Comparative study of three angiotensin II type 1 receptor antagonists in preventing liver fibrosis in diabetic rats: stereology, histopathology, and electron microscopy

Thrombospondin-1: A Key Protein That Induces Fibrosis in Diabetic Complications

Fibrosis accompanies most common pathophysiological features of diabetes complications in different organs. It is characterized by an excessive accumulation of extracellular matrix (ECM) components, the response to which contributes to inevitable organ injury. The extracellular protein thrombospondin-1 (TSP-1), a kind of extracellular glycoprotein, is upregulated by the increased activity of some transcription factors and results in fibrosis by activating multiple pathways in diabetes. The results of studies from our team and other colleagues indicate that TSP-1 is associated with the pathological process leading to diabetic complications and is considered to be the most important factor in fibrosis. This review summarizes the molecular mechanism of increased TSP-1 induced by hyperglycemia and the role of TSP-1 in fibrosis during the development of diabetes complications.

The lung endothelin system: a potent therapeutic target with bosentan for the amelioration of lung alterations in a rat model of diabetes mellitus

PURPOSE

The aim of this study is to show the effect of a new mechanism on endothelin (ET) receptors in the physiopathology of diabetes-related pulmonary injury. We tested the hypothesis that dual ET-1 receptor antagonism via bosentan can reverse diabetes-induced lung injury.

METHODS

The rats (24 male) were separated into four groups: group 1 (HEALTHY): Control group; group 2 (DM): Streptozotocin 60 mg/kg (i.p.); group 3 (DM + BOS-1): Diabetes + bosentan 50 mg/kg per-os; group 4 (DM + BOS-2): Diabetes + bosentan 100 mg/kg per-os. The bosentan treatment was initiated immediately after the onset of STZ-induced diabetes and continued for 6 weeks.

RESULTS

In the treatment group, SOD activity was significantly increased, although GSH and MDA levels and TNF-α and TGF-β gene expression were decreased. Bosentan 50 mg/kg and bosentan 100 mg/kg showed a significantly down-regulatory effect on ET-1, ET-A, and ET-B mRNA expression.

CONCLUSIONS

In conclusion, increased endothelin levels in the lung associated with diabetes may be one cause of endothelial dysfunction, cytokine increase, and oxidant/antioxidant imbalance in the pathogenesis of complications that may develop during diabetes. With its multiple effects, bosentan therapy may be an effective option against complications that may develop in association with diabetes.

The role of renin-angiotensin system modulation on treatment and prevention of liver diseases

The renin-angiotensin system (RAS) is now recognized as an important modulator of body metabolic processes. The discovery of angiotensin-converting enzyme 2 (ACE2) has renewed interest in the potential therapeutic role of RAS modulation. Recent studies have pointed out the importance of the local balance between ACE/Ang-II/AT1 and ACE2/Ang-(1-7)/Mas arms to avoid liver metabolic diseases. Furthermore, non-alcoholic fatty liver disease is an increasing health problem that includes a spectrum of hepatic steatosis, steatohepatitis and fibrosis. Some new studies revealed that RAS imbalance appears to promote hepatic fibrogenesis; while the activation of ACE2/Ang-(1-7)/Mas counter-regulatory axis is able to prevent liver injuries. In this context, the aim of the present review is to discuss the importance of RAS in the development and prevention of liver disease. AT1 receptor activation by Ang II induces hepatic stellate cell contraction and proliferation, causes oxidative stress, endothelial dysfunction, cell growth and inflammation. In addition, both AT1 blocker administration and ACE inhibitors lead to a reduction in inflammation and improvement of hepatic fibrosis. Conversely, Ang-(1-7) infusion reduces fibrosis and proliferation mainly by suppression of hepatic stellate cell activation; Mas receptor antagonism aggravates liver fibrosis and severe liver steatosis. In conclusion, the use of ACE/Ang II/AT1 axis inhibitors associated with ACE2/Ang(1-7)/Mas axis activation is a promising new strategy serving as a novel therapeutic regimen to prevent and treat chronic liver diseases as well as acute liver injury.

