Insecticide detoxification indicator strains as tools for enhancing chemical discovery screens

BACKGROUND: Insecticide discovery screens carried out on whole organisms screen for potency resulting from chemical activity at the target site. However, many potentially insecticidal compounds are naturally detoxified in vivo and do not make it to the target site. It is hypothesised that insect strains with their xenobiotic detoxification machinery compromised could be used to identify such compounds that normally fail to show up in screens; these compounds could then be more rationally designed to increase their bioavailability. This strategy was tested with transgenic Drosophila lines with altered expression of Cyp6g1 and Dhr96. RESULTS: It was observed that Cyp6g1 knockdown transgenic lines have increased susceptibility to the test compound imidacloprid, while Dhr96 knockdown transgenic lines are resistant. Evidence was found for a systemic response to xenobiotic exposure, uncovered by piperonyl butoxide treatment and by gene expression profiling. Sex-specific gene expression regulated by DHR96 was also observed. CONCLUSION: The results confirm that this approach to chemical discovery could identify compounds that escape traditional screens. The complexity of the system means that a panel of single and multiple gene knockdown transgenic lines may be required. Copyright © 2011 Society of Chemical Industry     

Phloem mobility of xenobiotics VI. A phloem-mobile pro-nematicide based on oxamyl exhibiting root-specific activation in transgenic tobacco

Phloem mobility is a desirable attribute for pesticides in many applications, and the physicochemical properties necessary for phloem mobility are now well understood. However, attempts to derivatize pesticides to make them phloem mobile are often frustrated by a concomitant loss of activity. This study describes a phloem-mobile pro-nematicide, a hydroxymethyloxamyl glucuronide (JR522) coupled with an in-situ activation mechanism in transgenic tobacco expressing Escherichia coli β-glucuronidase in its root tips. When applied foliarly to the transgenic tobacco, JR522 and its methyl ester (JM775) showed greater nematicidal activity than oxamyl against root-knot nematodes. This example of combining pro-pesticide chemistry with crop genetic engineering for site-specific activation provides a model system for demonstrating how to circumvent the often mutual exclusivity of phloem mobility and pesticidal activity. Additional advantages of this scheme include the potential mammalian safety of the propesticide, as exhibited by JR522 in this study, and a high degree of site-specific release of xenobiotics in plants.     

A Survey of the Literature (1995–1999) on the Kinetics of Drugs in Camels (Camelus dromedarius)

Recent publications dealing mainly with the kinetics of antiparasitic and antibacterial agents, NSAIDs, and other drugs in camels are briefly reviewed. The kinetic data for most of these drugs indicated that they have longer absorption and elimination half-lives and slower systemic clearance in the camel compared to other animals. This corroborates earlier reports that suggested that the activities of drug-metabolizing enzymes and the capacity to biotransform and eliminate xenobiotics is lower in camels than in other ruminants. There is a clear need to establish basic kinetic data for the camel in order to avoid extrapolation of drug dosage regimens and withdrawal times from data for other animals, as this may result in irrational use of drugs in camels.     

Characterization of the Purified Glutathione S-transferases from Two Psocids Liposcelis bostrychophila and L.entomophila

Glutathione S-transferases（GSTs） from Liposcelis bostrychophila Badonnel and L.entomophila（Enderlein）（Psocoptera：Liposcelididae） were purified by glutathione-agarose affinity chromatography,and characterized subsequently by their Michaelis-Menten kinetics toward the artificial substrates 1-chloro-2,4-dinitrobenzene（CDNB） and reduced glutathione（GSH）,respectively.The specific activity of the purified GST toward CDNB was 2.3-fold higher in L.bostrychophila than in L.entomophila.Though the specific activities of purified enzymes varied between the two species,the purification yields were similar.SDS-PAGE revealed one band at 23 kDa for both the species.GSTs of L.entomophila exhibited higher Michaelis-Menten constants（Km） but lower maximal velocity（Vmax） values than those of L.bostrychophila.The optimum pH for CDNB conjugation of L.bostrychophila and L.entomophila GSTs was 7.0 and 7.5,and optimum temperature was 35 and 40°C,respectively.Inhibition kinetics showed that cibacron blue,curcumin,bromosulfalein,ethacrynic acid,and carbosulfan had excellent inhibitory effects on GSTs in both species,but the inhibitory effects of beta-cypermethrin,fenpropathrin,tetraethylthiuram disulfide,and diethyl maleate were not significant.     

