Anti-fibrogenic function of angiotensin II type 2 receptor in CCl4-induced liver fibrosis

The Renin-Angiotensin System in Liver Disease

The renin-angiotensin system (RAS) is a complex homeostatic entity with multiorgan systemic and local effects. Traditionally, RAS works in conjunction with the kidney to control effective arterial circulation, systemic vascular resistance, and electrolyte balance. However, chronic hepatic injury and resulting splanchnic dilation may disrupt this delicate balance. The role of RAS in liver disease, however, is even more extensive, modulating hepatic fibrosis and portal hypertension. Recognition of an alternative RAS pathway in the past few decades has changed our understanding of RAS in liver disease, and the concept of opposing vs. "rebalanced" forces is an ongoing focus of research. Whether RAS inhibition is beneficial in patients with chronic liver disease appears to be context-dependent, but further study is needed to optimize clinical management and reduce organ-specific morbidity and mortality. This review presents the current understanding of RAS in liver disease, acknowledges areas of uncertainty, and describes potential areas of future investigation.

An Egg White-Derived Peptide Enhances Systemic Insulin Sensitivity and Modulates Markers of Non-Alcoholic Fatty Liver Disease in Obese, Insulin Resistant Mice

Non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, is a global health problem. Currently, no pharmacological treatment is approved for NAFLD. Natural health products, including bioactive peptides, are potential candidates to aid in the management of metabolic syndrome-related conditions, including insulin resistance and obesity. In this study, we hypothesized that an egg-white-derived bioactive peptide QAMPFRVTEQE (Peptide 2) would improve systemic and local white adipose tissue insulin sensitivity, thereby preventing high-fat diet-induced exacerbation of pathological features associated with NAFLD, such as lipid droplet size and number, inflammation, and hepatocyte hypertrophy in high-fat diet-fed mice. Similar to rosiglitazone, Peptide 2 supplementation improved systemic insulin resistance during the hyperinsulinemic-euglycemic clamp and enhanced insulin signalling in white adipose tissue, modulating ex vivo lipolysis. In the liver, compared with high-fat diet fed animals, Peptide 2 supplemented animals presented decreased hepatic cholesterol accumulation (p < 0.05) and area of individual hepatic lipid droplet by around 50% (p = 0.09) and reduced hepatic inflammatory infiltration (p < 0.05) whereas rosiglitazone exacerbated steatosis. In conclusion, Peptide 2 supplementation improved insulin sensitivity and decreased hepatic steatosis, unlike the insulin-sensitizing drug rosiglitazone.

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.

ASK1 Enhances Angiotensin II-Induced Liver Fibrosis In Vitro by Mediating Endoplasmic Reticulum Stress-Dependent Exosomes

Background

Apoptosis signal-regulating kinase 1 (ASK1) has been reported to induce fibrotic signaling in the setting of oxidative stress. However, the role of ASK1 and its mechanism of action in angiotensin II- (Ang II-) induced liver fibrosis remain largely unknown.

Methods

Human hepatic LX-2 stellate cells were treated with Ang II alone or cotreated with Ang II plus an ASK1 inhibitor (GS-4997) or siRNA-targeting ASK1. Immunofluorescent staining, real-time PCR, and western blotting were used to determine the expressionof α-SMA, Col I, and Col III expression. Cell viability was assessed by the CCK-8 assay. The concentrations of IL-1β, IL-18, and TNF-α in conditioned medium were determined by ELISA. The levels of intracellular ROS in LX-2 cells were analyzed using a ROS assay kit. Exosome size was determined by electron microscopy.

Results

Ang II markedly increased the expression of extracellular matrix (ECM) proteins (α-SMA, Col I, and Col III) and proinflammatory cytokines (IL-1β, IL-18, and TNF-α). Ang II also increased the expression of endoplasmic reticulum stress (ERS) markers (GRP78, p-PERK, and CHOP) and p-ASK1. Results also showed that pretreatment with GS-4997 or siRNA could abolish all the abovementioned effects on LX-2 cells. Furthermore, we found that exosome release caused by ASK1-mediated ERS was involved in the activation of LX-2 cells by Ang II. The activation of LX-2 cells could be blocked by treating the exosomes with annexin.

Conclusions

In summary, we found that ASK1 mediates Ang II-activated ERS in HSCs and the subsequent activation of HSCs, suggesting a promising strategy for treating liver fibrosis.

Activation of AT2 receptors prevents diabetic complications in female db/db mice by NO-mediated mechanisms

BACKGROUND AND PURPOSE

The AT₂ receptor plays a role in metabolism by opposing the actions triggered by the AT₁ receptors. Activation of AT₂ receptors has been shown to enhance insulin sensitivity in both normal and insulin resistance animal models. In this study, we investigated the mechanism by which AT₂ receptors activation improves metabolism in diabetic mice.

EXPERIMENTAL APPROACH

Female diabetic (db/db) and non-diabetic (db/+) mice were treated for 1 month with the selective AT₂ agonist, compound 21 (C21, 0.3 mg·kg^-1 ·day^-1 , s.c.). To evaluate whether the effects of C21 depend on NO production, a subgroup of mice was treated with C21 plus a sub-pressor dose of the NOS inhibitor l-NAME (0.1 mg·ml^-1 , drinking water).

KEY RESULTS

C21-treated db/db mice displayed improved glucose and pyruvate tolerance compared with saline-treated db/db mice. Also, C21-treated db/db mice showed reduced liver weight and decreased hepatic lipid accumulation compared with saline-treated db/db mice. Insulin signalling analysis showed increased phosphorylation of the insulin receptor, Akt and FOXO1 in the livers of C21-treated db/db mice compared with saline-treated counterparts. These findings were associated with increased adiponectin levels in plasma and adipose tissue and reduced adipocyte size in inguinal fat. The beneficial effects of AT₂ receptors activation were associated with increased eNOS phosphorylation and higher levels of NO metabolites and were abolished by l-NAME.

CONCLUSION AND IMPLICATIONS

Chronic C21 infusion exerts beneficial metabolic effects in female diabetic db/db mice, alleviating type 2 diabetes complications, through a mechanism that involves NO production.

Pathways of hepatic and renal damage through non-classical activation of the renin-angiotensin system in chronic liver disease

In liver cirrhosis, renin-angiotensin system (RAS) activation sustains renal sodium retention and hepatic fibrogenesis. New information has recently enlivened the traditional concept of RAS. For instance, renin and prorenin bind their ubiquitous receptors, resulting in the local production of angiotensin (Ang) II; increased serum calcium and calcimimetic agents, through stimulation of extracellular calcium-sensing receptors (CaSR), blunt renin production and lead to natriuretic effects in human and experimental cirrhosis. Alongside systemic production, there is Ang II tissue production within various organs through RAS enzymes different from angiotensin-converting enzyme (ACE), that is chymase, tissue plasminogen activator and several cathepsins. In experimental cirrhosis, inhibition of chymase leads to natriuretic and hepatic antifibrotic effects, without changes in systemic haemodynamics. In the kidney, local RAS coordinates proximal and distal tubular sodium reabsorption. However, renalase, whose plasma and tissue levels are severely altered in experimental cirrhosis, degrades systemic and renal tubule catecholamines, antagonizing the effects of renal RAS. Angiotensinogen-derived natriuretic and vasodilating peptides (Ang1-9, Ang1-7, Ang3-8) and their receptors have been described. Receptor agonists or antagonists are available to affect portal hypertension and sodium retention in cirrhosis. ACE2-dependent generation of Ang1-7 may inhibit experimental liver fibrosis. inhibition of Ang1-7 clearance by means of neprilysin blockade has portal hypotensive and natriuretic effects. Ang1-12, whose production renin does not regulate, is converted to several different angiotensin peptides via chymase. Finally, Ang II behaves as either an antinatriuretic or a natriuretic agent, based on the tissue content of AT₁ R and AT₂ R receptors, their ratio being prone to pharmacological modulation.

