Karina M. Mata

Combining two potential causes of metalloproteinase secretion causes abdominal aortic aneurysms in rats: a new experimental model

Progress in understanding the pathophysiology of abdominal aortic aneurysms (AAA) is dependent in part on the development and application of effective animal models that recapitulate key aspects of the disease. The objective was to produce an experimental model of AAA in rats by combining two potential causes of metalloproteinase (MMP) secretion: inflammation and turbulent blood flow. Male Wistar rats were randomly divided in four groups: Injury, Stenosis, Aneurysm and Control (40/group). The Injury group received a traumatic injury to the external aortic wall. The Stenosis group received an extrinsic stenosis at a corresponding location. The Aneurysm group received both the injury and stenosis simultaneously, and the Control group received a sham operation. Animals were euthanized at days 1, 3, 7 and 15. Aorta and/or aneurysms were collected and the fragments were fixed for morphologic, immunohistochemistry and morphometric analyses or frozen for MMP assays. AAAs had developed by day 3 in 60–70% of the animals, reaching an aortic dilatation ratio of more than 300%, exhibiting intense wall remodelling initiated at the adventitia and characterized by an obvious inflammatory infiltrate, mesenchymal proliferation, neoangiogenesis, elastin degradation and collagen deposition. Immunohistochemistry and zymography studies displayed significantly increased expressions of MMP‐2 and MMP‐9 in aneurysm walls compared to other groups. The haemo‐dynamic alterations caused by the stenosis may have provided additional contribution to the MMPs liberation. This new model illustrated that AAA can be multifactorial and confirmed the key roles of MMP‐2 and MMP‐9 in this dynamic remodelling process.

Interference of doxycycline pretreatment in a model of abdominal aortic aneurysms.

BACKGROUND Abdominal aortic aneurysm (AAA) is characterized by chronic inflammation and degradation of the extracellular matrix, mediated by matrix metalloproteinases (MMPs). Doxycycline has been reported to control the progression of AAA by regulation of MMP. We hypothesized that doxycycline pretreatment in a rat model of AAA would cause reduction in gelatinolytic activity of MMP-2 and -9 and the inflammatory response in the wall of an aneurysm, consequently decreasing the formation and development of AAAs. METHODS Male Wistar rats were divided into the following four groups: aneurysm (A); control (C); aneurysm+doxycycline (A+D) and control+doxycycline (C+D), with 24 animals per group subdivided into n=6 animals at different time points [1, 3, 7, and 15 days postsurgery (dps)]. The (A) and (A+D) groups simultaneously received the injury and extrinsic stenosis of the aortic wall. The (C) and (C+D) groups received sham operation. The treated animals received doxycycline via gavage (30 mg/kg/day) from 48 h before surgery until the end of experiment. At 1, 3, 7, and 15 dps, the animals were euthanized, and the aortas were collected for morphological analyses, immunohistochemistry, and zymography. RESULTS The animals from the (A) group developed AAAs. However, the animals treated with doxycycline showed a 85% decrease in AAA development, which was associated with a large reduction in gelatinolytic activity of MMP-2 and -9, and decreased inflammatory response (P<.05). CONCLUSIONS These results suggest that pretreatment with doxycycline before surgery inhibited the activity of MMP-2 and -9, as well as the inflammatory response, and may play an important role in the prevention of the development of AAAs.

Giant right coronary artery aneurysm presenting as a paracardiac mass

Coronary artery aneurysms, commonly atherosclerotic, are usually asymptomatic and can be diagnosed incidentally during investigation for ischemic heart disease or on autopsy. An asymptomatic giant right coronary artery aneurysm presenting as a paracardiac mass discovered on autopsy is reported here. Even though there was great concern due to its large size, complex atherosclerotic lesions, and potential obstruction of blood flow, it had no direct link to the cause of death. We also review the literature on giant right coronary artery aneurysms exceeding 5 cm in the last 10 years.