The influence of dietary energy levels with and without PCB induction on the growth of tilapia,Oreochromis niloticos x O. aureus

The effects of three dietary energy levels, 323, 365 and 408 Kcal/100g diet, on the growth performance of hybrid tilapia, Oreochromis niloticus x O. aureus, were studied. The experiment was carried out for 3 months in a recirculating rearing system. Growth and feed conversion ratios were significantly reduced (p<0.05) in fish exposed to 100 ppm polychlorinated biphenyl (PCB), fed high energy diets (365 and 408 Kcal/100g diet). The hepatic cytochrome P-450 and NADPH-cytochrome c reductase activities were also significantly (p<0.05) lower in PCB-treated fish fed high energy diets (365 and 408 Kcal/100g diet) than fish fed lower energy diet (323 Kcal/100g diet). The malic enzyme activity and the body lipid content in fish generally increased as the dietary energy level increased.     

Cytochrome P-450-dependent metabolism in isolated liver cells from fed and starved rainbow trout,Salmo gairdneri

The cytochrome P-450 content in liver cells from rainbow trout was not affected by starvation for 12 weeks whereas the rate of cytochrome P-450-dependent deethylation of 7-ethoxycoumarin in liver cells from 6 or 12 weeks starved fish was 60% of the rate in fed fish. Treatment of fish with -naphthoflavone increased the 7-ethoxycoumarin metabolism several-fold in both starved and fed fish.Optimal cytochrome P-450 monooxygenation in liver cells from fed or starved fish was not affected by addition of glucose or 2-bromooctanoate, an inhibitor of fatty acid -oxidation which is the main source of metabolic fuel in trout liver. The cellular content of NADPH, an obligatory cofactor for cytochrome P-450 monooxygenation, was not affected by addition of substrate to cytochrome P-450, inhibition of fatty acid -oxidation or inhibition of the oxidative phosphorylation. This indicates a great capacity of rainbow trout liver cells to retain high NADPH/NADP⁺ ratios. These results suggest that the cytochrome P-450 mediated metabolism of xenobiotics in liver cells from fed or starved trout is not limited by the availability of reducing equivalents.     

Aldrin epoxidation and dihydroisodrin hydroxylation as probes of in vivo and in vitro oxidative metabolic capability of some caterpillars

Comparative biochemical studies are productive means to study factors that limit both beneficial and harmful effects of chemicals. Reactions such as aldrin epoxidation and dihydroisodrin hydroxylation are valuable assays of oxidative metabolism in scientific studies of chemical biology in insects, subhuman primates and other living things. The tissue distribution of activity in caterpillars may have functional significance. Localization of relatively high concentrations of these cytochrome P450 monooxygenases in gut tissue of lepidoptera may represent an important means to minimize absorption of lipophilic foreign chemicals in food. Some polychlorocycloalkanes permit in vivo and in vitro studies owing to their stability, acceptable toxicity and relatively simple pattern of metabolism. In vivo studies to assess the significance of in vitro findings are feasible with substrates such as aldrin, dihydroisodrin (DHI) and oxidative methylenedioxyphenyl inhibitors such as piperonyl butoxide (PBO) or carbon monoxide. Biphasic dose-dependent decreased and increased DHI-OH formation resulted from PBO pretreatment by gut, fat body, head and Malpighian tubule homogenates of cutworms and gut and fat body (the only tissues tested) of cabbage looper Trichplusia ni (Hübner) and black cutworm Agrotis ipsilon (Hüfnagel). The biphasic in vivo responses of caterpillars to PBO are a reminder of the complexity of biochemical and physiological responses of organisms coexposed to chemicals that are classified, often glibly, as toxic substances and metabolic inhibitors and inducers. Knowledge of dose and time relationships demands very careful evaluation in living things in the environment.     

A degree-day concept for estimating degradation time under field conditions

Development of degradation rate information for crop protection products in soil is typically a time consuming and costly process. Therefore, development of methodology that would allow extrapolation of limited degradation information to wider field conditions in a predictive fashion would be desirable. This study presents an approach that uses a modified heat unit model to estimate organic compound degradation time using limited datasets. The model requires daily soil or air temperature and volumetric water content. Predictions based on the model for three different compounds in five different field studies were within 80% of measured values based on soil analysis. Results from this research indicate that the model was able to predict compound half-life values across all sites with r2 = 0.99.     

白腐菌漆酶特性及异生芳香化合物的降解

漆酶是一种含铜多酚氧化酶，在白腐菌中普遍存在。漆酶可催化酚类化合物和芳香胺的氧化，在小分子介体物质存在下，漆酶氧化范围可进一步扩大。本文对漆酶降解纺织染料、多环芳香化合物、氯化芳香化合物的机理及最新研究进展作一介绍。在纺织染料中，蒽醌类染料为漆酶底物，可被漆酶直接氧化，而偶氮染料和靛青染料为非酶底物。当小分子的还原介体存在下，可介导酶与非酮底物染料之间的氧化；漆酶对多环芳烃的氧化也多属于酶与非酶底物之间的氧化，因此，选择合适的介体物质非常重要；漆酶可氧化氯酚类物质形成自由基，然后形成低溶性聚合物，可通过沉淀去除，介体物质的存在也有助于氯化芳香化合物的降解。