Allopurinol attenuates oxidative stress and cardiac fibrosis in angiotensin II-induced cardiac diastolic dysfunction

Aims: Oxidative stress and fibrosis is implicated in cardiac remodeling and failure. We tested whether allopurinol could decrease myocardial oxidative stress and attenuate cardiac fibrosis and left ventricular diastolic dysfunction in angiotensin II (AngII)‐induced hypertensive mice. Methodology: We used 8‐week‐old male C57BL/6J mice, in which angiotensin II was subcutaneously infused for 4 weeks to mimic cardiac remodeling and fibrosis. They were treated with either normal saline or allopurinol in daily doses, which did not lower blood pressure. Results: Allopurinol improved diastolic dysfunction in angiotensin II‐induced hypertensive mice, which was associated with the amelioration of cardiac fibrosis. However, allopurinol showed no effect on the increased systolic blood pressure by angiotensin II infusion. The ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) [GSH/GSSG] was decreased and malondialdehyde levels were increased in the hearts of AngII‐treated mice. Allopurinol also inhibited both the decrease in the GSH/GSSG ratio and the increase in malondialdehyde levels in the heart. Infusion of AngII‐induced upregulation of transfer growth factor (TGF)‐β1, Smad3 expression and downregulation of Smad7 expression. Treatment with allopurinol reduced cardiac levels of TGF‐β1, Smad3, and increased Smad7 expression. Conclusions: These results suggest that allopurinol prevents pathological remodeling of the heart in AngII‐induced hypertensive mice. The antioxidative effect of allopurinol contributes to the regression of AngII‐induced cardiac diastolic dysfunction. These effects of allopurinol to prevent cardiac fibrosis are mediated at least partly through modulation of the TGF‐β1/Smad signaling pathway.     

Prevention of angiotensin II-mediated renal oxidative stress, inflammation, and fibrosis by angiotensin-converting enzyme 2

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase capable of metabolizing angiotensin (Ang) II into Ang 1 to 7. We hypothesized that ACE2 is a negative regulator of Ang II signaling and its adverse effects on the kidneys. Ang II infusion (1.5 mg/kg?1/d?1) for 4 days resulted in higher renal Ang II levels and increased nicotinamide adenine dinucleotide phosphate oxidase activity in ACE2 knockout (Ace2(-/y)) mice compared to wild-type mice. Expression of proinflammatory cytokines, interleukin-1β and chemokine (C-C motif) ligand 5, were increased in association with greater activation of extracellular-regulated kinase 1/2 and increase of protein kinase C-α levels. These changes were associated with increased expression of fibrosis-associated genes (α-smooth muscle actin, transforming growth factor-β, procollagen type Iα1) and increased protein levels of collagen I with histological evidence of increased tubulointerstitial fibrosis. Ang II-infused wild-type mice were then treated with recombinant human ACE2 (2 mg/kg?1/d?1, intraperitoneal). Daily treatment with recombinant human ACE2 reduced Ang II-induced pressor response and normalized renal Ang II levels and oxidative stress. These changes were associated with a suppression of Ang II-mediated activation of extracellular-regulated kinase 1/2 and protein kinase C pathway and Ang II-mediated renal fibrosis and T-lymphocyte-mediated inflammation. We conclude that loss of ACE2 enhances renal Ang II levels and Ang II-induced renal oxidative stress, resulting in greater renal injury, whereas recombinant human ACE2 prevents Ang II-induced hypertension, renal oxidative stress, and tubulointerstitial fibrosis. ACE2 is an important negative regulator of Ang II-induced renal disease and enhancing ACE2 action may have therapeutic potential for patients with kidney disease.     

Pressure overload-induced cardiac hypertrophy with and without dilation.

OBJECTIVES. The present study was designed to produce a small animal model showing compensated hypertrophy followed by congestive heart failure within a reasonable time period. BACKGROUND. Although there are various large animal experimental models of hypertrophy and heart failure, the occurrence of these two stages within a reasonable time period has not been shown very successfully in small animals. METHODS. A mildly constricting band was placed around the ascending aorta of very young guinea pigs (mean age 25 +/- 3 days) to impose a gradually increasing pressure overload. The animals were examined at different postoperative intervals up to 20 weeks. RESULTS. At 10 weeks, there was a 56% increase in ventricular weight/body weight ratio, a 33% increase in left ventricular wall thickness and a significant increase in left ventricular systolic pressure. The animals with 20 weeks of banding had developed various clinical symptoms of congestive heart failure including dyspnea, cyanotic appearance of the extremities, hydrothorax and ascites. Although at this stage there was 86% hypertrophy, the increase in wall thickness was only 20%, indicating cardiac dilation. Depressed left ventricular systolic pressure and increased left ventricular end-diastolic pressure and the increase in wet weight/dry weight ratio in the lungs and liver at 20 weeks also indicated the occurrence of heart failure. The collagen content in the heart of animals with banding for 10 and 20 weeks was 160% and 240%, respectively, of that in corresponding sham control animals. CONCLUSIONS. The data suggest that the heart was in a stage of compensated hypertrophy for up to 10 weeks, whereas heart failure was seen at 20 weeks. The two functional stages, compensatory hypertrophy followed by prolonged failure, make this model appropriate for studies on the transition of heart hypertrophy to congestive heart failure.     

