水中有机磷农药二嗪农的臭氧化降解机制及影响因素

目的臭氧是一种清洁高效的饮用水消毒剂，并能氧化水中有机污染物而不产生消毒副产物，广泛地用于饮用水处理。方法臭氧与有机磷农药二嗪农反应后，采用GC-MS对中间产物进行定性分析，用HPLC监测二嗪农的残留量和中间产物的生成量，研究二嗪农的臭氧降解动力、机制及影响因素。结果二嗪农的臭氧降解由臭氧直接氧化和羟基自由基间接氧化共同作用，并遵循假一级动力学。降解受离子清除剂与溶液pH的影响。加入50mmol／L的离子清除剂和降低溶液pH都使二嗪农的臭氧降解速率常数明显减小。结论通过GC-MS分析，确定了二嗪氧磷为二嗪农的臭氧化中间产物，提高溶液pH有利于二嗪氧磷进一步降解，而加入离子清除剂则不利于二嗪氧磷的降解。     

CYP-specific bioactivation of four organophosphorothioate pesticides by human liver microsomes

The bioactivation of azinphos-methyl (AZIN), chlorpyrifos (CPF), diazinon (DIA), and parathion (PAR), four widely used organophosphorothioate (OPT) pesticides has been investigated in human liver microsomes (HLM). In addition, the role of human cytochrome P450 (CYPs) in OPT desulfuration at pesticide levels representative of human exposure have been defined by means of correlation and immunoinhibition studies. CYP-mediated oxon formation from the four OPTs is efficiently catalyzed by HLM, although showing a high variability (>40-fold) among samples. Two distinct phases were involved in the desulfuration of AZIN, DIA, and PAR, characterized by different affinity constants (K(mapp1) = 0.13-9 microM and K(mapp2) = 5- 269 microM). Within the range of CPF concentrations tested, only the high-affinity component was evidenced (K(mapp1) = 0.27-0.94 microM). Oxon formation in phenotyped individual HLM showed a significant correlation with CYP1A2-, 3A4-, and 2B6-related activities, at different levels depending on the OPT concentration. Anti-human CYP1A2, 2B6, and 3A4 antibodies significantly inhibited oxon formation, showing the same OPT concentration dependence. Our data indicated that CYP1A2 is mainly involved in OPT desulfuration at low pesticide concentrations, while the role of CYP3A4 is more significant to the low-affinity component of OPT bioactivation. The contribution of CYP2B6 to total hepatic oxon formation was relevant in a wide range of pesticide concentrations, being a very efficient catalyst of both the high- and low-affinity phase. These results suggest CYP1A2 and 2B6 as possible metabolic biomarkers of susceptibility to OPT toxic effect at the actual human exposure levels.     

Paraoxonase 1 (PON1) status and substrate hydrolysis

Paraoxonase 1 (PON1) hydrolyzes a number of organophosphorus (OP) compounds including insecticides and nerve agents. The in vivo efficacy of PON1 to protect against a specific OP exposure depends on the catalytic efficiency of hydrolysis. The Q192R polymorphism affects the catalytic efficiency of hydrolysis of some substrates and not others. While PON1_R192 hydrolyzes paraoxon approximately 9-times as efficiently as PON1_Q192, the efficiency is insufficient to provide in vivo protection against paraoxon/parathion exposure. The two PON1₁₉₂ alloforms have nearly equivalent but higher catalytic efficiencies for hydrolyzing diazoxon (DZO) and provide equivalent in vivo protection against DZO exposures. On the other hand, PON1_R192 is significantly more efficient in hydrolyzing chlorpyrifos oxon (CPO) than PON1_Q192 and provides better protection against CPO exposure. Thus, for some exposures it is only the level of plasma PON1 that is important, whereas for others it is both plasma level and the PON1₁₉₂ alloform(s) present in plasma that are important. In no case is the plasma level of PON1 unimportant, provided that the catalytic efficiency is sufficient to protect against the exposure. Two-substrate enzyme assay/analysis protocols that reveal both PON1 plasma levels and PON1₁₉₂ phenotype (QQ; QR; RR) are designed to optimize the separation of PON1₁₉₂ phenotypes; however, they have not been optimized for evaluating in vivo rates of OP detoxication. This study describes the adaptation of a non-OP, two-substrate determination of PON1 status to the conversion of the PON1 status data to physiologically relevant rates of DZO and CPO detoxication. Conversion factors were generated for rates of hydrolysis of different substrates.     

