Cibele M. Prado

Imbalance between matrix metalloproteinases and tissue inhibitor of metalloproteinases in hypertensive vascular remodeling.

Structural vascular changes in two-kidney, one-clip (2K-1C) hypertension may result from increased matrix metalloproteinase (MMP)-2 activity. MMP-2 activation is regulated by other MMPs, including transmembrane-MMPs, and by tissue inhibitors of MMPs (TIMPs). We have investigated the localization of MMP-2, -9, -14, and TIMPs 1-4 in hypertensive aortas and measured their levels by zymography/Western blotting and immunohistochemistry. Gelatinolytic activity was assayed in tissues by in situ zymography. Sham-operated and 2K-1C hypertensive rats were treated with doxycycline (or vehicle) for 8 weeks, and the systolic blood pressure was monitored weekly. Doxycycline attenuated 2K-1C hypertension (165 + or - 11.7 mmHg versus 213 + or - 7.9 mm Hg in hypertensive controls, P<0.01), and completely prevented increase in the thicknesses of the media and the intima in 2K-1C animals (P<0.01). Increased amounts of MMP-2, -9, and -14 were found in hypertensive aortas, as well as enhanced gelatinolytic activity. A gradient in the localization of MMP-2, -9, and -14 was found, with increased amounts detected in the intima, at sites with higher gelatinolytic activity. Doxycycline attenuated hypertension induced increases in all the 3 investigated MMPs in both the media and the intima (all P<0.05), but it did not change the amounts of TIMPs 1-4 (P>0.05). Therefore, an imbalance between increased amounts of MMPs at the tissue level without a corresponding increase in the quantities of TIMPs, particularly in the intima and inner media layers, appears to account for the increased proteolytic activity found in 2K-1C hypertension-induced maladaptive vascular remodeling.

Coronary Microvascular Disease in Chronic Chagas Cardiomyopathy Including an Overview on History, Pathology, and Other Proposed Pathogenic Mechanisms

This review focuses on the short and bewildered history of Brazilian scientist Carlos Chagass discovery and subsequent developments, the anatomopathological features of chronic Chagas cardiomyopathy (CCC), an overview on the controversies surrounding theories concerning its pathogenesis, and studies that support the microvascular hypothesis to further explain the pathological features and clinical course of CCC. It is our belief that knowledge of this particular and remarkable cardiomyopathy will shed light not only on the microvascular involvement of its pathogenesis, but also on the pathogenetic processes of other cardiomyopathies, which will hopefully provide a better understanding of the various changes that may lead to an end-stage heart disease with similar features. This review is written to celebrate the 100th anniversary of the discovery of Chagas disease.

Chagas Heart Disease: Report on Recent Developments

Chagas disease, caused by the parasite Trypanosoma cruzi, is an important cause of cardiac disease in endemic areas of Latin America. It is now being diagnosed in nonendemic areas because of immigration. Typical cardiac manifestations of Chagas disease include dilated cardiomyopathy, congestive heart failure, arrhythmias, cardioembolism, and stroke. Clinical and laboratory-based research to define the pathology resulting from T. cruzi infection has shed light on many of the cellular and molecular mechanisms leading to these manifestations. Antiparasitic treatment may not be appropriate for patients with advanced cardiac disease. Clinical management of Chagas heart disease is similar to that used for cardiomyopathies caused by other processes. Cardiac transplantation has been successfully performed in a small number of patients with Chagas heart disease.

Sepsis: Going to the Heart of the Matter

Although myocardial depression is the predominant cause of death in severe sepsis/septic shock, it remains disputed whether the functional changes are a consequence of structural alterations. If we look at myocardial dysfunction from the perspective of a critically ill patient, there are a few questions to be asked: What causes myocardial dysfunction? What is the pathophysiology of cardiac dysfunction and death? Is there something that could be done to prevent the outcome? Each of these questions is interrelated and the answers will be more easily addressed if we continue to understand the basic mechanisms that are implicated. The principal mechanisms proposed for the pathogenesis of myocardial dysfunction support a prominent role for functional rather than anatomical abnormalities. However, attempts to reduce the high mortality in septic patients by manipulating the functional alterations have provided limited success. In recent years, the concept of septic cardiomyopathy has evolved, which implies alterations in the myocardial phenotype. This review includes an overview on the activation of the immune system and therapeutic approaches in sepsis, myocardial structural changes in the human septic heart, experimental models of sepsis, and cellular, molecular and functional myocardial changes seen in a variety of experimental sepsis models. The abnormal parameters discussed may emerge as therapeutic targets, for which modulation might provide beneficial effects on cardiovascular outcome and mortality in sepsis in the future.

