An update on the islet renin-angiotensin system

Gluco-regulation & type 2 diabetes: entrenched misconceptions updated to new governing principles for gold standard management

Our understanding of type 2 diabetes (T2D) has evolved dramatically. Advances have upended entrenched dogmas pertaining to the onset and progression of T2D, beliefs that have prevailed from the early era of diabetes research-and continue to populate our medical textbooks and continuing medical education materials. This review article highlights key insights that lend new governing principles for gold standard management of T2D. From the historical context upon which old beliefs arose to new findings, this article outlines evidence and perspectives on beta cell function, the underlying defects in glucoregulation, the remediable nature of T2D, and, the rationale supporting the shift to complication-centric prescribing. Practical approaches translate this rectified understanding of T2D into strategies that fill gaps in current management practices of prediabetes through late type 2 diabetes.

Preliminary investigation of the effect of non-cardiac surgery on intraoperative islet and renal function: a single-center prospective cohort study

Background

The effect of different non-cardiac surgical methods on islet and renal function remains unclear. We conducted a preliminary investigation to determine whether different surgical methods affect islet function or cause further damage to renal function.

Methods

In this prospective cohort study, the clinical data of 63 adult patients who underwent non-cardiac surgery under general anesthesia were evaluated from February 2019 to January 2020. Patients were divided into the abdominal surgery group, the laparoscopic surgery group, and the breast cancer surgery group. The primary outcome was the difference between the effects of different surgical methods on renal function.

Results

Islet and renal function were not significantly different between the groups. The correlation analysis showed that hematocrit (HCT) and hemoglobin (HB) were negatively correlated with fasting plasma glucose (FPG) (p < 0.05), MAP was positively correlated with C-peptide (p < 0.05), and HCT and Hb were positively correlated with serum creatinine (SCr) (p < 0.05). Fasting insulin (FINS) and C-peptide were negatively correlated with SCr (p < 0.05), and the homeostatic model assessment of insulin resistance (HOMA-IR) was positively correlated with SCr (p < 0.05). FINS, C-peptide, HOMA-IR, and the homeostatic model assessment of β-cell function (HOMA-β) were positively correlated with cystatin C (Cys C) (p < 0.05).

Conclusion

FINS, C-peptide, and HOMA-IR had positive effects on beta-2-microglobulin (β2-MG). FINS, C-peptide, and HOMA-IR were positively correlated with Cys C and β2-Mg. While FINS and C-peptide were negatively correlated with SCr, HOMA-IR was positively correlated with SCr.

The Counteracting Effects of Ang II and Ang-(1-7) on the Function andGrowth of Insulin-secreting NIT-1 Cells

INTRODUCTION

China now has the highest number of diabetes in the world. Angiotensin II (Ang II) causes insulin resistance by acting on the insulin signaling pathway of peripheral target tissues. However, its effect on islet β-cells remains unclear. The possible role of Angiotensin-( 1-7) [Ang-(1-7)] as an antagonist to the effects of Ang II and in treating diabetes needs to be elucidated.

OBJECTIVES

To assess the effects of Ang II and Ang-(1-7) on the function and growth of islet β cell line NIT-1, which is derived from the islets of non-obese diabetic/large T-antigen (NOD/LT) mice with insulinoma.

METHODS

NIT-1 cells were treated with Ang II, Ang-(1-7) and their respective receptor antagonists. The impact on cell function and growth was then evaluated.

RESULTS

Ang II significantly reduced insulin-stimulated IR-β-Tyr and Akt-Ser; while Ang-(1-7), saralasin (an Ang II receptor antagonist), and diphenyleneiodonium [DPI, a nicotinamide adenine dinucleotide phosphate oxidase (NOX) antagonist] reversed the inhibiting effect. Conversely, Ang II significantly increased insulin-stimulated intracellular H2O2 and P47 phox, while saralasin and DPI reverted the effect. Furthermore, Ang-(1-7) reduced the elevated concentrations of ROS and MDA while increasing the proliferation rate that was reduced by high glucose, all of which were reversed by A-779, an antagonist of the Mas receptor (MasR).

