Inactivation of proteolytic enzymes by Eubothrium rugosum (Cestoda) from the gut of burbot Lota lota

Abstract

Parasitic organisms inhabiting the alimentary canal should permanently resist the destructive action of host digestive enzymes. The intestinal parasites were shown to produce specific protease inhibitors protecting them from proteolysis. However, little is known about this adaptive mechanism in cestodes so far, especially for the tapeworms dwelling inside the fish intestines. Here, we explored the ability to inactivate proteolytic enzymes in the fish tapeworm Eubothrium rugosum (Batsch, 1786) (Bothriocephalidea) parasitising the intestine of wild burbot, Lota lota (Linnaeus). The assays were conducted with different concentrations of commercial trypsin and homogenate of intestinal mucosa both being the sources of proteinases. The incubation of live E. rugosum in trypsin solutions of two different concentrations caused a significant decrease in the enzyme activity. The extent of activity reduction was dependent on trypsin concentration. At the same time, the inhibitory effect of the worm incubation medium turned out to be statistically insignificant. These findings suggest partial adsorption of the enzyme to the tegument surface, with its further inactivation. In contrast to the incubation medium, the worm extract suppressed over 80% of trypsin activity and nearly half of the proteolytic activity in the mucosa homogenate. Notably, the inhibitory activity of the tapeworms hardly depended on their size characteristics. Finally, the research has demonstrated secretion of proteinase inhibitor in E. rugosum, which appears to be essential for its survival in enzymatically hostile environment.

Localization of the proteinase inhibitor activity in the fish cestode Eubothrium rugosum

“…Therefore, the tapeworm body apparently contains no substances responsible for inhibition of the host digestive proteinases. Thus, the data obtained show that it is possible to use the whole worms for similar studies, which proves the validity of the basic conclusions from some previous works that were made using the extracts of the homogenized worms (Izvekova et al, 2017a).…”

“…Previously, we found that the extracts from E. rugosum cestodes have an inhibitory effect on trypsin activity, as well as on the proteolytic activity of homogenized intestinal mucosa from its host fish, the burbot (Izvekova et al, 2017a). In the present study, we tried to determine whether the incubation medium of this tapeworm has an inhibitory ability and whether this ability is associated with the brush border of the worm or with its body.…”

“…To this end, the incubation medium of living worms was tested for inhibitory capacities first. In a previous study, we found no significant inhibitory effect of E. rugosum incubation medium on trypsin activity (Izvekova et al, 2017a). However, since the incubation medium of another cestode, Triaenophorus nodulosus, living in the pike intestine was found to inhibit trypsin samples (Izvekova et al, 2017b), we have changed the experimental design to search for a similar capacity in E. rugosum.…”

“…The infection by this large parasitic worm may limit the nutrient uptake by the host, which entails changes in the catalytic capacity of intestinal enzymes. The infection-induced effects in fish are attributable to protease inhibitors produced by the tapeworms, the damages in the intestinal epithelial cells caused by the attachment structures of the parasite (Izvekova et al, 2017a), and associated changes in the composition of the host microbiota (Kashinskaya et al, 2020). Sometimes, to reduce the economic costs of Eubothrium infection, attempts have been made to treat fish with anthelmintics (Bristow & Berland, 1991).…”

Composition of the microbial communities in the gastrointestinal tract of perch (Perca fluviatilis L. 1758) and cestodes parasitizing the perch digestive tract

“…In order to inhabit the fish gut, tapeworms possess different features that facilitate their ability to survive under specific conditions of the fish gut. Thus, cestodes are characterized by specific surface epithelium or, tegument, associated with feeding processes and parasite protection from the host enzymes (inhibition of host proteinase activity) (Izvekova, Frolova, & Izvekov, ). It was shown that cestodes, as a component of intestinal communities, can also impact digestive processes and be an important factor that effect on the fish gut microbiota (Izvekova, ; Izvekova & Korneva, ).…”