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.
Treatment of drug resistant protozoa, bacteria, and viruses requires new drugs with alternative chemotypes. Such compounds could be found from Southeast Asian medicinal plants. The present study examines the cytotoxic, antileishmanial, and antiplasmodial effects of 11 ethnopharmacologically important plant species in Malaysia. Chloroform extracts were tested for their toxicity against MRC-5 cells and Leishmania donovani by MTT, and chloroquine-resistant Plasmodium falciparum K1 strain by Histidine-Rich Protein II ELISA assays. None of the extract tested was cytotoxic to MRC-5 cells. Extracts of Uvaria grandiflora, Chilocarpus costatus, Tabernaemontana peduncularis, and Leuconotis eugenifolius had good activities against L. donovani with IC50 C. costatus, T. peduncularis, L. eugenifolius, A. subulatum, and C. aeruginosa had good activities against P. falciparum K1 with IC50 C. costatus was inactive against L. donovani and P. falciparum. C. costatus extract and pinoresinol increased the sensitivity of Staphylococcus epidermidis to cefotaxime. Pinoresinol demonstrated moderate activity against influenza virus (IC50 = 30.4 ± 11 μg/mL) and was active against Coxsackie virus B3 (IC50 = 7.1 ± 3.0 μg/mL). β-Amyrin from L. eugenifolius inhibited L. donovani with IC50 value of 15.4 ± 0.01 μM. Furanodienone from C. aeruginosa inhibited L. donovani and P. falciparum K1 with IC50 value of 39.5 ± 0.2 and 17.0 ± 0.05 μM, respectively. Furanodienone also inhibited the replication of influenza and Coxsackie virus B3 with IC50 value of 4.0 ± 0.5 and 7.2 ± 1.4 μg/mL (Ribavirin: IC50: 15.6 ± 2.0 μg/mL), respectively. Our study provides evidence that medicinal plants in Malaysia have potentials as a source of chemotypes for the development of anti-infective leads.