Effect of high-dose cyclophosphamide on ultrastructural changes and gene expression profiles in cardiomyocytes of C57BL/6J mice

Abstract The pathogenesis of cyclophosphamide (CY)-induced cardiotoxicity remains unknown, and methods for its prevention have not been established. To elucidate acute structural changes in myocardial cells and pathways leading to myocardial damage in mice treated with high-dose CY, we performed detailed pathological analyses of myocardial tissue obtained from C57BL/6J mice that received high-dose CY. In addition, we analyzed the genome-wide cardiomyocyte expression profile of mice that received high-dose CY. Treatment with CY caused marked ultrastructural aberrations with electron microscopy, although these could not be observed with optical microscopy. Expansion of the transverse tubule and sarcoplasmic reticulum, turbulence of myocardial fiber travel, and low contractile protein density in cardiomyocytes were observed. High-dose CY treatment changed cardiomyocyte expression of 1,210 genes associated with cell-cell junctions, inflammatory responses, cardiomyopathy, and cardiac muscle function, as detected by microarray analysis (│Z-score│ > 2.0). The expression of functionally important genes related to myocardial contraction and the regulation of calcium ions was validated using real-time polymerase chain reaction analysis. Our results of gene expression profiles, functional annotation clustering, and the Kyoto Encyclopedia of Genes and Genomes pathway functional classification analysis suggest that cardiotoxicity induced by CY is associated with a disruption of the Ca2+ signaling pathway.