CONCLUSION

Angiotensin II poses a negative regulatory effect on insulin signal transduction, increases oxidative stress, and may inhibit the transcription of insulin genes stimulated by insulin in NIT-1 cells. Meanwhile, angiotensin-(1-7) blocked these effects via MasR. These results corroborate the rising potential of the renin-angiotensin system (RAS) in treating diabetes.

Metabolic and Genetic Association of Vitamin D with Calcium Signaling and Insulin Resistance

Various evidences have unveiled the significance of Vitamin D in diverse processes which include its action in prevention of immune dysfunction, cancer and cardiometabolic disorders. Studies have confirmed the function of VD in controlling the expression of approximately nine hundred genes including gene expression of insulin. VD insufficiency may be linked with the pathogenesis of diseases that are associated with insulin resistance (IR) including diabetes as well as obesity. Thus, VD lowers IR-related disorders such as inflammation and oxidative stress. This review provides an insight regarding the molecular mechanism manifesting, how insufficiency of VD may be connected with the IR and diabetes. It also discusses the effect of VD in maintaining the Ca2+ levels in beta cells of the pancreas and in the tissues that are responsive to insulin.

Vitamin D improves hepatic alterations in ACE1 and ACE2 expression in experimentally induced metabolic syndrome

Metabolic Syndrome (MetS) is a term used to describe a cluster of pathophysiological, biochemical, and metabolic criteria; including high Blood Pressure (BP), high cholesterol, dyslipidaemia, central obesity and Insulin Resistance (IR). The Renin Angiotensin System (RAS) has a regulatory function in BP, hydroelectrolyte balance, and cardiovascular function. RAS is composed of angiotensinogen (AGT), (Ang I), (Ang II), (ACE1), (ACE2), (AT1R), (AT2R), and (Ang 1-7). Vitamin D had been proved to act as a protective factor against MetS. Therefore, the study is pursued to explore vitamin D supplementation roles on hepatic RAS in MetS experimental model. At first, 36 males Albino rats were separated into 4 groups and induced to MetS under controlled circumstances for 3 months. Then, data were collected from blood samples, whereas RNA extracted from liver were analyzed using biochemical and statistical analysis tests. As a result, the major finding was proving that vitamin D can balance the expression of ACE1 and ACE2. Also, confirming that it can improve MetS components by elevating HDL and insulin levels while reducing the levels of BP, cholesterol, LDL, TG, GLU, ALT, AST, and IR. These outcomes may give a new insight into the RAS pathways associated with MetS.

Ang II Controls the Expression of Mapkap1 by miR-375 and Affects the Function of Islet β Cells

BACKGROUND

The RAS system is involved in the regulation of islet function, but its regulation remains unclear.

OBJECTIVE

This study investigates the role of an islet-specific miR-375 in the effect of RAS system on islet β-cells.

METHODS

miR-375 mimics and inhibitors were transfected into insulin-secreting MIN6 cells in the presence or absence of RAS component.

RESULTS

Compared to control, in Ang II-treated MIN6 cells, miR-375 mimic transfection results in a decrement in cell viability and Akt-Ser levels (0.739±0.05 vs. 0.883±0.06 and 0.40±0.04 vs. 0.79±0.04, respectively), while the opposite occurred in miR-375 inhibitor-transfected cells (1.032±0.11 vs. 0.883±0.06 and 0.98±0.05 vs. 0.79±0.04, respectively, P<0.05). Mechanistically, transfection of miR- 375 mimics into Ang II-treated MIN6 cells significantly reduced the expression of Mapkap1 protein (0.97±0.15 vs. 0.63±0.06, P<0.05); while miR-375 inhibitor-transfected cells elevated Mapkap1 expression level (0.35±0.11 vs. 0.90±0.05, P<0.05), without changes in mRNA expression. Transfection of miR-375 specific inhibitors TSB-Mapkap1 could elevate Mapkap1 (1.62±0.02 vs. 0.68±0.01, P<0.05), while inhibition of Mapkap1 could significantly reduce the level of Akt-Ser473 phosphorylation (0.60±0.14 vs. 1.80±0.27, P<0.05).

