The role of the pancreatic renin-angiotensin system in acinar digestive enzyme secretion and in acute pancreatitis

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

The potential therapeutic use of renin-angiotensin system inhibitors in the treatment of inflammatory diseases

Inflammation is a normal part of the immune response to injury or infection but its dysregulation promotes the development of inflammatory diseases, which cause considerable human suffering. Nonsteroidal anti-inflammatory agents are the most commonly prescribed agents for the treatment of inflammatory diseases, but they are accompanied by a broad range of side effects, including gastrointestinal and cardiovascular events. The renin-angiotensin system (RAS) is traditionally known for its role in blood pressure regulation. However, there is increasing evidence that RAS signaling is also involved in the inflammatory response associated with several disease states. Angiotensin II increases blood pressure by binding to angiotensin type 1 (AT₁ ) receptor, and direct renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors and AT₁ receptor blockers (ARBs) are clinically used as antihypertensive agents. Recent data suggest that these drugs also have anti-inflammatory effects. Therefore, this review summarizes these recent findings for the efficacy of two of the most widely used antihypertensive drug classes, ACE inhibitors and ARBs, to reduce or treat inflammatory diseases such as atherosclerosis, arthritis, steatohepatitis, colitis, pancreatitis, and nephritis.

Angiotensin II receptor blockers and risk of acute pancreatitis - a population based case-control study in Sweden

Background

Acute pancreatitis is a potentially lethal disease, with a rising incidence in the Western world. Yet, no pharmacological prevention or specific treatment for acute pancreatitis exists. Also, the connection with severity of acute pancreatitis is unknown. Experimental and epidemiological research suggests a protective effect of angiotensin II receptor blockers.

Methods

During 2006 to 2008, we performed a nationwide case–control study on Swedish residents aged 40–84 years. First-time cases with acute pancreatitis were identified in the National Patient Register and data on dispensed prescriptions was retrieved from the Prescribed Drug Register. Controls were randomly selected from the general population in Sweden frequency-matched on sex, age, and calendar year. To estimate relative risk of acute pancreatitis, by degree of severity, among users of angiotensin II receptor blockers, as compared to non-users, we used multivariable logistic regression analysis to calculate odds ratios (OR) with 95% confidence interval (CI).

Results

Among 6,161 cases of acute pancreatitis and 61,637 controls, current use of angiotensin II receptor blockers was followed by a decreased risk of acute pancreatitis, compared to non-users, adjusted OR 0 · 77 (95% CI 0 · 69–0 · 86). No protective association, but an increased risk was found for users of angiotensin-converting enzyme inhibitors (adjusted OR 1 · 11, 95% CI: 1 · 01–1 · 21), analysed for comparison reasons. There was a significant decreased risk associated with both severe acute pancreatitis, (OR 0 · 71 (0 · 59–0 · 85), and mild acute pancreatitis; adjusted OR 0 · 81 (0 · 70–0 · 94).

Conclusion

This population-based case–control study indicates that use of angiotensin II receptor blockers might be associated with a lesser risk of acute pancreatitis, and that the protective association was significant among cases of both severe and mild acute pancreatitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12876-017-0595-8) contains supplementary material, which is available to authorized users.

Fatal Acute Pancreatitis in a Patient Chronically Treated with Candesartan

Objective:

To summarize a case of acute pancreatitis in a patient receiving the angiotensin II receptor blocker (ARB) candesartan.

Case Summary:

A previously healthy 75-year-old white man presented with acute pancreatitis complicated by anuric renal failure, respiratory failure, circulatory collapse, and died within 24 hours despite resuscitation efforts. He had been receiving candesartan 32 mg/day for more than one year with no apparent adverse effects.

Discussion:

In recent years, angiotensin-converting enzyme (ACE) inhibitors have been linked with sporadic cases of acute pancreatitis. Recent case reports suggest a similar association between pancreatitis and the related drug class of ARBs. Animal data indicate that the renin–angiotensin system plays an important role in pancreatic hemodynamics and exocrine function and is activated in the setting of acute pancreatitis. Because both ARBs and ACE inhibitors affect angiotensin II, we hypothesize that a common pathophysiologic mechanism might apply to both ARB- and ACE inhibitor–induced pancreatitis.

Conclusions:

Although acute pancreatitis appears to be a rare complication of both ARBs and ACE inhibitors, the catastrophic outcome in this case mandates that clinicians be aware of this adverse effect. Further research into the role of the renin–angiotensin system in the pathogenesis of acute pancreatitis appears warranted.

No association between losartan use and acute pancreatitis in hypertensive patients

Background and objective

Clinical evidence is scarce about the relationship between losartan use and acute pancreatitis. We therefore conducted a population-based case-control study using the database from the Taiwan National Health Insurance Program to investigate this question.

Methods

The study consisted of 1449 hypertensive subjects aged 20-84 years with a first episode of acute pancreatitis during the period 2000-2011 as the case group and 2479 hypertensive subjects without acute pancreatitis as the control group. Both the case and control groups were matched for sex, age, comorbidities and index year of acute pancreatitis diagnosis. According to the history of losartan prescription before the date of diagnosis of acute pancreatitis, subjects who had never received a prescription for losartan were defined as 'never use of losartan', those whose last remaining losartan tablet was detected within 7 days before the date of diagnosis of acute pancreatitis were defined as 'current use of losartan' and those whose last remaining tablet of losartan was detected ≥8 days before the date of diagnosis of acute pancreatitis were defined as 'late use of losartan'. ORs and 95% CIs were measured to investigate the risk of acute pancreatitis associated with losartan use by the multivariable unconditional logistic regression model.

Results

After adjustment for potentially confounding factors, the adjusted OR of acute pancreatitis was 0.96 (95% CI 0.68 to 1.37) for subjects with current use of losartan compared with those with never use of losartan, but the difference was not statistically significant. For subjects with late use of losartan the adjusted OR of acute pancreatitis was 1.05 (95% CI 0.80 to 1.37), which also was not statistically significant.

Conclusions

No significant association can be detected between losartan use and acute pancreatitis in hypertensive patients. More research is required to determine the potential role of losartan in the risk of acute pancreatitis.

Inhibition of pancreatic oxidative damage by stilbene derivative dihydro-resveratrol: implication for treatment of acute pancreatitis

Trans-resveratrol is a natural stilbenoid possessing multifarious pharmacological benefits; however, when orally consumed, it is rapidly metabolised by colonic microflora and converted to dihydro-resveratrol. Thus, this microbial metabolite is of great therapeutic relevance. In the present study, upon the oral administration of dihydro-resveratrol (10–50 mg/kg), the severity of acute pancreatitis in the cerulein-treated rats was significantly ameliorated as evidenced by decreased α-amylase activities in the plasma and lessened oedema formation in the pancreatic parenchyma. In addition, the generation of intracellular reactive oxidative products, including malondialdehyde and protein carbonyls, was accordingly reduced, so as the production of pro-inflammatory cytokines. While inhibiting the activities of NADPH oxidase and myeloperoxidase, the depletion of glutathione was considerably restored. Importantly, the attenuation of pancreatic oxidative damage by dihydro-resveratrol was associated with a down-regulation of the nuclear factor-kappaB and phosphatidylinositol 3′-kinase-serine/threonine kinase signalling pathways. Furthermore, we demonstrated that the solubility of dihydro-resveratrol was at least 5 times higher than trans-resveratrol whilst exhibiting a much lower cytotoxicity. Collectively, the current findings accentuate new mechanistic insight of dihydro-resveratrol in pancreatic oxidative damage, and advocate its therapeutic potential for the management of acute pancreatitis, particularly for patients unresponsive to trans-resveratrol due to the lack of proper microbial strains.

