Novel fluorescence-based methods to determine infarct and scar size in murine models of reperfused myocardial infarction

Background Determination of infarct area and scar size following myocardial infarction (MI) is commonly used to evaluate the efficacy of potential cardioprotective treatments in mice and other animal models. Methods For both, early and late time points following MI, we compared classical histochemical approaches with fluorescence staining methods. Reperfused MI was induced in male C57BL/6J mice and hearts were extracted 24 hours, 7-, 21-, or 28-days following MI and stained with 2,3,5-Triphenyltetrazolium chloride (TTC) and Evans Blue, Hoechst, phalloidin, Sirius Red, Masson’s or Gomorís Trichrome or Wheat Germ Agglutinin (WGA). Results Fluorescent staining combining Hoechst and phalloidin constitutes an alternative for TTC and Evans Blue, enabling a clear visualization of infarct area, area at risk, as well as remote area unaffected by MI. Infarct size early after reperfusion determined with TTC staining correlates strongly with that demarcated by phalloidin while combination of Hoechst and phalloidin staining can emulate classical TTC/Evans Blue staining 24 h post-MI. Moreover, WGA is equally accurate as the classical Sirius Red, Masson’s and Gomorís Trichrome stainings in identifying scar size in later phases (>7d) post-MI. Finally, we demonstrate feasibility of combining conventional fluorescence staining by localizing CD45 + leukocytes to specific regions of the infarcted myocardium. Conclusion We established staining procedure is not inferior to classical TTC staining while providing substantial benefits including the option for unbiased software-assisted analysis while sparing ample residual tissue for additional analyses. Overall, this enhances the data quality and reduces the required animal numbers consistent with the 3R concept of animal experimentation. Graphical abstract