Metabolism of radiolabeled methionine in hepatocellular carcinoma.
Metabolism of radiolabeled methionine in hepatocellular carcinoma.
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DOI：
10.1007/s11307-013-0678-z
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发表时间：
2014-02
影响因子：
3.1
通讯作者：
Lee Z
中科院分区：
文献类型：
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作者：
Kuang Y;Wang F;Corn DJ;Tian H;Lee Z
放射性标记的甲硫氨酸（Met）有望用于肝细胞癌（HCC）的正电子发射断层扫描（PET）成像。然而，其在HCC中的代谢途径尚未完全了解。在这项研究中，放射性标记的Met在HCC中的代谢途径进行了研究。为了模拟放射性标记的Met的快速血液清除，进行脉冲追踪实验。将L-[甲基-3H]-Met或L-[1- 14 C]-Met在对照或放线菌酮处理的WCH 17细胞和大鼠肝细胞上脉冲5分钟，并用冷培养基追踪。随后从全细胞的酸可沉淀和酸可溶部分中提取并测量水溶性、脂溶性、DNA、RNA和蛋白质相。通过放射性薄层色谱法进一步分离放射性代谢产物Met、S-腺苷甲硫氨酸（SAM）、S-腺苷高半胱氨酸、Met亚砜和Met砜。(1)两种细胞对L-[甲基-3H]-Met的摄取均高于L-[1- 14 C]-Met。在大鼠肝细胞中，L-[甲基-3H]-Met的摄取显著高于L-[1- 14 C]-Met，这可能有助于其在使用L-[甲基-11 C]-Met的HCC PET成像中观察到的周围肝组织中的生理蓄积。与大鼠肝细胞相比，WCH 17细胞对这两种放射性示踪剂的摄取显著更高。(2)对于L-[甲基-3H]-Met，主要的细胞内摄取主要在蛋白相中，在较小程度上在磷脂酰乙醇胺（PE）甲基化途径中，其在55分钟追踪期内相当稳定（主要代谢产物为SAM、Met、Met亚砜和Met砜）。相比之下，大鼠肝细胞中Met的摄取主要指向通过PE甲基化途径合成磷脂酰胆碱（PC）（主要代谢产物为PC）。(3)两种细胞类型都将L-[1- 14 C]-Met主要掺入蛋白质合成中。(4)最后，当蛋白质合成途径被抑制时，在WCH 17细胞中，来自L-[甲基-3H]-Met的SAM掺入脂质类（PC是主要代谢产物）的速率降低，表明该途径可能在HCC中受损。这项研究表明，不同的代谢途径的放射性标记的甲硫氨酸之间存在的肝癌和周围的肝组织，并有助于增加摄取的放射性标记的甲硫氨酸在肝癌的模式。
Radiolabeled methionine (Met) promises to be useful in the positron emission tomography (PET) imaging of hepatocellular carcinoma (HCC). However, its metabolic routes in HCC have not yet been fully understood. In this study, the metabolic pathway(s) of radiolabeled Met in HCC were investigated. To simulate the rapid blood clearance of radiolabeled Met, pulse–chase experiments were conducted. L-[methyl-3H]-Met or L-[1-14C]-Met was pulsed over control or cycloheximide- treated WCH17 cells and rat hepatocytes for 5 min and chased with cold media. The water-soluble, lipid-soluble, DNA, RNA, and protein phases were subsequently extracted and measured from the acid-precipitable and acid-soluble fractions of whole cells. The radioactive metabolites Met, S- adenosylmethionine (SAM), S-adenosylhomocysteine, Met sulfoxide, and Met sulfone were further separated by radio thin layer chromatography. (1) The uptake of L-[methyl-3H]-Met in both cell types was higher than that of L-[1-14C]-Met. In rat hepatocytes, the uptake of L-[methyl-3H]-Met was significantly higher than that of L-[1-14C]-Met, which may contribute to its physiologic accumulation in surrounding hepatic tissues seen in PET imaging of HCC using L-[methyl-11C]-Met. Compared to rat hepatocytes, WCH17 cells had significantly higher uptake of both radiotracers. (2) For L-[methyl-3H]-Met, the major intracellular uptake was found mostly in the protein phase and, to a lesser degree, in the phosphatidylethanolamine (PE) methylation pathway, which is fairly stabilized within the 55-min chase period (the main metabolites were SAM, Met, Met sulfoxide, and Met sulfone). In contrast, the uptake of Met in rat hepatocytes mainly points to phosphatidylcholine (PC) synthesis through the PE methylation pathway (the main metabolite was PC). (3) Both cell types incorporated L-[1-14C]-Met predominantly into protein synthesis. (4) Finally, when the protein synthesis pathway was inhibited, the incorporation of SAM derived from L-[methyl-3H]-Met to lipid class (PC was the main metabolite) occurred at a reduced rate in WCH17 cells, suggesting that the route may be impaired in HCC. This study demonstrated that different metabolic pathways of radiolabeled Met exist between HCC and surrounding hepatic tissue and contribute to the patterns of increased uptake of radiolabeled Met in HCC.