Liver disease and the renin-angiotensin system: recent discoveries and clinical implications

Angiotensin 1-7: a peptide for preventing and treating metabolic syndrome

Angiotensin-(1-7) is one of the most important active peptides of the renin-angiotensin system (RAS) with recognized cardiovascular relevance; however several studies have shown the potential therapeutic role of Ang-(1-7) on treating and preventing metabolic disorders as well. This peptide achieves a special importance considering that in the last few decades obesity and metabolic syndrome (MS) have become a growing worldwide health problem. Angiotensin (Ang) II is the most studied component of RAS and is increased during obesity, diabetes and dyslipidemia (MS); some experimental evidence has shown that Ang II modulates appetite and metabolism as well as mechanisms that induce adipose tissue growth and metabolism in peripheral organs. Recent articles demonstrated that Ang-(1-7)/Mas axis modulates lipid and glucose metabolism and counterregulates the effects of Ang II. Based on these data, angiotensin-converting enzyme 2 (ACE2)/Ang-(1-7)/Mas pathway activation have been advocated as a new tool for treating metabolic diseases. This review summarizes the new evidence from animal and human experiments indicating the use of Ang-(1-7) in prevention and treatment of obesity and metabolic disorders.

Improving long-term outcomes after liver transplantation

Long-term survival following liver transplantation is profoundly affected by conditions unrelated to graft function. Many causes of mortality are contributed to by the metabolic syndrome. The approach to metabolic syndrome in liver transplant recipients requires consideration of transplant-specific factors, particularly immunosuppression. Enhancing long-term outcomes for liver transplant recipients necessitates minimizing the amount of immunosuppression required to prevent rejection. Studies to determine the optimal approach to minimize the impact of metabolic syndrome and complications of immunosuppression in transplant recipients are needed.

The Ang-(1-7)/Mas-1 axis attenuates the expression and signalling of TGF-β1 induced by AngII in mouse skeletal muscle

AngII (angiotensin II) induces pathological conditions such as fibrosis in skeletal muscle. In this process, AngII increases ROS (reactive oxygen species) and induces a biphasic phosphorylation of p38 MAPK (mitogen-activated protein kinase). In addition, AngII stimulates the expression and production of TGF (transforming growth factor)-β1 via a mechanism dependent on ROS production mediated by NADPH oxidase (NOX) and p38 MAPK activation. In the present study, we investigated whether Ang-(1-7) [angiotensin-(1-7)], through the Mas-1 receptor, can counteract the signalling induced by AngII in mouse skeletal muscle and cause a decrease in the expression and further activity of TGF-β1 in skeletal muscle cells. Our results show that Ang-(1-7) decreased the expression of TGF-β1 induced by AngII in a dose-dependent manner. In addition, we observed that Ang-(1-7) prevented the increase in TGF-β1 expression induced by AngII, ROS production dependent on NOX and the early phase of p38 MAPK phosphorylation. Interestingly, Ang-(1-7) also prevented the late phase of p38 MAPK phosphorylation, Smad-2 phosphorylation and Smad-4 nuclear translocation, an increase in transcriptional activity, as determined using the p3TP-lux reporter, and fibronectin levels, all of which are dependent on the TGF-β1 levels induced by AngII. We also demonstrated that Ang-(1-7) prevented the increase in TGF-β1, fibronectin and collagen content in the diaphragm of mice infused with AngII. All of these effects were reversed by the administration of A779, indicating the participation of Mas-1. In conclusion, our findings support the hypothesis that Ang-(1-7) decreases the expression and further biological activity of TGF-β1 induced by AngII in vitro and in vivo.

Angiotensin blockade does not affect fibrosis progression in recurrent hepatitis C after liver transplantation

BACKGROUND

Liver transplantation (LT) for hepatitis C virus (HCV)-related end-stage liver disease is impaired by universal disease recurrence and suboptimal response to antiviral therapy. Inhibition of angiotensin-II signalling by angiotensin-converting enzyme inhibitors (ACE-I) or angiotensin-II receptor blockers (ARB) decreases hepatic stellate cell activation in vitro and hepatic fibrogenesis in animal models. A single-center retrospective analysis suggested that angiotensin blockade (AB) inhibits fibrosis progression in recurrent HCV post-LT. This study assessed the effect of AB on fibrosis progression in an independent patient cohort.

METHODS

Chart review of all patients who underwent transplantation in our institution for HCV-related ESLD between January 2000 and February 2008 revealed 109 patients with ≥2 protocol liver biopsies and free of antiviral therapy post-LT up to the last biopsy analyzed; 27 of 109 patients were treated with ACE-I/ARB for ≥12 months, 82 were not. Fibrosis was staged using METAVIR.

RESULTS

Live-donor LT was more frequent in controls than in the AB group (25% vs 11%; P < .05). However, parameters known to affect outcome of recurrent HCV, including donor age, prevalence of diabetes, acute cellular rejection, and immunosuppression, were similar in both groups. Time between first and last biopsy (median, 23 months), stage of fibrosis, fibrosis progression rates (median 0.47 vs 0.45 unit/y; P = .46), and time to develop fibrosis stage ≥2 did not differ between groups. Results held true if deceased-donor LT were analyzed separately.

CONCLUSION

Our study does not support the contention of a previous report that use of AB reduces fibrosis progression in recurrent HCV post-LT.

Upregulation of circulating components of the alternative renin-angiotensin system in inflammatory bowel disease: A pilot study

INTRODUCTION

The relationship between intestinal inflammation and circulating components of the renin-angiotensin system (RAS) is poorly understood.

MATERIALS AND METHODS

Demographic and clinical data were obtained from healthy controls and patients with inflammatory bowel disease (IBD). Plasma concentrations of the classical RAS components (angiotensin-converting enzyme (ACE) and angiotensin II (Ang II)) and alternative RAS components (ACE2 and angiotensin (1-7) (Ang (1-7))) were analysed by radioimmuno- and enzymatic assays. Systemic inflammation was assessed using serum C-reactive protein (CRP), white cell count, platelet count and albumin, and intestinal inflammation by faecal calprotectin.

RESULTS

Nineteen healthy controls (11 female; mean age 38 years, range 23-68), 19 patients with Crohn's disease (11 female; aged 45 years, range 23-76) and 15 patients with ulcerative colitis (6 female; aged 42 years, 26-64) were studied. Circulating classical RAS component levels were similar across the three groups, whereas ACE2 activity and Ang (1-7) concentrations were higher in patients with IBD compared to controls (ACE2: 21.5 vs 13.3 pmol/ml/min, p<0.05; Ang (1-7): 22.8 vs 14.1 pg/ml, p<0.001). Ang (1-7) correlated weakly with platelet and white cell counts, but not calprotectin or CRP, in patients with IBD.

CONCLUSIONS

Circulating components of the alternative RAS are increased in patients with IBD.

