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, littleis known about this adaptive mechanism in cestodes so far, especially for the tapeworms dwelling inside the fish intestines. Here, weexplored 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 commercialtrypsin and homogenate of intestinal mucosa both being the sources of proteinases. The incubation of live E. rugosum in trypsinsolutions of two different concentrations caused a significant decrease in the enzyme activity. The extent of activity reduction wasdependent on trypsin concentration. At the same time, the inhibitory effect of the worm incubation medium turned out to be statisticallyinsignificant. These findings suggest partial adsorption of the enzyme to the tegument surface, with its further inactivation. In contrastto the incubation medium, the worm extract suppressed over 80% of trypsin activity and nearly half of the proteolytic activity in themucosa homogenate. Notably, the inhibitory activity of the tapeworms hardly depended on their size characteristics. Finally, the researchhas demonstrated secretion of proteinase inhibitor in E. rugosum, which appears to be essential for its survival in enzymaticallyhostile environment.