A xanthone O-glucoside isolated from Iris setosa Pall. ex Link exhibits promising anti-amoebic activity against the brain-eating amoeba Naegleria fowleri

Abstract

Background: Primary amoebic meningoencephalitis (PAM), caused by Naegleria fowleri, poses a significant challenge in humans owing to its high mortality rate, exceeding 97 %. Current therapeutics have been unable to deliver satisfactory treatment outcomes, due to suboptimal efficacy and toxicity, highlighting the critical need for efficacious drug development. In this study, we identified a natural compound, 3,5-Dihydroxy-8‑methoxy-1-O-β-D-glucopyranosyl xanthone (DX), which exhibited promising anti-N. fowleri activity, and investigated its underlying anti-N. fowleri mechanisms. Methods: The anti-amoebic activity of DX against N. fowleri trophozoites and its cytotoxicity against C6 glial cells were evaluated using a cell viability assay. The anti-N. fowleri mechanism of DX involved analyses of apoptosis-necrosis, TUNEL, caspase-3, ROS production, mitochondrial dysfunction, ATP production, qRT-PCR, and actin integrity. The efficacy of DX in protecting C6 glial cells from the amoebae was assessed using a co-culture method. Results: DX, isolated from Iris setosa Pall. ex Link, demonstrated significant anti-N. fowleri activity with an IC50 of 55.37 ± 2.58 µM, exhibiting a high selectivity index (> 9.03) and negligible cytotoxicity to C6 glial cells. DX induced apoptosis-like programmed cell death in the amoebae, characterized by DNA fragmentation, increased caspase-3 activity, and mitochondrial dysfunction. DX also disrupted actin cytoskeletal integrity in the amoebae. DX significantly protected C6 glial cells against phagocytosis of N. fowleri trophozoites. Conclusion: The selective anti-amoebic activity of DX for N. fowleri underscores its potential as a promising candidate drug or a supplemental compound in the development or optimization of therapeutic drugs for PAM.