A disintegrin and metalloproteinase 17 (ADAM17) mediates epidermal growth factor receptor transactivation by angiotensin II on hepatic stellate cells

AIMS

Epidermal growth factor receptor (EGFR) transactivation induced by angiotensin II (Ang II) participates in the progression of various diseases. A disintegrin and metalloproteinase 17 (ADAM17) is thought to promote renal fibrosis, cardiac hypertrophy with fibrosis and atherosclerosis by activation of the EGFR through secretion of EGFR ligands. The purpose of this study was to investigate whether Ang II-induced EGFR transactivation occurs on hepatic stellate cells (HSCs) and whether the reaction is mediated via ADAM17.

MAIN METHODS

Ang II-induced EGFR transactivation and cellular proliferation of the human HSC line LI90 were investigated using Western blotting and ATP assay, respectively. Ang II-induced secretion of mature amphiregulin into the cell culture medium was evaluated by enzyme-linked immunosorbent assay (ELISA).

KEY FINDINGS

An inhibitor of ADAM17, TAPI-1, as well as antagonists of EGFR and angiotensin II type-1 receptor (AT1), attenuated Ang II-induced EGFR transactivation and proliferation of LI90 cells. Furthermore, silencing of ADAM17 inhibited Ang II-induced secretion of mature amphiregulin in addition to EGFR transactivation.

SIGNIFICANCE

These results indicate that ADAM17 mediates Ang II-induced EGFR transactivation on HSCs, and that this process may participate in the progression of liver fibrosis.

The role of angiotensin II in nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is now considered the most prevalent chronic liver disease, affecting over 30% of the US adult population. NAFLD is strongly linked to insulin resistance and is considered the hepatic manifestation of the metabolic syndrome. Activation of the renin-angiotensin-aldosterone system (RAAS) is known to play a role in the hypertension observed in the metabolic syndrome and also is thought to play a central role in insulin resistance and NAFLD. Angiotensin II (AngII) is considered the primary effector of the physiological outcomes of RAAS signaling, both at the systemic and local tissue level. Herein, we review data describing the potential involvement of AngII-mediated signaling at multiple levels in the development and progression of NAFLD, including increased steatosis, inflammation, insulin resistance, and fibrosis. Additionally, we present recent work on the potential therapeutic benefits of RAAS and angiotensin II signaling inhibition in rodent models and patients with NAFLD.

Therapeutic potential of targeting the renin angiotensin system in portal hypertension

Portal hypertension is responsible for the bulk of the morbidity and mortality in patients with cirrhosis. Drug therapy to reduce portal pressure involves targeting two vascular beds. The first approach is to reduce intra hepatic vascular tone induced by the activity of powerful vasocontrictors such as angiotensin II, endothelin-1 and the sympathetic system and mediated via contraction of perisinusoidal myofibroblasts and pervascular smooth muscle cells. The second approach is to reduce mesenteric and portal blood flow. Non-selective β-blockers are widely used and have been shown to prolong patient survival and reduce oesophageal variceal bleeding in advanced cirrhosis. However many patients are unable to tolerate these drugs and they are ineffective in a significant proportion of patients. Unfortunately there are no other drug therapies that have proven efficacy in the treatment of portal hypertension and prevention of variceal bleeding. This review briefly outlines current therapeutic approaches to the management of portal hypertension, and the evidence supporting the role of the renin angiotensin system (RAS) and the use of RAS blockers in this condition. It will also outline recent advances in RAS research that could lead to the development of new treatments focusing in particular on the recently discovered "alternate axis" of the RAS.

Nonalcoholic fatty liver disease and the renin-angiotensin system: Implications for treatment

Nonalcoholic fatty liver disease (NAFLD) is the commonest liver disease in Western countries. Treatment of NAFLD is currently based on lifestyle measures and no effective pharmacologic treatment is available so far. Emerging evidence, mainly from animal studies, suggests that the renin-angiotensin-aldosterone system may be of major importance in the pathogenesis of NAFLD and indicates that angiotensin-converting enzyme inhibitors (ACE-I) and angiotensin receptor blockers (ARBs) as a potentially useful therapeutic approach. However, data from human studies are limited and contradictory. In addition, there are few randomized controlled trials (RCTs) on the effects of ACE-I or ARB in patients with NAFLD and most data are from retrospective studies, pilot prospective studies and post hoc analyses of clinical trials. Accordingly, more and larger RCTs are needed to directly assess the effectiveness of ACE-I and ARBs in NAFLD.

Aliskiren attenuates chronic carbon tetrachloride-induced liver injury in mice

BACKGROUND

Increased angiotensin II (Ang II) plays an important role in liver inflammation and fibrogenesis. Chronic administration of aliskiren, a newly developed direct renin inhibitor, decreases Ang II in the hypertensive patients and animals.

AIMS

Our study aims to evaluate the possible protective effects of chronic administration of aliskiren in a chronic liver injury model.

METHODS

C57BL6 mice were injected intraperitoneally with carbon tetrachloride (CCl(4)) to induce chronic liver injury. The injured mice were randomly assigned to aliskiren-treated (25 mg/kg per day for 2 weeks, the CCl(4) + Ali group) or untreated group (the CCl(4) group). Mice without CCl(4) and aliskiren administration served as the normal control.

RESULTS

In the CCl(4)-injured mice, aliskiren attenuated liver inflammation and fibrosis. The levels of hepatocyte apoptosis, lipid peroxidation production, the activation of hepatic stellate cells and Kupffer cells, hepatic expression of p47 phox, inflammatory mediators and profibrotic markers were reduced in the CCl(4) + Ali group. Furthermore, aliskiren decreased Ang II, activated the renal expression of renin, but down-regulated the hepatic expression of renin and renin receptor in the CCl(4)-injected mice.

CONCLUSIONS

Aliskiren attenuates chronic liver injury in the CCl(4)-treated mice by reducing Ang II. Direct renin inhibition may serve as a potential treatment for chronic liver injury.

Telmisartan attenuates hepatic fibrosis in bile duct-ligated rats

AIM

To evaluate the antifibrotic effect of telmisartan, an angiotensin II receptor blocker, in bile duct-ligated rats.

METHODS

Adult Sprague-Dawley rats were allocated to 3 groups: sham-operated rats, model rats underwent common bile duct ligation (BDL), and BDL rats treated with telmisartan (8 mg/kg, po, for 4 weeks). The animals were sacrificed on d 29, and liver histology was examined, the Knodell and Ishak scores were assigned, and the expression of angiotensin-converting enzyme (ACE) and ACE2 was evaluated with immunohistochemical staining. The mRNAs and proteins associated with liver fibrosis were evaluated using RTQ-PCR and Western blot, respectively.

