Anthracyclines are widely used in chemotherapy regimens for several malignancies, with cardiotoxicity being the major limiting factor in high-dose schedules. Recently, it was reported that doxorubicin induces apoptosis in cardiac muscle cells in vivo and, as such, is expected to be involved in the genesis of doxorubicin-induced cardiomyopathy. The aim of this study was to validate an animal model for in vivo monitoring of doxorubicin cardiotoxicity by means of scintigraphic detection of apoptosis.
Methods: Three groups of 5 male Wistar rats each were treated for 3, 4, and 5 times with a weekly intraperitoneal injection of doxorubicin at 2.5 mg/kg. At 24 h before and 24 h after the final treatment, (99m)Tc-annexin pinhole scintigraphy was performed. A control group of 5 rats was scanned without doxorubicin treatment. A cardiac uptake ratio was calculated from planar scintigraphy results with the following formula: (mediastinum - fat)/fat. After scintigraphy, the rats were sacrificed, and the heart was processed for histologic analysis.
Results: Incremental general signs of illness were observed with increasing total cumulative doxorubicin dose. Rats treated for 3, 4, and 5 wk with doxorubicin showed significantly higher uptake ratios of, respectively, 4.0 +/- 0.52 (mean +/- SEM), 4.8 +/- 0.46, and 5.2 +/- 0.17 after the final treatment; the ratio for controls was 1.84 +/- 0.05 (P < 0.05). Histologic analysis confirmed cardiac stress in treated groups, with an increasing left ventricular atrial natriuretic factor messenger RNA expression level with increasing cumulative doxorubicin dose. Late apoptosis was confirmed by terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling in the rats treated for 5 wk.
Conclusion: Acute doxorubicin-induced cardiomyopathy based on early apoptosis can be assessed and imaged with annexin V scintigraphy in rats. This finding makes it possible to use this animal model for repetitive noninvasive evaluation of cardioprotective regimens for anthracycline cardiotoxicity.