CONCLUSION

The effects of Ang II on mouse islet β cells were mediated by miR-375 through miR- 375/Mapkap 1 axis. This targeted regulation may occur by affecting Akt phosphorylation of β cells. These results may provide new ideas and a scientific basis for further development of miRNA-targeted islet protection measures.

The Surging Mechanistic Role of Angiotensin Converting Enzyme 2 in Human Pathologies: A Potential Approach for Herbal Therapeutics

Advancements in biological sciences revealed the significant role of angiotensin-converting enzyme 2 (ACE2), a key cell surface receptor in various human pathologies. ACE2 is a metalloproteinase that not only functions in the regulation of Angiotensin II but also possesses some non-catalytic roles in the human body. There is considerable uncertainty regarding its protein expression, despite its presence in virtually all organs. The level of ACE2 expression and its subcellular localisation in humans may be a key determinant of susceptibility to various infections, symptoms, and outcomes of numerous diseases. Therefore, we summarize the distribution and expression pattern of ACE2 in different cell types related to all major human tissues and organs. Moreover, this review constitutes accumulated evidences of the important resources for further studies on ACE2 Inhibitory capacity via different natural compounds in order to understand its mechanism as the potential drug target in disease pathophysiology and to aid in the development of an effective therapeutic approach towards the various diseases.

Prenatal dexamethasone exposure induced pancreatic β-cell dysfunction and glucose intolerance of male offspring rats: Role of the epigenetic repression of ACE2

The prevalence of diabetes in children and adolescents has been rising gradually, which is relevant to adverse environment during development, especially prepartum. We aimed to explore the effects of prenatal dexamethasone exposure (PDE) on β-cell function and glucose homeostasis in juvenile offspring rats. Pregnant Wistar rats were subcutaneously administered with dexamethasone [0.1, 0.2, 0.4mg/(kg.d)] from gestational day 9 to 20. PDE impaired glucose tolerance in the male offspring rather than the females. In male offspring, PDE impaired the development and function of β-cells, accompanied with lower H3K9ac, H3K14ac and H3K27ac levels in the promoter region of angiotensin-converting enzyme 2 (ACE2) as well as suppressed ACE2 expression. Meanwhile, PDE increased expression of glucocorticoid receptor (GR) and histone deacetylase 3 (HDAC3) in fetal pancreas. Dexamethasone also inhibited ACE2 expression and insulin production in vitro. Recombinant expression of ACE2 restored insulin production inhibited by dexamethasone. In addition, dexamethasone activated GR and HDAC3, increased protein interaction of GR with HDAC3, and promoted the binding of GR-HDAC3 complex to ACE2 promoter region. Both RU486 and TSA abolished dexamethasone-induced decline of histone acetylation and ACE2 expression. In summary, suppression of ACE2 is involved in PDE induced β-cell dysfunction and glucose intolerance in juvenile male offspring rats.

Novel severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) infection: Microbiologic perspectives and anatomic considerations for sanctuary sites

Introduction

A significant chunk of global life – the economy, sports, aviation, academic, and entertainment activities – has significantly been affected by the ravaging outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) with devastating consequences on morbidity and mortality in many countries of the world.

Methods

This review utilized search engines such as google scholar, PubMed, ResearchGate, and web of science to retrieve articles and information using keywords like “Coronavirus”, “SARS-CoV-2”, “COVID-19”, “Origin of coronavirus and SARS-CoV-2”, “microbiology of coronavirus”, “microbiology of SARS-CoV-2”, COVID-19”, “Coronavirus reservoir sites”, “Anatomic sanctuary sites and SARS-CoV-2”, biological barriers and coronavirus”, biological barrier and SARS-CoV-2”.

