Yan Weili, Xiong Ping, Liu Zhengwei, Huang Gang
Department of Nuclear Medicine, Renji Hospital Affiliated to Shanghai Second Medical University, Shanghai 200127, China.
Rapid Commun Mass Spectrom. 2006;20(4):602-8. doi: 10.1002/rcm.2345.
The L-[1-13C]phenylalanine breath test (PheBT) could potentially advance the evaluation of hepatocyte function and liver functional reserve. However, because the factors influencing PheBT results have not been clarified, the clinical application of the test has been limited. This study investigated the relationship between the parameters of PheBT, performed with air isotope ratio mass spectrometry, and the activity of phenylalanine hydroxylase (PAH), the phenylalanine metabolism rate-limiting enzyme, in rat liver, and proposes valid parameters for the assessment of liver function. Chronic injury to the liver was induced by the administration of CCl4 to male Sprague-Dawley rats for either 8 or 12 weeks. Livers from rats in the two cirrhotic groups were discolored, enlarged and roughly textured, with cells filled with fat granules of various sizes, pseudolobuli formations, and regenerated tubercles. Of the 12 parameters tested, only the unit liver weight (LW) breath test parameters, including the maximum abundance of 13C in breath (13Cmax/LW), 13C abundance in breaths 2 and 7 min after administration of L-[1-(13)C]phenylalanine (13C-phe) (13C2/LW and 13C7/LW), cumulative 13C excretion 10 and 30 min after 13C-phe administration (AUC10/LW and AUC30/LW), and the 13C excretion rate constant (PheBT-k/LW) were significantly affected in the chronic liver injury groups. There was no significant difference in the total PAH activity in liver among the three groups, but there was significant difference in unit LW PAH activity. Total PAH activity in the liver was significantly correlated with 13Cmax, 13C2, 13C7, AUC10, AUC30 and PheBT-k, while the unit LW PAH activity was significantly correlated with 13Cmax/LW, 13C2/LW, 13C7/LW, AUC10/LW, AUC30/LW and PheBT-k/LW. PheBT-k/LW was also correlated with biochemical indices that are used to assess liver function. The present findings indicate that the PheBT results based on air isotope ratio mass spectrometry can quantitatively reflect the change in total PAH activity in the livers of chronically injured rats. PheBT-k and PheBT-k/LW are the most sensitive among the test parameters, and can be used to assess liver functional reserve and hepatocyte damage at the molecular level.
L-[1-¹³C]苯丙氨酸呼气试验（PheBT）可能会推动对肝细胞功能和肝功能储备的评估。然而，由于影响PheBT结果的因素尚未明确，该试验的临床应用受到了限制。本研究调查了采用空气同位素比质谱法进行的PheBT参数与大鼠肝脏中苯丙氨酸羟化酶（PAH）活性（苯丙氨酸代谢的限速酶）之间的关系，并提出了评估肝功能的有效参数。通过给雄性Sprague-Dawley大鼠腹腔注射四氯化碳8周或12周来诱导慢性肝损伤。两个肝硬化组大鼠的肝脏变色、肿大且质地粗糙，细胞内充满大小不一的脂肪颗粒，有假小叶形成和再生结节。在测试的12个参数中，只有单位肝脏重量（LW）呼气试验参数，包括呼气中¹³C的最大丰度（¹³Cmax/LW）、注射L-[1-(¹³)C]苯丙氨酸（¹³C-苯丙氨酸）后第2分钟和第7分钟呼气中的¹³C丰度（¹³C2/LW和¹³C7/LW）、¹³C-苯丙氨酸给药后第10分钟和第30分钟的¹³C累积排泄量（AUC10/LW和AUC30/LW）以及¹³C排泄速率常数（PheBT-k/LW）在慢性肝损伤组中受到显著影响。三组肝脏中的总PAH活性无显著差异，但单位LW的PAH活性有显著差异。肝脏中的总PAH活性与¹³Cmax、¹³C2、¹³C7/AUC10、AUC30和PheBT-k显著相关，而单位LW的PAH活性与¹³Cmax/LW、¹³C2/LW、¹³C7/LW、AUC10/LW、AUC30/LW和PheBT-k/LW显著相关。PheBT-k/LW也与用于评估肝功能的生化指标相关。目前的研究结果表明，基于空气同位素比质谱法的PheBT结果可以定量反映慢性损伤大鼠肝脏中总PAH活性的变化。PheBT-k和PheBT-k/LW在测试参数中最为敏感，可用于在分子水平评估肝功能储备和肝细胞损伤。
