Imaging Of Acute Myocardial Infarction With TSPO Ligand CB86 Labeled ^99mTc Based SPECT/CT

Backgrounds and PurposeIn recent years,with the development of aging society,the prevalence of acute myocardial infarction has been high,and has become a disease with the highest mortality after cancer.Therefore,how to improve the early diagnosis of acute myocardial infarction is of great significance for the treatment of acute myocardial infarction and the prognosis of acute myocardial infarction.More and more studies have shown that acute myocardial infarction will be accompanied by a large number of mononuclear/macrophage infiltration in the infarct myocardial region.The severity of acute myocardial infarction is also related to the degree of myocardial inflammatory cell infiltration.So long as we can design a probe that can accurately target mononuclear/macrophages in the infarcted myocardial region at the early stage of onset,we can diagnose acute myocardial infarction at an early stage.At the same time,the severity of acute myocardial infarction can be judged.TSPO-formerly known as the Peripheral Benzodiazepine Receptor(PBR)-is an ubiquitous 18 kDa molecule located on the outer mitochondrial membrane(OMM)and has a high evolutionnary conservation,it can be expressed in CNS microglia and correlates with the inflammatory states of the CNS(Central Nervous System),because of which it is widely applied in the detection of diseases in CNS.In peripheral tissues,it exists in monouclear cells s lymphocyte、multinucleargiant cell and bronchial and bronchiole epithelium、pneumocytes and alveolar macrophages in lung,so it also been used in some peripheral inflammation.Besides,TSPO is also expressed in tumor cell,which is thought positively assosiatant with tumor progression and malignancy.Many radioligands have been explored for imaging the 18-kDa translocator protein(TSPO),a diagnostic and therapeutic target for acute myocardial infarction.Here,we aimed to evaluate the TSPO novel radioligand 99mTc-CB86 for positron emissiontomography(SPECT)imaging of acute myocardial infarction by the estimation of physicochemical characteristic、the perform of cell assays and immunohistology,as well as MicroSPECT imaging to achieve early acute myocardial infarction inflammatory infiltration imaging.Procedures1、The preparation of 99mTc-CB86 was made by making 99mTc-radiolabeled on the tosylate substrate and the physicochemical characteristic was evaluated including the stability in saline snd mouse serum in vitro.2、The rat model of acute myocardial infarction was established by permanent transmural coronary artery ligation.3、After the establishment of acute myocardial infarction(AMI)rat model,the success of the model was detected,including echocardiography and electrocardiogram to detect the changes of St segment.4、The infarct myocardial area was mainly determined by intravenous injection of 18 F-FDG under MicroPET.5、MicroSPECT imaging was performed to determine whether the tracer could be used in the imaging of acute myocardial infarction.6、It was verified that the tracer was targeted at the inflammatory infarct area of rat myocardium,and the biological distribution was mainly used to observe the tracer in the infarcted myocardial area of rats.The distribution of normal myocardial region and other organs was confirmed by autoradiography on rat myocardium to confirm the reliability of MicroSPECT.Finally,the high expression of TSPO in myocardial infarction area was confirmed by immunohistochemical staining-anti-PBR.Results1、The radiochemical purity of 4h was still more than 95%both in saline and serum,which showed 99mTc-CB86 had a good stabiliity in vitro.2、After ligation of coronary artery,the cardiac function of rats was obviously damaged,and the amplitude of myocardial anterior wall systolic motion was decreased significantly(EF=84.5%of normal;EF=58.0%of Myocardial infarction);At the same time,St segment elevation can be seen by electrocardiogram,indicating that myocardial infarction has occurred in rats.3.The area of myocardial infarction was located by MicroPET,and the MicroSPECT was performed by injecting 1mG99mTc-CB86 into penile vein.An image shows that the infarct area is filled with radioactive signals.It is feasible to infer that 99mTc-CB86 has targeted myocardial infarction area by MicroSPECT imaging.4、The area of myocardial infarction was measured quantitatively by γ-counter.myocardial uptake of 99mTc-CB86(0.52 + 0.07ID%/g,MI area;0.16 + 0.02ID%/g,non-MI area)proved the high expression of CB86 in the infarct region,and there was obvious contrast between liver,spleen,lung and kidney.The higher uptake of thyroid gland tissue probes may be related to the presence of TSPO targets in the gland tissue.After the heart sections of the model rats were taken,TTC staining and autoradiography were performed.TTC staining can clearly show the infarct area.The myocardial infarction area was observed to be filled with radioactive signals.This confirms that MicroSPECT imaging radionuclide signals do appear at myocardial infarction.5.further validation of MicroSPECT imaging of myocardial infarction area radioactivity is due to the 99mTc-CB86 target to the infarct zone of high expression of TSPO,thus we remove the myocardial infarction myocardial sections immunohistochemical,proved that the high expression of the area is TSPO.The myocardial sections stained by HE,inflammatory cells by immunohistochemistry(Anti-PBR)staining,we found that the infiltration of inflammatory cells with high expression of TSPO significantly.ConclusionIn this experiment,99mTc-CB86 has good physical and chemical properties in vitro and can be used for in vivo imaging.Then we completed the preliminary study of 99mTc-CB86 probe MicroSPECT imaging in rat myocardial infarction model.This will provide some guidance for the pharmacokinetic study of probes in animals and information on the pathological mechanism of acute myocardial infarction.And applied to the early diagnosis of disease.