Neurotoxins are substances that are toxic to nerve cells. They can originate from plants, animals, minerals, or the atmosphere. Common neurotoxins include botulinum toxin, tetrodotoxin, and toxic metals like mercury and lead. Botulinum toxin, produced by Clostridium botulinum bacteria, is the most potent toxin known and works by inhibiting the release of acetylcholine at neuromuscular junctions, causing paralysis. Tetrodotoxin blocks sodium channels, leading to paralysis and respiratory failure. Heavy metals like mercury and lead can cross the blood-brain barrier and cause central nervous system damage. While some neurotoxins like glutamate and nitric oxide are normally present in the body, higher concentrations can

1. NEUROTOXINS
PRATHAMESH KUDALKAR
13FET1011

2. What are Neurotoxins?
 Neurotoxins are the substances that are poisonous or
destructive to the nerve cells.
 The term is also used for classifying endogenous compounds
which when present in higher concentrations may prove
neurologically toxic.
 They affect the functioning of developing as well as mature
nervous tissues.
 Neurotoxins can be of plant, animal, mineral or atmospheric
origins.
 Neurotoxins inhibit neuron control over ion concentrations
across cell membrane or communication between neurons
across a synapse.

3. COMMON NEUROTOXINS
Botulinum Toxin Lead
Teradotoxin Ethanol
Tetanus Toxin Glutamate
Nitric Oxide Tetraethylammonia
Chlorotoxin Arsenic
Conotoxin Mercury

4. Botulinum Toxin
 Botulinum Toxin (BTX) is a group of neurotoxins consisting
of eight distinct compounds, referred to as BTX-
A,B,C,D,E,F,G,H
 Botulinum Toxin (BoNT) causes a rare disease termed as
Botulism.
 It is the most potent of all the known poisons. 1g is
sufficient to kill approximately 30 billion mice.
 LD50 value for humans is 0.2ng/kg.
 It is produced by bacterium Clostridium Botulinum.

5. Botulinum Toxin
Biology of C.Botulinum
Gram Positive
Rod Shaped
Anaerobic
Spore forming
Motile
Large
Growth Conditions
pH (>4.6)
Water activity (>0.93)
Anaerobic
Moderately High Salt
(5.5%)
Temperature(35-37
degree Celsius)

6. Botulinum Toxin
 Toxin
Seven serotypes (A, B, C, D, E, F and G) of botulism
are recognized, based on the antigenic specificity of
the neurotoxin produced by each strain.
Types A, B, E and F cause human botulism
Types C and D cause most cases of botulism in
animals. As they are highly potent toxins only a very
small amount (1ng/kg body weight) is necessary for
severe symptoms and even death.
The toxins are heat labile and can be destroyed by
high and uniform heat at 950C for 15 minutes or
boiling for 5 minutes.

7. Botulinum Toxin
Groups I II III IV
Neurotoxin Types A, B, F B, E, F C, D G
Gene Location Chromosome Chromosome Bacteriophage
Activity Proteolytic Non Proteolytic Non Proteolytic Proteolytic
Optimum Temp. 35-40 18-25 15 ND
Minimum aw 0.94 0.97 ND ND
Minimum pH 4.6 5.0 ND ND
D100 (min) 25 <0.1 0.1-0.9 0.8-1.12
D121 (min) 0.1-0.2 <0.001 ND ND

8. STRUCTURE
 The toxin is in the form of a non-covalently bound
complex that contains several nontoxic proteins that
consist of hemegglutinin and nonhemegglutinin, and
weighs 150 kDa
 In order for this polypeptide molecule to become
toxic, it is cleaved by a protease at one-third the
distance from the N terminus.
 The exact enzyme that performs this function has still
yet to be been determined.
 This action yields two fragments: a smaller, lighter
fragment weighing 50 kDa and a heavier fragment
with a larger weight of 100 kDa
 Proteolytic activity is located at the N-terminal end of
the light chain of botulinum toxin

9. MECHANISM OF ACTION
 Outside the body.
 Food
Heat

12. MECHANISM OF ACTION
Inside the body
 The neurotoxin targets the body’s peripheral nervous system.
 After entering the body, it is transported by blood stream to the nerve
cells
 They pass through the presynaptic membrane of motor nerve terminals
and enter into the neuron cell by endocytosis.
 The heavier chain forms a channel within the membrane in which the
lighter chain can then pass through into the cytoplasm.
 The botulinum toxin produces specified cleaving proteases that allow
the pathogen to successfully attach to the synaptic vesicles.

13. MECHANISM OF ACTION
 The carboxy-terminal domain of the heavy chain recognizes a specific binding
site, while the nitrogen-terminus transports the lighter chain into the nerve cytosol
 The lighter chain contains metalloproteases that target SNARE proteins involved in
controlling the exocytosis machinery.
 Neurotoxin types depend upon the characteristic of lighter chain.
 SNARE proteins are group of proteins which facilitate the release of acetylcholine
from Synaptic vesicles.
 Type B,D,F,G cleaves Synaptobrevin
 Type A,C,E cleaves SNAP-25
 Type C cleaves Syntaxin
 Thus membranes of vesicles carrying acetylcholine and presynaptic membranes
do not fuse, in turn blocking the exocytosis of neurotransmitter acetylcholine

14. MECHANISM OF ACTION
 Acetylcholine plays an essential role in the body
 It is responsible for regulating the somatic nervous system,
which controls the voluntary movements of the skeletal
muscles, and is the only of its kind.
 If acetylcholine is absent, muscle contraction cannot take
place resulting in regional flaccid paralysis of muscle.
 It affects the cardiovascular as well as respiratory muscles
 Death is caused mainly due to respiratory failure.

