Ursos L M, DuBay K F, Roepe P D
Department of Chemistry and Program in Tumor Biology, Lombardi Cancer Center, Georgetown University, 37th and O Streets, Washington, DC 20057, USA.
Mol Biochem Parasitol. 2001 Jan 15;112(1):11-7. doi: 10.1016/s0166-6851(00)00342-x.
Recently, we measured a more acid digestive vacuolar pH for drug resistant Plasmodium falciparum [Dzekunov S, Ursos LMB, Roepe PD. Mol Biochem Parasitol 2000;in press; Ursos LMB, Dzekunov S, Roepe PD. Mol Biochem Parasitol 2000;in press]. We suggested this acidification contributes to drug resistance via the profound effects that pH has on the solubility of unpolymerized heme found in the vacuole (ferriprotoporphyrin IX mu oxo dimers). In this report, we measure how FPIX concentration, time, NaCl concentration, and several antimalarial drugs affect FPIX pH dependent solubility. Aggregation is essentially instantaneous below pH 5.3, but at vacuolar pH previously measured for HB3 parasites [Dzekunov S, Ursos LMB, Roepe PD. Mol Biochem Parasitol 2000;in press] can increase to several minutes as NaCl is lowered. As FPIX is decreased, the midpoint of the pH dependent solubility curve shifts to higher values. Addition of antimalarial drugs also increases the midpoint of the pH dependent FPIX solubility curve, with the net shift proportional to the relative affinity of the drug for FPIX. Surprisingly, however, for all drugs tested shifts of essentially identical magnitude are found at all drug: FPIX molar ratios inspected, spanning eight orders of magnitude (to as low as 0.0000001:1). This suggests that changes in pH dependent FPIX solubility by addition of antimalarial drugs is via previously unrecognized drug/FPIX nucleation phenomena. These data could have important implications for understanding the role of previously observed changes in pH(vac) [Dzekunov S, Ursos LMB, Roepe PD. Mol Biochem Parasitol 2000;in press; Ursos LMB, Dzekunov S, Roepe PD. Mol Biochem Parasitol 2000;in press] upon development of antimalarial drug resistance.
最近，我们测定了耐药恶性疟原虫消化泡的pH值更偏酸性[泽库诺夫S，乌尔索斯LMB，罗普PD。《分子生物化学寄生虫学》2000年；即将发表；乌尔索斯LMB，泽库诺夫S，罗普PD。《分子生物化学寄生虫学》2000年；即将发表]。我们认为这种酸化通过pH值对泡内未聚合血红素（铁原卟啉IXμ氧二聚体）溶解度的深远影响而导致耐药性。在本报告中，我们测定了铁原卟啉IX（FPIX）浓度、时间、氯化钠浓度以及几种抗疟药物如何影响FPIX的pH依赖性溶解度。在pH 5.3以下，聚集基本上是瞬间发生的，但在先前测定的HB3寄生虫泡内pH值下[泽库诺夫S，乌尔索斯LMB，罗普PD。《分子生物化学寄生虫学》2000年；即将发表]，随着氯化钠浓度降低，聚集时间可增加到几分钟。随着FPIX浓度降低，pH依赖性溶解度曲线的中点向更高值移动。添加抗疟药物也会增加pH依赖性FPIX溶解度曲线的中点，净移动与药物对FPIX的相对亲和力成正比。然而，令人惊讶的是，在所检测的所有药物中，在检查的所有药物：FPIX摩尔比范围内（低至0.0000001:1，跨越八个数量级），发现的移动幅度基本相同。这表明添加抗疟药物导致的pH依赖性FPIX溶解度变化是通过以前未被认识的药物/FPIX成核现象实现的。这些数据对于理解先前观察到的pH（vac）变化[泽库诺夫S，乌尔索斯LMB，罗普PD。《分子生物化学寄生虫学》2000年；即将发表；乌尔索斯LMB，泽库诺夫S，罗普PD。《分子生物化学寄生虫学》2000年；即将发表]在抗疟药物耐药性发展中的作用可能具有重要意义。