Results

While this pandemic has caught the global scientific community at its lowest level of preparedness, it has inadvertently created a unified and wholesome approach towards developing potential vaccine (s) candidates by escalating clinical trial protocols in many countries of Europe, China and the United States. Interestingly, viral pathobiology continues to be an evolving aspect that potentially shows that the management of the current outbreak may largely depend on the discovery of a vaccine as the administration of known antiviral drugs are proving to offer some respite. Unfortunately, discontinuation and longtime administration of these drugs have been implicated in endocrine, reproductive and neurological disorders owing to the development of pathological lesions at anatomical sanctuary sites such as the brain and testis, as well as the presence of complex biological barriers that permit the entry of viruses but selective to the entrance of chemical substances and drugs.

Conclusion

This review focuses on the microbiologic perspectives and importance of anatomical sanctuary sites in the possible viral rebound or reinfection into the system and their implications in viral re-entry and development of reproductive and neurological disorders in COVID-19 patients.

Angiotensin-(1-7) Improves Islet Function in a Rat Model of Streptozotocin- Induced Diabetes Mellitus by Up-Regulating the Expression of Pdx1/Glut2

OBJECTIVE

To observe the effects of angiotensin-(1-7) (Ang-(1-7)) on glucose metabolism, islet function and insulin resistance in a rat model of streptozotocin-induced diabetes mellitus (DM) and investigate its mechanism.

METHODS

Thirty-four male Wistar rats were randomly divided into 3 groups: control group, which was fed a standard diet, DM group, high-fat diet and injected with streptozotocin, and Ang-(1-7) group receiving an injection of streptozotocin followed by Ang-(1-7) treatment. Blood glucose level, fasting serum Ang II and insulin levels, and homeostasis model assessment of insulin resistance (HOMA-IR) were measured. The pancreases were collected for histological examination, protein and gene expression analysis.

RESULTS

Compared with the control group, fasting blood glucose, serum angiotensin II level, and HOMA-IR value increased, while serum insulin level decreased in the DM group. Moreover, islet structure was damaged, β cells were irregularly arranged, the cytoplasm was loose in the DM group. Expressions of Pancreatic duodenal homeobox-1 (Pdx1), glucose transporter-2 (Glut2) and glucokinase (Gk) were significantly decreased in the DM group compared with the control group. However, the DM-associated changes were dramatically reversed following Ang-(1-7) treatment.

CONCLUSION

Ang-(1-7) protects against streptozotocin-induced DM through the improvement of insulin secretion, insulin resistance and islet fibrosis, which is associated with the upregulation of Pdx1, Glut2 and Gk expressions.

Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans

The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.

Activation of ACE2/angiotensin (1-7) attenuates pancreatic β cell dedifferentiation in a high-fat-diet mouse model

OBJECTIVE

Angiotensin-converting enzyme 2 (ACE2) has been identified in pancreatic islets and can preserve β cells. In this study, we aimed to examine the possible role of ACE2 and its end product, angiotensin 1-7 (A1-7), in reducing β cell dedifferentiation during metabolic stress.

METHODS

First, a lineage-tracing experiment was performed to track β cells in mice fed a high-fat diet (HFD). Second, the ACE2/A1-7 axis was evaluated in the HFD mouse model. Intraperitoneal glucose tolerance tests (IPGTTs) and intraperitoneal insulin tolerance tests (IPITTs) were conducted. Phenotypic changes in β cells were detected by immunohistochemistry and quantitative real-time PCR. Pancreatic sections were immunostained for vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase (iNOS). Finally, the effects of the ACE2/A1-7 axis were explored in isolated mouse islets exposed to different concentrations of glucose. Glucose-stimulated insulin release and levels of insulin mRNA and OCT4 mRNA were measured.

