Carter K C, Hutchison S, Henriquez F L, Légaré D, Ouellette M, Roberts C W, Mullen A B
Department of Immunology, SIBS, University of Strathclyde, 31 Taylor Street, Glasgow G4 0NR, United Kingdom.
Antimicrob Agents Chemother. 2006 Jan;50(1):88-95. doi: 10.1128/AAC.50.1.88-95.2006.
Sequencing studies showed that the gamma-glutamylcysteine synthetase (gamma-GCS) heavy chain genes from sodium stibogluconate (SSG)-resistant (SSG-R) and SSG-susceptible (SSG-S) Leishmania donovani strains were identical, indicating that SSG resistance was related to quantitative differences in gamma-GCS expression rather than gene interstrain polymorphisms. In vitro infection of murine macrophages with the SSG-R strain, but not the SSG-S strain, down regulated expression of host gamma-GCS, which would result in a reduction in intramacrophage glutathione (GSH) levels and promote an oxidative intramacrophage environment. This would inhibit, or minimize, the reduction of SSG pentavalent antimony to its more toxic trivalent form. Macrophage studies showed that the SSG-R strain expressed higher levels of gamma-GCS compared to the SSG-S strain, which would result in higher GSH levels, giving increased protection against oxidative stress and facilitating SSG efflux. However a similar differential effect on host and parasite gamma-GCS expression was not obtained when using tissues from infected mice. In this case gamma-GCS expression was organ and strain dependent for both the host and the parasite, indicating that environmental conditions have a profound effect on gamma-GCS expression. Consistent with the proposed mechanism from in vitro studies, increasing tissue GSH levels in the presence of SSG by cotreatment of L. donovani-infected mice with SSG solution and GSH incorporated into nonionic surfactant vesicles was more effective in reducing liver, spleen, and bone marrow parasite burdens than monotherapy with SSG. Together, these results indicate that SSG resistance is associated with manipulation of both host and parasite GSH levels by L. donovani.
测序研究表明，抗葡萄糖酸锑钠（SSG）和对SSG敏感的杜氏利什曼原虫菌株的γ-谷氨酰半胱氨酸合成酶（γ-GCS）重链基因是相同的，这表明SSG抗性与γ-GCS表达的定量差异有关，而不是基因株间多态性。用SSG抗性菌株而非SSG敏感菌株体外感染小鼠巨噬细胞，会下调宿主γ-GCS的表达，这将导致巨噬细胞内谷胱甘肽（GSH）水平降低，并促进巨噬细胞内的氧化环境。这将抑制或最小化SSG五价锑还原为毒性更强的三价形式。巨噬细胞研究表明，与SSG敏感菌株相比，SSG抗性菌株表达更高水平的γ-GCS，这将导致更高的GSH水平，增强对氧化应激的保护并促进SSG外流。然而，当使用感染小鼠的组织时，未获得对宿主和寄生虫γ-GCS表达的类似差异效应。在这种情况下，宿主和寄生虫的γ-GCS表达均取决于器官和菌株，表明环境条件对γ-GCS表达有深远影响。与体外研究提出的机制一致，用SSG溶液和掺入非离子表面活性剂囊泡的GSH联合处理感染杜氏利什曼原虫的小鼠，在存在SSG的情况下提高组织GSH水平，比单独使用SSG治疗更有效地降低肝脏、脾脏和骨髓中的寄生虫负荷。总之，这些结果表明，SSG抗性与杜氏利什曼原虫对宿主和寄生虫GSH水平的操纵有关。
