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BTX
(Batrachotoxin)
Jenny Johnston, Mat Ley, Michael
Miller, Tony Nguyen
Outline
What is Batrachotoxin?
History
Sources of BTX
Uses of Batrachotoxin
Absorption of BTX
BTX Effects
Action Potentials
Synthesis and Mechanism
BTX Treatments
BTX and other Toxins
Evolution
Mimicry and Batrachotoxins
Exogenous vs. Endogenous Acquisition
A bird with batrachotoxins?
Watch the video below to
learn how the Pitohui bird’s
toxic feathers were
discovered by Dr. Jack
Dumbacher. (California
Academy of Sciences)
CLICK HERE!
http://www.greenexpander.com/wp-content/uploads/2007/11/pitohui.jpg
Hooded Pitohui (Pitohui dichrous)
What is Batrachotoxin?
• BTX is a class of
extremely toxic steroidal
alkaloids
• Lipid solubility greatly
increases the toxicity of
BTX
• BTX has an LD50 of
approximately 2 µg/kg (in
mice)
• BTXs are found across a
wide range of organisms
• BTX is a neurotoxin
• Irreversible activator
of Na+ channels
• Affects both nerve
and muscle cells
• Stabilizes the open
conformation of
voltage gated ion
channels
History of Batrachotoxin
• BTX was first
isolated from frogs
• “batrachos” = frog
(Greek)
• BTX is found in
several species of
frogs from the genus
Phyllobates and
Dendrobates
• Phyllobates bicolor
(seen right)
History of Batrachotoxin
• Indigenous people
from parts of South
and Central America
used the toxic frogs
to make poisonous
blow darts
• Much like the toxin
curare which also a
neurotoxin
Batrachotoxin in New Guinea
• BTX is also found in
passerine birds of
New Guinea
• 6 species of birds
mostly from the
genus Pitohui
express BTX
• Birds express BTX
mostly in the skin
and feathers
Batrachotoxin in New Guinea
• Indigenous people in
New Guinea do not
hunt/eat the birds
• Simply handling the
birds causes respiratory
irritation
• The meat is reportedly
bitter tasting and
nauseating
Source of Batrachotoxin
Phyllobates lugubris
• Neither frogs nor birds are believed to be able
to synthesize BTX de novo
• The source of BTX is most likely dietary
• Frogs raised in captivity do not produce BTX
• Birds show varying levels of BTX congruent with
dietary variation
Uses of Batrachotoxin
• BTX has been used to experimentally
probe and characterize Na+ channels
• Research has revealed that some
mutations (point mutations and deletions)
can reduce or increase susceptibility to
BTX
Absorption
• The common pathways
for absorption are:
•
•
•
•
Ingestion
Inhalation
Tissue Contact
Skin Contact
http://www.canaryzoo.com/Spectacular%20Animals/hooded%20pitohui%2002.jpg
http://www.aquariumofpacific.org/images/olc/golden_dart_frog600ar.jpg
Absorption by Inhalation
• Its been reported by the indigenous
people of New Guinea that handling the
Pitohui birds will cause respiratory
irritation because the skin particles and
feathers of these birds contain BTX.
Absorption by Ingestion
• Of these absorption pathways, ingestion
is the most common and is most
represented when predators of poison
dart frogs succumb to the toxic effects
of BTX when attempting to prey upon
these frogs. The same can be said of
the Pitohui birds and natives noted
these birds as non-consumable.
Absorption by Tissue Contact
• Indigenous people of Central and
South America often coat their hunting
darts with toxins obtained from poison
dart frogs and use them to hunt. The
darts will puncture the skin of the animal
and thereby distributing the toxin within
the animal by exposing muscle tissue to
this toxin.
Absorption by Skin Contact
• Because tissue contact with BTX
causes numbness any contact with BTX
by skin in small amounts can result in
numbness of the skin as well is the
senses within the area affected by BTX.
BTX Effects
• BTX’s bind with high affinity to voltage gated
sodium channels in nerve and muscle
membranes, locking them in an open state.(1)
• Highly toxic to cardiac muscle tissue.
• (BTX) toxin causes muscle and nerve depolarization,
fibrillation, arrhythmias, and heart failure(2)
• Binding is irreversible, suggesting a chemical change in
the Na+ channel that locks it open.
• Since binding only occurs in open sodium channels, “it has
been hypothesized that batrachotoxin binds within the pore of
the channel.”(3)
• This binding causes disruption of action potentials
across the membrane.
Action Potential Overview
• An action potential is a rapid,
temporary change in
electrical potential across a
membrane, from negative to
positive back to negative.(4)
• Created by an unequal
distribution of ions.