RESULTS

Pancreatic β cell dedifferentiation occurred both in vitro and in vivo in response to metabolic stress and was accompanied by ACE2 reduction. HFD-induced insulin resistance and glucose intolerance were exacerbated in ACE2-knockout (ACE2KO) mice but were alleviated by exogenous A1-7 in C57BL/6J mice. Approximately 20% of β cells were dedifferentiated in ACE2KO mice fed a standard rodent chow diet (SD). A higher percentage of dedifferentiated β cells was detected in ACE2KO mice than in wild-type (WT) mice under HFD conditions. In contrast, the administration of A1-7 alleviated HFD-induced β cell dedifferentiation in C57BL/6J mice. Moreover, the exogenous injection of A1-7 improved microcirculation in islets and decreased the production of iNOS in islets of C57BL/6J mice fed an HFD. Additionally, ACE2 was found to be mainly expressed in α cells of mice, while Mas, the receptor of A1-7, was distributed in β cells.

CONCLUSIONS

Overall, this study is the first to demonstrate that the ACE2/A1-7/Mas axis may be one of the intra-islet paracrine mechanisms of communication between α and β cells. Enhancing the ACE2/A1-7 axis exerts a protective effect by ameliorating β cell dedifferentiation, and this effect might be partially mediated through improvements in islet microcirculation and suppression of islet iNOS.

The inositol-requiring enzyme 1 (IRE1α) RNAse inhibitor, 4µ8C, is also a potent cellular antioxidant

Inositol-requiring enzyme 1 alpha (IRE1α) is an endoplasmic reticulum (ER)-transmembrane endonuclease that is activated in response to ER stress as part of the unfolded protein response (UPR). Chronic activation of the UPR has been implicated in the pathogenesis of many common diseases including diabetes, cancer, and neurological pathologies such as Huntington's and Alzheimer's disease. 7-Hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde (4µ8C) is widely used as a specific inhibitor of IRE1α ribonuclease activity (IC50 of 6.89 µM in cultured cells). However, in this paper, we demonstrate that 4µ8C acts as a potent reactive oxygen species (ROS) scavenger, both in a cell-free assay and in cultured cells, at concentrations lower than that widely used to inhibit IRE1α activity. In vitro we show that, 4µ8C effectively decreases xanthine/xanthine oxidase catalysed superoxide production with an IC50 of 0.2 µM whereas in cultured endothelial and clonal pancreatic β-cells, 4µ8C inhibits angiotensin II-induced ROS production with IC50 values of 1.92 and 0.29 µM, respectively. In light of this discovery, conclusions reached using 4µ8C as an inhibitor of IRE1α should be carefully evaluated. However, this unexpected off-target effect of 4µ8C may prove therapeutically advantageous for the treatment of pathologies that are thought to be caused by, or exacerbated by, both oxidative and ER stress such as endothelial dysfunction and/or diabetes.

Pericardial Parietal Mesothelial Cells: Source of the Angiotensin-Converting-Enzyme of the Bovine Pericardial Fluid

Background

Angiotensin II (Ang II), the primary effector hormone of the renin-angiotensin system (RAS), acts systemically or locally, being produced by the action of angiotensin-converting-enzyme (ACE) on angiotensin I. Although several tissue RASs, such as cardiac RAS, have been described, little is known about the presence of an RAS in the pericardial fluid and its possible sources. Locally produced Ang II has paracrine and autocrine effects, inducing left ventricular hypertrophy, fibrosis, heart failure and cardiac dysfunction. Because of the difficulties inherent in human pericardial fluid collection, appropriate experimental models are useful to obtain data regarding the characteristics of the pericardial fluid and surrounding tissues.

Objectives

To evidence the presence of constituents of the Ang II production paths in bovine pericardial fluid and parietal pericardium.

