T OX I N S 4 4 5

SAXITOXIN

Pablita Mendez

WHAT IS SAXITOXIN?

Introduction • A saxitoxin is a naturally

occurring neurotoxin found in both fresh and salt water ecosystems.

• It is produced by certain species of Dinoflagellates and Cyanobacteria.

• Saxitoxin is odorless and tasteless. It is heat and acid resistant.

• Water soluble

HISTORY OF SAXITOXIN

• 1950’s first started being used by CIA as a suicide pill• 1970 president Nixon orders the destruction of all the stock

of saxitoxin. (Did not happen, all stock was not destroyed.)• 1977 saxitoxin first synthesized by Kishi at Harvard

USES OF SAXITOXIN

Bioterrorism and Biological Warfare• Saxitoxin has been explored by

the United States biological and chemical weapons programs.

• Schedule 1 chemical agent • Water soluble• In biological/chemical warfare,

saxitoxin could become an agent of mass destruction through dissemination of aerosolized toxin.

Figure 1. Toxicity in LD50 vs. quantityof toxin required to provide a theoretically effectiveopen-air exposure, under ideal meteorologicalconditions. to an area 100 km2

ORGANISMS PRODUCING SAXITOXIN

• Cyanobacteria are a photosynthetic aquatic bacteria• Specific cyanobacteria that

produce saxitoxin:• Anabaena, Aphanizomenona, and

Cylindrospermopsis

• Dinoflagellates are photosynthetic marine plankton • Specific Dinoflagellates that

produce saxitoxin:• Alexandrium, Gymnodinium and

Pyrodinium

RED TIDE

• It is not always possible to “see” when saxitoxin levels are elevated but some saxitoxin producing organism are responsible for red tide events which is quite a sight!

• Red tide is a natural occurring event known as harmful algal blooms where marine organism such as Dinoflagellates rapidly accumulate turning the water a red/brown color.

• Millions of dollars are lost every year due to contaminated shellfish during red tide

• Factors affecting red tide include: • systematic increase in sea water temperature • seasonal occurrence resulting from coastal

upwelling• increased nutrient loading from human activities

• nitrates and phosphates can be abundant in agricultural run-off as well as coastal upwelling zones

TRANS-VECTORS

Saxitoxin is usually consumed by humans through the consumption of infected shellfish. (There have been reported cases of humans being infected by consuming infected fish as well but this is less common)

• molluscs (mussels, clams, oysters, etc.) • Filter feed on these organisms and the toxins accumulate in the

tissue.

MECHANISM OF SAXITOXIN

• With a high affinity for binding on site 1 of the voltage-gated sodium ion channel, saxitoxin inhibits the temporary permeability of Na+ ions by binding tightly to a receptor site on the outside surface of the membrane very close to the external orifice of the sodium channel.

• This prevents sodium ions from passing through the membranes of nerve cells, thus interfering with the transmission of signals along the nerves.

• The widespread blockade prevents impulse-generation in peripheral nerves and skeletal muscles.

EXPOSURE PATHWAYS

The following chart shows the route of exposure and LD50 for rats.

Route LD50(micrograms/kg)

Intravenous 3-9

Intraperitoneal 10

Oral 263

Inhalation <2 (in hamsters)

ORAL INGESTION

• This is the most probable pathway in humans.

• The classic presentation of saxitoxin intoxication is that of recent shellfish ingestion followed closely in time by an acute gastrointestinal illness with neurological symptoms.

• Symptoms appear 30min- a few hours after exposure.

• Human LD50 10 micrograms/kg

INHALATION

• Inhalation is the most lethal pathway for humans.

• After respiratory exposure with aerosolized saxitoxin, the patient may have only the neurological syndrome.

• If not treated may result in respiratory failure.

• Symptoms may occur within minuets of inhalation.

