The Role Of Dopamine As An Endogenous Toxin Triggered By Inhibition Of VMAT In The Pathogenesis Of The Parkinson Disease

Parkinson Disease (PD) is a kind of progressive neural degeneration of nigrostriatal system. There are several hypothesis about the pathogenesis of PD. In recent years, from the selective cell lose in substantia nigra scientists found that dopamine as an endogenous toxin triggered by inhibition of VMAT, might play a key role in the pathogenesis of PD. Dopamine is a kind of catecholamines which is easy to be oxidized. It can be oxidized by oxidase or no-oxidase. The metabolites of dopamine and free radicals can damage cells and even lead them to death. VAMT can transport the monoamine neurotransmitters including dopamine trom cytoplasm into secretive vesicle. Thus, the dopamine level in the cytoplasm is very low and not high enough to act as an endogenous toxin. In this study we tested the dopamine toxicity of various concentration to PC 12 cells and the synergism of the selective VMAT inhibitor - reserpine and detected the role of dopamine as an endogenous toxin triggered by inhibition of VMAT which might play a key role in the pathogenesis of PD and thus to illuminate an pathogenesis which could interpret the progressive and selective characteristic of PD more perfectively and rationally.Methods: 1.PC12 cells were cultured and various concentration of dopamine was added when these cells were in logarithmicperiod, then the influence of dopamine with PC 12 cells was observed by MTT methods after 48h of culture. 2.To detect the death way of PC 12 cells that were disposed of by dopamine and reserpine with Annexin V-FITC duel dyeing methods with the aid of flow cytometer; To measure MDA and SOD in cytoplasm of PC 12 cells dealed with dopamine and reserpine . The cells were freezed and melted for three times. To observe the protecting function of anti-oxidizer: DTT, GSH and Chinese traditional medicine Maichong 1 for PC 12 cells that were also dealed with dopamine and reserpine.Results 1.Dopamine has poisonous effect on PC 12 cells and the effect has an dose relationship with dopamine. Reserpine has no poisonous effect when acting lonely, but has synergetic effect with dopamine.2. The poisonous effect of dopamine and reserpine with PC 12 cells was related with the increase of MDA and the increase of SOD reflects the oxidative metabolite toxicity of dopamine indirectly. The PC 12 cells that was disposed by dopamine and reserpine went to death with three ways: apoptosis, apoptosis then with secondary necrosis and necrosis. The unti-oxidants have protecting function for PC 12 cells dealed with medicine.The basic pathologic change of PD is that the decreased dopamine neurons in substantia nigra reach to 60-80%. This loss is necrosis or apoptosis about which we have no conclusion until now. PC12 cells is a kind of catecholamine cell line. It serve as a useful tool for neurotoxicology for its similarity with dopamine neurons in structure and function. Reserpine is a powful and selective inhibitor for VMAT. Our research indicated that dopamine has poisonous effect for PC 12 cells and become stronger with the increase of its concentration. Reserpine has no poisonous effect lonely but has synergetic effect with dopamine and this supports VMAT possesses protecting function by sequestering toxin from cytoplasm into vesicle. As PC 12 cells has no phenylalanine hydroxylase and can not synthetize-5-dopamine with phenylalanine in the cell culture liquid,so when acting lonely, reserpine has no poisonous effect even its concentration reaching at 1600 nmol/L. By the aid flow cytometer and dual dyeing ,we found the endogenous toxin of dopamine inducing death of PC 12 cells maily expresses by apoptosis, apoptosis with secondary necrosis and necrosis. The reason why dopamine as a kind of neurotransmitter in normal condition changes into endogenous toxin is because the protecting function of VMAT is inhibited. Thus, the dopamine which is easy to be oxidized produces free radicals by enzyme oxidation and no-enzyme oxidation . These free radicals attack the polyunsatured fatty acid in the cell membrane, then lipid...