Methods

Albumin-free crude extracts of bovine pericardial fluid, immunoprecipitated with anti-ACE antibody, were submitted to electrophoresis (SDS-PAGE) and gels stained with coomassie blue. Duplicates of gels were probed with anti-ACE antibody. In the pericardial membranes, ACE was detected by use of immunofluorescence.

Results

Immunodetection on nitrocellulose membranes showed a 146-KDa ACE isoform in the bovine pericardial fluid. On the pericardial membrane sections, ACE was immunolocalized in the mesothelial layer.

Conclusions

The ACE isoform in the bovine pericardial fluid and parietal pericardium should account at least partially for the production of Ang II in the pericardial space, and should be considered when assessing the cardiac RAS.

Functional status of microvascular vasomotion is impaired in spontaneously hypertensive rat

Accumulating evidence demonstrates that microcirculation plays a role in the pathogenesis of hypertension. In the current study, we demonstrated that pancreatic islet microvascular vasomotion of spontaneously hypertensive rats (SHRs) lost the ability to regulate blood flow perfusion and exhibited a lower microvascular blood perfusion pattern which was negative correlated with blood glucose level. SHRs administrated with insulin revealed an improvement of pancreatic islet microvascular vasomotion and blood perfusion pattern. In vitro, the expressions of endothelial nitric oxide synthase (eNOS) and phospho-eNOS^ser1177 (p-eNOS^ser1177) were significantly decreased in high glucose exposed islet endothelial cells (iECs), accompanied with a higher ratio of eNOS monomer to eNOS dimer and a significantly increased malondialdehyde and nitrite levels. Meanwhile, barrier function, tube formation and migration capacities of high glucose exposed iECs were significantly inhibited. In contrast, iECs dysfunction induced by glucose toxicity and oxidative stress was attenuated or improved by supplement with insulin, L-arginine and β-mercaptoethanol. In summary, our findings suggest that functional status of pancreatic islet microvascular vasomotion is impaired in SHRs and provide evidence that treatment with insulin, L-arginine and β-mercaptoethanol improves endothelium-dependent microvascular vasomotion and meliorates iECs function due to anti-hyperglycemic and anti-oxidative effects, partly through mechanism involving regulation of eNOS and p-eNOS^ser1177.

Characterization of ACE and ACE2 Expression within Different Organs of the NOD Mouse

Renin angiotensin system (RAS) is known to play a key role in several diseases such as diabetes, and renal and cardiovascular pathologies. Its blockade has been demonstrated to delay chronic kidney disease progression and cardiovascular damage in diabetic patients. In this sense, since local RAS has been described, the aim of this study is to characterize angiotensin converting enzyme (ACE) and ACE2 activities, as well as protein expression, in several tissues of the non-obese diabetic (NOD) mice model. After 21 or 40 days of diabetes onset, mouse serums and tissues were analyzed for ACE and ACE2 enzyme activities and protein expression. ACE and ACE2 enzyme activities were detected in different tissues. Their expressions vary depending on the studied tissue. Thus, whereas ACE activity was highly expressed in lungs, ACE2 activity was highly expressed in pancreas among the studied tissues. Interestingly, we also observed that diabetes up-regulates ACE mainly in serum, lung, heart, and liver, and ACE2 mainly in serum, liver, and pancreas. In conclusion, we found a marked serum and pulmonary alteration in ACE activity of diabetic mice, suggesting a common regulation. The increase of ACE2 activity within the circulation in diabetic mice may be ascribed to a compensatory mechanism of RAS.

