not AT(1) , receptor was a key mediator of Ang II-induced upregulation of transcription factors important in β-cell development. Furthermore, lentivirus-mediated knockdown of AT(2) receptor suppressed the expression of these transcription factors in ICCs. Transplantation of AT(2) receptor-depleted ICCs into immune-privileged diabetic mice failed to ameliorate hyperglycemia, implying that AT(2) receptors are indispensable during ICC maturation in vivo. These data strongly indicate that a local RAS is involved in governing the functional maturation of pancreatic progenitors toward the endocrine lineage.

The renin-angiotensin system in the pathophysiology of type 2 diabetes

Increased activation of the renin-angiotensin system (RAS) has been related to cardiovascular disease and type 2 diabetes mellitus. Most randomized clinical trials have demonstrated that RAS blockade reduces the incidence of type 2 diabetes, which has been explained by improved insulin secretion and insulin sensitivity. In this review, an overview of the mechanisms that may underlie the association between the RAS and type 2 diabetes will be provided, with focus on skeletal muscle and adipose tissue function. This will include discussion of several human studies performed in our laboratory to investigate the metabolic and hemodynamic effects of the RAS, combining in vivo measurements of whole-body and tissue metabolism with molecular and immunohistochemical approaches. Available data suggest that the detrimental effects of the RAS on insulin secretion are mediated by a reduction in pancreatic blood flow and induction of islet fibrosis, oxidative stress as well as inflammation, whereas both impaired skeletal muscle function and adipose tissue dysfunction may underlie RAS-induced insulin resistance. Thus, although future studies in humans are warranted, current evidence supports that targeting the RAS in intervention studies may improve metabolic and cardiovascular function in conditions of insulin resistance like obesity and type 2 diabetes.

Effects of whey protein supplements on metabolism: evidence from human intervention studies

PURPOSE OF REVIEW

Epidemiological studies indicate that the consumption of milk and dairy products is inversely associated with a lower risk of metabolic disorders and cardiovascular diseases. In particular, whey protein seems to induce these effects because of bioactive compounds such as lactoferrin, immunoglobulins, glutamine and lactalbumin. In addition, it is an excellent source of branch chained amino acids. This review summarizes recent findings on the effects of whey protein on metabolic disorders and the musculoskeletal system.

RECENT FINDINGS

We identified 25 recently published intervention trials examining chronic and/or acute effects of whey protein supplementation on lipid and glucose metabolism, blood pressure, vascular function and on the musculoskeletal system. Whey protein appears to have a blood glucose and/or insulin lowering effect partly mediated by incretins. In addition, whey protein may increase muscle protein synthesis. In contrast there are no clear-cut effects shown on blood lipids and lipoproteins, blood pressure and vascular function. For bone metabolism the data are scarce.

SUMMARY

In summary, whey protein may affect glucose metabolism and muscle protein synthesis. However, the evidence for a clinical efficacy is not strong enough to make final recommendations with respect to a specific dose and the duration of supplementation.

Evidence of an intracellular angiotensin-generating system and non-AT1, non-AT2 binding site in a human pancreatic cell line

OBJECTIVES

To assess the presence of a local angiotensin-generating systems (LAGS) and its participation in tumor growth in the human pancreatic cancer derived cell line Capan-1.

METHODS

Capan-1 cells were cultured in Dulbecco modified Eagle medium, and angiotensin I was assayed by radioimmunoassay and angiotensin II and vascular endothelial growth factor were assayed by enzyme-linked immunosorbent assay in the supernatant. Immunohistochemistry and reverse transcription-polymerase chain reaction were performed for the expression of AT1 and AT2 receptors. Angiotensin II binding assays and blockade were studied.

RESULTS

High levels of both angiotensins I and II were found in Capan-1 cells, although neither angiotensin I nor angiotensin II was detected in the cell culture supernatant. Reverse transcription-polymerase chain reaction and immunocytochemistry revealed that Capan-1 cells do not express AT1 and AT2 receptors; however, specific binding to the cell membrane was identified for angiotensin II. Neither exogenous angiotensin II nor Dup753 (specific AT1 receptor blocker) affected Capan-1 cells' proliferation or vascular endothelial growth factor secretion.

