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Effect of the P-glycoprotein inhibitor, R(+)-verapamil on the drug susceptibility of a triclabendazole-resistant isolate of Fasciola hepatica.

Vet Parasitol. 2013 Mar 22;

Authors: Savage J, Meaney M, Brennan GP, Hoey E, Trudgett A, Fairweather I


A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by the inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Sligo TCBZ-resistant and Cullompton TCBZ-susceptible fluke isolates were used for these experiments and the Pgp inhibitor selected was R(+)-verapamil [R-VPL]. In the first experiment, flukes were initially incubated for 2h in R-VPL (100μM), then incubated for a further 22h in R-VPL+triclabendazole sulphoxide (TCBZ.SO) (50μg/ml, or 0.1327μM). For controls, flukes were incubated for 24h in R-VPL and TCBZ.SO on their own. In a second experiment, flukes were removed from the incubation media following cessation of movement. In the third experiment, Sligo flukes were incubated in lower concentrations of R-VPL (10μM) and TCBZ.SO (15μg/ml, or 0.0398μM). Morphological changes resulting from drug treatment and following Pgp inhibition were assessed by means of scanning electron microscopy. Incubation in R-VPL alone had minimal effect on either isolate. After treatment with TCBZ.SO alone, there was greater surface disruption to the Cullompton than Sligo isolate. However, combined treatment of R-VPL+TCBZ.SO led to more severe surface changes to the Sligo isolate than with TCBZ.SO on its own; this potentiation of drug activity was not seen with the Cullompton isolate. The phenomenon was evident at both concentrations of TCBZ.SO. Inclusion of R-VPL in the incubation medium also reduced the time taken for the flukes to become inactive; again, this effect was more distinct with the Sligo isolate. The results of this study support the concept of altered drug efflux in TCBZ-resistant flukes and indicate that drug transporters may play a role in the development of drug resistance.

PMID: 23597772 [PubMed - as supplied by publisher]