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BOT 380 > Plant Toxins > Flashcards

Plant Toxins Flashcards

1
Q

Define Toxin

A

poisonous substance produced by cells or living organisms

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2
Q

‘Toxin’ origin

A
  • from the greek ‘toxikon’
  • meaning ‘poison for use on arrows’
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3
Q

Dosage of Toxins

A
  • is often the critical difference between medical or recreational effect vs. toxic effect
  • effect can range from an adverse physiological reaction to death
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4
Q

History of Poisons

A
  • Assyrians wrote of plant poisons over 3000 years ago
  • greeks attribute discovery of poisonous plants to Hecate
  • Roman herbalists were often accomplices to murder
  • Arab cultures in 9th century perfect the art of poisoning
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5
Q

Who is Hecate

A

greek goddess of sorcery

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6
Q

How were poisoning with herbs popular with Roman herbalists

A
  • most poisonous herbs were readily available for other uses
  • murder from a distance
  • calculate dosage so that victim was killed slowly over time
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7
Q

Death of Cleopatra

A
  • Queen Pharaoh of Egypt 51 to 30 BC
  • has son with Julius Caesar and Rome becomes involved with the ruling of Egypt
  • following Caesar’s death, she forms an alliance with Mark Antony
  • eventually overthrown by Octavian
  • she first experiments with different plant extracts on slaves
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8
Q

what plant extracts does cleopatra experiment with?

A
  • henbane and belladona work quickly but are painful
  • strychnine works quickly, but leaves the face distorted
  • supposedly, she decides on Asp’s venom
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9
Q

Historic ways to avoid being poisoned

A
  • avoid eating foods that smell or taste ‘wrong’
  • use of special goblets (“unicorn horn”,embedded with amethyst or emeralds)
  • use special stones to neutralize poison (toadstones, bezoar stones)
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10
Q

Historic Antidotes and Cures

A
  • most cures instruct victim to induce vomiting
  • use antidotes called Theriaca (remedies for venomous bites)
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11
Q

Nero

A
  • poisons his stepbrother to gain the throne
  • worries he will be poisoned as well
  • has his physician, Andromachus, make a theriac containing 78 ingredients
  • contains opium, lizard, snake flesh
  • antidote becomes popular through rome
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12
Q

Mithridates Eupator

A
  • 120-66 BC
  • king of Pontus (on the black sea)
  • is extremely paranoid of being poisoned
  • takes small doses of the herbal poison/antidote to make himself immune
  • romans attack in 66 BC
  • he tries to poison himself, but has become too tolerant
  • has a slave stab him to death
  • Mithridatism means acquired tolerance to poisons
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13
Q

Toxic Alkaloids

A
  • piperdines (coniine)
  • tropane alkaloids (anticholinergics from hallucinogenic plants)
  • pyrrolidines (nicotine)
  • quinolizidines (lupinine)
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14
Q

Examples of Terpenoid alkaloids

A
  • cyclopamine (veratrum californicum)
  • aconitine (aconitum species)
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15
Q

Examples of Indoles

A
  • ergot (claviceps pupurea)
  • strychnine
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16
Q

Examples of Complex alkaloids

A
  • tubocuraine (Chondrodendron tomentosum)
  • physostigine (physostigms venonosum)
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17
Q

Cyclopamine

A
  • is a teratogen
  • grazing animals who ingest it have offspring with severe defects
  • inhibits normal protein patterning in developing organisms
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18
Q

What is the compound Cyclopamine named after?

A

named after the mythical cyclops spoken of in Homer’s odyssey

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19
Q

Sonic Hedgehog Signaling and Development

A
  • normal development involves sonic hegdehog activation of a signaling pathway
  • failure of the cerebral hemispheres of the brain to divide (holoprosencephaly)
  • affects the same development signaling pathway (without cyclopamine)
  • phenotypes can range from mild to severe
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20
Q

Aconitum napellus

A
  • aconitine or aconite
  • known as monkshood, friar’s cap, auld wife’s huid, brute killer, leopard killer, wolf’s bane
  • has hooded flowers in shades of greenish and purplish hues
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21
Q

Mechanism of Aconitum napellus

A
  • reduces ion selectivity of sodium channels
  • increases uptake of sodium
  • produces cardiac arrhythmias (depression of respiration, death)
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22
Q

Strychnine (production and historic uses)

A
  • strychnos nux-vomica
  • tree produces strychnine in fleshy orange-red berries
  • native to tropical southeast asia and Australia
  • used by Indigenous people to make poison arrows for hunting
  • also used in rat poison
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23
Q

Physiological effects of Strychnine

A
  • has stimulant effects
  • increases respiration and circulation
  • once used as an antidote in cases of poisoning by alcohol or barbs
  • minimal therapeutic index limited clinical use
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24
Q

Low dose vs. High dose in Strychnine

A
  • low dose = CNS stimulant
  • high dose = acts as a convulsant, seizure activity in the brain, contract all muscle, face contorts, breathing is cut off, death follows
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25
Q

How is Strychnine a complex structure?