15. Exposure and transmission
 Foodborne botulism
 Infant botulism
 It occurs when infants ingest Clostridium botulinum spores, which germinate into
bacteria that colonize in the gut and release toxins.
 In most adults and children older than about six months, this would not happen
because natural defense that develops over time prevent germination and
growth of the bacterium.
 Wound botulism
 Wound botulism is rare and occurs when the spores get into an open wound and
are able to reproduce in an anaerobic environment.
 Other types of intoxication
 Water borne
 Airborne

16. FOOD SOURCES
 The spores are heat-resistant (killed at 1150C) and can
survive in foods that are incorrectly or minimally
processed.
 Spores do not germinate in the presence of nitrate (250
ppm).
 Foods most commonly associated are low acid
vegetables (green beans, corn, spinach, asparagus,
pepper and mushrooms) and fruits (figs and peaches)
and also fermented, improperly cooked and smoked
fish, meat, poultry and fish eggs in hermatically sealed
containers.

17. SYMPTOMS & TREATMENT
 At the initial stage (generally 12h to 36h, but can be 2h), some
gastrointestinal symptoms (nausea, vomiting, diarrhea and
constipation) are evident.
 Neurological symptoms appear in a short time particularly when the
amount of toxin consumed is more, which includes blurred or
double vision, difficulty in swallowing, breathing and speaking,
dryness of the mouth, and paralysis of different involuntary muscles
that spreads to the lung and heart.
 The person who has been intoxicated by botulinum toxin should be
given supportive care for breathing like Ventilator
 Equine antitoxin must be administered within 18 hrs
 Even if extremely small dosage is ingested, antitoxins must be taken
immediately or it may lead to paralysis.

18. DETECTION OF TOXIN
 Mouse bioassay was the earliest method used for detection of
Botulinum toxin
 Modern Methods:
 ELISA
 PCR
 HPLC
 DNA Microarrays
 Real time PCR
 GC

19. TETRODOTOXIN
 Tetrodotoxin, frequently
abbreviated as TTX, is a extremely
toxic neurotoxin.
 It is found mainly in fishes such
as pufferfish, porcupinefish, ocean
sunfish etc.
 TTX is found in
the liver, gonads, ovaries,
intestines, and skin of these fish.
 LD50 value for humans is 25mg/kg
 Tetrodotoxin intoxication is found
mainly in Japan

20. POISONING
 The toxin can enter the body by ingestion, injection, or
inhalation, or through abraded skin.
 The mechanism of toxicity is through the blockage of fast
voltage-gated sodium channels.
 These are required for the normal transmission of signals
between the body and brain.
 As a result, TTX causes paralysis of voluntary muscles (including
the diaphragm and intercostal muscles, stopping breathing),
loss of vagal regulation of heart rate (causing it to increase to
around 100bpm), and loss of sensation etc.

21. SYMPTOMS & TREATMENT
 The diagnosis of pufferfish poisoning is based on the observed
symptomology and recent dietary history.
 Symptoms develop within 30 minutes after ingestion and include
paresthesia of the lips and tongue is followed by hyper-salivation,
sweating, headache, weakness, lethargy, incoordination, tremor,
paralysis etc
 Death usually occurs in 4-6 hrs. if proper treatment is not provided.
 Therapy is supportive.
 If ingested, treatment can consist of emptying the stomach, feeding
the victim activated charcoal to bind the toxin, and taking standard
life-support measures to keep the victim alive until the effect of the
poison has worn off.

22. CONOTOXIN
 Conotoxins are found mainly in creatures having shells
like snail, oyster and sometimes even crabs.
 It inhibits the activity of Ca channel. Some Conotoxins
were found to have different activity.
 Cases of Conotoxin intoxication have not been reported
yet.
 Nowadays, Conotoxins are permitted by FDA for their
use as Pain Killers.
 Not much research has been done on Conotoxins.

23. TOXIC METALS
 Metal contamination in food is easily possible during cultivation,
harvesting and processing
 Mercury ( Dimethyl mercury) is the most potent toxin ever.
 Aluminium and Mercury are capable of inducing CNS damage by
migrating into brain by crossing brain, bone barrier
 Arsenic is widely found in the soil. It is destructive towards
cytoskeleton
 Lead is a potent neurotoxin whose toxicity has been recognized for
at least thousands of years.
 Lead results in increased absorption of calcium in cell leading to
apoptosis (cell death)

24. GLUTAMATE & NITRIC OXIDE
 Glutamate and Nitric Oxide are widely used in food as an additives.
 Glutamate and Nitric Oxide are part of CNS and hence termed as
endogenous neurotoxins.
 Nitric oxide (NO) is commonly used by the nervous system in inter-
neuron communication and signaling.
 Glutamate is its functions as an excitatory neurotransmitter.
 It is only when these endogenous compounds become highly
concentrated that they lead to dangerous effects.
 Increased concentrations lead to DNA damage, swelling and
apoptosis.
 Also, NO is carcinogenic.

25. THANK YOU!