Moriyama Mitsuaki, Fujimoto Yuki, Rikimaru Shizuka, Ushikai Miharu, Kuroda Eishi, Kawabe Kenji, Takano Katsura, Asakawa Akihiro, Inui Akio, Eto Kazuhiro, Kadowaki Takashi, Sinasac David S, Okano Yoshiyuki, Yazaki Masahide, Ikeda Shu-Ichi, Zhang Chunhua, Song Yuan-Zong, Sakamoto Osamu, Kure Shigeo, Mitsubuchi Hiroshi, Endo Fumio, Horiuchi Masahisa, Nakamura Yoichi, Yamamura Ken-Ichi, Saheki Takeyori
Laboratory of Integrative Physiology in Veterinary Sciences, Osaka Prefecture University, Izumisano, Japan.
Laboratory of Yamamura Project, Institute of Resource Development and Analysis, Kumamoto University, Kumamoto, Japan; Institute for Health Sciences, Tokushima Bunri University, Tokushima, Japan.
Biochim Biophys Acta. 2015 Sep;1852(9):1787-95. doi: 10.1016/j.bbadis.2015.04.023. Epub 2015 May 5.
The mitochondrial aspartate-glutamate carrier isoform 2 (citrin) and mitochondrial glycerol-3-phosphate dehydrogenase (mGPD) double-knockout mouse has been a useful model of human citrin deficiency. One of the most prominent findings has been markedly increased hepatic glycerol 3-phosphate (G3P) following oral administration of a sucrose solution. We aimed to investigate whether this change is detectable outside of the liver, and to explore the mechanism underlying the increased hepatic G3P in these mice. We measured G3P and its metabolite glycerol in plasma and urine of the mice under various conditions. Glycerol synthesis from fructose was also studied using the liver perfusion system. The citrin/mGPD double-knockout mice showed increased urine G3P and glycerol under normal, fed conditions. We also found increased plasma glycerol under fasted conditions, while oral administration of different carbohydrates or ethanol led to substantially increased plasma glycerol. Fructose infusion to the perfused liver of the double-knockout mice augmented hepatic glycerol synthesis, and was accompanied by a concomitant increase in the lactate/pyruvate (L/P) ratio. Co-infusion of either pyruvate or phenazine methosulfate, a cytosolic oxidant, with fructose corrected the high L/P ratio, leading to reduced glycerol synthesis. Overall, these findings suggest that hepatic glycerol synthesis is cytosolic NADH/NAD(+) ratio-dependent and reveal a likely regulatory mechanism for hepatic glycerol synthesis following a high carbohydrate load in citrin-deficient patients. Therefore, urine G3P and glycerol may represent potential diagnostic markers for human citrin deficiency.
线粒体天冬氨酸-谷氨酸载体亚型2（柠素）和线粒体甘油-3-磷酸脱氢酶（mGPD）双敲除小鼠已成为人类柠素缺乏症的有用模型。最显著的发现之一是口服蔗糖溶液后肝脏甘油3-磷酸（G3P）明显增加。我们旨在研究这种变化在肝脏外是否可检测到，并探讨这些小鼠肝脏G3P增加的潜在机制。我们在各种条件下测量了小鼠血浆和尿液中的G3P及其代谢产物甘油。还使用肝脏灌注系统研究了果糖的甘油合成。在正常进食条件下，柠素/mGPD双敲除小鼠的尿液G3P和甘油增加。我们还发现禁食条件下血浆甘油增加，而口服不同的碳水化合物或乙醇会导致血浆甘油大幅增加。向双敲除小鼠的灌注肝脏中注入果糖可增强肝脏甘油合成，并伴随着乳酸/丙酮酸（L/P）比值的相应增加。与果糖共同注入丙酮酸或吩嗪硫酸甲酯（一种胞质氧化剂）可纠正高L/P比值，从而减少甘油合成。总体而言，这些发现表明肝脏甘油合成依赖于胞质NADH/NAD(+)比值，并揭示了柠素缺乏患者高碳水化合物负荷后肝脏甘油合成的可能调节机制。因此，尿液G3P和甘油可能代表人类柠素缺乏症的潜在诊断标志物。