Coronary Artery Aneurysms: An Update

Coronary artery aneurysm (CAA) is a neglected topic in the pathology literature; most descriptions of CAAs have been limited to reports of single cases and some reviews. Because CAAs are usually found incidentally during cardiac examinations, most of the reported cases have been diagnosed by coronary angiography, intravascular ultrasound and, on rare occasions, during autopsy (Ramos et al., 2008). Although they are rare, CAAs can be potentially fatal if they are not managed in a judicious and timely manner.

Increased Atrial β-Adrenergic Receptors and GRK-2 Gene Expression Can Play a Fundamental Role in Heart Failure After Repair of Congenital Heart Disease with Cardiopulmonary Bypass

Surgeries to correct congenital heart diseases are increasing in Brazil and worldwide. However, even with the advances in surgical techniques and perfusion, some cases, especially the more complex ones, can develop heart failure and death. A retrospective study of patients who underwent surgery for correction of congenital heart diseases with cardiopulmonary bypass (CPB) in a university tertiary-care hospital that died, showed infarction in different stages of evolution and scattered microcalcifications in the myocardium, even without coronary obstruction. CPB is a process routinely used during cardiac surgery for congenital heart disease. However, CPB has been related to increased endogenous catecholamines that can lead to major injuries in cardiomyocytes. The mechanisms involved are not completely understood. The aim of this study was to evaluate the alterations induced in the β-adrenergic receptors and GRK-2 present in atrial cardiomyocytes of infants with congenital heart disease undergoing surgical repair with CPB and correlate the alterations with functional and biochemical markers of ischemia/myocardial injury. The study consisted of right atrial biopsies of infants undergoing surgical correction in HC-FMRPUSP. Thirty-three cases were selected. Atrial biopsies were obtained at the beginning of CPB (group G1) and at the end of CPB (group G2). Real-time PCR, Western blotting, and immunofluorescence analysis were conducted to evaluate the expression of β1, β2-adrenergic receptors, and GRK-2 in atrial myocardium. Cardiac function was evaluated by echocardiography and biochemical analysis (N-terminal pro-brain natriuretic peptide (NT-ProBNP), lactate, and cardiac troponin I). We observed an increase in serum lactate, NT-proBNP, and troponin I at the end of CPB indicating tissue hypoxia/ischemia. Even without major clinical consequences in cardiac function, these alterations were followed by a significant increase in gene expression of β1 and β2 receptors and GRK-2, suggesting that this is one of the mechanisms responsible for the exacerbated response of cardiomyocytes to circulating catecholamines. These alterations could explain the irreversible myocardial damage and lipid peroxidation of membranes classically attributed to catecholamine excess, observed in some infants who develop heart failure and postoperative death. Although other factors may be involved, this study confirms that CPB acts as a potent inducer of increased gene expression of β- adrenergic receptors and GRK-2, making the myocardium of these infants more susceptible to the effects of circulating endogenous catecholamines, which may contribute to the development of irreversible myocardial damage and death.

High-Fat and Fat-Enriched Diets Impair the Benefits of Moderate Physical Training in the Aorta and the Heart in Rats

