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CYP450 Bioactivation of Organnophosphorothioate Pesticides in Fish Liver Misrosomes

Author: ZhangLi
Tutor: LiuXin;LiShaoNan
School: Fujian Agriculture and Forestry University
Course: Pesticides
Keywords: cytochrome P450 organophosphate pesiticides inhibition rate metabolism
CLC: X174
Type: Master's thesis
Year: 2009
Downloads: 56
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Abstract

Organophosphorous insecticides are prone to contaminate aquatic environment and intoxicate aquatic organisms reside in it due to their large application amount and relatively high solubility in water. One outstanding character of some of the organophosphorous insecticides is selective toxicity towards different species of fish. This character results in difficulty for assessing risk of this group of insecticide upon fish community. In present study a monoxygenase related capacity that converts organothiophosphorous insecticides into their more toxic oxon analogs was measured by an indirect method and a direct one, respectively. The indirect method was designed to measure inhibition of an exogenesis acetylcholinesterase (AChE) by the oxon analogs, while the direct method was to detect the oxon analogs being produced by means of high performance liquid chromatography (HPLC and GC). In present study, three kinds of organothionphosphorous insecticide, i.e., parathion, malathion, and chlorpyrifos were used as the parent compounds, and microsome from livers of four species of freshwater fish, i.e., Brachydanio rerio, Pseudorasbora parva, Lepomis gibbosus, and Xiphophorus helleri were used as enzyme sources. Aim of the study was to investigate correlation between capacity in terms of oxidative activation and sensitivity of fish toward organothiophosphorous insecticides.Indirect measure: 1) The best suitable condition for inhibiting of endogenesis cholinesterase was 30μmol/L iso-OMPA and 15 min for the Lepomis gibbosus, and it was 50μmol/L iso-OMPA and 15 min for the Brachydanio rerio, the Pseudorasbora parva, and the Xiphophorus helleri, respectively. 2) Statistically significant difference in terms of inhibition of the probe AChE, resulted from production of the oxon analogs, was detected in case that microsome from the four species of fish was spiked with a series of concentration (5μmol/L, 10μmol/L, 100μmol/L) of parathion, respectively, and the case was the same for malathion and chlorpyrifos.Chromatography analysis: 1) Statistically significant difference in terms of monoxygenase involved production of paraoxon and chlorpyrifos-oxon were detected in the four species in case that the microsomes were spiked with 10μmol/L and 100μmol/L parathion and chlorpyrifos, respectively. No paraoxon was detected in the four species as 5μmol/L parathion was added. Whereas in case that the same amount of chlorpyrifos was added, statistically significant difference, in terms of production of its oxon analog, was detected among the four species except for the Brachydanio rerio and the Pseudorasbora parva. 2) Statistically significant difference, in terms of production of malaoxon, was detected among the four species in case the microsomes were spiked with 10μmol/L and 100μmol/L malathion except in case that microsomes from the Brachydanio rerio and the Pseudorasbora parva were spiked with 10μmol/L malathion. No malaoxon was detected in any one of the four species as their microsomes were spiked with 5μmol/L malathion.

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