Alteration of the renin-angiotensin system in caerulein induced acute pancreatitis in the mouse

BACKGROUND

The objective of this study was to determine if RAS bioactive enzymes and peptides are perturbed in acute pancreatitis and associated lung injury.

METHODS

The intervention group of mice were treated with ten hourly intraperitoneal (i.p.) injections of caerulein (50 μg/kg) to induce acute pancreatitis. Animals were euthanized, samples of pancreas, lung and blood were collected, and plasma was prepared and stored for subsequent analysis. ACE and ACE2 activities were determined by spectrofluorometric assay. ACE, ACE2, Ang II and Ang-(1-7) levels were quantified by ELISA.

RESULTS

There was a significant decrease in ACE2 enzymatic activity in pancreatic and lung tissues of mice with acute pancreatitis. In contrast, there were no significant changes in measured levels of ACE and ACE2 in the pancreas, and lung or activity of ACE in pancreatic and lung tissue following acute pancreatitis. There were no significant differences in the activities and levels of circulating ACE and ACE2 following acute pancreatitis. The ACE to ACE2 activity ratio was markedly increased in pancreatic and lung tissues of mice with acute pancreatitis. No significant changes were observed in the levels of Ang II except for a decrease in lung tissue. No changes were observed in Ang-(1-7) levels in pancreas, lung and plasma between the groups. The Ang II to Ang-(1-7) ratio was increased in the pancreas but was decreased in the lung following caerulein treatment.

CONCLUSION

These data suggest dysregulation of RAS in acute pancreatitis as evidenced by altered Ang II/Ang-(1-7) levels induced by the imbalance of ACE/ACE2 activity.

Effects of Local Pancreatic Renin-Angiotensin System on the Microcirculation of Rat with Severe Acute Pancreatitis

Severe acute pancreatitis (SAP) is normally related to multiorgan dysfunction and local complications. Studies have found that local pancreatic renin-angiotensin system (RAS) was significantly upregulated in drug-induced SAP. The present study aimed to investigate the effects of angiotensin II receptors inhibitor valsartan on dual role of RAS in SAP in a rat model and to elucidate the underlying mechanisms. 3.8% sodium taurocholate (1 ml/kg) was injected to the pancreatic capsule in order for pancreatitis induction. Rats in the sham group were injected with normal saline in identical locations. We also investigated the regulation of experimentally induced SAP on local RAS expression in the pancreas through determination of the activities of serum amylase, lipase and myeloperoxidase, histological and biochemical analysis, radioimmunoassay, fluorescence quantitative PCR and Western blot analysis. The results indicated that valsartan could effectively suppress the local RAS to protect against experimental acute pancreatitis through inhibition of microcirculation disturbances and inflammation. The results suggest that pancreatic RAS plays a critical role in the regulation of pancreatic functions and demonstrates application potential as AT1 receptor antagonists. Moreover, other RAS inhibitors could be a new therapeutic target in acute pancreatitis.

Dietary Sodium Suppresses Digestive Efficiency via the Renin-Angiotensin System

Dietary fats and sodium are both palatable and are hypothesized to synergistically contribute to ingestive behavior and thereby obesity. Contrary to this hypothesis, C57BL/6J mice fed a 45% high fat diet exhibited weight gain that was inhibited by increased dietary sodium content. This suppressive effect of dietary sodium upon weight gain was mediated specifically through a reduction in digestive efficiency, with no effects on food intake behavior, physical activity, or resting metabolism. Replacement of circulating angiotensin II levels reversed the effects of high dietary sodium to suppress digestive efficiency. While the AT₁ receptor antagonist losartan had no effect in mice fed low sodium, the AT₂ receptor antagonist PD-123,319 suppressed digestive efficiency. Correspondingly, genetic deletion of the AT₂ receptor in FVB/NCrl mice resulted in suppressed digestive efficiency even on a standard chow diet. Together these data underscore the importance of digestive efficiency in the pathogenesis of obesity, and implicate dietary sodium, the renin-angiotensin system, and the AT₂ receptor in the control of digestive efficiency regardless of mouse strain or macronutrient composition of the diet. These findings highlight the need for greater understanding of nutrient absorption control physiology, and prompt more uniform assessment of digestive efficiency in animal studies of energy balance.

The ACE2-angiotensin-(1-7)-Mas axis protects against pancreatic cell damage in cell culture

OBJECTIVE

Angiotensin-converting enzyme 2 (ACE2), its product angiotensin-(1-7), and its receptor Mas have been shown to moderate the adverse effects of the ACE-angiotensin II-AT1 axis in many diseases. The aim of this study was to determine whether the ACE2-Ang-(1-7)-Mas axis could have similar effects in a cell culture model of pancreatic damage.

METHODS

AR42J cells were stimulated with 10 nmol/L cerulein to simulate acute pancreatitis. ACE2, Ang-(1-7), Mas receptor, and PI3K/AKT pathway were measured by quantitative real-time polymerase chain reaction and Western blot analysis.

RESULTS

ACE2 and Mas receptor protein levels in AR42J cells were significantly increased (P < 0.05) between 30 minutes and 6 hours postdisease induction compared with the control group. Mas receptor gene expression was significantly increased (P < 0.05) at 2 hours postdisease induction, and Ang-(1-7) was increased at 6 hours. Treatment with Ang-(1-7) in AR42J cells increased IL-10, decreased IL-6 and IL-8, and reduced the damage to pancreatic cells. Levels of IL-6 and IL-8 in AR42J cell culture were increased significantly after treatment with A779. Moreover, Ang-(1-7) increased the concentration of PI3K/AKT pathway and eNOSin AR42J cells.

CONCLUSIONS

ACE2-angiotensin-(1-7)-Mas axis significantly inhibits pancreatitis in response to decreased inflammatory factors by the activation of endothelial nitric oxide synthase and NO signaling pathways.

Evidence for a role of mitogen-activated protein kinases in the treatment of experimental acute pancreatitis

Acute pancreatitis (AP) is an inflammatory disease characterized by acute inflammation and necrosis of the pancreatic parenchyma. AP is often associated with organ failure, sepsis, and high mortality. The pathogenesis of AP is still not well understood. In recent years several papers have highlighted the cellular and molecular events of acute pancreatitis. Pancreatitis is initiated by activation of digestive enzymes within the acinar cells that are involved in autodigestion of the gland, followed by a massive infiltration of neutrophils and macrophages and release of inflammatory mediators, responsible for the local and systemic inflammatory response. The hallmark of AP is parenchymal cell necrosis that represents the cause of the high morbidity and mortality, so that new potential therapeutic approaches are indispensable for the treatment of patients at high risk of complications. However, not all factors that determine the onset and course of the disease have been explained. Aim of this article is to review the role of mitogen-activated protein kinases in pathogenesis of acute pancreatitis.

