Effect of Diafenthiuron exposure under short and long term experimental conditions on hematology, serum biochemical profile and elemental composition of a non-target organism, Labeo rohita.

Diafenthiuron is a thiourea compound that has a novel mode of action as it inhibits mitochondrial functioning in insect pests. It has been reported in local newspapers that this pesticide is entering in our fresh water bodies on regular basis and it is a potential threat for aquatic life. The present study was designed to determine effect of Diafenthiuron, a commonly used pesticide in Pakistan, on the hematology, serum biochemical profile and elemental composition of a non-target organism, Labeo rohita (L. rohita). A sub-lethal dose (0.0075 mg L-1) of Diafenthiuron was applied under short (2, 4 and 8 days) and long term (16, 32 and 64 days) experimental conditions. Our results indicated that the pesticide exposed fish had significantly higher white blood count, lymphocyte, red blood cell count, hemoglobin, hematocrit, mean corpuscular volume, red cell distribution width than the control group. However, platelets count, plateletcrit and platelet distribution width were significantly reduced in Diafenthiuron treatments than their respective control groups. Concentration of total serum proteins, albumin, globulin, cholesterol, triglycerides and AST were disturbed in pesticide exposed treatments compared to control groups. Comparison of elemental concentrations revealed that calcium, potassium and cadmium concentration varied significantly when compared between Diafenthiuron treated and untreated L. rohita. In conclusion, we are reporting that Diafenthiuron can adversely affect the hematological, serum and elemental concentrations of a non-target organism like L. rohita and may therefore pose a threat to the food web.

Comparative analysis of goitrogenic effects of phenylthiourea and methimazole in zebrafish embryos.

Craniofacial malformations, reduced locomotion and induction of genes encoding for enzymes involved in thyroid hormone synthesis were assessed using methimazole and N-phenylthiourea in zebrafish embryos. Gene expression, the most sensitive endpoint (EC50_MMI=372-765µM, EC50_PTU=7.6-8.6µM), was analysed in wild-type and in a transgenic strain, tg(tg:mCherry), expressing mCherry fluorescence protein under the control of the thyroglobulin gene. Reduction of locomotion and craniofacial malformations were observed at one or two orders of magnitude above concentrations affecting gene expression, respectively. Both effects could be linked to the malformations caused by reduced thyroxin levels. Our results show that due to the presence of the autoregulatory loop of the hypothalamus-pituitary-thyroid axis, various molecular initiating events of thyroid disruption are amenable for the zebrafish embryo. We propose the tg(tg:mCherry) bioassay as a sensitive tool in medium scale screening of goitrogens, given the minimal effort for sample preparation and analysis of gene expression.

Isoxyl particles for pulmonary delivery: In vitro cytotoxicity and potency.

Pulmonary delivery of isoxyl may increase drug efficacy by targeting alveolar macrophages which are host cells for Mycobacteria. Isoxyl microparticles (1-2microm) were obtained by antisolvent precipitation and simultaneous spray drying method. The controls were made by mixing isoxyl solution in DMSO with cell culture media. Depending on the drug concentration, either isoxyl solution or nanosuspension was obtained in these controls. In the study, MTT (methylthiazol tetrazolium) and LDH (lactose dehydrogenase) assays were utilized to test cytotoxicity of these particle suspensions or solutions toward macrophages. Isoxyl microparticles and controls in concentrations up to 100microg/ml were not toxic to macrophages. Both isoxyl microparticle suspensions and controls showed bactericidal activity, as estimated by death of mycobacteria inside the macrophages, at a concentration of 5microg/ml.

Toxicity of diafenthiuron to honey bees in laboratory, semi-field and field conditions.

BACKGROUND: Cardamom, an important spice crop often attacked by many insect pests, is controlled mainly using synthetic insecticides. As honey bees play a vital role in pollination in cardamom, the impact of insecticides on honey bees needs to be explored to assess its safety. RESULTS: Risk assessment based on contact toxicity revealed diafenthiuron to be a non-selective insecticide to bees with a low selectivity ratio (the ratio between the LD(50) for beneficial and pest species). A dose of diafenthiuron that killed 90% of cardamom borer, Conogethes punctiferalis Guenee, was found to kill 100% of Indian bees. Based on the hazard ratio (the ratio between the field-recommended dose and the LD(50) for the beneficial), diafenthiuron was found to be slightly to moderately toxic to bees. Diafenthiuron, even at low concentrations of LC(1) (the concentration that killed 1% of bees), was found to affect the foraging and homing behaviour of Indian bees. Of bees fed with 30 microg mL(-1) of diafenthiuron, 40% were found missing on the third day after exposure. However, diafenthiuron did not affect bee visits to the cardamom fields. CONCLUSION: Diafenthiuron is more highly toxic to Apis cerana indica F. than to C. punctiferalis by contact, using selectivity ratio and probit substitution methods of risk assessment, but the hazard ratio revealed diafenthiuron to be a slightly to moderately toxic chemical. Diafenthiuron was found to affect the foraging and homing behaviour of bees at sublethal concentrations. Thus, sublethal effects are more relevant in risk assessment than lethal and acute effects.

