Bushman J E, Palmieri D, Whinna H C, Church F C
Department of Chemistry, The University of North Carolina at Chapel Hill, NC 27599-3290, USA.
Leuk Res. 2000 Jul;24(7):559-65. doi: 10.1016/s0145-2126(00)00017-5.
Asparaginase (ASNase) is a widely used and successful agent against childhood acute lymphoblastic leukemia (ALL). Asparaginase cleaves asparagine (Asn) to give aspartic acid and ammonia, thereby depleting free Asn in the blood. However, treatment with ASNase has been implicated in significant reduction of plasma levels of the coagulation serine protease inhibitor (serpin) antithrombin III (AT3), predisposing patients to thromboembolic complications. Our investigation was designed to delineate the biochemical mechanism of AT3 depletion that can occur in the plasma of ALL patients undergoing ASNase therapy. SDS-PAGE showed no cleavage of purified AT3 following treatment with ASNase. Furthermore, purified AT3 treated with ASNase demonstrated no decrease in inhibitory activity. Human plasma and whole blood treated with approximate therapeutic concentrations of ASNase showed no loss of AT3 activity as detected by a plasma-based factor Xa inhibition assay. Treatment of a confluent monolayer of HepG2 (hepatocarcinoma) cells with ASNase showed no gross loss in AT3 message levels detected by rtPCR. However, a decrease of cell viability was observed in cultures treated with ASNase. Interestingly, medium from HepG2 cells treated with ASNase showed a marked decrease in secretion of AT3 and another serpin, heparin cofactor II. Collectively, these data show that ASNase has no direct effect on AT3 in blood or plasma, but that ASNase may affect plasma levels of AT3 by interfering with translation and/or secretion of the protein in liver cells.
天冬酰胺酶（ASNase）是一种广泛应用且成功用于治疗儿童急性淋巴细胞白血病（ALL）的药物。天冬酰胺酶可将天冬酰胺（Asn）裂解为天冬氨酸和氨，从而消耗血液中的游离天冬酰胺。然而，使用天冬酰胺酶治疗与凝血丝氨酸蛋白酶抑制剂（丝氨酸蛋白酶抑制剂）抗凝血酶III（AT3）的血浆水平显著降低有关，使患者易发生血栓栓塞并发症。我们的研究旨在阐明接受天冬酰胺酶治疗的ALL患者血浆中AT3消耗的生化机制。SDS-PAGE显示用天冬酰胺酶处理后纯化的AT3未发生裂解。此外，用天冬酰胺酶处理的纯化AT3的抑制活性未降低。用近似治疗浓度的天冬酰胺酶处理的人血浆和全血，通过基于血浆的因子Xa抑制试验检测，未显示AT3活性丧失。用天冬酰胺酶处理汇合的HepG2（肝癌）细胞单层，通过rtPCR检测，AT3信息水平未出现明显下降。然而，在用天冬酰胺酶处理的培养物中观察到细胞活力下降。有趣的是，用天冬酰胺酶处理的HepG2细胞的培养基显示AT3和另一种丝氨酸蛋白酶抑制剂肝素辅因子II的分泌显著减少。总体而言，这些数据表明天冬酰胺酶对血液或血浆中的AT3没有直接影响，但天冬酰胺酶可能通过干扰肝细胞中该蛋白的翻译和/或分泌来影响AT3的血浆水平。