Resveratrol suppresses microcirculatory disturbance in a rat model of severe acute pancreatitis

The present study sought to understand the mechanisms of attenuation of severe acute pancreatitis (SAP) by resveratrol (RES). SAP was experimentally induced in rats by injection of 4% sodium taurocholate in the retrograde pancreatic duct. Three study groups were evaluated: Group I (sham-operated animals), Group II (SAP animals), and Group III (SAP animals treated with RES at 20 mg/kg/body weight, 5 min after induction of SAP). The study outcomes were histopathologic changes and alterations in biochemical markers: plasma renin activity and levels of angiotensin II, endothelin, and nitric oxide in plasma. Biochemical markers were evaluated at 3, 6, and 12 h after induction of SAP. SAP was associated with significant (p < 0.05) histopathologic changes (saponification spots in the intraperitoneal cavity, severe pancreatic edema, blood congestion, varying degrees of necrosis, etc.), as well as with elevation of biochemical markers in blood plasma. RES treatment significantly (p < 0.05) attenuated changes of both histopathologic and biochemical markers induced by SAP. In conclusion, this study provides evidence that RES treatment is a promising therapeutic approach to suppress microcirculatory disturbance in SAP.

Ulinastatin activates the renin-angiotensin system to ameliorate the pathophysiology of severe acute pancreatitis

BACKGROUND AND AIM

Ulinastatin is a drug used effectively to alleviate symptoms and improve the pathophysiology of various types of pancreatitis. However, the molecular mechanism responsible for its action remains unknown. Therefore, we further explore the therapeutic effects of ulinastatin and investigate possible molecular pathways modulated by this drug in the development of severe acute pancreatitis (SAP).

METHODS

SAP mouse model was created by administering intraperitoneal injections of cerulein and lipopolysaccharide. Pancreatic injury was assessed by performing biochemical and histological assays and by measuring the inflammatory response of the pancreas. Specifically, we examined changes in the expression of components of the rennin-angiotensin system (RAS), including angiotensin-converting enzyme (ACE)-angiotensin II (Ang II)-angiotensin type 1 receptor (AT-1R), and ACE2-Ang-(1-7)-Mas receptor.

RESULTS

When SAP mouse models were treated with ulinastatin at a dosage of 50,000 U/kg body weight, we found, through biochemical and histopathological analyses, that the pancreatic injury was significantly ameliorated. Administration of ulinastatin to SAP mice led to increased expression of ACE2, Ang-(1-7), and Mas receptor, decreased expression of serum Ang II and pancreatic AT-1R, and no alterations in the expression of pancreatic ACE and Ang II when compared to cerulein-treated control group that did not receive ulinastatin.

CONCLUSIONS

This study shows that ulinastatin has differential effects on the two axes of the RAS during SAP. Our results further suggest that upregulation of components of the ACE2-Ang-(1-7)-Mas pathway might be an important mechanism contributing to the therapeutic role of ulinastatin in alleviating pancreatitis-associated symptoms.

Angiotensin-converting enzyme (ACE and ACE2) imbalance correlates with the severity of cerulein-induced acute pancreatitis in mice

Angiotensin-converting enzyme (ACE) and its effector peptide angiotensin II (Ang II) have been implicated in the pathogenesis of pancreatitis. Angiotensin-converting enzyme 2 (ACE2) degrades Ang II to angiotensin-(1-7) [Ang-(1-7)] and has recently been described to have an antagonistic effect on ACE signalling. However, the specific underlying role of ACE2 in the pathogenesis of severe acute pancreatitis (SAP) is unclear. In the present study, the local imbalance of ACE and ACE2, as well as Ang II and Ang-(1-7) expression, was compared in wild-type (WT) and ACE2 knock-out (KO) or ACE2 transgenic (TG) mice subjected to cerulein-induced SAP. Serum amylase, tumour necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-10 levels and histological morphometry were used to determine the severity of pancreatitis. In WT mice, pancreatic ACE and Ang II and serum Ang II expression increased (P < 0.05), while pancreatic ACE2 and Ang-(1-7) and serum Ang-(1-7) levels were also significantly elevated (P < 0.05) from 2 to 72 h after the onset of SAP. However, the ratio of pancreatic ACE2 to ACE expression was significantly reduced (from 1.46 ± 0.09 to 0.27 ± 0.05, P < 0.001) and paralleled the severity of pancreatitis. The Ace2 KO mice exhibited increased levels of tumour necrosis factor-α, IL-1β, IL-6, multifocal coagulative necrosis and inflammatory infiltrate, and lower levels of serum IL-10 and pancreatic Ang-(1-7) (4.70 ± 2.13 versus 10.87 ± 2.51, P < 0.001) compared with cerulein-treated WT mice at the same time point. Conversely, Ace2 TG mice with normal ACE expression were more resistant to SAP challenge as evidenced by a decreased inflammatory response, attenuated pathological changes and increased survival rates. These data suggest that the ACE2-ACE imbalance plays an important role in the pathogenesis of SAP and that pancreatic ACE2 is an important factor in determining the severity of SAP.

Valsartan-induced acute pancreatitis

Gastrointestinal toxicity is uncommon among patients treated with angiotensin II receptor antagonists. A 58-year-old man presented with nausea, vomiting and constant pain in the epigastrium that radiated to the flanks. He received treatment with valsartan (160 mg daily) for hypertension. The clinical, biochemical and radiological findings were compatible with a diagnosis of acute pancreatitis. After the patient achieved a clinical and biochemical recovery, the valsartan therapy was started again. Six weeks later, he returned to the hospital with an attack of pancreatitis. Subsequently, he returned with repeated attacks of pancreatitis twice, and the valsartan was discontinued. Ten months after the treatment, the patient had no complaints. When severe abdominal symptoms occur for no apparent reason during treatment with valsartan, a diagnosis of pancreatitis should be considered.

Overview of exocrine pancreatic pathobiology

Exocrine pancreas is a source of several enzymes that are essential for the digestive process. The exocrine pancreatic secretion is tightly regulated by the neuroendocrine system. The endocrine pancreas is tightly integrated anatomically and physiologically with the exocrine pancreas and modulates its function. Compound-induced pancreatitis is not a common event in toxicology or drug development, but it becomes a significant liability when encountered. Understanding the species-specific differences in physiology is essential to understand the underlying pathobiology of pancreatic disease in animal models and its relevance to human disease. This review will mainly focus on understanding the morphology and physiology of the pancreas, unique islet-exocrine interactions, and pancreatitis.

The Angiotensin II Type 2 Receptor in Brain Functions: An Update

Angiotensin II (Ang II) is the main active product of the renin-angiotensin system (RAS), mediating its action via two major receptors, namely, the Ang II type 1 (AT₁) receptor and the type 2 (AT₂) receptor. Recent results also implicate several other members of the renin-angiotensin system in various aspects of brain functions. The first aim of this paper is to summarize the current state of knowledge regarding the properties and signaling of the AT₂ receptor, its expression in the brain, and its well-established effects. Secondly, we will highlight the potential role of the AT₂ receptor in cognitive function, neurological disorders and in the regulation of appetite and the possible link with development of metabolic disorders. The potential utility of novel nonpeptide selective AT₂ receptor ligands in clarifying potential roles of this receptor in physiology will also be discussed. If confirmed, these new pharmacological tools should help to improve impaired cognitive performance, not only through its action on brain microcirculation and inflammation, but also through more specific effects on neurons. However, the overall physiological relevance of the AT₂ receptor in the brain must also consider the Ang IV/AT₄ receptor.

Losartan to prevent hyperenzymemia after endoscopic retrograde cholangiopan-creatography: A randomized clinical trial

AIM: To study if the angiotensin II receptor blockers (ARB) losartan counteracts pancreatic hyperenzymemia as measured 24 h after endoscopic retrograde cholangiopancreatography (ERCP).

