Differential Genes Expression Analysis of Chronic Organophosphorus Pesticide Toxicity in Low Dose Exposure Using Oligonucleotide Microarrays

摘要

We completed the organophosphorus pesticide (OP) triazophos chronic toxicity studies according to the requirements of good laboratory practice (GLP) in Sprague-Dawley rats for 12 months and investigated the application of DNA microarray. Four doses of triazophos and control groups were used. The highest dosing regimen, a constant diet concentration of 100 mg triazophos/kg feed, inhibited blood and plasma cholinesterase activity, which reached the peaks of 14.5% and 7.6% respectively at the end of four weeks in the absence of any clinical manifestations. Alkaline phosphatase (AKP), red blood cells (RBC) and hemoglobin (Hb) decreased and other clinical pathology variables did not show significant differences. In the present study we used the Rat Toxicology U34 genechip to analyze differential gene expression induced by triazophos. Liver samples were collected from Sprague-Dawley rats at 6 and 12 months termination periods in different dose subgroups. Calculated with respect to the constant diet concentration of 100 mg/kg, the average dose of triazophos was 5.21 mg/kg BW/d in the six months test. There were 30 genes and expressed sequence tags (EST) that were differentially expressed (with a minimum of twofold change) between the treatment groups and control groups. The differentially expressed genes involved metabolism enzymes, immune response-related genes, DNA damage repair genes, stress response genes and membrane proteins. Cell structure components changes were confirmed through pathology. Calculated with respect to the constant diet concentrations of 100 and 3 mg/kg, the average doses of triazophos were 3.86 and 0.11 mg.kg~(-1) BW.d~(-1) respectively at 12 months. Self-Organizing Map (SOM) clustering algorithm showed that 184 expressed genes had a linear increase in gene expression in a dose-response relationship and 145 expressed genes had decreased expression levels. The multi-endpoint results showed that chronic OPs toxicity differs from the acute cholinergic episodes and suggest its metabolic pathway and intoxication. Some candidate genes may be used as biomarkers of chronic triazophos toxicity. This study demonstrates that changes in gene expression levels can predict toxicity events unidentified by routine preclinical safety testing and also shows the documented changes in many genes not previously shown to be involved in the organophosphate toxicity response.