RESULTS

The mean fibrosis score of BDL rats treated with telmisartan was significantly lower than that of the model rats (1.66±0.87 vs 2.13±0.35, P=0.015). However, there was no significant difference in inflammation between the two groups, both of which showed moderate inflammation. Histologically, treatment with telmisartan significantly ameliorated BDL-caused the hepatic fibrosis. Treatment with telmisartan significantly upregulated the mRNA levels of ACE2 and MAS, and decreased the mRNA levels of ACE, angiotensin II type 1 receptor (AT1-R), collagen type III, and transforming growth factor β1 (TGF-β1). Moreover, treatment with telmisartan significantly increased the expression levels of ACE2 and MAS proteins, and inhibited the expression levels of ACE and AT1-R protein.

CONCLUSION

Telmisartan attenuates liver fibrosis in bile duct-ligated rats via increasing ACE2 expression level.

Angiotensin II receptor type 1 blockade decreases CTGF/CCN2-mediated damage and fibrosis in normal and dystrophic skeletal muscles

Connective tissue growth factor (CTGF/CCN-2) is mainly involved in the induction of extracellular matrix (ECM) proteins. The levels of CTGF correlate with the degree and severity of fibrosis in many tissues, including dystrophic skeletal muscle. The CTGF overexpression in tibialis anterior skeletal muscle using an adenoviral vector reproduced many of the features observed in dystrophic muscles including muscle damage and regeneration, fibrotic response and decrease in the skeletal muscle strength. The renin-angiotensin system is involved in the genesis and progression of fibrotic diseases through its main fibrotic components angiotensin-II and its transducer receptor AT-1. The use of AT-1 receptor blockers (ARB) has been shown to decrease fibrosis. In this paper, we show the effect of AT-1 receptor blockade on CTGF-dependent biological activity in skeletal muscle cells as well as the response to CTGF overexpression in normal skeletal muscle. Our results show that in myoblasts ARB decreased CTGF-mediated increase of ECM protein levels, extracellular signal regulated kinases 1/2 (ERK-1/2) phosphorylation and stress fibres formation. In tibialis anterior muscle overexpressing CTGF using an adenovirus, ARB treatment decreased CTGF-mediated increase of ECM molecules, α-SMA and ERK-1/2 phosphorylation levels. Quite remarkable, ARB was able to prevent the loss of contractile force of tibialis anterior muscles overexpressing CTGF. Finally, we show that ARB decreased the levels of fibrotic proteins, CTGF and ERK-1/2 phosphorylation augmented in a dystrophic skeletal muscle from mdx mice. We propose that ARB is a novel pharmacological tool that can be used to decrease the fibrosis induced by CTGF in skeletal muscle associated with muscular dystrophies.

Long-term medical management of the liver transplant recipient: what the primary care physician needs to know

Recognition, management, and prevention of medical complications and comorbidities after liver transplant is the key to improved long-term outcomes. Beyond allograft-related complications, metabolic syndrome, cardiovascular disease, renal dysfunction, and malignancies are leading causes of morbidity and mortality in this patient population. Primary care physicians have an important role in improving outcomes of liver transplant recipients and are increasingly relied on for managing these complex patients. This review serves to assist the primary care physician in the long-term management issues of liver transplant recipients.

Update on new aspects of the renin-angiotensin system in liver disease: clinical implications and new therapeutic options

The RAS (renin-angiotensin system) is now recognized as an important regulator of liver fibrosis and portal pressure. Liver injury stimulates the hepatic expression of components of the RAS, such as ACE (angiotensin-converting enzyme) and the AT(1) receptor [AngII (angiotensin II) type 1 receptor], which play an active role in promoting inflammation and deposition of extracellular matrix. In addition, the more recently recognized structural homologue of ACE, ACE2, is also up-regulated. ACE2 catalyses the conversion of AngII into Ang-(1-7) [angiotensin-(1-7)], and there is accumulating evidence that this 'alternative axis' of the RAS has anti-fibrotic, vasodilatory and anti-proliferative effects, thus counterbalancing the effects of AngII in the liver. The RAS is also emerging as an important contributor to the pathophysiology of portal hypertension in cirrhosis. Although the intrahepatic circulation in cirrhosis is hypercontractile in response to AngII, resulting in increased hepatic resistance, the splanchnic vasculature is hyporesponsive, promoting the development of the hyperdynamic circulation that characterizes portal hypertension. Both liver fibrosis and portal hypertension represent important therapeutic challenges for the clinician, and there is accumulating evidence that RAS blockade may be beneficial in these circumstances. The present review outlines new aspects of the RAS and explores its role in the pathogenesis and treatment of liver fibrosis and portal hypertension.

Elevated serum angiotensin converting enzyme levels as a reflection of bone marrow renin-angiotensin system activation in multiple myeloma

INTRODUCTION

Angiotensin converting enzyme (ACE) is a circulating enzyme that participates in the body's renin-angiotensin system (RAS) and is localized on the endothelial cell surface in the lung and other vascular beds. It catalyses the conversion of decapeptide angiotensin I to octapeptide angiotensin II. In the present study, we aimed to analyse the possible relationship between the levels of ACE in the context of RAS in multiple myeloma (MM) pathogenesis.

MATERIALS AND METHODS

The study was conducted on 25 MM patients (13 males, 12 females; median age 66 years, range 47-88) and 20 healthy controls. The clinical features of MM patients including demographics and laboratory findings were summarized. Serum ACE levels were measured by using commercially available kits.

RESULTS

The serum ACE levels of MM patients and controls were 32.60±20.26 and 15.35±6.47 respectively. Serum ACE levels were significantly higher in MM patients compared with control groups (p<0.001).

CONCLUSIONS

Being an important component of RAS, circulating ACE might be associated with clonal proliferation of malignant plasma cells in the bone marrow microenvironment. Identification of the pathobiological activity of the local RAS in MM would enlighten the biologic basis and clinical management of haematologic disorders.

Review article: the pathophysiological roles of the renin-angiotensin system in the gastrointestinal tract

BACKGROUND

The renin-angiotensin system (RAS) is a homeostatic pathway widely known to regulate cardiovascular and renal physiology; however, little is known about its influence in gastrointestinal tissues.

AIM

To elicit the anatomical distribution and physiological significance of the components of the RAS in the gastrointestinal tract.

METHODS

An extensive online literature review including Pubmed and Medline.

RESULTS

There is evidence for RAS involvement in gastrointestinal physiology and pathophysiology, with all the components required for autonomous regulation identified throughout the gastrointestinal tract. The RAS is implicated in the regulation of glucose, amino acid, fluid and electrolyte absorption and secretion, motility, inflammation, blood flow and possibly malignant disease within the gastrointestinal tract. Animal studies investigating the effects of RAS blockade in a range of conditions including inflammatory bowel disease, functional gut disorders, gastrointestinal malignancy and even intestinal ischaemia have been encouraging to date. Given the ready availability of drugs that modify the RAS and their excellent safety profile, an opportunity exists for investigation of their possible therapeutic role in a variety of human gastrointestinal diseases.

CONCLUSIONS

The gastrointestinal renin-angiotensin system appears to be intricately involved in a number of physiological processes, and provides a possible target for novel investigative and therapeutic approaches.