Aim Millions of people die each year due to cardiovascular disease (CVD). A Western lifestyle not only fuses a significant intake of fat with physical inactivity and obesity but also promotes CVD. Recent evidence suggests that dietary fat intake impairs the benefits of physical training. We investigated whether aerobic training could reverse the adverse effects of a high-fat diet (HFD) on the aorta. Then, we explored whether this type of exercise could reverse the damage to the heart that is imposed by fat-enriched diet (FED). Methods Rats were randomly assigned to two experiments, which lasted 8 weeks each. First, rats swam for 60 min and were fed either a regular diet [standard diet (STD)] or an HFD. After aortic samples had been collected, the rats underwent a histopathological analysis for different biomarkers. Another experiment subjected rats that were fed either an STD or an FED to swimming for 20 or 90 min. Results The first experiment revealed that rats that were subjected to an HFD-endured increased oxidative damage in the aorta that exercises could not counteract. Together with increased cyclooxygenase 2 expression, an HFD in combination with physical training increased the number of macrophages. A reduction in collagen fibers with an increased number of positive α-actin cells and expression of matrix metalloproteinase-2 occurred concomitantly. Upon analyzing the second experiment, we found that physically training rats that were given an FED for 90 min/day decreased the cardiac adipose tissue density, although it did not protect the heart from fat-induced oxidative damage. Even though the physical training lowered cholesterol levels that were promoted by the FED, the levels were still higher than those in the animals that were given an STD. Feeding rats an FED impaired the swimming protocol’s effects on lowering triglyceride concentration. Additionally, exercise was unable to reverse the fat-induced deregulation in hepatic antioxidant and lipid peroxidation activities. Conclusion Our findings reveal that an increased intake of fat undermines the potential benefits of physical exercise on the heart and the aorta.

Myocardial Ischemia in Congenital Heart Disease: A Review

Patients with congenital heart disease (CxHD) are surviving into adulthood, as well as living longer and growing older [1], due the major achievements in their diagnosis, medical man‐ agement, surgical repair, and postoperative treatment in the last three to four decades. An increasing numbers of patients with CxHD are encountered in our everyday practice. It is therefore timely and appropriate to start addressing the somewhat-neglected issue of myo‐ cardial ischemia in this patient population [2].

175 PATHOGENESIS OF ABDOMINAL AORTIC ANEURYSMS: THE ROLE OF METALLOPROTEINASES AND THEIR INHIBITORS

An abdominal aortic aneurysm (AAA) represents a complex pathophysiological process of weakening and dilatation of the aortic wall, which is associated with atherosclerosis, a chronic inflammatory response and hemodynamic alterations. Degradation of the extracellular matrix by the matrix metalloproteinases (MMPs) and an imbalance between MMPs and their tissue inhibitors (TIMPs), as well as the production of reactive oxygen species, have fundamental roles in the development of AAA. The exact pathogenetic mechanisms remain incompletely elucidated. In this study, we used an experimental model that was developed in our laboratory to induce AAA by combining two potential causes of MMP secretion: inflammation and turbulent blood flow. Male Wistar rats were divided into a control group (C) and an aneurysm group (A). The rats in group A received both an injury and extrinsic stenosis of the wall of the abdominal aorta. The rats in group C received a sham operation. The rats were euthanized at 3, 7 or 15 days post-surgery (dps). Sections of the aorta including the aneurysm were collected for morphological studies and MMP-2 and -9 and TIMP-1 and -2 assays. Dilatation to more than 300% of the normal aortic diameter was observed on 3 dps in 65% of the rats in group A and was similar at 7 and 15 dps. The AAA wall underwent an intense remodeling process characterized by a severe inflammatory response (neutrophils, macrophages and lymphocytes), considerable destruction of elastin fibers and deposition of collagen as well as an increase in the myofibroblast population and neovascularization. These alterations were directly related to the dramatic increase of the levels of MMP-2 and -9 and TIMP-1 and -2 throughout the study period. Immunohistochemistry revealed an increase in the level of inducible nitric oxide synthase (iNOS) in A group rats, suggesting that reactive oxygen species (ROS) contribute to the degeneration of the aortic wall. AAA results from a cascade of events that culminate in dilatation of the aortic wall. The inflammatory process associated with turbulent intraluminal flow most likely causes endothelial dysfunction that creates a milieu favorable to the release of MMPs. The MMPs cause massive destruction of elastin fibers which significantly remodels the arterial wall, resulting in dilatation and AAA formation. Reactive oxygen species play a role in the development of aneurysms. Increasing the levels of TIMPs, proportional to the increased levels of ROS, was not sufficient to block the formation of AAA. Further studies are being conducted to elucidate the role of inflammatory cells and turbulent blood flow in the pathogenesis of AAAs in this experimental model.