Angiotensin II type 1 receptor blockers increase tolerance of cells to copper and cisplatin

The human pathology Wilson disease (WD) is characterized by toxic copper (Cu) accumulation in brain and liver, resulting in, among other indications, mitochondrial dysfunction and apoptosis of hepatocytes. In an effort to identify novel compounds that can alleviate Cu-induced toxicity, we screened the Pharmakon 1600 repositioning library using a Cu-toxicity yeast screen. We identified 2 members of the drug class of Angiotensin II Type 1 receptor blockers (ARBs) that could increase yeast tolerance to Cu, namely Candesartan and Losartan. Subsequently, we show that specific ARBs can increase yeast tolerance to Cu and/or the chemotherapeutic agent cisplatin (Cp). The latter also induces mitochondrial dysfunction and apoptosis in mammalian cells. We further demonstrate that specific ARBs can prevent the prevalence of Cu-induced apoptotic markers in yeast, with Candesartan Cilexetil being the ARB which demonstrated most pronounced reduction of apoptosis-related markers. Next, we tested the sensitivity of a selection of yeast knockout mutants affected in detoxification of reactive oxygen species (ROS) and Cu for Candesartan Cilexetil rescue in presence of Cu. These data indicate that Candesartan Cilexetil increases yeast tolerance to Cu irrespectively of major ROS-detoxifying proteins. Finally, we show that specific ARBs can increase mammalian cell tolerance to Cu, as well as decrease the prevalence of Cu-induced apoptotic markers. All the above point to the potential of ARBs in preventing Cu-induced toxicity in yeast and mammalian cells.

Valsartan improves portal hypertensive gastropathy in rats possibly via TGF-β1/Smad signaling pathway

AIM: To investigate the efficacy and mechanisms of action of valsartan on portal hypertensive gastropathy in rats with gastric mucosa lesions.

METHODS: Forty-eight SD rats were randomly divided into a sham-operated group, a portal hypertension gastropathy group, a valsartan prevention group, a normal dose valsartan group and a high dose valsartan group. Portal hypertensive gastropathy was induced by the partial portal vein ligation method. Gastric mucosa TGF-beta1 expression and microvessel density (MVD) were detected by immunohistochemical staining method. Gastric mucosa Smad2 and Smad7 protein expression was detected by Western blot. Plasma levels of rennin activity (PRA), angiotensin II (Ang II), alanine aminotransferase (ALT), and albumin (ALB) were determined by ELISA.

RESULTS: Compared with the model group, gastric mucosa TGF-β1 (11.58 ± 2.27, 13.29 ± 2.82, 13.15 ± 3.36 vs 24.25 ± 3.48, all P <0.05) and Smad2 (0.86 ± 0.59, 0.82±0.36, 0.83 ± 0.49 vs 1.60 ± 0.77, P < 0.05) protein expression was significantly decreased in the valsartan prevention group, normal dose valsartan group and high dose valsartan group. Smad7 protein expression in the valsartan prevention group, normal dose valsartan group and high dose valsartan group was significantly higher than that in the model group (1.59 ± 0.72, 1.65 ± 0.80, 1.69 ± 0.85 vs 0.58 ± 0.35, all P < 0.05). Plasma PRA (16.49 ng/mL ± 2.77 ng/mL, 15.92 ng/mL ± 4.30 ng/mL, 16.72 ng/mL ± 5.48 ng/mL vs 11.49 ng/mL ± 2.12 ng/mL, all P <0.05) and Ang II (1664.44 pg/mL ± 285.47 pg/mL, 1686.82 pg/mL ± 499.16 pg/mL, 1734.07 pg/mL ± 326.66 pg/mL vs 1110.38 pg/mL ± 193.85 pg/mL, all P <0.01) were also significantly higher in the valsartan prevention group, normal dose valsartan group and high dose valsartan group than in the model group.