Comparative study on pesticide mixture of organophosphorus and pyrethroid in commercial formulation

The marketing of mixtures of organophosphate and pyrethroid insecticides has become very common in developing countries and has resulted in an increase in the prevalence of toxicity. The present study aimed to evaluate the toxic effects of a commercial preparation of the pesticide mixture durasin, which contains 60% diazinon and 0.5% deltamethrin, compared with the individual commercial pesticides of diazinon 30% and deltamethrin 5%. Forty male albino rats weighing 160 ± 20 g were divided into; DA (diazinon 20 mg/Kg b.w.), DA (deltamethrin 2 mg/Kg b.w.), M (durasin 20 mg/Kg b.w.) and control (C); cholinesterase (ChE), malonaldehyde (MDA), glutathione (GSH), glutathione-S-transferase (GST), superoxide dismutase (SOD), total cholesterol (TC), triglyceride (TG) and non-specific esterase's isoenzymes in rat's blood were determined following 7 and 14 days of treatment. The weekly- recorded biochemical results were used as criteria for estimating the joint effects of the tested pesticide mixture. Antioxidant defense mechanisms and lipid peroxidation in rat plasma displayed the same responses with intensities which were related to the different treatments. Biochemical analysis showed that (DA) or (DM) individually cause alteration in lipid metabolism and non-specific esterase, while mixture treatment (M) induced antagonistic effects toward all the tested parameters except total reduced glutathione level, which was synergistic at the 2nd week. In conclusion the commercial mixture (M) under study has potentially greater toxic impact than the components alone in the rat.     

Paraoxonase 1 (PON1) modulates the toxicity of mixed organophosphorus compounds

A transgenic mouse model of the human hPON1_Q192R polymorphism was used to address the role of paraoxonase (PON1) in modulating toxicity associated with exposure to mixtures of organophosphorus (OP) compounds. Chlorpyrifos oxon (CPO), diazoxon (DZO), and paraoxon (PO) are potent inhibitors of carboxylesterases (CaE). We hypothesized that a prior exposure to these OPs would increase sensitivity to malaoxon (MO), a CaE substrate, and the degree of the effect would vary among PON1 genotypes if the OP was a physiologically significant PON1 substrate in vivo. CPO and DZO are detoxified by PON1. For CPO hydrolysis, hPON1_R192 has a higher catalytic efficiency than hPON1_Q192. For DZO hydrolysis, the two alloforms have nearly equal catalytic efficiencies. For PO hydrolysis, the catalytic efficiency of PON1 is too low to be physiologically relevant. When wild-type mice were exposed dermally to CPO, DZO, or PO followed 4-h later by increasing doses of MO, toxicity was increased compared to mice receiving MO alone, presumably due to CaE inhibition. Potentiation of MO toxicity by CPO and DZO was greater in PON1^−/− mice, which have greatly reduced capacity to detoxify CPO or DZO. Potentiation by CPO was more pronounced in hPON1_Q192 mice than in hPON1_R192 mice due to the decreased efficiency of hPON1_Q192 for detoxifying CPO. Potentiation by DZO was similar in hPON1_Q192 and hPON1_R192 mice, which are equally efficient at hydrolyzing DZO. Potentiation by PO was equivalent among all four genotypes. These results indicate that PON1 status can have a major influence on CaE-mediated detoxication of OP compounds.     

Effects of organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on brain acetylcholine content and acetylcholinesterase activity in Japanese quail

Effects of 2 organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on the brain cholinergic system were investigated in Japanese quail. Cholinergic signs, such as salivation and convulsions in legs and wings, were seen 7–15 min after administration with DDVP (3–4 mg/kg) or 6–120 min after administration with fenitrothion (250–350 mg/kg). In the DDVP-treated quail (10 min after dosage of 3 mg/kg), free acetylcholine (ACh), labile-bound ACh, increased significantly and acetylcholinesterase (AChE) decreased to 28% of the value determined in untreated quail. In the fenitrothion-treated group (60 min after dosage of 300 mg/kg), only free ACh increased and AChE activity decreased to 20% of the control value. In vitro, DDVP and fenitrothion inhibited AChE activity in brain homogenate with an I₅₀ of 10^?8 M and 10^?5 M, respectively. It appeared that both organophosphorus compounds might have essentially the same effect on the brain cholinergic system. There were only small differences in the effect on various fractions of ACh between the 2 compounds, although there was a hundred-fold range in dose.     

Sublethal Effects of Organophosphate Diazinon on the Brain of Cyprinus Carpio

Effects of diazinon, at different concentrations and exposure times, were investigated in freshwater fish, Cyprinus carpio, to elucidate the possible mode of action on lipid peroxidation together with the inhibitory effect of diazinon on acetylcholinesterase activity and changes in tissue protein levels. Cholinesterase inhibition is considered to be a specific biomarker of exposure to organophosphorus pesticides. Fish were exposed to 0.0036 μg/L, 0.018 μg/L, and 0.036 μg/L (sublethal) concentrations of diazinon for 5, 15, and 30 days, and biochemical measurements were carried out spectrophotometrically. Brain was chosen as an indicator tissue because it is a target system for the organophosphorus action. More than 20% decline in acetylcholinesterase activity relative to mean activity of the controls was observed in the diazinon-exposed groups. Protein content decreased significantly after 15 days of exposure to 0.018 μg/L and 0.036 μg/L diazinon and after 30 days of exposure to 0.036 μg/L. Malondialdehyde level declined markedly compared with the control levels. This study showed that prolonged exposures of C. carpio to diazinon had significant effects on brain acetylcholinesterase activity and that environmentally relevant concentrations of diazinon can significantly inhibit brain acetylcholinesterase activity. Altered protein content was probably due to the high energy demand under pesticide stress or inhibition of de novo enzyme synthesis. The decreased malondialdehyde content may reflect the possibility of better protection against oxidative stress.     