Hepatoprotective potential of Ferula communis extract for carbon tetrachloride induced hepatotoxicity and oxidative damage in rats

We investigated the hepatoprotective potential of Ferula communis extract for CCI₄ induced liver damage. We used six groups of rats: group 1, untreated control; group 2, CCl₄ treated (hepatotoxic); group 3, treated with 150 mg/kg F. communis; group 4, treated with 300 mg/kg F. communis; group 5, treated with CCl₄ + 150 mg/kg F. communis; and group 6, treated with CCl₄ + 300 mg/kg F. communis. Liver damage was produced by injection of 1 ml/kg CCI₄ twice/week. Extracts of F. communis, 150 and 300 mg/kg/day, were administered for 8 weeks. The effects of F. communis were assessed by measuring aspartate aminotransferase (AST), alanine aminotransferase (ALT), γ-glutamyl transferase (GGT) and total bilirubin (T-BIL) levels, and the activities of antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase (GPx) in the liver. The histology and immunohistochemistry of liver tissue were evaluated using hematoxylin and eosin staining, and caspase 3 and 8-OHdG immunostaining. F. communis extract produced significant reductions in elevated levels of ALT, AST, GGT and T-BIL and increased levels of GPx and SOD in rats treated with CCl₄. F. communis extract decreased CCl₄ induced 8-OHdG formation and caspase 3 activation significantly in hepatocytes, especially at the 150 mg/kg dose. Our findings demonstrate the potential efficacy of F. communis for attenuating CCl₄ induced hepatotoxicity and oxidative damage.

Renin-angiotensin system inhibition ameliorates CCl4-induced liver fibrosis in mice through the inactivation of nuclear transcription factor kappa B

Therapeutic interventions for liver fibrosis are still limited due to the complicated molecular pathogenesis. Renin-angiotensin system (RAS) seems to contribute to the development of hepatic fibrosis. Therefore, we aimed to examine the effect of RAS inhibition on CCl₄-induced liver fibrosis. Mice were treated with silymarin (30 mg·kg^-1), perindopril (1 mg·kg^-1), fosinopril (2 mg·kg^-1), or losartan (10 mg·kg^-1). The administration of RAS inhibitors improved liver histology and decreased protein expression of alpha smooth muscle actin (α-SMA) and hepatic content of hydroxyproline. These effects found to be mediated via inactivation of nuclear transcription factor kappa B (NFκB) pathway by the inhibition of NFκB p65 phosphorylation at the Ser536 residue and phosphorylation-induced degradation of nuclear factor kappa-B inhibitor alpha (NFκBia) subsequently inhibited NFκB-induced TNF-α and TGF-β1, leading to lower levels of tissue inhibitor of metalloproteinase-1 (TIMP-1) and vascular endothelial growth factor (VEGF). We concluded that the tissue affinity of the angiotensin converting enzyme inhibitors (ACEIs) has no impact on its antifibrotic activity and that interfering the RAS either through the inhibition of ACE or the blockade of AT1R has the same therapeutic benefit. These results suggest RAS inhibitors as promising candidates for further clinical trials in the management of hepatic fibrosis.

Sildenafil, a phosphodiesterase-5 inhibitor, offers protection against carbon tetrachloride-induced hepatotoxicity in rat

BACKGROUND

Elevation of phosphodiesterase-5 (PDE5) activity converts cyclic guanosine monophosphate (cGMP) to 5'-GMP, a mechanism that could be associated with drug-mediated hepatotoxicity. This study investigated whether selective inhibition of PDE5 by sildenafil could offer protection against hepatotoxicity induced by carbon tetrachloride (CCl4).

METHODS

CCl4 (0.5 mL/kg) was administered intraperitoneally to induce hepatotoxicity. The control group received normal saline. Sildenafil (5 mg, 10 mg, and 20 mg/kg, p.o.) was administered to CCl4-treated rats.

RESULTS

CCl4 significantly increased the serum levels of gamma glutamyl transferase (γ-GT), alkaline phosphatase (ALP), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) and reduced total protein (TP) (p<0.05). Pretreatment with sildenafil moderately reduced ALP, AST, and ALT activities with modest increase in TP level. CCl4-induced changes in the antioxidant status of the liver were significantly improved by sildenafil, especially at the lowest dose of 5 mg/kg by elevating the levels of reduced glutathione (GSH), glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) and preventing lipid peroxidation (p<0.05). Sildenafil did not significantly alter the total cholesterol and triglyceride levels. However, high-density lipoprotein (HDL) level was significantly increased by sildenafil (p<0.05).

CONCLUSIONS

The results from this study suggest that sildenafil, when used at low doses, may be a useful pharmacological protective agent against CCl4-induced hepatotoxicity.

AT2 receptor agonist Compound 21: A silver lining for diabetic nephropathy

The currently available therapies for diabetic nephropathy, one of the leading causes of renal failure globally are based on inhibition of renin angiotensin system. However, recently, the focus has shifted towards activation of its protective arm rather than the inhibition of deteriorative axis, using specific agonists. Compound 21 (C21), a novel non-peptide Angiotensin II type 2 receptor (AT₂) agonist, recently granted orphan drug status for the treatment of a rare disease, idiopathic pulmonary fibrosis has also shown a potent anti-inflammatory, anti-fibrotic, antioxidant and anti-apoptotic potential in various diseases including heart failure, myocardial infarction, chronic inflammatory diseases, and neurological diseases such as ischemic stroke. A pool of evidences suggest that C21, either alone or in combination with angiotensin receptor blockers could be extremely beneficial in the treatment of diabetic nephropathy, a chronic inflammatory condition sharing its pathogenesis with aforementioned diseases. The review analyses the new therapeutic tool, C21, its mechanisms of action for renoprotection in diabetic nephropathy, and its future perspectives and thereby provides an insight into the potential application of C21 as a novel therapeutic tool in the eradication of diabetic nephropathy.

Anti-fibrotic Potential of AT2 Receptor Agonists

There are a number of therapeutic targets to treat organ fibrosis that are under investigation in preclinical models. There is increasing evidence that stimulation of the angiotensin II type 2 receptor (AT₂R) is a novel anti-fibrotic strategy and we have reviewed the published in vivo preclinical data relating to the effects of compound 21 (C21), which is the only nonpeptide AT₂R agonist that is currently available for use in chronic preclinical studies. In particular, the differential influence of AT₂R on extracellular matrix status in various preclinical fibrotic models is discussed. Collectively, these studies demonstrate that pharmacological AT₂R stimulation using C21 decreases organ fibrosis, which has been most studied in the setting of cardiovascular and renal disease. In addition, AT₂R-mediated anti-inflammatory effects may contribute to the beneficial AT₂R-mediated anti-fibrotic effects seen in preclinical models.

