Anti-Acanthamoeba Activities of Silica Nanoformulated Quercetin Compound Derived From Annona muricata L. Leaves.

Acanthamoeba spp., free-living amoebae (FLA), are the causative agents of Acanthamoeba keratitis (AK) and granulomatous amoebic encephalitis (GAE). These diseases have limited treatment options; therefore, drug discovery remains a critical priority. This study evaluated the leaf extract of Annona muricata L., which contains quercetin, formulated in silica nanoparticles against Acanthamoeba species. The anti-Acanthamoeba effect of the nanoformulation was determined by its MIC and percentage viability. Scanning electron microscopy confirmed the nanocompound-directed effect on trophozoites and cysts. The nanoquercetin exhibited anti-Acanthamoeba activity, showing greater effectiveness against the trophozoites of Acanthamoeba polyphaga ATCC 30461 (AP) (MIC > 2 mg/mL) compared to cysts (MIC > 8 mg/mL) and against A. triangularis WU19001 (AT) trophozoites (MIC > 4 mg/mL) compared to cysts (MIC > 8 mg/mL). It also showed reduced activity against Acanthamoeba castellanii ATCC 30010 (AC3) trophozoites (MIC > 4 mg/mL) compared to cysts (MIC > 8 mg/mL) and A. castellanii ATCC50739 (AC5) trophozoites (MIC > 4 mg/mL) compared to cysts (MIC > 8 mg/mL). The anti-Acanthamoeba activity of A. muricata on all four species was compared to chlorhexidine, which had MIC values of 0.008 mg/mL for AC3 and AT trophozoites and 0.016 mg/mL for AC5 and AP trophozoites. For cysts, chlorhexidine exhibited MIC values of > 0.0128 mg/mL for AC3 and AP, 0.032 mg/mL for AC5, and 0.064 mg/mL for AT. All MIC values demonstrated inhibition of Acanthamoeba species with reduced viability exceeding 90%. SEM findings revealed morphological changes in Acanthamoeba, indicating parasitic inhibition. Quercetin-loaded silica nanoparticles demonstrated anti-Acanthamoeba activity with low cytotoxicity. This indicates the potential of quercetin as a nano-enhanced natural therapeutic or contact lens-care agent. This study is limited by its in vitro design, small parasite strain panel, and potential nanoparticle variability. This highlights the need for in vivo validation, ocular/contact lens model testing, and formulation optimization for improved cysticidal efficacy.