title: Increased susceptibility of a triclabendazole (TCBZ)-resistant isolate of Fasciola hepatica to TCBZ following co-incubation in vitro with the P-glycoprotein inhibitor, R(+)-verapamil.
abstract: A study was carried out to investigate whether the action of triclabendazole sulphoxide (TCBZ.SO) against the liver fluke, Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible fluke isolates were used for this in vitro study and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. For experiments with the Oberon isolate, flukes were incubated for 24 h with either R(+)-VPL (1×10-4 m) on its own, TCBZ.SO (15 μg mL-1) alone, a combination of R(+)-VPL (1×10-4 m) plus TCBZ.SO (15 μg mL-1), TCBZ.SO (50 μg mL-1) on its own, or a combination of TCBZ.SO (50 μg mL-1) plus R(+)-VPL (1×10-4 m). They were also incubated in TCBZ.SO (50 μg mL-1) alone or in combination with R(+)-VPL (1×10-4 m) until they became inactive; and in TCBZ.SO (50 μg mL-1) alone for a time to match that of the combination inactivity time. Flukes from the Cullompton isolate were treated with either TCBZ.SO (50 μg mL-1) alone or in combination with R(+)-VPL (1×10-4 m) until they became inactive, or with TCBZ.SO (50 μg mL-1) alone time-matched to the combination inactivity time. Morphological changes resulting from drug treatment and following Pgp inhibition were assessed by means of scanning electron microscopy. Incubation in R(+)-VPL alone had a minimal effect on either isolate. TCBZ.SO treatment had a relatively greater impact on the TCBZ-susceptible Cullompton isolate. When R(+)-VPL was combined with TCBZ.SO in the incubation medium, however, the surface disruption to both isolates was more severe than that seen after TCBZ.SO treatment alone; also, the time taken to reach inactivity was shorter. More significantly, though, the potentiation of drug activity was greater in the Oberon isolate; also, it was more distinct at the higher concentration of TCBZ.SO. So, the Oberon isolate appears to be particularly sensitive to efflux pump inhibition. The results of this study suggest that enhanced drug efflux in the Oberon isolate may be involved in the mechanism of resistance to TCBZ.
authors.affiliation: Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland.
authors.forename: M
authors.initials: M
authors.lastname: Meaney
authors.affiliation: Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland.
authors.forename: J
authors.initials: J
authors.lastname: Savage
authors.affiliation: Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland.
authors.forename: G P
authors.initials: GP
authors.lastname: Brennan
authors.affiliation: Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland.
authors.forename: E
authors.initials: E
authors.lastname: Hoey
authors.affiliation: Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland.
authors.forename: A
authors.initials: A
authors.lastname: Trudgett
authors.affiliation: Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland.
authors.forename: I
authors.initials: I
authors.lastname: Fairweather
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology*; D001562:Benzimidazoles / Q000494:pharmacology*; D004351:Drug Resistance / Q000187:drug effects*; D005210:Fasciola hepatica / Q000187:drug effects* / Q000648:ultrastructure; D008297:Male; D008855:Microscopy, Electron, Scanning; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013454:Sulfoxides / Q000494:pharmacology*; D000077682:Triclabendazole; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D000871:Anthelmintics; D001562:Benzimidazoles; D013454:Sulfoxides; D000077682:Triclabendazole; D014700:Verapamil; C085104:triclabendazole sulfoxide