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Investigations on selected enzyme systems in Caenorhabditis elegans in response to representative insecticides of different classes.

Leelaja, B. C. (2013) Investigations on selected enzyme systems in Caenorhabditis elegans in response to representative insecticides of different classes. PhD thesis, University of Mysore.

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The present work was carried out to investigate (a) the effect of pesticides belonging to different classes on selected enzyme systems in C. elegans with special reference to enzymes of detoxification mechanism (b) the induction of oxidative stress by pesticides belonging to different classes in C. elegans by studying the changes in enzymatic and non-enzymatic oxidative stress parameters (c) the role of altered enzyme systems (detoxification mechanisms) and oxidative imbalance in toxic manifestations of selected pesticides in C. elegans. Our study showed that sublethal concentrations monocrotophos (MCP, an organophosphorus insecticide) induced a concentration related increase in the number of paralyzed worms and decrease in progeny besides inhibiting acetylcholinesterase (AChE) activity significantly in a concentration dependent manner. A good correlation was evident between AChE inhibition and extent of paralysis. MCP also induced marked decrease in glutathione-s-transferase (GST) activity, concentration- dependent decrease in uridine diphospho glucuronyl transferase (UDPGT), and significant decrease in carboxylesterase (CaE) activity. MCP was also found to induced oxidative stress in the worms. C. elegans exposed to various sublethal concentrations of deltamethrin (DEL, a synthetic pyrethroid insecticide), exhibited significant decrease in brood size. DEL induced significant oxidative stress and upregulated the CaE, the major detoxification enzyme. Worms exposed to sublethal concentrations of phosphine (PH3, a fumigant insecticide) exhibited significant decrease in brood size. Eggs exposed to sublethal concentrations of PH3 showed a significant delay in development. PH3 induced developmental delay was associated with up regulation of reduced glutathione (GSH) levels. Depletion of GSH by diethyl maleate further delayed development in worms, suggesting the role of GSH in the developmental toxicity of PH3. Exposure to PH3 resulted in elevation in GST activity and marginal decrease in UDPGT activity besides inducing oxidative stress in the worms. In conclusion, our studies revealed that of the three insecticides – MCP, DEL and PH3 - MCP and PH3 were highly toxic to the worms while DEL did not induce mortality in the worms at the highest tested concentration. However, all the three insecticides elicited adverse biochemical and physiological responses in the worms at sublethal concentrations. The three insecticides at sublethal concentrations also affected the brood size in the worms to varying extent. The impact of phosphine was the most significant and the relative impact on brood size was: PH3 > MCP> DEL. Characteristically, MCP at sublethal concentrations induced paralysis in worms, the extent of which correlated with the degree of AChE inhibition. PH3 induced distinct developmental delay in the worms and GSH was found to play a major role in PH3-induced developmental toxicity. The three insecticides affected the detoxification enzymes in C. elegans differently. While GST activity was significantly up-regulated in worms exposed to PH3 , CaE was up-regulated in worms exposed to DEL. Interestingly, MCP inhibited all the three assayed detoxification enzymes. Oxidative imbalance was induced in worms by sublethal concentrations of all the three insecticides as evident by increased ROS levels. Studies with oxidative stress sensitive and resistant mutants revealed that the OS sensitive mutant (mev-1) was oxidatively stressed to a greater extent on exposure to the three insecticides. Based on the results obtained, C. elegans appears to be an ideal model organism to study insecticide toxicity and resistance mechanisms in insects. C. elegans also seems to be a good model to study mechanistic strategies to ameliorate insecticide toxicity in mammals.

Item Type: Thesis (PhD)
Uncontrolled Keywords: pesticides, enzyme systems, C. elegans
Subjects: 600 Technology > 03 Agriculture > 05 Insect/Pest Control
600 Technology > 08 Food technology > 16 Nutritive value > 05 Enzymes
Divisions: Food Protectants and Infestation Control
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 19 Mar 2015 10:29
Last Modified: 19 Mar 2015 10:29
URI: http://ir.cftri.com/id/eprint/11758

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