• Depolarization
• caused by voltage gated Na+
channels opening and an
influx of Na+ . (event 1)
• Causes an action in the
cell(such as muscle
contraction, or nerve impulse)
• During depolarization, K+
channels open and k+ exits
the cell. (event 2)
Figure 1 (5)
Action Potential Overview
(Cont.)
• Repolarization
• Begins with closing of
voltage gated Na+
channels.(event 3)
• The now open K+
channels allow for efflux of
K+ ions(event 4).
• As the charge nears the
resting potential, K+
channels close(event 5)
and the cell returns to its
resting potential.
• Excess K+ diffuses
away(event 5)
• All events occur in a very
short time(<1 millisecond)
Figure 1 (5)
BTX Effects (Cont.)
• The permanent
opening of the
Na+ channels
would cause
permanent
depolarization of
the cell. Figure 2
to figure 3.
• This would lead to
paralysis, and
abnormal heart
function.
• Figure 4 shows
the effect of BTX
on Na+ channels.
BTX and Other Toxins
• BTX is similar to other
neurotoxins in function. One
example is tetrodotoxin.
• Both affect voltage gated
sodium channels. Causing
paralysis among other
effects.
• BTX however is more toxic
than many other toxins.
• The ld50 in mice is 2
micrograms/kg. Convulsions
and death after 8 min at 10
micrograms/kg.(6) This
means that an amount
equivalent to a grain of salt
could kill an average human.
Tetrodotoxin
Batrachotoxin
Synthesis (7)
• A complete synthesis of a
Batrachotoxinin A was
discovered in 1998.
• The synthesis of
Batrachotoninin A is
considered a synthesis of
Batrachotoxin because it is
readily converted into
Batrachotoxin.
• Link to complete synthesis
• www.unc.edu/depts/mtcgrou
p/litmeetings/batrachotoxini
n.pdf
H
Batrachotoxinin A
Batrachotoxin
Synthesis Summary
Ketone
Synthesis
Note: Stereo-selectivity of
product varies.
Synthesis of Diels-Alder
Precursor
Synthesis Summary (Cont.)
Synthesis of
Methyl Ketal
Final Steps
BTX Treatment Options
• There is currently no safe and effective treatment for
batrachotoxin. But tetrodotoxin seems to be the most
likely candidate for treatment.
• Tetrodotoxin targets the same voltage-gated
sodium channels, but instead of permanently
opening them and creating a huge influx of ions, it
shuts them off and prevents the movement of ions.\
• Although it is not an ideal antitoxin it serves to slow
down the effects of BTX and more research is
being done to understand neurotoxins and their
effects before any type of treatment can be
approved.
Evolution of Batrachotoxins
•
•
•
Both the Poison Dart Frogs and Pitohiu birds have acquired there toxicity from
outside sources. These organisms obtain the toxins fully synthezised in their
diet. Once ingested, batrachotoxin is secreted by glands on the skin.
• This is called the “Diet-Toxicity” Hypothesis
• Specic species of ants and beetles producebatrachotoxins that ultimately
end up on the frogs skin. (Darst, 2005)
Poison Dart Frog (family Dendrobatidae) use coloration a warning of their
toxicity. The frog’s coloring and use of batrachotoxin are believed to have to
coevolved.
Toxicity is an anti-predator defense. Predators learn to avoid prey of certain
colors to minimize the chances of eating toxic prey. (Summers, 2001)
A Pitohui bird next to a
Choresine pulchra. This
beetle is believed to be
responsible for the bird’s
acquisition of
batrachotoxins.
http://www.calacademy.org/blogs/jdumbacher/?m
=200901
Blue Poison Dart Frog (Dendrobates azureus)
http://animaldiversity.ummz.umich.edu/site/resources/lazette_gifford/117bluepoisondartfrog.jpg/view_large.html
Mimicry and Batrachotoxins
•
Pitohui birds of New Guinea contain
batrachotoxins in their feathers.
Highest concentrations of the toxins
are found in feathers on the
stomach, legs and breast of the bird.
(Dumbacher, 2000)
•
The Pitohui birds and poison dart
frogs display Mullerian mimicry. The
animals send an honest signal to
predators to make them aware they
are not edible. Other animals that
are palatable mimic the coloration of
the Pitohui birds or poison dart frogs
in order to avoid predation (called
Can you identify the harmless species
Batesian mimicry).
from the picture above?
We recommend a taste test to figure
this one out. :)
http://www.biosci.utexas.edu/graduate/eeb/spot1.aspx
Homobatrachotoxins as a Lice Repellant
•
•
•
Dr. John Dumbacher of the California Academy of Sciences
found that lice preferred feathers of birds without
homobatrachotoxins.
Lice living on feathers containing the toxin also had a reduced
life span.
