Identification, recombinant protein production, and functional analysis of a M60-like metallopeptidase, secreted by the liver fluke Opisthorchis viverrini.

The carcinogenic liver fluke Opisthorchis viverrini (O. viverrini) is endemic in Thailand and neighboring countries including Laos PDR, Vietnam and Cambodia. Infections with O. viverrini lead to hepatobiliary abnormalities including bile duct cancer-cholangiocarcinoma (CCA). Despite decades of extensive studies, the underlying mechanisms of how this parasite survives in the bile duct and causes disease are still unclear. Therefore, this study aims to identify and characterize the most abundant protein secreted by the parasite. Proteomics and bioinformatics analysis revealed that the most abundant secretory protein is a metallopeptidase, named Ov-M60-like-1. This protein contains an N-terminal carbohydrate-binding domain and a C-terminal M60-like domain with a zinc metallopeptidase HEXXH motif. Further analysis by mass spectrometry revealed that Ov-M60-like-1 is N-glycosylated. Recombinant Ov-M60-like-1 (rOv-M60-like-1) expressed in Escherichia coli (E. coli) was able to digest bovine submaxillary mucin (BSM). The mucinase activity was inhibited by the ion chelating agent EDTA, confirming its metallopeptidase identity. The enzyme was active at temperatures ranging 25-37 °C in a broad pH range (pH 2-10). The identification of Ov-M60-like-1 mucinase as the major secretory protein of O. viverrini worms warrants further research into the role of this glycoprotein in the pathology induced by this carcinogenic worm.

How would publication bias distort the estimated effect size of prototypic antidepressants in the forced swim test?

This commentary aims to discuss the impact of publication bias on the estimated effect of prototypic antidepressants in the forced swim test (FST). A systematic review and meta-analysis (SRMA) recently reported by Kara et al. (2018) showed that selected prototypic antidepressants reduced immobility time of mice in the FST across a variety of experimental designs. Despite differences in the procedures for SRMA, these results resemble the interim data collected by our research group according to a protocol deposited in the Systematic Review Facility (http://syrf.org.uk/) and Open Science Framework (osf.io/9kxm4). Both studies detected a high amount of publications reporting statistically significant results and agreement with the primary hypothesis raising the possibility of publication bias in the field of FST. In our preliminary analysis, no evidence for publication bias was observed. However, the present work was limited to the effects of imipramine (doses ranging from 4 to 64 mg/kg) in different strains of mice. Therefore, more comprehensive studies are required to evaluate the risk of publication bias in the field of basic antidepressant research. We see the need to expand the current preliminary studies to evaluate the risk of publication bias within the preclinical research using the FST. Appraisal of the risk of publication bias may avoid misestimated effects of drugs in the FST providing better bases for the discovery of new antidepressants.