The application of autofluorescence lifetime metrology to the study of heart failure models and heart disease

Abstract

Autofluorescence spectroscopy offers a promising label-free approach to characterise biological samples and has already shown diagnostic potential in a number of medical applications, although study of myocardium has been relatively limited. A number of myocardial molecules display autofluorescence, including those involved in energetics, e.g. NADH and flavoproteins, as well as structural molecules, e.g. collagen. This thesis discusses the application of a custom-built single point fibre-optic probe-based instrumentation for time-resolved spectrofluorometry utilising spectrally resolved time-correlated single photon counting detection (TCSPC) and white light reflectometry to the investigation of models of heart failure, both ex vivo and in vivo. Heart failure (HF) is a pathophysiological state in which an abnormality of cardiac function causes failure of the heart to pump blood at a rate commensurate with the requirements of the metabolising tissues. It affects 1-2% of the population rising to greater than 10% aged over 70 years. Despite recent therapeutic advances, annualized mortality can still approach 10%. HF results from a myocardial injury (e.g. myocardial infarction, chemotherapy) causing loss of myocytes, and maladaptive changes in surviving myocytes and extracellular matrix by ‘pathological remodelling’. That HF is characterized by structural and energetic changes was the principal motivation for the creation of an instrument to investigate changes in myocardial autofluorescence signature in disease states in vivo. If the signatures associated with known pathological diagnoses could be ascertained, such a technique could perform ‘virtual biopsy’ to aid diagnosis. This thesis describes the application of autofluorescence technique to an ex vivo Langendorff-heart to characterise the changes in autofluorescence signature with controlled insults of glucose deprivation and hypoxia. Additionally, it reports for the first-time the characterization of the autofluorescence lifetime signature in vivo at different time points in an established rat post-myocardial infarction heart failure. The thesis describes development of in vivo intravenous doxorubicin chemotherapy-cardiomyopathy heart failure model (DOX-HF) and subsequent characterization of in vivo autofluorescence signature. This investigation prompted development of a clinically viable instrument and the progress to date is described.