| Objective:(-)-MHED is an analogue of metaraminol,and it is concentrated selectively in the regionals that the sympathetic nerves distributed richly,such as the heart and the adrenal medulla.The uptake of(-)-MHED reflects the transport,storage of catecholamine and the reuptake of neuron.Its alpha methyl side chain can resist oxidative deamination of MAO,and so,(-)-MHED has the characteristic that it can not be metabolized by MAO and COMT by comparision to NE.The study of animal models and the pharmacokinetic of isolated organ system suggests that NE's concentration is related to the clearance rate of(-)-MHED.Therefore,the use of carbon-11 radionuclide labeled(-)-[11C]MHED is a radiotracer which is suitable for human mapping of sympathetic nervous system using PET.The aim of this study is that,firstly,regard metaraminol and norepinephrine as the positive control,and compare the effection between(-)-MHED and calA adrenergic receptor using the molecular simulation method.At the same time,make this effection comparison to the other 3 optical isomers of(-)-MHED.Furthermore,explore that the reason why(-)-MHED can be chosen as one of the radiotracer of PET among the 4 optical isomers at the atomic level.Secondly,(-)-[11C]MHED is radiosynthesized and purified by cyclotron and carbon-11 mutifunciton module automatically.The quality control system of(-)-[11C]MHED is established for confirming that it is suitable for human injection.The relationship between the radiolabel rates and reaction conditions are researched as well.The optimal reaction conditions are also determined.At present,there is no reports that(-)-[11C]MHED has been used in the detection of PHEO in and out of adrenal.In this study,MHED PET are given to healthy controls to confirm the normal distribution;for suspected PHEO/paraganglioma patients,with surgical pathology results as the golden standard,the feasibility of checking(-)-[11C]MHED in detection of sympathetic nerve tumor in PET/CT is discusse.At the same time,its value in diagnosis of PHEO/paraganglioma is compared with FDG PET.Methods:The 3D structure of alA adrenergic receptor was built by homology modeling method,using the turkey ?1 adrenergic receptor/isopropylnoradrenaline X-ray crystal structre as template.Metaraminol,noradrenaline,and four MHED isomers were then docked into the active site of alA adrenergic receptor using Schrodinger Suite 2009 Update 1 software.Finally,the above complexes were used to carry out molecular dynamics simulations using Gromacs 4.5.3.The synthesis processes are as follows:the[11C]methylation reagent is prepared via 14N(p,a)11C nuclear reaction and certain chemical methods,then(-)-[11C]MHED is synthesized by direct N-methylation of metaraminol with the[11C]methylation reagent and purified by semi-preparative reversed-phase HPLC.In PET imaging studies,healthy controls and the patients whose blood pressure abnormal and the urine VMA level within 24h increased are selected in the MHED and FDG PET.These patients are suspected patients with PHEO/paraganglioma in clinical.The diagnosis and the corresponding treatments are determined according to the results of biochemical and PET/CT examinations.The value of MHED and FDG PET imaging in PHEO/paraganglioma are verified on the basis of surgical pathology and clinical follow-up results.Results:In this work,the alA adrenergic receptors share high homology with the template.The Ramachandran plot shows that resultant homology model have acceptable stereochemical parameters.The docking models of positive control(agonists)appear to provide agreement with site directed mutagenesis results.Therefore,it could suggest that the constructed protein 3 dimensional structure is reliable.Molecular dynamics simulation results show that the impact of four MHED isomers on the receptor backbone movement is similar with positive control.The process of radiochemical synthesis and purification of(-)-[11C]MHED is convenient,and the method is mature.The results of quality controls presents(-)-[11C]MHED is suitable for human injection.The results of MHED PET imaging of healthy controls are similar to the previous report.Although the SUVmax and the SUVmean are different,the metabolism differences of each organ are consistent.The level of MHED concentration is increased significantly in the tissues of sympathetic nerves distribution,especially in the tissues that the norepinephrine metabolised and excretioin.Suspected PHEO/paraganglioma can be diagnosed accurately by MHED PET.The benign and malignant diagnosis of PHEO can be achived combined with the results of FDG PET.Conclusion:The results of molecular simulation suggests that the electrostatic interaction of(-)-MHED with Ser1 88 and Asp 106 is stronger than the other three isomers,which might be the reasons why(-)-MHED is more suitable to be used as PET/CT tracer.The whole process of radiosynthesis and purification of(-)-[11C]MHED is easy to operation.It can provide radiotracer for scientific researches and clinical imaging in animals and humans.The results of MHED PET imaging of healthy controls and the suspected PHEO/paraganglioma are ideal,building on a good basis for further clinical imaging works. |
PDF Full Text Request