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mechanisms > Neurotoxic Insecticides > Flashcards

Neurotoxic Insecticides Flashcards

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
Q

What is the general structure of organophosphates?

A

O=P(OR)3

a central phosphate molecule with alkyl or aromatic substituents

26
Q

Acetylcholinesterase

A

enzyme located in synaptic space that rapidly breaks down acetylcholine

27
Q

Where do organochloride pesticides bind?

A

sodium ion channels

28
Q

What are acetylcholine’s active sites?

A

anionic site and esteratic site

29
Q

anionic site

A

electrostatic interaction with quaternary nitrogen in choline

30
Q

esteratic site

A

serine residue that covalently binds to the ester carbonyl group

31
Q

acetylcholine-acetylcholine esterase complex

A

forms an unstable tetrahedral intermediate which rapidly decomposes, liberating choline and leaving the enzyme covalently bound to esteric site

32
Q

How is acetate removed from acetylcholinesterase?

A

water spontaneously hydrolyzes the bond in the esteric site, regenerating the free enzyme

33
Q

How do organophosphates block acetylcholinesterase?

A

interact with the serine hydroxyl residue in the esteratic site to block enzyme regeneration

34
Q

Organophosphate aging

A

chemical stabilization of phosphate bond to AChE occurs over time
R group leaves via hydrolysis strengthing the serine-phosphate bond

35
Q

Two fates of OP-adducts

A
  1. spontaneously hydrolyze and restore enzyme activity

2. Irreversible process known as “aging”

36
Q

How long until OPs are fully aged?

A

24-48 hours

37
Q

What is used to treat OP poisoning?

A

pralidoxime (2-PAM)

prevents aging by bonding to organophosphate group

38
Q

Feature of carbamates

A

carbamate-ester functional group

commonly used for agriculture, residential lawn, and garden applications

39
Q

What do carbamates inhibit?

A

AChE

40
Q

How do carbamates differ from OPs?

A

They don’t age

41
Q

A draw back of carbamates?

A

tend to hydrolyze easily, resulting in low level persistence in soil and water

42
Q

How long does it take AChE to be recovered after carbamate exposure?

A

24-48 hour window

43
Q

How do insects develop resistance to insecticides?

A
  1. behavioral – avoid lethal dose

2. physiological

44
Q

3 examples of physiological resistance (insects)

A
  1. reduced penetration
  2. target site insensitivity
  3. enhanced detoxification
45
Q

What human neurological disease is associated with organochlorides?

A

Parkinson’s

46
Q

What human neurological disease is associated with organophosphates and carbamates?

A

Parkinson’s
organophosphate-induced delayed neuropathy (OPIDN)
chronic organophosphate-induced neuropsychiatric disorder (COPIND)

47
Q

What are some major challenges to chronic exposure?

A
  1. untangling acute vs. chronic
  2. multiple compound exposures
  3. many different endpoints beyond neuropathy
48
Q

neurodegenerative disorders are considered an interaction between:

A

environmental factors and genetic predisposition

49
Q

Motor manifestations of Parkinson’s disease are attributed to what?

A

progressive loss of dopaminergic neurons in substantia nigra pars compacta (SNpc)

50
Q

The misfolding of what protein is linked to Parkinson’s disease?

A

alpha-synuclein

51
Q

Misfolding of alpha-synuclein leads to what?

A

Lewy bodies

52
Q

Pesticides may play a role in parkinson’s by the production of what?

A

ROS

53
Q

What neuron type are associated with Parkinson’s?

A

dopaminergic

54
Q

ROS in dopaminergic neurons

A

oxidative metabolism of dopamine in the substantia nigra

55
Q

ROS in resident macrophages

A

redox cycling initiates inflammatory cytokine production (NADPH oxidase)

56
Q

Acute cholinergic syndrome

A

organophosphates
due to the inhibition of AChE activity
subsides within days
blood AChE activity used to monitor exposure

57
Q

intermediate syndrome

A

organophosphates
usually starts 24-96 hours after the acute syndrome
respiratory paresis, weakness, depressed tendon reflexes without response to treatment

58
Q

Organophosphate-induced delayed neuropathy (OPIDN)

A

weeks following an acute exposure
symmetric distal neuropathy
inhibition of the enzyme neuropathy-target esterase(NTE)

59
Q

Example of OPIDN epidemic?

A

Ginger Jake from 1930s

product found to be contaminated with TOCP

60
Q

Chronic Organophosphate induced neuropsychiatric disorder (COPIND)

A

mechanisms unclear but are not related to enzyme inhibition.
pesticide applicators
prolonged exposure to OPs

mechanisms (5 decks)

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