Serum angiotensin-converting enzyme level as a marker of fibrosis in patients with chronic hepatitis B

BACKGROUND

and aims: Hepatitis B virus (HBV) infection is a public health problem and affects nearly 350 million people worldwide. The present study was conducted in order to investigate the role of circulating angiotensin-converting enzyme (ACE) in the context of renin-angiotensin-aldosterone in newly diagnosed chronic hepatitis B infection. Moreover the association between liver fibrosis and serum ACE levels was also investigated.

MATERIALS AND METHODS

The study was performed on 50 chronic hepatitis B (CHB) patients (24 males, 26 females; median age 39.4 years, range 18-63) and 20 healthy controls. The clinical features of CHB patients including demographics, laboratory and liver biopsy findings were summarized. Serum ACE levels were measured by using commercially available kits.

RESULTS

Serum median ACE levels were 48.4 (14-83) U/L and 26.2 (12-48) U/L for the CHB patients and controls, respectively. Serum ACE levels were significantly higher in patients with CHB compared with the control group (p<0.001). Twenty-two patients (44%) had advanced liver fibrosis (Ishak score >2) and 28 patients (56%) had mild liver fibrosis (Ishak score ≤ 2). Mean serum levels of ACE were significantly higher among patients with advanced fibrosis as compared with those without advanced fibrosis (60.3±14.2 U/L vs. 39.0±10.5 U/L, p<0.001). Receiver operating characteristic (ROC) curve analysis suggested that the optimum ACE level cut-off point for advanced fibrosis was 52.5 U/L (sensitivity: 81.8%, specificity: 82.1%, PPV 78.3%, NPV 85.2%, accuracy 82%, AUC: 0.890).

CONCLUSIONS

Our study showed that elevated circulating ACE levels are commonly observed in CHB patients. This finding was more prominent in patients with advanced fibrosis in liver. When evaluating a patient along with other parameters, the inclusion of ACE levels in the evaluation of CHB patients may grant additional prognostic information.

Increased ACE in extrahepatic cholangiocarcinoma as a clue for activated RAS in biliary neoplasms

AIM

Cholangiocarcinoma (CCA) is a primary neoplastic tumor of the epithelial lining of the biliary tree which carries a poor prognosis despite combined therapeutic strategies. Although the exact etiology remains obscure, it has been suggested that locally produced Angiotensin II (Ang II) in intrahepatic CCA tissues plays a key role in the proliferation and activation of CCA. In the present study, we aimed to analyze the relationship between the levels of circulating angiotensin converting enzyme (ACE), an important molecule of the renin-angiotensin system (RAS), and biliary disorders.

PATIENTS AND METHODS

The study group comprised 19 extrahepatic cholangiocarcinoma (EHCC) (16 patients with hilar, three patients with distal CCA), and 15 choledocolithiasis (CL) patients, with 15 controls. Median age of EHCC, CL and healthy controls were 67 (48-82), 65 (29-87) and 56 (23-74) respectively. ACE was measured by monitoring the alteration in absorbance at 340 nm of the hydrolysis of furylacrylolylphenylalanylglycylglycine (FAPGG) to FAP and GG on an analyzer. The ACE activity in the sample was determined by comparing the sample reaction rate to that obtained with the ACE calibrator.

RESULTS

Serum mean ACE levels were 56.6±27.4 U/L, 32.9±14.6 U/L and 28.6±10.6 U/L for patients with EHCC, CL and healthy controls, respectively. Serum ACE levels were significantly higher in patients with EHCC compared to CL and control groups. No significant differences with respect to ACE levels were observed between CL and control groups.

CONCLUSION

Circulating ACE in the context of RAS might be associated with EHCC development by creating a local environment enriched with cytokines and other growth factors that may promote cholangiocyte turnover.

A meta-analysis of the association between angiotensin-converting enzyme insertion/deletion gene polymorphism and steroid-sensitive nephrotic syndrome in children

BACKGROUND AND OBJECTIVE

Angiotensin-converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism correlates with circulating and cellular ACE concentration. Association between ACE I/D gene polymorphism and steroid-sensitive nephrotic syndrome (SSNS) risk in children is still controversial. This meta-analysis was performed to evaluate the relation between ACE I/D gene polymorphism and SSNS susceptibility in children.

METHODS

The relevant investigations were screened from the search engines of PubMed, Cochrane Library and CBM-disc (China Biological Medicine Database) as of 1 March 2011, and eligible studies were synthesized using meta-analysis methods.

RESULTS

Ten studies were identified for the analysis of association between ACE I/D gene polymorphism and SSNS risk in children, including seven in Asians, one for Caucasians and two in Africans. There was no markedly positive association between D allele or DD genotype and SSNS susceptibility in Asians, Caucasians and Africans (D: Asians OR = 1.24, p = 0.28; Caucasians OR = 1.61, p = 0.15; Africans OR = 1.61, p = 0.53; DD: Asians OR = 1.72, p = 0.15; Caucasians OR = 1.39, p = 0.48; Africans OR = 1.80, p = 0.56). Furthermore, II homozygous seemed not to play a protective role against SSNS onset for Asians, Caucasians and Africans (Asians OR = 0.95, p = 0.85; Caucasians OR = 0.30, p = 0.11; Africans OR = 0.60, p = 0.65).

CONCLUSIONS

There was no association between ACE I/D gene polymorphism and SSNS susceptibility in Asians, Caucasians and Africans. However, the conclusions for Caucasians and Africans were less powerful.

Association of angiotensin converting enzyme insertion/deletion gene polymorphism with idiopathic nephrotic syndrome susceptibility in children: a meta-analysis

Background and objective: Angiotensin converting enzyme (ACE) gene contains either an insertion (I) allele or a deletion (D) allele forming three potential genotypes: II, ID and DD. The D allele or DD genotype has been reported to be associated with higher plasma ACE level. An assessment of the association between ACE I/D gene polymorphism and idiopathic nephrotic syndrome (INS) susceptibility in children is still controversial. This meta-analysis was performed to evaluate the association between ACE I/D gene polymorphism and the onset of INS.

Method: A predefined literature search and selection of eligible relevant studies were performed to collect data from electronic databases, and eligible investigations were synthesized using the meta-analysis method.

Results: Nine investigations were identified for the analysis of association between ACE I/D gene polymorphism and INS risk in children, including six in Asians, one study for Caucasians and two for Africans. There was positive association between D allele or DD genotype and INS susceptibility in Asians (OR = 1.75, p = 0.01; OR = 2.01, p = 0.02), but not for Caucasian children and Africans (for Caucasians, D: OR=1.35, p = 0.27, DD: OR = 0.95, p = 0.91; for Africans, D: OR = 1.70, p = 0.56, DD: OR = 1.60, p = 0.73). Furthermore, II homozygous seemed to play a positive role against INS onset for Asians (OR = 0.59, p = 0.02), but the link between II genotype and INS risk was not observed in Caucasian children and Africans (Caucasians: OR = 0.31, p = 0.06; Africans: OR = 0.50, p = 0.59).