Increase in parasympathetic tone by pyridostigmine prevents ventricular dysfunction during the onset of heart failure

Heart failure (HF) is characterized by elevated sympathetic activity and reduced parasympathetic control of the heart. Experimental evidence suggests that the increase in parasympathetic function can be a therapeutic alternative to slow HF evolution. The parasympathetic neurotransmission can be improved by acetylcholinesterase inhibition. We investigated the long-term (4 wk) effects of the acetylcholinesterase inhibitor pyridostigmine on sympathovagal balance, cardiac remodeling, and cardiac function in the onset of HF following myocardial infarction. Myocardial infarction was elicited in adult male Wistar rats. After 4 wk of pyridostigmine administration, per os, methylatropine and propranolol were used to evaluate the cardiac sympathovagal balance. The tachycardic response caused by methylatropine was considered to be the vagal tone, whereas the bradycardic response caused by propranolol was considered to be the sympathetic tone. In conscious HF rats, pyridostigmine reduced the basal heart rate, increased vagal, and reduced sympathetic control of heart rate. Pyridostigmine reduced the myocyte diameter and collagen density of the surviving left ventricle. Pyridostigmine also increased vascular endothelial growth factor protein in the left ventricle, suggesting myocardial angiogenesis. Cardiac function was assessed by means of the pressure-volume conductance catheter system. HF rats treated with pyridostigmine exhibited a higher stroke volume, ejection fraction, cardiac output, and contractility of the left ventricle. It was demonstrated that the long-term administration of pyridostigmine started right after coronary artery ligation augmented cardiac vagal and reduced sympathetic tone, attenuating cardiac remodeling and left ventricular dysfunction during the progression of HF in rats.

Tempol inhibits TGF-β and MMPs upregulation and prevents cardiac hypertensive changes.

BACKGROUND Increased oxidative stress upregulates matrix metalloproteinases (MMPs) and transforming grow factor (TGF-β), which are involved in hypertensive cardiac remodeling. We tested the hypothesis that tempol (an antioxidant) could prevent these alterations in two-kidney, one-clip (2K1C) hypertension. METHODS Sham-operated or hypertensive rats were treated with tempol (18 mg.kg(-1)day(-1) or vehicle) for 8 weeks. Systolic blood pressure was monitored weekly. At the end of the treatment, a catheter was inserted into the left carotid artery and into the left ventricle (LV) to assess arterial blood pressure and contractile function. Morphometry of the LV was carried out in hematoxylin/eosin sections and fibrosis was assessed in picrosirius red-stained sections. Cardiac TGF-β level was evaluated by immunofluorescence. Cardiac MMP-2 levels and activity were determined by gelatin zymography, in situ zymography, and immunofluorescence. Cardiac superoxide production was evaluated by dihydroethidium probe. RESULTS Tempol treatment attenuated 2K1C-induced hypertension and reversed the contractile dysfunction in 2K1C rats. Cardiac hypertrophy was ameliorated by antioxidant treatment. Hypertensive rats showed increased cardiac MMP-2 levels, however tempol did not decrease MMP-2 levels. Increased TGF-β level, total gelatinolytic activity and oxidative stress were found in untreated 2K1C rats. Tempol treatment decreased oxidative stress, TGF-β levels, and gelatinolytic activity in 2K1C rats to control levels. CONCLUSIONS Tempol blunted the increases in TGF-β, the proteolytic imbalance, and the morphological and functional alterations found in 2K1C-induced cardiac hypertrophy. These findings are consistent with the idea that antioxidants may help to prevent hypertension-induced cardiac hypertrophy.

5-Lipoxygenase is a key determinant of acute myocardial inflammation and mortality during Trypanosoma cruzi infection

This study provides evidence supporting the idea that although inflammatory cells migration to the cardiac tissue is necessary to control the growth of Trypanosoma cruzi, the excessive influx of such cells during acute myocarditis may be deleterious to the host. Production of lipid mediators of inflammation like leukotrienes (LTs) along with cytokines and chemokines largely influences the severity of inflammatory injury in response to tissue parasitism. T. cruzi infection in mice deficient in 5-lipoxygenase (5-LO), the enzyme responsible for the synthesis of LTs and other lipid inflammatory mediators, resulted in transiently increased parasitemia, and improved survival rate compared with WT mice. Myocardia from 5-LO(-/-) mice exhibited reduced inflammation, collagen deposition, and migration of CD4(+), CD8(+), and IFN-gamma-producer cells compared with WT littermates. Moreover, decreased amounts of TNF-alpha, IFN-gamma, and nitric oxide synthase were found in the hearts of 5-LO(-/-) mice. Interestingly, despite of early higher parasitic load, 5-LO(-/-) mice survived, and controlled T. cruzi infection. These results show that efficient parasite clearance is possible in a context of moderate inflammatory response, as occurred in 5-LO(-/-) mice, in which reduced myocarditis protects the animals during T. cruzi infection.