The expression of ETAR in liver cirrhosis and liver cancer

BACKGROUND

To investigate the expression of endothelin receptors in liver diseases and discuss its role in the process of liver cirrhosis and liver cancer.

RESEARCH DESIGN AND METHODS

We examined the expressions of ETAR, ETBR and α-SMA in tissue samples using western blotting analysis. Furthermore, immunofluorescence was used to locate ETAR expression in hepatic stellate cells (HSCs) and hepatic sinusoidal endothelial cells (HSECs), we calculated the percentage of positive cells and then analyzed its relation with clinical indexes.

RESULTS

According to the western blotting analysis, the expression of ETAR was high in hepatic hemangioma and liver cancer tissues and ETBR was highly expressed in cirrhosis tissues. The immunofluorescence results demonstrated that the expression of ETAR was elevated in hepatic hemangioma and liver cancer tissues. Moreover, ETAR expression was found in both HSCs and HSECs. Finally, the statistical analysis revealed that the number of positive ETAR cells was correlated with the clinical index platelets (PLT), alanine transaminase (ALT) and diameter of portal vein.

CONCLUSION

Endothelin receptors express differently in liver cirrhosis and liver cancer tissues and play a role in hepatic diseases by affecting HSCs and HSECs.

Role of renin-angiotensin system in liver diseases: an outline on the potential therapeutic points of intervention

The current review aimed to outline the functions of the renin angiotensin system (RAS) in the context of the oxidative stress-associated liver disease. Areas covered: Angiotensin II (Ang II) as the major effector peptide of the RAS is a pro-oxidant and fibrogenic cytokine. Mechanistically, NADPH oxidase (NOX) is a multicomponent enzyme complex that is able to generate reactive oxygen species (ROS) as a downstream signaling pathway of Ang II which is expressed in liver. Ang II has a detrimental role in the pathogenesis of chronic liver disease through possessing pro-oxidant, fibrogenic, and pro-inflammatory impact in the liver. The alternative axis (ACE2/Ang(1-7)/mas) of the RAS serves as an anti-inflammatory, antioxidant and anti-fibrotic component of the RAS. Expert commentary: In summary, the use of alternative axis inhibitors accompanying with ACE2/ Ang(1-7)/mas axis activation is a promising new strategy serving as a novel therapeutic option to prevent and treat chronic liver diseases.

Molecular Cues Guiding Matrix Stiffness in Liver Fibrosis

Tissue and matrix stiffness affect cell properties during morphogenesis, cell growth, differentiation, and migration and are altered in the tissue remodeling following injury and the pathological progression. However, detailed molecular mechanisms underlying alterations of stiffness in vivo are still poorly understood. Recent engineering technologies have developed powerful techniques to characterize the mechanical properties of cell and matrix at nanoscale levels. Extracellular matrix (ECM) influences mechanical tension and activation of pathogenic signaling during the development of chronic fibrotic diseases. In this short review, we will focus on the present knowledge of the mechanisms of how ECM stiffness is regulated during the development of liver fibrosis and the molecules involved in ECM stiffness as a potential therapeutic target for liver fibrosis.

Amomum cardamomum L. ethyl acetate fraction protects against carbon tetrachloride-induced liver injury via an antioxidant mechanism in rats

Background

Medicinal herb-derived drug development has become important in the relief of liver pathology. Amomun cardamomum is traditionally used therapeutically in Korea to treat various human ailments including dyspepsia, hiccupping, and vomiting. We investigated to assess the protective effect of A. cardamomum on carbon tetrachloride (CCl₄)-induced liver damage through antioxidant activity in hepatic tissues of Sprague–Dawley rats.

Methods

Antioxidant properties of different fractions from A. cardamomum from ethanol extracts were evaluated by an in vitro free radical scavenging systems. The protective effect of the ethyl acetate fraction from A. cardamomum (EAAC) against CCl₄-induced cytotoxicity was determined by a cell viability assay using HepG2 hepatocarcinoma cells. In vivo study, the influence of EAAC concentrations of 100 and 200 mg/kg following CCl₄-induced hepatic injury was assessed. Serum levels of glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), and alkaline phosphatase (ALP) were determined, as was lipid peroxidation (malondialdehyde, MDA). Effect of EAAC on liver detoxification enzymes including superoxide dismutase (SOD), total glutathione (GSH), and glutathione S-transferase (GST) activity was measured in rat liver homogenates. Liver cytochrome P450 (CYP2E1) expression level was determined by quantification of mRNA.

Results

Phytochemical analysis of A. cardamomum indicated that EAAC was enriched in total polyphenol and total flavonoid. Most of the tannins were confined to the hexane fraction. Hepatoprotective properties of EAAC were evident, with significantly reduced serum levels of GOT, GPT, and ALP compared with the control group. Improved hepatic antioxidant status was evident by increased SOD, GSH, and GST enzymes in rat liver tissue. Liver lipid peroxidation induced by CCl₄ was apparent by increased intracellular MDA level. EAAC suppressed lipid peroxidation as evidenced by the significant decrease in MDA production. Expression of CYP2E1 was also significantly decreased at the higher concentration of EAAC, indicating the hepatoprotective efficacy of EAAC on acute liver damage.

Conclusion

These results indicated that EAAC has a significant hepatoprotective activity on CCl₄-induced acute hepatic injury in rats, which might be derived from its antioxidant properties and CYP2E1 downregulation.

Angiotensin-converting enzyme inhibitor prevents oxidative stress, inflammation, and fibrosis in carbon tetrachloride-treated rat liver

Hepatic fibrosis is a common feature of chronic liver injury, and the involvement of angiotensin II in such process has been studied earlier. We hypothesized that anti-angiotensin II agents may be effective in preventing hepatic fibrosis. In this study, Long Evans female rats were used and divided into four groups such as Group-I, Control; Group-II, Control + ramipril; Group-III, CCl4; and Group-IV, CCl4 + ramipril. Group II and IV are treated with ramipril for 14 d. At the end of treatment, the livers were removed, and the level of hepatic marker enzymes (aspartate aminotransferase, Alanine aminotransferase, and alkaline phosphatase), nitric oxide, advanced protein oxidation product , catalase activity, and lipid peroxidation were determined. The degree of fibrosis was evaluated through histopathological staining with Sirius red and trichrome milligan staining. Carbon-tetrachloride (CCl4) administration in rats developed hepatic dysfunction and raised the hepatic marker enzymes activities significantly. CCl4 administration in rats also produced oxidative stress, inflammation, and fibrosis in liver. Furthermore, angiotensinogen-inhibitor ramipril normalized the hepatic enzymes activities and improved the antioxidant enzyme catalase activity. Moreover, ramipril treatment ameliorated lipid peroxidation and hepatic inflammation in CCl4-treated rats. Ramipril treatment also significantly reduced hepatic fibrosis in CCl4-administered rats. In conclusion, our investigation suggests that the antifibrotic effect of ramipril may be attributed to inhibition of angiotensin-II mediated oxidative stress and inflammation in liver CCl4-administered rats.

Impact of hepatic immunoreactivity of angiotensin-converting enzyme 2 on liver fibrosis due to non-alcoholic steatohepatitis

BACKGROUND

We aimed to evaluate the hepatic immunoreactivity of angiotensin-converting enzyme 2 (ACE2) in non-alcoholic steatohepatitis (NASH) patients, elucidate its association with the clinicopathological characteristics and also determine its role in fibrosis progression.

