Department of Molecular Biology, Rajendra Memorial Research Institute of Medical Sciences, Agamkuan, Patna, Bihar, India.
Antimicrob Agents Chemother. 2012 Feb;56(2):1031-41. doi: 10.1128/AAC.00030-11. Epub 2011 Nov 28.
The clinical value of amphotericin B, the mainstay therapy for visceral leishmaniasis in sodium antimony gluconate-nonresponsive zones of Bihar, India, is now threatened by the emergence of acquired drug resistance, and a comprehensive understanding of the underlying mechanisms is the need of the hour. We have selected an amphotericin B-resistant clinical isolate which demonstrated 8-fold-higher 50% lethal doses (LD(50)) than an amphotericin B-sensitive strain to explore the mechanism of amphotericin B resistance. Fluorimetric analysis demonstrated lower anisotropy in the motion of the diphenylhexatriene fluorescent probe in the resistant strain, which indicated a higher fluidity of the membrane for the resistant strain than for the sensitive strain. The expression patterns of the two transcripts of S-adenosyl-l-methionine:C-24-Δ-sterol methyltransferase and the absence of ergosterol, replaced by cholesta-5,7,24-trien-3β-ol in the membrane of the resistant parasite, indicate a decreased amphotericin B affinity, which is evidenced by decreased amphotericin B uptake. The expression level of MDR1 is found to be higher in the resistant strain, suggesting a higher rate of efflux of amphotericin B. The resistant parasite also possesses an upregulated tryparedoxin cascade and a more-reduced intracellular thiol level, which helps in better scavenging of reactive oxygen species produced by amphotericin B. The resistance to amphotericin B was partially reverted by the thiol metabolic pathway and ABC transporter inhibitors. Thus, it can be concluded that altered membrane composition, ATP-binding cassette transporters, and an upregulated thiol metabolic pathway have a role in conferring amphotericin B resistance in clinical isolates of Leishmania donovani.
两性霉素 B 是印度比哈尔邦葡萄糖酸锑钠无反应区内脏利什曼病的主要治疗药物，其临床价值现在受到获得性耐药性出现的威胁，因此，全面了解潜在机制是当务之急。我们选择了两性霉素 B 耐药的临床分离株，该分离株的 50%致死剂量（LD(50)）比两性霉素 B 敏感株高 8 倍，以探索两性霉素 B 耐药的机制。荧光分析表明，耐药株中二苯基十六碳三烯荧光探针的运动各向异性较低，这表明耐药株的膜流动性高于敏感株。S-腺苷甲硫氨酸：C-24-Δ-甾醇甲基转移酶的两种转录物的表达模式以及甾醇缺失，在耐药寄生虫的膜中被胆固醇-5,7,24-三烯-3β-醇取代，表明两性霉素 B 的亲和力降低，这表现在两性霉素 B 摄取减少。耐药株中 MDR1 的表达水平较高，表明两性霉素 B 的外排率较高。耐药寄生虫还具有上调的硫氧还蛋白级联和更低的细胞内巯基水平，这有助于更好地清除两性霉素 B 产生的活性氧。巯基代谢途径和 ABC 转运体抑制剂部分逆转了对两性霉素 B 的耐药性。因此，可以得出结论，改变的膜组成、ATP 结合盒转运体和上调的巯基代谢途径在利什曼原虫临床分离株中赋予了两性霉素 B 耐药性。