Conclusions: D allele and DD homozygous might become significant genetic molecular markers for INS susceptibility in Asian children, but the association was not observed in Caucasians or Africans. However, the conclusion from our study cannot be sustained and more investigations on larger sample in different populations are required to further clarify the role of D allele or DD homozygous in the onset of INS in difference races.

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

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

β-Amino acid substitution to investigate the recognition of angiotensin II (AngII) by angiotensin converting enzyme 2 (ACE2)

In spite of the important role of angiotensin converting enzyme 2 (ACE2) in the cardiovascular system, little is known about the substrate structural requirements of the AngII-ACE2 interaction. Here we investigate how changes in angiotensin II (AngII) structure affect binding and cleavage by ACE2. A series of C3 β-amino acid AngII analogs were generated and their secondary structure, ACE2 inhibition, and proteolytic stability assessed by circular dichroism (CD), quenched fluorescence substrate (QFS) assay, and LC-MS analysis, respectively. The β-amino acid-substituted AngII analogs showed differences in secondary structure, ACE2 binding and proteolytic stability. In particular, three different subsets of structure-activity profiles were observed corresponding to substitutions in the N-terminus, the central region and the C-terminal region of AngII. The results show that β-substitution can dramatically alter the structure of AngII and changes in structure correlated with ACE2 inhibition and/or substrate cleavage. β-amino acid substitution in the N-terminal region of AngII caused little change in structure or substrate cleavage, while substitution in the central region of AngII lead to increased β-turn structure and enhanced substrate cleavage. β-amino acid substitution in the C-terminal region significantly diminished both secondary structure and proteolytic processing by ACE2. The β-AngII analogs with enhanced or decreased proteolytic stability have potential application for therapeutic intervention in cardiovascular disease.

The association between angiotensin-converting enzyme insertion/deletion gene variant and risk of focal segmental glomerulosclerosis: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

The association of the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism with the risk of focal segmental glomerulosclerosis (FSGS) is still controversial. A meta-analysis was performed to evaluate the association between ACE I/D gene polymorphism and FSGS susceptibility.

METHOD

We performed a predefined literature search and selection of eligible relevant studies to collect data from electronic databases.

RESULTS

In total, 12 articles were identified for the analysis of the association between ACE I/D gene polymorphism and FSGS risk. One report included an investigation in Arab and Jewish populations separately. Thus, there were seven reports in Asians, two in Caucasians, one in Africans, two in Arabs and one in Jews. In Asians, there was a markedly positive association between the D allele or DD genotype and FSGS susceptibility (p = 0.008; p = 0.002), and the II genotype may play a protective role against FSGS onset (p = 0.002). However, a link between ACE I/D gene polymorphism and FSGS risk was not found in Caucasians, Africans, Arabs or Jews (Caucasians: D: p = 0.11, DD: p = 0.19, II: p = 0.70; Africans: D: p = 0.40, DD: p = 0.49, II: p = 0.61; Arabs: D: p = 0.34, DD: p = 0.10, II: p = 0.42; Jews: D: p = 0.90, DD: p = 0.97, II: p = 0.83).

CONCLUSION

The D allele or DD homozygosity may become a significant genetic molecular marker for the onset of FSGS in Asians, but not for Caucasians, Africans, Arabs or Jews.

ACE I/D gene polymorphism can't predict the steroid responsiveness in Asian children with idiopathic nephrotic syndrome: a meta-analysis

Background

The results from the published studies on the association between angiotensin-converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism and the treatment response to steroid in Asian children with idiopathic nephrotic syndrome (INS) is still conflicting. This meta-analysis was performed to evaluate the relation between ACE I/D gene polymorphism and treatment response to steroid in Asian children and to explore whether ACE D allele or DD genotype could become a predictive marker for steroid responsiveness.

Methodology/Principal Findings

Association studies were identified from the databases of PubMed, Embase, Cochrane Library and CBM-disc (China Biological Medicine Database) as of September 1, 2010, and eligible investigations were synthesized using meta-analysis method. Five investigations were identified for the analysis of association between ACE I/D gene polymorphism and steroid-resistant nephrotic syndrome (SRNS) risk in Asian children and seven studies were included to explore the relationship between ACE I/D gene polymorphism and steroid-sensitive nephrotic syndrome (SSNS) susceptibility. Five investigations were recruited to explore the difference of ACE I/D gene distribution between SRNS and SSNS. There was no a markedly association between D allele or DD genotype and SRNS susceptibility or SSNS risk, and the gene distribution differences of ACE between SRNS and SSNS were not statistically significant. II genotype might play a positive role against SRNS onset but not for SSNS (OR = 0.51, P = 0.02; OR = 0.95, P = 0.85; respectively), however, the result for the association of II genotype with SRNS risk was not stable.

Conclusions/Significance

Our results indicate that D allele or DD homozygous can't become a significant genetic molecular marker to predict the treatment response to steroid in Asian children with INS.

Relationship between Angiotensin-Converting Enzyme Insertion/Deletion Gene Polymorphism and Susceptibility of Minimal Change Nephrotic Syndrome: A Meta-Analysis

Aim. This meta-analysis was performed to evaluate the association between ACE I/D gene polymorphism and MCNS susceptibility. Method. A predefined literature search and selection of eligible relevant studies were performed to collect the data from electronic databases. Results. Six articles were identified for the analysis of association between ACE I/D gene polymorphism and MCNS risk, including 4 for Asians, one in Caucasian population and one for Africans. There was a markedly positive association between D allele or DD genotype and MCNS susceptibility in Asians (D: P = .01, DD: P = .02), but not for Caucasians and Africans (Caucasians: D: P = .16, DD: P = .98; Africans: D: P = .81, DD: P = .49). Furthermore, the II genotype seemed not to play a protective role against MCNS risk for Asians, Caucasians and Africans (P = .12, P = .09, P = .76, resp.). Interestingly, there was also significant association between ACE I/D gene polymorphism and MCNS susceptibility in overall populations (D: P = .007, DD: P = .04, II: P = .03). Conclusion. D allele or DD genotype might be a significant genetic molecular marker for MCNS susceptibility in Asians and overall populations, but not for Caucasians and Africans. More larger and rigorous genetic epidemiological investigations are required to further explore this association.

