Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Centre Rotterdam, Rotterdam, The Netherlands.
PLoS One. 2013 Oct 14;8(10):e75848. doi: 10.1371/journal.pone.0075848. eCollection 2013.
Caspofungin, currently used as salvage therapy for invasive pulmonary aspergillosis (IPA), strangely only causes morphological changes in fungal growth in vitro but does not inhibit the growth. In vivo it has good efficacy. Therefore the question arises how this in vivo activity is reached. Caspofungin is known to increase the amount of chitin in the fungal cell wall. Mammals produce two chitinases, chitotriosidase and AMCase, which can hydrolyse chitin. We hypothesized that the mammalian chitinases play a role in the in vivo efficacy of caspofungin.
In order to determine the role of chitotriosidase and AMCase in IPA, both chitinases were measured in rats which did or did not receive caspofungin treatment. In order to understand the role of each chitinase in the breakdown of the caspofungin-exposed cells, we also exposed caspofungin treated fungi to recombinant enzymes in vitro.
IPA in immunocompromised rats caused a dramatic increase in chitinase activity. This increase in chitinase activity was still noted when rats were treated with caspofungin. In vitro, it was demonstrated that the action of both chitinases were needed to lyse the fungal cell wall upon caspofungin exposure.
Caspofungin seemed to alter the cell wall in such a way that the two chitinases, when combined, could lyse the fungal cell wall and assisted in clearing the fungal pathogen. We also found that both chitinases combined had a direct effect on the fungus in vitro.
卡泊芬净目前被用作侵袭性肺曲霉病（IPA）的补救治疗药物，但奇怪的是，它仅在体外引起真菌生长的形态学变化，而不抑制其生长。在体内它具有良好的疗效。因此，人们不禁要问这种体内活性是如何达到的。卡泊芬净已知会增加真菌细胞壁中的几丁质含量。哺乳动物产生两种几丁质酶，即壳三糖苷酶和 AMCase，它们可以水解几丁质。我们假设哺乳动物的几丁质酶在卡泊芬净的体内疗效中发挥作用。
为了确定壳三糖苷酶和 AMCase 在 IPA 中的作用，分别测量了接受或未接受卡泊芬净治疗的大鼠中的这两种几丁质酶。为了了解每种几丁质酶在分解暴露于卡泊芬净的细胞中的作用，我们还在体外将暴露于卡泊芬净的真菌与重组酶一起孵育。
免疫功能低下的大鼠中的 IPA 导致几丁质酶活性显著增加。当大鼠接受卡泊芬净治疗时，仍然观察到几丁质酶活性的增加。体外实验表明，在暴露于卡泊芬净后，需要两种几丁质酶的共同作用才能裂解真菌细胞壁。
卡泊芬净似乎改变了细胞壁，使得两种几丁质酶在联合作用时能够裂解真菌细胞壁，并有助于清除真菌病原体。我们还发现，两种几丁质酶在体外对真菌均具有直接作用。