The Potential Protective Action of Vitamin D in Hepatic Insulin Resistance and Pancreatic Islet Dysfunction in Type 2 Diabetes Mellitus

Vitamin D deficiency (i.e., hypovitaminosis D) is associated with increased insulin resistance, impaired insulin secretion, and poorly controlled glucose homeostasis, and thus is correlated with the risk of metabolic diseases, including type 2 diabetes mellitus (T2DM). The liver plays key roles in glucose and lipid metabolism, and its dysregulation leads to abnormalities in hepatic glucose output and triglyceride accumulation. Meanwhile, the pancreatic islets are constituted in large part by insulin-secreting β cells. Consequently, islet dysfunction, such as occurs in T2DM, produces hyperglycemia. In this review, we provide a critical appraisal of the modulatory actions of vitamin D in hepatic insulin sensitivity and islet insulin secretion, and we discuss the potential roles of a local vitamin D signaling in regulating hepatic and pancreatic islet functions. This information provides a scientific basis for establishing the benefits of the maintenance, or dietary manipulation, of adequate vitamin D status in the prevention and management of obesity-induced T2DM and non-alcoholic fatty liver disease.

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.

Mitochondrial uncoupling proteins regulate angiotensin-converting enzyme expression: crosstalk between cellular and endocrine metabolic regulators suggested by RNA interference and genetic studies

Uncoupling proteins (UCPs) regulate mitochondrial function, and thus cellular metabolism. Angiotensin‐converting enzyme (ACE) is the central component of endocrine and local tissue renin–angiotensin systems (RAS), which also regulate diverse aspects of whole‐body metabolism and mitochondrial function (partly through altering mitochondrial UCP expression). We show that ACE expression also appears to be regulated by mitochondrial UCPs. In genetic analysis of two unrelated populations (healthy young UK men and Scandinavian diabetic patients) serum ACE (sACE) activity was significantly higher amongst UCP3‐55C (rather than T) and UCP2 I (rather than D) allele carriers. RNA interference against UCP2 in human umbilical vein endothelial cells reduced UCP2 mRNA sixfold (P < 0·01) whilst increasing ACE expression within a physiological range (<1·8‐fold at 48 h; P < 0·01). Our findings suggest novel hypotheses. Firstly, cellular feedback regulation may occur between UCPs and ACE. Secondly, cellular UCP regulation of sACE suggests a novel means of crosstalk between (and mutual regulation of) cellular and endocrine metabolism. This might partly explain the reduced risk of developing diabetes and metabolic syndrome with RAS antagonists and offer insight into the origins of cardiovascular disease in which UCPs and ACE both play a role.

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.

The role of renin-angiotensin system in cellular differentiation: implications in pancreatic islet cell development and islet transplantation

In addition to the well-characterized circulating renin-angiotensin system (RAS), local RAS has been identified recently in diverse tissues and organs. The presence of key components of the RAS in local tissues is important for our understanding of the patho-physiological mechanism(s) of several metabolic diseases, and may serve as a major therapeutic target for cardiometabolic syndromes. Locally generated and physiologically active RAS components have functions that are distinct from the classical vasoconstriction and fluid homeostasis actions of systemic RAS and cater specifically for local tissues. Local RAS can affect islet-cell function and structure in the adult pancreas as well as proliferation and differentiation of pancreatic stem/progenitor cells during development. Differentiation of stem/progenitor cells into insulin-expressing cells suitable for therapeutic transplantation offers a desperately needed new approach for replacement of glucose-responsive insulin producing cells in diabetic patients. Given that the generation of functional and transplantable islet cells has proven to be difficult, elucidation of RAS involvement in cellular regeneration and differentiation may propel pancreatic stem/progenitor cell development and thus β-cell regeneration forward. This review provides a critical appraisal of current research progress on the role of the RAS, including the newly characterized ACE2/Ang-(1-7)/Mas axis in the proliferation, differentiation, and maturation of pancreatic stem/progenitor cells. It is thus plausible to propose that the AT1 stimulation could be a repair mechanism involving the AT2R as well as the ACE2/Ang-(1-7)/Mas axis in directing β-cell development in diabetic patients using genetic and pharmaceutical manipulation of the RAS.

