Transcript Hemlock toxin - UNM Biology Department Home Page

Hemlock Toxin
Gregory N. Ortiz
Biology 445
May 4, 2007
Topics
• Hemlock – The Plant
– Description
– Location
– Chemical Composition
• Biochemical Properties of Toxin
– Nicotinic-Acetylcholine Channel
– Effects of Toxin
• Medicinal Properties
– Can it be used as a treatment?
• Hemlock in History
– Fate of Socrates
Drawing courtesy of USDA (http://plants.usda.gov/java/profile?symbol=COMA2)
Hemlock – The Plant
Photos courtesy of USDA (http://plants.usda.gov/java/profile?symbol=COMA2)
Description of Hemlock
• By far the most familiar species is Conium maculatum - the
most common of several species of hemlock characterized by
their toxicity.
• It is a herbaceous biennial plant which grows between 1.5-2.5 m
tall, with a smooth green stem, usually spotted or streaked with
red or purple on the lower half of the stem.
• The leaves are finely divided and lacy, overall triangular in shape,
up to 50 cm long and 40 cm broad. The flowers are small, white,
clustered in umbels up to 10-15 cm across.
• The plant is often mistaken for fennel, parsley or wild carrot
although the characteristic stem hairs of the wild carrots are
missing. The Conium root is fleshy, white and often unbranched
and can be mistaken for parsnip.
Poison Hemlock Classified
Kingdom
Plantae (Plants)
Subkingdom
Tracheobionta (Vascular plants)
Superdivision
Spermatophyta (Seed plants)
Division
Magnoliophyta (Flowering plants)
Class
Magnoliopsida (Dicotyledons)
Subclass
Rosidae
Order
Apiales
Family
Apiaceae (Carrot family)
Genus
Conium L. (poison hemlock)
Species
Conium maculatum L.
(poison hemlock)
More Hemlock Info.
• A useful trick to determine whether a plant is poison
hemlock rather than fennel (which it resembles) is to crush
some leaves and smell the result. Fennel smells like
liquorice, but poison hemlock smells “mouse-like” or
musty. Discard it if you can’t tell the difference.
• Poison hemlock flourishes in the spring, when most other
forage is gone. All parts of the plant are poisonous but
once the plant is dried the poison is greatly reduced (but
not gone completely).
• Hemlock goes by other names such as: "poison parsley" or
"spotted parsley".
Distribution of Hemlock in U.S.
Conium maculatum has been introduced and naturalized in many other areas,
including much of Asia, N. America and Australia. Poison hemlock is often found
on poorly drained soils, particularly near streams, ditches, and other surface water.
Map courtesy of USDA (http://plants.usda.gov/java/profile?symbol=COMA2)
Chemical Composition
• Hemlock contains the following alkaloids:
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–
–
–
–
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Coniine
N-methylconiine
Conhydrine
Pseudoconhydrine
g-coniceïne
Atropine
The most important and toxic of these is Coniine. Coniine is a
neurotoxin, which disrupts the workings of the central
nervous system (CNS).
Picture courtesy of Wikipedia
Biochemical Properties
• There are two main classes of acetylcholine receptor (AChR),
nicotinic acetylcholine receptors (nAChR) and muscarinic
acetylcholine receptors (mAChR). They are named for the
ligands used to discover the receptors.
• Nicotinic AChRs are ionotropic receptors permeable to sodium,
potassium, and chloride ions. They are stimulated by nicotine
(low concentrations) and acetylcholine and blocked by nicotine
(high concentrations) and hemlock toxin.
• Nicotinic acetylcholine receptors are present in many tissues in
the body. The neuronal receptors are found in the central
nervous system and the peripheral nervous system. The
neuromuscular receptors are found in the neuromuscular
junctions of somatic muscles; stimulation of these receptors
causes muscular contraction.
Acetylcholine and its Receptor
Acetylcholine Receptor (nAChR)
Acetylcholine (Ach)
Pictures courtesy of Wikipedia
Effect of Toxin
• Hemlock toxin funtions
by binding to the postsynaptic cell receptor of
the of the target cell (#4)
• This results in decreased
transmitter (#3) biding,
which causes CNS and
muscle cell inhibition and
eventual cessation of cell
signaling (boxes with X’s)
Diagram courtesy of Wikipedia
Toxin bound to Receptor
Picture courtesy of Wikipedia
Effects of Toxin
• In poisonous/lethal doses:
– it produces complete paralysis including loss of
speech
– respiration initially becomes depressed
– respiration eventually ceases completely
– death results from asphyxia
– brain and the rational faculties remain
unaffected and alert up to the time of death
Medicinal Properties
• Treatment wasn't always effective as the difference between a
therapeutic and a toxic amount is very slight.
• Poison hemlock has been used as a sedative and for its
antispasmodic properties.
• Also used by Greek and Persian physicians for a variety of
problems, such as arthritis.
• As an inhalant it is said to relieve cough in bronchitis, whoopingcough, asthma, etc.
• Hemlock juice (Succus conii) has been prescribed as a remedy in
cases of undue nervous motor excitability, such as:
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–
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teething in children
epilepsy
spasms of the larynx and gullet
in acute mania
Hemlock in History
In ancient Greece, hemlock was used to poison condemned
prisoners, with the most famous victim being the philosopher
Socrates. After being condemned to death for impiety in 399
BC, Socrates was given a strong solution of the hemlock plant.
Plato described Socrates' death in the “Phaedo”:
"The man … laid his hands on him and after a while examined his feet and legs,
then pinched his foot hard and asked if he felt it. He said ‘No’; then after
that, his thighs; and passing upwards in this way he showed us that he was
growing cold and rigid. And then again he touched him and said that when it
reached his heart, he would be gone. The chill had now reached the region
about the groin, and uncovering his face, which had been covered, he said –
and these were his last words – 'Crito, we owe a cock to Asclepius. Pay it and
do not neglect it.' 'That,' said Crito, 'shall be done; but see if you have
anything else to say.' To this question he made no reply, but after a little while
he moved; the attendant uncovered him; his eyes were fixed. And Crito when
he saw it, closed his mouth and eyes."
Socrates
Death of Socrates
Photos courtesy of Wikipedia
Bust of Socrates
References
• Assorted authors. 2003. State noxious weed lists for 46 states. State agriculture
or natural resource departments.
• Haragan, P.D. 1991. Weeds of Kentucky and adjacent states: a field guide. The
University Press of Kentucky. Lexington, Kentucky. 278pp.
• Plato, Phaedo 117e-118a, trans. Loeb Classical Library, Harvard University
Press, Cambridge, Mass., 1990 edition, pp. 401-3.
• Southeast Exotic Pest Plant Council. 1996. Invasive exotic pest plants in
Tennessee (19 October 1999). Research Committee of the Tennessee Exotic
Pest Plant Council. Tennessee.
• United States Department of Agriculture (USDA) - Plants database.
http://plants.usda.gov/java/profile?symbol=COMA2.
• Uva, R.H., J.C. Neal, & J.M. DiTomaso. 1997. Weeds of the Northeast.
Cornell University Press. Ithaca, New York. 397pp.
• Whitson, T.D. (ed.) et al. 1996. Weeds of the West. Western Society of Weed
Science in cooperation with Cooperative Extension Services, University of
Wyoming. Laramie, Wyoming. 630pp.
• Wikipedia. http://en.wikipedia.org/wiki/Main_Page.