Human flavin-containing monooxygenase form 2 S-oxygenation: sulfenic acid formation from thioureas and oxidation of glutathione.

Thioureas are oxygenated by flavin-containing monooxygenases (FMOs), forming reactive sulfenic and/or sulfinic acids. Sulfenic acids can reversibly react with GSH and drive oxidative stress through a redox cycle. For this reason, thiourea S-oxygenation is an example of FMO-dependent bioactivation of a xenobiotic. Functional FMO2 is expressed in the lung of 26% of individuals of African descent and 5% of Hispanics but not in Caucasians or Asians. We have previously demonstrated that human FMO2.1 protein expressed in Sf9 microsomes has high activity toward a series of thioureas that are known or suspected lung toxicants including thiourea, 1-phenylthiourea, and ethylenethiourea. We now show by HPLC and LC-MS that 1-phenylthiourea and alpha-naphthylthiourea are converted to their sulfenic acids. GSH in the incubations at concentrations of 0.5-1.0 mM completely eliminated the sulfenic acid with resultant production of GSSG. These results indicate that individuals with the FMO21 allele may be at enhanced risk of pulmonary damage upon exposure to thioureas.

Field efficacy and baseline toxicities of pyriproxifen, acetamiprid, and diafenthiuron against Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) in Burkina Faso (West Africa).

Bioassays were conducted in 2001 and 2002 to estimate toxicities and dose-response relationships of 24 Bemisica tabaci Gennadius populations to pyriproxifen, acemitaprid, and diafenthiuron. LC50s ranging from 0.014 to 0.096 mgL(-1), 0.60 to 1.3 mgL(-1), and 3.5 to 6.7 mgL(-1) were observed respectively for pyriproxifen, acemitaprid, and diafenthiuron. These LC50s much lower than the field doses recommended for each compound. A fast increase in rates of mortality within a narrow range of lethal concentrations was observed for each compound. indicating that all three compounds were highly effective at killing whiteflies. In a separate experiment, pyriproxifen, acemitaprid, and diafenthiuron were tested in 2001 and 2002 to compare their effectiveness and assess their impact on parasitism in the field. In both years all three compounds significantly prevented B. tabaci populations from reaching economic injury levels in cotton and minimized adverse effects on parasitism. Our results provide for the first time baseline toxicological, field efficacy, and effect on parasitism data for pyriproxifen, acemitaprid, and diafenthiuron against B. tabaci in West Africa. These compounds should be included in a resistance management program of the cotton pest complex and their use should be restricted to prevent the building of resistance in B. tabaci populations.

Accumulation of chlorpromazine and thiouracil by human melanoma cells in culture.

The uptake (total radioactivity in intact cells) and incorporation (radioactivity bound to acid-precipitable material) of 14C-chlorpromazine (CPZ) and 14C-thiouracil (TU) were studied using a library of 3 human fibroblast strains and 13 tumour cell lines. In contrast to previous studies using rodent melanomas in vivo, the melanoma lines, including lines with high tyrosinase and melanin contents, did not take up more CPZ and TU than non-melanoma cells (fibroblasts, HeLa cells). Incorporation of CPZ was also broadly similar in all cell types studied. TU was selectively incorporated into the melanoma line having a high tyrosinase and melanin content but not into lines with high tyrosinase activity and low melanin content. While supporting the possibility of selective therapy for heavily-pigmented melanomas using labelled TU derivatives, these results suggest that the action of potentially melanoma-affined compounds should be further evaluated in human cells. Unlabelled CPZ or TU was not selectively toxic to melanoma cells. Unexpectedly, methylation-sensitive tumour cells (Mer-phenotype) were highly resistant to TU, thus providing a new experimental tool for understanding the genesis of this phenotype in vivo.