Toxicity Equialcr Evaluation Fo Moncrophos In Caenrohaditis Elgans

Lethality is one of the most important endpoints for evaluating the toxicities of xenobiotic compounds on the organisms. However, the actual environmental concentrations of xenobiotic compounds are generally too low to lead to death of the organisms. More and more studies have shown that xenobiotic compounds at sublethal doses could induce a variety of toxicities on the organisms. Typically, these multiple toxicities simultaneously exist, and each of them has a different toxic equivalence from others. There are both correlation and difference between these toxicities from which the harm are different. One prime question in toxic evaluation of xenobiotic compounds is how to determine the major toxicity and select the biomarker responding to the major toxicity of xenobiotic compounds fast. And determining the major toxicity would provide scientific basis for biological testing of an unknown xenobiotic compounds.Monocrotophos （MCP） is a broad spectrum systemic organophosphorus pesticide （OPs）, of which the main toxic mechanism is the inhibition of acetylcholinesterase （AChE）, influencing normal metabolism of acetylcholine （ACh） and resulting in neurotoxicity. Moreover, MCP showed cytotoxicity, genotoxic, reproductive toxicity, developmental toxicity and estrogenic property. It was focused on by us that what was the correlation between these above toxicities of MCP and which effect was the most harmful action to the organism. In order to solve these questions, using the nematode Caenorhabditis elegans as the animal model, we investigated multiple toxicities of MCP, evaluated the toxicity equivalence by correlation analysis and principal component analysis, and determined the correlation between these multiple toxicities of MCP, as well as the major toxicity among them.This paper investigated the developmental and reproductive toxicity, using body length and eggs per nematode as endpoints respectively, the neurotoxicity using acetylcholinesterase （AChE） activity and behaviors as endpoints, and the cytotoxicity, reproductive toxicity, developmental toxicity and estrogenic effects were evaluated by the expression of stress-related gene. Then we evaluated the equivalence of these above toxicity of MCP by correlation analysis and principal component analysis.The results indicated that:（1） After 24 h exposure to 0.5, 5.0 and 50.0 mg·L^-1 MCP, it could be seen that MCP inhibited body length, eggs per nematode and AChE activity significantly in a dose-dependent manner, which showed MCP had reproductive toxicity, developmental toxicity and neurotoxicity.（2） After 24 h exposure to 0.5, 5.0 and 50.0 mg·L^-1 MCP, it could be seen that treatment with MCP caused a highly significant decrease in both head thrashes and body bends of C. elegans （P < 0.01）. The exposure to MCP caused a decrease in forward turns of which inhibitory effect was significant for 0.5 mg·L^-1 MCP （0.01 < P < 0.05） and highly significant for 5.0 and 50.0 mg·L^-1 MCP （P < 0.01）. Treatment with 5.0 or 50.0 mg·L^-1 MCP caused a highly significant decrease in chemotaxis towards NaCl （P < 0.01）. Compared to the control of the observation points （2, 4, 6, 8, 24 h）, the attainment levels of C. elegans exposed to 50.0 mg·L^-1 MCP were significantly decreased （0.01 < P < 0.05） at 2, 4, 6, and 8 h and highly significantly （P < 0.01） at 24 h. Above results showed that MCP caused severe defects of locomotion, learning and foraging behaviors in C. elegans, which showed that MCP had neurotoxicity.（3） Several stress-related genes mRNA expression levels were examined by real-time PCR in C. elegans following a 24 h exposure to 0.5, 5.0 and 50.0 mg·L^-1 MCP. Treatment with MCP resulted in increased hsp^-16.41, hsp-70, cyp-35a2, vit-2, vit-6 and age^-1 mRNA expression, while it caused a decrease in cep^-1, ape^-1, sod^-1, sod-3, ctl-2, ctl-3, gst^-1, daf^-12 and daf-21 mRNA expression. There was no significant change in hsp^-16.2, mtl^-1 and mtl-2 mRNA expression after exposure to MCP. Above results showed that MCP had environmental estrogenic effects, cytotoxicity, developmental toxicity and neurotoxicity.（4） Correlation analysis indicated that there was significant correlation between endpoints of 192 pairs. This showed MCP could induce multiple correlated toxicities. Principal component analysis indicated that load of body bends or chemotaxis towards NaCl was higher than others in the first principal component, load of expression of ctl-3 or vit-6 was higher than others in the second principal component, and load of expression of vit-2 or age^-1 was higher than others in the third principal component. Results suggested that neurotoxicity was the most major toxicity of MCP, followed by the environmental estrogenic effects. This is in accordance with the major toxicity of MCP reported in previous studies, thus proved the validity of our method.Consequently, we identified that correlation analysis and principal component analysis could be used for the determining the major toxicity of MCP by evaluating the equivalence of multiple toxicities. We suggested a selection procedure should be set up to determine the major toxicities, which will provide scientific basis for both fast selection of sensitive biomarkers and biological test of xenobiotic compounds.