Simvastatin prevents angiotensin II-induced cardiac alteration and oxidative stress

The influence of the HMG-CoA reductase inhibitor simvastatin was assessed on the cardiovascular alterations and production of free radicals associated with chronic angiotensin II (Ang II) infusion. Simvastatin (60 mg/kg per day PO) or placebo were given concomitantly for 10 days in Sprague-Dawley rats infused with Ang II (200 ng/kg per minute SC, osmotic pump). In addition, simvastatin or placebo was also given in vehicle-infused rats. Tail-cuff pressure and albuminuria were measured before and at the end of the treatment period. Cardiac weight, carotid structure, production of reactive oxygen species (ROS, by chemiluminescence) by polymorphonuclear leukocytes and aortic wall as well as protein and lipid oxidation products were determined at the end of the study. Ang II increased tail-cuff pressure by 56+/-12 mm Hg and simvastatin blunted the development of hypertension by approximately 70% (19+/-5 mm Hg). Increases in heart weight index and carotid cross-sectional area induced by Ang II were obliterated by simvastatin (3.18+/-0.09 versus 3.46+/-0.11 mg/g body wt and 0.125+/-0.010 versus 0.177+/-0.010 mm2, respectively). The Ang II-induced increases in leukocyte and aortic production of ROS as well as protein and lipid oxidation products were prevented by simvastatin. No effect of simvastatin was detected in non-Ang II-infused rats. These results indicate that simvastatin prevented the development of hypertension and cardiovascular hypertrophy together with inhibition of the induced angiotensin II production of ROS. Therefore, inhibition of HMG CoA reductase by statins may have a beneficial effect on cardiovascular alterations through its antioxidant action in experimental Ang II-dependent hypertension.     

Cannabinoid receptor 2 activation alleviates diabetes-induced cardiac dysfunction,inflammation, oxidative stress,and fibrosis

GeroScience - Diabetes mellitus promotes accelerated cardiovascular aging and inflammation, which in turn facilitate the development of cardiomyopathy/heart failure. High glucose-induced...     

Deletion of angiotensin-converting enzyme 2 accelerates pressure overload-induced cardiac dysfunction by increasing local angiotensin II

Angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase that cleaves angiotensin II to angiotensin 1-7. Recently, it was reported that mice lacking ACE2 (ACE2(-/y) mice) exhibited reduced cardiac contractility. Because mechanical pressure overload activates the cardiac renin-angiotensin system, we used ACE2(-/y) mice to analyze the role of ACE2 in the response to pressure overload. Twelve-week-old ACE2(-/y) mice and wild-type (WT) mice received transverse aortic constriction (TAC) or sham operation. Sham-operated ACE2(-/y) mice exhibited normal cardiac function and had morphologically normal hearts. In response to TAC, ACE2(-/y) mice developed cardiac hypertrophy and dilatation. Furthermore, their hearts displayed decreased cardiac contractility and increased fetal cardiac gene induction, compared with WT mice. In response to chronic pressure overload, ACE2(-/y) mice developed pulmonary congestion and increased incidence of cardiac death compared with WT mice. On a biochemical level, cardiac angiotensin II concentration and activity of mitogen-activated protein (MAP) kinases were markedly increased in ACE2(-/y) mice in response to TAC. Administration of candesartan, an AT1 subtype angiotensin receptor blocker, attenuated the hypertrophic response and suppressed the activation of MAP kinases in ACE2(-/y) mice. Activation of MAP kinases in response to angiotensin II was greater in cardiomyocytes isolated from ACE2(-/y) mice than in those isolated from WT mice. ACE2 plays an important role in dampening the hypertrophic response to pressure overload mediated by angiotensin II. Disruption of this regulatory function may accelerate cardiac hypertrophy and shorten the transition period from compensated hypertrophy to cardiac failure.     

Exercise and cardiac oxidative stress.

Cardiac muscle is frequently affected by many stimuli responsible for loss of cell homeostasis, including physical exercise. While exercise has been presented as a recommended activity for health reasons, it also provides favorable conditions for additional production of reactive oxygen species. These compounds are associated with fundamental mechanisms of cell metabolism but are also related to the etiology and pathophysiology of some cardiac diseases. Cardiac muscle tissue has a high oxidative metabolic rate and relatively low activity of the main antioxidant enzymes, which could enhance its susceptibility to oxidative injury after acute exercise. However, physical training could be considered an important stimulus for the different antioxidant systems like glutathione and those related to the activity of some important antioxidant enzymes in myocardial protection such as superoxide dismutase and glutathione peroxidase. Endurance training seems to induce up-regulation in some antioxidant defenses, protecting cardiac muscle in potentially harmful situations that induce additional oxidative stress. Nevertheless, the mechanisms related to this cross-tolerance effect of training are not yet well understood.     

