ORIGINAL PAPER Expression and characterization of glutathione peroxidase of the liver fluke, Fasciola gigantica Narin Changklungmoa 1 & Kulathida Chaithirayanon 2 & Werachon Cheukamud 1 & Athit Chaiwichien 1 & Supawadee Osotprasit 1 & Tepparit Samrit 1 & Prasert Sobhon 1,2 & Pornanan Kueakhai 1 Received: 17 June 2018 /Accepted: 7 August 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Glutathione peroxidase (GPx) is a key member of the family of antioxidant enzymes in trematode parasites including Fasciola spp. Because of its abundance and central role as an anti-oxidant that helps to protect parasites from damage by free radicals released from the host immune cells, it has both diagnostic as well as vaccine potential against fasciolosis. In this study, we have cloned, characterized, and detected the expression of the GPx protein in Fasciola gigantica (Fg). FgGPx (582 bp) was cloned by polymerase chain reaction (PCR) from complementary DNA (cDNA) from an adult fluke. Its putative peptide has no signal sequence and is composed of 168 amino acids, with a molecular weight of 19.1 kDa, and conserved sequences at NVACKUG, FPCNQFGGQ, and WNF. Phylogenetic analysis showed that GPx is present from protozoa to mammals and FgGPx was closely related to Fasciola hepatica GPx. A recombinant FgGPx (rFgGPx) was expressed in Escherichia coli BL21 (DE3) and used for immunizing mice to obtain polyclonal antibodies (anti-rFgGPx) for immunoblotting and immunolocalization. In immunoblotting analysis, the FgGPx was expressed in all stages of F. gigantica (eggs, metacercariae, newly excysted juveniles (NEJ), 4-week-old juveniles, and adults). This mouse anti-rFgGPx reacted with the native FgGPx at a molecular weight of 19.1 kDa in adult whole body (WB) and tegumental antigens (TA) as detected by immunoblotting. The FgGPx protein was expressed at a high level in the tegument, vitelline glands, and eggs of the parasite. Anti-rFgGPx exhibited no cross-reactivity with the other parasite antigens, including Eurytrema pancreaticum, Cotylophoron cotylophorum, Fischoederius cobboldi, Gastrothylax crumenifer, Paramphistomum cervi, and Setaria labiato papillosa. The possibility of using rFgGPx for immunodiagnosis and/or as a vaccine for fasciolosis in animals of economic importance will be explored in the future. Keywords Fasciola gigantica . Glutathione peroxidase . Cloning . Molecular characteristics . Tissue expression Introduction Fasciolosis is a disease that is caused by infection with Fasciola spp., including F. hepatica and F. gigantica. It is a serious health problem for both domesticated animals and humans in the trop- ical and subtropical regions. Metacercariae are the infective stage, and after excystation in the duodenum of the definitive host, the juveniles migrate through the intestinal wall and the peritoneal cavity to reach the liver and eventually the bile ducts. During penetration and migration, juvenile parasites come into contact with and are damaged by reactive oxygen species (ROS) released by the host immune cells, such as macrophages and inflamma- tory cells. Therefore, the parasites must defend themselves by posing anti-oxidation mechanism. F. gigantica possesses and expresses a series of antioxidant enzymes, such as superoxide dismutase (SOD, Jaikua et al. 2016), thioredoxin glutathione reductase (TGR, Kalita et al. 2018; Changklungmoa et al. 2015), thioredoxin (Trx, Gupta et al. 2015; Changklungmoa et al. 2014), and peroxiredoxin (Prx, Chaithirayanon and Sobhon 2010; Sangpairoj et al. 2014) to neutralize oxidative stress. GPx was the first seleno-protein anti-oxidant enzyme being discovered (Rotruck et al. 1973) and functions as an antioxi- dant by catalyzing the reduction of hydrogen peroxide (H 2 O 2 ), a more potent member of ROS, by using selenocysteine * Pornanan Kueakhai earn_patho@hotmail.com; pornanan@buu.ac.th 1 Faculty of Allied Health Sciences, Burapha University, Long-Hard Bangsaen Road, Saen Sook Sub-district, Mueang District, Chonburi 20131, Thailand 2 Department of Anatomy, Faculty of Science, Mahidol University, Rama VI Rd, Bangkok 10400, Thailand Parasitology Research https://doi.org/10.1007/s00436-018-6046-9