METHODS

The consecutive biopsy proven NASH patients were subdivided into two groups according to their fibrosis score. Fibrotic stages<3 in mild fibrosis group and fibrotic stages ≥ 3 in advanced fibrosis depending on the presence of bridging fibrosis. Liver biopsy specimens were immunohistochemically stained for ACE2 immunoreactivity. Demographics and clinical properties were compared between the groups. Univariate and multivariate analysis were also performed to evaluate the independent predicting factors for the presence of advanced liver fibrosis caused by NASH.

RESULTS

One hundred and eight patients were enrolled in the study. Out of this, ninety-four patients representing 87% were classified as mild fibrosis group, whilst fourteen representing 13% were in advanced fibrosis group. We compared high hepatic immunoreactivity of ACE2 between mild and advanced fibrosis groups and found a statistically significant difference 65.9% vs 28.5%, respectively and P=0.008. Hepatic ACE2 immunoreactivity was inversely correlated with the fibrosis score (r: -0.337; P<0.001). The significant variables in the univariate analysis were then evaluated in multivariate logistic regression analysis and hepatic ACE2 immunoreactivity was an independent predicting factor of liver fibrosis [odds ratio (OR): 0.194; 95% confidence interval (CI): 0.082-0.897, P=0.036].

CONCLUSION

Hepatic immunoreactivity of ACE2 was inversely correlated with the liver fibrosis among biopsy proven NASH patients and it was also an independent predicting factor of advanced fibrosis.

Protective effects of Carissa opaca fruits against CCl4-induced oxidative kidney lipid peroxidation and trauma in rat

BACKGROUND

Carbon tetrachloride (CCl4) is a potent nephrotoxin, as it causes acute as well as chronic toxicity in kidneys. Therefore, this study was carried out to assess the pharmacological potential of different fractions of Carissa opaca fruits on CCl4-induced oxidative trauma in the kidney.

METHODS

The parameters studied in this respect were the kidney function tests viz, serum profile, urine profile, genotoxicity, characteristic morphological findings, and antioxidant enzymatic level of kidneys.

RESULT

The protective effects of various fractions of C. opaca fruits against CCl4 administration were reviewed by rat renal function alterations. Chronic toxicity caused by 8-week treatment of CCl4 to the rats significantly decreased the pH level, activities of antioxidant enzymes, and glutathione contents, whereas a significant increase was found in the case of specific gravity, red blood cells, white blood cells, level of urea, and lipid peroxidation in comparison to control group. Administration of various fractions of C. opaca fruit with CCl4 showed protective ability against CCl4 intoxication by restoring the urine profile, activities of antioxidant enzymes, and lipid peroxidation in rat. CCl4 induction in rats also caused DNA fragmentation and glomerular atrophy by means of dilation, disappearance of Bowmen's space, congestion in the capillary loops, dilation in renal tubules, and foamy look of epithelial cells of tubular region, which were restored by co-admiration of various fractions of C. opaca.

CONCLUSION

Results revealed that the methanolic fractions of C. opaca are the most potent and helpful in kidney trauma.

The pathophysiologic basis of abdominal aortic aneurysm progression: a critical appraisal

An aneurysm of the abdominal aorta is a common pathology and a major cause of sudden death in the elderly. Currently, abdominal aortic aneurysms (AAAs) can only be treated by surgery and an effective medical therapy is urgently missing. The pathophysiology of AAAs is complex and is believed to be best described as a comprehensive inflammatory response with an accompanying proteolytic imbalance; the latter being held responsible for the progressive weakening of the aortic wall. Remarkably, while interference in inflammatory and/or proteolytic cascades proves highly effective in preclinical studies, emerging clinical studies consistently fail to show a benefit. In fact, some anti-inflammatory interventions appear to adversely influence the disease process. Altogether, recent clinical observations not only challenge the prevailing concepts of AAA progression, but also raise doubt on the translatability of findings from rodent models for growing AAA.

Selective activation of angiotensin AT2 receptors attenuates progression of pulmonary hypertension and inhibits cardiopulmonary fibrosis

BACKGROUND AND PURPOSE

Pulmonary hypertension (PH) is a devastating disease characterized by increased pulmonary arterial pressure, which progressively leads to right-heart failure and death. A dys-regulated renin angiotensin system (RAS) has been implicated in the development and progression of PH. However, the role of the angiotensin AT2 receptor in PH has not been fully elucidated. We have taken advantage of a recently identified non-peptide AT2 receptor agonist, Compound 21 (C21), to investigate its effects on the well-established monocrotaline (MCT) rat model of PH.

EXPERIMENTAL APPROACH

A single s.c. injection of MCT (50 mg·kg(-1) ) was used to induce PH in 8-week-old male Sprague Dawley rats. After 2 weeks of MCT administration, a subset of animals began receiving either 0.03 mg·kg(-1) C21, 3 mg·kg(-1) PD-123319 or 0.5 mg·kg(-1) A779 for an additional 2 weeks, after which right ventricular haemodynamic parameters were measured and tissues were collected for gene expression and histological analyses.

KEY RESULTS

Initiation of C21 treatment significantly attenuated much of the pathophysiology associated with MCT-induced PH. Most notably, C21 reversed pulmonary fibrosis and prevented right ventricular fibrosis. These beneficial effects were associated with improvement in right heart function, decreased pulmonary vessel wall thickness, reduced pro-inflammatory cytokines and favourable modulation of the lung RAS. Conversely, co-administration of the AT2 receptor antagonist, PD-123319, or the Mas antagonist, A779, abolished the protective actions of C21.

CONCLUSIONS AND IMPLICATIONS

Taken together, our results suggest that the AT2 receptor agonist, C21, may hold promise for patients with PH.

The protective role of ellagitannins flavonoids pretreatment against N-nitrosodiethylamine induced-hepatocellular carcinoma

Ellagitannins are esters of glucose with hexahydroxydiphenic acid; when hydrolyzed, they yield ellagic acid (EA), the dilactone of hexahydroxydiphenic acid. EA has been receiving the most attention, because it has potent antioxidant activity, radical scavenging capacity, chemopreventive and antiapoptotic properties. Hepatocellular carcinoma (HCC) is the most frequent primary malignancy of liver, and accounts for as many as one million deaths worldwide in a year. The aim of the present study was to evaluate the antioxidant and chemopreventive efficiency of ellagic acid against N-nitrosodiethylamine (NDEA) induced hepatocarcinogenesis in rats. Rats were classified into four groups as follows: normal control group, group injected i.p. with a single dose (200 mg/kg b.wt.) of NDEA, third group daily administered orally EA with a dose of 50 mg/kg b.wt. for 7 days before and 14 days after NDEA administration, and fourth group received a similar dose of EA for 21 days after the dose of NDEA administration. The model of NDEA-injected hepatocellular carcinomic (HCC) rats elicited significant declines in liver antioxidant enzyme activities; glutathione peroxidase (GPX), gamma glutamyl transferase (γ-GT) and glutathione-S-transferase (GST), with a reduction in reduced glutathione (GSH) and serum total protein with concomitant significant elevations in tumor markers arginase and α-l-fucosidase, and liver enzymes; aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and glutathione-S-transferase (GST), glucose-6-phosphate dehydrogenase (G6PD), direct and total bilirubin. The oral administration of EA as a protective agent, produced significant increases in tested antioxidant enzyme activities and serum total protein concomitant with significant decreases in the levels of tumor markers arginase and α-l-fucosidase as well as liver enzymes, direct and total bilirubin. Similarly, the oral administration of EA, as a curative agent produced similar changes to those when EA was used as a protective agent, but to a lesser extent. In addition, it was noted that HCC rats exhibited a degree of DNA fragmentation; however, EA administration partially inhibited the DNA fragmentation. Therefore, EA has the ability to scavenge free radicals, prevent DNA fragmentation, reduce liver injury and protect against oxidative stress.