The role of the renin-angiotensin system in liver fibrosis

Hepatic fibrosis, which is characterized by progressive inflammation and deposition of extracellular matrix components, is a common response to chronic liver disease. Hepatic fibrogenesis is a dynamic process that involves several liver cell types including hepatic stellate cells and Kupffer cells. In addition, recent evidence indicates that bile duct epithelial cells (i.e. cholangiocytes) also participate in the progression of biliary fibrosis that is observed during chronic cholestatic liver diseases, such as primary sclerosing cholangitis. To date, there are no effective treatments for hepatic fibrosis. Several recent studies have demonstrated that the renin-angiotensin system (RAS) plays a key role in hepatic fibrosis. Therapies targeting the RAS may represent a promising paradigm for the prevention and treatment of hepatic fibrosis in the setting of chronic liver disease. In this review, we provide a comprehensive update on the role of RAS in the pathogenesis of hepatic fibrosis in both animal models and human studies. We will discuss the profibrotic mechanisms activated by the RAS and the cell types involved. Studies that have utilized angiotensin receptor blockers (ARBs) and angiotensin-converting enzyme (ACE) inhibitors to modulate the RAS in order to ameliorate hepatic fibrosis will also be discussed. Although the cumulative evidence supports the potential for the use of ARBs and ACE inhibitors as treatment for hepatic fibrosis, extensive studies of the effectiveness of RAS therapeutics are necessary in patients with chronic liver disease.

Pharmacologic inhibition of the renin-angiotensin system did not attenuate hepatic toxicity induced by carbon tetrachloride in rats

The renin-angiotensin system (RAS) subserves vital physiological functions and also implicated in certain pathological states. Modulation of this system has been proposed in recent studies to be a promising strategy in treating liver fibrosis. We investigated the effect of the pharmacologic inhibition of RAS with angiotensin-converting enzyme inhibitor or angiotensin receptor blocker in CCl4-induced liver injury with a view to ascertaining the chemopreventive benefit. Fifty-six Wistar albino rats were divided into eight experimental groups of seven rats/group. Groups 1–4 received normal saline (10 ml/kg), enalapril (0.6 mg/kg), losartan (1.4 mg/kg) and CCl4 (80 mg/kg), respectively. Groups 5–8 were pretreated with enalapril (0.3 mg/kg), enalapril (0.6 mg/kg), losartan (0.7 mg/kg) and losartan (1.4 mg/kg) 1 hour before CCl4 administration. Experiment lasted 11 days and dosing was via oral route. Rats were killed 24 hours after the last treatment. Serum activities of alkaline phosphatase, aspartate and alanine aminotransferases increased significantly ( p < 0.05) by 46.0%, 90.6% and 122.3%, respectively, with severe hepatic centrilobular necrosis, fatty infiltration and increase in liver weight ( p < 0.05) in the CCl4-treated rats. Enalapril (0.6 mg/kg) and losartan (1.4 mg/kg) significantly ( p < 0.05) increased aspartate aminotransferase activity by 37.0% and 94.7% and produced mild centrilobular and periportal hepatic necrosis, respectively, with enalapril significantly ( p < 0.05) increasing liver weight. Serum total cholesterol, triglyceride, albumin and total protein did not change significantly in these rats. Also, glutathione, malondialdehyde and uric acid levels were not significantly altered. Enalapril and losartan failed to attenuate liver injury associated with CCl4 treatment. Although both drugs did not significantly alter serum biochemistry in the CCl4-treated rats, they however produced slight elevations in biomarkers of liver function and appear to worsen liver histopathology. Overall, the chemopreventive benefits of RAS inhibitors in liver disease remain doubtful and should be used with caution during hepatic dysfunction.

The renin-angiotensin system and the gastrointestinal mucosa

The gastrointestinal (GI) tract is fundamental for the intake of fluid and electrolytes and accommodates a large proportion of bodily hemodynamics and host defence systems. Despite that the renin-angiotensin system (RAS) is a prominent regulatory system for fluid and electrolyte homeostasis its impact on GI physiology is only little explored. Recent data indicate that RAS is well expressed and active in the GI tract although exact physiological roles are to be settled. There are several reports showing influences by RAS and its key mediator angiotensin II (AngII) on intestinal epithelial fluid and electrolyte transport and data are accumulating, suggesting involvement in GI mucosal inflammation and carcinogenesis. Of particular interest is the increasing amount of experimental support for the involvement of AngII formation and actions via the AngII subtype 1 (AT1) receptor in the pathogenesis and treatment of inflammatory bowel disease. The picture of RAS in the GI tract is, however, far from complete. Because RAS is an important application area for reno-cardiovascular diseases, a number of pharmacological agents as well as research technologies already exist and can in the future be used for GI research. A marked expansion of knowledge concerning the role of RAS in GI physiology and pathophysiology is to be expected.

Advances in understanding the role of the UII/UT system in the pathogenesis of portal hypertension

Urotensin II (UII), a vasoactive peptide with structural similarity to somatostatin, is the most potent vasoconstrictor known in systemic resistance vessels and has multiple biological effects related to a variety of human diseases. Numerous studies have found that UII and its receptor (UT) play an important role in the pathogenesis of portal hypertension. This paper reviews the recent advances in understanding the role of the UII/UT system in the pathogenesis of portal hypertension.

Preservation of basal AcSDKP attenuates carbon tetrachloride-induced fibrosis in the rat liver

BACKGROUND & AIMS

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous tetrapeptide which has antifibrogenic effects at physiological concentrations in various tissues. AcSDKP is produced locally in the liver, however, little is known about its biological effect in this organ. We hypothesize that basal levels of endogenous AcSDKP decrease during the development of liver fibrosis and preservation of basal AcSDKP attenuates liver fibrosis.

METHODS

Endogenous levels of AcSDKP in the liver were measured by enzyme immunoassay after 2, 6, and 10 weeks of carbon tetrachloride (CCl(4))-induced liver fibrosis in rats. Subcutaneous osmotic pump infusion of vehicle or AcSDKP (800 microg/kg/day) was administered to CCl(4)-treated rats for 8 weeks to study the effect of exogenous AcSDKP on liver fibrosis. The effect of AcSDKP on profibrogenic properties of hepatic stellate cells was studied in vitro.

RESULTS

Endogenous AcSDKP was significantly decreased in the liver of CCl(4)-treated rats. Chronic AcSDKP infusion preserved basal levels of AcSDKP and reduced liver injury, inflammation, fibrosis, and profibrogenic transforming growth factor-beta signaling. This was demonstrated by decreased aminotransferase serum levels, CD45 positive cells, collagen accumulation, alpha-smooth muscle actin positivity, transforming growth factor-beta1, phosphorylated Smad2/3 protein, increased bone morphogenetic protein-7, and phosphorylated Smad1/5/8. Further, AcSDKP exerts antifibrogenic effects on hepatic stellate cells (HSCs) by downregulation of HSC activation in vitro.

CONCLUSIONS

Maintaining physiological levels of AcSDKP is critical in negatively regulating the development of fibrosis in chronic liver injury. Preservation of AcSDKP may be a useful therapeutic approach in the management of liver fibrosis.