METHODS: A triple-blind and placebo-controlled randomized clinical trial was performed at two Swedish hospitals in 2006-2008. Patients over 18 years of age undergoing ERCP, excluding those with current pancreatitis, current use of ARB, and severe disease, such as sepsis, liver and renal failure. One oral dose of 50 mg losartan or placebo was given one hour before ERCP. The relative risk of hyperenzymemia 24 h after ERCP was estimated using multivariable logistic regression, and expressed as odds ratio with 95% confidence intervals (CIs), including adjustment for potential remaining confounding.

RESULTS: Among 76 participating patients, 38 were randomized to the losartan and the placebo group, respectively. The incidence rates of hyperenzymemia and acute pancreatitis among all 76 participating patients were 21% and 12%, respectively. Hyperenzymemia was detected in 9 and 7 patients in the losartan and placebo group, respectively. There were no major differences between the comparison groups regarding cannulation difficulty, findings, or proportion of patients requiring drainage of the bile ducts. There were, however, more pancreatic duct injections, a greater extent of pancreatography, and more biliary sphincterotomies in the losartan group than in the placebo group. Losartan was not associated with risk of hyperenzymemia compared to the placebo group after multi-varible logistic regression analysis (odds ratio 1.6, 95%CI 0.3-7.8).

CONCLUSION: In this randomized trial 50 mg losartan given orally had no prophylactic effect on development of hyperenzymemia after ERCP.

Severe acute pancreatitis is associated with upregulation of the ACE2-angiotensin-(1-7)-Mas axis and promotes increased circulating angiotensin-(1-7)

BACKGROUND/OBJECTIVES

Angiotensin-converting enzyme 2 (ACE2), its product angiotensin-(1-7) and its receptor Mas may counteract the adverse effects of the ACE-angiotensin receptor II-AT(1) axis in many diseases. We examined the expression of these novel components of the rennin-angiotensin system in an experimental mouse model of severe acute pancreatitis (SAP).

METHODS

SAP was induced by six intraperitoneal injections of caerulein, and mice were sacrificed at 2, 12, 24, 48 and 72 h post disease-induction (normal control group mice were sacrificed at 2 h post disease-induction). Tissue and blood were collected for biochemical detection, gene and protein expression by qRT-PCR and western blot analysis, enzyme-linked immunosorbent assay and immunohistology detection.

RESULTS

Pancreatic ACE2 gene and protein expression, plasma and pancreatic angiotensin-(1-7) levels and Mas receptor gene and protein expression were significantly increased (p < 0.05) following SAP induction compared with the normal control group.

CONCLUSIONS

Severe acute pancreatitis is associated with upregulation of the ACE2-angiotensin-(1-7)-Mas axis and promotes increased circulating angiotensin-(1-7). These results support the presence of an ACE2-angiotensin-(1-7)-Mas axis in pancreatitis.

The role of stroma in pancreatic cancer: diagnostic and therapeutic implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the five most lethal malignancies worldwide and survival has not improved substantially in the past 30 years. Desmoplasia (abundant fibrotic stroma) is a typical feature of PDAC in humans, and stromal activation commonly starts around precancerous lesions. It is becoming clear that this stromal tissue is not a bystander in disease progression. Cancer-stroma interactions effect tumorigenesis, angiogenesis, therapy resistance and possibly the metastatic spread of tumour cells. Therefore, targeting the tumour stroma, in combination with chemotherapy, is a promising new option for the treatment of PDAC. In this Review, we focus on four issues. First, how can stromal activity be used to detect early steps of pancreatic carcinogenesis? Second, what is the effect of perpetual pancreatic stellate cell activity on angiogenesis and tissue perfusion? Third, what are the (experimental) antifibrotic therapy options in PDAC? Fourth, what lessons can be learned from Langton's Ant (a simple mathematical model) regarding the unpredictability of genetically engineered mouse models?

The role of stroma in pancreatic cancer: diagnostic and therapeutic implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the five most lethal malignancies worldwide and survival has not improved substantially in the past 30 years. Desmoplasia (abundant fibrotic stroma) is a typical feature of PDAC in humans, and stromal activation commonly starts around precancerous lesions. It is becoming clear that this stromal tissue is not a bystander in disease progression. Cancer-stroma interactions effect tumorigenesis, angiogenesis, therapy resistance and possibly the metastatic spread of tumour cells. Therefore, targeting the tumour stroma, in combination with chemotherapy, is a promising new option for the treatment of PDAC. In this Review, we focus on four issues. First, how can stromal activity be used to detect early steps of pancreatic carcinogenesis? Second, what is the effect of perpetual pancreatic stellate cell activity on angiogenesis and tissue perfusion? Third, what are the (experimental) antifibrotic therapy options in PDAC? Fourth, what lessons can be learned from Langton's Ant (a simple mathematical model) regarding the unpredictability of genetically engineered mouse models?

Can we expect progress in the treatment of fibrosis in the course of chronic pancreatitis?

Chronic pancreatitis (CP) is a necroinflammatory process characterized by loss of both exocrine and endocrine function. To date, the disease has been treated symptomatically. Real advances in CP management can be expected once the pathophysiology of the disease is elucidated and individual stages of its development are properly managed. A key role in the CP pathogenesis is played by activation of pancreatic stellate cells (PSCs) that cooperate with the remaining pancreatic cells. All these cells produce cytokines, growth factors, angiotensin and other substances, which paracrinally or autocrinally induce further, persistent activation of PSCs. The activated PSCs are capable of producing and modifying the extracellular matrix. An optimal therapeutic preparation should exert beneficial effects on all the above-mentioned phenomena observed in CP. The most promising treatment modalities include blocking of the renin-angiotensin system (RAS), activation of peroxisome proliferator-activated receptors gamma (PPAR-γ), influence on the remaining PSC signaling pathways, blocking of substances produced by activated PSCs, and antioxidants. The findings of many recent experimental studies are highly encouraging; however, their efficacy should be confirmed in well-designed clinical trials.

Chronic activation of endogenous angiotensin-converting enzyme 2 protects diabetic rats from cardiovascular autonomic dysfunction

In this study, we evaluated whether the activation of endogenous angiotensin-converting enzyme 2 (ACE2) would improve the cardiovascular autonomic dysfunction of diabetic rats. Ten days after induction of type 1 diabetes (streptozotocin, 50 mg kg(-1) i.v.), the rats were treated orally with 1-[(2-dimethylamino)ethylamino]-4-(hydroxymethyl)-7-[(4-methylphenyl) sulfonyl oxy]-9H-xanthene-9-one (XNT), a newly discovered ACE2 activator (1 mg kg(-1) day(-1)), or saline (equivalent volume) for 30 days. Autonomic cardiovascular parameters were evaluated in conscious animals, and an isolated heart preparation was used to analyse cardiac function. Diabetes induced a significant decrease in the baroreflex bradycardia sensitivity, as well as in the chemoreflex chronotropic response and parasympathetic tone. The XNT treatment improved these parameters by ≈ 76% [0.82 ± 0.09 versus 1.44 ± 0.17 Ratio between changes in pulse interval and changes in mean arterial pressure (ΔPI/ΔmmHg)], ∼85% (-57 ± 9 versus -105 ± 10 beats min(-1)) and ≈ 205% (22 ± 2 versus 66 ± 12 beats min(-1)), respectively. Also, XNT administration enhanced the bradycardia induced by the chemoreflex activation by v 74% in non-diabetic animals (-98 ± 16 versus -170 ± 9 Δbeats min(-1)). No significant changes were observed in the mean arterial pressure, baroreflex tachycardia sensitivity, chemoreflex pressor response and sympathetic tone among any of the groups. Furthermore, chronic XNT treatment ameliorated the cardiac function of diabetic animals. However, the coronary vasoconstriction observed in diabetic rats was unchanged by ACE2 activation. These findings indicate that XNT protects against the autonomic and cardiac dysfunction induced by diabetes. Thus, our results provide evidence for the viability and effectiveness of oral administration of an ACE2 activator for the treatment of the cardiovascular autonomic dysfunction caused by diabetes.