A
  • is a monoterpene alkaloid
  • amino acid (tryptophan)
  • monoterpene isoprene units
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26
Q

Strychnine one of three alkaloids used by athletes:

A
  • 1800-1900s
  • used to improve performance
  • two others were cocaine and amphetamine
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27
Q

Thomas Hicks

A
  • used a mixture of strychnine and brandy to win the marathon in 1904 olympics
  • collapsed at the end of race, but survived
28
Q

Arrow Toxins

A
  • alkaloids and cardiac glycosides
  • aids to hunting
  • arrow toxins contain water soluble mixture of cardiac poison and muscle paralyzing poison
29
Q

Arrow toxins used in south america (example)

A
  • muscle paralyzers
  • antidotes exist and artificial respiration can be used to revive those affected
  • example: curare and phytostigmine
30
Q

Arrow toxins used in Africa and Asia

A
  • cardiac poisons
  • no antidotes or treatments for cardiac poisons
  • examples: ouabain and strophanthidin
31
Q

Curare used in South America blowpipe dart poison

A
  • 16th century explorers report that indigenous people in brazil, peru, ecuador and columbia use arrows tipped with curari or woorali
  • crude dried plant extract
  • usually mixed with various strychnos species
32
Q

Potency of Curare

A
  • preparation involves making an aqueous extract of bark from plant vines
  • concentrate it into a tar-like mass
  • classified as ‘one tree curare’ if a wounded monkey could one leap before dying
  • ‘three tree curare’ could be used to capture animals alive
33
Q

Charles Waterton (1820s)

A
  • revived a donkey dead from curare poisoning by artificial ventilation using a bellows
  • curare causes death by asphyxiation
34
Q

Claude Bernard (1850s)

A
  • french physiologist
  • shows that curare preparations block transmission of nerve impulses in frogs
  • death is caused because the chest and abdominal muscles become paralyzed
35
Q

Why is Curare so complex?

A
  • is a complex mix of alkaloids
  • structure is plant species dependent
  • major components are Curarines and Strychnine derivatives
36
Q

Richard Gill (1920s)

A
  • brings back 30 pounds of curare and lobbies drug companies
  • eventually Squibb and Burroughs Welcome experiment with curare as a muscle relaxant during anasthesia
  • experimental animals died until it was realized that artificial ventilation was necessary during the surgery
37
Q

Mechanism of Actions of Curare

A
  • curare is a competitive antagonist at NAChR
  • in the neuromuscular junction, this inhibits the ability for acetylcholine to elicit muscle contraction, resulting in paralysis
38
Q

Physosotigmine

A
  • physostigms venenosum
  • known as Eserine
  • produced from the Calabar bean
  • interacts with and inhibits acetylcholinesterase
  • results in more ACh in the synapses
39
Q

Functions of Physostigmine

A
  • has been used to treat myasthenia gravis
  • recently used to treat Alzheimer’s disease
40
Q

Acetylcholinesterase and Physostigmine

A
  • acetylcholinesterase quickly removes acetylcholine from the synapse
  • physostigmine inhibits acetylcholinesterase, resulting in more acetylcholine in the synapse
41
Q

Historical use of Physostigmine (Britain)

A
  • calaber bean was used in ‘trials by ordeal’
  • 1840 British Army medical officer observes the African natives
  • used to reveal witches
42
Q

Ouabain

A
  • African Arrow poison
  • Cardiac glycosides
  • used on arrows by hunters in Africa
  • described by Victorian explorer David Livingstone : lowers heart rate and regulates arrythmias, high doses can kill
  • not absorbed be GI tract so it is safe to eat poisoned animals
43
Q

Ouabain Mechanism of Action

A
  • inhibits the sodium/potassium ATPase that maintains ion gradients in heart muscle cells
44
Q

Toxic Phenolics

A
  • Lignans (podophyllotoxin)
  • coumarins (methoxypsoralen, aflatoxins)
  • tannins
  • other phenolics (urushiol)
45
Q

Aflatoxin (aspergillus sp.)

A
  • fungus, difuranocoumarins
  • contaminate corn, cereals, sorghum, peanuts
46
Q

How are aflatoxins carcinogenic?