• Human LD50(2 micrograms/kg)

THE LONG LIST OF SYMPTOMS OF SAXITOXIN POISONING

• Symptoms: • Disorientation • Dizziness • Memory loss• headache• Vomiting • Numbness (tongue, lips, fingertips)• Weakness • Diarrhea • Motor incoordination• Diplopia (double vision)• Swallowing difficulties• Flaccid paralysis• Respiratory failure

DIAGNOSIS

• Diagnosis of saxitoxin poisoning is by history and clinical signs and symptoms.

• Radioimmunoassay or by indirect enzyme linked immuno adsorbent antibody test (ELISA) or by mouse bioassay confirms the diagnosis.

• Clinical specimens that may be tested for saxitoxin include stomach contents, serum, and, after respiratory exposure, respiratory secretions. • The best early diagnostic sample for most aerosolized

toxins is a swab of the nasal mucosa.

HOW TO TREAT SAXITOXIN POISONING

• Treatment: Treatment of saxitoxin poisoning is supportive. • Attention must be given to the patient’s respiratory status.

Temporary mechanical ventilation may be required. • Activated charcoal to adsorb toxin from the gut may be

effective if given within 1 to 2 hours of ingestion.

• Prophylaxis and Antidotes: No vaccines or effective prophylactic treatments exist for Saxitoxin. • There is no antidote for it.

RESEARCH

• In this study by Barash et al.,2009 they developed prolonged duration local anesthetics based entirely on site 1 sodium-channel blockers.• Their hypothesis being that there would be less

harm to local tissue. • To allow increased loading without systemic

toxicity they used liposomes, which are biocompatible microscopic lipid vesicles with a bilayer membrane structure.• Saxitoxin was used as the model site 1 sodium-

channel blocker.

RESEARCH CONTINUED

• The resulting formulation produced nerve blocks lasting many days in the rat, with minimal local or systemic toxicity and inflammation.

• Free Saxitoxin (0.005–0.05 mg/mL) was not myotoxic at any of the concentrations or any durations of exposure tested.

• Conclusion: ultra long-acting saxitoxin-based liposomal local anesthetics were developed that were biocompatible in terms of myotoxicity, neurotoxicity, inflammation, and systemic toxicity.

Figure 2. Graph showing that cell survival was 100% when using saxitoxin based liposomal local anesthetics.

CONCLUSION

• The control of saxitoxin is of vital importance in the shellfish industry. Millions of dollars are lost each year to toxic blooms. • Research using saxitoxin in the development of

prolonged duration local anesthetics shows great promise in new anesthetic usage with no toxic affects. • Saxitoxin continues to be of concern in biological

warfare. It may be used as an agent of mass destruction especially in its aerosolized form.

SOURCES

• Agarwal, A. 2012. The future of anesthesiology. Indian J Anaesth. Vol56(6): 524–528. • Barash,H. et al. 2009. Prolonged duration local anesthesia with minimal toxicity. Proc

Natl Acad Sci U S A. Vol 106(17): 7125–7130• Cusick, A., Sayler, G. 2013. An Overview on the Marine Neurotoxin, Saxitoxin: Genetics,

Molecular Targets, Methods of Detection and Ecological Functions Mar. Drugs.11: 991-1018

• Faber, S. 2012. Saxitoxin and the induction of paralytic shellfish poisoning. Journal of Young Investigators.Vol. 23 Issue 1

• Hallegraeff, GM. 1993. A review of harmful algal blooms and their apparent global increase. Phycologia. 32:79-99.

• Johnson, R. 2009. Quantification of Saxitoxin and Neosaxitoxin in Human Urine Utilizing Isotope Dilution Tandem Mass Spectrometry. Journal of Analytical Toxicology, Vol. 33: 8-14

• Dekker, M. Seafood and Freshwater Toxins : Pharmacology, Physiology, and Detection.• Sullivan, J., and W.T. Iwaoka. 1983. High pressure liquid chromatography determination

of toxins associated with paralytic shellfish poisoning. J. Assoc. Off. Anal. Chem. 66: 297–303

• http://www.usamriid.army.mil/education/defensetox/toxdefbook.pdf• http://www.globalsecurity.org/wmd/intro/bio_saxitoxin.htm