It has now been confirmed that Kim Jong-nam, the half-brother of North Korean Leader Kim Jong-un, may have been assassinated using a highly toxic nerve agent known as VX. The attack occurred last week (13^th February) in Kuala Lumpur airport, suspected to have been committed by two women who reportedly sprayed the chemical into his face before fleeing the scene.

VX, or S-[2-(Diisopropylamino)ethyl] methylphosphonothioate, is a nerve agent initially developed at the Porton Down Chemical Weapons Research Centre in Wiltshire, UK in 1952. Having originally been the focus of research elsewhere into the development of new organophosphate compounds as pesticides, the British military soon established an interest in the compound and continued its development.

Typically encountered in liquid form, this clear or sometimes amber-coloured, oily substance is notoriously difficult to detect, lacking in both taste and odour. Its toxicity makes it one of the deadliest chemical warfare agents, requiring as little as 10mg adsorbed through the skin to be fatal. Its deadliness is only further increased by the persistence of the agent, making it difficult to decontaminate people and areas tainted with the chemical.

Mechanism

The mechanism of action of VX is identical to many similar nerve agents. The compound can enter the body by a range of potential routes, including ingestion, inhalation or skin contact. Once inside the body, VX inhibits the function of acetylcholinesterase (AChE), an enzyme responsible for catalysing the breakdown of acetylcholine. Acetylcholine is released over a synapse following an electric nerve impulse, ultimately resulting in a muscle contraction. However when VX binds to the active site of acetylcholinesterase, it renders the enzyme inactive, thus preventing it from breaking down the acetylcholine. As the nervous system is flooded with excess acetylcholine,  repeated muscle contractions occur, eventually resulting in asphyxiation due to constant contraction of the diaphragm muscle.

The effects of VX will typically occur immediately after exposure, beginning with coughing, shortness of breath and a tightness in the chest. A headache and blurred vision soon follows, along with symptoms such as vomiting, diarrhoea and abdominal pains. Given a sufficient dose, seizures will then occur as the drug attacks the nervous system, eventually resulting in a coma and asphyxiation.

If administered promptly, there are antidotes for VX. Atropine, typically administered by injection, is an anti-nerve agent that blocks the acetylcholine receptors, alleviating the symptoms brought on by the nerve agent. However it is worth noting that compounds such as atropine are toxic in their own right and, although they may save the person’s life by alleviating the effects of the nerve agent, they will still have an adverse effect on the patient. In addition to this, pralidoxime (or 2-PAM), can be administered to reactivate the enzyme, thus reversing the effects of VX. 2-PAM is a safer compound to use than atropine, but its effects are much slower.

Other Nerve Agents

VX is just one of many known toxic nerve agents. Nerve agents can typically be classed as either G-series or V-series. G-series agents were first synthesised by German scientists during World War II, and include tabun (GA), sarin (GB), soman (GD), and cyclosarin (GF). The first compound to be discovered, tabun, was accidentally synthesised by Dr Gebhardt Schraeder, who was investigating the development of organophosphate-based pesticides. The German army soon realised the potential use of such compounds, and went on to fund the development of other nerve agents such as sarin. The G-series chemicals are all clear, colourless liquids at room temperature, but are largely utilised as gases due to their high volatility.

The V-series nerve agents, which include VX, VE, VG, VM and VR, were developed a few years later, initially in the UK but some later in Russia. Unlike the G-series compounds, V-agents are very persistent and are not easily washed away or degraded, meaning they can remain on surfaces for long periods of time.

Fortunately the V-series nerve agents have generally not been exploited outside of military research, and the death of Kim Jong-nam may well be the first known use of the toxic agent in an assassination. However the G-series have received a great deal of malicious use and attention over the years, ranging from the Tokyo sarin subway attack in 1995 to its recent use in the Syrian civil war

VX, along with numerous other toxic nerve agents, were banned under the Chemical Weapons Convention of 1993, rendering the manufacture, possession and use of such substances illegal.

 

References

BBC News. VX nerve agent: The chemical that may have killed Kim Jong-nam. [online] Available: http://www.bbc.co.uk/news/world-asia-39073558

University of Bristol Chemistry on the Screen. VX Nerve Gas. [online] Available: http://www.chm.bris.ac.uk/webprojects2006/Macgee/Web%20Project/nerve_gas.htm