CONCLUSION: Valsartan can improve portal hypertensive gastropathy probably by down-regulating TGF-β1 and Smad2 expression and up-regulating Smad7 expression.

Liraglutide Exerts Antidiabetic Effect via PTP1B and PI3K/Akt2 Signaling Pathway in Skeletal Muscle of KKAy Mice

Background. Liraglutide (a glucagon-like peptide 1 analog) was used for the treatment of type 2 diabetes (T2DM) which could produce glucose-dependent insulin secretion. Aim. The aim was to investigate whether liraglutide could improve myofibril and mitochondria injury in skeletal muscle and the mechanisms in diabetic KKAy mice. Method. We divided the male KKAy mice into 2 groups: liraglutide group (250 μg/kg/day liraglutide subcutaneous injection) and model group; meanwhile, the male C57BL/6J mice were considered as the control. After 6 weeks, the ultrastructure of skeletal muscle was observed by electron microscope. The gene expressions of protein tyrosine phosphatase 1B (PTP1B), phosphatidylinositol 3-kinase (PI3K), and glucose transporter type 4 (GLUT4) were determined by real-time PCR. The protein levels of the above molecules and phospho-Akt2 (p-Akt2) were measured by Western blot. Results. Liraglutide significantly ameliorated the injury of mitochondria by increasing the number (+441%) and the area (+113%) of mitochondria and mitochondrial area/100 µm(2) (+396%) in skeletal muscle of KKAy mice. The results of real-time PCR and Western blot showed that liraglutide downregulated PTP1B while it upregulated PI3K and GLUT4 (P < 0.01). The protein level of p-Akt2/Akt2 was also increased (P < 0.01). Conclusion. These results revealed that liraglutide could improve myofibril and mitochondria injury in skeletal muscle against T2DM via PTP1B and PI3K/Akt2 signaling pathway.

Telmisartan ameliorates fibrocystic liver disease in an orthologous rat model of human autosomal recessive polycystic kidney disease

Human autosomal recessive polycystic kidney disease (ARPKD) produces kidneys which are massively enlarged due to multiple cysts, hypertension, and congenital hepatic fibrosis characterized by dilated bile ducts and portal hypertension. The PCK rat is an orthologous model of human ARPKD with numerous fluid-filled cysts caused by stimulated cellular proliferation in the renal tubules and hepatic bile duct epithelia, with interstitial fibrosis developed in the liver. We previously reported that a peroxisome proliferator activated receptor (PPAR)-γ full agonist ameliorated kidney and liver disease in PCK rats. Telmisartan is an angiotensin receptor blocker (ARB) used widely as an antihypertensive drug and shows partial PPAR-γ agonist activity. It also has nephroprotective activity in diabetes and renal injury and prevents the effects of drug-induced hepatotoxicity and hepatic fibrosis. In the present study, we determined whether telmisartan ameliorates progression of polycystic kidney and fibrocystic liver disease in PCK rats. Five male and 5 female PCK and normal control (+/+) rats were orally administered 3 mg/kg telmisartan or vehicle every day from 4 to 20 weeks of age. Treatment with telmisartan decreased blood pressure in both PCK and +/+ rats. Blood levels of aspartate amino transferase, alanine amino transferase and urea nitrogen were unaffected by telmisartan treatment. There was no effect on kidney disease progression, but liver weight relative to body weight, liver cystic area, hepatic fibrosis index, expression levels of Ki67 and TGF-β, and the number of Ki67- and TGF-β-positive interstitial cells in the liver were significantly decreased in telmisartan-treated PCK rats. Therefore, telmisartan ameliorates congenital hepatic fibrosis in ARPKD, possibly through the inhibition of signaling cascades responsible for cellular proliferation and interstitial fibrosis in PCK rats. The present results support the potential therapeutic use of ARBs for the treatment of fibrocystic liver disease in ARPKD patients.