The Renin-angiotensin system and reactive oxygen species: implications in pancreatitis

SIGNIFICANCE

The renin-angiotensin system (RAS) is a circulating hormonal system involved in the regulation of blood pressure and circulating fluid electrolytes. Recent findings have revealed that locally generated angiotensin (Ang) II plays a pivotal role in normal physiology as well as pathophysiology in various tissues and organs, including the pancreas. This review article summarizes current progress that has been made in elucidating the putative roles of Ang II in both acute and chronic pancreatitis.

RECENT ADVANCES

A convergence of evidence suggests that the underlying mechanism may involve reactive oxygen species (ROS)-generating systems, such as nicotinamide adenine dinucleotide phosphate oxidase, and subsequent elevation of proinflammatory and profibrogenic gene expression as well as protein activity. More importantly, Ang II-induced ROS interacts with other ROS-generating systems to positively feed-forward the ROS-induced signaling.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Advances in basic research indicate that RAS blockers may provide potential therapeutic role for the management of pancreatic inflammation and, more importantly, pancreatitis-associated complications. Genetic alterations resulting from a malfunction in the epigenetic control of pancreatic RAS could be a causative factor in the development of pancreatitis.

Review article: pancreatic renin-angiotensin systems in health and disease

BACKGROUND

In addition to the circulating (endocrine) renin-angiotensin system (RAS), local renin-angiotensin systems are now known to exist in diverse cells and tissues. Amongst these, pancreatic renin-angiotensin systems have recently been identified and may play roles in the physiological regulation of pancreatic function, as well as being implicated in the pathogenesis of pancreatic diseases including diabetes, pancreatitis and pancreatic cancer.

AIM

To review and summarise current knowledge of pancreatic renin-angiotensin systems.

METHODS

We performed an extensive PubMed, Medline and online review of all relevant literature.

RESULTS

Pancreatic RAS appear to play various roles in the regulation of pancreatic physiology and pathophysiology. Ang II may play a role in the development of pancreatic ductal adenocarcinoma, via stimulation of angiogenesis and prevention of chemotherapy toxicity, as well as in the initiation and propagation of acute pancreatitis (AP); whereas, RAS antagonism is capable of preventing new-onset diabetes and improving glycaemic control in diabetic patients. Current evidence for the roles of pancreatic RAS is largely based upon cell and animal models, whilst definitive evidence from human studies remains lacking.

CONCLUSIONS

The therapeutic potential for RAS antagonism, using cheap and widely available agents, and may be untapped and such roles are worthy of active investigation in diverse pancreatic disease states.

Co-operative effects of angiotensin II and caerulein in NFκB activation in pancreatic acinar cells in vitro

Angiotensin II is a vasoactive peptide that controls blood pressure and homeostasis. Emerging evidence shows that locally generated angiotensin II plays a crucial role in normal physiology, as well as pathophysiological conditions such as pancreatitis. We recently reported that angiotensin II activates pancreatic NFκB in obstructive pancreatitis. However, the specific cell type responsible for this activation remains unclear. In this study, we investigated whether pancreatic acinar cells respond to angiotensin II. These cells are the most abundant pancreatic cells and the most vulnerable to pancreatitis. Pancreatic acinar AR42J cells were used as an in vitro model of pancreatic inflammation. Our results demonstrated that treatment with caerulein, a cholecystokinin receptor agonist, induced hypersecretion and NFκB activation, as demonstrated by elevated amylase secretion and degradation of inhibitor of NFκB (IκBβ). Angiotensin II, either alone or in combination with caerulein, augmented IκBβ degradation. Pre-treatment with losartan, an antagonist of the angiotensin type I (AT₁) receptor, abolished NFκB activation by angiotensin II and caerulein in a dose-dependent manner. Treatment with PD123319, a blocker of the angiotensin type II (AT₂) receptor, enhanced the activation of NFκB by angiotensin II and caerulein. Preliminary data further demonstrated that angiotensin II could extend caerulein-induced ERK1/2 activation in acinar cells. These results indicated that inflammation triggered by hyperstimulation of pancreatic acinar cells is enhanced by angiotensin II, via the AT₁ receptor. In contrast, stimulation of the AT₂ receptor protects against caerulein-induced NFκB activation. The differential roles of the AT₁ and AT₂ receptors might be useful in developing potential therapies for pancreatic inflammation.

The islet-acinar axis of the pancreas: more than just insulin

Although the role of the islets in the regulation of acinar cell function seemed a mystery to investigators who observed their dispersion among pancreatic acini, over time an appreciation for this intricate and unique structural arrangement has developed. The last three decades have witnessed a steadily growing understanding of the interrelationship of the endocrine and the exocrine pancreas. The islet innervation and vascular anatomy have been more fully characterized and provide an appropriate background for our current understanding. The interrelationship between the endocrine and exocrine pancreas is mediated by islet-derived hormones such as insulin and somatostatin, other humoral factors including pancreastatin and ghrelin, and also neurotransmitters (nitric oxide, peptide YY, substance P, and galanin) released by the nerves innervating the pancreas. Although considerable progress has been achieved, further work is required to fully delineate the complex interplay of the numerous mechanisms involved. This review aims to provide a comprehensive update of the current literature available, bringing together data gleaned from studies addressing the actions of individual hormones, humoral factors, and neurotransmitters on the regulation of amylase secretion from the acinar cell. This comprehensive view of the islet-acinar axis of the pancreas while acknowledging the dominant role played by insulin and somatostatin on exocrine secretion sheds light on the influence of the various neuropeptides on amylase secretion.

The renin angiotensin system and the metabolic syndrome

The renin angiotensin system (RAS; most well-known for its critical roles in the regulation of cardiovascular function and hydromineral balance) has regained the spotlight for its potential roles in various aspects of the metabolic syndrome. It may serve as a causal link among obesity and several co-morbidities. Drugs that reduce the synthesis or action of angiotensin-II (A-II; the primary effector peptide of the RAS) have been used to treat hypertension for decades and, more recently, clinical trials have determined the utility of these pharmacological agents to prevent insulin resistance. Moreover, there is evidence that the RAS contributes to body weight regulation by acting in various tissues. This review summarizes what is known of the actions of the RAS in the brain and throughout the body to influence various metabolic disorders. Special emphasis is given to the role of the RAS in body weight regulation. The paper represents an invited review by a symposium, award winner or keynote speaker at the Society for the Study of Ingestive Behavior [SSIB] Annual Meeting in Portland, July 2009.

