An in vitro larval migration assay for assessing anthelmintic activity of different drug classes against Ascaris suum.

In vitro methods have been developed for the detection of anthelmintic resistance in a range of nematode species. However, the life cycle of Ascaris suum renders the commonly used egg hatch assay and larval development assay unusable. In this study we developed a combined multi-well culture and agar gel larval migration assay to test the effect of benzimidazole and tetrahydropyrimidin/imidazothiazole anthelmintics against nine isolates of A. suum collected from locations in China and Denmark. Drugs tested were thiabendazole, fenbendazole, mebendazole, levamisole, and pyrantel. The percentages of larvae that migrated to the surface of each treated and control well were used to calculate the drug concentration which inhibits 50% of the larvae migration (EC50). The values of EC50 of thiabendazole, fenbendazole, mebendazole, levamisole, and pyrantel against A. suum isolates ranged 74-150, 4.9-13.9, 2.3-4.3, 358-1150 and 1100-4000nM, respectively. This combined multi-well culture and agar gel larval migration assay was a sensitive bioassay for anthelmintic activity and could serve as an in vitro method to detect for lowered drug efficacy against A. suum or possibly to screen for anthelmintic drug candidates.

Structural Basis of the Substrate Specificity and Enzyme Catalysis of a Papaver somniferum Tyrosine Decarboxylase.

Tyrosine decarboxylase (TyDC), a type II pyridoxal 5'-phosphate decarboxylase, catalyzes the decarboxylation of tyrosine. Due to a generally high sequence identity to other aromatic amino acid decarboxylases (AAADs), primary sequence information is not enough to understand substrate specificities with structural information. In this study, we selected a typical TyDC from Papaver somniferum as a model to study the structural basis of AAAD substrate specificities. Analysis of the native P. somniferum TyDC crystal structure and subsequent molecular docking and dynamics simulation provide some structural bases that explain substrate specificity for tyrosine. The result confirmed the previous proposed mechanism for the enzyme selectivity of indolic and phenolic substrates. Additionally, this study yields the first crystal structure for a plant type II pyridoxal-5'-phosphate decarboxylase.