Green Tea Anti-Acanthamoeba Activity Regulated by Silver Nanoparticles

Efforts to utilise naturally derived substances in parasitology are gaining increasing interest. Among these are nanoparticles, whose antiparasitic properties may be enhanced when combined with plant extracts rich in bioactive compounds, beneficial to the host but toxic to parasites. This study evaluated whether silver nanoparticles coated with green tea (GT(AgNPs)), enhance the antiparasitic effects of silver nanoparticles (AgNPs) or green tea extract (GT) alone. Transmission electron microscopy revealed phagocytosis of nanoparticles, which accumulate in the vacuoles of amoebae. Notably, amoebae exposed to GT(AgNPs) exhibit cytoplasmic vacuolization and advanced cytoplasmic organelle disintegration, indicating strong toxicity even at lower levels of nanoparticle accumulation. Green tea extract alone is also toxic to amoebae, but without induction of cytosolic vacuolization. GT extract alone induced high expression of cysteine proteinase, paralleled by active autophagy. GT(AgNPs) did not have such effect on cysteine proteinase gene expression in amoebae. The mechanisms underlying the toxicity of silver nanoparticles and green tea appear to differ and are probably influenced by the condition of vacuole formation in trophozoites of Acanthamoeba castellanii.