Technetium-99m Cysteine; A Novel Radiopharmaceutical for Detection of Experimental Myocardial Infarction in Rats

Infarct avid radiopharmaceuticals are necessary for rapid and timely diagnosis of acute myocardial infarction. None of the infarct avid radiopharmaceuticals so far developed fulfill all the required criteria like rapid localization at the infarct, high avidity and specificity, and reasonable duration of scan positivity. 99mTc Cysteine was already reported from this laboratory as a suitable radiopharmaceutical to determine both morphology and function of kidney. The chemical structure of this radiopharmaceutical was also established. The present study demonstrates the affinity of the same chelate for damaged myocardial mass. 99mTc-cysteine was first tested on isoproterenol induced damaged rat myocardium, when ECG and histological studies demonstrated significant damage of the heart muscle following isoproterenol injection. The results were compared to that of 99mTc-glucarate. The uptake of 99mTc-cysteine in damaged rat myocardium was maximum (0.45% ID/g) when the animals were treated with isoproterenol 18 hrs before radiopharmaceutical injection; under the same experimental protocol 99mTc glucarate exhibited maximum heart uptake (0.263% ID/g) when injected 8 hrs after isoproterenol treatment. Evaluation was also performed on rat models of reperfused and non reperfused acute myocardial infarction. Animals were sacrificed after radiopharmaceutical injection and the excised hearts were subjected to radionuclide imaging, TTC and H-E staining. 99mTc-Cysteine chelate localized predominantly in the damaged portion. The highest infarct/viable tissue activity ratio (12/1) was obtained in 90 min occlusion model (protocol-2).