CONCLUSIONS

Detection of both angiotensin I and angiotensin II along with specific binding of angiotensin II in Capan-1 cells provides evidence of the existence of a LAGS that operates in an intracrine manner. Intracellular angiotensin II may play a role in the aggressiveness of pancreatic cancer and is a possible target for therapeutic agents.

Functional expression of angiotensinogen depends on splicing enhancers in exon 2

Angiotensinogen belongs to the family of serpins and is the only precursor of the potent cardiovascular peptide, angiotensin II, the main effector of the renin-angiotensin system. The gene coding for this protein carries an internal exon (exon 2), the length of which (859 bp) by far exceeds the mean length of internal exons in vertebrates (<300 bp). Here, we show that this essential exon is skipped in about 20% of all transcripts in liver, brain, and kidney of rats and mice. Deletion mutants of exon 2 revealed a 62 bp region located at its 5'-end which is important for its inclusion in the mature angiotensinogen mRNA in transfected COS7 cells. Using an artificial minigene, we defined sequences inside this region as exonic splicing enhancers. These data reveal a novel molecular mechanism important for the renin-angiotensin system with implications in the basic understanding and the therapeutical assessment of cardiovascular diseases.

Association of hematological parameters with insulin resistance and beta-cell dysfunction in nondiabetic subjects

OBJECTIVE

Previous studies reported independent associations of hematological parameters with risk of incident type 2 diabetes, although limited data are available on associations of these parameters with insulin resistance (IR) and (especially) pancreatic beta-cell dysfunction in large epidemiological studies. Our objective was to evaluate the associations of hematological parameters, including hematocrit (HCT), hemoglobin (Hgb), red blood cell count (RBC), and white blood cell count with IR and beta-cell dysfunction in a cohort of nondiabetic subjects at high metabolic risk.

METHODS

Nondiabetic subjects (n = 712) were recruited in Toronto and London, Ontario, Canada, between 2004 and 2006, based on the presence of one or more risk factors for type 2 diabetes mellitus including obesity, hypertension, a family history of diabetes, and/or a history of gestational diabetes. Fasting blood samples were collected and oral glucose tolerance tests administered, with additional samples for glucose and insulin drawn at 30 and 120 min. Measures of IR included the homeostasis model assessment (HOMA-IR) and Matsuda's insulin sensitivity index, whereas measures of beta-cell dysfunction included the insulinogenic index divided by HOMA-IR as well as the insulin secretion-sensitivity index-2. Associations of hematological parameters with IR and beta-cell dysfunction were assessed using multiple linear regression and analysis of covariance with adjustments for age, gender, ethnicity, smoking, cardiovascular disease, systolic and diastolic blood pressure, and waist circumference.

RESULTS

HOMA-IR increased across quartiles of HCT, Hgb, RBC, and white blood cell count after adjustment for age, gender, ethnicity, and smoking (all P (trend) <0.0001). Similarly, there was a strong stepwise decrease in the Matsuda's insulin sensitivity index across increasing quartiles of these hematological measures (all P (trend) <0.0001). The associations remained significant after further adjustment for previous cardiovascular disease, blood pressure, and waist circumference (all P (trend) <0.0001). Similarly, there was a strong pattern of decreasing beta-cell function across increasing quartiles of all hematological patterns (all P (trend) <0.0001). The findings for HCT, Hgb, and RBC were attenuated slightly after full multivariate adjustment, although the trend across quartiles remained highly significant.

CONCLUSION

These findings suggest that standard, clinically relevant hematological variables may be related to the underlying pathophysiological changes associated with type 2 diabetes mellitus.

