Growth inhibition and ultrastructural alterations induced by Delta24(25)-sterol methyltransferase inhibitors in Candida spp. isolates, including non-albicans organisms.
BACKGROUND
Although Candida species are commensal microorganisms, they can cause many invasive fungal infections. In addition, antifungal resistance can contribute to failure of treatment.The purpose of this study was to evaluate the antifungal activity of inhibitors of Delta24(25)-sterol methyltransferase (24-SMTI), 20-piperidin-2-yl-5alpha-pregnan-3beta-20(R)-diol (AZA), and 24(R,S),25-epiminolanosterol (EIL), against clinical isolates of Candida spp., analysing the ultrastructural changes.


RESULTS
AZA and EIL were found to be potent growth inhibitors of Candida spp. isolates. The median MIC50 was 0.5 microg.ml-1 for AZA and 2 microg.ml-1 for EIL, and the MIC90 was 2 microg.ml-1 for both compounds. All strains used in this study were susceptible to amphotericin B; however, some isolates were fluconazole- and itraconazole-resistant. Most of the azole-resistant isolates were Candida non-albicans (CNA) species, but several of them, such as C. guilliermondii, C. zeylanoides, and C. lipolytica, were susceptible to 24-SMTI, indicating a lack of cross-resistance. Reference strain C. krusei (ATCC 6258, FLC-resistant) was consistently susceptible to AZA, although not to EIL. The fungicidal activity of 24-SMTI was particularly high against CNA isolates. Treatment with sub-inhibitory concentrations of AZA and EIL induced several ultrastructural alterations, including changes in the cell-wall shape and thickness, a pronounced disconnection between the cell wall and cytoplasm with an electron-lucent zone between them, mitochondrial swelling, and the presence of electron-dense vacuoles. Fluorescence microscopy analyses indicated an accumulation of lipid bodies and alterations in the cell cycle of the yeasts. The selectivity of 24-SMTI for fungal cells versus mammalian cells was assessed by the sulforhodamine B viability assay.


CONCLUSIONS
Taken together, these results suggest that inhibition of 24-SMT may be a novel approach to control Candida spp. infections, including those caused by azole-resistant strains.
Ishida
Kelly
K
Laboratório de Biologia Celular de Fungos, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil. ishidakelly@biof.ufrj.br
Rodrigues
Juliany Cola Fernandes
JC
Ribeiro
Marcos Dornelas
MD
Vila
Taíssa Vieira Machado
TV
de Souza
Wanderley
W
Urbina
Julio A
JA
Nakamura
Celso Vataru
CV
Rozental
Sonia
S
D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D002175:Candida / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D002522:Chlorocebus aethiops; D025141:Drug Resistance, Fungal; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007810:Lanosterol / Q000031:analogs & derivatives* / Q000494:pharmacology; D008780:Methyltransferases / Q000037:antagonists & inhibitors*; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D011276:Pregnanediol / Q000031:analogs & derivatives* / Q000494:pharmacology; D014709:Vero Cells
C443579:20-piperidin-2-yl-5-pregnan-3,20-diol; D000935:Antifungal Agents; D004791:Enzyme Inhibitors; C059162:24,25-iminolanosterol; D007810:Lanosterol; D008780:Methyltransferases; C022670:delta 24-sterol methyltransferase; D011276:Pregnanediol