Treatment options for primary sclerosing cholangitis

Primary sclerosing cholangitis is a cholestatic liver disease characterized by inflammation and fibrosis of intra-/extrahepatic bile ducts, leading to multifocal strictures. Primary sclerosing cholangitis exhibits a progressive course resulting in cirrhosis and the need for liver transplantation over a median period of 12 years. The disease is frequently associated with inflammatory bowel disease and carries an increased risk of colorectal cancer and cholangiocarcinoma. Despite extensive research, there is currently no effective medical treatment. Multiple drugs are shown to be ineffective in halting disease progression, including ursodeoxycholic acid, the most widely evaluated drug. High-dose ursodeoxycholic acid (28-30 mg/kg/day) was recently shown to increase the adverse events rate. Endoscopic or radiological dilatation of a 'dominant' stricture may lead to symptomatic and biochemical improvement. However, liver transplantation is the only life-prolonging treatment for patients with end-stage disease. Studies with promising drugs, such as antibiotics, antifibrotic agents and bile acid derivatives, are eagerly awaited.

Angiotensin II signaling through the AT1a and AT1b receptors does not have a role in the development of cerulein-induced chronic pancreatitis in the mouse

The intraorgan renin-angiotensin system (RAS) plays an important role in the pathophysiology of a variety of diseases and has been implicated in fibrogenesis. The role of RAS in the development of chronic pancreatitis is not well established. The blockade of RAS in rat models with angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptor 1 (AT1) blockers (ARBs) mostly have reduced pancreatic inflammation and fibrosis with a few exceptions. At the same time, the use of ACEi and ARBs in humans is associated with a modest risk of acute pancreatitis. The aim of this study was to elucidate the effect of the AT1 signaling pathway in the development of pancreatitis using AT1a- and AT1b-deficient mice as well as the ARB losartan. Chronic pancreatitis was induced by repetitive cerulein administration in C57BL/6J wild-type (WT) and AT1a- and AT1b-deficient mice (AT1a-/- and AT1b-/-), and pancreatic injury was assessed at day 10. Pancreatic weight of cerulein treated groups was significantly reduced. There was severe parenchymal atrophy and fibrosis assessed by histological examination. Fibrosis was accompanied by activation of pancreatic stellate cells (PSC) evaluated by Western blot analysis for alpha-smooth muscle actin. No differences were seen between cerulein-treated WT, AT1a-/- , AT1b-/- mice, or losartan treated-WT mice with regards to morphological or molecular alterations induced by cerulein. Our results demonstrate that AT1a and AT1b receptor pathways do not seem to be essential for the development of pancreatitis in the mouse model of pancreatitis induced by repetitive cerulein injury.

Metabolic syndrome and liver transplantation: a review and guide to management

Metabolic syndrome is common among liver transplant recipients before and after transplantation. The components of metabolic syndrome are often exacerbated in the post-transplant period by transplant specific factors, such as immunosuppression, and are strong predictors of patient morbidity and mortality. Many aspects of the metabolic syndrome are modifiable. Early recognition, prevention and treatment of post-transplant hypertension, obesity, dyslipidemia and diabetes may impact long-term post-transplant survival. Further study into the prevention and management of these issues in the transplant patient are needed.

Local RAS

The concept of a circulating RAS is well established and known to play an endocrine role in the regulation of fluid homeostasis (see Section 4.1, Chapter 4). However, it is more appropriate to view the RAS in the contemporary notion as an “angiotensin-generating system”, which consists of angiotensinogen, angiotensin-generating enzymes, and angiotensins, as well as their receptors. Some RASs can be termed as “complete”, having renin and ACE involved in the biosynthesis of angiotensin II peptide, i.e. in a renin and/or ACE-dependent manner which is exemplified in the circulating RAS. On the other hand, some RAS can be termed as “partial”, having alternate enzymes to renin and ACE, such as chymase and ACE2 (see Section 4.3, Chapter 4) available for the generation of angiotensin II and other bioactive angiotensin peptides in the biosynthetic cascade, i.e. in a renin and/or ACE-independent manner. Complete vs. partial RASs can be exemplified in the so-called intrinsic angiotensin-generating system or local RAS; for example, a local and functional RAS with renin and ACE-dependent but a renin-independent pathway have been indentified in the pancreas and carotid body, respectively. In the past two decades, local RASs have gained increasing recognition especially with regards to their clinical importance. Distinct from the circulating RAS, these functional local RASs exist in such diverse tissues and organs as the pancreas, liver, intestine, heart, kidney, vasculature, carotid body, and adipose, as well as the nervous, reproductive, and digestive systems. Taken into previous findings from our laboratory and others together, Table 5.1 is a summary of some recently identified local RASs in various levels of tissues and organs.

Role of angiotensin II in liver fibrosis-induced portal hypertension and therapeutic implications

Angiotensin II (AT-II) is a peptide that plays an important role in the renin-angiotensin-aldosterone (RAA) system. Traditionally, the RAA system has been related with states of systemic hypertension and hypoperfusion as a counterbalance mechanism. Recently, AT-II has been studied for its properties in the process of fibrosis in several organs, especially in the liver. AT-II is capable to stimulate the activated hepatic stellate cells, which increase expression of profibrogenic molecules like tumor growth factor-beta, tissue inhibitor of metalloproteinase-1 and collagen I, among others. At the same time, AT-II is implied in the hemodynamic balance of cirrhosis and portal hypertension. Due to its profibrogenic and vasoactive properties, blockade of AT-II actions constitutes an important therapeutic target to inhibit fibrotic processes and reduction of risk of complications of portal hypertension as well. Some drugs like angiotensin-converting enzyme inhibitors or the angiotensin II receptor blockers have been studied as alternatives for the treatment of patients with cirrhosis with promising results. Nonetheless, additional research is required in order to consider these drugs as a part of the integral treatment of the patient with cirrhosis and portal hypertension.

Advances in the renin angiotensin system focus on angiotensin-converting enzyme 2 and angiotensin-(1-7)

The contribution of the renin angiotensin system to physiology and pathology is undergoing a rapid reconsideration of its mechanisms from emerging new concepts implicating angiotensin-converting enzyme 2 and angiotensin-(1-7) as new elements negatively influencing the vasoconstrictor, trophic, and pro-inflammatory actions of angiotensin II. This component of the system acts to oppose the vasoconstrictor and proliferative effects on angiotensin II through signaling mechanisms mediated by the mas receptor. In addition, a reduced expression of the vasodepressor axis composed by angiotensin-converting enzyme 2 and angiotensin-(1-7) may contribute to the expression of essential hypertension, the remodeling of heart and renal function associated with this disease, and even the physiology of pregnancy and the development of eclampsia.

Fatty liver and lipotoxicity

Fatty liver disease comprises a spectrum ranging from simple steatosis to steatohepatitis which can progress to liver cirrhosis and hepatocellular cancer. Hepatic lipotoxicity may ensue when the hepatic capacity to utilize, store and export fatty acids (FA) as triglycerides is overwhelmed. Additional mechanisms of hepatic lipotoxicity include abnormal FA oxidation with formation of reactive oxygen species, disturbances in cellular membrane FA and phospholipid composition, alterations of cholesterol content and ceramide signalling. Lipotoxicity is a key factor for the progression of fatty liver disease by inducing hepatocellular death, activating Kupffer cells and an inflammatory response, impairing hepatic insulin signalling resulting in insulin resistance, and activation of a fibrogenic response in hepatic stellate cells that can ultimately lead to cirrhosis. Therefore, the concept of hepatic lipotoxicity should be considered in future therapeutic concepts for fatty liver disease.