Regulatory role of the rennin-angiotensin system in acute pancreatitis

The renin-angiotensin system (RAS) is known as a circulating or hormonal system regulating blood pressure, electrolyte and fluid homeostasis. Recent studies have found that, in addition to the circulating RAS, local renin-angiotensin systems also exist in several tissues and organs. Pancreatic renin-angiotensin system can not only regulate exocrine and endocrine function but also, via paracrine and (or) autocrine mechanisms, participate in the pathology and pathophysiology of pancreas-related diseases such as acute pancreatitis, diabetes, and pancreatic cancer. Acute pancreatitis (AP) is a common acute abdominal disease of the digestive system, which is often complicated with many other serious diseases and is therefore associated with a high overall mortality. At present, the etiology and pathogenesis of AP have not been fully elucidated yet. Thus, the proposed concept of a local RAS in the pancreas may provide a new avenue for the development of new treatments for AP.

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.

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.

Perinatal taurine imbalance alters the interplay of renin-angiotensin system and estrogen on glucose-insulin regulation in adult female rats

Perinatal taurine depletion followed by high sugar intake (postweaning) alters the renin-angiotensin system (RAS) and glucose regulation in adult female rats. This study tests the hypothesis that in adult female rats, RAS and estrogen contribute to insulin resistance resulting from perinatal taurine imbalance. Female Sprague-Dawley rats were fed normal rat chow with 3% β-alanine (taurine depletion, TD), 3% taurine (taurine supplementation, TS), or water alone (control, C) from conception to weaning. Their female offspring were fed normal rat chow with 5% glucose in water (TDG, TSG, CG) or water alone (TDW, TSW, CW) throughout the experiment. At 7-8 weeks of age, animals were studied with or without captopril inhibition of the RAS and with or without estrogen receptor inhibition by tamoxifen. Compared to CW and CG groups, perinatal taurine depletion but not supplementation slightly increased plasma insulin levels. High sugar intake slightly increased plasma insulin only in TSG. Captopril treatment significantly increased plasma insulin in all groups except CG (the greatest increase was in TDG). Changes in insulin resistance and insulin secretion paralleled the changes in plasma insulin levels. In contrast, tamoxifen treatment increased insulin resistance and decreased insulin secretion only in TDG and this group displayed hyperglycemia and glucose intolerance. These data indicate that perinatal taurine imbalance alters the interplay of RAS and estrogen on glucose-insulin regulation in adult female rats.

New insights and perspectives on intrarenal renin-angiotensin system: focus on intracrine/intracellular angiotensin II

Although renin, the rate-limiting enzyme of the renin-angiotensin system (RAS), was first discovered by Robert Tigerstedt and Bergman more than a century ago, the research on the RAS still remains stronger than ever. The RAS, once considered to be an endocrine system, is now widely recognized as dual (circulating and local/tissue) or multiple hormonal systems (endocrine, paracrine and intracrine). In addition to the classical renin/angiotensin I-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II receptor (AT₁/AT₂) axis, the prorenin/(Pro)renin receptor (PRR)/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, and the Ang IV/AT₄/insulin-regulated aminopeptidase (IRAP) axis have recently been discovered. Furthermore, the roles of the evolving RAS have been extended far beyond blood pressure control, aldosterone synthesis, and body fluid and electrolyte homeostasis. Indeed, novel actions and underlying signaling mechanisms for each member of the RAS in physiology and diseases are continuously uncovered. However, many challenges still remain in the RAS research field despite of more than one century's research effort. It is expected that the research on the expanded RAS will continue to play a prominent role in cardiovascular, renal and hypertension research. The purpose of this article is to review the progress recently being made in the RAS research, with special emphasis on the local RAS in the kidney and the newly discovered prorenin/PRR/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, the Ang IV/AT₄/IRAP axis, and intracrine/intracellular Ang II. The improved knowledge of the expanded RAS will help us better understand how the classical renin/ACE/Ang II/AT₁ receptor axis, extracellular and/or intracellular origin, interacts with other novel RAS axes to regulate blood pressure and cardiovascular and kidney function in both physiological and diseased states.