Hong-Sheng Wang, PhD - US grants

[unreadable] DESCRIPTION (provided by applicant): The Brugada syndrome is a malignant form of ventricular arrhythmia that is associated with a high mortality rate of approximately 10% per year. It is believed to be responsible for at least 4% of all sudden deaths. Although important progress has been made in our understanding of the Brugada syndrome, significant gaps remain. Much of the dominating the theory on the pathophysiological mechanism of the syndrome is based on a few studies using perfused ventricular wedges. The way by which the Brugada-like ECG is generated in these studies is questionable, and the proposed ionic mechanisms have not been vigorously tested. Our goal is to bridge these gaps by delineating the role of Ito and late INa in the cellular electrical abnormalities as well as contractile dysfunction of the Brugada syndrome. A second goal of our study is to explore potential new therapeutic strategies for the treatment of the disease. [unreadable] [unreadable] Our specific aims are 1) to determine the role of Ito in generating the AP abnormalities in the Brugada phenotype. We will examine whether Ito, when coupled with a reduced Na+ current, is sufficient to produce the abnormal epicardial AP repolarization properties in Brugada syndrome, and whether blockade of Ito restores the normal AP morphology. 2) To determine the ionic basis of the contractile abnormality in Brugada syndrome. Wall-motion abnormality has been described in Brugada patients, and the basis of such abnormality is directly relevant to our understanding of the arrhythmogenic substrate of the disease. We will examine myocyte contractile and Ca2+ transient abnormalities under Brugada cellular electrical settings. And 3) to determine the role of late INa in the AP abnormalities in the Brugada syndrome. We will examine whether reduction of the late INa in addition to the fast Na+ current is required to produce the abnormal AP morphology of the Brugada syndrome, and test the therapeutic potential of restoration of the late INa as a treatment of the syndrome. The key approach we employment is a novel technique, the dynamic clamp. It will allow us to selectively and quantitatively manipulate the conductance of interest in single myocytes, and gain in depth knowledge of the cellular mechanisms of the Brugada syndrome. Our proposed study closely fits the stated purpose of the R21 Program Announcement because it is innovative and exploratory, and it is consistent with the goal of the funding program. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): The goal of our proposed study is to elucidate the toxicological effects of exposure to estrogenic xenobiotics on the cardiac system, and to define the underlying pharmacological mechanisms of actions of these agents. We will also investigate the molecular basis for the sex-specific susceptibility to estrogenic xenobiotics-induced cardio-toxic effect. Estrogenic endocrine-disrupting chemicals (EDCs) are structurally diverse compounds that mimic, or antagonize the actions of endogenous estrogens. A particularly significant example of EDCs to human health is the nearly ubiquitous estrogenic xenobiotic bisphenol A (BPA). Estrogenic EDCs have the ability to impact the actions of endogenous estrogen, i.e. 17?-estradiol (E2), and it is increasingly recognized that BPA and other EDCs can have harmful effects on the reproductive, nervous and immune systems. A notable gap in our current knowledge on health risks of EDC exposure is its impact on cardiac physiology and health. Importantly, a recent epidemiologic study has shown that in the US adult population, higher urine BPA concentrations are associated with adverse health effects, including cardiovascular disease (Lang et al, 2008). This new evidence highlights the critical need to understand the effects of exposure to environmentally relevant concentrations of estrogenic EDCs on the heart, which are currently unknown. This fundamental lack of knowledge regarding the effects of estrogenic xenobiotics in the heart hinders effective protection against environmental cardiac risk factors, and the development of preventive-therapeutic strategies. We present compelling preliminary results showing that exposure to environmentally or physiologically relevant low-dose of BPA and E2 rapidly promotes arrhythmogenic activity in female ventricular myocytes and female hearts, but not in male. We have shown that the underlying mechanism of the rapid pro-arrhythmic effects of estrogenic agents likely involve increased spontaneous Ca leak from the sarcoplasmic reticulum, and that the mechanism of the sex-specific susceptibility to EDCs involves the opposing effects of membrane estrogen receptors (ER)s. These findings lead to our central hypothesis that E2 and estrogenic EDCs, via activation of membrane associated ER mechanisms, alter cardiac Ca2+ handling in a sex-specific manner, and that the actions of at least some estrogenic agents contribute to arrhythmogenesis in female hearts. We propose three Specific Aims to address this hypothesis: Aim 1 is to determine the cellular mechanism(s) underlying the pro- arrythmogenic effects of EDCs and E2 in rat ventricular myocytes;Aim 2 is to define the molecular basis for the sex-specificity of susceptibility to rapid E2/EDC effects on contractile function and arrhythmogenesis of ventricular myocytes;and Aim 3 is to determine the effects of E2/EDCs on cardiac arrhythmias at the whole organ level, especially during pathologic stress, including catecholamine stimulation and ischemia, and explore potential preventive/therapeutic strategies for protection against such arrhythmias. PUBLIC HEALTH RELEVANCE: Our proposed study investigates the toxicological effects and underlying mechanism of exposure to estrogenic xenobiotics and other environmental estrogenic compounds on the cardiac system, particularly in women. These studies have high clinical relevance, particularly with respect to arrhythmias in women in the at risk population. The results will provide critical knowledge for the development of protective measures against environmental estrogenic cardiac risk factors, and the development of novel preventive or therapeutic strategies for cardiac diseases related to these risk factors.

