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Neurotoxic Insecticides Flashcards

(60 cards)

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1
Q

Examples of natural pesticides used prior to 1940s?

A

inorganic metals and sulfur based products

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2
Q

mechanism of natural insecticides?

A

inhibited respiration via ATP

impaired heme synthesis

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3
Q

when were organochlorides first deployed?

A

during WW2 to combat typhus, malaria and dengue fever

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4
Q

Organochloride desired properties

A

persistent stimulation of the CNS

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5
Q

organochloride example

A

DDT

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6
Q

organophosphate example

A

Parathion and Malathion

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7
Q

organophosphate desired properties

A

irreversible/reversible stimulation of the CNS

degrade rapidly

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8
Q

Why were carbamates developed?

A

Wanted an insecticide with neuronal activity but with greater specificity and lower mammalian toxicity than organophosphates

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9
Q

carbamate properties

A

effects on neural system are reversible

degrade rapidly

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10
Q

Why is there a reduction in the use of insecticides?

A

Rise in GMOs and increased resistance

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11
Q

What is the half-life of DDT?

A

2-15 years

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12
Q

structure of organochlorides

A

chlorine substituted aliphatic or aromatic rings

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13
Q

What 2 properties make organochlorides so dangerous to the natural environment?

A

bio-accumulation and bio-magnification

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14
Q

How does DDT cause over-stimulation?

A

Keeps voltage gated sodium ion channels open causing them to fire spontaneously, leading to spasms and eventual death
highly processed alpha subunits associated with auxiliary beta subunits
prevents neuronal re-polarization
acts on pre-synaptic cell

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15
Q

Where do organochlorides bind?

A

open sodium channels

stabilize the open state and cause prolonged currents

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16
Q

sodium channel – resting state

A

polarized

electrical charge on the outside of the membrane is positive and contains excess sodium ions

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17
Q

sodium channel – action potential

A

sodium ions move inside the membrane

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18
Q

sodium channel – depolarized

A

threshold reached when chain of channel open sequentially

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19
Q

sodum channel sequence

A

resting potential > threshold > depolarization > repolarization > hyperpolarization

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20
Q

How does dieldrin work?

A

Causes overstimulation like DDT, but through GABA receptors

acts on post-synaptic cell

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21
Q

GABA receptor

A

ion-gated chlorine channel composed of 5 subunits

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22
Q

Role of GABA (neurotransmitter)

A

inhibit the activity of neurons

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23
Q

Action with GABA binding

A

channels open to Cl, this leads to hyperpolarization and inhibits the firing of new action potentials

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24
Q

Action of dieldrin

A

binds to the GABA receptor, blocking the GABA induced uptake of Cl ions and inhibiting hyperpolarization

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25
What is the general structure of organophosphates?
O=P(OR)3 | a central phosphate molecule with alkyl or aromatic substituents
26
Acetylcholinesterase
enzyme located in synaptic space that rapidly breaks down acetylcholine
27
Where do organochloride pesticides bind?
sodium ion channels
28
What are acetylcholine's active sites?
anionic site and esteratic site
29
anionic site
electrostatic interaction with quaternary nitrogen in choline
30
esteratic site
serine residue that covalently binds to the ester carbonyl group
31
acetylcholine-acetylcholine esterase complex
forms an unstable tetrahedral intermediate which rapidly decomposes, liberating choline and leaving the enzyme covalently bound to esteric site
32
How is acetate removed from acetylcholinesterase?
water spontaneously hydrolyzes the bond in the esteric site, regenerating the free enzyme
33
How do organophosphates block acetylcholinesterase?
interact with the serine hydroxyl residue in the esteratic site to block enzyme regeneration
34
Organophosphate aging
chemical stabilization of phosphate bond to AChE occurs over time R group leaves via hydrolysis strengthing the serine-phosphate bond
35
Two fates of OP-adducts
1. spontaneously hydrolyze and restore enzyme activity | 2. Irreversible process known as "aging"
36
How long until OPs are fully aged?
24-48 hours
37
What is used to treat OP poisoning?
pralidoxime (2-PAM) | prevents aging by bonding to organophosphate group
38
Feature of carbamates
carbamate-ester functional group | commonly used for agriculture, residential lawn, and garden applications
39
What do carbamates inhibit?
AChE
40
How do carbamates differ from OPs?
They don't age
41
A draw back of carbamates?
tend to hydrolyze easily, resulting in low level persistence in soil and water
42
How long does it take AChE to be recovered after carbamate exposure?
24-48 hour window
43
How do insects develop resistance to insecticides?
1. behavioral -- avoid lethal dose | 2. physiological
44
3 examples of physiological resistance (insects)
1. reduced penetration 2. target site insensitivity 3. enhanced detoxification
45
What human neurological disease is associated with organochlorides?
Parkinson's
46
What human neurological disease is associated with organophosphates and carbamates?
Parkinson's organophosphate-induced delayed neuropathy (OPIDN) chronic organophosphate-induced neuropsychiatric disorder (COPIND)
47
What are some major challenges to chronic exposure?
1. untangling acute vs. chronic 2. multiple compound exposures 3. many different endpoints beyond neuropathy
48
neurodegenerative disorders are considered an interaction between:
environmental factors and genetic predisposition
49
Motor manifestations of Parkinson's disease are attributed to what?
progressive loss of dopaminergic neurons in substantia nigra pars compacta (SNpc)
50
The misfolding of what protein is linked to Parkinson's disease?
alpha-synuclein
51
Misfolding of alpha-synuclein leads to what?
Lewy bodies
52
Pesticides may play a role in parkinson's by the production of what?
ROS
53
What neuron type are associated with Parkinson's?
dopaminergic
54
ROS in dopaminergic neurons
oxidative metabolism of dopamine in the substantia nigra
55
ROS in resident macrophages
redox cycling initiates inflammatory cytokine production (NADPH oxidase)
56
Acute cholinergic syndrome
organophosphates due to the inhibition of AChE activity subsides within days blood AChE activity used to monitor exposure
57
intermediate syndrome
organophosphates usually starts 24-96 hours after the acute syndrome respiratory paresis, weakness, depressed tendon reflexes without response to treatment
58
Organophosphate-induced delayed neuropathy (OPIDN)
weeks following an acute exposure symmetric distal neuropathy inhibition of the enzyme neuropathy-target esterase(NTE)
59
Example of OPIDN epidemic?
Ginger Jake from 1930s | product found to be contaminated with TOCP
60
Chronic Organophosphate induced neuropsychiatric disorder (COPIND)
mechanisms unclear but are not related to enzyme inhibition. pesticide applicators prolonged exposure to OPs

mechanisms (5 decks)

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