Gregus Z, Fekete T, Halászi E, Klaassen C D
Department of Pharmacology, University Medical School of Pécs, Hungary.
Drug Metab Dispos. 1996 Dec;24(12):1347-54.
Conjugation with glycine, a reaction important in the elimination of carboxylic acids (e.g. benzoic and salicylic acids), takes place in hepatic mitochondria and uses ATP, coenzyme A, and glycine. Although normal ATP supply does not limit glycine conjugation in vivo (Gregus, Z., et al., Drug Metab. Dispos. 20, 234, 1992), ATP deficiency may impair it. This hypothesis was tested by examining the effect of ATP depletors (oligomycin, fructose, and ethionine) on glycine conjugation and elimination of benzoic acid in rats. Pretreatment with the mitochondrial ATP synthesis inhibitor oligomycin (0.5-2 mg/kg, intraportally) decreased glycine conjugation of benzoic acid markedly and in a dose-dependent manner, as indicated by the delayed elimination of benzoate and delayed appearance of benzoylglycine in blood. Oligomycin also dramatically diminished urinary excretion of benzoylglycine, because it inhibited not only formation of benzoylglycine from benzoate, but also the renal transport of benzoylglycine. Treatment with fructose (a consumer of both cytosolic and mitochondrial ATP) or ethionine (a consumer of cytosolic ATP) depleted hepatic ATP from approximately 2.5 micromol/g to levels comparable with those observed after administration of 1 mg/kg oligomycin (approximately 1.2 micromol/g). Despite this, elimination of benzoate and formation of benzoylglycine were decreased less by fructose than by oligomycin and only negligibly by ethionine. ATP depletors did not influence hepatic glycine levels, and only oligomycin lowered coenzyme A levels in liver. However, the oligomycin-induced decline of hepatic coenzyme A levels was delayed, contrary to impairment of glycine conjugation, which was almost immediate. In summary, impairment of benzoylglycine formation by ATP depletors apparently correlates with their capacity to diminish ATP levels in hepatic mitochondria (i.e. at the site of glycine conjugation). These observations suggest that limited availability of mitochondrial (but not cytosolic) ATP reduces glycine conjugation capacity. Therefore, mitochondrium toxic agents and pathological mitochondrial injuries acting in liver may compromise glycine conjugation by decreasing ATP supply.
与甘氨酸结合是羧酸（如苯甲酸和水杨酸）消除过程中的一个重要反应，该反应发生在肝脏线粒体中，需要消耗三磷酸腺苷（ATP）、辅酶A和甘氨酸。虽然正常的ATP供应在体内并不限制甘氨酸结合反应（Gregus, Z., 等人，《药物代谢与处置》20, 234, 1992），但ATP缺乏可能会损害该反应。通过研究ATP消耗剂（寡霉素、果糖和乙硫氨酸）对大鼠体内甘氨酸结合反应以及苯甲酸消除的影响，对这一假设进行了验证。用线粒体ATP合成抑制剂寡霉素（0.5 - 2毫克/千克，经门静脉注射）预处理，可显著降低苯甲酸的甘氨酸结合反应，且呈剂量依赖性，这表现为苯甲酸消除延迟以及血液中苯甲酰甘氨酸出现延迟。寡霉素还显著减少了苯甲酰甘氨酸的尿排泄，因为它不仅抑制了苯甲酸生成苯甲酰甘氨酸，还抑制了苯甲酰甘氨酸的肾脏转运。用果糖（一种同时消耗胞质和线粒体ATP的物质）或乙硫氨酸（一种消耗胞质ATP的物质）处理后，肝脏ATP从约2.5微摩尔/克降至与给予1毫克/千克寡霉素后观察到的水平相当（约1.2微摩尔/克）。尽管如此，果糖对苯甲酸消除和苯甲酰甘氨酸生成的减少程度小于寡霉素，而乙硫氨酸的影响可忽略不计。ATP消耗剂不影响肝脏甘氨酸水平，只有寡霉素降低了肝脏中的辅酶A水平。然而，与几乎立即出现的甘氨酸结合反应受损相反，寡霉素引起的肝脏辅酶A水平下降出现延迟。总之，ATP消耗剂对苯甲酰甘氨酸生成的损害显然与其降低肝脏线粒体（即甘氨酸结合反应发生部位）ATP水平的能力相关。这些观察结果表明，线粒体（而非胞质）ATP供应受限会降低甘氨酸结合能力。因此，作用于肝脏的线粒体毒性剂和病理性线粒体损伤可能会通过减少ATP供应而损害甘氨酸结合反应。
