Expression of renin in the rat liver

Renin–Angiotensin System in Liver Metabolism: Gender Differences and Role of Incretins

The impaired hepatic lipids and carbohydrates metabolism result in various metabolic disorders, including obesity, diabetes, insulin resistance, hyperlipidemia and metabolic syndrome. The renin–angiotensin system (RAS) has been identified in the liver and it is now recognized as an important modulator of body metabolic processes. This review is intended to provide an update of the impact of the renin–angiotensin system on lipid and carbohydrate metabolism, regarding gender difference and prenatal undernutrition, specifically focused on the role of the liver. The discovery of angiotensin-converting enzyme 2 (ACE2) has renewed interest in the potential therapeutic role of RAS modulation. RAS is over activated in non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma. Glucagon-like peptide-1 (GLP-1) has been shown to modulate RAS. The GLP-I analogue liraglutide antagonizes hepatocellular steatosis and exhibits liver protection. Liraglutide has a negative effect on the ACE/AngII/AT1R axis and a positive impact on the ACE2/Ang(1-7)/Mas axis. Activation of the ACE2/Ang(1-7)/Mas counter-regulatory axis is able to prevent liver injuries. Angiotensin(1-7) and ACE2 shows more favorable effects on lipid homeostasis in males but there is a need to do more investigation in female models. Prenatal undernutrition exerts long-term effects in the liver of offspring and is associated with a number of metabolic and endocrine alterations. These findings provide a novel therapeutic regimen to prevent and treat many chronic diseases by accelerating the effect of the ACE2/Ang1-7/Mas axis and inhibiting the ACE/AngII/AT1R axis.

Up-regulation of components of the renin-angiotensin system in the bile duct-ligated rat liver

BACKGROUND & AIMS

Angiotensin II (ANG II) has profibrotic actions in the heart and kidney, whereas blockade of the renin angiotensin system (RAS) attenuates injury. This study examines whether the RAS is present in the liver and examines its regulation in the bile duct-ligation model of hepatic fibrogenesis.

METHODS

Sham-operated and bile duct-ligated (BDL) Sprague-Dawley rats were studied. Gene and protein expression of hepatic renin, angiotensinogen, angiotensin-converting enzyme (ACE), and the angiotensin receptors AT1 and AT2 were assessed using real-time reverse-transcription polymerase chain reaction, in vitro autoradiography, and immunohistochemistry.

RESULTS

Angiotensinogen and renin messenger RNA were detected in sham liver but were not increased following BDL. Angiotensinogen protein was widely distributed in hepatocytes in both normal and injured livers, but in BDL livers, it was also expressed within areas of active fibrogenesis. Both ACE and AT1 receptor genes were up-regulated following BDL. The low level of ACE activity in sham animals was significantly increased in areas of active fibrogenesis in BDL livers. The AT1 receptor was present in both normal and diseased liver parenchyma, with increased AT1 receptor binding seen in fibrotic areas in the diseased liver. The AT2 receptor gene was not detected in normal or diseased liver.

CONCLUSIONS

Key elements of the RAS are present in normal liver tissue, and there is major up-regulation of the system in the bile duct-ligated liver. These findings are in keeping with recent experimental studies that have demonstrated antifibrotic effects of RAS blockade in the bile duct-ligated liver.

Effect of angiotensin II type 1 receptor blockade on experimental hepatic fibrogenesis

BACKGROUND/AIMS

The aim of this study was to investigate whether in the liver, as in other tissues, there is evidence that angiotensin II, acting via the angiotensin II type 1 receptor (AT1-R), plays a role in fibrogenesis.

METHODS

Sprague-Dawley rats were divided into three groups; sham, bile duct ligated (BDL) and BDL + AT1-R antagonist, irbesartan. Real time RT-PCR was utilised to assess gene expression of the AT1 receptor, TGF-beta1 and alpha1 (I) collagen in the liver. TGF-beta1 and alpha1 (I) collagen mRNA expression and localisation were also assessed by in situ hybridisation. TGF-beta1 activity was assessed by using the TGF-beta inducible gene product betaig-h3. Fibrosis was assessed by the Knodell scoring system, tissue hydroxyproline content and picro-sirius red staining.

RESULTS

Real time RT-PCR revealed that there was a 6-fold up-regulation in AT1 receptor expression in BDL animals compared with shams. This was associated with marked increases in TGF-beta1, betaig-h3 and alpha1 (I) collagen gene expression which were attenuated by AT1-RA treatment. However, AT1-RA therapy produced no significant change in liver histology or hydroxyproline content.

CONCLUSIONS

These results suggest that in the liver angiotensin II may play an important role in the fibrogenic response to injury. However, whether treatment with an AT1-RA will be of therapeutic benefit remains to be determined.