Angiotensin II induces endothelin-1 expression in human hepatic stellate cells

BACKGROUND

Both angiotensin (Ang)-II and endothelin-1 (ET-1) are involved in the pathogenesis of liver fibrosis. Activated hepatic stellate cells (HSCs) are considered a key effector of liver fibrosis.

AIMS

To explore the effect of Ang-II on ET-1 expression in cultured human HSCs and the underlying mechanisms.

METHODS

Human HSCs were treated with Ang-II in different concentrations (0.1, 0.5, 1, 5, or 10 nM) for different lengths of time (0.5, 1, 2, 4, or 6 h) with or without transcription inhibitor actinomycin D, Ang-II type 1 (AT1) receptor blocker losartan, AT2 receptor blocker PD123177, or different kinase inhibitors.

RESULTS

Ang-II increased the ET-1 mRNA level in a statistically significant dose- and time-dependent manner within 4 h, which led to dose-dependent up-regulation of the ET-1 protein level. Actinomycin D (1 mg/ml), losartan (50 μM), and phosphatidylinositol-3 kinase inhibitor LY294002 (50 μM) abolished the promoting effect of Ang-II on ET-1 expression. Ang-II (10 nM) significantly increased the expression of α-smooth muscle actin and type I collagen in HSCs, which was abolished by losartan, LY294002, ET A receptor blocker BQ123, and ET-1 siRNA, but not PD123177 and ET B receptor blocker BQ788.

CONCLUSIONS

Ang-II induces ET-1 expression in human HSCs via the AT1 receptor by the PI3 K/Akt signaling pathway. The ET-1/ET A receptor axis could mediate the promoting effects of Ang-II on HSCs' transdifferentiation into myofibroblast-like cells. This is the first evidence of crosstalk between the Ang-II/AT1 axis and the ET-1 system in regard to the pathogenesis of liver fibrosis.

Non-alcoholic steatohepatitis and preneoplastic lesions develop in the liver of obese and hypertensive rats: suppressing effects of EGCG on the development of liver lesions

Non-alcoholic steatohepatitis (NASH), which involves hepatic inflammation and fibrosis, is associated with liver carcinogenesis. The activation of the renin-angiotensin system (RAS), which plays a key role in blood pressure regulation, promotes hepatic fibrogenesis. In this study, we investigated the effects of (-)-epigallocatechin-3-gallate (EGCG), a major component of green tea catechins, on the development of glutathione S-transferase placental form (GST-P)-positive (GST-P(+)) foci, a hepatic preneoplastic lesion, in SHRSP.Z-Lepr(fa)/IzmDmcr (SHRSP-ZF) obese and hypertensive rats. Male 7-week-old SHRSP-ZF rats and control non-obese and normotensive WKY rats were fed a high fat diet and received intraperitoneal injections of carbon tetrachloride twice a week for 8weeks. The rats were also provided tap water containing 0.1% EGCG during the experiment. SHRSP-ZF rats presented with obesity, insulin resistance, dyslipidemia, an imbalance of adipokines in the serum, and hepatic steatosis. The development of GST-P(+) foci and liver fibrosis was markedly accelerated in SHRSP-ZF rats compared to that in control rats. Additionally, in SHRSP-ZF rats, RAS was activated and inflammation and oxidative stress were induced. Administration of EGCG, however, inhibited the development of hepatic premalignant lesions by improving liver fibrosis, inhibiting RAS activation, and attenuating inflammation and oxidative stress in SHRSP-ZF rats. In conclusion, obese and hypertensive SHRSP-ZF rats treated with a high fat diet and carbon tetrachloride displayed the histopathological and pathophysiological characteristics of NASH and developed GST-P(+) foci hepatic premalignant lesions, suggesting the model might be useful for the evaluation of NASH-related liver tumorigenesis. EGCG might also be able to prevent NASH-related liver fibrosis and tumorigenesis.

Role of the renin-angiotensin system in liver fibrosis

Hepatic fibrosis is characterized by progressive inflammation and deposition of extracellular matrix components. Several recent studies have demonstrated that the rennin-angiotensin system (RAS) plays a key role in hepatic fibrosis. In this review, we provide a comprehensive update of the role of the RAS in the pathogenesis of hepatic fibrosis. We will discuss the profibrotic mechanisms activated by the RAS. Studies that have utilized angiotensin receptor blockers and angiotensin-converting enzyme inhibitors to modulate the RAS to ameliorate hepatic fibrosis will also be discussed.

Matrix metalloproteinase Mmp-1a is dispensable for normal growth and fertility in mice and promotes lung cancer progression by modulating inflammatory responses

Human MMP-1 is a matrix metalloproteinase repeatedly associated with many pathological conditions, including cancer. Thus, MMP1 overexpression is a poor prognosis marker in a variety of advanced cancers, including colorectal, breast, and lung carcinomas. Moreover, MMP-1 plays a key role in the metastatic behavior of melanoma, breast, and prostate cancer cells. However, functional and mechanistic studies on the relevance of MMP-1 in cancer have been hampered by the absence of an in vivo model. In this work, we have generated mice deficient in Mmp1a, the murine ortholog of human MMP1. Mmp1a(-/-) mice are viable and fertile and do not exhibit obvious abnormalities, which has facilitated studies of cancer susceptibility. These studies have shown a decreased susceptibility to develop lung carcinomas induced by chemical carcinogens in Mmp1a(-/-) mice. Histopathological analysis indicated that tumors generated in Mmp1a(-/-) mice are smaller than those of wild-type mice, consistently with the idea that the absence of Mmp-1a hampers tumor progression. Proteomic analysis revealed decreased levels of chitinase-3-like 3 and accumulation of the receptor for advanced glycation end-products and its ligand S100A8 in lung samples from Mmp1a(-/-) mice compared with those from wild-type. These findings suggest that Mmp-1a could play a role in tumor progression by modulating the polarization of a Th1/Th2 inflammatory response to chemical carcinogens. On the basis of these results, we propose that Mmp1a knock-out mice provide an excellent in vivo model for the functional analysis of human MMP-1 in both physiological and pathological conditions.

