A high-throughput colorimetric assay for detection of Schistosoma mansoni viability based on the tetrazolium salt XTT

Pedro Henrique Nascimento Aguiar, Núbia Monteiro Gonçalves Soares Fernandes, Carlos Leomar Zani, Marina Moraes Mourão

Schistosoma mansoni is a trematode parasite that causes schistosomiasis, one of the most prevalent neglected tropical diseases, leading to the loss of 2.6 million disability-adjusted life years. Praziquantel is the only drug available, and new drugs are required. The most common strategy in schistosomiasis drug discovery is the use of the schistosomula larval-stage for a pre-screen in drug sensitivity assays. However, assessing schistosomula viability by microscopy has always been a limitation to the throughput of such assays. Hence, the development of validated, robust high-throughput in vitro assays for Schistosoma with simple readouts is needed. Here, we present a simple and affordable alternative to assess schistosomula viability. The method employed is based on the hydrosoluble tetrazolium salt XTT which has been widely used in other organisms but has never been used to drug screen in schistosomes. We showed that schistosomula reduce XTT salt to a coloured formazan product and that absorbance levels reflected the viability and parasites number. This XTT viability assay was validated for high throughput screening of compounds in schistosomula, and dose-response curves of compounds could be reproduced. We conclude that the XTT viability assay could be applied for the screening of large compounds collections in S. mansoni and accelerate the identification of novel antischistosomal compounds.