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

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Relation http://ir.cftri.com/11758/
 
Title Investigations on selected
enzyme systems in Caenorhabditis elegans in response to representative
insecticides of different classes.
 
Creator Leelaja, B. C.
 
Subject 05 Insect/Pest Control
05 Enzymes
 
Description 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.
 
Contributor Rajini, P. S.
 
Date 2013
 
Type Thesis
NonPeerReviewed
 
Format application/pdf
 
Language en
 
Rights —
 
Identifier http://ir.cftri.com/11758/1/Leelaja%20BC-Biochemistry%20%28Aug-2013%29.pdf
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.