No description available.

No description available.

Avermectins are macrocyclic lactones insecticides, used as antihelminthics in humans and animals, since they have low human toxicity. There is a clear role for the efflux transporter mdr1 controlling CNS exposure to avermectins in polymorphic animal models, but the role of MDR1 in limiting human avermectin exposure is less well defined, although no such knockout MDR1 polymorphisms have been identified to date. The aim of this study was to characterise the kinetics of avermectin interactions with efflux transporters in the human SHSY5Y neuroblastoma cell line, and compare them with mouse isoforms expressed in N2a cells to determine the relevance of mouse data to human avermectin exposure. Protein and mRNA expression of human MDR1, MRP and mouse mdr1a were identified in the cell lines, similar to the blood-brain barrier except BCRP and bcrp were absent. Ki values for inhibition of MDR1 or MRP substrate efflux by avermectins did not differ significantly between human and mouse cells (P > 0.05); abamectin (MDR1 Ki = 0.95 ± 0.08μM; mdr1a Ki = 0.77 ± 0.25μM), emamectin benzoate (MDR1 Ki = 0.60 ± 0.07μM; mdr1a Ki = 0.56 ± 0.02μM) and ivermectin (MDR1 Ki = 0.24 ± 0.08μM; mdr1a Ki = 0.18 ± 0.02μM), but ivermectin has the highest affinity for inhibition of MDR1- and mdr1a-substrate efflux. Cytotoxicity was apparent for emamectin benzoate above 6μM, which is 100-fold higher than peak exposure concentrations, but not for abamectin or ivermectin. Expression levels of the chemokine genes SDF-2, AIMP1 and BDNF are candidates for biomarkers of avermectin exposure. These data show that SH-SY5Y cells are a good model in which to investigate avermectin exposure and to compare to mouse cells and have confirmed the involvement of MDR1 and MRP transporters. Avermectins are of global importance, so a greater understanding of mechanisms of human exposure is pertinent.

No description available.

In order to control insect populations that are resistant to the currently used insecticides, new compounds with completely different modes of action need to be developed. One such novel insecticide is Pyridalyl; it shows high specificity towards lepidopteran pests, no phytotoxicity and it is capable of controlling lepidopteran populations that are resistant to the currently used insecticides. The main aim of this project was to elucidate the mode of action of Pyridalyl using biochemical and proteomic techniques.

The exposure of primary and secondary non-target species to Second Generation Anticoagulant Rodenticides (SGARs) is widespread and is a cause for concern amongst conservationists. Levels found in wild non-target species range from trace amounts to lethal levels and occur in up to 81% of barn owl carcasses surveyed. The harm caused by low level AR residues carried by many animals in the wild is not well understood, as is the relative toxicity of the different AR compounds to bird species. My experimental work investigated both sub-lethal residues carried by laboratory mice, Mus musculus, and the comparative toxicity of three SGARs (bromadiolone, difenacoum and brodifacoum) to feral pigeon, Columba livia. Laboratory mice were given >LDso doses of three SGAR compounds and were maintained initially with vitamin K supplements. These mice were monitored for 175 days post-dosing, including through pregnancy. No measurable effect of carrying a SGAR-residue was seen on the growth and breeding activity of mice. Using blood-clotting response testing in pigeons, an EDso was determined for SGAR compounds. Bromadiolone was the least toxic compound to pigeons while the toxicity of difenacoum did not differ significantly from brodifacoum. Data from field trials conducted against AR-resistant rat populations was modelled to compare the exposure levels posed by three SGAR compounds used to control the wild rat infestations. The model was in two parts, the uptake and persistence in the rat population, and the secondary exposure posed by the trials. The AR-resistant rat populations were not controlled completely by bromadiolone or difenacoum and this resulted in much higher levels of SGAR entering the food chain through the rats. This in turn led to higher exposure levels in the secondary non-target species. The need for understanding the toxicity level of each compound to the non-target species of concern was highlighted by this work.

No description available.

The aim of this project was to develop azadirachtin as an insecticide that is applied to the soil, using a granular formulation, for root uptake and subsequent systemic plant protection. A method was developed whereby azadirachtin could be rapidly isolated to approximately 95% purity using flash chromatography. This material was used in all subsequent chemical and biochemical studies. To increase the speed of crude extract analysis, a colorimetric technique was assessed to rapidly quantify azadirachtin. However, this method was generally unsuitable for the requirements of this project because it was non-specific and not stable. Granular formulations based on sodium alginate, starch-kaolin and poly(e-caprolactone), and containing different neem seed extracts were successfully prepared. These granules exhibited differnces in the rate of azadirachtin release into water. Additives such as kaolin clay and rapeseed oil could be used to modify the speed of release. Following application to soil, the position of granules did not affect release rates. However, granule application method was shown to affect the rate at which the limonoid was accumulated within the nasturtium plants. Azadirachtin was shown to be moderately water-soluble (1.29 g/l). During mixing studies between distilled water and n-octanol, the limonoid partitioned more favourably into the non-aqueous phase at a ratio of 7:1. Based on calculated Koc values (<40), azadirachtin was classified as very highly soil mobile. Adsorption occurred principally to the organic matter of soils. Clay minerals were comparably non-sorbent. Desorption from both of these sites occurred readily. Azadirachtin was not persistent within soil where the limonoid’s DT50 was as short as 1.06 days. Initial breakdown resulted in the acetyl moiety being cleaved from the molecule. In addition, azadirachtin was shown to exhibit a pH sensitive hydrolytic degradation. The limonoid’s half-life in solution ranged from 57 days at pH 5 to 7.15 hours at pH 9. In conclusion a suitable granule for a controlled-release of azadirachtin was developed.