SarinAdarsh Vangala

Introduction: Why Sarin?

• It is one of the most famous and widely used agents of modern chemical warfare – It has been involved in many recent conflicts– We have a better understanding of its effects on

humans than other nerve agents• It serves as good illustration of the mechanism

and effects of other nerve agents.

Introduction: Presentation Contents

• Uses of Nerve Agents• History of Sarin• Production • Mechanism • Physiological response and symptoms• Detection • Current Treatments

Nerve Agents• Organophosphate compounds that disrupt transmission

of information in nervous system– All act with similar mechanism

• Tabun (GA), Sarin (GB), Soman (GD), Cyclosarin (GF), VX are examples used in chemical warfareSmythies, Journal of the Royal Society of Medicine,

2004, 97.

Uses of Nerve Agents

• 1st synthesized nerve agent Tabun developed by IG Farben in Germany as insecticide in late 30s– Toxic effects on humans discovered

when lab assistants accidentally exposed

• Sarin and Tabun now used almost exclusively for chemical warfare

Ivarsson, National Defence Research Establishment, 1992.

Civilian Uses of Nerve Agents

• Organophosphate compounds very similar to Sarin such as parathion and chloropyrifos are still used as pesticides in the U.S. today– Quickly degraded and

rendered nontoxic by exposure to sunlight, air, etc.

Reigart, EPA, 2013, 43-55

Potential Medical Uses of Organophosphates

• Cholinesterase inhibitors might be used to treat dementia

• Organophosphates pyridostigmine and physostigmine used to treat neruomuscular disease myasthenia gravis

Ellis, J.M., 2005, J AM Osteopathic Assoc, 145-158Flacke, W., 1973, N Engl J Med., 27-31

History of Sarin

• Sarin (C4H10FO2P) first synthesized by German scientist Gerhard Schrader

• part of G-series of synthetic nerve agents developed for use in chemical warfare by German military

• never actually used during WWII

Sample, Guardian, 2013

Ivarsson, National Defence Research Establishment, 1992.

Use in Warfare and terrorism

• One of several chemical agents used by Iraqi government in 1988 Halabja attack killing over 5,000

• Most famously used by terrorist Aum Shinrikyo sect during 1994 Matsumoto attack and 1995 Tokyo Subway attack in Japan killing over 20 people.

Sample, Guardian, 2013

Modern Incidents

• rocket attacks on August 21st 2013 on Ghouta area of Damascus during Syrian Civil war claimed between 350 and 1400 lives

Sample, Guardian, 2013

Production of Sarin

• Several different methods used to synthesize Sarin– Many components such as isopropanol (rubbing

alcohol) are very common– Most major precursors are heavily restricted by

Chemical Weapons Convention guidelines that went into effect in 1997• Can only easily be made in large quantities by

governments and militaries

Sample, Guardian, 2013

Acetylcholine

• Common neurotransmitter involved in signaling muscle contraction.

• Acetylcholinesterase (AChE) is an enzyme that hydrolyzes ACh into choline and acetic acid.

Pohanka, 2011, Biomed. Pap. Med. Fac. Univ. Palacky Olomouc Czech Repub., 219-230CDC, 2007

Sarin Mechanism

• Sarin prevents the breakdown of Ach through competitive inhibition.

• Sarin forms phosphate ester bond to serine residue on AChe active site.

CDC,2007

Wang, 2006, Phys. Chem. B. 7567-7573

Mechanism Continued

• sarin-AChE complex undergoes irreversible dealkylation that results in the cleavage of the phosphonate ester bond. – This irreversible process, called “aging”, permanently

removes the enzyme’s functionality.

CDC, 207

Wang, 2006, Phys. Chem. B. 7567-7573

Physiological response

• Sarin exposure causes buildup of ACh• Causes uncontrollable muscle contractions– May cause paralysis when ATP depleted

• Most of the acute symptoms observed when 75-80% of the AChE inhibited– 1995 Tokyo subway victims showed decreased

erythrocyte cholinesterase activity 3 years after the attack

Yanagisawa, 2006, Journal of the Neurological Sciences, 76-85

Okumura, 2005, Toxicol. Appl. Pharmacol., 471-476

Symptoms

• Symptoms of inhalation usually appear within five minutes – symptoms of liquid exposure generally arise much

later– Respiratory failure was main cause of death in

1994 Matsumoto attack• weakness and paralysis in respiratory muscles, mixes

with inhibition of the respiratory center of the CNS and thick mucus secretions in the respiratory tract

Yanagisawa, 2006, Journal of the Neurological Sciences, 76-85

Okumura, 2005, Toxicol. Appl. Pharmacol., 471-476

Other Symptoms

• bradycardia (depressed heart rate) due to effects on muscarine ACh receptors

• tachycardia (elevated heart rate) due to effects on nicotinic ACh receptors

• blurred vision, headaches, and coughing.