Cardiocirculatory pathophysiological mechanisms in severe acute pancreatitis

Acute pancreatitis (AP) is a common and potentially lethal acute inflammatory process. Although the majority of patients have a mild episode of AP, 10%-20% develop a severe acute pancreatitis (SAP) and suffer systemic inflammatory response syndrome (SIRS) and/or pancreatic necrosis. The main aim of this article is to review the set of events, first localized in the pancreas, that lead to pancreatic inflammation and to the spread to other organs contributing to multiorganic shock. The early pathogenic mechanisms in SAP are not completely understood but both premature activation of enzymes inside the pancreas, related to an impaired cytosolic Ca²⁺ homeostasis, as well as release of pancreatic enzymes into the bloodstream are considered important events in the onset of pancreatitis disease. Moreover, afferent fibers within the pancreas release neurotransmitters in response to tissue damage. The vasodilator effects of these neurotransmitters and the activation of pro-inflammatory substances play a crucial role in amplifying the inflammatory response, which leads to systemic manifestation of AP. Damage extension to other organs leads to SIRS, which is usually associated with cardiocirculatory physiology impairment and a hypotensive state. Hypotension is a risk factor for death and is associated with a significant hyporesponsiveness to vasoconstrictors. This indicates that stabilization of the patient, once this pathological situation has been established, would be a very difficult task. Therefore, it seems particularly necessary to understand the pathological mechanisms involved in the first phases of AP to avoid damage beyond the pancreas. Moreover, efforts must also be directed to identify those patients who are at risk of developing SAP.

Use of angiotensin II receptor blockers and the risk of acute pancreatitis: a nested case-control study

BACKGROUND

There is no specific treatment against acute pancreatitis (AP). A protective effect by angiotensin II receptor blockers (ARB) on AP has been suggested experimentally, but clinical evidence is scarce.

METHODS

We conducted a population-based case-control study using The Health Improvement Network in the United Kingdom, comprising about 167,000 hypertensive patients in the study period 1996-2005. In multivariate logistic regression analysis, odds ratios were calculated with 95% confidence intervals (CI). Adjustments included sex, age, calendar year, body mass index, tobacco smoking, alcohol, general practitioner visits per year, and various antihypertensive medications with regard to exposure to ARB, and risk of AP.

RESULTS

Among 633,281 person-years at risk, 265 new cases of AP were identified. Current users of ARB had a 37% statistically non-significant reduced risk of developing AP as compared to non-users (OR 0.63, 95% CI 0.38-1.02). No clear association was found between use of other antihypertensive drugs and risk of AP.

CONCLUSION

Our study adds some support to previous experimental findings. Use of ARB might be associated with a reduced risk of AP. More research is needed to elucidate the potential role of ARB in the development of AP in the clinical setting.

Role of reactive oxygen species in brucein D-mediated p38-mitogen-activated protein kinase and nuclear factor-kappaB signalling pathways in human pancreatic adenocarcinoma cells

BACKGROUND

In human pancreatic adenocarcinoma, nuclear factor-kappa-B (NF-kappaB) transcription factor is constitutively activated that contributes to the resistance of the tumour cells to induced apoptosis. In our earlier studies, we have shown that brucein D (BD) mediated apoptosis through activation of the p38-mitogen-activated protein kinase (MAPK) signalling pathway in pancreatic cancer cells. This study investigated the function of reactive oxygen species (ROS) in BD-mediated p38-MAPK and NF-kappaB signalling pathways in PANC-1 cells.

METHODS

Glutathione and dihydroethidium assays were used to measure the antioxidant and superoxide levels, respectively. The protein expression of p22(phox), p67(phox) and p38-MAPK were examined by western blot. The NF-kappaB activity was evaluated by electrophoretic mobility shift assay.

RESULTS

Treatment with BD depleted the intracellular glutathione levels in PANC-1 cells. Brucein D triggered the activation of NADPH oxidase isoforms, p22(phox) and p67(phox) while enhancing the generation of superoxide. Increases in both intracellular ROS and NADPH oxidase activity were inhibited by an antioxidant, N-acetylcysteine (NAC). Brucein D-mediated activation of p38-MAPK was also inhibited by NAC. However, inhibition of NF-kappaB activity in BD-treated cells was independent of ROS. In vivo studies showed that BD treatment effectively reduced the rate of xenograft human pancreatic tumour in nude mice with no significant toxicity.

CONCLUSION

These data suggest that BD is an apoptogenic agent for pancreatic cancer cells through activation of the redox-sensitive p38-MAPK pathway and inhibition of NF-kappaB anti-apoptotic activity in pancreatic cancer cells.

Role of oxidative stress in pancreatic inflammation

Reactive oxygen and reactive nitrogen species (ROS/RNS) have been implicated in the pathogenesis of acute and chronic pancreatitis. Clinical and basic science studies have indicated that ROS/RNS formation processes are intimately linked to the development of the inflammatory disorders. The detrimental effects of highly reactive ROS/RNS are mediated by their direct actions on biomolecules (lipids, proteins, and nucleic acids) and activation of proinflammatory signal cascades, which subsequently lead to activation of immune responses. The present article summarizes the possible sources of ROS/RNS formation and the detailed signaling cascades implicated in the pathogenesis of pancreatic inflammation, as observed in acute and chronic pancreatitis. A therapeutic ROS/RNS-scavenging strategy has been advocated for decades; however, clinical studies examining such approaches have been inconsistent in their results. Emerging evidence indicates that pancreatitis-inducing ROS/RNS generation may be attenuated by targeting ROS/RNS-generating enzymes and upstream mediators.

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

Emerging evidence indicates that pancreatic tissue expresses all components of the renin-angiotensin system. However, the functional role is not well understood. This investigation examined renin inhibition on pancreas structure/function in the transgenic Ren2 rat harboring the mouse renin gene, a model of tissue renin overexpression. Renin is the rate-limiting step in the generation of angiotensin II (Ang II), which stimulates the generation of reactive oxygen species in a variety of tissues. Overexpression of renin in Ren2 rats results in hypertension, insulin resistance, and cardiovascular and renal damage. Young (6-7 wk old) insulin-resistant male Ren2 and age-matched insulin sensitive Sprague Dawley rats were treated with the renin inhibitor, aliskiren (50 mg/kg.d by ip injection), or placebo for 21 d. At 21 d, the Ren2 demonstrated insulin resistance with increased islet insulin, Ang II, and reduced total insulin receptor substrate (IRS)-1, IRS-2, and Akt immunostaining. There was increased islet nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and subunits (p47(phox) and Rac1) as well as increased nitrotyrosine immunostaining (each P < 0.05). These functional abnormalities were associated with a disordered islet architecture; increased islet-exocrine interface, pericapillary fibrosis, and structurally abnormal mitochondria and content in endocrine and exocrine pancreas. In vivo treatment with aliskiren normalized systemic insulin resistance and islet insulin, Ang II, NADPH oxidase activity/subunits, and nitrotyrosine and improved total IRS-1 and Akt phosphorylation (each P < 0.05) as well as islet/exocrine structural abnormalities. Collectively, these data suggest that pancreatic functional/structural changes are driven, in part, by tissue renin-angiotensin system-mediated increases in NADPH oxidase and reactive oxygen species generation, abnormalities attenuated with direct renin inhibition.

Cardiovascular homeostasis in hypotension associated with initial stages of severe acute pancreatitis

OBJECTIVES

To identify the mechanisms underlying hypotension during the early phase of severe acute pancreatitis (SAP) by analyzing whether an impaired response to vasoactive substances occurs in this pathological process.

METHODS

Experimental SAP was induced by infusing 5% sodium taurocholate through the main pancreatic duct in rats. Once mean arterial pressure (MAP) in animals with pancreatitis was reduced, different vasoactive substances and inhibitors were administered.

