Abstract
Ethnopharmacological relevance Sea cucumbers are known to have beneficial effects towards many ailments. Among traditional documented use of edible sea cucumbers are as anti-infective tonic food. Metabolites with immunomodulatory properties have also been reported from temperate sea cucumber species. The black sea cucumber (Holothuria atra) is a widely distributed tropical marine sea cucumber species traditionally consumed by Asian populations for its medicinal values.
Aim of the study A strategy to circumvent the problem of multidrug resistant Pseudomonas aeruginosa is discovery of novel anti-infectives targeting bacterial virulence or host immunity. This study aims to decipher the anti-infective properties of H. atra.
Materials and methods Here, we utilized the Caenorhabditis elegans-P. aeruginosa infection model to assess the anti-infective properties of H atra. We conducted the C. elegans-P. aeruginosa slow killing assay to isolate a fraction with capable of conferring survival to pathogen-infected worms, followed by a series of tests to assess the anti-virulence and immune-related properties of the sea cucumber bioactive fraction.
Results The H. atra methanol extract improved survival of infected worms without affecting pathogen viability. Further extraction and assays sequestered a fraction with significant anti-infective activities and was able to attenuate the secretion of virulence factors and biofilm formation. Treatment of P. aeruginosa-infected transgenic lys-7::GFP worms with this fraction also restored the repressed expression of host lys-7, a defense enzyme. QTOF-LCMS analysis of this fraction revealed the presence of aspidospermatidine, an indole alkaloid and inosine.
Conclusion Collectively, results shows that H atra confers survival advantage against P. aeruginosa infection through inhibition of pathogen virulence and the restitution of host lys-7 expression.
Authors and respective contribution
Wan-Ting Lee: Conducted killing assays, anti-virulence and gene expression studies, draft of manuscript
Boon-Khai Tan: Involved in supervision of experiments involving C. elegans
Su-Anne Eng: Data analysis, manuscript preparation
Gan Chee Yuen: Natural product extraction and fractionation
Kit Lam Chan: Natural product extraction and fractionation
Yee Kwang Sim: collection and handling of sea cucumbers
Shaida Fariza Sulaiman: Identification of compounds, manuscript preparation
Alexander Chong Shu-Chien: Overall design of studies, funding, flow of work, supervision of WT Lee, BK Tan, S Eng, draft and finalization of manuscript