Fig 1.
(A) The infection cycle of G. lamblia (green) and E. histolytica (red). The protozoan cysts are ingested through contaminated food or water. Viable cysts undergo excystation after passing through the acidic environment of the stomach to release the trophozoites that attach or migrate to the intestines. Trophozoites will either remain in the lumen of the small intestines (G. lamblia) or invade through the colon mucosa (E. histolytica). The parasites also undergo encystation and excretion from the host body to further infect human populations through contaminated food and water supplies. (B) N. fowleri thrives in warm fresh water and hot springs. Under these conditions, N. fowleri infects humans via the nasal sinuses invading the brain and its infection causes swelling of the brain, termed primary amoebic meningoencephalitis (PAM).
Fig 2.
Structures of compound 1–9.
Table 1.
1H (400 MHz) and 13C NMR (100 MHz) data for 8 compared to the crude reported 1H NMR data ((CD3)2CO) a.
Table 2.
1H (400 MHz) and 13C NMR (100 MHz) data for 9 (CDCl3 + CD3OD) compared to the crude reported 1H NMR data (CD3OD)a.
Table 3.
EC50a antiparasitic activity of L. tridentata lignans 1–8 and flavonol 9.
Fig 3.
(A) Key HMBC correlations of compound 8. (B) Key 1D gradient enhanced NOESY correlations of compound 8. 3D energy minimized conformers were generated using BIOVIA Discovery Studio 2017 software.
Fig 4.
Key HMBC correlations of compound 9.
The 3D energy minimized conformer was generated using BIOVIA Discovery Studio 2017 software.
Fig 5.
Percent inhibition of N. fowleri and human HUVEC cell proliferation by 1 and 2.
(A) The EC50 dose response curves for 1 and 2 against N. fowleri trophozoites. (B) The EC50 dose response curves for 1 and 2 against HUVEC cells. (C) Compound 1 and 2 displayed more potent inhibition of N. fowleri proliferation compared to HUVEC cells, which was statistically significant by Student’s t test analysis.
Fig 6.
Percent Inhibition of cysteine protease activity present in N. fowleri crude extract after treating the cells with different concentrations of compound 1 (A) and compound 2 (B). One microgram of lysate protein was used in the cysteine protease assay. Cysteine protease activity was determined as described in Experimental Section and measured as RFU/min/μg protein. The data represent the mean and standard error of mean of three independent experiments. *P < 0.05 by Student’s t test compared to DMSO-treated N. fowleri lysate.