Abstract 28: Automated Characterization and Quantification of Cardiomyocyte Proliferation and Apoptosis in Post Myocardial Infarction Tissue Images

Detection of cardiac cell death and cardiomyocyte (CM) proliferation after ischemic injury often hinges on quantitative image analysis of cardiac histopathology. Currently, the analysis of cardiac images has greatly relied on manual measurements of the number or percentages of apoptotic CM nuclei, as well as newly forming CM nuclei. The current manual methodology for image analysis is a tedious, subjective and inconsistent approach. Nuquantus (Nuclei quantification utility software) is a novel machine learning-based analytical method, which classifies and quantifies CM nuclei in post myocardial infarction (MI) fluorescent images. Nuquantus accelerated the image analysis by 6 fold from 12.6 ± 5.6 minutes per image by manual approach to 2.2 ± 0.9 minutes (mean ± standard deviation). The analysis variability reflected by the inter-observer agreement Fleiss Kappa was improved from 0.511 ± 0.006 to 0.695 ± 0.006 (Fleiss Kappa ± standard error (***P<0.0001). The percentage of proliferating CMs out of all proliferating cell types in the heart was compared between Nuquantus and manual approaches in 1 week post MI mouse heart. CM nuclei positive to 5-ethynyl-2′-deoxyuridine (EdU) and DAPI stainings were determined to undergo DNA synthesis in the following regions: Infarct Area 0.95 ± 0.26% vs. 0.24 ± 0.07%, Border Zone 0.67±0.40% vs. 0.21±0.10%, Remote Zone 1.39±0.80% vs. 1.40±0.60% and sham 3.85±2.56% vs. 1.32±1.32% (mean ± standard error) Nuquantus vs. manual count, respectively (N=4). Nuquantus identified and quantified CM nuclear DNA fragmentation in wild-type mouse hearts stained by TUNEL assay and DAPI. In the TUNEL negative controls, we detected 0% vs. 0.1±0.1% apoptotic CM nuclei, and in the positive TUNEL control 84.77±3.49% vs. 95.64±0.69% apoptotic CM nuclei (mean ± standard error, Nuquantus vs. manual). No statistical significance was detected between the different methods. In summary, Nuquantus provides innovative computerized methodology to reliably analyze cardiac tissue images, significantly facilitates image analysis and minimizes human bias. Moreover, validation of Nuquantus indicates that CM proliferation in the remodeling heart is a very rare event.

Sorafenib cardiotoxicity increases mortality after myocardial infarction

RATIONALE

Sorafenib is an effective treatment for renal cell carcinoma, but recent clinical reports have documented its cardiotoxicity through an unknown mechanism.

OBJECTIVE

Determining the mechanism of sorafenib-mediated cardiotoxicity.

METHODS AND RESULTS

Mice treated with sorafenib or vehicle for 3 weeks underwent induced myocardial infarction (MI) after 1 week of treatment. Sorafenib markedly decreased 2-week survival relative to vehicle-treated controls, but echocardiography at 1 and 2 weeks post MI detected no differences in cardiac function. Sorafenib-treated hearts had significantly smaller diastolic and systolic volumes and reduced heart weights. High doses of sorafenib induced necrotic death of isolated myocytes in vitro, but lower doses did not induce myocyte death or affect inotropy. Histological analysis documented increased myocyte cross-sectional area despite smaller heart sizes after sorafenib treatment, further suggesting myocyte loss. Sorafenib caused apoptotic cell death of cardiac- and bone-derived c-kit+ stem cells in vitro and decreased the number of BrdU+ (5-bromo-2'-deoxyuridine+) myocytes detected at the infarct border zone in fixed tissues. Sorafenib had no effect on infarct size, fibrosis, or post-MI neovascularization. When sorafenib-treated animals received metoprolol treatment post MI, the sorafenib-induced increase in post-MI mortality was eliminated, cardiac function was improved, and myocyte loss was ameliorated.

CONCLUSIONS

Sorafenib cardiotoxicity results from myocyte necrosis rather than from any direct effect on myocyte function. Surviving myocytes undergo pathological hypertrophy. Inhibition of c-kit+ stem cell proliferation by inducing apoptosis exacerbates damage by decreasing endogenous cardiac repair. In the setting of MI, which also causes large-scale cell loss, sorafenib cardiotoxicity dramatically increases mortality.