A
  • carcinogenic to humans and animals
  • toxin intercalates and alkylates DNA, inducing mutation
  • linked to hepatocellular carcinoma
47
Q

Case of Aflatoxicosis

A
  • 200 villages in Western India
  • poor people ate badly molded corm
  • high mortality rate due to massive GI bleeding
  • possible use of aflatoxin as a biological weapon
48
Q

Tannins Uses

A
  • astringent phenols
  • bind proteins and precipitates them out of solution
  • used in medicines to draw irritants out of the skin
  • used to transform animal hides into leather
  • tannin action can be oncogenic or anti-oncogenic
49
Q

What kind of taste do tannins produce and why?

A

produce bitter tasting tannins as defense against predation

50
Q

Human consumption of tannins

A
  • tea, coffee, wine
  • frequent drinking of strong tea linked with esophageal cancer
  • reduce risk by taking tea with milk (casein fixed the tannin, preventing its action on mucous membranes of mouth)
51
Q

Toxic Amino Acids and Proteins

A
  • coprine
  • amatoxin and phallotoxin
  • lectins (ex. ricin)
52
Q

Coprinus atramentarius

A
  • toxis amino acid
  • inky cap mushrooms (edible)
  • produces coprine (aa that interferes with body’s alcohol metabolism)
  • inhibits acetaldehyde dehydrogenase (mitochondrial enzyme)
53
Q

Toxic Mushrooms

A
  • amanita phallosides (death cap mushroom or Angel of death)
  • Amanita vivrosa (destroying angel)
  • both contain deadly amatoxins and phallotoxins
54
Q

Symptoms of Amanita phallosides and Amanita vivrosa?

A
  • 12-24 hours after ingestion: violent and prolonged abdominal pains, vomiting, diarrhea, respiratory distress, symptoms subside
  • 4-11 days after ingestion: liver damage and failure, coma and death
55
Q

Amatoxin

A
  • selectively absorbed by hepatocytes
  • specifically inhibit RNA polymerase II
  • transcription inhibited
  • used as a research tool to study transcriptional regulation in animal and plant cells
56
Q

Phallotoxin

A
  • binds protein on hepatocyte plasma membrane
  • results in membrane leakiness that comprises cellular function (efflux of K and Ca)
  • phalloidin binds to actin subunits (used as a research tool to study cytoskeletal function)
57
Q

Lectins

A
  • highly toxic proteins of non-immune origin
  • has two sugar binding sites
  • cause agglutination and precipitation of sugar molecule complexes
58
Q

Ricinus communis

A
  • castor bean plant
  • acts as a ribosome inactivating protein
  • is the most toxic naturally occuring compound
59
Q

Ricin Poisoning

A
  • ingestion of 3 seeds is fatal to most adults
  • inhibition of protein synthesis in intestinal wall
  • causes clumping of red blood cell
60
Q

Symptoms of Ricin Poisoning

A
  • nausea, vomiting, burning sensation in throat and mouth
  • followed by hemorrhaging in the GI tract, liver and kidneys
  • kidney failure and death
61
Q

Ricin Mechanism of Action

A
  • heterodimer (2 different polypeptides, RTA and RTB)
  • RTA and RTB linked by disulphide bridge
  • RTA, enzyme
  • RTA, lectin
62
Q

RTB

A
  • sugar-binding lectin
  • binds to target cell surfaces
  • interacts with any galactose or N-acetylgalatosamine terminating olgosaccharide
  • mammalian cells have many such surface binding sites
63
Q

RTA

A
  • N-glycosidase, prevents mRNA translation
  • inactivates 60S subunits of eukaryotic ribosomes
  • irreversibly hydrolyzes a specific adenine-ribose bone of the 23S rRNA that is part of the 60S ribosomal subunit
  • one RTA molecule can remove adenines from 1500- 2000 ribosomes per minute
64
Q

Ricin mechanism as a cell toxin

A
  • requires both parts of the ricin molecule
  • entry via endocytosis
  • RTA enters cytoplasm and accesses its rRNA substrate
65
Q

Two functions of RTB in the Ricin mechanism as a cell toxin

A
  • binds to specific cell surfaces
  • aids entry of ricin (RTA-RTB) into target cell
66
Q

Georgi Markov

A
  • was a successful playwright and novelist
  • was stabbed in his right thigh by an umbrella and was rushed to the hospital the next day
  • autopsy showed that death was due to blood poisoning
  • discovered a metallic bead located just under the skin

BOT 380 (17 decks)

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