BACKGROUND Therapies targeting altered activity of pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) have been proposed for hepatomas. However, the activities of these pathways in hepatomas in vivo have not been distinguished. Here we examined pyruvate entry into the tricarboxylic acid (TCA) cycle through PDH versus PC in vivo using hepatoma-bearing rats. METHODS Hepatoma-bearing rats were generated by intrahepatic injection of H4IIE cells. Metabolism of 13C-labeled glycerol, a physiological substrate for both gluconeogenesis and energy production, was measured with 13C NMR analysis. The concentration of key metabolites and the expression of relevant enzymes were measured in hepatoma, surrounding liver, and normal liver. RESULTS In orthotopic hepatomas, pyruvate entry into the TCA cycle occurred exclusively through PDH and the excess PDH activity compared to normal liver was attributed to downregulated pyruvate dehydrogenase kinase (PDK) 2/4. However, pyruvate carboxylation via PC and gluconeogenesis were minimal, which was linked to downregulated forkhead box O1 (FoxO1) by Akt activity. In contrast to many studies of cancer metabolism, lactate production in hepatomas was not increased which corresponded to reduced expression of lactate dehydrogenase. The production of serine and glycine in hepatomas was enhanced, but glycine decarboxylase was downregulated. CONCLUSIONS The combination of [U-13C3]glycerol and NMR analysis enabled investigation of multiple biochemical processes in hepatomas and surrounding liver. We demonstrated active PDH and other related metabolic alterations in orthotopic hepatomas that differed substantially not only from the host organ but also from many earlier studies with cancer cells.

中文翻译：

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活性丙酮酸脱氢酶和大鼠原位肝瘤糖异生受损。

背景技术已经提出了针对丙酮酸脱氢酶（PDH）和丙酮酸羧化酶（PC）的活性改变的疗法。然而，这些途径在体内肝癌中的活性尚未被区分。在这里，我们研究了携带肝癌的大鼠体内丙酮酸通过PDH相对于PC进入三羧酸（TCA）循环的过程。方法通过肝内注射H4IIE细胞产生荷瘤大鼠。用13 C NMR分析测量13 C标记的甘油（糖异生和能量产生的生理底物）的代谢。在肝癌，周围肝脏和正常肝脏中测量关键代谢物的浓度和相关酶的表达。结果在原位肝癌中，丙酮酸仅通过PDH进入TCA周期，与正常肝脏相比，PDH活性过高归因于丙酮酸脱氢酶激酶（PDK）2/4的下调。然而，丙酮酸通过PC的羧化和糖异生作用极少，这通过Akt活性与下调的叉头盒O1（FoxO1）相关。与许多癌症代谢研究相反，肝癌中乳酸的产生并未增加，这对应于乳酸脱氢酶表达的降低。肝癌中丝氨酸和甘氨酸的产生增加，但是甘氨酸脱羧酶被下调。结论[U-13C3]甘油和NMR分析相结合可以研究肝癌和周围肝脏的多种生化过程。