Salutary effects of attenuation of angiotensin II on coronary perivascular fibrosis associated with insulin resistance and obesity

Obesity and insulin resistance confer increased risk for accelerated coronary disease and cardiomyopathic phenomena. We have previously shown that inhibition of angiotensin-converting enzyme (ACE) prevents coronary perimicrovascular fibrosis in genetically obese mice that develop insulin resistance. This study was performed to elucidate mechanism(s) implicated and to determine the effects of attenuation of angiotensin II (Ang) II. Genetically obese ob/ob mice were given ACE inhibitor (temocapril) or Ang II type 1 (AT(1)) receptor blocker (olmesartan) from 10 to 20 weeks. Cardiac expressions of plasminogen activator inhibitor (PAI)-1, the major physiologic inhibitor of fibrinolysis, and transforming growth factor (TGF)-beta(1), a prototypic profibrotic molecule, were determined and extent of perivascular coronary fibrosis was measured. Twenty-week-old obese mice exhibited increased plasma levels of PAI-1 and TGF-beta(1) compared with the values in lean counterpart. Perivascular coronary fibrosis in arterioles and small arteries was evident in obese mice that also showed increased left ventricular collagen as measured by hydroxyproline assay. Immunohistochemistry confirmed the deposition of perivascular type 1 collagen. Markedly increased PAI-1 and TGF-beta were seen immunohistochemically in coronary vascular wall and confirmed by western blotting. When obese mice were treated with temocapril or olmesartan from 10 to 20 weeks, both were equally effective and prevented increases in perivascular fibrosis, plasma PAI-1 and TGF-beta(1), left ventricular collagen and mural immunoreactivity for PAI-1, TGF-beta and collagen type 1. The c-Jun NH(2)-terminal kinase (JNK) activity was elevated in the left ventricle of obese mice (western) and blocked by temocapril and olmesartan. Ang II-mediated upregulation of PAI-1 and TGF-beta(1) with collagen deposition may explain the mechanism of perivascular fibrosis in obese mice. ACE inhibition and blockade of AT(1) receptor may prevent coronary perivascular fibrosis and collagen deposition even before development of overt diabetes. JNK activation may be a mediator of obesity-related cardiac dysfunction and a potential therapeutic target.     

Chronic inflammation and oxidative stress

Helicobacter pylori is the leading risk factor associated with gastric carcinogenesis. H. pylori leads to chronic inflammation because of the failure of the host to eradicate the infection. Chronic inflammation leads to oxidative stress, deriving from immune cells and from within gastric epithelial cells. This is a main contributor to DNA damage, apoptosis and neoplastic transformation. Both pathogen and host factors directly contribute to oxidative stress, including H. pylori virulence factors, and pathways involving DNA damage and repair, polyamine synthesis and metabolism, and oxidative stress response. Our laboratory has recently uncovered a mechanism by which polyamine oxidation by spermine oxidase causes H₂O₂ release, DNA damage and apoptosis. Our studies indicate novel targets for therapeutic intervention and risk assessment in H. pylori-induced gastric cancer. More studies addressing the many potential contributors to oxidative stress, chronic inflammation, and gastric carcinogenesis are essential for development of therapeutics and identification of gastric cancer biomarkers.     

Simvastatin attenuates cardiovascular effects and oxidative stress induced by angiotensin II]

The effects of an HMG-CoA reductase inhibitor, simvastatin (statin, 60 mg/Kg/24 h by forced feeding), were studied on the development of hypertension, cardiac hypertrophy and oxidating stress induced by chronic perfusion of angiotensin II (ANG II, 200 ng/Kg/min s.c., for 10 days) in the rat. The statin was giver 24 hours before, and during the 10 days of ANG II. At the end of the study, mean blood pressure was measured and blood sampling performed under anaesthesia (sodium pentobarbital). The cardiac mass index was measured (cardiac mass/body weight, mg/Kg). TBARS (thiobarbituric acid reactive substances), representing the index of lipid peroxidation, was assessed by fluorimetry. The statin attenuated the development of hypertension (131 +/- 9 vs 164 +/- 4 mmHg) and the increase in cardiac mass (3.13 +/- 0.09 vs 3.46 +/- 0.09 mg/g) associated with ANG II. The overproduction of TBARS induced by ANG II was partially prevented by simvastatin (598 +/- 40 vs 794 +/- 79 pmol/mL). These results indicate that simvastatin attenuates the cardiovascular effects and lipid peroxidation induced by chronic administration of angiotensin II.