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Metaiodobenzylguanidine: Evaluation of Its Potential as a Tracer for Monitoring Doxorubicin Cardiomyopathy

Division of Nuclear Medicine of the Department of Radiology, Massachusetts General Hospital and the Departments of Radiology, Harvard Medical School
Department of Pathology, New England Deaconess Hospital, Boston, Massachusetts

Correspondence: For correspondence or reprints contact: Alan J. Fischman, MD, PhD, Div. of Nuclear Medicine, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114.

ABSTRACT

We evaluated alterations in cardiac adrenergic neuron activity and progression of left ventricular dysfunction in comparison with the severity of structural changes using a rat model of adriamycin cardiomyopathy. Rats were treated with adriamycin (2 mg/kg s.c. once a week) for 6, 7, 8 and 9 wk. Accumulation of ¹²⁵I-metaiodobenzylguanidine (MIBG) 4 hr after intravenous administration was determined and left ventricular ejection fraction (LVEF) was calculated from gated blood-pool images. H & E and Masson-Trichrome stained specimens of the myocardium were examined by light microscopy. Histopathologic examination demonstrated dose-dependent myocyte damage, although there were no differences between the 8-wk and 9-wk groups. LVEF did not differ between controls and the 6-wk group (81.3% ± 5.5% versus 82.1% ± 4.8%, p = ns). LVEF began to decrease slightly in the 7-wk group (75.0% ± 5.7%, p < 0.05) and showed a remarkable decrease in the 8-wk group (53.7% ± 2.6%, p < 0.001). In the 9-wk group, LVEF diminished to 47.9% ± 3.1% (p < 0.001), accompanied by massive pleural effusions and ascites. MIBG accumulation in the heart (%ID/heart) significantly and progressively diminished; 1.42% ± 0.15% in the 6-wk group, 1.06% ± 0.16% in the 7-wk group, 0.77% ± 0.13% in the 8-wk group and 0.34% ± 0.11% in the 9-wk group, respectively p < 0.001, compared to controls (1.99% ± 0.30%). These results demonstrate that MIBG accumulation in the heart showed a greater and more linear dose-dependent decrease than LVEF. Furthermore, MIBG uptake was significantly reduced in the 6-wk group where only mild myocyte damage (isolated vacuolation or myofibrillar loss) was observed. Thus, MIBG may be a sensitive biochemical marker of adriamycin cardiomyopathy.

FOOTNOTES

Note: Review of the manuscript was made under the supervision of Guest Editor Steven M. Larson, Memorial Sloan-Kettering Cancer Center, New York, NY