PROMOTION OF LIVER CARCINOGENESIS BY OROTIC ACID

目前的建议审查的假设，乳清酸诱导肝 通过在细胞中创造不同的有丝分裂抑制环境来促进肿瘤 同时允许启动的肝细胞对 生长刺激形成肝病灶和结节。 在过去的赠款 期间，观察到乳清酸对肝细胞有丝分裂抑制 无论是在体外还是在体内。 此外，肝结节似乎是 对乳清酸的有丝分裂抑制作用具有相对抗性。 基于 根据这些最近的初步意见， 被提议。 (1)为了确定乳清酸发挥其 线粒体抑制作用;（2）确定肝细胞凋亡的机制， 结节对乳清酸的有丝分裂抑制作用产生抗性; (3)以确定乳清酸是否诱导有丝分裂抑制环境 当与肝细胞增殖刺激相结合时， 促进作用。 在第一个具体目标中，我们将确定 核糖核苷二磷酸还原酶（RNR）是线粒体的一个靶位点， 乳清酸的抑制作用。 乳清酸对大鼠肝细胞凋亡的影响 RNR活性和表达的调节将在 体外分离的原代肝细胞暴露于EGF和体内， 部分肝切除术（PH）后的肝脏。 乳清酸的抑制作用 酸将与核苷酸的不平衡相关， 乳清酸在肝细胞中诱导的脱氧核苷酸池。 第二 具体目的是研究肝细胞的抵抗是否 结节的有丝分裂抑制作用的乳清酸是由于缺陷， （i）乳清酸摄取和/或代谢为尿苷酸和/或 (ii)由于RNR改变，即对不平衡的影响不太敏感 在核苷酸/脱氧核苷酸池中。 两个体外实验都使用 来自结节的肝细胞和使用携带结节的大鼠的体内实验 将被雇用。 在第三个具体目标中，大鼠将开始与 二乙基亚硝胺和乳清酸诱导的有丝分裂抑制 环境与PH耦合，以确定这样的协议是否 选择性快速促进肝细胞生长形成病灶， 肝结节 由于核苷酸池和RNR是正常的细胞成分， 很容易推测乳清酸促进肝肿瘤的模型 也有可能扩展到其他器官。

The present proposal examines the hypothesis that orotic acid induces liver tumor promotion by creating differential mito-inhibitory environment in the surrounding liver while permitting the initiated hepatocytes to respond to growth stimuli to form hepatic foci and nodules. During the past grant period, it was observed that orotic acid is mito-inhibitory to hepatocytes both in vitro and in vivo. Further, hepatic nodules appear to be relatively resistant to the mito-inhibitory effect of orotic acid. Based on these recent preliminary observations the following three specific aims are proposed. (1) To determine the site at which orotic acid exerts its mito-inhibitory effect; (2) to determine the mechanism by which hepatic nodules become resistant to the mito-inhibitory effect of orotic acid; and (3) to determine whether orotic acid induced mito-inhibitory environment when coupled with a liver cell proliferative stimulus will exert a rapid promoting effect. In the first specific aim we will determine whether ribonucleosidedliphosphate reductase (RNR) is one target site of the mito- inhibitory effect of orotic acid. The effect of orotic acid on the regulation of the activity and expression of RNR will be examined both in vitro in isolated primary hepatocytes exposed to EGF and in vivo in the liver following partial hepatectomy (PH). The inhibitory effect of orotic acid will be correlated with the imbalances in nucleotide and deoxynucleotide pools induced in hepatocytes by orotic acid. The second specific aim examines the question whether the resistance of hepatic nodules to the mito-inhibitory effects of orotic acid is due to a defect in the (i) uptake and/or metabolism of orotic acid to uridylic acid and/or (ii) due to an altered RNR i.e. less sensitive to the effects of imbalances in nucleotide/deoxynucleotide pools. Both in vitro experiments using hepatocytes from nodules and in vivo experiments using rats bearing nodules will be employed. In the third specific aim, rats will be initiated with diethylnitrosamine and subjected to orotic acid induced mito-inhibitory environment coupled with PH to determine whether such a protocol selectively and rapidly promote the growth of hepatocytes to form foci and hepatic nodules. Since nucleotide pools and RNR are normal cellular constituents, it was tempting to speculate that orotic acid model of liver tumor promotion has the potential to be extended to other organs as well.