RESULTS

Administration of the nonspecific nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester caused a similar increase in MAP in rats with pancreatitis and control rats, whereas inducible nitric oxide synthase inhibition did not cause changes in MAP. Moreover, the hypertensive response to endothelin and angiotensin II was lower in pancreatitis. Inhibition of angiotensin II synthesis by the angiotensin-converting enzyme inhibitor perindopril in animals with pancreatitis caused severe hypotension, causing death in 40% of them. Finally, pressor hyporesponsiveness to angiotensin II in animals with pancreatitis was avoided by previous administration of perindopril and N omega-nitro-L-arginine methyl ester.

CONCLUSIONS

The SAP-induced hypotension is associated with a deficient pressor responsiveness to angiotensin II and endothelin-1. The renin-angiotensin system plays an important role in the control of MAP in animals with pancreatitis.

Increased energy expenditure, dietary fat wasting, and resistance to diet-induced obesity in mice lacking renin

An overactive renin-angiotensin system is associated with obesity and the metabolic syndrome. However, the mechanisms behind it are unclear. Cleaving angiotensinogen to angiotensin I by renin is a rate-limiting step of angiotensin II production, but renin is suggested to have angiotensin-independent effects. We generated mice lacking renin (Ren1c) using embryonic stem cells from C57BL/6 mice, a strain prone to diet-induced obesity. Ren1c(-/-) mice are lean, insulin sensitive, and resistant to diet-induced obesity without changes in food intake and physical activity. The lean phenotype is likely due to a higher metabolic rate and gastrointestinal loss of dietary fat. Most of the metabolic changes in Ren1c(-/-) mice were reversed by angiotensin II administration. These results support a role for angiotensin II in the pathogenesis of diet-induced obesity and insulin resistance.

The ghrelin system in acinar cells: localization, expression, and regulation in the exocrine pancreas

OBJECTIVES

Ghrelin and its receptor are expressed abundantly in the stomach and pituitary. Recently, a ghrelin system, consisting of both ligand and receptor, has also been found to exist in the endocrine cells of pancreatic islets. This ghrelin system may play a role in regulating insulin secretion and glucose homeostasis. The aim of the present study was to investigate whether a functional ghrelin system also exists in the exocrine pancreas.

METHODS

Precise localization and expression of ghrelin and its receptor in rat pancreatic acinar cells were examined by immunocytochemistry and Western blot, whereas messenger RNA levels were examined by semiquantitative reverse transcription-polymerase chain reaction. The roles of physiological and pathophysiological conditions, such as gastric acid inhibition, starvation, and acute pancreatitis, in regulation of ghrelin and its receptor were also examined.

RESULTS

Both ghrelin and its receptor were detected, at both protein and messenger RNA levels, in the acinar cells of the exocrine pancreas. Ghrelin receptor expression was up-regulated by gastric acid inhibition and down-regulated by acute pancreatitis, whereas levels remained unchanged after food deprivation. In contrast, ghrelin expression did not exhibit significant changes in any condition.

CONCLUSIONS

Our data indicate that a ghrelin system exists in the acinar cells of the exocrine pancreas. This system is subject to regulation by physiological and pathophysiological stimuli and may thus regulate exocrine functions by paracrine and/or autocrine mechanisms.

Effects of Enalaprilat on Acute Necrotizing Pancreatitis in Rats

The aim of this study was to investigate the influence of enalaprilat on acute necrotizing pancreatitis (ANP) induced by glycodeoxycholic acid in rats. The induction of ANP resulted in a significant increase in the mortality rate, pancreatic necrosis, serum activity of amylase, alanine aminotransferase (ALT), and interleukin-6 (IL-6), lactate dehydrogenase (LDH) in bronchoalveolar lavage (BAL) fluid, serum concentration of urea, and tissue activity of myeloperoxidase (MPO) and maondialdehyde (MDA) in the pancreas and lung, and a significant decrease in concentrations of calcium, blood pressure, urine output and p0(2). The use of enalaprilat inhibited the changes in urine output, blood pressure, serum concentration of urea, p0(2), and tissue activity of MPO and MDA in the pancreas and lungs. It reduced the mortality and pancreatic damage. Enalaprilat demonstrated a beneficial effect on the course of ANP in rats; therefore, it may be used in the treatment of acute pancreatitis.

Angiotensin II type 1 receptor-dependent nuclear factor-kappaB activation-mediated proinflammatory actions in a rat model of obstructive acute pancreatitis

Angiotensin II is a key mediator of inflammation, and nuclear factor-kappaB (NF-kappaB) plays a critical role in various inflammatory diseases, including acute pancreatitis (AP). This study sought to elucidate the mechanism mediating angiotensin II involvement in angiotensin II type 1 (AT1) receptor-mediated NF-kappaB activation, and ultimately in proinflammatory actions of AP pathogenesis. A rat model of obstructive pancreatitis was induced by ligation of the common biliopancreatic duct. Pancreatic injury was determined by assessing pancreatic histology, myeloperoxidase activity, and serum interleukin-6. Protein levels of pancreatic angiotensinogen and AT1 receptor as well as NF-kappaB inhibitory subunits (IkappaBalpha and IkappaBbeta) and phospho-NF-kappaB p65, kappaB-related proteins (intercellular adhesion molecule-1, cyclooxygenase-2, and interleukin-1), and NADPH oxidase isoforms p67 and p22 were examined by Western blot. Nuclear kappaB binding activity and degree of oxidative stress were determined by electrophoretic mobility shift assay and glutathione/nitrotyrosine examination, respectively. The effects of losartan, an AT1 receptor antagonist, on NF-kappaB-mediated proinflammatory actions were also assessed. Induction of AP was associated with a time-dependent increase in pancreatic angiotensinogen levels. AT1 receptor blockade with losartan improved the pancreatic histological damage, myeloperoxidase activity, and serum interleukin-6. Losartan treatment also reduced AP-associated depletion of IkappaBbeta and elevation of phospho-NF-kappaB p65 protein expression as well as the enhanced nuclear kappaB binding activity and elevated levels of kappaB-related proteins. In addition, losartan treatment suppressed pancreatic glutathione and nitrotyrosine levels, which were consistent with decreased NADPH oxidase expression. These data provide substantial evidence that angiotensin II is involved in AT1 receptor-mediated NADPH oxidase-dependent NF-kappaB activation; thus, it might ultimately promote proinflammatory actions during AP pathogenesis.

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

Large clinical trials have shown that inhibition of the renin-angiotensin system (RAS) can delay and/or prevent the onset of Type 2 diabetes mellitus (T2DM) in high-risk individuals, such as those with hypertension or chronic heart failure. Moreover, a meta-analysis of these randomized clinical studies concluded that the mean weighted relative risk of development of T2DM was reduced by 25% in those patients treated with angiotensin II receptor blockers or angiotensin-converting enzyme inhibitors. In spite of these firm clinical data, the mechanistic pathways mediating the protective activity of RAS blockade have yet to be resolved. Of particular interest is the recently identified local pancreatic RAS and, perhaps more importantly, the finding that it is up-regulated in animal models of T2DM. This putative local RAS may regulate pancreatic islet blood flow, oxygen tension, and islet (pro)insulin biosynthesis. It might also mediate the generation of reactive oxygen species, thereby causing oxidative stress-induced pancreatic beta-cell apoptosis and fibrosis. Moreover, findings that RAS blockade improved beta-cell secretory function and cell mass in experimental animal models of Type 2 diabetes indicate that inhibition of RAS activation may play a pivotal role in protecting islet cell function, and furthermore may prevent the development of overt T2DM. Such data supporting the involvement of the local pancreatic RAS in islet function, as well as a causal relationship between RAS activation and T2DM, and RAS induced beta-cell dysfunction, mandate further investigation into the role of RAS in the pathogenesis of the progressive islet impairment observed in patients with T2DM.

