Influence of Pluronic 85 and ketoconazole on disposition and efficacy of ivermectin in sheep infected with a multiple resistant Haemonchus contortus isolate.

Non-specific mechanisms involving ATP-binding cassette drug efflux transporters may play an important role in xenobiotic clearance in ovine gastro-intestinal nematodes. By using transporter inhibitors, the aim of this trial was to assess the possibility of increasing drug bioavailability in the host in an attempt to improve treatment efficacy. Thirty-six lambs were infected with 5000 multiple-drug resistant Haemonchus contortus third stage larvae and separated into six groups (n=6): ivermectin alone (IVM; 0.2 mg/kg body-weight, BW), ketoconazole alone (KET; 10 mg/kg BW), Pluronic 85 alone (P85; 4 mg/kg BW), IVM+KET, IVM+P85 or untreated control. Ivermectin was administered once on day 28 post-infection for all appropriate groups, whereas KET and P85 were administered as five separate doses on day 26-30 post-infection inclusive. The resultant data showed that concomitant administration of KET or P85 with IVM induced increases in plasma and tissue concentrations of IVM in treated animals, resulting in a two-fold increase in the area under the time-concentration curve (p<0.05). Faecal egg counts and worm burdens of the IVM+KET and IVM+P85 groups were lower than in the untreated, KET and P85 alone control animals. Worm burdens were reduced by between 16% and 51% with IVM+KET and IVM+P85 respectively compared to untreated control animals. The co-administration of P85 with IVM increased the efficacy by 34%, compared with IVM alone, in terms of worm count reduction of the multi-resistant isolate of H. contortus.

In vitro screening of plant lectins and tropical plant extracts for anthelmintic properties.

Lectins are plant secondary metabolites (PSM) found in many forages and which may confer anthelmintic properties to gastrointestinal parasites through disrupting the development of parasitic larvae throughout its life cycle. In experiment 1, the ability of the plant lectins jacalin (JAC), concanavalin A (Con A), phytohemagglutinin E2L2 (PHA-E2L2), phytohemagglutinin L4 (PHA-L4), phytohemagglutinin E3L (PHA-E3L), kidney bean albumin (KBA), Robinia pseudoacacia agglutinin (RPA), Maackia amurensis lectin (MAA), Maclura pomifera agglutinin (MAA), Dolichos biflorus agglutinin (DBA), wheat germ agglutinin (WGA) and Galanthus nivalis agglutinin (GNA) to disrupt the feeding of the first stage larvae (L(1)) of the sheep gastro-intestinal nematodes (GIN) Teladorsagia circumcincta, Haemonchus contortus and Trichostrongylus colubriformis was investigated using a larval feeding inhibition test (LFIT). Only PHA-E3L, WGA and Con A had a potent effect on disrupting larval feeding of all of the three species of GIN investigated. The lectin concentration required to inhibit feeding in 50% of L(1) (IC50) was 7.3±1.2, 8.3±1.4 and 4.3±1.7 µg/ml for PHA-E3L; 59.1±32.4, 58.7±11.9 and 8.1±7.0 µg/ml for Con A and 78.9±11.2, 69.4±8.1 and 28.0±14.1 µg/ml for WGA for T. circumcincta, H. contortus and T. colubriformis larvae, respectively (P=0.006). The addition of the lectin inhibitors fetuin, glucose/mannose or N-acetylglucosamine for PHA-E3L, Con A and WGA, respectively, caused an increase in the proportion of larvae that had fed at all concentrations for PHA-E3L only. In experiment 2, the effect of extracts from the tropical plants Azadiractha indica, Trichanthera gigantea, Morus alba, Gliricidia sepium and Leucaena leucocephala on the feeding behaviour of H. contortus L(1,) was examined. A. indica, T. gigantea and M. alba failed to inhibit 50% of larvae from feeding at concentrations up to 10mg plant extract per ml. In contrast, both G. sepium and L. leucocephala demonstrated a dose-dependent effect on larval feeding with respective IC50 estimates (mean±s.e.) of 0.015 mg/ml ±0.001 and 3.465 mg/ml ±0.144, effects which were partly reversed by the inclusion of either the tannin inhibitor polyethylene glycol or the lectin inhibitor Fetuin. These studies demonstrate that plant lectins can have an inhibitory effect on the feeding behaviour of first stage larvae of ovine GIN in vitro. Moreover they also provide novel evidence that lectins may contribute to the anthelmintic properties of some tropical forage plant extracts, such as G. sepium and L. leucocephala.

P-glycoprotein interfering agents potentiate ivermectin susceptibility in ivermectin sensitive and resistant isolates of Teladorsagia circumcincta and Haemonchus contortus.

P-glycoprotein (P-gp) homologues, belonging to the ATP Binding Cassette (ABC) transporter family, are thought to play an important role in the resistance of gastro-intestinal nematode parasites against macrocyclic lactones. The aim of this study was to investigate the influence of various P-gp interfering compounds on the efficacy of ivermectin (IVM) in sensitive and resistant nematode isolates. The feeding of IVM resistant and sensitive Teladorsagia circumcincta and Haemonchus contortus first-stage larvae (L1) was assessed using a range of IVM concentrations (0.08-40 nm) with or without P-gp inhibitors: valspodar, verapamil, quercetin, ketoconazole and pluronic P85. The P-gp inhibitors were selected on the basis of their ability to interfere with P-gp transport activity in an epithelial cell line over-expressing murine P-gp. In the presence of P-gp interfering agents, the in vitro susceptibility to IVM of both sensitive and resistant isolates of T. circumcincta and H. contortus was increased. These results show that compounds interfering with P-gp transport activity could enhance IVM efficacy in sensitive isolates, and also restore IVM sensitivity in resistant nematodes. These results support the view that ABC transporters can play an important role in resistance to IVM, at least in the free-living stages of these economically important gastro-intestinal nematodes.