SLIDE 1 Jeff Scott Guest Lecture Spring 2015
NBB 4910 Principles of Neurobiology
INSECTICIDE NEUROTOXICOLOGY
SLIDE 2 Soderlund, D., 2012 Molecular mechanisms of pyrethroid insecticide neurotoxicity: recent advances. Archives of Toxicology 86: 165–181. Raymond-Delpuch, V., K. Matsuda, B. M. Sattelle, J. J. Rauh & D. B. Sattelle. 2005. Ion channels: molecular targets of neuroactive insecticides. Invert Neurosci 5: 119- 133. Zlotkin, E. 2001. Insecticides Affecting Voltage-Gated Ion Channels In: Biochemical Sites of Insecticide Action and Resistance (I. Ishaaya ed) pp. 43-76. Springer-Verlag Berlin, Heidelberg.E.
- J. R. Bloomquist, 1996. Ion channels as targets for insecticides, Ann. Rev. Entomol.
41: 163-90.
References
SLIDE 3
Pesticides
The USA uses 1.0-1.5 billion pounds of pesticides (herbicides, insecticides, etc.) per year
SLIDE 4 Long, long ago Inorganics Long ago botanicals
Historical Perspective
1880 Commercial production (inorganics) 1941 DDT 1946 Cyclodienes 1947 Organophosphates 1950 Carbamates 1970 Insect Growth regulators 1980 Pyrethroids 1995 Genetic engineering 2000 Neonicotinoids
Effective insect control
#1 #2
SLIDE 5 Long, long ago Inorganics Long ago botanicals
Historical Perspective
1880 Commercial production (inorganics) 1941 DDT 1946 Cyclodienes 1947 Organophosphates 1950 Carbamates 1970 Insect Growth regulators 1980 Pyrethroids 1995 Genetic engineering 2000 Neonicotinoids
Effective insect control
#1 #2
SLIDE 6 Perspective and Predictions
In addition to pest control, neurotoxic insecticides have played key roles in characterization of the nervous system (e.g. DFP characterized serine in active site of AChE) Synthetic insecticides w ill continue to be a major factor for pest control into the foreseeable future.
SLIDE 7 Neurophysiology of insecticides acting on sodium channels
DDT & pyrethroids Usually both provide very useful information
To investigate the mechanism of action of neurotoxins there are two main types of data one can gather: behavior and neurophysiology
SLIDE 8 HISTORY OF DDT
(DichloroDiphenylTrichloroethane)
- Synthesized in 1874 by Ziedler
- Insecticidal activity discovered by Paul Muller of Geigy in 1939.
- Won the Nobel prize in 1948.
- DDT opened the era of synthetic organic insecticides and
"efficient" insect control. Called "miracle insecticide" or "the insecticide that won the w ar" in the mid 1940s.
- Extremely effective against a broad range of insects (LD50
1 - 1000 ug/g to insects).
Cl C CCl3 H Cl
SLIDE 9 HISTORY OF DDT
- Relatively safe to humans (oral LD50 to humans 250
mg/kg, 115 mg/kg to rats, practically non-toxic by dermal exposure).
- Cheap !!!!!!! ~$0.50 per pound.
- DDT has saved millions of lives. Controls vectors of
diseases such as typhus, yellow fever or malaria. Use
- f DDT nearly eradicated malaria from the planet.
Some areas still are malaria free w hile other have resurgence in the number of cases.
- >2,000,000 tons of DDT have been manufactured
(Mellanby 1992)
- 1962 Silent Spring labels DDT the “Elixir of Death”
SLIDE 10
Military use of DDT
SLIDE 11
Civilian use of DDT
SLIDE 12
In vivo poisoning symptoms
SLIDE 13 American Cockroach CNS
Cockroach cercal nerve-giant axon preparation
SLIDE 14
In situ poisoning symptoms
SLIDE 15
Voltage Clamp
SLIDE 16
Voltage Clamp Normal
SLIDE 17
Voltage Clamp TTX
SLIDE 18
Voltage Clamp Normal vs. TTX
SLIDE 19
Voltage Clamp TEA
SLIDE 20
Voltage Clamp Normal vs. TEA
SLIDE 21
Voltage Clamp DDT
SLIDE 22
Voltage Clamp Normal vs. DDT
SLIDE 23
Voltage Clamp DDT + TEA
SLIDE 24
Voltage Clamp DDT alone vs.. DDT + TEA
SLIDE 25
Voltage Clamp DDT + TTX
SLIDE 26
Voltage Clamp TTX alone vs.. DDT + TTX
SLIDE 27
Do the voltage clamp experiments explain the repetitive discharges?
Do repetitive discharges explain the symptoms?
SLIDE 28 Pyrethroids
- Based upon a natural product - pyrethrins
- First pyrethroids w ere synthesized in the
1940s, but they w ere not stable under field conditions.
- Field stable pyrethroids discovered in the
1960s.
- The 2nd largest class of insecticides in
use today
SLIDE 29 Pyrethrins and the first pyrethroids
But then something unusual happened
These insecticides appear to be “super DDT” Symptoms are similar Both cause repetitive discharges Both prolong the opening of the sodium channel Both are more toxic at low er temperatures
Cl C CCl3 H
DDT
Cl O O C O H H
H
Pyrethrin I
? =
VIDEO
SLIDE 30 α-CN pyrethroids (Type II)
Symptoms of poisoning are radically different from DDT or Type I pyrethroids
VIDEO
There are no repetitive discharges
VIDEO
SLIDE 31 Structures
C O N O O O Cl C C CN O O C O O O CN Cl Cl C O O O Cl Cl C O O O CN C O O O O
Type I Type II
tetramethrin fenvalerate cypermethrin permethrin cyphenothrin phenothrin
SLIDE 32
Identify the site of action type II pyrethroids
What w ould you do?
SLIDE 33 Patch clamp data Type I
Yamamoto et al (1983)
SLIDE 34 Patch clamp data Type II
Control 10 μM deltamethrin
Chinn and Narahashi 1986
SLIDE 35 Patch clamp summary
How does this explain the lack of repetitive discharges?
Insecticide Open Time none 1-2 msec DDT 10-20 msec Type I pyrethroid 20-80 msec Type II pyrethroid >80 msec
SLIDE 36
Both DDT and pyrethroids (both Type I and Type II) hold the voltage gated sodium channel in the open state
Differences in symptoms (and potencies) can be explained by differences in kinetics
SLIDE 37
Any questions?
