Synergism between ivermectin and the tyrosine kinase/P-glycoprotein inhibitor crizotinib against Haemonchus contortus larvae in vitro

Anthelmintic resistance is a major problem in parasitic nematodes of livestock worldwide. One means to counter resistance is to use synergists that specifically inhibit resistance mechanisms in order to restore the toxicity, and hence preserve the usefulness, of currently available anthelmintics. P-glycoproteins (P-gps) eliminate a wide variety of structurally unrelated xenobiotics from cells, and have been implicated in anthelmintic resistance. Crizotinib is a tyrosine kinase inhibitor under development as a cancer therapeutic. The compound also inhibits P-gps, and has been shown to reverse multidrug resistance in cancer cells. We were therefore interested in determining if the compound was able to increase the sensitivity of Haemonchus contortus larvae to ivermectin, as measured by in vitro larval development and migration assays with a drug-resistant and a –susceptible isolate. In migration assays, co-administration of crizotinib increased the toxicity of ivermectin to resistant larvae (up to 5.7-fold decrease in ivermectin IC), and rendered the resistant larvae equally or more sensitive to ivermectin than the susceptible isolate. On the other hand, co-administration of crizotinib had no effect on ivermectin sensitivity in the susceptible isolate. In development assays, significant increases in the sensitivity of both the resistant (up to 1.9-fold) and susceptible (up to 1.6-fold) larvae to ivermectin were observed, although the magnitude of the observed synergism was less than seen in migration assays, and the resistant larvae retained significant levels of ivermectin resistance. By highlighting the ability of the P-gp inhibitor crizotinib to increase the sensitivity of H. contortus larvae to ivermectin, this study provides further evidence that P-gp inhibitors are potential tools for modulating the efficacy of anthelmintics. In addition, the differences in the outcomes of the two assays, with ‘resistance-breaking’ effects being much more marked in migration assays, suggest that some life-stage-specific aspects may exist in the interaction of ivermectin with P-gps in the two worm isolates

Drug-efflux and target-site gene expression patterns in Haemonchus contortus larvae able to survive increasing concentrations of levamisole in vitro

While there is some evidence that changes in nicotinic acetylcholine receptor (nAChR) subunits confer resistance to levamisole in gastrointestinal helminth parasites, the exact nature of the resistance mechanism(s) is unclear. We utilised the presence of a resistant fraction within the Wallangra 2003 isolate of Haemonchus contortus larvae in order to subdivide the population into three subpopulations of larvae able to survive increasing concentrations of the drug. We then measured gene expression levels in the subpopulations and the larval population as a whole, focusing on genes encoding the subunit components of levamisole-sensitive receptors, genes encoding ancillary proteins involved in receptor assembly, and P-glycoprotein (P-gp) genes. The subpopulation surviving the lowest levamisole concentration showed increases of 1.5- to 3-fold in a number of P-gp genes (Hco-pgp-3, -4, -10, and -14) alongside unchanged receptor genes, compared to the whole Wallangra larval population. On the other hand, the subpopulation surviving the intermediate levamisole concentration showed an increase in only a single P-gp (Hco-pgp-14), alongside decreases in some receptor subunit (Hco-unc-63a) and ancillary protein genes (Hco-unc-50, Hco-ric-3.1 and 3.1). The subpopulation surviving the highest levamisole concentration showed further decreases in receptor subunit genes (Hco-unc-63a and Hco-unc-29 paralogs) as well as genes involved in receptor assembly (Hco-unc-74, Hco-unc-50, Hco-ric-3.1 and 3.1), alongside no increased P-gp gene levels. This suggests a biphasic pattern of drug resistance in the larvae of this worm isolate, in which a non-specific P-gp-mediated mechanism confers low levels of resistance, while higher level resistance is due to altered receptor subunit composition as a result of changes in both subunit composition and in the levels of proteins involved in receptor assembly

The Effect of Egg Embryonation on Field-Use of a Hookworm Benzimidazole-Sensitivity Egg Hatch Assay in Yunnan Province, People's Republic of China

With the implementation of mass drug administration programmes for the control of human soil transmitted helminths there is a need to develop drug sensitivity monitoring tools to detect the emergence of resistance. The present study aimed to use an egg hatch assay to measure benzimidazole sensitivity in human hookworms in a field setting in Yunnan province, People's Republic of China, in order to assess whether the assay offered a practical means of monitoring drug sensitivity in human hookworms in such a location. The assay proved able to generate dose response data, which allowed for the drug sensitivity of the hookworms in the local children to be described; the mean IC50 was 0.10 ug/ml thiabendazole. The study also found that practical issues associated with stool collection procedures, specifically the embryonation of some eggs during the time elapsing between stool deposition and egg recovery, can have an impact on the drug sensitivity data. We suggest means for data analysis that overcome the impact of egg embryonation on drug dose response data, which should allow for the use of such assays at different field sites worldwide

The mediating role of innovation in the relationship between market orientation and university performance in Pakistan

Universities globally are going through a paradigm shift with a need to become more innovatively market-oriented to handle the issue of growing competition for funding, as well as attracting/retaining the international/local competent students and academicians. However, there appears to be a dearth of research on how such state of affairs could be addressed, particularly in the emerging economies like Pakistan. In the light of resource-based theory (RBT), as well as organizational-learning theory (OLT), literature suggests that market-orientation (MO) and innovation are to be the desirable unique resources, as well as the guiding philosophies, to enable universities for a more competitive performance. Hence, this study investigated how resources like marketorientation (MO), and innovation, can influence university performance (UP). The study also tested empirically the potential mediating effect of innovation on the MOUP relationship. In addition, how the dimensions of MO influenced the innovation and university performance (UP) were also tested empirically in the universities of Pakistan. Results of the PLS path modelling (with 369 respondents from the target public-sector universities) firstly confirmed significant effect of the “universal construct of MO” and two of its dimensions “the advising and mentoring, as well as the intelligencegeneration and response” on UP. However, one dimension of MO, which is the administration-leadership, was not significantly supported to directly influence the UP. Secondly, the study confirmed that there were significant direct effects of the “universal construct of MO”, as well as all of its dimensions, on innovation. Thirdly, the study also found that there was a significant effect of innovation on UP. Furthermore, the bootstrapping results found significant mediation of innovation between the MO-UP relationship. Hence, the results show that UP can be directly enhanced through MO and innovation. Even the use of innovation as a mediator can further strengthen the MO-UP relationship. Based on the findings, the study offers theoretical and practical implications, followed by its limitations and directions, for future research

Making Decisions to Identify Forage Shrub Species for Versatile Grazing Systems

Grazing systems in many parts of the world face large challenges, including a declining natural resource base (e.g. soil fertility), marked fluctuations in feed production across seasons and years, climate change (including the contribution of greenhouse gases from livestock), and market demands for sustainable and ethical production systems. The ‘Enrich’ project was established in Australia (Revell et al. 2008; Bennell et al. 2010) within this broad context of emerging challenges to explore the potential of using Australian native perennial shrub species as part of the feedbase for sheep and cattle in southern Australia. The underlying rationale was to: add perennial shrub species into the existing annual-based pasture feedbase so that the forage system could tolerate extended dry periods but provide green edible plant material during periods where a ‘feed gap’ would otherwise exist; be productive on marginal soils where other productive options are limited (Masters et al. 2010); and have a positive effect on gut function and health (Vercoe et al. 2007); i.e. a versatile grazing system. This paper outlines the research approach that was taken, and reports on a ‘decision tree’ to prioritise species from an initial large list, based on a wide range of plant characteristics and how they can be used in a grazing system