Yanagisawa, 2006, Journal of the Neurological Sciences, 76-85

Okumura, 2005, Toxicol. Appl. Pharmacol., 471-476

Detection

• Sarin is very volatile and can be very dangerous even in small quantities.– Degrades quickly under environmental conditions– Exposes workers to risk

• detection methods focus on identifying more stable Sarin metabolites

Abu-Qare, 2002, Food and Chemical Toxicology, 1327-1333

Okumura, 2005, Toxicol. Appl. Pharmacol., 471-476

Methods of Detection

• Gas chromatography, mass spectrometry identify metabolites– Metabolites

methylphosphonic acid (MPA) or IMPA) isolated from soil samples, urine of victims, etc.

Abu-Qare, 2002, Food and Chemical Toxicology, 1327-1333

Okumura, 2005, Toxicol. Appl. Pharmacol., 471-476

Treatment

• Currently mostly focuses on alleviating symptoms– diazepam to treat seizure symptoms– Atropine injections limit ACh activity in muscarine

response– oximes injections (such as 2-pralidoxime chloride)

can reactivate AChE split sarin into easier to metabolize fragments• Oximes are ineffective once enzyme aging has occurred

Okumura, 2005, Toxicol. Appl. Pharmacol., 471-476.

Newmark, 2004, Arch. Nerol, 649-652.

Smythies, 2004, Journal of the Royal Society of Medicine, 32.

Reasons for use of Sarin

• Highly toxic– The LD50 of sarin gas is 179 μg/kg in mice

• Highly volatile (mostly gas at room temperature)– Can be easily inhaled or absorbed through skin

• Sarin much less toxic and less stable than other G-series nerve agents and more modern V-series nerve gases developed by U.S.– But manufacturing generally easier

Barriers to effective treatment

• “Aging” is nearly impossible to reverse– Sarin-AChe complex relatively stable as well

• Sarin is quick acting and very toxic even in small quantities– Difficult to detect– Victims often die before they can receive medical care– Medical personnel in many areas not equipped/trained

to treat Sarin exposure– Poor access to medical care in regions where Sarin

most likely to be usedOkumura, 2005, Toxicol. Appl. Pharmacol., 471-476.Newmark, 2004, Arch. Nerol, 649-652.Smythies, 2004, Journal of the Royal Society of Medicine, 32.

Conclusions

• Sarin is widely used in chemical warfare – Very toxic and relatively easy to produce

• Similar organophosphates are relevant for both chemical warfare and pesticides

• Current treatment methods are largely ineffective

• Likely to remain relevant in future conflicts due to effectiveness

Avenues for future research

• More effective treatments • Better protective gear• More rapid and efficient detection methods• Potential long term health effects of exposure

on cholinesterase activity

References• Smythies, J, Golomb, B. 2004. Nerve gas antidotes. Journal of the Royal Society of Medicine. 97, 32.• Ivarsson U, Nilsson H, Santesson J, eds. 1992 A FOA briefing book on chemical weapons: threat, effects, and

protection. Umeå, National Defence Research Establishment.• Reigart, J.R. and J.R. Roberts. 2013. "Recognition and Management of Pesticide Poisonings." (6 th ed.) United

States Environmental Protection Agency Publication EPA-735K-13001.• Sample, I., 2013. Sarin: the deadly history of the nerve agent used in Syria. The Guardian. • Wang, J., Gu, J., Leszczynski, J. (2006) Phosphonylation Mechanisms of Sarin and Acetylcholinesterase: A

Model DFT Study. J. Phys. Chem. B. 110, 7567-7573• CDC. 2007. Cholinesterase Inhibitors: Including Insecticides and Chemical Warfare Nerve Agents. Agency for

Toxic Substances and Disease Registry.• Yanagisawa, N., Morita, H., Nakajima, T. (2006) Sarin experience in Japan: Acute toxicity and long-• term effects. Journal of the Neurological Sciences. 249(1), 76-85• Newmark, J. (2004) Therapy for Nerve Agent Poisoning. Arch. Nerol. 61(5):649-652• Okumura, T., Hisaoka, T., Yamada, A., Naito, T., Isonuma, H., Okumura, S., Miura, K., Sakurada, M., Maekawa,

H., Ishimatsu, S., Takasu, N., Suzuki, K. (2005) The Tokyo subway sarin attack—lessons learned. Toxicol. Appl. Pharmacol. 207, 471-476

• Smythies, J, Golomb, B. (2004). Nerve gas antidotes. Journal of the Royal Society of Medicine. 97, 32.• Ellis, J.M., 2005. Cholinesterase Inhibitors in the treatment of dementia. J AM Osteopathic Assoc. 105, 145-

158• Flacke, W., 1973, Treatment of Myasthenia Gravis. N Engl J Med., 288, 27-31