The present study was designed to explore the protective effects of melatonin and its analogs, 6-hydroxymelatonin and 8-methoxy-2-propionamidotetralin, on the survival of doxorubicin-treated mice and on doxorubicin-induced cardiac dysfunction, ultrastructural alterations, and apoptosis in mouse hearts. Whereas 60% of the mice treated with doxorubicin (25 mg/kg ip) died in 5 days, almost all the doxorubicin-treated mice survived when melatonin or 6-hydroxymelatonin (10 mg/l) was administered in their drinking water. Perfusion of mouse hearts with 5 μM doxorubicin for 60 min led to a 50% suppression of heart rate × left ventricular developed pressure and a 50% reduction of coronary flow. Exposure of hearts to 1 μM melatonin or 6-hydroxymelatonin reversed doxorubicin-induced cardiac dysfunction. 8-Methoxy-2-propionamidotetralin had no protective effects on animal survival and on in vitro cardiac function. Infusion of melatonin or 6-hydroxymelatonin (2.5 μg/h) significantly attenuated doxorubicin-induced cardiac dysfunction, ultrastructural alterations, and apoptosis in mouse hearts. Neither melatonin nor 6-hydroxymelatonin compromised the antitumor activity of doxorubicin in cultured PC-3 cells. These results suggest that melatonin protect against doxorubicin-induced cardiotoxicity without interfering with its antitumor effect.

Left ventricular (LV) filling increases during exercise, but left atrial (LA) phasic function and its contribution to LV filling is poorly understood. Sixteen endurance-trained middle-aged males were studied at rest and during light (LE) and moderate (ME) intensity cycle-ergometry. Atrioventricular-plane displacement (AVPD) increased from rest to LE (from 14±2 mm to 18±2 mm, p<0.01), but did not increase further at ME. LA reservoir volume increased from rest to LE (from 32±8 mL to 40±10 mL, p<0.01). LA passive contribution increased at LE (from 21±5 mL to 27±8 mL, p<0.01), while LA active contribution increased from rest only at ME (from 12±5 mL to 23±9 mL, p<0.01). AVPD, and thus the longitudinal shortening of LV systole, contributes to LA filling primarily during LE, but is a limited mechanism beyond LE. These data suggest that LV filling appears to shift to a reliance on conduit function to increase LV filling at ME.

Left ventricular (LV) filling increases during exercise, but left atrial (LA) phasic function and its contribution to LV filling is poorly understood. Sixteen endurance-trained middle-aged males were studied at rest and during light (LE) and moderate (ME) intensity cycle-ergometry. Atrioventricular-plane displacement (AVPD) increased from rest to LE (from 14±2 mm to 18±2 mm, p<0.01), but did not increase further at ME. LA reservoir volume increased from rest to LE (from 32±8 mL to 40±10 mL, p<0.01). LA passive contribution increased at LE (from 21±5 mL to 27±8 mL, p<0.01), while LA active contribution increased from rest only at ME (from 12±5 mL to 23±9 mL, p<0.01). AVPD, and thus the longitudinal shortening of LV systole, contributes to LA filling primarily during LE, but is a limited mechanism beyond LE. These data suggest that LV filling appears to shift to a reliance on conduit function to increase LV filling at ME.

The present experiments were designed to evaluate the effects of pifithrin-α (PFT-α), which is a p53 inhibitor, on doxorubicin (DOX)-induced apoptosis and cardiac injury. Administration of DOX (22.5 mg/kg ip) in mice upregulated the mRNA levels of Bax and MDM2, whereas PFT-α attenuated those levels when administered at a total dose of 4.4 mg/kg at 30 min before and 3 h after DOX challenge. DOX treatment led to an upregulation of p53 protein levels, which was preceded by elevated levels of phosphorylated p53 at Ser15. PFT-α had no effect on the level of p53 or its phosphorylated form. The protein levels of Bax and MDM2 were elevated by DOX and attenuated by PFT-α. DOX gave rise to increased apoptosis-positive nuclei in cardiac cells, elevated serum creatine phosphokinase, ultrastructural alterations, and cardiac dysfunction. PFT-α offered protection against all of the aforementioned changes. Finally, PFT-α did not interfere with the antitumor potency of DOX. This study demonstrates that PFT-α effectively inhibits DOX-induced cardiomyocyte apoptosis, which suggests that PFT-α has the potential to protect cancer patients against DOX-induced cardiac injury.

No description available.

