Mechanism underlying the selective removal of copper accumulating in the liver of LEC rats and development of the therapy for Wilson disease

肝豆状核变性（Wilson disease，Wilson病）是由于遗传性铜代谢缺陷导致铜（Cu）在肝脏中异常蓄积而引起的，Cu以与金属硫蛋白（MT）结合的形式蓄积，即Cu，Zn-MT。当铜的积累超过MT的生物合成能力时，不含锌的Cu-MT开始作为促氧化剂发挥作用并导致急性肝炎。肝、血、肾、尿中Cu的形态研究揭示了这一机制，肝豆状核变性的治疗必须通过以下途径来降低Cu在肝中的蓄积：i）喂低Cu含量的饲料，ii）降低胃肠道的吸收，iii）从肝中的Cu，Zn-MT中去除Cu。在本研究报告中，审查了第三种办法。基于Cu、Mo、S之间形成络合物的原理，采用四硫代钼酸盐（TTM）去除Wilson病动物模型LEC大鼠肝脏中的Cu。已经提出了TTM和与MT结合的Cu之间的反应以及Cu从肝脏中去除的精确机制。TTM不仅是特定的各种金属之间的铜，但也铜结合MT。TTM的选择性去除铜被证明在体内，它也表明，从肝脏中去除的铜不重新分配到其他器官。从MT中去除的Cu以Cu/TTM复合物的形式流出到胆汁和血液中，然后排泄到粪便中，但不进入尿液。作为副作用，已经表明，过度使用TTM治疗会导致严重的Cu缺乏症，并且在酸性条件下水解产生的硫离子会急性影响肝功能。因此，建议将TTM作为单次或多次注射给药，但不要重复，以避免由于过量而引起的副作用。

Wilson disease is caused by an abnormal accumulation of copper (Cu) in the liver owing to the inherited defect in Cu metabolism, and the Cu accumulates in the form bound to metallothionein (MT), Cu,Zn-MT. When Cu accumulates more than the biosynthetic capacity of MT, Cu-MT without Zn starts to work as a prooxidant and causes acute hepatitis. This mechanism was revealed by the speciation study of Cu in the liver, bloodstream, kidneys and urine.Cu accumulating in the liver has to be lowered in the therapy of Wilson disease either by i) feeding diets of low Cu content, ii) lowering the absorption at the gastro-intestinal tract or iii) removing Cu from Cu, Zn-MT in the liver. In the present study, the third approach was examined. Based on the complex formation between Cu, Mo and S, tetrathiomolybdate (TTM) was used to remove Cu in the liver of LEC rats, an animal model of Wilson disease. Precise mechanisms underlying the reaction between TTM and Cu bound to MT and underlying the removal of Cu from liver have been presented. TTM is specific not only to Cu among various metals but also to Cu bound to MT.The selective removal of Cu by TTM was demonstrated in vivo, and it was also shown that the Cu removed from the liver does not redistribute to other organs. The Cu removed from MT is effluxed into bile and bloodstream in the form of the Cu/TTM complex, and then excreted into feces but not into urine.As side-effects, it was shown that excessive treatment with TTM causes a severe Cu deficiency, and that sulfide ions produced by hydrolysis under acidic conditions affect acutely liver function. As a result, it has been recommended to administer TTM as a single or several injections but not repeatedly to avoid the side-effects due to overdose.