Acanthamoeba castellanii trophozoites need oxygen for normal functioning and lipids are their preferred substrate, offering new possibilities for treatment

Maarten J Sarink; Anna Z Mykytyn; Aïsha Jedidi; Martin Houweling; Jos F Brouwers; George Ruijter; Annelies Verbon; Jaap J van Hellemond; Aloysius G M Tielens

doi:10.1016/j.ijpara.2024.10.004

Acanthamoeba castellanii trophozoites need oxygen for normal functioning and lipids are their preferred substrate, offering new possibilities for treatment

Int J Parasitol. 2024 Oct 26:S0020-7519(24)00187-5. doi: 10.1016/j.ijpara.2024.10.004. Online ahead of print.

Authors

Maarten J Sarink¹, Anna Z Mykytyn¹, Aïsha Jedidi¹, Martin Houweling², Jos F Brouwers³, George Ruijter⁴, Annelies Verbon¹, Jaap J van Hellemond¹, Aloysius G M Tielens⁵

Affiliations

¹ Department of Medical Microbiology and Infectious Diseases, Erasmus MC University Medical Center, Rotterdam, the Netherlands.
² Department Biomolecular Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
³ Avans University of Applied Sciences, School of Life Sciences and Technology, Research Group for Analysis Techniques in the Life Sciences, Breda, the Netherlands.
⁴ Department of Clinical Genetics, Erasmus MC University Medical Center, Rotterdam, the Netherlands.
⁵ Department of Medical Microbiology and Infectious Diseases, Erasmus MC University Medical Center, Rotterdam, the Netherlands. Electronic address: a.tielens@erasmusmc.nl.

PMID: 39490506
DOI: 10.1016/j.ijpara.2024.10.004

Abstract

Acanthamoebae, pathogenic free-living amoebae, can cause Granulomatous Amoebic Encephalitis (GAE) and keratitis, and for both types of infection, no adequate treatment options are available. As the metabolism of pathogens is an attractive treatment target, we set out to examine the energy metabolism of Acanthamoeba castellanii and studied the aerobic and anaerobic capacities of the trophozoites. Under anaerobic conditions, or in the presence of inhibitors of the electron-transport chain, A. castellanii trophozoites became rounded, moved sluggishly and stopped multiplying. This demonstrates that oxygen and the respiratory chain are essential for movement and replication. Furthermore, the simultaneous activities of both terminal oxidases, cytochrome c oxidase and the plant-like alternative oxidase, are essential for normal functioning and replication. The inhibition of normal function caused by the inactivity of the respiratory chain was reversible. Once respiration was made possible again, the rounded, rather inactive amoebae formed acanthopodia within 4 h and resumed moving, feeding and multiplying. Experiments with radiolabelled nutrients revealed a preference for lipids over glucose and amino acids as food. Subsequent experiments showed that adding lipids to a standard culture medium of trophozoites strongly increased the growth rate. Acanthamoeba castellanii trophozoites have a strictly aerobic energy metabolism and β-oxidation of fatty acids, the Krebs cycle, and an aerobic electron-transport chain coupled to the ATP synthase, producing most of the used ATP. The preference for lipids can be exploited, as we show that three known inhibitors of lipid oxidation strongly inhibited the growth of A. castellanii. In particular, thioridazine and perhexiline showed potent effects in low micromolar concentrations. Therefore, this study revealed a new drug target with possibly new options to treat Acanthamoeba infections.

Keywords: Acanthamoeba; Cell respiration; Drug target; Energy metabolism; Lipid metabolism; Treatment.