Localised lipid accumulation detected in infarcted mouse heart tissue using ToF-SIMS

Abstract

Cardiovascular disease (CVD) is largely related to complications from atherosclerotic disease such as myocardial infarction (MI) and ischemic stroke and accounts for more than 30% of overall global mortality. Understanding the biochemical changes that occur in cardiac tissue following myocardial infarction is critical for clarifying the mechanisms underlying the impaired heart function seen after a myocardial infarction. Lipids have been shown to accumulate in ischemic cardiac tissue following an infarction. Recent data indicate that this cardiac lipid accumulation induces apoptosis and loss of muscle cells during the post-infarction period, which aggravate the functional impairment in the heart and limit its adaptive capacity for compensatory remodelling. It is therefore important to identify the lipids and molecular mechanisms that induce these destructive responses. In this study, the spatial distribution of lipids in mouse cardiac tissue after surgically induced infarction were identified using ToF-SIMS imaging with a gas cluster ion beam (GCIB). The benefits of frozen hydrated analysis versus freeze dried sample preparation were assessed as was the suitability of different multivariate analysis techniques for identification of localised chemical changes in the tissue. Results show that differences in intensity of the peaks in the mass spectrum corresponding to different lipids can be detected between the infarcted region of the heart and normal tissue region as well as specific accumulation of acyl-carnitine species at the boundary of the damaged region. Different spatial distributions of lipids were detected in both positive and negative ion mode providing insights into the changes in lipid metabolism following infarction. The ToF-SIMS results were compared with conventional lipidomics where although many lipid classes show similar changes between infarcted and non-infarcted hearts the ToF-SIMS data revealed differences due to salt adduct formation and most importantly where the changes in lipid signal are highly localised at the border between the infarcted and non-infarcted regions of the heart.