Up-regulation of components of the renin-angiotensin system in liver fibrosis in the rat induced by CCL₄

The purpose of this study was to investigate the components of renin-angiotensin system (RAS), liver function and histology in liver fibrogenesis in the rats induced by low-dose chronic carbon tetrachloride (CCL4) administration and evaluate the relationship between biochemical variables and components of RAS. Male Sprague-Dawley (SD) rats were randomly divided into the CCL4 group which received intraperitoneal injection of 40% CCL4 dissolved in olive oil every three days for four consecutive weeks (Initial dose was 5 mL/kg, other dose: 3 mL/kg) and the control group which received the same dose of olive oil. The micro-structure of the liver was examined by H&E. Hepatic Ang II and Ang(1-7) was detected. Real-time PCR and Western-blot were performed to determine the gene and protein expression of the RAS. The components of RAS were all up-regulated in CCL4 group, and the increased extent of ACE-Ang II-AT1 axis was higher than the ACE2-Ang(1-7)-Mas axis. There was a significant correlation between ACE and ACE2 gene expression, AT1 and MAS gene expression, Ang II and Ang(1-7) in the liver of rats. ACE (or ACE2) gene expression strongly correlated with the index of liver injury significantly. These results suggest hepatic fibrogenesis induced by chronic CCL4 administration may be associated with the relationship of ACE-Ang II-AT1 axis and ACE2-Ang(1-7)-MAS axis.

Angiotensin inhibition enhances drug delivery and potentiates chemotherapy by decompressing tumour blood vessels

Cancer and stromal cells actively exert physical forces (solid stress) to compress tumour blood vessels, thus reducing vascular perfusion. Tumour interstitial matrix also contributes to solid stress, with hyaluronan implicated as the primary matrix molecule responsible for vessel compression because of its swelling behaviour. Here we show, unexpectedly, that hyaluronan compresses vessels only in collagen-rich tumours, suggesting that collagen and hyaluronan together are critical targets for decompressing tumour vessels. We demonstrate that the angiotensin inhibitor losartan reduces stromal collagen and hyaluronan production, associated with decreased expression of profibrotic signals TGF-β1, CCN2 and ET-1, downstream of angiotensin-II-receptor-1 inhibition. Consequently, losartan reduces solid stress in tumours resulting in increased vascular perfusion. Through this physical mechanism, losartan improves drug and oxygen delivery to tumours, thereby potentiating chemotherapy and reducing hypoxia in breast and pancreatic cancer models. Thus, angiotensin inhibitors -inexpensive drugs with decades of safe use - could be rapidly repurposed as cancer therapeutics.

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.

Salvianolic Acid B Attenuates Rat Hepatic Fibrosis via Downregulating Angiotensin II Signaling

The renin-angiotensin system (RAS) plays an important role in hepatic fibrosis. Salvianolic acid B (Sal B), one of the water-soluble components from Radix Salviae miltiorrhizae, has been used to treat hepatic fibrosis, but it is still not clear whether the effect of Sal B is related to angiotensin II (Ang II) signaling pathway. In the present study, we studied Sal B effect on rat liver fibrosis and Ang-II related signaling mediators in dimethylnitrosamine-(DMN-) induced rat fibrotic model in vivo and Ang-II stimulated hepatic stellate cells (HSCs) in vitro, with perindopril or losartan as control drug, respectively. The results showed that Sal B and perindopril inhibited rat hepatic fibrosis and reduced expression of Ang II receptor type 1 (AT1R) and ERK activation in fibrotic liver. Sal B and losartan also inhibited Ang II-stimulated HSC activation including cell proliferation and expression of type I collagen I (Col-I) and α-smooth muscle actin (α-SMA) production in vitro, reduced the gene expression of transforming growth factor beta (TGF-β), and downregulated AT1R expression and ERK and c-Jun phosphorylation. In conclusion, our results indicate that Sal B may exert an antihepatic fibrosis effect via downregulating Ang II signaling in HSC activation.

Agaricus blazei Murill as an efficient hepatoprotective and antioxidant agent against CCl4-induced liver injury in rats

Agaricus blazei Murill is one of the very popular edible medicinal mushrooms. The present study investigated the protective effect of this biologically active mushroom on the tissue peroxidative damage and abnormal antioxidant levels in carbon tetrachloride induced hepatotoxicity in male albino rats. Male albino rats of Sprague-Dawley strain weighting (120-150 g) were categorized into five groups. The first group served as the normal control, the second and the third groups were treated with Agaricus blazei Mushroom extract and carbon tetrachloride dose, respectively. Fourth group (protective group) was first treated with Agaricus blazei Mushroom extract followed by carbon tetrachloride treatment and fifth (therapeutic group) with carbon tetrachloride first followed by Agaricus blazei Mushroom treatment. The wet fruiting bodies of mushroom Agaricus blazei Murill, crushed and suspended in distilled water was administered orally to the treated groups of male albino rats. The activities of various enzymes (aspartate and alanine transaminase, lactate dehydrogenase, glutathione reductase), levels of non-enzymatic antioxidants (glutathione, vitamin C, vitamin E) and level of lipid peroxidation (malondialdehyde) were determined in the serum of all the experimental animals. Decrease in all the enzymes and non-enzymatic antioxidant, along with an increase in the lipid peroxidative index (malondialdehyde) was found in all the carbon tetrachloride treated rats as compared with normal controls. Also increase level of non-enzymatic antioxidant along with the decrease level in malondialdehyde was found in all experimental animals which were treated with Agaricus blazei Mushroom extract as compared with normal controls. The findings indicate that the extract of Agaricus blazei Murill can protect the liver against carbon tetrachloride induced oxidative damage in rats and is an efficient hepatoprotective and antioxidant agent against carbon tetrachloride induced liver injury.

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.

Animal models of cutaneous and hepatic fibrosis

Fibrosis occurs as a part of normal wound healing. However, excessive or dysregulated fibrosis can lead to severe organ dysfunction and is a feature of a variety of diseases. Due to its insidious onset, fibrosis tends to go undetected in its early stages. This is in part why these diseases remain so poorly understood. Animal models have provided a means to examine these early stages and to isolate and understand the effect of perturbations in signaling pathways, chemokines, and cytokines. Here, we summarize recent progress in the understanding of the molecular pathogenesis of fibrosis, both its initiation and its maintenance phases, from animal models of fibrosis in the skin and liver. Due to these organs' properties, modeling fibrosis in them poses unique challenges. Elegant solutions have therefore been developed for modeling fibrosis in each, and now, great potential for animal models to contribute to our understanding appears scientifically imminent.

Hepatoprotective effects of methanol extract of Carissa opaca leaves on CCl4-induced damage in rat

BACKGROUND

Carissa opaca (Apocynaceae) leaves possess antioxidant activity and hepatoprotective effects, and so may provide a possible therapeutic alternative in hepatic disorders. The effect produced by methanolic extract of Carissa opaca leaves (MCL) was investigated on CCl4-induced liver damages in rat.

METHODS

30 rats were divided into five groups of six animals of each, having free access to food and water ad libitum. Group I (control) was given olive oil and DMSO, while group II, III and IV were injected intraperitoneally with CCl4 (0.5 ml/kg) as a 20% (v/v) solution in olive oil twice a week for 8 weeks. Animals of group II received only CCl4. Rats of group III were given MCL intragastrically at a dose of 200 mg/kg bw while that of group IV received silymarin at a dose of 50 mg/kg bw twice a week for 8 weeks. However, animals of group V received MCL only at a dose of 200 mg/kg bw twice a week for 8 weeks. The activities of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and γ-glutamyltransferase (γ-GT) were determined in serum. Catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), glutathione-S-transferase (GST), glutathione peroxidase (GSH-Px), glutathione reductase (GSR) and quinone reductase (QR) activity was measured in liver homogenates. Lipid peroxidation (thiobarbituric acid reactive substances; TBARS), glutathione (GSH) and hydrogen peroxide (H2O2) concentration was also assessed in liver homogenates. Phytochemicals in MCL were determined through qualitative and high performance liquid chromatography (HPLC) analysis.

