Transcriptional responses in Parascaris univalens after in vitro exposure to ivermectin, pyrantel citrate and thiabendazole

The aim of this study was to investigate the transcriptional responses in adult Parascaris univalens after in vitro exposure to different concentrations of three anthelmintic drugs, focusing on drug targets and drug metabolising pathways. Adult worms were collected from the intestines of two foals at slaughter. The foals were naturally infected and had never been treated with anthelmintics. The worms were incubated in cell culture medium containing different concentrations of either ivermectin (10-9 M, 10-11 M, 10-13 M), pyrantel citrate (10-6 M, 10-8 M, 10-10 M) or thiabendazole (10-5 M, 10-7 M, 10-9 M) at 37 °C for 24 h. In parallel, control worms were incubated under the same conditions without anthelmintics. After incubation the viability of the worms was assessed and RNA extracted from the anterior end of 36 worms and sequenced on Illumina NovaSeq. All worms were alive at the end of the incubation but showed varying degrees of viability depending on the drug and concentration used. Differential expression (p < 0.05 and fold change = 2) analysis showed similarities and differences in the transcriptional response after exposure to the different drug classes. Candidate genes up- or downregulated in drug exposed worms include members of the phase I metabolic pathway short-chain dehydrogenase/reductase superfamily (SDR), flavin containing monooxygenase superfamily (FMO) and cytochrome P450-family (CYP) as well as members of the membrane transporters major facilitator superfamily (MFS) and solute carrier superfamily (SLC). Generally, different targets of the anthelmintics used were found to be up- and downregulated in an unspecific pattern after drug exposure, apart from the GABA receptor subunit lgc-37, which was upregulated only in worms exposed to 10-9 M of ivermectin. In summary, we have identified a number of novel candidate genes putatively involved in drug metabolism and possibly involved in anthelmintic resistance in P. univalens.