This suggests that the evolution of the toxin on the Pitohui’s
feathers may protect the bird from lice infestation. Selective
pressures for birds without lice may have attributed to the
evolution of the toxin. (Dumbacher, 1999)
Vs.
http://waynesword.palomar.edu/images/lice2.jpg
http://www.swarthmore.edu/NatSci/cpurrin1/bio97/images/pitohui.jpg
¿Una Pregunta?
• Why is batrachotoxin presence in
poison dart frogs and Pitohui birds
unique?
¿Una Pregunta?
• Why is batrachotoxin presence in
poison dart frogs and Pitohui birds
unique?
There is no de novo synthesis of batrachotoxin
within the organism. Many amphibians utilize
toxins, but very few acquire the toxin
exogenously. Most amphibians acquire
monomers from their diet and synthesize the
toxin within their body (endogenous acquisition).
Toxins Comparison
Name
Toxic
Compound
Defense
Exogenous or
Endogenous
Warning
Coloration?
Dendrobatids,
Phyllobates (Poison
Dart Frogs), and
Pitohui Birds
Batrachotoxins
(a neurotoxin)
Secreted by
glands on the
skin. Prevents
closing of sodium
channels in nerve
cells
Exogenous
Yes - Bright
body
coloration
Rough-Skinned Newt
(Taricha granulosa)
Tetrodotoxin (a
neurotoxin)
When ingested,
results in
manipulation of
sodium channels
Believed to be
Endogenous
Yes - Bright
coloration on
belly
Marine Toad
(Bufo marinus)
Bufotoxin
(a cardiotoxin)
Secreted by
glands on skin.
Manipulation of
SodiumPotassium
Channels in
myocardial cells
Endogenous
No
Works Cited
Daly, John W., Myers, Charles W. and Borys Malkin. “A Dangerously Toxic New Frog (Phyllobates) used by Embera Indians of Western
Colombia with Discussion of Blowgun Fabrication and Dart Poisoning.” Bulletin of the American Museum of Natural History.
161.2 (1978): 311-363).
Darst, Catherine, Pablo Menendez-Guerrero, Luis Coloma, and David Cannatella. "Evolution of Dietary Specialization and Chemical
Defense in Poison Frogs (Dendrobatidae): A Comparative Analysis." The American Naturalist 165.1 (2005): 56-69.
"Dr. Jack Dumbacher: California Academy of Sciences." California Academy of Sciences - San
Francisco Museum and Planetarium - Bay Area Natural History Museum. Web. 17 Mar. 2010.
<http://www.calacademy.org/science/heroes/jdumbacher/>.
Duellman, William, and Linda Trueb. Baltimore: John Hopkins UP, 1986.
Dumbacher, J. P., T. F. Spande, and J. W. Daly. "Batrachotoxin Alkaloids from Passerine Birds:
A Second Toxic Bird Genus (Ifrita Kowaldi) from New Guinea." Proceedings of the National
Academy of Sciences of the United States of America 97.24 (2000): 12970-2975.
Dumbacher, John P. "Evolution of Toxicity in Pitohuis: I. Effects of Homobatrachotoxin on
Chewing Lice (Order Phthiraptera)." The Auk 116.4 (1999): 957-63.
Hanifin, Charles, Edmund III Brodie, and Edmund Jr. Brodie. "Tetrodotoxin Levels of the Rough-skin Newt, Taricha Granulosa, Increase
in Long-term Captivity." Toxicon 40 (2002): 1149-153
Hilgris, R. 2001. "Bufo marinus" (On-line), Animal Diversity Web. Accessed April 17, 2010 at
http://animaldiversity.ummz.umich.edu/site/accounts/information/Bufo_marinus.html.
Lorenz, A. and J. Harding. 2008. "Taricha granulosa" (On-line), Animal Diversity Web. Accessed April 17, 2010 at
http://animaldiversity.ummz.umich.edu/site/accounts/information/Taricha_granulosa.html.
Summers, Kyle, and Mark Clough. "The Evolution of Coloration and Toxicity in the Poison Frog Family (Dendrobatidae)." Proceedings
of the National Academy of Sciences of the United States of America 98.11 (2001): 6227-232.
1.
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Albuquerque, E. X., et. all. (1971) science 172, 995-1002.
Bosmans, F. et. all. The poison Dart frog's batrachotoxin modulates Nav1.8. FEBS Lett. (2004), 577, 245-248.
Hadid, D. et. all. The Batrachotoxin Receptor on the Voltage-Gated Sodium Channel is Guarded by the Channel Activation
Gate. Mol. Pharmacol. (2002), 61, 905-912.
Freeman, Scott. Biological Science. (2005), 2nd edition, G1. Pearson Education, London.
http://www.psych.uiuc.edu/~etaylor4/neuralnets.html
http://www.batrachotoxin.com/
www.unc.edu/depts/mtcgroup/litmeetings/batrachotoxinin.pdf