Gregus Z, Fekete T, Halászi E, Gyurasics A, Klaassen C D
Department of Pharmacology, University Medical School of Pécs, Szigeti, Hungary.
Drug Metab Dispos. 1998 Nov;26(11):1082-8.
In the course of glycine conjugation, benzoic acid is successively converted into benzoyl-CoA and benzoylglycine by mitochondrial enzymes (i.e. benzoyl-CoA synthetase and benzoyl-CoA/glycine N-acyltransferase, respectively), utilizing ATP, CoA, and glycine. Large doses of benzoate deplete CoA from the liver, suggesting that the supply of CoA may limit the capacity for glycine conjugation. Because fibrates are known to increase hepatic CoA synthesis, we examined whether treatment with fenofibrate or bezafibrate enhanced the capacity of rats to conjugate benzoic acid with glycine. Dietary administration of fenofibrate or bezafibrate (2.5 mmol/kg of feed, for 10 days) increased hepatic CoA levels 8-10-fold, while not affecting hepatic ATP levels; only fenofibrate elevated, albeit moderately, the concentration of glycine in liver. Hepatic mitochondria isolated from fibrate-fed rats, compared with those from controls, exhibited unchanged benzoyl-CoA synthetase activity but higher benzoyl-CoA hydrolase and lower benzoyl-CoA/glycine N-acyltransferase activities. Feeding with either fibrate increased liver mass by 50-60%. Control and fibrate-fed rats were administered benzoate at different doses, one to produce a large demand for CoA (i.e. 2 mmol/kg, iv) and two others to produce smaller demands for CoA (i.e. 1 mmol/kg or 2 mmol/kg plus glycine, iv). Fenofibrate-fed rats, and to a lesser extent bezafibrate-fed animals, exhibited increased glycine conjugation capacity, as indicated by faster disappearance of benzoate from the blood and appearance of benzoylglycine in the blood and urine, compared with controls; however, fibrates were not more effective in rats receiving the benzoate dose that produced the greatest demand for CoA. In contrast, benzoylglycine formation from benzoate (0.1-1 mM) was not enhanced in liver slices from fibrate-fed rats; moreover, it was lower than control levels in slices from bezafibrate-fed animals. Bezafibrate, but not fenofibrate, given to rats in a single dose (0.5 mmol/kg, ip) decreased the elimination and glycine conjugation of benzoate, indicating that bezafibrate is a direct inhibitor of glycine conjugation. In summary, fibrates influence glycine conjugation in a complex manner. Some fibrate-induced alterations (i.e. increased benzoyl-CoA hydrolase and decreased glycine transferase activities and direct inhibition by bezafibrate) can potentially hinder conjugation of benzoate with glycine, thus precluding conclusions regarding whether increased CoA availability enhances glycine conjugation. Fibrate-induced hepatomegaly appears to significantly contribute to the increased glycine conjugation capacity of rats treated with fenofibrate or bezafibrate.
在甘氨酸结合过程中，苯甲酸先后被线粒体酶（即分别为苯甲酰辅酶A合成酶和苯甲酰辅酶A/甘氨酸N - 酰基转移酶）转化为苯甲酰辅酶A和苯甲酰甘氨酸，同时利用ATP、辅酶A和甘氨酸。大剂量的苯甲酸盐会耗尽肝脏中的辅酶A，这表明辅酶A的供应可能会限制甘氨酸结合的能力。由于已知贝特类药物可增加肝脏辅酶A的合成，我们研究了用非诺贝特或苯扎贝特治疗是否能增强大鼠将苯甲酸与甘氨酸结合的能力。经口给予非诺贝特或苯扎贝特（2.5 mmol/kg饲料，持续10天）可使肝脏辅酶A水平提高8 - 10倍，而不影响肝脏ATP水平；只有非诺贝特适度提高了肝脏中甘氨酸的浓度。与对照组相比，从喂食贝特类药物的大鼠分离出的肝线粒体，其苯甲酰辅酶A合成酶活性未变，但苯甲酰辅酶A水解酶活性较高，而苯甲酰辅酶A/甘氨酸N - 酰基转移酶活性较低。喂食任何一种贝特类药物都会使肝脏重量增加50 - 60%。给对照组和喂食贝特类药物的大鼠静脉注射不同剂量的苯甲酸盐，一种剂量会产生对辅酶A的大量需求（即2 mmol/kg），另外两种剂量会产生对辅酶A较小的需求（即1 mmol/kg或2 mmol/kg加甘氨酸）。与对照组相比，喂食非诺贝特的大鼠以及程度稍轻的喂食苯扎贝特的动物，其甘氨酸结合能力增强，表现为血液中苯甲酸盐更快消失以及血液和尿液中苯甲酰甘氨酸的出现；然而，贝特类药物对接受产生最大辅酶A需求剂量苯甲酸盐的大鼠效果并不更显著。相反，喂食贝特类药物的大鼠肝脏切片中，由苯甲酸（0.1 - 1 mM）形成苯甲酰甘氨酸的过程并未增强；此外，在喂食苯扎贝特的动物的切片中，该过程低于对照水平。给大鼠单次腹腔注射苯扎贝特（0.5 mmol/kg）而非非诺贝特，会降低苯甲酸盐的消除和甘氨酸结合，这表明苯扎贝特是甘氨酸结合的直接抑制剂。总之，贝特类药物以复杂的方式影响甘氨酸结合。一些贝特类药物诱导的改变（即苯甲酰辅酶A水解酶增加、甘氨酸转移酶活性降低以及苯扎贝特的直接抑制作用）可能会潜在地阻碍苯甲酸与甘氨酸的结合，因此无法得出关于辅酶A可用性增加是否增强甘氨酸结合的结论。贝特类药物诱导的肝肿大似乎对用非诺贝特或苯扎贝特治疗的大鼠甘氨酸结合能力的增加有显著贡献。