RESULTS

Hepatotoxicity induced with CCl4 was evidenced by significant increase in lipid peroxidation (TBARS) and H2O2 level, serum activities of AST, ALT, ALP, LDH and γ-GT. Level of GSH determined in liver was significantly reduced, as were the activities of antioxidant enzymes; CAT, POD, SOD, GSH-Px, GSR, GST and QR. On cirrhotic animals treated with CCl4, histological studies showed centrilobular necrosis and infiltration of lymphocytes. MCL (200 mg/kg bw) and silymarin (50 mg/kg bw) co-treatment prevented all the changes observed with CCl4-treated rats. The phytochemical analysis of MCL indicated the presence of flavonoids, tannins, alkaloids, phlobatannins, terpenoids, coumarins, anthraquinones, and cardiac glycosides. Isoquercetin, hyperoside, vitexin, myricetin and kaempherol was determined in MCL.

CONCLUSION

These results indicate that MCL has a significant protective effect against CCl4 induced hepatotoxicity in rat, which may be due to its antioxidant and membrane stabilizing properties.

Animal models for the study of liver fibrosis: new insights from knockout mouse models

Fibrosis arises as part of a would-healing response that maintains organ structure and integrity following tissue damage but also contributes to a variety of human pathologies such as liver fibrosis. Liver fibrosis is an abnormal response of the liver to persistent injury with the excessive accumulation of collagenous extracellular matrices. Currently there is no effective treatment, and many patients end up with a progressive form of the disease, eventually requiring a liver transplant. The clarification of mechanisms underlying pathogenesis of liver fibrosis and the development of effective therapy are of clinical importance. Experimental animal models, in particular targeted gene knockouts (loss of function) in mice, have become a powerful resource to address the molecular mechanisms or significance of the targeted gene in hepatic functions and diseases. This review will focus on the recent advances in knowledge obtained from genetically engineered mice that provide novel insights into the pathophysiology of liver fibrosis.

An update on the islet renin-angiotensin system

The traditional renin-angiotensin system (RAS) components have been studied extensively since the rate-limiting component of RAS, renin, was first characterized. The ongoing identification of various novel RAS components and signaling pathways continues to elaborate the complexity of this system. Regulation of RAS according to the conventional and contemporary views of its functions in various tissues under pathophysiological conditions is a main treatment strategy for many metabolic diseases. The local pancreatic RAS, first proposed to exist in pancreatic islets two decades ago, could regulate islet function and glycemic control via influences on islet cell mass, inflammation, and ion channels. Insulin secretion, the major function of pancreatic islets, is controlled by numerous factors. Among these factors and of particular interest are glucagon-like peptide-1 (GLP-1) and vitamin D, which may regulate islet function by directly binding receptors on islet beta cells. These factors may work with local RAS signaling in islets to protect and maintain islet function under diabetic and hyperglycemic conditions. In this concise review, the local islet RAS will be discussed with particular attention being paid to recent notable findings.

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.

Texture analysis of liver fibrosis microscopic images: a study on the effect of biomarkers

Chronic hepatic injury results in liver fibrosis with eventual progression to irreversible cirrhosis. Liver fibrogenesis involves the activation of the quiescent hepatic stellate cell into an activated myofibroblast that is characterized by α-smooth muscle actin (α-SMA) expression and the production of collagens (types I and III). In the present study, rats were randomly divided into three groups: (i) control group, where rats were only treated with a vehicle; (ii) fibrosis group, where rats were treated with carbon tetrachloride (CCl(4)) to induce liver fibrosis; and (iii) silymarin group, where rats were protected with silymarin during CCl(4) treatment. Rats were sacrificed and sections of liver tissue were counterstained with hematoxylin and eosin and Masson's trichrome. Other sections were immunostained using collagens and α-SMA primary antibodies. Fibrosis was confirmed using serum marker measurements. Microscopic images of the stained sections were acquired and digitized. The Biomarker Index of Fibrosis (BIF) was calculated from the images by quantifying the percentage of stained fibers. Statistical methods of texture analysis (TA), namely co-occurrence and run-length matrices, were applied on the digital images followed by classification using agglomerative hierarchical clustering and linear discriminant analysis with cross validation. TA applied on different biomarkers was successful in discriminating between the groups, showing 100% sensitivity and specificity for classification between the control and fibrosis groups using any biomarker. Some classification attempts showed dependence on the biomarker used, especially for classification between the silymarin and fibrosis groups, which showed optimal results using Masson's trichrome. TA results were consistent with both BIF and serum marker measurements.

Hepatoprotection by freshwater clam extract against CCl4-induced hepatic damage in rats

Freshwater clam is traditionally used as a food and has been mentioned in ancient books to have a hepatoprotective effect. The hepatoprotective effect of freshwater clam extract was evaluated in the model of chronic hepatic fibrosis induced by carbon tetrachloride (CCl4). Male Sprague-Dawley rats were orally treated with freshwater clam extract (0.3, 0.6 and 1.5 g/kg of bw) or silymarin (0.2 g/kg of bw) along with the administration of CCl4 (0.5 ml/rat, 20% CCl4 in olive oil) for eight consecutive weeks. Blood samples were collected for assaying serum biochemical parameters. The livers were excised for evaluating peroxidation products and antioxidant substances, as well as the activities of antioxidant enzymes. Pathological histology was also performed. The data showed that supplementation of freshwater clam extract (0.6 g/kg bw) significantly reduced the serum levels of alanine aminotransferase and aspartate aminotransferase in rats treated with CCl4, and also decreased the thiobarbituric acid reactive substances, hydroxyproline and excessive inflammation in the livers of CCl4-treated rats. Histopathological analysis of the liver showed that freshwater clam extract (0.6 g/kg bw) markedly reduced the injury score of the fibrosis induced by CCl4 in rats. The data suggest that oral administration with freshwater clam extract might provide a novel and alternative approach for treating chronic liver failure.

Genetic determinants of hepatic steatosis in man

Hepatic steatosis is one of the most common liver disorders in the general population. The main cause of hepatic steatosis is nonalcoholic fatty liver disease (NAFLD), representing the hepatic component of the metabolic syndrome, which is characterized by type 2 diabetes, obesity, and dyslipidemia. Insulin resistance and excess adiposity are considered to play key roles in the pathogenesis of NAFLD. Although the risk factors for NAFLD are well established, the genetic basis of hepatic steatosis is largely unknown. Here we review recent progress on genomic variants and their association with hepatic steatosis and discuss the potential impact of these genetic studies on clinical practice. Identifying the genetic determinants of hepatic steatosis will lead to a better understanding of the pathogenesis and progression of NAFLD.

Dietary olive oil prevents carbon tetrachloride-induced hepatic fibrosis in mice

AIM

The specific purpose of this study was to investigate the effects of dietary olive oil on hepatic fibrosis induced by chronic administration of carbon tetrachloride (CCl(4)) in the mouse. In addition, the effects of oleic acid, a major component of olive oil, on activation of hepatic stellate cells (HSCs) were investigated in vitro.

