P611Imaging mass spectrometry for direct Heart tissue analysis : a new frontier for molecular histology

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The conversion of fatty acids into complex lipids such as triacylglycerol (TAG), diacylglycerol (DAG), has recently received considerable interest, as the accumulation of these intermediates has been implicated in the development of cardiac dysfunction, and heart failure. However, the effects of heart failure on fatty acid metabolism are complex, due mainly to the complexity of heart failure itself. Molecular discovery in cardiovascular disease processes and its integration in diagnostic pathology need a new technology, such as image mass spectrometry, which provides an ideal vehicle into this arena. Secondary ion mass spectrometry (SIMS) is a new innovative technology for local lipids analysis directly on heart tissue surfaces.

The aim of our study is to identify novel and useful fragments of biomolecules in specific major areas of the explanted heart tissue at the time of trasplantation: the pericardium, the myocardium, and endocardium.

Sample (left ventricle) from explanted heart (heart failure) were frozen and stored at -80°C until sectioning. 12 µm thick heart tissue sections were cut using a cryomicrotome and then mounted onto an ITO slide. To correlate heart's molecular profile with morphological features, the tissue sections were stained with Haematoxylin and Eosin after SIMS analysis. An abundant pseudomolecular ion signal of cholesterol (m/z 385) [M-H] together with the dominant fragment ion (m/z 369) [M-OH] can be observed. Cholesterol related ions show high intensity in the myocardium. This ion show low intensity in the pericardium and endocardium. Results from animal models of heart failure generally support the concept of decreased fatty acid β-oxidation in heart failure. These findings are consistent with the data presented below showing that DAG species were tentatively identified as [P–Po] + (Palmitic, Palmitoleic) at m/z 550, [P–O] + (Palmitic, Oleic) at m/z 578 and [O–O] + (Oleic, Oleic) at m/z 604, and could be detected with high intensity in the pericardium and low intensity in the myocardium . The mass spectrometry imaging results overlayed with the optical images demonstrates how this label-free approach takes advantage of the availability of the multitude of mass spectral peaks. This implies that the molecular basis of morphological structures observed in human heart can be detected.

This work would challenge existing paradigms and address an innovative technologies to progress in heart failure by the characterization of molecules that map the spatial organization in heart's structure.

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