The physiology of a local renin-angiotensin system in the pancreas

The systemic renin-angiotensin system (RAS) plays an important role in regulating blood pressure, electrolyte and fluid homeostasis. However, local RASs also exist in diverse tissues and organs, where they play a multitude of autocrine, paracrine and intracrine physiological roles. The existence of a local RAS is now recognized in pancreatic acinar, islet, duct, endothelial and stellate cells, the expression of which is modulated in response to physiological and pathophysiological stimuli such as hypoxia, pancreatitis, islet transplantation, hyperglycaemia, and diabetes mellitus. This pancreatic RAS has been proposed to have important endocrine and exocrine roles in the pancreas, regulating local blood flow, duct cell sodium bicarbonate secretion, acinar cell digestive enzyme secretion, islet beta-cell (pro)insulin biosynthesis, and thus, glucose-stimulated insulin release, delta-cell somatostatin secretion, and pancreatic cell proliferation and differentiation. It may further mediate oxidative stress-induced cell inflammation, apoptosis and fibrosis. Further exploration of this system would probably offer new insights into the pathogenesis of pancreatitis, diabetes, cystic fibrosis and pancreatic cancer formation. New therapeutic targets and strategies might thus be suggested.

Acute pancreatitis: animal models and recent advances in basic research

Acute pancreatitis (AP) is characterized by edema, acinar cell necrosis, hemorrhage, and severe inflammation of the pancreas. Patients with AP present with elevated blood and urine levels of pancreatic digestive enzymes, such as amylase and lipase. Severe AP may lead to systemic inflammatory response syndrome and multiorgan dysfunction syndrome, which account for the high mortality rate of AP. Although most (>80%) cases of AP are associated with gallstones and alcoholism, some are idiopathic. Although the pathogenesis of AP has not yet been elucidated, a common feature is the premature activation of trypsinogen within pancreatic tissues, which triggers autodigestion of the gland. Recent advances in basic research suggest that etiologic factors including cyclooxygenase-2, substance P, and angiotensin II may have novel roles in this disease. Basic research data obtained thus far have been based on animal models of AP ranging from mild edematous pancreatitis to severe necrotizing pancreatitis. In view of this, an adequate selection of experimental animal models is of paramount importance. Notwithstanding these animal models, it should be emphasized that none of these models mimic the clinical situation where varying degrees of severity usually occur. In this review, commonly used animal models of AP will be critically evaluated. A discussion of recent advances in our knowledge about AP risk factors is also included.

Blockade of the renin-angiotensin system improves insulin sensitivity in thermal injury

Insulin resistance after burn is associated with alterations in postreceptor insulin signaling and abnormal glucose homeostasis. The renin-angiotensin system (RAS) exerts a largely inhibitory role on insulin action and is activated after burn injury. We hypothesized that upregulation of RAS is involved in the development of insulin resistance in burned rats. We examined the possibility that an angiotensin II type 1 (AT1) receptor blocker, losartan, enhances insulin sensitivity and thereby increases glucose tolerance in thermally injured rats. A 30% body surface area burn was induced by immersion of the dorsum into water with a temperature level of 95 degrees C for 15 s. Sham-burned rats were immersed in water with a temperature level of 23 degrees C. Losartan (30 mg/kg per day) or placebo (water) was given by gavage immediately after the burn injury and daily for 3 days postburn injury, resulting in sham-burned, burn placebo, and burn losartan groups. Plasma angiotensin II levels between burn placebo and sham-burned groups were not different 3 days after burn injury. However, losartan significantly increased plasma angiotensin II levels (P < 0.05), suggesting blockade of the AT1 receptor. An oral glucose tolerance test was performed 3 days postburn injury. There was an increase in the area under the curve for insulin and the glucose insulin index in burn placebo group as compared with sham-burned group, indicating insulin resistance. Losartan treatment abolished the insulin resistance in burn as evidenced by an area under the curve for insulin and glucose insulin index lower than that in the burn placebo group and similar to that in the sham-burned group. This suggests that insulin resistance and glucose intolerance associated with burn injury is, in part, caused by RAS.

Captopril, an Angiotensin-converting enzyme inhibitor, attenuates the severity of acute pancreatitis in rats by reducing expression of matrix metalloproteinase 9

It has been reported that matrix metalloproteinase 9 (MMP-9) disrupts basement membrane and increases vascular permeability. MMP-9 therefore might participate in the pathogenesis of severe acute pancreatitis (SAP). Captopril, an angiotensin-converting enzyme inhibitor, could reduce MMP-9 expression. However, the effect of captopril on the outcome of SAP is not ascertained. The aim of this study was to determine whether captopril attenuates the severity of SAP by reducing MMP-9 expression. Thirty Sprague-Dawley rats were randomly divided into 3 groups (n = 10 for each). Rats were given intraperitoneal injection of saline (SAP group) or captopril (4 mg/kg) (treated group), and then given retrograde infusion of 5% sodium taurocholate (1.5 ml/kg) into the pancreatic duct under laparotomy to induce SAP. One group of rats, injected with saline, underwent only sham operation (Control). Experimental samples were collected at 24 hrs after the induction of SAP or sham operation. Various markers of severity of SAP, such as serum levels of amylase and trypsinogen activation peptide and the vascular permeability, were increased in rats with SAP, but were significantly decreased in captopril-treated rats (p < 0.01). Likewise, the serum MMP-9 levels and expression levels of pancreatic tissue MMP-9 were significantly higher in rats with SAP than those in captopril-treated rats and control rats (p < 0.01 for both parameters), but showed no difference between captopril-treated and control rats. These results suggest that captopril may attenuate vascular permeability by reducing MMP-9 expression in SAP, thereby ameliorating severity of the disease. The use of captopril might become a new therapeutic agent for SAP.

Angiotensin II type 1 receptor blockade improves beta-cell function and glucose tolerance in a mouse model of type 2 diabetes

We identified an angiotensin-generating system in pancreatic islets and found that exogenously administered angiotensin II, after binding to its receptors (angiotensin II type 1 receptor [AT1R]), inhibits insulin release in a manner associated with decreased islet blood flow and (pro)insulin biosynthesis. The present study tested the hypothesis that there is a change in AT1R expression in the pancreatic islets of the obesity-induced type 2 diabetes model, the db/db mouse, which enables endogenous levels of angiotensin II to impair islet function. Islets from 10-week-old db/db and control mice were isolated and investigated. In addition, the AT1R antagonist losartan was administered orally to 4-week-old db/db mice for an 8-week period. We found that AT1R mRNA was upregulated markedly in db/db islets and double immunolabeling confirmed that the AT1R was localized to beta-cells. Losartan selectively improved glucose-induced insulin release and (pro)insulin biosynthesis in db/db islets. Oral losartan treatment delayed the onset of diabetes, and reduced hyperglycemia and glucose intolerance in db/db mice, but did not affect the insulin sensitivity of peripheral tissues. The present findings indicate that AT1R antagonism improves beta-cell function and glucose tolerance in young type 2 diabetic mice. Whether islet AT1R activation plays a role in the pathogenesis of human type 2 diabetes remains to be determined.