Fatty Acid Esters and Acyclic Monoterpenoid from Justicia insularis Leaf Fractions Attenuated Malaria Pathogenesis Through Docking with Plasmodium falciparum Serine Hydroxymethyl Transferase and Plasmodium falciparum Erythrocyte Membrane Protein 1 Proteins

Background Justicia insularis (Acanthaceae) T. Anderson is ethnopharmacologically used in Nigeria for the treatment of diseases including malaria. Therefore, this study was designed to investigate in vivo antiplasmodial effect of J. insularis leaf in Plasmodium berghei-infected mice, characterize its constituents, and carryout in silico studies of its compounds. Methods Standard protocols were followed in the processing of the plant leaves, extraction, fractionation, isolation, and characterization, evaluation of in vivo antiplasmodial assay, retrieval of Plasmodium falciparum serine hydroxymethyl transferase (PfSHMT) and Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1) proteins, absorption, distribution, metabolism, excretion, and toxicity (ADMET), and docking studies. Gas chromatography-mass spectrometry (GC-MS) was employed to isolate and characterize the compounds; SWISSADME and ADMET lab 2 enhanced the evaluation of pharmacokinetic properties, PyRx for docking analysis; Biovia discovery studio for 2D visualization, and PyMol software for 3D visualization of the ligand-protein interactions. Results The dichloromethane (61.59%) and ethyl acetate (73.15%) fractions had the best therapeutic indices and compared favorably with chloroquine (81.58%) in the curative antiplasmodial assay. The GC-MS analysis revealed 20 already reported antiplasmodial compounds with hexanoic acid 1,1-dimethylethyl ester, octadecanoic acid docosyl ester, and trans-β-ocimene as the lead compounds based on their binding affinities, permeation of the blood-brain-barrier, non-inhibition of metabolizing enzymes, ease of excretion, non-carcinogenicity, as well as non-violation of Lipinski's criteria. Conclusion Octadecanoic acid docosyl ester and hexanoic acid 1,1-dimethylethyl ester bonded the tetrahydrofolate-binding sites of PfSHMT, caused inhibition of DNA synthesis, and apoptosis, whereas trans-β-ocimene inhibited PfEMP-1, reversed the attachment of parasitized red blood cells to micro-vascular endothelium as their mechanism of action for parasitemia clearance. Moreover, these lead compounds reported for the first time in the dichloromethane and EtoAc fractions of this plant are responsible for the remarkable antiplasmodial activity observed in this study.