Measurement of pesticides in hair samples from pemphigus foliaceus and pemphigus vulgaris patients in Southeastern Brazil

BackgroundPesticides, mainly organophosphates (OP), have been related to increased risk of pemphigus vulgaris (PV) and pemphigus foliaceus (PF), nevertheless, their measurement has not been determined in pemphigus patients.ObjectiveTo evaluate pesticide exposure and pesticide measurement, comparing PV, PF and control groups in Southeastern Brazil.MethodsInformation about urban or rural residency and exposure to pesticides at the onset of pemphigus was assessed by questionnaire interview; hair samples from the scalp of PV, PF, and controls were tested for OP and organochlorines (OC) by gas-phase chromatography coupled to mass spectrometry.ResultsThe minority of PV (2 [7.1%] of 28) and PF (7 [18%] of 39), but none of the 48 controls, informed living in rural areas at the onset of pemphigus (p = 0.2853). PV (33.3%), PF (38.5%), and controls (20%) informed exposure to pesticides (p = 0.186). Twenty-one (14.8%) of 142 individuals tested positive for OP and/or OC: PV (2 [6.3%] of 32) and PF (11 [25.6%] of 43) had similar pesticides contamination as controls (8 [11.9%] of 67) (p = 0.4928; p = 0.0753, respectively), but PF presented higher contamination than PV (p = 0.034). PV did not present any positivity for OP. Three (7%) PF tested positive for both OP and OC. Some PF tested positive for three or four OP, mainly diazinon and dichlorvos.Study limitationLack of data for some controls.ConclusionAlthough the frequency of PV and PF patients exposed to pesticides was similar, pesticides were more frequently detected in hair samples from PF compared to PV. The cause-effect relationship still needs to be determined.     

Protective effect of thymoquinone against diazinon-induced hematotoxicity,genotoxicity and immunotoxicity in rats

Several studies have shown that oxidative stress and cell damage can occur in the very early stages of diazinon (DZN) exposure. The present study was designed to determine the beneficial effect of thymoquinone (Thy), the main component of Nigella sativa (black seed or black cumin) against DZN immunotoxicity, hematotoxicity and genotoxicity in rats. In the present experimental study, 48 male Wistar rats were randomly divided into six groups, (eight per group) as follows: control (receiving corn oil as the DZN solvent), DZN (20 mg/kg), Thy (10 mg/kg), Thy (2.5 mg/kg) + DZN, Thy (5 mg/kg) + DZN and Thy (10 mg/kg) + DZN. After four weeks of treatment, the hematological parameters of red blood cells (RBCs), white blood cells (WBCs), hemoglobin (Hb), hematocrit (Hct) and platelets (PLTs) were evaluated. The evaluation of genotoxicity was carried out using the micronucleus assay. For measurement of cytokine production, interferon gamma (IFN-γ), interleukin 10 (IL10) and interleukin 4 (IL4) were chosen as immunotoxicity indicators of DZN toxicity. DZN was found to decrease RBCs, WBCs, Hb, Hct, PLTs, butyrl- and acetyl-cholinesterase activity and I FN-γ and increased the micronucleus indices of IL10 and IL4 as compared with the control group. Treatment with Thy reduced DZN hematotoxicity and immunotoxicity, but, significantly, did not prevent genotoxicity. This study showed that Thy (without the significant effect on genotoxicity) decreased the hematological toxicity, immunotoxicity and butyrl and acetyl cholinesterase activity induced by DZN. The success of Thy supplementation against DZN toxicity can be attributed to the antioxidant effects of its constituents.     

Toxicity of diazinon and its metabolites increases in diabetic rats

The effect of diazinon (DZN) on the activities of cholinesterase (ChE) in plasma and acetylcholinesterase (AChE) in erythrocyte and brain was investigated in normal and streptozotocin-induced diabetic rats. Hepatic drug-metabolizing enzyme activity was also estimated by measuring the systemic clearance of antipyrine, and the expression of hepatic cytochrome P450 (CYP) 3A2 and CYP1A2, which is closely related to the metabolism from DZN to DZN-oxon, a strong inhibitor of both ChE and AChE. No significant differences in the activities of ChE in plasma and AChE in erythrocyte were observed between normal and diabetic rats. Treatment with DZN significantly decreased these activities in diabetic rats more than in normal rats 6 h after injection (6.5 mg/kg). Treatment with DZN significantly decreased the activity of AChE in brain of diabetic rats than normal rats 3 h after injection (65 mg/kg), although no significant difference in the activity was found between normal and diabetic rats. The urinary recovery of diethylphosphate (DEP), a metabolite of DZN-oxon, was significantly increased in diabetic rats, but that of diethylthiophosphate (DETP), a metabolite of DZN, was unchanged. Significant increases in the systemic clearance of antipyrine and protein levels of hepatic CYP1A2, not CYP3A2, were observed in diabetic rats. These results suggest the possibility that a metabolite of DZN, DZN-oxon, causes higher toxicity in diabetic rats due to the enhancement of hepatic CYP1A2-mediated metabolism of DZN.