Atherosclerosis is a multifactorial, chronic inflammatory condition characterised by endothelial dysfunction, hyperlipidaemia and the accumulation of fatty deposits within the tunica intima of medium-to-large sized muscular arteries. This disease can prove fatal with patients suffering lethal myocardial infarction or stroke. Recently, two studies investigating the role of G-protein-coupled receptor 55 (GPR55) in atherosclerosis reported conflicting results; one reported a pro-atherogenic role for GPR55 and the other, an anti-atherogenic role for this receptor. Interestingly, another study demonstrated that the activation of GPR55 by lysophosphatidylinositol (LPI) in cultured rat neonatal ventricular cardiomyocytes provokes distinct cellular functions that are dependent on the location of GPR55, leading to suggestions that GPR55 may regulate cardiomyocyte function at two cellular sites and be a potential therapeutic target for cardiac disorders. While it has been demonstrated that GPR55 is important in the maintenance of cardiac function of healthy mice, what is currently unknown is if GPR55 has a role in the cardiovascular remodelling and cardiac function of atherosclerosis prone mice. To address this, the present studies were conducted to investigate 1) the role of GPR55 in atherogenesis, 2) if GPR55 has a role in the cardiac function of mice suffering from atherosclerosis, 3) the signalling pathway by which LPI activates cardiomyocytes, 4) the impact of GPR55 activation on the outcome of myocardial ischaemia/reperfusion (I/R) injury and, 5) the signalling mechanisms by which GPR55 elicits any observed effects on the myocardium in response to such injury. Using C57BL/6 (wildtype; WT), apolipoprotein E knockout (ApoE-/-; mouse model of atherosclerosis), GPR55 knockout (GPR55-/-) and novel ApoE-/-/GPR55-/- mice, this study has established that in the presence of high fat feeding (to accelerate atherosclerosis), GPR55 has a complex role whereby it both regulates risk factors associated with atherosclerosis (i.e. body weight and fat mass) yet promotes the development of fatty streaks within the vasculature, via a lipid independent mechanism. In terms of cardiac function, GPR55 exerted a protective role by maintaining the systolic function of high fat fed ApoE-/- mice, yet negatively affected the contractile reserve of these mice. With regard to infarct size, the present study established that LPI-induced activation of GPR55 (pre-global ischaemia) exacerbates myocardial tissue injury via a Rho-associated protein kinase (ROCK) dependent mechanism. Finally, this study established that LPI signals through the same signalling pathway as it did in the isolated heart, in both mouse and human-induced pluripotent stem cell-derived cardiomyocytes thus suggesting a translational role for GPR55 in the human heart. In conclusion, despite further research being required, the data presented within this thesis provides evidence that GPR55 may have the potential to be targeted for therapeutic gains in atherosclerosis and myocardial I/R injury.

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-22Bitstream added on 2014-06-13T20:41:16Z : No. of bitstreams: 1 leopoldo_as_dr_botfm_prot.pdf: 3513369 bytes, checksum: 922f5bbd3b24a15e940c8cfa86cf1680 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / not available

CapZ is an actin capping protein that locates at cardiac Z-discs and anchors sarcomeric actin [1]. Transgenic (TG) mice overexpressing CapZ in cardiac myocytes develop a lethal cardiac hypertrophy [2], while a large reduction in CapZ protein causes severe myofibrillar disarray and death [2]. However, a TG model that contains a modest reduction in cardiac CapZ protein levels is viable and is associated with decreased PKC-dependent regulation of myofilament function [3]. Given the well known role of PKC in myocardial pathogenesis, the general aim of this thesis was to investigate how the modest reduction in CapZ protein affects cardiac function in models of cardiac stress. I found that PKC-translocation to cardiac myofilaments during cold cardioplegic arrest impairs myofilament activation, and that decreased cardiac CapZ protein disrupts this pathway and provides cardioprotective benefit. Using an in vivo model of ischemia-reperfusion (IR), I made the novel discovery that myofilament-associated PKC is altered during prolonged global ischemia, and found that a CapZ deficiency affects the translocation of PKC to myofilaments in a time-dependent manner. Furthermore, I found that TG mice deficient in CapZ demonstrate significant reductions in IR injury, while providing enhanced cardioprotection following ischemic preconditioning. The cardioprotected phenotype of CapZ-deficient TG mice is associated with altered translocation of several PKC-isoforms to cardiac myofilaments. Finally, having uncovered new information about the activation of protein phosphatase type 2A (PP2A) in IR, I investigated the role of CapZ in PP2A-dependent myofilament regulation. I found that reductions in CapZ may affect cardiac contractility by interrupting the association of PP2A with myofilaments. Together these findings expand the role of CapZ as a regulator of intracellular signaling molecules and demonstrate the novel ability of reduced CapZ to protect the heart against significant pathological threats. / Canadian Institutes of Health Research (CIHR), Heart and Stroke Foundation of Ontario (HSFO), Heart and Stroke Foundation of Canada (HSFC), The Premier's Research Excellence Award (PREA), Ontario Graduate Scholarship Program (OGS).

