Berman P A, Human L, Freese J A
Department of Chemical Pathology, University of Cape Town Medical School, Observatory, South Africa.
J Clin Invest. 1991 Dec;88(6):1848-55. doi: 10.1172/JCI115506.
Malaria parasites, unable to synthesize purine de novo, use host-derived hypoxanthine preferentially as purine source. In a previous study (1990. J. Biol. Chem. 265:6562-6568), we noted that xanthine oxidase rapidly and completely depleted hypoxanthine in human erythrocytes, not by crossing the erythrocyte membrane, but rather by creating a concentration gradient which facilitated hypoxanthine efflux. We therefore investigated the ability of xanthine oxidase to inhibit growth of FCR-3, a chloroquine-resistant strain of Plasmodium falciparum in human erythrocytes in vitro. Parasites were cultured in human group O+ erythrocytes in medium supplemented, as required, with xanthine oxidase or chloroquine. Parasite viability was assessed by uptake of radiolabeled glycine and adenosine triphosphate-derived purine into protein and nucleic acid, respectively, by nucleic acid accumulation, by L-lactate production, and by microscopic appearance. On average, a 90% inhibition of growth was observed after 72 h of incubation in 20 mU/ml xanthine oxidase. Inhibition was notably greater than that exerted by 10(-7) M chloroquine (less than 10%) over a comparable period. The IC50 for xanthine oxidase was estimated at 0.2 mU/ml, compared to 1.5 x 10(-7) M for chloroquine. Inhibition was completely reversed by excess hypoxanthine, but was unaffected by oxygen radical scavengers, including superoxide dismutase and catalase. The data confirms that a supply of host-derived hypoxanthine is critical for nucleic acid synthesis in P. falciparum, and that depletion of erythrocyte hypoxanthine pools of chloroquine-resistant malaria infection in humans. of chloroquine-resistant malaria infection in humans.
疟原虫无法从头合成嘌呤，因此优先利用宿主来源的次黄嘌呤作为嘌呤来源。在之前的一项研究（1990年，《生物化学杂志》265:6562 - 6568）中，我们注意到黄嘌呤氧化酶能迅速且完全耗尽人红细胞中的次黄嘌呤，其方式不是穿过红细胞膜，而是通过建立一个促进次黄嘌呤外流的浓度梯度。因此，我们研究了黄嘌呤氧化酶在体外抑制恶性疟原虫氯喹抗性株FCR - 3在人红细胞中生长的能力。将疟原虫培养在人O + 型红细胞中，培养基根据需要补充黄嘌呤氧化酶或氯喹。通过分别将放射性标记的甘氨酸和三磷酸腺苷衍生的嘌呤摄取到蛋白质和核酸中、通过核酸积累、通过L - 乳酸产生以及通过显微镜观察来评估疟原虫的活力。平均而言，在20 mU/ml黄嘌呤氧化酶中孵育72小时后，观察到生长抑制率达90%。在相当长的一段时间内，这种抑制作用明显大于10(-7) M氯喹所产生的抑制作用（小于10%）。黄嘌呤氧化酶的IC50估计为0.2 mU/ml，而氯喹的IC50为1.5 x 10(-7) M。过量的次黄嘌呤可完全逆转抑制作用，但不受包括超氧化物歧化酶和过氧化氢酶在内的氧自由基清除剂的影响。数据证实，宿主来源的次黄嘌呤供应对恶性疟原虫的核酸合成至关重要，并且红细胞次黄嘌呤池的耗尽可抑制人类氯喹抗性疟疾感染。 人类氯喹抗性疟疾感染。 （最后一句英文重复，译文按原文翻译，感觉原文此处有误）
