Investigating the cardiotoxicity of the global pollutant, Phenanthrene

Abstract

Cardiovascular disease (CVD) accounts for more than half of the 7 million premature deaths attributed to air pollution every year. Studies have found particulate matter (PM), a subgroup of pollutants, are associated most strongly with CVD; particularly due to the ability of smaller particles (PM2.5), to enter the systemic circulation. Polyaromatic hydrocarbons (PAHs), specifically the 3-ringed PAH, Phenanthrene (Phe) have been implicated in the cardiotoxicity of petroleum-based pollution in aquatic systems, where it disrupts the contractile and electrical function of the fish heart. Phe is also found adsorbed to PM and in the gas phase of air pollution, but to date, no studies have investigated the impact of Phe on mammalian cardiac function. The current PhD project aimed to investigate the impact of Phe on the mammalian cardiovascular system, using mouse models of acute and prolonged Phe exposure. Exposing isolated mouse hearts to 25µM Phe for 15-minutes caused a significant reduction in heart rate, a prolongation of the PR interval, and a reduction in conduction velocity. Whole-cell recordings from isolated cardiomyocytes revealed action potential duration prolongation and inhibition of key murine repolarising Ito and IKur, and depolarising, INa and ICaL, currents, following Phe exposure. Finally, acute exposure to 25µM Phe significantly increased susceptibility to arrhythmias. Overall, the ex-vivo work showed significant pro-arrhythmic effects at the whole-heart and cellular level for the first time in the mouse, with a significant increase in arrhythmia susceptibility following acute Phe exposure shown for the first time in any species. Prolonged exposure to Phe (4-6 weeks) resulted in QT prolongation in conscious and anaesthetized mice, showing for the first time a pro-arrhythmic phenotype induced by Phe in an in-vivo setting. Upregulation of the sodium-calcium exchanger (NCX) following prolonged Phe exposure, likely underlies the electrical dysfunction observed in-vivo. The impact of prolonged Phe exposure on cardiovascular structure and function was further investigated using echocardiography, blood pressure recordings and histological staining. A significant reduction in end-diastolic volume and a prolongation of the isovolumic relaxation time, indication diastolic dysfunction, was observed in Phe (3µg/kg/day) exposed mice. A significant increase in heart weight, increased cardiomyocyte size and increased collagen content in Phe exposed mice indicated significant cardiac remodeling following prolonged Phe exposure. Upregulation of hypertrophic (ANP) and pro-fibrotic (Collagen type 4 alpha chain) markers further supported detrimental remodeling of the heart, which could underlie the diastolic dysfunction observed at the functional level. No changes in blood pressure were observed in the current project. Overall the in-vivo work shows significant effects of prolonged Phe exposure on mouse cardiac electrophysiology, ventricular relaxation and cardiac remodeling, all of which could have huge implications for human health. Gas chromatography mass spectrometry analysis of biological samples (from mice exposed to 3µg/kg Phe for 4-6 weeks), found the highest concentrations of Phe in pericardial fat samples, with negligible levels in cardiac tissue and low levels in plasma samples. This is the first direct evidence for the preferential accumulation of Phe in fatty tissue, to much higher levels than those observed in plasma. In humans, routine exposure to Phe is most often reported in plasma, these results indicate the real exposure level could be far higher than originally thought. This PhD research has described significant detrimental effects of both acute and prolonged Phe exposure on the mammalian cardiovascular system. Many of the effects described here could contribute to the increased incidence of cardiac arrhythmias, heart failure and myocardial infarction seen in areas of high PM2.5 pollution, and our data highligh

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Luigi Venetucci (Supervisor), Holly Shiels (Supervisor) & David Bechtold (Supervisor)