Combination of the dipeptidyl peptidase IV inhibitor LAF237 [(S)-1-[(3-hydroxy-1-adamantyl)ammo]acetyl-2-cyanopyrrolidine] with the angiotensin II type 1 receptor antagonist valsartan [N-(1-oxopentyl)-N-[[2'-(1H-tetrazol-5-yl)-[1,1'-biphenyl]-4-yl]methyl]-L-valine] enhances pancreatic islet morphology and function in a mouse model of type 2 diabetes

LAF237 [(S)-1-[(3-hydroxy-1-adamantyl)ammo]acetyl-2-cyanopyrrolidine] is an inhibitor of dipeptidyl peptidase IV that delays the degradation of glucagon-like peptide-1 (GLP-1). Valsartan [N-(1-oxopentyl)-N-[[2'-(1H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl]-l-valine] is an antagonist of the angiotensin II type 1 receptor (AT1R) that reduces the incidence of type 2 diabetes mellitus. LAF237 and valsartan act on a common target through separate pathways to improve pancreatic islet cell function. We hypothesize that the combination of these two drugs acts in a synergistic or additive manner on islet function and structure. To test this hypothesis, we performed in vitro and in vivo studies. To measure the acute effect of the treatment, pancreatic islets of db/db mice were isolated and stimulated in vitro with glucose in the presence of valsartan (1 microM) and exendin-4 (100 nM), a GLP-1 receptor agonist. Combination treatment with valsartan and exendin-4 significantly enhanced glucose-stimulated insulin secretion from isolated islets. For studies of chronic effect, db/db mice received LAF237 (1 mg/kg/day) and/or valsartan (10 mg/kg/day). Islet cell reactive oxygen species (ROS), proliferation, apoptosis, fibrosis, beta-cell area, and glucose homeostasis were evaluated after 8 weeks of treatment, which showed that combination treatment resulted in a significant increase in pancreatic islet beta-cell area compared with monotherapy. This beneficial effect correlated with an increase in beta-cell proliferation and a decrease in ROS-induced islet apoptosis and fibrosis. These in vitro and in vivo data indicate that combination treatment with LAF237 and valsartan has significant beneficial additive effects on pancreatic beta-cell structure and function compared with their respective monotherapeutic effects.

The renin-angiotensin-aldosterone system: a pivotal role in insulin sensitivity and glycemic control

PURPOSE OF REVIEW

Diabetes mellitus is an exploding epidemic costing billions of dollars yearly. Type 2 diabetes mellitus is characterized by insulin resistance and is closely associated with arterial hypertension. Emerging literature has demonstrated that modulation of the renin-angiotensin-aldosterone system by use of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers leads to improved insulin sensitivity, glycemic control and possibly prevention of type 2 diabetes mellitus.

RECENT FINDINGS

Several major studies investigating angiotensin II receptor blocker or angiotensin-converting enzyme inhibitor use in either hypertensive or heart failure patients have found lower incidence of type 2 diabetes mellitus when compared with placebo, beta-blocker, calcium-channel blocker or diuretic. None of these trials, however, studied prevention of diabetes as a primary endpoint. The Dream Trial and upcoming NAVIGATOR, ONTARGET/TRANSCEND trials specifically look at the prevention of diabetes as a primary endpoint. Several studies have evaluated possible mechanisms of how the renin-angiotensin-aldosterone system can alter insulin sensitivity and glycemic control.

SUMMARY

This review will focus on the recent literature that demonstrates renin-angiotensin-aldosterone system modulation and its effects on diabetes prevention, glycemic control and insulin sensitivity, as well as possible mechanisms for achieving this goal.

Preserving insulin secretion in Type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a complex disease characterized by insulin resistance and a progressive decline in β-cell function and mass. Current evidence suggests that β-cell dysfunction is present early in the course of the disease and that this dysfunction, rather than insulin resistance, is primarily responsible for the progression of T2DM. β-cell dysfunction can be accelerated by glucose toxicity, lipotoxicity, oxidative stress, chronic increases in inflammatory mediators and, potentially, the use of sulfonylureas. This review suggests that future efforts to limit the impact of T2DM must focus on strategies to preserve β-cell function. Several interventions have shown promise in this regard, including lifestyle modifications, thiazolidinediones, potassium channel openers, incretin mimetics, cytokine antagonists, bariatric surgery and dipeptidyl peptidase IV inhibitors, although therapeutic insulin remains the most robust and physiological approach.

