Amebicidal and Antiadhesion Activities of Knema retusa Extract Against Acanthamoeba triangularis T4 Genotype on Contact Lenses and Modeling Simulation of Its Main Compound, E2N, Against Acanthamoeba Beta-Tubulin

Medicinal plants have been used as alternative agents for the treatment of infections. This study aimed to investigate bioactivities of medicinal plant extracts including Knema retusa extract (Kre) against Acanthamoeba triangularis T4 in vitro and in silico. Anti-Acanthamoeba activities of 44 extracts from 5 plant species were determined. From 44 tested extracts, a chloroform extract of Kre bark showed the strongest anti-Acanthamoeba activities against both trophozoites and cysts, with MIC values of 32.25 and 62.50 μg/mL, respectively. Then, amebicidal and antiadhesion activities of Kre against A. triangularis were investigated. Kre reduced the growth by 3 logs within 8 h at 4 × MIC. Disruption of the cells with abnormal shapes was observed when trophozoites were treated with Kre. Trophozoites had lost their robust acanthopodia and began to shrink after treatment with Kre. Treated cysts exhibited wall disruption and dramatically showed forms of marked retraction. Treatment of Kre at 1/2 × MIC showed about 87% reduction in the trophozoite adhesion, while treatment at 2 × MIC exhibited a 59% reduction in the trophozoite adhesion to the plastic surface, compared with the control. Furthermore, 1 log cells/mL (90%) of the contact lens adhesive trophozoites were reduced and removed after treatment with Kre. Molecular docking indicated that E2N, the main compound in Kre, exhibited strong binding to the ligand binding sites at β-tubulin, with a binding energy of -7.01 kcal/mol and an inhibitory constant of 2.43-7.32 μM. E2N generated multiple connections via hydrogen, hydrophobic, ionic, and water bridge bonding and maintained these connections until the simulation finished, facilitating the creation of stable bindings with the β-tubulin protein as measured by molecular dynamics simulation. These findings suggest that Kre exhibits amebicidal and antiadhesion activities which could be used for the prevention of A. triangularis adhesion to contact lenses.