Turbulent flow/low wall shear stress and stretch differentially affect aorta remodeling in rats.

Objective The present investigation was carried out to evaluate the relationship between local hemodynamic forces and intimal and medial remodeling in the proximal and distal segments of the arterial walls of rats in relation to severe infradiaphragmatic stenosis of the aorta. Methods Young male rats were divided randomly into an operated group, animals submitted to surgical abdominal aorta stenosis, and a sham-operated group, a control group of animals submitted to sham operation to simulate abdominal aorta stenosis. Results and conclusions Constricted aortas showed two distinct adaptive remodeling responses to hemodynamic stimuli induced by infradiaphragmatic coarctation. The first is remodeling in the hypertensive prestenotic segment with increased circumferential wall tension (CWT), associated with normal tensile stress, laminar flow/normal wall shear stress characterized by enlarged heterogeneous endothelial cells, elongated in the direction of the blood flow, diffusely distributed neointimal plaques, appearing as discrete bulging towards the vascular lumen and medial thickening. Our findings suggest that increased CWT caused by hypertension play a pivotal role in the remodeling of the prestenotic segment through biomechanical effects on oxidative stress and increased expression of transforming growth factor beta. The second is remodeling in the normotensive poststenotic segment with turbulent flow/low wall shear stress and normal CWT and tensile stress characterized by groups of endothelial cells with phenotypic alterations and focally distributed neointimal plaques, similar but many of them larger than those found in the prestenotic segments. Further studies are needed to determine how the mechanical forces of turbulent flow/low shear stress are detected and transduced into chemical signaling by the cells of the artery walls and then converted into pathophysiologically relevant phenotypic changes.

Circumferential wall tension due to hypertension plays a pivotal role in aorta remodelling

The present study was carried out to investigate the role of hypertension in the genesis and localization of intimal lesions and medial remodelling found in the prestenotic segment in relation to a severe stenosis of the abdominal aorta just below the diaphragm. Male young rats were divided randomly into operated group, animals submitted to surgical abdominal aorta stenosis, and sham‐operated group, a control group of animals submitted to sham operation to simulate abdominal aorta stenosis. Aortas in the hypertensive prestenotic segment with increased circumferential wall tension associated with normal tensile stress, laminar flow/normal wall shear stress were characterized by enlarged heterogeneous endothelial cells elongated in the direction of the blood flow, diffusely distributed conspicuous neointimal plaques and medial thickening. The immunohistochemical analysis revealed an increased expression of eNOS, iNOS, nitrotyrosine and transforming growth factor‐β (TGF‐β) in endothelial cells and/or smooth muscle cells in this segment. Our findings suggest that increased circumferential wall tension due to hypertension plays a pivotal role in the remodelling of the prestenotic segment through biomechanical effects on oxidative stress and increased TGF‐β expression. Further studies are needed to clarify the intrinsic pathogenetic mechanism of focal distribution of the neointimal plaques in the hypertensive segment.

Temporal changes in cardiac matrix metalloproteinase activity, oxidative stress, and TGF-β in renovascular hypertension-induced cardiac hypertrophy

Cardiovascular remodeling found in later phases of two-kidney, one-clip (2K1C) hypertension may involve key mechanisms particularly including MMP-2, oxidative stress, transforming growth factor-β (TGF-β), and inactivation of the endogenous MMP inhibitor, the tissue inhibitor of MMP (TIMP)-4. We examined whether temporal cardiac remodeling resulting from 2K1C hypertension occurs concomitantly with alterations in cardiac collagen, MMP activity, MMP-2, TIMP-4, TGF-β, and reactive oxygen species (ROS) levels during the development of 2K1C hypertension. Sham-operated and 2K1C hypertensive rats were studied after 15, 30, and 75 days of hypertension. Systolic blood pressure was monitored weekly. Left ventricle (LV) morphometry and fibrosis were evaluated in hematoxylin/eosin and picrosirius red-stained sections, respectively. Cardiac MMP-2 levels/activity was determined by gelatin zymography, immunofluorescence, and in situ zymography. TIMP-4 levels were determined by western blotting. Cardiac TGF-β levels were evaluated by immunofluorescence and ROS levels were evaluated with a dihydroethidium probe. 2K1C hypertension induced LV hypertrophy associated with augmented gelatinolytic activity at an early phase of hypertension and further increased after 75 days of hypertension. These alterations were associated with increased cardiac MMP-2, TGF-β, and ROS in hypertensive rats. Higher TIMP-4 levels were found in hypertensive rats only after 75 days after surgery. Our findings show that increased MMP-2 activity is associated with concomitant development of LV hypertrophy and increased TGF-β and ROS levels.