Enalapril treatment corrects the reduced response to bradykinin in diabetes increasing the B2 protein expression

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the effect of enalapril on the reduced response of bradykinin and on the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems, in an insulin-resistance model of diabetes. For the above purpose, the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. In n-STZ diabetic rats, enalapril treatment restored the reduced response to BK but not the potentiation of BK by Ang-(1-7) present in non-diabetic rats. The restorative effect of enalapril was observed at a dose that did not correct the altered parameters induced by diabetes such as hyperglycemia, glicosuria, insulin resistance but did reduce the high blood pressure levels of n-SZT diabetic rats. There was no difference in mRNA and protein expressions of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Enalapril treatment increased the B2 kinin receptor expression. From our data, we conclude that in diabetes enalapril corrects the impaired BK response probably by increasing the expression of B2 receptors. The lack of potentiation of BK by Ang-(1-7) is not corrected by this agent.

An update on non-peptide angiotensin receptor antagonists and related RAAS modulators

The renin-angiotensin-aldosterone-system (RAAS) is an important regulator of blood pressure and fluid-electrolyte homeostasis. RAAS has been implicated in pathogenesis of hypertension, congestive heart failure, and chronic renal failure. Aliskiren is the first non-peptide orally active renin inhibitor approved by FDA. Angiotensin Converting Enzyme (ACE) Inhibitors are associated with frequent side effects such as cough and angio-oedema. Recently, the role of ACE2 and neutral endopeptidase (NEP) in the formation of an important active metabolite/mediator of RAAS, ang 1-7, has initiated attempts towards development of ACE2 inhibitors and combined ACE/NEP inhibitors. Furukawa and colleagues developed a series of low molecular weight nonpeptide imidazole analogues that possess weak but selective, competitive AT1 receptor blocking property. Till date, many compounds have exhibited promising AT1 blocking activity which cause a more complete RAAS blockade than ACE inhibitors. Many have reached the market for alternative treatment of hypertension, heart failure and diabetic nephropathy in ACE inhibitor intolerant patients and still more are waiting in the queue. But, the hallmark of this area of drug research is marked by a progress in understanding molecular interaction of these blockers at the AT1 receptor and unraveling the enigmatic influence of AT2 receptors on growth/anti-growth, differentiation and the regeneration of neuronal tissue. Different modeling strategies are underway to develop tailor made molecules with the best of properties like Dual Action (Angiotensin And Endothelin) Receptor Antagonists (DARA), ACE/NEP inhibitors, triple inhibitors, AT2 agonists, AT1/TxA2 antagonists, balanced AT1/AT2 antagonists, and nonpeptide renin inhibitors. This abstract gives an overview of these various angiotensin receptor antagonists.

Lack of potentiation of bradykinin by angiotensin-(1-7) in a type 2 diabetes model: role of insulin

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems in an insulin resistance model of diabetes, and the effect of insulin on it. For this the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in n-STZ rats. Chronic but not acute insulin treatment restored the potentiation. This restorative effect of insulin was abolished by a K+ channel blocker (tetraethylammonium), by nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester) and by a cyclooxygenase inhibitor (indomethacin). On the other hand, Na(+)-,K(+)-ATPase inhibition (by ouabain) did not abolish the effect of insulin. There was no difference in mRNA and protein expression of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Insulin treatment did not alter the kinin receptor expression. Our data allow us to conclude that diabetes impaired the interaction between BK and Ang-(1-7) and that insulin restores it. The restoring effect of insulin depends on membrane hyperpolarization, nitric oxide release and cyclooxygenease metabolites but not Na+K+-ATPase. Alteration of kinin receptor expression might not be involved in the restoring effect of insulin on the potentiation of BK by Ang-(1-7).