METHODS

Mice were fed liquid diets containing either corn oil (control, AIN-93) or olive oil (6.25 g/L) throughout experiments. Animals were treated with CCl(4) for 4 weeks intraperitoneally. The mRNA expression of TGF-beta1 and collagen 1alpha2 (col1alpha2) in the liver was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). The HSCs were isolated from mice, and co-cultured with either oleic acid (100 microM) or linoleic acid (100 microM) for 2 days. The expression of alpha-smooth muscle actin (alpha-SMA) was assessed by immunohistochemistry. In addition, the production of hydroxyproline was determined.

RESULTS

Serum alanine aminotransferase levels and the mRNA expression of TGF-beta and collalpha2 were significantly reduced by treatment of olive oil. Dietary olive oil blunted the expression of alpha-SMA in the liverand liver injury and hepatic fibrosis were prevented by treatment of olive oil. The number of alpha-SMA positive cells was significantly lower in HSCs co-cultured with oleic acid than in those co-cultured with linoleic acid. Concentration of hydroxyproline in culture medium was significantly lower in cells co-cultured with oleic acid than in the control.

CONCLUSIONS

Dietary olive oil prevents CCl(4)-induced tissue injury and fibrosis in the liver. Since oleic acid inhibited activation of HSCs, oleic acid may play a key role on this mechanism.

The metabolic syndrome: how it may influence hepatic stellate cell activation and hepatic fibrosis

PURPOSE OF REVIEW

To highlight the metabolic or inflammatory components, deregulated in or pathogenic for the metabolic syndrome, that may, directly or indirectly, modulate hepatic fibrogenesis.

RECENT FINDINGS

Advanced glycation end products signal profibrogenetic transformation of hepatic stellate cells. Altered adipocytokines favor insulin resistance and steatosis. They participate to the proinflammatory status of the metabolic syndrome. Among them, leptin has been shown to directly enhance fibrogenesis, whereas adiponectin has shown antifibrotic properties. The renin-angiotensin system, a component of arterial hypertension, is activated in the diseased liver, and there is convincing evidence that blockade of angiotensin II signaling attenuates fibrosis. Endocannabinoids, whose hepatic production and signaling capability are increased with insulin resistance and obesity, signal profibrotic response via the preponderant receptor, cannabinoid receptor 1, whereas antifibrotic and anti-inflammatory signals are rather generated via stimulation of cannabinoid receptor 2. Finally, recent data demonstrate that modulation of innate immunity, particularly modulation of natural killer and natural killer T cells, has potential roles in the resolution of steatohepatitis and fibrosis.

SUMMARY

Several features associated with the metabolic syndrome can undoubtedly modulate liver fibrosis. More studies are needed to identify those that are prominent determinants of fibrosis in the metabolic syndrome and the benefit of their targeting for fibrosis prevention and treatment.

Zizyphus spina-christi protects against carbon tetrachloride-induced liver fibrosis in rats

The study of chronic hepatic fibrosis has been receiving an escalating attention in the past two decades. The aim of the study was to examine the effects of the water extract of Zizyphus spina-christi (L.) (ZSC) on carbon tetrachloride (CCl(4))-induced hepatic fibrosis. ZSC extract was daily administered [alone (ZSC-control group) or along with CCl(4) (protected groups)] at 0.125 (low dose), 0.250 (medium dose) and 0.350 (high dose) g/kg b.wt. for 8 weeks. Histo-pathological, biochemical and histology texture analyses revealed that ZSC significantly impede the progression of hepatic fibrosis. ZSC resulted in a significant amelioration of liver injury judged by the reduced activities of serum ALT and AST. Oral administration of ZSC has also restored normal levels of malondialdehyde and retained control activities of endogenous antioxidants such as SOD, CAT and GSH. Furthermore, ZSC reduced the expression of alpha-smooth muscle actin, the deposition of types I and III collagen in CCl(4)-injured rats. Texture analysis of microscopic images along with fibrosis index calculation showed improvement in the quality of type I collagen distribution and its quantity after administration of ZSC extract. These results demonstrate that administration of ZSC may be useful in the treatment and prevention of hepatic fibrosis.

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.

Inhibition of mitochondrial respiratory chain in the brain of rats after hepatic failure induced by carbon tetrachloride is reversed by antioxidants

Hepatic encephalopathy is an important cause of morbidity and mortality in patients with severe hepatic failure. This disease is clinically characterized by a large variety of symptoms including motor symptoms, cognitive deficits, as well as changes in the level of alertness up to hepatic coma. Carbon tetrachloride is frequently used in animals to produce an experimental model to study the mechanisms involved in the progression of hepatic disease and the impact of various drugs on this progression. The brain is highly dependent on ATP and most cell energy is obtained through oxidative phosphorylation, a process requiring the action of various respiratory enzyme complexes located in a special structure of the inner mitochondrial membrane. In this context, we evaluated the activities of mitochondrial respiratory chain complexes in the brain of rats submitted to acute administration of carbon tetrachloride and treated with NAC and DFX alone or in combination. Our results showed that complexes I, II and IV were inhibited after carbon tetrachloride administration and that NAC and DFX alone or in combination were able to prevent the inhibition of these enzymes. On the other hand, complex III was not affected. The participation of oxidative stress has been postulated in the hepatic encephalopathy and it is well known that the electron transport chain itself is vulnerable to damage by this species. Based on our findings, we suggest that oxidative stress may be involved in the inhibition of complexes from mitochondrial respiratory chain.

Angiotensin-receptor blockers as therapy for mild-to-moderate hypertension-associated non-alcoholic steatohepatitis

AIM: To evaluate insulin resistance, cytolysis and non-alcoholic steatohepatitis (NASH) score (NAS) using the Kleiner and Brunt criteria in 54 patients with NASH and mild-to-moderate hypertension, treated with telmisartan vs valsartan for 20 mo.

METHODS: All patients met the NCEP-ATP III criteria for metabolic syndrome. Histology confirmed steatohepatitis, defined as a NAS greater than five up to 3 wk prior inclusion, using the current criteria. Patients with viral hepatitis, chronic alcohol intake, drug abuse or other significant immune or metabolic hepatic pathology were excluded. Subjects were randomly assigned either to the valsartan (V) group (standard dose 80 mg o.d., n = 26), or to the telmisartan (T) group (standard dose 20 mg o.d., n = 28). Treatment had to be taken daily at the same hour with no concomitant medication or alcohol consumption allowed. Neither the patient nor the medical staff was aware of treatment group allocation. Paired liver biopsies obtained at inclusion (visit 1) and end of treatment (EOT) were assessed by a single blinded pathologist, not aware of patient or treatment group. Blood pressure, BMI, ALT, AST, HOMA-IR, plasma triglycerides (TG) and total cholesterol (TC) were evaluated at inclusion and every 4 mo until EOT (visit 6).

RESULTS: At EOT we noticed a significant decrease in ALT levels vs inclusion in all patients and this decrease did not differ significantly in group T vs group V. HOMA-IR significantly decreased at EOT vs inclusion in all patients but in group T, the mean HOMA-IR decrease per month was higher than in group V. NAS significantly diminished at EOT in all patients with a higher decrease in group T vs group V.

CONCLUSION: Angiotensin receptor blockers seem to be efficient in hypertension-associated NASH. Telmisartan showed a higher efficacy regarding insulin resistance and histology, perhaps because of its specific PPAR-gamma ligand effect.