Portal pressure responses and angiotensin peptide production in rat liver are determined by relative activity of ACE and ACE2

Angiotensin converting enzyme (ACE) 2 activity and angiotensin-(1-7) [Ang-(1-7)] levels are increased in experimental cirrhosis; however, the pathways of hepatic Ang-(1-7) production have not been studied. This study investigated the role of ACE2, ACE, and neutral endopeptidase (NEP) in the hepatic formation of Ang-(1-7) from angiotensin I (Ang I) and Ang II and their effects on portal resistance. Ang I or Ang II were administered to rat bile duct ligated (BDL) and control livers alone and in combination with the ACE inhibitor lisinopril, the ACE and NEP inhibitor omapatrilat, or the ACE2 inhibitor MLN4760 (n = 5 per group). BDL markedly upregulated ACE, ACE2, and NEP. Ang-(1-7) was produced from Ang II in healthy and in BDL livers and was increased following ACE inhibition and decreased by ACE2 inhibition. In contrast, Ang-(1-7) production from Ang I was minimal and not affected by ACE or NEP inhibition. Surprisingly, ACE2 inhibition in BDLs dramatically increased Ang-(1-7) production from Ang I, an effect abolished by ACE2/NEP inhibition. Ang II and Ang I induced greater portal pressure increases in BDL livers than controls. The effects of Ang I were closely correlated with Ang II production and were strongly attenuated by both ACE and ACE/NEP inhibition. These findings show that the major substrate for hepatic production of Ang-(1-7) is Ang II and this is catalyzed by ACE2. Ang I is largely converted to Ang II by ACE, and net conversion of Ang I to Ang-(1-7) is small. NEP has the ability to generate large amounts of Ang-(1-7) in the BDL liver from Ang I only when ACE2 activity is greatly decreased or inhibited.

Renin-angiotensin system in the pathogenesis of liver fibrosis

Hepatic fibrosis is considered a common response to many chronic hepatic injuries. It is a multifunctional process that involves several cell types, cytokines, chemokines and growth factors leading to a disruption of homeostatic mechanisms that maintain the liver ecosystem. In spite of many studies regarding the development of fibrosis, the understanding of the pathogenesis remains obscure. The hepatic tissue remodeling process is highly complex, resulting from the balance between collagen degradation and synthesis. Among the many mediators that take part in this process, the components of the Renin angiotensin system (RAS) have progressively assumed an important role. Angiotensin (Ang) II acts as a profibrotic mediator and Ang-(1-7), the newly recognized RAS component, appears to exert a counter-regulatory role in liver tissue. We briefly review the liver fibrosis process and current aspects of the RAS. This review also aims to discuss some experimental evidence regarding the participation of RAS mediators in the pathogenesis of liver fibrosis, focusing on the putative role of the ACE2-Ang-(1-7)-Mas receptor axis.

Angiotensin II activates I kappaB kinase phosphorylation of RelA at Ser 536 to promote myofibroblast survival and liver fibrosis

BACKGROUND & AIMS

The transcription factor nuclear factor-kappaB (NF)-kappaB promotes survival of hepatic myofibroblasts and fibrogenesis through poorly defined mechanisms. We investigated the activities of angiotensin II and I kappaB kinase (IKK) in regulation of NF-kappaB activity and the role of these proteins in liver fibrosis in rodents and humans.

METHODS

Phosphorylation of the NF-kappaB subunit RelA at serine 536 (P-Ser(536)-RelA) was detected by immunoblot and immunohistochemical analyses. P-Ser(536)-RelA function was assessed using vectors that expressed mutant forms of RelA, cell-permeable blocking peptides, and assays for RelA nuclear transport and apoptosis. Levels of P-Ser(536)-RelA were compared with degree of fibrosis in liver sections from chronically injured rats and patients with hepatitis C virus-mediated fibrosis who had been treated with the AT1 antagonist losartan.

RESULTS

Constitutive P-Ser(536)-RelA is a feature of human hepatic myofibroblasts, both in vitro and in situ in diseased livers. Autocrine angiotensin II stimulated IKK-mediated phosphorylation of RelA at Ser(536), which was required for nuclear transport and transcriptional activity of NF-kappaB. Inhibition of angiotensin II, the angiotensin II receptor type 1 (AT1), or IKK blocked Ser(536) phosphorylation and stimulated myofibroblast apoptosis. Treatment of fibrotic rodent liver with the angiotensin converting enzyme (ACE) inhibitor captopril or the IKK inhibitor sulphasalazine resulted in loss of P-Ser(536)-RelA-positive myofibroblasts and fibrosis regression. In human liver samples, increased numbers of P-Ser(536)-RelA-positive cells were associated with fibrosis that regressed following exposure to losartan.

CONCLUSIONS

An autocrine pathway that includes angiotensin II, IKK, and P-Ser(536)-RelA regulates myofibroblast survival and can be targeted to stimulate therapeutic regression of liver fibrosis.

Effect of propranolol on the splanchnic and peripheral renin angiotensin system in cirrhotic patients

AIM: To evaluate the effect of β-blockade on angiotensins in the splanchnic and peripheral circulation of cirrhotic patients and also to compare hemodynamic parameters during liver transplantation according to propranolol pre-treatment or not.

METHODS: Patients were allocated into two groups: outpatients with advanced liver disease(LD) and during liver transplantation(LT). Both groups were subdivided according to treatment with propranolol or not. Plasma was collected through peripheral venipuncture to determine plasma renin activity(PRA), Angiotensin(Ang) I, Ang II, and Ang-(1-7) levels by radioimmunoassay in LD group. During liver transplantation, hemodynamic parameters were determined and blood samples were obtained from the portal vein to measure renin angiotensin system(RAS) components.

RESULTS: PRA, Ang I, Ang II and Ang-(1-7) were significantly lower in the portal vein and periphery in all subgroups treated with propranolol as compared to non-treated. The relationships between Ang-(1-7) and Ang I levels and between Ang II and Ang I were significantly increased in LD group receiving propranolol. The ratio between Ang-(1-7) and Ang II remained unchanged in splanchnic and peripheral circulation in patients under β-blockade, whereas the relationship between Ang II and Ang I was significantly increased in splanchnic circulation of LT patients treated with propranolol. During liver transplantation, cardiac output and index as well systemic vascular resistance and index were reduced in propranolol-treated subgroup.

CONCLUSION: In LD group, propranolol treatment reduced RAS mediators, but did not change the ratio between Ang-(1-7) and Ang II in splanchnic and peripheral circulation. Furthermore, the modification of hemodynamic parameters in propranolol treated patients was not associated with changes in the angiotensin ratio.