The Ornate Tinamou (Nothoprocta ornata), an ancient bird, has adapted to life at high altitude (&gt;2.400 m.a.s.l) for a longer period than the domestic chicken (Gallus domesticus), which came to South America with the Spanish conquerors. Ornate tinamous have a smaller heart in relation to body size than domestic chickens. This study was made to evaluate heart morphometric measurements comparing Ornate Tinamou and domestic chicken using echocardiography measurements to determine wall thickness and chamber size and to evaluate whether it can retrieve measurements consistent with previous results on dissected hearts. I was also interested in evaluating potential adaptations of the Ornate Tinamou to life in hypoxic environments by exposing the heart to positive inotropic stimulation. The results were compared with those previously obtained on dissected hearts. The results showed that the chamber size of the domestic chicken was significantly larger than in Ornate Tinamou, both in conscious and anesthetized birds. Injection of 1µg/kg isoproterenol caused domestic chickens’ systolic chamber size to decrease significantly and fractional shortening to increase significantly. The same changes were seen in the Ornate Tinamou but they were not significant. In conclusion, this study confirms that echocardiography is a valid method for retrieving cardiac measurements without euthanizing animals, opening for the possibility of taking several measurements at different ages.

Made available in DSpace on 2014-06-11T19:25:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-11Bitstream added on 2014-06-13T18:26:28Z : No. of bitstreams: 1 nascimento_tb_me_botib.pdf: 563358 bytes, checksum: f368726d0ce2a3b729d717d9b8eed2e9 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O estresse é entendido como um processo complexo e multidimensional, cuja resposta adaptativa é vista como um processo dinâmico no qual mecanismos fisiológicos do indivíduo mudam continuamente para ajustarem-se ao ambiente. Esse fator pode contribuir para alterações na função cardíaca, associada, ou não, ao trânsito de Ca2+ e a alteração vascular devido ao aumento da atividade da via l-arginina/óxido nítrico. A obesidade é uma doença complexa, caracterizada pelo acúmulo excessivo de tecido adiposo, levando a disfunções cardíacas e vasculares, que podem estar envolvidas com alteração no fluxo de Ca2+ e comprometimento da resposta vasodilatadora. O estresse é considerado um fator ambiental, portanto, responsável por alterações no balanço energético e peso corpóreo, uma vez que o peso corpóreo é a interação entre fatores genéticos e ambientais. Devido à escassez de estudos que avaliam o estresse crônico e dieta hipercalórica nas alterações cardiovasculares, e considerando a hipótese de que esta associação é capaz de atenuar o desenvolvimento da obesidade e intensificar as alterações cardiovasculares, o objetivo do presente trabalho foi confirmar essa hipótese em animais submetidos à dieta hipercalórica e ao estresse crônico. Ratos machos Wistar, divididos em quatro grupos: DN: dieta normocalórica; DN/Es: dieta normocalórica e submetidos ao estresse crônico; DH: dieta hipercalórica; DH/Es: dieta hipercalórica e submetidos ao estresse crônico, foram avaliados quanto aos perfis nutricionais, metabólicos e a remodelação cardiovascular. Os dados demonstraram que o estresse crônico impediu o desenvolvimento da obesidade, e em oposição à hipótese, o estresse crônico melhorou a função cardíaca e vascular, independente do tipo de dieta utilizada / The stress is a complex and multidimensional process, the adaptive response is a dynamic process, in which individual physiologic mechanisms change to adjust to the environment, that causes alteration in the cardiac function, involved, or not, with Ca2+ flux and vascular alterations due to the increase of the l-arginine/nitric oxide pathway activity. The obesity is a complex disease, characterized by the excess of adipose tissue that causes cardiac and vascular dysfunction, involved with Ca2+ flux alterations and injury the vasodilating response. The stress is considered an environmental factor, therefore, it is responsible for the energetic balance alterations and weight gain, once the body weight is an interaction between genetic and environmental factors. There are few studies about chronic stress associated with the hypercaloric diet that evaluate the cardiovascular alterations, and considering the idea that this association can decrease the obesity development and increase the cardiovascular alterations, the aim of this research was evaluate the cardiovascular alterations and the obesity development in animals submitted to the hypercaloric diet and chronic stress. Male Wistar rats were separated into four groups: DN: standard diet; DN/Es: standard diet and chronic stress; DH: hypercaloric diet; DH/Es: hypercaloric diet and chronic stress were evaluated in relation to the nutritional and metabolic profile and cardiovascular remodellating. The data show that the chronic stress inhibited the obesity development, and different of the initial idea, the chronic stress improved the cardiac and vascular function, in both diets