Telmisartan in the diabetic murine model of acute myocardial infarction: dual contrast manganese-enhanced and delayed enhancement MRI evaluation of the peri-infarct region

Abstract

Background: A novel MRI technique, employing dual contrast manganese-enhanced MRI (MEMRI) and delayed enhancement MRI (DEMRI), can evaluate the physiologically unstable peri-infarct region. Dual contrast MEMRI-DEMRI enables comprehensive evaluation of telmisartan to salvage the peri-infarct injury to elucidate the underlying mechanism of restoring the ischemic cardiomyopathy in the diabetic mouse model.

Methods and results: Dual contrast MEMRI-DEMRI was performed on weeks 1, 2, and 4 following initiation of telmisartan treatment in 24 left anterior descendent artery ligated diabetic mice. The MRI images were analyzed for core infarct, peri-infarct, left ventricular end-diastolic, end-systolic volumes, and the left ventricular ejection fraction (LVEF). Transmission electron microscopy (TEM) and real-time PCR were used for ex vivo analysis of the myocardium. Telmisartan vs. control groups demonstrated significantly improved LVEF at weeks 1, 2, and 4, respectively (33 ± 7 %*** vs. 19 ± 5 %, 29 ± 3 %*** vs. 22 ± 4 %, and 31 ± 2 %*** vs 18 ± 6 %, ***p < 0.001). The control group demonstrated significant differences in the scar volume measured by MEMRI and DEMRI, demonstrating peri-infarct injury. Telmisartan group significantly salvaged the peri-infarct injury. The myocardial effects were validated by TEM, which confirmed the presence of the injured but viable cardiomyocyte morphology in the peri-infarct region and by flow cytometry of venous blood, which demonstrated significantly increased circulating endothelial progenitor cells (EPCs).

Conclusion: The improved cardiac function in ischemic cardiomyopathy of diabetic mice by telmisartan is attributed to the attenuation of the peri-infarct injury by the angiogenic effects of EPCs to salvage the injured cardiomyocytes. Dual-contrast MEMRI-DEMRI technique tracked the therapeutic effects of telmisartan on the injured myocardium longitudinally.

Fig. 1

Functional measurement of telmisartan versus control groups. Significantly improved LVEF at weeks 1, 2, and 4 (***p < 0.001) in the telmisartan-treated (red bar) diabetic mice compared to control diabetic mice (white bar)

Fig. 2

Invasive hemodynamic analysis. No significant difference is seen in the telmisartan-treated (red bar) diabetic mice compared to control diabetic mice (white bar) for both systemic end-diastolic pressure and the isovolumic relaxation constant, Tau, calculated by the Glantz method

Fig. 3

Corresponding short-axis MEMRI and DEMRI. a MEMRI defect representing myocardial scar (red tracing), b DEMRI enhancement depicting myocardial scar (red tracing), and c overlapping area between MEMRI and DEMRI in the border zone illustrates the viable peri-infarct region (yellow tracing)

Fig. 4

MEMRI and DEMRI enable peri-infarct volume measurements. DEMRI % scar volume does not differ significantly from the MEMRI % scar volume in the a telmisartan group (red and dark red bars) while b the DEMRI and MEMRI % scar volume difference is significant in the control (white and black bars) group for weeks 2 and 4. c The telmisartan group demonstrates decreased % peri-infarct volume compared to the control group at week 4

Fig. 5

Myocardial fibrosis and apoptosis. Real-time PCR quantitative analysis of fibrotic (collagen I, collagen III, connective tissue growth factor (CTGF), TGFβ, and fibronectin) and apoptotic (thymoma viral proto-oncogene 1: Akt) genes in the injured myocardium of telmisartan and control groups. There was a trend towards increased expression of fibrotic genes, collagen I, collagen III, CTGF and fibronectin in the telmisartan group compared to the control group. Red bar: telmisartan group, white bar: control group

Fig. 6

Hematoxylin and eosin stain and TEM of myocardial injury. a Hematoxylin and eosin stained heart with ROI of remote zone (black line), peri-infarct region (blue line), and infarct region (green line). b–d TEM images of remote, border, and infarct regions. The three regions exhibited healthy, injured but viable, and non-viable cells, respectively. M mitochondria, N nucleus, S sarcomeric structure

Fig. 7

Flow cytometry of circulating CD34 + cells. The telmisartan group demonstrates significantly increased population of circulating CD34 + cells compared to the control group (*p < 0.05)