Central Institute of Isotope Science, Hokkaido University, Hokkaido 060-0815, Japan; Graduate School of Biomedical Science and Engineering, Hokkaido University, Hokkaido 060-0815, Japan.
Faculty of Pharmaceutical Sciences, Hokkaido University, Hokkaido 060-0812, Japan.
Nucl Med Biol. 2020 Mar-Apr;82-83:25-32. doi: 10.1016/j.nucmedbio.2019.12.006. Epub 2019 Dec 16.
Although liver biopsy is the gold standard for the diagnosis of nonalcoholic steatohepatitis (NASH), it has several problems including high invasiveness and sampling errors. Therefore, the development of alternative methods to overcome these disadvantages is strongly required. In this study, we evaluated the potential use of our tracer targeting thymidine phosphorylase (TYMP), 5-[I]iodo-6-[(2-iminoimidazolidinyl)methyl]uracil ([I]IIMU) for the diagnosis of NASH.
The mice used as the NASH model (hereafter, NASH mice) were prepared by feeding a methionine- and choline-deficient diet for 4 weeks. A control group was similarly given a control diet. The expression levels of the TYMP gene and protein in the liver were examined by real-time reverse-transcription polymerase chain reaction and western blot analyses. The localizations of [I]IIMU and the TYMP protein in the liver were examined by autoradiography and immunohistochemical staining, respectively. Finally, the mice were injected with [I]IIMU and single-photon emission tomography (SPECT) imaging was conducted.
The hepatic expression levels of TYMP were significantly lower in the NASH mice than in the control mice at both mRNA and protein levels, suggesting that a decrease in TYMP level could be an indicator of NASH. [I]IIMU was uniformly distributed in the liver of the control mice, whereas it showed a patchy distribution in that of the NASH mice. The localization of [I]IIMU was visually consistent with that of the TYMP protein in the liver of the control and NASH mice. SPECT analysis indicated that the hepatic accumulation of [I]IIMU in the NASH mice was significantly lower than that in the control mice [SUV (g/ml): 4.14 ± 0.87 (Control) vs 2.31 ± 0.29 (NASH)].
[I]IIMU may provide a noninvasive means for imaging TYMP expression in the liver and may be applicable to the diagnosis of NASH.
尽管肝活检是诊断非酒精性脂肪性肝炎（NASH）的金标准，但它存在一些问题，包括高侵袭性和取样误差。因此，强烈需要开发替代方法来克服这些缺点。在这项研究中，我们评估了我们的胸腺嘧啶磷酸化酶（TYMP）靶向示踪剂 5-[I]碘-6-[[2-亚氨基咪唑烷-1-基]甲基]尿嘧啶（[I]IIMU）用于诊断 NASH 的潜力。
使用蛋氨酸和胆碱缺乏饮食喂养 4 周制备 NASH 模型（以下简称 NASH 小鼠）。对照组同样给予对照饮食。通过实时逆转录聚合酶链反应和 Western blot 分析检查肝 TYMP 基因和蛋白的表达水平。通过放射自显影和免疫组织化学染色分别检查 [I]IIMU 和 TYMP 蛋白在肝脏中的定位。最后，给小鼠注射 [I]IIMU 并进行单光子发射计算机断层扫描（SPECT）成像。
在 mRNA 和蛋白水平上，NASH 小鼠的肝 TYMP 表达水平均明显低于对照组，表明 TYMP 水平降低可能是 NASH 的一个指标。[I]IIMU 在对照组小鼠的肝脏中均匀分布，而在 NASH 小鼠的肝脏中则呈斑片状分布。[I]IIMU 的定位与对照组和 NASH 小鼠肝脏中 TYMP 蛋白的定位在视觉上一致。SPECT 分析表明，NASH 小鼠肝内 [I]IIMU 的摄取明显低于对照组 [SUV（g/ml）：4.14±0.87（对照组）比 2.31±0.29（NASH）]。
[I]IIMU 可能为肝 TYMP 表达的成像提供一种非侵入性手段，可用于 NASH 的诊断。