Bisphenol A (BPA) is a common environmental endocrine disrupting chemical (EDC) with a range of potential adverse health effects. Growing epidemiologic and experimental studies have demonstrated a potential link between higher BPA exposure and cardiovascular diseases. In previous studies, we reported some of the first evidence on the arrhythmogenic actions of BPA in rodent hearts. We further showed that the pro-arrhythmic effects of BPA was shared by bisphenol S (BPS), a BPA analog that is used in many of the ?BPA-free? products. Our findings demonstrate the potential pro-arrhythmic toxicity of BPA, and highlight the need to further define the impact of BPA and related EDCs on human heart health. The goal of our proposal is to determine the pro-arrhythmic toxicity of BPA and BPS in larger animals, including humans, particularly through prolongation of the QT interval of the electrocardiogram (ECG). QT interval reflects the duration of ventricular excitation of the heart. In human and other larger species, a distinct arrhythmogenic mechanism is QT prolongation. Importantly, QT prolongation is a common forms of cardiac toxicity for chemical and pharmaceutical agents, and is well recognized as a central issue in cardiac safety. It has been shown that female sex hormones, including estrogen, prolong QT interval in both human females and animal models. However, the impact of BPA, a near ubiquitous estrogenic EDC, on the risk of QT prolongation and related arrhythmias is entirely unknown. Supported by compelling preliminary studies, we propose to address the central hypothesis that in the hearts of larger species including human, low-dose BPA and BPS have pro-arrhythmic toxicity through delay of ventricular repolarization and prolongation of the QT interval; this pro-arrhythmic action is particularly significant in hearts with existing QT prolongation, such as those of idiopathic long QT syndrome (LQT) patients. The study uses a combination of animal experiments using rabbits, and epidemiology analysis using biospecimens and data from the Fernald Community Cohort. The gender-specificity of the actions of the bisphenol chemicals will be addressed in each Aim. Three aims are proposed. The long-term (Aim 1) and rapid (Aim 2) effects of BPA and BPS exposure on cardiac electrophysiology and arrhythmogenesis will be examined using the rabbit model. In Aim 3, the correlation of BPA exposure in human adults and ECG markers of cardiac electrical abnormalities will be examined in the Fernald Community Cohort. The proposed research is significant because it is expected to provide important insights into the action and underlying mechanism of BPA and BPS on larger animal hearts. Further, our study will provide better understanding of the risk factors of cardiac arrhythmia, particularly in vulnerable subpopulations with cardiac disease. The Fernald Cohort study represents the first epidemiologic study on the association between BPA exposure and cardiac electrical abnormalities, bridging a major knowledge gap in our understanding of the toxicity of BPA.

SUMMARY/ABSTRACT This application seeks administrative supplement, under the Research Supplements to Promote Diversity in Health-Related Research category (PA 20-222), to provide support for Latia Tucker, an African American graduate student in my laboratory. Her graduate research project focuses on the impact of environmental disrupting chemicals (EDCs) on the cardiovascular-circulatory system, including the heart and blood coagulation. Bisphenol A (BPA) and its related analogues are common EDCs with a range of potential adverse health effects. Growing epidemiologic and experimental studies have demonstrated a potential link between higher BPA exposure and cardiovascular diseases. In previous studies, my laboratory reported some of the first evidence on the arrhythmogenic actions of BPA in rodent hearts. We further showed that the pro-arrhythmic effects of BPA was shared by its analogue chemical bisphenol S (BPS). Our findings demonstrate the potential cardiovascular toxicity of BPA, and highlight the need to further define the impact of BPA and related EDCs on human heart health. While the cardiac toxicities of bisphenol chemicals have received increasing attention, an area that is currently completely unknown is the potential impact of these chemicals on hemostasis. Increased blood coagulation leads to thrombosis, which can result in life threatening conditions including myocardial infarction (heart attack), ischemic stroke, and pulmonary embolism. Importantly, it has been well established that gonadal hormones impact blood coagulation; in particular, estrogen has been shown to increase coagulation. However, the potential influence of environmental chemicals, including EDCs, on these processes is entirely unknown. The overall goal of Latia's thesis research is to determine the impact of both BPA and a mixture of BPA analogue chemicals on the circulatory system. Her study will focus on 1) the impact of these chemicals on cardiac electrical properties and markers of electrical abnormality in the hearts of larger animals; and 2) the effects of exposure to BPA and a mixture of BPA-related bisphenols on blood coagulation and thrombotic risks. These studies are innovative and has high significance, and will provide important understanding of the potential cardiovascular-circulatory toxicity of bisphenol type EDCs. They will also provide comprehensive training for Latia on environmental health and toxicology, cardiac physiology and electrophysiology, and hemostasis regulation, thus equipping her well for pursuing future independent research career.