Hymenolepis diminuta and H. microstoma: uptake of cyclosporin A and drug binding to parasite cyclophilins.

Cyclosporin A (CsA) acts as a powerful immunosuppressant through its binding to the cytosolic isomerase, cyclophilin (CyP), forming a complex which inhibits the phosphatase activity of calcineurin. The drug is also selectively anti-parasitic but its mode of action remains unknown. The mouse tapeworm, Hymenolepis microstoma is sensitive to CsA, but the rat tapeworm, H. diminuta is not susceptible either in rats, mice or in vitro. Using these two tapeworm models, the uptake and binding of CsA were examined in relation to parasite cyclophilins. Uptake and compartmentalization of the drug were markedly different in the two species: H. microstoma takes up more drug than does H. diminuta and sequesters more drug into intracellular compartments. Characterization of cyclophilins using both CsA binding and isomerase activity assays reveals that H. microstoma possesses two cyclophilin isoforms (M(r) 17,700 and 21,400) with isomerase activity that is inhibited by CsA. using identical assays, we have been unable to demonstrate CsA-binding proteins or CsA-sensitive isomerase activity in H. diminuta. These data suggest that the anthelmintic action of CsA relates in some way to the presence and function of parasite cyclophilins.