Anthelmintic activity of traditional medicinal plant extracts

Abstract

Parasitic nematode diseases cause major morbidity and mortality in humans globally and impact the world economy through extensive infection of crops and livestock. Resistance to anthelmintics is widespread in worm populations and therefore there is a continuous need for the new anthelmintic. Using parasitic worms in screens for new anthelmintics is extremely costly and has a low hit rate. This thesis aimed to overcome those problems by selecting ethnomedicinal plants based on their traditional use by indigenous people, and combine this preselection tool with the most studied nematode Caenorhabditis elegans as a model to screen selected ethnomedicinal plant extracts for their anthelmintic activity. The first aim of this thesis was to screen traditional medicinal plant extracts for their anthelmintic activity using C. elegans. The plant extracts were selected by indigenous communities from Sarawak, Malaysia, based on their use in de-worming remedies. A 96 well plate based assay was developed to screen the nematocidal activity of the plant extracts. The effective plant extracts were tested against Haemonchus contortus, the most economically important animal parasitic nematode in the world. To further investigate their effect on C. elegans, we took advantage of the vast genetic resource of C. elegans to characterize the stress responses of the effective plant extracts and discovered effective plant extracts elicit unique stress reporter profiles compared to the commercially available anthelmintics. The second aim of this project was designed to illustrate the most effective plant extract and investigate its killing mechanism. We fractionated the most effective plant extract, and tested fractions on C. elegans. The anthelmintic activity was determined to exist in a single fraction which killed 90% of C. elegans adults. The efficacy of this fraction on parasitic nematodes was validated via H. contortus motility assay. Analysis of gene expression of selected genes by qRT-PCR confirmed iv the stress reporter strain findings and gave temporal changes in gene expression post exposure to the most effective fraction. Transcriptome-wide analysis of gene expression by next-generation sequencing discovered the effects of compounds on ER, mitochondria and lipid metabolism affecting energy production in C. elegans. Our findings showed that C. elegans is not only a good tool for preliminary screening, but may also be useful for examining the effects of compounds on nematodes and to understand the mechanism of action of the compounds. Moreover, the project demonstrates that selecting plants on the basis of their traditional application is an important approach to identify new anthelmintic compounds.